textural characteristics and genesis of the aeolian sediments in the kuwaiti desert several types of aeolian deposits have been recognized in kuwait a smooth sand sheets that resemble desert floor sand b immobile sands that include rugged vegetated sand sheets and wadi fill deposits and c mobile sands that form active sand sheets and sand dunes simple size frequency curves illustrate the genetic relationship between the various aeolian sediment types the four size parameters namely mean size sorting skewness and kurtosis were calculated scatter plot diagrams of sorting versus mean size and sorting versus kurtosis are effective in differentiating smooth sand sheet deposits from dune sands active sand sheet deposits can also be recognized because they are usually located between the two end members smooth sand sheets and dune sands size parameters change with location regardless of their types coarsening and positive skewness usually increase downwind mineralogical and textural characteristics of the aeolian deposits in kuwait revealed that they are mostly derived from the lower mesopotamian muddy flood plain deposits the sand fraction of the al dibdibba gravelly deposits and the disintegrated material from calcretic and gypcretic duricrusts distribution of depositional and deflational areas indicates that the northern desert of kuwait is characterized by a positive sand budget whereas the southern desert has a negative sand budget

grain size distribution patterns of a point bar system in the usri river india grain size distribution patterns in a point bar system of the usri river india were critically analysed in the light of log normal log hyperbolic and log skew laplace distribution models sand samples were collected from the cross bedding foreset of different sizes of bedform the objectives were to i study whether bedform heights have any role in grain size distribution patterns ii offer a best fit statistical model iii study the downstream variation of size sorting in a point bar system and iv study the mechanism of grain sorting the results indicate that the bedform heights have no role in grain size distribution patterns quantitatively when the errors in three distribution models were analysed it was observed that the log normal distribution is the best fit statistical model and the next one is the log skew laplace however in the upper reaches of the river log normal distribution is the best fit model in the case of large bedforms whereas in the lower reaches the log normal model is the best fit one in the case of small bed forms it is also observed that within a point bar for large and small bedforms there is a tendency for mean grain size to decrease downstream between point bars for large bedforms there is no consistency in decreasing grain size downstream whereas for small bed forms the decrease of grain size downstream is observed except near the confluence at palkia with distance of transport the coarser and finer fractions of sediments are gradually chopped off the coarser fractions are buried below the advancing bedforms on the lee sides and the finer ones are transported further downstream thus the finer admixture giving rise to the fining upward sequence overlies a carpet of coarser materials this mechanism provides a clue to the process of grain sorting in the fluvial environment an interpretation has been offered for the log normality of the grain size distribution pattern during prolonged transportation in a fluvial environment the larger grain size fractions are gradually chopped off and buried below the advancing bedforms on their lee sides on the other hand the finer fractions are transported further downstream in suspension thus the narrow intermediate size fraction takes active part in the distribution patterns leading to the generation of unimodality and a symmetric distribution pattern downstream which are the main criteria for log normality similarly increase of bedform size is the effect of increase of stream power and froude number leading to the selective segregation of bed materials thus the intermediate size fractions take a more active part than the coarser and the finer size fractions in developing log normality besides the hydrodynamic parameters of the usri coarsening of grain size downstream has been attributed to i the aggrading nature of the usri downstream and ii the contribution of coarser materials to the usri by its tributaries and bank erosion copyright 2006 john wiley sons ltd

discriminating depositional environments of sands from modern source terranes using modal analysis abstract composition of modern beach dune and fluvial sands from the gulf of mexico coast and the kapiti and foxton coasts new zealand were compared in order to establish petrological criteria that discriminate between depositional environments and subenvironments the three areas were chosen because of their different sand compositions sand from the gulf of mexico is quartzofeldspathic to feldspatholithic sand from the kapiti coast sands is feldspatholithic and sand from the foxton is lithofeldspathic using a confidence level of 95 petrographic data were plotted as bar charts for each environment beach dune river and for each subenvironment inshore foreshore backshore of the beaches stoss crest lee face of eolian dunes upstream and mouths of the river the best discrimination of beach dune and river environments was achieved for the gulf of mexico sands using q f l and qm k p plots terranes with multiple source rock types such as the gulf of mexico enhance petrological discrimination between sands from beach dune and river subenvironments and environments in terranes with few rock source types such as the kapiti coast only the river sands can be discriminated from those of other environments the single rock source of the foxton coast allows little petrological discrimination between the beach dune and river sands this study examines compositional differences between beach dune and river subenvironments and environments and the degree to which these differences are dependent on the variation of rock types in the source terrane the study also shows the usefulness of q f l qm k p and lv lm ls bar charts the discrimination among beach dune and river sands is partly due to grain size variation

