A late Cenozoic regional mesofracture system in southern England and northern France

Abstract

The Upper Cretaceous and Palaeogene rocks of S England and N France are cut by a NW-trending system of fractures, characterized by swarms of vertical extension joints accompanied by conjugate sets of hybrid and shear joints, and normal mesofaults. Many major photolineaments exhibit the same NW trend as the fractures, and are particularly conspicuous in N France where they are coincident with rectilinear drainage channels, suggesting a relationship between fracture orientation and physiography. In S England, this relationship is absent; possibly because of the influence of additional fracture systems related to major flexures trending obliquely to the NW-SE direction. These major E-W trending flexures and associated fracture systems were formed during the Oligocene to Early Miocene 'Helvetic' phase of deformation, and are cross-cut obliquely by fractures in the NW-trending system. The NW-trending fractures and lineaments are parallel to neotectonic normal faults in the Lower Rhine embayment, and become less well developed to the west with increasing distance from these major structures. The Lower Rhine faults were reactivated and propagated into the Quaternary cover as a consequence of NE-SW regional tension generated during the late Neogene to Recent 'Jura' phase of NW-SE Alpine convergence. The NW-trending extensional structures in S England and N France are considered to be of about the same age and related to the same stress regime as the neotectonic normal faults of the Lower Rhine embayment. However, because fractures of the NW-system cutting Palaeogene sediments in SE England are truncated by the erosion surface beneath the Plio-Pleistocene Red Crag deposits, it is possible that in England fracture initiation did not continue into Quaternary times.

The spatial distribution of groundwater flooding in a chalk catchment in southern England

“…The valley of the Pang between East Ilsley and Compton is parallel to the line of the valley of the river Lambourn, suggesting that it is likely to have a structural control. This suggests that the dominant structural line is west-northwest and there is a secondary line normal to this, north-northeast, which is in general agreement with previous work (Bevan and Hancock, 1986). The major increases in the flow of the Pang at Hampstead Norreys and about 1Ð5 km upstream coincide with intersections of the main valley with north-northeast-trending side valleys.…”

Active tectonics, seismicity and geomorphology with special reference to Normandy (France)

“…8). This orientation is consistent with the Alpine compression, as envisaged previously (Bevan and Hancock, 1986;Nicolas et al, 1990). 2.…”

“…The post-Variscan history of Normandy can be summarized as follows: (i) Late Variscan planation, (ii) early Jurassic (limestones) to Cretaceous (chalk) marine deposits (Rioult et al, 1991), (iii) uplift of western and central Normandy during the early Tertiary, with formation of erosion surfaces and weathering of Mesozoic limestones giving rise to layers of clay-with-flints, (iv) lower Tertiary marine transgression in the Paris Basin and eastern Normandy, (v) extensive marine regression during the late Pliocene, and (vi) incision of the erosion surfaces and drainage network development during the Quaternary (Gibbard, 1988). The structural context involves (i) post-Variscan extensional strain that probably lasted throughout the Permian and Mesozoic, (ii) tectonic inversion in the Oligocene and (iii) weak compressional strain during the Quaternary (Bevan and Hancock, 1986;Gö lke and Coblentz, 1996).…”

The formation of the hot springs at Bath Spa, UK

“…The region was extensively deformed during the Variscan Orogeny with the result that there are numerous major thrusts and faults within the basin (Kellaway & Welch, 1993). Many of the faults in the region were repeatedly reactivated throughout the Mesozoic, and deformation probably continued until the Miocene (Kellaway & Welch 1948;Bevan & Hancock 1986). …”