a note on the amount of wave energy transmitted over nearshore sand bars the wave energy loss as waves break on nearshore bars is an important geomorphological process as it controls the stability of the adjacent beaches and dunes the effect is particularly important during storms as it serves to guard against severe shoreline erosion field measurements from florida and ireland of waves crossing both single and multiple bar bedforms indicate that where bar breaking occurs between 78 and 99 per cent of wave energy may be dissipated from individual waves however a further 20 per cent energy may reach the shore if wave frequencies increase during the reformation process this latter effect was not noted at the multiple bar site where spilling mode breakers dominate the level of energy dissipation is related to the time taken to cross that section of the submerged bar below the critical depth d 1 28h in the field this may be approximated by the ratio of wave speed to the width of the bar breaker zone

eolian dune interdune sand sheet and siliciclastic sabkha sediments of an offshore prograding sand sea dhahran area saudi arabia an offshore prograding sand sea exists along portions of the arabian gulf coastline near dhahran saudi arabia in this region sediments of eolian dune interdune sand sheet and siliciclastic sabkha intercalate with marine deposits this depositional setting is characterized by strong offshore winds which supply abundant sand to the coastline and cause at present time the outbuilding of the dune system this quartz detrital dominant setting contrasts markedly with the carbonate dominant setting resulting from onshore winds in the trucial coast area to the south the broad intercalation of eolian and marine deposits which results creates ideal potential for subregional stratigraphic petroleum traps due to pinch out of porous and permeable dune sands into impermeable m rine mudstones within the eolian system itself are potential reservoir rocks dunes sources organic rich sabkha and interdune deposits and seals zones of early cementation in all deposits early cementation is very common in all facies of the eolian sand sea the early cementation occurs owing to 1 soil formation 2 deposition of pore filling gypsiferous cements from saturated solutions near water table and 3 addition of sand size windblown evaporitic material to sands downwind of sabkhas

clustering of fracture orientations using a mixed bingham distribution and its application to paleostress analysis from dike or vein orientations abstract the clustering and classification of fracture orientations are important in rock mechanics and in brittle tectonics the latter of which includes the paleostress analysis of extension fractures hosting dikes or mineral veins here we present an unsupervised clustering method for the orientations of extension fractures using mixed bingham distributions the method not only detects the elliptical clusters and girdles made by the poles to such planar features but also determines the appropriate number of those groups by means of bayesian information criterion bic without a priori information the method was tested with artificial data sets and successfully detected the assumed groups when the clusters had little overlaps however clusters with the common maximum concentration orientation and large aspect ratios were distinguished provided that their minimum concentration orientations were separated by a large angle our method separated two stress states from natural data from a miocene dike swarm in sw japan the method also evaluated the probabilities of the stresses to form each of the dike

upper flow regime mud floodplains lower flow regime sand channels sediment transport and deposition in a drylands mud aggregate river abstract dryland rivers in which fine sediments travel as aggregates are increasingly recognized in modern and ancient fluvial systems fowlers creek australia is an ephemeral dryland mud aggregate river whose sediments provide insights into the dynamics of mud aggregate floodplains the origin of massive mudrocks from arid depositional environments and the nature of planar bedding fowlers creek s flow conditions were inferred from relationships between landforms and the sediment texture bedforms and sedimentary structures remaming after flow ceases floodplain muds consisting of fine sand and sand size mud aggregates are distributed over the floodplain in suspension as flow decelerates they are deposited as bedload the shallow depth high sediment load and low aggregate particle density promote flow conditions ranging from high in the lower flow regime to upper flow regime producing coexisting ripples scours flat beds and clay layers with time visible signs of aggregate structure are lost leaving a massive cohesive mud consolidation is not achieved by burial aggregates reappear when muds reenter fluvial transport in unchanneled reaches sheetflows deposit sediment with a pervasive horizontal fabric channel sediments coarse sands and gravels are a minor component of fowlers creek s deposits widespread lower flow regime conditions produce planar beds and 2 d dunes usually deposited without internal stratification or in horizontal laminae lower flow regime planar bedding is also observed in fine silty sands near the close of flow rapid shallowing may move channel conditions from lower to upper flow regime or from lower to higher positions in the lower flow regime bedform stability spectrum leading to unusual bedform associations in the rock record sediments from a river like fowlers creek would be characterized by structureless gravelly sands channel facies massive red mudstones floodplain facies and sediments with horizontal fabric but poorly expressed bedding sheetflow facies

factors determining desert dune type while most observers recognize four elemental types of desert dunes longitudinal transverse barchan and star1 3 there is little agreement about which factors determine these types the angular relationships between the resultant of sand shifting winds and both the crest and principal slipfaces of the elemental types have been discussed qualitatively for many decades these relationships have been quantified but the wide range of dune types that combine the elemental forms and the juxtaposition of different dune types show that wind regime is not the only determinant for example sand availability has been considered important we have now quantified the importance of both wind regime and sand availability as determinants of dune type we show here that the four elemental types occur in areas uniquely defined by both the equivalent sand thickness of sediments held in the dunes and a measure of directional variability of sand moving winds wind strength does not appear to be important vegetation has an ambiguous role and the particle size of dune sediments is unimportant

