Field Trips in the , USA

Field Guide 5

Edited by Eric P. Nelson and Eric A. Erslev Downloaded from http://pubs.geoscienceworld.org/books/book/chapter-pdf/3734269/9780813756059_frontmatter.pdf by guest on 25 September 2021 Field Trips in the Southern Rocky Mountains, USA

Edited by

Eric P. Nelson Department of Geology and Geological Engineering Colorado School of Mines Golden, Colorado 80401 USA

and

Eric A. Erslev Department of Geosciences Colorado State University Fort Collins, Colorado 80523 USA

Field Guide 5 3300 Penrose Place, P.O. Box 9140 Boulder, Colorado 80301-9140 USA 2004

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Copyright is not claimed on any material prepared wholly by government employees within the scope of their employment.

Published by The Geological Society of America, Inc. 3300 Penrose Place, P.O. Box 9140, Boulder, Colorado 80301-9140, USA www.geosociety.org

Printed in U.S.A.

GSA Books Science Editor: Abhijit Basu

Library of Congress Cataloging-in-Publication Data

Field trips in the southern Rocky Mountains, USA / edited by Eric P. Nelson and Eric A. Erslev. p. cm. -- (Field guide ; 5) Includes bibliographical references. ISBN 0-8137-0005-1 (pbk.) 1. Geology--Colorado--Guidebooks. 2. Geology----Guidebooks. 3. Geology--Rocky Mountains Region--Guidebooks. 4. Geology, Stratigraphic--Guidebooks. 5. Colorado--Guidebooks. 6. New Mexico--Guidebooks. 7. Rocky Mountains Region--Guidebooks. I. Nelson, Eric P., 1951- II. Erslev, Eric A. III. Field guide (Geological Society of America) ; 5.

QE91.F43 2004 557.88-dc22 2004058060

Cover: Digital elevation model of the Colorado Front Range between Golden and Ft. Collins created from a mosaic of 7.5 min U.S. Geological Survey topographic quadrangles using Natural Scene Designer; data were gridded at 30 m (courtesy of Karl Mueller, University of Colorado, Boulder). The eastern mar- gin of the Front Range near Boulder, shown in purple and blue, is formed of east-vergent folds and thrust faults. As the range front steps eastward farther to the north, structures are smaller and are west vergent above reactivated NW-trending basement faults. The central part of the region (from north to south) shows gently east-dipping surfaces of Quaternary age that are now deeply incised by river networks. The elevation of these surfaces once marked regional base levels along the base of the Front Range, which has now been significantly lowered by removal of easily eroded and Tertiary strata. Regions of higher elevation show glacial cirques and valleys sculpted by alpine glaciers. The western edge of the Front Range is marked by yellow and green where west-vergent thrust faults emplace basement rocks over late Cretaceous and Tertiary strata. This region also marks the headwaters of the Colorado River that drains the Front Range to the west.

10 9 8 7 6 5 4 3 2 1 ii

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Preface ...... v

1. Navajo sand sea of near-equatorial Pangea: Tropical westerlies, slumps, and giant stromatolites...... 1 David Loope, Len Eisenberg, and Erik Waiss

2. Strike-slip tectonics and thermochronology of northern New Mexico: A field guide to critical exposures in the southern Sangre de Cristo Mountains...... 15 Eric A. Erslev, Seth D. Fankhauser, Matthew T. Heizler, Robert E. Sanders, and Steven M. Cather

3. Structural implications of underground coal mining in the Mesaverde Group in the Somerset Coal Field, Delta and Gunnison Counties, Colorado ...... 41 Christopher J. Carroll, Eric Robeck, Greg Hunt, and Wendell Koontz

4. West Bijou Site Cretaceous-Tertiary boundary, Basin, Colorado ...... 59 Richard S. Barclay and Kirk R. Johnson

5. Buried Paleo-Indian landscapes and sites on the High Plains of northwestern Kansas...... 69 Rolfe D. Mandel, Jack L. Hofman, Steven Holen, and Jeanette M. Blackmar