differentiation of modern beach and coastal dune sands a logistic regression approach using the parameters of the hyperbolic function abstract particle size data have been obtained from sieved samples of sand from beach and coastal dune environments at ainsdale northwest england the four parameters of the hyperbolic distribution were calculated for each sample these together with additional derived parameters were the basis of a binomial logit regression model which sought to distinguish the two sand environments seventy five percent of the samples were correctly assigned by logistic equation containing a single independent variable which is a measure of the skewness of the hyperbolic distribution

deposition of sand by suspension currents experimental and theoretical studies abstract flume experients with heterogeneous sediment mixtures show that all the grain sizes present in suspension are involved in the process of formation of a bed when the flow velocity is decreased the size distribution deposited closely reflects the one present in suspension this finding is contradictory to the common belief that the coarser grains are the first to be discarded at decreasing current velocity the existing equations after rouse 1938 and hunt 1969 also tend to overestimate depletion of the coarser grains a mathematical model for deposition based on the idea that the process of depletion of the coarser grains is actually dampened in nature has been developed in this work this model gives results which compare well particularly for low velocities with the observed values comprising wide range of grain sizes using the model it should be possible to estimate the grain size distribution of the deposited material given the size distribution present in suspension at a higher velocity since the size distribution of the deposits closely reflects that present in suspension it should also be possible to work out paleoflow velocities of suspension currents from grain size parameters of ancient deposits following the relationship established earlier between mean grain size in suspension and the shear velocity ghosh and mazumder 1981

palynological evidence for prolonged cooling along the tunisian continental shelf following the k pg boundary impact abstract the cretaceous palaeogene k pg boundary mass extinction event is related to major global environmental changes resulting from a large extraterrestrial impact organic walled cyst producing marine dinoflagellates dinocysts survived the k pg mass extinction relatively unscathed making them ideally suited for reconstructing these environmental changes so far one of the best dinocyst records available is from the k pg boundary global stratotype section and point gssp at el kef nw tunisia there the dinocyst record shows major fluctuations across the boundary likely reflecting strong responses to environmental changes these fluctuations have so far not been confirmed by other studies therefore in this study we performed a high resolution marine palynological study on a closely spaced sample set from the elles section some 75 km south of el kef in order to generate a palaeoenvironmental and palaeoclimatic record across the k pg boundary to allow verification and refinement of earlier reported environmental changes to better constrain the reconstructions based on qualitative biotic proxies we employed the quantitative sea surface temperature proxy tex86 unfortunately the tex86 proxy record of the studied section is compromised because of post depositional oxidation however the diverse dinocyst assemblages at elles show strong fluctuations similar to the el kef record therefore confirming the earlier recorded signals showing rapid regionally consistent changes these records imply that the latest cretaceous was characterized by a gradual cooling trend and the onset of relative sea level fall within the immediate post extinction interval in the first thousands of years after the impact dinocyst assemblages reveal multiple incursions of higher latitude dinocyst species implying repeated pulses of cooling these results signify that the earliest danian climatic and environmental conditions were relatively unstable across the tunisian shelf

the manumiella seelandica global spike cooling during regression at the close of the maastrichtian abstract manumiella seelandica lange 1969 bujak and davies 1983 emend firth 1987 occurs in great abundance together with a closely related and possibly conspecific form isabelidinium sp virtually at the end of the maastrichtian the abundance of m seelandica immediately adjacent the cretaceous paleogene kpg boundary and its global distribution serve as an excellent biostratigraphic marker for dating it the abundance spike is widely distributed in both northern and southern hemispheres and ranges from locations as far south as seymour island antarctica to as far north as west greenland the global distribution of the m seelandica spike in such widely separated areas and the ease with which it is recognized in closely sampled sections underscores its value in dating until recently this short lived event was correlated within an interval of global sea level fall and regression which extended from the latest maastrichtian into the earliest danian that is that the species became numerically abundant as the shoreline approached however based on our study of the boundary interval at bass river in southern new jersey usa we propose that an additional factor may have contributed to its origin our investigation of this section shows that there is a prominent abundance spike in the 20 cm 7 8 in interval immediately beneath the boundary and that this interval correlates precisely with the 18o isotope evidence of cooling at bass river the last 500 ky of the maastrichtian was a period of global warmth as revealed by geochemical evidence however based on the geochemical evidence a mild cooling period began within tens of thousands of years of the close of the cretaceous period based on this correlation we present the hypothesis that the cooling event played an important role in producing this global assemblage of dinoflagellates study of a large number of fossils in the sample situated 15 cm 5 85 in beneath the boundary shows that there is considerable variation in overall form and archeopyle excystment in manumiella seelandica the same degree of variation was not observed in the samples with fewer specimens

recognition of cyclic and non cyclic environmental changes in the mediterranean pliocene a palynological approach the interval between 2 8 and 2 3 ma b p from the south italian singa section has been investigated for its dinoflagellate cyst and sporomorph contents in order to facilitate palaeoenvironmental interpretation the following curves are derived from the data the ratios sporomorphs dinoflagellate cysts protoperidinioid gonyaulacoid dinoflagellate cysts warm cold water indicating dinoflagellate cysts inner neritic oceanic dinoflagellate cysts outer neritic oceanic dinoflagellate cysts and the reworked dinoflagellate cysts per gram of sediment furthermore the already available 18o curve has been used calibration of changes in the sporomorph dinoflagellate ratio against the computed astronomical insolation curve leads to an improved age assessment for the section frequency analysis on the curves shows the 23 41 and 100 ka frequency components to be most important phase and amplitude differences between the filtered 23 41 and 100 ka frequency components are used for environmental interpretation the 23 ka frequency band is best explained by changes in runoff induced transport the 41 ka frequency components are classified in a group with short response time to orbital forcing and a group with longer response time those signals having a short response time are attributed to local precipitation induced changes in runoff those signals having a longer response time are mainly attributed to changes in global temperature and to a lesser extent to changes in global ice volume finally longer term cyclic and non cyclic changes are mainly attributed to temperature and sea level variation

the use of grain size distribution patterns to elucidate aeolian processes on a transverse dune of thar desert india the grain size distribution of aeolian dune sands in the thar desert india was analyzed and compared with three model distributions log normal log hyberbolic and log skew laplace to determine the best fit statistical model in total 51 samples were collected along a single transect over a transverse dune of which 15 were from the stoss side 12 from the crest and 24 from the lee side samples were collected during a calm period in the afternoon of a winter s day it was observed that of these 51 samples 33 fit best to a log hyperbolic distribution 14 fit best to a normal distribution and only four fit best to a laplace distribution however it was further observed that of 24 samples from the lee side 13 fit best to a normal distribution eight fit best to a hyperbolic distribution and three fit best to a laplace distribution of 12 samples from the crest of the dune 11 fit best to the log hyperbolic distribution only one to the laplace distribution but none to a normal distribution of 15 samples from the stoss side of the dune only one sample best fits a normal distribution 14 fit best to a log hyperbolic distribution and none best fit to a laplace distribution during sample collection a calm period prevailed and there was no dusty wind it was therefore assumed that in the initial stage a mixture of coarse medium and fine sands was laid down on the stoss side of the dune as wind speeds increased and saltation started the coarser fractions were segregated and lagged behind on the stoss slope in the final stage when the remaining intermediate and finer fractions reached the dune crest the finer fractions were winnowed away to suspension from the crest of the dune as a result a narrow range of intermediate sized sediments was deposited by rolling down the lee side to explain the development of log normality in such a situation both the coarser and finer fractions to which the skewed distributions can be attributed are separated from the initial mixture of coarse intermediate and fine fractions hence the main criteria for the development of a normal distribution is the lack of skewed fractions and the concentration of the narrow intermediate size fractions in the final grain size distribution this is also corroborated with the index of symmetry which is a measure of the difference between the angle of two slopes of the hyperbolic distribution as represented by the coarser and finer fractions copyright 2010 john wiley sons ltd

