retracted the influence of sand bed temperature on lift off and falling parameters in windblown sand flux in deserts the temperature of the sand bed can reach up to more than 50 degrees c however existing knowledge on the lift off and falling velocities and angles of sand particles in windblown sand flux is based mainly on experimental results over a temperature range of 20 degrees c to 30 degrees c consequently existing experimental results cannot reflect the actual interaction between saltating sands and the bed in this study the influence of the sand bed temperature on the probability distribution of lift off and falling velocities and angles of sand particles is investigated through an improved particle image velocimetry piv system results demonstrate that the distribution shape of lift off and falling velocities and angles of sand particles is not greatly influenced by the temperature of sand bed however it has a certain influence on the center of the probability distributions of horizontal velocities as well as the average decay constant and amplitude of the distributions of vertical velocities and angles we present formulas to describe the probability distributions of lift off and falling velocities and angles with regard to the influence of sand bed temperature c 2013 elsevier b v all rights reserved

wind tunnel evaluation of a wedge shaped aeolian sediment trap abstract a detailed set of tests in a wind tunnel investigated the characteristics of flow and sampling efficiency of a low cost sediment trap that can be used in wind tunnels and field applications the trap is constructed of thin sheet aluminum and has a wedge shape 32 internal inlet angle with a 20 500 mm rectangular inlet orifice that extends 40 mm beyond the wedge form relatively unimpeded airflow through the trap is achieved by the large exit area 130 500 mm which is covered with fine stainless steel mesh 62 5 m openings 60 porosity and collected all but the finer silt sediment sizes despite its angular shape the trap has good characteristics of flow and a very high sampling efficiency 90 over a wide range of wind velocities because of its near isokinetic characteristics of flow results also indicate that this trap and others that have wide side profiles are very sensitive to incident wind angle incident angles 5 significantly reduce the sampling efficiency and promote scour around the trap inlet

niveo aeolian sand deposition in subarctic dunes eastern coast of hudson bay quebec canada aeolian sand transport during winter and the snow free season was assessed quantitatively by direct year round field measurements along transects on the lee side of parabolic dunes in subarctic quebec in 1987 1988 niveo aeolian deposition was more important than aeolian sedimentation in three of the four study sites and contributed 75 of the total annual accumulation in exposed sites and 25 in protected forest sites the maximum depth of interstratified snow and sand deposits 3 5 m was recorded in march semi permanent snow lenses may persist longer than 2 years in the aeolian sediments after dissipation of snow 22 cm of sand as a maximum accumulated on the slipface of the most active dunes whereas only minor sand accumulation occurred in distant areas from active sand erosion wind driven sand was dispersed over 7 4 km2 in the whapmagoostui kuujjuarapik area the acumulation of snow and sand during the snow season together with spring thaw and collapse of the niveo aeolian deposit caused different types of injuries to trees especially in 1985 and 1987 when a maximum of torn branches was recorded over the last 10 year period

analysis of velocity profile measurements from wind tunnel experiments with saltation abstract investigations of wind field modification due to the presence of saltating sediments have relied heavily on wind tunnels which are known to impose geometric constraints on full boundary layer development there remains great uncertainty as to which portion of the vertical wind speed profile to analyze when deriving estimates of shear velocity or surface roughness length because the lower sections are modified to varying degree by saltation whereas the upper segments may be altered by artificially induced wake like effects thus it is not obvious which of several alternative velocity profile parameterizations e g law of the wall velocity defect law wake law should be employed under such circumstances a series of experimental wind tunnel runs was conducted across a range of wind speed using fine and coarse grained sand to collect high quality fine resolution data within and above the saltation layer using thermal anemometry and ruggedized probes after each run the rippled bottom was fixed with fine mist and the experiment repeated without saltation the measured wind speed profiles were analyzed using six different approaches to derive estimates of shear velocity and roughness length the results were compared to parameter estimates derived directly from sediment transport rate measurements and on this basis it is suggested that one of the six approaches is more robust than the others specifically the best estimate of shear velocity during saltation is provided by the logarithmic law applied to the profile data within about 0 05 m of the bottom despite the fact that this near surface region is where profile modification by saltating sediments is most pronounced uncertainty remains as to whether this conclusion can be generalized to field situations because progressive downwind adjustments in the interrelationship between the saltation layer and the wind field are anticipated in wind tunnels thereby confounding most analyses based on equilibrium assumptions

aeolian sand drift from the intertidal zone on a temperate beach potential and actual rates this paper compares the amount of sand that is potentially moved into a coastal dune system from a beach using estimates based solely on the wind force with actual measured amounts the actual sand inputs are determined by measuring sand level changes each month over a period of eighteen months along a 1760 m section of foredune on braunton burrows southwest england the calculation procedure used to estimate the potential rates of sand drift is based on the capacity of the wind force to transport sand using a published transport equation white 1979 the results show that the actual movement rates are markedly smaller than the potential rates for all months except in the summer meteorological variables and the watertable level in the adjacent dune system are used in an empirically derived regression equation in an attempt to explain the large discrepancy between the potential and actual movement rates the resulting corrected potential movement rates are a closer estimate to the actual rates but there remains much unexplained variance

the carolina sandhills quaternary eolian sand sheets and dunes along the updip margin of the atlantic coastal plain province southeastern united states the carolina sandhills is a physiographic region of the atlantic coastal plain province in the southeastern united states in chesterfield county south carolina the surficial sand of this region is the pinehurst formation which is interpreted as eolian sand derived from the underlying cretaceous middendorf formation this sand has yielded three clusters of optically stimulated luminescence ages 1 75 to 37 thousand years ago ka coincident with growth of the laurentide ice sheet 2 28 to 18 ka coincident with the last glacial maximum lgm and 3 12 to 6 ka mostly coincident with the younger dryas through final collapse of the laurentide ice sheet relict dune morphologies are consistent with winds from the west or northwest coincident with modern and inferred lgm january wind directions sand sheets are more common than dunes because of effects of coarse grain size mean range 0 35 0 59 mm and vegetation the coarse grain size would have required lgm wind velocities of at least 4 6 m sec accounting for effects of colder air temperatures on eolian sand transport the eolian interpretation of the carolina sandhills is consistent with other evidence for eolian activity in the southeastern united states during the last glaciation

