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41.
STEPHEN J. LIVINGSTONE COLM Ó COFAIGH DAVID J.A. EVANS ADRIAN PALMER 《Boreas: An International Journal of Quaternary Research》2010,39(3):505-527
Livingstone, S. J., Ó Cofaigh, C., Evans, D. J. A. & Palmer, A. 2010: Sedimentary evidence for a major glacial oscillation and proglacial lake formation in the Solway Lowlands (Cumbria, UK) during Late Devensian deglaciation. Boreas, Vol. 39, pp. 505–527. 10.1111/j.1502‐3885.2010.00149.x. ISSN 0300‐9483. This paper is a sedimentological investigation of Late Devensian glacial deposits from the Solway Lowlands, northwest England, in the central sector of the last British–Irish Ice Sheet. In this region, laminated glaciolacustrine sediments occur, sandwiched between diamictons interpreted as subglacial tills. At one location the laminated sediments are interpreted as varves, and indicate the former presence of a proglacial lake. Correlation of these varves with other laminated sediments indicates that the glacial lake was at least 140 km2 in area and probably much larger. Extensive beds of sand, silt and gravel throughout the Solway Basin associated with the lake demonstrate ice‐free conditions over a large area. Based on the number of varves, the lake was in existence for at least 261 years. The stratigraphic sequence of varves bracketed by tills implies a major glacial oscillation prior to the Scottish Re‐advance (16.8 cal. ka BP). This oscillation is tentatively correlated with the Gosforth oscillation at c.19.5 cal. ka BP. Subsequent overriding of these glaciolacustrine sediments during a westward‐moving re‐advance demonstrates rapid ice loss and then gain within the Solway Lowlands from ice‐dispersal centres in the Lake District, Pennines and Southern Uplands. It is speculated that the existence of this and other lakes along the northeastern edge of the Irish Sea Basin would have influenced ice‐sheet dynamics. 相似文献
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ADRIAN ARMSTRONG 《地球表面变化过程与地形》1996,21(8):769-771
In estimating the form of a peat mound from the equilibrium water table position, the assumption that hydraulic conductivity shows an exponential decline with depth (as used in the Armstrong (Earth Surface Processes and Landforms, 1995, 20 , 473–477) analysis) may be questioned in some circumstances. However, this does not invalidate the use of the hydrologic model for peat mounds, and results are presented which could be used to evaluate other forms of the depth-dependent relationship. 相似文献
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Abstract– The CO3s Colony and Ornans and LL3s Chainpur and Bishunpur were analyzed for the first time for amino acids using gas chromatography–mass spectrometry (GC‐MS). Type 3 chondrites have relatively unaltered metamorphic and petrological histories. Chainpur was the most amino acid rich of the four type 3 chondrites with a total amino acid abundance of 3330 parts per billion (ppb). The other type 3 chondrites had total amino acid abundances that ranged from 660 to 1110 ppb. A d /l ratio of <0.7 for all proteic amino acids suggests at least some amino acid terrestrial contamination. However, a small fraction of indigenous extraterrestrial amino acids cannot be excluded because of the presence of the nonprotein amino acid α‐aminoisobutyric acid (α‐AIB), and unusually high relative abundances (to glycine) of β‐alanine and γ‐ABA. The comparisons between the free and total amino acid contents of the samples also indicate a low free/total amino acid ratio (ranging from about 1:4 in CO chondrites to about 1:50 in Chainpur), which indicate that amino acids are present mainly in the bound form and were made detectable after acid hydrolysis. 相似文献
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为研究剧毒卡尔藻(Karlodinium veneficum)与东海原甲藻(Prorocentrum donghaiense)之间的化感作用,在f/2营养盐条件下,分别采用了混合培养及滤液培养的方法。结果表明:剧毒卡尔藻指数生长后期的无藻细胞滤液明显抑制了东海原甲藻的生长,而东海原甲藻滤液对剧毒卡尔藻的生长几乎无影响,化感作用作为重要的影响因素使剧毒卡尔藻获得竞争优势。将剧毒卡尔藻指数生长末期的无藻细胞滤液置于固相萃取(SPE) C18小柱,经吸附、不同比例的甲醇溶液洗脱,考察不同洗脱部分对东海原甲藻生长的影响,发现80%的甲醇洗脱部分明显抑制了东海原甲藻的生长。本研究为了解剧毒卡尔藻的竞争机制提供了重要的科学依据,今后将重点分析剧毒卡尔藻释放的有效抑制东海原甲藻生长的化感物质。 相似文献
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ADRIAN M. HALL NEIL F. GLASSER 《Boreas: An International Journal of Quaternary Research》2003,32(1):191-207
The Cairngorm Mountain area of Scotland is a classic example of a landscape of selective linear glacial erosion, with sharp contrasts in the intensity of glacial erosion between the deeply incised troughs and valleys and the undulating high plateau. This article examines the Quaternary development of Glen Avon, a 200 m deep glacial trough set within the high plateau of the mountains. Evidence concerning the aggregate basal thermal regimes of the topographically controlled ice streams that formerly developed in this area is reconstructed from the geomorphological record, including bedforms indicative of wet-based, sliding ice and of dry-based ice frozen to its bed. This mapping indicates that basal sliding was not confined exclusively to the troughs but extended towards valley heads and on to parts of the plateau adjacent to troughs. The extent of basal sliding appears to have been greatest beneath pre-Late Devensian ice sheets. Basal ice temperatures are modelled under steady-state conditions for the last ice sheet at c. 18 ka BP. Basal thermal regimes are predicted using a reconstruction of the preglacial relief and for the current topography of the area. Convergent flow of ice through the preglacial valley system appears to have been sufficient to induce basal melting and therefore to initiate valley deepening. This effect is enhanced when the model is run across the present topography. Comparison of results of the geomorphological mapping and the modelling reveals significant differences between the actual and predicted extent of basal sliding outside the main ice stream. The overall conclusion is that many ice streams in mountainous terrain are inherited from the locations of preglacial valleys, which serve to accelerate ice flow and promote frictional heating beneath ice sheets. 相似文献
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