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OLIVE ]ÝY'[f[f S`ÅX10ê0Ý0¸0È0ê

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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
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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 geo- logy 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 par- ticular area was selected for several reasons, such as, the hitherto accepted deposits ex- tensively 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
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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 conglo- merate, 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 dis- tributed 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
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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 distri- buted 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
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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 for- mation. 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…

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