Palaeostress records in Cretaceous formations in NW Europe: extensional and strike–slip events in relationships with Cretaceous–Tertiary inversion tectonics

Abstract

The Chalk formations in NW Europe have been investigated in terms of brittle tectonics and palaeostress analysis. Studies of mesofaults and joints reveal that extension has prevailed since the Cretaceous. The palaeostresses recorded in the Chalk formations of the Isle of Wight, Sussex, Kent, Boulonnais, the Mons Basin and NE Belgium are characterised by an extensional regime interrupted periodically by compressional events related to regional inversions. Four principal extensional events have been distinguished. The early synsedimentary Cretaceous extensional event is present in the whole studied domain. It is related to basin subsidence. The E–W and N–S extension regimes are related to the opening dynamics of the English Channel and the North Sea. The younger NE–SW extension is the most important system of faults, in terms of amount and extent. It is active since the Late Cretaceous and related to recent tectonics. In Boulonnais and the Mons Basin, strike–slip events are related to right-lateral motion on the regional crustal-scale North Artois Shear Zone (NASZ). In Boulonnais and Kent, strike–slip events are Cenomanian in age (the so-called Subhercynian phase). In the Mons Basin and NE Belgium, Early Maastrichtian compressional events are related to the Laramide inversion phase. In Sussex and the Isle of Wight, faulting is principally related to Tertiary (Eocene–Oligocene) inversion. A strike–slip system in N–S compression is dominant in Sussex. Successive strike–slip fault and reverse fault system have been identified in the Isle of Wight flexure. The palaeostress field evolution in NW Europe recorded in Chalk formations is complex but representative of a relay zone between the Atlantic opening and the Tethysian dynamics, where compressional events along crustal regional structures periodically interrupted a regional extensional regime.