bluuebunny/crossref_metadata_2025 huggingface dataset:
FLUME STUDY OF RIPPLE PROPAGATION BEHIND MOUNDS ON FLAT SAND BEDS
Authors: SOUTHARD JOHN B. , DINGLER JOHN R.
Published: June 2006

Propagation of sediment ripples behind mounds of sediment in uniform flows of water over flat beds of fine sand was studied in a recirculating open channel. If the flow is strong enough, scour downstream of the mound, due to flow separation and impingement of strong eddies on the bed, generates a ripple, which itself grows large enough to cause downstream scour and production of a second ripple; the result is a widening train of ripples. Propagation vs. non‐propagation, as a function of mound height and bed shear stress, is interpreted in terms of the tentative hypothesis that ripple development is governed by the relationship between minimum height of bed irregularity necessary to generate ripples on an otherwise flat bed and the maximum height of bed irregularity that can be built up by flow over an originally flat bed. Minimum mound height for propagation of ripples was found to be non‐zero even when there was some sediment movement on the surrounding flat bed, but there was no sign of spontaneous development of ripples on the flat bed under these conditions; this suggests that there is a range of bed shear stresses for which a flat bed in uniform flow is metastable rather than unstable.
FLOOD DEPOSITS OF THE SAND‐BED EPHEMERAL STREAMS OF CENTRAL AUSTRALIA
Authors: WILLIAMS GEORGE E.
Published: June 2006

This study investigates the deposits of sand‐bed ephemeral streams within an area of 250,000 km2 in the western Lake Eyre basin, central Australia, being initiated after the record floods of February–March 1967.

Large‐scale ripples were the most common bed forms preserved in the majority of channels, covering 30–40% of the depositional area. Other bed forms included longitudinal, transverse and linguoid bars (20%), upper‐regime plane beds (<5%), small‐scale ripples (25–30%), and flute marks (<1%). Major bed forms could be related to flood stage: plane beds (upper regime), large‐scale ripples, and longitudinal bars usually were generated by high‐stage flow, and transverse and linguoid bars by waning and low‐stage flow.

Trough cross‐stratification was produced by migrating small‐scale and large‐scale ripples, large‐scale sets comprising about 60% of the deposits. Tabular cross‐stratification (25% of deposits) resulted from the downstream and lateral growth of channel bars. Flat‐bedding with parting lineation (<5%) was dominant only along the middle reach of the Finke, the major stream in the western Lake Eyre basin. Disturbed bedding was almost totally absent. Bed forms, in order of increasing overall mean grain size (?) of deposits, are plane beds (upper regime), small‐scale ripples, transverse and linguoid bars, and large‐scale ripples. Sorting (σI) and skewness (SkI) are dependent on mean grain size (Mz).

Lower‐regime flow prevailed for the majority of streams, upper‐regime flow being dominant only in the middle reach of the Finke. Using estimated Froude numbers and Darcy‐Weisbach resistance coefficients, the greatest mean velocities of flow have been calculated at about 0.8–3.7 m/sec.
ANTIDUNE CROSS‐STRATIFICATION IN A TURBIDITE SEQUENCE, CLORIDORME FORMATION, GASPÉ, QUEBEC
Authors: SKIPPER KEITH
Published: June 2006

Single‐set cross‐stratification, considered to have been produced by the upstream migration of antidunes, is present in the basal division of certain thick turbidite beds.

The basal divisions of these turbidites consist of very coarse to medium sand with a smooth or fluted base and sinusoid top. Internal laminae are inclined upstream at a shallow angle (less than 15°), opposing the local paleocurrent direction shown by flutes and ripple‐drift cross‐lamination.

The sinusoid (antidune) bed forms and their associated internal cross‐strata were preserved by the rapid fall‐out of sediment from suspension normal to the bed.

A paleohydraulic analysis suggests that during the final stages of antidune growth and migration, the currents moved at approx. 1 m/sec over very low slopes (much less than 1°).
DIFFERENT SOURCES CONTRIBUTING TO A BEACH SAND, SOUTHEASTERN BORNHOLM (DENMARK)
Authors: And HANS FÜCHTBAUER , ELROD JOHN M.
Published: June 2006

An abnormal relationship between quartz roundness and grain size, and unusual K‐feldspar accumulation in the medium sand fraction, quartz grains with overgrowths, and a differentiated heavy‐mineral community made it possible to calculate quantitatively the contributions of four sources to a modern beach sand in southeastern Bornholm. The quartz grains with overgrowths were particularly sensitive to transport and clearly showed an increase in roundness away from their origin, the Balka Quartzite. This rock, due to its high resistance, contributed only about 1% to the beach sands.
CONTROL OF SLOPE ON DEPOSITION FROM SMALL‐SCALE TURBIDITY CURRENTS: EXPERIMENTAL RESULTS AND POSSIBLE GEOLOGICAL SIGNIFICANCE
Authors: LOVELL J. P. B.
Published: June 2006

The experiments involved pouring aqueous starting suspensions of pumice sand and kaolinite silt into a submerged trough. The steepness of the bottom slope of the trough was varied from run to run. Heights of sand and silt were recorded at 10‐cm intervals away from source. The results: (1) support earlier suggestions that the ratio of sandstone to shale is a sensitive indicator of proximality in ancient turbidites, but do not support clearly the suggestion that the rate of decrease in that ratio away from source may indicate steepness of bottom slope; (2) suggest that the rate of decrease in sandstone thickness away from source in ancient turbidites may be inversely proportional to steepness of bottom slope.

