Evaluating optically stimulated luminescence rock surface exposure dating as a novel approach for reconstructing coastal boulder movement on decadal to centennial timescales

Abstract

Abstract. Wave-transported boulders represent important records of storm and tsunami impact over geological timescales. Their use for hazard assessment requires chronological information on their displacement that in many cases cannot be achieved by established dating approaches. To fill this gap, this study investigated, for the first time, the potential of optically stimulated luminescence rock surface exposure dating (OSL-RSED) for estimating cliff-detachment ages of wave-transported coastal boulders. The approach was tested on calcarenite clasts at the Rabat coast, Morocco. Calibration of the OSL-RSED model was based on samples with rock surfaces exposed to sunlight for ∼ 2 years, and OSL exposure ages were evaluated against age control deduced from satellite images. Our results show that the dating precision is limited for all targeted boulders due to the local source rock lithology which has low amounts of quartz and feldspar. The dating accuracy may be affected by erosion rates on boulder surfaces of 0.02–0.18 mm yr−1. Nevertheless, we propose a robust relative chronology for boulders that are not affected by significant post-depositional erosion and that share surface angles of inclination with the calibration samples. The relative chronology indicates that (i) most boulders were detached from the cliff by storm waves; (ii) these storms lifted boulders with masses of up to ∼ 24 t; and (iii) the role of storms in the formation of boulder deposits along the Rabat coast is more significant than previously assumed. Although OSL-RSED cannot provide reliable absolute exposure ages for the coastal boulders in this study, the approach has large potential for boulder deposits composed of rocks with larger amounts of quartz or feldspar and less susceptibility to erosion.

Erosion rates in a wet, temperate climate derived from rock luminescence techniques

“…Beyond this, it is possible that the MET-pIRIR protocol may be useful in identifying complex burial or exposure histories of rocks, similar to those that have been reported in previous studies but solely using the IR 50 signal (e.g. Freiesleben et al, 2015;Brill et al, 2021). There is also potential to explore whether the different temperature IRSL signals of the MET protocol record different states of erosion (i.e.…”

“…Studies have applied rock luminescence techniques (mostly exposure dating) to a variety of lithologies including granites, gneisses (Lehmann et al, 2018(Lehmann et al, , 2019aMeyer et al, 2018), sandstones (Sohbati et al, 2012b;Chapot et al, 2012;Pederson et al, 2014), quartzites (Gliganic et al, 2019) and carbonate limestone (Brill et al, 2021). These studies showed that µ is highly dependent upon the rock lithology, where mineralogy has a strong control on the rock transparency.…”

“…Improved understanding of this fundamental principle has led to the development of new applications of luminescence; constraining the timing of rock exposure events (Laskaris and Liritzis, 2011;Sohbati et al, 2011;Lehmann et al, 2018) and rock surface erosion rates (Sohbati et al, 2018;Lehmann et al, 2019a, b). Brown (2020) combines these phenomena within model simulations to explore different sample histories of exposure and burial, informing geomorphological interpretations of luminescence depth profiles measured in samples collected from the natural environment. Here, we investigate erosion rates, rather than weathering rates, as the luminescence technique specifically measures the light penetration into a rock surface after the removal of material (i.e.…”

The Imprint of Recent Meteorological Events on Boulder Deposits along the Mediterranean Rocky Coasts

“…Two prominent methods have recently been used to date the boulder dynamics in medium-low latitudes. Oliveira et al [92] applied lichenometry techniques to date boulder movement on the western coast of Portugal, while Brill et al [93] used optically stimulated luminescence on CBDs located on the Moroccan Atlantic coast, both with encouraging results.…”

“…The interaction of the different scientific disciplines involved in the study of CBDs as natural archives for intense storms is the final point discussed here. Assuming that the identification of suitable CBDs is geomorphological expertise, the contribution of atmospheric physicists, physical oceanographers, hydrodynamics researchers, and other natural science scholars is crucial to establishing the processes that determined their formation (see, e.g., [8,17,21,92,93]). While the intrinsically interdisciplinary nature of such a field of research is strongly emerging, it is necessary to ensure that disciplinary differences do not hinder interdisciplinary research efforts (Sections 1 and 2).…”