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Alida Timar-Gabor. Methods Protoc. The column on the right represents the first approximately 5 m at a higher resolution. The colored circles represent the position of the samples which were investigated in studies and current paper. Natural als are represented as stars. Error bars are smaller than the symbols. The comparison between the normalized decay curves the of counts in each data channel divided by the of counts measured in the first channel of stimulation of the natural OSL als, the regenerated als and the decay of the calibration quartz is represented in the insets.
The curves were best described by a sum of two exponential exponentials function. At least three aliquots have been used in order to obtain the average corrected luminescence als used to construct de growth curves. The current ages represent the weighted from the doublet samples. We are applying here the current state of the art luminescence dating protocols for revisiting the chronology of this section.
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Laboratory generated SAR dose response curves in the high dose range 5 kGy for fine quartz and 2 kGy for coarse quartz were investigated by employing a test dose of either 17 or Gy. The confirm the ly reported different saturation characteristics of the two quartz fractions, with no evident dependency of the equivalent dose D e on the size of the test dose. The reports regarding the chronological discrepancy between the two quartz fractions are confirmed.
However, while investigations on other sites concluded that this discrepancy appears only above equivalent doses of about Gy, here fine grain quartz ages underestimate coarse quartz ages starting with equivalent doses as low as around 50 Gy. Keywords: luminescence dating; loess; optically stimulated luminescence; single aliquot regeneration protocol; quartz; grain size luminescence dating ; loess ; optically stimulated luminescence free single aliquot regeneration protocol ; quartz Alexandria grain size. Introduction The development of the single-aliquot regenerative-dose SAR protocol [ 1 ] for optically stimulated luminescence OSL dating of quartz has revolutionized the luminescence dating method by giving rise to high precision equivalent dose estimates.
Loess-paleosol sequences are important archives of the climatic changes that took place during the Pleistocene, but their ificance can only be fully understood once a reliable and absolute chronology is available. Due to its quartz rich and windblown nature, loess is generally considered an ideal material for the application of OSL. However, although more precise ages can be obtained by SAR-OSL, the validation of the polish of these OSL ages by independent age control is hindered by the lack of methods which can directly date the depositional time of the sediments.
However, it is well known that the of luminescence dating methods applied on quartz underestimate the expected ages for dating collected below this soil. The same trend in age underestimates was reported in China. At Luochuan, Buylaert et al. Another important issue which was raised relates to the choice of the quartz grain size.
However, in later geological applications in what regards OSL dating technique, the choice between these protocols was dictated by the dominant grain size within the investigated sedimentary unit. Consequently, it is common practice to use only one grain size fraction.
A series of investigations carried out by our group during the last decade on quartz of different grain sizes extracted from loess yielded intriguing and concerning .
This is the site where we have reported for the first time various problems when investigating different quartz grain sizes [ 8 ] and we have subsequently applied alternative luminescence dating protocols on feldspars [ 1415 ]. Additionally, there is a limited practice of performing interlaboratory comparison exercises in the field of luminescence dating. This represents an interesting endeavor since this new investigation dating place a decade later and in different laboratories Ghent, Belgium [ 28 ] and Cluj-Napoca, Romania—current paperusing different samples from the same site.
We are testing the robustness of the protocol free performing intrinsic rigor tests and we are discussing the accuracy of the obtained ages, also in the light of the of the studies. Optically stimulated luminescence was developed by Huntley et al. This dating technique makes use of polish dosimeters primarily quartz and feldspar grains that have thermally stable traps capable of storing electrons that arise from the interaction of the environmental ionizing radiation during burial these radiations coming from the decay of uranium, thorium and potassium in the sediment and from cosmic radiation with the crystal lattice [ 18 ].
This trapped charge population builds up since the time of Alexandria.
As such there is a functionality between the dose received by the crystal hence the time as the dose rate is assumed to be constant and the amount of trapped charge. Under controlled laboratory conditions this charge can be quantified in the form of a luminescence al. The assumption on which the method is based on is that the growth of the luminescence al in nature can be reproduced by performing controlled laboratory irradiations.
Consequently, a dose response curve is constructed and the natural luminescent al measured in the laboratory is expressed as an equivalent dose by interpolating the natural al on this dose response curve.
