The characteristics of n-alkanes from the Palaeogene lacustrine oil shale in the Kanggale area, Nyima Basin, and their paleoenvironment and Paleoclimate significance

Continuous lacustrine dark oil shale with numerous biomolecular fossils were deposited in the Nyima Basin on the central Qinghai-Tibet Plateau since Cenozoic, It is of great significance to reconstruct the paleoclimate and paleoenvironment of the Qinghai-Tibet Plateau. By analyzing the distribution characteristics of n-alkanes and related parameters of the Palaeocene Niubao Formation in the Kanggale section, the results show that the distribution of n-alkanes in the oil shale varies from bottom to top from a single peak type to a single behind peak type with two cycles; The CPI is relatively stable, but the TAR, ACL, P_aq and nC≤₂₁/nC≥₂₅ are more variable, indicating a shift in the sedimentary organic matter of the lake from endogenous-dominated lower algae to higher aquatic and exogenous terrestrial higher plants, and a gradual evolution of the regional climatic environment from cool and humid to hot and arid. To sum up, we believe that the climate change in the Nyima Basin during the Eocene was mainly influenced by westerly circulation and monsoon systems, which is related to the global climate. During periods of global warming, there is less effective precipitation from the central plateau (provided by westerly circulation and moisture from the residual ocean) and the climate dries up as westerly circulation weakens. Instead, the intensification of westerly circulation and Indian monsoons enriched the central of the plateau with repeated effective precipitation, resulting in a wetter climate.