Tectonic and Sea Level Control on the Transport and Depositional Processes in a Siliciclastic Sedimentary Basin. Insights from the Ganges-Brahmaputra Delta, Bengal Basin, Bangladesh.

Abstract

Climate, tectonic and sea level changes are the primary drivers for sedimentary basin dynamics at any time and space scale. Their mutual interaction during late Quaternary is studied in the Ganges-Brahmaputra Delta. High-resolution Multichannel Seismic and acoustic data collected during the SO188 Expedition, were processed and interpreted. It results that sea level cycles cannot be addressed as a fulfilling explanation for the uneven sediment depocentre distribution on the Bengal Shelf, whereas monsoon climate and the long term tectonic subsidence (0.18 mm/yr) are dominating the offshore export and the margin accretion respectively. Moreover active tectonic processes might have contributed to the initial formation ca. 245 ka ago and consolidation of the Swatch of No Ground shelf incised canyon, the main modern shelf depocentre. The Ganges-Brahmaputra subaqueous delta, during the last 300 years, has instead decreased from 22% to 13% the storage rate, possibly due to the global reduction in the monsoon precipitation and/or to the intensified anthropogenic stress.