Quaternary environment and climate change reconstruction from geochemical and geoarchaeological evidences of paleosols in east-central Barind, NW Bangladesh

Abstract

This research focuses on analyzing paleosols, major and trace element geochemistry, organic carbon levels, and geo-archaeological aspects of Quaternary deposits investigated in two sedimentary successions located in the east-central Barind region of NW Bangladesh. Several factors that influence the paleosol development can be used to decipher the paleoenvironment and paleoclimatic conditions of the study area. Sedimentary succession of the studied sections have been grouped into two broad categories i.e., Gray unit/Newer Alluvium (NA) of Late Holocene and Red unit/Older Alluvium (OA) of Early Pleistocene age. Some geoarchaeological evidences have been found at the bottom of the gray unit and the top of the red unit in Durgadaha (DD) section indicating the existence of paleo-settlement at about ∼1300 years BP. The age is determined by the relative dating of several artifacts found at the paleo-settlement surface. Interpretation of several field characteristics and geochemical parameters i.e., clayeyness, salinization, base loss, calcification, leaching (Ba/Sr), aeolian input (Zr/Al), CIA, CIW, CIA-K, etc. revealed that the paleosols in gray unit are weakly developed; whereas, paleosols in red unit are relatively moderate, strong to very strongly developed. In the red unit, the MAP and MAT range from 1000 ± 181 mm to 1478 ± 181 mm and 9° ± 4.4°–14° ± 4.4 °C respectively. On the other hand, MAT ranges from 23.1° ± 0.6 °C to 28.3° ± 0.6 °C in gray unit paleosols. Depending on the depositional pattern and estimated MAT, five short-term climatic cycles (i.e., alternating phases of dry and wet) have been recognized in gray/newer alluvium units during the last 1300 years. The demise of paleo settlement (1300 years BP) due to the abrupt climatic change towards a dry and cooler phase where the MAT was estimated as 23.1° ± 0.6° which is at least 3 °C lower than the present. This study also revealed that the estimated MAP and MAT are more analogous to paleoclimatic records of the Asian regions.