bluuebunny/crossref_metadata_2025 huggingface dataset:
TEMPERATURE EFFECT ON PRECIPITATION OF CALCIUM CARBONATE FROM CALCIUM BICARBONATE SOLUTIONS AND ITS APPLICATION TO CAVERN ENVIRONMENTS
Authors: SIEGEL FREDERIC R. , REAMS MAX W.
Published: June 2006

Solutions of calcium bicarbonate were allowed to lose carbon dioxide and evaporate to dryness under controlled temperature conditions. With filtered solutions prepared from spar calcite, precipitates were 100% calcite in the 2° to 100°C temperature range. When, in analogous experiments, coralline aragonite was the starting material, the precipitates were 100% calcite. Essentially the same was true when carbonate rocks from karst areas were used to prepare the experimental solutions. An artificially prepared mixture (maximum crystal size of about 7 u) of 70% aragonite and 30% calcite was also used in the study. The precipitates from this starting material were apparently affected by seed nuclei which passed through the filter. The stability of calcium carbonate seed nuclei appears to vary with temperature. Natural calcium bicarbonate solutions from caves yielded only calcite at 25°C.

Calcite should be the dominant or only polymorph of CaCO3 formed by the loss of carbon dioxide and evaporation of natural calcium bicarbonate solutions if temperature is the controlling factor. Since appreciable amounts of aragonite are found in many cave deposits, factors other than temperature must influence the polymorphs formed.

POBEGUIN (1955) proposed that rapid evaporation and slow diffusion of solutions favor aragonite. If so, layers of aragonite and calcite in speleothems may reprsent alternate wet and dry paleoclimates. During these periods, rate of introduction of solution and rate of evaporation would change markedly.
CRUSHING OF SEDIMENTARY ROCK SAMPLES AND ITS EFFECT ON SHAPE AND NUMBER OF HEAVY MINERALS
Authors: HENNINGSEN DIERK
Published: June 2006

Few examples are given to demonstrate that crushing of hard sedimentary rocks practically does not break up the heavy minerals present in the rock. Also the ratios of the various minerals mostly are not changed.
THE CARBONATE FRACTION OF BEACH AND DUNE SANDS
Authors: Pilkey ORRIN H. , MORTON ROBERT W. , LUTERNAUER JOHN
Published: June 2006

The sand size carbonate fractions of beach and dune sands from the southeastern U.S. Atlantic coast were investigated from the standpoint of mineralogy, roundness and size distribution. The carbonate fractions of beach‐dune sands used in this study range in abundance from less than 1% to over 40% and average about 10%. Calcium carbonate is least abundant in Georgia beaches and increases slightly to the north and greatly to the south. The size distribution of the carbonate fraction is similar to that of the non‐carbonate fraction since both have been distributed by the same processes. The variable flat shape of calcareous fragments causes the carbonate fraction to be usually coarser and more poorly sorted than the acid insoluble residues of the samples. No regional relationship between roundness and wave energies was found in sand size materials although field observations indicate high energies strikingly round gravel sized calcareous fragments. There is some tendency for angularity to increase with decreasing grain size in the sand sizes as with quartz grains. The mineralogy of beach sand carbonate fractions is characterized by the almost total absence of high My calcite. Aragonite is the dominant mineral.
A COMPARATIVE STUDY OF GLAUCONITE AND THE ASSOCIATED CLAY FRACTION IN MODERN MARINE SEDIMENTS
Authors: BELL DAVID L. , GOODELL H. GRANT
Published: June 2006

The crystallinity and mineralogy of both the glauconite and the clay fraction of samples from six contemporary marine environments were investigated by X‐ray diffraction. In those areas where glauconite is now forming, the mineralogy and the degree of crystallinity of both the glauconite pellets and the associated clay fraction are similar. In contrast, detrital and relic glauconites are observed to have mineralogies that are different from their clay fractions. No consistent relationship was observed between degree of crystallinity and color of the pellets. Further, only two classes of glauconite as defined by BURST (1958) were common: expandable, interlayered clays and two or more clay minerals in a mixed assemblage.

Based on the clay fraction‐glauconite similarities and other supporting evidence, glauconite on the Scotia Ridge is concluded to be authigenic. Glauconite from Santa Monica Bay, California and from the continental shelf off Morocco appear to be detrital. Glauconite pellets in the shelf sediments off Guinea and the southeastern Atlantic Shelf of the United States are both detrital and authigenic. The poor crystallinity exhibited by the Chatham Rise glauconite is in contrast to the well‐crystallized associated clay fraction and indicates that they are not genetically related. However, the origin of this glauconite remains in doubt.
THE DETERMINATION OF THE GRAIN‐SIZE DISTRIBUTION OF A SPHERICAL GRANULAR MATERIAL EMBEDDED IN A MATRIX
Authors: ROSE H. E.
Published: June 2006

In this paper the problem of the evaluation of the grain‐size distribution of a spherical granular material embedded in a matrix, upon the basis of the measured distribution of the sizes of the figures formed by the intersection of the grains with a random plane, is discussed and a solution, based upon matrix algebra, is developed.

There are no limitations on the method, with respect to the type of particle‐size distribution function involved and, in theory, the grain‐size distribution may be determined to any desired degree of accuracy by the use of a conversion table.

