False drainage anomalies (?) in a granite area, Kvalöya in Troms, Norway — a case study     

Henrik Stendal  Maria Douglas Petersen 《Journal of Geochemical Exploration》1993,47(1-3)

An anomalous area (100 km²) revealed by a previous regional overbank sediment sampling survey by the Geological Survey of Norway was followed-up for Ti, Nb, Y, Zr, La and Ce by drainage and lithogeochemical sampling and analyses. The drainage samples were anomalous in the same elements as in the overbank samples and contained similar concentrations. The lithogeochemical results did not indicate mineralization and showed only a small enhancement of Ti, Zr, La and Ce in mylonitic rocks.Mineralogical studies of the drainage samples revealed, apart from proportions of quartz and feldspars, that stream sediments and heavy mineral concentrates are similar in mineralogy, with epidote predomination and several vol% of fine-grained titanite and zircon. Drainage samples contained amounts of Nb, Y, and Zr up to ten times larger than average contents of rock samples. Enhanced light REE (La and Ce) and Nb reflect host minerals, titanite, and enhanced Y possibly zircon and/or allanite.Anomalies in both media do not relate to mineralization. The overbank samples and the drainage samples provide comparable geochemical data.  相似文献   

On the significance of CO2 inclusions in plagioclase microphenocrysts in tholeiite from Moeraki,New Zealand   总被引：1，自引：0，他引：1  

Douglas S. Coombs  Edwin Roedder 《Bulletin of Volcanology》1994,56(1):23-28

Liquid plus vapour inclusions of CO₂ are widespread in plagioclase microphenocrysts in small tholeiitic intrusions and tephra of the Moeraki and adjacent areas of northeast Otago, New Zealand. They imply the presence of immiscible CO₂ droplets in the magma at depths of about 7–14 km. Their presence within 5 μm of the edges of microphenocrysts as little as 35 μm thick and 118 μm long indicates minimal feldspar crystal growth during the final ascent and quenching of the magma. Delicate branching clusters of lath-like microphenocrysts escaped disruption during this ascent. Such CO₂ inclusions are a potential source of ‘excess argon’ perturbing K-Ar age determinations. Received March 24, 1993/Accepted September 10, 1993  相似文献   

THE TROPICS: ENVIRONMENTS AND HUMAN IMPACTS UNDERSTOOD AND REINTERPRETED     

Ian Douglas  M.A.  B.Litt.  Ph.D. 《Singapore journal of tropical geography》1994,14(2):103-122

In the 1950s, few people had travelled widely through different parts of the tropics and interpretations on tropical landforms, soils, vegetation and climate largely rested on impressions gained from residence or long sojourns in particular tropical countries. Most academic geography on the tropics was then written by expatriates and lacked the perspective gained from long experience of tropical regions. Particular problems of understanding arose as people attempted to extrapolate from one part of the tropics to another. Since then, understanding has advanced enormously, largely through the efforts of tropical scientists working in their own institutions and through the greater technological ability to study tropical lands both remotely and through easier field access. The establishment of a number of field stations, aimed primarily at the biological sciences, but also facilitating the work of geographers, has been a major stimulus to this effort. Concerns over practical issues, particularly local development and global climatic change have prompted new avenues of research, many of which have been assisted by the great increase in data collection in tropical countries. For the future, South-South dialogue between tropical physical geographers is needed to improve their ability to ask meaningful questions so that they can contribute to teach the rest of their discipline more about serious applied and applicable geography.  相似文献   

Paleolimnological significance of observed distribution patterns of chrysophyte cysts in arctic pond environments     

Marianne S. V. Douglas  John P. Smol 《Journal of Paleolimnology》1995,13(1):79-83

In a survey of 35 high arctic ponds, chrysophycean cysts were relatively more common in moss periphyton and epilithon habitats, than in surface sediment samples. The highest percentages of cysts relative to diatoms were found in the semi-aquatic mosses. Although chrysophytes are generally considered to be planktonic, periphytic taxa may be common in high latitudes. The ratio of diatom frustules to chrysophyte cysts in arctic sediment cores may be tracking different environmental variables than paleolimnologists may intuitively expect based on observations from more temperate regions.  相似文献   

Book reviews     

Kacper R. Rybicki  Brian J. Mitchell  Louise H. Kellogg  Andrea Borgia  Allan M. Rubin  Douglas R. Schmitt  Douglas R. Schmitt  Edo Nyland  Zbigniew Fajklewicz  David Stevenson  Janusz L. Borkowski 《Pure and Applied Geophysics》1990,133(1):179-180

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Reliability of inexpensive charcoal and alpha-track radon monitors     

Douglas G. Mose  George W. Mushrush  Charles E. Chrosniak 《Natural Hazards》1990,3(4):341-355

