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Evolution géomorphologique du littoral granitique sud-armoricain : approche terre-mer

Abstract : The granitic rocky coast evolution, in passive margin context, is still not completely understood as its evolution is lower. The aim of the South-Finistère shore zone studying is to better understand its development and erosive dynamic on a time scale ranging between Cenozoic and Quaternary. A detailed onshore/offshore mapping has been realized, highlighting several erosional features. From land seaward, a rasa (≈15m-high), a marine terrace (≈7m-high), a shore platform (0-5 m-high) and a rocky marine platform (-70 à 0m) have been emphasized. These objects evidence temporal variations in the response of the tectonic or eustatic processes. The 3D architecture of rocky marine platform demonstrates a highly fractured domain with major faults bounding several micro-blocks, reactivated between the Eocene (Pyrenean compression) and Late / Post-Oligocene (Rhine continental transform zone activation). The quantitative geomorphology applied on the western part of studying zone reveals none late-Cenozoic uplift. Consequently, the rasa and marine terrace have been shaped during a high paleo-sea level. The granitic surface’s erosion produces horizontal joint planes, as a result of weathering processes. The combination between planar and horizontal granitic jointing and the marine eustatic purge explains the large width of granitic eroded surfaces.Two eustatic purges (MIS 5 and Holocene) have been shaped the granitic shore zone and the vertical erosion, rate obtained for various lateritic horizon in onshore and shore domains, is ranging between 3.35 ±0.32 m.Ma-1 and 6.20 ± 0.80 m.Ma-1.
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  • HAL Id : tel-01703380, version 1

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Céline Raimbault. Evolution géomorphologique du littoral granitique sud-armoricain : approche terre-mer. Géomorphologie. Normandie Université, 2017. Français. ⟨NNT : 2017NORMLH19⟩. ⟨tel-01703380⟩

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