A multivariate statistical and geostatistical study on the geochemistry of allochtonous karst bauxite deposits in Hungary

A geochemical evaluation of the Szc-Halimba-Kisld area, Hungary, covering an area of more than 200 km² is presented using different statistical and geostatistical methods. The study area is a representative example of allochtonous karst bauxite accumulation. The three groups of deposits studied here have been explored and mined since 1950. Several thousand boreholes have been drilled, and bauxite cores were analyzed for the five main chemical components. A total of 80,000 pleces of analytical data were processed, followed by a geological examination of borehole logs and of mining excavations.The quantitative geochemical evaluation of the data set led to both geochemical and practical results: The geochemical behavior of the allochtonous, clastic karst bauxite deposits differs essentially from that of the autochtonous and parautochtonous ones, as well as that of the lateritic bauxite deposits. The deposits of the study area can be split into several subsequent geochemical-sedimentological units, each representing an event of bauxite transport and accumulation. Clear regional patterns can be revealed in the composition of these units. The geostatistically measured chemical variability of the geochemical units is rather different, the lowest units showing the smallest variability. The interrelations of the main chemical components are weaker and more irregular in the studied deposits than in the autochtonous lateritic bauxite deposits. Additional local genetic features, such as transport routes, can be delineated by the methods applied. Within each deposit, local changes of chemical composition and of its variability can be determined more precisely. These results can be used in bauxite prospecting and exploration, because areas of high or low bauxite quality can be predicted.     

VHF double-peaked spectra at negative Doppler shifts in the morning sector of radio aurora

This paper presents a new Doppler spectral type of VHP (42 MHz) radio auroral backscatter. This spectrum, which has a double-peaked structure, was observed repeatedly during the morning sector of an exceptionally strong event (A_p = 48) and is due to irregularities moving northwards with quite different velocities. The stronger spectral component, which has a smaller Doppler shift, is centred in frequency at ～?130 Hz, corresponding to the ion-acoustic velocity range in the medium; the weak component, which has a greater frequency shift, usually is centred at about ?300 Hz (～ 1050 m s^?1). Evidence based on spectral analysis of sequential short time sequences shows that the spectral power alternates in time between the two distinct frequency bands where the peaks are located, suggesting that the double-peaked spectrum may result from two competing processes which cannot operate simultaneously. The possibility exists that the theoretical model proposed by Sato (1977), which predicts two different quasi-linear stabilization mechanisms for the two-stream instability, could explain the observed double-peaked spectral type.     

Telescopic investigation of relative spectral reflectivity of mare grounds of lunar surface

A study of the variation of the spectral relative ratios of reflectivity of selected mare lunar grounds between wavelengths 4000 and 8000 Å is given in comparison with lunar craters. The intensities at different wavelengths of each lunar region are corrected for the angles of illumination and viewing, and they are scaled to unity at =5538Å. Distinct variety in the spectral reflectivity values of mare grounds at short wavelengths are confirmed. The Mare Tranquillitatis type grounds (similar to Apollo-11 site), have relative ratio of reflectivity at short wavelength at =4035 Å; larger than or equal to 1.03 in addition to a bigger difference in reflectivity between the short and the long wavelength. The Mare Serenitatis type grounds (similar to Apollo-12) are characterized to give relative ratio of reflectivity less than 1.03 at =4035 Å, and smaller difference in reflectivity between short and long wavelengths. This is due to the variation in the colour of the Mare Tranquillitatis and Mare Serenitatis type ground due to compositional differences. The mare type grounds are generally different in shape than that of lunar craters grounds.Presented at the IAU-COSPAR Julian Schmidt Symposium on 100 Years of Lunar Mapping held at Lagonissi, Greece, 25–27 May, 1978.     

On the astrometric detection of neighboring planetary systems,II

Extensive testing suggests that astrometric techniques can be employed to detect and study virtually any planetary system that may exist within 40 light years (12.5 parsec) of the Sun. Following the conclusion of Paper I [G. Gatewood, Icarus27 (1976), 1–12], the astrometric group at the Allegheny Observatory began an intensive survey of 20 nearby stars to detect the nonlinear variations in their motion that planetary systems would induce. Several tests conducted to further our understanding of the limitations of this survey indicated that the photographic detector itself is responsible for the majority of the random error. A new photoelectric detector has been designed and a simplified prototype of it successfully tested. The new detector is expected to be able to utilize virtually all of the astrometric information transmitted through the Earth's atmosphere. This is sufficient to determine relative positions to within an accuracy of approximately 1 milliarcsec/hr. Such precisions exceed the design capabilities of the best existing astrometric telescopes, thus a feasibility study has been conducted for the design of an improved instrument. The study concludes that a new ground-based telescope and the new detector combined should be able to study stars as faint as the 17th magnitude with an annual accuracy of a few tenths of a milliarcsecond. However, to obtain the ultimate accuracy possible from current technology, we must place an astrometric system above the Earth's atmosphere. A space-borne instrument utilizing the new detector would in theory have sufficient accuracy to detect any Earth-like planet orbiting any of the several hundred stars nearest the Sun.     

Exospheric perturbations by radiation pressure: II. Solution for orbits in the ecliptic plane

An earlier paper gave solutions for the mean time rates of change of orbital elements of satellite atoms in an exosphere influenced by solar radiation pressure. Each element was assumet to beahve independently. Here the instantaneous rates of change for three elements $\text{(e, ω,}\text{and}\text{θ = ω + Ω)}$ are integrated simultaneously for the case of the inclination i = 0. The results (a) confirm the validity of using mean rates when the orbits are tightly bound to the planet and (b) serve as examples to be reproduced by the complicated numerical solutions required for arbitrary inclination. Strongly bound hydrogen atoms perturbed in Earth orbit by radiation pressure do not seem a likely cause of the geotail extending in the anti-Sun direction. Instead, radiation pressure wil cause those particles' orbits to form a broad fan-shaped tail and to deteriorate into the Earth's atmosphere. Whether loosely bound H atoms are plentiful enough to create the geotail depends on their source function versusr; that question is beyond the scope of this paper.     

Lyman-alpha observations of Comet West (1975n)

Images of Comet West in atomic hydrogen (1216 Å) emission were obtained from a sounding rocket on 1976 March 5.5 (R = 0.38 AU). The hydrogen production rate derived from the fit of a simple radial-outflow model to the observed inner isophotes was 3.2 × 10³⁰ atoms/sec. The outer isophotes did not fit the predictions of the complex dynamic model of Keller and Meier, partly because of optical depth effects, but also because the nucleus was breaking up at about this time and it is quite possible that additional hydrogen was being emitted from smaller chunks of the nucleus distributed along the orbit. The above production rate, taken with data on C and O obtained simultaneously by Feldman and Brune, gives Q_H: Q_o: Q_c = 8:3.5:1. For Comet Kohoutek we obtained the ratio 7:1.7:1. The difference, if real, may be due to minor differences in composition or evolution, but in any case it appears that the two comets are similar.     

Complex refractive index of Martian dust: Wavelength dependence and composition

Mariner 9 ultraviolet spectra of the 1971 dust clouds were analyzed to obtain the phase function times single scattering albedo of the dust particles. The phase functions were matched with Mie scattering calculations for size distributions of spheres of homogeneous and isotropic material. The absorption index of the dust particles was found to increase with decreasing wavelenght from 350 nm down to about 210 nm, and drop off shortward of this wavelength. A structural shoulder occurs in the absorption spectrum between 240 and 250 nm. Titanium dioxide (anatase) has the correct transitions at 210 and 250 nm to match the absorption curve of Martian dust, and is proposed as a candidate constituent in Martian surface material. The spectral neutrality of TiO₂ between 0.5 and 4 μm is consistent with visible and infrared observations of Mars. The high refractive index of TiO₂ can explain the large refringence of Martian dust. The titanium dioxide content of the dust particles is estimated to be a few percent or less. Uncertainties in the results due to limitations in the model and data are discussed.     

Boundary-layer parameterizations for applied dispersion modeling over urban areas

Many applied dispersion models require the knowledge of boundary-layer parameters such as sensible heat flux,Q _H , friction velocity,u _*, and turbulent energy components, _w and _v . Formulas are suggested for calculating these parameters over a wide variety of types of ground surfaces, based on simple observations of wind speed near the ground and fractional cloud cover, and specification of constants such as roughness length, albedo, and soil moisture availability. Observations ofu _*,Q _H , _w , and _v during field experiments in St. Louis and Indianapolis are used to test the formulas for urban sites. Relative errors of about ±20% in the predictions are seen to occur whenu _*,Q _H , _w , and _v are large. However, when these quantities are small (e.g.,u _* < 0.2 m/s), the errors in the predictions are as large as the mean value of the quantity itself.In addition, it is concluded from studies of available field data and theories that the magnitude of _w is not well-known at elevations above about 100m during the late afternoon and night. Some simple parameterizations for _w . are suggested that are consistent with the observed steady decrease in ground-level concentration in the afternoon and the sudden increase in concentration that can occur a few hours after sunset due to wind shears associated with a low-level jet, for continuous plumes emitted from moderate to tall stacks.     

Fossil-pollen evidence for abrupt climate changes during the past 18 000 years in eastern North America

A quantitative measure of the rate at which fossil-pollen abundances changed over the last 18 000 years at 18 sites spread across eastern North America distinguishes local from regionally synchronous changes. Abrupt regional changes occurred at most sites in late-glacial time (at 13700, 12 300, and 10000 radiocarbon yr BP) and during the last 1000 years. The record of abrupt late-glacial vegetation changes in eastern North America correlates well with abrupt global changes in ice-sheet volume, mountain snow-lines, North Atlantic deep-water production, atmospheric CO₂, and atmospheric dust, although the palynological signal varies from site to site. Changes in vegetation during most of the Holocene, although locally significant, were not regionally synchronous. The analysis reveals non-alpine evidence for Neoglacial/Little Ice Age climate change during the last 1000 years, which was the only time during the Holocene when climate change was of sufficient magnitude to cause a synchronous vegetational response throughout the subcontinent. During the two millennia preceding this widespread synchronous change, the rate of change at all sites was low and the average rate of change was the lowest of the Holocene.Contribution to Clima Locarno Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate Program     

Chemical study of tectonically controlled hydrothermal dolomitization: an example from the Lessini mountains,Italy

In the Central Southern Alps (Feltre, Verona — Italy), a 750 m thick interval of Jurassic and Cretaceous pelagic limestones shows post-depositional partial brecciation and dolomitization. The overlying 500 m thick Tertiary sedimentary sequence is unaffected. Through the Paleogene, mostly submarine, mafic volcanism has been documented in the area. Small-scale extensional features were observed in the limestone near the contact with the dolomitized breccias. Their orientations measured in the field correspond to the tectonic framework of the area and give evidence for the contemporaneousness of the volcanic activity and the brecciation. The distribution and petrologic characteristics of the basalts, combined with the orientation of the extensional features observed in the field, allow a paleotectonic reconstruction. This tectonic scenario can be viewed as a back-arc extension, an eastward prolongation of the spreading that divided Southern France from the Sardinia-Corsica-Calabria block, generating the Ligurian-balearic basin in the Late Oligocene.The dolomite is fine-grained to sucrosic, with a microamygdaloidal porosity, partially filled with ankerite and calcite. The matrix shows a homogeneous, orange-red cathodoluminescence, indicating a single phase of iron-poor dolomite. The carbonate fraction consists of more than 90% dolomite. The dolomite is almost stoichiometric (Ca_0.6Mg_0.4 to Ca_0.5Mg_0.5). The ¹³C values of the dolomite are less than 1%. more negative than the unaffected limestone. The ¹⁸O values are between –5%. to –13%., with a depletion of 2–11%. relative to the undolomitized limestone. The depleted oxygen isotope ratios in the dolomitized rock can be derived either from fluids impoverished in the heavy isotopes (e.g. meteoric water) or high temperatures. The unvaried carbon isotopic ratios make the second interpretation the most acceptable. As the⁸⁷Sr/⁸⁶Sr values increase from a mean of 0.7077 in the unaffected limestones to 0.7085 in the dolomitized limestones, a derivation of the dolomitizing fluids from the volcanic rocks can be excluded. Comparing the obtained data with the Phanerozoic seawater isotope curve, however, the radiogenic Sr may be derived from marine waters of Late Oligocene-Early Miocene age. Microthermometric analyses of the fluid inclusions in the dolomite crystals from the bulk rocks and from the veins suggest a trapping temperature ranging from a minimum of 70°C (dolomite rock) to a maximum of 120°C (dolomite in veins). The solution contained in the inclusions is water with NaCl and MgCl₂ with salinities of 46%. (dolomite bulk rock) and 17%. (dolomite in veins). The pressure correction calculated from the fluid inclusion data is about 250 bars, which roughly correspond to the lithostatic pressure over the Mesozoic limestones in the Early Miocene.These results point to a hydrothermal origin of the dolomitization during the Late Oligocene-Early Miocene, as ascertained from the strontium isotope and fluid inclusion data. The circulation of hot marine water through the brecciated limestones in convective cells, triggered by the geothermal gradient related to the volcanic activity, is the proposed hydrodynamic model. Hydrologie considerations demonstrate that the proposed model is feasible.

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Zusammenfassung In den zentralen Südalpen (Feltre, Verona — Italien) findet sich eine etwa 750 m dicke Abfolge jurassischer und kretazischer pelagischer Kalke, die nach der Ablagerung zum Teil breckziert und dolomitisiert wurde, während die darüberliegenden 500 m mächtigen tertiären Sedimente keine Dolomitisierung zeigen. Im Paläogen ist im Gebiet ein mafischer, überwiegend mariner Vulkanismus dokumentiert. Kleinmaßstäbliche listrische Brüche in Kalken am Kontakt mit der dolomitisierten Breckzie entsprechen geometrisch einem großräumigen extensiven Regime im Paläogen. Sie beweisen die Gleichzeitigkeit der vulkanischen Aktivität und der Breckzierung. Die Verteilung und petrographischen Eigenschaften der Basalte, mit der Geometrie der Extensionsstrukturen, erlauben eine paläotektonische Rekonstruktion. Diese tektonische Situation entspricht einem Back-arc-basin und stellt die östliche Verlängerung des ligurisch-balearischen Beckens dar, das Südfrankreich vom Sardisch-Korsisch-Kalabrischen-Block im späten Oligozän getrennt hat.Die ¹³C Werte der Dolomite sind weniger als 1%. negativer als die entsprechender nicht dolomitisierter Kalke. Die ¹⁸O-Werte (relativ zum PDB Standard) variieren zwischen –5%. und –13%., das ist 2 bis 11%. negativer als die nicht dolomitisierter Kalke. Dies wird auf erhöhte Bildungstemperaturen zurückgeführt. Ein Anstieg der⁸⁷Sr/⁸⁶Sr-Signaturen im Mittel von 0.7077 in den nicht dolomitisierten Kalken auf 0.7085 in den dolomitisierten Kalken schließt eine Herkunft der dolomitisierenden Fluide von den vulkanischen Gesteinen aus. Beim Vergleich der Isotopensignaturen mit der phanerozoischen Meerwasser-Isotopenkurve, könnte aber das radiogene Strontium von spät oligozänem — früh miozänem Meerwasser kommen. Mikrothermometrische Analysen flüssiger Einschlüsse in Dolomitkristallen im Gestein und in Adern deutet auf eine Einschlußtemperatur von 70°C (Dolomitgestein) bzw. 120°C (Dolomit in Adern) hin. Die Lösung in den Einschlüssen ist Wasser mit NaCl und MgCl₂, mit einer Salinität von 46%. (Dolomitgestein) bzw. 17%. (Adern). Die aus den Einschlüssen berechnete Druckkorrektur ist etwa 250 bar. Dies entspricht ungefähr der früh miozänen Gesteinssäule über den mesozoischen Kalken.Aufgrund dieser Daten wird eine hydrothermale Bildung der Dolomite im späten Oligozän - frühen Miozän postuliert. Es wird ein hydrodynamisches Modell vorgeschlagen, in dem aufgeheiztes Meerwasser konvektiv durch die breckzierte mesozoische Abfolge zirkuliert. Als Motor wirkt ein vulkanischer geothermischer Gradient. Dieses Modell läßt sich mit hydrologischen Betrachtungen testen und stützen.

