Nachweis der allgemeinen Gültigkeit des Gefrierkernspektrums

Zusammenfassung Durch weitere experimentelle Untersuchungen wird festgestellt, dass das an destillierten Wassertropfen ermittelte Gefrierkernspektrum von speziellen Versuchsbedingungen unabhängig ist und auch für Wasserarten mit verschiedenen natürlichen oder künstlichen Verunreinigungen gilt. Es kann ausserdem in allen bisher im Laboratorium und in der Atmosphäre durchgeführten Untersuchungen über die Eiskeimbildung nachgewiesen werden. Dieser Befund stützt als notwendige Bedingung die Deutung des Gefrierkernspektrums durch Strukturänderungen des Wassers und besagt, dass im Laboratorium und in der Atmosphäre dieselben Gefrierkerne vorhanden sind und dass bei der atmosphärischen Eiskeimbildung auch nur die aus Untersuchungen im Laboratorium bekannten Besonderheiten des Gefrieveorgangs (im unterkühlten Wasser) vorliegen.

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Summary Further experimental investigations demonstrate the «Gefrierkernspektrum», which was found for droplets from destilled water, to be independent from special experimental conditions and valid for sorts of water containing natural or artificial impurities, too. Furthermore it can be pointed out from all existing investigations on ice-nucleation, made in laboratory and in the atmosphere. This result supports, as a necessary condition, the interpretation of the «Gefrierkernspektrum» by means of changes in the structure of water itself and proves, that there are the same freezing nuclei both in the laboratory and the fre atmosphere and that ice-nucleation in the atmosphere holds but the same peculiarities of freezing (of supercooled water), known from laboratory work.

     

Sea-level and reef accretion history of Marine Oxygen Isotope Stage 7 and late Stage 5 based on age and facies of submerged late Pleistocene reefs,Oahu, Hawaii

In situ Pleistocene reefs form a gently sloping nearshore terrace around the island of Oahu. TIMS Th–U ages of in situ corals indicate that most of the terrace is composed of reefal limestones correlating to Marine Oxygen Isotope Stage 7 (MIS 7, ~ 190–245 ka). The position of the in situ MIS 7 reef complex indicates that it formed during periods when local sea level was ~ 9 to 20 m below present sea level. Its extensiveness and geomorphic prominence as well as a paucity of emergent in situ MIS 7 reef-framework deposits on Oahu suggest that much of MIS 7 was characterized by regional sea levels below present. Later accretion along the seaward front of the terrace occurred during the latter part of MIS 5 (i.e., MIS 5a–5d, ~ 76–113 ka). The position of the late MIS 5 reefal limestones is consistent with formation during a period when local sea level was below present. The extensiveness of the submerged Pleistocene reefs around Oahu compared to the relative dearth of Holocene accretion is due to the fact that Pleistocene reefs had both more time and more accommodation space available for accretion than their Holocene counterparts.     

The Bayesian approach to an internally consistent thermodynamic database: theory, database, and generation of phase diagrams

An internally consistent thermodynamic dataset has been derived for 148 endmember phases (145 solids and 3 fluids) comprising the elements Li, Na, K, Be, Mg, Ca, Ti, Cr, Mn, Fe, Zn, Al, Si, C, H, and O. This has been achieved by simultaneous treatment of phase property (like standard enthalpy of formation, standard entropy, molar heat capacity, molar volume, thermal expansivity, bulk modulus etc.) and reaction reversal data by the Bayesian method. The theory underlying the approach, and the computational methods involved, are briefly outlined. (For the benefit of readers unfamiliar with inference statistics, the basic concepts of the Bayes method are also presented in such a way that they can be grasped intuitively.) Although not yet addressed, this method can be extended to refine the thermodynamic mixing properties of crystalline solutions. The sources of the input data, culled from the literature, are summarized in the Appendix. The resulting database is succinctly documented in this paper. It includes the enthalpies of formation and entropies, their uncertainties, and the correlation among them. The database allows calculation of P-T, T-X _CO2, P-X _CO2, and T-f _O2 sections, with error propagation into the computed phase diagrams on a routine basis. A user-friendly computer program has been written to generate such phase diagrams. It is public domain software. The software and the thermodynamic database (which includes a complete documentation of the thermodynamic data above and beyond those listed (Table 2, here) may be downloaded from the web site http://homepage.ruhr-uni-bochum.de/niranjan.chatterjee/Index.htm. Examples of computed phase diagrams are given to illustrate the quality of the data and the capabilities of the software. Received: 11 March 1998 / Accepted: 11 June 1998     

Zur Stratigraphie,Petrologie und Genese einer Bentonit-Lage aus dem oberen Mittel-Turon (Oberkreide) des südöstlichen Münsterlandes

Zusammenfassung Die Bentonit-Lage kann möglicherweise mit der Lage M₆₈ aus dem Turon von Lüneburg (Norddeutschland) korreliert werden. Identifiziert wurden vulkanische Glasfragmente, Quarz, Na-, K-Feldspat, Oligoklas, Biotit, Muskovit, Calcit, Schwerminerale (u. a. Olivin, Hornblende) und Tonminerale (Kaolinit, Illit, mixed-layer Illit/Smektit, FeBeidellit - z. T. in großen Aggregaten). Die vulkanoklastischen Gläser zeigen alle Übergänge von intakt zu völlig devitriert. Mit Hilfe der Elektronenstrahl-Mikrosonde konnten, bei Berücksichtigung der Kathoden-Lumineszenz, die Feldspäte chemisch analysiert und genetisch in solche mit niedrigerer und solche mit höherer (vulkanoklastisch) Bildungstemperatur gegliedert werden. Von den Schwermineralen dürften vor allem Olivin und Hornblende vulkanogener Herkunft sein. Untersuchungen der durch Umwandlung vulkanischen Materials entstandenen kompakten Smektit-Aggregate mittels Mikrosonde, Röntgendiffraktometrie und Mössbauer-Spektroskopie zeigten, daß es sich hier um ein AI-reiches Glied der Mischungsreihe Nontronit-Beidellit (Fe-reicher Beidellit) handelt. Differentialthermoanalytische Untersuchungen ergaben für Fe-reiche, dioktaedrische, smektitische Tonminerale typische Kurven. Das Ausgangsmaterial des Bentonits war intermediär bis basisch. Äolischer oder kombiniert äolischer und mariner Transport von Exhalationspunkten im mitteleuropäischen Raum werden diskutiert.

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The bentonite can probably be correlated with horizon M₆₈ in the Turonian of Lüneburg in northern Germany. Volcanic glass fragments, quartz, Na and K feldspars, oligoclase, biotite, muscovite, calcite, heavy minerals (i. a. olivine, hornblende) and clay minerals (kaolinite, illite, mixed-layer illite/smectite and Fe-beidellite) were identified. The glass shows a spectrum of all states from unaltered to completely devitrified. Analysis of feldspars by means of electron microprobe and cathodo-luminescence has allowed to divide them into genetically high (pyroclastic) and low temperature forms. Of the heavy minerals, olivine and hornblende most clearly are of volcanic origin. Examinations of smectite aggregates (alteration products of volcanic material) by electron microprobe, x-ray diffractometry, and Mössbauer spectroscopy demonstrated the presence of a member of the continuous series nontronite-beidellite (Fe-rich beidellite). Differential thermal analysis gave typical curves for dioctahedral Fe-rich smectites. The chemical composition of the original material of the bentonite was intermediate to basic. Eolian or eolian and marine current transport from sources in central Europe are considered.

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Résumé La couche de bentonite peut probablement être corrélée avec la couche M₆₈ du Turonien de Lunebourg (au nord de l'Allemagne). Des fragments de verre volcanique, du quartz, du feldspath sodique, du feldspath potassique, de l'oligoclase de la biotite, de la muscovite, de la calcite, des minéraux lourds (p. ex. olivine, hornblende) et des minéraux argileux (kaolinite, illite, mixed-layer illite/smectite, beidellite ferreux — en partie en grands agrégates) ont été identifiés. Les verres pyroclastiques montrent tous les passages du verre intact jusqu'au verre entièrement dévitrifié. A l'aide de la microsonde électronique et en prenant en considération la cathodoluminescence, les feldspaths pouvaient être analysés chimiquement et ordonnés génétiquement selon leur température de formation. Ceux à haute temperature de formation sont pyroclastiques. Parmi les minéraux lourds pouvaient avant tout être d'origine volcanogène, l'olivine et la hornblende. Les études des agrégats de smectites compacts formés par la transformation de matériaux volcaniques montrent grâce à la microsonde, la diffractométrie X et de la spectrométrie de Mössbauer qu'il s'agit dans ce cas là d'un membre riche en Al de la série des mélanges nontronite-beidellite (beidellite ferreux). Des analyses thermiques différentielles donnèrent des courbes typiques pour les minéraux argileux smectitiques, dioctaédriques et riches en Fe. La matière de base de la bentonite était intermédiaire à basique. Transport éolien ou transport combiné, éolien et marin des points d'exhalation dans l'espace européen central seront dicutés.

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“Transgenic treadmill”: Responses to the emergence and spread of glyphosate-resistant johnsongrass in Argentina

The broad-spectrum herbicide glyphosate has become the largest-selling crop-protection product worldwide. The increased use of glyphosate is associated with the appearance of a growing number of tolerant or resistant weeds, with socio-environmental consequences apart from the loss of productivity. In 2002, a glyphosate-resistant biotype of johnsongrass (Sorghum halepense (L.)) appeared in Argentina and now covers at least 10,000 ha. This paper analyzes the driving forces behind the emergence and spread of this weed and also examines management responses and their implications.Preventive strategies against glyphosate-resistant johnsongrass fail because of the institutional setting. Reactive measures, however, transfer the risks to the society and the environment through the introduction of novel genetically modified crops that allow the use of yet more herbicide. This in turn reinforces the emergence of herbicide-resistant weeds, constituting a new phenomenon of intensification, the “transgenic treadmill”.     

