EARLY TRIASSIC METAZOAN REEFS FROM THE WESTERN USA
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.