Advances

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

Probably the biggest advance in Utah thrust system studies has come through improved dating and correlation methods.

In an active thrust system, coarse alluvium is shed from rapidly eroding mountains formed by the thrusted rock. In some cases, soon after deposition, the advancing thrust plates override, fold, and fault these “synorogenic deposits.” To unravel thrust history, it is essential to accurately date these rocks.

In Utah, geologists scoured many miles of outcrops searching for datable materials. They collected and identified pollen, spores, and volcanic ash, then correlated the samples with well-dated strata elsewhere. They also mapped the conglomerates, unconformities, and cross-cutting relationships, and matched conglomerate clasts with the formations from which they were derived. Analyzing this data with new tools and thrust models has significantly refined our knowledge of timing and the sequence of events that formed the Utah thrust system.

This paper is extracted from: Willis, G.C., 1999, The Utah Thrust System - An Overview, in Spangler, L.W., and Allen, C.J., editors, Geology of northern Utah and vicinity: Utah Geological Association Publication 27, p. 1-9. Sources used to prepare this paper are listed in that publication.