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1.
A late glacial to early Holocene lacustrine and peat succession, rich in conifer remains and including some palaeolithic flint artefacts, has been investigated in the Palughetto intermorainic basin (Venetian Pre‐Alps). The geomorphological and stratigraphical relationships, 14C dates and pollen analyses allow a reconstruction of the environmental history of the basin and provide significant insights into the reforestation and peopling of the Pre‐Alps. The onset of peat accumulation is dated to 14.4–14.1 kyr cal. BP, coinciding with reforestation at middle altitudes that immediately post‐dates the immigration of Larix decidua and Picea abies subsp. europaea. Plant macrofossils point to the expansion of spruce about 14.3 kyr cal. BP, so far one of the earliest directly dated in the late glacial period of southern Europe. The previous hypothesis of an early Holocene spruce immigration in the Southern Alps from Slovenia needs reconsideration. Organic sedimentation stopped at the end of the Younger Dryas and was followed by the evolution of hydromorphic soils containing lithic artefacts, anthropic structures and wood charcoal. The typological features of the flint implements refer human occupation of the site to the end of the recent Epigravettian. Charcoals yielded dates either consistent with, or younger than, the archaeological chronology, in the early and middle Holocene. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

2.
Sedimentological, micropalaeontological (benthic foraminifers and dinoflagellate cysts), stable isotope data and AMS 14C datings on cores and surface samples, in addition to acoustic data, have been obtained from Voldafjorden, western Norway. Based on these data the late glacial and Holocene sedimentological processes and variability in circulation and fjord environments are outlined. Glacial marine sedimentation prevailed in the Voldafjorden between 11.0 kyr and 9.2 kyr BP (radiocarbon years). In the later part of the Allerød period, and for the rest of the Holocene, there was deposition of fine‐grained normal marine sediments in the fjord basin. Turbidite layers, recorded in core material and on acoustic profiles, dated to ca. 2.1, 6.9–7.6, ca. 9.6 and ca. 11.0 kyr BP, interrupted the marine sedimentation. The event dated to between 6.9 and 7.6 kyr BP probably corresponds to a tsunami resulting from large‐scale sliding on the continental margin off Norway (the Storegga Tsunami). During the later part of the Allerød period, Voldafjorden had a strongly stratified water column with cold bottom water and warm surface water, reaching interglacial temperatures during the summer seasons. During the Younger Dryas cold event there was a return to arctic sea‐surface summer temperatures, possibly with year‐round sea‐ice cover, the entire benthic fauna being composed of arctic species. The first strong Holocene warming, observed simultaneously in bottom and sea‐surface temperature proxies, occurred at ca. 10.1 kyr BP. Bottom water proxies indicate two cold periods, possibly with 2°C lowering of temperatures, at ca. 10.0 (PBO 1) and at 9.8 kyr BP (PBO 2). These events may both result from catastrophic outbursts of Baltic glacial lake water. The remainder of the Holocene experienced variability in basin water temperature, indicated by oxygen isotope measurements with an amplitude of ca. 2°C, with cooler periods at ca. 8.4–9.0, 5.6, 5.2, 4.6, 4.2, 3.5, 2.2, 1.2 and 0.4–0.8 kyr BP. Changes in the fjord hydrology through the past 11.3 kyr show a close correspondence, both in amplitude and timing of events, recorded in cores from the Norwegian Sea region and the North Atlantic. These data suggest a close relationship between fjord environments and variability in large‐scale oceanic circulation. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

