『Abstract
Erosion is fundamental player of the interactions existing between
internal geodynamics and climate, in particular through its influence
on the carbon dioxide budget. However, long term (>1 Ma) erosion
rates, estimated indirectly from sediment budget, remain poorly
constrained. While some studies suggest that worldwide erosion
rates increased at the Plio-Pleistocene climatic transition (〜4-2
Ma), the validity of this observation and its significance is
a matter of debate due to potential biases of the sedimentary
record and to the influence of sea level fall on the global sedimentary
flux to marginal basins. In the present study, we estimate erosion
rates over the last 〜9 Ma using in situ produced cosmogenic 10Be
concentrations measured in magnetostratigraphically dated continental
sediments. We focus on an intracontinental endorheic watershed
draining the northern Tianshan in Central Asia, a key region regarding
the ongoing debate. While erosion rates between 0.1 and 1 mm・yr-1
are derived from most of our record, they reach values as high
as 〜2.5 mm・yr-1 from 2.5 to 1.7 Ma. Then, after 1.7
Ma, recent and modern erosion rates fell below 1 mm・yr-1.
This temporary increase is correlated with the onset of Quaternary
ice ages and suggests that global climate had a significant and
transient impact on erosion.
Keywords: Quaternary glaciation; erosion rates; Tianshan; cosmogenic
nuclide; magnetostratigraphy; 10Be
1. Introduction
2. Geological settings and sampling
3. Methods and measurements
3.1. Cosmogenic isotopes in modern river sediments
3.2. Cosmogenic isotopes in buried sediments
3.2.1. Estimation of the cosmogenic paleo-production rate
3.2.2. Corrections of the post-depositional 10Be
accumulation
3.3. Samples treatment and measurement of 10Be concentrations
4. Results
5. Discussion and conclusion
Acknowledgements
References