Geometry, Scale and Distribution of Shelf-Edge Collapse Features and Their Control of Deepwater Sedimentation, Offshore NW Sabah, Borneo, Malaysia
Azli Abu Bakar1, Christopher A. Jackson2, and Howard D. Johnson2
1Basin Analysis, Petronas Carigali Sdn Bhd, Kuala Lumpur City Centre, Malaysia
2Earth Science & Engineering, Imperial College, London, United Kingdom
Exploration offshore NW Sabah, Malaysia, is currently focused on slope-to-basin floor sands, which are interpreted to be derived from slumping of the shelf-edge and cannibalisation of sand-rich, shelf-edge deltas. In this study, 3D seismic and well data are utilised to understand the linkage between shelf-edge collapse and deposition of sands downdip. The study interval is Late Miocene age and consists of two prograding slope complexes: SDC1, which prograded towards the W, and SDC2, which prograded towards the NW. Both slope complexes are expressed seismically as ca. 800 m high, low-angle clinoforms. Seismic data indicates that during progradation of SDC1 the shelf-edge periodically collapsed in response to tectonic uplift of NW Borneo. Shelf-edge collapse resulted in the formation of large (2 km wide by 500 m deep), arcuate scars which can be mapped for 20 km along-strike of the shelf-edge. Further downdip, on the clinoform toesets, fan-shaped amplitude anomalies are observed which correlate to thin (ca. 10 m) sandy turbidites identified in wells. Large-scale shelf-edge collapse is not stratigraphically restricted to SDC1, but also occurred in the overlying SDC2 slope complex which downlaps onto the underlying, slump-scarred slope complex. Seismic isochron maps and the distribution of slump scars in both slope complexes indicate that neither system was affected by gravity-driven growth faults present elsewhere within the area and which developed later during the Pliocene. This study demonstrates that shelf-edge collapse was probably a key control on sediment supply to the slope and basin floor, offshore NW Borneo. Crucially, although present exploration is focused on Pliocene reservoirs, the development of shelf-edge collapse features in Late Miocene slope complexes suggests that deeper exploration potential may exist in this interval further downdip to the NW.
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