ALBERT

Notes: An objective procedure is described for quantifying the shape of two-dimensional closed curves from projections or sections of particles, e.g., sand grains. The curves are plotted in polar coordinates r and θ, and a harmonic analysis is made of the function r(θ) by numerical analysis of measurements at equally spaced sample points along the curves. Quantities corresponding to the conventional properties of sphericity and roundness are derived from the Fourier coefficients. Three different measures of roundness are proposed and shown to correlate with visually estimated roundness classes, though also depending to some extent on sphericity. An attempt is described to study the interaction between these two properties by analysis of synthetically rounded plastic particles.

Notes: Many, but not all, current ripples show log-normal grain-size distribution and good sorting (P. D. Trask). A range in medians was measured from fifty to several hundred microns. Turbidite ripples are log-normal, very well-sorted and are restricted to medians of very fine sand to silt (〈 130 μ) because the particles have been supplied in suspension at rippling velocity. Experimental suspension current ripples formed at about 50–60 cm/sec are similar in composition and structure to turbidite ripples. The continuous supply results in climbing ripples. The restricted grain size and the internal structure of turbidite ripples both form strong evidence against the action of normal currents. The number of grain-size analyses is still rather small.

Notes: An attempt was made to find the ways for quantitative estimation of changes of the sedimentation processes and paleogeographic environments in the geological past. Quantitative regularities on the basis of rock volume measurements were found in the history of sedimentation and environmental conditions on the Russian Platform beginning in Late Riphean (Pt3) until Quaternary, through the main geotectonic cycles (Caledonian, Hercynian and Alpine).It was shown that there were no major differences between sand and clay abundance (26.0% and 30.1%, respectively). Limestones are most abundant among carbonate rocks (17.0%), followed by dolomites (10.2%), then marls (7.5%) and finally chalk (2.0%). Surprising was the very high abundance of gypsum and anhydrite (2.7%) and of salts (3.1 %). Being in agreement with data of many other regions of the world, this fact has far reaching consequences, first of all, concerning the history of ocean salinity and, secondly, for the knowledge of geochemical cycles of Na, C1 and S.A predominance of terrigenous sedimentation has been found for the Caledonian and Alpine cycles, whereas a greater abundance of chemical and biochemical sedimentation occurred in the Hercynian (Variscian) cycle. Each of these cycles is characterized by the common scheme of periodical recurrence of main rock types from the initial to the final stages. (Fig. 2).Fig. 8 shows the prevailing role of uplift and erosion on the Russian Platform (76% of the total platform area); only 5.7% of the area falls on the continental sedimentation, 1.8% on the lagoon environments, and 16.5% on the marine sedimentation. This is in contrast to the geosynclines which were dominated by marine sedimentation. Considering now only the regions of stable subsidence and “fixed” sedimentation of the Russian Platform (Fig. 5) we find that here marine sedimentation dominated (68.9% of the areas of stable subsidence) in comparison with the continental environments (23.6%). As well as the abundance of sediments, the distribution of the main types of paleogeographical conditions changed during the cycles with extreme regularity according the periodic law. (Fig. 6,7). The periodicity of sedimentation and the alteration of paleogeographical conditions were finally determined by the periodical rhythm of platform epirogenic movements.

Notes: A clastic deposit is represented by several diagrams. C-M diagrams in which C is the one-percentile, M the median of the grain-size distribution, characterize the coarsest fractions of the samples. F-M, L-M and A-M diagrams in which F, L and A, respectively, are the percentages by weight in the samples of grains finer than 125, 31 and 4 μ characterize the finest fractions. As a group, these diagrams form the “grain-size image” of a deposit.The above parameters were selected because they are closely related to transport and deposition mechanisms. As a consequence, the grain-size image gives fairly precise information on hydraulic conditions under which a deposit is formed.A large number of deposits were compared by means of their grain-size images. This comparison shows that some texture characteristics are related to the environment of deposition while others are controlled by basin mobility. Mobility should, therefore, be considered when comparing sediments of different basins and particularly recent and ancient sediments.Relationships which exist between certain sizes of clastic grains and the most probable deposition mechanism are used to classify clastic sediments by subdividing them into types indicative of their genesis.Grain-size types can be represented on maps and cross-sections. Grain-size facies maps of ancient formations represent lateral variations of texture and of hydraulic conditions across all basin environments and do not necessitate a reconstruction of these environments, which, often, is questionable. These maps, sell suited to show and project sedimentary trends, complete conventional isopach and sand/shale ratio maps. Integrated with ecological determinations and sedimentary structure descriptions, grain-size facies maps are a means of environment analysis.

Notes: Relative mineral frequencies (number or weight) are not suitable to study variations in the absolute frequencies of individual heavy-mineral species in a turbidite. A particular grain size can be selected as the “nominal grain” and numbers of grains of a particular mineral in all size classes can be converted to nominal grains. The total number of nominal grains per gram of sediment sample has been defined as the “nominal grain abundance”, which is a function of the volume (or weight) of the total mineral in the sample.Study of a simple, graded, Tertiary turbidite indicates that the least vertical change in heavy-mineral content occurs at, or slightly above, the middle part of the bed. Heavy minerals in the distal part of the turbidite have more uniform vertical distribution than in the proximal part.

Notes: Devonian limestone turbidites from North Cornwall, composed mainly of crinoidal debris, are considered to have been derived from an oceanic rise or schwelle. Large-scale cross-bedding (representing division C) occurs in some limestone bands. The turbidites lack a pelitic division and there is usually a sharp contact with the shales above. Typical flutes are rare but broad grooves and channels are present on the soles.

Notes: It is shown that in calculating the viscous force on a non-spherical particle suspended in a fluid, it is necessary to use the largest dimension of the particle. This may be calculated from the diameter of the equivalent sphere obtained from a hydrometer analysis provided the shape of the particle is known.

Notes: A new instrument to measure a functional-shape property of sand grains is presented. This property, which is called “rollability”, is measured on the inside of a slightly inclined, revolving cylinder mantle. During the rolling shape segregation takes place and the time it takes the grains to emerge from the cylinder is a measure for their rollability.The measurements are performed on 1/4–phi sieve fractions. Only very little material is needed for a measurement (30–200 mg) and the measurements last on the average 70 sec. Sizes between 88–700 μ are most suitable. Static electricity on quartz—the snag in most similar methods—is eliminated. The repeatability is 1% plus or minus. Since the measurement is completely automatized, personal bias is excluded.This paper is meant to enable copying of the instrument,/〉 whereas methodology and results in regional applications have been treated elsewhere (WINKELMOLEN, 1969).

Notes: Handbook of Palynology (Morphology-Taxonomy-Ecology). An Introduction to the Study of Pollen Grains and Spores. G. ERDTMAN. Elemental Analysis in Geochemistry, Part A: Major Elements. (Methods in Geochemistry and Geophysics, 8). A. VOLBORTH. Physical Geology. C. R. LONGWELL, R. F. FLINT and J. E. SANDERS. Les Ordinateurs en Géologie Pétroliére et dans les études de Production.(Collection Colloques et Séminaires, 7.)