Macroscopic representation of structural geometry for simulating water and solute movement in dual-porosity media

The structure of macroporous or aggregated soils and fractured rocks is generally so complex that it is impractical to measure the geometry at the microscale (i.e., the size and the shape of soil aggregates or rock matrix blocks, and the myriad of fissures or fractures), and use such data in geometry-dependent macroscale flow and transport models. This paper analyzes a first-order type dual-porosity model which contains a geometry-dependent coefficient, β, in the mass transfer term to macroscopically represent the size and shape of soil or rock matrix blocks. As a reference, one- and two-dimensional geometry-based diffusion models were used to simulate mass transport into and out of porous blocks of defined shapes. Estimates for β were obtained analytically for four different matrix block geometries. Values for β were also calculated by directly matching analytical solutions of the diffusion models for a number of selected matrix block geometries to results obtained with the first-order model assuming standard boundary conditions. Direct matching improved previous results for cylindrical macropore geometries, especially when relatively small ratios between the outer soil mantle and the radius of the inner cylinder were used. Results of our analysis show that β is closely related to the ratio of the effective surface area available for mass transfer, and the soil matrix volume normalized by the effective characteristic length of the matrix system. Using values of β obtained by direct matching, an empirical function is derived to estimate macroscopic geometry coefficients from medium properties which in principle are measurable. The method permits independent estimates of β, thus allowing the dual-porosity approach eventually to be applied to media with complex and mixed types of structural geometry.     

Inclined K–Ar illite age spectra in brittle fault gouges: effects of fault reactivation and wall‐rock contamination

K–Ar clay fraction ages of brittle faults often vary with grain size, decreasing in the finer size fractions, producing an inclined age–grain‐size spectrum. K–Ar ages and mineralogical characterization of gouges from two normal faults in the Kongsberg silver mines, southern Norway, suggest that inclined spectra derived from brittle fault rocks reflect the mixing of inherited components with authigenic mineral phases. The ages of the coarsest and finest fractions constrain faulting at c. 260–270 Ma and reactivation around 200–210 Ma, respectively. This study demonstrates how wall‐rock contamination influences the K–Ar age of the coarsest size fractions and that authigenic illite and K‐feldspar can crystallize synkinematically under equivalent conditions and thus yield the same K–Ar ages.     

Eh ph Diagrams for mn, fe, co, ni, cu and as Under Seawater Conditions: Application of two new Types of eh ph Diagrams to the Study of Specific Problems in Marine Geochemistry

E_H pH diagrams have been calculated using the PHREEQC programme in order to establish the predominance fields of Mn, Fe, Co, Ni, Cu and As in bottom waters from the Angola Basin. Predominance fields are presented separately for both aquatic species and solid mineral phases in order to simplify interpretation of the data. The diagrams show significant differences from standard E_H pH diagrams for these elements calculated for freshwater at 25 °C and 1 bar which assume an element concentration of 10^-6 M. In particular, our diagrams show that Mn²⁺ and NiCO ₃ ⁰ are the predominant aquatic species for Mn and Ni in bottom seawater and FeOOH, Fe₂O₃, Fe₃O₄, CoFe₂O₄, CuFe₂O₄, CuFeO₂, and Ba₃ (AsO₄)₂ the predominant solid phases for Fe, Co, Cu and As, respectively. Mn and Ni are therefore undersaturated and Fe, Co, Cu and As supersaturated in bottom seawater from the Angola Basin. Neither rhodochrosite (MnCO₃) nor siderite (FeCO₃) can form in this marine environment in equilibrium with seawater. A mixed Mn-Ca carbonate is therefore formed within the pore waters of reducing sediments. The high Ni/Cu ratios in cobalt-rich manganese crusts formed adjacent to the oxygen minimum zone may be explained by the change from Cu²⁺ to CuCl ₃ ^2- as the dominant aquatic species of Cu in seawater at an E_H of +0.48 V.     

Sodic Pyroxene and Sodic Amphibole as Potential Reference Materials for In Situ Lithium Isotope Determinations by SIMS

