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1.
Timing of the last deglaciation in Lithuania   总被引：1，自引：1，他引：0  
Boulders from the Grūda Moraine, which is associated with the maximum extent of the Scandinavian Ice Sheet (SIS) during the last glaciation, and the Baltija (also referred to as the South Lithuanian), the Middle and North Lithuanian moraines, which are associated with recessional stages of the SIS, were sampled for surface exposure dating using 10Be. By combining these data with existing radiocarbon ages, we developed a chronology for the retreat of the SIS margin in Lithuania. Our new 10Be ages suggest that the SIS margin began to retreat from its maximum extent at 18.3 ± 0.8 10Be kyr. Based on a probable correlation of the Baltija Moraine with the Pomeranian Moraine in Poland, we infer that the Baltija Moraine was formed following a re-advance of the SIS margin. The ice margin retreated from the Baltija position at 14.0 ± 0.4 10Be kyr. The SIS-margin retreat paused at least two more times to form the Middle Lithuanian Moraine at 13.5 ± 0.6 10Be kyr and the North Lithuanian Moraine (tentatively correlated to the Pajūris Moraine) at 13.3 ± 0.7 10Be kyr. Subsequent ice-margin retreat from the North Lithuanian Moraine represented the final deglaciation of Lithuania. Direct dating of these moraines better constrains the relation of ice-margin positions in Lithuania to those in adjacent countries as well as the SIS response to climate change.  相似文献   

2.
A well-preserved moraine on the northern coast of County Donegal, Ireland, has played a critical role in our understanding of the glacial history of this sector of the Irish Ice Sheet (IIS). Because of a lack of numerical dating of the moraine, however, previous interpretations of its age and significance to the glacial history of this region have varied widely. Here we report eight in situ cosmogenic 10Be ages on boulders sampled from the moraine. Two of these ages are outliers, with the remaining six ranging from 18.8±1.0 10Be kyr to 20.9±1.3 10Be kyr, with an uncertainty-weighted mean age of 19.4±0.3 10Be kyr (19.4±1.2 kyr accounting for production rate uncertainty). Our results confirm one previous 10Be age obtained from the moraine, with the combined data ( n =7) constraining the age of initial deglaciation of the IIS from its LGM position on the continental shelf to be 19.3±0.3 10Be kyr (19.3±1.2 kyr accounting for production rate uncertainty). These ages are in excellent agreement with calibrated 14C ages that constrain retreat of the IIS margin from the continental shelf elsewhere in northwestern and western Ireland and the Irish Sea Basin associated with the start of the Cooley Point Interstadial (≥20–≤18.2 cal. kyr BP), suggesting widespread deglaciation of the IIS ∼19.5–20 kyr ago.  相似文献   

3.
We measured 10Be concentrations in boulders collected from the Orsha and Braslav moraines, associated with the Last Glacial Maximum extent and a recessional stage of the Scandinavian Ice Sheet (SIS), respectively, providing a direct dating of the southeastern sector of the ice-sheet margin in Belarus. By combining these data with selected existing radiocarbon ages, we developed a chronology for the last deglaciation of Belarus. The northeastern part of the country remained ice free until at least 19.2±0.2 cal. kyr BP, whereas the northwestern part of the country was ice free until 22.3±1.5 cal. kyr BP. A lobate ice margin subsequently advanced to its maximum extent and deposited the Orsha Moraine. The ice margin retreated from this moraine at 17.7±2.0 10Be kyr to a position in the northern part of the country, where it deposited the Braslav Moraine. Subsequent ice-margin retreat from that moraine at 13.1±0.5 10Be kyr represented the final deglaciation of Belarus. Direct dating of these moraines better constrains the relation of ice-margin positions in Belarus to those in adjacent countries as well as the SIS response to climate change.  相似文献   

