on the mechanism of wavelength selection of self organized shoreline sand waves sandy shorelines exposed to very oblique wave incidence can be unstable and develop self organized shoreline sand waves different types of models predict the formation of these sand waves with an initially dominant alongshore wavelength in the range 1 10 km which is quite common in nature here we investigate the physical reasons for such wavelength selection with the use of a linear stability model the existence of a minimum wavelength for sand wave growth is explained by an interplay of three physical effects a largest relative to the local shoreline wave angle at the downdrift flank of the sand wave b wave energy concentration at the updrift flank due to less refractive energy dispersion and c wave energy concentration slightly downdrift of the crest due to refractive focusing for small wavelengths effects a and c dominate and cause decay while for larger wavelengths effect b becomes dominant and causes growth however the alongshore gradients in sediment transport decrease for increasing wavelength making the growth rate diminish there is therefore a growth rate maximum giving a dominant wavelength lm in contrast with previous studies we show that lm scales with 0 0 is the wavelength of the offshore waves and is the mean shoreface slope from shore to the wave base an estimate of the order of magnitude of the distance waves travel to undergo appreciable transformation our model investigations show that the proportionality constant between lm and 0 is typically in the range 0 1 0 4 depending mainly on the wave incidence angle

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

grain size controls on the morphology and internal geometry of river dominated deltas predictions of a delta s morphology facies and stratigraphy are typically derived from its relative wave tide and river energies with sediment type playing a lesser role here we test the hypothesis that all other factors being equal the topset of a relatively noncohesive sandy delta will have more active distributaries a less rugose shoreline morphology less topographic variation in its topset and less variability in foreset dip directions than a highly cohesive muddy delta as a consequence its stratigraphy will have greater clinoform dip magnitudes and clinoform concavity a greater percentage of channel facies and less rugose sand bodies than a highly cohesive muddy delta nine self formed deltas having different sediment grain sizes and critical shear stresses required for re entrainment of mud are simulated using deflt3d a 2d flow and sediment transport model model results indicate that sand dominated deltas are more fan shaped while mud dominated deltas are more birdsfoot in planform because the sand dominated deltas have more active distributaries and a smaller variance of topset elevations and thereby experience a more equitable distribution of sediment to their perimeters this results in a larger proportion of channel facies in sand dominated deltas and more uniformly distributed clinoform dip directions steeper dips and greater clinoform concavity these conclusions are consistent with data collected from the goose river delta a coarse grained fan delta prograding into goose bay labrador canada a reinterpretation of the kf 1 parasequence set of the cretaceous last chance delta a unit of the ferron sandstone near emery utah usa uses ferron grain size data clinoform dip data clinoform concavity and variance of dip directions to hindcast the delta s planform the kf 1 last chance delta is predicted to have been more like a fan delta in planform than a birdsfoot delta

tidal dynamics and residual circulation in a well mixed inverse estuary the tidal and residual circulations in laguna san ignacio lsi a well mixed evaporative lagoon located on the pacific coast of the baja california peninsula in mexico is described based on surveys and moored observations at tidal periods pressure and axial current fluctuations are about one quarter of a period out of phase and so the tidal wave is close to standing pressure fluctuations increase and axial currents decrease with distance from the ocean the fluctuating axial momentum balance is nonlinear and involves local acceleration advection barotropic pressure gradients and friction the structure of the residual circulation depends on the internal froude number fri a measure of the relative strength of tidal and buoyancy forcing most of the time fr i is large and the residual flow is laterally variable driven by the tidally averaged nonlinear advective terms the sense of this residual circulation is shown to depend on the lateral structure of the tidal stress and is away from the ocean in the deep channels when the tidal wave is standing as in lsi and in the opposite direction for a progressive wave during neap tides when fri is small the residual circulation is vertically stratified with a dense near bottom flow toward the ocean and relatively fresh inflow at the surface

erg margin of the permian white rim sandstone se utah the permian white rim sandstone of the canyonlands national park utah contains a wide variety of sedimentary structures and features that largely result from stages in erg migration and marine influence on an erg margin three spatially distinct lithological and depositional facies are recognized and can be distinguished as informal units within the formation the aeolian dune facies is composed predominantly of fine grained cross stratified sandstone of the white rim erg this facies is the most widespread and comprises the bulk of the formation within the aeolian dune facies are small subfacies that represent interdune deposits a sheet sand facies composed of parallel bedded sandstone makes up a significant part of the lowest part of the white rim formation this facies appears to have been the precursor or leading progradational edge to the main erg system the final facies is a reworked or veneer facies of rippled to disturbed sandstone that is localized in its extent it is restricted to the upper few metres of the formation and is transitional in some places to the triassic moenkopi formation this veneer facies contains many structures which indicate marine reworking as well as periods of desiccation or subaerial exposure some previous interpretations of the white rim sandstone have tended to classify the whole formation as one depositional setting it is clear that at the margin of a sand sea as shown in the white rim sandstone there are transitional facies due to the interactions with other environments additionally variation in the stratigraphic relationships of facies can be related to stages of erg migration erg margin deposits preceded central erg development erg initiation occurred during a probable relative sea level low sea level influence is recorded at the top of the formation because erg termination accompanied a relative sea level high with cut off of sand supply transgression of the permian kaibab sea over the white rim erg was probably the main process in preservation of original dune topographic relief sea level fluctuations also may have affected distribution of facies and the complexities of structures at the erg margin subsequent fluvial reworking of the veneer facies may have obliterated late permian features during lowest triassic moenkopi deposition

significant effect of sediment cohesion on delta morphology delta morphology is thought to be controlled by factors such as river discharge tides and waves numerical modelling shows that sediment cohesion also strongly influences the development of a delta s characteristics the morphologies of the world s deltas are thought to be determined by river discharge tidal range and wave action 1 more recently sea level rise 2 3 and human engineering4 have been shown to shape delta evolution the effects of factors such as sediment type and the overall amount of sediment carried by rivers are considered secondary4 5 6 in particular the role of sediment cohesion which is controlled by sediment size and type of vegetation is unclear here we use a numerical flow and transport model7 8 9 10 to show that sediment cohesiveness also strongly influences the morphology of deltas we find that holding all other factors constant highly cohesive sediments form bird s foot deltas with rugose shorelines and highly complex floodplains whereas less cohesive sediments result in fan like deltas with smooth shorelines and flat floodplains in our simulations sediment cohesiveness also controls the number of channels that form within the deltas and the average angle of bifurcation of those channels as vegetation generally acts as a cohesive agent we suggest that deltas that formed before the expansion of land plants in the devonian period should show fan like characteristics a finding consistent with the limited data from the sedimentological record11

coastline sand waves on a low energy beach at el puntal spit spain abstract coastline sand waves have been observed at el puntal spit located on the north coast of spain the spit has been monitored by an argus video system since 2003 and the formation and destruction of sand waves has been observed coastline data from the video images are analyzed by means of principal components analysis obtaining a mean sand wave length of 125 150 m and a maximum amplitude of 15 m it is also observed that sand waves reach their maximum amplitude at about 15 days no propagation of these sand waves is noticed during the approximately two month long events analyzed sand wave formation and evolution are examined in relation with the prevailing local wave conditions during that period incident waves at the west end of the spit approach from the east northeast with a very high angle with respect to the shoreline field observations suggest that sand waves may result from an instability in alongshore sediment transport caused by moderate energy waves with a high angle incidence

aeolian to shallow marine shelf architecture off a major desert since the late pleistocene northern mauritania abstract continental shelves off major desert regions are not expected to host substantial amounts of sediments due to long lasting and unfocused material supply and a high re mobilization potential of aeolian material this study in contrast demonstrates that significant volumes of sediments have accumulated on the northern mauritanian shelf under the arid climate conditions and prevail over consecutive climatic cycles eight late pleistocene to holocene depositional units each formed under contrasting depositional conditions are identified in high resolution seismo acoustic data and dated sediment cores these are 1 a highly differentiated pleistocene paleo landscape older than the past climatic cycle 2 a continental dune complex mis 4 3 a thick regressive shallow water clinoform late mis 3 4 a regressive to lowstand shore deposit latest mis 3 and 5 a local transgressive cover lgm to deglacial additionally 6 an open shelf highstand cover 7 an outer shelf highstand wedge and 8 mid shelf mud depocenters have formed during the holocene sea level highstand the common local offshore formation and preservation of confined stratigraphic units in particular from during mis 3 mark the interplay of a episodes of pronounced arid climatic conditions resulting in enhanced aeolian and coastal sediment input b shelf current patterns focusing sediment deposition locally and c early post depositional sediment stabilization providing protection against erosion prominent internal surfaces at 63 and 115 m modern water depths indicate widespread and intense erosional activity during late mis 3 regression and mis 2 lowstand to post lgm transgression hosting coarse shell sands and gravels from beach and shoreface paleo environments the reasons for the high preservation potential of confined stratigraphic units are a carbonaceous cementation b sediment composition massive widespread shore related gravel and shell beds with subtle minor admixtures of cohesive material and c morphological protection inside seafloor depressions and behind sheltering relief

tidally flooded back barrier dunefield guerrero negro area baja california mexico a 45 km long barrier island exists west of the town of guerrero negro mexico along the western coast of the baja california peninsula about 720 km south of san diego california this barrier has developed in a mesotidal arid climate regime characterized by steady strong onshore winds from the nw the barrier island w of guerrero negro has prograded seaward about 1 6 km in the last 1800 years while an aeolian dunefield fed by sand blown from beaches has advanced inland up to 13 km landward progradation of the dune system from the barrier has occurred during relative rise in sea level thus aeolian sediments exist at or below the water table over a wide area the progradation of dunes across marshes tidal flats and tidal channels as well as the repeated submergence of interdune areas by tidal waters has created a complex suite of mixed aeolian and subaqueous sediments in the back barrier the complexity of the suites of aeolian sedimentary structures together with the inclusion of subaqueously formed structures such as current and oscillation ripples would make recognition of the aeolian origin of much of the sediments difficult in ancient rocks in addition to the scientific importance of recognizing the aeolian deposits the sedimentation model represented by the guerrero negro barrier has applications in petroleum exploration and development currently most preservational models for barrier islands attach little volumetric importance to aeolian deposits this modern example suggests that volumetrically significant aeolian deposits can be preserved behind a barrier particularly in an arid climate regime if preserved and charged with oil the resulting productive sandstone could have an extremely irregular landward edge comprised in part of onshore prograded aeolian dune sandstone with excellent reservoir characteristics as with current barrier models the reservoir would be sealed landward and above by lagoonal mudstone and silt evaporites or evaporitic sandy sabkha deposits high organic productivity occurs in lagoons immediately adjacent to the dunefields of guerrero negro suggesting that organic rich source rock may exist near aeolian sandstone in ancient settings similar to guerrero negro