Conversion tables, which are sufficiently comprehensive to give results of worthwhile accuracy in most practical cases, are presented and the necessary calculations can be carried out, without recourse to complicated mathematics, by the use of a slide‐rule or a desk calculating machine.

If the grain‐size distribution must be divided into a number of classes greater than that covered by these tables, then extended tables must be prepared. This can be done, by application of the methods of the present work but evaluation upon a computer, by use of a standard fast‐running routine, is then practically unavoidable.

The present treatment also leads directly to the number of particles of each size present in a unit volume of compact, this being a figure of technical importance which is not easily established by other methods.
GRADED RHYTHMIC BEDDING IN THE CAPE EEAR FORMATION, CAROLINA COASTAL PLAIN
Authors: HERON S. DUNCAN , SWIFT DONALD J. P. , DILL CHARLES E.
Published: June 2006

The Cape Fear Formation rests on basement rocks in the Cape Fear River valley of the North Carolina Coastal Plain. It consists primarily of graded muddy sand—sandy mud couplets. A typical sequence for each couplet starts with a disconformity, followed by a basal gravelly sand with megaclasts of quartz and clay pebbles, cross‐bedded sand, and finally a structureless mud bed. Fossils are absent. The sand fraction is poorly sorted and the sediment has a clayey texture. Structures and textures suggest that each couplet is the product of a current waning from an upper flow regime, to the lower part of a lower flow regime. Turbidity current and fluvial origins are considered. Cross‐bedding and textural criteria indicate that normal, low‐density currents are responsible for at least part of the typical sequence. A normal fluvial origin is rendered less likely by the absence of mud cracking, root casts, and textural criteria of a partitioned subaerial environment. Stratigraphic and geochemical considerations suggest that the formation may have been deposited in estuaries or coastal lagoons; if so, the stratification may record sedimentation during the periodic flushing of saline water by river floods.
SOME EXPERIMENTS ON THE GENESIS OF TURBIDITY CURRENTS
Authors: VAN DER KNAAP W. , EIJPE R.
Published: June 2006

Turbidity currents are thought to be the agency responsible for the transport and deposition of the sediments known as turbidites. The way in which such currents may arise has been studied experimentally in a glass‐walled tank.

The starting point of the experiments was setting the sediments in motion by raising their pore pressure via a shock or vibration. This was achieved in the experiments by striking the metal bottom of the tank with a mallet.

The response of a heap of homogeneous sand to such a shock was merely to change the angle of its slope. If a layer of sand was draped over a core of coarser, homogeneous sand, sliding occurred along the plane of permeability contrast and the less coarse sand was deposited at the toe of the slope. When the layer consisted of kaolin, which has a much lower permeability than sand, sliding again took place, but the clay subsequently mixed with the water and was moved along the bottom of the tank in the manner attributed to turbidity currents.

An attempt is made to set up a scaling rule for experiments of this type and the consequences that such a rule may have in subsequent study are briefly discussed.
WEATHERING AND ROUNDNESS OF QUARTZ SAND GRAINS
Authors: CROOK KEITH A. W.
Published: June 2006

Photographs and descriptions of quartz sand grains from soils, paleosols and silcretes show that grain shape can be modified by solution in situ. Dissolution is attributed to solutions rich in organic molecules present in weathering profiles, and commonly results in rounding of protuberances and re‐entrants on grains. The incidence of this process may vary with climate. It is postulated that solution rounding during weathering plays an important role in shaping quartz sand grains in general, its significance varying with climate. This postulate, which remains unconfirmed, has considerable implications for the interpretation of textural maturity of sandy sediments. If true, super‐mature sands may be as much a climatic indicator as an indicator of tectonic quiesence.
AN OPTICAL METHOD OF MEASURING GRAIN ORIENTATION IN SEDIMENTS
Authors: WINKELMOLEN A. M. , VAN DER KNAAP W. , EIJPE R.
Published: June 2006

A new method is presented for the measurement of grain orientation in clastic sediments.

The method is based on the principle that when an inclined beam of light passes through an elliptical hole in a plate of a certain thickness, the amount of light passing through depends on the orientation of the long axis of the ellipse with respect to the direction of incidence of the light beam. If such a plate is rotated in its own plane, the amount of light passing through will fluctuate. Such fluctuations are larger the greater the eccentricity of the ellipse, the amount of light passed being maximal when the long axis coincides with the plane of incidence of the light.

If the plate contains many holes, which need not be elliptical but for the ease of reasoning can be approximated by ellipses, their main orientation direction can be inferred from the maximum intensity of passed light.

It is shown in the paper that results of a similar kind can be obtained by using a black and white picture of the grain packing in combination with a mirror. These pictures can be obtained either from thin‐sections or from printed replicas of etched polished sections of impregnated samples.

The resulting data represent an integrated orientation pattern instead of a long‐axis distribution pattern as given by the grain‐by‐grain counting technique.

The new method has been thoroughly checked against the visual counting method. Excellent agreement was observed.
PARTICLE SHAPE AND INFERENCE OF SIZE FROM SIEVING
Authors: LUDWICK JOHN C. , HENDERSON PATRICIA L.
Published: June 2006

Accurate particle‐size measurement by sieving requires that consideration is given to particle shape and screen opening size variations. The effect of particle shape has been studied by determining experimentally the probability of passage through each of five woven‐wire screens of 35 different mm‐sized ellipsoids. These range in shape from T/D= 0.2 to 1.0 and from L/D= 1.125 to 2.625, where T is particle thickness, L is particle length, and D is particle intermediate diameter. Passage tests were performed for both static and dynamic conditions of sieving.

