Geology of Kubor Anticline PNG

8/9/2019 Geology of Kubor Anticline PNG

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GEOLOGY OF THE KUBOR ANTICLINE - CENTRAL HIGHLANDS OF NEW GUINEA

by

J.H.C. Bain, D.E. Mackenzie, and R.J. Ryburn

RECORD 1970/79

Page

SUMMARY

INTRODUCTION

Physiography

Climate

Airphotographs and base maps

Access and method of working

PREVIOUS GEOLOGICAL INVESTIGATIONS

OUTLINE OF GEOLOGY

PRE-PERMIAN

Omung Metamorphics

PERMIAN-TRIASSIC

Kuta Formation

TRIASSIC

Kana Volcanics

JURASSIC .

Balimbu Greywacke

Mongum Volcanics

Maril Shale

CRETACEOUS

9

1 0

4

1 7

2 1

23

23


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I.

1

Q U A T E R N A R Y

Pleistocene

he Highlands Volcanoes

Wahgi Fanglomerate

Recent

Page

5 3

58

Alluvium

5 9

Talus and scree

5 9

I N T R U S I V E R O C K S

Ku bor Granodiorite

6 0

Kimil Diorite

6 2

Bismarck Intrusive Complex

6 4

Michael Diorite

6 7

Minor Intrusives

Kera Sill

6 8

Kenangi Ga bbro

6 9

Benembi Diorite

7 0

S T R U C T U R E

70

The Ku bor Anticline

7 1

The Yaveufa Syncline

7 2

Bismarck Fault Zone

7 3

G E O L O G I C A L H I S T O R Y

74

E C O N O M I C G E O L O G Y

76

Gold

7 6

Copper

7 7

Bedded pyrite

7 7

Limestone

7 8

Stone axe quarries

7 8

Blue metal

7 9


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T EX T F I G U R E S

Figure 1:

he Ku bor Range and Wahgi Valle y

2 :

Mount Wilhelm

3 : Ku bor Range

-4

ount Sigul Mugal

:

ubor Range and Mount Oga

ubor Range

7

1

Vegetation and physiography

8: Roads and airstrips

9:

Omkalai airstrip

1 0 :

Summar y of stratigraphic units

1 1 :

Bedding and cleavage in Omung Metamorphics

1 2 : Chiastolite slate, Omung Metamorphics

1 2 a :

ana Volcanics - Chimbu River Section

1 3 :

Monoclinal fold, Kondaku Tuff

Chim Formation, Tua River

1 5: Faulted Kondaku Tuff

1 6:

Chim Formation and suspension bridge, Tua River

1 6 a :

him Formation - Chimbu River section graphic log

1 7 : Lower Wahgi Valle y

1 8:

Mount Elimbari

1 9 :

Mount Elimbari

2 0 : N o r t h e a s t f la n k o f K u b o r A n ti c li n e

2 1 :

Wahgi River Gorge


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(iv)

TEXT FIGURES (contd)

34:

Northeast slopes of Mount Karimui volcano

35:

Mount Suaru volcano

36:

High potash olivine basalt, Mount Hagen

37:

Shoshonitel Mount Suaru

38:

Shoshonitet Mount Suaru

39:

High potash olivine andesite, Mount Karimui

40:

Hornblende-2-pyroxene basalt t

Crater Mountain

41:

Wahgi Valle y

42:

Fanglomerate deposits, Wahgi Valley

43:

Upper Wahgi Valley lake deposits

4:

aip Valley and Upper Wahgi Valley

- 4 5 :

ornb1ende-augitelgabbro4 Bismarck Intrusive Complex

46

II

47

outheastern nose of Kubor Anticline

48:

Structural Sketch Map of New G uinea

49:

Development of the Bismarck Fault Zone

0 :

tructure

50a:

eological History - Summary

5 1 :

conomic rock and mineral deposits

P L A T E S

:

eological map of the Kub or Anticline 1:500 1000 scale


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(v)

PLATES (contd)

16:

Geological map: Lufa Sheet

:100,000 scale

17:

: part of Gonomi Sheet

1 8 :

t

: Index to map sheets.

T A B L E S

1 :

Estimated compositions of samples of K ondaku Tuff

Page

2: Subdivisions of the Tertiary and the nomenclature used

in this report

3:

Estimated modes Of samples of the Daub

o Volcanic

Member

1 + : stimated modes of samples from the Highlands

Volcanoes

5:

Estimated modes of specimens of the Kubor

Granodiorite

6:

Estimates modes of samples of the Bismarck

Intrusive Complex

7:

Estimated modes of some specimens of Michael

Diorite

8:

Estimated modes of samples of Kenangi Gabb ro

A P P E N D IX

Geographical localities mentioned in text.


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S U M M A R Y

The Kubor Anticline is situated in the Goroka-Mount Hagen area

of the central highlands of Papua-New Guinea. It is a mountainous region_

with peaks up to 4,500 m, drained by the Kaugel and Wahgi River systems

which flow to the Gulf of Papua via t he Purari River. The area was mapped

as part of a continuing programme of regional mapping by the Bureau of

Mineral Resources. Field work was carried out in 1968 (four months) and

1970 (two months). Regional g eology is shown at 1:500,000 scale (Plate 1),

and all detail at 1:100,000 scale (P lates 2-17). A bout 450 thin sections

and 250 palaeontological samples were examined; their locations are shown

on the 1:100,000 maps.

The Kubor Anticline is a large double plunging b asement arch

(60 x 125 km) which exposes metamorphic, igneous, and sedimentary rocks

ranging in age from Palaeozoic to upper Tertiary. The core of the anticline

consists of low g rade (greenschist) metamorphics of Palaeozoic age intruded

by late Permian composite plutons of acid to basic composition. Unconformably

overlying the basement core are small remnants of Upper Permian to Lower

Triassic reef limestone„, and Upper Triassic dacitic and basaltic volcanics.

About 7000 m of folded and faulted Upper Jurassic to Upper Cretaceous fine

clastics and volcanolithic sediments unconformably overlie the basement

complex, the Permian-T riassic limestone, and the Triassic•volcanics; the

Jurassic and Cretaceous rocks form the topographically prominent limbs of

the anticline. The volcanolithic sediments, which have been buried to

depths of 4500 m or more, contain lime zeolites, prehnite, pumpellyite,

and zoisite*

Two slightly smaller synclinal folds that flank the eastern end

of the anticline are developed in Tertiary rocks which surround the Kubor

Anticline on all but the northern side, Upper Palaeocene clastics occur

only south and west of the anticline. Eocene-Oligocene shelf and reef

limestone overlie Palaeocene and Cretaceous rocks west, south, east, and

northeast of the anticline.* The limestone is overlain by lower and middle

Miocene volcanolithic sediments and volcanics east and west of the anticline,


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The Ku bor Granodiorite plutons, emplaced in the Omung

Metamorphics during the late Permian, were uplifted, eroded

*

and exposed

within a period of

5

m. y.: after emplacement. This was the first development

of a topographic high in the Kubor area

*

D u r i n g P e r m i a n t o T r i a s s i c t i m e

-reef limestone developed on and around the exposed Kubor

Granodiorite.

Episodic

sedimentation

+

volcanism,, and erosion continued in the Kubor area

from Upper Triassic until Cenomanian time

*

although at least part of the

Kubor area remained above sea level from Lower Jurassic time onwards. In

Lower Cretaceous time

*

the Ku bor area began to rise (first stage in the

d e v e l o p m e n t o f t h e K u b o r A n t i c l i n e ) a n d t h e s o u r c e o f v o l c a n i c m a t e r i a l

in the sediments moved northwards, The Bismarck Fault Zone became active

_during late Cretaceous to Palaeocene time,, resulting in vertical scissor

and possi ble horizontal displacement of the Mesozoic sediments north of t he

•

K u b o r R a n g e * S e d i m e n t a t i o n r e c o m m e n c e d t o t h e s o u t h a n d w e s t o f t h e K u b o r

area during the upper Palaeocene

*

and became more extensive to the west

+

south

*

a n d e a s t d u r i n g m i d d l e E o c e n e t o e a r l y O l i g o c e n e t i m e , T w o b a s i n s

•

developed in lower and middle Miocene time to t he east and west of the

Kubor area

*

T h e y w e r e c o n n e c t e d t o t h e s o u t h b y a n ext e n s i v e s h al l o w s e a

in which shelf limestone formed, Andesitic volcanism occurred in the

basins during middle Miocene time, and numerous large and small plutonic

b o d i e s w e r e e m p l a c e d t o t h e n o r t h o f t h e K u b o r a r e a . C o m m e n c i n g i n t h e

late middle Miocene there followed major orogenic events which probably.

reached a peak during the Pliocene: the Bismarck Fault Zone was reactivated,

the Yaveufa Syncline formed,, and the Kubor Anticline was further arched.

Numberous minor folds and faults formed and a hypa byssal pluton was

emplaced in the eastern nose of the Kubor Ant icline. The Tertiary limestone

on the southern flank of the Ku b or Anticline slid southwards over the

•

Cretaceous shale

+

and a 50 km-wide belt of o verthrust diapiric folds

resulted.. The whole region was further upl ifted and eroded during late

Pliocene and early Pleistocene time,* Several large stratovolcanoes then

formed to the west and south of the Kub or Anticline, The summit areas of

volcanoes and mountains above 3000 m were glaciated during l ate Pleistocene

to Recent time*


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Fig.

The Kubor Anticl ine, forming the Kubor Range and Wahgi

Valley.

View to W.N.W. 5RT 5RGL M718 338RS 948 6 25,000 feet CPC 7614.


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INTRODUCTION

The Ku bor Anticline forms a mountain range (Ku bor Range)

-75

gm long in the central highlands of New Guinea between

1 4 4 ° E

and

145 E. The range is rugged, forest-covered, and almost uninhabited; the

crest is a bove 3000 m, and a number of peaks have gl acial landforms and

alpine vegetation. The surrounding countr y forms part of a high,. deeply

dissected, southward sloping plateau (Purari Pl ateau)

1 the northern part

of which is mostly grass-covered, supports more than a quarter of a million

inhabitants and is served by numerous roads, tracks and airstrips; the

southern part is forested and sparsely populated.

The Ku bor A nticline was mapped in the course of producing Ramu

and Karimui 1:250

1

000 scale geological sheets; a part of the Bureau of

Mineral Resources' programme of regional mapping at 1:250.000 scale in the

Territory of Papua and New Guinea.

Field work from June until October 1968 was carried out by

J.H,C. Bain

*

D.E. Mackenzie, and R.J. Ryb urn, who were assisted during

helicopter operations by D.B. Dow

*

R.J. Tinge y, I.E. Smith

*

G. Cifali, and

R.W. Page.. Detailed follow- up work was carried out by Bain, Mackenzie,

and D.J. Belford during June and July„ 1970.

The area mapped covers the Purari Plateau from the Ne b ilyer Valle y

in the west to the Asaro-Wahgi divide in t he east. In the north it is

bounded by the Jimi,Wahgi divide and to the south by t he Poru River and

Karimui and Crater volcanoes. The southeastern portion of the Plateau

extending to the Aziana and Lamari Rivers was also mapped (but is not

discussed here)..

This report deals only with the Ku b or Range and the area

immediately adjacent to it. It incorporates the unpublished results of some

traverses made by D.B. Dow and F.E. Dekker in 1964, but does not include

data from the L amari River area.


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Dominant on the P urari Plateau in the central part of the map

area, is the Ku b or Range which rises to over 3,500 metres a bove sea

level at a number of places along its

75

k m l e n g t h ( F i g . i )• T h e c e n t r e

of the range is the Palaeozoic zco

r i o f : A h s : K u b o l t

A n t i c l i n e , a n d i t s f o o t h i l l s a r e t h e M e s o z o i c l i m b s . T o t h e w e s t , w h e r e

the range is widest (35 km).„ and composed largely of granitic rocks.,

the drainage is more complex, and the topography more rugged, than at the

t a p e r i n g e a s te r n e n d . D e e p l y e r o d e d ,

l t , Y 1 f l g o u 1 i e r s

of volcanic

rocks cap the highest points on the range (Fig, 3)., and commonly form

sharp, rugged, bare rock peaks such as Mount Sigul Mugal (Fig..

4 ) .

Elsewhere the range is bush covered and is everywhere devoid of human

habitation.

A late P leistocene glaciation has modified the landscape a bove

.3,200 metres elevation,,,.and cirques are

,

developed at a number of places on

the Ku bor R ange and on plounts Giluwe, Hagen (justwest of the m ap area),

Michael, and Wilhelm (Loffler„ 1970), . Small moraine, deposits remain at a

few places on Mount Giluwe and on the flanks of Mount Wilhelm, and

fanglomerate deposits, in part of proba bl e fluvioglacial origin, cover the

floor of the central Wahgi Valle y,

A prominent limestone cuesta (Chimbu Lim estone) with cliff faces

. up to 300 m high, runs for. 60 km southeast of Kerowagi. It presents an

almost impenetrata ble b arrier to eastwest travel except where it is cut by

the southwesterly flowing Chimb u and Mai Rivers. The Chimbu River forms a

spectacular pass; it 'flows from a small t arn high on the slopes of Mount

Wilhelm, falls steeply to the east

*

then swings southwestwards past Gembogl

and flows through a series of straight-walled gorges cut in the more

resistant rocks at the b ottom of a deep valle y,- and finally breaks through

a deep V-shaped notch in the Chimbu Limestone dipslope near Kundiawa. It

dissipates much of its energy in a short stretch of broad, flat-floored

valle y before joining the Wahgi River.

The main river in the map area, the Wahgi River, starts its course

as a small yout hful 'stream on the steep eastern slope of Mount Hagen. In


12/164

...

W HGI

V LLEY

I

MT UDON

MT WILHElM

I

Fig. 2.

Glaciated

summit

area of

Mount

Wilhelm

viewed from the south

east .

Note seasonal

snow cap

Altitude

4500

metres

above

sea level .

Q SCO

N

25/11.


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Fig. 3

Kubo

r Range approx 4000 metres ASL showing massive

f l t - lying Kana

Volcanics capping

Omung Metamorphics

and Kubo r Granodiorite. Local

Relief

is

about

2000

metres . Neg. GA1233


14/164


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The Kaugel River enters the westerly flowing T ua (Wahgi) River

southwest of Mount Suaru and the resultant much swollen Tua flows south out

of the map area where it is joined by the Erave River, and becomes the

Purari River.

On the deeply dissected land surface descri bed a bove are

superimposed

L

a number of large st ratovolcanoes, surrounded by thick and

extensive gently sloping volcanic aprons, which have been deeply g ullied by

recent erosion. Lavas and lahar deposits from the larg er volcanoes

(e.g., Mount Hagen) have filled deep valle ys (e.g., Ne bilyer) and changed

the courses of numerous streams.

C l i m a t e

On the Purari Plat eau mean annual rainfall is a b out 2,500 mm

and there is a pronounced 'dry' period during the season of southeast winds

(May-October); annual rainfall is l ower in sheltered areas, and higher

(probably up to 3,800 mm) in more exposed areas. More rain (in the order

of 3,800-5,000 mm per year) falls on the southern flanks of t he Ku bor Range,

and Crater and Karimui volcanoes where there is a poorly-defined wet season

during the southeast trades.

During the surve y (June-September) tem peratures recorded at Gumine

base camp (1700 m a.s..1.) in 1968 ranged bet ween mean maxima and m inima of

26,8

0

C and 12..8°C. These figures show a greater diurnal range t han would be

expected for the more humid remainder of the y ear. Occasional night frosts

are known to occur at ground level in cold air pockets down to as low as

2000 m a.s.l.

Bik (1967) descri bed a ver y similar climate for part of the

Western and Southern Highlands..

Brookfield and Hart (1966) show that g reat variations in weather

conditions prevail in different parts of the Wahgi Valle y at t he same time


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Geological data were plotted on 1:50,000 scale topographic b ases.

For the northern part of the map area these were obtained b y enlarging

1:63,360 scale Pl animetric Series (uncontoured) Preliminar y Edition maps

prepared by the Division of National Mapping. B ases for the southern half

of the area were obtained by assembling the airphotographs in uncontrolled

m o s a i c s , a n d t r a c i n g o f f t h e m ajo r s t r e a m s . T h e s e m a p s w e r e t h e n r e d u c e d

to 1:50,000 scale, and adjusted so that on further reduction to 1:250,000

scale the drainage would approximately match th e generalized stream data on

the Royal Australian Surve y Corps 1:250,000 scale topographic maps.

U.S.A.F. A eronautical Approach Charts (1:250,000 scale) with hill shading

and some form lines were also availa ble, but as the Army Surve y maps

contained the same stream data and more complete cultural data t he y were used

in preference to the Approach Chart s. The 1:50,000 scale geological sheets

have been photographically reduced to 1:100,000 scale (Plates 2-17).

Access and Method of Working

The Lae-Mount Hagen road runs through t he area, and there are

numerous poorly formed roads in the Wahg i Valle y bet ween Mount Hagen and

G o r o k a . M a n y o f t h e s e m i n o r r o a d s , h o w e v e r , b e c o m e i m p a s s a b l e a f t e r

h e a v y r a i n . T h e r e a r e n i n e t e e n a i r s t r i p s w i t h i n t h e m a p p e d a r e a , a l t h o u g h

all but three are open only to light aircraft (Figs.

8 and 9).

In 1968, a base camp, with access to Omkalai airstrip (Figs.

8

a n d 9 ) , w a s e s t a b l i s h e d n e a r G u m i n e . R o a d s w e r e t r a v e r s e d u s i n g f o u r -

wheel-drive vehicles, and the intervening 'country mapped by one and two-day

traverses along streams and walking tracks.

During the last five weeks of the ,

1968 survey a Bell 47G3B1

helicopter was used to extend the area mapped, and to position parties in

the Okapa area, and in the densely forested, sparsely populated area south of

t h e K u b o r R a n g e . A n i n f l a t a b l e r u b b e r r a f t w a s u s e d d u r i n g m a p p i n g o f a

65 km •

ection of the Tua River.


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Kegisugl

Nan

ug l

1 4

vet

1

1\ Mount

.2 .

Haw

G

, , , , . - - . . _

..., .....•

7 . . :

‘

N....›

•

...

•

. . . . 14 , . . . . . e

Togobo

o/ i

\

M)

in)-1

1 %,

/0 Tsigmul .

"1" Pabarobuk

(A)

•

on :

Fig, 8

Th. Highlands Highsrog

ROADS AND AIRSTRIPS

0

irfield

in

irstrips

M

ass camps

■■■■•• MIND WNW

Roads (4whasi drivo only)

Raft r

N) — Mission


19/164Fig. Omkalai airstr ip restricted B category) on a


20/164

-7-

( 2 )

Geologiat and native assistant placed in the field in the

morning, and picked up the same afternoon. (This method is

economical only whilst working close to the helicopter base,

i.e., within 30 km).

( 3 )

Geologist and three carriers positioned for traverse of up

to four or five da ys' duration.

