bluuebunny/crossref_metadata_2025 huggingface dataset:
Origin of red beds in a Cambrian flysch sequence, Canadian Appalachians, Quebec
Authors: LAJOIE JEAN , CHAGNON ANDRÉ
Published: June 2006

The basal unit of this flysch sequence consists of about 700 m of rhythmically interlayered red and green claystone intercalated with feldspathic sandstone and lithic conglomerate. Chemical analyses show that both types of claystones have approximately the same Fe2O3 content (8%).

The presence within green claystone of inarticulate brachiopods, thin laminations of phosphate and pyrite, coupled with a high Mn content (Fe/Mn : 27) together with the composition of the chlorites, suggest that green mud was deposited slowly in a marine environment under reducing conditions. The hematite content of red claystone averages 4%. The Fe/Mn is high (71), and the clay fraction contains chamosite in addition to chlorite and illite. These characteristics favour a paralic oxidizing environment for the red muds.

Rapid resedimentation of red sediment from a paralic environment into the green lithotope, rather than a lateral variation of facies, is suggested by: (1) the distribution of the two hemirhythms in the stratigraphic column, (2) the presence in the red hemirhythm of large slump structures, contorted laminations, and pebbly claystone, and (3) by the internal sedimentary structures of the coarse fraction.
Lithified carbonate sediment and zeolitic tuff in basalts, Mid‐Atlantic Ridge
Authors: GARRISON ROBERT E. , HEIN JAMES R. , ANDERSON THOMAS F.
Published: June 2006

Basaltic boulders dredged from the Mid‐Atlantic Ridge contain lithified coccolith‐foraminiferal ooze in fractures and small pockets. Textural and isotopic studies of this sediment provide no evidence for high temperature metamorphism. The lithified carbonate sediment occurs together with palagonitized basaltic glass and zeolitic tuff, and appears to have been squeezed into cracks and other voids within the congealed margins of partly‐cooled basalt pillows which intruded soft carbonate ooze. Thermal metamorphism probably was precluded by rapid heat dissipation in convecting pore waters and by the thermal stability of calcareous microplankton. Low temperature alteration of basaltic glass appears to have provided the chemical milieu for precipitation of calcite cement as well as zeolites in the sediment.
Selective transport of heavy minerals by shoaling waves
Authors: MAY JAMES P.
Published: June 2006

A model to account for the occurrence of heavy mineral concentrations as discrete lamina on beaches is presented. The model is based on the shoreward variation in the distribution of bottom fluid velocities due to shoaling, progressive, gravity, water waves. This variation causes certain portions of the sediment population to be transported shoreward at a faster rate than other portions. On moderate energy shorelines composed of sand‐sized sediment the selectively transported portion may include the relatively hard‐to‐move heavy mineral fraction. Wave tank experiments with artificially prepared sediment populations provide empirical support for the proposed model. Under certain wave conditions it was found that the heavy mineral fraction of the sediment population moved shoreward at a faster rate than did the light mineral fraction.
Whistling sand beaches in the British Isles
Authors: RIDGWAY K. , SCOTTON J. B.
Published: June 2006

Beaches which squeak or whistle when walked on have been known for many years. The phenomenon is shown to be more common than has previously been thought: sand from thirty‐three beaches in the British Isles has been found to whistle. Size distributions of all these sands have been obtained by sieving, and the particle shape distribution in the peak size fractions has been measured by using a vibratory shape‐sorting table. A physical mechanism has been suggested for the production of the whistle, which depends upon a close size grading coupled with a spherical grain shape. The locations at which whistling sand occurs correlate quite well with the landward ends of bed‐load partings in the continental shelf sand transportation pattern as determined from side‐scan Asdic surveys.
Transportation of detrital materials on the lunar surface: evidence from Apollo 15
Authors: LINDSAY JOHN F.
Published: June 2006

The thickness frequency distribution of stratigraphic layers intersected by the Apollo 15 deep core suggests that the majority of impact events reworking the lunar soil are small and produce ejecta blankets with an average thickness of less than 1·D5 cm. The energy frequency distribution of the meteorites producing the layers may be bimodal. The impacting meteorites produce both normal and reverse graded beds which appear to be the end products of two depositional mechanisms. First, the normally graded beds appear to be produced in base surges as escaping gases fluidize the flowing debris and larger particles move downwards in response to Stokes Law. Second, if the gas loss from the base surge is excessive the fluidization may cease and inertial grain flow dominates. In this situation the beds are reverse graded as larger particles move under dispersive pressure to the region of minimum shear stress at the upper boundary of the base surge. The same processes also produce measurable shape sorting of the particles in the beds.
An evaluation of CM patterns for grain‐size studies of fine grained sediments
Authors: VANDENBERGHE N.
Published: June 2006

Grain‐size data of Boom clay (Belgium) are represented on CM, AM, LM diagrams as suggested by Passega. They show a typical ‘uniform suspension’ pattern. It is argued that a ‘uniform suspension’ pattern can be due simply to the clay‐rich nature of the sediments. As these sediments are not deposited by a single transport mechanism, the ‘uniform suspension’pattern does not necessarily indicate a specific transport mechanism.
Glacial retreat sedimentation in the Smalfjord Formation, Late Precambrian, North Norway
Authors: EDWARDS M. B.
Published: June 2006

Tillites, conglomerates and sandstones occurring in the basal part of the Smalfjord Formation along the Varangerfjord, East Finnmark, North Norway are believed to have formed during the retreat of a glacier.

