Echinoids from the Belpberg Beds (Obere Meeresmolasse, Middle Burdigalian) in the area of Bern (Switzerland)

The present paper deals with the echinoid fauna of the Belpberg Beds, a lithostratigraphic unit in the Upper Marine Molasse cropping out southeast of Bern (Switzerland). In this unit, echinoids, in contrast to mollusks, are rare and of low diversity. The scarcity of echinoids is related to the environmental setting dominated by monotonous siliciclastic deposits and strong diagenetic alteration. The echinoid fauna consists of three species Psammechinus dubius dubius, Echinocardium deikei and Hemipatagus ocellatus? Psammechinus dubius dubius and H. ocellatus typically occur in Burdigalian sediments in the Paratethys and help to confirm the dating obtained from the microfossils and molluscs of the Belpberg Beds. Furthermore, the Belpberg echinoid fauna is especially relevant for the palaeobiogeography with species common to both the Rh?ne Basin and the Central Paratethyan faunas.

---

Zusammenfassung. Die vorliegende Arbeit besch?ftigt sich mit der Echinidenfauna der Belpberg Schichten (Obere Meeresmolasse) bei Bern. Im Gegensatz zu den Mollusken sind die Echiniden selten und wenig divers. Dies kann einerseits auf das sediment?re Regime, und andererseits auf diagenetische Ursachen zurückgeführt werden. Insgesamt konnten drei Arten nachgewiesen werden (Psammechinus dubius dubius, Echinocardium deikei und Hemipatagus ocellatus?). Zwei davon treten in der Paratethys charakteristischerweise im Burdigalium auf und lassen ein ebensolches Alter für die Belpberg Schichten als wahrscheinlich erscheinen. Aus pal?obiogeographischer Sicht ist die Belpberg-Echinidenfauna von besonderem Interesse, das sie ein Bindeglied zwischen Rh?ne Becken und Zentraler Paratethys darstellt.

     

Formation and stability of schwertmannite in acidic mining lakes

Schwertmannite (ideal formula: Fe₈O₈(OH)₆SO₄) is typically found as a secondary iron mineral in pyrite oxidizing environments. In this study, geochemical constraints upon its formation are established and its role in the geochemical cycling of iron between reducing and oxidizing conditions are discussed. The composition of surface waters was analyzed and sediments characterized by X-ray diffraction, FTIR spectroscopy and determination of the Fe:S ratio in the oxalate extractable fraction from 18 acidic mining lakes. The lakes are exposed to a permanent supply of pyritegenous ferrous iron from adjacent ground water. In 3 of the lakes the suspended matter was fractionated using ultra filtration and analyzed with respect to their mineral composition. In addition, stability experiments with synthetic schwertmannite were performed. The examined lake surface waters were O₂-saturated and have sulfate concentrations (10.3 ± 5.5 mM) and pH values (3.0 ± 0.6) that are characteristic for the stability window of schwertmannite. Geochemical modeling implied that i) the waters were saturated with respect to schwertmannite, which controlled the activity of Fe³⁺ and sulfate, and ii) a redox equilibrium exists between Fe²⁺ and schwertmannite. In the uppermost sediment layers (1 to 5 cm depth), schwertmannite was detectable in 16 lakes—in 5 of them by all three methods. FTIR spectroscopy also proved its occurrence in the colloidal fraction (1-10 kDa) in all of the 3 investigated lake surface waters. The stability of synthetic schwertmannite was examined as a function of pH (2-7) by a 1-yr experiment. The transformation rate into goethite increased with increasing pH. Our study suggests that schwertmannite is the first mineral formed after oxidation and hydrolysis of a slightly acidic (pH 5-6), Fe(II)-SO₄ solution, a process that directly affects the pH of the receiving water. Its occurrence is transient and restricted to environments, such as acidic mining lakes, where the coordination chemistry of Fe³⁺ is controlled by the competition between sulfate and hydroxy ions (i.e. mildly acidic).     

Forecasting terrestrial water storage for drought management in Ethiopia

ABSTRACT

Reliable seasonal forecasting of water resources variability may be of great value for agriculture and energy management in Ethiopia. This work aims to develop statistical forecasting of seasonal total water storage (TWS) anomalies in Ethiopia using sea-surface temperature and sea-level pressure indices. Because of the spatial and temporal variability of TWS over the country, Ethiopia is divided into four regions each having similar TWS dynamics. Periods of long-term water deficit observed in GRACE TWS products for the region are found to coincide with periods of meteorological drought. Multiple linear regression is employed to generate seasonal forecasting models for each region. We find that the skill of the resulting models varies from region to region, with R ² from 0.33 to 0.73 and correlation from 0.27 to 0.77 between predicted and observed values (using leave-one-out cross-validation). The skill of the models is better than the climatology in all regions.     

