hummocky cross stratification and megaripples a geological double standard abstract hummocky cross stratification in ancient sedimentary deposits is considered to be diagnostic of inner shelf storm deposits the geometry of the cross strata sets implies a low relief oval bedform of a few meters spacing orientation is poorly defined or random hummocky cross strata sets have been attributed to the action of strong storm wave surges megaripples of 2 5 m spacing are typical responses of the inner atlantic shelf of north america to storm flows side scan sonar records have shown that megaripples on the inner shelf are commonly hummocky oval to circular in plan view and lack asymmetry box cores and vibracores reveal gently inclined to horizontal lamination as the characteristic primary structure the megaripples am produced by combined flow storm currents these are alongcoast geostrophic flows with a mean flow component of 20 60 cm sec 1 a high frequency wave orbital current of similar or weaker intensity is present but its role in megaripple formation is subordinate to that of the mean flow the high velocity coastal margin of the flow is often jetlike and downwelling in nature and is characterize by a down current decrease in sand flux and rapid deposition of sand the bottom boundary layer of such flows is characterized by dense sediment suspensions 40 60 mgl 1 and is highly turbulent due to the interaction of the mean flow and wave orbital current components eddy diffusivity up to 200 cm2 sect at 40 cm above the bed sand transport in this coastal boundary zone is obliquely offshore but neither the density of the sediment suspension nor storm surge ebb appear to be important driving forces it is difficult to account for either modern hummocky megaripples or ancient hummocky cross stratification as responses to purely oscillatory flows combined flow currents are the typical response of mostmodern shelves and epicontinental seas to storms and presumably were so in the past hummocky cross stratified beds are generally too thick 20 80 cm to be accounted for by in situ resuspension they are more likely to have been despoited by combined flow currents in areas where these currents were experiencing a downstream velocity decrease and sediment deposition throughout much of the storm s duration evidence for strong scour in swales between hummocks and the smoothly rounded surface of the hummocks suggests a transitionlike bed regime measurements on the atlantic shelf likewi e suggest a transitionlike regime whose boundary layer is characterized by lower velocity than the transitional regime of unidirectional flow in flumes but more intense turbulence and a higher suspended sand concentration the lack of normal cross bedding in bothmodern and ancient hummocky bedforms indicates that these features did not migrate this characteristic may be a consequence of the complex trajectories followed by near bottom water particles in response to combined flow currents

subtidal occurrences of ladder back ripples their significance in palaeo environmental reconstruction ladder back ripples are common on modern intertidal flats and have been thought to be diagnostic of deposition in this environment recognition of superimposed asymmetric ladder back ripples in a subtidal back barrier estuary and superimposed symmetric ladder back ripples in an embayed shallow marine environment indicates that these features are not diagnostic of deposition in the intertidal zone only but can occur in other depositional environments produced by different mechanisms and on different scales the presence of ladder back ripples in the subtidal zones challenges aspects of a model used to determine the palaeotidal range of ancient tidal sequences

origin of giant wave ripples in snowball earth cap carbonate the most extreme climate transitions in earth history are recorded by the juxtaposition of neoproterozoic glacial deposits with overlying cap carbonate beds some of the most remarkable sedimentary structures within these beds are sharp crested trochoidal bedforms with regular spacing of as much as several meters that are often interpreted as giant wave ripples formed under extreme wave conditions in a nonuniform postglacial climate here we evaluate this hypothesis using a new bedform stability diagram for symmetric oscillatory fl ows that indicates that the fi rst order control on the formation of trochoidal rather than hummocky bedforms is sediment size not wave climate new measurements of bedform wavelengths and particle sizes from the ca 635 ma nuccaleena formation australia indicate that the giant ripples are generally composed of coarse to very coarse sand most are within the trochoidal bedform stability phase space for normal wave climates moreover numerical simulations of flover fi xed bedforms show that symmetric trochoidal ripples with a nearly vertical angle of climb may be produced over long time periods with variable wave climates in conjunction with rapid seabed cementation these data reveal that rather than extreme wave conditions the giant wave ripples are a consequence of the unusual mode of carbonate precipitation during a global carbon cycle perturbation unprecedented in earth history

combined flow processes and sedimentary structures on the shoreface of the wave dominated grande riviere de la baleine delta abstract shoreface sediments exposed in raised deltaic deposits along the hudson bay coast are characterized by a thick succession of predominantly parallel laminated and small scale cross laminated fine sand ripple forms where preserved include both combined flow and wave ripple geometries hummocky cross stratification is present in lower parts of the section similar facies have been found in cores from the present day shoreface measurements of waves currents and suspended sediment concentrations in 10 m water depth conducted over a 15 day period in the fall of 1999 captured four different meteorological periods these included an intense four day storm which sustained significant wave heights over 3 m for 15 hours and a storm surge of over 1 m height fair weather conditions produce weak alongshore tidal flows but oscillatory motions generated by small local waves predominate during storms orbital motions dominate the flow but a strong inertial flow generated by wind forcing is also present comparison with a published combined flow bedform stability diagram suggests that the predominant bedforms at 10 m depth would be small 2 d wave dominated ripples and small weakly asymmetrical 3 d ripples under fair weather conditions and large 3 d ripples and upper plane bed under storm wave conditions the predominantly interbedded parallel laminated and small scale cross laminated facies is therefore interpreted to be characteristic of the upper shoreface where the seabed experiences intense oscillatory motions under all storms and even some fair weather conditions combined flow ripples would form during storm events because of the stronger wind driven mean residual current hummocky cross stratification forms in deeper water during storms where the ratio of maximum orbital velocity to mean residual current velocity remains for longer periods in the large 3 d ripple field during the waning phase of storms a numerical bed predictor model using the 15 day data set as input also suggests bimodal conditions fluctuating between wave ripples and upper plane bed at 10 m water depth this model further indicates that combined flow ripples would form rarely but tends to underestimate the threshold of sediment suspension

storm influences on a tidal sandbank s surface middelkerke bank southern north sea the results are presented of two types of pre storm and post storm surveys carried out on the middelkerke bank southern north sea the first type of survey was planned to detect detailed morphological changes in two selected areas of the bank totalling 3 km2 for the survey in these shallow waters to be completed in a fast and accurate way use was made of a special hovercraft based hydrographic system the other type of survey concerned grab samplings covering the sandbank in order to study spatial variations in surficial grain size the pre storm and post storm morphological surveys showed that small and medium dunes disappear under stormy conditions a 5 m westerly displacement of most of the large and very large dunes has been interpreted as the result of bedform migration under normal fair weather locally dominant ebb flow the lowering of the large dunes crests by up to 1 2 m is considered an effect of the storms the accretion of the lower part of the northwestern flank is attributed to the deposition of sand derived from shallow parts of the sandbank during storms the grain size surveys showed that especially the central and northern parts of the sandbank were affected by grain size changes the northwestern flank showing a clear coarsening and the landward southeastern flank a fining with respect to the fair weather situation it is put forward that the waves approaching from the north cause an extra winnowing on the exposed flank of the bank on the southeastern flank of the bank which is better protected against the wave action fine particles are then deposited

infrasonic tremor in the diffraction zone 1 volcanic tremor signals recorded by an infrasound array 12 5 km from the active vent of k lauea volcano show clear diurnal amplitude variations and originate from a well defined direction pointing to the active pu u crater complex spectral amplitudes between 0 02 0 3 hz a proxy for wind speed increase when the wind speeds increase during the daytime spectral amplitudes between 0 5 3 hz where infrasonic tremor is concentrated increase when the wind speeds decrease at night power spectrum analysis shows that when ambient noise levels drop infrasonic tremor amplitudes rise array processing confirms this relationship and reveals tremor detections and amplitudes decrease during the day these changes in infrasonic tremor spectral amplitude and coherence are most likely due to diurnal variations in atmospheric boundary layers affecting infrasonic propagation within the diffraction zone recognition of these regional atmospheric patterns is necessary to permit robust infrasonic remote sensing of volcanic processes

observations of time dependent bedform transformation in combined wave current flows although combined wave current flows in the nearshore coastal zone are common there are few observations of bedform response and inherent geometric scaling in combined flows our effort presents observations of bedform dynamics that were strongly influenced by waves currents and combined wave current flow at two sampling locations separated by 60 m in the cross shore observations were collected in 2014 at the sand engine mega nourishment on the delfland coast of the netherlands the bedforms had wavelengths ranging from 14 cm to over 2 m and transformed shape and orientation within at times as little as 20 min and up to 6 hr the dynamic set of observations was used to evaluate a fully unsteady description of changes in the bedform growth with the sediment transport continuity equation exner equation relating changes in bedform volume to bedload sediment transport analysis shows that bedform volume was a function of the integrated transport rate over the bedform development time period the bedform development time period time lag of bedform growth adjustment is important for estimating changes in bedform volume results show that this continuity principle held for wave current and combined wave current generated bedforms

field investigation of bedform morphodynamics under combined flow abstract fieldwork was conducted at the red cliff sandbar located in the upper humber estuary in order to investigate bedform dynamics under different hydrodynamic conditions related to combinations in tidal and wave generated currents a fixed mooring was deployed to obtain current flow and wave properties across the sand bar site at both spring and neap tidal flows and during conditions of high wind generated waves a terrestrial laser scanner was used to scan the sandbar during low water across the various forcing conditions acquiring detailed information of ripple geometries under spring tide and calm wave conditions two dimensional asymmetrical ripples with straight crest lines were generated on the sandbar surveys were also conducted during strong winds prior to high wind waves two dimensional symmetrical and washed out ripples were observed during spring and neap tidal conditions respectively the lengths of these ripples were almost the same as those generated under current only conditions but their heights were relatively smaller after the strong wind periods 2d current induced ripples were replaced by flatbed conditions and 2d symmetrical wash out ripples which indicates wave induced bed shear stress is enhanced by the presence of a tidal current most pertinently our study reveals discrepancies between field observations and existing predictions of bed configurations that are largely based on laboratory investigations this is likely due to a larger grain size distribution in field conditions and due to turbulence dampening by high concentrations of suspended clay particles the study thus highlights a need to extend a range of field investigations that explore the current deficiencies in our abilities to predict bedforms and bedform dynamics in estuarine systems

geological and oceanographic perspectives on event bed formation during hurricane katrina 1 storm deposits in ancient shelf sediments typically form thick sequences of interbedded sand and mud deposited during shoreline regression whereas modern shelf sediments are generally thin veneers deposited during shoreline transgression in this paper we present a preliminary comparison between ancient and modern storm beds deposited in these disparate contexts hurricane katrina deposited a storm bed on the louisiana shelf with a maximum observed thickness of 0 58 m which thinned to approximately 0 1 m at 200 km west of landfall this thickness is similar to event beds observed in both ancient and modern sediments using data for tropical cyclone landfalls in the gulf of mexico we estimate the return time for a storm of this size to be 40 50 years in this region this estimated frequency for deposition of storm beds is useful in evaluating ancient storm sequences that were deposited during similar climatic conditions

deltaic sedimentation in the devonian of western libya abstract middle and upper devonian deposits from the aouinet ouenine formation in the southern ghadames basin of western libya provide a well exposed example of a deltaic complex containing both progradational and transgressive facies progradational facies comprise both laterally accreting and incised distributary channels overlying prodelta deposits also present is a progradational beach environment showing build up from an offshore shelf through nearshore shelf to shoreface and foreshore sub environments over lying these progradational facies are transgressive tidal flat washover fan foreshore and nearshore deposits the characteristics and interrelationships of the different facies are explained by two sedimentation models progradational facies existed contemporaneously during phases of active sediment supply whereas the transgressive facies existed contemporaneously during periods of diminished or absent detrital influx

sediment transport patterns in the san francisco bay coastal system from cross validation of bedform asymmetry and modeled residual flux abstract the morphology of 45 000 bedforms from 13 multibeam bathymetry surveys was used as a proxy for identifying net bedload sediment transport directions and pathways throughout the san francisco bay estuary and adjacent outer coast the spatially averaged shape asymmetry of the bedforms reveals distinct pathways of ebb and flood transport additionally the region wide ebb oriented asymmetry of 5 suggests net seaward directed transport within the estuarine coastal system with significant seaward asymmetry at the mouth of san francisco bay 11 through the northern reaches of the bay 7 8 and among the largest bedforms 21 for 50 m this general indication for the net transport of sand to the open coast strongly suggests that anthropogenic removal of sediment from the estuary particularly along clearly defined seaward transport pathways will limit the supply of sand to chronically eroding open coast beaches the bedform asymmetry measurements significantly agree up to 76 with modeled annual residual transport directions derived from a hydrodynamically calibrated numerical model and the orientation of adjacent flow sculpted seafloor features such as mega flute structures providing a comprehensive validation of the technique the methods described in this paper to determine well defined cross validated sediment transport pathways can be applied to estuarine coastal systems globally where bedforms are present the results can inform and improve regional sediment management practices to more efficiently utilize often limited sediment resources and mitigate current and future sediment supply related impacts

skin friction behind isolated hemispheres and the formation of obstacle marks we have measured the mean magnitude and direction and the rms fluctuation intensity of the skin friction behind plain hemispherical obstacles and behind hemispheres with tapered artificial tails one and four obstacle heights long downstream of reattachment the mean skin friction magnitude is about 20 greater than its free stream value along the centre line and comparably reduced to either side of it the horizontal divergence of the skin friction vector field is positive divergent along the centre line and negative convergent to either side of it neither of these conditions favours development of a ridge longer than the separation length along the centre line the development of ridges or tails many obstacle heights long commonly observed in nature requires considerable modification of the simple sediment free wakes we have studied

impact of a rocky outcrop on hydrodynamics and geomorphology in a mesotidal channel abstract the purpose of the present work is to study the effect of an isolated depression and a related rocky outcrop on the flow field in a mesotidal channel of the bahia blanca estuary argentina to this end measurements of current velocity adcp swath bathymetry multibeam and seismostratigraphic surveys 3 5 khz were made in the study area in general the channel bed studied cabeza de buey channel is flat and mainly composed of clayey silts in the inner sector there is a depression 6 m deep and 50 60 m in diameter and on either side in a streamwise sense there are two isolated rocky outcrops that extend up to 2 m in height relative to the prevailing bed level the two features differ in that the up estuary outcrop is longer and extends over the whole width of the hole while the down estuary outcrop is shorter and only extends over part of the diameter of the hole seismostratigraphic analysis in correlation with bathymetric and lithological data indicates that these high points correspond to the outcropping of relict deltaic materials that formed part of a regional late pleistocene drainage system fine grained estuarine sediments deposited above the old deltaic materials show evidence of the present day sedimentological conditions related to the hydrodynamics of the channel the flow patterns within the depression observed over a complete tidal cycle demonstrate that the flow behaves differently depending on the stage of the tide the depth averaged flow shows higher velocities during the ebb tide generating a net flow directed towards the sea results reveal the generation of return flows turbulent eddies at the bottom of the hole which expand immediately towards the water surface during the ebb tide intense vertical currents develop inside the hole the eddy formation is attributed to the unequal size of the outcrops hence the larger upstream channel outcrop plays an important role in eddy generation just as downwelling upwelling interaction produces erosion and transport of sediments which exerts a strong influence on the deepening of the hole

sand waves on an epicontinental shelf northern bering sea abstract sand waves and current ripples occupy the crests and flanks of a series of large linear sand ridges 20 km 5 km 10 m high lying in an open marine setting in the northern bering sea the sand wave area which lies west of seward peninsula and southeast of bering strait is exposed to the strong continuous flow of coastal water northward toward bering strait a hierarchy of three sizes of superimposed bedforms all facing northward was observed in successive cruises in 1976 and 1977 large sand waves height 2 m spacing 200 m have smaller sand waves height 1 m spacing 20 m lying at a small oblique angle on their stoss slopes the smaller sand waves in turn have linguoid ripples on their stoss slopes repeated studies of the sand wave fields were made both years with high resolution seismic reflection profiles side scan sonographs underwater photographs current meter stations vibracores and suspended sediment samplers comparison of seismic and side scan data collected along profile lines run both years showed changes in sand wave shape that indicate significant bedload transport within the year gouge marks made in sediment by keels of floating ice also showed significantly different patterns each year further documenting modification to the bottom by sediment transport during calm sea conditions in 1977 underwater video and camera observations showed formation and active migration of linguoid and straight crested current ripples current speeds 1 m above the bottom were between 20 and 30 cm s maximum current velocities and sand wave migration apparently occur when strong southwesterly winds enhance the steady northerly flow of coastal water many cross stratified sand bodies in the geologic record are interpreted as having formed in a tidal or storm dominated setting this study provides an example of formation and migration of large bedforms by the interaction of storms with strong uniform coastal currents in an open marine setting

a note on megaripples in the surf zone evidence for their relation to steady flow dunes megaripples in the combined flow environment of the nearshore are proposed to behave like dunes or large ripples in rivers tidal estuaries and deserts their profile basically is symmetric and thus significantly different from the traditional asymmetric triangular features observed in steady flows similarly their planform often exhibits little directionality unlike crescentic or lunate steady flow dunes that point in the downstream direction these characteristics are the result of complex combined flows in the nearshore including oscillatory flows wave skewness and steady currents undertow rips and alongshore flows recent observations of megaripples in the nearshore suggest that they occur frequently however they are rarely considered in studies of flow resistance or sediment transport in addition megaripples are thought to be the source of hummocky cross stratification in sedimentary sequences and are generally attributed to storm waves on inner continental shelves however observations show that they also exist inside the surf zone and under lower energy conditions a better understanding of their dynamics and thus their occurrence and characteristics would improve the understanding of nearshore wave and circulation dynamics sediment transport large scale morphodynamics and the resulting sedimentary sequences it is hypothesized that megaripples in the nearshore are dynamically similar to steady flow features which are observed in rivers estuaries and deserts and have been studied in much more detail

a study of model bivalve siphonal currents we carried out experiments studying the hydrodynamics of bivalve siphonal currents in a laboratory flume rather than usc living animals we devised a simple model siphon pair connected to a pump fluorescence based flow visualization was used to characterize siphon jet flows for several geometric configurations and flow speeds these measurements show that the boundarylayer velocity profile siphon height siphon pair orientation and size of siphon structure all affect the vertical distribution of the excurrent flow downstream of the siphon pair and the fraction of cxcurrent that is refiltered the observed flows may effect both the clearance rate of an entire population of siphonate bivalves as well as the efficiency of feeding of any individual our results imply that field conditions arc properly represented in laboratory flume studies of phytoplankton biomass losses to benthic bivalves when the shear velocity and bottom roughness are matched to values found in the field numerical models of feeding by a bivalve population should include an effcctivc sink distribution which is created by the combined incurrent excurrcnt flow field nearbed flows need to be accounted for to properly represent these benthic pelagic exchanges we also present velocity measurements made with a laser doppler anemometer lda for a single configuration siphons flush with bed inlet downstream that show that the siphonal currents have a significant local effect on the properties of a turbulent boundary layer

infrasound from the 2007 fissure eruptions of kīlauea volcano hawai i 1 varied acoustic signals were recorded at k lauea volcano in mid 2007 coincident with dramatic changes in the volcano s activity prior to this time period pu u crater produced near continuous infrasonic tremor and was the primary source of degassing and lava effusion at k lauea collapse and draining of pu u crater in mid june produced impulsive infrasonic signals and fluctuations in infrasonic tremor fissure eruptions on 19 june and 21 july were clearly located spatially and temporally using infrasound arrays the 19 june eruption from a fissure approximately mid way between k lauea s summit and pu u produced infrasound for 30 minutes the only observed geophysical signal associated with the fissure opening the infrasound signal from the 21 july eruption just east of pu u shows a clear azimuthal progression over time indicative of fissure propagation over 12 9 hours the total fissure propagation rate is relatively slow at 164 m hr although the fissure system ruptured discontinuously individual fissure rupture times are estimated using the acoustic data combined with visual observations

infrasonic harmonic tremor and degassing bursts from halema uma u crater kilauea volcano hawaii 1 the formation evolution collapse and subsequent resurrection of a vent within halema uma u crater kilauea volcano produced energetic and varied degassing signals recorded by a nearby infrasound array between 2008 and early 2009 after 25 years of quiescence a vent clearing explosive burst on 19 march 2008 produced a clear complex acoustic signal near continuous harmonic infrasonic tremor followed this burst until 4 december 2008 when a period of decreased degassing occurred the tremor spectra suggest volume oscillation and reverberation of a shallow gas filled cavity beneath the vent the dominant tremor peak can be sustained through helmholtz oscillations of the cavity while the secondary tremor peak and overtones are interpreted assuming acoustic resonance the dominant tremor frequency matches the oscillation frequency of the gas emanating from the vent observed by video tremor spectra and power are also correlated with cavity geometry and dynamics with the cavity depth estimated at 219 m and volume 3 106 m3 in november 2008 over 21 varied degassing bursts were observed with extended burst durations and frequency content consistent with a transient release of gas exciting the cavity into resonance correlation of infrasound with seismicity suggests an open system connecting the atmosphere to the seismic excitation process at depth numerous degassing bursts produced very long period 0 03 0 1 hz infrasound the first recorded at kilauea indicative of long duration atmospheric accelerations kilauea infrasound appears controlled by the exsolution of gas from the magma and the interaction of this gas with the conduits and cavities confining it

field observations of bedforms and sediment transport thresholds of fine sand under combined waves and currents abstract seabed video images and s4 wave current meter data collected during the build up of a moderate storm on the scotian shelf are analysed for bedform development and sediment transport threshold of fine sand under combined waves and currents as the storm built up the following sequence of bedforms was observed 1 relict wave dominant ripples with worm tubes and animal tracks during the preceding fairweather period 2 irregular sinuous asymmetrical current dominant and intermediate wave current ripples under bedload transport 3 regular nearly straight or sinuous asymmetrical to slightly asymmetrical wave dominant ripples under saltation suspension 4 upper plane bed under sheet flow conditions 5 small crest reversing transitory ripples at the peak of the storm and 6 large scale lunate megaripples which developed when the storm decayed these data also show that only single sets of asymmetrical intermediate wave current ripples will form when waves and currents are co linear the development of the crest reversing transitory ripples indicates a high energy transition stage under quasi sheet flow conditions a direct comparison of the skin friction combined shear velocity and the critical shear velocities for bedload suspension and sheet flow transport under estimated the onset of these sediment transport modes as the presence of ripples causes the shear stress to increase from ripple trough to ripple crest the ripple enhanced skin friction shear velocity must be used to determine properly the initiation of bedload transport at high transport stages the boundary layer dynamics is controlled mainly by the thickness of the bedload transport layer thus a transport related bedload shear velocity predicted based upon the sum of the grain roughness and bedload roughness has to be compared against the conventional threshold criterion to properly define the onset of suspension and sheet flow transport modes

