Middle Pleistocene raised beach anomalies in the English Channel: regional and global stratigraphic implications - Archive ouverte HAL
Article Dans Une Revue Journal of Geodynamics Année : 2000

Middle Pleistocene raised beach anomalies in the English Channel: regional and global stratigraphic implications

Résumé

Palaeo-shore positions help to evidence long-term eustatic changes and assist in the understanding of tectonic movements at a regional scale. Raised beaches anomalies exist in the Channel region and may result from deformations induced by neotectonic or by glacio-isostasy. The aim of this paper is to re-analyse, within their geodynamic context in the Channel and Dover Strait regions, the stratigraphy and the datings of palaeo-shores of Middle and Upper Pleistocene ages. This sector of Europe is characterised by strong geological contrasts and is controlled by two main geological boundaries: in the north, the Variscan Overthrust (corresponding approximately to the position of the Dover Strait) and, in the south, the Northern Branch of the Southern Brittany shearing zone. These two boundaries border a domain which seems to behave rather homogeneously on a large scale under the control of plate tectonics. Today, shorelines are subsiding north and south of this ‘Channel’ region. Episodic uplift largely controlled the open or closed status of the Dover Strait, especially after the Messinian and Early Quaternary, by reactivating Variscan structures. After 400 ka, global cooling allowed supplementary deformations in the area to be induced by glacio-isostatic rebound and clustered seismic activity during the phase of ice sheet building. Evidence of eight different transgressions dated by ESR from Oxygen Isotopic Stage (OIS) 13 to the end of OIS 5 shows the complexity of the sea-level records in a region unstable for isostatic and neotectonic reasons. Due to glacio-isostatic depression, transgressions are possible in late glacial times as well as during full interglacials. Most platforms were initially cut, during the Late Miocene, and seem to have been re-trimmed several times, especially by shore ice rafting since OIS 9. Regionally, the sea apparently rose to about the same level in O.I. Stages 11, 9 and 7. Glacio-isostatic and glacio-eustatic relative displacements of the sea level together with background tectonic movements have modified coastal positions and have temporarily altered the intensity of tidal currents. The oldest shoreline deposits are preserved only in subsiding areas, controlled by the deep crustal pattern. Neotectonics related to Variscan structure reactivation still dominates glacio-isostatic deformation and basin subsidence. The OIS 7 positive anomaly seems related to a regional relaxation event.

Dates et versions

hal-04718336 , version 1 (02-10-2024)

Identifiants

Citer

Brigitte van Vliet-Lanoë, Michel Laurent, Jean-Jacques Bahain, Sanda Balescu, Christophe Falguères, et al.. Middle Pleistocene raised beach anomalies in the English Channel: regional and global stratigraphic implications. Journal of Geodynamics, 2000, 29 (1-2), pp.15-41. ⟨10.1016/S0264-3707(99)00063-0⟩. ⟨hal-04718336⟩
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