bluuebunny/crossref_metadata_2025_split huggingface dataset:
COCCOLITHS: IMPORTANT ROCK‐FORMING ELEMENTS IN BITUMINOUS SHALES OF CENTRAL EUROPE
Authors: MÜLLER GERMAN , BLASCHKE ROCHUS 
Published: June 2006

ABSTRACTCoccoliths 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

ABSTRACTExamination 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

ABSTRACTConcretions 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

ABSTRACTHalite 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

ABSTRACTStatistical 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

ABSTRACTSemi‐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

ABSTRACTAll 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

ABSTRACTSediments 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

ABSTRACTAn 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

ABSTRACTWe 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

ABSTRACTMagnesian 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

ABSTRACTThe 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

ABSTRACTPyrenean 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

ABSTRACTThe 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

ABSTRACTWholesale 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

ABSTRACTMineralogical 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

ABSTRACTGrey 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

ABSTRACTTwo 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.