40Ar/39Ar Thermochronology west of the Main Uralian fault, southern Urals, Russia

West of the Main Uralian fault, the main suture in the southern Urals, ⁴⁰Ar/³⁹Ar apparent ages of amphibole, muscovite and potassium feldspar are interpreted as cooling ages. A fast exhumation of the metamorphic complex of Kurtinsky during Upper Carboniferous time is indicated by the small age difference (15 Ma) between cogenetic amphibole and muscovite. Differentiated movement in the footwall of the Main Uralian fault along strike is indicated by the age difference of 70 Ma between the metamorphic complexes of Kurtinsky (north) and Maksyutov (south). No Upper Paleozoic (Uralian) medium- to high-temperature event is recorded in ⁴⁰Ar/³⁹Ar data from the metamorphic complex of Beloretzk (MCB). An amphibole age of 718±5 Ma and the occurrence of mafic intrusions might signal the break-up of Rodinia and therefore indicate the rifting period followed by the separate movement of the "Beloretzk terrane". Muscovite ages of approximately 550±5 Ma, the unique pre-Ordovician tectonometamorphic evolution of the MCB and the Late Vendian sedimentary history of the western Bashkirian Megaanticlinorium (BMA) imply the existence of a Neoproterozoic orogeny at the eastern margin of Baltica. This orogeny might have been initiated by the accretion of the "Beloretzk terrane". The metamorphic grade of the overlain Silurian shales and the K/Ar microcline ages from the "Beloretzk terrane" give evidence for a new thermal event at approximately 370 Ma. A microcline age of 530–550 Ma obtained for the Vendian conglomerate in the western BMA suggests that a maximum temperature of approximately 200°C was reached in Cambrian or Vendian times. An orthoclase age (590–630 Ma) of the Vendian Zigan flysch deposits might be inherited from the eastern source area, the Cadomian orogen. An orthoclase age (910–950 Ma) from the Riphean Zilmerdak conglomerate coincides with a documented decrease in the subsidence rate of the Upper Riphean basin.     

Chemical structural units of macromolecular coal components

Chemical degradations of coal resins, coal asphaltenes and coal residues have been performed with selective, non-oxidative reagents. The coal comprise samples a rank interval 0.30–1.21 %R_m. Degraded low-molecular-weight compounds were analyzed by GC-MS. The distributions of pentacyclic terpanes, isoprenoids, n-alkanes, acids and alcohols obtained as degradation products illustrate a considerable variability between the macromolecular coal fractions. A structural study on the molecular level of the degraded compounds from coal resins and coal asphaltenes show their potential to generate hydrocarbons during coalification process.     

Biogeochemistry of Mono Lake,California

Modern sediments of Mono Lake show marked variation in lipid composition with depositional environment. Constituents derived from the drainage basin, characterized by high molecular weight alkane hydrocarbons (C₂₅–C₃₁), and the steroids β-sitosterol and brassicasterol, predominate in near-shore environments. In the deepest part of the lake, sediments exhibit a combination of externally-derived constituents, and lipids derived from the lake biota; the latter characterized by low molecular-weight alkanes and alkenes (C₁₅–C₁₇), phytane, and the steroids ergost-7-en-3β-ol and 24-ethylcholest-7-en-3-β-ol. Steranes, 4-methylsteranes, and the C₁₈ and C₁₉ isoprenoids appear to be forming in the intensely reducing bottom sediments at the present time.The compositions of samples from the Pleistocene succession of Mono Basin suggest that sample-to-sample variation within the same stratum is negligible so long as unweathered samples from the same depositional environment are compared. Sediments having equivalent lithologies may or may not have similar compositions, but sediments having similar fossil contents do show similar lipid compositions. Subaerial weathering of sediments causes a marked decrease in the amount of extractable organic material, as well as distinct changes in its hydrocarbon composition. Specifically, weathered sediments exhibit a decrease in relative content of low molecular weight hydrocarbons and a relative increase in nC₂₂.Organic composition of sediments from the Pleistocene stratigraphie column cannot be correlated with depth of burial. Compositional changes with stratigraphie position are probably related to paleo-ecological factors such as population or productivity rather than depth of burial. Lithology and organic composition provide mutually-corroborating evidence regarding glacial advances in the adjacent Sierra Nevada Mountains. During glaciations, the lake sediments are rich in sandstones, and the organic composition shows a predominance of externally-derived debris, with no evidence for contributions from the lake biota.     

Zu den Kondensationskernverhältnissen von Wien

Zusammenfassung Nach allgemeinen und quantitativen Angaben über die Ursachen der Zu-und Abnahmen der Kondensationskerndichte wird auf die natürliche und industrielle Kernproduktion verwiesen. Auf Grund einjähriger Morgen- und Mittagsbeobachtungen in Wien mit einem Pollak-Kondensationskernzähler wird besonders die Sedimentation, der Washout- und Rainouteffekt, der Einfluss von Austausch und Windadvektion sowie der Jahres- und Wochengang besprochen.

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Summary General as well as quantitative details of reasons of the variations of the density of condensation nuclei is mentioned. Based on one year's records of observations in the morning and at noon in Vienna, executed by menas of a Pollak-condensation nucleus counter especially the effects of sedimentation, washout, rainout, exchange, wind advection, annual and weekly variation is discussed.