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GEOLOGY of the INTERMOUNTAIN WEST an Open-Access Journal of the Utah Geological Association GEOLOGY OF THE INTERMOUNTAIN WEST an open-access journal of the Utah Geological Association Volume 3 2016 RISE OF THE ERG—PALEONTOLOGY AND PALEOENVIRONMENTS OF THE TRIASSIC-JURASSIC TRANSITION IN NORTHEASTERN UTAH Brooks B. Britt, Daniel J. Chure, George F. Engelmann, and Jesse Dean Shumway A Field Guide Prepared For SOCIETY OF VERTEBRATE PALEONTOLOGY Annual Meeting, October 26 – 29, 2016 Grand America Hotel Salt Lake City, Utah, USA Pre-Meeting Field Trip October 23–25, 2016 © 2016 Utah Geological Association. All rights reserved. For permission to copy and distribute, see the following page or visit the UGA website at www.utahgeology.org for information. Email inquiries to [email protected]. GEOLOGY OF THE INTERMOUNTAIN WEST an open-access journal of the Utah Geological Association Volume 3 2016 Editors UGA Board Douglas A. Sprinkel Thomas C. Chidsey, Jr. 2016 President Bill Loughlin [email protected] 435.649.4005 Utah Geological Survey Utah Geological Survey 2016 President-Elect Paul Inkenbrandt [email protected] 801.537.3361 801.391.1977 801.537.3364 2016 Program Chair Andrew Rupke [email protected] 801.537.3366 [email protected] [email protected] 2016 Treasurer Robert Ressetar [email protected] 801.949.3312 2016 Secretary Tom Nicolaysen [email protected] 801.538.5360 Bart J. Kowallis Steven Schamel 2016 Past-President Jason Blake [email protected] 435.658.3423 Brigham Young University GeoX Consulting, Inc. 801.422.2467 801.583-1146 UGA Committees [email protected] [email protected] Education/Scholarship Loren Morton [email protected] 801.536.4262 Environmental Affairs Craig Eaton [email protected] 801.633.9396 Geologic Road Sign Terry Massoth [email protected] 801.541.6258 Historian Paul Anderson [email protected] 801.364.6613 Membership Rick Ford [email protected] 801.626.6942 Public Education Paul Jewell [email protected] 801.581.6636 Matt Affolter [email protected] Publications Roger Bon [email protected] 801.942.0533 Publicity Paul Inkenbrandt [email protected] 801.537.3361 Social/Recreation Roger Bon [email protected] 801.942.0533 Society of Vertebrate Paleontology AAPG House of Delegates Editors 2016-2018 Term Craig Morgan [email protected] 801.422.3761 James I. Kirkland (Editor-in-Chief) — Utah Geological Survey State Mapping Advisory Committe ReBecca Hunt-Foster — Bureau of Land Management UGA Representative Jason Blake [email protected] 435.658.3423 Greg McDonald — Bureau of Land Management Martha Hayden — Utah Geological Survey Earthquake Safety Committe Chair Grant Willis [email protected] 801.537.3355 Production Cover Design and Desktop Publishing UGA Website Douglas A. Sprinkel www.utahgeology.org Cover Webmasters Paul Inkenbrandt [email protected] 801.537.3361 Lance Weaver [email protected] 801.403.1636 Three articulated sphenosuchians from the Saints & Sinners Quarry, which is Stop 5 of this field trip. UGA Newsletter The voids of various colors are weathered concretion Newsletter Editor Bob Biek [email protected] 801.537.3356 sites. Become a member of the UGA to help support the work of the Association and receive notices for monthly meetings, annual field conferences, and new publi- cations. Annual membership is $20 and annual student membership is only $5. Visit the UGA website at www.utahgeology.org for information and membership application. This is an open-access article in which the Utah The UGA board is elected annually by a voting process through UGA Members. Geological Association permits unrestricted use, However, the UGA is a volunteer driven organization, and we welcome your distribution, and reproduction of text and figures that voluntary service. If you would like to participate please contact the current are not noted as copyrighted, provided the original president or committee member corresponding with the area in which you would author and source are credited. like to volunteer. Utah Geological Association formed in 1970 from a merger of the Utah Geological Society, founded in 1946, and the Intermountain Association of Geologists, founded in 1949. Affiliated with the American Association of Petroleum Geologists. i GEOLOGY OF THE INTERMOUNTAIN WEST an open-access journal of the Utah Geological Association Volume 3 2016 Rise of the Erg—Paleontology and Paleoenvironments of the Triassic-Jurassic Transition in Northeastern Utah Brooks B. Britt1, Daniel J. Chure2, George F. Engelmann3, and Jesse Dean Shumway1 1Museum of Paleontology and Department of Geological Sciences, Brigham Young University, Provo, UT, 84602; [email protected], [email protected] 2Dinosaur National Monument, Jensen, UT 84035; [email protected] 3Department of Geography and Geology, University of Nebraska at Omaha, Omaha, NE 