bluuebunny/crossref_metadata_2025 huggingface dataset:
THE APPLICATION OF A CHEMICAL STAINING TECHNIQUE TO A STUDY OF DEDOLOMITISATION
Authors: EVAMY B. D.
Published: June 2006

A staining technique is described which detects variations in ferrous iron content within calcite and dolomite, whilst simultaneously differentiating the dolomite from the calcite. The application of this technique to a study of dedolomitisation is pre‐ sented.

Ferroan dolomite, in certain pyrite bearing limestones of the southern Jura, is shown to have been dedolomitised, that is replaced by calcite, while at the same time the pyrite content of the rock was oxidised to haematite. One of the oxidation products of the pyrite is considered to have caused the dedolomitisation.
SEDIMENTARY FOLDS AND THE DEVELOPMENT OF LIMESTONE IN AN EARLY ORDOVICIAN SEA
Authors: LINDSTRÖM MAURITS
Published: June 2006

In a vast region in Scandinavia, a monotonous and extremely slow deposition of anaerobic mud persisted through the Late Cambrian. After a long time with no or very little sedimentation, deposition was recommenced in the Early Ordovician at an equally slow rate, but with calciumcarbonate as the main component. pH at the bottom was so low that the deposition of the carbonate in the long run only just outweighed the solution, which occurred frequently and sometimes during long periods. By oscil‐ lating solution and precipitation in the pores, lime mud could set into limestone on the sea‐bed. By more definite phases of solution, most of the limestone could be reduced to a marl bed with remains of undissolved limestone. Single limestone beds formed over such marl were apt to glide and deform into anticlines, which rose from the sea‐ bottom to heights up to 20 cm. These folds were rarely destroyed mechanically, which speaks for a tranquil bottom environment. Their crests were, however, cheinically corroded in the same way as discontinuity surfaces, which were also formed at many intervals. The processes by which the discontinuity surfaces were formed never affected a fold mechanically. The corrosion of the fold crests and of the discontinuity surfaces took place on the bottom of the sea, at safe distance from the surface. The corrosion was most frequently associated with the formation, and maintenance, of a glauconite skin. The abundance of preserved fold structures indicates that the region was relatively deep under the sea for most of the Early Ordovician. Later on, already in the middle‐Late Arenigian, the sea may have become shallower. The findings are extrapolated, with some probable interpretations and new observations, to include a hypothetical explanation for the passage from black shale to limestone facies.
ORIGIN AND MAINTENANCE OF RIPPLE MARKS
Authors: TANNER WILLIAM F.
Published: June 2006

A mechanical analog has been designed, constructed, and operated to produce a variety of ripple marks. Ripple‐mark maintenance has been studied in a wave tank, in an experimental flume, on tidal flats, and on dune fields.
VISCOSITY MEASUREMENTS OF AQUEOS CLAY SUSPENSIONS AS A TOOL FOR DETERMINING MINERALOGIC TYPE OF CLAYS
Authors: ROBERTSON JOHN O. , RIEKE HERMAN H. , CHILINGAR GEORGE V.
Published: June 2006

The possibility of using viscosities of clay plus water systems for determining the mineralogic type of clays was investigated by the writers.
TEXTURAL STUDIES OF GRADED BEDDING. OBSERVATION AND THEORY
Authors: SCHEIDEGGER ADRIAN E. , POTTER PAUL EDWIN
Published: June 2006

Published data and new observations from the Tertiary and Ordovician show that non‐multiple, continuously graded beds from turbidite sequences have size decline curves that are either convex, concave, or straight.

Utilizing a physical model and knowledge of fluid mechanics of turbulent transport, a formula relating both median and maximum grain‐size to height above the base of the graded bed was obtained. This analysis suggests that the shape of the size decline curve in a continuously graded bed depends on the initial size distribution of particles carried by the turbulent current.
RED BEDS IN NORTHEASTERN NIGERIA
Authors: JONES G. P.
Published: June 2006

