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1.
Shoreline displacement data from the Trondheimsfjord area have been collected and a synthesis of the Late Weichselian and Holocene relative uplift is presented. The isobase direction is N 30–35°E during the whole period. The gradients of the shorelines are 1.7? m/km at 11,800 years B.P., 1.3 m/km at 10,000 years B.P., gradually decreasing towards the present with a value of 0.2 m/km at 5,000 years B.P. Some irregularities in the shoreline gradient curve in the Late Weichselian and Preboreal chronozones may be ascribed to crustal readjustments by faults. An interpolation of the 9,500 years B.P. shoreline to the Ångermanland and Baltic area shows a relative uplift at 11,800 years B.P. of 400–450 m in the central area of glaciation. The island of Hitra was probably deglaciated at about 12,000 years B.P. and Ørlandet/Bjugn somewhat later. The Younger Dryas ice marginal deposits at Tautra have been deposited early in this chronozone, and deposits proximal to this at Hoklingen and Levanger were probably deposited in the late part of the same chronozone.  相似文献   

2.
New palaeoenvironmental data from the Lateglacial in Southwest Iceland add to the record of climatic events during deglaciation of the region. Recently exposed sediments on the north coast of Seltjarnarnes Peninsula in the Reykjavik area, Southwest Iceland, contain evidence of marine deposition during the Bølling Interstadial. The glaciomarine sediments contain both slightly reworked marine macrofossils and microfossils indicating normal marine salinity and subarctic climate conditions. Previous sedimentological studies and radiocarbon dating of the sporadic sediments covering the lava bedrock in Reykjavik have revealed lateglacial marine units from the Allerød, the Allerød—Younger Dryas transition, the Younger Dryas and from the Preboreal. Until now, the only Bølling evidence has consisted of scattered radiocarbon-dated redeposited shell fragments. From the Bollagardar deposits we report the first faunas dated to the Bølling chronozone preserved in marine sediments in the Reykjavik area. Recently published work in Hvalfjördur and Borgarfjördur, West Iceland, has shown that sea level was relatively high during the Bølling and that deglaciation was rapid. Bølling, Allerød and Younger Dryas deposits in the coastal areas of the Reykjavík region accumulated in a relatively open marine environment in oceanographic conditions similar to the present ones. Combined previous and present results indicate that several episodes of glaciomarine deposition occurred.  相似文献   

3.
Recent research based primarily on exposure ages of boulders on moraines has suggested that extensive ice masses persisted in fjords and across low ground in north‐west Scotland throughout the Lateglacial Interstade (≈ Greenland Interstade 1, ca. 14.7–12.9 ka), and that glacier ice was much more extensive in this area during the Older Dryas chronozone (ca. 14.0 ka) than during the Younger Dryas Stade (ca. 12.9–11.7 ka). We have recalibrated the same exposure age data using locally derived 10Be production rates. This increases the original mean ages by 6.5–12%, implying moraine deposition between ca. 14.3 and ca. 15.1 ka, and we infer a most probable age of ca. 14.7 ka based on palaeoclimatic considerations. The internal consistency of the ages implies that the dated moraines represent a single readvance of the ice margin (the Wester Ross Readvance). Pollen–stratigraphic evidence from a Lateglacial site at Loch Droma on the present drainage divide demonstrates deglaciation before ca. 14.0 ka, and therefore implies extensive deglaciation of all low ground and fjords in this area during the first half of the interstade (ca. 14.7–14.0 ka). This inference appears consistent with Lateglacial radiocarbon dates for shells recovered from glacimarine sediments and a dated tephra layer. Our revised chronology conflicts with earlier proposals that substantial dynamic ice caps persisted in Scotland between 14 and 13 ka, that large active glaciers probably survived throughout the Lateglacial Interstade and that ice extent was greater during the Older Dryas period than during the Younger Dryas Stade. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

