Facies and Stratigraphic Architecture of the Fox Hills Sandstone, Eastern Wyoming: Insight Into Depositional Processes During Long-Transit Shoreline Regression

Abstract

The stratigraphic architecture and detailed facies successions that develop during long-transit (>100's km) forced regressions are not well documented. The Fox Hills Sandstone (Horseshoe Canyon Formation equivalent) is an extensive, marginal marine sandstone that records rapid progradation during the terminal regression of the Western Interior Seaway- a >1500 km regression. Although the Fox Hills Sandstone has been thoroughly studied in the Washakie basin, the detailed sedimentary architecture and processes are not well known in eastern Wyoming where subsidence was likely broader and slower. This study documents the detailed stratigraphic architecture and constituent facies that resulted from rapid regression of the Fox Hills Sandstone shorelines using exceptional outcrops northeast of Casper, WY. We document 11 facies associations across a network of measured sections that include offshore marine, lower shoreface, tide-influenced incised valley-fill, cyclic wave and tide-dominated deltaic and terrestrial. These facies stack into three high-frequency cycles encompassed by one complete depositional sequence. Furthermore, we define a new incised valley system at the base of the succession that is not documented in the Fox Hills S.s. in the Denver Basin, or northward in Montana. The depositional processes within the Fox Hills Sandstone alternate between estuarine within the basal valley-fill, and cyclic tide- and wave-dominated deltaic processes towards the top. In conclusion, this study: 1) highlights a new incised valley at the base of the Fox Hills Sandstone, 2) defines 3 high-frequency, transgressive-to-regressive cycles within the overall forced regressive succession of the Fox Hills Sandstone, and 3) a mixed-energy forced regressive deltaic system within a long-transit regressive shoreline. Collectively, these observations contribute new insight into the resultant deposition and stratigraphy of long-transit forced regressive systems.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016