Sequence stratigraphy of the Upper Miocene Stage IVC in the Labuan-Paisley Syncline, northwest Sabah Basin

Abstract

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 shelf-edges. 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.