6. The Colorado Front Range—Anatomy of a Laramide Uplift...... 89 Karl S. Kellogg, Bruce Bryant, and John C. Reed Jr.

7. Continental accretion, Colorado style: Proterozoic island arcs and backarcs of the Central Front Range...... 109 Lisa Rae Fisher and Thomas R. Fisher

8. Eco-geo hike along the , north of Boulder, Colorado...... 131 Peter W. Birkeland, E.E. Larson, C.S.V. Barclay III, E. Evanoff, and J. Pitlick

9. The South Cañon Number 1 Coal Mine fire: Glenwood Springs, Colorado ...... 143 Glenn B. Stracher, Steven Renner, Gary Colaizzi, and Tammy P. Taylor

10. Field guide to the paleontology and volcanic setting of the Florissant fossil beds, Colorado. . . . 151 Herbert W. Meyer, Steven W. Veatch, and Amanda Cook

11. Paleoceanographic events and faunal crises recorded in the Upper Cambrian and Lower Ordovician of west Texas and southern New Mexico ...... 167 John F. Taylor, Paul M. Myrow, Robert L. Ripperdan, James D. Loch, and Raymond L. Ethington

iii

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12. The consequences of living with geology: A model field trip for the general public (second edition) ...... 185 David M. Abbott Jr. and David C. Noe

13. Surface and underground geology of the world-class Henderson molybdenum porphyry mine, Colorado ...... 207 James R. Shannon, Eric P. Nelson, and Robert J. Golden Jr.

14. Walking with dinosaurs (and other extinct animals) along Colorado’s Front Range: A field trip to Paleozoic and Mesozoic terrestrial localities ...... 219 Joanna L. Wright

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The theme of the 2004 Geological Society of America Annual Meeting and Exposition is “Geoscience in a Changing World,” a theme that covers both new and traditional areas of the sciences. Traditionally, fi eld trips are a very important part of the GSA Annual Meeting, both for disseminating the results of current research as well as for educational purposes. Education is an important goal implicit in the mission of GSA, and in the broader earth science community, and students in our changing world come from academic, indus- try, governmental, and political arenas as well as interested laypersons. The Front Range of the Rocky Moun- tains and the High Plains preserve an outstanding record of geological processes from Precambrian through Quaternary times, and thus serve as an excellent educational exhibit. With its energy and mineral resources, geological hazards, water issues, geoarcheological sites, and famous dinosaur fossil sites, the Front Range and adjacent High Plains region provide ample opportunities for fi eld trips focusing on our changing world. The chapters in this fi eld guide all contain technical content as well as a fi eld trip log describing fi eld trip routes and stops. Of the 25 fi eld trips offered at the meeting, 14 are described in this guidebook and are presented in the order that the trips were listed and organized at the meeting. In keeping with the theme of the meeting, the guidebook chapters cover a wide variety of geoscience disciplines, with chapters on tectonics (Precambrian and Laramide), stratigraphy and paleoenvironments (for example, early Paleozoic environments, Jurassic eolian environments, the K-T boundary, the famous Oligocene Florissant fossil beds), economic deposits (coal and molybdenum), geological hazards, and geoarchaeology. Chapter top- ics are summarized below. Three chapters discuss tectonics. Fisher and Fisher (chapter 7) present fi eld evidence in the Front Range for the existence and paleoenvironments of Proterozoic island arc and backarc rock packages that formed during the accretion of the North American Craton. Although most basement rocks in the Front Range have undergone high T-low P amphibolite facies metamorphism under anatectic conditions, the rocks examined on this trip are slightly lower grade and without anatectic melting. Kellogg and coauthors (chapter 6), who have extensive past and recent mapping experience in the Front Range, present a spec- tacular transect across the Front Range to explore Precambrian through Rio Grande Rift tectonics, with a special focus on the controversy surrounding interpretations of Laramide structure along the fl anks of the range. Erslev and coauthors (chapter 2) examine the fl anks of the southern Sangre de Cristo arch in New Mexico and address its history of uplift and the large (>35 km) dextral offsets of Precambrian lithologic belts on N-striking fault zones that have been attributed to Proterozoic, Ancestral Rocky Mountain, and Laramide events by recent authors. This fi eld trip tests these confl icting hypotheses by combining new and old mapping with new thermochronological techniques. Six chapters discuss stratigraphy and paleoenvironmental interpretations. Taylor and coauthors (chap- ter 11) present a revised, and more useful, lithostratigraphy for Lower Paleozoic strata in New Mexico and west Texas based on new biostratigraphic (trilobite and conodonts) and chemostratigraphic (carbon isotope) data. Wright (chapter 14) examines terrestrial sedimentary units exposed along the east fl ank of the Front Range, with a focus on sedimentological and trace fossil evidence for paleoenvironmental interpretations during of Ancestral and Laramide mountains. Loope and coauthors (chapter 1) present new research results on eolian deposits of the Early Jurassic Navajo Sandstone in Utah that suggest that pluvial episodes punctuated the history of dune sea development during this otherwise arid period. Spectacular outcrops of v

