Modelling the Velocity Field in a Regular Grid in the Area of Poland on the Basis of the Velocities of European Permanent Stations

The paper presents the results of testing the various methods of permanent stations’ velocity residua interpolation in a regular grid, which constitutes a continuous model of the velocity field in the territory of Poland. Three packages of software were used in the research from the point of view of interpolation: GMT (The Generic Mapping Tools), Surfer and ArcGIS. The following methods were tested in the softwares: the Nearest Neighbor, Triangulation (TIN), Spline Interpolation, Surface, Inverse Distance to a Power, Minimum Curvature and Kriging. The presented research used the absolute velocities’ values expressed in the ITRF2005 reference frame and the intraplate velocities related to the NUVEL model of over 300 permanent reference stations of the EPN and ASG-EUPOS networks covering the area of Europe. Interpolation for the area of Poland was done using data from the whole area of Europe to make the results at the borders of the interpolation area reliable. As a result of this research, an optimum method of such data interpolation was developed. All the mentioned methods were tested for being local or global, for the possibility to compute errors of the interpolated values, for explicitness and fidelity of the interpolation functions or the smoothing mode. In the authors’ opinion, the best data interpolation method is Kriging with the linear semivariogram model run in the Surfer programme because it allows for the computation of errors in the interpolated values and it is a global method (it distorts the results in the least way). Alternately, it is acceptable to use the Minimum Curvature method. Empirical analysis of the interpolation results obtained by means of the two methods showed that the results are identical. The tests were conducted using the intraplate velocities of the European sites. Statistics in the form of computing the minimum, maximum and mean values of the interpolated North and East components of the velocity residuum were prepared for all the tested methods, and each of the resulting continuous velocity fields was visualized by means of the GMT programme. The interpolated components of the velocities and their residua are presented in the form of tables and bar diagrams.     

Electrical Resistance Heating of Clay Layers in Water‐Saturated Sand

Electrical resistance heating (ERH) experiments were performed in a two‐dimensional water‐saturated porous medium comprising an electrically conductive, low‐permeability clay lens embedded within a less electrically conductive, higher permeability silica sand. These were compared to experiments performed in homogeneous silica sand. All experiments were performed in the absence of a non‐aqueous phase liquid (NAPL) or dissolved volatile organic compound (VOC). Temperature monitoring showed preferential heating in the clay lens and higher overall heating rates throughout the test cell compared to the homogeneous case. Gas production was localized around the sand–clay interface due to high temperature and low capillary displacement pressure. Above the clay lens, unexpected temperature plateaus were observed, similar to those observed in previous experiments during NAPL–water co‐boiling. A conceptual model based on the consumption of thermal energy as latent heat of vaporization in the highly localized heating and gas production region adjacent to the clay lens is proposed to explain the temperature plateaus. Supporting data is drawn from images of the gas phase and electric current measurements. These results show that the use of co‐boiling plateaus as an indicator of NAPL–water co‐boiling could be misleading during applications of ERH at sites containing electrically conductive, low‐permeability clay lenses embedded within less electrically conductive, higher‐permeability sands.     

Sources of dissolved silica to the fjords of northern Patagonia (44–48°S): the importance of volcanic ash soil distribution and weathering

Dissolved silica (DSi) plays an important biogeochemical role in the fjords of northern Chilean Patagonia (44–48°S), where it drives high biogenic productivity and promotes carbon burial. It is generally believed that the DSi riverine input to lakes and coastal environments is controlled by a combination of factors including lithology, climate, topography, vegetation, and meltwater input. In northern Chilean Patagonia several authors have proposed that the postglacial volcanic ash soils (andosols) may play a significant role in the high supply of DSi to the regional fjords. To assess the influence of andosols on DSi concentrations in north Patagonian rivers, we mapped andosol thickness and compared our results with river chemistry. The mineralogical and geochemical composition of three representative andosol profiles was also examined to evaluate the efficiency of weathering processes. The andosol thickness map clearly demonstrates that volcanic ash was predominantly deposited on the eastern side of the regional volcanoes, reflecting the influence of the prevailing westerly winds on the distribution of pyroclastic material. Mineralogical and geochemical results show that the andosol parent material has the typical andesitic basaltic signature of the regional volcanoes, i.e. high amounts of amorphous material, plagioclase, K‐feldspar, and pyroxene. Down‐profile variations in soil mineralogy and geochemistry indicate increased leaching of silica with depth, resulting from weathering of the volcanic parent material. For the five studied watersheds, a highly positive correlation (R²=0.98) was found between average andosol thickness and DSi concentrations, suggesting that andosol thickness is the main parameter affecting DSi concentrations in north Patagonian river systems. On seasonal timescales, increased precipitation (winter) and glacial meltwater (summer) input can significantly reduce DSi concentrations. We argue that the weathering of andosols constitutes the most important source of DSi to the lakes and fjords of northern Chilean Patagonia, explaining the particularly high regional rates of biogenic silica production. Copyright © 2015 John Wiley & Sons, Ltd.     

