Tectonostratigraphy of Foreland Basins: The Upper Cretaceous in Southwestern Wyoming

Hongjun Luo¹ and Dag Nummedal^2
1 BP America Inc, Houston, TX
² Colorado School of Mines, Golden, CO

Tectonostratigraphic analysis and 3D flexural and stratigraphic modeling were used to improve the understanding of the tectonostratigraphy of the Late Cretaceous foreland basin in southwestern Wyoming. Detailed outcrop control and well log correlations were used to document the sequence stratigraphic framework along three 2-D profiles across the Greater Green River Basin. Five cycles of thrusting controls the Late Cretaceous stratigraphic stacking patterns in southwestern Wyoming: the Meade-Laketown (Cenomanian to middle-Turonian), the Crawford (Coniacian to Santonian), the early Absaroka (late Santonian to early Campanian), the late Absaroka (late Campanian to early Maastrichtian), and the basement-involved Wind River (late Turonian to Eocene) thrusting. Subsidence analysis showed the dynamic topography provides a significant regional background subsidence for the study area.

The Meade-Laketown thrusting accounts for the thick retrogradational interval from the Chalk Creek to the Allen Hollow Members of the Frontier Formation in front of the Wyoming thrust belt. The Crawford thrusting caused the transgression associated with the Hilliard Shale and formed a forebulge at the Moxa arch. During the Early Absaroka thrusting (late Santonian to early Campanian), another shoreline transgression occurred (Steele and Baxter Shales) and the forebulge migrated eastward to the Rock Springs uplift. The basement-involved Moxa arch was uplifted at the same time, forming the base-Trail and base-Canyon Creek unconformities. The late Absaroka thrusting caused another regional transgression (Almond Formation and Lewis Shale) augmented by concurrent global sea-level rise. The forebulge migrated eastward to the west flank of the Washakie basin where its stratigraphic impact became obscured by the concurrent rapid subsidence of that basin due to basement-involved Laramide tectonism.