The Formation and Distribution of Source Rocks for Deep Water Area in the Northern of South China Sea

Source rocks in deep water basins in the north of South China Sea are obviously different from the passive margin basins in Atlantic Ocean.Mesozoic lacustrine source rock in the rifting sequence and marine source rock in the post-rift depression are the main source rocks in the passive margin basins of Atlantic Ocean,and their organic matters in lacustrine and marine source rocks all mainly came from aquatic lower organisms.There maybe exist three kinds of source rocks,including lacustrine source rock,transitional coal-bearing source rock and marine source rock in deep water basins in the north of South China Sea,but the correlation of oil/gas and source showed that Tertiary coal-bearing source rocks in transitional sequence is the main source rock there.Organic matters in transitional coal-bearing source rock and marine source rock mainly came from terrestrial higher plants in the north of South China Sea,and fluvial deltaic system is one of the very important factors for controlling the growth of terrestrial higher plants and abundance of organic matter.Because of the influence of the Paleo-pearl River,coal-bearing source rock of Enping Formation distribute relatively widespread and stable in the Pearl River Mouth basin.But there is no large river system,and fan-delta is the main type of delta,so coal-bearing source rock of Yacheng Formation distributed relatively limited in Qiongdongnan basin.The formation of marine source rocks is influenced by the quantity of terrestrial organic matter and accumulation and reservation of organic matter.Because of the difference of paleo-geography condition between the Pearl River Mouth basin and Qiongdongnan basin,origin of terrestrial organic matter in the Pearl River Mouth basin is much more abundant than Qiongdongnan basin,and the content of total organic carbon for marine source rock in the Pearl River Mouth basin is higher than the same geological time source rocks in Qiongdongnan basin.Because the supply of terrestrial organic matter decrease from land to ocean,so the organic matter content of marine source rock also lower from land to ocean.Seen from the distribution of source rocks in north of South China Sea,source rocks with relative high organic matter content mainly distributed in the surrounding area of basin or depression,they are mainly composed of coal-bearing source rock,also include some marine source rock with abundant organic matter,but the organic matter content is popularly low in the depocenter of basin or depression,the surrounding area of basin or depression is more profit for oil and gas exploration.