Elemental Geochemistry, Paleoproductivity Variations and Their Controlling Factors of Lower Cambrian Organic-Rich Strata in the Tarim Basin

Marine source rocks in the Tarim Basin are generally highly mature to overmature, and conventional organic geochemical parameters may not fully reflect their original organic matter accumulation under such conditions. In this study, a comprehensive dataset including major elements, trace elements, and rare earth elements was used to systematically evaluate paleoproductivity variations, spatial distribution patterns, and geochemical controls of the Lower Cambrian (Є1) source rocks in the Tarim Basin. The results show that paleoproductivity in the Lower Cambrian source rocks exhibits clear stratigraphic and regional differentiation. Vertically, the lower intervals are characterized by relatively higher paleoproductivity, whereas the overlying intervals show a gradual decrease in productivity-related signals. Spatially, paleoproductivity in northwestern Tarim was generally higher and more variable than that in eastern Tarim, reflecting differences in depositional environments and material supply among different parts of the basin. These variations were jointly controlled by basin paleogeography, redox conditions, hydrothermal input, and terrigenous supply. Further analysis indicates that inorganic elements can provide complementary information on nutrient supply, export productivity, and organic matter preservation. Among these proxies, P and Ba and their excess indicators record enhanced nutrient availability and increased organic matter export, respectively; however, their variations may be decoupled from TOC because they are strongly influenced by redox conditions and post-depositional processes. In contrast, Ni, Cu, and Zn show relatively weaker enrichment but may better reflect the preserved organic matter component under reducing conditions. This study emphasizes that the application of inorganic geochemical proxies to highly mature marine source rocks requires integrated consideration of lithological heterogeneity, redox conditions, hydrothermal influence, terrigenous input, and diagenetic modification. This work represents a quantitative, data-based review and statistical reanalysis of published geochemical datasets.