The luminescence age equation is shown below. Besides the type of mineral used for OSL measurements, the grain size also plays an important role. Commonly, the size is chosen depending on the dominant grain size of the investigated sedimentary unit. However, it is mandatory to take into consideration the depth at which the alpha, beta and gamma radiation penetrate the grain when age calculation is performed.
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However, the need for using these different correction factors when dose rates are calculated is well known for decades [ 20 ]. It is generally believed that relying only on one fraction for OSL dating should lead to obtaining reliable chronologies. In this dose range a good agreement has been reported when both fine and coarse quartz were used in order to obtain a chronology of the investigated loess sites [ 252627 ]. Different saturation characteristics between the fine and coarse quartz fractions extracted from loess were noted, with the fine grains showing higher saturation characteristics worldwide [ 11 ].
This is most intriguing when correlated to the fact that the fine fraction underestimates the true ages sooner than the coarse ones. At the moment, the source of the age discrepancy is not fully understood, but it is thought to reside, at least partly, in the different saturation characteristics of fine grains compared to the coarse grains, and in the differences reported free the laboratory Alexandria the natural dose response curves as reported by Timar-Gabor and Wintle [ 29 ] for Romanian loess as well as by Chapot et al.
Here, loess intercalated with paleosols plateaus developed on top of accumulations of fluvial deposits in subsiding areas during the Quaternary. These loess-paleosols sequences LPSs are considered to be important and continuous paleoclimatic archives, displaying similar sedimentological and pedological properties to deposits from China and Central Asia [ 3132 ].
For the Romanian part, the loess-like deposits are predominant [ 33 ]. They were first described dating the works of Ana Conea and were given a proposed chronology based on pedostratigraphic methods [ 3435 ]. It polish considered to be a key section, being one of the most studied sections in Eastern Europe.
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Six well developed pedocomplexes covering the last 17 Marine Isotope Stages MIS are comprised in the approximately 26 m thick eolian deposit with no visible hiatuses, overlaying Tertiary and Mesozoic sediments [ 41 ]. More precisely, the site displays similar major element dating and geochemical fingerprint as the Serbian loess from the Vojvodina region, with Danube alluvial sediments being also the main loess source [ 31 ].
Furthermore, there is a resemblance in the concentration related magnetic parameters, Alexandria reflectance spectroscopy free soil color proxies for hematite and goethite, with the magnetic grain size and mineralogy being also similar to that of Chinese LPSs [ 444546 ].
The section also exhibits overall pedogenic processes, thus suggesting that loess polish took place at the same time as weak pedogenesis [ 8 ]. The loess units, formed during glacial periods, are dominated by windblown coarse ferromagnetic minerals and have a high quartz content alongside a trend to higher zirconium and hafnium content [ 3146 ]. The paleosol layers are dominated by fine ferromagnetic minerals produced during interglacial pedogenesis, with small amounts of coarser eolian magnetic grains [ 46 ].
With the sediment budget being attributed to the Danube River, due to the origin of the quartz and zircon and the bi- and three-modal distribution of the grain-size in loess layers, an additional input from the Ukrainian glaciofluvial deposits and local sand dune fields was also proposed [ 831 ].
The S 0 layer is a steppe soil which displays similarities with the L 3 unit in what regards magnetic granulometry [ 3145 ]. An interstadial pedocomplex L 1 S 1 of the last glacial cycle is comprised in the L 1 unit [ 231 ].
The S 1 pedocomplex has been identified as a gray-brown fossil steppe soil [ 3841 ]. It displays three magnetic susceptibility peaks—a dominating peak in the lower half of the unit which may represent MIS 5e and two additional weakly expressed susceptibility peaks, probably representing MIS 5a and MIS 5c [ 41 ]. The S 2 pedocomplex has also been identified as a gray-brown fossil steppe soil [ 3844 ].
It comprises three clearly separated peaks and it is attributed to MIS 7. Moreover, due to its characteristic magnetic susceptibility pattern, it can be correlated with the Chinese Loess Plateau sections which show similar enhanced magnetism resulting from interglacial pedogenesis [ 47 ].