palaeoenvironment of braided fluvial systems in different tectonic realms of the triassic sherwood sandstone group uk abstract fluvial successions comprising the fills of sedimentary basins occur in a variety of tectonic realms related to extensional compressional and strike slip settings as well as on slowly subsiding passive basin margins a major rifting phase affected nw europe during the triassic and resulted in the generation of numerous sedimentary basins in the uk much of the fill of these basins is represented by fluvial and aeolian successions of the sherwood sandstone group additionally regions that experienced slow rates of mesozoic subsidence unrelated to triassic rifting also acted as sites of accumulation of the sherwood sandstone group one well exposed example being the eastern england shelf the fluvial depositional architecture of deposits of the sherwood sandstone group of the eastern england shelf a shelf edge basin is compared with similar fluvial deposits of the st bees sandstone formation eastern irish sea basin a half graben the two studied successions represent the preserved deposits of braided fluvial systems that were influenced by common allogenic factors climate sediment source delivery style differences in preserved sedimentary style principally reflect their different tectonics settings analysis of lithofacies and architectural elements demonstrates that both studied successions are characterized by amalgamated channel fill elements that are recorded predominantly by downstream accreting sandy barforms the different tectonic settings in which the two braided fluvial systems accumulated exerted a dominant control on preserved sedimentary style and long term preservation potential on the eastern england shelf the vertical stacking of pebbly units and the general absence of fine grained units reflect a slow rate of sediment accommodation generation 18 19 4 m myr in this shelf edge basin successive fluvial cycles repeatedly reworked the uppermost parts of earlier fluvial deposits such that only the lowermost channel lags tend to be preserved by contrast in the eastern irish sea basin of west cumbria the rate of sediment accommodation generation was substantially greater 119 m myr such that space was available to preserve complete fluvial cycles including silty drape units that cap the channelized deposits

hoanib river flood deposits of namib desert interdunes asanalogues for thin permeability barrier mudstone layers inaeolianite reservoirs abstract the ephemeral braided hoanib river of nw namibia ows for a few days ayear and only high discharges enable the river to pass through interdunaldepressions within the northern namib desert dune eld to the atlantic thedune eld comprises mainly large transverse dunes resulting frompredominant ssw winds river ood deposits between aeolian dunes areanalogous to mudstone layers conformably interbedded with ancientaeolianite dune foresets deep oods pond laterally to considerable depths metres to 10 m in adjacent interdunes depositing mud layers 1 50 cm toconsiderable heights on avalanche and stoss faces of bounding dunes fairlypassive ooding only disturbs aeolian strati cation minimally floodwaterclay in ltrates and settles as an impermeable seal with a ood pond on top perched above regional groundwater flood ponds evaporate slowly for longperiods 3 years early emergence desiccates higher parts of a mud layer subsequent oods can re ll a predecessor pond bene ting from the existingimpervious seal potential preservation of such mud layers is lower on thestoss face but high on the avalanche face after burial by subsequent dunereactivation and migration the leeward right hoanib bank a dune stoss face is river and wind eroded to exhume fossil interdune pond mud layers of anearlier hoanib channel the highly inclined layers are interbedded with duneavalanche foresets and represent the edges of two successive fossil pondsexposed in plan ancient ood pond mudstones occur in the permian triassichydrocarbon reservoir the sherwood sandstone group of the cheshire basin kinnerton formation and irish sea basin and were previously usederroneously to argue against the aeolian origin of cross bed sets hoanibstudies show that primary river interaction with a dune eld might preserveonly localized erosional omission surfaces in ancient aeolianites with littlesandy barform preservation prone to aeolian reworking around the main uvial channel locus however ood pond mudstone layers should form apredictable halo within which uid permeability will decrease keywords aeolian dunes aeolianite reservoir ash ood interdune namibdesert namibia permeability introductionhigh discharge oods of the hoanib river occa sionally break through the skeleton coast dune eld which forms part of the extensive namibdesert that parallels the western margin of thesouthern african subcontinent this arid regionis 140 km wide and over 2000 km long fromsouth western angola to the northern capeprovince south africa the northern namib dune eld termed the skeleton coast dune eld bywilson 1973 lancaster 1982 and ward sedimentology 2002 49 719 736

loose boundary hydraulics and fluid mechanics selected advances since 1961 s u m m a r y a maj or and acknowledged role in the advance o f sedimentological knowledge is played by the methods of physics as expressed through fluid mechanics and loose boundary hydraulics turbulence is increasingly being seen as involving orderly flow structures and these are significant for the origin of several sedimentary structures and for suspension transport recent advances in sediment transport theory are rooted in the concept of the sediment load as a downward acting force and in the notion of the flow as a transporting machine laboratory experiments are increasing our understanding of bedforms due to rivers and waves but there is a need for well framed field studies to clarify the influence of change in natural environments physical explanations are being proposed for tidal bedforms field studies in both modern environments and the stratigraphic record suggest that tidal patterns and strengths are recognizable from the internal features of cross bedded units formed by sand waves tidal patterns are complex however and a wider range of situations needs to be explored than has hitherto been the case mathematical modelling could help to define the expectable bedding patterns although successful mathematical models have been constructed of flow and sedimentation in channel bends secondary flow in real bends and the evolution of those bends are not yet well understood turbidity currents on a geologically significant scale have not been observed directly but valuable insights into their character and processes have come from laboratory experiments recent laboratory work points to the limitations of lock exchange experiments and emphasizes the various ways in which turbidity currents mix with the ambient medium these studies seem to have implications yet to be worked out for the internal features and some sole marks of turbidites

resonant wave reflection by transverse bedforms and its relation to beaches and offshore bars abstract on an erodible sand bed there may be a coupling between the reflection of incident wave energy and the development of transverse bedforms the nature of this interaction is examined with particular reference to a laboratory experiment in which a veneer of sand was introduced into a pre existing fixed pattern of bars the observed motion of the mobile sand suggested potential development of this existing bar system in the up wave direction but not in the down wave direction it is argued here that this phenomenon may be significant in terms of the growth of shore parallel bars off beaches and for coastal protection in general

the enigma of fine grained alluvial basin fills the permo triassic cumbrian coastal and sherwood sandstone groups of the solway basin nw england and sw scotland the late permian to triassic sediments of the solway basin consist of a layer cake succession of mature predominantly fine grained red clastics laid down in semi arid alluvial plain to arid sabkha and saline marginal marine or lacustrine environments the cumbrian coastal group consists of basal clastics and eden shales the basal clastics are thin regolith deposits resting unconformably on all underlying units and are composed of mixtures of angular local gravel and far transported fine to very fine grained sands deposited as basal lag the eden shales are predominantly gypsiferous red silty mudstones with thin very fine grained sandstone beds and with thick marine gypsum beds at the base deposited at a saline lake margin the overlying triassic sherwood sandstone group consists of the annan and kirklinton sandstones the annan sandstones are predominantly thick bedded multi storied fine grained mature red quartz sandstones in which coarse sand is practically absent despite channels with clay pebbles up to 30 cm in diameter the overlying predominantly aeolian kirklinton sandstones consist of festoon cross bedded and parallel laminated fine grained sandstones almost identical to the annan sandstones except that mica and clay are absent the stanwix shales located above consist of interbedded red blue and green mudstones siltstones and thin very fine grained sandstones with gypsum layers although the entire succession can plausibly be interpreted as deposited in a large desert basin opening into a hypersaline marine or lacustrine embayment to the southwest the uniformly fine grained nature of the succession is unusual as is the absence of paleosols and body and trace fossils there is almost no coarse sand even in the river channel units and it seems likely that the basin was not only extremely arid but supplied predominantly by wind rather than water

seabed wave resonance and sand bar growth the interaction of surface water waves with undulating sea bed topography is of fundamental importance to coastal engineersand sedimentologists for example wave reflection from submerged bars on beaches may provide a mechanism for protecting the beach from further wave attack additionally the interaction of surface water waves with other tidally or wave generated bedforms such as sandwaves on offshore banks may modify wave climates on adjacent coastlines while there have been numerous studies of the interaction of sea waves with engineering structures such as breakwaters piers and jetties there have been comparatively few investigations of wave interactions with naturally occurring bedforms predictions have recently been made of the amount of wave energy reflected as a result of resonant interactions between surface water waves and undulating sea bed topography but with no supporting experimental proof i describe here preliminary results from what are believed to be the first published laboratory measurements of resonant interactions between surface water waves and submerged bars which show that significant and large amounts of wave energy may be reflected and that these reflections are brought about by resonant interactions between surface water waves and the bedforms in particular at resonance incident surface water wavelengths are approximately twice the bedform wavelengths these results have implications not only in terms of wave reflection from naturally occurring bedforms say bars on beaches but also for sediment transport processes in general

fluvial aeolian interactions part i modern systems two modern fluvial aeolian depositional systems great sand dunes national monument colorado and the mojave river wash california are remarkably similar in spite of different climates sizes fluvial sediment textures and relative directions of aeolian and fluvial transport dune growth and migration and deflation of blowouts create 8 10 m of local relief in unflooded aeolian landscapes there are six prominent fluvial aeolian interactions 1 fluvial flow extends into the aeolian system until it is dammed by aeolian landforms 2 interdune areas overbank interdunes upstream of aeolian dams and alongside channels are flooded 3 water erodes dunes alongside channels and interdunes 4 flood waters deposit sediment in interdune areas 5 fluvially derived groundwater floods interdunes interdune playas 6 wind erodes fluvial sediment and redeposits it in the aeolian system unique and characteristic sediments are deposited in overbank interdunes and in interdune playas reflecting alternate fluvial and aeolian processes and rapidly changing flow and salinity conditions these fluvial aeolian interdune deposits are characterized by irregular concave up bases and flat upper surfaces containing mudcracks or evaporite cement characteristic low relief surfaces form in aeolian systems as an effect of flooding fluvial deposits are resistant to aeolian deflation aeolian sand is preserved when flood sediments are deposited around the bases of the dunes thus repetitive fluvial and aeolian aggradation tends to be stepwise as interdune floors are suddenly raised during floods the effects of flooding should be easy to recognize in ancient aeolianites even beyond the area covered with overbank muds

