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1.
Thermoluminescence dating has been carried out on feldspar sand grains from the distal sandur of the Godøya Formation and correlated sediments at Sunnmøre, western Norway. The accumulated dose was determined by the regeneration method. The Godøya Formation, which was earlier assumed to be of Middle Weichselian age, was dated to 105–130 ka and is now assumed to postdate immediately the Eemian interglacial. Dates of sediments previously correlated to the Godøya Formation yielded ages in the ranges of 70–90 and 40–50 ka, thus indicating at least three Weichselian ice-free periods predating the Ålesund interstadial in the area.  相似文献   

2.
Detailed investigations of sediments exposed along river sections in the coastal part of Jameson Land have revealed a Saalian to Holocene glacial history. Eleven sedimentary units have been distinguished. most of which are found in superposition at one single large section. Four subglacially formed till beds are recognized; three of which are of Weichselian age. All the tills are considered to have been deposited at the base of fjord glaciers restricted to the Scoresby Sund basin. The tills are separated by marine, fluvial or deltaic sediments, and demonstrate changes in the depositional environnient considered to represent changes in relative sea level during the ice-free periods. The fossil content. supported by a series of luminescence dates, suggest that most of the succession is of Eemian and Early Weichselian age. From the luminescence dates, a short duration of <10ka is suggested for the Early Weichselian glacial stades. Sedimentation during this period was partly controlled by glacio-isostatic subsidence caused by net growth of the Greenland Ice Sheet. The Middle Weichselian is represented by a large hiatus. whereas the Late Weichselian is represented by a subglacial till.  相似文献   

3.
From central East Greenland, C14 ages between 19,500 > 40,000 years B.P. have been obtained for six samples of marine bivalve shells. The ages seem to be consistent with geological observations and form the basis for a tentative chronology for the Weichselian ice age in the region. It appears that the maximum glaciation during Weichselian times was attained more than 40,000 years ago, and that since then ice-free areas have existed. This assumption agrees with evidence of botanical refugia in the region, and the restricted glacier activity especially during the Upper Pleniglacial (ca. 30,000–15,000 years B.P.) is explained by a reduced supply of moisture. A comparison with evidence from other parts of Greenland indicates that different glacial histories can be expected for different sectors of the Greenland Inland Ice.  相似文献   

4.
Isoleucine epimerization (alle/Ue) ratios in the pelecypod Mya truncata and benthic foraminifer Cibicides lobalulus from emerged marine units in western Norway allow construction of a regional relative chronostratigraphy for the Ecmian and Weichselian. Two in situ interglacial sections are considered correlative by the similar biostratigraphy and alle/Ile ratios in C. lobalulus. Overlying sediments at the two sites are of both marine and glacial origin. Neither site contains a complete Weichselian record, but allelic ratios, lithostratigraphy and fauna! changes suggest at least four stadial and three interstadial events occurred along the western Norwegian coast during Early and Middle Weichselian time. Kinetic data defining the relationship between the isoleucine epimerization rate constant and temperature for the species studied allow the estimation of paleotemperatures for samples of known age. Accepting published age estimates for the Eemian interglacial beds, the average Weichselian temperature in western Norway is calculated to have been ca. 4°C below the average Holocene temperature, whereas the last interglacial was 1 to 2°C warmer that the Holocene. The limited temperature depression over this region during the Weichselian implies that coastal western Norway was ice-covered only about 30% of this period, and that Atlantic water, although not necessarily in a warm surface current as today, entered the Norwegian Sea during much of marine isotope stage 5 and intermittently during stage 3. Interpolated amino acid ages date interstadial events at ca. 94 ka, 78 ka and 52 ka, B.P., whereas glacial events are dated ca. 103 ka and bracketed by limiting dates between 78 and 89 ka, between 52 and 63 ka and less than 36 ka B.P.  相似文献   

5.
At Godøya near Ålesund sequences of unconsolidated fine sand and silt below two till beds are interpreted as remains of a sandur. Two facies sequences dominate: One comprises erosional scours followed by horizontally and current-ripple laminated fine sand, massive silt and erosional scours. The other sequence differs by planar wedge-shaped cross-beds replacing the horizontal lamination. The planar cross-beds are assumed to represent migrating linguoid or transverse bars, with an orientation partly at a high angle to current ripples in the same beds. The frequent silt beds are interpreted as a result of rapid vertical accretion due to isostatic subsidence during deposition. A Middle Weichselian age is assumed from thermoluminescence, radiocarbon and amino acid dates.  相似文献   

