Seismic sequence stratigraphy of the Tertiary sediments, offshore Sarawak deepwater area, Malaysia

Abdul Manaf Mohammad and Wong, Robert H. F. (1995) Seismic sequence stratigraphy of the Tertiary sediments, offshore Sarawak deepwater area, Malaysia. Bulletin of the Geological Society of Malaysia, 37. pp. 345-361. ISSN 2637-109X

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Abstract

A seismic sequence stratigraphic interpretation was carried out in the Sarawak deepwater area with the main objective of developing a workable chronostratigraphic chart that defines stratigraphic boundaries within which depositional systems and lithofacies can be identified, mapped and interpreted. The dataset includes 8,000 km of seismic lines and well data from four drilled locations. The study has resulted in the identification and correlation of eight seismic horizons representing the tops of eight depositional sequences which are grouped into four mega/supersequences (A, B, C and D) based on regional tectonic events of the South China Sea. Six of the seismic horizons have been tied to the four wells and dated based on paleontologic data. Two other older horizons are dated based on correlation to the global sea-level chart. Higher order sequences are also interpreted from paleontologic lithologic, paleofacies data and GR-Iogs from the four wells. Seismic facies analysis have also been carried out in the study area where four main seismic facies (Facies I-IV) ranging from non-marine to deepmarine facies are interpreted. Seismic facies maps constructed for lower and upper portions of Oligocene-Lower Miocene Supersequence C indicate that it contains all four main facies. This supersequence is overall transgressive and its paleoshoreline runs in a NW-SE direction. A seismic facies map generated for Middle Miocene-Recent Supersequence D suggests that it contains mainly outer shelf to deepmarine facies (Facies III-IV) and its paleoshoreline runs in an East-West direction. A workable chronostratigraphic chart has been developed where second to fourth-order sequences can be correlated within the study area. The chart is able to correlate the episodic rifting of Ru and Pigott (1986), the local structural history and Shell‘s sedimentary Cycles I-VIII (Ho, 1978) to the global sea-level curve (Haq et al., 1988). This study also assisted in identifying potential play-types. Structural traps of non-marine to shallow marine facies are mainly confined to Supersequence C while stratigraphic traps of basin floor fans are located mainly in Supersequence D.

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