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BARBARA WOHLFARTH OLE BENNIKE LARS BRUNNBERG IGOR DEMEDOV GÖRAN POSSNERT SERGEI VYAHIREV 《Boreas: An International Journal of Quaternary Research》1999,28(4):575-586
The laminated sediments at Pudozh in eastern Karelia are generally assumed to have been deposited between 13 000 and 16 000 14 C yr BP and have been used to date the recession of the active ice margin. However, 17 AMS 14 C measurements performed on terrestrial plant macrofossils contained in these sediments show that deposition began during the late Allerφd, when the ice margin had already receded to the northern part of Lake Onega. Based on an age model, we assume that the 1933-year-long varved sequence covers the time period between c. 12 900 and 11 000 calendar years BP. During this period, which comprises the later part of the Late Weichselian and the early Holocene, the local vegetation consisted of open, tree-less dwarf shrub heaths. Increased soil erosion may have occurred before 12 550 calendar years BP. 相似文献
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BARBARA A. LUSARDI CARRIE E. JENNINGS KENNETH L. HARRIS 《Boreas: An International Journal of Quaternary Research》2011,40(4):585-597
Lusardi, B. A., Jennings, C. E. & Harris, K. L. 2011: Provenance of Des Moines lobe till records ice‐stream catchment evolution during Laurentide deglaciation. Boreas, 10.1111/j.1502‐3885.2011.00208.x. ISSN 0300‐9483. Mapping and analysis of deposits of the Des Moines lobe of the Laurentide Ice Sheet, active after the Last Glacial Maximum (LGM), reveal several texturally and lithologically distinct tills within what had been considered to be a homogeneous deposit. Although the differences between tills are subtle, minor distinctions are predictable and mappable, and till sheets within the area covered by the lobe can be correlated for hundreds of kilometres parallel to ice flow. Lateral till‐sheet contacts are abrupt or overlap in a narrow zone, coincident with a geomorphic discontinuity interpreted to be a shear margin. Till sheets 10 to 20 m thick show mixing in their lower 2 to 3 m. We suggest that: (i) lithologically distinct till sheets correspond to unique ice‐stream source areas; (ii) the sequence of tills deposited by the Des Moines lobe was the result of the evolution and varying dominance of nearby and competing ice streams and their tributaries; and (iii) in at least one instance, more than one ice stream simultaneously contributed to the lobe. Therefore the complex sequence of tills of subtly different provenances, and the unconformities between them record the evolution of an ice‐catchment area during Laurentide Ice Sheet drawdown. Till provenance data suggest that, after till is created in the ice‐stream source area, the subglacial conditions required for transporting till decline and incorporation of new material is limited. 相似文献
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DANIEL VERES SIWAN M. DAVIES BARBARA WOHLFARTH FRANK PREUSSER STEFAN WASTEGÅRD LINDA AMPEL ANNE HORMES GÖRAN POSSNERT JEAN-PAUL RAYNAL GÉRARD VERNET 《Boreas: An International Journal of Quaternary Research》2008,37(3):434-443
A new tephra has been identified within a long core (EC 3) sequence recovered from Les Echets, near Lyon, France. This visible tephra was discovered as part of a high resolution multiproxy re-investigation of the Les Echets sequence. Independent chronological information suggests that the tephra is c . 2 000–45 000 years old, and geochemical analysis indicates that it is of basanitic composition. The latter suggests a possible origin in the Eifel; however, as yet, no other volcanic events or deposits can be correlated to the Les Echets tephra. New sedimentological and chronological data are presented indicating that the tephra falls within an interval that most likely correlates with Dansgaard–Oeschger events 12-9. Thus, this tephra could potentially be an important middle MIS 3 marker horizon in central Europe if it can be traced in other palaeorecords. 相似文献
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BARBARA WOHLFARTH 《Boreas: An International Journal of Quaternary Research》2010,39(2):377-398
Wohlfarth, B. 2010: Ice‐free conditions in Sweden during Marine Oxygen Isotope Stage 3? Boreas, 10.1111/j.1502‐3885.2009.00137.x. ISSN 0300‐9483 Published and unpublished 14C dates for Sweden older than the Last Glacial Maximum ice advance were evaluated. Acceptable 14C dates indicate that age ranges for interstadial organic material in northern and central Sweden are between c. 60 and c. 35 cal. kyr BP and for similar deposits in southern Sweden are between c. 40 and c. 25 cal. kyr BP, which is in good agreement with recently derived Optical Stimulated Luminescence ages. 14C dates on mammoth remains show a larger scatter, possibly as a result of incomplete laboratory pretreatment. A possible scenario based on calibrated 14C dates from interstadial deposits is that central and northern Sweden was ice‐free during the early and middle part of Marine Oxygen Isotope Stage 3 and that southern Sweden remained ice‐free until c. 25 cal. kyr BP. A first ice advance into northern and central Sweden might have occurred as late as around 35 cal. kyr BP, more or less coeval with the Last Glacial Maximum ice advance onto the Norwegian shelf. To test the conclusions drawn here, new multi‐proxy and high‐resolution investigations of several key sites in north, central and south Sweden are required. 相似文献
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NIGEL R. J. POOLTON LARS BØTTER-JENSEN ANN G. WINTLE PETER J. YPMA KAREN LUISE KNUDSEN VAGN MEJDAHL BARBARA MAUZ HENRIK E. CHRISTIANSEN JØRGEN JAKOBSEN FINN JØRGENSEN FINN WILLUMSEN 《Boreas: An International Journal of Quaternary Research》1996,25(3):195-208
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 instrument. 相似文献
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Heavy metals and sulphur in mosses from southern Spitsbergen 总被引：1，自引：0，他引：1
Concentrations of Cd, Pb. Ni, Cu. Zn and S were determined in 16 moss species collected from 9 localities in southern Spitsbergen (mostly within the Hornsund region). Two species, Sanionia uncinata and Hylocomium splendens , were objects of more thorough studies. In Sanionia uncinata the mean concentrations were (ug/g): Cd-0.59, Pb-7.07, Ni-4.25, Cu-6.01. Zn-21.13 and S- 1, 481. Hylocomium splendent accumulated similar quantities of these elements. The concentrations of metals and sulphur in mosses differed significantly {p 0 .05) from site to site, depending on geological and climatic conditions specific to the Arctic region. The effect of remote sources of pollution reaching Spitsbergen on the levels of heavy metal concentrations was taken into account, as well as the effect of local emissions from the Polish Polar Station. At 10-25 metre distances from the Station, the levels of heavy metals and sulphur were 3-10 times higher than at a 300-metre distance. 相似文献
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BARBARA G. SHORTRIDGE 《Geographical review》2003,93(4):507-529
ABSTRACT. This article explores the regional identity of the Great Plains through its foodways using 744 responses from a mailed survey that asked participants to plan a representative menu for their locale. The strongest association is with beef—not surprising in an area known for cattle ranching. Other commonalities include potatoes, beans, and corn. Differentiation within the region is marked by preparation methods for beef as well as emphases on cornbread and peach cobbler in the south, rhubarb pie in the north, tortillas and sopapillas in the southwest, and pickles in two separate clusterings. 相似文献
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Concetrations of 16 elements (Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Zn, C, N, S, P, Ca, Mg) were determined in the lichen Cladina stellaris (Opiz) Brodo collected from 26 localities on the Kola Peninsula. Concentrations were higher closer to the emission sources. In Arctic regions affected by local emissions. lichens can be recommended as sensitive indicators of atmospheric pollution. 相似文献