The study of relative density in some dune and beach sands

A new method was developed for the measurement of relative density in natural sand deposits. The method is based on hardening sand in the field, so that undisturbed samples can be obtained, and the later removal of the organic hardener in the laboratory. In the study of two coastal dunes use was made of “peels” which reveal in detail the internal structure of the sand. A definite relationship was established between relative density of the dune sand, its internal structure and mode of deposition. Very high relative densities, approaching and even exceeding 100%, were found in sand deposited by accretion on the top of the dunes. Low to very low relative densities were measured in slip deposits formed by avalanching of sand on the leeward slope of the dunes. High densities in accretion deposits are attributed to sand movement by saltation taking place during the accumulation of the sand and the very high kinetic energies expended during this transportation process. Low densities in the slip deposits are attributed to the process of avalanching which involves minimum energy expenditure. A more or less constant relative density of around 80% was found in the stretch of beach sand studied.     

Marine Plio-Pleistocene of Iceland and problems of its correlation

The marine Pliocene-Pleistocene sequence of Iceland contains four main assemblages of mollusks: (1) Venerupis rhomboides et al., (2) Serripes groenlandicus et al., (3) Portlandia arctica et al., and (4) recent species. Analysis of the stratigraphic distribution of 100 species shows that the percentage of extinct species in the assemblages decreases from 40% in the oldest to 4–8% in the youngest. There is also a change from south boreal affinities in the oldest assemblage to north boreal in the youngest. The molluskan assemblages of Iceland can be correlated with Pliocene-Pleistocene assemblages of England and North Europe: (1) Coralline Crag, (2) Red Crag—lower part of the Icenian strata, (3) upper part of the Icenian-Cromerian strata. The upper boundaries of the Pliocene and Eopleistocene are defined by paleomagnetic data and radiological dating. The upper boundary of the Pliocene presumably should be established in the basalts lying between the Tjörnes and the Breidavik deposits by changes between the second and third mollusk assemblages and by the Gilsa paleomagnetic event.     

An application of Mie's series to soft particles

Summary The scattering of electromagnetic radiation from soft particles has been studied by a new method which allows to transform the Mie series into a simplified form through the use of some auxiliary expansions derived in the Appendix of this article. This simplified form (eq. 1) converts into the Hulst and Rayleigh-Debye-Gans' formulae if the parameters of eq. I are properly restricted. A further simplified form (eq. II), improves the well-known Hulst approximation.     

Melting of Mg2GeO4 under pressure

Melting point of germanate forsterite, Mg₂GeO₄, was raised by compression at the rate of 30°C/GPa. The triple point, at which three phases of olivine- and spinel-type solids and liquid coexisted, was fixed at 1950°C and 3.5GPa. Wen these results are combined with the thermodynamical data of forsterite, Mg₂SiO₄, it is estimated that the triple point of forsterite lies in a region ranging from 2700° to 3000°C in temperature and from 20 to 30GPa in pressure.     

Elastic modulus and internal friction in enstatite,forsterite and peridotite at seismic frequencies and high temperatures

Spectra of internal friction between 2 and 8 Hz were studied in a single crystal of enstatite, in a polycrystal of synthetic forsterite and in several samples of natural peridotite. Measurements of Q^?1 and μ were performed in vacuum (10^?6 torr), from room temperature up to 1100°C. For these experimental conditions no peak was observed in the polycrystalline undeformed forsterite, but the background attenuation irregularly increased from 5 · 10^?3 to 10^?2.A peak Q^?1 = 7 · 10^?2 appears in a deformed peridotite at 930°C. It is reduced of 60% after 5 h of annealing at 1100°C. But the background attenuation persists. In the single crystal of enstatite, a peak is observed at 760°C (Q^?1 = 6 · 10^?2). A mechanism involving dislocations is suggested as a possible explanation for the peak obtained with the peridotite samples. If this hypothesis is right, the observed effect would be diffusion controlled so that one can expect pressure to translate it towards higher temperature. This mechanism could therefore appear in the upper mantle. Background attenuation could be the result of intergranular thermal losses.     

