bluuebunny/crossref_metadata_2025 huggingface dataset:
THE CONTINENTAL MARGIN OFF THE ATLANTIC COAST OF THE UNITED STATES: CARBONATE IN SEDIMENTS, NOVA SCOTIA TO HUDSON CANYON1
Authors: HÜLSEMANN JOBST
Published: June 2006

A joint survey by the Woods Hole Oceanographic Institution and the U. S. Geological Survey, begun in 1962, aims at the geologic exploration of the Atlantic continental margin. This report describes the distribution of carbonate in the surface sediments between Nova Scotia and Hudson Canyon. Samples of surface sediment on a 10‐mile grid reveal that over more than 90% of its area the shelf sediment contains less than 5% calcium carbonate. These low values are due to low production by aquatic organisms, a consequence of low average water temperatures. A few locales on the shelf have high carbonate concentration owing to a prolific sessile or nearly sessile fauna. Seaward of the shelf concentrations of calcium carbonate increase regularly with depth to about 30% on the upper continental rise; this increase reflects a greater relative abundance of planktonic Foraminifera due to a decrease in the rate of deposition of land derived detritus. Limestone outcrops are very rare in the area.
WOODY DEBRIS ON THE MAINLAND SHELF OFF VENTURA, SOUTHERN CALIFORNIA
Authors: UCHUPI ELAZAR , JONES GILBERT F.
Published: June 2006

Land plant debris occurs in appreciable quantities in the shelf sediments off Ventura, southern California. Concentrations range from less than 2 g (wet weight)/1 (less than 250 g/m2) to 53 g/1 (10,662 g/m2). The highest values are found near the outer edge of the shelf.
OCCURRENCE OF HIGH‐ANGLE STRATIFICATION IN LITTORAL AND SHALLOW NERITIC ENVIRONMENTS, CENTRAL GEORGIA COAST, U.S.A.1
Authors: HOYT JOHN H.
Published: June 2006

High‐angle stratification (greater than 20°) is produced in several areas of shallow marine sedimentation along the barrier islands of the central Georgia coast. The maximum angle of inclination is 30° which is the angle of repose for the saturated, fine‐grained, angular sand of this area. High‐angle stratification forms in the following locations:

(1) The depositional margin of tidal channel inlets. Under some wave and current conditions, sand accumulates near low tide level and steepens the depositional interface to the angle of repose.

(2) The steep face of asymmetrical megaripples developed by tidal currents. Ripples with amplitudes as much as 3 ft. and wave lengths of 20–40 ft. commonly develop in channel inlets and other areas of sand sediments.

(3) The steep face of sand waves formed in channel inlets. These large asymmetrical ripples have amplitudes as great as 12 ft. and wave lengths of ca. 300 ft. Lengths along the crests are over 600 ft.

(4) The landward side of low bars developed on the beach. Bars and troughs (ridges and runnels) are common on the beaches of this area. The bars, which are as much as 5 ft. high, shift landward by deposition on the steep landward face.

(5) The oceanward side of large sand waves at the mouth of offshore tidal channels. Large sand waves are located 6 miles offshore from Doboy Sound inlet in 20–25 ft. of water. The steep face of these asymmetrical sand waves is orientated toward the ocean. Amplitude of these large ripples is as much as 17 ft. and length along the crests is over 1/2 mile.
AN ELECTRON MICROSCOPE STUDY OF THE SURFACE TEXTURE OF SAND GRAINS FROM A BASAL CONGLOMERATE
Authors: WOLFE M. J.
Published: June 2006

Quartz grain surface textures from the basal glauconitic chalk of the Belemnitella mucronata Zone southwest of Belfast, Northern Ireland, show the effects of solution during the last stages of diagenesis of the limestone. The postulated chemical environment, in which quartz is more soluble than calcite, is one of moderate temperature and pressure and alkaline circulating ground water.
14C DATES OF CALCAREOUS SAMPLES, HERON ISLAND, GREAT BARRIER REEF1
Authors: WOLF KARL H. , ÖSTLUND GÖTE
Published: June 2006

Two samples of plant‐rich limy sand collected from the 9‐ and 11‐ft.‐level of the Heron Island cay were subjected to 14C dating. Uncertainties related to secondary changes and contaminations, and the unknown transportation history of the woody material prior to accumulation at Heron Island, in combination with the relatively young age of the carbon, did not result in 14C values useful for correlation and absolute dating purposes.
DEFINING GRADIENTS IN A SAMPLE OF SEDIMENTARY ROCK
Authors: DAHLBERG E. C. , GRIFFITHS J. C.
Published: June 2006

Three orthogonal planes (two vertical and one horizontal with respect to the apparent bedding structure) of a core sample of seemingly graded graywacke sandstone have been petrographically analyzed in order to determine the form and characteristics of the lithologic gradients in the specimen.

Compositional and textural properties were sampled in thin section according to an orthogonal grid pattern on each of the three faces.

Variability among rows and columns (plus interaction) with respect to each petrographic variable was tested by analysis of variance using a two way classification. A larger number of properties show significant variation among the rows of the sampling grid (thus in a vertical direction) than in the horizontal plane of the apparent bedding.

Quality control models with confidence limits, which display graphically trends in the individual constituents, indicate that feldspar proportion, mica proportion, and quartz grain size exhibit significant gradients (above the level of analytical error) in the direction perpendicular to the bedding. Quartz proportion oscillates in a non‐systematic fashion, and quartz grain shape shows no trend in the vertical planes of the specimen. The petrographic variability observed in the horizontal plane of the bedding is generally trendless.

