two cryogenian glacial successions compared aspects of the sturt and elatina sediment records of south australia abstract two cryogenian glacial sequences the sturt and elatina occur within the adelaide rift complex s australia and are part of an 8 km thick succession recording rodinia fragmentation and subsequent passive margin development we compare and contrast these glacial successions presenting new data including detailed logged sections for both glacial sequences facies analysis reveals a total of six facies associations recording a range of glacial and glacially related processes these are a diamictite facies association ice proximal debris flows a sheet sandstone facies association fluvial deposits a flaser and rhythmically bedded facies association tidal flat a hummocky cross stratified sandstone facies association shoreface to offshore transition zone deposits and an underflow facies association recording offshore deposition a sixth facies association a ferruginous lonestone bearing siltstone is restricted to the top of the elatina formation and records rapid environmental amelioration and emergence from glaciation in the central flinders ranges the sturt succession commences with a glacial erosion surface ges which in agreement with previous workers was probably enhanced by rifting this ges is overlain in ascending order by the pualco tillite holowilena ironstone and wilyerpa formation with the warcowie dolomite member at the base of this latter formation a second ges is preserved within this latter unit and is overlain by a stratigraphic motif that records an alternation of offshore transition zone and offshore deposits significant base level falls within the wilyerpa formation are identified by fluvial deposits sitting disconformably upon offshore deposits in contrast within the elatina formation a single ges is proposed which defines the base of the formation the elatina formation is split into two informal members on the basis of analysis of sediment stacking patterns and the recognition of a sharp stratigraphic surface that divides the formation apart from a locally preserved basal diamictite the lower member consists of fluvial deposits whereas the upper member is dominated by a mixture of tidal flat sediments and debris flow deposits the boundary between these units is therefore interpreted as a hybrid surface recording tidal ravinement in some areas and a glacial advance in others deglaciation left contrasting deposits the sturt deglaciation culminated in deposition of black shale of the tindelpina shale member of the tapley hill formation seemingly as a sheet like deposit over the adelaide rift complex and beyond into the amadeus basin of central australia the elatina deglaciation meanwhile began first with deposition of the sixth facies association ferruginous dropstone bearing siltstone then proceeded with deposition of cap dolostone of the nuccaleena formation

rhythmic shelf storm beds proterozoic kaimur formation india abstract the shallow marine turbidite like storm beds of the proterozoic kaimur formation exhibit intrabed rhythmic vertical variations in sedimentary structure and texture attributable to different patterns of velocity pulsations within an event of storm current deposition the alternate repetition of parallel laminated s b and ripple cross laminated s c divisions s bcbc within individual storm beds has been interpreted to represent periodic fluctuation in flow intensity beyond the stability limits of ripple and upper flat bed during sedimentation sandstone beds characterised by successively occurring thin internal mud partings indicate pulsing discontinuous flows with alternate periods of slack water within an event of storm current deposition successive mud drapes occurring within the ripple cross laminated divisions s c of some of the storm beds also represent pulsing discontinuous flows palaeoccurrent analyses of these storm beds of the kaimur formation reveal a northwesterly current mode against an e w trending shoreline these storm beds thus may be interpreted to have deposited from geostrophic storm currents that were pulsating in nature with a periodicity of the order of tens of hours similar to that observed on present day storm dominated shelves

evidence of superimposition of storm waves on tidal currents in rocks from the tithonian neocomian umia member kutch india abstract the general opinion is that hummocky cross stratification is generated from superposition of storm waves on a unidirectional current however constraints on the type of the current field have not been clearly established sedimentary structures preserved in rocks of the tithonian neocomian umia member kutch india indicate hummocky cross stratification developed from storm wave interference with ebb tide currents facies indicate repeated progradation of the shoreline and the increasingly important role of sand transport by currents in offshore direction stratigraphic analyses identify two major stages of shoreline progradation each is composed of distinctive shelf to shoreface transitions in the tidally influenced shoreface parts of these transitions the azimuths of units with nearly unidirectional hummocky cross stratification are consistent with the direction of ebb tidal cross stratification suggesting offshore sand transport by superposition of waves on an ebb tidal current

