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Geological Society, London, Memoirs; 2004; v. 29; p. 83-90;
DOI: 10.1144/GSL.MEM.2004.029.01.09
© 2004 Geological Society of London

Depositional Systems

3D Seismic Analysis Reveals the Origin of Ambiguous Erosional Features at a Major Sequence Boundary in the Eastern North Sea: near Top Oligocene

J. P. V. Hansen1, O. R. Clausen1 & M. Huuse2

1 Department of Earth Sciences, University of Aarhus, , 8000 Arhus C, Denmark (e-mail: jenspeter{at}geo.au.dk)
2 3D-Lab, School of Earth, Ocean and Planetary Sciences, Cardiff University, , Main Building, Park Place, Cardiff CE10 3YE, UK

The near top Oligocene unconformity is a major sequence boundary in the eastern North Sea Basin. It is characterized by erosional scarps below the boundary and a pronounced basinward shift in onlap above. The shift in onlap has previously been interpreted as caused by a major fall in sea level. Detailed 3D seismic analysis of a 20 by 20 km area at and basinward of the uppermost Oligocene clinoform breakpoint reveals that the erosional scarps were caused by undercutting of steep clinoforms by contour-parallel currents and resulting mass wasting whilst the lowermost onlap package consists of a contour-parallel drift deposited as the erosive currents waned. The 3D seismic analysis corroborates a recent analysis based on regional 2D seismic data, which found that the erosional scarps and the geometry of the onlap sequence were indicative of a major shift in sediment input directions and not necessarily associated with any change of sea level. The paper thus demonstrates the utility of local 3D seismic analyses as a form of 'ground truthing' regional basin analyses based on widely spaced 2D seismic grids.