bluuebunny/crossref_metadata_2025_split huggingface dataset:
AUTHIGENIC SILICATE MINERALS IN SEARLES LAKE, CALIFORNIA
Authors: HAY R. L. , MOIOLA R. J. 
Published: June 2006

SUMMARYMonoclinic K‐feldspar, analcime, searlesite and phillipsite of diagenetic origin are present in samples of clay and tuff from U. S. Geological Survey cores of Pleistocene and Recent sediments of Searles Lake, California. Authigenic K‐feldspar was identified in 37 of the 72 samples studied; analcime was identified in 21, searlesite in 8, and phillipsite in 3. Most of the K‐feldspar, analcime, and searlesite occur in non‐tuffaceous claystones, which form about 46% of the 875‐ft. thickness of sediments that was cored. Phillipsite was found only in three rhyolitic tuff laminae within the upper 110 ft. of beds. Most of the K‐feldspar and analcime crystals are less than 2 μ in diameter, and maximum diameters are 0.10 mm for K‐feldspar and 0.02 mm for analcime. Phillipsite occurs as lath‐shaped crystals 0.01–0.02 mm long, and searlesite principally forms spherulites 0.02–0.2 mm in diameter.Microcline, orthoclase, albite, andesine, and quartz predominate in the sand and silt fraction of the clays; illite, montmorillonite, chlorite, and kaolinite predominate in the detrital clay fraction. Grains of quartz and andesine are extensively etched at various levels below a depth of 220 ft., and only skeletal crystals of andesine remain in some clays. Volcanic glass has been completely dissolved or replaced by authigenic silicate minerals in the few tuffs. Distribution of clay minerals in the core suggests that montmorillonite and chlorite have been destroyed in many of the clays.Alkaline brine saturates the surface and subsurface sediments, and the high activity ratio of alkali ions to hydrogen ions in this brine probably accounts for the widespread formation of K‐feldspar, zeolites, and searlesite. Na, K, and B for the authigenic silicates were probably supplied by the brine and by saline minerals in contact with the brine. Montmorillonite may have provided additional K. Solution of glass provided the Si and Al required to form authigenic silicate minerals in the tuffs, and solution of quartz, plagioclase, and montmorillonite most likely supplied the Si and Al for authigenic silicates in the clays.
CYCLIC SEDIMENTATION IN THE LOWER WESTPHALIAN OF NO DEVON, ENGLAND
Authors: DE RAAF J. F. M. , READING H. G. , WALKER R. G. 
Published: June 2006

SUMMARYEleven facies of the (Lower Westphalian) Abbotsham Formation and upper portion of the Northam Formation of north Devon are described: black mudstone, silty mudstone, “turbidite”, silty streak, sandy streak, three kinds of oscillatory beds, cross‐stratified sandstones and mudstones, fining‐upwards units and major sandstones. Their relationships to each other are determined and they are shown to recur in a cyclic pattern.Six cycles are distinguished in the 1,200 ft. of the Abbotsham Formation. Each passes upwards gradually from black mudstone into coarser beds, the top of which is sharply separated from the black mudstone of the succeeding cycle.We suggest that the environment of deposition of these cycles ranges from a moderately deep basin, in which mudstones and occasional turbidites were deposited, through the sediments of an advancing coastline, fronted by deltas, to coastal plains in which fluviatile sediments were laid down.
ENVIRONMENT RECONSTRUCTION FOR A PART OF THE GLEN ROSE LIMESTONE, CENTRAL TEXAS
Authors: BEHRENS E. WILLIAM 
Published: June 2006

