Untersuchungen mit der Elektronenmikrosonde über die natiirlichen Mischkristallbereiche der Skutterudite

This paper demonstrates with approximately 140 electron micro probe analyses of minerals from the classic localities the areas of solid solution in the ternary diagram of the natural iron-cobalt-nickel-skutterudites. The skutterudites analyses show a. much more scattered pattern over all the diagram than presumed by the analyses or by the experimental determined areas of solid solution in the recent literature. Furthermore, a fluctuation in the metalarsenic-ratio between 1:1.9 to 1:3.3 was ascertained for this mineral type. The iron-skutterudites favour the lower metal-arsenic-ratios, the cobalt-skutterudites and respectively the cobalt-nickel-skutterudites more the medium, and the nickel-skutterudites more the higher ratios.With solely microscopic determination of the iron-skutterudite mineral phase an error could be possible, whereas the determination of the nearly pure nickee-skutterudite (which is a new mineral phase) seems certain to the author.Finally, the author tries to explain the extreme fluctuation of stochiometry in the same structure to be caused by a chiefly metalic bond in an alloy type.Zusammenfassung Anhand von über 140 Mikrosondenanalysen von Mineralien der klassischen Vorkommen wird in dieser Arbeit versucht die Mischkristallfelder im Dreieckdiagramm der natütlichen Eisen-Kobalt-Nickel-Skutterudite zu ermitteln. Dabei zeigte sick einmal eine wesentlich größere Streuung der Skutteruditanalysen, als dies aus den Analysenangaben und den experimentell bestimmten Mischkristallfeldern der bisherigen Literatur zu vermuten war. Weiterhin konnte ein außergewohnliches Schwanken des Metall-Arsenverhaltnisses zwischen etwa 1:1,9 bis 1: 3,3 bei dieser Mineralart festgestellt werden. Es zeigte sich, daß die niederen Metall-Arsenverhältnisse bevorzugt an die Eisen-Skutterudite, die mittleren mehr an die Kobalt-Skutterudite bzw. an die Kobalt-Nickel-Skutterudite und die höheren bevorzugt an die eigentlichen Nickel- Skutterudite gebunden sind.Während bei den Eisen-Skutteruditen aufgrund der rein mikroskopischen Bestimmung die Möglichkeit eineir Fehldiagnose nicht völlig ausgeschlossen werden kann, erscheint der Nachweis eines fast reinen Nickel- Skutterudites dem Verfasser als gesichert.Das kristallchemisch interessante Problem, wie these großen Stöchiometrie-schwankungen in ein und derselben Struktur ohne wesentliehe Änderungelr auftreten können, versucht der Verfasser durch eine vorwiegend metallische Bindung in einem Legierungstyp zu erklären.

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Diese Arbeit wurde auszugsweise am 9. September 1964 vor der Deutschen Mineralogischen Gesellschaft auf deren Jahrestagung in Wiesbaden vorgetragen.     

The Late Cenozoic Eridanos delta system in the Southern North Sea Basin: a climate signal in sediment supply?

ABSTRACT The Eridanos fluvio‐deltaic system, draining most of north‐western Europe, developed during the Late Cenozoic as a result of simultaneous uplift of the Fennoscandian shield and accelerated subsidence in the North Sea Basin. This seismo‐stratigraphic study aims to reconstruct the large‐scale depositional architecture of the deltaic portion of the basin fill and relate it to external controls. A total of 27 units have been recognized. They comprise over 62×10³ km³ in the Southern North Sea Basin alone, and have an average delta surface area of 28×10³ km², which suggests that the size of the drainage area was about 1.1×10⁶ km². Water depth in the depocentre is seen to decrease systematically over time. This trend is interrupted by a deepening phase between 6.5 and 4.5 Ma that can be correlated with the simultaneous occurrence of increased uplift of the Fennoscandian shield, increased subsidence of the Southern North Sea Basin, and a long‐term eustatic highstand. All these observations point to a tectonic control on long‐term average rates of accommodation and supply. Controls on short‐term variations are inferred from variations in rates of sediment supply and bifurcation of the delta channel network. Both rates were initially low under warm, moist, relatively stable climate conditions. The straight wave‐dominated delta front gradually developed into a lobate fluvial‐dominated delta front. Two high‐amplitude sea‐level falls affected the Pliocene units, which are characterized by widespread delta‐front failures. Changes in relative sea level and climate became more frequent from the late Pliocene onward, as the system experienced the effects of glacial–interglacial transitions. Peaks in sedimentation and bifurcation rates were coeval with cold (glacial) conditions. The positive correlation between rates of supply and bifurcation on the one hand, and climate proxies (pollen and δ¹⁸O records) on the other hand is highly significant. The evidence presented in this study convincingly demonstrates the control of climate on time‐averaged sediment supply and channel‐network characteristics, despite the expected nonuniformity and time lags in system response. The presence of a clearly discernible climate signal in time‐averaged sediment supply illustrates the usefulness of integrated seismo‐stratigraphic studies for basin‐wide analysis of delta evolution on geological time scales.     

