Palaeostress analysis and geodynamical implications of CretaceousTertiary faulting in Kent and Boulonnais

Abstract: Detailed studies of fracture patterns and palaeostress reconstruction based on fault slip data analysis allow identification of five main palaeostress fields in the Cretaceous formations of the Boulonnais and Kent areas. These stress patterns correspond to six successive tectonic events: (1) a N-S compression/E-W extension of early Cenomanian age, (2) an E-W extension of late Cenoma-nian age, and (3) four post-Santonian events with N-S, E-W, NW-SE and NE-SW extensions, respectively. The first event, interpreted from conjugate strike-slip faults is related to the beginning of the Sub-Hercynian phase and linked to a right-lateral motion of the Nord-Artois Shear Zone. The first E-W extensional event and the N-S extensional event could be related to the last rifting episodes of the North Sea graben and English Channel (Wessex basin). The others post-Santonian extensional events are related to Late Cretaceous, Tertiary and Recent tectonic episodes. The purpose of this study is to describe and interpret in terms of palaeostress tensors the different fault systems that affect Upper Cretaceous formations in the Boulonnais and Kent areas. The palaeostresses deduced in this way are discussed in the tectonic framework of Northwest Europe