feasibility study of spectral pattern recognition reveals distinct classes of volcanic tremor abstract systematic investigations of the similarities and differences among volcanic tremor at a range of volcano types may hold crucial information about the plausibility of inferred source mechanisms which in turn may be important for eruption forecasting however such studies are rare in part because of an intrinsic difficulty with identifying tremor signals within very long time series of volcano seismic data accordingly we develop an efficient tremor detection algorithm and identify over 12 000h of volcanic tremor on 24 stations at k lauea okmok pavlof and redoubt volcanoes we estimate spectral content over 5 minute tremor windows and apply a novel combination of principal component analysis pca and hierarchical clustering to identify patterns in the tremor spectra analyzing several stations from a given volcano together reveals different styles of tremor within individual volcanic settings in addition to identifying tremor properties common to all stations in a given network we find localized tremor signals including those related to processes such as lahars or dike intrusions that are only observed on some of the stations within a network subsequent application of our analysis to a combination of stations from the different volcanoes reveals that at least three main tremor classes can be detected across all settings whereas a regime with a ridge of high power distributed over 1 2hz and a gradual decay of spectral power towards higher frequencies is observed dominantly at three volcanoes k lauea okmok redoubt with magma reservoirs centered at less than 5km below sea level b s l a spectrum with a steeper slope and a narrower peak at 1 2hz is observed only in association with open vents k lauea and pavlof a third regime with a peak at approximately 3hz is confined to two stratovolcanoes pavlof and redoubt these observations suggest generic relationships between the spectral character of the observed signals and volcano characteristics such as magma viscosity storage depths and the physical properties of volcanic edifices similarities among the spectral patterns detected at stations 4km and 8 10km distance from the centers of volcanic activity respectively indicate that path effects do not strongly influence spectral shapes at distances of a few kilometers from the inferred source of the signals our preliminary work shows that a global comparison of tremor is feasible our results suggest that further work on data from a larger sample and diverse range of volcano types will reveal additional classes of tremor signals and plausibly identify fingerprints of source processes that are specific to volcano type but independent of volcano location

monitoring underwater nourishments using multibeam bathymetric and backscatter time series natural and man induced coastal erosion endanger life and environment in coastal areas worldwide for sedimentary barrier coasts beach and underwater nourishments are an efficient coastal protection strategy to optimize nourishments and to understand their impact on the marine environment monitoring strategies are required in this study we investigate the potential of multibeam echosounder mbes data providing both bathymetry and backscatter bs for monitoring the evolution of the nourished sediment and morphodynamics over time a time series of seven mbes measurements as well as two sets of box cores vibrocores and seismic data were acquired of a channel side nourishment near the wadden sea island ameland the netherlands between april 2017 and may 2019 in general a high confidence of the acoustic reliability of the bs time series measurements is demonstrated the unsupervised bayesian classification method supported by ground truthing is employed to produce a time series of sediment maps revealing sediments ranging from sandy mud to sand with varying amounts of shell fragments based on the sediment maps the nourished sediment could be distinguished from the natural sediment within one year the shell rich pre nourishment seabed is recreated by washing out finer sediments which are deposited towards the main tidal channel using the seismic data and vibrocores the shell rich pre nourishment seabed could be identified in the subsurface after being buried by the nourishments supporting the general findings furthermore a rapid development of steep bedforms with increasing sediment sorting is observed in parts of the nourished areas this study shows that high resolution sediment maps obtained from a time series of mbes bs together with bathymetry reveal morphodynamic and sedimentary processes of nourishment evolution and can advance underwater nourishment strategies

sedimentological effects and palaeoecological implications of the tube building polychaete lanice conchilega pallas the tube building polychaete lanice conchilega forms intertidal mounds in association with macroalgae this assemblage produces structures that can record tidal and seasonal cycles in the stratigraphic record they mark low tide levels because the assemblage occurs below neap low tide and many of the structures form when water drains off the assemblage mounds are created by disturbance of the sediment surface around aggregations of the assemblage and accumulation of sediments within the aggregations the initial aggregations may be relict patches of adult worms new clumps of juveniles or both juvenile worms and drift algae easily settle and survive in high density patches whereas predators and waves more readily disturb low density patches algae and tubes extend through accumulated sediment and create a new higher surface through this interactive process the high density patches increase height rapidly while the low density patches erode regardless of density when the initial distribution is regular the surface remains flat rising evenly or eroding evenly accumulation and erosion increases during spring tides and decreases during neap tides mound development also follows a seasonal pattern the recruitment of juvenile worms in spring facilitates algal settlement and initiates mound buildup the rate of tube building and algal growth increases in early summer as the erosive forces of storms decline this leads to the greatest development of mounds in late summer just before the macroalgae begin to die the loss of algae coincides with autumnal storms and causes catastrophic erosion of the mounds into relict patches of dormant tube worms patches of tubes that survive the winter enhance spring recruitment and renewal of mound development the shape of the mounds is often obscured during burial and preservation because of this it may be difficult to distinguish the original form of ancient mounds without contemporaneous cementing organisms but cycles of deposition and erosion are recorded in lanice tubes and other biogenic structures these structures can be used in conjunction with physical structures to define tidal height seasonality or current regime in general however the presence of tube aggregations per se is not diagnostic of a specific hydraulic environment

a 3 d ground penetrating radar and wavelet transform analysis of the morphology of shoreface deposits in the upper cretaceous ferron sandstone member utah wavelengths of hummocky cross stratified hcs beds a common sedimentary feature of storm dominated shorefaces are documented for the first time using measurements in three dimensional 3 d ground penetrating radar gpr data for a well developed upper cretaceous lower shoreface succession at dry wash in the ferron sandstone member utah the shallow marine sequence consists of upward thickening hcs sand beds alternating with interstorm deposits the thickness variation of the storm beds indicates locally steadily growing storm intensity with at least four cycles weakly coarsening upward mud to very fine grained sand fair weather background deposits suggest a slow progradation of deposition with no significant change in environment the gpr interpretation mapped three conformable high continuity high amplitude reflections throughout the 3 d gpr data volume the interpreted radar surfaces rss are well correlated with tops of hcs sand beds and thus paleotopographic surfaces the associated radar units rus have a uniform thickness on average 0 8 m 2 6 ft the rus and the adjacent outcrop observations suggest that the shoreface sandstone at the dry wash site has a simple layered internal architecture the hummocky swaley surfaces generally dip westerly as a product of postdepositional structural alterations that are mostly in the shoreline direction and contain variable size structurally undulating rounded features a 2 d continuous wavelet transform analysis is applied to the detrended rss producing a multiresolution image decomposition of the gpr surfaces surface features with a wavelength range of 1 7 m 3 23 ft are in good agreement with the observations on modern hummocky shallow marine seabeds quantitative measurements indicate that the hummocky surfaces at the dry wash site are dominated by uniformly distributed circular to elongate bed forms with maximum correlation at 1 5 3 5 m 4 9 11 4 ft wavelength and that the deltaic sedimentary layers were simultaneously deformed by the middle campanian compressional stress of the sevier orogeny transmitted from the northwest quantitative information on the subseismic scale surface geometry of the hcs beds is expected to result in more refined reservoir models in addition the connectivity of units indicated by the scale of the morphology can be an indirect indicator of unit correlation and permeability paths

experiments on bed configurations in fine sands under bidirectional purely oscillatory flow and the origin of hummocky cross stratification abstract we made experiments on bed configurations in bidirectional purely oscillatory flows at a wide range of oscillation periods t and maximum orbital velocities um in two closed flow ducts 0 1 m and 0 4 m wide the motivation was that understanding of bed configurations in oscillatory flows with long periods and high velocities during storm induced deposition in the shallow ocean is needed for interpreting the stratification in such deposits the ripples produced were classified geometrically as two dimensional 2d or three dimensional 3d in plan view geometry and dynamically as oscillatory current ripples dependent upon the patterns of flow and sediment transport specific to the existence of the oscillation itself and reversing current ripples dependent on he existence of the current in one direction or the other during the oscillation runs in the small duct with effectively 0 19 mm and 0 30 mm sand showed the familiar small 2d oscillatory current ripples at short t and low um passing into much larger ripples with spacing up to 2 m at periods of 6 20 s and velocities up to 1 m s with no apparent limit on size with increasing t and um even in such a narrow duct there was some evidence of 3d geometry of the large ripples runs in the large duct with effectively 0 11 mm sand at a single period of about 9 5 s showed a progression from small 2d oscillatory current ripples through small 3d reversing current ripples to large round crested 3d oscillatory current ripples with prominent superimposed 3d to 2d reversing current ripples the large 3d ripples which increased in spacing to 1 3 m at the h ghest attainable um of 1 m s shifted in position and changed in size with time seemingly at random causing substantial local and temporary erosion and deposition at a given point on the bed there was no net aggradation during the runs but a deposit was synthesized by taking a time series of sidewall bed profiles during a run in which large 3d ripples developed from an initially plane bed and changed irregularly in size and position as they grew toward equilibrium and then plotting the profiles one above the previous with a constant upward increment the resulting stratification is strikingly similar to much hummocky cross stratification in ancient sandstones this suggests that some hummocky cross stratification is generated during sediment fallout from strong purely oscillatory flows at moderate to long oscillation periods as large 3d oscillatory current bed forms develop from a planar bed during strong but waning flow

the role of scour in shipwreck site formation processes and the preservation of wreck associated scour signatures in the sedimentary record evidence from seabed and sub surface data fully submerged shipwreck sites act as open systems with the exchange of material sediment water organic and inorganic objects and energy wave tidal storm across system boundaries formation processes at wreck sites are driven by some combination of chemical biological and physical processes with physical processes dominant in initial phases of site formation scouring and associated depositional patterns that form in response to hydrodynamic forcing are commonly the dominant physical processes acting at shipwreck sites scour is initiated by the introduction of a shipwreck to the seafloor leading to increases in flow velocity and turbulent intensity around the structure near field and far field scour pits form at wreck sites due to the interaction of horseshoe and lee wake vortices with the mobile substrate the morphology of resultant scour signatures are controlled by the orientation of the wreck structure in relation to the prevailing hydrodynamic regime the morphology and size of the wreck and individual site components the hydrodynamic regime currents waves or combined waves and currents bathymetry and the geology of the site seafloor and sub surface conditions individual objects or artefacts may act as nuclei to promote scour at a local scale under high energy conditions groups of artefacts and or disarticulated structural components emanating from a wreck may compound natural scour processes by rolling or sliding under suitable environmental conditions wreck associated scour features can be preserved in the sedimentary record

