Tectonostratigraphy of foreland basins: The Upper Cretaceous in southwestern Wyoming

Most previous stratigraphic studies in foreland basins were based on a two-phase model producing a wedge-shaped stratigraphic record in the foredeep area. Other parts of the complete foreland basin systems were generally ignored. This study examines the stratigraphy of a complete foreland basin including the wedge-top, foredeep, forebulge and back-bulge depozones. 3-D numerical modeling produced a 3-D synthetic stratigraphy, which demonstrates that different sub-basins may have different stratal stacking patterns in a same time-stratigraphic interval. The modeling accounts for the dominant geological factors, such as initial topography, erosion and sedimentation rates, flexural as well as dynamic subsidence, and global sea-level change.; The synthetic stratigraphic model was tested against the tectonostratigraphy of the Late Cretaceous foreland basin in front of the Sevier fold-and-thrust belt in western Wyoming. Five thrust events influenced the Late Cretaceous stratigraphy and structure of the region: the Meade-Laketown, Crawford, early Absaroka, late Absaroka, and the basement-involved Wind River thrusting. The analysis shows that dynamic subsidence provided a significant regional background subsidence for the study area.; The stratigraphic patterns across the foreland basin system in response to the Crawford and the early Absaroka thrusts were documented in detailed outcrop to subsurface cross sections, and the 3-D stratigraphic model results were tested against these geologic observations.; Forebulge migration is recognized in the subsurface cross sections. The amplitude of the forebulges is 40 to 80 m, based on observed stratal erosion and thinning. In response to eastward progressive movement of the Crawford, early Absaroka, and late Absaroka thrusts, the forebulges migrated eastward to the Moxa arch, the Rock Springs uplift, and the Washakie basin, respectively. Tectonic analysis shows that the Late Cretaceous forebulges resulted from the combined elastic response of the lithosphere by the Sevier thrust belt and Wind River thrust. 3-D flexural modeling further supports this explanation.