bluuebunny/crossref_metadata_2025_split huggingface dataset:
Deposition of fine‐grained sediments in the abyssal environment of the Algéro‐Balearic Basin, Western Mediterranean Sea
Authors: RUPKE N. A. 
Published: June 2006

ABSTRACTTwo depositional processes control the mud accumulation on the southern Balearic Abyssal Plain: pelagic settling at a rate of 10 cm/1000 years, and turbidity currents at an average frequency of > 3 per 2000 years. Thermo‐haline bottom flow has little effect on the abyssal sediment distribution. Just over half of the Late Quaternary section is made up of turbidite mud. Distinctive properties of turbidite mud are: structural, textural, and compositional continuity from the underlying turbidite sand‐silt layer into the overlying mud, grading within the mud layer, a ratio of carbonate percent with the underlying turbidite sand‐silt layer of about 0.5, and a proportion of sand of > 1%. Those of (hemi)pelagic mud are: bioturbation, an average of 8% of sand consisting largely of remains of foraminifera and pteropods, a grain size distribution which is virtually normal with a median around 9 φ, and very poor sorting; in general, the properties of (hemi)pelagic muds are the same in widely separated localities and depths in cores. In some instances the clay mineral ratios of the turbidite mud layer are markedly different from those of the overlying (hemi)pelagic mud layer.
Relict magnesian calcite oolite and subsidence of the Amazon shelf
Authors: MILLIMAN JOHN D. , BARRETTO HENYO T. 
Published: June 2006

ABSTRACTOolitic sediments occur over large portions of the outer continental shelf off northernmost Brazil and southern French Guiana. Carbon‐14 dates, stable isotope values and analogies with similar deposits from other areas in the world indicate that the ooids were formed in shallow water (possibly protected hypersaline environments) during low stands of sea level. In contrast to both modern ooids and other relict ooids, however, the Amazon shelf ooids are composed entirely of magnesian calcite (12 mol % MgCO3) and possess radial crystal microstructures.A comparison of water depths and ages of the Amazon ooids with the generally accepted eustatic sea level curve indicates that the Amazon shelf subsided more than 100 m 16‐21 thousand years ago. Prior to and subsequent to the subsidence, however, the outer shelf remained relatively stable.
Mass‐emplaced sand‐fingers at Mararoa construction site, southern New Zealand
Authors: CARTER R. M. 
Published: June 2006

ABSTRACTDuring work on a dam construction site in South Island, New Zealand, outflowing ground water resulted in extensive local mass‐transport of the sands being excavated. A series of small scale sand fans was built up, probably mainly by laminar mass‐flow processes. The surfaces of the fans were made up of a series of complexly interdigitating sand‐fingers that are inferred to have been emplaced by viscous plug‐flow. Other sedimentary processes associated with the building and synsedimentary destruction of the fans included rapid grain‐flow, liquefaction and progressive slumping. Although small in scale, the Mararoa mass‐flow fans may be a close analogue for some of the many‘fluxoturbidite’ or‘proximal flysch’ facies described in the sedimentological literature, and their geologic implications are therefore briefly discussed.
Possibilities of palaeopedology
Authors: BUURMAN P. 
Published: June 2006

ABSTRACTAlthough fossil hydromorphic soils are very abundant in both Tertiary and older deposits in Western Europe, they are either not recognized or their study is not undertaken. A short account is given on the pedogenetical processes in hydromorphic soils and some of the features that can be traced and others that cannot are discussed. Two examples illustrate conclusions that can be drawn from the study of fossil hydromorphic soils.
Calcareous crust (caliche) profiles and early subaerial exposure of Carboniferous carbonates, northeastern Kentucky
Authors: WALLS RICHARD A. , HARRIS W. BURLEIGH , NUNAN W. E. 
Published: June 2006

