HR: 0830h
AN: H51E-1121    [PDF]
TI: Using Fill Terraces and Multiple Dating Techniques to Calculate Incision Rates for Grand Canyon
AU: * Pederson, J L
EM: bolo@cc.usu.edu
AF: Geology Department, Utah State University, Logan, UT 84321 United States
AU: Anders, M D
EM: matt.anders@nau.edu
AF: Geology Department, Utah State University, Logan, UT 84321 United States
AU: Rittenour, T M
EM: tammyr@unlserve.unl.edu
AF: Department of Geosciences, University of Nebraska-Lincoln, Lincoln, NE 68588 United States
AU: Sharp, W D
EM: wsharp@bgc.org
AF: Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709 United States
AU: Gosse, J C
EM: jcgosse@dal.ca
AF: Earth Sciences Department, Dalhousie University, Halifax, NS B3H 4R2 Canada
AU: Karlstrom, K E
EM: kek1@unm.edu
AF: Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131 United States
AB: OSL, U-series, and terrestrial-cosmogenic-nucleid dating applied to the impressive fill-terrace record of eastern Grand Canyon provide a relatively complete reconstruction of fluvial history, including long-term bedrock incision rates. Despite how common and information-rich fill terraces like these are, the cyclic alluviation and incision they record complicates their use for calculating incision rates relative to strath terraces. This has frequently resulted in overestimates of true bedrock incision that are exacerbated in shorter records. Multiple dating techniques applied to the well-exposed eastern Grand Canyon Quaternary stratigraphy allow us to date the timing of aggradation, the abandonment of terraces, and even incision. We use this record to illustrate a widely applicable methodology of extracting high quality bedrock incision rates by linking episodes when the river is on bedrock. Our long-term bedrock incision rate for eastern Grand Canyon of 155 m/my is greater than rates from near the hangingwall of the Hurricane and Toroweap faults in western Grand Canyon, but less than long-term incision rates reported upstream in and near western Colorado. This increase in rate upstream could be due either to differential uplift in Colorado, to a knickzone passing through the system from faulting or the major drainage capture ~6 Ma at the southwestern edge of the Colorado Plateau, or to different timescales and methods of rate calculation. More, consistent data are needed about bedrock incision along the profile of this major river to investigate the role of these factors in the erosion of the Colorado Plateau.
DE: 1035 Geochronology
DE: 1815 Erosion and sedimentation
DE: 1824 Geomorphology (1625)
DE: 8107 Continental neotectonics
SC: Hydrology [H]
MN: 2003 Fall Meeting