ECHINODERM EPIBOLES IN THE HELDERBERG GROUP (PŘÍDOLÍ – LOCHKOVIAN) OF NEW YORK AND THEIR STRATIGRAPHIC UTILITY

Seven distinct echinoderm epiboles are recognized in the carbonate formations of the Helderberg Group. Six epiboles are characterized by unique holdfast morphologies that permit recognition of individual taxa even in extensively reworked encrinites. Two epiboles display unusual taphonomic signatures. These epiboles facilitate regional correlations, clarify stratigraphic relationships, and enable recognition of facies variations within individual units.

In ascending stratigraphic order, the epiboles are: 1) Scyphocrinites/Camarocrinus - Green Vedder Mbr. of the Manlius Fm., 2) Lepocrinites n. sp. - lower Dayville Mbr. of the Manlius Fm., 3) Ctenocrinus - upper Dayville Mbr., 4) Lepocrinites gebhardi - upper 2-4 m of the Ravena Mbr. of the Coeymans Fm., 5) Mariacrinus stoloniferous - upper Kalkberg Fm., 6) Aspidocrinus scutelliformis - lower Becraft Fm. and 7) Clonocrinus sp. (?) - uppermost Becraft Fm.

The Silurian-Devonian boundary is marked by the Scyphocrinites/Camarocrinus epibole comprised of whole and fragmental loboliths (floats) and dispersed ossicles, associated with numerous orthocones. Abundant dart-like holdfasts and obrution-preserved, fully articulated cystoids characterize the Lepocrinites n. sp. epibole in the Dayville. Higher in the Dayville, Lepocrinites becomes less abundant and the tops of tempestite beds are strewn with long, ropy stems of Ctenocrinus. The upper beds of the Ravena are characterized by profuse club-like holdfasts of the cystoid L. gebhardi. Rhizoidal holdfasts of M. stoloniferous are restricted to the upper half of the Kalkberg Fm. The Mariacrinus epibole helps demonstrate westward thinning of the Kalkberg as it laps onto the Punch Kill Unconformity. The lower half of the Becraft Fm. displays countless shield-like holdfasts of A. scutelliformis. Thinner and flatter A. scutelliformis occur in packstones to wackestones between Schoharie and Sharon Springs. Occurrence of this guide fossil enables reinterpretation of the “upper tongue of the Kalkberg Fm.” in this region as a muddy facies of the Becraft Fm. (typically a grainstone). Restricted to the uppermost 1.5 m of the Becraft Fm. in the central Hudson Valley, the Clonocrinus sp. (?) epibole exhibits clusters of root-like holdfasts in grainstones with abundant Gypidula pseudogaleata, a robust pentamerid.