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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.
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   

3.
Glacial landforms on the Barton and Weaver peninsulas of King George Island in the South Shetland Islands, West Antarctica were mapped and dated using terrestrial cosmogenic 36Cl methods to provide the first quantitative terrestrial record for late Quaternary deglaciation in the South Shetland Islands. 36Cl ages on glacially eroded and striated bedrock surfaces range from 15.5±2.5 kyr to 1.0±0.7 kyr. The 36Cl ages are younger with decreasing altitude, indicating progressive downwasting of the southwestern part of the Collins Ice Cap at a rate of ∼12 mm yr−1 since 15.5±2.5 kyr ago, supporting the previously published marine records for the timing and estimate of the rate of deglaciation in this region.  相似文献   

4.
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   

5.
Rinterknecht, V. R., Marks, L., Piotrowski, J. A., Raisbeck, G. M., Yiou, F., Brook, E. J. & Clark, P. U. 2005 (May): Cosmogenic 10Be ages on the Pomeranian Moraine, Poland. Boreas , Vol. 34, pp. 186–191. Oslo. ISSN 0300–9483.
We measured the 10Be concentrations in boulders collected from the Pomeranian Moraine in Poland, providing the first direct dating of the southern margin of the Scandinavian Ice Sheet (SIS) in the Polish Lowland. The mean age of 8 10Be ages of the Pomeranian Moraine in northwestern Poland is 14.30.8 10Be ka, while in northeastern Poland the mean age of 19 10Be ages of the moraine is 15.00.5 10Be ka. Given the excellent agreement between the two age groups, we calculate a mean age of 14.80.4 10Be ka for final deposition of the Pomeranian Moraine of northern Poland. The age of the Pomeranian Moraine suggests that the southern margin of the SIS was near its maximum extent in Poland at a younger time than previously inferred, and that retreat from the moraine at 14.80.4 10Be ka probably occurred in response to the onset of the Bølling interstade.  相似文献   

6.
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   

7.
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   

8.
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   

9.
The timing of the extinction of the Australian Megafauna and whether it was simultaneous and widespread has been a much researched topic in Quaternary geoscience. The Black Creek Swamp Megafauna site on Kangaroo Island was thought to be a refugium for Megafauna; however, recent and multidiscipline age determinations have established that the fossils are considerably older than the well-quoted extinction age of 45 kyr. Further radiocarbon age determinations, δ13C isotope analysis and 13C-NMR spectroscopy of the fossil containing organic matter demonstrates that it is highly soluble and accumulated as recently as 31–18 cal. kyr BP. These radiocarbon ages are much younger than the 100–50 kyr age bracket ascertained for the fossil material itself, implying separate episodes of death, deposition and burial. The soluble nature of the organic matter and increasing radiocarbon ages with depth suggests lateral accumulation, probably transported by subsurface waters from elevated areas proximal to the low-lying swamp. Such depositional conditions and 14C age range implies that the site may have experienced an unusually wet Last Glacial Maximum, due maybe to its proximity to the continental shelf and thus to maritime conditions. C3 vegetation dominates the Black Creek Swamp and its organic matter (δ13C; −30‰ and −23‰); however, variations in δ13C may indicate climatic shifts. 13C-enrichment and an abundance of salt-tolerant gastropods within the site's final phase of sediment accumulation (<6 cal. kyr BP) suggest that conditions during this most recent period were not as wet as those of the Last Glacial Maximum.  相似文献   

10.
Rock samples from the Kanin Peninsula and the Timan Ridge were analysed for in situ cosmogenic 10Be for exposure age dating purposes. Crystalline rocks were sampled at four sites on the Kanin Peninsula, either from bedrock outcrops or from glacial erratics, giving overall similar 10Be ages. Outcropping sandstone and crystalline erratics were available from three sites at the Timan Ridge. The highly weathered sandstone gives substantially younger 10Be ages than the adjacent erratics. The exposure ages from the Kanin Peninsula suggest that the last deglaciation of this area took place between 55 and 37 10Be kyr ago, in agreement with a preceding Kara Sea glaciation (55-45 kyr BP). The northwest coast of the peninsula was probably just outside the maximum limit of the last Scandinavian glaciation (20-17 kyr BP). Glacial erratic exposure ages from the Timan Ridge suggest that the 55-45 kyr BP Kara Sea glaciation reached the northern part of the ridge. The exposure dates do not show conclusive evidence regarding the existence of a Timan Ridge ice cap.  相似文献   

11.
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   

12.
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   

13.
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   

14.
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   

15.
Four stratigraphic sections in the southern part of the Columbia Basin preserve a sequence of aeolian and non-aeolian sediments ranging in age from 9·43 to >47·0 14C ka based on accelerator mass spectrometry radiocarbon dating of fossil molluscs, geochemistry of Cascade Mountain-sourced tephra and association with formally recognized pedostratigraphic units (the Washtucna and Old Maid Coulee soils). Study sections are interpreted as representing concurrent deposition of loess and distal Missoula Flood rhythmites in valleys tributary to main drainages backflooded during the Missoula Floods, and formation of carbonate and iron-rich soils. Sediments belong to the formally recognized L-1 and L-2 loess units established for the Palouse loess, which were deposited in the Columbia Basin subsequent to events of glacial outburst flooding. Sediments associated with the Mount Saint Helens set S and set C tephras in the study sections preserve a fauna of five species of gastropod mollusc which have not been reported previously from sediments of late Pleistocene age in the Palouse region. The fossils comprise two distinct faunules stratigraphically separated by the Mount Saint Helens So tephra. Accelerator mass spectrometry radiocarbon dating of the fossils collected above the tephra in two of the sections yielded ages of 12·48 ± 0·06 and 9·43 ± 0·05 14C kyr. These ages suggest that independent determinations of the 13·35 14C kyr age of the So tephra in other areas where Missoula Flood sediments are preserved are probably accurate, and help to refine the age of the latest events in the most recent sequence of catastrophic glacial outburst flooding.  相似文献   

16.
Direct absolute dating of the Penninic Frontal Thrust tectonic motion is achieved using the 40Ar/39Ar technique in the Pelvoux Crystalline Massif (Western Alps). The dated phengites were formed syn-kinematically in shear zones. They underline the brittle-ductile stretching lineation, pressure-shadow fibres and slickensides consistent with underthrusting of the European continental slab below the propagating Penninic Thrust. Chlorite–phengite thermobarometry yields 10–15 km and T ∼280 °C, while 40Ar/39Ar phengite ages mainly range between 34 and 30 Ma, with one younger age at 27 Ma. This Early Oligocene age range matches a major tectonic rearrangement of the Alpine chain. Preservation of prograde 40Ar/39Ar ages is ascribed to passive exhumation of the Pelvoux shear zone network, sandwiched between more external thrusts and the Penninic Front reactivated as an E-dipping detachment fault. Partial resetting in the Low Temperature part of argon spectra below 24 Ma is ascribed to brittle deformation and alteration of phengites.  相似文献   

17.
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   

18.
U–Pb age, trace element and Hf isotope compositions of zircon were analysed for a metasedimentary rock and two amphibolites from the Kongling terrane in the northern part of the Yangtze Craton. The zircon shows distinct morphological and chemical characteristics. Most zircon in an amphibolite shows oscillatory zoning, high Th/U and 176Lu/177Hf ratios, high formation temperature, high trace element contents, clear negative Eu anomaly, as well as HREE-enriched patterns, suggesting that it is igneous. The zircon yields a weighted mean 207Pb/206Pb age of 2857 ± 8 Ma, representing the age of the magmatic protolith. The zircon in the other two samples is metamorphic. It has low Th/U ratios, low trace element concentrations, variable HREE contents (33.8 ≥ LuN≥2213; 14.7 ≤ LuN/SmN ≤ 354) and 176Lu/177Hf ratios (0.000030–0.001168). The data indicate that the zircon formed in the presence of garnet and under upper amphibolite facies conditions. The metamorphic zircon yields a weighted mean 207Pb/206Pb age of 2010 ± 13 Ma. These results combined with previously obtained Palaeoproterozoic metamorphic ages suggest a c. 2.0 Ga Palaeoproterozoic collisional event in the Yangtze Craton, which may result from the assembly of the supercontinent Columbia. The zircon in two samples yields weighted mean two-stage Hf model ( T DM2) ages of 3217 ± 110 and 2943 ± 50 Ma, respectively, indicating that their protoliths were mainly derived from Archean crust.  相似文献   

19.
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   

20.
New 40Ar/39Ar ages are presented from the giant Sulu ultrahigh-pressure (UHP) terrane and surrounding areas. Combined with U-Pb ages, Sm-Nd ages, Rb-Sr ages, inclusion relationships, and geological relationships, they help define the orogenic events before, during and after the Triassic collision between the Sino–Korean and Yangtze Cratons. In the Qinling microcontinent, tectonism occurred between 2.0 and 1.4 Ga. The UHP metamorphism occurred in the Yangtze Craton between 240 and 222 Ma; its thermal effect on the Qinling microcontinent was limited to partial resetting of K-feldspar 40Ar/39Ar ages. Subsequent unroofing at rates of 5–25 km Myr−1 brought the UHP terrane to crustal levels where it underwent a relatively short amphibolite facies metamorphism. The end of that metamorphism is marked by 40Ar/39Ar ages in the 219–210 Ma range, implying cooling at crustal depths at rates of 50–200 °C Myr−1. Ages in the 210–170 Ma range may reflect protracted cooling or partial resetting by Jurassic or Cretaceous magmatism. Jurassic 166–149 Ma plutonism was followed by cooling at rates of c. 15 °C Myr−1, suggesting relatively deep crustal conditions, whereas Cretaceous 129–118 Ma plutonism was succeeded by cooling at rates of c. 50 C Myr−1, suggesting relatively shallow crustal depths.  相似文献   

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