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Holocene valley-floor deposition and incision in a small drainage basin in western Colorado, USA |
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| Authors: | Lawrence S Jones Margaret Rosenburg Kathleen McKee Jenna Hunter |
| Institution: | a Department of Geology, Mesa State College, 1100 North Avenue, Grand Junction, CO 81501, USA b Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA c Halliburton, Inc., Lafayette, LA 70508, USA d Geological & Mining Engineering & Sciences, Michigan Technological University, Houghton, MI 49931, USA e Department of Earth Sciences, University of Southern California, Los Angeles, CA 90089, USA f High School for Environmental Studies, New York, NY 10019, USA |
| Abstract: | The valley floor of a 33.9 km2 watershed in western Colorado experienced gradual sedimentation from before ∼ 6765 to ∼ 500 cal yr BP followed by deep incision, renewed aggradation, and secondary incision. In contrast, at least four terraces and widespread cut-and-fill architecture in the valley floor downstream indicate multiple episodes of incision and deposition occurred during the same time interval. The upper valley fill history is atypical compared to other drainages in the Colorado Plateau.One possible reason for these differences is that a bedrock canyon between the upper and lower valley prevented headward erosion from reaching the upper valley fill. Another possibility is that widespread, sand-rich, clay-poor lithologies in the upper drainage limited surface runoff and generally favored alluviation, whereas more clay-rich lithologies in the lower drainage resulted in increased surface runoff and more frequent incision. Twenty-two dates from valley fill charcoal indicate an approximate forest fire recurrence interval of several hundred years, similar to that from other studies in juniper-piñon woodlands. Results show that closely spaced vertical sampling of alluvium in headwater valleys where linkages between hillslope processes and fluvial activity are relatively direct can provide insight about the role of fires in alluvial chronologies of semi-arid watersheds. |
| Keywords: | Holocene Incision Aggradation Geomorphology Colorado Sedimentation Arroyo 14C Forest fire Recurrence interval Charcoal |
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