Repeated folding at Boscastle, North Cornwall, England

Abstract

Repeated folding of the Boscastle Measures, a group of thinly bedded sandstones and shales of presumed Upper Carboniferous age, has led to the development of small-scale superimposed structures. The earliest folds are now isoclinal with a strongly developed axial-plane slaty cleavage and a prominent mineral elongation parallel to fold axes. Although the regional trend of the southern margin of the Culm Measures trough of north Cornwall and mid-Devon is east to west, the early folds at Boscastle are recumbent with predominantly a gentle plunge to the north. Of lesser importance is the more nearly east to west trend of some isoclines. It is suggested that the two trends of isoclines may be linked in synchronous right-angled combinations, and that this pattern may be reflected on a large scale in the outcrops south of Boscastle. The isoclines are deformed by small-scale east to west zigzags, believed to be related to northwards movements down major low-angle normal faults which are parallel to the gently inclined bedding.