Geol. Soc. Malaysia, Bulletin 22, December 1988; pp. 153-187

Stratigraphy and Palaeofacies Development of Carigali's Operating Areas in the Malay Basin,

South China Sea

MD NAZRI RAMLI

Exploration Division PETRONAS Carigali

Kuala Lumpur, Malaysia

Abstract: CARIGALI had recently undertaken a regional stratigraphic review with the aim of establishing a coherent stratigraphic scheme for correlation within and across Blocks PM 6 and PM 12 which are situated 120 km apart in the Malay Basin. Results of this study had led to the formulation of a time-stratigraphic framework for regional geological studies and seismic mapping over these two areas. This has significantly contributed to a better understanding of these parts of the Malay Basin.

The oldest sediments in these areas were deposited during Oligocene times in upper coastal plain environment and later in lower coastal plain environment. The Early Miocene section is basically com­posed of coastal fluviomarine sediments in PM 12 and lower coastal plain sediments in PM 6. Middle to Late Miocene sediments were predominantly laid down in coastal fluviomarine environment while those of Pliocene to Recent in holomarine environment.

INTRODUCTION

The Malay Bas~n is situated offshore east coast Peninsular Malaysia and is closely associated with the Thai Basin in the north and Penyu Basin and West Natuna Basin in the south (Figure 1). It is bounded ~t the north-eastern flanks by the Khorat Swell and Tenggol Arch respectively. PETRONAS Carigali's main operating areas in this basin are Blocks PM 6 and PM 12 (Figure 2). These blocks are parts of larger areas previously held by Esso Pro­duction Malaysia Incorporated (EPMI) and Continental Oil Company (CONOCO).

This paper is an attempt to introduce CARl GALl's present stratigraphic scheme (Samad & Nazri, 1985) which has provided the means of establishing a time-stratigraphic framework for regional evaluations within and across Block PM 6 and PM 12. It will also discuss the stratigraphy and palaeofacies development of these two areas which should provide some insight of the sedimentation history of these areas of the Malay Basin.

STRATIGRAPHIC SCHEME

When CARIGALI acquired Blocks PM 6 and PM 12, it adopted, out of operational convenience, EPMI's seismostratigraphic scheme for PM 6 and CONOCO's lithostrsatigra­phic scheme for PM 12 (Figures 3 and 4). Due to their obvious differences in nomenclature and application, CARIGALI had experienced difficulties in conducting regional correlation between PM 6 and PM 12 areas which are located 120 km apart. This had hampered the understanding of the sedimentary history of these two areas due to the inavailability of a coherent stratigraphic scheme. To resolve this problem, CARIGALI undertook a regional stratigraphic review of these two areas in two phases. The first phase was to carry out a bi-

Presented at GSM Petroleum Geology Seminar 1986.

·10•N

PENINSULAR MALAYSIA

104• E 108• E

INDO - CHINA

KHORAT SWELL

108• E 110• E

BASIN SETTING DEPTH IN METRES

112• E'

SOUTH CHINA

SARAWAK BASIN

Figure 1: Sedimentary basin setting map of South China Sea. The Malay Basin can be seen to be closely associated with the Thai Basin in the north and Penyu Basin and West Natul!a Basin to the south.

DEVELOPMENT OF CARIGALr's OPERATING AREAs

104°00'E 106°00'E 108°00'E

LEGEND:

-2. 0- TWT In sec .

...-.-..... Fault. a•oo'

-··- International boundary. N'

KHORAT SWELL

LOCATION MAP

WEST NATUNA

BASIN

40 • 80 120 160 zoo Km.

SCALE

155

Figure 2: Location map of CARIGALI's main operating areas i.e. Blocks PM 6 and PM 12 in the Malay Basin. It can be observed that Block PM 12 covers 3 major geological provinces, namely; Malay Basin, Tenggol Arch and Penyu Basin.

ostratigraphic re-evaluation of thirteen key wells from these areas (Figure 5) in order to provide good age controls and better definition of depositional environments. The second was to integrate these data with wireline log data and seismic in an attempt to formulate a time-stratigraphic framework for regional correlation within and across the two areas.

The first phase of the study has resulted in more consistent biostratigraphic zonations (Figure 6); the most notable being the Cicatricosisporites palynomorph zonation and Spenolithus heteromorphus (NN5) and Helicosphaera ampliaperta (NN4) nannofossil zo­nation. The former has provided the means of distinguishing the Oligocene-Miocene bound­ary and the latter the Early and Middle Miocene boundary. Another important result of this study is in the recognition of well defined depositional environment subdivisions (eg. Figure 7) which were based on florf» ooli faunal assemblages and wireline log shapes and patterns. The terminology used for desP.rtbiJlg the various depositional environments is shown in the environment of deposition sch~mt.' (figure 8).

The second phase of the study has given rise to the recognition of two sets of stratigraphic markers, ie. IIUUine transgressive pulses and regional shales (eg. Figure 9). These markers

156 MD NAZRI RAMLI

GP EUSTATIC CYCLES AGE MY

A PLIEIS

B PLIO 5 .· D w

t-E <( _. 10 F c w - z H ::& w

0 15 I 0

> -_. :E a: 20 <(

J UJ

K _. 25

L Q·. UJ -:E z 30 w

0 ~ 0 a: £! 35 <( _.

M UJ 0

SEISMO STRATIGRAPHIC SCHEME (AFTER EPMI)

Figure 3: EPMI's seismostratigraphic scheme used previously in Block PM 6. The Tertiary sequence, in this scheme, is subdivided into 11 seismic groups.

DEVELOPMENT OF CARIGALI's OPERATING AREAs·

LITHOSTRATIGRAPHIC SCHEME (MODIFIED AFTER CONOCO)

. .. ··-·· .

EPOCH FORMATION MEMBER .. .. ... .. ·- .. . .

QUATERNARY PI LONG

·-··-.

PLIOCENE ···-.

EARLY TO MIDDLE UPPER

MIOCENE "iflllll!!"!"! ---...- -. SAND COAL

LOWER

TERENGGANU EARLY SHALE

MIOCENE

UPPER

. -· ....

TAPIS MIDDLE

~--- ~---~ LOWER

EARLY .. ..

MIOCENE UPPER

TO SO TONG

OLIGOCENE LOWER

MESOZOIC

Figure 4; CONOCO's lithostratigraphic scheme adopted for Block PM 12 previously. In this scheme, The Tertiary sequence is subdivided into 5 lithological formations.

157

158

N

30'

30'

30'

DUNG UN

TANJUNG BERHALA

104°00'(

0 DULANG

RESAK 0

BERANANG 0

MD NAZRI RAMI..I

30' 30'

!BLOCK PM12J I / lou<?oNG /

r-------..L-------:0:----' 0

SOTONGO 0

ANDING 0 BARAT

MALONGO

KEMP AS 0

DUYONG / BARAT

I I

. I

~--------------------------~~ /

\ I

I I

I

SCIILE I 0 :"0 «t~n"

1!!!1 !!!!!l;;;;;;;;;e!!t.' -;;;;a;;;j

Figure 5: Location map of key wells identified for the biostratigraphic re-evalution exercise.

DEVELOPMENT OF CARioALI's OPERATING AREAs

BIOSTRATIGRAPHIC ZONATION co!Z _,

uc - ll:z ~ ~0

159

EPOCH

II:W ceo ww >II: zA. ow --=

~!~ z!z

PALYNOLOGICAL ZONATION

~fl ::EW

ID

c 0 _, N A.O ... ZONE SUBZONE

' PLEISTOCENE N22-23 NN21-19

1.6 ---------PLIOCENE _N~0-2.~ NN18-16

_!:1 .!_9.::. 'U_ ~ NN 12---1·-5.t---;l----t _pACRYDIIl~(

w z w 0 0

w z w 0 0 Cl ...I 0

NOTE:

w t­< ...J

5.2

r-- 11.3 w ...I c c :::E

r-- 16.5

> ...I a: < w

w t­< ...I

24

r-- 32 > ...I a: < w

37

---~ z en w Ci5

NN11

----

< z 6 w Ocn < z w ;:) w 1- 0..

tic ~

FLORSCHUET­ZIA M ERI DIONALIS

-NN5·---- -+-------1

NN4 FLORSCHUET­ZIA

1----~ LEVIPOLI

F_SEMIL DBATA l'li,llo.6 r!'!~OL

CICATRICOSIS PORITES

__ 1[ __ _ __ ""!:' __ _ __ ..... __ _

c ------d t------- ------

CYCLOPHORUS

PRE-TERTIARY BASEMENT

a- CICATRICOSIS PORITES c- CELPHALOMAPPA

b- C. V ANRAADSHOVENI c- SCOLOCY AMUS

Figure 6: Biostratigraphic zonations recognised from the biostratigraphic re-evalution exercise.

160

DEPOSITIONAL ENVIRONMENT SUBDIVISIONS OF THE TERTIARY SEQUENCE

LEGEND jucpj UPPER COASTAL PLAIN

jLcP!l.OWER COASTAL PLAIN

jcoFj COASTAL FI.,UVIOMAAINE

IF'"' FLUVIOMAR!NE INNER NERmC

IHINI HOLOMARINE INNER NERI11C

(;=~ REGIONAL SHAI,..E

Figure 7: Depositional Cl\Vironments recognised within the Tertiary sequence of a cypical well section in Block PM 1~. It can be ~n that the sedimentary sequence in this area is overall transgressive in nature.

