Orbital eccentricity, clinker formation,
and the climate-landscape evolution link in the North American
Rockies and High Plains
Kadegis,
Jeffrey, Sewall,
Jacob, and Riihimaki,
Catherine A., 2011, Orbital eccentricity, clinker formation,
and the climate-landscape evolution link in the North American
Rockies and High Plains [abs]: Geological Society of America -
Annual Meeting in Minneapolis, Minnesota (9–12 October 2011), Vol.
43, No. 5, p. 272.
While surface processes are sensitive to changes in the moisture
balance of drainage basins, proxies for paleo-hydrology are rare in
the geologic record. Consequently, the observed correlation between
orbital eccentricity and high rates of landscape evolution in the
Powder River Basin of Wyoming and Montana, U.S.A. is difficult to
explain with only empirical data. High orbital eccentricity,
particularly if enhanced by precession, could lead to a highly
seasonal climate with strong mid-continental summer warming and
increased precipitation that would drive an increase in local
incision rates and the exhumation of coal. We test this hypothesis
with the National Center for Atmospheric Research, Community
Atmosphere Model v.3 at a spectral resolution of T85 (~1.4° lat.
x 1.4° lon.). Orbital eccentricity in our simulations was
0.05767 or 0.0034 with each eccentricity value paired with a moving
vernal equinox latitude of perihelion (MVELP) of 270° and
90° for four total atmosphere-only simulations. Planetary
obliquity was constant at a maximum of 24.5°; all other boundary
conditions were held static at modern values. Simulations were
integrated for 30 years with the final 10 years averaged for
analyses. Comparisons across the simulations suggest that, under
eccentricity maxima, increasing seasonality (MVELP=270°)
substantially increases summer (June, July, and August average)
precipitation totals in much of Wyoming, western Nebraska, and
northeastern Colorado (32-48 cm; >14 cm more than with
MVELP=90°). Under minimum eccentricity, summer precipitation is
~33% lower than under maximum eccentricity and precession’s impact
is negligible (~4 cm change over MVELP=270° to 90°). By
linking high values of planetary eccentricity and precession to
enhanced mid-continental precipitation, these results provide a
possible mechanism to explain the observed association between
increased erosion, clinker formation, and orbital eccentricity in
sediments of the Powder River Basin and, thus, a direct link between
orbital parameters and landscape evolution in this region. We
predict similar relationships between surface processes and
insolation across much of the central Rocky Mountains and High
Plains.
Orbital eccentricity, clinker formation,
and the climate-landscape evolution link in the North American
Rockies and High Plains 
