27 Paleontology (Posters) I: Ecology and Phylogeny

Sunday, 9 October 2011
9:00 AM - 6:00 PM
Hall C

DEPTH TRANSECT OF AN UPPER TRIASSIC REEF FROM GOSAU, AUSTRIA; MICROFACIES AND COMMUNITY ECOLOGY

Paper number: 27-9
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

In the Late Triassic (~235–200 Ma) scleractinian corals and calcareous sponges built large, diverse reef ecosystems, which are some of the most notable fossil reefs. We present a depth transect along an Upper Triassic barrier reef from Gosau, Austria: the early Rhaetian Dachsteinrifkalk of the Gosausee margin. The Gosausee reef is relatively intact, with good preservation of microfacies and fossil organisms. The lack of tectonic deformation allows for an almost continuous transect from the fore reef zone at the bottom of the hill, up through the reef front, and laterally northward into the back reef and lagoonal facies at the top of the hill. The Gosausee reef exhibits strong depth zonation in both the community paleoecology and the inorganic reef fabrics (brecciation, cementation etc.) as well as zonation of the cryptobionts, which demonstrate a shift in encruster communities as the cavities in which they lived were filled.

The fore reef facies of the Gosausee reef is characterized by delicate, branching corals, calcareous sponges, Tubiphytes epibionts, and thin microbial encrusters. The reef front facies typically features more robust branching corals, calcareous sponges, calcareous algae, and a diverse suite of epibionts and cryptobionts (foraminifera, microproblematica e.g. Microtubis, and clotting or encrusting microbialites), with thick (probably marine) isopachous cements, and in places, autobrecciation of the reef front. In outcrop, large (decimeter to meter scale) branching corals (Retiophyllia) dominate the back reef facies, but in thin section there are diverse epibionts and cryptobionts (Microtubis, encrusting microbialites, sponges etc.) associated with these corals, and numerous generations of marine cements.

The Gosausee reef features classic depth zonation and intriguing epibiont and cryptobiont zonation, which can inform models of the community ecology and niche utilization in these reef ecosystems, which were evolving rapidly in the Mesozoic.