bluuebunny/crossref_metadata_2025_split huggingface dataset:
RE‐INTERPRETATION OF THE CYRTINA SEPTOSA BAND DATA, LOWER CARBONIFEROUS OF DERBYSHIRE, ENGLAND, BY COMPUTER ANALYSIS
Authors: SADLER HELEN E. , MERRIAM DANIEL F. 
Published: June 2006

SUMMARYRe‐interpretation of Cyrtina septosa Band (Lower Carboniferous) data from Derbyshire (England) by trend analysis reveals previously unrecognised but meaningful sedimentational patterns. Trends in geographic variation of number of shells; their disarticulation, orientation, and size; and thickness of the Band are judged to be indicative of water depth and turbulence, conditions of accumulation, and source.
FORMATION OF LARGE‐SCALE CROSS‐BEDDING IN A CARBONATE UNIT
Authors: SWINCHATT JONATHAN P. 
Published: June 2006

SUMMARYThe type Lindsey Bridge Member of the Moorefield Formation of northeastern Oklahoma consists of 24 ft. of massively cross‐bedded limestone. Cross‐bed shape, lithologic variation, grain size and sorting, distribution of insolubles, and distribution of fossils and fossil burrows can be explained with reference to a hydrodynamic model developed in recent flume studies.Three facies can be distinguished in this unit: (1 Thei) foresets, thick‐bedded, well‐sorted, fine to medium crinoidal grainstones, dipping at angles up to 1° (2) toesets, which are thin‐bedded, poorly sorted, skeletal packstones notably more fossiliferous than the foresets, with which they are laterally gradational; toesets dip at approximately 5°‐8° (3) bottomsets, composed of argillaceous, fine‐grained (mainly silt‐size), skeletal limestones. Foresets overlie previously deposited bottomsets; this geometry is typical of regressive sedimentation.The exposure is adjacent to a pre‐Moorefield topographic high. As currents crossing this high entered a basin on the downcurrent side, flow separation occurred. Bed material load was deposited mainly on the foreset slope, suspension material mainly in toeset and bottomset areas. The poor sorting of the toesets is in part due to reverse circulation, formed by the flow separation, which transported bottomset sediment back toward the foreset. Jopling (1965b) has shown that this depositional geometry produces tangential cross‐beds similar to those seen in this outcrop. Differential settling velocity, substrate stability, and abundance of organic detritus influenced other sedimentologic properties of the deposit.
RIPPLE MARK INDICES AND THEIR USES
Authors: TANNER WILLIAM F. 
Published: June 2006

SUMMARYThe following dimensionless parameters (two of them well‐known and five of them new) are defined for determination of ripple mark geometry: ripple index (RI), ripple symmetry index (RSI), continuity index (CI), bifurcation index (BI), straightness index (SI), and two different parallelism indices (PI1 and PI2).In general, RI = 15 or less indicates wave or water current origin; RI = 17 or more indicates wind or swash origin. RSI = 1.5 or less indicates wave or swash types; RSI = 3 or more indicates wind or water current types. CI = 15 or more suggests wind or wave origin; CI = 10 or less suggests water current origin. BI = 10 or more suggests wave varieties; BI = 1 or less suggests wind varieties. SI = 102 or more indicates wind or deep‐water wave types; SI = 15 to 102 indicates wind or wave types; SI =4 or less indicates current types. PI1 = 7 or more suggests wave origin; PI1 = 1 or less suggests water current origin. PI2 = 0.4 or more is probably the result of swash or water current action. PI2 = 0.2 or less is probably the result of wind or wave action. Longitudinal ripple marks (such as rib‐and‐furrow) and deformed or modified varieties (such as flat‐topped tidal‐flat ripple marks and nearly‐ flat‐topped intermittent creek ripple marks) have been excluded, inasmuch as (1)they are commonly easy to identify from their appearance, and (2)they are difficult to measure with ordinary methods.Plots of two indices against each other on coordinate paper can be particularly useful; the best combinations are RI vs. RSI, and RI vs. PI1, although several other pairs are almost as good. Where all seven parameters can be obtained, the confidence one can have in the interpretation is close to 98%.The effects of current bias, or depth bias, on wave‐type ripple marks, extend to both the symmetry (RSI) and to sediment‐transport interpretations. Unless the investigator is reasonably sure that no such bias is present (i.e., RSI = 1.0 instead of some significantly higher value such as 1.5), wave‐type ripple marks cannot be used to determine direction of either wave approach or sediment transport. If no such bias is present, wave‐type ripple marks still cannot be used to determine precise sediment transport direction. If RSI = 1.0 precisely, it is not even necessary that the ripple crests parallel the waves that formed them. The same restrictions apply to the interpretation of micro‐crossbedding (that is, ripple mark internal structure). Despite these seemingly severe limitations, general geometry commonly permits a reliable interpretation, and hence ripple marks can provide a great deal of useful data for paleogeographic interpretations.The swash‐zone variety of ripple marks includes two sub‐types: those modified by a small but unmistakeable hydraulic jump, and those not so modified. The RI can be used to distinguish between these two, even when they were not observed to form.
THE PRESENT STATUS OF ZIRCON
Authors: MARSHALL BRIAN 
Published: June 2006

