Portal de Periódicos da CAPES

Geology of the northern part of the Toquima Range, Lander, Eureka, and Nye counties, Nevada

1976; United States Government Publishing Office; Linguagem: Inglês

10.3133/pp931

2330-7102

Edwin H. McKee,

Hydrocarbon exploration and reservoir analysis

Rocks exposed in the Toquima Range of central Nevada (centering at lat 39°20 ' N. and long 117°50 ' W. ) are early and middle Paleozoic marine strata, middle and late Mesozoic intrusive igneous rocks, and late Cenozoic volcanic and sedimentary rocks.The Paleozoic rocks are divided into three assemblages: an eastern, predominately carbonate assemblage; a western, siliceous assemblage consisting mostly of chert and dark shale; and an overlapping assemblage of limestone and conglomerate.The carbonate assemblage is composed of four sequences that have been brought together on thrust faults with displacements of 10 miles (16 km) or more.Each sequence contains a generally similar yet significantly different series of strata that were deposited across a wide r egion of central Nevada.The four distinct stratigraphic sequences of correlative carbonate rocks are exposed at localities only a few kilometres apart in the northern Toquima Range.Three of the sequences are stacked in a series of thrust plates in the Ikes Canyon window in the southern part of the area; the fourth is exposed in Petes Canyon window about 12 miles (19 km) to t he north.The Ikes Canyon window contains, from lowest to highest, the August Canyon, Mill Canyon, and June Canyon sequences.The August Canyon sequence is presumed to be autochthonous; the others, allochthonous.The Petes Canyon window contains the Petes Canyon sequence.Most of the units of the carbonate assemblage can be correlated with the well-known formations from the Eureka-Antelope Valley region of east-central Nevada, and many of the names used for these Ordovician, Silurian, and Lower Devonian rocks are derived from the classic sections of the Eureka-Antelope Valley region to the east.These formations include the Goodwin Limestone, Ninemile Formation, Antelope Valley Limestone, Hanson Creek Formation, and Roberts Mountains Formation.Formations defined from localities in the Toquima Range are the Tor and McMonnigal Limestones and the Caesar Canyon Limestone, the Gatecliff Formation, and the Masket Shale of Kay and Crawford (1964).The western, siliceous assemblage, composed of Ordovician rocks, , is called the Vinini Formation and is similar to allochthonous silicic rocks in other parts of central Nevada.These strate have been thrust 40 miles (64 km) or more eastward from their site of deposition on the regionally extensive Roberts Mountains thrust.The overlapping assemblage of conglomerate and limestone lies with angular unconformity on both the older Paleozoic siliceous and carbonate assemblages and is presumed to represent detritus that accumulated near the edges of the allochthonous thrust plates.Kay and Crawford's (1964) name Wildcat Peak Fromation is adopted for rocks of the overlapping assemblage in the Toquima Range.These rocks are of Pennsylvanian age.The Paleozoic history of the region can be divided into three phases.The first is recorded by strata of Early Ordovician to Early Devonian age deposited in deep water in regions west of central Nevada and in shallow seas in central Nevada and eastward.The Toquima Range lies in the shallow shelf zone near the transition into 2 TOQUIMA RANGE, LANDER, EURE KA, AND NYE COUNTIES, NEVADA of collapse of this volcanic center after eruption-the pyroclastic material simply formed a thick pile of weakly welded to non welded debris.Other ash-flow sheets of regional extent are the Pancake Summit Tuff, dated at about 31 m.y.; the Bates Mountain Tuff, comprising three cooling units all about 24 m.y.old; and the tuff of Clipper Gap, which at about 22 m.y.old is the youngest volcanic formation in the area.All the ash flows except the tuff of Hoodoo Canyon are of rhyolitic composition; the tuff of Hoodoo Canyon is quartz latite.The older units including the tuff of Hoodoo Canyon, tuff of Stoneberger Canyon, Pancake Summit Tuff, and Northumberland Tuff are rich in crystals and contain as much as 40 percent phenocrysts; the younger units including the Bates Mountain Tuff and the tuff of Clipper Gap are poor in crystals and contain 10 percent phenocrysts or less.The thickness of the ash flows and the stratigraphic sequence they form vary within the area.