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Research about Nevada

Source-linked reports with geographic coverage including Nevada.

At least 883 records · Page 49Linked to original sources
USGS1984

Depositional environments and paleogeography of the Upper Miocene Wassuk Group, west-central Nevada

Fluvial and lacustrine deposits of the Miocene Wassuk Group, exposed in Coal Valley, west-central Nevada, are divided into five lithofacies: (1) diatomite, claystone, siltstone, and carbonaceous siltstone deposited in a lake with paludal conditions at the margin; (2) upward-coarsening sequences of sandstone deposited on a delta and fan-delta; (3) channel-form sandstone deposited on a distal braided alluvial plain; (4) clast-supported conglomerate deposited on a proxial braided alluvial plain or distal alluvial fan; and (5) matrix-supported conglomerate deposited on a distal to middle alluvial fan. Petrographic analysis records an upsection change from a predominantly andesitic to a predominantly plutonic provenance. This change, combined with the overall upward-coarsening of the Wassuk Group and the great thickness (2400 m) of the sequence, suggests active uplift and rapid subsidence during deposition of the group. Facies relationships and paleocurrent directions indicate source areas to the south, southeast and west of Coal Valley. The Miocene Wassuk Group was deposited in an intra-arc basin with penecontemporaneous volcanism and tectonic activity. Syndepositional faulting at the southern margin of Coal Valley between 13 and 11 m.y. ago suggests an early episode of northeast-southwest extension prior to the onset of east-west basin and range extension.

Nevada↗
USGS1984

Major carbon-14 deficiency in modern snail shells from southern Nevada springs

Carbon-14 contents as low as 3.3 ± 0.2 percent modern (apparent age, 27,000 years) measured from the shells of snails Melanoides tuberculatus living in artesian springs in southern Nevada are attributed to fixation of dissolved HCO 3 - with which the shells are in carbon isotope equilibrium. Recognition of the existence of such extreme deficiencies is necessary so that erroneous ages are not attributed to freshwater biogenic carbonates.

Nevada↗
USGS1984

Recent studies indicate that major structures in northeastern Nevada and the Golconda thrust in north-central Nevada are of Jurassic or Cretaceous age

Geologic mapping recently completed in four areas of northeastern Nevada indicates that major folds and thrusts are of post-Early Triassic age and probably are Jurassic or Cretaceous. Previously published data for northeastern Nevada lead to, or permit, the same conclusion. Basinal deposits of Early Triassic age in the northern Adobe Range are easterly derived clay and carbonate. The apparent lack of westerly derived siliceous orogenic sediments of Sonoma age (Late Permian to Early Triassic) suggests that the Sonoma orogeny took place at some unknown location far from northeastern Nevada and that rocks deformed then, the Golconda allochthon, were emplaced in northern Nevada at a later date.

Nevada↗
USGS1984

Stratigraphic and volcano-tectonic relations of Crater Flat Tuff and some older volcanic units, Nye County, Nevada

The Crater Flat Tuff is herein revised to include a newly recognized lowest unit, the Tram Member, exposed at scattered localities in the southwest Nevada Test Site region, and in several drill holes in the Yucca Mountain area. The overlying Bullfrog and Prow Pass Members are well exposed at the type locality of the formation near the southeast edge of Crater Flat, just north of U.S. Highway 95. In previous work, the Tram Member was thought to be the Bullfrog Member, and therefore was shown as Bullfrog or as undifferentiated Crater Flat Tuff on published maps. The revised Crater Flat Tuff is stratigraphically below the Topopah Spring Member of the Paintbrush Tuff and above the Grouse Canyon Member of the Belted Range Tuff, and is approximately 13.6 m.y. old. Drill holes on Yucca Mountain and near Fortymile Wash penetrate all three members of the Crater Flat as well as an underlying quartz-poor unit, which is herein defined as the Lithic Ridge Tuff from exposures on Lithic Ridge near the head of Topopah Wash. In outcrops between Calico Hills and Yucca Flat, the Lithic Ridge Tuff overlies a Bullfrog-like unit of reverse magnetic polarity that probably correlates with a widespread unit around and under Yucca Flat, referred to previously as Crater Flat Tuff. This unit is here informally designated as the tuff of Yucca Flat. Although older, it may be genetically related to the Crater Flat Tuff. Although the rocks are poorly exposed, geophysical and geologic evidence to date suggests that (1) the source of the Crater Flat Tuff is a caldera complex in the Crater Flat area between Yucca Mountain and Bare Mountain, and (2) there are at least two cauldrons within this complex--one probably associated with eruption of the Tram, the other with the Bullfrog and Prow Pass Members. The complex is named the Crater Flat-Prospector Pass caldera complex. The northern part of the Yucca Mountain area is suggested as the general location of the source of pre-Crater Flat tuffs, but a caldera related to the Lithic Ridge Tuff has not been specifically identified.

Nevada↗