Abstract

Biostratigraphic and lithologic correlations of Lower and Middle Cambrian strata are made in eastern and southeastern Nevada at Eureka, Cave Valley, Pioche, Delamar, Mormon Range, and Virgin Mountains, and in Arizona at the western end of the Grand Canyon near Grand Wash Cliffs, and in the Granite Gorge area of the Canyon.

These correlations, together with others in the better-known areas of Lower and Middle Cambrian strata in central Arizona, western Utah, and southeastern Idaho, disclose widespread faunal and lithogenetic continuity over a large part of the Great Basin area of the Southern Cordilleran geosyncline and thus permit unification and consequent simplification of formational nomenclature.

The Prospect Mountain quartzite (Eureka district, Nevada) is present throughout the entire region, ranging from Upper Algonkian (?) and Lower Cambrian in eastern Nevada and western Utah to lower Middle Cambrian in northwestern Arizona (Granite Gorge), central Arizona, northwestern Utah, and southeastern Idaho. The quartzite has been locally designated as Tapeats sandstone, Tintic, and Brigham quartzites.

The overlying Pioche shale (Pioche district, Nevada) is recognized from Eureka to western Grand Canyon and eastward throughout most of western Utah. In southeastern Nevada and north-westernmost Arizona the Pioche has previously been regarded as part of the Bright Angel shale; and in western Utah it has been called Ophir and Cabin. The Pioche formation is both Lower and Middle Cambrian over most of the Great Basin area but is Lower Cambrian at Eureka and Cave Valley (?), Nevada, and in the House and Deep Creek (?) ranges of western Utah, and Middle Cambrian in the Tintic and Sheeprock ranges of central Utah.

The Middle Cambrian Lyndon limestone and Chisholm shale (both of the Pioche district) may be traced northward to Cave Valley and southward to western Grand Canyon. Farther east in the Grand Canyon, the Lyndon limestone disappears, and the combined Pioche and Chisholm shales constitute the Bright Angel shale.

The Peasley and Burrows limestones and portions of the Highland Peak limestone are recognized at Cave Valley and Delamar in eastern Nevada as well as in their type area, the Pioche district, and the first of these is traced southward to western Grand Canyon.

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