SUMMARYSaxena (1966a) proposed that zircon could be authigenic and low‐grade metamorphic, as well as magmatic in origin. He questioned the mechanical and chemical stability of zircon, the use of crystal morphology in correlation, and the use of roundness as a criterion of detrital origin. In so doing, he challenged the role of zircon in problems of stratigraphy, pedogenesis, and sedimentary, igneous, and metamorphic petrology.SAXENA'S(1966a, b) evidence for authigenic and low‐grade metamorphic zircon is unconvincing, since conventional explanations adequately encompass his obser‐ vations, and do not conflict with established knowledge of zircon behaviour.During weathering, authigenesis, and metamorphism, zircon is shown to conform with the concepts that:(1) its removal and transport in solution is minimal, (2) zircon formation during authigenesis and low‐grade metamorphism is insignificant. Rare occurrences of hydrozircon confirm this paucity of authigenic zirconium minerals. At high metamorphic grades zircon‐transformation is favoured by the “wet” metasomatic processes of the amphibolite facies and impaired by the “dryness” of the granulite facies. The occurrence of zircon transformation in the granulite facies may also be prevented by incorporation of zirconium in the lattice of newly‐formed pyroxene. Release of this zirconium during diaphthoresis of pyroxene‐bearing granulites could give rise to new zircon.The formation of zircon during authigenesis, and its formation and transfor‐ mation during low‐grade metamorphism, would diversify initially homogeneous assemblages; but Saxena has failed to prove that either process does in fact occur. It is contended that, since the positive correlation of zircon assemblages from co‐eval sedimentary and metamorphic rocks of the Kingsbridge area is opposed to Saxena's views regarding the origin and behaviour of zircon, the roles of authigenesis in the formation of zircon, and of low‐grade metamorphism in its formation and transformation, are insignificant or non‐existent.
EARLY DIAGENETIC IRON SULPHIDE IN RECENT SEDIMENTS OF THE WASH (ENGLAND)
Authors: LOVE L. G. 
Published: June 2006

SUMMARYMicroscopical and chemical examination of intertidal flats of the Wash indicate that phases of iron corresponding to ferric hydroxide and iron monosulphide are involved in the early diagenetic formation of pyrite, the first being an important source of the iron. Sedimentological data are tested against analyses of total iron extractable by hydrochloric acid and concentrated nitric acid, and of the pyritic fraction of this iron; ignition data for residual organic matter are considered. The occurrence of the pyrite as isolated grains and spherules of framboidal texture is recorded, their size ranges given, and iron monosulphide recognised as the precursor of both forms. Ordering in the pyrite framboidal spherules is recorded and internal coalescence confirmed as a feature of primary growth which obscures the ordering.
DIE LITHOGENESE DER STEINMÜHL‐KALKE DES ARRACHER STEINBRUCHES (JURA, ÖSTERREICH)
Authors: FLÜGEL HELMUT W. 
Published: June 2006