tidal deposition in the basal upper cambrian mt simon formation in wisconsin the upper cambrian mt simon formation 0 65 m thick is a basal quartz arenite exposed in westcentral wisconsin a detailed field investigation of the physical and biogenic sedimentary structures of the mt simon has led to the recognition of three distinct lithofacies the lower one unconformably overlies precambrian basement rocks it consists of medium to very large scale sets of tabular and trough cross bedded medium to very coarse grained sandstone and pebbly sandstone with minor intercalated horizontal beds of very fine to medium grained sandstone siltstone and shale sparse examples of skolithos and arenicolites are present this facies consists of a very thin sequence of possible braided fluvial and marine foreshore deposits overlain by probable marine shoreface and tidal channel deposits much of the facies seems to represent shallow subtidal deposition in a relatively high energy regime the middle lithofacies consists of two distinctly different subfacies which probably were deposited in a low tidal flat setting the higher energy subfacies consists of small to medium scale sets of tabular and trough crossbedded fine to coarse grained sandstones containing distinct zones dominated by skolithos and arenicolites this subfacies probably represents deposition in meandering tidal channels the lower energy subfacies consists of thinbedded horizontally laminated and ripple cross laminated very fine to medium grained sandstone siltstone and shale with common specimens of cruziana rusophycus and planolites this subfacies probably represents deposition on lower energy tidal flats adjacent to the tidal channels the upper lithofacies consists predominantly of structureless densely bioturbated very fine to coarse grained sandstone containing abundant specimens of skolithos the upper few meters of the facies consists of small to medium scale sets of trough cross bedded very fine to coarse grained sandstone with layers of disarticulated valves of the brachiopod obolus the upper facies probably represents deposition on tidal flats perhaps in a midtidal flat setting characterized by slower sedimentation rates a correspondingly higher degree of bioturbation persistent reworking of shelled macrobenthos and periodic subaerial exposure the mt simon formation is interpreted as a largely progradational regressive shoaling and fining upward tidal sequence a marine interpretation is supported by the widespread occurrence of marine trace fossils within this unit evidence for a tidal origin is seen in the presence of unimodal cross strata associated with reactivation surfaces compound cross strata numerous scour and truncation surfaces lined with intraformational conglomerates common clay drape laminae separating sets of cross strata interference and flat topped ripple marks and desiccation cracks sedimentation continued without apparent interruption as the overlying eau claire formation was deposited also under tidal influence recent reinterpretations of other basal cambrian cratonic quartz arenites together with this new interpretation for the mt simon formation suggest that the long held concept of basal transgressive sandstones deposited as blankets across the craton may be too simplistic for deposition in braided fluvial marginal marine tidal flat tidal channel and marine foreshore and shoreface environments seems indicated

tidal induced large scale regular bed form patterns in a three dimensional shallow water model the three dimensional model presented in this paper is used to study how tidal currents form wave like bottom patterns inclusion of vertical flow structure turns out to be necessary to describe the formation or absence of all known large scale regular bottom features the tide and topography are treated as a coupled system and the potential free instabilities in this system are investigated a linear stability analysis is used to study the dynamics of bed forms this yields information on the role of physical mechanisms such information cannot be obtained by direct numerical nonlinear simulation the basic state represents a horizontal elliptical flow veering in vertical direction over a flat bottom it is shown that in such a system modes can grow which have characteristics of both tidal sand banks and sand waves the model predictions are compared with observations and show good agreement

abundant and diverse early paleozoic infauna indicated by the stratigraphic record marine benthic animals have lived within the sediment since the late precambrian an abundant early paleozoic infauna is indicated by bioturbated zones and diversity of deposit feeder and suspension feeder trace fossil genera burrow depths extended tens of centimetres below the sediment water interface trace fossil evidence of an abundant early paleozoic infauna conflicts with evidence from the shelled fauna which lacks infauna this requires reinterpretation of early paleozoic community structure and raises new questions about interactions between early paleozoic soft bodied and skeletonized animals

processes controlling the dynamics of compound sand waves in the north sea netherlands the understanding of the morphodynamics of harmonic bed forms on the seabed is essential for modeling marine sediment transport and coastal morphologic development previous research has mainly focused on the type and distribution of bed forms but areally extensive data and time series of seabed features are scarce multibeam and side scan sonar data from four expeditions reveal the contrasts between a coastal site with asymmetric and flattened three dimensional 3 d compound sand waves on a shoreface connected ridge and an offshore site with asymmetric and sharp crested 2 d compound sand waves migration rates of the coastal sand waves are 6 5 20 m yr 1 while migration rates of the offshore sand waves are 3 6 to 10 m yr 1 this contrasting morphology and dynamic behavior of compound sand waves at the two north sea sites is explained by differences in the relative importance of tidal currents and wave activity near the bed these new field data provide parameters and boundary conditions for sand transport models while the empirically derived behavior of sand waves may be used to validate sand transport and sand wave models 2005

exploratory flow duct experiments on combined flow bed configurations and some implications for interpreting storm event stratification abstract experiments were conducted to define equilibrium combined flow bed configurations developed under a wide range of oscillatory uo and unidirectional uu velocity components with a constant oscillation period of 8 5 sec and median grain size of 0 09 mm in the range of flows studied uo 0 0 80 m sec uu 0 0 25 m sec the bed phases are no movement small 2d ripples small 3d ripples large 3d ripples and plane bed small 2d ripples are stable at low uo and uu by increasing either velocity component the plan view bed configuration becomes progressively less regular as small 3d ripples develop small 3d ripples are stable at low to moderate uo and a wide r nge of uu under purely oscillatory flow as uo increases beyond about 0 40 m sec large scale hummocky bed forms become stable when a unidirectional component is applied these bed forms quickly develop a downstream asymmetry and generally move in the direction of uu the dip angles of the lee flanks increase with increasing uu although they remain less than the angle of repose at high oscillatory velocities uo 0 70 0 80 m sec plane bed is the stable bed phase when uu 0 05 m sec much hummocky cross stratification shows a preferred dip direction of the coset laminae our experiments support the idea that such cross stratification is produced by combined flow the large 3d ripples produced at high oscillatory velocities and small to moderate unidirectional velocities would presumably generate what might be called anisotropic hummocky cross stratification if we had been able to aggrade the bed during the runs this would be the case even in dominantly oscillatory flow the experiments show that even a weak unidirectional current of several centimeters per second superimposed upon a strong oscillatory flow results in bed forms that move predominantly in a single direction and that leave sets of laminae that dip predominantly in that direction in runs at large uo the purely oscillatory large scale bed forms were quickly planed off as uu was increased from zero but a series of almost stationary gentle undulations on the bed surface persisted for indefinitely long times where the original topographic highs were situated even at the highest unidirectional flow investigated 0 25 m sec this suggests a possible origin for the gentle undulation observed in cretaceous parallel laminated shallow marine sandstones described by arnott 1987 1988 with spacings up to a few meters and heights not much more than a centimeter

physical irrigation of relict burrows implications for sediment chemistry abstract relict biogenic structures are common in some areas of the sea floor particularly the deep sea and are potentially irrigated by flow induced by overlying water currents such physically induced irrigation could have major effects on sedimentary solutes and influence interpretation of their measured distributions experiments show that the rate of flow through these uninhabited burrow structures is in some cases comparable to irrigation rates by animals even at the very low mean current velocities expected in the deep sea boundary layer induced irrigation is often sufficient to hold the concentrations of solutes in the burrow water close to that of the overlying water as a result these relict structures may in some ways be functionally equivalent to inhabited burrows with respect to modification of sediment chemistry

episode 49 of the pu u o o kupaianaha eruption of kilauea volcano breakdown of a steady state eruptive era the pu u o o kupaianaha eruption 1983 present is the longest lived rift eruption of either kilauea or neighboring mauna loa in recorded history the initial fissure opening in january 1983 was followed by three years of episodic fire fountaining at the pu u o o vent on kilauea s east rift zone 19km from the summit episodes 4 47 these spectacular events gave way in july 1986 to five and a half years of nearcontinuous low level effusion from the kupaianaha vent 3km to the cast episode 48 a 49th episode began in november 1991 with the opening of a new fissure between pu u o o and kupaianaha this three week long outburst heralded an era of more erratic eruptive behavior characterized by the shut down of kupaianaha in february 1992 and subsequent intermittent eruption from vents on the west flank of pu u o o episodes 50 and 51 the events occurring over this period are due to progressive shrinkage of the rift zone reservoir beneath the eruption site and had limited impact on eruption temperatures and lava composition

observations of bedform migration and bedload sediment transport in combined wave current flows bedload transport is an important mechanism for sediment flux in the nearshore yet few studies examine the relationship between bedform evolution and net sediment transport our work contributes concurrent observations of bedform mobility and bedload transport in response to wave dominant current dominant and combined wave current flows in the nearshore bedload sediment flux from migrating bedforms during combined wave current conditions accounted for at least 20 more bedload transport when compared with wave dominant flows and at least 80 more than current dominant flows bedforms were observed to transport the most sediment during periods with strong currents with high energy skewed waves and while bedform orientation and transport direction were aligned regardless of flow type bedform migration rates were directly proportional to the total kinetic energy contained in the flow field eleven bedload transport models formulated to be used in combined flows both shear and energetics based were compared with sediment flux estimated from measured bedform migration an energetics based sediment transport model was most representative for our data

an automatic seismic event processing for detection and location the p m c c method we present a new method for automatic detection and location of seismic events recorded on a network it is based on a progressive study of the interstation correlation functions which leads to a consistent set of time delays when a seismic phase is present three different examples are processed on networks of different sizes

horizontal and vertical sediment sorting in tidal sand waves modeling the finite amplitude stage the bed of coastal seas displays a large number of rhythmic bed features of which sand waves are relevant to study from an engineering perspective sediments tend to be well sorted over these bed forms which is so far poorly understood in terms of modeling of finite amplitude sand waves using delft3d we employ bed stratigraphy and consider four different grain size classes which are normally distributed on the phi scale the standard deviation sortedness is then varied whereas the geometric mean grain size is kept constant the results show that typically the crests of sand waves are coarser than the troughs residual flow causes net sedimentation on the lee side of the crest and consequently the general sorting pattern is distorted since larger grains experience a larger settling velocity they are deposited on the upper lee slope whereas the smaller grains are found on the lower lee slope due to sand wave migration also the internal structure of the sand wave is revealed which follows the same sedimentation pattern as the lee slope surface these results qualitatively agree with sorting patterns observed offshore the sorting processes lead to longer wavelengths and lower wave heights as a function of standard deviation this relates to the dampening effect of suspended sediment transport for fine grains finally it appears that the modeled wave heights fall in the same range as observations in the north sea these results are valuable for e g predicting the morphological response after engineering activities and determining suitable aggregates for sand extraction

controls on local scour and deposition induced by obstacles in fluvial environments abstract obstacles in fluvial environments cause flow separation and the emergence of three dimensional flow fields that can lead to scour and deposition even when no general sediment transport at the bed occurs resulting forms are commonly denoted as fluvial obstacle marks the morphology and dynamics of these forms is depended on obstacle flow and sediment characteristics as no generally approved approach for analysis of these forms exists yet a process based method is developed that relates certain dependent morphometric variables to an adapted obstacle reynolds number the novel approach was applied by conducting experiments in a laboratory flume and validated against other laboratory and field data the results of this work have shown a significant relationship between the morphometry of fluvial obstacle marks and obstacle reynolds number especially when morphometric variables were combined further validation calibration and extension and of this approach will help to adequately asses the influence of obstacles in the fluvial environment on micro and meso scale processes of sediment transport

runoff microdeltas a potential emergence indicator in cross bedded sandstones abstract microdeltas produced by slope controlled runoff are useful emergence indicators in cross bedded tidal and fluvial sandstones because they occur abundantly have high preservation potential and are identifiable in cross section each microdelta normally consists of a lenticular shaped linguoid cross bed that sits within a scour at the base of a larger cross bed delta thickness approximates the relief on the base of the overlying set while their lateral extent is normally less than 1 m the deltas are closely associated with reactivation surfaces in the overlying set and are generally oriented perpendicular to the over and underlying cross beds the lowest occurrence of microdeltas in a sequence provides an estimate of the low water level the identification of which should great y aid in the quantification of paleotidal or stage fluctuation ranges

tiering in suspension feeding communities on soft substrata throughout the phanerozoic tiering of benthic marine suspension feeding communities on soft substrata has varied throughout the phanerozoic epifaunal tiering was most developed during the middle and late paleozoic and the triassic to jurassic with large scale reductions in tiering occurring during the permian triassic extinctions and after the jurassic infaunal tiering reached its highest level of organization after the paleozoic

