bluuebunny/crossref_metadata_2025 huggingface dataset:
GRAIN‐SIZE IMAGE OF CLASTIC DEPOSITS
Authors: PASSEGA R. , BYRAMJEE R.
Published: June 2006

A clastic deposit is represented by several diagrams. C‐M diagrams in which C is the one‐percentile, M the median of the grain‐size distribution, characterize the coarsest fractions of the samples. F‐M, L‐M and A‐M diagrams in which F, L and A, respectively, are the percentages by weight in the samples of grains finer than 125, 31 and 4 μ characterize the finest fractions. As a group, these diagrams form the “grain‐size image” of a deposit.

The above parameters were selected because they are closely related to transport and deposition mechanisms. As a consequence, the grain‐size image gives fairly precise information on hydraulic conditions under which a deposit is formed.

A large number of deposits were compared by means of their grain‐size images. This comparison shows that some texture characteristics are related to the environment of deposition while others are controlled by basin mobility. Mobility should, therefore, be considered when comparing sediments of different basins and particularly recent and ancient sediments.

Relationships which exist between certain sizes of clastic grains and the most probable deposition mechanism are used to classify clastic sediments by subdividing them into types indicative of their genesis.

Grain‐size types can be represented on maps and cross‐sections. Grain‐size facies maps of ancient formations represent lateral variations of texture and of hydraulic conditions across all basin environments and do not necessitate a reconstruction of these environments, which, often, is questionable. These maps, sell suited to show and project sedimentary trends, complete conventional isopach and sand/shale ratio maps. Integrated with ecological determinations and sedimentary structure descriptions, grain‐size facies maps are a means of environment analysis.
GRAIN SIZE OF TURBIDITE RIPPLES
Authors: KUENEN PH. H. , HUMBERT F. L.
Published: June 2006

Many, but not all, current ripples show log‐normal grain‐size distribution and good sorting (P. D. Trask). A range in medians was measured from fifty to several hundred microns. Turbidite ripples are log‐normal, very well‐sorted and are restricted to medians of very fine sand to silt (< 130 μ) because the particles have been supplied in suspension at rippling velocity. Experimental suspension current ripples formed at about 50–60 cm/sec are similar in composition and structure to turbidite ripples. The continuous supply results in climbing ripples. The restricted grain size and the internal structure of turbidite ripples both form strong evidence against the action of normal currents. The number of grain‐size analyses is still rather small.
A PYRITIZED LIMESTONE HARDGROUND IN THE LOWER JURASSIC OF DORSET (ENGLAND)
Authors: HALLAM A.
Published: June 2006

SUMMARY

Detailed documentation and interpretation is given of a thin band of limestone nodules in the Lower Lias of Dorset, which has been subjected to early lithification, exhumation on the sea bed and incrustation and boring by organisms in a more turbulent and shallow‐water regime than that of deposition. Final burial has been followed by extensive pyritization. The stratigraphical gap during which these events took place is less than two ammonite zones.
STRUCTURAL AND TEXTURAL EVIDENCE OF EARLY LITHIFICATION IN FINE‐GRAINED CARBONATE ROCKS
Authors: ZANKL H.
Published: June 2006

SUMMARY

Absence of compaction, intraformational breccias, resedimention, internal sediments and synsedimentary hardgrounds indicate early lithification of finegrained carbonate rocks. One of the factors controlling early lithification is the purity of lime mud. Less than 2% of insoluble residue (especially clay minerals) favours cementation and recrystallisation before further sediment accumulation causes compaction. Thus, early lithification is terminated in or near the environment of sedimentation. “Electrodiagenesis” is considered to be a possible mechanism for cementation.
THE DISTRIBUTION OF CLAY MINERALS IN THE OCEANS
Authors: RATEEV M. A. , GORBUNOVA Z. N. , LISITZYN A. P. , NOSOV G. L.
Published: June 2006

In order to obtain data comparable to those of Biscaye (1965) on the Atlantic Ocean, the authors carried out quantitative X‐ray determinations of clay minerals in the sediments of the Indian and Pacific oceans using the Biscayemethod.
MINERALOGY AND CHEMISTRY OF TONSTEINS FROM CARBONIFEROUS SEQUENCES IN GREAT BRITAIN
Authors: PRICE N. B. , DUFF P. McL. D.
Published: June 2006

Tonsteins from Westphalian Coal Measures in England are compared mineralogically and chemically with tonsteins of volcanic origin from coalbearing sequences of Namurian and Westphalian age in Scotland. Differences are apparent between tonsteins occurring as partings within coals (“coal tonsteins”) and those interbedded with inter‐seam sedimentary rocks (“non‐coal tonsteins”). The coal tonsteins show higher titanium values and in some cases contain minerals of the goyazite series. Sedimentological, mineralogical and chemical evidence is reviewed and the conclusion reached that all tonsteins examined could have originated as thin layers of volcanic ash. Subsequent alteration depended upon the environment of deposition into which the ash fell.
THE OBLIQUE ASDIC AND ITS USE IN AN INVESTIGATION OF A MARINE HIGH‐ENERGY ENVIRONMENT1
Authors: DOBSON MAX
Published: June 2006