Two large pegmatitic crystals of sodic pyroxene (aegirine) and sodic amphibole (arfvedsonite) from the agpaitic igneous Ilímaussaq Complex, south Greenland were found to be suitable as reference materials for in situ Li isotope determinations. Lithium concentrations determined by SIMS and micro‐drilled material analysed by MC‐ICP‐MS generally agreed within analytical uncertainty. The arfvedsonite crystal was homogeneous with [Li] = 639 ± 51 μg g^?1 (2s, n = 69, MC‐ICP‐MS and SIMS results). The aegirine crystal shows strongly developed sector zoning, which is a common feature of aegirines. Using qualitative element mapping techniques (EPMA), the homogeneous core of the crystal was easily distinguished from the outermost sectors of the crystals. The core had a mean [Li] of 47.6 ± 3.6 μg g^?1 (2s, n = 33) as determined by SIMS. The seven micro‐drilled regions measured by solution MC‐ICP‐MS returned slightly lower concentrations (41–46 μg g^?1), but still overlap with the SIMS data within uncertainty. Based on MC‐ICP‐MS and SIMS analyses, the variation in δ⁷Li was about 1‰ in each of the two crystals, which is smaller than that in widely used glass reference materials, making these two samples suitable to serve as reference materials. There was, however, a significant offset between the results of MC‐ICP‐MS and SIMS. The latter deviated from the MC‐ICP‐MS results by ?6.0 ± 1.9‰ (2s) for the amphibole and by ?3.9 ± 1.9‰ (2s) for the aegirine. This indicates the presence of a significant matrix effect in SIMS determinations of Li isotopes for amphibole and pyroxene relative to the basalt glasses used for calibration. Based on the MC‐ICP‐MS results, mean δ⁷Li values of +0.7 ± 1.2‰ (2s, n = 10) for the arfvedsonite crystal and of ?3.7 ± 1.2‰ (2s, n = 7) for the core of the aegirine crystal were calculated. Adopting these values, SIMS users can correct for the specific IMF (instrumental mass fractionation) of the ion probe used. We propose that these two crystals serve as reference materials for in situ Li isotope determinations by SIMS and pieces of these two crystals are available from the first author upon request.     

Factors shaping submerged bryophyte communities: A conceptual model for small mountain streams in Germany

Several models explaining species composition of aquatic bryophytes are available for specific regions. However, a more general, conceptual model applicable to a broader range of regions is lacking.We present a conceptual model ranking environmental factors determining submerged bryophyte communities in small mountain streams. It was tested on a dataset of 54 stream sections after removing the effect of stream size and altitude. Species responses were modeled with pH as predictor variable based on 97 stream sites covering six mountain regions all over Germany. Multiple regressions revealed the importance of primary growth factors (light, Ep(CO₂)) and substrate for the total submerged bryophyte coverage.The known distinction of hard- and softwater bryoflora was clearly supported. The floristic composition of headwaters was predominantly determined by the bicarbonate/ionic strength complex. Species response to pH values supported this result and thus our conceptual model. The primary growth resources light, Ep(CO₂) and availability of coarse streambed material explained one third (R_adjusted² = 0.34) of total submerged bryophyte cover. Disturbances, predominantly spates, reduce biomass but do not affect the basic floristic structure.In conclusion, conceptual models and monitoring methods focusing on aquatic bryophytes need to clearly distinguish “aquatic” from “submersed by chance”. All “aquatic bryophytes” found in Germany can also occur at least temporarily at non-submerged sites. Therefore, a distinction between primary growth factors and additional resources is recommended to disentangle factors determining aquatic bryophyte communities.     

K–Ar dating of authigenic minerals in siliciclastic sequences: an example from the south Sanfranciscana Basin (Western Minas Gerais,Brazil)

K–Ar dating was applied on authigenic potassic minerals which are abundant in sandstones from the south of the Sanfranciscana Basin, Western Minas Gerais State, central Brazil. The Quintinos Member fluvial sandstones (Três Barras Formation, Areado Group) contain significant amounts of authigenic K‐feldspar as microcrystals of adularia and sanidine habits. The ages of these microcrystals cluster into three groups: 106.1 ± 2.2, 89.9 ± 1.9 and 88.8 ± 1.8 Ma (from Albian to Coniacian). The older age of 106.1 ± 2.2 Ma was obtained from the coarse fraction analysed (10–20 µm) that can contain a mixture of detrital potassic minerals (K‐feldspar, muscovite, biotite and illite) and different authigenesis of K‐feldspar (overgrowths and microcrystals). Thus, only the younger ages were interpreted as precipitation of K‐feldspar microcrystals during the Late Cretaceous into the Quintinos Member sandstones. Moreover, these ages can document the formation of microcrystals within a few million years after deposition of the sandstones. The ages of authigenic illite from the Capacete Formation epiclastic sandstones (Mata da Corda Group) range from 88.5 ± 1.9 to 71.5 ± 1.9 Ma (Coniacian–Campanian). These results suggest the timing of the illitization event in these sandstones as well as a synchrony with K‐feldspar authigenesis in the Quintinos Member sandstones. These results are well constrained and are in agreement with stratigraphic, biostratigraphic and radiometric ages previously reported for the Sanfranciscana Basin. Copyright © 2014 John Wiley & Sons, Ltd.     