4.
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   

5.
We determined in situ cosmogenic 10Be ages for nine boulders sampled on the Salpausselkä I (Ss I) Moraine. Previous dating of this moraine indicated that it formed during the Younger Dryas Stadial along the southern margin of the Scandinavian Ice Sheet in southern Finland. Our new exposure ages range from 10.9±1.0 to 13.5±1.2 10Be ka, with an error-weighted mean age of 12.4±0.7 10Be ka. Our results confirm four previous 10Be ages obtained 40 km northeast of our sample location. The combined data (n=13) indicate that retreat from the Ss I Moraine occurred at 12.5±0.7 10Be ka, in excellent agreement with an age of 12.1 ka for retreat from the Ss I Moraine based on varve chronologies. These results identify the Ss I Moraine as among the best-dated margins associated with Late Quaternary ice sheets.  相似文献   

6.
Four boulder samples from the Piano del Praiet frontal moraine in the Gesso della Barra Valley (Maritime Alps) have been 10Be dated. The results give a weighted mean age of 11 340±370 (870) yr, constraining the frontal moraine to the Egesen glacial stadial, during the Younger Dryas cold phase. By applying the same 10Be production rate to other Egesen moraines previously dated in the Alps, we obtain similar ages for all of them. This suggests a synchroneity of the Egesen deglaciation in the European Alps at the end of the Younger Dryas. From the palaeoshape of the Egesen glacier, reconstructed by means of geomorphological mapping, an Equilibrium Line Altitude depression (δELA) of −520 to −530 m, with respect to the present-day ELA, and of −260 to −320 m, with respect to the Little Ice Age ELA, has been calculated. Comparison with other Alpine sector δELAs indicates that the Maritime Alps experienced humid climatic conditions during the Younger Dryas.  相似文献   

7.
We report in-situ produced 10Be data from the Gorge du Diable (French Western Alps) to date and quantify bedrock gorge incision into a glacial hanging valley. We sampled gorge sidewalls and the active channel bed to derive both long-term and present-day incision rates. 10Be ages of sidewall profiles reveal rapid incision through the late Holocene (ca 5 ka) at rates ranging from 6.5 to 13 mm yr−1. Present-day incision rates are significantly lower and vary from 0.5 to 3 mm yr−1 within the gorge. Our data imply either delayed initiation of gorge incision after final ice retreat from internal Alpine valleys at ca 12 ka, or post-glacial surface reburial of the gorge. Our results suggest that fluvial incision rates >1 cm yr−1 into crystalline bedrock may be encountered in transient landscape features induced by glacial-interglacial transitions.  相似文献   

8.
Surface exposure dating, using in situ produced cosmogenic 10Be, is applied to determine the time since deglaciation of bedrock surfaces in the Grimsel Pass region. Nine 10Be dates from bedrock surfaces corrected for cover by snow are minimum ages for deglaciation of the pass. Four 10Be dates from surfaces below 2500 meters above sea level (m a.s.l.) on Nägelisgrätli, east of Grimsel Pass, yield ages that range from about 14 000 to 11 300 years. Three 10Be dates from locations above 2600 m a.s.l. on Nägelisgrätli are between about 11 700 and 10 400 years. Two 10Be dates from locations at 2560 m a.s.l. below Juchlistock are about 12 100 and 11 000 years. The geographical distribution of 10Be dates on Nägelisgrätli either may show the timing of progressive deglaciation of Grimsel Pass or may reflect differences in subglacial erosion of bedrock in the pass region. All dates are discussed in the context of deglaciation of the late Würmian Alpine ice cap and deglaciation from Last Glacial Maximum (LGM) ice extents in other regions.  相似文献   

9.
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   

10.
Accurate chronological records are critical for studying the alluvial fan sequences emplaced during local/global climatic changes but, in general, there are no satisfactory, quantitative dating methods available. In situ -produced 10Be concentrations have been measured in quartz boulders exposed on Sulawesian late Quaternary fan surfaces. These concentrations suggest that the two fan units evidenced by geomorphic study were emplaced during two distinct major climatic events. The calculated minimum exposure ages imply abandonment ages of 11 kyr and 120 kyr, for the younger and older units, respectively. This study demonstrates that using both the neutron and muon components implicated in the in situ 10Be production, surficial erosion rates can be estimated and alluvial fans dated. In particular, it shows that in situ 10Be may be used to date fan emplacement during the last 120 kyr under humid tropical conditions, significantly helping to constrain continental palaeoclimatology.  相似文献   

