2002 Denver Annual Meeting (October 27-30, 2002)

Paper No. 38
Presentation Time: 8:00 AM-12:00 PM


AUSICH, W.I., Department of Geological Sciences, The Ohio State Univ, 125 South Oval Mall, Columbus, OH 43210 and COPPER, P., Department of Earth Sciences, Laurentian Univ, Sudbury, ON P3E 2C6, Canada, ausich.1@osu.edu

The Ordovician-Silurian strata on Anticosti Island are, apparently, a complete succession from the Rawtheyan (Richmondian) through the Telychian. These strata were deposited in a shallow-water mixed carbonate-siliciclastic setting that supported an abundant and diverse fauna. For the first time, crinoids have been systematically sampled through this section. Relatively few Hirnantian and Llandoverian crinoid faunas were known previously, so these faunas provide an unparalleled opportunity to examine the fabric of extinctions and evolution across the Ordovician-Silurian boundary, which witnessed a macroevolutionary change in the composition of crinoid faunas. Crinoids are known from ten members of two Ordovician formations on Anticosti Island: the Rawtheyan Vauréal Formation and the Hirnantian Ellis Bay Formation. A rarefaction analysis considering the history of collections of each formation indicates that these faunas are reasonably well sampled. The Rawtheyan crinoid fauna has 12 species, organized in communities with various diversities, one to eight species, with the highest diversity in the LaVache Member. The Vauréal fauna is typical for the Rawtheyan with Gaurocrinus, Xenocrinus, Dendrocrinus, Cupulocrinus, Plicodendrocrinus, and Carabocrinus. It also contains Clidochirus, Chirocrinus, and Eomyelodactyus. However, this fauna is lower in total diversity than other Rawtheyan faunas such as the Cincinnati, Ohio area (17), the Maquoketa Shale of Iowa and Illinois (20), and the Threave Glen Starfish bed of Scotland (19). Nine species occur in the Hirnantian Ellis Bay Formation, with community diversity of one to four. The most diverse communities occur in the two upper members, the Lousy Cove and Laframboise, with four species each. Crinoids in this fauna include a new rhodocrinitid camerate, a new monorathrid camerate, Xenocrinus, Dendrocrinus, Euspirocrinus, Calceocrinus, and Charactocrinus. The best documented Hirnantian crinoid fauna is the Girardeau Limestone in Missouri, which is much more diverse (15 species).