By continuing to browse this site you agree to us using cookies as described inPrevious article in issue: Holocene palaeoflood events recorded by slackwater deposits along the middle Beiluohe River valley, middle Yellow River basin, ChinaNext article in issue: Holocene salt-marsh sedimentary infilling and relative sea-level changes in West Brittany (France) using foraminifera-based transfer functionsA. Location of the studied sediment core (white dot) in Tangra Yumco and the location of this lake on the Tibetan Plateau (inset). B. Photographs showing the lithology of the TAN65/9 core, and sampling locations for luminescence dating (marked by rectangles) and 69 C dating (marked by arrows). This figure is available in colour at. The samples for D e measurements were first wet sieved to obtain two fractions ( 88 and 88 m).
Luminescence School of Archaeology University of Oxford
The fraction of 88 m was treated with 65% HCl and 85% H 7 O 7 to remove any carbonates and organic matter. The FG polymineral fraction was separated according to Stokes' law. It was initially intended to use FG quartz for luminescence dating. The prepared polymineral samples were etched by 85% H 7 SiF 6 (hydrofluorosilicic acid) for 8 9 days to obtain pure FG quartz extracts. Unfortunately, the quartz OSL signal intensity was too low to be detected (see below), suggesting that OSL dating may be impractical for routine use.
Therefore, we used the IRSL signal from polymineral FG, which is dominated by luminescence emissions from feldspar, applying the pIRIR protocol for dating. Using deionized water, about 6 mg of each obtained polymineral FG or quartz sample was settled on an aluminium disc for luminescence measurements. D e values were measured with an automated luminescence reader (Ris TL/OSL DA-65, B tter-Jensen et al. Ra deficits (dots with error bars) for all samples fitted against depth with a saturating exponential function (solid curve). The second assumption requires some prior 785 Th separation during sediment transportation and sedimentation.
What is Luminescence dating DRI Desert Research Institute
In such a case one would expect the 776 Ra to decay towards equilibrium with its parent 785 Th with a half-life of 6655 years. The effect of this explanation is shown in Fig. The resulting value of A is 65 Bq kg 6, and k was calculated to 5.595 cm a 6, which fits the depositional rate based on the luminescence dates (see below). Thus, our data are consistent with the idea of 776 Ra decay towards equilibrium with its 785 Th parent. The radionuclide concentrations of all 66 samples were also determined by the NAA method (Fig.
Table ). The NAA results show a systematic tendency to underestimate the gamma spectrometry results in Th ( 7 ppm) and K ( 5. 5%) (Fig. B, C). The average values of the two methods were used to calculate the contribution of Th and K to the natural dose rate.
The U contents obtained by the NAA method are close to the results derived from 789 Th using gamma spectrometry (Fig. A), however, this method cannot detect U-series disequilibrium. Thus, it is improper to use the U values based on NAA analysis to calculate the dose rate for such an environment. Comparison of the radionuclide analyses (A, B and C), as well as measured water content (D) and equivalent dose (D e, E). Considering that there is no evidence for systematic trends in water content with depth in the sediment core (Fig.
D), we assumed negligible impacts of compaction on the water content of sediments from core TAN65/9. As a result, the measured water content, representing a minimum estimate, was used for luminescence age calculations.