Ecology,sedimentology, and diagenesis of recent and fossil reefs

At the VIII. International Sedimentological Congress held in Heidelberg in 1971, a symposium with the above title was convened; a selection of the papers presented is assembled in this issue. In the introduction the approaches of the following studies are reviewed to show some trends and problems in reef research.     

Die Berechnung der Globalstrahlung aus Trübungswert und Bewölkung

Zusammenfassung Es werden einfache halbempirische Formeln zur Berechnung der Globalstrahlung angegeben. Die Abhängigkeit der Globalstrahlung von den meteorologischen Parametern Trübungsgrad (Linke'scher TrübungsfaktorT _g) sowie Bewölkungsart und-bedeckung wurde empirisch aus Messungen in Frankfurt (Main) und Potsdam ermittelt. Die nach diesen Formeln berechnete Globalstrahlungsleistung in ly min^–1 und die 24-stündige Globalstrahlungsenergiesumme in ly wird mit Messergebnissen anderer Autoren in den Tropen, bzw. in Polargebieten, verglichen, wobei sich eine sehr gute Übereinstimmung zeigt.

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Summary Simple halfempirical formulas for the calculation of the global radiation are presented. The dependence of global radiation on the meteorological parameters: turbidity (turbidity factorT _g afterLinke) and type and amount of cloud was find empirically from the measurements in Frankfurt (Main) and Potsdam. The flux of global radiation (in ly min^–1) and the daily sum of global radiation energy, calculated by these formulas, was compared with measured values of other authors in the tropics and in polar regions, respectively, and shows satisfactory agreement.

     

Mineralbestand und Genese südbayerischer Lösse

Zusammenfassung An ausgewählten, stratigraphisch gut gegliederten Profilen wurden Mineralbestand und Bildungsumstände der würmeiszeitlichen Lösse sowie ihrer unterlagernden Schichten mit geologischen, sedimentpetrographischen und mineralogischen Methoden untersucht. Schwermineralgehalt und paläogeographische Folgerungen machen die Alpen als primäres Liefergebiet wahrscheinlich. Die vorwiegend detritischen Tonminerale wurden postsedimentär durch Klima und Bodenbildung regional unterschiedlich beeinflußt. Während in den alpennahen, niederschlagsreichen Gebieten mit hoher Bodenauswaschung der Tonmineralbestand (vorherrschend Illit, neben Kaolinit und Chlorit) keine merkliche Veränderung zeigt, werden in den alpenfernen, relativ trockenen Gebieten Umwandlungen von Illit in Montmorillonit beobachtet. Ein Absinken des pH-Wertes (pH 4 bis 5) unter dem Einfluß von Staunässe und Bodenbildung führte zu einer verstärkten Verwitterung der Silikate und begünstigte eine Neubildung von Kaolinit.

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In the last glacial period (Würm) the origin of loess in Southern Bavaria is to be found in the Alps, as the mineral components of the loess indicate. After the glacial deposit the mainly detrital clay minerals were influenced in different ways by climate and soil formation. In regions rich in rainfall the clay mineral component (Illit, Kaolinit, Chlorit) remained almost the same, while in regions poor in rainfall a transformation from Illit to Montmorillonit was to be observed. Constant moisture of the soil produced in acid reaction (pH 4–5) a more intensive weathering of the silicates and supported a new formation of Kaolinit.

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Résumé En Bavarie du Sud, se trouver la région d'origin du loess de la dernière période glaciale (Würm) dans les Alpes, a qui est indique par les composants minéraux dans le loess. Aprés le dépôt l'argile assentiellement détritique fut inffuencée de manière différente par le climat et la pédogénèse. Dans les régions riche en pluie le composant d'argile (Illit, Kaolinit, Chlorit) restait presque inchangé, tandis que dans les régions qui out peude pluie on observait une transformation de Illit en Montmorillonit. L'humidité constante du sol accidité pH 4–5 causait une plus forte altération des silicates et favorisait la nouvelle formation de Kaolinit.

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— , , . — pH 5 — .

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Aus dem Geologischen Institut der Technischen Hochschule München und dem Mineralogischen Institut der Universität Erlangen-Nürnberg.     