The possible application of the results to the geological record is discussed.
THE CONDITIONS OF GROWTH OF THE WENLOCK REEFS OF SHROPSHIRE (ENGLAND)
Authors: SCOFFIN TERENCE P.
Published: June 2006

Distribution and size of the reefs in the Wenlock Limestone (Mid‐Silurian, Wenlock area) indicate that the most suitable site for growth was at the seaward fringe of the reef belt. The reef development increased through time as clay‐mineral concentration reduced. Many reefs colonized small mounds of coarse crinoidal debris but growth also started on soft muddy substrates. The Wenlock structures have similar characteristics to modern patch reefs: they are small—the average width is 12 m and the thickness 4.5 m—and roughly oval in section. During growth reef surfaces were gently convex and reached heights of between 50 cm and 3 m above the sea bed.

The organic framework of all reefs examined consisted of massive and branching tabulate corals, stromatoporoids, branching rugose corals and bryozoans; with stromatolites, laminar corals and stromatoporoids and bryozoans playing the role of reef binders. Most reef builders grew contiguously and are preserved in growth position. Biotic zoning within reefs was not detected. Biomicrites accumulated in interstices near the surface of the reef at the time of, and just shortly after, organic growth. The sea was probably less than 30 m deep and extreme shallowing at the close of the Wenlockian terminated reef development. However, reefs were not broken up by wave or current action. The inter‐reef sediments, which were deposited at the same rate as reef growth, are predominantly argillaceous crinoidal biomicrites alternating with thin shale bands. Very few beds of reef‐derived talus occur (Fig. 13–15). High influxes of clay minerals—especially bentonites—brought about local reef death.

Diagenetic processes of dissolution, recrystallisation and compaction greatly modified the original fabric of the reefs.
SEDIMENTATION IN THE ICE‐CONTACT ENVIRONMENT, WITH EXAMPLES FROM SHROPSHIRE (ENGLAND)
Authors: SHAW J.
Published: June 2006

Glacial sedimentation is assigned to two environments, the pro‐glacial and the ice‐contact. This paper is concerned with sedimentation in the ice‐contact environment. The sub‐drift topography of the area of study and the direction of ice movement are shown to be conducive to ice stagnation which is necessary for widespread ice‐contact sedimentation. Ridges of glacigenic sediment show faulted, collapsed margins and lateral kettle holes characteristic of ice‐contact landforms. The internal structure of these ridges is analysed in terms of primary and secondary sedimentary structure and texture. The spatial distribution of sedimentary structure and texture is shown to be similar to the fluvial models of Allen (1964) and Visher (1965). The absence of lateral extension of the fluvial members is interpreted as being due to stream training by ice walls preventing lateral migration. Large thicknesses of horizontal stratification and strongly unimodal palaeocurrent estimates are believed to be a result of this low sinuosity. Primary sedimentary structure and texture are used to designate facies. The distribution of the facies is thought to be diagnostic of the ice‐contact environment. Downstream facies migration is thought to have occurred as a result of changes in the ratio of sediment supply to stream power.
LINAER SAND BANKS IN THE SOUTHERN NORTH SEA
Authors: CASTON V. N. D.
Published: June 2006

The majority of the linear sand banks in the Norfolk Banks area of the southern North Sea are considered to be large‐scale mobile bed forms in dynamic equilibrium with the environment, thus confirming much of the earlier work of Houbolt (1968). Sand streams moving in opposing directions on either side of a bank are shown to be deflected to the right, upslope, and converge at the crestline, whilst the asymmetry of a bank is considered to be a reflection of the dominance of one of these streams. Convergence of sand streams causes an accumulation of sand which is believed to result in the continuing growth of the bank parallel to the direction of flow of the tidal currents. Migration of asymmetric banks is in the direction of the steeper side; the predominant direction is to the northeast, but it is suggested that the opposing movement of sand streams may magnify localized irregularities into a complex “S” shaped bank surrounding a pair of ebb and flood channels. The apices of this bank may eventually disappear, leaving a line of en echelon banks. Confirmatory evidence is forthcoming from a study of a linear sand bank lying off the Belgian coast, and it is suggested that the general sequence of bank development may be of far wider application.
GENESIS OF LAMINATED SAND AND GRADED RHYTHMITES IN STORM‐SAND LAYERS OF SHELF MUD
Authors: REINECK H. E. , SINGH INDRA B.
Published: June 2006

The formation of laminated sand and graded rhythmites — so‐called storm‐sand layers — found embedded in shelf mud is discussed. With decreasing energy of a storm, the sand eroded on the coast is transported away by the retreating waters into the open sea, and is retained in suspension because of the high wave energy of the rough sea. With decreasing wave energy, the individual suspension clouds settle, forming parallel sand layers. As generally only slow bottom currents are present, the sediment deposited is not reformed into ripples, but sedimented in the form of laminated sand.
STRUCTURE AND PROCESS IN A BRAIDED RIVER
Authors: RUST BRIAN R.
Published: June 2006

The Donjek is a proglacial braided river with a coarse heterogeneous bedload ranging from −7 to +8 φ. The three reaches studied comprise, in downstream order, a zig‐zag reach formed by the interaction of the river and tributary fans, a straight reach, and a meandering reach, all with internal braids. The straight to meandering junction is unusual in that slope and discharge both increase.

The dominant bed‐forms are longitudinal gravel bars, which migrate only during flood. Their internal structure is poorly defined horizontal bedding, which suggests that gravel deposition takes place on the upper bar surfaces, rather than on foreset slopes at the downstream margins. At lower stage sand accumulates in wedge‐shaped units lateral to the bars, with internal high‐angle cross‐stratification and ripple cross‐lamination; other sedimentary structures are rare. A simple facies model can be constructed on the basis of two trends: a proximal‐distal trend, and an active‐stable trend. Both result in the increased abundance of fine‐grained sediment.

Random directional measurements give good estimates of the river trend from small‐scale structures (mainly ripples) and from channels, the latter giving the closest approximation. The variability of ripple orientation always exceeds that of channels. Both increase in the meandering reach, although the divergence of the vector mean from the river trend is not significantly greater than in the straight reach.
ORIGIN AND DISTRIBUTION OF CALCAREOUS FINES ON THE CAROLINA CONTINENTAL SHELF
Authors: MOLNIA BRUCE F. , PILKEY ORRIN H.
Published: June 2006

The fine carbonate fraction (less than 63 μ in diameter) in 175 sediment samples collected from the Carolina continental margin has been studied. This fraction, generally under 5% of the total sample, averages 43% CaCO3. By comparison, the CaCO3 fraction of the total samples averages only 25%. On the inner shelf, the percentage CaCO3 in the fine fraction is twenty or more times greater than the percentage CaCO3 in the total sample. With increased distance offshore, the percentages of CaCO3 in the fine fraction and the total sample approach equality. Beyond the shelf break the percentage of CaCO3 in the total sample is greater than that in the fines.

The CaCO3 faunal components are primarily foraminifera, fragments of foraminifera, mollusc‐barnacle fragments and echinoid material. Minor constituents include alcyonarian and tunicate spi‐cules, Halimeda and other calcified green algae. Many grains are bored and show solution effects. The coarse carbonate fraction shows distinct regional faunal assemblages, but the fines are essentially uniformly distributed. Two exceptions are a zone of mollusc fragments around Cape Hatteras and a foraminifera zone on a portion of the outer shelf. The average carbonate mineral assemblage consists of 44% low‐Mg calcite, 38% aragonite and 18% high‐Mg calcite. The principal modes of origin of calcareous fines on the Carolina continental margin are probably biological and physical destruction of coarser particles and primary formation in fine size fraction (as in the case of some foraminifera).
EVOLUTION OF ROCK COMPOSITION AND GEOCHEMICAL PROCESSES IN THE SEDIMENTARY SHELL OF THE EARTH*
Authors: RONOV A. B.
Published: June 2006

Analyses of the chemistry of the earth's sedimentary shell (and the crystalline crust) reveal evolutionary trends in sedimentary rock composition, depositional environments, and the intensity and relative importance of geochemical processes. Successive changes in the mode of crustal movement, the intensity of volcanic and intrusive activity, and in the structural plan of continents (reduction of the area of active geosynclines, increase of the area of platforms) caused a regular transformation of the petrographic composition of ancient erosion areas and corresponding changes in the composition of terrigenous material that at different stages was supplied to depositional areas (gradually lower amounts of greywacke, decrease of average Na, Mg, Fe and Al content, inverse development of K and Ca). Sediment‐composition and lithological proportion in the sedimentary shell changed in the course of time: the abundance of volcanogenic rocks decreased, the abundance of carbonates and evaporites increased, the types of prevailing carbonate accumulation changed (siderite→dolomite→calcite), the degree of compositional differentiation of terrigenous sediments increased. These changes were accompanied by regular evolutionary changes in the chemical composition of the most important sedimentary rock types: the lowering of average Na and Fegen contents, the increase of Corg, Ssulf and Spyr concentration, the inverse K development, the increase of the Ca/Mg ratio, the rise of the iron oxidation degree, the displacement of isotope ratios of oxygen and sulfur, etc.

A definite trend in the development of the main types of sedimentary geochemical processes is established. The processes of clastogenesis and hydrolysis developed inversely: the importance of the first process decreased, but that of the second increased in the course of time. The intensity of oxidation and precipitation processes also increased through time; chemical precipitation was predominant during the early development stages, and biogenic precipitation predominated during the later stages. Characteristic boundaries in the evolution of sedimentary rock composition and geochemical processes are traced, which correspond to the boundaries A and Pt1, Pt1 and Pt3, Rf3 and V, Pz3 and Mz. Discontinuous variations in the concentrations and ratios of elements in sediments and in the intensity of some geochemical processes are confined to these boundaries. They were determined by changes in the composition of erosion areas, by the increasing importance of platform types of sedimentary processes, by large changes in the biosphere, by the evolution of the atmosphere and ocean composition, and by changes in the types of surface equilibria in the dynamic system: atmosphere‐ocean‐stratisphere.
AUTHIGENIC QUARTZ PRESERVING SKELETAL MATERIAL
Authors: RICHTER DETLEV K.
Published: June 2006

Authigenic quartz crystals formed within skeleton walls frequently contain carbonate inclusions which may characteristically differ from the composition of the skeletons. Whereas the skeletons suffered diagenetic alteration, the inclusions in the quartz crystals were more or less preserved and thus may indicate the original composition of the skeletons, provided the quartz crystals formed not too late in diagenesis. Because they generally grew after the aragonite‐calcite transformation, original aragonite skeletons are characterized by low‐Mg calcite inclusions in the quartz crystals whereas original high‐Mg calcite skeletons differ clearly by the Mg‐content of the inclusions. There is no difference between inclusions within quartz of original low‐Mg calcite and transformed aragonite skeletons, but the former skeletons are well and the latter are poorly preserved.

By this method, it is shown that Paleozoic Stromatopora and Actinostroma as well as Triassic Ammonoidea presumably were composed of aragonite, whereas the shells of articulate brachiopods (Stringocephalus, Terebratula, Rhynchonella, Gigantoproductus) were composed of low‐Mg calcite. The skeletons of Crinoidea (Devonian, Muschelkalk, Jurassic) and of Devonian rugose and tabulate corals, however, were composed of high‐Mg calcite.
AN INTERPRETATION AND ANALYSIS OF RECUMBENT‐FOLDED DEFORMED CROSS‐BEDDING
Authors: ALLEN J. R. L. , BANKS N. L.
Published: June 2006

Three main kinds of syndepositional deformation are found in cross‐bedded sand‐grade sediments. The first type is characterized by simple recumbent folds of broadly parabolic form. The second is marked by series of folds, with or without overturning. The third type is much more complex, presenting a combination of faulting, folding, and the local destruction of bedding.

The type marked by recumbent folds is interpreted as due to the deformation of a liquefied (or perhaps fluidized) sand by current drag following an event in the majority of cases suspected to be an earthquake shock. By reference to empirical and theoretical studies of sedimenting systems, and the behaviour under small shear stresses of liquids of high viscosity, this physical model is developed analytically to yield equations describing the geometry of the deformations in terms of the thickness of the deformed bed, the settling velocity and concentration of particles in the liquefied sand, the viscosity of the liquefied sand, and the magnitude of the deforming force. The equations describe a fold surface that is a portion of a flat‐lying parabola, and show that the proposed circumstances of deformation are plausible in terms of what is known of the real situation. They further reveal that, under the assumptions made in the analysis, the vertical height of the fold hinge above the base of the bed is a function only of the initial shape of the deformed cross‐stratum, the shear rate in the liquefied materials, and the falling velocity and concentration of particles in the liquefied bed. The shapes of deformations calculated from the equations agree well with patterns observed from the geological record.
OBSERVATIONS NOUVELLES SUR LA STRUCTURE DE LA GLAUCONIE EN ACCORDEON (“VERMICULAR PELLETS”); DESCRIPTION DU PROCESSUS DE GENESE DE CES GRANULES PAR NEOFORMATION
Authors: ODIN G. S.
Published: June 2006

Since Galliher's studies on the sediments from the Monterey bay (California), vermicular pellets have been considered to be derived from mica flakes by a transformation phenomenon. Generally, it is considered that all the glauconite pellets result from the transformation of degraded smectitic‐ or illitic‐type sheets into more ordered sheets. In the present study, it is shown that the vermicular pellets cannot be derived from the transformation of a mica flake. The mass obtained is several orders higher than the initial mass. Secondly it is noticed that the transformation process invoked do not allow for the continuing existence of the sheets. Finally, the ions of the micaceous sheet are never involved in the “transformation”, for sometimes they are found intact in the vermicular pellet. A study carried out through an electron microscope by reflexion indicates that there is crystal growth between the mica sheets. These sheets are merely a support favourable for glauconite neoformation. If the ions of the mica flake are involved in this genesis to any extent, they yield only a very low quantity of the mass of the final granule. As in the cracks of quartz grains, in feldspar cleavages or in limestone pores, the important surface constituted by the mica sheets is a catalyst for glauconite neoformation.
RAPID FIELD TECHNIQUE USING SPRAY ADHESIVE TO OBTAIN PEELS OF UNCONSOLIDATED SEDIMENT
Authors: YASSO WARREN E. , HARTMAN ELLIOTT M.
Published: June 2006

A synthetic rubber base spray adhesive was used to obtain high‐relief, rapidly drying peels of moist unconsolidated beach sand. Samples from vertical planar trench walls and box coring devices were obtained instantaneously and completely hardened in about fifteen additional minutes, with drying times dependent primarily on air temperature. This technique can also be used for preservation of sediment‐core structures in the laboratory.
GEOCHEMICAL HISTORY OF THE CRYSTALLINE BASEMENT AND THE SEDIMENTARY COVER OF THE RUSSIAN AND NORTH AMERICAN PLATFORMS—A DISCUSSION
Authors: SCHWAB FREDERIC L.
Published: June 2006

Ronov and Migdisov (1971) very effectively document and explain the apparent compositional evolution of the shield and platform rocks of the world in terms of secular changes in source composition, the mode and intensity of weathering (in turn a reflection of secular variations in the composition of the biosphere, atmosphere, and hydrosphere), and compositional differentiation resulting from repetitious episodes of granitization, metamorphism, erosion, and sedimentation. Based on modifications of my own analysis of geosynclinal sediment compositions (Schwab, 1971), I suggest some additional comparisons and interpretations (Fig.1, Table I).
EXEMPLES DE DIAGENÈSE SOUS‐MARINE DANS LES SÈDIMENTS PLIOCÈNES ET PLÉISTOCÈNES: DOLOMITISATION, FERRUGINISATION (MÉDITERRANÉE NORD‐OCCIDENTALE, SUD DE MARSEILLE)
Authors: FROGET CLAUDE
Published: June 2006

