Fossil Heavy Mineral Concentrations

Zusammenfassung Fossile Schwermineralanreicherungen (Seifen), die wirtschaftlich nicht nutzbar sind, treten gelegentlich in Sandsteinen und Konglomeraten auf. Die Konfiguration, die Mineralzusammensetzung und der vermutete Ablagerungsraum von sechs Schwermineralanreicherungen aus Westdeutschland, die ein unterschiedliches stratigraphisches Alter (Unterdevon, Oberdevon, Rotliegendes, RhÄt, Dogger und OligozÄn) haben, werden beschrieben und illustriert. Die Bildungsbedingungen von Seifen im allgemeinen sind kurz erwÄhnt. Radiographien werden als methodisches Hilfsmittel zur Untersuchung von Seifen demonstriert.Die geographische und stratigraphische Verteilung — vom PrÄkambrium bis zum QuartÄr — von bekannten, wirtschaftlich nutzbaren und nicht nutzbaren Anreicherungen ist tabellarisch zusammengefa\t. Ferner werden Schwermineralanreicherungen nach der Art des Ablagerungsraums klassifiziert. Abschlie\end werden aus diesen Beobachtungen über fossile Seifen Folgerungen auf die physiographische Verteilung rezenter Seifen gezogen.

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Noneconomic fossil heavy mineral concentrations (streaks) are a conspicuous feature in some sandstones and conglomerates. Configuration, mineral composition, and presumable environment of deposition of such concentrations are described based on six examples of varying stratigraphic age from West Germany. Conditions of placer formation are briefly mentioned. Radiographs are demonstrated as an auxiliary tool to studying placers.Geographic and stratigraphic distribution (from Precambrian to Quaternary) of known noneconomic and economic accumulations are tabulated. A tentative classification of heavy mineral concentrations as to their depositional environment is presented. As a result of these observations on ancient placers, conclusions can be drawn regarding the physiographic distribution of Recent placers.

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Résumé Des enrichissements fossiles de minéraux lourds (placers), sans valeur commerciale, peuvent Être observés occasionnellement dans des grès et des conglomérats. L'auteur décrit et illustre la configuration, la composition minéralogique et l'aire de sédimentation présumée de six concentrations de minéraux lourds, d'âges stratigraphiques différents (Dévonien inférieur, Dévonien supérieur, Rotliegend, Rhétien, Dogger et Oligocène), tous en République Fédérale Allemande. Les conditions générales de genèse des placers sont brièvement mentionnées. La radiographie se montre comme une méthode auxiliaire dans la recherche des placers.La distribution géographique et stratigraphique — du Précambrien au Quaternaire — des placers commerciaux et non-commerciaux connus est résumée dans un tableau. Les placers sont ensuite classifiés selon le milieu de sédimentation. A partir de ces observations sur les placers fossiles, on peut tirer quelques conclusions sur la distribution physiographique des placers récents.

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This paper was presented at the VIII International Sedimentological Congress 1971, Heidelberg.     

Dynamic stresses in an elastic half-space

This paper deals with the problem of time-varying point loads applied onto the surface of an elastic half-space and the stresses that such loads elicit within that medium. The emphasis is on the evaluation of the isobaric contours for all six of the stress components at various frequencies of engineering interest and for a full range of Poisson’s ratios. The extensive set of pressure bulbs presented herein may be of help in predicting the severity of dynamic effects in common practical situations in engineering—or even the lack thereof.     

A Middle‐Late Triassic 40Ar/39Ar age for the Paasselkä impact structure (SE Finland)

Abstract– ⁴⁰Ar/³⁹Ar dating of recrystallized feldspar glass particles separated from clast‐rich impact melt rocks from the approximately 10 km Paasselkä impact structure (SE Finland) yielded a Middle to Late Triassic (Ladinian‐Karnian) pseudo‐plateau age of 228.7 ± 3.0 (3.4) Ma (2σ). This new age makes Paasselkä the first known Triassic impact structure dated by isotopic methods on the Baltic Shield. The new Paasselkä impact age is, within uncertainty, coeval with isotopic ages recently obtained for the Lake Saint Martin impact structure in Canada, indicating a new Middle to Late Triassic impact crater population on Earth. The comparatively small crater size, however, suggests no relationship between the Paasselkä impact and a postulated extinction event at the Middle/Late Triassic boundary.     

