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Note relative à deux grabens tertiaires de Bretagne : graben de Plessala (Côte-du-Nord) et graben de Messac (Ille-et-Vilaine)

Authors
Journal
Norois
0029-182X
Publisher
PERSEE Program
Publication Date
Volume
79
Issue
1
Identifiers
DOI: 10.3406/noroi.1973.3305
Disciplines
  • Earth Science
  • Geography

Abstract

SUMMARY The Plessala depression, which gashes the jumbled relief of the Mené, in the , department ' of Côtes du Nord, and the Messac depression, in the Silurian zone of Appalachian relief which lies to the south of the Rennes basin, are two subsidence trenches which cannot be explained other than by tectonic changes in the tertiary era. Here, morphological arguments can be of great help to anyone wanting to give an account of these hollowed-out shapes which have few links with liihology and ancient tectonic changes. But each of these two trenches has a distinctive character : they open out at different altitudes, into different structures, and evolution in the post-Miocene era was more complicated in the Messac trench than in that of Plessala. An examination of the hydrographie network also provides interesting data for the study of this evolution, and suggests that, in the region crossed by the Vilaine valley, tectonic deformations went on right up to the Pliocene era and even after it.

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