Shale and Mudstone : Essential Source Rocks in the Proterozoic to Paleozoic Marine Basins in China

Carbonates are main sedimentary rock in the Proterozoic to the Paleozoic sedimentary basins of China and regarded as the main source rock for hydrocarbon , but less attention has been given to marine mudstone and shale.The statistics of organic carbon contents for more than 11200 samples from 147 outcrop sections and 289 wells in the Yangtze area , Yunnan , Guizhou and Guangxi provinces of the southern-western China , Tarim and ordos basins of the northwestern-northern China , show that shales/mudstones are rich in organic matter and are the essential source rocks in the Proterozoic to the Paleozoic marine basins.The Carbonates are poor in organic matter and are secondary source rock for hydrocarbon. The TOC is inweak negative relation to carbonate content in marine carbonatic rock.Mud input is favorable for the formation of organic-rich carbonate source rock , but is not an essential condition.Major factors determining the concentration of organic matters are productivity , sedimentary and preservation environments.The Proterozoic to the Paleozoic marine basins of China are not lack of organic-rich shale or mudstone ,which occur widely in the Doushantuo Formation of the Neoproterozoic , the Lower Cambrian , the Upper ordovician-Lower Silurian and the Upper Permian in the Yangtze area , the Lower-Middle Devonian in the Yunnan , Guangxi and southern Guizhou provinces , the Lower Cambrian , the Lower or dovician and the Middle-Upper ordovician in the Tarim basin ; the Hongshuizhuang and Xiamaling formations of the Mesoproterozoic to the Neoproterozoic in the Northern China.Carbonate source rocks , such as lime mudstone , marl and argillaceous limestone ,occur locally in the Cambrian and or dovician , Tarim basin , and in the Lower Permian , Southern China.Source rock of hydrocarbon argillaceous carbonatic rock is well developed within the Tarim basin and relatively enriched in the Lower Permian in southern China.