Calcium carbonate distribution in the Late Quaternary sediments of Bay of Bengal

摘要

Spatial distribution of calcium carbonate concentration in sixteen core top sediments indicates an increasing trend towards the deep-sea, and suggests that the carbonate concentration in the western Bay of Bengal is mainly controlled by terrigenous dilution. The temporal distribution, in general, shows a higher concentration of biogenic calcium carbonate in the middle segment of the cores (between 80 and 150 cm) compared to upper and lower half segments. The gradual enrichment of in-situ biogenic carbonate at this level is probably due to a reduced terrigenous supply by the Ganga-Brahmaputra river system owing either to a weak SW monsoon or tectonic trapping of sediments in the subsiding Indo-Gangetic Foredeep during the Last Glacial Period in late Pleistocene. However, towards the Godavari river mouth (E-W traverse) as the calcium carbonate concentration demonstrates no variation in temporal distribution, this indicates a higher Godavari river influx probably related to a strong NE monsoon during the glacial period. The presence of low-carbonate content in the upper part of the cores is attributed to an increased terrigenous supply in the post-glacial period. The temporal distribution also shows three abrupt increases in calcium carbonate concentration related to transported nature of biogenic and chemogenic (ooids) materials from the shelf regime under turbidity current/gravity flow activity. [References: 30]