Title

The Late Paleozoic Tectonostratigraphy of the Central Pequop Mountains, Elko County, Nevada

Publication Date

6-2003

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Geology

Department

Geosciences

Major Advisor

Walt Snyder

Abstract

This study documents two upper Paleozoic tectonic unconformities within the Central Pequop Mountains (CPM) in northeastern Nevada. The two unconformities record tectonisim during the interval between the classic Antler orogeny (Late Devonian- Early Mississippian) and the Sonoma orogeny (latest Permian-earliest Triassic) of the western U.S. In the CPM, the stratigraphic succession is comprised of mixed siliciclastic-carbonate strata and is approximately 2580 m thick. From oldest to youngest, the lithostratigraphic units studied are the Diamond Peak Formation (~490 m), Ely Limestone (~43l m), Hogan Formation (~306 m), and Pequop Formation (~1659 m). The unconformities have been recognized and constrained by field relationships, fusulinacean data, and conodont data. Regionally, these tectonic unconformities have been sequentially labeled Cl to C6 (for the Carboniferous), and P1 to P5 (Permian). The C5 unconformity in the CPM (early late Atokan-early middle Desmoinesian) is bounded by the Ely Limestone and the Hogan Formation and the P2 unconformity (late Desmoinesian-Artinskian) is bounded by the Hogan Formation and Pequop Formation, The C5 unconformity represents a maximum hiatus of approximately 5 Ma and is associated with sub-C5 deformation, This deformation consists primarily of small scale thrusts, which displace strata 10's of meters, and outcrop scale folding. Orientations of the compressional structures suggest a northwest-southeast shortening axis. This study postulates that the C5 unconformity reflects the destruction of the Ely Basin and the tectonic initiation of the Hogan Basin. The P2 unconformity is bounded on the top by a pebble-cobble conglomerate with chert, limestone, and quartzite clasts. The largest clast size is 27 cm in diameter. On a regional scale, where the P2 unconformity is present, a similar basal conglomerate occurs. Tectonostratigraphic comparisons of the CPM and a section 15 Km to the south, Nine Mile Canyon (NMC), show that NMC experienced relatively continuous deposition and thicker lithostratigraphic units than the CPM suggesting that NMC was a locus of subsidence, while the CPM was periodically uplifted during the Middle Pennsylvanian to Early Permian.

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