ABSTRACTSequences of laminated limestones found within thin Carboniferous carbonate strata of northeastern Kentucky were studied to determine their origin and palaeo‐environmental significance. These laminated zones are strikingly similar to Holocene and Pleistocene surficial calcareous crusts (caliche) profiles that occur in various parts of the world.Carboniferous laminated carbonates are associated with shallow marine carbonate units, palaeokarst, and overlying palaeosol zones. A typical laminated profile ranges in thickness from 1 to 2 m and contains brecciated, light olive‐grey to brown micrite that lacks distinctive bedding. Structures and textures common in most profiles include: (1) calcareous and silicious laminae (laminae form diffuse, alternating light and dark bands that generally parallel bedding but often fill fractures and vugs within the rocks); (2) particles (allochems, and micrite and microspar fragments) coated by brown microcrystalline calcite; (3) brecciated texture; (4) circular to elliptical fossil moulds (occur in sinuous patterns and fill fractures within the rocks); (5) large and small scale fracture patterns.Subaerial weathering and vadose diagenesis of carbonate mud banks or islands is suggested as a mechanism for the formation of these Carboniferous calcareous crust profiles. These ‘crusts’ formed by a combination of solution (karsting), brecciation, and soil development that transformed an exposed marine biomicrite (‘host’ rock) into a porous subsoil rubble. Laminated ‘crusts’ and coated particles developed as the result of dissolution and reprecipitation of CaCO3 and SiO3 from the soil and carbonate bedrock.Carboniferous laminated carbonates in northeastern Kentucky are often referred to as ‘algal limestones’ because of their superficial similarity to some modern and ancient algal structures. This study, however, reveals numerous characteristics that can only be explained by diagenesis in a subaerial environment.
Computer program for presentation of grain‐size data by the graphic method
Authors: SLATT ROGER M. , PRESS DAVID E. 
Published: June 2006

ABSTRACTA computer program is described for a Hewlett‐Packard desk‐top Calculator (Model 9820A)‐Plotter (Model 9862A) which plots a histogram, frequency polygon and/or cumulative curve, as well as standard statistical parameters and percentages of gravel, sand, silt, and clay from raw weight data from a sediment grain‐size analysis. The program utilizes the graphic method for calculating statistical parameters in contrast to other commonly used computer programs derived for the method of moments.This program is advantageous because (1) it is rapid, (2) it allows direct comparison with grain‐size data in the literature which have been computed by the graphic method, (3) either a complete presentation of a distribution can be obtained on one sheet of paper or a series of cumulative curves or frequency polygons can be prepared on a single graph which is ready for publication photocopying, (4) automatic extrapolation of data points from a cumulative curve eliminates inconsistencies arising from manual extrapolation, and (5) the desk‐top calculator is more convenient to use, eliminates punching of data cards, and can be operated by someone without a knowledge of computers and programming. Disadvantages of the program are: (1) some authors feel critical percentiles are more accurately read off cumulative curves plotted on a probability ordinate than on an arithmetic ordinate, (2) the cumulative curve is a series of straight‐line segments, (3) the frequency polygon is not as accurate a representation of grain‐size distribution as a frequency curve and (4) size class intervals for the histogram and frequency polygon are standardized at 0.5φ, even though gravel and mud fractions are analysed at whole φ intervals. For most studies, the advantages of the program outweigh the disadvantages.
87Sr/86Sr composition of evaporitic carbonates and sulphates from Miocene sediment cores in the Mediterranean Sea (D.S.D.P., Leg 13)
Authors: CLAUER NORBERT 
Published: June 2006

ABSTRACTThe 87Sr/86Sr ratios of evaporitic carbonates and sulphates from Miocene sediment cored in the Mediterranean Sea show a depletion of 87Sr when compared to the isotopic composition of the Miocene contemporaneous marine strontium: 0.70803 versus 0.70936. The arrival into the evaporitic environment of strontium brought by continental waters can explain this difference.The variation of the 87Sr/86Sr ratios is, nevertheless, noticeable only when the influence of the continental waters is already well marked. This is proved when one compares the results obtained with strontium, to the results of isotopic analysis made on oxygen, carbon, sulphur and hydrogen taken from the same samples.
Depositional environments of Upper Miocene (Messinian) evaporites of Sicily as determined from analysis of intercalated carbonates
Authors: SCHREIBER B. CHARLOTTE , FRIEDMAN GERALD M. 
Published: June 2006

