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This paper focuses on the Cenozoic evolution of the northern North Sea and surrounding areas, with emphasis on sediment distribution, composition and provenance, as well as on timing, amplitude and wavelength of differential vertical movements. Quantitative information about palaeo-water depth and tectonic vertical movements has been integrated with a seismic stratigraphic framework to better constrain the Cenozoic evolution. The data and modelling results support a probable tectonic control on sediment supply and on the formation of regional unconformities. The sedimentary architecture and breaks are related to tectonic uplift of surrounding clastic source areas, thus the offshore sedimentary record provides the best age constraints on Cenozoic exhumation of the adjacent onshore areas. Tectonic subsidence accelerated in Paleocene time throughout the basin, with uplifted areas to the east and west sourcing prograding wedges, which resulted in large depocentres close to the basin margins. Subsidence rates outpaced sedimentation rates along the basin axis, and water depths in excess of 600 m are indicated. In Eocene times progradation from the East Shetland Platform was dominant and major depocentres were constructed in the Viking Graben area, with deep water along the basin axis. At the Eocene-Oligocene transition, southern Norway and the eastern basin flank became uplifted. The uplift, in combination with prograding units from both the east and west, gave rise to a shallow threshold in the northern North Sea, separating deeper waters to the south and north. The uplift and shallowing continued into Miocene time when a widespread hiatus formed in the northern North Sea, as indicated by biostratigraphic data. The Pliocene basin configuration was dominated by outbuilding of thick clastic wedges from the east and south. Considerable late Cenozoic uplift of the eastern basin flank is documented by the strong angular relationship and tilting of the complete Tertiary package below the Pleistocene unconformity. Cenozoic exhumation is documented on both sides of the North Sea, but the timing is not well constrained. Two major uplift phases in early Paleogene and late Neogene times are related to rifting, magmatism and break-up in the NE Atlantic and isostatic response to glacial erosion, respectively. Additional uplift events may be related to mantle processes and the episodic behaviour of the Iceland plume.

We have undertaken 2D forward modelling across the northern North Sea, based on reprocessed, interpreted and depth-converted deep reflection seismic lines NSDP84-1 and −2 (15 s twt) and refraction data. Two separate stretching phases, Permo-Triassic and Jurassic, are recognized. The cumulative stretching is consistent with the observed crustal structure and the overall basin configuration, as reproduced by forward modelling. Good agreement between observed and modelled top basement level, and crustal thickness below the platform areas are particularly emphasized. Crustal-scale modelling indicates that crustal thickness varied across the northern North Sea at the onset of the Permo-Triassic rifting, from c. 35 km in the platform areas to less than 30 km in the interior of the basin. This may be ascribed to Devonian(-Carboniferous?) crustal stretching. Thinning of the crust has progressively been narrowed, from post-Caledonian extensional collapse, to less regional Permo-Triassic basins, and finally development of the Viking Graben area in the Jurassic-early Cretaceous time. Most of the Permo-Triassic stretching occurred between the Øygarden Fault Zone to the east and the Shetland Platform (southern transect) and the Hutton Fault alignment to the west. The width of the Permo-Triassic basin was c. 120–125 km, with calculated βmean between 1.38 and 1.40. Permo-Triassic βmean estimates across the present Horda Platform vary between 1.33 and 1.39. The Jurassic βmean estimates for the same area vary between 1.08 and 1.13. Across the Viking Graben, Permo-Triassic βmean varies between 1.28 (southern transect) and 1.41 (northern transect). This is lower than estimates for the Jurassic βmean, which amounts to 1.53 and 1.42. Permo-Triassic and Jurassic βmean estimates across the East Shetland Basin are 1.29 and 1.11, respectively. Lithospheric thermal evolution reflects the general differences between Permo-Triassic and Jurassic stretching, with a much wider thermal perturbation during the former and a focusing and lateral migration towards the east of the peak thermal elevation during the latter. There are still uncertainties related to the degree of (de)coupling between the upper crust and upper mantle during the Permo-Triassic and the Jurassic rift phases. These uncertainties are related to the interplay between age, strain rate, crustal rheology, crustal thickness and long-lived zones of weaknesses.

The southwestern Barents Sea shows a complicated network of fault complexes and systems with various geometrical and genetic characteristics: trend, relation to basement, reactivation, fault plane geometry, and regional significance. Using these parameters, a classification of the fault complexes has been made, and a correlation to onshore faults has been attempted. The area is subdivided into several fault blocks separated by deep-seated zones of weakness (first and second class fault systems). These are reactivated in connection with later (Mesozoic) movements in the area, and have acted as foci of strain so leaving the central area of the blocks relatively strain free. A third class of fault systems is of local significance, and reflects deformation limited to the interior of the fault blocks.

[1] Using analog modeling aided by digital image analysis (DPIV), we constrained the long-term kinematic evolution of strain partitioning in transpressional brittle wedges as a function of convergence angle. We ran a series of dry quartz sand experiments representing highly oblique continent-continent collision (convergence angles of 4°to 30°). The digital image analysis provided high-resolution constraints on the long-term kinematic evolution of these wedges, which could be subdivided in distinct kinematic stages, comprising (1) an initial "distributed strain" stage and (2) an "oblique wedge" stage before (3) the stage of strain partitioning is reached. Thus, we document the evolution of different deformation stages from a single plate tectonic boundary condition. In addition, the relationship between convergence angle, kinematic stages, and wedge geometry (including fault dips and fault hierarchy) was established. The modeling results show that smaller convergence angles lead to steeper faults. Besides, for a constant convergence angle, the proshears that evolved during the strain partitioning stage were less steep than those formed during the oblique wedge stage. The fault slip vector on individual fault segments was derived from the DPIV data set for each time increment, quantifying the magnitude and orientation of slip on fault segments during the different kinematic stages. In addition, in the 7.5°and 15°models, rotation of the slip vector by up to 40°was observed on a single proshear during the strain partitioning stage. These observations allow to some degree a validation of existing analytical models of strain partitioning, in particular the assumption of steady state.Citation: Leever, K. A., R. H. Gabrielsen, D. Sokoutis, and E. Willingshofer (2011), The effect of convergence angle on the kinematic evolution of strain partitioning in transpressional brittle wedges: Insight from analog modeling and high-resolution digital image analysis, Tectonics, 30, TC2013,