Partial trend surfaces show that the trends in quartz grain size are dominant, but are not simple in form according to the comparative reductions in total variation achieved by fitted surfaces of successively higher degree. Again, the major portions of variability are explained by the surfaces fitted to planes perpendicular to the bedding. The textural homogeneity of the rock in the horizontal (bedding) plane is reflected in the relatively subdued trends exposed by the surfaces in this direction.

Taking grain size as an example, a 1: 1 correspondence is established between this property and the theoretical effects of settling in a liquid medium by a functional relationship; it is shown that only 25 to 40% of the total grain size variation in the specimen is attributable to this process.

It is concluded that the interpretation of natural sedimentation processes from analysis of petrographic properties is complex due to the interaction of the processes and the interdependencies among the measurable properties which result.
AUTHIGENIC CEMENTATION OF SCORIACEOUS DEEP‐SEA SEDIMENTS WEST OF THE SOCIETY RIDGE, SOUTH PACIFIC1
Authors: MORGENSTEIN MAURY
Published: June 2006

Harmotome‐rich scorias and indurated tuffaceous mudstones occur in sediments west of the Society Ridge, South Pacific. Diagenetic alteration of mafic palagonite produces the following authigenic minerals: harmotome, phillipsite, goethite, limonite and montmorillonite. A major mode of induration of pyroclastic‐rich marine sediments is the devitrification of mafic palagonite producing the following diagenetic cementing minerals: phillipsite, harmotome, limonite, and to some extent, manganese and ferromanganese oxides.
LESSONS FROM A FEASIBILITY STUDY FOR COMPUTER MODELS OF COAL‐BEARING DELTAS
Authors: OERTEL G. , WALTON E. K.
Published: June 2006

A computer‐generated model of a coal‐bearing delta would be desirable if it included enough detail to reproduce the cyclical nature of the sediments. At the present stage of development of computers, and with the present state of knowledge of the quantitative aspects of transportation and sedimentation, it is not yet possible to set up such a model. However, the logical arrangement in a flow‐diagram of the processes and parameters involved in delta formation strongly suggests that cyclical sedimentation can occur without the need for an external cyclical cause, such as tectonic or climatic oscillations. Attempts to provide for appropriate checks of a computer model bring out overall regularities in the assemblages of cyclic types in three different coal basins.
NOTES ON SOME FUNDAMENTALS OF PALAEOCURRENT ANALYSIS, WITH REFERENCE TO PRESERVATION POTENTIAL AND SOURCES OF VARIANCE
Authors: ALLEN J. R. L.
Published: June 2006

Arguments are developed to show that a factor termed preservation potential could bias the operational data of palaeocurrent analysis, and hence any palaeogeo‐ graphical inferences that are drawn. Flow systems and their directional sedimentary response elements are hierarchically organised in the geological present. A flow system can therefore be characterised (within the limitations imposed by preservation potential) only by reference to all the ranks of sedimentary structure generated therein. The operational rock structures generally employed in palaeocurrent analysis are usually low‐ranking and subject to several sources of variance.
X‐RAY RADIOGRAPHY FOR EXAMINATION OF BURROWING IN SEDIMENTS BY MARINE INVERTEBRATE ORGANISMS1
Authors: HOWARD JAMES D.
Published: June 2006

Examination of the primary sedimentary texture of rocks and sediments by X‐radiography can be extended to include the study of bioturbation and burrowing by living organisms. This technique involves making time‐lapse X‐radiographs while the animals are in the process of disturbing the sediment.

Artificially and naturally stratified sediments are contained in plexiglass aquaria connected to a continuously flowing seawater system. The burrowing animals to be studied are introduced into these aquaria and the effect of their activities on the sediments is recorded by X‐radiography over a period of hours, days or weeks.
DENDRITIC HALITE PSEUDOMORPHS FROM THE KEUPER MARL OF LEICESTERSHIRE, ENGLAND
Authors: LLEWELLYN P. G.
Published: June 2006

Small, dendritic structures in probable playa lake sediments of the basal Keuper Marl in Leicestershire are interpreted as habit‐modified halite pseudomorphs.
SOME HYDRAULIC PROPERTIES OF BIOCLASTIC CARBONATE GRAINS
Authors: MAIKLEM W. R.
Published: June 2006

A simple experiment demonstrates that shape and bulk density of bioclastic carbonate crains are important factors affecting the grain‐size distribution of a clastic carbonate sediment deposited in water.
A QUANTITATIVE STUDY OF A SEQUENCE OF COAL‐BEARING CYCLES IN THE NAMURIAN OF CENTRAL SCOTLAND, 2
Authors: READ W. A. , DEAN J. M.
Published: June 2006

The quantitative relationships between stratigraphical variables from a succession of coal‐bearing cycles deposited in a subsiding basin have been investigated using principal component‐ and factor analysis, in an attempt to reveal simple relationships undetected by conventional qualitative methods. Knowledge of such relationships will undoubtedly be useful in future computer simulation studies of cyclical sedimentation. Principal component analysis and factor analysis yield similar results, which confirm and amplify those of the trend surface analysis described in Read and Dean (1967).
THIN‐SECTION SIZE ANALYSIS AND THE MOMENT PROBLEM
Authors: SAHU BASANTA K.
Published: June 2006