11.
In this study we have obtained 17 cosmogenic exposure ages from three well‐developed moraine systems – Halland Coastal Moraines (HCM), Göteborg Moraine (GM) and Levene Moraine (LM) – which were formed during the last deglaciation in southwest Sweden by the Scandinavian Ice Sheet (SIS). The inferred ages of the inner HCM, GM and LM are 16.7 ± 1.6, 16.1 ± 1.4 and 13.6 ± 1.4 ka, respectively, which is slightly older than previous estimates of the deglaciation based on the minimum limiting radiocarbon ages and pollen stratigraphy. During this short interval from 16.7 ± 1.6 to 13.6 ± 1.4 ka a large part (100–125 km) of the marine‐based sector of the SIS in southwest Sweden was deglaciated, giving an average ice margin retreat between 20 to 50 m a?1. The inception of the deglaciation pre‐dated the Bølling/Allerød warming, the rapid sea level rise at 14.6 cal. ka BP and the first inflow of warm Atlantic waters into Skagerrak. We suggest that ice retreat in southwest Sweden is mainly a dynamical response governed by the disintegration of the Norwegian Channel Ice Stream and not primarily driven by climatic changes. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

12.
A survey of the revised lateglacial varve chronology is given. Almost all revisions are based on new, independent measurements not yet finished. Compared with the old time scale, the preliminary datings (calendar years ± a margin of error) of the ice margin retreat are 'older', mainly due to the fact that the postglacial varve chronology has been extended by 365 years. This implies that the so-called zero year ( sensu De Geer 1940: limit of late glacial and beginning of postglacial varve sedimentation). earlier estimated at 6,923 B.C. (Nilsson 1964), is now dated 7,288 B.C. According to the new time scale, deglaciation from Stockholm to the area of zero-year formation in Indalsälven's valley lasted about 1,190 ± 40 years, compared with 1,073 years in De Geer's (1940) time scale or 1,092 in Jarnefors' (1963). Preliminary varve graph correlations, which are still very weak concerning the Fennoscandian moraine zone, indicate that the ice receded from Högsby, northwest of Kalmar at approximately 10,700+200−300 B.C. At localities just to the north of the Fennoscandian moraines, deglaciation started about 8,750+50−150 years B.C. according to the new varve measurements, and the ice front receded in southern Stockholm 8,470+40−140 B.C. Varve dating now gives older ages (calendar years) than 14C-dating; about 200–400 years older regarding some ice margin positions in south Sweden.  相似文献   

13.
Heeremans  & Wijbrans 《地学学报》1999,11(5):216-222
The post-Svecofennian tectonic development of southern Finland is controlled by intrusion of rapakivi granites (and associated rocks), reactivation of Svecofennian wrench zones, formation of sedimentary basins and successive intrusion of olivine dolerite dykes and sills. Relative age determinations have revealed that fault reactivation acted before, simultaneously and after intrusion of the rapakivi granites. Results of 40Ar/39Ar geochronometry of the Porkkala–Mäntsälä fault (30 km west of Helsinki) reveal ages predominantly in the range 950–1300 Myr. These ages are all significantly younger than the intrusion age of the rapakivi granites. It is suggested that these ages represent tectonic events related to the intrusion of olivine dolerite dykes and sills in SW Finland and the Sveconorwegian Orogeny active further west. 40Ar/39Ar ages of a sample taken from the Obbnäs granite (U–Pb zircon ages of 1645 ± 5 Myr) show ages predom-inantly in the range of 1400–1550 Myr. These ages are suggested to represent either cooling ages of the granite or ages associated with the formation of the sedimentary grabens.  相似文献   

