Pre-Tertiary Stratigraphy and Structure of Northwestern Nevada
N. J. SILBERLING, RALPH J. ROBERTS, 1962. "Pre-Tertiary Stratigraphy and Structure of Northwestern Nevada", Pre-Tertiary Stratigraphy and Structure of Northwestern Nevada, N. J. Silberling, Ralph J. Roberts
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Despite their remarkable diversity, the Paleozoic and Mesozoic rocks of northwestern Nevada are related in both their depositional and structural history. In the northern part of the region, lower and middle Paleozoic rocks were greatly deformed during the Antler orogeny, after which shallow-water limestone and clastic rocks of the Antler sequence of Pennsylvanian and Permian age were deposited upon them. The Havallah sequence, an entirely different facies of upper Paleozoic rocks including several thousand feet of fine-grained clastics, chert, and volcanic rocks, is thrust eastward over the Antler sequence and older rocks. Overlying the Havallah are Permian and Triassic volcanic rocks of the Koipato sequence and two different facies of lower Mesozoic sedimentary rocks, the Winnemucca and Augusta sequences. Part of the Augusta sequence of latest Early to Late Triassic age is interpreted as an eastern and more shoreward facies of the Winnemucca sequence, which ranges from Middle Triassic to Early Jurassic in age.
The rocks in the southern part of the region, south of a belt in which there are few pre-Tertiary outcrops, represent the same time span as those farther north, but rock units and structural features differ. Greatly deformed lower Paleozoic rocks along the southeastern and southern margin of the region are unconformably overlain by the Diablo sequence, the lower part of which resembles the Antler sequence and the upper dominantly volcanic part, the Koipato sequence. Overlying the Diablo is the Luning sequence, mainly of calcareous sedimentary rocks ranging from latest Middle Triassic through Early Jurassic in age. The upper part of the Luning sequence was laid down during the initial folding and thrusting of Mesozoic orogeny. Volcanic rocks of the Gillis sequence, tentatively dated as Middle or Late Triassic, are thrust over the Luning sequence from the west.
Three periods of orogeny deformed the Paleozoic and Mesozoic rocks of the area. The Antler orogeny took place during late middle Paleozoic time; this was followed by the Sonoma orogeny during the middle or Late Permian and by folding and thrusting that commenced in the late Early Jurassic and persisted into Cretaceous time. Thrust faulting, represented in some places by faults with great horizontal displacement, characterized all three orogenies. The sequence of thrusts in the northern part of the area, and therefore the paleogeographic interpretation of the upper Paleozoic and Mesozoic rocks, has not been completely resolved. Two interpretations can be made: that the Golconda thrust, bringing the Havallah over the Antler sequence from the west, is one of the youngest of the Mesozoic thrusts and controls the distribution of the Augusta sequence of Triassic rocks; or that the Golconda thrust is older, developed during the Sonoma orogeny, and did not affect the geographic relationships of the Augusta to the Winnemucca sequence.