1997 sedimentary and tectonic evolution of the tertiary kutai basin

8/10/2019 1997 Sedimentary and Tectonic Evolution of the Tertiary Kutai Basin

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doi:10.1144/GSL.SP.1997.126.01.241997; v. 126; p. 395-416Geological Society, London, Special Publications

Milsom and Andy CarterSteve J. Moss, John Chambers, Ian Cloke, Dharma Satria, Jason R. Ali, Simon Baker, John Tertiary Kutai Basin, East Kalimantan

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Ne w o b s e r v a t i o n s o n t h e s e d i me n t a r y a n d t e c t o n i c e v o l u t i o n o f t h e

T e r t ia r y K u t a i B a s i n E a s t K a l i m a n t a n

S T E V E J . M O S S 1,2, J O H N C H A M B E R S 3, I A N C L O K E 4, D H A R M A S A T R I A 4,

J A S O N R . A L I 5, S I M O N B A K E R 6 , J O H N M I L S O M 6 A N D Y C A R T E R 7

1 Present ad dress: Schoo l o f Applied G eology, Curtin Universi ty o f Technology,

Perth, 6845, WA, Australia (e-mail: [email protected])

2 Universi ty o f London Southea st As ia Research Grou p, Dep artmen t o f Geology,

Royal Hol loway , UK

3 L A S M O Runtu Ltd, Jakartal Indonesia

4 Geological Research De velopm ent Centre, Bandung, Indonesia

5 Depa rtment o f Earth Sciences, Universi ty o f Ho ng K ong

6 Universi ty o f London Southeas t A sia Research Grou p, Dep artmen t o f Geological Sciences,

University College London, U K

7 University o f London Fission Track Research Labor atory, D epartm ent o f Geological

Sciences, University College London, UK

Abs t rac t The Kutai Basin, Kalimantan, is one of several large Tertiary basins which

opened during the mid- to late Eocene in Borneo. Extensional tectonics are responsible for

basin formation, and not crustal flexure as has been suggested previously. Extensional

faulting did, however, occur within a general foreland sett ing located to the south o f the late

Cretaceous/Palaeogene Ce ntral Ka lim ant an fold belt. The basin post-dates late Cretaceous/

early Tertiary orogenic activity which affected the Central K alim antan foldbelt and formed

several upper Cretaceous granites. The Palaeogene stratigraphy of the basin includes basal

conglomerates , shallow m arine clastics and min or clastics an d thick sequences of b athya l

marine shales . Neogene s tratigraphy is dominated by deltaic clastics and carbonate

platforms. Several phases of Tertiary igneous activity are seen intruded into and interbedded

with Tertiary sediments of the Kutai Basin. Three suites are recognized and have been

variously interpreted as the products of melting of an orogenic root, extensional driven

melting and/ or su bduction related melting. We review Tertiary sedim entation in the ba sin

and propose a new m odel which relates the form ation of the Kutai Basin to the opening of

Celebes Sea and collapse o f an uplifted Late Cretaceous/Palaeogene oroge nic belt.

T h e 6 0 0 00 k m 2 K u t a i B a s i n o f e a s t K a l i m a n t a n

(F ig . 1 ) i s t he l a rges t an d deepe s t ( 15 00 0m )

b a s i n i n I n d o n e s i a ( R o s e H a r t o n o 1 97 8;

H u t c h i s o n 1 98 9; C C O P 1 99 1). T h e N e o g e n e

s e c t i o n i n t h e S a m a r i n d a r e g i o n r e a c h e s t h i c k -

n e s se s o f u p t o 9 0 0 0 m . T e r t i a r y s e d i m e n t a t i o n i n

t h e b a s i n h a s b e e n f a i r l y c o n t i n u o u s s i n c e i t s

i n c e p t i o n i n t h e m i d - t o l a t e E o c e n e , a l t h o u g h

t h e c e n t re o f d e p o s i ti o n h a s g r a d u a l l y m o v e d

t o w a r d t h e e a s t ( t h e p r e s e n t - d a y M a h a k a m

D e l t a ) . T h e e a s t e r n p a r t o f t h e K u t a i B a s i n

( s o m e t i m e s c a l l e d t h e l o w e r o r E a s t K u t a i B a s i n )

i s a m a j o r o i l a n d g a s p r o v i n c e w i t h r e s e r v e s o f

o i l a n d o i l - e q u i v a l e n t ga s o f u p t o 5 b i l li o n b b ls ,

a n d s e v e r a l g i a n t o i l f i e l d s . T h e S a n g a - S a n g a

F ie ld was d i s cove red in 1897 (Verd ie r

et al.

1980) . Th i s and s ubs equen t s ucces s es r e s u l t ed in

t h e c o n c e n t r a t e d e x p l o r a t i o n o f t h e c o a s t al a n d

e v e n t u a l l y o f f s h o r e a r e a s .

T h e K u t a i B a s i n is b o u n d e d t o t h e s o u t h w e s t

b y t h e S c h w a n e r M o u n t a i n s (F i gs 1 2 ) a n d to

t h e n o r t h w e s t b y l a te C r e t a c e o u s / e a r l y T e r t i a r y

t u r b i d i t e s ( R a j a n g a n d E m b a l u h G r o u p s ) , a n d

o l d e r b a s i c ig n e o u s r o c k s a n d c h e r t o f t h e

v a r i o u s ly n a m e d K a l i m a n t a n C e n t r a l R a n g e s,

K a p u a s R a n g e s o r K u c h i n g u p l i f t ( F i g. 1 ). O n

t h e e a s t e r n s id e o f t h e K u t a i B a s i n i s t h e d e e p

N o r t h M a k a s s a r B a s in (F i g. 1) b o u n d e d b y t w o

N W - S E - t r e n d i n g f a u l t s z o n e s , t h e A d a n g a n d

t h e S a n g k u l i r a n g t o t h e s o u t h a n d n o r t h r e s p e c -

t iv e ly . T o t h e s o u t h a r e t he M e r a t u s M o u n t a i n s

a n d T e r t i a r y B a r i t o a n d P a s i r B a s i n s ( F i g . 2 ) ,

w h i c h a r e s e p a r a te d f r o m t h e K u t a i B a s i n b y t h e

A d a n g f a u l t z o n e ( o r C r os s B a r i t o H i g h ) . T h e

w e s t e r n ( o r u p p e r ) p a r t o f t h e K u t a i B a s i n i s

c o n n e c t e d t o t h e B a r i t o B a s i n v i a a n a r r o w s t r ip

o f T e r t i a r y s e d i m e n t s i n t h e a r e a s o u t h e a s t o f

M u a r a T e w e h ( F ig s 1 2 ). T h e M u l l e r M o u n -

t a i n s f o r m t h e w e s t e r n b a s i n m a r g i n a n d c o m -

p r i s e C r e t a c e o u s s h e l f s a n d s t o n e s a n d l i m e s t o n e s

o f th e S e l a n g k a i F o r m a t i o n a n d g r a n it e s a n d

m e t a m o r p h i c s o f t h e B u s a n g c o m p l ex . T h e

From Fraser, A. J . , Matthew s, S. J . M urphy , R. W. (eds), 1997, Petroleum Geology of Southeast Asia,

Ge ologica l Society Special Pub licatio n No . 126, pp. 395-416.



396 S. J. MO SS E T A L .

Fig. 1. Location m ap for the K utai B asin. Inset map o f Borneo. Localities mentioned in the text are show n on

this figure.

Mul le r Mounta ins a lso te rmina te eas te rn end of

the Semitau Ridge (Fig. 2). The Te rt iary o f the

Kut ai Basin is continuous with sediments of the

Mandai and Melawi Bas ins v ia a nar row rou te

through the Muller Mountains (Pieters et al.

1987; Pieters Sup riatn a 1990; Fig. 2).

The Tert iary succession within the Kutai Basin

is divided into a sy n-rift pha se in the mid-Eocen e,

a sag phase in the late Eocene to Oligocene and a

renewed phase of tectonic activi ty and subsi-

dence in the late Oligocene to Miocene. Inversion

beginning at least as early as the end of the early

Miocene and probably as early as the la te

Oligocene and has been responsible for the

rework ing of earl ier sediments and continuing

deposit ion of ' syn-inversion ' delta ic packages.

Continuing erosion from the hinterland in

response to Miocene and Pliocene tectonic

activity results in continuing deltaic deposition.

Geologic al evolution of the Kutai asin

P r e T e r t i a r y e v e n ts

With in the Kal imantan Cent ra l Ranges the

Mesozoic sequence comprises of spillites, ultra-

basics and serpentinites ( 'ophioli tes ' ) and radi-

olarian cherts of Jurass ic-ear ly Cretaceous age,

and tu rb idi tes o f the Ra jang /Emb aluh Group s

a n d Me n ta r e n g F o rm a t io n . R a ja n g /E m b a lu h

Groups and Menta reng Format ion a re the

names given to s imilar sediments in Sarawak

and par ts o f Kal imantan , we use Embaluh

Group here . The Cent ra l Kal imantan Ranges

(Fig. 1) have been interpreted as an accretiona ry

prism result ing from SW-directed subduction

of oceanic crust beneath the continental core

of Borneo (Ham il ton 1979; Hutch ison 1989;

B6nard

et al.

1990; Ton gku l 1991). The geo logy

of this area and an al ternative interpretat ion is

presented in Moss (in press).

The Schwaner Mo untain s (Figs 1 2) contain

numerous granit ic and tonali t ic batholi ths of

Cretaceous age (Will iams et al. 1988; Amir rud-

din 1989). These are intruded into slates,

amphibolites, schist and gneiss of ?Silurian to

Permian age. Hutchison (1989) proposed that

the Schwaner Mounta ins fo rmed a con t inen ta l

core to the is land and that throughout the

(?)Jurassic/Cretaceous this part of Sund aland

buil t outwards by the accretion of margin al

basin fill, island arc and ophiolitic material. Tate

(1992) has questioned the continental origin of

the Schwaner Mountains and al ternatively

suggested an magmatic arc origin for the



EVOLU TION OF KUT AI BASIN 397

Fig. 2. Tecton ic provinces' map of Borneo, based on references cited and our fieldwork. Radiometric age s of

Cretaceous granites north of the Schwaner Mountains are from Pieters et al (1993a , b, c, e).

Schwaner Mounta ins but the nature of the

country rock in to which the Schwaner Moun-

ta ins grani tes have been in t ruded and the

locat ion of lower to upper Cretaceous grani tes

(Alan, Era , Topai , Pesinduk and Peuh, Fig . 2)

and Pe rmian-Tr ia ss ic g rani t es and me tamor -

phics (Busang and Embuoi complexes , Fig . 2)

to the nor th of the Schwaner Mounta ins , imply-

ing the presence of cont inenta l c rus t nor th of

the Schwaner Mounta ins , a rgues against th is

hypothesis.

In the SE co rne r o f Ka l im an tan oph io l i ti c and

volcanic is land arc rocks exposed in the M eratus

M ounta ins (Fig . 2) were f ina l ly emplaced by the

la te Cretaceous (Sikum bang 199 0) . Several

phases of NNE-SSW-oriented s t r ike-s l ip defor-

mation are suggested to have affected these

rocks dur ing both the Cretaceous and Ter t iary

(S ikumbang 1990 ; Kus um a Dar in 1989).

Grani te genera t ion is a lso l inked with deforma-

t ion in th is region. The Kintap Grani te p luton

(K -A r dated a t 95 Ma, Sikum bang 1990) and

the Rimuh Granod io r i t e p lu ton in t rude the

volcanic arc sequence of the lower Cretaceous

Al ino Group . The Al ino Group i s in the

footwall to thrust sheets carrying peridotites of

the ophiol i te (Yuw ono e t a l 1988). The reported

Ka l im an tan oph io li te s , apa r t f rom the M era tus

ophiolite (Sikumbang 1990), have yet to be

s tudied in deta i l and in outcrop typica l ly conta in

only part of the classical Penrose sub-divisions

of an ophiol i te . In par t icular , p i l low lavas and

sheeted-dyke complexes , the upper par ts of an

ophiol i te sequence , are n ot iceably lacking f rom

outcrops and o utcrop descr ip tions of pre-

Ter t iary rocks in both K al im anta n and Sarawak.

The Mera tus Complex (SE Ka l iman tan ) and

Danau Maf ic Complex (Wes t Ka l iman tan ;

Fig. 2) m ay re present true ophiolit ic sequences in

Kal imantan. Cretaceous grani te in t rus ions and

Ter t iary rhyo-daci t ic volcanics and quar tz-r ich

sedim ents overlying these mafic rocks all suggest

the involvement of cont inenta l c rus t . In the

upper Belayan river (Fig. 1), tectonically inter-

ca la ted basal ts , gabbros and microg abbros show

severa l phases of deformat ion and are in t ruded

by granitic dykes. These dykes only show a single

phase of tensional deformat ion and hence post-

date ear l ier deformat ion.

The Boyan melange of the Semitau Ridge

(Fig . 2) comprises predominant ly b locks of

shal low marine carbonates and sands f rom the



398 S. J. M OS S

E T A L .

l o w e r - m i d d l e C r e t a c e o u s S e l a n g k a i F o r m a t i o n

w i t h m o r e e x o t i c f r a g m e n t s o f m e t a m o r p h i c

r o c k s a n d g r a n i t e d e r i v e d f r o m t h e B u s a n g a n d

Em buo i com plexes enc losed i n sca ly c l ay . The

s c a l y c l a y c o n t a i n s C e n o m a n i a n t o S a n t o n i a n

nanno foss i l s , a l t hou gh the b locks w i th in t he c lay

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

e n t p a r ts o f t h e S e l a n g k a i F o r m a t i o n y i e ld

l o w e r t o m i d d l e C r e t a c e o u s d i a g n o s t i c f a u n a s

( H e r y a n t o et al. 1993) . Bo th t he S em i t au R idge

and the Lupar L ine (F ig . 2 ) reco rd seve ra l

p h a s e s o f c o n t r a c t i o n a l / t r a n s p r e s s i o n a l d e f o r -

m a t i o n . T h e S e m i t a u R i d g e h a s b e e n t h r u s t

s o u t h w a r d s o n t o t h e M e l a w i B a si n , a s s h o w n b y

nor th - sou th se i sm ic sec t ions ac ross the M elawi

B a s i n ( P e r t a m i n a - B e i c i p - F r a n l a b 1 9 9 2 ) . T h e

younges t foo twa l l sed im en t s t o t hese t h rus t s

a re uppe r Eocene / lower O l igocene i n age

(K . G lazeb rook , Can-Oxy , pe rs . com m . 1994) .

F i s s ion - t rack a na lys i s o f apa t i t e s f rom a C re t ac -

e o u s s a n d s t o n e f r o m t h e B o y a n m e l a n g e ( B o y a n

r ive r, see F ig . 1 ) o f t he S em i t au R idge y i e lded an

lower O l igocene (35 + 4 M a) age o f coo l ing an d

(by inference) upl i f t .