At Kvalnes, on the south side of the fjord, the following sequence, up to 20 m thick, is found: (1) massive monomict tillite interpreted as a subglacial till, (2) massive polymict tillite with lenticular intercalations of stratified sandstone and tillite, interpreted as supraglacial/proglacial drift, (3) polymict conglomerate interstratified with laminated sandstones, interpreted as braided stream deposits. The last named interfingers laterally and is overlain by marine sandstones.

At Bigganjargga, near the head of the fjord, a lens of tillite about 3 m thick rests on a striated pavement and is overlain by sandstones and shales. Part of the tillite, containing irregular patches of slightly winnowed tillite, is interpreted as a melt‐out till, while a marginal part consisting of inclined tillite beds is interpreted as a series of flow till deposits. The lens is believed to be an oblique section through what was originally an ice‐cored moraine ridge. During a subsequent transgression, the moraine was partially eroded, a lag conglomerate was formed, and overlying marine sediments were deposited.

Bedded flow tills formed in a supraglacial/proglacial environment may be preserved where the extent of current reworking is very low (such as an isolated end moraine). Stratified conglomerate and sandstone, intimately intercalated with tillite, is to be expected at a glacier margin where glacial meltwater is locally and occasionally abundant, and glacier ablation permits downslope flowage of mobilized supraglacial fluid till.
Sediment deposition from flocculated suspensions
Authors: KRANCK KATE
Published: June 2006

Suspended sediment in coastal environments with high inorganic content have characteristic broad size distributions and are composed of both single grains and flocculated aggregates. These flocculated suspensions have stable size distributions the modal size of which is dependent on the modal size of the deflocculated single grain distributions. Comparison between theoretical settling speeds of quartz grains and the settling speed of particles in natural suspensions indicates that most grains smaller than the deflocculated single grain mode settle as part of flocs, whereas the particles larger than the mode settle as single grains. As a result the size distribution curves of sediment populations which settle out during consecutive intervals are composed of a modal peak of larger grains and a low flat portion of smaller grains and resemble the asymmetrical non‐normal curves common for muddy sediments.
Miniacina miniacea: modern foraminiferal sands on the Outer Moroccan shelf*
Authors: MILLIMAN JOHN D.
Published: June 2006

The attached foraminifera, Miniacina miniacea, is a major sedimentary component on the outer shelf off central and southern Morocco, particularly in water depths between 95 and 115 m, where concentrations generally exceed 40% of the carbonate fraction. Predominance of this species may be largely a function of the relatively great water depths which preclude optimal growth of other encrusting organisms.
Equantcy versus sphericity
Authors: TELLER JAMES T.
Published: June 2006

The shape of a particle is commonly characterized by its sphericity. In geology, sphericity is determined by comparing a grain's length, width and breadth diameters. This type of measurement does not indicate how close the particle is to a true spherical shape, and cubes, tetrahedrons, and true spheres all have the same degree of sphericity.

Because the term sphericity is misleading, implying that its determination takes roundness into account, a different term should be used. I propose that whenever the shape of a grain is determined by measuring or estimating the lengths of its main axes, we regard this as determining its degree of equantcy.
La sédimentologie: Reflexions sur son développement et sa place parmi les sciences de la terre
Authors: LOMBARD AUGUSTIN
Published: June 2006

La sédimentologie est une des disciplines des sciences de la terre dont le développement est extrêmement rapide. Elle est par définition la connaissance des sédiments mais cette formule trop laconique demande un développement.

Les sédiments sont aussi bien ceux qui se forment actuellement que ceux qui constituent les dépôts fossiles, du milieu terrestre, lacustre, fluviatile, marin ou océanique.

Les méthodes d'investigation sont celles du terrain et du laboratoire, qu'il s'agisse de la mécanique, de la physique (géophysique), de la chimie (géochimie), de l'analyse au microscope ou aux rayons X. L'expérimentation est limitée.

L'analyse des sédiments emprunte des méthodes à d'autres sciences de la terre: stratigraphie, tectonique et sédimentation actuelle.

II y a donc un aspect limitatif et descriptif de la sédimentologie. Ce n'est pas le seul. Les congrès de sédimentologie ont montré que cette science opère des synthèses, remonte aux origines des sédiments, de leurs facteurs génétiques et par là‐même apporte une information complémentaire à la géologie générale.
Size selection: a source of error in sphericity determination
Authors: BARDECKI M. J.
Published: June 2006

It is suggested that a relationship may exist between the measured sphericity of clasts selected from a sediment and the criterion of size selection employed in the sampling. This relationship is exhibited clearly in cases where the size selection results in a change in the shape of the size distribution of the clasts.

A study of glacial and beach pebbles statistically illustrates the correlation between sphericity and the skewness of the size distribution of the pebbles for each mode of size selection employed.

