Element concentrations and variations along a 120-km transect in southern Norway – Anthropogenic vs. geogenic vs. biogenic element sources and cycles

Rock samples and the C-, B- and O-horizons of soils developed on these rocks were collected in forested areas along a 120-km south–north transect in southern Norway, passing through the city of Oslo. Forty samples (1 site/3 km) were analysed for 37 chemical elements (Ag, Al, As, Au, B, Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ga, Hg, K, La, Mg, Mn, Mo, Na, Ni, P, Pb, S, Sb, Sc, Se, Sr, Te, Th, Ti, Tl, U, V, W and Zn) following an aqua regia digestion; pH (water extract) and loss on ignition were also determined. The O-horizon soils were additionally analysed for Pt. Gold is the only element that shows a clear anthropogenic peak in the O-horizon soils collected from the city of Oslo. Silver, Au, Bi, Cd, Hg, Pb, S, Sb, Se and Sr all show a strong enrichment in the O-horizon when compared to the underlying C-horizon or the bedrock along the full length of the transect. Neither geology nor anthropogenic input of elements dominate the observed patterns. The most important factors for the observed element concentrations in the O-horizon are weathering, uptake (or rejection) of elements by plants and the kinetics of decay of the organic material in the O-horizon. Climate, especially temperature and precipitation, has an important influence on the formation and decay rates of the organic soil layer. Acid precipitation will delay the decomposition of the organic layer and lead to a natural enrichment of several metals in the O-horizon. Land use change, deforestation and liming can all increase the decay kinetics of organic matter and thus result in a release of the stored element pool.     

A Bayesian approach to estimating tectonic stress from seismological data

Earthquakes are conspicuous manifestations of tectonic stress, but the non-linear relationships between the stresses acting on a fault plane, its frictional slip, and the ensuing seismic radiation are such that a single earthquake by itself provides little information about the ambient state of stress. Moreover, observational uncertainties and inherent ambiguities in the nodal planes of earthquake focal mechanisms preclude straightforward inferences about stress being drawn on the basis of individual focal mechanism observations. However, by assuming that each earthquake in a small volume of the crust represents a single, uniform state of stress, the combined constraints imposed on that stress by a suite of focal mechanism observations can be estimated. Here, we outline a probabilistic (Bayesian) technique for estimating tectonic stress directions from primary seismological observations. The Bayesian formulation combines a geologically motivated prior model of the state of stress with an observation model that implements the physical relationship between the stresses acting on a fault and the resultant seismological observation. We show our Bayesian formulation to be equivalent to a well-known analytical solution for a single, errorless focal mechanism observation. The new approach has the distinct advantage, however, of including (1) multiple earthquakes, (2) fault plane ambiguities, (3) observational errors and (4) any prior knowledge of the stress field. Our approach, while computationally demanding in some cases, is intended to yield reliable tectonic stress estimates that can be confidently compared with other tectonic parameters, such as seismic anisotropy and geodetic strain rate observations, and used to investigate spatial and temporal variations in stress associated with major faults and coseismic stress perturbations.     

Deutung diskordanter Zirkonalter der Silvrettadecke und des Gotthardmassivs (Schweizer Alpen)

U-Pb isotopic analyses are reported for zircons of nine igneous rocks and high grade metamorphic paragneisses from the Silvretta nappe and the Gotthard massif, Switzerland.Following Silver and Deutsch (1961) the zircon populations isolated from six of these rocks were devided into series of size fractions with varying uranium content. An extensive Rb-Sr investigation has been made on some of these rock samples and their minerals (Arnold and Jäger, 1965: Gotthard massif, Grauert, 1966: Silvretta nappe). Rb-Sr measurements on biotites and mineral isochrons of individual gneiss samples yield ages which indicate the end of the Alpine and the Hercynian (=Variscan) metamorphism. Other measurements give mixed ages between these events. The U-Pb investigation of zircons, however, yield criteria for an even older event, 400 to 500 m.y. ago.The isotopic relationship indicates a strong episodic disturbance of the U-Pb systems in the paragneiss zircons with high losses of radiogenic lead. In a Concordia diagram the best fit lines to the data points of the paragneiss zircons from the Gotthard massif as well as from the Silvretta nappe trend both toward the data points of the orthogneiss zircons and intersect the Concordia at approximately 440 m.y. Rb-Sr analyses of the granitic orthogneisses from the Silvretta nappe (Flüela granite gneisses) gave a well defined isochron of 428 m.y. (=1.47×10^–11y^–1). This value agrees rather well with the age given by the intersection of the best fit lines to the paragneiss zircons with the Concordia.Considering the geological and petrographical observations we interpret this disturbance of the U-Pb systems in the paragneiss zircons as the result of an influence of regional high grade metamorphism and anatectic melting together with the formation of igneous rocks during the Caledonian petrogenesis.In the Silvretta the uranium rich zircons from the Flüela granite gneisses reflect a disturbance and lead loss probably during the Hercynian metamorphism. In the Gotthardmassif the zircons from a quartz diorite and an ultrabasic inclusion in this diorite, however, show no or only a slight influence of the later Hercynian and Alpine metamorphisms. The apparent ages of the zircons in the ultrabasic inclusion are nearly concordant (Pb²⁰⁶/U²³⁸: 448 m.y., Pb²⁰⁷/ U²³⁵: 452 m.y., Pb²⁰⁷/Pb²⁰⁶: 472 m.y.). There is in all orthogneiss zircons some evidence of older inhereted U-Pb components besides new zircon growth.If we assume an episodic model for the lead loss and a disturbance 450 m.y. ago the minimum primary age of the detrital zircon components in the paragneisses would be 1500 m.y.

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Der eine von uns (B.G.) möchte den Herren Prof. Dr. M. Grünenfelder und Prof. Dr. P. Signer vom Labor für Geochronologie des Instituts für Kristallographie und Petrographie der Eidgenössischen Technischen Hochschule Zürich seinen Dank für ihr Interesse und die großzügige Unterstützung bei der Durchführung dieser Arbeit aussprechen. Herr Prof. Dr. M. Grünenfelder und Herr Dr. R. Pidgeon haben ihn in die Arbeitsweise der U-Pb-Isotopenanalyse eingeführt. Herr Dr. V. Köppel sowie alle oben genannten Herren haben durch ihre wertvollen Ratschläge und kritischen Diskussionen diese Arbeit wesentlich gefördert. Ihnen und auch allen anderen Angehörigen des Labors für Geochronologie, die zum Gelingen der Arbeit beigetragen haben, sei herzlichst gedankt.

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Herr Dr. L. Rybach hat in dankenswerter Weise von vier Zirkonfraktionen die Urankonzentration durch Gamma-Spektrometrie bestimmt.

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Wir beide möchten Frau Prof. Dr. E. Jäger und Herrn Prof. Dr. E. Niggli vom Mineralogisch-Petrographischen Institut der Universität Bern für ihr wohlwollendes Interesse und die kritische Durchsicht des Manuskriptes danken.     

Carbon on surfaces of magnesium oxide and olivine single crystals. Diffusion from the bulk or surface contamination?

We have conducted detailed studies of the behavior of carbon on the surfaces of MgO and olivine single crystals using various surface analytical techniques: viz. secondary ion mass spectrometry (SIMS), Auger electron spectrometry (AES) and X-ray photoelectron spectrometry (XPS). In order to distinguish without ambiguity the effect of diffusion of carbon from the bulk to the surface and the effect of surface contamination by carbon-containing species, the experiments were conducted in ultrahigh vacuum, i.e. 10^?11–10^?9 torr. In addition to MgO and olivine single crystals, we have conducted the same studies on TiO₂, MnO, SiO₂ and Ta₂O₅ which serve as blank samples. The MgO and olivine samples were also intentionally implanted with known doses of carbon and the mobility of this particular carbon was investigated in detail. Our results show that the bulk carbon content in MgO is around 40 wt. ppm, considerably lower than the quantities quoted by Freund and co-workers in the past. We also show that the carbon in both MgO and olivine does not display any rapid diffusion behaviour leading to surface segreation in the temperature range 78–723 K, in contrast to the previous findings of Freund and co-workers.     

