A palaeomagnetic and petromagnetic study of Upper-Carboniferous,Permian and Triassic sediments,NW Bulgaria

Summary In order to obtain basic palaeomagnetic data on Upper Carboniferous, Permian and Triassic sediments collected from the NW Bulgaria, laboratory stability tests were extended from A.C. and thermal treatments to studies of mineral phase changes and to investigations of changes of magnetic anisotropy during laboratory procedures. Laboratory criteria were found which permitted to distinguish samples suitable for palaeomagnetic analyses from those representing rocks totally or almost totally chemically reworked during their history. Palaeomagnetic directions and pole positions derived from Stephanian, Lower Permian and Triassic rocks from the southern margin of the Moesian Platform are compatible with the values obtained for the tectonically stable North-European Platform.     

Sur la couche absorbante élevée observée par glenn pendant le vol spatial mercury-atlas-6

Studia Geophysica et Geodaetica - Нафняодения высокого...     

Improved indirect phase reflection height measurements at Panská ves - first results

Summary Indirect phase reflection height measurements have been performed at the Panská Ves Observatory, Czechoslovakia, on two frequencies of 162 (earlier 164) and 153 kHz (earlier 155) for 30 years. However, they were used only for solar flare effect (SFA) monitoring. After introducing new measuring equipment in 1985, the quality of the 162 kHz records became sufficient to apply the indirect phase height analysis (IPHA) method in full. The method itself, the measuring equipment, and the method of evaluation are described in [1]. The purpose of this paper is to describe the first results and to verify the reliability of the 162 kHz IPHA data. The IPHA method as applied to the 162 kHz measurements made at Panská Ves, allows ionospheric and neutral atmospheric parameters to be studied simultaneously and appears to provide reliable and good quality data. The expected seasonal variation and response to sudden stratospheric warmings are observed. The use of the 162 kHz IPHA data in the international MAC/SINE and DYANA campaigns and for monitoring pressure variability at 80 km are briefly described.     

Spectrum of geomagnetic activity in the period range 5–60 days: possible lunar influences

The series of daily Ap-indices has been subdivided into pentades (1932–1936 etc.) and spectra with fine-frequency resolution have been calculated for the indices in each of these intervals. Daily sunspot numbers have been processed in the same way. The average spectrum from all spectra in the pentades, as well as the spectrum from the whole interval have been calculated, and significant peaks have been determined. There is a significant difference between the spectra in the pentades containing the solar activity minimum (1932–1936, 1942–1946 etc.) and those containing the solar activity maximum (1937–1941, 1947–1951 etc.). Most peaks can be interpreted as a response to solar rotation and to the structure of solar wind speed (two high-speed streams per solar rotation), both modulated by the 11-year, annual and semi-annual waves. No significant peak corresponding to the period of the synodic month, or its half has been found. This result suggests that the influence of lunar cycles on some natural phenomena (if any) is not mediated by geomagnetic activity.     

Available potential energy of the daily coastal circulation at Zadar (Croatia)

Summary The aim of this study is the evaluation of the sea breeze speed on the basis of its energy. Energetics of the sea breeze can be studied by means of the available potential energy (APE). Part of this energy is transformed into the kinetic energy of the sea breeze. Some similarity exists between the large scale processes of the circulation and the small coastal air circulation due to the fact that both circulations are triggered by the same physics, i.e., solenoidal activity of the baroclinic atmosphere. To evaluate the sea breeze speed, APE was calculated by use of the Lorenz’s equation (1955), and which is possible if the coastal circulation is considered to be a closed system in a hydrostatic equilibrium. For calculations and verifications hourly sea-surface temperatures, near-ground air temperatures and wind speed measurements, as well as the radio-sounding measurements at 12 UTC were used at the Zadar station (ϕ = 44° 08′ N, λ = 15° 13′ E), which is situated in the central part of the eastern Adriatic coast. Two days with an undisturbed sea breeze circulation were extracted using the methods for minimizing other atmospheric influences. Calculated hourly near ground sea breeze speeds obtained in this way were higher than the measured ones. With the assumption that some of the APE is transformed into the kinetic energy it is possible to obtain characteristic speed of the developed sea breeze with small discrepancies to the near-ground measurements. If 6.6% of the mean daily near ground APE was taken to be transformed to the mean daily kinetic sea breeze energy on the 29th and 4.2% on the 30th September 2002, the best agreement was obtained with the mean daily measured near ground sea breeze speed. This range of values can be attributed to inability to extract precise values for the lapse-rate needed in the APE sea breeze calculations. Results show similarities to the general circulation of the atmosphere, since about 10% of the APE is transformed to the kinetic energy of the sea breeze. On the other hand calculated wind speed at the lower branch of the borderline coastal circulation was not dependent on the integral value of the APE over the land, but on its value at the near-ground level.     

