sediment trend models fail to reproduce small scale sediment transport patterns on an intertidal beach a rigorous test is presented of the application of sediment trend models to an intertidal beach environment characterized by bar morphology sediment samples were collected during low tide from a regular grid and their sediment fall velocity distributions obtained using a settling tube were analysed using moment analysis the net sediment transport direction determined from beach surveys hydrodynamic measurements wave ripple observations and sediment transport modelling was compared with predictions by sediment trend models based on the spatial distribution of sediment parameters it was found that the sediment transport pathways and patterns of sedimentation predicted using sediment trend models were at odds with field observations and varied significantly depending on whether surface or sub surface sediment samples were used the sediment trend models are thought to fail because in energetic and morphologically variable beach environments spatial patterns in sediment characteristics are mainly attributed to the presence of different hydrodynamic regions and associated morphology rather than sediment pathways the use of sediment trend models cannot replace the collection of morphological hydrodynamic and sediment transport data in the field to define relationships between flows forms and sedimentation patterns on a dynamic intertidal beach

the role of bore collapse and local shear stresses on the spatial distribution of sediment load in the uprush of an intermediate state beach abstract spatial variations in sediment load in the swash uprush and textural properties of sediment in transport were evaluated to investigate the mechanisms responsible for sediment transport during wave uprush four streamer traps were deployed at 2 0 m intervals across the swash zone of a sheltered microtidal sandy beach at port beach western australia over a 4 day period during these trapping experiments offshore significant wave heights were 0 3 0 5 m and wave periods were about 10 s the average width of the uprush zone was 6 9 m and the average uprush duration was 5 9 s cross shore distributions of sediment load for 70 uprush events reveal a maximum in sediment load landward of the base of the swash at about 20 of swash width during single events and a maximum closer to mid swash at about 40 of swash width during multiple events characterized by swash interactions settling velocity distributions of trap samples during individual uprush events are similar to distributions found on the beach surface with the lowest settling velocities finest sediments near the base of the swash zone and maximum settling velocities coarsest sediments around the mid swash position it was found that sediment transport during wave uprush occurs through two distinct mechanisms 1 sediment entrainment during bore collapse seaward of the base of the swash zone and subsequent advection of this bore entrained sediment up the beach by wave uprush and 2 in situ sediment entrainment and transport induced by local shear stresses during wave uprush both mechanisms are considered important but the first mechanism is considered most significant during the early stages of wave uprush when sediment is transported mainly in suspension while the second mechanism is likely to dominate the mid to later stages of wave uprush when sediment is transported mainly by sheet flow the relative importance of the two mechanisms will vary between different beaches with the morphodynamic state of the beach reflective versus dissipative expected to play a major role

retrogressive development of glaucophane in some eclogites from massif armoricain east of nantes france a petrological and mineralogical study using an electron microprobe of a blue amphibole eclogite occurring near nantes massif armoricain france has enabled us to characterize this amphibole as glaucophane resulting from a secondary reaction in the rock this sodic amphibole was formed at the expense of primary eclogite paragenesis including omphacite garnet and quartz according to a sliding reaction which it was possible to study quantitatively 3 24 omphacite 0 90 sio2 0 76 garnet 1 08 h2o 1 glaucophane 0 55 grossular s s in the garnet 0 04 paragonite

precambrian u pb zircon ages in eclogites and garnet pyroxenites from south brittany france an old oceanic crust in the west european hercynian belt abstract u pb zircon ages have been determined for two eclogites from the vendee and for two garnet pyroxenites from the baie d audierne in an episodic pb loss model the two discordia would give upper intercept ages around 1300 1250 ma and lower intercepts ages of 436 384 ma two interpretations are proposed 1 the 1250 1300 ma ages may reflect an unspecified upper mantle event or process the paleozoic ages correspond to the tectonic emplacement of an eclogitic mantle fragment into the continental crust 2 the protolith may have been extracted from the upper mantle 1250 1300 ma ago and stored in a crustal environment until it was metamorphosed under high pressure conditions around 400 ma ago this latter model is favoured by available geologic and isotopic data consequently we propose that a 1300 ma old oceanic crust was tectonicly incorporated into a sialic basement during the proterozoic this mixture was subsequently subducted during the paleozoic

