Weathering processes in baked sediments and their effects on archaeomagnetic field-intensity measurements

Thellier-type measurements of ancient field intensity on specimens of clay and other sediments, which were apparently well-baked and oxidised in ancient times, often fail to give consistent results over part or even most of the blocking-temperature spectrum. It is suggested that post-baking chemical alteration, or weathering, leading to the presence of hydrated Fe minerals, is a major cause of non-ideal behaviour in such material. The behaviour of hypothetical specimens containing either goethite or lepidocrocite can be predicted using simple models, and actual examples are given from two sites in southern Australia which show some similarities with the predicted model behaviour. The results of the Thellier measurements, after interpretations, agree closely with previously published results from the northern hemisphere for the period 4700-4200 yr. B.P. The presence of hydrated minerals may not be readily detected by methods other than the Thellier technique and, if so, would result in estimates of the ancient geomagnetic field strength that are systematically too low.     

Mössbauer and high field magnetization studies of the solid solution CoFexAl2-xO4

By means of paramagnetic Mössbauer spectra the cation distribution of the solid solution CoFe _x Al_2?x O₄ with 0≦x≦1.5 has been determined. The existence of high field magnetic susceptibility at low temperature for samples with x≧0.4 has been interpreted in terms of non-collinear ferrimagnetic arrangements. Below the Neel temperature the spinel CoAl₂O₄ has a complex antiferromagnetic behavior.     

Measurements of free radicals in the atmosphere by matrix isolation and electron paramagnetic resonance

With some special adaptations the technique of matrix isolation followed by detection through electron paramagnetic resonance (EPR) can also be used for the measurement of atmospheric radical concentrations. A light weight cryogenic sampling device has been constructed. It uses condensation of atmospheric CO₂ or H₂O at 77 K for matrix formation and trapping of the radicals. The sampler has been flown on a balloon for stratospheric sampling. First data on stratospheric, HO₂ and NO₂ at 32 km altitude have been obtained on a flight on 8 August 1976 and will be reported.     

The influence of ionic radii of cations and covalent forces on the unit cell dimensions of spinels

Fe-, Cr- and Al-spinels were synthesized and their unit cell sizes determined by means of X-rays. Differential thermal curves show that the magnetic inversion of Fe₂O₃ at 680° C accelerates the formation of the ferrites when the constituent oxides are heated together.A correlation can be made between ionic radii of cations and unit cell dimensions provided the effect of covalent forces in the lattice is taken into account. The values for ionic radii of cations as given byAhrens (1952) permit a better correlation than those ofGoldschmidt.A shrinkage of 0.01 Å in the unit cell size per 0.01 Å decrease in the ionic radius of the divalent cations was determined when spinels with the same cation arrangement in the same group were compared. A shrinkage of 0.027 Å in the unit cell size per 0.01 Å decrease in the ionic radius of the trivalent cations was determined in spinels having the same divalent cation and cation arrangement when the trivalent cations form the same type of bonds.The half-occupation of the 3d orbits in Mn²⁺ and Fe³⁺ causes abnormally high unit cell dimensions in spinels where these ions are incorporated in octahedral sites. This is attributed to the formation of electrovalent bonds by these ions. Variable forces of contraction in the lattice are revealed when the unit cell dimensions are correlated with the ionic radii of cations. The force of contraction can be satisfactorily explained as being due to covalent forces in the spinel structure. The magnitude of this force or the degree of covalence in the bonds increases in the following order of cations where these are situated in tetrahedral sites:The divalent transition element ions, Fe²⁺, Co²⁺ and Ni²⁺; the B-Sub-group element ions Cd²⁺ and Zn²⁺; Fe³⁺ in tetrahedral co-ordination.     

Die spannungsoptische Meßpatrone in ihrer Anwendung im gebirgsmechanischen Modellversuch

ZusammenfassungDie spannungsoptische Meßpatrone in ihrer Anwendung im gebirgsmechanischen Modellversuch Die in den letzten Jahren für in-situ-Messungen von Gebirgsspannungen entwickelte spannungsoptische Meßpatrone kann in entsprechender Ausführung auch in Modelle für gebirgsmechanische Untersuchungen eingesetzt werden. Die Anwendung im Modellversuch, die Eichung und ein Beispiel werden erläutert.