DEvELOPMENT OF CARIGALI's OPERATING AREAs 161

ENVIRONMENT OF DEPOSITION SCHEME

LEGEND

MFi.i UPPER COASTAL PLAIN (··."·) LOWER COASTAL PLAIN IZ:!] COASTAL FLUVIOMARINE E:-;-'1 COASTAL

.. J::!::J FLUVIOMARINE INNER NERITIC f:::-:-:3 HOLOMARINE INNER NERITIC

I§M FLUVIOMARINE MIDDLE NERITIC f·:-:-,g HOLOMARINE MIDDLE NERITIC

Figure 8: Environment of deposition scheme as used for an open marine setting. The direction ofJI!arine invasion is indicated by the solid arrow while the ttansition zone between holomarine and fluviomarine environments is shown by the jagged line.

162 MD NAZRI RAMLI

RECOGNITION OF MARINE TRANSGRESSIVE PULSES AND REGIONAL SHALES .

LEGEND lucPI UPPER COASTAL PLAIN

ILcPI LOWER COASTAL PLAIN

lcoFI COASTAL FLUVIOMARIN.E

LCP

IFtNI FLUVIOMARIN.E INNER NERITIC

IHtNI HOLOMARINE INNER NERITIC ~ REGIONAL ~ MARINE TRANSGR. ~SHALE \ PULSE

Figure 9: Marine transgressive pulses and regional shales identified from the integration of biostratigraphic, wireline log and sedimentological data.

DEVELOPMENT OF CARioAU's OPERATING AREAs 163

have been found to be useful in defining time-stratigraphic boundaries since they are dated by biostratigraphic means and supported by seismic correlation. Henceforth, based on the occurrence of these stratigraphic markers, eight stratigraphic units have been recognised in the Tertiary sedimentary sequence of Block PM 6 and PM 12 (Figure 10). Examples of how these markers are being used to define stratigraphic unit boundaries are shown in figures 11 and 12.

In summary, tops of Tertiary I and II are defined by tops of regional shales, ie. Shale 'A' and Shale 'B' respectively while those of Tertiary m to IV by both regional shales and marine transgressive pulses (eg. Figure 13). The top of Tertiary VII though not identified by a transgressive pulse or shale marker is however distinguished by the onset of holomarine sedimentation occuring around the closing phase of Late Miocene times in these areas.

STRATIGRAPHY AND PALAEOFACIES DEVELOPMENT

The establishment of this coherent stratigraphic scheme and the resultant time-stratigra­phic framework (Figure 14) created the avenue for regional correlation and seismic mapping within and across Blocks PM 6 and PM 12 (Figures 15a, 15b, 16a & 16b). The most significant contribution made by this stratigraphic scheme is the provision of a framework for the integration of geological, geophysical and geochemical data for regional evaluations.

Among the most important conclusion deljved from these regional evaluation is that a relationship exists between environment of deposition and the distribution of reservoir and source rocks. The best reservoirs are observed to occur in the coastal environments and to a . lesser degree in lower coastal plain environment (refer Figure 8). However, good quality source rocks are found to be concentrated in lower coastal plain environment and to a certain extent in coastal fluviomarine environment. Palaeofacies maps constructed can therefore now be used for the prediction of source rock and reservoir rock distribution in these areas.

TERTIARY I AND II (OLIGOCENE AND OLDER?)

The progressive collision of the Indian subcontinent with the Eurasian Plate (Figure 17) during early Tertiary times (Eocene or older?) had resulted in the interior fracturing of the Sundalandmass where Thai, Malay, Penyu and WestNatuna basins now lie (Hamilton, 1979 and Tapponier et al, 1982). This was later followed by block faulting and subsequent subsidence of the Malay Basin during Early Oligocene times (Figure 18). This early period of extensional tectonics in the basin had given rise to the formation of a series of grabens/half­garbens and horst blocks where in certain areas formed large scale depressions providing the physiographic lows for lake development.