a quantitative analysis of recent arid coastal sedimentary facies from the arabian gulf coastline of abu dhabi united arab emirates abstract this study presents the results of the first quantitative analysis of surface sediments along multiple transects of the arabian gulf shoreline of abu dhabi united arab emirates the natural coastline of this low angle carbonate ramp depositional system is being anthropogenically modified at an unprecedented rate as this system is much employed as a recent analogue for many ancient depositional sequences it is imperative that sedimentological characteristics of natural facies occurrences are accurately recorded for employment in future applications we establish distinct relationships between the geomorphic setting and sediment characteristics siliciclastic grains admixed to this system are naturally sourced from the pliocene ghayathi formation and from aeolian sediment influx during dust storms this natural source of siliciclastic detritus is being increasingly superseded by siliciclastic material derived from anthropogenic activities evaporite minerals are similarly being contributed from anthropogenic sources the occurrence of mud to silt grade sediments is primarily controlled by the presence of a sediment binding microbial mat that prevents the removal of fine material during high energy events similarly the presence of a halite crust in the upper tidal flats and supratidal zone prevents aeolian deflation this study did not establish any clear relationship between coastal geomorphic setting and the bioclastic components present in the sediments this finding has major implications for the application of bioclasts in fine tuning palaeoenvironmental interpretation of ancient carbonate ramp coastal systems

classification of large scale subaqueous bedforms a new look at an old problem sepm bedforms and bedding structures abstract a symposium entitled classification of large scale flow transverse bedforms was convened at the 1987 mid year meeting of sepm in austin texas with the purpose of examining the problems involved in classifying large subaqueous flow transverse bedforms developed in fluvial intertidal and marine environments and recommending changes in nomenclature the consensus of the participants is that despite the wide spectrum of morphologies of large scale flow transverse bedforms excluding antidunes they all occupy a similar position in the lower flow regime sequence between ripples and upper plane bed the wide variety of forms is a reflection of secondary effects such as channelization fluctuating water levels and unsteady and reversing flows the bedforms appear not to fall into size classes with naturally occurring boundaries but rather form a continuum with spacing from just under 1 m to over 1 000 m the symposium panel proposes therefore that they should have only one name dune dune is preferred as it has historical precedence over other terms in use such as megaripple and sand wave the term dune should be modified by rimary descriptors of shape i e 2 d or 3 d and size based on spacing small 0 6 5 m medium 5 10 m large 10 100 m or very large 100 m and the adjective subaqueous when it is important to distinguish them from eolian dunes the panel recommends a morphologically based classification that is descriptive with an underlying genetic rationale second order descriptors such a sediment size and bedform superposition may be used to describe more thoroughly the variety of subaqueous dunes in nature

coastal dune facies permian cutler formation white rim sandstone capitol reef national park area southern utah abstract the permian cutler formation white rim sandstone in the capitol reef national park area in southern utah is an excellent example of a coastal dune complex subjected to periodic flooding by marine waters wind ripple grainfall and grainflow laminae compose the cross sets deposited by eolian dunes however wave reworked structures such as oscillation ripples the occurrence of the characteristically marine trace fossils thalassinoides and chondrites and interfingering marine carbonate beds of the kaibab formation collectively indicate marine interaction with the eolian environment four facies are distinguished cross stratified sandstone burrowed to bioturbated sandstone brecciated and deformed sandstone and ripple laminated sandstone and thin carbonate beds one unusual aspect of the cross stratified sandstone facies is the abundance of coarse grained sand coarse grained sand is atypical in many ancient eolian slipface deposits but occurs here in large slipface foresets as both grainflow and wind ripple deposits no water laid structures are found in these slipface deposits coarse grained sand was probably transported to the cutler shoreline by fluvial systems draining the uncompahgre uplift to the east and then concentrated as coarse grained ripples in interdune areas some of these coarse grained ripples migrated up the stoss side of the dunes and accumulations of coarse grained sand avalanched down the crest to form grainflow deposits an extensive amount of soft sediment deformation is indicated by the presence of convolute bedding and brecciation these features occur near the zone of interfingering with marine carbonate beds of the kaibab formation the water saturated and moist conditions required for extensive deformation may have been controlled by the proximity of these sandstones to the shoreline and fluctuations in the associated groundwater table

stratigraphic analysis of eolian interactions with marine and fluvial deposits middle jurassic page sandstone and carmel formation colorado plateau u s a abstract the eolian page sandstone middle jurassic in south central utah and adjacent arizona consists of multiple mostly eolian sequences and sequence bounding unconformities super surfaces the super surfaces are a powerful correlation tool that provide the basis for a detailed regional stratigraphic analysis of the page sandstone and coeval parts of the marine and coastal plain carmel formation some page sandstone super surfaces correlate with sharp lithologic breaks in the carmel formation that are interpreted as marine flooding surfaces others correlate with fluvial surfaces in the carmel formation the lower part of the page carmel interval encompasses seven onlapping accumulation sequences bounded by marine flooding surfaces the uppermost two represent the middle jurassic marine high water mark these seven units comprise marine transgressive and marine highstand system tracts each interval is composed of progradational eolian deposits over marine deposits major tectonic and sedimentologic changes affected accumulation sequences 8 and 9 the two intervals are continental in origin fluvial to the west and eolian to the east a major slightly angular regional unconformity marks the top of accumulation sequence 9 the unconformity reflects regional tilting up to the northeast and ensuing erosion of older units in the page sandstone accumulation sequence 10 the top of the s udy interval displays complexly juxtaposed continental and marine facies that buried the unconformity as regional subsidence continued the broad patterns described above can be correlated with thick marine carbonate and minor siliciclastic deposits of the twin creek limestone 400 km north of the study area the resulting depositional patterns define three broad depositional events the oldest of these sequences defines a regional marine transgression and highstand the second sequence reflects strong siliciclastic influx and slight regional tilting that resulted in widespread continental deposition regional tilting and erosion closed out this event the youngest sequence indicates a partial return to marine transgressive conditions but was complicated by regional uplift and tilting related to are tectonism this study demonstrates that a sequence stratigraphic framework can be applied to sparsely fossiliferous eolian sabkha and restricted marine deposits in a marine coastal setting using detailed sedimentologic and stratigraphic studies tectonic eustatic and possibly climatic signals can be differentiated within the complex cyclic facies patterns displayed in the page sandstone and carmel formation

