A graphical approach to polar paths: Paleomagnetic cycles and global tectonics

Some problems of the conventional “minimum polar distance” approach to Precambrian pole path construction are discussed. An alternative technique, based on a less restricted approach, is proposed and assessed by using all presently-available Precambrian and Paleozoic data from the world. In the construction of any pole path, assumptions are always made on the shape of the path through regions of apparently missing data. Many different assumptions are possible. Assuming that the Precambrian tectono-stratigraphic record conforms to repeated sequences of geological events suggests we should observe cycles in the paleomagnetic data. Empirically, it is found that the pole paths for the periods Cambrian-Devonian, and 750–1000 Ma, define cycles of pole motion from equator, up to and over the pole, and back down to the equator. Similar cycles of 250-Ma periodicity can be identified in paleomagnetic data back to 2500-Ma. Global wide changes in the phase of the cycles appears to be coincident with the major subdivisions of geological time i.e., Phanerozoic + Hadrynian, Helikian, Aphebian, and Archean. Finally, the geological implications of these cyclic changes in Precambrian pole paths are briefly discussed.     

Reaction pathways and reaction progress for the smectite-to-chlorite transformation: evidence from hydrothermally altered metabasites

The transformation from smectite to chlorite has been interpreted as involving either a disequilibrium chlorite/smectite mixed‐layering sequence, or an equilibrated discontinuous sequence involving smectite–corrensite–chlorite. Here, analysis of the smectite to chlorite transition in different geothermal systems leads us to propose that the transformation proceeds via three contrasting reaction pathways involving (i) a continuous mixed‐layer chlorite/smectite series; (ii) a discontinuous smectite–corrensite–chlorite series and (iii) a direct smectite to chlorite transition. Such contrasting pathways are not in accord with an equilibrium mineral reaction series, suggesting that these pathways record kinetically controlled reaction progress. In the geothermal systems reviewed the style of reaction pathway and degree of reaction progress is closely correlated with intensity of recrystallization, and not to differences in thermal gradients or clay grain size. This suggests a kinetic effect linked to variation in fluid/rock ratios and/or a contrast between advective or diffusive fluid transport. The mode of fluid transport provides a means by which the rates of dissolution/nucleation/growth can control the reaction style and the reaction progress of the smectite to chlorite transition. Slow rates of growth are linked to the first reaction pathway involving mixed‐layering, while increasing rates of growth, relative to nucleation, promote the generation of more ordered structures and ultimately lead to the direct smectite to chlorite transition, representative of the third pathway.     

Snowfall into a forest and clearing

Experiments in February–March 1987 at Fraser Experimental Forest in Colorado, U.S.A., compared the number flux of snow particles above the center of an 80-m wide clearing with simultaneous samples in and above the forest 85 m upwind. Numbers of snow particles counted with electronic sensors on towers decreased with decreasing height below the canopy top in the forest and also nearer the surface in the clearing. Average fluxes were greater in the clearing than in the forest, and these differences increased with increasing average wind speed, in the 0–6 m s⁻¹ range, measured during the experiments. The greater flux at the tower in the clearing could not be completely explained by interception of snow in the forest canopy, indicating that aerodynamics may have played a part in creating the difference, even in those light winds. A plumer or concentration of snow particles appeared to have developed near the top of the canopy and spread into the clearing.     

Field campaign for the comparison of SOUSY radar wind measurements with rawinsonde and model data

A field campaign was carried out from 26 October to 7 November 1992, using the SOUSY-VHF radar and a mobile rawinsonde system installed and operated nearby to produce vertical wind profiles. The purpose of this campaign was to compare the two types of wind measurements with one another and with results from forecast models. Numerical algorithms were developed and applied to the radar data in order to eliminate random errors, correct for velocity aliasing, and calculate the effective zenith angle of the off-vertical beams. Differences between wind profiler data and rawinsonde or model results depend not only upon the errors of the different systems, but also on temporal and spatial variations of the wind field. Therefore, methods for the comparison of radar and rawinsonde data were developed which take into consideration these variations. The practical potential of these methods is demonstrated by comparisons of rawinsonde and radar wind profiles. The comparison of radar data and model output shows excellent agreement in the direction and in the speed of the wind at virtually all altitudes. An evaluation of the quality of wind profiler measurements is possible using the estimation of variance and variability of wind components.     

Geo-/Object-Coding for Local-Change Assessment

Missing availability of reliable and specific landscape data may pose substantial restrictions to successful exploitation of remote sensing data and fast implementation of GIS (Geo-Information Systems). The possibilities to document conditions with high spacial resolution at a given time and to review changing aspects by different disciplines represent opportunities for complex environmental programs.The article covers: geodata acquisition and processing, research, execution, and ergonomical/cognitive aspects. Application in inpenetrable terrain for research, landuse, and engineering requirements proved the feasibility especially in areas with high demand for timely, accurate, and comprehensive surveys.Airborne close-range sensing was developed to survey localities and regions. It is no competition to global-change monitoring and large area are mapping programs possible with remote sensing. Substituting only the bulk of field-work, leaving time for in-depth review in the field or in the office, the system provides a possibility to restudy points of interest.Exploitation of advanced metric cameras, specialized airborne platforms, and spatial overlay, recognition, and discrimination techniques form the backbone of the TOPOGRAMM approach. Multi-sectoral, multi-temporal, multi-spectral survey and processing methods rely basically on enlarged image scales additional to conventional aero-photogrammetry and analytic plotting. Measurements and identification, not primarily interpretation, allow to establish high-fidelity and high resolution geo-frameworks. Focussing on micro- and mesoscales, no emphasis is given to highest geometric accuracy used for geodetic surveys. Drawing near to the object allows extraction of thematical and semantical information, dimensions, and phenomelogy of objects hitherto only singularily available.

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