wAbstract
@Apparent increases in sedimentation rates during the past 5 Ma
have been inferred at sites around the globe to document increased
terrestrial erosion rates, but direct erosion rate records spanning
this period are sparse. Modern and paleo-erosion rates for a small
alpine catchment (3108 m above sea level) in the Southern Rocky
Mountains are measured using the cosmogenic radionuclides (CRNs)
10Be and 26Al in cave sediment, bedrock
on the overlying landscape surface, and coarse bedload in a modern
fluvial drainage. The unique setting of the Marble Mountain cave
system allows the inherited erosion rates to be interpreted as
basin-averaged erosion rates, resulting in the first CRN-based
erosion rate record from the Rocky Mountains spanning 5 Myr. Pliocene
erosion rates, derived from the oldest cave sample(4.9}0.4 Ma),
for the landscape above the cave are 4.9}1.1 m Myr-1.
Mid Pleistocene erosion rates are nearly an order of magnitude
higher (33.1}2.7 to 41.3}3.9 m Myr-1), and modern erosion
rates are similar; due to the effects of snow shielding, these
erosion rate estimates are likely higher than actual rates by
10-15. The most likely explanation for this dramatic increase
in erosion rates, which likely occurred shortly before 1.2 Ma,
is an increase in the effectiveness of periglacial weathering
processes at high elevations related to a cooler and wetter climate
during the Pleistocene, providing support for the hypothesis that
changes in late Cenozoic climate are responsible for increased
continental erosion.
Keywords: erosion rate; cosmogenic nuclide; cave; Rocky Mountains;
Pliocene and Pleistocene climate; periglacial weatheringx
1. Introduction
2. Marble Mountain cave system
3. Methods
4. Results
5. Discussion
@5.1. Water table lowering and paleo-erosion rates
@5.2. The erosion rate increase
6. Conclusions
Acknowledgements
References