6.
A complete interglacial cycle, named the Fjøsangerian and correlated with the Eemian by means of its pollen stratigraphy, is found in marine sediments just above the present day sea level outside Bergen, western Norway. At the base of the section there are two basal tills of assumed Saalian ( sensu lato ) age in which the mineralogy and geochemistry indicate local provenance. Above occur beds of marine silt, sand and gravel, deposited at water depths of between 10 and 50 m. The terrestrial pollen and the marine foraminifera and molluscs indicate a cold-warm-cold sequence with parallel development of the atmospheric and sea surface temperatures. In both environments the flora/fauna indicate an interglacial climatic optimum at least as warm as that during the Holocene. The high relative sea level during the Eemian (at least 30 m above sea level) requires younger neotectonic uplift. The uppermost marine beds are partly glaciomarine silts, as indicated by their mineralogy, drop stones and fauna, and partly interstadial gravels. The pollen indicates an open vegetation throughout these upper beds, and the correlation of the described interstadial with Early Weichselian interstadials elsewhere is essentially unknown. The section is capped by an Early Weichselian basal till containing redeposited fossils, sediments, and weathering products. Several clastic dikes injected from the glacier sole penetrate the till and the interglacial sediments. Radiocarbon dates on wood and shells gave infinite ages. Amino acid epimerization ratios in molluscs support the inferred Eemian age of the deposit. The Fjøsangerian is correlated with the Eemian and deep sea oxygen isotope stage 5e; other possible correlations are also discussed.  相似文献   

7.
Skjonghclleren is a marine-cut cave with 15–20. m thick pre-Holocene sediments. Corings and excavations reveal three beds of extremely fine-grained, laminated sediments alternating with blocky sediments. The laminated beds are interpreted as glaciolacustrine sediments deposited subglacially at times when ice sheets covered the area, suggesting at least three glaciations after the cave was formed. The blocky/diamictic sediments were formed by frost-shattered blocks from the roof of the cave during ice-free periods, and mixing with the fines through slow mass movements along the floor of the cave. In the diamictic sediment beneath the uppermost laminated bed, almost 7,000 bone and teeth fragments of birds, mammals and fish were found. Birds dominated, with little auk and brunnich's guillemot as the most frequently occurring species. Arctic fox was the dominating mammal. During climatic optimum of the interstadial, conditions seem to have been similar to present-day coastal Finnmark, with North Atlantic warm water entering the Norwegian Sea. Two radiocarbon dates on bones and three Uranium series dates on speleothems from this bed all cluster around 30,000 B.P., i.e., the end of the Ålesund interstadial. Above the uppermost laminated bed, bone fragments of birds, fish and mammals, deposited between c . 12,000 and c . 10,000 B.P., were found. Little auk dominate. The occurrence of squirrel is worth noting since it is limited mainly to areas with coniferous forest today. The beds below the 30,000B.P. bed are poorly dated or undated, but it is tentatively concluded that the entire sediment sequence was deposited during the Weichselian stage. It seems that the cave was formed at a high relative sea-level stand sometime during the Early Weichsclian. Two recorded palaeomagnetic excursions seem to correlate with the Laschamp/Olby and the Lake Mungo events, respectively.  相似文献   

8.
On the basis of studies of many stratigraphical profiles, together with radiocarbon dates, Thorium-Uranium dates and amino-acid dates, the following preliminary stratigraphy is proposed: (1)Late Weichselian. Stavanger Stadial. The glacier covered the coast and deposited the upper drift sheet. - (2) Middle Weichselian.(a)Sandnes Interstadial (30,000?-39,000 years B.P.). Thick units of marine deposits underlie the Stavanger Stadial drift. The lithology, the foraminiferal fauna, the molluscan fauna and the pollen flora all record cold, partly near-ice environment during their deposition. Elements of a boreal type foraminiferal fauna suggest that certain phases of the Sandnes Interstadial could have been slightly warmer. The shore level was very high. (b) Jæren Stadial (40,000? 1000 years B.P.). Tills and glaciomarine deposits at several locailites are correlated with a Jæren Stadial. (c) Nygaard Interstadial (41,000–50,000? years B.P.). Marine deposits representing a low shore-level phase, record cool to cold conditions. - (3)Early Weichselian. (a) Karmøy Stadial (older than 47,000 years B.P.). Gravelly and very bouldery tills at low stratigraphical levels in several prifles are correlated with a Karmøy Staidial.(b) Older deposits. Marine deposits which lie below the Karmøy Stadial till and on top of Eemian deposits at Bø II on Karmøy are being studies.  相似文献   

9.
Th/U dating and radiocarbon dating of 'old' shells are discussed, and amino acid ratios from shells are used as a method of relative-age dating. The Svalbard area has been completely covered by an extensive ice sheet at leats once. New data from Sjuøyane indicate that such glaciation took place in the Early Weichselian. The Middle Weichselian was a period of interstadial conditions. Series of beaches of assumed Middle Weichselian age occur in several places in western Spitsbergen while no such beaches are known in the eastern part of the archipelago. The maximum glaciation in the Late Weichselian is assumed to have taken place about 18,000 B.P. In the western part of Spitsbergen, the Late Weichselian glaciation was limited and local, while the eastern part of the archipelago was covered by an ice sheet. Kongsøya has a pattern of Holocene shoreline displacement which indicates that the centre of this ice sheet was east of kong karts Land.  相似文献   

10.
A historical review is given of the stratigraphic and chronological research of the Weichselian glaciation in Finland. Submorainic interglacial organogenic deposits have been found in Finnish Lapland and Ostrobothnia. Radiocarbon analyses give ages of over 50,000 years B.P. and the microfissil assemblages indicate climatic conditions that are more fovourable than at present. Interstadial deposits with radiocarbon ages of 42,000 to over 50,000 years B.P. contain fossil assemblages in dicating a poorer climate than at present. A tentative correlation of the Weichselian stratigraphy by various authors is presented.  相似文献   

11.
Coastal Jameson Land is characterized by thick Quaternary deposits from the last interglacial/glacial cycle. The successions at the mouth of Langelandselv exhibit a key stratigraphy where sediments from the Langelandselv interglaciation (Eemian) are overlain by three till units interbedded with glacimarine and deltaic interstadial successions. Immediately after the retreat of glaciers after the extensive Scoresby Sund glaciation (Saalian). advection of warm Atlantic surface water surpassed what is known from the Holocene. The two lowermost Weichselian tills, deposited during the Aucellaelv and Jyllandselv stades (Early Weichselian), reflect short-lasting readvances of fjord glaciers. Luminescence dates and correlation with adjacent areas suggest ages of 110–80 ka and 70–60 ka for the Hugin Sø and the Møselv interstades, respectively.  相似文献   

12.
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13.
A pre-Holocene marine level is found at 109 m a.s.1. on Hopen. Fragments of Mya truncata and Hiatella arctica occurring on a raised coastal spit at that altitude have been radiocarbon dated to >45,000 BP. The amino acid epimerization of these shells, a clearly mixed sample, correlates with samples from Kongsøya that are of Eemian or Early Weichselian age (alloisoleucine/isoleucine ratios, hydrolysed fraction, between 0.084 and 0.213). No direct evidence, such as striations or roche moutonées, of overriding glacier ice has been found, and no erratics were found above the pre-Holocene marine limit. The existing Holocene shoreline displacement curve, with its upper limit at 60 m a.s.1., is supported by four new radiocarbon dates.  相似文献   

14.
The highest shoreline features of paleo-Lake Malheur are undated gravelly barrier beaches south of Harney Lake that lie ca. 3.5 m higher than the hydrographic outlet of Harney Basin at Malheur Gap (1254 m). The earliest Quaternary record for Lake Malheur consists of occurrences of water-deposited tephra dated to ca. 70,000–80,000 yr ago. The next identified lake interval is dated by shells with ages of ca. 32,000 and 29,500 yr B.P. No dates are available for the terminal-Pleistocene Lake Malheur. Lake(s) were present between ca. 9600 and 7400 yr B.P., although periodic low levels or desiccation are suggested by a paleosol dated as ca. 8000 yr B.P. The lake system probably dried further after 7400 yr B.P., although dates are lacking for the period between ca. 7400 and 5000 yr B.P. Dune deposits on the lake floor are ca. 5000 yr old and indicate generally dry conditions. Fluctuating shallow lakes have probably characterized the last 2000 years. A date of 1000 yr B.P. gives a maximum age for beach deposits at 1254 m, near the basin threshold elevation. Thus, the Malheur Lake system may have drained to the Pacific Ocean by way of Malheur Gap during the latest Holocene.  相似文献   

15.
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16.
General problems in determining and interpreting shell C14 dates are discussed: calculation methods, factors influencing primary activity (apparent age), and determination of contamination. It is concluded that shell dates are reliable when handled carefully. Measurements on ten shells, collected between 1898 and 1923 on the Norwegian coast, gave apparent ages from 340±75 to 550±80 years, indicating that apparent age is not a significant problem in dating of Norwegian shells.  相似文献   

