Landslides and stratigraphy in the coastal outcrop of the Barton Clay

Geological surveying in soft rock landslide terrain with compound shaped landslides formed by slide prone horizons (SPH) cannot normally be comprehensive without subsurface investigations: the sharp angled shear surfaces of the compound slides result in the complete deformation of the in situ fabric and prevents exposure of the intact material located just above the SPH. The problem is illustrated with respect to the coastal outcrop of the Barton Clay in its type area in Christchurch Bay, Hampshire, UK. The extensive historical literature is briefly reviewed to show the difficulties experienced by the geologists seeking to give a comprehensive account of the stratigraphic sequence. Recent drilling through the most prominent SPH and a fortuitous exposure revealing details of a higher SPH has allowed details of the normally obscured part of the sequence to be revealed.