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Neogene and Quaternary depositional environments on the Norwegian continental margin, 62°N–68°N
Marine Geology 213 (2004) 257 – 276 www.elsevier.com/locate/margeo
Neogene and Quaternary depositional environments on the Norwegian continental margin, 628N–688N Berit Oline Hjelstuena,*, Hans Petter Sejrupa, Haflidi Haflidasona, Kjell Bergb, Petter Brynb a
Department of Earth Science, University of Bergen, Alle`gt. 41, N-5007 Bergen, Norway b Norsk Hydro ASA, N-0256 Oslo, Norway Accepted 30 September 2004
Abstract 2D multichannel seismic and mini-sleeve gun profiles reveal that an up to 1.5 s(twt) thick sedimentary succession has been deposited on the Norwegian continental margin (628N–688N) during Neogene and Quaternary. Well-defined Miocene depocentres have evolved both in the North Sea Fan region and along the flanks of structural highs in the Vbring Basin. Miocene sediments are, on the other hand, mainly absent within the Storegga Slide scar. Seismic facies analyses show that these deposits locally are characterised by a mounded and/or migration–aggradation pattern, which we relate to a current-influenced depositional environment. Hence, the early Neogene sediments on the Norwegian continental margin are classified as contourites. The contourites have most likely been deposited in connection with the establishment of a deep-water exchange in the Norwegian–Greenland Sea, due to the opening of the Fram Strait and subsidence of the Greenland–Scotland Ridge. At about 2.5 Ma, a significant change in this depositional environment took place. Down-slope sedimentary processes became now more important and throughout the late Plio-Pleistocene sediments were mainly sourced from the Norwegian mainland and the adjacent continental shelf, causing depocentres to evolve along the shelf edge. D 2004 Elsevier B.V. All rights reserved. Keywords: Norwegian margin; seismic facies; contourites; Neogene; Quaternary
1. Introduction The Neogene and Quaternary time periods on the Norwegian continental margin (628N–688N; Figs. 1
* Corresponding author. Tel.: +47 55 58 35 07; fax: +47 55 58 36 60. E-mail address: [email protected] (B.O. Hjelstuen). 0025-3227/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.margeo.2004.10.009
and 2) represent an important geological time span with respect to tectonism and climate. The Norwegian margin has been shaped into its present structural configuration by repeated tectonic events, which culminated with the ca. 55 Ma break-up of the Norwegian–Greenland Sea and compressional episodes during post-break-up times. These tectonic events most likely influenced the oceanic circulation pattern, thereby affecting both sediment distribution
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Fig. 1. North Atlantic overview map. Study area within box. Bathymetry in metres. NC—Norwegian Channel; NCC—Norwegian Coastal Current; NwAC—Norwegian Atlantic Current. NwAC flow pattern from Orvik and Niiler (2002).
and depositional environments. Throughout Cenozoicum, the climate on the Northern Hemisphere gradually cooled, and a glacial regime characterise the late Plio-Pleistocene Norwegian margin. The sediments deposited during this ca. 2.5-my-long time span have been severely dissected by slides (e.g. Evans et al., 2002; Nyga˚rd et al., in press), of which the most recent one is the ca. 7250 14C BP Storegga Slide (Bugge et al., 1987; Haflidason et al., in press)
and the ca. 4000 14C BP Tr&nadjupet Slide (Laberg et al., 2002) (Fig. 2). To evaluate slope stability and possible trigger mechanisms for these slides, it is of importance to understand, and to have knowledge on, sedimentary processes and depositional environments that have acted through time. In this paper, mini-sleeve gun records and multichannel seismic profiles are interpreted to study sediment geometries, source areas,
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sediment distribution and seismic facies in order to refine our understanding of the Neogene and Quaternary development of the Norwegian continental margin.
2. Physiographic setting The Norwegian margin between 628N and 688N comprises the North Sea Fan, the Storegga Slide region and the Vbring Plateau (Figs. 1 and 2). During break-up, the volcanic-related Vbring and Mbre marginal highs, which define the western boundaries of the Vbring and Mbre basins (Fig. 2), were created. The basin areas are separated from each other by the Jan Mayen Frature Zone and its landward extension, the Jan Mayen Lineament (Blystad et al., 1995). The Vbring Basin has been structured into two provinces, divided by the Fles Fault Complex (Fig. 2). The eastern province consists of the R3s and Tr&na basins, whereas in the western province, the Gjallar Ridge and the Nyk High separate the Vigrid and N3grind synclines from the Fenris and Hel Grabens (Blystad et al., 1995). Five Cenozoic dome structures have evolved along the studied margin segment (Fig. 2). These structures are aligned into a N–S trending chain, with the Ormen Lange Dome to the south and the Naglfar Dome to the north. Various mechanisms, such as interaction by the Iceland Hotspot (Lundin and Dore`, 2002), differences in seafloor spreading rates (Mosar et al., 2002) and differential sediment loading (Stuevold et al., 1992; Hjelstuen et al., 1997) have been suggested as possible doming mechanisms. During post-break-up time, the Norwegian margin subsided, and a thick sedimentary succession was deposited (e.g., Skogseid and Eldholm, 1989). These sediments were divided by Dalland et al. (1988) into three formal units: the Eocene–Oligocene Brygge Fm, the Miocene–early Pliocene Kai Fm and the late PlioPleistocene Naust Fm, where the deposition of the late Plio-Pleistocene sediments is reflected in the bathymetry by the North Sea Fan complex at the outlet of the Norwegian Channel and the broad continental shelf off mid-Norway (Fig. 2). At present, three water masses characterise the hydrographic regime within the studied area: the Atlantic Water in the Norwegian Atlantic Current (NwAC), Coastal Current Water in the Norwegian
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Coastal Current (NCC) and homohaline deep-water in the Norway Basin (Fig. 1) (Mosby, 1972). The Atlantic Water enters the Norwegian Sea over the Iceland–Faroe Ridge and through the Faroe–Shetland Channel as two separate branches (Fig. 1) (Orvik and Niiler, 2002). The eastern NwAC branch follows the outer part of the shelf, and has strongly influenced the seabed sediment distribution in the region (Holtedahl, 1981; Sejrup et al., 1981). The Atlantic Water is sharply bounded towards the Coastal Current Water in the NCC, which parallels the coast of Norway (Fig. 1).
3. Sequence stratigraphy, seismic facies and sediment distribution The data set used in this study is composed of a regional grid of multichannel seismic profiles and high-resolution minisleeve gun data covering the Vbring margin, the Storegga Slide region and the northeastern part of the North Sea Fan. The seismic profiles are limited to the Vbring and Mbre basins (Fig. 2). Seismic unconformities as well as changes in seismic facies have been used to identify sequence boundaries (Figs. 3 and 4). The chronostratigraphy is based on Hjelstuen et al. (1999), which dated the Cenozoic sediments by seismic ties to 18 commercial wells on the mid-Norwegian continental shelf. We have identified and mapped five regional reflectors: base late Pliocene (BP), lower Miocene (LM), intra-Oligocene (IO), middle Oligocene (MO) and top Paleocene (TP) (Figs. 3–7). These reflectors bound three mega-sequences comprising Eocene– Oligocene, Miocene and late Plio-Pleistocene sediments. Although the main focus of this study will be the Miocene–Pleistocene sedimentary succession, the Paleogene time period will briefly be discussed because of its importance for the understanding of the Neogene and Quaternary margin evolution. 3.1. Eocene–Oligocene The Eocene–early Oligocene deposits are limited by the top Paleocene (TP) and the middle Oligocene (MO) sequence boundaries (Fig. 3). An acoustic non-structural seismic reflection pattern characterises the lower part of this succession, whereas parallel
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Fig. 3. Identified sequence boundaries, description of seismic facies characteristic and lithologies of mapped Cenozoic mega-sequences.
high-amplitude reflectors dominate the early Oligocene deposits. The late Oligocene sediments, defined by MO and the lower Miocene (LM) sequence boundary, are characterised by high-amplitude reflectors that have been heavily faulted. A chaotic seismic pattern is locally observed near the lower bounding surface of these deposits. Diapirism has furthermore disturbed the Oligocene sediments in a few places (Fig. 4). The Eocene–Oligocene sediment distribution has not been fully mapped, however, the seismic profiles reveal that these deposits vary considerably in thickness (Figs. 4–6). In the Vbring Basin and on the continental shelf off mid-Norway, the Eocene– Oligocene sediments mainly consist of clay (Eidvin et al., 2000). On the Mbre margin, the Eocene deposits are also mostly fine-grained; however, layers of sandstone are observed (Martinsen et al., 1999). Commercial drillings in the northernmost North Sea have shown that Oligocene sediments consist of clay and silt with minor amounts of sand (Eidvin and Rundberg, 2001).
3.2. Miocene The Miocene sediments are bounded by LM and the base late Pliocene (BP) sequence boundary (Figs. 3 and 4). In the Vbring Basin, the Miocene sediments are commonly characterised by parallel, low- to medium-amplitude reflectors (Fig. 5). Due to numerous small-offset faults, these sediments are heavily deformed, making it difficult to trace internal reflectors regionally. The faults are characterised as both normal and reverse and are occasionally penetrating into the overlying late PlioPleistocene unit (Hjelstuen et al., 1997). Berndt et al. (2003) have classified these features as polygonal faults. The layering of the Miocene sediments deposited in the Vbring Basin has apparently changed through time. This is revealed in the seismic sections by a change from SE-ward-dipping to convex-shaped reflectors (Fig. 5). Profiles cross-cutting this seismic pattern (Fig. 7a) show an asymmetrical mound, built up by thin sheet-like sequences that pinch out towards
Fig. 2. Study area showing location of interpreted seismic profiles. Filled and open fault symbols refer to Late Cretaceous–Early Tertiary and reactivated Late Jurassic–Early Cretaceous structures, respectively. Bathymetry in metres. Structural elements from Blystad et al. (1995). DSDP—deep sea drilling project; FFC—Fles Fault Complex; FG—Fles Graben; FSE—Faroe–Shetland Escarpment; GR—Gjallar Ridge; HG—Hel Graben; HHA—Helland–Hansen Arch; JMFZ—Jan Mayen Fracture Zone; MA—Modgunn Arch; MCS—multichannel seismic; MMH—Mbre Marginal High; MSG—minisleeve gun; ND—Naglfar Dome; NH—Nyk High; NS—N3grind Syncline; ODP—ocean drilling program; OL—Ormen Lange Dome; RB—R3s Basin; TB—Tr&na Basin; UH—Utgard High; VD—Vema Dome; VMH—Vbring Marginal High; VE—Vbring Escarpment; VS—Vigrid Syncline.
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Fig. 4. Geoseismic section crossing the Vbring Plateau, Storegga Slide area and the northeastern North Sea Fan, showing distribution of Quaternary, Neogene and Paleogene sediments. Profile location in Fig. 2. BP—base late Pliocene; LM—lower Miocene; MO—middle Oligocene; IO—intra-Oligocene; TP—top Paleocene.
north. The sheets are stacked on top of each other, and show a NE-trending migration–aggradation pattern. Furthermore, along the flanks of the Helland–Hansen and Modgunn arches, the Miocene sediments are characterised by mounded reflectors with an aggradating onlap pattern. Apparently, two generations of onlap features are observed along the western Helland–Hansen Arch flank (Fig. 7b). Near the northern Storegga Slide scar, the Miocene sediments are dominated by convex parallel reflectors, whereas within the slide scar itself, the Miocene sediments that are still preserved show medium- to high-amplitude parallel reflectors. In the northeastern North Sea Fan region, the Miocene sediments locally display a mounded seismic appearance along the slope (Fig. 6). Both within the Storegga Slide scar and in the North Sea Fan region, the Miocene succession is faulted. However, the deformation within these regions has been less intense than that observed on the Vbring Plateau. A well-defined high-amplitude reflector, crosscutting the Miocene bedding, is observed within the entire studied region (Figs. 4–7). This high-amplitude reflector also crosses LM and is neither parallel to the seafloor nor to the layering of the late Plio-Pleistocene deposits. Most likely, it is a diagenetic surface, representing the transition from Opal A to Opal CT (Brekke, 2000; Berndt et al., 2004). Brekke (2000) suggested that this boundary was formed during the latest Miocene–earliest Pliocene. The Miocene sediments show a complex distribution along the Norwegian margin. In the Vbring
Basin, the Miocene deposits reach a maximum thickness between 0.75 and 1.0 s(twt) within a SW–NEelongated depocentre (Fig. 8). The Miocene sediments are thin or absent across the Modgunn Arch, Helland– Hansen Arch, Vema Dome and Naglfar Dome. Previous studies within the region have furthermore revealed that the Miocene sediments on the midNorwegian continental shelf are rather thin (e.g., Hjelstuen et al., 1999). In the Storegga Slide region, the Miocene sediments are mainly absent (Figs. 4 and 8), whereas at the northeastern flank of the North Sea Fan, a depocentre reaching a thickness of about 0.75 s(twt) has evolved. The Miocene succession was first sampled in the northwestern Vbring Basin and on the northern Vbring Marginal High during Deep Sea Drilling Project (DSDP) Leg 38 (Fig. 2) (Talwani et al., 1976). The DSDP sites show that the Miocene sediments, in water depths N1250 m, almost exclusively consist of pelagic siliceous oozes with varying clay and calcareous nannoplakton contents, where the terrigenous input increases upwards in the succession (Caston, 1976). Similar ooze-rich sediments have been reported from ODP Leg 104 sites on the Vbring Marginal High (Fig. 2) (e.g., Eldholm et al., 1989). ODP Site 644 (Fig. 2) from the Vbring Basin apparently penetrates into Miocene sediments at about 230 m core depth (Fig. 9), i.e., at a level characterised by a significant increase in the biogenic opal content. Goll and Hansen (1992) investigated seven wells at the continental shelf off mid-Norway, showing that the Miocene succession consists of calcareous mudstone.