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

infrasonic tremor wavefield of the pu u ō ō crater complex and lava tube system hawaii in april 2007 1 long lived effusive volcanism at the pu u crater complex kilauea volcano hawaii produces persistent infrasonic tremor that has been recorded almost continuously for months to years previous studies showed that this infrasonic tremor wavefield can be recorded at a range of 10 km however the low signal power of this tremor relative to ambient noise levels results in significant propagation effects on signal detectability at this range in april 2007 we supplemented a broadband infrasound array at 12 5 km from pu u mene with a similar array at 2 4 km from the source kipu the additional closer range data enable further evaluation of tropospheric propagation effects and provide higher signal to noise ratios for studying volcanic source processes the infrasonic tremor source appears to consist of at least two separate physical processes we suggest that bubble cloud oscillation in a roiling magma conduit beneath the crater complex may produce a broadband component of the tremor low frequency sound sourced in a shallow magma conduit may radiate infrasound efficiently into the atmosphere due to the anomalous transparency of the magma air interface we further propose that more sharply peaked tones with complex temporal evolution may result from oscillatory interactions of a low velocity gas jet with solid vent boundaries in a process analogous to the hole tone or whistler nozzle the infrasonic tremor arrives with a median azimuth of 67 at kipu additional infrasonic signals and audible sounds originating from the extended lava tube system to the south of the crater complex median azimuth 77 coincided with turbulent degassing activity at a new lava tube skylight our observations indicate that acoustic studies may aid in understanding persistent continuous degassing and unsteady flow dynamics at kilauea volcano

linking the morphology and ecology of subtidal soft bottom marine benthic habitats a novel multiscale approach high resolution surveying techniques of subtidal soft bottom seafloor habitats show higher small scale variation in topography and sediment type than previously thought but the ecological relevance of this variation remains unclear in addition high resolution surveys of benthic fauna show a large spatial variability in community composition but this has yet poorly been linked to seafloor morphology and sediment composition for instance on soft bottom coastal shelves hydrodynamic forces from winds and tidal currents can cause nested multiscale morphological features ranging from metre scale mega ripples to sand waves and kilometre scale linear sandbanks this multiscale habitat heterogeneity is generally disregarded in the ecological assessments of benthic habitats we therefore developed and tested a novel multiscale assessment toolbox that combines standard bathymetry multibeam backscatter classification video surveying of epibenthos and box core samples of sediment and macrobenthos in a study on the brown bank a sandbank in the southern north sea we found that these methods are greatly complementary and allow for more detail in the interpretation of benthic surveys acoustic and video data characterised the seafloor surface and subsurface and macrobenthos communities were found to be structured by both sandbank and sand wave topography we found indications that acoustic techniques can be used to determine the location of epibenthic reefs the multiscale assessment toolbox furthermore allows formulating recommendations for conservation management related to the impact of sea floor disturbances through dredging and trawling

observations of sand waves megaripples and hummocks in the dutch coastal area and their relation to currents and combined flow conditions 1 this paper aims to investigate the distribution and stability of large scale bed forms in response to storm and fair weather conditions in a shallow marine environment multibeam and side scan sonar data off the dutch coast median grain size 0 25 0 35 mm were collected to monitor sand waves 100 800 m and superimposed megaripples 1 40 m through multiple storm and fair weather events box cores were used to observe the vertical bed structure and grain size in the dutch coastal area two dimensional 2 d megaripples x 1 15 m are the dominant bed forms in current dominated 0 4 m s tidal flow regimes with oscillatory flows 0 4 m s undulating bed topography of mound like 3 d bed forms 20 40 m is observed immediately after storms these bed forms are covered by smaller 3 d megaripples which are related to sets of low angle converging laminae in box cores interpreted as hummocky cross stratification hcs the sand waves form compound bed forms of sets of 2 d and 3 d megaripples the morphology of the sand waves is a function of the general wind wave climate of the marine environmental setting with flat topped 3 d sand waves occurring in shallow wave dominated settings and 2 d sand waves occurring in the tide dominated environment farther offshore copyright 2005 by the american geophysical union

an overview of volcano infrasound from hawaiian to plinian local to global abstract volcano infrasound is an increasingly useful technique for detecting locating characterizing and quantifying eruptive activity and can be used to constrain eruption source parameters in recent years studies of infrasound data from active volcanoes have shown clear progress towards mitigating volcanic hazards and understanding volcanic source processes volcano acoustic sources are shallow or aerial thus volcano infrasound data provide valuable information on eruption dynamics and are readily combined with direct and remote observations of gas ash and other eruptive phenomena the infrasound signals produced by volcanoes are indicative of the eruption style and dynamics here we review the diversity of infrasound signals generated by a wide variety of volcanic eruptions from hawaiian to plinian and the physical processes inferred to produce them we place particular emphasis on regional 15 250 km distance and global 250 km distance volcano infrasound studies as recent work in this area has made significant advances in monitoring and characterizing remote and difficult to monitor eruptions long range infrasonic detection of explosive volcanic eruptions is possible due to the energetic source mechanisms involved minor atmospheric attenuation at low frequencies and the existence of waveguides in the atmosphere however accurate characterization of the atmosphere and its spatiotemporal variability is required for reliable long range sound propagation modeling and correct interpretation of global infrasound recordings conversely because volcanic explosions are energetic and sometimes repetitive infrasound sources they can be used to validate atmospheric and acoustic propagation models

the hydrodynamics of particle clusters and sediment entrapment in coarse alluvial channels particles projecting from the bed of an alluvial channel distort the fluid stream to produce a distinctive pressure field this has considerable significance for both the entrapment and entrainment of other particles and is a primary cause of the widespread occurrence of pebble clusters and boulder shadows lift and drag forces are determined on clustered hemispherical particles of varying size in the wake of an obstructing particle both forces are shown to vary directly with particle separation in a linear fashion on the stoss side of the cluster drag is uniform regardless of the separation of the component particles but lift is shown to increase when particle separation is small so affecting stability this mutual interference of neighbouring clustered bed particles is a vital consideration of incipient motion and is shown by field evidence to cause a wide range in transport stage for particles of similar size and shape on average 46 of clustered particles are entrained by flood flow compared to 87 of particles in open plane beds the influence of clusters is a major determinant of sedimentary sorting

palaeogeographical changes in response to glacial interglacial cycles as recorded in middle and late pleistocene seismic stratigraphy southern north sea offshore stratigraphic records from the north sea contain information to reconstruct palaeo ice sheet extent and understand sedimentary processes and landscape response to pleistocene glacial interglacial cycles we document three major middle to late pleistocene stratigraphic packages over a 401 km2 area norfolk vanguard boreas offshore wind farm offshore east anglia uk through the integration of 2d seismic borehole and cone penetration test data the lowermost unit is predominantly fluviatile yarmouth roads formation marine isotope stage mis 19 13 including three northward draining valleys the middle unit swarte bank formation records the southernmost extent of tunnel valley fills in this area of the north sea providing evidence for subglacial conditions most likely during the anglian stage mis 12 glaciation the yarmouth roads and swarte bank deposits are truncated and overlain by low energy estuarine silts and clays brown bank formation mis 5d 4 smaller scale features including dune scale bedforms and abrupt changes in cone penetration test parameters provide evidence for episodic changes in relative sea level within mis 5 the landscape evolution recorded in deposits of mis 19 5 are strongly related to glacial interglacial cycles although a distinctive aspect of this low relief ice marginal setting are opposing sediment transport directions under contrasting sedimentary process regimes

the fauna of the hebble site patterns in standing stock and sediment dynamic effects abstract at the high energy benthic boundary layer experiment hebble site at 4820 m depth on the nova scotia rise 40 27 n 62 20 w abundances of polychaetes bivalves tanaids and isopods were conspicuously greater than expected for the depth whereas those of nematodes and harpacticoids the two dominant meiofaunal taxa were not further the abundances of polychaetes bivalves tanaids and nematodes were consistent over time and appeared to be unaffected by the periods of strong near bottom flow that characterized the site in contrast isopods and harpacticoid copepods were less abundant in samples taken as a storm abated apparently because they were eroded during benthic storms we explore implications of the difference between macrofaunal and meiofaunal abundance for community structure in addition because a goal of the hebble project was the parameterization of sediment transport in the deep sea we summarize ways that the biota affects sediment transport at this high energy site

aeolian features on venus preliminary magellan results magellan synthetic aperture radar data reveal numerous surface features that are attributed to aeolian or wind processes wind streaks are the most common aeolian feature they consist of radar backscatter patterns that are high low or mixed in relation to the surface on which they occur a data base of more than 3400 wind streaks shows that low backscatter linear forms long narrow streaks are the most common and that most streaks occur between 17 s to 30 s and 5 n to 53 n on smooth plains moreover most streaks are associated with deposits from certain impact craters and some tectonically deformed terrains we infer that both of these geological settings provide fine particulate material that can be entrained by the low velocity winds on venus turbulence and wind patterns generated by the topographic features with which many streaks are associated can account for differences in particle distributions and in the patterns of the wind streaks thus some high backscatter streaks are considered to be zones that are swept free of sedimentary particles to expose rough bedrock other high backscatter streaks may be lag deposits of dense materials from which low density grains have been removed dense materials such as ilmenite or pyrite have dielectric properties that would produce high backscatter patterns wind streaks generally occur on slopes 2 and tend to be oriented toward the equator consistent with the hadley model of atmospheric circulation in addition to wind streaks other aeolian features on venus include yardangs and dune fields the aglaonice dune field centered at 25 s 340 e covers 1290 km 2 and is located in an ejecta flow channel from the aglaonice impact crater the meshkenet dune field located at 67 n 90 e covers 17 120 km 2 in a valley between ishtar terra and meshkenet tessera wind streaks associated with both dune fields suggest that the dunes are of transverse forms in which the dune crests are perpendicular to the prevailing winds dunes on venus signal the presence of sand size 60 to 2 000 m grains the possible yardangs are found at 9 n 60 5 e about 300 km southeast of the crater mead although most aeolian features are concentrated in smooth plains near the equator the occurrence of wind streaks is widespread and some have been found at all latitudes and elevations they demonstrate that aeolian processes operate widely on venus the intensity of wind erosion and deposits however varies with locality and is dependent on the wind regime and supply of particles

