21 Jul 2020

21 Jul 2020

Review status: a revised version of this preprint is currently under review for the journal ESurf.

OSL rock surface exposure dating as a novel approach for reconstructing transport histories of coastal boulders over decadal to centennial timescales

Dominik Brill1, Simon Matthias May1, Nadia Mhammdi2, Georgina King3, Christoph Burow1, Dennis Wolf1, Anja Zander1, Benjamin Lehmann4, and Helmut Brückner1 Dominik Brill et al.
  • 1Institute of Geography, University of Cologne, Köln, Germany
  • 2Institut Scientifique, Laboratory LGRN and GEOPAC Research Center, UniversitéMohammed V, Rabat, Rabat, Morocco
  • 3Institute for Geology, University of Lausanne, Switzerland
  • 4Centro de Estudios Avanzados en Zonas Áridas (CEAZA), ULS-Campus Andrés Bello, Raúl Britán 1305, La Serena, Chile

Abstract. Wave-transported boulders represent important records of storm and tsunami impact over geological timescales. Their use for hazard assessment requires chronological information 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 transport ages of wave-emplaced coastal boulders. The approach was applied to 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 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 0.06–0.2 mm/year. 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 moved by storm waves; (ii) these storms lifted boulders with masses of up to ~ 40 t; and (iii) the role of storms for the formation of boulder deposits along the Rabat coast is much 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, older formation histories and less susceptibility to erosion.

Dominik Brill et al.

Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

Dominik Brill et al.

Data sets

OSL rock surface exposure dating data for wave-emplaced boulders from the Rabat coast (Morocco) Brill, Dominik, May, Simon Matthias, Mhammdi, Nadia, King, Georgina, Burow, Christoph, Wolf, Dennis, Zander, Anja, Lehmann, Benjamin, and Brückner, Helmut

Dominik Brill et al.


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Short summary
Wave-transported boulders are important records for storm and tsunami impact over geological timescales. Their use for hazard assessment requires chronological information. We investigated the potential of a new dating technique, luminescence rock surface exposure dating, for estimating transport ages of wave-emplaced boulders. Our results show that the new approach may provide chronological information over decadal to millennial timescales for boulders not datable by any other method so far.