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The Sr/Sr ratios and Sr concentrations of detrital noncarbonate fractions of sediment deposited in the central basin of the Black Sea are controlled to a first approximation by varying proportions of sialic and mafic components. The sialic component consists of weathering products of igneous, metamorphic, and sedimentary rocks of Precambrian to Tertiary age in the northern watershed. The mafic component originates from ophiolite complexes and associated volcanic rocks and volcanogenic sediment of Mesozoic to Cenozoic age in Turkey and Bulgaria. Quantitative interpretations of the data yield mixing equations from which the Sr concentrations of the sialic and mafic components are estimated using reasonable assumed values of their Sr/Sr ratios. For the mafic component we assumed Sr/Sr = 0.705 ±0.001 and obtained a Sr content of 215 ±28 ppm. The concentration of Sr in the sialic component is 50.4±?J ppm, assuming that its Sr/Sr ratio is 0.735 ±0.005. The data suggest that slight variations of these values occurred for limited intervals of time. The concentrations of the sialic component, calculated from the two-component mixing model, vary systematically as a function of depth in the hole and indicate a strong climatic influence on the input of sialic detritus from the northern watershed, as follows: Würm glacial: 59%; Würm/Riss interglacial: 51%; Riss glacial: 67%; Mindel/Riss interglacial (?): 37%; Mindel glacial: 84%. The Sr/Sr ratios of the calcium carbonate fractions in Cores 1 through 22 range from 0.7070 to 0.7084 and are less than the value of this ratio in modern seawater (0.709). The low values are attributable to the presence of reworked older coccoliths of Cretaceous and Eocene to Oligocene age which have lower Sr/Sr ratios than indigenous species of Quaternary age. The average Sr/Sr ratio of carbonates deposited during the Würm/Riss interglacial is greater than that of the Würm glacial period due to the predominance of the indigenous species Emiliania huxleyi during periods of increased salinity (interglacials) in the Black Sea. The isotopic composition of Sr in the carbonate phases therefore has some value as an indicator of salinity in the Black Sea.

A Study of Sedimentation at DSDP Hole 379A, Black Sea, Based on the Isotopic Composition of Strontium