Tectonics of the Coldingham Bay Area of Berwickshire, in the Southern Uplands of Scotland

Summary Structures are described from two sequences of Lower Palaeozoic rocks exposed in the Coldingham Bay area. In the north of the region the Coldingham Beds consist of alternating greywackes, shales and distinctive calcareous siltstones; thin greywackes and shales of the Linkim Beds occupy the shore to the south. The minor folds in the Coldingham Beds are much more complex than those found in the Linkim Beds. In the Coldingham Beds early folds were refolded to form a series of cross-folds; these, subsequently compressed into isoclines, were in turn refolded into a series of open concentric structures. In contrast, the minor folds within the Linkim Beds consist only of the late open structures. The major structure of the area is considered to be a southward-facing recumbent anticline involving both the Coldingham Beds and the Linkim Beds. The Lower Old Red Sandstone rocks which succeed the Linkim Beds to the south are folded into two asymmetrical anticlines, the southern having broadly arched the brow of the underlying recumbent structure. It is postulated that one phase of deformation affected the Coldingham Beds before the Linkim Beds were deposited and that, if so, the Coldingham Beds may be early Ordovician or older, rather than Silurian as previously thought. The major recumbent fold, the superimposed open folds and the refolded isoclines represent fold styles and structures which have not been recognized before in the Southern Uplands.