A Depositional Model and the Stratigraphic Development of Modern and Ancient Tide-Dominated Deltas in NW Borneo
Joseph J. Lambiase, Abdul Razak Damit, Michael D. Simmons, Raden Abdoerrias, Azhar Hussin, 2003. "A Depositional Model and the Stratigraphic Development of Modern and Ancient Tide-Dominated Deltas in NW Borneo", 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 modern deltas of NW Borneo have long been regarded as wave-dominated, as typified by the Baram River Delta. However, the sedimentary facies associated with several modern deltas within Brunei Bay are strongly tide-dominated. A notable example is the Trusan River Delta, which occurs within a subsiding sub-basin and has an intertidal morphology and facies distribution that indicates tidal dominance, although the shoreline geometry suggests significant fluvial influence. The succession becomes sandier upward from embayment muds through mixed sand and mud flats to tidal-channel and bar sands near mean sea level, and then fines upward to tidal sand flats and finally mud flats near the high-tide shoreline.
Tide-dominated sediments also are common in the outcropping strata of the mid-Miocene and younger Belait Formation. The Seven-Up Beach succession is interpreted as the distal ends of progradational lobes of a tide-dominated delta that coarsen upward from brackish-water mudstone through muddy and sandy tide-dominated mouth-bar deposits to tidal-channel and bar sandstones. The tidal-flat and tidal-channel and bar sandstones and interbedded tidal-flat mudstones of the Jalan Sungai Akar succession are more proximal deposits of a similar delta. Examples of distributary channels that eroded into lobe deposits during a relative sea-level fall and were backfilled during the subsequent relative sea-level rise are exposed in the Tanjong Batu succession. All three outcropping successions are strongly aggradational.
A model for tide-dominated deltas in NW Borneo derived from the modern facies distribution and outcrop stratigraphy indicates that stratigraphic architecture is controlled primarily by the interaction of tectonic and compaction-driven subsidence, a relatively high rate of sediment supply, and basin hydrodynamics. The result is a largely aggradational, sandy intertidal succession on the delta plain and muddy delta-front deposits, with aggradational stacking of individual delta lobes.
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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.