validating novel boundary conditions for three dimensional mechanics based restoration an extensional sandbox model example geomechanical restoration methods are dependent on boundary conditions to ensure geological consistency of the restored model in terms of geometry and strain classical restoration boundary conditions such as flattening a datum horizon may lead to inconsistent displacement and strain fields we restore a laboratory structural sandbox model with known deformation history to develop guidelines for definition of boundary conditions that produce improved results from geomechanical restorations the sandbox model has a basal silicone layer includes synkinematic deposition and is characterized by structures analogous to those found in suprasalt extensional environments the deformed geometry is interpreted from three dimensional tomography imaging and a time series of cross section tomography images provides a benchmark to quantify restoration error and inform boundary conditions we confirm that imposing a lateral displacement equal and opposite to far field tectonic shortening or extension provides a more accurate restoration however the amount of displacement may not be known in real cases we therefore test several established methods using only the unrestored geometries to assess the amount of shortening that should be used to guide geomechanical restorations an accurate estimation is provided by the area depth method and potentially by a dilatation analysis additionally novel fault compliance boundary conditions produce improved results in the vicinity of crossing and branching faults application of similar methods should produce improved restoration of natural geologic structures

channel margins in a pennsylvanian braided fluvial deposit the morien group near sydney nova scotia canada abstract braided fluvial deposits in the pennsylvanian morien group contain an unusual association of erosional features at contacts between sandstone and mudstone units which represent flat lying to vertical channel margins mudstone intraclasts up to 2 m in diameter form lensoid lags at channel bases and are interpreted as bank collapse rubble flutes on vertical channel walls channel floors and intraclasts indicate active flow whereas rills on steep surfaces resulted from downslope drainage over the edges of banks or mudclasts delicate plumose patterns on vertical fracture surfaces modified by flow formed during cracking of the muds by desiccation and bank collapse scoured desiccation cracks are common on flat lying surfaces where flow parallel linear scours 50 cm deep may have expl ited orthogonal desiccation cracks the channel margin features described here require deposition and subsequent reworking of cohesive fines on high topographic levels of a fluvial system due to alternating periods of flooding and subaerial exposure braided and ephemeral river systems with variable discharge are likely to provide the most suitable setting for these features

geometry spatial arrangement and origin of carbonate grain dominated scour fill and event bed deposits late jurassic jubaila formation and arab d member saudi arabia

the importance of small scale faulting in regional extension a recurring observation in many studies of extensional basins has been that the amount of extension visible on normal faults for example on seismic reflection profiles is significantly less than the amount of extension indicated by crustal thickness and thermal subsidence1 5 one mechanism suggested to account for this discrepancy is small scale faulting with offsets too small to be resolved seismically6 7 but earthquake studies8 10 indicate that small faults are responsible for only a small fraction of the total seismic moment in an active area scholz and cowie11 have recently attempted to extend this approach to the total strain at the end of a finite deformation interval by combining scaling laws describing the distributions of fault lengths and displacements here we present fault displacement data that directly conflict with scholz and cowie s conclusions and imply that up to 40 of the extension may be missed by summing fault offsets on basin profiles the fault population at the end of a long deformation interval may differ substantially from that responsible for the earthquake population at any one time

infragravity energy modulation by tides infragravity waves motions with frequencies immediately below wind generated sea and swell are believed to be radiated seaward from the surf zone where they are excited by nonlinear interactions between waves in the sea swell frequency band we describe tidal modulation of sea surface elevation variance at infragravity frequencies observed in 8 30 m water depth a few kilometers from shore at several california sites infragravity spectral levels vary by as much as a factor of 10 between high and low tide possibly because the surf zone width and beach face slope vary significantly with tidal level on the usually concave shaped beaches onshore of the observations at a fixed sensor and with approximately constant sea swell energy the observed infragravity energy is lowest at low tide

infragravity wave dynamics in a barred coastal region a numerical study this paper presents a comprehensive numerical study into the infragravity wave dynamics at a field site characterized by a gently sloping barred beach the nonhydrostatic wave flow model swash was used to simulate the local wavefield for a range of wave conditions including mild and storm conditions the extensive spatial coverage of the model allowed us to analyze the infragravity wave dynamics at spatial scales not often covered before overall the model predicted a wavefield that was representative of the natural conditions supporting the model application to analyze the wave dynamics the infragravity wave field was typically dominated by leaky waves except near the outer bar where bar trapped edge waves were observed relative contributions of bar trapped waves peaked during mild conditions when they explained up to 50 of the infragravity variance near the outer bar the infragravity wave growth was partly explained by nonlinear energy transfers from short waves this growth was strongest for mild conditions and decreased for more energetic conditions when short waves were breaking at the outer bar further shoreward infragravity waves lost most of their energy due to a combination of nonlinear transfers bottom friction and infragravity wave breaking nonlinear transfers were only effective near the inner bar whereas near the shoreline where losses were strongest the dissipation was caused by the combined effect of bottom friction and breaking this study demonstrated the model s potential to study wave dynamics at field scales not easily covered by in situ observations

edge waves on nonplanar bathymetry and alongshore currents a model and data comparison the numerical solutions for the dispersion of linear shallow water edge waves are compared with observed alongshore wavenumber frequency spectra of edge wave variance to examine their prediction of the effects of nonplanar bathymetry and moderate mean alongshore currents field observations were made at the two southern california nearshore sediment transport study field sites torrey pines 1978 and leadbetter 1980 beaches on torrey pines beach where the bathymetry is very planar except for a concave steepening landward beach face observed departures from the analytical plane beach dispersion solution attributed to the concave face are predicted by numerical dispersion solutions using the measured cross shore depth profile on both beaches asymmetry in observed dispersion curves of upstream and downstream progressing edge waves are well predicted by numerical dispersion solutions using the cross shore profile of measured mean alongshore current spectra of the alongshore velocity component from both beaches show changes in edge wave mode dominance with increased frequency oltman shay and guza 1987 demonstrated that mode dominance transition with frequency as observed from a fixed offshore location is associated with the seaward decay of edge waves and that the approximate frequency of mode transition is predicted by the profile solutions for edge wave variance and the assumption of equal shoreline elevation variance amongst modes a submerged concave beach face at torrey pines beach is shown to alter the predicted cross shore scaling of the edge wave profiles from that predicted when mean water is below the concave beach face and therefore to alter the mode transition frequency predictions different mode transition frequencies are observed in spectra from data runs with mean water levels both above and below the concave beach face and the differences are shown to be reasonably predicted using edge wave profile solutions for the measured beach profile for these data observed and predicted mode transition frequencies did not change appreciably in the presence of mean alongshore current implying that large changes in cross shore scaling of the edge wave profiles did not occur however as has been previously shown by howd et al 1992 there are also local edge wave profile shape changes because of the cross shore shear of the mean alongshore current verification of these predicted local shape changes can not be made with these data confidence in cross shore profile solutions is of practical importance for estimates of shoreline variances from offshore measurements on these two beaches estimates using both numerical solutions for the measured depth and current profiles and analytical solutions for plane beach approximations typically differ by only 10 to 40

geometry distribution and fill of erosional scours in a heterolithic distal lower shoreface sandstone reservoir analogue grassy member blackhawk formation book cliffs utah usa

origin of shore normal channels from the shoreface of sable island canada a suite of modern shore normal channels was discovered on the southern shoreface of sable island canada repetitive multibeam and sidescan surveys of these features as well as box coring and sampling showed that the depressions were perennial features of the shoreface they occurred in fine and medium sand and were most abundant in depths less than 20 m they were up to 1 m deep and 50 m wide increased in size seawards and generally followed the seabed slope the channels dominated the inner shoreface becoming wider and deeper seawards to depths in excess of 40 m there is a continuum of scales in width and depth of these channels the smallest of which are equated with gutters preserved in the geological record the internal structure of the shoreface sediments where the gutters are found is characterised by normally graded tempestites composed of cut and fill structures overlying an erosion surface thus the environmental setting internal structure and scale are similar to ancient counterparts gutters have been interpreted to result from downwelling over palaeo shorefaces during ancient storms myrow 1992b the composition of gutter infill as well as the stability evolution associated bedforms and hydrodynamic conditions under which they formed were examined to verify genetic interpretations of the ancient counterparts the multi sensor benthic lander ralph was deployed within a field of shore normal channels for 17 days during late winter 1998 ralph burst sampled flow at hourly intervals whilst imaging the seabed resulting sequential imagery revealed the genesis of a group of five gutters during storm spin down that was coincident with the formation of large scale wave ripples this was followed by infilling of the gutters and wave ripple destruction within 20 hours by longshore sand transport the gutters were located within and parallel to a larger channel 50 m wide and 0 50 m deep they were formed by coastal set up and subsequent downwelling that was triggered by the rotation of storm winds from seawards onshore wind to landwards offshore wind the gutters formed within 2 to 3 hours during spin down of a winter storm under live bed conditions of sand transport wave height and mean tidal flows were well below those of the storm peak and so they were not directly responsible for creating the gutters the mechanism we propose for the evolution of gutters supports the geological interpretations that is a storm driven downwelling event as described by swift and niedoroda 1985 however the downwelling event appeared to take place suddenly rapid acceleration in flow briefly few hours duration and within narrow corridors guided by wider and deeper channels of the shoreface high turbidity during the time of gutter formation leads us to believe that the phenomenon of inner shelf turbidity currents as suggested by walker 1985 exists and may be instrumental in channel formation

multibeam bathymetry of glaciated terrain off southwest newfoundland abstract inner st george s bay newfoundland was mapped in 1988 using a suite of conventional geophysical and sampling tools the quaternary deposits sea level history and holocene littoral sediments were described in a series of papers in 1995 part of the previously mapped area was imaged using a multibeam mapping system the resulting high resolution images of bathymetry and backscatter are interpreted with reference to the previously collected data the multibeam imagery shows a late wisconsinan morainal bank that has been modified by marine processes during and following a t2 5 m postglacial sea level lowstand two types of terrain occur on the morainal bank in the extreme west where morainal till is close to the seabed the image shows areas with high reflectivity and rough texture that consist of bouldery gravel farther east the flanks of the moraine are buried by a prograded wedge of sediment eroded from the bank during the holocene transgression and transported towards the adjacent basin by waves and currents here areas of relatively smooth seabed on the multibeam bathymetry image consist of either mobile rippled poorly sorted gravel high reflectivity or sand lower reflectivity the image shows a submarine valley which according to the previous data was glacially overdeepened and subsequently partly filled by glacial marine and postglacial sediments shallow areas with high reflectivity on either side of the valley are seafloor exposures of a draped glacial marine unit that was deposited when the former ice margin was located close to the present coast between 13 3 and 10 8 ka an area of mounded morphology and high backscatter located below the level of the postglacial sea level lowstand is interpreted as till that has not been modified by wave processes the multibeam bathymetry and backscatter images reveal the inadequacies of the previous map that was compiled using data from conventional survey techniques

