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

GLOBALAND PLANETARY CHANGE

ELSEVIER

Global and Planetary Change 12 (1996) 53-74

Late Cenozoic evolution of the western Barents Sea-Svalbard continental margin Jan Inge Faleide a, *, Anders Solheim b Anne Fiedler b, Befit O. Hjelstuen Espen S. Andersen a, Kris Vanneste c

a

a Department of Geology, University of Oslo, P.O. Box 1047, Blindern, N-O316Oslo, Norway Norwegtan Polar Insntute, P.O. Box 5072, Majorstua, N-O3Ol Oslo, Norway c Renard Centre of Marine Geology, University of Gent, Krijgslaan 281, B-9OOOGent, Belgium b

.

,

Received 28 November 1994; accepted 11 May 1995

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

1. Introduction The western Barents Sea and Svalbard continental margin extends about 1000 km in a n o r t h - s o u t h direction (Fig. 1). The plate tectonic evolution of the margin and the spreading history o f the N o r w e g i a n Greenland Sea are well established through several studies (Talwani and Eldholm, 1977; Reksnes and * Corresponding author.

V~gnes, 1985; Eldholm et al., 1987; Faleide et al., 1991). A large number of geological and geophysical investigations have been carried out during the last two decades, but no attempt has been made to interpret the sedimentological evolution o f the entire margin. The main reason for this has been the lack of regional seismic lines with which to correlate borehole data. Limited stratigraphic control remains the major limitation for a detailed analysis of the margin.

0921-8181/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved SSDI 0921-8181(95)00012-7

J.l. Faleide et a l . / Global and Planetary Change 12 (1996) 53-74

54

However, recently published results from both exploration wells (Eidvin et al., 1993, 1994) and shallow boreholes (S~ettem et al., 1992, 1994; M~rk and Duncan, 1993) from the southwestern Barents Sea have provided new and significant contributions to the understanding of the evolution of the southern part of the margin. The results have supported the suggestion that the area was fed by sediments from the Barents Sea region. Based on Pliocene ages established for large parts of the sedimentary section on the southwestern Barents Sea margin, a late Cenozoic erosion in the order of 1 km in the central Barents Sea was proposed (Eidvin and Riis, 1989). These new results have during the last few years given rise to an increased discussion of the glacial evolution of the Barents Sea margin. In the present study, key seismic lines are used to correlate seismic sequences along the entire western Barents Sea and Svalbard margin (Fig. 2). The paper will focus mainly on the younger part of the sedimentary succession which is interpreted to be of

20"

0°

glacial origin with less emphasis given to the preglacial deposits. The main objectives of the study are: --Seismic identification and correlation of the base of the glacial sediments in order to determine its stratigraphic position and age of the onset of glaciations in this region. --Correlation of the main seismic sequences together with a study of the lateral and vertical changes in seismic character in order to document spatial and temporal variations in the paleoclimatic and sedimentologic evolution of the margin. --Estimation of erosional and depositional rates and their temporal and spatial variations in order to improve the understanding of the glacial history of Svalbard and the Barents Sea. This volume also includes two complementary papers which document and discuss the most prominent fans along the western Barents Sea margin, notably the Bjornoya Fan (Fiedler and Faleide, 1996) and the Storfjorden Fan (Hjelstuen et al., 1996). The

20 °

40 °

60"

80"

80 °

70"

70 °

60"

60 ° 20 °

0°

20 °

40"

60 °

Fig. 1. Location o f the study a r e a along the western Barents S e a - S v a l b a r d continental margin. Selected b a t h y m e t r i c contours (500, 1000, 2 0 0 0 m). B T = B j o r n o y a T r o u g h , LB = Lofoten Basin, NGS = N o r w e g i a n - G r e e n l a n d Sea, ST = Storfjorden T r o u g h .

J.I. Faleide et al. / Global and Planetary Change 12 (1996) 5 3 - 7 4 0°

10 °

20 °

o

55 30 °

~ ]

Magnetic lineations

~

Multichannel seismic lines km

200

78 °

GREENLAND SEA

76 ° 76 °

BARENTS SEA

BJ~RN®YA 74 °

... ..f/./"

/

.... ...j

-f'""

--'1/"

72 °

..-- ..............

jf

j--/"f

..... .- k,,g "¸ ....... 7 ---"

70 ° -

LOFOTEN ~ BASIN ~ ..................

. .....

............... ~.i7

70 °

I

10 °

20 °

Fig. 2. Location of regional seismic lines and boreholes used in this study. Thick lines show location of the regional profiles 1-6 presented in Figs. 5-8. BeT = Bellsund Trough, HR = Hovgaard Ridge, IT = lsfjorden Trough, K T = Kongsfjorden Trough.

56

J.l. F a l e i d e et al. / G l o b a l a n d P l a n e t a r y C h a n g e 12 ( 1 9 9 6 ) 5 3 - 7 4

0°

10 °

20 °

30 °

80 ° 1

- -

i

2oo0

2

..... 5

3

. . . .

80 °

4 ~\~

5 y//~

6

78 °

7

78 °

/ bi I

"

\

I

~

\

/

76 ° 76 °

74 ° • -- -,I/

s.S'° ! "IN

74 °

s Is ~ t

i /

s

LH

,

,

72 ° • _

..... ~i

.....

70 °

_

'<

~V5

/

"20" ~ " ~ "

::::::::::::::::::::: •..

24A--

- ~22.-'" 2

2

..... :iii!....................... ~............ 100 krn

~

70 °

,

Polar Stereographic

10 °

15 °

20 °

25 °

J.l. Faleide et al. / Global and Planetary Change 12 (1996) 5 3 - 7 4

sequence stratigraphic framework of the present paper forms the basis for discussions of mass balance studies focussing on Late Cenozoic erosion, sediment yield and paleoenvironment in the western Barents Sea.

2. Geological background 2.1. Topography The present-day topography of the Barents Sea is influenced partly by the underlying bedrock and structural trends, but also by moulding by late Cenozoic glacial erosion. It is characterized by relatively shallow banks separated by deep troughs. Along the western margin, the Bjomoya and Storfjorden Troughs represent the most prominent morphological features (Fig. 1 and 2). Similar, but smaller, troughs are found along the western Svalbard margin, forming the westerly continuation of fjords in Svalbard extending across the relatively narrow shelf. The most prominent troughs along the western Svalbard margin are the Bellsund-, lsfjorden- and Kongsfjorden Troughs (Fig. 2). Large submarine fans, reflected as seaward-convex bulges in the bathymetry, are found at the mouth of each of the troughs (Figs. 1 and 2). The size of the individual fans reflects both the size of the troughs and their corresponding drainage area. The Bjornoya Fan is by far the largest (comparable in areal extent with the Amazon and Mississippi Fans) and the fans along the Svalbard margin are the smallest. In general, the continental slope exhibits a smooth bathymetry, essentially lacking canyons or significant channels. Within the Bjornoya Fan however, the bathymetry is modified by a major slide scar at its southern flank (Kristoffersen et al., 1978; Laberg and Vorren, 1993). High-resolution seismic surveys and SeaMARC II side-scan sonar investigations have

57

revealed an extensive system of debris flows with associated shallow channels on the Bjom0ya Fan (Vogt et al., 1990, 1993; Laberg and Vorren, 1996; Crane and Solheim, 1995). The slope gradient varies from less than 1° in the south to about 4 ° adjacent to Isfjorden on Svalbard. The width of the continental slope varies also in a N - S direction, due to the asymmetric location of the active spreading centre, the Knipovich Ridge, within the Greenland Sea. North of Isfjorden the proximity of the Knipovich Ridge has permitted the glacial sediments partly to bury the spreading axis. Further south the distance between the shelf edge and spreading axis increases.