3.
Mangerud, J., Gulliksen, S. & Larsen, E. 2009: 14C‐dated fluctuations of the western flank of the Scandinavian Ice Sheet 45–25 kyr BP compared with Bølling–Younger Dryas fluctuations and Dansgaard–Oeschger events in Greenland. Boreas, 10.1111/j.1502‐3885.2009.00127.x. ISSN 0300‐9483. We present 32 accelerator mass spectrometry (AMS) 14C dates obtained on well‐preserved bones from caves in western Norway. The resulting ages of 34–28 14C kyr BP demonstrate that the coast was ice‐free during the so‐called Ålesund Interstadial. New AMS 14C dates on shells aged 41–38 14C kyr BP are evidence of an earlier (Austnes) ice‐free period. The Ålesund Interstadial correlates with Greenland interstadials 8–7 and the Austnes Interstadial with Greenland interstadials 12–11. Between and after the two interstadials, the ice margin reached onto the continental shelf west of Norway. These events can be closely correlated with the Greenland ice core stratigraphy, partly based on identification of the Laschamp and Mono Lake palaeomagnetic excursions. We found that the pattern of the NGRIP δ18O curves for the two periods Greenland Interstadial (GI) 8 to Greenland Stadial (GS) 8 and GI 1–GS 1 (Bølling–Younger Dryas) were strikingly similar, which leads us to suggest that the underlying causes of these climate shifts could have been the same. We therefore discuss some aspects of glacial fluctuations during the Bølling–Younger Dryas in order to elucidate processes during Dansgaard–Oeschger events.  相似文献   

4.
High‐resolution gravity cores and box cores from the North Icelandic shelf have been studied for palaeoceanographic history based on lithological and biostratigraphical foraminiferal data. Results from two outer shelf cores covering the last 13.6 k 14C yr BP are presented in this paper. The sediments accumulated in north–south trending basins on each side of the Kolbeinsey Ridge at water depths of ca. 400 m. Sedimentation rates up to 1.5 m kyr−1 are observed during the Late‐glacial and Holocene. The Vedde and Saksunarvatn tephras are present in the cores as well as the Hekla 1104. A new tephra, KOL‐GS‐2, has been identified and dated to 13.4 k 14C yr BP, and another tephra, geochemically identical to the Borrobol Tephra, has been found at the same level. At present, the oceanographic Polar Front is located on the North Icelandic shelf, which experiences sharp oceanographic surface boundaries between the cold East Icelandic Current and the warmer Irminger Current. Past changes in sedimentological and biological processes in the study area are assumed to be related to fluctuations of the Polar Front. The area was deglaciated before ca. 14 kyr BP, but there is evidence of ice rafting up to the end of the GS‐1 (Greenland Stadial 1, Younger Dryas) period, increasing again towards the end of the Holocene. Foraminiferal studies show a relatively strong GS‐2 (pre‐13 kyr BP) palaeo‐Irminger Current, followed by severe cooling and then by unstable conditions during the remainder of the GI‐1 (Greenland Interstadial 1, Bølling–Allerød) and GS‐1 (Younger Dryas). Another cooling event occurred during the Preboreal before the Holocene current system was established at about 9 kyr BP. After a climatic optimum between 9 and 6 kyr BP the climate began to deteriorate and fluctuate. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

5.
Kirkbride, M.P. & Bell, C.M. 2009: Edge‐roundness of boulders of Torridonian Sandstone (northwest Scotland): applications for relative dating and implications for warm and cold climate weathering rates. Boreas, 10.1111/j. 1502‐3885.2009.00131.x. ISSN 0300‐9483. The relative ages of late Quaternary morainic and rock avalanche deposits on Late Precambrian Torridonian Sandstone are determined from the characteristic edge‐roundness of constituent boulders. Because weathering of sandstone is manifest as edge‐rounding by granular disintegration, a relative chronology can be derived by measuring the effective radii of curvature of a sample of boulder edges. Thirteen samples totalling 597 individual boulder edges fall into two statistically distinct groups. Moraines of inferred Younger Dryas age (12.9–11.5 kyr BP) are distinguished from moraines of the Wester Ross Re‐advance (≤14.0 kyr BP). One moraine previously assumed to be of Younger Dryas age is reassigned to the older group. The method allows spatial extrapolation of deposit ages from dated sites where lithological and sampling criteria are met. Calculated rates of edge‐rounding imply that granular disintegration was several times more rapid during cold stadial climates than during the Holocene. Used as a proxy for boulder ‘erosion rate’, this indicates that surface loss of grains in glacial climates exceeds that during interglacials by a factor of 2–5, with implications for the calculation of exposure ages from cosmogenic nuclides.  相似文献   

6.
This paper presents an event stratigraphy based on data documenting the history of vegetation cover, lake‐level changes and fire frequency, as well as volcanic eruptions, over the Last Glacial–early Holocene transition from a terrestrial sediment sequence recovered at Lake Accesa in Tuscany (north‐central Italy). On the basis of an age–depth model inferred from 13 radiocarbon dates and six tephra horizons, the Oldest Dryas–Bølling warming event was dated to ca. 14 560 cal. yr BP and the Younger Dryas event to ca. 12 700–11 650 cal. yr BP. Four sub‐millennial scale cooling phases were recognised from pollen data at ca. 14 300–14 200, 13 900–13 700, 13 400–13 100 and 11 350–11 150 cal. yr BP. The last three may be Mediterranean equivalents to the Older Dryas (GI‐1d), Intra‐Allerød (GI‐1b) and Preboreal Oscillation (PBO) cooling events defined from the GRIP ice‐core and indicate strong climatic linkages between the North Atlantic and Mediterranean areas during the last Termination. The first may correspond to Intra‐Bølling cold oscillations registered by various palaeoclimatic records in the North Atlantic region. The lake‐level record shows that the sub‐millennial scale climatic oscillations which punctuated the last deglaciation were associated in central Italy with different successive patterns of hydrological changes from the Bølling warming to the 8.2 ka cold reversal. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

7.
Zech, M., Andreev, A., Zech, R., Müller, S., Hambach, U., Frechen, M. & Zech, W.: Quaternary vegetation changes derived from a loess‐like permafrost palaeosol sequence in northeast Siberia using alkane biomarker and pollen analyses. Boreas, Vol. 39, pp. 540–550. 10.1111/j.1502‐3885.2009.00132.x. ISSN 0300‐9483 Alkane biomarker and pollen data were obtained from a 15‐m‐high and probably c. 240‐kyr‐old loess‐like permafrost palaeosol sequence (‘Tumara Palaeosol Sequence’, TPS) in northeast Siberia. The alkane results were corrected for degradation effects by applying an end‐member model and were evaluated by comparing them with the palynological results. The two data sets are generally in good agreement and suggest that the lower part of the TPS developed mainly under larch forests, whereas the upper part of the sequence reflects the expansion of mammoth steppes during the Weichselian glaciation and finally reforestation during the Lateglacial and the early Holocene. For the lower part of the TPS, the palaeoclimatic interpretation according to modern analogue methods would indicate warm, interglacial conditions, but this is at odds with the climate chronostratigraphy based on a multi‐proxy palaeopedological approach and numeric dating. Provided that the correlation of the discussed stratigraphic unit with the Late Saalian glaciation and the Marine Oxygen Isotope Stage 6 is correct, our results suggest that temperature was not a limiting factor for tree growth at that time. Furthermore, it seems very likely that it was not mainly temperature changes but rather increasing aridity and continentality during the course of the last glacial that favoured the expansion of the mammoth steppe.  相似文献   

8.
The deglaciation history of the Malangen‐Målselv fjord and valley area proximally to the Tromsø‐Lyngen (Younger Dryas) moraine at Bakkejord, Malangen, northern Norway, is reconstructed based on morphostratigraphic, lithostratigraphic and geophysical evidence, and 25 radiocarbon dates from marine shells and foraminifera. The results show that following the Skarpnes event c. 12 200 14Cyr BP, and prior to the Younger Dryas readvance, the area was deglaciated at least as far as Sandmo situated 22 km proximally to the Tromsø‐Lyngen moraine. Two moraine ridges crossing the fjord at Sandmo and buried beneath thick glaciomarine sediments are correlated with this period. The area was subsequently deglaciated between 10 300 and 9200 14Cyr BP, following the Tromsø‐Lyngen (Younger Dryas) readvance. Five ice‐front accumulations post‐dating the Tromsø‐Lyngen moraine and situated 19, 27, 42, 55 and 77 km behind it are identified and dated based on radiocarbon dates and correlation of marine limits: Målsnes (c. 10 050 14Cyr BP), Kjerresnes (c. 10 000 14Cyr BP), Solli (c. 9750 14Cyr BP), Bardufoss‐Brentmoen‐Storskogmoen (c. 9600–9700 14Cyr BP) and Alapmoen (c. 9200 Cyr BP). The largest of these, at Bardufoss‐Storskogmoen, possibly accumulated as a response to an ice advance. Fourteen dates of apparent late Allerød/Younger Dryas age (11 100–10 000 14Cyr BP), obtained from fossils in glaciomarine sediments in the Målselv valley up to 77 km proximally to the Tromsø‐Lyngen moraine, are interpreted as postdating rather than predating this moraine. Several of these are considered to be too old because of uncertain reservoir age, carbon‐dating plateaus and/or contamination. This highlights uncertainties associated with radiocarbon‐dating and the profound effect such uncertainties may have on interpreting geological events.  相似文献   

9.
The boundary between the last two geological epochs, the Pleistocene and the Holocene, is placed at 'the date 10,000 B.P., measured in radiocarbon years'. In the European chronostratigraphy, this corresponds to the Younger Dryas/Preboreal boundary, the pollen zone III/IV boundary and the Late Glacial/Postglacial boundary. The stratal sequence in the Botanical Garden of Gothenburg is proposed as a suitable boundary-stratotype of the Pleistocene/Holocene that fulfils the stratigraphical rules of marine environment and accessibility. A core, labelled B 873, has been analyzed for multiple parameters by various authors. The suggested Pleistocene/Holocene boundary in Core B 873 is indicated by a lithologic boundary, a palynological change tentatively correlated with the pollen zone III/IV boundary, and a distinct palaeomagnetic intensity maximum, the 'Gålön Magnetic Intensity Maximum', identified in numerous other cores at the Younger Dryas/Preboreal boundary and at the drainage of the Baltic Ice Lake in varved clay sequences (with the peak dated at the drainage ±4 varves). This boundary is closely radiocarbon dated at 10,000 B.P. (10,000–9950 B.P.) in terrestrial-lacustrine sequences within the proposed type area in Gothenburg and in Southern Sweden, the established type region for the Pleistocene/Holocene boundary. The corresponding varve date is 9965 varves B.P. (De Geer's varve –1073). The various parameters directly and indirectly connected with the study of Core B 873 make global correlations possible. Because every region has its own local characteristics, however, it will be necessary to establish regional type sections, hypostratotypes.  相似文献   

10.
Northern Folgefonna (c. 23 km2), is a nearly circular maritime ice cap located on the Folgefonna Peninsula in Hardanger, western Norway. By combining the position of marginal moraines with AMS radiocarbon dated glacier‐meltwater induced sediments in proglacial lakes draining northern Folgefonna, a continuous high‐resolution record of variations in glacier size and equilibrium‐line altitudes (ELAs) during the Lateglacial and early Holocene has been obtained. After the termination of the Younger Dryas (c. 11 500 cal. yr BP), a short‐lived (100–150 years) climatically induced glacier readvance termed the ‘Jondal Event 1’ occurred within the ‘Preboreal Oscillation’ (PBO) c. 11 100 cal. yr BP. Bracketed to 10 550–10 450 cal. yr BP, a second glacier readvance is named the ‘Jondal Event 2’. A third readvance occurred about 10 000 cal. yr BP and corresponds with the ‘Erdalen Event 1’ recorded at Jostedalsbreen. An exponential relationship between mean solid winter precipitation and ablation‐season temperature at the ELA of Norwegian glaciers is used to reconstruct former variations in winter precipitation based on the corresponding ELA and an independent proxy for summer temperature. Compared to the present, the Younger Dryas was much colder and drier, the ‘Jondal Event 1’/PBO was colder and somewhat drier, and the ‘Jondal Event 2’ was much wetter. The ‘Erdalen Event 1’ started as rather dry and terminated as somewhat wetter. Variations in glacier magnitude/ELAs and corresponding palaeoclimatic reconstructions at northern Folgefonna suggest that low‐altitude cirque glaciers (lowest altitude of marginal moraines 290 m) in the area existed for the last time during the Younger Dryas. These low‐altitude cirque glaciers of suggested Younger Dryas age do not fit into the previous reconstructions of the Younger Dryas ice sheet in Hardanger. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