Red beds are present in the dominantly drab Bima Sandstone at two main localities in northeastern Nigeria. Their lithology and petrography are described and chemical analyses quoted. It is deduced that the climate at the source area was conducive to the production of red soils. Alternating humid and dry periods are believed to have provided the conditions favourable for the accelerated erosion of a provenance of igneous and metamorphic rocks of marked relief. For the most part the pigment appears to have been finely‐divided material that was sorted prior to deposition; local environmental conditions determined whether the pigment subsequently remained red or was reduced. The association of oxidising and reducing conditions with shallow‐water sedimentary structures may best be explained by the postulation of seasonal flooding of an alluvial plain in a savanna‐type environment.
THE CLASSIFICATION OF CROSS‐STRATIFIED UNITS, COMMENT ON A PAPER BY J. R. L. ALLEN
Authors: CROOK KEITH A. W.
Published: June 2006

Examination of the criteria employed by ALLEN (1963) in his classification of cross‐stratified units suggests (a) that an additional criterion, the three‐dimensional shape of cross‐strata, should be used in describing and recognizing varieties of cross‐stratification, (b) that the character of the lower bounding surface of sets should be expressed in descriptive rather than genetic terms, and (c) that in describing the relation between cross‐strata and lower bounding surfaces, an additional term, asymptotic, should be used.

The recent discussion of the morphological features of cross‐stratification by ALLEN (1963) represents a significant advance in our appreciation of the variability of this type of sedimentary structure. The valuable classification of McKEE and WEIR (1953) generated a concern for precise description of cross‐stratification which has, in 10 years, made the classification inadequate. Allen's proposed classification, based as it is on observable morphological criteria and utilising a nongenetic terminology, should promote further rapid progress.

Allen has discussed the problems that arise in naming varieties of cross‐stratification. He very properly avoids terms with genetic implications and his use of Greek letters results in commendably brief names. Almost inevitably, his chosen nomenclature is not readily applicable in the field due to the difficulty of remembering which letter is associated with which assemblage of morphological features. This difficulty will increase as the number of defined varieties increases. It seems probable that workers will prefer for the most part to give names to varieties of cross‐stratification only in the laboratory where reference to literature can be made. The basis for recognition of varieties will be detailed field notes and photographs of morphological features. Nor is this undesirable, for it necessitates the making of detailed observations in the field which will lead to the recognition of new varieties. An easily remembered nomenclature too often leads to the suppression of significant differences in the interests of “pigeon‐holing” the structure in question.

It is therefore important that all significant morphological features should be noted. Consideration of the differences between certain varieties of cross‐stratification.
MATRIX OF TURBIDITES: EXPERIMENTAL APPROACH
Authors: KUENEN PH. H.
Published: June 2006

The matrix (< 40 μ) of turbidites forms a possible clue to the density of turbidity currents and the origin of the graywacke matrix. Experiments in a circular flume provide a mechanism to study the relation between composition of suspensions at various speeds and their deposits. There is a close analogy to the lower part of turbidity currents. The lutum content of samples with median diameters greater than 400 or 500 μ is found to correspond to the suspended load of the pore water. The higher value for finer deposits can be recalculated to suspension concentration by use of the “sedimentation factor”. Hence, each turbidite carries, as it were, a sample of its depositing current. The lutum content depends not on the ratio of sand to lutum in the current, as tacitly assumed by many authors, but mainly on the ratio lutum to water, although also influenced by velocity.

The average lutum density of coarser recent deep‐sea sands is 1‐2%. This indicates turbidity currents with 5‐10% lutum by weight (density 1.03–1.07). The sand must be added to ascertain the current density. In first approximation turbidity currents tend to have densities at their nose of 1.1–1.2, but higher and much lower values also occur.

The maximum original lutum percentage of coarse turbidites is below 10%. Higher values are very scarce and are due to post‐depositional mixing, or we are dealing with slides. However, in fine‐grained turbidites there is more matrix up to 20% for a median of 100 p. Hence, coarse graded marine graywackes with 20 or more per cent matrix are presumably weakly metamorphic turbidites, that originally held the same modest amount of lutum as recent turbidites of the same grain size. The Trask sorting of the experimental deposits is very good, like the average of natural turbidites. Most cumulative curves of turbidite grain‐size analyses on arithmetic probability paper show a characteristic bend in fine sand or silt sizes.
A REVIEW OF GRAIN‐SIZE PARAMETERS
Authors: FOLK ROBERT L.
Published: June 2006

