evolving fluvial transitional marine deposition through the cambrian sequence of jordan abstract the cambrian sequence in jordan crops out in a belt like pattern extending over more than 300 km from the arabian nubian shield source rock in the south located on a stable shelf platform to the invading southern baltic side of the tethys seaway the analysis of the lithofacies association ichnofossil content together with the architecture of fluvial and paralic sandstone bodies reveals the development of the depositional environments of the cambrian deposits of jordan the depositional environment evolved from proximal alluvial fans into major sand flats of braided rivers or directly into distal braidplains dominated by 3 d megaripples in the following depositional phase various marine environments prevailed including platform carbonates clastic carbonate and mixed tidal flats and supratidal sabkhas and less common lagoons all these marine or marine influenced environments changed back into distal braidplains or sand flats of braided streams the latter persisted through the remaining period of the cambrian the study has revealed that shales containing cruziana interbedded within the fluviatile sandstone sequence are time markers that can be used for correlation and could be deposited in a braidplain if the detrital influx was very low it is the latter that enabled the cruziana producing trilobites to migrate from the sea through river mouths to reach distal braidplains and lagoons

geology and petroleum potential of upper cretaceous and tertiary strata beaufort mackenzie area northwest canada 1 upper cretaceous to holocene strata on the beaufort sea continental margin were deposited as a series of northward prograding delta complexes totaling 12 16 km thick the succession contains eleven regionally extensive transgressive regressive sequences that were deposited during four large scale tectonostratigraphic phases each phase terminated by a major tectonic event during the cenomanian to middle maastrichtian sedimentation was limited to relatively thin organic rich muds on an outer shelf to basinal environment from the late maastrichtian to middle eocene deltaic depocenters were located along the southwestern margin of the canadian beaufort sea during the third depositional phase middle eocene to late miocene sedimentation was concentrated in the central canadian beaufort sea depocenters shifted to the eastern beaufort sea during the fourth depositional phase pliocene to early pleistocene the modern mackenzie delta may represent a new phase of deposition considerable volumes of oil and gas have been discovered in tertiary rocks principally in eocene and oligocene delta front strata with lesser volumes in paleocene and miocene strata three families of oils have been recognized in tertiary reservoirs the most important of which appears to have been derived from the eocene richards sequence in general tertiary strata have modest toc total organic carbon values 1 2 and low thermal maturity to drilled depths 4000 4500 m in the more extensively explored central beaufort mackenzie area however thermal and subsidence modeling of tertiary strata suggest that maturity rapidly increases between 5000 and 6000 m

thirty five year creep rates for the creeping segment of the san andreas fault and the effects of the 2004 parkfield earthquake constraints from alignment arrays continuous global positioning system and creepmeters we present results from differential global positioning system gps surveys of seven alignment arrays and four continuous gps sites along the creeping segment of the san andreas fault surveys of four alignment arrays from the central creeping segment yield 33 to 36 year average minimum slip rates of 21 26 mm yr these rates are consistent with previous alignment array surveys spanning a 10 year period and with rates determined by creepmeters indicating approximate steady state creep along the central creeping segment for at least 35 years motion between continuous gps sites that span the central creeping segment is 28 2 0 5 mm yr for two sites that are 1 km apart and 33 6 1 mm yr for two sites that are 70 km apart slip rates therefore increase with distance from the creeping segment of the san andreas fault all rates reported here are significantly slower than the 39 2 mm yr rate predicted for motion between the sierra nevada great valley block and the pacific plate repeat surveys of three alignment arrays following the 2004 parkfield earthquake demonstrate that its coseismic and short term postseismic offsets decrease rapidly with distance from the epicenter from 150 mm to 15 mm to 5 mm at respective distances of 9 36 and 54 km to the northwest continuous gps data confirm that little coseismic and postseismic slip occurred along the central creeping segment geodetic and geologic slip rates are compared and different models for the accommodation of transcurrent deformation across the creeping segment are discussed

