Abstract. 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.