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1.
BOREAS Griffey, N. J. & Worsley, P. 1978 03 01: The pattern of Neoglacial glacier variations in the Okstindan region of northern Norway during the last three millennia (Okstindan Research Project Report 26). Boreas, Vol. 7, pp. 1–17. Oslo. ISSN 0300–9483.
Historical, lichenometrical and stratigraphical evidence is combined to establish a provisional history of Neoglacial glacier variation in a mountainous environment approx. 66oN. Attention is focussed on end moraine chronology. At five sites, derived organic materials have been located within end moraines and at two others in situ palaeosols occur buried beneath distal slopes. Organic rich samples from all the sites have been radiocarbon dated and the results permit the recognition of three major glacier expansion episodes, each of which contributes to the diachronous nature of the Okstindan outer Neoglacial limit. A widespread 'Little Ice Age' event with a maximum extent of probable eighteenth century age is confirmed. Limited areas of older moraine ridges peripheral to the 'Little Ice Age' maximal limit appear to date from about 3000-2500 14C years B.P. and a younger period tentatively dated as about 1250-1000 14C years B. P. which agrees with recent data from Engabreen in northwest Svartisen. No evidence for any extensive glacial activity after the inlandice wastage approx. 9000 14C years B. P. and prior to 3000 14C years B.P. was forthcoming.  相似文献   

2.
A Schmidt hammer was used in conjunction with lichenometry to examine the relative age of the outermost Neoglacial moraines in front of glaciers in the Jotunheimen mountains of southern Norway. Particular attention was directed at (1) the magnitude of the 'Little Ice Age' glacier expansion episode relative to any others of Neoglacial age, and (2) the potential and limitations of the Schmidt hammer in the context of Holocene glacial chronologies. Schmidt hammer R-values were measured at 34 glaciers and the sizes of the lichen Rhizocarpon geographicum agg. at 80 glaciers. Unusually low R-values and large lichens suggest the occurrence of pre- 'Little lee Age' Neoglacial moraines at only a small minority (< 10 %) of the sampled glaciers. The traditional model of relatively large southern Norwegian glaciers during the 'Little Ice Age' is substantiated and it is tentatively suggested that differences in climate or glacier type may account for a regional difference in the status of the 'Little Ice Age' between northern and southern Scandinavia. The incorporation of weathered boulders into 'Little Ice Age' moraines by glacier push mechanisms, and the altitudinally-related variation in boulder surface textures, are identified as major sources of potential error in the use of the Schmidt hammer R-values for relative-age determination of Neoglacial surfaces.  相似文献   

3.
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4.
Pollen analysis of the organic surface (FH) horizon of a radiocarbon-dated palaeopodzol buried beneath the 'Little Ice Age' outer moraine of Haugabreen west of the Jostedalsbrecn ice-cap, southern Norway, provided evidence for environmental change in the area between ca. 4,000 B. P. and the 13th century A. D. Radiocarbon dating of the profile, apart from providing a chronology for the changes interpreted, also allowed estimation of pollen incorporation rates into the soil which can be compared with pollen influx rates established elsewhere. Two periods of local woodland recession were identified, the first between ca. 3,300 B. P. and ca. 3,600 B. P., after the initiation of the FH horizon, and the second in the 13th century A. D. at the onset of the Little Ice Age.  相似文献   

5.
When viewed from the air, Scottish ‘hummocky moraine’ can be resolved into a series of linear ridges that resemble those found at the margins of actively retreating glaciers today. Recent work has supported the interpretation of these linear ridges as ice-marginal landforms and the authors believe that the majority of ‘hummocky moraine’ deposits can be interpreted in this way. Consequently the pattern of deglaciation can be established fairly precisely from the pattern of linear ridges. This approach is applied to the landforms of the northern part of the Loch Lomond Stadial ice-field in order to reconstruct the regional pattern of deglaciation. This leads to important inferences about the significance of topographic control during deglaciation and more importantly it provides fresh insight into the environment of the British Isles during the Loch Lomond Stadial.  相似文献   

