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The Geology of Kagawa and Northern Ehime Prefectures,

Shikoku, Japan

Minoru SAITO

List of Contents Page

Abstract 1 Introduction 2 Acknowledgements 3 I Historical Review of the Works on the Geology and Paleontology of the Setouchi Area 3 IT. Geology of the Inner Zone of Shikoku 12

A -Sambagawa Metamorphics 12 B -Yamaguchi Group 14 C -Ryoke Metamorphics 14 D -GI anite 15 E -1zumi Group 17 F -Kuma Group 19 G -Tonosh0 Group 20 H-Sanuki Group 21 I -1shizuchi Group 23 J -The Lacustrine Deposits 24 K-Yakeotoge Gravels 36 L -Ter r ace and Fan Deposits 37

a. Igneous Activity 38 IV. Geological Structures 40

A-Unconf or mities 40 B -Faults 42 C -Median Line 44 D -Folding 45 E-Basin Structure 46

V . Sedimentary Structures 46 VI. Geological Ages of the Formations 5 1 W Boundary between the Pliocene and Pleistocene Deposits in Kagawa and Ehime Prefectures 56 m. Correlation 58 M Geological History 61 Bibliography 67 Explanation to Plates

Abstract

More than ten years field and laboratory work on the geology and paleontology of the deposits ranging from Cretaceous to Pleistocene distributed in Kagawa and northern Ehime Prefectures has resulted in the distinction of lacustrine deposits of Pliocene age, the establishments of stratigraphic units, recognition of geological structures hitherto left unnoticed, concrete evidence for the number of activities of the Median Line and others

The previously considered Quaternary deposits are shown to belong to the Pliocene and to represent lacustrine deposits. These lacustrine deposits have extensive distribution throughout Ehime and Kagawa Prefectures and continue farther eastwards to Nara, Mie and Aichi Prefectures and are characterized everywhere by the yield of Metasequoia-Stegodon assemblage.

Throughout northern Shikoku deposits of Miocene marine sediments are missing except in small patches in the island of ShBdo-shima, whereas those of the Paleogene are represented by the Kuma group of Eocene age This shows that the period of denudation was a long and varied one, ranging from Oligocene throughout the Miocene in northern Shikoku aside from ShBdo-shima


2 M. Saito

Similary the restricted distribution of marine Pleistocene deposits i n the Setouchi area also shows that the conditions were varied during the late Pliocene to Pleistocene ages I t i s shown that the marine Pleistocene invasion into the Setouchi area was contemporaneous with the intense crustal movement during the post-Pliocene pre-Pleistocene break

The long debated problem of number of time of activity of the Median Line is now proved by field evidence have taken place a t least three time, namely, during the post-Cretaceous pre-Kuma, post- Kuma pre-Ishizuchi, and post - lacustr ine deposits and pre-Yakeotoge gravels

Although i t may be problem that other ages of the movements may be discovered, at least in no r the~n Shikoku, i t is deemed that the stated three movements are well established. From sedimentary structure preserved in the Cretaceous Izumi group and in the Pliocene lacustrine deposits, it i s shown that deposition was rapid in the rapidly downsinking through of the Izumi sea in which turbidities are well developed and have dist~ibution, showing there many interesting structures However, in the lacustrine deposits where sedimentary structure also well preserved, the inferred conditions are quite different from that of the Izumi group because deposition was in a linear basin, shallow, now preserved only in the depressed areas, in that major structure are not developed Another characteristics of the lacustrine sedimentary structures is the development of local features However, i t is noticeable that the local structures reflect the sedimentary environment of the different part of the extensive paleo-Setouchi Lake

Aside from the geological structure which is given in detail considerable details are given to the correlation of the Pliocene and Pleistocene deposits in the Setouchi area a s well as also with adjacent areas From this correlation table i t i s evident that the climatic conditions were varied from cold to moderate or warm and i t is well reflected in the flora, fauna and also in the kinds of sediments distributed in the different parts of the Pleistocene deposits

Introduction

The present work which commenced more than ten years ago concentrates on the geology of the rocks ranging pre-Cretaceous, Cretaceous up to and through the Pleistocene distributed in the northern part of Ehime Prefecture and Kagawa Prefecture. This particular area was selected for several reasons, such as, the hitherto accepted deposits extensively distributed in the two Prefectures actually comprise sediments of the Pliocene and of the Pleistocene, the number of time of activity of the Median Line had been interpreted variously and the field evidence had been obscure in many cases, and the sequence of the different deposits (volcanic and sedimentary) had been clear.

Also the geological structures of the deposits ranging from Cretaceous to Pleistocene had been left almost untouched. For such reasons as well a s for others, the writer studied the area in detail and for the purpose several provinces were distinguished for the sake of brevity. Since rocks of pre-Cretaceous age are not well distributed in the studied area and because they are better developed in other areas, details concerning them have not been included into the present work.

The chief purpose of the present study is to clarify the sedimentary environment of the lacustrine deposits of Pliocene age, to settle the boundary between the Pliocene and Pleistocene deposits to find their relationship within the Setouchi areas as well a s in the adjacent ones. For the study mechanical analysis of many samples from different stratigraphic levels and geographic positions were undertaken, detail stratigraphic columns were whereas possible, sedimentary structures were recorded in detail and their occurrences plotted, data from drilled wells as well a s those dug for irrigation purposes were also included into the study, and paleontological evidence was incoporated.

By field and laboratory works just outlined, this work was brought to i ts present condition and although i t is felt that more evidence is necessary i t also is considered that our knowledge to date should be into a published to advance our knowledge on the geology of Shikoku and also of Japan


The Geolog,y gf' Kagawa and Nortlzern Ehime Prefectures 3

Acknowledgements

The writer wishes to express his thanks to Professor Kotora HATAI of the Institute of Geology and Paleontology, Tohoku University, for his kind guidance in the field and in the laboratory .

The writer, who wzs first introduced to the study of geology by Dr. Shbshiro HANZAWA, Professor Emeritus of the Tohoku University, takes this opportunity to express his deep gratitude to him for his continued encouragement.

Sincere thanks are expressed to Prfessors Enzb KONNO and Kiyoshi ASANO, both of the Institute of Geology and Paleontology, Faculty of Science, Tohoku University for their encouragements.

He deeply appreciates the kindness of Professor Tadao MAEKAWA, Dean of the Faculty of Agriculture of the Kagawa University who made possible the writer's research during 1960 to 1961 in the Institute of Geology and Paleontology, Tohoku University.

During the course of the present work the writer has received valuable support from the following persons to whom he tskes this opportunity to express his deep gratitude, Dr. Hisakatsu YABE, Professor E~ner i tus of the Tohoku University and P~ofessor Motoki EGUCHI of the Faculty of Technology of the Tohoku University for their encouragements in various way; Dr. Shigeru MIKI, Professor of the Bsaka City University and Dr. Keiji SUZUKI of the Fukushima University for their valuable suggestions concerning the plant fossils; Professor Koz6 NAGAI of the Ehime University for his permission to study his data and Dr. Kankichi SOHMA of the Tohoku University for his pollen analysis of peaty matter and Dr. Taiji KUROKAMI for his encouragement in various way.

Acknowledgements are also due to the following persons for their help in many ways; Dr. Tamio KOTAKA, Dr. Shozb HAYASAKA, Dr. Koichiro MASUDA, Dr. Shin KITAMURA, Dr. Masafumi MURATA, and the members of the Institute of Geology and Paleontology, Tohoku University; Professor Wataru ISHIJIMA of the Rikkyo University; Dr. Rikii SHOJI of the Tohoku University; Dr. Yoshio ARAKI and Mr . Jun YAMADA, both of the Mie University; Dr Jiro KATTO and Dr. Jun NAKAMURA, both of the Kochi University; Dr. Jun AKUTSU of the Utsunomiya University; Mr. Shigeichi YAGI of the Matsuyama Museum; Mr. Katsuaki HIYAMA of the B o ~ r d of Education of Ehime Prefecture; Mr . Kazu TAKAHASHI of the Mizukue Middle School, Ehime Prefecture; Mr Shoichi KONDO of the Kaneko Primary School, Niihama City; Mr. Yuji BANDO of the Faculty of Liberal Arts and Education of the Kagawa University ; Dr Masaki UEHARA, DI . Hachiro KIRA, Mr Hiroo INOUE, Mr. Kazuyoshi NAKAYAMA, Mr. Yutaka UMEDA, Mr. Takeshi WAKIYA, and the members of the Faculty of Agriculture, Kagawa University.

For Photographic work of Mr . Kimiji KUMAGAI of the Tohoku University, the writer's thanks are also expressed.

Thanks are also due to the Ministry of Education, for financial support from the Sci- ence Expeditur e Fund,

I . Historical Review of the Works on the Geology and Paleontology of the Setouchi Area

In 1894, K . WAKABAYASHI wrote on the discovery of mammalian fossils from the vicinity of Shaganohana in Sh6do-shima, but gave neither generic or specific names.

U. OGAMI (1895) reported that Mt. Iyatani in the Sanuki district consists of conglomerate, but made no mention as to i ts age.

T . SUZUKI (1896) in his explanatory text to the geological map of Tokushima in the scale of 1:200,000; wrote that the pyroclastic group bearing sanukite (including the coal


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bearing strata) belong to Pliocene in age. E. SAKAWA (1898) reported that Mt. Iino in Sanuki province is independent of the

older volcano. M. YAMAGAMI (1898) made a geological map of the Marugame area in the scale of

1 : 200,000; but did not distinguish the different rocks from one another. D. SATO (1900) in his survey of the sanukite in the vicinity of Sanno, Sakaide City,

stated that there are diabase xenoliths in the sanukitic rocks. T . OGAWA (1898, 1902, 1907) found a kind of conglomerate developed in the small

valley of Ichinokawa in Iyo province and called i t "Ichinokawa conglomerate". He thought that i t is a relic of a Cretaceous valley cut through the crystalline schist and so he regarded the Izumi sandstone as sediments deposited in a more or less narrow, shallow inland sea.

S . NODA and Y . Kozu (1910) in their explanatory text to the geological map of the Matsuyama, wlote on the general geology and geomorphology of Matsuyama district.

H. YABE (1915) from the paleontological basis, inferred that the marine Cretaceous rocks well developed along the northern and southern sides of the island of Shikoku and the adjacent parts of Honshu and Kyushu were deposited in an open sea and he maintained that a t least, there is no data favourable for the opposite assumption by NAUMANN, HARADA and OGAWA.

B. KOTO (1916) made a petrographical study of the sanukite distributed in the Kokubudai district and classified i t into two types, sanukite proper and bronzite andesite.

H. MATSUMOTO (1916) reported on the occurrence of Stegodon orientalzs, Stegodon sznensis, Elephas namadzcus, Bzson sp. and Cervus sp. from the sea-bottom near ShBdo- shima .

T . OGAWA (1919, 1920) wrote on the Tertiary deposits of the Ise district and called the younger Tertiaty sediments the AgC coal-bearing formation.

J. MAKIYAMA (1924) described Elephas trogontheriz PHOLIG dredged from the bottom of the Inland Sea off Shirahama, ShGdo-shima, Sanuki province. At the same time, he listed 18 named species of Mollusca from the Maiko shell bed near Kobe, and described some important species and stated that the age of this fauna is not younger than that of the upper Musashino series.

M. MORISHITA (1921, 1929) stated that the Ishizuchi-yama Tertiary system is distributed in the Inner Zone in the vicinity of Takahama, Matsuyama City, and reported on the relation between this system and the Median Line.

H. MATSUMOTO (1924, 1929) described Loxodonta namadzca naumanni (MAKIYAMA) and Loxodonta namadzca namadz were dredged from the Inland Sea, and stated that i ts age belongs to the mid-Pleistocene.

In 1926, Y. OZAWA in his paper on the primitive elephants from the Setonaikai area and on the sanukite bearing pyroclastic rocks included the Yashima gravel into his namely proposed Setouchi group.

The age, according to H. MATSUMOTO (1924) and J. MAKIYAMA (1924) from their studies on the mammalian fossils from the Inland Sea, is stated by OZAWA to be middle to lower Pleistocene.

S. NAKAMURA (1926) stated that the all of the lake deposits distributed in Nara, Yamashiro, Kyoto and Osaka are older Plesitocene in age.

S. YEHARA (1926) reported on the stratigraphy of the Izumi group in the eastern part of the Sanuki mountain range and cited the stratigraphical sequence as follows, from the lower,

(1) Basal conglomerate (2) Hiketa shale (3) Fucoid sandstone (4) Hashikura shale.

K. AKAGI (1927) in his explanatory text to the geological map of Okayama in the


The Geo1og.y o f Kagawa and Northern Ehime Prefectures 5

scale of 1 : 75,000, wrote that the young sediments distributed in Namigata and Obie, Okayama Pr efectur e , belong to the Tertiary System, because the sediments correspond to the Miocene strata developed in the Shobara district, Hiroshima Prefecture, on the basis of the lithological similarity and the distribution.

H. SATO (1929) surveyed the Kuma district, Ehime Prefecture and described the geological sequence as follows in ascending order, pre -Carbonif erous , upper Paleozoic, upper Cretaceous (Izumi group) , Miocene (Ishizuchiyama group), Pleistocene.

T. OSE (1929) in his study of the sediments of the Chita Peninsula in Aichi Prefec- ture, discovered lake deposits which he called the Tokoname formation and stated that i t belongs questionably to the Pleistocene.

M. SATO (1929) wrote on the discovery of a graphite-schist pebble in the gravel bed at Goshikihama of Awaji Island and discussed the origin.

K. KORIBA and S . MIKI (1931) described Archaeozosma from the Izumi sandstone. T. MIZUCHI (1931) described the geology of the Onomichi area in considerable details. T. KOBAYASHI (1931) reported on an outline of the stlatigraphy of the Izumi group in

the Izumi mountain range. M. SATO (1932, 1935) in his explanatory text to the geological maps of Takamatsu,

Marugame, and Saidaiji in the scale of 1 : 75,000, wrote that the pyroclastic and lava bearing formations are to be defined as the Setouchi series, but does not include the strata from which the primitive elephants were found. This group comprise from the lower, acidic tuff, two-pyroxene andesite agglomerate, basic tuff breccia and from the lower horizon he leported Quercus crzsPula and F a g u s japonzca, but did not mention the geological age. With regard to the position of the primitive elephant, he said that i t belongs to the Pleistocene. He also said that the Yashima gravel is a relic of the alluvial deposits.

T. YAGI (1932) made a petrographical study of the green sandstone of the Izumi group and he described that i ts green color is due to chloritic mineral derived from the crystalline schist (Sambagawa series) .

In 1933, N. IKEBE in his study of the deposits of the so-called paleo-Biwa Lake, di - vided the sediments into two formations. From the lower he reported Stegodon orientalzs OWEN and stated that the horizon is a little younger than that of the AgC formation.

In 1933, T . TAKEYAMA described the Pleistocene gravel deposits developed on the Kibi peneplain and its environs, and said that these gravels are relic of alluvial deposits

At the same time, he wrote on the younger marine deposits of the Okayama district and called them the Namigata and Obie formations and from them reported several marine fossil shells, namely Ostrea sp . , Lzma golzath SOWERBY, L. smzthz SOWERBY, B n l a n u s sp. , from the former, and Cerzthzdea czngzclata from the latter The age is stated to be early Pleistocene.

In 1934, B. YOSHIKI studied the sillimanite deposit in the vicinity of Nagasumi, Kagawa Prefecture, and stated that the granite in the environs of the ore deposit shows schistosity with strike of east-west.

In 1935, S . TOKUNAGA described Parastegodon sugz,yamaz TOKUNAGA from the ter- r estrial deposits near Iruhi of Saida -mura , Kagawa Pr efectur e.

H. KUNO (1935) described the sequence of volcanic activity, and lithic character of the sanukite bearing pyroclastic rocks developed at Kokubudai in Sanuki province.

T . MATSUMOTO (1935) described the stratigraphic sequence of the Izumi group distributed in the Takanawa Peninsula near Matsuyama City.

In 1936, H. SASAI studied the Izumi group which is exposed in the southern part of Awaji Island and established the stratigraphic sequence as follows, from the lower,

(a) Tsui conlgomerate (200m) (b) Minato shale (500) (c) Yo~oizaki sandstone (1400) (d) Shichi


M. Saito

shale (400) (e) Kitaama sandstone and shale (3300) (f ) Nada sandstone and conglomerate (1100) (g) Shimonada fine sandy siltstone (370) (h) Shimonada sandstone (250)

In 1936, T . SHIKAMA studied the Akashi and Harima groups and stated that the former group yields fresh water molluscs, plant remains , and Parastegodon akashzenszs , and from these fossils and the sediments, concluded that the group was deposited in the littoral zone of a paleo-lake and that the majority of the fossils were transported after death.

From the condition of sedimentation he considers that the Akashi resembles that of the paleo-Biwa lake deposits. The conditions of the Akashi become shallow upwards. The geological age of the Akashi is stated to be upper Pliocene or Villafranchian. The Akashi is separated from the Harima with distinct umconformity.

The Harima is a 140 meters thick gravel deposit intercalating the Maiko shell beds, Higashifutami formation and the Nishiyagi formation.

From the occurrence of Palaeoloxodon namadzcus f nom the Nishiyagi formation, he states that the age is not younger than middle Pleistocene.

F . TAKAI (1936) described Parastegodon akashzenszs TAKAI from 0kubo-mura, Akashi district.

H. SATO (1937) in his explanatory text to the geological map of the Niihama sheet in the scale of 1 : 75,000, described the lake deposits and referred them to Pleistocene in age.

K. SUGI (1938) studied the xenocryst in the sanukite distributed in the vicinity of Takamatsu City.

T . SHIKAMA (1943) from the sea-bottom of ShGdo-shima reported on the occurrence of Stegodo~z sznenszs , Parelephas :trogontherzz, Palaeoloxodon namadzcns naumanni, P. namadzcns setoenszs, P. namadzcus yabez, P. aomorzenszs, Sus cfr nzpponicns, and Bzson occzdentalzs. These are considered to have been derived from the Nishiyagi formation. The geogical age is middle Pleistocene according to him.

N. IKEBE (1948) in his paper on the letter nomination of the Japanese Cenozoic stated that the Pleistocene groups of S. NAKAMURA (1926) should be subdivided into different horizons according to area and that the age ranges from Pliocene to Pleistocene.

His subdivision comprises five groups as follows, A - Stegodon elephantozdes, Vzviparus kosananus or the Ag& group B - Stegodon akashzenszs - Tuglans cine? ea - Metasequoia - Gl yptostrobus - Sequoia or the Kuwana

group, Akashi group and the lower part of the paleo-Biwako group and the age is indicated to be 11

C - Stegodon orzentalz s bearing fresh water molluscs and plant yielding group or the upper part of the paleo-Biwako group and the age is 1 2

D - Elephas namadzcus naumannz or the Ha~ima group, Kyoto and Osaka older Pleistocene and is equal to JI

E - Mountain gravel beds or J2

S. Miki (1948) as a result of his studies on the fossil plants recognized seven horizon and gave detail discussions on them. His seven horizons are, in ascending order ,

Pinus t tzfolza bed - lower Pliocene; Metasequoza bed - upper Pliocene; Palzurus bed - lower Pleistocene; Cryptomeria bed - middle Pleistocene; Larix bed - middle Pleistocene; Sapium bed - upper Pleistocene; Aphananthe bed-Holocene

S. TORII (1948) surveyed the Pleistocene deposits in the vicinity of Higashiyama, Kyoto City, and divided them into, from the lower, DGgahara bed, Taniguchi marine shell bed, and Nakanochaya gravel. The geological age of the marine shell bed is stated to be lower Pleistocene.

N. KURATA (1948) summarized the boring data and electric prospecting data from below the Mitoyo alluvial plain of werstern Kagawa Prefecture, and stated that there is a lignite bearing blue silt in the horizon about 100 meters below the ground surface.


The Geo1og.y o,f Kagawa and Northern Ehime Pre,fectures 7

K. SUZUKI and others (1948) surveyed the Agi! group and from the occurrence of Stegodon elephantozdes, fresh-water molluscs and plant fossils stated that its age is early or middle Pliocene in age.

T . SHIKAMA and E. TAKAHASHI (1949) reported on the mammals occurring from Akiyoshi in Yamaguchi Prefecture, and stated that the fauna corresponds to his upper Kuzuu formation in Tochigi Prefecture. The age is stated to be J2 .

M. YAMAGUCHI (1949) in his survey of the sanukite of ShGdo-shima stated that the eruption was during or after the deposition of the lower part of the Setouchi group and before sedimentation of i ts upper part. From the lower part of the group he reports Lzquzdambar formosana and Rosa sp . , and stated that the age is Pliocene.

T . MATSUMOTO (1950) in his petrographical study of the Setouchi volcanic rocks, said that Mt. Iino, Mt. Kiyama, Mt. Kokubudai and others which are composed of sanukitic rocks are not the Mesa or Butte made by erosion but independent volcanos.

K. HIRAYAMA (1950) surveyed the Wakimachi district, Tokushima Prefecture, and described the stratigraphy of the Sambagawa series and Izumi group.

S. MIKI (1950, 52, 53) wrote many short articles on the occurrences of plant fossils, all of which are related to the sequence of the plants younger than the Pliocene in southwestern Japan.

In these paper he reports that Metasequoza occurs from Saida -mura and Sogo-mura in Kagawa Prefecture and from the Ajina basin in Yamaguchi Prefecture.

M. NAKANO and G. IMAMURA (1950) surveyed the Izumi group in the vicinity of Kubo, Nakatado-gun, Kagawa Prefecture, and stated that the Izumi group is thrust over the older Pleistocene gravels and is covered with the younger Pleistocene gravels.

G. KOJIMA (1951) studied on the stratigraphy and geological structure of the Sambagawa metamorphics in central Shikoku and divided i t into from the lower, Nishiiya group and the Yoshinogawa group. The latter group is divided into three subgroups.

H. YO~HIDA (1951) studied the igneous rocks of the neighbourhood of Ishizuchi-yama and gave some descriptions .

H. HIGASHINAKA (1951) studied in Awaji-shima, especially the lignite bearing deposits and found that the sediments amount to 150 meters in thickness and overlie the Izumi group and granite with unconformity. He also reported on the occurrence of Anodonta and other fresh-water shells.

0. FUKUDA and Y. ANDO (1951) listed 11 named species of molluscs from the Takatsukayama shell bed near Maiko. They also emphasized that the boundary between the upper (Takatsukayama bed) and lower (Maiko bed) is a conformity and reported Metasequoza from middle horizon of these strata and from it stated that the age of the Mollusca bearing strata is Pliocene.

In 1951, K. FUJITA and others wrote on the young deposits in the vicinity of Osaka and Kyoto and called these the Osaka group. This group is subdivided into, from the lower, Senriyama formation, and the Ibaragi formation, and from the former they reported on the occurrence of benthonic foraminifers as Nonzon , Bulzmzna , planktonic for aminif er a as Globiger ina , and marine diatoms.

From this data they consider that the previously called lake deposits are marine in their larger part. From the occurx ence of Metasequoia from the Senr iyama for mation, they correlate i t with the Akashi group and state the age to be 11.

R. MORIMOTO and others (1952) in their study of the Osaka and Futagamiyama groups, inferred that the age of the Setouchi volcanic activity in the Kinki region is Mio -Pliocene.

In 1953, K. FUJITA studied the Setouchi supergroup and stated that the strata comprised Metasequoza, all are correlated to the lower Osaka group and considered to be 11 in age.

Y. ANDO (1953) described the molluscan fossils from the Maiko and Takatsukayama


8 M. Saito

shell beds near Kobe City. E. TAKAHASHI (1953) gave a brief outline of the mode of occurrences and the sequence

of the fossil plants in different parts of Yamaguchi Prefecture based upon the works of other authors .

M. NAKANO (1955) studied the Izumi sandstone developed in the Sanuki mountain and stated that the young deposits distributed on its northern flank is probably Plio- Pleistocene in age although no fossils have been found.

T . SHUT^ (1953) made a study on the oita group which he divided into from the lower, Takio formation and the Tsuruzaki formation, and these correspond to 11 and I2 in age. The latter formation represents a aew cycle in marine transgression.

G. KOJIMA (1953) in his study of the structure of the basement of Chugoku and Shikoku, described the distribution and characteristic features of the Cretaceous Hiroshima granite.

T . MATSUMOTO and others (7953) compiled the Cretaceous System in the Japanse Island. K. NAGAI and K. HORIKOSHI (19.53, 1954, 1955) surveyed the Ishizuchi group in the

neighbornhood of Ishizuchi-yama and they divided the group into two formations. J. KATTO and J . NAKAMURA (1954) discovered pollen of Metasequoza, Lzquidambar,

Nyssa and others from the peat bed of Kitano in Saida-mura, Kagawa Prefecture. M. SAITO (1954) in his article on the sequence of volcanic activity, and stratigraphy

of the sanukite bearing pyroclastic rocks of eastern Kagawa Prefecture gave descriptions and discussion in concern to them.

In the same year, M. SAITO wrote on the young sediments distributed in western Kagawa Prefecture and called them the Mitoyo group and from the occurrence of Metasequoza, Sequoza, Pseudotsuga, he correlated i t with the Akashi group.

M. SAITO (1955) wrote on the gravel beds on the Yashima hill-tops, and stated that they may occupy the upper horizon of the Metasequoza bed and be Plio-Pleistocene in age

R . SAKAMOTO (1955) in his study of the Cenozoic rocks in the southern part of Nara stated that the Shirakawa-ike formation and Sabo formaion are contemporaneous and range in age from I1 to 12.

S . KOKAWA (1955) studied the plant fossils from the Sabo formation and subdivided the Shirakawa-ike formation into two parts and stated that there is no break between them, from the lower part Metasequoza occurs and from the upper Menyanthes, Trapa and SczrPus but not Metasequoza. Although the age is not certain, the lower part is taken to be a correlative with the Akashi.

S. YAGI (7955) reported on the plant fossils from Gunchu-cho in Iyo province. Here also Metasequoza besides others occur.

Y. KONDO and others (1956) reported on the discovery of Metasequoza from the Tokoname group in Chita Peninsula, Aichi Prefecture and stated that the age is 11.

H. OZAKI (1956) studied the molluscan fossils from the Namigata formation, Okayama Prefecture, and said that i t should better be referred to the Tertiary than to the Pleistocene.

M. SAITO (1956) in his explanatory text to the geological map of Kagawa, in the scale of 1 : 200,000, described the geological sequence as follows, from the lower,

Ryoke complex; Izumi group; Teshima formation (Miocene) ; Sanuki group (Mio-Pliocene) ; Mitoyo group (Pliocene) ; Yashima gravel (early Pleistocene)

K. NAGAI (1956) made a study on the Tertiary rocks of Ishizuchi- yama which he divided into from the lower, Kuma group and the Ishizuchi group and he reported several plant fossils and two larger foraminifers indicating the Eocene froni the former group.

K. NAGAI (1957) reported on the upper Eocene flora from the Kuma group, in the Ishizuchi range , and described some important species, namely, Nelumbo nippo~zzcnus ENDO and Sabalztes nzpflonicus ENDO.

S . YAGI (1957) from the plant beds near Gunchu-cho in Iyo province, reports on the occurrence of some fresh- water shells.


The Geo1og:y o,f Kagawa and Northern Ehime Prefectures 9

T . KASAMA and K. FUJITA (1957) based upon their survey and the works of other authors, described the geological features of the Setouchi area and discussed about the inter correlation of the Cenozoic strata developed in the Setouchi geological province.

Y. TAKAHASHI (1958) reported on the discovery of Metasequoza from the south of Komatsu City, Ehime Prefecture and named the deposit which yield the fossil as the Okamura formation. He stated that the age is Pliocene and gave a brief account of its distribution.

E. TAKAHASHI and others (1958) called the silt deposits distributed on the sea-bottom of Ube area, the Kusae s i l t ; this measures 100 meters in thickness and is sometimes intercalated with tuff layers Besides fossil crabs it yielded A n a d a r a , Tellzna and Ostrea. Pznus and Tzlza are also recorded from this silt and the age is stated to be Iz. Similar facies occur on the sea coast of Murazaki near Yasuoka in the north of Shimonoseki City.

M. HASHIMOTO and H. KUSUMI (19.58) wrote on the lake deposits developed in Saijo, Hiroshima Prefectune. These are divided by them into two parts, the lower of 30 meters in thickness and intercalated with two or three peat beds, and the upper is ten meters in thickness. These are correlated with the Ekoda stage.

M. ICHIHARA and J. OGURO (1958) surveyed the Akashi and Harima groups and stated that the Maiko shell beds are interbedded in the Akashi group.

C. NAKAGAWA (1958) studied the Izumi group in the upper course of the Shigenobu River in Onsen-gun, Ehime Prefecture. On this occasion from the older Pleistocene beds and from the silt a t the lower of the terrace deposits he found the pollen remains and from an analyses discovered pollen of A l n u s , Pznus , Pzcea, Metasequoza, Fagus, LycoPodzum and stated that they correspond to the Akashi group.

Y. ARAKI (1958) reported on the occurrence of Pleistocene marine fossils from the Mitachi and Konobe formations which unconformably overlie the Pliocene lake deposits known as the AgC group.

S . HANZAWA (1959) described two larger foraminifers from the basal conglomerate of the Tertiary formation of the Ishizuchi mountains, namely Fabzanza casszs (OPPENHEIM) and Discocyclzna sp. .

N. IKEBE (1959) wrote on the distribution of the primitive elephants in the Kinki region and recognized four horizons, these are from the lower,

Horizon I - Stegodon elephantozdes - Hz, Horizon 2 -Stegodon znsignzs sugz yamai, S shodoenszs, S . akashiensz s - 11, Horizon 3 - Stegodon orzentalzs and Elephas namadzcus naumanni - 12, and Horizon 4 - Elephas namadzcus naumannz - Jz

Y . TAI (1959) in his study of the Miocene microbiostratigraphy of West Honshu, reported that the marine sediments are distributed a t Nadazaki -machi, KO jima -gun, Okayama Prefecture, based upon the boring data of a well lowered to 161 meters in depth.

E. TAKAHASHI (1959) compiled on the occurrence of plant fossil, all of which are related to the sequence of the plants younger than the Paleozoic in West Honshu.

Y. ARAKI (1960) studied the geology of Mie Prefecture and subdivided the AgC group into several formations and sedimentary facies. This group, a lake deposit is unconformably superposed on the Miocene and unconformably overlain with marine Pleistocene deposits. The age of the lake deposits is stated to be Pliocene.

S. HAYASAKA and I . IWAI (1960) in their study of the Pleistocene marine fauna of Chita Peninsula, Aichi Prefecture, wrote that the lower Tokoname formation (lake deposit) is unconformably over lain with the marine shell bearing siltstone referred to the upper Tokoname for mation.

M. SAITO and Y. BANDO (1960) studied the Plio-Pleistocene strata of the Inner Zone of Shikoku, and described the geological structure.

M. ICHIHARA, J OGURO and H KINUGASA (1960) studied the loose sediments construct


10 M. Saito

ing the Harima hills in the Akashi district and divided i t into, from the lower, Akashi group and the terrace formation. In the same year, M. ICHIHARA discussed the Plio- Pleistocene boundary in the Kinki district.

M. SAITO (1960) reported on several types of sedimentary structures observed in the Pliocene lacustrine sediments in Kagawa Prefecture.

Median Line, with regard to work on this tectonic line, the following ones are of im- por tance .

Edmund NAUMANN (1885, 1890) was the first geologist to describe the major geological structure of the Japanese Islands. He divided the Japanese arc into four grand parts based upon geological and geomorphological considerations, as,

Southwestern Japan Northeastern Japan Inner zone

Inner zone{ Middle zone

Inner zone('nner Middle zone

Outer zone Outer zone

He called the divisional line between the inner and outer sides of Southwest Japan "Grosse Medianspalte" and said that this line is a fissure and older than the "Fossa Magna". I t is said to be an essential structure of the folded mountain arc. Also he called the Setouchi zone of the outer side of the Inner Zone of Southwest Japan "Trummer Zone" and believed that this "fragmentation" is a geological event of very much later date, because Pliocene agglomerate and tuff breccia are developed on Sh8do -shima , Setouchi district.

T . HARADA (1888, 1890) distinguished in southwestern Japan three longitudinal d i - visions and two longitudinal tectonic divisions.

The former are called (1) the outer and (2) the inner zones of sedimentary rocks and (3) the core zone of gneisses and crystalline schists, and the latter (1) the outer and (2) the inner sides

He described that this Median Line runs almost along the geological boundary between the Izumi group and Ryoke complex in the islands of Shikoku and Awaji, and along the upper coutse of the Tenr yu River in central Honshu.

Further he remarked on the inner side of Southwest Japan, and said that there are developed four volcanic lines, almost parallel to one another and also to the Median Line.

T. OGAWA (1899-1902) drew the Median Line quite correctly, and described that i t was formed a t a much later date than the construction of the general folded structure of the land, preceded the Cretaceous marine transgression and expressed that a t least a part of the line represents a zone of overthrust.

He pointed out the development of imbricate structure due to overthrusts in the Outer Zone of Southwest Japan, as the effect of a horizontal thrust directed from the inner side towards the outer and explained, as did NAUMANN and HARADA, the formation of the Inland Sea as being due to the fragmentaion of the land and the depression of certain blocks.

H. YABE (1915) described that the dividing line between the inner or northern side and the outer or southern side in Southwest Japan is a plane of separation of tectonic origin and to mark the boundary line between the Izumi sandstone and gneiss (including older granite) on one side and the crystalline schists and the lower Chichibu formation on the other and this came first to existence a t the end of the Mesozoic Era or a t the beginning of the Cenozoic.

H. YABE (1917) with regard to NAUMANN'S opinion on the formation of the Inland Sea, wrote as follows,

"The fragmentation of the earth's crust and the subsequent block-movement I believe certainly took place in the reigon now occupied by the Inland Sea; I am doubtful only as to whether th is was the sole agent which took part in the formation of the water basin, that is whether i t was without the association of another action, as for instance the positive movement of sea level.


The Geology o f ' Kagawa and Northern Ehime Pre,fectu~es 11

The positive movement of the sea level can be wholly or at least partly the direct cause, though the present configuration of the water basin was certainly modeled after the pre-existing faults and joints which have rendered the erosion of the encroaching marine water easier

The encroachment of the marine water to a basin may or may not be consequent to the formation of the tectonic basin"

H. YABE (1926) in his paper on the MedianLine of Southwest Japan and its position on the island of Kyushu, emphasized that the date of the first: appearance of the Median Dislocation Line of Southwest Japan is post-Urakawa Epoch (the Japanese Senonian) and pre- Akitsu (the Japanese Paleogene) .

Y. OTUKA (1935) from field evidence stated that the Median Line was developed between the time after the deposition of the Izumi sandstone and before the deposition of the Izumi sandstone and before the deposition of the Eocene formations. It has been active a t least three times, of which the latter two are reverse faults.

$5. YEHARA (1936) stated that there are four activities of the Median Line, the first i s post -Cr etaceous to pr e -early Tertiary , the second is early Miocene, the third is post. Tertiary to pre-Pleistocene , and the fourth is post-Pleistocene.

S. YEHARA (1937) stated that the Izumi sandstone is thrust over the schist along the Median Line and the outcrops are well observed at Yuyaguchi, Tobe, and Inuyose-tBge, all in Ehime Prefecture.

K. KAWADA (1939) stated that the schist and Izumi sandstone are thrust up on young deposits a t Shobudani along the Kino River in Wakayama Prefecture.

R . SUGIYAMA (1939) studied the different rocks distributed along the Median Line in Nagano and Shizuoka Prefectures .

S. TSUBOI (1939) on the basis of SUGIYAMA'S study described that the boundary line between the Inner and the Outer was covered with the Izumi group. He called i t the Median M ylonitization Zone.

K. WATANABE (1939) wrote on the origin of the Median Line in southwestern Japan. T . KOBAYASHI (1941) recognized four activities of the Median Line, differing from

YEHARA'S view in that a Kashio phase may be established in which the Sambagawa-, Mikabu-, zones were invaded by the Ryoke gneiss. He states that the Median Line was completed just after Miyako time.

H. FUJIMOTO (1953) recognized four times of activity of the Median Line. G. KOJIMA (1953) in the petrographical study of the Sambagawa series, described that

the Sambagawa metamorphic zone was formed under the influence of southernly up- thrusting movement of the Ryoke Kratogen, in other words, Sambagawa metamorphism is a type of dislocation metamorphism of relatively large scale. I t seems to him to be meaningless to draw a clear line of demarcation between the Inner and the Outer Zones.