The helicopter base was moved twice to ensure that the machine

operated only within its most economical range (50 km radius). Light

aircraft were used to provide rapid and economical movement of personnel

and equipment between base camps. To make full use of the helicopter it

was found imperative that the Party consist of at least five or six

geologists. The party leader generally remained in base as co-ordinator,

and made use of any free t ime on the helicopter with reconnaissance and

one day.traverses. His duties were to ensure the smooth and efficient

functioning of the helicopter programme which had to be as flexible as

possible to accommodate contingencies such as bad weather, unexpected

geological problems, or sickness of party memb ers.


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-8-

PREVIOUS GEOLOGICAL INVESTIGATIONS

N.H. Fisher, Government Geologist, visited the Highlands in

1 9 3 7 .

His brief reconnaissance followed earlier prospecting forays by the Leahy

brothers and others, and the discovery of small alluvial gold deposits at

K u t a a n d B e n a B e n a. I n

1 9 3 9 L.C. Noakes, Assistant Government Geologist,

measured a section of Mesozoic and Tertiary rocks exposed in the Chimbu

River, and collected specimens from this section and from the l imestone at

K u t a . L a b o r a t o r y s t u d i e s o f t h e s e s p e c i m e n s w e r e m a d e b y E d w a r d s a n d

Glaessner (1953), and Crook (1961). In 1949 Australasian Petroleum C ompany

(A.P.C.) geologistsG.A.V. Stanley, K.M. Llewellyn, and M.F. Glaessner

.

(Stanley, 1950) made a reconnaissance of the Central Highlands from Aiyura

(east of Kainantu) to Mount Hagen. The Miocene rocks east of the Chimbu

Limestone were described, and the Kuta limestone :resampled. Subsequent .

palaeontological examination of the.Kuta limestone b y Glaessner et al.

(1950) established its

age

a s P e r m i a n . T h e K u b o r g r a n i t e a n d m e t a m o r p h i c

rocks, which are unconformably overlain by the limestone were therefore

thought to b e Palaeozoic, and the oldest known rocks in eastern New G uinea.

In December, 1950, F.K. Rickwood (1955) mapped the area from

Chuave to Wabag, including the Kubor Range and the Wahgi Valley .

Unfortunately he and earlier workers had no base maps or airphotographs of

the area, and consequently m uch. of their data is not easily refera ble to

existing maps or airphotographs. However, Rickwood recognized the broad

structure of the area, and mapped and defined the formations proposed by

Edwards and Glaessner (1953), Petroleum exploration geologists t hen

regarded the geological knowledge of the Highlands as adequate for the

purposes of oil exploration in Papua. Rickwood and other A.P.C. geologists

(Rickwood and Kent, 1956) subsequently mapped the area to the south of

Mount Michael and the Tua River (Pio-Purari Survey), b ut without accurate

base maps.

In 1956 Bureau of Mineral Resources geologists (McMillan and


22/164

-9-

O U T L I N E O F G E O L O G Y

The Kubor Anticline is a basement fold on what was the northeast

margin of the Australian continental block during Palaeozoic time. It is

bounded on the north b y the N ew Guinea Mobile Belt (Dow et al. 1968), a

tectonically active zone within younger continental crust which accreted

to the northern edge of the continent during Mesozoic time. Uplift of the

northern edge of the older continental block resulted in gravity sliding

which has strongly deformed the uppermost layers of the overlying Mesozoic

and Tertiary sediments. The lower layers of this sedimentary sequence are

only broadly folded and faulted (e.g., Kubor Anticline). Within the Mobile

Belt these sediments have been strongly deformed and intensely faulted.

The oldest rocks exposed in the map area are l ow-grade regionally

metamorphosed (greenschist facies) sedimentary and volcanic rocks of

probable Palaeozoic age called the Omung Metamorphics. These are exposed

only in the core of the Kubor A nticline, where they are intruded by large

composite plutons and small stocks of acid to basic composition

(Kubor Granodiorite) which are thought to be of late Permian age.

Unconformably overlying the Kubor Granodiorite at the western

and northeastern extent of the basement core are small patches of sandy

limestone and arkose (Kuta Formation) of Upper Permian - Lower Triassic

age. Also unconformable on the metamorphic and plutonic rocks, but not

seen in contact with the K uta Formation, are Upper Triassic dacitic and

basaltic volcanics (Kana Volcanics) which form flat outliers on the crest

of the Kubor Range and overturned fault wedges on the southern and western

slopes of Mount Wilhelm.. To the north of the Anticline the Kana Volcanics

are unconformably overlain by Lower Jurassic greywacke (Balimbu Greywacke)

and Middle Jurassic basic volcanics (Mongum Volcanics). I n the map area

these formations are present only as small fault wedges in the Jimi-

Wahgi divide and Bismarck Mountains.

Unconformably overlying the basement core, the Kuta Formation,


23/164

-10-

(undifferentiated Aure Group) which grade southwards into m assive shelf

l i m e s t o n e ( Da r a i L i me s t o n e ). T h e M i o c e n e l i me s t o n e h a s s l i d s o u t h w a r d s

off the flanks of the K u bor Range, and now rests with marked unconformity

on highly distur bed U pper Cretaceous shale.

Unconforma bly overlying the Chimbu Limestone in the Yaveufa

Syncline is a sequence of siltstone, tuffaceous sandstone, conglomerate,

and limestone (Movi Beds), and volcanic and volcanolithic rocks (Asaro

Formation and Daub

o Volcanic Member) which thicken towards the southeast.

Intruding the Mesozoic formations in the Jimi-W ahgi divide

and Bismarck Mountains are large composite plutons o f middle Miocene age

(Kimil Diorite„ and Bismarck Intrusive Complex), A large hypaby ssal

diorite stock (Michael Diorite) forms Mount Michael, and is of upper

M i o c e n e a g e . N u m e r o u s s m a l l i n t r u s i v e b o d i e s ( K e n a n g i G a b b r o ) i n t h e

vicinity of the Daub

o Volcanics, and a small stock Benembi Diorite)

near Kuta, are proba bly also of Miocene age,

T h e

northern limb of the Ku b or Anticline is cut by t he extensive

Bismarck Fault Zone which marks the southern m argin of the New Guinea

Mobile Belt, The Bismarck Fault Zone is a 20 km-wide., highly disturbed

zone of su bparaliel anastomosing faults„ thrust faults, and tight

o v e r t u r n e d f o l d s , T h e r e i s a t l e a s t 3 , 0 0 0 m o f v e r t i c a l d i s p l a c e m e n t

(north side up) spread over the width of t he fault zone in the vicinity

of Mount Wilhelm.

P R E - P E R M I A N

Omung Metamorphics

Name

The oldest rocks in the Central Highl ands are low-grade meta-

sedimentar y rocks which form part of t he pre-Permian basement exposed in

t h e c o r e o f t h e K u b o r A n t i c l i n e . T h e s e r o c k s w e r e f i r st d e s c r i b e d b y


24/164


25/164


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-12-

Petrography

In thin section the fine-grained metasediments are seen to be

poorly sorted, nota bly quartzose silty shales and matrix-rich siltstones

t h a t h a v e u n d e r g o n e v a r i o u s d e g r e e s o f m e t a m o r p h i c r e c o n s t i t u t i o n. I n

relatively unmetamorphos ed examples, clastic texture is largely preserved,

and the detritus is predominantly quartz with progressively smaller amounts

of albitized plag ioclase, muscovite, chloritized and epidotized

f e r r o m a g n e s i a n m i n e r a l s , b i o t i t e , s p h e n e , e p i d o t e , a n d z i r c o n . T h e m a t r ix

material in all cases is largely recr ystallized to fine-grained sericite,

quartz, chlorite, and albite(?) with m uch disseminated opaque material.

Cleavage in the m atrix is marked by preferred orientation of micaceous

m i n e r a l s . W i t h i n c r e a s i n g m e t a m o r p h i c r e c o n s t i t u t i o n, r e c r y s t a l l i z a t i o n

and directional structure become more pronounced but some relict detrital

g r a i n s a r e p r e s e n t i n a l l s p e c i m e n s . F i n e - g r a i n e d , m e t a m o r p h i c b i o t i t e i s

p r e s e n t i n s o m e p h y l l i t e s p e c i m e n s . M a n y t h i n s e c t i o n s a r e t r a n s e c t e d b y

veinlets of quartz, albite, and chlorite.

Metagre ywackes consist of angular poorly sort ed grains of quartz

(a bout 60%), albitized plagioclase, muscovite, potash -feldspar (micro-

cline and orthoclase), intermediate to basic volcanics, biotite, sphene,

opaques, epidote, apatite, and zircon in a matrix similar to th at of the

f i n e r m e t a s e d i m e n t s . S h e a r i n g a n d c a t a c l a s i s a r e a p p a r e n t i n m a n y

s p e c i m e n s . A s i n t h e p h y l l i t e s , m e t a m o r p h i c b i o t i t e ( o r i n s o m e c a s e s

possi bly stilpnomelane) is present in some of the more highly metamorphosed

specimens.

Most of the met avolcanic rocks appear to have been lavas of basic

or intermediate composition, but are now largely recr ystallized to

greenschist facies assemblages made up of alb ite, chlorite, epidote,

actinolite, quartz, and calcite, not all of which are necessarily found

i n t h e o n e r o c k . A c c e s s o r y s p h e n e a n d o p a q u e s a r e u bi q u i t o u s . A l b i t i z e d

plagioclase laths are commonly preserved in relict su bophitic texture

(sometimes flow-aligned), and relict phenocr ysts of plagioclase and augite


27/164

Fig.

11:

Strain

s l ip

cleavage

a t

an

ang

l e

to

bedding

in

finely

interbedded

s laty

shale and s i l ts tone of the Omung

Metamorphics. Specimen 21NG0523) from the Kundiawa-

Gumine

road.

