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