Seismic and well evidence for the early development of the Faeroe–Shetland Basin

Abstract

Synopsis The Faeroe–Shetland Basin occurs between the Faeroe and Shetland Islands north of the United Kingdom mainland. Most geologists currently favour an early Cretaceous rifting event for the origin of this basin. However, data from cores, cuttings, geophysical logs and seismic reflection profiles pertaining to well 206/5–1 show that Lower, Middle and Upper Jurassic marine sediments were deposited within the Faeroe–Shetland Basin. Therefore this basin had formed by the early Jurassic. The early and mid-Jurassic sediments probably record submarine fan sequences; the late Jurassic sediments are interpreted as fault scarp talus marginal to a deep muddy marine basin. As well 206/5–1 did not reach metamorphic basement, older sediments must also be present within the Faeroe-Shetland Basin. Southeast of the Faeroe-Shetland Basin, the West Shetland Basin accumulated a wedge of Middle and Upper Jurassic nearshore sediments showing that both basins were then subsiding under the same regional tectonic influence. Three wells in the West Shetland Basin terminated at approximately 2.2 km, 2.6 km and 2.7 km within Triassic sediments. Below this, seismic data demonstrate that up to 3.9 km of older sediment remains undrilled above metamorphic basement. We therefore confidently infer a Permian or older origin for the West Shetland Basin. Seismic data shows the Jurassic and pre-Jurassic shapes of the West Shetland Basin to be almost identical. If the same tectonic control also influenced the Faeroe-Shetland Basin, we must infer a Permian or older age for the Faeroe-Shetland Basin. A long-lived deep marine Faeroe-Shetland Basin implies the presence of pre-Mesozoic hydrocarbon source rocks, plus the possibility of deeply buried reservoirs.