Abstract

During the Mesozoic, the sedimentary rocks of the miogeocline of western Utah and eastern Nevada were thrust eastward over the North American continental margin. During the Cenozoic, this folded and thrusted terrain extended westward, essentially opposite to Mesozoic vergence. The miogeocline consists of Eocambrian to Jurassic paraconformable sedimentary rocks over 12 kilometers (40,000 feet) thick in western Utah and eastern Nevada.

Stratigraphic/structural Relief across the twenty mile width of Steptoe Valley, between outcrops of the Jurassic Navajo (Aztec) Sandstone at Curry Junction and outcrops of Eocambrian quartzite north of Cherry Creek, is as much as twelve kilometers. Clasts of Prospect Mountain Quartzite in the basal conglomerate of the Cretaceous(?) to Eocene Sheep Pass Formation indicate at least seven and a half kilometers of EXPOSED stratigraphic relief by early Sheep Pass time.

Regional Outcrop Patterns - The major mountain ranges (Fish Springs/House/Wah Wah Range; Raft River/Pilot/Goshute/Deep Creek Range/Snake/Highland; Ruby/White Pine/Grant/Quinn Canyon/Groom Range; Toiyabe Range) form antiformal linear structural culminations. Cambrian quartzite and older sedimentary rocks are in the core. The ranges are separated by synclinoria of structurally dismembered younger sedimentary rocks (Confusion Range; Buttes Range; Sulphur Springs-Monitor Ranges). The synclinoria show significant packages with clear westward structural vergence on their eastern limb. These synclinoria preserve miogeoclinal sedimentary rocks as young as Jurassic Navajo Sandstone in their cores (Buttes Range Synclinorium near Curry, Nevada). Outcrops of Cretaceous sedimentary rocks are rare and consist of nonmarine elastics. Outcrops of pre-miogeocline crystalline basement are rare beneath the thick sections of Eocambrian clastic rocks.

Structural Models – This poster presents a series of simplified balanced cross sections illustrating a model of Basin and Range tectonic development in time and space. The model demonstrates that the key to understanding of the Basin and Ranges tectonic development lies in understanding the style of Mesozoic thrusting.