PROVENANCE OF PALEOGENE COLTON FORMATION (UINTA BASIN, NE UTAH): CONSTRAINTS FROM COMBINED PETROFACIES AND DZ ANALYSIS

The Paleocene-Eocene Colton Formation (fluviodeltaic arkosic sandstone and interbedded mudstone of the Roan Cliffs) interfingers laterally with and grades upward into the lacustrine Green River Formation of the Laramide Uinta basin. Preserved Colton sediment (~15,000 cu km) occupies half a geometric cone with its apex (~1000 m thick) at Desolation Canyon of the Green River and a basal radius of ~100 km. Paleocurrents (n~100 troughset intrachannel crossbed stations along and near Desolation Canyon) indicate northward (mean N9W) Colton sediment delivery into the Uinta basin. Arkosic Colton petrofacies (Qm50, F35, Lt15) implies a granitoid provenance for Colton sand, and Mesozoic U-Pb ages for ~50% of Colton detrital zircons document sources in plutons of the Cordilleran magmatic arc. Paleogene drainage divides in the Great Basin well to the east of the Sierra Nevada batholith, and well into Mexico east of the Peninsular Ranges batholith, indicate that the principal arc provenance was the Mojave segment of the Cordilleran batholith belt adjacent to the restored (pre-San Andreas) Salinian block, with sediment transport to the Uinta basin via the California paleoriver of Davis et al. (2010). Quartzose sandstones with only minor (≤5%) Mesozoic DZ grains in the sub-Colton North Horn Formation and Colton-equivalent strata of the Gunnison Plateau were derived from the Sevier thrust belt to the west. Colton-equivalent strata (Debeque) of the Piceance basin to the east and supra-Colton (Green River) sandstones contain 10%-25% Mesozoic DZ grains, suggesting that Colton arkosic detritus was spread widely within Lake Uinta but diluted by mixture with more locally derived sediment. DZ facies in Upper Cretaceous sandstones of the central Utah foreland reflect pre-Colton longitudinal sediment transport northward along the Sevier foredeep throughout Late Cretaceous time to augment transverse sediment derivation from the nearby Sevier thrust belt. Petrofacies more quartzose than Colton and/or contrasting U-Pb ages for arc-derived DZ grains (P~0 from K-S analysis) in the Cretaceous units preclude recycling of arkosic detritus into the Colton Formation from Utah Cretaceous strata. Colton deposition reflected the continuation of a persistent pattern of longitudinal sediment dispersal within the Cordilleran foreland.