B.O. Hjelstuen et al. / Marine Geology 213 (2004) 257–276 Fig. 5. (a) NW–SE trending geoseismic section (NH9651-405) across the central part of the Vbring Plateau. Profile location in Fig. 2. Abbreviations as in Fig. 4. (b) Seismic facies characteristic of Cenozoic sediments. Profile location in panel (a). Abbreviations as in Fig. 4. 263
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Fig. 6. (a) NW–SE trending geoseismic section (MB6-92/MB6-91) across northeastern part of the North Sea Fan. Profile location in Fig. 2. Abbreviations as in Fig. 4. (b) Seismic facies characteristic of Cenozoic sediments. Profile location in Fig. 2. Abbreviation as in Fig. 4.
At the Utgard High (Fig. 2), the Miocene sediments are characterised as claystone with a small content of sand/ silt and sparse occurrences of radiolarian ooze (Eidvin et al., 1998, 2000; Poole and Vorren, 1993). The lithological information about the Miocene sedimentary succession in the southern part of the study area is rather sparse. Eidvin et al. (2000) identified the Utsira Formation near the outlet of the Norwegian Channel (Figs. 2 and 8). Galloway (2002) suggested a middle–late Miocene age for the Utsira Formation and described it as a unit composed of marine sand deposited in a water depth of 100–200 m. The Utsira Formation fine westwards, and the lower
part of the unit is glauconitic (Martinsen et al., 1999). The Miocene succession within the main Mbre Basin has not been sampled. However, the seismic facies indicate that it may consist of similar sediments as deposited on the Vbring Plateau. 3.3. Late Plio-Pleistocene It is well documented that the base late Pliocene sequence boundary (BP) represents an unconformity on the Norwegian margin (Hjelstuen et al., 1999; Eidvin et al., 2000; STRATAGEM partners, 2002). Seismic investigations and cores along the entire
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northeastern European margin have furthermore revealed that BP is related to the main initiation of the Northern Hemisphere glaciations at ca. 2.5 Ma (e.g., Eidvin and Riis, 1989; Thiede et al., 1989; Jansen and Sjbholm, 1991; Solheim et al., 1998). There is a distinct change in the seismic facies pattern between Miocene and late Plio-Pleistocene sediments (Figs. 5 and 6), thus generally making it
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easy to trace BP within the study area. On the Vbring margin, BP represents a well-defined downlapping surface for late Plio-Pleistocene prograding clinoforms. The clinoforms are commonly characterised by high-amplitude reflectors and separate sequences showing a chaotic, structureless or weakly layered seismic pattern (Fig. 5). The clinoforms reach their westernmost extent in a water depth of ca. 1000–1200
Fig. 7. (a) Seismic example (above) and interpretation (below), showing characteristic depositional pattern of current-influenced sediments on the Vbring Plateau. Profile location in Fig. 2. Abbreviations as in Fig. 4. (b) Seismic example (above) and interpretation (below), showing characteristic depositional pattern of current-influenced sediments along the western flank of the Helland–Hansen Arch. Profile location in Fig. 2. Abbreviations as in Fig. 4.
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Fig. 7 (continued).
m. In deeper water, the late Plio-Pleistocene sediments are lying conformable above BP, and the deposits are characterised by parallel medium- to high-amplitude reflectors (Fig. 5b). At several places in the Vbring Basin, the late Plio-Pleistocene sediments are disturbed by diapirs (Fig. 4) (Hjelstuen et al., 1997; Hovland et al., 1998). Within the Storegga Slide region, the base late Pliocene boundary is defined as an erosional surface, whereas the late Plio-Pleistocene sediments are domi-
nated by an internal non-structural acoustic facies and a few high-amplitude continuous reflectors. Slide scars, up to 200 ms(twt) (ca. 200 m) high, are observed at the base late Pliocene level, causing deep intersections into the underlying sedimentary succession on the North Sea Fan. The fan succession itself has also been severely eroded due to repeated slide events (Evans et al., 2002; Nyga˚rd et al., in press; Sejrup et al., 2004). The slide debrites left by these slide events are dominated by a chaotic, pattern, limited by smooth
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Fig. 8. Isopach map of Miocene sediments. Stippled lines indicate location of seismic profiles defining the database of this study. Major dome structures, the Storegga Slide and the North Sea Fan are outlined. Isopach contour interval is 250 ms(twt). HHA—Helland–Hansen Arch; MA— Modgunn Arch; ND—Naglfar Dome; NH—Nyk High; OL—Ormen Lange Dome; VD—Vema Dome.
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Fig. 9. Compilation of ODP Site 644, geotechnical boring 6405/2-GB1 and the commercial well 34/2-4, showing lithology and grain size of late Paleogene–Neogene–Quaternary sediments on the Norwegian continental margin. Based on Haflidason et al. (1998), Eidvin et al. (2000) and Henrich et al. (1989). Core locations in Fig. 2. MIS—marine isotope stage; LGM—last glacial maximum; WD—water depth.
lower and irregular upper boundaries. The North Sea Fan complex is furthermore characterised by sequences composed of acoustically transparent, mounded, lensoid-stacked glacigenic debris flows (King et al., 1996; Nyga˚rd et al., 2002, in press). The isopach map of the late Plio-Pleistocene deposits (Fig. 10) shows that an up to 1.5 s(twt) thick sequence has been deposited along the shelf edge on the Vbring margin. The sedimentary succession is however thinning rapidly westward, and in water depths exceeding 1000 m, this unit is commonly less than 0.5 s(twt) thick. At the mouth of the Norwegian Channel, the sediment thicknesses exceeds 1.5 s(twt),
whereas in the Storegga Slide scar, the isopach map shows that the late Plio-Pleistocene sediments are b1.0 s(twt) thick. The composition of the late Plio-Pleistocene sediments has been well documented by DSDP/ODP borings, recently raised shallow cores and geotechnical borings within the study area (e.g. Eldholm et al., 1989, Eidvin et al., 2000; Dahlgren and Vorren, 2003; Hjelstuen et al., 2004; Berstad et al., in press). ODP Site 644 in the central Vbring Basin (Fig. 2) revealed that these deposits consist of sandy mud (Fig. 9). Detailed lithological analyses furthermore show that there is a strong cyclicity in the carbonate and
Fig. 10. Isopach map of late Plio-Pleistocene sediments. Stippled lines indicate location of seismic profiles defining the database of this study. Outline of major dome structures, the Storegga Slide and the North Sea Fan are shown. Isopach contour interval is 250 ms(twt). Stippled contours on the North Sea Fan indicate uncertain sediment thickness. HHA—Helland–Hansen Arch; MA—Modgunn Arch; ND—Naglfar Dome; NH—Nyk High; OL—Ormen Lange Dome; VD—Vema Dome.
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terrigenous particle content through time, and that the observed carbonate peaks correlate with minima in the terrigenous input (Henrich et al., 1989). These repetitive changes are related to the climatic variations during this time period, with waxing and waning ice sheets over Fennoscandia (Henrich, 1989). Detailed analyses of gravity cores from the northern part of the study area (Dahlgren and Vorren, 2003) indicate that the very uppermost part of the late Plio-Pleistocene sediment succession is composed of mud and diamicton. Geotechnical borings (Fig. 9) from the southern Vbring Plateau show that the sediments deposited during the last 250 ka are composed of clay/ silt and sand/gravel units, with the coarsest sediments deposited during glacial stages. Coring of the uppermost-identified glacigenic debris flow unit on the North Sea Fan reveals a diamictic composition (King et al., 1998). Caston (1976) has further showed that the late Plio-Pleistocene sediments have a mean wet bulk density of 1.85 g/cm3 and a porosity of 51%, whereas the underlying Eocene–Miocene sediments have densities of 1.32 g/cm3 and a porosity of about 82%.
4. Depositional environments 4.1. Pre-Neogene The opening of the Norwegian–Greenland Sea at the Paleocene–Eocene boundary established a gateway for exchange of surface- and deep-waters between the Arctic Ocean and the North Atlantic. However, the emplacement of extrusive complexes and syn-rift uplift controlled the water circulation, and in the Paleocene–Eocene, the Norwegian–Greenland Sea was characterised by a series of shallow basins with restricted surface–water interactions (Eldholm et al., 1994). The sediments deposited furthermore evidence isolation of intermediate and deep-water masses throughout the early Paleogene (Thiede and Myhre, 1996). During the earliest Eocene, the Norwegian margin subsided rapidly (Eldholm et al., 1989), and in the middle–late Eocene, the Norwegian–Greenland Sea had evolved into an ocean basin of modest size (Vogt et al., 1981). Regional surface– water interaction may have existed during the middle Eocene (Eldholm and Thomas, 1993); however,
circulation and exchange of bottom-waters were most likely restricted until the end of the Paleogene. The elevated structures on the Norwegian margin largely controlled the pre-Neogene sediment distribution (Fig. 4), as has been documented for the Paleocene sediments on the Vbring margin. In this region, these deposits are restricted to a basin area limited by the Gjallar Ridge, the Fles Fault Complex and the Nyk and Utgard highs (Fig. 2) (Hjelstuen et al., 1999), which also, in addition to the Vbring and Mbre marginal highs, represent important Paleogene source areas (Skogseid and Eldholm, 1989; Martinsen et al., 1999; Brekke, 2000; Hjelstuen et al., 1999). 4.2. Early Neogene Both seismic facies characteristics (Figs. 5–7) and sediment distribution pattern of the Miocene sediments (Fig. 8) on the Vbring continental margin indicate that these sediments have been influenced by currents during deposition; thus classifying them as contourites. At the northern Vbring Plateau, the characteristic aggradation–migration seismic pattern and the thinning of the unit towards the Nyk High (Figs. 4 and 7a) are features comparable to drift systems described by Wood and Davy (1994), which Fauge`res et al. (1999) and Rebesco and Stow (2001) defined as mounded elongated drift structures. Similar structures have also been described in Miocene sediments from the western Rockall Trough (Stoker, 2002) and the continental margin off northern Norway (Laberg et al., 2001). The Paleocene–Eocene break-up caused the Vbring Basin to be structured into several sub-provinces separated by ridges and highs (Fig. 2). The seismic records show that some of these ridges, as the Nyk High, remained as positive structures until they were rapidly covered by glacigenic sediments in the late Plio-Pleistocene. The Modgunn and Helland–Hansen arches that most likely underwent a period of growth in the late Oligocene–early Miocene (Lundin and Dore`, 2002) were also positive structures throughout the time span during which the drifts were deposited. We therefore suggest a model where oceanic currents followed the flanks of these structures (Fig. 11), causing non-deposition along the Nyk High, currentrelated structures along the Modgunn and Helland– Hansen arches and a mounded depositional pattern
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Fig. 11. (a) North Atlantic bathymetry. Contours shown are 500, 1000, 2000 and 3000 m. Box indicates location of panels (b) and (c). (b) Paleogeographical reconstruction, showing anticipated deep-water pathways on the Norwegian continental margin in the Miocene. The reconstruction is based on a 3D display of a gridded surface just below the lower Miocene sequence boundary, clearly showing the elevated dome structures and ridges at this time. (c) 3D visualisation, based on the interpreted seismic lines, of present day seabed within the studied region. Note that the Miocene dome structures and ridges have been completely covered by late Plio-Pleistocene deposits.
