Geol Rundsch (1995) 84:665-682
D. Ntirnberg - M. A. Levitan
© Springer-Verlag 1995
" J. A .
Pavlidis
E. S. Shelekhova
Distribution of clay minerals in surface sediments from the eastern Barents and south-western Kara seas
Received: 24 June 1994 / Accepted: 5 February 1995
Abstract Surface samples from the eastern Barents and south-western Kara seas have been analysed for clay mineralogy. Transport paths, the role of regional sources and local bedrock outcrops and the influence of hydrodynamic and glacigenous processes for clay distribution on the shelves are discussed in relation to central Arctic Ocean deep sea and sea ice sediments. Franz Josef Land and Novaya Zemlya show significantly different clay mineral associations. Although smectite concentrations are fairly high, Franz Josef Land can be excluded as a source for central Arctic sea ice sediments, which are relatively rich in smectite. In the Kara Sea, smectite concentrations in coastal sediments surpass even the Franz Josef Land concentrations. The large cyclonic gyre in the eastern Barents Sea between Novaya Zemlya and Franz Josef Land, which serves as a mixing zone between Arctic and North Atlantic water, is apparently reflected within the smectite distribution pattern. With the exception of Franz Josef Land, the area of investigation is typically low in kaolinite. In particular, coastal areas and areas north of Novaya Zemlya, influenced by the inflow of Arctic waters, show the lowest kaolinite concentrations. A high kaolinite occurrence within the Nansen Basin is most probably related to Franz Josef Land and emphasizes the importance of long-range downslope transport of sediments across the continental slope. The surface water circulation pattern in close interaction with local outcrops onshore Novaya Zemlya and locally restricted occurrences within the eastern Barents Sea significantly alter the illite dispersal pattern. Illite concentrations are lowest around Franz Josef Land. Chlorite is generally low in the area of investigation. Submarine outcrops D. Ntirnberg (EN) Alfred Wegener Institute for Polar and Marine Research, D-27568 Bremerhaven, Germany, Tel.: 0471 4831 238, Fax: 0471 4831 149, e-mail:
[email protected] M. A. Levitan - J. A. Pavlidis • E. S. Shelekhova P. P. Shirshov Institute of Oceanology, Moscow, Russia
and important chlorite occurrences onshore Novaya Zemlya bias its distribution pattern. Key words Clay mineralogy • Eurasian Arctic shelves • Dispersal processes • Potential source areas • Lithogenic tracers • Sea ice transport
Introduction In the Arctic region, clay mineral data are available for most shelf areas (e.g. Naidu et al, 1971; Silverberg, 1972; Andrew and Kravitz 1974; Wright 1974; Elverh¢i et al. 1989), coastal areas (e.g Kalinenko et al. 1974) and adjacent shallow seas (Kalinenko et aI. 1974). In the deep Arctic Ocean, investigations were performed by Berner (1991), Bohrmann (1991) and Stein et al. (1994). Distribution maps of the eastern Barents and south-western Kara seas, however, have not yet been published. In this study, we present distribution charts of the common clay mineral groups within the surface sediments of these shelf areas. The samples presented were collected in a joint research program between the Shirshov Institute of Oceanology (Moscow) and the Alfred Wegener Institute for Polar and Marine Research (AWI, Bremerhaven). It is tested whether the clay mineral distribution can be used to define sedimentary processes and wether it can be applied to relate depositional centers to specific source or provenance areas of clay minerals. In particular the role of sea ice in the dispersal of clay minerals is investigated. In the Arctic Ocean, transport agents and processes, pathways, depositional centers and the corresponding source areas of clay minerals are relatively unknown (e.g. Andrew and Kravitz 1974; Wright 1974; Naidu et al. 1982; Naidu and Mowatt 1983). Sea ice has been proved to be an important agent in transporting large amounts of mainly fine-grained sediments across the Arctic Ocean (e.g. Pfirman et al. 1989; Wollenburg 1993; Ntirnberg et al. 1994). A few studies have shown that clay minerals can be used to trace the pathways of
666 Fig. 1 Bathymetric map of the study area showing geological sampling sites. Bathymetry is given in meters. For the RV Professor Shtockrnan stations (B), the clay mineralogy (< 1 ~m fraction) was analysed at the Shirshov Institute of Oceanology. For the RV Professor Shtockman stations (0), the clay mineralogy (< 1 ~m fraction) was studied at the AWI; and at the RV Dalnie Zelentsy stations (A), the clay mineralogy (< 2 ~xm fraction) was investigated at the AWL Inset shows the location of the study area
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sea ice, to decipher the source areas of sea ice and deep-sea sediments and to elucidate transport processes (e.g. Darby et al. 1989; Wollenburg 1993; Ntirnberg et al. 1994; Stein et al. 1994).
