4.5 Article

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

期刊

MARINE GEOLOGY
卷 433, 期 -, 页码 -

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ELSEVIER
DOI: 10.1016/j.margeo.2020.106405

关键词

Coastal cliffs; Chalk; Erosion; Rock platform; Holocene; Cosmogenic dating

资金

  1. Le Havre Normandie Universite allocation
  2. INSU/CNRS French national program EC2CO (Ecosphere Continentale et Cotiere) -DRIL (CROCO-DYL project 2015)

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By using a shallow water high-resolution mapping system to survey the Normandy coastline, a new submarine platform has been identified, showing different levels of erosion from the past. The study estimated cliff retreat rates since 6.5 ky +/- 1 ky and found that long-term retreat rates are 33% to 57% lower than contemporary ones, confirming an acceleration of chalk cliff system retreat rates.
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 Be-10 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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