T w o w e l ls i n t h e K e r e n d a n g a s f ie ld a r e a n e a r

M u a r a T e w e h ( F ig . 1 ) p e n e t r a t e d b a s e m e n t

g r a n o d i o r i te s w h i c h y i e ld e d K - A r a g e s o f

6 8 + 3 a n d 6 3 + 2 M a ( V a n d e W e e r d

et al .

1987) . O the r w e l ls i n t he sam e a rea have

p e n e t r a t e d u p p e r J u r a s s i c t o l o w e r C r e t a c e o u s

s h a le s a n d i n t r u si v e r oc k s a n d u p p e r P a l a e o z o ic

m e t a s e d i m e n t s ( V a n d e W e e r d et al. 1987).

T h e s e m a y b e t h e l a t e r a l e q u i v a l e n t s o f t h e

S e l a n g k a i F o r m a t i o n a n d B u s a n g C o m p l e x t o

the no r thwes t .

G e o l o g i c a l d a t a f o r t h e p r e - T e r t i a r y o f K a l i -

m a n t a n i s f a r f r o m c o m p l e te a n d m a n y p r o b l e m s

r e m a i n , n o t l e a s t t h e g e o m e t r y o f C r e t a c e o u s

subduc t ion com plexes (Moss i n p re ss ) . These

p rob lem s a re t he sub j ec t o f on -go ing re sea rch .

T i m i n g o f b a s i n i t i a t i o n

T h e t i m i n g o f i n i t i a t i o n o f t h e K u t a i B a s i n i s

poo r ly cons t ra ined re f l ec t i ng t he absence o f

re l i ab l e b io s t ra t i g ra ph ic i nd i ca to rs i n t he t e r re s -

t r ia l d o m i n a t e d i n i t ia l b a s i n f il l a n d t h e l a c k o f

we l l pene t ra t i on i n to t he deepes t pa r t s o f t he

s y n - r if t se q u e nc e . O n l a p o f s y n - r i f t a n d y o u n g e r

sed im en t s on to t he bas in f l anks , and a l so t he

poss ib i l i t y t ha t pa r t s o f t he b as in f i l l have b een

t h r u s t o v e r t h e b a s i n m a r g i n s d u r i n g i n v e r s io n ,

i m p l i e s t h a t o u t c r o p s a l o n g t h e b a s i n m a r g i n s

m ay no t be rep resen t a t i ve o f t he o ldes t sed i-

m e n t s i n t h e b a s i n . M o s t a u t h o r s s u g g e s t t h a t

t he base o f t he T e r t i a ry bas in f i l l i s m idd le t o

u p p e r E o c e n e i n a g e. U p p e r m o s t m i d d l e a n d l a t e

E o c e n e n a n n o f o s s i l s (N P 1 6 - 1 9) a n d f o r a m i n i -

fe ra (Tb o r P 14 -16 ) a re p re sen t i n t he bas in . Th i s

ag rees w i th t he ages sugges t ed by Van de Weerd

Arm in (1992) and P i e t e rs et al . (1993a) on

t h e b a s i s o f r a d i o m e t r i c a n d b i o s t r a t i g r a p h i c

d e t e r m i n a t i o n s . S e d i m e n t s o f P a l a e o c e n e - l o w e r

Eocene age have ye t t o be found wi th in t he

K u t a i B a s i n . A l t h o u g h a P a l a e o c e n e a g e f o r

t h e K i h a m H a l o q S a n d s t o n e F o r m a t i o n o f th e

u p p e r K u t a i B a s i n h a s b e e n s u g g e s t e d ( W a i n

Berod 1989) , t he o ldes t fo ss i l s a re m idd le t o

u p p e r E o c e n e f o r a m i n i f e r a f ro m b e d s o f th e

R i t a n L i m e s t o n e M e m b e r i n t e r c a l a t e d i n t h e

u p p e r p a r t o f t h e f o r m a t i o n .

Rhyo l i t e l ava f l ows and a ssoc i a t ed sub -ae r i a l

v o l c a n ic l a s ti c r o c k s o c c u r b o t h b e l o w a n d p a s s

l a t e ra l l y i n to i n i t i a l bas in sed im en t s i n bas in

m a r g i n a n d i n t r a - b a s i n l o c a t i o n s ( d i s c u s s e d

l a t e r ) . I n t h e u p p e r M a h a k a m R i v e r ( F i g . 1 )

t h e s e a r e c a l l e d t h e N y a a n v o l c a n i c s a n d h a v e

K - A r r a d i o m e t r i c a g e s o f 4 8 - 5 0 4 -1 M a ( e a r ly

m id -Eocene , P i e t e rs et al. 198 7, 1993a) an d a t

Ke l i an (F ig . 1 ) fe l si c vo l can i c s and l avas a re

c o n f o r m a b l e w i t h i n a s e d i m e n t a r y s u c c e s s i o n

con ta in ing l im es tone l enses w i th l a t e Eocene

( T b ) b e n t h i c f o r a m i n i f e r a ( V a n L e e u w e n et al.

1990). A l a t e m id - t o l a t e Eocene t im ing fo r

t h e f o r m a t i o n o f t h e K u t a i B a s i n i s m o s t l i k e l y

(Fig . 3a b) .

M i d d l e E o c e n e

T h e u p p e r m i d d l e E o c e n e r e p r e s e n t s a s y n - r i f t

s e c ti o n a n d i s r e m a r k a b l y s i m i l a r t h r o u g h o u t

K a l i m a n t a n . A p a r t i c u l a r l y c o m m o n f e a tu r e is

t h e p r e s en c e o f a b a s a l c o n g l o m e r a t e v a r i a b l y

r e f e r r e d t o a s t h e T a n j u n g F o r m a t i o n ( B a r i t o

b a s i n a n d s o u t h e r n K u t a i B a s in , K u s u m a

D a r i n 1 9 89 ), K u a r o F o r m a t i o n ( s o u t h e r n p a r t o f

t h e K u t a i B a s in ) a n d K i h a m H a l o q S a n d s t o n e

F o r m a t i o n ( u p p e r p a r ts o f t h e M a h a k a m R i v er )

w e s t e rn b a s i n m a r g i n , a n d M e l a w i B a s in , ( V a n d e

W e e r d A r m i n 1 99 2 ). S i m i l a r d e p o s i ts h a v e a l so

b e e n l o c a te d a l o n g t h e n o r t h e r n b a s i n m a r g i n

n o r t h o f t h e W a h a u R i v e r ( F i g s 1 , 3 a b ) .

D e p o s i t i o n o f t h e s e u n i t s m a y h a v e b e e n r a p i d

a n d c o n t r o l l e d b y p a l a e o t o p o g r a p h y ( W a i n

Berod 1989). In ou t c rops a long the uppe r reaches

o f t h e W a h a u R i v e r t h ic k b e d s ( 80 c m t o 2 m ) o f

b r e c c i o- c o n g l o m e r a te , s o m e o f w h i c h a r e c h a n -

ne l l ed , fo rm package s 6 -7 m th i ck . C las t s va ry

f r o m s u b - a n g u l a r t o r o u n d e d a n d l ie w i t h i n th e

p e b b l e s i ze r an g e . A b u n d a n t c h e r t w i t h p h y l li t e ,

q u a r t z it e , m i l k y q u a r t z a n d o t h e r m e t a m o r p h i c

rocks a re seen wi th in t hese cong lom era t e s .

In t e rca l a t ed ove r a d i s t ance o f seve ra l m e t re s



EVOL UTIO N OF KUTA I BASIN 399

~ 0 c~

0 , . ~ ~

~ ~ ~ ~

e ~ N

0 ,~ , '~ - - '

9 ~ , ,

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9 , - ~ ~ , - ~

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400 S. J . M OS S

E T A L

with the b re c c io -c ong lome ra te s a re l a te ra l ly

d i sc on t inuo us l e nse s o f c oa r se l i th ic s a nds

whic h in f il l sha l low c ha nne l f e a tu re s . T he b re c -

c i o - c o n g lo m e r a t e s a r e f r a m e w o r k s u p p o r t e d a n d

d o w n c u t i n t o c o a r s e s a n d s t o n e a n d / o r c o n g l o m -

e ra te be ds . Re dd ish purp le ma r l s wi th a g re e n

mot t l ing a nd f ine r e d , l i th ic s a nds a re a l so

in te rbe dde d wi th b re c c io -c ong lome ra te s . T he se

a r e c o n t i n e n t a l i n o r i g i n a n d t h e p r o d u c t o f

a l luv ia l f a n de pos i t ion th rough se d ime nt g ra v i ty

f low a nd f luv ia l c ha nn e l p roc e s se s. O ve r ly ing a nd

la te ra l ly e qu iva le n t in de e pe r pa r t s o f the ba s in

a re ba thya l sha le s a nd tu rb id i t i c s a nds c on ta in ing

u p p e r m i d d l e - u p p e r E o c e n e f o r a m i n i f e r a a n d

na nnofos s i l s (P15-16 o r T b ; NP16-19) .

I s o l a te d o u t c r o p s o f m i d d l e t o u p p e r E o c e n e

fora min i fe ra l l ime s tone s (T b be n thon ic fo rms ,

F . Ba nne r pe r s . c omm. 1995) oc c ur a long the

M a h a k a m R i v e r a n d W a h a u R i v e r ( F ig s 1 3 a) .

Al tho ugh d i re c t f ie ld obse rva t ions o f the i r

r e la t ive pos i t ions wi th r e spe c t to c ong lome ra te s

ha ve no t be e n poss ib le , m ic rofa c ie s a na lys i s o f

the c a rbona te s ind ic a te s a sha l low ma r ine e nv i r -

onm e nt o f de pos i t ion . T he oc c a s iona l p re se nc e

o f r o u n d e d t o s u b - r o u n d e d b a s e m e n t c l a st s

within these l imestones sugges ts the inf luence

of a n up l i f t e d ba se m e nt h igh she dd ing c la s ti c

ma te r ia l . T o the nor the a s t in the uppe r r e a c he s

of the Ka ra n ga n R ive r (F ig . 1 ) f ine s a nds

a nd sha le s o f upp e r midd le E oc e ne (P14) a ge

a re ba thya l to a byssa l , c onf i rming tha t the

pa la e o c oa s t in the E oc e ne wa s e a s t o f c e n t ra l

K a l i m a n t a n .

o f s a nds tone be ds a nd so le s t ruc tu re s in the fo rm

of g roove , p rod a nd loa d c a s t s a re se e n on the

ba se o f be ds . Pa r t i a l Bou ma se que nc es , o f te n

wi th on ly T a bc o r T a -c pa r t s p re se n t , a re

c o m m o n w i t h i n t h e s a n d s t o n e b e d s . T h e s e a r e

in te rp re te d to be tu rb id i te s , a n in te rp re ta t ion

s u p p o r t e d b y t h e g e n e r a ll y b a t h y a l f o r a m i n i f e r a .

T urb id i te s e d ime nts o f th i s a ge a re pa r t i c u la r ly

w e l l e x p o s e d a l o n g t h e T e l e n , M a r a h a n d

W a h a u R i v e r s e c t i o n s i n t h e n o r t h e r n p a r t o f

the c e n t ra l Kuta i Ba s in (F ig . 1 ) a nd a long the

u p p e r M a h a k a m R i v e r i n t h e n o r t h w e s te r n p a r t

o f th e u p p e r K u t a i B a s in . L i t h o s t r a t i g r a p h i c

na m e s o f these s e d ime nts inc lude the na me s

B a t u K e l a u F o r m a t i o n , A t a n F o r m a t i o n , t h e

B o n g a n F o r m a t i o n ( V a n d e W e e r d

et al

1987)

a n d M a r a h F o r m a t i o n ( S u p r i a t n a 1 9 9 0 ) . I n t h e

u p p e r M a h a k a m R i v e r a r e a t h e d i s t a l t u r b i d i t e s

o f th e B a t u K a l a u F o r m a t i o n a r e ov e r la i n

c o n f o r m a b l y b y u p p e r E o c e n e t o u p p e r O l i g o -

c e ne she l fa l qua r tz s a nds a nd m uds to ne s o f the

B a t u A y a u a n d U j o h B i l a n g F o r m a t i o n s . T h e

pre se nc e o f she l fa l s e d ime nts in th i s pa r t o f the

b a s i n a n d t h e p r e d o m i n a n t l y t e r re s t ri a l n a t u r e o f

the E oc e ne -Ol igoc e ne se d ime nts in the Me la wi ,

K e t u n g a u a n d M a n d a i B a s i n s t o t h e w e s t i s

p r o b a b l y l i n k e d , w i t h t h e w e s t e r n p a r t o f

the ba s in sha l lowe r tha n e a s te rn a re a s a t th i s

po in t in t ime . Ma r ine de pos i t s in the Me la wi

a n d M a n d a i B a s i n s a r e l i m i t e d t o t h e e x t r e m e

e a s te rn e dge s o f the ba s ins a nd to f e a tu re s suc h

the t ida l s a nds wi th in the ba sa l s e c t ion o f the

M a n d a i G r o u p .

