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Mineral modes have been determined for specimens of eight rocktypes from CuK X-ray powder diffraction data using the Rietveldmethod. The samples include two granites, a granodiorite, adamellite,gabbro, basalt, trachyte, and two granulite-facies metamorphicrocks. Up to eight individual mineral components have been measuredin each sample (no glassy phases were observed), with a detectionlimit of {small tilde}1 wt.%, depending on the mineral assemblage.Marked variations in grain size (i.e., granite vs. trachyte)provide no difficulties for the X-ray method. The X-ray resultscompare very favourably with (1) optical modes determined forthe medium–coarse-grained samples by point counting, (2)normative calculations obtained using locally enhanced catanormand mesonorm software, and (3) corresponding Rietveld modesdetermined, for two samples, from neutron powder data. Wheredifferences occur, these are discussed in relation to the limitationsof each of the methods. The improved accuracy of the X-ray method is due primarily tothe incorporation of the full diffraction profile in the Rietveldanalysis calculations, and the elimination of preferred orientationby collecting the data from samples packed in glass capillaries(i.e., Debye–Scherrer mode). The good agreement of theX-ray and neutron modes shows that the usual problems encounteredwith microabsorption, extinction, and sampling are of littleconcern in these rocks. The results highlight one of the majoradvantages provided by Rietveld modal analysis over the moretraditional ‘reference intensity’ X-ray methods,namely, that the crystal chemistry (and thus the calibrationconstants) of the individual phases can be adjusted dynamicallyduring each individual analysis. This not only provides moreaccurate phase abundances, but also gives important supplementaryinformation about the mineralogy of the major components. 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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AFSOON M. KAZEROUNI METTE L. K. POULSEN HENRIK FRIIS JOHAN B. SVENDSEN JENS P. V. HANSEN 《Sedimentology》2013,60(3):679-692
Detrital glaucony in the Palaeogene glauconitic sandstones in Siri Canyon, Danish North Sea, has been analysed from 15 exploration wells by X‐ray diffraction, electron microprobe and scanning electron microscopy. These sandstones consist of mixed‐layer illite/smectite and have a large variability in chemical composition and structure. In the most shallow wells (ca 1700 m), the glaucony is rich in Fe and consists of mixed‐layer illite/smectite with random‐interstratification (R = 0). In the depth interval from 1700 to 2000 m, the composition changes as Si is incorporated. The structure changes to ordered R = 1. Further increase in burial leads to the loss of Fe. Ordered R = 3 mixed‐layer illite/smectite is recognized from burial depths of 2200 m. The proportion of illite in illite/smectite mixed layers increases only slightly with depth and temperature. Although the structural changes generally are associated with chemical changes, they can also take place isochemically when the detrital glaucony is tightly embedded in earlier cement, which prevented chemical exchange. The glaucony transformation in the Siri Canyon sandstones partly reflects a supply of Si and partly significant loss of Fe. Thus, the glaucony transformation relates to the general diagenesis of the host sandstone. These sandstones are cemented by microquartz at an early stage, followed by precipitation of Fe‐rich grain‐coating berthierine or chlorite. 相似文献
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HANNE BIRGIT MADSEN KAREN LUISE KNUDSEN 《Boreas: An International Journal of Quaternary Research》1994,23(4):495-504
A study of sea-bottom samples from shallow waters in the northern part of Scoresby Sund, off Jameson Land, East Greenland, reveals four different foraminiferal assemblages between 1.3 and 35.6 m water depth. The shallowest samples. Assemblage SA (1.3–2.2 m), contain only very few foraminifera, presumably due to the annual repeated formation of an ice foot. Assemblage SB (3.7 and 4.3 m) is characterized by the calcareous species Haynesina nivea and H. orbiculare , while the arenaceous species Spiropleclammina biformis, Reophax arctica , and Recurvoides turbinatus dominate all the faunas of Assemblage SC (9.3–25.9 m depth). The change in fauna to the succeeding Portatrochammina bipolaris - Spiropleclammina biformis fauna (Assemblage SD, 29.6 and 35.6 m) presumably corresponds to the transition from the shallow Fjord water layer to the deeper and relatively more stable Polar water. Elphidiella hannai (Cushman & Grant) is recorded live for the first time in recent assemblages from the Atlantic Ocean. 相似文献
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dr. agro. LEIF PETERSEN mag.scient. HENRIK BREUNING MADSEN 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):25-35
Petersen, Leif og Madsen, Henrik Breuning: Possible Effects of Ground Water Lowering on Some Peat Soils in Sjælland. Geografisk Tidsskrift 77:25–35 København, June 1, 1978. In four peatlands in the central part of Zealand nine profiles have been investigated to estimate the effect of a lowering of the groundwater level. 相似文献
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Spit systems are seldom recognized in the pre‐Quaternary sedimentary record compared to their common occurrence along present‐day coasts and in Quaternary successions. This lack of recognition may partly be due to the lack of widely accepted depositional models describing the facies characteristics of spit systems and their subaqueous platforms in particular. The Skagen spit system is a large active system that began to form 7150 yr bp and from 5500 bp to Recent times it has prograded 4 m year?1 and accumulated 3·5 × 109 m3 of sand. The spit system provides a unique opportunity for establishing a well‐constrained depositional model because uplift and erosion have made large windows into the preserved facies, while active spit‐forming processes can be examined at the young prograding end of the same system. The depositional model presented here thus builds on excellent outcrops, surface morphology, a well‐defined palaeogeography and detailed C14 age control supplemented with observations from continuous well cores and profiles obtained by ground‐penetrating radar and transient electromagnetic surveys. The factors that have governed the development of the spit system, such as relative sea‐level change, wave and current climate, tidal range, sediment transport and depositional rates are also well‐understood. The sedimentary facies of the spit system are grouped into four principal units consisting from below of thick storm sand beds, dune and bar‐trough deposits, beach deposits and peat beds. These four units form a coarsening and shallowing upward sand‐dominated succession, up to 32 m thick, which overlies offshore silt with a transition zone and is topped by a diastem overlain by young aeolian dune sand. The sedimentary structures and depositional processes are described in detail and integrated into a depositional model, which is compared to other spit systems and linear shoreface models. 相似文献
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KENNETH D. MADSEN 《Geographical review》2002,92(1):63-72
ABSTRACT. Recent presidents of the Association of American Geographers have made it clear that as a discipline we need to do more to reach outside the confines of academia. Since 1985, the J. B. Jackson Award has recognized individuals whose books provide examples of how to share professional geographical knowledge with the educated lay public. Through correspondence with these individuals, recommendations for improving geographers' outreach are presented. 相似文献
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Predictability of seasonal precipitation in the Nordic region 总被引：1，自引：0，他引：1
HENRIK FEDDERSEN 《地球，A辑:动力气象学与海洋学》2003,55(5):385-400