On the importance of grain size in luminescence dating using quartz

Abstract

h i g h l i g h t sDiscrepancy between quartz SAR-OSL ages obtained on fine and coarse grains. Dose response curve adequately fitted by a sum of two saturating exponentials. Isothermal decay fitted by a single exponential. Clear dependency between the saturation characteristics (D 0 s) and the quartz grain size. No correlation between the 2 D 0 value and the maximum attainable accurate equivalent dose. a r t i c l e i n f o a b s t r a c tThere are two major problems commonly encountered when applying Optically Stimulated Luminescence (OSL) dating in the high dose range: (i) age discrepancy between different grain sizes, and (ii) age underestimation. A marked and systematic discrepancy between fine-grain (4e11 mm) and coarse-grain (63e90 mm) quartz single aliquot regeneration protocol (SAR) ages has been reported previously for Romanian and Serbian loess >40 ka (D e of~100 Gy), generally with fine-grain ages underestimating the depositional age. In this paper, we show a similar age pattern for two grain size fractions from Chinese loess, thus pointing to a potential worldwide phenomenon. While age underestimation is often attributed to signal saturation problems, this is not the case for fine grain material, which saturates at higher doses than coarse grains, yet begins to underestimate true ages earlier. Here we examine the dose response curves of quartz from different sedimentary contexts around the world, using a range of grain sizes (diameters of 4e11 mm, 11e30 mm, 35e50 mm, 63e90 mm, 90e125 mm, 125e180 mm, and 180 e250 mm). All dose response curves can be adequately described by a sum of two saturating exponential functions, whose saturation characteristics (D 0 values) are clearly anticorrelated with grain diameter (4) through an inverse square root relationship, D 0 ¼ A/√4, where A is a scaling factor. While the mechanism behind this grain-size dependency of saturation characteristics still needs to be understood, our results show that the observation of an extended SAR laboratory dose response curve does not necessarily enable high doses to be recorded accurately, or provide a corresponding extended age range.

A luminescence‐based chronology for the Harletz loess sequence, Bulgaria

“…However, previous studies have observed this growth behaviour for other quartz fine grain samples, and have come to the conclusion that it may lead to D e and age underestimation (e.g. Lowick et al 2010;Lowick & Preusser 2011;Kreutzer et al 2012;Timar-Gabor et al 2017).…”

“…However, the thermal stability of the quartz luminescence signal seems to be regionally different. For example, the quartz fine grain signal of Romanian loess samples has been shown to be thermally stable enough to theoretically obtain ages up to 20 Ma (Timar-Gabor et al 2017). However, the true maximum age limit is much lower, due to the limited number of electron traps.…”

Direct and indirect luminescence dating of tephra: A review

“…Although age estimates differ by grain size, weighted means of 40.4 ± 1.3 and 40.7 ± 1.2 ka agree well with the independent age. Different age results depending on the grain size fraction used were also obtained by Trandafir et al (2015) and Timar-Gabor et al (2017). Figure 9 shows the extent of tephra deposits in south-eastern Europe and investigated loess deposits containing these tephras (cf .…”

“…() and Timar‐Gabor et al . (). Figure shows the extent of tephra deposits in south‐eastern Europe and investigated loess deposits containing these tephras (cf.…”

Luminescence as a Sediment Tracer and Provenance Tool

“…Values of D 0 may be due to source lithology, but further evidence is needed to confirm this (Lowick et al, ). Recently, Timar‐Gabor et al () demonstrated that an inverse square relationship exists between quartz grain size and D 0 ( , where δ is grain size and k is a constant).…”