Role of pre-Tertiary fractures in formation and development of the Malay and Penyu basins

Abstract

Major faults in Sundaland trend NNW to NW, WNW, N and E. Some of the NNW to NW and N-striking faults across Mesozoic areas of the Malay Peninsula were active until mid-Eocene time. Small, fault-bounded Tertiary basins onshore may be pull-apart basins associated with such faults. Mainly from seismic data, NNW to NW, N and E-striking faults have been recognized in the pre-Tertiary basement of the Malay and Penyu basins off the east coast of the peninsula. These faults were reactivated before the Late Oligocene and during the Middle to Late Miocene. N-striking faults in pre-Tertiary areas are common throughout Sundaland. In the field, these faults are found to be the oldest (possibly Jurassic) regional fractures. The regional NNW-NW and WNW fractures are believed to have originated as strike-slip faults when the peninsula was subjected to late Mesozoic deformation. The onshore E-W faults were probably extensional fractures that developed as secondary structures associated with sinistral slip motions along NNW-NW faults. Upper Cretaceous dolerite dykes fill some of the E-W fractures. NWstriking basement faults of the Malay basin continue onshore SE Asia as the Three Pagodas fault zone. Initially these were sinistral basement wrench faults creating secondary E-W extensional fractures. In the Middle to Late Miocene the regional stress field changed, resulting in reversal of slip movement along major wrench faults and structural inversion of the sedimentary basins. This inversion is manifested as E-W anticlines located over half-graben. In the Penyu basin similarly striking half-graben probably developed in the same fashion. There, the NW-striking Rumbia fault divides the basin into two parts. Half-graben in the western part remained orientated E-W, but those in the eastern part became rotated clockwise by continued left-lateral slip along the Rumbia fault. After the Miocene the two basins continued to subside, developing an almost undisturbed blanket of post-Miocene sediments. Locally, residual stress caused some of the structures to grow.

Petroleum systems of the Malay Basin Province, Malaysia

“…Left-lateral shear during the late Eocene to Oligocene formed pull-apart basins and half grabens into which thick sedimentary sequences were deposited (Ngah andothers 1996, andTjia andLiew, 1996). Expulsion of portions of continental Southeast Asia resulted from collision between the India plate and the Eurasia plate in the midEocene (Tjia, 1994, andNgah andothers, 1996).…”

“…Expulsion of portions of continental Southeast Asia resulted from collision between the India plate and the Eurasia plate in the midEocene (Tjia, 1994, andNgah andothers, 1996). This expulsion produced left-lateral shear on a southeastern extension of the Three Pagoda fault zone in the Malay Basin (a major fault system onshore Thailand) (Tjia, 1994;Ngah and others, 1996;Mazlan B. Hj.…”

“…3) (Ngah andothers, 1996, McCaffrey andothers, 1998). Marine influences in the basin began during deposition of the I Group ( Fig.…”

“…The overlying J Group reservoirs consist of fluvial and shoreline deposited sandstones of early Miocene age (Nik Ramli, 1986;Ngah, andothers, 1996, Tjia andLiew, 1996;Tjia 1994). The J sandstone studied by Nik Ramli (1986) Ramli, 1986;Ngah, 1996).…”

Kinematics and Timing of Brittle-Ductile Shearing of Mylonites along the Bok Bak Fault, Peninsular Malaysia

“…Thermochronological analysis of granitic rocks of the Malay Peninsula shows several periods of exhumation, during Late Cretaceous to early Paleogene and Eocene 45,47 . The Late Eocene to Oligocene rapid exhumation coincides with significant subsidence in offshore areas 47 , during the time when sinistral transtensional movement along pre-existing NW-SE fault zones formed the Tertiary offshore and onshore basins [51][52][53] . From this study, it is shown that the Bok Bak fault underwent an early brittle-ductile dextral strike-slip, possibly initiated as early as Late Jurassic, with the fault undergoing cooling during Early Cretaceous.…”