wave energy saturation on a natural beach of variable slope time series of flow were measured across the inner surf zone during a storm these data were used to quantify the dependence of wave height transformed from measured flow and velocity on local slope and depth similar to previous studies as incident waves broke and propagated into the surf zone wave energy became saturated and wave height was strongly dependent on depth however the ratio of rms wave height to local depth rms was found not to be constant but to vary between 0 29 and 0 55 rms increased with local slope and was independent of deepwater wave steepness thus the surf zone similarity parameter the ratio of slope to the square root of steepness did not adequately parameterize rms

control of estuarine sediment dynamics by interactions between currents and waves at several scales abstract the effect of interactions between continuous tidal currents and intermittent waves processes on sediment dynamics and transport is addressed by presenting detailed field measurements of waves boundary layer currents and suspended sediment from an estuarine channel and an adjacent intertidal sandflat in manukau harbour new zealand the aim is to determine in what ways it is necessary to couple waves and currents in numerical models and thereby put limits on the fundamental structure of process based estuarine sediment transport models waves were important on the intertidal flat turbidity switched on and off with the appearance and disappearance of waves wave groups dominated entrainment of bed sediment a wave current boundary layer model explained measured bed shear stress and hydraulic roughness and the measured near bed time averaged suspended sediment concentration was mostly well predicted by a pure wave model both the waves themselves and wave related processes varied markedly over the tidal cycle the variation in the former principally changes in wave height was related to changes in fetch caused by the harbour wide emergence and submergence of intertidal regions the variation in the latter was related to changes in water depth relative to the wavelength of the waves which controlled the penetration to the bed of wave orbital currents in addition to the variation over the tidal cycle in the intensity of wave processes there was also a change in kind which occurred with the arrival at the measurement site of the turbid fringe which is the narrow highly turbid edge of the estuarine water body the relationship between suspended sediment concentration and wave orbital velocity in the turbid fringe was radically different to the relationship in the estuarine water body proper which suggests a change in dynamics perhaps related to breaking waves a hybrid modelling approach is required i e one that treats discrete events but resolves tidal cycle scale variation within the event there is a need to resolve the variation in the wave train over the tidal cycle and the penetration to the bed of wave orbital motions both of which could only be done adequately within an estuary tidal model in contrast to the situation on the intertidal flat where waves intermittently entrained sediment sediment transport in the channel was continuous driven by tidal currents to predict sediment flux in the channel we need to know the upstream sediment transporting capacity of the flow including that contributed by waves the character of the bed sediment and the sediment settling time scale these factors confounded even the simplest notion of flood and ebb dominance which frequently has been applied to understand estuarine morphodynamics

run up from impact tsunami summary we report on calculations of the on shore run up of waves that might be generated by the impact of subkilometre asteroids into the deep ocean the calculations were done with the coulwave code which models the propagation and shore interaction of non linear moderate to long wavelength waves kh using the extended boussinesq approximation we carried out run up calculations for several different situations 1 laboratory scale monochromatic wave trains onto simple slopes 2 10 100 m monochromatic wave trains onto simple slopes 3 10 100 m monochromatic wave trains onto a compound slope representing a typical bathymetric profile of the pacific coast of north america 4 time variable scaled trains generated by the collapse of an impact cavity in deep water onto simple slopes and 5 full amplitude trains onto the pacific coast profile for the last case we also investigated the effects of bottom friction on the run up for all cases we compare our results with the so called irribaren scaling the relative run up r h0 s h0 l0 1 2 where the run up is r h0 is the deep water waveheight l0 is the deep water wavelength s is the slope and is a dimensionless quantity known as the irribaren number our results suggest that irribaren scaling breaks down for shallow slopes s 0 01 when 0 1 0 2 below which r h0 is approximately constant this regime corresponds to steep waves and very shallow slopes which are the most relevant for impact tsunami but also the most difficult to access experimentally

modeling the tectonic development of the tucano and sergipe alagoas rift basins brazil abstract the tucano and sergipe alagoas basins of northeast brazil form part of a regional extensional basin system that was operative during the mesozoic breakup of south america and africa with both basins developing on precambrian crust the synchronous development of the rift basins suggest that they are genetically linked in space and time whereas the offshore sergipe alagoas basin is characterized by a substantial thickness of post rift sediment the tucano basin either failed to develop or at least preserve a significant thickness of post rift sediment observed primary porosities within both pre and syn rift tucano basin sediment imply that significant post rift sedimentation never occurred failure to develop significant post rift subsidence has important thermal and mechanical implications for the reaction of the lithosphere to rifting and can be explained in terms of 1 depth dependent lithospheric extension in which intracrustal detachments allow the extension of the crust to be decoupled from the thinning of the lithospheric mantle 2 small rates of extension that allow the lithosphere to cool during rifting and or 3 lithospheric rifting during which the flexural strength of the lithosphere remains high with respect to points 2 and 3 forward modeling demonstrates that finite rifting rates over a 20 25 m y period are insufficient to cool the lithosphere to the point where post rift subsidence fails to develop an interesting complication arises when the flexural strength of the lithosphere remains large during rifting it tends to suppress the vertical motions of the lithosphere such as those engendered by the cooling of the lithosphere following rifting thereby reducing significantly the amplitude of the post rift subsidence thus the lack of post rift sedimentation within a basin does not necessarily imply that extension has been limited to the crust from our kinematic modeling of the tucano basin the observed negative free air and bouguer gravity anomalies 120 mgals suggest that the flexural strength of the lithosphere has remained sufficiently large to maintain the load of the sediment we can model successfully the observed tucano basin architecture and gravity anomaly irrespective of whether we assume depth dependent or depth independent lithospheric extension primarily because the flexural strength of the lithosphere tends to buffer or suppress the amplitude of the post rift subsidence in contrast the adjacent sergipe alagoas basin is associated with low amplitude gravity anomalies which may reflect a resetting of flexural strength during rifting prior to rifting however there was no appreciable elevation difference between the tucano and sergipe alagoas regions as might be induced by a hot spot for example implying that the flexural strength of the lithosphere was similar the total thickness of the syn and post rift sediments within the sergipe alagoas basin is about the same as the thickness of rift phase sediments in the tucano basin thus the amount of crustal extension responsible for each basin was similar however since the sergipe alagoas basin contains 4 5 km of post rift sediments lithospheric mantle thinning in this region must have been significantly greater than the crustal extension to overcome the effects of flexural bufferring the need for lithospheric mantle thinning to be greater that crustal extension in the sergipe alagoas region was also a result obtained by modeling the development of the ocean continent boundary between brazil and africa from our coupled kinematic and rheological model of lithospheric extension we predict that the ocean continent boundary should form preferentially at the location of greatest crustal and lithospheric mantle thinning that is within the region of maximum depth independent lithospheric extension the ocean continent boundary formed east of the sergipe alagoas basin despite the fact that the tucano basin represents the region of greatest crustal thinning if extension had been uniform with depth beneath these basins the ocean continent boundary should have formed in the tucano basin as it did not some form of intracrustal detachment appears to have been operative to reduce lithospheric mantle thinning beneath the tucano basin while enhancing it beneath the offshore regions of the sergipe alagoas basin

erosion and accretion processes in a muddy dissipative coast the chao phraya river delta thailand seasonal variation in seabed elevation in the muddy intertidal zone of the chao phraya river delta an area of serious coastal erosion for 40 years was assessed using information on waves and tides predicted by numerical simulations the study area is under the influence of the southeast asian monsoon climate and lies in the innermost part of a sheltered gulf across which a low gradient slope has developed observations aimed at evaluating the effectiveness of a prototype breakwater on mitigating coastal erosion indicated that the seasonal variation in the seabed elevation typically about 30 cm was caused primarily by seasonal changes in wave direction and height the breakwater seems to have contributed to a net rise in the seabed level at sites behind the structure seabed erosion was most apparent during the northeast monsoon when waves are weak erosion under this low wave energy state was attributed to the combined effect of wave breaking and the low tidal level a difference in the observed seabed accretion rate between the transitional intermonsoon period and the succeeding southwest monsoon period was attributed to the direction of the wave energy flux offshore sediments seem to have been supplied efficiently to the study area by waves during the transitional period another potential cause of seabed erosion and accretion during the wet southwest monsoon season was the discharge of water and sediments from local canals associated with intense tropical rainfall this discharge seems to be linked to land use in the coastal area the results of this study show the importance of monitoring across shore sediment transport for better understanding of coastal erosion processes copyright 2010 john wiley sons ltd

swash on steep and shallow beaches extensive field observations of swash on natural beaches are used to relate the magnitudes of swash oscillations to incident wave conditions and the beach slope swash fluctuations at wind wave frequencies defined here as f 05 hz appear to be saturated as in laboratory experiments with monochromatic waves wave breaking prevents the magnitudes of swash oscillations at incident wave frequencies from increasing past a certain level which depends on the beach slope all data sets considered support this conclusion in contrast the magnitude of swash oscillations at surf beat frequencies defined as f 05 hz varies between data sets possible reasons for the discrepancy are discussed despite their differences all data sets show that motions at surf beat frequencies dominate the swash spectrum on dissipative beaches as in previous studies the frequencies of spectral hills and valleys in the spectra of surf zone sensors suggests that a significant fraction of the surf beat energy is contained in motions which are standing in the cross shore direction preliminary analysis indicates that shoreward propagating surf beat is coupled to incident wave groups

surficial sediments of the outer banks scotian shelf canada the distribution thickness and mean grain size of surficial sediments on sable island bank middle bank and banquereau scotian shelf are used to re evaluate interpretations made by others on mechanisms controlling long term stability and net transport pathways of surface sand a holocene sand ridge complex the sable island catena extends 300 km across sable island bank and banquereau this sand ridge complex which is up to 50 m thick formed as a result of holocene sediment transport on the outer banks and controls the modern day distribution of bedforms and sediment size a clockwise circulation of sand centred around sable island which had been proposed as the mechanism maintaining the island does not take place sand is transported from southwest to northeast across sable island bank towards the sable island catena thereafter sand is dispersed eastward spillover of sand from the banks to the gully is not significant sand is trapped in depths less than 100 m the processes proposed to ha

rotary sidescan images of nearshore bedform evolution during a storm abstract high resolution acoustic images are presented of bedform development on the crest of a nearshore bar during a storm the images were obtained using a 2 25 mhz rotating sidescan sonar the sonar system provides a continuous record of the evolution of the bedform field through time within a 10 m diameter field of view the images document the occurrence of ripples cross ripples and megaripples during the waning stages of the storm transitions among ripple types occurred on time scales of 1 3 h beginning with flat bed and culminating in highly 3 d short crested ripples

