江西萍乐坳陷带西段早三叠世地层划分与对比及沉积环境分析

Stratigraphic classification and correlation and sedimentary environment analysis of the Early Triassic in western Pingxiang-Leping depression, Jiangxi Province

萍乡—宜春一带地处萍乐坳陷带西段,早三叠世地层广泛发育,长期以来对其地层单元划分、时代归属、分布范围、名称使用均不统一,给萍乐坳陷西段的研究工作带来诸多问题。笔者通过萍乐坳陷带西段萍乡—宜春一带1∶5万区域地质调查,首次系统地从岩石地层、生物地层方面对早三叠世地层进行了划分与对比,将该地区早三叠世地层自下而上划分为:殷坑组、青龙组、周冲村组,又将周冲村组进一步划分为四个段,并依据牙形石成果资料,将殷坑组、青龙组、周冲村组一段定为印度阶,周冲村组二段至四段定为奥伦尼克阶。同时根据岩性组合及沉积相特征对其沉积环境进行了分析,认为该地区早三叠世沉积环境为"台-坡-盆"古地貌结构的"陆缘海"。

Pingxiang-Yichun area is located in western Pingxiang-Leping depression, where the Early Triassic strata are developed extensively. The stratigraphic nomenclature, age, distribution, and the classification of the stratigraphic units in this area have been controversial for a long time, which considerably hinders the study of the Pingxiang-Leping depression. Through a 1：50000 regional geological survey in Pingxiang - Yichun area, the authors systematically classified the Early Triassic strata of that area for the first time on the basis of investigating lithostratigraphy and biostratigraphy. The Early Triassic strata in the area can be divided in upward sucession into Yinkeng, Qinglong and Zhouchongcun Formations, and the Zhouchongcun Formation can be further subdivided into four members. On the basis of conodont data, the Yinkeng Formation, the Qinglong Formation, and the first member of the Zhouchongcun Formation are assigned to India Stage, and the second member to the fourth member of the Zhouchongcun Formation are assigned to Olenekian Stage. At the same time, according to the characteristics of the lithologic association and sedimentary facies, an analysis of the sedimentary environment was carried out. The sedimentary environment of the Early Triassic strata in the study area was ＂terrace-continental slope-basin＂ epicontinental sea with the ancient landform structure.