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1.
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 cm 14C 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 14C 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   

2.
An exhaustive 14C 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 14C age distribution (standard deviation of ±235 years) of molluscs from all localities and from successive marine units in vertical sections. The weighted mean conventional 14C 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 14C 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. δ13C and δ18O results suggest that temperatures may have ranged up to 60°C.  相似文献   

3.
Neptune's Cave in the Velfjord–Tosenfjord area of Nordland, Norway is described, together with its various organic deposits. Samples of attached barnacles, loose marine molluscs, animal bones and organic sediments were dated, with radiocarbon ages of 9840 ± 90 and 9570 ± 80 yr BP being derived for the barnacles and molluscs, based on the superseded but locally used marine reservoir age of 440 years. A growth temperature of c . 7.5 °C in undiluted seawater is deduced from the δ13C and δ18O values of both types of marine shell, which is consistent with their early Holocene age. From the dates, and an assessment of local Holocene uplift and Weichselian deglaciation, a scenario is constructed that could explain the situation and condition of the various deposits. The analysis uses assumed local isobases and sea-level curve to give results: that are consistent with previous data, that equate the demise of the barnacles to the collapse of a tidewater glacier in Tosenfjord, and that constrain the minimum extent of local Holocene uplift. An elk fell into the cave in the mid-Holocene at 5100 ± 70 yr BP, after which a much later single 'bog-burst' event at 1780 ± 70 yr BP could explain the transport of the various loose deposits further into the cave.  相似文献   

4.
This paper reviews the deglaciation history and palaeoclimate from 22 to 9.5 14Cka BP in the Andfjord-Vagsfjord area. Eight main glacial events are recorded: The Egga-I (>22 14Cka BP), the Bjerka, the Egga-II (>14.6 14Cka BP), the Flesen (14.5 14Cka BP), the D (13.8–13.2 14Cka BP), the Skarpnes (12.2 14Cka BP), the Tromsø–Lyngen (10.7–10.3 14C ka BP) and the Stordal (10.0–9.5 14Cka BP). Onset of the final deglaciation occurred about 14.6 14Cka BP. Most of the western part of the Fennoscandian and Barents Sea Ice Sheets receded from the outer continental shelf 15–14 14Cka 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 14Cka BP, and an atmospheric warming commenced 12.9/12.8 14Cka 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 14Cka BP and retreated from this position before about 10.3 14Cka BP.  相似文献   

5.
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 14C 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 14C 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 14C 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 14C ka BP coincided with this event. The onset of postglacial marine sedimentation occurred along with increasing evidence of Atlantic water c. 9.94 14C ka BP and was interrupted by a short-lived Pre-boreal cooling of the Irminger Current c. 9.91 14C ka BP. Conditions similar to those today were established by 9.7 14C ka BP.  相似文献   

6.
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   

7.
Lake Boksehandsken, the largest lake on Jameson Land, central East Greenland, is situated 54 m a.s.l. and holds a long (6.3 m) and complex stratigraphy. It was analysed with respect to lithology, carbon content, 14C, micro- and macrofossils. The diamict material in the bottom is overlain by a fining-upwards sequence, possibly deposited close to a receding ice margin in a glaciomarine environment. These deposits are interpreted to have been formed at the time of the marine limit ( c . 70 m) in the area. In spite of a large series of 14C datings, very few of the obtained dates were considered reliable. This is because the sediments contain coal fragments and old redeposited plant remains. Based on a set of arguments and correlations to the surrounding glacial stratigraphy it is implied that the marine limit and deglaciation cannot be much older than 10,000 BP. The lithology of the lake sediments, in combination with occurrence of marine macrofossils. shows that deglaciation was succeeded by a (glacio)marine depositional environment. The lake was isolated from the sea at c . 9000 BP. followed by a short transgression and a final isolation at c . 8400 BP. This sequence of events is demonstrated by both litho-and biostratigraphy and possible causes are discussed. A later oscillation some time between 8000 and 7500 BP. evidenced by litho-, carbon-, pollen- and Pecliastrum stratigraphy, is interpreted as a regional climatic cooling possibly correlatable to a distinct δ18O minima in the Greenland ice cores.  相似文献   