Methods whereby an Asdic may be used empirically to examine the sea bed are discussed. They indicate that on flat sea bottoms the effects of impedance and attenuation combine to produce a record usually distinctive enough to broadly classify the sediment over which the vessel is passing. These methods were used to interpret an area of unconsolidated sand, gravel and mud in the region of Arklow off the east Irish Coast. Echo‐sounder traverses and sea bed sampling were also employed to assist with the interpretations. The sea bed is composed of dissected residual gravels covered in places with mobile sand displaying a great variety of high‐energy bed forms. Mechanisms of sub‐littoral sediment circulation, based largely on the bed forms recognized in the Asdic records, are also discussed.
A BURET CYLINDER FOR GRAIN‐SIZE ANALYSIS OF SILT AND CLAY (WITH ALGOL‐PROGRAM)
Authors: FABRICIUS F. , MÜLLER ST.
Published: June 2006

A new apparatus, the “buret cylinder”, was constructed in order to increase the efficiency of the size analysis of fine‐grained sediments. Its uncomplicated operation and automatic levelling enables working in series of ten samples or more at a time. This method, an improvement of the “pipet method”, works with an accuracy comparable to that of the “Atterberg method”.

An ALGOL‐program was compiled to compute all data, obtained from the granulometric analysis of the entire sediment. In the output, the numerical parameters are printed out and a simple frequency and a cumulative diagram is plotted. The computer program works for grain sizes from −6 phi (64 mm φ) to +9 phi (2 u φ). Two procedures can be applied alternatively: (a) sieving—buret analysis; and (b) sieving—visual accumulation tube—buret analysis.
FACIES OF AN EARLY MIOCENE VOLCANIC ARC, MALEKULA ISLAND, NEW HEBRIDES
Authors: MITCHELL A. H. G.
Published: June 2006

On Malekula Island pre‐Miocene pelagic red mudstones are in tectonic contact with a thick marine succession of Early Miocene age, which is intruded by basaltic and andesitic dykes and sills with a calc‐alkaline composition and by plutons. This succession is in faulted contact with Middle Miocene sedimentary rocks.

The Lower Miocene succession consists of quartz‐free volcanoclastic rocks, detrital limestones and pelagic sediments, and rare lava flows. Fifteen sedimentary facies have been recognized, all of which accumulated below the zone of strong wave or current action. Vertical changes in facies are common; facies relationships and associations and internal sedimentary structures indicate that many facies were transported by mass gravity processes. Texture and composition of clasts in the volcanoclastic rocks show that some facies were derived from subaerially erupted volcanic rocks, and others from submarine volcanoes. Clastic limestones consist largely of algal and coral fragments and benthonic foraminifers.

The Lower Miocene palaeogeography resembled that in and around volcanic chains in present island arcs. Subaerial and submarine volcanoes fed by minor intrusions supplied epiclastic, pyroclastic and autoclastic debris which accumulated in deep water around the volcanic chain. Carbonate detritus was derived from reefs bordering the volcanic islands.

The Middle Miocene succession consists of volcanic and reef‐derived turbid‐ites, pelagic sediments and tuffs. The epiclastic rocks in this succession were derived from the uplifted rocks of Early Miocene age and from bordering reefs.

The presence of some ancient volcanic arcs, now located either within existing ares or within geosynclinal successions lying in or on the borders of continents, may be indicated only by quartz‐poor turbidites containing abundant calc‐alkaline volcanic detritus.
DOWNCURRENT TEXTURAL CHANGES IN ORDOVICIAN TURBIDITE GREYWACKES
Authors: PARKASH BARHAM , MIDDLETON GERARD V.
Published: June 2006

Longitudinal and vertical variation in grain orientation and size has been studied in eight turbidite greywacke beds from the Cloridorme Formation (Middle Ordovician), Gaspé, Quebec, Canada. The beds are exposed on a wave‐cut platform near Grande Vallée, Gaspé. These beds were traced for about two miles along the strike (276°), which is almost parallel to the average current direction (274°) as indicated by sole marks.

Agreement between grain orientation and other internal current‐direction indicators such as graptolites and intra‐bed lineation shows that grain fabric is primary in nature and that grains are typically aligned parallel to the current direction. Grain orientations are generally statistically non‐significant in the upper massive part of the beds in the proximal region and significant in the rest of the beds. Most of the significant grain orientations are close to the sole direction in the proximal region and deviate from the sole direction by as much as 90° in the distal region. Grain orientations are increasingly divergent from the base towards the top of the bed. Current‐normal grain orientations are observed in a plane‐laminated part of a bed.

The beds show a good grading in the proximal area and are ungraded or slightly reverse graded in the distal area. These grading characteristics are exhibited by both the mean and maximum grain size. Most beds show no appreciable variation in the mean grain size at the base of the bed along the strike. However, for one bed, the largest mean size at the base occurs in the middle of the outcrop and grain size decreases from this point both in the upstream and downstream directions.
COMPARISON OF POST‐SEDIMENTARY ALTERATIONS OF OIL‐, GAS‐ AND WATER‐BEARING ROCKS
Authors: YURKOVA R. M.
Published: June 2006