ABSTRACTVarious workers have suggested that the Upper Miocene (Messinian) evaporites of the Sicilian Basin formed in a topographic basin of considerable relief, filled with hypersaline water. Our studies indicate that this basin contained shallow water, at least during the deposition of the carbonate rocks intercalated between the gypsum beds. We recognize four basic kinds of limestone: (1) pelletal and pisolitic limestone; (2) skeletal limestone; (3) oöitic limestone, and (4) laminated lime‐stone‐dolostone. Modern analogs suggest that three of these four kinds of carbonate must have formed close to or above sea level. The evidence supporting this contention includes pellets with algal coatings, pisolites, quiet‐water oöids, and algal laminates. Therefore we suggest that the evaporites associated with these carbonates may likewise have formed in relatively shallow water. An alternative conclusion would be that the level of the sea, and the salinity, underwent irregular patterns of profound change.
Changes in intertidal dunes during two spring‐neap cycles, Lifeboat Station Bank, Wells‐next‐the‐Sea, Norfolk (England)
Authors: ALLEN J. R. L. , FRIEND P. F. 
Published: June 2006

ABSTRACTTwice‐daily observations over a fixed range were made covering three consecutive sets of spring tides. Some dune population dimensions (e.g. mean wavelength) show a long‐lasting (at least weeks) alteration during the most vigorous springs, but a short‐lived (tides or days only) change over the weaker ones. Other properties (e.g. mean height) experience merely short‐lived alterations. The changes seem to be linked to the creation during spring tides of new dunes of an initially small size (minor dunes), which introduces new matured dunes into the populations if there is sufficient subsequent sediment transport, and to the limited ability of individual dunes to respond to changing hydraulic conditions during their life‐spans. The dunes are active during only a very small proportion of each spring‐neap cycle, but the bank is permanently covered by them, and cross‐stratification caused by dune movement is the only internal structure. Without a knowledge of the history and dynamics of the dune populations, the quality of the environment at Lifeboat Station Bank cannot be satisfactorily assessed from the sedimentary products.
Lower Silurian transgressive barrier islands, southwest Wales
Authors: BRIDGES PAUL H. 
Published: June 2006

ABSTRACTBarrier islands developed on the southeastern flanks of a volcanic terrain during the Lower Silurian transgression of southwest Wales. The barriers are preserved in transgressive sequences overlying basalts and comprising from base upwards: lagoon→barrier island→offshore marine sediments. The thickness of the barrier island sediments varies from 5 m to 28 m. Comparison with modern barriers suggests that the thin sequences result from narrow (<2 km), steadily transgressing barrier islands, whereas the thicker sequences represent broad (2–4 km), slowly transgressing forms. In one case the barrier became narrower as the rate of migration accelerated in response to decreased fluviatile sediment supply caused by rising sea‐level. Despite the high preservation potential of inlet fill deposits, the latter are generally absent in these Silurian barriers because inlet migration was slow compared with the rate of barrier retreat. Possibly much shell material was dissolved during early diagenesis.
Bed topography and grain size in open channel bends
Authors: BRIDGE JOHN S. 
Published: June 2006

ABSTRACTEngelund's (1974a, b) theoretical bed topography model for curved channels is modified and shown to fit natural channels when using values for the dynamic bed load friction coefficient of about 0·4–0·5. The dependence of this coefficient on grain size for flow in the lower flow regime is discussed. Using the bed topography model simultaneously, Allen's (1970a, b) theory for grain size variation over point bar profiles is shown to be broadly applicable. The interaction between sediment, flow and bed topography in bends is therefore adequately described.
Glacial lake sedimentation, Austerdalsisen, Norway
Authors: THEAKSTONE WILFRED H. 
Published: June 2006

