Abstract

A detailed study of the size distribution of framboidal pyrites in the black shales of the Upper Permian Ravnefjeld Formation was performed to evaluate the redox state of the Late Permian ocean. In contrast to framboidal pyrites in bioturbated sediments, the smaller and less variable size distribution of pyrite framboids in the laminated shales of the Ravnefjeld Formation provides persuasive evidence for sulfidic (H2S-rich) bottom-water conditions in the East Greenland Basin. However, the S isotope compositions of both pyrite populations show a similar distribution. The widespread δ34S values of pyrites (−41.2‰ to −28.2‰) in the black shales of the Ravnefjeld Formation indicate a large fractionation (up to 52.7‰) relative to seawater sulfate, and may record different pathways of sulfur cycling in sulfidic water columns as well as within sediments. The new data from the East Greenland Basin indicate that environmental stress such as widespread sulfidic conditions could have caused the biotic crisis in the Late Permian.

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