Numerical Calculation of Equivalent Cell Permeability Tensors for General Quadrilateral Control Volumes

A new method for upscaling fine scale permeability fields to general quadrilateral-shaped coarse cells is presented. The procedure, referred to as the conforming scale up method, applies a triangle-based finite element technique, capable of accurately resolving both the coarse cell geometry and the subgrid heterogeneity, to the solution of the local fine scale problem. An appropriate averaging of this solution provides the equivalent permeability tensor for the coarse scale quadrilateral cell. The general level of accuracy of the technique is demonstrated through application to a number of flow problems. The real strength of the conforming scale up method is demonstrated when the method is applied in conjunction with a flow-based gridding technique. In this case, the approach is shown to provide results that are significantly more accurate than those obtained using standard techniques.     

Prehistoric soil and water detention structures (gabarbands) at Phang,Sindh Kohistan,Pakistan: An adaptation to environmental change?

Five gabarbands (dams), components of integrated soil and water conservation systems, were investigated in the arid region of Sindh Kohistan. The dams are associated with two prehistoric Kot Dijian settlements, Phang and Kohtrash (3200–2800 B. C.). The dams were constructed with relatively permeable materials. Three of the dams, South, East, and North, close off water gaps and a strike valley, respectively, to form a detention basin. The West Dam, located on Phang Nai, upstream of the detention basin removed the coarser sediment fraction from the flows. Spring Dam, located in a water gap to the north of the detention basin, acted as a low-head weir to distribute flow from a perennial spring onto the floodplain of Baran Nai, where double-cropping was probably practiced. Faulting eliminated the spring, which had probably supported the Kohtrash site, and led to construction of the detection basin for the purposes of subsurface storage of detained flows. Association of both modern and prehistoric sites with springs suggests that there has not been appreciable climate change in Sindh Kohistan in the last 5000 years. © 1993 John Wiley & Sons, Inc.     

Effects of variable winds on biological productivity on continental shelves in coastal upwelling systems

The production and distribution of biological material in wind-driven coastal upwelling systems are of global importance, yet they remain poorly understood. Production is frequently presumed to be proportional to upwelling rate, yet high winds can lead to advective losses from continental shelves, where many species at higher trophic levels reside. An idealized mixed-layer conveyor (MLC) model of biological production from constant upwelling winds demonstrated previously that the amount of new production available to shelf species increased with upwelling at low winds, but declined at high winds [Botsford, L.W., Lawrence, C.A., Dever, E.P., Hastings, A., Largier, J., 2003. Wind strength and biological productivity in upwelling systems: an idealized study. Fisheries Oceanography 12, 245–259]. Here we analyze the response of this model to time-varying winds for parameter values and observed winds from the Wind Events and Shelf Transport (WEST) study region. We compare this response to the conventional view that the results of upwelling are proportional to upwelled volume. Most new production per volume upwelled available to shelf species occurs following rapid increases in shelf transit time due to decreases in wind (i.e. relaxations). However, on synoptic, event time-scales shelf production is positively correlated with upwelling rate. This is primarily due to the effect of synchronous periods of low values in these time series, paradoxically due to wind relaxations. On inter-annual time-scales, computing model production from wind forcing from 20 previous years shows that these synchronous periods of low values have little effect on correlations between upwelling and production. Comparison of model production from 20 years of wind data over a range of shelf widths shows that upwelling rate will predict biological production well only in locations where cross-shelf transit times are greater than the time required for phytoplankton or zooplankton production. For stronger mean winds (narrower shelves), annual production falls below the peak of constant wind prediction [Botsford et al., 2003. Wind strength and biological productivity in upwelling systems: an idealized study. Fisheries Oceanography 12, 245–259], then as winds increase further (shelves become narrower) production does not decline as steeply as the constant wind prediction.     

Low‐energy helium ion irradiation‐induced amorphization and chemical changes in olivine: Insights for silicate dust evolution in the interstellar medium

Abstract— We present the results of irradiation experiments aimed at understanding the structural and chemical evolution of silicate grains in the interstellar medium. A series of He+ irradiation experiments have been performed on ultra‐thin olivine, (Mg,Fe)₂SiO₄, samples having a high surface/volume (S/V) ratio, comparable to the expected S/V ratio of interstellar dust. The energies and fluences of the helium ions used in this study have been chosen to simulate the irradiation of interstellar dust grains in supernovae shock waves. The samples were mainly studied using analytical transmission electron microscopy. Our results show that olivine is amorphized by low‐energy ion irradiation. Changes in composition are also observed. In particular, irradiation leads to a decrease of the atomic ratios O/Si and Mg/Si as determined by x‐ray photoelectron spectroscopy and by x‐ray energy dispersive spectroscopy. This chemical evolution is due to the differential sputtering of atoms near the surfaces. We also observe a reduction process resulting in the formation of metallic iron. The use of very thin samples emphasizes the role of surface/volume ratio and thus the importance of the particle size in the irradiation‐induced effects. These results allow us to account qualitatively for the observed properties of interstellar grains in different environments, that is, at different stages of their evolution: chemical and structural evolution in the interstellar medium, from olivine to pyroxene‐type and from crystalline to amorphous silicates, porosity of cometary grains as well as the formation of metallic inclusions in silicates.     

