Évolution sédimentaire cénozoïque (Paléocène à Pléistocène inférieur) de la Normandie

Abstract

In the NW Normandy, only the Cotentin peninsula has preserved record of a thick Cenozoic sedimentary series (about 280 m) covered partially by Holocene sediments. As late as the Eocene, the Cotentin basin was open toward the Atlantic Ocean and separated from it by Paleozoic rocky shoals which controlled the tidal currents. During the Cenozoic times, it was a bay or a tidal estuary between the North and the South Cotentin reliefs. The Cenozoic sedimentary series may be explained by the high eustatic sea-levels due to repetitive transgressions of Atlantic Ocean over the Armorican massif (Middle Lutetian to Bartonian; Lower Oligocene; Middle Miocene; Plio-Pleistocene) which transported shelly sands and gravels (faluns) or tidal quartzose sands. The Cenozoic sedimentary series are also characterized by few sedimentary gaps (Paleocene, Lower to Middle Eocene, Middle to Upper Oligocene, Lower to Upper Miocene, Lower Pliocene) which may be due to deformations, uplifts and erosions. The repetitive Atlantic transgressions over the Armorican massif were extended through the Channel basin to the present-day Seine valley and finally to the Paris basin. These repeated transgressions can account for the presence of shelly or quartzose marine sands in the Seine valley of which few were eroded or remained during the Plio-Pleistocene times. At the same times, the paleo-Seine river drained the North margin of the Massif Central, transported and deposited the fluvial coarse-grained sands in this gateway between the Pliocene and the Lower Pleistocene.