14.
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   

15.
Glacial drifts perched alongside outlet glaciers that drain through the Transantarctic Mountains constrain inland polar plateau ice elevations. The Taylor Glacier, which heads in the Taylor Dome (a peripheral dome of the East Antarctic Ice Sheet), drains East Antarctic ice into the Dry Valleys sector of Transantarctic Mountains and terminates in central Taylor Valley, about 24 km west of the Ross Sea. Five gravel-rich drifts (including 39 distinct moraine ridges) fringe a lateral lobe of the Taylor Glacier in the lower Arena Valley, Quartermain Mountains, southern Victoria Land. 3He and 10Be exposure age dating (from Brook et al . 1992), together with Arena Valley stratigraphy and soil morphologic data, provide chronologic control for these drifts and constrain maximum Quaternary thickening of the inland Taylor ice dome to less than 160 m. These minor Quaternary expansions of Taylor Glacier were out-of-phase with outlet glaciers that pass through the Transantarctic Mountains and terminate in the Ross Sea north and south of the Dry Valleys region. Textural analyses suggest that drift deposition occurred from cold-based ice, even though Taylor Glacier advances most likely occurred during global interglaciations. The thermal regime of former Taylor Glacier ice lobes, the character of geomorphic features superimposed on individual drifts, the chemical composition of soils developed on Taylor drifts, and the stability of in situ moraine ridges on steep valley walls suggest that the present cold-desert climate in Arena Valley has persisted for at least the last 2.2 Ma.  相似文献   

16.
Previous work has presented contrasting views of the last glaciation on Jameson Land, central East Greenland, and still there is debate about whether the area was: (i) ice-free, (ii) covered with a local non-erosive ice cap(s), or (iii) overridden by the Greenland Ice Sheet during the Last Glacial Maximum (LGM). Here, we use cosmogenic exposure ages from erratics to reconcile these contrasting views. A total of 43 erratics resting on weathered sandstone and on sediment-covered surfaces were sampled from four areas on interior Jameson Land; they give 10Be ages between 10.9 and 269.1 kyr. Eight erratics on weathered sandstone and till-covered surfaces cluster around ∼70 kyr, whereas 10Be ages from erratics on glaciofluvial landforms are substantially younger and range between 10.9 and 47.2 kyr. Deflation is thought to be an important process on the sediment-covered surfaces and the youngest exposure ages are suggested to result from exhumation. The older (>70 kyr) samples have discordant 26Al and 10Be data and are interpreted to have been deposited by the Greenland Ice Sheet several glacial cycles ago. The younger exposure ages (≤70 kyr) are interpreted to represent deposition by the ice sheet during the Late Saalian and by an advance from the local Liverpool Land ice cap in the Early Weichselian. The exposure ages younger than Saalian are explained by periods of shielding by non-erosive ice during the Weichselian glaciation. Our work supports previous studies in that the Saalian Ice Sheet advance was the last to deposit thick sediment sequences and western erratics on interior Jameson Land. However, instead of Jameson Land being ice-free throughout the Weichselian, we document that local ice with limited erosion potential covered and shielded large areas for substantial periods of the last glacial cycle.  相似文献   

17.
During the last (MIS 2) and older glaciations of the North Sea, a North Sea Lobe (NSL) of the British-Irish Ice Sheet flowed onshore and terminated on the lowlands of eastern England, constructing inset sequences of either substantial ice-marginal deposits and tills or only a thin till veneer, indicative of complex and highly dynamic glaciological behaviour. The glaciation limit represented by the Marsh Tills and the Stickney and Horkstow Moraines in Lincolnshire is regarded as the maximum margin of the NSL during MIS 2 and was attained at ∼19.5 ka as determined by OSL dating of overridden lake sediments at Welton le Wold. A later ice marginal position is recorded by the Hogsthorpe-Killingholme Moraine belt, within which ice-walled lake plains indicate large scale ice stagnation rapidly followed ice advance at ∼18.4 ka based on dates from supraglacial lake deposits. The NSL advanced onshore in North Norfolk slightly earlier constructing a moraine ridge at Garrett Hill at ∼21.5ka. In addition to the large ice-dammed lakes in the Humber and Wash lowlands, we propose that an extensive Glacial Lake Lymn was dammed in the southern Lincolnshire Wolds by the NSL ice margin at the Stickney Moraine. Previous proposals that older glacier limits might be recorded in the region, lying between MIS 2 and MIS 12 deposits, are verified by our OSL dates on the Stiffkey moraine, which lies immediately outside the Garrett Hill moraine and appears to be of MIS 6 age.  相似文献   

