Spatial Differences In The Luminescence Sensitivity Of Quartz Extracted From Carpathian Basin Fluvial Sediments

The luminescence sensitivity of a sample is the luminescence intensity measured in response to unit radioactive dose. Sensitivity is by no means a stable parameter, it might change during measurements, or in nature as well. The primary or natural magnitude of luminescence sensitivity is basically determined by mineralogical background (number of crystal impurities) and sedimentary prehistory (repeated exposure of the sediment to sunlight).In the present study we have investigated the luminescence properties and sensitivity of coarse-grain (90-150 mu m) quartz samples related to four major rivers of the Carpathian Basin (River Danube, Tisza, Szamos and Maros). In case of each region of interest 5 previously dated Late Pleistocene and/or Holocene samples were selected, each representing similar sedimentary environments, i.e. coarse grain channel deposits related to point bars and medial bars. Sensitivity was investigated using CW-OSL, LM-OSL and TL techniques using a multi-grain approach. By determining the normalised luminescence response to the same regeneration dose administered after bleaching, sensitivity base values were obtained for each sample. Using repeated cycles of dosing laboratory sensitivity change was also recorded. The base values and sensitivity change of the 20 investigated samples were then compared on a regional basis to identify potential differences, which might be used later for fingerprinting the sediments of the investigated rivers.When considering mean sensitivity base values, calculated from several aliquots of the same sample, Danube related, mostly Alpine origin sediments exhibited 50-60% lower values compared to those with a Carpathian origin, and even at the considerable standard deviation obtained (coefficient of variation being 25-60%) they could be clearly separated using any of the measured luminescence sensitivity parameters. The discrimination of fluvial sediments with a Carpathian origin, but representing different catchments, is less straightforward, though, plotting against different sensitivity parameters can offer an opportunity to define fairly distinct groups of sample mean values. From this aspect total LM-OSL and fast component ratio seemed to be the best candidates, however, at the characteristic standard deviation and standard error separation can be unclear. No clear relationship was found in terms of sensitivity change, however some samples, related to River Maros showed practically no change during the laboratory sensitisation process. When plotting OSL ages against quartz sensitivity clear trends could be recognised, which can partly be explained by geomorphological reasons. Results in all, point to the possibility to differentiate Carpathian Basin fluvial sediments on the basis of their quartz luminescence sensitivity, a parameter that can be assessed easily during the routine dating process.