SCALING THE CALIFORNIA PALEORIVER: A SOURCE TO SINK APPROACH APPLIED TO FLASHY FULVIAL DEPOSITS IN THE EALRY EOCENE WASATCH AND GREEN RIVER FORMATIONS, UINTA BASIN, UT

Channel dimension is a key variable in source to sink analysis of ancient fluvial deposits. Relationships between discharge and catchment area in modern river systems are well documented (Syvitski and Milliman, 2007 ; Syvitski et al., 2014), but using this as a tool for paleoreconstruction, espescially in flashy fluvial deposits (Plink-Bjorklund, 2015) with multiple order of magnitude differences in channel dimensions, can be problematic. The Wasatch and Green River Fms. in the Uinta Basin contain fluvial deposits that record the Paleocene-Eocene Thermal Maximum in the Western Cordillaran Foreland Basin of North America, and are hypothesized to have been sourced from catchments as far as 600 km away in the Mogollon Highlands (Dickinson et al., 2012). This study presents integrated stratigraphic and sedimentologic characterization of the terminus of the “California Plaeoriver” (Dickinson et al., 2012), where clastic sediments deposited in a fluvial megafan interfinger with basinal lacustrine carbonates. An outcrop dataset oriented across depositional strike for ~100 km shows an axial-distal decrease in average channel dimensions from fan apex to margin. Calculated bankful paleodischarge rates (~1,000 – 20,000 m³/sec) and corresponding estimates of catchment area (~1.5 x 10⁶ and1.2 x 10⁷ km² respectively) vary depending on fan position and calculation methodology (e.g.Bhattacharya and Tye, 2004, Lynds et al., 2014). The minimum of these range of estimates is in agreement with the proposed catchment of the “California Paleoriver”, but the maximum estimates would require a much larger source area. We evaluate the relationship between channel dimensions and fan position in datasets from modern fluvial megafans where catchment size is reported, and use this analysis to 1) inform our interpretation of the most reasonable estimates of the catchment size of the “California Paleoriver” and 2) evaluate how to best apply scaling relationships to highly ephemeral fluvial deposits.