Geology of Porcupine Bank and Goban Spur, Northeastern Atlantic — Preliminary results of the Cyaporc submersible cruise

Abstract

During the Cyaporc cruise, five submersible traverses and four dredge hauls were made up the steep western slopes of Porcupine Bank and Goban Spur on the continental margin west of Ireland. The major aims of the study were to examine the syn- and post-rift evolution of the margin during the Mesozoic and Cenozoic, and to compare the “basement” rocks of Porcupine Bank and Goban Spur with those of the Hercynian and Caledonian orogens of the western British Isles. On Porcupine Bank, sampling and observational data show a metamorphic basement overlain by a sequence of Upper Palaeozoic siltstones and sandstones. Mesozoic sediments are restricted to isolated patches of Lower Cretaceous shallow-marine deposits. On Goban Spur, the oldest rocks are weakly metamorphosed sandstones of Late Palaeozoic age (Hercynian basement). In contrast to Porcupine Bank, these are overlain by a thick sequence of shallow-water Barremian limestones deposited during the late Early Cretaceous rifting event. Upper Cretaceous and Tertiary sediments have only a patchy development in both areas. Comparison with onshore areas suggest that the Porcupine Bank Palaeozoic sequence is comparable with that of the Hercynian foreland seen in Ireland. The Palaeozoic sequence at Goban Spur, with granites intruded along its southern flank, is less easily compared with onshore sequences, but most closely resembles that seen in onshore southwest England. The development of a thick syn-rift sequence on Goban Spur resulted from faulting and subsidence related to crustal thinning during the Early Cretaceous rifting event. In contrast, seismic refraction results show little crustal thinning beneath Porcupine Bank, offering an explanation for the absence of Mesozoic subsidence and the lack of preserved Mesozoic sediments.