K. NAGAI (1954) stated that the activity of the Median Line differs according to region, especially in western Shikoku there can be recognized three places. The first between Mishima and Ichinokawa, the second between Ichinokawa and Kaminada, and the third between Kaminada and Nagahama. The first has been active to recent time and is a normal fault, and its vertical displacement is the greatest. The second has not moved since the building of the Takano tuff (Ishizuchi group). The third shows evidence of recent movement but its vertical displacement is not as great as that of the first mentioned.

K. NAGAI (1955) classified the alluvial deposits in the east of Ehime Prefecture, and stated that the oldest is probably middle Pleistocene in age and the Izumi sandstone is thrust over i t and is named the Okamura fault. From the distributions of the alluvial deposits i t can be inferred that the fault has been recently active.

T. SAWAMURA (1955) from seismic records and crustal movements during the Nankai Earthquake of 1946, assumed that the Median Line passes near the north of the Yoshino Biver bridge in the north of Tokushima City.


12 M. Saito

K. NAGAI (1958) stated that there are four activities of the Median Line in Shikoku. The first i s post -1zumi pre-Kuma (Ichinokawa phase) , the second is post-Kuma pre- Ishizuchi (Tobe phase) , the third is early Pleistocene (Niihama phase) , and the fourth is Holocene (Shobudani phase).

11. Geology sf the Inner Zone of Shikoku

The area in which the geology was studied extends from the southwestern part of Matsuyama City in Ehime Precture, northeastwards along the northern foot of the Ishizuchi and Asan mountains, via Niihama City in the same Prefecture to Sambonmatsu City in Kagawa Prefecture through Mishima City in Ehime Prefecture and Kanonji City in Kagawa Prefecture. This covers a distance of about 200 kilometers in east-northeast to west -southwest direction and a breadth of about 30 kilometers in maximum, thus the area is more or less in belt form.

For the sake of descriptions as well as of the development of the different formations, this belt -like area is subdivided into several provinces as , 1 ) Matsuyama Province, including the area from the environs of Matsuyama City northeastwards to near the Nakayama River in Shus6-gun, Ehime Prefecture ; 2) Niihama- Saijo Province, extending from the Nakayama River just mentioned, east -nor theastwards to Iyo-Mishima City ; 3 ) Mitoyo- Nakatado Province, extending from Iyo-Mishima City northeastwards to the Doki River in Kagawa Prefecture, and 4 ) Eastern Province, which includes the area from the Doki River east -northeastwards to Tomita in Okawa -gun, Kagawa Prefecture . Descriptions of the paleo- lake deposits will be undertaken according to each respective province.

The stratigraphical relationship between the Sambagawa metamorphics and the Ryoke complex and the granite remains unknown owing to their areas of development being different, the latter two being in the Inner Zone of Southwest Japan and the former in the Outer Zone of the same region. The Izumi group unconformably covers both the granite and Ryoke metamorphics, but not the Sambagawa metamorphics. The granite has intruded the Yamaguchi group. Although the direct relationship of the Sambagawa to the other two remains unknown, the general descriptions are given because they form the foundation of the present area. The descriptions of the different rock units are given in the following lines.

A Sambagawa Wetamorphics

Although the stratigraphical relationship of the Sambagawa metamorphics to the Ryoke complex, younger granite and the granodiorite remains unknown, their development a s the foundation rocks in the studied area is important, and the description now follows

The Sambagawa metamorphics with the type locality in the Sambagawa valley of the province of Kozuke in the Kwanto district of central Japan is a name applied to the crystalline complex developed there. Since i t is generally believed that the crystalline schists in Shikoku is closely connected with those of Kii, Chubu and the Kwanto districts the name is also applied to similar rocks distributed in the present district The Sambagawa system or metamorphics as they may be called include in the present area black schist and green schist, the latter in a position lower than that of the former .

The green schist is very compact, well indurated and shows excellent schistosity with a general trend of east-west and dips towards the north a t above 30'-50" This schist i s developed in the southern part of the Shikoku mountain range especially in the Matsuyama and Niihama-Saijo p~ovinces. It i s distributed parallel with the Median Line and extends from the western sea coast i n the Matsuyama province, northeastwards to the south of Komatsu City in the Niihama-Saijo p~ovince , where i t is overlain with black schist

The black schist is mainly graphite schist with good luster, rather soft, showing schistosity with a general trend of east-west with northward dips of about 30-50 degrees similar t o those of t he green schist This schist i s developed in the northern half of the Shikoku mountain range extendnig


The Geolog,y o,f' Kagawa and Northern Ehzme Pre,f'ectures .13

from the south of Komatsu City northeastwards to the south of Mishima City in the Niihama-Saijo province. In the farther south of the black schist there is developed the green schist and on i t s southern side again the black schist appears, because there is developed an anticlinal structure

In the Matsuyama province the green schist with approximately east-west trend and northward dip

Table 1 , Stratigraphic Classification of the Rocks distributed in the Present Area

Age 1 Group 1 Formation Predominant Lithofacies 1 Thickness

Pleistocene

-. - . - ..

L " ~ ~ p ~ ~ ~ ~ a c e I Gravel, sand and clay 1 l0m

Hig2:b2::ace I Gravel, sand and tuffaceous clay 1 10-15m Unconfor mity

Yakeotoge gravel 1 Gravel and granule sand 1 20-50m Unconfor mity

Kawauchi

Taman

Upper member : granule sand, pebbly gravel 30-50m

Lower member : alternation of sand and silt 1 O m

mity

Sanuki

Sanukite lava Hornblende andesitic and pyroxene andesitic

agglomerate unconformity

Compact white tuff Biotite dacitic tuff breccia Conglomerate and stratified sandy tuff

Unconf or

Kokubudai

Local

Oda

loom(+)

50-100m

Miocene

Eocene

Tonosho

Kuma

Local unconformity

Yashima / Basic tuff and tuff breccia 1 50m

Unconformity

Shikai 1 Alternation of coarse- and medium grained sandstone 1 40-80m

Late Cretaceous

Paleozoic

30-50m Ikisue

Unconf or mity

Myojin Alternation of sandstone and mudstone / Conglomerate I 4mm

Alternation of sandstone and calcareous Nimyo sandstone 1 300m

Basal conglomerate Unconformity and thrust fault

Alternation of granule sandstone and siltstone intercalating three or four thin lignite layers

Basal conglomerate

I Muya 1 Alternation of sandstone and shale 1 1600m

Izumi

Osakagoe I Alternation of sandstone and shale intercalating conglomerate and tuff layers 1 2000m

1 Massive mudstone~predominant, with strati- Hiketa fied shale 1 2000m

Tsubasayama I Medium-grained sandstone intercalating thin mudstone and thin conglomerate layers 1 30-300m

Shiroyama I Ar kose sandstone and conglomerate 1 100-3OOm

Unconfor mity

Ryoke complex

Hornblende -biotite granite, biotite granite, granodiorite , gneissic granite, mica-schist, banded gneiss, hornfels, unaltered Yama- guchi facies of clayslate, greywacke, chert, schalstein

Stratigraphic relation uncertain Sambagawa metamoIphics I Black-schist (mainly graphite-schist) and

green -schist (mainly chlorite -schist)


14 M . Saito

makes about five to six anticlinal and synclinal structures and on the southern side of this folding structure there is distributed the black schist, which is situated above that of the green schist. The general trend of the axis of the mentioned anticlines and synclines i s parallel with the general trend of the schistosity Near the boundary of the Matsuyama and Niihama-Saijo provinces, the green schist has developed about five to six anticlines and synclines also with east-west trends and on the southern side of this folding structure there is developed the black schist also in a stratigraphic position higher than the green schist In the Niihama-Saijo province there is developed only a single very large anticlinal structure having the same trends a s the schistosity of t he schists and on i ts southern side is distributed the black schist

The northern limit in distribution of the green schist in the Matsuyama province is defined by the Median Line, whereas in the Niihama-Saijo province the northern limit in distribntion of the black schist is also the Median Line and the Pliocene lacustrine deposits These schists are in contact with the Izumi group in the larger part of their distribution and with the lacustrine deposits just mentioned only in a small portion

In the Niihama-Saijo province, the black schist i s cut by the Shimona-Tsuneyama fault which trends almost east-west and dips towards the south a t 45 degrees, being a thrust from the south Along this fault there are found several intrusions of dolerite In the same province, the black schist is cut by the Ryudzan fault which trends in northeast-southwest direction and with dips of 80 degrees towards the west ; this is a normal fault not associated with intrusive igneous rocks The exact dating of these two faults is difficult to determine, but i t can be said that both were developed before one of the movements of the Median Line, but which of the movements is difficult to determine

Since the extension northwards of the Median Line of both of the faults cannot be determined in the field from structural evidence, i t may be considered that they were associated or had relation with the folding structures which they cut and were developed a t an early date. Their date of development may be after the deposition of the Cretaceous Izumi group

B . Yamaguchi Group

The stratigraphical relationship between the Yamaguchi group and the Sambagawa metamorphics i s unknown because no contact between them has been observed by anyone in the field On the other hand the relation between the Yamaguchi group and the Ryoke metamorphics can be observed in the field, and the latter are only the metamorphosed facies of the former, and without superposition This metamorphism is related to granite plutonism, accompanied of intense granitization. The metamorphosed zone extends in the south of t he longitudinal axis of the Setouchi Sea and in the northern side there is distributed the Yamaguchi group

The Yamaguchi group consists of nearly 4000 meters thick clayslate with intercalated layers of schalstein (about f ive) , each of which measure from 100-500 meters in thickness The general trend of the group is N 60"-80" E with dips of 50"-80" towards the NNW as measured in the vicinity of the Kojima Peninsula in Okayama Prefecture, and in the vicinity of northwest of Shddo-shima in Kagawa Prefecture. Elsewhere in the distribution of the Yamaguchi group measurements have not been made for the strike and dip but the general trend is east-west with northward dips although sometimes with southward dips. There is developed in the Kojima Peninsula an anticline with axis trending east-west with the wings dipping a t 60 80 degrees to the north and south respectively.

C . Ryoke Metamorphics

The Ryoke metamorphics are the metamorphosed Yamaguchi group rocks and consist of brownish- I ed mica-schist, banded gneiss, blackish purple hornf els, grayish white quartzite, and in part with milky white crystalline limestone These have a general trend of nearly east-west and dips to the north and to the south according to places The distribution of the metamorphic rocks is rather patchy. These rocks ar e distributed along the coastal regions of Ehime and Kagawa PI ef ectures The most intense degree in metamorphism is along the coastal areas of the two Prefectures

In the Matsuyama province, the Ryoke is distributed from Matsuyama City in the west via Fukumiyama eastwards to Tambara-cho, trending roughly in east -west direction with northward dip of 40-60 degrees ; i t s width is about two kilometers and is distributed in belt form. On i t s northern side is developed the granite which is related to the Ryoke metamorphic rocks and on i ts southern side is distributed Izumi group, which is not altered In the islands offing the Takanawa Peninsula


The Geo1og.y of' Kagawa and Northern Ehirne Preftctures

the Ryoke has strikes of east-west with northward dip of about 50 degrees. In the Niihama-Saijo province the Ryoke metamorphic is distributed on 8-shima(island), where

the strike i s east-west with northward dip of 50 degrees The mica-schist in this island has on i ts southern side the distribution of granite, which is the eastern extension of the granite mass mentioned in the Matsuyama province

In Kagawa province, the Ryoke metamorphics are distributed on the islands offing the coast and along the coastal area, and the granite i s developed on both northern and southern sides of i t . In the island of ShBdo-shima, where a t Yasuda, Uchinoumi-cho, the Ryoke metamorphic measures about 400 meters in thickness and consists of mica-schist, quartzite and hornfels and the diabase has been observed a t Kuroiwa, Tonosho-cho in the same island. The strike is east-west with northward dip of 60 degrees. In the Shioaku islets offing the coast of Kagawa Prefecture, the Ryoke shows a general strike of east- west with northward dips of about 60-70 degrees, and a t places as on Ushi- jima t h e Ryoke dips at about 50 degrees to the south Here the rocks consist of mica-schist, hornfels with subordinate crystalline limestone on Shishi-jima Mica-schist of the Ryoke has also been observed on the eastern side of Kiyama hill in the south of Sakaide City in Kagawa Prefecture. The strike is east -west with northward dip of 50 degrees At Nagasumi, Manno-cho, Kagawa Prefecture, the1 e is exposed hornfels with strike of east-west and is intervened in granite; it carries sillimanite ore.

The Ryoke metamorphics are thought to have been developed as a result of granite plutonism, accompanied of intense granitization, probably beginning from and during late Paleozoic according to KOJIMA (1952), and is thought to have intimate relationship with the orogenic phase which occurred before the deposition of the Carnic Mine series and after deposition of the late Permian Akiyoshi limestone group. On the other hand, T KOBAYASH~ (1941) stated that the Ryoke metamorphics were developed during the Jurassic-Cretaceous associated with the Sakawa orogeny, and he considers the Akiyoshi orogenic phase to be late-Paleozoic to early Mesozoic in age , for which there seems to be no direct field evidence. The writer considers the development of the Ryoke metamorphics associated with the Akiyoshi orogenic phase and to be post-late Permian and pre-Carnic to be in

age

D. Granite

The granitic rocks intimately related to Ryoke metamorphic rocks comprise hornblende-biotite granite, biotite granite and granodiorite These granitic rocks are distributed throughout the four provinces distinguished in this article, being developed particularly in their northern parts, in the islands offing the coasts of Ehime and Kagawa Prefectures and in the southern half of t he Setouchi area Within this area of distribution of the said granitic rocks there are found fine grained granite and porphyr itic granites intruding the aforementioned granites Aplite and pegmatite are found in association with older granites along the eastern coast of Kagawa Prefecture. Diorite in the form of stocks and dikes intruding the older granites.

There is another granite mass which has intruded the two different ones above mentioned This i s found in the northern half of the Setouchi area and in the southern half of Chugoku district and is considered to be Cretaceous in age according to G KOJIMA (1952). This intrusion is the largest one of batholithic type in Japan The one which is related to the Ryoke is called the Ryoke granite and i t s age of intrusion is considered to be post-Paleozoic to pre-Izumi in the present area, but when viewed from a broader area, the age of intrusion is post-Paleozoic to pre-Carnic.

The Ryoke granite i s characteristic in showing the development of schistosity with almost east- west trend, and according to M. MORISHITA (1934) the granite in the Takanawa Peninsula also shows east-west trend of i ts schistosity. According to B YOSHIKI (1934) the granite exposed a t Manno-cho, Kagawa Prefecture also shows east-west trend of its schistosity, and that this direction is in agreement with that of the Median Line.

Measurement of the joints of the granite in the marginal portions of the Pliocene lacustrine d e - posits a t Manno-cho and Kotohira-cho both in Nakatado-gun ; Kagawa-cho in Kagawa-gun ; Aji-mura, Kida-gun; it was found that ENE-WSW and NNW-SSE directions are developed. The dips are generally about over 60 degrees. Unconformably overlying the Ryoke granites just mentioned are the Izumi group with basal conglomerate or basal arkoses, the Miocene Tonosho group, the late Miocene Sanuki volcanics, the Pliocene Mitoyo group and the Pleistocene deposits, according to areas a s will be mentioned in later pages


Table 2: Correlation of the Cretaceous Deposits In the Izumi Belt (After T.MATSUMOTO, K.TANAKA, M.NAKANO and H .MATSUWO, 1952)

Takanawa Peninsula

(Near Matsuyama) (T.Matsumoto, 1950 em.)

6500m.

Age

a g 6 .i a -

Sanuki Mountaln -Range

(West) (M.Nakano. 1951)

9 4 h

Shimonada white sandstone (200) * -- Shimonada fine sandy siltstone (300) (Ia,Ih , Ps)

Nada ss. + cgl . (800 ? !

- Kitaama ss. +sh.

sh.>ss. ss .=sh. (tf) ss .>sh . (Isk)

(ca. 3300)

W

, - &'

2

$

; h

Hiketa sh . (Ib, Pe)

7!?

(ss.>sh.) !- I 2 Minato sh. ss. (500) (Ism, Ib , Ba) (500) i

Areas (Authors) -

m s , s - 6 $?G C n

Abbreviation - cgl : conglomerate, ss - sandstone, sh shale, tf - tuff , * : marine fossils, x - plant fossils, Ia : I?eoceramus awaje'ens~s, Ib - Inoc.baltzcus, Ih : Inoc. hetonazanus, Isk : Inoc. shikotaenszs, Ism - Inoc. schrnzdti, Pe I Pachydiscus aff. egertoni, Pk : Pachy. kobayashii, Ps: Pachy, subcornpressurn

1 sh. $if t f .

ss. +sh. (ss.>sh.)

(Wedge-form)

sh .+ss . / (sh.>ss.)

cgl. +ss. (275)

8 1 5

i-z

Sanuki Mountain - Range

(East) (S.Yehara em. K . Hirayama, 1950)

--

Awaji Island (Southern Part) (H. Sasakl, 1936, em. K. Tanaka, T . Matsu- moto, and Y. Maeda, 1951)

--

Not yet identified

.................................... Muya ss. +sh.

Osakagoe

ss. t s h . +cgl.

(ca. 2000)

Tsul cgl. / cgl. +arkose (200) i c loesoo)

....................................

Sanukl Mountain - Range

(Central) (M.Nakano, 1951)

--

Thickness

i --- I

1 sh . (700) I (Ib)

! ss .+sh. sh . i (ss.>sh.) ( ~ b ) (1500)

sh . +ss. * 1 (sh.>ss.) (600)

1

1 cgl. I ................................................................................................................................................

/ Granodiorite and Underlying / quartz-porphyry Granodiorite

>4600m. 7000m.

White sandstone (700)

sh . +ss . (250) (sh . >ss . ) (Ba)

W -

ss. +sh. (630) (sh<ss)

Tuf faceous ss. (200)

ss. +sh. (650) (ss.<sh.)

ss. +sh. (1330)

(e) sh. +ss. with 1 .z t f . (400) (Ib) I m

( d ) s s . + s h . ( 5 0 0 )

(c) sh . +ss. (500) (sh.>ss.) 4 I 0

(b) Banded ss . (1 100) (a) cgl. +ss. (500) 1 (Ism) i? ......... Granites and meta-

i'..."".: Granitic rocks I Granitic rocks

ca. 6000m. I I

( s s .>s~ . )

morphlc group 1 I

(ss.>sh.) (1900) 1-1- I s ? -

Not yet identified

....................................

ss. +sh.

(i) Fine-sandy * siltstone (300)

(h) ss. +cgl. (850)

(g) sh . with ss .

and t f . (450)

(f) ss .+sh.

-- , - .- -. 1 E l

IK 9 .d

m

5 4 a 3

.s 3 .- c z


The Geolog,y o,f Kagawa and Norther% Ehime Pre,fectures

E Izumi Group

The Cretaceous Izumi group is subdivided into five formations all of which a re developed in the areas studied by the writer. These formations are all distributed in east-west directiox and show homoclinal structur e dipping towards the south and form a modified syncline near t he southernmost margin of the belt. The syncline generally pitches eastwards but the distribution of the strata i s particularly repeated in the Sanuki mountain raage owing to faults of NNW-SSE trends

T h e Izumi group is distributed in the northern and southern sides of the Pliocene deposits in the Matsuyama and the Niihama-Saijo provinces, but elsewhere the Izumi group occurs only on the southern side of the Pliocene lacustrine deposits

Although the Izumi group consists of f ive formations, owing to that the present work is concentrated to t he lacustrice deposits, t he Izumi group i s subdivided into two parts, each representing two cycles, the lower three forrnations given in the Table 2 , indicate the first two cycles. and the upper two a re included into the upper two cycles Descriptions will be given from the lower to t he upper Here i t must be added tha t although i t had been considered that the five formations of the Izumi group a re developed throughout t he distribution of the group, i t is found that the upper half of t he Izumi group in the Niihama-Saijo province has not been classified into the two cycles representing i t s upper half as found in other areas Whether a part of the Izumi is missing in this area due to subsequent erosion and to fault displacement or whether the original strata were only thinly deposited is difficult to determine Further since the type localites of the five formations making the Izumi group are situated outside of the studied ares of the writer, details concerning type locality, lithofacies and other features will be omitted and the stratigraphic names will be employed in the sense of the Committee on the Cretaceous Stratigraphy of Shikoku (1953)

E - I Shcroyama Formation (named by NAKAGAWA, 1960) This for mation unconf or mably over lies the Ryoke metamor phics and granites and is estimated to

measure about 100-300 meters in total thickness This formation consists of arkose sandstone and conglomerate The conglomerate in this for mation comprises pebble to cobble size, subrounded chert , slate, Ryoke granite, hor nstone, quartz-porphyr y cemented with arkose sandstone This i s typically developed in t he areas where granitic rocks are exposed, or throughout all of the four provinces This conglomerate measures about 5 to 200 meters in thickness and unconformably covers t he granite Although of the same horizon the conglomerate is sometimes replaced with arkose sandstone such as in the vicinity of Shionoe and tha t of Kasuga in the Eastern province This measures about 10-50 meters in thickness and unconformably covers granitic rocks, but i t s boundary i s indis- t inct , being a blended unconformity A t S a i ~ a 1.1 the Mitoyo province, t h e formation commences with black shale without t he development of conglomerate or arkose sandstone ; this shale measures about 5 to 10 meters in thickness In this area i t may also be said that the formation is represented by a n alternation of sandstone and shale instead of conglomerate or arlrose sandstone

Thus i t may be noticed that the Shiroyama i s variable in i ts lateral facies, being of conglomerte, arkose sandstone or black shale, the latter of which represents the original land surface a t t he t ime of marine transgression of the Izumi group

In t he vicinity of Shionoe the arkose sandstone i s i n fault contact with t he granitic rocks and the boundary is extruded with trachyte andesite for a distance of about two kilometers This trachyte andesite is in dike form Trcgonza laponica YEHARA and Ostrea sp have been found by YEMARA from the basal member

E - 2 Tsubasayama Sandstone The type locality of the Tsubasayama sandstone first named by C NAKAGAWA (1960), is in t he

northwest of Tsubasa- yama, Hiketa-cho, Kagawa Prefecture This for mation conformably overlies t he Shiroyama and is estimated to measure about 30 meters to 300 meters in total thickness.

This sandstone is gray-greenish and consists of fine to medium sand graines Sometimes the thin mudstose layer and the conglomerate layer are intercalated

Pleuograrnatodon splendens ICHIKAWA and MAEDA, Steznmannela(Setotrzgonra) s/~inol~araz KOBAYASHI and AMANO, and Znoceramus baltzcus BOHM have been found by NAKAGAWA from th is formation

In the small valley of Gesho, Miki-cho, Kagawa Prefecture, there was observed alternating layers of bedded sandstone with intercalated thin dark sha!y layers These alternating layers of sandstone were found to be graded and to form many cycles, each of which is incomplete i n lacking lutite deposits which occur in the uppermost in a complete graded deposit They were also note-


18 M. Saito

worthy for the many interesting structures they preserve such as many problematica resembling burrows of marine annelids, soft rock pebbles and fragments, strings and slices of dark coloured lutite, very small scale cross-laminations, apparent flowage sands and distortions within the graded deposits themselves These sandstones consist of graded deposits due to turbidity currents and therefore comprise turbidities As many be readily noticed from the outcrop along the Doki River below Nakato, Kotonai-mura, Kagawa Prefecture, which shows abundant oyster shells incorporated in turbidite, the origin of the turbidity currents was shallow water near the coast

E- 3 Hiketa Shale This formation conformably overlies the Tsubasayama and is estimated to measure about 2000

meters in total thickness. This formation consists of an alternation of sandstone and shale, with the latter rock being most dominant and partly massive The layers are about 30 centimeters and one meter for the sandstone and shale respectively, thus making a muddy flysch-like deposit. In the upper part of the formation shale becomes dominant and sometimes a layer of green, rather coarse grained tuff layers about two meters in thickness i s intercalated Fossils are sporadically found in the lower and upper member of this formation. The important species are Inoceramus balticuc BOIIM and Bostrychoceras cf . awalzense (YABE) (after NAKAGAWA 1960)

E - 4 . Osakagoe Formatzon This formation comprises an alternation of sandstone and shale with thin conglomerate and tuff

totalling about 2000 meters in thickness The sandstones are medium graines and yellowish brown, while the shales are black Archaeozostrea, and Inoceranms occur. This formation is conformably superposed upon the aforementioned stratigraphical units I t is conformably overlain with the Muya for mation.

E - 5 , Muya Formatzon This formation consists of an alternation of sandstone and shale amounting to about 1500 meters

in thickness. It can be subdivided into the following members in the central part of the Asan range according to NAKANO (1953), but is not divisible in the eastern and western parts of the range.

E - 5 a Lower Member Sandstone is more predominant than shale, estimated a t about 600 meters in thickness.

E - 5 6 . Middle Member Shale predominates over sandstone and is measured to be about 250 meters thick E - 5 c . Upper Member This consists of white-gray sandstone measuring more than 700 meters in thickness The formation is not developed in the Niihama-Saijo province but occurs all of the others Every-

where i t i s conformable with the underlying Osakagoe for mation, and is unconformably covered with the Kuma group in Ehime Prefecture The Muya is devoid of fossils so far a s i s known, but from a stratigraphically higher horizon in Awaji Island in the Setouchi Sea, such fossils as Inoceramus and Pachydzscus have been found Thus i t is evident that the Muya does not represent the highest part of the Cretaceous in this area

Of the metioned five formations, the first two have been referred to the first cycle, the third formation to the second cycle, the fourth one to the third cycle and the five one to the fourth cycle, according to the classification of T M n r s u ~ o r o (1953)

In the Matsuyama province the Izumi group is separated into two areas of distribution by the Shigenobu River flowing from east to west in the central part In the northern part of the river, the Izumi group unconformably overlies the Ryoke metamorphic with eastnortheast-westsouthwest strike and dips of 30-50 degrees to the south But in the vicinity of Matsuyama Castle, the Izumi is i n fault contact with the granitic rocks and the strike is N 70° E and the dip is 40' N. In the southern slope of the northern area there is developed the Yamanouchi syncline whose axis trends in eastnortheast-westsouthwest and the wings dip a t about 30 degrees toward the north on the southern side and a t about the same angle towards the south on the northern side This syncline extends from the Sasage-toge in Tambara-cho in the northeast, to Sone in Iyo City in the southwest In the southern side and parallel with the Yamanouchi syncline there i s developed a small anticline called the Hodono anticline This trends in parallel direction and its wings dip a t abut 45 degrees on both sides Near the central portion near the boundary between the northern and southern sides the dip of the strata becomes a s low as about five degrees towards the south

In the eastern part of the southern side of the river there are developed several anticlines and


The Geolog,y of Kagawa and Northern Ehirne P~ef'ectures 19

synclines having the same trend of east-northeast-west-southwest and with general dips of wings of about 40 degrees According to NAKAGAWA (1957) there are developed in this area numerous normal faults with north to south trends by which the area i s cut into many blocks However, the writer failed to observe such features

At Inuyose-toge in Iyo-gun the Izumi group is thrust over green schist with strike of N 40"-55" E and with dips of 40" N, and here the Izumi near the contact i s a pseudoconglomerate measuring about 4 - 5 meters in thickness At Tobe-cho in Ehime Prefecture the Izumi group is thrust over a thick conglomerate of the Eocene Kuma group and the boundary is a five to six meters thick tectonic conglomerate The strike is N 45' E and the dip is 45' N Eoth are typical thrust faults of large magnitude.

In the Niihama-Saijo province granitic rocks are exposed along the coastal area over which the Izumi is superposed unconformably The strike of the Izumi is ENE-WSW with dips of 35 degrees to the south. In the eastern half of this province the Izumi shows rather simple homoclinal structure and comes into contact with the Median Line, where the strike is ENE-WSW with dips of 30-45 degrees towards the north However, in the western half of this province, the Izumi is bounded in i t s southern side by the Median Line, on i t s northern side by the Okamura fault , and within this about three kilometers wide belt, the Izumi shows several small anticlinal and synclinal folds The northern side of the Okamura fault shows the development of the Pliocene lacustrine deposits

At Yuyaguchi in Tambara-cho the Izumi rides over the green schists and the fault plane strikes almost east-west and the dip is about 20 degrees towards the north In this area the Izumi group has a strike of N 70" E with 50" S dips, and the green schists strike N 40" W and dip a t about 40' N

In the south of Saijo a t Banya, near Ichinokawa, the Izumi is thrust over the graphite schist, the fault plane shows a strike of N 70' E and with dips of 40" N, whereas the Izumi strikes almost the same as that of the fault plane and i t s dip is also similar, but the schist strikes east-west and dips a t 30 degrees towards the north

The northern side of the Izumi in this area is everywhere cut by the Okamura fault which has a strike is about ENE-WSW but in the south of Himicho the dip is 80 degrees towards the north and appears like a normal fault, but in the south of Okamura the dip changes to about 80 degrees towards the south appearing as if a reverse fault From the changes in dip angles of the Okamura fault i t appears as if this represents a rotational fault and not a simple normal or simple reverse fault This fault is a reverse fault according to K NAGAI (1955)

In Kagawa province the Izumi group is distributed on the northern side of the Median Line and is unconformably supe~posed upon the Byoke granites and shows a general strike of ENE-WSW and the dip is about 30-40 degrees towards the south Along the southern margin of distribution of the Izumi group especially immediately north of the Median Line there is developed a synclinal structure with general trend of ENE-WSW of i t s axis and the wings dip a t about 40-50 degrees This syncline, called the Iwakurayama syncline extends parallel with the Median Line, and the syncline axis pitches a t about 5-10 degrees towards the east As the result of north to south trends but with deviations to both east and west, the syncline has been cut so that i t s strata show repetition several times in east-west direction.

In the western part of the northern margin of the Izumi group in this area, i t s shows a strike of ENE-WSW and dips a t 40-50 degrees towards the south and is thrust over the Pliocene lacustrine deposits Ten to 20 centimeters thick fault clay is developed along the fault plane In the south of Zota in Kotonami-mura towards the eas t , the thrust fault extends into the Izumi group and i t s continuation is difficult to trace in the field because of the homoclinal structure The thrust faul t extends from Icawauchikami in Yamamoto-cho in the west, eastwards to Zota, from where i t s farther eastward extension is in the Izumi group a s already mentioned

In the southern part of distribution of the Izumi group, i t rides over the Pliocene lacustrine deposits with thrust fault of the Median Line According to IMAMURA and NAKANO (1953) this fault inclines a t 30 degrees towards the north and thus extending down under the Izumi group This was called by them the Shibafu thrust fault

F. Kuma Group

According to NAGAI (1954, 55), the Kuma group consists of two formations, the lower is named the Nimyo and the upper the Myojin, and these will be described from the lower Here i t may be added that the Kuma lies on the Izumi group with clino-unconformity and also on the Sambagawa


20 M. Saito

metamorphics The group is distributed only in the vicinity of the Ishizuchi mountains F - I . N i m yo Formation This formation consists of basal conglomerate followed upwards with an alternation of sandstone

and calcareous sandstone, measuring about 300 meters in total thickness In the conglomerate are found pebble to cobble size, breccia in the lower part and rounded in the upper of graphite schist and green schist derived from the Sambagawa metamorphics The fossils reported from this for - mation are such as Fabzania cassis (OPPENHEIM), D Z S C O C ~ C ~ Z ~ ~ sp , and calcareous algae, thus indicating its Eocene age. The distribution of this formation is the environs of Kamibayashi in Onsen- gun, Iwayadera in Kamiukena-gun and Shimosakabatoge in southwest of Kuma-cho, all in Ehime Prefecture

F - 2 Myolin Formatzon This formation conformably overlies the Nimyo and comprises conglomerate and an alternation of

sandstone and mudstone, amounting to about 400 meters in total thickness.. The conglomerate consists of pebbles and cobbles, well rounded, and derived from the Izumi group, granite, and Paleozoic System. They comprise sandstone, granite, hornfels, quartzite, mica-schist, chert and clay -slate. Fossils as Sabalites, Lrquidambar, Nelumbo and others have been reported and the age i s considered as upper Eocene, while the underlying Nimyo is middle Eocene from the foraminifers. The distribution is wider than the underlying Nimyo and is in the environs of the Saragamine, Aotaki mountains.

The Kuma group lies clino-unconformably upon the folded and truncated Izumi group The strata of the Kuma group are almost horizontal in general but in the northern part they dip southwards, in the south they dip northwards and with a ENE-WSW axis they show gentle synclinal structure In the northern part the Kuma group is over riden with the Izumi group by a thrust fault of the Median Line, the dip of which is about 40 degrees towards the north and the general strike of this fault is N 45" E.

The sea which deposited the Eocene Kuma group is thought to have invaded the area from the north and west into a depressed area bounded on the eastern and southern sides by the Sambagawa crystalline schists, but not on its northern and western sides I t is considered that deposition took place in a depressed area of trough like nature parallel or roughly so with the Median Line

G . Tonosho Group

The Tonosho group of Miocene age is a name here newly proposed for the deposits distributed extensively in the north of Tonosho-cho, ShOdo-shima and which can be divided into two stratigraphic units, the lower of which is here designated as the Ikisue formation and the upper or Shikai formation which is redesignated and redefined Both formations are conformable with one another but of different facies, the lower being brackish to lagoonal whereas the upper is typically marine and yields many marine shells The 'Tonosho group shows no direct contact with the Eocene Kuma group, but since its age is Miocene, i t is considered that the relation is one of unconformity. The Tonosho group is superposed upon the Yamaguchi group of Paleozoic age and also the Ryoke granite with remarkable unconformity and is overlain by the Sanuki group with unconformity The total thickness of the Tonosho is estimated to be about 100-150 meters, of which the Ikisue occupies about 30-50 meters and the remaining consists of the Shikai formation

G -1 Ikisue Formatzon The Ikisue formation with its type locality along the road leading from Ikisue to Oe in Tonosho-cho

(Pl. 3, Fig 1) . In this type locality the formation lies upon the clayslate of the Paleozoic Yamaguchi group with angular unconformity upon which i t i s thrust up in part The basal conglomerate of the formation comprises pebble size rocks, rounded of granite, quar tz-porphyr y , subangular clayslate in a matrix of arkose sand, the thickness being about one meter This is superposed with a 10 meters thick arkose sandstone which is cross-bedded, 1 5 meters thick gray siltstone, 10 centimers thick lignite, two meters thick siltstone, 10 centimeters thick lignite, 15 meters thick arkose sandstone in upwards succession and totalling 30 meters in thickness The formation i s distributed in the northwestern part of the island

In the vicinity of Umagoe-hama and Hidoyama, the lignites become thick and attain about 30-50 centimeters in thickness and three layers of about 30-50 centimeters thick bentonitic clay layers develop No other changes are noticed in the lithology

Plant fossils were collected from the lignite layers exposed in sea cliff in the northeast of Nagahama, Tonosho-cho ; these comprise Metasequoia dzsticha MIKI, Cinnamomum lanceolatum HEER,




The Geolog,y q f ' Kagawa and Northern Ehirne Pref 'ectu~es

Comptoniphyllum sp. , Sasafras sp , Quercus sp (ever green). (P1 15, Figs 1 - 6) . G - 2. Shzkaz Formatzon

The Shikai formation is here designated a s the sandstone and siltstone of marine origin which covers the Ikisue formation with conformity and has i ts type locality in the cliff in the northeast of Nagahama, Tonosho-cho, and does not include the brackish water or lagoonal facies referred to the Ikisue formation a s done by previous workers Thus the name is restricted to the marine facies The formation commences with a one meter thick light gray fine grained sandstone with sandpipes, a two meters thick gray coarse grained sandstone with calcareous concretions and fragments of Ostrea and other molluscs, a one meter thick fine grained sandstone, 0 3 meters thick light green sandy siltstone, a two meters thick medium grained quartzose sandstone, 10 meters thick bluish gray fine grained sandstone, 10 meters thick gray very fine grained sandy siltstone, two meters thick brown silty sandstone and a one meter thick black sandstone The formation is unconformably overlain with the Sanuki volcanics The distribution of the formation is almost the same as that of the Ikisue for mation.

In the east of the type locality in the vicinity of Umagoe and Mime, the formation changes to a nearly 80 meters thick yellowish gray, medium to fine grained sandstone At the vicinity of Nagahama the Shikai formation directly covers the basement with unconformity, suggesting that during deposition of the Ikisue formation with which i t is conformable, there existed either a small land surface or a small island

Fossils of molluscs were collected from Takinomiya and Nagahama, both in Tonosho-cho, and these are determined to comprise, Glycymerzs c f . crassa KURODA, Cardcum sp , Callzsta sp , Siratoria s p . , Turrztel la cf. s-hataii NOMURA, T oyaszo IDA, Calyptrasa sp , Euspzra mezsenszs (MAKIYAMA) and Nassarzus sp (P1 14, Figs. 7-34)

The similar facies are developed in the Teshima islands in the west of ShBdo-shima From the sequence of the rocks making the two formations and alslo from the fossils collected from them as well a s their relationship with the basement i t is clear that prior to the marine transgression in this area there was developed a lagoonal or brackish water facies in which the lignites were deposited, and that this was followed with continued subsidence leading to the flooding by the marine waters which deposited the Shikai formstion After which there occurred marine regression shown by the unconf or mity above the for mation

The Tonosho group is distributed in the northwestern parts of Shodo-shima and Te-shima, two islands offing the coast of Yashima in Kagawa Prefecture

The Tonosho group is largely covered with the Setouchi volcanic detritus and i t s talus, and exposures are exceedingly f ew These deposits a re in nor th-south and eastnor theast- westsouthwest faults with the Paleozoic rocks and granites The age of these faults is thought to be post-Tonosho deposition and pre-Setouchi volcanics At Onude and Hidoyama, both in Tonosho-cho in the south of distributed area of the Tonoshog roup, i ts strike is ENE- WSW and the dips 5-10 degrees towards the northwest, on the contrary, a t Kitaura, Tonosho-cho in the north area, the dips 3 -5 degrees towards the southeast In general. i t shows a synclinal basin structure and its general trends is ENE-WSW being more or less oval in shape Small gentle syncline with axis trending N 45" W is found in these deposits in the vicinity of Nagahama, Tonosho-cho However, on Teshima island, the strike is almost north-south and the dips 10-15 degrees towards the east Therefore the strikes of both islands are almost perpendicular to one another

I3 Sanuki Group

The Sanuki group consists mainly of pyroclastic rocks such a s tuff , tuff breccia and agglomerate and lava, and is classified into three formations These are named the Yashima basic tuff breccia, Oda formation and the Kokubudai formation in upward sequence. Because all of these formations are considered to be terrestrial in origin. the development of unconformities which are not extensive but observed only locally may also be a common phenomenon

H - l Yas l~zma Basic T u f f Breccza

Yashima basic tuff breccia with i t s type locality is the northern summit of Yashima hill to along the road descending to Nagasaki-no- hana in Takamatsu City. This formation covers the basement of biotite granite unconformably and measures about 50 meters in thickness I t consists of dark blue shards measuring about 2 - 4 millimeters in diameters, and quartz, biotite flakes and plagioclase


22 M . Saito

derived from granite and olivine fragments cemented with basic andesitic tuff and is a tuff breccia In i t s middle part there is sometimes developed cross-lamination and stratification

This formation is distributed only in the vicinity of Yashima and Sh6do-shima and i t s th ick- ness varies according to places, being about 50 meters thick a t the type locality, and about 30 meters on Shbdo shima Generally i t i s horizontal.

H - 2 Oda Formatzon

This formation is situated unconformably upon the Yashima, and begins with cobbles and pebbles of granite I t consists mainly of basal conglomerate, pitchstone and biotite andesititic white tuff and tuff breccia. I t covers the Yashima basic tuff unconformably, whereas in other areas i t covers the granitic rocks directly In the vicinity of the type locality which is Oda in Shido-cho. Kagawa Prefecture, i t has the following sequence in upward order, sandstone with cobbles and pebbles of granite, sandy tuff and biotite andesitic tuff breccia, compact white tuff in the uppermost The total thickness a t the type locality i s about 50 meters, but the thickness varies according to places and may be 70-100 meters in maximum and 10 meters in minimum

In general the strata are nearly horizontal but a t some places they dip a t about 10-50 degrees They are generally stratified and thus suggest deposition under aqueous conditions The strata according to localities are follows.

Goshokurenpo hills i n the east of Sakaide City, Kagawa Prefecture Here unconformably overlying the basement of gianite is developed a stratified gray tuff and tuff breccia in which the fragments of pitchstone and quartz-mica andesite are included, but show distinct stratification In the northern part the strata are horizontal but in the southern part a t Hashioka in Kokubunji-cho the strike is N 70' W and dip a t 30-50 degrees SW, and there can be observed no faults nearby 01

in the vicinity At the same point, they have some clastic dikes oblique to the stratification (PI 9, Figs 4-6).

Kiyama hills in the south of Sakaide City In this area the hills attain the height of 460 meters above sea-level The lower 80 meters i s occupied by the basement of granite and on i t s eroded surface is developed a conglomerate consisting of fragments of granite and mica-schist embeded in a matrix of arkose sandstone measuring about 20 meters in thickness and overlain conformably with a nearly 100 meters thick biotite andesitic tuff and tuff breccia; the tuff becomes yellowish towards i ts upper part In this area the strata are nearly horizontal

Iyatani and Amakiri hills in the south of the Kaiganji Station on the Yosan Railway Line Here unconformably overlying the basement of granite is developed a stratified gray tuff and tuff breceia in which the f r a g m e ~ t s of pitchstone, quartz-mica andesite, hornblende andesite and granite are included

In the southern part a t near the Iyatani temple the strata become about 100 meters thick, the strike and dip are N-S , 25" E Hiage and Gahaishi hills in the west of Zentsuji City, Kagawa Pre- fecture In this area the hills attain the height of 480 meters above sea-level The lower 250 meters is occupied by the basement of Ryoke complex and on i t s eroded surface is developed a gray tuff and tuff breccia measuring about 100-150 meters in which the fragments of pitchstone and granite are included, but show distinct stratification. Towards i ts upper part the tuff and tuff breccia become yellow and agglomeratic in which the large fragments of hyperthene-hornblende andesite are included Near the temple, the strike and dip of this formation are N 30' W , 25' E

Iwaseo-sankai in the west oi Takamatsu City Here a 10 to 20 meters thick tuff breccia unconformably overlies the basement granite and the strike is N 20" E and the dip is 10-50 degrees NW

Gokenzan hills a t Yaguri in Mure-cho, Kida-gun, Kagawa Prefecture Here the formation is well developed and begins with a 10 meters thick glassy quartz-mica andesite flow unconformably overlying the basement granite The base of this flow consists of angular pebbles of the basement granite are incorporated into the flow Above this comes a five meters thick brownish tuff superposed with a one meter thick stratified sandy tuff and then a 10 meters thick quartz-mica andesite pebbles bearing greenish-gray massive tuff

At places where the flow is not developed and the tuff is i n direct contact with the basement of granite, the boundary appears to be blended a s in the northern part of Yaguri especially in the Aji Peninsula In this region the tuff becomes about 50 meters thick, being well stratified, compact and white in color At the marginal parts that is to say i t s lower part is pisolitic, the middle part becomes pumiceous and the upper i s of fine compact white tuff In the upper part are found frag


The Geology o,f Kagawa and Northern Ehime Prefectures 23

ments of silicified woods and plant leaves. The plant leaves a s determined consist o f , Fagus japonzca MAXIM , F . ferrugznea AIT , Quercus

sp. , Salzx sp and Quercus crzspula BLUME In 1948, YAMAGUCHI discovered the leaves of Lzquzdambar formosana HANCE from the same horizon in Sh6do-shima, offing the coast of Kagawa Prefecture In Sh6do-shima this tuff becomes yellowish pyroxene andesitic towards i t s upper part

The thick tuff just mentioned above is distributed eastwards to the Oda Peninsula in Kida-gun, showing no changes in i t s lithological facies and the thickness is uniform

Kitayama hills in Tsuda-cho in dkawa-gun In this area the formation measures about 25 meters in thickness and covers the basement of granite unconformably The strike i s east-west with dips of 20 degrees towards the north The formation here consists of stratified tuff breccia, yellowish gray tuffaceous sandstone which changes upwards to cobbly tuff and the uppermost consists of a five meters thick agglomeratic tuff

H-3. Kokubudai Formatron The type locality of this formation is a t Hashioka in the southern slope of Kokubudai i n the east

of Sakaide City I t consists of purplish red hornblende andesitic agglomerate, two pyroxene andesitic agglomerate, and flows of the sanukitic rocks The thickness of the formation a t the type locality is 100 meters, consisting of the 30 meters thick hornblende andesitic agglomerate, 50 meters thick bronzite andesite lava flow succeeded upwards with a 20 meters thick sanukite lava A t the type locality the formation unconformably covers the Oda formation, the strike and dip of the Oda are N 70" W, 50-50" SW, whereas that of the Kokubudai is almost horizontal The top of the Oda here consists of tuff breccia whereas the basal part of the Kokubudai i s of hornblende andesitic agglomerate

The succession of the Kokubudai formation as observed a t the type locality can also be observed in the western part of the Kokubudai hills, whereas in the eastern part such a s Yashima, and Kitayama, the development of the andesitic agglomerate is not good, and the sanukitic lava directly covers the Oda formation The characters of this lava are the development of platy joints in the upper part and of columnar joints in the lower In the eastern par t a t Yaguri- Gokenzan in Mure.cho, i t i s observed that the two pyroxene andesitic agglomerate covers the hornblende andesitic agglomerate, both amounting to about 60 meters in thickness, and here the lava of the sanukitic rocks are missing The succession of this formation as observed a t Yaguri-Gokenzan can also be observed in Sh6do-shima

From the development, succession and distribution of the rocks making up the Sanuki group i t can be said that quartz mica andesite or liparite flows, i t s tuff and i t s tuff breccia were the first volcanic eruption in the present area This was followed by biotite andesite flows, hornblende andesitic agglomerate, two pyroxene andesitic agglomerate and sanukitic rock flows This order of volcanism can be observed in many localities within the present field The geolgical age of the Sanuki group will be considered from the following mentioned facts The group unconformably overlies the Tonosho group in Sh6do-shima The gravels derived from the sanukitic rocks are found in the Pliocene lacustrine deposits From this evidence i t can be said that the Sanuki group is post-Tonosho and pre-lacustrine deposits in age, and more precisely, from the fossil flora i t may be late Miocene

I t should also be mentioned that a t Tsuzuno, Okawa-cho, Okawa-gun in Kagawa Prefecture there is observed a thrust fault trending east-west with southwards dip of 50 degrees, and this thrsut occurs between the Ryoke and the liparite and between them there is developed a 20 meters thick crushed zone This fault is considered to extend westward from Tomita to Kikaku Park in Nagao-cho Another fault is observed a t Iwaseo-san in the west of Takamatsu City cutting the sanukite lava with east-west trend and almost vertical dip This fault also cannot be traced for any great distance, but associated with i t are others also of similar magnitude and not tracealbe for any noteworthy distance There i s no crushed zone following this fault but only the development of thin fault clay Also similar faults are observed a t Kashoku-san in the southwest of Zentsuji City cutting the pitch- -stone and liparite with north-south trend and with eastwards dip of 40-60 degrees

I . Ishizuchi Group

The correlative of the Sanuki group is the Ishizuchi group developed in the vicinity of the Ishizuchi- yama range in Onsen-gun in Ehime Prefecture The Ishizuchi group covers the Sambagawa-, Kuma and Izumi groups with clino-unconformity According to NAGAI and HORIKOSHI (1954, 55), the Ishizuchi group can be classified into [our formations, which are described in the following lines These are from the lower, the rakano tuff, Kuromoritoge tuff and andesite, Saragamine volcanics,


M. Saito

and Omogo acidic rocks I - 1. Takano T u f f The type locality of this formation is a t Takano. Kuma-cho, Ehime Prefecture I t consists of

from the lower, tuff with schist and pumice pebbles, overlain with biotite dacite tuff , an alternation of sandstone and mudstone, and agglomeratic tuff , measuring about 150 meters in toal thickness. A t places this formation attains 300 meters in thickness Generally the tuff is stratified and thus indicating i t subaqueous origin This is developed in the marginal portions of the Ishizuchi volcanics

I - 2 Kuromorztoge Formatton The type locality of this formation is in the vicinity of the Kuromoritoge in Onsen-gun, Ehime

Prefecture I t i s conformable with the Takano tuff and consists of in upward sequence, rhombic pyroxene andesite, tuff , r hombic pyroxene andesite, biotite r hombic pyroxene andesite From the tuff there have been found ill-preserved plant remains a s of Carpznus sp , Fagus sp , Quercus sp , Ftcus s p , Hedera sp The rhombic pyroxene andesite has wide distribution and makes the 1000 meters high flat surface

I - 3 Saragaml ne Volcanzc s This is conformable with the aforementioned and has i t s type locality near the summit of the

Saragamine hill in Onsen-gun, Ehime Prefecture I t consists of tuff and thick sanukite lava

1-4 Omogo Aczdic Rocks This i s probably conformable with the foregoing, i t s type locality being a t Omogo, Kamiukena-

gun, Ehime Prefecture I t consists of granodioritic rocks and quartz-porphyry, being intrusive The former has strongly metamorphosed the chlorite schist This i s thought to have been derived from the residual magma of the biotite rhombic pyroxene andesite

The Ishizuchi group is also considered to be of lacustrine origin, but i t s present height i s about 500- 1800 meters, whereas the corresponding Sanuki group in Kagawa Prefecture is situated upon the granitic rocks which are a t a height of about 200 meters, and upon this are developed the volcanics range up to about 450 meters in height above sea-level This difference in height of the corresponding deposits may be explained as due to differential movements in the Outer and Inner Zones if i t i s to be considered that both occupied the same height a t the time of deposition However, if the lacustrine deposits were deposited a t different heights originally, then the present differences in heights may not be due directly to the different movements in the Outer and Inner Zones But, i t is evident that considerable movements took place after the deposition of the two lacustrine deposits, and this movement cannot be neglected

The Ishizuchi volcanics besides having Iavas there are also dikes which are directed parallel with the Median Line, thus being east- west in trends There are east -west trending faults cutting the volcanics just mentioned, especially there two in the north of Saragamine in Onsen-gun One of these is called the Saragamine fault, this trends in N 70" E and dlps 70' S , the other is called the Inaitoge fault and this i s directed east-west and with dips of 80" S The Ishizuchi group is not cut by the Median Line, but can be seen covering the Median Line in the valley situated in the south- southwest of Kariba, Kawauchi-machi, Onsen-gun The Takano tuff in the lower part of the Ishizuchi group covers the Median Line. From this evidence i t is ceratain that the Median Line was not subjected to movement after the deposition of the Takano tuff in Matsuyama province

J. Lacustrine Deposits

Along the northern slope of the Shikoku Massif consisting of crystalline rocks and the Asan mountain range oi the Cretaceous Izumi group, there are developed unconsolidated sands, muds and gravels which make the 100-150 meters high hills or fill the low areas of the foundation rocks, and these sediments are in general distributed in east-west direction. These deposits are well developed in the Mitoyo district in Kagawa Prefecture and have been named the Mitoyo group.

Previously these unconsolidated sediments were regarded as Quaternary in age, but from various localities there have been found the remains of Metasequoza and Para - stegodon, and from this paleontoiogical evidence, i t has been proved that they are not Quaternary deposits but should be included into the Tertiary System, and as Pliocene in age. This geological age may be upheld from stratigraphical evidence as will be explained


The Geology qf' Kagawa and Northern Ehime Prqf'ectures 25

in another section of this article. These unconsolidated sediments are distributed in the four provinces distinguished in the present work, and unconformably cover the older rocks of basement granite, and the Cretaceous Izumi group.

Because the hinterland or the original sources of the unconsolidated sediments dif fered according to locality, the developed deposits likewise differ according to area, and for this reason i t i s difficult to apply to them the same stratigraphical name. As the result deecliptions of the deposits are given according to area and different stratigraphical terms have become necessary . Another reason for the aforementioned procedure is because these deposits owing to intense subsequent erosion, are now non-continuous and exposed only in separated areas. After the areal descriptions are given for each of the provinces in which they are developed, correlation of them is presented to show their interrelationships.

For the sake of convenience descriptions are given in the order from west to east according to the respective provinces.

J - 1 Mat su yama Province The lacustrine deposits in this province are found distributed along the southern part adjacent to

the foundation rocks Along the sea coast of Mori about three kilometers southwest of Iyo City about 10 kilometers south of Matsuyama City, there is developed the Gunchu formation This for - mstion makes the 100 meters high hills in that area, attains about 500 meters in width and is distributed for about two kilometers in northeast-southwest direction

The type locality of the Gunchu formation first named by K NAGAI (1°53), i s the sea coast of Mori i n Iyo City (formerly called Gunchu-cho) (PI 3, Figs 5-7) .

In this area the formation is overriden by the Cretaceous Izumi group and thus i ts base remains unknown and from i ts dip, i t can be considered that the upper part extends to the Iyo Sea, so the upper limit of the formation is not ascertainable

In general this formation measures about 300 meters a t the type locality and consists of an alter - nation of sandstone and siltstone in i t s lower, and gravels in the upper

Although the base remains unknown because of being thrust over with the Izumi group, the part thought to be very near the basal parts consists of a nearly 15 meters thick gravel deposits consisting of rounded pebbles ranging from large to very large in size of chert , granite and sand stone are embeded in a matrix of arkose sandstone These are thought to be derived from the basal conglomerate of the Izumi group This i s overlain with 70-80 meters thick strata consisting of yellowish gray sandstone and blue siltstone Plant fragments and fresh water molluscs have been collected from the sandy siltstone layer Amog the plant remains, leaves, stems, braches and trunks a re common, and so far determined are such a s , namely, Pzcea Korzbaz MIKI, Cunnznghawzia Konzshzz HAY, Metasequoza dzstzclia MIKI, Carya ovatocarpa MIKI, S ty rax obasszoides MIKI, Spondzas axillarz s Box, Magnolza Kobus Dc, Pseudotsuga laponzca SHIRASAWA Fresh water molluscs a s Unto margarztzfera (LINNE), Lymnzum douglastz nzpponense (V MARIENS), Anodonta woodzana lauta MART , Semzsulcosppzsa bibestzna (GOULD), Czpangopaludzna sp , Corbicula sp. have been reported by YAGI (1957)

The lower part just described is overlain conformably with the upper comprises an alternation of thin sandy siltstone and gravels measuring about 200 meters in thickness In this alternation are intercalated five, 20-30 centimeters thick layers of coaly sands and peat Plant fragments and pollen have been collected from the carbonaceous layer From this member Metasequoza dzstzcha MIKI, Pseudolarzx Kaempherz GORD , Chamaeczparz s pz s z f cra FNDL , Juglans megacznerea CHANEY, Pterocarya multzstrzata Miki, Corylus heterophylla FISCH , Q U ~ Y C U S Hzkztaz MIKI, etc

From the lower, middle and upper peat layers the pollen determined from them are a s shown in Table 3 Common throughout the layers of the present middle part are, Metasequoza, Pznus, Chamec yparz s, Sal ix , Alnus, Quercus and Ulmus, among which Metaseqzcoza i s most dominant followed by Alnus Particularly from the lower peat layer Nyssa was found From the lower to the upper, Metasequoia decreases in abundancy, GZyptostrobus is not found in the upper but is common in the middle and lower parts, although not common Cryptomeria has been found in the upper Especially the upper part is characterized with abundant Alnus

The upper layer i s thought to be represented with plants living in a moist area, these are such


M. Saito

Table 3 The Results of Pollen Analysis of Peat as Orchidaceae, Chenopodiaceae, Spiaceae, Matter from the Gunchu Formation Compositae. The gravels of the alternating

Upper Middle Lower layers consist in the lower part of sub- Peat bed Peat bed Peat bed angular cobbles and pebbles of the Izumi

Cunnighamza 1 5 sandstone, crystalline schist, where in the Metasequoza 6.0(%) 53.9 44 0 middle part of the alternation there are Cr yptomer i a 1.5 found large pebbles of liparitic gravels and Glyptostrobus 11 4 8 0 the gravels consist of green schist, liparitic Picea 4 0 rocks are dominant and their shapes are Tsuga

1 8 subangular and large pebbles to small Pseudotsuga Pznus 7 5 3 0 15 cobbles in size. The upper part comprising

Chamec ypart s 3 0 3 6 4 0 subangular to subrounded, large pabbles to Salz x 1 5 1 2 5 5 small cobbles of schist, liparite and of the Pter ocar ya 1 0 Izumi sandstone in about the same propor - Juglans 0 5 1 8 1 0 tion; the matrix consists of sand derived Carpznus 0 6 from decomposed schist and Izumi sand- Cor ylus 1 5 3 6

57 0 13 2 stone and medium to coarse grained Alnu s 4 5 Fagus 1 5 In the vicinity of the water reservoir of

Quercus 5 5 3 0 5 0 Mori, the gravel deposits are exposed and Ulmu s 2 0 3 0 2 0 this gravel belongs to the basal horizon of Zelkova 1 5 1 0 the upper part of the Gunchu formation Rhus 1 5 1.0 This gravels are almost vertical in position, Ilex 3.5 the longer axis of the respective gravels Ac er 0"5 being almost vertical, and sometimes the Nyssa Symplzcos 0 5

O gravels are much disturbed and their ori-

Fraxznus 0 5 entation is a t random and appear as a

B.P./T P 91 8 94 5 96 tectonic conglomerate

1 The geological structure of the Gunchu

Polypodiaceae Gramineae 3 6 1 formation in the type area has a strike of

Cyperaceae 3 3 7 N 50-55' E with dips of 30-70' NW and

Chenopodiaceae 2 near the contact with the Izumi the dip Spiaceae 6 Col by SAITO becomes almost vertical Near the bounda- Compositae 4 Analy. by SOHMA ry in the northeastern part of the area,

the actual exposure of the fault cannot be observed, but a t the southwestern part along the coast, the strike of the lacustrine deposits do not change but the dip changes to the opposite direction, being towards about 20" SE and the Izumi group can be seen riding over the lacustrine deposits with low angle Especially from the coast to Kono-gawa, the strike of the Izumi group is varied ranging from east-west to north-south and the dip may be north or east, thus showing a crushed zone In this area east-west directed faults are abundant and taken together appear to indicate a crushed zone

The Gunchu formation in eastward direction is exposed sporadically in the bed of the Mori River, and from its strike and dip it can be considered that the formation extends northwards to Iyo-nada, and eastwards under the alluvial plain In the east of Iyo City where there is developed a 50-60 meters high hill along the northern slope of the mountains consisting of the Izumi group, consisting of talus deposits Below this talus deposit a t Ueno, Kamimitani and Kamiagawa, in Iyo City, exposures of the lacustrine deposits can be observed

At Aso about five kilometers south of Matsuyama City, the lacustrine deposits are exposed along the cliffs of the Tobe River. Here the strike is east-west and the dip is 15" N Although the lower part cannot be observed, from the lower the rocks consist of three meters thick large pebbles of subangular to subrounded Izumi sandstone and schist rocks in a matrix of coarse sand derived by decomposition of the Izumi sandstone and schists This is overlain with a one meter thick yellowish medium grained sandstone covered with about a 10 meters thick small to large cobbles of subrounded to subangular Izumi sandstone and schist rocks; the matrix is coarse to medium grained sand This is covered with the alluvial deposits

No fossils have been found from these localities, but the facies is considered to correspond to the uppermost part of the Gunchu formation of type area


The Geolog,y o,f Kagawa and Northern Ehime Prefectures 27

In the eastern part of Matsuyama province in the cuttings along the road leading from Sangenya to Torinoko, Kawauchi-cho, Onsen-gun, the lacustrine deposits are observed underlying the Yakeo- toge gravels which make the Kawakami hills The lower part of the deposits can not be observed, but from the distribution of the different rocks i t is thought that these deposits cover the basement rocks of the Izumi group The lowest observed part consists of 2 - 3 meters thick white sandy silt becoming darker in i t s upper part and this i s overlain with a 10 centimeters thick coaly mud. This mud when weathered is grayish white in color This i s overlain with a 30 centimeters thick medium pebbles bed consisting of subangular slate rocks The surface of this gravel bed is very irregular and uneven and is unconformably covered with the Yakeotoge gravels

Pollen analysis of the coaly mud above mentioned shows that the abundant genera a re , in the following order, Pzcea, Alnus , Metasequoia, Pznus, Tsuga , Compositae, Fagus and Carpznus (after NAKAGAWA, 1953) The first two are most dominant From the assemblage of this pollen flora i t is considered that i t corresponds to the upper part of the Gunchu formation in the type area

Although the exposures under the Yakeotoge gravels are scattered and small, the dip is towards the south a t about five degrees Similar exposures a s just described also occur in the hills of Suno- uchi, Kawauchi- cho, below the talus deposits

Aside from the type area of the Gunchu formation, the rocks referable to i t a re distributed only sporadically and expose only different parts They are generally covered either with talus deposits or by the Yakeotoge gravels, and in the northward parts they are covered with the alluvial deposits.

J - 2 Nzzhama-Sai jo Provznce In the Niihama-Saiio province, lacustrine deposits are called by the name of Okamura formation

(first named by TAKA HAS HI,^^^^) whose type locality is in the vicinity of Okamura a t about two kilometers south of Komatsu City in Ehime Prefecture (P1 4 , Figs 1-2) Although i t i s considered that the Okamura formation was deposited unconformably upon the Izumi group. the contact of the two could not be observed in the present province

The lower part of the formation consits of about 20 meters thick gravel beds consisting of small to large pebbles of subangular to subrounded sandstone of and slate of Izumi group cemented with sandy silt In this gravel there are four 50 centimeters thick sandy silt layers intercalated. In the upper part there is a dark blue sandy silt measuring one meter in thickness, overlain with a 30 centimeters thick sandy silt which yielded Metasequoza dzstzcha MIKI, Styrax mzcrocarpa MIKI, S japonzca MIKI, Pterocarya multzstriala MIKI Th i s i s covered with one meter thick rounded medium slate pebble bed, then a two meters thick subrounded large pebbles to small cobbles of schist and the Izumi sandstone, overlain with a three meters thick subangular large pebbles to small cobbles of sandstone rarely with those of schist , quartzite and andesite Sometimes rounded pebbles of the Izumi sandstone are intercalated This is covered with a 30 centimeters thick muddy silt which yielded such pollens a s , Metasequoza 61 5 pre cent, Glyptostrobus 17 5 per cent, Pznus 5 per cent , Juglans 2 per cent, A l n u ~ 2 per cent , Quercus 4 5 per cent, Ulmus 3 5 per cent , and Betula 1 0 per cent The analysis indicates that Mefasequoza and Glyptostrobus are predominant This pollen flora i s analogous with that derived from the Gunchu formation This pollen bed is overlain with a one meter thick, subrounded large pebbles of the Izumi sandstone So far i s the constituents of the lower part The upper part is distinguished from the lower by the abrupt change in kinds and shapes of gravels (P1 5, Fig. 3) The upper part consists of a 30 meters thick angular large pebbles to small cobbles size Izumi sandstone only, cemented with sandy silt or sand In the lower part of this gravel there are two, 40 centimeters thick sandy silt layers intercalated In the upper part there a re intercalated four or five layers of 10-20 centimeters thick sandy silt with limonite layers forming their boundaries

The Okamura formation in the type locality is almost horizontal but with slgiht dips towards the northeast and the general strike is N 50-60' W In the hills i n the south of Himi the formation consists almost wholly of gravels consisting of angular pebbles to cobbles of the Izumi sandstone, totalling about 50-60 meters in thickness As in the type locality there are also intercalated several 10-20 centimeters thick layers of sandy silt

In the northeastern part of the Okamura hills near the temple, although the base can not be observed, the lower consists of one meter thick subangular pebbles to cobbles of sandstone and slate of Izumi group, overlain with 50 centimeters thick angular to subangular pebbles of the Izumi sandstone, then a 10 meters thick pebbly sand followed with a 50 centimeters thick angular to subangular large cobbles of Izumi sandstone, covered with five meters thick tuffaceous sand with


28 M. Saito

pebbles of the Izumi sandstone, and fragments of pitchstone intercalated In general i t seems that the gravels i n the northern part of the Okamura hills are smaller than those developed in the southern par t

The geological structure of the Okamura hills i s almost horizontal except near the Okamura fault where the strata dip about 3 - 5 degrees towards the northeast and the general strike i s roughly N 50-60" W in trend Also faults are observed in the Okamura hills, although their number i s only two, they a re briefly described in the following

Okamura faul t This fault separates the Okamura formation from the Izumi group In the cliff of the road leading from Himi to Kurose in the south of Himi-cho, the contact consists of a 20 centimeters thick fault clay and the fault trends N 60-80" W , with dip of 70" NE The Izumi is considerably disturbed and within about five meters from the fault plane the Izumi is crushed in the form of blocks and measurement of the Izumi group is almost impossible Here i t appears a s a nor ma1 fault.

In the 10-15 meters deep valley consisting of the lacustirne deposits, following the road leading from Himi to Uenohara Here the Okamura formation near the fault consists of angular pebbles to cobbles of Izumi sandstone cemented with sandy silt which is i n contact with the fault separating i t from t h e Izumi group The east valley wall exposing the fault shows that the strike of the lzumi group is N 70" E with 50" SE dip. Within a thickness of about five meters from the fault t he Izumi group is badly crushed in the form of blocks and the nature of the fault cannot be determined The west cliff of the same valley opposite the one just described shows the same strike and dip of the Izumi group as aforementioned, but the f au l t has a two meters thick black fault clay ; th is measures N 70-80" E, with dip of 60' N , and is a normal fault Near the water reservoir in the south of Okamura there are observed two cliffs, the eastern and western, which are both different The eastern one shows that brecciated gravels, probably of tectonic origin and of the Izumi group, appears to gradually change laterally into the Izumi group The strike of the Izumi group is N 60' W with dip of 50" N, however, about 10 meters distant the strike becomes N 60" E with dip of 30" S. This may be interpretated either as a anticlinal structure or part of a crushed zone The west cliff oppositing the one just described shows the Izumi group striking N 80" E with 70' S dip and is in contact with the Okamura formation with reverse fault This is the reverse fault reported by NAGAI (1954), by which he came to the opinion that the relation between the Izumi group and the Okamura is a reverse fault, a s the result of his survey of the Median Line In the western part of the Okamura hills in the south of Minamigawa, Komatsu City in the south of Otani lake, there i s a fault almost vertical and i t appears a s if the Izumi group was thrust up against the lacustrine deposits

Besides the major fault just described there are also seen others cutting the Okamura formation. Near the water reservoir in the south of Okamura there is seen a fault trending in east-west direction and dipping 80' S The downthrow side shows the development of minor step-faults similar i n aspect with the step down conglomerate of KUNNEN except for being due to fault movement. Tracing this fault eastwards i t i s noticed that waterfalls are made just in the position where the faults are thought to extend Such can be traced to a s far a s in the valleys south of Himi-cho; such waterfalls are charcteristic of all of the valleys situated between the two extremes of the fault

The Okamura formation besides being typically developed in the Okamura hills is also distributed to the cliffs of the Shi River, a tributary of t he Nakayama River in Kurumi, Tambara-cho Here the formation is exposed under the thick alluvial deposits From this locality Metasequoza and Pseudotsuga were found by TAKAHASHI (1958) In the eastern part of this province, t he formation is developed a t Toyanohana five kilometers southwest of Niihama City, where i t makes the 100 meters high hills which consists almost wholly of gravels The gravels measure about 50 meters in thickness and comprise predominantly graphite schist and Izumi sandstone The gravels a re large pebbles, subangular and with a matrix of decomposed graphite schist and Izumi sandstone, thus being medium to coarse grained sands. In i t s northern part there i s intercalated a 30-50 centimeters thick layer of micaceous sand from where pollen have been found In general the formation dips g~adual ly northwards and the strike i s roughly east-west in direction

A fault i s observed a t Masaki in Nakahagi, Niihama City with east-west strike and with 80" N dip, being a normal fault

A t Kishinoshita in Nakahagi, Niihama City the formation is exposed below the covering of thick fan deposits Here i t consists of blue sandy silt and small pebbly sand in alternation and measuring


The Geolog,y o f ' Kagawa and Northern Ehirne Pre,fectures 29

about 10 meters in thickness; i t contains drift woods The deposits strike N 45' E and with 30° SE dip, there being developed here a small fault of east -west trend

In the Toyanohana hills the southern margin of the Okamura formation is defined by the Median Line with which i t is in contact with Where i t i s in contact with the Median Line i t i s generally covered with talus, and in the stream beds l t is covered with recent stream gravels, and although the direct relationship between the Okamura and the Sambagawa metamorphics cannot be seen, but in a small stream a t Kawaguchi east of Nakahagi, Niihama City, i t i s observed that the gravels of the Okamura are underlain with a 10 centimeters thick fault clay under which is a felsite dike, which lies above the schist of the older formations This sequence is covered clino-unconformably with younger gravel deposits This fault dips a t about 30' N with almost east-west trend and is considered to be a normal fault, the younger or Okamura having been thrown dcwn. This same relationship can be observed a t Mikura in Niihama City where a one meter thick fault clay separates the older schists from the angular schist gravels of the Okamura formation

In the eastern part of the Niihama-Saijo province the formations is thought to exist under the covering of alluvial deposits, because parts of the formation can be seen exposed in the beds of the streams in that area In the middle part of the province, especially a t Kishinoshita, Niihama City, there is seen a fault cutting the alluvial fans This was named by TSUJIMURA (1932) the Kishinoshita fault 'This fault i s considered to extend westwards and to cut the Okamura formation, but to be covered in the ar.ea north of the Okamura hills by the thick alluvial deposits.