The results suggest the need for a more critical treatment of sphericity data. It is not unlikely that statistically different sphericities may be largely or even entirely a result of the effect of differing size distributions of the sampled sediments; or conversely, the selection process may augment or obscure any real differences which are present.
Packing and angle of repose of naturally sedimented fine silica solids immersed in natural aqueous electrolytes
Authors: MANTZ P. A.
Published: June 2006

Six grades of near uniformly sized silica solids (ranging in median size from 15 μm to 160 μm) were sedimented in various natural aqueous electrolytes. The influence of surface forces on these silica‐electrolyte systems was then inferred from measurements of the packing coefficient, C, of each sediment. It was found that the packings were uninfluenced by surface chemical forces when the grade size was greater than about 100 μm. For smaller grades immersed in naturally concentrated aqueous electrolytes, C was found to decrease from an initial value of about 0·50, and this was explained by the onset of surface chemical attractive forces. For smaller grades immersed in pure water, C was found to increase to a maximum of 0·58. Three explanations for this phenomenon, namely a difference in shape with grade size, a decrease in intensity of deposition, and the onset of surface chemical repelling forces were examined and the latter explanation seemed the most probable. Measurements of the angle of repose for the sediments also showed the influence of surface chemical repelling as well as attractive forces in fine silica solids. The results may be used to aid interpretation of the fabric and stability of pre‐lithified sedimentary units.
Clinoptilolite, paragenesis and stratigraphy
Authors: NATHAN YAACOV , FLEXER AKIVA
Published: June 2006

Clinoptilolite, a zeolite of the heulandite group, occurs commonly in sediments as an authigenic mineral. In the Middle Eocene of southern Israel, it constitutes from a few per cent up to 80 per cent of the insoluble residue of the chalks and limestones. It is associated with opal C‐T, montmorillonite and palygorskite. These chalks and limestones overlie the Danian‐Palaeocene Taqiya marls which also contain a well‐established clay mineral sequence consisting of opal C‐T, montmorillonite, palygorskite, sepiolite, and clinoptilolite.

This paragenesis of minerals is shown to be typical of the Upper Cretaceous to Eocene times. It is world‐wide, occurs in deep‐sea sediments as well as in shallow water sediments, and results from the abundance of silica which probably reflects a warmer climate during this time period.

The concentration of magnesium in the sea‐water and its ratio to the other cations seem to determine which authigenic silicate will be formed.
Suspended matter in surface waters: influence of river discharge and of upwelling*
Authors: EMERY K. O. , MILLIMAN J. D.
Published: June 2006

About 4100 samples of suspended matter were collected by filtration of surface ocean waters in three large regions on the western sides of oceans and two on the eastern sides. Comparison of results shows that the non‐combustible fraction (chiefly detrital clays and silts with some siliceous and calcareous skeletal debris) generally dominates along the western sides of oceans, where large contributions of solid detrital sediment are made by rivers that drain much of the adjacent continents. The combustible fraction also is important off these rivers, but it is more important (both relative to the non‐combustible fraction and in absolute terms) along the eastern sides of oceans, where upwelling is intense.
Large‐scale rhomboid bed forms and sedimentary structures associated with hurricane washover*
Authors: MORTON ROBERT A.
Published: June 2006

Hurricane washover fans from the Texas Gulf Coast exhibit large‐scale rhomboid bed forms developed on washover deposits of fine sand with varying shell content. Washover processes inferred from aerial photographs, storm characteristics, and physical settings suggest that these bed forms are the product of (1) storm surge flooding or (2) high wind shear stress.

Multiple bed forms, including large‐scale rhombs, are responsible for sedimentary structures preserved in washover deposits. Proximal channels exhibit scour and fill sequences capped by mud drapes. Mid‐channel fan deposits also have scour bases marked by shell lags which are overlain by horizontal laminations and foreset and backset laminae. Distal fan sediments are relatively shell free and are interbedded with tidal flat deposits characterized by bioturbated, alternating sand and mud laminae.

Rhomboidal patterns can form on the free surface of water in response to five processes: (1) wave interference from two externally independent sources, (2) wave interference from refraction of a single set of wave fronts, (3) standing oblique waves caused by bed roughness elements, (4) standing oblique waves formed at channel boundaries and channel transitions, and (5) wind stress. Geologically, standing oblique waves from unidirectional nearly supercritical flow is probably the most important process in rhomboid bed form development.
Micritization of crinoids by diagenetic dissolution
Authors: NEUGEBAUER JOACHIM
Published: June 2006

Bands within the Chalk of Kansas made up of masses of Uintacrinus socialis show an unusual preservation of crinoid ossicles: in contrast to their normal preservation in full relief as single large calcite crystals the ossicles are compressed and transformed to micrite.

The micrite originated by a process different from the well‐known micritization by algal and fungal borings and subsequent cementation of the borings: it is the outcome of partial dissolution.

Dissolution proceeded inside the sediment and preferentially attacked the echinoderms as the most soluble calcareous component of the chalk sediment. Later, the remains of the Uintacrinus crystals preferentially attracted syntaxial cement so that the layer changed to a hard band of limestone within the soft chalk.