application of grain size trend analysis for the determination of sediment transport pathways in intertidal areas abstract in this paper we apply the gao and collins procedure of grain size trend analysis for the first time in an intertidal sedimentary system our purpose is to evaluate a reliable method to determine residual transport directions in intertidal environments where sediment movement is not well understood residual transport patterns can be determined by grain size trend analysis if the following criteria are applied 1 a single sediment transport unit must be precisely defined and investigated 2 the thickness of sampling has to be chosen in order to investigate the most recent sedimentary event and 3 a regular mesh grid is sampled to avoid bias in the calculation of grain size trends the gao and collins method was undertaken simultaneously with a topographic survey and a tracer experiment during consecutive meteorological conditions of fair weather and a storm event the topographic changes observed between these two situations and the directions of sediment movement deduced from tracer tracking are coherent with the residual transport pattern calculated from the grain size trend analysis the method was tested on a ridge and runnel system which corresponds to the intertidal part of a macrotidal beach called la salie beach located along the southwest french coast in a high wave energy environment this study permits us to recognize two different residual transport patterns for this intertidal ridge and runnel system one for fair weather and a second for storm conditions during fair weather specific sites are subject to sand accretion while during storm conditions these sand stocks are subsequently spread out over the whole area and remain partly on the beach

beach steps an evolutionary perspective abstract field observation of contrasting beach step behavior at canaveral national seashore on two subsequent days when incident wave conditions in the inner surf zone were similar prompted this re examination of our conceptual and quantitative understanding of beach steps these lower foreshore features are more complex than previously assumed evolving through erosional as well as accretional phases and displaying equifinality in geometric form but not necessarily internal sedimentary structure past and recent evidence is reviewed that links beach steps to incident waves at the surging plunging transition and to the action of a backwash vortex tides and low frequency waves likely play no direct role in beach step initiation although their presence can have pronounced influences on modulating nearshore hydrodynamics and thus on beach step maintenance and evolution a generalized conceptual model capturing these aspects of beach step dynamics is presented beach step initiation proceeds via step carving excavation or building depending on the erosional accretional character of the beach foreshore system subsequent evolution of the step form may take one of several alternative morphodynamic pathways including stepface retreat step drag down or step infilling elimination depending on tidal stage range or wave set up setdown additional data on equilibrium beach step forms and associated morphodynamic and hydrodynamic conditions in the field are necessary before quantitative models of beach step existence and evolution can be formulated with realistic results

observations of sand bar evolution on a natural beach waves currents and the location of the seafloor were measured on a barred beach for about 2 months at nine locations along a cross shore transect extending 255 m from 1 to 4 m water depth the seafloor location was measured nearly continuously even in the surf zone during storms with sonar altimeters mounted on fixed frames the crest of a sand bar initially located about 60 m from the shoreline moved 130 m offshore primarily when the offshore significant wave height exceeded about 2 m with 1 5 m of erosion near the initial location and 1 m of accretion at the final location an energetics type sediment transport model driven by locally measured near bottom currents predicts the observed offshore bar migration but not the slow onshore migration observed during low energy wave conditions the predicted offshore bar migration is driven primarily by cross shore gradients in predicted suspended sediment transport associated with quasi steady near bottom offshore flows these strong 50 cm s currents intensified near the bar crest by wave breaking are predicted to cause erosion on the shoreward slope of the bar and deposition on the seaward side the feedback amoung morphology waves circulation and sediment transport thus forces offshore bar migration during storms

simulating the influence of groundwater seepage on sediment transported by the sweep of the swash zone across macro tidal beaches abstract a numerical model is developed to simulate the influence of groundwater seepage on swash zone sediment transport across macro tidal beaches the emergence of equilibrium profile morphology is examined in response to varying tide sediment and initial profile characteristics due to the unresolved complexities of boundary layer flow and corresponding shear stresses in the swash zone sediment transport across the beach face is modelled by incorporating an uprush phase described by the shallow water wave equations within an heuristic model of equilibrium beach face slope a new parameter termed the m net transport parameter is defined to parameterize the net flux of sediment per uprush backrush cycle the definition of differing equilibrium gradients across saturated versus unsaturated regions of the intertidal profile permits the saturation characteristics of the bed to be incorporated the dynamics of the watertable exit point on the beach face is central to the scheme as this defines the time varying extent of saturated and unsaturated regions of the intertidal profile the sensitivity of coastal seepage face development to tide profile and sediment characteristics is highlighted through the derivation of a new seepage face parameter the simulation model is found to successfully reproduce key aspects of observed profile adjustment and resulting equilibrium morphology complex morphodynamic feedback is observed between the tidal stage net transport per uprush backrush cycle profile slope and the dynamics of the watertable outcrop net upper profile steepening and lower profile lowering is simulated on beaches composed of medium to coarse sand this results in the emergence of a distinctive break in slope within the intertidal profile such morphology is commonly observed on macro tidal coasts

correlation of the nappe stack in the ibero armorican arc across the bay of biscay a joint french spanish project a correlation between allochthonous units exposed in the nw iberian massif and the southern armorican massif is carried out based on lithological associations structural position age and geochemistry of protoliths and tectonometamorphic evolution the units on both sides of the bay of biscay are grouped into upper middle and lower allochthons whereas an underlying allochthonous thrust sheet identified in both massifs is referred to as the parautochthon the lower allochthon represents a fragment of the outermost edge of gondwana that underwent continental subduction shortly after the closure of a palaeozoic ocean which in turn is represented by the middle allochthon the latter consists of supra subduction ophiolites and metasedimentary sequences alternating with basic mid ocean ridge basalt morb type volcanics with inheritances suggesting the proximity of a continental domain seafloor spreading began at the cambro ordovician boundary and oceanic crust was still formed during the late devonian covering the lifetime of the rheic ocean which is possibly represented by the middle allochthon the opening of the oceanic domain was related to pulling apart the peri gondwanan continental magmatic arc which is represented by the upper allochthon

grain size trends used to assess the effective discharge for floodplain sedimentation river waal the netherlands abstract the importance of floods of different magnitude on floodplain sedimentation can be estimated from sedimentation measurements carried out during a series of floods however because these measurements represent sediment accumulation during the entire flood they cannot be used to estimate the importance of individual flood stages on sediment deposition in this study the importance of different flood stages on floodplain sedimentation was assessed from analysis of spatial variations in grain size distributions which are indicative of sediment transport directions as a secondary objective the applicability of grain size trend analysis to fine grained floodplain sediments was tested the grain size trend analyses were carried out in a geographical information system and applied to sediment deposited on an embanked floodplain section along the river waal in the netherlands during a large flood in december 1993 because flow patterns at the studied floodplain section vary with flood stage comparison of the identified sediment transport pathways with computed flow patterns indicates at which discharge most sediment is deposited the results indicate that large discharges with a recurrence time of more than two years are most effective in depositing suspended sediment on floodplain areas enclosed by a minor river dike on floodplain sections that directly border the main channel moderate discharges with a recurrence time of about one year seem to be more efficient contrary to the results of floodplain sedimentation models low but increasing discharges with a recurrence time of less than one year and during which only low lying areas near residual channels are inundated appear important for deposition of suspended sediment in these low lying areas this observation is confirmed by measurements of spatial concentration gradients and by floodplain sedimentation measurements comparison of the trends with additional information on sediment transport directions indicates that trends in which sediment becomes finer better sorted and more negatively skewed when measured in units are most suitable for defining transport pathways on river floodplains trends may however deviate up to 90 from true transport directions flocculation does not seem to have any negative effects on the applicability of grain size trend analysis

comparing sieve and sedimentation balance analysis of beach lake and eolian sediments using log hyperbolic parameters abstract sieving and settling analyses of 29 samples from different sedimentary environments have been compared with the use of invariant log hyperbolic parameters settling velocities were not converted into millimetre size the comparison was based on kurtosis skewness and sorting of the distributions the comparison of the parameter values have been evaluated by a two tailed t test the log hyperbolic parameters values for kurtosis between the two methods differed significantly for the beach sediments skewness differed significantly in all three environments and sorting only differed significantly for the beach sediments q n a measure of fit between observations and the estimated log hyperbolic distribution differed significantly in the beach and eolian sediments the study shows that settling velocities give a better fit to the log hyperbolic distribution opposed to sieve analysis the study shows that the differences in the log hyperbolic sediment parameter values differ significantly in nearly half of the comparisons it is concluded that great attention must be paid to the method of grain size analysis

