Frontiers and Opportunities in Antarctic Geosciences * Certosa di Pontignano * 29-31 July 2004
Episodic Cenozoic Tectonism and the Shaping of
the NW European 'Passive' Continental Margin
PRAEG, D.1*, STOKER, M.2, SHANNON, P.1, CERAMICOLA, S.3, HJELSTUEN,
B.4, LABERG, J.S.5, MATHIESEN, A.6
1
Department of Geology, University College Dublin (UCD) *(daniel.praeg@ucd.ie)
2
British Geological Survey (BGS)
3
Istituto Nazionale di Oceanografia e Geofisica Sperimentale (OGS)
4
Department of Earth Science, University of Bergen (UiB)
5
Department of Geology, University of Tromsø (UiT)
6
Geological Survey of Denmark & Greenland (GEUS)
A. Differential Tectonic Movements
The Atlantic continental margin of NW Europe is classed as 'passive', or tectonically quiescent, yet its Cenozoic post-rift
development has included differential vertical movements of up to km-scale. These movements have found expression in
epeirogenic (domal) uplifts, in episodic subsidence of basins and in the formation of compressive structures. However, the
nature and the succession of movements remains uncertain, which has in turn contributed to uncertainty over their cause(s)
in relation to models of intra-plate stress variations versus different forms of lithosphere-mantle interaction.
B. Absolute & Relative Measures of Subsidence/Uplift
We examine the history of the margin, from Ireland to Norway, by integrating published measures of absolute subsidence
and/or uplift with the records of relative movements available from tectono-stratigraphic analyses, including the results of
the STRATAGEM project (STRATAGEM Partners 2002, 2003; Stoker et al. in press; Praeg et al. in prep.). Absolute
measures are of low temporal resolution, but indicate two episodes of coeval uplift and subsidence (tilting), in the early and
late Cenozoic, separated by an episode of rapid differential subsidence (sagging) in the mid-Cenozoic. These three
epeirogenic episodes are reflected in higher resolution tectono-stratigraphic indicators (e.g. regional unconformities,
prograding shelf-slope wedges, tilted surfaces), which also provide structural evidence of at least one additional phase of
compressive tectonism (anticlinal domes).
C. A Succession of Cenozoic Tectonic Episodes
Four tectonic episodes are recognised, comprising three types of movement, each of which resulted in changes in the
patterns of sedimentation and deep-water current circulation: i) early Cenozoic tilting, in which coeval uplift and subsidence
of the margin resulted in the seaward progradation of (Eocene) shelf-slope wedges; ii) mid-Cenozoic sagging, during which
rapid differential subsidence outstripped sediment supply to drive a km-scale deepening; iii) compressive flexure and failure
in the late Oligocene to mid-Miocene, recorded by basin-margin to deep-water unconformities and by inversion anticlines;
iv) late Cenozoic tilting again resulted in the seaward progradation of (Plio-Quaternary) shelf-slope wedges. Each type of
movement was rapid (5-50 cm/ka) and coincided with plate reorganisations of regional to global scale.
D. Driving Forces - Plate Stresses vs Upper Mantle Convection
The early to mid-Miocene compressive phase coincides with a ridge jump across the adjacent Jan Mayen microplate and is
consistent with responses to intra-plate stress variations during a local plate reorganisation. However, this mechanism
cannot generate deflections large enough to account for epeirogenic movements of km-scale. The observed epeirogenic
movements are proposed to record dynamic topographic responses to small-scale (upper mantle) mantle convection cells:
tilting to an edge-driven convection cell (flowing upward beneath the continent), sagging to loss of support above a former
upwelling. Small-scale convection has been proposed to account for episodic Cenozoic tectonism on other Atlantic margins
and to be the cause of global plate reorganisations.
REFERENCES
Praeg, D., Stoker, M., Shannon, P.M., Ceramicola, S., Hjelstuen, B.O. & Mathiesen, A., in prep. Episodic Cenozoic tectonism and the development of the
NW European ‘passive’ continental margin. Marine & Petroleum Geology, thematic issue (P.M. Shannon & M.S. Stoker, eds), to be published 2005.
Stoker, M.S., Praeg, D., Shannon, P.M., Hjelstuen, B.O., Laberg, J.S., Nielsen, T., van Weering, T.C.E., Sejrup, H.P. & Evans, D., in press. Neogene
evolution of the Atlantic continental margin of NW Europe (Lofoten Islands to SW Ireland): anything but passive. In Petroleum Geology: North-West
Europe and Global Perspectives - Proceedings of the 6th Petroleum Geology Conference (Dore, A.G. & Vining, B., eds); The Geological Society,
London (to be published in early 2005).
STRATAGEM Partners, 2003. Neogene Evolution of the Glaciated European Margin (M.S. Stoker, compiler). A product of the EC-supported
STRATAGEM project, contract EVK3-CT-1999-00011; Svitzer Ltd, Great Yarmouth, UK, 165 pp.
STRATAGEM Partners, 2002. The Neogene Stratigraphy of the Glaciated European Margin from Lofoten to Porcupine (M.S. Stoker, compiler). A
product of the EC-supported STRATAGEM project, contract EVK3-CT-1999-00011; Svitzer Ltd, Great Yarmouth, UK, 75 pp.