摘要:

Up to now the best Quaternary climatic sequences come from oceanic isotope studies, but terrestrial sequences are also well known, usually for pollen or ice core data. A new sequence providing climatic information for the last 500,000 years has been studied in the loess series of Achenheim (Alsace), using the mollusc record in relation to other stratigraphical data. Mollusc assemblages are analysed using a multivariate method. The correspondence analysis used here allows us to explain, in ecological terms, the general variability of the Achenheim set. Most Pleistocene mollusc species have the advantage that modem individuals live in the same assemhlages. So, the known ecology and distribution of the modern molluscs allow us to conclude that the first two factors explain variations in temperature and moisture. Each loading, on a factor, of each association in its stratigraphical level contributes to characterizing the evolution of each climatic parameter through time. For the last five climatic cycles, these evolutions are expressed as a function of the depth within the series. As they are well preserved, the last three glacial cycles are studied in detail. They correspond to the last 350,000 years, are compared with SPECMAP data and particularly show correlations between continental and marine climatic indicators. The mollusc assemblages of the loess sequence also provide information on temperature and moisture conditions. The evolutions of each parameter are not identical during the last three cycles, indicating that the climatic history of one cycle cannot be transferred to the others. The mollusc assemblages also record the occurrence of an oscillatory system, especially during the Weichselian Upper Pleniglacial (isotopic stage 2) when it announces the Late Glacial variations. Similar oscillating excursions seem to have occurred during the older glacial stages.

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1990.tb00446.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Till stratigraphical investigations in Berlin have been evaluated using the gravel counting method (4–12.5 mm). The results are compared with studies of several authors from the coastal area north of Berlin (Rügen and Stoltera Cliff near Warnemünde); the gravel counting results from Stoltera Cliff (Cepek 1973) are re‐evaluated by means of cluster analysis, and a new stratigraphical interpretation of the sequence in the cliff is given. These results, together with a discussion of correlation problems of Weichselian and especially Saalian tills south of the Baltic Sea, lead to the following hypothesis: it is proposed that the ice margin of each glaciation has been nourished by several ice flows coming from different directions, for the most part turning from north‐northeast at onset to east‐northeast in later phases. Consequently, differences of composition are found in tills of the

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1990.tb00447.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Six measurements of surface‐boulder weathering and seven measures of moraine morphometrics were taken at 57 sites in the Kigluaik Mountains, Alaska, to test the morphostratigraphic division of five Quaternary glacial units, to test a threefold subdivision of the late Pleistocene glacial unit, and to estimate the timing of glacial advances. Group means from 70% of the relative‐age measures exhibit a positive relationship with relative age of the glacial units. The measures most effective at differentiating between moraine groups were: boulder frequency, tall‐boulder frequency, boulder height, distal slope, and boulder angularity. Results of dixriminant analysis indicate that moraine‐morphometric measures provided slightly better classification results than those of boulder weathering. Discriminant analysis correctly classified 89% of thea priorigrouped sites. Multivariate analysis supports the attempted threefold subdivision of the latest Pleistocene Mount Osborn moraines at the 0.056 level of significance. Estimated ages of 60,000 BP for the Salmon Lake and 165,000 BP for the Stewart River glacial units were interpolated by using the relative‐age data and ages of 18,000 BP for the Mount Osborn and 810,000 BP for the Nome Ri

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1990.tb00448.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The occurrence of pollen and macrofossils of larch in Eemian deposits in northern Finland indicates that this species must have grown in the area during the last interglacial. Lark spread to Finland from the east, its date of arrival being deducible from the general vegetational succession. It probably did not grow in central or southern Finland during the interglacial, but is thought to have extended fairly far south in Sweden and Noway along the Fennoscandian mountain range. The Lark pollen found at the upper boundary of the interglacial deposits at Margreteberg and Stenberget in southern Sweden may suggest that it did reach southern Sweden by the very end of the Eemian, but it cannot be said for certain whethcr this pollen represents an influx ofLarixfrom the north or from Central Europe.

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1990.tb00449.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Sub‐bottom sediment profiles and sediment cores show that the lacustrine sediments in lake Linnevatnet are underlain by marine sediments and a basal till that mantles the bedrock. The till was probably deposited by the glacier that during the Late Weichselian glacial maximum removed all pre‐existing sediments from the basin. The cores were collected in closed basins, where continuous deposition is expected. The marine sediment in the studied cores is up to 8 m thick and consists of bioturbated clay and silt. Radiocarbon dates on shells from the base of the marine sequence suggest that glacial retreat from the lake basin occurred around 12,500BP. This is more than a thousand years older than basal shell dates from raised marine sediments on the slopes above the lake. Typical ice proximal litbofacies were not identified in the cores. stratigraphic record indicates both a rapid glacial retreat and that no younger glacial re‐advances occurred. During the Younger Dryas local glaciers on western Svalbard were smaller than during the Little Ice Age. This is in sharp contrast to western Europe, where Younger Dryas glaciers were much larger than those the Little Ic

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1990.tb00450.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Glaciostratigraphic investigations at one key locality (Haldum), 9 major and about 160 minor localities in East and Central Jutland, Denmark, together with laboratory work, have led to the establishment of a stratigraphy consisting of 10 till units, usually separated by meltwater deposits. The stratigraphy is in some degree supported by thermoluminescence datings. The complete sequence includes one till unit with associated meltwater deposits of Menapian age, three till units with intercalated meltwater deposits of Elsterian age, marine sediments deposited during the Holsteininan, and three till units with intercalated of Elsterian age, marine sediments deposited during the Holsteinian, and three till units with intercalated glaciofluvial sedimants of Saalian age. Eemian deposits are present above this level, and the whole sequence is capped by till and meltwater deposits related to three glacial advances during the Weichselian.

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1990.tb00451.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0300-9483    

DOI:10.1111/j.1502-3885.1990.tb00452.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY