Die Paleozän-Eozän-Transgression in Südlibyen

Zusammenfassung An der Peripherie der Serir Tibesti (Südlibyen und nördlicher Grenzbereich der Rebublik Tschad) wurden 10 lithostratigraphische Profile aufgenommen und miteinander korreliert, um das Vorgreifen der Paleozän-Eozän-Transgression auf den afrikanischen Kontinent zu verfolgen. Es zeigt sich, daß der Höhepunkt der in der Oberkreide begonnenen Transgression während der Ablagerung der oberpaleozänen Operculinoides-Schichten und des untereozänen Kheir Mergels erreicht war. Ein direkter Zusammenhang zwischen dem Sedimentationsraum nördlich des Tibesti und dem Niger-Becken mittels der Hoggar-Tibesti-Pforte (Furon 1951, p. 71) wird abgelehnt, da die größte Verbreitung des mer saharienne südlich des Hoggar-Tibesti in der Oberkreide und nicht im Paleozän stattfand.

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10 lithostratigraphic sections were surveyed along the periphery of the Serir Tibesti (southern Libya and northern border area of Republic Chad). Their correlation resulted in analysing the Paleocene-Eocene transgression on the African continent. It was found out that this transgression starting with the Upper Cretaceous reached its climax during sedimentation of the upper Paleocene Operculinoides-Schichten and lower Eocene Kheir Marl. A direct connection between the sedimentation area north of the Tibesti mountains and the Niger basin via the Hoggar-Tibesti-Straits (Furon 1951, p. 71) is not encountered as the climax of the extension of the mer saharienne south of Hoggar-Tibesti coincides with the Upper Cretaceous and not with the Paleocene.

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Résumé A la périphérie du Sérir Tibesti (Libye méridionale et zone frontière septentrionale de la République du Tchad) 10 coupes lithostratigraphiques ont été établies. Une corrélation effectuée entre eux démontre le caractère progressif de la transgression du Paléocène-Eocène vers le continent africain. Cette transgression dont le début a été daté au Crétacé supérieur a atteint son extension la plus large au temps de la sédimentation des séries à Operculinoides (Paléocène supérieur) et des marnes Kheir (Eocène inférieur). L'idée d'une connexion directe entre l'aréal de sédimentation au nord du Tibesti et celui du bassin de Niger par moyen du détroit Hoggar-Tibesti (Furon 1951, p. 71) n'a pas pu être acceptée étant donné que l'extension la plus large de la «mer saharienne» au sud du Hoggar-Tibesti s'est passée au Crétacé supérieur et non pas au Paléocène.

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Soil frost effects on soil water and runoff dynamics along a boreal forest transect: 1. Field investigations

To determine how soil frost changes flowpaths of runoff water along a hillslope, a transect consisting of four soil profiles directed towards a small stream in a mature forest stand was investigated at Svartberget, near Vindeln in northern Sweden. Soil temperature, unfrozen water content, groundwater level and snow depth were investigated along the transect, which started at the riparian peat, and extended 30 m upslope into mineral soils. The two, more organic‐rich profiles closest to the stream had higher water retention and wetter autumn conditions than the sandy mineral soils further upslope. The organic content of the soil influenced the variation in frost along the transect. The first winter (1995–96) had abnormally low snow precipitation, which gave a deep frost down to 40–80 cm, whereas the two following winters had frost depths of 5–20 cm. During winter 1995–96, the two organic profiles close to the stream had a shallower frost depth than the mineral soil profile higher upslope, but a considerably larger amount of frozen water. The fraction of water that did not freeze despite several minus degrees in the soil was 5–7 vol.% in the mineral soil and 10–15 vol.% in the organic soil. From the measurements there were no signs of perched water tables during any of the three snowmelt periods, which would have been strong evidence for changed water flowpaths due to soil frost. When shallow soil layers became saturated during snowmelt, especially in 1997 and 1998, it was because of rising groundwater levels. Several rain on frozen ground events during spring 1996 resulted in little runoff, since most of the rain either froze in the soil or filled up the soil water storage. Copyright © 2001 John Wiley & Sons, Ltd.     

Schwammbänke,Riffe und submarines Relief im oberen weissen Jura der Schwäbischen Alb (Württemberg)

Zusammenfassung Im Weißen Jura der Schwäbisch-fränkischen Alb treten Schwammriffe auf. Diese Erscheinung wurde bisher nur in diesem Gebiet und nur in dieser Formation beobachtet. Im oberen Weißjura schließen sich diese Riffe zu mächtigen Massenkalkkomplexen zusammen. Das submarine Relief, wie es bei Ende der Massenkalkbildung bestand, wird für Teilgebiete der Schwäbischen Alb rekonstruiert. Auffällige Eigenschaft dieses Reliefs ist ein einheitliches höchstes Niveau der Rifferhebungen, das sich regional verfolgen läßt. Lagerungsbeziehungen des Massenkalks zur gleichzeitig abgelagerten und später an das Relief angelagerten geschichteten Fazies werden beschrieben und benannt.     

