摘要:

Measures of degree of rock surface weathering on three fjell summits in Finnish Lapland provide an independent test of the extent of continuously cold‐based ice during the Late Weichselian. The surface hardness of exposed surfaces is compared with that of surfaces that have remained covered and protected from subaerial weathering. Roughness measurements from granite gneiss surfaces are compared with results from similar lithologies that are known to have been eroded during the Late Weichselian. The results suggest that the summits have been covered and actively eroded by warm‐based ice and are difficult to reconcile with suggestions that large parts of Fennoscandia have not been glacially abraded since the Early Weichsel

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1996.tb00830.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Stable oxygen and carbon isotope data from a lacustrine sequence at Grænge, southeast Denmark, revealed distinct cnvironmental changes related to Late Weichselian climatic development in the region. Comparison of isotopic records obtained from sedimentary carbonates and freshwater molluscs enabled reconstruction of changes in the lacustrine environment. The degree of thermal and chemical stratification of the lake was evaluated and supported by pollen data from an earlier study of the site. During the Allerød interstadial, dimictic and stagnant conditions characterized the lake, whereas the stratification was disturbed during thc Younger Dryas stadial probably as a result of deforestation and increased wind impact. The origin of sedimentary carbonates was examined by mineralogic and morphologic studies. A considerable input of clastics and detrital carbonates, associated with pronounced enrichment of18O and13C. wds recorded in the Younger Dryas sediments indicating soil degradation and increased erosion. A climatic warming preceding the Pleis‐tocene/Holocene boundary is clearly reflected in the different stable isotope records and in the lithostratigra

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1996.tb00831.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Subglacial and subaqueous sediments deposited near the margin of a Late‐glacial ice‐dammed lake near Achnasheen, northern Scotland, are described and interpreted. The subglacial sediments consist of deformation tills and glacitectonites derived from pre‐existing glaciolacustrine deposits, and the subaqueous sediments consist of ice‐proximal outwash and sediment flow deposits, and distal turbidites. Sediment was delivered from the glacier to the lake by two main processes: (1) subglacial till deformation, which fed debris flows at the grounding line; and (2) meltwater transport, which fed sediment‐gravity flows on prograding outwash fans. Beyond the ice‐marginal environment, deposition was from turbidity currents, ice‐rafting and settling of suspended sediments. The exposures support the conclusion that the presence of a subglacial deforming layer can exert an important influence on sedimentation at the grounding lines of cal

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1996.tb00832.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Traditional views of glacigenic processes focus on erosion of hard bedrock and deposition of unconsolidated till. In the 1960s and 1970s attention was directed towards the glacier debris cascade, which linked these two end members. A limited understanding of the relationship between bedrock character, the supposed processes of erosion, debris comminution and texture emerged. In the 1980s researchers began to appreciate the important role which glaciotectonism plays in the spectrum of glacigenic processes, although little attention has been paid to the interface between glacial erosion, glaciotectonism and the early stages of the debris cascade system. A coastal section at Fanore, County Clare, Ireland affords a unique opportunity to examine a range of glacial deposits which represent a series in the erosion, tectonism and comminution stages of till genesis. Major elements of the site are bedrock rafts, glaciotectonic breecias, immature till and mature till. In all cases>98% of the elements comprise Carboniferous limestone. Research at Fanore has focused on textural properties. Analysis of bulk samples of the sediments demonstrates a continuum of textural development from the glaciotectonism of the bedrock (breecia production and bedrock raft comminution) to a homogenized but immature till and to a more mature matrix‐dominated deposi

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1996.tb00833.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The history of postglacial emergence on the Murman coast, Kola Peninsula, is reconstructed based on twelve new radiocarbon ages from three marine sections and regional shoreline observations. Two pronounced shore levels are recognized below the Late Weichselian marine limit. The lower shoreline (11 ‐16 m a.s.l.) is associated with a transgression dated to 6200–6600 BP, correlative to the Tapes transgression on the Norwegian coastline. The upper shoreline (36–47 m a.s.l.) is not yet dated directly but probably correlates to the Main (Younger Dryas) shoreline. Strandline elevations descend eastward along the Murman coast. Observed emergence trends suggest the greatest regional Late Weichselian glacier load over the west‐central Kola Peninsula rather than in the southern Bare

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1996.tb00834.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Throughout the 1980s the annual cycle of ice‐front activity along the stationary north margin of the ice‐cap Myrdalsjökull, southern Iceland, produced a complex ridge, 4 m high, composed of imbricately stacked slabs of frozen, clast‐paved lodgement till dipping up‐glacier. Further observations in 1994 revealed that glaciofluvial processes and associated deposits may be involved in the final stage of ridge production depending on local climate and meltwater drainage pattern. It is concluded that at the margin of Myrdalsjökull the progressive stacking of subglacial frozen‐on sediment slabs to form a moraine ridge is a fundamentally similar mechanism to that involved in the incremental double‐layer model reported from Styggesdalsbreen, southern Norway. This study has also identified internal characteristics which are of potential use for distinguishing between moraine ridges formed by this mechanism and push moraines formed by proglac

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1996.tb00835.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY