Stable isotopic geochemistry of organic carbon and pyrite sulfur from the Early Cambrian black shales in Northwestern Hunan, China

摘要

The early Cambrian black shale sequence in Northwestern Hunan Province has been invesiigated for its stable isotopic geochemistry of organic carbon and pyrite sulfur. The relatively low δ ~(34)S values of organic matter, - 29.7 per thousand ～ 34.2 per thousand, are interpreted as caused by the high CO_2 concentration in atmosphere/ocean and an atioxic depositional environment in early Cambrian. Variable, but significantly positive δ ~(34)S values, + 10. 2 per thousand ～ 4 28. 2 per thousand, lorsedimentary pyrite reveals bacterial sulfate reduction as the pyrite-forming process but under sulfate-limited conditions. A protected anoxic basin, which had very limited access to open ocean, and its sediments, where metabolizable organic matter was rich and bioturbation was absent, are supposed to be the sulfate-limited environments and might have existed in South China in the early Cambrian.