tidally modulated occurrence of megaripples in a saturated surf zone 1 an abstracted model for saturated surf zone megaripple occurrence based on the hypothesis that megaripples form and persist unless flow conditions change too rapidly or the bed passes through the swash zone correctly predicts the bed state presence or absence of megaripples for 73 of measurements over 1 year at scripps beach more than seven standard deviations above the agreement between a random model and the measurements transitions between bed states are predicted within 1 5 hours for 54 of measurements compared with 6 agreement for a random model the model is forced with a record of water depth over the beach h from offshore tide measurements and inferred changes in bed elevation assuming that changes in flow conditions and depth are determined by tide level alone in a saturated surf zone model parameter values are estimated independent of model results megaripple formation time t 2 5 hours maximum rms depth change over time t hrms 0 1 m and minimum depth averaged over time t below which megaripples are smoothed hsw 0 3 m allowing model parameters to vary increases agreement between measurements and model predictions to a maximum 82 for parameter values t 3 hours hrms 0 05 m and hsw 0 1 m neither bed state nor bed state transitions are correlated with offshore wave conditions

genesis of palimpsest cool water carbonate sediment on the continental margin of southern australia abstract the continental margin of southern australia is a site of extensive quaternary cool water carbonate sedimentation seafloor sediments are a mixture of holocene biofragments and late pleistocene relict and stranded particles relict sediments produced during marine isotope stages 3 and 4 are generally preserved as iron stained intraclasts such grains in the great australian bight are photozoan in character they include symbiont bearing benthic foraminifers and coralline algal particles and indicate that the wide shelves were bathed in shallow relatively warm oligotrophic waters and floored by marine grasses similar to many modern shallow inboard embayments in the region today in contrast east of the great australian bight relict sediments are more heterozoan in character with coralline algal and molluscan facies on the inner shelf and bryozoan sediments on the outer shelf stranded sediments marooned during the sea level rise associated with marine isotope stage 2 are gray to buff in color and composed of both biofragments and intraclasts these particles are mainly heterozoan in character throughout the region with subtropical photozoan marine grassbank facies localized to portions of the inner great australian bight stranded sediments are interpreted to have accumulated in an areally restricted photic zone and upon an overall narrow shelf covered in cool nutrient rich waters swell driven seafloor sediment disturbance to depths of 100 m along the southern australian margin in conjunction with reduced rates of sedimentation that characterize the cool water carbonate realm have resulted in mixing of sediment currently being produced with exhumed relict and stranded sediments generated during previous sea level stands the composition of these deposits and the nature of their pre burial alteration are a function of sea level history late pleistocene relict sediments originally accumulated in low energy inboard environments but were modified in the surf zone during subsequent sea level fluctuations this resulted in the formation of intraclasts abraded infilled and cemented biofragments of local origin the widespread distribution of intraclasts and of composite grain assemblages derived from multiple sedimentary environments that display highly variable degrees of seafloor alteration may be signatures of modern cool water carbonate assemblages worldwide while such palimpsest sediments may complicate paleoenvironmental interpretation their differentiation in the rock record can be utilized to discern subtleties in paleoceanography and sea level history