a wind tunnel study of aeolian sediment transport response to unsteady winds abstract although moderate attention has been paid to the response of the aeolian mass transport rate to wind gusts it is still unclear how the particle size and volumetric concentration affect this relation very little is known about the response time of the particle speed and specifically how the sensor scale and elevation affect measurements of this variable the present study addresses this knowledge gap through a series of wind tunnel experiments in which a gusty wind was generated by programming the fan motor to adjust to a randomly selected rpm every 10 s beds consisting of either medium or coarse sand were investigated through synchronous co located measurements of the local wind speed and particle speed count rate obtained via a customized laser doppler anemometry lda system the vertically integrated sand transport rate q and the wind speed in the freestream were quantified using a passive sand trap and pitot tube respectively the results of the experiments indicate that the response of the aeolian transport system to wind gusts is generally faster in terms of the particle speed than the mass transport rate while the degree of correlation is found to vary with the sensor elevation as well as with the particle size and volumetric concentration in essence the coupling within the transport system is demonstrated to be strongly scale dependent

high resolution stratigraphy and depositional model of wind and water laid deposits in the ordovician guaritas rift southernmost brazil abstract the upper portion of the pedra pintada alloformation includes about 100 m of mostly eolian deposits this paper emphasizes the vertical succession and lateral association of sedimentary facies based on analysis of outcrop data and aerial photographs as well as the hierarchy and origin of bounding surfaces it aims to propose a high resolution stratigraphic and depositional model that may be useful to exploitation of eolian reservoirs the succession has been preserved due to basin subsidence and is described in terms of four facies associations that constitute three dominantly eolian units these units are sharply bounded by major flooding surfaces super surfaces that in turn are overlain by 1 to 2 m thick dominantly water laid facies lacustrine fluvial deltaic and eolian both their internal organization and boundaries were controlled by changes in the base level rise rate the basal eolian unit is composed of crescentic eolian dunes and damp interdune deposits ascribed to a wet eolian system on the other hand eolian units ii and iii also characterized by crescentic eolian dunes simple and compound deposits were related to dry eolian systems since they comprise dry eventually wet interdune facies eolian unit iii is truncated by basinwide unconformity which is then overlain by the ephemeral fluvial deposits varzinha alloformation this second type of super surface is related to climate induced wind erosion deflation down to the water table level regional stokes surface followed by fluvial incision linked to tectonic activity

effects of time dependent moisture content of surface sediments on aeolian transport rates across a beach wildwood new jersey u s a a one day field investigation on an unvegetated backbeach documents the importance of surface sediment drying to aeolian transport surface sediments were well sorted fine sand moisture content of samples taken in the moist areas on the backbeach varied from 2 9 to 9 2 per cent lack of dry sediment inhibited transport prior to 08 50 by 09 10 conspicuous streamers of dry sand moved across the moist surface barchan shaped bedforms 30 to 40 mm high and composed of dry sand moisture content 0 10 per cent formed where sand streamers converged the surface composed of dry sand increased from 5 per cent of the area of the backbeach at 09 50 to 90 per cent by 12 50 mean wind speeds were beetween 5 6 and 8 6 m s 1 at 6 m above the backbeach corresponding shear velocities were always above the entrainment threshold for dry sand and below the threshold for the moist sand on the backbeach measured rates of sand trapped by vertical cylindrical traps increased during the day relative to calculated rates the measured rate of sand trapped on the moist foreshore was higher than the rate trapped on the backbeach during the same interval indicating that the moist foreshore moisture content 18 per cent was an efficient transport surface for sediment delivered from the dry portion of the beach upwind measured rates of sand trapped show no clear relationship to shear velocities unless time dependent surface moisture content is considered results document conditions that describe transport across moist surfaces in terms of four stages including 1 entrainment of moist sediment from a moist surface 2 in situ drying of surface grains from a moist surface followed by transport across the surface 3 entrainment and transport of dry sediment from bedforms that have accumulated on the moist surface and 4 entrainment of sand from a dry upwind source and transport across a moist downwind surface 1997 john wiley sons ltd

niveo aeolian deposits and denivation forms with special reference to the great kobuk sand dunes northwestern alaska the geomorphology lithology and chronostratigraphy of extensive late pleistocene inland and river dune sands aeolian sand sheets cover sands and loess deposits of periglacial origin in northwestern europe are well known however the idea that some of these aeolian sediments result from niveo aeolian processes is still an open question as no diagnostic sedimentary features have yet been reported moreover actual niveo aeolian sediments and related denivation forms reported from various cold climate regions are not suitable analogues recent observations in active dune fields in northwestern alaska indicate that interstratification of wind driven snow and sand preferentially occurs on slip faces of transverse barchanoid or parabolic dune ridges annual denivation forms develop e g snow ramparts sinkholes snow hummocks snow meltwater fans and tensional cracks the surface consists of a cracked wet sand layer with a dimpled surface and spongy structure although the preservation potential of these features is low in this specific case similar features may be observed in ancient sediments elsewhere and provide useful palaeoclimatic indicators the niveo aeolian concept should therefore not specifically be related to late pleistocene cover sand deposition in northwestern europe as previously assumed

an experimental study of multiple grain size ejecta produced by collisions of saltating grains with a flat bed collision data are presented from coloured high speed films of three size fractions of sand grains saltating over a bed of the total grain population each fraction was colour tagged and the proportion of each size ejected by grains colliding with the surface was recorded on a number of films taken as the bed was progressively eroded the results confirm earlier findings that v3 v1 0 5 0 6 vn v1 08 and the rebound angle increases with decreasing grain size ejected grains are examined in relation to their size the impactor size ejection speed and angle and the number of ejecta per collision in addition changes in grain parameters are observed with time for fine impactors ejection speeds generally increase with a decrease in ejecta size but the fine fraction does not follow this trend for the coarse and medium impactors ejection angles are typically between 40 and 60 with coarse grains having shallower mean angles than fine ejecta the number of ejections per collision increases with a decrease in particle size for each impactor size the general tendency for coarse particles to be ejected at lower speeds and shallower angles than fine particles will lead to sorting of the grain sizes there is poor correlation between the forward momentum loss of the saltating grams at collision and both the forward momentum of the ejected grains and the number of ejected grains much of the forward momentum of the saltating grains is transfered to creeping grains the composition and geometry of the bed are considered to be important factors in the evolution of the saltation cloud