6.
A difference in the size of Neoglacial lateral moraines on either side of a valley axis (within-valley asymmetry of lateral moraine development) is described. Analysis of clast roundness has revealed subangular material in latero-terminal and terminal moraines; lateral moraines, however, exhibit a compositional gradient of increasing angularity with distance from the former glacier snout. Comparisons with clasts of known origin suggest that this 'roundness gradient' may be explained with reference to either or both of two hypotheses: (1) a variable proportion of supraglacial (or englacial) to subglacial transported material; and (2) the variable composition of regolith incorporated by a push mechanism from the valley sides. Within-valley asymmetry is inferred to result where the supply of debris to lateral moraines from these sources is unequal either side of a valley axis. Both interpretations are also consistent with the relatively large size of latero-terminal sections of end moraines. In order to account for the discrepancy between moraine size and apparent debris supply rates, it is suggested that the largest lateral moraines may have been formed over a longer time scale than the 'Little Ice Age', and that reworking of deposits may have occurred. The supply of debris to the north-facing lateral moraine at Nordre Illåbreen has been so great that it has developed into a rock glacier; this suggests the possibility that subglacial material and valley-side regolith, as well as supraglacial material, contributes to the formation of ice-cored rock glaciers.  相似文献   

7.
This paper considers the controversial issue of the existence of pre-'Little Ice Age' Neoglacial moraines in southern Norway. Schmidt hammer rebound values are combined with measures of boulder roundness and weathering rind thickness in an attempt to isolate moraines that include weathered boulders. A critical approach is used in distinguishing sites where boulders have weathered in situ from those where previously weathered clasts have been incorporated into relatively young moraines. The results confirm that possible pre-'Little Ice Age' Neoglacial moraines seem to be restricted to small, high-altitude glaciers in eastern Jotunheimen. It is concluded that at these glaciers a particularly large response to a short-lived earlier Holocene climatic event is more likely to explain the survival of such moraines than a particularly subdued response to the climatic deterioration of the 'Little Ice Age'. More refined dating techniques are required to determine the age of formation of the anomalous moraines, but before the palaeoclimatic significance of such dates can be assessed, a critical test is required to establish whether the moraines mark former ice-front positions, and therefore reflect lowering of equilibrium line altitudes, or whether they have been displaced forwards by later and more extensive glacier advances.  相似文献   

8.
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9.
We present results from three geophysical campaigns using high‐resolution sub‐bottom profiling to image sediments deposited in Loch Ness, Scotland. Sonar profiles show distinct packages of sediment, providing insight into the loch's deglacial history. A recessional moraine complex in the north of the loch indicates initial punctuated retreat. Subsequent retreat was rapid before stabilisation at Foyers Rise formed a large stillstand moraine. Here, the calving margin produced significant volumes of laminated sediments in a proglacial fjord‐like environment. Subsequent to this, ice retreated rapidly to the southern end of the loch, where it again deposited a sequence of proglacial laminated sediments. Sediment sequences were then disturbed by the deposition of a thick gravel layer and a large turbidite deposit as a result of a jökulhlaup from the Spean/Roy ice‐dammed lake. These sediments are overlain by a Holocene sheet drape. Data indicate: (i) a former tributary of the Moray Firth Ice Stream migrated back into Loch Ness as a major outlet glacier with a calving margin in a fjord‐like setting; (ii) there was significant sediment supply to the terminus of this outlet glacier in Loch Ness; and (iii) that jökulhlaups are important for sediment supply into proglacial fjord/lake environments and may compose >20% of proglacial sedimentary sequences. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

10.
The last British-Irish Ice Sheet (BIIS) created a landscape with many sedimentary basins that preserve archives of paleoenvironmental and paleoclimatic change during the Last Glacial-Interglacial Transition (LGIT; ~ 18-8 ka BP). The typical lithostratigraphic succession of these archives is composed of minerogenic/allogenic sediments formed during cold climatic conditions and organic-rich/authigenic sediments during warmer climates. This paper presents a multi-core lithostratigraphy compiled from the extant lake and surrounding basin at Llangorse Lake, south Wales, a basin lying within the southernmost limits of the last BIIS. This lake contains one of the longest continuous terrestrial sediment successions in the UK. Uncertainty previously existed concerning the presence and distribution of sediments at the site related to the Windermere Interstadial (~ 14.7 to ~ 12.9 ka BP) and Loch Lomond Stadial (~ 12.9 to 11.7 ka BP). A new borehole survey demonstrates that LGIT-age sediments are present at the site with nekron mud (gyttja), corresponding to the Lateglacial Interstadial, deposited in the deeper part of the lake waters and that these deposits are equivalent in age to marl deposits found at shallower depths at the margins of the basin. These deposits are associated with warmer conditions experienced during the Windermere Interstadial and Holocene, whilst minerogenic-rich sediments were deposited during the colder climatic conditions of the Dimlington Stadial and the Loch Lomond Stadial with rangefinder radiocarbon dates confirming this attribution. A model of lake level changes shows that drainage of the Dimlington Stadial glacial lake caused the largest fall, but there was also a further, smaller lake level fall at the end of the Windermere Interstadial and/or the start of the Loch Lomond Stadial, before the level rose in the early Holocene. The lithostratigraphic results presented here form the framework for further paleoenvironmental and paleoclimatic research at Llangorse Lake.  相似文献   