suspended sediment transport in the surf zone response to cross shore infragravity motion a field experiment to investigate the magnitude and temporal and spatial scales of suspended sediment transport in the inner surf zone was conducted at san marine oregon on october 7 13 1984 instrumentation consisted of five electromagnetic current meters three strain gauge type pressure transducers and 25 optical backscatter sensors to measure the concentrations of suspended sediment the instruments were deployed approximately 70 m x seaward of the mean high water line mean depth h 1 1 1 3 m in a closely spaced cross shaped pattern data were collected for 68 min periods spanning high tide during the 7 day experiment during the experiment waves varied in angle of approach from shore normal to southwesterly offshore significant swell heights were 3 5 m with periods of 12 14 s local sea conditions with wind waves of approximately 8 s also occurred a visual estimation of the width of the surf zone indicated it to be approximately 500 m and the breaker pattern suggested that there were two longshore bars at approximately 200 and 500 m offshore the data resulting from the experiment encompass a broad range of wave and current conditions which included periods of extreme infragravity motion 30 t 300 s and weak longshore currents and periods of low infragravity motion and strong longshore currents periods of incident wave dominance also occurred the field study section of this paper qualitatively describes the sediment response to strong 240 cm s 1 low frequency 0 01 hz cross shore fluid motions which dominated the inner surf zone during two of the data runs the infragravity band accounted for 85 of the cross shore velocity variance the peak 0 01 hz of which was associated with shore normal standing waves concentration gradients of suspended sediment appear to be associated with diffusive processes and develop and decay on time scales of the infragravity motions rather than those of incident waves suspension events during times of infragravity dominance often persisted for periods of 30 45 s and reached peak concentrations of 20 40 g l 1 at elevations in excess of 26 cm mean suspended load was 3 4 times larger than that associated with incident wave motions the modeling section of the paper attempts to quantitatively describe the observed time dependent vertical suspended sediment distribution with a one dimensional turbulent diffusion model formulations of eddy diffusion and erosion rate coefficients associated with peak cross shore flows are found to agree with or fall within the range of values from previous laboratory and field studies and are used in the model the model is evaluated by its ability to reproduce the time dependent vertical distribution of suspended sediment and to estimate the observed mean suspended load and the correct direction and magnitude of the mean longshore and cross shore flux level above the bed z 31 cm of suspended sediment

storm induced response of a nearshore bar system abstract a nearshore bar system was surveyed periodically through a storm and the following recovery period the data showed a very rapid response of morphology to changing wave conditions and allowed various models on bar formation to be tested under low energy conditions prior to the storm a small bar was surveyed 13 m offshore both the high reflectivity of the beach and the cross shore distance to the bar are consistent with a model of sediment convergence at the node or antinode of a standing wave of incident period such a small scale bar may be a common feature on beaches with steep foreshores and more gentle offshore slopes with the increase in wave height during the storm the bar became better developed and migrated offshore at rates up to 2 2 m h 1 the bar maintained its form in that the ratio of trough depth to crest depth h t h c remained roughly constant the bar was in no way related to processes which would cause the convergence of sediment in the breaker zone through most of the storm the bar crest distance offshore was typically only 10 of the surf zone width analysis of the bar distance offshore in terms of a standing wave motion showed that the causative wave period must have been much longer than that of incident waves probably on the order of a minute surf zone wave data showed significant energy in the infragravity band at these periods although no definite link has been made after the height of the storm the bar had a crescentic morphology the development of this morphology occurred very rapidly with parts of the bar migrating onshore at rates up to 1 2 m h 1 in contrast to the storm during the recovery period h t h c varied by nearly a factor of three analysis of the offshore and longshore length scales showed the bar to be similar to one which would be generated by a standing mode 1 edge wave of period on the order of one minute

foraminiferal biofacies on the mid latitude lincoln shelf south australia oceanographic and sedimentological implications foraminiferal assemblages on the southern mid latitude lincoln shelf comprise mixtures more strongly in shallow waters of holocene and relict pleistocene specimens over 200 benthic and 15 planktonic species were recorded and a higher diversity was found in the central and deeper parts of the shelf and slope cluster analysis identified five assemblages or biofacies nearshore assemblage a 50 m and inner mid shelf assemblage b 50 90 m are dominated by relict and recent shallow water species the outer mid shelf assemblage c 90 120 m contains more cibicidids and is transitional between the shallow and deep water assemblages outer shelf assemblage d 120 170 m is characterized by cibicidids and anomalinids and by a higher planktonic and benthic diversity and it can be subdivided into three sub assemblages d1 d3 unlike others assemblage d was not recognized from the most western transect samples the outer shelf to slope assemblage e 170 400 m is typically deep water having forms like hoeglundina elegans pullenia bulloides and melonis affinis the western great australian bight sector has the larger epifaunal benthic sorites marginopora group while the infauna is higher in the eastern neptune sector of the shelf we attribute these contrasts to the influence of the warm leeuwin current and to the mixing between gulf shelf and oceanic waters respectively a former lagoonal environment is largely responsible for the accumulation of relict tests during lower sea level periods of the late pleistocene when climate was more arid the lack of recent sediments preserved on the inner shelf is considered to be due to strong wave abrasion causing sediment starvation richer forarniniferal assemblages from the outer shelf to upper slope parallel an increasingly calcareous sediment faunal evidence indicates a warmer nearly oligotrophic condition on lincoln shelf compared to the mesotrophy on the adjacent lacepede shelf this difference may be due to the separation of these two shelves by kangaroo island acting as a local oceanographic environmental and biogeographic barrier

