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.