# Dating of Quaternary deposits on the Coast of Brittany (W France) by Optically Stimulated Luminescence and Terrestrial Cosmogenic Nuclides: Preliminary results of the cronBRET Project

Carlos Arce Chamorro, Benjamin Sautter, Guillaume Guérin, Pierre Dietrich, Steven Binnie, Tibor Dunai, François Guillocheau, David Menier

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Carlos Arce Chamorro, Benjamin Sautter, Guillaume Guérin, Pierre Dietrich, Steven Binnie, et al. Dating of Quaternary deposits on the Coast of Brittany (W France) by Optically Stimulated Luminescence and Terrestrial Cosmogenic Nuclides: Preliminary results of the cronBRET Project. 29 ème édition de la réunion des sciences de la Terre (RST 2025), Société Géologique de France (SGF), Oct 2025, Montpellier, France. pp.646794. insu-05350352

HAL Id: insu-05350352

https://insu.hal.science/insu-05350352v1

Submitted on 6 Nov 2025

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# Dating of Quaternary deposits on the Coast of Brittany (W France) by Optically Stimulated Luminescence and Terrestrial Cosmogenic Nuclides: Preliminary results of the cronBRET Project.

Arce Chamorro Carlos*<fnref n="1" />,<fnref n="2" />,<fnref n="3" />, Benjamin Sautter<fnref n="4" />, Guillaume Guérin<fnref n="5" />, Pierre Dietrich<fnref n="6" />, Steven Binnie<fnref n="7" />, Tibor Dunai<fnref n="7" />, François Guillocheau<fnref n="2" />, and David Menier<fnref n="4" />

## Résumé

The Quaternary record along the Coast of Brittany (W France) is well represented, offering important information about the geomorphological processes that have shaped this coast during this period. However, chronological data using numerical dating methods are very scarce leading to uncertain hypotheses put forward on the basis of correlations and extrapolations. Thanks to the cronBRET Project (MSCA-Bienvenüe Bretagne COFUND 2023) from the Geo-Ocean Lab of the Université de Bretagne Sud and the RenDaL laboratory of Géosciences-Rennes (Univ. Renes), in collaboration with the Cosmogenic Laboratory of the Institute of Geology and Mineralogy of the University of Cologne (Germany) and the Institute of Geology of the University of Coruña (Spain), numerous sedimentary outcrops along the Bretagne Coast are currently dated. For the burial age calculation, the optically stimulated luminescence (OSL) signal of quartz sands included in the sedimentary matrix is analyzed, as well as the concentration of 10Be and 26Al produced *in situ*, as a consequence of cosmic-ray interaction with quartzite cobbles, by using the isochron method. The first results include those obtained in the Falaisse de La Mine D'Or at Pénestin (SE Brittany), with a lower unit dated at 2.7 My (Plio-Quaternary boundary). The upper unit has been dated by OSL between 410 and 260 ky (Middle Pleistocene). As for the coastal deposits dated in Morbihan (ie, Betahon, Rhuys, Ploemeur), ages between 265 and 125 ky have been obtained. These data will be complemented with the dating of several sedimentary deposits from Brittany's West Coast (Finisterre) and North Coast (Côtes d'Armor) to achieve a comprehensive analysis at regional scale. This study highlights the importance of numerical

<footnote n="1">¹Laboratoire Gésociences Océan UMR 6538 - UBS - UBO – Université de Bretagne Sud [UBS] – France</footnote>

<footnote n="2">²Géosciences-Rennes, UMR6118, Université de Rennes 1, 35042 Rennes Cedex, France – Univ Rennes - CNRS, UMR 6118 – France</footnote>

<footnote n="3">³Instituto Universitario de Geología Universidade da Coruña – Espagne</footnote>

<footnote n="4">⁴Laboratoire Géosciences Océan UMR 6538 – CNRS -UBS - UBO – CNRS : UMR6538 – France</footnote>

<footnote n="5">⁵Géosciences-Rennes, UMR6118, Université de Rennes 1, 35042 Rennes Cedex, France – Géosciences Rennes UMR6118 – France</footnote>

<footnote n="6">⁶Géosciences-Rennes, UMR6118, Université de Rennes 1, 35042 Rennes Cedex, France – CNRS : UMR6118 – France</footnote>

<footnote n="7">⁷Institute of Geology and Mineralogy, University of Cologne – Allemagne</footnote>

<footnote>*Intervenant</footnote>
dating as an essential tool to constrain the formation of coastal sediments within a more
accurate paleoclimatic framework and integrate them in the glacioeustatic and neotectonic
processes linked to the Glacial-Interglacial cycles of the Quaternary, and more specifically
during the last 500,000 years.

**Mots-Clés:** Coastal sediments, OSL dating, TCN dating, Pleistocene, Brittany, W France.