Palaeoclimatic record in the loess–palaeosol sequence of the Strelitsa type section (Don glaciation area,Russia) deduced from rock magnetic and palynological data

Until now, palaeoclimatic reconstructions for the major stages in the development of the Quaternary loess–palaeosol sequence on the Russian Plain have been based on pedological, palynological and faunal (vertebrates and molluscs) analyses. In order to demonstrate the palaeoclimatic influence on the magnetic properties of this sequence, the magnetic susceptibility signature of the Strelitsa type section in the Upper Don basin is compared with a detailed landscape – climate reconstruction of loess and soil from palynological data. Large amplitude fluctuations of palaeoclimate and palaeoenvironment are reflected clearly in the lithology and in the rock magnetic properties, which usually are enhanced in wet and warm interglacial periods, but stay at low levels during cold glacial epochs. Palynological climate zonation, however, is sometimes in conflict with the pedologic–magnetic record. Strong climate fluctuations, as indicated by changing pollen assemblages, are not always paralleled by corresponding changes in lithology and/or rock magnetic properties. Alternatively, light coloured illuvial horizons with low magnetic signal sometimes appear to have formed during early stages of interglacials, and the top parts of some palaeosols apparently formed during glacial stages. Copyright © 2000 John Wiley & Sons, Ltd.     

Weathering fluxes of arsenic from a small catchment in Slovak Republic

Inputs of As to a small catchment due to chemical weathering of bedrock, mechanical weathering of bedrock, and atmospheric precipitation were 71.53, 23.98 and 0.02 g ha⁻¹ year⁻¹, respectively. The output fluxes of As due to mechanical erosion of soil, biological uptake, stream discharge, and groundwater flow were 6.32, 4.77, 0.37 and 0.02 g ha⁻¹ year⁻¹, respectively. The results indicate that arsenic accumulates in soil and regolith with a very high rate. This is attributed to the selective weathering and erosion with respect to arsenic and fixation of arsenic in the secondary solids produced by weathering. The output fluxes of As in stream and groundwater in Vydrica catchment in Slovak Republic (0.39 g ha⁻¹ year⁻¹) based on muscovite–biotite granites and granodiorites were much lower compared to catchments in a gold district in the Czech Republic. These results may be ascribed to the low levels of arsenic pollution measured in Vydrica catchment. The arsenic fluxes were estimated by calculation of mechanical and chemical weathering rates of the bedrocks in Vydrica catchment from mass balance data on sodium and silica. The justification of the steady state of Na and Si is that neither of the elements is appreciably accumulated in plants and in exchangeable pool of ions in soil.     

The ševĚtín astrobleme,southern Bohemia,Czechoslovakia

The geological, geomorphological, petrological, and geophysical data for the 46 km circular structure evtín (4905N, 1435E), southern Bohemia, are consistent with characteristic of moderately eroded structures that have originated by hypervelocity meteorite impact. The astrobleme, dated as late Cretaceous (probably Coniac-Santon, 85-75 m.y.), is dissected into radial fault segments, which exhibit a variable level of erosion. The classification of the evtín astrobleme as a probable impact structure is based on the geological and geophysical evidence of central »scar« about 8 km in diameter, shock metamorphism in the centre of the structure, and relics of silicified impact breccia including globular and suevite types with structural indications of molten material. Shatter coning and shock metamorphism are documented for several formations and lithologies ranging in age from the hercynian granite of the crystalline basement, through Stephanian-Permian, to the Upper Cretaceous-Lower Klikov Formation. The morphological expression of the crater rim is preserved in the less eroded segments. The central uplift (d=21 km, approximately 0.5 of the total diameter), still preserved in part as a positive morphological feature, is partly burried under the post-impact Upper Klikov Formation. The impact event provided the major tectonic, geomorphological, and paleogeographic resetting, which was known for some time in the evolution of the continental Upper Cretaceous of this area and expressed in the splitting of the Klikov Formation into two divisions.

