Abstract The exploratory drilling of 200 wildcat wells along the NE Atlantic margin has yielded 30 finds with total discovered resources of c. 4.1×10 9 barrels of oil equivalent (BOE). Exploration has been highly concentrated in specific regions. Only 32 of 144 quadrants have been drilled, with only one prolific province discovered – the Faroe–Shetland Basin, where 23 finds have resources totalling c. 3.7×10 9 BOE. Along the margin, the pattern of discoveries can best be assessed in terms of petroleum systems. The Faroe–Shetland finds belong to an Upper Jurassic petroleum system. On the east flank of the Rockall Basin, the Benbecula gas and the Dooish condensate/gas discoveries have proven the existence of a petroleum system of unknown source – probably Upper Jurassic. The Corrib gas field in the Slyne Basin is evidence of a Carboniferous petroleum system. The three finds in the northern Porcupine Basin are from Upper Jurassic source rocks; in the south, the Dunquin well (44/23-1) suggests the presence of a petroleum system there, but of unknown source. This pattern of petroleum systems can be explained by considering the distribution of Jurassic source rocks related to the break-up of Pangaea and marine inundations of the resulting basins. The prolific synrift marine Upper Jurassic source rock (of the Northern North Sea) was not developed throughout the pre-Atlantic Ocean break-up basin system west of Britain and Ireland. Instead, lacustrine–fluvio-deltaic–marginal marine shales of predominantly Late Jurassic age are the main source rocks and have generated oils throughout the region. The structural position, in particular relating to the subsequent Early Cretaceous hyperextension adjacent to the continental margin, is critical in determining where this Upper Jurassic petroleum system will be most effective.

Abstract The northern North Atlantic margins are classic examples of ‘volcanic’ rifted continental margins, where breakup was accompanied by massive volcanism. We discuss strategies used to obtain good intra- and sub-basalt seismic penetration so as to map the structure and the extruded and intruded igneous volume. We recorded deep penetration reflection data using a 12 000 m long single sensor (Q-)streamer and wide-angle seismic profiles with 85 4-component ocean bottom seismometers, along two transects across the Faroe and Hatton Bank continental margins in the NE Atlantic. Tomographic inversion of both compressional (P) and shear (S) wave crustal velocities are crucial in improving the reflection image and in constraining the nature of the sub-basalt lithology and the volume of extruded and intruded melt. Beneath the basalts, which reach 5 km thickness, is a low-velocity zone with P- and S-wave velocities characteristic of sedimentary rocks intruded by basalt sills. The underlying stretched continental basement contains abundant intrusive igneous sills on the rifted margin. Near the Faroe Islands, for every 1 km along-strike, 340–420 km 3 of basalt was extruded, while 560–780 km 3 was intruded into the continent–ocean transition (COT). Lower-crustal intrusions are focussed mainly into a narrow zone less than 50 km wide on the COT, whereas extruded basalts flow >100 km from the rift. Melt on the COT is intruded into the lower crust as sills which cross-cut the stretched and tilted continental fabric, rather than as ‘underplate’ of 100% melt, as has often been assumed previously. Our igneous thickness and velocity observations are consistent with the dominant control on the melt production being rifting above mantle with a temperature elevated above normal. The mantle temperature anomaly was up to 150°C above normal at the time of continental breakup, decreasing by c . 70–80°C over the first 10 Ma of seafloor spreading.

Abstract The occurrence of failed breakup basins and deepwater blocks of thinned continental crust is commonplace in the rifting and breakup of continents, as part of passive margin development. This paper examines the rifting of Pangaea–Gondwanaland and subsequent breakup to form the South Atlantic Ocean, with development of a failed breakup basin and seafloor spreading axis (the deepwater Santos Basin) and an adjacent deepwater block of thinned continental crust (the Sao Paulo Plateau) using a combination of 2D flexural backstripping and gravity inversion modelling. The effects of the varying amounts of continental crustal thinning on the contrasting depositional and petroleum systems in the Santos Basin and on the São Paulo Plateau are discussed, the former having a predominant post-breakup petroleum system compared with a pre-breakup system in the latter. An analogy is also made to a potentially similar failed breakup basin/thinned continental crustal block pairing in the Faroes region in the NE Atlantic Ocean.

Abstract Improved seismic imaging of the deep structures in the Faroe–Shetland Basin has revealed a complex Mesozoic rift system with shifting block polarity along the West Shetland Platform. Newly acquired seismic data has led to the focus of hydrocarbon exploration on structurally defined Mesozoic traps and has re-opened exploration in the deeper stratigraphic sections beyond the stratigraphic, Paleocene deep-water play. In the study area, rift geometry changes from symmetrical (south) to asymmetrical (north), the latter creating a large-scale seaward-dipping flexure. The polarity shift may link up with deep-seated basement structures (rift-oblique lineaments) segmenting the rift zone. The initial rifting along the West Shetland Platform strongly influenced the depositional setting and lateral distribution of the Lower Cretaceous sediments. During rift initiation in the Early Cretaceous faulting took place along numerous small faults, which eventually linked up, creating a set of basin master faults in the main rift phase. Sand derived from rivers and longshore currents on the West Shetland Platform was transported down the axis of relay ramps and filled the juvenile rift basins. These sediments formed thick onlapping wedges, reflecting the continuous creation of accommodation space and the overall transgressive nature of the syn-rift and early post-rift succession. In this period, rift basins were elongated, which to some extent hindered cross-rift transport of coarse material except at relay ramps and rift-oblique lineaments. As fault movements ceased, the rift topography was levelled out and allowed gravity-driven systems to reach further into the basin, overstepping former cross-rift barriers. Lower Cretaceous syn-rift sediments are well exposed at several localities along the margins of the northern North Atlantic including onshore NE Greenland. The close analogy to the syn-rift structural setting imaged in the west of Shetland seismic succession may provide valuable information on structurally controlled depositional systems, reservoir architecture and properties.

Abstract Recent exploration activities in the basalt covered part of the offshore Faroe Island region has stressed the need for a better understanding of the volcanic succession, especially the lowermost part and the transition to the underlying non-volcanic succession. Using the proposed interpretation methods, which include careful identification of inclined reflector segments and flattening to various reflectors representing pronounced continuous markers embedded horizontally and 3D visualization, six volcanic units have been identified. The upper three units consist of plane-parallel reflector packages and probably represent subaerially extruded lava flows. The three lower units are characterized by irregular hummocky and inclined reflectors and are interpreted as lava deltas composed mainly of hyaloclastites. Within the data coverage area, the direction of extrusion is inferred from the seismic interpretation and four units originate from the NW and two from the SE. It is believed that the base of the volcanic succession is situated at a deeper level than the base of the parallel bedded units. At the base of the basalt succession and in the lower part of the volcanic succession pronounced reflector segments are ascribed to saucer-shaped sills. Analysing the seismic data using principles of seismic stratigraphy and observing them in a 3D environment, it is possible to obtain a broader understanding of the volcanic succession in the area and thereby divide the volcanic succession into characteristic facies units and separate it from the non-volcanic lithology and sills. The study shows that applying the proposed interpretation technique allows an evolution model to be put forward and it is suggested that the approach used in the study can be of use for hydrocarbon exploration in other basalt-covered areas.