Abstract Mesozoic extensional basins of the Southern Permian Basin (SPB) System became inverted from Late Cretaceous time onwards. Following a first Cretaceous ‘Subhercynian’ pulse of contractional deformation and basin uplift, several distinct inversion events of Cenozoic age were often described. The oldest of these is the ‘Laramide’ event of Paleocene age which coincides with the termination of chalk deposition and widespread regression around the North Sea Basin, whose axial part continued to subside. The spatial extent of these effects is too wide to be compatible with inversion by folding and reverse faulting. The width of the uplifting and subsiding regions was also too large to be consistent with folding of the entire lithosphere under tangential compression. There appears to be no unequivocal evidence of discrete structures formed or reactivated in the Laramide event. By contrast, well-documented younger inversion of approximately Late Eocene to Late Oligocene–(Miocene?) age affected the region from the Celtic Sea to the western Netherlands. The associated deformation is weaker than that of the Late Cretaceous event and spatially overlaps with it only in the Southern North Sea. Structural inversion of the SPB thus comprised only two events separated in time and mostly also in space.

Abstract The inversion of a sedimentary basin could be associated with compressional reactivation of basin-forming normal faults, upwards movement of the basement blocks and partial or complete erosion of its sedimentary infill. Basin inversion might be also related to whole-basin uplift that is not linked to the reactivation of basement faults, and results in the development of regional stratigraphic gaps and unconformities. Both types of basin inversion have been documented in SE Poland using seismic data. Regional NW–SE seismic profiles illustrate earliest Late Jurassic (earliest Oxfordian) and earliest Late Cretaceous (Cenomanian) regional unconformities related to regional basin-scale uplifts in the SE segment of the Polish Basin. Late Cretaceous (Turonian?–Maastrichtian) progressive uplift of the Mid-Polish Swell has been documented along the NE border zone of this regional anticlinal structure. The Upper Cretaceous inversion-related sedimentary succession is characterized by an overall progradational character directed from the SW towards the NE. Buried contourite drifts that were detected within the Upper Cretaceous succession using seismic data indicate the existence of contour currents encircling inversion-related intrabasinal morphological barriers. A new tectonic scenario of the Mesozoic evolution of SE Poland would have a significant impact on the modelling of tectonic subsidence and the history of petroleum systems.

Abstract Wintershall Noordzee BV recently discovered and appraised two Chalk oil fields (Rembrandt and Vermeer) in the Dutch North Sea with wells F17-10, F17-11, F17-12 and F17-13x. Extensive core material is available, and biostratigraphical analysis plus sedimentological evaluation results are presented here. Integration of these data with detailed 3D seismic interpretation results in interesting conclusions on the tectonic inversion of the Dutch Central Graben. It can be determined that the main inversion event is the Sub-Hercynian Phase, after which an island was formed in the Chalk sea during the Campanian and Maastrichtian. Around this island, erosion products can be found in the Chalk intervals. These sediments are time and facies comparable to the Vaals Formation in the south of The Netherlands, adjacent to the inverted Roer Valley Graben. Maastrichtian sediments are seen to onlap onto the island, decreasing it in size and influence as a sediment source. It is proposed that the Laramide inversion phase in the Dutch Central Graben is a period of non-deposition and, possibly, this is also the case for most of the other Dutch inverted basins.

Abstract We present a consistent synthesis of palaeothermal (apatite fission track analysis (AFTA) and vitrinite reflectance) data from UK Southern North Sea wells with the regional pattern of exhumation defined from sonic velocity data. Cenozoic exhumation across most of the region began in the Paleocene between 63 and 59 Ma. Amounts of removed section are around 1 km across the offshore platform, increasing to 2 km or more on the Sole Pit axis. Neogene exhumation within this area began between 22 and 15 Ma, and led to removal of up to 1 km of section. Along the eastern flank of the Sole Pit axis, sonic data define a pre-Chalk event, and AFTA data from these wells show that exhumation began between 120 and 93 Ma. This timing correlates with events defined from AFTA data in the Sorgenfrei–Tornquist Zone, further east, presumably reflecting a response to regional tectonic stresses. East of the Sole Pit axis, AFTA and sonic velocities suggest that Neogene exhumation dominates, while further east towards the central parts of the North Sea Mesozoic sediments appear to be at maximum burial today except for local effects related to salt movement. The multiple episodes of exhumation and burial defined here have important implications for exploration.