A mathematical sieving theory stemming from the idea of particle passing probability is developed. The theory is put to use by computer‐simulated sieving of idealized input samples of simple shape make‐up. When near‐spheres are sieved it is found that a bar‐type histogram is a justifiable depiction. For some other more realistic shape inputs, what is obtained are broad, overlapping bell‐shaped fraction distributions considerably offset from the nominal openings of the limiting screens. For these distributions, conventional representation in histogram form is incongruous.

The treatment presented contains allowance for screen opening size variations. Some apparently polymodal distributions are probably explainable as a result of unsuspected differences between the screens used and an ideal screen series.
DIAGENETIC RE‐CRYSTALLIZATION AND ORIENTATION OF TWO CARBONATE SPECIES
Authors: ATTEWELL P. B. , HIRST D. M. , TAYLOR R. K.
Published: June 2006

Results of X‐ray textural studies of dolomite and the clay minerals in the Marl Slate and of siderite from the top of the Mansfield Marine Band are interpreted in terms of the possible diagenetic development of the re‐crystallized carbonates in these two rocks. From computer processed (1014) fabrics of the two trigonal carbonates it is deduced that there is a c‐axis preferred orientation concordant with the normal to the stratification. An early diagenesis in this oriented mode must be a function of both a threshold stress difference in a non‐hydrostatic stress field (in effect a necessary minimum depth of burial) and also of the presence of connate solutions. The existance of a minor percentage of dolomite oriented with the rhomb faces parallel to the stratification probably reflects an even earlier crystallization within the top few metres of sediment, when the confining pressures and pressure differences were of insignificant amplitude. It is concluded that a higher rate of sedimentation associated with the Coal Measure sequence is responsible for the singular preferred orientation of the siderite.
GRAIN‐SIZE INDICES, CLASSIFICATION AND ENVIRONMENT
Authors: DOEGLAS D.J.
Published: June 2006

Indices based on Wentworth phi values of Q1, Md and Q3 are used for textural classification of sediments. Wentworth phi values enable a detailed subdivision. A nomenclature based on the Wentworth phi indices is developed. The indices, and to a smaller degree the names, show sorting and skewness based on integer phi units. The classification scheme gives a continuous scale from gravel to fine clay. The Q1MdQ3‐indices can be used for distinction of river, marine and loess deposits. The addition of indices of the 1st and 99th percentile, giving 5‐digit indices, augments the possibilities for a determination of the environment: river deposits can be distinguished from beach and dune sediments and in more detail from shallow marine and coastal deposits. The indices can be handled by data‐processing machines.
SUR LA CRISTALLINITÉ DE L'ILLITE DANS LA DIAGENÈSE ET L'ANCHIMÉTAMORPHISME
Authors: DE SEGONZAC G. DUNOYER , FERRERO J. , KUBLER B.
Published: June 2006

On the crystallinity of illite in diagenesis and anchimetamorphism

A simple method to estimate the degree of “crystallinity” of illite has been used for several years in three French laboratories. Many results, which are unpublished, were obtained; three examples are presented in this paper. They show the sensibility of the method, which allows one to appreciate, above all other methods, burial diagenesis, the front of metamorphism, or some regional areas of very weak metamorphism.
MORPHOLOGIE MATHÉMATIQUE ET GENÈSE DES CONCRÉTIONS CARBONATÉES DES MINERAIS DE PER DE LORRAINE
Authors: SERRA J.
Published: June 2006

Matheinatical morphology and genesis of Lorraine iron ore carbonated concretions

Mathematical morphology provides strong theoretical tools for the description of geological structures. Here, the intrinsic function of MATHERON'S (1965) regionalized variables theory, is used to describe a limestone migration phenomcnon, and the genesis of carbonate nodules in the sedimentary ore deposits of Lorraine. In this intrinsic function:

image

is x a moving point through the mineraliLed space v, and k(x) a boolean value associated to x. The characteristics of γ (h) represent the structure of the regionalisation k(x).

This descriptive step leads to models of stochastic processes to interpret the genesis of those migrations. The theoretical models allow to resolve or to compute the intrinsic functions and to confront them with experimental data.

In conclusion mathematical morphology ‐ the acute efficiency of which is manifest in the description of the evolutions ‐ appears to be unable to explain why those evolutions occur.

The different steps of this study can be presented as follows. The beginning is shown by the pictures of Fig. I. White limestone concretions can be distinguished set against a dark background of iron ore. It is clear that the structure of the concretion is the same in Fig.lA and 1B though the two photos are different. How could this structural identity be measured?

For this purpose we shall use the “variogram”‐concept of Matheron's theory (FORTET et al., 1953). The “regionalized variable” is the function k(x), of wich the value is 1 when x is in the concretions, and zero when not. “x” is a moving point through the mineralized space v. The intrinsic function, or “half variogram”, γ (h) is then:

image

which depends only on the vector h and not on the moving point x. y(h) represents an increment variance. It mathematizes the concept of the influence zone of the sample.