One of the productive horizons (17th) of north Sakhalin has been studied. The areas within and beyond oil and gas pools, near the top and at the flanks of structures were compared with areas where the horizon under study was waterbearing. The rocks were least transformed by secondary processes within oil accumulations, where a sudden increase was observed in the content of feldspars and accessory minerals (epidote, ilmenite and sphene) which had not undergone intrastratal solution. Inside gas pools, however, no deceleration of epigenesis has been observed. This points to a more recent (post‐Pliocene) accumulation of gas, whereas the first oil migration in these Miocene strata occurred in the Upper Pliocene, according to the hampered epigenesis.
THE VARIABILITY OF MICACEOUS MINERALS IN SEDIMENTARY ROCKS
Authors: KOSSOVSKAYA A. G. , DRITS V. A.
Published: June 2006

Relationships between crystal chemistry and genetic conditions are presented for a series of dioctahedral micaceous minerals. Using a ferruginicity index, three groups of micaceous minerals are distinguished: Al‐micas, Fe‐illites, and glauconites. The degree of Al‐for‐Si substitution in the tetrahedral sheets of micaceous minerals depends on their thermodynamic genetic conditions. If pressure and temperature increase, the Al‐IV content increases and the octahedral sheet is “cleaned” from divalent cations. This process is accompanied by structural alteration with a polytype sequence 1Md‐1M‐2M1. Tetrahedral and octahedral charges are the same for micaceous minerals formed at the surface (sedimentogenesis/diagenesis) and are independent of the iron content. For most illites of sedimentary rocks an authigenic origin is suggested.
EXPERIMENTAL STUDY OF THE SORPTION OF POTASSIUM BY MONTMORILLONITE
Authors: MURAVYOV V. I. , SAKHAROV B. A.
Published: June 2006

Experimental studies on saturation of montmorillonite with potassium showed that sorption of potassium tends to produce a regular alternation of the interlayer regions.

The sorptive nature of the potassium fixation by montmorillonite appears to form the basis of the epigenetic formation of rectorite.
LONGITUDINAL DUNES OF THE NORTHWESTERN EDGE OF THE SIMPSON DESERT, NORTHERN TERRITORY, AUSTRALIA, 1. GEOMORPHOLOGY AND GRAIN SIZE RELATIONSHIPS
Authors: FOLK ROBERT L.
Published: June 2006

Origin of the longitudinal dune form is reviewed. The spectacular longitudinal dunes of the Simpson desert are caused by helicoidal wind flow of the prevailing south‐southeastern winds, acting upon ancient alluvial plains. Critical in this theory is the evidence from tuning‐fork junctures, which open upwind as do similar features in other geologic realms of primarily one‐directional currents undergoing second‐order helicoidal circulation.

A summary of previous work on using grain size to distinguish beach from dune sands reveals the consistent good sorting and positive skewness of coastal dunes. Simpson desert dunes are also positively‐skewed, but are not as well sorted as coastal dunes because they are only recently derived from poorly‐sorted alluvial source sediments. Dune crests are coarsest and best sorted because they are made out of the most easily saltated fine sand (about 2.5 ø); windward flanks, leeward flanks, and reg are progressively finer and also show regular and explainable changes in the higher‐order grain‐size parameters. Both dune and reg sediments are made of polymodal mixtures, giving rise to a “quantum theory” of aeolian deposition.
SLUMPING ON A CONTINENTAL SLOPE INCLINED AT 1°–4°
Authors: LEWIS K. B.
Published: June 2006

Continuous seismic profiles from the upper continental slope east of North Islands, New Zealand, show that surface sediment 10–50 m thick has slumped down bedding planes sloping at 1°–4°.

There are four slumps, the Kidnappers Slump which has an area of 250 km2, the Paoanui Slump of 80 km2, a small slump of only several square kilometers and a slump of undetermined extent. All occurred during the last 20,000 years in Last Glacial Age sediments. A glide plane is exposed at the head of each slump and beds are thrust or contorted at the toe of some slumps.

Slumping was probably caused by the failure of loosely packed sandy silt during major earthquakes.
CORRELATION OF SEDIMENT CORES ON THE BASIS OF THEIR MAGNETIZATION
Authors: HEYE DIETRICH
Published: June 2006

Sediment cores originating from the Indian and the Atlantic Ocean were investigated. The declination of the cores was measured non‐destructively. In both regions it was possible to correlate several cores on the basis of their magnetization (intensity correlation in contrast to correlation of paleomagnetic reversals). Additional layers of turbidity‐currents and a layer of volcanic material were detected.
EFFECT OF CLAY ON THE ACCURACY OF THE HYDROMETER METHOD
Authors: MADHAV M. R. , SUBRAMANYA K.
Published: June 2006

Even small colloidal clay fractions in suspension affect markedly the results from a hydrometer test. The discrepancies are due to non‐consideration of specific gravity and relative viscosity of the actual clay‐water suspension. Therefore, actual—i.e., experimentally or otherwise determined—values of specific gravity and relative viscosity should be used instead of the conventionally used values for the specific gravity and the coefficient of viscosity. Expressed in terms of this study, in equations 1 and 2 the values of G1 and n should be replaced by G11 and nr, respectively. Another simple but time‐consuming remedy is to remove the clay content from the soil by repeated decantation before conducting the hydrometer analysis.
TEXTURAL DIFFERENTIATION ON THE SHORE FACE DURING EROSIONAL RETREAT OF AN UNCONSOLIDATED COAST, CAPE HENRY TO CAPE HATTERAS, WESTERN NORTH ATLANTIC SHELF
Authors: SWIFT DONALD J. P. , SANFORD ROBERT B. , JR CHARLES E. DILL , AVIGNONE NICHOLAS F.
Published: June 2006

