effects of wave current interactions on suspended sediment dynamics during strong wave events in jiaozhou bay qingdao china abstractwave current interactions are crucial to suspended sediment dynamics but the roles of the associated physical mechanisms the depth dependent wave radiation stress stokes drift velocity

barotropic tides in the global oceans from a nonlinear tidal model assimilating altimetric tides 1 model description and results in this first part of a two part paper we present results from a high resolution data assimilative fully nonlinear barotropic tidal model of the global oceans that excludes the arctic the model assimilates in waters deeper than 1000 m altimetric tides derived from the analysis of 2 years of topex altimetric data it also assimilates tide gage data from coastal tide gages the model domain includes that covered by the altimeter and extends to the antarctic in the first part we present tidal results for the primary semidiurnal m2 s2 n2 and k2 and diurnal k1 o1 p1 and q1 constituents the second part deals with applications kantha et al this issue the model results are compared with observational data from pelagic gages these comparisons show that overall in the open ocean in deep waters away from the margins of the primary basins the model performance is comparable to other tidal models derived using topex data except for m2 and s2 however one advantage of this model compared with those based solely on the analysis of altimetric data is that the altimetry derived tides are subjected to dynamical constraints by the model this results in reduction of subtidal variability often folded into tidal signals by topex data analysis it is also shown that in shallow waters along the margins especially in east asian marginal seas the model differs substantially from these other models in addition to sea surface heights we also present dynamically consistent barotropic currents in the form of tidal ellipses for m2 and k1 constituents since the goal of this research is a global tidal model uniformly valid in both deep and shallow waters we finally present tidal elevations and currents on two well known shallow water areas the northwest european shelf and the northeast american shelf and a semienclosed western pacific marginal sea the bering sea the model results are compared with independent observations and where possible with results from other numerical models the results highlight the importance of bottom topography on the northwest european shelf where accurate bottom topography was included in the model the results are much better than on the northeast american shelf where the digital bathymetric data base 5 dbdb5 topographic database has significant errors results from the bering sea where the topography is more accurate than the dbdb5 compare well with known tides in the region

shelf wide erosion deposition and suspended sediment tranport during cyclone winifred central great barrier reef australia abstract observation of shelf sediments collected immediately before and after cyclone winifred crossed the central great barrier reef shelf 1 february 1986 confirmed that the storm produced a normally graded mixed terrigenous carbonate storm layer extending 30 km offshore in water up to 43 m deep distinct post winifred changes in the cross shelf distribution of organic carbon and carbonate in the mud fraction of the sediment suggest that suspended sediment transport was extensive and that the storm layer had multiple sediment sources on a shelf wide scale the storm layer is composed almost entirely of reworked shelf sediment erosion depths were greater on the mid shelf 20 40 m water depth than on the inner shelf 6 9 cm and 5 1 cm respectively particles finer than medium sand were eroded and transported out of the mid shelf the inner shelf portion of the storm layer formed by the combination of three sediment sources including 1 seaward transport of terrigenous sediment in buoyant freshwater flood plumes 2 resuspension and settling of inner shelf sediment and 3 resuspension and shoreward transport of mid shelf sediment mass balance calculations predict that at least 10 30 of the inner shelf storm layer is composed of mid shelf mud combined wave and wind forced currents probably resuspended mid shelf material and drove the suspended fraction alongshelf and shoreward a minimum distance of 15 km the results suggest that tropical cyclones are capable of sporadic but efficient cross shelf transport of suspended sediment on shallow cyclone prone shelves suspended sediment may easily be exchanged between adjacent sedimentary facies in ancient shelf sequences the transport history of the mud will be complex and stratigraphically equivalent facies may have similar mud types but completely different sands

intercomparison of recent ocean tide models one of the tremendous achievements of the topex poseidon t p satellite mission is the release of 12 new global ocean tide models during 1994 virtually all of these models are based on the high precision altimetry obtainable from the t p satellite and all of the models are superior to both the cartwright and ray 1990 1991 model as well as to the schwiderski 1980a b model when compared to tide gauges in the present intercomparison only global ocean tide models released during 1994 have been tested as t p continues to operate new ocean tide models will continue to be released and existing ocean models will be updated hence this intercomparison can only present a snapshot of the state of the art within ocean tide modeling however the intercomparison demonstrates the high accuracy and consistency of all these recent ocean tide models from a comparison with a common 104 tide gauge data set compiled by le provost and others unpublished data the general result is that six of the new ocean tide models have rms agreement better than 3 cm the obtainable accuracy with different tide gauge types raises the question about the accuracy of ground truth as ocean tide models become increasingly more accurate the accuracy of the harmonic constants derived from the tide gauge recordings becomes significant generally the rms agreement between models based on 2 years of t p altimetry is significantly better than the agreement between models based on 1 year of t p altimetry for models based on two years of t p altimetry the rms agreement has values around 2 0 1 4 1 0 and 0 7 cm for the m2 s2 k1 and o1 constituents respectively as a preliminary evaluation these values might be taken as a measure of the consistency of ocean tides estimated from the first part of the t p mission which is extremely promising for future ocean tide models derived from t p altimetry using 3 or more years of data this also suggests that further improvement using 3 or more years of data will only be marginal the differences arise when studying the ocean tides on continental shelves surrounding the ocean major differences are seen especially on the patagonian shelf as the continental shelves are critical for tidal dissipation it will be very important to improve tide models on the shelves in future global ocean tide models

accuracy assessment of recent ocean tide models over 20 global ocean tide models have been developed since 1994 primarily as a consequence of analysis of the precise altimetric measurements from topex poseidon and as a result of parallel developments in numerical tidal modeling and data assimilation this paper provides an accuracy assessment of 10 such tide models and discusses their benefits in many fields including geodesy oceanography and geophysics a variety of tests indicate that all these tide models agree within 2 3 cm in the deep ocean and they represent a significant improvement over the classical schwiderski 1980 model by approximately 5 cm rms as a result two tide models were selected for the reprocessing of topex poseidon geophysical data records in late 1995 current ocean tide models allow an improved observation of deep ocean surface dynamic topography using satellite altimetry other significant contributions include theft applications in an improved orbit computation for topex poseidon and other geodetic satellites to yield accurate predictions of earth rotation excitations and improved estimates of ocean loading corrections for geodetic observatories and to allow better separation of astronomical tides from phenomena with meteorological and geophysical origins the largest differences between these tide models occur in shallow waters indicating that the current models are still problematic in these areas future improvement of global tide models is anticipated with additional high quality altimeter data and with advances in numerical techniques to assimilate data into high resolution hydrodynamic models

seismic structure of the lithosphere from teleseismic converted arrivals observed at small arrays in the southern sierra nevada and vicinity california 21 well distributed teleseisms 30 to 100 distance were recorded by mixed broad band bb and short period sp seismic arrays at mineral king mk and horseshoe meadow hm in the southern sierra nevada and at darwin plateau dp between the inyo and argus ranges these arrays permit identification and separation of direct p and s arrivals reflections from topography scattered energy and arrivals from different back azimuths multipath arrivals p to s conversions can be identified from beamed bb or sp seismograms least squares time domain processing recovered single event receiver functions from these beamed seismograms converted phases attributable to the moho are clear and uncomplicated at dp ps p times of 3 9 4 2 s correspond to crustal thicknesses of 31 33 km assuming a mean p crustal velocity of 6 2 km s and a poisson s ratio of 0 255 ps p times at hm eastern sierra are 3 9 4 6 s 32 37 km excepting some unusual seismograms from events at back azimuths of 225 239 mk western sierra times for ps p show a strong e w asymmetry 3 9 4 1 s 31 33 km from the east and 4 8 5 3 s 39 42 km from the west the mk arrivals from the east are multiple and substantially weaker by comparison with hm and dp these results confirm the absence of a thick crust under the southern high sierra inferred from both a refraction experiment coincident with this experiment and some earlier studies at dp the moho event follows an intracrustal negative polarity event defining the top of an s wave low velocity zone this feature dips west under the sierran crest at hm but is absent farther west at mk this feature appears to be a manifestation of extensional strain and thus indicates that the surficially undeformed sierra overlies a tectonized lower crust sub moho energy is absent under the basin and range dp but is conspicuous under the high sierra at positive arrivals 7 3 s mk and 9 s hm after the p these arrivals might be from the base of a low velocity low density upper mantle body supporting the sierra

