Late Holocene continental shelf sediments, off Cuddalore, East coast, Bay of Bengal, India: Geochemical implications for source-area weathering and provenance

In the present study, a 60 cm sediment gravity core collected off the Cuddalore shore (11°42.419 N, 79°57.993 E) from a water depth of 150 m was radiocarbon dated and analysed for major elements (Si, Al, Na, K, Ca, Mg and P), trace elements (Fe, Cr, Mn, Co, Ni, Cu, Zn and Pb), calcium carbonate, and organic matter content to understand their behavior and probable sources and also to understand the monsoon variability. The sediment core has been radiocarbon dated from around 4100 to 3100 BP. High sand around 4000, 3700, 1500 BP with low CaCO3 content suggests high sediment flux coupled with higher precipitation corresponding to increased erosion during these periods, and more fresh water runoff from rivers in the late Holocene, thus reflecting intensification of the SW and NE monsoon. The results of the major elemental analyses show the fine-grained, detrital nature of sediments with high values of Si and lower values of Al and Fe. The present study clearly demarcates that the distribution patterns of Cr, Cu, Pb and Zn that are controlled by the distribution of the fine grained fractions. The increased Mn content towards the lower end of the sediment core denotes the allogenic supply of Mn from oxic to-sub-oxic recycling within the sediment column in fine grain sediments. The mean CIA values (56.47) reflect immature, moderately weathered sediments that are mostly derived from sandstone and clay.