This paper comprises a review of the many graphical and mathematical techniques that have been proposed for the statistical summary of grain‐size data. Satellitic problems, such as laboratory techniques, choice of size scales, and interpretation, are only considered briefly.
SEDIMENTATION IN A MEANDERING ESTUARY1
Authors: LAND LYNTON S. , HOYT JOHN H.
Published: June 2006

Sand is being deposited in a meandering estuary separating Sapelo and Blackbeard Islands, Georgia, in the channel of the estuary and on two point bars associated with meanders. Sand is being eroded by the meandering channel from slightly lithified Pleistocene and unconsolidated Holocene strandline deposits, and is being redeposited by the ebb tidal currents. The estuary‐channel deposits are coarse grained and their grain‐size decreases down ebb current from the source outcrops. The point bars are elongated in the direction of the ebb current, and increase in grain‐size from their crests downward as they grade into the channel deposits. Festoon cross‐bedding and ripple marks on the point bars record the ebb direction, while elongate plant fragments are preferentially oriented normal to the bar elongation (current). Horizontally stratified muds and muddy sands are being deposited behind the bars, and contain a rich fauna (primarily annelids, arthropods, and molluscs). However, the fauna is represented in the deposits more by burrows and disturbed stratification than by preserved organisms. The sands of the bars and channel are biologically less productive, but the bioclastic content of the sediment is high.
SOME FLUME EXPERIMENTS WITH A FINE SILT
Authors: REES A. I.
Published: June 2006

Four flume experiments have been performed in which the behaviour was investigated of a bed of fine silt under running water with and without an excess of material introduced into suspension.

In the presence of excess material, bed features were formed in the tangential stress range 0.1 < θ < 0.4, and the bed was found to remain plane in the ranges 0 < θF < 0.1 and 0.4 < θF < 1.3. In the absence of excess material the stable condition over the entire range appeared to be that of the plane bed.

Dual values of the threshold stress for grain movement were postulated to explain these results, and a relationship has been found between the magnitude of the tangential stress and the upstream slope of the features.
ENVIRONMENTAL SIGNIFICANCE OF SAND DIKES
Authors: OOMKENS E.
Published: June 2006

Sand dikes that have been found in Recent desert sediments are described, and an explanation of their origin is presented. The Recent dikes are compared with ancient ones of Permian age.
AN OBJECTIVE EVALUATION OF THE SEDIMENTARY STRUCTURAL COMPLEXITY OF A FLUVIAL BAR
Authors: DAVIES DAVID K. , EHRLICH ROBERT
Published: June 2006

The objective characterisation of sedimentary structures has not had as robust a development as more qualitative approaches. Using KRYNINE'S definition (1948, p. 145) that sedimentary structure is the “visible expression of non‐uniformity in texture and composition”, a method is here developed that yields data which are a function of the thickness and orientation of the visually homogeneous elements that, juxtaposed, comprise a sedimentary structure. This method, based upon a progressive enlargement of the field of vision about a point until the included area is first non‐uniform, yields a series of diameters which are related to both structural type and sampling plan. Exposures of sediment on a point‐bar in the Mississippi River were studied in this manner and it was determined that the method efficiently discriminated between structural varieties, and additionally allows the structural complexity of a point‐bar to be given a succinct quantitative description.
BED THICKNESS AND GRAIN SIZE: GRADED BEDS
Authors: POTTER PAUL EDWIN , SCHEIDEGGER ADRIAN E.
Published: June 2006

Data from Ordovician and Tertiary turbidites and from the Hekla ash fall show good correlation between bed thickness and grain size. Most of the thicker beds are coarser grained. The relation between bed thickness and grain size in graded beds can be explained by a theory which uses a sedimentation formula based on the decay law of turbulence in the deposition zone of a turbidity current.
TEXTURAL CLASSIFICATION OF SEDIMENTS
Authors: LINK ALBERT G.
Published: June 2006

In the light of present‐day requirements and the author's personal experience, existing systems of nomenclature and classification of sediments on a textural basis need revision. A system is proposed that is based on a three end‐member relationship involving sand‐, silt‐ and clay‐size particles. The construction, nomenclature and application proposed, fulfils the purpose of a classification because it is simple, easily remembered, practical, has wide application, is needed; and above all it groups sediments into useful categories that make communication more effective and easier.
THIN‐SECTION SIZE ANALYSIS: A FURTHER NOTE
Authors: STAUFFER PETER H.
Published: June 2006

Criticisms by VAN DER PLAS (1962) of thin‐section point counting as a method of size analysis appear to be based on confusion between number percent and volume percent. Points are samples of volume, and point counts yield volume percents. This is as much true of size classes as of other types of constituents, though distortions are caused in the distribution by the sectioning effect. The “ribbon” method advocated by Van der Plas counts individuals rather than points and hence yields number percents. The two types of statistic are fundamentally different.
MOUNTING SAND GRAINS FOR THREE‐DIMENSIONAL ANALYSIS
Authors: HUMPHRIES D. W.
Published: June 2006

A technique for mounting sand grains in transparent plastic rods is outlined. Four simple devices to facilitate the preparation and handling of the rods are described. These comprise a demountable mould, a grain lifter, a polishing jig and a microscope stage jig.
LAMINA, LAMINASET, BED AND BEDSET
Authors: CAMPBELL CHARLES V.
Published: June 2006

From smallest to largest, the component layers of a sedimentary body are laminae, laminasets, beds and bedsets. Different arrangements of these layers characterize different types of sedimentary bodies and identify different depositional processes. Concepts of these layers are redescribed because previous definitions are not adequate for modern quantitative descriptions of sedimentary bodies. The four kinds of layers are genetically similar; when compared with each other, they differ principally in areal extent and interval of time for formation. Because beds are usually the most readily recognized layers, they are considered the basic “building blocks” of sedimentary bodies.

Beds are bounded by depositional surfaces termed bedding surfaces; each surface is practically synchronous, and a bed can be considered an informal time stratigraphic unit of limited areal extent and of relatively short time span. This concept broadens the scope of intrabasinal correlations, permitting time correlations more refined than possible using fossils or radioactive age dating. Also, a better understanding of the mode of genesis and recognition of distinguishing characteristics of different types of sedimentary bodies follow from this concept.
BED THICKNESS AND GRAIN SIZE: CROSS‐BEDDING
Authors: SCHEIDEGGER ADRIAN E. , POTTER PAUL EDWIN
Published: June 2006

Qualitative and quantitative observations show a general positive correlation between grain size and thickness of cross‐bedded units. Greater sand‐wave height correlates with greater turbulence which permits more and coarser grains to be transported. A theory is developed which qualitatively explains these relationships.
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

Re‐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

The 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

The 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

Saxena (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

Microscopical 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.
AN UNUSUAL CARBONATE BAND IN THE EAST PENNINE COALFIELD (ENGLAND)
Authors: TAYLOR R. K. , SPEARS D. A.
Published: June 2006

A combined petrographical and geochemical study has been made on a per‐ sistent carbonate horizon from the Mansfield Marine Band, an important marker horizon in the Westphalian Coal Measures of the east Pennines. The composition of this carbonate is unusual for it normally consists of ankerite, but in some localities the carbonate is siderite and not ankerite. The position of the carbonate in the sedimentary cycle is discussed and the conclusion drawn that physicochemical conditions were suitable for the precipitation of CaC03 to occur. Furthermore the detrital material in the carbonate band continued to accumulate at a similar rate to the shales above and below the carbonate. The alteration of the CaC03 is thought to have been a diagenetic effect and the result of a change in the physicochemical environment. Variations in the concentration of dissolved sulphur species and their effect on the solubilities of iron and manganese provide an adequate mechanism to explain how CaC03 may alter to siderite on the one hand or ankerite on the other.
EMPLACEMENT OF FLYSCH‐TYPE SAND BEDS
Authors: KUENEN PH. H.
Published: June 2006

Recently 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

In 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

Electron 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

Analysis 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

The 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

SUMMARY1

Of 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

A 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

Wave‐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

Curved 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

Three 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.
PROBABLE CHANGES IN THE COMPOSITION OF SEA WATER DURING THE COURSE OF GEOLOGICAL TIME1
Authors: RONOV A. B.
Published: June 2006

The initial geological facts are considered on which the author bases on of the possible variants of the evolutionary scheme of the stratisphere, ocean and atmosphere composition from the Early Precambrian to the Recent. Some general tendencies and causal relationships in the development of these external shells of the earth are traced.

The object of this paper is to trace the evolution of the compositions of the sedimentary shell, the world ocean and the atmosphere from the Early Precambrian to the Recent period. Further, an attempt is made to elucidate some general tendencies in the development of these outer shells of the earth, in the changes of magmatic rock composition and in the history of tectonic movements and to establish causal relationships between them. The solution suggested is one of the possible variants, as the data used and the assumptions that have been made are not uniformly reliable for the different stages of geological history.
ON ENVIRONMENT‐SENSITIVE GRAIN‐SIZE PARAMETERS
Authors: KOLDIJK W. S.
Published: June 2006

Moment measures are to be preferred over graphic measures for a reliable description of the depositional environment of sands. This is demonstrated by coarse beach and river sands from the Ria de Arosa (northwestern Spain). A PL/1 computerprogram for the calculation of graphic and moment measures has been added to stimulate other comparative studies.
PRELIMINARY EXPERIMENTS ON HYDRODYNAMIC MOVEMENT INDUCED BY EVAPORATION AND THEIR BEARING ON THE DOLOMITE PROBLEM
Authors: HSÜ K. JINGHWA , SIEGENTHALER CHRISTOPH
Published: June 2006

Experiments were performed to demonstrate that saline interstitial waters under an arid coastal plain could be set in hydrodynamic movement to replace the evaporative loss near the surface.

In contrast to movement in a vadose zone, which is related to capillary forces caused by surface tension, the type of movement we observed was induced by a vertical hydraulic gradient under the evaporated area. Fluid flow through porous media was induced by an upward decrease in hydrodynamic potential during evaporation. We propose to call this type of movement evaporative pumping.

Experiments further verified that flow rate induced by evaporative pumping was directly governed by evaporation alone; linear flow rate through coarse sand and that through very fine silt was approximately the same under the same evaporative condition. Yet the movement apparently obeyed Darcy's law. Since the permeability of the medium was fixed, and the flow rate was dictated by evaporation, only the hydraulic gradient could be the dependent variable in the Darcy equation. We observed that the gradient was indeed much greater in relative impermeable silt than in permeable sand, when the water to replace evaporative loss must flow with the same rate through those media.

Our experiments suggested that hydrodynamic movement induced by evaporation could be an effective mechanism to transport magnesium‐bearing solutions through relatively impermeable sediments of an arid coastal plain. Computations showed that dolomitization by evaporative pumping could proceed at a rate to account for the origin of Recent dolomite crusts, and for the great thickness of ancient supratidal dolomites. In contrast, we believed that dolomitization by seepage reflux or by groundwaters cannot be extensive, because of the inadequate magnesium‐supply rates by such waters.
THE CHEMISTRY OF SUBMARINE CEMENT FORMATION AT DOHAT HUSSAIN IN THE PERSIAN GULF
Authors: DE GROOT K.
Published: June 2006

A chemical study made at Dohat Hussain lagoon in Qatar, has supported other field observations that submarine carbonate cementation is probably active there today. The source of the cement is the lagoon water, supersaturated with aragonite. In the lagoon the supersaturation is too low to effect spontaneous nucleation and thus precipitation of carbonate, but just below the sediment‐water interface both the presence of a stable substrate and supersaturation promote aragonite precipitation. In soft sediment layers in between cemented layers no supersaturation was found. The carbonate saturation of various water samples is tabulated below:

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STRATIGRAPHY AND GEOLOGIC HISTORY OF THE SABKHA, ABU DHABI, PERSIAN GULF
Authors: EVANS G. , SCHMIDT V. , BUSH P. , NELSON H.
Published: June 2006

The sabkha of Abu Dhabi was formed during the past 7,000 years by wind erosion of pre‐existing dunes and progradation of subaqueous, intertidal, and supratidal carbonate sediments. Marine transgression began in this area about 7,000 years ago and reached an apparent high about 1 m above its present level somewhat prior to 4,000 years B.P. Since then progradation of intertidal and supratidal sediments has taken place; this began 3,750 years ago. Arid conditions over the sabkha have produced large amounts of gypsum and anhydrite and lesser amounts of dolomite, magnesite, celestite and halite.