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Interpretation of soil erosion in a Polish loess area using OSL, 137Cs, 210Pbex, dendrochronology and micromorphology – case study: Biedrzykowice site (s Poland)

Poręba Grzegorz, Śnieszko Zbigniew, Moska Piotr, Mroczek Przemysław, Malik Ireneusz

Geochronometria

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2019

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Vol. 46, no. 1

57--78

EN

Loess areas used for agriculture are susceptible to soil erosion. The intensive process of soil erosion in Polish loess areas began with the onset of the Neolithic and has continued intermittently until today. This work presents the results of soil erosion from simultaneous use of the 137Cs and 210Pbex methods on an agricultural field located on loess slope. Moreover, to establish the age of accumulated sediment connected with water slope erosion, OSL dating, selected physicochemical and micromorphological analyses were applied. The reference values of the 137Cs and 210Pbex fallout for the studied site (Biedrzykowice, the Proszowice Plateau, Małopolska Upland) equal 2627 (45% connected with Chernobyl) and 4835 Bq·m–2, respectively. The results of the 137Cs and 210Pbex inventories measured for the agricultural field range from 730 to 7911 and from 1615 to 11136 Bq·m–2, respectively. The mean soil erosion is about 2.1 kg·m–2·a–1 (about 1.4 mm·a–1). The accumulation of the colluvial sediments started in the Neolithic and drastically increased in the Middle Ages. The examined gully catchment in Biedrzykowice has probably developed quite rapidly as a result of increased erosion. This resulted in the abandonment of this area as farmland and, consequently, in the minimization of water erosion on the slope due to the entrance of woody vegetation in this area. Erosion processes were highly intensified during the last 70 years as a result of deforestation after World War II and intensive agricultural reuse of this area after a break, as indicated by isotope measurements and dendrochronology.

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Distribution in SAR palaeodoses due to spatial heterogeniety of natural beta dose

Chauhan N., Singhvi A. K.

Geochronometria

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2011

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Vol. 38, no. 3

190-198

EN

In luminescence dating of sediments, Mayya et al. (2006) pointed out that at single grain level, the beta dose for quartz grains is heterogeneous. This heterogeneity arises due the fact that the total potassium in sediment is contributed by few feldspar grains with up to 11-14% stoichiometric potassium (Huntley and Baril, 1997). Beta particles have a range of ~2 mm, which is comparable to grain sizes and inter-grain distances. This fact implies that the spatial fluctuation of beta emitters (K-feldspars) around individual quartz grains results in heterogeneous dose deposition. These fluctua-tions therefore, lead to an inherent spread in palaeodoses received by individual quartz grains. In this study, we compute the spread in single aliquot palaeodoses that arises exclusively due to het-erogeneity in beta radiation dose received by individual grains. We thus postulate that ‘single ali-quots’ (comprising several – typically 100 – heterogeneously irradiated single grains) would have an inherent spread in the palaeodose. In this work, we used Monte Carlo simulations to quantify the ex-tent of spread in palaeodoses arising due to heterogeneity of beta dose and hence put a limit on the precision of age estimation. Simulations results indicated, that, 1) the average of the single aliquot palaeodoses provides the closest approximation to the true palaeodose, 2) the minimum number of al-iquots that are needed to obtain a robust estimate of average palaeodose value depend upon desired precision and the concentration of K, and 3) the ratio of maximum to minimum single aliquot palaeo-dose values for a given K concentration provides a measure of inherent spread arising due to beta dose heterogeneity. Any spread over and above this range, can be ascribed to other sources such as heterogeneous bleaching and sensitivity changes. Radiation dose from other uniformly distributed sources of beta particles (U, Th and Rb) however would reduce this spread.

3

Dating mortar by optically stimulated luminescence: a feasibility study

Goedicke C.

Geochronometria

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2011

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Vol. 38, no. 1

42-49

EN

Quartz is the datable component in mortar. Although its luminescence properties are very well studied, the problem of mortar dating arises from a low level of optical bleaching. In order to reduce the time consuming efforts for dating lime mortar in monuments by optically stimulated luminescence, we investigated the most suitable methods of dose and dose rate determination, and we explored tests which are suitable to predict the datability of a given material. Reverting to the large number of publications on sedimentary partially bleached quartz we found linear modulation techniques especially useful, equally we also recommend the determination of the level of optical depletion before starting analyses. Single grain analysis is regarded as an ultimate but infallible tool to date very poorly bleached quartz from mortar. Dose rate measurements need to take into account the radioactive equilibrium of the uranium decay and the short range inhomogeneity of the environmental gamma radiation field: gamma spectrometry and on-site TLD measurements are best suited.

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Changes in natural OSL sensitivity during single aliquot regeneration procedure and their implications for equivalent dose determination

Singhvi A. K., Stokes S. C., Chauhan N., Nagar Y. C., Jaiswal M. K.

Geochronometria

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2011

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Vol. 38, no. 3

231-241

EN

Measurement of low temperature (90o, C-120o,C) Thermoluminescence (TL) sensitivity of natural quartz samples subjected to pre-heating and optical stimulation indicate that significant sensi-tivity changes can occur during measurement of the natural Optically Stimulated Luminescence (OSL). During the measurement of natural signal, the luminescence sensitivity of samples can change by 40%. The sensitivity changes both during the initial preheat and the measurement of natural OSL. The currently used version of Single Aliquot Regeneration (SAR) protocol measures and corrects for the sensitivity changes after preheat and readout of natural OSL. However, it does not take into ac-count the changes in sensitivity during the readout of the natural signal. We therefore developed a correction procedure so that both the natural and the regenerated OSL in-tensities can be measured and plotted with the same sensitivity and suggest that in the absence of such a correction, a considerable fraction of the SAR based ages could have systematic errors. The correc-tion for the sensitivity is based on the use of sensitivity of 110o, C TL quartz peak, which is correlated to OSL signal (Murray and Roberts, 1998). The use of 110o, C peak provides a reasonable measure of the changes in OSL sensitivity of quartz. A modified Natural Sensitivity Corrected–SAR (NSC-SAR) procedure, that comprises the measurement of, 1) the TL intensity of 110o, C peak for a test dose on sample as received (i.e. natural sample) and, 2) the sensitivity of the 110o,C peak of the same sample after the preheat and read out of the natural OSL, is proposed. This ratio, termed as Natural Correc-tion Factor (NCF), then provides a way to correct for sensitivity changes. Results on samples from diverse depositional environments indicated that the NSC-SAR consistently (without exception) provided improved distribution in paleodoses i.e. a lower scatter compared to the standard SAR protocol. In addition, the use of this protocol also resolved anomalous cases where the intensity of natural OSL was significantly above the saturation intensity of the regenerated OSL. Implicitly, this study implies a caution on the use of palaeodoses obtained from single grains as such a correction is not possible in the currently used automated single grain OSL measurement systems. The only way now on will be to analyze aliquots with only a grain on them.

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A high resolution optical dating study of the Mostiştea loess-palaeosol sequence (SE Romania) using sand-sized quartz

Vasiliniuc S., Timar-Gabor A., Vandenberghe D. A. G., Panaiotu C. G., Begy R. CS., Cosma C.

Geochronometria

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2011

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Vol. 38, no. 1

34-41

EN

We report on SAR-OSL dating of closely-spaced samples from the loess-palaeosol sequence near Mostiştea lake (Danube Plain, SE Romania). We used sand-sized quartz and a SAR protocol that involved a preheat of 10s at 220°C and a test dose cutheat to 180°C. It is shown that these thermal pretreatments isolate a quartz OSL signal that is dominated by the fast component. The behavior of this signal in the SAR protocol is then documented. The ratio of the measured to given dose tends to lie slightly but systematically above unity (~5% on average) and the recycling ratio below unity (~6% on average); for all samples, the recuperated signal is negligible. Within analytical uncertainty, the nineteen optical ages are internally consistent and agree with the predictions from a palaeomagnetic age-depth model. Although it may be possible to optimize the SAR measurement procedure, the optical ages already confirm the chronostratigraphic position of the uppermost welldeveloped palaeosol in that it formed during MIS 5.The established chronology allows correlating the sequence near Mostiştea lake with that near Mircea Vodă that we investigated earlier.

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Residual luminescence in quartz from slack water deposits in Kaveri Basin, South India : a single aliquot approach

Jaiswal M. K., Chen Y. G., Kale V. S., Achyuthan H.

