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A sequence stratigraphic study was performed in the southern offshore Sandakan Basin with the aim of deriving a workable chronostratigraphic scheme and identifying plays, including stratigraphic traps. The data set includes 1800 km of high quality 1990 seismic and 8 wells. The study area can be divided into a structurally complex landward northern province and a relatively undisturbed basinward southern province. Three chronostratigraphic units were identified, each bounded by Type 1 third-order sequence boundaries. Each unit consists ofthird to fourth-order sequences which can be correlated from landward coastal plain facies to basinward bathyal facies. Unit 1 (Middle Miocene-early Upper Miocene) is characterised by moderate progradation, moderate aggradation; Unit 2 (middle Upper Miocene) by high progradation, low aggradation; and Unit 3 Oate Upper Miocene-Pliocene) by high aggradation, low progradation.. The positions of the prominent shelf edges in Unit 1, Unit 2 and lower Unit 3 indicate a southeastward progradation from Middle to Upper Miocene. Pliocene progradation was probably eastwards as suggested by N-S growth faults in the northeastern part of the study area, and is interpreted to have occurred within a ramp setting, as prominent shelf edges are lacking. The study led to the recognition of two play-types in the southern province, both associated with lowstand systems tract sediments. The fIrst is a slope fan play in Unit 1. The second is a basin floor fan play in Unit 2. Comparison of the locally derived onlap chart and the global onlap chart of Haq et al. (1987) highlighted some differences. The main difference is major Upper Miocene progradation in the study area versus Upper Miocene aggradation in the global chart, testifying to the importance of the interplay of local tectonics and sedimentation in the Sandakan Basin.

A sequence stratigraphic study of the Upper Miocene Stage IVe has been carried out in the Labuan-Paisley Syncline, Northwest Sabah Basin with the aim of identifying new hydrocarbon plays in the study area. The Stage IVe contains up to 4,000 m thick, clastic sediments deposited in coastal plain to bathyal environments probably between 8.2 Ma and 10.5 Ma indicating an immense sedimentation rate of approximately 1,700 metreslMa. The top and base of the Stage IVe are marked by the Shallow Regional and Upper Intermediate Unconformities respectively which are pronounced tectonic boundaries in the NW Sabah Basin. The overall regressive Stage IVe sediments are characterised by oblique to shingled progradation towards the westerly-northwesterly directions as suggested by the mapping of the pronounced shelfedges. A generalised third-order sequence witlUn the Stage IVe includes very thin transgressive systems tract and very thick highstand and lowstand systems tracts. A Type-I, third order sequence boundary separates the Stage IVe into two third-order sequences. This sequence boundary is evidenced by the occurrence of a major erosional slump scar at the western part of the syncline. The depositional model derived from this study includes thick shelf sands and basin floor/submarine fans interspersed by thinner sands of the levee-channel complexes at the shelf slopes."The Intra Stage IVe sequence boundary is thought likely to be caused by the fall in sea-level probably between 8.5 Ma and 9.0 Ma. This fall in.sea-Ievel is not represented in the global sea-level chart of Haq et al. (1987), suggesting that this fall in sea-level could be small and localised but it is evident in a basin with large sediment supply.This sequence stratigraphic study has resulted in the identification of various hydrocarbon plays. They comprise basin floor/submarine fans, slope fan/levee channel complex and shelf-edge/slump scar plays. The 'basin floor /submarine fan play is considered the highest ranked but requires additional seismic coverage for detailed mapping.

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) lunging 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 ofRu and Pigott (1986), the local structural history and Shell's sedimentary Cycles I-VIII (Ho, 1978) to the global sealevel 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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