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111.
Alberto C. Montefinale Gianna L. Petriconi Enrico G. Gori Henry M. Papee 《Pure and Applied Geophysics》1970,83(1):201-221
Summary Results of intercorrelations between daily average visibilities, at 18 Observatories situated in the Po-Valley, indicate the existence there of several areas within which conditions of fog are similarly affected. The position of those areas reflects the influence of geographic and topographic factors on fogs which regularly recur, during the cold seasons, in that extensive part of Northern Italy. 相似文献
112.
113.
Hydrothermal submarine metalliferous deposits, common in areas of the ocean floor with high heat flow, contain generally about 10 ppm U as an order of magnitude. The ratio is in the majority of cases close to that of seawater; only in a few cases is it anomalously high. Anomalous ratios are coupled with low U concentrations. These data are explained by a model where thermal water (essentially heated seawater) in its sub-bottom circulation often is unable to leach U from the basaltic oceanic crust; in fact, these thermal waters may in some cases lose U. When leaching of U from the basalt does take place, probably during shallow stages of the sub-bottom circulation, the resulting anomalous ratio can be preserved in the hydrothermal deposit only if mixing with ‘seawater’ U is prevented. 相似文献
114.
Summary The photodecomposition of ammonium nitrate at various concentrations, in ventilated, aqueous solutions, is investigated as a function of radiation intensity, both under sunlight illumination and under artificial ultraviolet light. The process of decomposition, to nitrogen and water, of ammonium nitrite formed, competes with the formation of NO
2
–
which is, otherwise, proportional to the radiation absorbed. 相似文献
115.
Summary The process of nitrite formation, by the action of the near-ultraviolet radiation on sodium nitrate solutions, is investigated both in the laboratory and at different elevations under sunlight. The release of NO
x
, from solutions irradiated, is found to compete with the generation of nitrite which is proportional to the radiation absorbed by the solution. 相似文献
116.
Enrico Bonatti 《Bulletin of Volcanology》1965,28(1):257-269
Palagonite is an hydrated and often altered glass usually associated with sub-aqueous basaltic volcanites. It is commonly considered as an alteration product of normal basaltic glass (sideromelane) with which it is associated in hyaloclastites. Existing information on the diffusion rates of water in natural glasses suggests, however, that the hydration which causes the formation of palagonite takes place at relatively high temperature, that is mainly during effusion and cooling of the lava under water. It is also suggested that generally palagonite is not formed in nature to any great extent from the alteration of sideromelane. Palagonite appears to devitrify much faster than normal unhydrated glass of the same composition. This fact may explain some previously unclear data on the occurrence of volcanic glasses on the floor of the oceans; namely, the existence of totally devitrified glasses in some recent sediments and the finding of unaltered glass in older deposits. 相似文献
117.
