Conodont biostratigraphy and paleoecology of the Lower Devonian Helderberg Group of Virginia

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Virginia Polytechnic Institute and State University

The occurrences of species of Delotaxis and Icriodus and the Ozarkodina remscheidensis eosteinhornensis--Ozarkodina remscheidensis remscheidensis lineage indicate that (1) most of the Keyser Formation of western Virginia is assignable to the uppermost Silurian eosteinhornensis zone; (2) the top of the upper limestone member of the Keyser is assignable to the basal Devonian woschmidti zone; (3) the remainder of the Helderberg Group is no younger than the delta zone; and (4) the basal Needmore Shale at the Price's Bluff section is assignable to the serotinus, patulus, or costatus costatus zones, of uppermost lower Devonian and lowermost Middle Devonian age, leaving a gap of at least six conodont zones represented by the Ridgeley Sandstone and its bounding unconformities.

Conodonts tend to avoid tidal flat and lagoonal environments. They are not uniformly distributed through the rest of the section, but the occurrence of all but two species is not related to water depth, energy, or substrate; Ozarkodina excavata and Pseudooneotodus beckmanni prefer moderate energy environments. Icriodus helderbergensis and most of the simple cone species are associated with each other.

There were 13,360 specimens collected, divided among 10 biological species and 15 form species; of the biological species, 3 are new and 2 are newly reconstructed apparatuses.