Constraining the aggradation mode of Pleistocene river deposits based on cosmogenic radionuclide depth profiling and numerical modelling

Abstract. Pleistocene braided-river deposits commonly represent long periods of non-deposition or erosion that are interrupted by rapid and short aggradation phases. When dating these sedimentary sequences with in situ-produced cosmic radionuclides (CRNs), simple concentration depth profiling approaches often fall short, as they assume the alluvial sequence has been deposited a constant rate exposed to radiations afterwards. Numerical modelling evolution CRNs permits one account for aggradation, phases can simulate which scenarios preservation most likely river dynamics. In this study, such model was developed applied Middle gravel sheet (Zutendaal gravels) NE Belgium. The parameters were optimised observed 10Be 26Al concentrations 17 sediment samples taken over interval 7 m constitutes top up 20 thick. studied sequence, (at least) three individual be distinguished, each interruption lasting ∼ 40 kyr. age onset upper further constrained 654-62+218 ka. This age, within error limits, does not invalidate previous correlations Cromerian Glacial B Marine Isotope Stage (MIS) 16. deposition entire represents more than climatic cycle demonstrates importance accounting depositional modes braided rivers when applying situ cosmogenic radionuclide techniques.