CONTEMPORANEOUS QUARTZ ARENITE FAN DELTA DEPOSITS AND FAR-TRAVELED FELDSPATHIC LITHARENITES DEPOSITED BY THE CALIFORNIA PALEORIVER: AN EXAMPLE OF CATCHMENT LITHOLOGY AND CLIMATE OBSCURING INTERPRETATION OF TECTONIC SETTING USING SANDSTONE PETROFACIES

Analysis of detrital modes from arkosic sandstones in the Lower Eocene Colton Fm. on the southern flank of the Uinta Basin, UT suggests derivation from nearby Laramide uplifts (Dickinson et al., 1986). Detrital zircon geochronology led to a revised interpretation that the Colton Fm. was deposited by a far-traveled paleoriver system with catchments 750 km to the south (Dickinson et al., 2012). This study has two main focuses: 1) analysis of paleoclimate and catchment lithology at the time of deposition of the Colton Fm. to explain why detrital modes do not fit the known tectonic setting and 2) a source-to-sink approach to constraining the size of the “California Paleoriver” that deposited the Colton Fm.

The steeper northern margin of the Early Eocene Uinta Basin was occupied by a series of fan deltas, while the low gradient southern margin was occupied by a large fluvial system. The deposits of the fan-deltas have quartz arenite composition while the far-traveled fluvial deposits have feldspathic litharenite composition. Detrital zircon chronofacies of the quartz-rich fan-delta systems suggest recycling from the eolianites of the Jurassic Glen Canyon Group, and therefore a bedrock control on sandstone composition. A terrestrial carbon isotope record collected from the fluvio-deltaic system records a negative carbon isotope excursion that is likely the Paleocene-Eocene Thermal Maximum. Sedimentological analysis suggest periods of extreme drought punctuated by flooding events that may have subdued chemical and physical weathering of the river’s sediment load. These bedrock and climatic controls obscure interpretation of tectonic setting using sandstone petrofacies (sensu Dickinson and Suczek, 1979)

We take an actualistic approach to constraining the size of the drainage basin of the river system that deposited the Colton Fm., the California Paleoriver. Gauging station data from 400+ modern rivers shows a correlation between bankfull discharge and drainage basin size. We reconstruct bankfull discharge conditions from fluvial channel deposits in the Colton Fm. exposed in the Roan Cliffs. Results suggest the drainage basin area of the California Paleoriver was ~300,000 km². This result supports the far-traveled California Paleoriver hypothesis of Dickinson et al. (2012) using source-to-sink analysis.