The purpose of this investigation was to test two hypotheses.
The first hypothesis interprets allochthonous rocks in the southern
Pinyon Range to lie on the Devonian Nevada Group. The second
hypothesis interprets allochthonous rocks to lie on the Mississippian
Dale Canyon Formation. Evidence presented here supports the second
During Late Silurian to Middle Devonian time, deposition in the
southern Pinyon Range occurred in a miogeoclinal shallow shelf
environment characterized by the Lone Mountain Dolomite and Nevada
Deposition of the Pilot Shale in an incipient basin developed
within the shelf, beginning no later,than marginifera-Lower velifer
Zone time, marked the onset of the Antler orogeny. A westward-dipping
subduction zone formed to the west, developing an accretionary
wedge which later became the Roberts Mountains allochthon. Incipient
subduction of continental crust resulted in obduction of the allochthon
onto the continential crust. The Antler foreland basin formed east of
the advancing allochthon where deposition of the Dale Canyon Formation
unconformably on the Pilot Shale formed a submarine fan complex
consisting of siliciclastic sediments shed from the rising allochthon.
The Roberts Mountains allochthon in the southern Pinyon Range
consists of the Devonian Woodruff Formation forming the base, the
Ordovician Vinini Formation thrust over the Woodruff, with slices of
the Devonian Roberts Mountains Formation occurring in between at
places. The allochthon was emplaced in the southern Pinyon Range,
over the Dale Canyon Formation during or after late isosticha-Upper
crenulata Zone time.
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