ABSTRACT: A Comparison of Two Late Pleistocene Shelf Edge Deltas (Indonesia and Gulf of Mexico)--Stratigraphic Architecture, Systems Tracts, Bounding Surfaces, and Reservoir Potential

Abstract

Abstract Thousands of kilometers of high-resolution seismic data have been collected over two late Pleistocene shelf-edge deltas in very different settings, the northern Gulf of Mexico and the eastern shelf of Borneo in Indonesia. Both deltas have been constructed by falling-to-lowstand deposition associated with the latest Pleistocene glacial maximum, the former by the temperate Mobile River, the latter by the equatorial Mahakam River. Four cores provide detailed stratigraphic control for the Mobile River delta while one long boring and numerous piston and vibracores provide stratigraphic control on the Mahakam delta. Systems tracts and key bounding surfaces have been related to the eustatic sea level curve in both settings over ca. 125 years. Sequence architectures differ significantly, an important consequence of different depositional settings. The tropical Mahakam shelf is tectonically active and has low wave energy, strong oceanic currents, upwelling, and a mixed siliciclastic - carbonate depositional system. The resulting falling-to-lowstand clinoforms downlap a highly irregular surface of isolated carbonate bioherms built above a transgressive surface that formed during the preceding sea level rise. The northeastern Gulf of Mexico is relatively stable, also has low wave energy, but is dominated by siliciclastic sedimentation. Falling-to-lowstand progradation of the Mobile River delta has occurred in numerous overlapping and spatially offset lobes incised by a complex channel network. Clinoforms downlap an isotope stage 5 interglacial condensed section. The Mobile depocenter has migrated from east to west; eastern lobes show evidence of wave reworking while the western flank is fluvially dominated. Both the Mahakam and Mobile deltas are composed of sand-rich clinoforms and channel deposits that possess excellent potential reservoir properties.