ABSTRACT The structure and geology of former rifted continental margins can exert significant influence on their subsequent incorporation into collisional orogens. While thinned continental crust attached to the subducting mantle lithosphere may be incorporated into subduction channels, the weakly rifted parts of the margin are likely to resist subduction and thus deform ahead of the main orogenic front. This expectation is corroborated by a case study from the external western Alps. The former Dauphinois basins have inverted to form external basement massifs. Much of the deformation was widely distributed, with few localized thrust structures. Existing models that invoke distinct deformation events separated in time by a major (late Eocene, “Nummulitic”) unconformity are abandoned here in favor of crustal shortening that was continuous in time. Integrated stratigraphic, paleothermal, and geochronological data reveal that basin inversion was protracted over 6–10 m.y., coeval with deformation in the more internal parts of the chain. The notion of continuous, rather than episodic, deformation raises issues for the ways in which rates and tectonic activity may be evaluated within ancient orogens.

Abstract: Fault inversion has been documented in many basins worldwide, yet the details of how the initial extensional faults impact on the geometry and growth of the reactivated contractional system is often poorly resolved by the available data. Two-dimensional (2D) and 3D seismic reflection, and well data have been used to chart the evolution of inverted faults from the Taranaki Basin, offshore New Zealand. Sedimentary rocks up to 8 km thick record Late Cretaceous–Paleocene normal faults inverted during Miocene and younger shortening. The displacement and length of early normal faults is a key determinant for the reactivation and size of the subsequent reverse faults. All normal faults with maximum vertical displacements ≥600 m and lengths ≥9 km were inverted along their entire length, while smaller faults were not inverted. The proportion of the total basin-wide strain accommodated on each fault is comparable between deformational episodes. The hierarchy of reverse fault lengths was established rapidly, with longer faults accruing a greater proportion of the total strain from an early stage of shortening. The reverse fault system is dominated by inverted normal faults, which accrue displacement at the expense of smaller faults, and utilize the largest crustal-scale elements of the pre-existing system. The size of pre-existing heterogeneities is an important control for the magnitude and spatial extent of elevated stresses during contraction, which, in turn, control the dimensions, locations and displacements of subsequent fault growth.

Abstract: Salt is mechanically weaker than other sedimentary rocks in rift basins. It commonly acts as a strain localizer, and decouples supra- and sub-salt deformation. In the rift basins discussed in this paper, sub-salt faults commonly form wide and deep ramp synclines controlled by the thickness and strength of the overlying salt section, as well as by the shapes of the extensional faults, and the magnitudes and slip rates along the faults. Upon inversion of these rift basins, the inherited extensional architectures, and particularly the continuity of the salt section, significantly controls the later contractional deformation. This paper utilizes scaled sandbox models to analyse the interplay between sub-salt structures and supra-salt units during both extension and inversion. Series 1 experiments involved baseline models run using isotropic sand packs for simple and ramp-flat listric faults, as well as for simple planar and kinked planar faults. Series 2 experiments involved the same fault geometries but also included a pre-extension polymer layer to simulate salt in the stratigraphy. In these experiments, the polymer layer decoupled the extensional and contractional strains, and inhibited the upwards propagation of sub-polymer faults. In all Series 2 experiments, the extension produced a synclinal hanging-wall basin above the polymer layer as a result of polymer migration during the deformation. During inversion, the supra-polymer synclinal basin was uplifted, folded and detached above the polymer layer. Changes in thickness of the polymer layer during the inversion produced primary welds and these permitted the sub-polymer deformation to propagate upwards into the supra-salt layers. The experimental results are compared with examples from the Parentis Basin (Bay of Biscay), the Broad Fourteens Basin (southern North Sea), the Feda Graben (central North Sea) and the Cameros Basin (Iberian Range, Spain).