A Late‐glacial chironomid record from Hawes Water,northwest England     

Alan Bedford  Richard. T. Jones  Barbara Lang  Stephen Brooks  Jim D. Marshall 《第四纪科学杂志》2004,19(3):281-290

This paper presents the results of a high‐resolution Late‐glacial chironomid stratigraphy from Hawes Water, a small carbonate lake in northern Lancashire. The samples were from a core taken from the terrestrialised margin of the present lake, which represents an intermediate depth between the true littoral and the profundal. The chironomid assemblage showed a high degree of sensitivity to both broad‐scale and short‐term temperature changes. Comparison with an existing proxy temperature record (δ¹⁸O) for the site confirmed the presence of four temperature inversions within the Late‐glacial Interstadial. A mean July air temperature inference model, derived from acid, soft‐water lakes in Norway and Svalbard, was applied to the data. Despite the absence of carbonate lakes within the Norwegian training set, there was a close similarity between trends in estimated July air temperature and the δ¹⁸O trace, with a particularly strong correspondence in the periods of clay deposition. This suggests that this model is highly robust. The inferred maximum Interstadial temperature was 13.4°C, dropping initially to 7.5°C in the Loch Lomond Stadial. Temperatures reach a maximum of nearly 10°C in this period, cool for a short period before rising rapidly to 13.2°C at the start of the Holocene. These temperatures are similar to but slightly higher than those estimated for Whitrig Bog, southeast Scotland, and lower than those inferred from coleopteran‐based models for sites in South Wales. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Relict sand wedges in soliflucted London Clay at Wimbledon, London, UK     

J.N. Hutchinson 《Proceedings of the Geologists' Association. Geologists' Association》2010,121(4):444-454

Exposures on Wimbledon Hill, SW London, in the Palaeogene London Clay Formation, are described. The 3° slopes are mantled by clayey solifluction (head) deposits, comprising two superimposed sheets, each around 1.2 m thick. The lower sheet exhibits relict sand wedges forming polygons 1.0-1.5 m across, up to 50 mm wide and 1.25 m deep. These have no surface expression. The wedges are sand-filled and modify significantly the hydrogeology and properties of the solifluction mantle. There are no sand wedges in the upper solifluction sheet.The mechanics of emplacement of the lower solifluction sheet are explored and the high initial water content estimated. Subsequent desiccation and consolidation have reduced the thickness of this sheet by at least 35%, thus distorting contained features such as the wedges. An active layer about 0.4 m thick is inferred to have formed in the top of the lower solifluction sheet. No direct dating was undertaken but, by analogy with relevant dated sites in southern Britain and the Netherlands it is inferred that the lower solifluction sheet was emplaced during the first part of the Loch Lomond Stadial and frost-cracked during a subsequent, colder and more arid part. On this basis, following filling of the cracks by sand, emplacement of the upper solifluction sheet would have occurred in the later part of the Loch Lomond Stadial.  相似文献   

Characteristics and implications of some Loch Lomond Stadial moraine ridges and later landforms,eastern Lake District,northern England     

Peter Wilson  Richard Clark 《Geological Journal》1998,33(2):73-87

Moraine ridges and mounds of inferred Loch Lomond Stadial (LLS) age have been mapped at three sites (Fordingdale, Swindale and Wet Sleddale) in part of the eastern Lake District, northern England, and indicate glaciers were more widespread than envisaged by Sissons (1980, Transactions of the Royal Society of Edinburgh: Earth Sciences, Vol. 71, pp. 13–27). The moraines delimit closely the downslope/downvalley limits of the former glaciers but there is no geomorphological evidence with which to define their upslope/upvalley margins. The former glaciers are considered to have been nourished within the confines of their individual valley, cirque and hillside embayment respectively, rather than being outlet glaciers of plateau icefields. Estimated equilibrium line altitudes (ELAs) are within the range of values determined previously for LLS glaciers in the Lake District and do not necessitate revision of established palaeoclimatic parameters. Individual ELAs were probably influenced by local factors; all three former glaciers had accumulation-area aspects between north and east, limiting the impact of direct solar radiation during the ablation season, and were adjacent to extensive areas of high ground to the west and/or south that would have facilitated transfer of snow to their surfaces by winds from those directions. In Fordingdale, three essentially contemporaneous depositional landforms occur upslope of the moraines and are considered to represent hillslope adjustments following wastage of glacier ice from the site. © 1998 John Wiley & Sons, Ltd.  相似文献   

Glaciomarine deltaic deposition and ice-marginal tectonics: The ‘Loch Don Sand Moraine’, Isle of Mull,Scotland     

Douglas I. Benn  David J. A. Evans 《第四纪科学杂志》1993,8(4):279-291

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In situ cosmogenic exposure ages from the Isle of Skye,northwest Scotland: implications for the timing of deglaciation and readvance from 15 to 11 ka     

David Small  Vincent Rinterknecht  William Austin  Derek Fabel  Maria Miguens‐Rodriguez  Sheng xu 《第四纪科学杂志》2012,27(2):150-158