The average “variogram” of Fig.1, and of a series of twelve photos taken in the same neighbourhood is giien by Fig.3B, in the vertical direction. The origin tangents of curves measure in each direction the diametral variation, whose average value in all directions of space represents the specific surface of concretions (cf. SERRA, 1966a). Practically the variograms do not increase after 50 cm in horizontal direction, and 25 cm in the vertical one. Those values mean average lengths of concretions in those directions. On the other hand, the curve of Fig. 3B represents a maximum, which reflects the limestone migration process itself.

This last remark leads to the establishment of stochastic models of the genesis of limestone migration. Realisations of those random functions are giwn in Fig. 9A, B, C, D. Their variograms are similar to those of Fig.3A and 3B. Such a model is, therefore, an adequate representation of natural regionalization, and expresses the genetic hypothesis. This mathematical method finally allows an easy and clear translation of structural notions in a quantitative language.
THE PRESENT STATUS OF ZIRCON
Authors: SAXENA S.K.
Published: June 2006

The present writer (SAXENA, 1966) does not propose that the use of zircons in problems of stratigraphy, pedogenesis and petrology should be discarded. His conclusions (pp.30–31) make a plea for caution in such use. The writer suggests several possible modes of the origin of Lircons and by no means the authigenic mode of origin is more important than any other. Igneous or detrital zircons could certainly be used provided due consideration is given to other possible modes of origin. The solution does not lie in abandoning the use of zircons but an individual case is to be judged according to the local geologic evidence. It may be possible to find the genctic history imprinted on the morphological features of Zircons. Most of MARSHALL'S (1967) criticism is because of his failure to realize the broader genetic aspects of zircons.
RECENT LITTORAL AND SUBLITTORAL HIGH‐MG CALCITE LITHIFICATION IN THE MEDITERRANEAN
Authors: ALEXANDERSSON TORBJÖRN
Published: June 2006

Lithification caused by inorganic precipitation of high‐Mg calcite is reported from several localities in the Mediterranean. A micritic calcite cement with 13–15 mol. % MgCO3 in solid solution lithifies internal sediments and forms open‐space fillings within a sublittoral algal framework down to 20 m, in which the biogenic structures are gradually obliterated through the activity of numerous boring organisms and the subsequent precipitation of micrite. The silt‐mud fraction of unconsolidated bottom sediments is to a large extent stable low‐Mg calcite, and is not the source for the mcrite; instead the cementing mineral is assumed to precipitate directly from interstitial sea water. The special physico‐chemical régime is attributed to organism activities.

The same phase of high‐Mg calcite also forms the cement in beachrock in the areas studied; also here the Mg‐content is an original property and not the result of diagenetic changes. The cement occurs partly as micrite, identical to the micrite in the lithified algal framework, and partly as radiating microspar fringes. The littoral and sublittoral lithification described here indicates that within several niches in the present marine environment high‐Mg calcite may substitute for aragonite as the mineral form of precipitated calcium carbonate.
HOLOCENE INTERTIDAL CALCIUM CARBONATE CEMENTATION, QATAR, PERSIAN GULF
Authors: TAYLOR J. C. M. , ILLING L. V.
Published: June 2006

Cemented layers in the shallow lagoonal, intertidal, and supratidal sediments surrounding the Qatar Peninsula, Persian Gulf, contain high‐magnesian calcite and aragonite cements. The magnesian calcite appears to occur both as a primary precipitate and as a replacement of aragonite. These cements are believed to be forming today from sea‐derived waters. Radiocarbon dating sets an upper age limit of about 4,500 years.

Two major types of cemented layer can be distinguished: beachrocks form variably cemented units about 1 m thick at the surface of freely draining exposed beaches: cemented sheets a few cm thick form beneath the surface of broad intertidal sand flats by the growth, hardening, and coalescence of small friable lumps near low‐tide level. Replacement of aragonite matrix, druse, and pellets by microcrystalline magnesian calcite is accomplished by dissolution and reprecipitation; detail is obliterated but the gross features of the original fabric are preserved. The process helps to explain the crystal fabrics of many older limestones.
SUBMARINE LITHIFICATION OF HOLOCENE CARBONATE SEDIMENTS IN THE PERSIAN GULF
Authors: SHINN EUGENE A.
Published: June 2006

Large areas of the sea floor in the Persian Gulf are composed of lithified carbonate sediment. That this cementation is contemporaneous and occurs within the present submarine environment has been proven by carbon dating, the presence of pottery and other artifacts within the lithified sediments, and other methods.

Although the chemistry of the processes resulting in lithification is unknown it would seem not to require any special conditions other than carbonate‐saturated sea water. The process seems to be operating in areas of relatively normal salinity and temperatures in depths ranging down to 30 m. It is deduced that the principal physical factors involved are relatively low rates of sedimentation, sediment stability, and high initial permeability of the sediments.

The principal types of cement filling the intergranular spaces and locally replacing grains are aragonite (in several growth forms) and microcrystalline magnesium calcite. The aragonite cement seems to be unstable and has inverted locally to more stable calcite within the marine environment.

