Carboniferous–Permian conodonts and the age of the lower Cutler Group in the Bears Ears National Monument and vicinity, Utah, USA

The Carboniferous–Permian (C–P) Cutler Group in southeastern Utah archives large-scale environmental changes along multiple facies belts, including major sea-level changes and continental aridification that intensified into earliest Permian times. Nevertheless, the stratigraphical position of the C–P boundary within the Cutler Group has been poorly constrained, until now. Here, we report the first biostratigraphically significant conodonts from shallow-water facies of the lower Cutler beds in the vicinity of Valley of the Gods, San Juan County, Utah. Bulk samples were collected from marine carbonate marker beds spanning up to 160 m of section through the middle Rico to Halgaito formations. Productive carbonates yielding diagnostic conodont elements included the informal marker beds: the McKim limestone and the ‘A’ limestone, representing a variety of shallow-water facies. C–P conodonts included Ellisonia conflexa, Hindeodus sp. and Adetognathus spp. We show that the first appearance of Adetognathus sp. B (Henderson), a species known from the C-P interval (latest Gzhelian – early Asselian) of the Canadian Arctic and east-central British Columbia, places the local base of the Permian at or above the ‘A’ limestone in southern San Juan County. The new records reinforce previous age assignments for the Rico–Halgaito transition beds established on the basis of land vertebrate faunachrons (LVFs) and offer a rare datum for correlating marine and terrestrial C–P faunal assemblages in western Pangaea.