2.2. Plate tectonic framework and pre-glacial geological evolution The western Barents Sea and Svalbard continental margin consists of three main structural segments (Fig. 3) (Faleide et al., 1991, Faleide et al., 1993): (1) a southern sheared margin along the Senja Fracture Zone (70-72°30'N), (2) a central rift complex associated with volcanism (72°30'-75°N) and (3) a northern initially sheared, and later rifted, margin along the Homsund Fault Zone (75-80°N). The evolution of the western Barents Sea as a passive shear margin is closely linked to the gradual northward opening of the Norwegian-Greenland Sea (Talwani and Eldholm, 1977; Myhre et al., 1982; Reksnes and V~ignes, 1985; Eldholm et al., 1987). Cenozoic sea floor spreading in the NorwegianGreenland Sea and Eurasia Basin began at the Paleocene-Eocene transition (anomaly 25/24B time; ca. 57 Ma). The Eocene opening history is well constrained by dated magnetic lineations (anomalies A24-A13) in the Lofoten Basin west of the Senja Fracture Zone. Larger uncertainties are however associated with the initiation of opening of the southem Greenland Sea. Myhre et al. (1982) proposed

Fig. 3. Main structural features along the western Barents S e a - S v a l b a r d margin (Faleide et al., 1991. Faleide et al., 1993). 1 = bathymetry (m), 2 = magnetic lineations, 3 = limit of identified oceanic crust on the seismic sections, 4 = Vestbakken Volcanic Province, 5 = stretched Tertiary continental crust, 6 = salt, 7 = faults, B B = B j o m 0 y a Basin, CB = Central Basin, F P = Finnmark Platform, H B = Harstad Basin, HfB = H a m m e r f e s t Basin, H F Z = Hornsund Fault Zone, K R = Knipovich Ridge, L B = Lofoten Basin, L H = Loppa High, M F Z = Molloy Fracture Zone, M R = Molloy Ridge, SB = S0rvestsnaget Basin, S F Z = Senja Fracture Zone, S H = Stappen High, S p F Z = Spitsbergen Fracture Zone, SR = Senja Ridge, TB = TromsO Basin.

58

J.l. Faleide et a l . / Global and Planetary Change 12 (1996) 53-74

initial sea floor spreading at anomaly 21 time (47 Ma). However, reconstructions by Reksnes and Vltgnes (1985) indicate that the southern part of the basin is somewhat older and probably started to open at about anomaly 23 time (52 Ma). In earliest Oligocene time (anomaly 13; 35 Ma) the opening direction altered orientation, giving rise to further extension and the opening of the northern Greenland Sea as well. Compressional structures of the Spitsbergen fold and thrust belt, formed mainly during late Paleocene-Eocene dextral shear movements, collapsed and grabens developed along the Svalbard margin (Schlfiter and Hinz, 1978; Eiken and Austegard, 1987). Since Oligocene time oceanic crust has been formed along the whole Barents Sea margin followed by subsidence and accumulation of a thick Late Cenozoic sedimentary wedge fed by erosional products from the Barents Shelf and Svalbard. 2.3. Glacial history Results from Ocean Drilling Program (ODP) sites on the Voring Plateau (Jansen and Sjoholm, 1991), indicate that glaciation of the northern hemisphere may have started as early as 5.5 Ma, or even earlier. Based on recent results from ODP Leg 151 (Myhre et al., 1995) and Leg 152 (Larsen et al., 1994), the earliest phases of glaciation may have occurred in southern Greenland in the Late Miocene. At approximately 2.6 Ma, a deterioration of the climate occurred and the glaciations became more regionally extensive. Local, alpine, high-Arctic regions, such as Svalbard, may, however, have had limited glaciations well prior to 2.6 Ma. After a transitional period between 1.2 and 0.8 Ma, a period of even greater climatic fluctuations followed, with colder and more intense glaciations alternating with warmer and longer interglacials, involving a shift in predominance from 40 k.y. to 100 k.y. cyclicity. This is documented in records of ice-rafted detritus (IRD) from the Norwegian Sea (Jansen et al., 1988; Jansen and Sjoholm, 1991) and in global oxygen isotope records (Shackleton et al., 1984; Raymo et al., 1989; Ruddiman et al., 1989). Seismic stratigraphic interpretations of high-resolution, single-channel seismic records (Solheim and Kristoffersen, 1984; Vorren et al., 1988) have indi-

cated that at least five glacial advances reached the shelf break in the Bj0moya Trough. A firm age control is not established for all these advances, but S~ettem et al. (1992) found morphologic evidence of glacial advance to the outermost Bjorn0ya Trough at their lowermost unit A 0 time, probably corresponding to the late Pliocene. Furthermore, amino acid analyses of material from shallow boreholes in the same area seem to indicate at least four major advances in the period between 440 ka and 130 ka (S~ettem et al., 1992). Hence, despite the uncertainties in the precise chronology, several lines of evidence point towards repeated glacial coverage of the Barents Sea during the Pleistocene. This is also supported by the young ages (late Pliocene-Pleistocene) reported by Eidvin et al. (1993, Eidvin et al. (1994) and S~ettem et al. (1992, S~ettem et al. (1994) for a main part of the Bjom0ya Fan sediments. Most of the unlithified sediments encountered in the Barents Sea are glacial and glaciomarine diamictons deposited during the last glaciation of the area, the Late Weichselian, which had its maximum extent at 18-20 ka. There is evidence for a grounded Late Weichselian glacier over the major part of the Barents Sea that reached the western margin (Vorren et al., 1988; Solheim et al., 1990; Elverhoi et al., 1990). At the west coast of Svalbard, three glacial advances are recorded during the Weichselian (115-10 ka) (Mangerud et al., 1992).

3. Seismic data

Several institutions have carried out seismic surveys along the western Barents Sea and Svalbard margin. In the present study we have mainly used selected seismic lines acquired by the Norwegian Petroleum Directorate (NPD) together with regional lines acquired by various universities (Fig. 2). The most important lines for the regional correlation between the sedimentary fans along the margin are the University of Bergen line BU-1 and NPD 1430. These are long strike-lines which cover the continental slope along most of the margin (Fig. 2). Line NPD 7620 was used to tie the two regional strikelines. The interpretation of regional profiles acquired by the University of Kiel, Germany, and covering the lower slope and basin floor (73-75°N; Fig. 2),

J.l. Faleide et al. / Global and Planetary Change 12 (1996) 53-74

strengthened the correlation between the Bjomoya and Storfjorden Fans. More detailed studies of individual submarine fans along the margin have been performed on denser grids of seismic data (Fiedler, 1992; Fiedler and Faleide, 1996; Hjelstuen, 1993; Hjelstuen et al., 1996; Andersen et al., 1994; Solheim et al., 1996). Seismic data from the Svalbard margin are of variable quality. On the deep continental slope and rise, the data quality is generally good, although the resolution of reflectors is variable. In shallow water however, sea floor multiples have caused large problems, and only a few surveys have yielded high quality data from the continental shelf area west of Svalbard. Most of the data from the Storfjorden Fan are of good quality as a result of modem acquisition techniques and successful reprocessing of older data. In the Bjcmoya Fan, the data quality varies. The oldest NPD-lines and the BFB/BGR-lines are characterized by multiples and poor resolution. The more recent data are of better quality with much of the multiple energy removed.

SVALBARD MARGIN 77"- 80"N SchlOter & Hinz (1978) Myhre & Eldholm (1988)

4. Seismic stratigraphy 4.1. Regional correlation Schli~ter and Hinz (1978) defined three seismic sequences offshore central Spitsbergen, SPI-I, SPI-II and SPI-III, separated by two unconformities, U1 and U2, respectively (Fig. 4). Sequence SPI-II exhibits a chaotic seismic character which is clearly different from both SPI-I and SPI-III. This has been interpreted in different ways. Schli~ter and Hinz (1978) and Myhre and Eldholm (1988) explained the chaotic character as resulting from sediments derived from mass movements triggered by high sedimentation rates. Eiken and Austegard (1987) related the chaotic character to mud diapirism, while Eiken and Hinz (1993) interpreted the chaotic reflection pattern to represent contourite deposits based on a comparison with similar observations from the Blake Outer Ridge. According to Schliiter and Hinz (1978), SPI-I consisted of Plio-Pleistocene glaciomarine sediments

BARENTS SEA MARGIN 70" - 7T N

This study~

G III

-R,~ ~

BARENTS SEA MARGIN 70"" 74" N Smttem et a1.(1991) Sasttem et aL(1992) Saettem et a1.(1994)

Eidvin& RUs (1989) Eidvinet al. ( 1 9 9 3 )

8-G o.,~-

59

< 0.44

Vorren et aL (1991) Richardsen et aL (1993) Knutsen et al. (1993) TeE

Re;;,6,c;or I

0.8

-'R2SPI-I A

TeD

GII Late Riocene/ Pleistocene

-R4"

-As-"~-~I.O-UI SPI-II 4 - - 5 . 5 ~ U ~ SPI-III

Late Pliocene/ Pleistocene

Reflector2 Ao

R6

-R7 C~I

2.3

2 3 3.0 / 5.5

TeC

Reflec~r3

GO

15.5 TeA-TeB

55

1Faleide et al. -I Hjelstuen et al. j % This volume Fiedler and Falelde

2 Vorren et al. (1991) 3 Richardsen et al. (1993) 4 Myhre & Eldholm (1988)

Fig. 4. Correlation of seismic sequences along the western Barents Sea-Svalbard margin with suggested ages (Ma) for the main sequence boundaries, and comparison with previously published stratigraphies (S~ettem et al., 1991).

J.l. Faleide et a l . / Global and Planetary Change 12 (1996) 53-74

60

and turbidites, while SPI-II consisted of Pliocene sediments and U2 represented a hiatus extending from pre-Middle Oligocene to Pliocene. Myhre et al. (1982) and Myhre and Eldholm (1988) argued that U2 was younger, and suggested a maximum age of 5.5 Ma based on the age of the underlying oceanic basement. Furthermore, Myhre and Eldholm (1988) proposed that the interpreted mass movements resulting in sequence SPI-II were due to drastically increased sedimentation rates after U2 time. In the present study U1 and U2 are termed R6 and R7, respectively (Fig. 4). These unconformities are important horizons in the regional correlation along the margin. Compared to earlier studies we have obtained an improved data base both for the regional correlation, and for the assignment of age brackets to

W

the main sequences. This improvement can be attributed to better data quality and greater seismic coverage, together with the stratigraphic constraints obtained from wells in the southwestern Barents Sea. Seven regionally significant reflectors (R1-R7) have been identified between oceanic basement and the sea floor along the margin (Fig. 4). The regional seismic sequences are well exemplified by a dip-line west of Svalbard (Fig. 5). The sequence between R7 and R6, corresponding to SPI-II of Schliater and Hinz (1978), is characterized by a chaotic reflection pattern with a lack of continuous internal reflectors, and by an eastward (landward) thinning of the sequence. In contrast, the sequences above R6 are well stratified, particularly the uppermost sequence, and have internal reflectors of great lateral extent. Both

KR

E

0 2

4

2

,

]

R6

/

I'n

@

"

0 I

km

-4

25

6

6 S lwt

StWt

, : I i

: ' ! I

: : i

, : I !'

:

t

! ~ ~" r ! r

~ i ~ ~

~ 4' ! : i:.r: i U ~ IT:

P--: ! t : l-r I I. I I

!-p i I

I I I

i 'l t I

' : ! !

! F I-

!-~--~ i !'~-I t F- I ! r i t "E-I ;U*~ [ t I : I I "t ¢

[ } r

! t i r

: , [ i

. . . . . , I '[ [ ~ ~l ~

; i q

~

i : i ~ " ~

' I :

! ~-~'!'i , ~ I i ": ~ ~ -.

~

, ..----'~ .

.~ , ~ ~. -- ~-,~--.~-.5

Fig. 5. Seismic line BEL-1 across the Svalbard margin. Location in Fig. 2 and reflector code in Fig. 4. Thick line = top oceanic basement, KR = Knipovich Ridge. Seismic example shows chaotic reflection pattern between R7 and R6.

J.l. Faleide et al. / Global and Planetary Change 12 (1996) 53-74

61

!

O0

----___. o

co ~r o to

Z

t'q

Ko.j

e

r~

o

o o.I ¢D

/

Z

o

E

8~ e~

o (9 o~

6

"-~Z

0 .*-~ .r'~

Z I

i

I

}

{

I

.~'~ ~

>

J.l. Faleide et al. / Global and Planetary Change 12 (1996) 53-74

62

R5 and R4 form important sequence boundaries on the Svalbard margin. The post-R5 seismic stratigraphy and an interpretation of depositional processes on the Svalbard margin are discussed by Solheim et al. (1996). The combined strike-line consisting of BU-1 and NPD 1430, linked by NPD 7620 (Fig. 6), shows the fan development along the margin. In the period corresponding to deposition of the sequence between R7 and R6, the Storfjorden Fan was the most important depocentre in the northern part of the region. This sequence changes character from north to south. The chaotic internal reflection pattern observed adjacent to the Svalbard margin and within the Storfjorden Fan disappears southwards and the sequence thins at the northern flank of the Bj0rnoya Fan. Further south, within the Bjornoya Fan proper, the sequence thickens again, but is now stratified. Interpretation of the NPD lines 1430, 1500 and 1530 (Fig. 2), which cross the upper continental slope and outer shelf, does not fully resolve uncertainties in the

W

north-south correlation at the northern flank of the Bj0rnoya Fan, where reflectors R7, R6 and R5 interfere with a strong sea floor multiple. North-south seismic lines farther west along the deeper parts of the slope between 73°N and 75°N (Fig. 2) support the regional correlation as described. However, there are still some uncertainties resulting from the limited record length and multiples present in these lines. R5 forms a well-defined erosional surface within the Storfjorden Fan (Fig. 7). The sequence between R6 and R5 thins significantly at the northern flank of the Bjorn0ya Fan (line NPD 1430; Fig. 6) before R6 is apparently truncated by R5 within the fan proper. This is also indicated in the east-west lines (Fig. 8). In the southwestern Barents Sea, reflector R5 truncates Paleogene strata east of the Senja Ridge (Fig. 9). Erosional channels of the same age have been reported by S~ettem et al. (1992) south of Bj0rnoya. Within the Bj0rn0ya Fan, the sequences younger than R5 are characterized by reflection patterns interpreted as representing sediments resulting from

DSDP

KR

,~.

HFZ E

o 2

(311

4 GO

68 $twt

stwt

KR

W

HFZ E o Gig GD

2 4 6

0

Rm

5O

8 slwl

slwt

Fig. 7. R e g i o n a l seismic lines across the Storfjorden Fan ( s h o w i n g seismic tie to D S D P Site 344). L o c a t i o n in Fig. 2 and reflector code in Fig. 4. OB (thick line) = top oceanic basement, HFZ = H o r n s u n d Fault Z o n e , KR = K n i p o v i c h Ridge.

63

J.l. Faleide et al. / Global and Planetary Change 12 (1996) 53-74

~a

i

o

Iii

t",q

.~ ;> ,..,

II

,,,,<

r~No

,.el

tl

,.~-o ¢0

()

.u

II

t~

o

J.l. Faleide et al. / Global and Planetary Change 12 (1996) 53-74

64

~_

~b

II

@

@

LI.I

E

Z r,n Q o> 0 rr F-

o III ,_1 n"

ku

E~

-~

u!~o!~

~.

~-

~:

oo en ku. Z oO 'mr.,O u.J rr ruO

! ~'"' ~i~k~ Zl~i ~:~

o

J.l. Faleide et al. / Global and Planetary Change 12 (1996) 5 3 - 7 4

65

Q

kl..l

I

I

I

I r

~5

II

Z

o e~

H e~

.=.

®

~

Ill

66

J.l. Faleide et a l . / Global and Planetary Change 12 (1996) 53-74

$ SVALBARD MARGIN

STORFJORDEN FAN

~ RI R2

~ ~

BJ~RN~fA FAN

~__

Ro I

R1

R'I

R2 ~

R2 - -

AGE

~, ,c o°44 Me

~

•

R6

R6

R5 ~

~ 1.0Ma 2.3Ma

Fig. 11. Seismic stratigraphic framework. Correlation of main seismic sequences between the Bj~rn~ya, Storfjorden and lsfjorden Fans. Internal reflection pattern varying from stratified to chaotic also indicated. OB = top oceanic basement.

large-scale mass movements (Fig. 10). They are somewhat different in character from those within the chaotic sequence between R7 and R6, adjacent to Svalbard, showing a greater predominance of larger scale structures. However, the implications for the sedimentation history are similar and the sequences are interpreted to result from increased sediment supply to the outer shelf, and subsequent mass movements caused by an unstable sediment configuration. Details of the structure of the Bjornoya Fan are presented by Fiedler and Faleide (1996), while Kuvaas and Kristoffersen (1996) discuss mass movements in the same area. The seismic character for the upper sequences is more uniform along the margin (Fig. 6). High resolution, single channel seismic data from the Svalbard margin have shown that the sequences above R4 in the Isfjorden Fan have a seismic character indicative of small-scale slumps (Andersen et al., 1994). Laberg

,5

~

"7

-0

SEA FLOOR

GHI 500.'

,~

/

O fl-

- 5o(3

1:11 ?

,,'

,~

•

2i

GII

ttl o

"R5 20O0

il I

2500-I (m) |

l

<~ vv v

-lOO0

-1500

BASEMENT(OR SILL?)

(m)

Fig. 12. Correlation of Late Cenozoic sequences in exploration wells and shallow boreholes from the Senja Ridge to the Knipovich Ridge. Location in Fig. 2.

J.L Faleide et a l . / Global and Planetary Change 12 (1996) 53-74

and Vorren (1996) have suggested that sediments younger than R1 within the Bjornoya Fan consist of overlapping lobes of laterally extensive debris flows. However, seismic character equivalent to the chaotic structures seen between R7 and R6 in the north, and between R5 and R2 in the south, are not observed in the youngest sequences. The boundary between the pre-glacial bedrock and the thin cover of glacial deposits on the continental shelf is termed the Upper Regional Unconformity (URU) (Solheim and Kristoffersen, 1984). Although direct correlation between the URU and the seismic stratigraphy defined at the margin is not straightforward, the seismic data used in this study indicate that the URU corresponds to progressively older slope reflectors from south to north along the outermost continental shelf (Fig. 11). In the Bj0rnoya Fan, URU corresponds to R1 (Fiedler and Faleide, 1996), whereas it corresponds to R3 in the Storfjorden Fan (Hjelstuen et al., 1996), and most likely to R5 in the Isfjorden Fan (Solheim et al., 1996). The regional correlation of the main seismic sequences is summarized in Fig. 11.

4.2. Chronology The age constraints for the seismic stratigraphic interpretation are sparse, and widely scattered and consequently, the possibilities for a detailed chronologic analysis of the margin evolution are restricted. Chronostratigraphic control is best for reflector R7 and the evidence can be summarized as follows (Figs. 2 and 12): --Plate tectonic evolution and dating of magnetic anomaly lineations in the oceanic basement (Talwani and Eldholm, 1977; Reksnes and V~tgnes, 1985; Fiedler, 1992). - - D S D P Site 344 at the eastern flank of the Knipovich Ridge (Talwani, Udintsev et al., 1976). - - D e e p exploration wells on the Senja Ridge in the southwestern Barents Sea (Eidvin and Riis, 1989; Eidvin et al., 1993), and southwest of Bjornoya (Eidvin et al., 1994). --Shallow boreholes in the outer parts of the Bj0rn0ya Trough (S~ettem et al., 1992, S~ettem et al., 1994; Mork and Duncan, 1993). - - I n addition, interpretations of the general paleo-

67

climatic evolution, based on ODP boreholes in the adjacent Norwegian Sea (Jansen and Sjoholm, 1991) may be used for support. The determination of maximum ages based on the termination of sequence boundaries against oceanic basement of known age has been performed successfully for a series of pre-glacial sequences in the Lofoten Basin (Fiedler, 1992; Fiedler and Faleide, 1996). However, for the younger sequences greater uncertainties are associated with this method due to the large relief of the oceanic basement near the spreading axis at the Mohns and Knipovich Ridges. R7 can be traced to its termination against oceanic basement 40-45 km from the present plate boundary at the Knipovich Ridge (Fig. 7). Projected onto flow-lines along the opening direction, this corresponds to 45-50 km. With an average spreading rate of 0.93 c m / y r in the southern Greenland Sea since anomaly 5 time (10 Ma) (Reksnes and V~ignes, 1985) this gives a maximum age of the sediments in the overlying sequence of 4.8-5.4 m.y. However, the sediments are probably younger than this, as the increasing basement relief limits the proximity to the spreading axis to which R7 can be identified with certainty. The results from DSDP Site 344 (Talwani, Udintsev et al., 1976) support a Pliocene age for R7. A seismic line published by Eiken and Hinz (1993) correlates the borehole to the seismic lines at the Svalbard margin. Though somewhat uncertain, a Pliocene age is suggested for the lowermost glacially influenced sediments, and these appear to be contained within the seismic sequence SPI-II of Schliiter and Hinz (1978) between R7 (U2) and R6 (U1) (Fig. 7). The unconformity R7 is tied seismically to exploration wells 7117/9-1 and 7117/9-2 on the Senja Ridge (Figs. 2 and 8 and 12) (Eidvin and Riis, 1989; Eidvin et al., 1993), where it corresponds to the base of the glacial sediments. Based on biostratigraphy, Eidvin et al. (1993) give the boundary an age slightly older than 2.3 Ma, whereas strontium-isotope analysis and correlation with the results from ODP boreholes on the Voring Plateau (Jansen et al., 1988), indicate 2.6 Ma. Reflector R7 has also been tied to well 7316/5-1 situated southwest of Bjorn0ya (Figs. 2 and 8 and 12), where glacially derived Upper Pliocene and Pleistocene sediments rest uncon-

68

J.l. Faleide et al. / Global and Planetary Change 12 (1996) 53-74

formably on a Lower Miocene sequence (Eidvin et al., 1994). A late Pliocene-Pleistocene age for the entire Late Cenozoic sedimentary wedge of the Bj0rn0ya Fan is further supported by recently published results from shallow boreholes southwest of Bj0rn0ya (Figs. 2 and 12) (Mork and Duncan, 1993; S~ettem et al., 1994). Two volcanic clasts from a core (7316/03-U01) just below the base of the wedge have been dated by the 4°Ar-39Ar method, indicating a late Pliocene age for the volcanism (2.35 + 0.12 Ma and 2.20 + 0.12 Ma). Boreholes on the Knipovich Ridge, the Senja Ridge and southwest of Bjornoya all show that glacial sediments are present in the sequence between R7 and R6 (Fig. 12). From this, and the seismic character of the same sequence at the northern part of the margin, we interpret this sequence to represent the first significant phase of extensive glaciation of the outer continental shelf along the Svalbard and Barents Sea margin. From the discussion above, the likely age of reflector R7 is about 2.3 Ma. The only other regional reflector with a seismic tie to well information is R1, which can be traced to the shallow boreholes in the outer Bjornoya Trough (S~ettem et al., 1992). The sediments above R1 (URU) all belong to the Bruhnes normal polarity epoch, and must therefore be younger than 790 ka (the Brunhes-Matuyama boundary). Amino acid analyses further indicate an age younger than 440 ka. Extrapolation of calculated sedimentation rates in piston cores on the Svalbard margin, led Elverhoi et al. (1995) to assign an approximate age of 200 ka to R1 in this area. Hence, the likely age for R1 is between 440 ka and 200 ka. The ages of the horizons between R7 and R1 can only be inferred from general knowledge regarding major geologic events which may have affected deposition patterns during the late Cenozoic. R6 forms the top of the chaotic reflection pattern of sequence R7 to R6 (SPI-II) in the north (Figs. 5 and 6) but it is truncated by R5 within the Bjorn0ya Fan (Figs. 6 and 8). R5 represents a significant erosional surface within the Storfjorden Fan where it truncates R6 on the upper slope, and east of the Senja Ridge where it truncates Paleogene strata (Fig. 9). R5 also forms the base of the sequence characterized by chaotic reflection patterns within the Bj0rnoya Fan (Fig. 10). It is

AVERAGE

SEDIMENTATION

- AND

RATES

EROSION

(crn/l o =year)

126

z w nO

°

ii

k 172

SEDIMENTATION m

EROSION

Z < Q z Q

44.5

37

in

2.2 0.6 UNIT

GO

AGE

55 - 2.3

GI 2.3 - 1.0

Gill

GII 1.0 - 0.44

0.44 - 0

(Ma)

Fig. 13. Average sedimentation and erosion rates for the Storfjorden and Bj0rn0ya Fans based on Hjelstuen et al. (this issue) and Fiedler and Faleide (this issue), respectively. therefore interpreted to represent a hiatus resulting from the most significant change in sedimentation patterns during the time interval corresponding to the sequences between R7 and R1. The erosion may be the result of increased glacial activity on the shelf. By correlation with increased amounts of ice-rafted detritus (IRD) and oxygen- isotope measurements showing a shift in climatic cyclicity and amplitudes in the time period 1.2-0.8 Ma (Shackleton et al., 1984; Jansen et al., 1988; Raymo et al., 1989; Ruddiman et al., 1989; Thiede et al., 1989), this sequence boundary is assigned a likely age of about 1.0 Ma. 4.3. Rates of erosion and sedimentation Average erosion and sedimentation rates based on mass balance studies of the Bj0rnoya (Fiedler and Faleide, 1996) and Storfjorden (Hjelstuen et al., 1996) Fans, are summarized in Fig. 13. The rates exhibit great temporal and spatial variations which reflect the great importance of glacial processes in the Late Cenozoic evolution of the margin. The onset of glacially-dominated deposition gave

69

J.l. Faleide et a l . / Global and Planetary Change 12 (1996) 5 3 - 7 4

rise to a dramatic increase in erosion and sedimentation rates. The maximum rates are calculated for unit GII (R5-R1). A younger age for R1 will reduce the difference in rates calculated for units GII and GIII. 0°

The highest rate of erosion is calculated for the drainage area of the Storfjorden Fan. The average sedimentation rates are however, comparable for the two fans.

10 °

GREENLAND SEA

20

°

l.u o

76 °

BARENTS SEA

74

°

72

°

/ /

/

/

I

/

IIII/ / / '

I

/

l

I

/

LOFOTEN BASIN

c

i

I

i

I 70

\

\

\

x~ /

10 °

I --

20 °

Fig. 14. Isopach map of the glacial sediments (R7 to seafloor). Contour interval 0.5 s twt.

°

70

J.l. Faleide et aL / Global and Planetary Change 12 (1996) 53-74

4.4. Late Cenozoic evolution

Thick glacial sediments have been deposited above reflector R7 along the entire margin (Fig. 14). Although the Bjomoya Fan is volumetrically the largest system, the thickest glacial deposits are found within the Storfjorden Fan, where total thicknesses reach more than 3 s twt, corresponding to about 4.5 km (Hjelstuen et al., 1996). The Bjorn0ya Fan also reaches a maximum thickness of 3 s twt, but due to lower seismic velocities, this corresponds to about 3.5 km (Fiedler and Faleide, 1996). However, thicknesses of the order of 1.5 s twt (1.5-2 km) and greater have been recorded along the entire margin segment presented in this study. These thick glacial deposits represent an important record of the late Cenozoic development of the entire Barents Sea and Svalbard region. Based on the glacial sediment distribution, sparse age control, and in combination with the seismic stratigraphic interpretation, we relate the following sequence of important depositional events to the glacial history of the margin: --Glacially influenced deposition became dominant on the continental slope at about 2.3 Ma. This event is represented by the unconformity R7 which forms the most important sequence boundary observed on the seismic sections. This interpretation does not exclude the possibility of smaller scale glaciomarine deposition prior to this time. --Adjacent to Svalbard and the Storfjorden Trough, glaciers reached the shelf already in R7 time (2.3 Ma), transporting large volumes of glacial sediments to the outer shelf and upper slope. As a result of this, frequent mass movements of unstable sediments built out and formed sequences now observed exhibiting chaotic seismic character between R7 and R6 (Fig. 5). This chaotic character is best developed in the Storfjorden Fan, where the thickness of the sequence between R7 and R6 is at its maximum (Figs. 6 and 7). Further south, within the Bjornoya Fan, the earlier deposition appears to have occurred by means of less dynamic mechanisms, with less extensive gravity-driven mass transport in the form of slumps or debris flows. - - O n the southern part of the margin, the sequence boundary R5 appears to represent an important change in depositional style. It indicates a clear erosional unconformity on the outer shelf and upper

slope within the Storfjorden Fan (Fig. 7). Within the Bjornoya Fan, reflector R5 truncates reflector R6 and marks the apparent onset of large-scale mass movements in this region (Figs. 6, 8, 9 and 10). Most likely this was initiated by increased sediment supply, analogous to the processes described for the lower sequence further north, i.e. extensive ice sheets reached the shelf edge at this time. This may have been related to the general intensification of the northern hemisphere glaciation cycles as described by Jansen et al. (1988) and Jansen and Sjoholm (1991), which commenced sometime between 1.2 and 0.8 Ma. - - S i n c e R5 time, both the Svalbard shelf and the Barents Sea have been repeatedly covered by extensive ice sheets, most of which reached the shelf break. The Upper Regional Unconformity (URU) was developed over the entire shelf as a result of repeated glacial erosion, that reached deep, pre-glacial stratigraphic levels. - - S i n c e RI time (440-200 ka), the outer shelf in the southern Barents Sea has experienced a net accumulation and shelf aggradation. This transition from net erosion (forming URU) to net accumulation in the outer continental shelf areas took place progressively earlier towards the north; at R3 time in the Storfjorden Trough (Hjelstuen et al., 1996) and at R5 time west of Svalbard (Solheim et al., 1996). The change may be related to changes in glacial regime, sediment supply and differential subsidence.

5. Discussion

Recently published studies of the southwestern Barents Sea margin (Richardsen et al., 1991, Richardsen et al., 1993; Vorren et al., 1991; Knutsen et al., 1993) have emphasized correlations with Cenozoic sea level curves (Haq et al., 1988; Wornardt and Vail, 1990) as means of determining the ages of sequence boundaries within the Bjornoya Fan. Starting with an age of 0.8 Ma for the URU, ages of 3.0/5.5 Ma and 15.5 Ma were assigned to the base of their units TeD and TeC (equivalent to reflectors R5 and R7, Fig. 4), respectively. However, regional correlations presented in this paper show that sequence TeC (between R7 and R5) comprises glacial sediments which cannot be older than Pliocene, and

J.l. Faleide et aL / Global and Planetary Change 12 (1996) 53-74

are probably younger than 2.3 Ma. With an age of 15.5 Ma, sediments at the base of sequence TeC cannot occur overlying oceanic basement younger than 15.5 Ma (between anomalies 5 and 6) which, given calculated spreading rates, corresponds to a distance of about 130 km from the present spreading axis. However, the present study has shown that the base of this sequence can be followed to less than 50 km from the Knipovich Ridge (Fig. 7). Such evidence also supports a Pliocene age for this sequence. The age determinations from these two interpretations give rise to large discrepancies in the calculation of erosion and sedimentation rates. The present study has shown that the age of the basal unconformity (R7) of the glacial sequences is relatively well constrained. An age range between 440 and 200 ka for R1, seems also likely. The age of approximately 1 Ma for the intermediate reflector R5 discussed in this paper is based admittently on assumptions rather than confident seismic correlation or stratigraphic calibration. A paleoenvironmental change such as that between 1.2 and 0.8 Ma reported by Jansen et al. (1988) and Jansen and Sjoholm (1991) is likely to have had major consequences in terms of the depositional regime, and until ages are determined through drilling we consider 1 Ma as the most likely age for R5. The seismic character of the sequences along the margin indicates that increased sedimentation promoted by glaciers at the shelf edge occurred at R5 time within the Bjorn0ya Fan, and at R7 time within both the Storfjorden Fan and adjacent to Svalbard. This interpretation lends some support to assumptions regarding the age of R5. While glaciers extended across the narrow continental shelf off Svalbard and the Storfjorden Trough during the earliest glacial phases, later and extended glacial periods were required in order for large ice masses to accumulate and to extend to the shelf edge within the extensive, low relief Barents Sea platform. However, a distinct change in glacial regime appears to have taken place at approximately R5 time on Svalbard as well (Solheim et al., 1996), further indicating the regional importance of this paleoenvironmental event. The total Cenozoic erosion of Svalbard is calculated to be of the order of 3000 m (Manum and Throndsen, 1978). The archipelago must therefore have had an alpine relief throughout the Pliocene and

71

Pleistocene. Svalbard thus acted as a more effective source area for glaciers extending to Storfjorden and western margin areas, than the wide, lower relief Barents Sea platform, even though the latter may also have been emergent during the initial phases (Rasmussen and Fjeldskaar, 1996-this issue). Furthermore, a delayed glaciation of the Barents Sea platform implies that much of the glacial sediments produced during the earliest phases, in R7 to R5 time, may have been deposited temporarily in shelf basins and thus made readily available for mass wasting on the continental slope. The interpretation of the depositional evolution of the western Barents Sea and Svalbard margin is based primarily on observed seismic character and its lateral and vertical changes. The existence of chaotic seismic sequences with few and discontinuous internal reflections as well as frequent diffraction hyperbolae, is taken to indicate sediments deposited under gravity-driven mass transport. This in turn can be interpreted as resulting from the rapid build-up of unstable sediment masses from grounded glaciers supplied directly to the outer shelf and upper slope. The first appearance of this slump-dominated facies is taken as the first indication of extensive glaciation of the continental shelves. As observed in the depositional environment in present-day glaciated regions, most sediments are deposited in fjord basins or within a few kilometres of the ice front (Pfirman and Solheim, 1989; Syvitski, 1989; Elverhoi et al., 1995; Hooke and Elverhoi, 1996). Extensive glaciers are therefore required to explain the rapid deposition of large volumes of glacial sediments over a wide area at or near the shelf break. The high sedimentation rates calculated, indicate efficient mechanisms for transporting sediments to the margin. Since submarine fans are located off the main fjord systems and associated transverse shelf troughs, topographically controlled ice stream dynamics may have played a major role, with the fjords and troughs representing the location of former fastflowing ice streams, analogous to those documented in Antarctica (Alley et al., 1989). Glacial sediments can be transported by different mechanisms, including meltwater, englacial transport, or within a subglacial layer of deformation till (Alley et al., 1989; Hooke and Elverh0i, 1996). Subglacial deformation has by far the highest transport capacity (R. Hooke,

72

J.l. Faleide et al. / Global arm Planetary Change 12 (1996) 53-74

pers. comm., 1993), and is therefore considered the most important mechanism here. This was also concluded by S~ettem et al. (1992), based on sedimentological data from the Bjarn~ya Trough.

6. Summary and conclusions Until stratigraphic drilling provides improved age control and new data regarding both lithology and depositional processes, the following main conclusions can be inferred, based on the discussions in this paper: - - S e v e n significant seismic reflectors, R7 to R1, can be correlated along the entire western Barents Sea and Svalbard continental margin. The seismic sequences exhibit both vertical and lateral variations in acoustic character. --Seismic character with a lack of internal structure, disrupted reflectors and frequent diffraction hyperbolae are interpreted as being indicative of gravity-driven mass wasting. This process is in turn interpreted to result from increased sediment supply directly to the margin by advancing glaciers. - - R 7 marks the onset of glacially-dominated deposition along the margin. An age of approximately 2.3 Ma for R7 is likely. - - O t h e r age constraints include a probable age window of 440-200 ka for RI, while R5 may have been formed as a response to the climatic shift between 1.2 Ma and 0.8 Ma. --Glaciers reached the shelf break off Svalbard and the Storfjorden Trough in R7 time, while expansion to the shelf break in the southwestern Barents Sea was delayed until R5 time. - - A change from erosion to accumulation and aggradation of the outer shelf is seen all along the margin. The transition took place at times corresponding to R5 (approximately 1 Ma), R3, and R1 (440-200 ka) adjacent to Svalbard, the Storfjorden Trough and the Bj~rn~ya Trough, respectively. - - T h e large volumes of glacial deposits in submarine fans along the margin imply high erosional and depositional rates. Transport in a subglacially deforming till layer is the most likely high capacity mechanism for transporting these sediments from Svalbard and the Barents Sea to the margin.

