UK Chalk Group stratigraphy (Cenomanian – Santonian) determined from borehole geophysical logs

Abstract

Borehole geophysical logs through the Chalk Group of SE England have distinctive profiles that correspond with formational boundaries, recognized by lithological changes in borehole core and mapped by the British Geological Survey on the basis of lithology and topographic features at outcrop. Borehole geophysics graphically demonstrates the validity of the stratigraphy of the Chalk Group used by the British Geological Survey, and can be used to refute recent arguments against lithostratigraphical subdivision of the White Chalk Subgroup. Although intra-formational changes in the detail of borehole geophysical logs may occur between regions, generalized trends can still be used for inter-regional recognition of formations in the subsurface. Much previous work has focused on the utility of borehole geophysics for marker-bed recognition and correlation in the Chalk Group, but little attention has been paid to the more fundamental task of characterizing formations. This approach allows a much greater appreciation of regional Chalk Group stratigraphy than might be evident from available outcrops, and is the first step in the development of three-dimensional digital geological models of the Chalk Group.