Climatic control on detrital sedimentation in the continental margin off Chennai, western Bay of Bengal – A 42 kyr record

Abstract

While the peninsular Indian rivers deliver considerable loads of detrital sediments to the Bay of Bengal, changes in their depositional patterns with time are relatively less constrained compared to those deposited by Himalayan Rivers. Here, we present a 42 kyr record of detrital sedimentation, studied using whole-core logging, environmental magnetism, and major element geochemistry from the continental margin near Chennai, in the western Bay of Bengal. The variations of magnetic mineral properties and elemental concentrations of detrital sediments combined with the published oxygen isotope record, suggest monsoonal control on detrital input to the margin. Four major periods of changes in sedimentation are identified 1) the lower section of the core representing marine isotope stage (MIS) 3 (42–24 ka) shows varying detrital input, while magnetic minerals are affected by early diagenesis, 2) the period between 24 and 15 ka exhibits increased detrital input as a result of subaerial erosion in southern India during the last glacial sea-level lowstand, 3) the deglacial period from 15 to 10 ka is marked by decreased detrital input and increased productivity, and 4) the Holocene (10–2 ka) period experienced increased detrital input and chemical weathering in the source areas. Although the post-depositional alteration of magnetic minerals in MIS 3 limits the use of environmental magnetism, major elements and δ18O record the variations in paleomonsoon and detrital input during this period. The increased detrital input during 24–15 ka, despite the glacial conditions and intensified NE winter monsoon, indicates the increased subaerial erosion of exposed continental shelf during the sea-level lowstand owing to the proximity of the sampling site to the coast. The high magnetic susceptibility (χlf), chemical index of alteration (CIA), Al and Ti content beginning at ∼10 ka marks the intensification of SW summer monsoon through the Holocene.