Silurian sponge spicules from the Racine Formation, Wisconsin

• Published in: Journal of Paleontology
• Main Authors: Watkins, Rodney, Coorough, P. J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Cambridge University Press (CUP) 1997
• Subjects: Arctic
• Online Access: http://dx.doi.org/10.1017/s0022336000039147; https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0022336000039147

The Silurian (Wenlockian) Racine Formation of Milwaukee, Wisconsin has yielded 22 types of siliceous and silicified sponge spicules. The spicules occur in bioturbated dolomite mudstone, and they are part of a high-diversity community of small crinozoans, brachiopods, and other taxa. Siliceous desmas of the order Lithistida comprise 79 percent of recovered spicules. Siliceous triaxons of the class Hexactinellida and silicified sexiradiates of the class Heteractinida each comprise 7 percent of spicules. Eleven additional types of siliceous spicules of uncertain taxonomic affinity form 7 percent of the assemblage. No complete sponge skeletons have been observed, probably because of slow deposition and high bioturbation. The Racine spicule assemblage resembles sponge faunas of Silurian offshore deposits in the Canadian Arctic and Great Basin, which suggests moderate bathymetric relief in the Michigan Basin during Wenlockian times.