Geochemistry of core sediments from the southeastern Bay of Bengal: Inferences on weathering and early diagenetic changes

摘要

A sediment core (ABP24/05), collected at a water depth of 3520??m from the southeastern Bay of Bengal was studied to determine the change in chemical weathering during the last glacial to deglacial periods and the factors of sedimentary environment which controlled earliest diagenetic changes in the sediment after its deposition. High ratios of K/Rb, Ti/Al and Zr/Rb during ~45 to ~18??cal??kyr B.P. in the core sediments may be attributed to the stronger physical erosion and turbidity currents activity during this period. This might have brought a higher quantity of unaltered minerals to the study area. Low ratios of K/Rb, Zr/Rb, and Ti/Al and increase of SiO2/TiO2, Rb/Al and Cs/Al from ~18??cal??kyr B.P. to present may be indicating an increase in the rate of chemical weathering during this period. The time of increased chemical weathering in the study area is consistent with deglaciation warming in the tropical Indian Ocean and strengthening of river runoff into the Andaman Sea. Climate change during the interglacial period by increased solar insolation thereby strengthened the summer monsoon which might have led to intensified chemical weathering in the source region since ~18??cal??kyr B.P. The low organic carbon (OC), high Mn/Al, Fe/Al and the Mn-oxides minerals precipitation indicate prevailing of oxic conditions during ~11??cal??kyr B.P. in the core sediments, which is contradictory to suboxic conditions developed in the deep ocean sediments in the western Bay of Bengal and the equatorial Indian Ocean. The low terrigenous influx and export of less OC to the bottom sediments might have created a favorable condition for the formation of Mn-oxides in the study area during Holocene.