Basin modelling of a lignite‐bearing salt rim syncline: insights into rim syncline evolution and salt diapirism in NW Germany

The Helmstedt‐Staßfurt salt wall is 70 km long, 6–8 km wide and one of the most important diapiric structures in northern Germany, based on the economically significant lignite‐bearing rim synclines. The analysed Schöningen rim syncline, located on the southwestern side of the Helmstedt‐Staßfurt structure, is 8 km long and 3 km wide. The basin‐fill is up to 366 m thick and characterized by 13 major lignite seams with thicknesses between 0.1 and 30 m. The key objectives of this article were to expand on the classical cross‐section based rim syncline analysis by the use of 3D models and basin simulations. Cross‐sections perpendicular to the basin axis indicate that the basin‐fill has a pronounced lenticular shape. This shape varies from more symmetric in the NW to clearly asymmetric in the SE. Isopach maps imply a two‐fold depocentre evolution. The depocentre migrated over time towards the salt wall and also showed some distinct shifts parallel to the salt wall. The basin modelling part of the study was carried out with the software PetroMod^®, which focused on the burial history of the rim syncline. Modelling results also show the progressive migration of the rim syncline depocentre towards the salt wall. The present‐day asymmetry of the basin‐fill was already developed in the early phases of rim syncline evolution. The extracted geohistory curve shows initial rapid subsidence between 57 and 50 Ma and more moderate subsidence from 50 to 34 Ma. This pattern is interpreted to reflect salt evacuation from the source layer into the salt wall. The initial salt‐withdrawal rate was rapid, but later decreased probably due to depletion of the source layer.     

Tropical cyclone hazard assessment using model-based track simulation

A method is introduced for assessing the probabilities and intensities of tropical cyclones at landfall and applied to data from the North Atlantic. First, a recently developed model for the basin-wide Monte-Carlo simulation of tropical cyclone tracks is enhanced and transferred to the North Atlantic basin. Subsequently, a large number of synthetic tracks is generated by means of an implementation of this model. This synthetic data is far more comprehensive than the available historical data, while exhibiting the same basic characteristics. It, thus, creates a more sound basis for assessing landfall probabilities than previously available, especially in areas with a low historical landfall frequency.     

Carbon isotope analyses of n-alkanes in dust from the lower atmosphere over the central eastern Atlantic

Atmospheric dust samples collected along a transect off the West African coast have been investigated for their lipid content and compound-specific stable carbon isotope compositions. The saturated hydrocarbon fractions of the organic solvent extracts consist mainly of long-chain n-alkanes derived from epicuticular wax coatings of terrestrial plants. Backward trajectories for each sampling day and location were calculated using a global atmospheric circulation model. The main atmospheric transport took place in the low-level trade-wind layer, except in the southern region, where long-range transport in the mid-troposphere occurred. Changes in the chain length distributions of the n-alkane homologous series are probably related to aridity, rather than temperature or vegetation type. The carbon preference of the leaf-wax n-alkanes shows significant variation, attributed to a variable contribution of fossil fuel- or marine-derived lipids. The effect of this nonwax contribution on the δ¹³C values of the two dominant n-alkanes in the aerosols, n-C₂₉ and n-C₃₁ alkane, is, however, insignificant. Their δ¹³C values were translated into a percentage of C₄ vs. C₃ plant type contribution, using a two-component mixing equation with isotopic end-member values from the literature. The data indicate that only regions with a predominant C₄ type vegetation, i.e. the Sahara, the Sahel, and Gabon, supply C₄ plant-derived lipids to dust organic matter. The stable carbon isotopic compositions of leaf-wax lipids in aerosols mainly reflect the modern vegetation type along their transport pathway. Wind abrasion of wax particles from leaf surfaces, enhanced by a sandblasting effect, is most probably the dominant process of terrigenous lipid contribution to aerosols.     

Zur geoelektrischen Untersuchung der Zementverpressungen von Staumauern und Staudämmen

Zusammenfassung a) Es werden die Ergebnisse eines Messverfahrens besprochen, dessen Aufgabe die überprüfung des Injektionserfolges ist. -b) Das Verfahren wurde an verschiedenen Baustellen bei sehr verschiedenen Bodenverhältnissen eingesetzt. Die Ergebnisse werden mitgeteilt. Es war in vielen Fällen möglich, die durch elektrische Messungen begründete Vorhersage mit den mechanisch gewonnenen Befunden zu vergleichen. Auch diese Ergebnisse werden mitgeteilt. -c) Im Zuge dieser Untersuchungen wurde die elektrische Mischtheorie experimentell untersucht und ein geoelektrisches Verfahren zur Bestimmung desK-Wertes entwickelt. -d) Die richtige Verbindung der elektrischen und mechanischen Messverfahren ermöglicht ein weit genaueres Studium des Injektionsvorganges und eine viel richtigere Beurteilung des Injektionserfolges als die bisher übliche blosse Wasserverpressung.

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Summary The results of a geoelectrical method of measurement for controlling cement injections are discussed. This method was practised already at several building-sites e. g. at building-sites in the bare and rocky Alpine region (Carso) of Yugoslavia. By means of this geoelectrical method the volumetric distribution of the injection mass can be controlled and therefore also the quantity discharged from the injection volume. In many cases the results obtained by geoelectrical measurements were later mechanically controlled. These results show the usefulness of this method. By means of this geoelectrical method more precise results may be obtained than by water pressure which method was used exclusively before. In this paper the fundamentals of this method and the geoelectrical mixture theory are discussed. Then the results obtained at the building-sites of Kaprun (Austria) and of Lokvarka and Cetina (Yugoslavia) are compared.

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Nach Referaten auf der Vierten Allgem. Tagung derSocietà Italiana di Geofisica e Meteorologia in Genova (5.–8. April 1956).

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Der Verfasser dankt allen, die ihm bei der Durchführung der Untersuchungen geholfen haben und insbesondere seinen Mitarbeitern. Besonderen Dank spricht er den Herren der Tauernkraftwerke A. G. und Geofizika in Zagreb aus.     

Einige Probleme der geoelektrischen Bodenverfestigung

Zusammenfassung 1. Eine Verfestigung über die «kritische Zeit» hinaus ist unwirtschaftlich. Daher sollten Elektroden verwendet werden, bei deren Anwendung die kritische Zeit sehr gross ist, oder die leicht verlegt werden können, wenn die kritische Zeit abgelaufen ist. Bei Stabelektroden geschieht dies durch Umstecken. Man kann aber auch Rollenelektroden verwenden, die über das zu verfestigende Volumen hinwegrollen. Dies ist allerdings nur dann zulässig, wenn nur eine ziemlich schwache Oberflächenschichte zu verfestigen ist. — 2. Um die günstigste Verfestigungsleistung zu erreichen, muss die Elektrodenspannung und der Elektrodenstrom den bodenphysikalischen Bestimmungsstücken richtig angepasst werden. — 3. Die geoelektrische Entwässerung ist nur dann anwendbar, wenn der Boden einen Mindestwassergehalt hat. Dieser ist durch die Kornverteilungskurve bestimmt. — 4. Durch die geoelektrische Behandlung des Bodens wird das Verhältnis zwischen Raumgewicht und Wassergehalt verändert und daher die Verfestigungskurve verformt.

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Summary In this article some geoelectrical problems of soil consolidation are discussed. The principal part of the electrical power is effective only near the electrodes. The resistance in this zone rises quickly during the course of time. After a «critical time» it becomes so high that no further consolidation of soil can be achieved. This time depends on the number, form and configuration of the electrodes. Rollings and plates are preferable to sticks. The voltage of electrodes has to be adapted to the specific resistivity of soil. The content of water of the soil can be reduced by electric means only if it surmounts a certain lowest value. By this geoelectrical consolidation the moisture-density relationship (Proctor-diagram) is deformed.

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Nach einem Vortrag auf der 2. Tagung der «Società Italiana di Geofisica e Meteorologia» in Genova, 23–25 April 1954.     

Discussion of the formation of major positive and negative ions up to the 50 km level

Summary An attempt has been made to predict the nature of positive and negative ions up to a level of 50 km. Considerable progress has been made in recent years in the understanding of the mechanism of formation of small ions at ground levels and the altitude profile of ions presented here for the first time will rely on this previous work. It should be understood that this discussion as related to negative ions is tentative due to the fact that many more rate constants are needed to provide a quantitative answer.It is also attempted to postulate the existence of condensation embryos formed by gas-to-particle conversion induced by radiation and chemical reaction throughout the atmosphere. As is known at the present time, this gas-to-particle conversion takes place in the troposphere and is also responsible for the so-called Junge layer at around 20 km. However, we have reason to believe that the formation of condensation embryos must take place to some degree at any altitude being considered here.     

Negative ions in air-like gas mixtures

Summary The nature of negative ions in an air-like gas mixture containing 300 ppm²) of carbon dioxide and 1 ppm of water has been investigated using a drift tube working at atmospheric pressure and interfaced with a quadrupole mass spectrometer. It was found that the most dominant ion under equilibrium conditions is CO₄–·(H₂O).

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Zusammenfassung Mittels einer Kombination eines Beweglichkeits-Spektrometers und eines Vierpol-Massenspektrometers, ersteres im Bereich des normalen Luftdrucks arbeitend, wurde die Natur der negativen Ionen in einer luftähnlichen Gasmischung untersucht. Die Gasmischung enthielt 300 ppm²) Kohlendioxid und 1 ppm Wasserdampf. Es wurde festgestellt, dass unter Gleichgewichts-bedingungen das vorherrschende Ion die Formel CO₄–·(H₂O) hat.