Structural patterns within the Tertiary basement of the Strait of Malacca

Transcription

1 Allllllal Gelgical Cnference '94 Jlllle Klli Terengganll Mali!fJUz Structural patterns within the Tertiary basement f the Strait f Malacca LEW KT KONG Petrnas Research & Scientific Services Sdn. Bhd. Lt 1026 PKNS ndustrial Estate Ulu Kelang Kuala Lumpur Abstract: The Tertiary basement f the Strait f Malacca (Malaysian waters) slpes gently twards suthwest. Nrtherly trending grabens have been mapped within the basement at discrete lcatins. These grabens frm suth t nrth are Kukup Graben Jhr Graben Prt Klang Graben Angsa Graben Sabak Graben Suthern Graben Central Graben Eastern Graben East Penang Graben West Penang Graben Nrth Penang Graben MSS-XA Graben and Nrthern Graben. The maximum depths f these grabens range frm 900 metres t 4000 metres. The Tertiary basement tpgraphy f sme grabens has been altered by structural mdificatin during?late Micene. These grabens can be gruped int (1) Bengkalis Trugh related grabens (2) Pematang-Balam Trugh related grabens (3) Asahan Arch-Kepulauan Aruah Nse related grabens and (4) Tamiang-Yang Besar High related grabens. These graben grupings are situated between reginal highs. These graben grupings are als elngated in nrtherly directin and may represent reginal fracture znes. The znes are initiated during Lwer Oligcene by right lateral shearing in the NW-SE directin. NTRODUCTON Reginal structures within Peninsular Malaysia and nrtheastern Sumatra trend nrtherly. Hwever the Malaysia/ndnesia (Sumatra) internatinal bundary which trends NW-SE has limited the knwledge f the extensin f these reginal structures. Structural cntinuity between these tw areas are ften extraplated. There are infrmatin gaps within the Strait f Malacca as published infrmatin abut the gelgy f the Strait is limited. This paper attempts t prvide sme infrmatin abut the Tertiary basement f the Strait fmalacca (Malaysian waters). The Tertiary basement referred in this study is the seismic basement r the ecnmic basement as seen in seismic sectins. The Strait f Malacca (Malaysian waters) has been demarcated as PM 1 and PM 15 explratin blcks by PETRONAS (Fig. 1). Sun Malaysia Petrleum Cmpany surveyed bth blcks and had relinquished bth blcks in Stratigraphic schemes (Fig. 2) utilised by the peratr are similar t thse f the Nrth Sumatra Basin (fr PM 1) and the Central Sumatra Basin (fr PM 15). t is believed that sedimentatin within bth blcks is related t these greater basins. The Tertiary basement (referred t the seismic basement) is interpreted t be the base f Upper Oligcene. Tertiary sedimentatin in PM 1 (nrth western margin area) began in a terrestrial envirnment with lacustrine t lagnal shales (Bamp frmatin). Hlmarine t inner neritic cnditin (Belumai frmatin) was established during Lwer Micene with carbnate reefs buildup n existing structural highs. nflux f carse clastics in the middle Micene marked the depsitin f the Bang frmatin. The tp fbang frmatin is the Upper Micene uncnfrmity. Reginal transgressin has resulted in Pst Bang sedimentatin within a shallw marine envirnment (Murray1991). Within PM 15 grabens three majr stratigraphic sequences are identified: (1) Early graben fill which cmprises lacustrine sediments (Pematang equivalent) (2) middle t late graben fill f fluvi-acustrine deltaic sediments (Sihapas equivalent) and (3) pst-graben fill (PetanilMinas equivalent) with sediments f marine influence. They are separated by uncnfrmities (Wng 1990). The bjective f this study is t determine the structural patterns within the Tertiary basement f the Strait f Malacca (Malaysian waters) and attempt t relate these patterns t reginal structures. T achieve these bjectives structural interpretatin is perfrmed n structural maps prduced by Sun Malaysia Petrleum C. These maps are scaled frm 1:50000 t 1: Gelgical reprts (in-huse unpublished and published) regarding this regin are als cmpiled. GeL. Sc. MaLaYJia BuLLetin 38 December 1995; pp