structural and climatic controls on facies distribution in a mixed fluvial and aeolian reservoir the triassic sherwood sandstone in the irish sea

magnetostratigraphy of the sherwood sandstone group lower and middle triassic south devon uk detailed correlation of the marine and non marine anisian the sherwood sandstone group in south devon consists of the budleigh salterton pebble beds and the otter sandstone formation the otter sandstone formation comprises four lithostratigraphic sub units from the base labelled a d and contains tetrapods corresponding to the perovkan land vertebrate faunachron and is consequently a key european non marine anisian succession a total of 181 palaeomagnetic specimens from 92 horizons were measured to determine the palaeomagnetic signal the magnetic properties and characteristic remanence is predominantly carried by haematite most of which probably formed early in the depositional and diagenetic history the lower part of the sherwood sandstone group budleigh salterton pebble beds and otter sandstone formation unit a lower part of unit b has predominantly normal polarity magnetozones bs1 bs2 and bs3n with three thin reversed polarity magnetozones the lower part of unit b to the lower part of unit c of the otter sandstone formation is predominantly reverse polarity magnetozones bs3r bs4 and bs5 but includes three short normal polarity intervals the upper ca 50 m of unit c shows a mix of normal and reverse polarity bs6 bs7 with normal dominating the ca 15 m thick unit d is entirely of normal polarity bs8n the magnetostratigraphy allows unambiguous comparison with conodont and ammonite calibrated magnetostratigraphies from elsewhere in europe these show that the bs2 and bs3n magnetozones of the otter sandstone formation are lower aegean to middle pelsonian lower to middle anisian the bs3r to bs5r magnetozone interval is middle pelsonian to lower illyrian middle to upper anisian and the bs6 to bs8n magnetozone interval is middle illyrian to lower fassanian the top of unit d is correlated to an interval in the middle of the nevadites zone close to the anisian ladinian boundary consequently the otter sandstone formation correlates with the muschelkalk in the polish basin but is equivalent to only part of the germanic basin muschelkalk the continuous magnetostratigraphy from the sherwood sandstone group provides additional details of the polarity pattern through the pelsonian to illyrian interval which appears to be lacking in discontinuous marine sections a synthesis of adjacent european sedimentary basins in combination with the magnetostratigraphy suggests that the budleigh salterton pebble beds are probably late spathian to lower aegean

paleostress and fluid pressure regimes inferred from the orientations of hishikari low sulfidation epithermal gold veins in southern japan abstract the orientation distribution of dilational fractures is affected by the state of stress around the fractures and by the pressure of the fluid that opened the fractures thus the distribution can be inverted to determine not only the stress but also the pressure condition at the time of vein formation however epithermal ore veins that we observe today are the results of a great number of intermittent upwelling of overpressured fluids with different pressures here we define driving pressure index dpi as the representative non dimensionalized fluid pressure for the fluids we collected the orientations of 1000 ore veins in the hishikari gold mine which were deposited at around 1 ma in southern kyushu japan it was found that the majority of the veins were deposited under an extensional stress with a nw se trending 3 axis and a northeasterly inclined 1 axis with relatively high stress ratio the representative driving pressure ratio was 0 2 data sets obtained at different depths in the mine indicated a positive correlation of representative driving pressure ratios with the depths the correlation suggests repeated formation and break of pressure seals during the mineralization our compilation of the pliocene quaternary stress regimes in southern kyushu including the result of the present study suggests that epithermal gold mineralization was associated with distributed extensional deformations in southern kyushu and strain localization into an intra arc rift seems to have terminated the mineralization

feedbacks between flow sediment motion and microbial growth on sand bars initiate and shape elongated stromatolite mounds abstract elongated stromatolites are often used as indicators of current direction and shoreline orientation especially in paleoenvironmental reconstructions however mechanisms that create shore parallel m scale elongated stromatolite mounds in carbonate sand are not well understood we propose that this geometry is initiated by microbial growth on the parts of sand bars that experience low wave induced bed shear stresses we test this idea by growing microbial mats on carbonate sand bars in a laboratory wave tank cyanobacterial mats grow on the bar runnels where sediment motion is negligible but are absent from the bar ridges where the waves generate migrating ripples when microbially promoted lithification reinforces and preserves this initial pattern elongated stromatolites should initiate in the runnels of sand bars with long wavelengths 5 100 m and small width to wavelength ratios 0 3 these dimensions are consistent with modern shore parallel stromatolites in hamelin pool western australia and with patterns of microbial colonization in other sandy sediments this model of elongated stromatolite mounds can inform paleoenvironmental reconstructions by clarifying and quantifying feedbacks among waves sediment transport and microbial growth

aeolian to marine transition in cambro ordovician cratonic sheet sandstones of the northern mississippi valley u s a cratonic quartz sandstones have presented several intractable problems besides their extreme textural and compositional maturity and paucity of shale their sheet like geometry is particularly notable if the sandstones were entirely marine as long supposed such geometry is difficult to explain in terms of modern shelf sediments which are generally held to be either relict or only slightly reworked by the holocene transgression palimpsest re study of two quartz sandstones in the northern mississippi valley region reveals evidence for significant non marine deposition followed by varying degrees of marine reworking during transgressions facies patterns are similar in the cambrian wonewoc and ordovician st peter sandstones both of which overlie unconformities in both a large scale cross stratified facies believed to represent aeolian ergs passes laterally into a planar and channelled facies inferred to represent sand plains composed of braided fluvial and aeolian sand sheet deposits criteria of aeolian deposition in both facies include adhesion structures large ripple index fine climbing translatent lamination grainfall and grainflow stratification criteria of braided fluvial deposition include shallow channels containing sequences of thinning upward sets of trough cross stratification reactivation surfaces low index ripples and polygonal cracks probable aeolian sand sheets contain flat bedding punctuated by small channels adhesion structures and coarse sand ripples with large index there is a conspicuous absence of trace and body fossils from these inferred non marine deposits in contrast is a burrowed and trough cross stratified facies characterized by medium scale cross bedding alternating with bioturbated intervals and rare brachiopod or trilobite mould coquinas which is interpreted as shallow marine in both formations this last facies replaces laterally and overlaps the other two reflecting transgression and variable reworking the main areas of non marine deposits in both formations are capped by a thin burrowed subfacies that represents the culmination of each transgression that is a stillstand during which sediment influx ceased and both physical winnowing and bioturbation were intense it is suggested that the sheet like geometry of many cratonic quartz sandstones is due primarily to initial sand dispersal by aeolian and fluvial processes that such processes must have been orders of magnitude more important on pre devonian vegetation free landscapes than they have been since not only helps to explain the sheet like character but also the exceptional maturity of the older cratonic sandstones

sand transport by unbroken water waves under sheet flow conditions a model of wave induced onshore sand transport and resulting topographical changes seaward of the break point on a sloping beach is presented for the specific case in which the waves are random normally incident weakly nonlinear and relatively long the bottom boundary layer is fully turbulent and sand transport occurs as sheet flow the model consists of the following components 1 a new empirical expression for sand transport as sheet flow in which the instantaneous transport rate is directly proportional to the instantaneous bottom shear stress 2 an expresssion for the mean bottom shear stress based on a theoretical analysis of the bottom boundary layer 3 a simple representation of the shoaling wave field in which the local properties are described by linear long wave theory the probability density function of the surface displacement is gaussian and the waves conserve energy flux as they shoal and 4 the equation for conservation of sediment mass computations based on the model compare favorably with recently reported field measurements of the onshore motion of a long offshore bar

bragg reflection of ocean waves from sandbars 1 resonant bragg reflection of ocean surface waves by a field of natural shore parallel sandbars was observed in cape cod bay ma waves transmitted through the bars were reflected strongly from the steep shoreline and the observed cross shore variations in the onshore and offshore directed energy fluxes are consistent with theory for resonant bragg reflection including a 20 decay of the incident wave energy flux that is an order of magnitude greater than expected for wave orbital velocity induced bottom friction bragg reflection was observed for a range of incident wave conditions including storms when sediment transported toward and away from nodes and antinodes caused by the reflecting waves might result in growth and maintenance of the sandbars

whitecap features induced by submarine sand waves in stereo optical imagery under high wind speed conditions waves break on the sea surface producing whitecaps which can be recorded in optical satellite images however the breaking of waves is also influenced by submarine topography in this study we investigate the whitecap features induced by submarine sand waves using optical stereo images we determine the whitecap coverage in images and estimate the probabilities of wave breaking the observed and estimated results are in agreement with some previous investigation results a physical model is used to discuss the mechanisms of wave breaking along sand wave crests the physical model is able to qualitatively explain the differences between the observed whitecap coverage and the estimated probability of wave breaking between the sand wave area swa and the background area bga further analysis shows that the periodic sand wave system may play the role of a frequency control device and may result in more broken waves in the swa than in the bga this study demonstrates that it is possible to observe submarine topography under high wind conditions by using whitecap features

stratigraphical relationships and a revised lithostratigraphical nomenclature for the carboniferous permian and triassic rocks of the offshore east irish sea basin

sandbar formation under surface waves theory and experiments 1 we report a combined theoretical and experimental study of sandbar formation under simple harmonic surface waves for coarse grains and weak waves an established empirical rule of bed load transport is used with an asymptotic theory for the fluid flow the surface waves are governed by potential theory and a depth linear eddy viscosity is employed in the turbulent boundary layer at the seabed the derived bed stress is used to predict the sand bed evolution laboratory experiments and corresponding numerical simulations for both high and low beach reflection are discussed for weak reflection the shear stress associated with the return current is found to be important partial simulation of a field record in cape cod bay is also described

