Geochemical Characterization and Proxy Development for Hydrocarbon Potential Assessment of Shale in Lower Cretaceous Yingcheng Formation of Songliao Basin, China: A Principal Component Analysis Approach

The Southern Shuangcheng Depression, located in the northern part of the Songliao Basin in northeast China, contains organic-rich lacustrine shale intervals within the Lower Cretaceous Yingcheng Formation that have recently gained attention for their oil-type shale potential. This study presents an integrated geochemical evaluation of the Southern Shuangcheng (SSC) shale formations using principal component analysis (PCA) applied to Rock-Eval pyrolysis, molecular biomarker, and elemental datasets. A total of six geochemical proxies were used to characterize organic richness, thermal maturity, depositional redox conditions, and detrital input. These include the Organic Productivity and Hydrocarbon Potential Proxy (OPHP), Thermal Maturity Proxy (TMP), Organic Source and Preservation Proxy (OSP), Redox and Maturity Proxy (RMP), Detrital Input and Productivity Proxy (DIP), and Redox and Organic Preservation Proxy (ROP). PCA effectively reduced the complexity of the multivariate dataset, with the first two principal components (PCs) explaining over 88% of the variance in Rock-Eval data, 67% in molecular data, and 73% in elemental data. Each proxy demonstrated strong statistical correlations with its respective PC (R 2 values between 79% and 99%), confirming their reliability. The combined analysis reveals a decoupling between organic richness and maturity across wells and highlights the role of depositional environment in organic matter preservation. This study offers a quantitative and transferable approach for shale characterization, improving predictive hydrocarbon potential assessment and supporting exploration strategies in complex lacustrine systems. The proposed methodology is adaptable to similar shale formations in other sedimentary basins.