Controls of Tectonic, Sedimentary and Paleoenvironmental Factors on Source Rock Formation of the Lower Wenchang Formation, Pearl River Mouth Basin

ABSTRACT The Kaiping–Baiyun Western Sag in the Pearl River Mouth Basin is a key area for deepwater petroleum exploration in China. However, due to complex tectonic changes and limited well coverage, the differential formation mechanisms and multi‐scale controlling factors of source rocks in rift basins remain unclarified. This study investigates the tectonic, sedimentary and paleoenvironmental controls on source rock formation through well‐seismic calibration, organic geochemical analysis and paleoenvironmental reconstruction. The results indicate that multi‐order faults exert hierarchical control on the distribution of source rocks. First‐order faults define the boundary of Kaiping, Panyu 25 and Baiyun Western Sag and govern the distributions of source rock. The second‐order faults dominate the thickness differentiation of source rock in the Sub‐sags, and third‐order faults regulate local heterogeneity. Sedimentary facies further determine the lithology and quality of source rocks. Source rocks exceeding 300 m in thickness with TOC over 2.0% are widely distributed in the lacustrine facies. In contrast, source rocks with mud‐sand interbed and low TOC are mainly deposited in fluvial environments. Paleoenvironment serves as the key control on differential organic matter enrichment. Warm climate, high productivity, and bottom‐water anoxia are the key factors driving TOC over 3.0%. In contrast, arid climate and elevated paleosalinity restrict organic matter enrichment. Accordingly, this study proposes a source rock formation model in which faults control distribution, lacustrine facies control thickness, and paleoenvironment controls quality, providing a theoretical basis for source rock prediction in the study area and similar rift basins.