Lithification results indirectly in the production of several characteristic macro‐structures, including superimposed bored surfaces, fine sediment overlying drusy cement, and several other features all of which in the past have been regarded as criteria for unconformity.
A METHOD TO STUDY THE DISTRIBUTION OF HEAVY‐MINERAL GRAIN ABUNDANCE IN A TURBIDITE
Authors: NORMAN TEOMAN N.
Published: June 2006

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.
DETACHMENT OF FIRST‐GENERATION CARBONATE CEMENT ON ONCOLITES BY CRYSTALLIZATION OF SECONDARY ANHYDRITE
Authors: ROTHE PETER
Published: June 2006

Regionally the “main dolomite” (Hauptdolomit) of northwestern German Zechstein (shallow water) is made up of 30–100 m thick oncolitic dolostones. In almost every case anhydrite is observed within the sequence suggesting an environment of elevated salinities (FÜCHTBAUER, 1968). Studies on thin sections of oncolitic carbonates of a gasfield in the Emsland area reveal a shallow marine environment, sometimes even intertidal as shown by intraformational flat pebbles of reworked material. Different stages of diagenesis within the carbonates occur. The most interesting fact concerning the detached rims of first‐generation carbonate cement is discussed below and shown by several thin‐section photomicrographs.
SUBAERIAL CEMENTATION AND SUBSEQUENT DOLOMITIZATION OF LACUSTRINE CARBONATE MUDS AND SANDS FROM PALEOTUZ GÖLÜ (“SALT LAKE”), TURKEY
Authors: MÜLLER GERMAN , IRION GEORG
Published: June 2006

SUMMARY

Along the eastern coast of the Gez Gölö, a salt lake formerly belonging to the larger “Paleo‐Tuz Gölö” in central Anatolia, about 6.5 m of lake sediments of probably Pleistocene age were studied.

The sediment series consists of fine‐grained unconsolidated dolomite muds representing the basin sedimentation of the old lake.

Nine lithified beds (oomicrites, intramicrites, intraoomicrites, intrabiomi‐crites and dololutites with smaller amounts of allochems) are intercalated. These beds were deposited in very shallow water in the littoral zone of the paleo‐lake. There is direct evidence that the beds were occasionally exposed to the air after deposition. This led to desiccation (with mud cracks, breaking up of intraclasts) and subaerial cementation due to the influx of fresh water (rain water, springs).

These now lithified carbonate sedimentary rocks were submerged and subsequently covered with mud. During this sub‐aquatic phase the rock beds as well as the unconsolidated muds were dolomitized by an extremely high Mg/Caratio of the lake water which in the present Tuz Gölü amounts to about 150! It cannot be excluded, however, that dolomitization already took place or was initiated during the subaerial phase (“supratidal dolomite”).
SYN‐SEDIMENTARY MARINE LITHIFICATION OF MIDDLE JURASSIC LIMESTONES IN THE PARIS BASIN
Authors: PURSER B. H.
Published: June 2006

SUMMARY

Bored surfaces in Middle Jurassic limestones in northeastern France indicate syn‐sedimentary lithification. The sedimentary structures and textures, and age relationships between the bored carbonates and the argillaceous sediments above them suggest that the lithification has occurred in both submarine and intertidal environments. The diagenetic fabrics which have resulted from this early marine lithification include three types of calcite druse, echinoderm overgrowths, and microcrystalline cements. Most of these cements are comparable with those forming today in inter‐ and subtidal environments of the Persian Gulf.

The localization of bored surfaces (“hard grounds”) at the tops of regressive carbonate sequences is interpreted as being the result of slow carbonate sedimentation and lithification of the Jurassic sea‐floor prior to the onset of argillaceous colder, or deeper‐water sedimentation.
REWORKED DOLOMITE CRUSTS IN THE WETTERSTEINKALK (LADINIAN, ALPINE TRIASSIC) AS INDICATORS OF EARLY SUPRATIDAL DOLOMITIZATION AND LITHIFICATION
Authors: GERMANN K.
Published: June 2006

SUMMARY

Dolomitic intraclastic sediments intercalated in a cyclic limestone‐dolostone sequence of the Wettersteinkalk represent a rock type with reworking fabrics demonstrating early lithification and dolomitization. The extreme flatness and the angularity of the pebble‐sized doloclasts, the lack in plastically deformed dolomitic fragments, and clasts of previously cementated arenites and oncolites testify to a pre‐reworking consolidation which, besides biogenic stabilization and dehydration, requires an early cementation. In the different types of doloclasts cementation both by dolomite and by calcite has been confirmed by stained peels and thin‐sections, electron‐microphotographs, and electron‐microprobe analysis.

The prevailing rock type, a very poorly sorted mixture of doloclasts and minor amounts of rounded limeclasts with a pelletal calcite mud matrix is interpreted as storm sediment formed by the introduction of subtidal lime muds to dolomite incrusted supratidal flats.
EARLY VOID‐FILLING CEMENTATION IN DEVONIAN FORE‐REEF LIMESTONES (GERMANY)
Authors: KREBS WOLFGANG
Published: June 2006

SUMMARY

Fibrous calcite is the main cement in the voids and cavities of Devonian fore‐reef limestones in Germany. Cementation occurs in some cases simultaneously with encrustation by blue‐green algae as well as internal deposition of calcarenites and calcilutites. These observations lead to the conclusion that the fore‐reef voids were exposed to light and were still in free communication with the sea, when the cementation began. Furthermore, redeposited fragments of former cavity fillings indicate that the formation of cavity‐filling fibrous calcium carbonate cement was already completed before the sea‐ward erosion took place. It is believed that the precipitation of fibrous calcium carbonate in most of the Devonian fore‐reef limestones, which show no signs of dissolution, occurred in a shallow subtidal environment. Only the voids showing larger solution phenomena were probably exposed to fresh water in the inter‐ to supratidal zone.
CLAY MINERAL POST‐SEDIMENTARY RANKS IN TERRIGENOUS ROCKS
Authors: KARPOVA G. V.
Published: June 2006

