摘要:

ABSTRACTThe early and late stages of the Weichselian glaciation of the Baltic Sea proper and the Baltic countries is tentatively suggested as having been by means of a thin ice with very low basal friction, to a great extent floating on a number of water-filled cavities. The terms 'captured ice shelf and‘captured lake’are introduced, suggesting that a floating ice is the norm, rather than an exception, in this concept. The captured ice shelf-hypothesis states, that a moving floating ice may, if and when the entire perimeter of the water body is reached by this floating ice (or‘captured ice shelf’), develop an‘ice rim’that acts as a hydrostatic seal, so that the water under the captured ice shelf cannot get out (it is a‘captured lake’). Meltwater inflow to the captured lake will lift the captured ice shelf, until the base of the latter reaches the level of the threshold, at which time the water will escape in a jökulhlaup. The water can escape to the next captured lake in a chain, or to the extra-marginal environment. Tunnel valleys and mid-sea channels with dead ends are suggested to be the product of these kinds of jökulhlaups.

ISSN:0435-3676    

DOI:10.1080/04353676.1994.11880401

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

ABSTRACTThe paper examines the‘captured ice shelf’-hypothesis through the construction of a numerical model. Based on ice surface elevation, ice thickness, and ground topography, the velocity is calculated. The thickness is adjusted, taking into account the effects of mass balance and deformation.By calculating the fluid potential, the location of the water divide in theice rimaround thecaptured lakeis found (the water always flows towards the lower fluid potential). Within the water divide, the ablation is summed up and added to the volume of the captured lake. Thus, the captured ice shelf floats on a water surface which is above the threshold level. Should the water divide cease to exist, the captured lake will be emptied in a jökulhlaup.The results showed that a quick glacier advance is possible with this mechanism. However, the final equilibrium situation of the model runs do not seem to include any captured ice shelf. This is expected, since the captured ice shelf lacks a stabilizing feed-back mechanism—it is an unstable feature, with a life time probably in the range of a few thousands to several tens of thousands of years.

ISSN:0435-3676    

DOI:10.1080/04353676.1994.11880402

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

ABSTRACTThe zonation of moraines and meltwater landforms in southern Norway indicates that the ice sheet was cold-based during the deglaciation of the central areas. Flutes, drumlins, Rogen moraines and end moraines in these central areas most probably predate the late Weichselian. There is also a vertical zonation of landforms which indicate that the highest areas became cold-based at an early stage during the last glaciation. These higher areas are characterized by blockfields and other weathering phenomena, and no traces of glaciation except meltwater channels and erratic boulders. Later the cold-based zone of the glacier expanded both downwards to lower parts of the terrain and outwards to areas further away from the culmination zone. In these areas the glacier stayed cold-based throughout the deglaciation period. Flutes, drumlins and end moraines were fossilized beneath cold-based ice, while Rogen moraines were formed by ice movement in warm-based patches with trapped water beneath a glacier that was otherwise frozen to the ground. In more distal areas of southern Norway the ice sheet was warm-based, and glacial landforms therefore directly reflect the course of deglaciation.

ISSN:0435-3676    

DOI:10.1080/04353676.1994.11880403

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

ABSTRACTA ridge of unconsolidated debris at an altitude of 2000 m, located beneath cliffs in the East Cape Drakensberg of South Africa, is interpreted on morphological and sedimentological evidence as a protalus rampart. The rampart is believed to have formed in the Bottelnek Stadial, after 27000 BP and before 13000 BP, and provides evidence of perennial snowbeds and at least discontinuous permafrost in the East Cape Drakensberg during that Stadial.

ISSN:0435-3676    

DOI:10.1080/04353676.1994.11880404

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

ABSTRACTSorted polygons, 0.4–1.8 m in diameter, are rapidly forming on vegetation-free, windswept regions of a drumlinized ground moraine, 570–580 m a.s.l., within an area from which the ice cap of Myrdalsjökull has receded over the past four decades and where permafrost is absent. The ground consists of clast-paved, sandy-silty lodgement till, which forms a continuous sheet, generally 0.5–1 m thick, resting on outwash deposits. It is concluded that in this area the formation of sorted polygons is connected with cracking of the seasonally frozen surface layer combined with rapid infilling of the cracks by sand, gravel, and stones as a result of sorting of surface material due to wind action, rainsplash, drifting snow, and probably also frost heaving.

