Sedimentary environments controlled by tectonics and induced differential subsidence: A perspective in the Permian Liangshan and Qixia Formations, northwestern Sichuan Basin, China

Abstract

Based on field observation, core description and well logging analysis, the tectonic-sedimentary framework of the Liangshan and Qixia Formations in the northwestern Sichuan Basin, China is deeply discussed. Two long-term sequence cycles were identified, denoted as LSC1 and LSC2, respectively. The sequence stratigraphic framework was established, suggesting the Liangshan Formation to be not isochronously deposited. Paleogeomorphy before deposition of LSC1 was reconstructed by the impression method. LSC1 was featured by thin, low-energy shoal deposits in the high topography, and thick inter-shoal sea and open sea deposits in the low topography. Meanwhile, paleogeomorphy before deposition of LSC2 was reconstructed using the residual thickness method, which was demonstrated to have primary high-energy, thick shoal deposits in the high topography, and thin inter-shoal and open sea deposits in the low topography. The results show that differential tectonic subsidence has already taken place during the Qixia Period, and thus the Dongwu Movement should occur earlier than previously expected. Meanwhile, pre-depositional paleogeomorphy has obvious controlling effects on the sequence stratigraphic filling and sedimentary facies distribution. Results of this study were expected to provide practical guidance to fine characterization of the sedimentary evolution process and prediction of high-quality reservoir distribution.

摘要

在野外观察、岩心描述及测井分析的基础上, 对川西北部地区梁山组-栖霞组的构造-沉积格架 进行深入探讨。共划分出2 个长期旋回LSC1、LSC2, 建立了川西北部梁山-栖霞组层序地层格架, 分 析认为梁山组并非等时沉积。采用印模法恢复出LSC1 沉积前古地貌、LSC1 在古地貌高部位沉积厚 度较薄的低能滩,, 而在低部位以厚度较大的滩间海、开阔海沉积为主。同时,, 采用残厚法恢复出LSC2 沉积前古地貌,, 地貌高部位以较厚的高能滩相沉积为主,, 地貌低部位为较薄的滩间海、开阔海沉积。 结果表明栖霞期已经发生了不同程度的构造差异沉降, 东吴运动发生时间可能在目前认识上进一步提 前, 沉积前古地貌对层序地层充填和沉积相分布具有明显的控制作用。研究结果对精细刻画沉积演化 过程和预测优质储层分布具有实际指导意义。