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preserved dune sand features are illustrated. Barclay and Johnson (chapter 4) present extensive data from the West Bijou K-T boundary site (only discovered in August 2000) that constrain the position of this important boundary preserved in a terrestrial environment. This is a great example of a multidisciplinary study directed at understanding the importance of the K-T boundary and, in general, of impact events in earth history. Birkeland and coauthors (chapter 8) offer a trip using public and human-powered transportation that gives an overview of the Front Range Phanerozoic stratigraphy and Laramide magmatism while focusing on the development of Quaternary geomorphology and surfi cial deposits in the Boulder area. Meyer and coauthors (chapter 10) illustrate how Oligocene volcanic activity and related landforms in the southern Front Range infl uenced sedimentation of the Florissant Formation, which houses a spectacularly diverse, world-famous fl ora and insect fauna consisting of more than 1,700 described species. This fossil site continues to provide signifi cant data for interpretations of paleoenvironments and the evolution of life. Two chapters cover aspects of economic geology. Carroll and coauthors (chapter 3) present recent results of structural studies on faults, fractures, and coal cleats in important coal mines within the Mesaverde Group in the Somerset Coal Field in westernmost Colorado. The results have important implications for mine plan- ning in the area and for the structural evolution of the Mesaverde Group during the Eocene and Neogene. Shannon and coauthors (chapter 13) present previously unpublished mapping data on veins and hydrother- mal alteration associated with the peripheral zones of the world-famous Urad-Henderson porphyry Mo deposits, and suggest that many features of the deposit and the peripheral zone were structurally controlled by old Precambrian shear zones. The geology and operations of this world-class mine are also illustrated. Two chapters cover important and current aspects of geological hazards. Abbott and Noe (chapter 12) present an excellent and updated version of this previously-run fi eld trip that examines the geological haz- ards present along the heavily populated east fl ank of the Front Range. This trip is an important model for future trips on the consequences of living with geology that could be offered to the general public, service clubs, politicians, and school groups anywhere in the world. One of the biggest challenges for geoscientists is appropriately disseminating the results and importance of geoscientifi c studies to society in general. Stracher and coauthors (chapter 9) present new, exciting data and methods of study on the composition and environ- mental effects of gases and mineral condensates related to an underground coal fi re in western Colorado. This is an important study because such underground fi res, combined with recent drought conditions in the west, have led to surface fi res with drastic effects on fl oral and faunal, including human, habitats. This study also illustrates how geoscience and fi re science are being combined to address associated hazards. In the chapter on geoarchaeology, Mandel and coauthors (chapter 5) present recent research on the High Plains of northwestern Kansas, where soil-stratigraphic and geomorphological studies have shed light on the buried landscapes that harbor the material record of what may be the earliest humans in the region. This is an excellent illustration of how classical geological techniques can aid in archeological interpretations of past civilizations and how these civilizations may have interacted with the physical environment. We hope that these guidebook chapters will illustrate to current and future readers how geoscience is changing and how it is addressing issues in a changing world.

Eric P. Nelson Eric A. Erslev

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