Characteristics of Sequencebased Lithofacies and Paleogeography of the Changxing Formation in the Eastern KaijiangLiangping Intraplatform Trough

Key words: 
• KaijiangLiangping intraplatform trough

Abstract: Based on the study of sedimentary facies and sequence stratigraphy, Changxing Formation is a thirdorder of type Ⅱ sequence and subdivided into three systems tracts: SMST, TST, and 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 was aggressive from the northwest to the southeast, all kinds of sedimentary facies well developed. In the troughplatform transition belt fringing reefs and shoals occur often, and they are also the main favorable 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.