Sedimentary facies and processes of deposition: Ice Island cores, Axel Heiberg Shelf, Canadian Polar Continental Margin

Marine Geology, 93 (1990) 243-265 Elsevier Science Publishers B.V., Amsterdam

243 Printed in The Netherlands

Sedimentary Facies and Processes of Deposition" Ice Island Cores, Axel Heiberg Shelf, Canadian Polar Continental Margin* F R A N C E S J. H E I N 1.*, N A N C Y A. v a n W A G O N E R / and P E T A J. M U D I E 3 1Centre for Marine Geology, Department of Geology, Dalhousie University, Halifax, N.S. B3H 3J5 (Canada) 2Department of Geology, Acadia University, Wolfville, BOP 1XO (Canada) 3Geological Survey of Canada, Atlantic Geoscience Centre, Box 1006, Dartmouth, N.S. B2Y 4A2 (Canada) (Received October 28, 1988; revision accepted M a r c h 16, 1989)

Abstract Hein, F.J., Van Wagoner, N.A. and Mudie, P.J., 1990. Sedimentary facies and processes of deposition: Ice Island cores, Axel Heiberg Shelf, Canadian Polar Continental Margin. In: J.R. Weber, D.A. Forsyth, A.F. Embry and S.M. Blasco (Editors), Arctic Geoscience. Mar. Geol., 93: 243-265. The sedimentological features are described of 24 piston and gravity cores recovered at depths from 140 to 283 m b e n e a t h the perennial ice cover of the Arctic Ocean, n o r t h of Axel Heiberg Island. Sample sites are located between Nansen and Sverdrup channels, along the drift path of the Canadian Ice Island. Eight facies are characterized and interpreted, as follows: (A) Soft, yellow-brown structureless pebbly sandy mud/silty mud interpreted as strongly bioturbated hemipelagic muds with ice-rafted meltout and fallout deposits; (B) burrowed sandy silty/clayey mud interpreted to be the result of slow continuous suspension fallout concommitant with bioturbation; (C) wispy, laminated sandy silty mud due to slow continuous suspension fallout with bioturbation punctuated by sudden deposition from nepheloid flows or fine-grained turbidity currents; (D) laminated sandy silty mud formed by underflow, turbidity current and suspension fallout; (E) firm, dark grey/olive grey-brown pebbly sandy/silty mud comprising ice-rafted debris or debris flow deposits; (F and G) indurated, reddish brown/ochre and black pebbly sandy mud/silty mud comprising exposed bedrock; and (H) firm, grey and brown structureless silty mud interpreted as suspension deposits with rare ice rafting. The indurated facies F and G occur on a topographic high on the inner shelf. This topographic high is interpreted as an offshore bank which may have provided a sedimentary source during deposition. Facies H is restricted to deeper cores within Nansen and Sverdrup channels, representing a possibly older relict deposit. Other facies show broad correlations throughout the study area. Facies A, B and C are more common in the upper parts of cores, Facies D and E in the lower parts of cores. Deposition by gravity flows in a realm of normal hemipelagic sedimentation is a more important process t h a n fallout and wasting of ice shelves and icebergs. Reworking by waves and bottom currents is minimal. The present facies model compares well with those for other high arctic areas, including Baffin Island fjords and the c o n t i n e n t a l rise of Canada Basin in the western Arctic Ocean. No till facies were cored on the Axel Heiberg Shelf, indicating t h a t this part of the shelf was probably not i n u n d a t e d by grounded ice during the last glaciation. The most a b u n d a n t mineral in the coarse fraction ( > 63 ~m) of the samples selected is common quartz. The mafic minerals are far less common t h a n quartz and feldspar, reflecting the instability of these grains; however, igneous augite, typically clinopyroxene, occurs in all samples. Rock fragments include fresh and altered basalt and gabbro, metamorphic and granitic rock fragments and a wide variety of sedimentary rock fragments, including mudstone, sandstone, chert and limestone. The v a r i a t i o n of shape and composition of rock and mineral fragments within and between facies suggests a mixed source area dominated by a plutonic terrain. The plutonic and metamorphic rock fragments were probably derived from Pearya, whereas the sedimentary rock fragments were eroded from the F r a n k l i n i a n Mobile Belt and Sverdrup Basin. The occurrence of augite suggests a nearby volcanic source, probably Ellesmere Island. The present data indicate t h a t the source terrains did not vary significantly during the time of the facies distribution of the Axel Heiberg Shelf. *Ice Island Contribution 16. Geological Survey of Canada Contribution 35189. **Now at University of Calgary, Calgary, Alta. T2N 1N4 (Canada). 0025-3227/90/$03.50

© 1990 Elsevier Science Publishers B.V.

Introduction This study describes the sedimentology of cores taken from the polar continental shelf beneath the perennial pack ice of the Arctic Ocean, north and west of Axel Heiberg Island (Fig.lA; see Fig.lB for the stratigraphic and structural geological framework of the area). Coring was from a drifting ice island (Mudie et al., 1985, 1986), formed by calving from a floating ice shelf. These are the first cores recovered from the submarine banks on the polar continental

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margin of the Canadian High Arctic and the} provide important insights into the palaeoenv ronmental development of this region during the late Tertiary to Recent. Since the Eurekan Orogeny this continental rnargi~ has undergone dramatic palaeoenvironmental changes, including transitions from fluvial to marine, glacial to interglacial and sea ice to glacial ice cover e.g. Pelletier, 1966: Miall, 1986; England, 1987). Many workers have speculated that the inter-island channels record a pre-existing Tertiary drainage pattern (e.g. Pelletier, 1966) that was overdeepened by

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SEDIMENTARY FACIES AND DEPOSITION, AXEL HEIBERG SHELF

ARCTIC COASTAL PLAIN Upper Tertiory- Recent SVERDRUP BASIN Car boni f erous - Cretaceous (include3 uppermost Cretaceouslower Tertiary elastics) PEARYA Middle Proterozoic (Neohelikion)Upper Silurian FRANKLINIAN MOBILE BELT Cambrian - Devonian predominantly d e e p - w a t e r sediments (includes volconice and shallow-marine and nonmorine sediments; may include Upper Proterozoic rocks) predominantly d e e p - w a t e r sediments {includes Lower Cambrian shelf sediments) predominantly shelf sediments (includes Upper Ordovicion- Lower Devonian deep- water sediments and Devonian nonmorine clostic~)

ARCTIC PLATFORM Cambrian - Cretaceous CANADIAN SHIELD Archeon - L o w e r Proterozoic (Aphebion}

Fig.1. A. The locations of piston and gravity cores collected beneath the Canadian Ice Island during the spring and summer of 1985 and 1986. Cores 85-3to 85-6(upper right of map) were collected during 1985; other cores (2-136; 41-58 refers to cores 41 to 58 inclusive) were collected during 1986. The numbering scheme is used for reference to the archival cores in storage at the Atlantic Geoscience Centre, Dartmouth, Nova Scotia. Bathymetry was mapped during the occupation of the Canadian Ice Island in the spring and summer of 1985 and 1986. Contour interval = 50 m. Inset map and arrow show the location of the study area in the Arctic Ocean. B. Stratigraphic-structura] framework of the Arctic Islands and index (from Trettin, 1987). glacial erosion. In these models for the Canadian H i g h A r c t i c p h y s i o g r a p h i c region, the implicit a s s u m p t i o n is t h a t sediments derived from the e r o d i n g l a n d m a s s e s were deposited on the c o n t i n e n t a l shelf ( H a t t e r s l e y - S m i t h , 1969); hence, t h e r e s h o u l d be some r e c o r d on the shelf of p o s t u l a t e d pre-existing T e r t i a r y fluvial systems and Q u a t e r n a r y glacier deposits. N e w d a t a r e l e v a n t to some of t h e s e models of l a n d f o r m e v o l u t i o n has been o b t a i n e d from the drift t r a c k t r a v e r s e d by the C a n a d i a n Ice Island. The cores discussed in this p a p e r i n c l u d e sediments of T e r t i a r y to R e c e n t age, a n d m a y possibly r e c o r d fluvial, marine, glaciom a r i n e or ice-shelf deposits. The facies models developed from these cores are c o m p a r e d with o t h e r g l a c i o m a r i n e s e d i m e n t facies and c a n be used for the d e v e l o p m e n t of a r e g i o n a l model of the C a n a d i a n H i g h A r c t i c c o n t i n e n t a l shelf.

Study area and methods This s t u d y examines 24 piston and g r a v i t y cores r e c o v e r e d from the Axel H e i b e r g Shelf in w a t e r depths r a n g i n g from 140 to 283 m (Fig.l). Sites o c c u r b e t w e e n N a n s e n C h a n n e l to the n o r t h e a s t and S v e r d r u p C h a n n e l to the southwest (Fig.l) and i n c l u d e t h o s e p a r t s of the Axel H e i b e r g shelf t r a v e r s e d by the C a n a d i a n Ice I s l a n d d u r i n g the 1985 a n d 1986 seasons ( G o r v e a t t a n d Chin Yee, 1988). Cores were logged on a scale r a n g i n g from millimetres to centimetres. Grain-size a n a l y s e s were made on 36 samples from i n t e r l a m i n a t e d zones in two cores (86-18 a n d 86-54) u s i n g the c o m p u t e r i z e d s e d i g r a p h system at the A t l a n t i c G e o s c i e n c e Centre. The c o a r s e - f r a c t i o n c o m p o s i t i o n was determ i n e d by p e t r o g r a p h i c a n a l y s i s of t h i n sections made from selected samples of the cores c o n t a i n i n g h i g h p r o p o r t i o n s of c o a r s e mate-

riM. The samples were wet sieved using a 63 Bm sieve to collect the coarse fraction, which was then air dried, and impregnated with epoxy resin in a 3 cm diameter plastic mould. A slice was cut from this mould and a standard petrographic thin section (0.03 mm) was made. The modal mineralogy of the coarse fraction was determined by point counting. The number of points counted per slide ranged from 120 for finer and smaller samples, to 390 for samples containing more varied grains. The average number of grains counted was 200 per thin section. The sediments are classified into facies following the rationale of De Raaf et al. (1965). The main criteria for the distinction of facies include the physical and biogenic sedimentary structures, the presence or absence of grading, and for the finer grained lithologies (silt and clay), the colour of the sediment. Except for the gravel fraction, grain-size variation in most of the cores is minimal, so texture was not especially useful in distinguishing the finer grained facies. Facies were defined mainly from the core as seen in split section, although reference was made to X-radiographs during core logging. More detailed descriptions of the facies variation and microfossil content are given elsewhere (Hein and Mudie, submitted).

Facies description Core sampling was carried out from the drifting ice island, the movement of which depends on winds and currents. Sea-ice movement is irregular on the Canadian polar margin (Mudie et al., 1985, 1986). The sampling scheme is thus erratic, with clusters of cores in some localities, and other cores widely spaced (Fig.l). Due to this uneven distribution, and the zig-zag path of the ice island, it is impossible to draw accurate facies maps or precise longitudinal or cross sections of the facies distributions. Therefore, the data are presented in two ways: (1) as detailed facies logs with respect to bathymetry at sites with good core control and bathymetric contouring (Fig.2) and (2) as a correlation chart with

respect to depth, showing the general distrlbw tions of facies in s h a l l o w versus d~:~ep-shelf sites (Fig.3). Representative photographs of t:h~ facies are shown in Fig.4

Facies A. Yellow-brown pebbly sandy mud This facies caps most of the cores (Figs.2 and 3) and consists of units which average about 5 cm in thickness in the cores and 10 cm in grab samples (thickness ranges from absent to a maximum of 22 cm). The mud is commonly brown, yellow-brown or slightly reddish yellow-brown in colour (10YR 4/2, 10YR 5/2, 10YR 5/3), and completely bioturbated. Planktic and benthic calcareous foraminifera are abundant (Schroeder-Adams et al., 1990). Pebbles have a maximum size of 4 cm, although they average 1-2 cm in length, occurring as angular to subangular outsized clasts dispersed within a finer grained sandy, silty-mud matrix. Sorting is poor to very poor.

Facies B. Burrowed~mottled mud This facies underlies Facies A in many cores. In the longer cores, there are a number of layers that are burrowed further downsection (e.g. 85-6, 86-6 and 86-18, Fig.3). Facies B ranges in thickness from ~1 to 55cm (average 20 cm, Fig.3). Burrow infills are generally of silty-clayey mud, and rarely of sand. Most of the mottles are irregular, with vague boundaries. Less commonly, distinct burow types can be recognized, including Thah~ssinoides, Rhizocorallium, Terebellina of the Cruziana ichnofacies, and Chondrites, Planolites and composite burrows (Ekdale et al., 1984). Rare, isolated Skolithos traces were noted in the sandier beds.