resolving bathymetric components of the upper shoreface on a wave dominated coast abstract the bathymetric components of a wave and storm dominated shoreface were examined as a key to understanding the controlling effects of hydrodynamic processes and geological factors that maintain the shoreface results of empirical orthogonal function analysis applied to bathymetric data from the upper shoreface of long island s south shore between fire island inlet and montauk point show that this area can be divided morphologically into a headland section and a barrier island section the headland section is characterized by well organized well correlated bathymetry in contrast to the barrier island section which has more complex and less organized less correlated bathymetry the first three spatial eigenfunctions modes account for nearly 90 of the variance among the headland shoreface bathymetry data whereas the first three eigenfunctions of the barrier island section account for 82 of the variance among the data the headland shoreface is steeper than the barrier island shoreface and is dominated by a primary nearshore bar mode which accounts for 70 of the variance among the shoreface bathymetry data for this section secondary bathymetric components of the headland shoreface account for less than 20 of the remaining variance the bathymetry of the barrier island shoreface is dominated by a terrace mode this mode accounts for only 54 of the variance among the bathymetric data however and secondary bathymetric components account for more than 27 of the remaining variance underlying factors determining the differences in shoreface bathymetry between the barrier island and headland sections of the study area include topographic control by the outwash plain backing much of the headland section and proximity to sediment source the factor directly responsible for differences in bathymetric components however is the relative difference in dissipative conditions between the two sections with respect to incident wave energy both sections have an outer dissipative domain and a more resonant inner domain however the barrier island section is twice as dissipative as the headland section

formation conditions of aluminum rich chondrules abstract we have studied the formation conditions of al rich chondrules by doing isothermal and dynamic crystallization experiments at one atmosphere on four different chondrule analogue compositions within the pure cao mgo al2o3 sio2 system for the dynamic crystallization experiments we cooled from both liquidus and subliquidus peak temperatures tmax at cooling rates from 5 1000 c h the starting compositions include two with anorthite and two with forsterite as the dominant liquidus phases all at or near spinel saturation one of each pair evolves towards diopside crystallization and the others cordierite or enstatite crystallization giving a total of four completely different crystallization sequences analogous to the four basic varieties of al rich chondrule recently proposed bulk composition is the main controlling factor both in terms of mineralogy and texture the textures of the anorthite rich compositions are more sensitive to tmax than they are to cooling rate whereas the textures of the forsterite rich compositions are more sensitive to cooling rate comparisons of natural al rich chondrules having similar compositions to our synthetic analogues indicate that the natural objects reflect a range of peak heating temperatures 1400 1500 c and cooling rates of 10 500 c h for porphyritic chondrules and possibly higher 1000 c h for barred chondrules these conditions are consistent with the conditions inferred for ferromagnesian chondrules but differ from those inferred for some calcium aluminum rich inclusions

wave beach and dune interactions in southeastern australia abstract a morphodynamic classification of surfzones beaches and dunes of the microtidal low to high energy southeast australian coast is presented the first section a waves and beaches briefly deals with the transformation of deep water wave energy as it crosses the shelf nearshore and surfzone depending on the deep water wave characteristics and shelf and inshore morphology resultant breaker wave energy may be high moderate or low and the accompanying beach surfzone morphodynamic state in fine to medium sand beaches either dissipative intermediate or reflective dissipative beaches have wide surfzones with shore parallel bar s and channel s and predominantly shore normal circulation intermediate beaches are characterised by rip circulation crescentic transverse bars and megacusps and reflective beaches by a barless surfzone and steep cusped or bermed beach each beach form has a characteristic level of beach stability zone of sediment storage and mode of beach and dune erosion landward aeolian sediment transport of swash deposited sand section b is dependent on the subaerial beach topography and the aerodynamic flow regime across that topography characteristic profile shapes are ascribed to each beach type dissipative intermediate and reflective aeolian sand transport rates are potentially highest on dissipative beaches moderate on intermediate beaches and lowest on reflective beaches these rates determine the potential size of foredunes which are correspondingly largest on dissipative beaches and smallest on reflective beaches the combination of mode and frequency of beach dune erosion rates of aeolian sand transport and foredune volume and morphology provide an explanation of the nature and morphology of landward occurring large scale dune systems dissipative beaches are frequently characterised by large scale transgressive dune sheets intermediate by a trend from large scale parabolic dune systems high wave energy to small scale blowouts low wave energy and reflective beaches by minimal dune development

a short duration of chondrule formation in the solar nebula evidence from 26al in semarkona ferromagnesian chondrules abstract the 26 al 26 mg systems of five ferromagnesian chondrules from the least metamorphosed ordinary chondrite semarkona ll3 0 were studied using a secondary ion mass spectrometer their glass or plagioclase portions contain excesses of 26 mg and in two chondrules the 26 mg excesses are well correlated with 27 al 24 mg which demonstrates the in situ decay of 26 al the initial 26 al 27 al ratios in these chondrules obtained from the slope of isochrons show a narrow range of between 6 10 6 and 9 10 6 indicating their short formation duration of less than 1 my if the solar nebula was initially homogeneous in al isotopes the chondrule formation ages are 2 my younger than those of cais our results based on the study of the least metamorphosed uoc are consistent with the previous studies on al rich chondrules that the chondrule formation started at least 2 my after cais alternatively the older records before 2 my were erased by chondrule recycling process it further suggests that the young apparent ages 3 to 5 my after cais for chondrules in type 3 4 uocs are due to the disturbance of the 26 al 26 mg system possibly during parent body metamorphism the result is not consistent with the extended nebular time scale of 5 my and the chondrule formation by planetary processes the ni isotopic analysis of the feo rich olivines in a type ii chondrule in semarkona did not show any detectable excess 60 ni in spite of their high fe ni ratios the upper limit of the initial 60 fe 56 fe ratio of the solar system was estimated to be 3 4 10 7 which is consistent with the previous estimate 0 2 1 9 10 7 from eucrites this result confirms that the 60 ni excess previously observed from cais was not due to the decay of the short lived nuclide 60 fe but a ni isotopic anomaly of nucleosynthetic origin

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

an analysis of the cross shore beach morphodynamics of a sandy and a composite gravel beach in this paper beach profile surveys acquired over more than a decade at a sandy beach narrabeen beach new south wales australia and a composite sand gravel beach milford on sea christchurch bay uk are analysed to compare and contrast cross shore morphodynamics of the two beach types the different behavioural characteristics of the two beach types at decadal inter annual and intra annual time scales are investigated comparisons of beach profiles with dean s equilibrium profile and vellinga s erosion profile show that the dean s profile satisfactorily represents the time mean profiles of both beach types statistical and empirical orthogonal function eof analyses confirm the generally accepted model that the inter tidal zone is the most morphodynamically active region on a sandy beach whereas the swash zone is the most dynamic region on a mixed sand gravel beach the results also imply that during storms composite sand gravel beaches may become unstable due to cutback of the upper beach while sandy beaches are more likely to be unstable as a result of beach lowering due to sediment transport from the inter tidal zone to the sub tidal zone during storms eof results also show that milford on sea beach is in a state of steady recession while the narrabeen beach shows a cyclic erosion accretion variability a multivariate technique canonical correlation analysis cca shows that on the composite beach a strong correlation exists between incident wave steepness and profile response which could be attributed to the unsaturated surf zone whereas on the sandy beach any correlation is much less evident

