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1.
BRIGITTA AMMANN RE F. LOTTER 《Boreas: An International Journal of Quaternary Research》1989,18(2):109-126
A detailed late-glacial radiocarbon stratigraphy for the Swiss Plateau has been established on the basis of over 90 accelerator 14 C dates on terrestrial plant macrofossils. Two plateaux of constant.,14 C age were observed, occurring at 12,700 B.P. and at 10,000 B.P. The consequences of these plateaux for palaeo-ecological investigations are threefold: (1) a more refined 14 C dating within the plateaux is not possible, (2) in teleconnections between different sites (if based on 14 C dating and concerning the periods around 12,700 B.P. and 10,000 B.P.) events are considered synchronous which are only synchronous within a plateau of constant age, and (3) exact time-depth relationship and therefore influx calculations are made impossible during these plateau periods. A comparison of the radiocarbon ages derived from terrestrial, telmatic and limnic material at different sites on the Swiss Plateau yields a proposal for modifying the zonation system of Welten for the Late-Glacial. By retaining the limits of chronozones (at 13, 12, 11 and 10ka B.P.) and by refining the palynostratigraphic criteria for the limits of biozones, a separation between chrono- and biozonation at the beginning of the Belling and at the beginning of the Younger Dryas becomes obvious. 相似文献
2.
CHRISTIAN BÉGIN LOUISE FILION 《Boreas: An International Journal of Quaternary Research》1988,17(3):289-299
A 12km long terrace along the estuary of the Grande Rivière de la Baleine, northern Québec (5517'N, 7747'W), has been locally modified by seven large landslides during the last 3,20014 C years. The oldest undated landslide occurred between 3,200 B.P(formation of the upper terrace) and 2,200B.P., i.e. the radio carbon age of the second oldest landslide. The third one occurred around 900B.P. sometime before peat started to accumulate on the flowbowl floor. The more recent landslides were dendrochronologically dated. They were formed in less than 30 years, i.e. in 1818 (2 synchronous landslides), 1839 and 1846 A.D. These 19th-century landslides were dated through a comparative analysis of growth curves derived from buried trees found in the flowing sediments or from tilted and cut trees, with the regional master chronologies and the northern Québec light-ring chronology, using more specifically the 1816 and 1817 light-ring years. The 1818 landslides occurred during the growing season (July), whereas the 1839 and 1846 landslides were formed during spring. The occurrence of numerous landslides during this short period seems to be related to sustained cool and humid climatic conditions that may have enhanced the subsoil water content. 相似文献
3.
NIGEL J. GRIFFEY PETER WORSLEY 《Boreas: An International Journal of Quaternary Research》1978,7(1):1-17
BOREAS Griffey, N. J. & Worsley, P. 1978 03 01: The pattern of Neoglacial glacier variations in the Okstindan region of northern Norway during the last three millennia (Okstindan Research Project Report 26). Boreas, Vol. 7, pp. 1–17. Oslo. ISSN 0300–9483.
Historical, lichenometrical and stratigraphical evidence is combined to establish a provisional history of Neoglacial glacier variation in a mountainous environment approx. 66o N. Attention is focussed on end moraine chronology. At five sites, derived organic materials have been located within end moraines and at two others in situ palaeosols occur buried beneath distal slopes. Organic rich samples from all the sites have been radiocarbon dated and the results permit the recognition of three major glacier expansion episodes, each of which contributes to the diachronous nature of the Okstindan outer Neoglacial limit. A widespread 'Little Ice Age' event with a maximum extent of probable eighteenth century age is confirmed. Limited areas of older moraine ridges peripheral to the 'Little Ice Age' maximal limit appear to date from about 3000-2500 14 C years B.P. and a younger period tentatively dated as about 1250-1000 14 C years B. P. which agrees with recent data from Engabreen in northwest Svartisen. No evidence for any extensive glacial activity after the inlandice wastage approx. 9000 14 C years B. P. and prior to 3000 14 C years B.P. was forthcoming. 相似文献
Historical, lichenometrical and stratigraphical evidence is combined to establish a provisional history of Neoglacial glacier variation in a mountainous environment approx. 66
4.
DAN HAMMAKLUND 《Boreas: An International Journal of Quaternary Research》1993,22(3):236-243
Values of δ13 C obtained from conventional bulk sediment radiocarbon dates encompassing the Pleistocene Holocene boundary have been compiled and plotted against 14 C age. In all. 286 lake sediment dates from southern Sweden in the range 8.000 to 13.000 BP have been evaluated. A significant decrease in δ13 C values, initiated shortly before 10.000 RP and amounting to 5%, is distinguished. This change is accompanied by increased limnic productivity. decreased erosive input and increased organic carbon content of the sediments. A probable explanation for the δ13 C decline in organic material is decreased importance of dissolution of silicates at the transition to the Holocene. During the Late Weichselian. extensive weathering of exposed minerogenic material with subsequent input of bicarbonate to the lake water may have caused a relative enrichment of 13 C in dissolved inorganic carbon. Furthermore, the early Holocene increase in terrestrial vegetation cover probably led to an increased supply of 13 C depleted carbon dioxide to the lake water by root respiration. Altered limnic vegetation, presumably towards increased production of phytoplankton. could also have contributed to the observed decreasing δ13 C trend. The importance of these processes compared to other possible influencing factors. mainly endogenic carbonate production and changes in the global carbon cycle. is discussed. 相似文献
5.
SOLVEIG FIMREITE KARL-DAG VORREN TORE O. VORREN 《Boreas: An International Journal of Quaternary Research》2001,30(2):89-100
Sediments from two small lakes distal to the Tromsø–Lyngen moraine at Tromsø, northern Norway, indicate that the area was deglaciated prior to c. 11.7 14 C ka BP. The earliest vegetation was dominated by calciphilous and heliophilous pioneer plants on unstable soils; this changed to a vegetation reflecting a dry continental climate until c. 10.7 14 Cka BP. A phase (10.7–10.5 14 Cka BP) with snow-bed communities was followed by one with a mosaic of plant communities. This was succeeded by Empetrum heaths c. 10.3 14 Cka BP, then by an open forest with Betula pubescens after 10.0 14 Cka BP. Ice-front oscillations in the Tromsø area are evaluated. The main part of the Younger Dryas glacial readvance, the Tromsø–Lyngen event, probably occurred between 10.7 and 10.3 14 Cka BP. 相似文献
6.
ATLE NYGÅRD HANS PETTER SEJRUP HAFLIDI HAFLIDASON MARCELLO CECCHI DAG OTTESEN 《Boreas: An International Journal of Quaternary Research》2004,33(1):1-17
Analysis of 2D and 3D seismic records from the continental shelf off western Norway, in combination with chronological constraints from 14 C dates, has led to a model for the glacial development in these shelf areas between c. 15 and 13 14 C ka BP. On the shallow Måløy Plateau adjacent to the Norwegian Channel, iceberg scours are preserved below a prominent moraine ridge, which by correlation to the Norwegian Channel indicate ice retreat at c. 15 14 C ka BP. Subsequently, the ice advanced across the scoured surface and deposited a till sheet before stabilizing to deposit a prominent moraine, termed the Bremanger Moraine. Based on location on the shelf, seismic stratigraphy, morphology and C dates the Bremanger Moraine is correlated with a significant moraine on the continental shelf off Trøndelag. We suggest that these features are products of a regional glacial event, the Bremanger Event, dated to <15–13.3 14 C ka BP. The Bremanger Event is probably a result of the deteriorating climatic conditions in the NE Atlantic during Heinrich event 1. 相似文献
7.
DAVID J. LUBINSKI SERGEY KORSUN LEONID POLYAK STEVEN L. FORMAN SCOTT J. LEHMAN FRANCES A. HERLIHY GIFFORD H. MILLER 《Boreas: An International Journal of Quaternary Research》1996,25(2):89-100
A study of two piston cores and a 3.5 kHz seismic profile from the Franz Victoria Trough provides new stratigraphic, stable isotopic and foraminiferal AMS 14 C data that help constrain the timing of ice-sheet retreat in the northern Barents Sea and the nature of the deglacial marine environment. Silty diamicton at the base of each core, interpreted as till or ice-marginal debris flow, suggests that the Barents ice sheet was grounded at the core sites (470 m water depth). Eight AMS 14 C dates on sediment overlying the diamicton indicate that the ice sheet retreated from both core sites by 12.9 ka and that postglacial sedimentation began 10 ka ago. These dates, combined with a recently published 14 C date from a nearby core, suggest that the Franz Victoria Trough may not have been deglaciated until c . 13 ka, 2000 years later than modeled ice-sheet reconstructions indicate. In the trough, oxygen isotopic ratios in planktonic foraminifera N . pachyderma (sinistral) were 0.5–0.750, lower during deglaciation than after, probably as a result of ice-sheet and/or iceberg melting. Foraminiferal assemblages suggest that Atlantic-derived intermediate water may have begun to penetrate the trough c . 13 ka ago. 相似文献
8.
