摘要:

At Grobern (51°52′N, 12°6′E, altitude 94–98 m a.s.l., 50km north of Leipzig), a succession of lacustrine sediments has yielded a fossil coleopterous fauna permitting the reconstruction of climatic conditions through out the Eemian/Early Weichselian transition. In accord with other indicators, the Coleoptera show that this period was characterized by three major climatic oscillations during which the thermal climate fluctuated between conditions of arctic severity and more temperate conditions. During the cold episodes, the beetle faunas were dominated by species which today have exclusively northern or even Asiatic ranges. In the intervening warm periods these cold‐adapted species were absent and the faunas included temperate species some of which are tree‐dependent. Quantitative palaeotemperature estimates using the Mutual Climatic Range method, show that the mean July temperatures during the relatively colder intervals were 5°C to 6°C lower than during the warmer periods, but the depression of winter temperatures during the colder periods was much greater than this. Because different species of Coleoptera have different thresholds of temperature tolerance, their indications of climatic change do not always coincide with the changes in the lithol

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1996.tb00843.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1996.tb00844.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The magnetic susceptibility of loess‐palaeosol sequences in southern Poland and western Ukraine varies mainly with the degree of decomposition of detrital magnetite grains conditioned by palaeoclimate. Relatively high susceptibility values were observed in the unweathered loess horizons and in accumulation horizons of the non‐gleyed soils which contain relatively high amounts of paramagnetic fraction and pedogenic (?) magnetite. The susceptibility curves characteristic for Polish and western Ukrainian loess‐palaeosol sequences may be directly correlated with oxygen‐isotope fluctuations in deep‐sea sediments. This correlation is more complex than that for the Chinese or Alaskan loess‐palaeosol sequences. The major causes of the complexities are the relatively small thicknesses of the investigated sections (especially their older horizons) and the heterogeneity of geochemical processes that affected loess surface in the interglacial and interst

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1996.tb00845.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The Chippewa and Wisconsin Valley Lobes of the Laurentide Ice Sheet reached their maximum extent in north‐central Wisconsin about 20 000 years ago. Their terminal positions are marked by a broad area of hummocky topography, containing many ice‐walled‐lake plains, which is bounded on the up‐ice and down‐ice sides by ice‐contact ridges and outwash fans. The distribution of these ice‐disintegration landforms shows that a wide zone of stagnant, debris‐covered, debris‐rich ice separated from the active margins of both lobes as they wasted northward during deglaciation. Accumulation of thick, uncollapsed sediment in ice‐walled lakes high in the ice‐cored landscape indicates a period of stability. In contrast, hummocky disintegration topography indicates unstable conditions. Thus, we interpret two phases of late‐glacial landscape evolution. During the first phase, ice buried beneath thick supraglacial sediment was stable. Supraglacial lakes formed on the ice surface and some melted their way to solid ground and formed ice‐walled lakes. During the second phase, buried ice began to melt rapidly, hummocky topography formed by topographic inversion, and supraglacial and ice‐walled lakes drained. We suggest that ice wastage was controlled primarily by climatic conditions and supraglacial‐debris thickness. Late‐glacial permafrost in northern Wisconsin likely delayed wastage of buried ice until after about 13 000 years ago, when clima

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1996.tb00846.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Fluvial and deltaic sediments from Jameson Land in East Greenland contain the first record of the leaf beetlePhratora of.polaris, not presently found in Greenland; the ground beetleBembidion grapii, north of this species' present northern range limit; and the true bugNysius gruenlandieus. In addition, there is a rather diverse flora. All of these records are in sediments of Early Holocene age. We suggest that most of these animals and plants immigrated to East Greenland in the Early Holocene by long‐distance chance dispersal, mostly from northwest Europe. The environment was physiognomically similar to that of today, butSalix areticaandCassiope tetragonuthat are important dwarf shrubs today had not yet immigrate

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1996.tb00847.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Book reviewed in this article:Donner, J. 1995:The Quaternary History of Scandinavia

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1996.tb00848.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

This article describes the development and performance of an integrated optical sensor system that has been designed for rapid analysis of split sediment cores. The primary aim of the system is to obtain information based on optically stimulated luminescence (OSL) techniques; these provide a record of the accrued radiation dose of material since deposition. Particularly after suitable normalization, the luminescence signal recorded along the length of the core will provide information on the relative age of the sediment. Two wavelengths of stimulation are used (infra‐red and green) and these probe the feldspar, and combined feldspar and quartz components of the sediment respectively; the ratio of the two signals can thus provide some indication of relative changes in the silicate mineralogy. A secondary use of the system is for optical reflectance measurements. With the addition of a monochromator, optical reflectance spectroscopy can be applied to obtain additional information on down‐core mineralogical changes. In this article we describe technical aspects of the sensor system, discuss measurement techniques and consider the relevance of data obtained. Two examples of sediment cores are presented, which demonstrate the applicability of the instrum

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1996.tb00849.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY