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Detrital Zircon Geochronology of Lower Cretaceous Conglomerates, San Rafael Swell— Wasatch Plateau, Central Utah

Hunt, Gary J.1, Timothy F. Lawton2, and George E. Gehrels3
1New Mexico State University, Las Cruces, NM
2New Mexico State University, las Cruces, NM
3University of Arizona, Tucson, AZ

     U-Pb ages of detrital zircon grains collected from four samples of Lower Cretaceous Cedar Mountain (Neocomian-Albian) and San Pitch (Aptian-Albian) Formations in central Utah exhibit discrete, distinctive peaks on age-probability plots. Detrital zircons were ultimately derived from Precambrian, Paleozoic, and Mesozoic igneous rocks. Paleoproterozoic grains (2475-1651 Ma; 62 of 100 grains) dominate the basal Cedar Mountain Formation in Salina Canyon. In contrast, the type Buckhorn Conglomerate on the San Rafael Swell and Member C of the San Pitch Formation in Salina Canyon contain mostly Mesoproterozoic grains (1579-1000 Ma; 61 and 64 of 100 grains, respectively). A population of Ordovician- Mississippian grains in the type Buckhorn Conglomerate indicates substantial contributions from Paleozoic and/or Mesozoic source rocks. Our data indicate that the basal Cedar Mountain Formation in Salina Canyon and the type Buckhorn Conglomerate were deposited by two different river systems, separated either geographically or temporally, or both. We postulate that clasts in the Buckhorn Conglomerate were derived from Paleozoic quartzarenites, the Triassic Chinle Formation and Permian and Jurassic eolianites. The San Pitch Formation clasts, which lack Paleozoic grains, may have been derived primarily from the Cambrian Prospect Mountain Quartzite and older rocks.
     Our data are consistent with progressive unroofing of siliciclastic units from the Sevier thrust belt. They corroborate and refine exposure gates for inverted clast stratigraphies documented in carbonate clast conglomerates of the foreland basin. Future work on these geochronologically distinctive quartzite-clast conglomerates should further elucidate correlations, which remain ambiguous, among conglomeratic strata of the foreland.


AAPG Search and Discovery Article #90071 © 2007 AAPG Rocky Mountain Meeting, Snowbird, Utah