J - 3 Mzto yo-Nakatado Provznce In the Mitoyo-Nakatado province the lacustrine deposits are best developed, especially along the

Saida River east to west flowing from the northern slope of the Asan mountain range. These lacustrine deposits usually extend up to about 150 meters in height above sea-level, but not higher The lower part of the deposits which consists of muddy sediments are now found in the valleys of the present area, which is evidence that the deposition surface of the lacustrine deposits had high and irregular relief

The Kawauchi formation, which is named for the lacustrine deposits i s best developed a t Kawauchi, Yamamoto-cho, Mitoyo-gun. which is the type locality (PI 4, Figs 4-5). Here the basal part of the formation is in thrust fault contact with the Izumi group and thus cannot be observed The lowest part of the formation is thought to be the four to f ive meters thick loose gravel which consists of subangular to angular small pebbles to large cobbles of the Izumi sandstone. This is overlain with a 20-30 centimeters thick plant-bearing gray silt layer, which has yielded, Metasequoza dzstzcha MIKI, Pseudot suga yaponzca SHIRASAWA, Cunnzngkamza Konz shzz HAY, Quercus rubrozdea MIKI, Coynus controversa HESML., Styrax mzcrocarpa MIKI, Nelumbo nuczfera GAERIN , Trapa mammzllzfera MIKI, Euryale akashzenszs MIKI, Pzcea Korzbaz MIKI, Zelkova sp Particularly the cones and pollen of Metasequoza are common and abundant Lying above this plant bearing bed is a two meters thick quartz bearing dark gray sil t , a one meter thick blue sand, a two meters thick T r a p a - bearing mudstone yielding the following species, Tr apa dz scozdpoda MIKI, T tetragona MIKI, T macropoda MIKI, Palzurus nzpponzcus MIKI Besides water plants about 14 species of fresh water diatoms have been distinguished, these are such a s Cymbella cf ventrzcosa K u r z , Cyclotella stellzgera C and G . , Eunotza graczlzs (EHR ) RABH., Synedra acus KUTZ. , S ulna NIIZSCH., Navzcula placentula (EHR ) GRUNOW, Dzplonezs ovalzs (HILSE) OLEVE, F ~ a g z l a r z a construens (EHR.) GRUNOW, F construens var venter (EHR ) GRUNOW, F . vzrescens RALFS, Gomphonea abbrevzatum AGARDH ? K u r z , Meloszra zslandzca 0 MULL , Stauronezs phomzcenteron EHR , Opephora Martzz HERIBAUD, Pznnular za sp Above this comes a one meter thick granule sand, a one meter thick dark micaceous sil t , 30 centimeters fine sandy silt with drift woods included, a 1 5 meters thick coarse sand with limonite layers, above with a 40 centimeters dark bluish mud which yields the following species, Metasequoza dzstzcha MIKI, Pseudotsuga yaponzca SHIRASAWA, B U X U S yaponzca MUELL. This overlain with a one meter thick reddish quartz sand This comprises the lower part of the formation The upper part i s distinguished from the lower part by the nearly 30 meters thick arkose sand with intercalated four layers of 30 centimeters thick silt and four - five limonite bands The arkose sand sometimes becomes pebbly

The geological structure of the formation a t the type locality. At Kawauchinaka in Yamamoto-cho the formation is in fault contact with the Izumi group The Izumi group within a distance of about five meters and situated a t about seven meters from the lower part of the lacustrine deposits i s folded with the folds more or less open and the sandstones taking part are broken a s if by compressive


30 M. Saito

forces These fo:ds show a general trend of N 70" E and a dip of 70" towards the south, and from this i t is thought that the Izumi was thrust over the lacustrine deposits (P1 6 , Fig. 9) In this area the !acustrine deposits strike z t about N 10-20' E and show a dip of about 3-5" towards the west From the structure 01 the lacustrine deposits i t is evident that they extend under the alluvial deposits

In the western part o i this province a t the northern part of the Izeki lake in Onohara-cho, the Izumi group is exposed as inliers Here the gravels thought to be near the basal part of the lacustrine deposits abut against the Izumi group (P1 5, Fig 6) Near the contact with the Izumi group, the Kawauchi formation has angular cobbles and boulders of the Izumi sandstone cemented with sandy silt; this measures about five to six meters in thickness Above this i s a 10 meters thick medium sandy shale and cross-bedded pebb!e gravel dipping a t about three to five degrees towards the northwest towards the Hiuchi Sea and i t can be postulated that the lacustrine deposits extend under the broad alluvial plain

Electrical prospecting in the area between Kinosato, a small granite hill in Yamamoto-cho, about four kilometers north of the Izeki lake, and the sea coast of Kanonji, indicates that a t the depth of about 60-80 meters near the granite hill the granite basement prevails Farther northeastwards the basement becomes deeper and is recorded a t 100-140 meters This prospecting indicates that the basement under the alluvial plain has very irregular relief From electrical prospecting and core boring data , i t is evident that lacustrine deposits occur filling the areas of low relief and even covering the ones of high relief below the plain These deposits are correlatable with the Kawauchi formation dipping northwads under the alluvial plain which were observed in the vicinity of the Izeki lake already mentioned The lignite layers recorded by KURATA upon boring data is thought to correspond to the writer's peat beds intercalated in the lower half of the formation

The gravel deposits lying above KURATA'S lignite layer measure about 50-60 meters in thickness i s thought to correspond the upper half of the Kawauchi formation and a part of Yakeotoge gravel This gravel deposit i s overlain with alluvial deposits under the plain and a t a depth of about 10 meters f rom the surface The boundary between the gravel deposits and the underlying lacustrine deposits i s recorded by the electrical prospecting by an abrupt curve

The Kawauchi formation is distributed also in the western part oi the province and is exposed in the cliff of the stream near the shrine in the south of Ikenouch;, Yamamoto-cho Here the lower part i s not exposed but the nearly 10 meters thick gravel consisting ot zngular cobbles of the Izumi sandstone Although the contact with the Izumi group cannot be observed, near to the boundary the gravels consist of boulders of the Izumi sandstone. Above this comes a blue sandy silt containing plant fragments covered with a one meter thick medium pehble layer and a five to six meters thick cross-bedded arkosic granule sand intercalating pebbles The sediments occupying a higher position occur in the south of Otani-ike in Onohara-cho. Here a one to two meters thick carbonaceous mudstone is exposed in the lower par t , and from i t the following plants were collected, namely, Pseudotsuga ~aponzca SHIRASAWA, Sequoza sempsrvzreny ENDL , Pterocarya multzstrzata MIKI, Corylus yostrata AIT , C heterophylla FISCH , Magnolza obovata THUNB , and Stewartza serrata MAZ This i s overlain by a seven to eight meters thick cross-bedded, pebble bearing granule arkosic sand This makes the lower part of the Kawauchi formation in this area

The upper part of the formation is exposed in the Ogiwara hills in Onohara-cho. Here i t consists of a 20-30 meters thick alternation of subangular pebbly gravel and white fine sandstone. Uncon- formably superposed upon the upper part of the Kawauchi formation is the Yakeotoge gravel, which consists of subangular, medium to large pebbles derived from the Izumi group, measuring about 10- 20 meters in thickness The Yakeotoge gravels when traced southwards towards the mountains made of the Izumi group become gradually thicker and a t places the matrix becomes a red loam showing lateritisation ; the thickness becomes 30-40 meters. In this area, Kawauchi formation is almost horizontal but a t Fukudahara their strike is east-west and dip is 20" N

In the cutting in the east of this locality between Kawauchi-kami in Yamamoto-cho and Iruhi, Saida-mura, a one meter thick medium sand is exposed in the lowest part and is overlain by a one meter thick limonite band bearing medium grained sand, covered with a 20 centimeters thick dark blue sandy silt, a 30 centimeters thick yellow fine grained sand, and a one meter thick dark blue micaceous sand The strike is N 40" E and dip is 30" NW. Although in the present area the strata are almost horizontal everywhere i t is only a t this one locality where the dip i s steep, and therefore, whether this strong inclination is due to the impregnation of limonitic waters or represents


The Ge0log.y o,f' Kagawa and Northern Ehime Pre,fectures 31

the true dip is difficult to interpret , but the dip may be due to some local disturbance. At Saidanaka in Saida-mura, the Izumi group and a part of the kawauchi formation are both

exposed in the bed of the Saidanaka River Although the contact between the two formations cannot be observed, the gravels of the Mawauchi formation consist of subrounded to subangular pebbles of green sandstone and crystalline schist , quartzite and black slate A fault is observed in this gravel deposit; i t s strikes east-west and dips 80" N, and is a normal fault. The gravels near the fault have their longer axis inclined. The thickness of this gravel deposit i s about five meters Tracing the fault eastwards to the Naka hills i t is thought that i t may be extend through the one meter thick blue silt and 30 centimerers thick gray silt and a one meter thick arkose sand; these sediments a re observed to dip northwestwards a t about 50 degrees and their strike is N 50" E

At Saidanaka above mentioned there occurs above the aforementioned five meters thick gravel deposit, a five meters thick coarse bluish silty sand containing grains of feldspar and quartz with dr i f t woods intercalated. The drift woods are sometimes horizontal, vertical or oblique to the bedding plane There are also intercalated in this coarse sandy silt two to three centimeters thick detached curved silt layers, which are not continuous The strike i s east-west and the dip is 5' N

In the east of this locality in a cliff of the Saida River a t Saida, the part near to the base of the Kawauchi formation abuts against the granitic rocks forming the basement in this area (P1.5, Fig. 7) . The boundary is almost vertical and the gravel deposits consist of angular boulders and cobbles of granite and andesite, and the cement consists of a cross-bedded arkosic sand Near ICijio in the east of this locality, this gravel is overlain with a five meters thick pebbly granule arkose sand; the pebbles become larger upwards. This gravel deposit intercalates a 20 centimeters thick layer of siltstone which shows evidence of slumping Scour and fill structures can also be observed in th is gravel deposit Below the pebbly sand there i s 50 centimeters thick micaceous sand and peaty mud in very thin alternation (P1 4, Fig 6) This alternation is not continuous and is thought to comprise a lens structure From this lens pollen have been found, these comprise Metasequoza (55%), Glyptostrobus (11.5%), Pznus (0 5%), Chamecyparzs (30%), Pterocar ya (1 5%), Juglans (4 OH), Corylus(1 O%), Alnus (10 5%), Fagus (1 O%), Quercus (3 5%), Ulmus (5.5%), Rhus (2.0%), Nyssa (1.0%), Eaum pollen/'Iotal pollen (89 7%) Next in upwards sequence are sediments exposed in the road cliff a t Miyazaka, Saida-mura, where in the lower i s developed a three meters thick cross-bedded sand with granite pebbles intercalated, overlain with a one meter thick arkosic coarse sand changing upwards into fine sand, covered with a 40 centimeters thick varved sandy silt and a three to five meters thick massive bluish gray siltstone intercalated 30 centimeters thick coaly silt with such plants a s , Potamogeton cf . perfolzatus L , P cf crzstatus R e t M , Sczrpus mucronatus L , Menyanthes sp , Metasequoza dz stzcha MIKI, Trapa Maxzmowzczzi KORSH., 7 mammillz fera MIKI, Trapella sp and Fagus sp . Nearly all of these plants are water plants or those growing in moist areas, and this suggests that deposition took place in a shallow muddy area. Pollen analysis of these pollen revealed the following, Sczadopz t y s (C 5%), Cunnznghamza (1 5%), Metasequoza (53.0%), Glyptostrobus (6.5%), Pzcea (5.5%), Pznus (9 0%), Chamecyparzs (2 5%), Salzx (2.0%), Jkglans (1 0%). Carpznus (1 0%) , Betula (1.2%), Alnus (2 5%) , Quepcus (8 0%), Ulmus (2 5%), Ilex (1 -0%) and Nyssa (0 5%). Besides these pollen there were also found Chenopodiacea, Spiacea and Compositae

Above this pollen bearing sediments there occur a three to five meters thick blue sandy siltstone with coarse quartz and feldspar grains, a 10-30 centimeters thick peat which is irregular bedded and has yielded such pollen similar to the one above mentioned The Baum pollen/Total pollen is 61 0, being of lower percentage and thus showing that the pollen of grasses predominate.

In this area the strata are generally nearly horizontal but there is developed a small anticlinal structure in the vicinity of Kitano in Saida-mura. This anticlinal axis trends in N 45" W and the wings dip a t about 5-10 degrees (Pl. 7, Fig. 3).

At about 500 meters east of Sako, Yamamoto-cho a nearly 20 meters thick arkose sandstone of the upper part of the Kawauchi formation is exposed This sandstone intercalates limonite layers and also iron-pipes are developed in i t . The lower part of the formation is exposed in the cliff in the north of the above locality, a t Nakayashiki Although the lowermost part i s not exposed a two meters thick pebbly sand above where there is developed a 10 meters thick blue sandy silt in which drift woods are intercalated In this area the strata are nearly horizontal

In the cliff of a stream in Imoo, Saida-mura in the east of the above mentioned locality there i s exposed above the tabular jointed granite making the basement with unconformity a seven to eight


32 M. Saito

meters thick gravel deposits consisting of angular pebbles and cobbles of granite and andesite, and cemented with greenish arkose sand Sometimes carbonized woods are intercalated and their orientation is almost horizontal

In the road cutting about 300 meters east of the Saida Station on the Dosan Railway Line, there is exposed the gravels of the upper part of the formation I hese gravels measure about 30 meters in thickness although its contact with the Izumi group is obscure, the strike of the alternation of black slate and sandstone of the Izumi gtoup is N 40" E with 50-60' S dips The exposure gives the impression that the Izumi group was thrust over the Kawauchi formation The gravels contained in the deposit are angular cobbles and boulders of the Izumi sandstone and also of black slate pebbles, and the matrix consists of granule sand and tuffaceous sand

The gravel deposits just described come into contact with a nearly 20 meters thick alternation of tuffaceous sandy silt and pebbly sand with an angle of about 25 degrees, and along this inclined surface there is developed a limonite layer measuring about one to two centimeters in thickness. The contact strikes N 80" E with 25O S dip This is thought to be a thrust plane and the fault clay to have changed into limonite

Eoth the gravel deposit and the Izumi group are covered clino-unconformably with the Yakeotoge gravels, which are horizontal T hus before deposition of the Yakeotoge gravels there was developed an imbricate structure consisting of twin thrust faults

In the cliffs of the Yamawaki valley, Saida-mura in the east of the above described locality, the Izumi group with a one meter thick black fault clay and breccia with N 50-60" E, and 40' S dip, is thrust up on a gravel deposit consisting of gravels quite indistinguishable from the basal conglomerate of the Izumi group (P1 8 , Fig 6) The basal conglomerate of the Izumi group consists of rounded pebbles of greywacke, quartzite, sandstone and chert These same kind of rocks are found below the thrust plane just mentioned However, laterally these Izumi-like gravels change into angular boulder and cobbles derived from the Izumi group and cemented with sandy silt. Therefore it is interpreted that the gravels giving the impression of the basal conglomerate of the Izumi group may have been derived from i t , but actually a te the gravel deposits of the Kawauchi formation The angular boulders above mentioned may attain as much as one meter in length and 20 centimeters in thickness and appear as large slabs (P1 8 , Fig 4) Such a development of the angular boulders continues laterally for about 30 meters and then they grade into angular cobbles also of sandstone derived from the Izumi group Where the angular cobbles are developed there is exposed below them a one meter thick gravel deposit consisting of subrouned cobbles and pebbles of sandstone also derived from the Izumi group, and below this there occurs a two meters thick dark gray sandstone in which intercalated are plant fragments and carbonized moods From this horizon Metasequoia dzstzcha MIKI, Pseudotsuga laponzca SHIRASAWA, Fagus crenata BLUME, Q U ~ Y L U S sp., Castanea sp , Pzcea Maxzmowzczzz REGEL were collected.

In the road cutting in the north of Yamawaki valley, there is exposed the gravels of upper part of the formation These gravels measure about 30 meters in thickness intercalating three to four 30 centimeters thick sandy silt layer and limonite band They are generally subangular to angular large pebble to small pebble size, and consist of sandstone, black slate derived from the Izumi

group Although its contact with the Izumi group is obscure, the strike of the alternation of gravel and

sandy silt of the Kawauchi formation is N 50" E with 20' NW dips and in the basal conglomerate of the Izumi group near the contact, there are several fault with E-W trend

At Shinme and Oguchi in Chunan-mura in the east of the above mentioned locality, there i s exposed a 20 meters thick alternation of brown arkose pebbly sand and quartz-bearing blue silt This is almost horizontal and from the blue silt in the lower part of the alternation there were found, Metasequoza dz stzcha MIKI , Cornus controver sa HEMSL , Hamamelzs parrotzozdea MIKI, T r a p a sp. and Styrax sp .

In the cliff of the Saida River in the south of Shinme. there is exposed a 15 meters thick pebbly arkose sand in which lower part there is a 10-50 centimeters thick silt layer upon which a five to 20 centimeters thick coaly mud layer is superposed, and it was subjected to pollen snalysis. The following pollens were found, Metasequoza (34 2%), Gl yptostrobus (15 8%), Chamecyparzs (7 0%), Salz x (3 5%), Juglans (3 5%), Carpznus (0 9 % ) , COY ylus (3 5%), Alnus (15 8%) , Quercus (6.1%), Ulmus ( 2 6%), Rhus (0 9%) and Fraxznus (6 1%) The strata here strike N 20" E and dip a t 15' towards the southeast, although in general in this area the strata are n e a ~ l y horizontal


The Geology o,f' Kagawa and Northern Ehirne Prgfbctu~es 33

In the valley south of Kasuga in Chunan-mura, the Izumi group can be observed to thrust over the Kawauchi formation. The strike is E-W and with dip of 40" S The Izumi group in this area has the same strike and dip a s that of the thrust plane A 70 centimeters thick fault clay is developed The Izumi group i s thrust over a gravel deposit consisting of gravels quite indistinguishable from those making the basal conglomerate of the Izumi group and are thought to have been reworked The gravels which are thought to have been reworked ones from the basal conglomerate of the Izumi group change laterally into sandy silt, characteristic of lacustrine deposits

In the vicinity of Manno. ike in Manno-cho, especially its southern part, the Kawauchi formation abuts against the granite which makes the basement Although the basal part is not exposed, the part thought to be near to base is exposed in the bed of a small stream in Mita in Manno.cho. Here a one meter thick blue silt covered with a one meter thick subrounded to subangular large to very large pebbles of the Izumi sandstone and of medium pebbles of granite and crystalline schist. This i s overlain unconformably with a 30 centimeters thick muddy peat which was subjected to pollen analysis with the iollowing results, namely, Cr yptomerza (23 0%) , Chamec yparzs (15.0%) , Salzx (0 5%), Pterocarya (1.5%), Juglans (1.0%), Carpznus (7 0%), Corylus (4.0%), Alnus (9.0%), Fagus (3.0%), Quercus (22.5%), ULmus (3 0%), Rhus (5 0%), and Fraxznus (2.5%). Here the Bp /Tp=47 4, thus showing that this pollen assemblage is different from those mentioned in earlier lines The age of this very restricted muddy peat may be Pleistocene probably i t was de. posited on the lowly swampy land on the erosion surface of Kawauchi formation The upper part of the for mation in this vicinity consists of a four or five meters thick alternation of arkose sand and gray -yellow silt whose respective layers measure about 5 - 10 centimers in thickness Especially the silt shows a wavy structure due to rapid deposition This is overlain with a nearly 10 meters thick alternation of arkose sand and light gray silt and this is covered unconformably with the Yakeotoge gravels The strata in this vicinity are generally horizontal.

In the northern part of the Manno-ike, gravels are found lying with unconformity upon the basement of granitic rocks. The gravels consist of subrounded to subangular pebbles and cobbles of sandstone derived from the Izumi group and sometimes boulders of sandstone are intercalated in the gravels 'I his gravel deposit measures about 10-1 5 meters in thickness. Laterally this deposit changes into granule arkose sand or pebbly sand Where the granule arkose sand changes into pebbly sand, there are developed a micaceous fine sand and grayish yellow sandy silt in layer form or as lenses. Also they may be developed as soft-rock pebbles

The gravel deposits are almost horizontal but there is a fault cutting i t , i t strikes north-south with dip of 15" W , and the longer axis of tabular gravels are aligned along the fault plane.

Along the upper reaches of the Kanakura River at Ebata in the southeast of Manno-ike, the boundary between the Kawauchi formation and the Izumi group can not be seen but a t least only a few meters is not exposed Here the basal part of the Kawauchi formation is almost vertical and the strike of the Izumi group is N 70" E with 30' S dip From this relationship it is thought that the stratigraphical relation is a thrust fault The order of succession of the rocks of the Kawauchi formation in upward sequence is as follows, a 50 centimeters thick blue silt, 10 centimetrs thick pebbly gravel, 50 centimeters thick gray sandy silt, 50 centimeters thick black silt with plant fragments, a 30 centimeters thick pebbly gravel, 20 centimeters thick micaceous sandy silt, 30 centimeters thick pebbly gravel and a five to seven meters thick greenish tuffaceous silt with load casts between this and the underlying pebbly gravel; this comprises the lower part of the formation in this area. Although near the fault the strata are almost vertical i t is noticed that at about 20 meters away, the strata return to almost horizontal

The upper part of the formation in this area consists of a nearly 20 meters thick medium to coarse grained ar kose sand.

The thrust fault above mentioned in the east, at Nakaebata valley and Higashiebata valley, can be well observed At the former locality the thrust plane strikes N 60" E with 40' S dip, being the same as the strike of the Izumi group A 10 centimeters thick black fault clay is developed along the plane thrust up over the Kawauchi formation. The Kawauchi near the fault shows the following sequence, a 50 centimeters thick greenish pebbly clay, 50 centimeters thick black silt which laterally changes into micaceous silt and has yielded Trapa sp , Metasequoia dzstzcha MIKI, Cunnznghamia Konzshiz HAY., Juglans megacznerea CHANEY, Fortunearia sznensis REHD et WILS This is over - lain with a one meter thick small pebbly gravel inclined at about 10-15 degrees subparallel with the thrust.


34 M. Saito

At the latter locality the thrust plane strikes N 80" W and dips 45' S, and the Izumi group in this vicinity has the same strike and dip The Izumi is disturbed within a distance of five to six meters from the fault plane, forming there a kind of brecciated zone The Kawauchi formation near the fault consists of angular pebbles of sandstone and slate derived from the Izumi group in a matrix of blue silt Laterally this grades into blue silt At about 10 meters north of this outcrop and in a lower horizon the subangular to angular pebbles and cobbles of sandstone derived from the Izumi group make a 20 meters deep gorge.

In the bed of the Doki River at Naiden in Kotonami-mura, the basal part of the Kawauchi formation is exposed, the lowest consisting of arkose sand and is thought to be the weathered products of the basement granitic rocks. In this sand are found erect stumps with their roots penetrating the arkose sand, all still in original position (P1 4, Figs. 7-8) A~ound the roots are found thin covering of greenish silt Above this sand there is a 50 centimeters thick green sandy silt with plant fragments and with lenticular carbonaceous matter From the lenticles were found .!etasequoza dzstzcha MIKI, Pseudotsuga japonica SHIRASAWA, and Pzcea Maxzmowzczzz REGEL This is succeeded with a one meter thick, gravel deposit consisting of subangular cobbles and boulders of sandstone derived from the Izumi group and of granite from the basement, and cemented with green arkose sand (PI. 4, Fig. 9) Tracing this gravel deposit eastwards along the river bottom, it found to directly cover the basement of granitic rocks near the shrine in Naiden, Kotonami-mura

In the cliff of the road at Inoo in Kotonami-mura is exposed a one meter thick varved structure sandy silt overlain with one to two meters thick pebbly arkose sand and a one to one and a half meters thick muddy silt yielding abundant remains of Trapa discoidpoda MIKI and 7 tetragona MIKI This is succeeded with a 20 centimeters thick medium grained sand layer in which a dense parallel arrangement of stems and leaves admixed with the sand, and from this layer were determined such fossils as Cunnznghamza Konzshzz HAY., Chamaecyparz s pz s z f era ENDL and Metaseguoza dzstzhca MIKI.

Above this plant bearing deposit there comes a four or five meters thick pebbly sand in which is intercalated a 30 centimeters thick silt layer and sedimentar y structures of east-west trend are developed These sedimentary structures consist of the dragging down of one part and squeezing of the other, and associated with it are stretched slabs of silt and on the sides of the dragged down part of the silt there can be observed injections of the surrounding sand into it. This suffices to indicate the plastic nature of the silt layer, its elasticity and unconsolidated nature at the time of its formation This may also suggest that the conditions of the sedimentary basin may have not been stable This is overlain with unconformity by the Yakeotoge gravels. At the north side cliff of Hazama-ike in Manno-cho, in the northern part of this province, within a very restricted area there is exposed a one meter thick white tuff, covered with a 20 centimeters thick muddy peat which abuts against the granite From this muddy peat, pollen have been found, these comprise, Metasequoia ( 8 %) , Pzcea ( 7 %), Tsuga (1 O % ) , Abzes (4 5%), Pinus (36%), Quercus (14%), Alnus (12%) This may be a relic of the lacustrine deposits

J - 4. Eastern Province In the eastern province there are developed 500-600 meters high hills of granite flanking the

northern side of the Asan mountains which consist of the Izumi group. The lacustrine deposits occur mostly on the northern side of this granitic hills or as valley filling deposits of the granitic hills and no lacustrine deposits have been found in association with the Izumi group as seen in other province. These will be described in the following lines and it may be stated that the present preservation of the lacustrine deposits in the lower parts of the ~el ief indicates the degree of erosion that had taken place after their deposition. Although plant fragments are found at several places of the lacustrine deposits in the province, no determinable ones have been collected.

The type locality of the Taman formation which is distributed in this eastern province is the road cutting in the low reliefs of the granitic hills between Taman and Kudarikura in Ayagami-mura. Here the lowest part of the formation is not exposed but below the Taman bridge in Taman, Ayagami-mura, a two meters thick blue sandy silt becoming white upon weathering and intercalating lenticular gravels and some plant fragments is developed, and above it is a two meters thick gravel bed of which gravels are subangular cobbles of hornfels, diorite, granite cemented with arkose sand included into the gravel bed as derived materials from the basal conglomerate of the Izumi group. Tracing this gravel deposits southwards along the stream bottom they abut against the basement granite and the boundary is obscure.


The Ge0log.y o,f' Kagawa and Northern Ehime Pre,f'eclu~es 35

The upper part is exposed in the east of this area at Shimowada, Ayagami-mura. Above the gravel deposit described above there is a four meters thick pebble deposit of subrounded gravels of granite and sandstone derived from the Izumi group, overlain with a one meter thick blue sandy silt and a five meters thick arkosic sand This is covered with a five meters thick gravel deposit of subrounded to subangular medium to large pebbles of sandstone derived from the Izumi group, and also small subrounded pebbles of both slate and granite and these are cemented with arkose sand. This is covered with unconformity by the Yakeotoge gravels.

In the north of this area in the vicinity of Kamisenbiki, Ryonan-cho, there is an alternation of tuffaceous silt and arkosoic sand measuring about 10-15 meters in thickness This facies is also of the lacustrine deposits.

In the eastern part in the vicinity of the Higashiueda Primary School in Yamada-cho, Kida-gun, a four meters thick srkose sand with limonite layers intercalated is exposed (PI 13, Fig. 3) .

At Nishiueda in the south of Jinnai-ike covering the granodiorite with unconformity there is exposed a 50 centimeters thick tuffaceous silt overlain with a four meters thick arkose sand with intercalated limonite layers, in upward succession.

In the vicinity of Nishihoji, Yamada-cho in Kida-gun there is exposed a 50 centimeters to one and a half meters thick gravel deposit consisting of weathered granite and andesite cobbles lying unconformably upon the 30 centimeters tuffaceous gray silt under which there is a one meter thick arkose sand with weathered grains of feldspar grains Under this, there is exposed a 30 centimeters thick tuffaceous clay. Here the formation strikes N 40' W with 30° SW dip, thus there is an angular unconformity between the lacustrine deposits and the terrace deposits

In the road cliff in Nakashiro in Miki-cho, Kida-gun there is exposed a five meters thick terrace gravel deposit covering a one to one and a half meters thick blackish purple, faintly stratified, brecciated tuff with angular fragments included. This facies is thought to correspond to the Taman for mation.

In the northern part of this province in the vicinity of the summit of Yashima hill, within a very restricted area there is exposed unconformably above the reddish purple agglomerate of the Sanuki group, a two to five meters thick granule sand deposit in which are intercalated small pebbles of subangular to subrounded glassy biotite andesite, biotite granite and rarely also of mica- schist, and the cement of decomposed coarse arkosic sand. Stratification is developed at about five centimeters intervals and the granule and sand zones alternate. The biotite flakes are parallel with the stratification being almost horizontal This deposit is also considered to belong to the lacustrine deposits (Pl. 5, Figs. 1, 5)

The lacustrine deposits which extend through the four provinces distinguished in this article occur only sporadically either as valley filling deposits of the basement of granitic rocks, along the northern sides of the granitic masses or along the foots of the Izumi group making up the mountain range extending in east-west direction. Also they are frequently covered with younger deposits and therefore their direct tracing in the field is often difficult. However, from the characteristic lithofacies as well as the relation with the older rocks, distinction of the lacustrine deposits is not difficult.

The differences in lithological characteristics according to locality within the four provinces seems to indicate the local environmental conditions of the lake. The good development of gravel facies and of arkose sands is a typical feature of the deposits and readily indicates the rapid deposition in those areas and also that weathering must have been progressive there. The rapid deposition of such deposits can be noticed from the orientation of the gravels and sands making the deposits as well as from the strong relief of the basement over which the lacustrine sediments were deposited.

As will be lepeated in another section of this article i t is evident that the lacustrine deposits originally had an extensive distribution, but are now only represented as erosion relics, being preserved in the depressed areas such as in the valley of the granite hills then existing. This may also be indicated from that true deep water lithofacies of lacustrine deposition are not found because the greater part of the lake has been removed by erosion, and only the lower parts of the originally deposited sediments are now preserved


M. Saito

K Yakeotoge Gravels

The Yakeotoge gravels are a name proposed for the gravels distributed a t the heights of about 80-300 meters, the latter at Yakeo-toge (pass) and the former Konan-cho, Kagawa-gun, Kagawa Prefecture These gravels are unconformable with the older deposits such as the lacustrine deposits, Izumi group and granite, and the younger deposits consist of terrace deposits with which it is unconformable. The gravels of the Yakeotoge are generally subrounded to subangular pebble to cobble size, rarely with boulders, and consist of sandstone and slate of the Izumi group, granite, crystalline schist, quartzite, hornf els and andesite, being derived from the older rocks. The proportions of the kinds of included gravels are related with the kind of rocks making the basement and those of the hinterland, thus they show considerable variation according to places The matrix is generally in the range of small pebbles, granule to coarse grained sand However, a t places the matrix may be reddish and loamy as at Kawakami hill in Kawauchi-cho in Ehime prefecture, the Nukita hill in Mishima City in Ehime Prefecture and the Kudarikura hill in Ayagami-mura in kagawa Prefecture. And to be mentioned is that the gravels are covered with an about one meter thick white ash layer a t the summits of the Shimowada hills in Ayagami-mura in Kagawa Prefecture, being found from no other locality.

These gravels are distributed in the four distinguished provinces and the thickness varies from 15-60 meters. The Yakeotoge is distributed chiefly in the southern part of the studied four provinces or in the northern parts of the mountain range traversing the island of Shikoku

The type locality of the Yakeotoge gravels is the pass leading from In6 to Nakato in Kotonami- mura, Nakatado-gun in Kagawa prefecture in the Mitoyo-Nakatado province (PI. 5, Fig. 3) Here the Yakeotoge gravels cover the basement granite, Cretaceous Izumi group and lacustrine deposits with marked unconformity (P1 5, Fig 6) At the type locality the gravels measure about 40 meters in thickness and the range is to about 20-50 meters in thickness in the vicinity. The gravels consist in the lower part of a two- five meters thick subrounded small cobbles of granite, sandstone and slate of Izumi group in addition to small pebbles cemented with arkose sand. Above this the 35 meters thick gravels consist of subrounded to subangular cobbles of sandstone and slate derived from the Izumi group sometimes with pebbles of slate and this deposit is cemented with coarse sand to small pebbles The distribution of the Yaketoge gravels is sporadic, but can be observed in the region of four provinces.

In the Aso hills about five kilometers south of Matsuyama City and the Kawakami hills in Kawauchi-cho, Onsen-gun in the Matsuyama province, a t the former locality the 30-50 meters thick Yakeotoge gravels cover the Izumi group with unconformity, and build the 200 meters high hills. These consist of subangular to subrounded pebble to cobble size sometimes with 50 centimeters in diameter boulders derived from the slate and sandstone of Izumi group, black schist, hornfels, andesite and of quartzite, in a matrix of granule to small pebbles and sometimes of tuffaceous sand In the valley south of Shigemitsu there is a N-S treding fault with vertical angle cutting the Yakeotoge gravels At the locality above mentioned, the Yakeotoge gravels cover the lacustrine deposits and the Izumi group with unconformity. sometimes abutting against the vertically inclined Izumi group (P1 6, Fig 5). The gravels measure 10-30 meters in thickness, and consist almost wholly of sandstone derived from the Izumi group, being subangular to subrounded, pebble to cobble size and sometimes with boulders intercalated and sometimes a 30-50 centimeters thick layers of small to medium sized pebbly zone, the matrix consists of coarse grained sand to small pebbles In the upper part of the Yakeotoge gravels the matrix becomes a reddish loam

In the Niihama-Saijo province the Yakeotoge gravels in the 80-150 meters high hill in the southwest of Doi-cho, measure about 10-30 meters in thickness and cover unconformably the Izumi group, and consist of angular schist cobbles and subrounded Izumi cobbles to boulders cemented with loam. In the Nukita hills in the east of Mishjma City, the Yakeotoge gravels are found at a height of 100 meters, measure about 20 meters in thickness and cover the Izumi group with unconformity. The gravels consist of subrounded cobbles of the Izumi sandstone and angular elongated cobbles of black schist cemented with reddish loam. In the immediate east in the vicinity of Kanagawa, the Yakeotoge gravels measure about 20 meters in thickness and cover the Izumi group with unconformity. The gravels consist of subrounded pebbles and cobbles of schist, angular cobbles of the Izumi sandstone with a matrix of decomposed schist and micaceous sand

In the Mitoyo- Nakatado province the Yakeotoge gravels in Saida-mura build the 200 meters high


The Geol0g.y o,f' Kagawa and Northern Ehime Pre,f'ectures 37

hills and meaure about 30 meters in thickness They consist of subangular to subrounded pebbles to cobbles with sandstone boulders in the lower part The gravels consist of the sandstone and slate of Izumi group, schist, quartzite and granite and the matrix consists of decomposed Izumi sandstone of medium to coarse grained size Of the sandstone gravels those of bluish-green color are outstanding and rarely soft-silt rocks are in the gravels. Near the Asan montains consisting of the Izumi group in the south, the gravels become covered with talus deposits and thus the boundary between i t and the Izumi group is not distinct.

Although there i s no distribution of the cr ystalline schist in the hinterland, it is interesting to notice that gravels of schist are included in the gravel deposit, and they are rather commonly intercalated. These schist gravels are thought to have been derived from the gravels intercalated in the lacustrine deposits

The type locality of the Yakeotoge gravels lies within this province and has already been described and will not be repeated a t this place.

In the eastern province, the Yakeotoge gravels are exposed in the 100-200 meters high hills distributed between Senbiki and Shimowada bordering the townships of Ryonan cho, Ayagami-mura and Konan-cho. The Yakeotoge gravels cover the basement granite and lacustrine deposits with unconformity. They measure about 20-30 meters in thickness, consist of subangular to subrounded pebbles and cobbles of Izumi sandstone predominating with subordinate granite, slate, liparite, and especially the slate gravels are well rounded and grade from small pebbles to granule size The matrix consists of sand derived from decomposed granite and Izumi sandstone, and especially in the upper part of the deposit the gravels are weathered and therefore soft, the matrix consists of reddish loam to whitish yellow kaolin (Pl. 13, Fig 5). In this province the gravels become smaller in size towards the north and the thickness decreases to about 10 meters

Viewing from the distribution of the Yakeotoge gravels in the present province and their relation with the basement, i t i s considered that their surface is an erosion surface. This may be upheld by that the basement granite is exposed a s inliers in the area of distribution of the Yakeotoge gravels, this indicates a prolonged period of erosion Also from the distribution and thickness of the gravels, i t can be assumed that they originally had very extensive distribution although now only developed sporadically.

The yakeotoge gravels are considered to be uplifted fan deposits and the oldest, while other fans are denoted as middle and younger The middle fan deposits are estimated to have about the same height as the older terrace deposits although their areas of development are not the same.

L Terrace and Fan Deposits

The higher terrace of 60-80 meters in height above sea-level i s covered with a 5 or 10 meters thick gravel deposit overlying silt and tuffaceous rocks referable to the lake deposits (P1 5, Fig. 2) . The contact although appearing to be conformable i s due to the reworking of the underlying silt and tuffaceous deposits at the time of the deposition of the overlying gravels and thus resulting in the production of a conformable-like bounndary The underlying sediments however are a continuation of the lake deposits.

In the Niihama-Saijo province in Ehime Prefecture there are no terrace deposits equivalent with the ones above mentioned, but instead there are fan deposits measuring 60-100 meters in height and consisting of gravels of schist and Izumi sandstone, being of rounded to subrounded cobbles From their degree of denudation these fan deposits can be correlated with the higher terraces developed in Kagawa Prefecture In this province the fan deposits are developed in the environs of Okamura in the south of Komatsu City and at Kishinoshita in the south of Niihama City, in the environs of Toyooka in the south of Mishima City.

The distribution of the higher terraces in the Matsuyama province are the hills of Harano-machi about five kilometers south of Matsuyama City, the hills of Shizugawa in Kawakami- cho in Onsen -gun where both range in height above sea-level at about 80-100 meters consisting of three to 10 meters thick gravel covering These gravels are subrounded to rounded cobbles and boulders of Izumi sandstone and schist

In the Mitoyo province the higher terraces are distributed in the environs of Komatsuo in Yamamoto- cho, in the vicinity of Mori in Saida-mura, where they measure about 80-100 meters in height and are covered with 5-10 meters thick gravels of the Izumi sandstone and granite of cobble to boulder size and subrounded to subangular i n shape


38 M . Saito

In the Eastern province the higher terraces are found between Ikenishi and Sue in Ryonan-cho, in the vicinity of Kawahigashi in Konan-cho, the environs of Sogo in Yamada-cho, where they are 70-110 meters in height and make the hills in those areas. These consist of 5 to 10 meters thick gravels in general but that of Sogo is only one to two meters in thickness and is characteristic in its lateritisation The gravels are rounded to subangular andesite and granite of pebble to cobble size.

The lower level terraces measuring in general about 60-70 meters in height and covered with 5 to 10 meters thick gravel deposits and are found in both Ehime and Kagawa Prefectures In Ehime Prefecture in the Matsuyama province the lower level terraces of Kagawa Prefecture cor~espond to the fans developed in Kawakami-cho in Onsen-gun. These fan deposits consist of five to more than 10 meters in thickness according to places of gravels of the Izumi sandstone which are subrounded and cobble to boulder size

In the Niihama-Saijo province the fans which correspond to the one of the Matsuyama province and to the low level terraces in Kagawa Prefecture are found along the Nakayama River in Tambara, Onsen-gun Here they measure about 60-140 meters in height, consist of gravels of the Izumi sandstone, Paleozoic sedimentaries and granite, which are subrounded to subangular cobble to boulder in size Their exact thickness could not be measured but it is thcught that they exceed 15 meters.

