Abstract This chapter provides comprehensive descriptions of 52 numbered formations/rock units of the Southeastern Oman Mountains, based on available literature. The oldest eight siliciclastic and carbonate formations are positioned below the ‘Hercynian’ Unconformity. The overlying formation (9–16) mostly represent carbonates which accumulated in a passive margin platform setting during or after the opening of the Neo-Tethys Ocean. The passive margin slope and platform collapsed during the late Cretaceous because of the obduction of the Semail Ophiolite along with the deep marine Hawasina sedimentary rocks. The collapsing passive margin interval was recorded within the syn-obductional Aruma Group (17; Muti Formation). Above this formation are the allochthonous units (18–42) of the tectonically lower Hawasina deep-sea basin and the structurally overlying Semail Ophiolite. The former contains Permian to Upper Cretaceous formations, while the latter is Cenomanian in age. Above the allochthonous rocks, the Neo-autochthonous formations were deposited, starting with the post-obductional uppermost Cretaceous Aruma Group (43; Al-Khod Formation) until the Quaternary deposits (52). All these formations/rock units are depicted on an accompanying map and stratigraphic chart.

ABSTRACT Recent seismic reflection data across the Japan Trench show that frontal accretion involves offscraping sediments on top of horsts and scooping-up sediment from grabens. However, seismic profiling does not illuminate the structure within the accretionary prism, and thus the processes of accretion and prism growth are unknown. Key data from scientific drilling at Integrated Ocean Drilling Program Site C0019 that penetrated the prism in the region of large displacement during the 2011 Tohoku earthquake support a model in which frontal accretion occurs by imbricate thrusting, folding, and stacking of thrust sheets that are composed of semicoherent-sediment strata. Using palinspastic restoration techniques, we conclude that out-of-sequence thrusting and duplex development during the underthrusting of horsts can form and displace hanging-wall ramps along the plate-boundary detachment, which helps to explain the formation of some unexpected tectonostratigraphic relations at C0019, such as the emplacement of a thick section of the youngest sediments at the base of the accretionary prism, and numerous juxtapositions of different-age sediments within the basal plate-boundary fault zone.

Abstract The Middle Jurassic–Lower Cretaceous in the eastern Dutch offshore provides excellent examples of sand-rich sediments that locally accumulated in the vicinity of rift basin margins affected by salt tectonics. These types of deposits are often geographically restricted and difficult to identify, but can be valuable targets for hydrocarbon exploration. The distribution, thickness and preservation potential of fluvio-lacustrine, shallow- and deep-marine sediments is discussed to provide new insights into the regional and local tectonostratigraphy of the Dutch Central Graben, the Terschelling Basin and their neighbouring platforms. New sedimentological, geochemical, biostratigraphic, stratigraphic and structural information have been analysed and integrated into a new tectonostratigraphic model for the Callovian Lower Graben Formation, Oxfordian Middle and Upper Graben formations, Early–Middle Volgian Terschelling Sandstone and Noordvaarder members, and the Late Volgian–Early Ryazanian Scruff Greensand Formation. It is demonstrated that salt withdrawal at the basin axis was the primary control on the generation of high accommodation during the Callovian–Early Kimmeridgian. Incised valleys developed on the platforms providing lateral sediment input. During the Late Kimmeridgian–Ryazanian salt migration shifted laterally towards the basin margins, providing accommodation adjacent to active salt bodies and deposition of overthickened sandy strata.

The NAG-TEC project was a collaborative effort by the British Geological Survey, the Geological Survey of Denmark and Greenland, the Geological Survey of Ireland, the Geological Survey of the Netherlands, the Geological Survey of Northern Ireland, the Geological Survey of Norway, Iceland GeoSurvey and the Faroese Geological Survey (Jarðfeingi), along with a number of academic partners and significant support from industry. The main focus was to investigate the tectonic evolution of the region with a particular emphasis on basin evolution along conjugate margins. A key outcome was the development of a new tectonostratigraphic atlas and database that includes comprehensive geological and geophysical information relevant for understanding the Devonian to present evolution of the NE Atlantic margins. These provide the foundation upon which ongoing research and exploration of the area can build. This Special Publication provides some of the first scientific results and analysis based on the project, including regional stratigraphic analysis and correlations, crustal structure and interpretation of geophysical data sets, plate kinematics and the evolution of igneous provinces.

