Crackington Haven recumbent folds interpretation

By special request: an interpretation of the zoomed-in view of the base of the cliff on the north side of Crackington Haven, north Cornwall.

Original photo here:



Grey shales and thin turbidite sandstones, (pale grey-brown) of the Crackington Formation (upper Carboniferous) have been strongly deformed into isoclinal recumbent folds by the Variscan earth movements at the end of the Carboniferous.

This is an attempt to interpret the main geological structures, as seen on the more-or-less 2-D vertical cliff face:
Yellow lines are arbitrary bedding traces
Blue dashed lines are synclinal axes
Red dashed lines are anticlinal axes

Sedimentary features (ripples, sole structures, etc) in the sandstones enable us to determine the 'way-up' of the beds and hence classify the folds into anticlines and synclines. In this photo, the general 'younging' direction is to the south east (right). The folds were probably initially upright as the Variscan compression developed but continuing deformation and complex thrusting rotated the whole stack of folds in a clockwise sense so that the fold axes became approximately horizontal.

The deformation is more intense here compared with Millook Haven 3.5 miles to the NE:



This probably reflects (a) more shales (weaker rocks which deform more readily) in the Crackington Haven section and (b) the more southerly location is slightly closer to the 'source' of the deformation. As a general rule, in Cornwall the most intensely deformed rocks are towards the south.