L'article présente une étude minéralogique et pétrographique de fragments rocheux pliocènes et pléistocènes recueillis sur le sommet de la pente continentale. Cette étude amène à distinguer trois groupes: Pliocène dolomitisé non ferrugineux, Pléistocène dolomitisé et ferrugineux, Pléistocène ferrugineux non dolomitisé. La diagenèse s'est effectuée en milieu sous‐marin. Les processus de dolomitisation sont discutés. La ferruginisation est rapportée au lessivage de sols riches en fer (limons rouges) élaborés sur le continent lors des périodes interglaciaires. Ces données sont utilisées pour tenter de classer les échantillons dans une chronologie relative.
Clastic sediments associated with radiolarites (Tauglboden—Schichten, Upper Jurassic, Eastern Alps)
Authors: SCHLAGER WOLFGANG , SCHLAGER MAX
Published: June 2006

During the early Upper Jurassic, widespread deep‐sea radiolarites were deposited in most parts of the Northern Limestone Alps. In the formation described (Tauglboden‐Schichten), these pelagic sediments interfinger with local‐source clastic material. Depending on the topography and the kind of material, either slides and slumps, mudflows, grain flows or turbidity currents operated and formed slump‐folded beds, mud‐flow breccias, fluxoturbidites or turbidites.

A breccia had been traced over an area of 20 km2. Its variation is described in terms of lithological columns, bed thicknesses, maximum grain sizes and grain orientations. It forms a tongue‐shaped body, which was probably a part of a submarine fan. The fluxoturbidites of the proximal area grade distally on three sides into turbidites within 3–5 km.

The clastic material consists of marls and limestones of Rhaetian and Jurassic age. It was probably derived from a tectonically uplifted palaeo‐high by an interplay of tectonics and gravity. The clastics were deposited on submarine fans bordering this high.

In its lithology the formation closely resembles certain marginal facies of flysch troughs.
Markov chain analysis applied to an ancient alluvial plain succession
Authors: MIALL ANDREW D.
Published: June 2006

Markov chain analysis is a comparatively simple statistical technique for the detection of repetitive processes in space or time. Coal measure cyclothems or fluvial fining‐upward cycles are good examples of sedimentary successions laid down under the control of Markovian processes.

Analyses of stratigraphic sections commence with a transition count matrix, a two‐dimensional array in which all possible vertical lithologic transitions are tabulated. Various probability matrices may be derived from this raw data, and these are then subjected to chi‐square tests to determine the presence or absence of the Markov property. This technique is applied to four types of stratigraphic succession which occur in the Devonian rocks of Prince of Wales Island, Arctic Canada.

(1) A conglomerate succession of alluvial fan origin. Markov analysis is of little or no assistance in the interpretation of these rocks, in which only two principal lithologies are present.

(2) A conglomerate‐sandstone succession. Fluvial fining‐upward cycles are detectable by visual examination of the sections and are strongly indicated by Markov analysis.

(3) A sandstone‐carbonate succession, of marginal marine origin, and including both marine and non‐marine strata. Cyclicity is weak in these rocks, but analysis suggests that regressions took place much more rapidly than transgressions during their period of deposition.

(4) A succession in which the relative proportions of the various lithologies vary markedly with age. The varying nature of the cyclic tendencies is emphasized in this case by dividing the succession into two subintervals, for the purpose of analysis.
Effect of compacton on chemistry of solutions expelled from montmorillonite clay saturated in sea water
Authors: CHILINGARIAN GEORGE V. , SAWABINI C. T. , RIEKE HERMAN H.
Published: June 2006

The total mineralization of solutions squeezed out of montmorillonite clay saturated in sea water was determined at different overburden pressures. The subsequent fractions of expelled solutions were also analysed for various anions (Cl−, SO2‐4, HCO−3, F−) and cations (Na+, K+, Mg2+, Ca2+, B3+).

The results indicate that the concentrations of squeezed‐out solutions during the initial stages of compaction (at pressures up to 35 kg/cm2) are slightly higher than that of interstitial solution present initially. The concentration of squeezed‐out solution goes through a maximum, or at least remains constant, before starting to decrease with increasing overburden pressure.
Fragmentation of granitic quartz in water
Authors: MOSS A. J. , WALKER P. H. , HUTKA J.
Published: June 2006

Studies of grain fragmentation in natural streams have the limitation that the full size range of the debris produced is virtually unobtainable. Experiments described here for grain fragmentation in a rotating drum permitted the study of all of the debris, and a fragmentation load technique was used to relate experimentally and naturally fragmented material. The present investigation has been focused on granitic quartz.

Relatively gentle collective movement in water can cause significant fragmentation of coarse, nascent, granitic quartz grains. The debris produced by rotating in a drum a range of single sieve fractions, taken from gravel in the headwaters of a stream draining granite, had continuous size distributions down to (and probably beyond) 0·06 μm. Quartz was the dominant fragmentation product in all fractions down to 2 μm and present in finer fractions. When pebbles moved with sand in these experiments, breakage of the latter was greatly increased. In comparison with that of breakage, the effect of attrition on granitic quartz was negligible. At least a proportion of granitic quartz grains are subject to a fatigue effect as a result of impacts in water. Evidently they are thus progressively weakened prior to being broken. Size analysis of debris showed a significant break at 20 μ, suggesting some special production of quartz particles just below this size.

