the norwegian-greenland sea continental margins, morphology and late quaternary sedimentary...

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Quaternary Science Re views , Vol. 17, pp. 273 — 302, 1998 1998 Elsevier Science Ltd.

Printed in Great Britain. All rights reserved.0277 — 3791/98, $19.00

PII: S0277-3791(97)00072-3

THE NORWEGIAN –

GREENLAND SEA CONTINENTAL MARGINS:MORPHOLOGY AND LATE QUATERNARY SEDIMENTARYPROCESSES AND ENVIRONMENT

TORE O. VORREN *- , JAN SVERRE LABERG - , FRANK BLAUME ‡, JULIANA. DOWDESWELL , NEIL H. KENYON , JU

$ RGEN MIENERT -- , JAN RUMOHR -- ,

FRIEDRICH WERNER ‡‡- Department of Geology, Uni versity of Troms ~ , N-9037 Troms ~ , Norway

( Email: torer @ ibg.uit.no)‡ Sonderforschungsbereich 313, Uni versity of Kiel, Heinrich-Hecht-Platz 10, D-24118 Kiel, Germany

Centre for Glaciology, Institute of Geography and Earth Studies, Uni versity of Wales, Aberystwyth, SY23 3DB,Wales, UK

Southampton Oceanography Centre, Empress Dock, Southampton, SO14 3ZH, UK -- GEOMAR, Forschungszentrum fu

( r marine Geowissenschaften, Wischhofstrasse 1-3, D-24148 Kiel, Germany

‡‡ Geologisch Pala( ontologisches Institut und Museum, Uni versity of Kiel, Olshausenstr. 40, D-24118 Kiel, Germany

Abstract —The continental margins surrounding the Norwegian — Greenland Sea are to a largedegree shaped by processes during the late Quaternary. The paper gives an overview of themorphology and the processes responsible for the formation of three main groups of mor-phological features: slides, trough mouth fans and channels.

Several large late Quaternary slides have been identied on the eastern Norwegian — GreenlandSea continental margin. The origin of the slides may be due to high sedimentation rates leading to

a build-up of excess pore water pressure, perhaps with additional pressure caused by gas bubbles.Triggering might have been prompted by earthquakes or by decomposition of gas hydrates.

Trough mouth fans (TMF) are fans at the mouths of transverse troughs on presently orformerly glaciated continental shelves. In the Norwegian — Greenland Sea, seven TMFs havebeen identied varying in area from 2700 km to 215 000 km . The Trough Mouth Fans aredepocentres of sediments which have accumulated in front of ice streams draining the largeNorthwest European ice sheets. The sediments deposited at the shelf break/upper slope by theice stream were remobilized and transported downslope, mostly as debris ows. The TroughMouth Fans hold the potential for giving information about the various ice streams feedingthem with regard to velocity and ice discharge.

Two large deep-sea channel systems have been observed along the Norwegian continentalmargin, the Lofoten Basin Channel and the Inbis Channel. Along the East Greenland margin,several channel systems have been identied. The deep-sea channels may have been formed bydense water originating from cooling, sea-ice formation and brine rejection close to the glaciermargin or they may originate from small slides on the upper slope transforming into debrisows and turbidity currents. 1998 Elsevier Science Ltd. All rights reserved.

INTRODUCTION

Objectives

This paper aims to explain the morphology and lateQuaternary sedimentary processes and palaeoenviron-ment of the Norwegian — Greenland Sea continentalmargin. In particular it concentrates on the North

Norwegian and Barents Sea continental margin.

Physiographic setting

The rst general description of the morphology of the continental margin, particularly the continental

* Corresponding author.

shelves, of the Norwegian — Greenland Sea was given byNansen (1904). A comprehensive review on themorphology, sediments and paleoenvironments of theNorwegian — Greenland deep-sea as well as the conti-nental margins was given by Vogt (1986).

The continental margins surrounding the Norwe-gian — Greenland Sea (Fig. 1) have been shaped by tec-tonic and sedimentary processes throughout theCenozoic. Morphodynamic patterns have evolved dur-ing the late Cenozoic under the inuence of the waxingand waning Fennoscandian-, Barents Sea- and Green-land ice sheets. An adequate understanding of thedevelopment of the continental margin surroundingthe Norwegian — Greenland Sea relies on thoroughknowledge of the morphodynamic features of the pres-ent sea oor as well as the hinterland.

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FIG. 1. Bathymetric map of the Norwegian Greenland Sea adapted from Perry et al . (1980). Water depth in meters.

The development of the Norwegian — Greenland Seaocean basins (Fig. 1) is governed by plate-tectonicevolution (Talwani and Eldholm, 1977; Myhre et al .,1992). In the Norwegian — Greenland Sea the mid-oceanridge comprises four active segments, the KolbeinseyRidge, the Mohns Ridge, the Knipovich Ridge and the

Molloy Ridge. The ridges are often interrupted bytransverse valleys created by fracture zones cuttingacross their topography. The mid-ocean ridge andfracture zones separate the deep Norwegian — Green-land Sea into four major basins (Norway, Lofoten,Greenland and Boreas Basins), and two minor basins(the Scoresby and Blosseville Basins) (Perry, 1986)(Fig. 1).

A key element in the understanding of the LateCenozoic evolution of the continental margin is anunderstanding of the Cenozoic uplift of Greenland,Scandinavia, the Barents Sea and Svalbard. A widevariety of hypotheses as to the timing and causes of theCenozoic uplift have been proposed. Recent studiesfrom the Barents Sea have suggested that much of theuplift occurred during the Plio — Pleistocene (Riis andFjeldskaar, 1992; Eidvin et al ., 1993; Henriksen andVorren, 1996; Stuevold and Eldholm, 1996). Duringand after the uplift large amounts of sediment weretransferred from the hinterland to the continental

slope. The outer part of the Norwegian — Barents Seacontinental margin has a wedge of mostly clastic LateCenozoic sediments up to 7 km (5 s twt) thick (Fig. 2).

The bathymetry of the East Greenland ContinentalShelf is characterised by shallow banks and local de-pressions, with large troughs cut into the shelf bedrock.

The maximum shelf width is 280 km at 77 °25 N andthe minimum width is 30 km at 81 °50 N. Shelf depthsrange between 100 and 300 m, but shoals of less than100 m exist (Perry, 1986). The continental slope off East Greenland varies in gradient from 1:38 at 70 °N to1:13 at 82 °N. The slope ranges in depth from 400 to1600 m in the south and from 400 to 3400 m in thenorth. A prominent feature of this margin is the fan-like feature offshore of Scoresby Sund (Fig. 1).

The continental shelf off Norway (Fig. 1) has greatvariations with regard to width and depth. Two re-gions are particularly narrow, namely offshore M + re(minimum width less than 65 km), and offshoreLofoten (minimum width less than 10 km). The shelf area between has a width exceeding 200 km (maximum260 km). The narrowest areas are also the shallowest,with depths less than 200 m, while the shelf between isgenerally more than 250 m deep and has maximumdepths of ca 500 m. Several troughs cross the shelf (Fig. 1). These transverse troughs often have a steep

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FIG. 2. Envelope surface of Norway (m 1000) (Gjessing, 1967) and isopach map of the Cenozoic sediments in the Norwegian Sea (s twt) (adaptedfrom Vorren et al ., 1991). Note the pronounced depocenters on the Barents Sea continental margin.

backwall aligned more or less along the longitudinaltrough situated at the boundary between the landwardcrystalline rocks and the seaward sedimentary rocks(Holtedahl, 1971). The continental slope is steepest off the narrowest shelf areas. Offshore mid Norway thecontinental margin broadens due to a marginal pla-teau, the V + ring Plateau which exhibits depths mainlybetween 1200 and 1600 m.

The Barents Sea covers one of the widest continentalshelves in the world (Fig. 1). At 40 °E the shelf reachesa width of 1500 km. The western sea oor of the Bare-

nts Sea comprises a series of broad troughs of whichthe Bear Island Trough is the most prominent. Thistrough ranges between 300 and 500 m in depth. It isbordered by a series of shallower banks and platformslike Spitsbergenbanken to the north (minimum depthof less than 20 m) and Troms + aket (200 m) andFugl + ybanken (200 m) to the south. The shelf west of Svalbard is narrow (30 — 60 km) and split into shallowbanks by several transverse troughs.

The western continental margin of the Barents Sea ischaracterised by fan-shaped protrusions. The most

T.O. Vorren et al .: The Norwegian — Greenland Sea continental margins 275


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FIG. 3. Bathymetric map showing location and extent of slides, small slides and large channels on the Norwegian — Greenland Sea continentalmargin. The gure is compiled from several sources, e.g. Bugge et al . (1987), Mienert et al . (1993), Laberg and Vorren (1993), Dowdeswell and

Kenyon (1995), Dowdeswell and Kenyon (1997) and Dowdeswell et al . (1996).

prominent is off the mouth of the Bear Island Troughextending more than 280 km beyond the shelf break.Further north are fans off the Storfjorden and smallerfans off Bellsund, Isfjorden and Kongsfjorden on Sval-bard (Fig. 1).

SLIDES

Norwegian margin

Several smaller and larger slides have been identiedon the Norwegian continental margin (Fig. 3). Hol-tedahl (1971) seems to have been the rst to indicatesliding activity on the Norwegian continental marginby writing: “off M + re the slope down to 1000 m ishighly irregular and partly very steep, and this particu-lar topography may be due to sliding activity, andperhaps also due to current activity ” (translated fromNorwegian). The existence of several slides on the con-tinental margin was indicated by Damuth (1978).

During the 1980s, a detailed research programmeorganised by the IKU (Continental Shelf and Petro-leum Technology Research Institute A/S, Norway) fo-cused on the Storegga Slide region (Fig. 3). This

resulted in a series of papers (Bugge, 1983; Bugge et al .,1987, 1988; Jansen et al ., 1987).

Based on GLORIA long-range side-scan sonar data,Bugge (1983) and Kenyon (1987) gave an overview of slides occurring along the Northwest European marginup to 73 °N. In the area between the Storegga Slide and67°N, Bugge (1983) found ‘‘no real sliding or slumpingof any reasonable size’’. Between 67 ° and 73 °N, severallarger and smaller slides were observed, noticeably theTr ænadjupet and Bj + rn + yrenna Slides (Fig. 3). RecentGLORIA mapping (Dowdeswell et al ., 1996) has in-dicated another large slide, the And + ya Slide and manysmall slides in this region. In the following we shallbriey describe these slides, and in Table 1 we havecompiled available data of the largest slides.

The Storegga Slide

The Storegga Slide is one of the world’s largestknown submarine slides. The 290-km long headwall islocated at the shelf break 100 km off the coast of M + re— Tr + ndelag (Fig. 4). About 5600 km was in-volved in the sliding (Bugge et al ., 1988). Bugge (1983)distinguished three slide events; the rst probably took



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FIG. 4. Bathymetric map of the Storegga Slide area (after Bugge et al ., 1987). Water depth in meters.

place at 30 — 50 ka, and the two younger events seem tohave occurred in close succession about 6 — 8 ka (Buggeet al ., 1987, 1988; Jansen et al ., 1987). The rst eventaffected almost the whole area of the present slide scar;the second slide cut up to 200 m into the former slidescar and formed a new headwall some 5 — 8 km furtherinto the shelf; the last slide was the smallest and wasconned to the upper part of the second slide. Largeareas of the Norway Basin seems to be covered byvarious types of slide deposits (Bugge et al ., 1987; Vogt,1997).

The Trænadjupet Slide

The existence of the Tr ænadjupet Slide (Fig. 3) wasrst indicated by Damuth (1978). Bugge (1983) andKenyon (1987) found that the headwall is at a waterdepth of about 300 m and the upper part of the slidecovers an area of about 4000 km . The sediments weretransported 200 km down a slope of about 1 ° toa depth of 3000 m. The slide deposits include manylarge blocks, which are up to kilometres wide andhave a relief of up to 100 m (Dowdeswell et al ., 1996).



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FIG. 5. Seismic sparker prole across the Bj + rn + yrenna Slide at about 1500 m water depth showing the inlling of the depression (dotted area)enclosed by a zone of several tilted blocks separated by faults. Location is given in Fig. 7. From Laberg and Vorren (1993).

The total slide affected area is about 12 000 km (Dow-deswell et al ., in 1996).

The And ~ ya Slide

The And + ya Slide is located within the steepest part

of the eastern Norwegian — Greenland Sea continentalmargin (Fig. 3). It originated on the upper continentalslope (Kenyon, 1987) where the present gradient is5— 18°. From GLORIA side-scan sonar records it isapparent that there is a complex of different kinds of slide deposits including three readily identiable thin,distal ow deposits (Fig. 3). The total slide affectedarea is about 8000 km (Dowdeswell et al ., 1996).

The Bj~ rn ~ yrenna Slide

The Bj + rn + yrenna Slide, located on the southernank of the Bear Island Trough Mouth Fan (Fig. 3),was rst described by Kristoffersen et al . (1978) andlater investigated by Bugge (1983), Vorren et al . (1989)and Laberg and Vorren (1993). According to Labergand Vorren (1993), the slide has a run out distance of about 400 km, is up to 400 m deep and a total volumeof about 1100 km has been displaced. The boundarybetween the erosional and depositional area appears tobe at a depth of about 2500 — 2700 m. Kristoffersen et al .(1978) suggested an age of about 200 ka and Laberg

and Vorren (1996a) found the failure to have occurredsometime between Isotope Stage 8 (313 ka) to IsotopeStage 6 (194 ka). Hemipelagic sediments, in excess of 160 m thick inll the slide scar (Fig. 5), and indicate

that the slide occurred prior to the last glacial — inter-glacial cycle.

Small slides

Several small slides have been identied from side-scan sonar and 3.5-kHz records between the Tr ænad- jupet and And + ya Slides, immediately north of theAnd + ya Slide and on the continental margin west of Bj+ rn + ya (Bugge, 1983; Kenyon, 1987; Crane and Sol-heim, 1995; Dowdeswell et al ., 1996) (Fig. 3). Little isknown about these small slides, which seem to be mostfrequent along the steepest part of the continentalmargin.

Buried slides

Recently, Evans et al . (1996) and King et al . (1996)found indications of two or more earlier sliding eventson the North Sea Trough Mouth Fan (TMF: see belowfor details), probably of Late Cenozoic age. On theBear Island TMF, Knutsen et al . (1992) mappeda Plio — Pleistocene slide covering an area of 12 000 kmand involving a total volume of 5100 km . A later slide,probably of Mid/Late Pleistocene age, was identiedby Laberg and Vorren (1996a). This slide also occurredon the central fan. It covered a comparable area, butseems to have been shallower, thus involving less vol-ume of sediment. Recently, Kuvaas and Kristoffersen

(1996) identied at least ve separate failure eventswithin the Pliocene and Pleistocene succession,documenting the importance of large-scale mass move-ments within the Bear Island TMF area.



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East Greenland margin

Compared to the Norwegian/Barents Sea continen-tal margin, relatively few detailed studies have so farbeen undertaken on the East Greenland continentalmargin. However, much of the East Greenland marginfrom 70 — 80° (Mienert et al ., 1993, 1995; Prman and

Kassens, 1995) and 68 — 70° (Dowdeswell et al ., 1997)has been mapped by GLORIA long-range side-scansonar and PARASOUND/3.5 kHz data (see below).These data reveal no large scale sliding. Thus, withinmuch of the East Greenland continental slope nolarge-scale sliding events seem to have occurred duringMid/Late Pleistocene time. Mass wasting does, how-ever, seem to have been pronounced on the SoutheastGreenland continental margin during the Oligocene(Clift, 1996).

Origin of the slides

Three of the large slide complexes on the Norwe-gian — Barents Sea margin (the Storegga, Tr ænadjupetand Bj + rn + yrenna Slides) occurred in areas character-ised by high sediment input (Fig. 2 and Fig. 3). Thus,relatively high sediment supply leading to unstablesediments may have been important for the initiationof slope failures in these areas. Another importantfactor may be the presence of shallow gas, suggested byKnutsen et al . (1992) as important for the instability of

sediments found on the central part of the Bear IslandTMF.

Studies of the present seismicity in the eastern Nor-wegian — Greenland Sea has shown relatively high activ-ity along older fault systems (Kvamme and Hansen,1989; Bungum et al ., 1991). From other continentalmargin areas, earthquakes have been recognised as oneof the most likely triggering mechanisms for submarineslides (e.g. Hampton et al ., 1996). Thus, for the trigger-ing of the large slides along the eastern Norwe-gian — Greenland Sea continental margin, earthquakes

have probably been an important mechanism (Bugge,1983; Bugge et al ., 1987; Kenyon, 1987; Knutsen et al .,1992; Laberg and Vorren, 1993, 1996a; Evans et al .,1996).

Decomposition of gas hydrates was also suggestedas a possible triggering mechanism for the StoreggaSlides (Bugge et al ., 1987). Andreassen and Hansen(1995) using a phase boundary diagram for a methanehydrate system infer that gas hydrates may be presentunder the Norwegian/Barents Sea continental slopetoday. Increased bottom water temperature and/orlowering of sea level would cause destabilization of thehydrate zone (McIver, 1982).

To summarise, high sedimentation rates, which inturn may have led to a build-up of excess pore waterpressure, and perhaps with additional pressure causedby gas bubbles, probably led to unstable or metastablesediments within relatively large parts of the easternNorwegian — Greenland Sea continental margin. De-stabilizing and triggering may have been prompted by

earthquakes or perhaps by decomposition of gas hy-drates.

TROUGH MOUTH FANS AND DEBRISFLOWS – GENERAL REMARKS

On the continental margins surrounding the Norwe-gian — Greenland Sea, fan or delta-like protrusions oc-cur in front of many of the glacial troughs or channelscrossing the continental shelf and ending on the shelf break (Fig. 6). Many of these protrusions were notedby Nansen (1904). Vogt and Perry (1978) pointed outthat these protrusions are probably prograded deltasand attached fans. Vorren et al . (1988, 1989) proposednaming these features, which also occur on other gla-ciated margins, “trough mouth fans ” (TMF). Not alltroughs ending on the shelf break have fans at theirmouths, but on the eastern margin of the Norwe-gian — Greenland Sea they are particularly frequent: theNorth Sea TMF, the Bear Island TMF, the StorfjordenTMF, and smaller TMFs off Svalbard (the BellsundTMF, the Isfjorden TMF and the Kongsfjorden TMF).On the Greenland continental margin, the ScoresbySund TMF is well developed (Dowdeswell et al ., 1997),but it is in fact difficult to identify other TMFs on thismargin from the available bathymetric, seismic andlong-range side-scan sonar data. The TMFs vary insize and shape (Table 2). In recent years the fans have

been investigated with regard to their architecture,sedimentological processes and origin, and their poten-tial as palaeoclimatic archives.

At least during the late Quaternary, the TMFs havebeen the sites of intense debris ow activity. Damuth(1978) was the rst to indicate their presence. From3.5-kHz records he noted that large areas of the BearIsland and North Sea TMFs had a characteristic echotype comprising ‘‘continuous, sharp bottom echoeswith one or two sharp, unconformable, wedging sub-bottom reections which generally persist for less than

10— 15 km’’. He suggested they may represent sometype of downslope progradation via gravity-controlledmass ows, and that ‘‘sediments deposited by the ice onthe continental slope and upper rise may have movedfurther downslope by localised debris ows, turbiditycurrents or other gravity-controlled bottom ows.’’

Vorren et al . (1988, 1989) using sparker data foundthat the debris ows, seen in cross section, are bundledin sets of lenses separated by high amplitude reec-tions, and pointed to their potential as a palaeoc-limatostratigraphic proxy. They suggested that in mostcases each of the lobes in the lens set represents a singledebris ow originating on the upper slope, emplacedduring periods when the glacier grounding line wasnear the shelf break. Then ‘‘there was probably a veryhigh sediment input all along the trough mouth. Thissituation caused oversteepened slopes and/or excesspore uid pressures in the accumulated sediments,creating instability and mass movement. The highamplitude reections between each lens-set probably



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F I G

. 6 .

B a t h y m e t r i c m a p o f t h e N o r w e g i a n — G r e e n l a n d S e a c o n t i n e n t a l m a r g i n s h o w i n g l o c a t i o n a n d e x t e n t o f t r o u g h m o u t h f a n s . A

r r o w s i n d i c a t e l a r g e s h e l f t r o u g h s

.



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TABLE 1 Dimensions of large scale slides on the Norwegian continental margin

Storegga Slide Tr ænadjupet Slide And + ya Slide Bj + rn + yrenna Slide

Run-out distance (km) 850 200 400Slide scar area (km ) 34 000Total slide inuenced area (km ) 112 500 12 000 8000 12 500Maximum thickness (m) 430Volume (km ) 5580 1100

Storegga Slide dimensions are from Bugge et al . (1988); Bj+ rn + yrenna Slide dimensions are from Laberg and Vorren (1993); Tr ænadjupet Slidedimensions are from Bugge (1983) and Dowdeswell et al . (1996) and And + ya Slide dimensions are from Dowdeswell et al . (1996) and this study.

represent periods of low sediment input/erosion duringinterstadials or interglacials’’ (Vorren et al ., 1989).

Later mapping by seismic and side-scan sonars hasconrmed that the debris ows are the main buildingblocks, and palaeoclimatic recorders, of the youngerpart of the TMFs in the Norwegian — Greenland Sea(Vogt et al ., 1993; Laberg and Vorren, 1995, 1996a,b;King et al ., 1996; Sejrup et al ., 1996; Dowdeswell et al .,1996, 1997). Similar ows have been reported from thecontinental margin off Northwest Britain (Stoker,1995) and the eastern Canadian continental margin(Aksu and Hiscott, 1992; Hiscott and Aksu, 1994).

The trough mouth fans along the eastern Norwe-gian — Greenland Sea continental margin south of Sval-bard all seem to have acquired their modern shapelater than the early Mid-Pleistocene. This indicates

that the north European ice sheets (i.e. The British IceCap, the Fennoscandian Ice Sheet and the (southern)Barents Sea Ice Sheet), did not extend to the shelf-break for any appreciable time before the Mid Pleis-tocene. This conforms with deep-sea as well as terres-trial data which show that the Mid and LatePleistocene was the time of the largest glaciations innorthern Europe (Vorren and Laberg, 1997).

MORPHOLOGY AND STRATIGRAPHY OFTHE TROUGH MOUTH FANS

The North Sea TMF

Morphology

The North Sea TMF is deposited in front of theNorwegian Channel (Fig. 6), and comprises a thickwedge extending into the Norway Basin. A N — S axialdip line along the fan body shows a uniform dip of about 0.7 ° attening out to about 0.3 ° in the distal fanarea (King et al ., 1996).

Stratigraphy

According to King et al . (1996), the fan stratigraphyindicates two main depositional phases. The earlyphase, of which a signicant part may be preglacial isrepresented by steeply dipping (1 — 2.5°) progradationalstrata comprising much of the most proximal fan,together with correspondingly thick uniform deposits

extending to the Faeroe — Shetland Escarpment. Thelate phase comprising an overlying wedge, extendsbeyond the escarpment exhibiting overall slopes lessthan 0.5 ° and is of Quaternary age and mainly of glacigenic origin.

The Quaternary part of the fan was subdivided byKing et al. (1996) into 12 seismic sequences. Theseismic sequences of the fan body are interpreted ascomprising three major depositional styles, namelyterrigenous hemipelagic, debris ow aprons and dis-turbed slide sediments. The glacially-related debrisow aprons represent ve of the seven uppermostsequences. A middle Pleistocene age is suggested forthe rst debris ow apron (sequence 7) and a (Late)Weichselian age for the youngest debris ow apron(sequence 1).

The Bear Island TMF

Morphology

The Bear Island TMF is situated in front of the BearIsland Trough (Fig. 6). This fan extends from the shelf break to depths greater than 3000 m, where it mergeswith the abyssal plain of the Lofoten Basin. To the westand Northwest the fan is bounded by the Mohns andKnipovich spreading ridges (Fig. 1). The Bear Island

TMF has a width of about 250 km at its proximal partand approximately 440 km at 2200 m water depth. Itcovers an area of approximately 215 000 km (Table 2).The morphology of the fan is inuenced by theBj+ rn + yrenna Slide scar on its southern ank (Fig. 1).Based on slope gradient and seismic facies distribution,Laberg and Vorren (1995) subdivided the fan into threemorphological zones. At about 1500 m a minor breakin slope occurs which separates the upper from themiddle fan. The upper fan extends from the shelf break,the average depth of which is 500 m, and has a slopegradient of about 0.8 ° along the central fan axis. Thesurface of the upper fan is generally hummocky. Thesurface of the middle fan, between 1500 and 2200 m, isboth hummocky and ridged on the northern and cen-tral fan, whilst smooth on the southern part. The aver-age gradients of the mid- and lower fan are about 0.5 °and 0.2 °, respectively. The slightly convex-upward sur-face of the lower fan is uneven on the northern fanank and smooth near the slide scar.



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TABLE 2 Dimensions and slope gradients of through mouth fans along the Norwegian — Greenland Sea continental margin

KongsfjordenTMF

IsfjordenTMF

BellsundTMF

StorfjordenTMF

Bear IslandTMF

North SeaTMF

Scoresby SundTMF

Radius (km) 55 50 70 190 590 560 110Width upper (km) 40 45 55 130 250 165 180Width lower (km) 60 75 85 210 550 300 240Depth upper (km) 0.2 0.25 0.15 0.4 0.5 0.4 0.3Depth lower proximal (km) 2.4 3.0 2.7 1.5Depth lower distal (km) 2.0 3.0 2.3 2.7 3.2 3.5 1.5Area (km ) 2700 3700 6000 35 000 215 000 142 000 19 000Gradient (upper) 1.8 ° 0.8° 0.6°Gradient (middle) 1.9 ° 3.2° 1.8° 1.0° 0.4° 0.8° 2°Gradient (lower) 0.2 ° 0.2° 0.3°

Radius " radius along the longest axis; Width upper " width at shelf break; Width lower " maximum width of the lower fan; Depthupper " depth at the shelf break; Depth lower proximal " depth at the base of the proximal part of the fan; Depth lower distal " depth of the baseof the distal part of the fan; Area " total fan area including shelf and distal areas (except for the Scoresby Sund TMF the shelf area constitutesa negligible part of the fan area and has not been included). Gradients of the upper, middle, and lower slope along the longest fan axis of theStorfjorden and Bear Island TMF according to Laberg and Vorren (1996b) and from King et al . (1996) for the North Sea TMF. Average gradients

of the whole fan slopes are given for the Kongsfjord TMF, the Isfjord TMF, the Bellsund TMF, and the Scoresby Sund TMF.

Stratigraphy

The overall seismic stratigraphy of the clastic wedgeof sediments comprising the fan has been studied bymany workers (Spencer et al ., 1984; Richardsen et al .,1991, 1992; Vorren et al ., 1991; Knutsen et al ., 1992;Eidvin et al ., 1993; Sættem et al ., 1994; Faleide et al .,1996) (Table 3). The age of the fan progradation and

also the origin of the sediment comprising the fan isdisputed. Recent dating suggests that most of the fansediments are of (Late) Pliocene — Pleistocene age (Eid-vin et al ., 1993; Sættem et al ., 1994; Faleide et al ., 1996).

Much of the sediment in the fan contains clasts of glacial origin (Eidvin et al ., 1993; Sættem et al ., 1994).The origin of the sediments comprising the lower partof the fan has to a large degree been a matter of discussion about the extent of the sediment-feedingglaciers through time. Many favour extensive gla-ciations of the Barents Sea throughout the deposition

of the fan/clastic wedge, e.g. ‘‘ 2 it is likely that the shelf was covered by ice sheets during a major part of thisperiod’’ (Eidvin et al ., 1993), ‘‘We argue that glaciersreached the position of the westernmost Barents shelf already at the very earliest stage of the deposition of the clastic wedge in front of Bj + rn + renna’’ (S ættem etal ., 1992). Vorren et al . (1991) favoured a graduallyincreasing glacial dominance, culminating with totalglaciation of the Barents Sea shelf during the depos-ition of the youngest sequence (i.e. unit TeE) only.Sættem et al . (1994) also indicate, in accordance withVorren et al . (1991), that the earliest glaciations werecentred on the Svalbard area. However, S ættem et al .(1994) indicate that glaciers reached the shelf break inthe Bear Island Trough, from the north, at the veryearliest time of the clastic wedge deposition.

In this work we will concentrate on the upper seis-mostratigraphic unit, corresponding to Unit IV of Spencer et al . (1984), Unit TeE of Vorren et al . (1991),and Unit G III of Faleide et al . (1996) (Table 3) and

also corresponding to the following units identied onthe continental shelf and uppermost slope: namelyunits I to IV of Solheim and Kristoffersen (1984); units1W to 4W of Vorren et al . (1990) and units B to G of Sættem et al . (1992). There is a general consensus thatthis upper part of the clastic wedge/fan was depositedduring a period when the whole of the Barents Sea shelf underwent repeated glaciations.

Eight seismostratigraphic units, I (oldest) to VIIIwere identied by Laberg and Vorren (1996a) in thisupper part of the clastic wedge. All these units weredominated by debris ows assumed to be depositedduring glacials (Fig. 7). The reections separating theseunits are interpreted to be formed during inter-glacials/interstadials (see below).