In the Mitoyo province the low level terraces are found in the vicinity of Komatsuo, Yamamoto-cho where they occupy the forepart of the higher terraces. The low level ones measure about 50-70 meters in height and are covered with subrounded cobbles of the Izumi sandstone attaining about five to 15 meters in thickness

Fan deposits corresponding to the low level terraces are found in the vicinity of Yoshino in Manno- cho, where they attain 50-60 meters in height and consist of subrounded cobbles of the Izumi sandstone

In the Eastern province the low level terraces are found below the higher terraces and in their foreground, measuring 50-70 meters in height and consist of subrounded and subangular cobbles of andesite and granite.. They are developed in the same areas as those of the higher terraces already mentioned.

Alluvial deposits are found in all of the provinces along the courses of the present day drainages. The alluvial deposits are developed as fans and the main drainages named from west to east are, Shigenobu River, Nakayama River, Kamo River, and the Kuniryo River all in Ehime Prefecture The Saida River, Doki River, Aya River, Godo River and the Kasuga River in Kagawa Prefecture.

In general all of the deposits become broader towards the north In the Takamatsu area boring data shows that the thickness attains about 30 meters and the sediments comprise an alternation of clay and gravel with admixture of marine shells only at about two meters from the surface

From the available data it is judged that the alluvial deposits in Kagawa Prefecture average about 20-30 meters in thickness.

111. Igneous Activity

The first igneous activity experienced in the present area consists of schalstein found in the lower to middle parts of the Yamaguchi group. This schalstein indicates intense volcanic activity during deposition of the Yamaguchi sediments in the geosyncline. This measures about 500 meters in thickness and is distributed extensively in the Okayama region, but in the surveyed area i t occurs only in the island of ShGdo-shima offing Kagawa Prefecture. The age of this activity is pre-Permian and post -lowest Yamaguchi.

The Ryoke granitic intrusion occurred a t the end of the Paleozoic. I ts distribution is mainly the area south of the median axis of the Setouchi Sea.

The next igneous activity is represented by the acidic tuff layers found in the upper part of the second cycle and in the upper part of the third cycle of the Izumi group; these measure about 10-15 meters in thickness and extend from the Sanuki mountains to Matsuyama City. This tuff is grayish or greenish, very compact, fine grained and liparitic. From that there could be observed no variation in the thickness of the ash layers, the origin could not be determined. These activities are during the Hetonaian stage, particular 1 y during the middle part .



The Geology o f Kagawa and Northern Ehime Pre,f'ectures. 39

The granitic batholith distributed in the area north of the median axis of the Setouchi Sea is thought to have intruded a t the end of the Cretaceous probably associated with the down sinking of the Izumi parageosyncline.

The only volcanic activity noticed in the Kuma group is represented by tuffaceous shales occurring in the basal part of the upper Eocene Myojin formation. This is white tuffaceous shale and it may be inferred that during deposition of muddy sediments there was ash falls from some distant volcano, but whether the tuffaceous sediments are reworked from some pre-existing tuffaceous rock or admixed by ash fall into the muddy sediments could not be determined. The distribution of this tuffacso~ls shale is confined to the vicinity of Tobe-cho, Ehime Prefecture.

In the Miocene Tonosho group there are found in its basal part in association with lignite beds three, 30-50 centimeters thick layers of bentonitic clay. This bentonitic material is derived from liparitic tuff by subaerial denudation. This is distributed in the vicinity of Kitaura, Tonosho -cho in Sh6do -shima.

The Sanuki group which ranges from late Miocene to early Pliocene is volcanic in its larger part and comprises tuff or tuff breccia, hornblende andesite agglomerate, two pyroxene andesite agglomerate and sanukite lava, attaining a total thickness of about 100-150 meters. This volcanic complex is distributed in the northern part of Kagawa Prefecture. Its correlative is the Ishizuchi group in the Matsuyama province which is also volcanic in origin, being composed of tuff, tuff breccia, sanukite and xhombic pyroxene andesite lava. Associated with this volcanisms is the development of abundant dikes showing north to south trends in Kagawa Prefecture, which in general, but in the vicinitys of Ishizuchiyama and Sar agamine in Ehime Prefecture, the dikes show east - west directions contrary to those found in Kagawa Prefecture This differences in directions of dike trends may reflect the pattern of the foundation roclirs in those areas.

Microscopical studies of the volcanic rocks show that there is a general tendency in the order of pitchstone -, quartz -mica andesite -, biotite andesite -, hornblende biotite andesite- , hornblende pyroxene andesite-, and sanukitic rocks by which the series ends.

Volcanism during deposition of the Pliocene Mitoyo group may be indicated by the tuff aceous sandstone in its upper part . This is distributed chiefly in Kagawa Prefecture and in the south of the Hiuchi Sea. Whether this tuffaceous sediments are reworked or actually represent ash falls during deposition of the sands could not be determined. It may be probably that the tuff is reworked from the Sanuki group of volcanic rocks.

A one meter thick white ash layer covers the Yakeotoge gravels only in a part of the Shimowada hills in Ryonan-cho in Kagawa Prefecture. Not being distributed in other parts of Kagawa Prefecture and do not cover the Higher or Lower Terraces, the origin is difficult to interpret. However, there is a one-two meters thick red soil covering the granitic areas in Kagawa Prefecture and in Ehime Prefecture there is a one meter thick red loam in the upper part oi the Yakeotoge gravels. Whether the red soil covering the granitic rocks is decomposed granitic material or correlative with the ash layer mentioned before may be problematical. However, i t can be interpreted that the white ash layer covering the Yakeotoge gravels in the Shimowada hills, the red loamy sediments in the upper part of the Yakeotoge gravels in Ehime Prefecture and the red loamy material covering the granitic rocks may all belong to a similar phenomena, being distinguished from one another by their grade of decomposition or weathering according to the rocks upon which they over lie.

On the summit of Kokubudai in Kagawa Prefecture there is found two meters thick red loam covering the sanukite. However, since weathering of the sanukite may result in the development of red loamy sediments, i t is questionable whether this stone artifact bearing red loam can be correlated with the ash layers in the upper part of the Yakeo-


40 M. Saito

toge gravels. I t may be suggested that the red loamy sediments and the white ash layer may corre-

spond in time with the older ash deposits covering the higher planes in the Kwanto region of central Japan, probably being nearly equivalent with the Tama plane.

IV. Geological Structures

For the sake of convenience the different geological structures will be described under subheadings follows.

A Unconformities

The unconforrnities recognized in the present field occur between the basement of Ryoke complex and the Cretaceous Izumi group, between the Izumi group and the Kuma group, between the Kuma group and the Tonosho group, the Tonosho-Sanuki break, between the Sanuki group and the Mitoyo gxoup, and the Mitoyo-Yakeotoge break.

A- I . Contact of the Ryoke Complex and the Cretaceous Izumz Group The unconformity between the Ryoke granite and the Izumi group can be observed at Kasuga,

Manno-cho, Kagawa Prefecture; Korobiishi, Kotonami -mura, Kagawa Prefecture; and Saida-naka, Saida-mura, Kagawa Prefecture The contact at the first mentioned locality is shown by the basal conglomerate of the Izumi group overlying a 20 meters thick arkose zone superposed on the Ryoke granite. Here the unconformity is obscure and no clear boundary can be drawn but it is considered that the basal conglomerate is conformable with the arkose This type of unconformity is a blended one and an unconformity zone is thought to exist

At the second mentiond locality the basal conglomerate of the Izumi consists of cobbles of hornfels and granite in a matrix of arkose sandstone and this directly covers the Ryoke granite (P1 6 , Fig 2).

At the third locality a dark colored slate forming the base of the Izumi directly covers the Ryoke granite. This slate is thought to be a surface soil at the time of marine transgression of the Izumi group (Pl. 6 , Fig 1) Also the unconformity between the Ryoke metamorphics or granites and the Izumi can be observed in the valley in the south of Aonami, Ehime Prefecture; in the valley of Shionoe, Kagawa Prefecture; Shiroyama, Hiketa-cho; and Kii, onohara-cho, both of Kagawa Prefecture.

A-2. Unconformzty between the Izumz Group and the Kuma Group The contact between the Izumi group and the Eocene Kuma group can be observed at the summit of

the 453 3 meters high hill in the south of Uemura, Shigenobu-cho, Onsen-gun, Ehime Prefecture. Here the lower palt of the Kuma group, the Nimyo fomation almost horizontal lies directly upon the eroded surface of the Izumi group whose strike is east-west with 45 degrees northward dip.

A-3 Unconformity between the Eocene Kuma Group and the Mzoene lonosho Group

Although no direct contact of the Eocene Kuma group with the Miocene Tonosho group can be observed in the field owing to their localities being remote, the great differences in geological ages suggest the existence of an unconf or mity .

A-4 Break between the Tonosho Group and the Sanukz Group The contact between the Tonosho group and the Sanuki group occurs at Hidoyama in Sh6do-shima

in Kagawa Prefecture Although the direct contact between the two groups can not be observed owing to the thick covering of talus deposits, i t is evident from the differences in structure that an unconformity exists. The structure of the Tonosho group strikes N 65' E and dips 10" NW whereas that of the Sanuki group trends N 70" W with dips of 20 degrees towards the northeast This discordance in structure reflects the existence of an unconformity between those two groups.

A-5 Break between the Sanukz Group and the Plzocene Mztoyo Group The contact between these two groups can be observed on the summit of Yashima in Takamatsu

City, Kagawa Prefecture, where the irregular surface of the agglomerate at the upper part of the Sanuki group is covered with the alternation strata of coarse sand and granule gravel of the Mitoyo group and is also horizontal or abuts at places (P1 5, Fig 5) Also abundant gravels derived from the Sanuki group occur as pebbles in the lower part of the Mitoyo group of lacustrine origin.

A-6 Break between the Mztoyo Group and the Yakeotoge Gravels The unconformity between the Pliocene Mitoyo group of lacustrine origin the Yakeotoge gravels can


The Ge0log.y of Kagawa and Northern Ehzme Prefectures 41

be observed near the Manno-ike , Manno-cho, Nakatado-gun , Kagawa Pref ecture, at Kawauchikami, Yamamoto-cho, Mitoyo-gun in the same Prefecture, and at Sangenya, Kawauchi-cho, Onsen-gun, Ehime Prefecture At the first mentioned locality the arkose sand in the upper part of the Mitoyo group is provided with irregular surface and many depressions in which the Yakeotoge gravels were deposited. (Pl. 6, Fig 7) This same kind of contact can be observed at the other two mentioned localities. Since the gravels in the uppermost part of the lake deposits are in contact with the gravels of the Yakeotoge distinction between them is at times quite difficult

I t may be mentioned that each of the different groups come into direct contact with the basement Ryoke granite and Ryoke metamorphics according to places and since such an unconformity is easily recognized and very distinct, thus they have not been described separately for each locality.

Among the outcrops showing the unconformity between the Pliocene lake deposits and older rocks there are several worthy of mentioning a t this place For example the contact between the lake deposits and the Izumi group in a cliff about 500 meters south of Togawa in Saida-mura, i t i s observed that

Table 4 Showing the Respective Geological Ages of the Diastrophic Movements and Volcanic Activities in the Present Area

, Directions of the \ tectonic struc- E-W NW-SE -,, tures according NE-SW 1 1 ! N-S 1 Remarks - . to age ENE-WSW

Geological age 1-Post -middle Pleistocene 1

I I I 1 I I Displacement o f i h e Pleistocene de-

I - 1 x 1 1 X I posits. (normal, thrust faults) Warv- Recent 1

Post -Pliocene

Pr e - Pleistocene

Late Pliocene --

Post -Miocene I 1 A X

Pre-middle Pliocene 1 - 1 I-- Late Miocene I x Post - middle Miocene 1 1 1

- X Pre-late Miocene

Early -

middle Miocene -

Post-Eocene 1 1 1 1 - I 1 -

Pr e-Miocene

Middle -,

I I x I late Eocene

Post -Cretaceous I I 1

I - -

Pre-middle Eocene 1 / 1 Late Cretaceous

Post - Per mian -

Pr e -late Cretaceous .. . - - - - - --- .----

Paleozoic

ing Third activity of the Median Line

(thrust, normal faults). Block move - ment, development 'of the thrust and normal faults and second Inland sea -

Deposition of the Mitoyo group and u ~ l i f t a t the close of the Pliocene

Pr olonged erosion, development of the lacustr ine basin

~

Intensive volcanism (Setouchi vol- c a n i c ~ ) . NW, N-S trending dikes

Block movement, development of normal and reverse faults with little or no folding - . .

Deposition of the Tonosho group accompanied with weak volcanism and uplift a t the close of the middle Miocene --

Second activity of the Median Line (thrust fault). Little or no folding. Development of the first Inland sea --- .

Deposition of the Kuma group ac - companied with weak volcanism and uplift a t the close of the Eocene-- - .. . . .

First activity of the Median Line.. Folding of the Izumi group. Prolong- ed erosion, development of the sedimentary basin of the Kuma group

- - - - Deposition of the Izumi group, a c - companied with weak volcanism and uplift a t the close of the Cretaceous.. Intrusion of Chugoku Cretaceous granite --- . . .. . .-

Folding of the Paleozoic group, dy- namic matamorphism Intrusion of Ryoke granite . Prolonged erosion, 1 development of the sedimentary basin of the Izumi group

- ~

Deposition of the Chichibu and Yama- guchi groups with intense volcan- Ism, plutonism and granitization .. IJolift a t the clnse nf the Per.mian


42 M. Saito

the former were deposited in a small crevice of the latter, abutting there against. Whether this was a mere small crevice, some kind of cave or cavern developed in the Izumi group could not be determined , but i t is thought that the original opening may have been something like a cavern, eroded on land before the filling by the lake deposits. (Pl. 6 , Fig. 4)

In the cliff of the Saida River at Kuboshita in Saida-mura, the lake deposits of arkose sand carrying up to boulders of granite lie directly upon the basement of granite without the development of an arkose sand deposit. This shows that the weathered granite products were transported into the lake as i ts basal sediments in this area (PI. 5, Fig. 7)

In a cliff near the Izeki pond at Izeki, Onohara-cho in Kagawa Prefecture, the lake deposits consisting of sandy silt with angular fragments and very large blocks of the Izumi group are found lying upon the very irregular surface of the Izumi group with marked unconformity. This shows that the lake sediments were deposited over the eroded and weathered surface of the Izumi group which may have formed a hill or mountain a t that time. The lake sediments abut against the layered rocks making the Izumi group. (PI. 5, Fig. 6)

B. Faults

In the present field several kinds of faults are recognized such as normal, thrust, reverse, rotational types. Among the many recognized faults several of the more important are named and only those which have direct relation with the geological structures are plotted in the geolgical map whereas the minor ones which are associated with major ones ox which do not have significance with the geological structure were omitted. Those given names will be described in the order mentioned above.

B-1. Kishinoshita Fault (PI 1, Fig. I ) This i s a normal fault stretching from Kishinoshita, Niihama City in Ehime Prefecture east-west with

the northern side thrown down, eastwards for two kilometers. By this fault only the upper Pleistocene alluvial deposits are cut, and a distinct fan-scarp is preserved. This was first recognized by TSUJIMURA and TANJI (1932).. This fault i s considered to extend westwards from Kishinoshita to fan-scarp in the vicinity of Ishioka Shrine in the north of Komatsu City for about 12 kilometers.

B-2. Saragamine Fault This is a normal fault extending along the northern slope of Saragamine in Onsen-gun, Ehime

Prefecture for six kilometers in east-west direction The strike i s N 70' E with 70' S dip. This fault cuts the Ishizuchi group. The fault of nearly the same type as above mentioned is developed about one kilometer in i ts north

B-3 Toyooka Fault This is a normal fault extending from Kobayashi, Doi-cho in Ehime Prefecture for about six kilo-

meters to Nishisangawa, Toyooka-cho The general trends E-W with the norhexn side thrown down. By this fault only the upper Pleistocene fan deposits are cut, and a distinct fan scarp is preserved. B-4. I,yo Fault This is a normal fault assumed to extend from Konogawa, Kaminada-cho, Ehime Prefecture for

about 10 kilometers to Ueno, Iyo City in the same Prefecture The general strike is ENE-WSW with northwestward throw. This fault occurs between the Izumi group and the Gunchu formation, and in the southwestern part, it exends into the Izumi group and is formed a crushed zone there B-5. Tambara Fault This is a normal fault assumed to strech from Nagano, Tambara-cho in Ehime Prefecture for about

10 kilometers to Kusunoki in the same township. The general strike is N 10" E with eastward throw. This fault cuts the Izumi group and is cut by the Okamura fault which is a rotational fault B-6. Ryuozan Fault This is a normal fault extending from Nishinokawayama, Saijo City, Ehime Prefecture north-northeast-

wards for about 12 kilometers to Tsugoshi in the same City where i t comes into contact with the Median Line. The strike is almost NNE-SSW dipping about 80 degrees to the west and extends through the Sambagawa metamorphics. This fault is covered by the Eocene Kuma group and is thought to have had relation with the folding of the Izumi group at the end of the Mesozic B-7. Kawauchi Fault This is a normal fault extending from Otoda, Kawauchi-cho, Onsen-gun, Ehime Prefecture to six

kilometers southwestwards through the Izumi group. In the vicinity of Otoda, this fault is nearly


The Geolog,y o,f Kagawa and Northern Ehime Pre,ftctures

vertical and cuts the sanukitic andesite B-8. Kaburazaki Fault (Pl. 7 , Fig. 1) This is a normal fault extending from Nagahama in Tonosho-cho in ShBdo-shima for about 1.5 kilo-

meters to Oe in the same township The general strike is N 55" E with dips of 65' SE. This fault occurs between the Tonosho group and the Paleozoic rocks and between them there is developed a 10 meters thick crushed zone and a 30 centimeters thick fault breccia and gouge, the latter above the former. At the road side cliff in Oe, there are found a number of fissure filling-like deposits developed in the Paleozoic rocks along the fault I t could not be determined whether the Miocene conglomerates were dragged into the clayslate of older rocks due to faulting or whether the former were deposited in a small crevice of the latter assoiated with faulting. From this evidence i t is considered that there were two times of fault activity, once before deposition of the Miocene sedimentaries and again after deposition of the Tonosho group and before deposition of the Sanuki group. In other words the southeastern part of the thrown down side was eroded away before deposition of the Miocene Tonosho group, and faulting occurred along the unconformity after deposition of the Tonosho group, The same type fault a s above mentioned occurs between the Tonosho group and the Paleozoic rocks or granitic rocks with N-S trends or ENE-WSW trends, namely the Mime fault. (P1 1, Fig. 2)

B-9 Monnyu Fault This is a normal fault and is observed at Monnyu-ike, Okawa-cho, Kagawa Prefecture. This fault

is conside~ed to be a large one because of having 20-30 centimeters thick fault clay or gouge, i t s strike is N 20" W with 40' NE dip. Although its extension can not be determined because of cutting the Ryoke g ~ a n i t e i t i s considered to be an important one B-10. Gunchu Fault (P1 7 , Figs. 4-5) This is a thrust fault extending from the reservoir in Mori about three kilometers southwest of

Iyo City to 1 5 kilometers farther southwestwards By this fault the Izumi group rides over the Gunchu formation. The general trends N 60" E with dip of 20" SE in the southwestern part whereas in the northeastern part the dip angle is not clear B-11. Okamura Fault (P1 8 , Fig. 7) This is a rotational fault extending or traced from Daito in Komatsu City, Ehime Prefecture east-

northeastwards to Kamenoko in Niihama City for a distance of 17 kilometers. This was first recognized by NAGAI (1954), who claimed it to be a reverse fault.. This fault comes between the Izumi group and the Okamura formation This fault is considered to extend westwards from Daito to the Matsuyama Castle in Matsuyama City for about 25 kilometers through the Izumi group but near the Matsuyama Castle the fault separates the Izumi group from the Ryoke granite with strike of N 70" E and 40" N dip. This fault is considered to be a rotational fault because the dips change and the fault is both a normal and reverse one along the same line.. B-12. Shimone- Tsune,yama Fault This is a thrust fault extending from Tsuneyama in Tomisato-mura, Uma-gun, Ehime Prefecture

west-northwestwards for about 20 kilometers to Daishoin, Niihama City where i t comes into contact with the Median Line. The strike is almost east-west dipping about 45 degrees to the south and extends through the Sambagawa metamorphics. This was named by KOJIMA (1955).

This is thought to have had relation with the folding of the Sambagawa matamorphics a t the end of the Paleozoic. B-13. Ebata Fault (Pl. 8 , Fig. 6) This is a thrust faul textending from Kawauchi, Yamamoto-cho, Kagawa Prefecture to Eabta in Manno-

cho for about 20 kilometers in N 60" E to east-west trend The dip is towards the south or southwest a t about 40--50 degrees. The Izumi group rides over the Kawauchi formation. Near Nakato in Kotonami- mura, Kagawa Prefecture, this fault extends into the Izumi group and because having the same strike and dip as the Izumi group its tracing is difficult but sometimes This is covered unconformably by the Yakeotoge gravels. This fault corresponds to the Kubo thrust of IMAMURA and NAKANO (1950). The thrust fault having the same strike and dip a s above mentioned fault extend into the Izumi group in its south and makes the crushed zone. B-14. Kikaku Fault (Pl. 8 , Fig. 8 ; PI. 9, Fig. 8) This is a thrust fault and is observed a t the road side cliff in the south of Kikaku-Park, Nagao-

cho, Kagawa prefecture. By this fault the Ryoke granite rides over the Taman formation and the higher terrace gravel and

between them there is developed a one meter thick white fault clay and the Ryoke was crushed and


44 M. Saito

disturbed for a fairly long distance in width. The strike is almost E-W dipping about 20-30 degrees to the south and although of considerable magnitude, this fault can not be traced for any great distance because of being covered by the lower terrace gravels or alluvial deposits.

Also similar thrust is observed at the south cliff of Kabutoyama in the west of Zentsuji-City. There the Ryoke rides over the tuff breccia of the Oda formation.

B-15. Setoucki Faults From the directions of the bays, crevices and inlets of the islands studied in the Setouchi Sea, the

peninsulas and the many blocks (namely, Yashima scarp) observed on the mainland, the orientations of the islands themselves, the relationships of them to the structures observed on the mainland, and faults observed on some of the islands, i t is thought that there are two different trends in the fault system of the Setouchi area. One system trends roughly in east-west direction (ENE-WSW) parallel with the shape of the present Setouchi Sea and the other is transverse to it or roughly north to south in direction (NNW or NNE) These different fault systems are thought to have had bearing on the development of basin of the Setouchi Sea and to have had control or at least great influence on the trends of the longer axis of the respective islands and of the directions of the inlets, coves, embayments and other features now preserved there.

C Median Line

The Median Line a t different localities shows certain features of interest as described below according to locality.

At Inuyose -toge (pass), Nakayama -cho, Iyo-gun, Ehime Prefecture, the strike of the Median Line is N 40' E with 40' N dip, and the sandstone of the upper part of the Izumi group in the form of pseudoconglomerate rides over the green schist of the Sambagawa metamorphics. At Oiwabashi, Tobe- cho in the same township, the Izumi group rides over the Kuma group with fault strike of N 45" E and 45" N dip. Here the Izumi group is considerably disturbed for a thickness of about seven meters where there is developed tectonic conglomerate cemented with black mud. At Inai in Kawauchi-cho, Onsen-gun, the Izumi group and Kuma group are in contact but the contact could not be observed However, the strike and dip of the Kuma group is N 80" W , 30" S whereas that of the Izumi is N 75" W, 50" N, and the relation is considered to be a thrust, with the latter riding over the former.

At Yuyaguchi, Tambara-cho, Onsen-gun, Izumi group rides over the black schist and the fault plane strikes almost east-west and the dip is about 20 degrees towards the north There is developed a one meter thick mixed breccia zone of sandstone and schist, and four or five meters thick felsitic rock having sandstone fragment as xenolith like and the black slate of the Izumi group in contact with the Sambagawa metamorphics is disturbed over a considerable distance Here the strike of the Izumi group is N 70" E with 50' S dip, whereas that of the Sambagawa is N 40" W with 40' N dip. (PI 8, Figs. 1-3; P1. 7, Fig. 2)

At Banya the vicinity of Ichinokawa, in the south of Saijo City, Ehime Prefecture, a fault plane striking N 70' E with 40' N dip separates the Izumi group and the graphite schist of the Sambagawa metamorphics This is probably a thrust fault.

In the valley in the east of Kawaguchi, Nakahagi in Niihama City, the black schist and felsite with east-west trend and dip of 30 degrees towards the north and 10 centimeters thick fault clay is in contact with the Okamura formation This is probably a normal fault (P1 8, Fig 5)

In the valley bottom a t Mikura in Niihama City, a one meter thick black colored fault clay lying over the schist of the Sambagawa metamorphics can be observed but because of being covered with the gravels of the present streams it could not be determined what formation is in contact with it

In the valley in the south of Kinogawa, Doi-cho in Ehime Prefecture, the Sambagawa metamorphics and Izumi group are in contact with a fault Although neither fault nor fault clay could be observed, i t is thought that a fault occurs because the Izumi group strikes east-west with N 40" dip whereas about 20-30 meters therefrom the dip becomes 30" S The strike of the schist near the assumed fault is N 40" E with 50" N dip Although the fault is assumed the kind remains unknown.

At Urayamatani, Doi-cho, Ehime Prefecture, the Izumi group is in contact with the Sambagawa schists, and the fault plane is N 70" E with 30' N dip For a thickness of about 30-40 meters from the fault plane the Izumi group is disturbed and forms a crushed zone and a t the place nearest to this zone the Izumi strikes east -west with 4S0 N dip, whereas the black schist of the Sambagawa metamor - phics the strike is N 70" E with 65' N dip At the road side cliff about 500 meters south of Tsubakido


The Geology o,f Kagawa and Northern Ehime Pre,fectures 45

(Temple), Kawanoe City, the black schist rides over the Izumi group and liparitic dyke and the fault plane strikes almost east-west and the dip is about 40 degrees toward the south which is the opposite direction in contrast to the other localities (P1 7, Figs. 6-7)

The observations given above are those made along the Median Line distributed in the present field. From the observations it can be noticed that the kinds of faults associated with the tectonic line vary according to places. I t is also evident that the Sambagawa metamorphics come into contact with the Izumi group, and the Okamura formation with fault relation. When the Izumi and kuma are in contact, the Izumi rides over the Kuma group and it is covered unconformably by the Ishizuchi group, and when the Sambagawa and Mitoyo group are in contact the relation is a normal fault with the northern side thrown down.

From the given evidence mentioned above and in early pages of this article i t is evident that the Median Line was subjected to movement three times, the first movemeut being post - Izumi and pr e - Kuma , the second one being post - Kuma and pr e - Ishizuchi group , and the third is post-Mitoyo group and pre- Yakeotoge gravels.

D. Folds D-1 Ishzzuchz yama Anticlzne This anticline occurs in the Sambagawa metamorphics extending in east-west direction along the

northern slope of Ishizuchi-yama for about 12 kilometers The dips of both wings are about the same being 30 degrees Only the Sambagawa metamorphics takes part in the folding In the vicinity of Nishinokawayama this anticline is cut by a north-south trending Ryuozan fault. There are several small anticlines and synclines accompanying this large one and are developed parallel with i t and separated by about 10 kilometers. This is thought to have had relation with the movement a t the end of the Paleozoic D-2 Yamanouchi S ynclzne This syncline occurs in the Izumi group, extending from Sone in Ehime Prefecture northeastwards

to Sasagetoge in Tambara-cho in Ehime Prefecture for about 30 kilometers The axis is almost s t~a igh t and both wings dip at about 30 degrees Only the Izumi group partakes in the development of this syncline Associated with this syncline is the Hodono anticline which is developed about 0 7 kilometers in i ts south. This anticline extends from Ohata in Kawauchi-cho, Onsen-gun, Ehime Prefecture northeastwards to Hodono in the same township for a distance of about ID kilometers. I t s wings dip a t about 45 degrees being about the same for both Only the Izumi group partakes in the folding. Several small foldings are associated with it in its south

0-3 T sunatsuke yama Antzclzne This anticline occurs in the Izumi group, extending from vicinity of Tsunatsukeyama in the south

of Komatsu City in Ehime Prefecture east-northeastwards for about eight kilometers Its north wing dips a t 50 degrees and the southern one a t 40 degrees. Several small anticlines and synclines are associated with it and developed parallel with i t

0 - 4 Iu~akurayama S ynclzne This occurs in the Izumi group, extending from Hikaidani, Ichiba-cho, Tokushima Prefecture west-

wards through Fujikawa, Iwakura-cho, the north of Iwakurayama to Myojin, Mino-cho in Tokushima Prefecture for a distance of about 50 kilometers Its strike is ENE-WSW and the wings dip a t 30 degrees a t the west, 35 degrees near the middle part and 40 degrees a t i ts eastern part, for both wings respectively In the vicinity of Tatsumiyama this syncline is cut by a north-south trending fault Two or three small associated folds are found

All of these folds are thought to have had relation with the final stage of the Izumi group Small foldings are found in the Tonosho group in the vicinity of Nagahama, Tonosho-cho, ShGdo-shima.

Of these there is a gentle syncline with axis trending N 45' W with the southwestern wing dipping a t 10 degrees and the northeastern a t five degrees. The Tonosho group shows a synclinorium structure although the one just mentiond is the most outstanding one These foldings are of post-Tonosho age.

In the lacustrine deposits there is a small anticlinal structure observed a t Kitano, Saida-mura, Kagawa Prefecture The direction is N 45' W with both wings dipping a t about three to five degrees and this may represent a type of warping rather than fold in the general sense (P1 7 , Fig 3)


M. Saito

E . Basin Structures

Basin structures are found in the Kuma group and Tonosho group, the former of Eocene age and the latter of Miocene age The basin structures have dips of about 10-15 degrees for the Kuma group and about 5-10 degrees for the Tonosho group, and the general trends of both basins is ENE-WSW being more or less oval in shape These structural basins are thought to have been related with volcanism which cover them and therefore to probably have been a result of collapse or depression due to the escaping magmatic material

V . Sedimentary Structures

Sedimentary structures are features rather common in marine formations and have been described by many workers both abroad and in Japan. However, the sedimentary structures of lacustrine or lake deposits have not been so extensively treated as those of the marine sediments. AKUTSU (1959) described many interesting types of sedimentary structures observed by him in the lacustrine deposits of the paleo-Shiobara lake of Pleistocene age distributed in Tochigi Prefecture, K. 0. EMERY has noticed contortions in lagoonal sediments of California, and thexe are works on the deltaic deposits of the Mississippi delta of North America, and the writer has described a few from the Pliocene lake deposits of Kagawa Pr ef ectur e .

The lacustrine deposits of Pliocene age extensively distributed in Kagawa and Ehime Pr ef ectur es also show many different types of sedimentary structures which are thought to be worthy of description because they have relation with the sedimentary environment in which the lacustrine sediments were deposited. These will be described in the following pages according to type, (including the sedimentary structures of the Sanuki and Tonosho groups) whereas the ones already described by the writer will be included for ref ex ence .

A Clastic Dikes

A-1. Segregatzon Clastic Dikes (P1 9 , Figs 1-3) Numerous string-like, closely arranged or segregated argillaceous laminae about up to three or four

millimeters in width and three to five meters in length (height), arranged more or less parallel to subparallel with one another, vertical to highly oblique with the bedding plane, and apparently intimately related with cracks, joints or others of similar nature are found jn arkose sandstone along the sea coast at Nagahama, Tonosho-cho in ShGdo-shima. These belong to the Ikisue formation of lagoonal or brackish origin and of Miocene age

This type of clastic dike can also be observed in a cliff of the sea coast at Ikisue in Tonosho- cho, but the intruded sediments comprise pebble arkose sandstone and the dikes themselves are oblique to the bedding and immediately above the unconformity separating the Ikisue formation from the Paleo- zoic Yamaguchi group These also are segregated, parallel to subparallel with one another, measure about one to two centimeters in width and up to three meters in length These consist of limonitic or kaolinitic argillaceous sediments and are thought to have invaded from below through minute cracks in the sandstone

This type of segregation clastic dikes are found only in the Ikisue formation of brackish to lagoonal origin and have not been observed in the Pliocene lacustrine sediments These segregation dikes are not related directly with faults, that is to say, they do not fill the crevices due to faulting However , one associated with faulting is observed also in the sea cliff at Ikisue above mentioned, where thin argillaceous sediment or gouge-like material fills the faulted planes, and although simulating the clastic dikes, there are not thought to be referable to typical clastic dikes

A-2. Upward Injectzon Dzkes (PI. 9 , Figs 4-6) Clastic dikes also occur in the Sauuki group particularly near the basal part and display several

different types as is mentioned below In the cliffs of the road leading from Hashioka in Kokubunji-cho to the summit of Kokubududai there are found a number of clastic dikes penetrating alternating layers of tuffaceous sandstone and tuff of the basal part of the Oda formation in the lower part of the Sanuki group The dikes are of two types according to the sediments which they are made of. One consists of


The Geo1og.y o,f Kagawa and Northeyn Ehime Pre,f'ectures 47

fine tuff and the other of conglomeratic materials. Both are branching types, the angles of branching being acute to nearly a t right angles to the main trunk From that aspect, thinning upwards in one case, completely covering in sill-like shape another and from the coarser material forming the middle part and the sides of fine materials, it can be judged that these were injected from below upwards. These may be included into the injection dike type after deposition but before consolidation of the country rocks and to be related with the activity of the Sanuki volcanics. These types of dikes measure about 20 centimeters in maximum width, and about five to six meters in length (height) Associated with these dikes are several minute ones, some of which appear in string-form and others in ribbon form None of these minor ones are extensive and thin out upwards within a short distance, and may have been formed penecontemporaneously with the larger ones as a result of the small fractures due to stress and strain developed during the upward injection of the major ones and movement by volcanism From the materials included into the dikes and their relation with the country rocks as well as their shapes it can be inferred that the injection is intimately related with and probably formed a t the time of volcanism of the upper part of the Sanuki group as already mentioned The only locality of the present structure is that above mentioned.

