Alpine and pre-Alpine magmatism in the root-zone of the western Central Alps

 The highest grade of metamorphism and associated structural elements in orogenic belts may be inherited from earlier orogenic events. We illustrate this point using magmatic and metamorphic rocks from the southern steep belt of the Lepontine Gneiss Dome (Central Alps). The U-Pb zircon ages from an anatectic granite at Verampio and migmatites at Corcapolo and Lavertezzo yield 280–290 Ma, i.e., Hercynian ages. These ages indicate that the highest grade of metamorphism in several crystalline nappes of the Lepontine Gneiss Dome is pre-Alpine. Alpine metamorphism reached sufficiently high grade to reset the Rb-Sr and K-Ar systematics of mica and amphibole, but generally did not result in crustal melting, except in the steep belt to the north of the Insubric Line, where numerous 29 to 26 Ma old pegmatites and aplites had intruded syn- and post-kinematically into gneisses of the ductile Simplon Shear Zone. The emplacement age of these pegmatites gives a minimum estimate for the age of the Alpine metamorphic peak in the Monte Rosa nappe. The U-Pb titanite ages of 33 to 31 Ma from felsic porphyritic veins represent a minimum-age estimate for Alpine metamorphism in the Sesia Zone. A porphyric vein emplaced at 448±5 Ma (U-Pb monazite) demonstrates that there existed a consolidated Caledonian basement in the Sesia Zone. Received: 23 May 1995/Accepted: 12 October 1995     

Modelling the response of glaciers to a doubling in atmospheric CO2: a case study of Storglaciären, northern Sweden

To predict the evolution of glaciers in an enhanced greenhouse climate, results from a global climate model, a glacier melt/accumulation model, and a glacier flow model were combined. The method was applied to Storglaciären, a small well-studied glacier in northern Sweden. The difference between the present climate and a 2 × CO₂ climate around the year 2050 was extracted from a model experiment with the ECHAM4-T106 high resolution climate model for time slices at present and in 2050, using prescribed boundary conditions of sea surface temperature and sea-ice distribution, which are derived from a lower resolution transient run of the ECHAM4-T42/OPIC-coupled atmosphere ocean model between present and 2050. The local climatic conditions on the glacier for 2050 were obtained by adding the modelled local climate changes to the observed local present-day climate. The combination of the comprehensive models presented offers a tool to test and calibrate simplified models which are applicable to a much larger sample of glaciers. For the region of Storglaciären, the GCM projected temperature is found to increase most strongly during the winter months, but also shows a warming during the transition from spring to summer, and again between summer and fall, thus extending the melt season by three to four weeks. Precipitation, on the other hand, decreases by approximately 5% during May to September while there is a stronger increase of approximately 14% for the rest of the year. The consequent increase in winter accumulation on Storglaciären is more than compensated by the increase in ablation during the melt season. The glacier flow model predicts a 300 m retreat of the glacier terminus by the middle of the next century, and a loss of 30% of the present ice mass.     

Faltung und Gangbildung im Gebiet der Eisenspatgrube “Ameise” bei Siegen

Zusammenfassung Die Bildung des Spateisensteinganges von Grube Ameise fällt wahrscheinlich in das Ende der Faltung.Der Gang entwickelt sich aus einer Scherfläche, an der Abschiebungen stattfanden, die die Faltenachsen antithetisch verwerfen.     

Simulation of the geochemical transformations of sterols: superacid effect of clay minerals

The heating of cholestanol 2a with kaolinite (140°C, 16 hr) mainly leads to a mixture of steranes (40%) and sterenes (35%). The major compounds which are formed have been identified as 5α(H)- and 5β(H)-cholestanes, 4a and 4b, the diacholestenes, 5, the diacholestanes, 6, and the D-homodiacholestanes 7. With the exception of the latter, these compounds have all been observed previously in ancient sediments and crude oils. Several of these compounds are identical or bear structural similarities with those obtained from cholestanol at low temperature in acidic or superacidic conditions. The comparison with the results obtained using other minerals (montmorillonite, talc, alumina, polyphos-phate-treated montmorillonite) shows that the observed transformations are catalysed by superacid sites which are present in kaolinite and montmorillonite.     