11.
The restricted environment of the Black Sea is particularly sensitive to climatic and oceanographic fluctuations, owing to its connection with the Mediterranean Sea via the narrow Bosphorus Strait. The exact mechanism and timing of the most recent connection between these water bodies is controversial with debate on the post-glacial history of the Black Sea being dependent on radiocarbon dating for numerical ages. Here we present new 23 accelerator mass spectrometer (AMS) radiocarbon ages on peat and bivalve molluscs, supported by the first amino acid racemization (AAR) dating of bivalve molluscs (n = 66) in the Black Sea. These data indicate infilling of the Black Sea during the early Holocene from an initial depth 107 m below sea-level, and 72 m below that of the Bosphorus Sill. These data combined with a review of previous radiocarbon ages has enabled a unique perspective on the post-glacial Black Sea. A sea-level curve based on conventional and AMS radiocarbon ages on peat and AMS-based ages on Dreissena sp. shells indicate the water-level in the earlier lake phase continued, until the early Holocene, to be lower than the Bosphorus Sill after the Younger Dryas ended. However, the absence of AMS-dated mollusc ages from the shelves of this basin older than the Younger Dryas is suggestive of sub-aerial exposure of the shelves, and comparatively lower water-levels when the Younger Dryas began. Thus post-glacial outflow from the Black Sea occurred through a lowered or open Bosphorus seaway. Basin-wide radiocarbon ages on peat indicate a prompt increase in water-level from that of the pre-existing and unconnected palaeo-lake during the earliest Holocene (9600–9200 cal a BP). Mass colonisation of the Black Sea by Mediterranean taxa did not occur until salinity had risen sufficiently, a process which took 1000 a or more from the initial transgressive event. This gradual change in salinity contrasts with the prompt transgression which would have taken ～400 a to occur.  相似文献   

12.
Here, we present and discuss results from geo‐archaeological and palaeo‐zoological investigations at the Palaeolithic site Pymva Shor, in the Russian Arctic. As many as 3324 vertebrate fauna remains were recovered during two excavations. This includes bones of mammals, birds and fish. Radiocarbon dates were obtained from 26 specimens. The results show ages in the range 30–3 cal. ka BP. Hare and reindeer are the best represented amongst the identified mammalian species, whilst ptarmigan and various wader species dominate the avian bones. The Pleistocene assemblage includes herbivorous herd animals such as horse, bison and musk ox. These species are typical of the treeless tundra‐steppe landscape that existed during the Lateglacial. Of particular interest is a cave lion specimen that has been radiocarbon dated to approximately 15.5 cal. ka BP. According to our knowledge, this is one of the latest dated examples of this species in Eurasia. The faunal composition in the Holocene assemblage is strikingly different and includes distinct forest taxa such as beaver and pine marten. The avifauna also supports a forested environment with the presence of black grouse. A few stone artefacts were found within the strata, and have been radiocarbon dated to 16–15 cal. ka BP, suggesting that there were humans in the Pymva Shore area at that time. We identified impact notches and cut marks on some radiocarbon‐dated reindeer and bison bones, showing that humans were present twice during the Younger Dryas period. A fourth occupation phase is identified during the mid‐Holocene (6–5 cal. ka BP). We also investigated river terraces and obtained a series of luminescence dates. These have been used to reconstruct the geological history and the relationship to the find‐bearing strata.  相似文献   