Paléo-bactéries et minéralisations plombo-zincifères du Bled Zelfane (tunisie centrale)

Résumé Le Bled Zelfane est un synclinal mio-pliocène sur la bordure septentriono-orientale de l'ile de Kasserine. L'ile de Kasserine est une plate-forme devenue insulaire à partir du Crétacé supérieur et restée émergée jusqu'au Miocène moyen. Ce môle a été soumis apparemment pendant sa période continentale à un climat oxydant de type méditerranéen relativement sec. On note une certaine diversification dans la nature des dépôts en zones basses (secteur de Kasserine) et en zones hautes (secteur du Bled Zelfane). En zones basses, la sécheresse climatique a favorisé la formation de dépôts de gypse, d'argiles rouges et de calcrêtes. En zones hautes, une érosion par lessivage acide a créé des dépressions karstiques dans les calcaires du Crétacé supérieur (Aïn Khamouda) et dans les calcaires du Maëstrichtien (Sidi Mabrouk et Guémata). Le remplissage des cavités karstiques (poches, crevasses) s'est fait avec de l'argile blanche (halloysite), contenant des micro-cristaux de galène, avec de la calamine et des oxydes de fer. Les conditions climatiques étaient trop oxydantes pour que le zinc se dépose autrement que sous forme de calamine. Elles expliquent aussi la présence de paléo-algobactéries (aérobies) sur la calamine. La présence de micro-cristaux de galène dans l'halloysite serait liée à un sulfuretum et non à des conditions réductrices réelles. Il semble en effet que dans ces karsts du Bled Zelfane une flore bactérienne très riche a joué un rôle essentiel dans le piégeage d'éléments lourds et notamment dans la genèse de galènes supergènes et dans la cristallisation de la calamine. Une minéralisation, elle aussi plombo-zincifère, de type stratiforme, s'observe à la base de Miocène inférieur et montre de même des bactéries fossiles à foison.

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Bled Zelfane is a Mio-Pliocene syncline on the NE edge of the palaeo-island of Kasserine, a platform which became insular at the beginning of the Upper Cretaceous and remained emergent until the Middle Miocene. During its long emergence this platform was affected by an oxidising, relatively dry, Mediterranaean-type climate. There exists a certain diversity in the sedimentary accumulations in both the lower (Kasserine area) and upper (Bled Zelfane area) sectors of this palaeo-relief. In the lower sectors the dry climate has favourised gypsum, red clays and calcrete formation. In the higher sectors erosion and leaching by acid waters has created karstic depressions in the Upper Cretaceous (Aïn Khamouda) and in the limestones of Maestrichtian (Sidi Mabrouk and Guémata). The karst cavities (pockets and fissures) are filled with white, halloysite clays containing micro-crystals of galena associated with calamine (Zn) and iron oxides. The climatic conditions were too oxidising to permit the formation of Zn other than in the form of calamine. The dry climate is also an explanation for the presence of aerobic palaeo-algobacteria on this calamine. The presence of micro-crystals of galena within the halloysite is probably related to a sulfuretum and not to effective reducing conditions. It would seem that the presence of a rich bacterial flora within the karst at Bled Zelfane has played a significant role in the stabilisation of heavy elements, and especially the supergene genesis of the galena. A Lead/Zinc mineralisation also exists at the base of the Miocene. This latter is diffused through the cement in conglomerates and sandstones.

     

Exploration geochemistry—Distribution of elements and recognition of anomalies

The exploration geochemist faces a serious problem in reconciling theoretical statistics with the empirical distribution of elements in materials in the earth's crust. The results of computer-simulation experiments being conducted by the Exploration Geochemistry Group at the University of New Brunswick illustrate some of the problems of the relation between frequency distributions and spatial distributions of elements and raise some interesting questions about sampling patterns and physical size of samples. Most importantly, the simulation experiments and empirical examples support the contention that attempts to make an assumption of normality more efficient by performing log transformations on positively skewed data may defeat the purpose of statistical analysis for exploration work. New developments in computer-data presentation and interpretation, including population sorting and classification, illustrate the increasing use of the computer in exploration geochemistry.     

Amino acids in equatorial Pacific Ocean water

Seawater samples from the Eastern Equatorial Pacific Ocean were analyzed for amino acids by a ligand-exchange chromatography technique. The results showed that dissolved free amino acids make up only 0.3% of DOC, much less than has been previously reported for open ocean waters. Substantially larger amounts of combined amino acids are present, however. Concentration variations of the combined amino acid fraction in the water column suggest their potential use as a water mass indicator.     

Diurnal variations in planetary boundary-layer winds over land

Windsonde data gathered over a nine-year period at three stations in the Southeast U.S. are stratified by season and by time of observation to provide average profiles depicting the diurnal variations in low-level winds. Significant variations are found (especially during the summer months) in wind speed, angle between wind direction and isobars, and the various terms of the kinetic energy budget equation. A qualitative model of the diurnal variations in planetary boundary-layer winds (over land) is developed. From a thesis submitted to the Graduate Faculty of Colorado State University in partial fulfillment of the requirements for the degree, Doctor of Philosophy.