The Neogene stratigraphy of the glaciated European margin from Lofoten to Porcupine

WP2 - FAROE-SHETLAND

Tectonic setting and evolution

The pre-Neogene framework of the Faroe–Shetland region is dominated by the development of the Faroe-Shetland Basin, a broad area of sub-basins and ridges, which separates the Faroe Platform from the West Shetland Platform (Fig. 16a). The Faroe-Shetland Basin is contiguous with the Møre Basin to the NE, and the Rockall Basin to the SW, from which it is separated by the Erlend, and Wyville-Thomson/ Judd transfer zones, respectively (Rumph et al. 1993). The structural configuration of the basin reflects the intersection of NE–SW Caledonian lineaments with NW–SE transfer zones, which may also have been inherited from Caledonian or older orogenic phases. The geoseismic profiles in Fig. 16b and Fig. 16c shows that the pre-Neogene depocentre does not coincide with the present-day bathymetric expression of the Faroe-Shetland Channel, hence the different structural terminology.

The geoseismic sections (Fig. 16b and Fig. 16c) indicate that the Faroe–Shetland region has undergone polyphase extension, possibly initiated in the Late Palaeozoic with further intermittent extension and basin infill during Jurassic and Early Cretaceous time. However, the main phase of basin development took place in the Late Cretaceous and early Palaeogene related to rift events that led to the opening of the NE Atlantic Ocean. The development of the Faroe-Shetland Basin has been determined by differential subsidence in different sub-basins in Late Cretaceous, Paleocene and Eocene time, (Rumph et al. 1993; Roberts et al. 1999; Doré et al. 1999). The NW–SE trending lineaments were especially active, largely as a consequence of the Atlantic break up, which took place only 100–120 km to the W and NW of the Faroes (Larsen et al. 1999). These transfer zones are orientated perpendicular to the central spreading axis. Located towards the centre of the basin, the Victory Transfer Zone offsets the Corona Ridge and possibly the Rona Ridge, and has a proven influence on sedimentation patterns in the Palaeogene. The thickest Paleocene and Eocene depocentres are located to the SW of the Victory Transfer Zone (Mitchell et al. 1993), and movement along this feature may still occur at the present time (Ritchie, J.D. pers. comm. 2002). Up to 3km of Paleocene sediment accumulated in the Flett Sub-Basin (Stoker et al. 1993), whilst the Flett, Foula (Fig. 16c) and Judd Sub-basins all preserve significant Upper Cretaceous fills. 

Volcanism

Widespread volcanism accompanied late Mesozoic–early Cenozoic extension across the Faroe–Shetland margin (Fig. 16a). To the north and west of the Faroes Platform the study area is bounded by oceanic crust, including the anomalous crust of the Iceland-Faroe Ridge, which represents the hotspot trail of the Iceland plume (Doré et al. 1999). On the platform, the central and NW part of the high is covered by more than 3500m of flood basalts and hyaloclastites. To the SE, the basalts extend into the Faroe-Shetland Basin. According to Ritchie et al. (1999), lavas that accumulated to the SW of the Munkagrunnur Ridge were mainly extruded from strato/shield volcano complexes, whereas to the NE the extrusives originated from the same source that formed the Seaward–Dipping Reflector Sequences that mark the continent–ocean boundary. The lavas are of Paleocene–early Eocene age. The Paleocene lavas include those associated with the development of the Faroe-Shetland Escarpment (Fig. 16), which formed when continental basalts froze against a contemporary shoreline (Ritchie et al. 1999). Younger basalts subsequently extended farther into the basin, eventually pinching out in the middle of the basin. Intrusive sills and dykes together with a number of igneous centres are also known within the study area, forming the Faroe-Shetland Intrusive Complex. The sills and dykes are mainly latest Paleocene–early Eocene in age. The igneous complexes include the Paleocene Erlend Complex, and the undated Faroe Channel Knoll, Faroe Bank, and West Suduroy intrusions, which are known only from geophysical data. In the north of the area, the Brendan Complex has been interpreted as pre-Turonian in age (cf. Ritchie et al. 1999 for summary and references therein).

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Sedimentation

Cretaceous: During the Early Cretaceous, NW propagation of sea-floor spreading into the Labrador Sea resulted in periodic compressional reactivation in the eastern part of the Faroe–Shetland region. NE-trending normal faults, such as the Shetland Spine Fault, were reactivated and the structural highs of the West Shetland Platform and Rona Ridge became partially emergent and acted as source areas for the adjacent West Shetland Basin and Foula sub-basins, where up to 2000m of sediment accumulated. In the Late Cretaceous, the style of subsidence changed to a predominantly passive, thermal-cooling subsidence, as the Faroe-Shetland Basin developed and acted more as a single entity (Stoker et al. 1993). Upper Cretaceous successions are generally thicker, more extensive and more uniform than those of the Lower Cretaceous, and up to 5000m of Upper Cretaceous sediments may exist locally in the central part of the basin. 

Paleocene: At the beginning of the Paleocene, the Faroe-Shetland Basin was still an extension of the northern North Sea, and this connection remained open until the early Eocene (Lammers & Carmichael 1999). Inversion of the Margarita Spur closed the link to the North Sea and erosion of this high provided Paleocene coarse clastics into the Faroe-Shetland Basin and northern North Sea. The main Paleocene depocentre was the Flett Sub-Basin, which accumulated up to 3000m of marine shales and turbiditic sandstones (Stoker et al. 1993). Widespread volcanism (noted above) and episodic tectonic movements accompanied sedimentation. In the SW of the area, the Wyville-Thomson Ridge was subaerially exposed during the Paleocene, before being inundated. The origin of the ridge remains unclear, but it is believed that it (and the Munkagrunnur Ridge to the NE) was initiated by a late Paleocene–early Eocene compressional event, the result of a change in spreading geometries in the NE Atlantic (Boldreel & Andersen 1993).

Eocene: Lower Eocene clastic sediments originating primarily from the West Shetland Platform overlie the Paleocene volcanics (Andersen et al. 2002). In the Judd Sub-Basin, a lower Eocene succession, up to 700m thick, consists primarily of base-of-slope fan deposits. Uplift and inversion of the basin took place during early mid-Eocene time and a regional unconformity developed. In the following Lutetian time, a thick transgressive wedge onlapping the Ypresian sediments was deposited. The wedge is disconformably overlain by an upper Eocene succession containing a number of slump deposits (Sørensen 2002).

Oligocene: Oligocene sediments thicken northwards, and have a depocentre to the SE of the Faroe-Shetland Escarpment. Oligocene strata may also be present in the western part of the Faroe Bank Channel. According to Davies et al. (2001) deep-water exchange between the Arctic and Atlantic oceans may have been initiated in the early Oligocene, although Eldholm (1990) favours a later (Neogene) onset of bottom-current flow. The latter is consistent with strong deep-water erosion in latest Oligocene–early Miocene time that sculpted a highly irregular sea-bed surface, which forms the Top Palaeogene Unconformity, in the southern part of the Faroe-Shetland Basin (Stoker et al. 2002). During late Oligocene time, strong erosion also took place on the central part of the Faroes Platform and on the Fugloy Ridge. Consequently, Oligocene sediments present in the central part of the Faroe-Shetland Channel area are sourced partly from the Faroes and partly from the West Shetland Platform (Andersen et al. 2002). The uplift is believed to have resulted from compression caused by plate reorganisations and movements along spreading zones in the North Atlantic or by influence of early Alpine tectonism (Doré & Lundin 1996; Boldreel & Andersen 1993). Further development of the Wyville-Thomson Ridge may also have occurred at this time in response to dextral transpression in this area (Boldreel & Andersen 1993).

Note on Cenozoic compression

Phases of compression and uplift that were active in late Paleocene–early Eocene and late Oligocene time continued into the Neogene, where a third phase of compression occurred in the mid–late Miocene interval. This event, which saw further reactivation and uplift of the Wyville-Thomson, Fugloy and Munkagrunnur ridges, is similarly attributed to a change of spreading axes in the North Atlantic and the probable impact of Alpine orogenic compression (Doré & Lundin 1996; Boldreel & Andersen 1993). The persistence of such activity in this area is significant for understanding the Neogene evolution of the Faroe–Shetland region, as the main Neogene basin developments continued to be affected by uplift, folding and periodic reactivation of ridges along the flanks of the developing depocentres.