Kaolinite, dioctahedral 1M and 2M1 hydromicas, trioctahedral Ib and IIb chlorites, montmorillonite and mixed‐layer phases from the terrigenous Carboniferous rocks of the Bolshoy Donbas at the southwestern border of the Russian Platform are described. Clay minerals form definite assemblages connected with the facies character and mineral composition of the rocks and with the intensity of post‐sedimentary alteration. This post‐sedimentary evolution of the terrigenous rocks is characterized by regional ranks of clay polytypes and clay isomorphous varieties, viz.:

image

The persistence of mineral assemblages in definite PT intervals leads to the possibility of their use for characterizing post‐sedimentary alteration stages.
NOUVELLE MÉTHODE DE DÉTERMINATION DE LA SPHÉRICITÉ DES SÉDIMENTS MEUBLES
Authors: WEYDERT PIERRE
Published: June 2006

A new method to determine the sphericity of mobile sediments

In this paper we show a new method to determine the sphericity of sand particles with sedimentary analysis. We use two different sieves: the one with open squares: the side is a and the diagonal d=a√2 the other with circular openings: the diameter is D. Experimentation shows that elements crossed the open‐square sieves in diagonal positions. When we reported the cumulative curves into arithmetic or semi‐logarithmic graphs, we used the value d and not the side square a.

A sediment C, which is composed of not very angular or subspherical par‐ ticles, is represented by two cumulativecurves on the same graph. If a sediment A is very angular, the two curves are disconcerted. The sediment B is subspherical, the difference between the two curves is maximum. We call this difference δ which is equal to d–D. For C this difference is Δ, which is always inferior to δ. The absolute sphericity index Sa is the ratio AId in yo. When the particles are very angular, sphericity values are 0—like A and when they are sphericals the index is 1—like B. This index is determined with graphic solutions. The values obtained are compa‐ rable with those of visual charts.
FAULT‐GRADED BEDS INTERPRETED AS SEISMITES
Authors: SEILACHER ADOLF
Published: June 2006

Fault grading is expressed by a regular structural sequence of (from top) liquified zone, rubble zone and step‐faulted zone, with gradational contacts between these zones and the bottom, but with a sharp boundary at the top. It is interpreted as an effect of strong earthquakes on gradationally compacted muds in quiet water basins. Fault‐graded beds are geopetal and paleoslope criteria. If interpreted as seismites they may also be used as paleo‐seismograms.
A QUANTITATIVE MODEL OF CLIMBING RIPPLES AND THEIR CROSS‐LAMINATED DEPOSITS
Authors: ALLEN J. R. L.
Published: June 2006

The angle of climb of ripples in cross‐laminated deposits is governed by the simple relation:

in which ζ is the angle of climb, M is the rate of sediment deposition normal to the rippled bed, H is the ripple height, and jb is the bedload sediment transport rate. After introducing sediment transport functions, this relation is developed using the assumptions of gradually varied flow to predict the spatial patterns of cross‐lamination types in deposits due to pure non‐uniform flow, pure unsteady flow, and simultaneous non‐uniform and unsteady flow. Most of the predicted patterns can be matched from the geological record, and the analysis affords a hitherto missing insight into the environmental significance of climbing‐ripple cross‐lamination. The analysis also results in a rigorous definition of the kinds of environmental interpretation that may legitimately be made from examples of this structure.
TREATMENT OF SPHERICITY AND ROUNDNESS DATA OF QUARTZ GRAINS OF CLASTIC SEDIMENTS
Authors: SAHU BASANTA K. , PATRO B. C.
Published: June 2006

Sphericity and roundness data of quartz grains (of varying size) of sieve fractions are empirically shown to be non‐normally distributed. It is also demonstrated that log10 [ψ/(1−ψ)] and −log10(P) transformations, respectively, normalize the sphericity and roundness data, where ψ denotes the two‐dimensional sphericity and P the roundness of the grains in a plane. Laboratory experiments on sampling quartz grains from a sieve fraction show that the cone‐and‐quartering method is preferable as it yields similar results to those of the more time‐consuming random sampling procedure. Results of laboratory measurement errors on two‐dimensional sphericity and roundness data are also presented. The frequency of sphericity and roundness data are noted on number basis.

For all parametric statistical studies of sphericity and roundness the sample statistics should, therefore, be calculated according to the above normalizing log functions. Suitable grade scales of sphericity and roundness data are proposed here basing on these log functions and the total range and the minimum range of the variates (sphericity and roundness).
THE IDENTIFICATION OF ANCIENT BEACH SANDS BY THE COMBINATION OF SIZE ANALYSIS AND ELECTRON MICROSCOPY
Authors: HODGSON A. V. , SCOTT W. B.
Published: June 2006

The combined use of size analysis and electron microscopy has indicated the presence of beach sands within the Lower Carboniferous Fell Sandstone of southeast Scotland and northern England.