on the origin of late holocene sea level highstands within equatorial ocean basins abstract late holocene sea level highstands of amplitude 3 m are endemic to equatorial ocean basins these highstands imply an ongoing and moderate sub mm yr sea level fall in the far field of the late pleistocene ice cover that has long been linked to the process of glacial isostatic adjustment gia clark et al 1978 mitrovica and peltier 1991 coined the term equatorial ocean syphoning to describe the gia induced sea level fall and they provided the first physical explanation for the process they argued that water migrated away from far field equatorial ocean basins in order to fill space vacated by collapsing forebulges at the periphery of previously glaciated regions we provide a complete physical explanation for the origin of equatorial ocean syphoning and the associated development of sea level highstands using numerical solutions of the equation that governs meltwater redistribution on spherical viscoelastic earth models in particular we separate the total predicted sea level change into contributions associated with ice and meltwater loading effects and by doing so isolate a second mechanism that contributes significantly to the ocean syphoning process ocean loading at continental margins induces a levering of continents and a subsidence of offshore regions that has also long been recognized within the gia literature walcott 1972 we show that the influx of water into the volume created by this subsidence produces a sea level fall at locations distant from these margins indeed over the major ocean basins that is comparable in amplitude to the syphoning mechanism isolated by mitrovica and peltier 1991

scale dependent compensational stacking an estimate of autogenic time scales in channelized sedimentary deposits recent studies show that paleoenvironmental allogenic signals preserved in the stratigraphic record may be contaminated or overprinted by internally generated autogenic sedimentation this is problematic but it is unclear over what temporal and spatial scales autogenic patterns are most prevalent we propose that scale breaks in basin fi lling trends can be used to identify the transition between allogenic and autogenic stratigraphy using data from numerical and physical experiments and an ancient outcrop we explore how compensation the tendency for sediment transport systems to preferentially fi ll topographic lows varies with stratigraphic scale object based models demonstrate the temporal scales at which stratigraphy changes from being partially infl uenced by autogenic processes to being completely determined by allo genic forcings and suggest that this transition occurs at a time scale set by the maximum scale of surface roughness in a transport system divided by the long term aggradation rate this hypothesis is validated in a physical experiment where delta topography was monitored along fl ow perpendicular transects at a high temporal resolution relative to channel kine matics the strength of compensation in the experiment changes at the predicted time scale where the maxi mum surface roughness is equal to the depth of the experimental channels above this compensation time scale deposits stack purely compensationally but below this time scale deposits stack somewhere between randomly and deterministically similar scale dependent stacking is also observed in the ferris formation cretaceous paleogene hanna basin wyoming united states this study demonstrates that scale dependent compensational stack ing may be useful for isolating allogenic and autogenic stratigraphy in sedimentary basins

the hellenic margin from eastern crete to rhodes preliminary results abstract complementary data on previously surveyed areas have been obtained and more than 3000 km of continuous seismic profiles along the eastern hellenic continental margin between eastern crete and rhodes have been made among the important preliminary observations we note the relatively great thickness due to probable coarse rapid fill of the margin sedimentary cover which is also intensively affected by extensional faulting the presence of a well defined sedimentary basin lying between the strabo and pliny trench where evaporitic strata exist but where the acoustic facies also suggest coarse fill is probably derived from surrounding topographical highs exposed to erosion during the messinian finally we observe a progressive and perplexing change of the strabo trench structural pattern from west to east which indicates a more complex tectonic regime than we expected we speculate that at the southern margin of the rhodes basin northward thrusting may now be occurring

generation and nonlinear evolution of shore oblique transverse sand bars the coupling between topography waves and currents in the surf zone may self organize to produce the formation of shore transverse or shore oblique sand bars on an otherwise alongshore uniform beach in the absence of shore parallel bars this has been shown by previous studies of linear stability analysis but is now extended to the finite amplitude regime to this end a nonlinear model coupling wave transformation and breaking a shallow water equations solver sediment transport and bed updating is developed the sediment flux consists of a stirring factor multiplied by the depth averaged current plus a downslope correction it is found that the cross shore profile of the ratio of stirring factor to water depth together with the wave incidence angle primarily determine the shape and the type of bars either transverse or oblique to the shore in the latter case they can open an acute angle against the current up current oriented or with the current down current oriented at the initial stages of development both the intensity of the instability which is responsible for the formation of the bars and the damping due to downslope transport grow at a similar rate with bar amplitude the former being somewhat stronger as bars keep on growing their finite amplitude shape either enhances downslope transport or weakens the instability mechanism so that an equilibrium between both opposing tendencies occurs leading to a final saturated amplitude the overall shape of the saturated bars in plan view is similar to that of the small amplitude ones however the final spacings may be up to a factor of 2 larger and final celerities can also be about a factor of 2 smaller or larger in the case of alongshore migrating bars the asymmetry of the longshore sections the lee being steeper than the stoss is well reproduced complex dynamics with merging and splitting of individual bars sometimes occur finally in the case of shore normal incidence the rip currents in the troughs between the bars are jet like while the onshore return flow is wider and weaker as is observed in nature

