Abstract

This report covers approximately 3,000 mi² (4,828 km²) of the northeast corner of Elko County, Nevada and a small portion of the extreme southwest corner of Cassia County, Idaho. The area lies along the north-central boundary of the geographic province known as the Great Basin, an area characterized by internal drainage and a series of fault-bounded mountain ranges with intervening valleys. The area contains thick deposits of sedimentary rocks. It is estimated that the Paleozoic section is at least 20,000 ft (6,096 m) thick, with preserved thicknesses varying widely due to differences in the original thicknesses, multiple unconformities, and removal by erosion. In general, the stratigraphy is more complicated in the northern half of the area and along the western border; in the north because of facies changes and interfingering of formations, in the west because of possible thrusting. The southern half and the eastern portions are much less complicated stratigraphically.

Structural trends observed from very limited mapping in the area indicated that pre-Tertiary rocks of the southwestern portion of the area have a different structural grain than those in the northeastern portion. This is probably the result of thrusting in the southern part which appears to have occurred during Paleozoic and Mesozoic time.

Several factors indicate that the area has potential for the production of oil and gas;

1. Regional studies of the north-central Great Basin indicate that the area probably is underlain by abundant source rocks, particularly the Mississippian Chainman Shale, and the phosphatic shales and mudstones of the Permian Phosphoria Formation.

2. Based on a variety of recent thermal maturity studies done in the area, a major portion of the potential source rocks have been determined to fall within the oil-to-dry gas fractionation range.

3. The abundance of moderately dipping Middle and Upper Permian rocks exposed throughout the area and the presence of large north-northeast trending folds implies both a preserved Paleozoic section and an absence of widespread extensional deformation.

4. A variety of potential structural and stratigraphic traps could exist beneath the area including abundant facies changes in the Paleozoic section, unconformities in the Tertiary section, north-northeast trending anticlines in Permian rocks, and possibly overthrusting in the southwestern portion of the area.

Overall, the data available for the area indicates that it should be considered a prime exploration target for oil and gas in Nevada.