ISSN: 2642-1283
Authors: Md Nijam Uddin, Md Hussain Monsur and Saha SK*
Bengal basin, the largest fluvio-deltaic sedimentary system on Earth, is located in Bangladesh and three eastern states of India. Sediment accumulates in the basin from the Ganges, Brahmaputra, and Meghna (GBM) river systems and is dispersed into the Bay of Bengal, forming the largest submarine fan in the world. The present-day geomorphology is dominated by the extensive Holocene GBM floodplain and delta. The initiation of the modern GBM delta at the onset of the Pleistocene glacial maximum and its evolution to the present configuration are intricately related to Holocene fluvio-dynamic processes, eustatic sea-level changes, and tectonic movements. Quaternary System in Bengal basin has varieties of depositional environment. Sediment characteristics of different geomorphic units are different. Late Quaternary monsoon climatic episodes played the vital role in creating the present morphology of the Madhupur surfaces. During the Holocene, the central part of the basin experienced cyclic transgression and regression phase in several times. This was the evidence by mangrove pollens. The presence of mangrove pollen specially Phoenix paludosa, Avicennia sp, Phoenix sylvestris, Prosopis grandis, Sonneratiopollis sp found in Chatbari, Dubadia and Mirertek area of Dhaka city along with radiocarbon dating indicated that marine influence occurred during Mid Holocene time. Two phases of transgression and regression have been recorded during mid Holocene time. First transgression was noticed around 6500 cal BP and then a subsequent regression of the bay had been observed around 5500-3500 cal BP. This was again followed by another transgression episode around 3500-1500 cal BP. and then a regression during between 1500 cal BP onwards.
Keywords: Sea-Level; Dhaka; Paleocoasts