grain size characteristics of dune sands in the central taklimakan sand sea abstract compared with the sand grain size of the other sand seas central taklimakan sand sea has some of the finest sands seen globally the dunes are composed of fine and very fine sands with a diameter between 2 00 and 4 00 0 25 0 063 mm there are differences in the grain size distributions for different dune types mean grain size of the compound complex crescent dune sands is 3 08 the compound dome dunes 3 21 the compound complex linear dune sands between 2 63 and 3 41 and the star dunes 2 81 from the northern edge of the sand sea towards southern edge the components of fine and very fine sands increase closely related to the wind regimes time scale for dune development and underlying sediments compared with the foregoing there are some differences for the compound complex linear dunes in the centre of taklimakan though the pattern of coarser crests does exist the sorting parameters indicate that the sands on the west flank of compound complex linear dunes are better sorted than that on the east flank and crest sampling on the superimposed dunes developed on the surface of the complex linear dunes suggests that the patterns of finer crest coarser crest all existed in central taklimakan under the conditions of low energy wind regime when fine sand is available the frequency of the pattern for finer crest and better sorting will increase sampling on the simple crescent dunes developed on the interdunes suggests that the simple dunes are developed originally with nearly the same grain size distributions and parameters with the development of the dunes and evolution of the dune morphology the grain size distributions of the dune sands varied under the actions of the wind regimes time scale and underlying sediments

variation in particle size distribution over a small dune the variation in particle size distribution for a sequence of sand samples collected from the surface of a small barchanoid dune along a sampling line parallel to the windflow is studied by means of the hyperbolic distribution the modal or typical value of the log size increases linearly with distance from the windward foot to the crest of the dune and falls off steeply on the lee side the spread of the log size distribution locally near the modal value is roughly constant on the windward side but decreases significantly down the slip face two other parameters of the four parameter hyperbolic distribution can be considered largely constant a comparison of the log size distributions for heavy and light mineral grains based on a selected set of the samples showed that heavy and light minerals follow different hyperbolic patterns however the difference in modal size of the distributions for the two types of minerals was virtually constant among the samples

changes in coiling direction of cibicidoides pseudoacutus nakkady across the cretaceous tertiary boundary of tunisia palaeoecological and biostratigraphic implications abstract the analysis of coiling direction preference in the benthic foraminifera cibicidoides pseudoacutus nakkady has been carried out across the cretaceous tertiary boundary k t boundary from four tunisian sections representing a palaeobathymetric transect from a middle outer neritic to lower upper bathyal depositional setting our study reveals that c pseudoacutus developed a preference for sinistral coiling in a short time period during the lowermost danian the comparison of the coiling ratio number of sinistral vs dextral individuals record with isotope data and dinoflagellate cyst assemblage distribution suggests that the development of sinistrally coiled populations of cibicidoides pseudoacutus might be related to a short term cooling of both surface and bottom waters which occurred at the k t boundary and lasted for some 7 kyr the continuous occurrence and the high abundance of cibicidoides pseudoacutus through the k t boundary in neritic to upper bathyal depositional environments around southern tethys make identification of the shift in its coiling ratio relatively easy the development of a sinistrally coiled population in this benthic foraminiferal species is regarded as a potential marker for the base of planktonic foraminiferal zone p0 in tethyan shallow water settings

distinguishing different sedimentary facies in a deltaic system abstract an attempt has been made to differentiate sedimentary facies in a modern deltaic system by means of grain size characteristics of the ganga alluvial plain of west bengal india three main energy environments marine mixed and riverine comprising the delta were considered sand samples were collected from rivers both tidal and non tidal coastal dunes beaches and tidal flats of the deltaic plain the grain size distribution patterns were compared with the two model distributions of log normal and log skew laplace different sedimentary facies were identified by discriminant functions the analytical results indicate that the energy gradient of the different sedimentary facies of the deltaic system is well reflected by the grain size characteristics of the individual facies while critically analyzing the role of different textural parameters in discriminating the individual facies associations it is observed that the mean size alpha slope of coarser fractions of laplace model and skewness have greater potential to distinguish different sedimentary facies of the deltaic system the results of discriminant analysis might be applicable to paleo environmental interpretation of a deltaic system by distinguishing the individual facies associations

distinguishing depositional setting for sandy deposits in coastal landscapes using grain shape abstract several methods exist that use sediment properties to characterize depositional setting and related mechanisms of transport including analysis of grain size distributions sediment petrology micromorphology and grain structure techniques that rely on electron or optical microscopy produce results with varying degrees of success and applicability here a new method is presented and used to differentiate between littoral and eolian sands that were extracted from recently formed landforms as well as landforms that are from mid to late holocene in age the method utilizes a standard optical microscope with a mounted digital camera paired with freely available software imagej to characterize grain shape parameters the method was tested on nearly 6000 sand grains from samples with varied transport histories and it was found that grain solidity was the most distinguishable characteristic between eolian and littoral samples differentiating them 86 of the time for calibration samples the method was used to correctly identify the mechanism of transport for 76 of the samples patterns in the results indicated that this method could be extended to link potential sediment sources to various depositional basins and future work includes testing the method in areas with a different mineralogy and or landscape history

topset dominated deltas a new model for river delta stratigraphy in the late 1800s g k gilbert provided the first stratigraphic description of river delta deposits but later work revealed that the gilbert type model long thought to be universal did not apply to all deltas here we propose that in addition to gilbert type deltas herein called foreset dominated there is a class of deltas with a basic first order stratigraphy that is topset dominated we develop a geometric model that predicts the occurrence of each delta type by calculating the topset and foreset thicknesses under different fluvial and basinal conditions our model predicts that topset dominated deltas have a novel characteristic their distributary channels commonly incise into pre delta sediment this type of delta should be common on shelves where the slope is less than 0 05 and the river feeding the delta has a discharge greater than 200 m 3 s field data from gulf of mexico deltas confirm the prediction that distributary channels often incise into pre delta sediment finally we propose a new stratigraphic model for topset dominated deltas and suggest that future stratigraphic interpretation must distinguish between delta types because the cause of channel incision for each is different and may be unrelated to allogenic changes

trace elements stable isotopes and clay mineralogy of the elles ii k t boundary section in tunisia indications for sea level fluctuations and primary productivity abstract trace elements and stable isotopes in bulk rocks and foraminifera bulk rock and clay mineral compositions are used as palaeoproxies to evaluate sea level fluctuations climatic changes and variations in primary productivity across the k t transition at elles ii in tunisia from 1 m 33 kyr below to 1 m 70 kyr above the k t boundary results on clay minerals major and trace elements stable isotopes in bulk rock samples e g ca cu zn rb sr zr ba 13c and 18o and in foraminifera sr ca 13c 18o indicate that the latest maastrichtian last 33 kyr in tunisia was marked by a relatively warm but humid climate and a rising sea level the transgressive surface is marked by deposition of a foraminiferal packstone just below the k t boundary followed by maximum flooding across the k t boundary red layer and black clay layer humid warm conditions accompanied the maximum flooding along with increased total organic carbon values and rapidly decreasing primary productivity at the k t boundary an impact event ir anomaly ni rich spinels spherules exacerbated already stressed environmental conditions leading to the mass extinction of tropical planktic foraminifera increasingly more humid conditions prevailed within the lowermost danian zone p0 50 kyr culminating in a sea level lowstand near the top of p0 a slow recovery of the ecosystem in zone p1a coincided with a rising sea level and gradually less humid climatic conditions