Theory of relativistic hydrodynamic fluctuations before H-recombination

Using a previously developed relativistic extension of the Landau-Lifshitz theory of hydrodynamic fluctuations, the spectrum of energy density fluctuations before hydrogen recombination is calculated both for the radiation-dominated and the matter-dominated cases. The spectrum consists of a high frequency adiabatic and a low frequency isobar part. The isobar part is proportional to the inverse proton number density multiplied by the squared ratio of the rest energy density and the radiation energy density in the radiation dominated era. In the matter dominated era it is proportional to the inverse proton number density.The adiabatic part is proportional to the inverse photon number density in both cases. In the spectrum of temperature fluctuations the adiabatic part is the dominating one.The general part of the analysis is performed within a gauge invariant formalism.     

The two Suvasvesi impact structures,Finland: Argon isotopic evidence for a “false” impact crater doublet

The two neighboring Suvasvesi North and South impact structures in central‐east Finland have been discussed as a possible impact crater doublet produced by the impact of a binary asteroid. This study presents ⁴⁰Ar/³⁹Ar geochronologic data for impact melt rocks recovered from the drilling into the center of the Suvasvesi North impact structure and melt rock from glacially transported boulders linked to Suvasvesi South. ⁴⁰Ar/³⁹Ar step‐heating analysis yielded two essentially flat age spectra indicating a Late Cretaceous age of ~85 Ma for the Suvasvesi North melt rock, whereas the Suvasvesi South melt sample gave a Neoproterozoic minimum (alteration) age of ~710 Ma. Although the statistical likelihood for two independent meteorite strikes in close proximity to each other is rather low, the remarkable difference in ⁴⁰Ar/³⁹Ar ages of >600 Myr for the two Suvasvesi impact melt samples is interpreted as evidence for two temporally separate, but geographically closely spaced, impacts into the Fennoscandian Shield. The Suvasvesi North and South impact structures are, thus, interpreted as a “false” crater doublet, similar to the larger East and West Clearwater Lake impact structures in Québec, Canada, recently shown to be unrelated. Our findings have implications for the reliable recognition of impact crater doublets and the apparent rate of binary asteroid impacts on Earth and other planetary bodies in the inner solar system.     

Variscan amphibolite-facies rocks from the Kurtoğlu metamorphic complex (Gümüşhane area,Eastern Pontides,Turkey)

The Kurtoğlu metamorphic complex, that forms part of the pre-Liassic basement of the Sakarya zone in northern Turkey, consists of at least two tectonic units. Blueschist-facies rocks of unknown metamorphic age in the southern part of the complex are tectonically overlain by Variscan low-pressure high-temperature metamorphic rocks. The latter comprise mica schists and fine-grained gneisses, cut by metaleucogranitic dikes, as well as migmatitic biotite gneisses and subordinate amphibolite intercalations. Structural data indicate that metamorphism and penetrative deformation occurred after dyke intrusion. Peak metamorphic conditions of the mica schists, fine-grained gneisses and metaleucogranites are estimated to ∼650°C and ∼0.4 GPa, based on phase relationships in the system NCKFMASH, Fe–Mg partitioning between garnet and biotite as well as garnet-aluminosilicate-quartz-plagioclase (GASP) and garnet-plagioclase-biotite-quartz (GBPQ) barometry. Peak temperatures of the migmatitic biotite gneisses and amphibolite intercalations are not well constrained but might have been significantly higher (690–740°C), as suggested from hornblende-plagioclase thermometry. ⁴⁰Ar–³⁹Ar incremental dating on muscovite and biotite fractions from the mica schists and fine-grained gneisses yielded plateau ages of ∼323 Ma. Significantly older model ages of ∼329 and ∼337 Ma were obtained on muscovite fractions from two metaleucogranite samples. These fractions contain both relict igneous and newly formed metamorphic muscovite.