Lake-basin Filling Types and Development of High Quality Hydrocarbon Source Rocks in Ordos Basin in Late Triassic Yanchang Period

Lake-basin filling types response to the basin structures and plaeoclimate and control the development of high quality hydrocarbon source rocks.Based on comprehensive analysis of the depositional environment of Chang91,Chang73 and Chang72-71 source rocks,the authors recommend a balanced-fill type for these source rocks.However,as the abundance of organic matter and the scale of resource of these source rocks are different,the further subdivision of the balanced-fill type is needed.It is subdivided into delta front-deep lake,purely deep lake and turbidites-deep lake sedimentary systems corresponding to Chang91,Chang73 and Chang72-71 source rocks respectively.A discussion on the forming setting of excellent hydrocarbon source rocks was made.The authors point out that the basin subsidence and the climate controlled the sedimentation and preservation of source rocks,and the primary productivity was closely related to the surrounding volcanic activity and deep fluids.Integrating the relationship of basin and mountain,lake-basin filling types and lithofacies assemblage,the authors provide an ideal model for the development of Chang73 excellent hydrocarbon source rocks.This study emphasizes that the strong dynamic of water(such as turbidity current or delta) might have diluted the basin and embarrassed the enrichment of organic matter,whereas the nutrition elements from volcanic ash or deep fluid might have enhanced the production of organic matter.This understanding gives an example for further study of lake-basin filling types and development of high quality hydrocarbon source rocks in similar continental depression basins.