Lithostratigraphy of Upper Proterozoic and Lower Cambrian McCoy Creek Group and Prospect Mountain Quartzite, Egan and Southern Cherry Creek Ranges, Nevada
William M. Schneck
The upper Proterozoic to Lower Cambrian McCoy Creek Group and the Prospect Mountain Quartzite have an exposed thickness of 1,978 m within the northern Egan and southern Cherry Creek Ranges, Nevada. The 1,415-m thick McCoy Creek Group is represented by four quartzite and four argillite formations. The lowest four formations are herein named in ascending order as Salvi, Cocomongo Mountain, Jenny Lind, and Egan Formations. The upper four units are the Willard Creek Formation, Strawberry Creek Formation, Shingle Creek Quartzite, and Osceola Argillite. Sedimentary structures recognized in the Osceola Argillite include flat laminations, small slumps, and subaerial exposures, which may depict intertidal mud-flat or lacustrine sedimentation. The Egan and Strawberry Creek Formations contain rhythmically bedded quartzite and argillite with slump structures, channels, graded bedding, and mud rip-up clasts. Three paleoenvironmental scenarios for deposition of the Egan and Strawberry Creek are postulated: (1) shallow-water marine turbidites, (2) lacustrine turbidites, and (3) mud-flat sedimentation with fluvial debris flows.
Dark-gray to black graphitic laminations within the Cocomongo Mountain Formation may represent euxinic marine deposition. The McCoy Creek Group is conformably overlain by the 563-m thick Prospect Mountain Quartzite. Three major Prospect Mountain rock types are petrographically described as (1) quartzarenite, (2) subarkose, and (3) argillite. Sedimentary structures include sandy-planar and sandy-trough cross-bedding, and sandy horizontal bedding. The Prospect Mountain Quartzite may represent both fluvial braided-plain and shallow marine sedimentation.
AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.