integration of seismic and sedimentological methods for analysis of quaternary alluvial depositional systems due to the high potential of unconsolidated sedimentary bodies to form aquifers and reservoirs an identification of their exact geometry and location is of great importance current conceptual models of these bodies are often developed using scattered data from hydrogeological wells more reliable results can be achieved by application of methods that can provide continuous subsurface record of the actual geological situation in the investigated area in this article a combination of two different approaches is used on a case study of alluvial quaternary sediments from the east slovakian basin including the discussion how these methods contribute to the final geological interpretation first a sedimentological analysis was performed with the use of data acquired from auger drilled hydrogeological wells which enabled identification of depositional processes depositional systems and the possible source areas due to the shallow depth of the studied area a second approach based on the geophysical measurement using seismic refraction and tomography was applied this method provided information mainly about the geometry of these systems the position of the sediments within them and highlighted where the main changes in the sediment texture and composition occurred integration of both methods allows us to obtain a more precise image of the subsurface which contributes to a better understanding and prediction of the occurring sediments in the studied area

sedimentology and palaeogeography of the regressive transgressive kurnub group early cretaceous of jordan abstract the early cretaceous kurnub group of jordan consists of three regressive transgressive fluvial marine depositional sequences in northern jordan recorded here for the first time whereas continental clastics dominated central and southern jordan deposition of the kurnub group started in the late neocomian above a regional angular unconformity by basal conglomerate and sandstone facies association of an alluvial braidplain origin during this time the tethys seaway was located to the north and northwest of jordan which afterwards during the barremian advanced in a south and southeastward direction flooding north jordan and giving rise to a tidal flat coastal swamp sequence following a subsequent regression of the sea unconfined braidplain deposits covered the area the most extensive transgression of the tethys inundated the region during the late aptian and early albian where a mixed siliciclastic carbonate sequence with interbedded inner shelf carbonates and tidal marsh coastal swamp black shales and lignites was deposited the next and last regression took place in the middle albian where a thin meandering river clastic sequence was deposited finally shallow marine sedimentation resumed over the region during the remaining time of the kurnub group which at the same time prepared for the subsequent regional cenomanian transgression upon comparison with global eustatic curves these three incursions of the tethys sea in jordan are to a great extent in accordance with the global sea level fluctuations the various formations of the kurnub group and their informal units that are established here for the first time can readily be correlated with equivalent deposits in adjacent countries the distribution of the shorelines of the barremian aptian and albian on both sides of the dead sea transform offers new evidence for 100 km northward displacement of the arabian plate against the sinai palestine plate

sedimentology and mineral composition of the kurnub sandstone in wadi qsieb sw jordan abstract the kurnub sandstone of early cretaceous age crops out in wadi qsieb in the southwest of jordan with a thickness of 130 m moderately developed fining upward cycles with irregular erosive bases together with the presence of plant fragments and the absence of body or trace fossils point to a fluviatile depositional environment probably a river of intermediate sinuosity results of grain size analysis confirm this interpretation the sandstones are compositionally and texturally supermature quartz arenites formed mainly by recycling from early palaeozoc sandstones and less commonly by direct supply from the arabian nubian shield the absence of feldspars and unstable heavy minerals is attributed to intense chemical weathering attacking sands that were deposited with a low rate on a craton bordering the tethys sea the thickness recorded here and the absolute absence of hornblende are in contradiction with what has been published by nasir and sadeddin 1989

weathering recycling hydraulic sorting and metamorphism metasomatism implications of the ne gondwana lower cambrian lower cretaceous siliciclastic succession of jordan abstract whole rock major elements detrital and authigenic light heavy and clay minerals and neoformed zeolite minerals of the ne gondwana lower cambrian lower cretaceous siliciclastic succession of jordan were investigated to evaluate the factors controlling the chemical composition of the sandstone the provenance source rocks controlled by the tectonic setting at the time of deposition of the subarkosic arenites and the quartzarenites were the principal mineral and chemical governing factor followed by an interplay of chemical weathering recycling hydraulic sorting diagenesis and very low grade metamorphism hydrothermal metasomatism the sandstone provenance was mainly granitoids of the arabian shield formed during the neoproterozoic gondwana amalgamation and minor paleozoic and mesozoic siliciclastic strata high cia and low wip weathering index values indicate an intensive chemical weathering event that affected the provenance during the early cambrian middle ordovician and gave rise to mature first cycle quartzarenites high cia wip and sio2 al2o3 ratios indicate a pronounced recycling in the early cretaceous responsible for super mature second poly cycled quartzarenites the subarkosic arenites were formed either under a thorough chemical weathering coupled with a high rate of erosion and a rapid deposition in adjacent braidplains or an arid glacial climate devoid of chemical weathering hydraulic sorting caused enrichment of al and k in the detrital clay minerals ti in the silt sized ti bearing minerals and si in the sand sized quartz the very low grade metamorphism hydrothermal metasomatism recorded here for the first time is indicated by illite crystallinity ic 0 36 2 illite sericite muscovite transformation zeolites apatite authigenesis and alteration of monazite and titanite ilmenite into thorite and leucoxene hematite

