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1.
Because of its well-developed ice-marginal zones, SW Sweden is an important reference area for the study of deglaciation, chronology and palaeoclimate 13,500-10,000 B.P. The ice-marginal zones are described and defined. Earlier research and opinions concerning the deglaciation are summarized. Based on radiocarbon dates from shells, vertebrate bones and limnic sediments, a revised deglaciation chronology is presented. This chronology is supported by biostratigraphic transects of time-space diagrams. The radiocarbon and varve chronologies are compared. Some ice-marginal zones are supposed to be 400 to 900 years older than expected from the varve chronology. The deglaciation chronology is correlated within the southern margin of the Scandinavian inland ice. Various consequences for the interpretation of glacial dynamics, shoreline displacement, and the biological environment are mentioned.  相似文献   

2.
Various concepts of the deglaciation of Finland are presented in the form of a historical review. The suggestions of an early (12,000–10,000 B.P) deglaciation of eastern and northern Finland are considered to be erroneous. A map depicting the ice recession as successive ice-marginal lines is presented. According to radiocarbon dates the Finnish territory was entirely deglaciated slightly after 9000 B. P.  相似文献   

3.
The deglaciation of Norway after 10,000 B.P.   总被引：1，自引：0，他引：1  
Several distinctive marginal moraines of Preboreal age have been observed in Norway. They are grouped into three major morainal zones that are radiocarbon dated at about 9900±100, 9600±100 and 9300±100 B.P. respectively. The following deglaciation of central Norway was rapid and most likely completed about 8500 B.P. Evidence of glacier fluctuations up to recent time is discussed. The results are based partly on observations by the field parties of the I.G.C.P. project 'Quaternary Glaciations in the Northern Hemisphere'.  相似文献   

4.
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   

5.
Deglaciation processes within different rock relief types are discussed. The lower parts of the fissure-valley landscape in western Sweden were covered by the late-glacial sea at deglaciation, while the rock plateaux between the valleys formed an arctic archipelago. The glacial movements, deposition activity and recession were intimately dependent on the variations of the topography and on the buoyancy of the seawater in the valleys. The opinion that a piedmont glaciation existed in eastern Halland during the deglaciation stage has been corroborated concerning areas above the marine limit. In the valleys below this limit the ice margin, however, was straight or slightly concave. The western part of the South Swedish Highland, situated high above the marine limit, is characterized by a zonal deglaciation; zone by zone of the ice margin was detached from the actively moving ice and became immobile. Subglacially formed eskers appear together with glaciofluvial deltas which formed extramarginally in ice-dammed lakes. The moraine forms are often dominated by 1–2 km long drumlins with rock cores. Where the ice diverged over a convex bedrock basement, Rogen-like moraine ridges, radial as well as transverse, were formed during the deglaciation stage when the ice was stagnating.  相似文献   

6.
Recent kineto-stratigraphic studies (Berthelsen, Bull. Geol. Soc. Denm. 27 , 1978) indicate repeated advances and recessions and a correspondingly complex pattern of deglaciation. From mainly morphological studies Marcussen ( Danm. Geol. Unders . II: 110. 1977) advocates that only one Weichselian advance (from N and NE) occurred. Two of his key areas are discussed. His deglaciation model involves the formation of successively lower plains during the late Middle Weichselian due to glaciofluvial and ablation processes. It is shown that this model must be abandoned, because its implications contradict its basic assumptions.  相似文献   

7.
《Geodinamica Acta》2013,26(1):81-100
The North Volcanic Zone of Iceland was unglaciated during most interglacials. Subsequently, the region was covered by the Weichselian ice cap. A widespread interglacial complex, the Sy?ra Formation, has been mapped in this zone. It covers probably O.I.S.5e, 5d and 5c. Its formation and preservation are discussed in terms of rift and volcanism activity, in interrelations with the former deglaciation. A topographic bulge, presumed of glacio-isostatic origin, limited the downstream drainage of the Jökulsa a Fjolum river enabling the interglacial sedimentation and the excavation of one of the canyons of Dettifoss. Effusive volcanic activity in the rift is important prior to the Sy?ra 4 unit in association with an early abrupt event (SY2: Sy?ra ash), related to a phreato-magmatic eruption at the eastern hyaloclastite ridge or from the Askja volcano and to jökulhlaup events. It corresponds probably to ash Zone B as defined by Sejrup et al., (1989) on the Northern Iceland shelf. The previous activity of hyaloclastite ridge is recorded during the Marine Isotope Stage 6 (MIS 6 = Saalian) and its deglaciation, a younger effusive event is dated at 80 ka. The Interglacial paleo-seismic region is similar to the present one; during deglaciation, the seismic zone is widened, up to 60 km to the East. Continuous micro-seismicity related to dyke intrusion and effusive or phreato-magmatic eruptions develop at the onset of deglaciation. It is discrete during the full interglacials, and most intense during pyroclastic eruptions. A comparison with the Late Glacial/Holocene deglaciation is provided in the same region.  相似文献   

