SM-ND ISOTOPIC SIGNATURES AND SIGNIFICANCE OF THE PRECAMBRIAN-CAMBRIAN SEAWATER IN CHINA

Sm-Nd isotopic determination on small shelly fossils and collophanites collected from 3 Precambrian-Cambrian boundary sections, namely Meish ucun of Jinning in Yunnan, Maidiping of Emei in Sichuan and Wushi of K alpin in Xinjiang, shows that the seawater masses of these three remot ely separated areas were co-oceanic in the Precambrian-Cambrian transi tional period, with a common seawater epsilon(Nd)(T) value of -6.6+/-0 .5. The epsilon(Nd)(T) value of the China's seawater ranges from -5.7 to -6.6 during the period from 610 Ma B. P. to 500 Ma B. P. The resear ch suggests that there could be an ''Asiaustralian Ocean'' besides the Panthalassa Ocean and the Iapetus Ocean at that time, and the China's seawater possibly belonged to the Asiaustralian Ocean. The Sm-Nd mode l age of the determined samples is about 1.8 Car which reflects the me an age of the continental source areas around the China's seawater.