Geology of the South Third of the Green Springs Quadrangle, Nevada

Résumé du livre

The Green Springs quadrangle is in east-central Nevada approximately 75 miles southwest of Ely. The central part of the area investigated is at the north end of Railroad Valley and is flanked by the White Pine Range to the east and the Pancake Range to the west. The exposed Paleozoic rocks range in age from Devonian to Permian. They consist of limestone, shale, and quartzite. No Mesozoic strata were recognized in the mapped area, although Cretaceous lake sediments crop out in the neighboring Illipah quadrangle. The Paleozoic rocks are unconformably overlain by lacustrine sediments of probable Eocene age. Crystal tuffs overlie the lake beds but the stratigraphic relationship of these beds is uncertain. During the late Tertiary basic lava flows covered a large portion of the quadrangle. Quaternary sedimentation is recorded in fanglomerates and terrace deposits which have been correlated with the flood stages of Pleistocene lakes by some workers. The principal structural features are found in the highly folded and faulted strata of the White Pine and Pancake Ranges. Folds developed in Paleozoic rocks during the Mesozoic were largely destroyed by subsequent block faulting in the Tertiary Period. However, the remnants of several folded structures are exposed near the north boundary of the area. Thrusting presumably took place during Mesozoic time contemporaneous with folding. The exact age of the normal faults in the area is not known but two periods of normal faulting are clearly evident. Faulting occurred between the Eocene and Miocene. Pleistocence and/or younger normal faults have moderately disrupted fanglomerates, alluvium and basalts. The first commercial oil well in Nevada is located in Railroad Valley approximately 40 miles south of the quadrangle. The lake deposits of the Green Springs region are of particular interest, for it is here that the beds which presumably are deeply buried at the well sites farther south appear to lap out against Paleozoic strata. No evidence for mineralization was found and the area is not considered promising from that standpoint.