on the evaluation of sediment transport models in tidal environments abstract the application of numerical models for the simulation of coastal hydro and sediment dynamics requires model verification calibration and validation with field data yet no commonly accepted rules for the evaluation of sediment transport models exist this paper discusses the significance of statistical parameters and their limitations considering common time lags in tidal environments it is shown that the occasionally used discrepancy ratio lacks quantitative and qualitative information on model performance as the time context information on time series characteristics is lost as an initial measure of association the simple linear correlation coefficient r2 is proposed to account for time lag errors in suspended transport models a separate cross correlation analysis for the flood and ebb tidal phase is proposed for a comparison with other model applications a concluding rating of model performance can be expressed by a dimensionless error definition which takes into account the quality of field data

characteristics and formation mechanism of multi source mixed sedimentary rocks in a saline lake a case study of the permian lucaogou formation in the jimusaer sag northwest china abstract the permian lucaogou formation in the jimusaer sag of the southeastern junggar basin in china is an uncommon set of mixed sedimentary rocks the mixed sediment content of the lucaogou formation is unusual due to the large amounts of tuffaceous material which makes the system more complex than the commonly mixed siliciclastic carbonate rocks in this study the volcanic material acts as a third end member component in a multi source mixed sedimentary system therefore a new type of mixed siliciclastic carbonate tuffaceous rocks has been introduced methods including core observations thin section analysis grain size measurements and x ray diffraction are used to investigate the characteristics of mineral components sedimentary structures and lithological assemblages in upper and lower sections of the formation these analyses are then used to determine the lateral distribution area of mixed sedimentation sedimentary mixing processes originally described for siliciclastic carbonate systems are used and expanded here for the multi source mixed rocks in a saline lacustrine basin controlling factors on mixed sedimentation included climate change lake level fluctuation tectonic activity and sediment supply rate mentioned in previous studies as well as variations of energy levels in different parts of the lake mixed depositional models for the lower and upper sections of the lucaogou formation in saline lacustrine basin have been established respectively

pore throat structure characteristics and its effect on flow behavior in gaotaizi tight siltstone reservoir northern songliao basin abstract the features of pore and throat structure of an unconventional reservoir are very complex due to multiscale pore throat size and various pore types and thus hard to characterize in this study thin sections field emission scanning electron microscope fe sem x ray diffraction xrd granulometry analysis physical properties measurements mercury intrusion capillary pressure micp and nitrogen gas adsorption analysis n2ga were combined to investigate the pore throat structures of the gaotaizi tight siltstone reservoir in the northern songliao basin the results of observation suggest that the pores are composed of intergranular pores dissolution pores intercrystalline pores within clay minerals and micro fractures the content of calcite cement has some negative effect on porosity the content and types of clay minerals have some negative influence on petrophysical properties of reservoir as well micp and n2ga are combined to get the full range of pore throat size distribution based on previous studies and the actual situation of the gaotaizi reservoir a new classification for pore throat size has been proposed including micropore 100 nm mesopore 100 nm 0 625 m and macropore 0 625 m on this basis the contents of pore throat in different scales have been calculated the gaotaizi tight siltstone reservoir has been divided into three types based on the pore throat structure there are big differences among the three types of reservoir with respect to the grain size the content of matrix the types of diagenetic minerals the dominant pore types the pore throat size distribution and the percentage of pore throats in different scales accordingly a pore structure model has been constructed for each type of reservoir in addtion it has been found that the pore throat structure has an important effect on the percolation capacity of the tight siltstone reservoir porosity and pore throat radius have a positive correlation with the permeability pore throats in different scales have different impact on the flow characteristics of tight reservoir the mesopores and macropores make a great contribution to the flow in the reservoir while the micropores and transition pores do not contribute and even have an inhibitional effect in general the permeability or the flow characteristics of the tight siltstone reservoir are mostly controlled by the pore throats larger than 0 1 m

