XMCD at Fe L<Subscript>2,3</Subscript> edges,Fe and S K edges on Fe<Subscript>7</Subscript>S<Subscript>8</Subscript>

Pyrrhotite (Fe₇S₈) is a natural iron sulphide that can participate in rock magnetisation. Its electronic structure is not yet surely described. X-ray magnetic circular dichroism (XMCD) at Fe L_2,3 edges on Fe₇S₈, coupled with multiplet calculations, shows that iron is present only as Fe²⁺ in this magnetic iron sulphide. It reveals a strong magnetic orbital moment. XMCD at Fe and S K edges shows the quite strong polarization of both Fe and S in Fe₇S₈.     

Über die echographische Aufzeichnung des Verhaltens von Meeresfischen während der Sonnenfinsternis vom 30. Juni 1954

Summary Echo records from the Atlantic west of the Faroe Islands are presented which, for the first time, give evidence of the influence exerted by day on the vertical movement of pelagic fishes by a considerable reduction of luminous intensity (solar eclipse). This phenomenon corresponds with the fact well known since some years from investigations in the North Sea which prove that by night pelagic fishes move in a vertical direction according to the variation in luminous intensity.

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Sur des enregistrements ultra-sonores caractérisant le comportement des poissons pélagiques pendant l'éclipsé de soleil au 30 juin 1954

Résumé On présente des enregistrements ultra-sonores faits en océan Atlantique à l'ouest de l'archipel de Færoé. Ces enregistrements font, pour la première fois, preuve de l'influence exercée de jour sur le mouvement vertical des poissons pélagiques par une réduction sensible de l'intensité lumineuse (éclipse de soleil). Ce phénomène correspond avec le fait bien connu depuis quelques ans par des recherches dans la mer du Nord. Suivant ces recherches, les poissons pélagiques se meuvent nuitamment dans la direction verticale suivant la variation de l'intensité lumineuse.

     

U-Pb and Rb-Sr dating of a polymetamorphic nappe terrain: The Caledonian Jotun nappe,southern Norway

The Caledonian Jotun nappe in the Tyin area of southern Norway has been investigated using U-Pb analysis of zircon and sphene and Rb-Sr measurements of minerals and whole rocks, with special reference to the reaction of the isotope systems to various kinds of metamorphic event. The nappe consists of Precambrian basement rocks and their cover, inversely thrust over the Baltic shield and its parautochthonous, presumably lower Paleozoic sediments during the Caledonian orogeny. While the nappe basement retained its pre-Caledonian structures, the nappe cover was penetratively deformed and metamorphosed to lower greenschist facies conditions.U-Pb analyses of zircon and sphene ofnappe basement rocks point to the crystallization of a syenitic to monzonitic magma at 1694± 20m.y., the intrusion of gabbros into the syenites and monzonites at 1252_?25⁺²⁸ m.y., and the metamorphism (upper greenschist-lower amphibolite facies) and deformation (gneissification and mylonitization) of the whole complex at 909± 16m.y. Although this latest event caused strong lead loss in all zircon populations, it had no influence on the Rb-Sr system on a whole rock scale. The Caledonian movements did not disturb the U-Pb system of zircon and sphene but strongly influenced the Rb-Sr system in certain minerals and zircon and/or its inclusions (K-feldspar and brown biotite partially, green biotite completely reset).In contrast to the nappe basement, zircons from thecover rocks show pronounced lead loss during the Caledonian metamorphism/deformation — U-Pb analysis give discordia lower intercept ages of 415± 21 m.y. and 395± 6m.y. Again, however, the Rb-Sr whole-rock system has not been reset in Caledonian time. Minerals from the same rocks which provided the zircons give Rb-Sr isochron ages of 390± 11m.y. and 386 ± 20 m.y.Comparison of U-Pb and Rb-Sr results from the nappe basement demonstrates that only the analysis of U-Pb systematics in zircon and especially sphene resolved the 900-m.y. event. Rb-Sr mineral data alone yield ambiguous results.The results from the nappe cover confirm that U-Pb analyses from penetratively deformed sediments are very useful in dating a metamorphic/tectonic event in lower greenschist facies conditions.From the measured cell dimensions of the zircon populations it is concluded that lead can be completely retained in zircon during recrystallization.     

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A new map of glacigenic features and glacial landsystems in central mainland Nunavut,Canada

A new digital map of glacial geomorphic features and interpreted glacial landsystems was produced for an area covering ~415 000 km² in the Keewatin Sector of the Laurentide Ice Sheet (LIS) in Nunavut. The map integrates information from previous surficial geology maps and >14 000 field stations, and is significantly improved by the detailed inventory of ~152 000 glacigenic features using high-resolution ArcticDEM data and Landsat 8 imagery. From this, we identify and map coherent patterns of landform development (landsystems) between the Manitoba border and the Arctic coast, many of which are entirely new and others that are significantly modified or updated. In particular, we recognize six separate ice streams, including one probable remnant ice stream, and we delineate numerous palimpsest streamlined landscapes with associated ice-flow trends and relative ages. A continuum of relict terrains with varying basal ice thermal conditions is mapped for the first time in the ice divide migration zone between Baker Lake and Wager Bay. In addition, deglacial cold-based retreat terrains and preserved warm-based landscapes unaffected by younger glacial events have been identified. These new georeferenced, multi-scale data sets and interpreted glacial landsystems provide a comprehensive framework to strengthen reconstructions of the glacial history and dynamics of one of the largest ice domes of the LIS, identify distinct glacial sediment transport paths for applications to mineral exploration, and test numerical modelling of the LIS in support of climate change studies and long-term evolution of modern ice sheets.     

Effect of the environment on the hydrochemical characteristics of an alluvial aquifer following an exceptional multiyear drought (Mediterranean Seashore,Hérault,France): Part II—Climatology and agronomy

The hydrochemical evolution of an alluvial groundwater located along the Mediterranean seashore is analyzed with respect to its agricultural and climatic environment, including degree of saturation of the soil; types of cultures, chemical fertilizers and phytosanitary treatments; selective irrigations of the cultivated areas; precipitations. It is shown that the environmental effect on the groundwater's vulnerability depends on two groups of factors:

1. Transfers from surface to groundwater of nitrates, chlorides, sulfates, and potassium, which are governed by: (a) the climatic conditions before the agricultural activities begin, (b) the kinds of agricultural activities and their distribution in time with respect to a given climatic context. Phenomena of retention of and/or rapid diffusion are related to the sedimentary heterogeneities of the reservoir and to the differences of temperatures between irrigation waters and precipitations.
2. Cationic exchanges related to the presence of clays of Montmorillonite-Kaolinite type.

     

How does landfill leachate affect the chemical processes in a lake system downgradient from a landfill site?

A field study on the geochemical properties of a chemically-stressed limnic environment was performed in Lake Silbersee, which receives leachate water of high inorganic loading from an upgradient landfill site. The highly concentrated sulfate ion in groundwater, when entering the pore water system of the lake, gives rise to an intensive microbial sulfate reduction. A diagenetic approach was used to explain the existence of a marine-like aqueous system within a geologically slightly acidic aquifer, consisting of a well-buffered lake water and an alkalinity producing, excess sulphide containing sediment pore water system.