摘要:

AbstractEnvironmental reconstructions utilising the evidence of relic or fossil periglacial features are necessarily based on the nature and present distribution of comparable active features. The most critical features are those indicative of permafrost, because of the negative mean annual temperatures required for permafrost, whereas many other cold climate features are much less informative as to temperature implications. (Washburn, Geocryology, 1980, 279).

ISSN:0267-8179    

DOI:10.1002/jqs.3390030102

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractObserved depths to the base of the ice‐bearing permafrost (!BPF) as determined from geophysical well‐log and survey information in the Mackenzie Delta and offshore Beaufort Sea continental shelf show significant variation. Depths range from over 700m beneath the northeastern portion of Richards Island and the adjacent offshore region to the north, to less than 100m in the modern Mackenzie Delta and offshore Mackenzie Bay regions. Along the Tuktoyaktuk Peninsula, permafrost thicknesses exceed 600m but tend to thin to less than 100m in a southeasterly direction.The wide variation in the thickness and distribution of permafrost is due in part to differences in the subsurface deltaic lithologies and to the complexity of the past surface temperature history, exhibited, for example, by fluctuations of the mean annual ground temperature. Geological cross‐sections showing variation in the Tertiary and Upper Cretaceous deltaic sequences indicate a good correlation with the permafrost distribution. In particular, where the sand and gravel units of the Iperk and Kugmallit Sequences predominate, permafrost is thick owing to the high thermal conductivities of the ice‐rich sediments. Conversely, where the low thermal conductivity shales and mudstones of the Richards Sequence are present, permafrost is accordingly thinner.Numerical models of permafrost aggradation in the Mackenzie Delta region suggest that Early and Late Wisconsinan surface temperatures were of the order −18°C. A mid‐Wisconsinan rise in temperature to approximately −8°C, similar to mean surface temperature today, is also indicated. This proposed palaeoclimate is sufficient to account for the observed maximum permafrost thicknesse

ISSN:0267-8179    

DOI:10.1002/jqs.3390030103

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractThick ice‐bearing permafrost is not observed today beneath the deeper channels of the central Queen Elizabeth Islands, Canadian Arctic Archipelago. Analysis of a precision temperature log recently obtained at an offshore well near Ellef Ringnes Island indicates that the thermal regime beneath the seabed is in equilibrium with today's marine environment. If thick permafrost similar to that observed on land today had existed in the Pleistocene in areas that are presently offshore, then such permafrost must have started melting no later than 25000 years ago in order to allow the present thermal regime to evolve. This suggests that the inter‐island channels must have been water‐filled at least by that

ISSN:0267-8179    

DOI:10.1002/jqs.3390030104

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractThe Sandhills Moraine is a Late Wisconsinan lateral moraine complex on southwest Banks Island. The occurrence of ice‐ablation landforms, ground ice slumps, kettle lakes and catastrophic lake drainage in winter suggests the presence of substantial bodies of massive ground ice. The distinctive hummocky topography of the Sandhills Moraine is thought to reflect partial melt‐out of this ice. Stratigraphic observations indicate that the ice is overlain irregularly and unconformably by glacigenic sediments, notably pebbly clay (till) and/or sandy gravels (outwash), while the ice itself possesses numerous and variable mineral inclusions, faults and foliations. Petrofabric analyses indicate a strongly preferred orientation to the ice crystals. It is suggested that these characteristics are best explained if the ground ice is interpreted as relict glacier

ISSN:0267-8179    

DOI:10.1002/jqs.3390030105

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractAn examination of soil thermal and hydrologic regimes at several sites near Mayo, Yukon Territory, and the ground‐ice stratigraphy of a thaw‐slump headwall close to these sites supports the hypothesis that an ice‐rich zone, frequently observed at the base of the active layer, may be due to the annual water balance of permafrost. Observations demonstrate that ice lenses have grown at the top of permafrost in soil tubes installed in 1983. In addition, 90 cm of segregated ice are exposed in the thaw‐slump headwall above a thaw unconformity, dated at 8870 ± 200 years BP, but below the base of the present active layer. These data suggest that the rate of water incorporation into permafrost over the last 8000 years in the Mayo area has been at least 0.1

ISSN:0267-8179    

DOI:10.1002/jqs.3390030106

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractFrost‐cracking and ice‐wedge growth are fundamental processes within the permafrost environment. Extensive areas of contemporary permafrost terrain are characterised by frost‐fissure polygons, formed by repeated thermal contraction‐cracking of the ground. The incremental growth of ice veins and wedges along the axes of contraction‐cracks contributes significantly to the volume of ground ice in near‐surface permafrost. In areas beyond the present limit of permafrost, the recognition of ice‐wedge pseudomorphs provides one of the few unambiguous indications of the former existence of permafrost conditions. An understanding of the processes of ice‐wedge growth and thaw transformation is essential if contemporary ice wedges are to be used as analogues for Pleistocene frost‐fissure structures, in palaeoenvironmenta

