FAUNAL PATTERNS OF PENNSYLVANIAN SILICIFIED MARINE GASTROPODA FROM INDIANA

A diverse, silicified marine invertebrate fauna from Weller Falls, Warren County, Indiana shows exceptional preservation. The limestone was correlated with the Holland Limestone and was assigned a lowest Desmoinesian (Pennsylvanian) age based on conodont zonations (Rexroad, Brown, Devera, and Suman, 1998). The silicified taxa are stratigraphically restricted to a 3 to 6 cm zone in a 1.5 m thick organic-rich micritic limestone. The fauna includes gastropods, bivalves, cephalopods, scaphopods, rostroconchs, sponges, brachiopods, crinoids, ophiuroids, foraminifera, trilobites, ostracodes, and bryozoans. Preliminary work has recovered 16 families and 30 genera of gastropods ranging from 0.15 to 12 mm in length. There is no evidence of silicification in taxa larger than 12 mm. Silicification at this locality preserves protoconchs, larval shells, and detailed ornament on teleoconchs.

Preliminary faunal comparisons among the Weller Falls Fauna and the lower Desmoinesian Flechado Formation from New Mexico (Kues and Batten, 2001) and the late Visean (Mississippian) Ruddle Shale from Arkansas (Nützel and Mapes, 2001) show Vetigastropods and Caenogastropods to be the two dominant groups in all three faunas with 70% or more specimens in these two groups. Bellerophonts are the third most abundant group containing 7% to 22% of specimens in these faunas. Heterostropha are a minor group in both the Weller Falls and the Flechado faunas but are absent in the Ruddle Shale fauna. Platyceratids are a minor group in the Flechado Formation but are absent in both the Weller Falls and the Ruddle Shale faunas.