Issues

A stratigraphy for fracture styles, fracture fills and fracture porosity/permeability is illustrated by the Upper Cretaceous Chalk coastal cliffs of Sussex, England. Here east of Birling Gap, the vertical joint sets are typical of the middle part of the Seaford Chalk Formation in the Cuckmere and Haven Brow Beds (Late Coniacian–Early Santonian). Vertical joint sets are present in these beds throughout southern England and much of the Paris Basin controlling the style and scale of cliff slope failures as well as fracture permeability of the rock mass. The clean chalk-on-chalk fracture surfaces contrast with other Chalk formations where clay mineralization along fractures or sheet-flint filled fractures control the mechanical properties and permeability of the Chalk rock mass and the interaction between fluids in the material pores with the fluids in fractures.

Photograph by Rory Mortimore