STRATIGRAPHY AND DETRITAL ZIRCON U-PB AGE PROVENANCE OF THE PALEOGENE CLARON FORMATION AND UNDERLYING STRATA, SOUTHWESTERN UTAH: TRANSITION FROM SEVIER TO LARAMIDE SOURCES

The Cretaceous to Paleogene North American Cordillera foreland basin records the effects of low-angle subduction and the transition from Sevier to Laramide deformation. We present new measured sections and detrital zircon (DZ) U-Pb age data from the Claron Formation, southwestern Utah, and underlying Cretaceous to Paleogene strata, that constrain how these tectonic drivers affected sedimentation between Sevier and Laramide structures in the southern Utah foreland basin.

The Claron Formation, typically <300 m thick, consists of conglomerates, sandstones, and carbonates that reflect fluvial and lacustrine depositional environments. Evidence of burrowing and nodular carbonate development is common. Western Claron Formation strata interfinger with underlying alluvial conglomerates, whereas eastern Claron Formation exposures lie unconformably over Cretaceous to Paleogene strata.

New DZ U-Pb ages (n = 1148, 11 samples) show significant geographic and stratigraphic variation. DZ grains from strata underlying the Claron Formation and stratigraphically low Claron Formation samples show age peaks at ca. 1.1, 1.45, and 1.7 Ga, along with variable Neoproterozoic to Paleozoic peaks, consistent with derivation from the Sevier orogenic highland. Stratigraphically higher Claron Formation samples include significant Mesozoic DZ age populations, but the particular Mesozoic age peaks present differ markedly between samples, suggesting recycling of Mesozoic strata in multiple, distinct source areas. The Mesozoic age peaks of several samples show good matches to published DZ age distributions of the Cretaceous Cedar Mountain Formation, Dakota Formation, and Kaiparowits Formation, suggesting erosion of those formations in different parts of the Claron source area. No sources outside the Sevier belt and Laramide uplifts are implicated by the DZ age data. Together, the age data suggest a transition from dominantly Sevier sources during early deposition of the Claron Formation, to derivation from catchments that underwent Laramide uplift during later deposition of the Claron Formation. This transition may reflect a progressive increase in erosion of Laramide, relative to Sevier, source areas during deposition of the Claron Formation.