Cambrian trilobites and biostratigraphy of the Abrigo Formation, southeastern Arizona, USA

A suite of Miaolingian to Furongian (i.e., traditional middle-upper Cambrian) trilobites are reported from the Abrigo Formation at exposures along Nugget Canyon and adjacent Peppersauce Canyon, Santa Catalina Mountains, Arizona, USA. These fossils are uncommon in the region because the unit predominantly comprises coarser-grained siliciclastic facies deposited near shoreface settings where fossils are not often preserved. Trilobites include Agnostidae gen. indet. sp. indet. and the ptychoparioids Ehmaniella sp. indet.; Neoblairella sp. indet.; Altiocculus sp. indet.; Arapahoia ransomei (Stoyanow, 1936); Bolaspidella sp. indet.; Bolaspididae gen. indet. sp. indet.; Brachyaspidion sp. indet.; Cedaria sp. indet.; Crepicephalus sp. indet.; Elburgia sp. indet.; Eldoradia linnarssoni (Walcott, 1884); Eldoradia prospectensis (Walcott, 1884); Iddingsia sp. indet.; Modocia centralis (Whitfield, 1877); Modocia cf. M. crassimarginata Rasetti, 1965b; Modocia oweni ? (Meek and Hayden, 1861); Strigambitus cf. S. transversus Palmer, 1965; and Tricrepicephalus texanus (Shumard, 1861). The type specimens of Arapahoia ransomei and Arapahoia butleri (Stoyanow, 1936) are refigured and considered synonymous. This fauna spans the Ehmaniella to Crepicephalus biozones and the Dunderbergia Biozone; the last has not been previously reported from the Abrigo Formation. This biostratigraphy is calibrated by correlation with regional strata constrained by detrital zircon U-Pb geochronology, which provides ages that are consistent with the observed biozones. Considered together, these data help correlate the Abrigo Formation to more fossiliferous and offshore successions elsewhere in Arizona, Sonora, New Mexico, Texas, USA, and beyond.