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September Gsat 03 VOL. 19, No. 7 A PUBLICATION OF THE GEOLOGICAL SOCIETY OF AMERICA JULY 2009 The impact of snowmelt on the late Cenozoic landscape of the southern Rocky Mountains, USA Inside: ▲ 2009 Medal and Award Recipients, p. 12 ▲ 2009 GSA Research Grant Recipients, p. 18 ▲ Groundwork: The state of interactions among tectonics, erosion, and climate: A polemic, p. 44 Not Just Software. RockWare. For Over 26 Years. 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All of these tools (and more!) are now available in an annual license for academic use: unlimited installations within a department for the same price as a single, standard license. $2,499 Since 1983 303.278.3534 • 800.775.6745 RockWare.com GSATodayJuly09.indd 1 5/29/2009 12:40:49 PM VOLUME 19, NUMBER 7 ▲ JULY 2009 Not Just Software. SCIENCE ARTICLE GSA TODAY publishes news and information for more than 22,000 GSA members and subscribing libraries. GSA TODAY 4 The impact of snowmelt on the RockWare. (ISSN 1052-5173 USPS 0456-530) is published 11 times per late Cenozoic landscape of the year, monthly, with a combined April/May issue, by The southern Rocky Mountains, USA Geological Society of America®, Inc., with offices at 3300 Penrose Place, Boulder, Colorado. Mailing address: P.O. Box Jon D. Pelletier For Over 26 Years. 9140, Boulder, CO 80301-9140, USA. Periodicals postage paid at Boulder, Colorado, and at additional mailing offices. Cover: View of snow-covered peaks and cirque lake Postmaster: Send address changes to GSA Today, GSA in Rocky Mountain National Park, Colorado, USA. This Sales and Service, P.O. Box 9140, Boulder, CO 80301-9140, issue’s science article argues that snowmelt-induced USA. GSA provides this and other forums for the presentation of diverse opinions and positions by scientists worldwide, flooding has played a major role in shaping the land- ® regardless of their race, citizenship, gender, religion, or political scape of the southern Rocky Mountains in the late Ce- viewpoint. Opinions presented in this publication do not reflect nozoic era. See “The impact of snowmelt on the late RockWorks Academic Site License official positions of the Society. Cenozoic landscape of the southern Rocky Mountains, USA” by Jon D. Pelletier, p. 4–11. Copyright © 2009, The Geological Society of America (GSA). All rights reserved. Copyright not claimed on content prepared wholly by U.S. government employees within the scope of their employment. Individual scientists are hereby granted 12 GSA Names 2009 Medal and Award Recipients permission, without fees or further requests to GSA, to use a single figure, a single table, and/or a brief paragraph of text in 13 GSA Divisions Announce 2009 Named Awards other subsequent works and to make unlimited photocopies of items in this journal for noncommercial use in classrooms to 14 2009 GSA Fellows further education and science. For any other use, contact Permissions, GSA, P.O. 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Claims are honored for one year; please allow 23 About People Downhole Data Management and Directional Analysis Gridding Tools sufficient delivery time for overseas copies, up to six months. Visualization • Rose diagrams • Contours 23 In Memoriam • 2D and 3D striplogs • Stereonets • 3D surface diagrams GSA TODAY STAFF: Executive Director and Publisher: John W. Hess 24 GSA Officers and Councilors • Cross-sections • Statistical analysis • Several interpolation options Science Editors: Stephen T. Johnston, University of Victoria, 25 • Profi les • Lineation mapping and gridding • Grid math and grid fi lters School of Earth & Ocean Sciences, Victoria, British New GSA Members Columbia V8W 3P6, Canada, [email protected]; and • Fence diagrams • Arrow maps • Boolean logic tools David E. Fastovsky, University of Rhode Island, 33 GSA Foundation Update Department of Geosciences, Woodward Hall, Rm. 317, • Contour maps and 3D surfaces • Slope and direction models • Polynomial trend fi tting 34 2008–2009 Congressional Science Fellow Report • Solid models and isosurfaces • Strike and dip maps, and more! Kingston, Rhode Island 02881, USA, [email protected]. Managing Editor: Kristen E. Asmus, [email protected] 35 • Relational database for storage of Graphics/Imports/Exports Graphics Production: Margo Y. 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Printed in the USA using pure soy inks. 43 Classified Advertising All of these tools (and more!) are now available in an annual license for academic use: unlimited installations within a department 44 Groundwork: The state of interactions among tectonics, for the same price as a single, standard license. erosion, and climate: A polemic $2,499 46 Journal Highlights Erratum: The 2009 Geologic Time Scale on p. 61 of the April-May GSA Today contained an error: Hirnantian was misspelled. A corrected time scale is posted at www.geosociety.org/science/timescale/. Since 1983 303.278.3534 • 800.775.6745 GSA celebrates our three-year association with the International Year of Planet Earth. RockWare.com GSATodayJuly09.indd 1 5/29/2009 12:40:49 PM The impact of snowmelt on the late Cenozoic landscape of the southern Rocky Mountains, USA Jon D. Pelletier, Dept. of Geosciences, University of Arizona, Shoshone River has incised at least 800 m into the Eocene Gould-Simpson Building, 1040 East Fourth Street, Tucson, Willwood Formation (near horizon) and lower units, exposing Arizona 85721-0077, USA; [email protected] sediments as old as Triassic. Shale maturation data suggest that Cenozoic erosion in this area could have been as great as 1.5 km (Heasler and Kharitonona, 1996), indicating that the ABSTRACT thickness of basin fill sediments could have been much greater The intramontane basins of the southern Rocky Mountains, than the 800 m exposed in Figure 1. Broad, low-relief Quater- USA, have undergone up to 1.5 km of erosion from the middle nary strath terraces illustrate that local downcutting took place Miocene to the present. Here I explore the hypothesis that this episodically, followed by periods of lateral erosion (Mackin, erosion could have been caused primarily by an increase in the 1937; Hancock and Anderson, 2002). Dated basalt flows within intensity of snowmelt flooding. In the middle Miocene, snow- basin fill remnants indicate that most of this erosion took place melt runoff was limited to the highest elevations (>3 km) and from the late Miocene to the present (McMillan et al., 2006). hence impacted only a small fraction of the regional landscape. The Bighorn Basin is not unique—significant magnitudes of As the global climate system cooled during the late Miocene late Cenozoic erosion took place in all of the intramontane and Plio-Quaternary periods, the fraction of total river dis- basins of the southern Rocky Mountains. McMillan et al. (2006) charge derived from snowmelt increased significantly in areas used GIS techniques and dated basin-fill remnants to map the between 1.5 and 3 km elevation, thereby increasing the magni- spatial distribution of minimum erosion in the region and tude of flooding during periods of snowmelt and the resulting found that up to 1.5 km of late Cenozoic erosion occurred in bedload sediment flux and erosion of rivers in that elevation the
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