ISSN:0267-8179    

DOI:10.1002/jqs.3390030107

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractIce‐wedge casts in Scandinavia frequently occur in three regions: (a) southwestern Jutland (outside the limit of the Weichselian glaciation); (b) southwestern Sweden; and (c) northernmost Norway. The latter two areas are both early deglaciated regions. Characteristics of casts in vertical sections are discussed with reference to the host and infilling material. Aerial photographs provide an effective tool for detecting relict ice‐wedge polygons (crop marks, micromorphology). Experience from present‐day permafrost regions with active ice‐wedge formation helps to explain the palaeoclimatic significance of the relict polygons. Attempts to establish the ages of formation are discussed from a methodological point

ISSN:0267-8179    

DOI:10.1002/jqs.3390030108

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractAlthough partly active aeolian sand sheets and dunes cover large areas in the zones of (dis)continuous permafrost, little precise information is available about the influence of cold‐climate conditions on modern aeolian processes. This means that palaeoenvironmental reconstructions in the stabilised, mainly Late Pleistocene dune fields and cover sand regions in the ‘sand belts’ of the European Lowlands and the Northern Great Plains of the USA and Canada, are necessarily still based on ancient evidence. Cold‐climate wind deposits are typically derived from areas of abundant sediment supply like unvegetated flood plains, glacial outwash plains, till plains and lake shores. The common parabolic and transverse dune forms resemble those observed in temperate regions. Although a variety of periglacial features has been identified in Late Pleistocene dune and cover sands none of them indicate that permafrost is crucial to aeolian activity. Specific structures in aeolian strata permit tentative interpretation of the moisture content of depositional sand surfaces, the nature of annual sedimentation cycles and the processes by which strata were deposited and/or contorted. But surprisingly little is known about the role of vegetation in the process of sand accumulation. Dunes are most informative with respect to reconstructions of past wind regimes, which offer important data for verification of palaeoclimatic simu

ISSN:0267-8179    

DOI:10.1002/jqs.3390030109

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractCryoturbation results mainly from differential heave related to (1) drainage and thermal conditions and (2) frost susceptibility. Loadcasting and cryostatic pressures are restricted to wet soils such as pure silt or silty sand. The translocation of fine particles resulting from repeated freezing and thawing can promote frost susceptibility in a previously non‐susceptible material, as well as a loss in stability of the surface horizons (liquefaction). Small and metric scale cryoturbations can be explained by this process. Large scale deformations and injections may be related to abnormal liquefaction not necessarily associated with frost. Regular patterns are associated with fissure nets. Upturned injections in a downslope direction attest to cryoturbation and frost creep. A lowering of the water table promotes the formation of drop‐like cryoturbations, most of which can be related to seasonal frost in imperfectly to poorly drained soils. They are not indicative of permafrost except in well drained situations or in the case of flat bottomed involuti

ISSN:0267-8179    

DOI:10.1002/jqs.3390030110

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY

摘要:

AbstractRock glaciers are distinct landforms whose wide distribution, occurrence, and significance often go unrecognised. They are deposits of poorly sorted, angular, blocky to tabular debris which are held together by an ice core or a matrix of ice‐cemented fine clastics. Rock glaciers have formed in glaciated and non‐glaciated areas. Many researchers have suggested that the absence of an ice core or the lack of movement indicates relict or fossil status. Active and inactive states can be viewed as the end members of a movement continuum. Movement rates, derived from world‐wide locations as reported in the literature, range from less than 1 cmyr−1to greater than 130cmyr−1. Unfortunately, lack of observed movement has been equated incorrectly with an inactive status.Rock glacier movement must be considered from a rheological point of view. Movement is controlled by the transformation of potential energy to kinetic energy as the system attempts to reach thermal equilibrium or stability. Whereas a glacier can completely disappear or redevelop, reactivation of a rock glacier requires only the re‐establishment of the conditions responsible for development and maintenance of interstitial ice. Although it might not be possible to re‐establish an ice core, interstitial areas can definitely be recharged with ice and thus facilitate movement. The concept of active versus inactive should be abandoned in favor of the view that a spatial and temporal continuum of form and mo

ISSN:0267-8179    

DOI:10.1002/jqs.3390030111

出版商:John Wiley&Sons, Ltd    

年代:1988

数据来源: WILEY