ANNE JENNINGS JAMES SYVITSKI LINDA GERSON KARL GRÖNVOLD ÁSLAUG GEIRSDÓTTIR JÓRUNN HARDARDÓTTIR JOHN ANDREWS SVEINUNG HAGEN 《Boreas: An International Journal of Quaternary Research》2000,29(3):163-183
Foraminifera, sedimentology, and tephra geochemistry in core 93030-006 LCF from the southwestern Iceland shelf were used to reconstruct paleoenvironments between 12.7 and 9.4 14 C ka BP. Seismic-reflection profiles place the core in glacial-marine and marine sediments within one meter of the underlying glacial till. Foraminifers in the earliest glacial-marine sediments provide a record of ice-distal conditions and immigration of slope species onto the shelf in association with warm Atlantic water. Meltwater increased during the Allerød under a weakened Atlantic water influence. Arctic conditions began by 11.14 14 C ka BP with an abrupt increase in meltwater and near exclusion of boreal fauna from the shelf. Meltwater diminished in the early Younger Dryas, coinciding with sea-surface cooling between 11.14 and 10.5 14 C ka BP. A slight warming recorded in the uppermost glacial-marine sediments was interrupted by an inferred jökulhlaup event emanating from glacier ice on the Western Volcanic Zone. Retreat of the ice margin from the sea sometime between c. 10.3 and 9.94 14 C ka BP coincided with this event. The onset of postglacial marine sedimentation occurred along with increasing evidence of Atlantic water c. 9.94 14 C ka BP and was interrupted by a short-lived Pre-boreal cooling of the Irminger Current c. 9.91 14 C ka BP. Conditions similar to those today were established by 9.7 14 C ka BP. 相似文献
9.
ÁRNÝ E. SVEINBJÖRNSOTTIR JÓN EIRÍKSSON ÁSLAUG GEIRSDÓTTIR JAN HEINEMEIER NIELS RUD 《Boreas: An International Journal of Quaternary Research》1993,22(2):147-157
An exhaustive 14 C dating programme of molluscs from the Fossvogur sediments in Reykjavik. Iceland is presented. For the first time all the fossiliferous units of the sediments are dated. The results confirm earlier conclusions of a widespread occurrence of marine sediments of Allerød age in Reykjavik. The set of dates from the Fossvogur sediments shows a narrow 14 C age distribution (standard deviation of ±235 years) of molluscs from all localities and from successive marine units in vertical sections. The weighted mean conventional 14 C age is 11,400 BP. Assuming a reservoir effect of 400 years. this corresponds to a reservoir-corrected age of I1,000 BP. i.e. the Allerød- Younger Dryas transition for the sampled units, These new 14 C dates from Fossvogur confirm the need for a revision of the Upper Pleistocene chronology of the Reykjavik region. They also have a bearing on the Late Weichselian record of glacier readvances and sea-level changes in the area. The dates suggest that the marine units in Fossvogur accumulated within a restricted time-span of a few hundred years. The sediments in Fossvogur are of volcaniclastic origin and are extremely lithified, indicating local geothermal activity soon after their deposition. This may explain anomalously high D/L amino acid ratios measured in molluscs from the Fossvogur sediments. δ13 C and δ18 O results suggest that temperatures may have ranged up to 60°C. 相似文献
10.
MEINRAD KÜTTEL 《Boreas: An International Journal of Quaternary Research》1977,6(3):259-274
New pollen-analytical investigations and two 14 C series indicate that, at the Bedrina on Mount Piottino (Tessin, Switzerland), the post-Allerød NAP phase (Piottino oscillation) represents the well-marked Younger Dryas at least for the most part. The late-glacial part of the profile is re-classified, and the term Piottino oscillation is rejected, as it is largely identical with the Younger Dryas. Individual 14 C dates from the transition between the Younger Dryas and the Preboreal should be considered critically. Considerable fluctuations in the 14 C level are supposed for this period. 相似文献
11.
Podzol development, vegetation change and glacier variations at Haugabreen, southern Norway 总被引:2,自引:0,他引:2
CHRISTOPHER J. CASELDINE JOHN A. MATTHEWS 《Boreas: An International Journal of Quaternary Research》1987,16(3):215-230
12.
MATS RUNDGREN ÓLAFUR INGÓLFSSON SVANTE BJÖRCK HUI JIANG HAFLIDI HAFLIDASON 《Boreas: An International Journal of Quaternary Research》1997,26(3):201-215
Rundgren, M., Ingólfsson, Ó., Björck, S., Jiang, H. & Haflioason, H. 1997 (September): Dynamic sea-level change during the last deglaciation of northern Iceland. Boreas , Vol. 26, pp. 201–215. Oslo. ISSN 0300–9483.
A detailed reconstruction of deglacial relative sea-level changes at the northern coast of Iceland, based on the litho- and biostratigraphy of lake basins, indicates an overall fall in relative sea level of about 45 m between 11300 and 9100 BP, corresponding to an isostatic rebound of 77 m. The overall regression was interrupted by two minor transgressions during the late Younger Dryas and in early Preboreal, and these were probably caused by a combination of expansions of local ice caps and readvances of the Icelandic inland ice-sheet margin. Maximum absolute uplift rates are recorded during the regressional phase between the two transgressions (10000–9850 BP), with a mean value of c . 15 cm14 C yr-1 or 11–12 cm cal. yr-1 . Mean absolute uplift during the regressional phase following the second transgression (9700–9100 BP) was around 6 cm 14 C yr-1 , corresponding to c . 3 cm cal. yr-1 , and relative sea level dropped below present-day sea level at 9000 BP. 相似文献
A detailed reconstruction of deglacial relative sea-level changes at the northern coast of Iceland, based on the litho- and biostratigraphy of lake basins, indicates an overall fall in relative sea level of about 45 m between 11300 and 9100 BP, corresponding to an isostatic rebound of 77 m. The overall regression was interrupted by two minor transgressions during the late Younger Dryas and in early Preboreal, and these were probably caused by a combination of expansions of local ice caps and readvances of the Icelandic inland ice-sheet margin. Maximum absolute uplift rates are recorded during the regressional phase between the two transgressions (10000–9850 BP), with a mean value of c . 15 cm
13.
TORE O. VORREN LIV PLASSEN 《Boreas: An International Journal of Quaternary Research》2002,31(2):97-125
This paper reviews the deglaciation history and palaeoclimate from 22 to 9.5 14 Cka BP in the Andfjord-Vagsfjord area. Eight main glacial events are recorded: The Egga-I (>22 14 Cka BP), the Bjerka, the Egga-II (>14.6 14 Cka BP), the Flesen (14.5 14 Cka BP), the D (13.8–13.2 14 Cka BP), the Skarpnes (12.2 14 Cka BP), the Tromsø–Lyngen (10.7–10.3 14 C ka BP) and the Stordal (10.0–9.5 14 Cka BP). Onset of the final deglaciation occurred about 14.6 14 Cka BP. Most of the western part of the Fennoscandian and Barents Sea Ice Sheets receded from the outer continental shelf 15–14 14 Cka BP. The delivery and melting of icebergs at this time to the Norwegian-Greenland Sea resulted in a low oxygen isotope event recorded in a number of cores in the region. Atlantic water intruded the area 13.2 14 Cka BP, and an atmospheric warming commenced 12.9/12.8 14 Cka BP. A marked glacial recession occurred before the Skarpnes event. During Allerød time, the glaciers retreated to the fjord heads or even farther inland. The Fennoscandian outlet glaciers readvanced (locally more than 40 km), reached their Younger Dryas outer limit after 10.7 14 Cka BP and retreated from this position before about 10.3 14 Cka BP. 相似文献
14.
Optimizing sampling strategy for radiocarbon dating of Holocene fluvial systems in a vertically aggrading setting 总被引:1,自引:0,他引:1
TORBJÖRN E. TÖRNQVIST GEO J. VAN DIJK 《Boreas: An International Journal of Quaternary Research》1993,22(2):129-145
In this paper we address the question of how to determine the period of activity (sedimentation) of fossil (Holocene) fluvial systems in vertically aggrading environments. Our data base consists of almost 100 14 C ages (partly AMS) from the Rhine–Meuse delta in the central Netherlands. Radiocarbon samples from the tops of lithostratigraphically correlative organic beds underneath overbank deposits (sample type 1) yield consistent ages, indicating a synchronous onset of overbank deposition over distances of at least up to 20 km along channel belts. Similarly, 14 C ages from the base of organic residual channel fills (sample type 3) generally indicate a clear termination of within-channel sedimentation. In contrast, 14 C ages from the base of organic beds overlying overbank deposits (sample type 2), commonly assumed to represent the end of fluvial sedimentation, show a large scatter reaching up to 1000 14 C years. This setting usually produces 14 C ages significantly younger than residual channels of the same fluvial system, indicating the presence of non-depositional unconformities. These usually occur on top of slightly elevated sediment bodies (especially natural levee deposits), which often contain palaeosols. Such hiatuses appear to be much more abundant than hitherto supposed. We conclude that a combination of sample types 1 and 3 generally yields a satisfactory delimitation of the period of activity of a fossil fluvial system. The problems associated with 14 C samples of type 2 may also be present in coastal areas with an alternation of tidal deposits and organic beds. 相似文献
15.
Carbon isotope measurements carried out on 201 carbonate samples from the early Proterozoic of the Kola Peninsula, N. Karelia and Norway yield δ13 C (PDB) spanning - 20.5% to + 11%. A general δ13 C secular trend shows that prior to 2.33 Ga values are typically 'normal' marine, averaging around - 3%0. Between 2.33 and 2.06 Ga, in Jatulian time, there follows a rapid excursion to positive δ13 C of around + 6%. Post-Jatulian time is characterized by δ13 C of sedimentary carbonates fluctuating between - 5% and +3%; also it is remarkable for the first pronounced development of diagenetic carbonates, which have δ13 C between - 14 % and - 6% . The c. 6% positive δ13 C shift with a duration of about 270 Myr coincides with a maximum in the diversity and abundance of stromatolites, and with widespread development of 'red beds', but does not coincide with the maximum of buried Corg mass. The Fennoscandian Shield represents the largest isotoically anomalous carbonate province yet reported, and the positive δ13 C excursion together with a series of major global palaeoenviromental changes seems to be more intense than the Precambrian/Cambrian transition events. However, it is still not clear what kind of mechanism this phenomenon could be attributed to. An increase of the 'Ronov ratio', and/or 'Broecker ratio' and other possible models are discussed as the target for future investigations. 相似文献
16.
BARBARA WOHLFARTH OLE BENNIKE LARS BRUNNBERG IGOR DEMEDOV GÖRAN POSSNERT SERGEI VYAHIREV 《Boreas: An International Journal of Quaternary Research》1999,28(4):575-586
The laminated sediments at Pudozh in eastern Karelia are generally assumed to have been deposited between 13 000 and 16 000 14 C yr BP and have been used to date the recession of the active ice margin. However, 17 AMS 14 C measurements performed on terrestrial plant macrofossils contained in these sediments show that deposition began during the late Allerφd, when the ice margin had already receded to the northern part of Lake Onega. Based on an age model, we assume that the 1933-year-long varved sequence covers the time period between c. 12 900 and 11 000 calendar years BP. During this period, which comprises the later part of the Late Weichselian and the early Holocene, the local vegetation consisted of open, tree-less dwarf shrub heaths. Increased soil erosion may have occurred before 12 550 calendar years BP. 相似文献
17.
