LOW OXYGEN AND EXTREME TEMPERATURES DISTURB THE ECOLOGICAL RECOVERY OF THE TETHYAN BENTHIC FAUNA FOLLOWING THE END-PERMIAN MASS EXTINCTION

The Werfen Formation in the Italian Dolomites contains an extremely complete record of the end-Permian mass extinction and the Early Triassic. We performed high resolution paleocommunity analysis on two sections from the Werfen in order to evaluate biological and ecological change associated with extreme temperature and low oxygen conditions. The Werfen was deposited in the Tethys Ocean which has been interpreted as a restricted basin prone to low oxygen stratification and overturn events during the Early Triassic. An additional extreme temperature event in the late-Smithian was globally widespread. Ecological analysis allows us to reinterpret the pre-supposed stagnant recovery as a complex set of rebounds and resets in response to environmental change.

Bulk samples were collected for diversity and paleoecological data and compared to previous analysis. Thin sections were analyzed for microfossil content and to improve sedimentological and environmental interpretations. A modified ecological recovery rubric was used to score each community from a level 1 to a level 4, which indicates pre-extinction levels of ecological complexity.

Directly following the end-Permian extinction event, the Griesbachian Mazzin Member was deposited in a low oxygen environment and represented a low, recovery level 1. In the Dienerian Suisi Member, an increase in taxonomic diversity, body size, and trace fossil complexity among other ecological metrics indicates a recovery level 3 in conjunction with a return to oxygenated conditions. The Smithian Campil Member was reset to a recovery level 2, likely due to extreme temperature rise. In the Spathian, recovery progressed to a level 3. Extreme temperatures in the Smithian inhibited body size and the repopulation of groups like echinoderms while low oxygen conditions at different time intervals throughout the Early Triassic perpetuated the dominance of low complexity, opportunistic groups. The benthic faunas response to environmental change dictated the pattern of recovery from the end-Permian mass extinction.