ISSN:0435-3676    

DOI:10.1080/04353676.1994.11880405

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

ABSTRACTCalcretes closely linked with fossil ice-wedge pseudomorphs in Pleistocene alluvial deposits are widespread in Patagonia from Rio Negro (Lat. 40°S) to Rio Gallegos (Lat. 53°S). As carbonate rocks are absent in the region, the questions to be asked are: where did the calcium carbonate come from, how did it accumulate, what does this relationship between calcium carbonate and cryogenic structures mean?Two Pleistocene alluvial levels (Puerto Madryn. at 90–100 m asl, Montemayor, 270 m asl) are described here using sedimentological, micromorphological, and chemical analyses. By comparing the characteristics of the alluvial bodies, ice-wedge cast infilling, and upper massive calerete it appears that there is no common origin of the alluvial deposit and the carbonate accumulation. This one is a mix of allochtonous silt and calcareous dust of littoral origin, blown and deposited by wind. Its close association with cryogenic structures as well as some14C datings demonstrate that it accumulated during cold periods, corresponding to marine regressions and the emergence of the highly carbonated continental platform. In South America, for a sea level lowering 100–120m, the continental shelf widened 400 to 1000km. The rim of strong easterly katabatic winds migrated northwards, sweeping the exposed platforms.This interpretation fits in well with the results obtained by geophysicists working on Antarctic ice cores, which show that during cold maxima, characterized by an aridification of climate, an increase of wind strength and the emergence of the continental platform, the aerosol amount increases 5 to 30 times. Isotopic analyses demonstrate that a large part of the aerosols collected in East Antarctic ice-cores came from South American continental shelves.If these conclusions cannot be systematically extrapolated to all calcretes, they should at least be taken into consideration for the explanation of the origin of Pleistocene calcretes.

ISSN:0435-3676    

DOI:10.1080/04353676.1994.11880406

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

ABSTRACTThe distribution of boulder fields situated in three different parishes inÅland is discussed. It has been found that the majority of the boulder fields are situated at altitudes that correspond toAncylus-transgressions and an earlyLitorina-transgression.

ISSN:0435-3676    

DOI:10.1080/04353676.1994.11880407

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

ABSTRACTThe paper discusses the relationship between eustasy, climate and shore-displacement. It is shown that there is a good correlation between periods of warm climate and rise of sea-level. However, the quantitative relationship is not fully established. In areas with land uplift such as Scandinavia and Finland the eustatic transgressions can be traced through accumulation of shore-marks, e.g. along the eskers of Lake Mälar valley.

ISSN:0435-3676    

DOI:10.1080/04353676.1994.11880408

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

ABSTRACT14C datings of whalebone and driftwood samples from Alexandra Land, Franz Josef Land, Russia, indicate deglaciation before 878014C years BP. The absence of a prominent beach morphology at the highest marine limit suggests that the sea reached this level during a short period of time, the highest marine limit thus being formed during a transgression ending at 6800 BP.

ISSN:0435-3676    

DOI:10.1080/04353676.1994.11880409

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

ABSTRACTThe caesium-137 technique has been used to derive hitherto unavailable information concerning erosion rates on gully slopes in a yuan area of the Loess Plateau in Gansu Province, China. The patterns shown by the caesium- 137 inventories were used to interpret the dominant erosion processes operating on cultivated and uncultivated land. These patterns demonstrate the importance of tillage redistribution and water erosion on cultivated terraces and suggest that both wind and water erosion processes operate on grassland areas. Rates of erosion derived from the caesium-137 inventories for the sites on uncultivated land indicate that the estimate of 61 km-2year-1provided by the local soil conservation station may be a serious underestimate, although the data do confirm the importance of full vegetation cover in controlling erosion. The erosion rates derived for terraced cultivated sites are in line with published estimates. Two terrace types were examined and these were characterized by widely divergent net erosion rates, indicating that narrow-strip terraces cultivated parallel to the contour should be used where possible, because these offer a clear soil conservation benefit.

ISSN:0435-3676    

DOI:10.1080/04353676.1994.11880410

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor