A thin (3-6) cm) interval in the Perth Limestone Member of the Staunton Formation (Pennsylvanian, Desmoinesian) in Warren County, Indiana, contains abundant small siliceous sponge spicules that form a spicule mat. The limestone is a grain-supported packstone with a micritic matrix, the predominant grains being small sponge spicules that range down to a few micrometers in size. The intermeshed spicules helped support a wide variety of vagile and sessile benthonic marine invertebrates on a lime mud bottom. In contrast to other spiculites that are basinal deposits, the spiculite reported here developed in shallow water, probably no more than 90 feet deep, as part of a cyclothemic sequence that includes coals and fluviatile channel sandstones above and below the Perth.

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