Late Cretaceous Thrust Faulting

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

Thrust faulting reached its zenith in Utah during the Late Cretaceous when most of the major thrust plates were emplaced. By this time, most of the forebulge high had migrated east of Utah. Many plates were pushed eastward 25 to 30 miles, and in some cases, more than 50 miles. Drill holes have penetrated up to five stacked plates at single locations.

Thrusted rock was folded, faulted, overturned, brecciated, and metamorphosed to a low grade as it was pushed eastward, forming large mountains and creating the spectacular tilted and complexly folded formations now exposed in many of the ranges of northern, central, and southwestern Utah (for example: Devils Slide in Weber Canyon, the complexly folded rocks in Parleys Canyon, and the great block of overturned strata that forms Mount Nebo).

The Late Cretaceous was also the time of peak oil and gas generation in the thrust belt. For example, Cretaceous organic-rich rocks buried by thrust sheets near the Wyoming border generated the oil and gas that migrated into reservoirs in the thrust-created folds in the Coalville area. A few of these folds became some of the best oil and gas fields in Utah (for example: the Pineview and Anshutz Ranch fields).

As the "thrust front" migrated eastward, it abandoned one thrust fault as the "wedge" of thrusted rock became too thick, and "stepped" forward to a new fault. Thrust faults to the rear "locked" into place or experienced only minor renewed movement. In general, thrust plates in the eastern part of the Sevier belt didn’t move as far as western plates. Likewise, the eastern plates were thinner and deformed into folds of smaller amplitude between wider spaced thrust faults than the thick western plates.

Because the Late Cretaceous was the time of peak thrusting, it was also the time of peak synorogenic sedimentation in wedge-top basins on the thrust plates and in the foredeep basin in front of the thrust belt. These deposits include the thick conglomerate beds along Interstate Highways 80 and 84 (Echo Canyon, Weber Canyon, and Evanston Conglomerates), near U.S. Highway 6 in Spanish Fork Canyon (Indianola and Price River Formation), in the mountains near Cedar City (Iron Springs Formation), and at several other places in Utah.

In general, synorogenic conglomerate beds grade eastward into fluvial sandstone and shale, coastal-plain deposits, and deltaic deposits comprising the extensive coal-bearing deposits of Utah (parts of the Frontier Formation of northern Utah, the Blackhawk Formation of central Utah, and the Straight Cliffs Formation of southern Utah, among others). These in turn grade eastward into fine sand, mud, and clay shallow-marine deposits (parts of the Mancos Shale of central and southern Utah, and most of the Frontier Formation and the Hilliard Shale north of the Uinta Mountains).