Problems of Pleistocene and Holocene Sea Level Shifts in Western Brittany, with References to Other Sites in the Armorican Massif and the Southwestern British Isles

Zusammenfassung

Recent research has shown that the sea has invaded the western part of Brittany more than one time during the Tertiary. In the Aber Ildut valley near Brest (Hallegouet et al. 1976; Guilcher and Hallegouet 1987) Oligocene marine deposits are recorded, showing that, already at that time, valleys 60 m deep had been cut by fluviatile erosion into the flat plateau, thus levelling the country, and subsequently converting into marine rias. Possibly during the Pliocene, the sea built up a pebble and sand beach at the present altitude of 125–130m at Menez Lus in the Crozon Peninsula (Guilcher and Saint-Requier 1969), and probably rose even higher in Western Brittany (Fig. 1). A better dated deposit lies at 15 m altitude in the Elorn valley at Lanrinou near Landerneau (Hallegouet 1982; Morzadec-Kerfourn 1982), belonging to the Reuverian-Pretiglian (Upper Pliocene), and was followed, after a regression, by two other marine sequences at 22 and 26 m during the Lower Pleistocene (Tiglian) and Middle Pleistocene. These three transgressions had changed into a ria, the Elorn valley, previously cut into plateau as the Aber Ildut during the Oligocene. These events are recorded as an introduction to the Pleistocene sea level shifts.