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| Titel |
Onshore-offshore morpho-structural pattern of coastal rocky shore in SW Brittany (France): polyphased generation of rocky, shore and exhumed platforms. |
| VerfasserIn |
Céline Raimbault, Anne Duperret, Bernard Le Gall, Robert Wyns, Vincent Regard, Christine Authemayou, Stephane Molliex |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250138340
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| Publikation (Nr.) |
 EGU/EGU2017-1321.pdf |
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| Zusammenfassung |
| A large granitic submarine and shore platform has been mapped in Western Brittany on 580 km² surfaces with the aid of several high-resolution (<1 m) aerial and marine surveys: topographic and bathymetric LiDAR using Litto3D project (SHOM, IGN, IFREMER) mixed with marine interferometric echosounding sonar (R/V Haliotis) and low depth multibeam echosondeur with high resolution seismic reflection profiles (R/V Thalia). The structural and geomorphological study of this rocky platform allows understanding its formation on time scale between Paleocene to Quaternary.
The marine rocky platform is composed of: (1) a tidal part (shore platform) with a very slight seaward mean slope and a maximal width of about 800 m, (2) a > 5 km-wide and weakly dipping subtidal part, labelled the rocky platform, (3) a rocky external part with varying mean slopes, rocky reefs and sedimentary deposits, corresponding to the continental shelf. The coastal continental domain is characterized by a low elevated (<10 m-high) and severely eroded area, ranging in width between 200 m to about 4 km, and referred to as marine terrace. Its continentward transition with granitic outcrops coincides with a 10 m-high scarp, assumed to represent a paleo-shoreline, hence allowing regarding the marine terrace as a presently exhumed paleo-shore platform.
In order to estimate the timing of the denudation process recorded by the rocky platform during Quaternary, 10Be cosmogenic nucleides analyses were performed on submarine and offshore granitic samples. On the basis of 10Be contents, the conceptual evolutionary model applied to the rocky platform implies a polyphased history controlled by continental granitic weathering and high-stand sea level marine erosion. The present-day coastal morphology may be explained by the action of two highstand sea levels since mid-Pleistocene at least, favoring successive eustatic purges of previously weathered granitic rocks. Exposure ages deduced from 10Be content may be considered as minimum age in the aerial part of the platform (marine terrace), with a rocky platform formation near 166 ± 18 kyrs. Whereas the submarine part of the platform may be considered as inherited, recording several exhumations, with a maximum exposure age of 30.5 ± 3.5 kyrs, acquired during the beginning Last Glacial Maximum on a previously cleaned surface. |
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