Berit Oline Hjelstuen

Late Cenozoic evolution of the western Barents Sea-Svalbard continental margin

Abstract Seven regionally correlatable reflectors, named R7 (oldest) to R1, have been identified in the Upper Cenozoic sedimentary succession along the western continental margin of Svalbard and the Barents Sea. Regional seismic profiles have been used to correlate between submarine fans that comprise major depocentres in this region. Glacial sediment thicknesses reach up to 3 seconds two-way time, corresponding to 3.5–4 km. Despite limited chronostratigraphic control, ages have been assigned to the major sequence boundaries based on ties both to exploration wells and to shallow boreholes, and by paleoenvironmental interpretations and correlations with other regions. Lateral and vertical variations in seismic facies, between stratified and chaotic with slump structures, have major implications for the interpretation of the depositional regime along the margin. The main phases of erosion and deposition at different segments of the margin are discussed in the paper, which also provides a regional seismic stratigraphic framework for two complementary papers in the present volume. Reflector R7 marks the onset of extensive continental shelf glaciations, but whereas the outer Svalbard shelf has been heavily and frequently glaciated since R7 time, this did not occur, or occurred to a much less extent, until R5 time in the southern Barents Sea. The present study provides the background for a quantification of the late Cenozoic glacial erosion of Svalbard and the Barents Sea. The rates of erosion and deposition exhibit large temporal and spatial variations reflecting the importance of glacial processes in the Late Cenozoic development of this nearly 1000 km long margin.

Configuration, history and impact of the Norwegian Channel Ice Stream

The Norwegian Channel between Skagerrak, in the southeast, and the continental margin of the northern North Sea, in the northwest, is the result of processes related to repeated ice stream activity through the last 1.1 m yr. In such periods the Skagerrak Trough (700 m deep) has acted as a confluence area for glacial ice from southeastern Norway, southern Sweden and parts of the Baltic. Possibly related to the threshold in the Norwegian Channel off Jaeren (250 m deep), the ice stream, on a number of occasions over the last 400 ka, inundated the coastal lowlands and left an imprint of NW-oriented ice directional features (drumlins, stone orientations in tills and striations). Marine interstadial sediments found up to 200 m a.s.l. on Jaeren have been suggested to reflect glacial isostasy related to the Norwegian Channel Ice Stream (NCIS). In the channel itself, the ice stream activity is evidenced by mega-scale glacial lineations on till surfaces. As a result of subsidence, the most complete sedimentary records of early phases of the NCIS are preserved close to the continental margin in the North Sea Fan region. The strongest evidence for ice stream erosion during the last glacial phase is found in the Skagerrak. On the continental slope the ice stream activity is evidenced by the large North Sea Fan, which is mainly a result of deposition of glacial-fed debris flows. Northwards of the North Sea Fan, rapid deposition of meltwater plume deposits, possibly related to the NCIS, is detected as far north as the Voring Plateau. The NCIS system offers a unique possibility to study ice stream related processes and the impact the ice stream development had on open ocean sedimentation and circulation.

Cenozoic erosion and sediment yield in the drainage area of the Storfjorden Fan

Abstract The western Barents Sea continental margin, between 74° and 77°N, comprises 7–8 km post-Paleocene sediments. The margin sediments have been divided into four seismic sequences dated by seismic correlation to adjacent areas. This chronostratigraphy shows that the uppermost three sequences are of glacial origin, deposited during the last 2.3 m.y. A huge sedimentary wedge, the Storfjorden Fan, was deposited in front of the Storfjorden Trough between 2.3 and 0.44 Ma, whereas during the last 0.44 m.y. a more evenly distribution pattern is observed. The outbuilding of the fan is related to the onset of the northern hemisphere glaciations causing intense glacial erosion of predominantly consolidated rocks. Seismic facies interpretations indicates that the fan outbuilding was connected to large-scale mass movements. Within the uppermost part of the glacial sequence parallel and continuous reflectors and locally disturbed pattern on the upper slope are associated with downslope change in facies. Volumetric calculations, based on velocity studies and isopach maps, have been used to quantify Cenozoic erosion, sediment yield, sedimentation and erosion rates. Approximately 3300 m of post-Paleocene erosion is calculated within the drainage area of the Storfjorden Fan, of which about 1700 m was eroded in late Pliocene-Pleistocene times giving an average denudation rate of 0.63 mm/yr.