Abstract The Dyfed Supergroup of SW Wales ranges from Terreneuvian to Furongian in age and represents a prolonged and nearly continuous phase of siliciclastic sedimentation on the southern margin of the Cambrian Welsh Basin. The lower 564 m of the Supergroup are included in an extended Caerfai Group (six formations), embracing strata previously assigned to the Solva Group. Predominantly arenaceous, the Caerfai Group has important units of conglomerate and pebbly sandstone at its base, middle and top. The Caerfai Group is overlain by 687 m of mainly argillaceous sedimentary deposits of the Porth-y-rhaw Group (five formations), a newly erected unit that includes strata previously assigned to the ‘Menevian Group’ and ‘Lingula Flags’. This two-fold division of the Dyfed Supergroup is comparable with the distinction of the laterally equivalent Harlech Grits and Mawddach groups exposed around the Harlech Dome in North Wales. High resolution sequence-stratigraphical techniques, constrained by biostratigraphical data wherever possible, are applied to the Dyfed Supergroup across southern Britain: the revised lithostratigraphy is thereby integrated with a slightly modified version of the Avalonian chronostratigraphy initially developed for the western Avalonian successions of maritime Canada. Sequences 1 and 2 are not recognized in the Dyfed supergroup of SW Wales, reflecting the inner platform setting of the area. Those sequences are represented in North Wales however, which was situated on the outer platform. The relative ease with which the Cambrian successions of southern Britain can be incorporated into the general Avalonian framework reflects the shared epeirogenic history, sediment sources and accumulation history of a microcontinent unified by early Cambrian times. The gross lithological similarities that exist between Cambrian successions across Avalonia, and between SW Wales and North Wales in particular, are better understood when basin chronostratigraphy is placed within a sequence stratigraphic framework defined by systems tracts. This is particularly evident during Unnamed Cambrian Series 3 (C3) and Furongian times, when clear systems links are demonstrated between paralic depositional environments in SW Wales and deeper basin turbidites in North Wales. Sequences 3–7 (Terreneuvian–C3) in the Welsh Basin and its hinterland were dominated by siliciclastic deposition on an epeirogenically active platform. An extensional rift-like tectonic regime is proposed, where elongate basins dominated by mudstone deposition have time equivalents formed on areas of apparent uplift that were probably tilt-block highs. Local accumulation history, the development of regional unconformities, the extent of marine onlap, and the secular succession of lithofacies were controlled principally by phases of fault-accommodated subsidence along the NE-trending lineaments that bounded these basins and their intervening horsts or platforms. In southern Britain, movements first along the Menai Straits Fault System then the Welsh Borderlands Fault System, both of which are terrane boundaries, were responsible for the dominantly coarse-grained arenaceous sedimentation of pre-Drumian times. In the Welsh Basin, this is highlighted by a change in sediment source from the Monian Superterrane to the Wrekin Terrane. A rapid switch from marginal to inner platform source areas accompanied a major phase of tectonic reorganization of the Avalonian Superterrane during the development of the boundary between sequences 3 and 4. Although the role of secular variations in eustatic sea level as a control on sequence development and architecture has been dismissed previously, prominent lowstands such as those recorded during the basal Ptychagnostus gibbus Biozone, ‘ Solenopleura ’ brachymetopa Biozone (mid- Paradoxides forchhammeri Biosuperzone), and the upper part of the forchhammeri Biosuperzone also influenced the depositional sequence stratigraphy. The broad subdivision of Cambrian Avalonian stratigraphy into tectonically active and passive phases of sedimentation allows two megasequences to be distinguished. Megasequence 1 (sequences 1–7) represents the transform termination of Avalonian subduction following oblique convergence, and the accretion of island arcs onto the northern periphery of Gondwana. Under transpressional regimes, late Precambrian arc-related basins were inverted and recycled into pull-apart successor basins. Initially, the margins of these were dominated by alluvial fans and coarse-grained fan-deltas built by flood-generated sediment dispersal processes. In the later transform stage of Cadomian–Avalonian orogenesis, there was a switch to sediment supplied from highlands to the east. Sequence 8, represented in Pembrokeshire by the Aber Llong and Ogof Velvet formations, lies at the base of Megasequence 2 (late C3–early Ordovician). Excellent sections occur through these formations and their equivalents in North Wales, and their interpretation significantly improves understanding of younger Cambrian sedimentary basins in Avalonia. These successions reflect passive margin sedimentation and the culmination of the Avalonian–Cadomian orogenic cycle. Deposition occurred in part of a subaqueous delta platform at the mouth of a huge river system that drained a substantial part of West Gondwana, with Avalonia acting as a sink for vast quantities of fine-grained sediment. Secular variations in eustatic sea level and/or sediment supply, rather than active tectonism, were the main mechanisms controlling sequence architecture and depositional environments at this time.

