B. C. BURCHFIEL Department of Geology, Rice University, Houston, Texas 77001 R. J. FLECK U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025 D. T. SECOR Department of Geology, University of South Carolina, Columbia, South Carolina 29210 R. R. VINCELETTE Trend Exploration Limited, 600 Capitol Life Center, Denver, Colorado 80203 G. A. DAVIS Department of Geology, University of Southern California, Los Angeles, California 90007 Geology of the Spring Mountains, Nevada ABSTRACT II6°-0" 115®- 0" The northwest-trending Spring Moun- tains, Nevada, contain a 45-mi-wide (75-km) cross section of the eastern part of the North American Cordilleran orogenic belt and geosyncline. This cross section is probably the most southerly exposed sec- tion which exhibits structure and stratig- raphy "typical" of the eastern part of the Cordillera. Stratigraphically, the transition from Paleozoic craton to miogeosyncline is pres- ent from east to west across the Spring Mountains. The sedimentary succession through the middle Permian thickens from 8,800 ft (2,660 m) east of the Spring Moun- tains to approximately 30,000 ft (9,000 m) in the west. Thickening of individual for- mations accounts for 6,800 ft (2,070 m) of added section, addition of formations at unconformities accounts for 4,600 ft (1,400 m) of added section, and addition of a thick terrigenous late Precambrian sequence ac- counts for 9,800 ft (3,000 m) of added sec- tion. Three major thrust plates are exposed in the Spring Mountains, each structurally higher plate containing a thicker sequence Figure 1. Location map of the Spring Mountains, Nevada, showing areas of mapping responsibility. Quadrangle names are shown for the Spring Mountains area. of Paleozoic rocks. The easternmost thrust is the Keystone thrust, except where the ear- lier Red Spring thrust plate is present below within the Spring Mountains only establish easternmost part of the North American the Keystone as isolated remnants. The a much wider time bracket, post-Early Cordilleran orogenic belt. Keystone thrust appears to be a Jurassic to pre—late Cenozoic for the east- The earliest geologic work in the Spring décollement thrust, but complications at ernmost thrust faults and post—Early Per- Mountains was by G. K. Gilbert (1875), depth suggest that additional thrust slices mian to pre—late Cenozoic for the west- who served as a geologic assistant for the may be present below the thrust or several ernmost thrusts. Wheeler expeditions of 1871-1872. R. B. thousand feet of late Precambrian terrige- Rowe of the U.S. Geological Survey did ex- nous rocks may be present above the thrust. INTRODUCTION tensive work in the central part of the The structurally higher Lee Canyon thrust The Spring Mountains are located in Spring Mountains during the period plate probably contains at least 4,000 ft southeastern Nevada, 10 mi west of Las 1900-1901, but he died before his results (1,200 m) of these terrigenous rocks at its Vegas (Fig. 1). Trending northwest more could be published. His field data were in- base, and the Wheeler Pass thrust plate con- than 45 mi, they form a southern boundary corporated in the regional report of J. E. tains at least 11,000 ft (3,300 m) of these for the general north or northeast-trending Spurr (1903). Rowe clearly recognized the rocks. Pregeosynclinal basement could be ranges farther north in Nevada. Because the fault along the east side of the Spring involved in some of the higher thrust plates, northwest topographic trend is transverse Mountains now referred to as the Keystone particularly the Wheeler Pass plate, but to the north- or northeast-trending regional thrust. depths of exposure are inadequate to de- structural strike, the Spring Mountains In 1919, C. R. Longwell began system- termine its role. offer a unique opportunity to study a wide atic mapping in the region of southeastern Thrust faulting has produced a shorten- cross section of continuously exposed pre- Nevada. His work, together with that of ing of from 22 to 45 mi (36.6 to 75 km) in Tertiary rocks. Stratigraphically, the Spring Nolan (1929) and Glock (1929), led to the the géosynclinal rocks based on geometric Mountains contain Paleozoic rocks which first regional geologic map of southeastern constructions of cross sections at depth. show the transition from craton to Nevada and of the Spring Mountains This range probably represents a minimum miogeosyncline. Structurally, they contain (Bowyer and others, 1958). Longwell's figure. Some folding and thrusting occurred rocks of the undeformed craton and of work forms the basis for most of our pres- during the early Late Cretaceous, but data three major thrust plates belonging to the ent understanding of the tectonics and Geological Society of America Bulletin, v. 85, p. 1013-1022, 6 figs., July 1974 1013 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/85/7/1013/3433314/i0016-7606-85-7-1013.pdf by guest on 27 September 2021 1014 BURCHFIEL AND OTHERS stratigraphy in this part of the Cordilleran tains; Fig. 1) to a geosynclinal sequence in tween the Spring Mountains