mesoscale coastal complexity and its relationship to structure and forcing from marine processes abstract this study investigates australia s coastline complexity to establish the relationship between geological inheritance and ocean processes as well as determine the characteristic length scales at which they operate each of australia s geological regions displays discrete complexity signatures indicating a correlation between coastal complexity and geology these mesoscale complexity signatures can vary enormously between regions over a range of length scales an angled measurement technique is used to quantify coastal complexity for a large number of random nodes at varying length scales around the australian continental margin cluster analysis are used to determine characteristic complexity signatures for random nodes and dimension reduction techniques and additive models are used to assess the relative effects of wave and tide power and physical variables in each geological region however although some geological regions are visibly distinct all geological regions are comprised of up to three basic classes or typologies furthermore this study demonstrates that at the mesoscale 1 100 km geological inheritance has the major influence in determining coastal complexity results show lithological mix to be an important factor and coastlines of a homogeneous lithology tend to be straighter than coastlines of mixed lithology they further demonstrate that wave action promotes a straight coastline if the lithology is homogeneous and a complex one if the lithology is heterogeneous this work will contribute to ongoing research in the classification of the australian continental margin by utilising available geophysical datasets that are fundamental to the establishment of rigorous boundaries in the regional marine planning process it provides important information about drivers responsible for coastal complexity at the mesoscale it is only from such studies that constructive quantitative approaches can be developed for robust regionalisation of coastal and marine systems

the impact of waves and tides on residual sand transport on a sediment poor energetic and macrotidal continental shelf 2019 the authors the energetic macrotidal shelf off south west england was used to investigate the influence of different tide and wave conditions and their interactions on regional sand transport patterns using a coupled hydrodynamic wave and sediment transport model residual currents and sediment transport patterns are important for the transport and distribution of littoral and shelf sea sediments morphological evolution of the coastal and inner continental shelf zones and coastal planning waves heavily influence sand transport across this macrotidal environment median 50 exceedance waves enhance transport in the tidal direction extreme 1 exceedance waves can reverse the dominant transport path shift the dominant transport phase from flood to ebb and activate sand transport below 120 m depth wave tide interactions encompassing radiation stresses stoke s drift enhanced bottom friction and bed shear stress refraction current induced doppler shift and wave blocking significantly and nonlinearly enhance sand transport determined by differencing transport between coupled wave only and tide only simulations a new continental shelf classification scheme is presented based on sand transport magnitude due to wave forcing tide forcing and nonlinear wave tide interactions classification changes between different wave tide conditions have implications for sand transport direction and distribution across the shelf nonlinear interactions dominate sand transport during extreme waves at springs across most of this macrotidal shelf at neaps nonlinear interactions drive a significant proportion of sand transport under median and extreme waves despite negligible tide induced transport this emphasizes the critical need to consider wave tide interactions when considering sand transport in energetic environments globally where previously tides alone or uncoupled waves have been considered

morphology and dynamics of large subtidal dunes in bahia blanca estuary argentina abstract the purpose of this paper is to carry out a detailed analysis of subtidal dune morphology and temporal variability and to estimate dune migration rate to improve knowledge of this topic and so enhance the existing data on different marine environments in the world and especially in south america where this information is limited two swath bathymetry surveys were conducted across a dune field in the bahia blanca estuary argentina morphometric parameters and migration rate according to the dune type were analyzed the field is composed of large dunes exhibiting two morphological configurations which are differentiated into sinuous and barchan dunes the dunes studied are the largest of the estuary with heights and wavelengths greater than 5 m and 130 m respectively the crests of the large dunes are arranged with an orientation perpendicular to the axis of the channel from geometrical analysis of the parameters the dunes show a weakly positive correlation between dune height and wavelength as too between dune height and water depth no clear relationship was observed between maximum height and wavelength parameters with water depth across the estuary the bedforms migrate in the ebb direction with mean rate of 43 m year 1 comparison of our results with previous data shows that during three decades the western boundary of dune field has been displaced 900 m towards the outer estuary however the dune field configuration and distribution of diverse types of bedform appear to be relatively stable

sediments and history of the rottnest shelf southwest australia a swell dominated non tropical carbonate margin abstract the rottnest shelf is a narrow wave dominated open shelf on the passive continental margin of southwest australia adjacent to a hinterland of low relief and sluggish drainage high physical energy low nutrients in cool subtropical waters and rapid postglacial transgression have limited carbonate productivity restricted grain types and reworked the transgressed surface to form only a thin given sufficient time the rottnest shelf could recover from drowning and form blanket like skeletal carbonates thin

positive relief over buried post glacial channels great barrier reef province australia abstract continuous seismic profiling on the continental shelf central great barrier reef province australia has delineated a major sub bottom reflector interpreted as the pre holocene surface channels eroded in this surface are infilled and overfilled by post glacial sediments filling is ascribed to estuarine backfilling during sea level rise followed by deposition of delta front deposits in many cases these fills create positive relief over buried channels hence modern shelf morphology may not be an accurate guide to the positions of pleistocene channels across the shelf

tidally incised valleys on tropical carbonate shelves an example from the northern great barrier reef australia the formation of incised valleys on continental shelves is generally attributed to fluvial erosion under low sea level conditions however there are exceptions a multibeam sonar survey at the northern end of australia s great barrier reef adjacent to the southern edge of the gulf of papua mapped a shelf valley system up to 220 m deep that extends for more than 90 km across the continental shelf this is the deepest shelf valley yet found in the great barrier reef and is well below the maximum depth of fluvial incision that could have occurred under a 120 m eustatic sea level low stand as what occurred on this margin during the last ice age these valleys appear to have formed by a combination of reef growth and tidal current scour probably in relation to a sea level at around 30 50 m below its present position tidally incised depressions in the valley floor exhibit closed bathymetric contours at both ends valley floor sediments are mainly calcareous muddy gravelly sand on the middle shelf giving way to well sorted gravely sand containing a large relict fraction on the outer shelf the valley extends between broad platform reefs and framework coral growth which accumulated through the late quaternary coincides with tidal current scour to produce steep sided locally vertical valley walls the deepest segments of the valley were probably the sites of lakes during the last ice age when torres strait formed an emergent land bridge between australia and papua new guinea numerical modeling predicts that the strongest tidal currents occur over the deepest outer shelf segment of the valley when sea level is about 40 50 m below its present position these results are consistent with a pleistocene age and relict origin of the valley based on these observations we propose a new conceptual model for the formation of tidally incised shelf valleys tidal erosion on meso to macro tidal rimmed carbonate shelves is enhanced during sea level rise and fall when a tidal hydraulic pressure gradient is established between the shelf lagoon and the adjacent ocean basin tidal flows attain a maximum and channel incision is greatest when a large hydraulic pressure gradient coincides with small channel cross sections our tidal incision model may explain the observation of other workers that sediment is exported from the great barrier reef shelf to the adjacent ocean basins during intermediate rather than last glacial maximum low stand sea level positions the model may apply to other rimmed shelves both modern and ancient

giant dune morphologies and dynamics in a deep continental shelf environment example of the banc du four western brittany france the aim of this paper is to improve the knowledge of spatio temporal variability of very large to giant dunes in deep tide dominated environment their growth mechanisms and dynamic evolution still remain in debate and constitute a significant scientific challenge in regard to difficulties to achieve accurate measures of migrations this motivated the realization of three recent swath bathymetry surveys across the wide dune field of the banc du four located offshore the western brittany the banc du four field is composed of more than 500 large dunes exhibiting a great diversity of morphologies ranging from 2d to 3d shapes and reaching the largest sizes of such sedimentary structure ever described wavelength over 1000 m and height over 30 m the analysis of the entire ensemble of dune parameters offers the opportunity to discuss the relative influence of forcings and the validity of the equations predicting the bedform geometry in shallow waters our results show a good height spacing power law correlation but do not strike the usual statistical regression observed in previous studies the steeper positive slope of the equation and the outstanding values of the height parameter reveal the complexity of local hydrodynamic regime interacting with bed load transport and sediment supply no clear relationship has been observed between asymmetry and size parameters water depth can not be considered as a major factor controlling the size of dunes otherwise the vertical sedimentary variation suggests the action of storm waves on dune crests and the horizontal migration rates of dunes in the eastern field of the banc du four were found to range from 3 to 20 m yr 1 such velocities were only mentioned before by van landeghem et al 2012 on deep continental shelves 70 m deep and attest of the still present morphodynamical equilibrium of the large dunes furthermore as was previously found for similar dunes in the irish sea no power law relationship between dune migration rates and dune size can be deduced similarly no strong correlation is established between migration rates and the degree of asymmetry nevertheless the dune asymmetry can be used to predict the migration direction as for dimension parameters the evolution asymmetry depends on the study area and migration rates more precisely when the crest lines of dunes form straight lines and their migration rates remain below 8 10 m yr 1 the degree of dune asymmetry increases with the migration rate this trend is reversed for the dunes with higher migration velocities and crests which are sinuous these results relativize the migratory predictions based on punctual geometrical observations

classification of the australian continental shelf based on predicted sediment threshold exceedance from tidal currents and swell waves abstract estimates of significant wave height and period together with tidal current speed over a semi lunar cycle were used to predict the area on the australian continental shelf over which unconsolidated sediment was mobilised threshold exceedance these sediment entraining processes were examined independently to quantify their relative importance on the continental shelf using observed grain size data mobilisation from swell waves occurred on 31 and tidal currents on 41 of the continental shelf swell wave energy is sufficient to mobilise fine sand 0 1 mm diameter to a water depth of 142 m on the otway shelf near the western entrance to bass strait tidal currents in king sound northwest shelf are capable of mobilising large areas of medium sand 0 35 mm diameter 100 of the time superimposing the distribution of threshold exceedance by wave and tidal currents indicates that there are areas on the shelf where either wave induced or tidal currents dominate some areas where waves and tides are of relatively equal importance and still other areas where neither is significant we define six shelf regions of relative wave and tidal energy zero no mobility waves only wave dominated mixed tide dominated and tides only our results provide a predictive process based understanding of the shelf sedimentary system that has applications to marine engineering projects and to regional studies of pollution dispersal and accumulation where significant shelf sediment mobilisation is a factor

australian shelf sediment transport responses to climate change driven ocean perturbations abstract how will australia s shelf and coastal seabed respond to climatic stress climate change is likely to impact ocean circulation ocean temperature and salinity and sea level fluctuations recent global ocean models have increased in reliability and predictability with considerable advances in coupling climatic oceanographic and sedimentary processes several models have been successful in reproducing surface sediment transport in both coastal and deep sea areas however studies have yet to attempt a predictive assessment of how climate change influences long term regional seabed responses using a process based stratigraphic forward model we have developed a method that could be applied worldwide to assess the impact of climate change driven ocean perturbations on the seabed here we present results of a fifty year seabed sediment transport forecast of selected regions of the australian shelf the results depict changes to sediment composition and seabed topography as a consequence of climate change driven sediment mobility erosion and carbonate growth the predicted maximum of seabed changes is around 2 m of erosion or accretion over the next fifty years most of the near shore seabed sediments are coarsening due to combined effects of waves and tides increasing floods storms and cyclonic events lead to significant changes to many coral reefs

p wave image of the peninsular ranges batholith southern california we invert earthquake p wave arrival times to image the 3d distribution of p wave velocities in the mesozoic peninsular ranges batholith and nearby areas in southern california there is a 3 velocity contrast between the eastern and western peninsular ranges at 4 and 20 km depth west side faster and a 1 to 1 5 velocity contrast across the san andreas fault zone south side faster in the san bernardino region at 4 to 14 km depth the san andreas velocity contrast is due to the juxtaposition of different rock types by slip along the fault zone the peninsular ranges batholith velocity contrast is due to a difference in rock composition across the batholith the maximum gradient in the crustal velocities is coincident with a compositional boundary within the batholith that reflects emplacement of the batholith across juxtaposed oceanic and continental crust quaternary fault development has been in part concentrated at this boundary

crustal thickness of the peninsular ranges and gulf extensional province in the californias we estimate crustal thickness along an east west transect of the baja california peninsula and gulf of california mexico and investigate its relationship to surface elevation and crustal extension we derive moho depth estimates from p to s converted phases identified on teleseismic recordings at 11 temporary broadband seismic stations deployed at 318n latitude depth to the moho is 33 63 km near the pacific coast of baja california and increases gradually toward the east reaching a maximum depth of 40 64 km beneath the western part of the peninsular ranges batholith the crust then thins rapidly under the topographically high eastern peninsular ranges and across the main gulf escarpment crustal thickness is 15 18 62 km within and on the margins of the gulf of california the moho shallowing beneath the eastern peninsular ranges represents an average apparent westward dip of 258 this range of moho depths within the peninsula ranges as well as the sharp east west gradient in depth in the eastern part of the range is in agreement with earlier observations from north of the international border the moho depth variations do not correlate with topography of the eastern batholith these findings suggest that a steeply dipping moho is a regional feature beneath the eastern peninsular ranges and that a local airy crustal root does not support the highest elevations we suggest that moho shallowing under the eastern peninsular ranges reflects extensional deformation of the lower crust in response to adjacent rifting of the gulf extensional province that commenced in the late cenozoic support of the eastern peninsular ranges topography may be achieved through a combination of flexural support and lateral density variations in the crust and or upper mantle

crustal thickness variations beneath the peninsular ranges southern california we investigate the crustal thickness under the peninsular ranges using p to s converted phases of teleseismic body waves recorded on a temporary broadband seismometer array and isolated by the receiver function method ps minus p times at sites west of a compositional boundary that separates the peninsular ranges batholith into east and west zones indicate a relatively flat deep moho ps minus p times at sites east of the compositional boundary decrease eastward moho depth estimates made from the ps delays and crustal velocities from seismic tomography indicate a relatively constant 36 to 41 km thick crust in the western zone in the eastern zone the crust thins rapidly from 35 km thick at the compositional boundary to 25 km at the edge of the salton trough a lateral distance of 30 km the lack of correlation between topography and moho depths suggests compensation via lateral density variations in the lower crust or upper mantle we propose that the compositional boundary decouples the eastern and western portions of the batholith and that the eastern portion has thinned in response to regional miocene extension or salton trough rifting or both

the flexural isostatic response of the lithosphere to extensional tectonics abstract the tectonic loading resulting from the extension of the lithosphere is examined loads resulting from crustal thinning thermal perturbations and basin infill are recognised and the resulting flexural isostatic deflection of the lithosphere is modelled in response to each of them in the presence of a listric fault during rifting regional uplift or rebound occurs as a result of both crustal thinning due to normal faulting simple shear and the elevation of the geothermal gradient while subsidence is generated by the downward acting loads created by both basin infill and thinning of the lower crust by stretching pure shear following rifting further flexural subsidence occurs in response to the cooling of the temperature field and associated sedimentary infill one of the major tectonic effects resulting dominantly from crustal thinning by normal faulting is the generation of footwall uplift the magnitude of this uplift along with basin depth and underlying crustal structure are strongly determined by the flexural rigidity of the lithosphere the amount of extension and the dip of the major basement fault along which extension is taking place depending upon the values of these parameters model calculations predict between a few tens of metres and 1 5 km of footwall uplift these values correlate closely with the magnitude of footwall uplift estimated from examples within the geological record the erosion of this rift induced topography is also proposed as a possible driving mechanism for the generation of major basin unconformities

three dimensional seismic analysis of sediment waves and related geomorphological features on a carbonate shelf exposed to large amplitude internal waves browse basin region australia this study analyses the three dimensional geometry of sedimentary features recorded on the modern sea floor and in the shallow subsurface of a shelf to upper slope region offshore australia that is characterized by a pronounced internal wave regime the data interpreted comprise an extensive 12 500 km2 industrial three dimensional seismic reflection survey that images the northern part of the browse basin australian north west shelf the most prominent seismic morphological features on the modern sea floor are submarine terrace escarpments fault scarps and incised channels as well as restricted areas of seismic distortion interpreted as mass wasting deposits besides these kilometre scale sea floor irregularities smaller bedforms were discovered also including a multitude of sediment waves with a lateral extent of several kilometres and heights up to 10 m these sedimentological features generally occur in extensive fields in water depths below 250 m mostly at the foot of submerged terraces along the scarps of modern faults and along the shelf break between the outer shelf and the upper continental rise additional bedforms that characterize the more planar regions of the outer shelf are elongate north west south east oriented furrows and ridges the formation of both sediment waves and furrow ridge systems requires flow velocities between 0 3 m sec 1 and 1 5 m sec 1 which could be generated by oceanic currents gravity currents or internal waves in the studied setting these velocities can be best explained as being generated by bottom currents induced by internal waves an interpretation that is discussed against oceanographic background data and modelling results in addition to the documentation of three dimensional seismic geomorphological features of the modern sea floor it was also possible to map kilometre scale buried sediment wave fields in the seismic volume down to ca 500 ms two way time below the present sea floor indicating the general potential for the preservation of such bedforms in the sedimentary record

estimating global shelf sediment mobility due to swell waves global climate models gcms such as those produced at the european centre for medium range weather forecasts ecmwf generate data that are relevant to the study of marine sedimentary processes we used estimates of significant wave height and period derived from an ecmwf gcm to predict for the first time the area of continental shelves over which sediment is mobilised the wave climatology was such that 0 1 mm diameter quartz sand had the potential to be mobilised on at least one occasion between july 1992 and july 1995 over 41 6 of the earth s continental shelves the north atlantic region has the most energetic global wave climate strong enough to mobilise 0 1 mm diameter quartz sand to water depths of up to 234 m at least once over a 3 year period

modern carbonate and terrigenous clastic sediments on a cool water high energy mid latitude shelf lacepede southern australia the wide lacepede shelf and narrow bonney shelf are contiguous parts of the south eastern passive continental margin of australia the shelves are open generally deeper than 40 m covered by waters cooler than 18 c and swept by oceanic swells that move sediments to depths of 140 m the lacepede shelf is proximal to the delta of the river murray and the coorong lagoon shelf and upper slope sediments are a variable mixture of holocene and late pleistocene quartzose terrigenous clastic and bryozoa dominated carbonate particles bryozoa grow in abundance to depths of 250 m and are conspicuous to depths of 350 m they can be grouped into four depth related assemblages coralline algae the only calcareous phototrophs are important sediment producers to depths of 70 m active benthic carbonate sediment production occurs to depths of 350 m but carbonate sediment accumulation is reduced on the open shelf by continuous high energy conditions the shelf is separated into five zones the strandline is typified by accretionary sequences of steep shoreface beach and dune carbonate siliciclastic sediments similar shoreline facies of relict bivalve limestone cobble ridges are stranded on the open shelf the shallow shelf c 40 70 m deep is a wide extremely flat plain with only subtle local relief it is a mosaic of grainy quartzose palimpsest facies which reflect the complex interaction of modern bioclastic sediment production dominated by bryozoa and molluscs numerous highstands of sea level over the last 80 000 years modern mixing of sediments from relatively recent highstands and local introduction of quartz rich sediments during lowstands the middle shelf c 70 140 m deep is a gentle incline with subtle relief where holocene carbonates veneer seaward dipping bedrock clinoforms and local lowstand beach complexes carbonates are mostly modern uniform clean coarse grained sands dominated by a diverse suite of robust to delicate bryozoa particles produced primarily in situ but swept into subaqueous dunes the deep shelf edge c 140 250 m deep is a site of diverse and active bryozoa growth resulting accumulations are characteristically muddy and distinguished by large numbers of delicate branching bryozoa the upper slope between 250 and 350 m depth contains the deepest platform related sediments which are very muddy and contain a low diversity suite of delicate branching cyclostome bryozoa this study provides fundamental environmental information critical for the interpretation of cenozoic cool water carbonates and the region is a good model for older mixed carbonate terrigenous clastic successions which were deposited on unrimmed shelves

sand and rhodolith gravel entrainment on the mid to outer shelf under a western boundary current fraser island continental shelf eastern australia abstract carbonate sediments on the east australian continental shelf off fraser island represent a transition from the warm water tropical carbonate deposits in the north i e the great barrier reef to cool water temperate carbonate deposits in the south on the outer shelf in 40 140 m water depth these deposits are characterised by pebble to cobble sized rhodoliths current meter data obtained from this area demonstrates that near bed southward flowing currents of up to 130 cm s occur episodically to depths of over 70 m these current events may last for several days and are probably related to intrusions of the east australian current a western boundary current onto the shelf flume experiments on different size classes of rhodoliths suggests that the threshold speed referenced to 100 cm above the bed u 100 cr for 10 mm diameter rhodoliths is of the order of 45 cm s whereas u 100 cr for 50 mm diameter rhodoliths is of the order of 80 cm s therefore the shelf currents measured are competent to initiate rhodolith movement percentage exceedence of these threshold speeds ranges from 1 to 10 surface waves also generate nearbed oscillatory flows which when combined with the steady current are considered to be important in initiating movement of the rhodoliths

swell dominated carbonates on a mississippian ramp in the canadian rocky mountain front ranges abstract the livingstone formation and the middle opal member of the mount head formation of western canada are mississippian carbonate deposits tens to hundreds of meters thick that are interpreted to have accumulated in a mid ramp wave dominated sub thermocline environment at water depths up to 100 m or more the rocks are predominantly pelmatozoan grainstones and packstones that contain abundant physical sedimentary structures the most common sedimentary structures are planar lamination swaly and hummocky cross stratification and normally graded event beds that are interpreted as having been formed by oscillatory wave currents or oscillatory dominated combined flows the abundant oscillatory currents are interpreted to have been generated by swell waves and to a lesser extent by local storms high angle planar tabular cross bedding is also present in rare discrete beds produced by unidirectional offshore directed currents the unidirectional currents that produced the dunes are interpreted to have been generated by coastal set up that produced downwelling storm currents during the rare storms that occurred along the mississippian coastline it is hypothesized that local storms were not common due to the west coast location and the tropical latitude of the study area instead it is postulated that swell waves approaching from the broad panthalassa ocean to the west were responsible for most sediment remobilization and deposition across the mid and outer ramp swell waves are believed to have resuspended sediment to greater depths than short period less organized storm waves these mississippian deposits suggest that in situ grain production on the ramp without need for the offshore transport of sediment from the shoreface resulted in two major differences from siliciclastic wave dominated settings 1 swaly cross stratification was not restricted to environments shallower than hummocky cross stratification on the upper shoreface because sand size sediment was generated across a large portion of the ramp and 2 aggradation by means other than sediment supply from shallower water caused preservation of deep water swell dominated deposits

mobility of maerl siliciclastic mixtures impact of waves currents and storm events abstract maerl beds are free living non geniculate coralline algae habitats which form biogenic reefs with high micro scale complexity supporting a diversity and abundance of rare epifauna and epiflora these habitats are highly mobile in shallow marine environments where substantial maerl beds co exist with siliciclastic sediment exemplified by our study site of galway bay coupled hydrodynamic wave sediment transport models have been used to explore the transport patterns of maerl siliciclastic sediment during calm summer conditions and severe winter storms the sediment distribution is strongly influenced by storm waves even in water depths greater than 100 m maerl is present at the periphery of wave induced residual current gyres during storm conditions a combined wave current sediment mobility index during storm conditions shows correlation with multibeam backscatter and surficial sediment distribution a combined wave current mobilization frequency index during storm conditions acts as a physical surrogate for the presence of maerl siliciclastic mixtures in galway bay both indices can provide useful integrated oceanographic and sediment information to complement coupled numerical hydrodynamic sediment transport and erosion deposition models

wave formed structures and paleoenvironmental reconstruction clifton h e and dingier j r 1984 wave formed structures and paleoenvironmental reconstruction in b greenwood and r a davis jr editors hydrodynamics and sedimentation in wave dominated coastal environments mar geol 60 165 198 wave formed sedimentary structures can be powerful interpretive tools because they reflect not only the velocity and direction of the oscillatory currents but also the length of the horizontal component of orbital motion and the presence of velocity asymmetry within the flow several of these aspects can be related through standard wave theories to combinations of wave dimensions and water depth that have definable natural limits for a particular grain size threshold of particle movement and that of conversion from a rippled to fiat bed indicate flow velocity limits the ratio of ripple spacing to grain size provides an estimate of the length of the near bottom orbital motion the degree of velocity asymmetry is related to the asymmetry of the bedforms though it presently cannot be estimated with confidence a plot of water depth versus wave height h h diagram provides a convenient approach for showing the combination of wave parameters and water depths capable of generating any particular structure in sand of a given grain size natural limits on wave height and inferences or assumptions regarding either water depth or wave period based on geologic evidence allow refinement of the paleoenvironmental reconstruction the assumptions and the degree of approximation involved in the different techniques impose significant constraints inferences based on wave formed structures are most reliable when they are drawn in the context of other evidence such as the association of sedimentary features or progradational sequences

early cretaceous intra arc ductile strain in triassic jurassic and cretaceous continental margin arc rocks peninsular ranges california the cuyamaca laguna mountain shear zone clmsz lies along the axis of the peninsular ranges batholith separating it into an eastern and western plutonic zones the shear zone involves triassic jurassic and early cretaceous plutonic units which intruded the triassic julian schist and transects the eastern edge of a cryptic lithospheric boundary separating oceanic crust on the west from continental crust on the east the julian schist crops out on either side of the cryptic lithospheric boundary and is interpreted to represent an overlap sequence this structural stratigraphic relationship indicates that the contrasting lithospheric types must have been juxtaposed prior to approximately the triassic time and as a result the clmsz probably developed in an intra arc setting at least two periods of deformation produced the polygenetic clmsz structures that formed during d1 include s1 and l1 in triassic jurassic and early cretaceous orthogneisses s1 a pervasive nw striking and ne dipping mylonitic gneissosity obliterates nearly all traces of an older magmatic fabric l1 plunges steeply to the ne lies within the plane of s1 and is locally a well developed stretching lineation d1 structures can be traced from the 115 ma oriflamme canyon protomylonite into the adjacent julian schist and are represented by a well developed s c mylonitic structures indicative of ne sw contraction d1 structures in the oriflamme canyon protomylonite and in the 118 ma pine valley granodiorite developed while these plutons were incompletely solidified hence d1 probably occurred between 118 and 115 ma and had culminated in the 105 my emplacement of the las bancas tonalite normal convergence 125 to 115 ma between the north american and farallon plates is coincident with d1 and the syntectonic emplacement of the pine valley granodiorite and the oriflamme canyon protomylonite this relationship suggests that the mechanically weak thermally and melt softened cryptic lithospheric interface between oceanic and continental lithosphere may have yielded during the normal convergence event resulting in the concentration of strain into the clmsz during arc magmatism such a conclusion underscores the possibility of using intra arc structures to deduce convergence patterns as elegantly argued in several recent papers a 12 km long normal sense shear zone transects d1 structures and formed during d2 mesoscopic structure associated with the normal sense shear zone includes s2 l2 and c2 d2 structures are the record of ne sw extension between 105 and 94 ma they may be related to the vertical loading of the clmsz by the hanging wall block of the westward verging santa rosa and borrego springs mylonite belts or they may represent an early local response to magmatically and structurally overthickened gravitationally unstable crust in the latter interpretation d2 structures are the harbingers of tertiary aged gravity driven collapse of the sw cordilleran margin

the characteristics of carbonate system recovery during a relatively dry event in a mixed carbonate siliciclastic environment in the pelsonian middle triassic proximal marginal marine basins a case study from the tropical tethyan northwest gondwana margins abstract eight early mid pelsonian middle triassic marine sedimentary successions an outcrop and subsurface sections of the ra af formation from the northwest gondwana margins facing the southeast corner of the tropical western tethyan seaway assigned to the southern intertropical convergence zone itcz south israel levant basin north arabian plate are the focus of this work the successions especially with the exclusive outcrop at har arief are a golden opportunity to observe the still connected transitional zone between the huge siliciclastic domains derived from gondwana hinterland parts north arabian plate and the open tropical tethyan marine carbonate domain and their mutual relationships this multidiscipline research tracks a carbonate recovery attempt in a dominant siliciclastic system the recovery effort was characterized by starved sedimentary conditions basin constrained oxygen stressed environments and low diverse autochthonous burrowed sediments barren of other faunal remains low diverse fossiliferous allochthonous beds transported from higher sites on the slopes revealed differential distributions of echinoids mollusks and especially foraminifera large pilammina pilamminella versus small glomospirids these variances were attributed to different environmental conditions on the slopes of each basin type and illuminate some constraints on their distribution pattern and climate affinity in the triassic southern itcz mixed carbonate siliciclastic sedimentary system the carbonate recovery phase is ascribed to a relatively dry period in the hinterland rather than to sea level rise this dry period which interrupted the relatively humid climate in the northern tropical gondwana during the pelsonian is represented by the constant although with some perturbations siliciclastic sedimentary system that prevailed in the southeastern corner of the tethys seaway during the anisian insights from the symmetric and asymmetric correlation of climate fluctuations in the hinterlands of the southeastern european basins northern hemisphere and this work from the southern hemisphere both embracing basins ascribed to the western tropical tethyan seaway illuminate the possible effects of the ictz behavior pattern and possible extra tropical forces on the climate variations

towards a statistically valid method of textural sea floor characterization of benthic habitats abstract multibeam bathymetric sonar technology and benthic habitat research require the systematic characterization of the seafloor necessitating reliable and accurate sea floor descriptors in combination with a robust means to statistically assess descriptor associations historically geoscientific sea floor characterisation involves identifying the spatial extent and relationship of geological units broadly following litho or chronostratigraphic criteria but these conventions may not be meaningful biologically because they incorporate temporal elements that stem from a geochronological qualifier textural properties of geological facies are typically given in terms of distribution dependent statistics which have been shown to be inappropriate with multimodal marine sediments such as on glaciated shelves as habitat classification is aimed at boundary definition the boundaries between groups in such cases could be arbitrary or based on very subtle differences or noise e g sampling bias this study uses an independent statistical approach pioneered by calinski and harabasz c h which offers significant advantages in determining the appropriate number of groups that might exist in any sample population used in conjunction with a multivariate extension to information entropy grain size populations can be clustered into statistically validated groups this study utilizes a 30 yr legacy of 4 class grain size data collected from the scotian shelf canadian atlantic continental margin we show that a traditional stratigraphic approach does not provide clear discrimination between basic textural types and hence basic benthic habitats considerable improvements in textural zonation are obtained using a combination of information entropy clustering and c h technique two high resolution 32 class particle size data sets yield a solution where no obvious textural groups exist contrary to published field based studies comparison of sediment grab samples to bottom photographs from other shelf sites show that photos capture sample a wider range of textural variability particularly the coarsest gravel component that is sometimes absent from grabs and therefore classification from photos creates more groups this study emphasizes that data resolution and sea floor sampling strategies should be intimately linked and to fully unravel high resolution textural data might require in excess of a four order of magnitude increase in the number of bottom sediment samples therefore data should be collected at the highest practical resolution but be reduced to a resolution meaningful for statistical analysis in accordance with the total sample population

late miocene to recent transtensional tectonics in the sierra san fermin northeastern baja california mexico basins and ranges within part of the gulf of california extensional province mexico have experienced complex distributed deformation including normal and strike slip faulting and block rotations linked to dextral shear at the pacific north america plate boundary in the sierra san fermin and southern sierra san felipe northeastern baja california normal faulting began between 12 5 and 6 ma although most extension occurred between about 6 and 3 ma strongly influencing thickness and distribution of ash flow tuffs and sedimentary deposits extension is generally 10 in 6 ma rocks and somewhat more in 12 5 ma rocks inversion of kinematic data interpreted together with published paleomagnetic data suggests that the axis of least principal stress was oriented between w e and sw ne in late miocene time our data indicate an important change in the amount of dextral shear but not necessarily the least principal stress direction wsw ene at about 3 ma structural constraints limit significant sinistral strike slip faulting conjugate to the dextral plate boundary to the last 3 my progressive changes in the geometry of faulting through time are consistent with regional strain partitioning within the pacific north america plate boundary zone and are predicted by physical and analytical models of oblique divergence as the orientation of the stretching vector changes to lower and lower values

a three dimensional barotropic model of the response of the australian north west shelf to tropical cyclones abstract a three dimensional barotropic model using a coordinate or depth transformation and forced with tropical cyclone wind and atmospheric pressure fields has been applied to the continental shelf and slope regions of the australian north west shelf the atmospheric pressure field of the cyclone causes a nearly isostatic sea level response and weak currents in an unbounded ocean the wind field would produce currents that circulate around the center of the cyclone and eject water thus tending to reduce sea level the coastline forms a boundary for the ejected water resulting in a large sea level rise and strong currents between the cyclone path and the coastline the model provides a good description of the vertical current shear as observed at a number of moorings during two different cyclones sea level rises are accurately modeled and a reasonable description of observed current strengths is achieved however the predicted currents and sea level changes at offshore stations are sensitive to the

mobility of sediment grain size distributions on a wave dominated continental shelf southeastern australia abstract seabed sediments comprise a full distribution of grain sizes previous models describing sediment mobility on the australian continental shelf have ignored the distribution of grain sizes presenting results for one size class only the mean grain size a simple model is presented which determines the probability of sediment entrainment which accounts for the full grain size distribution the model is applied to the wave dominated new south wales nsw continental shelf south eastern australia using observed grain size distribution data wave data from the port kembla waverider buoy are used to calculate sediment mobility in response to waves via two methods a simple empirical approach where maximum bed orbital velocity must exceed a critical bottom velocity and a more theoretically based approach where skin friction shear stresses must exceed a shields curve determined threshold for sediment entrainment results from the two methods compare to within 10 the effects of a variable sea are investigated by comparing sediment mobility in response to both significant and maximum waves maximum waves are found to mobilise medium fine sand fraction sediments on the mid shelf whereas significant waves mobilise medium fine sand fraction sediments on the inner shelf and only rarely the mid shelf maximum waves are capable of mobilising mud fraction size sediments if non cohesive beyond the shelf break combined wave wind generated current bed shear stresses were determined and indicate that waves dominate mobilisation on the inner and mid shelf but only wind driven currents are capable of mobilising sediments on the outer shelf during extreme wind events the distribution of bed shear stresses is consistent with the previously reported observed sediment distribution on the continental shelf determination of the sediment mobility of grain size distributions on the continental shelf is limited to available grain size distribution data consolidation of existing grain size datasets and newly collected data will allow for rapid extension of the method on a large scale

self organizing maps in geothermal exploration a new approach for understanding geochemical processes and fluid evolution understanding geochemical processes is an important part of geothermal exploration to get information about the source and evolution of geothermal fluids however in most cases knowledge of fluid properties is based on few parameters determined in samples from the shallow subsurface this study presents a new approach that allows to conclude from the combination of a variety of these data on processes occurring at depth in a geothermal reservoir the neural network clustering technique called self organizing maps soms successfully distinguished two different geothermal settings based on a hydrochemical database and disclosed the source evolution and flow pathways of geothermal fluids scatter plots as shown in this study are appropriate presentations of element concentrations and the chemical interaction of water and rock at depth one geological setting presented here is marked by fault dominated fluid pathways and minor influence of volcanic affected fluids with high concentrations of hco3 ca and sr the second is a magmatically dominated setting showing strong alteration features in volcanic rocks and accommodates acidic fluids with high so4 and si concentrations former studies i e giggenbach 1988 suggested cl hco3 and so4 to be generally the most important elements for understanding hydrochemical processes in geothermal reservoirs their relation has been widely used to classify different water types in geothermal fields however this study showed that non standard elements are at least of same importance to reveal different fluid types in geothermal systems therefore this study is an extended water classification approach using som for element correlations som have been proven to be a successful method for analyzing even relatively small hydrochemical datasets in geothermal applications

wave mechanisms responsible for grain sorting and non uniform ripple distribution across two moderate energy sandy continental shelves abstract mechanisms responsible for observed ripple geometry and grain size trends at two open coast sites are considered the field sites are two moderate energy sandy shelves on the inner continental shelf out to 50 m depth at east gippsland in southeastern australia and at pakiri in northeast new zealand both are characterised by bands of medium sediments inshore and offshore separated at 20 45 m depth by a zone with significantly coarser grain size 0 9 mm cf 0 3 mm video observations of the seabed at 126 sites on the east gippsland shelf revealed that the band was also characterised by larger wavelength ripples 1 0 m cf 0 3 m the size of the band stretching over an average of 20 km from 20 45 m depth and its presence at both field sites suggests that the observed characteristics are a long term response to physical forcing possibly in near equilibrium with modern processes numerical modelling demonstrated that grain sorting on the shelf is initiated by the presence of maxima in predicted ripple activity and seabed roughness around 35 m depth the local grain size evidently increases due to winnowing of the fines positive feedback through dependence of ripple size on grain size causes further lengthening of ripple wavelength until the pattern has evolved to become highly pronounced on the shelf and self sustaining but limited by reducing sediment mobility as grain size increases

