DETRITAL ZIRCON U-Pb AGES INDICATE LOCAL SOURCING FOR THE EOCENE CLARON FORMATION, SOUTHWESTERN UTAH: IMPLICATIONS FOR THE PALEOGENE CALIFORNIA RIVER

Late Cretaceous to Paleoogene sedimentary rocks of the western US record how Cordilleran basin systems are influenced by complex tectonic transitions including slab shallowing and migration of deformation into the foreland. The Eocene Claron Formation, SW Utah, records deposition in a ponded Laramide basin near the Sevier thrust front, several Laramide uplifts, the Mogollon highlands, and the hypothesized course of the Paleogene California River. We present 1,299 detrital zircon U-Pb ages from 12 samples from the Claron Formation and underlying Late Cretaceous or Paleogene strata. The majority of the samples have wide age peaks ca. 1100, 1300, 1700, and 2700 Ma, with additional scattered Neoproterozoic to Paleozoic ages and very few Mesozoic ages, similar to quartzites and sandstones exposed in the Sevier thrust belt. Other samples less similar to Sevier belt sources have prominent Triassic, Jurassic, or Cretaceous age peaks or distinct Proterozoic age distributions and are strongly dissimilar to one another. Each of these latter sample age distributions are similar to Cretaceous units exposed in Laramide uplifts adjacent to the basin. The samples together indicate derivation from nearby sources exposed in the Sevier thrust belt and adjacent Laramide uplifts. No significant input from the Mogollon highlands or the Mojave region, the proposed headwaters of the Paleogene California River, is inferred.

Local derivation of the Claron Formation has implications for routing of the Paleogene California River, which is hypothesized to have delivered sediment from the Mojave region to the Uinta Basin. The Claron basin was either hydrologically isolated from the California River or post-dated its existence. In the former case, the California River may have followed a course that ran in between and subparallel to Laramide uplifts of northern Arizona and southern Utah, circumventing the Claron basin to the east. Alternatively, the distinct provenance of the relatively poorly dated Claron Formation and the California River may reflect a transition from far-traveled sources, exemplified by the California River, to local sources, exemplified by the Claron Formation, in the Laramide foreland. Such a transition may have been caused by defeat of the California River by Laramide uplifts during early Eocene time.