Multiple constraints on the age of a Pleistocene lava dam across the Little Colorado River at Grand Falls, Arizona

Abstract

Research Article| March 01, 2006 Multiple constraints on the age of a Pleistocene lava dam across the Little Colorado River at Grand Falls, Arizona Wendell Duffield; Wendell Duffield 1Department of Geology, Northern Arizona University, Flagstaff, Arizona 86011, USA Search for other works by this author on: GSW Google Scholar Nancy Riggs; Nancy Riggs 1Department of Geology, Northern Arizona University, Flagstaff, Arizona 86011, USA Search for other works by this author on: GSW Google Scholar Darrell Kaufman; Darrell Kaufman 1Department of Geology, Northern Arizona University, Flagstaff, Arizona 86011, USA Search for other works by this author on: GSW Google Scholar Duane Champion; Duane Champion 2U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, USA Search for other works by this author on: GSW Google Scholar Cassandra Fenton; Cassandra Fenton 3GeoForschungsZentrum Potsdam, Telegrafenberg, Haus B, D-14473 Potsdam, Germany Search for other works by this author on: GSW Google Scholar Steven Forman; Steven Forman 4Department of Earth and Environmental Sciences, University of Illinois, Chicago, Illinois 60607, USA Search for other works by this author on: GSW Google Scholar William McIntosh; William McIntosh 5New Mexico Bureau of Mines and Mineral Resources, 801 Leroy Place, Socorro, New Mexico 87801, USA Search for other works by this author on: GSW Google Scholar Richard Hereford; Richard Hereford 6U.S. Geological Survey, 2255 North Gemini Drive, Flagstaff, Arizona 86001, USA Search for other works by this author on: GSW Google Scholar Jeffery Plescia; Jeffery Plescia 7Johns Hopkins Applied Physics Lab, 11100 Johns Hopkins Drive, Laurel, Maryland 20723, USA Search for other works by this author on: GSW Google Scholar Michael Ort Michael Ort 8Department of Geology, Northern Arizona University, Flagstaff, Arizona 86011, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2006) 118 (3-4): 421–429. https://doi.org/10.1130/B25814.1 Article history received: 11 Feb 2005 rev-recd: 02 Jun 2005 accepted: 13 Jul 2005 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Wendell Duffield, Nancy Riggs, Darrell Kaufman, Duane Champion, Cassandra Fenton, Steven Forman, William McIntosh, Richard Hereford, Jeffery Plescia, Michael Ort; Multiple constraints on the age of a Pleistocene lava dam across the Little Colorado River at Grand Falls, Arizona. GSA Bulletin 2006;; 118 (3-4): 421–429. doi: https://doi.org/10.1130/B25814.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The Grand Falls basalt lava flow in northern Arizona was emplaced in late Pleistocene time. It flowed 10 km from its vent area to the Little Colorado River, where it cascaded into and filled a 65-m-deep canyon to form the Grand Falls lava dam. Lava continued ∼25 km downstream and ∼1 km onto the far rim beyond where the canyon was filled. Subsequent fluvial sedimentation filled the reservoir behind the dam, and eventually the river established a channel along the margin of the lava flow to the site where water falls back into the preeruption canyon.The ca. 150 ka age of the Grand Falls flow provided by whole-rock K-Ar analysis in the 1970s is inconsistent with the preservation of centimeter-scale flow-top features on the surface of the flow and the near absence of physical and chemical weathering on the flow downstream of the falls. The buried Little Colorado River channel and the present-day channel are at nearly the same elevation, indicating that very little, if any, regional downcutting has occurred since emplacement of the flow.Newly applied dating techniques better define the age of the lava dam. Infrared- stimulated luminescence dating of silty mudstone baked by the lava yielded an age of 19.6 ± 1.2 ka. Samples from three noneroded or slightly eroded outcrops at the top of the lava flow yielded 3He cosmogenic ages of 16 ± 1 ka, 17 ± 1 ka, and 20 ± 1 ka. A mean age of 8 ± 19 ka was obtained from averaging four samples using the 40Ar/39Ar step-heating method. Finally, paleomagnetic directions in lava samples from two sites at Grand Falls and one at the vent area are nearly identical and match the curve of magnetic secular variation at ca. 15 ka, 19 ka, 23 ka, and 28 ka. We conclude that the Grand Falls flow was emplaced at ca. 20 ka. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.