Compression and unconformity formation in the NE Atlantic passive continental margin

Category Tectonic & Seismotectonic
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Tuitt, Adrian۱; Underhill, John۲; Ritchie, Derek۳; Johnson, Howard۳; Ken, Hitchen۳; Scrutton, Roger۲
Holding Date 11 October 2008

Passive continental margins are generally thought to be characterised by tectonic quiescence following the extensional events that originally formed them. Analysis of newly acquired and existing 2-D seismic data from the Faroe Shelf to the Rockall Plateau, however, has demonstrated that the NE Atlantic Margin is the site of significant active deformation. Results of well-calibrated, seismic interpretation have revealed the presence of compression-related Cenozoic anticlines (e.g. Alpin Dome, Ymir and Wyville Thomson Ridges) and have provided new insights into the timing of, controls on and effects of contractional deformation that characterise the region.
Gravity and magnetic models support the presence of low-density sediments in the core of folds. This is consistent with folds developing due to the inversion of sedimentary basins. The spatial extent of the deformation could thus reflect the differing underlying basin morphologies. The mapping and dating of angular and erosional unconformities that define folding suggest that the growth of these compressional features occurred in five main phases — late Paleocene-early Ypresian, late Ypresian, late Lutetian, Late Eocene (C30) and Mid Oligocene. These compressional phases all appear to be driven by regional events affecting the NE Atlantic Margin, namely ridge push, Alpine and Pyrenean orogenies and depth-dependent stretching.
The regional studies make clear that compression can have a profound effect on sea-bed bathymetry and consequent bottom-water current activity. Bottom-water currents have directly formed the Early — Mid Miocene (C20), Late Miocene - Early Pliocene, and late Early Pliocene (C10) unconformities. However, the entry of bottom-water currents from the Faroe-Shetland Channel into the Rockall Trough is restricted by the Wyville-Ymir Ridge Complex, and takes place only via the syncline between the two ridges (Auًhumla Basin). The growth of this compressional feature is now thought to have controlled the timing and distribution of bottom-water currents in the Rockall Trough, and unconformity formation therein.