The stratigraphy of the Middle Chalk (Upper Cretaceous) succession at Mundford, Norfolk, UK

Four continuously cored boreholes and 82 observation shafts were drilled over an area of c. 45 km2 at Mundford, Norfolk in 1966–67 as part of a geological and geotechnical investigation of for a large (2.4 km diameter) proton accelerator and attendant experimental target areas that was to be commissioned by the Committé Européan pour Recherche Nucleaire (CERN). The site is a low-relief area underlain by Middle Chalk and the oldest part of the Upper Chalk in a region where the stratigraphy of the Chalk was poorly known prior to the investigation. The shafts enabled the unweathered succession to be examined in detail, both vertically and laterally, and proved numerous lithological marker beds, mostly flint bands and marl seams. Some were restricted to the site area; others remained unchanged over a much larger area. Penecontemporaneous erosion channels in the Middle Chalk that probably resulted from minor tectonic activity locally cut out some of the marker beds. The Mundford succession falls within the northern part of the Transitional Chalk Province. A few of the marker beds, notably the thicker marl seams, have been correlated with marker beds in the Southern and Northern Provinces. Some of the on-site names for marker beds were used to illustrate the geological succession and structure in the geotechnical report on the proposed site. As a result, the site subsequently became the de facto standard for the Middle Chalk stratigraphy of the region. A description of the full succession is included here for the first time.