Some results from phytoplankton counting intercalibrations

Phytoplankton samples from 7 different lakes were processed in 2 intercalibration series using Utermöhl's sedimentation method. Total biomass volumes obtained by most of the investigators give reliable results in respect to the mean. Numbers of individuals and mean volumes of selected species obtained by the different participants were compared and show larger variations than the overall results. Therefore a certain delimitation of particular sources of errors was tried in the 2nd intercalibration series by giving recommendations for the different steps of the whole procedure.     

Mineral-chemical and isotopic studies of Namaqualand granulites,South Africa: A grenville analogue

The northwestern part of South Africa and southern South-West Africa/Namibia is amongst the most extensive granulite terranes in Africa. This work reports the results of electron microprobe studies of minerals from two-pyroxene, cordieriteorthopyroxene (-gedrite) (-sapphirine) and garnet and/or cordierite parageneses from Namaqualand, in the N.W. Cape Province of South Africa. Determined PT conditions of prograde metamorphism based on thermodynamic calculations are 800°–900° C and ca. 6–7 Kb; and it is argued that rocks of unusual composition, notably cordierite-orthopyroxene rocks, are restites after the extraction of granitic liquid from former argillites. This interpretation is consistent with previously published data on similar rocks, and with McCarthy's (1976) suggestion of extensive partial melting in the quartzofeldspathic rocks in the area. U-Pb isotopic studies of some 50 zircon fractions have been carried out and confirm an age of 1,200 m.y. for the high-grade regional metamorphism; but certain zircon populations record inherited ages greater than 1,700 m.y. Garnet-sillimanite rocks that contain retrograde kyanite reflect PT conditions of 550°–650° C and ca. 7–8 Kb; and constituent biotite has yielded a K-Ar age of ca. 950 m.y. These data, the regional stratigraphy and structure, and the mineralisation are compared with data from the Grenville Province of Canada. Notable similarities are the possible basement-cover relationships, and the calendar of tectonothermal events, while differences include the important stratiform base-metal mineralisation in the supracrustal sequence in Namaqualand, and the Cu-mineralisation in hypersthenebearing intrusives, emplaced some 1,100 m.y. ago, that are areally, and believed to be genetically, related to the granulite facies metamorphic regime.     

Neues aus dem Geologen-Archiv (1988)

Ohne Zusammenfassung     

Detailed analysis of the geomagnetic ground survey performed in middle-northern Croatia over the time interval 2003–2005

During the time interval 2003–2005 a ground survey of the total magnetic field intensity in the middle-northern part of Croatia was performed, in order to get a detailed insight of the field distribution over the region. A special effort was done to understand the uncertainty and errors in data reduction, namely different amplitudes of the diurnal variations and different secular variations at the ground stations with respect to the observatories. For data reduction to epoch 2004.5 the total field recordings from AQU, FUR, NCK and THY geomagnetic observatories have been used. We estimate the mean determination error to be one order of magnitude smaller than the maximal reduction error. Multiple linear regression and the method of empirical orthogonal functions were applied on the ground survey and observatory time series. This allowed us to explain the correlations among them and the variance of the total field. Furthermore, we identified two sources of serious artificial disturbances caused by DC leakage: the tramway system of the capital and one railway station in neighbouring Slovenia. Also, we estimate the region free of these disturbances. The magnitude of one of them is estimated to be more than five nT at the distance of about 10 km.     

Probabilistic failure analysis of riprap as riverbank protection under flood uncertainties

Existing riverbank riprap could face the risk of failure if the flood regime changes in future. Additionally, changed sediment transport in rivers, as a possible result of climate change, impacts the failure risk of flood protection measures. Evaluation of this potential failure is the primary issue of riprap stability and safety assessment. The consequences of the bank failure are probably uncontrolled erosion and flooding with disastrous consequences in residential areas or damage to infrastructures. Thus, a probabilistic analysis of riprap failure considering different mechanisms due to the flood and sediment transport uncertainties is required to assess embankment stability. In this article, the concept of a probabilistic assessment model based on Monte Carlo simulation method, moment analysis methods, and Rosenblueth point estimation method are presented to define the failure risk of riprap as the river bank protection. The probability of failure in different modes, namely direct block erosion, toe scouring and overtopping, has been defined by taking into account the river bed level variation based on bedload transport described with a probabilistic function of the peak discharge. The result of three models comparison revealed a good agreement (the average deviation of less than 2%) in estimation of riprap failure probability. This model is a strategical tool to search the critical river reaches and helps to evaluate the risk maps. So that, the model could cover the engineering aspect of environmental stability in the rivers with riprap as the bank protections.     

Criteria for recognizing shelf-slope clinoforms in outcrop; Jurassic Lajas and Los Molles formations,S. Neuquén Basin,Argentina