U p p e r E o c e n e t o L o w e r O l i g o e e n e

Ma r ine in f lue nc e i s inc re a s ing ly a ppa re n t in the

s e d im e n t s t o w a r d s t h e e n d o f t h e m i d d l e E o c e n e

a nd in to the upp e r E oc e ne (F ig . 3a b ) . L oc a l ly

a l luv ia l s a nds a nd c ong lome ra te s g ive wa y to a n

in te rva l o f de lta ic s e d ime nts wi th c oa l s e a ms ,

c r o s s b e d d e d c h a n n e l s a n d s , c a r b o n a c e o u s

sha le s a nd the oc c a s iona l h igh to mode ra te

e n e r g y s a n d y f o r a m i n i f e r a l w a c k e s t o n e s o f

u p p e r E o c e n e a g e . A l o n g t h e u p p e r r e a c h e s o f

t h e M a h a k a m R i v er , se d im e n ts o f t h e K i h a m

H a l o q S a n d s t o n e F o r m a t i o n p a s s u p f r o m a

c oa r se f luv ia l c ong lome ra te - sa nds tone ba sa l

se c t ion , w i th me t re s c a le c ha nne l s t ruc tu re s ,

i n t o h i g h e n e r g y s h a l l o w m a r i n e a n d t i d a l

s a nds wi th in te rc a la t ions o f upp e r E oc e ne (T b)

N u m m u l i t e s

f o r a m i n i f e r a l p a c k s t o n e s ( R i t a n

L i m e s t o n e M e m b e r ) . A b o v e a n d l a t e r a l l y

e qu iva le n t to the se l i tho log ie s a re l i th ic a nd

qua r tz a re n i te s , sha le s , s i l t s tone s a nd c ong lom-

e r a t e s . S y n - s e d i m e n t a r y s l u m p i n g i s c o m m o n

wi th in the se s e d ime nts , a s i s the a ma lga ma t ion

U p p e r O l i g o c e n e

T he la te Ol igoc e ne wa s a s ign i f ic a n t t ime in the

e v o l u t i o n o f t h e K u t a i B a s in . A f t e r a p e r io d o f

d e e p m a r i n e s e d i m e n t a t i o n t h r o u g h o u t m u c h

of the ba s in in the l a te E oc e ne a n d O l igoc ene , a

m a j o r c h a n g e i n b a s i n t o p o g r a p h y o c c u r r e d

(F igs 3a b ) . In the Ke la i R ive r (F ig . 1 ), on

t h e n o r t h e r n m a r g i n o f th e b a s i n , a b a sa l

c o n g l o m e r a t e r e s t s u n c o n f o r m a b l y o n C r e t a c -

e ous me ta se d ime nt . Sha le s a s soc ia te d wi th the

c o n g l o m e r a t e c o n t a i n N 3 p l a n k t o n i c f o r a m i n i -

fe ra a nd ind ic a te lowe r sub l i t to ra l to ba thya l

e n v i r o n m e n t s o f d ep o s i ti o n . A d i s c o n f o r m a b l e

re la t ionsh ip be twe e n the lowe r Ol igoc e ne sha le s

a nd uppe r Ol igoc e ne l ime s tone s i s sugge s te d

f rom se i smic a nd f ie ld e v ide nc e in the Ke re nda n

ga s f ie ld (F ig . 1 ) (Va n de W e e rd

et al

1987). This

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

o n e w i t h i n t h e c e n t r e o f t h e b a s i n . U p w a r d s

wi th in the Ke la i R ive r s e que nc e the se c ong lom-

e ra te s a nd sha le s pa s s in to s e ve ra l hundre d

me t re s o f p la t f o rm l ime s tone s s e en on the



E V O L U T I O N O F K U T A I B A S I N 401

n o r t h e r n b a s i n m a r g i n i n l a r g e k a r s t i f i e d a r e a s

(F ig . 1 ). The fo ram in i fe ra l fau na o f these ca r -

bona t e s sugges t an uppe r O l igocene t o l ower

M i o c e n e a g e r a n g e ( u p p e r a n d l o w e r T e ) ,

a l t h o u g h m o s t i n d i c a t e A q u i t a n i a n a g e ( t o p

N 4 - N 5 ) . W i t h i n t h e b a s a l s e c t i o n a n d f r i n g i n g

t h es e t h i c k c a r b o n a t e s a l o n g t h e K e l a i r iv e r a n d

o the r l oca t i ons , m e t re sca l e beds o f l im es tone

b recc i a s cons i s t o f pebb le t o cobb le s i zed ,

r o u n d e d t o s u b - r o u n d e d c l as t s o f g ra i n s to n e s ,

p a c k s t o n e s , b o u n d s t o n e s , f o r a m i n i f e r a l p a c k -

s t o n e s , f r a g m e n t s o f c o r a l l i n e o r g a n i s m s a n d

wackes tones and c l a s t s o f l i t h i c m a te r i a l (phy l -

l i t e s , m e tased im en t s , m e tabas i c s , che r t , m i lky

quar t z ) . S i li c ic c l a s t s a re s ub -a ngu la r t o sub -

r o u n d e d a n d a r e a l s o s e e n i n d e c i m e t r e b e d s

o f c a l c a r e o u s c e m e n t e d c h e r t - r i c h c o n g l o m e r -

a t e s . These b recc i a s and cong lom era t e s a re

in t e rp re t ed a s deb r i s f l ows and ou t c rops o f

s im i l a r sed im en t s occu r i n t he v i c in i t y o f o the r

u p p e r O l i g o c e n e t o l o w e r M i o c e n e p l a t f o r m

l im es tones . The round ing o f t he l i t h i c c l a s t s

sugges t s t hey were t ranspo r t ed fu r the r t han t he

l im es tone c l a s t s . No ind i ca t i on o f sub -ae r i a l

e x p o s u r e o f a d j a c e n t p l a t f o r m a r e as , s u c h a s

v a d o s e c e m e n t f a b r i c s a n d / o r m i c r o - k a r s t i c

d i s s o l u t i o n a l f e a t u r e s , h a v e b e e n f o u n d w i t h i n

any o f t he l im es ton e c la s t s . The l im es tone c la s t s

were a t l ea s t pa r t i a l l y cem en ted wi th in t he

m a r i n e d i a g e n e t i c r e a l m p r i o r t o e r o s i o n a n d

s h o w n o s i g n o f s o f t s e d i m e n t d e f o r m a t i o n .

These b recc i a s m ay be t he re su l t o f reac t i va t i on

o f p r e - e x i s t i n g f a u l t s b o u n d i n g h i g h s u p o n

w h i c h c a r b o n a t e s w e r e a c c u m u l a t i n g , a l l o w i n g

e r o s i o n o f c a r b o n a t e s e d i m e n t a n d a n u n d e r -

l y i n g b a s a l c o n g l o m e r a t e . T h i s c o u l d e x p l a i n t h e

s i m i l a r it y i n t h e c l a s t c o m p o s i t i o n o f t h e b a s a l

c o n g l o m e r a t e s a n d t h e b a s e m e n t r o c k s s e e n i n

the l im es ton e b recc i a s . A l t e rna t i ve ly the b rec c i a s

m ay be t he re su l t o f renewed up l i f t i n t he

h i n t e r l a n d a n d s h e d d i n g o f b a s e m e n t c la s t s in t o

m a r i n e e n v i r o n m e n t ( p o s s i b l y a x i a l l y a l o n g

grabens o r a t by -pass channe l s ) where i t i s

m i x e d w i t h p r o x i m a l l y d e r i v ed c a r b o n a t e m a t e -

r i a l shed o f f h ighs . The b recc i a s m a y a l so be due

t o p r o g r a d a t i o n o f a h i g h s t a n d s y s te m s tr a c t a n d

p r o d u c t i o n o f 0 v e r s te e p e n e d s lo p e s. T h e l a c k o f

m e te ro i c fea tu res a rgues aga ins t a l ows tand

fo rm a t ion fo r t hese b recc i a s . The b recc i a s

d i f fe r f rom those seen i n t he sou the rn Ku ta i

B a s i n , w h i c h c o n t a i n o n l y c l a s t s o f c a r b o n a t e

m a te r i a l ( ' l i t hoc l a s t cong lom era t e s ' ) and a re

in t e rp re t ed t o be t he re su l t o f depos i t i on

d u r i n g a h i g h s t a n d o f s e a -l ev e l a n d b a c k s t e p p i n g

o f t h e p l a t f o r m a n d p r o d u c t i o n o f o v e r st e e p e n ed

cl i ffs (Sai ler

e t a l

1994). The uppe r sec t ion o f t he

U j o h B i la n g G r o u p i n t h e u p p e r M a h a k a m R i v e r

a rea c on ta in s o l i s t o l it h i c b locks an d de b r i s f lows

o f l i m e s t o n e a n d v o l c a n i c m a t e r i a l w i t h i n b a t h y a l

sha l e s and the vo l can i c l a s t i c t u rb id i t e s o f t he

L e n M u r i n g S a n d s t o n e ( W a i n B e r o d 1 98 9) .

O n t h e u p p er r e a c he s o f t h e M a h a k a m R i v e r

(F ig . 1 ) , i n t e rbedd ed dec im e t re t h i ckness beds o f

m u d s t o n e s a n d w a c k e s t o n e s w i t h f r a g m e n t s

of cora ls , f i sh tee th , oyster shel l s , ro ta l in id(?)

f o r a m i n i f e r a a n d u p p e r O l i g o c e n e n a n n o f o s s i l s

(NP 24-25 ) pass up i n to t h i cke r (m e t re -sca l e )

b e d d e d f o r a m i n i f e r a - c o r a l l i n e a l g a e p a c k s t o n e s

exposed in spec t acu l a r 100 -150m h igh c l i f f s .

The sou theas t e rn edge o f t hese c li f fs show a

p r o b a b l e N E - S W - t r e n d i n g s y n - s e d i m e n t a r y

fau l t , wh ich cu t s t he o lde r beds w i th in t he c l i f f

f a c e b u t i s i t s el f t r u n c a t e d b y y o u n g e r b e d s

h ighe r up wi th in t he c l i f f sec ti on . The na tu re o f

t h e o u t c r o p d o e s n o t a l l o w c lo s e e x a m i n a t i o n o f

t h i s r e l a t i o n s h i p . T h e p r e s e n c e o f a N E - S W -

t rend ing g rav i ty h igh (P i e t e rs

e t a l

1993a)

assoc i a t ed wi th t he a rea o f t he l im es tone ou t -

c r o p i n d i c a t i n g l i m e s t o n e d e v e l o p e d u p o n a

N E - S W - t r e n d i n g h o r s t b l o c k p a r t i a l l y r e a c t i -

va t ed du r ing depos i t i on o f t he l im es tones .

A t t he sam e t im e a s t hese l im es tones were

b e i n g d e p os i te d , m a j o r u p l i f t m a y h a v e o c c u r r e d

i n t h e u p p e r K u t a i B a s i n . V a n L e e u w e n

e t a l

(1990) an d W ain Bero d (1989) suggest a

pe r iod o f fo ld ing and fau l t i ng i n t he l a t e

Ol igocene and ea r ly Miocene . Apa t i t e f i s s ion -

t ra c k a ge s o f 2 2 + 2 a n d 2 5 + 2 M a a n d t he

n a r r o w t r a c k l e n g t h d i s t r i b u t i o n s o b t a i n e d f o r

S a n t o n i a n - C a m p a n i a n a g e d t u r b i d i t i c s a n d s

(KUS 148 /150) reco rd rap id coo l ing and the re -

f o r e b y i m p l i c a t i o n r a p i d u p l i f t a n d / o r e r o s i o n a l

denuda t ion ( i n t he sam ple a rea a t l ea s t ; F ig . 1 )

a r o u n d t h e O l ig o c e n e - M i o c e n e b o u n d a r y ( M o s s

e t a l 1997) . These sands , w h ich l i e unco nfo rm -

a b l y b e l o w t h e m i d d l e - u p p e r E o c e n e K i h a m

H a l o q S a n d s t o n e F o r m a t i o n , a r e l es s t h a n 5 k m

n o r t h o f th e p r e s e n t - d a y n o r t h e r n m a r g i n o f th e

u p p e r K u t a i B a s i n .

L o w e r M i o c e n e

D a t i n g o f f o r a m i n i f e r a w i t h i n s h a l l o w m a r i n e

c a r b o n a t e s s u g g es t d e p o s i t io n o f p l a t f o r m l im e -

s tones and re l a t ed l im es tone b recc i a s con t inued

f rom the l a te O l igocene i n to ea r ly Mioce ne

o n b o t h t h e n o r t h e r n a n d s o u t h e r n m a r g i n s o f

the bas in (F ig . 3a b ) . S eve ra l ou t c rops a long

the Wa ha u Rive r (F ig . 1 ) expose rubb ly b recc ia s

c o n t a i n i n g a v a r i e t y o f l i m e s t o n e a n d l i t h i c

c l a s t s and a re o f s im i l a r o r ig in t o t hose desc r ibed

above . A sequence o f de l t a i c c l a s ti c s was depos i -

t e d w i t h th e e a s t w a r d p r o g r a d a t i o n o f t h e d e lt a

sys t em s t a r t i ng i n t he wes t o f t he K u ta i Bas in i n



402 S. J. M OS S

ET AL

the early Miocene ( lower Miocene, N5/6,

LASMO pers. comm. 1995) and continuing to

the p resen t -day Mahakam Del ta .

Middle to upper Miocene

Thick middle M iocene sediments east of the

Samarinda anticl inorium (Fig. 4) were rapidly

deposited following an inversion event a t the end

of the early Miocene (Cham bers Daley 1995).

The deltaic sediments aggraded to form what is

now the coastal plain and present-day delta .

Over 3000 m of delta plain sediments o f middle

to la te Miocene age are present indicating

signif icant amounts of subsidence occurred in

parallel with deposition and sea level change. It

is likely that these sediments were derived from

erosion o f the lower M iocene delta ic sediments

(Ch am bers Dal ey 1995) as well as contin uing

erosion of the central hinterland.

The Neogene strat igraphy and l i thostrat igra-

phy for the Lower Kutai Basin has been

generally established (Marks

et al

1982, Van

de Weerd Arm in 1992). Howev er the l i thos-

trat igraphic terminology proposed is cumber-

some and fai ls to recognize that the lower

Miocene and middle Miocene delta ics are

different megasequences (Siemers

et al

1994;

Ca rte r Mo rley 1995). Siemers et al (1994)

presen t a more comprehens ive s t ra t ig raphy and

li thostrat igraphy for the area. Several megase-

quences are recognized which overall represent a

shallowing upward sequence from bathyal shales

to pro-delta shales with localized shallow marine

carbonate buildups, delta sands and delta plain/

f luvial sands. This sequence was produced with

the eas tward prograda t ion of a de l ta sys tem

start ing in the west of the Ku tai Basin in the

lower Miocene (N5/6, LASMO pers. comm.

1995) and continuing to the present day and the

Ma h a k a m D e l t a .

Pliocene to Recent

The Kuta i Lakes a re loca ted wes t o f Samar inda

(Fig. 1), lacustrine sedimentation within these

lakes began in the Pliocene (Anap Formation)

and continues to the present day. The formation

of the lakes area is the result of ponding of the

Pl iocene Mahakam River d ra inage bas in wi th

the uplif t of the Samarinda anticl inorium, a

domal a rea wes t o f Samar inda . Upl i f t o f the

Fig. 4. Geological map o f the Kutai B asin and E ast Kalimantan. The approximate basement-Tertiary contact,

Eocene, Oligocene and Miocene positions are shown.



EVOLU TION OF KUT AI BASIN 403

eas te rn edge of the Samar ind a ant i c l inor ium in

the Pliocene is also suggested to be responsible

for f resh water f lushing of de lta ic sediments on

the edge of the Mahakam de l t a (Bur rus

et al

1994) (Fig. 3a b).

tructure of the basin

B a s e m e n t

The mos t prominent f ea ture of the Kuta i Bas in

Bouguer gravi ty map (Fig. 5) i s a nor th-south-

t r ending high wi th an ampl i tude of about

40mGal . The Kuta i Lakes region (Fig. 1) ,

an area of subsidence and Pl iocene to Recent

lake deposi t ion, rough ly coincides wi th the crest

of the high and hence the fea ture has been

referred to as the Kuta i Lakes Gravi ty High

(KL GH , Fig. 5). A s im ilar corre la t ion between

gravi ty high and subsidence is observed in the

Kap uas Lakes d is t ri c t of Wes t Ka l im anta n

(Fig. 1), where the lakes are associated with an

eas t -west-e longated p osi t ive anom aly, the Lub ok

Antu-Kapuas gravi ty r idge , which has ampl i -

tudes of up to 70 mG al (Wi l l i ams

et al

1988; Fo ss

1993). The a nom aly is associa ted with the Pak ong

and D ana u maf ic complexes which outc rop nea r

the Lupar Line (Fig. 2) in Sarawak and Kal i -

mantan respectively. Foss (1993) suggested that

the Qua te rna ry subs idence of the Kapu as Lakes

dis t r ic t was due to isos ta t ic readjus tm ent fol low-

ing re laxat ion of the comp ress ive forces which led

to the em placem ent of the high densi ty rocks. I t

seems poss ible tha t a s im ilar explan at ion could be

appl ied in the Kuta i Lakes region, wi th the

gravi ty high marking a subsurface extension of

the ophiol i t ic rocks of the Meratus Mounta ins ;

serpent ini tes and layered gabbros crop out a t

the nor the rn margin of the bas in due nor th

of the Ku ta i Lakes . However , W ain Berod

(1989) and Ch am bers Daley (1995) a t t r ibute

the high to bas in upl i f t , re la t ing the gravi ty

response to invers ion of once deeply bur ied and

compacted Eocene and Oligocene sediments

over an upl i f t in the under lying basement .

Fig. 5. Simplified Bouguer gravity anomaly map for part of the K utai B asin. Re-drawn from Ch ambers

Daley (1995).



404 S. J . M OS S

E T A L .

Seismic re f lec t ion surveys in this a rea have not

a c h ie ve d pe ne t ra t ion to l e ve l s de e p e nough to

d is t ingu ish be twe e n the se s c e na r ios .

E a s t o f th e K u t a i L a k e s h i g h B o u g u e r g r a v i t y

va lue s d rop to a low of a l i tt l e a bov e 0 mG a l a n d

the n r i s e g ra dua l ly towa rds the c oa s t , whe re

v a lu e s ar e o f t h e o r d e r o f + 3 0 m G a l . B o u g u e r

gra v i ty l e ve l s a re thus s l igh t ly to mode ra te ly

p o s i t i v e t h r o u g h o u t t h e a r e a a n d n o t d r a m a t i -

ca l ly dif fe rent for the leve ls recorded over the

a re a s o f ba se m e nt o u tc ro p to the e a s t (P ie te rs

Sup r ia tna 1990), de sp ite the p re se nc e o f a th ic k

Ne oge ne se d ime nt s e c t ion , whic h shou ld r e pre -

se n t a c ons ide ra b le ma ss de f ic ie n t . A ba la nc ing

ma ss e xc e s s s e e ms to be r e g iona l a t de p th , whic h

c ou ld be a c c oun te d fo r by the c rus t be ing e i the r

t h i n n e r o r d e n s e r t h a n i n a r e as b e y o n d t h e b a s in

ma rg ins . I t i s pos s ib le tha t the ba s in de ve lope d

o n t o p o f o c ea n i c c ru s t c o n t i n u o u s w i t h t h a t

b e n e a t h t h e N o r t h M a k a s s a r B a s i n , o r o n

g r e a t l y e x t e n d e d a n d a t t e n u a t e d c o n t i n e n t a l

c rus t . T he obse rva t ions , inc lud ing the s te a dy

r i s e in g ra v i ty l e ve l s towa rds the Ma ka ssa r

S t ra i t s , a re c ompa t ib le wi th e i the r pos s ib i l i ty ,

bu t no t wi th o r ig in a s a fo re la nd (o r f l e xura l )

ba s in . De pre s s ion o f fo re la nd ba s ins oc c urs

be c a use o f loa d ing o f e la s t ic l i thosphe re , a nd

the loa d i s , by de f in i t ion , d i sp la c e d f rom the

de poc e n t re . L oc a l i sos ta t i c c ompe nsa t ions do

n o t a p p l y a n d l o w g r a v i t y i s o b s e r v e d o v e r t h e

se d ime nt a c c umu la t ions . I t i s p rob a b le th a t

t h e p r e s e n t - d a y M a h a k a m d e l t a i s p r o g r a d i n g

ou t o ve r oc e a n ic c rus t . Mode l l ing o f the g ra v i ty

a noma l ie s wi l l he lp to de te rmine whe the r th i s i s

l ike ly or not .

M a gne t ic su rve ys a long the we s te rn e dge o f the

u p p e r K u t a i B a s i n s u g g e s t t h a t t h e p r e - T e r t i a r y

ba se m e nt ha s a ge ne ra l e a s t -we s t s t ruc tu ra l t r e nd

( W a i n B e r o d 1 98 9) . H o w e v e r , n o r t h - s o u t h -

t r e nd ing fe a tu re s in the se low ma gne t ic l a t i tude s

w o u l d t e n d t o p r o d u c e w e a k e r a n o m a l i e s t h a n

fe a tu re s wi th s ign i f ic a n t e a s t -we s t c ompone n ts .

I n p a r t i c u l a r t h e N N E - S S W - t o N E - S W -

o r i e n te d s t r u c t u r a l h i g h s a n d l o w s o f th e M e r a t u s

t r e nd , whic h fo rme d a s ign i f ic a n t pa la e o topo-

gra phy a nd e xe r te d a s t rong c on t ro l on in i t i a l

P a l a e o g e n e s e d i m e n t a t i o n i n t h e u p p e r K u t a i

Ba s in (W a in Be rod 1989) , wo uld be e xpe c te d

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

N W - S E to W N W - E S E t re nd s o f th e A d a n g

f a u l t / C r o s s B a r i t o H i g h a n d s i m i l a r l i n e a m e n t s

w h i c h s e p a r a t e t h e K u t a i a n d t h e B a r i t o d e p o s i-

t iona l a re a s , ma y be more c le a r ly de fine d . Inde e d

a n i m p o r t a n t f e a t u r e o f t h i s b a s e m e n t c o n -

f i g u r a t io n a l o n g t h e s o u t h e r n e d g e o f t he

b a s i n a r e N W - S E a l i g n e d l i n e a m e n t s . H o w e v e r

N N E - S S W t o N E - S W ( M e r at u s tr en d ) or ie n te d

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

T h e K L G H r i d g e i s n o t i c e a b l y o f f - s e t b y a

n a r r o w , N W - S E - o r i e n t e d , r i g h t l a t e r a l s h e a r ,

(Be la ya n a x i s, W a in Be rod 1989) (F ig . 5 ).

N W - S E l i n e am e n t s w i t h i n t h e b a s in c e n t r e o ff -

s e tt i n g N N E - S S W a l ig n e d r e s id u a l g r a v it y

a nom a l ie s c o inc ide n t w i th su r fa c e fo lds a ffe c t ing

L o w e r M i o c e n e s e d im e n t s ( C h a m b e r s D a l e y

1995). A NW -S E fa br ic s ee ms to be a n inhe r i t e d

ba se me nt f e a tu re pos s ib ly r e la te d to the Cre ta c -

e ous a nd e a r ly T e r t i a ry de forma t ion . I t a f f e c t s

t h e l a t e C r e t a c e o u s t o P a l a e o c e n e E m b a l u h

G r o u p a n d i s o n e o f th e d o m i n a n t f r a c t u r e s e ts

s e en w i t h i n o u t c r o p s o f J u r a s s i c - C r e t a c e o u s

g a b b r o , l a y e r e d g a b b r o , m i c r o - g a b b r o a n d

b a s a l t o u t c r o p s a l o n g t h e u p p e r B e l a y a n R i v e r

a n d i n t r i b u ta r i es o f th e W a h a u R i v e r o n t h e

n o r t h e r n m a r g i n o f th e K u t a i B a s i n . L e f t -l a t e ra l

S - C f a b r ic s w i t h i n s e rp e n t in i t es s o u t h - w e s t o f

M u a r a L a s a n ( F i g. 1 ), a r e a l so o r i e n t ed N W - S E .

B a s i n b o u n d i n g f a u l t s

T h e r e a r e n o o b v i o u s b a s i n - b o u n d i n g f a u l t s t o

t h e K u t a i B a s in . A l o n g t h e u p p e r r e a ch e s o f th e

W a h a u , B e l a y a n , a n d M a h a k a m R i v e r s ( F i g . 1 )

t h e c o n t a c t b e t w e e n t h e T e r t i a r y a n d p r e -

T e r t i a ry i s a n a ngu la r unc onformi ty (F ig . 4 ) .

T h e n o r t h e r n a n d s o u t h e r n m a r g i n s o f t h e b as i n

a r e m a r k e d b y a t h i n n i n g o f se d i m e nt s . I n t h e

n o r t h a N W - S E - t r e n d i n g l i n e a m e n t t h a t p a r -

t i a l ly fo l lows the Be nga lon Rive r s e pa ra te s the

E o c e ne o u t c ro p s o f th e G u n u n g G o n g n y a y

(F ig . 1 ) a re a to the nor th f rom a de e p e a r ly

Mioc e ne ba s in to the sou th . T h is a ppe a r s to be a

n o r m a l d o w n t o t h e s o u t h f a u l t f o r m e d o r r e -

a c t iva te d dur ing the l a te Ol igoc e ne . I t c a n be

c ons ide re d a s a ba s in bounding fa u l t fo r the

N e o g e n e o r l o w e r K u t a i B a s i n , a l t h o u g h a t h i n

Ne o ge ne in te rva l i s p re se n t no r th o f th i s . T he

Be nga lon Rive r f a u l t i s o r ie n te d s imi la r ly to

t h e N W - S E o f f s h o r e S a n g k u l i r a n g f a u l t z o n e

( w h i c h f o r m s t h e n o r t h e r n m a r g i n t o t h e N o r t h

M a k a s s a r B a s i n ) ( F i g s 1 4 ) . T h e s o u t h e r n

ma rg in o f the Ku ta i B a s in is de l ine a te d by the

o n s h o r e c o n ti n u a t io n o f t h e N W - S E - t r e n d i n g

A da n g fa u l t (F igs 1 4 ). T h is f a u l t i s a dow n to

t h e n o r t h f a u l t , b o r d e r i n g t h e n o r t h e r n m a r g i n

o f t h e P a t e r n o s t e r P l a t f o r m o n t h e w e s t er n s i de

o f t h e M a k a s s a r S t r a i t . T h e f a u l t co m e s o n s h o r e

j u s t t o t h e n o r t h o f A d a n g B a y b u t i t s s u r f ac e

express io n is l imited to a se r ies of shor t

l ine a me nts pa ra l l e l to the t r e nd o f the o f f shore

A d a n g F a u l t , r e c o g n i s e d f r o m S A R i m a g e s

(W a in Be rod 1989). Se i smic da ta (Un oc a l

pe r s . c omm. 1995) shows tha t the Ada ng fa u l t

z one sp la ys in to a syn the t ic t r a ns fe r z one




i m m e d i a t e l y o f f s h o r e K a l i m a n t a n . T h e d o w n t o

the nor th Ba l ikpa pa n fa u l t z one , loc a te d to the

n o r t h o f t h e A d a n g f a u l t i s o ne s u c h s p l a y .

S p l a y i n g o f t h e f a u l t m a y e x p l a i n i t s l a c k o f

m a r k e d s u r f a c e e x p r e s s i o n o n s h o r e K a l i m a n t a n .

De sp i te i t s l a c k o f a ma rke d su r fa c e e xpre s s ion

t h e A d a n g f a u l t c l e ar l y h a s b e e n i m p o r t a n t i n t h e

e vo lu t ion o f the K uta i Ba s in . T he B a r i to Ba s in

a n d t h e K u t a i B a s i n a r e s e p a r a t e d a l o n g t h e

onsh ore c on t inua t io n o f th is f a u l t line (he nc e

' C r o s s B a r i to H i g h ' ) . T h e l in e o f th e A d a n g f a u l t

c o i n c i d e s w i t h t h e b o u n d a r y b e t w e e n t h e u p p e r

O l i g o c e n e B e r a i L i m e s t o n e F o r m a t i o n p l a t f o r m

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

B a s i n t o t h e n o r t h ( V a n d e W e e r d A r m i n 1 99 2;

Sa i le r e t a l 1992) . The s imila r i ty to the s i tua t ion

a t t h e n o r t h e r n b a s i n m a r g i n d e s c r i b e d a b o v e

( B e n g a l o n / S a n g k u l i r a n g f a u l ts ) s h o u l d b e n o t e d .

T h e e x t e n si v e d e v el o p m e n t o f c a rb o n a t e s o n

b o t h t h e n o r t h e r n a n d s o u t h e r n b a s i n m a r g i n s

a n d t h e r a p i d d e e p e n i n g o f th e c e n t r a l p a r t o f th e

ba s in in the l a te Ol igoc e ne (F igs 3a b ) sugge s t s

tha t th i s i s a pe r iod o f e x te ns ion a n d b a s in

f o r m a t i o n a n d n o t i n v e r s io n a s is o f te n q u o t e d i n

t h e l i te r a t u re ( W a i n B e r o d 1 9 8 9 ; V a n d e

W e e r d A r m i n 19 92 ). I n v e r s i o n w o u l d t e n d t o

ra d ic a l ly up l i f t the h in te r la nd a nd c a use a f lood

of s e d ime nts r a th e r tha n c re a t ing re la t ive ly s ta b le

c a rb ona te sh e l f a re a s a s obse rve d .

T h e A d a n g f a u l t z o n e is al s o p r o p o s e d t o b e a

m a j o r s t r ik e -s l ip f a u l t ( W o o d s 1 9 8 5 ; H u t c h i s o n

1 9 8 9 ) w i t h t h e o f f s e t o f t h e N o r t h M a k a s s a r

B a s i n fr o m t h e S o u t h M a k a s s a r B a s i n in d i c a ti n g

s in i s t r a l d i sp la c e me nt . Bo th Hutc h ison (1989)

a n d B i a n t o r o e t a l (1992) f a vour de x t ra l

d i sp la c e me nt on th i s f a u l t l ine . Ra ng in e t a l

( 1 9 9 0 ) s h o w t h e A d a n g a n d S a n g k u l i r a n g f a u l t

z o n e s a s t w o m a j o r n o r m a l f a u l t s b o r d e r i n g t h e

m i d - E o c e n e t o e a r ly M i o c e n e d e p o c e n t r e o f t h e

Nor th Ma ka ssa r Ba s in . S in i s t r a l s t r ike - s l ip

r e a c t i v a t i o n a l o n g t h e A d a n g f a u l t z o n e i s

sugge s te d to ha ve oc c ur re d in the mid-Mioc e ne

( R a n g i n

e t a l

1990). Gre a te r impo r ta nc e o f the

A d a n g f a u l t i s i m p l i e d b y a u t h o r s w h o h a v e

l i n k e d i t a c r o s s B o r n e o w i t h t h e L u p a r L i n e ( o f

w e s t S a r a w a k ) t o f o r m a ' t r a n s - B o r n e o s h e a r '

( W o o d s 1 9 8 5; B r a n s d e n M a t t h e w s 1 99 2 ; W a i n

B e r o d 1 98 9) . I n t u r n a n u m b e r o f th e m a j o r S E

As ia n fa u l t l ine s suc h a s the Re d Rive r f a u l t ( e .g .

Wi l l i a ms e t a l 1988) a nd the T hre e Pa g oda s f a u l t

a r e a d v o c a t e d t o l i n k u p w i t h t h e L u p a r L i n e i n

w e s t B o r n e o ( B i a n t o r o e t a l 1992; T . F ra se r ,

pe r s . c omm . 1995). Some a u tho rs fu r th e r sugge s t

t h a t t h e S a n g k u l i r a n g f a u l t z o n e l i n k s u p w i t h

s imi la r ly o r ie n te d fa u l t l ine s r e c ogn ise d in Sa r -

a w a k (W ood s 1985 ; T a te 1992). L inka ge o f the se

f a u l t l i n e s d o e s n o t a p p e a r t o b e s u p p o r t e d b y

a ny o f the ge ophys ic a l o r ge o log ic a l da ta ove r

B o r n e o . A m a j o r b e n d o r t r a n s f e r f a u l t a n d

re s t r a in ing o r r e le a s ing be nd s t ruc tu re s ma y

re a sona b ly be e xpe c te d to ha ve de ve lope d i f

t h e se t w o f a u l ts w e r e j o i n e d a n d h o r i z o n t a l

move me nts took p la c e . L inka ge i s the re fo re

d e e m e d u n l i k e l y , a l t h o u g h t h e d a t a c u r r e n t l y

a va i la b le c a n ne i the r p rove o r d i sp rove th i s .

T he T in ja u we l l (F ig . 1 ) d r i l le d by M obi l w a s

l o c a t e d u p o n a N E - S W - t r e n d i n g h o r s t b l o c k .

U p p e r O l i g o c e n e c a r b o n a t e s n e a r L o n g L a h a m

(F ig . 1 ) , ba se d on the i r ou tc rop pa t te rn a nd

sha pe o f a s soc ia te d g ra v i ty h igh (Fo ss 1993)

a r e d e v e l o p e d u p o n a N E - S W - t r e n d i n g h o r s t .

T h e o r i e n t a ti o n o f t h e o r ig i n a l r i ft - b o u n d i n g

fa u l t s a re p ropose d to be s imi la r ly o r ie n te d .

N E - S W - t r e n d i n g , u p r i g h t , t i g h t , c h e v r o n f o l d s

wi th in ba se me nt c he r t s a nd me ta - s i l t s tone s a nd

o t h e r N E - S W - t r e n d i n g s t r u c t u r e s w i t h i n t h e

b a s e m e n t o n t h e n o r t h e r n e d g e o f t h e b a s i n

ind ic a te tha t ba se me nt he te roge n ie t i e s ma y ha ve

in f lue nc e d the o r ie n ta t io n o f ba s in - fo rm ing r i f ts .

T h e A d a n g a n d S a n g k u l i r a n g f a u l t z o n e s a r e

m a j o r N W - S E l i n e am e n t s t h a t e f f ec ti v el y d e li n e-

a t e t h e n o r t h e r n a n d s o u t h e r n b o u n d a r i e s o f t h e

ba s in ; how e ve r i t i s sugge s te d he re tha t the t r e n d

o f m a j o r f a u l t s u p o n w h i c h b a s i n o p e n i n g

o c cu r re d w e re o r ie n te d N E - S W t o N N E - S S W

( C l o k e e t a l 1997).

O r i e n t a t io n a n d n a t u r e o f t h e f o l d s

Figure 4 shows the o r ie n ta t ion o f the fo lds in

the Kuta i Ba s in . T he T e r t i a ry s e d ime nts o f the

Kuta i Ba s in c on ta in ope n fo lds wi th a ge ne ra l

N E - S W t r e n d , e x c e p t n e a r t o t h e n o r t h e r n

m a r g i n t h e b a s i n w h e r e t h e t r e n d i s N - N N E

(F ig . 4 ) . Imm e dia te ly to the no r th o f the

M e r a t u s M o u n t a i n s , f o l d s w i t h i n t h e T e r t i a r y

a r e o r i e n t e d E N E - W S W . W i t h i n t h e c e n t r a l

r e g ion o f the L owe r K uta i Ba s in , r e fe r re d to a s

the Sa ma r inda a n t ic l inor ium (F ig . 4 ) , fo lds

t r en d N N E - S S W a n d f o r m c o n t in u o u s a n t ic li -

na l r idge s fo r ove r 100 km. In th e v ic in i ty o f the

M a n g k a l i h a t P e n i n s u l a a n E - W t r e n d d o m i -

n a t e s ( O t t 1 9 8 7 ; S u n a r y o e t a l 1 9 8 8 ; B i a n t o r o

e t a l 1992; Va n de W e e rd Ar m in 1992) a nd

f u r t h e r i n l a n d t o t h e w e s t o f th e M a n g k a l i h a t

P e n i n s u l a t h e N N E - S S W t r e n d r e a p p e a r s

( e . g . B e r i u n f a u l t t r e n d , L A S M O t e r m i n o l o g y ) .

T he c urva tu re o f fo ld t r e nds i s s imi la r in i t s

ove ra l l pa t te rn to tha t s e e n in the fo lds a f fe c t ing

t h e R a j a n g - E m a b a l u h G r o u p a n d C r o c k e r

F o r m a t i o n s e di m e nt s o f S a r a w a k a n d S a b a h .

W i t h i n t h e u p p e r K u t a i B a s i n fo l d t r en d s h a v e a

m o r e N E - S W t r e n d t h a n t h e S a m a r i n d a a n t i -

c l inor ium, a nd se ve ra l ope n a n t ic l ine - sync l ine



406 S. J. M OS S

E T A L

p a ir s e x p os e d a lo n g t h e u p p e r M a h a k a m R i v e r

u p s t r e a m f r o m L o n g I r a m ( F i g . 1 ) .

F i e l d a n d p u b l i s h e d s e i sm i c d a t a s h o w f o l d s o f

t h e S a m a r i n d a a n t i c l i n o r i u m a n d t h e ea s t K u t a i

Bas in a re t i gh t , gene ra l l y sha l e co red , a sym -

m et r i c t o sym m et r i c , an t ic l i nes sepa ra t ed by

b road , open , sa nd - r i ch sync l ines (B ian to ro

e t a l

1992 ; Ben dang 1993 ; Ch am ber s Da ley 1995).

Ax ia l t races o f fo ld s a re l ong , be tween 20 and

100k m a long s t r i ke (F ig . 4) . An t i c l i nes m ay be

cu t by re l a t i ve ly h igh ang le t h rus t fau l t s w i th

s i m i l a r t r e n d s , p r e d o m i n a n t l y d i p p i n g t o w a r d

t h e w e s t ( O t t 1 9 8 7 ; B i a n t o r o

e t a l

1992 ;

B e n d a n g 1 9 9 3 ) . D e t a c h m e n t f o l d s a r e t y p i c a l

w i t h b o t h b o x a n d c h e v r o n s ty le s . F o l d s d e t a c h

over ex t ens ive va r i ab ly i nve r t ed ove r -p ressu red

?Ol igocene sha l e w i th va r i ed dep th o f de t ach -

m e n t sugges t ed (Ch am bers Da ley 1995).

F o l d o r i g i n

M a n y a t t e m p t s h a v e b e e n m a d e t o e x p l a i n t h e

o r i g in a n d n a t u r e o f th e p r o m i n e n t f o l d c u rv e d

p a t t e r n o f t h e S a m a r i n d a a n t i c l in o r i u m . M o d e l s

invok ing d i ap i r i sm , g rowth fau l t i ng , g rav i ty

g l id ing , com press ion upon a r i f t shou lde r ,

s t r i ke -s l i p m ovem en t s , t h rus t i ng and re l a t ed

f o l d i n g a n d i n v e r s i o n h a v e b e e n p r o p o s e d ,

a l t h o u g h n o t a l l o f t h es e h a v e b e e n p u b l i s h e d .

A l l t h es e m o d e l s a r e p o s s i b l e m e c h a n i s m s o f f o l d

f o r m a t i o n . H o w e v e r , t h e y d o n o t e x p l a i n a l l t h e

f e a tu r e s o f f o l d i n g in t h e K u t a i B a s i n

D i a p i r i s m o f t h i c k p r o - d e l t a f i n e - g r a i n e d

c l a s t i c s i s desc r ibed by Ot t (1987) and by

B i a n t o r o

e t a l

(1992). However, i t i s d i ff icu l t

t o e x p l a i n t h e l i n e a r a n d c o n t i n u o u s n a t u r e o f

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

q u a l i t y s e is m i c d a t a a c q u i r e d b y o n s h o r e o p e r a -

to rs a l so cas ts doub t o n t he ea r l i e r i n t e rp re t a t i on

o f d i ap i r s i n t he an t i c l i no r ium . A l t e rna t i ve ly ,

g rav i ty s l i d ing o f m a te r i a l w i th up l i f t o f t he

C e n t r a l K a l i m a n t a n R a n g e s t o t h e w e s t w a s

p r o p o s e d ( O t t 1 9 8 7 ) . T h i s m a y e x p l a i n f o ld

f o r m a t i o n i n s o m e s e t ti n g s b u t d o e s n o t e x p l a i n

t h e v a r i a b l e d e p t h t o d e t a c h m e n t a c r o s s t h e

a n t i c l i n o r i u m a n d t h e d e c r e a s e i n i n t e n s i t y o f

d e f o r m a t i o n t o b o t h t h e e as t a n d w e s t o f t h e

an t i c l i no r ium . Bendang (1993) p roposed com -

press ion on a r i f t shou lde r w i th t he open ing and

ex tens ion o f t he Makassa r S t ra i t s , bu t t h i s

t i m i n g d o e s n o t a g r e e w i t h M i o c e n e d e f o r m a t i o n

o f t h e S a m a r i n d a a n t i c l i n o r i u m . S t r i k e - s l i p

m o v e m e n t s a lo n g b o t h t h e A d a n g a n d S a n g ku -

l i r a n g fa u l t s h a v e b e e n i n v o k e d a s a m e c h a n i s m

o f v a r i a b l e i n v e r s i o n ( B i a n t o r o

e t a l

1992) bu t i t

i s d i ff i cu l t t o exp l a in t he ex t ens ive li nea r n a tu re

o f t h e f o l d a x e s u s in g s u c h a m o d e l . N o n e o f t h e

m o d e l s s o f a r d e s c r i b e d a d e q u a t e l y e x p l a i n t h e

f o r m a t i o n o f t h e f o l d s.

The s t ruc tu ra l s t y l e o f t he fo ld s , bes t seen on

se i sm ic p ro f il e s (B ian to ro

e t a l

1 9 9 2; C h a m b e r s

D a l e y 1 9 9 5) c o m b i n e d w i t h t h e i r g e o m e t r y i n

m a p v i e w a n d t h e i r n a t u r e a t o u t c r o p i s m o r e

s u g g es t iv e o f f o r m a t i o n t h r o u g h i n v e r s i o n o f t h e

f i l l o f an ea r l i e r r i f t sy s t em . Inve rs ion wou ld

have p re fe ren t i a l l y a f fec ted t he deepe r pa r t s o f

the f i l l o f t he p re -ex i s t i ng Eocene r i f t depocen -

t re s . Ch am ber s Da ley (1995) advoca t e a

p u n c t u a t e d i n v e r s i o n m o d e l f o r th e f o r m a t i o n

o f t he an t i c l i no r ium , wh ich t hey desc r ibe a s a

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

fau l t s above a va r i a b ly up l i f ted reg iona l ove r -

p ressu red sha l e . P re - fo ld ing con t rac t i on i s i nd i -

c a t e d b y t h e p r es e n c e o f n o w d o w n w a r d f a c i n g

cm -sca l e dup lex s t ruc tu res exposed on t he l im bs

o f a n t i c li n e s o f u p p e r E o c e n e s e d i m e n t s o n t h e

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

reve rse fau l t s a ssoc i a t ed wi th t he fo ld s a re l a t e r

f e a tu r e s d e v e l o p e d a s a c c o m m o d a t i o n s t ru c t u re s

a l l o w i n g t ig h t e n i n g o f f o l d s a n d e v e n t u a l b r e a k -

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

m o d e l i s c o r r e c t a n d c a n b e e x t e n d e d i n t o t h e

wes t K u ta i Bas in s ign i f i can t up l i f t , i nve rs ion and

e ros ion o f t he P a l aeogene sec t i on du r ing t he

ea r ly Miocene i s im p l i ed .

I n v e r s i o n h i s t o r y

A s s u m i n g i n v e r s io n i s t h e c a u s e o f f o l d in g , w h a t

i s kno wn o f t he fo ld ing ( i nve rs ion ) h i s to ry o f t he

K u t a i B a s i n i s o u t l i n e d b e l o w a s a n a t t e m p t t o

c l a r i fy t he s i t ua t i on . T he cause o f i nve rs ion i s

s t i l l u n k n o w n a n d a l l m o d e l s p r o p o s e d s t i l l

r e m a i n i n t h e r e a l m o f s p e c u l a t i o n . T h e i n v e r -

s i o n a p p e a r s t o h a v e r e a c t i v a t e d a n d n u c l e a t e d

u p o n t h e o ri gi na l N E - S W / N N E - S S W r if t-

bound ing fau l t s . The o f f - se t t i ng o f fo ld axes

a n d t h r u s t s a l o n g N W - S E t r e n d i n g l i n e a m e n t s

sugges t s t ha t basem en t fab r i c was a l so reac t i -

va t ed (C loke

et al

1997).