In order to evaluate a model of Holocene shelf sediment distribution requiring a nearshore modern sand facies and an offshore relict sand facies, we have undertaken a textural reconnaissance of the Virginia‐North Carolina Coast between Capes Henry and Hatteras. Grab samples were subjected to grain‐size analysis by means of a modified Woods Hole Rapid Sediment Analyser. Textural provinces were erected with the aid of factor vector analysis. These include medium‐grained sands of the beach and surf zones; seaward fining, fine‐grained sands of the shore face, and heterogenous sands of the sea floor. In this latter province, grain size is controlled by a ridge and swale topography, with coarser sand on the crests. Coast‐wise grain‐size trends on the beach and shore face can be explained by assuming that wave heights increase toward the south, and that the Pleistocene sediment source is exposed higher on the shore face in the north than it is in the south. The shore face is retrograding, except in the vicinity of Diamond Shoals. There is textural evidence for a former Albemarle River channel, which bisects the study area. A model for sediment fractionation on a retreating barrier coast with low sediment input is proposed, based on studies which indicate that on such coasts: (1) barrier superstructures retreat more or less continuously by upper shore‐face erosion and storm washover; and (2) lower shore‐face erosion results in an equal‐volume aggradation of the adjacent sea floor, and forms the leading edge of the Holocene transgressive sand sheet. The nearshore “modern” sands and offshore “relict” sands are both present in the study area, but the terms are unnecessarily restrictive. Both are “relict” in the sense of being derived from a Pleistocene substrate, and both are “modern” in the sense of having undergone adjustment to a modern hydraulic regime. While modern and relict are useful general terms, it is convenient in this area to refer to a Holocene barrier sand prism, versus a Holocene transgressive sand sheet.
COCCOLITHS: IMPORTANT ROCK‐FORMING ELEMENTS IN BITUMINOUS SHALES OF CENTRAL EUROPE
Authors: MÜLLER GERMAN , BLASCHKE ROCHUS
Published: June 2006

Coccoliths are the main constituents of the carbonate layers in several Oligocene bituminous shales as well as in the Oligocene “Helle Mergelkalke” limestone, Upper Rhine Graben and Bavarian Molasse Trough.
MICROTEXTURES OF PARTICLES FROM SOME EUROPEAN LOESS DEPOSITS
Authors: CEGLA J. , BUCKLEY T. , SMALLEY I. J.
Published: June 2006

Examination of loess particles with the scanning electron microscope (SEM) allows several previously unresolvable features to be distinguished. SEM observations confirm that the majority of loess particles are angular but reveal a distinct proportion of rounded particles. Most particles have very fine particulate material adhering to their surfaces and virtually all show signs of surface attack to a greater or lesser degree. Contrary to some published statements it appears that European loess particles tend to show signs of weathering.
THE GROWTH OF CAMBRIAN AND LIASSIC CONCRETIONS
Authors: RAISWELL R.
Published: June 2006

Concretions from Upper Cambrian sediments in South Wales can be divided into two groups of different ages. An early group (type) are characterised by the association of septarian structures and deformed laminae; whilst later (type Ha) concretions developed both cone‐in‐cone structures and parallel laminae.

Determinations of the cement content of individual concretions revealed centrifugal variations related to the porosity changes within the sediment during concretionary growth. Growth of type‐I concretions began in sediment of approx. 70% porosity and continued until compaction had reduced the porosity to less than 40%. Later, type‐IIa concretions began growth in sediment of approx. 30–40% porosity and experienced only slight compaction over their growth spans.

Liassic concretions from a prolific concretionary horizon in Dorset developed parallel laminae, but grew early in the absence of compaction (type IIIb) concretions at this horizon grew within the sediment during a pause in deposition.

Evidence is described for distinguishing between concretions formed in systems open or closed to seawater. It is concluded that Cambrian concretions grew in closed systems, but the early Liassic concretions may have developed in a partially open system.

A model is offered to explain the closed system growth of prolific concretionary horizons. The Cambrian concretions often proliferated along 2–3 cm thick siltstone units, which it is suggested were more permeable than the surrounding mudstones and therefore became pore‐water migration paths. Along these migration paths concretionary growth may have relieved the supersaturation of mobile pore waters.
POSSIBLE DISPLACIVE HALITE IN THE PERMIAN UPPER EVAPORITE GROUP OF NORTHEAST YORKSHIRE1
Authors: SMITH DENYS B.
Published: June 2006

Halite lying above the potash‐rich interval of the Permian Upper Evaporite Group of northeast Yorkshire, England, is intimately associated with fine red clastics in such a way as strongly to suggest that the former originated by nucleation and growth within the latter. It is inferred that this process took place in distal sediments of a mature basin‐margin plain, probably in a belt subject to repeated inundation caused by periodic large‐scale expansions and contractions of an extensive basin‐centre playa. Such an environment is consistent with the generally shallow‐water to continental origin of the underlying Carnallitic Marl and the overlying Permian Upper Marls, and contrasts with the deep‐basin depositional model customarily applied to the Zechstein evaporites.
SIMPLE METRIC SEDIMENTARY STATISTICS USED TO RECOGNIZE DIFFERENT ENVIRONMENTS
Authors: And A. T. BULLER , McMANUS J.
Published: June 2006