accretionary history and crustal evolution of the variscan belt in western europe abstract the variscan belt of western europe is part of a large intra paleozoic belt extending on both sides of the atlantic from the ouachitas in the us and the mauritanides in west africa to the bohemian massif in czechoslovakia and poland the belt was constructed between 500 and 250 ma as a result of convergence and collision between two main continents laurentia baltica and africa after the closure of various oceanic basins iapetus rheic and galicia massif central now recorded as discrete in part cryptic sutures which form the roots of large crystalline nappes in which are found dismembered remnants of oceanic crust and mantle the accretionary history of the variscan belt in western europe is related to the progressive closure of probably two oceanic basins the rheic in the north and another the galicia massif central in the south by respectively southward and northward intraoceanic subduction followed by obduction and intracontinental lithospheric subduction the result is a broad 700 800 km fan like divergent belt which must be considered as a classical obduction collision orogen with a long intracontinental history of about 100 150 ma its arcuate shape is probably due to the northwestward impingement of a promontory of the african continent into laurentia baltica

an alternative approach to the identification of net sediment transport paths based on grain size trends abstract progressive changes in grain size parameters have long been linked to net sediment transport paths however the methods employed to date suffer from limitations potentially leading to serious interpretational errors which necessitate the formulation of an integrated quantitative technique the approach advocated here is a step in this direction as it eliminates some of the problems inherent in the older methods previously trend vectors were obtained by comparing the grain size parameters of only two sampling stations at a time which gives a low probability of identifying the actual transport direction in the proposed method groups of five stations comprising a central station and four satellite stations are used for each trend vector grain size parameters are first combined in such a way that bias towards any one of them is climated the resultant dimensionless numbers are then substituted for the proportional frequencies of recorded directions in conventional vector analysis the satellite stations must be located equally far from the central station on radials 90 from each other which is seldom the case an iterative trigometric technique is therefore employed to determine the combined grain size parameters at these localities conventional vector analysis adapted to the situation of using four raials instead of 10 sectors allows the calculation of a vector mean azimuth and vector magnitude

metamorphic amphiboles composition and coexistence amphiboles have long been key players in metamorphic petrology the concept of facies was developed for rocks of basaltic composition eskola 1920 1939 fyfe et al 1958 and within this concept amphiboles had a leading role the first appearance of amphiboles the presence of amphiboles of certain compositions or last appearance of amphiboles that are replaced by pyroxene bearing assemblages mark a number of major facies boundaries the transition from greenschist to amphibolite facies is marked in part by hornblende replacing actinolite and the granulite facies is defined by the breakdown of hornblende to orthopyroxene bearing assemblages the blueschist facies is defined by the appearance of glaucophane while the transition from blueschist facies to eclogite facies conditions is indicated by the breakdown of glaucophane to omphacitic pyroxene bearing assemblages references to amphibole names actinolite glaucophane or rocks characterized by certain amphiboles amphibolite hornblende figure prominently in six facies names turner 1981 liou et al 1985 oh et al 1988 evans 1990 peacock 1993 a large part of the literature that is devoted to metamorphic petrology of amphiboles concerns reactions which produce amphiboles from more hydrated mafic igneous rocks or lead to the destruction of amphiboles as they break down to form anhydrous or nearly anhydrous mineral assemblages consequently amphiboles can be thought of as occupying the wide intermediate portion of p t xfluid space in which metamorphic rocks are found the number of citations of the published amphibole nomenclature serves as a yardstick meterstick of the interest in amphiboles and a minimum estimate of the amount of literature devoted to this mineral two versions of the nomenclature of amphiboles have appeared 1978 and 1997 leake 1978 leake et al 1997 and they have been cited a over 2300 times in the past 28 years this works out to a minimum

relaxation time effects of wave ripples on tidal beaches 1 seabed roughness due to wave ripples is a key factor in controlling sediment transport processes in the nearshore zone roughness is commonly considered a function of the ripple geometry which in turn can be predicted from sediment and hydrodynamic parameters existing ripple predictors consider the bed morphology to be in equilibrium with the hydrodynamics whereas recent laboratory measurements show that the time scale for ripple development is of the order of tens of minutes to hours here we show that wave ripples on tidal beaches are significantly affected by relaxation time effects with ripple height and length progressively increasing during the rising tide and remaining constant during the falling tide moreover we examine the ripples in the context of existing empirical models and suggest how the temporal evolution over a tidal cycle may be predicted

