Contrasting developments of Pleistocene calcareous clay units in the middle Bengal Fan and their implications for paleoenvironmental changes

Abstract

This study details sedimentary and compositional characteristics of the Middle to Late and Early Pleistocene calcareous clay units recovered from Site U1453 in the middle Bengal Fan. The sedimentary characteristics reveal that the calcareous clay units consist of calcareous hemipelagic muds and terrigenous hemiturbidite muds which represent intervening periods of hemipelagic sedimentation sensu stricto and a slow sedimentation from suspension clouds of low-concentration turbidity currents on the fan surface, otherwise dominated by sand and mud turbidites. Variations in compositions, such as organic and inorganic carbon contents and delta C-13 of bulk organic matters of the calcareous hemipelagic muds, indicate the glacial-interglacial climate forcing of carbonate dissolution, surface marine productivity, and sources of particulate organic matters in the middle Bengal Fan during the Middle to Late Pleistocene. The glacial-interglacial climate forcing on hemipelagic sedimentation seems to be much obscure during the Early Pleistocene because of dilution by terrigenous clay inputs. Grain-size distribution of bulk sediments suggests the presence of coarse foraminifer and finer nannofossil modes in the calcareous clay units and the size of dominant foraminifer species could have been finer in the Early Pleistocene.