S eve ra l pe r iods o f i nve rs ion a re sugges t ed he re

to have a f fec t ed t he Ku ta i Bas in . A m a jo r

t ec tono -vo lcan i c even t occu r red i n t he l a t e

Ol igocene , bu t i t s o r ig in s a re unce r t a in (Moss

e t a l 1 9 9 7 ) . M a n y a u t h o r s r e g a r d t h i s a s a n

i n v e r s i o n e v e n t a n d a s m a r k i n g a s w i t c h f r o m

p r e d o m i n a n t l y d e e p m a r i n e s h a le a n d s a n d

d e p o s i t i o n to d e l t a d e p o s i t i o n a n d p r o g r a d a t i o n

occu r red . Th i s even t i s reco rded by l oca l d i s -

c o n f o r m i t i e s a n d d e p o s i t i o n o f d e b r i s f l o w

s e d i m e n t s f o l l o w e d b y c a r b o n a t e p l a t f o r m

d e p o s i t i o n o n b o t h t h e n o r t h a n d s o u t h b a s i n

m a r g i n s . T h e e x t r e m e n o r t h w e s t e r n m a r g i n o f

the ba s in was be ing up l i f t ed in t he l a t e O l igocene




( M o s s e t a l 1997). De l ta ic s e d ime nta t ion d id no t

a p p e a r i n t he b a s i n u n t il N 5 t i m e ( V a n d e W e e r d

A r m i n 1 9 9 2; L A S M O p e rs c o m m . 1 99 5) b u t

the inve r s ion i s da te d a s N3 or e a r l i e r . Inve r s ion

e ve n ts a re e a s ie r to da te wi th in the pos t N5

d e l ta i c s e c ti o n b y o b s e r v a t i o n o f t h i n n i n g o f

pa c ka ge s o f se i smic r e f le c to r s on to h ighs . T he

e a r l i e s t c le a r ly doc ume nte d e ve n t a nd the e ve n t

t h a t w a s r e s p o n s i b le f o r t h e b u l k o f th e d e f o r m a -

t ion in the lowe r M ioc e ne se d ime nts o f the

S a m a r i n d a a n t i c l i n o r i u m o c c u r r e d a t t h e e n d o f

t h e e a r ly M i o c e n e ( e n d N 8 ) ( C h a m b e r s D a l e y

1995) , but ea r l ie r events a re poss ible .

A t K e l i a n t h e u p p e r E o c e n e t o u p p e r O l i g o -

c e ne se que nc e ha s be e n fo lde d in to a b roa d

a n t ic l ine a nd fa u l te d , w i th ma jor s t ruc tu re s

t r e n d i n g t o t h e n o r t h / n o r t h e a s t . M o s t o f t h is

de forma t ion i s sugge s te d to ha ve oc c ur re d by the

t ime the Ke l ia n a nde s i te s ha d be e n in t rude d in

the l a te Ol igoc e ne /e a r ly Mioc e ne (Va n L e e uwe n

e t a l

1990). L a te r inve r s ion e ve n ts in the mid- to

l a te M i o c e n e a n d i n t h e P li o c en e a r e d o c u m e n t e d

by se d ime nta ry th inn ing ove r a n t ic l ine s (Al le n

Ga s t sa ldo 1987) a nd g rowth se c t ions s e e n

on re g iona l s e ismic l ine s (Ch a m be rs Da le y

1995) . Upl i f t in the Me ra tus Mounta ins a re a i s

a l so sugge s te d to ha ve oc c ur re d in the l a te

M i o c e n e - P l i o c e n e f r o m t h e p r e s e n ce o f th e

t h i c k , n o n - m a r i n e u p p e r M i o c e n e D a h o r F o r -

ma t ion (Hutc h ison 1992) .

S i g n i f i c a n t a m o u n t s o f r o c k h a v e b e e n

re move d s inc e the e nd o f the e a r ly Mioc e ne

t h r o u g h d e n u d a t i o n . B u r i a l h i s t o r y m o d e l l i n g o f

the Ba tuq we l l (F ig . 1 ) sugge s t s a n e s t ima te d

3 50 0 m o f s e d im e n t h a s b e e n r e m o v e d b y e r o s i o n

in i t i a te d by up l i f t (W a in Be rod 1989) . T he

M a w a i we l l (F ig . 1 ) , d r i l le d by M obi l , pe n e t ra te d

Ol igoc e ne a t su r fa c e wi th a n R0(a ve ra ge ) o f 1 . 2 ,

imply ing b ur ia l fo r s e ve ra l m i l l ion ye a r s a t de p ths

o f a r o u n d 3 - 4 k m , a s s um i n g a v e r a g e g e o t h e rm a l

gra d ie n t s . V i t r in i te r e f le c ta nc e da ta fo r the lowe r

M i o c e n e o f t h e u p p e r K u t a i B a s i n a l so i m p l y

u p l i f t a n d e r o s i o n o f 's e v e ra l th o u s a n d s o f

m e t r e s ' o f s e c ti o n ( V a n d e W e e r d A r m i n

1992) sugge s t ing tha t some of the se roc ks we re

bur ie d to 2 -3 km de p th p r io r to up l i f t , whi l s t

o the r s h a ve e xpe r ie nc e d re la t ive ly sha l low bu r ia l .

A p o p u l a r e x p l a n a t i o n f o r t h e i n v e r s i o n ( s )

i s the c o ll i s ion o f mic ro-c o n t ine n ts a nd c on-

t ine n ta l f r a gme nts , suc h a s Ba nga i -Su la ,

T u k a n g B e s i f r a g m e n t s , A u s t r a l i a ( D a l y

e t a l

1991) a nd sou th China de r ive d f r a gme nt ( s ) , w i th

B o r n e o - S u l a w e s i . D a l y e t a l (1991) invoke d

NW-di re c te d inve r s ion fo l lowing the c o l l i s ion o f

A u s t r a l i a w i t h t h e S u n d a t r e n c h . A u s t r a l i a n

c o l l i s i o n w i t h t h e B a n d a A r c o c c u r r e d a r o u n d

5 M a ( D a l y e t a l 1991) so is too la te to have

c a use d inve r s ion a t the e nd o f the e a r ly M ioc e ne .

Col l i s ion o f Ba ng a i -S u la i s sugge s te d to be

r e s p o n si b l e f o r th e t h i n n e d - s k i n n e d d e f o r m a t i o n

in the Ka los i PSC a re a a nd we s te rn Su la we s i

(Coff ie ld

e t a l

1 9 9 3 ; B e r g m a n

e t a l

1996).

Howe ve r a r e g iona l s e i smic l ine (CGG-104)

a c r o s s t h e M a k a s s a r S t r a i t s s h o w s t h a t t h e

d e f o r m a t i o n f r o n t c l e a r l y s t o p s o f f s h o r e w e s t

S u l a w e s i a n d t h a t O l i g o c e n e a n d M i o c e n e

s e c t i o n s i n t h e n o r t h e r n M a k a s s a r S t r a i t s a r e

u n d e f o r m e d . A l o w - a n g l e ( f l a t ) d e t a c h m e n t

would be r e qu i re d to t r a nsmi t s t r e s se s f rom the

B a n g a i - S u l a c o l l i s i o n t o c a u s e d e f o r m a t i o n i n

E a s t K a l i m a n t a n . C o l l is i o n o f s o u t h - C h i n a -

de r ive d f r a gme nt ( s ) , suc h a s the Re e d Ba nk/

D a n g e r o u s G r o u n d s , w i t h n o r t h e r n m a r g i n o f

Born e o i s a no the r pos s ib le source o f c omp re s -

s iona l s t resses to induce invers ion. Coll is ion

o f t h e R e ed B a n k / D a n g e r o u s G r o u n d s m i c r o -

c o n t i n e n t a l b l o c k w i t h t h e n o r t h e r n m a r g i n o f

B o r n e o m a y h a v e c a u s e d c o n t r a c t i o n f r o m t h e

nor thw e s t . T h is d i r e c t ion i s a ppro x im a te ly 45 ~

or more to the ge ne ra l d i r e c t ion o f o r ig ina l

b a s i n - b o u n d i n g f a u l t s i n t h e R u n t u B l o c k . E v e n

i f the o r ie n ta t ion o f the p r inc ipa l s t r e s s d i re c t ion

wa s ob l ique to the o r ig ina l f a u l t s , ne w fa u l t s a re

l ike ly to nuc le a te upon the e a r l i e r s t ruc tu re s

s inc e a we a kne ss a l r e a dy e x i s t s . Howe ve r , the

o r i g i n a n d t i m i n g a n y p r o p o s e d c o n t i n e n t a l

c o l l i s ion re ma ins unc le a r . T he la te Ol igoc e ne -

e a r ly Mioc e ne up l i f t in Borne o ma y be the r e su l t

o f S o u t h C h i n a S e a s p r e a d i n g a n d e x t e n s i o n

c a us ing c on t ra c t ion in the a d ja c e n t r e g ions .

T h e r m a l d o m i n g , p o s s i b l y r e l a t e d t o t h e o n s e t

of the Sintang Intrus ive sui te (see be low), is

a no the r pos s ib le c a use o f th i s up l i f t. H ow e ve r ,

suc h doming usua l ly induc e s e x te ns iona l b loc k

fa u l t ing ra the r tha n inve r s ion , a s ha s be e n

v a r i o u s l y d e s c r i b e d f o r t h e N o r t h S e a . D o m i n g

re la te d up l i f t r a re ly e xc e e ds 500m a nd i s

typ ic a l ly loc a l iz e d , bu t ma y in i t i a te a pha se o f

e r o s i o n a l r e b o u n d t h a t c o u l d r e m o v e s e v e r a l

k i l o m e t re s o f c o v e r. H o w e v e r , i f t h e r m a l d o m i n g

is the c a use o f the inve r s ion , a m ore e x te ns ive

a re a o f in t rus ive a nd e x t rus ive roc ks a s soc ia te d

wi th the ma in inve r s ion loc us migh t be e xpe c te d ,

bu t i s no t s ee n. I sos ta t i c a d ju s tme n ts o f the c rus t

fo l lowing th ic ke n ing o f the c rus t o r r e m ova l o f a

l o a d c a n a l s o c a u s e u p l i f t b u t a g a i n a r e m o r e

l ike ly to p roduc e e x te ns iona l f e a tu re s r a the r

tha n fo lds . T he c a use o f inve r s ion the re fo re

re ma ins unc le a r .

ert iary igne ou s activ i ty

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

T e r t i a r y K u t a i B a s i n , a n d h a s p r e v i o u s l y b e e n

u s e d t o c o n s t r a i n t h e T e r t i a r y s t r a t i g r a p h y



408 S. J. MO SS E T A L

cf. Pieters et a l 1987). Three suites of volcanic

and int rus ive rocks are recognized wi thin the

Ter t i a ry o f Ka l im antan F ig . 6 ), t he Ny aan

volcanics , Sintang Int rus ives sui te and the

Metu lang Volcanics or Platea u volcanics) .

The fels ic Nyaan volcanics in the upper

Ma ha ka m River F ig. 1 ) have K -A r ages o f

48-50 4- 1 Ma have been obtained Pieters et al

1987, 1993a) . On the bas is of comp osi t ion and

age the Nyaan volcanics correlate wi th the

Fig. 6. Distribution of Tertiary igneous activity in Borneo/Kalimantan. The nature, relationships and genesis of

the features shown in the diagram are discussed in the text.




P i y a b u n g V o l c a n i c s o f t h e S e m i t a u R i d g e i n

w e s t e r n K a l i m a n t a n , t h e S e r a n t e k V o l c a n i c s o n

w e s t e r n e d g e o f K a l i m a n t a n a n d t h e K e l i a n

Volcan i c s i n t he cen t re o f t he Ku ta i Bas in

(F igs 1 6 ). The t h i ck (ove r 1200 m ) S em bu lu

Tuf t s o f ?uppe r E ocene t o l ower O l igocene

age a re repo r t ed f rom exp lo ra t i on we l l s i n

t h e B u n g a l o n a r e a i n t he n o r t h e a s t c o r n e r o f t h e

K u t a i B a s i n a d j a c e n t t o t h e M a n g k a l i h a t

P e n i n s u l a ( S u n a r y o

e t a l

1988) . Ac id i c vo l can i c s

a l s o o c c u r w i t h i n S a r a w a k ( A r i p v o l c a n i c s a n d

P i r ing g ranod io r i t e i n t ru s ion ) , a l t hough these

m ay be s l i gh t ly younger . P i e t e rs

e t a l

(1987)

sugges t t he Nyaan vo l can i c s su i t e a re s t ra t i g ra -

ph i ca l l y be low the Te r t i a ry success ion , a l t hough

W ain Berod (1989) p l ace t he vo l can i c s w i th in

t h e b a s a l p a r t o f th e i r T a n j u n g F o r m a t i o n . A t t h e

K el ia n gold min e s i te (F ig . 1), fe l s ic bed ded tuft s ,

a g g l o m e r a t e s , r h y o l i t e l a v a a n d r e w o r k e d p y r -

o c l as t ic s a re p a r t o f a n u p p e r E o c e n e s e d i m e n t a r y

success ion (Van Leeuwen e t a l 1 9 9 0 ) . A t t h e

Nyaan vo l can i c s t ype l oca l i t y (F ig . 1 ) , f l ow

b a n d e d , v e s i c u l a r r h y o l t i c l a v a s a n d s u b - a e r i a l

vo l can i c s c rop ou t , bu t a s t hey a re no t i n con t ac t

wi th any Te r t i a ry sed im en t s , s t ra t i g raph ic re l a -

t i onsh ips canno t be a sce r t a ined . The basa l t i c t o

andes i t i c Mul l e r vo l can i c s , no r thwes t o f t he

M u l l e r M o u n t a i n s ( F i g . 1 ) , h a v e a K - A r r a d i o -

m e t r i c age o f 41 + 0 .4M a (P i e te rs

e t a l

1993b)

a n d m a y r e p r e s e n t a la t e st a g e e ve n t o f t h e N y a a n

su i t e . One exp lana t ion fo r t he o r ig in o f t hese

vo lcan i c s i s t ha t t hey a re re l a t ed t o ex t ens io na l

tec tonics (Hutchison 1996).

The S in t ang In t ru s ive su i t e i s de f ined a s

s p a n n i n g t h e u p p e r O l ig o c e n e to e a r l y M i o c e n e

i n t e r v a l , a l t h o u g h , a w i d e r r a n g e o f K - A r

r a d i o m e t r i c a g e s ( 4 1 -8 M a ) h a v e b e e n o b t a i n e d

f rom rocks a ss igned to t h i s su it e (Hery an to e t a l

1993; Pieters

e t a l

1993a; Moss

e t a l

1997) . The

S in t ang In t ru s ives ha ve a m af i c t o fe l s i c com po-

s i t i on and cons i s t o f d io r i t e s , m ic rod io r i t e s ,

dac i t e , m ic rog ran i t e s and andes i t e s . In t ru s ions

o f t he S in t ang In t ru s ive su i t e a re w ide ly d i s -

t r ib u t e d a s p l u g s a n d o t h e r h y p a b y s s a l i n t r u s io n s

t h r o u g h o u t p a r t s o f W e s t , C e n t r a l a n d E a s t,

K a l i m a n t a n , o f t e n f o r m i n g l o w c o n i c a l h i ll s ( F i g.

6 ). The f i ne ly c rys t a l l i ne na tu re and l im i t ed

c o n t a c t a u r e o l e o f t h es e i n t r u s i o n s i m p l i e s h i g h

l eve l em placem en t . Andes i t i c b recc i a s and

agg lom era t e s a re t yp i ca l l y a ssoc i a t ed wi th t he

plugs. P ie ters

e t a l

(1993a) co r re l a t e t he S in t ang

I n t r u s i v e s w i t h t h e c o m p o s i t i o n a l l y s i m i l a r

coeva l O l igo -Miocene i n t ru s ives o f K i rk (1968)

i n S a r a w a k .