Materials and methods The study area covers the eastern Barents and southwestern Kara seas (approximately 30°E to 70°E and 68°N to 81°N) (Fig. 1). The sample density decreases to the north, mainly caused by unfavorable ice conditions during the expeditions. Samples from 115 sites, which were obtained during cruises 8, 10 and 12 of R V Professor Shtockman between 1982 and 1984 and cruise 68 of R V Dalnie Zelentsy in 1992 (Matishov et al. 1993; Ntirnberg and Groth 1993) have been investigated (Ta-
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ble 1). Surface sediments were sampled by Van Veen grab and a giant box corer, and comprise approximately the upper 1 cm of the sediment column. Before analyses, sediment samples were oxidized and disaggregated with a 3-10% H202 solution. The < 63 txm fraction was obtained by washing through a 63 ~m sieve. Silt and clay fractions were separated in settling tubes by the Atterberg m e t h o d (Mtiller 1967). During this stage, differences between the Russian and G e r m a n analytical procedures became evident. In Russia, clay mineralogy is determined on sediment fractions of < 1 txm, whereas in G e r m a n y the < 2 txm fraction is used. Slight differences, especially in smectite concentrations, may therefore occur. In this paper, we concentrate on the main clay mineral groups of smectite, illite, kaolinite and chlorite. Although different methods have been applied, the comparison of closely located sediment samples elucidates that semiquantita-
667 Table 1 Sampling sites, clay mineral contents of the carbonate-free clay ( < 1 and < 2 txm) fraction (%) and portion of the clay fraction ( < 1 and < 2 txm) in relation to the bulk sediment, n . d . = N o data Station-#
Latitude (°N)
Longitude (°E)
Smectite (%)
Illite (%)
Kaolinite (%)
Barents Sea Samples processed at the Alfred Wegener Institute 1367 1369 1295 1299 1300 1302 1303 1306 1307 1308 1323 1326 1327 1328 1332 1333 1334 1335 1341 1343 1346 1350 1352 1266 1268 1284 1310
72°42.90 72°28.40 73°41.70 75°40.60 75°21.70 74°43.00 74°34.80 75°05.20 74°51.70 74°42.80 77°00.00 76°01.80 75°44.90 75°29.20 77°07.40 77°33.60 77°49.00 77°21.30 78°22.40 77°22.80 76°25.80 77°01.30 77°24.00 72°53.70 73°34.20 71°00.50 74°06.60
36°20.60 33°32.80 50°23.70 46°54.60 48°39.10 52°13.20 52°58.30 51°47.60 52°56.60 53°50.30 52°29.70 55%7.50 56°30.80 57°16.60 66°00.50 64°52.10 64°05.80 63°38.60 58°00.00 57°59.20 60°10.50 62°08.80 62°30.00 43°46.40 41°30.80 53°21.50 55°41.90
Chlorite (%)
< 1 ~m fraction ( % )
R V Prof. Shtockman Samples < 1 ~ m 7 0 0 35 17 3 0 35 13 17 5 13 3 0 0 21 0 0 0 0 3 0 0 0 0 27 0
47 79 63 40 57 56 67 40 55 54 62 55 74 72 78 48 58 69 65 57 69 100 74 57 60 47 76
24 10 20 12 12 12 13 11 13 11 14 18 7 8 11 14 23 13 18 14 11 0 8 21 21 11 6
22 11 17 14 14 28 20 13 19 18 18 14 17 20 10 17 19 18 16 29 17 0 17 21 19 15 18
33.10 31.63 n.d. 34.20 53.76 25.08 33.49 18.44 25.42 44.47 n.d. 13.30 47.23 38.72 25.19 13.45 26.47 26.98 24.29 12.97 32.00 19.46 26.36 44.64 50.04 24.64 45.80
54 49 55 49 38 28 30 43 33 42 47 23 61 53 50 40 25 4 56 14 39 53 47 49 43 32 48
26 31 27 31 40 49 46 34 43 33 30 45 39 31 35 37 42 71 27 62 42 33 31 32 37 46 36
7 9 8 8 8 6 4 11 4 9 10 13 0 6 7 12 14 4 5 5 8 7 7 9 11 6 6
12 11 10 11 14 16 20 12 21 16 13 18 0 10 8 12 18 21 12 19 11 8 15 10 9 16 10
n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. n.d. 43.02 40.22 n.d. n.d. 55.86 n.d. n.d. 37.06 17.70 31.56 n.d. 48.59 n.d. n.d. n.d. n.d. n.d.
