REBOUNDS AND RESETS IN THE BENTHIC RECOVERY FROM THE END-PERMIAN MASS EXTINCTION

The recovery from the end-Permian mass extinction is unusually long, lasting 5 My. Debates over the cause of the delayed recovery for the benthic, sea floor dwelling, marine communities have shifted from a focus on the sheer magnitude of the mass extinction to the continued environmental stress that was experienced by the benthic fauna throughout the Early Triassic. Recent publications have suggested that the benthic recovery progressed through stages of increasing ecological complexity, by the addition of higher trophic levels or through a community successional model (Solé et al. 2002, Chen and Benton 2012). The recovery is typically viewed as having been completed in the Middle Triassic, although the pace may have varied regionally. We present a modified recovery rubric that was used to assess benthic body and trace fossil diversity and complexity. The Moenkopi Formation and the Thaynes Formation from the Southwest US represent Panthalassa and the Werfen Formation in Italy represents Tethyan conditions. In Italy, low oxygen conditions in the Griesbachian prevented a rebound and only during the Dienerian Suisi Member, when oxygenated conditions returned, was the environmental limitation on the benthic fauna lifted. Persistent low oxygen conditions also limited the recovery of the benthic fauna in the Spathian Virgin Limestone in the Southwest United States. An extreme temperature event at the end of the Smithian was globally devastating and resulted in a short-lived decrease in diversity, body size, and complexity of the benthic shelly and trace fossil fauna in both the Southwest USA and Italy. The rebounds and resets caused by extreme temperature rise and regional low oxygen environments resulted in the appearance of a prolonged recovery for the benthic fauna. The benthic recovery was not delayed, it did not necessarily progress through step-like increases in trophic complexity, but was perturbed by repeated environmental catastrophes.