within the Vigrid Syncline (Figs. 4–7). Two generations of current-influenced sediment packages are observed along the western flank of the Helland–
Hansen Arch (Fig. 7b), possibly reflecting a Miocene change in the current system. However, this sediment distribution may also reflect a doming event along the
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Helland–Hansen Arch, where the first drift generation were bended along the elevating dome flanks before covered by a new generation of drift deposits during post-doming time. Parts of the Miocene succession within the North Sea Fan–Storegga Slide region have been removed during late Plio-Pleistocene, and seismic evidence indicative to interpret depositional environments is thus limited. We note that Martinsen et al. (1999) defined a prograding wedge at the continental slope on the Mbre margin. However, the convex build-up of this wedge (Fig. 6) may also be compatible with deposition under a current-influenced regime. Miller and Tucholke (1983) suggested that the present-day surface and deep-water circulation system within the Norwegian–Greenland Sea was established in the middle Miocene. This was agreed by Bohrmann et al. (1990), which dated the onset of overflow over the ridge system between Greenland and the Faroe Islands (Fig. 1) to ca. 11–13 Ma. We note that Thiede and Eldholm (1983) suggested that the shallowest parts of the Iceland–Faroe Ridge might have remained emerged until the latest Miocene. Based on plate tectonic considerations and depth anomalies, Eldholm (1990) found that the deep-water pathway through the Danmark Strait (Fig. 1) was established in the middle–late Miocene. This is consistent with results from ODP Leg 105, indicating late Miocene deep-water circulation within this region (Kaminski et al., 1989). The Fram Strait gateway (Fig. 1) to the north was also probably established during Miocene (Kristoffersen, 1990). Thus, it is reasonable to relate the establishment of a deep-water exchange within the North Atlantic and the opening of the Fram Strait gateway to the observed current-related structures within the studied region. The evolution of Miocene drift systems in the Faroe–Shetland Channel and along the northern Norwegian continental margin have also been related to the same changes in the Miocene current regime (Stoker et al., 1998; Laberg et al., 1999). 4.3. Late Neogene and Quaternary As revealed by the seismic data (Figs. 5–7) and the isopach maps (Figs. 8 and 10), the depositional pattern changed significantly at the start of the late Neogene time period. Sedimentary depocentres now evolved along the shelf edge, and westward prograd-
ing clinoforms and evolution of huge fan complexes on the uppermost slope indicate that the sediments mainly were sourced from the continental shelf and the Norwegian mainland. By the end of the late PlioPleistocene, this depositional pattern had completely smoothed the Miocene seabed relief (Fig. 11c). This change from dominantly along-slope to dominantly down-slope sedimentary processes is related both to the uplift of Fennoscandia (Stuevold and Eldholm, 1996) and the climatic cooling trend which started at ca. 2.5 Ma by the onset of the Northern Hemisphere Glaciations (e.g., Jansen and Sjbholm, 1991). The first shelf edge glaciation within the study area did, however, not occur before about 1.1 Ma (Haflidason et al., 1991; Sejrup et al., 2000), whereas marine isotope stage 12 (ca. 0.5 Ma) marks the onset of a time period characterised by repetitive shelf edge glaciations along the entire northwestern European margin (Sejrup et al., in press). Both sedimentary processes and the geological evolution of the Norwegian continental margin within this Pleistocene glacial–interglacial regime have been fully described by Sejrup et al. (2004); noting that, during glacial maximums, when ice sheets covered the continental shelf, till were transported to the shelf edge. The till material was transported down-slope by gravity processes as glacigenic debris flows (e.g., Nyga˚rd et al., 2002), thus building up the prograding wedge on the Vbring Plateau and the North Sea Fan complex. However, as for the Miocene unit, it appears that oceanic currents locally have influenced the late PlioPleistocene depositional pattern (Laberg et al., 2001; Hjelstuen et al., 2004). Within the Storegga Slide region and on the North Sea Fan, late Plio-Pleistocene erosion and sliding have caused removal of the underlying unit. This is in contrast to the Vbring continental margin where there is no evidence of erosion near the base of the late Plio-Pleistocene prograding wedge. The deposition of the thick glacigenic succession on the Norwegian margin most likely also caused significant compaction, and changes in geometry, of the pre–late Neogene deposits. This is confirmed by palinospastic restoration along depth-converted seismic profiles from the Vbring Basin, showing that Miocene sediments have been compacted by some hundred metres since ca. 2.5 Ma (Hjelstuen et al., in press). The late Plio-Pleistocene differential loading
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might therefore represent a trigger mechanism for the generation of the observed Miocene small-offset faults and the diapirs within the studied region (Hjelstuen et al., 1997, 1999). The rather rapid late Plio-Pleistocene covering of the fine-grained Miocene deposits might also provide an effective seal between Miocene and Pliocene sediments, possibly inhibiting dewatering of the Miocene sediments, leading to a low velocity zone in the upper part of the Miocene units (Reemst et al., 1996; Watterson et al., 2000). Bryn et al. (2003) have further suggested that late Plio-Pleistocene loading of Oligocene and Miocene oozes, which has a much higher permeability than the overlying glacigenic deposits, have caused transfer of excess pore pressure to the Storegga Slide region, thereby promoting conditions favourable for failure.
5. Conclusions Based on interpretation of seismic profiles, the Neogene and Quaternary time periods on the Norwegian margin have been studied, and the following conclusions have been made: !
!
!
!
Fine-grained Miocene sediments have been deposited unevenly along the Norwegian margin. A N0.75 s(twt) SW–NE-elongated depocentre is located within the western Vbring Basin. A welldefined Miocene depocentre has furthermore evolved at the northeastern flank of the North Sea Fan. Miocene sediments have been removed in the Storegga Slide–North Sea Fan region due to late Plio-Pleistocene erosion and sliding events. Similar erosion is not observed on the Vbring Plateau. Seismic facies interpretations indicate that oceanic currents influenced the Miocene sediments during deposition, classifying these deposits as contourites. We relate the contourites to the establishment of the present day deep-water current regime in the Norwegian–Greenland Sea. Observation of several generations of contourites along the western flank of the Helland–Hansen Arch may indicate changes in ocean circulation pattern.
!
!
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At the beginning of the late Pliocene, a change from dominantly along-slope to down-slope sedimentary processes occurred. During late Plio-Pleistocene, up to 1.5 s(twt)-thick depocentres evolved locally in the studied region. The Norwegian mainland and continental shelf areas have been the main source areas for these sediments. Late Plio-Pleistocene differential loading caused compaction of the underlying fine-grained Miocene sequence, probably causing pressure transfer to the Storegga Slide region, promoting instabilities in this region and thereby favourable conditions for sediment failure.
Acknowledgements We are grateful to the SEABED and Ormen Lange industry consortiums for providing seismic data to this study and for the permission to publish selected seismic sections. Atle Nyg3rd is acknowledged for constructive discussions and technical assistance. Anders Solheim offered valuable comments on an early draft of this paper. Constructive review comments from Dan Evans, Anders Mathiesen and Dag Ottesen are greatly appreciated. This work has been funded by Norsk Hydro ASA and by the EC through the STRATAGEM (EVT-CT-199900011) and COSTA (EVK3-1999-00006) projects.
References Berndt, C., Bqnz, S., Mienert, J., 2003. Polygonal fault systems on the mid-Norwegian margin: a long-term source for fluid flow. In: van Rensbergen, P., Hillis, R.R., Maltman, A.J., Morley, C. (Eds.), Subsurface Sediment Mobilization, Geol. Soc. London Spec. Publ. 216, 283 – 290. Berndt, C., Bqnz, S., Clayton, T., Mienert, J., Saunders, M., 2004. Seismic character of bottom simulating reflectors: examples from the mid-Norwegian margin. Mar. Pet. Geol. 21, 723 – 733. Berstad, I.M., Sejrup, H.P., Haflidason, H., Hjelstuen, B.O., Richter, T., Allaway, T., in press. Linkages between ocean circulation and ice sheet dynamics during the past 40 ka in the Norwegian Sea area. Bjerknes Special Publication, bClimate variability in the Nordic SeasQ. Blystad, P., Brekke, H., F&rseth, R.B., Larsen, B.T., Skogseid, J., Tbrudbakken, B., 1995. Structural elements of the Norwegian continental shelf: Part II. The Norwegian Sea region. Norw. Pet. Dir.-Bull. 8, 45 pp.
274
B.O. Hjelstuen et al. / Marine Geology 213 (2004) 257–276
Bohrmann, G., Henrich, R., Thiede, J., 1990. Miocene to Quaternary paleoceanography in the northern North Atlantic: variability in carbonate and biogenic opal accumulations. In: Bleil, U., Thiede, J. (Eds.), Geological History of the Polar Oceans: Arctic Versus Antarctic. Kluwer Academic Publishers, Netherlands, pp. 647 – 675. Brekke, H., 2000. The tectonic evolution of the Norwegian Sea continental margin, with emphasis on the Vbring and Mbre basins. In: Nbttvedt, A., et al., (Eds.), Dynamics of the Norwegian Margin, Geol. Soc. London Spec. Publ. 167, 327 – 378. Bryn, P., Solheim, A., Berg, K., Lien, R., Forsberg, C.F., Haflidason, H., Ottesen, D., Rise, L., 2003. The Storegga Slide Complex; repeated large scale sliding in response to climatic cyclicity. In: Locat, J., Mienert, J. (Eds.), Submarine Mass Movements and their Consequences. Kluwer Academic Publishers, Netherlands, pp. 215 – 222. 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 Mar. Lett. 7, 191 – 198. Caston, V.N.D., 1976. Tertiary sediments of the Vbring Plateau, Norwegian Sea, recovered by Leg 38 of the Deep Sea Drilling Project. In: Talwani, M., Udintsev, G., et al. (Eds.), Init. Rep. DSDP 38, 761 – 782. Dahlgren, K.I.T., Vorren, T.O., 2003. Sedimentary environment and glacial history during the last 40 ka f the Vbring continental margin, mid-Norway. Mar. Geol. 193, 127 – 193. Dalland, A., Worsley, D., Ofstad, K., 1988. A lithostratigraphic scheme for the Mesozoic and Cenozoic succession offshore mid- and northern Norway. Norw. Pet. Dir.-Bull. 4, 65 pp. Eidvin, T., Riis, F., 1989. Nye dateringer av de tre vestlige borehullene i Barentshavet. Resultater og konsekvenser for den terti&re hevingen. Norw. Pet. Cont. 27, 32 pp. 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. Nor. Geol. Tidsskr. 81, 119 – 160. Eidvin, T., Brekke, H., Riis, F., Renshaw, D.K., 1998. Cenozoic stratigraphy of the Norwegian Sea continental shelf, 64 8N–68 8N. Nor. Geol. Tidsskr. 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. Mar. Pet. Geol. 17, 579 – 600. Eldholm, O., 1990. Paleogene North Atlantic magmatic–tectonic events: environmental implications. Mem. Soc. Geol. Ital. 44, 13 – 28. Eldholm, O., Thomas, E., 1993. Environmental impact of volcanic margin formation. Earth Planet. Sci. Lett. 117, 319 – 329. Eldholm, O., Thiede, J., Taylor, E., 1989. Evolution of the Vbring volcanic margin. In: Eldholm, O., Thiede, J., Taylor, E., et al.,Sci. Res. ODP, vol. 104. , pp. 1033 – 1065. Eldholm, O., Myhre, A.M., Thiede, J., 1994. Cainozoic tectonomagmatic events in the North Atlantic: potential paleoenvironmental implications. NATO ASI Ser. I27, 35 – 55.
