Lithofacies palaeogeography of Middle Permian in the Sichuan Basin and its petroleum geological significance

Exploration discoveries have been made in the Middle Permian of the Sichuan Basin, indicating great exploration potential. However, the Middle Permian has obvious tectonic-sedimentary variation, resulting in complexity of hydrocarbon accumulation mechanism. The reconstruction of sequence lithofacies paleogeography is of great significance to understand the tectonic-sedimentary evolution, sedimentary formation and hydrocarbon exploration. In this paper, the lithofacies palaeogeography during the Middle Permian Qixia-Maokou period in the Sichuan Basin was reconstructed with the third order sequence as the minimum longitudinal mapping unit based on oil and gas exploration results as well as typical drilling and outcropping data. Five third-order sequences for the Middle Permian in the Sichuan Basin were supposed in this study including: SQq1 (from the Liangshan Formation to the section B of the first member of the Qixia Formation), SQq2 (from the section A of the first member to the second member of the Qixia Fo