Tectonostratigraphic evolution of the Slyne Basin

The Slyne Basin, located offshore NW Ireland, is a narrow and elongated basin composed of a series of interconnected grabens and half-grabens, separated by transfer zones coincident with deep crustal structures formed during the Silurian- to Devonian-aged Caledonian Orogeny. The basin is the product of a complex, polyphase structural evolution stretching from the Permian to the Miocene. Initially, relatively low-strain rifting occurred in the Late Permian and again in the latest Triassic to Middle Jurassic, followed by a third phase of high-strain rifting during the Late Jurassic. These extensional events were punctuated by periods of tectonic quiescence during the Early Triassic and Middle Jurassic. Late Jurassic strain was primarily accommodated by several kilometres of slip on the basin-bounding faults, which formed through the breaching of relay ramps between left-stepping fault segments developed during earlier Permian and Early–Middle Jurassic rift phases. Following the cessation of rifting at the end of the Jurassic, the area experienced kilometre-scale uplift and erosion during the Early Cretaceous and a second, less severe phase of denudation during the Palaeocene. These post-rift events formed distinct regional post-rift unconformities and resulted in a reduced post-rift sedimentary section. The structural evolution of the Slyne Basin was influenced by pre-existing Caledonian structures at a high angle to the basinal trend. The basin illustrates a rarely documented style of fault reactivation in which basin-bounding faults are oblique to the earlier structural trend, but the initial fault segments are parallel to this trend. The result is a reversal of the sense of stepping of the initial fault segments generally associated with basement control on basin-bounding faults.