Age estimates

The Holocene interglacial sedimentation rate has

been about 15 cm/1000 years within the uppermostpart of slide scar C (Laberg and Vorren, 1993). This isrelatively low compared to the up to 124 cm/1000years inferred during the Late Weichselian glacialmaxima (Laberg and Vorren, 1996a). Hence the keyreections which separate the seismic units were infer-red to reect palaeo-fan surfaces formed during sedi-ment-starved interstadials and/or interglacials. Theseismic correlation of the debris ow units (I — VIII) tothe glacigenic sedimentary units on the continentalshelf, shows that the diamicton in the debris ows wasdeposited during glacials (Laberg and Vorren, 1996a).

Based on the assumption that: (1) all the identiedseismic units on the fan comprise mainly sedimentsdeposited during glacial maxima; (2) the Barents Sea IceSheet advanced to the shelf break during each Middleand Late Pleistocene glacial maximum; and (3) theMiddle and Late Pleistocene fan stratigraphic record iscomplete, then ‘back-counting’ from the last glacialmaximum (Stage 2) indicates that seismo-stratigraphic



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TABLE 3 Suggested ages and correlation of seismostratigraphic units of the western Barents Sea and Svalbard continental margin

Barents Sea margin (70 — 74°N) Barents Seamargin (70 — 77°N)

Svalbard margin (77 — 80°N)

Spencer et al .(1984)

Eidvin and Riis(1989); Eidvinet al . (1993)

Vorren et al .(1991); Knutsenet al . (1992);Richardsen et al .(1992)

Sættem et al .(1992, 1994)

Faleide et al .(1996); Fiedlerand Faleide(1996); Hjelstuenet al . (1996)

Schlü ter andHinz (1978);Myhre andEldholm (1988)

Andersen et al .(1994)

unit VI was deposited mainly during Isotope Stage 6,V during Stage 8, IV during Stage 10, III during Stage12, II during Stage 14 and seismostratigraphic unit

I during Isotope Stage 16 (Fig. 8). This correlationindicates that the studied sediments on the fan areyounger than 622 ka (Laberg and Vorren, 1996a). Thisage estimate is somewhat younger than the 0.8 Masuggestion of Vorren et al . (1990), and somewhat olderthan the maximum 440 ka amino acid dating of Sættem et al . (1992). By using the isotope time scale, theinterval during which the individual seismo-strati-graphic units were deposited can be bracketed moreprecisely (Fig. 8).

However, the suggested ages may be maximum ages,

because more than one unit can be deposited duringeach glacial maximum, as exemplied by units VII andVIII. On the other hand, some of the isotope glacialmaxima may not be represented by an ice sheet extend-ing to the shelf break. Therefore, it must be stressedthat the suggested datings should be considered asa rst approximation for the seismic units (Laberg andVorren, 1996a).

The Trough Mouth Fans as proxies for ice streamvelocities and ice sheet mass balance

Vorren and Laberg (1996) estimated the velocities of the Bear Island Ice Stream as well as the icebergcalving ux and the snow accumulation of the drainagearea of this ice stream during the last glacial maximum(18— 15 ka). Their estimate was based on the measuredamount of sediments in the debris ows transported tothe Bear Island TMF (1500 km ), and estimates andassumptions on the origin of the sediments (deforma-

tion till), thickness of the deforming basal till layer(4 m), duration of input (3 ka), and width (150 km) andthickness (500 m) of the feeding ice stream. They con-

cluded that the speed of the basal ice was 2.5 km/yearat the front and that the ice discharge to the ocean wasabout 200 km /year.

When more data are available one could, by usingthe same type of reasoning, estimate the ice velocitiesand calving ux of other ice streams feeding troughmouth fans during the last glacial maximum and pos-sibly older glacials.

THE STORFJORDEN TMF

Morphology

The Storfjorden TMF which covers an area of about40 000 km and has a radius of about 190 km, de-veloped concentrically off the Storfjorden trough(Fig. 6). The water depth is mostly between 400 and2500 m. The fan extends from the shelf break westwardto the damming Knipovich Ridge. The upper andmiddle fan gradients along the central fan axis are 1.8 °and 1.0 °, respectively, while the lower fan gradient isabout 0.2 ° or less (Laberg and Vorren, 1996b).

Stratigraphy

The Storfjorden TMF is an integral part of theCenozoic sediment wedge which has been deposited atthe western Barents Sea margin (Myhre and Eldholm,1988; Vorren et al ., 1991). The Cenozoic sediment inthe Storfjorden TMF area has been divided into three



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FIG. 7. Map of the Bear Island TMF and the Storfjorden TMF indicating the extent of the youngest debris lobes and location of large channelsand gullies. Location of seismic proles (Fig. 5, Fig. 11, Fig. 14, Fig. 15 and Fig. 18) are given. Positions of gravity cores (Fig. 10) are given by

heavy dots. Bold frame outlines Fig. 19.



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FIG. 8. Tentative correlation of seismic (debris ow) units from the Bear Island and Storfjord TMFs to the oxygen isotope stratigraphy (Williamset al ., 1988). Isotope Stages 2 — 16 are indicated. Dating of units E, F and G are based on correlation to the Svalbard land record (Mangerud and

Svendsen, 1992). The gure has been adapted from Laberg and Vorren (1996b).

seismic sequences by Schlü ter and Hinz (1978), SPI-I,II and III, and four sequences by Hjelstuen et al . (1996),G0 (oldest), GI, II and III. In this study, we will focuson the youngest part of seismic sequence SPI-I, whichcomprises sequence GIII and the youngest part of GII.This part of the fan sequence is dominated by debrisows, and tentatively dated to be of Mid and LateQuaternary age (Laberg and Vorren, 1996b).

Seven seismic units have been identied within the

study area of the Storfjorden TMF; A (oldest) toG (Laberg and Vorren, 1996b). The units are boundedby regional key seismic reections; a (oldest) to g, of which reection b correlates to reection R1 of Hjel-stuen et al . (1996). However, due to the data coverageand penetration, some of the deepest reections (a — d)could not be traced with condence on the middle andlower fan, preventing a precise correlation in theseareas.

Age estimate

There are no published dates from the studied partof the Storfjorden TMF or the nearby shelf. The onlyresults available are from the DSDP Site 344 whichwas located on the distal part of the fan, and whichshowed that sequence SPI-I of Schlü ter and Hinz(1978) comprises sediments of Pliocene — Pleistoceneage (Talwani et al ., 1976). By seismic correlation tocommercial wells in the southwestern Barents Sea,Hjelstuen et al . (1996) propose that their sequence GIIIcomprises sediments younger than 440 ka.

Correlation with the Svalbard land record ledLaberg and Vorren (1996b) to suggest that the threemajor glaciations known to have extended beyond thecoast of western Svalbard were probably mirrored byice advances through the Storfjorden Trough from thesoutheastern part of Svalbard. Based on the aboveconsiderations, and the dating results of Mangerudand Svendsen (1992), Laberg and Vorren (1996b) tenta-tively suggest that there may have been two ice ad-

vances to the shelf break in the outer StorfjordenTrough during the Weichselian; in Middle (65 — 55 ka)and Late Weichselian (20 — 10 ka) respectively, and oneadvance during the Late Saalian. During these iceadvances, units E (Late Saalian), F (Mid Weichselian)and G (Late Weichselian) may have been deposited.

As a rst approximation, the older units (A — D) weretentatively correlated to the oxygen isotope curve(Fig. 8) (Williams et al ., 1988). Based on this correla-

tion, Laberg and Vorren (1996b) suggest that seismicunit D can be correlated to Isotope Stage 8, unit C toStage 10, unit B to Stage 12 and seismic unit A to Stage14. Hence the studied succession is found to comprisesediments younger than about 600 ka. In this correla-tion we have made similar assumptions as for thedating of the Bear Island TMF (see above).

The Svalbard TMFs

Morphology

Along the western shelf-margin of Svalbard threetrough mouth fans can be discerned on bathymetricmaps, Bellsund TMF off Bellsund, Isfjorden TMF off Isfjorden and Kongsfjorden TMF off Kongsfjord(Fig. 6). The three fans are of much the same size andshape (Table 2), and partly merge in their distal areas(Andersen et al ., 1994). These fans cover an area of about 4000 km each, have radii of 50 — 70 km andrelatively steep slopes, i.e. on average between 1.8 ° and3.2° (Table 2).

Stratigraphy

Schlü ter and Hinz (1978) recognised three sequencesoff western Svalbard, SPI-I, II and III, separated bytwounconformities, U1 and U2. The U2-unconformity,separating the oldest SPI-III from the SPI-II, has beentaken to correspond to the onset of glacigenic sedi-mentation (Myhre and Eldholm, 1988). Andersen et al .



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FIG. 9. Interpretation of a seismic reection prole (100 km inlength) across the East Greenland continental margin on the south-ern part of the Scoresby Sund TMF (Dowdeswell et al ., 1997;redrawn from Vanneste et al ., 1995). The prole was acquired by

Vanneste et al . during RV ‘Polarstern’ cruise ARKVII/3b.

(1994) have indicated that the Late Cenozoic suc-cession consists of two primary sequences (A and B)which are separated by a regional unconformity, R4.Sequence A corresponding to the youngest part of seismic sequence SPI-I, and is responsible for the fangrowth. Andersen et al . (1994) suggest that this tookplace at about 1 — 0.8 Ma ago and that this marks theadvent of more extensive glaciations.

The Scoresby Sund TMF

Morphology

On the East Greenland continental margin between69° and 71 °N, the presence of a major submarine fanoffshore of the 14 000 km Scoresby Sund fjord systemis indicated by the crescent-shape of the shelf break andthe contours of the continental slope (Dowdeswellet al ., 1997) (Fig. 6). The fan has a gradient of about1.8— 2° and terminates in about 1500 m of water to thewest of the Kolbeinsey Ridge. The glacier-inuencedfan volume is about 15 000 $ 5000 km (Dowdeswellet al ., 1997), based on seismic reection studies (Larsen,1990; Vanneste et al ., 1995). The seismic evidence sug-gests a smaller total volume for underlying non-glacialsediments of possible riverine origin (Vanneste et al .,1995). Thus, the total volume of the Scoresby SundTMF is unlikely to exceed 30 000 $ 10000 km .

Stratigraphy

A seismic reection prole across the southern partof the Scoresby Sund TMF, published by Vanneste etal . (1995), together with a west to east prole from justnorth of the mouth of Scoresby Sund (Larsen, 1990),provide information on fan thickness and internalstructure. Larsen (1990) also gives a total isopach mapof sediment thickness above basement for most of thefan and adjacent basin. There are three major unitsabove oceanic basement rocks, with a total sediment

thickness of up to about 2000 m (Fig. 9; Vanneste et al .,1995). However, the lower units, I and II in Fig. 9, areinterpreted by Vanneste et al . (1995) to be of preglacialorigin and to be related at least in part to riverineprocesses. The uppermost unit (III) is on the order of 275 m thick on the prograding continental shelf, and

up to 1000 m in thickness on the outer shelf and upperslope, thinning to less than 140 m on the Iceland Pla-teau (Fig. 9). The base of Unit III is represented bya clearly identied erosion surface on the continentalshelf, and this is interpreted to indicate the rst ice-sheet advance across the shelf. Unit III also has veerosional unconformities within it, probably related tofurther ice advances, and the entire unit is inferred tobe of predominantly glacial origin. The age of thetransition from preglacial to glacial sedimentation atthe base of Unit III is still in doubt, but it may corres-pond to the inception of glaciation reaching to sea-level in East Greenland at about 7 million years ago(Larsen et al ., 1994).

Sedimentary patterns and processes on the Scoresby Sund TMF

The character and spatial distribution of acousticfacies provide a view, in plan from GLORIA imagery,and in section from 3.5-kHz records, of Late Pleis-tocene sedimentation on the Scoresby Sund TMF andin the adjacent ocean basin truncated by the Kolbein-sey Ridge and Iceland Plateau to the east (Dowdeswellet al ., 1997). A series of acoustically transparent fea-tures, with irregular surface topography and elongatedownslope, are interpreted as debris ows of varyingwidth (0.5 — 2 km) and thickness (5 — 15 m). This acousticfacies makes up the bulk of relatively recent sedimenta-

tion on the upper fan, and marks the area of mostrecent active fan growth. However, on the northern-most one-third of the fan, a draping unit is presentclose to the surface. This is underlain by irregulartopography, similar in form to the debris ow de-scribed above. This northern region is interpreted torepresent the least active area of the Late Pleistocenefan, in which predominantly hemipelagic sedimentswith a contribution from ice-rafted debris (Nam et al .,1995) overlie older debris-ow deposits (Dowdeswellet al ., 1997). These debris ows, interpreted from

GLORIA and 3.5-kHz data, are the basic buildingblocks in the long-term development of the ScoresbySund TMF. The more distal area of the ocean basinhas a at oor with parallel sub-bottom reections.This facies is interpreted as an area of predominantlylow-energy hemipelagic sedimentation, punctuated byoccasional ice rafting and turbidity current activitywhich serves to produce the internal reections withinthe records (Dowdeswell et al ., 1997). It lies beyonda break of slope which presumably represents the toe of the prograding Scoresby Sund TMF and the limit of debris-ow activity. It is possible that the debris owsactive on the upper slope are related to, and in somecases trigger, turbidity currents which travel beyondthis topographic and acoustic stratigraphic boundaryinto the most distal parts of the basin (Hampton, 1972).During full glacials in East Greenland, the inland icesheet advanced to ll the Scoresby Sund fjord systemand extended across the shelf to reach the shelf break insome glacial cycles (Dowdeswell et al ., 1994; Funder et



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TABLE 4 Dimensions of individual debris ows on trough mouth fans in the Norwegian — Greenland Sea

Isfjorden TMF Storfjorden TMF Bear Island TMF North Sea TMF Scoresby Sund TMF

Width (km) 2 — 5 1— 5 3— 24 2— 40, (5) 0.5— 2Thickness (m) 10 — 30 15 5— 50 ( 60, (15— 30) 5— 15Length (km) 10 — 20 50— 100 100— 200Area (km ) ( 100 ( 500 850— 1880Volume (km ) 0.5— 1 3— 8 10— 32 10— 50

Data from this work and King et al . (1996) and Elverh + i et al . (1997) (North Sea TMF); Laberg and Vorren (1995) (Bear Island TMF); Laberg andVorren (1996b) (Storfjorden TMF); Elverh + i et al . (1997) (Isfjorden TMF) and Dowdeswell et al . (1997) (Scoresby Sund TMF).

al ., 1994). Debris ows formed in areas of most rapidsediment ux, which were probably related to the de-livery of glacial sediments to the ice margin in an activedeforming subglacial layer. The Scoresby Sund TMF isrelatively similar to the Storfjorden TMF on the east-ern Polar North Atlantic margin, but differs from thelarger Bear Island TMF in having a steeper fan gradi-ent, much smaller debris ows and no large-scaleslides.

DEBRIS FLOWS — DIMENSIONS ANDCOMPOSITIONS

Dimensions

The dimensions of the debris ows vary from fan tofan. The width varies between 0.5 and 40 km, thickness

between 5 and 60 m, length from less than 10 km up to200 km, the areas covered are up to 1880 km and thevolumes from 0.5 to 50 km (Table 4). There is a cleartendency towards larger fans having the larger andmore voluminous debris ows (Table 4).

Lithology

King et al . (1996) report that the debris ow materialof the North Sea TMF is an extremely homogenousdiamicton with 38% clay, 34% silt, 28% sand and

usually less than one percent greater than 1 mm indiameter. It is remarkably consistent in texture bothwith depth and across the fan.

From the Isfjorden TMF, Elverh + i et al . (1997) re-port that the debris ow sediments comprise 35 — 40%clay, 35 — 40% silt and 20 — 30% sand.

Four cores were recovered from one specic BearIsland TMF-debris lobe at different depths (Fig. 10).A massive dark grey diamicton was found to representthe basal unit in all cores (Laberg and Vorren, 1995).The diamicton has a sharp upper boundary. The sedi-

ment is poorly sorted and has high clast content, de-rived from both crystalline and sedimentary rocks. Thegrain-size distribution of the diamicton is 30 — 55%clay, 30 — 50% silt, 10 — 30% sand and 1 — 10% gravel.There is no systematic variation in grain-size distribu-tion between the upper and lower fan. The undrainedshear strength of the diamicton increases downcore;values between 3.3 — 16 kPa have been measured. Water

contents between 19 and 30% (of wet weight) havebeen found in most of the unit comprising debris owsediments in the cores, increasing to 30 — 35% at the topof the unit. The grain-size distribution and water con-tent are compatible with the youngest glacigenic dia-micton on the outer Barents Sea shelf (S ættem et al .,1992; Poole et al ., 1994). Foraminiferal analysis of coreJM93-6/1 (Fig. 10) shows that the benthic fauna isdominated by Arctic species like Cassidulina teretis andCassidulina reniforme . A shelf provenance of the sedi-ments is indicated by species related to shelf and upperslope environment (e.g. Elphidum excavatum f . clavata )being very frequent (Laberg and Vorren, 1995). Thefrequent appearance of the planktic foraminifer Neog -loboquadrina pacyderma (sin.) indicates that somehemipelagic sediments were also entrained into thedebris ow deposits.

Seismic signature

Here we will describe and interpret the seismic signa-ture as revealed on the Bear Island and StorfjordenTMFs. Published information from the North Sea andIsfjorden TMFs appear to be quite similar to this.

Key seismic re ections

Key seismic reections separate the identied seis-mostratigraphic units. The reections have medium to

high amplitude. On the upper part of the fan, they arepartly discontinuous, whereas they are continuous fur-ther downslope. The reections dene the base and topof units dominated by debris ows, but also comprisechannel erosion as well as slide deposits. By analogy tothe present interglacial, the key seismic reectionsprobably represent the presence of thin inter-beddedunits of hemipelagic interglacial/interstadial sediments.

Shelf break — upper fan

The upper part of the fans have a chaotic seismicsignature indicating reworking by sliding activity. Insome places remains of slide deposits can be identied(Fig. 11), while other places show a prograding delta-like feature having more gently dipping foresets thanthe general slope gradient (Fig. 12).

The middle part of the fans are dominated bya mounded signature in cross section (Fig. 13 and



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F I G

. 1 0 . S t r a t i g r a p h y a n d l i t h o l o g y o f f o u r g r a v i t y c o r e s r e c o v e r e d a l o n g a d e p t h t r a n s e c t o f o n e d e b r i s l o b e o n t h e B e a r I s l a n d T M F ( s e e F i g

. 7 f o r l o c a t i o n ) . F

r o m L a b e r g a n d V

o r r e n ( 1 9 9 5 )

.



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FIG. 11. Part of sparker prole UiT + 6B-87 across the shelf break of the Bear Island TMF (see Fig. 7 for location). Gravity sliding just below theshelf break is evident. Units I, II, III, VII and VIII refer to the seismic units of Laberg and Vorren (1996a) and unit 4W to the seismic units of Vorren

et al . (1990). M" multiple (slightly modied from Vorren et al ., 1990).

FIG. 12. Sparker prole along Andfjorden, a transverse trough north of And + ya, north Norway (see Fig. 6 for location). The sparker-recordindicates a prograding delta-like unit which ends at the steep shelf break to the right. We suggest that this feature may be a till delta. In this area theupper slope is so steep that sediments transported to the shelf break probably were directly transported further downslope by gravity ows

(modied from Vorren et al ., 1984).



