Tectonic and climatic interplay controls organic matter enrichment in Eocene low-latitude rift lakes: Insights from the Asian continental margin

Abstract

Organic matter enrichment in lacustrine rift basins remains enigmatic compared to marine systems, despite their significant role in global carbon cycling. The Eocene Liushagang Formation (South China Sea) provides valuable insight into how tectonic-climatic interactions control organic matter accumulation during active rifting. While conventional models emphasize productivity-anoxia interplay, the role of tectonic-climatic controls on organic matter deposition was less discussed. By integrating sedimentology, petrology, organic geochemistry, palynology, and elemental geochemistry, this multidisciplinary dataset seeks to elucidate the relationships between regional tectonism, climate change, and lake environment. Our results suggest that: (1) Intense rift activity, warm-humid climate, and moderate chemical weathering promoted a deep and stratified lake with high productivity and anoxia; (2) A distinct vertical variation in organic matter enrichment, with exceptional TOC contents in lower E₂l² shales contrasting sharply with diminished accumulation in upper E₂l² due to climate cooling and nutrient depletion; (3) Three predictive models of organic matter enrichment that correlate specific depositional conditions with accumulation efficiency. These results fundamentally advance our understanding of rift lake organic matter enrichment by highlighting tectonic accommodation space and Early Eocene Climatic Optimum (EECO) perturbations as primary drivers. The established models provide a valuable framework for evaluating lacustrine source rocks potential in Cenozoic basins worldwide, with particular relevance for low-latitude rift systems.