Publication Details

Roberts, R. G., Jacobs, Z. & Li, B. (2018). Optical dating of sediment samples from Chagyrskaya Cave. In M. V. Shunkov (Ed.), Multidisciplinary Studies of Chagyrskaya Cave - A Middle Paleolithic Site in Altai (pp. 353-369). Novosibirsk: Russian Academy of Sciences Publishing.


The existing chronology for the Chagyrskaya Cave is based on 19 radiocarbon (14C) age determinations (Derevianko et al., 2013; Rudaya et al., 2017) made on bison bones from stratigraphic layers 5 (n = 2) and 6 (n = 17). Several of the bones from layer 6 have cut marks consistent with those made by stone tools. Except for the uppermost sample from layer 5 (which has a calendar-year 14C age of 37,670–38,690 cal. BP at the 95 % confidence interval), all other age estimates fell at or beyond the reliable dating limit for these materials (Wood, 2015) and the current ceiling on 14C age calibration of c. 50,000 cal. BP (Reimer et al., 2013). Minimum (infinite) measured ages of 49,000 BP and 52,000 BP were obtained for 9 and 6 of the samples, respectively (Derevianko et al., 2013; Rudaya et al., 2017).

The 14C chronology for Chagyrskaya Cave indicates, therefore, that layer 6, the underlying layer 7 and part of the overlying layer 5 were deposited 50,000 years or more ago. Finite ages for these deposits can be obtained by optical dating of the sediments, which provides an estimate of the time since grains of luminescent minerals, such as quartz and potassium-rich feldspar (K-feldspar), were last exposed to sunlight (Huntley, Godfrey-Smith, Thewalt, 1985; Hütt, Jaek, Tchonka, 1988; Aitken, 1998; Jacobs, Roberts, 2007; Wintle, 2014; Roberts et al., 2015). The burial age is estimated by dividing the equivalent dose (De, a measure of the radiation energy absorbed by grains during their period of burial) by the environmental dose rate (the rate of supply of ionising radiation to the grains over the same period). The De is determined from laboratory measurements of the optically stimulated luminescence (OSL) from quartz or the infrared stimulated luminescence (IRSL) from K-feldspar, and the dose rate is estimated from field and laboratory measurements of environmental radioactivity, plus the small contribution from cosmic rays.

Each of these minerals has advantages and shortcomings compared to the other. In particular, the quartz OSL signal is bleached by light more rapidly and completely than is the feldspar IRSL signal, which is advantageous if grains were exposed to sunlight only briefly at deposition. K-feldspar, on the other hand, saturates a much higher dose than does the quartz OSL signal, thereby enabling finite ages to be determined for samples with larger De values and, hence, older deposits.