peraluminous sapphirine formed during retrogression of a kyanite bearing eclogite from pays de leon armorican massif france abstract in a quartz free eclogite from pays de leon armorican massif france kyanite has been replaced by a symplectite of plagioclase corundum spinel and sapphirine the sapphirine is amongst the most aluminous yet reported in the literature one analysis mg 1 38 fe 0 17 2 fe 0 05 3 cr 0 01 al 2 37 vi al 2 43 iv si 0 57 o 10 shows the highest degree of tschermak s substitution si 1 mg 1 al iv al vi yet reported for sapphirine omphacite has been completely transformed into clinopyroxene plagioclase symplectite a quantification of material transfer indicates that kyanite and omphacite breakdowns were coupled the kyanite and omphacite pseudomorphs exchanged components during their formation but the two pseudomorphs together behaved as a more or less closed system the kyanite symplectitisation is the source of the silica required for the omphacite breakdown i e jadeite ss sio 2 albite ss the kyanite and omphacite pseudomorphs display all the characteristics of a metasomatic system at a microscopic scale zonation diffusion fronts etc these features are explained in terms of relative mobility of the chemical components the kyanite and omphacite pseudomorphs give information about the p t path of the leon eclogites during retrograde metamorphism the appearance of sapphirine after kyanite is attributed to a low pressure and high temperature evolution from eclogite facies to granulite facies conditions

slow slip phenomena in cascadia from 2007 and beyond a review recent technological advances combined with more detailed analyses of seismologic and geodetic observations have fundamentally changed our understanding of the ways in which tectonic stresses arising from plate motions are accommodated by slip on faults the traditional view that relative plate motions are accommodated by a simple cycle of stress accumulation and release on locked plate boundary faults has been revolutionized by the serendipitous discovery and recognition of the significance of slow slip phenomena mostly in the deeper reaches of subduction zones the cascadia subduction zone located in the pacific northwest of the conterminous united states and adjacent canada is an archetype of exploration and learning about slow slip phenomena these phenomena are manifest as geodetically observed aseismic transient deformations accompanied by a previously unrecognized class of seismic signals although secondary failure processes may be involved in generating the seismic signals the primary origins of both aseismic and seismic phenomena appear to be episodic fault slip probably facilitated by fluids on a plate interface that is critically stressed or weakened in cascadia this transient slip evolves more slowly and over more prolonged durations relative to the slip in earthquakes and it occurs between the 30 and 40 km depth contours of the plate interface where information was previously elusive although there is some underlying organization that relaxes nearly all the accrued plate motion stresses along the entirety of cascadia we now infer that slow slip evolves in complex patterns indicative of propagating stress fronts our new understanding provides key constraints not only on the region where the slow slip originates but also on the probable characteristics of future megathrust earthquakes in cascadia herein we review the most significant scientific issues and progress related to understanding slow slip phenomena in cascadia and highlight some of their societal implications we provide a comprehensive review from the big picture as inferred from studies of regional scale monitoring data to the details revealed by innovative focused experiments and new instrumentation we focus on what has been learned largely since 2007 when several major investments in monitoring and temporary deployments dramatically increased the quality and quantity of available data

an energetics total load sediment transport model for a plane sloping beach bagnold s energetics based total load sediment transport model for streams is used as a basis for the development of a total load model of time varying sediment transport over a plane sloping bed in both the bedload and suspended load the transport rate vectors are found to be composed of a velocity induced component directed parallel to the instantaneous velocity vector and a gravity induced component directed down slope the model is applied to idealized surfzone conditions leading to estimates of the local longshore and onshore offshore sediment transport rates as well as the equilibrium beach slope as a function of the local wave and current conditions the model is combined with a nonlinear longshore current model and spatially integrated to obtain predictions of the total longshore transport rate as a function of the incident wave conditions the results support the general form of the wave power equation except that the wave power coefficient is no longer constant but is instead a complex function of the incident wave and beach characteristics

an interpretation of trends in grain size measures abstract the mean grain size sorting and skewness of a sedimentary deposit are dependent on the sediment grain size distribution of its source and the sedimentary processes of i winnowing erosion ii selective deposition of the grain size distribution in transport and iii total deposition of the sediment in transport if a source sediment undergoes erosion and the resultant sediment in transport is deposited completely the deposit must be finer better sorted and more negatively skewed than the source this trend is referred to as case i the lag remaining after erosion on the other hand must be coarser better sorted and more positively skewed case ii if sediment in transport undergoes selective deposition the resultant deposit can either be finer case iiia or coarser cas iiib than the source but the sorting will be better and the skew more positive although exceptions to these trends may occur they suggest that comparison of one sediment must be made with another for the proper identification of the sedimentary process and therefore it is not possible for a single grain size distribution to identify the depositional environment the trends also suggest that the skewness of a grain size distribution has been widely misinterpreted and implies neither the truncation of one of the tails nor the mixing of more than one mode rather a skewed sediment is the natural result of the sedimentary process in a system of related environments these trends can be used to identify both the probable source and the probable deposit and by inference the net sediment transport paths among sedimentary deposits such an analysis provides a rapid understanding of the sedimentary processes identifies patterns of erosion and accretion and may suggest transport processes