Secular non-random variations of cosmogenic carbon-14 in the terrestrial atmosphere

The time dependence of the¹⁴C content of bristlecone pine wood samples dated by their tree rings and grown during the last 8000 years was examined. The¹⁴C values as measured by the La Jolla Radiocarbon Laboratory were used for the investigation.Two different smoothing techniques were used for constructing values for equal time intervals. In this manner the introduction of regularities, that could have resulted from applied mathematical techniques, could be excluded.There is good evidence for non-random features in the power spectrum, in particular for a 200-year periodicity.The regularities in the power spectrum are further indications supporting the assumption that the¹⁴C variations reflect a property of the sun.     

Lake Shala: Water chemistry,mineralogy and geochemistry of sediments in an Ethiopian Rift lake

Lake Shala, the deepest lake in the internal Galla lakes basin of the Ethiopian Rift, fills a depression in Pleistocene volcanic rocks. Its sodium-bicarbonate (-chloride) water (salinity 16 g/l) is remarkably low in earth alkalines and sulphate. Stratification is indicated by different ion concentrations in the surface and bottom waters and by a thermocline in a water depth of 50–70 m. Hot soda springs emerging on the shores of Lakes Shala and Langano are believed to be derived from a hot saline underground reservoir recharged by meteoric waters. The ion composition of the hot spring waters is uniform and matches that in the Galla Lakes except for total salinities. Anomalous heavy metal concentrations are lacking in lake and hot spring waters. Sediments of Lake Shala belong to an extremely fine-grained group of deposits. They are poorly sorted and the lateral distribution of the grain sizes does not follow the normal scheme for aquatic depositional environments. A belt, 50–100 m below lake level containing the finest-grained sediments, separates the shallow periphery of the lake bottom from the deep center, both characterized by coarser-grained deposits. The sediments consist of a large portion of glassy components. A poorly cristallized smectite is most abundant in the clay mineral group. The components of the sand fraction are quartz, feldspar, glass particles and occasionally calcite. Nickel, cobalt and lead are depleted in the Lake Shala sediments compared with the averages of shales. Iron, manganese and zinc are relatively high. Silver, cadmium and some of the rare earth elements are enriched by factors of > 5.     

Die Liegendschichten der devonischen Pyrit- u. Schwerspat-Lager von Eisen (Saarland), Meggen und des Rammelsberges

Detailed petrographic and geochemical investigations on the rocks underlying the Devonian stratiforme pyrite and barite deposits of Eisen (Saar district), Meggen (Westphalia), and Rammeisberg (Harz Mountains) in the Rhenish Schiefergebirge have led to the following conclusions:

1. These deposits are tied to dark shales of the pelagic basin facies. In all cases a local depression of the sea floor coincides largely with the spatial extension of the overlying pyrite and barite bodies. These depressions are marked by a large number of sand and silt intercalations, accumulations of reef debris and a significant lower carbonate content.
2. The dark shales underneath the deposits have conspicuously high, but strongly varying contents of Mn, Zn and Pb. This, corresponding with the low carbonate content, is characteristic for the presence of hydrothermal, metalliferous emissions.
3. Predepositional phases of sulfide and barite emplacement are indicated by small layers and lenses.

     

A Comparison of an Ecological Model and GIS Spatial Analysis to Describe Niche Partitioning Amongst Carrion Beetles in Nebraska

Carrion beetles depend on vertebrate carcasses to rear their young. Carcasses are a limited resource with patchy distribution, and there is an intense competition among many species for these carcasses. This situation is expected to lead to niche partitioning, such that different beetle species use different resources and thus escape direct competition. Our project used a geographic information system (GIS) and pitfall sampling to characterize carrion beetle preferences for soil texture and land use in Kearney County, Nebraska. The GIS was used to select sites where sampling was conducted using pitfall traps baited with rat carcasses. Attracted beetles were counted, identified to species, and released. The resulting data were used to construct occurrence maps of eleven species of carrion beetles by overlaying soil texture and land use. We then compared the results of EcoSim (an ecological simulation model of niche overlap) with GIS–generated maps of probability of carrion beetle occurrence. Our results are consistent with landscape–level niche partitioning by seven of the eleven examined species. Our application of GIS to the spatial analysis of carrion beetle distributions demonstrates how this technology can be used to test ecological and evolutionary hypotheses, predict habitat associations, and examine the effects of land use on a community of insects. This work could easily be extended to study the habitat preferences of the federally endangered American burying beetle, Nicrophorus americanus .