Evans, D., McGiveron, S., Harrison, Z., Bryn, P., Berg, K., 2002. Along-slope variation in the late Neogene evolution of the midNorwegian margin in response to uplift and tectonism. In: Dore´, A.G., Cartwright, J.A., Stoker, M.S., Turner, J.P., White, N. (Eds.), Exhumation of the North Atlantic Margin: Timing, Mechanisms and Implications for Petroleum Exploration, Geol. Soc. London Spec. Publ. 196, 139 – 151. Fauge`res, J.-C., Stow, D.A.V., Imbert, P., Viana, A., 1999. Seismic features diagnostic of contourite drifts. Mar. Geol. 162, 1 – 38. Galloway, W.E., 2002. Seismic expression of deep-shelf depositional and erosional morphologies, Miocene Utsira formation, North Sea Basin. Mar. Geophys. Res. 22, 309 – 321. Goll, R.M., Hansen, J.W., 1992. The Cenozoic sequence stratigraphy of the Halten Terrace and the outer Vbring Plateau based on seismic and biostratigraphic data. Nor. Geol. Tidsskr. 72, 295 – 299. Haflidason, H., Aarseth, I., Haugen, J.-E., Sejrup., H.P., Lbvlie, R., Reither, E., 1991. Quaternary stratigraphy of the Draugen area, Mid-Norwegian Shelf. Mar. Geol. 101, 125 – 146. Haflidason, H., Iversen, M., Lbvlie, R., 1998. Mbre and Vbring Basins Geological Investigation: lithological and chronological analyses of the geotechnical borings. Unpubl. report, Dep. of Geology, Univ. of Bergen, Norway, 50 pp. Haflidason, H., Lien, R., Sejrup, H.P., Forsberg, C.F., Bryn, P., in press. The dating and morphometry of the Storegga Slide. Mar. Pet. Geol. Henrich, R., 1989. Glacial/interglacial cycles in the Norwegian Sea: sedimentology, paleocenaography, and evolution of late Pliocene to Quaternary Northern Hemisphere climate. In: Eldholm, O., Thiede, J., Taylor, E., et al. (Eds.), Sci. Results ODP 104, 189 – 243. Henrich, R., Wolf, T., Bohrmann, G., Thiede, J., 1989. Cenozoic paleoclimatic and paleoceographic changes in the northern hemisphere revealed by variablity of coarse-fraction composition in sediments from the Vbring Plateau—ODP Leg 104 drill sites. In: Eldholm, O., Thiede, J., Taylor, E., et al. (Eds.), Sci. Results ODP 104, 75 – 188. Hjelstuen, B.O., Eldholm, O., Skogseid, J., 1997. Vbring Plateau diapir fields and their structural and depositional settings. Mar. Geol. 144, 33 – 57. Hjelstuen, B.O., Eldholm, O., Skogseid, J., 1999. Cenozoic evolution of the northern Vbring margin. Geol. Soc. Amer. Bull. 111, 1792 – 1807. Hjelstuen, B.O., Sejrup, H.P., Haflidason, H., Nyg3rd, A., Berstad, I.M., Knorr, G., 2004. Late Quaternary seismic stratigraphy and geological evolution of the south Vbring Margin, Norwegian Sea. Quat. Sci. Rev. 23, 1847 – 1865. Hjelstuen, H., Sejrup, H.P., Haflidason, H., Nyg3rd, A., Ceramicola, S., Bryn, P., in press. Late Cenozoic glacial history and evolution of the Storegga Slide area and adjacent slide flanks regions, Norwegian continental margin. Mar. Pet. Geol. Holtedahl, H., 1981. Distribution and origin of surface sediments on the Norwegian continental margin between 62 8N and 65 8N, with some remarks on the Late Quaternary lithoand biostratigraphy. In: S&tre, R., Mork, M. (Eds.), The Norwegian Coastal Current, Proc. Norwegian Coastal Current Symp., vol. II, pp. 768 – 792.
B.O. Hjelstuen et al. / Marine Geology 213 (2004) 257–276 Hovland, M., Nygaard, E., Thorbjbrnsen, S., 1998. Piercement shale diapirism in the deep-water Vema Dome area, Vbring Basin, offshore Norway. Mar. Pet. Geol. 15, 191 – 201. Jansen, E., Sjbholm, J., 1991. Reconstruction of glaciation over the past 6 Myr from ice-borne deposits in the Norwegian Sea. Nature 349, 600 – 603. Kaminski, M.A., Gradstein, F.M., Scott, D.B., Mackinnon, K.D., 1989. Neogene benthic foraminifer biostratigraphy and deepwater history of Sites 645, 646 and 647 Baffin Bay and Labrador Sea. In: Srivastava, S.P., Arthur, M., Clement, B., et al., Proc. ODP Sci. Results 105, 731 – 747. King, E.L., Sejrup, H.P., Haflidason, H., Elverhbi, A., Aarseth, I., 1996. Quaternary seismic stratigraphy of the North Sea Fan: glacially-fed gravity flow aprons, hemipelagic sediments, and large submarine slides. Mar. Geol. 130, 293 – 315. King, E.L., Haflidason, H., Sejrup, H.P., Lbvlie, R., 1998. Glacigenic debris flows on the North Sea Trough Mouth Fan during ice stream maxima. Mar. Geol. 152, 217 – 246. Kristoffersen, Y., 1990. On the tectonic evolution and paleocenaographic significance of the Fram Strait gateway. In: Bleil, U., Thiede, J. (Eds.), Geological History of the Polar Oceans: Arctic Versus Antarctic. Kluwer Academic Publishers, Netherlands, pp. 63 – 76. Laberg, J.S., Vorren, T.O., Knutsen, S.-M., 1999. The Lofoten contourite off Norway. Mar. Geol. 159, 1 – 6. Laberg, J.S., Dahlgren, T., Vorren, T.O., Haflidason, H., Bryn, P., 2001. Seismic analyses of Cenozoic contourite drift development in the Northern Norwegian Sea. In: Rebesco, M., Stow, D.A.V (Eds.), Seismic Expression of Contourites and Related Deposits, Mar. Geophys. Res. 22, 401 – 416. Laberg, J.S., Vorren, T.O., Mienert, J., Bryn, P., Lien, R., 2002. The Tr&nadjupet Slide: a large slope failure affecting the continental margin of Norway 4000 years ago. Geo Mar. Lett. 22, 19 – 24. Lundin, E., Dore`, A.G., 2002. Mid-Cenozoic post-breakup deformation in the bpassiveQ margins bordering the Norwegian– Greenland Sea. Mar. Pet. Geol. 19, 79 – 93. Martinsen, O.J., Bben, F., Charnock, M.A., Mangerud, G., Nbttvedt, A., 1999. Cenozoic development of the Norwegian margin 60– 64 8N: sequences and sedimentary response to variable basin physiography and tectonic setting. In: Fleet, A.J., Boldy, S.A.R. (Eds.), Petroleum Geology of Northwest Europe. Proc. 5th Conf. , pp. 293 – 304. Miller, K.G., Tucholke, B.E., 1983. Development of Cenozoic abyssal circulation south of the Greenland–Scotland Ridge. In: Bott, M.P.H., et al., (Eds.), Structural Development of the Greenland–Scotland Ridge. Plenum Publishing, pp. 449 – 589. Mosar, J., Lewis, G., Torsvik, T.H., 2002. North Atlantic sea-floor spreading rates: implications for the Tertiary development of inversion structures of the Norwegian–Greenland Sea. J. Geol. Soc. (London) 159, 503 – 515. Mosby, H., 1972. Basic problems in the Norwegian Sea. Ambio Spec. Rep. 2, 7 – 10. Nyg3rd, A., Sejrup, H.P., Haflidason, H., King, E.L., 2002. Geometry and genesis of Glacigenic Debris Flows on the North Sea Fan; TOBI imagery and deep tow boomer evidence. Mar. Geol. 188, 15 – 33.
275
Nyg3rd, A., Sejrup, H.P., Haflidason, H., Bryn, P., in press. The glacial North Sea Fan, southern Norwegian Margin: architecture and evolution from the upper continental slope to the deep-sea basin. Mar. Pet. Geol. Orvik, K.A., Niiler, P., 2002. Major pathways of Atlantic water in the northern North Atlantic and Nordic Seas toward Arctic. Geophys. Res. Lett. 29, X1 – X4. Poole, D.A.R., Vorren, T.O., 1993. Miocene to Quaternary paleoenvironments and uplift history on the mid Norwegian shelf. Mar. Geol. 115, 173 – 205. Rebesco, M., Stow, D., 2001. Seismic expression of contourites and related deposits: a preface. Mar. Geophys. Res. 22, 303 – 308. Reemst, P., Skogseid, J., Larsen, B.T., 1996. Base Pliocene velocity inversion on the eastern Vbring Margin—causes and implications. Glob. Planet. Change 12, 201 – 211. Sejrup, H.P., Fj&ran, T., Hald, M., Beck, L., Hagen, J., Miljeteig, I., Morvik, I., Norvik, O., 1981. Bentonic foraminifera in surface samples from the Norwegian continental margin between 62 8N and 64 8N. J. Foraminiferal Res. 11, 277 – 295. Sejrup, H.P., Larsen, E., Landvik, J., King, E.L., Haflidason, H., Nesje, A., 2000. Quaternary glaciations in southern Fennoscandia: evidence from southwestern Norway and the northern North Sea region. Quat. Sci. Rev. 19, 667 – 685. Sejrup, H.P., Haflidason, H., Hjelstuen, B.O., Nyg3rd, A., Bryn, P., Lien, R., 2004. Pleistocene development of the SE Nordic Seas Margin. Mar. Geol. 213, 169–200. Sejrup, H.P., Hjelstuen, B.O., Dahlgren, K.I.T., Haflidason, H., Kuijpers, A., Nyg3rd, A., Praeg, D., Stoker, M.S., Vorren, T.O., in press. Pleistocene glacial history of the NW European Continental Margin. Mar. Pet. Geol. Skogseid, J., Eldholm, O., 1989. Vbring Plateau continental margin: seismic interpretation, stratigraphy, and vertical movements. In: Eldholm, O., Thiede, J., Taylor, E., et al.,Sci. Results ODP 104, 993 – 1030. Solheim, A., Faleide, J.I., Andersen, E.S., Elverhbi, A., Forsberg, C.F., Vanneste, K., Uenzelmann-Neben, G., Channell, J.E.T., 1998. Late Cenozoic seismic stratigraphy and glacial geological development of the Svalbard–Barents Sea continental margins. Quat. Sci. Rev. 17, 155 – 184. Stoker, M.S., 2002. Late Neogene development of the UK Atlantic margin. In: Dore`, A., Cartwright, J.A., Stoker, M.S., Turner, J.P., White, N. (Eds.), Exhumation of the North Atlantic Margin: Timing, Mechanism and Implications for Petroleum Exploration, Geol. Soc. London Spec. Publ. 196, 313 – 329. Stoker, M.S., Akhurst, M.C., Howe, J.A., Stow, D.A.V., 1998. Sediment drifts and contourites on the continental margin off northwest Britain. Sediment. Geol. 115, 33 – 51. STRATAGEM partners, 2002. The Neogene stratigraphy of the glaciated European Margin from Lofoten to Porcupine. A product of the EC supported STRATAGEM project, Contract No. EVK3-CT-1999-00011, Atlas. 75 pp. Stuevold, L.M., Eldholm, O., 1996. Cenozoic uplift of Fennoscandia inferred from a study of the mid-Norwegian margin. Glob. Planet. Change 12, 359 – 386. Stuevold, L.M., Skogseid, J., Eldholm, O., 1992. Post-cretaceous uplift events on the Vbring continental margin. Geology 20, 919 – 922.
276
B.O. Hjelstuen et al. / Marine Geology 213 (2004) 257–276
Talwani, M., Udintsev, G., et al., 1976. Init. Rep. DSDP vol. 38. U.S. Govt. Printing Office, Washington. Thiede, J., Eldholm, O., 1983. Speculation about the paleodepth of the Greenland–Scotland Ridge during the late Miocene and Cenozoic times. In: Bott, M.P.H. (Ed.), Structural Development of the Greenland–Scotland Ridge. Plenum Publishing, pp. 445 – 456. Thiede, J., Myhre, A.M., 1996. Introduction to the North Atlantic– Arctic Gateway: plate tectonic–paleoceanographic history and significance. In: Thiede, J., Myhre, A.M., Firth, J.V., Johnson, G.L., Ruddiman, W., Proc. ODP Sci. Results 151, 3 – 23. Thiede, J., Eldholm, O., Taylor, E., 1989. Variability of Cainozoic Norwegian–Greenland Sea paleoceanography and Northern
Hemisphere paleoclimate. In: Eldholm, O., Thiede, J., Taylor, E., et al.,Sci. Results ODP 104, 1067 – 1118. Vogt, P., Perry, R., Feden, R.K., Fleming, R.H., Cherkis, H., 1981. The Greenland–Norwegian Sea and Iceland environment: geology and geophysics. In: Nairn, A.E.M., Churkin, M., Stenli, F.G.The Ocean Basins and Margins vol. 5. The Arctic Oceans, pp. 493 – 598. Watterson, J., Walsh, J., Nicol, A., Nell, P.A.R., Bretan, P.G., 2000. Geometry and origin of a polygon fault system. J. Geol. Soc. (London) 157, 151 – 162. Wood, R., Davy, B., 1994. The Hikurangi Plateau. Mar. Geol. 118, 153 – 173.
