Abstract

Three stratigraphic sequences of lower Paleozoic rocks in the Seetoya Mountains east of Tuscarora, Nevada, are of partly equivalent age. The highest sequence is Lower Silurian and younger, composed of bedded cherts, quartzite, volcanic rocks, and graptolitic shales, deposited in a western eugeosynclinal belt, and thrust southward or southeastward for some scores of miles. Each of two lower sequences includes the same five Ordovician and Silurian formations which differ markedly in thickness and slightly in lithology. They are predominantly carbonate rocks with some quartz sandstones, deposited in an eastern miogeosynclinal belt. The upper of these latter sequences has been thrust about 6 miles southward or southeastward.

The eastern sequences were folded, faulted, and eroded, probably in pre-Carboniferous or Permian time. Siltstones, laid unconformably on the southern of the two eastern sequences, may have been derived from rising lands in the eugeosynclinal belt. Thrusting of uncertain age carried a thick plate of allochthonous rock of the western belt southerly or southeasterly. Presence of younger rocks beneath the thrust in the south suggests that there was a regional southward slope at this time. A second thrust, which developed within the eastern belt, carried parautochthonous rocks and may be a subsidiary thrust initiated by movement of the overriding rocks of the western belt. This thrust shows a close similarity to the peel thrusts of the Western Alps. Block faulting during Tertiary is largely responsible for the present-day north-south trend of the range.

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