Petrographic study of Maestrichtian and Post-Paleocene Formations of North-Western Nigeria (Iullemmeden Basin)

The results obtained from the study of over 100 samples from boreholes in North-Western Nigeria reveal striking petrographic differences between two Maestrichtian formations (Taloka and Wurno) and the Post-Paleocene Gwandu Formation. Two entirely different environments of sedimentation can be recognised and each delineates the end of one cycle of sedimentation and the beginning of another. The Maestrichtian sediments are characteristic of a detritic sedimentation in an alkaline, brackish water environment and the Gwandu Formation sediments are also detritic but are continental and in an oxidizing environment.     

Mineralogical and geochemical alteration of low-grade metamorphic black slates due to oxidative weathering

Low-grade metamorphic black slates of Silurian and Lower Devonian ages (from the Thüringisches Schiefergebirge in Germany) were investigated to identify mineralogical and geochemical alterations that occur during the oxidative weathering black slates.The slates exhibit an intense total organic carbon decrease (>90 wt%) due to oxidative weathering. The organic matter in black slate consists mainly of non-pyrolysable material with only minor portions of pyrolysable material. In contrast to the non-pyrolysable organic matter, the concentration of pyrolysable organic matter is not decreased during weathering. Heating experiments have yielded information about a potential protection of pyrolysable organic matter against weathering, which is probably caused by a structural configuration or the intergrowth of organic matter and illite.The slates consist mainly of illite. Iron oxide (goethite) and phosphate encrustations were formed on slate surfaces as a result of oxidative and acid weathering of both iron sulfide and monazite. Kaolinite often occurs as an older encrustation beneath the iron oxide encrustations. Encrustations of iron oxide and phosphate are major sinks for trace elements, released during oxidative weathering.     

Rhythmic Patterns in the Shoreline Contour of the Gulf of Terpenya,Sakhalin Island

Oceanology - The paper considers the results of long-term observations of megacusp (large-scale shoreline cusps) on the coast of the Gulf of Terpenya (Gulf of Patience), Sakhalin Island. The...     

The organisational context of retail locational planning

Retailers have a large number of techniques at their disposal to assist them in their locational planning, but the use made of them is varied, regardless of their intrinsic merits. The reasons for this lie very much in the organisational context in which the techniques are applied. This paper discusses the nature of locational planning and decision making, and puts forward a framework which links locational planning and the organisational settings in which it takes place. The preliminary results of a survey of the use of techniques by U.K. retailers are presented, which show that while most companies use more than ‘Rules of Thumb’, it is the simplest techniques which are the most widely used. The application of the more advanced knowledge based methods is still relatively uncommon. The explanation for the variations lies in the attributes of the techniques themselves, the types of locational planning undertaken, and the structural and cultural characteristics of the companies. This revised version was published online in July 2006 with corrections to the Cover Date.     

Zur Vorgeschichte der Alpenfaltung

Ohne Zusammenfassung     

Power and cross-power spectral studies of electric and meteorological parameters under fair weather conditions in the atmospheric surface layer

The influence of micrometeorological parameters (wind speed, temperature stratification and atmospheric stability) upon electric polar conductivity, potential gradient, vertical total current density and vertical convection current density is studied by means of power spectral and coherence spectral analysis. The analyses show great variations in the atmospheric electric parameters for frequencies corresponding to the diurnal wave (0.042 cph) and in many cases great variances are noted for the frequencies 0.083, 0.125 and 0.17 cph. The influence of the micrometeorological parameters upon atmospheric electricity seems to be significant for these frequencies. Annual changes of the power and coherence spectra are also observed.     

Weathering of Fruchtschiefer building stones: mineral dissolution or rock disaggregation?

Building stones manufactured from contact metamorphic slates (Fruchtschiefer slate) from Theuma (Sachsen, Germany) were investigated for mineralogical alterations as well as for changes in porosity and surface roughness due to weathering. After weathering periods of several years to decades, the originally dark gray-colored slates show pale spots of several centimeters in size at the surface of building stones. The dark-colored and light-colored sections of the slate show no differences in mineralogy. Surface weathering did not result in newly precipitated minerals. It was also found that the observed differences in color are not caused by variations in sedimentary organic carbon concentration or in sulfide/sulfate concentrations. Obtained results instead indicate that dark surface sections may show a thin cover of recent organic matter (OM), e.g., living OM, soot, dirt, etc. Microscopic investigations suggested that this cover was exfoliated at light-colored surface sections. The observed disaggregation of the upper 2 mm of the building block material results in an increase in porosity. Porosity of black (unweathered) slate is <2 vol.%. Due to weathering, the slate’s pores with diameters >1 μm show a significant increase in frequency compared to the original pore size distribution. Porosity of weathered rock volumes increased to approx. 8 vol.%. Discolored surface sections show a higher surface roughness (root-mean-square roughness, Rq ~ 1 μm) compared to dark-colored slate surfaces (Rq ~ 200 nm), both data are for cleavage planes. Preferentially, the discolored surface sections are located close to the edges of cut stones. This and the alteration in porosity, pore size, and surface roughness indicate that color changes of the slate are largely influenced by rock disaggregation proceeding from the edges into the center rather than by mineral dissolution/precipitation processes.     

