The significance of fixed ammonium in Palaeozoic sediments for the generation of nitrogen-rich natural gases in the North German Basin

In contrast to predominantly hydrocarbon-rich natural gases in the western part of the Central European Basin (CEB), accumulations of natural gases from the eastern part of the North German Basin (NGB) are nitrogen-rich with up to 90% N₂. This study is focused on the behaviour of fixed ammonium in clay minerals of organic-rich Palaeozoic sediments in the eastern part of the NGB as a major source of nitrogen-rich natural gases. Carboniferous shales have been investigated for a better understanding of nitrogen fixing during diagenesis, storage during burial and release during devolatilization processes or fluid–rock interactions. The total nitrogen contents in the studied Carboniferous shales of the NGB reach up to 2700 ppm with an inorganic fixed portion (in the form of NH₄ ⁺–N) of more than 60%. The results of this study indicate an increasing proportion of the mineralogically fixed ammonium with increasing thermal maturity and storage up to catagenetic conditions. The isotopic composition of fixed-NH₄ is relatively homogeneous in the majority of the shales and ranges from +1 to +3.5‰. In contrast, samples from the basin centre show a significant decrease in ammonium contents down to 460 ppm coupled with a shift in δ¹⁵N up to +5.6‰ suggesting a release of nitrogen on a large scale. Calculation of nitrogen loss and isotopic fractionation indicate that more than 30% of nitrogen was released as ammonium probably as a consequence of fluid-rock interaction with highly saline brines.     

Morphological development of the retention basin “Hartheim”: A case study

Flow in rivers and on floodplains is complex as it is affected by several interconnected factors such as topography, sediment transport and vegetation characteristics. The resulting processes are explained by the measure “Hartheim” planned for retention purposes at the Upper Rhine river. On the basis of existing formulas and instruments it is demonstrated that a good estimation of the development of the measure is possible. The proposed procedure is a useful tool for estimating morphological developments of restored river sections.     

Characterising thermal water circulation in fractured bedrock using a multidisciplinary approach: a case study of St. Gorman’s Well,Ireland

A hydrogeological conceptual model of the source, circulation pathways and temporal variation of a low-enthalpy thermal spring in a fractured limestone setting is derived from a multidisciplinary approach. St. Gorman’s Well is a thermal spring in east-central Ireland with a complex and variable temperature profile (maximum of 21.8 °C). Geophysical data from a three-dimensional(3D)audio-magnetotelluric(AMT) survey are combined with time-lapse hydrogeological data and information from a previously published hydrochemical analysis to investigate the operation of this intriguing hydrothermal system. Hydrochemical analysis and time-lapse measurements suggest that the thermal waters flow within the fractured limestones of the Carboniferous Dublin Basin at all times but display variability in discharge and temperature. The 3D electrical resistivity model of the subsurface revealed two prominent structures: (1) a NW-aligned faulted contact between two limestone lithologies; and (2) a dissolutionally enhanced, N-aligned, fault of probable Cenozoic age. The intersection of these two structures, which has allowed for karstification of the limestone bedrock, has created conduits facilitating the operation of relatively deep hydrothermal circulation (likely estimated depths between 240 and 1,000 m) within the limestone succession of the Dublin Basin. The results of this study support a hypothesis that the maximum temperature and simultaneous increased discharge observed at St. Gorman’s Well each winter is the result of rapid infiltration, heating and recirculation of meteoric waters within a structurally controlled hydrothermal circulation system.

     

Major fracture zones of Morocco: The South Atlas and the Transalboran fault systems

Within the fracturai pattern of Morocco, 35–45° and 70–90° directions are predominant. Most of the faults originated already during the Upper Palaeozoic and were repeatedly reactivated, later on. Two of the large fracture systems are considered here.The South Atlas fault system (SAF) is composed of different faults with directions varying between 45–90°. They were not functionally connected to the southern hinge of the High Atlas until its Miocene uplift. Today, it seems to be inactive on the whole. Both the tectonic data and the facies distribution of Mesozoic strata contradict clearly the interpretation that the SAF is a huge wrench-fault or even the Mesozoic plate margin of Africa. The SW striking Transalboran fault system (TAF) is still active. It crosses Morocco from Melilla to Agadir, showing again singular faults which are unified to extended lineaments only in a few areas. The intervals between the faults are bridged by linear arrangements of earthquake hypocenters. Sinistral massflow within the deeper parts of the lithosphere seems to be compensated at the surface by movements along pre-existing faults. For the Moroccan segment of the TAF, a sinsitral displacement is testified at least since the Oligocene, while the northeastern segments from the Rif to Spain did not even originate until the Pliocene. This would mean that sinistral shear was transmitted from Africa into the accreted Alboran and Iberia blocks after the Miocene collision.

