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.
Highlights
Faulting of sedimentary basin fills in the subsurface is an important process in producing structurally constrained aquifers and reservoirs, as well as providing potential conduits and barriers to fluid resource migration and accumulation
We present data from the Flamborough Head Fault Zone (FHFZ), which forms the southern boundary to the Mesozoic Cleveland Basin, and for which there is no present consensus as to the timing and kinematic history
Our findings show that at Selwicks Bay, and by inference, along the FHFZ, a regionally significant extensional phase of deformation occurred over a protracted period during the earliest Palaeocene to early Eocene times
Summary
Faulting of sedimentary basin fills in the subsurface is an important process in producing structurally constrained aquifers and reservoirs, as well as providing potential conduits and barriers to fluid resource migration and accumulation. Fault- and fracture-hosted infill and mineralisation allow us to assess the character and scale of along-fault fluid migration. Open or partially open fractures can be propped open and preserved in the subsurface when they become infilled by wall rock collapse breccias, waterborne sediments and/or hydrothermal mineralisation Walker et al, 2011; Holdsworth et al, 2019, 2020) These so-called fissure systems have the potential to act as significant channelways for the migration and storage of subsurface fluids such as water, hydrocarbons or geothermal fluids. In carbonate aquifers, they can act as pathways for the development of larger dissolutional conduits and cave systems
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