Facies C. Wispy laminated~mottled mud This facies generally underlies Facies B (core 86-18, Figs.2 and 3; cores 85-3 and 85-4, Fig.3) and repeated zones of Facies C occur downsection in cores 85-6, 86-54 and 86-53

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(Fig.3). Laminae consist of wispy sands or silts 2 mm thick (thickness ranges from 0.3 mm to 4 cm). These laminae alternate with silty mud and mud in stacked units up to ~0.65 m thick (core 86-18, Fig.3). The silt/sand commonly occurs as brown/tan grey to olive grey lenses within a medium to dark grey clayey mud (i.e. 10YR 3/1 with 10YR 5/3; 10YR 4/1 with 10YR 5/2). The bases of the silt and sand lenses are generally sharp and horizontal. The tops of the lenses are gradational and mottled. The sand/ silt lenses are laterally discontinuous, and thinner laminae appear mainly as silty or sandy "streaks" within a muddy sediment.

Facies D. Laminated mud This facies generally underlies or is interbedded with the Facies C muds (core 86-18, Figs.2 and 3; cores 85-3, 85-4, 85-6, 86-53, 86-54 and 86-102, Fig.3). Within the upper parts of the cores, medium to dark brownish silty clay (10YR 5/2, 5Y 4/2) grades upwards into a lighter silty yellow or light grey silty clay. Further downsection, the mud is a darker olive grey or grey colour (5Y 3/1, 5Y 3/2, 5Y 4/2, 5Y 5/2). Laminae consist of sands, silts or sandy/ silty muds ~ 2 mm thick (thickness ranges from 0.3 to 4 mm). The laminae alternate with silty mud and mud in stacked units up to ~0.35 m thick (core 85-6, Fig.3) and are continuous across the core width and usually have sharp, horizontal bases. Five types of laminated muds occur (Table 1): (D1) Normally graded bands of lighter brownish silty clay, grading into medium to dark grey clay (Turbidite Tae beds, Bouma, 1962). (Dz) Normally graded and laminated bands of lighter brownish silty clay, grading into medium to dark grey clay. Rare graded, low-angle crossbedded or convolute laminated beds occur (Turbidite Tade and Tace beds, Bouma, 1962). (D 3) Ungraded, alternating strips of lighter brown silty clay and medium dark grey clay. Contacts between stripes are sharp or gradational. (D 4) Inverse-to-normally graded "triplets" of fine, medium-dark brownish clay, grading into

249

a lighter yellow silty or light grey clay, which is overlain by a fine medium-dark brownish clay. Rare occurrences of brown-white-brown and brown-ochre-brown triplets were noted. (Ds) Inversely graded lighter brownish to grey silty clay, grading into darker coarser grained medium to dark grey or brown silty/ sandy clay.

Facies E. Dark grey pebbly sandy mud This facies occurs towards the bases of most of the longer cores (cores 86-6, 86-7, 86-18, 86-54 and 86-102, Fig.3). Another pebbly sandy mud occurs upsection in some cores, at a depth of ~40 70 cm (cores 86-11, 86-12 and 86-28, Fig.2; core 85-4, Fig.3). Sediment consistency is firm to very firm. The thickness of the units ranges from a few centimetres (core 86-112) to > 0.45 m (cores 86-7 and 86-102) (Fig.3). Beds are very poorly sorted and are dominantly structureless. Most of the beds have a chaotic appearance, with outsized clasts dispersed randomly within a finer grained sandy or silty mud. Several of the thinner pebbly muds overlie or are interbedded with convoluted/folded or disturbed sandy silty mud (cores 86-11, 86-12 and 86-28, Fig.2). Clasts are angular, subangular or subrounded, ranging from granules to pebbles > 5 cm across.

Facies F. Reddish brown~ochre pebbly sandy mud This facies occurs only in the short cores 8652, 86-56, 86-57 and 86-58 (Figs.l, 2 and 3). Core penetration at these sites was limited by the presence of boulder beds (in part dredged) and semiconsolidated or indurated sandstone. Sediments appear oxidized, with reddish brown, red and ochre colouration (7.5YR 3/2 4/4; 5YR 2/2, 5YR 4/1, 5YR 3/3, 5YR 3/2). The reddish pebbly sandy muds are very firm to semi-indurated, and alternate with reddish brown sand interbeds and ochre sand-silt interbeds. Clast size reaches a maximum of 4 cm. Units are quite thin, reaching a maximum of ~ 15 cm in core 86-52. Petrified/chertified wood fragments and

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well-preserved Cretaceous to Paleogene palynomorphs have been recovered from this facies.

Facies G. Dark grey-black pebbly mud This facies locally underlies the reddish Facies F pebbly muds and occurs at the base of

cores 86-57 and 86-58 (Figs.2 and 3). The sediments are very firm to semi-indurated. Units average ~ 5 cm in thickness and are poorly sorted, consisting of sandy mud with minor to common rock fragments. Clasts are subangular, subrounded and rounded.

SEDIMENTARY FACIES AND DEPOSITION, AXEL HEIBERG SHELF

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Facies H. Grey and brown silty mud This facies occurs at the base of cores recovered from the deeper water sites (> 280 m) of Nansen and Sverdrup channels (cores 85-3, 85-4, 85-6 and 85-18, Figs.1 and 2). The sediments are mainly firm, structureless silty muds

ranging in colour from brown (10YR 4/2) to dark grey (5Y 3/1). Faint laminae (2-5 mm thick) of yellow-brown (10YR 5/2) sand or silt interbeds occur locally. Isolated granule or pebble clasts are occasionally scattered within the mud. Units range from <5 cm thick to ~ 30 cm thick.