Statistical data computed from analyses of present‐day sediments may be useful for the recognition of ancient environments. Phi‐based measures may be used for the separation of sands. An arithmetic technique is suitable for suites of samples with a considerable range of grain sizes. This paper presents a re‐exploration of arithmetic scales and statistical measures which may facilitate environmental recognition. To test this technique, analyses from approximately 800 samples were used. Quar‐tile and median values were substituted into Trask's arithmetic measures of quartile deviation QDa and skewness Ska. Values of QDa were plotted against the median M/d mm on double‐log paper for four environments. On each graph the plots indicate a linear trend and both the positions and slopes of the individual trend curves are different. There is a decrease of gradient of the curves in the sequence: aeolian‐fluviatile‐beach‐ “quiet‐water”. Values of QDa against Ska were plotted similarly, the gradients of the curves decreasing in the reverse sequence. Thus each set of curves (QDa vs. Md mm; QDa vs. Ska) establishes a method for comparing and differentiating sediments from these environments.
CLAY MINERALOGY OF BLACK SEA SEDIMENTS
Authors: STOFFERS PETER , MÜLLER GERMAN
Published: June 2006

Semi‐quantitative clay. mineral analysis was carried out on the clay and silt fractions of approximately three hundred Black Sea core samples. Relative abundance of montmorillonite, illite, kaolinite and chlorite was determined.

Illite is the most frequent clay mineral in the Black Sea surface sediments. Highest values are obtained in the northern and central Black Sea. Approaching the Anatolian coast, the illite portion gradually decreases at the expense of montmorillonite. Chlorite and kaolinite occur generally only in small quantities. The lateral changes in the composition of the clay minerals can easily be traced back to the petrology of a northern (rich in illite) and a southern (rich in montmorillonite) distributive area.

In almost all cores a periodical fluctuation of the montmorillonite/illite ratio with depth could be observed which may be related to the changing influence of the two distributive provinces during the Holocene and Late Pleistocene (Würm). Higher montmorillonite contents indicate arctic and subarctic climate periods in the northern distributive area during which the illite supply was diminished to a large extent.
GRADED‐BED SEQUENCES EMPLACED BY TURBIDITY CURRENTS NORTH OF 20°N IN THE PACIFIC, ATLANTIC AND MEDITERRANEAN1
Authors: HORN D. R. , EWING J. I. , EWING M.
Published: June 2006

All core evidence supports the conclusion that abyssal plains are sites of graded‐bed sequences deposited from turbidity flows. The deposits appear to be present‐day equivalents of thin‐ to medium‐bedded, graded, flysch‐type sands and silts of many ancient geosynclines and sedimentary basins.
THE ORIGIN OF FERROMANGANESE SEDIMENTS ASSOCIATED WITH THE TROODOS MASSIF OF CYPRUS
Authors: ELDERFIELD H. , GASS I. G. , HAMMOND A. , BEAR L. M.
Published: June 2006

Sediments within and immediately above pillow lavas of the Troodos Massif of Cyprus show abnormally high concentrations of iron, manganese, arsenic and copper. Most likely they contain precipitates related to volcanism along a Tethyan rise. In addition, silica has been leached from lavas and has partly remobilized to form chert layers above the ferromanganese sediments. As a result of hydrothermal activity some horizons are enriched in copper, lead, zinc and nickel, and manganese and arsenic have been mobilized in the sediment column.
DISTINCTION OF ELEMENTARY SAND POPULATIONS IN THE GIRONDE ESTUARY (FRANCE) BY R‐MODE FACTOR ANALYSIS OF GRAIN‐SIZE DATA
Authors: ALLEN GEORGE P. , CASTAING PATRICE , KLINGEBIEL ANDRE
Published: June 2006

An R‐mode factor analysis was made on the grain‐size classes of the sediments in the Gironde estuary in order to group the sieve sizes into dynamically significant factors. It was found that three main groups of sand populations exist within the distributional province investigated. Comparison with previous works suggests that each group reflects a specific transport mechanism. The main group boundaries are the same as those observed on the log‐probability cumulative size curves of the sediments. The three main groups consist of the following sizes: finer than 3.0 Φ, 3.0 Φ‐0.6 Φ, and coarser than 0.6 Φ. The three groups are thought to represent respectively “pure” (or uniform) suspension transport, mixed suspension bed‐load, and “pure” bed‐load (surface creep) transport. Furthermore, a subdivision exists in the mixed‐suspension‐bed‐load group: the sediments between 3.0 Φ and 2.0 Φ seem to represent a “graded suspension” transport while the sizes between 2.0 Φ and 0.6 Φ are thought to represent “saltation” (graded suspension plus bed‐load). All the samples containing more than 5% of the surface creep population plot either as “graded‐suspension plus rolling” or as “rolling” in the CM pattern of the sediments.
Depositional theme of a marginal marine evaporite
Authors: BOSELLINI ALFONSO , HARDIE LAWRENCE A.
Published: June 2006

We have reconstructed the depositional environment of the gypsum‐carbonate‐shale sequence that comprises the Upper Permian Bellerophon Formation of the southeastern Alps in northern Italy. This formation, which reaches a maximum thickness of 600 m, is roughly divided into two facies: (a) a lower dolomite‐gypsum facies, and (2) an upper micritic‐skeletal limestone facies. It directly overlies, with transitional contact, a thick red‐bed sequence (alluvial fanglomerates, fluviatile sandstones and flood‐plain siltstones) and is sharply overlain by Lower Triassic calcarenites (oolites, grapestones, pellets, flat‐pebble conglomerates).

