Optically stimulated luminescence (OSL) dating of sediments and thermoluminescence (TL) dating of heated ceramics, terracotta figurines and potteries has proven to be useful in investigating geo-archaeological sites. Especially single-grain quartz optically stimulated luminescence dating has shown to provide reliable ages for samples from a range of archaeological contexts (Guérin
Our study examines single-grain chronologies for the archaeological site “the burials in Khutag Uul Mountains (Mongolia)”, associated with human activities from the Xiongnu period (3rd century BC – 2nd century AD) and from Turk period (552–745 AD) – using pottery and sedimentary samples from the same archaeological context. Based on the previous findings, e.g. the advantage of luminescence dating at the archaeological site using different dating materials (Solongo
The Orkhon Valley was the centre of numerous nomadic states; the Xiongnu (3rd century BC – 1st century AD), Turkic (552–745 AD), and Mongol Empires (12th – 14th centuries) succeeded one another in the steppes of Mongolia. Archaeological research in Orkhon Valley has concentrated on numerous steles with runic inscriptions, but also on numerous archaeological burials. Khutag Uul Mountains (47°36′N, 102°47′) is located on the left bank of the Khogshin Orkhon River on the eastern edge of the upper Orkhon valley; it was once a tribute to the people of ancient times. The Khutag Uul Cemetery is the largest in its territory. In 2009, during the fieldwork, a total of 121 burial sites were recorded in the south and additionally 43 burials on the east (Bayar
The settlement history at this site and the characteristic types of archaeological monuments, especially the sections of burial structures and tombs have been associated with human activities from the Turkic period. However, the graves under study had similar exterior surface structures mounded by an oval or circular stone construction with a diameter of 6–8 m, reflecting a standard tomb of the Xiongnu period. Pottery fragments L-EVA1201 and associated sedimentary samples L-EVA-1202 and L-EVA-1203, L-EVA-1204 from nearby sites ‘MKC 65’ (layer 2) and ‘MKC 4’ (layer 1) were collected taken for single grain measurements (
Sample preparation and luminescence measurements were carried out in the Luminescence laboratory at the MPI for evolutionary anthropology, Leipzig (Germany) and followed the standard procedure reported in (Solongo
Single grains of quartz were measured using a Risø TL-DA-20 reader (Bøtter-Jensen
To obtain
Grains were rejected if the resulting OSL data failed to satisfy the criteria similar to those proposed by (Jacobs
The dose-response curves for individual quartz grains of the heated quartz sample L-EVA1201, showing Lx/Tx as a function of regeneration doses. The corresponding luminescence decay curves from the individual grains are shown on the right side: natural OSL (N – black line), test dose (T1 – red line and T after IRSL – blue line) OSL decay curves as a function of stimulation time obtained from single grains. In addition, the corresponding TL measured from the aliquot at the end of the SAR protocol served as additional criteria for examining the presence of feldspar.
a) and c) The dose-response curves for individual quartz grains of the sedimentary quartz L-EVA1202, showing Lx/Tx as a function of regeneration doses. The corresponding luminescence decay curves from the individual grains are shown on the right side: natural OSL (N – blue line), test dose (T1 – red line and T after IRSL – blue line) OSL decay curves as a function of stimulation time obtained from single grains. In addition, LM-OSL from a bright grain (e) indicated the presence of a significant slow component in addition to the fast component; however those bright grains were rejected.
For each grain, the sensitivity-corrected regenerated OSL signals (Lx/Tx) were fitted with a single saturating-exponential function in the form:
Previously, Roberts and Duller (2004) reported for multi-grain Imax values of 36 to 52 and
Following this first analysis, we calculated the dose estimates obtained when the relative uncertainty on the natural test dose, and the error in
Effect of precision on De a). for sample L-EVA1201. Central Age Model (CAM, squares) dose and the relative standard error (as circles) on CAM De; b). for sample L-EVA1202. FMM and MAM De (triangles and squares) as function of precision on De.
For the sedimentary samples L-EVA1202 and L-EVA1203, the quartz grains exhibit significant grain-to-grain variability in terms of OSL decay rate and inherent brightness. The sensitivity of sedimentary quartz grains has been suggested to be associated with different factors such as the source of origin of the mineral grains (Fitzsimmons, 2011), and their sedimentary/thermal history (Sawakuchi
The dose-response curves of a selection of grains (L-EVA1202,
Similarly, we calculated the dose estimates for precision in
It is worth to note that 51 grains (with signals up to 30,000 cts in the first 0.035 s of stimulation of the natural signal) were registered; however, these bright grains failed the rejection criteria; specifically, the sensitivity-corrected natural signal does not result in a finite dose estimate. In addition, the bright grains failed the TL 110°C test and the IR depletion test, suggesting the presence of a feldspar component. The LM-OSL measurements from a bright grain (
The addition of the ‘fast ratio’ (Durcan and Duller, 2011) and thus removing the grains with low fast ratios as a criterion for selecting single grains for dose estimation was proposed recently (Duller, 2012); however, it might also lead to the removal of a high proportion of signals (Thomsen
The results of the fitting showed up to three components with decay rates on average of 53 ± 1 s−1, 13.4 ± 0.7 s−1 and 1.2 ± 0.2 s−1. Our results are in agreement with the decay rates of 10.3 ± 3.4 s−1 for the fast and 2.1 ± 0.7 s−1 for the medium components reported by (Feathers and Pagonis, 2015), and of 11 ± 4.3 s−1 and 1.9 ± 1.0 s−1 obtained by (Duller, 2012). We assume that the additional component with the decay rate of 56.6 ± 2.4 s−1 obtained in our measurements may correspond to a very rapidly decaying ultrafast OSL (UF component) in quartz samples, reported earlier for multi-grain OSL by (Jain
This ultrafast component was identified in samples from different areas around the world, and the optical cross-section of the responsible trap under blue light stimulation is about 14 times larger than that of the fast component (Jain
The initial OSL signal integration interval is assumed to include the fast component preferentially, and rejection of the very initial OSL signal might remove the UF. In the following we examined the effect of variation for the integration intervals on
The results are displayed in
a) The fitting results for pottery L-EVA1201, and for sedimentary quartz LEVA1202 showing the presence of UF, F and medium OSL components. b) The corresponding constant and increasing De-t-plots for L-EVA1201 and L_EVA1202 are shown.
Growth curves for naturally sedimentary and heated quartz grains.
Radial plots of the single grain dose distributions a) fast De from accepted 167 grains (closed triangles) for heated quartz L-EVA1201 and UF De from n = 159 (circles). The solid grey band is centered on the weighted mean, De determined using Central Age Model, over-dispersion of 14.7%. b) De from accepted 134 grains of L-EVA1202 channels 6–9. The solid grey lines indicate the CAM De = 15.13 ± 1.47 Gy and overdispersion of 96.8%. MAM De = 5.91±1.38 Gy.
In contrast,
The archaeological site at the Khutag Uul Mountains (Mongolia) was investigated using single-grain quartz OSL on pottery and sedimentary samples. Detailed luminescence investigations revealed a presence of an ultra-fast component – not detected previously in the single grain measurements – which might lead to erroneous ‘fast ratio’ estimates. As the fitting results of pottery quartz display, fitting was done using ultrafast, fast plus background. It is worth mentioning that the introduction of the third component, namely the medium or slow component did not improve the fit and was equal the background. For the sedimentary quartz grains, fitting was done using a combination of ultrafast and medium with a small fast contribution, whereas the other datasets were fitted using fast and medium components only. Therefore, it was impossible to obtain fast ratio values for the whole dataset.
The CAM