Cambrian and Precambrian rocks of the Groom district, Nevada, southern Great Basin

Abstract

More than 14,000 feet of conformable Cambrian and Precambrian rocks is exposed in the Groom district in southwestern Lincoln County, Nev. The lower half of this stratigraphic section is chiefly quartzite and siltstone, the upper half chiefly limestone and dolomite. Included are part of the Johnnie Formation (>300 ft) and the Stirling Quartzite (>2,930 ft) of Precambrian age; the Wood Canyon Formation (2,285 ft) of Cambrian and Precambrian age; and the Zabriskie Quartzite (220 ft), Carrara Formation (1,879 ft), Bonanza King Formation (4,355 ft), and Nopah Formation (2,035 ft) of Cambrian age. The stratigraphic units exposed in the Groom Range can be recognized for more than 100 miles to the west and south, and the same formational names can be used throughout that region. The units can also be correlated with the Cambrian and Precambrian rocks of the Pioche district, but different stratigraphic nomenclature is preferred for the Pioche area. INTRODUCTION A nearly complete conformable section of Cambrian and upper Precambrian rocks is exposed in the Groom mining district, at the south end of the Groom Range in southwestern Lincoln County, Nev. (fig. 1). Although the section was described by Humphrey in 1945, redescription and reinterpretation seem worthwhile because considerably more is now known of regional stratigraphic relations in the southern Great Basin and because the revised interpretation of the Groom section affects the regional picture significantly. Also1, on the basis of more complete data, this report revises an earlier outline of stratigraphic nomenclature for Cambrian rocks in the Nevada Test Site area (Barnes and Palmer, 1961). Because it is on the Nellis Air Force Range, the Groom district is not readily accessible at present. Measurement of the stratigraphic section and preparation of the reconnaissance geologic map (fig. 2) were done with permission of the Air Force as part of geologic mapping at the Nevada Test Site of the U.S. Atomic Energy Commission. Gl G2 CONTRIBUTIONS TO STRATIGRAPHY