Near-surface Palaeocene fluid flow, mineralisation and faulting at Flamborough Head, UK: new field observations and U–Pb calcite dating constraints

Abstract

Abstract. We present new field observations from Selwicks Bay, NE England, an exposure of the Flamborough Head Fault Zone (FHFZ). We combine these with U–Pb geochronology of syn- to post-tectonic calcite mineralisation to provide absolute constraints on the timing of deformation. The extensional frontal fault zone, located within the FHFZ, was active at ca. 63 Ma, with protracted fluid activity occurring as late as ca. 55 Ma. Other dated tensile fractures overlap this time frame and also cross-cut earlier formed fold structures, providing a lower bracket for the timing of folding and compressional deformation. The frontal fault zone acted as a conduit for voluminous fluid flow, linking deeper sedimentary units to the shallow subsurface, potentially hosting open voids at depth for a significant period of time, and exhibiting a protracted history of fracturing and fluid flow over several million years. Such fault-hosted fluid pathways are important considerations in understanding chalk reservoirs and utilisation of the subsurface for exploration, extraction and storage of raw and waste materials. Most structures at Selwicks Bay may have formed in a deformation history that is simpler than previously interpreted, with a protracted phase of extensional and strike-slip motion along the FHFZ. The timing of this deformation overlaps that of the nearby Cleveland Dyke intrusion and of regional uplift in NW Britain, opening the possibility that extensional deformation and hydrothermal mineralisation at Selwicks Bay are linked to these regional and far-field processes during the Palaeocene.