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FIG. 13. Cross prole ME72-31 (3.5 kHz) of debris lobes on the lower slope of the Storfjorden TMF (see Fig. 19 for location). Verticalexaggeration is approximately 1:50. The prole was acquired during RV ‘METEOR’ cruise 7-2, 1988.

Fig. 14), representing sections through debris ows.There is a central depression along the top of some of the debris ows (Vogt et al ., 1993; Laberg and Vorren,1995). As revealed from seismic proles, the depress-ions are up to 250 m wide and 1.5 m deep (Fig. 15). Thedebris ows are deposited into bathymetric lows be-tween older deposits. The ows end on the lower fan.The snouts of the debris ows are mostly very welldelineated, as can be observed both from seismic(Fig. 13) and side-scan sonar data (Vogt et al ., 1993)(Fig. 16). The distinct downslope margin of the debrislobes indicate a sudden halt on the lower fan.

The base reections are not commonly found on theupslope part of the debris lobes. This, together with thefact that the regional reections immediately below themounds have in some places an irregular character,indicates disturbance and probably incorporation of underlying sediments during downslope ow. Aksuand Hiscott (1992) and Stoker (1995), investigatingdebris ows on the Newfoundland continental slopeand Hebrides slope, respectively, also found that thebasal reection of a small number of lenses exhibiteddown-cutting into the underlying acoustically stratiedunit.



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FIG. 14. Cross prole (sparker) of stacked debris lobe sets. See Fig. 7 for location. After Laberg and Vorren (1996a).

FIG. 15. Sparker prole illustrating the stacked, mounded signature

found within seismic unit VIII on the Bear Island TMF. A centraldepression is found on top of one of the mounds (arrow). Waterdepth is indicated (see Fig. 7 for location) (after Laberg and Vorren,

1995).

ORIGIN OF THE DEBRIS FLOWS

In discussing the origin of the debris ows we aim toelucidate the following questions:

What was the source area of the material involved inthe slump/slide that evolved into the debris ow?

How and when was this material transported to theshelf break/upper slope?

How and when was this material accumulated at theshelf break/upper slope?

What release factors caused the material toslump/slide?

Why did the slide evolve into a debris ow?Did the debris ow erode the base and incorporate

material?What was the ow behaviour of the debris ows?

Source area

Laberg and Vorren (1995) pointed to the similaritiesin textural composition and water content of the debrisow diamicton to the youngest glacigenic diamictonon the outer shelf (S ættem et al ., 1992; Poole et al .,1994). The lithology as well as the fossil content in-dicated clearly that most of the debris ow sedimentwas derived from glacigenic shelf diamictons (see be-low). Radiocarbon dating also strongly indicated thatthe material of the debris ow was deposited duringpeak glaciations (Laberg and Vorren, 1995). Thus, thedata from the Bear Island TMF strongly suggest thatthe adjoining shelf is the source area, and that thematerial was accumulated when the ice sheet was at theshelf break. Similar conclusions are also reached forthe debris ows on the North Sea TMF (King et al .,



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FIG. 16. SeaMARC II sidescan data from the northern, lower Bear Island TMF showing the lower part of one debris lobe (adapted from Vogt etal ., 1993) (see Fig. 7 for location).

1996), the Storfjorden TMF (Laberg and Vorren,1996b) and the Isfjorden TMF (Elverh + i et al ., 1997).

Transport to and accumulation at the shelf break

It has been suggested that the diamicton on theouter continental shelf of the Barents Sea was rstdeposited as deformation till at the glacier bed (S ættemet al ., 1992; Laberg and Vorren, 1995). We favour thismodel (Fig. 17), which implies that glacigenic sedi-ments were brought to the grounding-line as a deform-ing till-layer (Boulton, 1979). This probably resulted ina build up, either of ‘till-deltas’ according to the modelof Alley et al . (1989) or as ‘diamict aprons’ (Hambreyet al ., 1992) along the glacier terminus. The glacigenicsediments could also have continued directly down-slope. The sediments deposited in the till deltas areprobably inherently unstable, and not preserved ona sloping subsurface. However, there are examples on

the seismic records across the shelf break which couldbe interpreted as till deltas (Fig. 12).

The relatively high water content of the outer shelf diamicton (S ættem et al ., 1992) indicates relatively littleglacier compaction of the source sediments. Thus thesediments deposited along the grounding line wererelatively unstable, and the water content was prob-ably high enough for the sediments to ow downslopewithout incorporation of additional water (Laberg andVorren, 1995, 1996b).

Release factors

The morphology, showing slide scars on the presentuppermost slope surface and a chaotic seismic facies onthe upper fan, indicates that several sediment slideswere released near the shelf break (Laberg and Vorren,1995). The slides may have been triggered by; (1) buildup of excess pore pressure due to high sediment input;



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FIG. 17. Schematic model showing the main sedimentary processes on the shelf break and upper slope during the presence of an ice sheet at theshelf break (from Laberg and Vorren, 1995).

(2) earthquakes; (3) oversteepening; (4) ice loading (e.g.Mulder and Moran, 1995); and/or (5) seepage of shal-low gas. The repeated release of slides on a regional

scale suggests a trigger mechanism common to theseparticular settings. Thus, most likely the slides werereleased by a build-up of excess pore pressure andoversteepening, and perhaps sometimes ice oscillationand iceberg calving.

Basal erosion?

Laberg and Vorren (1996b) observed that the basereections are not often found on the upslope part of

the debris ows on Bear Island and Storfjorden TMF.This, together with the fact that the regional reectionsimmediately below the mounds have in some places anirregular character, indicates disturbance and probablyincorporation of underlying sediments during down-slope ow. King et al . (1996) report that occasionalbasal indentations, presumably troughs, occur in theNorth Sea TMF, indicating the possibility of minorerosion at the base. Aksu and Hiscott (1992), inves-tigating debris ows on the Newfoundland continentalslope, also found that the basal reection of a smallnumber of lenses exhibited down-cutting into theunderlying acoustically stratied unit. Hiscott andAksu (1994) showed that the snout of a large debrislobe had erosional power and that a remoulded zoneoccurred beneath the lobe. Thus, it appears safe toconclude that the debris lobes comprise sediments bothfrom the original shelf diamicton and, additionally, insome cases, sediments from the more distal continentalslope.

Flow behaviour

The debris ows moved downslope following

bathymetric lows between older deposits (Aksu andHiscott, 1992; Laberg and Vorren, 1995). Flows thatmoved further downslope than their forerunnersspread out laterally, resulting in a width and thicknessincrease on the lower fan. Generally, the debris owscontaining the largest sediment volume have the lon-gest run out distance (Laberg and Vorren, 1995).

On several of the debris lobes on the Bear IslandTMF and on Storfjorden TMF, Laberg and Vorren(1995, 1996b) observed central depressions on the de-bris lobes (Fig. 15). They concluded that these depress-

ions most likely originated from freezing of themarginal parts of the ow. This may leave a centralmobile core which, in turn, caused a channel-like col-lapse on the crest of the debris lobe.

According to Elverh + i et al . (1997), the high claycontent of the debris ows indicates that the lobesconsist of cohesive material, which favours a plug owmechanism for their origin. Plug ow is characterisedby no internal movement in the sediments during theow. The original structure of the sediments is thusretained from the release of the slide to its nal posi-tion.

Many of the observed debris ows have a large runout distance on low gradient slopes, particularly on theBear Island and North Sea TMF. This indicates lowviscosity behaviour. The mobility of debris ows in-volves an important contribution from excess poreuid in allowing long run out distances. As indicatedabove, the water content of the diamicton transportedto the shelf break was probably high enough to cause



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FIG. 18. Sparker proles along the upper continental slope south of the Bear Island TMF in water depths of ca 400 and 600 m (see Fig. 7 forlocation). The proles cross gullies up to 150 m deep. Note the buried gullies below the lightly stippled upper seismic unit (after Vorren et al ., 1989).

ow. Furthermore, in the marine environment, excesspore uid pressures are probably generated both dur-ing remoulding of porous and saturated materials fol-lowing slope failure, and during ow, as wet muds areoverridden and incorporated into the base of the ows(Aksu and Hiscott, 1992). The latter process may havebeen of some importance on the upper slopes, asdocumented here, because sediments deposited rapidlyfrom suspension just beyond the glacial margin wouldhave been extremely rich in pore water.

Textural variations might also control the spatialdistribution of the debris ows as discussed by Hiscottand Aksu (1994). They suggested that ‘high efficiency’debris ows with a long runout distance are more mudrich than ‘low efficiency’ debris ows. The higher shearstrength of the mud-rich sediments, caused by highcohesive strength (Hampton, 1972), results in thebuild-up of larger amounts of sediment on the upperslope prior to sediment release. However, the scantydata at hand so far indicate that the observed debrisows on the Norwegian Sea continental margin havevery similar textural composition. Thus, the size of thefeeding slide and/or the slope gradient seem to be thedecisive factors regarding the run out distance.

CHANNELS

Norwegian margin

The observed channels on the Norwegian margincan be grouped into two types according to their sizeand morphology: (1) Gullies on the upper and middle

continental slope; (2) Large channels on the continen-tal slope, rise, and in the deep sea.

Gullies

On the upper continental slope south of Bear IslandTMF, there are several gullies (Bugge, 1983; Kenyon,1987; Vorren et al ., 1989). Many of these begin at theshelf break and merge together further downslope.Some of the gullies terminate at a depth of 1000 mwhile others continue to greater depths (Bugge, 1983).The gullies are up to 150 m deep and 1 km wide. Buriedfossil gullies of similar size also occur (Vorren et al .,1989) (Fig. 18). In interpreting the gullies there are twoimportant features: (1) The gullies seem to be erodedinto older glacial deposits and they are cutting intoprimary bedding planes; (2) The gullies have a ‘fresh’relief and do not appear to contain any sediment inll(Fig. 18). These observations indicate that the gulliesprobably did not form during full glaciations. Erosionby density currents/cold dense water formed on theshelf was suggested by Bugge (1983) and Vorren et al .(1989). Gullies which are probably of similar originhave also been found on the upper Bear Island TMF(Laberg and Vorren, 1995) and the Storfjorden TMF(Laberg and Vorren, 1996b) (Fig. 7).