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SummaryThe Hard-Inclusion Stressmeter and Its Use in Rock Mechanical Model Tests The hard-inclusion stressmeter, developed during recent years for determination of in-situ stress in rock masses, is in principle applicable also to model tests. This application, the calibration and an example are described.

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Vortrag, gehalten beim XIX. Geomechanik-Kolloquium am 16. Oktober 1969 in Salzburg.

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Mit 6 Abbildungen     

Zur Trias des Iran

Zusammenfassung In der Faziesentwicklung der iranischen Trias spiegelt sich der tektonische Zustand und die paläogeographische Position der Arabischen-, der Iran- und der Turan Platte wider. Die Iran Platte bildete während des Paläozoikums mit der Arabischen Platte eine Einheit und wurde durch die Paläotethys von der Turan Platte getrennt. Im Jungpaläozoikum bzw. zu Beginn der Trias löste sie sich aus diesem Verband und kollidierte gegen Ende der Mitteltrias mit der Turan Platte. Die ehemaligen Plattengrenzen werden heute durch die Nordiran Sutur markiert.Unter Berücksichtigung neuer paläotektonischer Ergebnisse werden folgende Fazieszonen unterschieden: Trias des Zagros-Gebietes (Arabische Platte), Trias des Alborz und Zentral-Iran (Iran Platte), Trias des südkaspischen Gebietes, des Kopet Dagh und von Nakhlak (Turan Platte). Die Faziesentwicklungen der Iran- und der Turan-Platte unterschieden sich während der Unter und Mittel-Trias erheblich. Auf der Iran-Platte bestand eine Karbonat-Plattform. Auf dem absinkenden Südrand der Turan-Platte hingegen wurden mächtige (1000–3000 m) klastische, zum Teil marine Sedimente deponiert. Nach der Kollision beider Platten erfolgte eine weitgehende Faziesangleichung in der Obertrias.Die kollisionsbedingten Deformationen (frükimmerische Bewegungen) hatten auf der Turan-Platte orogenen Charakter, auf der Iran-Platte bewirkten sie Hebungen und eine verstärkte Erosion.Da die Iran Platte im Jura durch spreading Vorgänge unter partiellen Rotationen in Teilschollen zerlegt wurde, muß zur paläogeographischen Rekonstruktion eine konstruktive Rückformung dieser Dislokationen durchgeführt werden. Hierbei kommt der Zentral-Ost-Iran Mikroplatte besondere Bedeutung zu.Die Iran Platte und der afghanische Block haben in der oberen Trias als Bestandteil Eurasiens zu gelten. Die Neotethy öffnete sich zwischen der Arabischen und der Iran Platte.

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The facies domains of the Iranian Triassic reflect the tectonic stage and paleogeographic position of the Arabian, Iran and Turan plates. In the Paleozoic Iran and Arabian plate formed a coherent unit and were separated from Turan plate by the Paleotethys. In Late Paleozoic or at the beginning of Triassic the Iran plate drifted apart by the opening of the Neotethys and collided with the Turan plate at the end of the Middle Triassic. The former plate margins are marked at present by the North-Iran suture.Considering new paleotectonic results the following facies types have been distinguished: Triassic of Zagros (Arabian plate), Triassic of Alborz and Central Iran (Iran plate), Triassic of South Caspian area, Kopet Dagh and Nakhlak (Turan plate). The Lower and Middle Triassic facies types of Iran and Turan plate are significantly different. On Iran plate cabonate platform conditions dominated whereas thick (1000–3000 m) clastic partly marine sediments were deposited on the subsiding margin of Turan plate.The collision induced deformations of the Turan plate (Early Kimmerian movements) were of orogenetic type, on the Iran plate however this tectonic event caused uplifting and strong erosion. In Jurassic the Iran plate was fragmented under partial block rotations. Therefore paleogeographic considerations require the reconstruction of the original tectonic situation. In this procedure the Central-East Iran microplate is of special interest. In Late Triassic the Iran plate and the Afghan block were constituents of Eurasia. The Neotethys opened between the Arabian and the Iran plate.