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   

Palaeoclimatic reconstruction from Loch Lomond Readvance glaciers in the West Drumochter Hills,Scotland     

Douglas I. Benn  Colin K. Ballantyne 《第四纪科学杂志》2005,20(6):577-592

Geomorphological mapping in the West Drumochter Hills provides evidence of a readvance of locally nourished glaciers during the Loch Lomond (Younger Dryas) Stade, in the form of an icefield 67.7 km² in area drained by outlet glaciers. The icefield limits accord broadly with those proposed by Sissons (1980) but all geomorphic, stratigraphic and sedimentological evidence conflicts with a recent proposal that the landforms in the area reflect southwestwards retreat of the last ice sheet. Up‐valley continuity of recessional moraines indicates that the ice remained active and close to climatic equilibrium during the earlier stages of glacier retreat, consistent with slow warming following the coldest part of the stade. The pattern of equilibrium line altitudes (ELAs) across the icefield is consistent with transfer of snow by westerly and southerly winds. The ELA of the reconstructed icefield as a whole is 622–629 m, although this figure is likely to be lower than the regional (climatic) ELA because the icefield probably received additional snow blown from adjacent plateau surfaces and slopes. Inclusion of potential snow‐blow areas in the ELA calculation yields a value of 648–656 m; the climatic ELA is therefore likely to have lain between 622 and 656 m. Mean June to August temperature at the ELA, based on chironomid assemblages at two sites, falls within the range 4.0 ± 0.7°C. Empirical relationships between temperature and precipitation at modern glacier ELAs indicate that mean annual precipitation (MAP) at the ELA was 1977 ± 464 mm, statistically indistinguishable from modern values. Comparison with precipitation values calculated for the Isle of Mull on the west coast suggest that the precipitation gradient across the Central Highlands of Scotland was steeper during the Loch Lomond Stade than at present, probably as the result of efficient scavenging of precipitation from westerly airflows by the West Highland Icefield. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Description and implications of valley moraines in upper Eskdale Lake District     

Peter Wilson 《Proceedings of the Geologists' Association. Geologists' Association》2004,115(1):55-61

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Historical and pooled flood frequency analysis for the River Tay at Perth, Scotland   总被引：1，自引：0，他引：1  

N Macdonald  A Werritty  A R Black  L J McEwen† 《Area》2006,38(1):34-46

Improved estimates of UK flood risk during a period of increased climatic variability place challenges on existing methods that rely on short instrumental records. This paper examines the value of using historical data (both documentary and epigraphic) to augment existing gauged records for the River Tay at Perth as part of a multi-method approach to assessing flood risk. Single station and pooled methods are compared with flood risk estimates based on an augmented historical series (1815–2000) using the Generalized Logistic and Generalized Pareto distributions. The value of using an even longer, but less reliable, extended historical series (1210–2000) is also examined. It is recommended that modelling flood risk for return periods >100 years should incorporate historical data, where available, and that a multi-method approach using a high threshold Generalized Pareto distribution can also add confidence in flood risk estimates for return periods <100 years based on standard methods.  相似文献   

Chironomid-based Lateglacial climatic reconstruction for southeast Scotland     

STEPHEN J. BROOKS  FRANCIS E. MAYLE  JOHN J. LOWE 《第四纪科学杂志》1997,12(2):161-167

This paper presents the first chironomid-based climatic reconstruction for the UK Lateglacial, obtained from a lake basin in southeast Scotland, Whitrig Bog. Comparison of chironomid, lithological, geochemical, and pollen data reveals a marked vegetation lag behind the warming following deglaciation; warm-water chironomid taxa (e.g. chironomus) had replaced cold-water chironomid taxa (e.g. Paracladius) prior to the arrival of shrubs and trees and when local soils were still poorly developed. In addition to clear evidence for the Younger Dryas Stadial, chironomid data also reveal two short-term cold episodes that punctuate the Lateglacial Interstadial, both of which are also reflected in pollen and lithological data as reversals from open birch scrub/woodland to open herbaceous tundra coinciding with inwash of minerogenic matter into the basin. © 1997 John Wiley & Sons, Ltd.  相似文献   

Debris transport by Loch Lomond Readvance glaciers in Northern Scotland: Basin form and the within-valley asymmetry of lateral moraines     

Douglas I. Benn  D. I. Benn 《第四纪科学杂志》1989,4(3):243-254

Moraines in six cirques in Northern Scotland are shown to be asymmetrically developed, being larger below north- or east-facing valley sides. Moraine asymmetry is strongly correlated with the distribution of free faces in the valleys, a relationship that is interpreted as the result of variation in slope retreat rates. Analysis of clast form and roundness demonstrates that following initial release from bedrock, debris entered both passive high-level glacial transport and tractive transport at the ice-bed interface. The importance of glacier velocities and medial moraines on debris flux is discussed. Consideration is also given to the implications of process asymmetry to long term landform development.  相似文献