Acknowledgements The Norwegian Petroleum Directorate (NPD), STATOIL, Saga Petroleum and Norsk Hydro are acknowledged for their financial support to this project. The NPD and the Universities of Bergen, Norway, and of Kiel, Germany, kindly provided seismic data used in this study, which forms a part of the European PONAM program. We thank Geir Mathisen for computer assistance in preparation of the figures and the referees Joar Sa~ttem, Paul Grogan and Yngve Kristoffersen for helpful comments and suggestions. Kris Vanneste conducted his work as research assistant at the Belgium National Fund for Scientific Research. This is the Norwegian Polar Institute Contribution no. 299.

References Alley, R.B., Blankenship, D.D., Rooney, S.T. and Bentley, C.R., 1989. Sedimentation beneath ice shelves--The view from Ice Stream B. Mar. Geol., 85: 101-120. Andersen, E.S., Solheim, A. and Elverh~i, A., 1994. Development of a glaciated arctic continental margin: Exemplified by the western margin of Svalbard. In: D.K. Thurston and K. Fujita (Editors), International Conference on Arctic Margins, Proceedings, Anchorage, Alaska 1992. U.S. Dep. Inter. Miner. Manage. Serv., Alaska Outer Shelf Reg., OCS Study, MMS 94-0040: 155-160. Crane, K. and Solheim, A. (Editors), 1995. Seafloor atlas of the northern Norwegian-Greenland Sea. Nor. Polarinst. Medd., 131. Eidvin, T. and Riis, F., 1989. Nye dateringer av de tre vestligste borhullene i Barentshavet. Resultater og konsekvenser for den tertiaere hevingen. Nor. Pet. Director. Contrib., 27, 44 pp. Eidvin, T., Jansen, E. and Riis, F., 1993. Chronology of Tertiary fan deposits off western Barents Sea: implications for the uplift and erosion history of the Barents Sea Shelf. Mar. Geol., !12: 109-131. Eidvin, T., Goll, R.M., Grogan, P., Smelror, M. and Ulleberg, K., 1994. En stratigrafisk unders~kelse av ~vre d e l a v brunn 7316/5-1 (Bj~rn~ya Vest). Nor. Pet. Director. Contrib., 38, 81 Pp. Eiken, O. and Austegard, A., 1987. The Tertiary orogenic belt of West Spitsbergen: Seismic expressions of the offshore sedimentary basins. Nor. Geol. Tidsskr., 67: 383-394. Eiken, O. and Hinz, K., 1993. Contourites in the Fram Strait. Sediment. Geol., 82: 15-32. Eldholm, O., Faleide, J.l. and Myhre, A.M., 1987. Continent-ocean transition at the western Barents Sea/Svalbard Margin. Geology, 15:1118-1122. Elverh~i, A., Nyland-Berg, M., Russwurm, L. and Solheim, A., 1990. Late Weichselian ice recession in the central Barents

J.l. Faleide et a L / Global and Planetary Change 12 (1996) 53-74 Sea. In: U. Bleil and J. Thiede (Editors), Geological History of the Polar Oceans: Arctic versus Antarctic. Kluwer, Dordrecht, pp. 289-307. Elverh0i, A., Svendsen, J.l., Solheim, A., Milliman, J.D., Mangernd, J. and Hooke, R. LeB., 1995. Late Quaternary sediment yield from the high Arctic Svalbard area. J. Geol. Faleide, J.l., Gudlaugsson, S.T., Eldholm, O., Myhre, A.M. and Jackson, H.R., 1991. Deep seismic transects across the sheared western Barents Sea-Svalbard continental margin. Tectonophysics, 189: 73-89. Faleide, J.l., Vlignes, E. and Gudlaugsson, S.T., 1993. Late Mesozoic-Cenozoic evolution of the southwestern Barents Sea in a regional rift-shear tectonic setting. Mar. Pet. Geol., 10: 186214. Fiedler, A., 1992. Kenozoisk sedimentasjon i Lofotenbassenget langs vestlige Barentshav-marginen. Thesis. Univ. Oslo, 114 PP. Fiedler, A. and Faleide, J.l., 1996. Cenozoic sedimentation along the southwestern Barents Sea margin in relation to uplift and erosion of the shelf. Global Planet. Change, 12: 75-93. Haq, B.U., Hardenbol, J. and Vail, P.R., 1988. Mesozoic and Cenozoic chronostratigraphy and cycles of sea-level change. In: C.K. Wilgus et al. (Editors), Sea-Level Changes: An Integrated Approach. Soc. Econ. Palaeontol. Mineral. Spec. Publ., 42: 71-108. Hjelstuen, B.O., 1993. Sen-kenozoisk utvikling av Stordfjordvifta, basert p~t reprosesserte multikanals data. Thesis, Univ. Oslo, 111 pp. Hjelstuen, B.O., Elverh~i, A. and Faleide, J.l., 1996. Cenozoic erosion and sediment yield in the drainage area of the Storfjorden Fan. Global Planet. Change, 12:95-117. Hooke, R. LeB. and Elverhoi, A., 1996. Sediment flux from a fjord during glacial periods, Isfjorden, Spitsbergen. Global Planet. Change, 12: 237-249. Jansen, E., Bleil, U., Hentich, R. and Slettemark, B., 1988. Paleoenvironmental changes in the Norwegian sea and the Northeast Atlantic during the last 2.8 Ma.: D S D P / O D P Sites 610, 642, 643 and 644. Paleoceanography, 3: 563-581. Jansen, E. and Sj0holm, J., 1991. Reconstruction of glaciation over the past 6 Ma based on Norwegian Sea records. Nature, 349: 600-603. Knutsen, S.-M., Richardsen, G. and Vorren, T.O., 1993. Late Miocene-Pleistocene sequence stratigraphy and mass-movements on the western Barents Sea margin. In: T. Vorren et al. (Editors), Arctic Geology and Petroleum Potential. Nor. Pet. Soc. Spec. Publ., 2: 569-602. Kristoffersen, Y., Elverhoi, A. and Vinje, T., 1978. Barentshavprosjektet, matin geofysikk, geologi og havis. Nor. Polatinst. Rep., 81 pp. (unpublished). Kuvaas, B. and Kristoffersen, Y., 1996. Mass movements in glaciomarine sediments on the Barents Sea continental slope. Global Planet. Change, 12: 287-307. Laberg, J.S. and Vorren, T.O., 1993. A Late Pleistocene submarine slide on the Bear Island Trough Mouth Fan. Geo-Mar. Lett., 13: 227-234. Laberg, J.S. and Vorren, T.O., 1996. Late Pleistocene evolution of

