Spatial patterns of subaerial coarse clasts

Lau, A. Y. Annie; Autret, Ronan

doi:10.1016/b978-0-12-815686-5.00024-9

Cited by 3 publications

(7 citation statements)

References 150 publications

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“…The OSL surface exposure ages derived for boulders and niches from the Rabat coast show two striking characteristics: (1) all exposure ages are associated with relatively large dating uncertainties compared to previous applications of OSL-RSED (e.g. Sohbati et al, 2012;Lehmann et al, 2018); and (2) 5 of the 13 dated boulder samples yield OSL exposure ages that underestimate minimum ages deduced from satellite imagery and rock-pool depth, even when their uncertainties are considered (Fig. 6c).…”

Section: Performance Of Osl Surface Exposure Dating On Calcarenite Bomentioning

confidence: 88%

“…(1) to calibra-tion samples with known exposure ages (e.g. Sohbati et al, 2012;Lehmann et al, 2018).…”

Section: Calibration Of the Osl Rock Surface Exposure Dating Model Usmentioning

confidence: 99%

“…This indicates that samplespecific values in this study may not only be imprecise but, due to large measurement uncertainties, may also be incorrect for some samples. Since the estimation of shared µ values for several rock samples can improve the accuracy of the estimate significantly (Lehmann et al, 2018), the use of a shared µ value for all samples was chosen as a reasonable and necessary compromise. The assumption of a common µ value for all boulders targeted in this study is supported by their very similar lithology, since all of the boulders are de- rived from the same local calcarenite facies.…”

Section: Calibration Of the Osl Rock Surface Exposure Dating Model Usmentioning

confidence: 99%

“…quartzite or quartz-dominated sandstone) or stronger feldspar signals to avoid using quartz OSL for dating (e.g. granite or gneiss) can provide much higher dating precision than achieved for the Rabat boulders (Sohbati et al, 2012;Freiesleben et al, 2015;Lehmann et al, 2018;Gliganic et al, 2019).…”

Section: Performance Of Osl Surface Exposure Dating On Calcarenite Bomentioning

confidence: 99%

“…Simms et al, 2011;Sohbati et al, 2015;Jenkins et al, 2018;Rades et al, 2018) is typically impeded for coastal boulders due to logistical problems with sampling the (inaccessible) light-shielded bottom surfaces of clasts weighing several tons, the OSL rock surface exposure dating (OSL-RSED) technique introduced by Sohbati et al (2011) can be applied to the light-exposed top surfaces of such clasts. For boulders that were overturned during wavedriven cliff detachment and that experienced no subsequent overturning events as well as negligible erosion and shielding of their top surfaces after deposition on the onshore platform, post-transport exposure periods may be estimated based on the time-dependent progression of OSL signal resetting, the so-called bleaching front, into the uppermost millimetres to centimetres of the rock (Sohbati et al, 2012;Freiesleben et al, 2015;Lehmann et al, 2018;Gliganic et al, 2019). OSL-RSED is applicable to a wide spectrum of lithologies, as long as they contain quartz and/or feldspar, and to timescales of decades, centuries and up to a few millennia.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2021

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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.

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Section: Performance Of Osl Surface Exposure Dating On Calcarenite Bomentioning

confidence: 88%

“…(1) to calibra-tion samples with known exposure ages (e.g. Sohbati et al, 2012;Lehmann et al, 2018).…”

Section: Calibration Of the Osl Rock Surface Exposure Dating Model Usmentioning

confidence: 99%

Section: Calibration Of the Osl Rock Surface Exposure Dating Model Usmentioning

confidence: 99%

Section: Performance Of Osl Surface Exposure Dating On Calcarenite Bomentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2021

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The Safi boulders (South of Morocco): another evidence of the 1755 Lisbon tsunami?

Khalfaoui,

Joudar,

Chahid

et al. 2023

Preprint

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Tsunamis and storm surges are among several hazards threatening the Atlantic coast of Morocco. During the last two decades, sedimentological deposits left by these events, in the form of fine-grained sediments (washover) and boulders, have been studied along the Moroccan shores to determine the return period of these events and how they fluctuate in terms of intensity. The present work investigates two new boulder fields located along the Safi coast (south of Morocco). Field surveys were accomplished in the two areas to collect the position/elevation and dimensions of 164 boulders using a GPS/DGPS and a traditional meter, respectively. The field data was combined with hydrodynamic equations to estimate the minimum velocity and storm/tsunami wave height to move the measured boulders. In site 1, the boulders are situated on a rocky intertidal platform, while in the second, they are on the top of a cliff. For both sites, the size of the boulders ranges from 0.6 to 5.60 m, 0.54 to 3.6 m, and 0.27 to 1.5 m on the major (a), medium (b), and minor (c) axes, respectively. They reach a volume of up to 25.20 m3 and a weight of 55.44 t. The maximum distance and elevation recorded are around 41.77 m and 13 m, respectively. According to hydrodynamic equations, the coastal platform boulders (site 1) can be moved by tsunami waves with heights between 0.31 and 2.50 m, and storm waves from 1.26 to 10 m. For the cliff-top boulders (site 2), they need tsunami and storm waves with at least 7.33 and 14.33 m, respectively, to be displaced. The results from the field surveys and hydrodynamic equations suggest that both, tsunami and storm waves, are capable of moving the boulders in site 1. For the cliff top-boulders, the data favours tsunamis as a source for this deposit.

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Interplay Between Coastal Elevation and Wave Height Controls the Occurrence of Coastal Boulder Deposits in the Aran Islands, Ireland

2021

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Coastal boulder deposits (CBD) are wave-emplaced supratidal accumulations that record extreme inundation on rocky coasts. They are poorly understood but are of growing importance as we seek to better understand the extremes of wave power on coastlines. The Aran Islands, Ireland, host CBD in varying settings ranging from sheer cliff tops to wide shore platforms, and at elevations to about 40 m above sea level. Deposits are known to be active during strong storm events and provide a unique opportunity to examine relationships between wave energy, setting, and CBD occurrence. We use topographic elevation (Z) and offshore 100-years significant wave height (Hs,100) to calculate a dimensionless elevation Z* = Z/Hs,100 at 25 m intervals all along the Atlantic-facing coasts of the Aran Islands, and record whether CBD were present or absent at each location. The data reveal universal CBD presence at locations with low dimensionless elevations and near-monotonic decreasing frequency of CBD occurrence as Z* increases. On the Aran Islands, CBD are restricted to locations with Z*<3.13. For high elevation deposits it appears that unresolved local factors may be the major determinants in whether CBD will form. This approach can be applied at any CBD-bearing coastline and has the potential to change the way that we think about these deposits. Evaluation of dimensionless elevations at CBD locations around the world will help build broader understanding of the impact local shoreline conditions have on CBD formation. Determining these relationships contributes to the ongoing need to better understand interactions between extreme waves and rocky coasts.

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Spatial patterns of subaerial coarse clasts

Cited by 3 publications

References 150 publications

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

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

The Safi boulders (South of Morocco): another evidence of the 1755 Lisbon tsunami?

Interplay Between Coastal Elevation and Wave Height Controls the Occurrence of Coastal Boulder Deposits in the Aran Islands, Ireland

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