Geology of Chinati Peak Quadrangle Trans-Pecos Texas

In the Chinati Mountains, Presidio County, Texas, a stratigraphic sequence of more than 15,000 feet of Paleozoic, Mesozoic, and Cenozoic rocks is exposed. Of five Paleozoic formations, aggregating 8,000 feet, the Cieneguita (Strawn through Cisco), Alta (Wolfcamp), and Cibolo (Leonard), are exposed north of Shafter. The Cibolo is restricted to Leonard age by raising the Alta-Cibolo boundary. The two exposed west of Shafter are respectively correlative with the Word and the Capitan but were mistakenly correlated with the Cibolo formation by previous writers except Skinner; for them the names Ross Mine formation and Mina Grande formation are proposed. Exposures of Paleozoic rocks in the upper Cibolo basin show a thinner, shoreward facies of the formations exposed typically in the vicinity of Shafter. A deep channel, formed during Wolfcamp time and trending southwestward through the quadrangle, is revealed by a 5,415 foot thick Wolfcamp section in the vicinity of Sierra Alta which thins northward to 2,610 feet in the upper Cibolo basin, and southeastward to 2,770 feet in the Argo Oil Corporation's Mitchell Bros.-State No. 1 well. The three Cretaceous formations, the Presidio (Travis Peak-Glen Rose), Shafter (Glen Rose), and "Finlay" (Walnut-Comanche Peak-Edwards), compose a total of 1,000 feet, which is correlative with the Yucca, Bluff, Cox, and Finlay formations, of the Quitman and Finlay mountains about 100 miles northwest. The Shafter is restricted to Trinity age. Extrusive rocks cover more than half the surface area of the quadrangle. The Buck Hill volcanic series is present on the eastern margin. The thick section of lava flows comprising the Chinati Mountains, for which the name Chinati Mountain volcanic series is proposed, lies above the Mitchell Mesa welded tuff of the Buck Hill series at the southern end of the Tierra Vieja and is therefore not older than Oligocene; it is probably Miocene or younger. Pleistocene and recent erosion and deposition has formed the prominent gravel terraces which surround the mountains. Four periods of crustal deformation affected the region: 1) post-Permian-pre-Cretaceous regional uplift and erosion; 2) post-Cretaceous uplift, thrusting, doming, folding, and erosion; 3) late Tertiary doming; and 4) late Cenozoic basin-and-range block faulting. Mineral deposits include ores of silver, lead, copper, zinc, and rare native lead.