bragg scattering of random surface gravity waves by irregular seabed topography the bragg scattering of random non stationary surface gravity waves by random topography on a gently sloping bottom is investigated a correction is given of previously published expressions for the triad wave wave bottom interaction source term in the spectral energy balance equation and the result is reconciled with deterministic theories for the reflection of waves from sinusoidal seabed undulations for both normal and oblique incidence the stochastic and deterministic theories are equivalent in the limit of long propagation distances even for relatively short distances for example two bottom undulations the reflected energy predicted by the stochastic source term formulation is generally within 15 of values predicted by deterministic theories the detuning of bragg resonance by refraction and shoaling is discussed suggesting practical validity conditions for the stochastic theory the effect of bottom scattering on swell propagation is illustrated with numerical model computations for the north carolina continental shelf using high resolution bathymetry and an efficient semi implicit scheme to evaluate the bottom scattering source term and integrate the energy balance equation model results demonstrate the importance of forward scattering of waves that propagate at large oblique angles over bottom features with typical scales of one to several surface wavelengths this process contributes significantly to the directional spread of swell on the continental shelf by diffusing energy in the spectrum around the mean wave direction back scattering caused by bottom features with crests parallel to those of the surface waves and wavelengths close to half the surface wavelength is weak owing to the sharp roll off of the bottom elevation spectrum at high wavenumbers model predictions are consistent with field measurements

recurrent deformations of aeolian desert dunes in the cretaceous of the south china block trigger mechanisms variability and implications for aeolian reservoirs abstract deposits of aeolian dunes accumulated in cretaceous intramontane deserts in the south china block underwent recurrent deformation processes affecting their toesets and foreset sediments the mid cretaceous matoushan formation preserves examples of soft sediment deformation deformations associated with theropod tracks in aeolian dune apron sandstones the late cretaceous tangbian formation in the xinjiang basin shows i seismites associated with dry interdune laminated deposits and sand injection into the interdune laminated facies generating intraclast breccias ii mass flow deposits associated with heavy rains generating interbedding of non deformed and deformed intervals in aeolian dune foresets deformed intervals display a variety of deformation styles including thrust duplexes upturned and deformed stratification recumbent folds and microfolds and liquefied intervals covered by overlying draa mega cross bedded sets animal tracks seismites monsoon rains and earthquakes are proposed as the main trigger mechanisms of the failures that led to deformation hydroseismicity associated with monsoon rains is a probable but difficult to prove trigger mechanism this process could be an important deformation agent in the case of large scale deformation recorded in ancient erg sequences mass wasting deposits in ancient erg extensive sandy deserts characterized by aeolian dunes sequences constitute significant heterogeneities for hydrocarbon migration and its architectural variability could determine the development of effective sedimentary traps in aeolian reservoirs

stokes surfaces and the effects of near surface groundwater table on aeolian deposition abstract stokes surfaces in aeolian deposits are caused by wind scour of unconsolidated material to a roughly planar horizon controlled by near surface water tables stokes 1968 a water table forms a downward limit of scour through the cohesion of damp or wet sand near water table and through early cementation by evaporites precipitated in the sediments as water evaporates near the sand air interface study of modern analogues reveals that stokes surfaces exist in a variety of depositional settings including a coastal offshore prograding sand sea jafurah saudi arabia a coastal onshore prograding sand sea guerrero negro mexico and a continental sand sea white sands new mexico usa these modern analogues indicate that our concept of stokes surfaces must be broadened to include the following i modern analogues for stokes surfaces described here cover areas on the order of 25 km2 these may be as representative of similar surfaces in ancient rocks as hypothesized plains of deflation requiring removal of entire sand seas ii stokes surfaces occupy a continuum in scale from local to extensive and erosional surfaces of different magnitude may be stacked closely in the sediments iii stokes surfaces although erosional in nature are commonly associated with deposits both above and below the stokes bounding surface which plainly reveal the influence of a near surface groundwater control on wind sedimentation moreover the erosional relief of the bounding surface itself as well as other features reveals the influence of a groundwater table iv stokes surfaces may be diachronous representing the lateral shift of a zone of scour within a sand sea rather than simultaneous removal of all dunes from the area encompassed by the erosional surface v stokes surfaces and associated deposits are often laterally transitional to surfaces and deposits of adjacent depositional environments including interdunes tidal flats lagoons beaches lakes and non aeolian sabkhas finally modern examples from different depositional settings suggest that while most stokes surfaces have many features in common such as erosional ridges due to early cementation there are some features which may with further study be revealed to be distinctive of an individual depositional setting