Tracing quartz through the environment

Quartz, SiO₂, a pure mineral with tight crystal structure, is widespread in rocks and soil. Cosmic rays produce¹⁰Be (t _1/2=1·5×10⁶, yr) and²⁶Al (t _1/2=7·05×10⁵ yr) in quartz exposed at or near the earth’s surface. The use of accelerator mass spectrometry permits measurement of these nuclides in samples exposed at sea level for typical periods.In situ production makes interpretation relatively straightforward. Potential applications include age determination, measurement of erosion and deposition rates, and use as a tracer for continental weathering processes.     

Die Nutzung des Wassers aus den Tagebauen nördlich Leipzigs

Außerordentlich große Wassermengen werden bei der Entwässerung der Tagebaue gehoben, aber bisher nur zu einem geringen Teil unmittelbar für die Wasserversorgung genutzt. Die planmäßige und abgestimmte Nutzung der Naturressourcen verlangt die Prüfung der Möglichkeiten zur Nutzbarmachung zumindest eines Teiles dieser Wässer für die Trinkwasserversorgung besonders in Ballungsgebieten. Auf Grund der besonderen geologischen Gegebenheiten im Raum nördlich Leipzigs bestehen günstige Voraussetzungen. Maßnahmen zum Schutze und der Nutzung dieser Wässer sind eingeleitet. Bauaufwand und technische Ausrüstungen für die Wasserversorgung sind den Besonderheiten der Tagebauwasserbereitstellung anzupassen.     

Professor Albert Defant siebzig Jahre

Ohne Zusammenfassung     

Late-Glacial radiocarbon- and palynostratigraphy on the Swiss Plateau

A detailed late-glacial radiocarbon stratigraphy for the Swiss Plateau has been established on the basis of over 90 accelerator ¹⁴C dates on terrestrial plant macrofossils. Two plateaux of constant.,¹⁴C age were observed, occurring at 12,700 B.P. and at 10,000 B.P. The consequences of these plateaux for palaeo-ecological investigations are threefold: (1) a more refined ¹⁴C dating within the plateaux is not possible, (2) in teleconnections between different sites (if based on ¹⁴C dating and concerning the periods around 12,700 B.P. and 10,000 B.P.) events are considered synchronous which are only synchronous within a plateau of constant age, and (3) exact time-depth relationship and therefore influx calculations are made impossible during these plateau periods. A comparison of the radiocarbon ages derived from terrestrial, telmatic and limnic material at different sites on the Swiss Plateau yields a proposal for modifying the zonation system of Welten for the Late-Glacial. By retaining the limits of chronozones (at 13, 12, 11 and 10ka B.P.) and by refining the palynostratigraphic criteria for the limits of biozones, a separation between chrono- and biozonation at the beginning of the Belling and at the beginning of the Younger Dryas becomes obvious.     

Geometry,bed topography and drainage system structure of the haut glacier d'Arolla,Switzerland

As part of an integrated study of the hydrology, meltwater quality and dynamics of the Haut Glacier d'Arolla, Switzerland, the glacier's drainage network structure was determined from patterns of dye recovery in 342 injection experiments conducted from 47 moulins distributed widely across the glacier. This structure was compared with theoretical predictions based upon reconstructed patterns of water flow governed by (a) the subglacial hydraulic potential surface, and (b) the subglacial bedrock surface. These reconstructions were based on measurements of ice surface and bedrock topography obtained by a combination of ground survey and radio-echo sounding techniques. The two reconstructions simulate the drainage system structures expected for (a) closed channels, in which water is pressurized by the overlying ice, and (b) gravity-driven, open-channel flow. The closed-channel model provides the best fit to the observed structure, even though theoretical calculations suggest that, under summer discharge conditions, open-channel flow may be widespread beneath the glacier. Possible reasons for this apparent discrepancy are discussed.