Tectonostratigraphic evolution of the Slyne Basin

Abstract. The Slyne Basin, located offshore NW Ireland, is a narrow and elongate basin composed of a series of interconnected grabens and half-grabens, separated by transfer zones coincident with deep Caledonian-aged crustal structures. The basin is the product of a complex, polyphase structural evolution stretching from the Permian to the Miocene. Relatively low-strain episodic rifting occurred in the Late Permian and the latest Triassic to Middle Jurassic, with the main phase of rifting occurring in the Late Jurassic. These extensional events were punctuated by periods of tectonic quiescence during the Early Triassic, and regional uplift and erosion during the late 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-Mid 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 second, less-severe phase of denudation during the Palaeocene. These post-rift events formed a distinct regional post-rift unconformity and resulted in a reduced post-rift sedimentary section. The structural evolution of the Slyne Basin is 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.