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Zusammenfassung Geologische, geomorphologische, petrologische und geophysikalische Daten, die über die 46 km im Durchmesser aufweisende Rundstruktur von evtín in Südböhmen (4905N, 1435E) ermittelt wurden, entsprechen der Charakteristik mittelmä\ig erodierten Strukturen, die infolge des Einschlags eines gro\en Meteoriten von Hypergeschwindigkeit entstanden sind. Das Astroblem wird als oberkretazisch (wahrscheinlich von Coniac- bis Santonalter, 85-75 Mill. Jahre) geologisch datiert. Es ist durch Brüche in Radialsegmente aufgegliedert, die verschieden intensiv erodiert sind. Geologische und geophysikalische Belege einer zentralen »Narbe« von 8 km im Durchmesser, eine Sto\wellenmetamorphose im Zentrum der Struktur sowie Relikte silizifierter Impaktbreccien, die globulare und suevitähnliche Typen mit Strukturanzeichen von aufgeschmolzenem Material umfassen, stellen Hauptangaben zur Klassifizierung des Astroblems von evtín als einer wahrscheinlichen Impaktstruktur dar. Die »shatter cones« und die Sto\wellenmetamorphose wurden in mehreren Formationen und verschiedenen Gesteinstypen von dem herzynischen Granit im kristallinen Untergrund, über die stefanischen und permischen Gesteine bis zu der oberkretazischen Klikov-Schichtenfolge (ihrem unteren Teil) ermittelt. Die Morphologie des Kraterrandes ist in weniger erodierten Segmenten durch die Erosion ausgeprägt. Die Zentralerhebung (Durchmesser von 21 km, d.h. ungefähr von einer Hälfte des Kratergesamtdurchmessers) ist morphologisch noch zum Teil erhalten, aber ihr östl. Teil ist von der oberen Abteilung der Klikov-Schichtenfolge überdeckt. In Zusammenhang mit dem Impaktereignis werden bedeutsame tektonische, geomorphologische und paläogeographische änderungen gestellt, die in der Entwicklung der kontmentalen Oberkreide dieses Gebietes bereits früher erkannt wurden und zur Aufgliederung der Klikov-Schichtenfolge in zwei Abteilungen führten.

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Résumé La structure circulaire de evtin (4905N - 1435E, 46 km de diamètre), examinée à la lumière des données géologiques, géomorphologiques, pétrologiques et géophysiques, présente les caractères d'une structure provoquée par l'impact d'une météorite de très grande vitesse, et modérément érodée. Cet astroblème est daté du Crétacé supérieur, probablement du Coniacien-Santonien (environ 85-75 Ma). Il est subdivisé par des cassures radiales en segments qui présentent divers degrés d'érosion. L'assimilation de l'astroblème de evtin à une structure d'impact se base sur les arguments suivants: cicatrice centrale de 8 km de diamètre, métamorphisme de choc dans la partie centrale, restes de brèche d'impact silicifiée comportant des types globulaires et de suévite avec indices de matériaux fondus. Les »shatter cones« et le métamorphisme de choc s'observent dans plusieurs formations, de lithologies diverses, qui s'échelonnent entre le granite hercynien du socle cristallin, le Stéphano-permien, et le Crétacé supérieur (partie inférieure de la formation de Klikov). La morphologie du rempart du cratère est préservée dans les segments les moins érodés. La zone surélevée centrale (21 km de diamètre, soit la moitié du diamètre total) est partiellement préservée et cachée pour le reste sous la partie supérieure de la formation de Klikov. Le phénomène d'impact a été accompagné de modifications tectoniques, géomorphologiques et paléogéographiques marquantes. Ces modifications étaient connues antérieurement dans l'évolution du Crétacé supérieur de cette région et avaient justifié la subdivision en deux parties de la formation de Klikov.

