ABSTRACT Cretaceous (131–92 Ma) plutonic rocks intruded two different NW-SE–oriented belts of host rocks in the southernmost tip of the Peninsular Ranges Batholith. The western belt, which was likely close to the paleotrench, consists of Jurassic metaigneous rocks with oceanic-arc affinity. Toward the continent, the eastern belt is composed of amphibolite, paragneiss and orthogneiss, schist, calc-silicate, marble, and undifferentiated metamorphic rocks, for which the sedimentary protoliths are interpreted as Triassic–Jurassic back-arc assemblages or Paleozoic continental slope and basin sediments. Here, we present U-Pb isotope data for detrital zircons from five paragneisses and two schists for maximum depositional age (MDA) and provenance analysis estimations. In addition, we obtained Sm-Nd isotope dilution–thermal ionization mass spectrometry isochron ages of leached garnet and whole-rock (WR) samples to establish the timing of metamorphism. Detrital zircon geochronology of three samples from the western belt and two from the eastern belt indicates Early Jurassic MDAs (193–177 Ma), whereas one sample from the western belt has a Late Triassic MDA (208 Ma), with zircon populations that were shed from similar sources. The compiled zircon data show four age modes, suggesting provenance from the Permian–Triassic Cordilleran arc and the Appalachian, Pan-African, and Grenville orogens. Based on these observations, we consider that the two proposed belts of host rocks from the southern Peninsular Ranges Batholith share a similar origin, where the sedimentary protoliths were deposited in ocean basins fed by continentally derived material with peri-Gondwanan affinity. One biotite-garnet paragneiss yielded a Sm-Nd garnet-WR age at 160 ± 2 Ma, coeval with metamorphic zircon growth (ca. 166 Ma) in the same sample, indicating a Middle–Late Jurassic metamorphic event. The other samples yielded Sm-Nd garnet-WR ages of 105 ± 3, 114 ± 2, and 214 ± 13 Ma. The Cretaceous ages are coeval with plutonism, whereas the Triassic age is the oldest metamorphic age documented in the Baja California Peninsula. The detrital zircon provenance ties the sedimentary protoliths to the ancient continental margin of Mexico since the Late Triassic. The Sm-Nd garnet-WR geochronology provides the first well-constrained dates for the timing of metamorphism in this region, which reveals not only a regional event, but also coeval metamorphism and magmatism.

The Southern Permian Basin, as its name suggests, is a historical heartland for hydrocarbon production from the Palaeozoic Rotliegend interval. However, in this mature basin the Mesozoic presents further possibilities to offer resource security to NW Europe. Such opportunities include increasing efficiency in the production of discovered hydrocarbons, exploration for further hydrocarbons (both conventional and unconventional) and efficient exploration for, and production of, geothermal energy. All these potential resources require a grounding in technically sound geoscience, via traditional scientific observation and the application of new technologies, to unlock their value. The main aim of this volume is to bring together the work of academics and industry workers to consider cross-border geoscience including contributions on Poland, Germany, The Netherlands, the United Kingdom and adjacent areas. The work presented intends to contribute to the development and discovery of further Mesozoic energy resources across the basin.

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 The Tornquist Fan, reflecting the northern part of the Trans-European Suture Zone, comprises a series of fault zones and major single faults, striking mainly subparallel to the SW margin of the Fennoscandian Shield. The deep-seated faults of Wiek, Nord Jasmund and Schaabe, which cross the northern part of Rügen Island and areas of the adjacent Baltic Sea from NW to SE, originated in the late Paleozoic. They are accompanied by younger faults, especially in the Pomeranian Bay, that were formed by Mesozoic tectonic processes. Based on reprocessed offshore seismic lines east of Rügen, a polyphase evolution for the Wiek Fault System is proposed. It implies changes in the stress field since the Caledonian Orogeny. Crustal extension in the Middle Devonian led to the formation of basins along the SW margin of Laurussia. Subsequent compressional movements, induced by the distant Variscan Orogeny, resulted in segmentation and block faulting of the Rügen Basin prior to the late Carboniferous. These Paleozoic faults were reactivated by Mesozoic extensional stress regimes. In addition, new en echelon faults were generated, contemporaneously with the formation of the Western Pomeranian Fault System. Since the Late Cretaceous (Africa–Iberia–Europe convergence), selected major normal faults have been reactivated as reverse faults.

Abstract Based on reprocessed offshore seismic lines acquired during oil and gas exploration in the 1980s, we reconstruct the formation and reactivation of major fault systems in the southern Baltic Sea area since the late Paleozoic. The geological evolution of different crustal blocks from the Caledonian Avalonia–Baltica collision until the Late Cretaceous–Paleogene inversion tectonics is also examined. The detected fault systems occur in the northern part of the Trans-European Suture Zone (TESZ) and belong either to the late Paleozoic Tornquist Fan or to the complex Western Pomeranian Fault System (WPFS) generated during Mesozoic extensional movements. While the NW–SE-trending deep Wiek Fault separates the Arkona High from the Middle Rügen Block, the NNW–SSE-trending Agricola Fault demarcates the Middle Rügen Block to the Falster Block in the west. Together with the Plantagenet Fault and numerous younger faults in the Mesozoic cover, it forms the Agricola Fault System. Furthermore, structural analyses of the Prerow Fault Zone above the Prerow salt pillow and the Werre Fault Zone crossing the Grimmen High indicate a complex fault history.

