Middle Pleistocene seismically induced clay diapirism in an intraplate zone, western Brittany, France
|Author(s)||Van Vliet-Lanoe Brigitte1, Authemayou Christine1, Molliex Stephane1, Field Michael Hugh2, Frechen Manfred3, Le Roy Pascal1, Perrot Julie1, Andrieu-Ponel Valerie4, Gregoire Gwendoline1, Hallegouet Bernard5|
|Affiliation(s)||1 : IUEM, CNRS, UBO, UMR Geosci Ocean 6538, Pl N Copernic, F-29280 Plouzane, France.
2 : Leiden Univ, Fac Archaeol, Archaeo & Palaeobot Lab, POB 9515, NL-2300 RA Leiden, Netherlands.
3 : Leibniz Inst Angew Geophys, Stilleweg 2, D-30655 Hannover, Germany.
4 : Avignon Univ, Aix Marseille Univ, CNRS, IRD,IMBE, Technopole Arbois Mediterranee,BP 80, F-13545 Aix En Provence, France.
5 : UBO, Geog Dept, 40 Rue Commandant Boennec, F-29490 Guipavas, France.
|Source||Quaternary Research (0033-5894) (Cambridge Univ Press), 2019-01 , Vol. 91 , N. 1 , P. 301-324|
|Keyword(s)||Clay diapirism, Liquefaction, Earthquake, Saprolite, Brittany, Variscan structures, Paleoseismology, Intraplate, Middle Pleistocene|
The Brittany region of France is located in a low seismicity intraplate zone. Most of the instrumented earthquakes are limited to a shallow crustal depth without surface rupture. A paleoseismological analysis was performed on deposits on the Crozon Peninsula and in the Elorn estuary. We highlight hydroplastic deformations induced by liquefaction leading to clay diapirism, which were likely triggered by past earthquakes. This diapirism seems to be frequent in continental nonconsolidated sediments and to develop on the inherited tectonic structures, when a shallow water table and confining layers exist. Timing of deformation is dated using paleoenvironmental data, and electron spin resonance and infrared-stimulated luminescence dating methods. Two seismic periods were identified in western Europe during early Marine Oxygen Isotope Stage (MIS) 10 (380 ka) and early MIS 8 (280-265 ka). The lack of similar deformations affecting the Holocene tidal deposits in the Bay of Brest suggests that the magnitude of the triggering paleoearthquakes is probably higher (M-w 6) than the recent events (M-w 5.4). These unusual intraplate major paleoearthquakes need specific factors affecting the far-field crustal stress loading to be triggered, such as a brief acceleration of the Africa-Eurasia lithospheric plate convergence, glacio-isostatic stress perturbations associated with the onset of major glaciations in northern Europe, or other processes induced by orbital forcing.