al mg systematics of cais poi and ferromagnesian chondrules from ningqiang we have made aluminum magnesium isotopic measurements on 4 melilite bearing calcium aluminum rich inclusions cais 1 plagioclase olivine inclusion poi and 2 ferromagnesian chondrules from the ningqiang carbonaceous chondrite all of the cais measured contain clear evidence for radiogenic 26 mg from the decay of 26 al 1 05 ma although the low al mg ratios of the melilites introduce large uncertainties the inferred initial 26 al 27 al ratios for the cais are generally consistent with the value of 5 x 10 5 there is clear evidence of 26 al in one poi and two chondrules but with considerable uncertainties in the value of 26 al 27 al 0 the 26 al 27 al 0 ratios for the poi and the chondrules are 0 3 0 6 x 10 5 roughly an order of magnitude lower than the canonical value ningqiang shows very little evidence of metamorphism as a bulk object and the 26 al 27 al 0 ratios in its refractory inclusions and chondrules are consistent with those found in other unmetamorphosed chondrites of several different classes our observations and those of other workers support the view that 26 al was widely and approximately homogeneously distributed throughout the condensed matter of the solar system the difference in 26 al 27 al 0 between cais and less refractory materials seems reasonably interpreted in terms of a 2 million year delay between the formation of cais and the onset of formation of less refractory objects the poi shows clear differences in 25 mg 24 mg between its constituent spinels and olivine which confirms that they are partially reprocessed material from different sources that were rapidly quenched

thermal metamorphic history of a ca al rich inclusion constrained by high spatial resolution mg isotopic measurements with nanosims 50l abstract mg isotope data were collected by nanosims with high precision and high spatial resolution from a coarse grained type b ca al rich inclusion cai ek1 6 3 in the allende cv3 chondrite to evaluate the time scale of parent body thermal metamorphism the cai melilite and fassaite contain excesses of 26mg 26mg from the in situ decay of 26al the inferred initial ratio 26al 27al 0 5 8 2 4 10 5 is consistent with many previously reported coarse grained cais from cv chondrites e g macpherson et al 1995 however the anorthite has heterogeneous 26al 27al 0 ranging from 1 8 10 5 to 3 3 10 6 the 26al 26mg systematics within the anorthite is consistent with thermal diffusion of mg isotopes during metamorphism we also show that the heterogeneous distribution of 26mg in anorthite could have resulted from thermal diffusion of 26mg over a 0 6 0 8 ma time span mg diffusion thus may be responsible for the 26al 27al 0 heterogeneity within anorthite in cais

sediment transport on dissipative intermediate and reflective beaches abstract in this paper we review and synthesize field measurements of suspended sediment transport on the shoreface of dissipative intermediate and reflective beach states the morphodynamic beach state continuum was originally established in the 1970s but at the time only hydrodynamic processes and morphologies in these various states were described since the early 1980s when sensors capable of resolving suspended sediment concentration at intra wave time scale became available many studies have examined suspended sediment transport by waves and currents on the shoreface the synthesis of this work shows that the two end states in the morphodynamic continuum which are the dissipative and reflective states exhibit relatively small rates of cross shore sediment transport and weak gradients in that transport which both ensure that the nearshore morphology is relatively stable the intervening intermediate beach states typically exhibit prominent bar topographies and in these states strong morphodynamic feedbacks between hydrodynamic processes and morphology create locally large transport rates and sharp transport gradients which is the reason for the dynamic nature of these beach states transport processes driving sediment onshore and offshore within beach states are discussed as well as the transport processes responsible for state transitions

hydrodynamics and sediment transport in the swash zone a review and perspectives the dominant hydrodynamic forcing and resulting sediment transport mechanisms in the swash zone are reviewed combined with a discussion of future measurement and modelling requirements the importance of swash zone processes in the overall behaviour of the nearshore littoral zone are identified with the paper subsequently focusing on aspects that directly relate to sediment transport on beaches the review considers analytical and numerical modelling work and both field and laboratory data the hydrodynamics of the swash zone are first discussed with reference to the surf zone boundary swash characteristics forcing mechanisms and shoreline oscillations subsequent sections consider more micro scale processes such as the internal flow kinematics turbulence the bed boundary layer and infiltration exfiltration through permeable beds the second part of the paper outlines the fundamental mechanics of sediment transport in the swash zone followed by a more detailed discussion of sediment transport modes induced by the dominant hydrodynamic conditions modelling concepts are reviewed and the strengths and weaknesses of different approaches identified a final summary and future modelling perspectives conclude the paper

