Quaternary Sedimentation in the Molengraaff Paleo-Delta, Northern Sunda Shelf (Southern South China Sea)
How Kin Wong, Thomas Lüdmann, Christiane Haft, Alke-Marit Paulsen, Christian Hübscher, Jianhua Geng, 2003. "Quaternary Sedimentation in the Molengraaff Paleo-Delta, Northern Sunda Shelf (Southern South China Sea)", Tropical Deltas of Southeast Asia—Sedimentology, Stratigraphy, and Petroleum Geology, F. Hasan Sidi, Dag Nummedal, Patrice Imbert, Herman Darman, Henry W. Posamentier
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The seven seismic units recognized in the Molengraaff paleo-delta on the Sunda Shelf underlying the postglacial unit can be interpreted as prograding shelf-margin lowstand wedges deposited during forced regressions. Speculative age estimates of these units were made by correlating the interpreted lowstand wedges with the SPECMAP δ18Ocurve. This correlation suggests that the oldest unit reaches back to 570 ka, that the mean sedimentation rates during glacial times are comparable to modern prodelta rates, and that the tectonic subsidence rate of the outermost shelf depressions during the latest Pleistocene was of the order of 27 cm/kyr. Subsidence (which was differential) also occurred in postglacial times. The rate at the shelf edge is of the order of 2.5 m/kyr, and the differential displacements are taken up by growth-fault activity.
The outer Sunda Shelf was the delta plain of the Molengraaff River system during the last glacial, during which major fluvial entrenchment did not take place because of the low gradient. Sand ridges formed by transgressive reworking of Late Pleistocene material mark the modern water-depth range of 135–145 m. Mass wasting and fan deposition are important processes on the continental slope during regressions and lowstands.
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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.