Alkali and alkaline earth metals in surface sediments off Bhimunipatnam-Amalapuram, central east coast of India (Bay of Bengal)

The alkali and alkaline earth metals both major (Na, K, Mg, Ca) and minor (Li, Rb, Cs, Sr) were analyzed in 75 surface sediment samples from an area covering the continental shelf, slope and the deep sea regions. Lithium, Rb, Cs and Sr averaged 7.2, 42.5, 12 and 27.2 ppm respectively. Rubidium and Sr showed north-south trends. Starting from the northern sector, the former increased and the latter decreased towards the mouth of R. Godavari. This behavior is explained by the dissolved transportation index (DTI) according to which the transport of Rb takes place mainly in the particulate and that of Sr in the dissolved phases. Lithium and Rb are correlated well to K suggesting a detrital origin for the elements. The alkali and alkaline earth metal distribution of the study area revealed a strong signature of R. Godavari. Strontium showed a good anticorrelation with the biogenic fraction of Mg (Mg-B). It: attained peak concentrations in the carbonate sands of the northern outer shelf which according to previous reports are of the late Pleistocene age. Sediments although rich equally in carbonate and from proximate stations, contain variable concentrations of Sr probably due to a differential time-dependent leaching of the metal as these carbonate deposits may have been formed at different stages of the regressive - progressive cycle of the late Quaternary sea level.