In addition to a second process of micritization the preservation of Uintacrinus demonstrates (1) that the magnesium content of magnesian calcites survives the earliest stages of diagenesis within chalk, and (2) that a diagenetic comminution of large crystals (in an optical sense) to smaller ones is possible. Provided the ossicles of echinoderms are true single crystals (the knowledge in this field is summarized), this is an example of the often discussed ‘crystal diminution’.
A barred‐basin marine evaporite in the Upper Proterozoic of the Amadeus Basin, central Australia
Authors: STEWART ALASTAIR J.
Published: June 2006

The Ringwood evaporite is part of the 900 m.y. old Bitter Springs Formation, a warm‐water shallow‐marine sequence of stromatolitic dolomite and limestone, microfossiliferous chert, red beds, quartzite, and evaporites. The evaporite at Ringwood comprises two parts: (i) a lower 127 m characterized by brecciated pyritic bituminous dolomite, together with smaller amounts of dolomite‐gypsum breccia, friable chloritic dololutite, coarsely crystalline anhydrite, and satin‐spar gypsum; and (ii) an upper 133 m which is similar except that bituminous dolomite forms only one bed, and the characteristic rock‐type is dolomite‐gypsum breccia. The evaporite is overlain by limestone breccia and massive stromatolitic limestone, interpreted as an algal reef. Gypsum is secondary after anhydrite, and the ratio of gypsum to anhydrite increases upwards. The evaporite shows none of the features of a sabkha or desiccated deep ocean basin deposit, and instead is interpreted as the filling of a barred basin which was cut off from the ocean by growth of an algal barrier reef. As circulation became restricted, bituminous dolomite deposited in the lagoon behind the reef, together with pyrite from the destruction by anaerobic bacteria of algal debris derived from the reef. With continued evaporation, brine concentration increased and gypsum precipitated. Occasional dust storms contributed wind‐blown clay to the deposit. The barrier reef transgressed diachronously across the evaporite lagoon, and was eventually drowned when normal marine conditions became established. Burial of the evaporite to about 7000 m beneath the succeeding sediments of the Amadeus Basin converted gypsum to anhydrite, and formed chlorite by reaction of clay with dolomite. Late Palaeozoic tectonism folded and brecciated the rocks, and was followed by erosion which eventually exposed the evaporite to ingress of meteoric water. Hydration of anhydrite to gypsum ensued, the reaction becoming less complete with increasing depth from the ground surface.
Sandstone pseudomorphs of aragonite fossils in an Ordovician vadose zone
Authors: HANKEN NILS‐MARTIN
Published: June 2006

Moulds after aragonite fossils from two Upper Ordovician limestones in the Oslo Region are filled with well sorted clastic fine sand. The fossil moulds are thought to have been formed by selective dissolution of aragonite shell material by fresh water in the vadose zone. Internal sedimentation post‐dates precipitation of a thin veneer of iron poor drusy calcite cement, but predates precipitation of ferroan blocky calcite cement. These age relationships and the texture of the fine sand suggests sedimentation in semiconsolidated sediment in the vadose zone of an island during early emergence.
Authigenie gypsum in deep‐sea manganese nodules
Authors: XAVIER A. , KLEMM D. D.
Published: June 2006

Gypsum crystals of authigenic origin have been found in manganese nodules of the deep‐sea sediment surface (4500‐5500 m water depth) from the Central Pacific Ocean.
Holocene evolution of a coastal lagoon, Lake of Tunis, Tunisia
Authors: THORNTON SCOTT E. , PILKEY ORRIN H. , DOYLE LARRY J. , WHALING PATRICK J.
Published: June 2006

Historical records demonstrate that the Lake of Tunis, Tunisia, was an open bay that became separated from the Mediterranean by an accreting barrier spit, forming a lagoon. Closure of the lagoon was caused by increased sedimentation as a consequence of Roman deforestation of the Medjerda River drainage basin to the north and subsequent accelerated longshore transport. The separation of the lagoon from the Mediterranean was completed in the early 1500s. At present, the 48 km2 lagoon averages less than 1 m in depth and reaches eutrophic conditions in the late summer. Consistent with the historical records, the lagoon sedimentary column shows three distinct successive environments of deposition: (1) an arid continental environment; (2) an open marine bay; and (3) the present brackish to hypersaline lagoon. These depositional environments are represented by the lower grey layer, which is less than 0‐5 m thick, the middle olive‐grey layer, which varies from 1 to 5 m in thickness, and the upper black layer, which is 1 m thick. All of the strata are predominantly silt plus clay, but usually contain at least 10% sand. The lower grey layer consists of pitted quartz sand, with very few abraded, broken molluscan fragments and benthic foraminifera with thick tests. An arid, subaerial depositional environment of latest Pleistocene time best explains these sediment and fossil assemblages. In the middle olive‐grey layer, coral, coralline algae, open marine graeses and the dominance of foraminifera over ostracods (expressed as a low percentage of ostracods/ostracods plus foraminifera) attest to a depositional environment of an open marine bay. A sharp increase in the percentage of ostracods/ostracods plus foraminifera and organic carbon from the middle olive‐grey layer to the upper black layer signifies a major change in depositional environment. The predominance of ostracods over foraminifera, abundance of gastropods characteristic of eutrophic conditions, high organic carbon content and absence of macro‐fossils characteristic of open marine conditions clearly indicate that the upper black layer was deposited in a brackish to hypersaline, eutrophic lagoon which has persisted to the present. Seismic records indicate a karstic bedrock surface underlying the lagoon. The surface is marked by considerable relief, and shows a linear depression which may represent an early sixteenth century ship canal. Heavy metal analyses of total samples in five cores demonstrate that Mn and Fe vary randomly, and are apparently derived from natural sources only. Cd, Cr, Pb, Cu and Zn are typically highest in the uppermost unit, which reflects levels of human contamination since closure of the lagoon.
Transformational changes of clay minerals, zeolites and silica minerals during diagenesis
Authors: AOYAGI KOICHI , KAZAMA TOSHIE
Published: June 2006