73

the Bear Island Trough Mouth Fan. Global Planet. Change, 12: 309-330. Larsen, H.C., Saunders, A.D., Clift, P.D., Beget, J., Wei, W., Spezzaferri, S. and ODP Leg 152 Scientific Party, 1994. Seven million years of glaciation in Greenland. Science, 264: 952-955. Mangerud, J., Bolstad, M., Elgersma, A., Helliksen, D., Landvik, J.Y., Lonne, I., Lycke, A.K., Salvigsen, O., Sandhal, T. and Svendsen, J.I., 1992. The last glacial maximum on Spitsbergen, Svalbard. Quat. Res., 38: 1-31. Manum, S.B. and Throndsen, T., 1978. Rank of coal and dispersed organic matter and its geological bearing in the Spitsbergen Tertiary. Nor. Polarinst. ~.rbok, 1977, pp. 159-177. Myhre, A.M., Eldholm, O. and Sundvor, E., 1982. The margin between Senja and Spitsbergen fracture zones: implications from plate tectonics. Tectonophysics, 89: 33-50. Myhre, A.M. and Eldholm, O., 1988. The western Svalbard margin (74-80°N). Mar. Pet. Geol., 5: 134-156. Myhre, A.M., Thiede, J., Firth, J.V. et al., 1995. Proc. ODP, Init. Rep., 151. M0rk, M.B.E. and Duncan, R.A., 1993. Late Pliocene basaltic volcanism on the Western Barents Shelf margin: implications from petrology and 4°Ar-39Ar dating of volcaniclastic debris from a shallow drill core. Nor. Geol. Tidsskr., 73: 209-225. Pfirman, S.L. and Solheim, A., 1989. Subglacial meltwater discharge in the open-marine tidewater glacier environment: Observations from Nordaustlandet, Svalbard Archipelago. Mar. Geol., 86: 265-281. Raymo, M.E., Ruddiman, W.F., Backman, J., Clement, B.M. and Martinson, D.G., 1989. Late Pliocene variation in northern hemisphere ice sheets and North Atlantic deep water circulation. Paleoceanography, 4: 413-446. Reksnes, P.A. and V~ignes, E., 1985. Evolution of the Greenland Sea and Eurasia Basin. Thesis. Univ. Oslo, 136 pp. Richardsen, G., Henriksen, E. and Vorren, T., 1991. Evolution of the Cenozoic sedimentary wedge during rifting and sea-floor spreading west of the Stappen High, western Barents Sea. In: T.O. Vorren, H.P. Sejrup and J. Thiede (Editors), Cenozoic Geology of the Northwest European Margin and Adjacent Deep Sea Areas. Mar. Geol., 101: 11-30. Richardsen, G., Knutsen, S.-M., Vail, P.R. and Vorren, T.O., 1993. Mid-Late Miocene sedimentation on the southwestern Barents Shelf Margin. In : T. Vorren et al. (Editors), Arctic Geology and Petroleum Potential. Nor. Pet. Soc. Spec. Publ. 2: 539-571. Ruddiman, W.F., Raymon, M.E., Martinson, D.G., Clement, B.M. and Backman, J., 1989. Pleistocene evolution: Northem hemisphere ice sheets and North Atlantic Ocean. Paleoceanography, 4: 353-412. Schliiter, H.U. and Hinz, K., 1978. The continental margin of West-Spitsbergen. Polarforschung, 48:151 - 169. Shackleton, N.J., Backman, J., Zimmerman, H., Kent, D.V., Hall, M.A., Roberts, D.G., Schnitker, D., Baldauf, J.G., Desprairies, A., Homrighausen, R., Huddlestun, P., Keene, J.B., Kaltenback, A.J., Krnmsiek, K.A.O., Morton, A.C., Murray, J.W. and Westberg-Smith, J., 1984. Oxygen isotope calibra-

74

J.1. Faleide et a l . / Global and Planetary Change 12 (1996) 53-74

tion of the onset of ice-rafting and history of glaciation in the North Atlantic region. Nature, 307: 620-623. Solheim, A. and Kristoffersen, Y., 1984. The physical environment, Western Barents Sea; Sediments above the upper regional unconformity: thickness, seismic stratigraphy and outline of the glacial history. Nor. Polarinst. Skr., 179B, 26 pp. Solheim, A., Russwurm, L., Elverhoi, A. and Nyland-Berg, M., 1990. Glacial geomorphic features: direct evidence for grounded ice in the northern Barents Sea and implications for the pattern of deglaciation and late glacial sedimentation. Geol. Soc. London Spec. Publ., 53: 253-268. Solheim, A., Andersen, E.S., Elverhoi, A. and Fiedler, A., 1996. Late Cenozoic depositional history of the western Svalbard continental shelf, controlled by subsidence and climate. Global Planet. Change, 12: 135-148. Syvitski, J.P.M., 1989. On the deposition within glacier-influenced fjords: Oceanographic controls. In: R.D. Powell and A. Elverh~i (Editors), Modern Glacimarine Environments: Glacial and Marine Controls of Modern Lithofacies and Biofacies. Mar. Geol., 85: 301-330. Saettem J., Poole, D.A.R., Ellingsen, L. and Sejrup, H.P., 1991. Glacial geology of outer Bjornoyrenna, western Barents Sea: preliminary results. Nor. Geol. Tidsskr., 71: 171-177. S~ettem, J., Poole, D.A.R., Ellingsen, K.L. and Sejrup, H.P., 1992. Glacial geology of outer BjornOyrenna, southwestern Barents Sea. Mar. Geol., 103: 15-51. S~ettem, J., Bugge, T., Fanavoll, S., Goll, R.M., Mork, A., Mork, M.B.E., Smelror, M. and Verdenius J.G., 1994. Cenozoic margin development and erosion of the Barents Sea: Core evidence from southwest of Bjornoya. Mar. Geol., 118: 257281.

Talwani, M. and Eldholm, O., 1977. Evolution of the Norwegian-Greenland Sea. Geol. Soc. Am. Bull., 88: 969999. Talwani, M., Udintsev, G. et al., 1976. lnit. Rep. DSDP, 38: 389-449. Thiede, J., Eldholm, O. and Taylor, E., 1989. Variability of Cenozoic Norwegian-Greenland Sea paleoceanography and northern hemisphere paleoclimatic. Proc. ODP, Sci. Res., 104: 1067-1118. Vogt, P., Sundvor, E., Crane, C., Pfirrnan, S., Nishimura, C. and Max, M., 1990. SeaMARCI! and associated Geophysical investigation of the Knipovich Ridge, Molloy Ridge/Fracture Zone, and Barents Spitsbergen Continental Margin: Part III Sedimentary Processes. EOS, 71 (17) (abstract). Vogt, P.R., Crane, K. and Sundvor, E., 1993. Glacigenic mudflows on the Bear Island submarine fan. EOS, Trans. Am. Geophys. Union, 74: 449, 452, 453. Vorren, T.O., Hald, M. and Lebesbye, E., 1988. Late Cenozoic environments in the Barents Sea. Paleoceanography, 3: 601612. Vorren, T.O., Richardsen, G., Knutsen, S.M. and Henriksen, E., 1991. Cenozoic erosion and sedimentation in the western Barents Sea. Mar. Pet. Geol., 8: 317-340. Wornardt, W.W. and Vail, P.R., 1990. Revision of the PlioPleistocene cycles and their application to the stratigraphy of the shelf and slope sediments in the Gulf of Mexico. In: Gulf Coast Section, SEPM Found., 1 lth Annu. Ress. Conf., Houston, Dec. 2-5, 1990, Progr. and Abstr., pp. 391-397.