Neogene and Quaternary depositional environments on the Norwegian continental margin, 628N–688N Berit Oline Hjelstuena,*, Hans Petter Sejrupa, Haflidi Haflidasona, Kjell Bergb, Petter Brynb a
Department of Earth Science, University of Bergen, Alle`gt. 41, N-5007 Bergen, Norway b Norsk Hydro ASA, N-0256 Oslo, Norway Accepted 30 September 2004
Abstract 2D multichannel seismic and mini-sleeve gun profiles reveal that an up to 1.5 s(twt) thick sedimentary succession has been deposited on the Norwegian continental margin (628N–688N) during Neogene and Quaternary. Well-defined Miocene depocentres have evolved both in the North Sea Fan region and along the flanks of structural highs in the Vbring Basin. Miocene sediments are, on the other hand, mainly absent within the Storegga Slide scar. Seismic facies analyses show that these deposits locally are characterised by a mounded and/or migration–aggradation pattern, which we relate to a current-influenced depositional environment. Hence, the early Neogene sediments on the Norwegian continental margin are classified as contourites. The contourites have most likely been deposited in connection with the establishment of a deep-water exchange in the Norwegian–Greenland Sea, due to the opening of the Fram Strait and subsidence of the Greenland–Scotland Ridge. At about 2.5 Ma, a significant change in this depositional environment took place. Down-slope sedimentary processes became now more important and throughout the late Plio-Pleistocene sediments were mainly sourced from the Norwegian mainland and the adjacent continental shelf, causing depocentres to evolve along the shelf edge. D 2004 Elsevier B.V. All rights reserved. Keywords: Norwegian margin; seismic facies; contourites; Neogene; Quaternary
1. Introduction The Neogene and Quaternary time periods on the Norwegian continental margin (628N–688N; Figs. 1
* Corresponding author. Tel.: +47 55 58 35 07; fax: +47 55 58 36 60. E-mail address: [email protected] (B.O. Hjelstuen). 0025-3227/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.margeo.2004.10.009
and 2) represent an important geological time span with respect to tectonism and climate. The Norwegian margin has been shaped into its present structural configuration by repeated tectonic events, which culminated with the ca. 55 Ma break-up of the Norwegian–Greenland Sea and compressional episodes during post-break-up times. These tectonic events most likely influenced the oceanic circulation pattern, thereby affecting both sediment distribution
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Fig. 1. North Atlantic overview map. Study area within box. Bathymetry in metres. NC—Norwegian Channel; NCC—Norwegian Coastal Current; NwAC—Norwegian Atlantic Current. NwAC flow pattern from Orvik and Niiler (2002).
and depositional environments. Throughout Cenozoicum, the climate on the Northern Hemisphere gradually cooled, and a glacial regime characterise the late Plio-Pleistocene Norwegian margin. The sediments deposited during this ca. 2.5-my-long time span have been severely dissected by slides (e.g. Evans et al., 2002; Nyga˚rd et al., in press), of which the most recent one is the ca. 7250 14C BP Storegga Slide (Bugge et al., 1987; Haflidason et al., in press)
and the ca. 4000 14C BP Tr&nadjupet Slide (Laberg et al., 2002) (Fig. 2). To evaluate slope stability and possible trigger mechanisms for these slides, it is of importance to understand, and to have knowledge on, sedimentary processes and depositional environments that have acted through time. In this paper, mini-sleeve gun records and multichannel seismic profiles are interpreted to study sediment geometries, source areas,
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sediment distribution and seismic facies in order to refine our understanding of the Neogene and Quaternary development of the Norwegian continental margin.
2. Physiographic setting The Norwegian margin between 628N and 688N comprises the North Sea Fan, the Storegga Slide region and the Vbring Plateau (Figs. 1 and 2). During break-up, the volcanic-related Vbring and Mbre marginal highs, which define the western boundaries of the Vbring and Mbre basins (Fig. 2), were created. The basin areas are separated from each other by the Jan Mayen Frature Zone and its landward extension, the Jan Mayen Lineament (Blystad et al., 1995). The Vbring Basin has been structured into two provinces, divided by the Fles Fault Complex (Fig. 2). The eastern province consists of the R3s and Tr&na basins, whereas in the western province, the Gjallar Ridge and the Nyk High separate the Vigrid and N3grind synclines from the Fenris and Hel Grabens (Blystad et al., 1995). Five Cenozoic dome structures have evolved along the studied margin segment (Fig. 2). These structures are aligned into a N–S trending chain, with the Ormen Lange Dome to the south and the Naglfar Dome to the north. Various mechanisms, such as interaction by the Iceland Hotspot (Lundin and Dore`, 2002), differences in seafloor spreading rates (Mosar et al., 2002) and differential sediment loading (Stuevold et al., 1992; Hjelstuen et al., 1997) have been suggested as possible doming mechanisms. During post-break-up time, the Norwegian margin subsided, and a thick sedimentary succession was deposited (e.g., Skogseid and Eldholm, 1989). These sediments were divided by Dalland et al. (1988) into three formal units: the Eocene–Oligocene Brygge Fm, the Miocene–early Pliocene Kai Fm and the late PlioPleistocene Naust Fm, where the deposition of the late Plio-Pleistocene sediments is reflected in the bathymetry by the North Sea Fan complex at the outlet of the Norwegian Channel and the broad continental shelf off mid-Norway (Fig. 2). At present, three water masses characterise the hydrographic regime within the studied area: the Atlantic Water in the Norwegian Atlantic Current (NwAC), Coastal Current Water in the Norwegian
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Coastal Current (NCC) and homohaline deep-water in the Norway Basin (Fig. 1) (Mosby, 1972). The Atlantic Water enters the Norwegian Sea over the Iceland–Faroe Ridge and through the Faroe–Shetland Channel as two separate branches (Fig. 1) (Orvik and Niiler, 2002). The eastern NwAC branch follows the outer part of the shelf, and has strongly influenced the seabed sediment distribution in the region (Holtedahl, 1981; Sejrup et al., 1981). The Atlantic Water is sharply bounded towards the Coastal Current Water in the NCC, which parallels the coast of Norway (Fig. 1).
3. Sequence stratigraphy, seismic facies and sediment distribution The data set used in this study is composed of a regional grid of multichannel seismic profiles and high-resolution minisleeve gun data covering the Vbring margin, the Storegga Slide region and the northeastern part of the North Sea Fan. The seismic profiles are limited to the Vbring and Mbre basins (Fig. 2). Seismic unconformities as well as changes in seismic facies have been used to identify sequence boundaries (Figs. 3 and 4). The chronostratigraphy is based on Hjelstuen et al. (1999), which dated the Cenozoic sediments by seismic ties to 18 commercial wells on the mid-Norwegian continental shelf. We have identified and mapped five regional reflectors: base late Pliocene (BP), lower Miocene (LM), intra-Oligocene (IO), middle Oligocene (MO) and top Paleocene (TP) (Figs. 3–7). These reflectors bound three mega-sequences comprising Eocene– Oligocene, Miocene and late Plio-Pleistocene sediments. Although the main focus of this study will be the Miocene–Pleistocene sedimentary succession, the Paleogene time period will briefly be discussed because of its importance for the understanding of the Neogene and Quaternary margin evolution. 3.1. Eocene–Oligocene The Eocene–early Oligocene deposits are limited by the top Paleocene (TP) and the middle Oligocene (MO) sequence boundaries (Fig. 3). An acoustic non-structural seismic reflection pattern characterises the lower part of this succession, whereas parallel
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Fig. 3. Identified sequence boundaries, description of seismic facies characteristic and lithologies of mapped Cenozoic mega-sequences.
high-amplitude reflectors dominate the early Oligocene deposits. The late Oligocene sediments, defined by MO and the lower Miocene (LM) sequence boundary, are characterised by high-amplitude reflectors that have been heavily faulted. A chaotic seismic pattern is locally observed near the lower bounding surface of these deposits. Diapirism has furthermore disturbed the Oligocene sediments in a few places (Fig. 4). The Eocene–Oligocene sediment distribution has not been fully mapped, however, the seismic profiles reveal that these deposits vary considerably in thickness (Figs. 4–6). In the Vbring Basin and on the continental shelf off mid-Norway, the Eocene– Oligocene sediments mainly consist of clay (Eidvin et al., 2000). On the Mbre margin, the Eocene deposits are also mostly fine-grained; however, layers of sandstone are observed (Martinsen et al., 1999). Commercial drillings in the northernmost North Sea have shown that Oligocene sediments consist of clay and silt with minor amounts of sand (Eidvin and Rundberg, 2001).
3.2. Miocene The Miocene sediments are bounded by LM and the base late Pliocene (BP) sequence boundary (Figs. 3 and 4). In the Vbring Basin, the Miocene sediments are commonly characterised by parallel, low- to medium-amplitude reflectors (Fig. 5). Due to numerous small-offset faults, these sediments are heavily deformed, making it difficult to trace internal reflectors regionally. The faults are characterised as both normal and reverse and are occasionally penetrating into the overlying late PlioPleistocene unit (Hjelstuen et al., 1997). Berndt et al. (2003) have classified these features as polygonal faults. The layering of the Miocene sediments deposited in the Vbring Basin has apparently changed through time. This is revealed in the seismic sections by a change from SE-ward-dipping to convex-shaped reflectors (Fig. 5). Profiles cross-cutting this seismic pattern (Fig. 7a) show an asymmetrical mound, built up by thin sheet-like sequences that pinch out towards
Fig. 2. Study area showing location of interpreted seismic profiles. Filled and open fault symbols refer to Late Cretaceous–Early Tertiary and reactivated Late Jurassic–Early Cretaceous structures, respectively. Bathymetry in metres. Structural elements from Blystad et al. (1995). DSDP—deep sea drilling project; FFC—Fles Fault Complex; FG—Fles Graben; FSE—Faroe–Shetland Escarpment; GR—Gjallar Ridge; HG—Hel Graben; HHA—Helland–Hansen Arch; JMFZ—Jan Mayen Fracture Zone; MA—Modgunn Arch; MCS—multichannel seismic; MMH—Mbre Marginal High; MSG—minisleeve gun; ND—Naglfar Dome; NH—Nyk High; NS—N3grind Syncline; ODP—ocean drilling program; OL—Ormen Lange Dome; RB—R3s Basin; TB—Tr&na Basin; UH—Utgard High; VD—Vema Dome; VMH—Vbring Marginal High; VE—Vbring Escarpment; VS—Vigrid Syncline.
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Fig. 4. Geoseismic section crossing the Vbring Plateau, Storegga Slide area and the northeastern North Sea Fan, showing distribution of Quaternary, Neogene and Paleogene sediments. Profile location in Fig. 2. BP—base late Pliocene; LM—lower Miocene; MO—middle Oligocene; IO—intra-Oligocene; TP—top Paleocene.
north. The sheets are stacked on top of each other, and show a NE-trending migration–aggradation pattern. Furthermore, along the flanks of the Helland–Hansen and Modgunn arches, the Miocene sediments are characterised by mounded reflectors with an aggradating onlap pattern. Apparently, two generations of onlap features are observed along the western Helland–Hansen Arch flank (Fig. 7b). Near the northern Storegga Slide scar, the Miocene sediments are dominated by convex parallel reflectors, whereas within the slide scar itself, the Miocene sediments that are still preserved show medium- to high-amplitude parallel reflectors. In the northeastern North Sea Fan region, the Miocene sediments locally display a mounded seismic appearance along the slope (Fig. 6). Both within the Storegga Slide scar and in the North Sea Fan region, the Miocene succession is faulted. However, the deformation within these regions has been less intense than that observed on the Vbring Plateau. A well-defined high-amplitude reflector, crosscutting the Miocene bedding, is observed within the entire studied region (Figs. 4–7). This high-amplitude reflector also crosses LM and is neither parallel to the seafloor nor to the layering of the late Plio-Pleistocene deposits. Most likely, it is a diagenetic surface, representing the transition from Opal A to Opal CT (Brekke, 2000; Berndt et al., 2004). Brekke (2000) suggested that this boundary was formed during the latest Miocene–earliest Pliocene. The Miocene sediments show a complex distribution along the Norwegian margin. In the Vbring
Basin, the Miocene deposits reach a maximum thickness between 0.75 and 1.0 s(twt) within a SW–NEelongated depocentre (Fig. 8). The Miocene sediments are thin or absent across the Modgunn Arch, Helland– Hansen Arch, Vema Dome and Naglfar Dome. Previous studies within the region have furthermore revealed that the Miocene sediments on the midNorwegian continental shelf are rather thin (e.g., Hjelstuen et al., 1999). In the Storegga Slide region, the Miocene sediments are mainly absent (Figs. 4 and 8), whereas at the northeastern flank of the North Sea Fan, a depocentre reaching a thickness of about 0.75 s(twt) has evolved. The Miocene succession was first sampled in the northwestern Vbring Basin and on the northern Vbring Marginal High during Deep Sea Drilling Project (DSDP) Leg 38 (Fig. 2) (Talwani et al., 1976). The DSDP sites show that the Miocene sediments, in water depths N1250 m, almost exclusively consist of pelagic siliceous oozes with varying clay and calcareous nannoplakton contents, where the terrigenous input increases upwards in the succession (Caston, 1976). Similar ooze-rich sediments have been reported from ODP Leg 104 sites on the Vbring Marginal High (Fig. 2) (e.g., Eldholm et al., 1989). ODP Site 644 (Fig. 2) from the Vbring Basin apparently penetrates into Miocene sediments at about 230 m core depth (Fig. 9), i.e., at a level characterised by a significant increase in the biogenic opal content. Goll and Hansen (1992) investigated seven wells at the continental shelf off mid-Norway, showing that the Miocene succession consists of calcareous mudstone.
