bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rare earth elements and strontium isotopes of polymetallic nodules from southeastern Pacific Ocean
Authors: COURTOIS CHANTAL , CLAUER NORBERT 
Published: June 2006

ABSTRACTRare 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

ABSTRACTThree 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

ABSTRACTAgglutinated 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

ABSTRACTNewly 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

ABSTRACTAdequate 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.
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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTA 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

ABSTRACTIrregular 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.
Origin of siltstones: glacial grinding versus weathering
Authors: NAHON D. , TROMPETTE R. 
Published: June 2006

ABSTRACTSiltstones are unusual rocks. They are mainly made up of quartz. Glacial grinding is considered by some authors to be the main, or even the only, process generating silt. This is supported by: (1) the presence of silt in basal tills from present ice‐caps and, above all, (2) by the volumetric importance of Quaternary loess. However, ancient glaciogenic sediments contain only a little silt scattered in the matrix of tillites, or forming thin intercalations in pro‐ and periglacial deposits. These siltstones represent less than 5% of the total volume of Upper Proterozoic and Upper Ordovician glaciogenic sequences of West Africa.On the other hand, silt is abundant in weathering profiles of tropical, equatorial and mediterranean zones. This silt is generated by splitting of minerals, mainly quartz, inherited from the parent rock. Quartz grains are partly dissolved in situ and their fragments cemented by iron oxi‐hydroxides in tropical and equatorial zones and by calcite in mediterranean zones. Silt is particularly abundant in tropical soils, comprising up to 50‐75%. Secondary dissolution of the iron or calcite matrix induces disaggregation of these soils and the release of silt which is later reworked and concentrated by wind or running water.Weathering processes, and especially those operating in tropical zones, are the main phenomena generating silt. Glacial grinding would generate only a little silt. A large part of the material of Quaternary loess may be derived from glacially reworked weathering profiles.
Bed‐thickness and grain size of turbidites
Authors: SADLER PETER M. 
Published: June 2006

ABSTRACTIn measured sequences of limestone‐ and greywacke‐turbidites the bed‐thickness is found to vary proportionally with the fall velocity of the maximum grain size, found at the base of the bed. A simple theoretical model, based on the decay of isotropic turbulence, suggests that bed‐thickness should be a function not only of this fall velocity, but also of bottom slope, flow depth and the concentration and grain‐size distribution of the sediment in the turbidity current. The field data do show some influence of these additional factors. Nevertheless, for many natural sequences of turbidites the flows must have carried very poorly sorted sediments and the inferred flow volumes and densities must cluster tightly about modal values. Thus, grain size remains the primary variable and the modal regression curve of bed‐thickness on maximum grain size is well defined and resembles a fall‐velocity curve. Relatively steep basin floors near to source can, theoretically, cause these modal regressions for distal and very proximal parts of a turbidite to diverge, introducing a crudely parabolic appearance in the form of the total regression curve. The form of this parabolic curve predicts the deposition of thin but relatively coarse proximal beds. Such beds do occur. They are different from the thin, but relatively fine, proximal beds that have been interpreted as the result of a fractionation of a turbidity current during levee‐forming processes.
Bed‐material size and the riffle‐pool sequence
Authors: MILNE J. A. 
Published: June 2006

ABSTRACTRelationships between the bed‐material size distribution and riffle‐pool geometry of a small coarse‐bedload upland stream channel are described. Downstream sequences of bed‐material size are highly variable, although series analysis reveals some persistence in the data over short distances. Cross‐correlation of bed‐material series with bed‐elevation series indicates riffles tend to coincide with coarser bed material sequences.Comparison of the bed‐material size distributions of individual riffles, pools and bars is, however, more revealing. Mean particle size was found to be the most useful criterion for distinguishing between bed forms, and in these terms bars are the most distinctive features. Moreover, riffles and pools can be viewed as simply downstream oscillations in elevation of a single coarser‐grained sedimentary unit. Coarse sediment supply from erosion scars created where the channel meets confining bluffs in valley‐fill deposits does mean that the average particle size of adjacent and downstream bed forms is increased. However, conclusions remained unchanged after reanalysis following the identification and subtraction of immobile particle diameters.Plan geometry and coarse sediment supply in the upland environment are also shown to influence bed‐material size distributions. Tightly curved pools tend to have the finest pool sediments but also the least difference between bar and pool sediments. Size of material in pools is also negatively related to an index of cross‐section asymmetry.
A new mechanism for seaward dispersion of midshelf sediments
Authors: LARSEN LAWRENCE H. 
Published: June 2006