Kara Sea Samples processed at the Alfred Wegener Institute 1371 1372 1373 1374 1375 1376 1378 1379 1380 1381 1382 1385 1386 1387 1388 1389 1391 1394 1395 1396 1397 1399 1400 1401 1402 1403 1407
70°47.40 70°19.40 69°48.00 69°28.00 69°44.60 69°17.80 70°49.09 70°30.90 70°12.00 69°57.40 72°00.40 71°27.10 71°12.00 72°03.60 72°18.50 72°30.90 73°59.90 73°29.90 73°45.00 74°53.90 74°37.70 73°57.03 73°01.00 73°19.10 73°35.30 73°48.40 72°15.00
58°51.30 60°07.60 63°51.80 65°15.10 65°49.60 66°24.60 65°24.01 64°14.10 63°04.00 62°13.30 62°01.70 64°52.20 66°10.00 68°02.80 66°43.70 65°36.60 65°59.90 68°10.00 66°59.40 61°35.30 62°53.00 66°04.20 63°01.20 61°28.60 59°59.20 58°43.40 60°44.10
For continuation of Table 1 please see the next page
668 Table 1 (continued) Station-#
Latitude (°N)
Longitude (°E)
Smectite (%)
Illite (%)
Kaolinite (%)
Franz Josef Land and Novaja Zemlja Samples processed at the Alfred Wegener Institute 180811 180821 100811 200811 200822 200831 210821 210842 210842 220811 220822 230812 240813 250811 260811 270811 270822 280811 300811 300821 300831 310822 010911
72°59.08 73°35.98 75°28.23 75°35.50 76°25.39 76°28.50 77°19.40 78°03.66 78003.66 78°54.50 79°50.00 81°07.11 80°20.57 80°37.20 80°44.30 80°30.40 80°24.04 80°19.92 75°33.30 75°28.50 75021.50 73°00.62 71°35.10
053°03.38 052°16.48 056°46.06 057°59.00 061°23.72 065°11.80 062°16.90 061°11.20 061°11.20 059°00.00 061°29.00 063°31.57 060°19.94 058o05.80 057°53.80 056°43.80 059°37.75 052°50.00 056°26.70 057°10.00 057°35.80 051°53.64 044°24.70
72°43.80 73°58.20 74°21.60 74°21.60 73°31.80 72°37.80 69°51.00 70%2.80 71°07.80 69°28.80 74%3.60 74°21.60 73°33.60 73°32.40 76°03.60 74°27.60 75°00.00 75°23.40 74°43.20 74°06.00 75°52.80 75%3.40 77°13.20 76°54.00 76%6.40 79°50.40 78%1.60 70°19.80 69°37.20 70°21.60 70°13.80 75°44.40 70°00.00 74°46.20 74°37.20 71°45.00 74°21.00
43°01.20 59°44.40 43°01.20 45°36.60 46°22.80 41°58.80 51°01.80 52°54.00 44°04.80 43°21.60 38°16.80 48°06.00 48°16.80 50°18.60 45°00.00 52°55.80 50°57.00 50°25.80 53°06.00 55°00.00 49°28.80 57°45.60 52°39.00 53°27.00 54°39.40 57°50.40 57°55.80 55°41.40 55°51.60 41°07.20 40°20.40 64°39.60 55°41.40 56°22.80 56°24.60 45°20.40 42°04.20
< 1 txm fraction ( % )
R V Prof. Dalnie Zelentsy < 2 ~ m 2 27 6 1 3 0 30 34 35 31 19 34 16 40 40 39 27 44 9 3 2 28 40
58 37 59 66 60 50 38 29 30 31 30 24 24 19 18 19 23 20 55 60 62 37 29
2 10 6 4 6 1 12 17 18 18 30 26 41 28 28 29 35 23 6 6 6 9 12
Barents Sea Samples processed at the Shirshov Institute 1267 1269 1272 1273 1275 1277 1280 1282 1286 1289 1292 1293 1294 1295 1298 1303 1301 1305 1307 1311 1317 1322 1323 1324 1325 1339 1342 1409 1412 594 595 2146 2149 2167 2163 1265 1271
Chlorite (%)
37 26 29 29 31 48 21 20 18 20 20 17 19 13 14 14 15 13 31 32 31 26 19
0.21 2.82 38.59 38.64 21.73 32.70 4.27 57.36 60.54 53.33 25.12 44.13 24.53 5.61 34.66 34.26 19.17 42.02 22.45 43.16 45.39 9.58 0.79
R V Prof. Shtockman Samples < 1 ~ m 23 22 24 23 14 33 16 28 22 37 26 34 31 29 11 7 38 16 17 0 14 24 3 16 6 23 5 25 37 10 31 7 18 0 0 24 17
51 56 46 58 62 43 59 55 67 47 38 47 47 47 67 75 39 52 55 82 52 54 57 44 60 66 67 40 48 75 51 57 54 68 72 49 49
9 7 14 8 10 9 7 0 3 0 17 6 7 3 7 0 0 7 0 0 17 6 20 20 3 4 0 9 0 8 0 10 10 0 0 19 0
17 15 17 11 14 17 19 16 8 16 20 12 15 22 15 19 23 26 28 18 17 17 20 20 31 7 29 27 16 8 18 27 18 33 28 8 33
36.49 32.72 30.83 35.36 41.12 40.45 22.85 37.77 25.72 10.23 18.00 12.52 15.63 41.67 39.09 n.d. 25.08 30.97 n.d. 38.81 22.55 47.65 56.29 9.96 6.03 36.87 48.62 32.46 3.72 n.d. n.d. n.d. n.d. n.d. n.d. 30.84 42.06
669 Fig. 2 Surface water circulation pattern superimposed on the bathymetry of the study area. Surface currents: A, Murmansk Current; B, Kanin Current; C, Murman Coastal Current; D, White Sea Current; E, Novaya Zemlya Current; F, Kolguev-Pechora Current; G, Central Current; H, Litke Current; I, Yamal Current; K, Eastern Novaya Zemlya Current; L, Zone of possible Ob influence; and M, Makarov/Persey Current. The probability of sea-ice coverage (%) at the end of April is adopted from Vinje and Kvambekk (1991)
tive differences are only of minor importance, particularly when drawing isolines in 10% gradations. A total of 37 samples according to Russian standards (Table 1) was processed at the Shirshov Institute of Oceanology and at the D e p a r t m e n t of Geology of Moscow State University. CaCO3 was not dissolved because concentrations were usually below 5%. Texturally oriented samples were prepared by dropping the suspended < 1 ~m fraction onto glass slides. These were analysed by X-ray diffractometry using a D R O N - 3 instrument with CuKa radiation. A three-step measurement was applied: (i) in an air-dry state; (ii) after exposure to ethylene glycol vapor; and (iii) after heating in an oven (580-600 ° C) for one hour. To destroy chlorite and to improve the determination of kaolinite, selected samples were boiled within a 7% solution of HC1 for one hour. Scans were performed on these samples from 2 ° to 40 ° 20 in 0.02 ° steps for two seconds at each step.
The individual clay minerals were identified by their basal reflections at ca. 17 A (glycol: smectite), 10 A (illite), 14.2, 7, 4.72 and 3.54 A (chlorite) and 7 and 3.58 (kaolinite). The relative percentage of each clay mineral was determined using the ratio and weight factors of peak areas (Biscaye 1965). Twenty-three samples gathered during the R V Dalnie Zelentsy cruise 68 (Table 1) were processed at the A W I according to a m e t h o d described in detail by Lange (1982) and E h r m a n n et al. (1992). Texturally oriented specimens were produced by vacuum filtration of the < 2 Izm fraction through a filter of 0.15 txm pore size and these were subsequently analysed with a Philips PW 1700 automated X-ray diffraction system with CoKa radiation (40kV, 4 0 m A ) . The density of the layer (ca. 40 Ixm thick) is ca. 10 mg/cm 2. Measurements were performed on untreated and glycolated (ca. 18 hours at 60 ° C) samples from 1° to 18 ° 20 and from 2 ° to
670 40 ° 20, respectively, in 0.02 ° steps for two seconds at each step. For the separation of kaolinite and chlorite, an additional scan was performed in 0.005 ° steps for two seconds at eachostep between 28 ° and 30.5 ° 20 to determine the 3.54 A peak of chlorite and the 3.58 peak of kaolinite (Biscaye 1964). Semi-quantitative evaluations were based on peak areas for the four clay mineral groups smectite, kaolinite, chlorite and illite at the angles described above. Fifty-five samples from the Barents and Kara seas comprising the < 1 txm fraction were provided by the Shirshov Institute of Oceanology (Table 1). The clay fraction (without dissolving CaCO3) was processed at the AWI. Owing to the low amount of material, we prepared specimens by evaporating the suspended < 1 ~m fraction onto aluminium slides. The resulting density of the layer (ca. 6 Ixm thick) is ca. 1.5 mg/cm 2. X-Ray analyses were subsequently applied using the parameters described earlier. Isolines have been manually drawn according to the relative percentages of the clay minerals in the < 2 txm fraction. In particular, at the edges of the charts, and in areas where the data density is reduced, isolines may differ from reality. The distribution pattern of the < 1 txm fraction has been drawn using data from Table 1 and following the pattern outlined in Gorshkov and Faleev (1980).
influences the current conditions, particularly around Spitsbergen Bank and along the northern coast of Norway (Sundby 1984; Vinje and Kvambekk 1991). During summer, Barents Sea shelf waters are clearly stratified, whereas the stratification is less developed during winter. The surface current pattern indicated in Fig. 2 is generally valid for the entire water column (Vinje and Kvambekk 1991). In places, however, there are changes in current direction with depth (Tantsyura 1959; Johansen et al. 1988; Loeng 1991). The southern Kara Sea is mainly disconnected from inflowing Atlantic waters (Dobrovolski and Zalogin 1982). The surface water circulation within the southwestern Kara Sea is characterized by a cyclonic cell (Fig. 2). The eastern, northward flowing branch consists of surface waters penetrating from the Barents Sea into the Kara Sea via straits south of Novaya Zemlya. These surface waters join with the Yamal Current and flow northward along the Yamal Peninsula. North of it, this current is strengthened by the Ob-Yenisey drainage system, bounds to the west and constitutes the southward flowing Eastern Novaya Zemlya Current. Near the southern straits, it joins with Barents Sea waters. The sea ice drift pattern largely reflects this surface water circulation pattern in the south-western Kara Sea. The discharge of freshwater from Ob and Yenisey (1243km3/a according to Kulikov 1961; Alexander 1973) strongly affects the hydrological balance of the Kara Sea.
