摘要:

Glacial hummocks associated with the Superior Lobe in western Wisconsin are stagnant‐ice features composed of melt‐out till, meltwater‐stream sediment, and flow till. The greater proportion of melt‐out till in these hummocks than in hummocks described elsewhere suggests that a model of extensive, supraglacial reworking of supraglacially released debris does not apply to the western Wisconsin hummocks. Interpretation of melt‐out till in hummock exposures is based on its strong fabric oriented parallel to regional ice‐flow direction. Other features of this melt‐out till include poorly developed stratification (color banding and discontinuous thin sandy lenses), and minor faulting, both of which support a melt‐out origin. We suggest that as stagnant, debris‐rich ice began to melt, supraglacially released debris was deposited as flow till and meltwater‐stream sediment (with some debris‐flow sediment and lake sediment), but as the thickness of supraglacial debris increased, debris melting out at depth was stabilized, allowing features characteristic of melt‐out till to be retained. Because the supraglacial debris was sandy and the stagnant ice was likely at the pressure‐melting point, the supraglacial debris was well drained and did not readily fail and flow. Debris volume in the glacier generally was greater at the glacier margin, but lateral and longitudinal variations within this zone were caused by thrusting, freezing‐on, or ice‐margin fluctuations, which in turn resulted in variations in hummock relief. Ice‐walled‐lake plains are commonly associated with the hummocks and develo

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1995.tb00630.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

A complete subglacial to glacial‐lacustrine facies transition is described from a temporary exposure in the Lake Michigan bluffs of southeastern Wisconsin. This transition occurs where a Late Woodfordian terminal moraine intersects the bluff line and grades from basal meltout till to chaotic diamicton to rhythmites over an abrupt 90 m lateral distance. The boundary of the subglacial meltout deposits is marked by an abrupt increase in pebbles and cobbles, which cluster at specific horizons, producing an incipient stratification. Thereafter, the diamicton develops contorted flow structures with progressive segregation into coarse and fine‐grained fractions, ultimately into well‐stratified rhyth

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1995.tb00631.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Andersen, B. G.&Borns Jr., H. W. 1994:The Ice Age World (an introduction to Quaternary history and research with emphasis on North America and Northern Europe during the last 2.5 million years). Scandinavian University Press.

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1995.tb00632.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Terminal‐moraine ridges up to 6 m high have been forming at the snout of Styggedalsbreen for two decades. Based on intermittent observations during this period, combined with a detailed study of ridge morphology, sedimentary structures and composition during the 1993 field season, a model of terminal‐moraine formation that involves the interaction of glacial and glacio‐fluvial processes at a seasonally oscillating ice margin is presented. In winter, subglacial debris is frozen‐on to the glacier sole; in summer, ice‐marginal and supraglacial streams deposit sediments on the wasting ice tongue. The ice tongue overrides an embryonic moraine ridge during a late‐winter advance and a double layer of sediment (diamicton overlain by sorted sands and gravels) is added to the moraine ridge during the subsequent ablation season. Particular ridges grow incrementally over many years and exert positive feedback by enhancing snout up‐arching during the winter advance and constraining the course of summer meltwater streams close to the ice margin. The double‐layer annual‐meltout model is related to moraine formation by the stacking of subglacial frozen‐on sediment slabs (Krüger 1993). Moraine ridges of this type have a complex origin. are not push moraines, and may be characteristic of dynamic high‐latitude and high‐alt

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1995.tb00633.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Olahola is a wavecut cave positioned well above the postglacial marine limit. The sediment sequence in the cave can be litho‐ and magnetostratigraphically correlated with the sequence in the Skjonghelleren cave, 36 km northeast of this locality. Three boulder formations in Olahola represent three ice‐free periods (including the Holocene) and two formations of laminated clay represent periods of ice‐cover. Paleomagnetic excursions in the laminated clays have been correlated with the Lake Mungo/Mono Lake excursion (28 ka), and with the Laschamp excursion (43 ka), but the resolution of these events is much better in the caves than anywhere else. The paleomagnetic records from Skjonghelleren and Olahola suggest that during the Laschamp excursion at least 0.75–1 m of sediment accumulated in Skjonghelleren before sedimentation started in Olahola, indicating also an earlier ice coverage at Skjongh

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1995.tb00634.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Lang, G. 1994:Quartäre Vrgetationsgeschichte Europas. Methoden und Ergebnisse. Gustav Fischer Verlag, Stuttgart/New York. 462 pp. (177 Figures, 54 Tables, 109 pp. addenda, index lists and references)

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1995.tb00635.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Lake‐level fluctuations in the Jura mountains (France) during the Younger Dryas and the early Holocene are reconstructed using sedimentological analyses. Major transgressive phases culminated just before the Laacher See tephra deposition, at the beginning of the Younger Dryas, between 9000 and 8000 BP and between 7000 and 6000 BP. The Younger Dryas appears to be characterized by increasing dryness. Other major lowering phases occurred during the middle Allerød and during the Preboreal. A transgressive event developed betweenc. 9700 and 9500 BP. These palaeohydrological changes can be related to climatic oscillations reconstructed from pollen and isotopic records in Swiss lakes, from glacier movements and timberline variations in the Alps, and from isotopic records in the Greenland ice she

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1995.tb00636.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Sediment profiles were obtained, from the basal sections of two mire basins located above the highest Litorina shore in the Helsinki region, for pollen, diatom and Cladocera analyses and radiocarbon dating with the aim of exploring the relative sea‐level changes during the Litorina stage of the Baltic Sea. Both profiles provided indications of ‘long‐distance effects’ of the Litorina transgression around 7500–6100 BP, in the form of eutrophication, inundation, increasedPediastrumabundances, declined chydorid diversity and the presence of saline water diatoms. The results support the idea that sea level rose during the Litorina stage in the Helsinki region and suggest that this transgressive event had considerable effects on natural conditions in the coastal ecosystems. The findings contradict earlier accounts of a shore level stillstand during the Littorina stage in the Helsinki

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1995.tb00637.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY