The Ganges-Brahmaputra Delta
Originating in the Himalayan Mountains within distinct drainage basins, the Ganges and Brahmaputra rivers coalesce in the Bengal Basin in Bangladesh, where they form one of the world’s great deltas. The delta has extensive subaerial and subaqueous expression, and this paper summarizes the current knowledge of the Late Glacial to Holocene sedimentation from the upper delta plain to the continental shelf break. Sedimentation patterns in the subaerial delta are strongly influenced by tectonics, which has compartmentalized the landscape into a mosaic of subsiding basins and uplifted Holocene and Pleistocene terraces. The Holocene evolution of the delta also has been mediated by changing river discharge, basin filling, and delta-lobe migration. Offshore, a large subaqueous delta is prograding seaward across the shelf, and is intersected in the west by a major submarine canyon which acts both as a barrier for the further westward transport of the rivers’ sediment and as a sink for about a third of the rivers’ sediment discharge. Subaerial and subaqueous progradation during the Holocene has produced a compound clinoform, a feature which appears to be common for large rivers discharging onto an energetic continental shelf.
Figures & Tables
Deltas are amongst the most environmentally and economically important coastal sedimentary environments. Studies of deltas lag behind research in both fluvial and deep-water depositional systems, as well as more geomorphologically oriented land studies. This knowledge lag reflects both a reorientation of the petroleum industry in the last two decades toward deep-water systems, as well as the difficulty of working across the shoreline with the traditional tools used for oceanographic or land-based work. However, deltaic studies are experiencing a renewed focus, because of their global importance in environmental and other societal concerns. This volume stems from a special session: Deltas: Old and New, held at the Annual Geological Society of America conference in October 2002, that was convened to highlight these new directions in deltaic research.