Diagenetic transformation of clay minerals, zeolites and silica minerals in Cretaceous and Tertiary argillaceous rocks from deeply drilled wells in Japan were studied. Transformations of these minerals during diagenesis were as follows: in clay minerals, montmorillonite → montmorillonite‐illite mixed‐layer mineral → illite; in zeolites, volcanic glass → clinoptilolite → heulandite and/or analcite → laumontite and/or albite; in silica minerals, amorphous silica → low‐cristobalite → low‐quartz. Maximum overburden pressures and geothermal temperatures corresponding to these transformations in each well studied were calculated. For clay minerals, a pressure of approximately 900 kg cm−2 and a temperature of about 100°C are necessary for the transformation from montmorillonite to mixed‐layer mineral and 920 kg cm−2 and 140°C for mixed‐layer mineral to illite. Transformation from kaolinite to other minerals requires much higher pressures and temperatures than from montmorillonite to mixed‐layer mineral. For zeolites, 330 kg cm−2 and 60°C are required for the transformation from volcanic glass to clinoptilolite, 860 kg cm−2 and 120°C for clinoptilolite to heulandite and/or analcite, and 930 kg cm−2 and 140°C for heulandite and/or analcite to laumontite and/or albite. For silica minerals, 250 kg cm−2 and 50°C are necessary for the transformation from amorphous silica to low‐cristobalite and 660 kg cm−2 and 70°C for low‐cristobalite to low‐quartz. Based on these diagenetic mineral transformations, seven mineral zones are recognized in argillaceous sediments. On the other hand, from the porosity studies of argillaceous sediments in Japan, the process of diagenesis is classified into the following three stages. The early compaction stage is marked by shallow burial and viscous rocks with more than 30% porosity. The late compaction stage is characterized by intermediate burial and plastic rocks with 30‐10% porosities. The transformation stage is marked by deep burial and elastic rocks with less than 10% porosity.
Fluidized bed elutriation of carbonate sands
Authors: COOKER B. , GOODWIN R.
Published: June 2006

Elutriation from a fluidized bed provides an accurate, economical, direct method of sediment grading by terminal velocity. This is of particular value in studying populations of irregular particles in the range medium sand to granule (e.g. carbonate sands). A column suitable for such material (terminal settling velocity 1‐30 cm s−1) is described and sample results from ConnemaraLithothamnionbeach material are given.
The formation and significance of irregularly shaped quartz grains in till
Authors: MAY RONALD W.
Published: June 2006

Thin sections and scanning electron microscopy of quartz sand grains from till show clearly that a number of grains have been modified in place. The irregular grains result from the action of circulating alkaline groundwater, episodically concentrated by evaporation on fracture surfaces within grains and on concave surfaces produced by fracture during glacial transport. Evaporation increases the pH of the pore water and localizes its effect in small pores with a high capillary potential. Subsequent dilution by rainwater or snow meltwater flushes the system so that evaporation can repeat the process again. Solution rounding in terrigenous sediments has a number of ramifications for any interpretation based on textural maturity of the sediment.
A modern oceanic hardground on the Carnegie Ridge in the eastern Equatorial Pacific
Authors: MALFAIT BRUCE T. , ANDEL TJEERD H. VAN
Published: June 2006

Fossil surfaces of erosion and non‐deposition are common in limestone sequences from the Mesozoic in western Europe and in the Tethys and have been described under the name ‘hardgrounds’. They are of shallow water as well as of oceanic origin. A modern example in the Pacific is described in this paper. The Carnegie Ridge, an east‐west trending shallow ridge between South America and the Galapagos Islands, has a central, deeper saddle where erosion has removed most of the sediment cover down to a hard chalk and chert bed (acoustic basement), and has cut intricate channel patterns on the south flank and two deep canyons on the north. The erosion has produced a karst‐like relief of steep‐walled channels, cliffs, and corroded chalk remnants. The floors of the channels are covered with ferromanganese oxide crusts or crust fragments over which loose sediment is being transported. In the two canyons on the north flank, this sediment consists of foraminiferal sand travelling downslope in the form of barchan dunes. All sediment down to acoustic basement has been stripped from the Carnegie Ridge crest except where it is protected behind basement ridges and pinnacles. Surface features of the eroded chalk are strongly reminiscent of features observed in Mesozoic hardgrounds. Current measurements over several days indicate a net northward movement, slow but possibly adequate to keep the sea floor free of fresh deposits. The rates, however, seem inadequate to explain the formation of the deep channels, and there is no evidence for the southward flow which is implied by the southern channel system. A process of combined carbonate dissolution and removal by the current of fresh sediment and dissolution residues can account for the required erosion in about two million years. Regional unconformities identifiable in seismic reflection profiles and dated in cores are of middle to late Pliocene age, suggesting that the formation of the erosion surface began 2‐3 million years ago. Buried Miocene unconformities of local extent show that the present erosion period had minor precursors possibly related to short‐lived increases in current action and carbonate dissolution.
Rare earth elements and strontium isotopes of polymetallic nodules from southeastern Pacific Ocean
Authors: COURTOIS CHANTAL , CLAUER NORBERT
Published: June 2006

