Fluvial Architecture and Longitudinal Variance within the Lower Castlegate Sandstone

The upper Campanian Castlegate Sandstone in the Book Cliffs of Utah is a highly amalgamated fluvial sandstone well known as a reservoir analog for oil and gas. This study focuses on the highly amalgamated deposits lower Castlegate. The Castlegate is among the most studied fluvial deposits in the world; Despite this, fluvial architecture analysis has yet to be completed for these deposits considering the longitudinal variance of the Castlegate fluvial system. The completion of a fluvial architecture analysis will further increase our understanding of the evolution of the paleochannels and valleys that comprise the lower Castlegate, and determine the relationship between channel depth and discharge and their effect on facies distribution, depositional style and fluvial architecture. This adds to our knowledge and understanding of the deposition and evolution of the lower Castlegate Sandstone and allows for a refined depositional model. This study has determined that the lower Castlegate Sandstone is a tributary fluvial system traveling primarily East to West comprised of coarse braided stacked fluvial upper-flow regime channel fill and side-attached and mid-channel bars updip, and low-upper-flow regime straight-meandering trunk channels with channel fills and lateral accretion sets downdip. Distal outcrops show three distinct depositional styles: the first representing low-flow distributary channels with maximum thickness of 1 m in a period highstand, the second representing localized tectonic uplift and incision containing large planar-trough cross bedded channel fill and lateral accretion sets up to 18 m, and a capping unit of small, braided low-flow channel fills represent a period of lowstand.