Records of environmental and climatic changes during the late Holocene from Svalbard: palaeolimnology of Kongressvatnet 总被引:2,自引:0,他引:2
Piero Guilizzoni Aldo Marchetto Andrea Lami Achim Brauer Luigi Vigliotti Simona Musazzi Leonardo Langone Marina Manca Federico Lucchini Natale Calanchi Enrico Dinelli Alceo Mordenti 《Journal of Paleolimnology》2006,36(4):325-351
A multi-core, multidisciplinary palaeolimnological study of the partially varved sediment of a deep, meromictic, arctic lake, Kongressvatnet (Svalbard, Western Spitsbergen), provides a record of environmental and climatic changes during last ca. 1800 years. The chronology of sedimentation was established using several dating techniques (137Cs, 210Pb, varve counts, palaeomagnetic correlation). A multiproxy record of palaeolimnological variability was compiled based on sedimentation rates, magnetic properties, varve thickness, organic matter, geochemistry, pigments from algal and photosynthetic bacteria, mineralogy and biological assemblages (diatoms, Cladocera). The major features recognised in our master core K99-3 include a shift in sediment source and supply (magnetic measurements, geochemistry) probably caused by glaciological changes in the catchment around 38–32 cm core depth (AD 700–820). Additional environmental changes are inferred at 20–18, 8–4.5 and 3–2 cm (AD ca. 1160–1255; 1715–1880; 1940–1963, respectively). During the past ca. 120 years a prominent sedimentological change from brownish-grey, partly laminated silt-clay (varves) to black organic-rich deposits was observed. From AD 1350 to AD1880 the sediment is comprised of a continuous sequence of varves, whereas the earlier sediments are mostly homogeneous with only a few short intercalated laminated sections between AD 860 and 1350. Sedimentation and accumulation rates increased during the last 30 years (modern warming). Pigment concentrations are very low in the lower ca. 32 cm of the core (AD 820) probably because of the high turbidity high energy environment. The high sulphur content in the uppermost 32 cm of sediment has given rise to two horizontally stratified populations of sulphur anaerobic photosynthetic bacteria, as inferred from their specific carotenoids. These bacteria populations are much more abundant during the Little Ice Age (LIA) than during warmer periods (e.g., during the Medieval Warm Period and 20th century). Diatoms are lacking from the core base up to 18 cm (ca. AD 1255); at this level, species indicative of mesotrophic water are present, whereas from 17 cm to the top of the core, oligotrophic taxa such as Staurosira construens/S. pinnata complex dominate, indicating extended ice coverage and more oligotrophic waters during the LIA. The concentration of Cladocera subfossil remains (dominated by Chydorus) are relatively high in the deepest sections (54–32 cm), whereas the upper 32 cm are characterized by a very low concentration of remains, possibly because of the strongly anoxic conditions, and in this upper sediment section rotifer resting eggs become prevalent. We interpret these changes as responses to climate forcing through its impact on glacial melt water, lake ice cover duration and mainly redox conditions in deep water. The observed changes suggest that at least some of our recorded changes may parallel the Greenland Ice core, although our study added more details about the inferred climatic changes. Further aspects are discussed, such as catchment processes, glacial activity, duration of the Medieval Warm Period, the Little Ice Age, local human activity, and limnology. 相似文献
118.
Paola Mameli Giovanni Mongelli Giacomo Oggiano Enrico Dinelli 《International Journal of Earth Sciences》2007,96(5):887-902
Bauxite deposits are widespread in NW Sardinia. They formed during the middle Cretaceous, in consequence of a period of emergence of the Mesozoic carbonate shelf. In the Nurra area the geometries derived by the Middle Cretaceous tectonic phases controlled the ore typologies. Two bauxite profiles, laying on different bedrocks, were sampled. The bauxitization proceeded from the surface downward, with the accumulation of Al2O3 and residual ‘immobile’ elements (Al, Ti, HFSE), and corresponding mobility and loss of SiO2 and Fe2O3. Epigenetic kaolinite formed close to faults and joints, probably as a result of silicification, introduced by low temperature hydrothermal solutions. Rare earth elements, especially LREE, are concentrated in Fe-rich bauxite horizons, probably due to scavenging by goethite. REE-enrichment is not observed in the boehmite-rich horizons. Very high REE contents are observed in a Fe-depleted horizon due to the occurrence of REE accessory minerals, probably of the bastnäsite group. Conservative indices, including TiO2/Al2O3 and Ti/Cr ratios, and Eu anomalies (Eu/Eu*), suggest that the deposits formed by weathering of sediments derived from mafic rocks of the Hercynian basement. This, in turn, implies that the basement was exposed during middle Cretaceous. 相似文献
119.
Simonetti Matteo Carosi Rodolfo Montomoli Chiara Langone Antonio D’Addario Enrico Mammoliti Elisa 《International Journal of Earth Sciences》2018,107(6):2163-2189
International Journal of Earth Sciences - In the Western Alps, a steeply dipping km-scale shear zone (the Ferriere-Mollières shear zone) cross-cuts Variscan migmatites in the... 相似文献
120.