a complex linear least squares method to derive relative and absolute orientations of seismic sensors summary determining the relative orientation of the horizontal components of seismic sensors is a common problem that limits data analysis and interpretation for several acquisition setups including linear arrays of geophones deployed in borehole installations or ocean bottom seismometers deployed at the seafloor to solve this problem we propose a new inversion method based on a complex linear algebra approach relative orientation angles are retrieved by minimizing in a least squares sense the l2 norm between the complex traces hodograms of adjacent pairs of sensors this methodology can be applied without restrictions only if the wavefield recorded by each pair of sensors is very similar in most cases it is possible to satisfy this condition by low pass filtering the recorded waveforms the main advantage of our methodology is that in the complex domain the relative orientations of seismic sensors can be viewed as a linear inverse problem which ensures that the preferred solution corresponds to the global minimum of a misfit function it is also possible to use simultaneously more than one independent data set other seismic events to better constrain the solution of the inverse problem furthermore by a computational point of view our method results faster than the relative orientation methods based on waveform cross correlation after several tests on synthetic data sets we applied successfully our methodology to different types of real data these applications include the alignment of borehole sensors relative to a vertical seismic profiling vsp acquisition and the orientation of ocean bottom seismometers obs relative to a neighbouring land station of known orientation using land stations the absolute orientation of obs can be retrieved finally as a last application we checked the correct orientation for land stations of a seismological array in germany

garnet chloritoid equilibria in eclogitic pelitic rocks from the sesia zone western alps their bearing on phase relations in high pressure metapelites abstract a detailed study of garnet chloritoid micaschists fom the sesia zone western alps is used to constrain phase relations in high pressure hp metapelitic rocks in addition to quartz phengite paragonite and rutile the micaschists display two distinct parageneses namely garnet chloritoid chlorite and garnet chloritoid kyanite talc has never been observed garnet and chloritoid are more magnesian when chlorite is present instead of kyanite the distinction of the two equilibria results from different bulk rock chemistries not from p t conditions or redox state estimated p t conditions for the eclogitic metamorphism are 550 600 c 15 18 kbar the presence of primary chlorite in association with garnet and chloritoid leads us to construct two possible afm topologies for the sesia metapelites the paper describes a kfmash multisystem for hp pelitic rocks which extends the grid of harte hudson 1979 towards higher pressures and adds the phase talc observed parageneses in hp metapelites are consistent with predicted phase relations critical associations are gt ctd chl and gt ctd ky at relatively low temperatures and gl chl ky and gt tc ky at relatively high temperatures

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

eclogites in the french palaeozoic orogen geodynamic significance abstract eclogites are widespread in the devonian internal zone of the french palaeozoic orogen they occur in different tectonic settings either in high pressure low temperature or in high pressure high temperature environments they are tectonically incorporated into several major allochthonous units as demonstrated either by their blastomylonitic texture or by their being in evident disequilibrium with their country rocks the protoliths of the presently well identified eclogite bearing series present different typical associations depending on their present location the igneous series include within plate basalts normal and transitional morbs and even calc alkaline rocks they were erupted mostly during the palaeozoic although they sometimes contain inherited precambrian zircons further some of them may be remnants of old precambrian oceanic crust most of the eclogitic parageneses were generated during the earliest silurian tectonometamorphic climax either in low temperature or in high temperature conditions later they followed various retrograde courses in still geographically distinct low temperature or high temperature associations the basic rocks in the leptynolitic amphibolitic complex and particularly the eclogites thus provide sufficiently clear evidence to support a new geodynamic scenario implying one or several subordinate narrow tensional zones in a thinned but well developed continental crust rather than in a true oceanic domain

net sediment transport patterns inferred from grain size trends based upon definition of transport vectors reply abstract a new approach to the analysis of the grain size trends associated with net sediment transport directions in shallow marine environments is developed here two specific trends modified from mclaren and bowles 1985 on the basis of a literature review are used to define a grid of trend vectors such vectors are filtered and transformed into transport vectors it is suggested that an ordered pattern of the transport vectors represents net transport paths the orderliness of the derived pattern is examined on the basis of a significance test using the average length of the transport vectors as a criterion both the filtering operation and the significance test procedure are based upon the assumption that the trend vectors which are not associated with net transport have the same probability of being in any direction the technique is applied to data from yangpu harbour southern china the technique can be applied to inner continental shelf and coastal environments for such an analysis the area under investigation should be sampled at an interval large enough to reflect the real grain size trends resulting from net sediment transport but small compared with the dimensions of the sedimentary environment the time scale of the results depends upon the sampling depth applicability of the technique is likely to be somewhat limited where the environment is highly variable over short distances furthermore due to its statistical character the analysis may fail to identify net transport patterns

deriving transport pathways in a sediment trend analysis sta abstract sediment trend analysis sta is a technique that enables patterns of net sediment transport to be determined by relative changes in grain size distributions of all naturally occurring sediments in addition sta can determine the dynamic behaviour of bottom sediments with respect to erosion accretion or dynamic equilibrium the data requirements for sta are the full grain size distributions taken from sediment grab samples collected at a regular spacing over a particular area of interest two types of methods are presently used in the derivation of the transport pathways a line by line approach in which transport pathways are determined by searching for sample sequences in which the distributions change in a statistically acceptable manner and various vector approaches in which each sample is compared to neighbouring sites from which a vector sum is calculated the basic assumption for sta is that the processes that cause sediment transport will affect the statistics of sediment distributions in a predictable way in reality this type of analysis is complicated through the inclusion of a number of uncertainties or noise the goal of sta is to extract the information the transport pathways from the noisy signal the grain size distributions an approach that is made difficult because neither the nature of the information nor the noise is known because of this obtaining results by simply applying its theory in a black box approach may provide poor solutions the line by line approach to sta draws from communications theory to achieve a solution in some communications systems the information from many sources is combined into one signal the resulting signal is from a statistical viewpoint nothing but noise the extraction of specific information assumes that information is indeed present and determines if that assumption is consistent with the received signal for sta the procedure is to assume a transport direction over an area comprising many sample sites from this assumption the predicted sediment trends are compared with the pathways determined by the actual samples the assumed transport direction is repeatedly modified until the best fit is achieved vector techniques may be very helpful to provide insights and guidance to the line by line approach however the approach is ultimately necessary to finalize a credible solution as well as providing important further information on the dynamic behaviour of the sediments and to delineate specific sediment transport environments

depth of activation of sediment by plunging breakers on a steep sand beach abstract field data were collected over a lunar tidal cycle on a meso tidal medium sand estuarine beach in delaware bay usa to document the relationship between wave height and depth of sediment activation in a low wave energy environment dominant energy was at the frequencies of locally generated waves and ocean swell significant wave heights ranged from 0 06 m to 0 52 m periods of locally generated waves averaged 4 0 s during strong onshore winds and 2 6 s during low speed winds waves on the foreshore were always plunging the foreshore maintained a slope of approximately 6 0 throughout the study period mean grain size at mid foreshore was 0 46 mm the greatest net surface elevation change in response to storm erosion and post storm recovery was 0 26 m results confirm previous observations that depths of sediment activation are greater for steeper beaches the spatial variability in depths of activation across the foreshore is comparable to results of tidal cycle studies where the ratio of depth of activation to wave height is great because a large percentage of the foreshore comes under the influence of the breakers the ratio of depth of activation to wave height on the portion of the foreshore that is not transgressed by the breakers is lower and comparable to results of short term investigations provided that the influence of beach slope is considered in the calculation of breaking wave height

sediment transport patterns determined from grain size parameters overview and state of the art abstract grain size trends have been applied in many diverse sedimentary environments to determine sediment transport paths generally coinciding with information from tracer studies current measurements and the orientation of sedimentary structures the different methods proposed to date are critically analysed and compared with reference to recent field studies it is concluded that the two dimensional methods produce comparable results and may in fact complement each other in spite of the advances several problems still exist which include the sampling method and density the choice of trend types the relative weight of grain size parameters and the interpretation of results these are discussed together with possible solutions