Modeling reactive transport in sediments subject to bioturbation and compaction

Current bioturbation models are marked by confusion in their treatment of porosity. Different equations appear to be needed for different biodiffusion mechanisms, i.e., interphase mixing, where biological activity causes bulk mixing of sediment affecting both tracer and porosity profiles, versus intraphase mixing, where the solid components are intermixed, but the porosity is left unchanged. Another issue is whether the model depends upon the particle type with which tracers are associated, e.g., ¹³⁷Cs on small clay particles versus ²¹⁰Pb on larger grains. This uncertainty has lead to conflicting conservation equations for radiotracers, and in particular, to the question whether the porosity should be placed inside or outside of the differential term that governs the biodiffusive flux. We have reexamined this situation in the context of multiphase, multicomponent continuum theory. Most importantly, we prove that under the assumption of steady-state porosity, there exists only one correct form of the steady-state conservation equation for a radiotracer, regardless of biodiffusion mechanism and particle type, i.e.,

     

SIMS analyses on trace and rare earth elements in coexisting clinopyroxene and mica from minette mafic enclaves in potassic syenites crystallized under high pressures

Trace and rare earth element contents were determined by SIMS technique in clinopyroxene and mica crystals from minette lamprophyric enclaves in a potassic syenite host. This co-mingled system was crystallized at high pressures, which varied about 3–5 GPa, as indicated by the presence of K-clinopyroxenes and pyrope-rich garnet with measurable amounts of K₂O and Na₂O, among the near-liquidus phases. Major and trace element composition of these lamprophyric enclaves is quite similar to those observed in silica-rich lamproites, suggesting that similar sources were involved in their origin. In a general view, the concentrations of most trace and rare earth elements in clinopyroxene of the studied enclaves are higher than those referred to by other authors. Clinopyroxene/melt partition coefficient for most trace elements are close to determinations in alkali-basalts and lamproites from Leucite Hills, with considerable differences relative to Gaussberg lamproites. Furthermore, these partition data are completely different from those determined for potassic lavas crystallized under crustal pressures. Spidergrams for clinopyroxenes exhibit negative-Sr anomalies relative to LREE, which have been associated by most authors to crystallization under low-pressures, out of garnet stability field. The presence of pyrope together with K-clinopyroxene excludes such hypotheses for the studied enclaves. Y and HREE are concentrated in clinopyroxene, whilst the other trace elements have Kd<1. LIL elements, except Rb, have incompatible (Kd<1) behavior in phlogopite. The high partition coefficient for Nb (Kd>3) determined in the studied phlogopite is unusual in lamproites, lamprophyres, and basalts, but frequently observed in phlogopite from metasomatic mantle samples, as well as in acid magmas. This partition value may indicate the lack of other mineral phase with high partition for this element during crystallization, and may be enhanced by the liquid composition progressively closer to alkali feldspar, an unsuitable structure for six-coordinated cations. Ce/Yb, Rb/Sr, and Zr/Hf ratios in clinopyroxene and mica suggest that the minettic magma could produce the host Piquiri potassic syenite by fractional crystallization. This hypothesis is not consistent with Ba concentrations in clinopyroxene and mica, which suggest that a Ba-bearing phase (e.g. alkali feldspar) should be among the fractionated phases in order to produce the potassic syenites.     