ABSTRACTSediments deposited in a lake at the front of a glacier in the Svartisen area, Norway, have been studied between 1957 and 1974. Until 1959, they were almost completely covered by an outwash plain (sandur), but subsequent erosion has exposed glacial lake sediments more than 70 m deep within a rock basin about 2·5 km long and 1 km wide. The basin was filled by sand and silt carried from beneath the glacier Austerdalsisen by two rivers, each of which deposited a delta in the lake. As the deltas advanced, laminated pro‐delta silt was covered by crossbeds of fine sand and silt, and by near‐horizontal sheets of fine sediments laid down between the delta‐fronts and the distal end of the rock basin. Although both slumping and loading caused minor disturbance of sediments at the lake floor, deformation was of local significance only. Movement of a mass of sediment across the floor, probably triggered by a ‘seismic event’ related to movement of the glacier or to calving at the floating tongue, created a recumbent fold in laminated sand and silt, but transfer of sediment over the lake bed was rare once it had been deposited. Varves are not common at Austerdalsisen, indicating that water temperature, lake chemistry or variations of water and sediment discharge from the glacier were unfavourable for their formation; rhythmic deposition from density flows of sediments carried from beneath the glacier rarely occurred within the Austerdalsisen basin.
Quantitative evaluation of the depth of the western Mediterranean before, during and after the Late Miocene salinity crisis
Authors: RYAN WILLIAM B.F. 
Published: June 2006

ABSTRACTQuantitative geophysical calculations which take into consideration the isostatic loading of sediment overburden, the overlying water cover, and the thermal cooling history of the continental edge, and its adjacent oceanic lithosphere, demonstrate the foundering of the margins of the western Mediterranean had already commenced in the Aquitanian stage of the early Miocene. The calculations are based on magnitudes and rates of sediment accumulation observed along a profile of three commercial boreholes into the subsurface of the continental shelf of southern France. By the time of the late Miocene (Messinian) salinity crisis, the depth of the seafloor within the Balearic basin exceeded 2.5 km.Sea‐level fluctuations induced by evaporitic draw‐down permitted the exposure of large tracts of the former submerged continental margins to subaerial processes. The measured magnitude of sediment removal by erosion and channel incision near the outer shelf of the modern Gulf of Lion surpasses 1 km.The subsidence history of this shelf platform south of France provides new evidence that the continental lithosphere behaves as if it is rigidly coupled to its oceanic counterpart commencing with the initial phase of the pull‐apart. No major vertical fault displacements have subsequently offset their overlying crustal layers.The sedimentary shaping and construction of the margin seaward of the Rhône delta resulted in a pronounced shelf edge migration and slope progradation during the pre‐salinity crisis Miocene. It has taken 5 million years of predominant upbuilding to establish a new equilibrium profile similar in cross‐section to the precrisis depositional surfaces created by outbuilding.
Size distribution of quartz in mudrocks
Authors: BLATT HARVEY , SCHULTZ DOUGLAS J. 
Published: June 2006

ABSTRACTSixteen penecontemporaneously deposited mudrock‐sandstone pairs ranging in age from Devonian to Cretaceous were treated chemically to isolate the quartz and chert fraction from the other constituents of the rocks. The amount of crystalline silica was determined from the chemical treatments; its size distribution was determined using a combination of normal and Micro Mesh sieving and settling tube analysis; the crystalline silica coarser than 10 μu was examined petrographically to determine the amount of chert.Percentages of crystalline silica in the mudrocks range from 6·7 to 46·7 % and average 27·6 (σ= 10·7). Mean grain size ranges from 4·4 φ to 7·3 φ and averages 6·1 φ. The crystalline silica fraction is a poorly sorted medium to fine silt consisting of one‐eighth sand, six‐eighths silt, and one‐eighth clay size sediment. Percentage of crystalline silica and mean size of crystalline silica in the thirty‐two mudrocks and sandstones are positively correlated; r= 0·685, which is significant at the 99 % level. The best fit linear regression line is: Y= 102·7–11·3X.Extrapolation of the regression line indicates that, on the average, crystalline silica is lacking in mudrocks in grain sizes finer than 9·1 φ (1·μm), a result consistent with observations by clay mineralogists.The crystalline silica fraction of both the mudrocks and associated sandstones averages 4% chert in the >10 μm portion. There is no correlation between the mean grain size of the crystalline silica and the percentage of chert in it.
Controls of variation in suspended sediment concentration in the River Rother, West Sussex, England
Authors: WOOD P. A. 
Published: June 2006

