The Bengal fan - Geomorphology and sediment distribution

Abstract

The Bay of Bengal is a large but relatively shallow embayment of the northeastern Indian Ocean. It receives a significant amount of freshwater and sediment, approximately 2000 million tonnes annually, from the Himalayan and the Indian peninsular rivers during the North East (NE) and the South West (SW) monsoons, respectively. The sediment flux to the bay is among the highest globally due to its size, location, and the catastrophic deposition of sediments. Long paleo-synoptic reconstructions and paleomonsoon interpretations from sediment cores in the Bay of Bengal are limited. This is largely because the enormous sediment load that enters the Bay through river discharge occurs under high-energy conditions, making it challenging to retrieve turbidity-free and undisturbed sediment cores. However, some recent reports (Ponton et al., 2012; Tripathy et al., 2014) have documented variations in paleoclimate and geochemical cycles from the Last Glacial Maximum to the late Holocene period in the Bay of Bengal. Sedimentological and geochronological studies conducted on the eastern Bengal shelf studied by Kuehl et al. (1989) revealed that the highest sediment accumulation from the Ganges-Brahmaputra river system occurs near the head of the Swatch of No Ground, which is located west of the present river mouths of Ganges-Brahmaputra. Additionally, Kolla and Rao (1990) analyzed sediment sources from the Bay of Bengal and reported high quartz and low calcium carbonate percentages adjacent to the Indian subcontinent, likely due to a substantial influx of terrigenous clastics. Furthermore, investigations on the mineralogy and heavy minerals in sands suggest that sediments of the western Bengal Fan, characterized by high levels of smectite, sillimanite, and garnet, are derived from peninsular Indian rivers.