The observed size in the thin‐section is less than the true grain sizes of the clastic rock as the thin‐section plane does not necessarily pass through the centre of gravity of the grains. Correction factors based on probability theory give corrected arithmetic moments of the size distribution in the clastic rock from the observed arithmetic moments of the size distribution in the thin‐section. The corrected arithmetic moments so obtained are transformed to their equivalent corrected phi moments which are useful to generate the unknown size distribution of the clastic rock by the help of Edgeworth's series.
TECTONIC CYCLES AND REGULARITIES IN THE DEVELOPMENT OF SEDIMENTARY ROCKS AND PALEOGEOGRAPHIC ENVIRONMENTS OF SEDIMENTATION OF THE RUSSIAN PLATFORM (AN APPROACH TO A QUANTITATIVE STUDY)
Authors: RONOV A. B. , MIGDISOV A. A. , BARSKAYA N. V.
Published: June 2006

An attempt was made to find the ways for quantitative estimation of changes of the sedimentation processes and paleogeographic environments in the geological past. Quantitative regularities on the basis of rock volume measurements were found in the history of sedimentation and environmental conditions on the Russian Platform beginning in Late Riphean (Pt3) until Quaternary, through the main geotectonic cycles (Caledonian, Hercynian and Alpine).

It was shown that there were no major differences between sand and clay abundance (26.0% and 30.1%, respectively). Limestones are most abundant among carbonate rocks (17.0%), followed by dolomites (10.2%), then marls (7.5%) and finally chalk (2.0%). Surprising was the very high abundance of gypsum and anhydrite (2.7%) and of salts (3.1 %). Being in agreement with data of many other regions of the world, this fact has far reaching consequences, first of all, concerning the history of ocean salinity and, secondly, for the knowledge of geochemical cycles of Na, C1 and S.

A predominance of terrigenous sedimentation has been found for the Caledonian and Alpine cycles, whereas a greater abundance of chemical and biochemical sedimentation occurred in the Hercynian (Variscian) cycle. Each of these cycles is characterized by the common scheme of periodical recurrence of main rock types from the initial to the final stages. (Fig. 2).

Fig. 8 shows the prevailing role of uplift and erosion on the Russian Platform (76% of the total platform area); only 5.7% of the area falls on the continental sedimentation, 1.8% on the lagoon environments, and 16.5% on the marine sedimentation. This is in contrast to the geosynclines which were dominated by marine sedimentation. Considering now only the regions of stable subsidence and “fixed” sedimentation of the Russian Platform (Fig. 5) we find that here marine sedimentation dominated (68.9% of the areas of stable subsidence) in comparison with the continental environments (23.6%). As well as the abundance of sediments, the distribution of the main types of paleogeographical conditions changed during the cycles with extreme regularity according the periodic law. (Fig. 6,7). The periodicity of sedimentation and the alteration of paleogeographical conditions were finally determined by the periodical rhythm of platform epirogenic movements.
THE MEASUREMENT OF THE SIZES OF NON‐SPHERICAL PARTICLES BY THE HYDROMETER METHOD
Authors: McCANN C.
Published: June 2006

It is shown that in calculating the viscous force on a non‐spherical particle suspended in a fluid, it is necessary to use the largest dimension of the particle. This may be calculated from the diameter of the equivalent sphere obtained from a hydrometer analysis provided the shape of the particle is known.
QUANTITATIVE ANALYSIS OF BEACH SAND MOVEMENT, VIRGINIA BEACH, VIRGINIA1
Authors: BOON JOHN D.
Published: June 2006

A simplified stochastic‐process model involving statistical procedures is used to analyze sand tracer displacement data on an ocean beach. The procedures provide meaningful estimates of the direction and magnitude of the movement of beach sand through set intervals of time.

Results of a single tracer experiment are reported for a beach located near Virginia Beach, Virginia. Using a rectangular sampling grid, tracers were recovered at fixed times, then considered as items in a sample of X and Y displacements from the point of release. Comparison of the adjusted means of these samples on a time‐ stratified basis gave estimates of average particle velocity in two dynamic zones:

(1) swash zone: v̄(X) = 0.44 ft./min (0.22 cm/sec) longshore; (2) surf zone: v̄(Y)= 0.37 ft./min (0.19 cm/sec) offshore.

Using an estimate of the thickness of the mobile layer (the depth interval in which semi‐continuous motion of beach sand occurs), a further estimate of the rate of longshore sand transport was computed at 440 yards3/day (336 m3/day).
SELF‐OPERATED PIPETTE FOR GRAIN‐SIZE ANALYSIS: A PROTOTYPE
Authors: BARTOLINI CARLO
Published: June 2006

The self‐operated pipette developed at the Geological Institute of the University of Florence, analyses the silt fraction of a sample at half‐phi intervals. Operator assistance is only required during the first four minutes of analysis.
FORMATION OF QUARTZ OVERGROWTHS IN THE PENRITH SANDSTONE (LOWER PERMIAN) OF NORTHWEST ENGLAND AS REVEALED BY SCANNING ELECTRON MICROSCOPY
Authors: WAUGH B.
Published: June 2006

The development of optically continuous quartz overgrowths is governed by the atomic structure and crystallographic orientation of the detrital quartz grains. Initial growth commences with the appearance of numerous oriented projections, with rhombohedral and prismatic form, on grain surfaces. Merging and overlap of the projections results in the formation of large crystal faces whose form is dependent upon the initial location of the projections with respect to the internal crystallographic axes. Growth is particularly rapid along the direction of the c‐axis. For unicrystalline quartz grains the ultimate growth phase is the production of polyhedral quartz crystals having the appearance of hexagonal dipyramids. In polycrystalline grains each quartz unit within a single grain develops a separate overgrowth, the form of which is similarly controlled by the internal structure of the individual quartz units. Hence, the completed overgrowth shows an irregular distribution of diversely oriented prism and rhombohedral faces.
AN EMPIRICAL EXPRESSION FOR THE PROBABILITY OF PARTICLE PASSAGE THROUGH IDEAL SCREENS
Authors: JANKE N. C.
Published: June 2006

Using a form factor, to represent particle shape, the dynamic sieve data of LUDWICK and HENDERSON (1968) can be presented as a single function, with a standard error of 4%.
PROBLEMS OF QUARTZ GRAIN MORPHOSCOPY
Authors: SCHNEIDER HORST E.
Published: June 2006

In a historical review of the development of quartz‐grain morphoscopy some unsolved problems such as the real aspects of the details on frosted grain surfaces and the interpretation of the origin of different surface textures are elaborated. Discrepancies in the presentation of quartz‐grain types as observed by electron microscopy are mentioned. It is proposed to relate such investigations to CAILLEUX's (1942) classical morphoscopic method; this could be facilitated by the modern scanning electron microscope. The possibilities and advantages of this instrument for morphoscopic research are presented by first results concerning the surface textures of original quartz grains derived from a weathered granite and of experimentally and naturally etched grain surfaces. For generalized conclusions a greater number of further observations must be made.
MINERAL STUDIES IN THE GRAVITATION‐GRADIENT FIELD, 2. CHANGES OF QUARTZ SAND DENSITY DUE TO NATURAL AND EXPERIMENTAL “MATURATION”
Authors: KATZ M. YA. , KATZ M. M. , RASSKAZOV A. A.
Published: June 2006

Based upon studies of natural quartz and upon laboratory experiments on mechanical and chemical destruction of quartz, it was established that the statistical density characteristics of detrital quartz change during sedimentary processes. Grains with defective structure, gas‐liquid inclusions, inclusions of organic matter and other lighter minerals have lesser densities, whereas grains with inclusions of heavier minerals have larger densities than those of optically pure grains. The susceptibility to destruction is less for optically pure grains than for grains with lower or higher density. This is responsible for the increasing maturity of quartz sand during weathering and transport as indicated by the increasing percentage of optically pure grains. Mathematical modelling of the dynamics of this process was carried out.
ON THE IDENTIFICATION OF MONTMORILLONITE MINERALS IN THE PRESENCE OF AMORPHOUS MATERIALS
Authors: MURAVYOV V. I.
Published: June 2006

The distinction of montmorillonite proper from beidellite is often based on the Li‐test proposed by GREENE‐KELLY (1953). However, when saturated with Li, true montmorillonite samples that contain considerable admixtures of SiO2 or Fe2O3hH2O behave in the same way as beidellites. An irreversible sorption of Li (after annealing at 250°C) is observed in such samples only after the admixed amorphous substance has been removed by leaching with a NaCO3 or HCI solution
MICRITIC ENVELOPES OF CARBONATE GRAINS ARE NOT EXCLUSIVELY OF PHOTOSYNTHETIC ALGAL ORIGIN
Authors: FRIEDMAN GERALD M. , GEBELEIN CONRAD D. , SANDERS JOHN E.
Published: June 2006

Micritic envelopes are commonly believed to develop from the lime‐mud infillings of circumferential perforations made in skeletal particles by algae. Because “algae” are usually taken to mean photosynthetic algae, the corollary has been proposed that micritic envelopes would not appear on carbonate skeletal particles originating in waters too deep for active growth of photosynthetic algae. Extensions of this “photosynthetic‐algae‐only” origin of micritic envelopes implies that: (1) the disappearance of envelopes with depth could mark a useful paleobathymetric datum; and (2) preservation of outlines of skeletal particles should be much better in “shallow”‐water carbonates than in “deep”‐water carbonates.

We doubt the validity of the depth‐limiting concept of the origin of micritic envelopes for two reasons: (1) petrographic study of a large number of thin sections thought to be representative of various paleo‐depth levels does not indicate any systematic variations in the preservation of the outlines of skeletal particles; and (2) molluscan skeletal debris displaying micritic envelopes and effects of borings identical with those generally ascribed to the activities of photosynthetic algae have been found in an aragonite‐cemented sandstone from the Atlantic shelf where geologic evidence indicates that the water at time of boring was too deep for active growth of photosynthetic algae.

Accordingly, we re‐emphasize the fact that organisms other than photosynthetic algae can bore into calcareous materials. In particular, fungi, bacteria, and heterotrophic algae (whose distribution does not depend on the penetration of light into seawater) are known to be active borers. Bacteria can be eliminated as producers of bores having diameters greater than approximately 10 μ. Fungi create boring structures with radiating or branching patterns or bores with nonuniform size. Some fungal bores appear to be indistinguishable from excavations known to have been bored by photosynthetic blue‐green algae. At present we do not know how to distinguish the results of boring activity of photosynthetic algae from those of algae living het‐erotrophically.
BREAK OF SLOPE IN PARTICLE‐SIZE CURVES OF GLACIAL TILLS
Authors: BEAUMONT PETER
Published: June 2006

In studies of particle‐size distribution of the less than 20‐mm fraction of glacial clays in eastern Durham it is noted that one particular characteristic seems common to them all. When the particle‐size data obtained by sieving and hydrometer analysis are plotted on semi‐logarithmic graph paper (BRITISH STANDARDS, 1961) it is seen that almost all the curves are made up of two shallow concave or straight sections separated by a small section of varying convexity. What is perhaps most surprising is that this convexity or marked break of slope is nearly always found in the range 0.2–0.8 mm. The break of slope shows that the material in the finer grain sizes is more abundant than the coarser material.

The question arises as to what is the cause of this break of slope and whether it is a sorting characteristic of sub‐glacial processes or is explicable in terms of parent‐material lithology.
DOWNCURRENT DECLINE OF GRAIN SIZE AND THICKNESS OF SINGLE TURBIDITE BEDS: A SEMI‐QUANTITATIVE ANALYSIS
Authors: SCHEIDEGGER A. E. , POTTER PAUL EDWIN
Published: June 2006

Sedimentologists have noted that turbidite sequences become thinner bedded and finer grained as traced downcurrent. We provide a semi‐quantitative explanation of this behavior based on the idea that turbulence in a turbidity current decays downcurrent so that in its zone of deposition both the total load in suspension and the grain size of that load decrease with increasing distance from the source. Semi‐empirical equations proposed by Chézy, Lokhtin and Sundborg are central to our argument.
FIGURES DE COURANT ET TRACES DE PATTES D'OISEAUX ASSOCIEES DANS LA MOLASSE MIOCENE DE DIGNE, BASSES ALPES (FRANCE)
Authors: BEAUDOIN B. , GIGOT P.
Published: June 2006

The Miocene “molasse” of Digne (subalpine chain) is studied in the profile along the Bramefan torrent. Gross lithological and paleontological contents, textures, structures and sole marks are described. All the types of sole marks are present (cf. the Plates), as in turbidites, but they point sometimes to opposite current directions on the same sole. Large‐scale (decimeter to meter) cross‐stratification is frequent. Graded bedding is very scarce. These observations do not indicate turbidites.

These coarse‐bedded, well‐sorted sediments are interpreted as high‐energy deposits. Bird tracks and Mya in living position suggest a beach environment.

Some “molasse” formations of Rumania and Spain are then discussed, especially with reference to MANGIN (1962) who shows, near a photograph of the Liedena formation, a picture of bird tracks from Barles: this example comes from the abovementioned Digne molasse, and is not an argument for the occurrence of such tracks in a new “flysch” near Digne.
LIMONITIC CONCRETIONS FROM THE EUROPEAN JURASSIC, WITH PARTICULAR REFERENCE TO THE “SNUFF‐BOXES” OF SOUTHERN ENGLAND
Authors: GATRALL MICHAEL , JENKYNS HUGH C. , PARSONS COLIN F.
Published: June 2006

Large discoid (1–30 cm), carbonate‐rich limonitic concretions or “snuff‐boxes” are contained in stratigraphically condensed limestones from the Jurassic of southern England and parts of Europe. Their general association with conglomerates and algal stromatolites suggests formation in turbulent shallow water on submarine swells, or a shallow marginal shelf. The surprisingly uniform growth‐form of the “snuff‐boxes”, together with their gradation into obvious calcareous oncolites and stromatolites, is taken as evidence that they too may have been formed, at least partially, under algal influence.

The geochemistry of the concretions, dominantly ferruginous, with subordinate phosphate, suggests deposition in an epicontinental environment, probably under the influence of considerable river drainage. They therefore contrast with the more trace‐element rich ferromanganese nodules which occur in some condensed pelagic sequences.
INTENSITY OF DEPOSITION FROM AVALANCHES AND THE LOOSE PACKING OF AVALANCHE DEPOSITS
Authors: ALLEN J. R. L.
Published: June 2006

An avalanche of granular solids deposits grains once its snout is arrested at the base of the surface of avalanching. During deposition the avalanche behaves as a settling column of dispersed particles; the surface of deposition within the column is marked by a distinct shadow, or continuity wave, which swiftly climbs the sliding mass. Empirically, the high intensities of deposition expected from avalanches behaving in this manner correspond to degrees of packing in the deposits that are very nearly the loosest possible for natural materials. This appears to explain why cross‐stratified sediments have low strengths and are readily deformed.
BEACH STRUCTURES PRODUCED BY CRAB PELLETS
Authors: CHAKRABARTI A.
Published: June 2006

It has been observed that seashore crabs produce various designs by the ejected faecal pellets. Study of such structures shows a clear association of them with different parts of the beach. Mossy structures are found only in the upper beach part, i.e., along the high‐water line, whereas concentric‐radiating and asteroid types are encountered in the middle beach area. In regions above mean high‐tide line burrow openings are surrounded by loose sediments and are devoid of any patterns. In the lower beach zone such structures are lacking. If the beach materials are more silty in character, faecal pellets congregate and stand out as knobby surfaces.

Closer examination of such structures, if preserved in ancient sediments, may not only help in delineating the ancient shoreline positions but also may help in demarcating littoral micro‐environments.
ANTIDUNE CROSS‐STRATIFICATION IN A TURBIDITE SEQUENCE, CLORIDORME FORMATION, GASPÉ, QUEBEC
Authors: HAND BRYCE M. , MIDDLETON GERARD V. , SKIPPER KEITH
Published: June 2006

The equation used by Skipper (1971) to derive flow velocity from antidune wavelength is satisfactory for open‐channel conditions, but must be modified for antidunes formed by density currents. Calculations based on the modified equation indicate a much higher flow density than was originally proposed for antidunes of the Cloridorme Formation. It further appears that the water waves accompanying these particular antidunes developed not at the upper boundary of the turbidity current, but at a density discontinuity within a few centimeters of the bed. Textural features of the Cloridorme turbidites are compatible with this interpretation.
BRECCIAS DEPOSITED BY MASS FLOW IN THE BRECCIA NAPPE OF THE FRENCH PRE‐ALPS
Authors: HENDRY HUGH E.
Published: June 2006

In the Lower Breccia Formation (Lower Jurassic), variations in thickness of the breccia sequence, in individual bed thickness, and in size of clasts suggest separate sources to the southwest and north of the study area. Large clasts, poor clast rounding, grading, and restriction of stratification towards the tops of individual beds indicate deposition by mechanisms other than normal marine bottom currents. The deposits are too thick to have been deposited from the bed load of many successive sandy turbidity currents. A mass‐flow origin is therefore favoured. The stratification in the breccias is believed to have formed at a late stage in their deposition. It is considered to be a result of traction of clasts at the tops of beds by fluid entrained by the flow, or turbidity currents associated with the flow.
OBSERVATIONS ON DUNES AND BI‐MODAL SANDS IN THE TÉNÉRÉ DESERT
Authors: WARREN A.
Published: June 2006

Observations of dune patterns in the central Ténéré desert, Niger, reveal a significant association between different dune morphologies and sand types. It is suggested that the bi‐modal sands that are associated with low dunes and flat areas can be explained by the protection of fine sands in the inter‐particle voids of the coarse creep fraction.
ORIGIN OF PHOSPHORITE OF THE LATE PRECAMBRIAN GANGOLIHAT DOLOMITES OF PITHORAGARH, KUMAUN HIMALAYA, INDIA
Authors: VALDIYA K. S.
Published: June 2006

The Precambrian Gangolihat Dolomites of the Pithoragarh area in the Kumaun Himalaya, characterized by rich and widespread development of the stromatolites belonging to theBaicalicagroup, are poorly to moderately phosphatic. The intimate and constant association of collophane with the branching stromatolites suggests that algae played a significant role in the localization of phosphate in the dolomites formed in very shallow and warm waters of the sea. The phosphatization of the stromatolites occurred during the later, almost penultimate period of the Gangolihat times, when theBaicalicagroup of algal stromatolites was in its heyday of development. The replacement of carbonates by collophane took place a little before and during the sedimentation of the clastic calcarenites that fill the space between the columns of algal structures. What is uniquely distinctive and significant in the Pithoragarh area is the association with algal bioherms of the lentiform deposits of very coarsely crystalline magnesite. The magnesite that has replaced the phosphatized stromatolite‐bearing dolomites not only preserves excellently the original stromatolitic structure, but its phosphatized parts as well. This shows that the phosphatization pre‐dates the origin of magnesite.
From limestones to distal turbidites: a facies and trace fossil analysis in the Zumaya flysch (Paleocene—Eocene), North Spain
Authors: CRIMES T. P.
Published: June 2006

The flysch of Paleocene to Eocene age outcropping in an almost unbroken cliff section at the Playa de San Telmo, Zumaya, North Spain, has been the subject of a quantitative sedimentological analysis. It is inferred that sedimentation commenced with deposition of a limestone‐red shale sequence below wave base and continued with proximal and then distal turbidite sandstones deposited in what may have been a gradually deepening trough. The trough was probably oriented approximately east‐west, parallel to the subsequent main tectonic trend. Sediment transport within the trough appears to have been essentially axial, with calcareous and siliceous sand derived from the east, but some siliceous sand was also laterally transported mainly from a land mass to the north.

The sediments contain an abundant and varied suite of trace fossils. Thus, with the depositional environment already defined sedimentologically, it was possible to critically examine the relationship between facies, trace fossil distribution and possible water depth. The facies variations were shown to be reflected in a changing ichnofauna. Spreite such as Zoophycos and Rhizocorallium were present in limestones apparently deposited not far below wave base. These traces are replaced by rosetted, winding and meandering forms in the more proximal turbidite facies. In the more distal facies spiral and patterned trace fossils appear, winding and meandering forms are common but Zoophycos, Rhizocorallium and rosetted traces are absent. It is inferred that these changes reflect faunal distribution on the sea floor rather than preservational factors.
Mathematical analysis to discriminate two types of sandstone‐shale alternations
Authors: HATTORI ISAMU
Published: June 2006

Sedimentation processes forming a series of bipartite layers have been studied mathematically. Two types of sedimentation processes are recognized, i.e. concurrent deposition of sandstone and shale by a turbidity current (Type I) and alternate deposition of each of them (Type II). A time series of events in a sedimentation process is reasonably considered a first‐order Markov chain, and the process is described with a Markov matrix including four state‐variables such as deposition of sandstone, erosion of sandstone, deposition of shale, and erosion of shale. Analysis of Markov matrix yields a fixed probability vector, which for Type I process is different from that for Type II process. The vector bears a close relation to Kolmogorov's coefficient, which is the ratio of the number of beds deposited and the number of beds preserved in a given sedimentary section. This coefficient can be computed on the basis of field observations. Substitution of the computed data determined the values of the fixed probability vector for two sedimentary sections in Japan. The results permitted a theoretical conclusion as to the genesis of observed sandstone‐shale alternations. This conclusion is in good agreement with the deductions from more conventional sedimentological methods.
Radiaxial fibrous calcite: a replacement after acicular carbonate
Authors: KENDALL A. C. , TUCKER M. E.
Published: June 2006

Radiaxial fibrous calcite, a common cavity fill in ancient limestones, is characterized by curved twin lamellae, optic axes that converge away from the substrate and subcrystals which diverge in this same direction. The optic axes radiate about three or four axes located in positions between adjacent crystals and orientated parallel with the crystal elongation. The crystals are commonly turbid with inclusions, which may be concentrated along twin lamellae and subcrystal and inter‐crystalline boundaries, or form zones parallel to the substrate. Some inclusion patterns reveal the position of former crystal faces.

From a consideration of the occurrences, gross morphological characters, the fabrics of the crystals and the inclusion patterns, radiaxial fibrous calcite is interpreted as a replacement of an early diagenetic acicular cement, composed of interfering bundles of radiating crystals. It is suggested that replacement takes place by a solution‐precipitation process and the migration of a fluid film through the acicular host, with replacement occurring most rapidly between bundles of acicular carbonate. The optic axis pattern of the fibrous calcite is considered to be inherited from the c‐axis orientations of the host acicular crystals. Fibrous calcite intercrystalline boundaries form as fractures after replacement. Some inclusion patterns record the characters of the replaced acicular cement; others, formed of impurities reorganized during the replacement, reveal the form of the replacement front.
Grain size studies on turbidite components from Tyrrhenian deep sea cores
Authors: SARNTHEIN M. , BARTOLINI C.
Published: June 2006

Through an analysis of their coarse‐grain composition (>63 μm), pumice‐rich sandy layers from deep sea cores were identified as shelf‐derived turbidites rather than deposits due to ash rain or drifting pumice. A comparison of median sizes of individual grain types and total samples yielded significant vertical and horizontal sorting trends, which allowed apparently unrelated samples from different cores to be grouped into proximal and distal parts of one turbidite type. A discrimination of samples belonging to unrelated turbidite layers was also possible. In addition, whatever the grain size, planktonic molluscs and foraminifera have Md‐diameters 1·1–2·75 times larger than those of pumice. Weathered shallow‐water skeletals have Md‐diameters approximately equal to pumice, whereas those of augite and hornblende are 1·25–2·3 times smaller. This results in a different proportion of components in proximal and distal turbidite samples. The Md‐values of planktonic foraminifera reach their upper natural limit at 250–350 μm.
Nature mineralogique et origine des glauconies du plateau continental du Gabon et du Congo
Authors: GIRESSE PIERRE , ODIN GILLES S.
Published: June 2006

Sur le plateau continental du Congo et du Gabon, on constate la formation de goethite, de berthiérine et de glauconies (smectite et glauconite). La berthiérine caractérise un milieu deltaïque a sedimentation active; les glauconies se forment sur le plateau continental à plus grande profondeur (—50à—300m). Dans un milieu original granulaire (généralement des coprolites) tous les stades d'une succession minéralogique depuis la kaolinite jusqu'à un minéral voisin de la glauconite ont été décelés. Cette formation passe nécessairement par le stade smectite ferrifère. La formation préalable de granules crée un milieu semi‐confiné remarquable qui est, ici, la condition primordiale des évolutions minérales.
Diagenetically formed ooids and intraclasts in South African calcretes
Authors: SIESSER WILLIAM G.
Published: June 2006

Certain South African calcrete (caliche) beds contain structures that very closely resemble normal marine ooids and intraclasts. The ooids/intraclasts are actually non‐marine in origin, and were formed by an in situ process of calcretization and selective neomorphism. The term ‘diagenetic ooids/intraclasts’ is thus applied to distinguish these grains from marine ooids/intraclasts. Quaternary calcretes contain the only known ooids/intraclasts in any South African Cretaceous or Cainozoic rocks.

The diagenetic grains are believed to have formed in the following manner. Rain water percolates through an unlithified calcareous sand deposit, dissolving carbonate along its downward path. This carbonate‐laden water is eventually checked in its descent and drawn upward somewhat by capillary action. Evaporation and soil suction in the uppermost zones of the sediment body cause precipitation of a concentric coating of carbonate mud around individual grains (incipient ooids) or composites of grains (incipient intraclasts). As this dissolution‐precipitation cycle is repeated the micritic coatings thicken and locally push grains apart. At this stage three things can happen: (a) sparry calcite may be introduced as an intergranular cement (very rare in these calcretes), (b) wet carbonate mud may fill the pore spaces and lithify to micrite (common), or (c) wet carbonate mud may fill the pore spaces and neomorphose to microspar (common). The last process causes ooids/intraclasts to stand out distinctively, since they are opaque, micrite‐coated grains set in a fabric of clear microspar. This selective neomorphism of the micritic mud in pore spaces, rather than the micritic mud forming ooids/intraclasts, is probably a function of rapidity of lithification. The micrite of the coatings must have lithified quickly, before neomorphic crystal enlargement could occur, whereas lithification of the intergranular mud was delayed long enough for the growth of microspar crystals.
Folding in intertidal sediments on the west Lancashire Coast, England
Authors: PARKER W. R.
Published: June 2006

Folded mud layers are observed to be spatially associated with dune bedforms in the runnels of a wide multi‐barred foreshore. An hypothesis is presented linking the formation of the folds, by porewater and sediment movements, to the growth of the dune bedforms. The hypothesis is supported by published reports of laboratory experiments by other authors.
Features of cross‐stratified units due to random and other changes in bed forms
Authors: ALLEN J. R. L.
Published: June 2006

Because cross‐stratified units depend upon the movement of bed forms, any change in the shape, size and direction of travel of the forms is reflected in the geometry of the units, notably in their relative length, breadth and thickness, mode of termination upstream and downstream, and internal discontinuities. Most models of cross‐stratification so far published are unsatisfactory because they ignore the fact that real bed forms are subject to change.

The changes are thought to occur at two levels of detail independently. Those at the coarser level depend on the essential non‐uniformity, unsteadiness and multi‐directionality of natural flows, when assessed on a suitably large scale. At the finer level, change is related to the random behaviour of individual bed forms as they interact with the adjacent flow, and it proceeds even when the flow is an equilibrium one overall.

Flume experiments on current ripples show that many features of cross‐stratified units can be explained by the random behaviour of bed forms. The finite streamwise length of such units, and their upstream and downstream erosional termination, is governed by the life‐span (finite) of individual ripples and by the extent of net deposition on the bed. Internal discontinuities, closely resembling features described as reactivation structures, were also found to depend on the relative motion of ripples, no change of flow discharge and stage being involved. The degree of relative motion in the ripple assemblages was substantial, as measured by the fluctuating component of the ripple celerity.
An Upper Carboniferous tonstein of volcanic origin
Authors: SPEARS D. A. , RICE C. M.
Published: June 2006

Previous work on the mineralogy of the volcanic supra‐Wyrley Yard tonstein is extended to include the opaque minerals. This has led to a better understanding of the major and trace element geochemistry of the tonstein. The complete mineral assemblage is kaolinite (dominant) with minor quartz, K‐mica, zircon, apatite, pyrite, sphalerite, galena, rutile, dolomite, barytes, goethite and organic matter.

Information on element location in the tonstein has been obtained by using autoradiography and fission track radiography, the electron probe and by analysing separated fractions with an optical spectrograph.

This has enabled the diagenetic history of individual elements to be determined, and the composition of the tonstein to be compared with igneous material. The high concentration of Th, U, Pb, Sn, Bi, Y, Be and B in the tonstein, and the low concentration of Ti, Cr, V, Ni, Cu and Co is indicative of an acidic ash. A source in the Armorican orogenic belt is postulated, based on the contrast with the basaltic Carboniferous volcanism and also the high concentrations of Sn, Pb and Zn.
Use of the Model T Coulter Counter* in size analysis of fine to coarse sand
Authors: MCCAVE I. N. , JARVIS J.
Published: June 2006

An electrical sensing‐zone particle size analyser has been calibrated for use with sands. A 10: 90 saline/glycerol electrolyte is used with a concentration of 0‐1‐0.5 g/1 of suspended sand. Calibration error is ± 1.6% (± 0.02 φ). Comparison of counter and sieving results shows close agreement. Advantages of the machine are rapidity—a prepared sample can be analysed in 60 sec—and the small size of the sample required.
The relationship of porosity and angle of repose to mixture proportions in assemblages of different sized materials
Authors: STATHAM IAN
Published: June 2006

Rotating drum experiments on the repose angles of mixtures of glass spheres have shown that φr (angle of shear) is strongly influenced by the proportions of the mixture. It was found that φr reached a peak value for the minimum porosity mixture; where the pore spaces between the large particles were just filled with small material; which was attributed to increased dilatation on the shear plane during avalanching. The geomorphic significance of these observations, in terms of slope development, is discussed.

Secondly, the results of the experiments showed that, although more constant than φi (limiting angle of repose), φr was subject to some variation. Thus φr, as measured in a rotating drum, is not a true constant and can not be exactly analogous to φ'cv (angle of internal sliding friction at constant volume) as measured in a shearbox test—as has been previously suggested. It is tentatively suggested that at least some of the variability in φr is attributable to the magnitude of the immediately preceding value of φi, in that an unusually high value of φi, favours a lower value of φr due to the greater amount of kinetic energy released on failure.
Halite oolites and ripples in the Dead Sea, Israel
Authors: WEILER Y. , SASS E. , ZAK I.
Published: June 2006

Clastic features in recent halite deposits are observed along the beaches of an artificially dammed part of the Dead Sea. These features include halite oolites (termed halolites in this paper) and ripples.

Halite precipitates initially either at the brine surface or on the floor. It is suggested that moderate increase of wave agitation shifts the balance towards brine‐surface crystallization, and keeps the growing halite grains in constant motion. In this way rippled structures are formed. A further increase of wave energy leads to the growth of coated halite grains.

The accumulation of the various halite grains along the beach, to form soft rippled floor and oolitic beach ridge is brought about during shoreward winds.

During calm periods the bulk of the halite crystallizes directly on the floor. It develops into a hard crust which assumes the morphology of the substrate, including the ripple forms.