V o l c a n i c s i n t e r b e d d e d w i t h l o w e r t o m i d d l e

M i o c e n e ( a n d y o u n g e r ) s e d i m e n t s , g e o g r a p h i -

ca l l y a ssoc i a t ed wi th t he a rea o f S in t ang su i t e ,

a re l i ke ly t o t he sub -ae r i a l p roduc t s o f S in t ang

in t ru s ive ac t i v i t y . Vo lcanogen ic t ons t e in s and

wa te r l a in c rys t a l and l i t h i c t u f t s a re i n t e rbedded

wi th l i t h i c a ren i t e s , ca rbonaceous sha l e s and

r a r e f o r a m i n i f e r a l l i m e s to n e s o f l o w e r M i o c e n e

age a long pa r t o f t he Te l en R ive r (F ig . 1 ) .

S eve ra l m ic rog ran i t i c , som e t im es g l a ssy , p lugs

i n t r u d e l o w e r M i o c e n e c o a l m e a s u r e s o n t h e

T e l e n R i v e r . T h e s i m i l a ri t ie s i n m i n e r a l o g y a n d

a l t e ra t i on s t a t e o f b io t i t e c rys t a l t u f ts an d g l a ssy

m i c r o g r a n i t i c p l u g s i m p l y a c l o s e r e l a t i o n . A n

u n c o n f o r m a b l e c o n t a c t i s i n f e r r e d t o e x i s t

be tween we lded b io t i t e t u f t s i n t e rbedded wi th

d i p p i n g l o w e r M i o c e n e s e d i m e n t s a n d s u b -

ho r i zon ta l wa te r - l a in pum ice r i ch t u f t s exposed

a sho r t d i s t ance downs t ream . Th i s sugges t s t ha t

v o l c a n i s m o cc u r r e d b o t h p r i o r t o a n d s u b se -

q u e n t t o e a r l y M i o c e n e i n v e rs i o n . A d d i s o n e t a l

(1983) de t a i l e igh t l a t e ra l l y con t inu ous t ons t e in

b a n d s w i t h i n l o w e r M i o c e n e d e l t a i c s i n t h e

S a m a r i n d a a r e a .

P l i o c e n e - P l e i s t o c e n e v o l c a n i c s o f t h e M e t u -

l a n g su i te a r e c o m m o n t h r o u g h o u t t h e c en t r e o f

K a l i m a n t a n a n d p a r ts o f S a ra w a k a n d h a v e

b e e n t e r m e d t h e M e t u l a n g o r P l a t e a u V o l c a n ic s .

T h e M e t u l a n g V o l ca n ic s h a v e K - A r r a d i om e t r i c

ages o f be tween 2 .4 and 1 .7 M a (P i e te rs e t a l

1993a) . The basa l t s o f t he N u i t vo l can i c s i n Wes t

K a l i m a n t a n (F i g . 1), w i t h K - A r r a d i o m e t r i c ag e

o f 4 .9 + 0 .1 M a ( S upr i a tna e t a l 1993), be lon g to

th i s su i t e (S upr i a tna

e t a l

1993). This su i te

c o m p r i s e s m e d i u m t o h i g h - K c a l c - a l k a l i n e

basa l t s and andes i t e s fo rm ing h igh - l eve l i n t ru -

s ions (o f t en sub -vo lcan i c ) , and l ava f l ows f rom

seve ra l ex t i nc t vo l can i c cen t re s . The P l a t eau /

M e t u l a n g V o l c a n i cs m a y r e c o rd a n e v o l u t i o n a r y

t r e n d t o w a r d m o r e m a f i c c o m p o s i t i o n s w i t h t im e

from the rhyo -dac i t i c S in t ang In t ru s ives su i t e .

O n e p r o p o s a l i s t h a t t h e y a r e p a r t o f a n

evo lu t i ona ry cyc l e w i th t he S in t ang In t ru s ive

S u i t e invo lv ing m e l t i ng o f a deep l i t hosphe r i c

roo t fo l l owing th i cken ing o f t he c rus t (P i e t e rs

e t a l

1993a).

T h e d i s t r i b u t i o n o f T e r t i a r y i g n e o u s a c t i v i t y

i n K a l i m a n t a n a n d B o r n e o i s s h o w n i n F i g . 6.

T h e r e w o u l d a p p e a r t o b e i n s uf f ic i e nt m a t e r i a l

fo r vo l can i c ac t i v i t y t o be re l a t ed t o sub duc t ion ,

a l t h o u g h t h is i m p r e s s i o n c o u l d b e d u e t o t h e

e f fec ts o f e ros ion . I t has been p rop osed f rom

the age da t a , m a jo r and t race e l em en t s i gna -

tu re s o f u ppe r M iocene (7.8 + 0 .3 , 7 .7 + 0 .3 M a

K - A r a g e s ) m i n e t t e d y k e s i n t h e K e r a m u r i v e r

( S W K u t a i b a s i n ; F i g . 1 ; B e r g m a n

e t a l

1988)

t h a t m a g r n a t i s m w a s n o t d i r e c tl y a s so c i a te d w i t h

s u b d u c t i o n . D y k e s , w h i c h p r o b a b l y c o r r e l a t e

wi th t he S in t ang In t ru s ive su i t e , a re v i ewed by

B e r g m a n

e t a l

(1988) t o have fo rm ed due t o

i n t r a p l a t e a l k a l i n e m a g m a t i s m a s s o c i a t e d w i t h

t h e m e l t i n g o f s u b c o n t i n e n t a l m a n t l e l i t h o s p h e r e



410 S. J . M OS S E T A L

a nd te n ta t ive ly r e la te d to c rus ta l th ic ke n ing

w i t h l a t e C r e t a c e o u s - m i d - T e r t i a r y c o n t r a c t i o n .

A s imi la r mode l fo r the e vo lu t ion o f the S in ta ng

su i te wa s p ropose d by P ie te r s e t a l (1993a) . The

P l ioc e ne -P le i s toc e ne Me tu la ng su i te we re ga rd

as the f ina l s tages of the Sintang sui te .

T he Ke l ia n go ld mine in the c e n t re o f the

Ku ta i Ba s in (F igs 1 & 6) r e c ords a l l th re e su i tes .

A w ide va r ie ty o f li tho log ie s , inc lud ing se d i-

me nts , some t ime s the rma l ly a l t e re d , tu f t s , rhyo-

l i tes , andes i tes , basa l t ic f lows, dykes , s i l ls and

s toc ks a re e xpose d in the mine . T he re we re a t

l e a s t th re e pha se s o f vo lc a n ic a nd in t rus ive

a c t iv i ty . F low ba nde d rhyo l i t e s a nd pyroc la s t i c

ma te r ia l (we lde d tu f t s , a gg lome ra te s ) o f the

in i t i a l pha se g ra de in to th ic k s a nds tone s , sha le s

a n d r a r e l im e s t o n es o f u p p e r E o c e n e a g e ( V a n

L e e u w e n e t a l 1990). L ime s ton e in te rc a la t ions in

o u t c ro p s o f th e u p p e r p a r t o f th e K i h a m H a l o q

S a n d s t o n e F o r m a t i o n a l o n g s t r i k e t o t h e n o r t h -

e a s t o f the K e l ia n s i t e y ie lde d uppe r E oc e ne

fora min i fe ra (T b o r P15-16) . T he f i r s t pha se o f

vo lc a n ism ma y we l l be c or re la ta b le wi th the

Nya a n vo lc a n ic s su i te . T he E oc e ne vo lc a n ic s

a nd se d ime nts a re in t rude d by sma l l s toc ks a nd

p l u g s o f a n d e s it e w h i c h h a v e y i el d e d K - A r

r a d i o m e t r i c a g e s o f 2 2 .9 + 0 .5 M a ( V a n L e e u w e n

e t a l 1990). T h is p ha se o f vo lc a n ic a c t iv i ty

be longs to the S in ta ng In t rus ive su i te . T he whole

se que nc e ha s be e n fo lde d in to a b roa d a n t ic l ine

a n d f a u l te d w i t h m a j o r s t r u c tu r e s t r e n d i n g t o t h e

n o r t h / n o r t h e a s t , p r o b a b l y i n t h e l a te O l i g o ce n e /

e a r l y M i o c e n e ( V a n L e e u w e n e t a l 1990).

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

go ld mine ra l iz a t ion oc c ur re d in the e a r ly Mio-

c e ne (Va n L e e uwe n e t a l 1990) . Uppe r Mioc e ne /

P l ioc e ne ba sa l t dyke s a nd ba sa l t f lows o f the

M e t u l a n g V o l c a n i c s i n t r u d e a n d u n c o n f o r m a b l y

I I I I I I

1 1 0 ~ 1 1 4 ~ 1 1 8 ~

9 SE A sia Re searc h Gro up - La te Eoc ene to Late/~.,Miocene ~" ,

L u m a d y o e t a l . ( 1 9 9 3 ) - L a t e E o c e n e t o P l i o - P l e i s t o c e n e / ~ / ~ _...._ ~ . J U g U

" S u n y a t a & W a h y o n o ( 1 9 9 1 ) - T r i a s s i c t o O l i g o - M i o c e n e / / _ .3

b ea

9 S c h m i d k t e e t a l . ( 1 9 9 0 ) & F u l l e r e t a l . ( 1 9 9 1 ) / 1M - K ar ~a / / ~ . 6 ~

- - 6 ~ - J u r a s s i c t o L a t e M i o c e n e / i n tr us io n13 M a v

9 H a i l e e t a l . ( 1 9 7 7 ) - L a t e C r e t a c e o u s ~ ~ A

PP = P l i . . . . P lei st . . . " - ) ~ n h a t '! / ,1 ) 1 1 /

IM = L a te M i . . . ( 8 M a ) ~ ~ U . O ' l t ~ l ~

Ti =Tertiary ntrusives two dated at 26 & 17 Ma) f..._..-./

Tu = Tertiaryundated (as yet) J ~ ~

O M = O lig . . . . M i . . . / ~ ' - ~ " " ~ " , , , - ~ o

- - 4 ~ Eo = Eo cen e / / [ _ " 3 4 - -

K i = C r etaceo us n tr us iv es J - ~ /~ /~ q .~ :~

IK = Late C . . . . . . . p lu tonics & volcanics

f , ~ l f ' l ~ a k I ~ ) ~ .

K = C . . . . . . . ~ ~ ' ' ' ' ' ~ ' ' ~ J ~ Celebes

J-K = Jurassic-Cretaceous ~ ~ " \ . . . . . . .

Tr = Triassic ~ (

~ S e a

[ 2 0 ~ ~ O M ~ , , , ~ f / 1 9 Tu- ( K J 7 4 - 7 6 ) ~ 2 0 - -

0 o 0 o - -

-2~ ~ ~ Straits 2~

- 4 ~ L O ~ a a ~ O m n a g f e

~w o r k n B o r n eo

4 0 0 k m

~ , ~

.. . .. . o, .... I I I I I I

F i g 7. Location of palaeomagnetic sam pling sites in Borneo and the location of University of London SE Asia

Group sites in the Kutai Basin.




o v e r l i e t h e e n t i r e s e q u e n c e . I t i s i n t e r e s t i n g t o

n o t e t h a t V a n L e e u w e n et al . ( 1 9 9 0 ) s h o w K e l i a n

a n d o t h e r e p i t h e r m a l g o l d d e p o s i t s o c c u r in a

r e m a r k a b l y l i n ea r N E - S W - t r e n d i n g l in e a m e n ts ,

a l t h o u g h t h e s i g n i f ic a n c e (i f a n y ) o f th i s w i t h

r e s p e c t t o o t h e r s t r u c t u r a l f e a t u r e s o f E a s t

K a l i m a n t a n is n o t c l e ar .

o t a t i o n h i s t o r y

T h e r o t a t i o n a l h i s t o r y o f B o r n e o is c o n t ro v e r s i a l

a n d a g o o d q u a l i ty , c o m p r e h e n s i v e d a t a s e t is

s t i l l l a c k i n g . P r e v i o u s p a l a e o m a g n e t i c s t u d i e s

h a v e c o n c e n t r a t e d u p o n W e s t S a r a w a k / W e s t

K a l i m a n t a n ( F ig . 7 ). A l a r g e v a r i a t i o n i n

Table 1 . Summary of previous and Universi ty of London palaeomagnetic work in Borneo

A g e / o r N o . o f D i r e c t i o n o f G r o s s T i m i n g t

f o r m a t i o n s it es * r o t a t i o n r o t a t i o n

Haile

et al.

(1977)

L a t e C r e t a c e o u s p l u t o n i c s

v o l c a n i c s

4 8 C C W 5 0 ~

Schmidtke

et a l .

(1990)

K e d a d o m F m , L a t e J u r a ss i c 3

P e d a w a n F m , L a t e 4

J u r a s s i c - C r e t a c e o u s ,

B a u F o r m a t i o n , L a t e 5

J u r a s s i c - C r e t a c e o u s

S i l a n ta k F m , E o c e n e t o 4

M i o c e n e

' T e r t i a r y i g n e o u s i n t r u s i o n s ' 1 0

Sunyata Wahyono (1991)

K a l u n g F o r m a t i o n T r ia s s ic (? )2

J u r a s s i c m u d s t o n e s 11

S e l a n g k a i F m , E a r l y / 3 9

M i d - C r e t a c e o u s

K i h a m H a l o q / o r B a t u 3 8

K e l a u F m , L a t e E o c e n e

U n d a t e d ? O l i g o -M i o c e n e 2

basal t s i l ls

Lumadyo

e t a l

(1993)

U n d a t e d E o c e n e b a s a lt f lo w

O l i g o - M i o c e n e b a s a l t

a n d e s i t e f l o w s

P l e i s t o c e n e - P l i o c e n e b a s a l t

f lows

C C W

C C W

C C W

C C W ( 1 s i t e

n o r o t a t io n )

C C W ( 4 s i t e s

neg l ig ib le

r o t a t i o n )

C C W

C C W

C C W

C C W

N e g l i g i b l e

r o t a t i o n

N e g l i g i b l e

r o t a t i o n

N e g l i g i b l e

r o t a t i o n

( s l ig h t C W )

N e g l i g i b l e

r o t a t i o n

Universi ty of London S E Asia Research Group

L a t e E o c e n e ( N P 1 7 -1 8 ) 4 C C W

s e d i m e n t s

E a r l y M i o c e n e (1 8 M a ) 4 C C W

d i o r i t e p l u g

U n d a t e d a n d e s it i c l a v a f lo w 3 C C W

? L a t e M i o c e n e

50 ~

90 ~

50 ~

41 ~

- 2 ~ t o 5 2 ~

8 1 - 7 3 ~

93 ~

76 ~

37 ~

0 o

~

1o

0 o

15 ~

16 ~

23 ~

S i nc e M i d - C r e t a c e o u s

S ince l a te Jur as s ic

S i n c e l a t e J u r a s s i c - C r e t a c e o u s

R e m a g n e t i z e d i n T e r t i a r y ,

t i m i n g n o t c o n s t r a i n e d

S i l a n ta k F m v e r y p o o r l y

d a t e d - n o t i m e c o n s t r a i n t s

O n l y t w o o f i n t ru s i o n s d a t e d

( 26 17 M a)

S ince the T r ia s s ic

S ince the Jur as s ic

S i n c e t h e C r e t a c e o u s

S i n c e t h e E o c e n e

S i n c e O l i g o - M i o c e n e

S i n c e t h e E o c e n e

S i nc e th e O l i g o - M i o c e n e

S i n c e t h e P l e i s t o c e n e - P l i o c e n e

L a t e E o c e n e

S i n c e e a r l y M i o c e n e

L a t e M i o c e n e

* 1 S i te = 1 hor izo n .

t T i m i n g = t i m i n g o f m a g n e t i z a t i o n .



