What drives incision along the Colorado River?

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What drives incision along the Colorado River?

• A working hypothesis

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Late Cenozoic incision in the Colorado watershed

• Drainage Integration - wave of incision
  propagates upstream from cutting of Grand Canyon
• Epirogenic uplift - differential surface uplift
  between Rockies and Colorado Plateau drives
  increase in topographic gradients
• Climate change - For unknown reasons,
  Miocene-Pliocene climates engender more erosive
  fluvial systems
• OUR CHALLENGE IS TO DECONVOLVE THESE FORCINGS

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Longitudinal Profile
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Comparison of tributary profiles
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Onset of incision

• Grand Canyonfairly well-known
• No evidence of Colorado river in Grand Wash
  trough at ca. 6 Ma (Bouse Fm. - Spencer et al. in
  press)
• First sediments with Colorado provenance in Gulf
  of CA at ca. 5.3 Ma (Dorsey et al., 2007)
• River at or near modern elevation at ca. 4.4 Ma
  (Faulds et al., 2001)
• Upper Coloradouncertain
• Ancestral rivers at 35-25? (Hansen, Hunt - 70s)
• Incision initiates at ca. 10 Ma (Larson et al.,
  1975, Anderson and Berlin)
• Most incision post-dates 3 Ma (Kunk et al., 2002)

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Timing of exhumation
MWX drill hole
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Kelley et al.
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Base of PAZ (AFT 110C)
Kelley et al.
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1D Thermal Models
Variable thermal conductivity
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1D thermal models - onset of exhumation
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1D thermal models - onset of exhumation
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Implications

• Onset of incision
• Appears to pre-date cutting of Grand Canyon
• Incision along western slope of Rockies NOT a
  response to canyon cutting on Colorado Plateau
• Subsequent incision rates
• Long-term - 200 m/My (since 6-8 Ma)
• Short-term - 150-200 m/My (since 0.6 Ma)
• Correspondence suggests maintenance of incision
  by geodynamic processes
• Steep river profiles on western slope reflect
  differential rock uplift across Rockies/Colorado
  Plateau boundary

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Where from here?

• Is onset of exhumation similar along western
  flank of Aspen Anomaly?
• Thermochronology (Kelley)
• What are space-time patterns of incision?
• Large gaps in knowledge between Miocene and
  Quaternary
• Working to fill these gaps (Anders, Darling,
  Karlstrom, Kirby)
• What are driving forces for incision?
• Requires linking
• Models of fluvial incision and mass removal
  (Kirby, Ouimet)
• Best estimates of crustal thickness, lithospheric
  temperature (Deuker, Hansen, Stachnik)
• Geodynamic models (Van Wijk, Coblentz, Aster)