Modern environment and oceanography The main element of surface water circulation within the Barents Sea is a relatively stable cyclonic gyre showing seasonal variations (Novitskiy 1961; Tantsyura 1973; Davidan 1974; Demenitskay 1974; Midttun and Loeng 1987). This gyre is generated by the eastward flowing continuation of relatively warm Atlantic water in the south and the inflow of Arctic waters in northern areas between Franz Josef Land and the northern tip of Novaya Zemlya (Dickson et al. 1970) (Fig. 2). The eastwest trending oceanic Polar Front at approximately 74-75 ° N (Johannessen and Foster 1978) separates these Arctic water masses to the north (Midttun and Loeng 1987) from the warm, saline north-eastward flowing North Atlantic water (Elverh0i et al. 1989). During summer, the southern edge of the Arctic pack ice traces the oceanic Polar Front (Elverh¢i et al. 1989). The Atlantic-type North Cape Current separates into several eastern branches. The northern and southern branches, the Murmansk and Murman Coastal currents, and the Kanin and Novaya Zemlya currents, form the southern part of the cyclonic cell (Tantsyura 1959) (Fig. 2). The eastern part of this system is called the Litke (Novaya Zemlya) Current. The northern part of the cyclonic gyre is presented by the Makarov, Persey and Bear Island currents transporting Arctic waters to the west and south-west (Novitskiy 1961; Dobrovolsky and Zalogin 1982). The bottom topography strongly
Geological setting Seafloor topography and geology In the Barents Sea, the average water depth of about 230 m (Elverh0i et al. 1989; Vinje and Kvambekk 1991) exceeds most other Eurasian shelves. The mean water depth of the Kara Sea is 118 m, with a maximum depth of about 600 m in the Novaya Zemlya Trough (Perry et al. 1986). According to geological, geophysical and geomorphological investigations, seven geomorphological provinces can be distinguished (Aksyonov 1987) (Fig. 3). These provinces reflect major tectonic elements of ancient Precambrian platforms, and Caledonian and Hercynian fold belts, which have been modified by neotectonic activity and Pliocene-Quaternary glacier activity (Nansen 1904; Elverh0i and Solheim 1983; E1verh¢i et al. 1989; Merklin et al. 1992; Pavlidis et al. 1992). In addition to glacier-proximal glaciomarine sediments sometimes forming positive bathymetric features (e.g. Spitsbergen Bank and Stor Bank westward of the study area; Elverh¢i and Solheim 1983; Solheim and Kristoffersen 1984; Solheim et al. 1988), Pleistocene till and moraines occur (Merklin et al. 1992; Pavlidis et al. 1992). Moraine deposits are of local distribution on the shelf and mark the extension of glaciers from Novaya Zemlya, Spitsbergen, Franz Josef Land and Scandina-
671 Fig. 3 Bathymetry map showing geomorphological structures and provinces used in this study: I, Yamal; II, Novaya Zemlya; III, Franz Josef Land; IV, Pechora; V, Scandinavia-Kanin; VI, eastern Barents Sea; and VII, eastern periphery of the western Barents Sea
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50% (Table 1). Relatively coarse sediments with a < 1 Ixm fraction below 10% are generally confined to shallow coastal areas (northern Kanin Bank, northern coast of Kola Peninsula, Bay of Kara, northern and north-western coasts of Yamal Peninsula) and bathymetric rises. Sediments become increasingly finer with water depth. The Eastern Novaya Zemlya Trough, the Northern and Southern Novaya Zemlya Trough, the central Kara Sea and most parts of the eastern Barents Sea comprise 25-50% of the < 1 txm fraction.
672 Fig. 4 Distribution of the < 1 txm fraction in surface sediments. Surface water circulation and geomorphological provinces are superimposed
Distribution of clay minerals in surface sediments The investigation of clay minerals within surface sediments of the eastern Barents and south-western Kara seas reveals a distribution pattern which is severely influenced by the oceanographic regime and the shape of geomorphological provinces. Franz Josef Land and Novaya Zemlya, which are characterized by significantly different clay mineral assemblages and serve as important source areas, overprint this clay mineral distribution pattern.
Smectite In the entire area of investigation, smectite concentrations range between ca. 0 and 60% (Fig. 5). The Franz
Josef Land area shows maximum values of 20-40%. The concentrations even reach values > 40% within the inner fjords of Franz Josef Land. These high values were also observed in the south-western Kara Sea along the southern island of Novaya Zemlya, the central part of the western coast of Yamal Peninsula and the southern boundary of the south-western Kara Sea. Here, concentrations even exceed 60%. Further north and in the Bay of Kara, smectite concentrations decrease to 20-40%. At a few sites at the northern tip of Yamal Peninsula and along the north-eastern coast of Novaya Zemlya concentrations decrease to < 20%. Sediments in the south-eastern Barents Sea and in coastal areas off southern Novaya Zemlya are generally characterized by smectite concentrations of 20-40%. The Pechora province, however, is low in smectite (ca. 16%). The sample density is very low in this area. Coas-
673 Fig. 5 Distribution of smectite in surface sediments. Sampling sites, surface water circulation and geomorphological provinces are superimposed
tal sediments from the northern island of Novaya Zemlya also exhibit low smectite concentrations around 0-20%. These low concentrations prevail within the north-eastern Barents Sea (Novaya Zemlya Province and the northern part of the Eastern Barents Sea Province).
