Geochemical Characteristics and Sedimentary Environment of the Lijiapan Shale from Yanchang Formation in Southeastern Ordos Basin

Investigating the geochemical properties and sedimentary environment of shale is crucial for reconstructing the basin's sedimentary framework, estimating paleogeothermal conditions, estimating paleotemperature, and exploring the origins of reservoir formation. Elemental geochemical analysis methods was applied to assess the major, trace, and rare earth elemental characteristics of the Lijiapan Shale from Yanchang Formation in southeastern Ordos Basin, aiming to explore the sedimentary environment during its formation period. The results indicate that compared with the upper crust, the main elements P2O5, K2O, TFe2O3, and Al2O3 are enriched in the Lijiapan shale, while trace elements such as U, Mo, and As are extremely enriched. The degree of differentiation between light and heavy rare earth elements is relatively high. The geochemical indicators indicate that the Lijiapan Shale of Yanchang Formation in southeastern Ordos Basin was formed under warm and humid conditions, reducing strong reducing conditions, semi-deep to deep lake facies with low-salinity freshwater, under weak hydrodynamic forces, and with high lake productivity. This stable, biologically thriving sedimentary environment favored the enrichment and preservation of organic matter.