Neogene evolution of the Atlantic continental margin of NW Europe (Lofoten Islands to SW Ireland): anything but passive

A regional stratigraphic framework for the Neogene succession along and across the NW European margin is presented, based on a regional seismic and sample database. The stratigraphy provides constraints on the timing and nature of the mid- to late Cenozoic differential tectonic movements that have drivenmajor changes in sediment supply, oceanographic circulation and climate (culminating in continental glaciation). The overall context for Neogene deposition on the margin was established in the mid-Cenozoic, when rapid, km-scale differential subsidence (sagging) created the present-day deep-water basins. The Neogene is subdivided into lower (Miocene–lower Pliocene) and upper (lower Pliocene–Holocene) intervals. The lower Neogene contains evidence of early to mid-Miocene compressive tectonism, including inversion anticlines and multiple unconformities that record uplift and erosion of basin margins, as well as changes in deep-water currents. These movements culminated in a major expansion of contourite drifts in the mid-Miocene, argued to reflect enhanced deep-water exchange across the Wyville-Thomson Ridge Complex, via the Faroe Conduit. The distribution and amplitude of the intra-Miocene movements are consistent with deformation and basin margin flexure in response to enhanced intra-plate compressive stresses during a local plate reorganization (transfer of the Jan Mayen Ridge from Greenland to Europe). The upper Neogene records a seaward tilting (

Cenozoic evolution of the northern Vøring margin

The northern Voring volcanic margin was initiated by late Campanian–Paleocene rifting, culminating with massive breakup-related igneous activity near the Paleocene-Eocene transition. Paleocene uplift of the central rift zone led to subaerial erosion and deposition in a restricted basin west of the Fles fault complex. The western source area was active toward the end of Eocene time. In the east, the low-relief land surface underwent modest relative uplift, which led to the construction of an early Oligocene delta system on the Trondelag platform. This event was followed by a period of margin subsidence and modest sedimentation until late Pliocene time. Although Miocene and early Pliocene biosiliceous hemipelagic sediments dominate on the outer margin, the influx of ice-rafted detritus records the climatic deterioration and the establishment of glaciers in late Miocene and early Pliocene time. Since ca. 2.6 Ma, ongoing epeirogenic uplift of Fennoscandia and the onset of Northern Hemisphere glaciation increased the erosion potential. A huge prograding wedge of glacial sediments was constructed from ca. 2.6 to 1.0 Ma, when the glacial mode changed from moderate, relatively stable icecaps to distinct glacial-interglacial cycles. The wedge overlies the base of the late Pliocene horizon, which marks pronounced changes in lithology and physical sediment properties, and corresponds to a distinct, regional velocity inversion. The differential glacial sediment load over unconsolidated and mobile biosiliceous oozes may have caused abundant small-offset faulting and diapirism in the western Voring basin.

Vøring Plateau diapir fields and their structural and depositional settings

Abstract Three fields of sea floor piercing diapiric structures, the Vema, Vigrid and Vivian diapir fields, exist on the marginal Voring Plateau, where individual structures rise as much as 150 m above the sea floor. The large Vema diapir field lies over two major arch structures, the Vema and Naglfar domes, whereas the Vigrid diapir field is located above relatively horizontally stratified basin sequences. Basin modelling shows, depending on the mode of lithospheric response, that 20–35% of the present 1800–3000 m Vema Dome relief is related to tectonism, whereas the remainder is caused by sediment loading and compaction. Backstripping reveals that the Vema Dome has changed from a lowrelief structural high in Paleocene-Oligocene to a much narrower Miocene-Present feature. Dome initiation is ascribed to local Paleocene relative structural uplift during the Maastrichtian-Paleocene rift episode. A later phase of tectonic uplift, most likely during the late Oligocene and Miocene, is ascribed to intraplate compressional stress. From seismic profiles and scientific drill holes we infer that Eocene-Miocene sediments, dominated by biosiliceous oozes and muds, are the source for the sea floor piercing structures, which are interpreted as mud diapirs and possibly also mud volcanoes. The ooze mobilization started in late Pliocene, and was induced by differential loading by more dense and less porous prograding late Pliocene-Pleistocene sediments. Abundant small-offset late Oligocene-Pliocene faults and zones of weakness are the most likely pathways for the oozes which have continued to move until Present.