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Textural properties of laminated Facies D units

laminated units to provide a data base for interpreting the laminae. Sampling intervals, descriptions of lamination types and grain-size statistics are given in Table 1. Detailed grain-size analyses of the D 3 ungraded, alternating stripes, the D4 inverse-tonormally graded ~'triplets", and the D 5 inversely graded bands show two main types of grain-size distribution (Table 1, Fig.5). Type ! is distinguished from Type II by its high

All of the well-developed laminated zones were logged on a scale of millimetres to ascertain the occurrence of any cyclicity in the laminations; however, in general, cycles in the patterns of lamination were not observed. In two cores (86-18 and 86-54, Fig.3) textural analyses were made on different types of

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standard deviation, broad range of skewness, lower percentage of clay (<50c~,), and relatively coarser grain size (3---8 ¢, as opposed to >8 4)) (Fig.5). These features are not necessarilly specifically restricted to the D3, D~ or D 5 lamination types (Table 1). Type II deposits resemble distributions produced by fine-grained, sediment gravity flows, including turbidity currents and underflows (Piper, 1973; Ashley, 1979; Lambert and Hsii, 1979; Mackiewicz et al., 1984; Schafer et al., 1989). Type I deposits are similar to those transported by plumes and deposited by suspension fallout in more distal basinal settings (Schafer et al., 1989). The rare Type I deposits with an average grain size in the sand-size fraction (three examples occur in Fig.5A) may represent deposits which originated as sediment gravity flows with an overriding sediment plume.

Depositional m e c h a n i s m s of facies Facies A

The coarseness and very poor sorting of the sediment, the absence of stratification and occurrence of dropstone structures (i.e. soft sediment deformation structures in sediments around the bases and sides of pebbles) suggests that the clastic component of this biogenic sediment was derived from melting and fallout of debris-laden ice. Multiyear sea ice, ice shelves and ice islands are the main sources of sediment transport into the western Arctic Ocean basins today (Clark and Hanson, 1983; Jeffries, 1986). The brown colour and textural properties of Facies A resembles that of the Holocene postglacial sediments which floor many other high-latitude seas (e.g. the Canadian inter-island channels, the eastern continental margin of Baffin Island, the Barents Shelf and slope off northern Norway, and the continental shelves of offshore U.S.S.R. (Tolmachev, 1982). Similar sediments occur on the extensive raised m a ~ n e terraces of Holocene age which occur along many of the high-

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Canada (,!

Facies B

The nearly complete obliteration of primary sedimentary structures by bioturbation implies that the rate of mixing associated with bioturbation exceeded the rate of sedimentation. The bioturbation pattern in Facies B most closely resembles Howard's (1978) models in which there is slow continuous deposition (characteristic of offshore shelf environments) accompanied by complete bioturbation of the sediment. Identifiable traces within Facies B belong to the Cruziana ichnofacies, which implies sedimentation between fair-weather and storm-weather wave base under conditions of low- to medium-energy level (Frey and Seilacher, 1980). The occurrence of these traces in deep shelf environments (i.e. at a water depth of 140 m, well below present wave base) suggests that traces of the Cruziana ichnofacies may not be solely representative of shallow-shelf conditions, and the range of Cruziana may possibly be extended to greater water depths. The local occurrence of isolated Chondrites indicates dysaerobic to anaerobic conditions within the sediment itself (i.e. after deposition, conditions within the pore water system become dysaerobic to anaerobic as sediment became buried and isolated from the more oxygenated water on the seafloor; cf. Ekdale et al., 1984). Facies C

Primary lamination is better preserved in Facies C than in Facies B. The type of bioturbation and sedimentary fabric most closely resembles Howard's (1978) model for rhythmic deposition interspersed with erosion. Individual wispy laminated to bioturbated Facies C beds have sharp bases and are normally graded, with fine to medium sand to coarse silt at the base, grading to clayey mud towards the top. These deposits closely resemble the "ribbon sands" of the shallow-

SEDIMENTARY FACIES AND DEPOSITION, AXEL HEIBERG SHELF

marine Cretaceous Swift Formation in Alberta (Harding and Hein, 1984; Harding, 1985) or the distal shelf deposits of the Arisaig Formation in Nova Scotia (Cant, 1980). Laboratory and field work (Carey and Roy, 1985) on the origins of laminated shales show that intermittent lamination is characteristic of silt/clay-laden currents which are decelerating at a constant silt content, loosing silt at a constant velocity, or both decelerating and loosing silt. Intermittent lamination occurs in mud deposited from flows bearing 40-60% silt. Non-laminated mud is deposited from flows bearing 20 40% silt. Current velocities are generally in the range of ~12-28 cm/s for deposition of the intermittent laminated muds. The Facies C beds are interpreted as the result of suspension fallout representing relatively low-energy conditions duirng deposition of the background clayey and silty muds. This low-energy setting is intermittently punctuated by sudden, more rapid erosion and deposition by fine-grained, silt/clay-laden currents which are more fluid than "normal" turbidity currents. These sediment gravity flows may be nepheloid flows or small-scale (low-density) turbidity currents. Nepheloid layers and bottom currents have been recorded from the deep abyssal, central Arctic Ocean, although these flows are mainly geostrophic in nature with measured velocities approximately one-third to one-half those inferred here for the origins of the wispy laminated sediment (4 6 cm/s, Hunkins et al., 1969; 1 2 cm/s, Amos, 1985). Examination of scour features on bottom photographs from the Alpha Ridge suggests that bottom current velocities may locally reach 20 cm/s (Amos, 1985). In shallower arctic continental shelf settings nepheloid flows may be associated with river flood discharge. (Reimnitz and Bruder, 1972; Dupre and Thompson, 1979), glacial meltwater, or return flows due to storm surges. At present, there are no Artic Island rivers of magnitude similar to the Yukon or Colville (Reimnitz and Bruder, 1972; Dupre and Thompson, 1979). During glacial inter-

255

vals, however, meltwater channels may have discharged sediment-laden flows into the nearshore shelf, these flows then becoming transformed into nepheloid flows or sediment gravity flows. These nepheloid or gravity flows may have transported material further offshore to the study area. Facies D

