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

Distribution

The Naust Formation forms a prograding sediment wedge that extends from the Norwegian coast westward into the Norwegian Basin. This wedge largely oversteps the major pre-Neogene depocentres of the Møre and Vøring basins.

External form and thickness

North of 65° 30´N, the Naust Formation forms an elongate, NNE–SSW-orientated shelf-margin succession, with a maximum thickness in excess of 1600ms TWTT. This decreases to the west and on the Vøring Plateau, above the Vøring Marginal High, the thickness is 100ms TWTT or less. South of 65°30'N, it can be divided into two thickness maxima. North of 63°N, a linear shelf-margin depocentre trends N–S to NNE–SSW. This is up to 1200ms TWTT thick, but thins westward to 200ms TWTT or less in the distal part of the Storegga Slide region. South of 63°N, the Naust Formation is dominated by the major depocentre of the North Sea Fan, which has a thickness in excess of 1600ms TWTT at the outlet of the Norwegian Channel. This decreases towards the NNW to less than 700 ms TWTT above the Faroe-Shetland Escarpment.

The thicknesses inferred by seismic mapping is verified by several wells. In well 6610/7-2, on the Mid-Norwegian Shelf, the Naust Formation is 767m thick. In well 6607/5-1, closer to the shelf-margin depocentre, the thickness is 1654m (Eidvin et al. 2000). Farther west, towards the base of the slope, the distal part of the wedge is greater than 253m in ODP Site 644 (base of unit not reached at this site), decreasing to 65–71m at ODP Sites 642 and 643 on the Vøring Plateau. In the North Sea Fan region, a thickness range from 718m in well 34/8-3A to 1089m in well 34/2-4 has been proved (Eidvin et al. 2001).

The slope apron has been locally modified by major slides, such as at the Storegga and Traenadjupet slides. South of 65°N, the extensive Storegga Slide scarp defines a major incision in the continental margin, and much of the Naust Formation has been extensively disturbed by mass-wasting processes.

Seismic facies

The seismic facies of the Naust Formation is a complex sigmoid-oblique clinoform signature, having a gentle (1–2°) west to south-west dip that reveals a repetitive pattern of unconformity-bounded, lensoid, sequences (Henriksen & Vorren 1996). On the inner shelf, the upper parts of the sequences are missing due to subsequent erosion. On the outer shelf, these sequences are better preserved. On the Vøring Plateau, the Naust Formation is characterised by a parallel-laminated internal acoustic signature. 

On the Møre and northern North Sea outer shelf, the lower part of the Naust Formation, below a pronounced angular unconformity (the upper regional unconformity: URU), is characterised by low-angle sigmoid-oblique clinoforms dipping to the NNW. Above the URU, the Naust Formation shows a sub-parallel, sub-horizontal reflector signature with moderate to good continuity. The North Sea Fan consists of low angle clinoforms bounding sequences that display a massive, laminated or lensoid internal signature (King et al. 1996). In the Storegga Slide region, the Naust Formation largely has an acoustically massive/transparent expression. 

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Upper boundary

The upper boundary is the present-day sea bed, which depicts the present bathymetric expression of the Mid-Norwegian margin and the adjacent Norwegian Basin.

Lower boundary

The lower boundary is the Base Naust Unconformity (BNU), an angular unconformity downlapped by clinoforms of the prograding Naust Formation onto the pre-Neogene structural surface, e.g Trøndelag Platform, or underlying Kai Formation in the Vøring Basin. Westwards it becomes a conformable surface, and above the Vøring Marginal High no hiatus has been identified (Bruns et al. 1998). In the northeastern part of the area, the BNU is draped over the Helland Hansen Arch, a mid-Cenozoic dome (McNeill et al. 1998).

On the northern Møre margin, at the north edge of the Storegga Slide, the BNU marks the top of the faulted, well-laminated Kai Formation. In the deeper parts of the Storegga Slide Complex, the unconformity is affected by slide events. Southwards on the Møre margin, the BNU marks the base of a seismically massive unit, showing both a conformable and an erosive character in this area. 

Below the North Sea Fan and the Storegga Slide area the boundary is generally conformable, or cutting the underlying bedding at a very low angle. It may locally be erosive, and truncated by slides in the distal parts. 

Lithology

On the shelf margin, much of the Naust Formation consists of clay-rich diamictons with lesser intervals of sandy diamictons (Sejrup et al. 1995; Eidvin et al. 2000). More distal areas, sampled by ODP sites 642–644, accumulated mainly muddy sediments containing ice-rafted debris (Eldholm et al. 1987).

