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Storms as Potential Change Agents on the Ganges-Brahmaputra Delta: Coevolving Clinoform and Canyon Morphology

K. G. Rogers1, S. L. Goodbred1, and S. R. Khan2
1Earth and Environmental Sciences, Vanderbilt University
2Geological Survey of Bangladesh

The Ganges-Brahmaputra delta is an end-member example of a highvolume discharge system that debouches onto a rapidly accreting, canyonincised margin. Active deposition and widespread sediment dispersal across the delta plain, shelf, and deep sea have been well documented here. However, transport mechanisms and pathways in the estuarine transition zone between these primary depocenters are poorly understood. Toward the goal of discerning how fluvial, oceanographic and climatic processes interact to control sediment dispersal at the subaerial-subaqueous transition, high-resolution subbottom sonar surveys were conducted on the inner shelf of the Bay of Bengal in March 2007. The data show shelf-wide acoustically transparent layers that extend across the topset-foreset boundary of the clinoform to the canyon edge. Based on accretion estimates, the tops of these layers terminate at a depth that corresponds to the timing of a 19th century category 4 cyclone in the Bay of Bengal and could be the result of wave pumping during this storm event. Feeder gullies and failure surfaces are visible in the data along the eastern edge of the canyon, and may also be linked to storm activity. A follow-up survey in March 2008 was conducted to characterize the impact of a November 2007 category 4 cyclone on the subsurface facies of the clinoform and the canyon. Correlation of post-storm canyon gullies and failure surfaces with acoustically transparent layers at the clinoform-canyon interface may lead to a more precise understanding of how storm events influence the dispersal of sediment to these depocenters.

AAPG Search and Discover Article #90087 © 2008 AAPG/SEG Student Expo, Houston, Texas