BARBARA WOHLFARTH SVANTE BJÖRCK GÖRAN POSSNERT GEOFFREY LEMDAHL LARS BRUNNBERG JONAS ISING SIV OLSSON NILS-OLF SVENSSON 《Boreas: An International Journal of Quaternary Research》1993,22(2):113-128
The increasing focus on the chronology of environmental and climatic changes of the last glacial-interglacial transition has led to several independent attempts to try to calibrate the 14 C time-scale beyond the Holocene. The Late Weichselian Gotiglacial varved clays of the Swedish Time Scale could potentially be used for this purpose. The reliability of the Swedish Time Scale is discussed as well as different ways of using the Swedish varved clays for calibrating the 14 C chronology. The strategy and initial results from an ongoing calibration project are presented. They show clearly that, if the right strategy is adopted, varved clay may be dated by accelerator mass spectrometry (AMS) 14 C measurement of terrestrial macrofossils. A Late Weichselian 'event stratigraphy', including the Vedde Ash fall-out, is established for south Scandinavia using three dating categories: clay varve measurements, terrestrial macrofossil measurement, and lake sediment (including aquatic mosses) measurements. It suggests that a 14 C chronology based on terrestrial organic remains is not consistent with the traditional Late Weichselian chronostratigraphy based on lake-sediment samples, and that 'clay varve years' exceed 'terrestrial 14 C years' by c. 900 years at the end of, and by 1100–1200 years at the beginning of the Younger Dryas Chronozone. Further back in time, the time-scales appear to converge. These results are compared with other recently published calibration studies. 相似文献
18.
Expanded sedimentary records from the Tethys reveal unique faunal and isotopic changes across the Palaeocene-Eocene (P-E) transition. Unlike in the open oceans, the Tethys exhibits a gradual decrease of 1.5% in δ13 C values prior to the rapid δ13 C excursion. Associated with the 613 C excursion is a decrease in calcite burial, increase in detrital content and appearance of a unique opportunistic planktic foraminifera1 assemblage (e.g. compressed acarininids). The existence of a prelude decrease in δ13 C values in the Tethys suggests that the P-E δ13 C excursion may have occurred in two steps and over a few hundred thousand years, rather than as one step over a few thousand years as previously suggested. This slower excursion rate is readily explained by changing organic carbon weathering or burial rates and avoids the need of invoking ad hoc scenarios. 相似文献
19.
PETER WILSON RICHARD M. BATEMAN 《Boreas: An International Journal of Quaternary Research》1986,15(2):137-153
Soil horizons delimit three periods of sand deposition and subsequent topographic stability at Magilligan Foreland, Co. Londonderry. All the deposits are composed of texturally and mineralogically similar material. The earliest topography is a beach ridge plain; podzols cap the ridges and peats occur in the inter-ridge depressions, together comprising a buried palaeocatena. The podzols are visually distinct but chemically and mineralogically immature. Peat and podzol genesis probably began between 3,000 and 2,500 years B.P., and were terminated between c . 1,100 years B.P. and c . 600 years B.P. by burial under an extensive layer of aeolian sand. This sand was eroded to a planar surface before developing a sand-pararendzina, which represents a second period of surface stability. The third deposit, a discontinuous dune sand, is presently also developing a sand-pararendzina. Difficulties of using 14 C dates to erect absolute chronologies are discussed. 相似文献
20.
ALLA SHARAPOVA MORTEN HALD KATRINE HUSUM CHRISTIN JENSEN 《Boreas: An International Journal of Quaternary Research》2008,37(3):444-457
A high-resolution Younger Dryas–late Holocene record of climate and environment from the Malangen fjord has been established on the basis of two marine sediment cores. Five pollen-spore assemblage zones have been defined covering the period c . 11 500 cal. yr BP (10 200 14 C yr BP) to c . 1600 cal. yr BP (1600 14 C yr BP) with a hiatus of c . 2000 cal. years between c . 10 200 and 8100 cal. yr BP (9000 and 7300 14 C yr BP). The Holocene vegetation development from pioneer vegetation to forest development, identified in the marine pollen record, correlates well with pollen records from terrestrial sections of northern Norway. The marine pollen record was also correlated directly with marine proxy records of the bottom water temperature investigated in the same sediment cores. Correlation between the marine and terrestrial proxies suggests that changes in the influx of warm Atlantic Water to the fjord led to an instant change in the vegetation of the surrounding land area. The results thus support a strong link between marine and atmospheric mean climatic states in the North Atlantic region throughout the Holocene. 相似文献