Lithogenesis of the Steinmiihl Limestone of the Arrach Quarry (Jurassic, Austria)The Upper Jurassic Steinmuhl Limestone Group on its type section (Arrach Quarry, Lower Austria) is subdivided into the following four members:
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These various sedimentary units represent a gradual change in the environments during sedimentation. The sequence sets in with the Filament Limestone. It possibly represents a sublittoral Lamellibranchiata debris and is of Callovian (?)age. Though the marine deposition continued without interruption to the Upper Jurassic, the environment changed markedly. The sea became deeper and the Filament Limestones were followed by pelagic‐bathyal Radiolaria Siliceous Limestones. A distinct difference in the degree of subsidence within the Upper Jurassic geosyncline led to the formation of bathyal furrows and swells. Over the latter the calcilutite Saccocoma and Calpionella Limestones with mainly pelagic fossils were deposited in Kimmeridgian and Port‐ landian. Their thickness is small, for currents swept much sediment into the deeper furrows, in which the Oberalm stratas arose in great thickness at this time.
EMPLACEMENT OF FLYSCH‐TYPE SAND BEDS
Authors: KUENEN PH. H. 
Published: June 2006

SUMMARYRecently several attempts have been made to explain deep‐sea sands or flysch‐type sandstone beds by normal currents, instead of by turbidity currents. The arguments that are offered against turbidity currents and those in favour of normal currents are inconclusive. Current measurements and calculations indicate 1 m from the bottom on abyssal plains velocities are less than 30 cm/sec. The ubiquitous structures: sole markings, graded bedding, fine‐grained ripple mark between a lower and a covering set of horizontal laminae, and convolution, are shown each in turn to be inexplicable on the basis of normal traction currents and the same holds for the uniform bed thickness. On the other hand these features develop readily in a circular flume from overloaded suspension currents. These experiments show that to support a heavy charge of fine sand in a clay suspension a current must exceed 100 cm/sec, and in clear water double that amount is needed.The inadequacy of normal currents both in velocity and kind is thus established. This lends powerful support to the case for turbidity currents.Many authors claim to have found evidence for the deflection of turbidity currents or for currents flowing across the paleo‐slope. Explanations offered include the Coriolis force, normal currents, multiple turbidity currents, or surge waves. Analysis shows that all are open to serious doubts. The author suggests, quite tentatively, that the deflections may be only simulated by the development of lamination and grain orientation oblique and perpendicular to the current direction. Sagging of the trough floor may also play a part by confusing the determination of paleo‐slope.Another possibility is that the turbidity current deviated from its original direction by “internal slope”, by momentum, by centrifugal force, or by lack of space.Admittedly, a problem remains, for the swift deposition deduced from the climbing ripples is in contradiction with the supposed stretching of the turbidity current inferred from grading.
DELTAIC SEDIMENTATION UNITS IN THE UPPER CARBONIFEROUS OF NORTHERN ENGLAND
Authors: COLLINSON JOHN D. 
Published: June 2006

SUMMARYIn the Kinderscout Grit (Namurian, R1c) of the southern half of the Central Pennine Basin, England, there occur tabular, isolated, cross‐bedded sets of coarse sandstone, between 4 and 40 m thick. The sets are up to 1 km wide and the foresets, in plan, are convex in the direction of dip. The sets interfere laterally to form extensive sheets. Foresets dip at up to 27° and are sometimes themselves internally cross‐bedded in trough‐shaped sets, here termed “intrasets”. The large sets are thought to be deltaic sedimentation units rather than sandwaves. In the delta top environment in which these sets were deposited, a high rate of bed‐load sediment supply and a sudden deepening were required to initiate the sets.Medium‐scale cross‐bedding, thought to have been laid down in migrating, fluviatile channels overlies the large‐scale sets and represents the topset member of the sedimentation units. From the spatial arrangement of the large‐ and medium‐scale cross‐bedding, it is possible to distinguish those areas where deposition took place during the deepening, from those where it took place essentially after the deepening. The causes of the deepening, which must have been on at least a basinal scale, may have been eustatic or tectonic.
ELECTRON‐MICROSCOPIC EXAMINATION OF NAMURIAN BEDDED CHERTS, NORTH WALES (GREAT BRITAIN)
Authors: OLDERSHAW ALAN E. 
Published: June 2006

SUMMARYElectron microscopic examination of Namurian bedded cherts in North Wales (Great Britain) has revealed the existence of two dominant surface textures, granular and spongy, with a range of textures intermediate between the two. These textures can be used to differentiate between three principal lithologies within the cherts and between laminae and colour bands within the lithologies. A positive relationship is demonstrated between the presence of spongy texture and a high volume of impurities; there is a gradation, with increasing argillaceous/organic content, from granular through intermediate to spongy surfaces. It is suggested that this gradation reflects an increase in chalcedony over micro‐crystalline quartz resulting from: (l) an increase in impurities; (2) an increase in the rate of precipitation of silica. The relationship between surface texture and type of lithology is considered to be consistent with the order of crystallisation for silica put forward by MILLOT (1960).
SEDIMENTOLOGICAL CONSEQUENCES OF A STEADY‐STATE OCEAN‐ATMOSPHERE
Authors: SIEVER RAYMOND 
Published: June 2006

SUMMARYAnalysis of influx and efflux of sediment and water to and from the ocean and of residence times of the elements indicates that the oceans and atmosphere are in a steady state with respect to erosion and sedimentation. A detailed examination of the ocean‐atmosphere model is needed to see how the system worked in the geological past. Weathering is characterized primarily by the absorption of H+ by silicates and secondarily by liberation of SiO2, alkalies and HCO3—to the oceans. The H+ is supplied mainly by the H2O‐CO2 system via the ionization of H2CO3 but some is supplied by HCI from volcanic emanations. Weathering of carbonate rocks results in the same absorption of H+, releasing Ca2+, Mg2+, and HCO3—. Sedimentation, silicate reconstitution, and diagenesis are seen as the reverse of weathering in that H+ is released and SiO2 and alkalies are precipitated from solution. Thus a constant H+ release is necessary to keep constant the CO2 pressure of the atmosphere by transforming the HCO3—of the ocean into CO2+ H2O. The sedimentary products that are part of the steady‐state model are reconstituted silicates (degraded clay minerals that become diagenetically altered to less hydrous, more siliceous illites and chlorites), limestone (precipitation reverses limestone weathering), salt (uses up alkalies), and chert (uses op free SiO2). It is concluded that the major site of silicate reconstitution is not on the open sea floor but in coastal subsiding sedimentation belts in which high‐grade diagenesis takes place and whose formation waters are ultimately connected with the ocean and so can buffer it. The obvious consequences of the model are that the global amounts of carbonate, reconstituted silicate, salt, and chert must be related in a systematic way for any time interval in which the system is steady. To keep CO2 constant, the total of carbonate precipitation and silicate reconstitution must be conserved. Similarly, salt precipitation and silicate reconstitution must be related to keep alkali removal constant. Finally, chert must be related to silicate reconstitution so that all silica released by weathering is removed from the ocean. A careful examination of the stratigraphic record is needed to objectively determine from such parameters whether the steady‐state system has always been operating much as today or whether there have been major secular changes or periodic perturbations.
ON SIEVING AND SETTLING TECHNIQUES FOR SAND ANALYSIS
Authors: SENGUPTA SUPRIYA , VEENSTRA HEMMO J. 
Published: June 2006

SUMMARYThe basic differences between mechanical analysis of sand by Ro‐Tap sieving and by settling in a sedimentation balance are discussed. The Groningen balance can continuously and rapidly record settling times of the grains (50–1,000 μ) of a 1.5‐g sample with a maximum recording and reading error of about 2%.The theory of sieving is not fully developed yet, nor has the theory of settling of sand‐sized particles been adequately expressed by any mathematical law. The drag coefficient (CD) and Reynolds number (Re) relation often used to derive diameter (d) from settling velocity (v) in this size range, are calculated from experimental data on diameter and velocity. Conversion of settling times to “sedimentation diameters” with the help of experimental curves for single, spherical quartz grains and their comparison with the corresponding “sieve diameters” are often found to be unsatisfactory in the case of natural sands, because shape and density variations of every individual grain in a sample can never be taken into account. Therefore, the use of settling velocity as a new grain parameter is advocated.
INTRICATED CROSS‐STRATIFICATION DUE TO INTERACTION OF A MEGA RIPPLE WITH ITS LEE‐SIDE SYSTEM OF BACKFLOW RIPPLES (UPPER‐POINTBAR DEPOSITS, LOWER RHINE)
Authors: BOERSMA J. R. , VAN DE MEENE E. A. , TJALSMA R. C. 
Published: June 2006

SUMMARY1Of the several uncommon types of large‐scale cross‐stratification encountered in Late Holocene upper‐pointbar sandy deposits of the Rhine, one is examined in detail. This type is structurally bipartite as it consists of a relatively coarse‐grained, upper interval of large‐scale foresets, which indentate with the oppositely dipping small‐scale foresets in the underlying finer interval. The lower interval is usually of smaller, and incidentally of the same thickness as the upper one. Together they constitute the so called “interwoven set”.The interwoven set is regarded as formed by a mega ripple (dune) with in front of it, a simultaneously active system of small‐scale, oppositely moving, ripples propelled by the backflow branch of the mega ripple's lee‐side vortex.Comparison of dip, strike, and principal bedding‐plane (= horizontal) sections brought to light dissimilarity in the crestline orientations of the mega‐ripple and backflow‐ripple systems. The latter's oblique, or incidentally perpendicular orientation with respect to the mega‐ripple front indicates a conspicious component of lateral water movement, which in the present outcrop was consistent from the left to the right, for the observer looking down(main)stream.It is suggested that this lateral water movement is due to the radial (transverse) flow in the bend of a meandering river. From the sense of the radial flow the river's bend configuration (here: right hand turn) can be inferred. Relative wander velocities of mega‐ and backflow‐ripple systems were deduced from the configuration in a horizontal section made through the interaction zone of the two structural intervals.
TEXTURAL STUDIES OF GRADING: VOLCANIC ASH FALLS
Authors: SCHEIDEGGER ADRIAN E. , POTTER PAUL EDWIN 
Published: June 2006

SUMMARYA theory of the lateral decrease of grain size and bed thickness with increasing distance of downwind transport is developed for ash falls. The theory is based on: the sediment load density of a turbulent slug of fluid, a turbulent diffusitivity coefficient, and the decay of turbulent velocity fluctuations. All three factors are founded on empirical observation and are generally accepted as having widespread applicability to turbulent sediment‐fluid mixtures. The theory yields good qualitative agreement with observational data.
INTERNAL STRUCTURE OF WAVE‐FORMED RIPPLE MARKS IN THE NEARSHORE ZONE
Authors: NEWTON ROBERT S. 
Published: June 2006

SUMMARYWave‐formed ripple marks in the nearshore zones of the Baltic Sea (tideless) and North Sea (tidal) exhibit a unidirectional internal lamination identical to that of current ripples. This holds true whether the ripples are symmetrical or asymmetrical. In most cases wave‐formed ripple laminae dip toward shore and can thereby provide a shoreline direction indicator when found in ancient sediments. The sediment transport direction, however, may be other than in the foreset laminae dip direction, and cross‐lamination as a sediment transport direction indicator should be used with caution.Ripple height, wave length and the orientation of the ripple internal structure are dependent upon both the orbital diameter and the velocity of the positive component of oscillation of the waves forming them. The thickness of the individual laminae making up ripples is highly dependent upon sediment grain size; the role hydrodynamics plays is problematic.
ROTATIONAL SLUMPS AND SLUMP SCARS IN SILURIAN ROCKS, WESTERN IRELAND
Authors: LAIRD M. G. 
Published: June 2006

SUMMARYCurved or planar discordant surfaces occurring within a limited stratigraphic range immediately beneath shallow marine deposits represent penecontemporaneous shear surfaces along which slumps have moved. Rotated packets of strata frequently retained within the curved discordant surfaces show both internal and external evidence of having moved laterally. Movement is considered to have been triggered off by a sudden shock or shocks which may have been either of sedimentary or tectonic origin. The slumping occurred at the change in gradient between slope and shallow marine shelf deposits.
STATISTICAL MODELS IN SEDIMENTOLOGY1
Authors: KRUMBEIN W. C. 
Published: June 2006

SUMMARYThree stages of statistical development can be recognized in sedimentology. The first is descriptive statistics, in which the sample is the object of interest, and the second is analytical statistics, in which the population assumes major importance. A very large variety of statistical techniques is available for estimating mean values, degrees of variability, tests of differences among population means, linear relations (correlations) among the variables, and ways of evaluating areal variations (trends) in sedimentary phenomena.The third stage of statistical development is the application of stochastic process models to sedimentology, in which the objective is to discern the probabilistic elements in sedimentary processes, in part by simulation with the high‐speed computer. Stochastic process models thus provide one way of examining sedimentary processes through time or over an area. In conjunction with deterministic models they provide a framework for exploring the underlying physical, chemical, and biological controls on sedimentary processes and deposits, with superimposed random fluctuations introduced by the “built–in” probabilistic mechanism.