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

Two regional Neogene unconformities, the Base Naust and Base Kai unconformities, bound the megasequences that comprise the Naust and Kai formations on the mid-Norwegian margin. These boundaries are illustrated in geoseismic sections (modified from Blystad et al. 1995) and seismic panels, opposite (Fig. 8). An intra-Naust unconformity, the Upper Regional Unconformity, is also highlighted as this surface forms an important late Pleistocene marker horizon on the Vøring margin. For ease of description, present-day physiographic and pre-Neogene structural terminologies are both utilised in the text and figures.

The Upper Regional Unconformity

The Upper Regional Unconformity (URU) represents an intra-Naust event, and is the youngest regional unconformity on the Mid-Norwegian Shelf. On the inner shelf it separates aggradational till units above the URU from variously dipping strata below (Fig. 8c). Sediments above the URU are correlated with oxygen isotope stage 6 or younger; those below the URU correlate with stage 8 and older. Farther west the URU becomes a conformable boundary at the top of Naust Unit B (Fig. 8b). The unconformity is a polycyclic surface formed by glacial erosion. To the south, on the Møre–North Sea Fan region the recognition of the URU or its equivalent remain uncertain at the present time.

The Base Naust Unconformity

The Base Naust Unconformity (BNU) is an angular unconformity downlapped by clinoforms of the prograding Naust Formation on the Trøndelag Platform and in the eastern Vøring Basin (Fig. 8a, Fig. 8b, and Fig. 8c). Westwards it gradually becomes a conformable surface, and on the Vøring Marginal High no hiatus has been identified (Bruns et al. 1998). On the northern Møre Margin, i.e. at the north edge of the Storegga Slide, the BNU defines the top of the faulted, well-laminated Kai Formation. In the deeper parts of the Storegga Slide the unconformity is affected by slide events. Southwards on the Møre Margin, the unconformity represents the base of a seismically massive unit. The BNU shows both a conformable and an erosive character in this area (Fig. 8d, Fig. 8e, and Fig. 8f).

The Base Kai Unconformity

For the most part, the Base Kai Unconformity (BKU) separates Miocene from Palaeogene strata, although some degree of diachroneity — extending from the late Oligocene — cannot be discounted. In the eastern Vøring Basin, the BKU is eroded into lower to middle Eocene sediments of the Brygge Formation (Eidvin et al. 1998) (Fig. 8a, Fig. 8b and Fig. 8c). Farther west, on the eastern side of the Vøring Marginal High, the BKU overlies lower Eocene volcaniclastic sediments. On the western Vøring Marginal High, a major break separates upper Oligocene from upper Eocene sediments with no apparent hiatus between Oligocene and Miocene strata (Eldholm et al. 1987). On the southern Trøndelag Platform the base of the Kai Formation is also manifest as an unconformity, as a hiatus was reported between the Kai and the underlying Brygge Formation in well 6506/12-4 (Eidvin et al. 1998) (Fig. 11). Commercial wells and seismic profiles also show that the BKU also exists on the southeastern Møre Margin (Eidvin et al. 2000) (Fig. 8d, Fig. 8e, and Fig. 8f, and Fig. 11).

References

Blystad, P., Brekke, H., Færseth, R.B., Larsen, B.T., Skogseid, J. & Tørudbakken, B. 1995. Structural Elements of the Norwegian Continental Shelf. Part II: The Norwegian Sea Region. Norwegian Petroleum Directorate, 8.

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. 

Eidvin, T., Brekke, H., Riis, F., & Renshaw, D.K. 1998. Cenozoic stratigraphy of the Norwegian Sea continental shelf, 64°N-68°N. 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.

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.). Initial Reports of the Ocean Drilling Program, 104: College Station, Tx (Ocean Drilling Program), 751-771.

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