SUMMARYAn approximately 50 ft. stratigraphic section of the Lower Cretaceous Glen Rose Limestone was sampled at 24 separate localities in central Texas from the standpoint of reconstructing the depositional environment. Among these samples 199 representative specimens were selected and subjected to point‐count analyses, X‐ray analyses, and insoluble residue determinations. Statistical analysis of the accumulated data with an IBM 7090 computer yielded the following facies: Corbula facies—characterized by a relative abundance of thick‐shelled ostracods, thin‐walled miliolid foraminifers, and the small pelecypod Corbula martinae; steinkern facies—characterized by large mollusc steinkerns, cellular mollusc shells and the foraminifer Orbitolina; mudstone facies—typified by less than 10% sand‐sized grains; and mixed particle facies—characterized by worn skeletal and nonskeletal carbonate grains. The mud‐stone facies subsequently was divided into two subfacies: (1) lime mudstones—characterized by delicate skeletal constituents and lime mud, and (2) marly mud‐stones—consisting of a mixture of lime mud and terrigenous clay‐sized material. Similarly the mixed particle facies was divided into four subfacies: skeletal calcarenites—characterized by sand‐sized skeletal debris; skeletal wackestones—consisting of sand‐sized skeletal particles floating in a mud matrix; nonskeletal calcarenites—characterized by nonskeletal carbonate grains; and nonskeletal wackestones—consisting of nonskeletal carbonate grains floating in a mud matrix. In addition limey sandstone, dolomite, and stromatolite facies were distinguished on the basis of relatively obvious textures and compositions.The attributes of these facies as evidenced by the 199 statistically analyzed specimens were then used to assign each of the additional samples (350) to a particular facies and to identify the distribution of these facies in the field. A reconstruction of the depositional environment was made for each facies, and the following depositional history was interpreted from the resulting facies pattern.The lowermost beds of the unit, consisting largely of stromatolites and nonskeletal calcarenites, are interpreted as representing deposition in very shallow, probably intertidal, waters, Following the deposition of these beds, the depth of water increased
BORON IN HOLOCENE ILLITES OF THE DOVEY ESTUARY, WALES, AND ITS RELATIONSHIP TO PALAEOSALINITY IN CYCLOTHEMS1
Authors: ADAMS T. D. , HAYNES J. R. , WALKER C. T. 
Published: June 2006

SUMMARYResults from modern and ancient sediments suggest that a boron‐illite equilibrium, reflecting salinity, is established at the time of deposition. This condition is not appreciably changed by subsequent processes of diagenesis and lithification. Equivalent boron in thirteen samples, from two augerholes through Dovey Estuary sediments, ranges between 260 p.p.m. and 370 p.p.m. and averages 336 ± 29 p.p.m. (95% confidence limits).Salinity conditions in the present estuary vary greatly. A very significant direct correlation exists between equivalent boron and inferred depositional salinity of Dovey Estuary sediments.
THE USE OF ANISOTROPY OF MAGNETIC SUSCEPTIBILITY IN THE ESTIMATION OF SEDIMENTARY FABRIC1
Authors: REES A. I. 
Published: June 2006

SUMMARYThe feasibility is discussed of using anisotropy of magnetic susceptibility to find preferred directions of grain orientation and current directions in sediments, and it is concluded that it should be possible to find these directions in silts and sands containing between 0.01 and 1% of magnetite.Some examples are given of the use of the method under controlled conditions, and it is shown to give the same result as optical grain orientation determination in one example and to predict the same current direction as macroscopic indications in two others. Some of the limitations of the method are suggested by examples in which the results would have been misleading if accepted unconditionally.
GRADATIONAL SEDIMENTARY PRODUCTS OF CALCAREOUS ALGAE
Authors: WOLF KARL H. 
Published: June 2006

