Litho-stratigraphy of the Ventnor Undercliff and determination of critical horizons through borehole geophysics

Ventnor is an area of notable landsliding. Concerns over the stability of a number of areas have in the past been investigated where possible with rotary cored boreholes. Landslide risk assessments which take account of future climate change will require further ground investigations of the landslide complex. Within Ventnor this may require the drilling of boreholes in excess of 100 m, at significant cost. This paper reviews and updates the published information regarding the litho-stratigraphy of the geological succession in Ventnor and demonstrates how geophysical gamma-logging can be used to correlate the succession thus providing an economic and useful investigative technique in place of rotary coring. The characteristics and index properties of the Gault are also described from the available data, particularly in relation to the occurrence of critical shear surfaces in this stratum.