Abstract
Abstract. Luminescence dating has become a pillar of the understanding of Pleistocene glacial advances in the northern foreland of the Swiss Alps. However, both quartz and feldspar from the region are equally challenging as dosimeters with anomalous fading and partial bleaching being some of the obstacles to overcome for the establishment of decisive chronologies. In this study, luminescence properties of coarse- and fine-grained quartz, feldspar, and polymineral fractions of eight samples from a palaeovalley, Rinikerfeld in northern Switzerland, are systematically assessed. Standard performance tests are conducted on all four fractions. Deconvolution of luminescence signals of the quartz fractions is implemented and shows the dominance of stable fast components. Reader-specific low preheat temperatures are investigated on the infrared stimulated luminescence (IRSL) signal of feldspar. Thermal stability of this signal is found for low preheats, and thermal quenching could be excluded for higher preheats. However, anomalous fading is observed in the feldspar and polymineral IRSL signals and two correction approaches are applied. For one approach, fading corrected coarse-grained feldspar ages are consistent with those derived from quartz. In general, coarse-grained quartz and feldspar, as well as the fine-grained polymineral fraction of one sample, are in chrono-stratigraphic agreement and present negligible evidence for partial bleaching. However, ages derived from fine-grained quartz are found to underestimate those of the coarse-grained quartz fractions. Hence, the impact of alpha efficiency and water content on the dose rate and thus the ages are assessed. A finite explanation for the observed discrepancies remains lacking, but this systematic investigation of different luminescence signals allows for the establishment of a chronology for the palaeovalley fill dating back to at least Marine Isotope Stage 6 (MIS 6).
Highlights
Pleistocene glaciations in the northern foreland of the Swiss Alps have been studied since the early 19th century
Luminescence dating of glacial and proglacial deposits can be complex (e.g. Duller, 1994, 2006; Spencer and Owen, 2004). In such environments sediment sources and sinks are often within a short distance of each other and transport may occur in turbid waters, both of which reduces the chance for grains to experience sufficient sunlight exposure to reset or bleach any pre-existing luminescence signals
Noteworthy is the presence of positively skewed De distributions for coarse-grained quartz, but the lack of a comparable pattern for the slower-bleaching feldspar suggests that partial bleaching is unlikely to influence these distributions
Summary
Pleistocene glaciations in the northern foreland of the Swiss Alps have been studied since the early 19th century (summarised in Preusser et al, 2011). Laboratory dose response curves for quartz were often best fitted with a double-saturating exponential function that accounts for high dose responses beyond single exponential behaviour (Lowick et al, 2010; Dehnert et al, 2012) This phenomenon is known for samples from other regions where luminescence ages are either in agreement These approaches rely on observing signal loss over hours to days within laboratory experiments and from this data the signal loss that has occurred over geological timescales is deduced In such storage tests, fading has been observed for most samples from northern Switzerland with g-values between 1 % and 3 % per decade (Dehnert et al, 2012; Lowick et al, 2012, 2015; Gaar and Preusser, 2012) and 2.7 ± 0.3 % per decade (normalised to 2 d; Buechi et al, 2017). Methods, results and discussion are jointly presented in aspect specific subsections
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