4.
Global climate change associated with the onset of the Younger Dryas chronozone affected different regions of the northern hemisphere in different ways. In the Great Basin of western North America, the effect was positive for human populations. Relatively cool temperatures causing effectively wetter conditions filled some pluvial basins with shallow but permanent lakes and other basins with well-watered marshes or meadows. Vegetation communities dominated by sagebrush and grasses promoted healthy and diverse animal populations. Ten archaeological sites from the region have been dated to the Younger Dryas chronozone. Evidence from these sites indicates that Paleoindians with skull shapes and mitochondrial DNA similar to modern western North American Indians occupied the region. These early humans produced a material culture characterized predominantly by large stemmed bifacial points, although one site contained a small fluted point. Curated tool forms and technological activities represented in analyzed lithic assemblages suggest a highly mobile settlement strategy, and redundant short-term occupations of sites indicate frequent and long-distance residential moves across territories spanning distances of up to 400 km. Paleoindian subsistence pursuits focused on artiodactyls (primarily mule deer, bighorn sheep, and pronghorn antelope), leporids (chiefly jackrabbits), birds (sage grouse and waterfowl), insects (grasshoppers), and possibly fish. Easy-to-process plants like cactus pads were also eaten, but small seeds do not seem to have been an important part of Great Basin human diets until long after the Younger Dryas, closer to 9500 cal BP. The Great Basin record contains no evidence for natural catastrophe at the onset of the chronozone. Instead, the Younger Dryas appears to have been among the best of times for human foragers in this region of North America.  相似文献   

5.
A clay varve chronology has been established for the Late Weichselian ice recession east of Mt. Billingen in Västergötland, Sweden. In this area the Middle-Swedish end moraine zone was built up as a consequence of cold climate during the Younger Dryas stadial. A change-over from rapid to slow retreat as a result of climatic deterioration at the Alleröd/Younger Dryas transition cannot be traced with certainty in the varve sequences, but it seems to have taken place just before 11,600 varve years BP. The following deglaciation was very slow for about 700 years — within the Middle-Swedish end moraine zone the annual ice-front retreat was only c . 10 m on average. A considerable time-lag is to be expected between the Younger Dryas climatic event and this period of slow retreat. The 700 years of slow retreat were succeeded by 200 years of more rapid recession, about 50–75 m annually, and then by a mainly rapid and uncomplicated retreat of the ice-front by 100–200 m/year or more, characterizing the next 1500 years of deglaciation in south and central Sweden. The change from about 50–75 m to 100–200 m of annual ice-front retreat may reflect the Younger Dryas/Preboreal transition. Clay-stratigraph-ically defined, the transition is dated at c . 10,740 varve years BP, with an error of +100 to -250 years. In the countings of ice layers in Greenland ice cores (GRIP and GISP-2) the end of the Younger Dryas climatic event is 800–900 years older. However, a climatic amelioration after the cold part of the Younger Dryas and in early Preboreal should rapidly be reflected by for example chemical components and dust in Greenland ice cores, and by increasing δ13C content in tree rings. On the other hand, the start of a rapid retreat of the inland ice margin can be delayed by several centuries. This can explain at least a part of the discrepancy between the time-scales.  相似文献   

6.
In an area in southwesternmost Värmland, western Sweden, ice-marginal deposits have been mapped and studied. They can be correlated with the Norwegian Younger Dryas to Preboreal Ås, Ski and Aker ice-marginal ridges, and with lines of ice recession earlier constructed in Dalsland. Together they give valuable information about the mode of deglaciation in southern Scandinavia. They indicate a pattern of deglaciation with intense upbreaking by calving of the ice eastwards from the Oslo Fjord and northwards in the Vänern basin. This process caused a downdraw of ice around the highland between those areas. Ice streams and, later, valley glaciers were formed in the large Årjäng-Koppom and Glafsfjorden-Byälven valleys. Between them a lobe-shaped, stagnant ice cap was isolated from further supply from the main ice sheet in the north. This ice cap, here called the Dal lobe, wasted down with a complicated pattern from the west, south and east.  相似文献   

7.
Diatoms in lower sediments from eight basins of the Frosta peninsula, Nord-Trødelag, Norway, have been analysed. All the basins have been isolated from the sea, and a succession from a flora influenced by marine and brackish water to a freshwater flora is always found. An attempt is made to establish a relative salinity range for the fjord basin around the investigated area, from the Younger Dryas chronozone to the end of the Atlantic chronozone. These changes seem to be controlled by the accumulation and ablation of the ice shield and also by major climatic changes in the early and middle Holocene. It is not possible to make a general list of lagoon taxa, because of great variation from basin to basin. The isolation contact (marine/brackish boundary) must be established at the end of the brackish water flora in the absence of lagoon types. The first period after isolation is characterized by a maximum in productivity with dominance of alkaliphilous types among the diatoms. A pioneer flora with dominance of Fragilaria taxa can be traced in the uppermost basins which were isolated just after the deglaciation of the area  相似文献   

