The Northeast Rockall Basin and its significance in the evolution of the Rockall-Faeroes/East Greenland rift system

Abstract

The newly mapped Northeast Rockall Basin lies between the Wyville-Thomson Ridge and an ESE lineament extending from the onshore Ness Shear Zone. It contains a window in the early Tertiary flood-basalts through which a syn-rift sedimentary succession is imaged on seismic data. This succession was mapped in detail, calibrated to wells and boreholes drilled on the basin margins, and integrated with results from gravity, magnetic and backstrip modelling. Modelling and seismic stratigraphic analysis show that the Wyville-Thomson Ridge is a late Eocene to Oligo-Miocene fault-propagation fold, comprising basalt at the seabed and folded low density sediments within its core. Together with the co-linear Munkegrunnur and Ymir Ridges, this fold developed from positive inversion above a composite, crustalscale ramp-flat detachment during N-S compression. Prior to mid-Tertiary inversion of the WyvilleThomson Ridge, the basin may have formed a link between the main part of the Rockall Trough to the south and the Faeroe-Shetland and East Greenland rift systems to the north. Triassic, Jurassic and Early Cretaceous syn-rift sediments have been penetrated in the adjoining West Lewis Basin, and the Northeast Rockall Basin may contain sediments with a similar age range beneath the Tertiary flood basalts. Estimates from modelling allude to a resurgence of rifting from mid-to latest Cretaceous times, perhaps coeval with voluminous axial volcanism in the adjacent Rockall Trough. This episode of syn-rift volcanism, underlying the Paleocene volcanics, prohibits deeper seismic resolution to the south of the lineament in the main part of the Rockall Trough. The present-day bathymetry has resulted from a complex interaction between the loci of Mesozoic stretching, renewed post-basalt subsidence and major late Eocene to Oligo-Miocene inversion.

Crustal structure of the NE Rockall Trough from wide‐angle seismic data modeling

“…Evidence for pre-Cretaceous rifting in the Rockall Trough has been found from two-dimensional (2-D) structural and stratigraphic forward modeling [Nadin et al, 1999]. The rift system might have continued into the Faeroe-Shetland Basin until the formation of the Wyville-Thomson Ridge through inversion in the midTertiary [Boldreel and Andersen, 1993;Tate et al, 1999].…”

“…Ridge push from the initiation of seafloor spreading in the North Atlantic has been proposed as cause for the NE-SW compressional stress necessary to form these structures [Boldreel and Andersen, 1994]. Recent investigations using reflection seismic data acquired in the region of the NE Rockall Basin show that the Wyville-Thomson Ridge has no igneous core and only a thin basalt cover overlying 3 -4 km thick sedimentary layers [Tate et al, 1999]. On the basis of these new data, the Wyville-Thomson Ridge together with the Ymir and Munkegrunnur ridges can be considered as positive inversion ramp anticlines above an inferred mid-lower crustal detachment, generated during N-S intraplate compression [Tate et al, 1999].…”

“…Recent investigations using reflection seismic data acquired in the region of the NE Rockall Basin show that the Wyville-Thomson Ridge has no igneous core and only a thin basalt cover overlying 3 -4 km thick sedimentary layers [Tate et al, 1999]. On the basis of these new data, the Wyville-Thomson Ridge together with the Ymir and Munkegrunnur ridges can be considered as positive inversion ramp anticlines above an inferred mid-lower crustal detachment, generated during N-S intraplate compression [Tate et al, 1999]. The origin of the deformation is proposed to be caused by compressional stress in the Pyrenean-Alpine foreland.…”

The Case for Large M > 7 Earthquakes Felt in the UK in Historical Times

“…The second is the existence of an apparent sea-floor-cutting fault on the northern flank of the Wyville-Thompson Ridge (Tate et al, 1999). This is shown on a seismic section ( Figure 3 in Tate et al, 1999) as a steep, south dipping fault cutting the sea bed.…”

“…This is shown on a seismic section ( Figure 3 in Tate et al, 1999) as a steep, south dipping fault cutting the sea bed. Uplift of the Wyville-Thompson Ridge started in the late Eocene and continued intermittently throughout the Oligocene, and possibly until Recent times (Tate et al, 1999). This north-bounding fault is possibly the only known instance of seabed fault displacement in UK waters, and it does rather suggest palaeoseismic evidence of a large earthquake.…”