Causes of Geochemical Diversity of Carbon Dioxide Water in Crystalline Rock Masses

The problem of the diversity of the geochemical types of carbon dioxide waters (CDW) in petrografically and mineralogically uniform crystalline rock masses is solved with allowance made for the effect of different boundary conditions (physicochemical parameters) on the geochemical effect of interaction in the rock–water system. The formation of the entire geochemical spectrum of CDW in crystalline rock masses is shown to be explicable on the basis of a model of interaction in granite–water systems at different mass ratios of reacting rock (S) and water (L), different temperatures T, and equilibrium concentrations of dissolved CO₂ (P _CO2).     

Reconstruction of the diagenesis of the fluvial-lacustrine- deltaic sandstones and its influence on the reservoir quality evolution-- Evidence from Jurassic and Triassic sandstones, Yanchang Oil Field, Ordos Basin

The reservoir quality of Jurassic and Triassic fluvial and lacustrine-deltaic sandstones of the Yanchang Oil Field in the Ordos Basin is strongly influenced by the burial history and facies-related diagenetic events. The fluvial sandstones have a higher average porosity (14.8%) and a higher permeability (12.7×10?3 ?m2) than those of the deltaic sandstones (9.8% and 5.8 ×10?3 ?m2, respectively). The burial compaction, which resulted in 15% and 20% porosity loss for Jurassic and Triassic sandstones, respectively, is the main factor causing the loss of porosity both for the Jurassic and Triassic sandstones. Among the cements, carbonate is the main one that reduced the reservoir quality of the sandstones. The organic acidic fluid derived from organic matter in the source rocks, the inorganic fluid from rock-water reaction during the late diagenesis, and meteoric waters during the epidiagenesis resulted in the formation of dissolution porosity, which is the main reason for the enhancement of reservoir-quality.     

Fracture induced emission of alkali atoms from feldspar

Emission of neutral atoms (K and Na) and molecules (H₂O and KOH) observed during fracture of K-feldspar have been accounted for by two independent mechanisms. H₂O and KOH emissions are attributed to the venting of fluid-filled inclusions, while emission of atomic K is due to surface effects accompanying cleavage of crystalline feldspar. The intensity of emitted potassium, at least 6 × 10¹⁴ atoms/cm² of surface area, is sufficient to affect K activities in solution during microbrecciation in the presence of rock-dominated fluids.     

THE TROPICS: ENVIRONMENTS AND HUMAN IMPACTS UNDERSTOOD AND REINTERPRETED

In the 1950s, few people had travelled widely through different parts of the tropics and interpretations on tropical landforms, soils, vegetation and climate largely rested on impressions gained from residence or long sojourns in particular tropical countries. Most academic geography on the tropics was then written by expatriates and lacked the perspective gained from long experience of tropical regions. Particular problems of understanding arose as people attempted to extrapolate from one part of the tropics to another. Since then, understanding has advanced enormously, largely through the efforts of tropical scientists working in their own institutions and through the greater technological ability to study tropical lands both remotely and through easier field access. The establishment of a number of field stations, aimed primarily at the biological sciences, but also facilitating the work of geographers, has been a major stimulus to this effort. Concerns over practical issues, particularly local development and global climatic change have prompted new avenues of research, many of which have been assisted by the great increase in data collection in tropical countries. For the future, South-South dialogue between tropical physical geographers is needed to improve their ability to ask meaningful questions so that they can contribute to teach the rest of their discipline more about serious applied and applicable geography.