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Abstract: Extensional Tectonics of a Part of the Southwestern White Pine Range, Nevada: Implications for Petroleum Occurrence in Railroad Valley

Holly Langrock, Wanda J. Taylor

Extension exerts controls on migration and trapping of petroleum in rift settings, such as the Great Basin. Extensional controls are critical to the accumulation of petroleum in Nevada, including in Pine and Railroad Valleys. In these fields, reservoir permeability increased due to extension-related fracturing. These fractured reservoirs and structural traps may be contained within upper plates to regional detachments.

Just northeast of Nevada's most productive oil fields, a regionally extensive detachment is exposed in the White Fine Range. This detachment, the Blackrock fault, is a presently low-angle normal fault which dips <30° along most of its surface trace. The Blackrock fault is nonplanar and exhibits drastic changes in both orientation and geometry along its length. The amount of stratigraphic separation across the fault is also highly variable ranging from <30 to ~3800 m.

Upper plate structures to the Blackrock fault may influence oil fields in Railroad Valley. The west-dipping Blackrock fault crops out only 2 km east of the White Pine range front and most likely extends westward-beneath Railroad Valley. Rocks in the hanging wall of the Blackrock fault are more intensely faulted than rocks in the footwall. The upper plate faults strike north, northwest, east, and northeast The ~east-striking faults are youngest because they typically cut the other structures. These faults are closely spaced and largely interconnected which allows migration of hydrocarbons. Most of the hanging wall faults are high-angle normal faults which cut both Paleozoic and Oligocene rocks. In the Blackrock upper plate, Paleozoic carbonate and minor siliciclastic rocks are unconfor ably overlain by Oligocene tuffs and tuffaceous sedimentary rocks of the Garret Ranch Group with interbedded rhyolites. Upper plate fracturing of the Paleozoic rocks and Garret Ranch Group is important because parts of both sections are producing reservoirs in Railroad Valley.

AAPG Search and Discovery Article #90959©1995 AAPG Rocky Mountain Section Meeting, Reno, Nevada