Effect of Late Cretaceous marine incursions on lacustrine organic carbon burial in East Asia: Perspectives from machine learning and geochemistry

Abstract

The relationship between lacustrine organic carbon burial and marine incursion has been investigated extensively, yet the mechanisms by which marine incursions control organic carbon burial remain unclear. The Songliao Basin, one of the largest continental basins in East Asia during the Cretaceous, provides an ideal natural laboratory to address this issue. This study focuses on the first member of the Qingshankou Formation (K₂qn¹) of the Late Cretaceous in the Songliao Basin, northeast China. Trace-element ratios, molecular biomarkers, and strontium isotopes demonstrate episodic marine incursions and indicate that the Southeastern Uplift was more strongly influenced by marine incursion than the Central Depression. As marine incursions intensified, the contribution of algae increased, primary productivity rose, anoxic conditions intensified, and salinity in the water column increased. Collectively, these processes markedly enhanced organic carbon burial. Spatial distributions of Sr/Ba, pristane/phytane (Pr/Ph), and total organic carbon (TOC) corroborate these lacustrine responses to marine incursions. A model was developed using XGBoost to quantify organic carbon burial using sedimentary environment indicators as input, specifically paleoclimate (Sr/Cu), paleosalinity (Sr/Ba), paleoredox (C_org/P), and paleoproductivity (Cu/Al); TOC served as the target variable. Results demonstrated that the XGBoost model captured the nonlinear relationship between depositional environments and organic carbon burial associated with marine incursion. Shapley Additive exPlanations (SHAP) identified paleoproductivity as the principal control on burial, followed by redox conditions. This study demonstrates the utility of machine learning in elemental geochemistry and provides a quantitative characterization of how marine–terrestrial interactions influence organic carbon burial in lacustrine depositional environments.