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MARTINA HÄTTESTRAND ANN‐MARIE ROBERTSSON 《Boreas: An International Journal of Quaternary Research》2010,39(2):296-311
Hättestrand, M. & Robertsson, A.‐M. 2010: Weichselian interstadials at Riipiharju, northern Sweden – interpretation of vegetation and climate from fossil and modern pollen records. Boreas, 10.1111/j.1502‐3885.2009.00129.x. ISSN 0300‐9483. The most complete records of Weichselian ice‐free conditions in northern Sweden have been retrieved from kettleholes in the Riipiharju esker. In an earlier study, the Riipiharju I core was described as containing two Weichselian interstadials and Riipiharju was chosen as type site for the second Weichselian interstadial in northern Sweden. Here, we present a palynological investigation of two new sediment cores (Riipiharju II and III) retrieved from Riipiharju. Together, the new cores comprise a late cold part of the first Weichselian interstadial recorded in northeastern Sweden (Tärendö I, earlier correlated with Peräpohjola in Finland) as well as a long sequence of the second Weichselian interstadial (Tärendö II, earlier named Tärendö). The results indicate that the climate during deposition of the Tärendö II sequence was more variable than earlier suggested. According to the present interpretation it was relatively warm in the early part of Tärendö II; thereafter a long cold phase persisted, and finally the climate was warmer again in the late part of Tärendö II. The warm phases are characterized by Betula‐dominant pollen assemblages, while the cold phase is characterized by high percentages of Artemisia and Gramineae pollen. Since there is still no firm chronology established of the interstadials in northeastern Sweden, two possible correlations are discussed; either Tärendö I and II are correlated with Brörup (MIS 5c) and Odderade (MIS 5a), or, perhaps more likely, they are correlated with Odderade and early Middle Weichselian (MIS 3) time. 相似文献
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ANN G. WINTLE JOHN A. CATT 《Boreas: An International Journal of Quaternary Research》1985,14(3):231-234
The loess component of a solifluction deposit of the Dimlington Stadial exposed at the inland site of Eppleworth in eastern England gave a thermoluminescence date of 17.5 ± 1.6 × 103 years. The solifluction deposit is overlain by a slightly weathered till correlated with the Skipsea Till of coastal exposures. which lies between organic horizons with radiocarbon dates of 18,500–18,240 B.P. and 13,045 B.P. Although the till must have been deposited during the Dimlington Stadial (after 18,240 B.P. at Dimlington and after 17,500 B.P. at Epplcworth), it gave apparent TL dates of 42.1 ± 3.6 × 103 years at Eppleworth and 102 ± 9 × 103 years at Dimlington, indicating that the components of the till were not exposed to light immediately before deposition. 相似文献
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Deposition of the Bear Gulch Limestone: a Carboniferous Plattenkalk from central Montana 总被引：1，自引：0，他引：1
LORETTA ANN WILLIAMS 《Sedimentology》1983,30(6):843-860
The Carboniferous Bear Gulch Limestone of the central Montana Big Snowy Trough is a lithographic limestone analogous to the plattenkalk carbonates of the Mesozoic European/Middle Eastern Tethyan belt. It contains an excellently preserved chitinous and phosphatic marine fauna. Petrographic and field studies synthesized with palaeontological data provide insights into depositional history. Tectonic activity initiated development of small en echelon basins. Rims of these basins were sites of high primary productivity. Photosynthesis by subtidal cyanobacterial mats and algae caused in situ precipitation of micrite. Cyanobacteria and algae also provided a food source for benthic and nektonic organisms, which provided food for predators. Respiration in turn provided carbon dioxide for continued photosynthesis. Thus a balanced ecosystem evolved. Productivity in the water column used up available oxygen, resulting in dysaerobic to anaerobic conditions in the bottom waters and sediments. This plus high sedimentation rates of carbonate ooze transported downslope, aided in preservation of whole-body fossils. There are no likely modern analogues known for the Bear Gulch Limestone. However, comparisons with Mesozoic plattenkalke demonstrate that it is most closely analogous to those deposited in shallow water back-reef areas of the Tethyan carbonate platform, rather than to those deposited in the deeper water shelf-edge environment. This is in agreement with the water depth of roughly 40 m estimated for the Bear Gulch Limestone. 相似文献
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Abstract— Optical and scanning electron microscope (SEM) observations of hematite impact bombs from the Araguainha astrobleme in central Brazil reveal an aerodynamically stable microstructure, which is interpreted to reflect the aerial crystallization of hypervelocity melt globules derived from Fe-rich sedimentary target rocks. The bombs are composed of an aggregate of preferentially oriented conic units with different degrees of packing, giving rise to porous and massive hematite varieties. These varieties generally occupy the front and rear of the bombs, respectively. Quartz fragments with planar deformation features are common in the porous domains and represent ejected solid particles captured by the bombs during cooling. The absence of typical contorted shapes in these bombs reflects the lack of spin during their ballistic trajectory. The bombs are enriched in Rh (4×); Ru, Ir, and Pd (5×); and Pt (>30×) relative to the indigenous level of target sediments. This suggests the presence of a projectile-derived component in their constitution. Single composition oxidic bombs (pure hematite and pure silica) predominate in this occurrence, indicating that a mechanism of segregation has operated in the ejected melt volumes. 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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C. LANA C. R. SOUZA FILHO Y. R. MARANGONI E. YOKOYAMA R. I. F. TRINDADE E. TOHVER W. U. REIMOLD 《Meteoritics & planetary science》2008,43(4):701-716
Abstract— The 40 km wide Araguainha structure in central Brazil is a shallowly eroded impact crater that presents unique insights into the final stages of complex crater formation. The dominant structural features preserved at Araguainha relate directly to the centripetal movement of the target rocks during the collapse of the transient cavity. Slumping of the transient cavity walls resulted in inward‐verging inclined folds and a km‐scale anticline in the outer ring of the structure. The folding stage was followed by radial and concentric faulting, with downward displacement of kilometer‐scale blocks around the crater rim. The central uplift records evidence for km‐scale upward movement of crystalline basement rocks from the transient cavity floor, and lateral moment of sedimentary target rocks detached from the cavity walls. Much of the structural grain in the central uplift relates to structural stacking of km‐scale thrust sheets of sedimentary strata onto the core of crystalline basement rocks. Outward‐plunging radial folds indicate tangential oblate shortening of the strata during the imbrication of the thrust sheets. Each individual sheet records an early stage of folding and thickening due to non‐coaxial strains, shortly before sheet imbrication. We attribute this folding and thickening phase to the kilometer‐scale inward movement of the target strata from the transient cavity walls to the central uplift. The outer parts of the central uplift record additional outward movement of the target rocks, possibly related to the collapse of the central uplift. An inner ring structure at 10–12 km from the crater center marks the extent of the deformation related to the outward movement of the target rocks. 相似文献
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ANN FORSTEN 《Boreas: An International Journal of Quaternary Research》1985,14(4):333-333
Book reviewed in this article:
Genoways, Hugh & Dawson, Mary (eds.) 1984: Contributions in Quaternary Vertebrate Palaeontology: A Volume in Memorial to John E. Guilday 相似文献
Genoways, Hugh & Dawson, Mary (eds.) 1984: Contributions in Quaternary Vertebrate Palaeontology: A Volume in Memorial to John E. Guilday 相似文献
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