B.O. Hjelstuen et al. / Marine Geology 213 (2004) 257–276 Fig. 5. (a) NW–SE trending geoseismic section (NH9651-405) across the central part of the Vbring Plateau. Profile location in Fig. 2. Abbreviations as in Fig. 4. (b) Seismic facies characteristic of Cenozoic sediments. Profile location in panel (a). Abbreviations as in Fig. 4. 263
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Fig. 6. (a) NW–SE trending geoseismic section (MB6-92/MB6-91) across northeastern part of the North Sea Fan. Profile location in Fig. 2. Abbreviations as in Fig. 4. (b) Seismic facies characteristic of Cenozoic sediments. Profile location in Fig. 2. Abbreviation as in Fig. 4.
At the Utgard High (Fig. 2), the Miocene sediments are characterised as claystone with a small content of sand/ silt and sparse occurrences of radiolarian ooze (Eidvin et al., 1998, 2000; Poole and Vorren, 1993). The lithological information about the Miocene sedimentary succession in the southern part of the study area is rather sparse. Eidvin et al. (2000) identified the Utsira Formation near the outlet of the Norwegian Channel (Figs. 2 and 8). Galloway (2002) suggested a middle–late Miocene age for the Utsira Formation and described it as a unit composed of marine sand deposited in a water depth of 100–200 m. The Utsira Formation fine westwards, and the lower
part of the unit is glauconitic (Martinsen et al., 1999). The Miocene succession within the main Mbre Basin has not been sampled. However, the seismic facies indicate that it may consist of similar sediments as deposited on the Vbring Plateau. 3.3. Late Plio-Pleistocene It is well documented that the base late Pliocene sequence boundary (BP) represents an unconformity on the Norwegian margin (Hjelstuen et al., 1999; Eidvin et al., 2000; STRATAGEM partners, 2002). Seismic investigations and cores along the entire
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northeastern European margin have furthermore revealed that BP is related to the main initiation of the Northern Hemisphere glaciations at ca. 2.5 Ma (e.g., Eidvin and Riis, 1989; Thiede et al., 1989; Jansen and Sjbholm, 1991; Solheim et al., 1998). There is a distinct change in the seismic facies pattern between Miocene and late Plio-Pleistocene sediments (Figs. 5 and 6), thus generally making it
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easy to trace BP within the study area. On the Vbring margin, BP represents a well-defined downlapping surface for late Plio-Pleistocene prograding clinoforms. The clinoforms are commonly characterised by high-amplitude reflectors and separate sequences showing a chaotic, structureless or weakly layered seismic pattern (Fig. 5). The clinoforms reach their westernmost extent in a water depth of ca. 1000–1200
Fig. 7. (a) Seismic example (above) and interpretation (below), showing characteristic depositional pattern of current-influenced sediments on the Vbring Plateau. Profile location in Fig. 2. Abbreviations as in Fig. 4. (b) Seismic example (above) and interpretation (below), showing characteristic depositional pattern of current-influenced sediments along the western flank of the Helland–Hansen Arch. Profile location in Fig. 2. Abbreviations as in Fig. 4.
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Fig. 7 (continued).
m. In deeper water, the late Plio-Pleistocene sediments are lying conformable above BP, and the deposits are characterised by parallel medium- to high-amplitude reflectors (Fig. 5b). At several places in the Vbring Basin, the late Plio-Pleistocene sediments are disturbed by diapirs (Fig. 4) (Hjelstuen et al., 1997; Hovland et al., 1998). Within the Storegga Slide region, the base late Pliocene boundary is defined as an erosional surface, whereas the late Plio-Pleistocene sediments are domi-
nated by an internal non-structural acoustic facies and a few high-amplitude continuous reflectors. Slide scars, up to 200 ms(twt) (ca. 200 m) high, are observed at the base late Pliocene level, causing deep intersections into the underlying sedimentary succession on the North Sea Fan. The fan succession itself has also been severely eroded due to repeated slide events (Evans et al., 2002; Nyga˚rd et al., in press; Sejrup et al., 2004). The slide debrites left by these slide events are dominated by a chaotic, pattern, limited by smooth
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Fig. 8. Isopach map of Miocene sediments. Stippled lines indicate location of seismic profiles defining the database of this study. Major dome structures, the Storegga Slide and the North Sea Fan are outlined. Isopach contour interval is 250 ms(twt). HHA—Helland–Hansen Arch; MA— Modgunn Arch; ND—Naglfar Dome; NH—Nyk High; OL—Ormen Lange Dome; VD—Vema Dome.
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Fig. 9. Compilation of ODP Site 644, geotechnical boring 6405/2-GB1 and the commercial well 34/2-4, showing lithology and grain size of late Paleogene–Neogene–Quaternary sediments on the Norwegian continental margin. Based on Haflidason et al. (1998), Eidvin et al. (2000) and Henrich et al. (1989). Core locations in Fig. 2. MIS—marine isotope stage; LGM—last glacial maximum; WD—water depth.
lower and irregular upper boundaries. The North Sea Fan complex is furthermore characterised by sequences composed of acoustically transparent, mounded, lensoid-stacked glacigenic debris flows (King et al., 1996; Nyga˚rd et al., 2002, in press). The isopach map of the late Plio-Pleistocene deposits (Fig. 10) shows that an up to 1.5 s(twt) thick sequence has been deposited along the shelf edge on the Vbring margin. The sedimentary succession is however thinning rapidly westward, and in water depths exceeding 1000 m, this unit is commonly less than 0.5 s(twt) thick. At the mouth of the Norwegian Channel, the sediment thicknesses exceeds 1.5 s(twt),
whereas in the Storegga Slide scar, the isopach map shows that the late Plio-Pleistocene sediments are b1.0 s(twt) thick. The composition of the late Plio-Pleistocene sediments has been well documented by DSDP/ODP borings, recently raised shallow cores and geotechnical borings within the study area (e.g. Eldholm et al., 1989, Eidvin et al., 2000; Dahlgren and Vorren, 2003; Hjelstuen et al., 2004; Berstad et al., in press). ODP Site 644 in the central Vbring Basin (Fig. 2) revealed that these deposits consist of sandy mud (Fig. 9). Detailed lithological analyses furthermore show that there is a strong cyclicity in the carbonate and
Fig. 10. Isopach map of late Plio-Pleistocene sediments. Stippled lines indicate location of seismic profiles defining the database of this study. Outline of major dome structures, the Storegga Slide and the North Sea Fan are shown. Isopach contour interval is 250 ms(twt). Stippled contours on the North Sea Fan indicate uncertain sediment thickness. HHA—Helland–Hansen Arch; MA—Modgunn Arch; ND—Naglfar Dome; NH—Nyk High; OL—Ormen Lange Dome; VD—Vema Dome.
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terrigenous particle content through time, and that the observed carbonate peaks correlate with minima in the terrigenous input (Henrich et al., 1989). These repetitive changes are related to the climatic variations during this time period, with waxing and waning ice sheets over Fennoscandia (Henrich, 1989). Detailed analyses of gravity cores from the northern part of the study area (Dahlgren and Vorren, 2003) indicate that the very uppermost part of the late Plio-Pleistocene sediment succession is composed of mud and diamicton. Geotechnical borings (Fig. 9) from the southern Vbring Plateau show that the sediments deposited during the last 250 ka are composed of clay/ silt and sand/gravel units, with the coarsest sediments deposited during glacial stages. Coring of the uppermost-identified glacigenic debris flow unit on the North Sea Fan reveals a diamictic composition (King et al., 1998). Caston (1976) has further showed that the late Plio-Pleistocene sediments have a mean wet bulk density of 1.85 g/cm3 and a porosity of 51%, whereas the underlying Eocene–Miocene sediments have densities of 1.32 g/cm3 and a porosity of about 82%.
4. Depositional environments 4.1. Pre-Neogene The opening of the Norwegian–Greenland Sea at the Paleocene–Eocene boundary established a gateway for exchange of surface- and deep-waters between the Arctic Ocean and the North Atlantic. However, the emplacement of extrusive complexes and syn-rift uplift controlled the water circulation, and in the Paleocene–Eocene, the Norwegian–Greenland Sea was characterised by a series of shallow basins with restricted surface–water interactions (Eldholm et al., 1994). The sediments deposited furthermore evidence isolation of intermediate and deep-water masses throughout the early Paleogene (Thiede and Myhre, 1996). During the earliest Eocene, the Norwegian margin subsided rapidly (Eldholm et al., 1989), and in the middle–late Eocene, the Norwegian–Greenland Sea had evolved into an ocean basin of modest size (Vogt et al., 1981). Regional surface– water interaction may have existed during the middle Eocene (Eldholm and Thomas, 1993); however,
circulation and exchange of bottom-waters were most likely restricted until the end of the Paleogene. The elevated structures on the Norwegian margin largely controlled the pre-Neogene sediment distribution (Fig. 4), as has been documented for the Paleocene sediments on the Vbring margin. In this region, these deposits are restricted to a basin area limited by the Gjallar Ridge, the Fles Fault Complex and the Nyk and Utgard highs (Fig. 2) (Hjelstuen et al., 1999), which also, in addition to the Vbring and Mbre marginal highs, represent important Paleogene source areas (Skogseid and Eldholm, 1989; Martinsen et al., 1999; Brekke, 2000; Hjelstuen et al., 1999). 4.2. Early Neogene Both seismic facies characteristics (Figs. 5–7) and sediment distribution pattern of the Miocene sediments (Fig. 8) on the Vbring continental margin indicate that these sediments have been influenced by currents during deposition; thus classifying them as contourites. At the northern Vbring Plateau, the characteristic aggradation–migration seismic pattern and the thinning of the unit towards the Nyk High (Figs. 4 and 7a) are features comparable to drift systems described by Wood and Davy (1994), which Fauge`res et al. (1999) and Rebesco and Stow (2001) defined as mounded elongated drift structures. Similar structures have also been described in Miocene sediments from the western Rockall Trough (Stoker, 2002) and the continental margin off northern Norway (Laberg et al., 2001). The Paleocene–Eocene break-up caused the Vbring Basin to be structured into several sub-provinces separated by ridges and highs (Fig. 2). The seismic records show that some of these ridges, as the Nyk High, remained as positive structures until they were rapidly covered by glacigenic sediments in the late Plio-Pleistocene. The Modgunn and Helland–Hansen arches that most likely underwent a period of growth in the late Oligocene–early Miocene (Lundin and Dore`, 2002) were also positive structures throughout the time span during which the drifts were deposited. We therefore suggest a model where oceanic currents followed the flanks of these structures (Fig. 11), causing non-deposition along the Nyk High, currentrelated structures along the Modgunn and Helland– Hansen arches and a mounded depositional pattern
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Fig. 11. (a) North Atlantic bathymetry. Contours shown are 500, 1000, 2000 and 3000 m. Box indicates location of panels (b) and (c). (b) Paleogeographical reconstruction, showing anticipated deep-water pathways on the Norwegian continental margin in the Miocene. The reconstruction is based on a 3D display of a gridded surface just below the lower Miocene sequence boundary, clearly showing the elevated dome structures and ridges at this time. (c) 3D visualisation, based on the interpreted seismic lines, of present day seabed within the studied region. Note that the Miocene dome structures and ridges have been completely covered by late Plio-Pleistocene deposits.
