T399 The Road to Recovery—The Nature of Biotic and Geochemical Cycles During the Early Triassic

Wednesday, 30 October 2013
1:00 PM - 5:00 PM
Room 504

EARLY TRIASSIC METAZOAN REEFS FROM THE WESTERN USA

Paper number: T399-6
Program: Technical Sessions
Time: 2:15 PM – 2:30 PM

Authors

Abstract

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.