Coastal chalk cliff retreat rates during the Holocene, inferred from submarine platform morphology and cosmogenic exposure along the Normandy coast (NW France)

Type Article
Date 2021-03
Language English
Author(s) Duguet Timothée1, Duperret Anne1, Costa Stéphane2, Regard Vincent3, Maillet Grégoire4
Affiliation(s) 1 : Normandie Université, UMR 6294 LOMC, CNRS, UNILEHAVRE, 53 rue de Prony, Le Havre 76600, France
2 : Normandie Université, UMR 6554 LETG-Caen, CNRS, UNICAEN, Esplanade de la Paix, Caen 14032, France
3 : Université de Toulouse, GET, CNRS, IRD, UPS, CNES, 14 Av. Edouard Belin, Toulouse 31400, France
4 : UMR 6112 LPG-Angers, CNRS, Université d’Angers, 2 boulevard Lavoisier, Angers 49000, France
Source Marine Geology (0025-3227) (Elsevier), 2021-03 , Vol. 433 , P. 106405 (23p.)
DOI 10.1016/j.margeo.2020.106405
WOS© Times Cited 11
Keyword(s) Coastal cliffs, Chalk, Erosion, Rock platform, Holocene, Cosmogenic dating
Abstract

Submerged marine terraces potentially provide crucial information on past sea-level variations and paleo-coastline locations that may be used to estimate long-term coastal erosion rates. The Normandy coastline has recently been surveyed using a shallow water high-resolution mapping system. We identified a new continuous submarine platform, called the inner platform, limited by a shore parallel edge located between -9 m and -10 m (NGF) along the Normandy chalk coastline. A lower rock platform, called the outer platform, ranging from about -14 m to -17 m (NGF) appears locally. This corresponds to inherited preserved submarine terraces created during a past sea level highstand. The high cosmogenic 10Be concentration measured at the end of Mesnil-Val inner shore platform (including intertidal and subtidal shore platforms) is attributed to the last glacial cliff location at 6.5 ky ± 1 ky. From the spatial edge location of the inner platform in Normandy, we estimated cliff retreat rates since 6.5 ky ± 1 ky ranging from 0.051 ± 0.008 m/y to 0.090 ± 0.014 m/y from place to place. Comparisons with the current coastal chalk cliffs indicate a mean retreat rate estimated over the contemporary period suggesting such long-term retreat rates are 33% to 57% lower than the contemporary ones (0.10 m/y to 0.18 m/y). This confirms a contemporary acceleration of chalk cliff system retreat rates.

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Duguet Timothée, Duperret Anne, Costa Stéphane, Regard Vincent, Maillet Grégoire (2021). Coastal chalk cliff retreat rates during the Holocene, inferred from submarine platform morphology and cosmogenic exposure along the Normandy coast (NW France). Marine Geology, 433, 106405 (23p.). Publisher's official version : https://doi.org/10.1016/j.margeo.2020.106405 , Open Access version : https://archimer.ifremer.fr/doc/00665/77687/