hummocky cross stratification tropical hurricanes and intense winter storms most previous workers have inferred a storm origin for hummocky cross stratification which typically occurs in shallow marine deposits on the modern earth the only storms capable of profoundly affecting shallow marine depositional environments are severe tropical cyclones hurricanes and mid latitude winter wave cyclones intense winter storms this paper examines the palaeogeographic distribution including palaeolatitude and palaeogeographic setting of 107 occurrences of hummocky cross stratification ranging in age from the proterozoic to recent in each of these stratigraphic units both palaeolatitude and palaeogeography are consistent with a direct storm influence associated with the passage of hurricanes or winter storms directly over the site of deposition this palaeogeographic evidence lends support to the inferred storm origin for hummocky cross stratification further the distribution of the structure suggests that most occurrences 73 were generated by tropical hurricanes the remaining 27 being generated by intense mid latitude winter storms the preferential generation of hummocky cross stratification by hurricanes is consistent with 1 the known differences in the nature of the bottom flows generated by the two major storm types and 2 the inferred nature of the flows which form hummocky cross stratification hurricanes couple less effectively with the water column than do intense winter storms due to this ineffective coupling hurricane generated bottom flows tend to be oscillatory or multidirectional dominant with only minor unidirectional components of motion in contrast intense winter storms generally do couple effectively with the water column generating bottom flows which possess a dominant or significant unidirectional component most previous workers have suggested that hummocky cross stratification forms under oscillatory or multidirectional dominant flow thus it is conceptually reasonable that the vast majority of ancient occurrences of hummocky cross stratification were probably hurricane generated as suggested by the aforementioned palaeogeographic distribution the proterozoic palaeozoic neogene and quaternary were times when global climate was similar to that of today the distribution of hummocky cross stratification deposited during these times suggests that both hurricanes and intense winter storms occupied latitudinal belts during these times which were essentially identical to those occupied by their modern counterparts the mesozoic and palaeogene were non glacial times when global climate was much warmer than that of today the distribution of hummocky cross stratification deposited during this interval suggests that hurricanes occurred more frequently at higher latitudes during non glacial times than they do at present the possibility of a broadened hurricane belt during the mesozoic and palaeogene is consistent with climatic considerations a limited number of mesozoic and palaeogene rock units containing hummocky cross stratification were deposited in palaeogeographic settings that preclude a direct hurricane influence these examples were deposited in the middle latitudes suggesting that intense winter storms continued to form hummocky cross stratification in the middle latitudes during these much warmer times some previous workers have suggested that tsunamis may be capable of generating hummocky cross stratification the palaeogeographic distribution of the structure does not support an origin due to tsunamis lacustrine examples of hummocky cross stratification reported herein are the first known non marine occurrences they suggest that storm effects strongly influence the sedimentary record of some lakes

allogenic controls on the evolution of storm to tidal shelf sequences in the early proterozoic uncompahgre group southwest colorado usa dominantly coarse grained shallow marine metasedimentary rocks of the early proterozoic uncompahgre group ug record periods of shoaling and drowning on different temporal scales that are attributed to episodic long term oscillations in relative sea level with superimposed shorter duration excursions in relative sea level long term events are probably tectonic whereas short term events are eustatic the 2 5 km thick uncompahgre group consists of 250 600 m thick dominantly coarse grained quartzite units q1 q4 and 200 300 m thick mudstone pelite units p1 p5 five depositional systems comprise the uncompahgre group the outer shelf system oss is composed of bouma type beds and intercalated mudstones that are transitional vertically to parallel laminated to wave rippled sandstones and hummocky cross stratified sandstones of the inner shelf system iss trough cross stratified sandstones comprise the shoreface system shs the tidal inner shelf shoreface system tis shs consists of a complex interlayering of cross bedded sandstones thin bedded conglomerates mudstones and rippled sandstones trough cross bedded pebbly sandstones and thin to thick bedded conglomerates represent the alluvial system alls depositional systems in the ug are associated in transgressive and highstand systems tracts that make up four sequences 1 to 4 sequence boundaries do not correspond with lithostratigraphic boundaries but are defined by subtle unconformities the basal q1 p1 unit lower sequence 1 consists of alls to tis shs to iss comprising a transgressive systems tract a maximum marine incursion is reflected by deposition of oss facies in stratigraphic units p1 p2 shoaling in the transition from p2 to the uppermedial portion of q2 oss iss shs to a thick tis shs alls records the highstand systems tract of upper sequence 1 a subtle disconformity paraconformity delineates a type 2 sequence boundary at the top of the highstand systems tract the drowning to shoaling pattern is replicated in sequence 2 upper q2 to p3 to upper medial q3 sequence 3 upper q3 to p4 to upper medial q4 and an incomplete sequence 4 upper q4 through p5 thinner shoaling intervals of oss iss shs in p3 and in lower q2 q3 and q4 represent parasequences sequences of 107 years duration are attributed to periods of increasing and decreasing subsidence rates due to tectonism marginal to the sedimentary basin parasequences record shorter duration temporal controls of c 104 to 105 years related to eustatic oscillations as a consequence of shoaling and aggradation progradation in the highstand systems tract tis shs and alls overlie and are temporally separated from oss to iss to shs this transition records filling of the basin to sea level leading to a shelf geometry that was conducive to tidal amplification a composite relative sea level curve integrating long term pulsatory subsidence and short term eustasy best explains the stratigraphic evolution of the uncompahgre group

soft sediment deformation structures in cambrian siliciclastic and carbonate storm deposits shandong province china differential liquefaction and fluidization triggered by storm wave loading abstract this paper focuses on soft sediment deformation structures ssds in both siliciclastic and carbonate storm deposits of the cambrian mantou and chaomidian formations shandong province china in order to understand their deformation mechanisms and possible triggers siliciclastic ssds e g sand volcanoes and pillows and carbonate ssds e g sedimentary dykes grainstone matrix breccias deformed cross beddings and marlstone matrix breccias occur exclusively in hummocky cross stratified fine sandstone and peloidal grainstone respectively the siliciclastic ssds formed in porous and permeable surface sediment whereas the carbonate ssds formed under shallow burial conditions when early marine cementation prevailed the various deformation structures resulted mainly from differences between siliciclastic and carbonate sediment conditions and resulting deformation mechanisms sand volcanoes formed by upward extrusion of over pressured fluidized sandy sediment whereas sand pillows resulted from upward injection of lower density muddy sediment into overlying liquefied sandy sediment sedimentary dykes and grainstone matrix limestone breccias formed as a result of differential liquefaction and fluidization of heterogeneously cemented carbonate sediment whereas deformed cross beddings and marlstone matrix limestone breccias developed by the thixotropic liquidization and injection of clayey sediment and further disruption of thin peloidal layers sedimentary facies analysis and analysis of the physical processes indicate that the ssds were most likely caused by cyclic loading of storm waves

cardium formation u cretaceous at seebe alberta storm transported sandstones and conglomerates in shallow marine depositional environments below fair weather wave base as a result of detailed mapping at seebe alberta we have defined five coarsening upward sequences in the turanian cardium formation the sequences begin with bioturbated mudstones and coarsen int

constraining turbulent heat flux parameterization over a temperate maritime glacier in new zealand the turbulent sensible and latent heat fluxes are important components of the surface energy balance over glaciers in the southern alps of new zealand contributing over half the energy available for ablation during large melt events to calculate these terms confidently in glacier mass balance models it is essential to use appropriate parameterizations for surface roughness and atmospheric stability eddy covariance measurements at brewster glacier were obtained over an ice surface to help facilitate an assessment of the calculation of the turbulent heat fluxes the roughness length for momentum was found to be 3 6 x 10 3 m while the roughness lengths for temperature and humidity were two orders of magnitude smaller in agreement with surface renewal theory a monte carlo approach was used to assess the uncertainty in turbulent heat fluxes calculated using the bulk aerodynamic method it was found that input data and roughness length uncertainty could not explain underestimates of observed sensible heat fluxes during periods with low wind speed and large temperature gradients during these periods a katabatic wind speed maximum alters the formulation of the turbulent exchange coefficient to that typically observed in a neutral atmosphere and this has implications for glacier mass balance sensitivity

