Abstract:In this study, we performed an inorganic geochemical study of EarlyMiddle Silurian bedded organic Cenriched cherts in the region between northern Ruoergai (Zoigê) County and Diebu (Têwo) County, central China. The goal of this study is to determine the origin and paleodepositional environment of the chert beds and to establish a depositional model for the Yangchanggou FormationLalong Formation in the study area. An integrated study, involving petrographic analysis, scanning electron microscopy (SEM) analysis, major, trace and rare earth element analyses, organic carbon content analysis, and Si, and O isotopic analyses, has been performed on twentyeight chert samples from the Yangchanggou Formation, Taer Formation and Lalong Formation of the Bailongjiang Group. Based on the petrographic, SEM, Fe/Ti, Al/(Al+Fe+Mn) (008~079; average 031), (Fe+Mn)/Ti (420~20523; average 6194), (La/Yb)N (012~141; average 054), δEu (081~336; average 155), ∑REE (759~25348; average 8290), Si isotope (-02‰~21‰; average 066‰), and O isotope (135‰~218‰) average 1953‰) results and the diagenetic temperatures inverted from the O and Si isotopic data, the chert samples are primarily hydrothermal in origin, with some evidence of biogenic chert (based on the Si and O isotopic compositions). During the deposition of the Taer Formation, terrigenous material mixed with the paleoseawater, promoting the growth of carbonateproducing organisms. Minor samples exhibit effect of terrigenous detrital material. Additionally, the petrographic, SEM, MnO2/TiO2, Al2O3/(Al2O3+Fe2O3) (011~084; average 037), Al/(Al+Fe) (008~080; average 033), Th/U, V (286×10-6~2261×10-6; average 45442 ×10-6), Ti/V, δCe (065~158; average 101), and (La/Ce)N (060~1314; average 097) results and the REE, TOC, and trace element (U, V, Mo, Cu, Ni) patterns indicate that the chert samples were deposited on a continental margin in an anoxic environment with strong hydrodynamic conditions. Portions of the chert samples have characteristics typical of midocean ridge and ocean basin environments (ie, they are enriched in hydrothermal elements). In combination with previous research results, we conclude that the siliceous rock formed in a continental margin extensional environment on the northern margin of the Yangtze Block. This environment was characterized by well developed hydrothermal activity and anaerobic condition, which was conducive to enrichment of U, V, Mo, Cu, and Ni. The lower Paleozoic (CambrianSilurian) black shale in the northern margin of the Yangtze Block deposited in anoxic to reducing conditions in the extensional continent margin.