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CENOZOIC DEFORMATION TIMING AND REGIME OF THE ARMORICAN MASSIF (WESTERN FRANCE): NEW INSIGHTS FROM A REPROCESSED HIGH RESOLUTION SEISMIC PROFILE (RENNES BASIN)

Abstract : The Armorican Massif is one of numerous Variscan basement blocks of Western Europe characterized by low to moderate elevation plateaus (e.g. Massif Central, Rhenish Massif) which have experienced several episodes of burial and exhumation in the Mesozoic and/or Cenozoic. This massif was twice buried then exhumed between Jurassic and Paleocene times in response to relative movements between Iberia and Eurasia. However, as other western European shields, its Paleogene to Neogene deformation history is still poorly constrained despite the presence of numerous Cenozoic (Ypresian to Piacenzian; 56-2.6 Ma) lacustrine to shallow marine deposits scattered upon it. Some of these deposits, mainly the Bartonian to Rupelian (41-28 Ma) ones, are preserved in small narrow grabens bounded by N140E faults. The Rennes Basin, a 2 to 4 km width for 400 m depth basin, is the largest and well-documented one with: i) a well-dated borehole which cross the whole Bartonian to Piacenzian series and reach the underlying basement (CDB1 Borehole, CINERGY Project, 2010); ii) a 5-km long high resolution seismic reflection profile which cut across the basin (HR1 profile, GeoFrance 3D program, 2000 – reprocessed in 2012). Here, we investigate this reprocessed seismic profile to bring new constraints about the Cenozoic deformation history of the Armoricain Massif. We converted the CDB1 borehole into seismic velocity and some shallow seismic reflectors in depth in order to date these reflectors then correlate seismic facies together with sedimentary facies of CDB1 and 58 neighboring shallow boreholes (50 m max.) from the French borehole database (BSS, via Infoterre). We show that Bartonian to lowermost Rupelian (41-33 Ma) series, which are affected by slight synsedimentary deformation, are gently bended and collapsed between two hidden highly dipping reverse faults. These faults are subsequently sealed by Lower Rupelian tabular and sparsely faulted deposits. Outcropping Late Langhian to Serravallian (15-11.6 Ma) crags (“faluns”) rest on and overflow these deposits above an angular unconformity (Upper Oligocene – Lower Miocene gap). They are affected by superficial normal faults gently dipping toward the pre-existing weathered basement. The sedimentary succession ends with Pliocene fluvial to estuarine deposits which overlain a second unconformity. Together with field observations, our results argue for Priabonian (?) to Early Rupelian transtensional to transpressional deformations associated with strike-slip movements along the N140E faults related to a NS tectonic stress. These deformations can be integrated within the Western European tectonic framework. They are likely to be related to the growth of numerous small sedimentary basins during Oligocene to middle Miocene times (ca. 35 – 10 Ma) along the western side of the British Isles (e.g. Cornwall) in a largely strikeslip regime, which led to local basin inversions. They also coeval with Oligocene (Eocene?) to Miocene shortwavelength deformation observed in surrounding basins and on the northwestern European platform that includes strike-slip to compressive folding (South Armorican Margin), major basin inversion (Western Approaches Basin) and NNE-SSW striking left-lateral transtensional wrenching of the European Cenozoic Rift System.
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https://hal-insu.archives-ouvertes.fr/insu-01717996
Contributor : Isabelle Dubigeon <>
Submitted on : Tuesday, February 27, 2018 - 8:40:53 AM
Last modification on : Wednesday, October 14, 2020 - 4:16:55 AM

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  • HAL Id : insu-01717996, version 1

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Paul Bessin, François Guillocheau, Cécile Robin, Hugues Bauer, Jean-Michel Schrötter. CENOZOIC DEFORMATION TIMING AND REGIME OF THE ARMORICAN MASSIF (WESTERN FRANCE): NEW INSIGHTS FROM A REPROCESSED HIGH RESOLUTION SEISMIC PROFILE (RENNES BASIN). International Meeting of Sedimentology 2017, Oct 2017, Toulouse, France. pp.99. ⟨insu-01717996⟩

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