AN INTEGRATED PETROLEUM EVALUATION OF NORTHEASTERN NEVADA
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AN INTEGRATED PETROLEUM EVALUATION OF NORTHEASTERN NEVADA
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CHINLE FORMATION Type Section Information The Chinle Formation was named by Gregory (1917) for shales overlying the Shinarump Conglomerate and underlying the La Plata Group near Chinle Valley in northern Arizona. The Shinarump Conglomerate is considered the basal member of the Chinle Formation. Geologic Age The Chinle is Upper Triassic in age. In northeastern Nevada the Chinle disconformably overlies the Thaynes Formation. General Lithology The Chinle is composed of fine-grained silty sandstone, siltstone, and shale that are dominantly red or pink, or brown. The basal Shinarump Member is poorly sorted, rusty brown-weathering, chert-pebble conglomerate, conglomeratic sandstone and sandstone. The Timothy Formation of Nelson (1956) is considered equivalent to the basal portion of the Shinarump member of the Chinle Formation. It is composed of 0 to 200 feet of friable, medium to coarse-grained, quartz sandstone beneath the conglomerates of the Shinarump. The Shinarump Conglomerate in the Currie area is about 42 feet of pale-yellowish-brown, massive, pebble conglomerate with subrounded gray, green, and red pebbles of quartz, chert, and quartzite in a fine-grained quartz sandstone and clay matrix (Scott, 1954; Nelson, 1956). Large pieces and blocks of petrified wood, common regionally within the formation, are present near Currie (Nelson, 1956). Overlying the Shinarump is what both Scott (1954) and Nelson (1956) described as the Chinle Formation. It is about 500 feet of light-gray to olive-green and deep-red shale, thin-bedded, micaceous, yellow-brown siltstone, and very fine-grained sandstone with a few 1 to 20 foot thick gray-brown limestone interbeds (Scott, 1954; Nelson, 1956). The upper portion of the Chinle Formation is locally gypsiferous and is overlain by the Jurassic Nugget Sandstone. Average Thickness The Chinle Formation has a total thickness of about 600 feet in the Currie area (Scott, 1954; Nelson, 1956). Areal Distribution The Chinle Formation is widely distributed in southern Nevada, northern Utah and is also present south of the study area in southernmost Lincoln County. The only rocks considered Chinle Formation in the evaluation area are exposed in a small series of outcrops in the Twin Springs and Currie Hills. Depositional Setting The Chinle Formation represents a Triassic continental red-bed sequence. The lower Shinarump member is a sequence of lenticular stream channels that contain silicified logs and wood fragments that are often uraniniferous. |
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