Title

Stratigraphy and Structure of the Devonian Autochthonous Rocks, North-Central Carlin Trend of the Southern Tuscarora Mountains, Northern Eureka County, Nevada

Publication Date

1989

Type of Culminating Activity

Thesis

Degree Title

Masters of Science in Geology

Department

Geosciences

Major Advisor

Dr. Walter S. Snyder

Advisor

Dr. David W. Rodgers

Abstract

During the Early Paleozoic, the western United States has considered to have been a passive Atlantic-type margin, with shallow-water shelf carbonates on the miogeocline and deeper-water basinal siliceous rocks to the west. During the Late Devonian to Early Mississippian Antler orogeny, the basinal siliceous rocks, of the Roberts Mountains allochthon are thought to have been thrust eastward over the carbonate shelf rocks.

In the north-central portion of the Carlin trend of the southern Tuscarora Mountains, northern Eureka County, windows within the Roberts Mountains allochthon along the crest of the Tuscarora Anticline expose lower plate carbonate rocks. The Roberts Mountains thrust has been mapped previously in the Carlin trend at the contact between siliceous rocks presumed to be part of the Ordovician Vinini Formation and subjacent carbonate rocks of the Popovich and Roberts Mountains Formations.

The Silurian-Devonian Roberts Mountains Formation is composed of platy weathering micritic mudstone and occasional interbeds of wackestones and bioclastic limestone conglomerates and is interpreted to have been deposited in a carbonate basinal to slope apron. The Devonian Popovich Formation is composed dominantly of micrite, micritic mudstone, peloidal limestone, and limestone conglomerate. The Popovich Formation is interpreted to reflect a carbonate base-of-slope environment. A thin unit (~100 m) of siliceous rocks, informally named the Rodeo Creek unit, is interpreted to lie conformably above the Popovich Formation. The Rodeo Creek unit is composed of radiolarian chert, shale, siltstone, quartzite, silicified limestones, and decalcified limestones. The chert yield abundant middle Devonian to younger Entactinosphaera sp. radiolaria. The Rodeo Creek unit is interpreted to have been deposited as hemipelagic and pelagic rain in a starved basinal environment as it deepened either tectonically or eustatically.

The recognition of the Rodeo Creek unit depositionally overlying the Popovich Formation has revised the mapping of the Roberts Mountains thrust in the north-central Carlin trend. The Roberts Mountains thrust has been located where Ordovician and Silurian rocks of the Vinini Formation and Ordovician carbonates overlie the Rodeo Creek unit. Chert folds measured within the Rodeo Creek unit suggest that tectonic shortening may have occurred in the lower plate during the Antler orogeny.

The slope to basinal rocks of the Popovich Formation and Rodeo Creek unit may be correlative to other units in central Nevada indicating a regional basin of deposition during the Devonian. Correlative rocks to the Popovich Formation include the McColley Canyon Formation, Denay Limestone, and Gabel Limestone and correlative rocks to the Rodeo Creek unit include the Woodruff Formation, the Pilot Shale in the Cortez Range, and the Angustidontus shale.

Comments

This thesis was issued by Idaho State University in collaboration with Boise State University.

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