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

Abstract

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.

Paleozoic Equatorial Records of Melting Ice Ages (PERMIA): calibrating the pace of paleotropical environmental and ecological change during Earth's previous icehouse

“…This bound-ary placement is just above the highest unambiguous marine unit, a wavy-laminated dark reddish-brown sandy siltstone between 323 and 318.9 m depth containing abundant disarticulated echinoderm elements. Locating the lower Cutler-Cedar Mesa boundary above the last marine unit and at the base of the first thick sandstone sequence is also consistent with its placement in outcrops by recent stratigraphic studies (e.g., Stanesco and Campbell, 1989;Loope et al, 1990;Dubiel et al, 1996Dubiel et al, , 2009Jordan and Mountney, 2012;Huttenlocker et al, 2021;Pettigrew et al, 2021). Our boundary placement is also associated with a noticeable decrease in magnetic susceptibility, gamma density, and natural gamma radiation values (Fig.…”

“…This is consistent with the lithologic changes observed in outcrops along the southern margin of Cedar Mesa (e.g., Valley of the Gods and Goosenecks of the San Juan State Park areas), where a mixed siliciclastic-carbonate succession with abundant marine limestones (the Honaker Trail Formation) is overlain by siltstone and sandstone redbeds with rare, thin marine limestones (the local equivalent of the lower Cutler beds called the Halgaito Formation) (Baker, 1936;G. S. Soreghan et al, 2002;Ritter et al, 2002;Huttenlocker et al, 2021). The color change associated with this boundary is apparent in the core line scan image stack (Fig.…”

“…7). These age constraints are consistent with outcrop work in nearby Arch Canyon and Valley of the Gods, where Huttenlocker et al (2021) identified the conodont Adetognathus sp. B in the upper part of the lower Cutler beds.…”

“…S. Soreghan et al, 2002;M. J. Soreghan et al, 2002;DiMichele et al, 2014;Golab, 2016;Huttenlocker et al, 2018Huttenlocker et al, , 2021Golab et al, 2018;Tobey, 2020) (Fig. 5).…”

Halgaitosaurus gregarius, a New Upper Carboniferous Araeoscelidian (Reptilia: Diapsida) from the Halgaito Formation, Bears Ears National Monument, Utah, USA

“…The primarily terrestrial Halgaito Formation has a conformable time transgressive contact with the Rico Formation (DiMichele et al 2014). In the western side of Valley of the Gods, the marine McKim limestone forms the upper bed of the Rico Formation, whereas the McKim is buried and the marine limestone ‘A’ comprises the upper bed in the eastern portion of the valley (Wengerd 1950; Orkild 1955a, b; Huttenlocker et al 2018, 2020). The Birthday bonebed is in the western part of the valley and several meters below the level of limestone ‘A’, indicating it is stratigraphically within the lower portion of the Halgaito Formation (Huttenlocker et al 2018).…”