Granitic quartz is criss‐crossed with partially healed cracks acquired before the zone of weathering is reached. The wholesale breakage that affects it, particularly in pebbly streams, is largely due to the reopening of these cracks. Progressive fragmentation of this material must eventually reach a stage wherein grains comprising single original crack‐bounded volume elements are produced. Such grains, lacking significant internal weaknesses, must strongly resist further breakage. Possibly the preferential production of quartz grains just below 20 μm in size may represent an accumulation of these single, crack‐bounded volume elements.
Carbonate cementation of some Pleistocene temperate marine sediments
Authors: WEST IAN M.
Published: June 2006

Carbonate cementation of some carbonate and quartz sands in three raised beaches of temperate origins was investigated. The carbonate of the cements was found to have been derived from the dissolution of skeletal debris. The sandstones, so produced, now possess only low‐magnesium calcite, but the original sediments, like adjacent modern beach and blown sands, probably contained low‐magnesium calcite, aragonite and some high‐magnesium calcite, all of skeletal origin. In meteoric water the dissolution has occurred of all carbonate within minute, tubulelike, volumes of sand. Concurrent deposition in adjacent volumes of sand of low‐magnesium calcite formed cements that are irregularly nodular or uneven on a small scale. Aragonite within the minute nodules has been replaced paramorphically by low‐magnesium calcite. Additional local carbonate cements were formed at later dates, around and within solution pipes.
The distribution of strontium in limestones on Barbuda, West Indies
Authors: WIGLEY PETER
Published: June 2006

The Sr2+ content of Barbudan limestones is proportional to the aragonite content. The Sr2+ content of calcite which has replaced aragonite varies from 3000 p.p.m. in the youngest limestones to 50 p.p.m., average values are approximately 300 p.p.m.

The (mSr2+/mCa2+)L ratios from well waters within the limestone fall within the predicted values assuming KSrC∼0·1. The high (mSr2+/mCa)2+L ratios expected by a lower value of KSrC do not occur.

The build up of (mSr2+/mCa2+)L ratios seen in waters from Barbados is not seen in the well waters from Barbuda. The Sr2+ content of calcite is generally lower than is seen in Barbados, but similar to that seen in parts of the Miami Oolite. Diagenesis of aragonite in Barbudan limestones is probably occurring in a more open system than in Barbados.
Holocene sediments and magnetic stratigraphy from Lakes Zug and Zurich, Switzerland
Authors: THOMPSON R. , KELTS K.
Published: June 2006

Piston cores 7 m and 6.5 m long were collected from Lakes Zug and Zurich respectively. Radiocarbon age determinations, pollen assemblage zones and varve counts indicate dates of 5000–6000 years B.P. (Zug), and 12,000–13,000 years B.P. (Zurich) for the base of the cores. Declination of the magnetic remanence varies through 70° and inclination varies through 30°. Although the correlation with the geomagnetic secular variation curve covering the last 15,000 years as determined from Lake Windermere, England (Creer et al., 1972) is not precise, the results suggest that Lake Zug and Lake Zurich sediments have been recording the broad outline of past secular variations of the earth's magnetic field. Since intensity of magnetization and susceptibility correlate markedly with lithology, a detailed sediment stratigraphy is presented. The amount and texture of the detrital input appears to be a controlling factor for the natural magnetic remanence. Intensity varies from 90 μG in zones of organic, sulphide pigmentation and those with ultra‐fine laminations to 0.8 μG in impure lacustrine chalk. Susceptibility ranges from 9 μG/Oe in laminated, fine‐grained glacially derived muds to 0.5 μG/Oe in impure lacustrine chalk. Intensity of magnetization also varies systematically within individual turbidites with lowest values in the coarse‐grained, basal fractions. Slumped beds were identified on the basis of erratic anomalies in magnetic declination and inclination measurements.
Regularities of rare‐earth element distribution in the sedimentary shell and in the crust of the earth
Authors: RONOV A. B. , BALASHOV YU. A. , GIRIN YU. P. , BRATISHKO R. KH. , KAZAKOV G. A.
Published: June 2006

After summarizing the vast analytical material it was possible to establish the differences in rare‐earth element (REE) distribution in geosynclines and on platforms. It is shown that the heavier REE composition in sediments of geosynclines and the lighter one in sediments of platforms was initially created by processes of endogenic differentiation and then inherited by sedimentary series of these zones. On the basis of the calculation of the REE content in rocks of various shells of the Earth crust the increase of the role of heavy lanthanides into the depths of the crust is shown. The obtained estimate of REE abundance in the lithosphere led to the conclusion that the crust of our planet, despite the repeated reworking of its matter by sedimentary processes, metamorphism and granitization, has inherited features peculiar to products of tholeiitic magmatism—the most widely spread type of mantle fusion.
Lithofacies relations in the Late Quaternary Niger Delta complex
Authors: OOMKENS EPPO
Published: June 2006

A study of cores from thirty‐three coreholes drilled in various parts of the Niger delta has shown tidal channel sand to be the dominant lithofacies type in the uppermost 30 m of the deltaic complex. Below 30 m fluviatile sand becomes predominant. Coastal barrier sand is present in the uppermost 5 m of the present coastal belt, but chances for preservation of this lithofacies appear to be small.

The Post‐Glacial deltaic sediments can be divided into three units.