Laminated zones are dominated by primary lamination with relatively minor biogenic structures. The preservation of the laminae implies that the sedimentation rate greatly exceeded bioturbation. The intermittent pattern of bioturbation resembles Howard's (1978) model in which there are intervals of rapid deposition (or deposition under anoxic conditions) and where animal activity is minor to non-existant. The D 1 graded bands and the D2 graded and laminated bands are similar to the banding produced in silt/mud turbidites (Bouma, 1962; Piper, 1973; Stow and Piper, 1984). As with coarser grained sandy turbidites which follow the Bouma sequence, the mud and silt laminae are interpreted as the result of deposition from decelerating flow in a single turbidity current. Although it is difficult to determine the range of current velocities for such flows, they may be ~40 50 cm/s at the base of beds, decelerating to 12-20 cm/s during deposition of the intermittent and wispy silt laminations, and to <10 cm/s during deposition of the massive upper parts of beds (Carey and Roy, 1985). As discussed previously, the other types of laminated deposits have textural properties that resemble those produced from (1) finegrained sediment gravity flows, including underflows and turbidity currents (Type II, Table l, Fig.5), and (2) suspension fallout deposits from plumes in more distal shelf settings (Type I, Table 1, Fig.5). Facies E

The massive character, random distribution of coarse clasts within a finer grained matrix,

the absence of dropstone structures (see Facies A) and the lack of grading suggests that Facies E deposits were emplaced very rapidly from highly concentrated, viscous, sediment gravity flows. Nevertheless, it is difficult to distinguish poorly sorted debris flows from till or glaciomarine sediments with abundant ice-rafted clasts (Dreimanis, 1979), especially in narrowdiameter cores. This is particularly problematic if the debris flows were generated by the slumping and resedimentation of glaciogenic or glaciomarine debris. Glacial tills would be more laterally extensive blankets of debris; glaciomarine sediments and debris flows would be more lenticular. As shown in the various diagrams (Figs.3-5) this facies is lenticular, and does not represent a widespread glacial till facies. Thin Facies E units commonly overlie or are laterally correlative with convoluted and/or slumped material (Figs.3- 5). These associations suggest t h a t the thin Facies E units are probably debris flow deposits. Thicker Facies E beds with rare foraminifera and sponge spicules may be ice-rafted deposits (core 86-63, Table 1). Facies F and G

The very firm to semi-indurated nature of these sediments, their distinct colouration, the occurrence of petrified/chertified wood fragments, and abundant well-preserved Cretaceous to Paleogene palynomorphs suggests that these sediments are much older than the other lithofacies. Facies F and G are restricted to cores 86-52, 86-56, 86-57 and 86-58 (Figs.3-5), all of which were taken on a submarine bank in the centre of the study area (Fig.l). These cores are closest to the present coast of Axel Heiberg Island. Facies F and G appear to represent bedrock belonging to the Paleogene Eureka Sound Group (Miall, 1986), which is distinguished from the younger (Neogene-Pleistocene) Beaufort Formation by its relatively unconsolidated character, by its yellow to orange colouration, and by the presence of only slightly altered wood rather than coal and silicified wood (Hill, 1969; Hills and Ogilvie, 1970).

Facies H

The massive nature of this facies, coupled with its uniform texture and only faint laminae, suggests that these muds are hemipelagic in origin. The low microfossil content and absence of biogenic traces suggests either that deposition was very rapid, or that bottom water conditions precluded the activity of" burrowing organisms. Occasional dropstones indicate t h a t there was some ice rafting at this time. It is difficult to ascertain the origin of this deposit, as it is restricted to the lower parts of the deeper cores from Nansen and Sverdrup channels (Fig.3). As such, this facies may represent an older stratigraphic zone not cored elsewhere in the study area. The firm nature of this facies also suggests that it is much older t h a n most of the other sediments examined in this study. However, it is not nearly as compact as Facies F and G, these two facies appearing to represent Tertiary bedrock.

Petrography o f the coarse (> 63 jim) fraction In most samples the particle shapes in the coarse fraction ranges from angular to well rounded. The most rounded grains are typically of medium to coarse sand. Grains larger than coarse sand are usually rounded or angular rock fragments, with rounded fragments being slightly more common. Fine sand and smaller grains are usually subangular or angular. The most abundant mineral in most samples is "common" or plutonic quartz (Folk, 1980), which is frequently rutilated (Table 2). Stretched metamorphic quartz is atso common, recrystallized metamorphic quartz occurs in a few samples, and vein quartz occurs less frequently. Volcanic quartz is rare. The dominance of common quartz and the occurrence of rutilated quartz is characteristic of plutonic source terrains, whereas other quartz grains display continuous authigenic quartz overgrowths over well-rounded grains, indicating reworking from sedimentary rocks.

SEDIMENTARY FACIESAND DEPOSITION,AXEL HEIBERG SHELF

257

TABLE 2 P e t r o g r a p h y of the coarse fraction, g = g r a v i t y core; P = p i s t o n core; cc = core c u t t e r Facies Core & d e p t h (cm)

E E 006 119 121 006g 130 132

E 006g c u t t e r

E E 007 121 123 007P cc

D H A 018 190 195 018P c u t t e r 052 8 18

C o m m o n qtz Volcanic qtz Recrystallized qtz S t r e t c h e d meta qtz Vein qtz

36.6 0.0 0.0 2.6 0.0

40.5 0.0 0.0 9.2 0.0

11.9 0.0 0.0 1.0 0.0

16.3 0.0 2.7 0.0 0.0

14.0 0.0 0.0 2.1 0.0

55.4 0.5 1.0 11.3 1.0

47.6 2.1 0.9 8.2 2.1

33.1 0.0 0.0 2.8 1.2

Total qtz

39.3

49.7

12.9

19.0

16.1

69.1

60.9

37.1

Plagioclase Alkali feld

6.3 15.2

6.9 19.7

3.0 6,9

1.1 2.7

3.0 11.0

4.4 13.7

3.0 3.9

2.8 13.5

Total feld

21.5

26.6

9~9

3.8

14.0

18.1

6.9

16.3

0.0 2.1 2.1 1.6 0.0 5.2

0.0 0.0 1.2 1.7 1.7 1.7

0.0 0,0 2.0 1.0 1.5 4.5

0.0 0.0 1.1 1.6 2.2 0.0

0.0 0.0 0.0 0.8 0.4 2.1

0.0 0.5 0.5 1.0 1.0 1.0

0.0 0.0 0.0 3.0 0.4 0.0

0.0 0.0 0.4 1.2 1.2 0.8

Total mafic m i n e r a l s

11.0

6.4

8.9

4.9

3.4

3.9

3.4

3.6

Mafic volcanic Sandstone, siltstone Mudstone Limestone Chert Metamorphic Granitic O t h e r rock frag

