Paleo-erosion rates in Central Asia since 9 Ma: A transient increase at the onset of Quaternary glaciations?
Résumé
Erosion is a 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.
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