Rare earth element (REE) distributions and 87Sr/86Sr ratios were determined for nodule crusts and associated surface sediments collected in the southeastern Pacific Ocean between South America and the Tuamotu archipelago. The shale‐normalized patterns of the REE from the surface sediments show pronounced negative anomalies in Ce which indicate a marine origin. One 87Sr/86Sr ratio also has a value characteristic for seawater strontium. REE patterns from the nodule crusts, when normalized to shales, seawater or associated surface sediment, show that a marine origin can also be proposed for the oxy‐hydroxides. Only the Ce shows a systematic scatter, which could be the result of fluctuations in the oxidation‐reduction conditions during nodule growth. The marine origin for REE is corroborated by the 87Sr/86Sr ratios which average 0 · 70905 ± 0 · 00019 (2σ), a value close to the seawater 87Sr/86Sr ratio of 0·70910 ± 0 · 00035. If the major metals of the polymetallic nodules have the same origin as these trace elements, then a direct precipitation from seawater can be postulated for the crusts studied here.
Evolution of the barrier islands of southern Long Island, New York
Authors: RAMPINO MICHAEL R. , SANDERS JOHN E.
Published: June 2006

Three lines of evidence based on data from more than 400 boreholes and vibrocores have been used to reconstruct the evolution of the barrier islands during the Holocene transgression in southern Long Island, New York: (1) the Holocene transgressive stratigraphic sequence behind the present barriers, (2) the stratigraphic patterns of the inner shelf, and (3) the morphology of the now‐buried late Pleistocene coastal features.

The extensive preservation of backbarrier sediments, radiocarbon dated between 7000 and 8000 yr BP, on the inner shelf of southern Long Island suggests that the barriers have not retreated by continuous shoreface erosion alone, but have also undergone discontinuous retreat by in‐place ‘drowning’ of barriers and stepwise retreat of the surf zone. Such stepwise retreat of the surf zone has prevented the backbarrier sediments from being reworked.

Based on the presence of submerged barrier sand bodies in seismic records, it is inferred that about 9000 years ago, when the sea stood about 24 m below the present sea level, a chain of barriers developed on the present shelf about 7 km offshore of the present barriers. With continued sea‐level rise, the – 24 m barrier built upward until the sea reached about – 15 m MSL, just prior to 7000 yr BP. The barriers were then submerged by the rapidly rising sea, and the surf zone shifted rapidly landward to a position about 2 km from the present shoreline. The surf zone overstepped to the landward margin of the old lagoon, which had become fixed at the steep seaward face of mid‐Wisconsinan (?) or Sangamonian coastal barriers. During the past 5000 or 6000 years, the shoreface has retreated continuously by about 2 km.

Evidence from southern Long Island and elsewhere in regions of coastal submergence indicates that rapid sea‐level rise and low sand supply seem to favour the stepwise retreat of barriers, whereas slow rates of submergence and a greater supply of sand generally favour continuous shoreface retreat. Stationary upbuilding, or seaward progradation of barriers may occur when supply of sand is great, and/or submergence is slowed or reversed. Morphologic highs on the pretransgression surface (such as old barrier ridges) tend to fix the migrating barrier shoreline during either continuous retreat, or stepwise retreat of barriers.
The use of phillipsite in test construction of agglutinated deep‐sea benthonic foraminifera*
Authors: CORLISS BRUCE H. , MILLIMAN JOHN D.
Published: June 2006

Agglutinated deep‐sea benthonic foraminifera with tests composed of phillipsite are documented and illustrated from a red clay sequence in a Giant Piston Core from the central North Pacific. Associated with the benthonic foraminifera are phillipsite crystal rosettes and aggregates of phiilipsite crystals. The benthonic foraminifera and phillipsite crystals constitute most of the > 38 μm fraction, but have little effect upon the mean size of the red clay sediments.
Carbonate tidal rhythmites from the Middle Jurassic of Britain
Authors: ASHTON MICHAEL
Published: June 2006

Newly discovered carbonate laminites are described from the Lincolnshire Limestone Formation (Middle Jurassic, Britain). These occur in the upper peloidal unit of fining‐upward rhythms which comprise much of the lagoonal lower Lincolnshire Limestone in south Lincolnshire. The flat, millimetre‐scale laminations are of three types: (1) alternating peloid‐rich, peloid‐poor laminae; (2) alternating bioclastic and peloidal laminae; (3) alternating bioclastic and micritic laminae. In all three types, small‐scale cross‐laminated sets (usually < 40 mm thick) also occur. The laminite horizons are usually < 150 mm thick and have, in some cases, been traced laterally for ∼100 m.

The close analogy of these carbonate laminites with siliciclastic counterparts favours their interpretation as tidal rhythmites, mechanically deposited in a low intertidal/shallow subtidal setting. The associated sedimentary features and overall stratigraphic‐sedimentologic position of the deposits support this conclusion.