8.
Environmental changes are reconstructed from a Lateglacial and early Holocene sequence at Conty, northern France. The molluscan succession is put into a chronostratigraphic framework supported by numerous radiocarbon dates. Malacofaunas from the Bølling chronozone are reported for the first time in northern France and show progressive expansion of marshy communities within organic deposits. This biozone ended in a calcareous silt with the appearance of several species of arctic-alpine affinities. These sedimentological and malacological data point to colder climatic conditions after 12 220 ± 90 BP, but before 11 640 ± 80 BP, allowing allocation to the Older Dryas event. The first part of the Allerød appears to have been drier and relatively stable. After 11 400 BP, a decline in species richness and diversity in the malacofaunas suggests increasing dryness. During the Younger Dryas, two molluscan biozones are identified in a homogeneous calcareous silt, reflecting an early wet phase followed by a drier episode. At the onset of the Holocene malacofaunas show a higher diversity, suggesting climatic improvement.  相似文献   

9.
Blomvåg, on the western coast of Norway north of Bergen, is a classical site in Norwegian Quaternary science. Foreshore marine sediments, named the Blomvåg Beds and now dated to the Bølling‐Allerød from 14.8 to 13.3 cal. ka BP, contain the richest Lateglacial bone fauna in Norway, numerous mollusc shells, driftwood, and flint that some archaeologists consider as the oldest traces of humans in Norway. The main theme of this paper is that the Blomvåg Beds are overlain by a compact diamicton, named the Ulvøy Diamicton, which was interpreted previously as a basal till deposited during a glacial re‐advance into the ocean during the Older Dryas (c. 14 cal. ka BP). Sediment sections of the Blomvåg Beds and the Ulvøy Diamicton were exposed in ditches in a cemetery that was constructed in 1941–42 and have subsequently not been accessible. A number of radiocarbon and cosmogenic 10Be exposure ages demonstrate that the diamicton is not likely to be a till because minimum deglaciation ages (14.8–14.5 cal. ka BP) from the vicinity pre‐date the Ulvøy Diamicton. We now consider that sea ice and icebergs formed the Ulvøy Diamicton during the Younger Dryas. The Scandinavian Ice Sheet margin was located on the outermost coastal islands between at least c. 18.5 and 14.8 cal. ka BP; however, no ice‐marginal deposits have been found offshore from this long period. The Older Dryas ice margin in this area was located slightly inside the Younger Dryas margin, whereas farther south it was located slightly beyond the Younger Dryas margin.  相似文献   

10.
Younger Dryas cirque glaciers are known to have existed beyond the Scandinavian Ice Sheet in parts of western Norway. At Kråkenes, on the outermost coast, a cirque glacier formed and subsequently wasted away during the Younger Dryas. No glacier existed there during the Allerød. Large cirque moraines, some with marine deltas and associated fans, extend into the western part of Sykkylvsfjorden. Comparison with existing late-glacial sea-level curves shows that the uppermost marine sediment in these features was deposited well above Younger Dryas sea-level, demonstrating that the cirques were occupied by glaciers before the Younger Dryas. During the Younger Dryas the cirque glaciers expanded, and some advanced across the deltas, depositing till and supplying the sediment to form lower-level fans and deltas controlled by Younger Dryas sea level. The extent of the Younger Dryas advance of some of the glaciers was, at least in part, controlled by grounding on material deposited before the Younger Dryas. The depositional history of the glacial–marine deposits in the Sykkylven area indicates that cirque glaciers existed throughout Late-glacial time and only expanded during the Younger Dryas. The sediment sequence in glacial lakes beyond cirque moraines and reconstructions of glacier equilibrium lines indicate that this was true for most cirques in western Norway. Only on the outermost coast were new glaciers formed in response to Younger Dryas climate cooling. © 1998 John Wiley & Sons Ltd.  相似文献   

11.
Marine transgression in Younger Dryas in Norway   总被引：1，自引：0，他引：1  
BOREAS Anundsen, K. 1978 03 01: Marine transgression in Younger Dryas in Norway. Boreas, Vol. 7, pp. 49–60. Oslo. ISSN 0300–9483.
The lithostratigraphy and biostratigraphy of sediment cores from two basins in southwestern Norway have been studied and radiocarbon dated. The diatom and the Hystrix content indicates a marine Younger Dryas transgression that reached its maximum level at the transition Younger Dryas/Preboreal Chronozone. No Allerød transgression to the same altitude can be demonstrated, and the suggested Allerød transgression at Bømlo (Faegri 1944) is most likely of Younger Dryas age, too.  相似文献   