infrasonic tremor observed at kīlauea volcano hawai i 1 infrasonic array data collected at k lauea volcano hawai i during november 12 21 2002 indicate that the active vents and lava tube system near the pu u vent complex emit almost continuous infrasound in the 0 3 10 hz frequency band the spectral content of these infrasonic signals matches well that of synchronous seismic tremor in sites protected from wind noise significant signal to noise ratios were recorded as far as 13 km from the crater of pu u the infrasonic recordings suggest that one or more tremor sources may be close to the surface in addition these results demonstrate that adequate site and instrument selections for infrasonic arrays are essential in order to obtain consistent and reliable infrasonic detections

a simple model of flow sediment organism interaction abstract previous models of organism sediment interaction have been limited primarily to eddy diffusion type mixing while such models are useful in interpreting some stratigraphic records they cannot be expected to provide mechanistic insights into the diversity of interactions among sedimentary processes organism activities and boundary layer flows to provide a more general formulation capable of dealing with all three types of processes in concert a simple discrete time markov model is generated this version of the model deals explicitly only with particulate and not liquid phases the initial formulation is a two compartment ergodic model of deposit feeding particle selection by deposit feeders results in incorporation of the selected particles into fecal pellets and fecal pellet disaggregation completes the cycle particles which are more strongly selected or which are incorporated into more robust pellets thus spend more time and reach higher relative concentration in the fecal pellet compartment the next level of complexity is achieved by adding burial from the free sediment non fecal pellet compartment this model predicts that particles which are more strongly selected or incorporated into more robust fecal pellets will have greater residence times in surficial sediments both pellets and free sediments before they become part of the stratigraphic record and will therefore achieve higher concentrations in surficial sediments than will less preferred particles the full flow sediment organism system is reached by adding the potential for lateral advection of particles the probability of such advection is allowed to differ between pellets and free sediments increasing selection and robustness of fecal pellets then can either increase or decrease relative concentration and residence time of a given particle type in surficial sediments the model thus provides a means of explaining differences in stratigraphic patterns among materials deposited simultaneously it also suggests that deposit feeder selection may increase the average age i e time since initial deposition of surficial sediments by maintaining preferred particle types near the surface selection may likewise control the texture of surficial sediments in a manner which is easily confused with purely physical sorting parameters which require careful measurement in testing these simple predictions are selectivity by deposit feeders probability of selection rate of fecal pellet breakdown under realistically simulated conditions probability of pelletal disaggregation differential erodibilities of pellets versus free sediments relative probabilities of lateral advection and rates of burial of free sediments versus pelletized sediments probabilities of burial

maintenance of strong rotational winds in venus middle atmosphere by thermal tides the cloud level atmosphere of venus takes little more than 4 days to complete one rotation whereas the solid planet below has a 243 day period computer simulations of the circulation of the venus middle atmosphere between 40 and 85 kilometers as driven by solar radiation absorbed in the clouds reproduce i the observed cloud level rotation rate ii strong vertical shears above and below the cloud tops and iii midlatitude jets and strong poleward flow on the day side simulated circulations converge to yield nearly the same zonal winds when initialized with both stronger or weaker rotation rates these results support the hypothesis that the observed cloud top rotation rate is maintained by statistical balance between fluxes of momentum by thermal tides and momentum advection by mean meridional circulation

seismic envelope based detection and location of ground coupled airwaves from volcanoes in alaska abstract volcanic explosions and other infrasonic sources frequently produce acoustic waves that are recorded by seismometers here we explore multiple techniques to detect locate and characterize ground coupled airwaves gca on volcano seismic networks in alaska gca waveforms are typically incoherent between stations thus we use envelope based techniques in our analyses for distant sources and planar waves we use f k beamforming to estimate back azimuth and trace velocity parameters for spherical waves originating within the network we use two related time difference of arrival tdoa methods to detect and localize the source we investigate a modified envelope function to enhance the signal to noise ratio and emphasize both high energies and energy contrasts within a spectrogram we apply these methods to recent eruptions from cleveland veniaminof and pavlof volcanoes alaska array processing of gca from cleveland volcano on 4 may 2013 produces robust detection and wave characterization our modified envelopes substantially improve the short term average long term average ratios enhancing explosion detection we detect gca within both the veniaminof and pavlof networks from the 2007 and 2013 2014 activity indicating repeated volcanic explosions event clustering and forward modeling suggests that high resolution localization is possible for gca on typical volcano seismic networks these results indicate that gca can be used to help detect locate characterize and monitor volcanic eruptions particularly in difficult to monitor regions we have implemented these gca detection algorithms into our operational volcano monitoring algorithms at the alaska volcano observatory

combined flow model for vertical stratification sequences in shallow marine storm deposited beds abstract we develop a model to help explain the wide variety of vertical stratification sequences in shallow marine sandstones this model embodied in a set of vertical sequence cartoons predicts or accounts for vertical stratification sequences in beds of free sandstone deposited from a full range of decelerating combined flows as well as from purely unidirectional and oscillatory flows according to the model vertical stratification sequences in storm deposited sandstone beds are the outcome of the time history of the bed configuration as deposition proceeds the idealized sequences are based on the initial velocities and subsequent deceleration histories of the unidirectional and oscillatory flow components twenty qualitatively different sequences starting with plane bed are generated and an additional 26 sequences result from omitting one or more of the lowermost intervals in succession the model thus accounts for 46 distinct kinds of sequences five major simplifying assumptions are built into the model bidirectional flows linear deceleration of both unidirectional and oscillatory flow components time independent deposition rate time independent sediment size and equilibrium bed configurations owing to these assumptions the model is likely to be applicable to only a small subset of vertical stratification sequences observed in shallow marine sandstones as more information on combined flow bed configurations becomes available these assumptions could be relaxed to provide a more refined and complete representation of vertical stratification sequences since the model generates vertical sequences formed from any kind of decelerating flow the bouma sequence for deposits from purely unidirectional turbidity currents and also sequences resulting from decelerating purely oscillatory flows similar in appearance to many proposed generalized tempestite sequences are end member cases in the model the model is also extended slightly to explain the geometry of the uppermost bedding surfaces of storm generated sandstones by consideration of disequilibrium effects

dissipative tides application to venus lower atmosphere abstract a linearized planetary scale wave model is used to investigate the effects of thermal and mechanical damping on atmospheric tides when the damping rate is comparable to the frequency of solar diurnal forcing omega 0 1 the circulation consists of three parts a classical vertically propagating atmospheric tide in the upper atmosphere a simple thermally direct subsolar to antisolar circulation or halley cell in most of the lower atmosphere and finally a reversed anti halley cell near the surface the near surface circulation produces horizontal divergence near the subsolar point while tides are a frequently encountered phenomenon venus earth and mars there is so far no observational evidence of a halley circulation in any planetary atmosphere a subsolar antisolar circulation might be possible in venus slowly rotating lower atmosphere if the mechanical dissipation time scale is of the order of or less than a venusian day such a circulation could be a factor in maintaining

on the behaviour of tidal current directions due to the presence of submarine sand waves abstract side scan sonar records reveal that the crestlines of megaripples in the troughs as well as on both sides of the slopes of sand waves form an angle with the crestline of the sand waves itself the existence of such an angle between the crestline of megaripples and sand waves indicates that changes of the tidal current direction across sand waves can be expected direct evidence that such tidal current direction changes occur above sand waves is derived from measurements of the air sea interaction drift buoy asib system at the sea surface and from side scan sonar records of the sea bed both systems were operated from on board research vessels during two c star field experiments in the hoek van holland study area off the dutch coast in april 1996 and in april 1997 measurements performed by electrical resistance wires on board the asib system indicate that variations of the short and moderate wave direction and the wave directional spread are associated with changes of the tidal current direction at the sea surface according to the results of the measurements derived from the asib system and the side scan sonar records it can be summarised that the variation of the direction of short and moderate period water waves as well as changes of the tidal current speed and direction across large sand waves must be considered for correct modelling of the wave current interaction mechanism

grain sorting effects on the formation of tidal sand waves a model is developed to investigate the process which leads to the formation of sand waves in shallow tidal seas characterized by a heterogeneous sea bed composition the main goal of the analysis is the evaluation of the effects that a graded sediment has on the formation of the bottom forms and the investigation of the sorting process induced by the growth of the bottom forms the analysis is based on the study of the stability of the flat bed configuration i e small amplitude perturbations are added to the flat bottom and a linear analysis of their time development is made for an oscillatory tidal current dominated by one tidal constituent the results show that the graded sediment can stabilize or destabilize the flat bottom configuration with respect to the uniform sediment case depending on the standard deviation sigma of the grain size distribution and on the ratio r over cap between the horizontal tidal excursion and the water depth for moderate values of r over cap i e values just larger than the critical value for which the sediment is moved and sand waves appear the presence of a sand mixture stabilizes the flat bed on the other hand for large values or r over cap the mixture has a destabilizing effect in both cases the effect that a sand mixture has on the stability of the flat bed configuration is relatively small moreover for moderate values of r over cap the fine fraction of the mixture tends to pile up at the crests of the bottom forms while the coarse fraction moves towards the troughs for large values or r over cap the grain size distribution depends on the value of sigma the results are physically interpreted and provide a possible explanation of the apparently conflicting field observations of the grain size distribution along the sand wave profile carried out in the north sea

very high resolution side scan sonar mapping of biogenic reefs of the tube worm lanice conchilega reefs of the tube building polychaete lattice conchilega are known to represent hotspots of biodiversity within inter and subtidal soft sediments of the north sea however because of their patchy distribution point sampling does not appropriately map their subtidal spatial distribution this study evaluated the feasibility to detect l conchilega reefs by very high resolution side scan sonar imagery a subtidal very high resolution 410 khz side scan survey combined with grab sampling revealed high densities of l conchilega up to 1979 ind m 2 to coincide with a higher reflectivity patchy and grainy acoustic facies from the side scan sonar imagery individual reefs were estimated to reach a maximum size of 15 m 2 to ground truth the acoustic facies the distribution of intertidal l conchilega reefs was mapped at low tide and side scan sonar imagery was recorded during the following high tide intertidal l conchilega reefs had a patch size of 0 8 m 2 up to 11 6 m 2 elevated 7 5 to 11 5 cm above the surrounding seafloor and covered approximately 10 of the selected area the very high 445 khz resolution side scan sonar imagery revealed a similar acoustic facies as in the subtidal lower resolution 132 khz side scan sonar imagery was less efficient to detect physically less developed l conchilega reefs we conclude that 1 there are no major technical restrictions to map l conchilega reefs using side scan sonar 2 the developmental stage of l conchilega reefs impacts the detectability of the reefs and 3 very high resolution side scan sonar imagery is considered a necessity when mapping small scale structures such as l conchilega reefs c 2008 elsevier inc all rights reserved