X 40

plane

polarized l i ght .


28/164


29/164

UPPER PERMIAN or TRIASSIC

Kuta Formation

(name varied)

Definition

Rickwoo d (1955, p.69) used the name Kuta Group for a sequence

of Permian? (Glaessner et al., 1950) calcareous arkoses, limestones, and

shales which unconforma bly overlies the Ku bor G ranodiorite and Omung

M e t a m o r p h i c s . T h e u n i t i s o v e r l a i n b y U p p e r J u r a s s i c M a r i l S h a l e a n d / o r

L o w e r C r e t a c e o u s K o n d a k u T u f f . T h e t y p e ar e a o f t h e K u t a G r o u p i s n e a r

Kuta villag e (145

0

13'11 E, 5

°

55'00 S), at t he western closure of the Ku b or

A n t i c l i n e . N o a t t e m p t w a s m a d e b y R i c k w o o d t o m a p a n y s u b - u n i t s w i t h i n

the Kuta Group , nor was an y su bdivision of the unit made in the 1968

B M R m a p p i n g . T h e r e f o r e t h e P e r m i a n l i m e s t o n e a n d a r k o s e a r e h e r e r e n a m e d

Kuta Formation in accordance with the Aust ralian Code of Stratigraphic

Nomenclature.

Distri bution and thickness

The largest exposure of the Kuta Formation is along the crest of

the range from just east of K uta south to latitude 6°10°S, at the western

e n d o f t h e K u b o r A n t i c l i n e . S m a l l e r exp o s u r e h a v e b e e n m a p p e d o n M o u n t O g a

(Figs.

5 and

4 4 ) ,

and at three localities on the southern side of the

Wahgi Valle y, a b out 26 km east of Mount Hagen township. Limestones 'of the

Kuta Format ion are exposed in Numans Creek, near Dek (144

°

45'E, 5°59'S ),

and near Gurumugl in the upper Wahgi Gorge, 20 km west of Kundiawa.

The Kuta F ormation attains a maximum t hickness of a bout 250 m

in the area southeast of Kuta; elsewhere it ranges in thickness from

about 30-40 m near the Korman River, to a bout 100 m in the Gurumugl area

(west of Kundiawa). Limestone makes up the bulk of the unit; arkose and

shale total only a few metres in thickness.

Stratigraphic relationships


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-15-

Fauna collected b y Rickwood (1955) from the Kut a Limestones at

various localities included:

Dielasma cf. elongatum (Schlotheim)

Dielasma cf. itiatubense Derby

Dielasma sp.

Spiriferina sp.

Rhynchonella sp.

Streptorhynchus cf. pyramidalis King

Marginifera sp.

Fistulotrypa sp.

Pseudomonotis sp.

Gastropod gen. et sp. indet.

This assemblage was also considered to be Permian, but Rickwood

states that it .... does not appear to have close affinities with either

the Australian or Timor Permian .

D.J. Belford (pers. comm., 1970) has identified the foraminfera

Geinitzina and

Robuloides

from locality 2 1NG2571, near Gurumugl Rest House (14

. I

° 47.5 1

E, 6

°

3'S), and

places them tentatively in the Upper Permian. A rhychonellid brachiopod

from the same locality is considered by K.S.W. Campbell (pers. comm., 1970)

to be Triassic or Permian. Although he likens it to a New Zealand Triassic

species, he does not consider it diagnostic. A collection of fauna from

the Kuta Formation, made in June 1970, included a variety of brachiopods,


31/164

-16-

w h i c h d i p s a t 38

°

to the southwest; this limestone bed was downfaulted

into the granitic basement before deposition of the Kondaku Tuff.

On the western side of the Kaip Valley, 10 km east- southeast of

Mount Hagen, a bed of massive, dark grey limestone which dips northwest

directly overlies granodiorite, and iS overlain by dark grey shale and

siltstone, probably of the Maril Shale.

Across the valley, on Mount Oga, the Kubor

Gram:diorite

and the

Omung Metamorphics are overlain by about twenty feet of brown-grey sandy

t o g r i t t y c r y s t a l l i n e l i m e s t o n e c o n t a i n i ng s p a r s e f o s s i l f r a g m e n t s . T h e

limestone is overlain by dark grey micateousVaril Shale A 8ffiala outlier

of Kuta limestone beside the main south road, close to the Wahgi River, is

made up of pale grey to b uff„ coarse to fine-grained crystalline limestone

which contains scattered sandy granitic detritus. A larger exposure, on the

eastern side of the Wahgi River is fossiliferous, very pale grey to buff

fine-grained limestone. Five kilometres farther east, also close to the

main road, is a small exposure of buff to grey medium to fine-grained

crystalline limestone with scattered granitic detritus and small

brachiopod remains.

Several prominent limestone masses on the northeast flank of

the Kubor Anticline, between the Om ung River and Neragaima Mission

(1440

47' E 6

°

02'S), were 'mapped by Rickwood (1953) as lenses within the

U p p e r

Jurassic Maril Shale., However, detailed examination in 1968

revealed that these masses are biohermal reefs which rest on a layer of

arkose unconformably overlying, Kubor Granodiorite, and are overlain by

Maria. Shale. The limestone is grey and compact, similar to that at the

type locality.

Near Minj, calcareous arkose and limestone typical of the Kuta

Formation grade laterally into calcareous breccias containing fragments of

metamorphic rocks (Rickwood, 1955). A thin shale (or phyllite) breccia


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-17-

and near Gurumugl

t

the limestone covers an irregular granitic b asement.

The Kuta Formation does not occur at el evations greater than 2,750 m in

the Kubor Range, and it is concluded that the limestone was deposited as

fringing reefs on granitic wash and on breccia derived from the adjacent

Palaeozoic basement.

Kana Volcanics

Nomenclature

Dow and Dekker (1964,. p.'12) proposed t he name 'Kana Form ation'

for Upper Triassic sediments of volcanic derivation exposed in the head-

waters of the Jimi River to the north of the map (Pl ate 1). In that area

the formation consists of at least 600 m of interbedded feldspathic arenite

and tuffaceous siltstone together with some beds of dacite pebble

conglomerate and minor quartz arenite and limestone. It conformably

overlies the Jimi Greywacke, also of Upper Triassic age, and is unconformab ly

overlain by the Lower Jurassic Balimbu Grey wacke. Macrofossils from the

Kane River (a tributary of the Jimi River) have been assigned an Upper

Triassic age (Skwarko, 1967, p.

46).

The formation was subsequently renamed Kana Volcanics by Dow

et al. (1968

4

. p. 24) who recognized the high volcanic content of the unit

in areas outside the Jimi River headwaters, notably t he Yuat River area

and near Tabibuga in the Jimi Vall ey. We have retained the name Kane

Volcanics as our mapping has confirmed that the unit as a whole is

characterized by volcanic rocks.

Distribution and thickness

The greater part of the Kana Volcanics crops out to the north

of the map area in the Jimi Valley and on the Jimi-Wahgi divide. The

formation is exposed extensively but discontinuously from the Jimi River

headwaters along the length of the Jimi Valley to the Yuat River in the


33/164


34/164


35/164

-19-

•

A stream section through part of the formation

7

km southeast

of the Chimbu River section exposes volcanolithic, feldspathic and

tuffaceous sediments. Much of the section consists of hard, grey, green,

or pink sandstone interbedded with red or grey tuffaceous siltstone and

shale. These rocks may be massive or thinly interbedded and finer

lithologies exhibit graded bedding in some places. The sandstones contain

rare calcareous beds up to 10 cm thick, and in two of these, poorly-

preserved bivalves, gastropods, and brachiopods were found. In places, the

sequence contains massive beds of volcanolithic conglomerate which consists

of well rounded pebbles and cobbl es of porphyritic andesite and dacite in

a grey or red tuffaceous matrix. Green, massive andesite was found in one

outcrop near the top of the sequence, but lavas are otherwise absent. Also

noted were fine green volcanic breccia, dark grey foetid limestone, and a

medium-grey limestone containing fragments of vesicular andesite.

Red and green volcanic breccias are abundant in the Jimi-Wahgi

divide northeast of Banz; red limestone and fossiliferous red shale

were also seen. No outcrop was seen in the headwaters of the Koro River,

b u t a b u n d a n t f l o a t i n d i c a t e s t h a t t h e f o r m a t i o n i s p r e s e n t . F a r t h er

downstream in the same river, green lavas of the Kana Volcanics crop out

over a short sect ion. On Mount U don, Dow and Dekker (1964) reported 600 m

of dolerite with some A ndesite grading upwards into

600

m of basalt,

agglomerate, greywacke, and siltstone.

Intermediate lavas and pyroclastics predominate on the Kubor

Range; outcrop on Mount Digini is mainly fine-grained, grey or green lava

and minor agglomerate. In the vicinity of Mount Kub or, agglomerates and

massive flow-banded or brecciated lavas are extensively chloritized and

epidotized. One outcrop of agglomerate appeared to contain fractured

remnants of pillow lava, suggesting subaqueous eruption. Other rock types

include epiclastic volcanic breccia, volcanolithic and feldspathic

sandstone, and fine-grained grey or green tuff. In hand specimen many


36/164

-20-

In the Kubor Anticline, the volcanics rest unconformably on Kubor

Granodiorite and Omung Metamorphics, Upper Jurassic Maril Shale overlies

the formation 20 km north of Mount Hagen, and possibly on the southern

limb of Kubor A nticline, west of the Mogono River.

Fossils collected from a few localities in the Bismarck Fault

Zone were too poorly preserved, or were otherwise unsuitable for precise

da t i n g . S k w a rk o ( 1 967, p .

