环境地球化学国家重点实验室知识库

Profound geotectonic, climatic and biological changes occur during the terminal Neoproterozoic and its transition into the early Cambrian. These are reflected in temporal variations of the chemical and isotopic composition of seawater. We are studying a sequence of sedimentary rocks at the Shatan section, northern Yangtze Platform. Sichuan Province of China. This succession comprises, in ascending stratigraphic order, predominantly calcareous sediments of the Sinian upper Dengying Formation and black shales of the lower Cambrian Guojiaba Formation (time equivalent of Niutitang Fm.). Paleoenvironmental setting represents shallow-water shelf deposits. The objective of our study is to provide temporal records for the isotopic compositions of organic and carbonate carbon throughout this time interval. Organic carbon isotope values display a range between −35.8‰. and −30.l‰. with clear stratigraphic variations. Carbonate carbon isotope data vary between −3.5‰. and +0.5‰. These secular variations are interpreted to reflect perturbations of the global carbon cycle specifically changes in the fractional burial of organic carbon. However, local conditions have further affected the isotopic signals.