Carbonate-rich melt infiltration in peridotite xenoliths from the Eurasian–North American modern plate boundary (Chersky Range,Yakutia)

A suite of mainly spinel peridotite and subordinate pyroxenite xenoliths and megacrysts were studied in detail, enabling us to characterize upper mantle conditions and processes beneath the modern North American–Eurasian continental plate boundary. The samples were collected from 37-Ma-old basanites cropping out in the Main Collision Belt of the Chersky Range, Yakutia Republic (Russian Far East). The spinel lherzolites reflect a mantle sequence, equilibrated at temperatures of 890–1,025 °C at pressures of 1.1–2 GPa, with melt extraction estimated to be around 2–6 %. The spinel harzburgites are characterized by lower P–T equilibration conditions and estimated melt extraction up to 12 %. Minor cryptic metasomatic processes are recorded in the clinopyroxene trace elements, revealing that percolating hydrous fluid-rich melts and basaltic melts affected the peridotites. One of the lherzolites preserves a unique melt droplet with primary dolomite in perfect phase contact with Na-rich aluminosilicate glass and sodalite. On the basis of the well-constrained P–T frame of the xenolith suite, as well as the rigorously documented melt extraction and metasomatic history of this upper mantle section, we discuss how a carbonated silicate melt infiltrated the lherzolite at depth and differentiated into an immiscible carbonate and silicate liquid shortly before the xenolith was transported to the surface by the host basalt. Decreasing temperatures triggered crystallization of primary dolomite from the carbonate melt fraction and sodalite as well as quenched glass from the Na-rich aluminosilicate melt fraction. Rapid entrainment and transport to the Earth’s surface prevented decarbonatization processes as well as reaction phenomena with the host lherzolite, preserving this exceptional snapshot of upper mantle carbonatization and liquid immiscibility.     

Change of black shale organic material surface area during oxidative weathering: Implications for rock-water surface evolution

Black shale oxidative weathering plays a significant role in a variety of processes including acid mine drainage and atmospheric CO₂ control. The modeling of weathering is highly dependent on reactive surface area. In this study it is shown that black shale oxidative weathering is regulated mainly by the external, geometrical surface area of rock polyhedrons and the organic matter’s (OM) internal surface area. The internal rock surface area decreases dramatically during OM dissolution from ∼15 m²/g to ∼5 m²/g. A linear relationship was found between the decrease of internal rock surface area and quantity of OM dissolved. Optical roughness analyses of black and bleached shale surface area reveal the formation of macropores due to the dissolution of mesoporous and probably microporous OM. However, due to deconsolidation, the geometrical external rock polyhedron surface area increases during weathering. Black shale polyhedrons show a doubling of their external surface area as OM decreases. This provokes an increase of the shale volume which is easily accessible by fluids. The increase of the external rock surface area seems to be self-accelerating during weathering. The upscaling of external and internal rock surface area evolution during weathering presented in this study demonstrates the possible application of these results to the improved understanding of a chemical transport in a variety of natural systems.     

A materials failure relation of accelerating creep as empirical description of damage accumulation

A general materials failure relation, , describes accelerating creep of materials with rate coefficients andA, by relating rates of deformation, , to changes in deformation rate, (Voight, 1988). Time of failure can be extrapolated from inverse rate versus time data, and andA may be derived to permit one to calculate the failure time. The method is of value for quantitative hazard assessments.Mechanisms leading to damage accumulation during accelerating creep include creep fracture by stress corrosion and power law lattice deformation. These mechanisms are examined here as phenomenologically related to the materials failure relation. Apparently, both mechanisms favour , where is the parameter of the materials failure relation controlling the sensitivity to accelerating activity. For pure shear governed by power law creep of powerp, under constant load, =2.0 andA=p. Stress corrosion is widely described by Charles' equation, relating crack velocity to stress intensity during subcritical crack growth by the stress corrosion indexn. The relationship betweenn and is given by =(2n–2)/n.