Abstract

Detrital zircon and petrographic provenance analysis of Upper Cretaceous (Campanian) strata corroborate correlation of the fluvial Kaiparowits Formation in southern Utah with post-Castlegate strata of the Mesaverde Group in eastcentral Utah. Sandstone samples of the Kaiparowits Formation in the Kaiparowits Plateau and Mesaverde Group (Neslen, Bluecastle Tongue of Castlegate, Farrer, and Tuscher formations) in Gray Canyon north of Green River, Utah, contain six U-Pb detrital zircon age populations ranging in age from Archean to Late Cretaceous. Thrust-belt-derived sublitharenite and quartzarenite of the lower part of the Mesaverde Group (Neslen and Bluecastle) lack or have only rare Mesozoic grains, but contain abundant Archean, Proterozoic, and Paleozoic grains that record recycling of Proterozoic, Paleozoic, and Jurassic sandstones exposed in uplifted thrust sheets to the west. South- and southwest-derived feldspathic litharenite of the Kaiparowits and Farrer formations contains Proterozoic grains and a diverse population of Mesozoic grain ages. Archean grains are rare to absent. Maximum depositional ages interpreted from young zircon grains in two Kaiparowits samples statistically overlap 40Ar/39Ar ages (76–74 Ma) from interbedded bentonitic tuffs and weighted mean ages of young grains from the Farrer Formation. Kolmogorov-Smirnoff statistics, in conjunction with young grain ages and detrital age spectra, corroborate petrographic evidence, which indicates that the Kaiparowits rivers were connected northward with a river system that deposited the Farrer Formation. The young grain ages, although imprecise, indicate that the uppermost Mesaverde Group strata of the Tuscher Formation are younger than the Kaiparowits Formation and record partitioning of the former foreland basin by Laramide uplifts.

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