Geology topics

Research about Northern Nevada

Source-linked reports with geographic coverage including Northern Nevada.

2 recordsLinked to original sources

USGS1997

Early Silurian radiolaria from northern Nevada, USA

Radiolarians recovered from three sites in the early Llandoverian Cherry Spring chert, north-central Nevada, provide the first Early Silurian radiolarian data from the conterminous United States. Two assemblages were recovered that contain abundant pylomate sphaerellarians, rotasphaerids, inaniguttids, and possible palaeoactinosphaerids. The pylomate taxa have an intermediate spine morphology with Cessipylorum and Aciferopylorum , bringing into question the present criteria for distinguishing these two genera. Rotasphaerids include both species of Rotasphaera and Secuicollacta , that have five primary rods per spine unit, similar to those present in Ordovician assemblages (Caradocian-Ashgillian) reported from Nevada and Australia. Oriundogutta is another common component shared between the Cherry Spring and Caradocian-Ashgillian age faunas. To a lesser extent, the Cherry Spring fauna resembles late Early-Late Silurian (Wenlockian-Ludlovian) assemblages that contain abundant inaniguttids and rotasphaerids. None of the younger species of inaniguttids have been recognized, however, and younger species of rotasphaerids differ in that they have six primary rods per spine unit and a more diverse spine morphology. These preliminary data indicate a stronger similarity between Late Ordovician and early Llandoverian assemblages than between early Llandoverian and Wenlockian-Ludlovian assemblages. The Cherry Spring chert faunas contain several distinct forms, such as Cessipylorum (?) sp. A and B, that may prove useful for biostratigraphic correlation.

Nevada↗

USGS1982

Mid-Paleozoic age of the Roberts thrust unsettled by new data from northern Nevada

The Roberts thrust is a major thrust in Nevada on which Ordovician to Devonian siliceous facies rocks were carried more than 80 km eastward over contemporaneous carbonate facies. For more than two decades, a mid-Paleozoic age for this structure has been widely accepted. The bases for dating the thrust are (1) the assumption that the Roberts thrust formed at the time of the Antler orogeny—a reliably dated mid-Paleozoic event, and (2) the concept of an overlapping assemblage consisting of sedimentary strata deposited on both the allochthon and autochthon. The first assumption is unproved, and the second relies on another assumption: that the overlap assemblage was not cut and telescoped by the Roberts thrust. In the years since a mid-Paleozoic age for the Roberts thrust became widely accepted, much new information on the stratigraphy and facies relations of Mississippian rocks in northern Nevada has accumulated. One interpretation of these new data suggests that in the Pinon Range, where a mid-Paleozoic age for the thrust was most convincingly displayed, the overlap assemblage actually may have been cut by a major thrust that juxtaposed contrasting facies of Mississippian rocks. If so, the principal evidence used to date the Roberts thrust is compromised, and the time has come for an agonizing reappraisal of all evidence bearing on the question. A mid-Paleozoic age can no longer be taken for granted, and a post-Paleozoic age cannot be ruled out.

Nevada↗