开江—梁平台内海槽东段长兴组层序—岩相古地理特征

通过沉积相和层序地层分析，将开江—梁平台内海槽东段长兴组层序划分为一个Ⅱ型三级层序和陆棚边缘（SMST）、海侵（TST）和高位（HST）三个体系域。以体系域为等时地层单元编制的岩相古地理图，表明四川盆地东北部晚二叠世长兴期碳酸盐岩沉积具有槽—台相间的古地理格局，其中:SMST沉积时，研究区自西南向北东方向依次发育有开江—梁平台内海槽和川东北开阔台地相带；TST沉积时，海水由西北往东南向侵进，各种沉积相带发育齐全，在槽—台相间的古地理格局背景上，于槽—台过渡带发育有台地边缘生物礁和浅滩相带，该相带也是最有利储层发育的相带；HST沉积时的沉积特征和展布格局与TST时期基本一致，但因受到晚二叠世末期构造抬升和侵蚀作用影响，所保存的地层很薄，台地边缘生物礁和浅滩基本不发育。

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

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.