Abstract

Two Devonian conodont faunas, which represent two distinct lithostratigraphic units, occur in strata that are generally assigned to the Woodford Formation in the subsurface of West Texas and eastern New Mexico. The lower fauna is latest Givetian to early Frasnian in age and occurs as stratigraphic “leaks” into the underlying heavily karsted carbonate section and in green and dark gray shales that locally overlie the carbonate section. This “pre-Woodford shale” represents the remnants of Devonian Transgressive-Regressive cycles IIa and IIb. The polygnathid-dominated conodont fauna indicates deposition in a subtidal setting. The upper conodont fauna from the black, organic-rich shale of the typical Woodford section is middle to late Famennian in age and places the black shale in T-R cycles IIe and IIf. No strata of T-R cycles IIe and IId have been identified and a significant unconformity exists between the “pre-Woodford shale” and the Woodford. The black shale fauna is typical of the palmatolepid/polygnathid biofacies, which is characteristic of deep subtidal, far offshore depositional environments. No Mississippian conodonts were recovered from the Woodford.