ABSTRACTSilt‐ to sand‐size particles may be transported across middle continental shelves by currents forced by the radiation stress of variable‐amplitude swell. With the passage of each group of waves of sufficient amplitude for the high waves in the group to resuspend bottom sediments, there is a seaward bias in the return of sediments to the seafloor. Over a storm season, with the passage of many wave groups, the net seaward sediment displacement may be 1‐5 km.
Practical representation of characteristic grain shape of sands: a comparison of methods
Authors: WILLETTS B. B. , RICE M. A. 
Published: June 2006

ABSTRACT A measure of grain shape is needed for incorporation in calculations of the behaviour of grain populations (for example during transport by fluids). Many shape measures have been proposed, most of them for application to single grains rather than to populations. In this paper three such shape parameters are evaluated for samples taken by size fraction from each of three parent sands. The chosen parameters are the maximum projection sphericity of Sneed & Folk (based on triaxial measurements made on the grains), the dynamic shape factor of Briggs (based on settling velocity in water), and rollability, after Winkelmolen (based on rolling behaviour in a specially mounted rotating cylinder).It is shown that the Sneed & Folk parameter and rollability both discriminate clearly between the shape characteristics of the three sands over the size range 150‐500 μm. Moreover the discrimination of the two parameters is mutually consistent. However, dynamic shape factor gives results which for sizes smaller than 300 μm are inconsistent with those of the other two methods and which do not discriminate reliably between the populations. This is inevitable because the differences between drag on spheres and on other shapes become very small at Reynolds Numbers corresponding to those which obtain in settling tests on grains smaller than 300 μm.
Size—frequency distribution of longitudinal dune rippled flank sands compared to that of slipface sands of various dune types
Authors: SNEH AMIHAI , WEISSBROD TUVIA 
Published: June 2006

ABSTRACTRippled flanks of longitudinal dunes and the slip faces of various dune types can be distinguished granulometrically by comparing the top to bottom trend of changes of sorting in the sand population of each individual slope. Flank sands, which are prone to sorting processes through migration of ripples alongslope, are always better sorted upslope whereas slipface sands, which are controlled by avalanche and grainfall of sands, become better sorted downslope. Considering the absolute values of the bottom samples, the sands of the slip faces are both better sorted and the size distribution more symmetrical than those of the rippled flanks.Applying this approach in investigating ancient sediments could improve palaeogeographical interpretations.
Progradation geometries of carbonate platforms: examples from the Triassic of the Dolomites, northern Italy
Authors: BOSELLINI ALFONSO 
Published: June 2006

ABSTRACTVarious types of progradation of Triassic carbonate platforms are described from the Dolomites of the Southern Alps. The internal and external geometric relationships are exposed in spectacular natural sections and, moreover, their scale (500–1000 m of thickness) is such that they can be compared with features found in seismic profiles.The different types of progradation are controlled by a number of factors which, normally, interact with each other. These factors include: rate of basinal sedimentation, rate of subsidence, width of the platform, depth of the surrounding basin and eustatic variations of sea‐level.Progradation is not a continuous process but episodic. Moments of massive debris input, during which the platform advances, alternate with long periods of negligible progradation, during which basinal sediments accrete and onlap the toe of slope. Upper boundary relationships of the prograding platforms include offlap, toplap and erosional truncation. Lower boundary relationships are horizontal, climbing and descending progradations. A variety of phenomena and circumstances have caused the cessation of progradation of the Triassic platforms. They include volcanism, collapse of margins, drowning (rapid relative rise of sea‐level), subaerial exposure (relative fall of sea‐level) and, probably, a natural decay of the system.In the Triassic of the Dolomites, two main progradation models can be put forward: in the Ladinian model, progradation took place simultaneously with aggradation (relative rise of sea‐level), whereas the characteristic feature of the Carnian model is toplap (relative stillstand of sea‐level).