ABSTRACTSuspended sediment concentrations were determined for samples collected from the River Rother, West Sussex, and rating loops constructed for several hydrographs. The rating loops often exhibit hysteresis with a greater suspended sediment concentration for a given discharge occurring on the rising limb than on the falling limb. A comparison of these loops indicates that the hysteresis, and the suspended sediment concentration (for a given discharge) become progressively reduced when storm events occur in rapid succession.Various types of rating curves can be identified, and a model of suspended sediment concentration and discharge constructed. Controlling factors of suspended sediment concentration are river discharge, duration and frequency of the storm event, the length of time between successive events, and the time of year.
The sliding bed facies in esker sands and gravels: a criterion for full‐pipe (tunnel) flow?
Authors: SAUNDERSON HOUSTON C. 
Published: June 2006

ABSTRACTThe Guelph esker (Ontario, Canada) consists of a sinuous, steep‐sided and segmented ridge which comprises poorly sorted, matrix‐supported sands and gravels. These sands and gravels were probably deposited during the sliding bed stage which has been observed by others in closed‐conduit hydraulic experiments. The poor sorting probably resulted from a high concentration of bed‐material load in the lower part of a subglacial tunnel, sorting being restricted to that produced by particle collisions. Inclusive graphic standard deviation is characteristically large for the sands and gravels, indicating that virtually all sizes available were in transport. The overall grain size distribution shows a characteristic undulatory shape on arithmetic probability paper, mostly because of selective removal of pebble gravel and granule sizes. This poorly sorted fades is believed to be diagnostic of transport in a subglacial tunnel flowing full of water, and may be used to identify subglacial conditions in other eskers. Deltaic sands and gravels occur downcurrent of the esker and contain a greater diversity of structures; climbing‐ripple cross‐laminae, parallel laminae and massive structure, deposited in large‐scale foresees at the end of a subglacial tunnel. These deltaic sands and gravels grade distally into outwash sands and gravels.
Caliche profile formation, Saldanha Bay (South Africa)
Authors: KNOX GORDON J. 
Published: June 2006

ABSTRACTA sequence of gradational lithification events can be observed in caliche profiles, in the Saldanha Bay area (South Africa), from friable lightly cemented aeolian calcarenites or littoral shelly deposits through an intermediate semi‐indurated zone to an upper strongly indurated zone (calcrete).Lightly cemented sediment fabrics exhibit bridge and meniscus cements, micritic druses and vadose compaction phenomena. The middle semi‐indurated zones exhibit coated grains in which irregular borings and/or tubules with tangential acicular fibres contribute to coated grains. Random networks of acicular fibres also occur in void spaces. In fully indurated upper layers of the caliche profiles, fabrics of micriteand microspar (in voids) occur in complex brecciated macro‐fabrics.The features represent changes in a sequence from the friable primary sediments to the calcretes. Fresh‐water vadose flushing leaches grains and causes formation of meniscus and bridge cements and uneven druses. In the middle zone, inorganic processes are aided by the action of micro‐organisms; fungi, bacteria or algae which produce tubules and irregular borings; the overall effect of which is to break down original detrital carbonate particles and enclose them in a crypto‐crystalline micrite. The acicular fibres probably result from evaporation of supersaturated solution. Mechanical processes cause fracturing, which repeated many times gives complicated brecciated fabrics within the upper indurated zone.
The development of sediment threshold curves for unusual environments (Mars) and for inadequately studied materials (foram sands)
Authors: MILLER M. C. , KOMAR P. D. 
Published: June 2006

ABSTRACTGeneralized curves for grain threshold under liquid flow and under gas flow (air), based on laboratory data summarized in a previous paper, are utilized to generate a series of threshold curves for unusual sedimentary environments and little‐studied sedimentary materials of interest to geologists. These are aeolian and water flow threshold on the planet Mars, and the threshold of foraminiferal sands in the deep‐sea. Such extrapolations from the generalized curves are necessary because of the difficulty or impossibility of obtaining satisfactory data for these sediments or environments, and the procedures demonstrate the importance of the general threshold curves.