Composition and construction of late Pleistocene end moraines, Durango, Colorado

Research Article| October 01, 1995 Composition and construction of late Pleistocene end moraines, Durango, Colorado Mark D. Johnson; Mark D. Johnson 1Department of Geology, Gustavus Adolphus College, 800 West College Avenue, St. Peter, Minnesota 56082 Search for other works by this author on: GSW Google Scholar Mary L. Gillam Mary L. Gillam 2Department of Geological Sciences, University of Colorado, Boulder, Colorado 80309-0250 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1995) 107 (10): 1241–1253. https://doi.org/10.1130/0016-7606(1995)107<1241:CACOLP>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Mark D. Johnson, Mary L. Gillam; Composition and construction of late Pleistocene end moraines, Durango, Colorado. GSA Bulletin 1995;; 107 (10): 1241–1253. doi: https://doi.org/10.1130/0016-7606(1995)107<1241:CACOLP>2.3.CO;2 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 late Pleistocene Animas City 2 and Animas City 3 end moraines at the north edge of Durango, Colorado, were built at the terminus of the Animas glacier as ice-marginal aprons of primarily debris-flow sediment interbedded with sandy stream sediment. Sorted sediment and three types of diamicton present in the moraines are interpreted as fluvial sediment, lacustrine sediment, debris-flow sediment, and melt-out till. Melt-out till at one locality represents deposition from the basal, debris-rich parts of the Animas glacier onto the proximal side of the Animas City 3 moraine. Glaciotectonic features in a coarsening-upward sequence of sediment, previously deposited in a proglacial moraine-dammed lake, mark a readvance of the Animas glacier to the Animas City 3 moraine.Based on the character of the sediments and their interbedding, we conclude that the existing moraines were built rapidly (in <10 yr to a few tens of years), immediately before the glacier retreated from the terminus position. Earlier moraine ridges would have been built continuously at the ice margin, but continuously removed by laterally migrating outwash streams. That the glacier stood at the terminus position for a long time is indicated not by the moraines, but by the extensive outwash deposits to the south and by the geomorphic constraint that coarse sediment could only be delivered to the river south of the moraine position when the ice was at the terminus position; otherwise, the large, scoured bedrock basin north of the moraine ridges would have acted as a sediment trap. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.