Tectono-geomorphic evolution of an alluvial fan along the Dauki fault system, Bengal Basin, Bangladesh: remote sensing and pedogenic approach

Abstract

Late Quaternary landform evolution of the Karnajhora fan and its adjacent areas of the mid northern Bengal Basin, Bangladesh have been studied using remote sensing and pedogenic approach. Based on pedogenic characteristics, different soil-geomorphic units can be arranged according to their maturity as Hill > Distal Fan > Mid Fan > Proximal Fan. Soil-geomorphic units are further grouped into a three member soil-chronoassociation and approximated inferred ages are QGSK1 < 1 ka; QGSK2 < 3–4 ka; and QGSK3 > 27 ka. The weakly developed youngest member QGSK1 and the moderately developed member QGSK2 represents inceptisols at fersiallitisation weathering stage. While the oldest QGSK3 member represents alfisols and show relict nature and at the initial phase of ferrugination weathering stage. Neotectonics controls the configuration of the local catena. Paleoclimate and base-level fluctuations have also played significant roles in the development of soils and landforms of the study area. The parent materials of Member QGSK3 were deposited during 80–27 ka. Since the beginning of deposition of QGSK3 soils till the Last Glacial Maximum (LGM~18 ka), the climatic conditions gradually changed from warmer-moist to cooler-drier, and the area might experienced dominantly channel incision with minor aggradation. During this period, the land between the Jamalpur Terrace and Susang Hills might be eroded and washed away while the Sherpur Terrace survived as a remnant terrace. After the LGM, the climate changed from a cooler-dry condition to warmer-moist condition and the present Holocene floodplain started to develop. The parent materials of QGSK2 and QGSK1 members then started to deposit by the paleo-Karnajhora synchronously with the old Brahmaputra River. As the Karnajhora River presently shifted toward east, soils of QGSK2 member are not presently affected and are relatively better developed compared to QGSK1 member soils.