sequence stratigraphic evolution and cyclicity of an ancient coastal desert system the pennsylvanian permian lower cutler beds paradox basin utah u s a abstract the lower cutler beds comprise a 200 m thick succession of at least 12 repeating cyclic packages of strata each 10 18 m thick that are of mixed eolian fluvial and shallow marine origin these accumulated during the latest pennsylvanian to early permian in the paradox foreland basin of southeast utah each depositional cycle comprises a lower unit composed of a bioclastic wackestone or a bioclastic sandy calcarenite facies both of shallow marine origin the upper units in each cycle are of nonmarine eolian dune and interdune and fluvial channel and floodplain origin the mixed nonmarine and shallow marine nature of the inferred paleoenvironments of the lower cutler beds is significant because the preserved expression of the nonmarine eolian and fluvial units in each cycle demonstrates an external climatic control on system development whereas the marine units in each cycle together with associated transgressive and regressive surfaces demonstrate repeated episodes of relative sea level change key stratigraphic surfaces have been traced from the continentally dominated northeastern portion of the basin into apparently contemporaneous shallow marine dominated sections in the southwest of the basin interdependent changes in both climate and relative sea level change are shown to have generated the preserved cycles which are interpreted to represent high frequency sequences that are bounded by erosional unconformities sequence boundaries and paraconformities diastems relative sea level lowstand was coincident with climatic aridity at which time exposure of a broad low relief coastal plain enabled the generation of a substantial eolian sediment supply that was available for transport by a paleowind aligned parallel to the trend of the paleocoastline resulting in dune field construction and accumulation along a coastal belt episodes of relative sea level rise were coincident with a transition to a more humid paleoclimate during which the eolian sediment supply was greatly reduced resulting in dune field deflation and associated expansion of the fluvial system across the deflated former dune field surface marine transgression occurred first in a series of estuarine embayments via the back flooding of broad but shallow fluvially incised valley systems later transgression culminated in marine incursion over the former low relief floodplain episodes of relative sea level highstand were coincident with maximum climatic humidity the high frequency sequences make up a composite sequence set which itself records a longer term relative sea level cycle at this larger scale a lowstand systems tract is recorded in the lower part of the studied lower cutler beds succession whereas a substantial transgressive systems tract is developed in the upper part a regionally extensive maximum flooding surface defines the top of the lower cutler beds the preserved thickness and number of high frequency cycles together with their relation to the long term subsidence trend of the paradox basin records a periodic switching of both climate and relative sea level the temporally linked nature of which demonstrates that glacio eustasy exerted a dominant control on the origin of the preserved succession the lower cutler beds preserve evidence for the linkage and feedback between combined climatic and eustatic allogenic controls on sedimentation and their role in generating high frequency milankovitch style cycles in mixed clastic carbonate successions

determination of water depth with high resolution satellite imagery over variable bottom types a standard algorithm for determining depth in clear water from passive sensors exists but it requires tuning of five parameters and does not retrieve depths where the bottom has an extremely low albedo to address these issues we developed an empirical solution using a ratio of reflectances that has only two tunable parameters and can be applied to low albedo features the two algorithms the standard linear transform and the new ratio transform were compared through analysis of ikonos satellite imagery against lidar bathymetry the coefficients for the ratio algorithm were tuned manually to a few depths from a nautical chart yet performed as well as the linear algorithm tuned using multiple linear regression against the lidar both algorithms compensate for variable bottom type and albedo sand pavement algae coral and retrieve bathymetry in water depths of less than 10 15 m however the linear transform does not distinguish depths 15 m and is more subject to variability across the studied atolls the ratio transform can in clear water retrieve depths in 25 m of water and shows greater stability between different areas it also performs slightly better in scattering turbidity than the linear transform the ratio algorithm is somewhat noisier and cannot always adequately resolve fine morphology structures smaller than 4 5 pixels in water depths 15 20 m in general the ratio transform is more robust than the linear transform

the extent of u series disequilibria produced during partial melting of the lower crust with implications for the formation of the mount st helens dacites the extent to which u series disequilibria can be produced during partial melting of mafic lower crust is quantified using a simple batch melting model and both experimental and theoretical partition coefficients for u th and ra we show that partial melting of mafic lower crust can only produce small disequilibria between 238u 230th and 226ra crystallisation of basalt and mixing between young basalt and crustal derived melts will have a similar or smaller effect consequently u series disequilibrium in arc andesites and dacites can generally only be an inherited feature derived from a mantle parent unless the timescales of silicic magma production within the crust are short compared to the half life of 226ra our results have profound implications for several recent models of silicic magma production by thermal incubation and partial melting of the lower crust we show that the 226ra excess observed in most arc andesites and dacites requires extremely rapid differentiation and or the involvement of mantle derived basalts less than a few thousand years old application to mount st helens suggests that crystallisation of young mantle derived magma is likely to be the dominant process in the formation of these dacites

the statistics and kinematics of transverse sand bars on an open coast abstract ten years 1987 1996 of time exposure video images of the nearshore region at duck nc were used to study transverse sand bars bathymetric features of intermediate length scales 10 200 m oriented oblique or perpendicular to the shoreline these transverse sand bars extend seaward from both the shoreline trough transverse bars and the shore parallel sand bar offshore transverse bars transverse bars had not previously been observed in an energetic coastal environment such as that at duck and their dynamics and role in nearshore processes is unknown frequency of occurrence statistics and length scales of the transverse bars were calculated using the video images trough and offshore transverse bars appeared a mean of 39 and 73 days per year respectively the offshore bars were found to be much larger features than the trough bars with mean wavelengths alongshore spacing between consecutive crests of 79 and 172 m for trough and offshore bars respectively both the trough and offshore bars were found to persist for periods of days to months the alongshore movement of the bars was measured and compared to estimates of surf zone longshore currents which were calculated from wave height and wave angle data both sets of bars were observed to move at rates up to 40 m day at times both trough and offshore bars were observed shifting in the same direction as the current was flowing and at other times both sets of bars remained stationary even under relatively strong longshore currents trough bars were also observed moving against the current an hypothesis proposed by barcilon and lau 1973 j geophys res 78 15 2656 2664 that the transverse bars were created as a sea bed instability under longshore currents was tested by comparing the magnitude of estimated surf zone longshore currents with times of formation or presence of transverse bars there was no evidence to suggest that the bars were formed by this simple longshore current instability mechanism instead it is plausible that the combined effects of waves and currents may drive the formation of these features

