Paper No. 32
Presentation Time: 9:00 AM-6:00 PM

TRANSIENT METAZOAN REEFS IN THE AFTERMATH OF THE END-PERMIAN MASS EXTINCTION


BRAYARD, Arnaud, Université de Bourgogne, Dijon, 21000, France, STANLEY Jr, George D., Geosciences, The University of Montana, Missoula, MT 59812, VENNIN, Emmanuelle, Laboratoire Biogéosciences, 6 Bd Gabriel, Dijon, 21000, France, OLIVIER, Nicolas, Laboratoire de géologie de Lyon: Terre, Planètes, Environnement, Université Lyon 1, 27-43 Boulevard du 11 novembre 1918, Villeurbanne, 69622, France, BYLUND, Kevin G., 140 South 700 East, Spanish Fork, UT 84660, JENKS, Jim, 1134 Johnson Ridge Lane, West Jordan, UT 84084, STEPHEN, Daniel A., Earth Science Department, Utah Valley University, 800 West University Parkway, Orem, UT 84058, HOFMANN, Richard, Paläontologisches Institut und Museum, Universität Zürich, Karl-Schmid Strasse 4, Zurich, 8006, Switzerland, GOUDEMAND, Nicolas, Paleobiology Group, Stanford University, 450 Serra Mall, Stanford, CA 94305 and ESCARGUEL, Gilles, Laboratoire de géologie de Lyon: Terre, Planètes, Environnement, Université Lyon 1, 2 rue Dubois, Villeurbanne, 69622, France, george.stanley@umontana.edu

Recovery from the devastating Permian-Triassic mass extinction about 252 myr ago is usually assumed to span ~5 myr, the entire Early Triassic epoch. The post-crisis interval was characterized by large-scale fluctuations of the global carbon cycle and harsh marine conditions, including a combination of ocean acidification, euxinia, and fluctuating productivity. During this interval, metazoan-dominated reefs are thought to have been replaced by various microbial deposits that are considered the hallmark of the Early Triassic. Contrasting with this consensual recovery scenario of a delayed recovery of complex benthic communities, we document metazoan-rich bioaccumulations and reefs from the western USA, formed only 1.5 myr after the extinction. These bioconstructions are comprised of various sponges and serpulids associated with microbialites and diverse eukaryotic organisms. We conclude that the predominance of microbial reefs following the mass extinction is restricted to short intervals during the earliest Triassic. We suggest that metazoan reef building continued throughout the Early Triassic wherever permitted by environmental conditions. However, the absence of corals, or their failure to calcify, remains remarkable for the Early Triassic and contrasts with their flourishing in later Triassic times. The absence could be due to the impossibility for these stenotypic reef builders to cope with intermittent deleterious conditions, especially potential acidification. While present-day reefs are most likely headed towards a severe extinction, these findings remind us that biotic recovery after an extinction event is a rapid phenomenon at the geological time scale, but a very long evolutionary process at the biological (human) time scale.