the dynamic effects of moisture on the entrainment and transport of sand by wind abstract there is an increasing awareness of the influence of surface moisture on aeolian entrainment and transport of sediment existing wind tunnel studies have shown the impact of a limited range of moisture contents on entrainment thresholds but similar investigations are lacking in the field the research reported here investigated the influence of changes in surface moisture content on sand entrainment and transport on a meso tidal beach in anglesey north wales high frequency 1 hz wind velocities measured with hot wire anemometers were combined with grain impact data from a sensit monitor and mass flux measurements from a standard sand trap surface and near surface moisture contents were assessed gravimetrically from surface sand scrapes and also directly by using a thetaprobe critical threshold values for entrainment were specified using a modified form of the time fraction equivalence method stout j e zobeck t m 1996a establishing the threshold condition for soil movement in wind eroding fields proceedings of the international conference on air pollution from agricultural operations mwps c 3 kansas city 7 9 february 1996 pp 65 71 results indicate a time dependent change in dominant control of the sand transport system from moisture to wind speed dependent upon the moisture content of the surface sediment this interchange between controlling parameters on both entrainment and transport was very sensitive to prevailing moisture conditions and took place over a period of minutes to hours under conditions experienced in the experiments presented here the critical moisture threshold for sediment entrainment was determined to be between 4 and 6 higher than the 1 4 specified in previous wind tunnel experiments furthermore a moisture content of nearly 2 where moisture was adhered to transported sediment appeared to have little or no impact on the rate of sand flux

the paleoclimatic significance of deformation structures in neoproterozoic successions abstract this paper reviews the different types of soft sediment deformation structures that can form in glacial and non glacial settings and explores the potential use of these structures in resolving long standing debates in paleoenvironmental reconstructions of neoproterozoic glacigenic successions soft sediment deformation structures are created when compressional gravitational or shear stress is applied to unlithified sediments during or shortly after deposition in subglacial or ice marginal glacial settings shear and compressional stress imparted by ice moving on top of a deformable substrate or advancing ice buldozing unlithified ice marginal sediments can result in a wide range of folding faulting and shear structures in glaciofluvial or stagnant ice marginal setting gravitational collapse and remobilization of sediments associated with the melting of buried ice can result in normal faulting and broad folding in glaciolacustrine or glaciomarine settings compressional shear and gravitational types of deformation structures can occur as a result of grounding ice or icebergs rapid sedimentation and reworking downslope associated with high sedimentation rates in non glacial settings similar deformation structures can form as a result of slope instability and reworking of sediments downslope rapid sedimentation seismic shaking wave induced shearing or loading in this context two case studies are presented to demonstrate the type of paleoenvironmental information that an analysis of deformation structures can provide in the first case study analysis of deformation in the port askaig formation scotland reveals a distinctive stratigraphic distribution of deformation structures the types of deformation observed together with their recurrence over several 100s of meters and their basinal context are used to infer a seismic origin for the deformation which in turn suggests a significant tectonic control on sedimentation atop a record of ice margin fluctuations in a glaciomarine setting in the second example analysis of deformation in the smalfjord formation northern norway provides strong evidence for deformation by active ice overriding glaciofluvial deposits the types of deformation in this example together with its complexity scale and associated facies provide the strongest case for ice marginal deformation in sum analysis of deformation structures together with analysis of structural geology stratigraphy facies and facies associations can provide additional constraints on paleoenvironmental conditions at the time of deposition which can help us refine or test paleoenvironmental models proposed for this critical time period in earth history

cenozoic alongslope processes and sedimentation on the nw european atlantic margin based on studies of sediment accumulations deposited from and erode by alongslope flowing ocean currents on the european continental margin from porcupine ireland to lofoten norway the evolution of the cenozoic paleocirculation was reconstructed as part of the stratagem project there is evidence of ocean current controlled erosion and deposition in the rockall trough in the faeroe shetland channel and on the voring plateau since the late eocene although the circulation pattern remains ambiguous the late palaeogene flow in the rockall trough was almost probably driven by southerly derived tethyan outflow water the extent and strength of any northerly derived flow is uncertain from the early neogene early mid miocene there was a massive regional expansion of contourite drift development both in the north atlantic and in the norwegian greenland sea this was most probably related to the development of the faroe conduit the opening of the fram strait and the general subsidence of the greenland scotland ridge these may have combined to cause a considerable acceleration in the exchange and overflow of deep waters between the arctic and atlantic oceans an early late neogene late early pliocene regional erosional event has been ascribed to a vigorous pulse of bottom current activity most probably the result of a global reorganisation of ocean currents associated with the closure of the central american seaway during the late neogene contourites and sediment drifts developed in deep water basins between units of glacigenic sediments as well as infill of several paleo slide scars these sediments were derived from areas of bottom current erosion as well as from the development of plio pleistocene prograding sediment wedges incorporating the extensive sediment supply derived from shelf wide ice sheets presently a profound winnowing prevails along the shelf and upper slope due to the inflowing currents of atlantic water depocentres of sediments derived from the winnowing are located locally in lower slope embayments and in slide scars

the initiation of particle movement by wind when air blows across the surface of dry loose sand a critical shear velocity fluid threshold ut must be achieved to initiate motion however since most natural sediments consist of a range of grain sizes fluid threshold for any sediment cannot be defined by a finite value but should be viewed as a threshold range which is a function of the size shape sorting and packing of the surface sediment in order to investigate the initiation of particle movement by wind a series of wind tunnel tests was carried out on a range of pre screened fluvial sands and commercially available glass beads with differing mean sizes and sorting characteristics a sensitive laser monitoring system was used in conjunction with a high speed counter to detect initial grain motion and to count individual grain movements test results indicate that when velocity is slowly increased over the sediment surface the smaller or more exposed grains are first entrained by the fluid drag and lift forces either in surface creep rolling or in saltation bouncing or hopping downwind as velocity continues to rise larger or less exposed grains may also be moved by fluid drag on striking the surface saltating grains impart momentum to stationary grains this impact may result in the rebound of the original grain as well as the ejection of one or more stationary grains into the air stream at shear velocities lower than that required to entrain a stationary particle by direct fluid pressure as a result there is a cascade effect with a few grains of varying size initially moving over a range of shear velocities the fluid threshold range and setting in motion a rapidly increasing number of grains results of the tests showed that the progression from fluid to dynamic threshold based on grain movement can be characterized by a power function the coefficients of which are directly related to the mean size and sorting characteristics of the sediment

