Quaternary denudation rates in the Tianshan

Abstract

The Earth surface, where life develops and stands, is strongly affected by denudation which is the sum of physical erosion and chemical weathering. Denudation impacts soil formation and agriculture, affects the relief stability and, at the geological time scale, controls the atmospheric CO2 via the weathering of silicates and the production of sediments that later bury organic matter in the oceans. In the context of global warming, it is particularly important to predict how denudation will change and hence impact the Earth Surface where we live. This requires to understand the links between past climate variability and denudation changes, especially during the Quaternary when Earth experienced rapid climate oscillations of amplitude similar to what is expected in the future due to anthropic impact. To reach this goal, quantitative estimate of past denudation rates during the Quaternary are needed. In this study, we reconstruct Quaternary paleo-denudation rates in the Tianshan range located in Central Asia because (1) it is a major orographic barrier that likely played an important role during the onset of Quaternary glaciations, (2) regional climate variations have been well documented by the geochemical and isotopic analyses of speleothems in caves and (3) well dated Quaternary deposits are abundant in the piedmonts To reconstruct basin average paleo-denudation rates we used the inherited 10Be concentrations derived from the inversion of 10Be cosmogenic depth profile collected across abandoned alluvial surfaces. We used a unique inversion technique to reprocess preexisting data and also analyze 5 new cosmogenic depth profiles located in the northern Tianshan. In this region, to extend the dataset we have also collected 9 ancient river sand samples along the magnetostratigraphically dated Jingou He section. For comparison between all data, paleo-denudation rates are normalized to modern 10Be derived denudation rates across the same drainage basin. This yields to a 0-1.5Ma record of paleo-denudation rates that is compared to climate variations to discuss the potential links between the two.