Geochronometria

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2009

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Vol. 33

1-8

EN

Optical bleaching of quartz may be incomplete due to decreased daylight intensity and narrower wavelength spectrum in water column, leading to age overestimation in young fluvial sediments. This hypothesis was tested on a low energy slack water deposits from Kaveri Basin in south India using the SAR protocol. Various tests suggest successful application of SAR on quartz from the study area despite low sensitivity and few numbers of bright grains. Partial bleaching can be ruled out if using SAR on small aliquots. The results suggest a uniform residual luminescence and a common sedimentary condition in this area. Due to partial bleaching, the lowest values of palaeodoses should be considered in preference to the average values.

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Overcoming environmental dose rate changes in luminescence dating of waterlain deposits

Li B., Li S-H., Wintle A. G.

Geochronometria

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2008

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Vol. 30

33-40

EN

This study investigates lacustrine and fluvial sediments on the Sala Us River in the Mu Us Desert in central north China. Significant changes in environmental dose rate in part of the section could be shown to have occurred from measurements of the present day radioactivity and by the age reversal for some samples that had been dated by optically stimulated luminescence (OSL) measurements on quartz. These changes in dose rate can be attributed to recent uptake of radioactive elements found in the sediments; this resulted in significant underestimation of the OSL ages. In this study, the new isochron method using K-feldspar grains has been applied to overcome the effects of changes in dose rate. Calculations are used to show that changes in the environmental dose rate factors, i.e. K, U, Th, water content and cosmic ray flux, and disequilibrium in the U and Th decay chains, e.g. radon escape, have a negligible effect on the isochron age. After applying the new isochron method, the effects of changes in dose rate caused by recent uptake of radioactive elements and changes in past water content were effectively overcome and true ages are obtained; this was verified by repeating the luminescence isochron measurements on samples of overlying and underlying sediments.

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Residual doses in recent alluvial sediments from the Ardenne (S Belgium)

Vandenberghe D., Derese C., Houbrechts G.

Geochronometria

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2007

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Vol. 28

1-8

EN

We report on our first investigations into the potential of optical dating for determining the rate of river flood sedimentation in the Ardenne region (S Belgium). Two samples collected from a recent alluvial deposit were used to investigate the extent of resetting in different particle size fractions of quartz (4-11 µm, 63-90 µm, 90-125 µm, 125-180 µm, 180-212 µm and 212-250 µm) as well as in polymineral fine (4-11 µm) grains. Both samples show satisfactory OSL and IRSL characteristics. The IRSL signals from the polymineral fine grains yield an equivalent dose (De) of 3-4 Gy, while a De of 0.3-0.6 Gy was measured using large aliquots of quartz. Small aliquot analyses of 63-90 µm and 212-250 µm quartz grains confirm that the coarser fraction contains more grains with lower De's. Furthermore, for a modern sample (‹ 3 years old), ˜60% of the aliquots yields a De consistent with zero, indicating that these contain only well-bleached grains. These findings suggest that it might be possible to extract the true burial dose from dose distributions measured using small aliquots of coarse-grained (e.g. 212-250 µm) quartz.

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The Influence of cesium activity on the annual dose for OSL dating

Moska P., Poręba G. J., Bluszcz A.

Geochronometria

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2004

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Vol. 23

15-19

EN

Introduction of single aliquot protocols dramatically improved the accuracy of absorbed dose measurements, so now dating of very recent events, which ages are of the order of tens of years or even single years, becomes possible. The overall accuracy of the OSL age is now limited by the correct assignment of the dose rate. Certain types of recent sediments may contain fall-out radioisotopes that increase the average annual dose. In this paper we demonstrate that the contribution from fall-out radioactivity may be significant and the way to take it into account by using a modified age equation.

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Zeroing of the osl signal as a function of grain size: investigating bleaching and thermal transfer for a young fluvial sample

Truelsen J. L., Wallinga J.

Geochronometria

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2003

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Vol. 22

1-8

EN

Previous studies have indicated that the OSL signal from coarser grain-size fractions might be more completely reset during fluvial transport. In this study we investigate whether this feature is real, or rather an artefact of thermal transfer effects that might affect finer grains more due to smaller thermal lag during heat treatment. Our experimental results obtained on three grain-size fractions (90-125, 180-212 and 425-500 mm) clearly show that better bleaching of coarser grains is not caused by differences in thermal transfer. On the basis of our results we advise selecting a coarse grain size for analysis when dating young fluvial deposits.