How a Sphagnum fuscum‐dominated bog changed into a calcareous fen: the unique Holocene history of a Slovak spring‐fed mire

In general, mires develop by autogenic succession from more groundwater‐fed to more rainwater‐fed. This study from a calcareous mire in the West Carpathians (Slovakia) describes a similar development in the Early Holocene, followed by a reverse development in the Middle and Late Holocene. Pollen, macrofossil and testate amoeba analyses show that the site started as a minerotrophic open fen woodland. After 10 700 cal a BP autogenic succession led to the accumulation of at least 1 m of Sphagnum fuscum peat. Around 9000 cal a BP, as climate could no longer sustain a stable water regime, the bog desiccated and a fire broke out. The fire removed part of the peat layer and as a consequence relative water levels rose, leading to the establishment of a wet minerotrophic swamp carr with Thelypteris palustris, Equisetum sp. and Alnus sp. with extremely slow peat accumulation. After 600 cal a BP, rapid peat accumulation with calcareous tufa formation resumed as a result of anthropogenic deforestation and hydrological changes in the catchment and resulting increased groundwater discharge. At present the mire still hosts a wealth of relict and endangered plant and animal species typical of calcareous fens and fen meadows. Copyright © 2011 John Wiley & Sons, Ltd.     

Bilateral recursive restitution of true ground motion from near-field and far-field seismograms

Summary A two-sided recursive inverse filtering procedure, originally proposed by R. Vích, is used to restore the true ground motion from digital records of inertial electromagnetic seismographs. Numerical simulations of far-field and near-field P-wave seismograms are used to test the performance of the procedure and to derive criteria for recognizing successful restorations. The procedure is applied to seismograms of local microearthquakes as well as of teleseismic events, and the restored signals are compared with those obtained by causal (one-sided) inverse filtering. In all cases the two-sided approach proved to have fundamental advantages: a higher accuracy of the approximation of the true ground motion, a faster convergence to the best attainable approximation, a lower sensitivity to incoherent noise, and a more reliable discrimination between veracious and dubious results.     

Rare earth elements and yttrium geochemistry of dolomite from post-Variscan vein-type mineralization of the Nízký Jeseník and Upper Silesian Basins, Czech Republic

Rare earth elements and yttrium geochemistry of dolomite from post-Variscan vein-type Zn–Pb–Cu mineralization was studied in the Nízký Jeseník and Upper Silesian Basins. Combined with crush–leach analyses of fluid inclusions, the study provided important information on fluid–rock interaction, physico-chemical and redox conditions during crystallization of the dolomite. The mineralization is hosted by Carboniferous siliciclastic rocks, representing Variscan flysch and molasse sedimentation. Dolomite samples contain highly variable contents of REE (between 18 and 295 ppm) and Y (between 17 and 95 ppm). REY patterns are divided into four different groups which differ in regional provenance, LREE vs. HREE enrichment/depletion and significance of Eu, Gd and Y anomalies. These patterns can be the result of 1) precipitation of dolomite from near neutral fluids with important concentrations of complexing ligands as a main factor for the REY partitioning, 2) interaction of migrating fluids with host or basement rocks, or, most probably, 3) a combination of both.Regarding the importance of complexing ligands, it is proposed that in all samples fluoride and chloride complexes prevailed over sulphate, bicarbonate and hydroxide complexes. Interaction of fluids with rocks was strongly affected by the fluid temperature. Dolomites which precipitated from fluids with homogenization temperature higher than 110 °C are mostly REY-enriched while fluids colder than 110 °C produced REY-depleted dolomite. The REY-enrichment may indicate higher effectiveness of leaching of REE-bearing minerals (probably monazite, allanite and biotite) at higher temperatures. The preferential loss of LREE can be caused by the recrystallization or remobilization of dolomite. Generally, an increase in salinity and contents of Cl and F in the fluids is mostly accompanied by a higher REY content in dolomite. Positive Eu anomalies and small negative Gd and Y anomalies are typical for most of the chondrite-normalized patterns. Positive Eu_CN anomalies in dolomites are most probably the result of an increase of Eh in the parent fluid. Distribution of Y is expected to be predominantly controlled by solution complexation.