Middle Jurassic Back-bulge Basin

Map
Sevier Thrust System
Middle Jurassic Back-bulge Basin
Late Jurassic to Early Cretaceous Forebulge High
Early Cretaceous Thrust Faulting
Late Cretaceous Thrust Faulting
Late-Phase Thrusting
The End of Thrusting
I Thought that was the Laramide Orogeny!
Advances

During the Middle to early Late Jurassic epochs, most of Utah was a broad, shallow back-bulge basin. The basin was covered by a shallow sea, tidal flats, sabkhas (flat evaporating pans), and coastal sand dunes (Twin Creek and Pruess Formations in northern Utah; Twin Creek, Arapien, and Twist Gulch Formations in central Utah; Carmel, Entrada, Curtis, and Summerville Formations in east-central and southern Utah), and later, by broad, low-elevation river floodplains (Stump and Morrison Formations in northern Utah, Morrison Formation in central and southern Utah, among others).

Late Jurassic to Early Cretaceous Forebulge High

By the Late Jurassic epoch, the backbulge basin had migrated east of Utah, and Utah was mostly a forebulge high. Modest erosion across this broad, gentle uplift produced an unconformity beveled across the Jurassic strata. The forebulge gradually migrated east of Utah during the Early Cretaceous. As the bulge subsided, sporadic deposition produced the late Early Cretaceous Cedar Mountain Formation (Kelvin Formation in northern Utah), a discontinuous unit noted for many minor internal unconformities and ancient soil horizons. This unit is also the most important producer of early Cretaceous dinosaurs in North America.

Early Cretaceous Thrust Faulting

Thrust faulting began in northwestern Utah in the latest Jurassic or earliest Cretaceous. Sparse evidence is found in Emigration Canyon near Salt Lake City, where boulder conglomerate strata near the base of the Kelvin Formation were derived from the westernmost and oldest thrust sheet. Additional evidence is preserved in synorogenic conglomerate beds in southern Idaho and western Wyoming.