A comparison between single short-term radon measurements and annual radon measurements in basements shows that significant uncertainties should be associated with the short-term measurements. Activated charcoal radon monitors which measure radon over a 3 to 7 day interval yield measurements that should carry a ± 90% uncertainty in terms of estimating annual radon concentration. Alpha-track radon monitors which measure radon over a 3 month interval should carry a ± 30% uncertainty. Decisions about home purchases, home remediation and the development of risk characterizations may often be incorrect if currently popular but unrealistically low estimates of uncertainty are applied to short-term radon measurements. Optimal results are obtained from year-long alpha-track measurements.  相似文献   

Book reviews     

Yukio Fujinawa  A. V. Koloskov  Gerardo G. Tango  Lech Stefaníak  Douglas R. Schmitt  Kei Katsumata  Vernon F. Cormier  Wladislaw Lyatsky  Krzysztof Haman  P. Vincent  Konrad Bajer  Henryk Piwkowski 《Pure and Applied Geophysics》1991,136(2-3):343-367

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How to Determine the End of Active Remediation     

Evan K. Nyer  Douglas G. Mehan 《Ground Water Monitoring & Remediation》1991,11(3):89-91

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Heat flow in the Ozark Plateau, Arkansas and Missouri: relationship to groundwater flow     

Joseph G. Meert  Douglas L. Smith  Len Fishkin 《Journal of Volcanology and Geothermal Research》1991,47(3-4)

Heat flow values were calculated from direct measurements of temperature and thermal conductivity at thirteen sites in the Arkansas-Missouri Ozark Plateau region. These thirteen values are augmented by 101 estimates of heat flow, based on thermal conductivity measurements and temperature gradients extrapolated from bottom-hole temperatures. The regional heat flow profile ranges from 9 mW m⁻² to over 80 mW m⁻², but at least two distinct thermal regimes have been identified. Seven new heat flow determinations are combined with three previously published values for the St. Francois Mountains (SFM), a Precambrian exposure of granitic and rhyolitic basement rocks, average 47 mW m⁻². Radioactive heat production of 76 samples of the exposed rocks in the SFM averages 2.4 μW m⁻² and a typical continental basement contribution of 14 mW m⁻² is implied. Conversely, the sedimentary rock sequence of the plateau is characterized by an anomalously low heat flow, averaging approximately 27 mW m⁻². Groundwater transmissivity values that are based on data from 153 wells in deep regional aquifers demonstrate an inverse relationship to the observed heat flow patterns. The areas of high transmissivity that correspond to areas of low total heat flux suggest that the non-conservative vertical heat flow within the Ozark sedimentary sequence can be attributed to the effects of groundwater flow.  相似文献   

Mg²⁺ removal in the system Mg²⁺—amorphous SiO₂—H₂O by adsorption and Mg-hydroxysilicate precipitation     

Douglas B. Kent  Miriam Kastner 《Geochimica et cosmochimica acta》1985,49(5):1123-1136

Two chemical processes can remove Mg²⁺ from suspensions containing amorphous silica (am-SiO₂) at low temperatures: adsorption and precipitation of a Mg-hydroxysilicate resembling sepiolite. Mg²⁺ removal from am-SiO₂ suspensions was investigated, and the relative role of the two removal processes evaluated, as a function of: pH, ionic strength, Mg²⁺ concentration, and temperature.The extent of Mg²⁺ adsorption onto am-SiO₂ decreases with increasing NaCl concentration due to displacement of Mg²⁺ by Na⁺. At NaCl concentrations of 0.05 M and above, adsorption occurs only at pH values above 8.5, where rapid dissolution of am-SiO₂ gives rise to high concentrations of dissolved silica, resulting in supersaturation with respect to sepiolite. Removal of Mg²⁺, at concentrations of 40 to 650 μM, from am-SiO₂ suspensions in 0.70 M NaCl at 25 °C occurs at pH 9.0 and above. Experiments show that under these conditions adsorption and Mg-hydroxysilicate precipitation remove Mg²⁺ at similar rates. For 0.05 M Mg²⁺, at 0.70 M ionic strength and 25 °C, measurable Mg²⁺ removal occurs down to ca. pH 7.5 but is primarily due to Mg-hydroxysilicate precipitation. For the same solution conditions at 5°C, Mg²⁺ removal occurs above pH 8.0 and is primarily due to adsorption.Assuming that increasing pressure does not greatly enhance adsorption, Mg²⁺ adsorption onto am-SiO₂ is an insignificant process in sea water. The surface charge of pristine am-SiO₂ in sea water is primarily controlled by interactions with Na⁺. The principal reaction between Mg²⁺ and am-SiO₂ in marine sediments is sepiolite precipitation.The age distribution of sepiolite in siliceous pelagic sediments is influenced by temperatures of bottom waters and by geothermal gradients.  相似文献