4 3 )

recorded Costatoria cf. melanesiana,-

Rhaphistomella? kumbrufensis and Spiriferina cf. abichi from l ocality H590

(of Dow and Dekker , 1964) in the Kana R iver. Because thes e forms were also

found in the Jimi Greywacke which was dated as Carnian-Norian, Skwarko

could not separate the two units on palaeontological grounds, and thus the

age of the Kana Volcanics is given as Upper Triassic.

Petrography

Specimens from the Chimbu River type section include lava,

agglomerate, tuff, volcaniclastic sediments, and a microdiorite porphyry.

The composition of volcanic constituents ranges from basaltic to rhyolitic,

b u t i s p r e d o m i na n t l y d a c i t i c t o r h y o d a c i t i c. A l l s p e c i m e n s h a v e s u f f e re d

low-grade metamorphism, and in most the original feldspar is albitized.

Chlorite and epidote are common; calcite

t

actinolite, biotite, and

muscovite are less so. The metamorphic grade decreases from epidote-

amphibolite facies close to the Bismarck Intrusive Complex to lowermost

greenschist facies at the downstream contact of the section. This suggests

that metamorphism accompanied intrusion of the adjacent plutonic mass.

A chloritized augite andesite pebble and a biotite dacite cobble from a

volcanolithic conglomerate were identified from Geirinigl Creek (Plate 7).

Specimens from north of Banz include volcanic breccia and arenite.

The breccia is composed of poorly sorted, angular, and commonly vesicular

lava fragments ranging from finely comminuted sandy m atrix material to

clasts of 10 cm diameter or more. The elastic volcanic material is


37/164

-21-

Provenance and depositional environment

The Kana Volcanics are composed almost entirely of the products

of basic to acid volcanism, and include both primary source rocks and

transported derivatives. Most, if not all, of the epiclastic sediments

were deposited in a marine environment, but some lavas and pyroclastics

were subaerial. The presence of massive beds of volcanolithic conglomerate

points to subaerial erosion, although the beds may have b een laid down

offshore. Features such as glassy rims on volcanic clasta and pillow forms

in agglomerate suggest that some volcanism may have been submarine.

The Kana Volcanics were probably deposited in and around volcanic

islands that were built up on the northern margin of t he Australian continent

in the Upper Triassic.

J U R A S S I C

Balimbu Gre ywacke

The name Balimbu Greywacke was proposed by Dow and Dekker

(1964,

p .

14) for interbedded greywacke and siltstone of Lower Jurassic

age which crops out in the headwaters of the Jimi River to the north of

the map area. The type section is exposed in Balimbu Creek on the northern

limb of the Kol Syncline. There,the formation is about 300 in thick.

Balimbu Greywacke unconformably overlies the Upper Triassic Kana Formation,

and is conformably overlain by the Mongum Volcanics of probable Middle

Jurassic age. Ammonites from the type area indicate a Sinemurian-

Pleinsbachian age (Skwarko, 1967, p.

46; and report in prep.).

Within the map area, rocks correlated with the Balimbu Greywacke

have been mapped in three areas to the north of the Wahgi Valley: in

the Chimbu River, in the K oro (Kworu) River, and along the southern fall

of the Jimi - Wahgi divide between Banz and Nondugl. All three areas lie


38/164

- . 2 2 -

The sandstone is typically well bedded, indurated, and moderately jointed.

Detritus is predominantly lithic-feldspathic, and appears to be largely

o f v o lc a n i c o r i gi n . G r a i n si z e r a n ge s f r o m f i n e s a n d t o g r i t. C a r b o n a c e ou s

fragments are common, if not characteristic. Thinly bedded to massive shale

and siltstone are interbedded with the sandstone; they make up less than

half the sequence. In some outcrops the finer lithologies have a tuffaceous

appearance.

A ver y large (a bout 20 cm long), but poorly preserved belemnite

was found in shale near Bogo Rest House (20NG2635), close to the Koro River

ammonite locality (H549) of D ow and Dekker (1964). This was subs equently

examined by G.R. S tevens, of the New Zealand Geological Survey, who was

unable to provide a positive identification. However, similar large

belemnites are known from the L ower Jurassic in other parts of the world.

Also noted were sinuous worm trials on a bedding plane in sandstone.

The Koro River sequence appears to overlie the Kana Volcanics to

the southwest and to underlie the Maril Shale to the northeast without the

interposition of the Mongum Volcanics. One or both contacts may be faulted,

and the sequence as a whole is structurally complex with numerous faults and

divergent bedding attitudes. From available data it seems that the Koro

River sequence is a southeastern extension of the Balimbu Greywacke on the

s o u t h e r n l i m b o f t h e K o l S y n c li n e . T h e p r o ba b l e m i n i mu m t h i c k n es s i s

1500 m .

Rocks correlated with the Balimbu Greywacke crop out in the

Chimbu River 15 km northeast of Kundiawa (Dow et al., 1968, p. 25).

Greywacke, siltstone, and shale form a 1500 m thick, overturned sequence

dipping steeply northeast. The sequence is faulted against overturned Kana

Volcanics to the northeast, and overlies overturned Maril Shale to the

southwest. Apart from incipient metamorphism the rock types are similar

to those exposed in the Koro River. Siltstone and shale are strongly

cleaved. In places the sequence is intruded by dolerite dykes up to


39/164

3-

The distribution and thickness of the formation suggest that

it was deposited in an elongate trough extending 170 km northwest from

the Chimbu River to the Yuat-Maramuni divide. Detritus was derived

largely from pre-existing volcanic rocks (Kana

VOIOaliied?) and possibly

from contemporary volcanism, as some rocks appear to be tuffaceous.

Mongum Volcanics

The Mongum Volcanics were first described by Dow and Dekker (1964,

p. 15) from the Kol Sy ncline, in the headwaters of t he Jimi River. In that

area the formation overlies the Lower Jurassic Balimbu Greywacke, and

u n d e r li e s t h e U p p e r J u r as s i c M a r l S h a le . T h e t y p e s e c ti o n i s o n t h e

northern limb of the Kol Syncline, 2 km north of Mongum Village. According

to Dow and Dekkerlthe formation comprises green basaltic agglomerate and

pillow lavas interbedded with pebble-cobbl e conglomerate and tuffaceous

g r e yw a c k e ; i t i s 250 m t h i c k i n t h e t y p e a r e a . F r o m i t s s t r a ti gr a p h i c

position, Dow and Dekker inferred a Middle Jurassic age b ut Lower or U pper

Jurassic ages are also possible*. Fossils from the type area were too

poorly preserved to b e identified.

The Mongum Volcanics crop out on both limb s of the northwest-

trending Kol Syncline. Only a small part of the exposure on the southern

limb occurs within the map area - to the northeast of Mount Udon. Here

the formation dips steeply northeast and appears to be no thicker than in

the type area. Its boundaries are interpreted from airphotos and from field

observations b y Dow an d Dekker in 1962; the area was not revisit ed in 1968.

The Mongum Volcanics do not appear in the Koro R iver sequence,

which is an extension of the southern limb of the Kol Syncline. This is

probably due to thinning or faulting-out east of Mount Udon. Elsewhere in

the Jimi Valley-Bismarck Fault Zone area, the Maril Shale rests directly,

and probably unconformably, on the Balimbu Greywacke. With the possible

exception of basic volcanics underlying Maril Shale in the Maramuni River


40/164

-24-

we place the bottom at the unconformity with the underlying Omung

Metamorphics and the top at the incoming of,volcanolithic sediments

characteristic of the overlying Kondaku Tuff. We have used the name

Maril Shale (singular) in line with current practises of stratigraphic

nomenclature, and following the usage of Dow and Dekker (1964).

Distribution and thickness

Recent mapping by the Bureau of Mineral Resources (e.g., Dow and

Dekker, 1964; Dow et al., 1968) has sho wn that the Maril S hale crops o ut

in a zone extending from the Kubor Anticline, 220 km northwest to the

Maramuni River in the South Sepik region. Within the map area, the

Maril Shale is exposed mainly around the basement core of the Kub cr Anticline

and in the Bismarck Fault Zone to the north of the Wahgi Valley.

The Maril Shale is thickest at the eastern end of t he Kubor

Anticline. Proceeding westwards along the northern limb, the thickness

diminishes from 1200 m in the Wahgi Gorge to about

400 m in the Omung River;

it remains roughly the same in the Minj

t

Tuman and Korman (Komun) Rivers

and lenses out beneath the Kondaku Tuff

8

k m s o u t h e a s t o f M t H a g e n . O n t h e

southern limb, the formation is about 1500 m thick in Olefa Creek,

7 km

west of Gumine; it thins to an estimated 1000 m in the Mogono River, and

pinches out altogether 30 km farther west. It reappears surrounding a small

window of Kubor Granodiorite in the Wembo River, 25 km south of Mt Hagen,

but is otherwise absent at the western end of the anticline. Small

outliers cap the summits of Mt Oga and Mt Mani at the northwestern end of

the Ku bor Range.

The Maril Shale also crops out overlying older rocks at t he

northwestern end of thesWahgi Valley. Only a small part of this occurrence

falls inside the map area: the main exposure lies to the northwest in the

Kuni and Muga Rivers (corresponding to the

9 Kileng Hill° area of Rickwood,

1966), where the thickness is at least 1200 m.


41/164

-25-

to be scarp-forming in areas of subhorizontal or gentle dips.

/ L i t h o l o g y

The Maril Shale is typified by dark-grey, m oderately-indurated

shale and siltstone with variable mica and carbonate content. Outcrops

may be either massive or well-bedded, but t hey commonly have two well

developed sets of joints at a high angle to bedding and to each other.

F l a g g y p a r t i n g p a r a l l e l t o b e d d i n g i s a l s o c o m m o n . A c h a r a ct e r i s t i c

feature of the calcareous shale and siltstone is the tendency of weathered

surfaces to disintegrate into small blocky fragments.

,Parts of the Maril Shale (especially

8

km west of G umine and

2 km south of Neragaima) include pyritic and carbonaceous shale and

siltstone. Pyrite occurs as concretions up to 30 cm in diameter, as thin

lensoid masses, or finely disseminated grains. Where pyritic, the sediments

are usually dark and carbonaceous. A 2 cm thick

t

lensoid mass of schungite,

a vitreous carbon mineraloid with a high TiO2 content, was collected from

the Maril River by inhabitants of the Gumine area.

The formation also contains subordinate beds of fine to medium-

grained sandstone up to 2 m, thick,but commonly about 10 cm thick. Minor

beds of grey to dark grey calcilutite occur widely, and red or green shales

have been noted at various localities.

In the Kubor Anticline, the base of the Maril.Shale is generally

marked by up to 20 m of breccia-conglomerate (see also p.16 ), poorly

sorted, angular to subrounded clasts of slate, phy llite, metagreywacke, and

granodiorite derived from the underlying basement, as well as clasts of

shale, greywacke, quartz, sandstone, chert, limestone, and volcanic rocks.

The matrix may be siltstone, sandstone, grit or limestone. The basal rudite

grades locally into coarse arkosic sandstone where the formation overlies

Hu ber G ranodiorite.


42/164

-26-

The basal parts of the formation at the eastern end of the

anticline include some large lenses of limestone up to 70 m thick.

Boulders derived from a large l ens west of the Gumine-Kundiawa road consist

of fine-grained dark grey limestone with conspicuous echinoid plates.

Some boulders are crowded with phyllite clasts derived from the underlying

metamorphic rocks.

Stratigraphic.rolationships and. age

In

most places around the Kubor Anticline, the Maril Shale rests

unconformably on the Omung Metamorphics or Kubor Granodiorite. At the

northwestern end, the formation locally overlies thin limestone of the Permian-

Triassic Kuta Formation, and in the Gurumugl area, 15

.

km south of Kerowagi

t

it abuts partly exhumed biohermal reefs Of the Kuta Formation. It unconforma-

bly overlies the Upper Triassic Kana Volcanics 20 km northeast of MOunt Hagen

town and probably also on the southern flank of the anticlineoest of the

Mogono River. In the Kubor Anticline, the formation is everywhere overlain

by the L ower Cretaceous Kondaku Tuff, in some areas with apparent conformity,

but in others with slight angular unconformity.

In the Kol Syncline, the Maril Shale conformably overlies the

Mongum Volcanics and is overlain, possibly unconfotmably, by Kondaku Tuff

(Dow and Dekker, 1964,

p. 16).

To the southeast in the Koro and Chimbu

Rivers, the Mongum Volcanics are absent, and the Maril Shale rests with

probable unconformity on Lower Jurassic Balimbu Greywacke, although the

relationship is not known with certainty.

A n U p p e r

Jurassic age is indicated by the widespread occurrence

of

M a l a y o m a o r i c a m a l a y o m a o r i c a

and to a lesser extent

I noceram us

cf.

haast i.

The age of this fauna is now considered to be Kimmeridgian

(Skwarko, 1967, p.

4 6 ) .

Rickwood

(1955) recognised °

B u c h i a ° m a l a y o m a o r i c a (=

M a l a y o m a o r i c a


43/164


44/164

-28-

Papua which is locally represented by the Ku b or Granodiorite and Omung

Metamorphics. In contrast with the overlying C retaceous sediments,

contemporar y volcanism has pla yed only a minor part.

The fine-grained calcareous sediments of the Maril Shal e were

deposited in a marine shelf environment during a period of relative tectonic

and volcanic quiescence. Except for the basal breccia-conglomerate and

arkose lenses in the vicinity of the Ku bor Anticline, coarse sediments are

generally a bsent, suggesting t hat the bulk of the formation was deposited

at some distance from land, or that l and, if present, was of su bdued relief.

The axis of the Kubor Anticline m ay have teen emergent in places. The

arkose member on the northern limb contains terrestrial plant fragments,

crossbedding, and ripple marks suggestive of a partly terrestrial environment.

This ma y indicate su baerial erosion of emergent islands of Ku bor Granodiorite.

S e d i m e n t a t i o n w a s v e r y e xt e n s i ve

.

i n . t h e U p p e r J u r a s s i c . A p a r t f r o m

the areas of Maril Shale, Upper Jurassic sedimats appear to underlie much

of the Western Highlands and . _Western Papua where they have b een located

in petroleum exploration wells (Australian Petroleum C ompany, 1961). In the

Western Highlands, fine-grained marine sediments containing

Malayomaorica

have been reported from the Wok Feneng„ a tri butar y of the Fl y River (Kua bgen

Group; Osborne, 1945) and also from the Strickland__Gorge(D. Jenkins,

British Petroleum Australia, pers.. comma. Thick marine sediments in t he

Telefomin area contain ammonites of Upper Jurassic age (Australasian

Petroleum Company , 1961) and

NAyliaz

. c a

occurs in the Sitipa Shale in

the April River area (Dow et al., 1

CRETACEOUS

Kondaku Tuff

Definition

T h e n a me 9

Kondaku TiLffs° was first used by Edwards and Glaessner

(1953) for the b asal sand y part of the C retaceous in the section along the


45/164

-29-

the other to the northeast of Kerowagi. Both are small masses caught up

in the Bismarck Fault Zone, and surrounded by older (Triassic and Jurassic)

rocks.

Noakes (1939) estimated the thickness of Lower Cretaceous in the

Chimbu measured section at 2,000 m, and this estimate was supported by

Rickwood (1955). However, more accurate mapping of the Chimbu section in

1968 showed the thickness to be about 2

2

450 m, and t his is a m aximum for

the formation. The average thickness elsewhere is about 2,000 m, but in

many areas the unit is partly repeated by faulting (Wahgi Valley) or folding

(southern flanks of the Ku bor Range).

Strati graphic relationships and age

T h e K o n d a k u T u f f i s u n d e r l a i n b y U p p e r J u r a s s i c M a r i l S h a l e . I n

some places there is clear evidence of angular unconformit y; in others there

is a paraconformable relationship. I n the Wilde River area, on the south-

western flanks of the Kubor Range

4

Kondaku Tuff directly overlies Kubor

Granodiorite and Omung Metamorphics. The unit grades upwards into Upper

Cretaceous Chim Formation; the contact is marked by the disappearance of

massive lithic sandstone beds.

T h e K o n d a k u T u f f i s p r o b a b l y o f L o w e r A p t i a n t o A l b i a n a g e; n o

Cenomanian fossils have been found. Edwards and Gl aessner (1953) list the

following fauna collected by G.A.V. Stanley near Kundiawa:

Deshayesites n. sp. (Lower Aptian),

Cymatoceras sp.,

fragment of a large phragmacone of

Belemnites sellheimi Tenison-Woods, and

P l e u r o m y a


46/164

-30-

At localities 20NG2625 and 2626, 18 km west-northwest of Kerowagi

l o n t h e

Highlands Highwa y, g astropods, bivalves and belemnites were found in

tuffaceous sandstone.

Lithology

The Kondaku Tuff consists largely of gre y-green, coarse-grained

lithic sandstone or gre y wacke, tuffaceous sandstone, and dark gre y or g reen-

grey shale and siltstone. Conglomerate, amygdaloidal lava, agglom erate, and

volcanic breccia make up a bout 10 percent of the formation, and are concentrat-

ed in the lower 500-1000 m of the unit.

Shale and siltstone are the most common b ut the least prominent

rock types in the K ondaku Tuff because of their soft

*

fissile nature and

consequent low resistance to erosion,. Inter bedded shale and siltst one occur

as beds ranging from 1 mm partings in sandstone* to beds up to 100 m thick

which contain minor sandstone la yers*. Shale beds are commonly massive and

uniform, though there is some la y ering

in 1 cm bands or 1 mm laminations*,

Silty beds are mostly banded* in 1-3 cm bands, or finely l aminated* with

laminae as thin as 0*2 mm* Soft sediment slump deformation is common in these

-

fine-grained beds* and has affected sequences up to 30 m thick* Dark grey to

-

b l a c k *

fine-grained calcareous nodules (Fig.. 15) occur in shale and siltstone,

but are larger and less comm on than similar nodules in the Chim Format ion; a

few of the nodules contain fossils* The calcareous nodules are ellipsoidal

or lenticular, 3-60 cm long (m ost commonly 15-20 cm)* and in man y cases displa y

surficial polygonal .desiccation cracks and deep gashes filled with white,.

coarsely-crystalline calcite* Less common features are small (10 to 30 cm

long

*

and

3 to 7 cm

thick) lenses of 1ight 4 powdery buff-coloured material

*

proba bly diatomites, and beds of impure limestone up to 20 cm thick* Vague

dark streaks and traces of worm(?) burrowings outlined by dark

*

organic

(faecal?) material are also a characteristic feature of the upper 400 m of

the Kondaku Tuff*. Most of the shale and silt-stone consists of clays

f

, f e l d s p a r

(mainly plag ioc1ase). quartz

*

and fragments of volcanic rock and altered

glass

*

Calcareous shale containing foraminifera is also common* and contains

Elm

=I

am

No

mo

am am so

I ow

oNENs

ow ow

TAMP

1. ESTIMATED COMPOSITIONS UP SAMPLES OF EDNOAKU


47/164

Sample

Number

Rock tyPe

.

s 4 7 , -

1

I

i 2S

: e ; .