Glaukonit aus der Regensburger Oberkreideformation

Some of the upper cretaceous sedimentary rocks near Regensburg, Germany, are rich in glauconite pellets of 63–200µ diameter. The clay fractions < 2µ of the same rocks are rich in glauconite-mica too.X-ray analysis, chemical analysis and petrographical tests show that, the glauconite pellets must be excrements of marine animals which took up glauconite-mica from sea-bottom.The glauconite materials from these rocks are 1M-micapolymorphs. A comparison of this glauconite with 1M-glauconites cited in literature by other authors shows close aggreement in K₂O/MgO- and K₂O/Fe₂O₃ ratios. Within the range of analytical errors the structure formulae of all these 1M-glauconites differ from one another only by the oxidation ratio of iron and — corresponding to this ratio — by the aluminum contents of the octahedral lattice layer. The differences of the 1M-glauconites in octahedral layer populations may due to different redox potentials during glauconite formation or to oxidation during rock diagenesis or rock weathering later on.In a similar manner 1Md-polymorphs of glauconite-mica may have developed from 1M-glauconite by oxidation of iron and corresponding removement of K⁺ and (H₃O)⁺ ions from interlayer lattice positions.     

Audiomagnetotelluric investigations of shallow sedimentary basins in northern Sudan

Audiomagnetotelluric (AMT) investigations were carried out to study shallow sedimentary basins in northern Sudan and southern Egypt. Unlike recordings in settled areas, the natural variations (atmospherics) in the eastern Sahara were completely unperturbed by cultural noise, usually yielding very high data quality. Typical recordings and spectra are presented. The atmospherics show distinct daily variations, with maximum amplitudes in the local afternoon/night hours. As a sort of calibration, AMT measurements together with DC-resistivity and electromagnetic soundings were conducted at several groundwater boreholes. Under favourable conditions, a vertical anisotropy may be resolved by joint inversion of DCR and AMT data. The results of a case study in the Es Safya basin (NW Sudan) are presented. The investigations were aimed at determining basement depths and groundwater levels, as well as the direction and dip of major bounding faults. 2-D modelling and inversion revealed the overall conductivity structure of this shallow graben. The AMT method proved to be a valuable tool for a comparatively swift reconnaissance study of shallow structures.     

Boron-isotope fractionation between tourmaline and fluid: an experimental re-investigation

The fractionation of boron isotopes between synthetic dravitic tourmaline and fluid was determined by hydrothermal experiments between 400 and 700°C at 200 MPa and at 500°C, 500 MPa. Tourmaline was crystallized from an oxide mix in presence of water that contained boron in excess. In one series of experiments, [B]_fluid/[B]_tour was 9 after the run; in another series it was 0.1. All experiments produced tourmaline as the sole boron-bearing solid, along with traces of quartz and talc. Powder XRD and Rietveld refinements revealed no significant amounts of tetrahedrally coordinated boron in tourmaline. ¹¹B always preferentially fractionated into the fluid. For experiments where [B]_fluid/[B]_tour was 9, a consistent temperature-dependent boron isotope fractionation curve resulted, approximated by Δ¹¹B_{(tour–fluid)} = −4.20 · [1,000/T (K)] + 3.52; R ² = 0.77, and valid from 400 to 700°C. No pressure dependence was observed. The fractionation (−2.7 ± 0.5‰ at 400°C; and −0.8 ± 0.5‰ at 700°C) is much lower than that previously presented by Palmer et al. (1992). Experiments where [B]_fluid/[B]_tour was 0.1 showed a significant larger apparent fractionation of up to −4.7‰. In one of these runs, the isotopic composition of handpicked tourmaline crystals of different size varied by 1.3‰. This is interpreted as resulting from fractional crystallization of boron isotopes during tourmaline growth due to the small boron reservoir of the fluid relative to tourmaline, thus indicating larger fractionation than observed at equilibrium. The effect is eliminated or minimized in experiments with very high boron excess in the fluid. We therefore suggest that values given by the above relation represent the true equilibrium fractionations.