Rapid ice sheet retreat triggered by ice stream debuttressing: Evidence from the North Sea

Using high-resolution bathymetric and shallow seismic data from the North Sea, we have mapped hitherto unknown glacial landforms that connect and resolve longstanding gaps in the Quaternary geological history of the basin. We use these data combined with published information and dates from sediment cores to reconstruct the extent of the Fennoscandian and British Ice Sheets (FIS and BIS) in the North Sea during the last phases of the last glacial stage. It is concluded that the BIS occupied a much larger part of the North Sea than previously suggested and that North Sea ice underwent a dramatic disintegration ~18,500 yr ago. This was triggered by grounding-line retreat of the Norwegian Channel Ice Stream, which debuttressed adjacent ice masses, and led to an unzipping of the BIS and FIS accompanied by drainage of a large ice-dammed lake. Our reconstruction of events provides an opportunity to improve understanding and modeling of the disintegration of marine-based ice sheets, and the complex interplay between ocean circulation and the cryosphere.

Shallow Landslides and Their Dynamics in Coastal and Deepwater Environments, Norway

In this manuscript, we present the first results of integrated slope stability studies to investigate smaller-scale mass movement processes in different physiographic settings of Norway. These include coastal areas (Sorfjord, Finneidfjord), and pristine open ocean settings in intermediate (Vesteralen) and deep waters (Lofoten) on the Norwegian margin. Triggers, pre-conditioning factors and sedimentary processes associated with these landslides are currently not well constrained.

Investigations of Slides at the Upper Continental Slope Off Vesterålen, North Norway

Multibeam bathymetry, high-resolution seismic profiles and sediment cores were collected from the upper continental slope outside Andoya, the northernmost island in Vesteralen, northern Norway (69°N). Eight small slides are identified at water depths between 500 and 800 m. These are linked to a larger slide related to the development of the Andoya Canyon by high resolution seismic. Slope angles adjacent to the headwalls of the small slides are 3–4° while slide deposits have accumulated where slope angles are 2–3°. The slides occurred in parallel-stratified glacial marine sediments, and three seismic horizons are interpreted. One of these horizons coincides with failure planes in four of the slides. A 12 m long core terminates above this level, but penetrates another horizon representing a slip plane in two of the slides. The core comprises silty clay with varying content of ice rafted debris. The upper slope shallower than 450 m appears stable although it may be up to 8° steep. Tension cracks up to 2 m deep on the lower slopes may suggest that deformation is active near the canyon systems.

An overview of the Upper Palaeozoic–Mesozoic stratigraphy of the NE Atlantic region

Abstract This study describes the distribution and stratigraphic range of the Upper Palaeozoic–Mesozoic succession in the NE Atlantic region, and is correlated between conjugate margins and along the axis of the NE Atlantic rift system. The stratigraphic framework has yielded important new constraints on the timing and nature of sedimentary basin development in the NE Atlantic, with implications for rifting and the break-up of the Pangaean supercontinent. From a regional perspective, the Permian–Triassic succession records a northwards transition from an arid interior to a passively subsiding, mixed carbonate–siliciclastic shelf margin. A Late Permian–earliest Triassic rift pulse has regional expression in the stratigraphic record. A fragmentary paralic to shallow-marine Lower Jurassic succession reflects Early Jurassic thermal subsidence and mild extensional tectonism; this was interrupted by widespread Mid-Jurassic uplift and erosion, and followed by an intense phase of Late Jurassic rifting in some (but not all) parts of the NE Atlantic region. The Cretaceous succession is dominated by thick basinal-marine deposits, which accumulated within and along a broad zone of extension and subsidence between Rockall and NE Greenland. There is no evidence for a substantive and continuous rift system along the proto-NE Atlantic until the Late Cretaceous.