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Late Weichselian glaciation of the northern - a discussion

ANDERS ELVERHOI AND ANDERS SOLHEIM

Elverhbi, A. & Solheim, A. 1987: Late Weichselian glaciation of the northern Barents Sea - a discussion. Polar Research 5 ns., 285-287.

j= Anders Elverhei and Anders Solheim, Norsk Polarimtitutt, Box 158, N-1330 Oslo lufthaun, .

The age of the raised beaches in eastern Svalbard (Figs. 1 & 2) are, until more data are available, interpreted in combined with the wide distribution of only a thin veneer the same way. of glacigenic sediments in the northern Barents Sea strongly The thickness of the proximal/iceberg dominated unit is in indicate the existence of a Late Weichselian in the general %5 m, except for local accumulations (Elverh~i& region (Salvigsen 1981; Elverh~i& Solheim 1983; Solheim et Solheim 1983; Solheim et al. 1988). A basic problem is to al. 1988) (Figs. 1 & 2). However, the maximum extent of the identify the onset of the proximal/iceberg glaciomarine sedi- ice sheet, the timing and pattern of are still much mentation, and thereby date the withdrawal of the grounded debated. Moraine ridges in the southwestern marginal parts of Late Weichselian ice sheet. The low content of foraminifera the Barents Sea may indicate a coalescence of the Fenno- indicates a harsh environment - cold water and a relatively scandian and Svalbard/northern Barents Sea ice sheet cover- rapid sedimentation rate. Application of a rate of 100 cm/ka ing the entire shelf (Vorren & Kristoffersen 1986). Ridge results in a depositional period of 3-5 ka. This, and also higher complexes fringing the northern Barents Sea bank areas at 25& rates, are comparable to rates found in modem ice proximal 300m water depth may represent a major stage during the regions (Elverhbi et al. 1983; Molnia 1983; Powell 1984). retreat, or alternatively represent the maximum extent (Elver- According to such a depositional rate, the breakup of the hbi & Solheim 1983). northern Barents Sea ice sheet took place relatively early, 1% The unlithified sediments on the sea floor (Fig. 1) are inter- 17 ky B.P. Indications of an early breakup may be found from preted as a continuous sequence consisting of till overlain by the increased input of terrigeneous material corresponding to proximal/iceberg dominated glaciomarine deposits, which termination IA in sediment cores from Framstretet and the grade into a distal glaciomarine facies representing the present eastern Arctic Ocean (Knudsen 1985; Zahn et al. 1985; Thiede day sea ice dominated environment (Elverhbi & Solheim 1983; et al. in press). If this timing is correct, the deglaciation of the Solheim et al. 1988). Laminated sediments may be present in the Barents Sea may have contributed significantly to the light transition zone between the two glaciomarine units, in particular isotope peak of termination I,, about 13 ky B.P. below 300m water depth. From extrapolation of the sedi- Former reconstructions of the Barents Sea ice sheet have mentation rate in the upper unit (based on datings of mainly included the existence of extensive ice shelves, both for a Astarte sp., Fig. 2), the transition between the distal and the maximum model with grounded ice to the shelf edge (Denton proximal/iceberg dominated glaciomarine deposits is tentatively & Hughes 1981) and for a more limited situation with grounded dated to 1&12 ky B.P. The 10 ky is a minimum age based on ice only on the banks in the northern regions (Matishov 1984). findings of Portlandia arctica with an age of 10,080 2 110 (south The current data background is inadequate for a thorough of Nordaustlandet). Accordingly, at 10 ky B.P. (at the latest) discussion of ice shelves associated with the Barents Sea ice the Late Weichselian ice sheet had retreated to onshore posi- sheet. However, for the limited model, we consider at least tions with only minor outlet and iceberg production. large ice shelves unlikely as the Barents Sea is too shallow and The proximal/iceberg dominated facies, a unit suggested to without sufficient topographic relief providing the necessary be associated with the withdrawal of the Late Weichselian anchor points. For the limited model the various troughs, e.g. Barents Sea ice sheet, has not been dated. The unit is char- Bjbrnbyrenna and Franz Victoriarenna (Fig. l), have acted as acterized by a low content (1&1,000 individuals per 100 g sedi- calving bays with sediment and iceberg supply from a grounded ment) of foraminifera. Accelerator dating of foraminifera and ice front. The 40-70 m thick glaciomarine accumulations in the calsispheres in two levels in a core from the central Barents Sea inner parts of the troughs and along the slopes of the banks (Figs. 1 & 2) shows reversed ages. 28 ka and 21 ka at 0.6 and (Elverhbi & Solieim 1983; Solheim et al. 1988) may represent 1.8 m sediment depth, respectively. (Each sample was collected the extensive sediment output during a recessional stage. from a 40 cm interval of a 110 mm split core, and approximately In conclusion, the Barents Sea was most likely covered by 5 mg were dated.) Due to the low microfossil content, a mixed grounded ice at least down to the present day 300 m contour (a assemblage had to be used, and the foraminifera showed clear limited model). The possibility that the northern Barents Sea evidences of abrasion. The dated samples are therefore inter- ice sheet coalesced with the Fennoscandian ice sheet and preted as consisting of foraminifera of mixed ages. Similarly, covered the entire Barents Sea to the shelf edge is still open to accelerator datings of foraminifera south of Nordaustlandet discussion. However, the timing of deglaciation is not known. 286 A. Elverh@i & A. Solheim

