Heliyon (Jan 2023)
Tectonic setting, provenance, depositional, and paleo-climatic conditions of the late quaternary subcrop sediments of the southeastern coastal region of the Bengal basin
Abstract
This is a systematic attempt to depict the genetic evolution of the Late Quaternary sediments of the southeastern (SE) coastal region of the Bengal basin regarding paleotectonic settings, sedimentation, provenance, paleo-climatic conditions, weathering condition and age. The study has considered multiple attributes such as, lithology/lithofacies, sedimentary features/records, major oxides, clay minerals, foraminifera, and radiocarbon dating. The lithological characters along with associated clay minerals confirmed that a Pleistocene paleosol horizon (over-bank deposits) of warm-humid nature is commonly encountered immediately on top of the sub-crop bed-rock in the area overlain by Holocene fluvio-marine sediments of the same nature. The lithofacies, foraminiferal assemblages, and sedimentary structures of the analyzed samples suggest that the Holocene sediments have been presumably deposited in a fluvio-marine condition after the Last Glacial Maximum (LGM) due to the transgression of the sea. Geochemically, the sediments are classified as Fe-rich shale, shale, and wake and primarily intermediate to felsic orogen provenance. These are possibly derived from intense weathered sources from the upheaval of Himalayan ranges of both active continental margin and Island Arc paleotectonic setting. The plot of the Index of Compositional Variability versus the Chemical Index of Alteration indicates that the sediments seemingly experienced intense weathering associated with warm and humid climatic conditions. The sedimentation rates of the area vary from place to place and layer to layer due to the complex delta-building process. The reconstructed Relative Sea Level Curve reveals that presumably, the sea level has reached its current position after the LGM. The deduction possibly will facilitate the (1) reconstruction of Late Quaternary coastal evolution after LGM, (2) support for future urbanization, land use plans, etc., and (3) also be helpful for international researchers to understand the possible sources of sediment input in the area from the complex interplay of the Indian-, Eurasian- and Myanmar-plates.
