Paper No. 6
Presentation Time: 2:15 PM
EARLY TRIASSIC METAZOAN REEFS FROM THE WESTERN USA
STEPHEN, Daniel A.1, BRAYARD, Arnaud
2, OLIVIER, Nicolas
3, VENNIN, Emmanuelle
4, BYLUND, Kevin G.
5, JENKS, Jim
6, ESCARGUEL, Gilles
7, FARA, Emmanuel
8, SNYDER, Dawn
1 and STANLEY Jr, George D.
9, (1)Earth Science Department, Utah Valley University, 800 West University Parkway, Orem, UT 84058, (2)UMR CNRS 6282 Biogéosciences, Université de Bourgogne, 6 boulevard Gabriel, Dijon, 21000, France, (3)Laboratoire de géologie de Lyon: Terre, Planètes, Environnement, Université Lyon 1, 27-43 Boulevard du 11 novembre 1918, Villeurbanne, 69622, France, (4)Laboratoire Biogéosciences, 6 Bd Gabriel, Dijon, 21000, France, (5)140 South 700 East, Spanish Fork, UT 84660, (6)1134 Johnson Ridge Lane, West Jordan, UT 84084, (7)Umr 5125 Cnrs, Université Lyon 1, 2 rue Dubois, Villeurbanne, 69622, France, (8)Biogeosciences, University of Burgundy, 6 bd Gabriel, Dijon, 21000, France, (9)Geosciences, The University of Montana, Missoula, MT 59812, daniel.stephen@uvu.edu
Previous work has suggested that biotic recovery from the devastating Permian-Triassic mass extinction ~ 252 Ma spanned the entire Early Triassic epoch (~ 5 m.y.) if not longer. Certainly, the post-crisis interval was characterized by reduced biodiversity, large-scale fluctuations in the global carbon cycle, and harsh marine conditions, including a combination of ocean acidification, euxinia, and variable productivity levels. During this timeframe, metazoan-dominated reefs were thought to have been completely replaced by microbial deposits considered the hallmark of the Early Triassic. However, in contrast with this scenario of a delayed recovery of complex benthic communities, we document several metazoan-rich bioaccumulations and reefs from Nevada and Utah, which formed only ~ 1.5 m.y. after the mass extinction.
These bioconstructions in our study are comprised of various sponges and serpulids associated with microbialites and diverse eukaryotic organisms, such as algae, ostracods, foraminifers, gastropods, brachiopods, echinoderms, and cephalopods. They also show different morphologies according to the sedimentary context, and their formation is apparently mainly controlled by water depth and energy.
We conclude that the predominance of microbial reefs following the Permian-Triassic mass extinction was restricted to brief intervals during the earliest Triassic and perhaps was previously overestimated because of poor preservation of sponges. We suggest that metazoan reef building continued throughout the Early Triassic wherever permitted by environmental conditions. Yet, 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 of corals could be due to physiological constraints for these stenotypic reef builders that limited their ability to cope with the intermittent deleterious oceanographic conditions, especially potential acidification.
