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Construction and destruction of an autogenic grade system: The late Holocene Mekong River delta, Vietnam


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Title: Construction and destruction of an autogenic grade system: The late Holocene Mekong River delta, Vietnam
Authors: Wang, Junhui / Tamura, Toru / Muto, Tetsuji
Issue Date: 13-May-2019
Publisher: Geological Society of America
Citation: Geology, 47(7), pp.669-672; 2019
Abstract: Grade, a fundamental concept in river geology and geomorphology, refers to a long-term sediment balance that is accompanied by zero net deposition and erosion. Recent physical and theoretical modeling proposed the notion that downstream alluvial rivers can autogenically attain grade only in a particular set of environmental conditions that include a constant fall of relative sea level. We here make the first successful identification of an autogenic grade system in the geological record: the late Holocene Mekong River delta, Vietnam. From 3.5 ka to subrecent, the record of the delta exhibits peculiar features, including (1) no trace of significant sediment accumulation and erosion on the delta plain surface, (2) a delta plain surface with the same slope as the underlying shelf surface, (3) distributary channels that are stabilized in transverse directions but extend linearly basinward, and (4) a delta set thickness that matches a theoretical value.These features in combination are indicative of autogenic grade. Coastal dispersal of river-derived sediment by tides, waves, and ocean currents, as well as tectonic features and mangrove vegetation, may have contributed to the attainment and maintenance of grade. Ongoing drastic changes in sea level and human activities have caused the downstream Mekong River to become ungraded and unstable with a much higher risk of channel avulsion and shifting than in the past.
URI: http://hdl.handle.net/10069/39330
ISSN: 00917613
DOI: 10.1130/G45872.1
Rights: © 2019 Geological Society of America. All Geology, GSA Bulletin, and GSA Books manuscripts may be published under the terms of Green Open Access.
Type: Journal Article
Text Version: author
Appears in Collections:Articles in academic journal

Citable URI : http://hdl.handle.net/10069/39330

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