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Résumé Dans la partie sud des Alpes Centrales (Feltre, Verone: Italie) il existe une succession, épaisse de 750 m, de calcaires pélagiques jurassiques et crétacés, qui ont subi après leur sédimentation une bréchification et une dolomitisation partielles. Les sédiments tertiaires surincombants, épais de 500 m, ne sont pas affectés par ces phénomènes. Un volcanisme paléogène mafique, essentiellement sousmarin, a été reconnu dans la région. Dans les calcaires, au contact de la brèche dolomitisée, existent des cassures listriques de petite échelle dont la géométrie témoigne d'un régime extensif général au Paléogène. Leurs orientations, mesurées sur le terrain, indiquent la contemporanéité de l'activité volcanique et de la bréchification. La distribution et les caractères pétrologiques des basaltes, combinés à la géometrie des structures extensives, permet une reconstitution paléotectonique. Celle-ci montre une extension dans un bassin d'arrière-arc, prolongement oriental de l'expansion qui, à l'Oligocène supérieur, a séparé du sud de la France le bloc corsico-sardo-calabrais en créant le bassin liguro-baléare.La dolomie, finement grenue à saccharoïde, possède une porosité à vides micro-amygdaloïdes, partiellement occupés par de l'ankérite et de la calcite. La matrice présente une cathodoluminescence homogène rouge-orange, indiquant la présence d'une seule phase constituée de dolomite pauvre en Fe. La fraction carbonatée consiste en dolomite pour plus de 90%. Cette dolomite est à peu près stoechiométrique (Ca_0,6Mg_0,4 à Ca_0,5Mg_0,5). Les rapports ¹³C de la dolomie sont inférieurs de moins de 1%. à ceux du calcaire intact. Les rapports ¹⁸O sont compris entre –5%. et –13%., soit 2 à 11%. inférieurs à ceux du calcaire non dolomitisé. Cette baisse du rapport isotopique peut provenir soit de fluides appauvris en isotopes lourds (p. ex. l'eau météorique), soit d'une température élevée; la constance des rapports isotopiques du C rend cette deuxième explication la plus plausible. Le rapport⁸⁷Sr/⁸⁶Sr passe d'une valeur moyenne de 0,7077 dans les calcaires non affectés à 0,7085 dans les calcaires dolomitisés; cet accroissement exclut une origine volcanique pour les fluides dolomitisants. En comparant ces valeurs à la courbe isotopique du Sr de l'eau de mer au Phanérozoïque, on peut déduire que le Sr radiogénique est dérivé d'eaux marines d'âge oligocène tardif à miocène inférieur. L'analyse microthermométrique des inclusions fluides contenues dans les cristaux de dolomite suggère une température de formation qui va de 70°C (dans la roche) à 120° (dans les veines). Le contenu de ces inclusions est une solution aqueuse de NaCl et MgCl₂ avec une salinité de 44%. (dans la roche) et de 17%. (dans les veines). La correction de pression calculée à partir des inclusions fluides est d'environ 250 bars, ce qui correspond grosso modo à la pression lithostatique qui s'exerçait au Miocène inférieur sur les calcaires mésozoïques.Sur la base de ces données, on conclut à une origine hydrothermale de la dolomie au cours de l'Oligocène supérieur - Miocène inférieur. Le modèle hydrodynamique proposé fait appel à la circulation convective, à travers le calcaire bréchié, d'eau marine échauffée grâce au gradient géothermique élevé dû à l'activité volcanique. Ce modèle est en accord avec des considérations hydrologiques.

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