the signal and the noise forward modeling of allocyclic and autocyclic processes influencing peritidal carbonate stacking patterns recent carbonate sequence stratigraphic models suggest that the degree of order present in successions of carbonate parasequences is determined by temporal variations in eustatic amplitude and by varying levels of autocyclicity ordered parasequence stacking is suggested to occur during greenhouse periods dominated by low amplitude eustatic oscillations conversely disordered vertical successions are said to occur when amplitudes of eustatic oscillations are high or when autocyclic processes dominate and thus drown the periodic external signal these assertions of causal mechanism are tested here by application of a three dimensional stratigraphic forward model the three dimensional model generates parasequences via a ginsburg type mechanism of sediment transport and shoreline progradation parasequence stacking is controlled by a superimposed longer term eustatic oscillation and parasequences generated are analyzed using runs analysis and durbin watson autocorrelation results from the modeling suggest that autocyclic parasequences generated by shoreline progradation form ordered vertical successions when accommodation changes driven by a low amplitude relative sea level oscillation suggesting that partly autocyclic strata may not be inherently any less ordered than entirely allocyclic strata addition of stochastic processes such as mosaic carbonate production and fluctuations in regional sediment transport direction tend to decrease the level of measurable order present in the autocyclic strata increasing the frequency and amplitude of relative sea level oscillations also tends to decrease the measurable order in stacked autocyclic peritidal parasequence thicknesses these results suggest that controls on parasequence stacking patterns are likely to be more complex and varied than suggested by recent sequence stratigraphic models more outcrop and modeling investigation is required with appropriately circumspect interpretations applied

eolianite grain size distributions as a proxy for large changes in planetary atmospheric density a digitized version of the ahlbrandt 1979 global dune dataset and data for distributions in figure are available at https github com erikgoosmann aeoliandata

a study of particle splash on developing ripple forms for two bed materials a custom designed particle tracking velocimetry ptv system was developed to measure particle splash dynamics in two materials mixed quartz sand and ground acrylic particles approximating the density of snow the strengths and limitations of the ptv system are described in the context of five experiments carried out at friction velocities slightly greater than the threshold friction velocity for particle entrainment and saltation analysis of particle collisions on the bed surface splash demonstrates that the simulated snow particles impact the surface at a smaller angle than quartz sand they also eject a greater number of particles though at lower velocities and angles than observed for the sand particles these relations appear to be highly sensitive to the porosity of the bed surface while particle shape and elasticity play a secondary role with regard to ptv measurements carried out along the wind aligned axis of migrating aeolian ripples particles ejected from the lee slope tend to be slightly larger than those on the stoss slope and in general are ejected with a lower speed and greater angle to the surface irrespective of the type of granular material when the average impact angle is close to or greater than the negative slope of the evolving bedform the particle ejection rate from the stoss slope was measured to be approximately twice that for the lee slope this empirical observation confirms the assumption made in models of ripple development that the ejection flux governs the bedform migration rate however systematic under prediction of this rate by an early model suggests that additional processes inclusive of surface creep must also be accounted for

cold water coral banks and submarine landslides a review this paper aims to review the relation between cold water coral bank development and submarine landslides both are common features on continental margins but so far it has not been reviewed which effect if at all they may have upon each other indirect and direct relations between coral banks and landslides are evaluated here based on four case studies the magellan mound province in the porcupine seabight where fossil coral banks appear partly on top of a buried slide deposit the sula ridge reef complex and the storegga landslide both off mid norway and the mauritania coral bank province associated with the mauritanian slide complex for each of these locations positive and negative relationships between both features are discussed based on available datasets locally submarine landslides might directly favour coral bank development by creating substratum where corals can settle on enhancing turbulence due to abrupt seabed morphological variations and in some cases causing fluid seepage in turn some of these processes may contribute to increased food availability and lower sedimentation rates landslides can also affect coral bank development by direct erosion of the coral banks and by the instantaneous increase of turbidity which may smother the corals on the other hand coral banks might have a stabilising function and delay or stop the headwall retrogradation of submarine landslides although local relationships can be deduced from these case studies no general and direct relationship exists between submarine landslides and cold water coral banks

response parameters for characterization of infiltration rainwater infiltration is of particular interest with respect to slope stability hazard management the process of rainfall infiltration into unsaturated soil is complex due to the number of soil parameters involved and the random nature of moisture flux boundary conditions in this paper the effect of rainfall intensity on infiltration is investigated through the use of finite element seepage modeling for a 5 m high soil column subjected to various rainfall intensities the numerical modeling study identified three response parameters that can be used to describe one dimensional infiltration into an unsaturated soil the response parameters are the depth of wetting front the matric suction reduction depth and the sectional infiltration rate the practical application of the rainfall response parameters in slope stability analysis is illustrated

measurements of turbulence in the benthic boundary layer over a gravel bed it is now generally recognized that the mathematical description of sediment dynamics will be improved through an understanding of geophysical turbulence in this study therefore the turbulence characteristics of the benthic boundary layer over coarse sediments are examined as a step towards the realization of such a description examination of the turbulence has been conducted using spectral correlation quadrant and statistical analyses and a number of features have been identified mean eddy length scales obtained using spectral and autocorrelation techniques were found to be similar the interpretation of the duration and interval between the intermittent bursting events scaled using outer flow variables was found to be dependent upon the sampling interval autocorrelation analysis revealed a high correlation between bedload transport and the instantaneous horizontal flow component rather than instantaneous kinematic stress from the standpoint of developing prognostic transport models based on physically realistic benthic flow processes it is considered that turbulence measurements will lead to such formulation