fluvial shallow marine glaciofluvial depositional environments of the ordovician system in jordan abstract the ordovician system cropping out in southern and west central jordan consists entirely of a 750 m thick clastic sequence that can be subdivided into six formations the lower disi formation starts conformably above the late cambrian umm ishrin formation according to cruziana furcifera occurring in the upper third of the disi formation an early ordovician age is confirmed the disi formation consisting mainly of downstream accretion da fluvial architectural element was deposited in a proximal braidplain flowing n ne from the southerly located arabian nubian shield towards the tethys seaway the braidplain depositional environment evolved into a braidplain dominated delta through the middle and upper parts of the disi formation and the lower part of the overlying um saham formation the delta was replaced by siliciclastic tidal flats that in turn evolved into an upper to lower shoreface environment through the upper part of the um saham formation the depositional environment attained the maximum bathymetric depth during the deposition of the lower and central parts of the third unit the hiswa formation where offshore graptolite rich mudstone with intercalated hummocky cross stratified tempestites were deposited the tethys seaway regressed back through the upper part of the hiswa formation promoting a resumption of the lower upper shoreface sedimentation oscillation between the lower to upper shoreface depositional environment characterized the entire fourth unit the dubaydib formation as well as the tubeiylliat sandstone member of the fifth unit the mudawwara formation the depositional history of the ordovician sequence was terminated by a glaciofluvial regime that finally was gradually replaced by a shoreface depositional environment throughout the last unit the ammar formation

a comparison of grain size analysis methods for sand dominated fluvial sediments abstract grain size distribution is a fundamental tool for interpreting sedimentary unitswithin depositional systems the techniques assessed in this study arecommonly used to determine grain size distributions for sand dominatedsediments however the degree of consistency and differences ininterpretation when using a combination of grain size methods have not yetbeen assessed systematically for sand dominated uvial sediments resultsobtained from laser diffraction x ray attenuation and scanning electronmicroscopy grain size analysis techniques were compared with those obtainedfrom the traditional sieve hydrometer method scanning electron microscopywas shown to provide an inaccurate quantitative analysis of grain sizedistributions because of dif culties in obtaining representative samples forexamination the x ray attenuation method is unsuitable for sand dominatedsediments because of its upper size range of only 300 lm the consistentlystrong correlation between the laser diffraction results and the sieve hydrometer results shows that these methods are comparable for sand dominated uvial sediments provided that sample preparation is consistent the latter two methods can be used together within a study of such sedimentswhile maintaining a high degree of accuracy these results indicate that datafor sand dominated uvial sediments gained from the long established sieve hydrometer method can be compared with con dence to those obtained bymodern studies using laser diffraction techniques keywords hydrometer laser diffraction scanning electron microscopy sieve x ray attenuation introductiongrain size distribution gsd analysis is a funda mental tool in sedimentology and uvial geo morphology it is particularly important indetermining environments of deposition andaspects of the ow regime at the time of deposi tion several methods of gsd analysis are pres ently available this study aimed at assessing thecomparability of sieve hydrometer x ray attenu ation scanning electron microscopy sem andlaser diffraction techniques for quantifying grain size distribution for sand dominated uvialsediments and the inconsistencies in interpreta tion that might occur when using a combinationof these methods such inconsistencies mayoccur when gsd data from contemporary studiesutilizing modern techniques such as laser dif fraction and x ray attenuation are compared withgsd data from prior studies gained by the use oflong established methods such as sieve hydro meter methods the wentworth 1922 scale is the most widelyused scale for sand dominated sediments colby 1964 smith 1970 schumm 1977 folk 1980 miall 2006 understanding the gsd of a depositsedimentology 2008 55 1905 1913

particle size scales and classification of sediment types based on particle size distributions review and recommended procedures this paper provides a review of different particle size scales size class terminology and particle size distribution textural classification schemes which are widely used in sedimentology geomorphology soil science aquatic ecology and civil engineering it is concluded that a revised system of size class nomenclature based on the udden 1898 and wentworth 1922 schemes provides the most logical and consistent framework for use with sediments and a wide range of other particulate materials a refined scheme is proposed which has five first order size classes boulder gravel sand silt and clay each of which has five second order subdivisions with limits defined at one phi intervals the scheme is simple and intuitively easy to understand the paper also provides a review of previous schemes that have been proposed to describe and classify sediments on the basis of the proportions of gravel sand and mud or sand silt and clay using trigons also termed ternary diagrams many of these schemes do not have a logical basis and provide limited or uneven resolution new gravel sand and mud and sand silt and clay classification systems are proposed that are both more logical and provide greater discriminatory power than previous schemes they are therefore more suitable for use in environmental and forensic investigations a new microsoft excel program freely available to download from http www kpal co uk allows rapid classification of sediments based on the proportions of gravel sand and mud and sand silt and clay proportions and graphical comparison of the data for different sample groups

variability in terrigenous sedimentation processes off northwest africa and its relation to climate changes inferences from grain size distributions of a holocene marine sediment record variations in deposition of terrigenous fine sediments and their grain size distributions from a high resolution marine sediment record offshore northwest africa 30 51 0 n 10 16 1 w document climate changes on the african continent during the holocene end member grain size distributions of the terrigenous silt fraction which are related to fluvial and aeolian dust transport indicate millennial scale variability in the dominant transport processes at the investigation site off northwest africa as well as recurring periods of dry conditions in northwest africa during the holocene the terrigenous record from the subtropical north atlantic reflects generally humid conditions before the younger dryas during the early to mid holocene as well as after 1 3 kyr bp by contrast continental runoff was reduced and arid conditions were prevalent at the beginning of the younger dryas and during the mid and late holocene a comparison with high and low latitude holocene climate records reveals a strong link between northwest african climate and northern hemisphere atmospheric circulation throughout the holocene due to its proximal position close to an ephemeral river system draining the atlas mountains as well as the adjacent saharan desert this detailed marine sediment record which has a temporal resolution between 15 and 120 years is ideally suited to enhance our understanding of ocean continent atmosphere interactions in african climates and the hydrological cycle of northern africa after the last deglaciation

depositional environments of the early cretaceous kurnub hathira sandstones north jordan abstract the kurnub hathira sandstones in north jordan which are most probably of early cretaceous age are about 300 m thick varicoloured friable quartz arenitic sandstones based on grain size analysis sedimentary structures palaeocurrent fossil content and petrography these sandstones are postulated to be dominantly of fluvial origin with a few interfingering shallow marine horizons a southward displacement of jordan by at least 100 km would bring these sandstones opposite to similar rocks west of the jordan araba rift with jordan being higher during the early cretaceous

deriving transport pathways in a sediment trend analysis sta abstract sediment trend analysis sta is a technique that enables patterns of net sediment transport to be determined by relative changes in grain size distributions of all naturally occurring sediments in addition sta can determine the dynamic behaviour of bottom sediments with respect to erosion accretion or dynamic equilibrium the data requirements for sta are the full grain size distributions taken from sediment grab samples collected at a regular spacing over a particular area of interest two types of methods are presently used in the derivation of the transport pathways a line by line approach in which transport pathways are determined by searching for sample sequences in which the distributions change in a statistically acceptable manner and various vector approaches in which each sample is compared to neighbouring sites from which a vector sum is calculated the basic assumption for sta is that the processes that cause sediment transport will affect the statistics of sediment distributions in a predictable way in reality this type of analysis is complicated through the inclusion of a number of uncertainties or noise the goal of sta is to extract the information the transport pathways from the noisy signal the grain size distributions an approach that is made difficult because neither the nature of the information nor the noise is known because of this obtaining results by simply applying its theory in a black box approach may provide poor solutions the line by line approach to sta draws from communications theory to achieve a solution in some communications systems the information from many sources is combined into one signal the resulting signal is from a statistical viewpoint nothing but noise the extraction of specific information assumes that information is indeed present and determines if that assumption is consistent with the received signal for sta the procedure is to assume a transport direction over an area comprising many sample sites from this assumption the predicted sediment trends are compared with the pathways determined by the actual samples the assumed transport direction is repeatedly modified until the best fit is achieved vector techniques may be very helpful to provide insights and guidance to the line by line approach however the approach is ultimately necessary to finalize a credible solution as well as providing important further information on the dynamic behaviour of the sediments and to delineate specific sediment transport environments

