Stratigraphic implications of Sinian-Early Cambrian volcanic ash beds on the Yangtze Platform.

Volcanic ash beds from shallow- to deep-water facies strata of the Sinian-Early Cambrian (Meishucunian) on the Yangtze Platform consist of bentonites and tuffites which are readily recognized in the field by their physical features and confirmed by geochemical analyses. Geochemistry suggests that the volcanic ash beds in Meishucunian time are rhyolite and rhyodacite while those in the Qiongzhusian and Sinian are andesite and trachyandesite. The ash beds in the time-equivalent strata, even in different areas display rather similar geochemical features, whereas the ash beds in different strata even in the same areas show large chemical difference. The results suggest that these ash beds can be used for intra- and extra-basinal correlations of the Sinian-Early Cambrian interval on the Yangtze Plat-form. Additionally, these ash beds suggest high potentials for further U-Pb dating strategies. [ABSTRACT FROM AUTHOR]