bluuebunny/crossref_metadata_2025_split huggingface dataset:
GRADED RHYTHMIC BEDDING IN THE CAPE EEAR FORMATION, CAROLINA COASTAL PLAIN
Authors: HERON S. DUNCAN , SWIFT DONALD J. P. , DILL CHARLES E. 
Published: June 2006

SUMMARYThe Cape Fear Formation rests on basement rocks in the Cape Fear River valley of the North Carolina Coastal Plain. It consists primarily of graded muddy sand—sandy mud couplets. A typical sequence for each couplet starts with a disconformity, followed by a basal gravelly sand with megaclasts of quartz and clay pebbles, cross‐bedded sand, and finally a structureless mud bed. Fossils are absent. The sand fraction is poorly sorted and the sediment has a clayey texture. Structures and textures suggest that each couplet is the product of a current waning from an upper flow regime, to the lower part of a lower flow regime. Turbidity current and fluvial origins are considered. Cross‐bedding and textural criteria indicate that normal, low‐density currents are responsible for at least part of the typical sequence. A normal fluvial origin is rendered less likely by the absence of mud cracking, root casts, and textural criteria of a partitioned subaerial environment. Stratigraphic and geochemical considerations suggest that the formation may have been deposited in estuaries or coastal lagoons; if so, the stratification may record sedimentation during the periodic flushing of saline water by river floods.
SOME EXPERIMENTS ON THE GENESIS OF TURBIDITY CURRENTS
Authors: VAN DER KNAAP W. , EIJPE R. 
Published: June 2006

SUMMARYTurbidity currents are thought to be the agency responsible for the transport and deposition of the sediments known as turbidites. The way in which such currents may arise has been studied experimentally in a glass‐walled tank.The starting point of the experiments was setting the sediments in motion by raising their pore pressure via a shock or vibration. This was achieved in the experiments by striking the metal bottom of the tank with a mallet.The response of a heap of homogeneous sand to such a shock was merely to change the angle of its slope. If a layer of sand was draped over a core of coarser, homogeneous sand, sliding occurred along the plane of permeability contrast and the less coarse sand was deposited at the toe of the slope. When the layer consisted of kaolin, which has a much lower permeability than sand, sliding again took place, but the clay subsequently mixed with the water and was moved along the bottom of the tank in the manner attributed to turbidity currents.An attempt is made to set up a scaling rule for experiments of this type and the consequences that such a rule may have in subsequent study are briefly discussed.
WEATHERING AND ROUNDNESS OF QUARTZ SAND GRAINS
Authors: CROOK KEITH A. W. 
Published: June 2006

SUMMARYPhotographs and descriptions of quartz sand grains from soils, paleosols and silcretes show that grain shape can be modified by solution in situ. Dissolution is attributed to solutions rich in organic molecules present in weathering profiles, and commonly results in rounding of protuberances and re‐entrants on grains. The incidence of this process may vary with climate. It is postulated that solution rounding during weathering plays an important role in shaping quartz sand grains in general, its significance varying with climate. This postulate, which remains unconfirmed, has considerable implications for the interpretation of textural maturity of sandy sediments. If true, super‐mature sands may be as much a climatic indicator as an indicator of tectonic quiesence.
AN OPTICAL METHOD OF MEASURING GRAIN ORIENTATION IN SEDIMENTS
Authors: WINKELMOLEN A. M. , VAN DER KNAAP W. , EIJPE R. 
Published: June 2006

SUMMARYA new method is presented for the measurement of grain orientation in clastic sediments.The method is based on the principle that when an inclined beam of light passes through an elliptical hole in a plate of a certain thickness, the amount of light passing through depends on the orientation of the long axis of the ellipse with respect to the direction of incidence of the light beam. If such a plate is rotated in its own plane, the amount of light passing through will fluctuate. Such fluctuations are larger the greater the eccentricity of the ellipse, the amount of light passed being maximal when the long axis coincides with the plane of incidence of the light.If the plate contains many holes, which need not be elliptical but for the ease of reasoning can be approximated by ellipses, their main orientation direction can be inferred from the maximum intensity of passed light.It is shown in the paper that results of a similar kind can be obtained by using a black and white picture of the grain packing in combination with a mirror. These pictures can be obtained either from thin‐sections or from printed replicas of etched polished sections of impregnated samples.The resulting data represent an integrated orientation pattern instead of a long‐axis distribution pattern as given by the grain‐by‐grain counting technique.The new method has been thoroughly checked against the visual counting method. Excellent agreement was observed.
PARTICLE SHAPE AND INFERENCE OF SIZE FROM SIEVING
Authors: LUDWICK JOHN C. , HENDERSON PATRICIA L. 
Published: June 2006

SUMMARYAccurate particle‐size measurement by sieving requires that consideration is given to particle shape and screen opening size variations. The effect of particle shape has been studied by determining experimentally the probability of passage through each of five woven‐wire screens of 35 different mm‐sized ellipsoids. These range in shape from T/D= 0.2 to 1.0 and from L/D= 1.125 to 2.625, where T is particle thickness, L is particle length, and D is particle intermediate diameter. Passage tests were performed for both static and dynamic conditions of sieving.A mathematical sieving theory stemming from the idea of particle passing probability is developed. The theory is put to use by computer‐simulated sieving of idealized input samples of simple shape make‐up. When near‐spheres are sieved it is found that a bar‐type histogram is a justifiable depiction. For some other more realistic shape inputs, what is obtained are broad, overlapping bell‐shaped fraction distributions considerably offset from the nominal openings of the limiting screens. For these distributions, conventional representation in histogram form is incongruous.The treatment presented contains allowance for screen opening size variations. Some apparently polymodal distributions are probably explainable as a result of unsuspected differences between the screens used and an ideal screen series.
DIAGENETIC RE‐CRYSTALLIZATION AND ORIENTATION OF TWO CARBONATE SPECIES
Authors: ATTEWELL P. B. , HIRST D. M. , TAYLOR R. K. 
Published: June 2006

SUMMARYResults of X‐ray textural studies of dolomite and the clay minerals in the Marl Slate and of siderite from the top of the Mansfield Marine Band are interpreted in terms of the possible diagenetic development of the re‐crystallized carbonates in these two rocks. From computer processed (1014) fabrics of the two trigonal carbonates it is deduced that there is a c‐axis preferred orientation concordant with the normal to the stratification. An early diagenesis in this oriented mode must be a function of both a threshold stress difference in a non‐hydrostatic stress field (in effect a necessary minimum depth of burial) and also of the presence of connate solutions. The existance of a minor percentage of dolomite oriented with the rhomb faces parallel to the stratification probably reflects an even earlier crystallization within the top few metres of sediment, when the confining pressures and pressure differences were of insignificant amplitude. It is concluded that a higher rate of sedimentation associated with the Coal Measure sequence is responsible for the singular preferred orientation of the siderite.
GRAIN‐SIZE INDICES, CLASSIFICATION AND ENVIRONMENT
Authors: DOEGLAS D.J. 
Published: June 2006

SUMMARYIndices based on Wentworth phi values of Q1, Md and Q3 are used for textural classification of sediments. Wentworth phi values enable a detailed subdivision. A nomenclature based on the Wentworth phi indices is developed. The indices, and to a smaller degree the names, show sorting and skewness based on integer phi units. The classification scheme gives a continuous scale from gravel to fine clay. The Q1MdQ3‐indices can be used for distinction of river, marine and loess deposits. The addition of indices of the 1st and 99th percentile, giving 5‐digit indices, augments the possibilities for a determination of the environment: river deposits can be distinguished from beach and dune sediments and in more detail from shallow marine and coastal deposits. The indices can be handled by data‐processing machines.
SUR LA CRISTALLINITÉ DE L'ILLITE DANS LA DIAGENÈSE ET L'ANCHIMÉTAMORPHISME
Authors: DE SEGONZAC G. DUNOYER , FERRERO J. , KUBLER B. 
Published: June 2006

SUMMARY On the crystallinity of illite in diagenesis and anchimetamorphism A simple method to estimate the degree of “crystallinity” of illite has been used for several years in three French laboratories. Many results, which are unpublished, were obtained; three examples are presented in this paper. They show the sensibility of the method, which allows one to appreciate, above all other methods, burial diagenesis, the front of metamorphism, or some regional areas of very weak metamorphism.
MORPHOLOGIE MATHÉMATIQUE ET GENÈSE DES CONCRÉTIONS CARBONATÉES DES MINERAIS DE PER DE LORRAINE
Authors: SERRA J. 
Published: June 2006