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Zusammenfassung Unter den großen Störungen Marokkos dominieren die Richtungen 35–45° und 70–90°. Sie wurden zumeist im Jungpaläozoikum angelegt und später wiederholt reaktiviert. Zwei der großen Bruchsysteme wurden näher untersucht:Die Südatlas-Störungszone (SAF) besteht aus unzusammenhängenden Brüchen unterschiedlichen Alters, deren Streichrichtung von 45–90° variiert. Diese wurden erst bei der miozänen Heraushebung des Hohen Atlas zu dessen südlichem Scharnier umfunktioniert. Heute sind nur wenige Störungen des Systems aktiv. Diese Befunde und ebenso die stratigraphisch-fazielle Entwicklung im Mesozoikum Marokkos verbieten, die SAF als bedeutende Lateralverschiebungszone oder gar als nördliche Plattengrenze Afrikas zu interpretieren.Das noch heute aktive, SW-streichende Transalboran-Störungssystem (TAF) setzt sich durch Marokko von Melilla bis Agadir fort. Es besteht an der Oberfläche ebenfals aus singulären Brüchen, die sich nur bereichsweise zu längeren Linien zusammenschließen. Zwischen den Störungen vermitteln linear angeordnete Herde rezenter Erdbeben: Sinistraler Massentransport an einer Tiefenstörung wird an der Oberfläche durch Teilbewegungen an präexistenten Störungen kompensiert. Während in Marokko südlich des Rifs sinistraler Versatz mindestens seit dem Oligozän nachgewiesen ist, entstand die TAF vom Rif bis nach Spanien erst im Pliozän. Die sinistrale Scherung tritt also erst nach der miozänen Kollision von Afrika aus auf die nunmehr akkretierten Mikroplatten- Alboran-Block und Iberia - über.

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Résumé Les grandes fractures du Maroc présentent les deux directions prédominantes de 35°-40° et 70°–90°. La plupart de ces fractures datent du Paléozoïque supérieur et ont été réactivées plusieurs fois au Mésozoïque et au Cénozoïque. Deux de ces grands systèmes de fractures sont considérés ici.L'accident sud-atlasien (SAF) est composé de fractures indépendantes d'âges divers dont la direction varie entre 45° et 90°. Ces fractures ne se sont connectées à la charnière du Haut Atlas qu'après le soulèvement miocène de celui-ci. Aujourd'hui, quelques failles seulement sont encore actives. Ces observations, ainsi que la distribution des faciès du Mésozoïque au Maroc sont en contradiction avec le modèle qui voit dans le SAF une grande zone de décrochement ou même la marge nord de la plaque africaine.L'accident transalboran (TAF), encore actif aujourd'hui, traverse le Maroc en direction sudouest de Mélilla à Agadir. Il est composé de failles discontinues, connectées entre elles seulement à quelques endroits. Les intervalles qui séparent ces failles sont jalonnés par des alignements rectilignes d'hypocentres de séismes récents. L'ensemble correspond à un décrochement sénestre profond compensé en surface par des mouvements le long de failles préexistantes. Ce décrochement sénestre, dans le segment du TAF situé au sud du Rif, s'est manifesté au moins depuis l'Oligocène, tandis que la partie qui s'étend du Rif à l'Espagne méridionale n'a été active qu'à partir du Pliocène. Ceci signifie que ce cisaillement sénestre ne s'est transmis de l'Afrique vers l'Europe qu'après l'accrétion, au Miocène, de la microplaque Alboran et du bloc ibérique.

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Numerical aspects of a spline-based multiresolution recovery of the harmonic mass density out of gravity functionals

We show the numerical applicability of a multiresolution method based on harmonic splines on the 3-D ball which allows the regularized recovery of the harmonic part of the Earth's mass density distribution out of different types of gravity data, for example, different radial derivatives of the potential, at various positions which need not be located on a common sphere. This approximated harmonic density can be combined with its orthogonal anharmonic complement, for example, determined out of the splitting function of free oscillations, to an approximation of the whole mass density function. The applicability of the presented tool is demonstrated by several test calculations based on simulated gravity values derived from EGM96. The method yields a multiresolution in the sense that the localization of the constructed spline basis functions can be increased which yields in combination with more data a higher resolution of the resulting spline. Moreover, we show that a locally improved data situation allows a highly resolved recovery in this particular area in combination with a coarse approximation elsewhere which is an essential advantage of this method, for example, compared to polynomial approximation.     

Vertical deformations from homogeneously processed GRACE and global GPS long-term series

Temporal variations in the geographic distribution of surface mass cause surface displacements. Surface displacements derived from GRACE gravity field coefficient time series also should be observed in GPS coordinate time series, if both time series are sufficiently free of systematic errors. A successful validation can be an important contribution to climate change research, as the biggest contributors to mass variability in the system Earth include the movement of oceanic, atmospheric, and continental water and ice. In our analysis, we find that if the signals are larger than their precision, both geodetic sensor systems see common signals for almost all the 115 stations surveyed. Almost 80% of the stations have their signal WRMS decreased, when we subtract monthly GRACE surface displacements from those observed by GPS data. Almost all other stations are on ocean islands or small peninsulas, where the physically expected loading signals are very small. For a fair comparison, the data (79 months from September 2002 to April 2009) had to be treated appropriately: the GPS data were completely reprocessed with state-of-the-art models. We used an objective cluster analysis to identify and eliminate stations, where local effects or technical artifacts dominated the signals. In addition, it was necessary for both sets of results to be expressed in equivalent reference frames, meaning that net translations between the GPS and GRACE data sets had to be treated adequately. These data sets are then compared and statistically analyzed: we determine the stability (precision) of GRACE-derived, monthly vertical deformation data to be ~1.2 mm, using the data from three GRACE processing centers. We statistically analyze the mean annual signals, computed from the GPS and GRACE series. There is a detailed discussion of the results for five overall representative stations, in order to help the reader to link the displayed criteria of similarity to real data. A series of tests were performed with the goal of explaining the remaining GPS–GRACE residuals.     

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.