the calibration of optical backscatter sensors for suspended sediment of varying darkness levels a series of calibration experiments were run in order to determine the effect of the colour of suspended sediment on the response of optical backscatter sensors obs munsell notation describes the properties of soil and sediment colour using the three parameters hue chroma and value which represent respectively the spectral position lightness level and amount of pure chromatic colour present the exposure of the obs to munsell soil chart patches revealed that the obs is sensitive to variations in munsell value and not munsell hue or chroma since obs output decreased with darkness level and increased with lightness level and munsell value it is suggested that the level of blackness of particles acts to absorb the near infrared ir signal of the obs modifying its output a strong correlation r2 0 984 was found between the observed and predicted obs outputs of varying concentrations and ratios of black and white suspended sediment the obs output was predicted using a linear mixture model incorporating end member calibrations of black and white sediment similar to green and boon green m o boon j d iii 1993 the measurement of constituent concentrations in nonhomogeneous sediment suspensions using optical backscatter sensors marine geology 110 pp 73 81 a strong correlation r2 0 907 was also observed between luminance factor and ir reflectance for various minerals suggesting a link between munsell notation and obs output formulae were developed to predict the ir reflectance of sediment of known munsell value concentration and size models predicting sediment transport should consider the effect of the level of blackness of particles on the obs response

analogue modelling of orthogonal and oblique rifting abstract the three dimensional progressive development of orthogonal and oblique rift systems has been simulated using scaled analogue sandbox models the orientation of the zone of rifting where angle between the rift axis and the extension direction was varied systematically from 90 orthogonal rifting to 75 60 and 45 oblique rifting completed models were impregnated and sectioned both vertically and horizontally orthogonal rift models are characterized by long straight rift border faults and intra rift faults perpendicular to the extension direction oblique rift models are characterized by shorter segmented rift border faults and intrarift faults in the oblique models the rift border faults formed en echelon arrays parallel to the inderlying zone of basement stretching whereas the intra rift faults formed at a high angle to the extension vector increased extension in the moderately oblique and oblique rift systems 60 and 45 caused the intra rift faults to rotate towards parallelism with the rift border faults no strike slip or oblique slip transfer faults were found in any experiments rift border faults and intra rift faults in the models are segmented along strike with relay ramp structures formed between overlapping fault tips along the strike of the rift variations in half graben polarities and offsets of depocentres are accomplished by accommodation zones formed by interlocking conjugate fault arrays the experimental fault patterns compare well with the fault architectures found in those modern or relatively young rift systems where well defined basement controlled strike slip or oblique slip transfer faults are absent an accommodation zone model consisting of interlocking conjugate extension faults is proposed for the along strike switching of half graben asymmetries and offsetting of depocentres in rift systems the fault geometries in the analogue models can be used as templates for recognition of fault styles in both orthogonal and in oblique rift environments

evolution of the grenada and tobago basins and implications for arc migration abstract the tectonic mechanisms controlling how volcanic arcs migrate through space and geologic time within dynamic subduction environments is a fundamental tectonic process that remains poorly understood this paper presents an integrated stratigraphic and tectonic evolution of late cretaceous to recent volcanic arcs and associated basins in the southeastern caribbean sea using seismic reflection data wide angle seismic refraction data well data and onland geologic data we propose a new tectonic model for the opening of the grenada and tobago basins and the 50 250 km eastward jump of arc volcanism from the late cretaceous aves ridge to the miocene to recent lesser antilles arc in the southeast caribbean based on the mapping of three seismic megasequences the striking similarity of the half graben structure of the grenada and tobago basins that flank the lesser antilles arc their similar smooth basement character their similar deep marine seismic facies and their similar paleogene sediment thickness mapped on a regional grid of seismic data suggest that the two basins formed as a single saucer shaped oceanic crust paleogene forearc basin adjacent to the now dormant aves ridge this single forearc basin continued to extend and widen through flexural subsidence during the early to middle eocene probably because of slow rollback of the subducting atlantic oceanic slab rollback may have been accelerated by oblique collision of the southern aves ridge and southern lesser antilles arc with the south american continent uplift and growth of the southern lesser antilles arc divided the grenada and tobago basins by early to middle miocene time inversion of normal faults and uplift effects along both edges of the lesser antilles arc are most pronounced in its southern zone of arc collision with the south american continent the late miocene to recent depositional histories of the grenada and tobago basins are distinct because of isolation of the grenada basin by growth and uplift of the neogene lesser antilles volcanic ridge

origin evolution and distribution of shoreface sand ridges atlantic inner shelf u s a abstract a computer mapping system was employed to document the location of 259 shoreface attached and detached sand ridges in water although shoreface attached sand ridges appear to have several different modes of formation a two step process for the development of most shoreface attached and detached sand ridges along u s atlantic barrier island and cape coastlines is proposed 1 sand is deposited as ebb tidal deltas or river deltas along the lower shoreface and or inner continental shelf prior to or during transgression followed by 2 further transgression which reworks the deltaic sand bodies into linear sand ridges at the base of the shoreface by shelf processes the best developed shoreface sand ridge fields along the u s atlantic shelf lie adjacent to shorelines characterized by all of the following 1 transgression 2 mixed energy wave dominated barrier islands and 3 laterally migrating tidal inlet systems tidal inlet systems are natural sediment sinks that capture sand carried by longshore sediment transport ebb tidal delta deposits associated with these migrating tidal inlets provide the initial sand body for the development of shoreface attached sand ridges the oblique orientation and linear form of shoreface attached sand ridges appear to be a function of shoreline transgression lateral inlet migration and wave reworking of ebb tidal delta deposits concentrated along an ebb tidal delta retreat path shelf processes act as modifying agents in the evolution of sand ridges during and after ebb tidal delta deposition in general shoreface attached sand ridges are poorly developed or absent along eroding headlands spits and barrier island shorelines characterized by naturally stabilized tidal inlets these latter inlets and shoreline types are dominated or influenced by one or all of the following 1 antecedent topography 2 higher tidal ranges 3 larger tidal prisms 4 lower wave energies or 5 finer grain sizes the coupling of shoreline and shallow marine sedimentary processes during a transgression is critical to the origin evolution and distribution of shoreface sand ridges in the study area modern shoreface attached sand ridges are also known to occur in different coastal and shelf settings where large amounts of sediment were supplied to the shoreface and inner shelf during or immediately before transgression commonly observed vertical and lateral interrelationships of holocene shoreface attached sand ridges and tidal inlets or distributary channels have important ramifications for the development of shelf sandstone facies models in addition the geometric relationship documented in this study provides predictive petroleum and hard mineral exploration models of the spatial and temporal distribution of shoreface and shelf sand ridges

observations of wave energy fluxes and swash motions on a low sloping dissipative beach 1 field observations of swash and ocean waves show that runup saturation at infragravity frequencies 0 025 0 035 hz infragravity waves where typically less than 5 of the linear energy flux was reflected from the beach and where similar to the sea swell band the swash energy was independent of offshore wave energy the infragravity frequency range of saturation was determined by the tide with saturation extending to lower frequencies at low tide when the local beach face slope over the concave shaped profile was gentler runup was strongly dominated by infragravity frequencies which accounted on average for 96 of the runup variance and its energy levels were entirely consistent with strong infragravity wave dissipation observed in the surfzone particularly when including the nonlinear contributions to the wave energy fluxes the infragravity wave dissipation was strongly associated with breaking of sea swell waves which abruptly decreased nonlinear transfers to infragravity frequencies and made infragravity dissipation prevail over forcing within the breaking region our observations show evidence of nonlinear interactions involving infragravity and high frequency harmonic waves and suggest that these harmonics could play a role in the wave energy balance near the shoreline on low sloping dissipative beaches

morphology lateral migration and internal structures of shoreface connected ridges sable island bank nova scotia canada an extensive complex of shoreface connected ridges is present around sable island near the outer edge of the canadian east coast shelf two orders or ridges occur the larger first order ridges are longer wider and higher than ridges along the east coast of the us whereas the superimposed second order ridges are smaller all of the ridges converge eastward with the shoreface at angles up to 90 sup 0 sediment grain size becomes finer eastward over each ridge the finest sediment occurring at the base of the eastern flank landward facing straight crested megaripples and sandwaves are present in the troughs whereas hummocky megaripples occur on the ridge crests eastward migration of the ridges will produce a 3 20 m thick upward coarsening sequence that rests on an upward fining basal lag cross bedding predominates throughout the sequence although the upper part may contain hummocky cross stratification the differences between the us and the canadian ridges are due to a more intense storm climate and to obliquely onshore rather than obliquely offshore geostrophic flows in the sable island area nevertheless the sedimentological patterns over the ridges in both areas are similar 17 references 5 figures

numerical modeling of infragravity wave response during delilah 1 the nearshore circulation model shorecirc is applied to simulate the infragravity wave conditions at two intervals during the 1990 delilah campaign at duck n c the model has been extended to solve the energy equation for random short waves on the timescale of the wave groups which acts as a wave driver for the long wave model to simulate the wave conditions an algorithm has been derived which synthesizes a directional offshore wavefield from measured data including the bound directional low frequency components the model data comparison shows that the mean short wave transformation and mean longshore current are predicted well the structure of the infragravity spectrum as measured in the nearshore array is correctly represented albeit that the energy levels are underpredicted in most locations the 2 d frequency longshore wavenumber spectra show that the infragravity wave energy consists mostly of edge waves and that the computations qualitatively resemble the measurements it is shown that for 1 day bar trapped edge waves are present the model is also used to show that the influence of the longshore variability is small for this particular beach and that the directional spreading in the offshore wave field is critical in predicting the nearshore infragravity wave conditions correctly edge waves which propagate against the current are generated by the directionally broad short wave forcing and to a lesser extent by back scattering the nonlinear terms are relatively unimportant for the prediction of the infragravity wave climate the cross shore gradient of the onshore directed radiation stress is the most important of the forcing terms

