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排序方式: 共有191条查询结果,搜索用时 15 毫秒
141.
142.
Decoding the Mediterranean salinity crisis 总被引:1,自引:0,他引:1
WILLIAM B. F. RYAN 《Sedimentology》2009,56(1):95-136
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Scanning electron microscopy of quartz grains in supraglacial debris, Adishy Glacier, Caucasus Mountains, USSR 总被引:7,自引:0,他引:7
WILLIAM C. MAHANEY REIN VAIKMAE KAI VARES 《Boreas: An International Journal of Quaternary Research》1991,20(4):395-404
The surface microtopography of quartz grains in glacial depostis has often been attributed to mechanical release from source rocks during weathering and prior to entrainment by glaciers. Fractures on quartz particles, including subparallel and conchoidal features, often attributed to cryostatic pressure in ice and stick-slip processes at the base of glaciers, have been considered, in part, to result from mechanical weathering of source rocks. To test this hypothesis we studied 15 samples of supraglacial debris from the Adishy Glacier in the central Caucasus Mountains, USSR. Clasts in transport on the surface of the glacier originate primarily from the cirque headwall by weathering and mass wasting processes; a minor amount is presumed to have been derived from aeolian influx following reworking of older sediments down valley. The results show unequivocally that mechanical weathering is only likely to produce grains with pronounced fracture faces that lack subparallel and conchoidal fracture features. No fresh glacial-crushing type features were observed on these samples. Grains that had been glacially crushed, weathered and retransported, presumably by aeolian processes, were observed in four samples of the data set. 相似文献
145.
Estimating regional carbon exchange in New England and Quebec by combining atmospheric, ground-based and satellite data 总被引:1,自引:0,他引:1
DANIEL M. MATROSS ARLYN ANDREWS MAHADEVAN PATHMATHEVAN CHRISTOPH GERBIG JOHN C. LIN STEVEN C. WOFSY BRUCE C. DAUBE ELAINE W. GOTTLIEB VICTORIA Y. CHOW JOHN T. LEE CONGLONG ZHAO PETER S. BAKWIN J. WILLIAM MUNGER DAVID Y. HOLLINGER 《Tellus. Series B, Chemical and physical meteorology》2006,58(5):344-358
146.
WILLIAM DE GENST FRANK CANTERS WOLFGANG JACQUET SOPHIE VERMEERSCH 《International journal of geographical information science》2013,27(6):591-614
In this article a technique is presented to estimate the proportions of different map categories in a series of heterogeneous mapping units, using information on the degree of spatial correlation with other categorical data. The technique has been applied to decompose ecotope complexes in a categorical map of the biotic environment in Flanders, using secondary information on land cover and soil type. Because the conditional probability of an ecotope occurring given a certain soil type depends on the frequency with which the ecotope occurs in an area, determining the probability of occurrence of an ecotope from the conditional probabilities can lead to predictions that contradict prior knowledge about the composition of the different mapping units. A measure expressing the affinity of an ecotope for a soil type is proposed and is used as an alternative to conditional probability in the estimation procedure. The proposed method has been tested in a study area for which detailed field observations were collected, and proves to work well if reliable a priori knowledge about the composition of complex mapping units is available. 相似文献
147.
WILLIAM C. MAHANEY 《Boreas: An International Journal of Quaternary Research》1995,24(4):293-304
Recent analyses of microtextures on quartz particles (63–2000 μm) from Quaternary tills in Antarctica, Germany, southern Ontario, western Wyoming, Tibet, the Austrian Alps, and Mount Kenya show that glacial fracture and abrasion microfeatures may be used to infer the thickness, transport history and ice dynamics of Pleistocene and Holocene glaciers. Quartz sands emplaced by continental and mountain ice were studied by SEM after transport over variable distances in glaciers estimated to range from 150 m to 1500 m in thickness. Relative differences in ice thicknesses, distances of transport, and/or ice dynamics appear to have determined the frequency of occurrence and type of microtextures occurring on sand-size particles. Subparallel fracture microfeatures tend to increase in frequency over a greater proportion of particle surfaces with increasing ice thickness and distance of transport. Conchoidal fractures, the most typical in quartz, and to some degree crescentic gouges abound on fragments emplaced by continental ice. Other possible fracture and fragmentation mechanisms, producing features of generally glacial origin, involve low velocity impacts induced by stick-slip mechanisms, under variable cryostatic stresses, producing fracturing and abrasion across particle surfaces. Their generation implies high local contact stresses associated with high strain rates. 相似文献
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WILLIAM A. S. SARJEANT 《Geology Today》1995,11(2):68-72
Following the'Golden Age'of Holmes and Thorndyke, geology and geological phenomena have figured in quite a number of crime novels. In a handful, geologists even serve as central characters — or as victims. These novels are here identified and briefly discussed, while the lack of a geologist as 'series character'is lamented. 相似文献