Paper No. 3
Presentation Time: 8:30 AM
PALEOECOLOGY AND TAPHONOMY OF CLYPEASTEROID MASS ACCUMULATIONS IN THE OLIGO-MIOCENE OF THE MEDITERRANEAN AND PARATETHYS
NEBELSICK, James H., University of Tübingen, Institute of Geosciences, Sigwartstrasse 10, Tübingen, 72076, Germany, BELAÚSTEGUI, Zain, Universitat de Barcelona, Departament d'Estratigrafía, Paleontologia i Geociències Marines, Martí i Franquès s/n, Barcelona, 08028, Spain, DE GIBERT, Jordi Maria, Estratigrafia, Paleontologia i Geociències Marines, Universitat de Barcelona, Facultat de Geologia, Martí Franquès s/n, Barcelona, 08028, Spain, MANCOSU, Andrea, Universita' degli Studi di Cagliari, Dipartimento Scienze della Terra, via Trentino, 51, Cagliari, 09127, Italy and KROH, Andreas, Naturhistorisches Museum, Burgring 7, Vienna, 1010, Austria, nebelsick@uni-tuebingen.de
Clypeasteroid echinoids are important contributors to sedimentary successions in shallow water environments during the Oligo-Miocene. Clypeasteroids form characteristic shell beds in both siliciclastic and carbonate sedimentary successions especially in the Mediterranean and Paratethys regions. The presence of these accumulations is promoted sturdy tests due to robust plate connections and internal supports. They can also occur in very large numbers in monospecific populations as documented for sand dollars in Recent higher energy, shallow water settings. In this presentation, new detailed sedimentological and palaeontological data from clypeasteroid occurrences are combined with previous studies from the Tethys and Paratethys in order to compare: 1) the diversity of constituent echinoids, 2) the sedimentary fabric and their position within sedimentary cycles, and 3) detailed biostratinomic aspects including disarticulation, fragmentation, abrasion, bioerosion and encrustation.
The results show a large variety of sedimentary and taphonomic features despite the fact only few genera (typically Clypeaster, Parascutella and Amphiope) are involved. Accumulations range from single taxa to multi-taxon assemblages. Sedimentary fabrics vary from accumulations a few decimeters thick to meter thick multi-event beds, with densities ranging from dispersed to very dense, imbricated and stacked individuals. Excellently preserved to strongly abraded and highly disarticulated specimens are present. Post-mortal encrustation by a variety of organisms and intense bioerosion especially by boring bivalves (Gastrochaenolites) can also be encountered though often missing. Commonalities include the fact that the clypeasteroids all occur in great numbers predominantly in near shore, trangressive settings. The disappearance of these accumulations in the study area goes hand in hand with the extinction of specific taxa as well environmental shifts related to paleogeography and paleoclimate.