The lower evaporite facies rocks are found in well‐defined cycles, each of which, from bottom to top, consists of (A) thin‐bedded, worm‐burrowed, vuggy ‘earthy’ micritic dolomite, (B) massive to poorly laminated dark grey to black sandy dolomite carrying isolated gypsum nodules, (C) layered (thin‐bedded) nodular gypsum (commonly with ‘enterolithic’ folds) with fragmented partings of dolomite, and (D) massive ‘chicken‐wire’ nodular gypsum. At Passo di Valles, just east of Predazzo, and 50 km from the basin margin, we measured forty‐six consecutive complete cycles, with an average thickness of 3 m per cycle.

We interpret the cyclic sequence as having been deposited in a prograding shallow lagoon—sabkha complex. The worm‐burrowed ‘earthy’ dolomite mud accumulated in a shallow hypersaline subtidal lagoon. The black sandy dolomite was an ‘intertidal’ sand‐flat devoid of algal mats and constantly churned by burrowers (likely crustaceans). As the shoreline prograded lagoonward evaporative concentration of the groundwater induced diagenetic growth of anhydrite nodules (now gypsum) within the porous sandy dolomite. The layered nodular and ‘chicken‐wire’ gypsum of the cycle cap is an extreme product of such displacive intra‐sediment growth of anhydrite (now gypsum) above the water table of a completely exposed sabkha, such as is found in the Persian Gulf today.

We have observed the same cyclically arranged lithologies in two other evaporite sequences in Italy: the Triassic Raibl Formation of the Southern Alps and the Upper Triassic Burano Formation of the central Apennines. We suggest that this mode of deposition is likely a very common one for at least the early stages of marine evaporite accumulation.
Precipitation and lithification of magnesian calcite in the deep‐sea sediments of the eastern Mediterranean Sea*
Authors: MILLIMAN JOHN D. , MÜLLER JENS
Published: June 2006

Magnesian calcite is an important sedimentary component in the deep‐sea sediments of the eastern Mediterranean Sea, comprising an average of 20–50% of the carbonate fraction in most areas. The lack of any obvious biogenic source, plus similarities with magnesian‐rich lutites from the Red Sea and deep‐sea cements from other areas suggest that this magnesian calcite was precipitated inorganically.

Although the exact mode of precipitation is not understood at present, it probably occurred at the water‐sediment interface under elevated salinity and temperature conditions, such as those present in the modern eastern Mediterranean. Precipitation did not occur during periods of lower temperatures and/or salinities such as during the stagnant conditions caused by the influx of fresh waters from melting Pleistocene glaciers.

The eastern Mediterranean magnesium‐rich sediments appear to represent an intermediate stage between normal deep‐sea sediments and those from the warm hpyersaline Red Sea. Normal deep‐sea carbonates are composed almost entirely of biogenic calcite, whereas the Red Sea magnesian calcite alternates with layers of aragonite that were precipitated under elevated salinity and temperature conditions brought about by lowered stands of sea level.
Distribution and nature of incorporation of trace elements in modern aragonitic corals*
Authors: AMIEL ABRAHAM J. , FRIEDMAN GERALD M. , MILLER DONALD S.
Published: June 2006

The objective of this study is to locate as closely as possible the sites of strontium, magnesium, sodium, and potassium in modern aragonitic corals, specifically whether these cations are adsorbed, or are substituted in the carbonate lattice or are incorporated in organic components. In addition to locating the sites of each of these four elements we wanted to find out quantitatively how much of each element occurs at each site. The experiments in this study are based on the dissolution rate of aragonite in distilled water and on the substitution of strontium and magnesium by calcium and sodium. Special attention has been given to the occurrence of strontium, magnesium, sodium, and potassium in the organic components of the corals.

The main site for strontium in the corals is in the aragonite lattice. Twenty‐five per cent of the total magnesium occurs in adsorbed sites and in organic compounds. The rest of the magnesium may be located in the aragonite lattice, but it is easily removed by repeated leaching or by replacement with calcium ions. Another possibility is that magnesium may occur in a dispersed mineral phase more soluble than aragonite because magnesium was released at a higher Mg to Ca ratio than is found in the solid coral; also because no local concentration of magnesium could be detected with an electron microprobe. About 12% of the total sodium is in adsorbed sites and is included in the organic compounds. The rest of the sodium might be in the lattice replacing calcium, but the low total exchange capacity is not enough to provide the needed charge balance. Another possibility is that sodium is located in a proposed mineral phase. Potassium is in adsorbed sites and incorporated in the organic compounds to an extent greater than all the other elements studied (30% of the total potassium), but again the evidence suggests that the remaining potassium is in a proposed mineral phase.

Calcite is detected on the surfaces of aragonite corals after 5 months in the substitution experiment. The change of argonite to calcite took place after the inhibitor magnesium was exchanged from the surface sites and replaced by calcium.