Seismic-reflection data show that most deepwater (>200 m water depth) basins are filled by sand and mud dispersed across clinoformal geometries characterized by gently dipping topsets, steeper foresets and gently dipping bottomsets. However, the entire geometry of these ubiquitous clinoforms is not always recognized in outcrops. Sometimes the infill is erroneously interpreted as “layer cake” or “ramp” stratigraphy because the topset-foreset-bottomset clinoforms are not well exposed. Regional 2-D seismic lines show clinoforms in the Lower to Middle Jurassic Challaco, Lajas, and Los Molles formations in S. Neuquén Basin in Argentina. Time equivalent shelf, slope and basin-floor segments of clinoforms are exposed, and can be walked out in hundreds of metres thick and kilometres-wide outcrops. The studied margin-scale clinoforms are not representing a continental-margin but a deepwater shelf margin that built out in a back-arc basin. Lajas-Los Molles clinoforms have been outcrop-mapped by tracing mudstones interpreted as flooding surfaces on the shelf and abandonment surfaces (low sedimentation rate) in the deepwater basin. The downslope and lateral facies variability in the outcrops is also consistent with a clinoform interpretation. The Lajas topset (shelf) is dominated by fluvial and tidal deposits. The shelf-edge rollover zone is occasionally occupied by a 40–50-m-thick coarse-grained shelf-edge delta, sometimes incising into the underlying slope mudstones, producing oblique clinoforms expressing toplap erosion on seismic. A muddy transgressive phase capping the shelf-edge deltas contains tidal sandbodies. Shelf-edge deltas transition downslope into turbidite- and debris flow-filled channels that penetrate down the mud-prone Los Molles slope. At the base-of-slope, some 300m below the shelf edge, there are basin-floor fan deposits (>200 m thick) composed of sandy submarine-fan lobes separated by muddy abandonment intervals. The large-scale outcrop correlation between topset–foreset–bottomset allows facies and depositional interpretation and sets outcrop criteria recognition for each clinoform segment.     

Wave propagation in protoplanetary disks: Formation of twin planets by ‘disk-brown dwarf’ collisions?

In this paper we derive a special linear non-vortical wave propagation solution in the shearing sheet, a model of a compressible two-dimensional fluid system with constant density, constant shear and constant Coriolis force, but without self-gravity. The linear analysis of the shearing sheet leads to a single differential equation for the azimuthal velocity perturbation. A detailed derivation of a special solution with a prescribed azimuthal wavenumber k is presented. More general wave solutions, eventually excited by large local ‘impacts’, can be derived by superimposing all k-modes. The special wave functions so obtained describe the formation of two independent spiral wave arms originating out of a ring-shaped structure. The motivation for this investigation lies in the fact that similar wave propagators can be excited by the transit of a solid or ‘clumpy’ object through a protoplanetary disk. We speculate that a disk-brown dwarf collision can produce in the disk a pair of two spiral density wave fragments triggering the rapid accretion of two giant planets by a gravitational shear instability simultaneously (Hypothesis of a mechanism for the production of giant planets in pairs).     

Zum Auf und Ab des Meeresspiegels in Skandinavien: Langer Streit um Eustasie oder Isostasie

The phenomenon of the rise of the Scandinavian shield during the Holocene and the concomitant fall in level of the Baltic Sea has been investigated for centuries. Already in medieval times, there were reports about the coastlines of the Gulf of Bothnia that are full of relevant observations. During the eighteenth century, scientists such as Celsius and Linnaeus collected observations such as these. The result was that the search for the possible explanations of this rise-and-fall phenomenon intensified. The generally favoured explanation was that there was an active sinking of sea level in the Baltic rather than an active rising of the land surface in Fennoscandia. This was because water was seen as mobile, in contrast to a „terra firma“. The relevant discussion was often emotional, and here, we try to illustrate it using material from the Geologenarchiv Freiburg (von Hoff, von Buch and Goethe). No more than a few decades later, it became obvious by the theory of Ice Age that both the sea level and the land could be mobile (eustatic sea level changes—glacial isostasy). Additionally, of course, plate tectonics had some influence: Norway is situated at the western end of the Eurasian plate and is part of a passive continental margin. There are still open research problems, many of which can be addressed using modern methods of satellite-based geophysics and geodesy. Some other aspects as the permanent uplift trend of Scandinavia since the Cambrium or the rhythmic to and fro of magma in the upper mantle during the Pleistocene are mentioned.     

The quantitative analysis of OH in vesuvianite: a polarized FTIR and SIMS study

A well-characterized suite of vesuvianite samples from the volcanic ejecta (skarn or syenites) from Latium (Italy) was studied by single-crystal, polarized radiation, Fourier-transform infrared (FTIR) spectroscopy and secondary-ion mass-spectrometry (SIMS). OH-stretching FTIR spectra consist of a rather well-defined triplet of broad bands at higher-frequency (3,700–3,300 cm^–1) and a very broad composite absorption below 3,300 cm^–1. Measurements with E//c or Ec show that all bands are strongly polarized with maximum absorption for E//c. They are in agreement with previous band assignments (Groat et al. Can Mineral 33:609, 1995) to the two O(11)–H(1) and O(10)–H(2) groups in the structure. Pleochroic measurements with changing direction of the E vector of the incident radiation show that the orientation of the O(11)–H(1) dipole is OHc~35°, in excellent agreement with the neutron data of Lager et al. (Can Mineral 37:763, 1999). A SIMS-based calibration curve at ~10% rel. accuracy has been worked out and used as reference for the quantitative analysis of H₂O in vesuvianite by FTIR. Based on previous SIMS results for silicate minerals (Ottolini and Hawthorne in J Anal At Spectrom 16:1266, 2001; Ottolini et al. in Am Mineral 87:1477, 2002) the SiO₂ and FeO content of the matrix were assumed as the major factors to be considered at a first approximation in the selection of the standards for H. The lack of vesuvianite standards for quantitative SIMS analysis of H₂O has been here overcome by selecting low-silica elbaite crystals (Ottolini et al. in Am Mineral 87:1477, 2002). The resulting integrated molar absorption FTIR coefficient for vesuvianite is _i=100.000±2.000 l mol^–1 cm^–2. SIMS data for Li, B, F, Sr, Y, Be, Ba REE, U and Th are also provided in the paper.