landscape and depositional controls on palaeosols of a distributive fluvial system upper cretaceous brazil abstract the stratigraphic record of distributive fluvial systems is commonly characterised by frequent and complex interstratification of palaeosols among channel and overbank deposits however current models focus primarily on sedimentation and pay only limited attention to palaeopedogenesis thereby failing to incorporate important palaeoenvironmental and stratigraphic information this study proposes a pedosedimentary model for distributive fluvial systems that depicts and accounts for two palaeopedogenetic trends one downdip in relation to distality from the fan apex and one along strike in relation to distance from active channel belts palaeosols are reported in detail from an upper cretaceous succession of the bauru basin southeastern brazil through the application of macro micromorphological and geochemical studies combined with facies and architectural element analyses of sediments in the downdip palaeopedogenetic trend the proximal zone of the depositional system is characterised by a dominance of well drained inceptisols that develop on amalgamated channel fills in the medial zone inceptisols occur interlayered with overbank deposits containing entisols and poorly drained vertisols the distal zone preserves more mature and poorly drained inceptisols developed on deposits of overbank and sporadic distal channel fills these pedotypes show an increase in maturity and hydromorphism moving away from the apex to the fan toe this is likely linked to i the progressive approach of the topographic surface to the water table and ii the average increase in distance to an active channel belt in distal locations the along strike palaeopedogenetic trend culminates in poorly developed palaeosols in floodplain regions that correspond to topographic depressions located between channel belts and which were subject to recurrent floods because palaeopedogenesis in the floodplain region is penecontemporaneous to sedimentation pedotypes show an increase in maturity bioinduced calcification and hydromorphism with distance from the active channels they pass laterally from entisols and inceptisols near active channels to vertisols away from active channels conversely following avulsion abandoned channel belts remain as topographically elevated alluvial ridges located at some distance from the newly active channels and positioned above the water table and this leads to the development of better drained and better developed inceptisols relative to pedotypes of the floodplain region overall both palaeopedogenetic trends demonstrate the overriding controls of topography sedimentation rate and parent material on pedogenesis with only minor climatic influence this work offers a novel pedosedimentary model for distributive fluvial systems and highlights the palaeoenvironmental significance of palaeosol trends providing new constraints for the recognition of distributive fluvial systems in the rock record

infragravity velocity profiles in the surf zone we present a theoretical solution for the vertical structure of the velocity profiles in infragravity waves the solution predicts that while the velocity without local forcing of the infragravity waves does not vary significantly with the vertical coordinate the velocity with local forcing of the infragravity waves has a substantial vertical structure

observations of swash under highly dissipative conditions video measurements of swash were made at the low sloping beach of the multiple bar system at terschelling netherlands the majority of the measurements were conducted under highly dissipative conditions with iribarren numbers 0 the ratio of beach slope to the square root of offshore wave steepness less than 0 2 infragravity 0 004 0 05 hz waves dominated the swash with an average ratio of infragravity and total swash height rig r of 0 85 using linear regression we investigated the dependence of swash parameters on environmental conditions such as short wave height period and local beach slope on average rig was about 30 of the offshore wave height h0 the slope in the linear h0 dependence of rig amounted to only 0 18 considerably smaller than that observed on steeper beaches the data set shows evidence for saturation of the higher infragravity frequencies for 0 less than roughly 0 27 in our opinion this saturation caused the constant of proportionality in the linear relationship between rig h0 and 0 to be significantly larger than that observed under higher iribarren number regimes the saturated tails of the swash spectra had an approximate f 3 roll off where f is frequency whereas in general the nonsaturated parts were white this lack of significant peaks casts doubt on the causality between infragravity waves and nearshore bars

tectonic control on the sequence stratigraphy of nonmarine retroarc foreland basin fills insights from the upper jurassic of central utah u s a abstract continental successions of the north american western interior retroarc foreland basin provide an excellent opportunity to evaluate the tectonic controls on nonmarine sequence stratigraphy the transition between the upper jurassic brushy basin member anastomosed fluvial system of the morrison formation and the gravelly braided river deposits of the buckhorn conglomerate has been studied to assess the dispersal of coarse clastics and the development of associated basin wide unconformities in a sequence stratigraphic framework the sharp contact between the two members is interpreted to be conformable based on stratigraphic sedimentologic and petrologic data collected at and near cedar mountain in central utah while a regional mature paleosol at the top of the buckhorn conglomerate indicates the presence of a major sequence boundary these interpretations are combined with paleoflow data and fluvial architectural analysis to reconstruct the evolution of the alluvial equilibrium profiles that controlled deposition of the succession the buckhorn conglomerate is interpreted as an example of a post orogenic deposit on the basis of 1 its tabular geometry 2 distance from the contemporaneous thrust belt 3 shift to transverse paleoflow direction from the preceding brushy basin axial drainage 4 conformable lower contact and 5 presence of an overlying sequence boundary with a westward expanding hiatus eroding the coeval foredeep the onset of a protracted period of low rate of orthogonal convergence between the farallon and north american plates resulted in tectonic quiescence and consequent isostatic rebound of the middle to late jurassic thrust belt and the contiguous contemporaneous foredeep as well as dynamic uplift the ensuing basin wide decrease in subsidence rate induced the progradation of the buckhorn alluvial plain into the morrison back bulge depozone and the subsequent generation of the overlying pedogenic unconformity which separates the deposits of the jurassic flexural event from the overlying sevier tectonostratigraphic unit

extensional tectonics in the jeanne d arc basin offshore newfoundland implications for the timing of break up between grand banks and iberia

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

the effects of tides on swash statistics on an intermediate beach 1 swash hydrodynamics were investigated on an intermediate beach using runup data obtained from video images under mild near constant offshore wave conditions the presence of a sandbar and the tidally controlled water depth over its crest determined whether most of the incoming waves broke before reaching the shoreline this forced a change in the pattern of wave energy dissipation across the surf zone between low and high tide which was reflected by changes to swash on time scales of a few hours significant runup height rs defined as 4 times the standard deviation of the waterline time series was found to vary by a factor of 2 between low tide when most of the waves were breaking over the sandbar rs hs 1 5 where hs is the offshore significant wave height and high tide when the waves were barely breaking rs hs 2 7 the increase in wave energy dissipation during low tide was also associated with changes in swash maxima distribution a decrease in mean swash period and increasing energy at infragravity frequencies bispectral analysis suggested that this infragravity modulation might have been connected with the presence of secondary waves

distribution morphology and origin of sedimentary furrows in cohesive sediments southampton water patches of sedimentary furrows are developed at several locations in the cohesive estuarine sediments of southampton water water depth 1 12 m these furrows apparently result from short periods of erosion followed by long periods of deposition although all the furrows are similar regularly spaced parallel troughs 0 5 15 m wide aligned with the dominant current furrows in different patches have different characteristics in some areas furrow width is 1 5 1 15 of furrow spacing termed narrow whereas in other areas furrow width is about 1 2 of the spacing termed wide narrow furrows have developed where sediment accumulation rates are greater than 3 6 cm yr 1 wide furrows where accumulation rates are lower cockle shells and other coarse sediments concentrated on the furrow floors and on floors of smaller 2 10 cm wide minifurrows play an important role in furrow formation and evolution as they act to widen the furrows when mobilized during current episodes uniform sedimentation across the profile during slack periods tends to narrow the furrow some of the larger furrows have remained in the same position for 12 years while mini furrows have duration scales of a few months or less well developed furrows are also found in a recently dredged channel bedforms similar to those described here may be preserved in the sedimentary record while no analogues to the larger furrows are presently known minifurrows may be morphologically similar to the gutter casts described from ancient rocks

flexural uplift of rift flanks due to mechanical unloading of the lithosphere during extension we suggest that the uplift of rift flanks results from mechanical unloading of the lithosphere during extension and consequent isostatic rebound this mechanism is presented as an alternative to explanations for rift flank uplift involving thermal or dynamic processes and magmatic thickening of the crust our hypothesis is based on two critical concepts first the lithosphere retains finite mechanical strength or flexural rigidity during extension second isostatic rebound uplift of the lithosphere follows when the kinematics of extension produces a surface topographic depression that is deeper than the level to which the surface of the extended lithosphere would subside assuming local isostatic compensation we develop and analyze two kinematic models for instantaneous extension of the lithosphere to show that flexural rebound is a viable explanation for the uplift of rift flanks we first investigate the isostatic consequences of finite simple slip on an initially planar dipping normal fault cutting the entire lithosphere when the lithosphere retains flexural rigidity during extension the topography resulting from this model resembles a half graben and the footwall rift flank is flexurally uplifted this simple normal faulting model explains free air gravity anomalies and topography observed at rift flanks in oceanic lithosphere such as broken ridge in the eastern indian ocean the caroline ridges sorol trough in the western equatorial pacific and the coriolis trough behind the new hebrides island arc we then investigate a general kinematic model for lithospheric extension where simple slip on a surface of arbitrary shape is accompanied by pure shear extension in the upper and lower plates when the simple slip component is not zero or the distribution of pure shear in the upper and lower plates is not identical the surface of slip can be regarded as a detachment by simplification our general model accounts for pure shear extension of the lithosphere that is uniform with depth in this case detachments have no meaning in the geologic sense however the kinematics of depth independent pure shear may nevertheless be described in terms of a surface which we term a kinematic reference surface at some depth in the lithosphere we speculate that the depth of this surface may be rheologically controlled the magnitude of rift flank uplift by flexure depends critically on the depth of this reference surface in contrast if local isostasy is assumed when the lithosphere undergoes a given amount of depth independent pure shear the resulting topography will be the same regardless of how the kinematics of that extension are formulated the basin and rift flank topography and free air gravity anomaly over young continental rifts such as the rhine graben can be satisfied using our general extensional model with a small amount 5 km of extension along a listric shaped detachment soling into the crust mantle boundary because the flexural rebound mechanism explains the observed topography and gravity anomaly over both oceanic and continental extensional domains we suggest that rheological differences between the two lithospheric types may not be important in their overall response to extension

edge wave trapping and amplification on barred beaches theoretical predictions show that edge waves may be trapped on bars providing a possible mechanism for bar growth simple solutions to the linear shallow water equations reveal that bar trapping is controlled by the depth of the water over the bar hbar and the geometry of the inshore trough relative to the bar for specific geometries amplification over the bar approaches an order of magnitude or more as the phase speed approaches where amplification is defined as the surface displacement over the bar relative to the surface displacement at the shoreline the amplification increases with the cross shore length scales of the profiles the amplification is somewhat frequency dependent generating stronger currents at the location of the bar in specific frequency ranges previous work showed that particular edge wave modes have the correct length scales to generate beach features such as bars and beach cusps but field observations notably shoreline run up data frequently show no evidence of edge wave energy being concentrated at the appropriate frequencies however for bar trapped modes edge wave energy is concentrated at the location of the bar therefore this edge wave energy will not necessarily be evident in shoreline measurements strong correlation exists between the energy distribution of the longshore component of the orbital velocity observed in data collected at superduck october 11 1986 and the distribution expected for a white edge wave spectrum at the shoreline this suggests that bar trapped edge waves exist in particular at incident wave frequencies

shoreface morphodynamics of a high energy steep and geologically constrained shoreline segment in northern ireland abstract the shoreface a complex and poorly understood part of the coastal zone plays a critical role in sediment transport processes between the beach and the inner shelf this two year study examined the surface and subsurface architecture and the process response mechanisms of a high energy steep and geologically constrained shoreface segment 1 20 m depth in northern ireland fourteen sequential bathymetric surveys covering an area of 2 km2 were compared and analysed in order to investigate seabed changes and their relationship to wave and wind forcing results reveal that the shoreface is highly dynamic and complex an examination of high energy conditions and lower than average energy conditions revealed significant periods of both accretion and erosion these complex morphodynamic responses are attributed mainly to a combination of antecedent pre survey morphology differences in wind forcing and coastal surges a comparison of seabed changes over 2 yr reveals net shoreface accretion which is attributed to inner shelf to shoreface sediment transport over the same period the adjacent west strand beach showed moderate erosion the study provides information on the morphodynamics of a steep high energy embayment shoreface a coastal environment which has received little previous attention

combined flow generation of sole structures including recurved groove casts associated with lower carboniferous lacustrine storm deposits in nova scotia canada abstract sole structures are common on bases of sandstone beds in lacustrine shoreline deposits of the horton bluff formation lower carboniferous nova scotia the structures include recurved groove casts the first reported occurrence other curvilinear grooves and opposed prod casts gutter casts and sinusoid like chevron marks are associated with these sole marks but flute casts and other undisputed indicators of unidirectional flow were not noted sole structures and gutter casts are oriented normal to the strike of wave ripple crests and to the elongation direction of hummocky cross stratified lenses inclined strata within the lenses locally show a preferred migration direction parallel to the elongation direction the erosional structures are inferred to have been generated during torms in a shallow lake by oscillatory and or combined flow the latter possibly associated with longshore currents these storms also produced hummocky cross stratification wave formed sole structures may be common in the rock record and can be recognized by curvilinear shapes including rare recurved shapes and bimodal orientations care should be taken when interpreting sole structures from wave influenced settings because they may not indicate directions of net sediment transport or the orientation of unidirectional currents

stress in the indo australian plate cloetingh s and wortel r 1986 stress in the ind austr ian plate in b johnson and a w bally editors intraplate deformation characteristics processes and causes tectonophysics 132 49 67 we modelled the state of stress in the indo australian plate in order to investigate quantitatively variations observed in tectonic style the numerical procedure incorporates the dependence of slab pull and ridge push on the age of the oceanic lithosphere estimates are presented for the average net resistive forces at the himalayan collision zone the suction force acting on the overriding indo australian plate segment at the tonga kermadec trench and the drag at the base of the lithosphere our modelhng shows a concen ation of compressive stresses of the order of 3 5 lcbar in the ninetyeast ridge area the effects of the compressive resistance associated with himalayan collision and subduction of young lithosphere off the northern part of the sunda arc are focused in this region the stress field as calculated gives a consistent explanation for the observed concentration of seismic activity stein and okal 1978 and significant deformation in the oceanic crust weissel et al 1980 mcadoo and sandwell 1985 in the area the calculated stress field in the area adjacent to the southeast and central india ridges is characterized by tension parallel to the spreading axis this explains the concentration of near ridge normal faulting seismicity with t axes subparaile1 to the spreading ridge in the indian ocean as recently observed by bergman et al 1984 and wiens and stein 1984 the regional stress field along the strike of the sunda arc varies from compression seaward of and parallel to the sumatra trench segment to tension perpendicular to the java flores segment this explains the selective occurrence of well developed grabens seaward off the java flores segment of the trench observed by hilde 1983 our modelling shows that the observed rotation of the stress field denham et al 1979 in the australian continent is mainly the consequence of its geographic position relative to the surrounding trench segments and the variations of the forces acting on the down going slab in each of these the state of compression in west and central australia is induced by the action of resistive forces at the himalayan and banda arc collision zones the joint occurrence of high levels of compression in the plate s interior and normal faulting seismicity in the near ridge areas is a transient feature unique to the present dynamic situation of the indo australian plate

bed shear stress coefficients for longshore currents over a barred profile abstract quantitative estimates are obtained of various terms in the momentum equation governing the mean alongshore flow in the surf zone on a barred beach a movable sled was instrumented with pressure current and wind sensors to measure wave and wind forcing during the superduck experiment mean currents and bottom shear stress at various locations across the surf zone were determined particular attention is devoted to precise estimation of the cross shore gradient of the radiation stress wind forcing is found to be a first order term along with wave forcing under certain conditions time dependence of the mean longshore current is due to variable wave forcing inside the surf zone as the tide modulates the depth of waves breaking on the bar bed shear stress coefficients determined as a residual of the local alongshore momentum balance tended to decrease in magnitude shoreward mean bed shear stress coefficients and estimated error are 0 004 0 0013 0 003 0 0006 and 0 001 0 0003 for offshore the bar on top and immediately in front of the bar and in the trough

the behaviour of a multiple bar system in the nearshore zone of terschelling the netherlands 1965 1993 abstract the behaviour of a multiple bar system in the nearshore zone of the island of terschelling the netherlands is investigated on the time scale of years using a data set of soundings the data set covers the period from 1965 to 1993 the behaviour is analysed in terms of bar crest position and in terms of morphometric parameters such as bar crest depth height width and volume two or three breaker bars are permanently present in the study area each individual bar passes through three stages during its existence 1 generation close to the shore 2 seaward migration and 3 degeneration at the outer margin of the nearshore bar zone the key factor controlling the behaviour of the inner bars is the crest depth of the outer bar three different couplings between the behaviour of the individual bars have been observed 1 bar stage changes due to the degeneration of the outer bar 2 prevention of the transition of an inner bar from the first to the second stage caused by the appearance from alongshore of a new outer bar having a small crest depth and 3 difference in mean annual seaward migration rate caused by the possible presence of a more seaward positioned bar it is hypothesized that the crest depth of the outer bar governs the relative importance of processes inducing shoreward and seaward migration in the inner nearshore bar zone and therefore controls the behaviour of the nearshore bar zone on the time scale of years

observations of infragravity waves infragravity wave periods of one half to a few minutes energy levels observed for about 1 year in 8 m water depth in the pacific and in 8 and 13 m depths in the atlantic are highly correlated with energy in the swell frequency band 7 to 20 s periods suggesting the infragravity waves were generated locally by the swell the amplification of infragravity wave energy between 13 and 8 m depth separated by 1 km in the cross shore is about 2 indicating that the observed infragravity motions are dominated by free waves not by group forced bound waves which in theory are amplified by an order of magnitude in energy between the two locations however bound waves are more important for the relatively few cases with very energetic swell when the observed amplification between 13 and 8 m depth of infragravity wave energy was sometimes 3 times greater than expected for free waves bispectra are consistent with increased coupling between infragravity waves and groups of swell and sea for high energy incident waves

wave variance partitioning in the trough of a barred beach the wave induced velocity field in the nearshore is composed of contributions from incident wind waves f 0 05 hz surface infragravity waves f 2 g where fis the frequency 2 f c is the radial alongshore wavenumber 2re l l being the alongshore wavelength is the beach slope and g is the acceleration due to gravity using an alongshore array of current meters located in the trough of a nearshore bar mean depth 1 5 m we investigate the bulk statistical behaviors of these wave bands over a wide range of incident wave conditions the behavior of each contributing wave type is parameterized in terms of commonly measured or easily predicted variables describing the beach profile wind waves and current field over the 10 day period the mean contributions to the total variance of the incident infragravity and shear wave bands were 71 5 14 3 and 13 6 for the alongshore component of flow mean rms oscillations of 44 20 and 19 cm s 1 respectively and 81 9 10 9 and 6 6 for the cross shore component mean rms oscillations of 92 32 and 25 cm s 1 respectively however the values varied considerably the contribution to the alongshore cross shore component of flow ranged from 44 888 4 58 5 95 8 for the incident band to 6 2 26 6 2 5 32 4 for the infragravity band and 3 433 1 0 6 14 3 for the shear wave band incident wave oscillations were limited by depth dependent saturation over the adjacent bar crest and varied only with the fide the infragravity wave rms oscillations on this barred beach are best parameterized by the offshore wave height consistent with previous studies on planar beaches comparison with data from four other beaches of widely differing geometries shows the shoreline infragravity amplitude to be a near constant ratio of the offshore wave height the magnitude of the ratio is found to be dependent on the iribarren number 0 h lo 1 2 shear waves are as previous observation and theory suggest oltman shay et al 1989 bowen and holman 1989 significantly correlated with a prediction of the seaward facing shear of the longshore current

predicting reservoir scale faults with area balance application to growth stratigraphy a reservoir that appears to lack faults at one scale of resolution or at one sampling density may nevertheless contain faults that are below the resolution of the observations the area depth relationship from a balanced cross section is shown to contain the necessary information for predicting the sub resolution fault heave existing area depth theory is extended to include growth units allowing structural length and thickness changes to be separated from the depositional changes the technique is validated with a numerical model of a growth full graben and a sand box model of a half graben then field tested in the gilbertown graben a growth structure within the regional peripheral fault trend along the northern margin of the gulf of mexico a cross section developed from wells alone is used to infer the abundance of sub resolution faults by the area balance technique a small but significant amount of sub resolution extension is predicted and then confirmed with a highresolution seismic line q 2003 elsevier science ltd all rights reserved

pot and gutter casts from the chapel island formation southeast newfoundland abstract member 2 of the chapel island formation of southeast newfoundland contains a diverse suite of erosional structures known as pot and gutter casts these are particularly abundant in a lithofacies deposited in a nearshore zone characterized by erosion and sediment bypass during storm emplacement of sands the steep to overhanging walls of both pot and gutter casts imply rapid filling during the same storm events that created these depressions erosion is thought to have taken place under strong offshore directed unidirectional flow storm surge or other relaxation flow as with many sandstone tempestites the initial stages of the storm events were dominated by strong and in this case highly erosive unidirectional flow and the latter stages by oscillatory flow as evidenced by wave diagnostic lamination in the sandy infills pot casts have geometries and soles indicating vortex flow similar to that which forms potholes in bedrock in glaciated regions gutter casts that lead into potholes do so at their edge a requirement for generating rotary currents within the depression pot casts are commonly tilted relative to paleohorizontal and their direction of plunge is either upcurrent or downcurrent variation in geometry of the erosional structures from the chapel island formation and from erosional structures in general can be accounted for by the following substrate type diagenetic history of substrate and flow parameters such as pattern of water motion velocity and intermittency of flow

longshore current and wave height modulation at tidal frequency inside the surf zone data were acquired continuously during the 19 day delilah nearshore experiment with a specific objective of examining variability of the longshore current at tidal frequencies it is hypothesized that breaking wave heights inside the surf zone are strong functions of the depth which are modulated by the tidal variations and since radiation stress is a function of the wave height longshore currents are forced at the tidal frequency inside the surf zone the measured longshore current variations at tidal frequency are the same order of magnitude as the mean longshore current variations for moderate wave height conditions indicating that the tide is a dominant mechanism associated with longshore current variability simulations of the magnitude and phase of the longshore current variability with tide elevation using the model by thornton and guza 1986 are used to explain observations the measured tidal elevation and longshore current are in phase in the inner surf zone and out of phase in the outer surf zone as predicted by the model verifying the hypothesis