regional variation in the distribution of trace metals in modern intertidal sediments of northern spencer gulf south australia abstract spencer gulf a sheltered marine inlet extending 270 km inland from the southern ocean is important to the maintenance of south australia s commercial fishery at the northern end of the gulf the tidal range of 3 m exposes 40 of the marine sediments at low water these intertidal flats vary from wide expanses of coarse sand to finer sediments colonized by blue green algal mats or mangroves dissecting channels are tidal with virtually no terrestrial runoff intertidal sediments from industrial and undeveloped shorelines have been analysed to determine the concentration of trace metals in the surface layer and factors influencing their local distribution physical and chemical characteristics of the depositional environment at sampling sites are defined by field measurements of temperature salinity ph and dissolved h 2 s in overlying water and by laboratory determination of the grain size organic matter and total carbonate content of the sediment samples nitric acid soluble metal content of surface sediments is highly variable with ranges of 5 mg 1 1 dissolved h 2 s indicate the highly variable chemical environment in shallow water overlying the sediments proximity to a point source the established pattern of littoral transport and the physical and chemical features of the depositional environment apparently control the distribution of trace metals in sediments

miocene to recent structural development of an extensional accommodation zone northeastern baja california mexico the gulf of california extensional province in northeastern baja california contains a major structural transition from a northern domain of widely spaced basins and ranges to a southern domain of closely spaced nnw striking high angle faults in the northern domain the western boundary of the province the main gulf escarpment is a single listric normal fault the san pedro martir fault in the southern domain it is a 5 km wide zone of numerous e dipping high angle normal faults the western half of this structural transition studied here does not occur by a single transfer fault but rather by 1 transfer of displacement from the san pedro martir fault onto multiple fault zones in the footwall without intervening cross faults and 2 increased southward disruption of the hanging wall by wnw striking strike slip faults oblique to the extension direction and nnw striking normal faults and extension fractures this structural transition involves both the hanging wall and the footwall of the escarpment the lack of a discrete transfer structure is attributed either to insufficient extension 10 or to a gradual change in geometry of the basal detachment

classifying seabed sediment type using simulated tidal induced bed shear stress abstract an ability to estimate the large scale spatial variability of seabed sediment type in the absence of extensive observational data is valuable for many applications in some physical e g morphodynamic models knowledge of seabed sediment type is important for inputting spatially varying bed roughness and in biological studies an ability to estimate the distribution of seabed sediment benefits habitat mapping e g scallop dredging although shelf sea sediment motion is complex driven by a combination of tidal currents waves and wind driven currents in many tidally energetic seas such as the irish sea long term seabed sediment transport is dominated by tidal currents we compare observations of seabed sediment grain size from 242 irish sea seabed samples with simulated tidal induced bed shear stress from a three dimensional tidal model roms to quantitatively define the relationship between observed grain size and simulated bed shear stress with focus on the median grain size of well sorted seabed sediment samples we present predictive maps of the distribution of seabed sediment classes in the irish sea ranging from mud to gravel when compared with the distribution of well sorted sediment classifications mud sand and gravel from the british geological survey digital seabed sediment map of irish sea sediments digsbs250 this grain size tidal current proxy gstcp correctly estimates the observed seabed sediment classification in over 73 of the area

wave climate sediment supply and the depth of the sand mud transition a global survey abstract the influences of wave climate and sediment supply on the depths of sand mud transitions hsmt are investigated depths of sand mud transitions smt are based on published granulometric data from surface samples gathered from 14 sites in different wave dominated coastal environments with fluvial input including high energy columbia eel russian san lorenzo copper and nepean rivers moderate energy ebro nile santa clara tseng wen and kao ping rivers and low energy po pescara and tronto rivers regimes geometric mean diameter gmd and mud percent are compiled from samples along shore normal transects and significant correlation is found between these two textural descriptors nominally the smt is defined as the transition from gmd 63 m to 25 mud this dual definition is applied to the 14 systems and hsmt is tabulated for each system correlation is found between hsmt and the depth at which wave induced bottom shear stress equals the critical erosion shear stress of the largest mud particles and also between hsmt and significant wave height lack of correlation between hsmt and sediment load of nearby rivers indicates either that the influence of sediment supply on depth of the sand mud transition is small or is not adequately represented in this study shelf width and slope do not correlate with residuals from a formalized linear relationship between hsmt and significant wave height the relationship between hsmt and wave climate is useful for calibration of numerical models of erosion and deposition in wave dominated coastal environments for prediction of seabed properties in remote or inaccessible areas and for reconstruction of paleodepth based on facies changes from sand to mud in ancient rocks

modelling seabed shear stress sediment mobility and sediment transport in the bay of fundy information about seabed stability and sediment dynamics is part of the fundamental geoscience knowledge required for the extraction of tidal energy in the bay of fundy and for the integrated management of the bay waves tidal currents and wind driven and circulation currents were obtained from oceanographic models to assess the wave and current processes for the broader bay of fundy the wave and current outputs were coupled with observed grain size in a sediment transport model to predict for the first time the seabed shear stresses sediment mobility and sediment transport patterns for the entire bay the root mean square tidal current highest in the upper bay 1 4 m s 1 is reduced to moderate in the central bay 0 5 0 8 m s 1 and decreases further in the outer bay 0 2 0 5 m s 1 the maximum tidal current occurs in the minas passage and is 5 m s 1 the mean significant wave height in contrast is the greatest in the outer bay 1 3 m and gradually decreases to the northeast in the centra

heterozoan carbonates when where and why a synthesis on parameters controlling carbonate production and occurrences abstract in modern and phanerozoic times heterozoan carbonates group a large array of depositional environments from the poles to the tropics this global assessment reviews the critical parameters and controlling factors of heterozoan carbonates i stratigraphic and global distributional trends ii oceanographic and trophic relationships and iii biological and sedimentary processes well documented case studies n 129 have been investigated when facies and stratigraphic attributes were available and when environmental settings such as oceanography climate and paleogeography were clearly identified these case studies occur during specific periods of time in the sedimentary record e g late ordovician early carboniferous early permian and neogene while they are absent during others e g triassic and jurassic periods during greenhouse to icehouse transitions and those with active thermohaline circulation are particularly conducive for heterozoan carbonates based on global oceanographic patterns and existing ecological and hydrodynamic regime classifications hallock 2001 pedley and carannante 2006 james and jones 2015 a process based classification scheme is proposed that distinguishes two main heterozoan carbonate systems i a highly productive system characterized by suspension feeding biota and ii an oligo mesotrophic warm temperate system characterized by red algal and seagrass derived biota eight depositional models are proposed that combine i the source of energy for metabolic activities that allow the carbonate producing biota to thrive and ii hydrodynamics and physiography of the depositional system that control the sediment accumulation the local and platform scale based profiles can be used to complement the facies approach of james and jones 2015

