Quarterly Journal of The Geological Society 

About: Quarterly Journal of The Geological Society is an academic journal. The journal publishes majorly in the area(s): Carboniferous & Devonian. Over the lifetime, 3410 publications have been published receiving 54578 citations.

On the Geology of Egypt

Abstract: I have deemed it advisable to preface this paper with a brief notice of the geographical position, extent, and more prominent physical features of Egypt, remarking at the same time that although much still remains to be done in this most interesting, and comparatively unexplored field for the geologist, yet it may not be wholly useless to lay before the Society a summary of what has already been effected.

On folding during three-dimensional progressive deformation

Abstract: This paper is concerned with the geometry of homogeneous strain in rocks. Equations relating rotation of planes and lines to the deformation of the rock containing them are derived with the aid of the deformation ellipsoid. The Fresnel construction is borrowed from optical mineralogy to determine from the deformation ellipsoid the principal axes of compression and extension in any plane, and an expression is derived for determining the lengths of these axes. Further equations are derived which define the surfaces of no infinitesimal strain and no finite strain for all possible ellipsoids, and it is shown that these surfaces may be used for rapidly determining whether the principal axes in any plane have suffered shortening or extension. With these tools the rather complex geometry of three-dimensional homogeneous strain is examined in detail. It is shown, for instance, that during deformation planes and lines develop preferred orientations reflecting the symmetry of the deformation, and pre-existing folds rotate bodily in space and either open or close or both during the deformation. In order to draw further conclusions of general interest the condition of homogeneous strain is relaxed in order to consider the deformation of layered rocks with competence differences between the layers. It is argued that during the deformation of such rocks folds and boudinage form parallel to the principal directions of strain in the layers. The conditions that determine whether folds or boudinage are formed are examined and the subsequent development of the structures after their generation is followed. These methods of analysis are used in the construction of models of superimposed fold-systems which are shown to be similar to some recently described field examples. It is argued that the tectonic axial cross must be replaced by the deformation ellipsoid. The structures treated in the paper are usually derived by shear-plane hypotheses, but it is considered that such hypotheses are superfluous.

The structural and geomorphic evolution of the dead sea rift

Abstract: The two methods of projected profiles and reconstructed stream profiles are applied in a geomorphic study of the region on both sides of the Dead Sea Rift. This supplements an earlier study of the tectonics. There are three recognizable surfaces at high levels. The earliest is cut partly in Eocene marine sediments. On both the Arabia and the Sinai–Palestine blocks the third surface has been well preserved and extends far into central Arabia. Warping, tilting and local uplift which affected these early erosion surfaces are related to the first phase of horizontal movement on the wrench-faults of the Rift. Along some sectors tendency to oblique overthrusting and underthrusting caused the downwarping or upwarping of the margins of the blocks ; along others the margins separated and there was an absence of distortion. There followed a period of quiescence, and base-level changed negatively and then remained stationary on more than seven occasions. The last major still-stand was interrupted by a second phase of horizontal movement on the Rift faults, which is continuing. Except for the outpouring of the plateau basalts of the Hauran of southern Syria, volcanism in the region was confined almost entirely to the Arabia block south of Amman. It was characterized by short-lived and occasionally violent eruptions. It began shortly after the initial warping of the early surfaces.

Notes on the compressibility of clays

Abstract: The consolidation of an argillaceous sediment may be simply described as the process by which it is compressed from a mud into a clay and finally, if the weight of the overburden is sufficient, into a shale. 1 This process is of importance in the interpretation of geological structure, and on a smaller scale it has an application in the design of foundations for engineering structures, since the weight of a structure founded on clay will cause settlements due to consolidation, and the magnitude of these settlements must be know. The practical aspects of consolidation have been considered in several papers in geological and engineering literature. In the present paper we shall be concerned with a quantitative study of the process of consolidation in argillaceous sediments, and the objects of our investigation will be as follows: (1) to examine the compressibility of a number of different types of clay, as demonstrated in laboratory consolidation tests; (2) to present field data on the compressibility of clays in nature; (3) to compare the ture compressibility of clays in nature with that found in the laboratory tests. The first experimental work on consolidation was published by K. Terzaghi in 1921 and 1923. This was collected together and considerably expanded in the book Erdbaumechanik which was published in 1925 and which formed the basis of the new applied science known as soil mechanics. In 1927 the same author gave results of laboratory consolidation tests on several different clays and showed that the compressibility was greater

The consolidation of clays by gravitational compaction

Abstract: Sedimentation compression curves, relating void ratio to effective overburden pressure, are presented for a wide lithological range of argillaceous deposits. These curves show the progressive changes from recently deposited muds on the sea floor, to Quaternary clays at depths of several tens of metres, and finally to hard clays and mudstones of Pliocene age at depths extending to about 3 000 m. Twelve localities are examined in some detail and information is also given from another eight previously published sites. In all cases the data are derived from ‘normally-consolidated’ deposits, strata which have never been under greater pressures than those existing at the present time. This procedure eliminates the difficulties of estimating the effect of pressure reduction by erosion. Clays containing high proportions of carbonates and organic matter are not included in this study. The water content (or void ratio or porosity) of any particular clay in the normally-consolidated condition is controlled by the effective overburden pressure p 0 , given by Terzaghi9s law p 0 = σ − u, where σ is the total vertical pressure exerted by all the material (particles and water) above the point considered, and u is the pore water pressure at that point. This law is shown to hold good even at porosities as low as 15 per cent. At any particular effective overburden pressure the water content of a normally-consolidated clay is directly related to the amount of clay minerals present and to their colloidal activity. The combined influence of these two factors can be indicated quantitatively by the Atterberg limits; and at a given value of p the water content is found to be a function of the Atterberg (liquid and plastic) limits for all inorganic non-calcareous clays except those with an extremely unstable microstructure, such as the so-called ‘quick clays’ of Scandinavia. Moreover, the water contents of muds on the sea bed or in tidal flats can also be expressed approximately by single-value parameters in terms of these limits. Thus if the water content, effective overburden pressure and Atterberg limits are known for an individual layer of normally-consolidated clay, it is possible to reconstruct the entire sedimentation compression curve for that clay with a reasonable degree of certainty; and hence an estimate can be made of the compaction which has occurred in the clay under its own weight and under the load of any overlying strata. At some of the sites, in addition to data relating to compaction, information is given on the increase in strength with depth and the rate of deposition as deduced from radiometric dating.