2 110 lew KT KONG REGONAL ELEMENTS Asahan Arch is a nrtherly trending reginal basement high that separates the Nrth Sumatra Basin frm the Central Sumatra Basin (see Fig. 1). This arch prbably extends t the west f Central Graben in PM 1. Based n sediment fill within the grabens Murray (1991) interpreted that grabens east f the Asahan Arch are assciated with th Central Sumatra Basin and thse west f the arc are assciated with the Nrth Sumatra Basin. n this paper grabens assciatin is based n Murray's (1991) criterin. Grabens r depressins west f the Asahan Arch verlie the Mergui Mircplate (see Pulunggn and Camern 1984). Mst f the area cnsists f THALAND STUDY AREA Kuala Terengganu PENNSULAR MALAYSA Kuimtan SUMATRA (NDONESA) Figure 1. General lcatin f the study area (PM 1 & PM 15). The area is within Malaysian waters f th e Strait f Malacca. Ce L. Sc. l11alaydia BuLLetin 58

3 STRUCTURAL PATERNS WTHN THE TERTARY BASEMENT OF THE STRAT OF MALACCA 111 shallw-depth pre-tertiary basement which slpes gently in suthwest directin. Thicker Tertiary sediments are lcated at the nrthwest margin f PM 1. ts nrth west margin area lies n the eastern shelfal (Malacca Platfrm) extensin f the Nrth Sumatra Basin (Fig. 3). Grabens east f the Asahan Arch are bunded by the Pre-Tertiary basement utcrpping nshre Peninsular Malaysia t the nrtheast and the Kuantan High t the suth east. Kepulauan Aruah Nse Sembilan High and Bengkalis Trugh are lcated n the suth west margin f these grabens (Fig. 4). Mst f this area als slpes gently in suthwest directin. PM1 PM15 M.Y AGE SedbnBlllary Sedbnentery Frmatin Envlrrunents frmatin Envirnments Pleistcene Castal t nner neritic Minas Shallw marine Plicene Equivalent t Lwer castal plains Pst Bang Middle neritic Upper nner neritic Petani Equivalent CD c 8 Middle Bang Castal t 0 nner neritic Sihapas :i Equivalent CD Lwer Upper Belumal Bamp Hlmarine nner neritic Cntinental at the base and marine twards thetp c CD ~ > 0 Lwer " " Pematang Equivalent Lacustrine t Ruvi-Deltaic Lacustrine 40 Tampur Ecene Uncertain Basement (Undifferentiated) 60 Palecene Basement. (Undifferentiated) Figure 2. Generalised stratigraphic schemes f PM 1 and PM 15 utilised by peratr. These schemes are similar t thse used in Nrth Sumatra Basin and Central Sumatra Basin respectively. Adapted frm Murray (1991) and Wng (1991). December 1995

4 112 liew KT KONG GRABENS ASSOCATED WTH NORTH SUMATRA BASN Davies (1984) described the Tertiary structural evlutin f the Nrth Sumatra Basin as a cnsequence f its psitin alng the trailing edge f the cunter-clckwise rtating "Sunda Mircplate". He elabrated that frm Ecene t Lwer Oligcene the Sunda Mircplate and the ndian-australia Plate cnverged at high acute angle. The cnvergence f these Plates has generated nrthward prpagating dextral verstepping wrench faults alng the western edge fthe cntinental mircplate. The cnfiguratin f the present Nrth Sumatra Basin was a cnsequence f the gemetrical inter-relatinship f these wrench fault systems. The grabens west f the Asahan Arch are n the eastern shelfal (Malacca Platfrm) extensin f the Nrth Sumatra Basin. These grabens lie in the nrthern part f the Strait f Malacca ffshre western Peninsular Malaysia. Gelgically they are situated n the nrtheast part f the Tampur Platfrm fthe Nrth Sumatra Basin. The nrtherly trending Tamiang High and Yang Besar High f the Tampur Platfrm extend int this grabenal area (see Fig. 3). Grabens in this area are generally nrtherly trending with the bunding fault t the east. The majr depcentre lies t the west in ndnesian waters and the grabens becme prgressivel shallwer twards the east (Murray 1991). Tw f the larger grabens are Nrthern and MSS-XA graben. Basement surface in this area inclines gently twards suthwest and faults trend NE-SW (Fig. 5). Acrss the internatinal brder twards Sumatra the basement surface becmes variable and basement highs are elngated in N-S r NNW SSE directin. NORTHERN GRABEN The NNE elngated Nrthern Graben i ~ situated near the western margin f PM 1 Blck and near the Malaysia/ndnesia internatinal bundary. Basement cntur deepens twards SW. 96' E 97' E Gl OJ 0- r ::>!!!.» ~ PM 1 5' N PASE SUB BASN 5 6 '1J 4' N ~ Right lateral mvement km 100 Figure 3. Tectnic elements f Nrth Sumatra Basin. Three main tectnic elements are Tampur Platfrm Pase Sub Basin and Sigli Platfrm. PM 1 is situated n the Malacca Shelf. Adapted frm Ssrmihardj (1988). Ce!. Sc. //i/alaylia BLLLetin 38

5 STRUCTURAL PATTERNS WTHN THE TERTARY BASEMENT OF THE STRAT OF MALACCA 113 Faults mapped in this graben trend nrth and NE and are intercnnected. Mst majr faults are lcated n the eastern flank f this graben. The size f this graben is estimated t be 20 km x 10 km. The maximum depth f this graben is 2400 metres (Fig. 6). Tw unnamed depressins have been mapped 90 km west fpulau Langkawi. These depressins are elngated in the nrth directin. Faults bunding these depressins are nrth and NE trending. Depressin c deepens eastward and depressin d deepens westward. The length f these grabens is abut 30 km (see Fig. 5). MSS-XA Graben This half graben is elngated in NNE directin with a majr fault demarcating its eastern margin. This NNE fault is 40 km lng. Basement deepens twards east. The maximum depth f this graben is 2600 metres (see Fig. 6). 4 N PM 15 PENNSULAR MALAYSA lid Kuala Lumpur PADANG ~ MAND~ SUBBASN Figure 4. Tectnic elements f Central Sumatra Basin. Nte the N-S and NW-SE rientatin f reginal Highs and Trughs. Kepulauan Aruah Nse is named as Perak Nse in Malaysian waters. Adapted frm BECEP (1985) in Greenway and Gh (1989). December 1995

6 114 lew KT KONG 9s E E PENNSULAR MALAYSA 6 N 6 N 4 N 4 N krn E NAME OF GRABEN a = NORTHERN b d = n name e 9 = NORTH PENANG h j = MSS-XA = CENTRAL = EASTPENANG = SOUTHERN c f = n name = WEST PENANG = EASTERN Figure 50 Nrtherly trending grabens in PM 1. Tamiang high and Yang besar High?extend int grabenal area Simplified frm graben summary map frm Dyer et al (1991) and Ssrmihardj (1988)0 Get Sc MataYJia Bulletin 38

7 STRUCTURAL PATERNS WTHN THE TERTARY BASEMENT OF THE STRAT OF MALACCA 115 n 20 CONTOUR NTERVAL' 0.2 SEC (lwt) NW ejf CARBONATE BULDUP SE NDONESA MALAYSA NORTHERN GRABEN POST-BAONG NOT TO SCALE (b) Figure 6. (a) nner Nrthern Graben with intercnnected N-S and NE-SW faults n the eastern flank. Extracted and simplified frm basement time structure map f Sun Malaysia Petrleum C. (1989). (b) Schematic crss sectin f Nrthern Graben. Majr faults are lcated at the eastern margin f the graben. Carbnate build-ups at lcal highs. Sectin simplified frm Sun Malaysia Petrleum C. (1989). December 1995

8 116 LEW KT KONG GRABENS ASSOCATED WTH CENTRAL SUMATRA BASN The Central Sumatra Basin is ne f a series f back arc basins develped linearly alng the leading edge f the Sunda Platfrm as a result f the subductin f the ndian Ocean Plate beneath the Sutheast Asian Plate. This basin was frmed during the east-west extensin in Late Cretaceus/ Early Tertiary (Dalyet al. 1987). The grabens east f the Asahan Arch are believed t be the nrth eastern extensins f the Central Sumatra Basin. These grabens lie in the suthern part fthe Strait fmalacca. They ccupy the nrth-eastern margin f the Central Sumatra Basin. Five main grabens (Central Sabak Angsa Prt Klang and J hr) are believed t be structurally and genetically similar t thse f Central Sumatra Basin. The structural styles within these grabens are characterised by Ecene t early Micene eastwest extensin related t rifting and graben frmatin fllwed by late Micene (r?pli Pleistcene) cmpressin and uplifting resulting in structural inversin change in basin depcentre and frmatin f structural traps. Wng (1990) suggested that this very active NE-SW cmpressin frmed mst fthe present day structures with fld axes generally paralleling the underlying NW-SE basement grain. The Jhr Graben appears t have undergne a relatively mre severe cmpressin phase during late Micene-Plicene time as indicated by intense faulting and uplift. CENTRAL GRABEN This graben is the largest mapped graben in PM 1. t is situated abut 80 km suthwest f Pulau Pinang. Gelgically it is lcated t the east f the intersectin fthe Malacca Platfrm and the Asahan Arch. The length f this graben is abut 60 km and the width is abut 20 km. Variable tpgraphy characterises the basement f Central Graben. Numerus depcentres within this graben are elngated NE-SW. Majr faults demarcating the limit f the graben are NE-SW trending whereas faults within the graben are nrth-suth trending. The deepest part f this graben is estimated t be ver 4000 metres. Basement surrunding this graben is abut 550 msec deep (Fig. 7a). Cmpressinal features such as flding f sedimentary sequences and?wrench-faulting have affected the basement and yunger sequences (Fig. 7b). These features indicated that basement tpgraphy has structural verprint. Structurally this graben can be divided int a number f sub-basins which have the appearance f full r half grabens. Murray (1991) interpreted that these features are frmed during a phase f extensin in the Oligcene with later structural mdificatin due t right lateral wrenching in the late Micene. A NNE half graben (Eastern Graben) is mapped 30 km east f Central Graben. A curvilinear NNE fault majr bunded the western margin f this graben. This fault is abut 35 km in length. The maximum depth f this graben is 970 metres. Basement slpes westward(see Fig. 5). Three grabens are mapped nrth f Central Graben; East Penang Graben Nrth Penang Graben and West Penang Graben. These grabens are prbably the nrthward extensin f the Central Graben. These grabens are situated abut 30 km west f Pulau Pinang. The maximum depths f these grabens are range frm 900 metres t 2800 metres. Basement f all these grabens slpes dwn westward with a majr fault demarcating its western margin. These curvilinear faults cntrl the size f these grabens and are parallel t the elngatin f the grabens. The length f these faults range frm 20 km t 55 km. East Penang Graben and Nrth Penang Graben are elngated in the NE directin whereas West Penang Graben is elngated in the nrth directin (see Fig. 5). SOUTHERN GRABEN This NE-SW elngated half graben is situated 90 km west f Pulau Pangkr. A majr SE dwnthrwing fault demarcates the western margin f this graben. This fault has a length f 50 km a maximum heave f 2.5 km and a vertical thrw f 800 msec. The graben deepens twards NW reaching a depth f mre than 2300 metres. The length f this graben is cntrlled by the majr fault and maximum width f this graben is 20 km. Faults parallel t the majr fault are fund within the graben (Fig. 7a). SABAK GRABEN This curvilinear N-S graben is situated 25 km suth f the Sg. Bernam muth. The Kepulauan Aruah Nse is lcated west f this graben. A majr fault is lcated n the western margin f this graben. The maximum depth f this graben is abut 2400 metre (Fig. 8). There are tw depcentres within this graben. They are separated by nrth trending faults. The suthern depcentre is elngated NNW and has been mapped seismically. This depcentre ccupies an area f 35 km x 15 km. The nrthern NNE trending depcentre has been defined by buguer gravity anmaly. This nrthern depcentre is estimated t be abut 1500 metres deep. Ce!. Sc. MalaYJitl l Bulletin 5S

9 STRUCTURAL PATERNS WTHN THE TERTARY BASEMENT OF THE STRAT OF MALACCA 117 H = High L= Lw High 5' N CENTRAL High High / km 10 (a) 99' 40' E ssw MNAS EQUVALENT NNE km NOT TO SCA::E BASEMENT CENTRAL GRABEN Decel/lber 1995 Figure 7. (a) Central and Suthern Graben. The basement f Central Graben has variable tpgraphy. NE-SW elngatin f numerus depcentres. Majr faults demarcating the limit f the graben are NE-SW trending. Faults within the graben are nrth-suth trending. Suthern Graben has a majr bunding fault n the western margin. Extracted and simplified frm basement time structure map f Sun Malaysia Petrleum C. (1989). (b) Simplified geseismic crss sectin f the suthern part f Central Graben. Basement tpgraphy is altered by later structural mdificatin. Simplified frm Dyer et al. (199 1).

10 118 LEW KT KONG Lw: '. \ \ \... 1 \ \ " " " -' PENNSULAR MALAYSA High SABAK GRABEN 3' 30' N CONTOUR NTERVAL = FT CONTOUR NTERVAL = MLLGAL (BOUGER GRAVTY ANOMALY) ANGSA GRABEN L=Lw 20 km Figure 8. Simplified basement utline fsabak Graben. The basement utline is curvilinear. The suthern part f the graben is defined by seismic whilst the nrthern part is defined by Bugeur gravity anmaly. The val Angsa Graben is suth fsabak Graben. Nte the difference in graben gemetry between these tw grabens. Extracted and simplified frm basement map f Wng (1990). Cel. Sc. MalaYdia Blllletin 38

11 STRUCTURAL PATTERNS WTHN THE TERTARY BASEMENT OF THE STRAT OF MALACCA 119 ANGSA GRABEN Angsa Graben is val in shape with a NNE trending fault bunding its western margin. This graben is situated between the Sabak Graben (see Fig. 8) and the Prt Klang Graben (see Fig. 9a). t is lcated 20 km west fpulau Ketam. Cnturs n western margin are aligned in NNE directin whereas cnturs n the eastern margin are cnvex twards ENE. This graben deepens twards west. The depth f the basement is estimated t be 3600 metres. Diameter f this graben is apprximately 25 km. Offshre gravity data indicate a pssible extensin f the Angsa Graben int the Angsa Bank area. Basement has tilted t the west after the depsitin f?petani Frmatin (Pli-Pleistcene) (Fig.9b). PORT KLANG GRABEN This NNW-SSE elngated graben is situated apprximately 25 km west f Bukit Jugra. The axis f this graben extended acrss the Malaysia! ndnesia internatinal bundary reaching a length f apprximately 80 km. The average width f this graben is 15 km. The NNW-SSE elngated depcentre is apprximately 3600 metres deep. N S faults have transected the depcentre f this graben. Nrmal faults have been mapped n the eastern and western flanks f the graben. The eastern flank f this graben is steeper than the western flank. Higher curvature is bserved n cnturs f the western flank f the graben. The higher linearity f the cntur n the eastern flank suggest that a majr fault has bunded the eastern margin f this graben and the graben deepens twards east (Fig. loa). Offshre gravity data suggest that the Prt Klang Graben may extend in nrtheast directin int the islands ffshre Kuala Selangr. Basement tpgraphy is altered by later structural events. Wrench faulting with flwer structure is bserved in this graben (Fig. lob). Separated by a N-S elngated basement high n the western margin f Prt Klang graben is a NNE-SSE riented depressin. This depressin is als bunded by a majr fault n the east margin. This depressin deepens twards east reaching a depth f 1700 msec. This depressin and Prt Klang graben culd be structurally related. These tw structural features are lcated n the eastern flank f Kepulauan Aruah Nse a reginal basement high (Fig. loa). JOHOR GRABEN The Jhr Graben is situated apprximately 20 km west f Pulau Pisang. This graben is elngated in NNE-SSW directin and is bunded by curvilinear faults which prgressively change nrthward frm NNE t N. The graben deepens twards ESE reaching a depth f 3300 metres (Fig. lla). Numerus curvilinear step faults have been mapped n the western bundary f this graben. Seismically this graben is apprximately 15 km wide alng its axis and 10 km wide acrss its bunding faults. Buguer gravity suggests that the depsitin area f this graben culd be extended landward int the Batu Pahat-Air Hitam area. On land the prbable extensin f the J hr Graben is elngated in NW SE directin and is parallel t the axis f the granite bdies in Jhr. Flwer structures and flded yunger sedimentary sequences within this graben indicate a structural verprint n the basement tpgraphy (Fig. llb). East f the Jhr Graben in the vicinity f Pulau Kukup Kukup Graben is mapped. This graben represents a N-S half graben with a majr fault n the eastern side f the graben. Gemetrically this graben culd be structurally related t the Jhr Graben (Fig. lla). DSCUSSON Based n the spatial relatinship between the grabens and reginal elements these grabens are gruped as fllw: (1) Bengkalis Trugh related grabens (2) Pematang-Balam Trugh related grabens (3) Asahan Arch-Kepulauan Aruah Nse related grabens and (4) Tamiang-Yang Besar High related grabens. Bengkalis Trugh related grabens include Jhr Graben and Kukup Graben. These grabens are situated abut 60 km east f the N-S trending Bengkalis Trugh. Bth grabens are aligned t the NNE directin (Fig. 12b). Tjia ( ) suggested that in late Cretaceus-early Tertiary time the Bengkalis segment f the Bentng Bengkalis suture experienced nrmal faulting that created the depressin. Lateral faulting ccurred in the Oligcene (?) and the Micene. Pleistcene NW striking reverse faults are superimpsed upn earlier trends. Wng (1990) believed that the Jhr Graben is genetically related t the Bengkalis Trugh in Central Sumatra. This graben culd have develped as a side graben f the Bengkalis Depressin (see Mulds 1989). Pematang-Balam Trugh related grabens are Prt Klang Graben Angsa Graben and Sabak Graben. These grabens are situated nrth f the N-S trending Balam Trugh and Pematang Trugh and culd be the nrthern extensin f the Trughs. Kepulauan Aruah Nse is situated west f these grabens. These grabens are aligned in NNW directin. Prt Klang Graben and Sabak Graben December 1995

12 120 lew KT KONG Cntur nterval = ft 101 E Cntur nterval = twt H = High km L= Lw 20 ANGSA 3 N \.: High / / - / \ \ \ \ '.. - '.. ~ '\ Figure 9. (a) Simplified basement utline f the val Angsa Graben. The steep cntur n the western margin suggest a majr bunding fault. Prt Klang Graben is suth f Angsa Graben. Nte the difference in graben gemetry between these tw grabens. Extracted and simplified frm basement map f Wng (1990). (b) Simplified geseismic crss sectin f the Angsa Graben. Basement tilted westward after depsitin f Petani Frmatin. Majr faults dip east with smaller antithetic faults dip west. Simplified frm Wng (1991). Ce!. S c. JilaLaYJla BuLLetin 38

13 STRUCTURAL PATERNS WTHN THE TERTARY BASEMENT OF THE STRAT OF MALACCA 121 J High < - J' / \ \ 1 / r" Lw... \ \ '\ H h g J /... / '... \ J \ " _ km '" \... \ \ _ 20 CONTOUR NTERVAL = FT CONTOUR NTERVAL = TWT H = High L = Lw. -- " ( -... \ \ \ (a) \. " "... \ " \ '... -" \ \ '": : -=- :.... \ \ '\... r' \ High '. \ " \ J ' " \ NW SE PLESTOCENE - RECENT PETAN MNAS EQUVALENT December 1995 Figure 10. (a) Simplified basement utline f Prt Klang Graben. The steep cntur n the eastern margin suggest a majr bunding fault. T the west is a similar elngated graben. Extracted and simplified frm basement map f Wng (1990). (b) Generalised crss sectin f Prt Klang Graben. Negative flwer structures and flded yunger sedimentary sequences indicated later structural verprint n the basement tpgraphy. Simplified frm Wng (1991).

14 122 lew KT KONG Batu Pahat 103 E \ \ ' '- 0 Air Hitam... \ \ \ \ \ Lw ' \ " \ \ J t - :"../..._-...:.' '"' ".."..' '' ' " \' ' "... \ \ \ \ J \ High \... \ \ \ km 20 CONTOUR NTERVAL = FT CONTOUR NTERVAL = MLLGAL (8uger Gravity Anmaly) H = High L = Lw 1 30' N OPulau Pisang (a) NW PETANl i MNAS EQUVALENT SE TELSA EQU VALENT BASEMENT JOHOR GRABEN NOT TO SCALE BASEMENT (b) Figure 11. (a) Simplified basement utline fjhr Graben. Graben may?extend nshre int the Batu Pahat-Air Hitam area. Extracted and simplified frm basement map f Wng (1990). (b) Simplified geseismic crss sectin fthe Jhr Graben. Basement slpes east. Flwer structures and flded yunger sedimentary sequences indicated mdificatin f basement tpgraphy by later structural event. Simplified frm Wng (1990). Ce!. Sc. l1a!ayjia BuLLetin 58

15 98'E 4'N 100' E SABAK GRABEN 102E PENNSULAR MALAYSA 4' N 6' N 4' N 1 :::r: : (9 ' - ::r: : 1 ~:. 1(9 :t:...- :~ : g: :. ::?! : fij' : ~ : i:5: :.'0: l : 1 '2: : /' : ~:.." 1. '0 1 1 '... 1 : ' ' '. ~ '. ~ \. :.. ~. ' 98' E SUMATRA ~... km 50. " : : : 1 ~ 'U :0:: :«:Z «~ ~ NAME OF GRABEN (a) 100' E :W : (fj :~4~N :~ «:0:: w :0.. 0' N SUMATRA PORT KLANG RABEN JOHOR GRABEN KUKUP GRABEN 2' N 0' N en -l :rj C -l C :rj :» r 'U :» :::j m :rj z en ::\! =i Z -l m -l m :rj -l l> :rj -< c :» en m ;:: m z -l. -l m en -l :rj :» =i. :s;: :» r; :» a = NORTHERN d N name b e 9 NORTH PENANG h j MSS-XA CENTRAL EAST PENANG SOUTHERN c = N name WESTPENANG EASTERN 100' E kin 50 Figure 12. (a) Lcatin f graben grupings with reginal elements Nte the rientatin f graben grupings with reginal elements Mdified frm Ssrmihardj (1988) and Dyer et al (1991) (b) Lcatin f graben grupings with reginal elements Nte the alignment f the Balam-Pematang Trugh related grabens with bth Trughs Jhr Graben and Kukup are east fthe Bengkalis Trugh Mdified frm Wng (1990)

