Geological mapping of the Late Cretaceous Chalk Group of southern England: a specialised application of landform interpretation

The modern Chalk Group lithostratigraphy divides the Chalk of southern England into nine formations, each with a characteristic lithological assemblage. It is more useful than the traditional subdivision into Lower Chalk, Middle Chalk and Upper Chalk because it can be applied more consistently over a wider area, it provides a better indication of lithological variation, it allows the recognition of more tectonic structures and it is thus more useful for practical application in engineering geology and hydrogeology.The process of surveying the Chalk that has been developed by the British Geological Survey over the past two decades is an empirical modification of the traditional methods used for detailed geological survey of sedimentary sequences in other parts of the United Kingdom. Each Chalk formation is closely associated with characteristic landforms, allowing them to be mapped with reasonable consistency and accuracy in largely unexposed ground and through built-up areas. This association of landform and lithostratigraphy reflects the response to weathering (and other surface processes) of relatively subtle variations in bulk lithological assemblage, rather than of individual beds of contrasting lithology.