Abstract The Late Cretaceous-Tertiary structural evolution of the northeastern part of the Vøring Basin, mid-Norway, is highly complicated. Although tectonic activity occurred throughout Cretaceous time in much of the Vøring Basin, including the Gjallar Ridge and along the Fles Fault Zone, in the Vema Dome-Nyk High area evidence of such activity is not observed until the latest Maastrichtian time. In the Vema Dome-Nyk High area, several faults with both a NW-SE orientation and a NE-SW orientation have experienced lateral movements. The NE-SW orientation is the old Caledonian trend. The complex structural evolution of the Vema Dome-Nyk High area is probably related to the existence of continental weakness zones, which are the onshore extension of known oceanic fracture zones. The two lineaments that delineate these weakness zones, and that delineate the Vema Dome-Nyk High area, namely the Bivrost and Surt Lineaments, diverge slightly from one another toward the SE. This complex structural framework of NW-SE oriented lineaments and NE-SW oriented deep-seated basement structures of Caledonian compressional and/or Mesozoic rift origin, facilitated minor clockwise rotation of the area between the two lineaments during the extensional regime before the break-up of the North Atlantic, as well as during the compressional regime that has been proposed after the break-up.

Abstract The effects of strong circulation for the generation of erosional surfaces in the deep sea are observed in the region of the Rio Grande Gap, Western South Atlantic. Conspicuous unconformities are observed on multichannel seismic lines shot by the University of Texas Institute of Geophysics (UTIG) research ship R/V Fred Moore in July 1979, while surveying the Rio Grande Gap and the Brazil basin for future locations of DSDP sites. The Rio Grande Gap, a low basement area with an average width of 150 km (93 mi), is located between the Rio Grande Rise and the basement high to the west (Figure 1). The Rio Grande Gap is the major connection between the Argentine basin to the south and the Brazil basin to the north. The 600-km (372-mi) long Vema Channel stretches along the western limit of the Gap (Figure 1). This channel allows significant quantities of northward-flowing Antarctic Bottom Water (AABW) to enter the Brazil basin. Abroad terrace extends from the Vema Channel to the base of the Rio Grande Rise. Regional seismic studies of this part of the South Atlantic (for example, Le Pichon et al, 1971; Gamboa, 1981) have revealed a complex depositional history in the area, mainly related to the onset and fluctuations of the Antarctic Bottom Water circulation. The purpose of this paper is to present some examples of these erosional and depositional events identified on seismic lines across the Rio Grande Gap and the southern portion of the Brazil basin. Analyses of UTIG multichannel seismic data in the Rio Grande Gap allow us to distinguish four major seismic sequences within the sedimentary cover of the region. The sediments in the Rio Grande Gap are about 1.2 km (.7 mi) thick and the sequences are designated by letters A to D from the base to the top (Figures 2 and 3). Sequence A lies on a strong reflector inferred to be top of oceanic crust. In general, the basement reflector is fairly smooth, but in places considerable relief is observed, which appears to indicate offset by faulting. Sequence A is characterized by weak (relatively low amplitude) but continuous subparallel internal reflectors. The lower part of this sequence onlaps and fills the relief on the basement. The upper limit of Sequence A is defined by a prominent regional unconformity (unconformity A) which truncates this sequence at several places. This unconformity is a fairly smooth and level surface and probably marks a major change in the bottom-water circulation through this area. Sequence B is acoustically transparent, showing only few discontinuous reflectors. Sequence B thins and pinches out locally beneath the axis of the Vema Channel. The upper boundary of Sequence B is a prominent regional reflector, unconformity B. Sequence B probably represents a regime of restricted sedimentation controlled by deep sea currents, which began to affect the Rio Grande Gap area. Initiation of these currents probably eroded sequence A to produce unconformity A. Sequence C forms the major part of the terrace to the east of the Vema Channel. This sequence is characterized by dipping (prograding) and contorted internal reflectors (Figures 2 and 3). In cross section Sequence C is somewhat similar in geometry to an alluvial terrace (Figures 1, 2 and 3). This sequence represents a striking change in the sedimentation pattern in the Rio Grande Gap area. Its dipping layers indicate a progradation of sediments transported along the bottom, which filled the gap and formed the terrace to the east of the Vema Channel.

Abstract A new approach to constrain the Cretaceous and early Palaeogene depositional systems in the Vøring Basin has been achieved by combining 3D palaeobathymetry reconstructed from seismic sequence geometries, indicators of zero or shallow water depth, compaction and isostasy. The restorations were calibrated to known exposed intrabasinal highs. The Vøring Basin started out as a segmented and locally deep syn-rift basin during the Late Ryazanian. Water depths in the range 1000–2000 m have been restored in the deeper areas. In Late Cenomanian broader deep-water areas formed in the eastern part of the basin. The broadening of the basin was accompanied by shallower water depths during the Coniacian. A switch in basin configuration was fully established during the Early Campanian. The previously deep areas in the Rås and Træna basins became very shallow and the Vigrid and Någrind synclines started to subside, as a response to the reactivation of the Fles Fault Complex. The shallowing trend continued during Late Cretaceous time until regional uplift of the basin floor, and total emergence of the intrabasinal highs known as Gjallar Ridge, Vema Dome, Nyk High and Utgard High occurred around Maastrichtian-Paleocene time. This was followed by deepening in the Early Paleocene expressed in the depocentres, where the Vigrid and Rås basins now attained water depths of 300–400 m. Further increased subsidence occurred during the Late Paleocene, resulting in water depths up to 1000 m in the eastern Vøring Basin.