mixed siliciclastic carbonate evaporite sedimentation in an arid eolian landscape the khor al adaid tide dominated coastal embayment qatar abstract the khor al adaid embayment of southern qatar represents a unique shallow water mixed siliciclastic carbonate coastal depositional system that developed in a hyper arid climatic setting over the past 6000 years the embayment which was formed during the flandrian transgression as a result of flooding across a partially fault controlled incised fluvial drainage is supplied by quartz rich sands delivered by wind blown dunes migrating southward across the surface of qatar these offshore migrating eolian derived sediments are being redistributed by tidal currents in an otherwise low energy coastal zone where in situ formation of carbonate mud and a low diversity skeletal assemblage is ongoing within salinity restricted environments three depositional sectors are delineated 1 an energetic linear fault controlled entrance channel into which the eolian dunes spill directly 2 a relatively deep up to 20 m outer lagoon interpreted to represent a flooded karst collapse structure and 3 a sprawling low energy shallow physical oceanographic modeling integrating multi seasonal current meter and tidal gage measurements demonstrates tidal current flow velocities are relatively high in both the entrance channel and at the constricted entrance to the inner lagoon associated flow expansion into less confined areas results in deposition of the eolian derived sands as flood tidal deltas one in the outer and two in the inner lagoon a weakly developed ebb tidal delta occurs where the entrance channel debouches into the arabian gulf flood tide dominance is also apparent in entrance channel deposits where sand accumulates in seaward terminating ebb barbs along the margins of the flood dominant thalweg such flood tide dominance of the thalweg is unusual and likely reflects the absence of river discharge evidence of significant inverse estuarine circulation seaward flow of a brine along the embayment floor is mostly absent in spite of the landward increase of salinity where concentrations reach more than double normal seawater salinity in the inner lagoon modeling results show that seaward flowing brines formed in the inner lagoon are trapped in the relatively deep outer lagoon and that mixing by tidal currents in the energetic entrance channel precludes the formation of vertical density gradients there because siliciclastic mud is essentially absent and most of the sediment forming the deltas consists of sand upper intertidal deltaic deposits that would normally consist of mud are absent resulting in the flood tide deltas having a pronounced lobate geometry similar to that of fluvial deltas formed predominantly of sand away from tidal deltas low energy lagoons are floored by carbonate mud of local production with minor gypsum precipitating in the inner lagoon wind generated waves only locally influence sedimentation forming complex nearshore bars along some lagoonal shorelines the overall landward increase in salinity is accompanied by a decrease in the diversity of benthic fauna and their skeletal remains a fairly diverse faunal assemblage is observed in the entrance channel near the arabian gulf including colonial corals whereas the inner lagoon assemblage is dominated gastropods belonging to pirenella cingulata the remnants of large eolian dunes are preserved in the low energy setting of the inner lagoon segmenting the waterbody and locally increasing restriction the sedimentology of the arid zone coastal khor al adaid embayment may serve as an analogue for environmental settings that were perhaps more commonplace in arid zones of flooded continents during greenhouse times

catastrophic flooding of an aeolian dune field jurassic entrada and todilto formations ghost ranch new mexico usa surveyed outcrops of the middle jurassic entrada sandstone at ghost ranch new mexico show the unusual occurrence of preserved aeolian dune palaeotopography buried beneath subaqueous strata the preserved dune remnants have relief up to 35 m trend nnw and show internal scalloped cross strata dipping to the wsw with small sets occurring as both topsets and bottomsets outcrop data are best satisfied in computer models by 50 m high sinuous bedforms that migrated to the wsw while the sinuosity migrated alongcrest to the nnw superimposed small dunes occurred upon the stoss slope and at the basal lee of the main bedform where they migrated alongslope to the nnw remnant dune palaeotopography is buried by onlapping subaqueous largely structureless sandstones believed to be derived by mass wasting of the upper portions of the dunes and deposited as sediment gravity flows that infilled between the dunes preservation of dune palaeotopography beneath mass flow deposits with no evidence for gradually rising water argues that flooding of the entrada dune field was geologically instantaneous the thickness and lithology of the overlying todilto formation conform to slight remnant palaeotopography on the entrada surface the todilto is a laminated limestone and thinnest over remnant dune crestal areas but thickens and increases in gypsum content downslope until it abruptly yields to a gypsum mound positioned over a remnant interdune hollow the todilto laminations are interpreted as seasonal varves deposited below wave base in a density stratified water body the flooding event that gave rise to the controversial todilto water body occurred during entrada time with todilto deposition occurring within an already substantial water body