11.
Many glaciated valleys in Scotland contain distinctive, closely spaced ridges and mounds, which have been termed ‘hummocky moraine’. The ridges and mounds are widely interpreted as ice-marginal moraines, constructed during active retreat of mainly temperate glaciers. However, hummocky terrain can form by various processes in glacial environments, and it may relate to a range of contrasting glaciodynamic regimes. Thus, detailed geomorphological and sedimentological studies of hummocky surfaces in Scottish glaciated valleys are important for robust interpretations of former depositional environments and glacier dynamics. In this contribution, we examine irregularly shaped ridges and mounds that occur outside the limits of former Loch Lomond Readvance (≈ Younger Dryas; ~ 12.9–11.7 ka) glaciers in the Gaick, Central Scotland. These ridges and mounds are intimately associated with series of sinuous channels, and their planform shape mimics the form of the adjacent channels. Available exposures through ridges in one valley reveal that those particular ridges contain lacustrine, subglacial, and glaciofluvial sediments. The internal sedimentary architecture is not related to the surface morphology; thus, we interpret the irregularly shaped ridges and mounds as erosional remnants (or interfluves). Based on the forms and spatial arrangement of the associated channels, we suggest that the ridges and mounds were generated by a combination of ice-marginal and proglacial glaciofluvial incision of glaciogenic sediments. The evidence for glaciofluvial incision, rather than ice-marginal moraine formation, at pre-Loch Lomond Readvance glacier margins in the Gaick may reflect differences in glaciodynamic regimes and/or efficient debris delivery from the glacier margins to the glaciofluvial systems.  相似文献   

12.
Ice-dammed lake Boverbrevatnet existed for 75–125 years in the 'Little Ice Age'. After about A.D. 1826, glacier retreat led to a fall in lake level and to exposure of the former shoreline, which includes well-developed platforms cut in metamorphic bedrock. The rock platforms, up to 5.3 m wide and backed by cliffs up to 1.55 m high, are partially covered by large angular boulders which form pavements. Accurate levelling has permitted correlation of platform fragments, overflow cols and related features of the shoreline, such as benches eroded in moraines, ice-push ridges, a perched delta, vegetation trim-lines, lichen limits and a 'lichen-kill' zone. The evolution of the lake, the chronology of deglaciation and the period of formation of the rock platforms have been dated by lichenometry, supported by 14C dating, Schmidt hammer 'R'-values and historical data. The morphology of the rock platforms, together with estimates of their rate of erosion ranging from 1.4 to 7.1 cm/year, indicate the importance of frost shattering (frost riving, frost wedging or macrogelivation) at the lake margin under a periglacial climate, while the permanence of such platforms as landscape features suggests their use in the reconstruction of former periglacial environments. A semi-quantitative model is outlined for the development of rock platforms which emphasises deep penetration of the annual freeze-thaw cycle, the movement of unfrozen lake water towards the freezing plane, and the growth of segregation ice in fissures and cracks at the interface between lake ice and bedrock. Ice-push and ice-pull processes are involved primarily as transporting agents in the formation of boulder pavements and in the removal of debris from the platforms. Analogous processes may occur on polar coasts producing coastal rock platforms.  相似文献   

13.
From mapping and consideration of prominent drift ridges at Stockdale Head, western Lake District, northern England it is inferred that the ridges are the products of dissection of a glacigenic or soliflual drift sheet rather than landforms constructed at the margins of a Loch Lomond Stade (LLS) valley‐head glacier. This proposal has implications for the recognition of LLS glacier limits and, possibly, understanding the dearth of moraine ridges associated with Dimlington ice in Lake District valleys. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