MUD/PEBBLY MUD "DISTAL" GLACIOMARINE / 7i:EcK 0- . 1. PEBBLY MUD "PROXIMAL" GLACIO- MARINE SEDIMENTS 2- BLUE GREY (LATE WEICHSELIAN) 3- STIFF PEBBLY MUD 4- TILL 5-10m (LATE WEICHSELIAN) 5- Fig. 1. Bathymetric map of the Barents Sea, including gener- 6- BEDROCK alized lithological description of the unlithified sediments in the 74 northern Barents Sea.

Based on the combination of datings and extrapolation of sedi- mentations rates, 10 ky B.P. is regarded as a minimum age of References the transition from a proximal/iceberg facies to the present day Denton, G. H. & Hughes, T. J. 1981: The Arctic Ice Sheet: An sea ice dominated sedimentary environment. Estimation of outrageous hypothesis. Pp. 437-467 in Denton. G. H. & sedimentation rates for the proximal facies may indicate degla- Hughes, T. J. (eds): The Last Great Ice Sheers. John Wiley ciation of the northern Barents Sea as early as W17 ky B.P. & Sons. The withdrawal of the Barents Sea ice sheet probably caused a Elverh~i,A. & Solheim. A. 1983: The Barents Sea ice sheet - significant support to the light isotope influx at isotope stage 1, a sedimentological discussion. Polar Res. 1 n.s.,23-42. and to the increased clastic supply in Framstretet and the eastern Elverh~i.A.. Lmne, 8.& Seland. R. 1983: Glaciomarine Arctic Basin during this interval, which is supposed to be about sedimentation in a modern environment, Spitsbergen. 13 ky B.P. Polar Res. 1 n.s, 127-149. Late Weichselian glaciation of the northern Bareiits Sea - a discussion 287

14 LITHOLOGY C-AGE, BP. 4 6 8 10 12 20 28 0.0 -

0.2

0.4 12 0.6 - - -E 0.8 - T. 5 1.0 I e a 1.2 - a 1.4 Sedimentation 1.6 - rate: Scm/ka

1.8 - I 2.0 -

DISTAL GLACIOMARINE 0 DISTAL GLACIOMARINE (HOLOCENE1 SEDIMENTS

A PROXIMAL GLACIOMARINE PROXIMAL GLACIOMARINE SEDIMENTS SEDIMENTS (LATE WEICHSELIAN)

SAMPLE NR. 1-8, fmn Elverhiii h Solheim 1983.

years BP are (in) nr. * Fig. 2. I4C-datings and sedi- port. Arct. 10080i170 Ua 302 10 103 Form 10390t170 50-58 Ua 301 mentation rate of Late Quat- 12 280 Forams/Calc. 28080i1125 175-200 Ua 304 ernary sediments in the 11 280 Form 21203t825 45-70 Ua 305 northerr, Barents Sea. (Dashed line: linear regression, locations * Tan&m accelerator, University of Gppsala, Sweden. in Fig. 1.)

Knudsen. B.-E. 1985: Sen-Kuarfrert paleomiljo i Framstretet. Solheim, A,, Miltiman, J. D. & Elverhei, A. 1988: Sediment Unpubl. Cand. Scient. thesis. Univ. of Oslo. 74 pp. distribution and sea floor morphology of Storbanken; impli- Matishov, G. G. 1984: Bottom of the ocean during glacial cations for the glacial history of the northern Barents Sea. periods Nauka, Leningrad. 176 pp. (in Russian). Canadian Journal of Earth Sciences (in press). Molnia, B. 1983: Subarctic glacial-marine sedimcntation: A Thiede, J., Clark, D. L. & Herman, Y. 1988: Late Mesozoic model. Pp. 95-144 in Molnia, B. (ed.): Glacial-Marine and Cenozoic paleoceanography of northern polar oceans. In Sedimentation. Plenum Press, NY. Grantz, A., Johnson, L. & Sweeny, W. (eds.): DNAGArctic Powell, R. D. 1984: Glaciomarine processes and inductive litho- Vol. (in press). facies modelling of ice shelf and tidewater sediments Vorren, T. 0. & Kristoffersen, Y. 1986: Late based on Quaternary examples. Marine Geol. 57, 1-52. glaciation in the south-western Barents Sea. Boreas IS. 51- Salvigsen, 0. 1981: Radiocarbon dated raised beaches in Kong 59. Karls Land, Svalbard, and their consequences for the glacial Zahn, R., Markussen, B. & Thiede, J. 1985: Stable isotope history of the Barents Sea area. Geogr. Ann. 63A, 283- data and depositional environment in the Late Quaternary 291. Arctic Ocean. Nature 314. 433-435.