Salt, wind, and acid: extreme continental environments in the Permian of Western Pangaea as precursors to the end Permian mass extinction

The quest to understand the end Permian mass extinction has mainly utilized rocks and fossils of the marine record. However, widespread mid Permian red beds and evaporites of the U.S. midcontinent, deposited in continental settings, may provide clues for environmental changes which set the stage for “the big kill”. Here we present sedimentological, geochemical, and paleontological data from the mid Permian Nippewalla Group of Kansas and the Opeche Shale of North Dakota. These rocks represent ephemeral acid saline lakes and surrounding mudflats and sandflats, wind-deposited loess, sand dunes, and desert paleosols. Analyses of primary, unaltered fluid inclusions in bedded and displacive halite, shows that lake waters and groundwaters were saline and acid, with pH as low as -1. Homogenization data from fluid inclusions suggest of extremely hot weather, with air temperatures as high as 70°C. Lakes were also enriched in iron, silica, and aluminum. Thick red siltstones and mudstone units commonly cemented by halite, are internally massive and blanket-like, suggesting that wind was the predominant depositional agent and groundwaters were saline. Signs of life in these rocks are notably scarce, restricted to back-filled insect burrows, rare roots, and possible lungfish burrows in some red beds and microbial suspects in bedded halite. We propose that the combination of extremely acid brines and strong winds may have caused geochemical products, including iron, silica, and alumina, as well as sulfates and chlorides, to be transported to epeiric seas and oceans during the mid-late Permian. This ‘seeding’ of ocean waters may have driven or contributed to the acidification and anoxia reported for late Permian oceans, as well as continental systems, resulting in extremely hostile conditions for most life.

Benison K. C., Zambito J. J. I., Soreghen G.S. & Soreghan M. J., 2012. Permian of Western Pangaea as precursors to the end Permian mass extinction. 2012 GSA Annual Meeting in Charlotte (4–7 November 2012). Presentation abstract.

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