Investigating the paleodelta type of the Ferron Sandstone in the Willow Spring Wash, East-Central Utah

The Upper Cretaceous Ferron Sandstone of east-central Utah is an important source of coal and contains sandstone bodies that serve as good quality petroleum reservoirs. The Ferron represents a wide range of paleo-environments ranging from alluvial plain to offshore marine. Meandering rivers transported sediment southward and eastward from the coastal plain to the shoreline, where deltaic sedimentation predominated. Previously published facies analyses of the Ferron Sandstone delta range from generally wave-dominated to fluvial-dominated. We examined a well exposed section of Ferron Sandstone in the Willow Spring Wash on the western flank of San Rafael Swell to differentiate between these two end members. We hypothesize that these end-member scenarios can be distinguished through analysis of outcrop and core of the Ferron. In the case of a fluvial dominated delta, isolated mouth bar deposits are encased in finer grained interdistributary bay deposits, whereas more interconnected, amalgamated sandstones are characteristic of a wave dominated system. Further, case studies showed that bioturbation is limited due to the fluctuating salinity levels in fluvially-dominated systems, whereas more extensive bioturbation with a diverse suite of trace fossils are present in a wave-dominated system. To distinguish between these two possibilities, we conducted photomosaic work, measured stratigraphic sections through key exposures, analysed paleoflow indicators, and investigated bioturbation indices in outcrop and core. Our results will have important implications for accesing the viability of the Ferron Sandstone as a reservoir for hydrocarbons