surficial cool water carbonate sediments on the otway continental margin southeastern australia abstract the otway continental margin of southern australia is a swell dominated open cool water carbonate platform it is partitioned into a series of depth related zones of biological sediment production and accumulation by three hydrodynamic interfaces 1 abrasion depth 70 m 2 swell wavebase 130 m and 3 storm wavebase 250 m the otway shelf profile drops steeply from the strandline the shallow shelf lies largely between 30 and 70 m and is a high energy zone of carbonate sediment production intensive destructive diagenesis and erosion the seafloor is characterized by widespread exhumed limestone substrates which host dense encrusting assemblages of molluscs sponges bryozoans and red algae loose sediment accumulation is patchy and consists of a thin quartz rich palimpsest gravel veneer the middle shelf 70 to 130 m is a zone of swell wave shoaling and production and accumulation of coarse mega rippled 2 d dunes bryozoan sands deep shelf areas 130 to 180 m accumulate finer bioclastic sands foraminiferal echinoid bryozoan that are intensely bioturbated and episodically reworked by storms grains are variably fragmented and marginally bored at the shelf edge and top of slope 180 to 350 m nutrient rich upwelling currents support laterally extensive aphotic biostromal hermal bryozoan sponge coral communities which generate and accumulate thick successions of muddy skeletal sand sediments of the upper slope 350 to 500 m are a bioturbated mixture of periplatform bioclastic debris and pelleted foraminiferal nannofossil mud turbidites and resedimentation features are common bioturbation and shelf derived skeletal content decrease progressively downslope and pelagic muds dominate below 500 m lower slope areas are cross cut by gullies and have low accumulation rates the base of slope is characterized by sediment apron deposits consisting of interbedded shelf derived coarse grained turbidites and pelagic ooze

morphodynamics of a macrotidal beach abstract an intensive field investigation of hydrodynamic processes processes of sediment entrainment and suspension and morphologic change was carried out on an unprotected macrotidal beach near broome in northwestern australia the spring tide range was 9 5 m waves had heights of 0 5 1 2 m and periods of 9 13 s the beach had an overall concave upward profile with low gradient and dissipative subtidal and low tidal zones and steeper more reflective mid tidal and high tidal zones direct measurement of energy flux dissipation over the intertidal profile showed dissipation rates on the order of 1 2 w m 2 of bed and indicated an approximate balance between shoaling and dissipation of unbroken waves so as to maintain a constant wave height time averaged predictive estimates of wave work over the lunar half cycle for different points on the intertidal profile show similar dissipation rates and reveal a relatively uniform distribution of work over most of the profile but with maxima in the middle of the low tidal zone and over the lower part of the high tidal zone most of the work over the low and mid tidal zones was performed by unbroken shoaling waves rather than by surf zone processes surf zone processes only dominate over the high tidal zone the nature of the surf zone processes varied across the profile as local gradient and degree of reflectivity changed with changing tide level the growth of standing waves and infragravity surf beat oscillations as identified from spectra and cross spectra of surface elevation and currents u and v was inhibited over most of the profile however well developed secondary standing wave energy particularly at infragravity frequencies was observed over the high tidal zone at spring high tide and over the mid tidal zone at neap high tide over the low tidal and subtidal zones strong shore parallel tidal currents were subordinate only to the orbital velocities of unbroken incident waves over the subtidal zone asymmetrical tidal currents skewed toward the north attained maximum speeds of 0 5 m s 1 just after high water field measurements of suspended sediment concentration profiles under broken and unbroken waves showed very good fit to a diffusion model for wave induced sediment suspension and suggested that sediment suspension was probably attributable largely to waves northerly advection of wave suspended sediment by asymmetrical tidal currents over the subtidal and low tidal zones accounted for a net northerly longshore transport the greatest morphologic mobility of the intertidal profile occurred over the lower high tidal and upper mid tidal zones corresponding to the position of the coarsest material and secondary maximum of time averaged wave work and to a beach state intermediate between the reflective and dissipative extremes temporally the greatest mobility of the profile as a whole was observed on the short within tidal cycle time scale net changes over the longest time scale of a lunar half cycle were negligible

