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

ROBERTS, HARRY H., CSI, Louisiana State Univ., Baton Rouge, LA 70803; JOHAN SYDOW, BP Amoco, Houston, TX 77210-4587; JOHN ROBALIN, Marathon, Houston, TX 77056; RICHARD FILLON, 3730 Rue Nichole, New Orleans, LA 70131

Thousands of kilometers of high-resolution seismic data were 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 were 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 ka. Sequence architectures differ significantly, an important consequence of different depositional settings. The tropical Mahakam shelf is tectonically active with low wave energy, strong oceanic currents, upwelling, and a mixed siliciclastic-carbonate deposystem. 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 with low wave energy, but dominated by siliciclastic sedimentation. Falling-to-lowstand progradation of the Mobile River delta 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 migrated from east to west with eastern lobes showing evidence of wave reworking while the western flank was fluvially dominated. Both the Mahakam and Mobile deltas are composed of sand-rich clinoforms and channel deposits that possess excellent potential reservoir properties.

ROBERTS, HARRY H., JOHAN SYDOW, JOHN ROBALIN, and RICHARD FILLON

AAPG Search and Discovery Article #90908©2000 GCAGS, Houston, Texas