Synopsis
In the central and northern British Isles the Carboniferous period was marked by normal faulting, trough formation and alkali basalt vulcanicity typical of rifting environments. This tectonomagmatic activity may have been the precursor to the opening of the Rockall and Faeroe-Shetland troughs and a Norway-Greenland rift. The opening itself is held to have taken place shortly after the intrusion of the tholeiitic dykes and sills near the end of Carboniferous times, just as similar intrusions of Late Triassic age in eastern North America and West Africa heralded the opening of the southern North Atlantic. The newly formed upstanding continental margins slowly subsided partly by basin formation and partly by oceanward sagging finally permitting the Boreal ocean to flood a portion of northwest Europe in the Upper Permian.