To understand probable influences of environmental changes on the decrease and rebound of biodiversity during the Late Ordovician, a detailed analysis of total organic carbon (TOC), pyrite, V/(V + Ni) ratios, and S isotopic compositions of pyrite in the Late Ordovician sediments from Poland was performed. The significant enrichments of TOC and pyrite as well as high V/(V + Ni) ratios (>0.6) for the Jeleniów Formation of the latest Darriwilian to middle Katian Stages provide evidence for predominant anoxic bottom-water conditions. In contrast, low TOC and pyrite as well as low V/(V + Ni) ratios for the Wólka Formation of late Katian age indicate oxic depositional conditions. The S isotopic data are consistent with the interpretations of oceanic redox conditions based on multiple proxies for paleoredox. The results from the Baltica area reveal a major oceanic redox condition change during the late Katian and suggest that oceanic oxygenation may have contributed to the rebound of marine animal diversity during the Late Ordovician.

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