14.
Holocene glacial variations in Sarek National Park, northern Sweden   总被引：3，自引：0，他引：3  
Detailed mapping of well-preserved moraine systems fronting 17 small alpine glaciers in Sarek National Park in Swedish Lapland reveals two Holocene intervals of prolonged glacier expansion, each involving a complex of minor fluctuations. The younger interval, which corresponds to the Little Ice Age, experienced advances that culminated about A.D. 1916–1920, 1880–1890, 1850–1860, 1800–1810, 1780, 1700–1720, 1680, 1650, and 1590–1620. The older expansion interval, which probably centered around 2500 14C yr B.P., experienced several minor fluctuations spread through about 600 years.
Lichen data collected on moraine systems in Sarek are internally consistent from glacier to glacier. Lichen measurements on surfaces of known age in Sarek and nearby Kebnekaise match closely, allowing moraine correlations between these areas. Several older expansion intervals are recorded in the Kebnekaise Mountains. Taken together, the two sequences suggest that a series of prolonged expansion intervals, each similar to the Little Ice Age, has characterized the Holocene in Lapland. Fluctuations of the Scandinavian Ice Sheet in Sweden suggest that this series of Little-Ice-Age events extends back into the late Weichsel in the form of the Younger Dryas and Oldest Dryas stadials.  相似文献   

15.
We present 10 in situ cosmogenic exposure ages from two moraines on the Isle of Skye. The Strollamus medial moraine was deposited during deglaciation of the Devensian ice sheet and yields a mean exposure age from five samples of 14.3 ± 0.9 ka. The moraine age indicates that a significant ice mass existed on Skye at the time of a regional readvance recorded in Wester Ross, northwest Scotland. Taken at face value the ages suggest that deglaciation did not occur until well into Greenland Interstade 1. The Slapin moraine represents the local limit of the Loch Lomond Readvance (LLR) and yields a mean exposure age from five samples of 11.5 ± 0.7 ka, which is consistent with deposition relating to the LLR. These ages suggest that the maximum extent may have been reached late in the stadial and that some glaciers may have remained active until after the climatic amelioration that marks its end. This scenario is considered unlikely given the nature of the climate during this period, which leads us to call for a locally calibrated production rate. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

16.
A core, recovered from a water depth of 53 m in Loch Assynt, North-West Scotland, has yielded a 9 m sequence comprising two distinct units, an upper, organic-rich unit (Unit I, ca. 6 m) overlying a sequence of laminated clays, silts and sands (Unit II, ca. 3 m). The upper unit is essentially Holocene in age based upon three bulk AMS radiocarbon dates while a fourth radiocarbon date from Unit II confirms a late-glacial age for that interval and supports a broadly linear age–depth relationship. Distinct variations in the magnetic susceptibility record of the lower unit can be visually correlated to major changes in the Greenland ice core (GISP2), this together with pollen evidence supports the radiocarbon dating suggesting an age of approximately 11,000 to around 17,000 cal. BP for Unit II, with evidence for the Younger Dryas (Loch Lomond) stadial and the Bolling–Allerød climatic phases. Variations in the magnetic susceptibility record of the late-glacial sediments are thought to relate to climatically driven changes in soil cover and erosion rates. The multiproxy record from Loch Assynt indicates relatively continuous, sub-aqueous sedimentation during the last ～17,000 years, providing an approximate age for the initiation of modern Loch Assynt and supporting recent dates of moraine retreat lines in the Loanan Valley from about 14–15 ka BP. Pollen and chironomid sampling provides further insights to the history of this relatively deep water body and compliment existing high-resolution palaeo-precipitation records for the mid to late Holocene interval from speleothem archives within the loch catchment.  相似文献   

