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Two raised marine sequences from Prins Karls Forland, western Svalbard, interpreted to have been deposited during part of isotope substage 5e (Eemian) and substage 5a, were studied for foraminifera content. Time constraints are given by 14 C ages, infrared stimulated luminescence age estimates and amino acid ratios in subfossil marine molluscs. A diamicton (unit B) separates the two marine sequences and reflects an advancement of local glaciers sometime late in isotope stage 5. The two marine sequences contain diverse benthic foraminiferal faunas, indicating periods of a relatively warm and seasonally ice-free marine shelf environment. Compared to the lowermost sequence (unit A), the upper marine sequence (unit C) seems to reflect a more shallow environment that could have resulted from the global lowering of the sea level towards the end of isotope stage 5. Our results further emphasise the problem of biostratigraphic distinction between interglacial and interstadial deposits at high latitudes, with temperature conditions for substage 5a close to those of substage 5e and present conditions. 相似文献
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PER MÖLLER DMITRY YU. BOLSHIYANOV HELENE BERGSTEN 《Boreas: An International Journal of Quaternary Research》1999,28(1):92-114
The Taymyr Peninsula constitutes the eastern delimitation of a possible Kara Sea basin ice sheet. The existence of such an ice sheet during the last global glacial maximum (LGM), i.e. during the Late Weichselian/Upper Zyryansk, is favoured by some Russian scientists. However, a growing number of studies point towards a more minimalistic view concerning the areal extent of Late Weichselian/Upper Zyryansk Siberian glaciation. Investigations carried out by us along the central Byrranga Mountains and in the Taymyr Lake basin south thereof, reject the possibility of a Late Weichselian/Upper Zyryansk glaciation of this area. Our conclusion is based on the following: Dating of a continuous lacustrine sediment sequence at Cape Sabler on the Taymyr Lake shows that it spans at least the period 39-17 ka BP. Even younger ages have been reported, suggesting that this lacustrine environment prevailed until shortly before the Holocene. The distribution of these sediments indicates the existence of a paleo-Taymyr lake reaching c. 60 m above present sea level. A reconnaissance of the central part of the Byrranga Mountains gave no evidence of any more recent glacial coverage. The only evidence of glaciation - an indirect one - is deltaic sequences around 100-120 m a.s.l., suggesting glacio-isostatic depression and a large input of glacial meltwater from the north. However, 14C and ESR datings of these marine sediments suggest that they are of Early Weichselian/Lower Zyryansk or older age. As they are not covered by till and show no glaciotectonic disturbances, they support our opinion that there was no Late Weichselian/Lower Zyryansk glaciation in this area. We thus suggest that the Taymyr Peninsula was most probably glaciated during the early part of the last glacial cycle (when there was only small- to medium-scale glaciation in Scandinavia), but not glaciated during the later part of that cycle (which had the maximum ice-sheet coverage over north-western Europe). This fits a climatic scenario suggesting that the Taymyr area, like most of Siberia, would come into precipitation shadow during times with large-scale ice-sheet coverage of Scandinavia and the rest of north-western Europe. 相似文献
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ÓLAFUR INGÓLFSSON FINNBOGI RÖGNVALDSSON HELENE BERGSTEN LARS HEDENÄS GEOFFREY LEMDAHL JUAN M. LIRIO HANS PETTER SEJRUP 《Polar research》1995,14(2):123-139
On western Kongsøya, Svalbard, three coarsening-upwards sequences of marine to littoral sediments, separated by tills, are recognised in sections at ca 50-92 m above present sea level. These sequences show major glaciations in the northern Barents Sea, resulting in substantial glacioisostatic downpressing of Kongsøya. Till fabrics indicate ice movements controlled by the local topography, while glaciotectonic deformations suggest that ice moved from an ice divide northeast of Kongsøya. independent of the local topography. The stratigraphical evidences show two pre-Holocene ice-free periods, when the climate was similar to or slightly warmer than at present. The age of these periods is not clear. It is suggested that the elder ice free interval is older than isotope stage 5e. The younger ice free interval could be of Eemian or Early Weichselian age. The uppermost succession of sublittoral-littoral sediments is of early Holocene age. It relates to the high (≥100 m) postglacial marine limit, dated to approximately 10,000 bp. 相似文献
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HELENE BERGSTEN KJELL NORDBERG 《Boreas: An International Journal of Quaternary Research》1992,21(3):223-252
From stratigraphic investigations of 38 piston and vibro cores, four fine-grained Late Weichselian sediment units can be defined in the southern Kattegat. A continuous stratigraphic record of the Late Weichselian sediments cannot be established from single cores due to the uneven distribution of the units, but by compilation of relative stratigraphies a composite record can be determined for sediments deposited between approximately 13,500 and 10,000 BP. The sediments contain both lithological and biostratigraphical evidence that the Baltic Ice Lake was suddenly drained through the Öresund Strait at about 12,700 BP. This drainage route appears to have been unchanged until about 10,300 BP when a passage opened in south central Sweden through which the final drainage of the Baltic Ice Lake took place. The Younger Dryas cold event appears to have had only marginal effects on the marine benthic life in the region. The data also indicate that drainage of fresh Baltic water through the Öresund Strait was the driving force for an inflow of marine water from the Skagerrak North Atlantic Ocean into the southern Kattegat, as occurring at the present. This paper is a contribution to IGCP 253, Termination of the Pleistocene . 相似文献
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HELENE BERGSTEN KJELL NORDBERG 《Boreas: An International Journal of Quaternary Research》1993,22(4):311-318
Foraminifera, pollen, lithology and radiocarbon dates from a core in the southern Kattegat provide a rare opportunity to obtain data relating to environmental conditions during the Middle Weichselian in the offshore Kattegat. This core is also correlated with an adjacent second core. Redeposited Eemian foraminifera and pollen occur in the Middle Weichselian sediments. This is interpreted as a result of reworking by an active Middle Weichselian ice present in, or advancing from, a northeasterly to easterly direction. During a second phase the Middle Weichselian sediments were compacted, probably a result of overriding by an ice from the northeast during the Middle Weichselian and/or the Late Weichselian Maximum. The Middle Weichselian sequence is overlain by a Holocene sequence which, in turn, is overlain by an admixture of Middle Weichselian and Holocene sediments. This mixing may be a result of tectonic activity some time between 7300 and 1000 BP. The core ends in Holocene fine sediments representing the last c. 1000 years. 相似文献
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HELENE BERGSTEN BENNETH DENNEGARD 《Boreas: An International Journal of Quaternary Research》1988,17(2):229-242
Marine clay from two cores (50 and 36m deep) from Gothenburg, southwestern Sweden, have been analysed using different stratigraphic methods. Foraminiferal stratigraphy complemented withe lithostratigraphy, pollen and mollusc analyses show an environmental succession from arctic conditions with water depths up to 100m during Late Welchselian time, to a boreal shallow water environment in early Holocene time. A comparison of the foraminiferal faunas with those from corresponding investigations from southern Bohuslän, NW of Gothenburg, shows a similar development in the two areas. The sudden environmental change around the Pleistocene/Holocene boundary (10,000 years B.P.) along the Swadish west coast is attributed to changes of the hydrographic patterns; a general shift of the circulation pattern of the Skagerrak/ Kattegat at that time and or a large supply of fresh water flowing into the area from the Lake Vanern basin. 相似文献
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