Sedimentary Characters of Wufeng Formation Upwelling Facies Source Rock in Lower Yangtze Area

Abstract:

The layered radiolarian cherty deposition of the latest ordovician Wufeng Formation is one of the regional excellent hydrocarbon source rocks in the lower Yangtze region and caused by the upwelling in the slope environment of the foreland flexural-break stagnation-flow basin margin. Under the control of the intensity and surging recurrence frequency of the upwelling,the Wufeng Formation is dominated by many siliceous rock/ siliceous shale couplets with different siliceous organisms and periodic variation in thickness.As the deposition under the anoxic environment, the Wufeng Formation mainly has high hydrocarbon potentional amorphous organic matters originated from algae and other pelagic organisms. In the impact from the upwelling, the different protection mechanisms of organic matter happen during the sedimentation of siliceous rock and siliceous shale, while organic carbon mainly relates to the adsorption protection of clay mineral and the loss of organic matter during the siliconoxide mineral transformation.