Based on detailed palynofacies and sedimentological data, three major depositional environment subdivisions ie. lake, lakeshore and lacustrine plain are envisaged for the lacustrine sediments of Tertiary Unit I and II (Figure 19). During Tertiary I and II times tlie Dulang and south ofDuyong areas were part of a lake while the rest of PM 6 and PM 12 areas were dominantly in lakeshore or shallower part of these lakes (Figures 20 and 21). During these times, Tenggol Arch Province was an area of erosion and/or non-deposition until Late Tertiary II times (Late Oligocene - Early Moicene) when a major portion of it was overstepped by lakeshore and lacustrine plain sediments. ·

164 MD NAZRI RAMLI

CAAIGALI'S STRATIGRAPHIC SCHEME FOR HYDROCAhBON EXPLORATION ... MALAY BASIN

. . .. ..

IIIIi: '"" :0:

~=:0: 1110

== ::>tiz .. Ill :o:wo 2!'ie PALYNOLOGICAL .. t; .. ... o~;:: TERTIARY f:POCH :.:"' .. i;c ""'"" .. ZONATiON uo•

~a~ STRATIGRAPHIC TRANSGRESSION Olll = :0: !i'""S UNit 32 j<fi 1!!0 .. tC:o: miU •2 u~~; if;! = . ZONE SUBZONE ... PUISTO- N22·23

NN2i·

I CENE 19

1.8 1---NNlf VIII I

PLIOCf:NE N20·21 I r--~ 16 I Nl9·?18 NNl2"= :1 PA~fb@M .. 8.2 r--- _~...§_ t: Ill llOLO-

R .. M~I\~NE .. Ill :0: II; Ill Iii

= HN11 = ~ vu -II

u = 'i'Ol'VI ..:I ~ .. BHAi.i -~- ...

INTRA .. Ill UTi f-- 11.3 ~~~~ loiiOCINl

rail N .. VI UNCOHf 101 .. '""

= ... < ..:I ::> ~ Q

u Q :a .. 0 - ~ e - * f-'- ill Ill :P.

NN!I ~ !i! v lBl.l 1-- 16.f r--NN4

Fi.ORSC• I t:OP IVB HUiTZIA

IVII!I SJiAU

II>< r--- LEVI POLl ..:1 lV 1111 F.IIMILOUT ~

".LiiATf~ioL. IVA INTRA IV 101 SHALE -.-- -·

=c~ U_l_ ~llA~E '()' ... 24 CICATRICOBIS 0

~------ SHAi.i:'B' PORITES il

.. --· n·

roi E-o -···

toll < CYCLOPHOBUII

IIHAU'A'

• ..:I

114 u 0 ....... ., ·-·· -t-··-?7 ell 1- 32 ...

~/ I ..:I 0 II><

..:I

lA 1111 ~ 101

137 -.- .. .. PRE ... _T)ilRTlABY .. IAB.IJ.IIll'fT. -

NOTE: a- cicatricoalaporites b- c.vanraadashoveni c- cephalomapPa d- acolocyamus

Figure 10: CARIGALI's sttatigraphic scheme now used for hydrocarbon exploration in Blocks PM 6 and PM 12. The subdivisions of each stratigraphic unit are based on the recognition of regional shales 1111.11/ormarine transgressive pulses and supported by seismic correlation. ·

DEVELOPMENT OF CARIGAu's OPERATING AREAs

TOP OF A STRATIGRAPHIC UNIT AS DEFINED BY A SHALE .

AG! PALYNOLOGICAL STRATIGRAPHIC ~-.--+----r-=Z~O~N~A~T~IO~N~-=-~- TOP

ZONE SUBZONE

~ t: a: 0 ~ 0 u a: ... c ... f w ~--~--------

~ > ~

ITOOm

iLl _. CICATRICOSISPOhi'I'ES < (,) a:: ~ IF.I00111~ 0 c - w ::&

iLl z iLl w u ... 0 oil(

" .... -... 0

(I) w ... a: 0 D. 0 ; 0 u ~ ... C( u -u

C. VANRA~DSHOVI:NI

CEPHALOMAPPA

SCOLOCYAMOS

.. 1-'-'--~--1-------

1900m

~ z iLl

COF

LCP

Figure 11: Example of a top of stratigraphic unit as defined by a regional shale. The top of Tertiary Unit n is defined by the top of regional shales which falls within the Cephalomappa subzone.

165

166

AGE

IU z > IU ... u 1111:

0 oc( - ·IU ::&

IU z IU Ill u ... 0 oc(

" ... ... 0

TOP o·F A STRATIGRAPHIC UNIT AS DEFINED BY A TRANSGRESSIVE PULSE

..: ~ TRANSGRESSION IU .....,.. __

COF

--------

---------(/) IU C. VANRAADSHOVENI ...

·1111: --------0 G. (/) -(/)

0 u CEPHALOMAPPA -1111: ... oc( u -u -------

SCOLOCYAMUS

---------

GAMMA NEUTRON RAY POROSITY

Figure 12: Example of a top of stratigraphic unit as defined by marine transgressive pulse. The top of Tertiary Unit m is defined by a transgressive pulse and also by the top of a regional shale.