steep rock lake sedimentology and geochemistry of an archean carbonate platform abstract the 2800 ma mosher carbonate formation at steep rock lake in south central canada is one of earth s oldest limestone deposits it is both thick up to 500 m and relatively well preserved and was one of the first precambrian successions to be noted for evidence of early life it continues to provide information on the antiquity of such processes as photosynthesis the carbonate contains a variety of fabrics and facies from apparently fine grained bedded limestones with domal and columnar stromatolites atikokania radial fans and sheet cracks to closely packed metric scale hybrid domes of originally aragonite seafloor crust interlayered with fenestral fabric here we review previous work provide new observations concerning these sediments and their geochemistry and discuss the inception overall development and ultimate demise of the steep rock platform we divide the mosher carbonate into the lower hogarth member and upper elbow point member these units constitute a shallow water carbonate platform succession the hogarth member overlies eroded 3000 ma tonalite and is at least 120 m thick thin horizons of domal pseudocolumnar columnar and fenestral stratiform stromatolites and occasional layers of atikokania radial crystal fans occur within relatively fine grained thin bedded limestone with iron carbonate horizons in the upper part meter scale domes occur locally with sheet cracks and stromatactis the irregular laminae that build the small domal and columnar stromatolites are interpreted to be lithified mats and biofilms presumably cyanobacteria dominated fine grained well bedded facies of the lower hogarth member and its varied association of small stromatolites is interpreted to have accumulated in a relatively protected inner platform environment numerous very thin horizons of iron carbonate in the lower and upper parts of the hogarth member suggest temporally limited influence of iron rich offshore waters vertical trends in fe mn ba sr ce and 13 c probably reflect progressive restriction of circulation with at least one abrupt but short lived change back to more open seawater conditions the upper hogarth member with large banded domes and fenestral crusts and stromatolites is interpreted as back margin facies the overlying elbow point member is at least 70 m thick and appears to be entirely composed of innumerable juxtaposed elongate smooth and thickly layered domes lacking intervening sediment each dome is typically several meters across and composed of centimetric alternations of cuspate fenestral fabric possibly microbial and crystal fan fabric that is probably abiotic seafloor aragonite precipitate adjacent cuspate fenestral and crystal fan fabric show significant differences in concentration of 13 c sr ba fe and mn this giant dome facies is interpreted as a platform margin deposit in which alternating calcite aragonite mineralogies within each dome reflect a laterally fluctuating offshore redox boundary negative ce anomalies positive gd anomalies and reduced positive eu anomalies relative to laterally correlative deep water iron formation occur in the majority of crystal fan samples and in some cuspate fenestral fabric samples ca carbonate precipitation at the margin of an anoxic iron rich sea would have been promoted by oxygenic removal of iron from seawater otherwise fe carbonate would have been favored over ca carbonate precipitation the mosher carbonate formation is interpreted as an early marine oxygen oasis a shallow platform that favored cyanobacterial productivity was sufficiently isolated from open marine circulation for the seawater to become relatively oxygenated and where carbonate sediment aggradation was a positive feedback that sustained these shallow water conditions limestone accumulation terminated as transgressive suboxic and anoxic seawater deposited first manganese oxide rich and then manganese oxide poor iron formation sediments

the pleistocene clastic sediments in the divje babe i cave slovenia geochemical characterisation and provenance part 2 different grain size fractions of clastic sediments 40 65 0 5 3 and 0 5 mm from the divje babe i cave were chemically analysed in the chemical composition of the medium and fine fractions four groups of variables were revealed 1 mgo loi tot c dolomite autochthonous terrigenous component 2 p2o5 tot s mo sr cu cao and so on bones apatite cement biochemical chemical components 3 sio2 al2o3 ree rb zr k2o th tio2 fe2o3 and so on non carbonate allochthonous terrigenous components and 4 u cd mno more mobile chemical components vertical distributions of p2o5 sio2 and u in the fine fraction suggest five geochemical boundaries the origin of p2o5 is attributed mainly to the cave bear a negative correlation between the content of sio2 and cavernously corroded clasts indicating a humidity indicates a dominant aeolian transport of non carbonate material into the cave vertical distribution of u indicates the migration of u and its enrichment in the deeper parts of the sedimentary sequence the mobilization of u was influenced by the duration of exposure of the sediments on the cave floor the chemical characteristics of non carbonate material indicate that source rocks probably belong to the triassic volcanic volcanogenic and terrigenous sedimentary rocks

multi disciplinary investigation of fluid seepage on an unstable margin the case of the central nile deep sea fan we report on a multidisciplinary study of cold seeps explored in the central nile deep sea fan of the egyptian margin our approach combines in situ seafloor observation geophysics sedimentological data measurement of bottom water methane anomalies pore water and sediment geochemistry and 230 th u dating of authigenic carbonates two areas were investigated which correspond to different sedimentary provinces the lower slope at 2100 m water depth indicates deformation of sediments by gravitational processes exhibiting slope parallel elongated ridges and seafloor depressions in contrast the middle slope at not vert 1650 m water depth exhibits a series of debris flow deposits not remobilized by post depositional gravity processes significant differences exist between fluid escape structures from the two studied areas at the lower slope methane anomalies were detected in bottom waters above the depressions whereas the adjacent ridges show a frequent coverage of fractured carbonate pavements associated with chemosynthetic vent communities carbonate u th age dates 8 kyr bp pore water sulphate and solid phase sediment data suggest that seepage activity at those carbonate ridges has decreased over the recent past in contrast large 1 km2 carbonate paved areas were discovered in the middle slope with u th isotope evidence for ongoing carbonate precipitation during the late holocene since 5 kyr bp at least our results suggest that fluid venting is closely related to sediment deformation in the central nile margin it is proposed that slope instability leads to focused fluid flow in the lower slope and exposure of fossil carbonate ridges whereas pervasive diffuse flow prevails at the unfailed middle slope

