IMPACT OF THE NORTH AMERICAN MONSOON ON ISOTOPE PALEOALTIMETERS: IMPLICATIONS FOR THE PALEOALTIMETRY OF THE AMERICAN SOUTHWEST
Por:
Licht, Alexis, Quade, Jay, Kowler, Andrew, De Los Santos, Marie, Hudson, Adam, Schauer, Andrew, Huntington, Katharine, Copeland, Peter, Lawton, Timothy
Publicada:
1 ene 2017
Categoría:
Earth and planetary sciences (miscellaneous)
Resumen:
Paleoaltimetric studies have characterized in detail the relationship
between carbonate oxygen isotope ratios (delta O-18(c)) and elevation in
orogens with simple, single-moisture-source hydrological systems, and
applied this relationship to ancient continental carbonates to provide
constraints on their past elevation. However, mixing of different
atmospheric moisture sources in low-elevation orogens should affect
delta O-18(c) values, but this effect has not yet been confirmed
unequivocally. In the American Southwest, summer monsoonal moisture,
sourced in the Equatorial Pacific and the Gulf of Mexico, and winter
moisture, sourced in the East Pacific, both contribute to annual
rainfall. We present stable isotope results from Quaternary carbonates
within the American Southwest to characterize the regional delta
O-18(c)-elevation relationship. We then provide stable isotope results
from local Eocene carbonates to reconstruct late Laramide
paleoelevations.
The Quaternary delta O-18(c)-elevation relationship in the American
Southwest is not as straightforward as in more simple hydrological
systems. delta O-18(c) changes with altitude are non-linear, scattered,
and display an apparent isotopic lapse rate inversion above 1200 m of
elevation. We speculate that decreasing surface temperatures at high
altitudes limit the duration of carbonate growth to the summer months,
biasing delta O-18(c) values toward higher values typical of the summer
monsoon and leading to lapse rate inversion.
delta O-18(c)-elevation relationships based on modern water isotope data
or distillation models predict paleoelevations that range up to as much
as 2 km higher than the modern elevations of 2000 to 2400 m for our late
Eocene sites located at the southern edge of the Colorado Plateau. By
contrast, our delta O-18(c)-elevation relationship for the American
Southwest yields lower paleoelevation estimates. These alternate
estimates nonetheless suggest that significant elevation (at least
similar to 1 km) had already been attained by the Eocene, but are also
compatible with <1 km of uplift by post-Laramide mechanisms. Our results
show the limitations of standard delta O-18(c)-elevation models in
complex hydrological systems and suggest that similar mechanisms may
have led to summer-biased paleoaltimetry estimates for the initial
stages of other orogenies -in the American Southwest and elsewhere.
Filiaciones:
Licht, Alexis:
Univ Arizona, Dept Geosci, Tucson, AZ 85721 USA
Univ Washington, Dept Earth & Space Sci, Seattle, WA 98195 USA
Quade, Jay:
Univ Arizona, Dept Geosci, Tucson, AZ 85721 USA
Kowler, Andrew:
Univ Arizona, Dept Geosci, Tucson, AZ 85721 USA
UCLA, Dept Earth Space & Planetary Sci, Los Angeles, CA USA
De Los Santos, Marie:
Univ Arizona, Dept Geosci, Tucson, AZ 85721 USA
Univ Houston, Dept Earth & Atmospher Sci, Houston, TX 77004 USA
Hudson, Adam:
Univ Arizona, Dept Geosci, Tucson, AZ 85721 USA
Schauer, Andrew:
Univ Washington, Dept Earth & Space Sci, Seattle, WA 98195 USA
Huntington, Katharine:
Univ Washington, Dept Earth & Space Sci, Seattle, WA 98195 USA
Copeland, Peter:
Univ Houston, Dept Earth & Atmospher Sci, Houston, TX 77004 USA
Lawton, Timothy:
Univ Nacl Autonoma Mexico, Ctr Geociencias, Queretaro, Mexico
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