the grain size characterisation of coastal sand from the somme estuary to belgium sediment sorting processes and mixing in a tide and storm dominated setting abstract sand rich holocene to modern clastic deposits in the eastern english channel and the southern north sea coasts of france and belgium occur extensively as nearshore sand bank estuarine tidal flat aeolian dune and beach sub environments sand samples n 665 collected from these deposits suggest the presence of three different populations a largely dominant 83 medium to fine quartz sand population b and finer 14 and coarser grained 4 populations respectively c and a the distribution of these populations among the four sub environments reflects tide and storm dominated sorting and transport processes and a variable degree of mixing these populations are derived from a mixture of very fine to very coarse grained fluvial outwash and paraglacial sediments deposited on the beds of the eastern english channel and southern north sea during the late pleistocene lowstand the nearshore sand bank environment which also corresponds to the main offshore source area of the coastal deposits exhibits population heterogeneity reflecting the variability of hydrodynamic conditions and sediment sorting in this zone the nearshore topography of tidal ridges banks and troughs in these tidal seas leads to variable bed and tide and storm induced shear stress conditions these conditions only allow for the mobilisation and onshore transport of some of the finer fractions populations b and c leaving an offshore mixture of these finer populations with coarser less mobilisable sediments population a once in the coastal zone these two finer populations undergo further hydrodynamic sorting and segregation variably sorted very fine sands to silts population c are trapped in the low energy estuarine tidal flat sub environment while the highly homogeneous population b is further sorted in aeolian dune and beach sub environments this sorting occurs via a coastal sand transport pathway linking the somme estuary mouth to the southern north sea bight where tidal range and wave energy decrease relative to the english channel since this sand transport pathway enables longshore transport of hydrodynamically sorted medium to fine sand derived directly from the immediate nearshore zone it has further contributed to a net flux of this sand population from the eastern english channel sea bed to the southern north sea

sediment transport patterns determined from grain size parameters overview and state of the art abstract grain size trends have been applied in many diverse sedimentary environments to determine sediment transport paths generally coinciding with information from tracer studies current measurements and the orientation of sedimentary structures the different methods proposed to date are critically analysed and compared with reference to recent field studies it is concluded that the two dimensional methods produce comparable results and may in fact complement each other in spite of the advances several problems still exist which include the sampling method and density the choice of trend types the relative weight of grain size parameters and the interpretation of results these are discussed together with possible solutions

grain size analysis of the lower cambrian lower cretaceous clastic sequence of jordan sedimentological and paleo hydrodynamical implications abstract 356 sand sized samples ranging in age from early cambrian epoch to late cretaceous epoch of known depositional environments were analyzed mechanically to obtain the grain size parameters of mode median mean and sorting the constructed grain size distribution curves for the various paleozoic and mesozoic formations were interpreted in terms of the paleo hydrodynamic processes prevailing through transportation and deposition the study proved that the grain size parameters of sand sized sediments most sensitive to paleo depositional environmental recognition were the graphic mean grain size and the inclusive graphic sorting mean grain size values below 1 77 of a sand sized sample could indicate a fluvial channel paleo depositional environment whereas the mean grain size values above 2 8 are indicative to a shallow marine paleo depositional environment sorting values above 1 1 may indicate a fluvial channel paleo depositional environment a bivariate discriminatory plot of mean grain size versus sorting yields two fields that can successfully discriminate between the fluvial channel paleo depositional environment and the shallow marine paleo depositional environment a new grain size parameter termed the mean sorting index was introduced in this study and calculated by dividing the mean grain size value over the sorting value it is recorded here that the mean sorting index is more sensitive to paleo depositional environment recognition than the individual mean grain size and sorting parameters

hydraulic interpretation of grain size distributions using a physical model for bedload transport abstract grain size distributions of bedload sediment are modelled by considering the time variation of sediment transport in a unidirectional turbulent flow a frequency distribution of instantaneous bed shear stress is divided into a large number of shear stress ranges with mean values of oi each oi is capable of transporting a range of sediment sizes as bedload the maximum size is just at its entrainment threshold the minimum size is just too large to be suspended rates of bedload transport are calculated for each size range using a theoretical bedload function and the proportion of time that these rates occur is obtained by integrating the frequency distribut on between the boundaries of each shear stress range the relative weights of sediment transported in particular size ranges determined for all oi values constitutes the grain size distribution obtained from bedload sampling at a fixed point on the bed cumulative grain size curves have been simulated using the model in order to demonstrate the effects of the various model parameters e g mean bed shear stress viscosity all curves show a distinct break in slope which represents the maximum grain size transportable in suspension when the shear stress attains its maximum fluctuating value examination of many natural bedload distributions shows close qualitative and quantitative agreement with the model and reasons for discrepancies can be fully explained typical grain size distributions of deposited sediments can be obtained by mixing of different flow related bedload distributions in various proportions thus although deposited sediments may primarily result from bedload transport during a steady flood flow flow unsteadiness also plays a part the effects of some deposition directly from suspended load can also be surmised

the influence of grain size analysis methods and sediment mixing on curve shapes and textural parameters implications for sediment trend analysis abstract to this day deterministic physical models capable of explaining the evolution of grain size distributions in the course of transport are still lacking for this reason various attributes of particle frequency distributions in particular curve shapes and textural parameters have for many decades been investigated for potential information about transport behaviour and size sorting processes of sediments in numerous environments such approaches are essentially conceptual and hence rely heavily on the validity of the assumptions on which they are based a factor which has to date been largely ignored in this context is the fact that different methods of grain size analysis e g sieving laser absorption and diffraction settling velocity measurements when applied to the same sample material produce variable curve shapes and hence incongruous textural data this is illustrated by selected examples showing the differences between sieving and settling results conversion of settling velocities into equivalent settling diameters psi phi transformations and the influences of particle shape particle density and water temperature it is demonstrated that particle size distributions are not only method dependent but also dependent on the adopted post processing procedure as a result only frequency curves generated by the same method and subsequently processed by identical computational procedures can be meaningfully compared furthermore the computation of textural parameters from bi or multimodal size distributions produces spurious results which are unrelated to the processes leading to the mixing of different size populations frequently observed in nature in such cases only the decomposition of such distributions into individual populations and the spatial comparison of such populations makes any sense because a physical explanation for the generation of size distributions is lacking a particular curve shape of a grain size population has no meaning on its own only a systematic comparison of progressively changing curve shapes and associated textural parameters of sediments collected on a closely spaced grid can yield data suitable for sediment trend analysis

grain size distribution function of polymodal sediments in hydraulic and aeolian environments and numerical partitioning of the sedimentary components most continental sediments are polymodal composed of overlapping components of which the grain size generally obeys some type of natural distribution the grain size components and their function types can be determined from frequency and cumulative curve plots in order to define the function formula of the grain size distribution the function parameters can be estimated by fitting a defined function formula to the measured grain size data of the sample which simultaneously achieves numerical partitioning of the sedimentary components genetic analysis of grain size components of hydraulic and aeolian sediments demonstrates the following environmental implications fluvial sediment is composed of isolated saltation and suspension components the sediments in closed lake basins are dominated by a suspension silt clay component with a small proportion of saltation sand the fine sand component makes up the majority of desert sand overlapping with a small proportion of fine dust aeolian loess is composed of two overlapping components a short suspension time silt component and a long suspension time fine component aeolian material in the north pacific deep sea sediments is dominated by long suspension time fine dust the fine component in aeolian sediments shows a consistent grain size distribution and genetic connection from the desert sand loess of northern china to the north pacific ocean which is mainly transported by westerly winds and is dispersed in the atmosphere forming a background dust c 2002 elsevier science b v all rights reserved