ABSTRACT: The Global Stratotype Section and Point (GSSP) for the base of the Roadian Stage is identifiedwithin the Cutoff Formation in Guadalupe Mountains National Park (GMNP). Previous mapping of the Cutoff Formation near the shelf margin of the buried late Kungurian (late Leonardian using North American terminology) Victorio Peak and equivalent Bone Spring platform proposed a three-member subdivision for this unit based upon the recognition of lithological changes and unconformities. New mapping conducted to the south of these previously studied outcrops identifies an undocumented succession of unconformity-bound carbonates, shales, and sandstones situated between the members described in previous work. These units are positioned demonstratively above the GSSP in Stratotype Canyon and thus represent a previously undocumented record of the earliest Roadian Stage in GMNP. In accordance with the NorthAmerican stratigraphic code, thiswork includes a description of the facies, boundaries, thickness, and lateral extent and correlations in a proposition for introducing two new members to the stratigraphy of the Cutoff Formation. In ascending order, these members include the Butterfield Member and the Rest Area Member. The Butterfield Member is an interval of grain- and mud-dominated carbonate deposits which are distinct from the underlying siliceous shale of the established El Centro Member and is bounded above by shales of the Rest Area Member. The Rest Area Member represents a lower shale, middlemud-dominated carbonate, and upper conglomerate and sandstone triplet, which is distinct from the overlying thin-bedded carbonate deposits of the established Williams Ranch Member. Both of these members pinch out to the south of the GSSP and have the potential to yield specimens of biota extant during the earliest Roadian Stage that are not currently sampled. Faunal specimens of this kind have the potential to improve correlations of the basal boundary for the Roadian Stage to areas with equivalent strata in other parts of the world. Furthermore, formal recognition of the Cutoff Formation as a basinward-thickening unit will aid in the correlation of stratigraphic units in the subsurface of the Delaware Basin and improve the understanding of the linked late Kungurian – early Roadian shelf, slope, and basinal architectures.
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