In Britain, thick limestones of early Carboniferous (Mississippian: 359-323 Ma) age are present in two provinces, respectively south and north of the Wales-Anglo-Brabant landmass. In the southern province, early Carboniferous limestones were deposited upon a southward-deepening shelf, laterally continuous from Ireland to the Rhineland. They now occupy a number of discrete minibasins as a consequence of Variscan orogenic thrusting and significant post-Carboniferous erosion. In the northern province, local tectonic controls led to the development of a mosaic of deepwater basins, ramps and platforms in response to Mississippian extensional stress. The interaction with glacioeustatic sea-level change led to the development of complex carbonate system tracts on these ramps and platforms.Given favourable conditions of palaeokarst development and fracturing, hydraulic transmissivity could be sufficient to allow development as a geothermal resource. Deep geothermal prospectivity is controlled by a hierarchy of factors, operating on scales ranging from provincial (1000-100 km) down to outcrop (1000-100 m), reflecting processes operating on the lithospheric down to sub-basinal scale respectively. On the scale of the individual prospect, these factors include the mode of carbonate deposition, particularly depth of water and angle of depositional slope, which are tectonically controlled; the history of synsedimentary exposure, erosion and karstification, strongly influenced by sea-level change; by the diagenetic history and subsequent basin evolution; by deformation and fracturing during Variscan basin inversion; and by the post-Carboniferous history of subsidence, uplift and karstification.The contrasting impact of these various processes upon hydraulic transmissivity in the two provinces is reviewed, and a preliminary assessment of the geothermal prospectivity of each is presented. The most prospective areas for deep geothermal exploitation are considered to be basins, shelves and platforms lying at depths of 2 to 5 km below sea level. Deepwater basins are considered less prospective because of the lack of thick limestones, except in the hanging wall at fault-bounded margins, where Waulsortian mud-mounds with good residual porosity and fault-zones with polyphase history are likely present. Granite underpinned highs in N England, where Carboniferous limestones are typically at crop, and shallow basins of Carboniferous age lying on the Wales-Anglo-Brabant Massif, are considered less prospective in the deep geothermal context.
<p>The Flamborough Head Fault Zone (FHFZ) is a regionally-significant structural zone in northeast England which dissects the Upper Cretaceous Chalk Group, a 500&#160;m thick limestone succession which is a principle aquifer and main source of water supply in the region. The geometry and physical characteristics of the Chalk succession, including the effects of faulting, influence groundwater flow across the region. Consequently, understanding the architecture of the FHFZ is vital to sustainably managing water resources in this area.</p> <p>The FHFZ marks the southern extent of the Cleveland Basin and the northern margin of the Market Weighton Block and has a complex history of Mesozoic-Cenozoic extension and compression. It is predominantly comprised of east-west trending faults which form a graben that is dissected by north-south trending faults, including the southern extension to the Peak Trough, the Hunmanby Fault. To the west, FHFZ links with the Howardian Fault System and offshore, in the east, it is truncated by the north-south trending Dowsing Fault. The FHFZ is well exposed and described in coastal cliff sections at Flamborough Head but the inland architecture of the faults has hitherto been poorly explored predominantly due to limited inland-exposure.</p> <p>To address this a multi-faceted approach to geological mapping has been undertaken in the region by the British Geological Survey, in collaboration with the Environment Agency and Yorkshire Water Limited. Remote sensing, targeted field mapping, palaeontological analysis, passive seismic and 2D onshore seismic interpretation have been integrated to understand the inland architecture of the FHFZ in unprecedented detail. Combining these techniques has enabled us to bridge the gap between the surface geology and deeper subsurface structure, increase our understanding of the geology of the region and produce an improved conceptual model at a range of depths which will be used to better manage water resources.</p>
<p>The Yorkshire Wolds Chalk aquifer, provides the main source of water supply in East Yorkshire and the city of Hull, which have a population over 900.000. Its structural configuration, including the effects of faulting, influence groundwater flow across the region. However, stratigraphic and structural characterisation is challenging due to limited bedrock being exposed at surface, with most of its extension covered by Quaternary glacial deposits and arable fields and pastures. While the coastal sections have been well characterised through the years, inland areas of the Yorkshire Wolds Chalk aquifer have not been systematically mapped since the late 19th century. The available maps do not reflect present-day stratigraphic divisions or current tectonic understanding, leading to an underestimation of the structural complexity of the aquifer.</p> <p>A multi-faceted approach to geological mapping is being undertaken in the region by the British Geological Survey, in collaboration with the Environment Agency and Yorkshire Water, integrating remote sensing, targeted field mapping, palaeontological analysis, 2D onshore seismic interpretation and borehole records. The objective of the project is to deliver an up-to-date geological map and structural model of the Chalk bedrock and Quaternary deposits which will impact on the groundwater resources management.</p> <p>The recent mapping campaigns have led to identifying and characterising numerous new faults in different structural trends, which were not present on previous maps. It has also led to a significant shifting of stratigraphic contacts and formation thicknesses, which have more lateral variability than previously thought. We present some of the most recent updates on the Yorkshire Wolds Chalk aquifer map, which highlight the importance of revising old cartography using modern tectonic and stratigraphic concepts and a multidisciplinary approach to field data collection and compilation. We are also interested in discussing with the hydrogeologist community how to better capture and represent structural complexity around fault zones, so it has an impact on hydrogeological modelling.</p>
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