Abstract The northern Dutch offshore is an area that has seen less hydrocarbon exploration activity than other areas of The Netherlands. Acquisition of a new regional 3D seismic dataset allowed further testing and re-evaluation of established geological concepts in this area. It is recognized that the presence and movement of Upper Permian Zechstein evaporites had a major impact on depositional patterns in Mesozoic sediments, structural development and hydrocarbon migration. As such, this study looks specifically at the role of salt tectonics in tectonosedimentary development. To assess this salt tectonic evolution within its structural context, a restoration of the Step Graben and Dutch Central Graben was performed. It follows that depositional patterns are closely linked to the nature of salt structure movement and the timing of regional tectonism. For example, during Late Triassic rifting, salt pillows developed and sedimentation focused away from salt structures into depocentres along regional fault trends. Restoration results show that this interplay between salt movement and tectonism is needed to accommodate the sedimentation patterns associated with the formation of the Step Graben and Central Graben during the Triassic and Jurassic, and later during Late Cretaceous and Cenozoic inversion tectonics.

Abstract In analytical models of salt diapirism, the initial salt-layer thickness and the post-deformation spacing of salt structures are key parameters. Here, 3D seismic data from The Netherlands offshore has enabled these parameters to be measured over large areas which can then be compared with model predictions. Estimates of the original salt-layer thickness were obtained by spatially filtering present thickness, using filters with varied spatial scales that remove local effects. Loss of evaporite minerals by dissolution or erosion during exposure, cannot be ruled out and, as such, thicknesses are minima. Spacing estimates were derived in two dimensions by locating the minimum separation of lines representing ridgelines of diapirs/walls. Because the length scale of spatial filtering was chosen based on the dependent variable, diapir spacing, the results are non-unique. Nevertheless, choosing an apparently optimal filter length of 50 km, a ratio between diapir spacing and original thickness from 12 to 20 is defined. This ratio is greater than has been reported for the pillow province of the UK North Sea Quadrant 44, which is as expected if pillows evolve into diapirs with progressive halokinetic deformation. This work is key to understanding the evolution of salt displacement, a necessity for unlocking remaining hydrocarbon resources.

Abstract A review of recent Triassic research across the Southern Permian Basin area demonstrates the role that high-resolution stratigraphic correlation has in identifying the main controls on sedimentary facies and, subsequently, the distribution of hydrocarbon reservoirs. The depositional and structural evolution of these sedimentary successions was the product of polyphase rifting controlled by antecedent structuration and halokinesis, fluctuating climate, and repeated marine flooding, leading to a wide range of reservoir types in a variety of structural configurations. Triassic hydrocarbon accumulations form an important energy resource across the basin, not only in the established Buntsandstein fairway but also in Rogenstein oolites and Muschelkalk carbonates. In addition, sand-prone sections in the Late Triassic, such as the Schilfsandstein, have the potential to be hydrocarbon reservoirs. Several Triassic intervals are now the focus for developing geothermal projects. A detailed understanding of Triassic reservoir quality and distribution is one of the main keys to efficiently unlocking the geothermal and remaining hydrocarbon potential across the basin.

Abstract Sandstones of the Main Buntsandstein Subgroup represent a key element of the well-established Lower Triassic hydrocarbon play in the southern North Sea area. Mixed aeolian and fluvial sediments of the Lower Volpriehausen and Detfurth Sandstone members form the main reservoir rock, sealed by the Solling Claystone and/or Röt Salt. It is generally perceived that reservoir presence and quality decrease towards the north and that the prospectivity of the Main Buntsandstein play in the northern Dutch offshore is therefore limited. Lack of access to hydrocarbon charge from the underlying Carboniferous sediments as a result of the thick Zechstein salt is often identified as an additional risk for this play. Consequently, only a few wells have tested Triassic reservoir and therefore this part of the basin remains under-explored. Seismic interpretation of the Lower Volpriehausen Sandstone Member was conducted and several untested Triassic structures are identified. A comprehensive, regional well analysis suggests the presence of reservoir sands north of the main fairway. The lithologic character and stratigraphic extent of these northern Triassic deposits may suggest an alternative reservoir provenance in the marginal Step Graben system. Fluvial sands with (local) northern provenance may have been preserved in the NW area of the Step Graben system, as seismic interpretation indicates the development of a local depocentre during the Early Triassic. These insights help to improve the chance of finding Lower Buntsandstein reservoir rocks in the northern Dutch offshore.

Abstract An analysis of the Lower Triassic ‘Buntsandstein’ gas play in the underexplored Mesozoic rift system of the German–Danish Horn Graben is presented. Dry hole information from four well penetrations is analysed alongside the development of a 3D basin model. It is demonstrated that the dry holes do not preclude the existence of a working hydrocarbon system. Reservoir and seal elements are present, although details of quality and distribution are uncertain. Carboniferous coal preservation is likely, in a limited area, within the graben and can be constrained through seismic mapping. Vertical gas migration through the Zechstein interval is considered likely due to a large thickness variability (driven by halokinesis and facies changes). The overlap of peak gas-expulsion timing and halokinetic movements make rollover/turtle-back traps risky in terms of breaching or underfill. Dry wells in Denmark are explained by a combination of this relative timing and uncertainty over longer distance migration. This play analysis demonstrates a general agreement with previously published 1D basin models with respect to gas-expulsion timing. However, in contrast to published examples, it is shown that the Zechstein interval can allow for vertical gas migration. Considerable uncertainty in parameters, such as depth conversion, amount of erosion and migration paths, are recognized. Exploration opportunities remain, albeit relatively high risk, in the German area of the graben both in the ‘Buntsandstein’ play and at other stratigraphic levels.