Frenchman Mountain Dolostone: A new formation of the Cambrian Tonto Group, Grand Canyon and Basin and Range, USA

Abstract We describe, interpret, and establish a stratotype for the Frenchman Mountain Dolostone (FMD), new Cambrian stratigraphic unit that records key global geochemical climate signals is well exposed throughout Grand Canyon central Basin Range, USA. This flat-topped carbonate platform deposit uppermost of Tonto Group, replacing informally named “undifferentiated dolomites.” The two chemostratigraphic events—the Drumian Carbon Isotope Excursion (DICE), when δ13Ccarb (refers to “marine rocks”) values in FMD dropped −2.7‰, Steptoean Positive (SPICE), rose +3.5‰. forma tion consists eight lithofacies deposited shallow subtidal peritidal paleoenvironments. At its at Mountain, Nevada, 371 m thick. Integration regional trilobite biostratigraphy geochronology with stratigraphy sedimentology FMD, together chemostratigraphy entire succession illustrates spans ~7.2 m.y., from Miaolingian (lower Drumian, Bolaspidella Zone) Furongian (Paibian, Dicanthopyge time. To west, correlates most Banded Member ~1100-m-thick Bonanza King Formation. east, Canyon’s Palisades Desert, thins 8 due pre–Middle Devonian erosion cut progressively deeper cratonward. Portions display visually striking, meterscale couplets alternating dark- light-colored facies, while other portions consist thick intervals single or facies. Statistical analysis strata section, involving Markov order runs analyses, yields no evidence cyclicity forms order. Autocyclic processes provide simplest mechanism have generated facies observed FMD.