Alluvial valley‐fill sands and conglomerates deposited during the strong Post‐Glacial sea level rise.

An onlapping complex of lower coastal plain deposits which contains a lower member of fine grained lagoonal and mangrove swamp deposits and an upper member of tidal channel and coastal barrier sands. This complex is thought to have been deposited during the strong Post‐Glacial rise in sea level and is locally as much as 25 m thick.

An offlapping complex of fluviomarine and coastal deposits which contains a lower member of marine clay and silt and an upper member of tidal channel and coastal barrier sand. The presence of this late Holocene complex indicates that deltaic progradation was resumed as soon as the rapid rise in sea level slowed down. The offlapping complex is locally as much as 35 m thick.
Measurements of sand transport by wind on a natural beach
Authors: SVASEK J. N. , TERWINDT J. H. J.
Published: June 2006

Bagnold's (1954) and Kawamura's (1951) formulae may be used for the calculation of the sand movement on a natural beach, provided the shear stress velocity U* > 0·D4 m/s. Great discrepancies have been found between calculated and measured sand transport rates for U* < 0·D4 m/s, mainly because of the capillary forces acting on a wet beach.

The measured critical shear velocity U*c at the beginning of sand movement on a clean dry beach agrees very well with that predicted by Bagnold's formula. On a dry beach where the sand grains are stuck together, U*c was found to be about 10% higher. On a wet beach U*c appeared to depend on the moisture content of the surface layer. Grain size is a determining parameter in the U*c‐moisture content relation.

When the angle a between the wind direction at sea and the dune face is between 15° and 85° the streamlines of the wind will bend in the vicinity of the dune face. In consequence this may influence the direction of sediment movement.
Diagenetic history of a North Sea chalk
Authors: MAPSTONE N. B.
Published: June 2006

A study of the petrofabrics of Danian and uppermost Maastrichtian chalk from the North Sea was undertaken to investigate its particulate components and diagenetic history.

Danian and Maastrichtian chalks are intensely mottled and burrowed globi‐gerinid lime mudstones. The Danian chalk matrix is composed of coccolith and thoracosphaerid debris, whereas the Maastrichtian chalk matrix contains mainly coccoliths. The lower part of the Danian is often argillaceous.

Three modes of lithification are evident—a spot‐welding of adjacent grains (important in Danian chalk), selective overgrowths (prolific in Maastrichtian chalk), and a sparry calcite pore filling associated with Maastrichtian stylolitization.

Not only does the scant cementation of chalk stem from an inadequate source of metastable calcium carbonate in the form of aragonite, but also indirectly in that extensive pressure‐solution is impeded by certain pore fluid compositions. Pressure‐solution can occur only at point contacts where a threshold linear pressure is exceeded and so allows an increase in calcite solubility. It is proposed that through the formation of spot‐welds an initial rigid intergranular framework is constructed in chalk relatively early during diagenesis. Subsequent increases in overburden eventually permit extensive stylolitization and the late diagenetic reprecipitation of a sparry calcite pore filling adjacent to stylolites. The time and genesis of selective overgrowths is less clear.
Sedimentology and petrology of Quaternary sediments from the Hellenic Trench, Mediterranean Ridge and the Nile Cone from D.S.D.P., Leg 13, cores
Authors: BARTOLINI C. , MALESANI P. G. , MANETTI P. , WEZEL FORESE C.
Published: June 2006

Fifty‐three samples from D.S.D.P. Sites 127, 128 (Hellenic Trench), 130 (Mediterranean Ridge) and 131 (Nile Cone) ranging in size from clayey silt to sand were submitted to grain‐size and compositional analyses. The former confirmed the evidences obtained from the visual observation of the sedimentary features as to the presence of turbidites (Sites 127, 128, 131) and fluxoturbidites (Site 131). The cumulative frequency distributions of the latter are closely similar to those obtained from ancient deposits of the same type.

The X‐ray quantitative analyses of the total samples showed that at both Site 127 and Site 128 calcite and phyllosilicates make up together, on average, about two‐thirds of the total composition. Quartz averages about 20%. Dolomite, plagioclase and K‐feldspars are present subordinately in this order; the former, observed in all samples, is both detrital and authigenic. In the Nile Cone quartz comprises, on average, about 70% of the composition. Phyllosilicates, plagio‐clases and K‐feldspars were observed in minor quantities.

The four samples of the Mediterranean Ridge, although Nile derived, show a composition closer to the Hellenic Trench samples than to the Nile Cone. This is due to the strong control exerted by the grain size on the quantitative mineralogical composition. The microscopic analyses carried out on both light and heavy minerals of the sand fraction and the clay mineralogy clearly differentiate between the Hellenic Trench and all the Nile derived sediments (Sites 130 and 131) and exclude an intermixing of even the finest fractions. Each group is well clustered in the compositional diagrams. The Hellenic Trench sediments could be classified as lithic arenites (Crook, 1960) or greywackes (Malesani & Manetti, 1970) and the Nile Cone sediments as sublabile lithic feldspathic arenites or feldspathic subgrey‐wackes.

The semi‐quantitative clay mineralogy showed that, on average, almost 50% of the Nile derived clay sized sediments is montmorillonite. Mixed layer minerals make up a relevant part of the remaining fraction. In contrast, the Hellenic Trench sediments show lower quantities of montmorillonite (about 10%) and prevailing percentages of illite and chlorite. Kaolinite is present only in the latter samples and not in the Nile Cone sediments.

The lack of relevant changes in the composition of the Nile Cone sediments along the cored sections of the holes suggests that the present hydrography of the Nile River dates from at least the Lower Pleistocene.
Sealers Bay submarine fan complex, Oligocene, southern New Zealand
Authors: CARTER ROBERT M. , LINDQVIST JON K.
Published: June 2006

The Oligocene Balleny Group of Chalky Island, southwestern Fiordland, comprises a typical continental margin sequence 900 m in thickness. Thin nearshore traction deposited sediments at the base are overlain by submarine canyon and fan lithofacies that were deposited by the full range of subaqueous mass‐transport processes. A steep‐walled channel within Balleny Group is interpreted as a fossil proximal fan‐channel. The sedimentary fill of the channel is texturally similar to sediments moving by slump‐creep in Recent submarine canyons and fan‐valleys. The field data presented indicate (1) that a small canyon complex at Sealers Bay was initially cut by subaqueous debris‐flows derived from an adjacent cliffed continental coast; (2) that transport within the upper parts of the canyon and fanchannel complex was primarily by inertia‐flow and slump‐creep; and (3) that these more proximal types of mass‐transport gave way gradationally and successively to fluxoturbidity and turbidity currents at locations further down‐slope, with consequent deposition of sediment in more distal fan‐channel and fan‐surface environments as fluxoturbidites and turbidites, with lesser contributions from inertia‐flows.
Measurements of density underflows from Walensee, Switzerland*
Authors: LAMBERT ANDRÉ M. , KELTS KERRY R. , MARSHALL NEIL F.
Published: June 2006

Speed and direction of bottom currents induced by density underflow of two sediment‐laden rivers were measured by oceanographic current meters in the Walensee (= Lake of Walenstadt), Switzerland. The apparently shooting flow of currents (up to 30 cm/s in this study) is suggested as an explanation for laminations in turbidite sequences. The current speed apparently stabilizes on slopes around 2°; this angle seems to correspond to the critical slope where the flow of the measured currents becomes steady. Current direction is controlled by bottom topography and direction of river inflow. Reversal of current direction observed at two sites is probably due to the underflow‐induced backward motion of the overlying lake water. Underflow activity in Walensee is correlative with density peaks of the river water input. The currents are compared to Lake Mead (Southwestern U.S.) underflows and sporadic currents in some submarine canyons.
Cycles and subsidence: their relationship in different sedimentary and tectonic environments in the Scottish Carboniferous*
Authors: READ W. A. , DEAN J. M.
Published: June 2006

Ten data sets have been collected from stratigraphical intervals in the Upper Carboniferous of Central Scotland. They represent six structural units and both distal and proximal deltaic environments, plus a meandering river environment. All show a definite tendency towards a linear relationship between the number of deltaic or fluvial cycles and the total thickness of strata in the interval. This relationship is, however, much stronger in sequences laid down in actively subsiding depositional basins than in areas where subsidence is thought to have been controlled by block faulting in the basement or in areas where there is no clearly defined pattern or subsidence. With respect to facies, the relationship is less close in successions that were frequently affected by widespread marine transgressions.

The slopes of linear regression lines fitted to the data sets vary much more than had hitherto been supposed. Thus they are no longer thought to provide possible evidence of some ubiquitous underlying process, such as ductile flow in the upper mantle, which affected all the structural units equally. The line which represents proximal deltaic deposits of Westphalian A age in the Kincardine Basin slopes twice as steeply as any of the eight lines representing other dominantly deltaic successions and considerably more steeply than the line representing a succession of Namurian fluvial cycles.

Second‐ and third‐degree polynomial regression lines were also fitted to each data set but these generally satisfy little more of the total variation than do the corresponding linear regression lines, and F‐test results indicate that the gains are not statistically significant. Eight of the second‐degree lines however share a common shape that suggests a general tendency for both deltaic and fluvial cycles to be somewhat thicker in the areas of greatest net subsidence.
Grain size variations in ignimbrites and implications for the transport of pyroclastic flows
Authors: SPARKS R. S. J.
Published: June 2006

Ignimbrite flow units commonly show reverse grading of large pumice clasts and normal grading of large lithic clasts. Ignimbrites show coarse‐tail grading, in which particles beneath a critical diameter, ranging from 64 to 2 mm, are ungraded. Above this size the larger the clast diameter the more pronounced the segregation. The grading is consistent with the theoretical settling rates of particles in a dispersion with a high particle concentration. Ignimbrite flow units show a reversely graded, fine grained basal layer which is attributed to the action of boundary forces during flow. Ignimbrites are commonly associated with cross‐stratified pyroclastic surge deposits and fine ash fall deposits formed in the same eruption. The fine ash fall deposit is depleted in crystals and is thought to be the deposit of the fine turbulent cloud observed making up the upper parts of nuées ardentes.

Pyroclastic flows are postulated to be dense, poorly expanded partly fluidized debris flows. Only its fine grained components can be fluidized by gas. Pyroclastic flows are believed to behave as a dispersion of larger clasts in a medium of fluidized fines, which acts as a lubricant similar to water in mud‐flows. Poor sorting in ignimbrites is attributed to high particle concentrations not turbulence. Many pyroclastic flows may be laminar in their movement with apparent viscosities, deduced from the lateral grading of large lithic clasts, in the range 101−103 poise.