Kaolinite In general, the area of investigation is low in kaolinite (Fig. 6). Concentrations normally range below 20%. Particularly along the coastal areas of the south-western Barents Sea, sediments around Novaya Zemlya, Yamal Peninsula and of the Pechora, ScandinavianKanin and southern parts of the Eastern Barents Sea provinces show values < 10%. Exceptionally high val-
ues (20-30%) occur locally in the southern part of the eastern Barents Sea Province. In contrast, the locally restricted area of the Franz Josef Land archipelago is an important source of kaolinite. Concentrations are around 20-30% and increase to a maximum of 3 0 4 0 % at a few sites. South of the Franz Josef Land archipelago, kaolinite concentrations decrease to 10-20%. These medium concentrations continue southward to approximately 74°N. F u r t h e r south, concentrations range between 0 and 10%, except in the center of the south-western Kara Sea (10-20%). Illite The dominant clay mineral in most surface sediments is illite (Fig. 7). Maximum concentrations increase to
674 Fig. 6 Distribution of kaolinite in surface sediments
> 8 0 % , whereas the minimum concentrations are around 20%. Franz Josef Land and adjacent areas significantly differ from the south-eastern Barents Sea and main parts of the south-western Kara Sea. Most samples collected within the inner fjords of Franz Josef Land have concentrations < 2 0 % . Sediments from areas further south have relatively low illite concentrations (20-40%) when compared to sediments from the remaining study area (40- > 60%). The eastern Barents Sea is generally characterized by relatively high concentrations of illite (40-60%). At locally restricted sites within the eastern Barents Sea, concentrations even exceed 60%. This is also true for coastal sediments of the northern island of Novaya Zemlya, the northern coast of Yamal Peninsula and Kola Peninsula. In contrast, the center part of the south-western Kara Sea as well as a west-east trending
region in the middle of the eastern Barents Sea exhibit lower illite concentrations (20-40%).
Chlorite Chlorite concentrations range between ca. 10% and a maximum of 48% (Fig. 8). The distribution of this mineral is fairly uniform. In large parts of the eastern Barents Sea, the south-western Kara Sea and around Franz Josef Land archipelago, concentrations are around 10-20%. Coastal surface sediments from the western side of the archipelago exhibit concentrations of > 2 0 % . The high concentrations continue much further seaward and are typical for nearly all of the western part of the Novaya Zemlya Province. At the northern tip of Novaya
675 Fig. 7 Distribution of illite in surface sediments
Zemlya, high chlorite concentrations can also be traced in coastal sediments east of the northern island. In addition, striking exceptions (>20%) from the overall low chlorite concentrations in the eastern Barents and south-western Kara seas can be found near the northern coast of Yamal Peninsula, at a few locally restricted sites and in the central part of the eastern Barents Sea.
Discussion Clay mineral sources and transport processes The contribution of clastic material to the Barents Sea and Kara Sea depositional environment is estimated by Suzdalskiy (1974), Leontyev (1984), Matishov (1985)
and Aksyonov (1987). Coastal abrasion of loose Quaternary material provides the dominant portion of the shelf deposits (ca. 60-110 x 106t/a), whereas the erosion of seafloor deposits (ca. 7-24 x 106t/a), and the contribution by river suspension (ca. 10-30 x 106t/a) and eolian transport (ca. 1 xl06t/a) is of minor importance. Glacial erosion of Mesozoic bedrock is reported by Gataullin et al. (1993) for the eastern Barents Sea. Today, large waves (up to 10-11 m height) caused by stable winds can lead to reworking and winnowing of shelf sediments down to 80-100 m water depth (Davidan 1974). Geological provinces, which often continue seaward as submarine outcrops, serve as potential source areas for the Barents and Kara seas terrigenous deposits. The Baltic Shield with Caledonian fold belts, the Timan fold outcropping on Kanin Peninsula, the Pleistocene de-
676 Fig. 8 Distribution of chlorite in surface sediments
posits within the Pechora Basin, Quaternary outcrops on Yamal Peninsula, the Novaya Zemlya Hercynides and the Franz Josef Land Caledonides with outcrops of Mesozoic sedimentary and volcanic rocks comprise the most important source rocks (Horn 1930; Dibner 1970; Vinogradov et al. 1975; Matishov 1977). In addition, local submarine outcrops of Devonian to Tertiary claystones, siltstones and sandstones are widely distributed over the south-eastern Barents Sea and south-western Kara Sea areas (Okulitch et al. 1989). Quaternary moraines from Kola Peninsula contain ca. 60% illite, 35% chlorite and 5% smectite (Blaszhchishin and Kheirov 1990). Moraines from the west coast of Kanin Peninsula also show illite-dominated clay mineral associations (55% illite, compared with 20% smectite, 20% kaolinite and 5% chlorite, Blaszhchishin and Kheirov 1990). Sediments from the White