B,, Load Casts (Pl. 9 , F i g . 7 ; P1. 10, Figs. 1,2)

Load casts (NAILAND and KUENEN, 1951) or the depressing of the substratum due to loading of the deposition surface is a feature common in sedimentary rocks of aqueous origin and also occurs in those of terrestrial nature. These kinds simple of structures are rather common in the lacustrine deposits and have already been described in a previous article (SAITO, 1960) These kinds of structures have been recognized at the following localities, namely, a cliff of a stream near Nishiebata in Manno-cho, Nakatado-gun, Kagawa Prefecture (Kawauchi formation), a stream cliff near Kawauchinaka in Yamamoto- cho, Mitoyo-gun, Kagawa Prefecture (Kawauchi f or mation) , the reservoir of Tamantoge in Ayagami-mura, Kagawa-gun, Kagawa Prefecture (Taman formation)

C.. Peculiar Structures due to Rapid Deposition and Transportation (P l , 10, Figs. 3-8; P1. 11, Figs. 1-7; P1. 12, Figs. 1,3,4)

A peculiar structure resulting from rapid deposition and the transportation of detached unconsolidated siltstone layers is observed in a cliff near the entrance of Ebata in Manno-cho, Kagawa Prefectu~e Here in a matrix of arkose sandstone measuring about six meters in thickness are found numerous detached siltstone with random orientation embedded in i t . These siltstones in the southern part of the cliff are much different from those in the northern part in their shapes, sizes, orientation and grade of development, that is to say, their thickness In the southern part of the cliff the siltstones are thicker and more massive, whereas northwards, these gradually change into soft-rock pebbles accumulated in a crowded mass The hard rocks found in the arkose sandstone are also with random orientation, scattered here and there, not touching one another and may or may not be in contact with the detached siltstone layer themselves. This is evidence that a part of the arkose sands were rapidly deposited not by turbidity currents but by flowage, during which process the unconsolidated silt layer was detached, incorporated into the moving sands to be deposited with varied orientation, shapes and sizes However, owing to the progressed transportation of the silts by the sands, many of the detached layers were subjected to rounding by abrasion and corrosion resulting in the development of the soft rock pebbles as may seen in the northern part of the cliff

This same phenomenon although of smaller scale is also observed in a cliff of a stream at Izumi, Saida-mura, Kagawa Prefecture. Here also in arkose sands there are found irregular silt blocks without definite orientation although more or less parallel with the general bedding and associated with detached and curved layers of silt with arkose sands injected upwards between them or even incorporated within them and vice versa

These above mentioned structures resulting from rapid deposition reflect the sedimentary conditions of the basin in which the lacustrine deposits were laid down. In other words during the early phase of the lacustrine deposits the area or sedimentary basin was not a stable one, being frequently filled penecontemporaneously with i ts sinking by secondary or reworked deposits

The wavy s t ructu~es described in the previous article (SAITO, 1960) is now considered to have been formed as a part of the same movement by which the ones above described were developed The formerly described phenomena or wavy structures were observed in a road side cliff along the road leading from Fukurami to Mita, Manno-cho, Kagawa Prefecture


M . Saito

Wherever arkose sands are exposed there is always found a sedimentary structure due to rapid deposition, exhibiting detached s ~ l t y fine grained sands and with the arkose sands injected between them This shows that where the arkose sands were deposited there must have been either uplift of the hinterland or the rapid sinking of the sedimentary basin by which the deposited sediments lost their equilibrium and were thus forced to move downwards towards the deeper parts of the basin. I t is during this time that silty fine sands or fine silts were subjected to distortion, detaching and transportation as well as to corrosion by the arkose sands together with their incorporation This leads to the development of disturbed sedimentary structures as shown also in the cliff in the north of Manno-ike in Manno-cho, Kagawa Prefecture This and the others belong to the upper part of the Kawauchi formation

In a cliff near the one just mentioned above there can be found a similar structure although differing in having remarkably recumbent folding observed best by the boundary of clean and brownish colored arkose sands This clearly shows that slumping structures were associated with the aforementioned structures developed by rapid deposition Here also the sands incorporate various sizes and shapes, more or less elongated silty fine sand blocks, soft rocks, and the included laminae which are variously curved as if due to torrential deposition, are well exposed This may also show that the movements by which the sediments were deposited may have been from the north

In the vicinity of the same locallty there are simrlar structures as already mentioned but differing in several important respects as in the development of detached wedges of silty fine sand layers, remarkable increase in gravel deposits which grade into arkose sands These gravels are poorly sorted, include large cobbles without definite orientation, large pebbles in ver tical, horizontal to oblique positions, incorporate sandy silt wedges showing curved laminae and grade laterally into the arkose sands exhibiting the interesting sedimentary structures The occurrence of the gravels and their general characters also suggest that they were deposited rapidly and not merely as marginal deposits generally found in lacustrine lake facies The degree of roundness being poor a s is the sorting, rather rapid grading into the arkose sands and the development of a number of varied sedimentary structures may all lead to the conclusion that the deposition was not only rapid but must have been associated with uplift of the hinterland, sinking of the sedimentary basin, both, or a t least the instability of the environment

In a cliff of the road leading from Saida-naka to Kitano in Saida-mura, there is exposed in the lower two meters of the cliff a bluish gray silt with sporadic sand grains incorporating numerous, irregular shaped but more or less elongated, different size coarse sand blocks some of which contain pebbles of silt The margins of these incorporated sands are generally highly irregular, often saw-teeth shaped, sometimes pinching to die out, roughly dentate- , bifurcate-, spatulate- or narrowly to more or less broadly rounded shapes, and neatly all have their longer axis parallel or nearly s o with the generally bedding of the superposed deposits of sands, silts and cross-bedded sands These blocks and fragments of coarse sands are all erratic to the grayish blue silts and represent a sedimentary structure due to rapid deposition and transportation of detached portions of a coarse sand layer During transportation of the detached layers which were still unco~~solidated silts were incorporated into them as shown by the silt pebbles included in them, and that the marginal portions are variously shaped in contact with the country rocks shows that most may have been developed a t the time of rest due to the resistance of the silts As in the case described in earlier lines this outcrop also reveals a similar history

In a stream cliff of the Saida River in Kijio, Saida-mura, Kagawa Prefecture there was observed a case of rapid deposition of pebbly arkose sand with incorporated detached sandy silt or silty layers of various sizes and shapes and hardstone gravels. In the lower part of the nearly five meters high cliff covered with unconformity by terrace gravels and consisting of a rubble structure a s mentioned above the following features were observed In the lowest part of the outcrop there is a highly irregular surface deposit of grayish blue sandy silt which is thin layered and intercalated with peaty or coaly layers in its upper part This sandy silt has its western side variously and very irregularly shaped where in contact with the slumped pebble arkose sand bearing the numerous, irregularly shaped, various sized, detached silt fragments ranging from size up to very large boulder although without spherical or rounded shapes The detached silty sediments, formerly of an extensive layer generally have their longer axis parallel or nearly so with the general bedding These detached parts are squeezed, pinched to show swell-and pinch shapes, uni-, b i - , to trifurcate a t their marginal parts, injected marginally with the arkose sands or with both pebbles and the arkose sands, and sometimes even with hard rock


The Geolog,y o,f' Kagawa and Northern Ehime Prefectures

pebbles of granite or quartzite The matrix of pebble arkose sand does not show normal deposition but appears as if scrambled with silty variously shaped thin ribbons and layers admixed without any definite orientation. The silty sediments themselves show upward and downward injections into the surrounding arkose sands which are scrambled. The intercalation of sandy sediments in the silty ones as if forced by compression during the process of both transportation and deposition is also well observed in many parts of the nearly 15 meters broad outcrop. From that the marginal parts of the underlying silty sediments in contact with the arkose rubble sand deposit show flame-like structures, elongated projections, sharp and angular to saw-teeth like portions, i t is readily inferred that the quick deposition served to preserve them rather than to erode them Erosion of parts of the underlying silts in contact with the arkose sands, however, is evident from the rounded and smoothed faces of the vertical parts and of the more or less horizontal parts, but this feature is rather in the middle part of the rubble deposit

From the features displayed by this outcrop it is evident that during deposition of the lower part of the Kawauchi formation there occurred rapid deposition of the arkose pebbly sands either by slumping due to various causes among which can be mentioned are earthquake shocks, after vibrations of volcanism, movement of the hinterland, migration of the sedimentary basin, deepening or shallowing of the basin, and probably others During the rapid movement of the sands there were incorporated into them by tearing up of the bottom sediments which were yet unconsolidated silty materials and hard-rock pebbles. Upon coming to rest these deposits by the abrupt loss in velocity were subjected to resistance resulting in the scrambling of the sediments as is inferred from the random orientation and up-or downward injections of the silty sediments and also of the matrix itself.

Another case of rather rapid deposition but of a cause different from those already mentioned is observed in a stream cliff near Shimowada, Ryonan-cho, Kagawa Prefecture and in the lower part of the Taman formation This outcrop shows two contrasting features, one is where gravels forming a bed overlie coarse arkose sands and the other is where gravels form a thin layer strewn over the sands These two conditions may be differently interpreted The former is the rapid deposits of gravels over unconsolidated sands whereby load cast structure is developed, or where the gravels are deposited on an uneven surface of the sand The other or latter is where the thinly strewn gravels are deposited over a shallowly scoured surface and separated from the main gravel bed by an arkose sand layer or bed Each of the cases are mutual in showing rapid deposition over an uneven surface of the arkose sands but load casts are not developed in one of the types because of the surface having already been scoured and thereby is more firm, whereas in the other case the sands (mobile or quick sand) are still water saturated and permitted the free development of load cast structures accompanying slight admix- ing of the subjacent sediments into the newly deposited gravels.

D. Apparent Interfinger Structure (PI. 12, Fig. 2)

An apparent interfinger structure of sandy silt intertonguing with pebbly arkose sand is developed near Okedoi in the north of Manno-ilre, Manno-cho Here there extend from the western side two narrow, rather long tongues of sandy silt extending laterally into massive pebbly arkose sand, and the boundary between the silts and sands is now represented by secondary limonitic deposition forming there are narrow zone curved in accordanced with the intertonguing sandy silts Whether this can be considered a typical interfingering structure or merely the lateral injection of sands moving into a massive silty sand layer thereby forcing it into two parts to represent tongues and to be a typical sedimentary structure indicating movement, or to be considered only a case of normal interfingering of marginal lake sediments may be open to question This may be questioned because of the good development of load cast structures at the contact of the arkose sands and silty sands being good, evidence of upward injection of the arkose sands into the sandy silts, presence of random hard round rocks in the silts, curving undersurface of the arkose sands and more or less rubble features of the silty sands Thus there remained doubt that the apparent interfingering may be only a particular case of rapid deposition of viscous material However, this problem will be reserved for another opportunity The only locality where such a peculiar structure was found is given in the above.

E. Cross-Bedding (P1 12, Fig. 5 ; P1. 13, Fig. 1)

Two types of lacustrine cross-bedding are observed in the present field, one indicates rapid deposition and is unidirectional whereas the other of less rapid deposition and is of the tabular or lenticular type Both are different from one another in their relation with the adjacent sediments and in magnitude of development and distribution. The latter mentioned type was observed in the stream


50 M. Saito

cliffs near Kubo in Chunan-mura in the upper part of the Kawauchi formation, and superposed on a pebbly arkose sand and covered with pebble to cobble size gravels also of the same formation. The cross-bedded part measures about four meters in height and each cross-stratified layer measures from 20 centimeters to 40 centimeters. The dip of the inclined parts is about 15-20 degrees whereas the dip of each set of cross-laminated layers is about 10 degrees thus presenting a more or less wedge shape but falls within the lenticular type, which is due to normal stream deposition

The other type which occurs in the lower part of the Kawauchi formation below the ones above described and at the same locality is confined within a layer measuring about 60 centimeters in thickness, overlain with gravels and superposed upon a gravel bed with thin silt and coaly layer at its uppermost in contact with the cross-bedded layer of pebbly arkose sand The unidirectional inclined sands dip at about 20 degrees towards the N 40" E contrary to the overlying gravels which are inclined towards the southwest. From the angle of repose of the sediments of coarse sands with pebbles it may be that deposition was due to rather rapid stream flow or current flowing over a thin deposit of silt and carbonaceous sediments, but so swift as to incorporate them into the cross-bedded deposits The overlying gravels which show southwestwards inclination of their platy ones shows that the currents depositing them came from the southwest as in the case of the one that deposited the cross-bedded sands If this is so, then it may be inferred that the conditions below were more tranquil than those above, the latter being of torrential nature whereas the former of steady unidirectional flow The latter type can be observed in the Okamura formation near the reservoir in Oka-mura, Ehime Prefecture.

F , Penecontemporaneous Fault (Pl. 13, Fig. 2)

In an exposure of the north side cliff in Manno-ike, Manno-cho, there are developed thick gravel deposits which are nothing but a lateral facies of the arkose sands However, this outcrop is of particular interest in that there can be observed a fault within the gravel deposits as is shown by the alignment of the gravels and also of the different orientaions of the sand and gravel laminae The oblique orientation of the more or less platy gravels can be seen extending into the overlying massive gravel deposits by the more or less obscure oblique line which separated the gravels on the underside and on the upperside of the line. This line is considered to be an extension of a fault plane extending from the gravels in the upper part, obliquely downward along the platy gravels into the underlying smaller gravel deposits Although not distinct, it can be seen that the gravels on the upper side of the plane are with oblique orientation against the more or less horizontal condition of the gravels situated on the underside of the plane This seems to be evidence for a fault passing through the gravels. Such faults are generally very difficult to determine and are generally not recognized unless the features are sought for in the orientations of the gravels, development and directions of the laminae and other minor structures which can be detected sometimes The development of the fault may be penecontemporaneous with deposition at least not before complete consolidation of the gravels as may be inferred from the alignments of the gravels, degree of disturbance of the respective laminae and differences between upper and lower sides of the fault plane.

G . Structures Caused by Ferruginous Cementation (P1 13, Figs. 3-4)

Although probably not a typical sedimentary structure but more or less related to structures developed after consolidation are found in the upper part of the Taman formation in a cliff near the Higashiueda Primary School in Yamada-cho, Kagawa Prefecture. In the cliff of arkose sand there can be observed layers of limonite in varied arrangement. Some of the layers are oblique to the bedding, some sharply inverted wedge-shaped, and others forming merely a gentle curvature more or less parallel with the bedding. These different arrangements appear to have different meanings, for example, the inverted wedge-shaped ones as well as the ones oblique to the bedding plane may reflect the structure of the arkose sands In other words deformation of the homogeneous and massive arkose sands, though difficult to observe because of the nature of the sediments, is reflected in the limonitic layers which were precipitated by ground water flowing more easily along the fractured or deformed parts of the sands These limonitic layers are generally underlain with thin layers of silty to clayey sediments which acts as the impervious stratum to the percolating gound waters upon which ferrous waters probably assisted with iron-oxidation resulted in the development of the ferrous layers If this is so, then these ferrous layers may be of value in interpreting the movements the sands were subjected to. The other type or false convolute lamination formed by ferruginous cementation can be observed at Kamitakaoka in Miki-cho, Kagawa Prefecture.



H . Imbricate Strpctures (Pl. 13, Figs. 5, 6)

Imbricated gravels are commonly found in the Yakeotoge gravels and on the hills of Takayashiki, Manno-cho, Kagawa Prefecture, the imbricated gravels measure up to about cobble size of sandstone derived from the Cretaceous Izumi group. The inclinations measure about 20 degrees towards the east, showing that the currents were from the east. Smaller gravels fill the interstices of the large ones and frequently smaller ones are found accumulated on the posterior parts Imbricated gravel as above mentioned can be observed on the Shimowada hill, Kagawa Prefecture and the Kawakami hill, Ehime Pref ecture

, VI. Geological Ages of the Formations

The oldest rocks developed in the area studied comprise the Sambagawa system of metamorphic rocks mostly of crystalline schists. At the present time there is no paleontological evidence to determine the geological age. However, H, FUJIMOTO (1938) discovered some radiolarian remains from the sericite schist at the type locality of the Sambagawa system which is Nagatoro in Kwanto Massif. He described and illustrated such radiolarians as Archicapsa cf . f zcz f ormzs HAECKEL, Trzcolocapsa cf . pzlula HINDE and Lzthocampe cf . cretacea RUST. From these fossils, FLJJIMOTO stated that the geological age is Jurassic because they are comparable with those occurring from similar ages in Europe and other parts of Japan.

Later FUJIMOTO and YAMADA (1949), found some crinoid remains in a limestone inter - calated in a chlorite schist exposed a t Fuppu, Yorii-machi, Saitama Prefecture. They considered that this crinoid limestone is very similar to those of the Chichibu system, and that i t is highly probable that the two are equivalent and of the same geological age. They stated that the Nagatoro system (Sambagawa and Mikabu system combined) compr ise various for mations ranging from the Carboniferous to the Jurassic.

T. KOBAYASHI (1951) based upon SUZUKI'S study (1930) on the crystalline schists of the Sambagawa system considered on the original rocks of the schists. KOBAYASHI found that the original rocks of the crystaIline schists are most closely similar to the unmeta- morphosed rocks of the Chichibu system. Particularly the original pyroclastic rocks of the Sambagawa system must be Devonian in geological age because the most intense volcanism in the geosyncline of the Chichibu system is of that age. Therefore, he considers that the geological age indicated by the radiolarians described by FUJIMOTO, as may be recognized from their value in foreign countries, must be subjected to question The Sambagawa therefore, should be considered a metamorphic facies of the non-metamorphosed Chichibu system and to be Paleozoic in age.

Accordingly a t the present time i t has not been determined whether a part of the Sambagawa system is Jurassic in age as maintained by FUJIMOTO or of Paleozoic age as advocated by KOBAYASHI. Although it is evident that the Sambagawa is a metamorphic facies of the Chichibu system, the complicate geological structure and the interrelation of the mentioned two rock groups makes it almost impossible to even determine the sequence in superposition of them.

The geological ages of the Yamaguchi group and the Ryoke complex are difficult to determine because in Shikoku only the Ryoke and scarcely the Yamaguchi is distributed. However, in Shishi- jima offing Kagawa Pref ecture crystalline limestone has been discovered inter bedded in the Ryoke complex, but unfortunately no fossils have been discovered to date. Therefore, there is no data by which the age of the Ryoke can be determined in Shikoku.

The Yamaguchi group has been best studied in the vicinity of Nishiyama in Kyoto Prefecture . According to NAKAMURA , MATSUSHITA and TAT EBAYASHI (19%) and subsequently by MATSUSHITA (1953), the group can be subdivided into, from the lower, A,


52 M. Saito

B, C, D and E. The lowest or A consists of a 800 meters thick sandstone, B is subdivided into from the lower BI, this is 800 meters thick chert formation, B2 of 120-130 meters thick sandstone, Bs is a 80-450 meters thick schalstein with lenticular limestone in its lower part which yielded Trzticztes cf. subobsoleta (OZAWA), and the uppermost part, Schwagerzna cf. vulgaris (SCHELLWIEN) . The subdivision C consists of an alternation of sandstone and clayslate measuring about 1450-1600 meters in thickness, and from the lower part there have been recorded Schwagerzna prisca (EHRENBERG) , Sch. cf . przsca var . parvula (SCHELLWIEN) , Sch. znczsa (SCHELLWIEN) , Sch. vulgarzs (SCHELLWIEN) , Trztzcites cf. subosokta (OZAWA) and Fusulznella spp.. The uppermost or D consists of 1400 meters thick clayslate, sandstone and chert with lenticular limestone in its lowermost part, which yielded Para fusulzna cf . edoenszs (OZAWA) .

MATSUSHITA (1953) stated that the B and C are Sakmarian in age, and that D is Artinskian in age, thus the larger part of the Yamaguchi group is Permian in geological age. However, the lowest or A may belong to the uppermost Carboniferous in age.

According to KOJIMA (1953, in the Tokuyama area in Yamaguchi Prefecture, the Paleozoic Yamaguchi group is subdivided into three parts of which the lower two, which are metamorphosed are called the Sangun metamorphics, while the upper part which is non-metamorphosed may be correlated to the Ota group of the Akiyoshi area, the age of which is believed to be the Pensylvanian- the upper Permian of TORIYAMA (1953).

KOJIMA and OKAMURA have named the Paleozoic formations (so-called Ryoke complex) in the Yanai-Iwakuni areas the Kuga group. The upper and the lower limits of the formations are not ascertainable. From the limestone lense of the Kuga group such fusulinids as Neoschwagerzna and Yabezna determined by YABE, according to KOJIMA (1953) are Permian in age. Thus it is evident that the upper part of the Yamaguchi group is Permian, but as to the ages of the middle and lower parts, there is at present no paleontological evidence.

The geological age of the Izumi group, according to MATSUMOTO and others (1953) is considered to Hetonaian (Campanian-Maestrichtian) because of the paleontological evidence mostly of the molluscan remains. Among the many fossils from the Izumi group, the important ones from its lower half are such as, Inoceramus orzentalzs SOKOLOW, I . cf. schmzdtz MICHAEL, I. baltzcus BOHM, Pachydzscus kobayashii (SHIMIZU), P. aff. egertonz (FORBES) and Bostr ychoceras awa jzense (YABE) . Of the named ones Inoceramus schmzdti is a zone marker of the lower Hetonaian in Japan, whereas Inoceramus balticus and I . ezoensis range from the upper Urakawan to lower Hetonaian. From the upper part of the second cycle I . balticus orientalis has been found, and this suggests that the part which yielded it may extend down to the upper Urakawan in age.

The upper half of the Izumi group has yielded such important fossils as Inoceramus awa jzensis MAT SUMOT o , I . hetonazanus MATSUMOTO , I. shikotanenszs NAGAO and MATSUMOTO, Pachydzscus subcompressus MATSUMOTO and Bostrychoceras awa jiense (YABE). Among these Inoceramus hetonaianus and I . shikotanenszs are zone markers in the upper Hetonaian of Japan. Pachydiscus subcompressus is also an index fossil of the Neohetonaian in age, approximately equivalent to the Maestr ichtian.

From paleontological evidence i t is certain that the larger part of the Izumi belongs to the Hetonaian in age, but with the probability of its basal part extending down to the upper Ur akawan.

The geological age of the Kuma group according to NAGAI (1956) and HANZAWA (1959) who found from the lower part of the Nimyo formation Dzscocyclina and Fabiania, two larger foraminifers of Eocene age, the latter or Fabzania seems to be the same as the European Fabiania cassis (OPPENHEIM) which has a world-wide distribution in the middle and upper Eocene of the tropical belt, and the former or the genus Discocyclina i s I estr icted to Eocene in chronological distribution, and its geological age is Eocene. From


The Geology 0,f Kagawa and Northern Ehime Prej'ectures 53

the stratigraphical evidence, i t is considered that the age of the Nimyo formation is middle Eocene.

From the Myojin formation which conformably over lies the Nimyo formation, NAGAI (1959) recorded such plant fossils as Cerczdzphyllum eo japonzcum ENDO, FZCUS tzlzaef olza HEER, and Nelumbo nipponzca ENDO. From the paleobotanical evidence that such an assemblage occurs only from the Paleogene in East Asia, i t is considered from stratigraphical position and paleobotanical evidence, that the age of the Myojin formation is upper Eocene.

The age of the Tonosho group from the molluscan and plant fossils collected from ShBdo-shima offing Kagawa Prefecture is determined as early-middle Miocene. The plant remains from the Ikisue formation ox the lower part of this group are such as, namely, Cznnamomum lanceolatum HEER (elongated type), Metasequoza dzstzcha MIKI , Sasa f ras sp . , Quercus sp. (ever green), especially Cznnamomum lanceolatum is abundant. The molluscan remains from the Shikai formation or the upper part of this group are such as, Glycymeris cf . crassa KURODA, Venerzcardza sp ., Cardzum sp., Callzsta sp. , Siratoria sp., Calyptraea sp., Turretella cf . s -lzatazz NOMURA, T . oyaszo IDA, Euspzra m~zsens i s (MAKIYAMA), Nassarzus sp. and lsurus hastalzs (AGASIZ).

The age of the Sanuki group is post Tonosho in age because the tuff breccia of its lower part covers the Tonosho group with distinct unconformity at Hidoyama, Tonosho- cho, ShBdo-shima (island). The sanukitic rocks in the upper part of the Sanuki group occur as gravels in the lower part of the overlying Pliocene lacustrine deposits, thus the group is pre-lacustrine in age. Near the summit of Yashima in kagawa Prefecture the agglomerate and sanukite of the Sanuki group are covered with unconformity by the granule sand of the lacustrine deposits. From such evidence it is certain that the geological age of the Sanuki group is post-Tonosho pre-lacustrine deposit. From the plant fossils discovered in the tuff layers interbedded in the Sanuki group, which are such as, Fagus japonzca MAXIMOWICZ, F . f errugznea AIT . , Quercus crzspula BLUME, Q . sp. , Salzx sp., Lzquzdambar formosana HANCE. I t may be judged that the age of the Sanuki group is late Miocene.

The age of the lacustrine Mitoyo group, which has yielded pollen as shown in Table 3, the plant leaves, cones, nuts, seeds and fruits shown in Table 5 , and Parastegodon sugzyamai TOKUNAGA (1936), is uppermost Pliocene. The Pliocene age of the Mitoyo g ~ o u p is upheld by the abundant occurrence of pollen of Taxodiaceae as Metasequoza and Glyptostrobus, which is analogous with the upper Pliocene of Europe (or older Villafranchian of Italy, which is subjacent to the younger Villafranchian of Pleistocene age) , the abundant yield of cones of Metasequoza, Sequoia, Pseudotsuga, Pzcea Korzbai and Cunnznghamza, the leaves of Metasequoza and Pseudotsuga, as shown in the above cited tables. Parastegodon is antecedent to the occurrence of Elephas from a still younger with which the stratigraphic relationship is an unconformity. SHIKAMA from his studies (1936, 1952) on the fossil elephants of Japan maintains that the genus Parastegodon is upper Pliocene, whereas TAKAI (1938, 1953) expresses the opinion that i t represents the lower Pleistocene. MATSUMOTO (1941) on the other hand is in the same view as SHIKAMA (1936) namely, that Parastegodon is late Pliocene. However, SHIKAMA (1957) adds that if the Akashi group which has yielded abundant remains of Parastegodon is Villafranchian in age and if that stage is Pleistocene, then the Akashi may also be Pleistocene. TAKAI (1938) considers that Stegodon elephantozdes in late Pliocene whereas all other Parastegodon and Stegodon species known from Japan are Pleistocene in age. However, i t is important to take into consider ation the important str atigr aphical hiatus separating deposits which have been known to Parastegodon and Elephas. Stegodon itself has been recorded from deposits of Pleistocene age, but as reworked materials from the late Pliocene, and


54 M. Saito

Table 5. List of Plant Fossils from the Mitoyo Group.

Plant fossils

Pzcea Koribaz MIKI - Maxzmowzczzz REGEL Pseudolarz x Kaempherz GORD Pseudotsuga japonzca SHIRASAWA Cunnznghamza Konz shzz HAY Chamaecyparis pzs i fera ENDLICH Metasequoza dzsticha MIKI Sequoia semper virens ENDLICH Salzx amygdarina LINNE var (%) Potamogeton cf . perfolzatus LINNE -- cf. crzstatus REG. e t MAACK Sczrpus mucronatus LINNE Xanthox yllum pzperatum Dc (%) Car ya ovatocar pa MIKI Juglans megacznerea CHANEY Pterocarya multistrzata MIKI Alnus tinctorza SARG. Corylus heterophylla FISCH - rostrata AITON Fagus crenata BLUME Quercus rubrozdea MIKI -- crzspula BLUME ---- alzena BLUME(%) -- Hzkztaz MIKI(%) Zelkova sp. Euryale akashiensz s MIKI Nelumbo nucz f e ra GAERTN Magnolza Kobus Dc. - obovata THUNBERG Fortunearza sznenszs REHD e t WILS. Wistarza florzbunda Dc (%) Hamamelis parrotzozdea MIKI(%) Melza Azedarach LINNE var. Aleur i tes cordata MUELL-ARG.(%) Sapzum japonzcum PAX e t K.HOFFM. Buxus yaponica MUELL Spondzas axzllarzs BOXB. (%) Staphylea Bumalda SIEB. e t Zucc (z) Acer sp. Palzurus nipponicus MIKI Stewartza monadelpha S I E B . ~ ~ Zucc.(%) - serrata MAZ. Trapa macropoda MIKI ---- mammzllz f e ra MIKI - dzscoidpoda MIKI - tetragona MIKI - angustzcerata MIKI - Maxzmowiczzz KORSH. COY nus contr over sa HEMSL. S t yrax obassioides MIKI(%) - rugasa MIKI(%) - japonzca SIEB e t Zucc. - microcarpa MIKI Menyanthes sp. Trapel la sp.

x present, X abundant, cs cone s seed, sh shoot, % from YAGI'S fosslls referred to the "On Metasequoia, Fossil and Living" by S. MIKI.

Occurrence Gunchu Okamura Kawauchi lp : j t l Remain Age

P. I X

x X x x X

x

x x X

x x

x

x x x

x

x x x x x x

x x

X

x x x

scale, e list. The

c s h

s c

c , sh c , c s s , c

c 1 s s

s n n n

f , s , s h n n 1

s , l 1

f , l s , l , sh

s s s s s 1

s , f f , l s

f , s 1,s e

1 f , sh f , s , l

f f f f f f e s

s s s

fruit , 1 distribution of

Mio. -Plio. Plio -Rec. Pliocene Mio.-Rec. Mio. -Pleist. P1io.-Rec Mio.-Plio. Mio.-Plio. Plio. -Rec. Plio. -Rec Plio. -Rec. Up. Plio -Rec. Up.Plio.-Rec. Mio. -Plio. Pliocene Pliocene Up.Mio -Rec Plio -Rec. Plio -Rec. Up Mio. -Rec. Pliocene Up Mio -Rec Up Mio. -Rec Pliocene

Pliocene Up.Plio.-Rec. Up.Mio.-Rec Plio. -Rec Pliocene Plio. -Rec Pliocene P1io.-Rec Plio. -Rec. Up.Mio.-Rec Plio -Rec. Pliocene Up.Plio. -Rec.

Plio -Pleist . Plio -Rec. Pliocene Up. Plio -Pleist . Pliocene Pliocene Pliocene Pliocene Up.Mio -Rec Up.Mio. -Rec. Pliocene Pliocene Plio. -Rec. Pliocene

(after MIKI)

leaf. n nut, the plant

F. 1 x

x

x

x

x x

endcap, c chronological

F .

x

X x x x x

X X x

x x x

X x x x x

x x X

x x

x

x x

x X X X X x x x

X x x x

cone, f


The Geolog,y of' Kagawa and Northern Ehime Pr.e,fectures 55

TAKAI'S opinion that Parastegodon sugz,yamaz is Pleistocene seems to be without satis- factory evidence.

The writer from the evidence of str atigr aphical sequence, str atigr aphical relationships, paleobotanical evidence and occurrence of the elephant above cited, is inclined to the view that the age of the Mitoyo group is late Pliocene as already stated. I t may be added that the climatic conditions indicated by the predominating flora of Metasequoza and Glyptostrobus is analogous with the older Villafranchian or late Pliocene flora of Italy, which is the classical locality for subdivision of geological time from late Tertiary to and including the Pleistocene.

The age of the next younger Yakeotoge gravels which is separated from the Mitoyo group with remarkably unconformity and non -f ossilif er ous can be determined from indirect evidence as to be mentioned in the following. However, from the stratigraphical relation between the Mitoyo and Yakeotoge and with their correlatives distributed in other parts of the Setouchi province, i t can be said at this place that the age of the Yakeotoge may be considered to be Pleistocene. Details will be given in the discussion on the boundary between the Pliocene and Pleistocene deposits in another section of this article.

The Yakeotoge gravels correspond to deposits yielding abundant remains of Stegodon orientalzs OWEN and Elephas namadzcus naumanni MAKIYAMA, elephant ranging throughout the Pleistocene. The mammalian fossils reported from the sea bottom in the vicinity of ShBdo-shima comprise elephants of the Elephas namadzcus horizon and i t is thought that they are those belonging to the Higher Terrace in age. Admixed with Elephas namadzcus are also specimens of Stegodon orientalzs, and this is considered to belong to the Yakeotoge gravels in age. In other words the mammalian remains from the sea bottom in the vicinity of ShBdo-shima comprise a mixed fauna of Yakeotoge and Higher Terrace elements.

I t may also be said that the Yakeotoge gravels whose surface are denudated are younger than the Pliocene lacustrine deposits and oldel than the Higher Terraces, which are developed at heights of about 80-90 meters above sea-level.

The geological age of the Higher Terraces which are the deposits next younger than the Yakeotoge gravels is considered to be Pleistocene, but to what part of the Pleistocene they belong is difficult to determine. It is evident that they are post-early Pleistocene in age because the Yakeotoge gravels can be considered to be early Pleistocene.

The age of the Lower Terraces which attain about 40-60 meters in height above present day sea-level is thought to be late Pleistocene. The age cannot be determined by fossils because such have not been found to date, however, i t is thought that the Higher Terraces are middle Pleistocene and from the differences in heights and grade of erosion, i t is considered that the Lower Terraces are late Pleistocene in age.

Here it is to be mentioned that in the vicinity of Ube the early Pleistocene marine deposits (Kusae formation) have yielded the early Pleistocene elephant Stegodon orientalis OWEN. The Stegodon elephants from the sea bottom of various parts of the Setouchi Sea are approximately correlative in age with the marine deposits distributed sporadically in the vicinity of Kobe City in Hyogo Prefecture, the Tsuruzaki formation in Oita Prefecture, the Taniguchi shell bed in Kyoto Prefecture, and the Hosoya group in Aichi Prefecture. I t is thought that these marine deposits are equivalent with the terrestrial facies, both being early Pleistocene in age. Further details will be given in another section of this article.

The alluvial deposits distributed on the plains and along the drainage system in the nor thern part of Kagawa Pr ef ectur e facing the Hiuchi Sea in Ehime Pr efectur e are thought to be Holocene in age.


56 M. Saito

VII . Boundary between the Pliocene and Pleistocene Deposits in Kagawa and Ehime Prefectures

The opinions diverge concerning the position of the boundary between the deposits referred to the Pliocene and Pleistocene ages in Kagawa and Ehime Prefectures as well as in other areas in the Japanese islands is well known. For reasons that various opinions concerning the present area and of the Kobe -Osaka areas have been published during recent years, i t has become necessary to present the view of the writer in order that the readers may understand where and why the boundary between the Pliocene and Pleistocene deposits has been drawn.

As is well known that in the classical locality in northern Italy, there are developed lacustrine deposits comprising older and younger Villafranchian and that the latter are a terrestrial facies of the marine Calabrian, whereas the older Villafranchian to which no formal name has yet been proposed corresponds in age to a part of the Plaisancian. Astian and to be Pliocene in age. The latter or younger Villafranchian and Calabrian deposits are generally accepted as comprising early Pleistocene formations. Since detail discussions have been published in many papers, it is not the purpose of the writer to make a review at this place, but for the sake of advancing discussions a brief account of the lacustrine deposits of Pliocene and Pleistocene ages in northern Italy will be given.

In northern Italy, the older lake deposits upon which the typical Villafranchian is superposed without stratigraphical break is said to yield, according to MIGLIORINI (1950), Sequoza, Taxodzum, Glyptostrobus, Alnus, Fagus, Quercus, Platanus, Lzquzdambar, Laurus, Cznnarnomum, Mag~zolza Acer, Juglans, Pterocarya, Casszs and others, and thus "indicating climate appreciably warmer than today's". The typical Villafranchian on the other hand has yielded pollen and other plant remains of Abies, Pzcea, Pinus, Fagus, Alnus, Tzlia and "indicate a perceptibly cooler than today's". The marine Calabrian deposits have yielded pollen of Alnus, Pznus, Abzes, Castanea, Ericaceae and ferns "denoting a cold temperate climate, while the Pliocene climate in Italy was considerably warmer than today's".

The data known in Italy for separating the Pliocene from the Pleistocene is that an "important mountain building phase took place in the Apennine region between the Plaisancian- Astian and the Calabrian , while no such event occurred between the latter and the Sicilian", also "fossil faunas and floras affored good evidence that between the Plaisancian- Astian and the Calabrian there was a pronounced climatic cooling which should herald the Ice Age". Further, the stratigraphical break between the Plaisancian- Astian and Calabrian corresponds to the first Alpine glaciation in the Alps, the first appearance of Elephas and a marked difference in climatic conditions. Such features as distinguished in northern Italy and in other regions of Europe are analogous with the conditions described by HATAI (1958) for the Pliocene to Pleistocene deposits distributed in the northern part of the Boso Peninsula, Chiba Prefecture where a continuous sequence of marine sediments ranging from early Pliocene to late Pleistocene are distinguished.

From the various opinions and discussions presented by Japanese geologists and paleon- tologists in Japan i t appears quite evident that the position of the boundary between the Pliocene and Pleistocene falls within a thickness of strata, which may be treated differently according to workers, but it is also evident that the fauna or flora yielded from the deposits are the same whatever name they may be given. HATAI (1958) has shown that the stratigraphical break between the Pliocene and Pleistocene strata in the Boso Peninsula is significant and in good correspondance with the change in marine fauna yielded from the deposits above and below the boundary. From this evidence presented by HATAI (1958) and particularly as the result of the Commission on the Pliocene- Pleistocene Problem on the ocasion of the Eighteenth Inter national Geological Congress held in Great Britain in 1948.


The Geology o f Kagawa and Northern Ehime Prefectures 57

In the Setouchi province i t is evident that lacustrine deposits have wide distribution being known from Kagawa and Ehime Prefectures as described in this article, and also the Ajina formation in Yamaguchi Prefecture, the Awaji group of Awaii Island, the Moriyama formation in Tokushima Prefecture, the Akashi group in the vicinity of Kobe City, lower part of the Osaka group in the vicinity of Osaka City, lower part of the pale0 Biwako group in the vicinity of Biwa-Lake in SHIGA Prefecture, a part of the Agb group in Mie Prefecture, Mihama group in Chita Peninsula in Aichi Prefecture and the Shirakawaike formation in Nara Pr ef ectur e. All of these mentioned group are lacustrine in origin and thought to be a continuation of the lake deposits distinguished as the Mitoyo group in the present paper.

In all of these lacustrine deposits, Metasequoza either as cone, leaves or pollen is distributed throughout and is accompanied with the so-called Metasequoia flora of MIKI (1948, 50, 53), thus showing that the climatic conditions then prevailing was the same throughout. All of these lacustrine deposits are superposed with marked unconformity upon deposits of different ages, such as the Miocene marine deposits in Mie and Aichi Prefectures , Ryoke granites as in Kagawa Prefecture , on volcanics as the Sanuki group in Kagawa Prefecture, Cretaceous Izumi group as in Ehime and Kagawa Prefectures, and also with sediments of other ages. Also i t is important to mention that these lacustrine deposits are everywhere covered with marked unconformity with the Yakeotoge gravels in Ehime and Kagawa Pxefectures, the Harima group in the vicinity of Kobe City, the Kentoyama gravel in Mie Prefecture, and with marine deposits in some other areas as already mentioned above.