13.
The authors discuss Late Pleistocene–Holocene depositional environments in one of the Fuegian Andes valleys on the basis of palynological, geomorphological, and sedimentological analyses from two sites located near the Beagle Channel. The results obtained at these localities reinforce and refine the Late Pleistocene–Holocene climatic pattern previously recorded there. A colder period, associated with the Younger Dryas stadial event, is suggested by low Nothofagus pollen frequency, and communities of grass, low scrub, and shrub heath expanded into the low/middle slopes (10,310 14C yr BP). By ca. 9500 14C yr BP, warmer and drier conditions occurred, as evidenced by the development of open-grown vegetation in the valley floors (pollen zone O-3), followed by the expansion of open Nothofagus woodland (pollen zone O-2) in the middle Holocene. The milder climate subsequently changed, as indicated by the spreading of the closed forest and mire (pollen zone O-1), to more humid and cooler conditions during the last ca. 5000 yr BP.  相似文献   

14.
Anjar, J., Larsen, N. K., Björck, S., Adrielsson, L. & Filipsson, H. L. 2010: MIS 3 marine and lacustrine sediments at Kriegers Flak, southwestern Baltic Sea. Boreas, 10.1111/j.1502‐3885.2010.00139.x. ISSN 0300‐9483. Sediment cores from the Kriegers Flak area in the southwestern Baltic Sea show a distinct lithological succession, starting with a lower diamict that is overlain by a c. 10 m thick clay unit that contains peat, gyttja and other organic remains. On top follows an upper diamict that is inter‐layered with sorted sediments and overlain by an upward‐coarsening sequence with molluscs. In this paper we focus on the clay unit, which has been subdivided into three subunits: (A) lower clay with benthic foraminifera and with diamict beds in the lower part; (B) thin beds of gyttja and peat, which have been radiocarbon‐dated to 31–35 14C kyr BP (c. 36–41 cal. kyr BP); and (C) upper clay unit. Based on the preliminary results we suggest the following depositional model: fine‐grained sediments interbedded with diamict in the lower part (subunit A) were deposited in a brackish basin during a retreat of the Scandinavian Ice Sheet, probably during the Middle Weichselian. Around 40 kyr BP the area turned into a wetland with small ponds (subunit B). A transgression, possibly caused by the damming of the Baltic Basin during the Kattegat advance at 29 kyr BP, led to the deposition of massive clay (subunit C). The data presented here provide new information about the paleoenvironmental changes occurring in the Baltic Basin following the Middle Weichselian glaciation.  相似文献   

15.
Krüger, L. C., Paus, A., Svendsen, J. I. & Bjune, A. E. 2011: Lateglacial vegetation and palaeoenvironment in W Norway, with new pollen data from the Sunnmøre region. Boreas, 10.1111/j.1502‐3885.2011.00213.x. ISSN 0300‐9483. Two sediment sequences from Sunnmøre, northern W Norway, were pollen‐analytically studied to reconstruct the Lateglacial vegetation history and climate. The coastal Dimnamyra was deglaciated around 15.3 ka BP, whereas Løkjingsmyra, further inland, became ice‐free around 14 ka BP. The pioneer vegetation dominated by snow‐bed communities was gradually replaced by grassland and sparse heath vegetation. A pronounced peak in Poaceae around 12.9 ka BP may reflect warmer and/or drier conditions. The Younger Dryas (YD) cooling phase shows increasing snow‐bed vegetation and the local establishment of Artemisia norvegica. A subsequent vegetation closure from grassland to heath signals the Holocene warming. Birch forests were established 500–600 years after the YD–Holocene transition. This development follows the pattern of the Sunnmøre region, which is clearly different from the Empetrum dominance in the Lateglacial interstadial further south in W Norway. The Lateglacial oscillations GI‐1d (Older Dryas) and GI‐1b (Gerzensee) are hardly traceable in the north, in contrast to southern W Norway. The southern vegetation was probably closer to an ecotone and more susceptible to climate changes.  相似文献   

