ND ISOTOPIC VARIATIONS OF CHINESE SEAWATER DURING NEOPROTEROZOIC THROUGH CAMBRIAN

Samples of sedimentary phosphatic rocks and manganese deposits were co llected from the Neoproterozoic Sinian System and the Lower Cambrian S eries in the Yangtze region, China. The results from Sm-Nd isotopic de terminations show a considerable change in Nd isotopic composition of the Chinese seawater during the Neoproterozoic Period, which was simil ar to that of the Panthalassa ocean, but with smaller swing. The epsil on(Nd)(T) values of the Chinese seawater were about -4.5 in the Nantuo ice age (corresponding to the Varanger ice age), falling within the r ange of the Panthalassa ocean, then gradually decreased and separated from the Panthalassa ocean after the Nantuo ice age, and finally reach ed the lowest point (about -8.0) at the beginning of the Early Cambria n, obviously distinct from the Panthalassa ocean (-20 to -10). As one might infer, the Chinese seawater was not co-oceanic with the Panthala ssa ocean in terms of Keto and Jacobsen (1988) and belonged to another major ocean as a result from reconstruction of the global palaeoceano geographic pattern during the Sinian (Vendian) through the Cambrian.