The marine deposits are character istic in having a cool temperature fauna whereas the underlying lacustrine deposits yield plant remains indicating a mild climate. I t is in the marine Kusae silt formation in the vicinity of Ube City in Yamaguchi Prefecture, and in the marine Tsuruzaki formation in Oita Prefecture, that the elephant called Stegodon orzentalzs OWEN was discovered, in association with marine shells indicating a thermal condition thought to be cool temperature.

The mammalian fauna from the sea bottom near ShGdo-shima offing Kagawa Prefecture has yielded Paleoloxodon namadzcus naumannz MAKIYAMA, P . n . yabei (MATSUMOTO), P. n . setoenszs (Makiyama) , P . aomorzenszs TOKUNAGA and TAKAI, SUS cf. nzpponicus MAT SUMOTO , Cervus praenzpponzcus SHIKAMA , C. yabez SHIKAMA , Capreolzna ma,yaz TOKUNAGA and TAKAI, Bzson occzdentalzs LUCAS, B . geron MATSUMOTO and Ursus sp.. This large mammalian fauna was ascribed to the Nishiyagi stage by SHIKAMA (1943,1952) and to be the upper part of the Harima group. On the other hand MAISUMOTO (1916) recorded Stegodon orzentalzs OWEN, S t . sinensz s OWEN, Elephas namadicus MAISUMOTO, Bzson sp., and Cervus sp. from the sea bottom near ShBdo-shima, thus its stratigraphical position is not definite.

MAKIYAMA (1924) recorded Elephas trogontherzz POI-ILIG from off ShGdo-shima and MATSUMOTO (1941) recorded Parastegodon shodoenszs MAISUMOTO from the sea bottom off Mitsugo- iima offing Nakatado-gun, Kagawa Prefecture. The precise stratigraphical horizons of the different pr oboscidean species r eco~ded by MAKIYAMA and MAT SUMOI o as well as by SHIKAMA remain unknown. However, since it is quite evident that the greater part of the lacustrine deposits called the Mitoyo group have been eroded away, and that the group extends below the sea surface to reappear in the areas already mentioned above, it can be inferred that the older types of those elephants may have been washed out from the Mitoyo group. Whereas on the other hand, the majority of the elephants derived from the sea bottom offing ShBdo-shima are thought to have been derived from now subme~ged terrestrial or brackish sediments corresponding to the Nishiyagi formation in the Kobe district now preserved sporadically on land. This being


58 M. Saito

explained by the differential crustal movements in the Setouchi area as will be described in another section of this article.

Since i t is appropriate to consider that the elephants may be arranged according to their general chronological distributions into the following way, namely, the oldest with Stegodon and Parastegodo%, the next younger with Stegodon orientalis OWEN and Elephas narnadzcus naumanni, and the youngest with varied forms of Elephas namadicus naumanni MAKIYAMA without the association of Stegodon. If this succession can be accepted then i t follows that the oldest are derived from the now submerged lacustrine Mitoyo group, the next younger are washed out specimens from the submerged by down warping terrestrial sediments corresponding to the early Pleistocene marine sediments, and the youngest are those corresponding in time to the Higher Terraces but it is also thought that they may have existed from a part of Yakeotoge time. I t should be added that Elephas namadzcus naumanni MAKIYAMA? was reported from a locality of the Higher Terrace by KOBAYASHI (1950), which may be taken as evidence verifying the above statement.

Accordingly, the writer is in the view that the significant unconformity above the lacustrine Mitoyo group and below the elephant bearing (Elephas namadicus naumannz MAKIYAMA , Stegodon orzentalzs O W E N ) deposits and the corresponding marine deposits marks the boundary between the Pliocene and Pleistocene in the studied area. I t is over this land bridge that the elephant migrated from the continent. Further the evidence from paleobotany (pollen, leaves, stems, cones, nuts, etc. ) indicates that the climatic conditions during Mitoyo time was warmer than that of the present at the same latitude, and that the cool temperate climate during early Pleistocene is one of the factors leading to the extinction of Metasequoia in the present area and in the inundation of shallow marine waters following the breaking of the extensive lake which permitted their invation.

This period of remarkably instability, change in climatic conditions, extinction of widespread Pliocene plants, migration of elephants from the continent, and birth of the present Setouchi Sea is taken as marking the boundary between the Pliocene and Pleistocene in the Setouchi province.

VIII . Correlation

The correlation undertaken in the present work includes the areas from western Kyushu to the Chita Peninsula in Aichi Prefecture because i t i s in this area that lacustrine deposits are well developed, yield the same or very similar kind of flora and elephants indicating the same or almost identical age have been reported therefrom. Another reason for including this extensive area into consideration is because marine deposits yielding a very similar fauna occur from subjacent deposits and all are situated above either Paleo- gene or pre-Tertiary rocks with significant unconformity. For the purpose of correlation the stratigraphic sequence of Ehime and Kagawa Prefectures are taken as the basis.

In the surveyed area the lower Neogene deposits are those referable to the Tonosho group which comprises two formations, the Ikisue in the lower and the Shikai in the upper, both in contact with one another with conformity From the lower or Ikisue formation which is a lagoonal facies with lignite beds with Cinnamomum Zanceolatum HEER, Sasa f ras sp., Metasequoza distzcha MIKI, QU~YCUS sp. (ever -green). This formation lies on the pre-Tertiar y rocks of granite, Ryoke complex and the Paleozoic with significant unconformity and is thought to correspond to the Shiomachi Iacustrine deposits in the Hiroshima Prefecture district, which has yielded Hemitrapa ,yoke yamae (NATH .) MIKI , Nelumbo nucz f era GAER T N , Liquidambar f ormosana HANCE , and Metasequoia japonica MIKI. This formation like the Ikisue is unconformable with the basement of granite and Paleozoic rocks. Both are lacustrine to lagoonal in character, yield a flora indicating a similar age, and are similarly superposed with deposits of marine sediments.


The Ge0log.y o,f Kagawa and Northern Ehime Pre,f'ectures 59

In the present area the Shikai formation with Glycymerzs cf. crassa KURODA, Turrztella cf . s-hatazi NOMURA, T . oyaszo IDA, EUSPZYU mezsenszs (MAKIYAMA) , and many others of Cardium, Siratoria , Nassarzus, etc. , whereas the corresponding lower part of the Bihoku group in the Hiroshima district has yielded besides abundant smaller for aminif er s , a molluscan fauna quite similar to that of the Shikai formation. Mzogypszna and Operculzna occur in the lower part of the Bihoku group which is superposed on the Shiomachi formation with local unconformity. Whether the whole Shikai marine facies corresponds to both upper and lower parts of the Bihoku group is difficult to determine from the absence of paleontological evidence. However , from the viewpoint of marine transgression , regression and local geological history of the two areas compared, it is thought that they may nearly contemporaneous in age.

The Tonosho group also corresponds to the Iwaya formation in Awaji Island, which is superjacent with unconformity upon the basement of granitic rocks and which yields Turritella kzzenszs YOKOYAMA, Trichlanzya hrrsuta (LAMARCK) , and many others yet in need of paleontological study. This formation commences with marine transgression, is situated not far away, ends with marine regression, and may belong to a position similar to that of the Bihoku group and Tonosho group already mentioned.

Correlatives of the Tonosho group are found in the vicinity of Lake Biwa in Shiga Prefecture where the Ayukawa group is developed. This group covers the basement of granitic rocks and the Paleozoic with significant unconformity, commences with transglession and ends with regression Its fauna comprises Vzcar ya yokoyamaz TAKEYAMA, Vzcar yella baculum (YOKOYAMA) , Soktellzna mznoenszs YOKOYAMA, Turrztella s-hatazz NOMURA, Katelysza nakamuraz IKEBE and many others. Thus from paleontological evidence i t is clear that the Ayukawa group is nothing but a correlative of the Tonosho and Bihoku groups already mentioned.

This is also the same as the Fujiwara group in Nara Prefecture which shows similar stratigraphic relation with the basement and yields a fauna comprising such as Cardita szogamenszs NOMURA, Macoma optzva (YOKOYAMA), Nuculana kongzenszs OTUKA, Yoldza sagittarza YOKOYAMA, Cardzum oguraz OTUKA and other typical early Miocene mollusca (pelecypoda as well as gastropoda) .

In Kyoto Prefecture there is developed the Tsuzuki group which covers the basement of Paleozoic with remarkable unconformity , commences with marine transgression over an eroded land surface and yields such marine molluscs as Protorotella yuantanzensis MAKIYAMA, Katelysza nakamuraz IKEBE, Turrztella s-hatazz NOMURA, besides others of the genera Anadara, Glycymerzs, Perzploma, Dosznza, etc.. All of the fossils known from this group are characteristic in the early to middle Miocene of Japan and are unknown from late Miocene deposits. From such evidence as well as stratigr aphical relationships i t is evident that this group can be considered a correlative of the Fujiwara, Ayukawa, Iwaya, Tonosho and Bihoku groups already mentioned.

In Mie Prefecture where the Isshi group is developed, A K A K ~ (1960) has described such molluscs as, Turrztella s - hatazz NOMURA, Turrztella oyaszo IDA, Aczla yanagawaenszs NOMURA and ZINBO, Glycymerzs cisshuenszs MAKIYAMA, Euspzra mezsenszs (MAKIYAMA) besides many others. This group transgresses over the Ryoke granite of pre-Tertiary age and its top is marked by a significant unconformity, just as in the cases already mentioned. Although the f acies and thickness may be different in the diff ex ent stratigraphical units already mentioned, this has nothing to do with the geological ages of the respective areas, which are all thought to range from early to middle Miocene and sediments of late Miocene age are considered to be missing because there are no fossils indicating such an age.

The Miocene sedimentar ies developed in the Chita Peninsula in Aichi Prefecture have yielded such fossils as Venerzcardza orbzca YOKOYAMA, Perzploma yokoyarnaz MAKIYAMA, Pallzolum peckhami (GABB.), Solemya tokunagaz YOKOYAMA and many others, all of which


60 M. Saito

are also typical in the early to middle Miocene deposits of Japan. The similarity in the marine fauna of all of the stratigraphic units so far mentioned is

only to be expected because all belong to the same geological age. I t is also noteworthy that the stratigraphical relation with subjacent and super jacent units is remarkably similar, although the thickness of the respective ones may be somewhat different and even though lacustr ine deposits or lagoonal ones are developed according to areas, because a land must have existed at that time.

I t is only in Oita Pr ef ecture where corresponding marine sediments are not developed, and in place there can be found the Usa group which is volcanic facies comprised of agglomerate, breccia, tuff and lava flows This is also another characteristic features of the early Miocene of Japan because even where marine facies predominate there are generally always accompanied volcanics which may be different in thickness and extension, but always accompany the first extensive marine transgression of the early Miocene in the Japanese islands.

In the Kagawa and Ehime areas the Tonosho group is covered with unconformity by thick volcanics assigned to the Sanuki group in the former and the Ishizuchi group in the latter area. This same period of volcanic activity i s widespread from Kyushu to Osaka Prefecture, being represented as the Higashi -Shonai volcanics in Oita Prefecture in Kyushu, and the Futagami group in Osaka Prefecture. In Kyushu the Higashi-Shonai comprises tu f f , sand, silt and lava with intercalated plant remains consisting of late Miocene floras as Fagus ferruginea AIT., Liquzdamdar formosana HANCE, Q U ~ Y C U S pseudocastanea GOPPERT, Metasequoza dzstzcha MIKI and Juglans cznersa LINNE, which occur in the Sanuki group, the Ishizuchi group, Futagami group. The volcanics of the Sanuki group consist of tuff, agglomerate and sanukitic lavas which also occur in the Ishizuchi group. The Futagami group comprises the same kind of volcanic ejecta.

The stratigraphic relationship of the four mentioned groups with subjacent and super - jacent units is quite similar being unconformable everywhere.

In all of the areas treated with in the present correlation, the Pliocene sediments are characterized with lacustrine or lake deposits, but the development of those deposits is not the same everywhere. However, all of them are unconformable with the subjacent units and the details are as follows.

The Taman and Kawauchi formations in Kagawa Prefecture are lateral extensions of the Okamura and the Gunchu for mations in Ehime Prefecture and the four formations are designated as the Mitoyo group. This group is characterized with Metasequoia distzcha MIKI , Pseudotsuga japonzca SHIRASAWA , S~quoza sempervzrens ENDLICH, Cunnigghamza Konishzi HAY, Pterocarya multistrzata M IKI, Eur yale akashienszs MIKI, Trapa mammzlz f era MIKI, Palzur us nzpponicus MIKI, Q U ~ Y C ~ L S rubrozdea MIKI, Pzcea Korzbaz MIKI, Juglans megacznerea CHANEY , besides many other plants. This f lor a1 assemblage (so-called the Metasequoza flora) occurs from the Ajina formation in the Yamaguchi-Hiroshima districts, the Miki gravel in the Kobe area, the Awaji group in Awaji Island, the Moriyama for - mation in Tokushima Pr ef ectur e , the Shobudani for mation in Wakayama Pr ef ectur e, the Koyozn formation in Osaka Prefecture, the upper part of the Yuhi formation in the vicinity of Biwa Lake in Shiga Prefecture, the Shirakawaike formation in Nara Prefecture, in the upper part of the Kuwana group in Mie Prefecture, the Mihama group in the Chita Peninsula in Aichi Prefecture and the lacustrine deposits in Nagoya in Aichi Prefecture. This horizon is also the one of Stegodon shodoenszs akashiensis (TAKAI) which occurs in the uppermost part of the Kuwana group and the Akashi formation, of Parastegodon sugzyamaz TOKUNAGA from the Kawauchi formation, and their discovery from the other mentioned units is expected.

Although the mentioned correspond with one another in their lake facies, floral assemblage, str atigraphical relationship with super jacent and sub jacent units, except for the


The Geolog:y o,f Kagawa and No~thern Ehime Pre,fectures 61

fact that the time range is different. I t is considered that the Higashiueda-, Handa-, and Takio formations in Oita Prefecture range from early to late Pliocene, the Yokkaichi group in Mie Prefecture, the Kuwana group in Mie Prefecture also range from early to late Pliocene. The Mihama group in the Chita Peninsula in Aichi Prefecture, the Uji group in Kyoto Pr ef ectur e, the Gunchu for mation in Ehime Prefecture, the Shimakumayama gravel in Osaka Prefecture, and the lower part of the Kobiwako group in Shiga Prefecture are considered to begin from middle Pliocene whereas the Jigokudani formation in Nara Prefecture is thought to be an early Pliocene deposit.

The position of the lower part of each of the stratigaphic sequences of the Pliocene lake deposits are thought to be different as already mentioned from the succession of the floral assemblages, the lower being characterized with old types of plants as Lzquzdambar formosana HANCE, Fagus ferrugznea AITON and Styrax obasszozdes MIKI which do not accompany so called the Metasequoza flora. The upper palt of the Pliocene lake deposits is characterized with the occurrence of Metasequoza distzcha MIKI and its associated flora, which do not occur from the lower part. This is the basis for leaving gaps between the Pliocene and Miocene deposits in several of the areas.

So far as is certain, the Pliocene lake deposits are overlain with younger sediments by distinct unconformity extending from Chita Peninsula and Nagoya in Aichi Prefecture southwards to Mie Prefecture, and again reappear in Kagawa, Tokushima and Ehime Prefectures, whereas elsewhere in the areas correlated with one another no sharp line of demarcation occurs until a higher horizon.

The Yakeotoge gravels typically developed in Kagawa and Ehime Prefectures is also found in Tokushima Prefecture. The extension of this kind of deposits is the Kentoyama gravels in Mie Prefecture, the Rengeji gravels in Aich Prefecture, the Taketoyo gravels in Chita Peninsula and the Osatsu gravels in Shima Peninsula. In the Nagoya area the Yakeotoge gravels are represented by the Shiroyama and Yagoto gravels which axe said to be separated from one another by an unco nformity. In the Nara, Biwa Lake, Osaka, Kyoto, Kobe, Yamaguchi-Hiroshima, Oita and western Kyushu areas the Pliocene lake deposits with Metasequoza flora are succeeded with marine facies and the Pleistocene lake facies, which are thought to correspond to the Yakeotoge gravels and its correlatives already mentioned. This horizon is characterized with the occurrence of Stegodon orzentalzs OWEN, ElePhas namadzcus naumannz MAKIYAMA, marine shells among which Volachlamys yagurai (MAKIYAMA), Chlamys ha1zmc;nszs (MAKIYAMA) , large size and elongate forms of Ostrea gzgas THUMBERG associated with TraPezzum lzratum REEVE and others, and Palzurus nipponzcus MIKI and its associated flora. This shows that marine transgression during the early Pleistocene was local, that is to say only fringing and drowning of the coastal area took place in the early phase although this was later followed by more extensive flooding.

Although paleontological evidence is insufficient in horizons higher than the Yakeotoge gravels and its correlatives, the differences in heights above sea -level, materials compr is- ing the units, and stratigraphical relationships with younger and older stratigraphical units served for correlating them, and the results are given in the correlation table (Table 6). I n the younger horizons ElePhas namadzcus naumannz MAKIYAMA occurs without the association of Stegodon orzentalzs OWEN, and may be considered as the horizon of that elephant.

IX . Geological History

In the present area du1in.g deposition of the Paleozoic rocks, in the geosyn.cline there occurred volcanic activity which produced diabase and schalstein in its middle part whereas there was also accompanied granitization and metamorphism which took place associated with the uplift of the geosynclinal sediments. During this phase faulting and folding


M. Saito

accompanied with intrusion of the Ryoke granite there was uplift of the Paleozoic sediments resulting in an orogenic phase. By the pressure and heat accompanied with oro- genesis an extensive area was subjected to metamorphism These metamorphic rocks under the name of Sambagawa and Ryoke metamorphics were aligned parallel with the Paleozoic sediments in east to west trend analogous with the lattel sediments. The folding of the Sambagawa metamorphics is considered to be a product of the Paleozoic oroqenesis.

The Paleozoic mountain range is considered to have been subjected to subaerial denudation during the Triassic and Jurassic whereby the entire region became almost a pene- plane, and the Ryoke granite was exposed there. With the opening of the Campanian stage this area was subjected to marine transgression resulting in deposition of the Izumi group.

The Izumi group commences with a 50-200 meters thick basal conglomerate or an arkose sandstone. The majority of the gravels of the conglomerate were derived from granitic rocks, except in the upper and middle parts, which comprises chert, slate, granite, quartz- porphyry, hornstone and sandstone, quartzite -hornfels gravels of granule to pebble sizes. The matrix consists of grains of quartz, feldspar , biotite and clayey matter thus showing a granitic origin. All of these different rocks are considered to have their source in the north of the distribution of the Izumi group, whereas there is no evidence of derivation of materials from the Sambagawa metamorphics which is situated in its south, except the fact that a part of the matrix of the green sandstone found in the middle part of the Izumi group consists of chlor itic mineral, which may have been derived from the weathered chlorite schists of the Sambagawa metamorphics.

Comparing the sand and silt proportions, 70 percent comprise the former and attain about 5,000 meters in thickness, which strongly suggests that deposition was rapid. This also suggests that the Izumi was deposited in a peculiar environment. The thickness and nature of the sediments making the Izumi group indicates that the hinterland must have been high or at least there was high relief of the land and rapid downsinking of the sedimentary basin, that is to say, by taphrogenesis.

Since there is hardly no inclusion of sediments from the Sambagawa metamorphics it can be inferred that a part of the Izumi sea covered the Sambagawa at least in part. However, in the northern part of the area, especially in the area north of the central part of the Setouchi Sea, it is inferred that the Paleozoic mountains were uplifted in order to produce clastic sediments. This uplift may have had relation with the batholithic intrusion of the Cretaceous Chugoku granite.

The Izumi sea is considered from its distribution to have had a general trend parallel with that of the Paleozoic and Sambagawa metamorphics and to have been deposited in a sinking trough roughly in east - west trend.

At the end of the Cretaceous and before deposition of the Eocene Kuma group, there occurred or ogenic movement which resulted in producing intense folding and faulting of the Izumi sediments. The faults in the form of normal faults of about east-northeast trend are the major ones and these comprise the incipient Median Line of Southwest Japan. By this fault movement the northern side slid down and the southern side together with a part of the Sambagawa metamorphics was pushed upwards and there was built a mountain range parallel with the structural trend. Owing to differential erosion a part of the Izumi and the uplifted higher part of the Sambagawa were removed whereby a part of the Sambagawa, and that of the Izumi were reduced to a similar height and in contact with one another by the aforementioned major normal fault.

The Kuma sea transgressed over the denudated land surface of the Sambagawa metamorphic~ and Izumi group filling the trough-like depression which resulted in part by diff ex ential erosion of the different str uctur a1 sediments. Although the original extension of the Eocene seas remains unknown it is evident from the Ichinokawa conglomerate


The Geolog,y o,f Kagawa and Northern Ehime Pre,fectures 63

developed in the south of Saijo, Ehime Prefecture is thought to be a marginal facies, whereby it is inferred that the seas must have been distributed in that area. This conglomerate, once thought to be a Cretaceous valley deposit of the Izumi by OGAWA (1907) was classified by YABE (1915) into friction breccia and sedimentary conglomerate, whereas KOBAYASHI (1950) stated that is very similar to the basal conglomerate of the Ishizuchi series developed in the vicinity of Tobe -cho, Ehime Prefecture, while recently NAGAI (1957) clarified that it belongs to the Kuma group especially to its lower part. From the conglomerate and its stratigraphic position i t cao be inferred that the Eocene seas reached Ichinokawa at least in distribution.

It is thought that the Kuma or Eocene extended farther eastwards based upon the fact that abundant Sambagawa schistose gravels occur in the vicinity of Mitoyo in Kagawa Prefecture near the basal part of the lacustrine deposits of Pliocene age. This inference is from that if the gravels were derived from the hinterland, they should comprise sandstone, slate or granitic rocks, since no schistose rocks are exposed there, and also since no such rocks are included in the Izumi group. The only units yielding schistose gravels prior to the Pliocene lake deposits is the Kuma group. Also i t should be stated that the conglomerate in the vicinity of Ichinokawa are nothing but erosion relics whereas the Kuma group itself is preserved by the covering of volcanic rocks of younger date. From such data i t can be inferred that the Eocene seas spread eastwards at least to the vicinity of Mitoyo in Kagawa Prefecture and that the invasion was from the west or southwest.

The Kuma group which is classified into two formations, the Nimyo in the lower and the Myojin in the upper. From the distribution in grain sizes of the sediments and characters of the gravels making; the conglomerate and also from the distribution of those rocks, it is considered that the invasion was from the west and the north during the earlier stage whereas during Myojin time the seas had already begun regression showing an offlap from the depositional area of the Nimyo. Fabzanza , Dzscocyclzna and molluscan remains from the lower part of the group indicate the Eocene age of the group. The upper part of the group has yielded Nelumbo, Sabalztes and other plant fossils. These plant fossils are similar to the Eocene flora from the Ube district in Chugoku.

By regression followed with uplift the Kuma group was uplifted but with no noteworthy folding or faulting and was subjected to subaerial denudation to the end of the Paleogene when the Median Line again became active. This reactivation of the Median Line resulted in a thrust fault by which the Izumi group in the northern part was thrust up upon the Sambagawa metamorphics and also over the Kuma group. This is the second activity of the Median Line. By this movement there were developed eastnortheast - westsouthwest trending faults within the Izumi group and the Kuma group in the vicinity of the faults was slightly disturbed.

This thrust movement from the north resulted in the depressed area in the north which was invaded by the Miocene seas whose deposits are now found on ShBdo-shima offing northern Kagawa Prefecture. The distribution of the Miocene seas extended from the ShBdo Islands northwards to Okayama Prefecture, but failed to invade Kagawa or Ehime Pre- fecture. The initial phase of the marine transgression resulted in the deposition of lagoonal facies with lignite called the Ikisue formation over which pure marine facies known as the Shikai formation. The similar facies are developed in the Kojima Peninsula and the vicinity of Ushimado in Okayama Prefecture, where their remnants are now found in the low area in the granitic regions. This may show that the seas were more or less restricted in distribution so far as concerning the present area.

During marine transgression of the Miocene in the present area, i t is thought that the land areas of Kagawa and Ehime Prefectures were the source areas of the sediments


64 M. Saito

making the formations of Miocene age. The two Prefectures were areas of erosion since uplift of the Eocene Kuma group and of the Cretaceous Izumi group, this clearly shows that the land area at the time of deposition of the Miocene seas was not high and therefore unable to supply abundant materials. This is well reflected in the Ikisue formation, which except for the small amounts of basal conglomerate, coarse clastic sediments aside from medium to coarse sands do not prevail, and also the kinds included into i t comprise granite, quartz-porphyr y , and clayslate, and do not incorporate sediments derived from the land area in its south. However, i t is judged that the land relief may have been moderate, though not high.

Near the end of the middle Miocene there occurred marine regression of the restricted seas, whereby uplift occurred. Associated with the uplift of the marine covered areas there occurred a gradually depressed area along the northern side of the Asan mountains and south of the Paleozoic rocks distributed along the northern side of the present day Setouchi Sea. Associated with the downwarping there occurred volcanisms throughout Kagawa Prefecture, a part of Ehime Prefecture and over the areas once covered by the middle Miocene sea. These volcanics of biotite andesitic tuff, hornblende andesite and pyroxene andesite agglomerates, and sanukitic lava flows. This extensive volcanism com- mencing from late Miocene continued in part into the early Pliocene, although the periods of volcanics may have been periodic and contiunous This intense volcanism was associated with fragmentation as a result of block movement which accompanied the volcanism. I t i s at this time that structural lines transverse to the longitudinal structure of the Setouchi were developed. By this movement the Tonosho group was faulted to come into contact with the basement and the north to south trending faults in the Izumi group were also developed at this same time.

With the close of this period of volcanism there occurred local down warping by which the basin structure of the Kuma group was developed, the basin structure of the Tonosho group was also a product of this time. The above mentioned faulting also took place at a similar time.

After a short period of subaerial denudation by which downwarping was still i n process, there was developed before late Pliocene a long depressed area extending from Ehime Prefecture via Kagawa Prefecture farther eastwards. I t is in this depressed areas that the late Pliocene lacustrine deposits were already being developed. These late Pliocene lacustrine deposits characterized with Metasequoza, Glyptostrobus, Juglans cznerea f lora, Parastegodon sugz,yamaz TOKUNAGA and some fresh-water shells as well as freshwater diatoms extend along the northern side of the Asan and Ishizuchi mountain ranges in belt form, probably also in the bottom of the Setouchi Sea, but not along the borderland of Honshu facing the Setouchi Sea. Their present distribution is more or less sporadic, being found in the areas of low relief of the basement. However, taking into consideration the extension of the sporadic deposits, existence in the bottom of the Setouchi Sea, similarity in sediments at each of the isolated localities, preserved thickness, heights in occurrence of the different sediments, it can be inferred that the original lacustrine deposits had very extensive distribution, ranging at least over the whole Setouchi Sea, the land areas in front of the Asan and Ishizuchi mountain ranges.

I t is also thought that the lacustrine deposits originally extended eastwards to the southern part of Aichi Prefecture via Nara Prefecture and to be also represented in Hyogo and Osaka Prefectures, though only in part.

The lacustrine deposits are characterized with sands and silts, but valved or rhythmic sediments are rare, and from the development of angular or more or less rounded rocks derived from the Izumi hinterland it can be inferred that sedimentation was rather rapid. The angular materials derived from the Izumi hinterland are thought to represent the


The Geolog,y o,f ' Kag'awa and Northern Ehime P~e f ' ec ture s 65

marginal facies of the lacustrine deposits. I t is thought that the early phase of the lacustrine deposits was a swampy environment which rapidly became deeper to form the lake and at times the lake waters even covered the granitic hills which then existed in many places.

From the boring data of the wells dug into the alluvial plain of Takamatsu City, it is evident that at a depth of 100 meters below the surface there is developed a 20-30 meters thick blue silt with intercalated lignite layers. This blue silt is thought to be a part of the lake facies. Except for a marine facies of Holocene age a t a depth of about 10 meters from the surface, no marine sediments are found throughout the remaining thickness of lacustrine sediments. This shows that there was rather continued denudation after upheaval of the Pliocene lacustr ine sediments Further , although down faulted , the lacustrine sediments from the nature of their grain size and thickness are thought to have been deposited far from the shore-line of the lake.

The lake deposits show many types of sedimentary structures as already mentioned in the earlier pages of this article, but whether such structures are the result of migration of the lake, uplift of the hinterland, or to other movements during deposition is difficult to determine owing to the sporadic preservation of the lacustrine deposits. However, i t is important that such structures are found because they reflect the conditions of the sedimentary basin during deposition of the lacustrine sediments.

At the end of the Pliocene the lacustrine deposits were rapidly filled by sand and gravel deposits accompanied with the uplift of the lake and extinction associated with rising of the hinterland. It is at this time that the Izumi group was thrust up over the lacustrine deposits or the Sambagawa was thrust up over the Izumi group (Tsubakido at Kawanoe City) thus marking the maximum uplift of the hinterland and the supply of abundant materials resulting in the deposition of the Yakeotoge gravels of early pleistocene age. I t i s at this time that the Bungo and Kii Straits were broken by either north- south trending faults or flexures or severely downwarped to permit the invasion of the seas which deposited the Maiko shell beds, and corresponding early Pleistocene deposits in a limited part of Oita Prefecture and western Kyushu, the southern part of Ube in Yamaguchi Prefecture .

This movement marks the third period of activity of the Median Line of Southwest Japan and the fault scarps of the Asan and Ishizuchi mountain ranges were developed a t this time. Also associated with this activity is probably the marine transgression in the various parts of Souhwest Japan mentioned above. The most structural feature at this time may be the depression of the Setouchi, which was flooded subsequently with Setouchi Sea, but at a date later than the marine invasion and breaking of the Bungo and Kii Straits above mentioned. Another feature of this time may be the small blocks produced as a result of differential movements which are now preserved as the many islands of the Setouchi Sea. These islands are nothing but blocks down- or uprisen, tilted or variously oriented as the result of the movement of the post-Pliocene pre -Pleistocene. Although faulting and block movements accompanied the movement in Southwest Japan there seems to be no direct evidence for the development of anticlinal or synclinal folds as seen in the oil-field region of Northwest Japan.

The first marine transgression of the Pleistocene may be correlated with the initial development of the Setouchi whereas the progressed marine transgression which extended as far northeastwards at Kyoto marks the maximum the former being structurally related with the depression of the Setouchi area and the latter continued rise of sea-level.

I t should also be added that lacustrine deposits in the vicinity of Lake Biwa in Shiga Prefecture which was formed in early Pliocene continued deposition throughout the Pliocene and extended into early Pleistocene. Although the Pliocene and Pleistocene lake


66 M. Saito

deposits are continuous, i t should also be noticed that the floral change from moderate to cold and the extinction of the Meiasequoza-GlyPtostrobus flora serve to mark the end of the Pliocene whereas the over whelming Tsuga , Cryptomerza, SaPzum, Palzurus and abundant fresh water shells. This conditions are similar to the Villafranchian lakes in northern Italy where the Pliocene lake deposits are conformably overlain with early Pleistocene lake deposits. In the present case, the prevailing topographic conditions did not permit the inundation of the seas into the area.

From the fact that the Pleistocene seas did not invade either Kagawa or Ehime Prefec- tures clearly shows that those areas including the present day Setouchi Sea were still land areas of deposition, ~eceiving thick gravels from the rising hinterland, although it is considered that sinking of those areas had already begun.

After regression of the early Pleistocene seas i t is thought that uplift again occurred rather extensively and that small swampy or lagoonal areas were developed as partial relics of the retreat of the sea at least along the marginal areas, whereas i n the land areas where sinking was still being continued relative to the uplift of the hinterland, alluvial deposits were being formed as may be inferred from the development of alluvial fans, river terraces and this also shows that erosion was also active. This erosion is marked by the unconformity on the Hosoya group in the Atsumi Peninsula in Aichi Prefecture, the one above the Kusae silt in Yamaguchi Prefecture, and by the non-deposition in other areas. The Higher Terraces in Kagawa Prefecture indicate this particular period.

The next subsidence or lowering of the land relative to the rising of the sea level flooded the depressed area now occupied by the Setouchi Inland Sea. The deposits of this stage are marked by the Nishiyagi formation of Akashi, the Uwamachi formation in Osaka, the Kurosaki clay in Ube, the Oe formation in western Kyushu, the Toyohashi group in the Atsumi Peninsula, the Konobe formation in Tsu, the Noma formation in the Chita Peninsula, the Benai formation in Kochi Prefecture. This period is marked by the horizon of Elephas namadzcus naumannz MAKIYAMA and also by the sediments yielding abundant elephant rcmains in the sea bottom off ShBdo-shima (island). On land this period is marked by the development of fans and river terraces as seen in Kagawa and Ehime Prefectures .

After a slight retreat of the sea there occurred in association a fault at Kishinoshita and Toyooka, both in Ehime Prefecture by which the late Pleistocene fan deposits are cut by a east-west trending normal fault. By this fault and a repeated iise in sea level the entire Setouchi was flooded extending over a large portion of the land surface, whereby Yashima and many other small islands came into existence and the alluvial deposits distributed there were deposited.

After the deposition of the alluvial deposits above mentioned there occurred a retreat of the seas followed with another but very local invasion probably associated with slight warping movement by which the marine shell deposits at about 10 meters below the alluvial deposits was deposited. I t is after this stage that the present geomorphological features of the Setouchi Inland Sea was attained.

I t should be added that slight movements in the position of the land relative to sea- level are resulting in the construction of various erosion features along the coasts of present day Kagawa and Ehime Prefectures, but this is thought to be related with local movements and not extensive ones as were responsible for the making of major features during the Pliocene and Pleistocene in the present area.

(Received December 20, 1961)


The Geo1og.y o,f Kagawa a~zd Northern Ehime Prefectures

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The Ge0log.y o,f Kagawa and Northern Ehime Pre,fLctur'es 71

475-505, (128) , 537-560, (130), 685-695, (132), 810-820 (1899-1902) (107) -- : Explanatory text of the geological map of Japan, Kochi sheet, scale 1 : 200,000, I m p Geol

Surv Japan (1902). (108)- : On the geotectonic of Southwest Japan, Bull Imp Geol Surv. Japan, 19 ( I ) , 1-100 (1906). (I 09) - : On the Tertiary Formation of the Ise district (in Japanese), Shzmazu N a t Hist Speczmens

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(121)- , NAKAYAMA, K : The younger Cenozoic slrata developed in the Tosan district, Kagawa Prefecture, with special reference to the Sanuki Group (in Japanese), Tech. Bu l l . Kagawa A g r . Coll., 5 (3), 272-278, 4 pls., 1 table, Imap (1954)

(122) ------, ------: Preliminar y note on the stratigraphical study of the Mitoyo Group, Kagawa Pre- fecture, Shikoku (in Japanese), Tech. Bul l Kagawa Agr . Coll., 6 ( I ) , 32-37, 2 figs. (1954).

( ~ ~ ? ~ ) S A I I O , M. : Plio-Pleistocene strata in western part of Kagawa Prefecture (in Japanese), R e p Kansaz Branch, Geol. Soc Japan, (26), 23-24 (1955) .

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(I%)--------, Studies on the distribution of bottom sediments in irrigational reservoir (in Japanese), Tech. Bul l Fac. Agr . , Kagawa Unzv , 11, 144-154, 1 pl. , 8 text-figs , 1 table (1959)

(127)- , BANDO, Y. : Plio- Pleistocene strata of the Inner Zone of Shikoku, Japan (in Japanese), Sci. R e p . Tohoku Unzv. , 2nd Ser , Spec. Vo l . , (4), 576-582, 5 text-figs (1960)

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72 M. Saito

Surv . Japan (1929) . (1 33)------ : Explantory text of the geological map of Japan, Matsuyama sheet, scale 1 : 75.000, I m p .

Geol. Surv. Japan (1931). (I 34) - : Explanatory text of the geological map of Japan, Niihama sheet, scale 1 : 75.000, I m p .