Sea (Kalinenko et al. 1974), as well as the river suspension from Pechora River (Blaszhchishin and Kheirov 1990), further contribute large amounts of illite to the eastern Barents Sea. Franz Josef Land with its high smectite concentrations has an exceptional status within the north-eastern Barents Sea. The lower Cretaceous trap basalts of Franz Josef Land are important source rocks of smectite. The smectite enrichment on Litke Plateau further south is presumably related to the southward dispersal from the Franz Josef Land archipelago. The distribution pattern of kaolinite points to Franz Josef Land with its Mesozoic sedimentary sequences as the main Arctic source ( > 20%). Relatively high kaolinite concentrations around Franz Josef Land have already been described by Andrew and Kravitz (1974). The high smectite and kaolinite concentrations charac-
677 teristic of the Franz Josef Land archipelago dilute the illite to minimum concentrations ( 50% (Berner 1991), supporting the assumption that North Atlantic water masses invading the Barents Sea serve as an important contributor for illite. Novaya Zemlya is another important source for illite and chlorite. In particular glaciers of the northern island of the Novaya Zemlya archipelago provide large amounts of terrigenous material annually (Aksyonov 1987). Within the western prolongations of these glaciers, illite concentrations reach more than 60%. Chlorite concentrations are strikingly high along the entire western coastal areas of Novaya Zemlya (>20%), therefore significantly differing from the fairly uniform chlorite content of the eastern Barents Sea (10-20%). The small chlorite concentrations at the eastern side of Novaya Zemlya may be related to the dilution by smectite. A kaolinite enrichment accompanied by a smectite low within the southern Barents Sea Basin (20-30%) is presumably caused by the local erosion of well-known outcrops of Triassic and Jurassic rocks (Okulitch et al. 1989). Similarly, the chlorite enrichment on Central Bank must be related to the erosion of submarine ancient rocks. South-west of the Central Bank, near-bottom currents of 25-50 cm/s were recorded in a water depth of 270 m (Loeng 1983), which may either redistribute sediments or prevent deposition.
The smectite enrichment within sediments from the central part of the south-western Kara Sea (40-60%) is due to the influx of smectite from adjacent land masses (Yamal Peninsula, southern coast of the south-western Kara Sea) in interaction with the cyclonic surface water circulation. The medium illite concentrations of only 20-40% in the vast areas of the central south-western Kara Sea as well as the low concentrations of kaolinite in coastal areas have also to be attributed to strong dilution by other clay minerals originating from nearby sources.
Clay mineral dispersal by oceanographic processes The role of Atlantic and Arctic waters as agents transporting sedimentary matter into the Barents Sea has not been intensively investigated. Elverh0i et al. (1989) report the possibility that carbonate-rich sediments, which accumulated east of Svalbard, might be transported in suspension by southerly currents of cold Arctic water. Atlantic water entering the Barents Sea from the Arctic Basin might also redistribute sediments and/ or prevent deposition, as is evident from observed sediment waves east of Nordaustlandet (Elverh¢i et al. 1989). The distribution pattern of smectite and kaolinite presented here clearly reflects the surface water circulation regime in the eastern Barents Sea. Inflowing North Atlantic water (Murmansk Current, Novaya Zemlya Current) leads to smectite-rich sediment in the southern and south-eastern Barents Sea. According to Berner (1991), suspended particulate matter from Norwegian Sea sediment traps is enriched in smectite. The concentration successively decreases from south to north, indicating the influx of suspended smectite by North Atlantic water masses to the Fram Strait and also to the Barents Sea. The kaolinite concentration is generally low in most parts of the study area ( 40%) to the central Arctic Ocean sea ice is considered to be of minor importance. The volume of ice exported to the Arctic Ocean is relatively low compared with the Laptev Sea (Wollenburg 1993). Moreover, the south-western Kara Sea Shelf is suspected to be too deep to allow large-scale sediment entrainment by 'suspension freezing'. This situation might have changed during the last glacial maximum when the sea level was drastically lowered. The exposed Laptev Sea Shelf was no longer the effective site of sediment entrainment, presumably explaining the late Weichselian deposits impoverished in smectite within the northern Barents Sea.