formation and maintenance of the extratropical tropopause by baroclinic eddies numerical simulations in a simple atmospheric model show that a realistic extratropical tropopause structure marked by a strong change both in meteorological variables such as lapse rate and in transport characteristics may be achieved solely through the stirring effects of baroclinic eddies acting against a smooth thermal relaxation the flow self organizes to give a transport structure that has a sharp transition in the vertical below the transition level the eddies stir across entire isentropic surfaces the transition level corresponds to the extratropical tropopause height above the transition level there is a midlatitude transport barrier corresponding to the subtropical transport barrier in the real atmosphere with eddy stirring on poleward and equatorward sides similar self organizing mechanisms are likely to be relevant in the stratosphere and in oceanic flows

a new method for environmental analysis of particle size distribution data from shoreline sediments the study of particle size distributions is commonly used to investigate sedimentary processes and environments originally such work concentrated on typifying these distributions by their sample moments while more recent statistical studies have proposed fitting parametric models to sample data and then using the resulting parameter estimates we have investigated the use of log hyperbolic and skew log laplace models to distinguish between beach and dune sands with the aim of classifying the depositional environment of some mesolithic middens we found that the former models were unsatisfactory for various numerical and physical reasons while the latter provide a simple and robust method which is useful for the classification of sand sediments

patterns of grain size distribution in some point bars of the usri river india abstract the patterns of grain size distribution of point bar sediments on the usri river india were compared to log normal log hyperbolic and log skew laplace distribution models sediment samples were collected from a specific size of bedform ranging in foreset thickness from 23 to 40 cm from the source to the mouth of the river over a distance of about 90 km the hydrodynamic parameters of the river were also measured at four point bars the results indicate that a the log normal distribution is the best fitted distribution model among the three distribution models b after a certain distance of transport the log normal distribution becomes log hyperbolic and c though there is a tendency for grain size to decrease downstream within each point bar together with improvement of sorting this pattern is not consistent along the entire course of the usri river from one equivalent bar position to the next or from the source to its mouth

heat transport deep waters and thermal gradients coupled simulation of an eocene greenhouse climate for the first time a coupled general circulation model with interactive and dynamical atmospheric oceanic and sea ice components is used to simulate an eocene 50 ma greenhouse climate we introduce efficient ocean spin up methods for coupled paleoclimate modeling sea surface temperatures ssts and salinities evolve unconstrained producing the first proxy data independent estimates for these eocene climate parameters tropical and extratropical model predicted ssts are warmer than modern values by 3 and 5 c respectively salinity driven deep water formation occurs in the north atlantic and tethys the zonal average overturning circulation is weaker than modern eocene ocean heat transport is 0 6 pw less than modern in the northern hemisphere and 0 4 pw greater in the southern hemisphere the model predicted near modern vertical and meridional eocene temperature gradients imply that the dominant theory for maintaining low gradients increased ocean heat transport is incorrect or incomplete and other mechanisms should be explored

effective grain size distribution analysis for interpretation of tidal deltaic facies west bengal sundarbans abstract research over the past two decades on the holocene sediments from the tide dominated west side of the lower ganges delta has focussed on constraining the sedimentary environment through grain size distributions gsd gsd has traditionally been assessed through the use of probability density function pdf methods e g log normal log skew laplace functions but these approaches do not acknowledge the compositional nature of the data which may compromise outcomes in lithofacies interpretations the use of pdf approaches in gsd analysis poses a series of challenges for the development of lithofacies models such as equifinal distribution coefficients and obscuring the empirical data variability in this study a methodological framework for characterising gsd is presented through compositional data analysis coda plus a multivariate statistical framework this provides a statistically robust analysis of the fine tidal estuary sediments from the west bengal sundarbans relative to alternative pdf approaches