Abundance Distribution of Various Elements in Sediment Cores from the Japan Sea Determined by Photon Activation Analysis

Abstract

Deep-sea sediment cores taken from 4 different regions in the Japan Sea were subjected to analyses for 5 major and 11 trace elements by means of instrumental photon acti vation analysis with 30 MeV bremsstrahlung. These elements were Ca, Fe, Mg, Na, Ti, Ba, Ce, Co, C r, Mn, Nb, Ni, Rb, Sr, Y and Zr. Additionally, Al was determined spectrophotometrically, and Si02 contents of selected specimens were determined by a conventional chemical method. Variation patterns of these elements along the core columns were derived, and discussions were give on the results from a viewpoint of element stratigraphy. Sedimentation rate ? was determined on the basis of the stratigraphic change of planktonic formainiferal assemblages, and found to be 9, 10 and 20 cm/10³ y for 3 of the 4 cores. The Holocene-Pleistocene boundary for these cores wa8 determined to be 90, 110 and 210 cm beneath the ocean floor, respectively. Variations in concentrations of the elements in deposits of post-glacial age are relatively small. On the contrary, abundance distributions of the elements are generally inhomogeneous in glacial zones. Below the boundary levels, enrichments of Ca and Sr by biogeneous process were observed, and, especially for a core from Yamato Basin, these Ca maxima were well correlated with Mn maxima which would be the result of lateral migration of Mn during glaciations. Cobalt and Ni tend to be associated with Mn. Qne core taken around the Yamato Ridge was found to have no detectable foraminiferals, but seems to have an extremely slow deposition rate. Sedimentation would have occurred under very calm conditions, thereby causing remarkable enrichments of Mn, Fe, Co and Ni characteristic of pelagic sediments. In the central parts of the Japan Sea, the oxidized post-glacial zone appears to be a typical pelagic sediment.