The organic compounds in corals contain small amounts of strontium, magnesium, sodium and potassium. Strontium is preferentially enriched in the organic compounds over magnesium.
Miocene point‐bar deposits in the Ebro Basin, Northern Spain*
Authors: PUIGDEFABREGAS CAYO
Published: June 2006

Pyrenean debris dispersed in relation to the Miocene tectonic phase filled the northern part of the Ebro basin. In the studied area (50 km south of Pamplona) the Miocene sediments are represented by fluviatile sequences consisting of flood basin and point‐bar deposits forming fining‐upward cycles.

The point‐bar character of part of these sediments is not only evidenced by the internal sedimentary structures, but also by the fact that the corresponding meander bends, about 200 m in radius, are clearly visible on aerial photographs. In this way a unique opportunity is given to compare directly the vertical profile and the surface pattern of ancient small size point bars.

The internal structure consists of many imbricated and concentrically arranged bundles corresponding to the accretional topography of the point bar. The separation planes between the bundles are erosional and dip toward the channel axis. The internal structure of each bundle is festoon mega‐cross‐stratification whose direction points toward the convex bank, away from the channel axis. The resulting structure resembles the Epsilon cross‐stratification of Allen (1965a) and its origin is the same as postulated by Allen for this kind of cross bedding.
Experimentally produced halite compared with Triassic layered halite‐rock from Cheshire, England
Authors: ARTHURTON RUSSELL S.
Published: June 2006

The experimental evaporation of brine in shallow vessels shows that layered halite can form by the overgrowth of crystals in mats that have foundered from their initial position of growth at the brine‐air interface; by the upward and lateral growth of crystals that have nucleated on the floor; and by the overgrowth on detrital halite. Each of these processes, and its resultant crystal fabric, is described in relation to the environmental factors which influence it.

The fabrics of primary halite crystals in layered halite‐rock and associated deposits from the Lower Keuper Saliferous Beds of the Cheshire Basin are described and compared with those of the experimentally produced halite. Some of the ancient halite‐rock may be matched with floor‐nucleated crystals, and some with detrital halite; none can be shown to have grown from foundered mats. The halite‐rock is regarded as having formed in shallow brine bodies, perhaps only a few centimetres deep, but of unknown extent, whilst the presence of planar solution or deflation surfaces at the top of the layered units, and disruptions in bedding similar to buckled salt‐crust structures, point to periodic and perhaps prolonged emergence.
Holocene meteoric dolomitization of Pleistocene limestones, North Jamaica
Authors: LAND LYNTON S.
Published: June 2006

Wholesale removal of the unstable carbonate phases aragonite and Mg‐calcite, and precipitation of calcite and dolomite is currently taking place where phreatic waters (the modern water table) invade 120,000‐year‐old Pleistocene biolithites (Falmouth Formation), North Jamaica.

Pleistocene rocks presently in the vadose zone are relatively unaltered, and consist of mineralogically unstable scleractinian biolithites. At the water table, a narrow zone of solution, a ‘water table cave’ is commonly encountered. Below the water table the rocks are invariably more highly altered than those above. Mg‐calcites are very rare, and considerable dissolution of aragonite has commonly occurred.

Dolomite occurs as 8–25 μm, subhedral to euhedral crystals replacing micrite, or precipitated as void linings. The isotopic composition of the dolomite (δO18=‐1·0 %0, δC13=‐8·4 %0), and its high strontium content (3000 p.p.m.) suggest precipitation as CO2‐oversaturated meteoric groundwaters invade the mineralogically unstable biolithites, dissolve Mg‐calcites and Sr‐rich aragonites, and de‐gas. Because some dolomitized rocks are enriched in magnesium relative to unaltered biolithites, addition of magnesium to the system is necessitated, and is probably derived from sea water in the mixing zone.

Phreatic meteoric diagenesis is thus demonstrated to be a rapid process, and to be capable of dolomitization.
Quantitative analysis of calcite and Mg‐calcite by X‐ray diffraction: effect of grinding on peak height and peak area
Authors: GAVISH ELIEZER , FRIEDMAN GERALD M.
Published: June 2006

Mineralogical analysis of calcite and Mg‐calcite by X‐ray diffraction requires that the samples be ground to a powder. Such grinding determines the particle size of the powder and the structural damage of the minerals. Both of these in turn affect the peak intensities recorded by the X‐ray machine. Most carbonate sediments are inhomogeneous; they contain both calcite and Mg‐calcite which are affected differently by grinding. Such differences cause quantitative analytical results to be inconsistent with the true mineralogical abundance. The two acceptable methods of analysis—(1) measurement of peak height from the base and (2) measurement of the area under the peak—were compared to determine if sample preparation affects the quantitative results. In samples with variable and relatively small amounts of calcite and Mg‐calcite the measurement of peak height yields more reproducible results than does the measurement of peak areas. Different proportions of particle size of the mineralogical components in a sample powder, affect proportionally more the peak areas than the peak heights. Extensive grinding causes structural damage of the component minerals which affects much more the peak areas than the peak heights. Thus for quantitative analyses of calcite and Mg‐calcite in inhomogeneous carbonate samples which require differing grinding times and have greatly variable amounts of calcite and Mg‐calcite, the peak height measurement seems to be a better method than peak area measurement.
Antidune and chute and pool structures in the base surge deposits of the Laacher See area, Germany
Authors: SCHMINCKE HANS‐ULRICH , FISHER RICHARD V. , WATERS AARON C.
Published: June 2006

