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In North-West Europe no evidence has been found for glaciations older than the Elsterian. The Elsterian seems to consist of at least two separate ice advances with a minor interval in between. During the Elsterian in the area south of the Baltic Sea over 400 m deep channels were cut into the underlying substratum by a combination of glacial erosion and meltwater activity. The channels were active until the Late Elsterian and were subsequently filled with meltwater deposits and glaciolacustrine silt and clay. During the Saalian no comparative channels were being formed. Three different ice advances can be distinguished within the Saalian, the stratigraphical correlation of which is to be discussed. No convincing evidence was found for any interglacial within the Saalian sequence. There are good reasons to assume that the ice advances were only separated from each other by minor ice-free intervals. 相似文献
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Eolian dusts collected after dust storms contain aggregates that are cemented by evaporitic salts, mainly halite. They vary in shape, fabrics, and surface roughness. Aggregation changes grainshape, density and size distribution of dust particles (i.e., characteristics determining erosion and transport); on deposition in the sea, cements dissolve and aggregates disintegrate, leaving the resultant eolo-marine sediment component with a misleading paleo-climatic record. The eolian transport of salts with dust from the arid coastal plain to the sea constitutes a portion of anticyclic salt movement and probably plays a role in the geochemical balance of the oceans. 相似文献
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Dmitrij V. Titov Wojciech J. Markiewicz Nikolay I. Ignatiev Li Song Sanjay S. Limaye Agustin Sanchez-Lavega Jonas Hesemann Miguel Almeida Thomas Roatsch Klaus-Dieter Matz Frank Scholten David Crisp Larry W. Esposito Stubbe F. Hviid Ralf Jaumann Horst U. Keller Richard Moissl 《Icarus》2012,217(2):682-701
Since the discovery of ultraviolet markings on Venus, their observations have been a powerful tool to study the morphology, motions and dynamical state at the cloud top level. Here we present the results of investigation of the cloud top morphology performed by the Venus Monitoring Camera (VMC) during more than 3 years of the Venus Express mission. The camera acquires images in four narrow-band filters centered at 365, 513, 965 and 1010 nm with spatial resolution from 50 km at apocentre to a few hundred of meters at pericentre. The VMC experiment provides a significant improvement in the Venus imaging as compared to the capabilities of the earlier missions. The camera discovered new cloud features like bright “lace clouds” and cloud columns at the low latitudes, dark polar oval and narrow circular and spiral “grooves” in the polar regions, different types of waves at the high latitudes. The VMC observations revealed detailed structure of the sub-solar region and the afternoon convective wake, the bow-shape features and convective cells, the mid-latitude transition region and the “polar cap”. The polar orbit of the satellite enables for the first time nadir viewing of the Southern polar regions and an opportunity to zoom in on the planet. The experiment returned numerous images of the Venus limb and documented global and local brightening events. VMC provided almost continuous monitoring of the planet with high temporal resolution that allowed one to follow changes in the cloud morphology at various scales.We present the in-flight performance of the instrument and focus in particular on the data from the ultraviolet channel, centered at the characteristic wavelength of the unknown UV absorber that yields the highest contrasts on the cloud top. Low latitudes are dominated by relatively dark clouds that have mottled and fragmented appearance clearly indicating convective activity in the sub-solar region. At ～50° latitude this pattern gives way to streaky clouds suggesting that horizontal, almost laminar, flow prevails here. Poleward from about 60°S the planet is covered by almost featureless bright polar hood sometimes crossed by dark narrow (～300 km) spiral or circular structures. This global cloud pattern can change on time scales of a few days resulting in global and local “brightening events” when the bright haze can extend far into low latitudes and/or increase its brightness by 30%. Close-up snapshots reveal plenty of morphological details like convective cells, cloud streaks, cumulus-like columns, wave trains. Different kinds of small scale waves are frequently observed at the cloud top. The wave activity is mainly observed in the 65–80° latitude band and is in particular concentrated in the region of Ishtar Terra that suggests their possible orographic origin. The VMC observations have important implications for the problems of the unknown UV absorber, microphysical processes, dynamics and radiative energy balance at the cloud tops. They are only briefly discussed in the paper, but each of them will be the subject of a dedicated study. 相似文献
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Klaus-Dieter Grevel Mirko Schoenitz Volker Skrok Alexandra Navrotsky Werner Schreyer 《Contributions to Mineralogy and Petrology》2001,142(3):298-308
The enthalpy of drop-solution in molten 2PbO·B2O3 of synthetic and natural lawsonite, CaAl2(Si2O7)(OH)2·H2O, was measured by high-temperature oxide melt calorimetry. The enthalpy of formation determined for the synthetic material is (fHOxides=-168.7Dž.4 kJ mol-1, or (fH0298=-4,872.5dž.0 kJ mol-1. These values are in reasonable agreement with previously published data, although previous calorimetric work yielded slightly more exothermic data and optimisation methods resulted in slightly less exothermic values. The equilibrium conditions for the dehydration of lawsonite to zoisite, kyanite and quartz/coesite at pressures and temperatures up to 5 GPa and 850 °C were determined by piston cylinder experiments. These results, other recent phase equilibrium data, and new calorimetric and thermophysical data for lawsonite and zoisite, Ca2Al3(SiO4)(Si2O7)O(OH), were used to constrain a mathematical programming analysis of the thermodynamic data for these two minerals in the chemical system CaO-Al2O3-SiO2-H2O (CASH). The following data for lawsonite and zoisite were obtained: (fH0298 (lawsonite)=-4,865.68 kJ mol-1 , S0298 (lawsonite)=229.27 J K-1 mol-1 , (fH0298 (zoisite)=-6,888.99 kJ mol-1 , S0298 (zoisite)=297.71 J K-1 mol-1 . Additionally, a recalculation of the bulk modulus of lawsonite yielded K=120.7 GPa, which is in good agreement with recent experimental work. 相似文献
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Experimental studies on the stability of several Mg-sulfate hydrates including epsomite (MgSO4·7H2O), hexahydrite (MgSO4·6H2O), starkeyite (MgSO4·4H2O), and kieserite (MgSO4·H2O) as a function of temperature and relative humidity are in poor agreement with calculations based on thermodynamic properties of these substances taken from the literature. Therefore, we synthesized four different MgSO4 hydrates and measured their enthalpies of formation by solution calorimetry at T = 298.15 K. The resulting enthalpies of formation from the elements are:
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- ΔfH0298 (epsomite) = −3387.7 ± 1.3 kJmol−1
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- ΔfH0298 (hexahydrite) = −3088.1 ± 1.1 kJmol−1
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- ΔfH0298 (sanderite, MgSO4·2H2O) = −1894.9 ± 1.3 kJmol−1
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- ΔfH0298 (kieserite) = −1612.4 ± 1.3 kJmol−1
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- Epsomite: ΔfH0298 = −3388.7 kJmol−1, S0298 = 371.3 Jmol−1 K−1, ΔfG0298 = −2871.0 kJmol−1
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- Hexahydrite: ΔfH0298 = −3087.3 kJmol−1, S0298 = 348.5 Jmol−1 K−1, ΔfG0298 = −2632.3 kJmol−1
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- Starkeyite: ΔfH0298 = −2496.1 kJmol−1, S0298 = 259.9 Jmol−1 K−1, ΔfG0298 = −2153.8 kJmol−1
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- Kieserite: ΔfH0298 = −1611.5 kJmol−1, S0298 = 126.0 Jmol−1 K−1, ΔfG0298 = −1437.9 kJmol−1
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Klaus-Dieter Meyer 《第四纪科学杂志》1998,13(3):282-282
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