Lowstand Deltas and a Basin-Floor Fan, Pleistocene, Offshore East Kalimantan, Indonesia
Arthur H. Sailer, Jesse T. Noah, Rhys Schneider, Alif Prama Ruzuar, 2013. "Lowstand Deltas and a Basin-Floor Fan, Pleistocene, Offshore East Kalimantan, Indonesia", Shelf Margin Deltas and Linked Down Slope Petroleum Systems–Global Significance and Future Exploration Potential, Harry H. Roberts, Norman C. Rosen, Richard H. Fillon, John B. Anderson
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The upper Pleistocene north of the Mahakam delta, offshore East Kalimantan has been studied from the inner shelf to basin floor, using 3D seismic data. Three cycles deposited between ~18 and ~370 ka are defined on the shelf by progradational packages separated by parallel reflectors with carbonate buildups. The prograding packages were apparently deposited during highstands and gradually falling eustatic sea level. Parallel reflectors and carbonate buildups are interpreted as transgressive deposits. During the lowest of the three cycles (~270-370 ka), a lowstand delta has prograded over the underlying shelf margin, and sand-rich sediment has spilled downslope, feeding a slope-channel complex and basin-floor fan. This slope-channel complex has: (1) a lower part consisting of an incised channel filled with high-amplitude reflectors that are inferred to be sand-rich, and (2) an upper part dominated by a low-amplitude channel-levee complex inferred to be shale-rich. The slope-channel complex passes downdip into a basin-floor fan. The basin-floor fan contains a lower part, which contains high-amplitude, continuous reflectors (interpreted as sand-rich fan lobes), and an upper part that represents an aggrading channel-levee complex. These levees also are inferred to be shale-dominated, whereas some channel-fills are apparently sand-rich. The channel-levee complex has prograded over the lower fan and fed additional unconfined high-amplitude (sand-rich?) lobes.
These Pleistocene cycles are significantly different from sequences and systems tracts defined in the late 1980s. Lowstand systems tracts can not be identified by onlap of the slope. Rather, lowstand strata on the slope and basin floor are generally parallel reflectors that have local variations caused by channels and fans. Lowstand strata extend down the slope from distal clinoforms of the prograding lowstand delta, and hence cannot be consistently separated from prograding highstand and falling stage systems tracts. Cycles are best separated at the tops of prograding packages (transgressive surfaces).