16 124 lew KT KONG are nrtherly elngated grabens whilst Angsa Graben which is situated between these tw grabens is val in shape (Fig. 12b). Grabens lcated between the Asahan Arch and the Kepulauan Aruah Nse are Central Grabens Suthern Graben Eastern Graben West Penang Graben Nrth Penang Graben and East Penang Graben. Cllectively these grabens are aligned in NNE directin. Majr bunding faults fr these grabens (except Central Graben) are situated n the western margin f these grabens (Fig. 12a). Grabens that are situated nrth f the N-S Tamiang and Yang Besar highs are Nrthern Graben MSS-XA Graben tw unnamed depressins (c and d). The Nrthern Graben and MSS-XA Graben which are situated n the suthern part f this graben gruping are aligned in the NNE directin. Depressins c and d are aligned in the N S directin. There is n preferred slping directin f these grabens (Fig. 12a). These graben grupings represent N-S depressins between N-S reginal highs. The first three depressins are?extensins f the Trughs f the Central Sumatra Basin. Tamiang-Yang Besar High related grabens are prbably extensin f lws within the Tamiang-Yang Besar High. The average hrizntal spacing between these graben grupings is 150 km. f these graben grupings represent reginal fracture znes then they depict a left-stepping en echeln array. Right-lateral shearing in the NW -SE directin culd have initiated the E-W transtensinal f these grabens (Fig. 13). Alternatively these graben grupings culd represent transtensinal bends within majr pre-tertiary N-S reginal lineaments. The N-S lineaments culd have experienced lateral mvement during Tertiary times. f the frmatin f the first three graben grupings are assciated with the Central Sumatra basin then the earliest Cenzic structural develpment is the E-Oligcene rifting alng ld basement breaks fn-nne strike and reactivatin f WNW trending reginal basement arches (Heidrick and Aulia 1993). f the Tamiang-Yang Besar High related grabens are related t Nrth Sumatra Basin then these depressins were develped during the Late Oligcene thrugh Early Micene as tensinal hrst and graben structures frmed between reactivated dextral wrench faults (Davies 1984). Pre-Tertiary structures exerted strng influence n the develpment f Tertiary basins. Pre-Tertiary lineaments patterns f the Strait f Malacca (Malaysian waters) trend nrtherly whilst thse ffshre east cast Peninsular Malaysia trend NW SE (see Liew 1993). Therefre the structural develpment f Tertiary basins/depressins in the Malay Basin and the Strait f Malacca depended n different kinematics. Tertiary depressins/grabens in Strait f Malacca are frmed alng?pre-tertiary?reactivated znes f weakness. The Strait f Malacca regin culd be a structural buffer zne between Peninsular Malaysia and Sumatra. t is pstulated that the scattered Tertiary basins nshre the west cast f the Peninsular Malaysia were prduced by late Tertiary structural adjustments mainly invlving. faulting. These basins are?aligned with the majr faults (Gbbett 1973; Stauffer 1973). ffrmatin f the depressins in these tw areas are gelgically related then age f the Tertiary basins nshre wuld nt be lder than that f the Central Graben r the Prt Klang Graben. Furthermre it can be inferred that sme f majr lineaments n Peninsular Malaysia have experienced mvement during Tertiary. CONCLUSONS Mst f the pre-tertiary basement in the Strait f Malacca (Malaysian waters) slpes gently in suthwest directin. Grabens/depressins are mapped within the basement at discrete lcatins.. These grabens/depressins may represent reginal fracture znes. All grabens are elngated in the nrtherly directin. Mst f the grabens have majr bunding faults n their western margin. The maximum depth f the grabens range frm 900 metres t 4000 metres. The Central Graben is the deepest graben. Basement tpgraphy f sme grabens has been altered by structural mdificatin during?late Micene. Flwer structures flded yunger sedimentary sequences and tilting f yunger sedimentary sequences are evidences f this structural verprint. These grabens can be gruped int (1) Bengkalis. Trugh related grabens (2) Pematang-Balam Trugh related grabens (3) Asahan Arch Kepulauan Aruah Nse related grabens and (41 Tamiang-Yang Besar High related grabens. These graben grupings are als elngated in the nrtherly directin. They represent reginal left-stepping fractures with an average hrizntal separatin f 150 km. These graben grupings are situated between reginal highs. These grabens were initiated during Lwer Oligcene by right lateral shearing in the NW-SE directin (Fig. 13). ACKNOWLEDGEMENT The authr expresses his gratitude t the managements f PETRONAS and PETRONAS Research & Scientific Services Sdn Bhd fr their Cel. Sc. MalaYJia Bulletin 58

17 STRUCTURAL PATERNS WTHN THE TERTARY BASEMENT OF THE STRAT OF MALACCA 125 Apprximate lcatin f THALAND (1) Bengkalis Trugh related grabens (2) Pematang-Balam related grabens (3) Asahan Arch-Kepulauan Aruah Nse related grabens (4) Tamiang-Yang Besar High related grabens PM1 PENNSULAR MALAYSA Kuantan Figure 13. Summary map f graben grupings and its reginal interpretatin. SNGAPORE DecemDer 1995

18 126 lew KT KONG permissin t publish this paper. This paper is part fprss Prject N. 123/92 "Tectnic Evlutin and Hydrcarbn Prspectivity f the Malay and Penyu Basins" which is funded by Petrleum Research Fund. The unpublished infrmatin quted in this paper is btained frm E&P Divisin PETRONAS. Sincere appreciatin is extended t Dr. H.D. Tjia fr prviding his cnstructive cmments and advice. REFERENCES DALY M.C. HPER B.G.D. AND SMTH D.G Tertiary plate tectnic and basin evlutin in ndnesia. Prceedings PA 10th Annual Cnventin DYER J. FNLAY A. MHO. GHAZAU AND WONG D Reprt n the gephysical and gelgical re-evaluatin f cntract area PM 1 Malacca Straits Malaysia. Sun Malaysia Petrleum C. (unpublished). DAVES P.R Tertiary structural evlutin and related hydrcarbn ccurrences Nrth Sumatra Basin. Prceedings 13th Ann. Cnv. ndnesian Petrleum Assciatin GOBBETT D.J ntrductin. n: Gbbett D.J. and Hutchisn C.S. (Eds.) Chapter 1 Gelgy f the Malay Peninsula West Malaysia and Singapre. New Yrk Wiley nterscience GREENAWAY P. AND GOH KT Preliminary gescience reprt cntract area Blck PM-15 Malaysia. Sun Malaysia Petrleum C. (unpublished). HEDRCK T.L. AND AUUA K A structural and tectnic mdel f the castal plains blck Central Sumatra Basin ndnesia. Prceedings 22nd Ann. Cnv. ndnesian Petrleum Assciatin LEw KK Strucfural develpment f the west-central margin f the Malay Basin. PETRONAS Research & Scientific Services Prject 123/92 Reprt N. RPS MOULDS P.J Develpment f the Bengkalis Depressin Central Sumatra and its subsequent defrmatin - A mdel fr ther Sumatran Grabens? Prceedings 18th Ann. Cnv. ndnesian Petrleum Assciatin MURRAY c Review f the prspectivity f Blck PM- 1 Straits f Malacca Malaysia. Sun Malaysia Petrleum C. (unpublished). PULUNGGONO A. AND CAMERON N.R Sumatran Mircplates their characteristics and their rle in the evlutin f the Central and Suth Sumatra Basins. Prceedings 13th Ann. Cnv. ndnesian Petrleum Assciatin SsROMHARDJO S.P.c Structural analysis f the Nrth Sumatra Basin - with emphasis n synthetic aperture radar data. Prceedings 17th Ann. Cnv. ndnesian Petrleum Assciatin ~.~.-~ Manuscript received 22 Octber 1994 STAUFFER P.H Cenzic. n: Gbbett D.J. and Hutchisn C.S. (Eds.) Chapter 6 Gelgy f the Malay Peninsula West Malaysia and Singapre. New Yrk Wiley nterscience SUN MALAYSA PETROLEUM C Preliminary evaluatin reprt: gephysics and structural gelgy. N.W. detail area. PM-. Sun Malaysia Petrleum C. (unpublished). TJA H.D Tectnic histry f the Bentng-Bengkalis Suture. Gelgical Sciety f Malaysia Petrleum Gelgy Seminar Abstracts f Papers. Warta Gelgi 14(6) TJA H.D Tectnic histry f the Bentng-Bengkalis Suture. Gel. ndn. 12(1) WONG Hydrcarbn ptential f PM-15 grabens (verview). Sun Malaysia Petrleum C. (unpublished). WONG D Review f the prspectivity f PSC blck PM-S (Pst Prt Klang-) Strait f Malacca. Sun Malaysia Petrleum C. (unpublished). Gel. Sc. MalaYJia Bulletin 38