17.
The tongue-shaped mass of debris and associated ridges on the cirque floor below Craig Cerrig-gleisiad, Brecon Beacons National Park is important and controversial because it has been attributed to more than one glacier advance during the Late Devensian. A new origin is proposed involving landslide development from the collapse of part of the western headwall followed by a single phase of glacier development in the Loch Lomond Stadial (Younger Dryas), which reworked the landslide sediments. Evidence for this landslide, which provides useful criteria for differentiating moraines formed by small glaciers from landslides, lies in tension cracks, backward-tilted blocks and bedrock joints dipping out of the western headwall, together with lateral levées, upstanding termini and angular clasts with only occasional, indistinct striae on the tongue-shaped mass, which is interpreted as a flowslide. Glacier reworking of debris in the upper part of the Cwm Cerrig-gleisiad landslide is indicated by subparallel ridges rising to 20 m above the cirque floor containing abraded clasts (16-32% striated). This interpretation is supported by a comparison with the morphological and sedimentary characteristics of a neighbouring landslide at Fan Dringarth, where no glacier developed in the Loch Lomond Stadial. The existence of paraglacial landsliding has significant palaeoenvironmental implications leading to: (1) erroneously large estimates of equilibrium line depression ($Δ$ELA) in the Loch Lomond Stadial; (2) consequent underestimates of summer palaeotemperatures and/or overestimates of the contribution of wind-drifted snow to glacier accumulation; and (3) larger moraines than usual and overestimation of the efficacy of glacial erosion because of antecedent processes.  相似文献   

18.
A detailed high‐resolution seismic stratigraphy, calibrated by core data and terrestrial geomorphological mapping, has been constructed for Loch Ainort, Isle of Skye. This study has provided a palaeoenvironmental history of the area as well as important corroborative evidence for the stepped deglaciation of the Loch Lomond Stadial ice‐field on Skye. The Ainort Glacier reworked pre‐Loch Lomond glacial deposits terminating in a grounded tidewater ice‐front potentially 800 m beyond the previously extrapolated limit. The first stage of deglaciation was characterised by the formation of De Geer moraines indicative of a period of interrupted retreat. The second phase, by contrast, produced hummocky relief with sporadic linear moraines suggesting periods of uninterrupted retreat with occasional stillstands/readvances. Paraglacial reworking of terrestrial slopes resulted in the deposition of thick, subaqueous, debris flows which graded into fluvioglacial dominated sediments and ultimately modern fjordic deposits. The identification of an initial period of active retreat punctuated by numerous readvances correlates directly with the terrestrial record. However, the offshore stratigraphy suggests that although the second phase was dominated by uninterrupted retreat, occasional stillstands/ readvances did occur. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

19.
The present day maritime climate of Scotland is primarily characterized by strong winds which, in very exposed sites, lead to modern windpolish of rock surfaces. The widespread existence of in situ relict windpolished boulders and bedrock surfaces in Scotland has enabled a reconstruction of prevalent Late Devensian (Late Weichselian) including Loch Lomond Stadial (Younger Dryas) palaeo-wind directions. Previous reconstructions of palaeo-wind directions have been indirect and based mainly on the distribution of aeolian sediments and former glaciers. Observations of relict windpolished microforms and their distribution on boulders and bedrock outcrops on various rock types at 55 sites in different parts of the Scottish Highlands have been used to establish a palaeo-wind map for the area. The reconstruction indicates two sets of dominating wind directions, one between SE and SW and one between NW and N. The maximum age of the windpolish is 16-10 cal. ka BP, but most of it presumably developed during the Loch Lomond Stadial 13-12 cal. ka BP, inferred from the distribution of windpolish sites in relation to the deglaciation chronology and establishment of vegetation.  相似文献   

20.
A sparker survey was undertaken of the sea area inshore of the peninsula of sleat and the islands of Eigg and Muck in Western Scotland. This revealed major submarine moraines across the mouths of Loch Nevis and Loch Ailort, which help define the margin of a major glacier readvance phase, presumed to be equivalent to the late-glacial Loch Lomond Readvance. Formation names are suggested for the seismic para-stratigraphy. West of the moraines, there is a till (Minch Para-formation) resting on bedrock, overlain by a stratum (Muck para-formation) with well-defined internal layering parallel to the substratum. The till is presumed to have been deposited by an ice cap which at its maximum reached the western edge of the continental shelf at some time after 27,000 B.P. The Muck para-formation probably represents a glaciomarine unit deposited during the retreat of this ice cap, and has been deeply eroded. Above this erosion surface occur a series of sediments which infill local basins, and which appear to be of Flandrian age (Arisaig para-formation). East of the moraines in Loch Nevis and Loch Ailort the draped sediments are missing and the till is overlain by apparent equivalents (Nevis para-formation) of the marine sediments of Flandrian age to the west  相似文献   

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