Fig. 1: Tectonic and stratigraphic background of the study area and adjacent regions.

a Map showing the geographic distribution of the Emeishan Large Igneous Province (ELIP) and Sichuan Basin in the Upper Yangtze platform, southwestern China^13,28. The administration boundaries in the map are originated from map products of National Geomatics Center of China (http://www.webmap.cn). b Tectonic setting of the study area and adjacent regions. The map of burial depth depicts the Cambrian bottom and constraints the boundary of Leshan-Longnvsi paleo-uplift²⁹. Nine gas samples for methane clumped isotope and noble gas analysis are indicated, samples not shown in the map are also collected from the same area in Sinian-Cambrian reservoirs. They are located on the Moxi-Gaoshiti Bulge as part of the Leshan-Longnvsi paleo-uplift, which is the center of the basin as well as the outer zone of ELIP. c Generalized stratigraphic column of the Sichuan Basin⁶⁵. Marine environments persisted in the basement from the Sinian to the Middle Triassic controlled by the Yangtze, Caledonian, and Hercynian movements, occurring unconformities of the Sinian-Cambrian by the deformation, the Devonian-Carboniferous by the late Paleozoic lifting, and the Permian-Triassic by the ELIP-induced dome and lifting^13,28,65. After the tectonic evolution during the middle Triassic, the terrestrial succession had become the main sedimentary facies until Late Cretaceous controlled by the Indosinian and Yanshannian movements^33,66. The Yanshannian-Himalayan lifting led to extensive absence of the Cenozoic in the basin^32,66. Symbols used in the figure include Є – Cambrian; O – Ordovician; C – Carboniferous; K – Cretaceous; E – Paleogene; N – Neogene; Q – Quaternary.