within the Vigrid Syncline (Figs. 4–7). Two generations of current-influenced sediment packages are observed along the western flank of the Helland–
Hansen Arch (Fig. 7b), possibly reflecting a Miocene change in the current system. However, this sediment distribution may also reflect a doming event along the
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Helland–Hansen Arch, where the first drift generation were bended along the elevating dome flanks before covered by a new generation of drift deposits during post-doming time. Parts of the Miocene succession within the North Sea Fan–Storegga Slide region have been removed during late Plio-Pleistocene, and seismic evidence indicative to interpret depositional environments is thus limited. We note that Martinsen et al. (1999) defined a prograding wedge at the continental slope on the Mbre margin. However, the convex build-up of this wedge (Fig. 6) may also be compatible with deposition under a current-influenced regime. Miller and Tucholke (1983) suggested that the present-day surface and deep-water circulation system within the Norwegian–Greenland Sea was established in the middle Miocene. This was agreed by Bohrmann et al. (1990), which dated the onset of overflow over the ridge system between Greenland and the Faroe Islands (Fig. 1) to ca. 11–13 Ma. We note that Thiede and Eldholm (1983) suggested that the shallowest parts of the Iceland–Faroe Ridge might have remained emerged until the latest Miocene. Based on plate tectonic considerations and depth anomalies, Eldholm (1990) found that the deep-water pathway through the Danmark Strait (Fig. 1) was established in the middle–late Miocene. This is consistent with results from ODP Leg 105, indicating late Miocene deep-water circulation within this region (Kaminski et al., 1989). The Fram Strait gateway (Fig. 1) to the north was also probably established during Miocene (Kristoffersen, 1990). Thus, it is reasonable to relate the establishment of a deep-water exchange within the North Atlantic and the opening of the Fram Strait gateway to the observed current-related structures within the studied region. The evolution of Miocene drift systems in the Faroe–Shetland Channel and along the northern Norwegian continental margin have also been related to the same changes in the Miocene current regime (Stoker et al., 1998; Laberg et al., 1999). 4.3. Late Neogene and Quaternary As revealed by the seismic data (Figs. 5–7) and the isopach maps (Figs. 8 and 10), the depositional pattern changed significantly at the start of the late Neogene time period. Sedimentary depocentres now evolved along the shelf edge, and westward prograd-
ing clinoforms and evolution of huge fan complexes on the uppermost slope indicate that the sediments mainly were sourced from the continental shelf and the Norwegian mainland. By the end of the late PlioPleistocene, this depositional pattern had completely smoothed the Miocene seabed relief (Fig. 11c). This change from dominantly along-slope to dominantly down-slope sedimentary processes is related both to the uplift of Fennoscandia (Stuevold and Eldholm, 1996) and the climatic cooling trend which started at ca. 2.5 Ma by the onset of the Northern Hemisphere Glaciations (e.g., Jansen and Sjbholm, 1991). The first shelf edge glaciation within the study area did, however, not occur before about 1.1 Ma (Haflidason et al., 1991; Sejrup et al., 2000), whereas marine isotope stage 12 (ca. 0.5 Ma) marks the onset of a time period characterised by repetitive shelf edge glaciations along the entire northwestern European margin (Sejrup et al., in press). Both sedimentary processes and the geological evolution of the Norwegian continental margin within this Pleistocene glacial–interglacial regime have been fully described by Sejrup et al. (2004); noting that, during glacial maximums, when ice sheets covered the continental shelf, till were transported to the shelf edge. The till material was transported down-slope by gravity processes as glacigenic debris flows (e.g., Nyga˚rd et al., 2002), thus building up the prograding wedge on the Vbring Plateau and the North Sea Fan complex. However, as for the Miocene unit, it appears that oceanic currents locally have influenced the late PlioPleistocene depositional pattern (Laberg et al., 2001; Hjelstuen et al., 2004). Within the Storegga Slide region and on the North Sea Fan, late Plio-Pleistocene erosion and sliding have caused removal of the underlying unit. This is in contrast to the Vbring continental margin where there is no evidence of erosion near the base of the late Plio-Pleistocene prograding wedge. The deposition of the thick glacigenic succession on the Norwegian margin most likely also caused significant compaction, and changes in geometry, of the pre–late Neogene deposits. This is confirmed by palinospastic restoration along depth-converted seismic profiles from the Vbring Basin, showing that Miocene sediments have been compacted by some hundred metres since ca. 2.5 Ma (Hjelstuen et al., in press). The late Plio-Pleistocene differential loading
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might therefore represent a trigger mechanism for the generation of the observed Miocene small-offset faults and the diapirs within the studied region (Hjelstuen et al., 1997, 1999). The rather rapid late Plio-Pleistocene covering of the fine-grained Miocene deposits might also provide an effective seal between Miocene and Pliocene sediments, possibly inhibiting dewatering of the Miocene sediments, leading to a low velocity zone in the upper part of the Miocene units (Reemst et al., 1996; Watterson et al., 2000). Bryn et al. (2003) have further suggested that late Plio-Pleistocene loading of Oligocene and Miocene oozes, which has a much higher permeability than the overlying glacigenic deposits, have caused transfer of excess pore pressure to the Storegga Slide region, thereby promoting conditions favourable for failure.
5. Conclusions Based on interpretation of seismic profiles, the Neogene and Quaternary time periods on the Norwegian margin have been studied, and the following conclusions have been made: !
!
!
!
Fine-grained Miocene sediments have been deposited unevenly along the Norwegian margin. A N0.75 s(twt) SW–NE-elongated depocentre is located within the western Vbring Basin. A welldefined Miocene depocentre has furthermore evolved at the northeastern flank of the North Sea Fan. Miocene sediments have been removed in the Storegga Slide–North Sea Fan region due to late Plio-Pleistocene erosion and sliding events. Similar erosion is not observed on the Vbring Plateau. Seismic facies interpretations indicate that oceanic currents influenced the Miocene sediments during deposition, classifying these deposits as contourites. We relate the contourites to the establishment of the present day deep-water current regime in the Norwegian–Greenland Sea. Observation of several generations of contourites along the western flank of the Helland–Hansen Arch may indicate changes in ocean circulation pattern.
!
!
!
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At the beginning of the late Pliocene, a change from dominantly along-slope to down-slope sedimentary processes occurred. During late Plio-Pleistocene, up to 1.5 s(twt)-thick depocentres evolved locally in the studied region. The Norwegian mainland and continental shelf areas have been the main source areas for these sediments. Late Plio-Pleistocene differential loading caused compaction of the underlying fine-grained Miocene sequence, probably causing pressure transfer to the Storegga Slide region, promoting instabilities in this region and thereby favourable conditions for sediment failure.
Acknowledgements We are grateful to the SEABED and Ormen Lange industry consortiums for providing seismic data to this study and for the permission to publish selected seismic sections. Atle Nyg3rd is acknowledged for constructive discussions and technical assistance. Anders Solheim offered valuable comments on an early draft of this paper. Constructive review comments from Dan Evans, Anders Mathiesen and Dag Ottesen are greatly appreciated. This work has been funded by Norsk Hydro ASA and by the EC through the STRATAGEM (EVT-CT-199900011) and COSTA (EVK3-1999-00006) projects.
References Berndt, C., Bqnz, S., Mienert, J., 2003. Polygonal fault systems on the mid-Norwegian margin: a long-term source for fluid flow. In: van Rensbergen, P., Hillis, R.R., Maltman, A.J., Morley, C. (Eds.), Subsurface Sediment Mobilization, Geol. Soc. London Spec. Publ. 216, 283 – 290. Berndt, C., Bqnz, S., Clayton, T., Mienert, J., Saunders, M., 2004. Seismic character of bottom simulating reflectors: examples from the mid-Norwegian margin. Mar. Pet. Geol. 21, 723 – 733. Berstad, I.M., Sejrup, H.P., Haflidason, H., Hjelstuen, B.O., Richter, T., Allaway, T., in press. Linkages between ocean circulation and ice sheet dynamics during the past 40 ka in the Norwegian Sea area. Bjerknes Special Publication, bClimate variability in the Nordic SeasQ. Blystad, P., Brekke, H., F&rseth, R.B., Larsen, B.T., Skogseid, J., Tbrudbakken, B., 1995. Structural elements of the Norwegian continental shelf: Part II. The Norwegian Sea region. Norw. Pet. Dir.-Bull. 8, 45 pp.
274
B.O. Hjelstuen et al. / Marine Geology 213 (2004) 257–276
Bohrmann, G., Henrich, R., Thiede, J., 1990. Miocene to Quaternary paleoceanography in the northern North Atlantic: variability in carbonate and biogenic opal accumulations. In: Bleil, U., Thiede, J. (Eds.), Geological History of the Polar Oceans: Arctic Versus Antarctic. Kluwer Academic Publishers, Netherlands, pp. 647 – 675. Brekke, H., 2000. The tectonic evolution of the Norwegian Sea continental margin, with emphasis on the Vbring and Mbre basins. In: Nbttvedt, A., et al., (Eds.), Dynamics of the Norwegian Margin, Geol. Soc. London Spec. Publ. 167, 327 – 378. Bryn, P., Solheim, A., Berg, K., Lien, R., Forsberg, C.F., Haflidason, H., Ottesen, D., Rise, L., 2003. The Storegga Slide Complex; repeated large scale sliding in response to climatic cyclicity. In: Locat, J., Mienert, J. (Eds.), Submarine Mass Movements and their Consequences. Kluwer Academic Publishers, Netherlands, pp. 215 – 222. 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 Mar. Lett. 7, 191 – 198. Caston, V.N.D., 1976. Tertiary sediments of the Vbring Plateau, Norwegian Sea, recovered by Leg 38 of the Deep Sea Drilling Project. In: Talwani, M., Udintsev, G., et al. (Eds.), Init. Rep. DSDP 38, 761 – 782. Dahlgren, K.I.T., Vorren, T.O., 2003. Sedimentary environment and glacial history during the last 40 ka f the Vbring continental margin, mid-Norway. Mar. Geol. 193, 127 – 193. Dalland, A., Worsley, D., Ofstad, K., 1988. A lithostratigraphic scheme for the Mesozoic and Cenozoic succession offshore mid- and northern Norway. Norw. Pet. Dir.-Bull. 4, 65 pp. Eidvin, T., Riis, F., 1989. Nye dateringer av de tre vestlige borehullene i Barentshavet. Resultater og konsekvenser for den terti&re hevingen. Norw. Pet. Cont. 27, 32 pp. 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. Nor. Geol. Tidsskr. 81, 119 – 160. Eidvin, T., Brekke, H., Riis, F., Renshaw, D.K., 1998. Cenozoic stratigraphy of the Norwegian Sea continental shelf, 64 8N–68 8N. Nor. Geol. Tidsskr. 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. Mar. Pet. Geol. 17, 579 – 600. Eldholm, O., 1990. Paleogene North Atlantic magmatic–tectonic events: environmental implications. Mem. Soc. Geol. Ital. 44, 13 – 28. Eldholm, O., Thomas, E., 1993. Environmental impact of volcanic margin formation. Earth Planet. Sci. Lett. 117, 319 – 329. Eldholm, O., Thiede, J., Taylor, E., 1989. Evolution of the Vbring volcanic margin. In: Eldholm, O., Thiede, J., Taylor, E., et al.,Sci. Res. ODP, vol. 104. , pp. 1033 – 1065. Eldholm, O., Myhre, A.M., Thiede, J., 1994. Cainozoic tectonomagmatic events in the North Atlantic: potential paleoenvironmental implications. NATO ASI Ser. I27, 35 – 55.