8.
Glaciomarine varves, in contrast to glaciolacustrine varves, are primarily dependent upon sedimentation from meltwater overflow. They are usually developed in proximal positions and are a more reliable reflection of deglaciation character within a specific area than 'classical' glaciolacustrine varves, which are generally more distal and greater influenced by bottom topography. The close relationship with ice-front processes in the glaciomarine environment is discussed and utilized to suggest correlations between the varve stratigraphy, ice-front positions and climate shifts during the deglaciation of the Savean valley, where two varve localities have been documented. A varve sequence outside this valley shows similar general trends in varve-thickness variation, and comparison between localities may help in extending the lines connecting positions of concurrent ice-marginal deposition. The study of glaciomarine varves provides a more continuous record of changes in the ice-front character than can be obtained from intermittent moraine positions.  相似文献   

9.
Deglaciation chronologies for some sectors of former ice sheets are relatively poorly constrained because of the paucity of features or materials traditionally used to constrain the timing of deglaciation. In areas without good deglaciation varve chronologies and/or without widespread occurrence of material that indicates the start of earliest organic radiocarbon accumulations suitable for radiocarbon dating, typically only general patterns and chronologies of deglaciation have been deduced. However, mid-latitude ice sheets that had warm-based conditions close to their margins often produced distinctive deglaciation landform assemblages, including eskers, deltas, meltwater channels and aligned lineation systems. Because these features were formed or significantly altered during the last glaciation, boulder or bedrock samples from them have the potential to yield reliable deglaciation ages using terrestrial cosmogenic nuclides (TCN) for exposure age dating. Here we present the results of a methodological study designed to examine the consistency of TCN-based deglaciation ages from a range of deglaciation landforms at a site in northern Norway. The strong coherence between exposure ages across several landforms indicates great potential for using TCN techniques on features such as eskers, deltas and meltwater channels to enhance the temporal resolution of ice-sheet deglaciation chronologies over a range of spatial scales.  相似文献   

10.
The nature and origin of glacial sediments at Wylfa Head are described, and their significance with regard to sedimentary environments during Late Devensian deglaciation of the Irish Sea Basin is discussed. Recent models of deglaciation under glaciomarine conditions are challenged. The Quaternary sequence at Wylfa consists of eroded and glaciotectonically deformed bedrock, locally derived lodgement till, calcareous silt-rich lodgement till containing northern erratics, discontinuous units of orange-brown silty sand of possible aeolian origin, and grey laminated freshwater silts filling a small kettle hole. The till units thicken to the south where the surface is drumlinised. It is concluded that the landforms and deposits result from a warm-based Irish Sea glacier, which moved towards the southwest. Spatial variation in basal water pressure resulted from localised drainage through zones of more heavily jointed bedrock. Rapid glacial erosion occurred in areas where subglacial water pressure was relatively high, while deposition of the resulting basal sediment took place where water pressures were reduced. The glacier also carried basal calcareous silty till onshore, which was deposited by lodgement processes. None of the deposits at Wylfa are interpreted as glaciomarine in origin, and there is no evidence at this site for an isostatically induced marine transgression prior to deglaciation.  相似文献   

11.
We present 23 cosmogenic surface exposure ages from 10 localities in southern Sweden. The new 10Be ages allow a direct correlation between the east and west coasts of southern Sweden, based on the same dating technique, and provide new information about the deglaciation of the Fennoscandian Ice Sheet in the circum‐Baltic area. In western Skåne, southernmost Sweden, a single cosmogenic surface exposure sample gave an age of 16.8±1.0 ka, whereas two samples from the central part of Skåne gave ages of 17.0±0.9 and 14.1±0.8 ka. Further northeast, in southern Småland, two localities gave ages ranging from 15.2±0.8 to 16.9±0.9 ka (n=5) indicating a somewhat earlier deglaciation of the area than has previously been suggested. Our third locality, in S Småland, gave ages ranging from 10.2±0.5 to 18.4±1.6 ka (n=3), which are probably not representative of the timing of deglaciation. In central Småland one locality was dated to 14.5±0.8 ka (n=3), whereas our northernmost locality, situated in northern Småland, was dated to 13.8±0.8 ka (n=3). Samples from the island of Gotland suggest deglaciation before 13 ka ago. We combined the new 10Be ages with previously published deglaciation ages to constrain the deglaciation chronology of southern Sweden. The combined deglaciation chronology suggests a rather steady deglaciation in southern Sweden starting at c. 17.9 cal. ka BP in NW Skåne and reaching northern Småland, ～200 km further north, c. 13.8 ka ago. Overall the new deglaciation ages agree reasonably well with existing deglaciation chronologies, but suggest a somewhat earlier deglaciation in Småland.  相似文献   

