Major oceanic redox condition change correlated with the rebound of marine animal diversity during the Late Ordovician

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 Jeleniow 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 Wolka 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.