Sedimentary environments of the Lower Cambrian source rocks in central Hunan

Tectonically, central Hunan lies on the southeastern margin of the middle-upper Yangtze plate. During the Early Cambrian, this region was in a relatively stable cratonic basin. The integration of upwelling oceanic currents, sea-level rises and anoxic events gave rise to the formation of the favourable environments for the generation of source rocks. Throughout the Early Cambrian, the central Hunan region was once developed as the anoxic stagnant basin above the continental shelf, and composed of a succession of black deposits comprising black carbonaceous tabular shales and siliceous-carbonaceous mudstones. The black deposits extend from the central Hunan region to the whole southeastern margin of the middle-upper Yangtze plate, implying that the study area was then enriched in hydrocarbons, and thus has great hydrocarbon potential. This region is selected as a key area not only for basic geological survey and oil and gas exploration, but also for the exploration of shale gas.