SUMMARY Matheinatical morphology and genesis of Lorraine iron ore carbonated concretions Mathematical morphology provides strong theoretical tools for the description of geological structures. Here, the intrinsic function of MATHERON'S (1965) regionalized variables theory, is used to describe a limestone migration phenomcnon, and the genesis of carbonate nodules in the sedimentary ore deposits of Lorraine. In this intrinsic function:
image

is x a moving point through the mineraliLed space v, and k(x) a boolean value associated to x. The characteristics of γ (h) represent the structure of the regionalisation k(x).This descriptive step leads to models of stochastic processes to interpret the genesis of those migrations. The theoretical models allow to resolve or to compute the intrinsic functions and to confront them with experimental data.In conclusion mathematical morphology ‐ the acute efficiency of which is manifest in the description of the evolutions ‐ appears to be unable to explain why those evolutions occur.The different steps of this study can be presented as follows. The beginning is shown by the pictures of Fig. I. White limestone concretions can be distinguished set against a dark background of iron ore. It is clear that the structure of the concretion is the same in Fig.lA and 1B though the two photos are different. How could this structural identity be measured?For this purpose we shall use the “variogram”‐concept of Matheron's theory (FORTET et al., 1953). The “regionalized variable” is the function k(x), of wich the value is 1 when x is in the concretions, and zero when not. “x” is a moving point through the mineralized space v. The intrinsic function, or “half variogram”, γ (h) is then:
image

which depends only on the vector h and not on the moving point x. y(h) represents an increment variance. It mathematizes the concept of the influence zone of the sample.The average “variogram” of Fig.1, and of a series of twelve photos taken in the same neighbourhood is giien by Fig.3B, in the vertical direction. The origin tangents of curves measure in each direction the diametral variation, whose average value in all directions of space represents the specific surface of concretions (cf. SERRA, 1966a). Practically the variograms do not increase after 50 cm in horizontal direction, and 25 cm in the vertical one. Those values mean average lengths of concretions in those directions. On the other hand, the curve of Fig. 3B represents a maximum, which reflects the limestone migration process itself.This last remark leads to the establishment of stochastic models of the genesis of limestone migration. Realisations of those random functions are giwn in Fig. 9A, B, C, D. Their variograms are similar to those of Fig.3A and 3B. Such a model is, therefore, an adequate representation of natural regionalization, and expresses the genetic hypothesis. This mathematical method finally allows an easy and clear translation of structural notions in a quantitative language.
THE PRESENT STATUS OF ZIRCON
Authors: SAXENA S.K. 
Published: June 2006

SUMMARYThe present writer (SAXENA, 1966) does not propose that the use of zircons in problems of stratigraphy, pedogenesis and petrology should be discarded. His conclusions (pp.30–31) make a plea for caution in such use. The writer suggests several possible modes of the origin of Lircons and by no means the authigenic mode of origin is more important than any other. Igneous or detrital zircons could certainly be used provided due consideration is given to other possible modes of origin. The solution does not lie in abandoning the use of zircons but an individual case is to be judged according to the local geologic evidence. It may be possible to find the genctic history imprinted on the morphological features of Zircons. Most of MARSHALL'S (1967) criticism is because of his failure to realize the broader genetic aspects of zircons.
RECENT LITTORAL AND SUBLITTORAL HIGH‐MG CALCITE LITHIFICATION IN THE MEDITERRANEAN
Authors: ALEXANDERSSON TORBJÖRN 
Published: June 2006

SUMMARYLithification caused by inorganic precipitation of high‐Mg calcite is reported from several localities in the Mediterranean. A micritic calcite cement with 13–15 mol. % MgCO3 in solid solution lithifies internal sediments and forms open‐space fillings within a sublittoral algal framework down to 20 m, in which the biogenic structures are gradually obliterated through the activity of numerous boring organisms and the subsequent precipitation of micrite. The silt‐mud fraction of unconsolidated bottom sediments is to a large extent stable low‐Mg calcite, and is not the source for the mcrite; instead the cementing mineral is assumed to precipitate directly from interstitial sea water. The special physico‐chemical régime is attributed to organism activities.The same phase of high‐Mg calcite also forms the cement in beachrock in the areas studied; also here the Mg‐content is an original property and not the result of diagenetic changes. The cement occurs partly as micrite, identical to the micrite in the lithified algal framework, and partly as radiating microspar fringes. The littoral and sublittoral lithification described here indicates that within several niches in the present marine environment high‐Mg calcite may substitute for aragonite as the mineral form of precipitated calcium carbonate.
HOLOCENE INTERTIDAL CALCIUM CARBONATE CEMENTATION, QATAR, PERSIAN GULF
Authors: TAYLOR J. C. M. , ILLING L. V. 
Published: June 2006

SUMMARYCemented layers in the shallow lagoonal, intertidal, and supratidal sediments surrounding the Qatar Peninsula, Persian Gulf, contain high‐magnesian calcite and aragonite cements. The magnesian calcite appears to occur both as a primary precipitate and as a replacement of aragonite. These cements are believed to be forming today from sea‐derived waters. Radiocarbon dating sets an upper age limit of about 4,500 years.Two major types of cemented layer can be distinguished: beachrocks form variably cemented units about 1 m thick at the surface of freely draining exposed beaches: cemented sheets a few cm thick form beneath the surface of broad intertidal sand flats by the growth, hardening, and coalescence of small friable lumps near low‐tide level. Replacement of aragonite matrix, druse, and pellets by microcrystalline magnesian calcite is accomplished by dissolution and reprecipitation; detail is obliterated but the gross features of the original fabric are preserved. The process helps to explain the crystal fabrics of many older limestones.
SUBMARINE LITHIFICATION OF HOLOCENE CARBONATE SEDIMENTS IN THE PERSIAN GULF
Authors: SHINN EUGENE A. 
Published: June 2006

SUMMARYLarge areas of the sea floor in the Persian Gulf are composed of lithified carbonate sediment. That this cementation is contemporaneous and occurs within the present submarine environment has been proven by carbon dating, the presence of pottery and other artifacts within the lithified sediments, and other methods.Although the chemistry of the processes resulting in lithification is unknown it would seem not to require any special conditions other than carbonate‐saturated sea water. The process seems to be operating in areas of relatively normal salinity and temperatures in depths ranging down to 30 m. It is deduced that the principal physical factors involved are relatively low rates of sedimentation, sediment stability, and high initial permeability of the sediments.The principal types of cement filling the intergranular spaces and locally replacing grains are aragonite (in several growth forms) and microcrystalline magnesium calcite. The aragonite cement seems to be unstable and has inverted locally to more stable calcite within the marine environment.Lithification results indirectly in the production of several characteristic macro‐structures, including superimposed bored surfaces, fine sediment overlying drusy cement, and several other features all of which in the past have been regarded as criteria for unconformity.
A METHOD TO STUDY THE DISTRIBUTION OF HEAVY‐MINERAL GRAIN ABUNDANCE IN A TURBIDITE
Authors: NORMAN TEOMAN N. 
Published: June 2006

SUMMARYRelative mineral frequencies (number or weight) are not suitable to study variations in the absolute frequencies of individual heavy‐mineral species in a turbidite. A particular grain size can be selected as the “nominal grain” and numbers of grains of a particular mineral in all size classes can be converted to nominal grains. The total number of nominal grains per gram of sediment sample has been defined as the “nominal grain abundance”, which is a function of the volume (or weight) of the total mineral in the sample.Study of a simple, graded, Tertiary turbidite indicates that the least vertical change in heavy‐mineral content occurs at, or slightly above, the middle part of the bed. Heavy minerals in the distal part of the turbidite have more uniform vertical distribution than in the proximal part.
DETACHMENT OF FIRST‐GENERATION CARBONATE CEMENT ON ONCOLITES BY CRYSTALLIZATION OF SECONDARY ANHYDRITE
Authors: ROTHE PETER 
Published: June 2006

SUMMARYRegionally the “main dolomite” (Hauptdolomit) of northwestern German Zechstein (shallow water) is made up of 30–100 m thick oncolitic dolostones. In almost every case anhydrite is observed within the sequence suggesting an environment of elevated salinities (FÜCHTBAUER, 1968). Studies on thin sections of oncolitic carbonates of a gasfield in the Emsland area reveal a shallow marine environment, sometimes even intertidal as shown by intraformational flat pebbles of reworked material. Different stages of diagenesis within the carbonates occur. The most interesting fact concerning the detached rims of first‐generation carbonate cement is discussed below and shown by several thin‐section photomicrographs.
SUBAERIAL CEMENTATION AND SUBSEQUENT DOLOMITIZATION OF LACUSTRINE CARBONATE MUDS AND SANDS FROM PALEOTUZ GÖLÜ (“SALT LAKE”), TURKEY
Authors: MÜLLER GERMAN , IRION GEORG 
Published: June 2006

SUMMARYAlong the eastern coast of the Gez Gölö, a salt lake formerly belonging to the larger “Paleo‐Tuz Gölö” in central Anatolia, about 6.5 m of lake sediments of probably Pleistocene age were studied.The sediment series consists of fine‐grained unconsolidated dolomite muds representing the basin sedimentation of the old lake.Nine lithified beds (oomicrites, intramicrites, intraoomicrites, intrabiomi‐crites and dololutites with smaller amounts of allochems) are intercalated. These beds were deposited in very shallow water in the littoral zone of the paleo‐lake. There is direct evidence that the beds were occasionally exposed to the air after deposition. This led to desiccation (with mud cracks, breaking up of intraclasts) and subaerial cementation due to the influx of fresh water (rain water, springs).These now lithified carbonate sedimentary rocks were submerged and subsequently covered with mud. During this sub‐aquatic phase the rock beds as well as the unconsolidated muds were dolomitized by an extremely high Mg/Caratio of the lake water which in the present Tuz Gölü amounts to about 150! It cannot be excluded, however, that dolomitization already took place or was initiated during the subaerial phase (“supratidal dolomite”).
SYN‐SEDIMENTARY MARINE LITHIFICATION OF MIDDLE JURASSIC LIMESTONES IN THE PARIS BASIN
Authors: PURSER B. H. 
Published: June 2006

SUMMARYBored surfaces in Middle Jurassic limestones in northeastern France indicate syn‐sedimentary lithification. The sedimentary structures and textures, and age relationships between the bored carbonates and the argillaceous sediments above them suggest that the lithification has occurred in both submarine and intertidal environments. The diagenetic fabrics which have resulted from this early marine lithification include three types of calcite druse, echinoderm overgrowths, and microcrystalline cements. Most of these cements are comparable with those forming today in inter‐ and subtidal environments of the Persian Gulf.The localization of bored surfaces (“hard grounds”) at the tops of regressive carbonate sequences is interpreted as being the result of slow carbonate sedimentation and lithification of the Jurassic sea‐floor prior to the onset of argillaceous colder, or deeper‐water sedimentation.
REWORKED DOLOMITE CRUSTS IN THE WETTERSTEINKALK (LADINIAN, ALPINE TRIASSIC) AS INDICATORS OF EARLY SUPRATIDAL DOLOMITIZATION AND LITHIFICATION
Authors: GERMANN K. 
Published: June 2006

SUMMARYDolomitic intraclastic sediments intercalated in a cyclic limestone‐dolostone sequence of the Wettersteinkalk represent a rock type with reworking fabrics demonstrating early lithification and dolomitization. The extreme flatness and the angularity of the pebble‐sized doloclasts, the lack in plastically deformed dolomitic fragments, and clasts of previously cementated arenites and oncolites testify to a pre‐reworking consolidation which, besides biogenic stabilization and dehydration, requires an early cementation. In the different types of doloclasts cementation both by dolomite and by calcite has been confirmed by stained peels and thin‐sections, electron‐microphotographs, and electron‐microprobe analysis.The prevailing rock type, a very poorly sorted mixture of doloclasts and minor amounts of rounded limeclasts with a pelletal calcite mud matrix is interpreted as storm sediment formed by the introduction of subtidal lime muds to dolomite incrusted supratidal flats.
EARLY VOID‐FILLING CEMENTATION IN DEVONIAN FORE‐REEF LIMESTONES (GERMANY)
Authors: KREBS WOLFGANG 
Published: June 2006

SUMMARYFibrous calcite is the main cement in the voids and cavities of Devonian fore‐reef limestones in Germany. Cementation occurs in some cases simultaneously with encrustation by blue‐green algae as well as internal deposition of calcarenites and calcilutites. These observations lead to the conclusion that the fore‐reef voids were exposed to light and were still in free communication with the sea, when the cementation began. Furthermore, redeposited fragments of former cavity fillings indicate that the formation of cavity‐filling fibrous calcium carbonate cement was already completed before the sea‐ward erosion took place. It is believed that the precipitation of fibrous calcium carbonate in most of the Devonian fore‐reef limestones, which show no signs of dissolution, occurred in a shallow subtidal environment. Only the voids showing larger solution phenomena were probably exposed to fresh water in the inter‐ to supratidal zone.