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Milton Blander H.N. Planner K. Keil L.S. Nelson N.L. Richardson 《Geochimica et cosmochimica acta》1976,40(8):889-896
Laser-melted magnesium silicate droplets, supercooled 400–750°C below their equilibrium liquidus temperatures before crystallization, were examined to provide a comparison with meteoritic and lunar chondrules and to examine physicochemical parameters that may indicate the conditions of their formation. Internal textures of the spherules strikingly resemble textures observed in some chondrules. Definite trends in crystal morphology, crystal width and texture were established with respect to nucleation temperature and bulk composition. Such trends provide a framework for determining the nucleation temperature of chondrules. The only phase to nucleate from the supercooled forsterite-enstatite normative melts was forsterite, which was present in more-than-normative amounts. Highly siliceous glass (~65wt. % SiO2) was identified interstitially to the forsterite crystals in seven of the spherules and is thought to be present in all. The presence of enstatite and the large proportion of crystals in some meteoritic chondrules implies that they were maintained at temperatures considerably in excess of 600°C at some point in their history. 相似文献
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KNUT KAISER ALEXANDRA HILGERS NORBERT SCHLAAK MICHA&#; JANKOWSKI PETER KÜHN SIXTEN BUSSEMER KRZYSZTOF PRZEGI&#;TKA 《Boreas: An International Journal of Quaternary Research》2009,38(3):591-609
Lateglacial buried soil horizons, which occur widely in sandy aeolian sequences of northern central Europe, were analysed in order to evaluate their regional pedostratigraphical and palaeoenvironmental potential. Data on stratigraphy, sedimentology, pedology, geochronology and palaeobotany from 29 palaeosol-bearing profiles at terrestrial sites are presented. Greyish Ahb and Eb horizons occur, as well as brownish Bwb and BwAhb horizons. They are 5–30 cm thick, showing similar pedological properties except colour, and they frequently bear charcoal typically from pine. Soil classification results in Albic Arenosols (Dystric) and Brunic Arenosols (Dystric) representing palaeosols of the Usselo and Finow types, respectively. Radiocarbon dating of the palaeosols reveals a dominance of Allerød ages followed by Younger Dryas and Preboreal ages. Most luminescence ages on overlying aeolian sands date into the Allerød–Younger Dryas interval. Mapping of all Usselo and Finow soil occurrences ( n =96) in northern central Europe known so far reveals a nearly closed Finow soil province between Usselo soil areas in NW Germany and central Poland, mainly situated in NE Germany. Most Usselo soils compiled contain charcoal, indicating widespread and repeated fires. Recent claims that the Usselo soil represents an event layer from rapid aeolian sedimentation caused by an extraterrestrial impact is rejected. Instead, both Usselo and Finow soils can be assumed to be pedostratigraphical marker horizons in northern central Europe and beyond. 相似文献
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This study investigates the potential for leaching of coal trace elements to seawater from a grounded bulk carrier. The coal type and ecological scenario was based on the grounding of the "Shen Neng" (April 2010) at Douglas Shoal located within the Great Barrier Reef (Queensland, Australia). The area is of high ecological value and the Queensland Water Quality Guidelines (2009) provided threshold limits to interpret potential impacts. Coal contains many trace elements that are of major and moderate concern to human health and the environment although many of these concerns are only realised when coal is combusted. However, "unburnt" coal contains trace elements that may be leached to natural waterways and few studies have investigated the potential ecological impact of such an occurrence. For example, coal maritime transport has increased by almost 35% over the last five reported years (Jaffrennou et al., 2007) and as a result there is an increased inherent risk of bulk carrier accidents. Upon grounding or becoming submerged, coal within a bulk carrier may become saturated with seawater and potentially leach trace elements to the environment and impact on water quality and ecological resilience. The worst case scenario is the breakup of a bulk carrier and dispersal of cargo to the seafloor. 相似文献
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