Timing of Cenozoic Basin Formation in Northern Sundaland, Southeast Asia
Total Page:16
File Type:pdf, Size:1020Kb
MPG InternatwlUll Conference d R"CbiDilwn '94 AI/gilA 21-24, 1994, Kuala Lumpur, MalaYJia Timing of Cenozoic basin formation in northern Sundaland, Southeast Asia LIEW KIT KONG PETRONAS Research and Scientific Services Sdn. Bhd. Lot 1026, PKNS Industrial Estate Ulu Kelang, 54200 Kuala Lumpur Abstract: Continental wrench shear basins and back-arc basins are developed on the present stable northern Sundaland. Different basin geometries and structural patterns among Cenozoic basins in northern Sundaland indicate different origins and/or timing of basin formation. Wrench faulting has played a significant role in the formation of these Cenozoic basins. The collision of the Indian Subplate with the Eurasian Plate during early Cenozoic has caused a redistribution of stress within this region. Zones of weakness have been reactivated or created by these stress field changes, thus initiating the subsidence of these basins. The episodic initiation of Cenozoic basins may have begun as early as Jurassic and continued in Eocene-early Oligocene and Late Miocene. INTRODUCTION areas whereas those onshore have not been studied in-depth. Based on the sedimentation history, the Tjia (1991) defined Sundaland as a geological study area is divided into three areas: Strait of designation for a semi-cratonic region of the Malacca, Peninsular Malaysia and west-central southern South China Sea and the Java Sea. This Malay Basin. geological province includes the land areas of the Stratigraphic schemes (Fig. 2) utilised by the Thai-Malay Peninsula, a narrow strip of eastern operator in the Strait of Malacca are similar to Sumatra, the tin islands and a triangular patch of those of the North Sumatra Basin (for PM 1) and Borneo enclosing West Kalimantan and western the Central Sumatra Basin (for PM 15). It is most Sarawak (Fig. 1 insert). This area was believed that sedimentation within both blocks is cratonised in Late Triassic (Hutchison, 1989). In related to these greater basins. The Tertiary this paper, the study area of northern Sundaland basement is interpreted to be Upper Oligocene. extends from the Strait of Malacca in the west to Tertiary sedimentation in PM 1 (north western the hingeline of the Malay Basin in the east. The margin area) began in a terrestrial environment northern and southern boundaries of the study area with lacustrine to lagoonal rich shales (Bampo are near latitudes 7°N and 1°N respectively (Fig. formation). Holomarine to inner neritic conditions 1). (Belumai formation) were established during Lower Tertiary basins of different geometries and Miocene with carbonate reefs buildup on existing structural patterns have been mapped in this region. structural highs. Influx of coarse clastics in the Most of the Tertiary basins in the study area are middle Miocene marked the deposition of the Baong half grabens or small depressions aligned to major formation. The top of Baong formation is the Upper fault zones. The kinematics and timing of the . Miocene unconformity. Regional transgression has formation of these basins are relatively unknown. resulted in Post Baong sedimentation within a Hence, the purpose of this paper is to investigate shallow marine environment (Murray, 1991). the possible kinematics and timing of Cenozoic Within PM 15 grabens, three major stratigraphic basins formation within the study area in northern sequences are identified: (1) Early graben fill which Sundaland. comprises lacustrine sediments (Pematang equivalent) (2) middle to late graben fill of fluvio STRATIGRAPHY lacustrine deltaic sediments (Sihapas equivalent) and, (3) post graben fill (PetanilMinas equivalent) Cenozoic sedimentation of the basins/ with sediments of marine influence. They are depressions began from ?Jura-Cretac~ous to Upper separated by unconformities (Wong, 1990, 1991). Oligocene (Fig. 2). The stratigraphic schemes of The stratigraphic scheme of Tertiary basins on offshore basins in northern Sundaland are well Peninsular Malaysia has not been established. documented by oil companies operating in these These basins have been mapped by the Geological GeoL. Soc. MalaYJia, Bulletin 37, July 1995; pp. 231-251 232 lIEW KIT KONG STUDY AREA THAILAND / "- , ~ -'---- JOINT DEVELOPMENT AREA TN \ \ --- (INDONESIA) ~ .2!JGAPORE l' N Figure 1. Location of the study area. Inset is the area of Sundaland (Adapted from Tjia, 1991). Pre Cenozoic tectonics domains of Sundaland consists of Mergui Plate and Indosinia Block. WEST STRAIT OF MALACCA EAST PENINSULAR M.Y AGE MALAYSIA PM 1 PM 15 WEST-CENTRAL MALAY BASIN Sedlmen!ary Sedlmentary SedlmanIDry SeIsmic FormaUan Formalian SedIment8ty Envlrunmonts Environmento EnvIronman1a Sequence EnvIronmenta Pleistocene Coastal to Inner neritic Minas Shallow marine to Pliocene Equivalent Lower coastal plains Middla naritic Post Baong - 4 Holomarina Upper Petani -I Innar-neritic Equivalent 10 Lacustrine to m RED- ..•..• .. 't- .•.. •..•.. .., ..•..• Littoral CD Fluvio-Deltaic c Coastal to 3 Middle Baang 8 Inner neritic Sihapas ;C Coastal Piain !-GREEN _Local .2 Equivalant ::E 2C Holomarine 20 ;C r--YELLOW- .. ~ •..•..•.. '.1" ..•..• Lower Coastal Halomarine 2B Lower Beiumai Plain Innar neritic '--- ORANGE- Pematang .". e· .. -............ .......... Lacustrina ..•. ";10 •. .m. ? . Continantal at the baSE Equivalent 2A Bampo Upper Coastal Upper and marine towards CD - PURPLE- Plain c ~ the top en fa: 30 8 0 .91 Alluvial 5 Lower --I 1A Plain .. ··1······· .•. ";10 ..•..•. .. •.. •.. • '1' ..•..•..•. ?- ... ;C Pre-Oliogocene riflinfill 40 Tampur - (possibly Cretaceous) Eocene » r 50 Basement Uncertain Basement (Undifferentiated) (Undifferentiated) ..... 'i .......... ~ ...... ..... ~ .....•..... ·1··· ... Basement 60 Paleocene (Undifferentiated) Figure 2. Generalised stratigraphic schemes ofthe study area. Compiled from Murray (1991), Wong (1991), and Lasmo Oil (1990). 234 llEW KIT KONG Survey of Malaysia. These Tertiary deposits appear Bengkalis Trough related grabens include Johor to be fully continental; they show facies association Graben and Kukup Graben. These grabens are oflacustrine, paludal and fluvial origin. Geological situated about 60 km east of the N-S trending Survey of Malaysia (1985) interpreted these basins Bengkalis Trough. Both grabens are aligned in the as isolated continental basin deposits of Late NNE direction. Tjia (1988,1989a) suggested that Tertiary age (?Late Miocene). Recent study on the in late Cretaceous-early Tertiary time, the Tertiary palynomorphs of Batu Arang suggested Bengkalis segment of the Bentong-Bengkalis suture that the initiation of Batu Arang basin is probably experienced normal faulting that created the Eocene to Oligocene (Ahmad Munif, 1993). Stauffer depression. Lateral faulting occurred in the (1973) concluded that the nature of the continental Oligocene(?) and the Miocene. Pleistocene NW deposits suggested that each basin has a discrete striking reverse faults have superimposed upon sedimentation history. The rapid lateral wedging earlier trends. Wong (1990) believed that the Johor of the deposits, e.g. Batu Arang, indicated that Graben is genetically related to the Bengkalis local downwarp controlled deposition. Trough in Central Sumatra. This graben could A joint regional study by Petronas, Lasmo and have developed as a side graben of Bengkalis Carigali on the northwest Malay Basin has proposed Depression (Moulds, 1989). a new stratigraphic system for the area (Lasmo Oil, Pematang-Balam Trough related grabens are 1990). This system is based on seismic sequence Port Klang Graben, Angsa Graben and Sabak stratigraphy (Fig. 2). Seismic sequence 1 (Purple Graben. These grabens are situated north of the to Basement isochron: ?Lower Oligocene to Middle N-S trending Balam Trough and Pematang Trough Upper Oligocene) is divided into two parasequences and could be the northern ?extension of the Troughs. separated by a local angular unconformity. Kepulauan Aruah Nose is situated west of these Sediments of this sequence were laid down under grabens. These grabens are aligned in a NNW alluvial to upper coastal plain conditions. Seismic d.ITection. Port Klang Graben and Sabak Graben sequence 2 (Green to Purple isochron: mid Upper are northerly elongated grabens whilst Angsa Oligocene to lower Middle Miocene) is divided into Graben which is situated between these two grabens three subsequences: Subsequence 2A was deposited is oval in shape. under lower coastal plain conditions with alluvial Grabens located between the Asahan Arch and plain dominated by braided and meandering the Kepulauan Aruah Nose are Central Grabens, channels. Subsequence 2B indicated the onset of Southern Graben, Eastern Graben, West Penang coastal conditions and subsequence 2C recorded Graben, North Penang Graben and East Penang the onset of marine conditions. Seismic sequence 3 Graben. Collectively, these grabens are aligned in (Red to Green isochron: lower Middle Miocene to the NNE direction. Major bounding faults for these Upper Miocene) was deposited under predominantly grabens are situated on the western margin of these lower coastal plain conditions (low energy estuarine grabens (except Central Graben). conditions) with widespread coastal swamp Grabens that are situated north of the N-S dominated by mangrove and a network of low Tamiang and Yang Besar High are Northern sinuosity distributary channel. Coastal conditions Graben, MSS-XA Graben, Thai Border East and are prevalent at the base of Seismic sequence 4 Thai Border West. The Northern and MSS-XA (above Red horizon; ?Upper Miocene to present) Graben