8

i

ii 03

A 4

.

. 1 g ,

z

.4

03

. . . . . — . .

, . . .

. 0 3 3 1 0 0 .

g

In

0

...,

vi ......

0

M

0

M

it

:

i

m

8

.,

8

tg

r

•M

4T .

2 C Z .

0

0

V

4.

: 1 1 1 C R 1 CR.

.

.1

01 g

4.

,

.., • P

m

otes

•

Tuffaceous/volcenclithic pediments

20(Ab)

tr.

5 1

tr.

tr. 5(6).)

tr.

40

0 Trace of muscovite15G 10353 Tuff. Zelda. -lith.erenite

20110 1254G Tuffaceous

areniteficrit 1

5 5+

1-2

3

10

0

2% glees

215(1 .

0548A.

Felda-lithcice_

tr.

tr. 60(?)

tr. tr.

5

2,500t

215G 1151

" labile amt- 2-3

15(Ab)

55 5

tr.

5

-10(g1) 10

1,000

_

205o

0599

"

prenite(T) 2-3

20 60

tr.

10(61)

2

5% leucoxene

2111G 2584A

"

granite

7

20

5(S)

55

8-10

3-

4

tr. tr.

1,400

21N G 10 240 " arenite

10 10(Ab) 20

40

20

tr.

tr.

•

15

0

20110 1212A

Qts4 feldslithic labile

.

renite(T)

10

15

5

45-

50

8 5(61)

2 top 5-10% leucoxene

2111G 10350 Felds-lithic ,vreimacke

15 25(Ab) 20

alt.

tr.

15

tr.

20

0

5% tourmaline

20110

1.239

Folds -qtz lithic arenite 15

5

60

1-2

tr.

15 0

20110 12544

Taft.

labile lithic

elitatone 15

5-10

50

tr. 10-15

tr.

tr.

o 10-15% alt. glees

2111C 1050A Tuff. lithic prevmacke 15

25

(25)*

20

tr.

25(61)

2 10

5

0

20110 2626A Calc.lithic labile

arenite 15

5 35

-

40

2

3 35 -40

?

201(0

12541

Qtz-felds-lithic labile

arenite

20

20

55

tr.

.

.

5

0(?)

2111G 1087A

Feldenathic sediments

"

renite 20

3

10(kb)

30(An0-30)

3 37

40 2

tr.

1

tr.

10

3 1

5(61)

15

20

top

300

0110 1295A

Tuff. felds.-lith.

labile arenite

21110 1024A

Tuff. felde.-lith.gair

Eke

5(2 )

40(kb)

8

10

10 10(61)

2

15

0

2111G 1024D

Quartzone arenites

Litho-felds (sublebile)

SENEcke-

10(2°)

40

60(01)

4.

10

10

40

5

2

tr.

1-2

5

5(61)

10

0

?

Trace of °phew

03G

0597

1

2tz

lithic labile prenite

2111G 2610A

Folds. -lith

ublabile

arenite

60

15(01-And)

2-3 15

1

2

1

900

20110

12958

Qtal

lithic labile arenite

40

10(

35

5

1

2

5

tr.

1

300

20110 1297

"

renite

50 10(

20

2

1

1 1-2 1-2 30

1-2% muscovite

2111G 06074 • Qtz folds. -lith. labile

arenite

30

25 25

tr.

10(61)

5

1,300 Rare zircon

21210 1101 •Calc.felde.qtz granite

35

3(Ab) 10

tr. tr.

10

5

35

300-600

Trace apatite

2111G 0540

Qtz lithic labile nrenite

50

30

tr. tr. 10 1,200 Minor tourmaline

21110 0544i

Calc.qtz lith.labile

50

tr(01)

20 2

25

tr. 1,200 Minor muscovite

2111G

0555

. renite 50 tr(01) 15

tr. tr.

30

900 Trace mtscovite

21No 1285

T u ff .

ranite

50

tr(Ab)

38(glass)

10,

2 600 Trace muscovite


48/164


49/164


50/164

-32-

and gastropod shells. Volcanic rock fragments dominate over other clasts,

and some conglomerates are made up entirely of greenish-grey, fine-grained

lava clasts.

Eight sampl es of lava were collected from the Kondaku Tuff,

all from b etween 300 and 1 9

200 m a bove the base of the unit, and all from

the area between Kundiawa and Minj. Five of the samples are almost

unaltered augite andesite made upoof oligoclase-andesine (80%), brown augite

(10%), opaque minerals, and some chlorite and calcite, Two samples are

spilites;

made up of albite, calcite and chlorite; one contains 5% quartz

a n d 2 0 % r e l i c t a u g i t e . T h e r e m a i n i n g s a m p l e (20NG1167) is an altered augite

rhyodacite porphyr y, consisting of plagioclase and sanidine (15%), augite

(10%), chlorite (30%), prehnite (5%), and a litt le calcite and epidote. This

rock also contains ovoid amygdales filled with quartz (20% of the rock) and

fine, fi brous, pleochroic g reen actinolite (15%).

Edwards and Glaessner (1

9 5 3 )

carried out some detailed petrological

w o r k o n a s m a l l n u m b e r o f s a m p l e s f r o m t h e K o n d a k u T u f f . A p a r t f r o m

features included in the a bove descriptions, the y recorded a wide variety

of heav y minerals, including topaz, to urmaline, zircon, apatite, rutile,

ilmenite and rare sulphides. Enstatite was found in one of the samples of

tuff.


Volcanic detritus and volcanic rocks make up the bulk of the

K o n d a k u T u f f , T h e a b u n d a n c e o f v o l c a n i c r o c k a n d g l a s s f r a g m e n t s , l a v a a n d

agglomerate in the K ondaku Tuff decreases markedly southwards awa y from the

Wahgi Valley. As Edwards and Glaessner.(1

9 5 3 )

inferred, this indicates a

source of the volcanic detritus and lava to the north of the Wahgi Valle y,

probably in the area of the Jimi-Wahgi divide. Some quartzose sandstones

in the Kondaku Tuff contain granitic detritus, including a variety of heav y

minerals which are not found in volcanic rocks. This granitic detritus was

proba bly derived from exposed parts of the ancestral Ku bo r Range.


51/164

-33-

On the basis of the more det ailed mapping carried out in the

1968 survey, it has been estimated that the depth of burial of t he base of

the Kondaka T uff is about 5,500 m, made up of 2 ,500 in of Kondaku T uff and

3,000 in of Chim Formation. I t is unlikely that there was a significant

thickness of Eocene-Miocene cover over the area of Kondaku Tuff that is

now exposed.. A liberal estimate of the total depth of burial could be no

more than 6,300 m, even if the Eocene-Miocene cover did extend to the Kub or

Range.

Zeolitization was noted in only two samples collected in 1968,

while prehnite was found to be abundant in the lowermost 100 in of the

Kondaku Tuff. This lower part of the formation is rich in volcanic detritus,

lava and agglomerate. With few exceptions, prehnite does not occur in

samples which contain calcite. Coombs et al. (1970) have pointed out that

under conditions of high partial'pressure of CO2 in burial metam orphism,

lime zeolites, prehnite, pumpellyite, and zoisite can al l be suppressed in

favour of calcite and chlorite. This is probabl y the explanation for the

absence of prehnite in calcareous rocks in the lower part of the Kondaku Tuffs,

and in all but a few samples of the underlying Maril Shale.

Effects of burial metamorphism have been manifested:at a deipth

of only 4,500 m in the W ahgi ieqUence in cOnträst to ,7,000 m for t he

Southland, New Zealand sequence, and 4,900 m for the Tamworth T rough

sequence (Crook, 1961). This is probably due to the litholog y of the rocks

involved. A thick pile of largely basic volcanic detritus, basic lava and

agglomerate, and interbedded siltstone and shale would probably retain

.

some

magmatic heat, and would generate an appreciable amount of radiogenic heat.

Volcanic and volcanic-derived rocks would also be chemically susceptib le to

diagenetic change, relative to pelitic, quartzo-feldspatic or siliceous

sediments which are more stable at the low temperatures of burial metamoithism.

Structure


52/164

k-

Chim Formation.

(name varied)

Definition

Specimens collected by Noakea_(1

9 3 9 )

in the Chim (nol Chimbu)

R i v e r , w e r e e x a mi n ed b y E d w a r d s a n d G I e S s n e r ( 1 953 ) w h o d i v i d ed t h e U p p e r

Cretaceous rocks into two units - the.Maram Shales and the Chimbu Tuffs.

Rickwood (1955) used the name Chim Group for a sequence of shales with

occasional cone-in-cone structure,-greywackes and tuffaceous mudstones

of Upper Cretaceous age exposed in the Chimbu area. No subdivision of the

Chim Group

. was attempted by Rickwoodi

:ajld no separate formations within

the U pper Cretaceous could b e mapped'in'.19684

so the unit is here renamed the

Chim Formation..

Distri bution and thickness

•

The'Chim Formation consists of grey to dark grey mUdstones and

siltstones, with Minor interbedded:lithió

-

or .

tuffaceous (Edwards &

Glaessner, 1953) siltstones and sandstones. It'cropS out around a large

part of the cuter flanksof the Kubor Anticline, from the Bismarck Fault

zone near Kerowagi, southeast to Mount Michael,and westwards from there to

Mount Ialibu and into the Nebilyer Valley.

Relief on the Chim F ormation is moderate to gentle, and ,dip slopes

are not commonly preserved, Streams cutting the formation generally have

broad V-shaped valleys, with very few gorges. Outcrop is restricted to the

streams, with only flaky shale fragments and scarce sandstone cobbles on

the ridges.