early permian palaeoenvironment in damodar valley coalfields india an overview abstract in the damodar valley basin coalfields containing coal bearing barakar formation are raniganj jharia bokaro ramgarh and karanpura the barakar formation is composed of conglomerate sandstone siltstone shale fireclay and coal the lower part of barakar formation represents a braided channel deposit and also in few places glacio fluvial deposit which changes to meandering channel system with the formation of some ox bow lake and cut off channel in the middle part in a few places deltaic brackish water condition possibly existed along with this meandering channel system in the upper part of barakar formation marine signatures are more prominant marine signatures influences have been reported from barakar formation of ramgarh south karanpura and west bokaro coalfields on the basis of trace fossil assemblage sedimentation character and trace element content although definite marine signatures have not been observed from jharia and raniganj coalfields high concentration of boron vanadium and chromium and presence of skolithos and thalassinoides burrows possibly suggest a brackish water condition the upper part clearly suggest that the sediments were deposited in a geographic setting very close to the sea or at the edge of the sea possibly in a peritidal setting where storm activity played a vital role during sedimentation which in turn suggests the presence of a broad shallow sea epeiric epicontinental sea that develop during times of high sea level the sea water possibly entered from the northeastern side as vast seaways or as embayment through the damodar valley which acted as a channel

biogeomorphological implications of microscale interactions between sediment geotechnics and marine benthos a review abstract at the foundations of biogeomorphological processes in the sea lie interactions between the activities of marine benthic animals and the geotechnical properties of their sedimentary environments the potential significance of these interactions which take place at a microscale level of millimetres to metres for the large scale geomorphology of the seabed has rarely been appreciated in the context of this review large scale is defined as greater than 50 m to hundreds of kilometres the present review addresses this link drawing examples from a wide range of marine environments including estuaries the intertidal zone continental shelves and slopes and the deep sea it firstly considers sediment stabilisation slope failure sediment mixing biodeposition sediment compaction and hydrodynamic effects this is followed by a consideration of two extremes of the ecological pyramid the effects of marine meiofauna and marine vertebrates the final section draws attention to the central role of faunal mucus and extracellular polymeric material ecpm in many of the microscale interactions that we describe the implications of these microscale biological processes and features are discussed in terms of their influence on and control of the large scale geomorphology of the seabed

the distribution of macrozoobenthos in the southern north sea in relation to meso scale bedforms this study investigates the distribution of macrozoobenthos in relation to meso scale bedforms in the southern north sea three sites on the dutch continental shelf were sampled that are representative of large areas of the north sea and show diverse morphological settings these sites are i part of a shoreface connected ridge ii the lower part of a concave shoreface and iii a sandwave area within these sites two or three different morphological units were distinguished sampling was undertaken in two seasons for two consecutive years the species composition was analysed for differences in benthic assemblage within sites based on the meso scale morphology and between sites and seasons in addition the benthic assemblage was correlated to water depth median grain size d50 and sorting d60 d10 results show that significant differences in the benthic assemblage can be found related to meso scale bedforms but macro scale morphological setting and seasonal effects are more important 2006 elsevier ltd all rights reserved

thin eolianites interbedded within a fluvial and marine succession early proterozoic whitworth formation mount isa inlier australia abstract the early proterozoic whitworth formation in the mount isa inlier australia contains the oldest known thinly bedded eolian dune and amalgamated interdune deposits and records the complex interplay of eolian fluvial and marginal marine depositional processes the whitworth formation accumulated during the waning phases of rifting in a north south trending trough that began between 1808 and 1790 ma and ended before 1740 ma three eolian facies are recognized 1 cosets of cross strata 2 sets of horizontal to low angle strata and 3 isolated sets of cross strata facies el records preservation of dunes with low angles of climb without intervening interdune deposits sets of facies e2 are interpreted as either sand sheet preserved dune plinths or amalgamated interdune deposits facies e3 is encased in facies e2 and consists of lenses of cross strata with irregular tops this association of facies is comparable to recent gypsum dune and interdune deposits at white sands new mexico facies e3 reflects limited dune preservation during migration and accumulation at or near the groundwater table vertical change from amalgamated interdune deposits to dune without interdune deposits records dunefield initiation or lateral migration from a peripheral to a more centralized position within the dunefield increased sedimentation rates promoted preservation of dune deposits represented by facies e1 decreased sedimentation rate and possible limited sediment bypassing resulted in amalgamation of interdune deposits on the dunefield periphery eolian facies e1 and e2 are interbedded with ephemeral river deposits three ephemeral river facies are recognized 1 cosets of horizontal strata 2 cosets of horizontal strata and overlying trough cross beds and 3 cosets of medium scale trough cross beds ephemeral river facies f3 often are preserved in channels incised into eolian facies e3 associated marginal marine facies consist of 1 thin bedded arenites of intertidal to supratidal origin and 2 trough and tabular planar cross bed sets and cosets that resulted from migration of subaqueous dunes within a tide dominated subtidal setting interbedded fluvial and eolian deposits reflect either autogenic processes such as reworking of fluvial sands by eolian processes or incursion of a fluvial system into a dunefield related to allogenic processes such as climatic change dune deposits in the whitworth formation probably developed under arid to semi arid conditions as indicated by extensive ephemeral river deposits presence of evaporite pseudomorphs and absence of wet interdune deposits interbedded eolian fluvial and marginal marine deposits resulted from relative sea level fluctuations related to a combination of eustasy and intrabasinal tectonics

infrasonic jet noise from volcanic eruptions 1 the lowermost section of a vulcanian or plinian volcanic eruption column may be thought of as a momentum driven turbulent free shear jet flow we propose that large amplitude and long duration infrasonic 20 hz signals recorded at ranges of tens of kilometers during powerful eruptions at mount st helens usa and tungurahua ecuador represent a low frequency form of jet noise a preliminary test of this hypothesis is made by comparing the observed infrasonic spectra to the empirically derived similarity spectra for pure air jets although the spectral shapes are in approximate agreement the observed volcanic signals have additional complexities not present in the pure air laboratory data these features may result from multiphase flow containing solid particles and liquid droplets very high temperatures and perhaps complex crater morphology however the overall similarity between the volcanic signals and jet noise indicates that broadband infrasound measurements at volcanoes may provide a quantitative link to eruption jet dynamics and would aid substantially in the remote assessment of volcanic hazard

behavioral plasticity of modern and cenozoic burrowing thalassinidean shrimp abstract the use of trace fossils as paleoenvironmental indicators is based on empirically derived and tested links between environmental conditions behavior and trace fossil morphology four approaches were used to assess how faithfully and at what resolution trace fossils as mirrors of behavior reflect environmental change 1 comparing the abundance and morphology of ophiomorpha nodosa in tidal channel margin and tidal channel axis facies miocene delaware 2 determining the range of morphology of o nodosa produced under unchanging environmental conditions within the channel margin facies 3 evaluating the behavioral response of the modern burrowing thalassinidean neotrypaea californiensis in mugu lagoon california to an environmental perturbation namely the burial of layers of glass plates and 4 assessing how ancient producers of ophiomorpha dealt with obstacles presented by dense shell and coral accumulations miocene maryland pleistocene bahamas comparison of ophiomorpha nodosa in channel margin versus channel axis facies indicated that o nodosa was significantly more abundant in the channel margin facies however there was no significant difference in burrow characteristics exterior or interior diameter wall thickness between the facies as recorded by o nodosa its thalassinidean producer did not modify its behavior in response to conditions in the tidal channel axis rather the tracemakers tended to avoid the channel axis as indicated by the reduced abundance of o nodosa in contrast o nodosa within the channel margin facies was highly variable in degree of pelletization of the burrow wall in burrow fill and definition of the burrow margin and in architecture of the burrow system variation in o nodosa found within the channel margin facies reflected behavioral flexibility in the absence of environmental change modern burrowing shrimp adapt to barriers layers of glass plates implanted within the substrate they alter the geometry and depth of their burrow systems they may even share shafts that penetrate the barrier meters thick miocene shell beds maryland in which the shells are not densely packed contain ophiomorpha and thalassinoides the producing thalassinideans were able to penetrate and move through the shell bed similarly pleistocene thalassinideans maneuvered around coral rubble in bahamian fossil coral reefs however miocene decimeter thick shell beds that are densely packed and well sorted are not penetrated by thalassinidean burrows implying that thalassinidean behavioral flexibility was not sufficient to penetrate densely packed shell beds likewise in the bahamian reefal settings ophiomorpha producers formed extensive maze systems immediately above impenetrable lithified surfaces in the reefal sequence behavior of thalassinidean shrimp is neither tightly constrained nor highly programmed and there is no indication that this has changed since miocene time small changes in morphology of traces produced by thalassinideans cannot be used to identify subtle changes in environmental conditions shrimp vary behavior apparently whimsically as well as in response to environmental change if this is true of animals other than thalassinideans the challenge to the ichnologist is to distinguish between background and environmentally triggered behavioral variation as recorded in the trace fossil record

deep burrowing in the early palaeozoic deep sea examples from the cambrian early ordovician meguma group of nova scotia enigmatic and heterogeneously deformed burrows are described from the cambrian early ordovician meguma group of nova scotia because of their morphological variability and the absence of previously defined morphotypes the burrows are unnamed yet do provide a cautionary note to the naming of trace fossils even at the ichnogeneric level by ichnologists the traces record the activity of unknown and mobile deposit feeding organisms that inhabited interchannel or levee areas immediately adjacent to and up to 5 m laterally from a 2 m deep channel developed on a deep sea mid outer submarine fan complex many of the vertically to subvertically oriented systems penetrate up to 40 cm suggesting that existing models on the depth of early palaeozoic benthic boundary layers obtained from shelf environments must be utilized with caution

infrasound from tungurahua volcano 2006 2008 strombolian to plinian eruptive activity abstract strombolian to plinian activity from tungurahua volcano ecuador has been recorded by the autonomous infrasound arrays of the acoustic surveillance for hazardous eruptions ashe project since early 2006 our studies suggest that acoustic energy release during large eruptions does appear to broadly scale with eruption intensity this manuscript provides a detailed chronology and characterization of tungurahua s eruptive activity between 2006 and 2008 and demonstrates the ability to constrain source parameters of significant eruptions such as onset duration and escalation at regional distances by combining infrasound and remote sensing techniques the ashe system in ecuador automatically detected over 20 000 volcanic explosions at an array 37 km from tungurahua and was successful at notifying the onset escalation and cessation of a hazardous february 2008 eruption with a latency of 5 min elevated infrasonic energy from sustained and intense tungurahua eruptions correlates well with ash column heights and their lateral extent during the study period the spectra of these sustained explosive eruptions appear to be recurrent readily recognizable and indicative of volcanic jetting and significant atmospheric ash injection the paroxysmal plinian phase of the august 2006 eruption produced an ash cloud that extended well into the stratosphere 24 km coinciding with a shift of the dominant jetting frequency from 0 25 hz to below 0 1 hz and radiation of over 5 107 w of acoustic power transient explosions were often marked by minor or no ash release and are presumed to be more gas rich a change in the acoustic spectrum of volcanic jetting was also detected in the transition from a sustained to collapsed eruption column at the end of the july 14 2006 eruption the jetting spectrum at tungurahua during a period of sustained pyroclastic density current production changes from a typical double peaked to a single peaked spectrum suggesting remote acoustic monitoring can help ascertain the stability and dynamics of an eruptive column