from opening to subduction of an oceanic domain constrained by la icp ms u pb zircon dating variscan belt southern armorican massif france in the variscan belt of western europe the lifetime and evolution of the oceanic domain is poorly constrained by sparse outdated and unreliable multigrain id tims u pb zircon dating in this article we present a complete in situ la icp ms dataset of about 300 u pb zircon analyses obtained on most of the ophiolitic and eclogitic outcrops of southern brittany comprising new dating of previously published zircon populations and newly discovered rock samples in situ dating and cathodo luminescence imaging of each zircon grain yields new absolute time constraints on the evolution of the galicia moldanubian ocean the new results confirm that the opening of this oceanic domain is well defined at about 490 ma in contrast the generally quoted 400 410 ma age for the high pressure event related to the subduction of the oceanic crust is definitely not recorded in the zircons of the eclogites in light of these new data we propose that the obduction of oceanic rocks occurred at about 370 380 ma while the high pressure event is recorded at 355 ma in only a few zircon grains of some eclogite samples additionally this large scale dating project demonstrates that the zircons from eclogites do not systematically recrystallise during the high pressure event and consequently their u pb systems do not record that metamorphism systematically these zircons rather preserve the isotopic memory of the magmatic crystallization of their igneous protolith another example of an eclogite sample from the french massif central illustrates the frequent mistake in the interpretation of the ages of the early hydrothermal alteration of zircons in the oceanic crust versus partial or complete recrystallization during eclogite facies metamorphism

hydraulic interpretation of grain size distributions using a physical model for bedload transport abstract grain size distributions of bedload sediment are modelled by considering the time variation of sediment transport in a unidirectional turbulent flow a frequency distribution of instantaneous bed shear stress is divided into a large number of shear stress ranges with mean values of oi each oi is capable of transporting a range of sediment sizes as bedload the maximum size is just at its entrainment threshold the minimum size is just too large to be suspended rates of bedload transport are calculated for each size range using a theoretical bedload function and the proportion of time that these rates occur is obtained by integrating the frequency distribut on between the boundaries of each shear stress range the relative weights of sediment transported in particular size ranges determined for all oi values constitutes the grain size distribution obtained from bedload sampling at a fixed point on the bed cumulative grain size curves have been simulated using the model in order to demonstrate the effects of the various model parameters e g mean bed shear stress viscosity all curves show a distinct break in slope which represents the maximum grain size transportable in suspension when the shear stress attains its maximum fluctuating value examination of many natural bedload distributions shows close qualitative and quantitative agreement with the model and reasons for discrepancies can be fully explained typical grain size distributions of deposited sediments can be obtained by mixing of different flow related bedload distributions in various proportions thus although deposited sediments may primarily result from bedload transport during a steady flood flow flow unsteadiness also plays a part the effects of some deposition directly from suspended load can also be surmised

a silent slip event on the deeper cascadia subduction interface continuous global positioning system sites in southwestern british columbia canada and northwestern washington state usa have been moving landward as a result of the locked state of the cascadia subduction fault offshore in the summer of 1999 a cluster of seven sites briefly reversed their direction of motion no seismicity was associated with this event the sudden displacements are best explained by 2 centimeters of aseismic slip over a 50 kilometer by 300 kilometer area on the subduction interface downdip from the seismogenic zone a rupture equivalent to an earthquake of moment magnitude 6 7 this provides evidence that slip of the hotter plastic part of the subduction interface and hence stress loading of the megathrust earthquake zone can occur in discrete pulses

etude par la methode pbpb de roches de haut grade metamorphique impliquees dans la chaine hercynienne abstract whole rock pb pb data on granulites from the french hercynian basement are presented the emphasis has been put on mafic rocks eclogites and eclogitoides since the possibilities of involvement of pb having an old crustal history like in metasediments are very limited the domains studied are the vosges the south armorican massif bay of audierne and vendee the east haut allier and the west of the massif central sauviat sur vige and the pyrenees castillon most of the observed 206 pb 204 pb and 207 pb 204 pb ratios are comprised between 18 0 and 19 8 and between 15 54 and 15 74 respectively the field defined by the mafic rocks in the 207 pb 204 pb vs 206 pb 204 pb diagram is not very different from that of the modern basalts and the regional variations probably indicate mantle source heterogeneities this pattern also allows to eliminate a very old emplacement age significantly older than 1 ga for the protoliths of these rocks except in the south armorican massif where an old crustal history as already indicated by u pb systematics on zircons on the same rocks has been recognized finally the high grade metamorphic rocks involved in the hercynian fold belt do not exhibit a strong depletion in u and rb in contrast to their archaean and proterozoic equivalents