late holocene morphodynamics in the littoral zone of the iwik peninsula area banc d arguin mauritania abstract in the littoral zone of the banc d arguin both littoral sedimentary units and man made deposits shell middens abound they were formed during the late holocene after the final onset of the post glacial transgression here a geo archaeological approach is used to study them the geomorphological and sedimentological characteristics of the coastal features define two distinct coastal sedimentary units in the iwik aouatil zone between an ancient shoreline which formed on the tafaritian substratum ca 6 7 5 7 cal ka bp and the present one i very extensive sand flats and ii linear relief features both covered by a thin veneer of anthropogenic anadara senilis shell middens they developed under a stable sea level regime the sand flats expanded at variable rates throughout the period the linear relief features represent beach barriers and coastal dunes which can be dated archaeologically thanks to the superimposed shell middens supplemented by 14 c dating two series of linear sedimentary units are identified first a complex north south system of dunes and hook ended sand barriers developed from 4 8 to 4 1 cal ka bp and secondly two regular and linear beach barriers developed between 3 7 and 3 3 cal ka bp their morphological characteristics suggest that they were generated through littoral drift processes directional changes observed between the first and the second groups demonstrate that the wave refraction pattern was dramatically modified after the closure of the strait between the former iwik island and the land a comparison with the nearby jerf el oustani coastal area in the late holocene shows that both sites shared similarities in depositional patterns but also differences in the chronology of the sedimentary units processes involved in the development of the linear units are indicative of the enhancement of both sand influx and longshore drift due to climatic change

rippled scour depressions on the inner continental shelf off central california abstract side scan sonar records taken during the recent coastal ocean dynamics experiment code show elongate shore normal rippled depressions of low relief on the inner continental shelf off central california between bodega bay and point arena these features extend up to 2 km from the coast into water depths of up to 65 m the proposed mechanism for their generation is storm generated bottom currents associated with coastal downwelling during the late fall and winter which scour the surficial fine sand sediment and expose the coarser sand substrate in the depressions the zones of most intense erosion and the irregular spacing of the features may be controlled by submerged rock ledges and other prominent coastal features the large straight crested ripples within the depressions heights to 40 cm wavelengths to 1 7 m are probably formed by large amplitude long period surface waves generated by winter storms

styles of interaction between aeolian fluvial and shallow marine environments in the pennsylvanian to permian lower cutler beds south east utah usa the pennsylvanian to permian lower cutler beds comprise a 200 m thick mixed continental and shallow marine succession that forms part of the paradox foreland basin fill exposed in and around the canyonlands region of south east utah aeolian facies comprise i sets and compound cosets of trough cross bedded dune sandstone dominated by grain flow and translatent wind ripple strata ii interdune strata characterized by sandstone siltstone and mudstone interbeds with wind ripple wavy and horizontal planar laminated strata resulting from accumulation on a range of dry damp or wet substrate types in the flats and hollows between migrating dunes and iii extensive near flat lying wind rippled sandsheet strata fluvial facies comprise channel fill sandstones lag conglomerates and finer grained overbank sheet flood deposits shallow marine facies comprise carbonate ramp limestones tidal sand ridges and bioturbated marine mudstones during episodes of sand sea construction and accumulation compound transverse dunes migrated primarily to the south and south east whereas south westerly flowing fluvial systems periodically punctuated the dune fields from the north east several vertically stacked aeolian sequences are each truncated at their top by regionally extensive surfaces that are associated with abundant calcified rhizoliths and bleaching of the underlying beds these surfaces record the periodic shutdown and deflation of the dune fields to the level of the palaeo water table during episodes of aeolian quiescence fluvial systems became more widespread forming unconfined braid plains that fed sediment to a coastline that lay to the south west and which ran approximately north west to south east for at least 200 km shallow marine systems repeatedly transgressed across the broad low relief coastal plain on at least 10 separate occasions resulting in the systematic preservation of units of marine limestone and calcarenite between units of non marine aeolian and fluvial strata to form a series of depositional cycles the top of the lower cutler beds is defined by a prominent and laterally extensive marine limestone that represents the last major north eastward directed marine transgression into the basin prior to the onset of exclusively non marine sedimentation of the overlying cedar mesa sandstone styles of interaction between aeolian fluvial and marine facies associations occur on two distinct scales and represent the preserved expression of both small scale autocyclic behaviour of competing coeval depositional systems and larger scale allocyclic changes that record system response to longer term interdependent variations in climatic and eustatic controlling mechanisms the architectural relationships and system interactions observed in the lower cutler beds demonstrate that the succession was generated by several cyclical changes in both climate and relative sea level and that these two external controls probably underwent cyclical change in harmony with each other in the paradox basin during late pennsylvanian and permian times this observation supports the hypothesis that both climate and eustasy were interdependent at this time and were probably responding to a glacio eustatic driving mechanism

erosional remnants and adjacent unconformities along an eolian marine boundary of the page sandstone and carmel formation middle jurassic south central utah sandstone ridges along the marine eolian boundary of the middle jurassic page sandstone eolian with the lower carmel formation restricted marine in south central utah have been identified as erosional remnants consisting of strata of siliciclastic sabkha and eolian origin the ridges lie within two distinct units of the thousand pockets tongue of the page two equally plausible models explain the genesis of these ridges one model involves 1 early cementation of eolian and sabkha strata 2 wind erosion leading to development of yardangs and unconformities 3 yardang tilting due to evaporite dissolution and 4 renewed deposition and burial the alternative model explains ridge development through 1 subsidence with tilting of eolian and sabkha strata into evaporites due to loading from linear dunes 2 evaporite dissolution and unconformity development and 3 renewed deposition and burial these models provide important clues about the nature of a missing part of the rock record reconstruction of units that were deposited but later eroded improves paleogeographic interpretation and here indicates that the carmel paleoshoreline was considerably farther to the northwest than previously believed