412 S. J . M OS S E T A L .

m e a s u r e d r o t a t i o n f o r b o t h t h e M e s o z o i c a n d

T e r t i a r y i s e v i d e n t ( T a b l e 1 ) . L u m a d y o

e t a l .

( 1 9 9 3 ) q u e s t i o n w h e t h e r B o r n e o h a s r o t a t e d a t

a l l i n t h e T e r t i a r y , b u t w e c o n t e s t f r o m t h e

l i m i te d d a t a a v a i la b l e th a t B o r n e o u n d e r w e n t

c o u n t e r c l o ck w i s e ( C C W ) r o t a t i o n o f n o m o r e

t h a n 2 5 ~ i n t h e N e o g e n e . T h i s i s i n d i r e c t

c o n t r a s t t o p r e v i o u s r e s u l t s , n o t a b l y S c h m i d k t e

e t a l . (1990 ) ; F u l l e r e t a l . ( 1 9 9 1 ) a n d S u n y a t a &

W a h y o n o ( 1 9 9 1 ) , w h o s u g g e s t m u c h l a r g e r

r o t a t i o n s i n t h e T e r t i a r y , p a r t i c u l a r l y i n t h e

e a r l y T e r t i a r y . D i s c r e p a n c i e s b e t w e e n t h e d i ff e r-

e n t s t u d i e s m a y b e a n i n d i c a t i o n o f s e p a r a t e

b l o c k r o t a t i o n s w i t h i n t h e i sl a n d o f B o r n e o a n d

t h e i n f l u e n c e o f m a j o r f a u l t l i n e s . B o r n e o i s a

v e r y l a r g e i s la n d w h i c h c o u l d e a s i ly b e d i v i d e d

i n t o s e v e r a l b l o c k s . F r o m t h e d a t a s e t a v a i l a b l e

i t i s n o t p o s s i b l e t o s a y w h e t h e r B o r n e o h a s

ro ta t ed a s a s ing le b lock o r s eve ra l s emi -

i n d e p e n d e n t b l o c k s w i t h s i m i l a r r o t a t i o n h i s -

t o r ie s . T h e v i e w t h a t B o r n e o b e h a v e d a s a s i n gl e

c r u s t a l b l o c k s h o u l d b e q u e s t i o n e d c e r t a i n l y fo r

t h e M e s o z o i c a n d p r o b a b l y f o r t he T e r t i a r y . T h e

L u p a r L i n e, A d a n g f a u l t z o n e , S e m i t a u R i d g e

a n d S a n g k u l i r a n g f a u l t z o n e a l l a r e p r o b a b l y

m a j o r s t r u c t u r al f e a t u re s o f B o r n e o a n d e v e n if

n o t l i n k e d m a y h a v e b e e n u t i l i z ed i n t h e r o t a t i o n

o f B o r n e o . C C W r o t a t i o n o f B o r n e o c on f li c ts

w i t h t h e e x t r u s i o n m o d e l ( T a p p o n n i e r

e t a l .

1 9 86 ) in w h i c h n o r o t a t i o n o f B o r n e o i s i m p l i c i t.

T h e d r i v i n g m e c h a n i s m s a n d t i m i n g o f th e

r o t a t i o n ( s ) r e m a i n u n c l e a r , b u t i t i s p l a u s i b l e

t h a t p e r i o d s o f i n v e r s io n i n t h e K u t a i B a s i n a n d

r o t a t i o n s o f B o r n e o m a y b e r e l a te d . T h e

p r e s e n c e a n d a c t i v i t y o f m a j o r f a u l t s s u c h a s

L u p a r L i n e a n d t h e W e s t B a r a m f a u l tl i n e i n

S a r a w a k a l o n g w h i c h d e f o r m a t i o n a s s o c i a t e d

w i t h t h e c o u n t e r - c l o c k w i se r o t a t i o n o f B o r n e o

m a y h a v e o c c u rr e d . T h e m a j o r o r o c l i n a l b e n d i n g

o f t u r b i d i t i c s e d i m e n t s o f t h e R a j a n g - E m b a l u h

G r o u p a n d C r o c k e r - T e m b u r o n g F o r m a t i o n s i n

S a b a h a n d S a r a w a k ( B 6 n a r d e t a l . 1990) cou ld

a l s o r e a s o n a b l y b e r e l a t e d t o t h i s c o u n t e r - c l o c k -

w i s e r o t a t i o n . F u r t h e r w e s u g g e s t t h a t t h e

a v a i l a b l e d a t a i m p l y v e r y l i t t l e l a t i t u d i n a l

c h a n g e i n t h e p o s i t io n o f B o r n e o t h r o u g h o u t

t h e M e s o z o i c a n d C a i n o z o i c.

M o d e l o f f o r m a t i o n o f th e K u t a i B a s in

T h e f o r m a t i o n o f K a l i m a n t a n b a s in s fo l l o w e d

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

a

0.

K a l i m a n t a n / B o r n e o e v e n t s R e g i o n a l e v e n ts

1 0

20-

30- ~ --

50

metamorph i s m

o

8

60

,Metu lang T Aus tra l ia co l l i s ion

-'Volcanics Deep &

h

Shallow ; SW Sulawe si 2nd ~ Bang gai-

i Sin tang ~ regional I ~ Sula

; vo lcanism invers ion

'- Intru sive 9 ,, - - U/C's i Sulu col lisio n

, _ . ~ ~am ara naa ~,. . . . West u

i ~mte ~ an t ic l inorium~ in ~at~an~ ; arc '. En d of

Natuna

Reed

B ank

!Major del ta ic progradat ion in Eas t [ lS ulu Sea

SCS

.~ -' Kalim antan - N5 i /ope ning openin g T 1st inversion collis ion

_ ~Wes t

i I M a j o r i n v e r s i o n - N 3 i Natuna Bas in

' - c a r b o n a t e d e p o s i t i o n Start of SCS

Crocker Group i spreading

"~ dep ositio n i

I B a s i n - T C e l e b e s " A c t i v e

Muller

[ o p e n i n g

Lubok An tu S ea Makas s ar

- Straits

~ volcanicc m elan ge- spr ea din g extens ion

~ ~- r / j~ ~ Defo rmation , ~ Hard

-' N ya an |

9 volcanics ~ of Rajang- ~ co l l i s ion

of India &

"~ Embaluh

Group i ~ Eurasia

~ (?)Emplacement Rajang-[ Exten sion on South Chin a

of the Sabah Em baluh i Ma rgin - Pearl Rive r

Mo uth bas in

70

J o p h io l i te Group_.dep0s it ion i

9Schwan er Era & I Meratus i- 'Mountain Topai ophio lite

igrani tes i g ranites emplacem ent

9Yenshanian magmat ic

i ac t iv i ty in South China , Ranai grani te

'& V ietn am -" Natuna

Fig. 8. Correlation of events within Ka lima ntan and su rrounding areas through the T ertiary.



EVO LUTIO N OF KUT AI BASIN 413

early Palaeogene deforma tion Fig. 8). Opening

of basins in Ka lima ntan overlaps with the sea

floor spreading in the Celebes Sea, whilst the

phases of la te Oligocene-M iocene inversion and

folding in Borneo overlap with inversions in the

West Na tun a Bas in , con tinued open ing of the

South C hina Sea, opening o f the Sulu Sea and

several microcontinent and continent coll is ions.

The Kutai Basin is an extensional basin that

formed in a foreland set t ing relat ive to the

deform ed Central Kalim anta n ranges Fig. 9).

In common wi th the Ketungau /Mandai Bas ins

in west Kalimantan, the f i l l of the Kutai

Basin unconformably overl ies the deformed

Creta ceou s-low er Eocene turbidites of the

Rajang-Embaluh and o lder oph io l i t ic and cher t

un i ts Lubok An tu and Ker iau melanges) w i th

marked angulari ty . We suggest basin exten-

sion was ini tia l ly driven by contin uation of coeval

extension in the Celebes Sea and M aka ssa r Strai ts

in to Kal im antan poss ib ly a ided by g rav i tat iona l

co llapse o f the Em baluh /R ajang orogen. The

presence of several thermal ano malies within the

upper crust from upper Cretaceous granite

in t rus ions and ear ly Ter t ia ry deformat ion may

have aided this process. The Permo-Triassic

gran ites and m etamorphics o f the Busang com-

plex on the basin edge may be signif icant , and the

complex is interpreted here to be basement core

complex unroofed via this extension. The depth

of the Kuta i Basin up to 15km) precludes

format ion o f the bas in th rough f lexural mechan-

isms as advocated by Pieters et al 1993a) for

Ter t ia ry bas ins o f Kal imantan . The o r ien ta t ion

of extensional faults and their evolution in the

Paleogene were s trongly controlled by the base-

ment s tructures. Extension had al l but ended by

the mid-Oligocene, by which t ime the basin had

move d into the sag phase of development.

Thermal doming and associated crustal thicken-

ing with the onset of the Sintang Intrusive suite

may have caused a shorter , less dramatic period

of subsidence and is related to late Oligocene

tectonism in the area. From the end of the

Oligocene to Pliocene the basin was affected by

a series of inversion events , most im porta nt of

which was the early Miocene event, which over-

laps with the f irs t phase of inversion in the Wes t

Na tun a Bas in N8, G inger et al 1994).

The Kutai Basin, as described, evolved in a

way quite different from that reported for other

Southeast Asia basins such as those in Sumatra

and Vietnam. Basins in Sumatra , for example,

show a rema rkab ly similar sequence of ?)upper

Eocene syn-rif t a l luvial and lacustr ine deposits

e .g . the Lahat Formation) passing up into

fluvial and fluvio deltaic sediments e.g. the

Sihapas and Ta lang Akar Format ions) and a

Miocene transgressive-regressive mega-sequence

e .g . Gumai and Air Benaka t Format ions) . The

majo r difference may be the location o f the Kuta i

Basin on the eastern edge of the Sund a crato n

during the Tert iary.

Fig. 9. Open ing and extension within the Kutai Basin.

Spreading within the Celebes Sea extends into the

Sunda Craton and is responsible for generating the

Eocene opening of the Makassar Straits and

extensional faulting in the Ku tai Basin area. Plate-

tectonic setting adapted from Hall 1996).

onclusions

The K utai Basin formed in the eastern part of the

Sunda craton. During the early Palaeogene the

Embaluh and Rajang Grou ps were deformed and

locally intruded by granites . This over thickened

crust was r if ted with extension driven by coeval

extension in the Celebes Sea and Makassar

Strai ts , between 44 and 34Ma. A deep basin

wi th marked depos i t iona l topography fo rmed

with ini tia l a l luvial fan conglom erates p assing up

into deep marine bathyal shales and fr inging

shallower marine clast ics and carbonates. The

orientat ion of basin-forming r if t faults was

strongly controlled by l ineaments in the base-

ment. A t the end of the Oligocene a majo r event is

recorded by the presence of a basin wide uncon-

formity reflecting a phase o f uplif t deduced from

fission track dat a Moss et al 1997). The cause

of this uplif t / inversion remains unclear . Follow-

ing this uplif t was a period of deep marine shale

and platform limestone deposit ion. A regressive



4 1 4 S . J . M O S S ET AL.

s e q u e n c e o f u p p e r l o w e r M i o c e n e d e l t a ic s w a s

t h e n d e p o s i t e d a n d d i a c h r o n o u s l y m i g r a t e d

f r o m w e s t t o e a st . D e l t a i c d e p o s i t i o n c o n t i n u e s

t o d a y i n t h e f o rm o f t h e M a h a k a m D e l ta .

S e v e r al p h a s e s o f in v e r s i o n d u r i n g t h e M i o c e n e

r e a c t i v a te d t h e o r i g in a l N E - S W - t r e n d i n g f a ul ts .

T h e S a m a r i n d a a n t i c li n o r iu m w a s f o r m e d

d u r i n g t h i s s t a g e. V o l c a n i c s a re i n t e r c a l a t e d

w i t h i n s e v e r a l p a r t s o f t h e s u c c e s s i o n , p a r t i c u -

l a r ly t h e u p p e r p a r t o f th e s e q u e n c e .

I . B a h a r , t h e D i r e c t o r o f t h e G e o l o g i c a l R e s e a rc h a n d

D e v e l o p m e n t C e n tr e , B a n d u n g , I n d o n e s i a , i s g r a te -

fu l ly ackno wled ged fo r h i s he lp and ass i s tance in the

o rgan isa t ion o f th i s p ro jec t . F . Bann er and T. F inch

are tha nke d fo r the i r exce l len t b ios t ra t ig raph ic work .

D i s c u s si o n s c o n c e rn i n g th e g e o l o g y o f B o rn e o a n d

SE As ia wi th T. Barber , I . Car te r , M. Clu t son ,

T. Daley , T . Doo ley , T . Fraser , N. H al le , R . Hal l ,

C . H u t c h i s o n , K . G l a z e b ro o k , M . K e e p , K . M c C l a y ,

S . Mi l l s , D. Murphy and M. Wi l son a re a l l g ra te fu l ly

a c k n o w l e d g e d . F u n d i n g fo r t h i s p ro je c t c a m e f ro m t h e

S o u t h e a s t A s i a C o n s o r t i u m (A rc o , C a n a d i a n O x y ,

Ex x o n , LA S M O , M o b i l a n d U n i o n Te x a s) w h o a r e a ll

g r a te fu ll y a c k n o w l e d g e d . C R A L i m i t e d a r e t h a n k e d

al lowing access to the w ork p i t s a t the K el ian go ld

m i n e a n d p ro v i d i n g e x c e ll e n t f ie l d a c c o m m o d a t i o n .

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