Late Paleocene-Early Eocene Climate Warming and Its Influence on Organic Matter Enrichment: Insights from the Kongdian Formation, Bohai Bay Basin, China

The late Paleocene to early Eocene was an interval of globally warm climate, during which organic-rich shales were developed in multiple basins. However, the impact of this climate warming on the mechanisms of organic matter enrichment remains unclear, primarily due to a scarcity of precise chronological data and continuous stratigraphic records from terrestrial basins. This study presents a continuous 400 m lacustrine core record from the GD-X borehole spanning the late Paleocene in the Bohai Bay Basin, East China. To reconstruct the palaeoenvironmental conditions and elucidate the mechanisms of organic matter enrichment of Paleocene shales, a series of analyses including total organic carbon (TOC), Rock-Eval pyrolysis, X-ray diffraction (XRD), major and trace elements testing, carbon and oxygen isotopes testing, and Gas Chromatography-Mass Spectrometry (GC-MS) were performed. The results indicate a high abundance of thermally mature Type I and II kerogen in the shales, with most samples exhibiting good to excellent generative potential. The mineralogical compositions are primarily comprised of quartz, feldspar, and dolomite, supplemented by calcite, clay minerals, and analcime. Vertical shifts in paleoenvironmental indicators suggest a climatic transition from semi-humid to arid conditions during the late Paleocene sedimentary period, characterized by reduced input of terrigenous detritus and increased water salinity. These findings indicate that rapid global warming from the late Paleocene to the early Eocene significantly altered precipitation patterns, leading to intensified lake evaporation, diminished surface runoff, and decreased inflow of terrigenous debris into lakes. Consequently, the organic matter enrichment model transitioned from a high productivity-dominated regime to one primarily driven by preservation conditions. Investigating the interplay between environment and biological evolution elucidates the enrichment mechanism of terrestrial organic matter against a backdrop of global climate warming. This research not only provides a scientific basis for predicting the distribution of continental organic-rich shale, but also offers geological insights into the carbon cycle under extreme climatic conditions in Earth's history.