Exploring the potential of luminescence methods for dating Alpine rock glaciers

Abstract

Rock glaciers contain valuable information about the spatial and temporal distribution of permafrost. The wide distribution of these landforms in high mountains promotes them as useful archives for the deciphering of the environmental conditions during their formation and evolution. However, age constraints are needed to unravel the palaeoclimatic context of rock glaciers, but numerical dating is difficult. Here, we present a case study assessing the potential of luminescence techniques (OSL, IRSL) to date the inner sand-rich layer of active rock glaciers. We focus on the signal properties and the resetting of the signal prior to deposition by investigating single grains. While most quartz shows low signal intensities and problematic luminescence characteristics, K-feldspar exhibits much brighter and well-performing signals. Most signals from plagioclases do not show suitable properties. Luminescence signals far below saturation indicate distinct but differential bleaching. The finite mixture model was used to determine the prominent populations in the equivalent dose distributions. The luminescence ages represent travel times of grains since incorporation into the rock glacier and hence, minimum ages of rock glacier formation. Luminescence ages between 3 kyr and 8 kyr for three rock glaciers from the Upper Engadine and Albula region (Swiss Alps) agree well with independent age estimates from relative and semi-quantitative approaches. Therefore, luminescence seems to have the potential of revealing age constraints about processes related to the formation of rock glaciers, but further investigations are required for solving some of the problems remaining and reducing the dating uncertainties.

Lithological controls on light penetration into rock surfaces – Implications for OSL and IRSL surface exposure dating

“…Aliquots obtained from the saturated inner part (depth > 25 mm) of the metamorphic boulders (HT-141, 144 and 145) yielded almost no blue-stimulated OSL signal but a bright response to stimulation with IR at 50°C for 100 s. This suggests the presence of insensitive quartz but high sensitivity Na-and/or K-feldspar grains and is in agreement with observations from other alpine catchments Fuchs et al, 2013) as well as with investigations into the luminescence characteristics of crystalline rocks (e.g. Sohbati et al, 2011).…”

Rates of river incision across the main tectonic units of the Pamir identified using optically stimulated luminescence dating of fluvial terraces

“…There was no significant variation of paleodoses. Low effects of changing overdispersion resemble findings of Fuchs et al (2013a) (supplementary data) for permafrost sediments of a high mountain setting in Switzerland. Best fit of the lowest data cluster (maximum in KDE estimates) was achieved for overdispersion values of 0.1 -0.25.…”

“…Compared to feldspars, the other commonly used mineral in luminescence dating, quartz does not show anomalous fading (Wintle, 1973) and has a faster signal reset (Wallinga, 2002). However, in mountain settings the OSL properties of quartz have been found to be problematic (e.g., Preusser et al, 2006;Fuchs et al, 2013a) due to low sensitization related to few sedimentation cycles (e.g., Pietsch et al, 2008;Jeong and Choi, 2012). In such settings OSL dating of quartz requires additional attention to measurement parameters.…”

Constraints on the timing of debris-covered and rock glaciers: An exploratory case study in the Hólar area, northern Iceland

“…(iv) Luminescence dating, a method which also presents serious complications of interpretation when applied to rock glaciers (Fuchs et al, 2013).…”