The use of maximum entropy to increase the informational content of hydrological networks by additional gauges

ABSTRACT

The optimization and extension of existing gauging networks are a challenging task, which can be done under consideration of many different aspects. One possibility is to maximize the obtained information on regional hydrological characteristics by new gauges compared to existing ones. For this, information theory approaches are most suitable. Here, the principle of maximum entropy is applied to calculate the probability of non-similarity of catchments to determine locations of new gauges according to the catchment characteristics that are most relevant for the hydrological conditions. The realization in an interactive application, provided online, makes use easy for practitioners and scientists. Goodness-of-fit measures are applied to investigate the explanatory power of the model and the contribution of each characteristic to the model, which gives information on the most influential properties of the catchment. The relevance of the proposed approach is proven by comparing hydrological signatures between similar and non-similar catchment.     

Das Nord-Süd-streichende Lineament von Elizondo in den westlichen Pyrenäen

Zusammenfassung In den spanischen Westpyrenäen läßt sich ein nord-süd-streichendes Lineament nachweisen, das sich vor allem im Aldudes-Quinto Real-Massiv zwischen Elizondo und Eugui bemerkbar macht. Die Magnesitlagerstätte von Eugui ist auf etwa 9 km nord-südlicher Erstreckung an das Lineament gebunden. Zahlreiche NW-SE streichende Diabasgänge zeigen in ihrer Gesamtheit in diesem Bereich eine lineare Anordnung von Nord nach Süd. Während des Devons und Unterkarbons bildete die Lineamentzone ein Becken mit größeren Sedimentmächtigkeiten und besonderer Fazies. Der Faltenspiegel der variszischen Strukturen fällt von Osten und Westen her in das Lineament ab. Die generell nordwestlich streichenden variszischen Faltenachsen schwenken innerhalb des Lineaments in eine nord-südliche bis rheinische Richtung ein. Bemerkenswert ist der Achsenfächer bei Berroeta.

---

Near by Elizondo in the Western Pyrenees (Spain) the massiv of Aldudes-Quinto Real is crossed by a lineament of NW direction. This lineament contains the magnisite deposit of Eugui. Diabas dykes show NW-SE direction, but the prevailing direction of the series is N-S. During devonian and lower carboniferous time the region of the lineament represented a sedimentary basin of great thickness and special facies. The axis of this large synclinorium shows the same direction as the lineament. The hercynian axes of folding are striking NW in general but NS in the region of the lineament. Remarkable is the fan of axes near Berroeta.

---

Compendio En los Pirineos occidentales españoles se encuentra un lineamiento con un rumbo de Norte a Sur, que se hace notable sobre todo en el macizo de Aldudes-Quinto Real entre Elizondo y Eugui. El yacimiento de magnesita de Eugui sigue este lineamiento en una extensión de 9 kms. Numerosas diques de diabasa muestran en su generalidad en esta región un orden en linea de Norte a Sur. Durante el devónico y el carbonífero inferior formaba esta zona de lineamiento una cuenca, en la que se depositaron sedimentos de gran espesor con una facies característica. Los niveles de eje de los anticlinales de las estmcturas varísticas buzan tanto del Este como del Oeste hacia el centro del lineamiento. Los ejes de los anticlinales que tienen en general un rumbo hacia el NO tuercen dentro del lineamiento en una dirección de N—S a NNE—SSO. Interesantes son los ejes en abanico cerca de Berroeta.

---

Résumé Dans l'ouest des Pyrénées espagnoles on a prouvé l'éxistance d'un linéament qui se montre particulièrement dans le massif des Aldudes-Quinto Real entre Elizondo et Eugui. Le gîte de magnésite d'Eugui est attaché à cette linéament du nord au sud sur une longueur de 9 km. Dans cette région de nombreux filons basaltiques montrent dans leur totalité un arrangement linéaire du nord au sud. Durant le dévonien et le carbonifère inférieur la zone de linéament a formé une cuvette de grandes epaisseurs sédimentaires et de faciès particulier. Dans cette linéament l'axe de plissement, en général de direction NW, se dirige du N—S jusqu'à une direction rhénale. L'axe en éventail près de Berroeta est remarquable.

---

: , . , NW NE. ( ) .

---

---

Anschrift der Verfasser: Dr. K.Mohr und Professor Dr. A.Pilger, Institut für Geologie und Paläontologie der Bergakademie Clausthal — Technische Hochschule 3392 Clausthal-Zellerf eld.     