On the sensitized photo-oxidation of alkylbenzenes in seawater

Several homologous monoalkylated benzenes were photo-oxidized as surface films on and dissolved in pure water and purified natural seawater by solar and equivalent artificial UV irradiation in the presence of anthraquinone as photo-sensitizer. The main reaction products were the 1-phenylalkanones, the corresponding secondary alcohols, benzaldehyde and, when the side chain contained four or more carbon atoms, the products of what appears to be a Norrish type II photo-degradation. The detection among the reaction products of an aldehyde with one carbon atom less than the olefin produced by the Norrish type II photo-degradation suggests a photolytic decomposition of 1-alkenes, resulting in the formation of highly reactive compounds capable of abiotic reactions in the electronic ground state with a variety of organic compounds occurring in seawater.     

Formation of low-pressure reaction textures during near-isothermal exhumation of hot orogenic crust (Bohemian Massif,Austria)

Two types of aluminous paragneiss from the Loosdorf complex (Bohemian Massif, NE Austria) contain coarse-grained granulite assemblages and retrograde reaction textures that are investigated to constrain the post-peak history of the Gföhl unit in the southern Bohemian Massif. Both types have a peak assemblage garnet–biotite–sillimanite–plagioclase–K-feldspar–quartz–granitic melt ± kyanite ± ilmenite ± rutile, recording peak metamorphic conditions of $$0.9–1.1 GPa and $$780–820°C estimated by isochemical phase equilibrium modelling. The first sample type (Ysper paragneiss) developed (i) cordierite coronae around garnet and (ii) cordierite–spinel and cordierite–quartz reaction textures at former garnet–sillimanite interfaces. Calculated chemical potential relationships indicate that the textures formed in the course of a post-peak near-isothermal decompression path reaching $$0.4 GPa. Texture formation follows a two-step process. Initially, cordierite coronae grow between garnet and sillimanite. As these coronae thicken, they facilitate the development of local compositional domains, leading to the formation of cordierite–spinel and cordierite–quartz symplectites. The second sample type (Pielach paragneiss) exhibits only discontinuous cordierite coronae around garnet porphyroblasts but lacks symplectites. The formation of cordierite there also indicates near-isothermal decompression to 0.4–0.5 GPa and 750–800°C. This relatively hot decompression path is explained by the contemporaneous exhumation of a large HP–UHT granulite body now underlying the Loosdorf complex. The timing of regional metamorphism in the granulites and the southern Bohemian Massif in general is well constrained and has its peak at $$340 Ma. Monazite from Loosdorf paragneiss samples yield a slightly younger age of $$335 Ma. Although the ages overlap within error, they are interpreted to reflect near-isothermal decompression and exhumation resulting in the formation of the observed reaction textures.     

Phenomenology of the Lense-Thirring effect in the Solar System: Measurement of frame-dragging with laser ranged satellites

In this paper we respond to the criticisms of “Phenomenology of the Lense-Thirring effect in the Solar System” by Iorio et al. about the general relativistic phenomena of gravitomagnetism and frame-dragging. The claims of the paper by Iorio et al. are not reproducible in any of our independent analyses.     

Highly radiative shock experiments driven by GEKKO XII

In this paper, recent results obtained on highly radiative shocks generated in a xenon filled gas cell using the GEKKO XII laser facility are presented. Data show extremely high shock velocity (??150 km/s) never achieved before in gas. Preliminary analyses based on theoretical dimensionless numbers and numerical simulations suggest that these radiative shocks reach a new radiative regime where the radiative pressure plays a role in the dynamics and structure of the shock. A major effect observed is a strong anisotropic emission in the downstream gas. This unexpected feature is discussed and compared to available 2D radiation hydrodynamic simulations.     

Characteristics and distribution patterns of snow and meteoric ice in the Weddell Sea and their contribution to the mass balance of sea ice

Based on snow- and ice-thickness measurements at >11 000 points augmented by snow- and icecore studies during 4 expeditions from 1986 - 92 in the Weddell Sea, we describe characteristics and distribution patterns of snow and meteoric ice and assess their importance for the mass balance of sea ice. For first-year ice (FY) in the central and eastern Weddell Sea, mean snow depth amounts to 0.16 m (mean ice thickness 0.75 m) compared to 0.53 m (mean ice thickness 1.70 m) for second-year ice (SY) in the northwestern Weddell Sea. Ridged ice retains a thicker snow cover than level ice, with ice thickness and snow depth negatively correlated for the latter, most likely due to aeolian redistribution. During the different expeditions, 8, 15, 17 and 40% of all drill holes exhibited negative freeboard. As a result of flooding and brine seepage into the snow pack, snow salinities averaged 4‰. Through ¹⁸O measurements the distribution of meteoric ice (i.e. precipitation) in the sea-ice cover was assessed. Roughly 4% of the total ice thickness consist of meteoric ice (FY 3%, SY 5%). With a mean density of 290 kg/m³, the snow cover itself contributes 8% to total ice mass (7% FY, 11% SY). Analysis of ¹⁸O in snow indicates a local maximum in accumulation in the 65 to 75^S latitude zone. Hydrogen peroxide in the snow has proven useful as a temporal tracer and for identification of second-year floes. Drawing on accumulation data from stations at the Weddell Sea coast, it becomes clear that the onset of ice growth is important for the evolution of ice thickness and the interaction between ice and snow. Loss of snow to leads due to wind drift may be considerable, yet is reduced owing to metamorphic processes in the snow column. This is confirmed by a comparison of accumulation data from coastal stations and from snow depths over sea ice. Temporal and spatial accumulation patterns of snow are shown to be important in controlling the sea-ice cover evolution.