68182; [email protected] ABSTRACT This field trip focuses on the Late Triassic-Early Jurassic transition in northeastern Utah. This tran- sition records one of the most striking terrestrial environmental transformations in the history of North America, wherein the fluvio-lacustrine Chinle Formation is transgressed by the vast erg system of the Nugget (Wingate+Navajo)/Navajo/Aztec Sandstones. Exposures in northeastern Utah are ideal for study- ing this transition as they are closely spaced and accessible. The uppermost Chinle Formation beds are lacustrine/fluvial fine-grained sediments which are overlain by increasingly drier, sandy, transitional beds. The non-eolian basal beds of the Nugget Sandstone preserve a Late Triassic ichnofauna, with some sites including Brachychirotherium tracks. Large-scale dune deposits comprise most of the Nugget Sandstone and contain vertebrate (Brasilichnium) tracks and a diverse invertebrate ichnofauna. Interdunal, carbonate, spring mounds, as much as 3 m tall, fed carbonate freshwater lake deposits containing gastropod body fossils and invertebrate ichnofossils. Another lacustrine deposit, located at the Saints & Sinners Quarry, is on the shoreline of a non-carbon- ate interdunal lake/oasis. Over 11,500 bones have been collected from the site and represent two thero- pod dinosaur taxa, sphenodonts, sphenosuchians, a pterosaur, and drepanosaurs (with many complete, three-dimensional, articulated skeletons). In addition to bones, dinosaur trackways are also preserved in shoreline and other interdunal beds. The fauna shows that this interdunal area of the Nugget Sandstone was the site of intense biological activity. The drepanosaurs are chronologically significant in that they are restricted globally to the Late Triassic, indicating that at least the lower one-fourth to one-third of the formation is Late Triassic in age. INTRODUCTION changes in the Phanerozoic of North America, where a fluvial and lacustrine environment is gradually replaced The Chinle-Nugget formational transition records by an eolian-dominated environment represented by a one of the most dramatic continental environmental vast erg that covered much of the western U.S. for mil- Citation for this article. Britt, B.B., Chure, D.J., Engelmann, G.F., and Shumway, J.D., 2016, Rise of the erg—paleontology and paleoenvironments of the Triassic- Jurassic transition in northeastern Utah: Geology of the Intermountain West, v. 3, p. 1–32. © 2016 Utah Geological Association. All rights reserved. For permission to use, copy, or distribute see the preceeding page or the UGA website, www.utahgeology.org, for information. Email inquiries to [email protected]. 1 Rise of the Erg—Paleontology and Paleoenvironments of the Triassic–Jurassic Transition in Northeastern Utah Britt, B.B., Chure, D.J., Engelmann, G.F., and Shumway, J.D. lions of years (Blakey and Ranney, 2008). Jurassic Carmel Formation rests unconformably on top These formations along the south flank of the Uinta of the Nugget Sandstone. In the absence of age-specif- Mountains have received less attention than equivalent ic invertebrate fossils, dating of the Nugget is based on exposures farther south on the Colorado Plateau. Over vertebrate tracks, with a Brachychirotherium suite in the the last decade, however, intensive work in the Chinle lower portions of the formation indicating a Late Trias- Formation by Randall Irmis (Utah Museum of Natural sic age (Lockley and others, 1992) and the Early Jurassic History), and at the Nugget Sandstone area of Dinosaur Grallator, Otozoum, Eubrontes assemblage near the top National Monument (DINO) by Dan Chure (National (Lockley and others, 1992; Lockley, 2011). These traces, Park Service), George Engelmann (University of Ne- however, do not help resolve the position of the Trias- braska), and Brooks Britt (Brigham Young University) sic-Jurassic boundary within the formation. The Saints has shed new light on the Chinle-Nugget transition & Sinners Quarry fauna sheds additional light on these (Irmis and others, 2015) and the paleontology and pa- issues by corroborating the ichnofossil-derived Early leoenvironments of the Nugget Sandstone (Chure and Triassic age for the lower portion of the formation with others, 2014a and 2014b). body fossils because the quarry contains a drepanosaur This field trip focuses on recent paleontological dis- and a sphenosuchian with a rod-like posterior expan- coveries in the Nugget Sandstone that provide insights sion of the coracoid. Drepanosaurs are known only into the rise of the erg, its biota, and paleoenvironments. from the Carnian to Norian (Renesto and Binelli, 2006; We have selected sites for their significance and to min- Renesto and others, 2010) and sphenosuchians with imize travel time so that more time
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