Geol. Surv. Japan (1937). ( ~ ~ ~ ) S A T O , M : Gravels of crystalline schist in the Goshikihama conglomerate beds in Awaji Island (in

Japanese), Jour . Geogr , 56 (490), 789 (1929) (I 36) - : Miscellaneous notes on the Sanuki district (in Japanese), Jour. Geogr . , 44 (520), 333-339,

44 (522), 436-449 (1932) (I 37) -- : "Setonaikai" (in Japanese), Jour Geogr , 44 (526), 672-680 (1932) (138) -- : Explanatory text of the geological map of Japan, Takamatsu sheet, scale 1 : 75.000, I m p .

Geol. Surv. Japan (1936). (139) - : Explantory text of the geological map of Japan, Marugame sheet, scale 1 : 75.000, I m p .

Geol. Surv Japan (1936). (140)------ : Explanatory text of the geological map of Japan, Saidaiji sheet, scale 1 :75.000, Imp . Geol.

Surv Japan (1938). ( ~ ~ ~ ) S A W A M U R A , T . : C~ustal movements by the Nankai Earthquake in 1946 (in Japanese), Kochr Unzv. ,

N a t . Scz , ( I ) , 20-33, 5 text-figs., 1 table (1951) (142)-----: On the position of the Median Line in the north of Tokushima City (in Japanese) , R e p .

Kansaz Branch, Geol. Soc Japan, (26), 60-61 (1955) ( ~ ~ ~ ) S H I K A M A , T : On the Akashi Group (in Japanese), Jour . Geol Soc. Japan, 43 (515), 565-589, 3 pls.,

2 text-figs. , 4 tables (1936). (144)-: Pleistocene problems iri Japan and its vicinity, some tentative considerations in palaeomam-

malogy, Bull . Cent. Nut Mus Manchoukuo, (6), 9-85, 29 tables, 6 text-figs. (in Japanese), 86-1 10, 13 tables (English Abstract) (1943)

( 145) ---- , TAKAHASHI, E. : Isa Formation, the spelean deposits in Akiyoshidai , Yamaguchi- ken (in Japanese), Mzneralog y and Geology, 3 (3) , 1-2, 3 pls (1949) .

(146) - : The Japanese Quaternary, its outline and historical review, Scz. Rep . Yokohama Na t . Univ , Sec 2 , ( I ) , 29-53, 7 tables, 2 text-figs. (1952)

( 1 4 7 ) S ~ u ~ o , T : Younger Cenozoic history of a i ta district, Kyushu (in Japanees) , Jour . Geol. Soc Japan, 59(693), 225-240, 8 text-figs., 6 tab., 59 (695), 372-384, 2 text-figs , 5 tables (1953)

( ~ ~ ~ ) S U G I , E . : On the sanukite rocks in the vicinity of Takamatsu, especially on the xenocryst contained in i t (Abstract) , Jour . Geol Soc. Japan, 45 (537), 451-452 (1938)

( ~ ~ ~ ) S U G I Y A M A , R : Studies on the rocks developed along the so-called "Median Line" (in Japanese), Jour. Geol. Soc. Japan, 46 (547) 169-187, 11 pls , 7 text-figs., 4 tables, 1 map (1939).

(150)Suzuk1, B. : Explanator y text of the geological map of Japan, Tokushima sheet 1 : 200.000, I m p . Geol. Surv. Japan (1896) .

( ~ ~ ~ ) S U Z U K I , K , H o s o ~ o , M , KUBO, K : On the coal bearing Tertiary of the Seki district, Mie Prefecture (in Japanese), Jour . Geol. Soc. Japan, 54 (631-633) , 50-55, 1 text-fig , 1 table (1948).

(152)T~1, Y. : Miocene microbiostratigraphy of West Honshu, Japan, Jour Scz , Hzroshima Unzv , Ser. C, 2 (4) , 265-395, 7 pls , 2 text-figs. , 34 tables (1959)

T TAKAHASH HAS HI, E. : Quaternat y chronology of Yamaguchi Prefecture (in Japanese), Chzgaku Kenkyu, 6 (3), 130-135 (1953) .

(154)- e t al. : Pleistocene deposits in Ube district (in Japanese) , R e p . Lz beral A r t s , Yamaguchi Unzv . , 7 (2), 115 (1958)

(155)------, Floral change since the Mesozoic age of Western Honshu, Japan (in Japanese), Scz. R e p Yamaguchz Unzv. , 10, 181-237, 23 tables (1959).

TAKA TAKA HAS HI, K : Consideration for the Tertiary Formation, Komatsu, Ehime Prefecture and neighbourhood (in Japanese), Chzgaku Kenkyu, 10 (4) , 156-159, 1 table, 1 map (1958).

( ~ ~ ~ ) T A K A I , F . : On a new fossil elephant from Okubo-mura, Akashi-gun, Hyogo Prefecture, Japan, Proc. Imp Acad Tokyo, 12 ( I ) , 19-21, 2 figs. (1936).

(158) - : On some Cenozoic mammals from Japan (Preliminar y report) (in Japanese), Jour Geol. Soc. Japan, 45 (541), 745-763 (1938).

(159)- : On some Cenozoic mammals from Japan (Part 1) (in Japanese) , Jour Geol Soc. Japan, 46 (552), 481-489 (1939)

(1 60) ---- , TANAI, T : On the so-called unconformity in the Akashi Formation (in Japanese), Jour.


T h e Geology o,f K a g a w a a n d Northern Ehime Pre-f'ectures 73

Geol. Soc. Japan, 55 (64&649), 192-193, 1 table (1959) (161) -- : A summary of the mammalian fauna of Eastern Asia and the interrelationships of Continents

since the Mesozoic, Japan. Jour . Geol. Geogr., 22, 169-205 (1952). ( ~ ~ ~ ) T A K A K U W A , T. : Erosion surfaces in the northern part of the Asan Mountainland (in Japanese), Mem

Fac. Lz beral Ar t s and Education, Kagawa Uniu. , 1 (4) , 1-1 3, 7 pls (1954). ( ~ ~ ~ ) T A K E H A R A , H. : Age Group and Kentoyama Gravel in the vicinity of Kameyama-cho, Mie Prefecture

(Abstract), Jour. Geol. Soc. Japan, 61 (718), 348-349 (1955). ( ~ ~ ~ ) T A K E Y A M A , T.: On the Pleistocene deposits and change in height in the Kibi plateau and its vicinity

(in Japanese), The Globe (Chikyu) , 20 (6) , 428-443, 7 tables, 1 text-fig. , 1 pl (1933). ( ~ ~ ~ ) T A K I M O T O , K. : On the Cenozoic System of the Isshi district (in Japanese), The Globe (Chzkyu) , 23

(5), 326-338, 7 text-figs (1935). ( ~ ~ ~ ) T O K U N A G A , S.: A few fossil elephant found in Shikoku, Japan, Proc I m p . Acad . 11, 432-434

(1935) (167)To~11, S. : Pleistocene deposits of Higashiyama in Kyoto (in Japanese), Mzneralog y and Geology,

Ser. 8 , 62-68, 2 tables, 1 fig. , I pl. (1948). ( 1 6 8 ) T s u ~ ~ , H. : Geology of the northern part of Suzuka Mountainland, Mie Prefecture (in Japanese) ,

Gakugez Kenkyu , Wakayama Unzv., ( ? I ) , 71-74 (1951). ( ~ ~ ~ ) T S U J I M U R A , T . : Fault scarp and fault line scarp (in Japanese), Jour . Geol. Soc. Japan , 30 (158),

266-279 (1923). (170)-------: Interpretation of Fault Topography (in Japanese), Kokzn Book Co. , Tokyo, 1-397 (1923). (172)------: Geomo~phological significance of the Median Dislocation L ~ n e of Southwest Japan (in Japanese),

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Tokyo, 1 (6), 306-307 (1894). ( ~ ~ ~ ) W A T A N A B E , H : The geomorphology of the coastal district of southeastern Shikoku; A contribution

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( ~ ~ ~ ) W A T A N A B E , Kyu : A study on the origin of a Median Line in southwest area of Japan (in Japanese), Jour . Geogr . , 51 (601), 122-125, 2 text-figs. (1939)

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(178)------: Problems concerning the geotectonics of the Japanese Islands; Critical reviews of various opinions expressed by previous authors on the geotectonics, Scz R e p . , Tohoku I m p Unzv. , 2nd Ser . , (Geology) , Sendaz, Japan , 4 ( I ) , 75-104, 5 maps (1917)

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( ~ ~ ~ ) Y A G I , S . , HIYAMA, K : On the Fusogi (lignite) of Iyo (Part 1) (in Japanese), Chzgaku Kenkyu, 6 (6), 311-314, 3 text-figs (1954)

( ~ ~ ~ ) Y A G I , S.: On the Fusogi (lighite) of Iyo (part 2) (in Japanese), Chzgaku Kenkyu, 7 (6), 206-209, 1 table (1955)

(182)------: On the Fusogi (lignite) of Iyo (Part 3) (in Japanese), Chzgaku Kenkyu, 9 (6), 223-225, 1 table (1957)

( ~ ~ ~ ) Y A G I , T : On the two species of elephants from the Setouchi and others (in Japanese), Jour Geogr ., 40 (473), 385-391, 1 text - f ig (1927).

( ~ ~ ~ ) Y A G I , TSU. : A petrographical study of the Izumi Sandstone (Preliminar y report) (in Japanese) , Part 1 , Jour. Japan Assoc. Mzner. Petro. Economzc Geol. , 7 (5), 220-228, 1 text-fig , Part 2, (6) , 267-274, 2 text-figs (1932).

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( ~ ~ ~ ) Y E H A R A , S.*: On the echelon structure of Shikoku and the origin of Japanese Arc, Japan Jour Geol. Geogr. , 13 ( I ) , 1-24, 8 pls., 3 text-figs (1936).


74 M. Saito

(187)- : Several types on the structure of Median Line (Abstract), Jour. Geol Soc. Japan, 44 (525), 599-600 (1937) .

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PLATES 1-


Explanation of Plate 1

Fig. 1. Distant view of the Ishizuchi fault scarp and the Kishinoshita fan scarp. seen from the north. Loc. Kishinoshita, Niihama City, Ehime Prefecture.

Fig. 2 Distant view of the fault scarp along the Mime fault which occurs between the Miocene Tonosho group and the Ryoke granite, seen from the west. Loc. Mime, Tonosho-cho, Kagawa Prefecture.

Figs.3, 4. Distant view of the Asan fault scarp along the Ebata thrust which occurs between the Pliocene Kawauchi formation and the Cretaceous Izumi group, seen from the northwest. Fig. 3; Loc. Saidanaka and Hayashikura, Saida-mura, Kagawa Prefecture., Fig. 4; Loc. South district of Shinme, Chunan-mura, Kagawa Prefecture.

Fig. 5. Distant view of the lava plateau and conic type mountain which are composed of pyroclastic rocks and lava flows, seen from the south. Loc. Hashioka and Enza, Takamatsu City, Kagawa Prefecture.

Fig. 6. Distant view of the Okamura hill, (100-120 meters above sea level) seen from the south. This hill is composed of the Pliocene Okamura formation. Loc. Okamura, Komatsu City, Ehime Prefecture.


M. Saito : Geology of Kagawa and Northexn Ehime PI. 1


M. Saito : Geology of Kagawa and Northern Ehime PI. 2



Fig. 1. Distant view of the low level terrace (40 meters above sea level) and high level terrace (80 meters above sea level) in the vicinity of Haramachi at about five kilometers south of Matsuyama City, Ehime Prefecture, seen from the west.

Fig. 2. Distant view of Aso hill, (200-250 meters above sea level) seen from the north. This hill is composed of the Pleistocene Yakeotoge gravel. Loc. Aso, Matsuyama City, Ehime Prefecture.

Fig. 3. Distant view of Masamune hill, (120-.I50 meters above sea level) seen from the north. This hill is composed of the Pliocene Kawauchi formation. Loc. Masamune, Saida. mura , Kagawa Prefecture.

Fig. 4. Distant view of the Senbiki hill, (100-150 meters above sea level) seen from the west. This hill is composed of the Pleistocene Yakeotoge gravel. Loc. Sen biki, Ryonan-cho, Kagawa Prefecture.

Fig. 5 Distant view of the Kasuga hill, (200 meters above sea level) seen from the north. Loc. Kasuga , Chunan - mura , kagawa Prefecture

Fig. 6. Distant view of the Ayudaki hill, (100-200 meters above sea level) seen from the east. This hill is composed of granite and the Yakeotoge gravel whose surface is an eroded plane Loc. Ayudaki, Konan -cho, Kagawa Prefecture

Fig. 7 Distant view of the high level terrace, (80-100 meters above sea level) seen from the west. Loc. Kawahigashi, Konan-cho, Kagawa Prefecture.



Fig 1 . Type locality of the Ikisue formation (Miocene) This formation consists of basal conglomerate, arkose sandstone and gray siltstone. Loc. A cliff along the road from Ikisue to Oe in Tonosho-cho, Kagawa Prefecture.

Fig 2 Basal conglomerate of the Cretaceous Izumi group. This conglomerate consists of subrounded cobbles to pebbles of granitic rocks, quartz-porphyr y, liparite, sandstone, chert and slate Loc. A cliff near the reservoir a t Kii, Yamamoto-cho, Kagawa Prefecture

Fig. 3 Relic of the terrestrial deposit (Pliocene) observed in the cave of the sanukitic andesite This deposit consists of angular gravel derived from the andesitic rocks intercalated with several thin dark yellow laminated silt layer. Loc. Sea cliff a t Tsukumo-san in the north of Kanonji-City, Kagawa Prefecture.

Fig. 4. Stratified tuff and tuffaceous sandstone in the lower part of the Oda formation (Late Miocene) Loc A cliff of the road leading from Hashioka in Kokubunji-cho to the summit of Kokubudai , Kagawa Prefecture.

Fig. 5. Type locality of the upper part of the Gunchu formation (Pliocene). Exposed is veI y thick gravel intercalating a fine to medium grained sandstone bed and a carbonaceous layer. Loc. Sea cliff along the beach leading from Mori in Iyo City to Konogawa in Kaminada- cho, Ehime Prefecture

Figs.6, 7 Type locality of the lower part of the Gunchu formation (Pliocene). Consists of gray sandstone and greenish sandy siltstone intercalated with thin conglomerate layers. Loc Sea cliff along the beach leading from Mori in Iyo City to Konogawa in Kaminada- cho, Ehime Prefecture


M. Saito : Geology of Kaga wa and Northern Ehime PI. 3





Fig 1. Type locality of the Okamura formation (Pliocene). Loc A cliff near the reservior of Okamura a t about two kilometers south of Komatsu City, Ehime Prefecture

Fig. 2. Exposure near the type locality of the Okamura formation. Showing the alternation of gravel and sandy silt

Fig. 3 Very characteristic angular gravel in the upper part of the Okamura formation. I t consists of angular pebbles to cobbles of sandstone derived from the Cretaceous Izumi group . Loc. Road side cliff a t about 500 meters west of Nagatani, Himi-machi, Komatsu City, Ehime Prefecture

Fig. 4 Type locality of the upper part of the Kawauchi formation, which consists of an alternation of pebbly arkose sandstone and white grayish sandy siltstone (Pliocene) Loc A cliff near the Shrine of Kawauchinaka, Yamamoto-cho, Kagawa Prefecture

Fig. 5. Type locality of the lower part of the Kawauchi formation, which consists of blue sandy silt intercalating drift wood (Pliocene). Loc. A stream cliff at Kawauchinaka, Yamamoto-cho, Kagawa Prefecture.

Fig 6. Very characteristic micaceous sandy siltstone observed in the lower part of the Kawauchi formation (Pliocene) Loc A small stream cliff of Nishiebata, Manno-cho, Kagawa Prefecture

Figs.7, 8 Erect stumps with their roots penetrating the arkose sandstone which is thought to be the weathered products from the basement granitic rocks Fig. 8 is an enlarged portion of Fig. 7 Loc In the bed of the Doki River a t Naiden, Kotonami-mura, Kagawa Prefecture

Fig 9. Gravel bed exposed in the bed of the Doki River. I t is the lower part of the Kawauchi for mation (Pliocene) . Loc. Naiden , Kotonami -mura, Kagawa Pr efectur e .



Fig. 1 .. Alternation of granule sand and coarse grained sand of the Pliocene lacustrine deposits. Loc,. A cliff on the summit of the Yashima hill, Kagawa Prefecture.

Fig 2 High terrace gravel (Pleistocene) comprising pebbles and cobbles of the Izumi sandstone, granite and andesite. Loc Road side cliff at Tomizuka, Kawaoka, Takamatsu City, Kagawa Prefecture

Fig 5 Type locality of the Yakeotoge gravel (Pleistocene) which has generally subrounded to subangular pebble to cobble size gravel and consists of sandstone and slate of the Izumi group, granite, crystalline schist, quartzite, hornf els and andesite. Loc. A cliff a t Yakeotoge (pass), Kotonami-mura, Kagawa Prefecture.

Fig 4 Yakeotoge gravel (Pleistocene) comprising pebbles and ccobbles of sandstone derived from the Izumi group. The sandstone cobbles are weathered and are cut by a knife easily and are very characteristic Loc South side cliff at otani-ike, Ryonan-cho, Kagawa Prefecture

Fig 5 Unconformable contact between the Pliocene lacustrine deposits (Taman formation) and the agglomerate of the Sanuki group Loc. A cliff on the summit of the Yashima hill, Takamatsu City, Kagawa Prefecture.

Fig 6. Showing the Kawauchi formation consisting of sandy silt with angular fragments and very large blocks of the Izumi sandstone abuts against the very irregular surface of the Izumi group. Loc. A cliff near the Izeki pond at Izeki, Onohara-cho, Kagawa Prefecture.

Fig 7. Showing the lake deposits of arkose sand carrying boulders of granite and andesite which lie directly upon the basement of granite without the development of an arkose sand deposit. Loc.. A cliff of the Saida River at Kuboshita, Saida-mura, Kagawa Prefecture..


M. Saito : Geology of Kagawa and Northern Ehime PI, 5


M. Saito : Geology of Kagawa and Norther'n Ehime P1. 6



Fig. 1 Unconformable contact between the Ryoke granite (right side) and a dark colored slate forming the base of the Izumi group This slate is thought to be a surface soil at the time of marine transgression of the Izumi group Loc A small stream cliff a t Saidanaka, Saida-mura, Kagawa Prefecture

Fig 2 Unconformable contact between the Ryoke granite (left side) and the basal conglomerate of the Izumi group, consists of cobbles of hornfels and granite in a matrix of arkose sandstone Loc A small stream cliff a t Korobiishi, Kotonami-mura, Kagawa Prefecture

Fig. 3 . Unconformable contact between the Yakeotoge gravel (upper) and the Pliocene Kawauchi for mation. Loc. A cliff of Saida River at Kubo, Chunan-mura, Kagawa Prefecture ..

Fig 4 Unconformable contact between the Pliocene Kawauchi formation and the Cretaceous Izumi group. Here it is observed that the former were deposited in a small crevice of the latter, abutting there against. Loc A cliff about 500 meters south of Togawa in Saida-mura, Kagawa Prefecture.

Fig 5. The Yakeotoge gravels abut against the Izumi group (left side). Loc A cliff at Sangenya , Kawauchi-cho, Ehime Prefecture.

Fig 6. Unconformable contact between the Yakeotoge gravel (Pleistocene) and the tuffaceous siltstone of the Izumi group (lower side). Loc. A cliff at Yakeotoge in Nakato, Kotonami-mura, Kagawa Pref ecture.

Fig. 7. Unconformable contact between the Yakeotoge gravel (Pleistocene) and the Pliocene Kawauchi formation (lower side) Loc A north side cliff of Manno-ike , Manno-cho, Kagawa Prefecture

Fig 8. Unconformable contact between the Pleistocene Yakeotoge gravels (upper part) and the Pliocene Kawauchi for mation. Loc. A cliff at Yamawaki, Saida-mura, Kagawa Prefecture

Fig. 9 Folding of the Izumi group in the vicinity of the boundary of the Izumi group and the Pliocene Kawauchi formation. The fold is more or less open and the sandstones taking part broken as if by compressive forces Loc A small stream cliff at Kawauchinaka, Yamamoto-cho, Kagawa Prefecture.



Fig 1 Fault contact between the siltstone of the Miocene Ikisue formation (left side) and the crushed zone of the clayslate of Paleozoic group formed by faulting before deposition of the Miocene sedimentaries The strike is N 50' E and the dip is 60' SE. Loc Sea cliff a t Kaburazaki. Tonosho-cho, ShBdo-shima, Kagawa Prefecture

Fig. 2 Crushed zone of the Izumi group along the Median Line a t Yuyaguchi, Tambara-cho, Ehime Prefecture

Fig 3 A small anticlinal structure observed in the Kawauchi formation (Pliocene) The direction is N 45" W with both wings dipping a t about three to five degrees. This may represent a type of warping rather than fold in the general sense Loc A cliff a t Kitano. Saida-mura, Kagawa Prefecture

Fig 4 Thrust fault between the clayslate of the Izumi group (upper) and the siltstone of the Pliocene Gunchu formation. Loc. A sea cliff a t Mori, Iyo City, Ehime Prefecture

Fig 5. Enlarged portion of the part shown by the pick in the middle lower half of Fig. 4 .

Figs 6, 7. Fault contact between the Izumi group (left side) and the Sambagawa metamorphics (Median Line). Here, the black schist rides over the Izumi group and liparitic dyke ? and the fault plane strikes almost east-west and the dip is about 40 degrees towards the south Fig 7 is an enlarged portion of the middle part of Fig. 6 Loc. Road side cliff about 500 meters south of Tsubakido (Temple), Kawanoe-City, Ehime Prefecture .


M. Saito : Geololyy of Kagawa and Northern Ehime PI. 7


M. Saito : Geology of Kagawa and Northern Ehime P1. 8



Figs. I, 3 Fault contact between the Izumi group (right side) and the Sambagawa metamor. phics (Median Line) Here, the Izumi group rides over the gIeen schist and the fault almost east-west and the dip is about 20 degrees towards the north. Felsitic dyke having sandstone fragments as xenolith-like are intruded along the fault plane. Fig. 1 is an enlarged portion of the left hand part of Fig. 3. Loc. Stream cliff a t Yuyaguchi, Tambara-cho, Ehime Prefecture.

Fig. 2 An undulated part of the gIeen schist of the Sambagawa System in the vicinity of Median Line a t Yuyaguchi, Tambara -cho, Ehime Prefecture.

Fig. 4 Lacustrine marginal conglomerates developed along the Ebata thrust. (Fig 6) This conglomerate consists of angular boulders (appear as large slabs) derived from the Izumi group and is cemented with sandy silt. Loc. A cliff of the Yamawaki valley, Saida-mura, Kagawa Prefecture.

Fig 5 Fault contact? between the gravels of the Okamura formation and a felsitic dyke, which lies above the schist of the older formations. (Median Line) Loc A cliff in a small stream at Kawaguchi, east of Nakahagi, Niihama-City, Ehime Prefecture

Fig 6. Thrust fault between the Izumi group (left side of the photograph) and the Pliocene Kawauchi formation. This is called the Ebata thrust The strike is N 50" E, and the dips is 40" S. Loc A cliff of the Yamawaki valley, Saida-mura, Kagawa Prefecture.

Fig. 7 Fault contact between the Izumi group (lower half of the photograph) and the Ryoke granite The strike is N 70' E and the dip is 40' N. Loc. A cliff near the Matsuyama Castle, Matsuyama City, Ehime Prefecture

Fig 8. is an enlarged portion of the middle part of Fig 8 of P1. 9



Figs.1, 2 , 3. Segregation clastic dikes observed in the Ikisue formation (Miocene) Loc Figs. 1 , 3. A cliff of the sea coast a t Ikisue in Tonosho-cho, Kagawa Prefecture Fig. 2. A cliff of the sea coast a t Nagahama, Tonosho-cho in shbdo-shima, Kagawa Prefecture.

Figs.4, 5, 6. Upward injection dike in the Oda formation (Miocene) The dikes are of two types according to the sediments which they are made of. One (Fig 5) consists of fine tuff and the other (Figs 4, 6) of conglomeratic material Both are branching types. Loc A cliff of the road leading from Hashioka in Kokubunji-cho to the summit of Kokubudai , Kagawa Prefecture

Fig 7 Load cast observed in the Kawauchi formation (Pliocene lacustrine deposit). The gravels are found loading deeply the underlying sandy silts in more or less wedge-shape. In this case the underlying sandy silt are injected upwards into the gravelly deposits Loc A cliff of a stream near Nishiebata in Manno-cho, Kagawa Prefecture

Fig 8 Thrust fault between the Ryoke granite (upper) and the Taman formation. (Kikaku thrust). Loc. A road side cliff in the south of Kikaku Park, Nagao-cho, Kagawa Prefecture


M . Saito : Geology of Kagawa and Northern Ehime P1. 9





Fig 1. Broad load cast observed in the Taman formation (Pliocene) In this place gravels are found to have been submerged into the underlying coarse sandy silt, and also to have formed broad load casts. Loc. A cliff near the reservoir of Taman-toge in Ayagami-mura, Kagawa Prefecture

Fig. 2 An interesting type of load cast in the Taman formation (Pliocene). Loc. A cliff near the reservoir of Taman-toge in Ayagami-mura, Kagawa Prefecture

Figs 3, 4, 5 Peculiar structures resulting from rapid deposition and the transportation of detached unconsolidated siltstone layer observed in the Kawauchi formation (Pliocene) These siltstones in the southern part (Figs 3, 4) of the cliff are much different from those in the northern part (Fig 5) in their shapes. sizes, orientation and grade of development In the southern part of the cliff the siltstones are thicker and more massive, whereas northwards, they gradually change into soft rock pebbles accumulated in a crowded mass Loc A cliff near the entrance of Ebata, Manno-cho, Kagawa Prefecture.

Fig 6 The same type structure a s Figs. 3, 4 , 5 observed in a cliff of a stream a t Izumi, Saida-mura, Kagawa Prefecture Here also in arkose sands there are found irregular silt blocks without definite orientation although more or less pa~allel with the general bedding

Figs.7, 8. A wavy structure formed as a part of the same movement a s Figs. 3, 4 , 5. Loc. Road cliff along the road leading from Fukurami to Mita, Manno-cho, Kagawa Prefecture



Figs 1 ,2, 3, 4 , 5 Various sedimentary structures observed in the upper part of the Kawauchi formation (Pliocene) These structure due to rapid depositions, exhibit detached sandy silts and with the arkose sands injected between them. Especially, Fig 1 shows that slumping structures were associated with the aforementioned structures developed by rapid deposition Loc Cliff in the north of Manno-ike in Manno-cho, Kagawa Prefecture

Figs 6, 7 A sedimentary structure due to rapid deposition and transportation of detached portions of a coarse sandy layer These blocks and fragments of coarse sands are all erratic to the grayish blue silt. (Pliocene Kawauchi f or mation) Loc Road cliff leading from Saidanaka to Kitano in Saida-mura, Kagawa P~efecture.


M.. Saito : Geology of Kagawa and Northern Ehime PI. 11





Fig 1. A sedimentary structure due to rapid deposition of pebbly arkose sand with incorporated detached sandy silt or silty layers of various sizes and shapes and hard stone gravels. (Pliocene Kawauchi for mation) . Loc. Stream cliff of the Saida River in Kijio, Saida-mura, Kagawa Prefecture.

Fig 2 An apparent interfinger structure of sandy silt with pebbly arkose sand. (Pliocene Kawauchi f or mation). Loc. A cliff near Okedoi in the north of Manno-ike, Manno-cho, Kagawa Prefecture.

Figs 3, 4 They show two contrasting features one (Fig. 3) is where gravels forming a bed overlie coarse sands and other (Fig 4) is where gravels form a layer strewn over the sands Fig 3 i s the rapid deposits of gravel over unconsolidated sands whereby load cast structutre is developed Fig 4 is where the thinly strewn gravels are deposited over a shallowly scoured surface and separated from the main gravel bed by an arkose sand layer (Pliocene Taman for mation). Loc Stream cliff near Shimowada, Ryonan-cho, Kagawa Prefecture.

Fig 5 Tabular or lenticular cross-bedding observed in the upper part of the lacustrine Kawauchi for mation (Pliocene) . Loc Stream cliff near Kubo in Chunan-mura, Kagawa Prefecture



Fig 1 . Torrential cross- bedding observed in the lower part of the Kawauchi for mation Loc. Stream cliff near Kubo in Chunan-mura, Kagawa Prefecture

Fig 2. A penecontemporaneous fault within the gravel deposits is shown by the alignment of the gravels and also of the different orientations of the sand and gravel laminae (Pliocene Kawauchi for mation) . Loc. North side cliff in Manno-ike, Manno-cho, Kagawa Prefecture.

Fig. 3. Peculiar structures caused by f er r uginous cementation. (Pliocene Taman f or mation) . Loc Cliff near the Higashiueda Primary School in Yamada-cho, Kagawa Prefecture

Fig. 4 A false convolute lamination by ferruginous cementation. (Pliocene Taman formation) Loc. Cliff near Kamitakaoka in Miki-cho, Kagawa Prefecture.

Fig. 5. Imbrication of the gravels of the Yakeotoge gravels (Pleistocene) The pebbles and the cobbles derived from the Izumi sandstone are weathered and very characteristic Loc Shimowada hill, Ryonan-cho, Kagawa Prefecture

Fig 6 Imbricated gravels observed in the Yakeotoge gravels (Pleistocene). The inclinatic-n measures about 20 degrees toward the east, showing that the current direction was from the east .. Loc. Takayashiki hill, Manno-cho, Kagawa Prefecture.




M . Saito : Geology of Kagawa and Noxthern Ehime PI. 14


Explanation of P l a t e 14

(All figures are in natural size unless otherwise stated)

Figs .I -3. Spond,ylus sp.

Fig. 4. Isurus hastalis (AGASSIZ)

Figs. 5, 6. Macrophthalunus sp.

Figs, 7-7 I . Si'ratoria sp. (nov.. ?)

Figs. 12-17. Gl,yc,ymeris cfr .. crassa KURODA

Fig. 18. Callista sp.

Fig.. 19.. Thracia sp.

Figs.20, 21. Ca1,yptraea sp.

Fig. 22. Eu.spira sp.. , x 2.0

Figs.23-25. Euspi'ya meisensis (MAKIYAMA) , X 2..0

Figs. 26,27. Nassariu.~ sp.. , x 2.0

Figs 28-32. Cancellaria sp , X 2.0

Figs.33,34 Turritella oyasio IDA, X 1.5 Loc. Figs. 1-3 Shimosakaba- toge (pass) , Kuma -cho, Ehime Prefecture. (Eocene Nimyo formation). collected by NAGAI Figs. 5,6 Sea bottom offing Nagahama, Tonosho-cho, Shbdo-shima, Kagawa Prefecture. (Pleistocene deposits) Figs 4, 7-34. Sea cliff at Nagahama, Tonosho-cho, Shbdo- shima, Kagawa Prefecture . (Miocene Shikai formation). (identified by KOTAKA and HAYASAKA)




Figs. 1 , 2 , 3. Cinnamomum lanceolatum HEER, (Miocene Ikisue formation). Loc. Sea cliff at Nagahama, Tonosho-cho, ShGdo-shima, Kagawa Prefecture .

Fig. 4 .. Quercus sp . (ever green) , (Miocene Ikisue for mation) . Loc. Same as above.

Fig. 5. Sasa f ra s sp , (Miocene Ikisue for mation) . Loc. Same as above.

Fig. 6. Metasequoza disticha MIKI, (Miocene Ikisue formation) Loc Same as above.

Fig. 7. Pzcea Maximowzczzz REGEL, Shoot, (Pliocene Kawauchi formation) Loc. Stream cliff at Yamawaki valley, Saida-mura, Kagawa Pref ecture.

Figs .8, 9. Pzcea Kor i baz MIKI, cone, (Pliocene Gunchu formation). Loc Sea cliff at Mori, Iyo-City, Ehime Prefecture

Fig. 10 Fagus cr enata BLUME, (Pliocene Kawauchi for mation). Loc Stream cliff at Yamawaki valley, Saida -mura, Kagawa Prefecture.

Fig. 1 I . Fagus CY enata BLUME, x 3 , (Pliocene Kawauchi for mation) . Loc Same as above.

Fig. 12. Metasequoia dzstzcka MIKI, cone, (Pliocene Gunchu formation) . Loc. Sea cliff at Mori, Iyo City, Ehime Prefecture.

Fig. 13 Pseudolari x sp., (Pliocene Kawauchi for mation) . Loc. Str eam cliff at Yamawaki valley, Saida- mura, Kagawa Pr efectur e

Fig. I 4 .. Metasequoi'a di'sticha MIKI, cone, (Pliocene Kawauchi for mation) Loc ,, Same as above.

Fig.15. Metasequoia disticha MIKI, cone, (Pliocene Kawauchi formation). Loc. Kawauchinaka, Yamamoto-cho, Kagawa Prefecture.

(identified by MIKI and SUZUKI)


M . Saito : Geology of Kagawa an.d Northern Ehime






Figs la-b. Pseudotsuga japonica SHIRASAWA, cone, (Pliocene Kawauchi formation) Loc Stream cliff a t Yamawaki valley, Saida-mura, Kagawa Prefecture.

F ig 2. Pseudotsuga japonica SHIRASAWA, cone, (Pliocene Kawauchi formation) .. Loc.. A str eam cliff a t Kawauchinaka, Yamamoto-cho, Kagawa Prefecture.

Fig. 3. Juglans megacznerea CHANEY, nut, (Pliocene Gunchu formation). Loc Sea cliff a t Mori, Iyo.City, Ehime Prefecture

Figs.4a-b Juglans megaczner ea CHANEY, nut, (Pliocene Kawauchi for mation) . Loc. Str eam cliff a t Nishiebata, Manno-cho, Kagawa Prefecture .

Figs. 5a- b Juglans megaczner ea CHANEY , nut, (Pliocene Kawauchi for mation) . Loc Stream bed in the Doki river, Naiden, Kotonami mura, Kagawa Prefecture

Fig 6 Car ya ovatocarpa MIKI, nut , (Pliocene Gunchu formation) Loc. Sea cliff a t Mori, Iyo-City, Ehime Prefecture.

F ig 7 Juglans manschur zca, nut, (Pliocene Gunchu formation) Loc Sea cliff a t Mori, Iyo-City, Ehime Prefecture

Fig. 8. Fortunearza sznenszs READ e t WILS , seed, x 5, (Pliocene Kawauchi formation) Loc. Stream cliff a t Nishiebata, Manno-cho, Kagawa Prefecture

Fig 9. COY ylus heterophylla FIRCH, nut, (Pliocene Kawauchi formation) . Loc . Str eam cliff a t Yamawaki valley, Saida-mura, Kagawa Pr efectur e

Fig 10 S ty rax obassza S e t Z , seed, (Pliocene Gunchu formation) Loc. Sea cliff a t Mori, Iyo-City, Ehime Prefecture

Fig . I I. Hamamelzs parrotzozdea MIKI, fruit , (Pliocene Gunchu for mation) . Loc. Same as above.

Fig.12. Melza Azedarach I, var . , fruit , (Pliocene Gunchu formation) Loc. Same as above.

Fig 13. S ty rax mzcrocarpa MIKI, seed, (Pliocene Okamura formation) Loc. A cliff near the reservoir of Okamura, Komatsu City, Ehime Prefecture.

Fig.14, Trapa macropoda f . bzcerata (MIKI) , (Pliocene Kawauchi formation). Loc. Road cliff a t Imoo, Kotonami-mura, Kagawa Prefecture.

(identified by MIKI)



Fig.. 1. Gomphonema abbreviatum AGARDHIZ ? Kutz., x 2,000.

Fig. 2.. Fragi lar ia vire.scens RALFS, X 2,000.

Fig. 3. Fragilaria con.st7uen.s (EHR.) GRUNOW, x 2,000.

Fig.. 4. Melosira islandica 0. MULLER, x 2,000.

Fig. 5. Fragilarza construens var . venter (EHR.) GRUNOW, x 2,000.

Fig. 6. Caloneis sp., x 1000

Fig. 7. Navicula placentula (EHR.) GRUNOW, x 1,000.

Fig. 8. Stauroneis phoenicenteron EHRENBERG, X 1,000.

Fig. 9 Stauroneis phoenicenteron EHRENBERG, X 2,000.

Fig.10. Diploneis ovalis (HILSE) CLEVE, X 2,000

Fig.11. Eunotia gracil is (EHR ) RABH., x 2,000.

Loc. A s t ~ e a m cliff at Kawauchinaka, Yamamoto-cho, Kagawa Prefecture. (Pliocene Kawauchi formation) (identified by AKUTSU)