Noakes (1939) measured .a section along the Chimbu River, and

estimated the thickness of the Upper. Cretaceous rocks to be 3 , 200 metres.

A thickness of about 2,400 metres was measured directly from Pl ate 10,

just east of the Chimbu River where dips are consistently about 3 0

0

NE.

Elsewhere the thickness of the Chim Formation varies considerably. It is


53/164


54/164


55/164

-35.-

In the Mount Michael area, middle Miocene Movi Beds unconformably

overlie the Chim Formation. East of Mount Suaru, the formation is

unconformably overlain by upper Palaeocene Pima Sandstone. In the

Nebilyer Valley, Chim Formation is overlain by calcareous Palaeocene

mudstone and Eocene to Oligocene Nebilyer Limestone.

At Mingende, specimens of ammonites were collected by Noakes

(1939), and these were found to be Cenomanian (Glaessner, 19k5)

0

T h e f a u n a

includes:

Euom haloceras hoeltkeri (Erni)

Puzosia sp.

Turrilites cf. scheuchzerianus Bosco

Inoceramus sp0

a few foraminifera, including

Textularia cf. washitensis Carsey

Specimens collected by Noakes in the Chimbu River section include

Textularia sp., and among the specimens from the Mingende area given to

G.A.V. Stanley b y natives (Stanley, 1950) were Mantelliceras S. Turrilites

cf. acutus Passy.

Only three specimens of Chim F ormation collected in 1968 contained

diagnostic m icrofauna; specimens 21NG0648 and 0651 from t he Tua R iver,

south of Mount Suaru contained the following:

0648

- plama2potruncana stephani (incl. turbinata forms)

Hed beratlla spp.

0651 - Gl obot runcana spp. (incl. G. lap parenti group)

aa n _ s p . c f . P

_. _0 stephani


56/164

-36-

Superimposed on the large scale folding and faulting are

numerous folds and' contortionsproduced by contemporaneous and intra-

formational slumping. Examples of this type of deformation are exposed

in many places, notably in the area west of Kerowagi. Deformation ranges

from gentle though irregular intraformational folds to intensely and

complexly contorted beds, and has occurred on all scales up to several

metres in amplitude.

Bedding in the Chim Formation ranges from very massive,

particularly in the siltstone and mudstones, to thinly and commonly

rhythmically interbedded (2-10 m m beds) siltstones and/or mudstones,and

laminated siltstones or sandstones (Fig. 14). Small-scale cross-bedding

and ripple marks in some of the laminated sandstones indicate shallow-water

deposition. The vague dark streaks and worm burrows not ed in the Kondaku

Tuff are also 'common in the Upper Cretaceous b eds.

The dominant lithology in the Chim Formation is grey, dark grey

or almost black mudstone to siltstone, commonly micaceous, and containing

in places grey fine-grained ovoid calcareous nodules ranging in size from

a few centimetres to over a metre across. Many of these nodules contain

microfauna and, macrofossils, including ammonites, gastropods, b ivalves

and.belemnites. The mudstones and siltstones consist of angular to

subrounded fine-:grained volcanic rock fragments, quartz (up to 30%),

plagioclase (usually oligoclase or andesine), and minor muscovite and/or

biotite, calcite and heavy minerals. The siltstones are well sorted and

contain only a small amount of clay matrix, but the shales and mudstones are

made up predominantly of clay minerals with minor quartz and micas. Heavy

minerals include opaques (magnetite and/or ilmenite), zircon, rare tourmaline,

and epidote. Some specimens contain irregular pat ches of coarser or finer-

g r a i n e d m a te r i a l, s u g g e s ti n g i n tr a f or ma ti o n a l e r o s i on , p o s s i b l y c a u s e d b y

slumping.

Very fine to medium-grained sandstone occurs as thin, widely to


57/164

Fla . 16s.

CHIM FORMATION- CHIMBU RIVER SECTION

SCALE

IN METRES

GRAPHIC

LO G

PETROGRAPHIC

SAMPLE NO.

LITHOLOGY

OSSILS

CNIM81/

LIMESTONE

1000-

•

•

0

: g .,

01

..

.9.0 .9

6 %

. . ; ; ; ; . 4 1 . ; ; ; ; I : ; ; ; ; .-> •. . 1 4

21 NO 0682

21 NG 0689

21N0 0693

21N0 0696

21 NO 0698

9014

9 0 1 8

3 .

• 21 N O 0 71 3 -4

9021

to

9024

21N6 OTIS

Shale, conglomerate

Calcarenite

Volconollthic greyw ache

M assive shale

}

Soft sediment

*Amp structures

Lamkated sandstone, sllistone

and shale with minor cola -

arenfte beds and tuff

Massive shale, tuff partings

Lam/noted tuff and slitstone,

altered volcanic* (Intermediate comp.)

9026

9 0 2 7

Massive shah, (calcareous)


58/164

-37-


Edwards and Glaessner (1953) noted the lack of obvious granitic

detritus in the Cretaceous sediments of the Wahgi Valley, and the apparent

subaerial origin of much of the tuffaceous detritus. They concluded that the

Wahgi sediments were derived from an andesitic volcanic source to the north,

and deposited in shallow geosynclinal waters.

Small-scale cross-bedding, ripple marks and fine laminations, and

the presence of well sorted sandy beds all point to shallow water, near

shore deposition. No detrital material that could be said with confidence

to have been derived from the core of the Kubor Anticline has been discovered

in the Chim Formation. These observations support the conclusions of

Edwards and Glaessner

( 1 9 5 3 )

(see discussion of Kondaku Tuff),

T E R T I A R Y

Ta Stage (U. Palaeocene-Eocene)

Pima Sandstone (new name)

Pima Sandstone is the name given to a sequence of fossiliferous

sandstone with interbedded siltstone and mudstone which is exposed over a

large area east of Mount Suaru,and extends across the Tua River to 145

°

E .

The name Pima Sandstone is derived from the Pima River (145

0

49

1

E , 60

23'S),

where the unit is well exposed.

Thickness of the unit probably exceeds 2,000 m in the t ype

area, and may be as much as 3,000 m elsewhere. The base of the unit is a

massive sandstone bed, at least 300 m t hick, which unconformably overlies


59/164


60/164


61/164


62/164

Fig.

7

Lower Wahgi Valley with Bismarck Mountains on the r ight .

Tertiary

Chimbu

Limestone

Tlc) overlying Upper and Lower Cretaceous

shale and sandstone

(Kuc &

Klk).

12-3 188x

B i s ~

to Kibagh

Vic

Chimbu 22,300

feet, 6 ,

1943.


63/164

-ko-

Nebilyer Limestone

The limestone unit which forms the prominent scarp on the western

side of the Nebilyer Valley was named Nebilyer Limestone by Rickwood

(1955). He described the unit as hard, grey, frequently argillaceous

limestone of Eocene to Oligocene age. Its maximum thickness was estimated

at 500 m.

Photogeological interpretation shows that t he limestone is exposed

for 30 km southwards from the southern slopes of Mount Hagen volcano to the

Kaugel River; the outcrop area is nowhere more than a kilometre in width.

The northern and southern extremities of the limestone are buried by

Quaternary volcanics. Recent field work (Jenkins et al., 1969) has shown

that the limestone due west of Togoba is only 106 m thick. This figure

appears to be representative of the thickness of the unit along most of its

north-south extent. The unit thins appreciably in the south and appears to

lens out completely near the Kaugel River.

The Nebilyer Lim estone consists entirely of limestone and

c a l c a r e ni t e w i t h s o m e v e r y m i n o r a r g i l l a c e o u s a n d s i l t y i n t e r b e d s . I n t h e

section described by Jenkins et al.,(1969),the lowermost 21 m consist of

dark grey to grey-b rown calcarenite with thin silty and argillaceous

interbeds, overlain by 45 m of dark grey-brown micrite. The upper part of

the micrite is coarser-grained, less argillaceous and l ighter coloured than

the lower part. The change is gradational. The micrite is homogeneous'in

beds about 2-5 cm thick except for the lowermost 10 m where 15-45 cm thick

b e d s a r e s l i g h t l y p y r i t i c a n d c a l c i t e v e i n e d . M a s s iv e l y b e d d e d m e d i u m -

grained grey and grey-brown calcarenite forms the uppermost

4o

m of the unit

in this section.

The limestone contains rare Glob igerina, Truncorotaloides and

keeled Globorotalia sp. suggesting an Eocene age (S.F. Schuy leman in Jenkins

et al., 1969). Common small Rotaliids, agglutinating forams, rare plankton,


64/164


65/164

Fig. 8

Hogback

of Eocene-Oligocene

Chimbu

Limestone

trending

southeastwards.

Lower to middle Miocene

sediments

crop

out to the

l f t of the

limestone, Cretaceous sediments

to the r ight .

The

highest point

on

the limestone is

Mount

Elimbari.

The peak in the l f t background is Mount

Michael.

(View from

pass

a t 3000 metres ASL on track

from Chuave

to

Kundiawa

behind the limestone .

Neg.GA2384.


66/164

Fig 20

Hogback of the Chimbu Limestone dark ridge, right

middle distance overlying Mesozoic sediments. Peak

on the right

skyline

is Mount Wilhelm 4,500 metres .

View i s to the north - west from the western side of

Mount Michael.

Neg. GA2379.


67/164

-42-

By far the greater part of the formation is composed of bioclastic

debris and chemically formed carbonate matrix or cement, clearly of l ocal

origin. However the lowermost beds and the outcrops nearest the Kubor Range

contain material derived from outside the zone of deposition. This clastic

material consists of quartz, feldspar,and siltstone which most probably

resul

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Geology of Kubor Anticline PNG

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