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Geological Society of America Bulletin Downloaded from gsabulletin.gsapubs.org on January 26, 2010 Geological Society of America Bulletin Sevier Orogenic Belt in Nevada and Utah RICHARD LEE ARMSTRONG Geological Society of America Bulletin 1968;79;429-458 doi: 10.1130/0016-7606(1968)79[429:SOBINA]2.0.CO;2 Email alerting services click www.gsapubs.org/cgi/alerts to receive free e-mail alerts when new articles cite this article Subscribe click www.gsapubs.org/subscriptions/ to subscribe to Geological Society of America Bulletin Permission request click http://www.geosociety.org/pubs/copyrt.htm#gsa to contact GSA Copyright not claimed on content prepared wholly by U.S. government employees within scope of their employment. Individual scientists are hereby granted permission, without fees or further requests to GSA, to use a single figure, a single table, and/or a brief paragraph of text in subsequent works and to make unlimited copies of items in GSA's journals for noncommercial use in classrooms to further education and science. This file may not be posted to any Web site, but authors may post the abstracts only of their articles on their own or their organization's Web site providing the posting includes a reference to the article's full citation. GSA provides this and other forums for the presentation of diverse opinions and positions by scientists worldwide, regardless of their race, citizenship, gender, religion, or political viewpoint. Opinions presented in this publication do not reflect official positions of the Society. Notes Copyright © 1968, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. Downloaded from gsabulletin.gsapubs.org on January 26, 2010 Downloaded from gsabulletin.gsapubs.org on January 26, 2010 RICHARD LEE ARMSTRONG Dept. Geology, Yale University, New Haven, Connecticut Sevier Orogenic Belt in Nevada and Utah Abstract: In Nevada and Utah, sedimentation in the Cordilleran miogeosyncline began before the appearance of Cambrian fossils and continued without erogenic interruption through the Triassic. During the Jurassic, deformation and regional metamorphism occurred in the western part of the miogeosyncline, and the area of sediment accumulation shifted onto the Colorado Plateau. A major source of clastic material appeared along the eastern margin of the Cordilleran miogeo- syncline in Early Cretaceous time; this source supplied the sediments that filled the Cretaceous to Paleocene Rocky Mountain geosyncline. Clasts in the Cretaceous conglomerates show an inverted stratigraphy, reflecting successive exposure of older and older rocks in an evolving orogenic belt along the eastern side of the Cordilleran miogeosyncline. This source area was the Sevier orogenic belt, which had a history of deformation through most of the Cretaceous (Sevier orogeny). Decollement thrusts with displacements of tens of miles are the characteristic structures of the belt, but several large folds are also known. The largest thrusts are overlain unconformably by uppermost Cretaceous conglomerates. Thrusting in the Sevier orogenic belt had virtually ceased by the time the Laramide orogeny began east of the Sevier belt in latest Cretaceous time. Laramide mountains were the result of uplift of great blocks of crystalline basement along nearly vertical, reverse, and steep thrust faults. The Uinta arch, which intersects the Sevier orogenic belt almost at a right angle, is the only one of these basement uplifts closely involved with the deformation of the Cordilleran miogeosyncline. North-south-trending regional normal faulting of post-Oligocene age has broken up the orogenic belt so that it is not immediately recognizable on geologic maps. Arch ranges, intrusive domes, and gravity slides are additional complications of the Tertiary geology, but widespread Tertiary de- posits, particularly Oligocene ignimbrites, make a paleogeologic reconstruction possible; thus, the Sevier orogenic belt can be viewed as it existed before the normal faulting. CONTENTS Introduction 430 Tertiary structures 450 Acknowledgments 430 Nevadan, Sevier, and Laramide orogenies . 451 Geologic setting and stratigraphic history . 430 References Cited 453 Pre-normal faulting paleogeology—Sevier orogenic belt 432 FiSure Paleogeologic map 432 1. Eastern Great Basin Tertiary correlation chart 433 Foreland 434 2. Index map for Sevier orogenic belt, Nevada and Sevier Orogenic Belt 435 Utah 436 General Statement 435 3. Relationship of Pole Canyon thrust to Sheep- Southern Nevada-southwestern Utah sector . 435 rock thrust, Sheeprock-West Tintic area, Wah Wah-Canyon Range sector 437 Utah 439 Nebo-Charleston sector 437 4. Reinterpretation of Taylor and Ogden thrusts 441 Northern Utah sector 438 5. Diagrammatic section across Rocky Mountain Amount of shortening in Sevier orogenic belt . 