Sur la mesure de l'intensité du champ magnétique terrestre et la distribution du magnétisme dans les aimants

The measurement of the horizontal component, H, of the geomagnetic field represents an important part of geomagneticians work from 1830 to the end of the 19th century. This measurement remained difficult at the required accuracy of ${10}^{\mathrm{?9}}\text{T}$ (1 nT or $1\gamma$), till the advent of proton and optical pumping magnetometers in geomagnetic observatories, around 1955. The measurement of H consisted in determining the mutual torque between two cylindrical magnets, by measuring either oscillation periods or angular deviations. Poisson was the first, indisputably, to propose the general principle of the measurement, in 1825. But Gauss, some years later (1832), successfully operated his famous oscillation–deviation method, described since then in all the elementary manuals of physics. The computation of the mutual torque depends on the tri-dimensional distribution of the magnetization in each one of the magnets. In the absence of an accurate-enough knowledge of these distributions, Poisson, Gauss, and their successors showed how to make the computations with a minimum number of hypotheses on them. Nevertheless physicists, in particular French ones, worked on the ‘distribution of magnetism’ in magnets; the first of them was Coulomb. We come back to this question through experiments conducted in the magnetic observatory of Chambon-la-Forêt, France. To cite this article: B. Leprêtre, J.-L. Le Mouël, C. R. Geoscience 337 (2005).     

Karsts polyphasés, faciès marins et continentaux dans le Paléocène de la partie orientale des Pyrénées fran?aises

In the Eastern part of French Pyrenees, the Cucugnan area (Southern Corbières) corresponded during the early/Mid-Paleocene (Danian/Selandian) to a narrow transitional zone between the sea to the South (Pyrenean Paleocene Trough) and the continent (fluvio-palustrine and lacustrine Vitrollian deposits) to the North. To the South, in the North-Pyrenean Zone, the polygenic marine breccias and the associated Dano-Selandian Globigerinid-bearing hemipelagites have been preserved within successive paleokarsts superimposed onto the carbonate substratum (ante-Albian). Four paleosurfaces are recognized, principally filled by marine internal sediments with proximal and distal facies. To the North, in the Sub-Pyrenean Zone, a continental foreland basin is characterized by four formations of variegated Microcodium-bearing marls and channelized conglomerates, separated by erosional paleosurfaces underlining well-marked unconformities. An event correlation (chronodiagrams) between the marine realm to the South and the continental realm to the North is proposed, using the successive paleosurfaces and the lithological sequences (same number within the two realms). Our paleogeographic reconstruction shows, to the North, the Lake of Cucugnan and, to the South, a calcareous mountainous zone broken by the juxtaposition of deep paleocanyons (eroded in a continental context) later converted into rias submitted to marine oscillations. Several palinspastic transects are reconstructed: they show the polyphase control of the Frontal North-Pyrenean Overthrust on the Paleocene sedimentation and the importance of the successive intra-Vitrollian compressions/ transpressions (phase fini-crétacée auct.) inducing, within the two juxtaposed realms, emersions, erosions and karstic features which give a very contrasted paleogeography during a period characterized by plate convergence and creation of steep topographies.Manuscrit reçu le 25 septembre 2003 Révision acceptée le 4 mai 2004     

Minor changes in surface-water fertility across the oceanic anoxic event 1d (latest Albian,SE France) evidenced by calcareous nannofossils

The latest Albian sediments deposited in the Vocontian basin in south-eastern France record the oceanic anoxic event (OAE) 1d, locally named the Breistroffer interval. They are represented by argillaceous marls and marls, containing organic matter (total organic carbon varying from 0.8 to 1%). Changes in calcareous nannofossil abundance and assemblage composition as well as macrofauna abundance, ichnofossil assemblage, and bioturbation intensity were analysed in order to evaluate the main palaeoenvironmental factors controlling the deposition of the OAE 1d sediments in this area. The pelagic carbonate production is limited and the carbonate fraction is predominantly of nektonic/benthic, and of allochthonous origin from carbonate platforms. The enrichment in organic carbon within the Breistroffer interval is weak and not associated with high surface-water productivity. The organic matter is mainly terrigenous. Its record is due to (1) a good preservation under dysoxic conditions within the sediments, and (2) a weak input of allochthonous carbonates. Eustatic fluctuations strongly influenced the variations of nannofossil and macrofauna abundances. Distinctive patterns in nannofossil assemblages and macrofauna abundances within the Breistroffer interval are also recognized, reflecting changes from mesotrophic to more oligotrophic conditions which are probably controlled by climate.