Sedimentary Controls on Migration Patterns and Developmental Model of Black Shales in the Foreland Lake Basin: Insights from the Middle Jurassic Lianggaoshan Formation in the Sichuan Basin, China

Abstract Research on the distribution and development of black shales in the Lianggaoshan Formation has been deficient, which has hindered exploration for lacustrine shale oil in the Sichuan Basin. Our study characterized the well logging data, core samples, outcrops, and geochemistry of black shales in the Lianggaoshan Formation in the Sichuan Basin. Our analysis focused on the lake basin evolution and the migration characteristics, paleoenvironmental features, formation mechanisms, and developmental model of the black shales. The results indicated that black shales in the Lianggaoshan Formation exhibited significant lateral migration, with an overall thickening trend from east to west. Within the 1st Member of the formation, black shale occurred as a single thick layer in the eastern region that gradually thinned toward the central region. Multiple sets of shale developed within the 2nd and 3rd members, and these had lower thicknesses than the 1st Member and migrated toward central Sichuan. Paleoproductivity and terrigenous input were the main factors controlling the deposition of black shales. A semi‐humid climate influenced the deposition of black shales, bringing abundant freshwater, terrigenous debris, and nutrients into the basin. Decomposition of organic matter consumed oxygen in sediment and bottom water, causing localized oxygen deficiency in the strata.