Kimberlites distribution in Angola and prospective areas for new discoveries

Based on a comprehensive analysis of kimberlite pipes of Angola, including the near surface structural setting, deep lithospheric structure, pipe morphology and emplacement, mineralogical and petrographic features, diamond characteristics and locations of secondary deposits four geographical regions have been outlined within Angola representing four types of diamond bearing potential. These areas include high diamond bearing potential pipes, possible potential, no potential, and unclear potential areas. It was found that the depth of magmatism and diamond potential of kimberlites increases from the Atlantic coast in southwestern Angola into the continent in the north-easterly direction. Areas prospective for the discovery of new primary diamond deposits have been identified.

     

Polarimetry and BVRI photometry of the potentially hazardous near-Earth Asteroid (23187) 2000 PN9

The results of V-band polarimetric observations of the potentially hazardous near-Earth Asteroid (23187) 2000 PN₉ at large phase angles are presented as well as its photometric observations in BVRI bands. Observations were made in March-April 2006 during its close approach to the Earth using the 1.82-m Asiago telescope (Italy) and the 0.7-m telescope at the Chuguevskaya Observational Station (Ukraine). We obtained polarimetric measurements at the phase angle of 115°, the largest phase angle ever observed in asteroid polarimetry. Our data show that the maximum value of the polarization phase curve reached 7.7% and occurred in the phase angle range of 90-115°. The measured values of linear polarization degree, BVRI colors and magnitude-phase dependence correspond to the S-type composition of this asteroid. Based on our observations the following characteristics of the Asteroid (23187) 2000 PN₉ were obtained: a rotation period of 2.5325±0.0004 h, a lightcurve amplitude of 0.13 mag, an albedo of 0.24±0.06 and a diameter of 1.6±0.3 km.     

Effects of variations in fluid properties and fracture geometry on dispersion,anisotropy, and reflection in media with planar fractures

Our objective was to discover the effect of variations in fluid properties and fracture geometry on the velocity of seismic wave propagation in fluid‐saturated media with parallel planar fractures. We used numerical models calculated by analytical solutions to examine the behaviour of P‐wave phase velocity dispersion in the normal direction to layering, in non‐porous and porous media with planar fractures. We also examined the anisotropy of low frequency phase and group velocities of fast and slow P‐waves and angular‐dependent reflection coefficients in media with planar fractures, under conditions of saturation by fluids with varying bulk moduli, densities, and fracture apertures. We defined several parametre , , and characterising dispersion, characterising anisotropy, characterising the difference between fast and slow modes, and R₀ and characterising reflection. Our results show that the behaviour of dispersion shows wider stopbands in the case of gas saturation. Concavity indicator of dispersion for gas saturation was greater than that for liquid saturation and is usually greater than one. Anisotropy is more sensitive to bulk modulus contrast than to density contrast between the solid and the fluid, and is more sensitive to density contrast than to bulk modulus contrast. The case of gas saturation usually had a greater negative R₀ and a greater value of compared with those of brine and heavy and light oil saturations. Our results are helpful in distinguishing fluid types saturating geophysical fractures and estimating the aperture and spacing of planar fractures. In seismic exploration, bulk modulus and fluid density can provide useful information in distinguishing among brine, oil, and gas; fracture geometry is important to estimate the permeability of reservoirs.     

Taphonomic phenomenon of ancient hair from Glacial Beringia: perspectives for palaeoecological reconstructions

An accumulation of mammoth hair, discovered in the Bol'shaya Chukochya River valley (northeast Yakutia, Russia), was found to contain remains of terrestrial and aquatic organisms, including plants, insects, crustaceans, birds and mammals. Radiocarbon dating indicated that this post‐mortem taphocoenosis represented multiple time periods. The mammoth hair was dated to older than 45 ka BP, the plants were dated to 12 750±50 a BP (which corresponds to a shift in the environmental conditions and landscapes during the formation of thermokarst in northeastern Russia) and the bird feathers were dated to 4115±40 a BP. A scenario of the formation of this fossil assemblage is proposed, covering the MIS 3‐1 time range. The hair also yielded various Arctic branchiopod crustaceans, which inhabit shallow temporary water bodies and therefore are important for reconstruction of palaeoenvironments. The cladoceran subgenus Daphnia (Ctenodaphnia), currently absent from the Asian part of Beringia, is reported from this region for the first time. The study demonstrates that the discovered permafrost‐preserved hair is a unique repository of Ice Age organisms.     

Caveats on tomographic images

Geological and geodynamic models of the mantle often rely on joint interpretations of published seismic tomography images and petrological/geochemical data. This approach tends to neglect the fundamental limitations of, and uncertainties in, seismic tomography results. These limitations and uncertainties involve theory, correcting for the crust, the lack of rays throughout much of the mantle, the difficulty in obtaining the true strength of anomalies, choice of what background model to subtract to reveal anomalies, and what cross‐sections to select for publication. The aim of this review is to provide a relatively non‐technical summary of the most important of these problems, collected together in a single paper, and presented in a form accessible to non‐seismologists. Appreciation of these issues is essential if final geodynamic models are to be robust, and required by the scientific observations.     

