The hydrocarbon source beds of the Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation were deposited in the Yangtze area.It is important in theory and practice to probe the mechanism of the development of marine hydrocarbon source beds,i.e.the precondition of breakthrough in the exploration of the marine strata in South China.From the Late Ordovician epoch,the Yangtze area began clastic shelf evolutionary phase.In Wufeng and Longmaxi age of the Late Ordovician and Early Silurian,the study area was mainly a restricted deep shelf.The paleogeographic framework was formed by the coexistence of shallow and deep shelves and bathyal environment.The distribution of sedimentary systems and sedimentary evolution were controlled by convergent squeezing of the Yangtze and Cathaysian platforms.The organic-rich source beds of the Upper Ordovician and the Lower Silurian in the Yangtze area are intimately related to these factors as following:the high organism production and bury,the rapid rise of sea level caused by a rapid increase of temperatures and melting of glaciers,between a glacial age and a postglacial age,enrichment of phosphorus element and the adsorption of clay minerals during the preservation of organic matter.