Mechanism and kinetics of the reaction: 1 dolomite + 2 quartz = 1 diopside + 2 CO2: a comparison of rock-sample and of powder experiments

Two experiments using cylindrical samples of a dolomite-quartz rock were carried out in a conventional hydrothermal apparatus for the forward reaction: 1 dolomite + 2 quartz = 1 diopside + 2 CO₂, in order to compare the mechanism and the kinetics with results from experiments using mineral powders of dolomite and quartz at the same P-T-X conditions. Experimental conditions were as follows: total pressure 500 MPa; temperature 680° C (overstepping 65° C); CO₂ content of the fluid phase, consisting of carbon dioxide and water, was nearly 90 mol%; the fluid/rock ratio was 1:37, and the H₂O/rock ratio was about 1:740; run duration was 92 days. Scanning electron microscope (SEM) examination of a polished axial section of the rock cylinders after the run, using back-scattered electrons (BSE), shows that the reaction produced corona textures. The diopside crystals nucleate and grow exclusively on dolomite surfaces adjacent to quartz grains, i.e. in regions where there is intimate contact between the reactants. The dolomite matrix, in contrast, is diopside free. A concept of microsystems is used to compare directly the rock cylinder results with those from runs done with mineral powders. The microsystems, which consist of quartz, dolomite and diopside, are connected by the intergranular space which is filled by the fluid phase. The SEM analysis of the rock cylinders indicates a dissolution-crystallization mechanism operating in the microsystems; this is consistent with the results of experiments using dolomite quartz powders (Lüttge et al. 1989). It can be demonstrated that reaction kinetics in mineral powder runs are interface controlled as long as the newly formed diopside crystals do not cover the dolomite surfaces completely (Lüttge and Metz 1991 c). This result is applicable to each microsystem of the rock cylinder, since the reaction mechanism and the resulting textures are the same in both kinds of experiments. The reaction is much slower outside the microsystems, i.e. in the dolomite matrix but in the close vicinity of the quartz grains. At these places, the reaction is controlled by the transport of Si-species in the CO₂-rich fluid phase filling the intergranular space. The reaction is absent in quartz-free regions of the dolomite matrix. Calculations and measurements of the extent of reaction progress in both kinds of experiments give results of the same order of magnitude: the conversion, and therefore the reaction rate, differs by less than a factor of two. The conclusion is that there are no differences, in principle, concerning mechanisms, rate controls, rates, and resulting textures between rock cylinder experiments, and mineral powder experiments.     

Middle to Late Pleistocene environments based on stable organic carbon and nitrogen isotopes of loess-palaeosol sequences from the Carpathian Basin

Stable organic carbon and nitrogen isotopes can be used to interpret past vegetation patterns and ecosystem qualities. Here we present these proxies for two loess-palaeosol sequences from the southern Carpathian Basin to reconstruct the palaeoenvironment during the past 350 ka and establish regional commonalities and differences. Before now, isotopic studies on loess sequences from this region were only conducted on deposits from the last glacial cycle. We conducted methodological tests involving the complete decalcification of the samples prior to stable isotope analyses. Two decalcification methods (fumigation method and wet chemical acidification), different treatment times, and the reproducibility of carbon isotope analyses were tested. Obtained results indicate that the choice of the decalcification method is important for organic carbon stable isotope analyses of loess-palaeosol sequences because ratios vary by more than 10‰ between the wet chemical and fumigation methods, due to incomplete carbonate removal by the latter. Therefore, we suggest avoiding the fumigation method for studies on loess-palaeosol sequences. In addition, our data show that samples with TOC content <0.2% bear increased potential for misinterpretation of their carbon isotope ratios. For our sites, C₃-vegetation is predominant and no palaeoenvironmental shifts leading to a change of the dominant photosynthesis pathway can be detected during the Middle to Late Pleistocene. Furthermore, the importance of further stable nitrogen isotope studies is highlighted, since this proxy seems to reflect past precipitation patterns and reveals favourable conditions in the southern Carpathian Basin, especially during interstadials.     

Leveraging HPC accelerator architectures with modern techniques — hydrologic modeling on GPUs with ParFlow

Computational Geosciences - Rapidly changing heterogeneous supercomputer architectures pose a great challenge to many scientific communities trying to leverage the latest technology in...     

The zircon evidence of temporally changing sediment transport—the NW Gondwana margin during Cambrian to Devonian time (Aoucert and Smara areas,Moroccan Sahara)

International Journal of Earth Sciences - Detrital zircon provenance studies are an established tool to develop palaeogeographic models, mostly based on zircon of siliciclastic rocks and isotope...