Cosmogenic nuclide 26Al10Be disequilibrium used to quantify Quaternary loess cover and integrated bedrock denudation rates in the Western Mecsek Mountains, Pannonian Basin

This study aims to quantify bedrock denudation rates of ridge tops and small catchments in the Western Mecsek Mts, a low-elevation hilly area currently being exhumed from under its Quaternary loess cover. Low 26 Al/ 10 Be ratios indicate unsteadiness caused by significant past burial of the bedrock surfaces. A Monte Carlo model was developed to determine the true rate of bedrock denudation by revealing and considering the temporal evolution of the loess cover as a function of glacial-interglacial climate. In case the most common single nuclide 10 Be approach was used, the true lowering rate of bedrock would have been overestimated by a factor that increases with the shielding time. The modelled integrated bedrock denudation rates were between 5 ± 5 m/Ma and 19 ± 8 m/Ma depending on the duration of the loess cover. They were similar for the ridge crests and basin-averaged samples suggesting a steady relief during the last 1 Ma. Our results suggest that the high risk radioactive waste disposal planned to be implemented in the study area is safe in terms of denudation: it is not threatened by exhumation in a million years timescale. Our study demonstrates that the use of a paired 26 Al/ 10 Be approach is recommended to avoid overestimation of the true bedrock denudation by testing the presumption of cosmogenic nuclide equilibrium. This is true not only for large catchments and formerly glaciated areas, but also in settings where past sediment cover may have lasted long enough to lower the CRN ratio.