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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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-2-
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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-3-
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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-4-
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
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...
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
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-5-
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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-6-
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
8/9/2019 Geology of Kubor Anticline PNG
19/164Fig. Omkalai airstr ip restricted B category) on a
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-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
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-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,
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-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
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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
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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 .
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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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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,
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-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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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
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-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
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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
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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
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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
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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
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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.
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-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.
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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
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-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
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-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
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-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
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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
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-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.
Provenance and depositional environment
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.
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-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
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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
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-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
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-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
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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)
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Provenance and depositional environment
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
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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.
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-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,
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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.
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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.
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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