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  • Author: Tamás Bartyik x
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Abstract

The alluvial development of the Great Hungarian Plain has greatly been determined by the subsidence of different areas in the Pannonian Basin. The temporal variation of subsidence rates significantly contributed to the avulsion and shifting of main rivers. This was the case in terms of the Hungarian Lower Danube when occupying its present day N-S directional course. The considerable role of tectonic forcing is also supported by the presence of different floodplain levels. Although, several channel forms are identifiable on these the timing of floodplain development has been reconstructed up till now mostly by the means of geomorphological analysis, and hardly any numerical dates were available. The main aim of this study is to provide the first OSL dates for palaeo-channels located on the high floodplain surface of the Hungarian Lower Danube, and to determine the maximum age of low and high floodplain separation on the Kalocsa Plain. For the analysis two meanders were sampled close to the edge of the step slope between the two levels. According to the results, the development of the investigated palaeo-meanders could be rapid. The formation of the older meander was dated to the Late Atlantic, while the possible separation of the high and low floodplain surfaces could start in the beginning of the Subboreal Phase.

Abstract

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.