How users interact with a 3D geo-browser under time pressure

Interactive 3D geo-browsers, also known as globe viewers, are popular, because they are easy and fun to use. However, it is still an open question whether highly interactive, 3D geographic data browsing, and visualization displays support effective and efficient spatio-temporal decision making. Moreover, little is known about the role of time constraints for spatio-temporal decision-making in an interactive, 3D context. In this article, we present an empirical approach to assess the effect of decision-time constraints on the quality of spatio-temporal decision-making when using 3D geo-browsers, such as GoogleEarth, in 3D task contexts of varying complexity. Our experimental results suggest that while, overall, people interact more with interactive geo-browsers when not under time pressure, this does not mean that they are also more accurate or more confident in their decisions when solving typical 3D cartometric tasks. Surprisingly, we also find that 2D interaction capabilities (i.e., zooming and panning) are more frequently used for 3D tasks than 3D interaction tools (i.e., rotating and tilting), regardless of time pressure. Finally, we find that background and training of tested users do not seem to influence 3D task performance. In summary, our study does not provide any evidence for the added value of using interactive 3D globe viewers when needing to solve 3D cartometric tasks with or without time pressure.     

Alfvén node-free vibrations of white dwarf in the model of solid star with toroidal magnetic field

In the context of white dwarf asteroseismology, we investigate the vibrational properties of a non-convective solid star with an axisymmetric purely toroidal intrinsic magnetic field of two different shapes. Focus is laid on the regime of node-free global Lorentz-force-driven vibrations about the symmetry axis at which material displacements have one and the same form as those for nodeless spheroidal and torsional vibrations restored by Hooke’s force of elastic shear stresses. Particular attention is given to the even-parity poloidal Alfvén modes whose frequency spectra are computed in analytic form, showing how the purely toroidal magnetic fields completely buried beneath the star surface can manifest itself in seismic vibrations of non-magnetic white dwarfs. The spectral formulae obtained are discussed in juxtaposition with those for Alfvén modes in the solid star model with the poloidal, homogeneous internal and dipolar external, magnetic field whose inferences are relevant to Alfvén vibrations in magnetic white dwarfs.     

A three-parameter magnitude phase function for asteroids

We develop a three-parameter H, G₁, G₂ magnitude phase function for asteroids starting from the current two-parameter H, G phase function. We describe stochastic optimization of the basis functions of the magnitude phase function based on a carefully chosen set of asteroid photometric observations covering the principal types of phase dependencies. We then illustrate the magnitude phase function with a chosen set of observations. It is shown that the H, G₁, G₂ phase function systematically improves fits to the existing data and considerably so, warranting the utilization of three parameters instead of two. With the help of the linear three-parameter phase function, we derive a nonlinear two-parameter H, G₁₂ phase function, and demonstrate its applicability in predicting phase dependencies based on small numbers of observations.     

Anomalous behaviour of specific electrical conductivity at a karst spring induced by variable catchment boundaries: the case of the Podstenjšek spring,Slovenia

Anomalous behaviour of specific electrical conductivity (SEC) was observed at a karst spring in Slovenia during 26 high‐flow events in an 18‐month monitoring period. A conceptual model explaining this anomalous SEC variability is presented and reproduced by numerical modelling, and the practical relevance for source protection zoning is discussed. After storm rainfall, discharge increases rapidly, which is typical for karst springs. SEC displays a first maximum during the rising limb of the spring hydrograph, followed by a minimum indicating the arrival of freshly infiltrated water, often confirmed by increased levels of total organic carbon (TOC). The anomalous behaviour starts after this SEC minimum, when SEC rises again and remains elevated during the entire high‐flow period, typically 20–40 µS/cm above the baseflow value. This is explained by variable catchment boundaries: When the water level in the aquifer rises, the catchment expands, incorporating zones of groundwater with higher SEC, caused by higher unsaturated zone thickness and subtle lithologic changes. This conceptual model has been checked by numerical investigations. A generalized finite‐difference model including high‐conductivity cells representing the conduit network (“discrete‐continuum approach”) was set up to simulate the observed behaviour of the karst system. The model reproduces the shifting groundwater divide and the nearly simultaneous increase of discharge and SEC during high‐flow periods. The observed behaviour is relevant for groundwater source protection zoning, which requires reliable delineation of catchment areas. Anomalous behaviour of SEC can point to variable catchment boundaries that can be checked by tracer tests during different hydrologic conditions. Copyright © 2011 John Wiley & Sons, Ltd.     

Mapping groundwater‐dependent ecosystems using remote sensing measures of vegetation and moisture dynamics

Protection of groundwater‐dependent ecosystems (GDEs) is an important criterion in sustainable groundwater management, particularly when human water consumption is in competition with environmental water demands; however, the delineation of GDEs is commonly a challenging task. The Groundwater‐dependent Ecosystem Mapping (GEM) method proposed here is based on interpretation of the land surface response to the drying process derived from combined changes in two multispectral indices, the Normalised Difference Vegetation Index and the Normalised Difference Wetness Index, both derived from Landsat imagery. The GEM method predicts three land cover classes used for delineation of potential GDEs: vegetation with permanent access to groundwater; vegetation with diminishing access to groundwater; and water bodies that can persist through a prolonged dry period. The method was applied to a study site in the Ellen Brook region of Western Australia, where a number of GDEs associated with localised groundwater, diffuse discharge zones, and riparian vegetation were known. The estimated accuracy of the method indicated a good agreement between the predicted and known GDEs; Producer's accuracy was calculated as up to 91% for some areas. The method is most applicable for mapping GDEs in regions with a distinct drying period. Copyright © 2012 John Wiley & Sons, Ltd.