Subdivision

On the Mid-Norwegian Shelf, Rokoengen et al. (1995) identified 12 units overlying an Oligocene coastal sandy sequence, deposited between 64° and 65°N. Henriksen & Vorren (1996) also described 12 sequences between 66° and 68 °N. Presently, no correlation exists between these two studies. McNeill et al. (1998) identified 8 units within the Naust Formation on the continental slope, simplified by Rise et al. (2002).

Farther south, King et al. (1996) identified 11 sequences on the upper part of the North Sea Fan. McNeill et al. (1998) also divided the North Sea Fan deposits into 11 units, and included the sequences of King et al. (1996) in their scheme. The two lowermost units identified extend below the Storegga Slide Complex. Further subdivision of the sediments in the Storegga Slide region has proven to be difficult, due to a complex succession of seismically massive/transparent slide sediments. The subdivision of the Naust Formation is considered further in the High-Resolution Stratigraphy section (pages 56 & 57).

Regional correlation

In the central and northern North Sea, the Naust Formation can be correlated with the upper part of the Nordland Group (Eidvin et al. 2000). In the Faroe–Shetland region, the Naust Formation corresponds to megasequence FSN-1. In the Rockall–Porcupine region, it correlates with megasequence RPa.

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Genetic interpretation

The lithology and fossil content indicates a glacigenic origin for these sediments (Eidvin & Riis 1991; Poole & Vorren 1993; Henriksen & Vorren 1996; Eidvin et al. 2000). Henriksen & Vorren (1996) suggested that most of the sediments were probably originally deposited in an ice-proximal position to a grounded ice sheet. According to their results, slope oversteepening caused instability and sediment transport downslope from the shelf break and upper slope. The diamictons found in flat-lying strata on the shelf have been interpreted to be deposited mainly as tills (King et al. 1987).

On the Møre and northern North Sea shelves, the prograding sequences in the upper Pliocene (lower part of Naust Fm) are probably a result of higher glacial activity and erosion of exposed shelf areas. The main constructive component of the prograding sequences on the North Sea Fan is glacigenic debris flows released at the shelf break, derived from material deposited in front of glaciers grounded on the shelf (King et al. 1996). In addition, episodic large slides have influenced the total volume of sediments deposited both on the North Sea Fan and in the Storegga region (Bugge et al. 1987; King et al. 1996; Evans et al. 2002). The diamictons found in flat-lying strata on the shelf have been interpreted to be deposited mainly as subglacial tills (Sejrup et al. 1995). 

Biostratigraphic characterisation

In well 6610/7-2, the Naust Formation corresponds to the Cibicides grossus–Elphidiella hanni–Globigerina bulloides–N. atlantica (Sinistral) zone (faunal zone M–D) of Eidvin et al. (1998). The base of this zone is marked by the highest consistent occurrence of Coscinodiscus sp. 1 while the top of the zone is taken at the highest occurrence of E. hanni, N. atlantica (sinistral) and G. bulloides and the highest consistent occurrence of C. grossus (Eidvin et al. 1998). Farther west, in well 6607/5-1, the base of the Naust Formation is characterised by the Cibicides grossus–Globigerina bulloides–N. atlantica (sinistral) zone (faunal zone M–C) where the base of the zone is marked by the highest consistent occurrence of N. atlantica (dextral) (Eidvin et al. 1998). In this well the top of the Naust Formation comprises the Cibicides grossus zone (faunal zone M–B) where the top of the zone is taken at the highest occurrence of Cibicides grossus (Eidvin et al. 1998). For details on the Naust Formation at ODP Sites 642 and 643, see Eldholm et al. (1987).

In well 6506/12-4, the oldest part of the Naust Formation corresponds to the Cibicides grossus–Elphidiella hannai–Globigerina bulloides–N. atlantica (sinistral) zone of Eidvin et al. (1998; 2001), and the base of the zone is marked by highest consistent occurrence of N. atlantica (dextral). In well 34/8-3A, the base of the Naust Formation is defined by the highest occurrence of Ehrenbergina variabilis (Eidvin et al. 2001).

Age

The age of the Naust Formation has been proposed to be late Pliocene by Dalland et al. (1988), and ca. 6 Ma to Recent by Swiecicki et al. (1998). Regional biostratigraphic data (Fig. 11) presented in this study suggest a ‘mid’-Pliocene–Holocene age range, with the BNU formed within the late early to early late Pliocene interval. The bulk of the strata comprising the Naust Formation are of late Pliocene–Holocene age. 

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References

Bruns, P., Dullo, W. C., Hay, W.W., Frank, M. & Kubik, P. 1998. Hiatuses on Vøring Plateau: sedimentary gaps or preservation artifacts? Marine Geology, 145, 61-84. 