LEGEND

DEVELOPMENT OF CARioALI's OPERATING AREAs·

STRATIGRAPHIC SUBDIVISIONS OF THE TERTIARY SEQUENCE

HIN

COF

FIN~

jucPj UPPER COASTAL PLAIN IFINI FLUVIOMARINE INNER NERITIC

(HINj HOLOMARINE INNER NERITIC.

167

(LcPJ LOWER COASTAL PLAIN

(coFJ COASTAL FLUVIOMARINE ~ REGIO~AL ~ MARINE TRANSGR. ~SHALE ~ PULSE

Figure 13: Stratigraphic subdivisions of the Tertiary sedimentary sequence of a typical well section in Block PM 12. Observe the top of Tertiary Unit VII, in the absence of a marine transgressive pulse and regional shale, is distinguished by the on set of holomarine sedimentation in this area.

168

TIME ... STRATIGRAPHIC CORRELATION IN CARIGALI'S OPERATING ARSAS

EPOCH

Pi.IEilt.

PLIO • ....____......,..... ....... -....~ ....•

IIi

• Iii

u 0

Ill .. c ..i

CD f'"-'-'"" U ... .... ... ... Ill:

'1'1UtTIARY ILOCK PM11

StRAtiGRAPHIC 8.._'tONG. 1 M.A. LONG./ UNIT b YO . .., "' · U Nu ANDING kEMPAt

VIII

VII

IVB IV

IVA .UJ

II

0.. c Iii 11 ...... 17

BLOCk

PM8

P it E "' 0 L I G 0 C E N E 8 A S IE M E N .t

Figure 14i 'tlnie sttatigraphic correlation between southem Malay Basin lilld Tenggol Arch areas ofBiock PM 12 and Biack PM 6. The hatched section at Middie Miocene titnes in Block PM 12 represents the non-deposition and/or erosion period due to Late Miocene tectonics.

:A A' STRATIGRAPHIC CO.R.RELATION

:MERANTI SF-H.~ A·LONG •D.EPOSITlO.NAL STRIKE

0 J

BERANAitG ·&f-18.1

.t.11DING BARA:r SG-11.~ SOTOftG SG-5.1 SOTONG 86 fO ·MALONG 'SG-117 .• 1

l 0 0

I

~'"' 0

UNIT VIII P.h ll . # . ~ ..

I I ; lo• - I r I r I UNIT.~ n ·INTRA I LATE MIOCECE It UNCONFORMITY I

UNatv I .' DATUM: TOP OF UNIT IV . I ' .

I ' I ..... I I I. .2· I, ' . ' '·" UNITIV , ~~

- · 1 r ,,. ~ SHALE 'C' , "~ ~ . · I - ---~ ;...:-:-:-:-~:~ 2 '

\. -2 --- -:- SH .----.:-2 -----~ ·--------'------- I!Iff:--..- ·, - -- - -\. 11ALE""T _ ,_-.:--- _ -------_-_..,, _ _ _ _ , -- -- _______ ~--

~ ~"""~··· - r . . - . I [ r, ! I ~ • \,.,__ . ~ • . li lNTII I~ I I ~ ,. ~--~ ~- ~ . I 3• ' . ·- . /1 ' --~ - -- . . .

. [\ Q/- \ r·o-o·o.cv/ .-.... ~~ '"-•if --.·.:----.:or;-- : ir----j . ~ : ~- ."---!!..--- ··- DEPTHS IN THOUSAND ME:rRES

N•u

Figure :J.Sa: Sttatigrapbic correlation along depositional strike from Block PM 12 to Block PM 6. Note the thickness variation of Tertiary I and n sediments being confonnable to the basement topography.

8 STRATIGRAPHIC CORRELATION ALONG DEPOSITIONAL DIP B' MALONG SG-17 .1 ANDING BARAT SG-11.1

•o.. •

~ UN~

I INTRA DATUM: TOP OF UNIT IV

,.

•0111•&

.~:~ ........ .

. ~ ... , .. ... '·"~·

I

I I \

L UNIT IV

DUYONG SH-2.1 DUYONG &H-32.1

01 I 10

I

?J

..........., ......

DEPTHS IN THOUSAND METRES

Figure 15b: Stratigraphic correlation along depo~itional dip within Block PM 12. Note the thickening of regional shales 'A' and 'B' and also the thinning of units V and VI in Duyong area.

S?

., 0 z

H !: w :I ;::

SOD

SEISMIC CORRELATION OF TERTIARY STRATIGRAPHIC UNITS

ANDING - FERI AREA 600 •oo

·.··-·-~~

200

r:'~£~~~~~!~~~:1!·::; v

~ I: m z

! c "'

Figure-168: Seismic correlation of Tertiary stratigraphic. units in Anding-Feri area of Block PM 12. The shallow basement area to the west is the Tenggol Arch Province .

-

s•

5?

.. Q z 0

~ :! Ill ::E ;::

DUYONG BARAT 1

SEISMIC CORRELATION OF TERTIARY STRATIGRAPHIC UNITS

DUYONG AREA

Figure l6b: Seismic correlation ofTertiary stratigraphic units in Duyong area of Block PM 12.

vm

::1 s: m z

I 0 (II

5?

•

DEvtn.oPMBNT OF CARIGALI1S OPERATING· AREAs 173

INDIA - ASIA COLLISION TECTONICS

Figure 171 Schematic map of India-Asia collision tectonics which triggered the fonnation of the Malay Basin. The white IU'l'l)\\islndicate major block motions with respect to Siberia while the black arrows shows the direction of extrusion·Nlated extension.

Tertiary I sediments which represent the basal part of the Tertiary sedimentary sequence lie unconformably on the pre-Tertiary basement and their thickness variation most probably reflects to a certain degree the pre-Tertiary basement topography (Figure 1Sa). Tertiary n sequence together with Tertiary I formed the initial basin fill which by the end of Tertiary n times had completely infilled the topography of the basin in PM 6 and PM 12 areas.

Tertiary t sequence as well as Tertiary n is composed of a lower sand-prone unit and an

WEST EAST

• EXTENSION • TENGGOL ARCH TENGGOL FAULT SOUTHERN PART OF MALAY BASIN

STABLE BLOCK

STRUCTURAL HISTORY - EARLY OLIGOCENE

Figure 18: East-west structural reconstruction during Early Oligocene times showing'the fonnation of half-grabens and horst blocks (after Ng. T. S., 1985)

LAK

DEPOSITIONAL SCHEME FOR UNITS I AND II (LACUSTRINE SETTING)

Figure 19: Environment of deposition scheme used for a lacustrine setting. The best reservoir rocks are found to occur in lakeshore environment. Good quality source rocks are observed to be dominant in lake environment and to a lesser degree in lacustrine plain environment.

176 MDNAZJURA.Mu

PALAEOFACIES OF TERTIARY UNIT I --- - ·---··- -- - .

liclt.Lt: 0 i!O ~ . ~?r!'ttttf

Figure 20: Paleofacies map of Tertiary Units 1 (early to middle Late Oligocene). 2 major blkes were developed in the major depocentre areas aroun4 Dulang and south of Duyong. Note the abse~ of Tertlary I seditnents In Tenggol Arch area.

3Q'

PALAEOFACIES OF TERTIARY UNIT II •Q••co·c

I I I f I I

I I

/ //

I I

I /

aos•Qo'£

1n

30'

Figure 2l: Palaoofacies map of Tertiary Unit ii (Late Oligocene to early Early Miocene}. O~orve the 2 major lakes still prevailing during this time while ~akeshore and lacustrine plain sediments have now covenld the Tonggol Mhatea.

178 MD NAZRI RAMu

upper shale unit (Figure 13). This cyclic pattern of sand and shale sedimentation signifies the interplay between sediment supply, basin subsidence and rise or fall in lake-water level. At this point of time there is very little evidence to suggest which of these processes dominated during the various phases of sedimentation. It is however believed that basin subsidence due to the sediment loading coupled by the continued encroachment of the South China sea due to sea floor spreading during these times could well be the major factors behind the cyclic sedimentation pattern observed in these Units.

TERTIARY ill AND IV (EARLY MIOCENE)

The continued opening of the South China Sea had caused a more pronounced marine influence in the PM 6 and PM 12 area during Tertiary m times. Because of this, a different set of depositional environment scheme is being used to cater for depositional environments of a marine setting during Tertiary m times and younger (refer Figure 8). Coastal fluviomar­ine conditions were established in PM 12 area while in PM 6 area located more distal to the marine incursion, sediments were still being iaid down in lower coastal plain environment (Figure 22). This sequence is also characterised by a lower sand-prone unit and an upper shale unit (Figure 13).

No significant change in depositional environments could be detected duriDg Tertiary IV times when compared to Tertiary m (Figures 23 and 24). However due to an obvious depletion of coarse clastic inputs and combined with the continued encroachment of the_ ancestral South China Sea, a substantial decrease in sand percentages can be observed throughout the entire sequence of Tertiary IV in both PM 6 and PM 12 areas (Figure 13).

TERTIARY V AND VI (MIDDLE MIOCENE TO EARLY LATE MIOCENE)

Towards the end of Tertiary VI times, massive regional uplift, compressive folding and faulting occurred in the PM 12 area. Fonner depocentre areas began to show positive growth and the initiation of this pervasive structuring seemed to have progressed northwesterly from one anticlinal trend to another (Ng, 1985) (Figure 25). This tectonic activity could have started as early as Tertiary m times in Block PM 12 area which could have therefore undergone maximum uplift when compared to areas north of it.

The uplift and subsequent erosion produced a striking regional unconformity in PM 12 which has been dated as an intra Late Miocene event (Late Tertiary VI times). In this area, · a major section of Tertiary V and VI was truncated due to this event. In the Duyong area, truncation of Tertiary V and VI sediments was followed by a period of non-deposition. This unconformity becomes less pronounced towards the northwest of PM 12 and finiilly disap­pears in PM 6 (Figure 15~).

By Tertiary V times, coastal fluviomarine conditions were established in Block PM 6 while fluviomarine inner neritic influence had progressed further north of Block PM 12 due to the continued advancement of the ancestral South China sea (Figure 26). However during Tertiary VI times, the coastal fluviomarine and fluviomarine inner neritic influences we~ reduced. This can be attributed to prograding coastline into a transgressive sea occurring during these times (Figure 27). ·

"00 N

30'

30'

DEVELOPMENT OF CARIGALI'S OPERATING AREAS

PALAEOFACIES OF TERTIARY UNIT Ill JO' 30'

' ' ,, MER"NTI

(.>

LOWER COASTAL PLAIN

DULANG c

RESAK

\ \

\ \

BERANANG

\ \ \

UPPER \ COASTAL \ ?PLAIN \

~\ \ ~·, \

I I I

I I

I /

AN!ll"'(' 0 BAIIAf

MALOtlG 0

/ / LOWER COASTAL PLAIN I

/ I

I I

\

\ UPPER \\ COASTAL PLAIN

\ \

\

'\.

' ' '-,

0 20 40km. ~~

......

179

Figure :Z:Z: Palaeofacies map of Tertiary Unit m (early Early Miocene). During this time, the first major marine influence was felt in Block PM 12 while Block PM 6 was marginally affected.

180

II

30'

MD NAZRI RAMu

PALAEOFACIES OF TERTIARY UNIT IV A

MERANTI 0

50'

LOWER COASTAL PLAIN

RESAK

DULANG r.

'\ • ... '\

' ' BERANANG

' '\ ' ' \ \

\ \ I I I I

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I I I I I I I

I I

'I I

/

I I

(

LOWER COASTAL PLAIN

PLUVIoMARINE 1 INNER N~RITICj

I

:::.'\/ ,.

~.~~' Ill f,'j"

,11 SCA~l.: • 0 20 4(1 .....

~I

Figure 23: Palaeofacies map of Terdary Unit IV A (middle Early Miocene), Depositional env~ents during this time remained similar to those in Tertiary m.

30'

\ \

\ \

DEVELOPMENT OF CARIOAL!'S OPERATING AREAS

PALAEOFACIES OF TERTIARY UNIT IV B

\ \

MERANT1 Q

RIISAI< Q

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\ \ \ \

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I

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181

Ftgure %41 Pl\laeofacies mpP ofTeniary Unit IVB (middle to bite Early Mi(K:ene). Note the enoroachmenl of the QOIISW fluviomarine bt;Jt row!lfds PM 6 area.

WEST

• EXTENSION •

STRUCTURAL HISTORY - LATE MIOCENE (REGIONAL UNCF.)

EAST

• COMPRESSION •

v TO Ill

TOP II

TOP I

Figure 25: East-west structural reconstruction during Late Miocene times indicating pervasive structuring in Duyong area (after Ng. T. S., 1985).

II

30'

DEVELOPMENT OF CARioALI's OPERATING AREAs

PALAEOFACIES OF TERTIARY UNIT V 30' 30' 10,0 00'[ 30'

_,.,..----------- LOWER COASTAL PLAIN

/ --1 -, \ COASTAL FLUVIOMARINE ..............................

\ ' \ DULANG '--

MERANTI 0 ,o

' ' AESAK ' 'J ,,

'o BERANANG

\ LOWER COASTAL PLAIN \

\ \

183

Figure 26: Palaeofacies map of Tertiary Unit V (early middle Miocene).Observe the fluviomarine influence stretching over PM 6 area.

184

PALAEOFACIES OF TERTIARY UNIT VI . 30' 50' 10°

' II

..... ''\ UPP!i:R COASTAl.

------- ' n~ ~ ~ ..... _ / ........... -

/ ...... ---...... f "",, L.OWE;R COASTAl. I ............... Pl,AIN \ OU~ANG "

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COASTAL \ LOWER COAST A~\ PI.AlN I PI.AlN

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\

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o eo «~""'· ........

Figure i7: Palaeofacies map of Tertiary Unit VI (middle to early Late Miocene), Note the sUsJlt retnmt of the fluviomarino belt south-eastwards.

II

ao·

DBVBLOl'MBNT OF CA1UoALt's Ol'ERATINo AREAs

PALAEOFACIES OF TERTIARY UNIT VII 30' JO' oos•oo'£ JO'

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,//

1 I \ II - ! I \

•i!.I<TA... I \ • j \

ISS

li'lgure 281 Palaeotlll:les map of 'tertiary Unit vn (tniddle Late Miocene). The coastal fluviomarine belt has now lt'llt\SCendl!d ovet the entire basin.

186 MD NAZRI RAMI..I

PALAEOFACIES OF TERTIARY UNIT Vlll 30' 104.00'£ )0' IO~·OO'E 30'

~

DULANG

MERANTI 0 0

RESAK 0

30' !)

BERANANG HOLOMARINE INNER NERITIC

I', / '\ \ I

5~0C \ OUYONG

DUYONG I 1- \ BARAT

Li 0 0

\ SO TONG I ·' \ 0 ;· \

ANOING 0 \ BARAT 0 ANDING // COASTAL/ COASTAL 0 FERI

FLUVIOI MALONGO I

I

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i.A.'<T#.H11 ( I

l

Figure 2.9: Palaeofac1es map ofTenary Umt vm. By this time, the entire basm has been covered predommantly by holomarine inner neritic sediments.

DEVELOPMENT OF CAIUGALI'S OPERATING AREAS 187

TERTIARY VII AND VIII (MIDDLE LATE MIOCENE TO RECENT)

Sedimentation within coastal fluviomarine environment continued to dominate during· Tertiary VII times in both PM 6 and PM 12 areas with the exception of the Duyong area where fluviomarine inner neritic sediments prevailed (Figure 28). Finally in Tertiary VIII times the entire Malay Basin was predominantly covered by holomarine inner neritic sediments until the present time (Figure 29).

CONCLUSION

The establishment of the eight stratigraphic units in the Oligocene to Recent sedimentary sequence has provided a practical stratigraphic scheme for regional geological correlation and seismic mapping. The present stratigraphic framework has also facilitated the integration of geological, geophysical and geochemical data for regional evaluations and has signifi­cantly contributed to a better understanding of the sedimentary history of PM 6 and PM 12 areas in the Malay Basin.

ACKNOWLEDGEMENT

The author expresses his gratitude to PETRONAS for their kind permission to present and publish this paper. Appreciation is accorded to Mr Tony Lim, the manager of the Exploration Division, PETRONAS Carigali for this paper. The paper has evolved to its present form through careful reviews by the management and staff of Geology Department, especially the manager Mr Abu Samad Nordin. Special thank is due to Mr Ho Kiam Fui, a consultant to the Division, for providing valuable comments and advice. Acknowledgement is also extended to Mr Raja Azmir Shah for draughting the text figures and Ms Siti Aisah for typing the text.

REFERENCES

Abu Samad Nordin and Md Nazri Ramli, 1985. Stratigraphic Scheme for Hydrocarbon Exploration in Carigali's Operating Areas, Offshore Peninsular Malaysia. GSM, Petroleum Geology Seminar 1985.

Hamilton W., 1979. Tectonics of The Indonesian Region. Geol. Survey Prof. Paper 1078, U.S. Govt Printing Office, Washington.

Ng Tong San, 1985. Trap Styles of The Tenggol Arch and the Southern Part of the Malay Basin. GSM Petroleum Geology Seminar 1985 (absctract). Also Bull. Geol. Soc. Malaysia No. 21, p 177-193, 1987.

Tapponier P., Peltzer G., Le Dain A.Y., Armijo R. and Cobbold P. Propagating Extrusion Tectonics in Asia: New Insights from Simple Experiments with Plasticine. Geology 10, p 611-616.

Taylor B. and Hayes D.E., 1982. Origin and History of South China Sea Basin. Am. Geophy U., Monograph 23, p 23-56.

White J.M. Jr and Wing R.S.,1978. Structural Development of The South China Sea with Particular Reference to Indonesia./PA, Proceedings of Seventh Annual Convention, p 159-172.

Manuscript received 12 October 1987.