Variation of OSL residual doses in terms of coarse and fine grain modern sediments along the Hungarian section of the Danube

Reliable OSL dating of fluvial sediments requires an assessment of incomplete bleaching and consequent residual dose in samples. A well-established way of this is determining the equivalent dose of modern samples from similar sedimentary environments as in the case of palaeo-samples. Meanwhile, relatively low, or close to zero doses are also greatly affected by the thermal transfer phenomenon, which can also lead to a palaeodose overestimation. The present study attempts to quantify both factors in coarse and fine grain modern sediments along the Hungarian section of the Danube River, with the aim of determining their significance when dating both young and palaeo-sediments. Investigations were performed at 30 sites along a 417 km long river section with varying morphological and erosive character. The studied samples were deposited during the record flood of 2013, mobilising and relocating a vast amount of sediment in the system. Tests have shown that thermal transfer can be minimized successfully by choosing preheat temperatures below 200°C, however it remains a significant factor when dating young or modern sediments. Based on equivalent dose measurements, coarse grain samples proved to be relatively well bleached, and residual doses showed only a minor spatial variation. Although in terms of fine grain samples residual doses were obviously much higher, results can enhance the reliability of dates retrieved later from fine grain palaeo-samples. In the meantime, the higher spatial variability of fine grain residual doses may also allow the assessment of the erosive character of different river reaches.