8.
Broughton Island is 50 km from the eastern margin of the 6,000 km2 Penny Ice Cap. During the early Wisconsin (> 54,000 BP) A younger glacial readvance is delimited by lateral moraines and glacio-marine deposits 14C dated at 24,100±850 BP; sea level was±18 m. During th last Wisconsin the glaciers terminated some distance inland from Broughton Island and sea alevel at 9,850±250BP was +5 m on Broughton Island. The head of Maktak Fiord, which presently contains a majour outlet glacier from the Penny Ice Cap, was deglaciated about 6,000 BP.  相似文献   

9.
Southwestern Finland was covered by the Weichselian ice sheet and experienced rapid glacio-isostatic rebound after early Holocene deglaciation. The present mean overall apparent uplift rate is of the order of 4-5 mm/yr, but immediately after deglaciation the rate of crustal rebound was several times higher. Concurrently with land uplift, relative sea level in the Baltic basin during the past more than 8000 years was also strongly affected by the eustatic changes in sea level. There is ample evidence from earlier studies that during the early Litorina Sea stage on the southeastern coast of Finland around 7000 yr BP (7800 cal. yr BP), the rise in sea level exceeded the rate of land uplift, resulting in a short-lived transgression. Because of a higher rate of uplift, the transgression was even more short-lived or of negligible magnitude in the southwestern part of coastal Finland, but even in this latter case a slowing down in the rate of regression can still be detected. We used evidence from isolation basins to obtain a set of 71 14C dates, and over 30 new sea-level index points. The age-elevation data, obtained from lakes in two different areas and located between c. 64 m and 1.5 m above present sea level, display a high degree of internal consistency. This suggests that the dates are reliable, even though most of them were based on bulk sediment samples. The two relative sea-level curves confirm the established model of relatively gradually decreasing rates of relative sea-level lowering since c. 6100 yr BP (7000 cal. yr BP) and clearly indicate that the more northerly of the two study areas experienced the higher rate of glacio-isostatic recovery. In the southerly study area, changes in diatom assemblages and lithostratigraphy suggest that during the early Litorina Sea stage (8300-7600 cal. yr BP) eustatic sea-level rise exceeded land uplift for hundreds of years. Evidence for this transgression was discovered in a lake with a basin threshold at an elevation of 41 m above sea level, which is markedly higher than any previously known site with evidence for the Litorina transgression in Finland. We also discuss evidence for subsequent short-term fluctuations superimposed on the main trends of relative sea-level changes.  相似文献   

10.
The island of Newfoundland, Canada, is situated close to the former margins of the Laurentide ice sheet. The post-glacial sea-level history is complex, dominated by the effects of an ice-marginal crustal forebulge produced by isostatic deformation of the lithosphere. Marine fossils found above present sea-level can be 14C dated, and examination of the temporal and geographical distribution of these 14C dates in combination with geomorphological indicators of past sea-levels indicates regional trends of relative sea-level change. For most of the island (apart from the Northern Peninsula) no samples have been recovered that date younger than 8000 BP. suggesting that sea-level lay below the present one in these areas for the last 8000 years. The same areas commonly show geomorphological evidence for stands of sea-level both above and below present sea-level. This evidence is interpreted as showing that over most of Newfoundland, following deglaciation, sea-level fell to below present levels, and subsequently rose to the modern level. Exceptions to this pattern are the north of the Northern Peninsula, which shows a history of continuous emergence, or a more complex pattern of sea-levels falling below present, subsequently rising above present, and currently falling; and the northeast Avalon Peninsula, which may have had sea-levels below present throughout post glacial times. This pattern of relative sea-level change is interpreted as being mostly due to isostatic recovery, with the main factor being northerly migration of the forebulge. Mapping the time at which sea-level fell below the present level allows estimation of the rate of northerly migration and collapse of the forebulge at between 4.5 and 11 km/100 years; this is considerably faster than previous estimates.  相似文献   

11.
New pollen-analytical investigations and two 14C 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 14C dates from the transition between the Younger Dryas and the Preboreal should be considered critically. Considerable fluctuations in the 14C level are supposed for this period.  相似文献   

12.
Previously published radiocarbon-dated horizons relating to early and middle Holocene relative sea-level change along the eastern coast of mainland Scotland are examined and trends determined. The data are modified to ensure comparability and are compared against the pattern of glacio-isostatic uplift in the area. Results show that the rate of relative sea-level rise during the Main Postglacial Transgression in the middle Holocene becomes greater towards the edge of the uplifted area, whilst the age of the Main Postglacial Shoreline becomes younger in the same direction. Linear and quadratic regression analyses disclose trends which indicate that at the 0 m HWMOST isobase of the Main Postglacial Shoreline the rate of relative sea level rise between c. 8400 and c . 7000 14 C years BP ( c . 9500 to c . 7900 cal. BP) was 5-11 mm/radiocarbon year or 6-11 mm/calibrated year, whilst at the same isobase the Main Postglacial Shoreline was reached between 5500 and 6100 14 C years BP (between 6300 and 7000 cal. BP). The relative sea-level changes identified are compatible with a rising sea surface level offshore, which may have involved three episodes, possibly related to regional and wider deglaciation.  相似文献   

13.
Romundset, A., Lohne, Ø. S., Mangerud, J. & Svendsen, J. I. 2009: The first Holocene relative sea-level curve from the middle part of Hardangerfjorden, western Norway. Boreas , 10.1111/j.1502-3885.2009.00108.x. ISSN 0300-9483.
The first relative sea-level (RSL) curve from the mid-Hardangerfjorden area covering the entire Holocene is presented. The curve is based on a series of AMS 14C dates on terrestrial plant macrofossils across the isolation level in each of five lakes located between 3.5 and 74.5 m a.s.l. During the first 1200 years, the RSL fell very rapidly from the marine limit at 98 m a.s.l. to 33 m a.s.l., i.e. at a rate of 5.4 cm yr−1. The emergence rate then slowed considerably and was close to standstill 8000–6500 cal. yr BP. However, an emergence of 16.5 m has taken place during the past 6000 years. Radiocarbon dates of terrestrial plant macrofossils from the basal strata in a lake above the marine limit and mollusc shells from glaciomarine silt in the isolation basins yielded a mean age for the local ice-margin retreat of 11 300 cal. yr BP. This verifies that Hardangerfjorden was glaciated during the Younger Dryas – an interpretation that has recently been disputed. The ice margin retreated at a rate of about 300 m yr−1 from the position of the Younger Dryas moraine to this site some 60 km further into the fjord.  相似文献   

14.
Four sites in northwestern Dalsland and southwestern VHrmland, southwestern Sweden were investigated. including studies of marine biostratigraphy and AMS datings. A marine foraminifera and mollusc fauna existed in the area between c . 10 400 and 9700 14C years BP. Arctic assemblages dominate the lowermost layers, deposited immediately after the deglaciation. A transition to more diverse faunas affected by a higher meltwater influence and decreasing water depths is recorded higher up in the succession. Northwestern Dalsland was dcglaciated between c . 10 400 and 10 200 BP, and southwestern Viirmland between c . 10 100 and 9800 BP. A stagnation in the retreat of the ice margin is suggested at 10 300 to 10 200 BP. The subsequent rapid ice recession was probably an effect of warmer conditions at the Pleistocene-Holocene climatic transition. A similar shift in the early Preboreal (c. 9900 BP) probably represents the dcglaciation which followed after the stagnation at the Ski moraines. Renewed glacial activity is indicated at c . 9700 BP.  相似文献   

