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

Two regional unconformities, the Top Palaeogene and Intra-Neogene unconformities, bound the megasequences that comprise FSN-1 and FSN-2 in the Faroe–Shetland region. These boundaries are illustrated in the seismic panels opposite (Fig. 9). A basinal Intra-Miocene unconformity and the shelf-to-upper slope glacial unconformity are also illustrated, as these surfaces form important, albeit more localised, marker horizons. 

Glacial Unconformity 

The Glacial Unconformity (GU) is best recognised on the West Shetland and Faroe shelves and upper slopes, and is interpreted to mark the onset of widespread shelf glaciation at about 0.44 Ma (Stoker 1999). In these areas, the GU is characteristically a planar to irregular and erosive surface that truncates underlying strata. On the lower slopes, the GU — where identified — appears more planar, less erosive and commonly a downlap surface. In areas with very steep slope angles, the GU cannot be traced on the seismic records (Fig. 9a and Fig. 9b). In the northern part of the Faroe-Shetland Channel, the GU is seismically indistinct and most probably either a conformable surface or a low-angle erosion surface. The GU is not readily identified at the SW end of the Faroe-Shetland Channel or in the Faroe Bank Channel where the Neogene succession is relatively thin. Similarly, the GU has not been reported from the north Faroes margin. 

Intra-Neogene Unconformity

The Intra-Neogene Unconformity (INU) forms the base of the FSN-1 megasequence, and is dated as early Pliocene in age on the basis of biostratigraphic data from well 214/4-1 (Davies & Cartwright In press). The general expression of the INU on seismic profiles is of a medium- to high-amplitude, continuous reflector, which forms an erosional, angular unconformity on the shelves, slopes and in the basins, except in the northernmost part of the Faroe-Shetland Channel where it forms a relatively flat conformity, (Fig. 9c). On the shelves and uppermost slopes the INU is commonly downlapped by prograding FSN-1 sediments, while it is onlapped by contouritic deposits at the base of the slopes. Landward, on the shelves, the INU is largely truncated by the GU.

Intra-Miocene Unconformity

The Intra-Miocene Unconformity (IMU) is defined in restricted areas across the northern part of the Faroe–Shetland region. Well 214/4-1 indicates a mid-Miocene age for the IMU (Davies & Cartwright In press), which has been used by Nielsen et al. (2002) to propose a preliminary subdivision of the FSN-2 megasequence into upper, FSN-2a, and lower, FSN-2b sequences (Fig. 9d). The IMU is an angular and erosive unconformity that truncates underlying strata. On the NE Faroe Shelf and in the northern Faroe-Shetland Channel the IMU becomes less erosive and appears more conformable with the underlying strata of FSN-2b. The IMU generally corresponds to CN-030 of Andersen et al. (2000).

TOP

Top Palaeogene Unconformity

The Top Palaeogene Unconformity (TPU) is a regional surface that defines the top of the Palaeogene FSP megasequence. The TPU is an angular unconformity that everywhere separates the Palaeogene and Neogene successions. It is best recognised in the SW Faroe-Shetland Channel, where a highly sculpted erosion surface still has sea-bed expression in the form of major erosional deeps, such as that shown on Fig. 9g (Stoker et al. In press). On the flanks of the basins, the TPU is commonly cut out by younger erosion surfaces, such as the INU and/or the GU, so forming a composite unconformity surface (Fig. 9a and Fig. 9d). Figure 9f shows the nature of the composite INU/TPU unconformity surface across an underlying, and neotectonically active, antiformal structure. The Sandoy Fan is also well illustrated in this figure. In the northern Faroe-Shetland Channel, a diagenetic horizon is observed on seismic profiles as a high-amplitude reflector. Locally, this reflector is coincident with the TPU, and hinders the definition of the unconformity in parts of the basin, as illustrated in Fig. 9e. Although having a broader definition, the TPU corresponds to a greater extend to the LOEMU (latest Oligocene–early Miocene unconformity) of Stoker (1999) and CN-010 of Andersen et al. (2000). 

References

Andersen, M.S., Nielsen, T., Sørensen, A.B., Boldreel, O.L. & Kuijpers, A. 2000. Cenozoic sediment distribution and tectonic movements in the Faroe region. Global and Planetary Changes, 24, 239-259.
Davies, R. & Cartwright, J. In press. Character and origin of a fossilised bottom simulating reflector originating from opal A to C/T transformation: an example from the Neogene of the NE Atlantic margin. Basin Research.

Nielsen, T., Mathiesen, A., Stevenson, A.G., Hoult, R., Sørensen, A.B., Kuijpers, A & Gillespie, E.G. 2002. Regional Stratigraphy — WP2. Stratagem Deliverable 19.

Stoker, M.S. 1999. Stratigraphic nomenclature of the UK North West Margin. 3. Mid- to late Cenozoic Stratigraphy. British Geological Survey, Edinburgh.

Stoker, M.S, 2002. Late Neogene development of the UK Atlantic margin. Doré, A.G.D., Cartwright, J., Stoker, M.S., Turner, J.P. & White, N. (eds), Exhumation of the North Atlantic Margin: Timing, Mechanisms and Implications for Petroleum Exploration. Geological Society, London, special Publications, 196, in press.

Stoker, M.S., Long, D. & Bulat, J. In press. A record of mid-Cenozoic strong deep-water erosion in the Faroe-Shetland Channel. In: Mienert, J. & Weaver, P. (eds), European Continental Margin Sedimentary Processes: An Atlas of Side-Scan Sonar and Seismic Images, Springer Verlag.

TOP