5.2 4.2 2.6 5.8 8.9 1.0 0.0 0.0

0.6 5.2 1.7 5,2 4,0 0,0 0~6 0,0

3.5 38.6 5.9 14.9 3.5 2.0 0.0 0.0

29.9 27.2 6.0 3.8 3.8 0.0 0.0 0.0

30.1 14.8 2.1 9.3 2.5 3.8 3.8 0.0

1.5 0.0 2.0 1.0 2.9 0.0 1.0 0.0

1.7 5.6 2.6 1.7 15.0 0.4 0.0 0.0

0.8 34.7 2.0 1.2 2.8 1.6 0.0 0.0

27.7

17.3

68.3

70.7

66.5

8.3

27.0

43.0

0.5

0.0

0.0

1.6

0.0

0.5

1.7

0.0

0.7 0.075

0.6 0.2

12 0.23

7 0.13

25 0.17

0.5 0.2

16 0.3

30 0.25

Biotite Hornblende Chlorite Clinopyroxene Haematite Other minerals

Total rock frag Unidentified

Approximate grain size Sample max, mm ts average, m m

Feldspars vary from fresh to highly altered in any given sample. Alkali feldspar is more common than plagioclase, and is usually perthitic. Alkali feldspar is also typical of a plutonic source. The mafic minerals (biotite, hornblende, chlorite and pyroxene) are far less common than quartz and feldspar (Fig.6), reflecting the instability of these mineral grains. Clinopyroxene, however, is common and occurs in all samples. It is typically augite, a common pyroxene of mafic igneous rocks.

Other minor and trace minerals include kyanite, tourmaline, actinolite, talc, garnet, pyrite and zeolite. Most of these trace minerals are consistent with a metamorphic or reworked sedimentary source. The tourmaline and garnet may originate from an igneous or metamorphic source. Rock fragments occur in most samples (Fig.6). Fragments of mafic volcanic rock make up to 30% of some samples, although the abundance of these fragments does not appear

25,~

:

!,]i~ t.:i

TABLE 2 (continued) Facies C,o r e & depth (cm)

F 052 8 22 bag

F 052 18 22

[i' 052 22 23

t'; 054 118 120

F 056 11

F 056 11 13

D 057 19 21

~57 2.3 2 5

C o m m o n qtz Volcanic qtz Recrystallized qtz Stretched m e t a qtz Vein qtz

47.1 0.5 1.0 3.4 2.4

40.5 0.0 0.0 5.1 0.8

57.4 0.0 0.5 9.4 1.0

65.1 0.0 0.0 0.9 0.0

50.2 0.5 0.5 3.5 0.0

40.5 0.0 0.0 3.8 0.0

45.7 0.8 2.4 5.5 0.0

30.6 !1.0 (}.0 2.7 0.5

Total qtz

54.4

46.4

68.3

65.9

54.7

44.3

54.3

33.8

Plagioclase Alkali feld

1.5 12.6

3.8 9.0

4.0 10.9

5.7 5.2

6.5 21.9

5.7 18.1

3.9 4.7

3.2 10.8

Total feld

14.1

12.8

14.9

10.9

28.4

23.8

8.7

14.0

Hornblende Chlorite Clinopyroxene Haematite Other minerals

0.5 0.0 0.5 2.4 1.9 1.9

0.0 0.0 0.3 1.0 0.3 1.5

0.0 1.0 0.0 1.0 0.5 0.0

0.0 0.0 0.0 3.9 2.2 1.7

1.5 0.0 1.0 1.5 2.0 2.5

0.0 0.5 0.0 0.0 1.0 2.4

0.8 0.0 0.8 2.4 3.9 2.4

0.9 0.5 0.5 0.9 1.4 5.0

Total mafic m i n e r a l s

7.3

3.1

2.5

7.9

8.5

3.8

10.2

9.0

Mafic volcanic Sandstone, siltstone Mudstone Limestone Chert Granitic O t h e r rock frag

5.8 8.7 1.0 3.4 1.5 3.4 0.0 0.0

6.7 1.3 0.8 0.0 2.3 26.7 0.0 0.0

2.0 2.5 1.5 0.0 4.0 4.0 0.0 0.5

1.3 2.6 2.6 7.0 1.7 0.0 0.0 0.0

0.5 0.5 0.0 1.0 6.0 0.5 0.0 0.0

5.2 9.5 4.8 1.4 2.4 4.3 0.5 0.0

2.4 2.4 1.6 7.1 5.5 4.7 1.6 0.0

4.5 5.0 1.4 14.0 4.5 14.0 0.0 0.0

Total rock frag

23.8

37.7

14.4

15.3

8.5

28.1

25.2

43.2

0.5

0.0

0.0

0.0

0.0

0.0

1.6

0.0

6 0.4

35 0.25

24 0.25

0.7 0.17

2.5 0.1

6 0.12

0.35 0.1

7 0.15

Biotite

Metamorphic

Unidentified

Approximate grain size Sample max, mm ts average, mm

to correlate with sedimentary facies (Fig.6). These mafic volcanic rocks include basalt and gabbro, many of which are fresh, although others are altered to greenschist facies. Granitic rock fragments are rare probably because they have the most distal provenance. A wide variety of sedimentary rocks occurs, with sandstone and siltstone fragments comprising up to 38% of some samples (Fig.6). One of these sandstones is distinctive, exhibiting a chert and mica matrix. It could be recognized in several samples from cores 86-52, 86-57 and 86-58 from the offshore bank where exposed

Tertiary bedrock was dredged (Mudie et al,, 1986). Mudstone fragments, typically haematite stained, occur in minor amounts (up to 6%) in most samples, but are most abundant in Facies E in cores 86-6 and 86-7 from Sverdrup Channel. Limestone fragments occur in all but three samples, and comprise up to 17% of the lithology. The limestones are m a i n l y micritic or coarsely crystalline, and they are mostly non-foasiliferous. Chert occurs in every sample but it is most abundant in core 86-18 from Sverdrup Channel. Most of the chert is not distinct; however,

259

SEDIMENTARY FACIESAND DEPOSITION,AXEL HE1BERG SHELF TABLE 2

(continued)

Facies Core & depth (cm)