Evans, D., McGiveron, S., Harrison, Z., Bryn, P., Berg, K., 2002. Along-slope variation in the late Neogene evolution of the midNorwegian margin in response to uplift and tectonism. In: Dore´, A.G., Cartwright, J.A., Stoker, M.S., Turner, J.P., White, N. (Eds.), Exhumation of the North Atlantic Margin: Timing, Mechanisms and Implications for Petroleum Exploration, Geol. Soc. London Spec. Publ. 196, 139 – 151. Fauge`res, J.-C., Stow, D.A.V., Imbert, P., Viana, A., 1999. Seismic features diagnostic of contourite drifts. Mar. Geol. 162, 1 – 38. Galloway, W.E., 2002. Seismic expression of deep-shelf depositional and erosional morphologies, Miocene Utsira formation, North Sea Basin. Mar. Geophys. Res. 22, 309 – 321. Goll, R.M., Hansen, J.W., 1992. The Cenozoic sequence stratigraphy of the Halten Terrace and the outer Vbring Plateau based on seismic and biostratigraphic data. Nor. Geol. Tidsskr. 72, 295 – 299. Haflidason, H., Aarseth, I., Haugen, J.-E., Sejrup., H.P., Lbvlie, R., Reither, E., 1991. Quaternary stratigraphy of the Draugen area, Mid-Norwegian Shelf. Mar. Geol. 101, 125 – 146. Haflidason, H., Iversen, M., Lbvlie, R., 1998. Mbre and Vbring Basins Geological Investigation: lithological and chronological analyses of the geotechnical borings. Unpubl. report, Dep. of Geology, Univ. of Bergen, Norway, 50 pp. Haflidason, H., Lien, R., Sejrup, H.P., Forsberg, C.F., Bryn, P., in press. The dating and morphometry of the Storegga Slide. Mar. Pet. Geol. Henrich, R., 1989. Glacial/interglacial cycles in the Norwegian Sea: sedimentology, paleocenaography, and evolution of late Pliocene to Quaternary Northern Hemisphere climate. In: Eldholm, O., Thiede, J., Taylor, E., et al. (Eds.), Sci. Results ODP 104, 189 – 243. Henrich, R., Wolf, T., Bohrmann, G., Thiede, J., 1989. Cenozoic paleoclimatic and paleoceographic changes in the northern hemisphere revealed by variablity of coarse-fraction composition in sediments from the Vbring Plateau—ODP Leg 104 drill sites. In: Eldholm, O., Thiede, J., Taylor, E., et al. (Eds.), Sci. Results ODP 104, 75 – 188. Hjelstuen, B.O., Eldholm, O., Skogseid, J., 1997. Vbring Plateau diapir fields and their structural and depositional settings. Mar. Geol. 144, 33 – 57. Hjelstuen, B.O., Eldholm, O., Skogseid, J., 1999. Cenozoic evolution of the northern Vbring margin. Geol. Soc. Amer. Bull. 111, 1792 – 1807. Hjelstuen, B.O., Sejrup, H.P., Haflidason, H., Nyg3rd, A., Berstad, I.M., Knorr, G., 2004. Late Quaternary seismic stratigraphy and geological evolution of the south Vbring Margin, Norwegian Sea. Quat. Sci. Rev. 23, 1847 – 1865. Hjelstuen, H., Sejrup, H.P., Haflidason, H., Nyg3rd, A., Ceramicola, S., Bryn, P., in press. Late Cenozoic glacial history and evolution of the Storegga Slide area and adjacent slide flanks regions, Norwegian continental margin. Mar. Pet. Geol. Holtedahl, H., 1981. Distribution and origin of surface sediments on the Norwegian continental margin between 62 8N and 65 8N, with some remarks on the Late Quaternary lithoand biostratigraphy. In: S&tre, R., Mork, M. (Eds.), The Norwegian Coastal Current, Proc. Norwegian Coastal Current Symp., vol. II, pp. 768 – 792.
B.O. Hjelstuen et al. / Marine Geology 213 (2004) 257–276 Hovland, M., Nygaard, E., Thorbjbrnsen, S., 1998. Piercement shale diapirism in the deep-water Vema Dome area, Vbring Basin, offshore Norway. Mar. Pet. Geol. 15, 191 – 201. Jansen, E., Sjbholm, J., 1991. Reconstruction of glaciation over the past 6 Myr from ice-borne deposits in the Norwegian Sea. Nature 349, 600 – 603. Kaminski, M.A., Gradstein, F.M., Scott, D.B., Mackinnon, K.D., 1989. Neogene benthic foraminifer biostratigraphy and deepwater history of Sites 645, 646 and 647 Baffin Bay and Labrador Sea. In: Srivastava, S.P., Arthur, M., Clement, B., et al., Proc. ODP Sci. Results 105, 731 – 747. King, E.L., Sejrup, H.P., Haflidason, H., Elverhbi, A., Aarseth, I., 1996. Quaternary seismic stratigraphy of the North Sea Fan: glacially-fed gravity flow aprons, hemipelagic sediments, and large submarine slides. Mar. Geol. 130, 293 – 315. King, E.L., Haflidason, H., Sejrup, H.P., Lbvlie, R., 1998. Glacigenic debris flows on the North Sea Trough Mouth Fan during ice stream maxima. Mar. Geol. 152, 217 – 246. Kristoffersen, Y., 1990. On the tectonic evolution and paleocenaographic significance of the Fram Strait gateway. In: Bleil, U., Thiede, J. (Eds.), Geological History of the Polar Oceans: Arctic Versus Antarctic. Kluwer Academic Publishers, Netherlands, pp. 63 – 76. Laberg, J.S., Vorren, T.O., Knutsen, S.-M., 1999. The Lofoten contourite off Norway. Mar. Geol. 159, 1 – 6. Laberg, J.S., Dahlgren, T., Vorren, T.O., Haflidason, H., Bryn, P., 2001. Seismic analyses of Cenozoic contourite drift development in the Northern Norwegian Sea. In: Rebesco, M., Stow, D.A.V (Eds.), Seismic Expression of Contourites and Related Deposits, Mar. Geophys. Res. 22, 401 – 416. Laberg, J.S., Vorren, T.O., Mienert, J., Bryn, P., Lien, R., 2002. The Tr&nadjupet Slide: a large slope failure affecting the continental margin of Norway 4000 years ago. Geo Mar. Lett. 22, 19 – 24. Lundin, E., Dore`, A.G., 2002. Mid-Cenozoic post-breakup deformation in the bpassiveQ margins bordering the Norwegian– Greenland Sea. Mar. Pet. Geol. 19, 79 – 93. Martinsen, O.J., Bben, F., Charnock, M.A., Mangerud, G., Nbttvedt, A., 1999. Cenozoic development of the Norwegian margin 60– 64 8N: sequences and sedimentary response to variable basin physiography and tectonic setting. In: Fleet, A.J., Boldy, S.A.R. (Eds.), Petroleum Geology of Northwest Europe. Proc. 5th Conf. , pp. 293 – 304. Miller, K.G., Tucholke, B.E., 1983. Development of Cenozoic abyssal circulation south of the Greenland–Scotland Ridge. In: Bott, M.P.H., et al., (Eds.), Structural Development of the Greenland–Scotland Ridge. Plenum Publishing, pp. 449 – 589. Mosar, J., Lewis, G., Torsvik, T.H., 2002. North Atlantic sea-floor spreading rates: implications for the Tertiary development of inversion structures of the Norwegian–Greenland Sea. J. Geol. Soc. (London) 159, 503 – 515. Mosby, H., 1972. Basic problems in the Norwegian Sea. Ambio Spec. Rep. 2, 7 – 10. Nyg3rd, A., Sejrup, H.P., Haflidason, H., King, E.L., 2002. Geometry and genesis of Glacigenic Debris Flows on the North Sea Fan; TOBI imagery and deep tow boomer evidence. Mar. Geol. 188, 15 – 33.
275
Nyg3rd, A., Sejrup, H.P., Haflidason, H., Bryn, P., in press. The glacial North Sea Fan, southern Norwegian Margin: architecture and evolution from the upper continental slope to the deep-sea basin. Mar. Pet. Geol. Orvik, K.A., Niiler, P., 2002. Major pathways of Atlantic water in the northern North Atlantic and Nordic Seas toward Arctic. Geophys. Res. Lett. 29, X1 – X4. Poole, D.A.R., Vorren, T.O., 1993. Miocene to Quaternary paleoenvironments and uplift history on the mid Norwegian shelf. Mar. Geol. 115, 173 – 205. Rebesco, M., Stow, D., 2001. Seismic expression of contourites and related deposits: a preface. Mar. Geophys. Res. 22, 303 – 308. Reemst, P., Skogseid, J., Larsen, B.T., 1996. Base Pliocene velocity inversion on the eastern Vbring Margin—causes and implications. Glob. Planet. Change 12, 201 – 211. Sejrup, H.P., Fj&ran, T., Hald, M., Beck, L., Hagen, J., Miljeteig, I., Morvik, I., Norvik, O., 1981. Bentonic foraminifera in surface samples from the Norwegian continental margin between 62 8N and 64 8N. J. Foraminiferal Res. 11, 277 – 295. Sejrup, H.P., Larsen, E., Landvik, J., King, E.L., Haflidason, H., Nesje, A., 2000. Quaternary glaciations in southern Fennoscandia: evidence from southwestern Norway and the northern North Sea region. Quat. Sci. Rev. 19, 667 – 685. Sejrup, H.P., Haflidason, H., Hjelstuen, B.O., Nyg3rd, A., Bryn, P., Lien, R., 2004. Pleistocene development of the SE Nordic Seas Margin. Mar. Geol. 213, 169–200. Sejrup, H.P., Hjelstuen, B.O., Dahlgren, K.I.T., Haflidason, H., Kuijpers, A., Nyg3rd, A., Praeg, D., Stoker, M.S., Vorren, T.O., in press. Pleistocene glacial history of the NW European Continental Margin. Mar. Pet. Geol. Skogseid, J., Eldholm, O., 1989. Vbring Plateau continental margin: seismic interpretation, stratigraphy, and vertical movements. In: Eldholm, O., Thiede, J., Taylor, E., et al.,Sci. Results ODP 104, 993 – 1030. Solheim, A., Faleide, J.I., Andersen, E.S., Elverhbi, A., Forsberg, C.F., Vanneste, K., Uenzelmann-Neben, G., Channell, J.E.T., 1998. Late Cenozoic seismic stratigraphy and glacial geological development of the Svalbard–Barents Sea continental margins. Quat. Sci. Rev. 17, 155 – 184. Stoker, M.S., 2002. Late Neogene development of the UK Atlantic margin. In: Dore`, A., Cartwright, J.A., Stoker, M.S., Turner, J.P., White, N. (Eds.), Exhumation of the North Atlantic Margin: Timing, Mechanism and Implications for Petroleum Exploration, Geol. Soc. London Spec. Publ. 196, 313 – 329. Stoker, M.S., Akhurst, M.C., Howe, J.A., Stow, D.A.V., 1998. Sediment drifts and contourites on the continental margin off northwest Britain. Sediment. Geol. 115, 33 – 51. STRATAGEM partners, 2002. The Neogene stratigraphy of the glaciated European Margin from Lofoten to Porcupine. A product of the EC supported STRATAGEM project, Contract No. EVK3-CT-1999-00011, Atlas. 75 pp. Stuevold, L.M., Eldholm, O., 1996. Cenozoic uplift of Fennoscandia inferred from a study of the mid-Norwegian margin. Glob. Planet. Change 12, 359 – 386. Stuevold, L.M., Skogseid, J., Eldholm, O., 1992. Post-cretaceous uplift events on the Vbring continental margin. Geology 20, 919 – 922.
276
B.O. Hjelstuen et al. / Marine Geology 213 (2004) 257–276
Talwani, M., Udintsev, G., et al., 1976. Init. Rep. DSDP vol. 38. U.S. Govt. Printing Office, Washington. Thiede, J., Eldholm, O., 1983. Speculation about the paleodepth of the Greenland–Scotland Ridge during the late Miocene and Cenozoic times. In: Bott, M.P.H. (Ed.), Structural Development of the Greenland–Scotland Ridge. Plenum Publishing, pp. 445 – 456. Thiede, J., Myhre, A.M., 1996. Introduction to the North Atlantic– Arctic Gateway: plate tectonic–paleoceanographic history and significance. In: Thiede, J., Myhre, A.M., Firth, J.V., Johnson, G.L., Ruddiman, W., Proc. ODP Sci. Results 151, 3 – 23. Thiede, J., Eldholm, O., Taylor, E., 1989. Variability of Cainozoic Norwegian–Greenland Sea paleoceanography and Northern
Hemisphere paleoclimate. In: Eldholm, O., Thiede, J., Taylor, E., et al.,Sci. Results ODP 104, 1067 – 1118. Vogt, P., Perry, R., Feden, R.K., Fleming, R.H., Cherkis, H., 1981. The Greenland–Norwegian Sea and Iceland environment: geology and geophysics. In: Nairn, A.E.M., Churkin, M., Stenli, F.G.The Ocean Basins and Margins vol. 5. The Arctic Oceans, pp. 493 – 598. Watterson, J., Walsh, J., Nicol, A., Nell, P.A.R., Bretan, P.G., 2000. Geometry and origin of a polygon fault system. J. Geol. Soc. (London) 157, 151 – 162. Wood, R., Davy, B., 1994. The Hikurangi Plateau. Mar. Geol. 118, 153 – 173.