440 geosyncline in central Utah 446 Structural continuity of thrust belt 441 6. Jurassic to Paleocene correlation chart showing Style and localization of thrusts 442 inverted stratigraphy of clasts in Rocky Hinterland 442 Mountain geosyncline 447 Stratigraphic evidence concerning age of deforma- 7. Geologic time scale 452 tion in Sevier orogenic belt 444 Evidence for pre-Cretaceous Sevier arch . 444 Plate Facing Cretaceous to Paleocene—Rocky Mountain geo- 1. Paleogeology of the Sevier Orogenic Belt . 429 syncline 445 Review of information provided by clast Table provenance 445 1. Geologic Maps of the Eastern Great Basin and Problem of Canyon Range fanglomerate . 448 Vicinity which were used for Construction Summary 449 of the Paleogeologic Map 434 Geological Society of America Bulletin, v. 79, p. 429-458, 7 figs., 1 pi., April 1968 429 Downloaded from gsabulletin.gsapubs.org on January 26, 2010 430 R. L. ARMSTRONG—SEVIER OROGENIC BELT IN NEVADA AND UTAH INTRODUCTION formed orogen now exposed at varied structural levels. The eastern Great Basin in eastern Nevada The existence of thrust faults and folds of and western Utah is characterized by north- Mesozoic age along the eastern edge of the south-trending fault-block ranges composed of Cordilleran geosyncline is common knowledge carbonate assemblage rocks of the Cordilleran (Eardley, 1962, 1963); the same area has been geosyncline. The area under consideration is clearly recognized as a source of clastic material bounded on the west by the mid-Paleozoic during the Cretaceous by Spieker (1946; 1949; Antler orogenic belt (Roberts and others, 1958), 1956) and his students and by Harris (1959) on the south by the Las Vegas shear zone who proposed the name, Sevier arch, for the (Longwell, I960), and on the east by the clastic source. This paper is a review and analysis Colorado Plateau. Although the Idaho bound- of the geology of this fold and thrust belt. ary has been taken as an arbitrary northern limit, it should be emphasized that structures ACKNOWLEDGMENTS described in the Great Basin persist without I am indebted to the large number of significant modification northward into, and geologists who contributed directly and in- even past, central Idaho. directly to this project through their studies in In order to understand the results of K-Ar the Great Basin. Without such previous work, dating studies of the region, a review of avail- this synthesis would be impossible. Kenneth F. able knowledge of Great Basin geology was es- Bick introduced me to the geology of the Great sential; the results of the K-Ar studies have Basin in 1956. Pierre Biscaye and, later, Julia been published elsewhere (Armstrong, 1963; Armstrong assisted in the field studies during 1966; Armstrong and Hansen, 1966). The only 1961. C. R. Longwell, Paul Williams, Robert complete synthesis of Basin and Range geology Scott, T. B. Nolan, Keith Ketner, Harold (Nolan, 1943) has become a classic. Since the Masursky, L. I. P. Muffler, J. C. Taylor, and appearance of that report, a great amount of Hoover Mackin provided hospitality and guid- work has been done in the area, particularly as ance in their respective field areas. During thesis projects. All Utah and approximately 80 preparation of the original manuscript, John percent of eastern Nevada have been mapped Rodgers, Edward Hansen, Keith Howard, in enough detail to show the most significant Clark Burchfiel, D. H. Adair, Kenneth Pierce, structural features. Osmond (1960) discussed and Pierre Biscaye provided helpful discussion. briefly the tectonic history of the Basin and K. K. Turekian, John Rodgers, P. M. Orville, Range province in Utah and Nevada; Misch C. R. Longwell, R. J. Roberts, Peter Misch (1960) discussed certain structural features of and D. H. Adair have read the present paper the eastern Great Basin; and Gilluly (1963) has at various stages of preparation and provided reviewed the tectonic history of the western helpful comments. Much of the drafting was United States. No up-to-date detailed synthesis done by Gary Audette. Field work was sup- of the geology of the eastern Great Basin exists, ported by National Science Foundation grant however, and this led King (1959, p. 142) to G14192. This research was done in major part say, after describing LongwelPs discoveries in while the writer was a National Science the Las Vegas region: Foundation graduate fellow (1959-1962). To pursue details of the structures in other parts GEOLOGIC SETTING AND of the eastern Great Basin would probably only bewilder the reader without profit. Many folds and STRATIGRAPHIC HISTORY thrusts are known, but the larger pattern is for the Two principal parts of the Cordilleran
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