Clay mineral distribution in relation to grain sizes The surface sediment distribution charts compiled by Bjelvin et al. (1993) show soft bottom sediments and diamictons to be the most prominent sediment types within the eastern Barents Sea. However, in the southeastern Barents Sea, which includes Goose Bank, Northern Kanin Bank and extensive areas of the Pechora Basin, hard bottom sediments with coarse grain sizes dominate. According to Aksyonov (1987), the lower boundaries of sand and silt range between 70-100 m and down to 200m, respectively. In the south-western Kara Sea, fine sediments are typical of the central part. Coarse material is bound to proximal areas, particularly north of Yamal Peninsula and within the Bay of Kara. Sand dominates down to ca. 30-70 m water depth, whereas silt reaches down to 100-110 m (Aksyonov 1987). The map of the < 1 pom fraction (Fig. 4) clearly resembles the distribution of surface sediments presented by Bjelvin et al. (1993) and shows the bathymetric control on grain sizes. Coarse material provided by rivers and glaciers is deposited rapidly along coastal areas and glacier-proximal zones. Velocities of surface currents in coastal areas of 8-13 cm/s and about 2.5 cm/s in the central Barents Sea Gyre (Tantsyura 1959), however, are sufficient to distribute fine material over the entire area of investigation, resulting in a high portion of the clay fraction. According to Elverh¢i et al. (1989), finegrained sediments in the intermediate and deep shelf areas are additionally contributed by sea-ice transport and winnowed sediments from shallow banks. The distribution patterns of the < 1 p~m fraction and of single clay mineral groups apparently have little in common. Correlation coefficients between the < 1 Ixm fraction
White Sea
)
Fig. 10 Main environmental controls on the clay mineral distribution in surface sediments from the eastern Barents and southwestern Kara seas. Boxes indicate clay minerals most characteristic for the clay mineral assemblages: C, chlorite;I, illite;Sm, smectite; and K, kaolinite
and single groups of clay minerals are < 0.2, indicating that both parameters are controlled by different processes.
Conclusions The investigation of clay minerals in surface sediments from the eastern Barents and south-western Kara seas provide insights into the processes shaping the depositional environment in the region. Perceptions derived from these surface sediment investigations can be transferred to the geological record and will subsequently allow the reconstruction of the paleocirculation and paleoenvironment. Figure 10 summarizes the major transport trajectories, depositional sites and source areas of the main clay mineral groups as inferred from this study. The principal conclusions are as follows: 1. The distribution of clay minerals within the study area depends largely on the close interaction of the surface water circulation, the erosion of local source areas and the mixing and dilution of clay minerals. Especially in the narrow south-eastern Kara Sea, di-
680
2.
3.
4.
5.
lution processes b e c o m e obvious. T h e role of sea ice for influencing the distribution o f clay minerals is difficult to assess. O u r data suggest that sea ice is o f subordinate importance. Coastal sediments f r o m F r a n z J o s e f L a n d and N o v aya Z e m l y a show v e r y different clay mineral associations that are m a i n l y caused by different source rocks. Smectite and kaolinite c o n c e n t r a t i o n s are exceptionally high a r o u n d F r a n z J o s e f L a n d . T h e occ u r r e n c e of these minerals is c a u s e d by the physical w e a t h e r i n g of M e s o z o i c basalts and s e d i m e n t a r y sequences. F o r the c o n t r i b u t i o n of sediments to the T r a n s p o l a r sea ice, F r a n z J o s e f L a n d plays only a m i n o r part. N o v a y a Z e m l y a is an i m p o r t a n t source for chlorite and illite. Especially along coastal areas, these minerals d o m i n a t e the clay m i n e r a l assemblages. Subm a r i n e o u t c r o p s of ancient rocks on the Central B a n k and within the s o u t h e r n B a r e n t s Sea Basin are definitely reflected within the surface clay mineral assemblages, and underline the i m p o r t a n c e of locally restricted source areas for the general distribution pattern. T h e mixing of N o r t h A t l a n t i c and A r c t i c waters in the f o r m of a large cyclonic gyre in the eastern Barents Sea is clearly reflected within the smectite distribution pattern. Sediments underlying the N o r t h A t l a n t i c w a t e r inflow exhibit high smectite c o n c e n trations, w h e r e a s areas c h a r a c t e r i z e d by the inflow of A r c t i c waters b e t w e e n N o v a y a Z e m l y a and F r a n z J o s e f L a n d show lowest smectite concentrations. T h e dispersal of clay minerals across the shelf areas is a p p a r e n t l y u n c o u p l e d f r o m processes being responsible for the distribution of the < 1 pom fraction. R e g i o n a l and local sources in c o m b i n a t i o n with the surface w a t e r circulation system significantly influence the mineralogical differentiation, w h e r e a s the grain size differentiation is largely controlled b y bathymetry.
Acknowledgements We thank the crews of RV Dalnie Zelentsy, RV Professor Shtockman, and members of the Murmansk Marine Biology Institute for generous support. We are grateful to D.K. F~itterer (AWI), G.G. Matishov (MMBI) and A. Lisitzin (Shirshov Institute) for making this joint Russian-German study possible. For the discussion of data and improvement of the manuscript, we thank J. Evans, S. Pfirman, E. Reimnitz, R. Stein, S. Schubert, C. Vogt and M. Wahsner. Thanks are also due to the technicians and students who helped during sampling and preparation. We also thank GEOMAR Research Center for Marine Geosciences (Kiel) for providing us with a giant box corer. We thank R. Petschik and an anonymous reviewer, who improved the manuscript. This is Contribution No. 830 of the Alfred Wegener Institute for Polar and Marine Research.
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