D 058 6-12

D 058 12-14

G 058 21 25

E 063 90-91

E 063 115 116

E 102 95 96

E 112 34 35

C 114 41 42

C o m m o n qtz Volcanic qtz Recrystallized qtz Stretched meta qtz Vein qtz

17.6 0.0 0.0 2.1 0.0

28.7 0.0 0.0 5.4 0.0

30.5 0.0 0.0 2.4 0.0

55.4 0.0 0.0 5.4 0.0

51.2 0.0 0.0 6.0 0.0

59.9 0.0 1.8 3.0 1.2

50.7 0.0 0.0 5.9 0.0

57.3 0.0 0.0 5.6 0.0

Total qtz

19.7

34.1

32.9

60.9

57.1

65.9

56.7

62.9

2.1 8.3

1.6 6.2

3.8 10.5

5.9 23.8

4.1 19.4

10.2 7.8

6.9 20.2

3.2 15.3

Plagioclase Alkali feld

10.4

7.8

14.3

29.7

23.5

18.0

27.1

18.5

Biotite Hornblende Chlorite Clinopyroxene Haematite Other minerals

Total feld

1.0 0.0 1.0 0.5 1.6 1.0

0.0 0.0 3.9 3.1 4.7 2.3

0.0 0.0 1.4 1.9 1.4 1.4

1.0 0.0 1.0 2.0 0.0 1.0

0.0 0.0 1.4 2.8 1.4 1.8

0.0 0.0 0.6 1.2 0.0 1.2

1.0 0.0 1.5 1.5 0.5 1.0

0.0 0.0 1.6 3.2 8.9 2.4

Total mafic m i n e r a l s

5.2

14.0

6.2

5.0

7.4

3.0

5.4

16.1

Mafic volcanic Sandstone, siltstone Mudstone Limestone Chert Metamorphic Granitic O t h e r rock frag

30.1 11.9 7.3 6.7 5.2 3.6 0.0 0.0

3.9 7.8 4.7 7.8 8.5 5.4 5.4 0.8

5.7 12.9 4.8 17.6 2.9 2.9 0.0 0.0

0.5 0.5 0.5 1.5 1.0 0.5 0.0 0.0

1.4 1.8 1.4 2.8 2.8 1.8 0.0 0.0

0.6 0.0 1.2 3.0 3.0 1.8 2.4 0.0

2.0 0.5 0.0 3.0 3.0 2.5 0.0 0.0

0.0 0.8 0.0 0.0 0.8 0.8 0.0 0.0

Total rock frag

64.8

44.2

46.7

4.5

12.0

12.0

10.8

2.4

0.0

0.0

0.0

0.0

0.0

1.2

0.0

0.0

23 0.18

1.3 0.2

20 0.18

0.5 0.12

2.5 0.2

0.6 0.15

0.7 0.15

0.6 0.15

Unidentified

Approximate grain size Sample max, mm ts average, mm

one chert fragment contains poorly perserved fossil outlines. The metamorphic rocks include micaschist, quartz micaschist, quartzite and gneiss. Metamorphic rock fragments occur in most samples, but are most abundant in Facies F (Fig.6) from the offshore highland. Distinct haematite rims occasionally occur around rock and mineral grains. Cursory examination of other coarse fractions throughout the cores shows a similar distribution of the rock and mineral types described here from thin section. The variety of rock and mineral fragments as well as the

variation in the grain shape indicates a mixed source area, dominated by a plutonic terrain. The plutonic and metamorphic rock and mineral fragments probably originated from Pearya (Fig.lB), whereas the sedimentary rock fragments were probably eroded from the adjacent Palaeozoic Franklinian Mobile Belt and from Sverdrup Basin (Fig.lB) (Trettin, 1987). Although only three of the samples have a large percentage of mafic volcanic rocks, the occurrence of augite in nearly all samples is indicative of a nearby volcanic source. This is probably the Upper Cretaceous volcanic

Quartz + F:e!aspar

/.

A' ?

0

Rock Fragments

Mafic Minerals

Metamorphic and Granitic Rock Fragments

FACIES •

A

C •

B

Sedimentary Rock Fragments

t:errain along northernmost Ellesmere island is very rugged, with both glaciers a~,d mass movement delivering rocks to the Arctic Ocean today (these rocks are easily rafted by sea ice or icebergs (J. England, pers. commun . 1988)), and (3) surface ocean currents travel westward along the coast of northernmost Ellesmere Island, transporting debris-laden ice across the Axel Heiberg Island Shelf. Many ice-rafted rocks have also been noted on raised marine shorelines in Phillips Inlet, northwestern Ellesmere Island (J. England, pers. commun., 1988). Consequently, the Shield of mainland Canada is a less likely source, more distant and not favoured by direct passage to the study area offshore of Axel Heiberg Island.

D

© E ~:i' F+G

Mafic Volcanic Rock Fragments

Fig.6. Petrography of the coarse ( > 63 ~m) fraction from selected samples, showing (A) the variation in textural maturity and (B) rock fragment composition as an indication of source area. Refer to Fig.3 for sample locations. Petrographic data are given in Table 2.

rock exposed along the cliffs of northwestern Ellesmere Island (Embry et al., 1988). The various sedimentary facies cannot be distinguished on the basis of sediment m a t u r i t y or source area as indicated by rock fragment composition (Fig.6). This suggests t h a t there has not been a major change in the source area during the time interval represented by the cores. The Pearya source for the plutonic and metamorphic rock fragments is favoured over a source on the Shield on mainland Canada for three reasons: (1) extensive plutonic and metamorphic terrains occur along northernmost Ellesmere Island (Fig.lB) (Trettin, 1987), (2) the

Discussion The sediments obtained from the inner continental shelf north of Axel Heiberg Island are predominantly fine-grained marine de~ posits overlying possible Tertiary bedrock (Facies F). The sedimentary facies described here are quite similar to those noted by Goldstein (1983) in more offshore settings on the outer continental rise in the western Arctic Ocean. The facies also resemble nearshore marine deposits in the Kane Basin between Greenland and Ellesmere Island (Kravitz, 1983). At the oceanic sites, Goldstein (1983) identified zones dominated by ice-rafted debris, turbidite sedimentation, and mixed ice-rafted and turbidite influences (Table 3). Although his study area was on the outer continental rise, he noted facies segregations similar to those noted in the present study on the deep inner shelf off Axel Heiberg Island. Coarse diamictons (which could be unequivocabty interpreted as till deposited from a former regional ice sheet) were not observed in our cores. This suggests that late Quaternary glaciers did not inundate the Axel Heiberg continental shelf. Furthermore, the sediment cores provide no evidence that glaciers regionally excavated the high arctic fjords and interisland channels. These observations support the model of England and his co-workers