the paleogeography of paleozoic and mesozoic storm depositional systems present day hurricane belts are confined to 5 45 latitude along the western edges of oceans whereas winter storms occur ubiquitously above 25 latitude both hurricanes and winter storms occur between 25 and 45 latitude in some areas storm zones can be identified on global paleogeographic maps with the assumption that this latitudinal zonation of storm systems existed in the geological past evaluation of 69 previously recognized paleozoic and mesozoic storm depositional systems on such maps showed that only 70 of them occur in ancient hurricane mixed hurricane and winter storm and winter storm belts the remainder occur on the western sides of continents and or at low paleolatitudes and therefore well may be of different origin mesozoic storm depositional systems containing hummocky stratification tend to occur in counterpart paleo winter storm belts whereas hummocky stratification in suggested paleozoic examples occur in both winter storm and hurricane belts and in paleolatitudes where we in

internal waves vs surface storm waves a review on the origin of hummocky cross stratification hummocky cross stratification hcs is considered a diagnos tic structure of surface storm activity at the shoreface offshore transition however the origin of hcs is still debated laboratory experiments have not yet reproduced it and direct observations on the continental shelves do not exist most hydrodynamic interpretations invoke pure oscilla tory flows unidirectional dominated combined flows and oscillatory dominated flows but they all share the assump tion of hcs to reflect the combined action of surface storm waves and related currents within this context of uncertain ties internal waves gravity waves propagating along the pycnocline provide an alternative mechanism to explain the origin of hcs internal waves breaking on the shelf create episodic high turbulence events and induce upslope and downslope currents as well as oscillatory flows at the depth where the pycnocline intersects the sea floor in this scenario both the oscillatory and the unidirectional components needed for hcs to form are not necessarily linked to surface storm waves but can occur at various depth as far and near there is a pycnocline where internal waves can form

hummocky cross stratification is not produced purely under progressive gravity waves hummocky cross stratification is a type of bedding in sedimentary rocks caused by the draping of sand around low steepness three dimensional bedforms this distinctive form of stratification has been thought to be diagnostic of the former action of storm waves and hence its occurrence has been used to reconstruct ancient palaeogeographies and marine processes here i examine theoretical and empirical aspects of hummocky cross stratification pertaining to its origin and argue that the notion that it was produced purely under progressive storm waves is incompatible with observed hummock spacings and possible values of the ratio a under waves a is the amplitude of oscillation near the bed and is the bedform spacing my view is supported by recent observations on naturally occurring hummocky megaripples from the sea floor of the inner atlantic shelf of north america

hindered bedload settling as a model of sand bed planation by water waves the interrelationships between fluid flows and the surface forms of underlying movable beds are crucial in interpreting sedimentary structures and in predicting hydraulic drag energetic flows can erode all features from a sediment bed and transition to such a planar bed is important to the processes of sediment transport by waves1 the following analysis connects bed planation to a threshold effect in hindered settling with increasing concentration of noncohesive sediment moving near the bed calculated fluid velocity from the resulting quantitative criterion for this bed transition agrees with extensive laboratory data2 3 in oscillatory flows

