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Pacing the post–Last Glacial Maximum demise of the Animas Valley glacier and the San Juan Mountain ice cap, Colorado

2007; Geological Society of America; Volume: 35; Issue: 8 Linguagem: Inglês

10.1130/g23596a.1

1943-2682

Zack Guido, Dylan J. Ward, Robert S. Anderson,

Pleistocene-Era Hominins and Archaeology

Research Article| August 01, 2007 Pacing the post–Last Glacial Maximum demise of the Animas Valley glacier and the San Juan Mountain ice cap, Colorado Zackry S. Guido; Zackry S. Guido 1Department of Geology and Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado 80309, USA Search for other works by this author on: GSW Google Scholar Dylan J. Ward; Dylan J. Ward 1Department of Geology and Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado 80309, USA Search for other works by this author on: GSW Google Scholar Robert S. Anderson Robert S. Anderson 1Department of Geology and Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado 80309, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Zackry S. Guido 1Department of Geology and Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado 80309, USA Dylan J. Ward 1Department of Geology and Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado 80309, USA Robert S. Anderson 1Department of Geology and Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado 80309, USA Publisher: Geological Society of America Received: 26 Dec 2006 Revision Received: 02 Apr 2007 Accepted: 04 Apr 2007 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (2007) 35 (8): 739–742. https://doi.org/10.1130/G23596A.1 Article history Received: 26 Dec 2006 Revision Received: 02 Apr 2007 Accepted: 04 Apr 2007 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Zackry S. Guido, Dylan J. Ward, Robert S. Anderson; Pacing the post–Last Glacial Maximum demise of the Animas Valley glacier and the San Juan Mountain ice cap, Colorado. Geology 2007;; 35 (8): 739–742. doi: https://doi.org/10.1130/G23596A.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 SocietyGeology Search Advanced Search Abstract During the Last Glacial Maximum (LGM), a 5000 km2 ice cap covered the San Juan Mountains of southwest Colorado. The largest valley glacier draining this ice cap occupied the Animas Valley and flowed 91 km to the south. To characterize the post-LGM demise of the Animas Valley glacier, we employ cosmogenic 10Be to date the LGM terrace outside the terminal moraines and a suite of seven glacially polished bedrock samples. The 10Be depth profile within the terrace sediments suggests abandonment at 19.4 ± 1.5 ka. As deglaciation began, the ponding of Glacial Lake Durango behind the terminal moraines shut off fluvial sediment supply and caused terrace abandonment. The age of the terrace therefore records the initiation of LGM retreat. Negligible 10Be inheritance in the terrace profile suggests that glacial erosion of the bedrock valley floor from which sediments were derived erased all cosmogenic inventory. Glacial polish exposure ages monotonically decrease up-valley from 17.1 to 12.3 ka, with the single exception of a sample collected from a quartzite rib, yielding an average retreat rate of 15.4 m/yr. This trend and the lack of inherited cosmogenic nuclides in the terrace sediments imply that polish ages accurately record the glacial retreat history. Retreat of the Animas lobe began at a time of regional drying recorded in sediments and shoreline elevations of large lakes. Deglaciation lasted for ∼7.2 k.y., and was complete by 12.3 ± 1.0 ka. The retreat history followed the pattern of increasing insolation and was perhaps fastest during a time of regional drying. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.