Paleozoic Facies from the Miogeosynclinal to the Eugeosynclinal Belt in Thrust Slices, Central Nevada

The Toquima Range, in the center of Nevada, has a remarkable set of thrust sheets of Paleozoic rocks that are displaced by Tertiary high-angle faults; these are mapped and described. Stratigraphically, the sequences in the successive slices when reconstructed show that the lower Ordovician rocks graded progressively from carbonate rocks on the east to argillites with volcanic interbeds on the west; clean quartzites in the latter must have originated to the east and been carried along the depositional trough. Upper Ordovician and Silurian rocks show an island belt of little or no subsidence between a carbonate trough on the east that subsided a mile or so, and an argillite- and chert-bearing belt on the west. The Ordovician stratigraphy is notable in having a fine section of early medial Ordovician fossiliferous carbonate rocks, the type section of the “Whiterock stage,” and representative graptolite zone successions in more westerly slices. Silurian has graptolite-bearing shales in several sequences, some carbonate rocks in the easterly ones. The Devonian limestones are notable in having brachiopods such as Septatrypa, Dubaria, and “Vagrania,” distinctive of Gedinnian in central Europe, previously unrecognized in North America; in the section of greatest span of disconformity, Devonian rocks lie on low Ordovician rocks.

The western belts show angular unconformity of Carboniferous sediments on lower Paleozoic rocks; as Carboniferous rocks are cut by thrusts, at least two times of orogeny are indicated. The area is not suited to determination of the time of emplacement of the allochthon, lower Paleozoic argillite-chert-volcanic rocks, on parautochthonous and autoch-thonous sequences, but the more westerly thrusts are younger than those separating the more easterly slices. The thrust faults require crustal shortening of scores of miles although not necessarily in the basement; the implications of crustal gliding are considered.