facies and stratigraphic architecture of the upper devonian lower mississippian sappington formation southwestern montana a potential outcrop analog for the bakken formation this study describes the sedimentology and stratigraphy of the devonian mississippian sappington formation in exceptional outcrop exposures in southwestern montana the goal was to assess the extent to which these outcrops could be used to define stratigraphic heterogeneity of time equivalent bakken formation reservoir and source rocks of the williston basin facies analysis of the sappington formation shows three depositional sequences deposited along a storm and wave influenced coastline the first sequence encompasses the lower sappington shale dominated by organic rich mudstones that represent an anoxic to dysoxic lower shelf environment the second sequence is marked by a basal transgressive surface and initial siltstone deposition these siltstones are abruptly overlain by basinward dipping low angle clinoforms 1 that represent a storm and wave influenced shoreface facies distributions along clinoforms change along depositional dip over approximately 17 km 11 mi from proximal to distal across the study area the best reservoir facies are present in the upper foresets of these clinoforms the upper shale of the sappington formation forms the lowest part of the third depositional sequence that continues into the overlying lodgepole limestone the outcrop based stratigraphy of the sappington formation provides insights into the scale of stratigraphic heterogeneity that is likely to be present in the time equivalent bakken formation over the length of a typical approximately 3 km long 2 mi long horizontal well geosteering horizontal wells in the bakken along bedding surfaces that is along gently dipping clinoforms is likely to cause variations in rock properties from the toe to heel of a horizontal well

seismic evidence for an ancient rift beneath the cumberland plateau tennessee a detailed analysis of broadband teleseismic p waveforms broadband receiver functions developed from teleseismic p waveforms recorded on the midperiod passband of regional seismic test network station rscp are inverted for vertical velocity structure beneath the cumberland plateau tennessee the detailed broadband receiver functions are obtained by stacking source equalizd horizontal components of teleseismic p waveforms the resulting receiver functions are most sensitive to the shear velocity structure near the station a time domain inversion routine utilizes the radial receiver function to determine this structure assuming a crustal model parameterized by many thin flat lying homogeneous layers lateral changes in structure are identified by examining azimuthal variations in the vertical structure the results reveal significant rapid lateral changes in the midcrustal structure beneath the station that are interpreted in relation to the origin of the east continent gravity high located northeast of rscp the results from events arriving from the northeast show a high velocity midcrustal layer not present in results from the southeast azimuth this velocity structure can be shown to support the idea that this feature is part of a keweenawan rift system another interesting feature of the derived velocity models is the indication that the crust mantle boundary beneath the cumberland plateau is a thick probably laminated transition zonemore between the depths of 40 and 55 km a result consistent with interpretations of early refraction work in the area less

the grain size characterisation of coastal sand from the somme estuary to belgium sediment sorting processes and mixing in a tide and storm dominated setting abstract sand rich holocene to modern clastic deposits in the eastern english channel and the southern north sea coasts of france and belgium occur extensively as nearshore sand bank estuarine tidal flat aeolian dune and beach sub environments sand samples n 665 collected from these deposits suggest the presence of three different populations a largely dominant 83 medium to fine quartz sand population b and finer 14 and coarser grained 4 populations respectively c and a the distribution of these populations among the four sub environments reflects tide and storm dominated sorting and transport processes and a variable degree of mixing these populations are derived from a mixture of very fine to very coarse grained fluvial outwash and paraglacial sediments deposited on the beds of the eastern english channel and southern north sea during the late pleistocene lowstand the nearshore sand bank environment which also corresponds to the main offshore source area of the coastal deposits exhibits population heterogeneity reflecting the variability of hydrodynamic conditions and sediment sorting in this zone the nearshore topography of tidal ridges banks and troughs in these tidal seas leads to variable bed and tide and storm induced shear stress conditions these conditions only allow for the mobilisation and onshore transport of some of the finer fractions populations b and c leaving an offshore mixture of these finer populations with coarser less mobilisable sediments population a once in the coastal zone these two finer populations undergo further hydrodynamic sorting and segregation variably sorted very fine sands to silts population c are trapped in the low energy estuarine tidal flat sub environment while the highly homogeneous population b is further sorted in aeolian dune and beach sub environments this sorting occurs via a coastal sand transport pathway linking the somme estuary mouth to the southern north sea bight where tidal range and wave energy decrease relative to the english channel since this sand transport pathway enables longshore transport of hydrodynamically sorted medium to fine sand derived directly from the immediate nearshore zone it has further contributed to a net flux of this sand population from the eastern english channel sea bed to the southern north sea

sand transport under the combined influence of waves and tidal currents an assessment of available formulae abstract various formulae are used to predict the transport of sand under the combined influence of waves and currents these approaches include the use of the unidirectional formulae of einstein 1950 frijlink 1952 yalin 1963 engelund and hansen 1967 sternberg 1972 ackers and white 1973 and gadd et al 1978 modified for the presence of waves in accordance with the techniques described by bijker 1967 and swart 1976 and those of bagnold 1963 madsen and grant 1976 and vincent et al 1981 predicted rates are compared with measurements based upon fluorescent sand tracer studies in an area of high tidal current and wave energy northern bristol channel u k in general predicted rates are lower than those measured and only the formulae of madsen and grant 1976 and the modified formula of sternberg 1972 appear to provide realistic estimates of transport under wave and tidally induced currents in comparison with the field measurements

testing for astronomical forcing of cycles and gamma ray signals in outer shelf upper slope mixed siliciclastic carbonates upper oligocene new zealand abstract we evaluate whether outer shelf upper slope settings preserve a record of astronomical forcing using gamma ray logs from the upper oligocene upper chattian tikorangi formation onshore taranaki basin north island new zealand the formation is a siliciclastic carbonate succession deposited in outer neritic to upper bathyal depths at paleolatitudes of c 45os gamma ray and sonic logs calibrated to core indicate four lithofacies based on percent carbonate these are calcareous siliciclastic mudrock highest gamma ray values highly calcareous siltstones high gamma ray values very fine to fine siliciclastic muddy packstones intermediate gamma and winnowed very fine to medium grain dominated packstones and grainstones low gamma detrended gamma ray logs were tuned using minimal tuning methods 405 kyr long eccentricity cycle or where this was poorly developed the 100 kyr short eccentricity cycle with sedimentation rates tested statistically against astronomical forcing the tuned data show well developed long and short term eccentricity obliquity and a weak precessional forcing obliquity modulation is observed at the 1 2 myr scale one well and 175 kyr scale two wells the floating time scale was tied to the absolute time scale via published biostratigraphy the la2004 eccentricity solution the atlantic odp site 1264 18o record and the mi 1 isotope event at c 23 ma sea level fluctuations typically were moderate 20 to 40 m estimated from the 18o record the high gamma siliciclastic prone units formed during warmer and wetter phases and possibly slightly higher sea levels whereas the cleaner carbonates with abundant inner shelf derived fine carbonate developed during cooler drier phases and possibly slightly lower sea levels gamma ray logs from outer shelf upper slope settings provide valuable data sets for documenting the effects of astronomical forcing on the sedimentary record the study supports climate models for new zealand which predict generally increased precipitation with warming over the next 100 years the study appears to be the first to record astronomical forcing in the oligocene marine record of new zealand

the australian coastal experiment a search for coastal trapped waves abstract the australian coastal experiment ace was conducted in the coastal waters of new south wales from september 1983 to 1984 the data obtained allow a detailed examination of the dynamics of flow on the continental shelf and slope and in particular allow a description of coastal trapped wave modes propagating within the coastal waveguide the trapped wave signal is contaminated by energy from the east australia current eddies approaching the continental slope however the data do allow a clear separation of the first three coastal trapped wave modes over the range of frequencies appropriate to the weather forcing band through that frequency range the phase speed is computed and an empirical dispersion relation determined for each mode the empirical dispersion relations compare well with the theoretical relations indicating that a large fraction of the variance in current velocities on the continental shelf can be accounted for by coastal trapped wave theory wind forcing of trapped waves is als