the longshore flow component in low energy rip channels the mediterranean israel abstract we examined in the field the near bed longshore v flow component in rip channels at the herzliyya beach israel on the southeastern mediterranean field experiments conducted under relatively calm wave conditions t sig 3 6 s h sig 0 3 1 1 m included current and wave monitoring and morphological mapping time series of instantaneous and smoothed shore parallel current velocities and of the orbital components were analysed including statistical and spectral processing the peak instantaneous velocities of waves and currents combined were in excess of the threshold motion of the local sand taken as 0 3 m s some velocities even exceeded the threshold for sheet flow transport 0 9 m s the feeder and the neck demonstrated the highest longshore flow components whereas the rip head typically showed the lowest longshore velocities the unsteadiness of the net longshore current was very high feeders typically showed a mean unidirectional longshore current however directional fluctuations gradually increased towards the rip head the data suggest a clear spectral structure most energy 46 67 was in the gravity range with 13 35 subharmonic and minor 13 16 in the infragravity band systematic cross shore spatial trends of the energy spectra components were linked to bar morphology and to exposure to incident waves

an extensive erosion surface of a strongly deformed limestone bed in the gushan and chaomidian formations late middle cambrian to furongian shandong province china sequence stratigraphic implications abstract in order to understand sequence development and sea level fluctuations during the late middle cambrian to early furongian on the north china epeiric platform the present study focuses on a unique subtle erosion surface of an extensive approx 100 km strongly deformed limestone bed in the uppermost part of the gushan formation shandong province china the gushan formation and the overlying chaomidian formation consist mainly of shales and a variety of carbonates that were deposited in subtidal environments e g deep subtidal shallow subtidal shoreface shoal subtidal microbial flat and restricted platform interior three third order depositional sequences s1 3 are identified each of which comprises a thin transgressive systems tract tst and a relatively thick highstand systems tract hst each sequence is bounded by a drowning unconformity sb1 a subaerial unconformity sb2 or a surface of submarine erosion sb3 the upper sequence boundary sb2 of sequence 1 s1 is represented by a subtle erosion surface of an extensive deformed limestone bed with a wide variety of soft sediment deformation structures e g lime mudstone breccias chaotic wacke packstone laminae and fragments homogenized oolites and clastic dykes and is overlain by small sporadic microbial buildups and an extensive bioclastic grainstone bed the deformed limestone was formed during early diagenesis by differential deformation processes brecciation liquefaction fluidization and injection which were most likely induced by pore water overpressure during the period of rapid sea level fall despite the lack of subaerial exposure features e g paleokarst paleosol etc the characteristics of the erosion surface cutting well lithified sediment below the missing of a significant geological record the prochuangia biozone and the worldwide correlatable positive carbon isotope excursion collectively indicate that the erosion surface developed under conditions of subaerial exposure after contemporaneous marine cementation of the deformed sediment the missing of the prochuangia biozone is most likely due to non deposition at a subaerial hiatal surface the erosion surface was submerged as a result of subsequent rise in sea level where sporadic microbial buildups formed under suitable conditions freshly deposited winnowed shell dominated transgressive lag deposits containing chuangia trilobite fragments brachiopod shells and abundant glauconite grains formed with continued rise in sea level which became in turn overlain by shale dominated facies the unique combination of the subtle erosion surface sensu stricto a subaerial unconformity and the underlying deformed limestone bed provides an important criterion for recognizing the subtle changes in relative sea level on shallow epeiric platforms

paleoenvironmental implications of an extensive maceriate microbialite bed in the furongian chaomidian formation shandong province china abstract this study focuses on the unique occurrence of an extensive microbialite bed 10 20 m thick in the chaomidian formation furongian in shandong province china in order to understand its paleoenvironmental implications the microbialite bed can be traced for over 6000 km2 in area the microbialites are characterized by centimeter to decimeter scale branching maze like constituents maceriae of microbial and muddy sediments with chaotic texture including tabular maceriate microbialite type 1 columnar maceriate microbialite type 2 and columnar chaotic microbialite type 3 within the bed each microbialite unit is generally well correlated for tens of kilometers the entire bed is bounded by limestone marlstone alternation at the base and an erosional surface at the top that is subsequently overlain by a grainstone bed of various thicknesses the microbialite bed formed when the seafloor reached suitable water depth for the microbial growth during sea level rise accompanied with carbonate production the maze like maceria structures formed to acquire a larger surface area under a relatively large input of lime mud the tabular maceriate microbialites initially formed in relatively deep water environments and flourished on broad and flat seafloor whereas the columnar microbialites types 2 and 3 developed under the influence of strong waves and currents the microbialite bed was eroded and terminated by frequent storm events and buried under the reworked grainstone further rise in sea level and increased metazoan activities afterwards limited the resurgence of microbes in the late furongian

experiments on oscillatory flow and combined flow bed forms implications for interpreting parts of the shallow marine sedimentary record abstract analog laboratory experiments were conducted to investigate subaqueous bed forms generated under storm like oscillatory and combined flow experiments were carried out in a large wave tunnel and used a range of sand sizes fine and very fine wave periods 10 5 and 8 s oscillatory velocities 0 to 125 cm s and unidirectional velocities 0 to 25 cm s at low unidirectional velocities 10 cm s addition of an increasing collinear oscillatory flow caused the bed to evolve from small scale wavelength 100 cm symmetric orbital ripples to plane bed at higher unidirectional velocities 10 cm s a similar trend was noted but ripples were more asymmetric three phase diagrams are presented to summarize the observed relationships of bed configurations to flow conditions these diagrams are intended to assist in the interpretation of shallow marine sedimentary environments where oscillatory and combined flow are thought to be omnipresent distinctive features of small scale asymmetric combined flow ripples generated are a 3d planform round crest and convex up sigmoidal profile with local pronounced scour at the toe of the stoss side giving the ripple profile a boxy appearance similarly large scale asymmetric combined flow ripples had broad and round crests convex up stoss sides and compressed profiles due to scouring at the toe of the stoss side hummocky bed forms were generated under moderate to high oscillatory velocities and low unidirectional velocities hummocks were not observed as a distinct bed state but rather appeared to mark transitions in bed form scale and symmetry hummocks were more prevalent at longer oscillatory periods and in finer grained sediment stratification produced by synthetically aggrading hummocky bed profiles closely resembles hummocky cross stratification with the introduction of only a small unidirectional flow component hummocks evolve into downstream migrating large scale asymmetric ripples and the resultant cross stratification becomes similar to that produced by unidirectional flow dunes accordingly these experiments suggest that much of the hummocky cross stratification observed in the stratigraphic record is produced by storm generated long period oscillatory dominant combined flows inasmuch as long period high energy waves require deep wide basins to form hummocky cross stratification may therefore serve as a useful indicator of deposition in unrestricted open water conditions

storm and fair weather wave base a relevant distinction surface waves are an important mechanism for the redistribution of sediment on shallow marine shelves and are commonly interpreted as comprising two distinct populations fairweather waves and storm waves the latter of which are generally thought to penetrate to greater water depths here we used 2 3 10 6 spectral density estimates for the surface ocean collected between 1996 and 2008 from 32 buoys in the caribbean the gulf of mexico and the western atlantic to test the hypothesis that surface waves in the modern ocean comprise two size modes although distinct wave size classes occur in some individual measurements and over the time scales of some individual storms time averaged frequency distributions of wave size are unimodal thus there is no empirical basis for presupposing a distinct bimodal separation in the size of fair weather and storm waves or in the manifestation of such differences in stratigraphic successions instead there is a continuously increasing probability that a wave will reach the bottom with decreasing water depth and a separate probability that describes the hydrodynamic state of the sediment water interface wave size does however exhibit signifi cant geographic bimodality locations in the relatively protected gulf of mexico and caribbean regions have modal wavelengths that are 50 m less than waves at locations along the western atlantic time integrated estimates of the depth of wave penetration provide empirical constraints on the paleo water depths of ancient sedimentary deposits and highlight differences between sheltered shelf environments such as those that characterized many ancient epeiric seas and open ocean facing narrow continental shelves

a lower permian sandwave containing shelf sequence exposed at zungwini mountain republic of south africa abstract as a result of railway excavations the pietermaritzburg shale vryheid formation transition is spectacularly exposed on the southern slope of zungwini mountain nine facies and three facies associations are recognised deposition occurred in a palaeoshelf and offshore setting the reconstructed coastline was sw ne with land to the northwest the inner shelf was tide and the outer shelf storm influenced fluvial input supplied sediment which was reworked into flood tidal sandwaves probably within the confines of an estuary a rising sea level brought the sandwaves into the realm of a more distal coast parallel storm tidal current regime where reworking of the sediment occurred intense storm augmented tidal currents swept some of the better sorted material seaward to be deposited as storm layers in the inner and outer shelf these same currents formed the low density turbidites and sediment plumes from which the offshore argillaceous deposits were formed the shelf edge poorly sorted rhythmite facies may have developed from sediment flushed out of the rivers during flood or from the flood tidal sandwave system as a result of exceptional coastal storms

equilibrium slopes and cross shore velocity asymmetries in a storm dominated barred nearshore system abstract the near bed 0 10 m elevation horizontal velocities were measured across a two barred lacustrine shoreface during a storm and reveal a spatially coherent but temporally variable pattern in the low order moments of the velocity field large cross shore velocity asymmetries indicated 1 1 spatially extensive and temporally persistent offshore mean flows up to 0 18 m s 1 across the landward slope of the linear outer bar reflecting an undertow driven by a wave induced setup 2 2 an onshore directed skewness opposing the mean flow of wind wave origin and persistent under propagating bores in the inner bar system long after this asymmetry had disappeared from the outer bar extensive sediment reactivation with near zero net sediment flux over the whole of the upper shoreface indicated a sediment prism in a steady state volumetrically over the storm cycle uniform depths of sediment reactivation with zero bed elevation change over the storm cycle revealed local slopes in a steady state in the outer linear bar however time integration of the near bed velocity field at this location indicated an offshore net flux of water while sedimentary structures indicated bedform migration and thus at least bedload almost uniformly onshore when ripples and megaripples were present the sediment transport giving rise to the local equilibrium cannot be explained therefore on the basis of the mean properties of the near bed velocity vector but requires knowledge of the time varying instantaneous sediment transport vector onshore migration of the inner bar correlated well with the large and persistent onshore skewness of the velocity distribution in the inner surf zone associated with translatory surf bores throughout the storm decay period low frequency oscillations were only significant close to the shoreline but may have influenced the development of a sinuous three dimensional inner bar form as it migrated onshore

paleoslope reconstruction in sandy suspended load dominant rivers constraining the depositional gradient of ancient alluvial river systems can aid in reconstructing landscapes and estimating paleodischarge by establishing boundaries on the climatic and tectonic history of continental sequences we present three methods for estimating ancient depositional gradients based on the interpreted mode of sediment transport for the range of particle sizes found on the beds of modern rivers or preserved in channel fills for sandy rivers with suspension as the dominant mode of sediment transport these methods take advantage of observations that can be directly obtained from preserved strata including measurements of paleo flow depth and grain size the first method relates river slope to shields number at bankfull flow the second method is similar to the first but allows for variation in shields number at bankfull flow with grain diameter the final method relies on criteria required for both suspended and bed material load sediment transport in the same system and is the most comprehensive and physically justified method we present each method and test them with modern river datasets to verify accuracy and help constrain uncertainty the first step to adapting them to ancient systems results indicate that all methods estimate slope within a factor of two these methods are potentially very powerful for interpreting sandy fluvial deposits because they can provide reasonably accurate quantitative estimates of paleoslope an elusive yet important environmental variable

hummocky cross stratification and post vortex ripples length scales and hydraulic analysis duke 1987 argues that the structure reported by greenwood sherman 1986 as hummocky cross stratification from a shallow lacustrine environment is instead bedding formed by simple post vortex oscillation ripples his primary concern is with the length scale of the structures identified in box cores however using measured flow data it is shown here that existing models of bedform generation based upon wave orbital velocity orbital diameter and grain diameter do not support a simple post vortex ripple interpretation in particular the relative steepness of the structure refutes such an origin the structural characteristics of the lacustrine cores most closely match those associated with classic hummocky cross stratification and were produced under a combined oscillatory quasi steady flow field