Northern North Sea Permo-Triassic Basin Architecture: A new vision

R.A. Hodgkinson1, J.R. Underhill1, M. Tomasso2, N. Banbury1, R. Cooper.3

1 Geology & Geophysics, University of Edinburgh, West Mains Rd, Edinburgh

2 Department of Geology, University College Dublin, Belfield, Dublin 4, Ireland

3 TotalFinaElf UK PLC, Crawpeel Road, Altens Industrial Estate, Aberdeen,

Richard.Hodgkinson@glg.ed.ac.uk

The presence of well-defined sedimentary basins in onshore and offshore areas of the UK which are unaffected by Jurassic extension (e.g. in the Horda Platform and Unst Basin areas) suggests that Permo-Triassic rifting played an important role in North Sea basin development. However, the exact role of the earlier rifting events has remained uncertain in the Northern North Sea largely due to the masking effect caused by the later Jurassic extensional overprint. Consequently, neither a precise definition of Permo-Triassic basins nor an accurate definition of their basin-bounding fault systems has previously been achieved. In the absence of clearly defined structures and knowledge of the general Permo-Triassic stratigraphic architectures many workers have presumed that the Jurassic fault configuration simply reflects reactivation and upward propagation of a fault system that was active in the Permo-Triassic.

Recent advances in the resolution and increased spatial density of 3D seismic data from areas such as the Moray Firth and Northern North Sea combined with the availability of new, deeper borehole penetrations, affords an opportunity to accurately map the Permo-Triassic structures. The integrated approach of structural and sedimentary geology enables an assessment of basin development and the interaction between older and younger extensional fault systems within the Northern North Sea to be realised. These data suggest that the Permo-Triassic rift system differs markedly from the Late Jurassic system, with many faults having different strikes and opposing tectonic polarities.

The positioning of the Jurassic North Viking Graben is frequently taken as a proxy for the axis of Permo-Triassic extension. However recognition of a thickened Permo-Triassic succession beneath the Horda Platform, accompanied by intrusive igneous rocks within the Bergen-Sunnhordland region of Norway suggests that this early stage of rifting within the region was asymmetric, with greater crustal stretching to the east.

This study, undertaken at the University of Edinburgh, wholly funded by TotalFinaElf UK PLC, as part of a proprietary study to investigate the Triassic evolution of the Northern North Sea.