Physical/chemical weathering and climate fluctuations during last ~6000 years-investigation through a sediment core, off Mahanadi River mouth, western Bay of Bengal

Abstract

Sediment core (GC 16) sampled off the Mahanadi River mouth from the western continental shelf region in the Bay of Bengal was investigated for sediment components, clay minerals, and metals with an objective to study the temporal distribution of clay minerals of the Middle and Late Holocene sediments to understand how the physical/chemical weathering and climate varied over the last 6000 years in the Mahanadi River basin. The chronology for the sediment core was obtained by two 14C dates, and the core spans the past ~5955 cal year BP. The study revealed the predominance of finer sediments and detrital clay mineral illite in the core suggesting a supply of material upon physical weathering of felsic rocks. The core was divided into different zones based on the distribution pattern of the sediment size, clay minerals, and metals. A decrease in silt content and illite + chlorite concentration along with a comparative increase in clay content, smectite and Fe concentrations, and high smectite/illite ratio in the upper half of the core indicated increased sediment supply after chemical weathering of mafic rocks, supported by metals, during warmer intervals and enhanced southwest monsoon. The cooler interval of climate and supply from physical weathering of felsic rocks was exhibited by high silt content and illite + chlorite content with lower smectite/illite ratio in the lower half of the core.