According to the literature, mechanically deposited as opposed to algally induced carbonate laminites are rare outside the supratidal realm. Possible reasons for the real or imagined scarcity of intertidal/ subtidal carbonate laminites in ancient sedimentary regimes are discussed.
Rank exposure index on a Silurian carbonate tidal flat
Authors: SMOSNA RICHARD , WARSHAUER STEVEN M.
Published: June 2006

Adequate discrimination between ancient intertidal and supratidal limestones and dolomites is often difficult because of vagueness of terms, problems of resolution, and the fact that most ‘diagnostic’sedimentary features are not restricted to narrow environmental zones. Furthermore, the rise and fall of sea‐level in restricted, epeiric seas is usually due more to storm surges than to true tides, and hence the occurrence and extent of tidal‐flat inundations are quite irregular. ‘Rank exposure index’is a concept introduced (1) to quantify the relative percentage of time that sediments are subaerially exposed and (2) to produce a more refined subdivision of shoreline carbonate rocks. The scheme employed to determine this index is a combination of numerical methods: cluster analysis separates 46 Tonoloway Limestone samples (Silurian of Maryland) into groups based on 16 sedimentary, mineralogic, and organic features, and minimum spanning tree produces a connected series of the five resultant groups. These groups are then ranked in sequence from 1 (greatest subaerial exposure) to 5 (least). Rocks of rank 1 are thought to have been deposited at the highest position within the tidal zone, as on a beach ridge. Rocks of decreasing rank reflect greater frequency of flooding. Those of rank 5 represent sediments deposited closest to low‐water level, as in a tidal pond. Rock type, mineralogy, fossil content, algal stromatolites, and sedimentary structures are closely related to exposure rank as interpreted for the Tonoloway carbonates. Rank exposure index, therefore, is a semi‐quantitative measure to aid in the detailed reconstruction of ancient shoreline environments.
Use of clay fabric to distinguish turbidites from hemipelagic siltstone
Authors: AZMON EMANUEL
Published: June 2006

In a recent paper O'Brien, Nakazawa & Tokuhashi (1980) summarized observations of clay fabric in some Pliocene and Holocene siltstones and silts. They demonstrated that clay fabric could be used, in combination with other sedimentary features, to distinguish hemipelagic sediments and turbidites.
REPLY
Authors: BARRETT P. J.
Published: June 2006

N. C. Janke's criticism of my paper seems aimed more at the title than the paper itself. I acknowledge the importance of shape in determining the style and rate of movement of particles in fluids (Janke, 1966), but my paper attempted a different task, clarifying the basic concepts of shape, which I believe are spatial, not behavioural. It did occur to me at the time of writing that a complementary review of the relationships between the shape of particles and their behaviour in different situations would be useful, but I saw this as a separate problem. The main purpose of Janke's 1966 paper was not to provide a measure of some particular aspect of shape, but to find a formula using different predetermined aspects of shape to predict settling velocities of particles. Nevertheless, points do arise in his discussion that could usefully have been taken up in my review, notably his acceptance of Prandtl's (1952) view that shape, as it affects settling velocity at least, has two components, a form component and a surface area component. Although Janke had considerable success in finding an appropriate mix of each component to allow prediction of settling velocity from two shape measures, he does not argue a basis for the measures themselves. For example he replaces Corey's shape factor with his shape factor E because the latter ‘allows more discrimination’for shapes with equal axial lengths. Corey's factor assigns a value of 1 to spheres, equant cylinders, equal double cones and cubes, whereas Janke's E gives 1, 0·866, 1 and 0·775 respectively. However, I have difficulty imagining a useful concept of form in which spheres and double cones are in some sense equal and distinct from cylinders and cubes, and it seems to me important that measures like Janke's are conceptually clear as well as efficacious. I would very much like to see someone with experience like Dr Janke undertake the review I mentioned earlier in the hope of achieving such a clarification.
The shape of sand‐sized crushed quartz particles
Authors: JANKE N. C.
Published: June 2006

The platy nature of sand‐sized quartz particles reported by Wellendorf & Krinsley (1980) is corroborated by the results of an exercise given in my optical crystallography course. In order to bridge the gap between the immersion oils technique and thin‐section work, the exercise asks the students to determine the sieve mesh‐size interval of crushed quartz particles that best corresponds to the standard thin‐section thickness of 0·03 mm, by determining the sieve interval which has the largest percentage of straw‐yellow interference colours. Consistently, this interval has been found to be the −140 to +170 mesh interval (0·10‐0·09 mm).
Holocene evolution of the Canet‐St Nazaire lagoon (Golfe du Lion, France) as determined from a study of sediment properties
Authors: MARTIN R. T. , GADEL F. Y. , BARUSSEAU J. P.
Published: June 2006

The sedimentation in the lagoons of the Golfe du Lion coast (Mediterranean Sea, France) records their post‐Holocene evolution. The Canet‐St Nazaire lagoon provides an example of such an evolution.

Eight cores (ranging from 13.5 to 19.7 m in length) from a transect of the lagoon provide a cross‐section of the late Quaternary stratigraphy. The sedimentary sequence comprises mud and sand layers. The two sand formations are identified as parts of two distinct shelf‐sedimentary prisms. Stratigraphic analysis defines three stages in the recent, muddy infilling, corresponding to the last divisions of the Holocene.