17.
A glacial chronology for northern East Greenland   总被引：3，自引：1，他引：3  
In East Greenland between 75 and 76N three different glacial episodes can be identified: (1) An early period with more or less total ice cover and in which the ice reached out onto the continental shelf - the Kap Mackenzie stadial; (2) a period with glaciation of intermediate extent, when nunataks and a few ice-free lowland areas existed - the Muschelbjerg stadial; and (3) a final period with glacial advance, when the glaciers were mainly restricted to fjords and larger valleys - the Nanok stadial. Each of these stadials was followed by a period with general deglaciation, from which marine shell-bearing sediments have been found; the Hochstetter Forland interstadial, the Peters Bugt interstadial and the Flandrian interglacial, respectively. The marine limit sank with each of these ice-free periods; probably an isostatic effect of the decreasing amplitude of the glacial advances. The deglaciation after the Nanok stadial began about 9500 B.P. It is not known for certain when this glacial advance started, but 13,000 B.P. or earlier is suggested. According to 14C datings the Peters Bugt interstadial dates from at least 45,000 B.P. and the Hochstetter Forland interstadial from at least 49,000 B.P. However, amino acid analyses indicate a distinct age difference between these two interstadial, and Th/U datings give age estimates of 70,000–115,000 B.P. for the Hochstetter Forland interstadial, which therefore seems to be of Early Weichselian age although a pre-Weichselian age cannot be excluded. The same applies to the preceding Kap Mackenzie stadial. The correspondence between the present glacial chronology and similar tripartite ones on Bafffin Island, Ellesmere Island and Svalbard seems reasonably good  相似文献   

18.
The Quaternary stratigraphy in Finland is discussed on the basis of an example from the Oulainen area of Ostrobothnia. Organogenic deposits found beneath till at this site are correlated with the Eemian Interglacial on biostratigraphical evidence. This is confirmed by TL dates of 97,000 ± 18,000 B.P. and 150,000 ± 30,000 B.P., whereas a finite radiocarbon date of 63,200 +5500 -3200 B.P. is probably too young. Correlation of the Weichselian stratigraphy is based on deep-sea oxygen isotope data, in which the variations in isotope ratios are assumed to reflect global changes in climate and fluctuations in the volume of the ice-caps. It is concluded on the latter grounds that Finland must have been free of ice at two periods during the Early Weichselian but at least for the most part covered by ice thereafter up to the final deglaciation. The sediments attributed to the only known Weichselian interstadial in Finland, the Perapohjola Interstadial, are taken to correspond most probably to the Brørup, although some may represent the Odderade, Information on the Weichselian till stratigraphy in the Oulainen area is largely confined to the deglaciation phase, the relatively complex nature of which suggests that complete reconstruction of the earlier phases of the Weichselian in an area such as Finland, located towards the centre of the ice sheet, is scarcely feasible by the methods currently available.  相似文献   

19.
The mandible of a polar bear (Ursus maritimus Phipps) found in about 1920 at Kjul Å, North Jutland, and described by Nordmann & Degerbol in 1930. has been l4C dated to 11.100 ± 160 B.P. It is so far the only find of polar bear in Denmark. Comparison with recent 14C datings of Swedish and Norwegian polar bears shows that the Danish specimen was a member of a southern Scandinavian Late Weichselian population. The contemporaneous Zirphaeu sea deposits can be regarded as the boreal-arctic shallow water equivalent of the arctic Upper Saxicava sand deposits from northern Jutland. The polar bear mandible, however, was deposited on land, as was the metacarpal bone of a brown bear ( Ursus arctos ) from the nearby Nr. Lyngby locality of Allerød age. The overall picture of the Late Weichselian mammal fauna in Denmark shows a mixed composition of different ecotypes. Their sympatric occurrence points at a unique environment not comparable to any now existing, and probably related to the very low latitude of the Weichselian ice sheet.  相似文献   

20.
Thermoluminescence (TL) dating of shallow marine sediments from the well studied interglacial-carly glacial sequence at Fjtfsangcr, western Norway has yielded ages that with few exceptions become progressively older with depth. For Ecmian samples the TL method yielded a mean of 111,000 ± 23,000 years, close to the often postulated age of 125,000 years. For the Early Weichselian the TL dates were younger than suggested by the amino-acid method.  相似文献   

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