insight into tube building behaviour and palaeoecology of some agglutinating worms from the upper devonian of nevada usa abstract agglutinated worm tubes from the upper devonian of the devils gate section in nevada usa are reported for the first time filling a major gap in their palaeozoic fossil record two small 5 mm and 6 7 mm in length tubes are composed entirely of tentaculitid shells and one large tube 55 mm in length is formed from particles including ostracode carapaces echinoderm ossicles tentaculitid shells and putative bryozoan fragments aligned perpendicularly to the tube s long axis the tubes in particular the large one have a cylindrical curved and tapering tube morphology that is very similar to that of modern agglutinating polychaetes of the families terebellidae and pectinariidae the large tube is dominated by objects that fall within a certain size range and although built from different types of particles echinoderm ossicles are prevalent in the posterior part whereas ostracode carapaces dominate in the middle and anterior parts of the tube tentaculitid shells are relatively rare in the large tube despite being abundant in the surrounding host deposit the faunal assemblage composing the tube suggests that the worm animal was rather specific in its selection of particles with a certain morphology this is common behaviour amongst many modern agglutinating terebellid and pectinariid polychaetes the preservation of such fragile tubes was enhanced by rapid burial likely caused by gravity flow of sediment in a deep slope setting

boundary skin friction and sediment transport about an animal tube mimic a flume study was made of fluid flow boundary skin friction and sediment transport about an animal tube mimic the effect of a tube on momentum transfer depends most strongly on its height a tube increases the net boundary skin friction locally and tends to promote sediment entrainment near its base flow in this region appears to be governed by the same similarity laws that apply to cylinders with much larger body reynolds number particles travelling as suspended load may be deposited immediately downstream of the tube the net sedimentological effect of any tube i e deposition or scour will depend both on its height and on the boundary shear stress imposed by the external flow the near wake region of a tube is dominated by a strong cross stream exchange of momentum wake perturbations decay downstream seemingly in accordance with similarity laws which also govern mounted two dimensional structures

sedimentary structures sorby and the last decade henry clifton sorby pioneered in the last century the description and especially the hydrodynamic interpretation of sedimentary structures together with their use as palaeocurrent indicators research completed since the last syntheses were published a decade ago shows that work along these lines continues to be necessary and relevant particularly as regards the physical explanation of structures and to present significant challenges and opportunities perhaps the most pressing needs are for a better understanding of 1 bedforms in gravels silts and carbonate sediments 2 tidal and especially sand wave bedding 3 hummocky and swaley cross stratification and 4 soft sediment and dewatering structures in turbidites many sedimentary structures present a little exploited opportunity to quantify process rates and define short time periods from the rock record

volcanic tremor and frequency gliding during dike intrusions at kilauea a tale of three eruptions to characterize syneruptive intrusive deviations from background volcanic tremor at kilauea hawai i we analyze the spatial and temporal properties of broadband tremor during dike intrusions into the east rift zone erz in 2007 and 2011 as well as during explosive eruptive activity at kilauea s summit in 2008 background tremor was similar for each event and the 2008 explosions did not affect its properties in contrast the intrusions were accompanied by departures from this background in the form of two phases of seismicity that were separated in space and time in both 2007 and 2011 phase i was characterized by a quick succession of discrete events which were most intense at the onset of intrusion near the presumed locations of the dikes intruding into the erz phase ii marked by continuous broadband tremor around the summit followed 10 14 h later in 2007 phase ii tremor was accompanied by a monotonic downward shift glide of spectral peaks between 0 6 and 1 5 hz over at least 15 h during phase ii in 2011 a gradual upward and subsequent symmetric downward glide between 0 6 and 6 6 hz occurred over 5 10 h respectively the spectra during both phases differed from the background and 2008 as well as from each other indicating different physical mechanisms phase i in 2007 and 2011 is probably related to the mechanics of dike intrusion phase ii tremor may be characteristic for evolving magma bubble dynamics related to the geometry of the plumbing system and the style of magma flow

a study of the dynamics of a marine sandwave the movement of the crest of a sandwave was studied using cross sectional profiles obtained from lines of sea bed reference stakes measurements were made over a six month period before and after flood and ebb tides in relation to both spring and neap tides and surface wave conditions additional observations were obtained on a daily basis over an equinoctial neap to spring to neap tidal period in conjunction with boundary layer flow measurements tracer experiments were conducted to study the dispersion of sediment from the sandwave crest the results showed that the sandwave was relatively stable at neap tides whilst at higher tidal ranges the crest position oscillated with successive flood and ebb tides net flank erosion occurred on the less steep upstream slope during the dominant ebb tide this together with increased deposition on the lee slope caused the crest to advance it was not possible to extrapolate sandwave migration over long periods as the tidal dynamic trends were interrupted by wind stress and surface wave activity high particle orbital velocities generated at the sea bed by storm waves caused major reductions in crestal heights calculated volumes of sediment eroded and accreted were used with boundary layer flow measurements to calculate threshold velocities for the movement of the sediment and sediment transport rates

accumulation and intense bioturbation of bioclastic muds along a carbonate platform margin dry tortugas florida abstract a sedimentological study was undertaken in the dry tortugas lowermost florida keys to examine processes influencing the accumulation and sedimentary fabric characteristics of carbonate muds along the shallow margin of a carbonate platform sedimentological studies physical properties 234th and 210pb geochronology were coordinated with observations of benthic biology and benthic boundary layer dynamics sampling was concentrated around a mud depocenter in southeast channel a reentrant 20 30 m deep in the southern edge of the dry tortugas platform in the depocenter of southeast channel accumulation rates of 0 10 0 32 cm y 1 are estimated from 210pb profiles likely sources of sediment are in shallower water and include reefs and beds of calcareous green algae fine sediment silt and clay sized is advected to the seabed of southeast channel by a combination of tidal and storm driven currents flows from shallow water decelerate upon entering deeper water in southeast channel producing conditions favorable to long term accumulation once deposited sediment in southeast channel is subjected to bioturbation by a two tiered benthic community the surface zone 0 5 cm is mixed biodiffusively by a surface community of small bivalves and polychaetes db 9 cm2 yr 1 over periods of weeks to months and is characterized by mm scale mottling other near surface structures include biodeposited fecal mounds of deep deposit feeders and ephemeral physical stratification as thin 1 5 cm layers of fine sediment below 5 cm the dominant post depositional process is bioadvective mixing by a deep deposit feeding community of callianassid shrimp and notomastid polychaetes the upper 10 15 cm is mixed completely every 6 21 years and bioturbation below this depth is slower even though the study area has been hit by 10 major hurricanes in the last 120 years winds 190 km h 1 sediments preserved i e below 5 cm depth in southeast channel during this period reveal wholly biogenic sedimentary fabric produced by the deep callianassid notomastid community bioturbation is thus capable of erasing the stratigraphic signature of the most extreme sediment transport events over decadal time scales

ichnology of prodeltaic hyperpycnite turbidite channel complexes and lobes from the upper cretaceous prairie canyon member of the mancos shale book cliffs utah usa

bioturbation of intertidal quartz rich sands a modern example and its sedimentologic and paleoecologic implications callianassa californiensis is a deep burrowing deposit feeding thalassinid shrimp which is abundant in intertidal areas of mugu lagoon california it occurs in greater densities 170 m 2 and is distributed more evenly to a depth of 50 cm below the sediment surface in quartz rich sands than in muddy sands 78 m 2 where most individuals live 15 to 30 cm below the sediment water interface callianassa californiensis produces extensive unlined burrow networks and deposits excavated material at the sediment surface given published excavation rates the population of c californiensis in the sandy area of mugu lagoon would deposit a layer 1 to 3 m thick each year it is also capable of rapidly reestablishing burrow openings after burial by up to 16 cm of sediment burrows act as conduits for fresh seawater and rapid overturn of sands inhibits compaction this results in flushing of nutrient and oxygen rich waters to considerable depth in the quartz rich sands as reflected by a depressed oxic anox

introduction to special section on marine sand wave and river dune dynamics marine sand waves and river dunes are rhythmic patterns formed at the interface between a sandy bed and turbulent flows driven by tidal and river currents their origin development and dynamics are far from being fully understood to enhance the discussion on this topic we organized the international conference marine sand wave and river dune dynamics marid in april 2004 in enschede netherlands scientific papers that originated from the marid conference are presented in this special section this introduction places these papers in the context of recent progress

wave ripple dynamics and the combined flow modification of wave ripples in the intertidal zone of ariake bay kyushu japan abstract intertidal sand bars occur as rhythmic features on the mesotidal foreshore in ariake bay in kyushu southern japan superimposed on the low gradient foreshore 2 1000 are seventeen low amplitude many wave ripples are constructed on the intertidal rhythmic bars by wind waves during high tide the crest line of the wave ripples is long parallel and straight to gently curved with bifurcation but often oblique to the crest of these rhythmic bars peaked crests of wave ripples on the gentle seaward slope of the bars are modified by combined flow of borelike waves and the return flow just before emergence and become rounded or flattened in contrast wave ripples on the landward slope are only slightly deformed through this process as the result the form of the wave ripples is diagnostic of the position on the rhythmic bars this difference in form is important as a criterion for discriminating the landward and seaward directions for such intertidal deposits

inner shelf to lower shoreface hummocky sandstone bodies with evidence for geostrophic influenced combined flow lower cretaceous west greenland abstract hummocky sandstone bodies were deposited on the margin of an early cretaceous rift basin in an overall progradational inner shelf to lower shoreface unit excellent outcrops of this unit permitted a detailed study of sedimentary structures and paleocurrents in relation to sandstone geometries the sandstone bodies are lensoid and 0 5 4 m thick with lateral extensions from a few meters to more than 30 m laterally they pinch into thin sandstone sheets that continue for at least 130 m along the entire outcrop or swell within a distance of 20 30 m to form another sandstone lens the lower boundaries are sharp with local erosional relief up to 1 m hummocky cross stratification wave ripple cross lamination and low angle cross stratification are closely interbedded within the sandstone aminated mudstone beds 10 60 cm thick separate the sandstone bodies and are generally continuous over the entire length of the outcrop sedimentary structures in the sandstone bodies were produced by high energy wave generated oscillatory currents and unidirectional geostrophic currents vertical stratification successions from individual storm events reflect deposition during both increasing storm current velocity succeeded by waning storm deposits and more typically waning storm facies successions deposition of the unusual vertical successions was probably controlled by an episodically high sediment supply the local presence of the hummocky sandstone bodies on a regional scale was controlled by a paleogeographic setting where the bathymetric contours locally caused geostrophic cu rents to decelerate

comparison between predicted and observed sand waves and sand banks in the north sea for the first time a prediction model of regular morphological patterns on the seabed was tested against observations of sand wave and sand bank occurrence in the entire north sea the model which originates from first physical principles predicts this occurrence via two dimensionless parameters on the basis of the water depth the tidal velocity amplitude the level of zero intercept above the seabed z0 and a viscosity variation parameter alt epsilon the latter two quantities were varied in a number of predictions for the entire north sea whereas for the first two local values were used the range of realistic values of alt epsilon and z0 was large enough to let these two parameters distinguish between the possible combinations of bed forms as is shown in the shallower southern bight of the north sea the results were more sensitive to variations in z0 than in alt epsilon a slightly more detailed approach focused on sand waves only in the southern north sea and estimated local values for z0 using depth information quantification of the results showed that the model was able to predict the contours of the sand wave patches but it could not account for the absence of the bed features within this area the type of bed deposit partly explains the smaller scale variation the work confirms the validity of the theoretical bed form prediction model and verifies the hypothesis that the large scale seabed features are formed as free instabilities of tide topography interactions