wetland sedimentation and associated diatoms in the pleistocene olorgesailie basin southern kenya rift valley abstract the olorgesailie basin in the southern kenya rift valley contains a variety of lacustrine wetland and terrestrial facies that were laid down during the last 1 2 million years this study integrates diatom ichnofossil and rhizolith silica and carbonate evidence in order to identify and characterize shallow wetland deposition at the top member 14 ca 493 ka of the olorgesailie formation a key feature of these deposits is the presence of facies with aquatic indicators diatoms that are overprinted by ichnofossils and rhizoliths that suggest drier conditions diatom floras include several fresh water aulacoseira spp and saline indicators such as thalassiosira rudolfi t faurii cyclotella meneghiniana and anomoeoneis sphaerophora the main indicators of shallow fresh to mildly saline waters include epithemia argus rhopalodia gibberula encyonema muelleri and synedra spp three main suites of ichnofossils indicate varying water table depths during their formation these consist of 1 horizontal tunnels that suggest saturated substrates 2 vertical burrows formed in substrates with relatively lower water tables and 3 termite hymenopteran and beetle ichnofossils that indicate dry substrates member 14 of the olorgesailie formation also contains carbonate and siliceous rhizoliths which occur both together and separately four possible models are suggested to explain the silica and carbonate rhizolith formation 1 a complex of spring fed marshes and dry areas 2 ephemeral wetlands and floodplains 3 wetlands with abundant organic decay and 4 initial carbonate rhizoliths that were replaced by silica preservation of cellular structures and the reworking and incorporation of rhizoliths in overlying younger strata suggest that they formed early during diagenesis

effects of temperature and humidity upon the transport of sedimentary particles by wind aeolian transport of sedimentary particles is a well recognized phenomenon in cold regions but the effect of low temperature t and specific humidity q upon particle entrainment has not previously been investigated this study reports on wind tunnel experiments 12 c t 32 c and 1 g kg 1 q 10 g kg 1 that suggest the aerodynamic drag required to entrain sand sized particles can be 30 lower in cold or high latitude settings as compared to hot deserts for any given regional wind velocity this effect will increase the wind strength index and thereby the proportion of time a surface is active at low temperature

on wind velocity profile measurements taken in wind tunnels with saltating grains this paper reviews some aspects of wind tunnel experiments on sand transporting winds it follows previous papers that have discussed the influence of the outer region of the boundary layer on wind velocity measurements this influence was quantified with the use coles wake function in this paper this correction is applied to six previously described wind velocity profiles an attempt is made to calculate the profile parameter ii from these measurements the values found were not consistent with the expected ii which was determined by coles for clean air flow this value ii 0 55 was assumed to be valid in previous analyses for sand transporting winds evidence for a mutual dependency of friction velocity and profile parameter is presented and the difficulty in determining u is pointed out it is suggested that the constant stress region of the boundary layer should be kept large enough for measurements when coles wake function is not to be used in the data analysis

stratigraphic evolution of a fluvial eolian succession the example of the upper jurassic lower cretaceous guara and botucatu formations parana basin southernmost brazil abstract the guara and botucatu formations comprise an 80 to 120 m thick continental succession that crops out on the western portion of the rio grande do sul state southernmost brazil the guara formation upper jurassic displays a well defined facies shift along its outcrop belt on its northern portion it is characterised by coarse grained to conglomeratic sandstones with trough and planar cross bedding as well as low angle lamination which are interpreted to represent braided river deposits southwards these fluvial facies thin out and interfinger with fine to medium grained sandstones with large scale cross stratification and horizontal lamination interpreted as eolian dune and eolian sand sheets deposits respectively the botucatu formation is characterised by large scale cross strata formed by successive climbing of eolian dunes without interdune and or fluvial accumulation dry eolian system the contact between the guara and the botucatu formations is delineated by a basin wide deflation surface supersurface the abrupt change in the depositional conditions that took place across this supersurface suggests a major climate change from semi arid upper jurassic to hyper arid lower cretaceous conditions a rearrangement of the parana basin depocenters is contemporaneous to this climate change which seems to have changed from a more restrict accumulation area in the guara formation to a wider sedimentary context in the botucatu formation

sublimation and aeolian sand movement from a frozen surface experimental results from presqu ile beach ontario abstract recent aeolian literature has indicated that sand movement can and does take place on frozen surfaces the winter aeolian process is influenced by the pore ice which binds the sand grains together and increases the surface resistance to wind action sublimation of the frozen moisture provides loose grains of sand which subsequently can be entrained by the wind field experiments carried out on the presqu ile beach ontario in the 1992 1993 winter provide some data on variables which affect sand loss from frozen surfaces because of sublimation sand moisture content determines the resistivity of the surface to sublimation induced sand loss frozen surfaces with higher moisture contents experience less sand loss the existing literature has indicated that temperature plays an important role in the occurrence of sublimation higher temperatures i e temperatures which are closer to 0 c result in higher rates of sublimation however the presqu ile experiments show that wind speed is more strongly correlated with sublimation induced particle loss than temperature or relative humidity higher wind speeds allow sand from the surface and sublimation produced water vapour to be removed from the area thus providing an incentive for further sublimation and sand loss to take place information on the variables which affect sublimation induced sand loss from frozen surfaces can be used to increase understanding of the processes involved in sand movement on frozen surfaces under subzero temperatures

late glacial to holocene aeolian deposition in northeastern europe the timing of sedimentation at the iisaku site ne estonia abstract the late glacial and holocene aeolian inland dune complex at iisaku ne estonia has been investigated using an accurate and detailed compilation of the sedimentary properties and chronological framework the quartz grains forming the dunes are very variable reflecting aeolian weathering and periglacial conditions both prior and after deposition although the morphological forms and the sedimentary record point to a dune like environment the transport record reflects either a short transport time or and distance and a contribution from neighbouring sedimentary environments dune development in the area was strongly controlled by the formation of the baltic ice lake bil in front of the retreating glacier luminescence ages from the aeolian complex suggest continuous deposition between 13 3 1 2 to 10 5 0 7 ka however the chronology of sand deposition also suggests phases in this aeolian activity 1 at 13 3 1 2 ka and onwards possibly correlated with the existence of an island separating the bil and peipsi lake 2 between 12 7 0 8 12 5 0 8 ka representing the younger dryas cold reversal 3 between 11 5 0 7 10 9 0 8 ka indicating that aeolian deposition continued over the younger dryas holocene boundary and 4 early holocene sand drift at 10 5 0 7 ka

