摘要:

Dispersal patterns of indicator rocks in central Gaspésie reveal that glacial debris is entrained in a basal debris‐rich zone of shearing where clast diffusion takes place. The Grand‐Volume Till forms a thin till sheet over the high plateaus of Gaspésie Peninsula and resulted from a succession of two Wisconsinan ice flows of distinct orientations (SSE and NE). The lithological composition of this till determined by pebble counts and the three‐dimensional dispersal patterns of indicator rocks in it suggest that debris transport occurred principally by simple shear deformation of glacial debris. In addition, the intermixing of clasts at the intersection of two lithologically distinct dispersal trains of SSE and NE orientations, respectively, suggests that extensive mixing takes place during shearing. Physical interactions among the clasts lead to both upward and downward movements which cause the clasts to diffuse across the zone of shearing. This process of shear‐diffusion results in continuous incorporation and mixing of the newly encountered rock types during glacial

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1995.tb00780.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Recent analyses of microtextures on quartz particles (63–2000 μm) from Quaternary tills in Antarctica, Germany, southern Ontario, western Wyoming, Tibet, the Austrian Alps, and Mount Kenya show that glacial fracture and abrasion microfeatures may be used to infer the thickness, transport history and ice dynamics of Pleistocene and Holocene glaciers. Quartz sands emplaced by continental and mountain ice were studied by SEM after transport over variable distances in glaciers estimated to range from 150 m to 1500 m in thickness. Relative differences in ice thicknesses, distances of transport, and/or ice dynamics appear to have determined the frequency of occurrence and type of microtextures occurring on sand‐size particles. Subparallel fracture microfeatures tend to increase in frequency over a greater proportion of particle surfaces with increasing ice thickness and distance of transport. Conchoidal fractures, the most typical in quartz, and to some degree crescentic gouges abound on fragments emplaced by continental ice. Other possible fracture and fragmentation mechanisms, producing features of generally glacial origin, involve low velocity impacts induced by stick‐slip mechanisms, under variable cryostatic stresses, producing fracturing and abrasion across particle surfaces. Their generation implies high local contact stresses associated with high strain

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1995.tb00781.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

High‐level weathering limits separating ice‐scoured topography from an upper zone of frost‐weathered detritus were identified on 17 mountains in NW Scotland at altitudes of<600 m to500 m over the extreme NW tip of Scotland and to 700–730 m at the head of

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1995.tb00782.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

An analysis of Late Weichselian sediments from basins in southern and central Halland, southwestern Sweden was carried out. Together with evaluation of previously reported data from the area (isolated basins, highest shore levels, glaciofluvial delta levels, periglacial features, and early Holocene shore levels), this has provided the basis for constructing shore displacement curves for the area, covering the approximate time interval 14 000–9000 BP. There is a general fall in relative sea level (RSL) during this period. The average regression rate until the late Younger Dryas (c. 10 300 BP) is 15–20 mm/yr. During the Younger Dryas the regression is possibly interrupted by minor transgressive phases. The RSL fall is rapid betweenc. 10 300 and 9500 BP. A halted glacio‐isostatic rebound during the Younger Dryas, as the result of glacier growth, is suggested as a cause of the observed pattern of RSL change. Previously reported transgressive events during the early late‐glacial phase are discussed with regard to global eustatic rise, glacio‐isostatic loading and glaciolacustrine dammi

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1995.tb00783.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

A 103‐cm core from a high arctic lake (80°49′N, 15°00′W) on Amdrup Land, NE Greenland has been analysed for pollen and other microfossils, as well as bulk samples from 10 cores for macrofossils. AMS14C‐dating of aquatic mosses (Drepanocladus exannulatusandScorpidiurn scorpioides) revealed that the lowermost 90 cm of the core was deposited during a 1.5‐2 ka interval in the early Holocene, before the appearance ofSalix arcticawhich immigrated to N Greenlandc. 7 ka BP.Armeria scabra, now extinct in the area, larval cases and apotomes ofApatcmiu zonella, today not known north of c. 77°N, and other indices point to a climate warmer than that of today. A thin, sandy layer 13 cm below the lake bottom, accompanied by marked changes in the content of pollen and macrofossils, such as the sudden occurrence of large amounts ofSalixpollen and leaves, indicates a large hiatus. This is confirmed by the dating toc. 7 ka BP of mosses just below the sand, and ofSalixleaves just above it toc. 1 ka BP. The hiatus must be caused by sediment slumping which transported all the sediment from the intervening period to the deeper part of the lake. A similar, sandy layer in the uppermost 2–6 cm may be caused by younger, (sub‐)recent slumping, or both may be the result of the same disturbance. The possibility of a reservoir effect causing too old14C‐ages for the

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1995.tb00784.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Investigations at a Late Weichselian freshwater basin in northwestern Jutland, Denmark, yielded a fairly rich assemblage of vertebrate remains, mostly bones and teeth of small mammals. The remains are primarily allochthonous and the bones have been subjected to different taphonomic pathways and agents. AMS14C‐dates on terrestrial organic remains provided ages of Middle to Late Allerød time. Identifications revealed the first fossil record in Scandinavia ofRana arvalis, Sorex minutus, Ochotonacf.pusilla, Microtus gregalis, Microtus oeconomus, andSicistacf.betulinu. Spermophiluscf.majorandDesmana moschata, previously found only once and twice respectively, were retrieved, andSorex araneusandArvicola terrestriswere recovered for the first time beyond the Atlantic chronozone. Ecologically, the Nørre Lyngby small mammal fauna can be characterized by its very high and almost equal proportions of boreal forest and steppe elements followed by a relatively high proportion of tundra elements. The fossil species share a modern area of sympatry north of the Caspian Sea from the river Volga in the west to the southern and western slopes of the Urals. If, however, the large Allerød mammals are added, the fauna is without modern analogues. The Nørre Lyngby fauna can be seen as a last expansion of the North European glacial fauna. Provided that an absolute chronology and a differentiated sea‐level curve for the area can be established, the Nsrre Lyngby fauna could become important for studies in mammalian dispersal and migratio

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1995.tb00785.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1995.tb00786.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY