An Early Pliocene tectonic episode on the NW European passive continental margin
|Category||Tectonic & Seismotectonic|
|Location||International Geological Congress,oslo 2008|
|Author||Praeg, Daniel۱; Stoker, Martyn۲; Shannon, Patrick۳|
|Holding Date||11 October 2008|
The NW European continental margin is inferred to have undergone a geologically recent episode of epeirogenic tectonism that drove large-scale changes in sediment fluxes to the ocean, deep-water circulation and possibly climate. The episode is identified from onshore-offshore correlation of published analyses of tectonic uplift and subsidence, integrated with a Neogene stratigraphic framework for the margin from Ireland to mid-Norway established during the STRATAGEM project. Tectonic analyses indicate differential vertical movements referred to as epeirogenic tilting: late Neogene uplift of onshore and shallow shelf areas (by up to 1-2 km) coincided with an early Pliocene acceleration of subsidence in offshore basins (of 100s of metres). Stratigraphic analyses indicated that the seaward tilting of the margin drove coeval changes in the patterns of offshore sedimentation, above a regional unconformity dated to 4 ± 0.5 Ma: the seaward progradation of shelf-slope wedges, by up to 100 km offshore Norway; and changes in deep water currents, linked to modifications of gateways between oceanic sub-basins. The onset of shelf-slope progradation along the NW European margin in the early Pliocene preceded the growth of continental ice sheets in Europe by 2-3 Ma, consistent with models in which tectonic uplift was the trigger for northern hemisphere glaciation. The observed surface deflections (up to a few kilometres in amplitude, 100s of kilometres in wavelength) are too large to be explained by variations in intra-plate stresses and too recent to be due to the influence of a hypothetical mantle plume. Epeirogenic tilting is proposed to record a dynamic topographic response to small-scale convective flow within the upper mantle, in particular to edge-driven flow cells generated across gradients in lithospheric thickness (i.e. the edges of cratons and of deep-water basins). The Early Pliocene epeirogenic episode on the NW European margin coincided with a global plate reorganization and preceded an increase in sediment supply to the world oceans. It is possible that similar epeirogenic movements have affected other "passive" margins in the late Neogene but have not been recognized due to the prevailing paradigm of passive post-rift thermal subsidence.