16.
The primary objective of this study is to further substantiate multistep climatic forcing of late‐glacial vegetation in southern South America. A secondary objective is to establish the age of deglaciation in Estrecho de Magallanes–Bahía Inútil. Pollen assemblages at 2‐cm intervals in a core of the mire at Puerto del Hambre (53°36′21″S, 70°55′53″W) provide the basis for reconstructing the vegetation and a detailed account of palaeoclimate in subantarctic Patagonia. Chronology over the 262‐cm length of core is regulated by 20 AMS radiocarbon dates between 14 455 and 10 089 14C yr BP. Of 13 pollen assemblage zones, the earliest representing the Oldest Dryas chronozone (14 455–13 000 14C yr BP) records impoverished steppe with decreasing frequencies and loss of southern beech (Nothofagus). Successive 100‐yr‐long episodes of grass/herbs and of heath (Empetrum/Ericaceae) before 14 000 14C yr BP infer deglacial successional communities under a climate of increased continentality prior to the establishment of grass‐dominated steppe. The Bølling–Allerød (13 000–11 000 14C yr BP) is characterised by mesic grassland under moderating climate that with abrupt change to heath dominance after 12 000 14C yr BP was warmer and not as humid. At the time of the Younger Dryas (11 000–10 000 14C yr BP), grass steppe expanded with a return of colder, more humid climate. Later, with gradual warming, communities were invaded by southern beech. The Puerto del Hambre record parallels multistep, deglacial palaeoclimatic sequences reported elsewhere in the Southern Andes and at Taylor Dome in Antarctica. Deglaciation of Estrecho de Magallanes–Bahía Inútil is dated close to 14 455 14C yr BP, invalidating earlier dates of between 15 800 and 16 590 14C yr BP. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

17.
A detailed shoreline displacement curve documents the Younger Dryas transgression in western Norway. The relative sea‐level rise was more than 9 m in an area which subsequently experienced an emergence of almost 60 m. The sea‐level curve is based on the stratigraphy of six isolation basins with bedrock thresholds. Effort has been made to establish an accurate chronology using a calendar year time‐scale by 14C wiggle matching and the use of time synchronic markers (the Vedde Ash Bed and the post‐glacial rise in Betula (birch) pollen). The sea‐level curve demonstrates that the Younger Dryas transgression started close to the Allerød–Younger Dryas transition and that the high stand was reached only 200 yr before the Younger Dryas–Holocene boundary. The sea level remained at the high stand for about 300 yr and 100 yr into Holocene it started to fall rapidly. The peak of the Younger Dryas transgression occurred simultaneously with the maximum extent of the ice‐sheet readvance in the area. Our results support earlier geophysical modelling concluding a causal relationship between the Younger Dryas glacier advance and Younger Dryas transgression in western Norway. We argue that the sea‐level curve indicates that the Younger Dryas glacial advance started in the late Allerød or close to the Allerød–Younger Dryas transition. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

18.
This paper presents a summary of Late-glacial environmental changes in southwestern Europe (lberian Peninsula, Pyrenees, Massif Central and the northern Apennines). The emphasis is on palaeoclimatic interpretations inferred from key sites in the region from which the most detailed records are available and which have been radiocarbon dated. The earliest evidence for climatic improvement following the end of the last glacial stage is dated to ca. 15 ka BP and is found at a few sites only. By 13 ka BP, a more widespread and marked climatic improvement is evident, although it is difficult to be precise in the timing and magnitude of the event. There are significant variations in detail between the Late-glacial records, but evidence for a significant cooling correlated with the Younger Dryas event is widespread throughout the region. Just two sites in the region provide evidence for an earlier, less emphatic phase of climatic cooling, which is tentatively equated with the ‘Older Dryas’ of continental northern Europe. Dry conditions appear to have predominated throughout the region in the later part of the Younger Dryas and the early Holocene.  相似文献   

19.
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   

20.
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   

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