18.
末次冰盛期（Last Glacial Maximum, LGM）结束后,全球经历末次冰消期进入全新世,这代表了过去十万年以来最为显著的气候转型事件。末次冰消期的开始在全球范围内近乎同步,但其背后的气候驱动机制仍不明确。中低纬度,如青藏高原及其周边地区的山地冰川对气候变化响应敏感,准确限定LGM结束前后冰川地貌的时代可为上述问题的解决提供可靠的古冰川信息。然而,目前青藏高原仍缺乏足够有针对性的研究。本文选取位于青藏高原东南部的岗日嘎布作为研究区,对该区格泥峰东侧的玉东曲谷口分布的冰碛垄序列进行了详细的地貌调查和宇宙成因核素10Be暴露测年研究。采自玉东曲谷口附近6道冰碛垄中地貌相对年代较老的4道冰碛垄的14个冰川漂砾10Be暴露年龄介于（13.3±1.0）~（19.3±1.4） ka。利用累积概率密度和简化卡方等统计分析方法排除异常值后,将这4道冰碛垄中地貌相对年代较年轻两道的形成时代限定为（17.0±0.5） ka和（18.4±1.0） ka,分别对应末次冰消期和LGM后期。与气候记录进行对比后,我们认为这两次冰川波动响应可能受控于印度洋-太平洋暖池海表温度的夏季气温变化。  相似文献   

19.
New U–Pb detrital zircon ages from Triassic metasandstones of the Torlesse Terrane in New Zealand are compared with 40Ar/39Ar muscovite data and together, reveal four main source components: (i) major, Triassic–Permian (210–270 Myr old) and (ii) minor, Permian–Carboniferous (280–350 Myr old) granitoids (recorded in zircon and muscovite data); (iii) minor, early middle Palaeozoic, metamorphic rocks, recorded mainly by muscovite, 420–460 Myr old, and (iv) minor, Late Precambrian–Cambrian igneous and metamorphic complexes, 480–570 Myr old, recorded by zircon only. There are also Proterozoic zircon ages with no clear grouping (580–1270 Myr). The relative absence of late Palaeozoic (350–420 Myr old) components excludes granitoid terranes in the southern Lachlan Fold Belt (Australia) and its continuation into North Victoria Land (East Antarctica) and Marie Byrd Land (West Antarctica) as a potential source for the Torlesse. The age data are compatible with derivation from granitoid terranes of the northern New England Orogen (and hinterland) in NE Australia. This confirms that the Torlesse Terrane of New Zealand is a suspect terrane, that probably originated at the NE Australian, Permian–Triassic, Gondwanaland margin and then (200–120 Ma) moved 2500 km southwards to its present New Zealand position by the Late Cretaceous (90 Ma). This sense of movement is analogous to that suggested for Palaeozoic Mesozoic terranes at the North American Pacific margin.  相似文献   

20.
他念他翁山位于横断山脉西部,是海洋性冰川向亚大陆性冰川的过渡区,维持冰川发育的降水补给主要由西南季风带来,该区第四纪冰川进退对西南季风波动有较为直接的反映。正是这一地理位置的特殊性,使得该区第四纪冰川研究具有重要意义。采用野外地貌调查与宇宙成因核素测年技术相结合的方法,试图查明他念他翁山青古隆槽谷全新世期间冰川地貌学特征,并确定其发生的具体时间,探讨其响应机制。结果显示：他念他翁山全新世早中期冰川波动的时限介于（6.13±0.37）~（8.83±0.50） ka,可能是当时西南季风强盛,降水增加的结果。研究可为探究冰川作用与西南季风气候变化及全球气候变化之间的动力学联系提供新依据。  相似文献   

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