energy saturation and phase speeds measured on a natural beach field measurements of wave height and speed from 7 m depth shoreward are described the experiment plan consisted of a shore normal transect of closely spaced compared to a dominant wave length velocity pressure and elevation sensors on an almost plane profile having an inshore slope of 1 50 as the waves shoal and begin to break the dominant dissipative mechanism is due to turbulence generated at the crest and wave heights become increasingly depth controlled as they progress across the surf zone wave heights in the inner surf zone are strongly depth independent the envelope of the wave heights is described by h sub rms 0 42 h the depth dependence of the breaking wave height is shown to be related to the kinematic instability criterion celerity spectra were measured by using phase spectra calculated between pairs of adjacent sensors inshore of 4 m depth the celerity was found distant over the energetic region of the spectrum a mean celerity was compared with linear theory and was within 20 and 10 showing good agreement for such a nonlinear dissipative region

the vertical structure of low frequency motions in the nearshore part i observations abstractfield observations of oscillating currents in the surfzone of a natural beach show significant vertical structure in energy phase and rotation at low frequencies around 0 005 hz where most of the energy is associated with vorticity motions energy levels in the cross shore component of the flow seaward of the sandbar decay near the bottom shoreward of the bar crest the flow decays nearly linearly over the water column conversely a weaker alongshore component of the flow increases near the bottom seaward of the sandbar and is roughly depth uniform inside the bar crest near this 0 005 hz frequency band the coherence between the uppermost and successive vertically separated sensors drops off quickly with as much as a 70 80 coherence drop over the water column ranging from 2 5 to 4 m the phase relative to the uppermost sensor shifts approximately linearly over depth with as much as 50 phase lag at the bottom that can lag or lead the surface rotary coefficients also vary across the su

morphodynamics of a bar trough surf zone abstract a field study was made of the distinguishing morphodynamic processes operating in a surf zone which perennially exhibits accentuated bar trough topography the longshore bar trough and rhytmic bar and beach states as described by wright and short 1984 characteristic features of the morphology include a shallow bar with a steep shoreward face a deep trough and a steep beach face this morphology which is favored by moderate breaker heights and small tidal ranges strongly controls the coupled suite of hydrodynamic processes in contrast to fully dissipative surf zones the bar trough surf zone is not at all saturated and oscillations at incident wave frequency remain dominant from the break point to the subaerial beach the degree of incident wave groupiness does not change appreciably across the surf zone infragravity standing waves which in dissipative surf zones dominate the inshore energy remain energetically secondary and occur at higher frequencies in the bar trough surf zone analyses of the field data combined with numerical simulations of leaky mode and edge wave nodal antinodal positions over observed surf zone profiles indicate that the frequencies which prevail are favored by the resonant condition of antinodes over the bar and nodes in the trough standing waves which would have nodes over the bar are suppressed sediment resuspension in the surf zone appears to be largely attributable to the incident waves which are the main source of bed shear stress in addition the extra near bottom eddy viscosity provided by the reformed non breaking waves traversing the trough significantly affects the vertical velocity profile of the longshore current whereas the bar is highly mobile in terms of onshore offshore migration rates the beach face and inner regions of the trough are remarkably stable over time

barrier island evolution middle atlantic shelf u s a part i shoreface dynamics abstract in part i of this paper near bottom fluid velocity and sediment concentration measurements from the shoreface of a middle atlantic barrier long island coast are analyzed to provide insight into the dynamics of erosional shoreface retreat in part ii these data are combined with observations of coastal stratigraphy in order to construct a model for the evolution and behavior of middle atlantic barriers wave motions on the long island shoreface tend to drive sediment onshore calculations of the onshore sediment flux driven by asymmetrical shoaling waves show that for the wave states commonly encountered on the middle atlantic shelf values become strongly positive landward of approximately 10 m water depth upper shoreface but drop to very low values shortly seaward of that isobath on the lower shoreface and inner shelf floor fair weather wave current interaction tends to cause a landward creep of sediment even though the wave orbital component of the near bottom velocity field is nearly symmetrical this movement occurs because the wave approach direction generally lies within 90 of the direction up coast or down coast of the alongshore wind driven current therefore fluid shear stress acting on the sediments tends to be reinforced during the shoreward stroke of the wave orbital motion and partially cancelled during the seaward stroke during major storms the rate of sediment transport increases by at least an order of magnitude and the role of wind driven currents becomes important much more sediment is resuspended by the wave orbital current component because storm waves are more powerful than fair weather swells but the wind driven flow component is also much stronger and is now available for transporting the resuspended sediment storm flows over the shoreface occur in distinct dynamic zones surf zone friction dominated zone transition zone geostrophic zone the zones are defined by dynamical considerations and expand or contract with the intensity of the causative wind stress during peak flow events the characteristic length scales of the friction dominated and geostrophic zones tend to correspond with the morphologic zones of the shoreface and inner shelf the storm intensified wind driven alongshore flows of the lower shoreface are frequently jet like in nature and may be upwelling or downwelling wind driven coastal flows with a strong downwelling component occur during most storms on the long island coast and are particularly important to the coastal sand budget during these events sand is entrained by the storm intensified upper shoreface circulation system of wave driven alongshore currents and rip currents and is fed into the main wind driven coastal current because of the offshore component of bottom flow sand is swept down the lower shoreface and onto the adjacent inner shelf fair weather processes may be unable to return storm deposited sand to the beach from such an offshore position the shoreface transport regime of the long island barrier coast thus consists of long periods of time months during which sand moves slowly toward the beach punctuated by short intense periods hours or days during which sand is transferred from the shoreface to the adjacent inner shelf the long term sense of movement of the shoreface whether retreating the long island case or prograding must depend on the loss or gain of sand by shoreface with respect to the inner shelf the data shows that the coastal sand budget is controlled not only by the upper shoreface cycle withdrawl of sand from the beach prism storage in the breakpoint bar and its subsequent return to the beach but by a cycle of larger spatial and temporal scale in which sand is exchanged between the shoreface as a whole and the adjacent inner shelf

laurentide glaciation in west central alberta a single late wisconsinan event the grande prairie region in west central alberta shows evidence of late wisconsinan laurentide glaciation in the form of a widespread till containing abundant erratic clasts derived from the canadian shield two sections located on the smoky river at watino and on the simonette river 80 km to the southwest expose sediment lying stratigraphically below the till a similar sequence is exposed in both localities 5 10 m of coarse quartzite gravel overlain by a thick sequence of sand and silt the gravel contains no laurentide erratics and is thus preglacial the contact between the basal gravel and the overlying sand and silt is sharp and conformable 14c dates from the base of the simonette section and throughout the watino section suggest a middle wisconsinan age thus the sediment exposed is interpreted as a conformable middle wisconsinan sequence the sedimentary sequences were deposited in a moderate to low energy braided stream system flowing towards the north the general fining up trend in the

field observations of shear waves in the surf zone 1 alongshore propagating meanders of the mean alongshore current in the surf zone called shear waves have periods of a few minutes and wavelengths of a few hundred meters here shear wave properties are estimated with arrays of current meters deployed for 4 months within 300 m of the shoreline of a sandy beach shear wave velocity fluctuations are approximately horizontally isotropic with root mean square values between 10 and 40 of the mean 3 hour averaged alongshore current v cross shore variations of the time averaged shear wave momentum flux are consistent with shear wave energy generation close to shore where the breaking wave driven mean alongshore current v and current shear vx are strong and with shear wave energy dissipation and transfer back to the mean flow farther offshore where v and vx are weak in case studies where v is a narrow jet near the shoreline the observed strong decay of shear wave energy levels seaward of the jet and the cross shore and alongshore structure of shear waves within the jet are similar to predictions based on the linearly unstable modes of the observed v shear wave energy levels also are high in a marginally unstable case with a strong but weakly sheared v

boundary layer dynamics and sediment transport under storm and non storm conditions on the scotian shelf abstract near bed measurements of waves currents seabed responses and ripple migration rates were obtained using an instrumented tripod at a water depth of 39 m on the scotian shelf during the winter of 1992 93 these data and the grant and madsen s 1986 grant w d madsen o s 1986 the continental shelf bottom boundary layer annu rev fluid mech 18 265 305 combined flow boundary layer model are used to examine wave current interaction various sediment dynamic thresholds and sediment transport on an exposed high energy continental shelf the seabed was found to be rippled for most time of the deployment and thus the ripple enhanced combined skin friction shear velocity had to be used to determine the initiation of bedload transport under combined flows this indirectly indicates adequate predictions of the skin friction shear velocities inside the wave boundary layer by the grant and madsen model at high transport stages bedload roughness must be added to the grain size roughness to obtain a transportrelated combined shear velocity in order to predict correctly the onsets of saltation suspension and sheet flow transports otherwise the initiation of suspended load transport and the total sediment transport rates will be severely under estimated the comparison between the prediction by the grant and madsen 1986 model and the calculation of a quadratic stress law suggests that the total current shear velocity was enhanced by a factor of 2 3 due to the wave current interaction during storms while the apparent bottom roughness was increased by more than an order of magnitude the non linear coupling between waves and currents also causes a 20 increase of the combined skinfriction shear velocity inside the wave boundary layer this non linear coupling is most important when waves and currents are roughly equal in magnitude and the angles between them are less than 30 four sediment transport formulae were tested while the engelund hansen total load and yalin bedload methods did not perform well the einstein brown and bagnold formulae were found to respectively give reasonable predictions of the bedload and total load sediment transport rates under the observed combined flow conditions the predicted sediment transport direction is also in good agreement with the observed ripple migration direction the gsc sediment transport model sedtrans92 predicts that the net daily transport rates during the storms reached 822 kg m 1 day 1 and were 2 3 orders of magnitude higher than the non storm transport suggesting the dominance of storm processes in sediment transport on the scotian shelf these values are in good agreement with the results from sand tracer experiments conducted in this region we thus conclude that sedtrans92 can properly simulate boundary layer dynamics and sediment transport on continental shelves

field observations of surf beat 1 progressive edge waves nineteen biaxial electromagnetic current meters have been used to determine the longshore and on offshore structure of currents at surf beat periods 1 4 min the sensors formed two linear arrays a long shore array within the surf zone and an on offshore array stretching from the shoreline to well beyond the breaker line analysis of the longshore current components yields a clear picture of progressive low mode edge waves with frequency wave number dispersion relations which are in remarkably good agreement with predictions some separation of edge wave modes is found with mode zero energy dominating in the frequency band 0 006 and 0 011 hz and mode one between 0 015 and 0 025 hz on offshore currents present a rather different picture which while not inconsistent with the longshore currents suggests that other sources of energy are also important to the on offshore currents these include standing edge waves probably formed by reflections at nearby scripps canyon and motions which are nonresonantly forced by incoming wave groups