New 1982 — 1990 photometry of λ Andromedae and its 11-year cycle

We present photoelectric photometry of λ And never before published, obtained between February 1982 and December 1990 at 29 different observatories. Then we combine it with all other photometry available to us (previously published, contained in the I.A.U. Commission 27 Archives, and obtained with the Vanderbilt 16-inch automatic telescope but not yet published), to yield a 14.8-year data base. Analysis reveals a long-term cycle in mean brightness, with a full range of 0^m.15 and a period of 11.4 ± 0.4 years. Because most of our new photometry was concentrated in the 1983-84 observing season, we analyze that one well-defined light curve with a two-spot model. Spot A keeps a 0^m.04 amplitude throughout four rotation cycles whereas the amplitude of spot B diminishes from 0^m.09 down almost to 0^m.03. The spot rotation periods were 55^d.9 ± 0^d.6 and 520^d.8 ± 1^d.0, respectively.     

Kinetic and equilibrium studies of copper-dissolved organic matter complexation in water column of the stratified Krka River estuary (Croatia)

An interaction of dissolved natural organic matter (DNOM) with copper ions in the water column of the stratified Krka River estuary (Croatia) was studied. The experimental methodology was based on the differential pulse anodic stripping voltammetric (DPASV) determination of labile copper species by titrating the sample using increments of copper additions uniformly distributed on the logarithmic scale. A classical at-equilibrium approach (determination of copper complexing capacity, CuCC) and a kinetic approach (tracing of equilibrium reconstitution) of copper complexation were considered and compared. A model of discrete distribution of organic ligands forming inert copper complexes was applied. For both approaches, a home-written fitting program was used for the determination of apparent stability constants (K_i^equ), total ligands concentration (L_iT) and association/dissociation rate constants (k_i¹,k_i^- 1).A non-conservative behaviour of dissolved organic matter (DOC) and total copper concentration in a water column was registered. An enhanced biological activity at the freshwater–seawater interface (FSI) triggered an increase of total copper concentration and total ligand concentration in this water layer. The copper complexation in fresh water of Krka River was characterised by one type of binding ligands, while in most of the estuarine and marine samples two classes of ligands were identified. The distribution of apparent stability constants (log K₁^equ: 11.2–13.0, log K₂^equ:8.8–10.0) showed increasing trend towards higher salinities, indicating stronger copper complexation by autochthonous seawater organic matter.Copper complexation parameters (ligand concentrations and apparent stability constants) obtained by at-equilibrium model are in very good accordance with those of kinetic model. Calculated association rate constants (k₁¹:6.1–20 × 10³ (M s)^− 1, k₂¹: 1.3–6.3 × 10³ (M s)^− 1) indicate that copper complexation by DNOM takes place relatively slowly. The time needed to achieve a new pseudo-equilibrium induced by an increase of copper concentration (which is common for Krka River estuary during summer period due to the nautical traffic), is estimated to be from 2 to 4 h.It is found that in such oligotrophic environment (dissolved organic carbon content under 83 µM_C, i.e. 1 mg_CL^− 1) an increase of the total copper concentration above 12 nM could enhance a free copper concentration exceeding the level considered as potentially toxic for microorganisms (10 pM).     

Les Facies de Transgression du Trias sur la Bordure Nord-est du Massif Central Français

Résumé La transgression triasique est suivie d'Est en Ouest sur la bordure du Massif Central français. Les formations sont de plus en plus récentes vers l'Ouest, indépendamment de leur faciès. Les limites du Buntsandstein et du Trias supérieur semblent locales et d'origine tectonique, tandis que la limite du Ladinien supérieur parait plus générale et correspond à la période où le caractère marin de la transgression sur les massifs hercyniens était le plus franc.Le début de la transgression aniso-ladinienne est daté pour l'Anisien par des empreintes de Reptiles et pour les faciès les plus marins du Ladinien par des Foraminifères et des pollens. A cette période, des microfaunes mésogéennes de mer ouverte apparaissent sur les bordures.Dans les faciès de transgression réduits, le Trias est constitué de grès fins silteux à pseudomorphoses de sel gemme et empreintes de Reptiles, étalés par une mer pelliculaire sur une surface plate. Le socle sous-jacent a fourni peu de matériel clastique et les courants sont orientés du Nord au Sud. Les évaporites sont plus concentrées sur la bordure que plus au large, ce qui implique une certaine aridité pendant toute la période de la transgression.Les faciès de bordure les plus avancés sur le socle sont formés d'une dolomie paralique supratidale déposée dans des lagunes évaporitiques. Sur les massifs hercyniens, des fractures et des failles ouvertes ont permis des circulations auxquelles sont liés des remplissages carbonates et des minéralisations.

