Latest Quaternary Baram Prodelta, Northwestern Borneo
Richard N. Hiscott, 2003. "Latest Quaternary Baram Prodelta, Northwestern Borneo", Tropical Deltas of Southeast Asia—Sedimentology, Stratigraphy, and Petroleum Geology, F. Hasan Sidi, Dag Nummedal, Patrice Imbert, Herman Darman, Henry W. Posamentier
Download citation file:
The Quaternary Baram Delta is more than 1 km thick on the outer continental shelf of Brunei, and includes mud-prone highstand delta lobes, sand-prone lowstand shelf-edge deltas, incised-valley fills, and transgressive sheet-like deposits lying on wave-cut ravinement surfaces. The shelf break is defined by a prominent fault scarp ∼ 130 m below sea level. Beyond, the seabed descends at an average of 2– 3° to the Borneo Trough at depths exceeding 2750 m. Uppermost Quaternary units thicken by a factor of 2–5 across en echelon shelf-edge growth faults, then progressively thin seaward as an extensive prodelta wedge that drapes irregular slope morphology. The slope owes its rugged relief to gravity-driven growth faulting, mud diapirism, cutting of submarine canyons, sediment sliding, and construction of levees alongside sporadically active turbidity-current channels that head in the region of shelf-edge deltas. During highstands, muddy lobes of the Baram Delta repeatedly extended to the upper slope as a consequence of high sediment yields and narrow shelf width. During the last lowstand, the Baram River cut an incised valley across the narrow shelf so that its muddy sediment load largely bypassed the continental margin through a major canyon. Delta deposits in the canyon head collapsed to generate a debris-flow complex that buries much of the canyon floor and that extends over large areas of the lower slope and Borneo Trough. This paper demonstrates that thick, extensive prodelta muds and associated turbidites can blanket basin slopes even during highstands in areas with high sediment supply and narrow shelves. Conversely, during lowstands, the suspended load of deltas can largely bypass the continental margin through incised valleys and canyons, resulting in reduced sedimentation on basin slopes.
Figures & Tables
It is the objective of this volume to bring to the fore a category of deltas with which many sedimentologists and stratigraphers are, at best, vaguely familiar. It is expected that this volume also will stimulate new research on tropical deltas by highlighting how their facies and stratigraphic architectures differ from mid- and high-latitude ones, by emphasizing their significance to the global sediment budget, and by stressing their uniqueness within a petroleum systems framework. This special publication emphasizes the need for models intrinsic to tropical deltas of Southeast Asia to supplement the more conventional general models currently in vogue, based on past studies of large and small mid-latitude deltas. The papers in this book explore how the combination of these complex factors has shaped deltas in this region. Sedimentological surprises such as distributary channels floored by thick accumulations of fluid mud lend a bit of “mystery” to tropical deltas. We hope that, rather than being merely a summary of tropical deltas, this book may open the door to a new and active phase of sedimentological and stratigraphic research in tropical environments across the globe.