Seismic stratigraphy of the Vendean-Armorican platform of the French Atlantic shelf: new insights into the history of the North Atlantic ocean

Abstract

The evolution of the North-Atlantic Ocean from its rifting stage during the Upper Jurassic until the present-day passive margin is recorded by the sedimentary wedge of eastern French-Atlantic platform. The study of a dense network of high resolution seismic profiles on the Vendean-Armorican platform (VAP) obtained during INSU-CNRS cruise "Geovend", led to the characterization of the architecture of the sediment wedge preserved between the coast and Armorican margin shelf edge. This sediment wedge lies on a substratum composed of metamorphic and magmatic rocks of Palaeozoic age (Ub). The sediment wedge comprises six seismic units (U1-U6) bounded by regional unconformities: Jurassic marine succession (U1), Upper Cretaceous marine rocks (U2), Eocene-Oligocene marine deposits of the incipient VAP (U3), Miocene (U4) and Plio-Quaternary (U5) marine deposits overlain by the last sea-level rise ravinement deposits (U6). Above the basal unconformity at the top of Ub, the units are bounded by angular unconformities (top of U1, U2, U3), truncation with channel incision (top U4) or planar marine ravinement (top of U5) surfaces.Most of these unconformities are due to the tectonic activity of the bay of Biscay during the Mesozoic including (1) the North Atlantic rifting during the Jurassic to Early Cretaceous, (2) the propagation of the ocean crust and counterclockwise rotation of the Iberian block during the Aptian-Albian to Coniacian (magnetic anomaly 33-34) producing troughs at the top of U1 filled by downlapping U2 sediment wedges, (3) the Alpine compression at the origin of folding and faulting and the unconformable deposition of U3, and (4) the late compressive deformation during the Miocene that affected U4. The VAP acquires its actual configuration during U4. Sedimentation on the platform was then affected by climatically-controlled relative sea-level changes (U5 to U6) that forced U5 shelf margin sediment deposition above an incised unconformity and subsequently overlain by U6 transgressive sediment blanketing.One of the main interest of the VAP area is the existence of pre-to post-rift units that helps to decipher with high resolution seismics the long-lived evolution of the Armorican margin. Such units are preserved because of the specific characters of this area located on the flank of the former Aquitaine basin (near the "celtaquitaine" flexure) and the presence of the Rochebonne basement high.The VAP thus displays most of the tectonosedimentary evolution of the West Atlantic margins. This paper would however constitute a basis for comparisons to other examples around the Atlantic ocean and then contribute to strengthen the running models of passive margin evolution. Stratigraphie sismique du plateau continental atlantique français (partie vendéo-armoricaine) : un nouvel aperçu de l'histoire de l'océan Atlantique NordMots-clés. -Vendée, Plate-forme aquitaine, Stratigraphie, Sédimentologie, Vallées fluviatiles, Activité tectonique Résumé. -L'évolution de l'océan Atlantique nord depuis son ouverture initiale au Jura...

Is the Machecoul fault the source of the ∼M6 1799 Vendée earthquake (France)?

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“…Lithologic and chronostratigraphic attributions of seismic units are based on previous studies of the south-armorican platform (e.g. Delanoë et al 1976;Menier 2004;Huerta et al 2010;Proust et al 2010). They are mostly speculative because they could not be complemented by appropriate in situ drilling.…”

New perspectives in studying active faults in metropolitan France: the “Active faults France” (FACT/ATS) research axis from the Resif-Epos consortium

“…Lithologic and chronostratigraphic attributions of seismic units are based on the acoustic facies variability defined in previous studies of the South-Armorican platform [e.g. Delanoë et al, 1976, Menier, 2004, Huerta et al, 2010 to infer the Neogene to Quaternary sediment thickness. To extend the sediment infilling data set and to better constrain the basin geometry onshore along the whole Machecoul Fault, gravity data from the Bureau Gravimétrique Interna-tional (BGI) 1 were used (data available at http://bgi.…”

Brittle tectonics and fluids overpressure during the early stage of the Bay of Biscay opening in the Jard-sur-Mer area, (northern Aquitaine Basin, France)

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“…1). Faulting is therefore inherited from latest Jurassic transtensional and/or from latest Aptian-earliest Albian crustal thinning (Huerta et al, 2010).…”