Bugge, T., Befring, S., Belderson, R.H., Eidvin, T., Jansen, E., Kenyon, N.H., Holtedahl, H., & Sejrup, H.P. 1987. A giant three-stage submarine slide off Norway. Geo-Marine Letters, 7, 191-198.

Dalland, A., Worsley, D. & Ofstad, K. 1988. A lithostratigraphic scheme for the Mesozoic and Cenozoic succession offshore mid- and northern Norway. Norwegian Petroleum Directorate Bulletin 4, 65pp.

Eidvin, T. & Rundberg, Y. 2001. Late Cainozoic stratigraphy of the Tampen area (Snorre and Visund fields) in the northern North Sea, with emphasis on the chronology of early Neogene sands. Norsk Geologisk Tidsskrift, 81, 119-160. 

Eidvin, T., Brekke, H., Riis, F. & Renshaw, D.K. 1998. Cenozoic stratigraphy of the Norwegian Sea continental shelf, 64oN-68oN. Norsk Geologisk Tidsskrift, 78, 125-151.

Eidvin, T., Jansen, E., Rundberg, Y., Brekke, H. & Grogan, P. 2000. The upper Cainozoic of the Norwegian continental shelf correlated with the deep-sea record of the Norwegian Sea and the North Atlantic. Marine and Petroleum Geology, 17, 579-600.

Eidvin, T. & Riis, F., 1991. En biostratigrafisk analyse av tertiære sedimenter på kontinentalmarginen av midt Norge, med hovedvekt på øvre Pliocene vifteavsetninger. Norwegian Petroleum Directorate Contribution 29, 57pp.

Eldholm, O., Thiede, J., Taylor, E. et al. 1987. Summary and preliminary conclusions, ODP Leg 104. In: Eldholm, O., Thiede, J., Taylor, E. et al. (eds), Proceedings, Initial Reports of the Ocean Drilling Program, 104: College Station, Tx (Ocean Drilling Program),751-771.

Evans, D., McGiveron, S., Harrison, Z., Bryn, P. & Berg, K. 2002. Along-slope variation in the late Neogene evolution of the mid-Norwegian margin in response to uplift and tectonism. 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.

Henriksen, S. & Vorren, T.O. 1996. Late Cenozoic sedimentation and uplift history on the mid-Norwegian continental shelf. Global and Planetary Change, 12, 171-199.

King, L.H., Rokoengen, K. & Gunleiksrud, T. 1987. Quaternary seismostratigraphy of the Mid Norwegian shelf, 65o - 67 o 30´N - A till tongue stratigraphy. The Continental Shelf and Petroleum Research Institute A/S (IKU), Publication 114, Trondheim, Norway, 58 pp. 

King, E.L., Sejrup, H.P., Haflidason, H., Elverhøi, A. & Aarseth, I. 1996. Quaternary seismic stratigraphy of the North Sea Fan: Glacially fed gravity flow aprons, hemipelagic sediments, and large submarine slides. Marine Geology, 130, 293-315.

McNeill, A.E., Salisbury, R.S.K., Østmo, S.R., Lien, R. & Evans, D. 1998. A regional shallow stratigraphic framework off Mid Norway and observations of deep water "special features". Offshore Technology Conference, Houston, USA, Paper 8639, 13 pp.

Poole, D.A.R. & Vorren, T.O. 1993. Miocene to Quaternary paleoenvironments and uplift history on the mid Norwegian shelf. Marine Geology, 115, 173-205.

Rise, L., Ottesen, D., Larsen, E., Lundin, E., Olsen, L. & Thorsnes, T. 2002. Large scale development of the Mid-Norwegian shelf and margin with emphasis on the last 3 million years. Norges Geologiske Undersøkelse, Report No. 2002.015.

Rokoengen, K., Rise, L., Bryn, P., Frengstad, B., Gustavsen, B., Nygaard, E. & Sættem, J. 1995. Upper Cenozoic stratigraphy on the Mid-Norwegian continental shelf. Norsk Geologisk Tidsskrift, 75, 88-104.

Sejrup, H.P., Aarseth, I., Haflidason, H., Løvlie, R., Bratten, Å., Tjøstheim, G., Forsberg, C.F. & Ellingsen, K.I. 1995. Quaternary of the Norwegian Channel: glaciation history and palaeoceanography. Norsk Geologisk Tidsskrift, 75, 65-87.

Swiecicki, T., Gibbs, P.B., Farrow, G.E. & Coward, M.P. 1998. A tectonostratigraphic framework for the Mid-Norway region. Marine and Petroleum Geology, 15, 245-276.

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