ASSESSMENT OF THE MAXIMUM AGE LIMIT FOR LUMINESCENCE DATING OF SEDIMENTARY QUARTZ

In recent years developments in single aliquot techniques applied to sedimentary quartz have significantly improved accuracy and precision of dating results. However, the maximum age obtainable in luminescence dating is dependent on the magnitude of the environmental radiation dose-rate, where age = equivalent dose (D_e) / dose-rate, and whether the luminescence signal has reached saturation. With respect to the latter, the growth of luminescence with increased radiation dose is typically described by a saturating exponential function of the form I = I₀(1-exp^-D/D0), where I is the luminescence intensity from dose D, I₀ is the luminescence saturation intensity and D₀ is the dose level that is characteristic of the saturating part of the dose-response curve. For older samples that we know are close to the maximum age limit, it is difficult to assess whether signal saturation may be influencing the luminescence data and leading to higher uncertainty or age underestimation. To ensure that saturation conditions are avoided, Wintle and Murray (2006) proposed the prerequisite that D_e < 2D₀, where the natural optically stimulated luminescence (OSL) level is about 15% lower than the saturated signal level obtained in the laboratory.

We are currently investigating the Quaternary history of an intermontane basin in northern Italy in the eastern European Alps. One of the sites in this study at Schabs consists of a sequence of ice-proximal shoaled or ponded sediments deposited in fine silt or sandy laterally continuous layers. In continuous-wave (CW) OSL data from extracted quartz we observe growth of luminescence with laboratory dose that indicates the natural OSL may be close to saturation, and the data are best described by a function that includes both saturating exponential and linear terms. This presentation will discuss results of both CW-OSL and linearly modulated (LM) OSL to assess the proximity to saturation using dose-response prerequisites (D_e < 2D₀) and the observed linear growth and saturation characteristics.

Wintle, A., Murray, A.S., 2006. A review of quartz optically stimulated luminescence characteristics and their relevance in single-aliquot regeneration dating protocols. Radiation Measurements 41, 369–391.