--> Abstract: Lessons from Holocene Deltas: Facies, Evolution, and Regime Shift, by Yoshiki Saito; #90039 (2005)

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Lessons from Holocene Deltas: Facies, Evolution, and Regime Shift

Yoshiki Saito
IGG, geological Survey of Japan, AIST, Tsukuba, Ibaraki, Japan

Modern delta studies give us a key to the past to help us better understand sedimentary rocks. In particular, modern sedimentary facies and processes and the evolution of deltas in response to known sea-level changes are useful modern analogues of past sedimentary processes. Ten of the top 16 largest rivers in the world in terms of sediment discharge are in Asia. Relatively stable or falling sea level for the last 7 ka and high sediment supply caused large, mature deltas to form at the mouths of Asian rivers, whereas transgressive coastal systems have developed in Europe and North America. Holocene deltas in Asia show a two-stage stacking pattern: an aggradational phase, as sea level slowly rises, and a subsequent progradational phase, when sea level is stable to falling. A rapid fall in sea level after the highest sea level leads to the emergence of delta plains and rapid seaward migration of delta systems with increasing wave influence. The coastal environmental regime, which was estuarine initially, changes to a tide-dominated bayhead, and then to a wave-dominated open shelf as the delta progrades. The surface morphology of the delta plain reflects only the sedimentary facies of the delta front platform, not those of the whole deltaic succession. Recent human activities such as deforestation have caused sediment discharge to increase, resulting in a regime shift to more fluvial-dominated deltas on a millennial timescale. However, because of dam construction, delta regimes are becoming more wave- or tide-dominated relatively on a decadal timescale.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005