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Geochemical and stable isotopic variability within two rivers rising under the same mountain,but belonging to two distant watersheds

Complementary geochemical and stable isotope investigations of the Gorski Kotar karst aquifer system in western Croatia were obtained for the first time, to answer the question whether both studied rivers drain the same aquifer system or not. The two main rivers, the Kupa and the Rje?ina, rise under the same mountain range, but belong to two different watersheds (Black Sea and Adriatic Sea). The karst aquifer of Gorski Kotar is a potentially important source of drinking water for two neighboring countries, Croatia and Slovenia (Central and South Europe), and is strongly influenced by both Mediterranean and continental weather conditions. It is a part of the Dinaric karst, which is “locus typicus” for karst worldwide and one of the most typical karst areas in the world.     

The AUSTRAL VLBI observing program

The AUSTRAL observing program was started in 2011, performing geodetic and astrometric very long baseline interferometry (VLBI) sessions using the new Australian AuScope VLBI antennas at Hobart, Katherine, and Yarragadee, with contribution from the Warkworth (New Zealand) 12 m and Hartebeesthoek (South Africa) 15 m antennas to make a southern hemisphere array of telescopes with similar design and capability. Designed in the style of the next-generation VLBI system, these small and fast antennas allow for a new way of observing, comprising higher data rates and more observations than the standard observing sessions coordinated by the International VLBI Service for Geodesy and Astrometry (IVS). In this contribution, the continuous development of the AUSTRAL sessions is described, leading to an improvement of the results in terms of baseline length repeatabilities by a factor of two since the start of this program. The focus is on the scheduling strategy and increased number of observations, aspects of automated operation, and data logistics, as well as results of the 151 AUSTRAL sessions performed so far. The high number of the AUSTRAL sessions makes them an important contributor to VLBI end-products, such as the terrestrial and celestial reference frames and Earth orientation parameters. We compare AUSTRAL results with other IVS sessions and discuss their suitability for the determination of baselines, station coordinates, source coordinates, and Earth orientation parameters.     

圣彼得堡土地利用格局现状特征及形成机制

以圣彼得堡市为例,依据1948、1987和2016年土地利用数据计算居住、工业和商业用地的区位熵值并分析其变化,基于统计小区、圈层式及扇形分布3个视角,运用GIS分析计划与市场经济影响下的城市用地空间分布特征。研究结果表明,居住、工业和商业用地的空间分布规律不同：① 3类用地在城市整体空间分布中均表现出一定的分散特征,其中,居住用地空间分布表现最为分散,工业用地呈现出分区域性布局特征,相比而言商业用地空间聚集程度最高;② 商业用地在核心圈层处于主导地位,工业用地在老城区圈层为主导地位,居住用地在近郊区圈层为主导地位,远郊区圈层仍处于初步发展阶段,城市景观发展尚未成熟;③ 对比圈层式和象限式结构各类用地区位熵值分布结果,提出圣彼得堡市3类用地空间分布扇形结构特征明显,说明沿主要交通线路是现代城市用地空间扩展主要方式,其中工业用地在城市空间分布中占据更为有利的交通区位优势,居住用地次之,商业用地在城市中心区域中分布不足。圣彼得堡城市用地空间分布形成主要机制总结为以下5个方面：前苏联时期城市用地空间结构主要框架的保持;行政区划调整为城市用地结构改善提供了路径;市场经济下住房体制改革推进了城市居住郊区化;土地市场对土地功能置换进程作用较弱;产业转型缓慢导致老城区仍主要为生产中心。     

A model of diffusion produced by a cellular surface flow

A model of diffusion induced by the joint action of random cells of two different sizes (granulation and supergranulation) is developed. The basic properties of the model are defined by the dimensionless ratio = (the life time)/(characteristic size/velocity) constructed for these two types of cells. An analytical expression for the diffusivity as a function of is derived. It is estimated that for the standard parameters used the contribution of granulation to the joint diffusion is small. A comparison between the model and numerical simulations of the kinematic diffusion of magnetic fields on the solar surface is made.