Influence of Volcanic Ash on Organic Matter Enrichment in the Late Permian Wuchiaping Formation, Eastern Sichuan Basin: Multiproxy Evidence and Implications for Shale Gas Exploration.

The relationship between volcanic activity and organic matter enrichment in sedimentary basins represents a critical yet incompletely understood control of source rock formation. Previous studies have documented correlations between these phenomena, but quantitative assessments of the volcanic input intensity and mechanistic models remain limited. This study employs a novel multiproxy approach to quantify volcanic ash intensity and evaluate its influence on organic matter enrichment in the Late Permian Wuchiaping Formation of the eastern Sichuan Basin, South China. Integration of mercury isotope systematics, high field strength element (HFSE) concentrations, and detailed mineralogical analyses reveals distinct pulses of volcanic activity associated with Paleo-Tethys subduction, with maximum intensity recorded in the upper Ws3 layer. Geochemical evidence demonstrates a robust coupling between volcanic ash input and organic matter enrichment through two interconnected mechanisms: (1) volcanic nutrient fertilization, evidenced by strong correlations between volcanic ash intensity indicators (Hg/Al) and paleoproductivity proxies (Ni/Al); and (2) maintenance of anoxic-euxinic conditions (V/(V + Ni) > 0.6, Ni/Co 8-19) conducive to organic matter preservation. Intervals with the highest volcanic ash intensity consistently exhibit elevated total organic carbon content (mean 6.2% in Ws3 versus 2.8-3.1% in Ws4-Ws5). These findings enhance our understanding of the complex interplay among tectonic processes, volcanic activity, and organic carbon burial in sedimentary basins, with significant implications for predicting source rock distribution and quality in convergent margin settings worldwide.