surf zone longshore currents and random waves field data and models abstract analytic and numerical models for longshore currents generated by obliquely incident random waves am compared with field observations five days of observations were selected during which the waves were narrow banded in both frequency and direction in keeping with model assumptions the extensive measurements included radiation stress and wave directional spectra in 9 m depth and a closely spaced array of current and pressure sensors on a line perpendicular to shore the longshore current models are based on balancing the gradient of the radiation stress with the alongshore bed shear and reynold s stresses assuming stationary wave conditions and straight and parallel bottom contours the spatial variation of wave height required to determine the gradient of the radiation stress is modeled using linear random wave theory given hrms in 9 m depth the model predicts hrms at shoreward locations with an average error of less than 9 using a nonlinear bottom shear stress formulation and the meas

geometry migration and evolution of wave orbital ripples at leo 15 observations of the temporal evolution of the geometric properties and migration of wave formed ripples are analyzed in terms of measured suspended sand profiles and water velocity measurements six weeks of bedform observations were taken at the sandy medium to coarse sized sand leo 15 site located on beach haven ridge during the late summer of 1995 with an autonomous rotary sidescan sonar during this period six tropical storms several of hurricane strength passed to the east of the study site ripples with wavelengths of up to 100 cm and with 15 cm amplitudes were observed the predominant ripples were found to be wave orbital scale ripples with ripple wavelengths equal to 3 4 of the wave orbital diameter although orbital diameters become larger than 130 cm during the maximum wave event it is unclear if a transition to non orbital scaling is occurring ripple migration is found to be directed primarily onshore at rates of up to 80 cm day suspended transport due to wave motions calculated by multiplying acoustic backscatter measurements of suspended sand concentrations by flow velocity measurements are unable to account for a sufficient amount of sand transport to force ripple migration and are in the opposite direction to ripple migration thus it is hypothesized that the onshore ripple migration is due to unobserved bedload transport or near bottom suspended transport bedload model calculations forced with measured wave velocities are able to predict the magnitude and direction of transport consistent with observed ripple migration rates sequences of ripple pattern temporal evolution are examined showing mechanisms for ripple directional change in response to changing wave direction as well as ripple wavelength adjustment and erosion due to changing wave orbital diameter and relative wave to current velocities

a numerical simulation of fabric development in polycrystalline aggregates with one slip system abstract fabric development and grain deformation behaviour in polycrystalline aggregrates involving one slip system have been numerically simulated the model allows inhomogeneous deformation while still ensuring strain compatibility and overall stress equilibrium two types of inhomogeneous deformation occur in deformed polycrystals inter grain strain inhomogeneity results from the contrasting deformability of neighbouring grains which is dominantly determined by the corresponding initial slip plane orientation intra grain strain inhomogeneity arises because of the need to achieve strain compatibility across grain boundaries grain boundaries are generally the places where strain compromise is reached between neighbouring grains various microstructures are developed in deformed polycrystals the development of kink subgrain structures a special type of subgrain observed in this model is closely controlled by initial lattice orientation the pattern of preferred orientations of slip planes is sensitive to strain history in contrast the preferred orientations of longer axes of deformed grains or passive plates in a deforming ductile medium are always parallel to the bulk extension direction not showing any relevance to deformation history

the quaternary sediments of banquereau scotian shelf the acoustic stratigraphy of quaternary sediments on banquereau scotian shelf interpreted from regional and site survey seismic lines is correlated with sedimentary units determined from undisturbed borehole samples the informal litho stratigraphic formations of the quaternary sequence on the scotian shelf are subdivided into members and litho chronozones diagnostic of depositional environments a late wisconsinan glacial advance dated by c 14 analysis of shell material took place ca 18 000 to 26 000 yr b p it formed a widespread gravel rich unit barren of fauna and capped by an erosional surface the unit occurs within stratified pro glacial marine sediments known locally as the emerald silt formation the minimum stand of sea level 110 m below present sea level occurred ca 14 000 yr b p and is confirmed by the presence of channel deposits at the top of the pleistocene section a marine transgression across banquereau took place ca 8 000 yr b p and is defined by a widespread erosion surface at the base of the holocene section this section known locally as the sable island sand and gravel formation comprises as much as 40 m of reworked sand which is divided into 3 members diagnostic of sand ridge generation eastern shoal an offshore storm ridge situated on banquereau was formed during holocene time created by modern day storm driven and tidal currents the intensity of these currents is the result of water mass acceleration over the shallow banks of the scotian shelf eastern shoal appears to have moved 30 km across the continental shelf at a rate of 3 5 m yr the regional setting of this sand body is similar to that postulated for the shannon and tocito sandstones of the western interior of the united states and shows that sand transport and large scale ridge development can take place in a shelf edge setting on present day storm dominated continental shelves

bar trapped edge waves and longshore currents edge waves react to the presence of a mean longshore current as though the current was a change in bottom topography in this way the cross shore shape of the edge wave can be amplified over the current relative to the shoreline in the same way as the edge wave shape can be amplified over bars on a beach with both longshore currents and bars the degree of edge wave amplification or trapping depends on the strength and location of the longshore current shear relative to the steepness of the bottom slope and also on the direction of edge wave propagation relative to the longshore current weak longshore current shear over well developed bars does not significantly alter edge wave trapping over bars simply enhancing or reducing the existing bar trapping effect conversely strong current shears over gentle topography can govern the existence and location of edge wave trapping the extreme example being edge wave trapping on plane beaches where the amplification is entirely due to the existence of mean longshore currents in reality the possibilities are restricted since the shape of the longshore current profile is primarily determined by the pattern of incident wave breaking which itself depends on the beach profile the importance of realistic current shear relative to realistic bottom slope in determining edge wave shape is demonstrated using frequency wavenumber spectra taken during the duck experiment on low frequency and incident band longshore and across shore hydrodynamics delilah at duck north carolina these frequency wavenumber spectra show a general dominance of edge waves traveling with the longshore current in cases where the current shear is strong relative to the bottom slope the location of edge wave trapping changes as the longshore current profile changes with the tide when the bar was well defined the longshore current shear was rarely strong enough to influence the existence or location of edge wave trapping but could have a enhancing effect while past work i e schonfeldt 1995 has suggested that edge waves trapped and amplified on longshore currents may cause bars to form on plane beaches and bars to move on barred beaches these observations suggest that under most conditions edge wave trapping on longshore currents is a subtle effect modulated by sea level changes and is unlikely to produce significant morphological change unless the current is very strong

the role of small scale extensional faulting in the evolution of basin geometries an example from the late palaeozoic petrel sub basin northwest australia abstract during continental extension the kinematic collapse of the hangingwall of major normal faults and the subsequent isostatic response imposes a strong control on the evolving basin geometry the interaction of the flexural wavelength and the magnitude and location of faults may allow the development of basin geometries which deviate from a classic half graben style particularly if some of this deformation is below the scale of observation commonly seismic reflection data in particular the development of a lateral partitioning between large and small scale faults within a basin may exert a significant control on the resulting basin geometry using the petrel sub basin in northwest australia as an example it is demonstrated that an extensional basin geometry consisting of a classic half graben can be overprinted by a significant sag geometry which can be related to the lateral offset of sub resolution faulting this lateral partitioning and resulting basin geometry may also have an application to other extensional basins particularly if a mechanism is present to allow this partitioning of fault styles to develop in the petrel sub basin this has been related to the presence of older basement features of the halls creek mobile zone beneath the axis of the basin however a comparison with physical models also suggests that this may be applicable to basins formed by oblique rifting a component of which may also be present within the petrel sub basin particularly if this is imposed upon a weak zone or suture within the upper mantle

on predicting infragravity energy in the surf zone flow data were obtained in the surf zone across a barred profile during a storm rms cross shore velocities due to waves in the infragravity band wave periods greater than 20 s had maxima in excess of 0 5 m s over the bar crest for comparison to measured spectra synthetic spectra of cross shore flow were computed using measured nearshore profiles the synthetic spectra were calculated assuming a white runup spectrum of mode 4 edge waves of unit amplitude although the results would be essentially the same for standing waves or any edge wave mode above 2 the structure in the infragravity band of these synthetic spectra corresponded reasonably well with the structure of the measured spectra total variances of measured cross shore flow within the infragravity band were nondimensionalized by dividing by total infragravity variances of synthetic spectra these nondimensional variances were independent of distance offshore and increased with the square of the breaker height thus cross shore flow due to infragravity waves can be estimated with knowledge of the nearshore profile and incident wave conditions

the sedimentary record of carboniferous rivers continuing influence of land plant evolution on alluvial processes and palaeozoic ecosystems abstract evidence from modern rivers and the deep time geological record attests to the fundamental importance of plant life for the construction of physical habitats within fluvial environments data from an extensive literature review and original fieldwork demonstrates that many landforms and geomorphic features of modern river systems appear in the palaeozoic stratigraphic record once terrestrial vegetation had adopted certain evolutionary advances for example stable point bars are associated with the onset of rooted plants in the siluro devonian and avulsive and anabranching fluvial systems become common at the same time as extensive arborescent vegetation in the carboniferous in this paper we demonstrate a correlation between the diversification of physical fluvial environments and the expansion of terrestrial fauna and flora with an emphasis on the culmination of these trends within carboniferous alluvial systems many extrinsic factors have been considered as possible controls on the evolutionary timelines of terrestrialization for organisms however a fundamental prerequisite for achieving terrestrial biodiversity was the variety of physical habitats especially riparian systems available for newly evolved organisms in association with abundant lowland meandering systems the widespread appearance across carboniferous alluvial plains of fixed channel and anabranching reaches created further physical landforms for colonization and would have promoted increasingly complex hyporheic flow regimes furthermore the associated increase in arborescent vegetation and supply of large woody debris to inland and coastal rivers would have created a wealth of microhabitats for continental organisms we argue that the expanding extent and diversity of physical alluvial niches during the palaeozoic is an underappreciated driver of the terrestrialization of early continental life the study of the deep time fossil and stratigraphic record also illustrates that vegetation is a fundamental prerequisite for the creation of biogeomorphic alluvial landforms and physical habitats and microhabitats

setup and swash on a natural beach wave setup and swash statistics were calculated from 154 runup time series measured on a moderately steep beach under incident waves varying from 0 4 to 4 0 m significant wave height when scaled by the incident wave height setup swash height and total runup the sum of setup and half the swash height were found to vary linearly with the surf zone similarity parameter 0 h0 l0 1 2 the foreshore slope appeared the appropriate value for the calculation of 0 although the setup data showed some influence of an offshore bar at low tide for low irribaren numbers the swash height in the incident frequency band becomes saturated while for high irribaren numbers no such signs of saturations were seen thus the infragravity band appears to become dominant in the swash below some value of 0 for these data that value is approximately 1 75 although there is considerable scatter associated with that estimate

