The concentration of folding and faulting in the Chalk at Staple Newk (Scale Nab), near Flamborough, East Yorkshire

摘要

At Staple Newk [TA 205 737], intensive folding and thrusting of the Chalk were restricted to a 200 m long section. The ENE-WSW folding and NNW-SSE thrusting resulted from dextral transpressive reactivation of the underlying ENE-WSW Bempton Fault. Detachment folding in the Welton Chalk Formation produced a monocline with a vertical limb that locked and was then cut by a thrust. This parallel style of folding contrasted with that in the overlying, more thinly bedded Burnham Chalk Formation, where tight and disharmonic, angular folding developed between the vertical limb and the north-north-west propagating thrust. When the tight, angular folding locked, south-south-eastward back-thrusts combined with the main thrust, but. both diminished and died out upwards. Later, low-angle extensional faulting was followed by steep normal faulting. Folding and thrusting also developed in the Chalk at Selwicks Bay, 6 km to the south-east. Here, four deformation phases ('D1-D4') can be separated and the later phases can be correlated with those that affected Staple Newk. At both localities, folding and thrusting were produced by a 'D3' N-S contraction which was more than cancelled later by 'D4' N-S extension, causing low-angle extensional faulting and subsequent steep normal faulting. Within the Howardian Hills-Flamborough Fault Belt, contractional features (folds and thrusts) and subsequent low-angle extensional faults were local developments and were replaced en echelon by similar structures. The later, steep normal faults produced the more-continuous E-W fault pattern.