12.
The deglaciation patterns of the Bergen and Nordfjord-Sunnmøre areas in western Norway are described and correlated. In the Bergen area the coast was first deglaciated at 12,600 B.P., with a succeeding re-advance into the North Sea around 12,200 B.P. Later, during the Allerød, the inland ice retreated at least 50 km, but nearly reached the sea again during the Younger Dryas re-advance, ending at 10,000 B.P. Sunnmøre was ice-free during an interstadial 28,000–38,000 B.P. Later the inland ice reached the sea. The final deglaciation is poorly dated in Sunnmøre, while further south in Nordfjord, it started slightly before 12,300 B.P., followed by a major retreat. No large re-advance of the inland ice occurred during the Younger Dryas. However, in the Sunnmøre-Nordfjord area many local glaciers formed outside the inland ice during the Younger Dryas. Limnic sediments outside one such cirque glacier have been cored and dated, proving that the glacier did not exist at 12,300-11,000 B.P., and that it was formed and disappeared in the time interval 11,000–10,000 B.P. (Younger Dryas). The erosion rate of the cirque glacier was 0.9 mm/year.  相似文献   

13.
14C-dated percentage and absolute late-glacial pollen diagrams from (1) Blelham Bog, north-west England and (2) Cam Loch, north-west Scotland arc subdivided into chronozones Bølling, Older Dryas, Allerød, and Younger Dryas as proposed for the Late-Weichselian sequence by Mangerud et al., Boreas 3 (1974), with boundaries defined in conventional 14C years. It is shown how these chronozone boundaries coincide in the two British pollen diagrams with boundaries between pollen assemblage zones which are interpreted as the results of environmental (climatic) changes. Differences between the pollen zones found in western Britain and those of the classic South Scandinavian profiles, which are interpreted as the consequence of regional differentiation in the vegetation of north-west Europe circa 14,500 to 10,000 years ago, pose serious problems in the correlation of Late-Weichselian and Late-Devensian subdivisions on the basis of pollen assemblage zones, but a chronostratigraphical classification makes it possible to compare the Late-Devensian profiles from western Britain with the Late-Weichselian subdivisions of Mangerud et al., in which 'chronozone boundaries seem to be climatically conditioned within southern Scandinavia'.  相似文献   

14.
The Getsjö area of Kolmärden is located within the Swedish terminal moraines. The pollen diagrams reflect a Younger Dryas flora. Some radiocarbon dates have been obtained from the oldest sediment with some organic matter. Diatom profiles show the Baltic Ice Lake diatom flora.  相似文献   

15.
Vandenberghe, Jef, Bohncke, Sjoerd, Lammers, Wim & Zilverberg, Liesbeth 1987 03 01: Geomorphology and palaeoecology of the Mark valley (southern Netherlands): geomorphological valley development during the Weichselian and Holocene. Boreas , Vol. 16, pp. 55–67. Oslo. ISSN 0300–9483.
The actual area of the Mark valley is limited by the borders of an Early Weichselian erosion phase. The subsequent accumulation has resulted in the formation of a Weichselian Pleniglacial terrace which has been deeply dissected by Late Glacial erosion. The present alluvial plain is formed by Late Glacial and Holocene infilling. The maximum incision of the Late Glacial fluvial phase was reached slightly before 11,780 B.P. and involved locally dry conditions which have given rise to aeolian activity during this period (Older Dryas). On the deepest parts of the Pleniglacial terrace, a backswamp environment was established until the end of the Alleröd. At the beginning of the Younger Dryas the river invaded the terrace but shortly afterwards aeolian activity progressively increased. At the climax of the Younger Dryas, deep seasonal frost or local permafrost characterized the Mark valley.  相似文献   

16.
The end of the Pleistocene in North America was marked by a wave of extinctions of large mammals, with the last known appearances of many species falling between ca. 11,000–10,000 14C yr BP. Temporally, this period overlaps with the Clovis Paleoindian cultural complex (11,190–10,530 14C yr BP) and with sudden climatic changes that define the beginning of the Younger Dryas chronozone (ca. 11,000–10,000 14C yr BP), both of which have been considered as potential proximal causes of this extinction event. Radiocarbon dating of enamel and filtered bone collagen from an extinct American Mastodon (Mammut americanum) from northern Indiana, USA, by accelerator mass spectrometer yielded direct dates of 10,055 ± 40 14C yr BP and 10,032 ± 40 14C yr BP, indicating that the animal survived beyond the Clovis time period and into the late Younger Dryas. Although the late survival of this species in mid-continental North America does not remove either humans or climatic change as contributing causes for the late Pleistocene extinctions, neither Clovis hunters nor the climatic perturbations initiating the Younger Dryas chronozone were immediately responsible for driving mastodons to extinction.  相似文献   

