Climate shifts vs. edaphic humidity and the difficulty of palaeoreconstructions – a malacological study on stable isotopes in Quaternary dune sequences of Fuerteventura

Dune palaeosurface sequences on the Eastern Canary Islands were investigated for stable isotope records in gastropod shells of the genus Theba. Due to the ecology of the taxon and the special oceanic insularity of the study site, we assume that δ¹⁸O_shell signals in our case mainly reflect shifts in δ¹⁸O signals of sea surface water. We found that a rapid decrease in δ¹⁸O_shell signals is associated with significant changes in gastropod associations. We suggest that these faunal changes were caused by strong (hot) winds at the end of glacial phases, that were described previously by Moreno et al. In addition, we assume that rapid declines in δ¹⁸O_shell signals due to marine transgressions were followed by geomorphologically stable phases, dominated by dust enrichment. Such palaeosurfaces correlate with maxima of gastropod biodiversity and with more negative δ¹³C_shell signals indicating a higher proportion of C3 plants. Based on our results, we also assume that these silty palaeosurfaces were associated with increased soil moisture conditions due to a higher water storage capacity of the finer substrate, independent of climatic moisture conditions.     

Iron biomineralization by anaerobic neutrophilic iron-oxidizing bacteria

Minerals formed by bio-oxidation of ferrous iron (Fe(II)) at neutral pH, their association with bacterial ultrastructures as well as their impact on the metabolism of iron-oxidizing bacteria remain poorly understood. Here, we investigated iron biomineralization by the anaerobic nitrate-dependent iron-oxidizing bacterium Acidovorax sp. strain BoFeN1 in the presence of dissolved Fe(II) using electron microscopy and Scanning Transmission X-ray Microscopy (STXM). All detected minerals consisted mainly of amorphous iron phosphates, but based on their morphology and localization, three types of precipitates could be discriminated: (1) mineralized filaments at distance from the cells, (2) globules of 100 ± 25 nm in diameter, at the cell surface and (3) a 40-nm thick mineralized layer within the periplasm. All of those phases were shown to be intimately associated with organic molecules. Periplasmic encrustation was accompanied by an accumulation of protein moieties. In the same way, exopolysaccharides were associated with the extracellular mineralized filaments. The evolution of cell encrustation was followed by TEM over the time course of a culture: cell encrustation proceeded progressively, with rapid precipitation in the periplasm (in a few tens of minutes), followed by the formation of surface-bound globules. Moreover, we frequently observed an asymmetric mineral thickening at the cell poles. In parallel, the evolution of iron oxidation was quantified by STXM: iron both contained in the bacteria and in the extracellular precipitates reached complete oxidation within 6 days. While a progressive oxidation of Fe in the bacteria and in the medium could be observed, spatial redox (oxido-reduction state) heterogeneities were detected at the cell poles and in the extracellular precipitates after 1 day. All these findings provide new information to further the understanding of molecular processes involved in iron biomineralization by anaerobic iron-oxidizing bacteria and offer potential signatures of those metabolisms that can be looked for in the geological record.     

Detrital blue amphiboles from the western Othrys Mountain and their relationship to the blueschist terrains of the Hellenides (Greece)

In contrast to blue amphiboles of the Ossa and Olympos tectonic windows in Thessaly, detrital blue amphiboles in Paleocene flysch deposits in the western Othrys Mountain (Pelagonian Zone s.l.) are chemically comparable with blue amphiboles from the Cyclades. For the detrital material, therefore, a source with "Cycladic" chemical affinities is assumed. The occurrence of these detrital minerals is in line with a Cretaceous onset of blueschist facies metamorphism in parts of the Hellenides, especially in the Cycladic belt. This was in response to Cretaceous subduction of the Pindos oceanic plate along the external margin of the Pelagonian micro-continent. Blueschist complexes were exhumed latest in the Paleocene when the terrigenous flysch sedimentation started in the Pelagonian and Pindos zones.     

Location and source mechanism of the Karlsruhe earthquake of 24 September 2014

On 24 September 2014, a M_L 2.3 earthquake occurred southwest of the urban area of Karlsruhe, Germany, which was felt by a few people (maximum intensity I ₀?=?III). It was the first seismic event in this highly populated area since an I ₀?=?VII earthquake in 1948. Data of 35 permanent and temporary seismometers were analysed to localise the event and to determine the focal mechanism to compare it to previous seismicity. Restricting the data to P- and S-phases from 18 nearby stations and optimising the local earth model result in an epicentre in the southwest of the city at 48.986°N/8.302°E and in a hypocentral depth of 10 km. To calculate the focal mechanism, 22 P- and 5 S_H-polarities were determined that constrain a stable left lateral strike-slip focal mechanism with a minor thrusting component and nodal planes striking NE-SW and NW-SE. The epicentre lies in the vicinity of the I ₀?=?VII earthquake of 1948. Both events are part of the graben-parallel flower structure beneath the Upper Rhine Graben, parallel to the active Rastatt source zone, which runs 5 km further east and included the epicentre of the 1933 Rastatt I ₀?=?VII earthquake. The focal mechanisms of the 2014 and 1948 earthquakes show NE-SW striking nodal planes that dip to the southeast. However, for the 1948 event, a normal faulting mechanism was determined earlier. Taking the uncertainty of the epicentre and focal mechanism in 1948 and its fault dimensions into account, both events might have happened on the same fault plane.     

STABILITY OF GRAVEL BED RIVERS BASED ON SIEVE ANALYSIS DATA

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Continental dispersion of seismic surface waves

Summary Continental dispersion curves for Love and Rayleigh waves have been determined by means of the Uppsala seismograph records for three earthquakes near the south coast of Turkey in April, 1957. To the authors' knowledge this is the first time dispersion curves have been determined for a relatively homogenous path across the whole of continental Europe and covering a good range of periods, namely from 3 to 86 sec for Love waves and from 5 to 61 sec for Rayleigh waves. The dispersion curves obtained are relevant to determinations of the average structure along the path traversed in particular, and to determinations of crustal structure of the European continent in general.

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Zusammenfassung Kontinentale Dispersionskurven für Love-und Rayleigh-Wellen wurden vermittels Registrierungen an der Station Uppsala von drei Erdbeben in der Nähe der Südküste der Türkei im April 1957 bestimmt. Soweit es den Autoren bekannt ist, wurden damit erstmalig Dispersionskurven für einen relativ homogenen Weg über das gesamte kontinentale Europa mit einem beträchtlichen Periodenbereich, der 3 bis 86 Sek für Love-Wellen und 5 bis 61 Sek für Rayleigh-Wellen umfasst, ausgearbeitet. Die erhaltenen Dispersionskurven haben ihre Bedeutung in der Festlegung der mittleren Krustenstruktur entlang dem durchlaufenen Wellenweg und überhaupt in der Festlegung der Krustenstruktur im Bereich des europäischen Kontinents.