Paleogeography

AN INTEGRATED PETROLEUM EVALUATION OF NORTHEASTERN NEVADA

REGIONAL PALEOGEOGRAPHY

Over the past 50 years, several stratigraphic classifications have been proposed for the major lithologic facies belts within central Nevada. Most tectono-stratigraphic schemes are based on an 1) initially rifted Precambrian margin with Cambrian through Late Devonian passive margin sedimentation, often expressed as the Cordilleran miogeocline, and 2) the acceptance of a Late Devonian through early Mississippian collisional tectonic event, the Antler orogeny, which emplaced basinal marine rocks over and against shelf and slope sediments along the Roberts Mountains thrust zone.

Early models proposed an east-dipping Late Devonian subduction zone with a continuous inner-arc basin and continental slope and shelf to the east (Stewart and Poole, 1974; Poole and others, 1977). Later models have emphasized a westward dipping subduction zone, and the obduction of an accretionary prism during incipient subduction (Dickinson, 1977; Johnson and Pendergast, 1981; Speed and Sleep, 1982).

The most common tectono-stratigraphic nomenclature used in the literature brackets Paleozoic stratigraphic units into contemporaneous north-trending and parallel facies belts. These are the western siliceous and volcanic, eastern carbonate, and transitional facies, and represent generally deep-water marine, stable shelf, and intervening slope depositional environments respectively (Merriam and Anderson, 1942; Kay, 1951; Roberts, 1951, 1972).

We have divided the Paleozoic rocks into Upper Paleozoic Western Siliceous-Volcanic, Transitional Detrital-Carbonate, and Eastern Carbonate-Detrital Assemblages, and Lower Paleozoic Western Siliceous-Volcanic, Transitional, and Eastern Carbonate Assemblages. The Lower and Upper Paleozoic subdivisions represent Cambrian through Devonian, and Mississippian through Permian rocks respectively. Cenozoic and Mesozoic rocks have been divided into Cenozoic Sedimentary Rocks, Cenozoic-Mesozoic Volcanic Rocks, Cenozoic-Mesozoic Plutonic Rocks, and Mesozoic Sedimentary Rocks.