evidence of across shelf transport of fine grained sediments turbidite filled shelf channels in the campanian aberdeen member book cliffs utah usa the shore normal transport of fine grained sediments by shelf turbidity currents has been the focus of intense debate over the last 20 years many have argued that turbidity currents are unlikely to be a major depositional agent on the shelf however sedimentological architectural stratigraphic and palaeogeographic data from the campanian aberdeen member book cliffs eastern utah suggests otherwise and clearly demonstrates that storm generated and river flood generated underflows can transport a significant volume of fine grained sediments across the shelf these across shelf flowing turbidity currents cut large subaqueous channel complexes up to 7 m deep tens of kilometres basinward of their time equivalent shoreface the shelf channels were filled with organic rich siltstones mudstones and very fine to fine grained bouma like sandstone beds including wave modified turbidites hyperpycnites and classical turbidites deposition was above storm wave base palaeocurrent data reveal an overwhelmingly dominant across shelf east south east offshore directed transport trend tectonic activity and or concomitant palaeogeographic reorganization of the basin may favour the generation of these turbidite rich shelf deposits by altering the relative balance of wave versus fluvial energy increased erosion and sediment supply rates because of tectonic uplift of the hinterland may have increased the probability of fluvial dominance along the coastline and hence the possibility of submarine channelization in front of the river mouths additionally the coastline may have become more sheltered from direct wave energy thus allowing the fluvial processes to dominate seasonal increases in rainfall and storm activity may also favour the generation of across shelf underflows on wave dominated shorelines isolated shelf channels and lobes are most likely to be found down dip of fluvial feeder systems in relatively high sediment supply settings these features are also most likely to occur in systems tracts that straddle a sequence boundary especially those which are tectonically generated as these would enhance the potential for altering basin morphology and hence the balance of fluvial and wave energy isolated shelf channels are recognized in older and younger strata in the book cliffs region implying that wave supported gravity flows were a recurrent phenomena in the campanian of utah it is probable that isolated shelf bodies are preserved in other stratigraphic intervals in the cretaceous western interior of north america and other basins worldwide and are currently being overlooked or misidentified shoreface to shelf facies models should be revised to incorporate turbidite rich shelf deposits in some shelf settings

bypass zone tempestite facies model and proximality trends for an ancient muddy shoreline and shelf member 2 of the late precambrian to lower cambrian chapel island formation of southeast newfoundland was primarily deposited in storm influenced nearshore and shelf environments along a fine grained coastline deposition took place within or adjacent to a deltaic system that supplied abundant silts and clays thin bedded graded sandstone beds hummocky cross stratified beds and a variety of very thin conglomerate units contain evidence for deposition by storm currents sedimentological and stratigraphic evidence is used to reconstruct the relative paleobathymetric position of the three major facies in member 2 the gutter cast facies is a shallow subtidal deposit characterized by very thin sandstone laminae and abundant pot and gutter casts the siltstone dominated facies contains more laterally extensive thin bedded sandstones and fewer erosional features and was deposited in the inner shelf the sandstone dominated facies consists of thin to medium graded and hummocky cross stratified sandstone beds deposited in a more distal shelf setting but above storm wave base the facies model and set of proximality trends developed for member 2 deposits may be applicable to other storm influenced fine grained shorelines in this model the shallow subtidal is a zone of throughput with high velocity sediment laden flows eroding deep narrow scours gutter casts and depositing very little sand outside of these scours as the storm generated flows move into deeper water they decelerate resulting in less erosion of the sea floor and depositing thicker and more continuous sand beds siltstone dominated facies further from shore bed thickness reaches a maximum sandstone dominated facies and hummocky crossstratification is abundant even more distally bed thickness decreases again represented by thinly laminated siltstones of the overlying member 3 analysis of sedimentary structures and paleocurrent data suggests deposition by storm currents that transported sediment nearly perpendicular to shore

evolution of infragravity variance during a storm data from an alongshore array of bidirectional current meters located in the surf zone were analyzed to provide estimates of the behavior of three bands of wave energy during the passage of a moderate storm the variance in the incident wave band is found to be saturated as is expected of depth limited waves the infragravity band variance is found to depend most strongly on the offshore wave height shear wave variance is found to be correlated with the magnitude of the measured longshore current during a period of nearly constant high waves the composition of the low frequency band motions f 0 05 hz changed dramatically this change is thought to be related to the directional characteristics of the incident band wind waves

alluvial channel bank collapse phenomena in the old red sandstone hitra group western central norway the old red sandstone ors on the island of hitra forms an approximately 1350 m thick succession of alternating continental mudstones sandstones and conglomerates of possibly latest silurian to devonian age within the middle part of this succession just above a major scoured surface a spectacular slump feature was observed the phenomenon is interpreted as a unit of overbank channel bank mudstones which because of undercutting and liquidization caved into a low sinuosity river channel the hitra sequence is the only one in the norwegian ors where such phenomena have as yet been identified

the quaternary stratigraphy of southwest sable island bank eastern canada three boreholes ten vibrocores and high resolution seismic reflection records were analyzed to reconstruct the stratigraphy of the topmost 50 m of the sedimentary column of southwest sable island bank the sequence is complex owing to the effects of two low stands of sea level two periods of ice influence and two periods of open water during the past 40 000 yr a low stand at 98 m occurred at 28 000 to 32 000 yr b p a second low stand occurred at 110 m between 13 000 and 15 000 yr b p ice covered the region prior to 32 000 yr b p and from 11 000 to 10 000 yr b p open water prevailed at other times the sequence of sediments follows the formational subdivision of king and the member subdivision of amos and knoll the sable island sand and gravel formation is subdivided into three members trough bedded sand cross bedded sand and conformably bedded sand the conformably bedded sand formed under heavy sea ice and represents the younger dryas event the uppermost two members result from shelf sediment reworking the emerald silt formation is subdivided into four members channel gravel upper stratified sand fines barren gravelly sand and lower stratified sand fines and two regional discontinuities r1 and r2 the coarser grained facies of the channel gravel and barren gravelly sand members are the result of reworking during late and mid wisconsinan transgressions of sable island bank the upper stratified sand fines member is interpreted as an open water marine deposit formed during the scotian stade the lower stratified sand fines member is interpreted as a glacio marine deposit formed during the digby stade

predicting ripple roughness and sand resuspension under combined flows in a shoreface environment ripple measurements and flow and sediment dynamical data obtained from the shoreface of the middle atlantic bight using instrumented tripods were analyzed to evaluate various predictors of ripple geometry and roughness ripple roughness controls on sand resuspension and suspended sediment concentration profiles under combined waves and currents were also evaluated the limited observation of sand ripples in the field indicates that the grant and madsen 1982 method overestimates ripple roughness while the nielsen 1981 method tends to under predict ripple roughness a modified ripple predictor is thus proposed based on the grant and madsen method and it is shown to give reasonable predictions under the present experiment conditions this modified ripple prediction along with wave current and suspended sediment concentration data recorded by the tripods were then brought into the combined flow bottom boundary layer model of grant and madsen 1986 and the modified rouse equation of glenn and grant 1987 to calculate sand resuspension coefficient 0 and to predict suspended sediment concentration profiles it was found that under low energy fair weather conditions sand ripples are in the equilibrium range and ripple roughness increases with the bed shear stress this causes strong vortex activity close to seabed and thus higher resuspension coefficient reference concentrations are moderate due to this high resuspension coefficient even though bed shear stresses are low under moderate storm conditions ripple break off occurs and ripple roughness will decrease with bed shear stress this reduces the vortex activity and hence sand resuspension coefficient 0 the combination of this moderately high bed shear stress and reduced but still moderate ripple roughness favours sand suspension and produces the highest reference concentration for the encountered experimental conditions as bed shear stress is further increased ripples are nearly washed out and sand resuspension coefficient is further decreased approaching the previously suggested constant value of 1 3 10 4 this corresponds with the lowest reference concentration despite the high bed shear stress suspended sediment concentrations predicted by the modified rouse equation using this time variable resuspension coefficient and properly calculated bottom boundary layer parameters are reasonable compared to the field measured concentration profiles

pot and gutter casts from the chapel island formation southeast newfoundland discussion and reply myrow has recently presented a case for pot and gutter casts produced by erosion under unidirectional flow most pot and gutter casts are considered to be storm generated features initially under strong offshore directed unidirectional flow the currents that produce the structures are related to nearshore marine setting where sediment by passes proximal area and where erosion is the dominant process pot and gutter casts are recognised from a wide range of environments from tidal flat to submarine fan it should be noted that linear erosional structures which have been given various names such as linear scours longitudinal furrows but falling under the general umbrella term of gutter casts are also known in ancient fluvial deposits

multibeam bathymetric investigations of the morphology of sand ridges and associated bedforms and their relation to storm processes sable island bank scotian shelf abstract storm formed sand ridges are important morphologic features occurring on many continental shelves of the world our understanding of the morphology migration and the controlling processes over this type of sand ridges under different environmental settings is still limited in the present study an integrated approach of combining multibeam bathymetry survey seabed sampling sidescan seismic surveys and seabed instrumentation measurements was used to characterize the surficial geology and morphology of offshore sand ridges on sable island bank scotian shelf and to evaluate the relationship between sand ridge morphology migration and the storm processes on this storm dominated outer shelf bank multibeam data obtained at selected sites demonstrated the series of ne sw oriented sand ridges with an average height of 4 3 m and wavelength of 1 5 km sand ridges attain maximum spacing height and steepness in the intermediate depths sand ridge size and steepness also decrease from west to east and this decrease is correlated with decreasing dynamic condition sediment grain size and depth sand ridge profiles show weak easterly asymmetry this morphological asymmetry augments the sediment texture and grain size asymmetry to suggest eastward long term sand ridge migration and net sediment transport in the study area sand ridge asymmetry also shows strong local variation and the number of sand ridges asymmetric to the west is nearly equal to that asymmetric to the east the likely cause is the nearly equal number of major storms passing to the south versus to the north of the island so that the westerly and easterly peak storm driven currents associated with these storm path scenarios affect equally the sand ridges on sable island bank a suite of smaller bedforms were found superimposed on the sand ridges sand waves widely superimposed on both flanks of sand ridges mixed 2d and 3d megaripples commonly occurring in the sand ridge troughs and on the lower western flanks and large wave ripples ubiquitously found in the troughs of all megaripples surficial sediment is coarsest coarse sand with shell fragments in the sand ridge trough and becomes progressively finer eastward toward the sand ridge crest and down the eastern flank while best sorting occurs near the sand ridge crest box cores collected across sand ridges reveal characteristic storm event bed structure that reflects the development and migration of bedforms with the evolution of storms