SUMMARYPenecontemporaneous calcareous algal products are very complex in both texture and mode of origin. For example, all gradations exist between stromatolites and pseudo‐stromata, different types of oncolites are transitional and are often difficult to distinguish from other allochthonous algal material, algal pellets form the final product of abrasion and they too are very similar despite variations independent of their original source; and some Algae may break down into “algal dust” or carbonate needles.Algal limestones of different ages and environments may supply detritus that is indistinguishable from one another. Therefore, in petrographic investigations of carbonate sediments the descriptive term “limeclast” is less ambiguous than the genetic terms “intraclast” and “calclithite”. If a combination of field‐work and thin‐section studies permits precise genetic and environmental interpretations, the limeclasts can be genetically described as “intraclasts” and “extraclasts”. If the extraclasts form the predominant components, the sediment is a “calclithite” and is a type of terrigenous rock (FOLK, 1959).In general, four possible relations exist between limestone frameworks and micrite matrices. Both allochthonous fragment accumulations and autochthonous growths may have either detrital matrices or matrices that formed in situ. The autochthonous algal micrite matrices give no indication of a degree of turbulence and winnowing in contrast to allochthonous matrices.Apparently minute differences, which are, however, significant in the genesis of limestone components may become more important with an increase in isotope, trace element and diagenetic investigations where the identity of the carbonate material is of special importance.
FALLING DROP USED FOR GRAIN‐SIZE ANALYSIS OF FINE‐GRAINED MATERIALS
Authors: MOUM JOHAN 
Published: June 2006

SUMMARYTo facilitate simultaneous performances of numerous grain‐size analyses covering the silt and clay fractions, a method has been worked out and the necessary equipment constructed for utilizing a falling drop for determining densities of particle suspensions. A drop is taken out by means of a micro‐syringe at the desired depth in a sedimentation vessel, and ejected into a column of an organic liquid with a slightly lower density. The drop then falls with a constant speed and the time measured with a stopwatch over a certain distance is a measure of the density of the drop, and hence also of the particle concentration in the sedimentation vessel where the drop is taken. In this way it is easily possible to work through twenty samples in a normal working day, including removal of organic matter, dispersion, washing (to remove effects of soluble salts) and evaluating the final results.
THE DEVELOPMENT OF OVERGROWTHS FROM ECHINODERM FRAGMENTS
Authors: EVAMY B. D. , SHEARMAN D. J. 
Published: June 2006

SUMMARYAn overgrowth from an echinoderm fragment is a single crystal of calcite in lattice continuity with the calcite crystal of the host. The development history of echinoderm overgrowths during cementation has been elucidated by the identification of iron‐bearing and iron‐free calcites within the overgrowths by employing staining techniques.The iron‐bearing parts of the overgrowths described do not stain uniformly for iron. Instead they exhibit a succession of light and dark stained sub‐zones, which represent the shapes of the overgrowths during their development.The pattern of zoning around basal sections of crinoid ossicles is comparatively simple. The innermost zones follow the outlines of the ossicles. Later zones adopt first quasi‐hexagonal outlines with curved sides, and then true hexagonal zones of prismatic habit. Such basal sections of ossicles give well‐centred conoscope images and are therefore, oriented perpendicular to the c‐axis directions of their calcites.Vertical sections through overgrowths show a more complex zoning: above and below the articulating surfaces of ossicles the zones are wide, and have a marked zig‐zag outline, with the axes of the spires parallel to the vertical axes of the ossicles and parallel to the c‐axes of the crystals. Along the sides of the ossicles the zones are narrow and straight. The multiple terminations in the c‐axis direction reduce in number away from the surface of the ossicle and, if the original pore‐spaces are sufficiently large, ultimately yield a single scalenohedron‐type termination. The multiple terminations have their origins on the articulating surfaces of the ossicles. In life these surfaces were perforated by the entrances to the numerous minor canals which ramify the ossicles. The multiplicity of terminations resulted from more rapid crystal growth from the surface of the ossicle between canals (c‐axis direction) than from the surfaces of the canals themselves (direction perpendicular to the c‐axis).
EVOLUTION OF ZIRCONS IN SEDIMENTARY AND METAMORPHIC ROCKS
Authors: SAXENA S. K. 
Published: June 2006

SUMMARYZircons have been studied in the sedimentary rocks of the Sparagmite Group (Eocambrian) and their metamorphic associates from the Trondheim area and the adjacent regions in Norway and Sweden. The majority of zircon population (type B) has been formed in the sediments by authigenesis. Another authigenic associate is rutile. The authigenic zircons have irregular, round and ellipsoidal habits. In metamorphic rocks the same grains show a greater tendency of euhedrism, forming drum‐like crystals with acute (331) pyramids and short prisms. Authigenic zircons are usually clear and transparent but some grains may show cloudy appearance. A few other grains (type A) with different habit and many inclusions appear to be of detritai nature.Dissolution of a metamictized zircon population in the source rock is possible in many ways. An important possibility is the dissolution of zircons in alkaline solution. Carbonated lime‐rich waters or other acidic solutions could be equally effective. Zirconates, so formed, are transported to the basin of deposition as colloidal particles or as ionic complexes. The authigenic process is visualized as a deposition of the zirconates by adsorption or by precipitation as zirconium hydroxide, possibly due to change in the Eh and pH in the environment. The hydrated oxide subsequently reacts with silica to form metastable hydrozircon. In course of time hydrozircon dehydrates and becomes a normal zircon.Numerous growths have been noted and are classified genetically into (l) late authigenic growths, and (2) growths syngenetic with metamorphism. The shape of the host grain usually controls the final shape of the overgrown grain.There is some effect of metamorphism on the morphology of the authigenic zircons. In view of the characters of the newly generated zircons, the use of shape, size, zoning and such other parameters of zircons in petrogenetic problems, has to be retested to ensure its reliability.Rather than being a mineral of igneous derivation only, zircon is from three parentages: igneous, authigenic and metamorphic. It is argued that the persistence of the authigenic zircons should be greatest because of very low concentration of radioactive elements.
ON BED FORMS AND PALAEOCURRENTS
Authors: ALLEN J. R. L. 
Published: June 2006

SUMMARYBed forms arise by interaction between a fluid flow and the sediment transported over or close to the bed. The geometry of bed forms is two‐dimensional or three‐dimensional. Two‐dimensional bed forms generate two‐dimensional internal sedimentary structures and are adjusted to two‐dimensional flow‐vector fields. Three‐dimensional bed forms generate three‐dimensional internal sedimentary structures and are adjusted to three‐dimensional flow‐vector fields. Many shallow‐water flow systems observable today are each characterised by flow‐vector fields of unequal rank, and hence are hierarchically structured. Hierarchies of bed forms and internal structures which parallel the hierarchies of flow‐vector fields can also be established in the case of these flow systems. A single type of bed form or internal structure from an hierarchically structured flow system cannot specify that system fully with regard to either its directional or flow‐dynamic characteristics. An approach to palaeocurrent analysis that is more flexible and comprehensive than previously attempted may therefore be desirable.
CORRELATION OF SOME ATLANTIC TURBIDITES
Authors: BELDERSON R. H. , LAUGHTO A. S. 
Published: June 2006

SUMMARYA study of six gravity cores from an abyssal plain at the western side of the Madeira‐Cape Verde Basin shows that individual turbidites can extend over a distance of at least 35 miles (65 km) in this area of final turbidity current deposition. Cores from the continental rise include relatively thinner turbidites; evidence from one of these indicates some local erosion of the sea floor: this apparently did not exceed 15 cm (as represented in the core).
APPLICATION OF THEORY TO AN ATLANTIC TURBIDITY‐CURRENT PATH
Authors: JOHNSON M. A. 
Published: June 2006

SUMMARYSome results of turbidity‐current theory are applied to analyses of turbidite layers in cores from the route of a large turbidity current of sheet‐flow type. Novel features are that current velocity is estimated from the sediment sizes deposited, and the lateral spreading of the current is considered. An approximate quantitative picture of the current is obtained. It is compared with the turbidity current which caused the Grand Banks cable breaks.
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

SUMMARYSolutions 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.
THE CARBONATE FRACTION OF BEACH AND DUNE SANDS
Authors: Pilkey ORRIN H. , MORTON ROBERT W. , LUTERNAUER JOHN 
Published: June 2006

SUMMARYThe 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

SUMMARYThe 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

SUMMARYIn 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.