261

SEDIMENTARY FACIES AND DEPOSITION, AXEL HEIBERG SHELF

o ¢. c~

,< 5~ oo

¢-

c~ 0 5f~ ~.9

n. oo

n: 0 0

0 r~

~ '~ ¢, c~

¢O

o

0

~o~

o

© ~D

O

o

<~ ..4

oO c~

c~ c2 c~

~

~o

~,0

n~ o0

c~

.<

"~o

o

m,

.~

¢. c~

N o

N cb~ o0

oo

<

0

~e ~r..-

(England and Bradley, 1978; England et al., 1978; England, 1985, 1987; Retelle, 1986), as well as models for the central Arctic Ocean (Clark and Hanson, 1983; Minicucci and Clark, 1983; Goldstein, 1983). Osterman and Andrews (1983), in their facies analysis of a core taken in Frobisher Bay, southeast Baffin Island, show a predominance of ice rafting, with secondary reworking by bottom currents in a nearshore glaciomarine setting (Table3). There is no evidence of significant slumping of material, nor of transport by debris flows or turbidity currents. This contrasts with the Axel Heiberg Shelf in which much of the laminated sediment is interpreted as being deposited from fine-grained turbidity currents, and the more lenticular pebbly muds from debris flows. In narrow Baflin Island fjords north of Frobisher Bay, however, preliminary analysis of surficial deposits from the floors of ten fjords shows that the facies are virtually identical to those described from the Axel Heiberg Shelf (Hein and Longstaffe, 1983; Reasoner and Hein, 1984). This is particularly true for the finer grained cores from the centres of the fjords. Differences arise in the more sanddominated systems, in which there is a greater influence of coarse-grained, sediment gravity flows (Syvitski and Farrow, 1989; Syvitski and Hein, in prep.) (Table 3). Only one of these fjords (Coronation) has a tidewater glacier. Other fjords receive most sediment from glacial meltwater, mass wasting and sediment gravity flows generated on the steep sides of the fjords, with minor input by surface runoff, aeolian transport or by ice rafting. By analogy, similar processes are interpreted to have emplaced the late Quaternary sediments on the Axel Heiberg Shelf. A generalized facies model for the glacial seas surrounding Antarctica is given by Anderson et al. (1979, 1983, 1984). The main distinction between the Antarctic and the arctic seas of the Northern Hemisphere is t h a t the West Antarctic glacial ice sheet is presently grounded at or below sea level over large coastal areas (depths between 0 and -500 m,

with a maximum depth of more than i000 m). Antarctic glaciomarine sedimentation is domb nated by ice rafting, with only a very minor meltwater input (Table 3). At this glacial ice sheet margin, sediment is deposited as lodgement till near the grounding line. Seaward of the grounding line, marine currents rework the material, removing the fine fractions and thus increasing the sorting of the glaciomarine sediments in comparison with the lodgement tills. In coastal regions of Antarctica where the ice sheets are grounded at or above sea level, facies tend to be more restricted. Here, debris flows and turbidity currents redistribute much of the sediment to the offshore (Table 3). Many of these offshore facies from Antarctica are similar to those observed on the Axel Heiberg Shelf. One very important difference is that on the central Axel Heiberg Shelf there is a lack of true subaqueous till or lodgement till, and little reworking of sediment by marine currents. The proportion of debris flow facies is also far lower than that reported from the Antarctic shelf. These observations indicate that the palaeoenvironment of the Axel Heiberg Shelf was not comparable with the setting in Antarctica where sediment is input mainly from glacial ice into the sea. Rather, the palaeoenvironment was more similar to that observed in Baffin Island fjord, where much sediment input is removed from direct glacial influence and sediment transport is mainly by meltwater, fluvial, mass-wasting, and aeolian mechanisms. Conclusions

(1) Various types of sediment gravity flows deposited material on the Axel Heiberg Shelf. These include submarine slumps, debris flows, turbidity currents, and possible underflows which were emplaced in a realm of normal hemipelagic sedimentation. Fallout from wasting of ice shelves or more solitary icebergs is less common. Reworking by wave or bottom currents is minimal. (2) An offshore submarine bank was cored in the study area. The recovered material is semi-

SEDIMENTARY FACIESAND DEPOSITION, AXELHEIBERGSHELF

indurated, reddish/ochre coloured, stratified sandy mud and gravel. It may be altered Tertiary bedrock. Although the interpreted marine currents are believed to be minor, sedimentation on high steep slopes may have generated sediment gravity flows which transported material off the bank, accounting for the thin veneer of sediment observed here. Thus, this bedrock may have provided a secondary source for sediment in the offshore deep-shelf setting. (3) Petrographic studies of the coarse fraction (>63 ~m) suggest a dominantly mixed source area, dominated by a plutonic terrain. The plutonic and metamorphic fragments were probably derived from Pearya, whereas the sedimentary rock fragments were eroded from the Franklinian Mobile Belt and Sverdrup Basin. The occurrence of augite in nearly all samples indicates a nearby volcanic source, probably the Cretaceous volcanics exposed on Ellesmere Island. (4) Comparisons with other glacial-marine facies models show that the Axel Heiberg Shelf sediments are most similar to the dominantly finer grained deposits (generally sand-sized and finer) in Baffin Island fjords and to the raised glaciomarine sequences exposed on Ellesmere Island. (5) There is no evidence from these cores (i.e. no till was recovered) that regional glacial ice sheets inundated the deep-shelf offshore Axe] Heiberg Island, nor is there any evidence from these cores to support the model that the fjords and inter-island channels were deepened by glacial erosion.

Acknowledgements This work was largely funded by D.S.S. contracts to Hein and Van Wagoner from the Atlantic Geoscience Centre. Funding for preparation of the manuscript was from N.S.E.R.C. grants to Hein and Van Wagoner. Grain-size analyses were made by Jean Dabros. J o h n England, Bob Gilbert and Donn Gorsline are thanked for their critical reviews of earlier versions of the manuscript. Logistical support

263

for the field work was provided by the Polar Continental Shelf Program (GSC Project 840086).

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