Abstract Palaeogeographic and tectono-stratigraphic considerations in the greater Barents Sea show that the distribution of reservoirs and hydrocarbon source rocks from the Late Palaeozoic to the Palaeogene can be related to three tectonic phases. Firstly, the Palaeozoic Caledonain Orogeny caused uplift to the west, followed by eastward sediment distribution across the shelf, towards carbonate platforms to the east. Secondly the Late Palaeozoic–Mesozoic Uralide Orogeny induced uplift to the east, causing widespread clastic deposition and reversal of the sediment distribution pattern. Thirdly, major Late Mesozoic–Cenozoic rifting and crustal breakup in the western Barents Sea led to the current basin configuration. Reservoir rocks comprise Late Palaeozoic carbonates and spiculites, Mesozoic terrestrial and marine sandstones and Palaeogene deep-water sandstones. Hydrocarbon source rocks range in age from Silurian to Early Cretaceous, and are grouped into three petroleum systems derived from Late Palaeozoic, Triassic and Late Jurassic source rocks. Multiple tectonic episodes caused formation of a variety of trap types, of which extensional fault blocks and gently folded domes have been the most prospective. Volumetric considerations of generated petroleum indicate that charging is not a limiting factor, except in the western margin.

Abstract Within the Appalachian–Variscan orogen of North America and southern Europe lie a collection of terranes that were distributed along the northern margin of West Gondwana in the late Neoproterozoic and early Palaeozoic. These peri-Gondwanan terranes are characterized by voluminous late Neoproterozoic ( c . 640–570 Ma) arc magmatism and cogenetic basins, and their tectonothermal histories provide fundamental constraints on the palaeogeography of this margin and on palaeocontinental reconstructions for this important period in Earth history. Field and geochemical studies indicate that arc magmatism generally terminated diachronously with the formation of a transform margin, leading by the Early–Middle Cambrian to the development of a shallow-marine platform–passive margin characterized by Gondwanan fauna. However, important differences exist between these terranes that constrain their relative palaeogeography in the late Neoproterozoic and permit changes in the geometry of the margin from the late Neoproterozoic to the Early Cambrian to be reconstructed. On the basis of basement isotopic composition, the terranes can be subdivided into: (1) Avalonian-type (e.g. West Avalonia, East Avalonia, Meguma, Carolinia, Moravia–Silesia), which developed on juvenile, c . 1.3–1.0 Ga crust originating within the Panthalassa-like Mirovoi Ocean surrounding Rodinia, and which were accreted to the northern Gondwanan margin by c . 650 Ma; (2) Cadomian-type (e.g. North Armorican Massif, Ossa–Morena, Saxo-Thuringia, Moldanubia), which formed along the West African margin by recycling ancient ( c . 2.0–2.2 Ga) West African crust; (3) Ganderian-type (e.g. Ganderia, Florida, the Maya terrane and possible the NW Iberian domain and South Armorican Massif), which formed along the Amazonian margin of Gondwana by recycling Avalonian and older Amazonian basement; and (4) cratonic terranes (e.g. Oaxaquia and the Chortis block), which represent displaced Amazonian portions of cratonic Gondwana. These contrasts imply the existence of fundamental sutures between these terranes prior to c . 650 Ma. Derivation of the Cadomian-type terranes from the West African craton is further supported by detrital zircon data from their Neoproterozoic–Ediacaran clastic rocks, which contrast with such data from the Avalonian- and Ganderian-type terranes that suggest derivation from the Amazonian craton. Differences in Neoproterozoic and Ediacaran palaeogeography are also matched in some terranes by contrasts in Cambrian faunal and sedimentary provenance data. Platformal assemblages in certain Avalonian-type terranes (e.g. West Avalonia and East Avalonia) have cool-water, high-latitude fauna and detrital zircon signatures consistent with proximity to the Amazonian craton. Conversely, platformal assemblages in certain Cadomian-type terranes (e.g. North Armorican Massif, Ossa–Morena) show a transition from tropical to temperate waters and detrital zircon signatures that suggest continuing proximity to the West African craton. Other terranes (e.g. NW Iberian domain, Meguma) show Avalonian-type basement and/or detrital zircon signatures in the Neoproterozoic, but develop Cadomian-type signatures in the Cambrian. This change suggests tectonic slivering and lateral transport of terranes along the northern margin of West Gondwana consistent with the transform termination of arc magmatism. In the early Palaeozoic, several peri-Gondwanan terranes (e.g. Avalonia, Carolinia, Ganderia, Meguma) separated from West Gondwana, either separately or together, and had accreted to Laurentia by the Silurian–Devonian. Others (e.g. Cadomian-type terranes, Florida, Maya terrane, Oaxaquia, Chortis block) remained attached to Gondwana and were transferred to Laurussia only with the closure of the Rheic Ocean in the late Palaeozoic.