Evidence for the 22-year-cycle in the longitudinal distribution of sunspots

It was shown in an earlier paper that preferred hemispheres of solar activity alternate with the 22-year magnetic cycle, when analyzed in the 27.0 day Bartels rotation. Using data which cover the time between 1818 and 1983 we trace back this result to 1880 (cycle 12). Before 1880 no significant correlations are found.     

Chemical and tectonic controls on the formation of sparry magnesite deposits — the deposits of the northern Greywacke Zone (Austria)

The sparry magnesite deposits of the northern Greywacke Zone are situated at the base of thrust sheets. Model calculations and natural examples suggest that an inverse temperature gradient can only be established at the base of a thrust sheet if thrusting is so rapid as to be geologically unrealistic. Independently of this thrusting induces a fluid flow from the lower units to the front of the moving thrust sheet. Stability data of magnesite and dolomite in contact with fluids with different Ca/(Ca+Mg) ratios suggest that this tectonically induced fluid flow produce magnesite from preexisting dolomite by metasomatism.

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Zusammenfassung Die Spatmagnesitvorkommen der Nördlichen Grauwackenzone liegen innerhalb von Deckengrenzen. Modellberechnungen zeigen, daß ein inverser Temperaturgradient sich nur dann an der Basis von Decken einstellen kann, wenn die Überschiebungsgeschwindigkeit so groß wird, daß sie geologisch unglaubwürdig ist. Deckenüberschiebungen erzeugen aber in jedem Fall in der überschobenen Einheit einen zur Deckenfront hin gerichteten Fluidstrom. Eine Betrachtung der Stabilitätsdaten für Magnesit und Dolomit im Gleichgewicht mit einer fluiden Phase mit unterschiedlichen Ca/(Ca+Mg)-Verhältnissen zeigt, daß durch einen solchen Fluidstrom metasomatisch Magnesit aus Dolomit gebildet werden kann.

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Résumé Les dépôts de magnésite spathique de la Grauwacken Zone septentrionale sont situés à la base d'unités charriées. Un calcul de modélisation et des exemples naturels montrent qu'un gradient inverse de température ne peut s'établir à la base d'une unité charriée qu'à la condition d'admettre une vitesse de charriage tellement élevée qu'elle est irréaliste. D'autre part, le phénomene de charriage induit un déplacement de fluide depuis les unités inférieures vers le front de la nappe. Les données relatives aux conditions de stabilité de la magnésite et de la dolomite en présence de fluides de divers rapports Ca/Ca+Mg permettent de déduire que le flux ainsi engendré par la tectonique peut engendrer la magnésite par métasomatose à partir de dolomite préexistante.

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. , , , , . . , Ca/(Ca+Mg) , , , , , , - .

     

Nachweis von Industriechemikalien (HPS,BPS und SPS) im Oberflächenwasser

Occurrence of Industrial Chemicals (HPS, BPS, and SPS) in Surface Water The paper gives the results of water examinations for different phenylsulfonamides. Random samples taken every month between May 1999 and August 2000 from surface water out of the river Rhine (kilometer 838), the river Ruhr (Mülheim Styrum) and the river Emscher (Oberhausen center) were tested for the corrosion inhibiting agent 6‐[methyl(phenylsulfonyl)amino]‐hexanoic acid (HPS) as well as its metabolites 4‐[methyl‐(phenylsulfonyl)amino]‐butanoic acid (BPS) and sarkosin‐N‐(phenylsulfonyl) (SPS). Furthermore, the sewage plant effluents of two municipal wastewater treatment plants from the rural area were also included in the monitoring program. The analytical method includes solid‐phase extraction (SPE), a derivatization step as well as gas chromatography mass spectrometry (GC‐MS). SPS is regularly found in all investigated surface waters, but only occasionally in the effluents of the two rural sewage plants. The median values for SPS amount to 0.09 μg/L in the river Rhine, 0.60 μg/L in the river Ruhr, and 0.70 μg/L in the river Emscher. BPS can only be found in the river Ruhr (median value: 0.08 μg/L) and in the river Emscher (median value: 0.41 μg/L). HPS was regularly found in a surface water for the first time. This substance can be detected in the Emscher through the whole measurement period. The median value for HPS amounts to 1.78 μg/L. Aditionally, the validation characteristics of an alternative analytical method including solid‐phase microextraction (SPME) is worked out. The fully automated process includes an on‐fiber methylation step and the GC‐MS. The repeatability standard deviation of the process amounts to RSD < 12%. Detection limits between 0.07 and 0.70 μg/L are achieved.