12.
Understanding the timing of mountain glacier and paleolake expansion and retraction in the Great Basin region of the western United States has important implications for regional-scale climate change during the last Pleistocene glaciation. The relative timing of mountain glacier maxima and the well-studied Lake Bonneville highstand has been unclear, however, owing to poor chronological limits on glacial deposits. Here, this problem is addressed by applying terrestrial cosmogenic 10Be exposure dating to a classic set of terminal moraines in Little Cottonwood and American Fork Canyons in the western Wasatch Mountains. The exposure ages indicate that the main phase of deglaciation began at 15.7 ± 1.3 ka in both canyons. This update to the glacial chronology of the western Wasatch Mountains can be reconciled with previous stratigraphic observations of glacial and paleolake deposits in this area, and indicates that the start of deglaciation occurred during or at the end of the Lake Bonneville hydrologic maximum. The glacial chronology reported here is consistent with the growing body of data suggesting that mountain glaciers in the western U.S. began retreating as many as 4 ka after the start of northern hemisphere deglaciation (at ca. 19 ka).  相似文献   

13.
The retreat of the Barents Sea Ice Sheet on the western Svalbard margin   总被引：1，自引：0，他引：1  
The deglaciation of the continental shelf to the west of Spitsbergen and the main fjord, Isfjorden. is discussed based on sub-bottom seismic records and scdirncnt cores. The sea lloor on the shelf to the west of Isfjorden is underlain by less than 2 m of glaciomarine sediments over a firm diamicton interpreted as till. In central Isfjordcn up to 10 m of deglaciation sediments were recorded, whereas in cores from the innermost tributary, Billefjorden, less than a meter of ice proximal sediments was recognized between the till and the 'normal' Holocene marine sediments. We conclude that the Barents Sea Ice Sheet terminated along the shelf break during the Late Weichselian glacial maximum. Radiocarbon dates from thc glaciomarine sediments above the till indicate a stepwise deglaciation. Apparently the ice front rctrcatcd from the outermost shelf around 14. 8 ka A dramatic increase in the flux of line-grained glaciomarine sediments around 13 ka is assumed to reflect increased melting and/or current activity due to a climatic warming. This second stage of deglaciation was intcrruptcd by a glacial readvance culminating on the mid-shelf area shortly after 12.4 ka. The glacial readvance, which is correlated with a simultaneous readvance of the Fennoscundian ice sheet along the western coast of Norway, is attributed to the so-called 'Older Dryas' cooling event in the North Atlantic region. Following this glacial readvance the outer part of Isljorden became rapidly deglaciated around 12.3 ka. During the Younger Dryas the inner fjord branches were occupied by large outlet glaciers and possibly the ice liont terminated far out in the main fjord. The remnants of the Harcnts Sea Ice Shcet melted quickly away as a response to the Holocene warming around 10 ka.  相似文献   

14.
Detailed field mapping of different lateral phenomena, striae, texture and till fabric forms the basis of a reconstruction of five deglaciation phases in the east Jotunheimen-Gudbrandsdalen area, a land scape with moderate relief in the vicinity of the ice divide. During wastage, the inland ice sheet separated into several ice lobes situated in valleys enclosed by large ice-free uplands. The slope of the ice surface varied with local changes in the ice movement pattern and with the breaking of ice dams, which caused reversal of drainage from ice-dammed lakes. Non-climatic, large margianl moraines are thought to have fomed as a result of locally increased steepness of the ice surface. By tracing the deglaciation phases through two different valley systems which converge in the lake Mjøsa area, deglaciation events in the ice divide zone are correlated with marginal deposits at the front of the ice lobes.  相似文献   

15.
The Liard Lobe formed a part of the north‐eastern sector of the Cordilleran Ice Sheet and drained ice from accumulation areas in the Selwyn, Pelly, Cassiar and Skeena mountains. This study reconstructs the ice retreat pattern of the Liard Lobe during the last deglaciation from the glacial landform record that comprises glacial lineations and landforms of the meltwater system such as eskers, meltwater channels, perched deltas and outwash fans. The spatial distribution of these landforms defines the successive configurations of the ice sheet during the deglaciation. The Liard Lobe retreated to the west and south‐west across the Hyland Highland from its local Last Glacial Maximum position in the south‐eastern Mackenzie Mountains where it coalesced with the Laurentide Ice Sheet. Retreat across the Liard Lowland is evidenced by large esker complexes that stretch across the Liard Lowland cutting across the contemporary drainage network. Ice margin positions from the late stage of deglaciation are reconstructed locally at the foot of the Cassiar Mountains and further up‐valley in an eastern‐facing valley of the Cassiar Mountains. The presented landform record indicates that the deglaciation of the Liard Lobe was accomplished mainly by active ice retreat and that ice stagnation played a minor role in the deglaciation of this region. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

