The Cenozoic Western Svalbard Margin: Sediment Geometry and Sedimentary Processes in an Area of Ultraslow Oceanic Spreading
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Mar Geophys Res (2011) 32:441–453 DOI 10.1007/s11001-011-9127-z ORIGINAL RESEARCH PAPER The Cenozoic western Svalbard margin: sediment geometry and sedimentary processes in an area of ultraslow oceanic spreading Ingrid Marie Hasle Amundsen • Maria Blinova • Berit Oline Hjelstuen • Rolf Mjelde • Haflidi Haflidason Received: 8 November 2010 / Accepted: 22 March 2011 / Published online: 17 April 2011 Ó The Author(s) 2011. This article is published with open access at Springerlink.com Abstract The northeastern high-latitude North Atlantic is continuous spreading and tectonic activity caused the characterised by the Bellsund and Isfjorden fans on the sediments to be transported out of the valley and westward. continental slope off west Svalbard, the asymmetrical ultraslow Knipovich spreading ridge and a 1,000 m deep Keywords Svalbard margin Á Ultraslow spreading ridge Á rift valley. Recently collected multichannel seismic profiles Trough mouth fans Á Glaciations Á Sedimentary processes and bathymetric records now provide a more complete picture of sedimentary processes and depositional envi- ronments within this region. Both downslope and alongs- Introduction lope sedimentary processes are identified in the study area. Turbidity currents and deposition of glacigenic debris flows The northern North Atlantic (Fig. 1) provides a region to are the dominating downslope processes, whereas mass study Cenozoic variations in ocean circulation, erosion, failures, which are a common process on glaciated mar- sedimentary processes and depositional environments in gins, appear to have been less significant. The slide debrite relations to tectonic events. The prominent Mid-Atlantic observed on the Bellsund Fan is most likely related to a spreading ridge (Fig. 1) stretches for a distance of about 2.5–1.7 Ma old failure on the northwestern Barents Sea 1,800 km through this part of the Atlantic Ocean and has margin. The seismic records further reveal that alongslope over the last 55 million years shaped the Norwegian- current processes played a major role in shaping the sedi- Greenland Sea into its present configuration. Through its ment packages in the study area. Within the Knipovich rift development, the ridge affected sediment distribution and valley and at the western rift flank accumulations as thick source areas (Skogseid and Eldholm 1989; Eldholm et al. as 950–1,000 m are deposited. We note that oceanic 1994; Bruvoll et al. 2009). The Fram Strait and the basement is locally exposed within the rift valley, and that Greenland-Scotland Ridge (Fig. 1), which limit the Nor- seismostratigraphic relationships indicate that fault activity wegian-Greenland Sea towards north and south, represent along the eastern rift flank lasted until at least as recently as significant gateways that during their Miocene opening and 1.5 Ma. A purely hemipelagic origin of the sediments in subsidence (Engen et al. 2003; Stoker et al. 2005) influ- the rift valley and on the western rift flank is unlikely. We enced oceanic circulation and depositional processes on suggest that these sediments, partly, have been sourced both regional and global scale. from the western Svalbard—northwestern Barents Sea The continental margin off west Svalbard and the margin and into the Knipovich Ridge rift valley before ultraslow Knipovich spreading ridge is the focus of this study (Figs. 1, 2). The availability of multichannel seismic transects, stretching from the continental shelf and across the Knipovich Ridge, now make it possible to get a more I. M. H. Amundsen Á M. Blinova (&) Á B. O. Hjelstuen Á complete picture of a shallow to deep sea depositional R. Mjelde Á H. Haflidason system. The seismic profiles, in addition to bathymetric Department of Earth Science, University of Bergen, Allegt 41, 5007 Bergen, Norway records, also document the structural setting and sedi- e-mail: [email protected] mentary record within a rift valley in much larger detail 123 442 Mar Geophys Res (2011) 32:441–453 Depth [m] Arctic Ocean 4000 80˚ 3000 FS 2000 Fig. 1000 S 0 2a −1000 Kn Barents −2000 R Greenland Sea 70˚ −3000 NGS BF −4000 Fig. MR 2c GS KR R 60˚ Iceland 320˚ GS RR 40˚ R NF Norway 340 NS 20˚ ˚ 0 km 500 1000 0˚ Fig. 1 Bathymetric map of the northern North Atlantic. Red box Greenland-Scotland Ridge, KnR Knipovich Ridge, KR Kolbeinsey indicates study area. Yellow line represents position of geoseismic Ridge, MR Mohns Ridge; NGS Norwegian-Greenland Sea, NS North profile shown in Fig. 2c. BF Bjørnøya Fan, FS Fram Strait, GSR Sea, NF North Sea Fan, RR Reykjanes Ridge, S Svalbard than previously possible. The objectives of this paper is characteristic of ultraslow spreading ridges is that their axes thus to: (1) establish a seismic stratigraphy for the sedi- are made up of a series of linked magmatic and amagmatic mentary succession within the study area, (2) describe rift accretionary segments. The rift valley of the Knipovich valley structures and sediment infill, (3) map out the sed- Ridge is no exception to this trend; it is segmented into iments on the western flank of the Knipovich Ridge, (4) extensional basins bounded by narrow, volcanically active study seismic facies in order to identify sedimentary pro- and tectonically modified axial highs (Crane et al. 2001). cesses and in which places along the margin each of these The spreading direction along the Knipovich Ridge is processes are active, and (5) extend our knowledge on NNW-SSE, which is highly oblique to the rift axis. At processes and depositional environments on glacial- present, the spreading rates along the Knipovich Ridge are dominated continental margins. slower in the north than in the south; estimated at 11.2 and 12.3 mm/year (full rates), respectively (Dick et al. 2003). Kandilarov et al. (2008) have shown that the Knipovich Background Ridge spreading rates have varied between 11 and 16 mm/ year (full rates) through time. The magnetic anomalies The opening of the northern North Atlantic (Fig. 1) generated around the Knipovich Ridge are diffuse. This is occurred at the Paleocene-Eocene transition and took place probably related to factors such as high heat flow and sed- in two stages, reflecting the change from a three- to two- iment loading (Engen et al. 2003). We note, however, that plate configuration (e.g. Talwani and Eldholm 1977). Anomalies 5 (9.8 Ma; Cande and Kent 1995), 6 (19.6 Ma) During the first stage the region between Greenland and and 7 (24.6 Ma) have been identified in a distance between Svalbard (Fig. 1) did not open but moved along a conti- c. 50 and 150 km from the Knipovich Ridge rift valley nent–continent mega-shear zone. In the early Oligocene, the (Fig. 2a) (Engen et al. 2008; Kandilarov et al. 2008, 2010). relative plate motion changed to a more east-westerly trend. The continental slope off west Svalbard is characterised This caused a northward opening of the Greenland Sea, first by Late Plio-Pleistocene fan complexes (e.g. Vorren et al. by continental extension and finally by sea floor spreading 1998). These fans have been deposited in front of troughs along the Knipovich Ridge (e.g. Mosar et al. 2002). on the continental shelf (Fig. 2a) and they are strongly The Knipovich Ridge (Fig. 1), which is characterised by a related to the glaciation history of the Barents Sea-Svalbard 1,000–2,000 m deep rift valley and a sea floor depth ranging region. Recently, it has been suggested that the growth of between 2,500 m and 3,800 m, has been classified as an the Barents Sea-Svalbard ice sheet have occurred in three ultraslow spreading ridge (Dick et al. 2003). An important stages (Knies et al. 2009): (1) An initial stage, between 123 Mar Geophys Res (2011) 32:441–453 443 123 444 Mar Geophys Res (2011) 32:441–453 b Fig. 2 a Study area. Location of interpreted MCS profiles are shown Data and methods by black lines, EM300 bathymetric coverage is outlined by red box, trough mouth fans are shown by a light grey colour, whereas the position of the Knipovich Ridge (KnR) rift valley is indicated by a This work is based on 2D multichannel seismic (MCS) dark grey zone. Positions of magnetic anomalies (A5–A7), shown by profiles and bathymetric records collected by the Univer- brown stippled lines, are from Kandilarov (2010). Blue stippled line sity of Bergen in 1999 and 2004 (Figs. 2a, 3, 4, 5, 6). The show location of geoseismic profile shown in c. Bathymetry in EM300 bathymetric records were acquired by R/V G.O. meters. Figure location shown in Fig. 1. BS Bellsund, BeF Bellsund 2 Fan, HR Hovgaard Ridge, IF Isfjorden Fan, KF Kongsfjorden Fan, SF Sars in 2004 and cover about 1,500 km of the Knipovich Storfjorden Fan. b Seismic sequence stratigraphy (Faleide et al. 1996) Ridge (Fig. 2a). The EM300 data were processed using a and ages (Butt et al. 2000) used in this study. R1–R7: Identified grid size of 50 9 50 m. The seismic profiles have a total sequence boundaries; G0–GIII: Identified sequences. c Interpreted length of 500 km. The main focus in this study will be the seismic transect from the Barents Sea-Svalbard margin. R1–R7: Identified sequence boundaries. Crossing with seismic profiles in MCS profiles that stretch from the continental shelf to the Figs. 3a and 6a are shown by grey lines. Profile location in Fig. 1 and deep ocean off Isfjorden and Bellsund (Fig. 2a). a. Figure modified from Faleide et al. (1996). d Examples of main The MCS data were acquired with a 3 km long streamer, seismic facies in the study area. (1) Chaotic facies (slide debrites), (2) containing 240 recording groups with 12.5 m spacing.