Environmental interpretations are based on a comparison of the statistical parameters summarizing the size distributions of the Fell Sandstone specimens with similar data from modern sediments. The spread of standard‐deviation values (sorting coefficients) indicates the presence of littoral, alluvial, and possibly offshore marine environments within the Fell Sandstone. These environments are further defined by plotting standard deviation against skewness on a scatter diagram.

Electron micrographs (E.M.G.'s) of the quartz grain surface textures of selected Fell Sandstone specimens corroborate the interpretations based on the size analysis.

E.M.G.'s of the Fell Sandstone beach specimens show all the diagnostic surface features developed on modern quartz beach sand grains.
PHYSIOGRAPHIC FEATURES AND STRATIFICATION TYPES OF COARSE‐GRAINED POINTBARS: MODERN AND ANCIENT EXAMPLES1
Authors: McGOWEN J. H. , GARNER L. E.
Published: June 2006

Primary sedimentary structures in modern point bar deposits of the Amite River in Louisiana and the Colorado River in Texas are analogous to features observed in Eocene Simsboro and Pleistocene Colorado River deposits of the Texas Gulf Coastal Plain.

Short‐duration peak flow, channel pattern, average stream gradient of about 2–3 ft./mile, and bank stabilization by dense vegetation are major parameters controlling the depositional pattern of coarse sand and pebble gravel of the Amite and Colorado rivers. Stratification is directly related to specific depositional features and consists of: large‐scale trough‐fill cross‐stratification in the scour pool; trough‐fill cross‐stratification and foreset cross‐stratification in the lower point bar; parallel laminae, large foreset cross‐stratification, and trough‐fill cross‐stratification in the chute bar; parallel inclined laminae, climbing ripple laminae, and mud drapes in the chute fill; and parallel inclined laminae, mud drape, and foreset cross‐stratification in overbank, flood‐plain deposits.

Fundamental differences between point bars of bed‐load streams (low suspended load/bed load ratio) and mixed‐load streams (high suspended load/bed load ratio) are that upper point bar sediments with small trough sets and parallel inclined laminae occur only in fine‐grained (mixed load) fluvial deposits, and large scale foresets of chute bars are common to coarse‐grained (bed load) fluvial deposits but are not found in fine‐grained fluvial deposits. Upward fining sequences, characteristic of fine‐grained fluvial deposits, are uncommon in sediments deposited by bed‐load streams such as the Amite and Colorado rivers.

The Simsboro Sandstone consists mainly of scour pool, lower point bar, and chute bar sediments. Chute fill and flood‐plain deposits are preserved only in the highest stratigraphic sequence. Pleistocene Colorado River deposits display the same sequence of stratification types as the Simsboro but are composed of coarser material.
EXPERIMENTS ON THE ANGLES OF REPOSE OF GRANULAR MATERIALS1
Authors: CARRIGY MAURICE A.
Published: June 2006

A simple apparatus for measuring the angles of repose of masses of granular material in various media, based on the rotating‐drum principle, is described. Two angles of repose are measured by this method. The critical angle of repose (ac), is defined as the angle through which a mass of granular material can be rotated before it fails by avalanching, and the angle of rest (aR), is defined as the inclination of the slope after avalanching has ceased.

Measurements of the angles of repose of several materials in air and under water with the “rotatable‐drum apparatus” indicate that for materials with similar surface characteristics the angles of repose increase with departure of the grains from a spherical form. For masses of spherical particles the angles of repose increase with increasing intergranular friction caused by changes in the surface characteristics of the spheres. For mixtures of spheres and cubes the angles of repose are proportional to the volumes of the end members present. For natural quartz sands the critical angle of repose (ac), is always greater in air than under water, but the angle of rest (aR), is the same in both media. Measurement of the inclinations of slip faces of subaerial dunes and subaqueous deltas indicates that these faces stand at, or less than, the angle of rest (aR), of the sand from which they are built.

It is concluded that shape and surface characteristics of the particles have the greatest effect on the angles of repose.
PHREATIC VERSUS VADOSE METEORIC DIAGENESIS OF LIMESTONES: EVIDENCE FROM A FOSSIL WATER TABLE
Authors: LAND LYNTON S.
Published: June 2006

The Middle Pleistocene Belmont Formation of Bermuda consists in part of beach‐dune biocalcarenites which underwent intense contemporaneous cementation and diagenesis. The beach deposits were contemporaneously cemented by fibrous isophacous cement to form beachrock, whereas previously deposited eolianites further inland underwent intense meteoric phreatic diagenesis, resulting in coarse‐grained cementation and stabilization of most of the metastable components of the rock. Above the Belmont water table, vadose diagenesis was relatively ineffective in cementing and altering the biocalcarenites. Phreatic meteoric diagenesis is interpreted to be a very rapid process, relative to vadose meteoric diagenesis, and to result in a much coarser‐grained sparite.
MIXED‐LAYER BIOTITE‐CHLORITE FORMED IN THE COURSE OF LOCAL EPIGENESIS IN THE WEATHERING CRUST OF A BIOTITE GNEISS
Authors: EROSHCHEV‐SHAK V. A.
Published: June 2006

In the course of deep weathering of a biotite gneiss, biotite is transformed into mixed‐layer biotite‐vermiculite hydrobiotite. Later biotite‐vermiculite is transformed into biotite‐chlorite under the action of hydrothermal solutions at the stage of epigenesis.
DENSITY AND OPTICAL DATA OF LOW‐TEMPERATURE FELDSPARS AND MICA
Authors: KATZ M. YA. , MURAVYOV V. I.
Published: June 2006

Precision measurements of the densities and the optical constants of authigenic low‐temperature orthoclases, albites, muscovites and quartz, and comparisons with those of their high‐temperature counterparts of identical or similar composition proved that the authigenic orthoclase and muscovite have significantly lower densities than the high‐temperature modifications.

