The Cambrian sedimentary characteristics and their implications for oil and gas exploration in north margin of Middle-Upper Yangtze Plate

Using data from tens of measured and observed outcrop successions, thin rock slices and sample analyses, we comprehensively studied the Cambrian sedimentary environments and evolutionary characteristics in the north margin of the Middle-Upper Yangtze Plate. During the Cambrian, platform, slope, and deep sea basin environments were developed in the study area. On the platform, both clastic rocks and carbonate rocks were deposited. Clastic rocks mainly occur in the Lower Cambrian, and were deposited in marine shore and shelf environments. Carbonate rocks are dominant in the Middle and Upper Cambrian, and were deposited in the open platform, restricted platform, tidal flat, beach, and reef environments. Carbonate gravity flow deposits were developed on the slope. In the basin, mainly black shales and chert beds were deposited. The Cambrian represents one large transgression-regression cycle, and maximum transgression occurred in the Qiongzhusi Age of the Early Cambrian. Tectonics and sea level fluctuations had important impacts on sedimentary environments. The Chengkou-Fangxian-Xiangfan Fracture controlled the position of the platform, slope and basin, as well as the silica supply for chert deposition in basin. Sea level fluctuations controlled types of sediments and sedimentary facies on the platform. In the study area, there are good reservoir rocks, including dolomites, grainstones, debris flow deposits, sandstones, and conglomerates; there are good source rocks, including black shales, dark micrites, and chert beds; and there are also good reservoir-source rock assemblages. The hydrocarbon potential of the study area is great.