Sedimentary succession and tectonic history of a marginal plateau (Goban Spur, southwest of Ireland)

Abstract

Goban Spur lies on the continental margin of northwest Europe, southwest of Ireland. It is a marginal plateau underlain by Hercynian granites and Palaeozoic sediments, which form large horsts, grabens and tilted fault blocks with a trend that is approximately parallel to the main Celtic/Armorican Shelf edge. The spur is thought to be a westward continuation of the buoyant Cornubian Ridge, and is bounded to the north and south by large fault lines which probably represent reactivation of Hercynian structural trends. The continental basement is further divided longitudinally into a low-lying outer zone (Intermediate Zone) and a high inner region (Goban Spur proper). The ocean/continent boundary is thought to lie at the outer edge of the Intermediate Zone, Sea-floor spreading anomalies immediately west of the Intermediate Zone suggest that the adjacent ocean crust was created prior to anomaly 33 (say at ca. 90 m.y. B.P.). The sedimentary sequence on Goban Spur can be subdivided into four layers which can be tentatively correlated with the stratigraphic succession on the Meriadzek Terrace (IPOD sites). Such a correlation suggests that the lowermost sediment layer (?Jurassic-Albian) represents a tectono-sedimentary rift infill, and that Layers 2–4 (Upper Cretaceous to Quaternary) were deposited during slow epeirogenic downwarping of the plateau and that the sedimentary processes involved both draping and strong current moulding. The relatively buoyant nature of Inner Goban Spur has inhibited the accumulation of a thick post-rifting sedimentary sequence (700–1000 m), and has shielded the Intermediate Zone from downslope mass movements of material. This has resulted in the accumulation of an anomalously thin post-rift stage outer margin sediment prism (ca. 1000 m) compared to most continent rises (up to 10 km).