topography deviating from values corresponding to isostatic equilibrium 15.Īlongside the distinct offshore subsidence, onshore areas around the North Sea are subject to large-scale uplift 16, 17, 18, 19, 20, 21. More generally, other modes of mantle convection are also suggested as causing dynamic topography, i.e. These include reactivation of faulting in association with a renewed rifting phase 2, 3, lithosphere buckling due to intraplate stresses 8, 9, 10, 11, metamorphic processes at the crust-mantel transition 12, and the influence of a mantle thermal anomaly 13, 14. Various potential mechanisms have been proposed as causes of the anomalously high rate of Quaternary subsidence 2, 3, 8, 9, 10, 10. During these 2.6 Ma, a thick package of more than 1000 m of sediments accumulated in the North Sea Basin, including the northwestern German North Sea (Figs 1 and 2). However, during the Quaternary (2.6 Ma), the Central Graben area of the North Sea rift experienced an unusually high degree of subsidence (i.e., anomalous subsidence), at about 140 Ma after the final rifting phase 2, 3.
The Mesozoic/Early Cenozoic subsidence pattern of the North Sea is interpreted as a result of thermally induced subsidence following Late Triassic to Early Cretaceous rifting events accompanied by sediment loading and isostatic adjustments 2, 3, 4, 5, 6, 7. During the subsequent post-rift phase, subsidence theoretically 1 declines exponentially. The widely accepted McKenzie model 1 predicts strong subsidence during the extension phase of continental rifts. Possibly a post-glacial collapse after the retreat of glaciers in the North Sea Basin, local lower crustal flow, or dynamic topography or a combination of these processes contributed to the residual subsidence.
From the orientation and extent of the depocentre, lithosphere buckling and subsidence due to salt movement are considered unlikely. The extensive seismic dataset interpreted here makes it possible to exclude a phase of renewed tectonic activity as the origin of the subsidence anomaly. However, a certain portion of the subsidence needs additional processes to be invoked. Here we show that compaction and load-induced subsidence alone explain about 75% of the observed Quaternary subsidence. Previously, a number of mechanisms have been proposed to explain the Quaternary subsidence. Distinct iceberg scour marks, identified in 3D seismic data are used to calibrate quantitative subsidence analysis and to document shallow marine conditions during the Quaternary interglacials. This indicates extremely fast subsidence, with a rate of up to 480 m/Ma during the Quaternary, resulting in a NNW-SSE oriented sedimentary depocentre. 3D and 2D seismic data reveal the base-reflection of the Quaternary in the northwestern German North Sea locally at depths of more than 1000 m.
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