Characteristics Of Sequence-based Lithofacies And Paleogeography Of The Changxing Formation In Upper Permian Of Kaijiang-Liangping Intraplatform Trough

The Sediment characteristics of Changxing Formation in Upper Permian of Kaijiang-Liangping intraplatform Trough is a set of relatively stable marine carbonate rocks deposition,combined the previous studies, and guided by the theories of sedimentology ,sequence stratigraphic,and on the basis of analysis of the rock structure ,surface profile and drilling datas ,it has studied in detail that the sequence-based lithofacies and paleogeography of the Changxing Formation in Upper Permian of Kaijiang-Liangping Trough,The main achievement and the understanding are generalized as follows:1.The carbonate rocks' deposition combination and evolution characteristic of the Changxing Formation in Upper Permian of Kaijiang-Liangping intraplatform Trough conforms to carbonate platform concept and the depositional mode.The carbonate platform (facies) could be classified into 6 facies: platform slope, platform margin reef, shallow, open platform, and restricted platform. The sedimentary models for the carbonate platform of the Changxing Formation in Upper Permian of Kaijiang-Liangping Trough have been established2.According to the previous studies, combined with the field profile, and analysis of the log data,Changxing Formation is a third-order of typeⅡsequence and subdivided into three systems tracts:SMST,TST,HST. The lithofacies paleogeographic map based on systems tract as the time—equivalent of the stratigraphic units indicates, that in Changxing stage of Late Permian in northeastern Sichuan basin a paleogeographic framework of platform alternating with basin(trough) was present. For instance,during the SMST sequence, from southwest to northeast of the study area Kaijiang-Liangping intraplatform trough and Northeast-Sichuan open platform facies successively developed. During the TST sequence, the sea water aggressived from the northwest to the southeast, all kinds of sedimentary facies well developed. In the trough-platform transition belt fringing reefs and shoals occurr often, and they are also the main favourate facies for reservoirs. During the development of HST sequence, the characteristics of sedimentary facies and distribution framework is basically the same with TST. However, because of the effect of structural uplifting and erosion at the end of Late Permian, the residual strata are very thin, and the fringing reefs and shoals almost are not absent.3.The lithofacies paleogeographic map indicates that the reef, beach-phase reservoir of Changxing formation is mainly developed in the TST, the reservoir development factors is controlled by lithology, sedimentary facies, diagenesis and the role of structural.