17.
The study of a c. 18 m thick Late Weichselian- Early Holocene (isotope stage 2/1) marine succession (original water depth 100–150 m) from the Skagen 3 borehole, northern Denmark, has led to a better understanding of the palaeoenvironmental changes during the last deglaciation. The palaeoenvironmental interpretation is based on benthic foraminifera, stable isotope composition and lithology, whereas the chronostratigraphy and sedimentation rates are based on AMS radiocarbon dates. Marine conditions were established in the area at between 15 000 and 14 500 BP (reservoir corrected 14C years), and the first influence of Atlantic water masses imported through the Norwegian Channel is registered from 13 100 BP to 10 900BP (the Bølling- Allerrad interstadial complex). This was followed by the Younger Dryas cooling event between 10 900 and 10 100 BP. The hydrographic change at the Pleistocene-Holocene transition after the Younger Dryas occurred in two stages. Arctic/subarctic deep-water assemblages persisted continuously at Skagen after the first stage at 10 200 BP, while cold boreal assemblages existed in shallower water environments in the Kattegat-Skagerrak basin during the same period of time. The slight warming in the early Holocene seems to have been interrupted by a short-term cooling at about 9700–9600 BP. Finally, at 9600 BP the arrival of warm Atlantic water masses created full-interglacial conditions in the whole region.  相似文献   

18.
Late Weichselian sea level changes at Sotra, Hordaland, western Norway   总被引：1，自引：0，他引：1  
Sediments from twenty-eight basins were surveyed; ten of these basins with a representative lithostrati-gfaphy wee studied to determine their isolation from the sea during Late Weichselian. Diatom analysis was used to determine salinity changes, which were dated by pollen analysis and the radiocarbon method. The area was deglaciated in the early Boiling, and a regression of about 5 m followed. A transgression of more than 10 m started in late Boiling and terminated in middle Younger Dryas, with a transgression maximum between 38.2 and 40 m above present sea level. All the investigated basins were finally isolated in late Younger Dryas/early Preboreal, during a rapid regression. Repeated cycles of chinophilous/ chinophobous plant communities in the area reflect climatic changes in the period. No evidence of an Older Dryas ice readvance was found.  相似文献   

19.
More than 50 varve-thickness diagrams, which were established from glacial varved clays in south-eastern Sweden were correlated with each other to form an 800-year long floating varve chronology. AMS |214|0C measurements on terrestrial macrofossils from the varved clays enabled synchronization of the record with other high-resolution archives. The synchronization indicates that the chronology spans between c. 13 150 and c. 12 350 calendar years BP and covers the later part of the Allerørd and the early part of the Younger Dryas. Calibrated radiocarbon dates, which were obtained on varved clays south of the floating chronology, indicate that the ice recession in south-eastern Sweden may have started during late Bølling. Our results indicate a longer time-span in varve years for the deglaciation than has been previously estimated  相似文献   

20.
The late‐glacial Bølling period was first identified by Johs. Iversen on the basis of pollen results from Lake Bølling Sø in Denmark. Because there were no radiocarbon dates from the sequence the Bølling Chronozone (12 000–13 000 14C yr BP) was later established on the basis of dates from other sites. A new project is reinvestigating the sediments from the Bølling Sø sequence with AMS radiocarbon dating and multiproxy analyses. Here we present results of AMS radiocarbon dating, macrofossil analyses, cladoceran analyses (Cladocera concentrations and chydorid ephippia) and Pediastrum analyses (concentrations). The AMS dates on land plant remains show that the lower part of the sequence is around 12 500 14C yr BP, and thus clearly pre‐dates the Allerød chronozone. However, construction of a chronology for the sequence was problematic, partly because of reworking of macroscopic plant remains. The climate ameliorated after glacial conditions to such an extent that growth of plants could begin at ca. 12 500 14C yr BP, but the results of multiproxy analyses show little evidence for a further warming period during the pre‐Allerød part of the sequence. Lake productivity was low, and tree birch rare or maybe absent. This may reflect widespread occurrence of dead ice, unstable soils, heavy in‐wash of minerogenic matter to the lake, resulting in turbid water and rapid sedimentation. The early pioneer vegetation was characterised by Salix polaris and Dryas octopetala, and by herbs. The Allerød Chronozone, and especially its initial part, appears to have been relatively warm but reduced cladoceran concentrations and increased proportion of chydorid ephippia suggest that climate cooled in the middle Allerød and that the late Allerød was colder than the early part. The early Younger Dryas was probably colder than the late Younger Dryas. Clear warming is apparent at the beginning of the Holocene, where the first macrofossil evidence of trees (Betula pubescens, Populus tremula) is found. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

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