15.
The ahermatypic coral Lophelia pertusa which produces aragonitic skeletons is widely distributed along the Norwegian coast. Specimens from a number of localities have been analyzed for oxygen and stable carbon isotope composition and 14C age. Stable isotope ratios of recent corals provide information on growth rate and seasonality of oceanographic conditions. Lophelia can be useful in paleoenvironmental reconstructions. 14C dates of fossil Lophelia from Drøak in the Oslofjord, collected from 20 m ahove and 40 m below present day sea-level, indicate regional extinction between 8700 and 7800 years ago. We suggest that the extinction resulted from the cut-off of deep waters by a rising sill in connection with the postglacial shoreline displacement. Radiocarbon dating of coral bushes suggests a fairly rapid growth rate as older and younger parts of recent corals do not reveal any difference in activity despite the short time scale of the history of bomb-produced 14C in the oceans.  相似文献   

16.
Bracketing ages on marine—freshwater transitions in isolation basins extending from sea level to 100 m elevation on Lasqueti Island, and data from shallow marine cores and outcrops on eastern Vancouver Island, constrain late Pleistocene and Holocene sea-level change in the central Strait of Georgia. Relative sea level fell from 150 m elevation to about —15 m from 14000 cal. yr BP to 11 500 cal. yr BP. Basins at higher elevations exhibit abrupt changes in diatom assemblages at the marine-freshwater transition. At lower elevations an intervening brackish phase suggests slower rates of uplift. Relative sea level rose to about +1 m about 9000 cal. yr BP to 8500 cal. yr BP, and then slowly fell to the modern datum. The mean rate of glacio-isostatic rebound in the first millennium after deglaciation was about 0.11 in a -1, similar to the peak rate at the centres of the former Laurentide and Fennoscandian ice complexes. The latter feature smooth, exponential-style declines in sea level up to the present day, whereas in the study area the uplift rate dropped to less than one-tenth of its initial value in only about 2500 years. Slower, more deeply seated isostatic recovery generated residual uplift rates of <0.01 m a-1 in the early Holocene after the late-Pleistocene wasting of the Cordilleran ice sheet.  相似文献   

17.
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 14C 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, 14C ages from the base of organic residual channel fills (sample type 3) generally indicate a clear termination of within-channel sedimentation. In contrast, 14C 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 14C years. This setting usually produces 14C 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 14C samples of type 2 may also be present in coastal areas with an alternation of tidal deposits and organic beds.  相似文献   

18.
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 14C 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 14Cka BP. A phase (10.7–10.5 14Cka BP) with snow-bed communities was followed by one with a mosaic of plant communities. This was succeeded by Empetrum heaths c. 10.3 14Cka BP, then by an open forest with Betula pubescens after 10.0 14Cka 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 14Cka BP.  相似文献   

19.
Studies on Cretaceous pelagic limestones have shown a close correspondence between putative sea-level curves and the carbon-isotope profile, suggesting a possible relationship between the two phenomena. Such a relationship could relate to shelf-sea area governing the global burial rate of organic carbon which, in turn, controls the 13C/12C ratio of dissolved inorganic carbon in the oceanic reservoir. In order to see whether or not this relationship might be of more general applicability, the major mid-Oxfordian (Jurassic) transgression is documented to zonal level and appropriate carbon-isotope data are presented. Although the applicability of ammonite zonation to the mid Oxfordian is problematic on a regional scale, a clear δ13C excursion is present in the trunsversariurn Zone, which is coincident with regional overstep and/or evidence of shoreline retreat and/or evidence of bathymetric deepening in Europe and elsewhere. The use of the carbon-isotope curve as a proxy for shelf-sea area or relative sea level is worthy of further exploration.  相似文献   

20.
Analysis of 2D and 3D seismic records from the continental shelf off western Norway, in combination with chronological constraints from 14C dates, has led to a model for the glacial development in these shelf areas between c. 15 and 13 14C 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 14C 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 14C 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   

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