16.
The morphology of paleosols and radiocarbon-dated charcoal from buried surface horizons of soils provide evidence to suggest that between periods of northward forest encroachment tundra climate has dominated areas at least 50 km south of the present forest/tundra border in southwest Keewatin. The present forest/tundra border climate is nearly as severe as any climate that has prevailed in the area since deglaciation.  相似文献   

17.
It generally is assumed that the Early Permian Gondwana deglaciation in South Africa started with a collapse of the marine ice‐sheet. The northeast part of the Karoo Basin became ice‐free as a result of this collapse. The deglaciation here probably took place under temperate glacial conditions. Three glacial phases have been identified. Phase 1: the marine ice retreat of 400 km over the northeast Karoo Basin, which may have been completed over a few thousand years. The glaciers grounded in the shallower areas around the shore of the basin. Phase 2: the smaller, now mainly continental ice‐sheet here re‐stabilised and remained more or less stationary for several tens of thousand years. During this phase, between 50 and 200 m of massive glaciomarine mud with dropstones accumulated in the open, marine basin that became ice‐free during Phase 1. Isostatic uplift, as a response to the first rapid deglaciation phase, can be traced in the inland part of the region. Phase 3: the final deglaciation may have taken 10 to 20 kyr. After this time no new ice sheet was built up over southern Africa. The entire Early Permian deglaciation of the northeast Karoo Basin was completed within thousands rather than millions of years. Phases 1 and 3 had lengths similar to typical Quaternary deglaciations, whereas Phase 2 was a long, stable phase, more similar to a full Quaternary glaciation. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

18.
The rate of displacement in Fennoscandia has been intensively discussed for many years. It is now widely accepted to be an isostatic response of the glacial history of the area. The Earth's present response to deglaciation in Fennoscandia is simulated using a three-dimensional (3D), viscoelastic model in which the asthenosphere and mantle viscosity are allowed to vary so that the maximum rate of present uplift matches its observed value. The deglaciation history is considered to be known, and the C14-datings are converted to sidereal years. The pattern of the present uplift gives a firm match with the observed data when a low-viscosity asthenosphere is introduced. Assuming a 15,000 years load cycle, i.e. the glacier was applied to the surface for 15,000 years before the melting started, the best fitting earth viscosity model is a 1024 Nm lithosphere overlying a 75 km-thick 2.0 × 1019 Pas asthenosphere and a 1.2 × 1021 Pas mantle. The simulations suggest a remaining maximum uplift of 40 m.  相似文献   

19.
The mode of deglaciation of the last Scottish ice sheet is assessed from evidence provided by geomorphological mapping and sedimentology. Ice-marginal deposits in the Dee valley have a distinctive morphological expression and a characteristically varied sedimentology that strongly resembles those from subpolar glaciers. The deposits tend to occur in certain topographic situations which can be accounted for by compression of ice near the margin and formation of an ice-cored supraglacial land system. A series of recessional stages of the ice-front can be mapped demonstrating that active retreat occurred. However, additional evidence shows there was probably a thin marginal zone of stagnant ice. Recessional stages are inferred to be stillstands that are considered to be topographically controlled rather than related to climate. Development of the supraglacial land system during deglaciation suggests that the ice sheet had a polythermal basal regime with a cold-based margin. This implies that deglaciation took place in northeast Scotland while the climate remained cold, probably due to a precipitation deficit, which agrees well with chronostratigraphic data.  相似文献   

20.
The deglaciation patterns of the Bergen and Nordfjord-Sunnmøre areas in western Norway are described and correlated. In the Bergen area the coast was first deglaciated at 12,600 B.P., with a succeeding re-advance into the North Sea around 12,200 B.P. Later, during the Allerød, the inland ice retreated at least 50 km, but nearly reached the sea again during the Younger Dryas re-advance, ending at 10,000 B.P. Sunnmøre was ice-free during an interstadial 28,000–38,000 B.P. Later the inland ice reached the sea. The final deglaciation is poorly dated in Sunnmøre, while further south in Nordfjord, it started slightly before 12,300 B.P., followed by a major retreat. No large re-advance of the inland ice occurred during the Younger Dryas. However, in the Sunnmøre-Nordfjord area many local glaciers formed outside the inland ice during the Younger Dryas. Limnic sediments outside one such cirque glacier have been cored and dated, proving that the glacier did not exist at 12,300-11,000 B.P., and that it was formed and disappeared in the time interval 11,000–10,000 B.P. (Younger Dryas). The erosion rate of the cirque glacier was 0.9 mm/year.  相似文献   

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