Sedimentation rates of the muds, related to climatic and palaeogeomorphological events, largely determine their geotechnical and geochemical properties. It appears, indeed, to be the most important factor in determining the compressibility index, the saturated bulk density and the organic and water contents of the deposits. Subboreal muds, poorly consolidated and rich in organic matter, correspond to a high rate of deposition. In the Subatlantic muds, in contrast, the sedimentation rate is lower whilst there is a decrease in the organic matter and an increase in the degree of cohesion.
Holocene carbonate sedimentation in Lake Manitoba, Canada
Authors: LAST W. M.
Published: June 2006

The carbonate mineral suite of the modern offshore bottom sediment of the South Basin of Lake Manitoba consists mainly of high magnesian calcite and dolomite with minor amounts of low‐Mg calcite and aragonite. The high‐Mg calcite is derived from inorganic precipitation within the water column in response to supersaturation brought about by high levels of organic productivity in the basin. Both dolomite and pure calcite are detrital in origin, derived from erosion of the surrounding carbonate‐rich glacial deposits. Aragonite, present only in trace amounts in the offshore sediments, is bioclastic in origin. The upward increase in the amount of magnesian calcite in the post‐glacial sediment record is attributed to increasing photosynthetic utilization of CO2 in the lake. Stratigraphic variation in the amount of magnesium incorporated into the calcite lattice is interpreted as reflecting a variable magnesium input to the lake from ground water and surface runoff, and possibly variable calcium removal in the precipitating lake water. The effects of long‐term chemical weathering at the source and size segregation explain the changes in dolomite content throughout the section.
Neogene non‐marine sedimentation and tectonics in small pull‐apart basins of the San Andreas fault system, Sonoma County, California
Authors: McLAUGHLIN ROBERT J. , NILSEN TOR H.
Published: June 2006

The San Andreas fault system in northern California forms an 80–90 km wide zone of right‐lateral shear. Extensional tectonism within this broad shear zone is indicated by both Neogene silicic volcanic rocks that gradually young in the direction of shear propagation to the north‐west and by numerous Neogene faultbounded structural basins filled with thick non‐marine sequences.

The Little Sulphur Creek basins, three well‐exposed 1·5–2 km wide pull apart basins within this shear system, have sedimentation patterns analogous to those of much larger pull‐apart basins. They were formed and subsequently deformed by east‐west extension and by north‐west to south‐east‐orientated right‐slip concurrently with basin filling. Palaeocurrent and maximum‐clast size data indicate both lateral sediment transport from fault‐bounded basin margins and longitudinal transport down the basin axes.

The basins are filled primarily with coarse alluvial‐fan and streamflow deposits derived from a surrounding igneous, sedimentary, and metamorphic provenance. Two of the basins contain basin‐plain‐type lacustrine turbidites that grade laterally into distal alluvial fan, fan‐delta, and sublacustrine delta deposits. Talus deposits along the south‐west margin of the basins contain megabreccia indicative of active uplift. Structures indicative of dewatering, liquefaction, and slumping suggest penecontemporaneous tectonism.
A small‐scale flood plain
Authors: HUGHES DENIS A. , LEWIN JOHN
Published: June 2006

A miniature, 9 m‐wide floodplain, developed along a gravel‐washing effluent stream, shows features such as levées, crevasse splays and floodbasins which compare with their larger‐scale counterparts. For sediments deposited overbank, median size decreases exponentially with distance from the channel whilst sorting increases, with coarser sediment on the outside of a meander bend. Overbank flows are only a few grain diameters in depth near the channel. This study shows potentially useful systematic relationships in floodplain sediment textures, but it involves only one of a possible variety of floodplain types dominated by overbank sedimentation. This suggests that further exploration of overbank depositional processes is desirable as an aid to field interpretation.
Pennsylvanian coalified rhizomorphs in Illinois: evidence for non‐compressive coalification to bituminous coal rank
Authors: BAIRD GORDON C. , WOODLAND BERTRAM G.
Published: June 2006

Irregular and discontinuous coalified objects, here termed rhizomorphs, occur above the Summum (No. 4) Coal Member (Carbondale Formation) at one locality in La Salle County, Illinois. These vitrinite structures, varying between 3 mm and 4 cm in diameter, occur in a blocky to structureless mottled claystone characterized by numerous carbonaceous streaks and small‐scale slickensides. The rhizomorphs twist and bend in a tightly coiled and kinked pattern, and may extend laterally through the claystone for 40 cm or more before bifurcating or terminating.

The rhizomorphs display little or no evidence of compressive distortion. They are composed of two types of material: structureless bright conchoidal collinite; and cellular woody structure. One or more vascular bundles occur as discrete steles within a groundmass of collinite gel; these are generally aligned longitudinally within the coal except where steles diverge laterally as offshoots.

The rhizomorphs are believed to be a diagenetic derivative of rooting structures; this is based on their occurrence in an underclay‐like sediment and on their irregular, kinked form, which differs from that of most vertical supportive plant stems. Non‐compressive coalification of the plant material may have occurred through: (1) aerobic alteration of cell walls to non‐compressive inertinite; (2) centripetal contraction and selective degradation of plant tissue; and (3) impregnation of more resistant stelar elements by organic gel derived from degradation of thin‐walled tissue.