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Conditions of the triassic transgression are analysed from East to West across the eastern border of the Central Massif. Formations directly overlying the basement get younger and younger westwards, without relation with the environment. Buntsandstein and upper Triassic boundaries appear to be syntectonic local limits. The upper Ladininian boundary seems to be more general and connected with the main period of the marine environment for the transgression on the variscan basement rocks. The anisoladinian transgression beginns during the anisian age as indicated by fooprints, while ladinian age is supported by mesogean foraminifera and palynology during the climax of the transgression, in an open sea environment.Silty fine sandstones with footprints and salt casts constitute the triassic transgression facies on the flattened border of the Central Massif. The underlying basement supplied only a little arenaceous material and the currents are oriented from Nord to South. Evaporites are more concentrated at the boundary of the transgression than towards the basin, what means aridity.Paralic supratidal dolomite constitutes the most external deposits at the transgression limit, in a syntectonic environment. Dolomite infillings and ore deposits are connected with water circulations along faults and fractures.

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Zusammenfassung Die Triastransgressionsschichten werden von Osten nach Westen am Nordrand des französischen Zentralmassivs beschrieben. Die auf dem Grundgebirge auflagernden Basisschichten werden, unabhängig von ihrer Faziesausbildung, nach Westen stets jünger. Die Begrenzungen der Ablagerungen des Buntsandsteins und der oberen Trias werden nur lokal, wahrscheinlich in Abhängigkeit von synsedimentären, tektonischen Strukturen angetroffen. Die Beckenausdehnung am Top des oberen Ladiniums ist dagegen zusammenhängend zu erkennen. Sie entspricht den eindeutigeren marinen Transgressionsverhältnissen auf dem variskischen Sockel.Die einsetzende Transgression des Aniso-Ladiniums wird durch Reptilienfährten als anisisch und die stärker marinen Ablagerungen durch Foraminiferen und Pollen als ladinisch datiert. In diesem Zeitabschnitt dringen offenmarine, mesogäische Mikrofossilien bis zum Beckenrand vor.Die geringmächtigen Transgressionsablagerungen bestehen aus siltigen Feinsanden mit Steinsalzpseudomorphosen und Reptilienfährten. Diese Sande wurden von einem sehr seichten Meer auf dem stark eingeebneten Grundgebirge verteilt. Das Grundgebirge hat nur sehr wenige klastische Abtragungsprodukte geliefert. Die Strömungen waren von Norden nach Süden ausgerichtet. Evaporite treten stärker in den randlichen Gebieten als zum offenen Becken hin auf. Dies zeigt auf eine ausgeprägte Aridität während der gesamten Transgressionszeit hin.Die am weitesten zum Festland hin vorgeschobenen Transgressionssedimente bestehen aus paralischen, subpratidalen Dolomiten, die sich in evaporitischen Lagunen bildeten. Die in den offenen Spalten und Verwerfungen des Grundgebirges zirkulierenden Lösungen führten zu Dolomitausfällungen und zu schichtgebundenen Vererzungen.

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Rauhwacken und ihre Entstehung

This publication comprises the results of a detailed investigation of rauhwackes regarding both their stratigraphic/tectonic positions and their macroscopic/microscopic aspects. The conclusion drawn is that rauhwackes are carbonate breccias of tectonic origin, which usually suffered extensive recrystallization and calcitization. Moreover, these breccias became strongly weathered as a result of which they acquired a typical porous to cavernous appearance. Rauhwackes were formed by way of brecciation of carbonate rocks with a comparatively slight cohesion of their constituting grains; these rocks have been deposited in a saline environment. Rauhwackes may be divided into two main varieties:

1. monomict rauhwaekes, formed by fragmentation of only one type of rock (usually a sucrose dolostone), and
2. polymict rauhwackes, formed by fragmentation and mixing of two or more types of rock.

The typical boxwork rauhwackes represent a subtype of monomict rauhwackes. They originated from fractured dolostones and are extensively developed in only slightly tectonized regions, e. g. in the German Zechstein and Muschelkalk. Polymict rauhwackes represent intraformational crush-breccias which were formed by sliding (décollement) parallel to the bedding. Examination of polymict rauhwackes occurring in the metamorphic nappes of Tertiary orogenes may increase our knowledge about the relation existing between the tectonic evolution and Alpine metamorphism in these orogenes.