bounding surfaces in a mixed aeolian fluvial system rotliegend wessex basin sw uk the dawlish sandstone formation is a late permian succession of mixed aeolian and fluvial deposits in the wessex basin sw england it is used to illustrate two contrasting types of fluvial aeolian bounding surface planar and incised planar bounding surfaces separate tabular bodies of fluvial conglomerate and aeolian dune sandstone they were produced primarily by wind scour to groundwater table with the later emplacement of conglomerates resulting in local fluvial erosion of cemented aeolian dune sandstones incised bounding surfaces were produced by fluvial downcutting the erosive relief was infilled with mixed aeolian fluvial deposits the dawlish sandstone formation may provide the first outcrop example of these incised valley fills which have recently been identified as a major component of the subsurface rotliegend in the southern north sea basin the potential variability of aeolian fluvial sedimentary architecture has important implications for well to well correlation and reservoir modelling

mass and hyperconcentrated flow deposits record dune damming and catastrophic breakthrough of ephemeral rivers skeleton coast erg namibia channel shaped deposits of well sorted sand with only 2 4 fine grained material being either massive and structureless or upward fining with basal lag are found interbedded with aeolian sand in the skeleton coast erg namibia detailed analyses of the channel shaped deposits suggest that they are formed as hyperconcentrated flows within the erg grain size analysis and whole rock geochemical modeling revealed that some of the fluvial sediments contain up to 70 aeolian sand interpreted as a result of dune collapse into the fluvial system in certain cases this instantaneous supply of sand resulted in generation of sandy mass flows with laminar flow behaviour the presence of smectite as dominant clay mineral proved to be of crucial importance in formation of mass flow deposits these mass flows had no erosional capacity and drape the palaeotopography they are comparable to those generated by catastrophic collapse of dunes described in the literature this paper suggests that all these deposits should be termed intra erg mass flows as several of them carry little if any debris based on their origin intra erg mass flows can be divided into two groups

conditions favourable for the formation of warm climate aeolian sand sheets aeolian sand sheets are areas of aeolian sand where dunes with slipfaces are generally absent sand sheets are ubiquitous to modern warm climate sand seas generally occurring marginal to dune fields although they may exist within the interior of a sand sea or independent of a dune field sand sheet deposits are recognized in ancient aeolian sequences where they may account for significant accumulations of low angle aeolian stratification we suggest that the occurrence of sand sheets instead of dunes indicates that conditions are outside the range within which dunes form or that one or more factors interfere with dune development while also favouring the accumulation of sand sheets a study of six modern sand sheets in north america located at great sand dunes gran desierto dumont algodones padre island and colorado river delta indicates that the factors favourable for sand sheet development are 1 a high water table 2 surface cementation or binding 3 periodic flooding 4 a significant coarse grained sediment population and 5 vegetation these factors are reflected in the nature of stratification and the accessory features of sand sheet accumulations within the areas of modern sand sheets as well as in their ancient counterparts in the triassic dolores and pennsylvanian permian rico formations

shore protection by oblique seabed bars shore protection by small seabed bars was once considered possible because seafloor undulations strongly reflect surface waves of twice the wavelength by the so called bragg resonance mechanism the idea however proved unreliable when it was realized that a patch of longshore seabed bars adjacent to a reflective shore could result in larger waves at the shoreline than for the case of a flat seabed here we propose to revamp the bragg resonance mechanism as a means of coastal protection by considering oblique seabed bars that divert rather than reflect shore normal incident waves to the shore parallel direction we show via multiple scale analysis supported by direct numerical simulations that the creation of a large protected wake near the shoreline requires a bi chromatic patch to deflect the incident waves to the shore parallel direction with two superposed sets of oblique seabed bars the incident wave energy becomes efficiently deflected far to the sides leaving a wake of decreased wave activity downstream of the patch we demonstrate that the shore protection efficiency provided by this novel arrangement is not affected by reflection of leaked waves at the shoreline and that it is relatively robust against small frequency detuning

do longshore bars shelter the shore in most past theories on bragg reflection of waves by a finite patch of rigid bars only outgoing waves are allowed on the transmission side simulating the effect of an idealized shoreline where all the incident wave energy is consumed by breaking in these theories the amplitudes of both the incident and reflected waves are found to decrease monotonically over the bar patch in the shoreward direction this result has motivated the idea of artificially constructing bars to protect a beach from incident waves however some numerical calculations have suggested that this tendency does not always hold when there is some reflection from the shore we show here that with finite reflection by the shoreline the spatial distribution of wave energy over the patch can indeed be reversed indicating that the mechanism can increase the hazards to the beach the phase relation between the bars and the shoreline reflection is found to be the key to this qualitative change of wave response

large scale linked drainage systems in the nw european triassic insights from the pb isotopic composition of detrital k feldspar pb isotopic data from k feldspars in middle triassic anisian sandstones in the wessex basin onshore sw uk and the east irish sea basin some 350 km to the north show that the same grain populations are present this indicates that the drainage system the budleighensis river feeding these basins originated from the same source s most probably the remnant variscan uplands to the south fluvial and aeolian sandstones have the same provenance suggesting that if water and wind driven sands were originally derived from different sources this has been obscured through reworking prior to final deposition significant recycling of feldspar from arkosic sandstones in earlier sedimentary basins can be ruled out the provenance data agree with previous depositional models indicating transport distances in excess of 400 km with a drainage pattern that linked separate basins this supports the idea that the regional fluvial system was driven by topography and episodic flooding events of sufficient magnitude to overcome evaporation and infiltration over hundreds of kilometres importantly this drainage system appears to have been isolated and independent from those operating contemporaneously to the nw of the irish and scottish massifs where the remnant variscan uplands apparently exerted no influence on drainage or sand supply