rating curves and estimation of average water depth at the upper negro river based on satellite altimeter data and modeled discharges summary the objective of this study is to derive the stage discharge relationship for 21 virtual gauge stations located at the upper negro river amazon basin brazil a virtual station can be defined as any crossing of water body surface i e large rivers by radar altimeter satellite tracks rating curve parameters are estimated by fitting with a power law the temporal series of water surface altitude derived from satellite measurements and the discharge discharges are calculated using progum a flow routing model based on the muskingum cunge m c approach considering a diffusion cum dynamic wave propagation leon j g bonnet m p cauhope m calmant s seyler f submitted for publication distributed water flow estimates of the upper negro river using a muskingum cunge routing model based on altimetric spatial data j hydrol among these parameters is the height of effective zero flow measured from the wgs84 ellipsoid used as reference it is shown that the height of effective zero flow is a good proxy of the mean water depth from which bottom slope of the reaches can be computed and manning roughness coefficients can be evaluated mean absolute difference lower than 1 1 m between estimated equivalent water depth and measured water depth indicates the good reliability of the method employed we computed the free surface water slope from envisat altimetry data for dry and rainy seasons these profiles are in good agreement with the bottom profile derived from the aforementioned water depths also the corresponding manning coefficients are consistent with the admitted ranges for natural channels with important flows superficial width 30 5 m chow v t 1959 open channel hydraulics mcgraw hill new york and irregular section

the carbonate evaporite lagoon of al dakhirah qatar an example of a modern depositional model controlled by longshore transport the southern coast of the arabian gulf is considered a good example of an arid carbonate depositional system the objective of this field investigation is to better elucidate the dynamic controls on the character and pattern of the depositional belts in a carbonate evaporite lagoonal setting the interpretation of this lagoon is based on combined field examination and laboratory analyses of surface samples and this has resulted in an updated depositional model for carbonate evaporite lagoonal settings this study highlights the effects of sediment transport by longshore currents with the formation of sand spits that gradually closed the lagoon during their southwards migration the associated narrow and elongated back barrier settings consist of tidal dominated muddy sediments affected by a network of tidal channels this wave dominated high energy system has generated several carbonate barrier and back barrier units that migrated southwards and seawards during the last few thousands of years this updated depositional model significantly differs from shoreline parallel facies tracts of the classical trucial coast model where the dominant wind is orientated perpendicular to the coastline conversely to the sediment belts of the trucial coast the al dakhirah lagoon displays a strongly asymmetrical pattern of the sediment belts marked by a southwards and seawards migration

the role of non uniform roughness in the formation of sand ribbons abstract sand ribbons typically are shallow water sedimentary features characterized as thin elongate bands of sand overlying a coarser lag sediment which is exposed between them the ribbons are oriented along the direction of the dominant current and are formed by a secondary circulation pattern that includes a small component of the boundary shear stress directed toward the center of the sand ribbons a perturbation expansion coupled with flume experiments indicates that this circulation pattern is linked to differences in the bottom roughness between the sand ribbons and the adjacent coarser strips the non uniform turbulence field arising from this roughness distribution drives a secondary helical flow the expansion indicates that there is a preferred ratio of sand ribbon spacing to water depth 4 1 for unstratified channel flow conditions the secondary flow pattern forces the downstream flow to readjust so that the boundary shear stress over the smooth sand strips is considerably smaller than the mean stress this serves to retard the movement of sand through such a system

whitings a sedimentologic dilemma whitings drifting clouds of water milky because of suspended carbonate have been claimed to originate from either the action of bottom feeding fish or direct precipitation of calcium carbonate five cruises during different seasons were made to the great bahama bank to collect data pertinent to the controversy measurements of particulate concentrations average 10 mg liter with a maximum of 20 mg liter of carbonate sediment suspended in whiting water compared with an average of 1 5 mg liter for clear water outside the whitings the particles are dominantly acicular aragonite but mg calcite composes as much as 20 percent of some whitings sedimentation rates measured with fixed and drifting sediment traps were as great as 34 g m 2 hr sediment suspended in whitings aggregated into silt and sand size fioccules and settled to the bottom of settling tanks within six hours even on a rocking ship sediment in artificial whitings created by stirring sediment from the bottom with a shrimp trawl settled to the bottom in about the same time natural whitings on the other hand were never observed to dissipate because sedimentation from whitings occurs at rates sufficient to cause dissipation of the whitings within six hours we conclude that the natural whitings are continually replenished by direct precipitation the search for fish in whitings utilized sidescan sonar and fathometer imaging shrimp trawls rotenone remote video and direct scuba observation these methods and 25 years of casual observations leading to this study indicate that fish are not involved in the formation of most bahamian whitings several whitings were found over rocky or sandy bottoms where there was no mud available for fish to suspend the distance of these whitings from areas of muddy bottom precluded their having been made elsewhere by fish stable carbon and oxygen isotopic analyses and delta 14 c activity are interpreted to indicate that the suspended sediment in whitings contains some precipitated calcium carbonate and is not merely bottom sediment stirred into suspension estimates indicate that the amount of new carbonate produced in whitings on the great bahama bank is substantially higher than that arising from algal production consequently the amount of sediment transported to deep water may be much greater than previously thought

changes in rate of transgression across the permian white rim sandstone southern utah abstract a change in the rate of transgression of the permian kaibab sea across southern utah is proposed on the basis of stratal relations and preserved paleotopography in the permian white rim sandstone as the kaibab sea transgressed southern utah across a generally west dipping continental margin the rate of transgression increased interbedded coastal dune sandstones white rim sandstone and marine carbonates kaibab limestone reflect slow transgression across what is now south central utah preserved paleotopography and the absence of intertonguing of carbonates and sandstones in southeastern utah reflects a more rapid transgression indicating that the rate of sea level rise increased with time throughout the transgression relative rise in sea level was discontinuous and punctuat d by stillstands in general intervening stillstands decreased in duration as the transgression progressed this change in transgression rate can be interpreted in one of two ways rate of regional sea level rise across southern utah increased with time or previously unrecognized and localized subsidence occurred in eastern utah during kaibab transgression although regional tectonism is important we favor the former interpretation because no independent evidence of local tectonic movement can be found