High authigenic Co enrichment in the non‐euxinic buff‐grey and black shale of the Chandarpur Group, Chhattisgarh Supergroup: Implication for the late Mesoproterozoic shallow marine redox condition

Abstract

AbstractPersistently low enrichment of conventional redox‐proxy trace metals, i.e., V, Cr, Mo and U in Mesoproterozoic black shale records, has generally been interpreted as an oxygen‐depleted surface environment. However, new evidence in this study contradicts this concept. We performed an integrated trace metals, major oxides and total organic carbon investigation on the late Mesoproterozoic black/buff‐grey shale of the Chandarpur Group. The results revealed no significant enrichment of V, Cr, Mo and U, however, intermittent high enrichment of non‐detrital Co, Fe and Mn. As the studied section is non‐euxinic, sulphidic Co scavenging seems to be an unlikely mechanism for the Co enrichment. A significantly positive correlation between Co and Mn, and CoEF covariation with Fe/Al, strongly suggests the co‐precipitation of Co and Fe/Mn in a well‐oxygenated environment. This intermittent oxygenation of the sediment‐water interface would have promoted the re‐dissolution loss of V, Cr, Mo and U from the sediments deposited under preceding anoxic conditions.