AN INTEGRATED METHODOLOGY FOR THE 3D CHARACTERISATION OF BEDROCK GEOLOGY IN AREAS OF LIMITED OUTCROP – CASE STUDY: THE YORKSHIRE WOLDS CHALK AQUIFER, UK

The geology of the UK is best characterised in coastal sections or in areas of steeper topography where there is sufficient density of rock outcrop. However, much of the UK has low relief and little or no bedrock exposed at surface, with most of the land covered by Quaternary glacial deposits or arable fields and pasture. This is the case of the Yorkshire Wolds Chalk aquifer, which 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. Some areas of the Yorkshire Wolds Chalk aquifer have not been systematically mapped since the late 19^th century, and do not reflect present-day stratigraphic divisions or current tectonic understanding, leading to an underestimation of the structural complexity of the aquifer.

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, which draws on a multidisciplinary skillset and collaboration between geologists of different specialisations. 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. Our methodology integrates remote sensing, field surveying, fracture analysis in coastal sections, borehole core and geophysics, seismic interpretation and biostratigraphy, drawing on new collection of geological data as well as reinterpretation of materials and logs held in the BGS collections.

This multidisciplinary approach to mapping has 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.