GRAND CANYON: A SIMPLY-FORMED, EQUILIBRIUM LANDSCAPE SINCE THE CRETACEOUS

Why would an object of such simplicity of form evolve from the complicated succession of processes and landscapes favored by most authors? Parsimony would suggest otherwise, if not the Second Law of Thermodynamics. The Grand Canyon Landscape passes two fundamental tests of equilibrium erosion:

(1) Perturb the landscape with hard rock, and it quickly erodes back very close its initial form, and no farther; the disequilibrium erosion rates are orders of magnitude greater than the long-term erosion rate (Hamblin, 1994, 2003);

(2) The thermal history of the surface is invariant with elevation (Flowers et al., 2008, GSAB; Flowers and Farley, 2012; 2013, Science; Wernicke, 2011, GSAB)

For convenience of discussion, the top dozen arguments made against the equilibrium model are outlined below with reference to their most recent airing. The strengths and weaknesses of these arguments will be discussed at the meeting.

1. Thermal history varies with elevation; system very complicated; short-wavelength thermal perturbations common

(Lee et al. 2013, Geosphere)

2. Proximity of the upper Verde River drainage to Grand Canyon

3. “Separation Point Hill” basalt: surrounded by tributaries to Grand Canyon

4. Rim gravel “backtilt” underestimated by extrap. of high SW dips near Pch. Spr.

5. No evidence of interruption of arc supply to foreland at KT boundary

(Dickinson, 2013, Geosphere)

6. Age of the Colorado River drainage system

(a) 5.6 arrival of “Colorado River sediment” in Gulf of California

(b) Oldest “Colorado River sediment” in Muddy Creek basin is 4.4 Ma

(c) Lack of pre-6 Ma “Colorado River sediment” at mouth of GC in 13-6 Ma deposits

7. Geometry of N-flowing 70-18 Ma paleocanyons in W Grand Canyon.

8. S-transported 60-50 Ma “Hindu fanglomerate" deposited across the modern course of W Grand Canyon.

9. Maximum incision rates since 4 Ma can carve most of Grand Canyon

(Karlstrom et al., 2013, Science)

10. Pierce Canyon fan and related Miocene lakes and playas deposited directly across the mouth of the western canyon:

An existing GC would impart a distinct signature on these deposits that is not observed

11. Precipitous topography a hallmark of geological youth

(Lucchitta, 2013, Science)

12. Lack of “Colorado Plateau detritus” (Plz zircon) in mid-T coastal deltas

(Ingersoll et al., 2013, Geology; Karlstrom et al. also mentions this)