Maer Cliff incompetent deformation

Chaotically deformed and disrupted thin sandstone bands within a horizon of highly sheared dark grey shale - behind the person - in the Bude Formation (upper Carboniferous) at Maer Cliff between Northcott Mouth and Bude, north Cornwall.

As a result of compression as part of the Variscan earth movements at the end of the Carboniferous, the weak (incompetent) shale has been strongly deformed, compared with the strong (competent) sandstone beds above and below the shale. Thin sandstone beds have been caught up in the deformed shale and have undergone severe folding and fracturing. The brown sandstone beds in the upper part of the cliff have moved to the left (north) relative to the lower sandstone beds, with the planes of thrusting and shearing being concentrated in the dark shale.

This deformation probably represents substantial slippage along the bedding planes of the weak shales to accommodate the 'space' problem in the series of chevron folds which characterise this area.