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Résumé Le développement des facies du Trias d'Iran reflète la situation tectonique et la position paléogéographique de la plaque turanienne, la plaque iranienne et la plaque arabe. Pendant le Paléozoïque la plaque iranienne et la plaque arabe formaient un ensemble, qui était séparé de la plaque turanienne par la Paléotéthys. A la fin du Paléozoïque, ou au début du Trias, la plaque iranienne se détachait de cet ensemble et entrait en collision vers la fin du Trias moyen avec la plaque turanienne. Les anciens confins des plaques sont aujourd' hui marqués par la suture nord-iranienne.En raison des nouveaux résultats paléotectoniques, on distingue les zones de faciès suivantes: Le Trias de la région du Zagros (plaque arabe), le Trias de l'Alborz et de l'Iran central (plaque iranienne), le Trias de la région sud-caspienne, Kopet Dagh, Nakhlak (plaque turanienne). Pendant le Trias moyen et inférieur le développement des facies des plaques iranienne et eurasienne différait considérablement. Sur la plaque iranienne existait une plate-forme carbonatique. Sur le bord méridional de la plaque eurasienne, qui était en subsidence lente, des sédiments clastiques épais (1000–3000 m), en partie marins, étaient par contre déposes. Après la collision des deux plaques les différences entre les deux faciès se perdaient durant le Trias supérieur.Les déformations produites par la collision (mouvements kimmériens précoces) avaient un caractère orogénique sur la plaque turanienne, alors qu'elles causaient, sur la plaque iranienne, un soulèvement et une accentuation de l'érosion.La plaque iranienne se décomposait en plusieurs fragments durant le Jurassique sous l'influence du spreading accompagné par des rotations partielles. Pour la reconstruction de la paléographie ces rotations doivent être prises en considération. Dans cette procédure le rôle de la microplaque de l'Iran central et oriental est d'une importance particulière. Pendant le Trias supérieur la plaque iranienne et le bloc de l'Afghanistan faisaint partie de l'Eurasie. La Néotéthys s'ouvrait entre les plaques arabe et iranienne.

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Diatom assemblages and quantitative reconstruction for paleosalinity from a sediment core of Chencuo Lake,southern Tibet

Changing salinity in lakes and especially in closed lakes depends mainly on the balance between precipitation, runoff and evaporation in arid and semi-arid areas, hence influencing lake levels di-rectly[1-4]. Past salinity has been recovered by a vari-ety of environmental indicators from lake sediments such as diatoms, chironomids, ostracoda, isotopes of ostracoda shells, geochemistry, and isotopes of authi-cabonates[3,5—10]. Recently, with extensive data-base study on diatom-salinity transfe…     

Modeling historical climate variability and slope stability

This study presents scenario models for historical variations of climate and slope stability. A model for historical annual patterns of temperature and rainfall was established on the basis of seasonal proxies. A process-based, spatio-temporal model for groundwater variations and slope stability was developed using the GIS environment of the software PCRaster. We applied the slope stability model to study the effects of the different climate scenarios on slope stability for three different hillslopes in the area around Bonn (Germany). The findings indicate three climatic phases with different annual temperature and precipitation patterns over the historic period. The modeling results show that a climatic scenario representing unstable conditions of a transition from the more humid Little Ice Age to dryer recent climate produces the highest slope instabilities. The intensity of this impact, however, varies with the sensitivity of the geomorphic system, i.e. local landforms and lithology, and cannot be generally related to the stability of a specific hillslope. More unstable areas are not necessarily more sensitive to climatic changes: the location of permeable layers (prone to groundwater rise) in relation to sensitive layers (lower strength) and higher gradients (higher stress) influences the sensitivity of a site with respect to climate changes. The presented method is capable of modeling landscape sensitivity to climate change with respect to groundwater-controlled landslides.