and Fren- thrust belt. The present report summarizes the northwest Spring Mountains. chman Mountain, but the general charac- the geology of most of the Spiing Moun- Stratigraphically, the oldest exposed teristics of the formations are maintained. tains compiled from work completed at var- parts of the most easterly and westerly sec- All the carbonate formations that have been ious times from 1961 to the present (Fig. 1). tions, and by inference the two central sec- studied suggest deposition in shallow The authors of this paper owe a great debt tions, begin with a nonmarine and shallow marine or marginal marine environments to Chester Longwell for assistance given, marine sequence of terrigenous rocks. At (Gans, 1970). ranging from selection of map areas, field Frenchman Mountain, these rocks are Early Thickening of the carbonate sequence excursions, and discussions to personal in- and early Middle Cambrian in age, approx- across the Spring Mountains takes place in spiration. imately 1,000 ft (300 m) thick, and rest un- two ways: (1) by thickening of individual conformably on Precambrian crystalline formations and (2) by addition of forma- GEOLOGY OF THE rocks. In the northwestern part of the tions at unconformities. Thickening is SPRING MOUNTAINS Spring Mountains, the terrigenous rocks marked in the Bird Spring Formation and The Spring Mountains contain geology are more than 11,000 ft (3.3 km) thick and equivalents of Late Mississippian to middle typical of the eastern part of the Cordilleran range from late Precambrian to early Mid- Perm an age which thicken from 1,600 ft orogenic belt which can be traced continu- dle Cambrian in age. South and southwest (485 m) at Frenchman Mountain (Callville ously from Canada to southern Nevada. of the Spring Mountains, the thick late Pre- Limestone and Permian red beds) to more Late Precambrian and Paleozoic rocks are cambrian terrigenous sequence rests uncon- than 6,700 ft (2,000 m) in the central characterized by a thin (approx. 8,800 ft or formably on either crystalline basement or Spring Mountains. Some formations thick- 2.6 km) cratonal sequence to the east which on an older sequence of unmetamorphosed en by 50 to 60 percent (for example, thickens northwestward (to approx. 30,000 to weakly metamorphosed late Precam- Bonanza King Formation), whereas others ft or 9.0 km) in the Spring Mountains into brian sedimentary rocks (Pahrump Group) show little if any thickening (for example, the miogeosynclinal part of the Cordilleran that rests unconformably on crystalline Monte Cristo Limestone and Sultan Lime- geosyncline (Fig. 2). Mesozoic rocks are basement. Regional correlations by Stewart stone). present only in the eastern part of the (1970) suggest that the upper part of the Addition of formations at unconformities Spring Mountains, and their relations to Tapeats Sandstone in some cratonal se- accounts for approximately 4,600 ft (1,400 Mesozoic geosynclinal development are not quences correlates with the Zabriskie m) ot thickening across the Spring Moun- clear (Stanley and others, 1971; Burchfiel Quartzite of the geosynclinal sequence (for tains. In the cratonal sequence at French- and Davis, 1972). Structures in the Spring example, northwestern Spring Mountains man Mountain, only one major unconfor- Mountains are dominated by east-directed section) and that the lower part of the mity is present in the Paleozoic carbonate thrust faults along which thicker sequences Tapeats correlates with the uppermost part sequence; the Middle Devonian Muddy of Paleozoic rocks have moved over thinner of the Wood Canyon Form ation. The transi- Peak Limestone rests unconformably on the ones. At present levels of exposure, thrust tion from the thin cratonal sequence to the Upper Cambrian Nopah Formation. In the plates carry only sedimentary reeks. These thick geosynclinal sequence must occur be- eastern part of the Spring Mountains above structural and stratigraphic characteristics neath the Spring Mountains; the thick Red Rock Canyon, two and possibly three are similar to those described from areas geosynclinal terrigenous sequence is first unconformities are present. One occurs be- farther north along the eastern oart of the exposed in the Wheeler Pass thrust plate tween Lower and Upper Ordovician rocks Cordilleran orogenic belt. where it is already fully developed. (Goodwin Limestone and Mountain Southward, however, the structural and The upper part of the terrigenous se- Sprin,s;s Formation of Gans, 1970) which stratigraphic relations change, such that the quence becomes calcareous and contains are here present below the Middle Devo- next exposed southeast cross section in the carbonate beds in lower Middle Cambrian nian unconformity. A second unconformity Mesquite and Clark Mountains, 30 mi rocks of the Bright Angel Shale, or its is present below Middle Devonian rocks farther south, contains Paleozoic sedimen- geosynclinal equivalent, the Carrara For- (Sultan Limestone) and is of regional ex- tary rocks characteristic of the craton and mation, and grades upward into a thick se- tent.