Joint 118th Annual Cordilleran/72nd Annual Rocky Mountain Section Meeting - 2022

Paper No. 18-5
Presentation Time: 9:20 AM


DEHLER, Carol1, YONKEE, Adolph2, SCHMITZ, Mark3, SUNDBERG, Fred A.4, COTHREN, Hannah1 and ELLISON, Matthew5, (1)Department of Geology, Utah State University, 4505 Old Main Hill, Logan, UT 84322, (2)Department of Earth and Environmental Sciences, Weber State University, 1415 Edvalson St - DEPT 2507, Ogden, UT 84408-2507, (3)Department of Geosciences, Boise State University, Boise, ID 83725, (4)Museum of Northern Arizona, 3101 N Fort Valley Rd, Flagstaff, AZ 86001, (5)Gerhart Cole, 7657 S. Holden Street, Midvale, UT 84047

Neoproterozoic-Cambrian strata in northern Utah to southeastern Idaho preserve a rich record of rifting during breakup of Rodinia leading to development of the western passive margin of Laurentia (modern day coordinates), and also documents Cryogenian glaciations and the evolving biosphere leading to the Cambrian explosion. In this presentation we integrate results from recent stratigraphic and geochronologic studies to develop a refined age and subsidence model for the Utah-Idaho area. The record includes: (1) development of intracratonic basins and deposition of largely siliciclastic strata (Uinta Mountain Gp) from ~766–730 Ma; (2) early rifting, bimodal volcanism, and deposition of glaciogenic strata (Perry Canyon and Pocatello Fms) variably bound by unconformities from ~720–635 Ma; (3) broad subsidence and deposition of mature siliciclastic strata (Caddy Canyon to Mutual Fms) from ~635–610 Ma, punctuated by incision during Caddy Canyon-Inkom time; (4) local mafic volcanism followed by mature siliciclastic deposition (Browns Hole Fm); (5) final rifting, local mafic volcanism, and transition to drift with deposition of variably mature siliciclastic strata above a regional unconformity (Geertsen Canyon Fm and correlatives) from ~<600–520 Ma; and (6) development of a passive margin with middle Cambrian deposition of carbonate-rich strata. Key age constraints include a detrital zircon MDA of 766 Ma for the Uinta Mountain Group (U-Pb, CA-ID-TIMS), a 697 Ma zircon crystallization date (U-Pb, CA-ID-TIMS) for dacite flows in the lower Pocatello Fm, five detrital zircon MDAs between ca. 670–635 Ma from sandstone and diamictite in the Pocatello Fm (U-Pb, CA-ID-TIMS); an apatite MDA of ca. 613 Ma for the Browns Hole Fm (U-Pb, electron microprobe); and trilobite biozones in the Cambrian shale and carbonate, with the lowermost, Mexicella Mexicana, constraining the uppermost Geertsen Canyon Quartzite to ca. 505.5 Ma. The new age model, combined with stratigraphic thicknesses, is consistent with protracted, multi-phase rifting, broadly similar to records along other parts of the Cordilleran margin.