For quartz and albite density differences are not established.

The optical constants of the low‐temperature minerals (except for quartz) likewise possess specific properties, manifested in the orientation of the optical indicatrix and the values of the angle 2V.
MINERAL STUDIES IN THE GRAVITATION‐GRADIENT FIELD, I. THE METHOD
Authors: KATZ M. YA.
Published: June 2006

This paper describes a new equipment for investigating the density properties of minerals and rocks. A description is given of the principle and operation of a gravitation gradient tube, of density standards and of a device for the precise density determination and separation of minerals. The possibility of using the method described for geological and mineralogical studies is discussed.
A COARSE‐GRAINED POCKET BEACH COMPLEX, TANAFJORD (NORWAY)
Authors: HOBDAY D. K. , BANKS N. L.
Published: June 2006

The bulk of the material comprising the pocket beach at the mouth of the Manndraperelv, Tanafjord, northern Norway, is supplied by the river. The stream bed consists of poorly sorted coarse sediments which show a crude upstream imbrication. Dampening of wave activity near the mouth of the stream by the outflow of water has caused relatively fine‐grained material to accumulate on spits. Size‐shape sorting by waves concentrates the finest pebbles on landward moving swash bars.

Away from the stream mouth beach deposits become finer grained landward, and are zoned in a manner similar to that described by BLUCK (1967). If similar deposits were preserved in the geological record they might be confused with coarse‐grained fluviatile sequences. Study of the textures of the Manndraperelv deposits establishes criteria for distinguishing between these two possibilities.
GEOCHEMICAL HISTORY OF THE CRYSTALLINE BASEMENT AND THE SEDIMENTARY COVER OF THE RUSSIAN AND NORTH AMERICAN PLATFORMS
Authors: RONOV A. B. , MIGDISOV A. A.
Published: June 2006

A vast amount of analytical material (more than 8,000 analyses) on the chemical composition of the main rock types occurring in the crystalline shields and sedimentary covers of the Russian and North American platforms has been compared, taking into account the abundance of these rocks. The comparison covers structures as a whole and separately—their sections representing very large stratigraphical complexes (A. Pt1_2, Pt3. Pz. Mz‐Cz). Based on generalization of these data, the more important development stages in the composition of the shields and platforms were traced for the last 3.5 billion years and the more general tendencies in their geochemical history were outlined. An almost complete uniformity of the “granite” shell's average composition, a striking similarity of the average composition of the sedimentary cover and similar ways of its development have been proved for different continents. At the same time a discrepancy was established in the average compositions of the rocks of the shields and derivative platform sediments, which by their composition are nearer to basic than to acid rocks. This fact obviously indicates a wider spread of the basic rocks during the earlier stages of the development of the Earth's crust. The more general tendencies in the evolution of the rock composition of shield and platform sediments have been retraced. They outlined a causal relationship, with the development of granitization processes of the primary, more basic material, with the passing of denudation products through numerous cycles of weathering and sedimentation and with the biosphere growth and life development which determined the change of the atmospheric and oceanic compositions as well as the oxidation‐reduction conditions on the surface of the Earth and in the formation of sedimentary series.
THE DEPOSITIONAL ENVIRONMENT OF MARINE EVAPORITES: A CASE FOR SHALLOW, CLASTIC ACCUMULATION
Authors: HARDIE LAWRENCE A. , EUGSTER HANS P.
Published: June 2006

The Upper Miocene Solfifera Series of Sicily contains very coarse, massive selenite; parallel laminated gypsum; wavy, stromatolitic laminated gypsum; planar‐ and ripple cross‐laminated gypsum‐skeletal calcite sandstones; flat‐pebble and fining‐upward gypsum conglomerates; and nodular gypsum. The assemblage of sedimentary features indicates deposition—much of it detrital—in a shallow lagoon‐littoral flat complex.

Using modern tidal flats as a guide, we interpret the laminations to form when onshore storms flood the shore‐line area with sediment‐charged seawater. Algal mats bind the newly deposited gypsiferous layer. Flat‐pebble conglomerates are formed when storm waves rip up mudcracked, algally‐bound laminated sediment. The gypsum nodules are similar to the anhydrite nodules of the modern Persian Gulf sabkhas. They form within sub‐aerially exposed skeletal sand just above the groundwater table. The gypsum sandstones accumulated periodically in very shallow shoals formed by wind‐driven currents. Large selenite crystals grew in increments during deposition, as indicated by flat‐topped pockets of gypsum sand between selenite crystals, selenite crystals draped by algal laminations, and intraformational conglomerates of selenite fragments.

We believe this model of very shallow strand‐line lagoonal accumulation, partly detrital and partly diagenetic, may apply to the early stages of many ancient marine evaporite deposits.