dikes emplaced into fractured basement timna igneous complex israel dikes are usually envisioned as arrays of parallel segments dilated perpendicular to the direction of the least compressive stress we describe here four dikes of highly irregular shape intruded in the fractured basement in the timna igneous complex southern israel the dikes include a doleritic dike 2 3 km long and 1 6 m to 32 m thick and three andesitic dikes up to 1 5 km long and 8 m thick the dikes each display significant variations of dip up to 60 strike up to 160 and thickness the thickness variations correlate better with the segment attitude than with the position along the dikes we show that the irregular shapes of the timna dikes are the result of emplacement into fractured host rock under different paleostress states and driving pressures three dilation styles that differ by the geometry of the initial cracks are analyzed an array of randomly oriented cracks style a a single linear crack style b and an array of interconnected nonparallel cracks style c the analysis of style a provides the stress state during dike emplacement including the orientations of the three principal stresses 1 2 3 the stress ratio 2 3 1 3 and the normalized driving pressure r pm 3 1 3 the stress ratio indicates the shape of the stress ellipsoid and it ranges from 0 for 2 3 prolate ellipsoid to 1 for 1 2 oblate ellipsoid the normalized driving pressure r indicates the relative magnitude of the internal magma pressure pm with respect to the tectonic stresses and it ranges from r 0 for pm 3 to r 1 for pm 1 we found that for three dikes in timna 0 25 indicating small differences between the two horizontal principal stresses and for one dike 0 9 indicating a large difference between the two horizontal principal stresses the normalized driving pressure r is about 0 08 in two horizontally propagating dikes and about 0 25 in two vertically propagating dikes style b predicts an elliptical thickness profile along the dike due to dilation of a linear crack this prediction agrees with the profile of one of the dikes the predicted thicknesses due to dilation of the interconnected array of cracks style c are in good agreement with the thickness variations of the doleritic dike and in fair agreement with two of the andesitic dikes deviations from the ideal geometry suggest separate stages of propagation and dilation in some of the dike segments

palaeoenvironments and palaeotectonics of the arid to hyperarid intracontinental latest permian late triassic solway basin u k abstract the late permian to late triassic sediments of the solway basin consist of an originally flat lying laterally persistent and consistent succession of mature dominantly fine grained red clastics laid down in part of a very large intracontinental basin the complete absence of body or trace fossils or palaeosols indicates a very arid hyperarid depositional environment for most of the sediments at the base of the succession thin regolith breccias and sandstones rest unconformably on basement and early permian rift clastics overlying gypsiferous red silty mudstones very fine sandstones and thick gypsum were deposited in either a playa lake or in a hypersaline estuary and their margins these pass upwards into thick bedded multi storied fine to very fine grained red quartzo felspathic and sublithic arenites in which even medium sand is rare despite channels with clay pebbles up to 30 cm in diameter above thick trough cross bedded and parallel laminated fine grained aeolian sandstones deposited in extensive barchanoid dune complexes pass up into very thick multicoloured mudstones and gypsum deposited in marginal marine or lacustrine sabkha environments the latter pass up into marine lower jurassic shales and limestones thirteen non marine clastic lithofacies are arranged into five main lithofacies associations whose facies architecture is reconstructed where possible by analysis of large exposures the five associations can be compared with the desert pavement arid ephemeral stream sabkha saline lake and aeolian sand dune environments of the arid to hyperarid areas of existing intracontinental basins such as lake eyre and lake chad the accommodation space in such basins is controlled by gradual tectonic subsidence moderated by large fluctuations in shallow lake extent caused by climatic change and local variation and this promotes a large scale layer cake stratigraphy as exemplified in the solway basin here the dominant fine grained mature sandstones above the local basal reg breccias suggest water reworking of wind transported sediment as in the northern part of the lake chad basin growth faulting occurs in places in the solway basin caused by underlying evaporite movement but these faults did not significantly affect pre late triassic sedimentation and did not expose pre permian units above the basal breccias there is no evidence of post early permian rifting anywhere during deposition of the late permian to middle triassic british succession although the succession is often interpreted with a rift basin model the arid to hyperarid palaeoclimate changed little during deposition of the solway basin succession in contrast to lakes eyre and chad and this is attributed to tectonic and palaeolatitude stability unlike the later mesozoic cenozoic only limited plate movements took place during the triassic in western europe palaeolatitude changed little and the solway basin remained in the northern latitudinal desert belt from early to mid triassic times however the influence of the early triassic impoverished biota on environmental interpretations needs further study