kinetic energy transfer through impact and its role in entrainment by wind of particles from frozen surfaces while extensive aeolian deposits are associated with glaciation little is known of the mechanisms which produced them observation of glaciofluvial sediments in pangnirtung pass n w t indicates that peak deflation occurs in the fall and winter months so that the nature of sediment transport involving frozen surfaces greatly differs from warm environments laboratory experiments indicate that such surfaces are mobilized through abrasion and are most susceptible at low volumetric water content less than 20 and low temperature 20 c stable surfaces have volumetric water contents in excess of 30 and temperatures of 15 c surface stability also increases with decreasing particle size density and possibly transport load collisions with frozen surfaces are relatively elastic with significantly greater kinetic energy transfer to ejected surface grains than observed for loose dry surfaces saltation transport in cold environments could therefore be sustained at lower windspeeds than for dry surfaces provided that some loose particles are available initially but do not accumulate at the surface

rates of aeolian transport on a beach in a temperate humid climate short term field measurements of aeolian transport using a saltiphone indicate that actual rates of transport deviate considerably from the potential rates predicted by transport equations when examined in detail however potential rates are approached during special conditions mostly when the wind blows offshore parallel or slightly oblique to the beach and relative humidity is below 85 also the potential rates of transport may be approached when wind speeds considerably exceed threshold speed even during showers the main cause of the large deviation of actual from potential rates is in the absence of transport during very wet conditions prolonged rainfall regardless of wind speed and the variation of threshold velocity with time the threshold velocity increases during wet conditions with onshore winds or because of the presence of algae therefore potential transport is defined as the transport optimum to predict the actual rates of transport accurately insight into the variation of the threshold velocity is essential aeolian transport of sand seems to be related to moderate events and not to extreme events conforming to the principle of magnitude and frequency

boundary layer turbulence characteristics during aeolian saltation 1 a great deal of effort has been expended in measuring turbulence phenomena in clean air flows however no previous measurements have been successfully made of the vertical distributions of turbulence intensity and reynolds stress in a fully adjusted boundary layer flow saturated with saltating particles the present wind tunnel study addresses this knowledge gap using a custom designed laser doppler anemometer lda the amount of turbulence is found to increase with the introduction of saltating particles to the airflow over the lowest 15 of boundary layer vertical profiles of the streamwise wind speed provide friction velocities that lie well within the narrow range of those derived from direct measurement of the reynolds stress relative to clean air aeolian saltation is demonstrated to increase the magnitude but not the frequency of burst sweep events that primarily contribute to the total fluid stress within several millimeters above the bed surface all vertical profiles of wind speed converge upon a focal point as the local fluid stress declines toward the mobile bed

the influence of rainfall on transport of beach sand by wind this paper deals with the effect of rainfall on the process of wind erosion of beach sands and presents results from both field and wind tunnel experiments although sediment transport by splash is of secondary importance on coastal dunes splash saltation processes can move sediments in conditions where no motion is predicted by aeolian processes the effect of raindrop impact on the movement of soil particles by wind was measured on a sand beach plain using an acoustic sediment sampler in general an increase of particle movement by wind at the sensor heights was observed during rainfall rainfall also affected the wind erosion process during and after rain by changing the cohesive conditions of the surface the influence of the surface moisture content on the initiation of wind erosion and on the vertical distribution of transported sand particles was studied in a wind tunnel moisture significantly increased threshold wind velocities for the initiation of sediment transport and modified vertical sediment profiles

saltation threshold on earth mars and venus new formulations valid for wide ranges of particle diameter and density and gas density are presented for prediction of saltation threshold speed for small particles a low air density wind tunnel was used to extend the range of previous investigations and to separate the effects of reynolds number and interparticle forces of cohesion the new formulations are used to predict saltation threshold for atmospheric conditions on the surface of the earth mars and venus

contemporary glacigenic inputs to the dust cycle the importance of glacigenic dust in the earth s system during glacial periods is widely acknowledged under contemporary conditions the world s largest dust sources are in low lying hot arid regions and this is where most aeolian research is focused however the processes of dust production and emissions are still operating in cold climate regions particularly in proglacial areas this paper assesses current understanding of the relationship between glacierised landscapes and dust emissions and inputs to the global dust cycle it focuses on how elements in the glacial and aeolian geomorphic sub systems interact to determine the magnitude frequency and timing of aeolian dust emissions and on feedback mechanisms between the systems where they have been measured dust emission intensity and deposition rates in glacierised catchments are very high in some cases far exceeding those in lower latitudes however few studies span long time scales the impact of future glacier retreat on the balance between sediment supply availability and aeolian transport capacity and implications for glacigenic dust emissions is also considered this balance depends on relative spatial and temporal changes in meltwater suspended sediment concentration and wind strengths which promote dust emissions and patterns and rates of soil development and vegetation succession on recently deglaciated terrain which protect sediments from deflation retreat of the antarctic ice sheet could mean that in future glacigenic contributions to the dust cycle exceed those of non glacigenic sources in the southern hemisphere copyright 2012 john wiley sons ltd

freshwater lens formation below juvenile dunes on a barrier island spiekeroog northwest germany abstract morphodynamic changes of barrier islands and the consequences for underlying freshwater reservoirs are of major interest for coastal environments and drinking water supply in coastal areas here a geomorphological and hydrological reconstruction of dune formation on a barrier island and their freshwater reservoirs is presented the aim was to provide an integrated analysis of the co evolution of dunes and freshwater resources during the development of a barrier island the study area is the eastern part of spiekeroog island the so called ostplate at the northwest german coast that expanded significantly in the last 360 years due to coastal land reclamation the first dune growth was initiated in the 1940s at the newly formed sand flat and dune freshening started around 1970 pore water measurements in november 2011 march and august 2012 confirm the existence of freshwater below the dune area and indicate a landward movement of the freshwater saltwater interface in winter and a seaward movement in summer respectively in response to storms and corresponding coastal flooding a density dependent groundwater flow model was used to estimate the present thickness and shape of the lenses as well as to reconstruct the evolution of the freshwater reservoirs the simulations suggest an asymmetric lens shape with a freshwater discharge tube below the beach to the sea and an extended brackish transition zone below the salt marsh area towards the tidal flat the simulation results also indicate that the freshwater reservoirs are still in a stage of development after 40 years of simulation time and are estimated to reach steady state after about 300 500 years under the given conditions without taking into account possible impacts of climate change

climatic and geochemical implications of archean pedogenic gypsum in the moodies group 3 2 ga barberton greenstone belt south africa abstract lithic sandstones of braided fluvial to supratidal facies in the paleoarchean moodies group 3 22 ga barberton greenstone belt south africa include several regionally traceable units with common to abundant in places rock forming nodular concretions of megaquartz pseudomorphs after gypsum barite and calcite concretionary accumulations are stratiform and commonly associated with aqueously reworked fine grained tuffaceous sediment of originally rhyodacitic composition and can grow to fist sized agglomerates in crusts tens of m in lateral extent weathering of tuffaceous material and feldspar delivered alkali cations such as ca ba and k while carbonates were likely supplied by silicate weathering of mafic to ultramafic volcanic rocks during exposure to a co2 rich atmosphere sulfate ions were partly delivered by oxidative pyrite dissolution which may have included microbial and abiotic disproportionation of volcanic s or so2 concretionary growth apparently took place under pedogenic to early diagenetic conditions within unconsolidated granular sediment in the vadose zone dominated by seasonal fluctuations of the groundwater level under evaporitic conditions the concretions likely represent the oldest terrestrial evaporites known to date and form part of the oldest known compound paleosols their formation and composition constrain the local occurrence of sulfate in the archean atmo and hydrosphere their interaction with the emerging biosphere archean weathering regime local climate and vadose zone hydrodynamics

geochemical stratigraphy sedimentology and mo isotope systematics of the ca 2 58 2 50 ga old transvaal supergroup carbonate platform south africa abstract the neoarchean paleoproterozoic transvaal supergroup in south africa contains the well preserved stromatolitic campbellrand malmani carbonate platform which was deposited in shallow seawater shortly before the 2 40 2 32 ga great oxidation event goe this platform is composed of alternating stromatolitic carbonates and mudstones and is a prominent candidate for isotope geochemical mapping to investigate the appearance of very small amounts of free oxygen that accumulated in shallow waters preceding the goe mo isotopes in sedimentary archives are widely used as a proxy for redox changes in modern and ancient environments and recent evidence suggests that oxy molybdate moo 4 2 is directly transferred from ocean water to inorganic carbonates with negligible fractionation thus reflecting oceanic mo isotope signatures in this study we analyzed major and trace element compositions as well as mo isotopic compositions of carbonate and mudstone samples from the kmf 5 drill core geochemical indicators such as fe and mn concentrations and fe to mn abundance ratios reveal the preservation of some geochemical indicators despite the widespread silicification and dolomitization of the platform heavy 30 si values of silicified carbonates between 0 53 and 2 35 point to si precipitation from surface water during early diagenesis rather than to a later hydrothermal overprint this assessment is supported by the frequent observation of rip up structures of silica chert layers within the entire sedimentary succession the 98 mo values of whole rock samples throughout the malmani campbellrand platform range between 0 82 and 1 40 similar to values reported for deeper slope carbonates from the griqualand west area but variations are independent from lithology or depositional water depth these large variations in 98 mo values indicate molybdenum redox cycling and thus the presence of free oxygen in the atmosphere ocean system at that time in agreement with earlier mo isotopic studies on campbellrand carbonates and shales a similar range in 98 mo values for carbonates between 0 40 and 0 87 however was also found on the hand specimen scale indicating the danger of a sample bias on the mo isotopic stratigraphy of this carbonate platform results of previously unpublished adsorption experiments of mo on caco 3 clearly indicate that the mo inventory of malmani campbellrand carbonates was not only influenced by primary adsorption from seawater but to a much larger degree by secondary processes during early diagenesis which also affected the mo isotopic composition of the samples on a local scale our results indicate that mo concentrations and isotopic compositions in ancient stromatolitic carbonates were subject to redox changes within microbial mats and within the soft sediment during early diagenesis and later lithification and as such cannot be used to quantitatively reconstruct the amount of free atmospheric oxygen or its fluctuations through earth s history nevertheless we interpret our heavy mo isotopic signatures from carbonates as a minimum value for neoarchean seawater and reinforce the assumption that free atmospheric oxygen built up a heavy oceanic mo reservoir at that time

anomalous depressions in the northern yellow sea basin evidences for their evolution processes abstract depressions of both known and unknown origin are observed in continental margin basins and ocean floors worldwide a field of anomalous depressions with dome structures within the centers are documented for the first time using sub bottom seismic profiles multibeam bathymetry data and well data in the northern yellow sea basin they have complex seabed morphologies circular elliptical polygonal linear and crescent shapes with kilometer scale diameters and shallow depths 10 s decimeters to meters focused fluid flow pathways such as gas chimneys faults and pipes and free gas enhanced amplitude anomalies are observed within the shallow strata the depressions are interpreted as immature pockmarks possibly caused by insufficient fluid supply compared to fully developed normal pockmarks they are suspected to still be in the middle stage of pockmark evolution their formation processes are suspected to be controlled by sub seabed plumbing fluid flux and bottom currents this study is important for geologic hazard assessments in the study area and it also contributes to the full understanding of pockmark evolution

on the entrainment of sediment and initiation of bed defects insights from recent developments within turbulent boundary layer research sediment entrainment and the initiation of bed defects has commonly been ascribed to the impact of high velocity sweeps upon mobile sand beds results of visualization experiments suggest that these sweep impacts are grouped and may define patches of entrainment upon a mobile bed that may be wider than an individual sweep impact additionally the presence of longitudinal ribs of sediment generated by sweep impacts may stabilize the position of sweeps and low speed streaks these observations are interpreted in the light of recent boundary layer research which suggests the formation of multiple hairpin shaped vortices within turbulent flows these are postulated to generate multiple sweeps that manifest themselves as entrainment patches on a mobile bed these features of the turbulent boundary layer and its modification by sweep generated sediment ridges can be used to propose a model for bed defect formation and the subsequent development of current ripples