Grey tuffs of late Pleistocene age form broad fans radiating from the Laacher See basin. They were derived from phreatomagmatic outbursts, and transported in turbulent pyroclastic flows, in contrast with the underlying white pumice tuffs of air fall origin. Flow origin of the grey tuffs is inferred from the well‐bedded plane parallel to cross‐bedded tephra characteristic of base surge deposits, and a variety of other sedimentary structures, as well as grain size distributions. We recognize a tentative sequence of five main kinds of dune structures or cross‐bedded strata. With some reservations these may be compared with the high flow‐regime alluvial bedforms produced experimentally in flumes.

Most of the cross‐bedded structures in the Laacher See deposits resemble antidunes, with steep stoss sides and very low‐dipping lee sides. Upcurrent migration of antidune crests is dominant close to the source, but changes to downcurrent migration at greater distances, presumably because of decay in flow energy.

The most spectacular cross‐bedding is somewhat similar to chute and pool structures formed under experimental condition in alluvial flumes, but not recognized in ancient sedimentary rocks. We suggest that these structures of the Laacher See tuffs formed during deposition from phreatic pyroclastic flows of very high flow energy and high sediment concentration. The antidunes apparently formed at lesser flow velocity than chute and pool structures, although interpretation of velocity conditions by examination of the deposits is difficult because of other factors such as the cohesiveness of wet material erupted by explosive phreatic volcanic activity. The large wave lengths of the dune‐like structures, however, suggest unusually high velocities. The Laacher See magmas were of phonolitic to tephritic composition, and may have erupted with greater explosive energy and in greater volume than comparable basaltic eruptions.
Pebble segregation and bed lenticularity in wave‐worked versus alluvial gravel*
Authors: CLIFTON H. EDWARD
Published: June 2006

Two aspects of bedding may permit visual discrimination between wave‐worked and alluvial gravel. Pebbles in gravel worked by waves tend to be better segregated into discrete beds than those in alluvial deposits, and bedding in wave‐worked gravel tends to be more laterally regular, or less lenticular, than that in stream gravel.

Pebble segregation and lenticularity were quantitatively analysed in twenty‐five different marine and fluvial deposits of Quaternary or Tertiary age in southwestern Oregon in order to evaluate their use as environmental indicators. The results indicate that these two factors combined provide a visual criterion for discriminating between many gravels of wave‐worked and alluvial origin.
Tide‐dominated offshore sedimentation, Lower Cambrian, north Norway
Authors: BANKS N. L.
Published: June 2006

The Duolbasgaissa Formation, Lower Cambrian, of northern Norway consists of 550 m of mineralogically and texturally mature sandstones with subordinate siltstones, mudstones and conglomerates. Four facies are defined on the basis of grain size, bed thickness and sedimentary structures. Facies 1–3 consist of a variety of erosively‐based, cross‐stratified and parallel‐stratified sandstones interbedded with siltstone and mudstone. Many of these sandstones show evidence of deposition from waning currents. Facies 4 consists of trough cross‐bedded sandstones with sets up to 4 m thick. Symmetrical ripples and bioturbation are ubiquitous. Bipolar palaeocurrent distributions are common to all facies and one mode is usually strongly dominant.

Lateral facies variations and sedimentary structures suggest that deposition took place in a tide‐dominated, offshore, shallow marine environment in which maximum sediment transport probably occurred when storm generated waves enhanced tidal currents.

The four facies are thought to represent the deposits of various parts of tidal sediment transport paths such as exist in modern seas around Great Britain. Small scale coarsening upward sequences may represent the superposition of facies independently of changing water depth. Lack of information prevents a detailed palaeogeographic reconstruction. It is suggested that sand body shape is not accurately predictable.
Settling behaviour related to sieve analysis of skeletal sands
Authors: BRAITHWAITE C. J. R.
Published: June 2006

One thousand grains selected from sieved samples of a bioclastic sand have been individually measured, weighed and timed in free unhindered fall at terminal velocity in a 250 cm column of sea water.

Four fall regimes are represented: straight fall, spinning and spiral modes and erratic tumbling. As size increases grains pass through this series at rates dependent upon shape and effective density.

Computed best‐fit curves for velocities/intermediate diameter and an equivalent sphere/intermediate diameter illustrate considerable divergencies in behaviour between the eleven grain types and five shape classes examined. Current methods of analysis of carbonate sediments, by sieving, by grain‐counting of components, and by sedimentation balance, provide different kinds of information which it is impractical to consider as having any simple relationship to each other.
High voltage electron microscopy of fine quartz particles from Norwegian marine clay
Authors: SMALLEY I. J. , MOON C. F.
Published: June 2006

The high voltage electron microscope allows the internal structure of fine quartz sediment particles to be examined. With high accelerating voltages sufficient penetration is obtained for actual particles to be directly examined in the transmission mode. Dislocations have been observed and also various substructures—indicated by Moire patterns—some of which may be due to Dauphine twinning. Some areas of great distortion have been observed at particle edges, but a certain degree of crystallinity appears to be retained.