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References

Andersen, M.S., Sørensen, A.B., Boldreel, L.O. & Nielsen, T. 2002. Cenozoic evolution of the Faroe Platform comparing denudation and deposition. In: Doré, A.G.D., Cartwright, J., Stoker, M.S., Turner, J.P. & White, N. (eds) In press. Exhumation of the North Atlantic Margin: Timing, Mechanisms and Implications for Petroleum Exploration. Geological Society, London, Special Publications, 196, in press.

Boldreel, L.O. & Andersen, M.S. 1993. Late Paleocene to Miocene compression in the Faroe-Rockall area. In: Parker, J.R. (ed.), Petroleum Geology of NW Europe: Proceedings of the 4th conference. Geological Society, London, 1025-1034.

Davies, R., Cartwright, J., Pike, J. & Line, C. 2001. Early Oligocene initiation of North Atlantic Deep Water formation. Nature, 410, 917-920.

Doré, A.G., & Lundin, E.R. 1996. Cenozoic compressional structures on the NE Atlantic margin: nature, origin and potential significance for hydrocarbon exploration. Petroleum Geoscience, 2, 299-311.

Doré, A.G.D., Lundin, E.R., Jensen, L.N., Birkeland, Ø., Eliassen, P.E. & Fichler, C. 1999. Principal tectonic events in the evolution of the northwest European Atlantic margin. In: Fleet, A.J. & Boldy, S.A.R. (eds), Petroleum Geology of Northwest Europe: Proceedings of the 5th Conference. Geological Society, London, 41-61.

Eldholm, O. 1990. Paleogene North Atlantic magmatic-tectonic events: environmental implications. Mem. Soc. Geol. It., 44, 13-28.

Lammers, E. and Carmichael, S.M.M. 1999. The Paleocene deepwater sandstone play West of Shetland. In: Fleet, A.J. and Boldy, S.A.R. (eds.), Petroleum Geology of NW Europe: Proceedings of the 5th conference. Geological Society, London, 645-659.

Larsen, L.M., Waagstein, R., Pedersen, A.K. & Storey, M. 1999. Trans-Atlantic correlation of the Palaeogene volcanic succession in the Faroe Islands and East Greenland. Journal of the Geological Society, London, 156, 1081-1095.

Mitchell, S.M., Beamish, G.W.J., Wood, M.V., Malacek, S.J., Armentrout, J.A., Damuth J.E. & Olson, H.C. 1993. Palaeogene sequence stratigraphic framework of the Faroe Basin. In: Parker, J.R. (ed.), Petroleum Geology of NW Europe: Proceedings of the 4th conference. Geological Society, London, 1011-1023.

Ritchie, J.D., Gatliff, R.W. & Richards, P.C. 1999. Early Tertiary magmatism in the offshore NW UK margin and surrounds. In: Fleet, A.J. & Boldy, S.A.R. (eds), Petroleum Geology of Northwest Europe: Proceedings of the 5th Conference. Geological Society, London, 573-584.

Roberts, D.G., Thomson, M., Mitchener, B., Hossack, J., Carmichael, S. & Bjrnseth. 1999. Palaeozoic to tertiary rift and basin dynamics: mid-Norway to the Bay of Biscay a new context for hydrocarbon prospectivity in the deep water frontier. In: Fleet, A.J. & Boldy, S.A.R. (eds), Petroleum Geology of Northwest Europe: Proceedings of the 5th Conference. Geological Society, London, 7-40.

Rumph, B., Reaves, C.M., Orange, V.G. and Robinson, D.L. 1993. Structuring and transfer zones in the Faroe Basin in a regional tectonic context. In: Parker, J.R. (ed.), Petroleum Geology of NW Europe: Proceedings of the 4th conference. Geological Society, London, 999-1009.

Stoker, M.S., Hitchen, K. & Graham, C.C. 1993. United Kingdom offshore regional report: the geology of the Hebrides and West Shetland shelves and adjacent deep-water areas. London: HMSO for the British Geological Survey

Stoker, M.S., Nielsen, T., van Weering, T.C.E. & Kuijpers, A. 2002. Towards an understanding of the Neogene tectonostratigraphic framework of the NE Atlantic margin between Ireland and the Faroe Islands. Marine Geology, in press.

Sørensen, A. B. 2002 Structural framework, basin development and stratigraphy around the Faroe Islands. Petroleum Geoscience, in press.

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