Large channels

Two channel systems have been observed along theNorwegian — Barents Sea continental margin, one oneither side of the Bear Island TMF (Fig. 3 and Fig. 7).We here propose to name the southern channel system



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FIG. 19. Map of the Inbis Channel on the western Barents Sea continental slope and rise (see Fig. 7 for location) with adjacent mud wave eldsand current lineations (bold arrows). North — south shaded lines indicate 3.5-kHz proles shown in Fig. 13 and Fig. 20. Location of sediment cores

is shown by circles.

‘the Lofoten Basin Channel’, and the northern ‘theInbis Channel’ (the Interfan Bear Island TMF andStorfjorden TMF channel system).

¹ he ¸ ofoten Basin Channel , located in the axis of the deep embayment south of the Bear Island TMFwas observed and described from long-range side-scansonar data by Dowdeswell et al . (1996). This channelsystem, which leads into the Lofoten Basin, increases indepth to about 30 m and the width, which is about3 km, increases greatly where it reaches the basin plain.The fairly at area beyond the channel has discontinu-ous, parallel bedding and medium 3.5-kHz penetrationof up to 25 m. Recent coring results lend support to theidea that this is a sandy channel mouth lobe (Dowdes-well et al ., 1996). Dowdeswell et al . (1996) interpret thechannel system as being formed either by cascadingdense cold water from the Barents Sea, formed throughbrine rejection during winter sea-ice formation, and/orby turbidity currents generated by the many debrisows on the slope above.

¹ he Inbis Channel . On the continental rise west of Bear Island in water depths of 2360 — 2520 m, a 60 kmlong and 5 — 15 km wide nearly at bottomed east — westoriented channel exists. To the south and the north, thechannel is bordered by the Bear Island and StorfjordenTMFs, respectively (Fig. 19).

The upslope part of the channel is buried underdebris ows having their origin on the upper slope infront of Kveitehola Trough (Fig. 7 and Fig. 13). The

southern limit is partly bordered by debris ows of theBear Island TMF (Laberg and Vorren, 1995, Fig. 7and Fig. 19).

At water depths of 2450 — 2500 m, the northern chan-nel ank is built up by a set of overbank depositsforming a 10 — 15 m high natural levee (Fig. 20). A fewhundred meters to the north the overbank depositschange into an area (up to 10 km wide) of well de-veloped asymmetric mud waves, having amplitudes of 2— 4 m and spacings of 200 — 400 m.

The steepest slopes and crest displacements of themud waves adjacent to the Inbis Channel (Fig. 20),suggest upslope migration against the sediment trans-porting currents (Allen, 1982; Blumsack and Weather-ly, 1989). Deep-towed high-resolution side-scan sonarproles displayed parallel linear features (width of thestripes are about 10 m) on the surface of the mudwaves. The stripes apparently have the character of current lineations, i.e. linear bedforms of extremely lowrelief oriented parallel to a strong downslope current.This interpretation is corroborated by the occasionalappearance of obstacle marks within the lineations.The orientation of the current lineations radiate fan-like downslope from the Inbis Channel (Fig. 19). Thus,both the mudwaves and the current lineations showthat density currents in the Inbis Channel have fre-quently been overowing the channel, depositing sedi-ments in the overbank areas.

The sediments in a 8.16-m long core (GIK 23257)from the northern levee (Fig. 19 and Fig. 21) comprisetwo sequences of very ne grained (95 wt.% of ( 20 m) turbidite mud; an upper sequence from 17 to

475 cm, and a lower sequence from 655 cm to thebase of the core (Fig. 21). Single sets up to 10 cmthick consist of dark basal cross-bedded silt laminae



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FIG. 20. Three 3.5-kHz-proles (RV ‘METEOR’ cruise 7-2, 1988) crossing the Inbis Channel, looking from the deep-sea oor upslope to the east.Vertical exaggeration is approx. 1:50. See Fig. 19 for location.

changing to brighter, very ne ungraded mud (Fig. 21).The units have a typical distal turbidite character asdescribed by Stow and Shanmugam (1980). Scatteredice rafted debris (IRD) in all levels of the laminated

mud indicates that the depositional time for one set haslasted longer than for a ‘normal’ distal turbidite and/orthat the IRD activity was high during the deposition of the turbidites. Both of the turbidite sequences are prob-ably of Late Weichselian age.

The sediment-echo character (3.5-kHz sub-bottomproling) of the relative at channel bed differs clearlyfrom the surrounding uneven and ridged sea bottomby its hard reecting irregular seismically laminatedsediment inll (Fig. 20). The deepest part of the chan-nel is along the southern side, whereas the sediment

bodies in the channel are thicker along the northern side.Beyond the upslope limit of the Inbis Channel(Fig. 19) a branched system of small V-shaped valleysbetween the debris ow deposits can be traced astributary channels by higher reectivity and smallmorphological irregularities in their deepest part. Alsoolder valleys lled up by debris ows are dominated bythis echo-character (cf. Fig. 13).

At the mouth of the Inbis Channel there isa ' 50 km wide fan-like accumulation, the Inbis Fan.A fan-like accumulation area is also deduced from theGLORIA and 3.5-kHz proler data (Dowdeswell et al .,1996). On prole ME72-08 (Fig. 20), sharp erosivechannel incisions 0.2 — 1 km wide and 5 — 10 m deep bor-dered by natural levees can be observed anking theInbis Fan.

The location of the Inbis Channel indicates that itsmain source area is the southern ank of the Storfjor-den TMF, the northern ank of the Bear Island TMFand the interfan area in front of Kveitehola Trough

(Fig. 7). Core GK 23257 (Fig. 21) indicates that turbid-ity currents were quite active during episodes with highIRD input, i.e. during glaciations. Also, the partialinlling of the Inbis Channel by debris ows, which

had their main activity during peak glaciations (Labergand Vorren, 1995; Vorren and Laberg, 1996), suggeststhat the density current activity mainly took placeduring glaciations.

The origin of the density currents running along theInbis Channel may have been dense water formed bycooling, sea-ice formation and brine rejection or theymay originate from small slides on the upper slopetransforming into turbidity currents. Along with de-creasing gravity energy of the turbidity current, thedistal portion of the suspension load was retarded and

deected to the right by the Coriolis force, where thelevee accumulated (Fig. 20). The Coriolis force, affect-ing predominantly the upper ne-grained level of thedensity current, may explain the greater thickness of the laminated mud along the northern side of thechannel.

The Holocene succession at the lower slope(' 2100 m water depth) is generally only a few cen-timetres thick (Blaume, 1992). Sandy turbidites havebeen identied within the Holocene sediments, but thethickness and frequency of the turbidity currents seemto have been far less than during glacial periods.

East Greenland margin

GLORIA long-range side-scan sonar and PARA-SOUND subbottom-proler records allow us to deter-mine the characteristic acoustic backscatter patternsalong the East Greenland continental margin, and toderive from it a better understanding of the interaction



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FIG. 21. (a) Schematic lithostratigraphy of sediment core GIK 23257, located on the northern levee near the mud wave eld (for location, seeFig. 19). The upper 17 cm comprise Holocene bioturbated sandy, silty mud. The Late Weichselian sediments comprise two sequences of muddyturbidites, an upper from 17 to 475 cm and a lower from 655 cm to the base of the core. Two zoomed X-ray radiographs show core interval290— 320 cm (A) of the upper turbidite sequence with repeating couplets of laminated, layered silts to nearly homogenous muds with IRD (mudpellets) in the upper parts of a turbidite set, and a core interval 411 — 422 cm (B) with a set of cross/parallel-laminated silty muds indicating turbidity

current origin.

between ice sheets, bottom-water currents and sedi-ment-transport processes (Mienert et al ., 1993).

Along the East Greenland Margin, southward ow-ing currents with a velocity of 2.3 cm/s at approxim-ately 1400 m water depth (Aagaard et al ., 1985) carrycold water masses from the Arctic Ocean through theDenmark Strait to the North Atlantic Ocean. Thesecurrents may cause an intense along-slope transport of ne-grained sediments. In contrast, the calving of ice-bergs from the Greenland Ice Sheet and the productionof melt water may transport large amounts of coarse-

and ne-grained sediments to the shelf, which arenally carried and deposited along the margin and inthe deep sea by down-slope gravity ows. Additionally,cold water may cascade from the margin and drive thedown-slope transport of sediments. Strong evidence of down-slope processes was found in the sonographsfrom the northern and southern Greenland Basin, butit was not evident in the Boreas Basin (Mienert et al .,1993; Hollender, 1996) (Fig. 1).

The southern Greenland Basin shows four distinctchannel systems which may have experienced several



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FIG. 22. GLORIA sonograph mosaic showing a major channel (black arrow) running with a low sinuosity towards the 3800 m deep GreenlandBasin. It passes the approximately 3000 m high Vesteris Seamount located east of the channel (modied from Mienert et al ., 1993). Location of

Fig. 23 is given.

events of active and inactive phases of sediment trans-port. These channels (Fig. 22) have a low sinuosity anda length of up to 300 km. The longest channel orig-inates from the upper slope (about 1500 m water depth)at ca 73 °10 N 16 °W and is possibly connected to aneast — west trending transverse trough leading intoKaiser Franz-Josef Fjord. However, the semi-perma-nent sea-ice cover on the shelf prevents bathymetricsurveys and, therefore, the bathymetric control on theshelf is poor and allows only preliminary interpreta-tions. Also, the uppermost part of the channels was notseen, due to sea ice and distortions from water strati-cation that limit the range of the side-scan sonar sys-tem. However, it is clearly seen that there is a well-developed tributary pattern of shallow ( ( 10 m deep)channels with a high order of branching on the upperslope (Mienert et al ., 1993). Downstream from thetributary channels, a deep ( ( 100 m) single channeldevelops which turns north and runs towards thedeepest part of the basin (3800 m water depth)(Fig. 22). This channel gradually changes from a U-shape to a V-shape, with characteristic steep slopes anda bulge of sediments at the levee on the eastern side of the wall (Fig. 23). PARASOUND proles across thechannel show that it can be narrow (2 km) and fairlystraight as well as wide (10 km), with a weak sinuositywhere the depth of the channel increases from 50 m inthe U-shaped section to 90 m in the V-shaped part.Sediment box-cores collected inside and outside the

channel (Mienert et al ., 1993) show ash layers and alsosandy sediments at their base (approximately 40 cmbelow sea-oor) and undisturbed sediments above.A pronounced ash layer in the cores may be the Veddeash, which has a C age of 10.3 ka (Bard et al ., 1994).This age may indicate that the channel system has beeninactive since the Younger Dryas. On some outsidewalls of the channels, regularly spaced bands of con-trasting backscatter exist, which possibly representsediment waves with wavelengths from 2 to 3 km. Thisfeature in deep-sea channelized systems is usuallyattributed to moulding of the muddy overbanksediments by turbidity currents. Turbidity-currentactivities may be related to large sediment supply rateswhich possibly occurred during times of ice-sheetadvances towards the shelf edge.

All four channels in both the southern and northernGreenland Basin show a similar pattern in that theynally turn north and then run towards the deepestpart of the basin (Fig. 22). Thus the channels runagainst the ow of the modern southward directeddeep-water currents. While these currents may causea vigorous southward directed transport of ne-grained sediments, the turbidity currents in the chan-nels may dominantly transport coarse-grained sedi-ments northward. Not only the erosional channel areasshow characteristic backscatter patterns. The mainlydepositional regions in the distal part of the channelsystems also have characteristic patterns. The pattern



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FIG. 23. Parasound prole showing a depth transect across the Greenland Basin channel at about 3040 m water depth (73 °34 N, 10 °03 W). Forlocation see Fig. 22 (modied from Hollender, 1996).

is braid-like, with overall higher backscattering that

has been attributed elsewhere to deposits of sand, forexample beyond a channel on the Orinoco deep-sea fan(Belderson et al ., 1984) and beyond channels on fans inthe Bering Sea (Kenyon and Millington, 1995). Ob-served features on the East Greenland margin areprobably very shallow channels and sandy lobes. Over-all, the four major sandy depositional lobes identiedin the Greenland Basin cover an area of about3000— 5000 km .

The northern Greenland Basin shows a contrastingpattern, seemingly devoid of channelized features

(Fig. 1). This non-channelized pattern extends down-slope in front of an approximately 300 km long and400 m deep transverse trough known as Belgica Strait(Perry, 1986). What kind of environmental conditionsfavour the development of channel systems on polarcontinental slopes is still not clear. One possible ex-planation may be related to the position of the ice sheeton the shelf which inuences the mass transport acrossthe shelf to the slope region.

CONCLUSIONSSeveral large late Quaternary slides have been iden-

tied on the eastern Norwegian — Greenland Sea conti-nental margin (the Storegga, Tr ænadjupet, And + yaand Bj + rn + yrenna slides). Buried slides have also beenidentied in the Storegga slide area and on the westernBarents Sea continental margin, indicating a long peri-od of slope instability.

The high sedimentation rate may have led to

a build-up of excess pore water pressure, perhaps withadditional pressure caused by gas bubbles, and may inturn have led to unstable sediments within relativelylarge parts of the Norwegian — Greenland Sea continen-tal margin. Triggering might have been prompted byearthquakes or by decomposition of gas hydrates.

Trough mouth fans (TMF) are fans at the mouths of transverse troughs/channels on presently or formerlyglaciated continental shelves. In the Norwegian — Greenland Sea, seven TMFs have been identied (theNorth Sea, Bear Island, Storfjorden, Bellsund, Isfjor-

den, Kongsfjorden and Scoresby Sund TMFs). Thearea of the TMFs varies from 2700 km (KongsfjordTMF) to 215000 km (the Bear Island TMF).

The Trough Mouth Fans are depocentres of sedi-ments accumulated in front of ice streams draining thelarge Northwest European ice sheets (Barents Sea,Fennoscandian and British ice sheets) and the Green-land Ice Sheet. The sediments deposited at the shelf break/upper slope by the ice stream were remobilizedand transported downslope, mostly as debris ows.

Besides being a locus for sediment deposition, theTrough Mouth Fans were also the main sites of freshwater supply to the oceans in front of glaciated margins(mainly in the form of icebergs) during the mid/latePleistocene ice ages. The Trough Mouth Fans hold thepotential for giving information about the various icestreams feeding them with regard to velocity and icedischarge.

Two large deep-sea channel systems have been ob-served along the Norwegian continental margin, the



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Lofoten Basin Channel and the Inbis Channel. Alongthe East Greenland margin, several channel systemshave been identied.

The deep-sea channels may have been formed bydense water originating from cooling, sea-ice forma-tion and brine rejection close to the glacier margin orthey may originate from small slides on the upper slopetransforming into debris ows and turbidity currents.

ACKNOWLEDGEMENTS

We thank J.P. Holm and A. Igesund who made thenal drawings and P. Vogt and M. Stoker for theircritical review.

REFERENCES

Aagaard, K., Darnall, C., Foldvik, A. and Toerresen, T. (1985) FramStrait Current Measurements 1985— 1986. Report no. 63. Jointdata report from University of Bergen, Department of Oceanog-raphy, Geophysical Institute, Bergen, Norway.

Aksu, A.E. and Hiscott, R.N. (1992) Shingled Quaternary debris owlenses on the north-east Newfoundland Slope. Sedimentology 39,193— 206.

Allen, J.R.L. (1982) Sedimentary Structures , ¹ heir Character andPhysical Basis . Developments in Sedimentology , 30B. Elsevier,Amsterdam, 663 pp.

Alley, R.B., Blankenship, D.D., Rooney, S.T. and Bentley, C.R. (1989)Sedimentation beneath ice shelves — the view from ice stream B.

Marine Geology 85, 101— 120.Andersen, E.S., Solheim, A. and Elverh + i, A. (1994) Development of

a glaciated continental margin: Exemplied by the western mar-gin of Svalbard. In : Thunston, D.K. and Fujita, K. (eds), Interna -tional Conference on Arctic Margins , pp. 155 — 160. ProceedingsAnchorage, Alaska 1992. U.S. Department of the Interior, Min-eral Management Service, Alaska Outer Continental Shelf Re-gion; OCS Study, MMS 94-0040.

Andreassen, K. and Hansen, T. (1995) Inferred gas hydrates offshoreNorway and Svalbard. In : Andreassen, K. Seismic reectionsasociated with submarine gas hydrales. Dr. Scient. thesis, Univer-sity of Tromsy, Norway.

Bard, E., Arnold, M., Mangerud, J., Paterne, M., Labeyrie, L., Dup-rat, J., Mé liè res, M.-A., S + nstegaard, E. and Duplessy, J.-C. (1994)The North Atlantic atmosphere — sea surface C gradient duringthe Younger Dryas climatic event. Earth and Planetary Science¸ etters 126, 275— 287.

Belderson, R.H., Kenyon, N.H., Stride, A.H., and Pelton, C.D. (1984)A ‘braided’ distributary system on the Orinoco deep-sea fan.Marine Geology 56, 195— 206.

Blaume, F. (1992) Hochakkumulationsgebiete am NorwegischenKontinentalhang: Sedimentologische Abbilder Topographie-gefü hrter Strö mungsmuster. Report Sonderforschungsbereich 313(36), 1— 151.

Blumsack, S.L. and Weatherly, G.L. (1989) Observations of thenearby ow and a model for the growth of mud waves. Deep-SeaResearch 36, 1327— 1339.

Boulton, G.S. (1979) Processes of glacier erosion on different substra-ta. Journal of Glaciology 23, 15— 38.

Bugge, T. (1983) Submarine Slides on the Norwegian ContinentalMargin , with Special Emphasis on the Storegga Area . ContinentalShelf and Petroleum Research Institute Publication, 110, 152 pp.Trondheim, Norway.

Bugge, T., Befring, S., Belderson, R.H., Eidvin, T., Jansen, E.,Kenyon, N.H., Holtedahl, H. and Sejrup, H.P. (1987) A giantthree-stage submarine slide off Norway. Geo -Marine ¸ etters 7,191— 198.

Bugge, T., Belderson, R.H. and Kenyon, N.H. (1988) The StoreggaSlide. Philosophical ¹ ransactions of the Royal Society of ¸ ondon325, 357— 388.

Bungum, H., Alsaker, A., Kvamme, L.B. and Hansen, R.A. (1991)Seismicity and seismotectonics of Norway and nearby continentalshelf areas. Journal of Geophysical Research 96 (B2), 2249— 2265.

Clift, P. (1996) Plume tectonics as a cause of mass wasting on thesouth east Greenland continental margin. Marine and PetroleumGeology 13, 771— 780.

Crane, K. and Solheim, A. (eds) (1995) Sea oor atlas of the northernNorwegian — Greenland Sea. Norsk Polarinstitutt Meddelelser137 , 172 pp.

Damuth, J.E. (1978) Echo character of the Norwegian — GreenlandSea: relationship to Quaternary sedimentation. Marine Geology28, 1— 36.

Dowdeswell, J.A., Uenzelmann-Neben, G., Whittington, R.J. andMarienfeld, P. (1994) The Late Quaternary sedimentary record inScoresby Sund, East Greenland . Boreas 23, 294— 310.

Dowdeswell, J.A. and Kenyon, N.H. (1995) Crui

the norwegian-greenland sea continental margins, morphology and late quaternary sedimentary...

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