early diagenesis of carbonates on a cool water carbonate shelf southern australia abstract the southern australian continental margin is an immense cool water carbonate factory the high energy open shelf is blanketed by heterozoan carbonates of both holocene and late pleistocene age three distinct grain types have been identified and radiocarbon dated these include 1 relict grains highly abraded iron stained intraclasts formed during the intermediate sea level stands of marine isotope stages 3 and 4 2 stranded grains gray and buff colored abraded biofragments and intraclasts marooned during the sea level rise associated with marine isotope stage 2 and 3 holocene grains unaltered biofragments formed during marine isotope stage 1 optical mineralogical and chemical characterization of grains of each age has revealed pathways of early diagenesis in this realm both calcitic and aragonite biogenic grains undergo dissolution while dissolution of calcitic components is minor and incomplete relict sediments are predominantly mg calcite aragonitic skeletons undergo significant dissolution within 30 000 years in contrast to early dissolution of aragonite micritic calcite cement with 12 mol mgco3 is a significant diagenetic phase in these sediments infilling many stranded and most relict skeletons similar cement precipitates between grains forming small numbers of cemented grain aggregates in most samples microprobe and icp ms analysis demonstrates fe oxides mn oxides and associated clay minerals discolor stranded and relict grains by coating grain surfaces and infesting micropores such coatings begin to form on holocene grains during or soon after formation the oxides scavenge trace elements including v ti cr and ree altering the elemental compositions of biogenic carbonate

spatial heterogeneity of 26al 27al and stable oxygen isotopes in the solar nebula the degree of isotopic spatial heterogeneity in the solar nebula has long been a puzzle with different isotopic systems implying either large scale initial spatial homogeneity e g 26al chronometry or a significant amount of preserved heterogeneity e g ratios of the three stable oxygen isotopes 16o 17o and 18o we show here that in a marginally gravitationally unstable mgu solar nebula the efficiency of large scale mixing and transport is sufficient to spatially homogenize an initially highly spatially heterogeneous nebula to dispersions of 10 about the mean value of 26al 27al on time scales of thousands of years a similar dispersion would be expected for 17o 16o and 18o 16o ratios produced by ultraviolet photolysis of self shielded molecular co gas at the surface of the outer solar nebula in addition to preserving a chronological interpretation of initial 26al 27al ratios and the self shielding explanation for the oxygen isotope ratios these solar nebula models offer a self consistent environment for achieving large scale mixing and transport of thermally annealed dust grains shock wave processing of chondrules and refractory inclusions and giant planet formation

nearshore bars and the break point hypothesis abstract the set of hypotheses calling for bar formation at the break point was tested with field data during two different experiments waves were measured across the surf zone coincident with the development of a nearshore bar we use a criterion based on the wave height to depth ratio to determine the offshore limit of the inner surf zone during the first experiment the bar became better developed and migrated offshore while remaining well within the inner surf zone during the second experiment the surf zone was narrower and we cannot rule out the possibility of break point processes contributing to bar development we conclude that bars are not necessarily coupled with the break point and can become better developed and migrate offshore while being in the inner surf zone landward from initial wave breaking in the outer surf zone

origin of plagioclase olivine inclusions in carbonaceous chondrites plagioclase olivine inclusions pois are an abundant group of chondrule like objects with igneous textures found in carbonaceous chondrites pois consist of plagioclase olivine pyroxene and spinel and cover a wide range of compositions between type c ca al rich inclusions cais and ferromagnesian chondrules pois are distinguished from cais by the absence of melilite lack of refractory siderophile rich opaque assemblages more sodic plagioclase and abundance of olivine and aluminousenstatite rare accessory minerals including armalcolite zirconolite rutile and sapphirine are found in several pois the petrographie and chemical properties of pois indicate that they are not condensates or evaporative residues but formed by melting or partial melting of pre existing solids seven of fourteen pois contain isotopically fractionated mg and despite their textures these pois are not isotopically homogeneous spinel is the major carrier of fractionated mg in six pois the magnitude of mg isotopic fractionation fmg of spinel ranges from 8 to 11 amu among the pois but f mg is always either positive or negative within an individual pol within a single inclusion f mg of coexisting spinel is not constant but varies by up to 7 amu isotopic fractionation of mg in silicates is less common and always positive f mg 0 pyroxenes in two pois and plagioclase in a third contain isotopically heavy mg radiogenic 26 mg is rare in pois as only two inclusions show evidence of excess 26 mg with 26 mg 27 al 4 10 6 the preservation of isotopic heterogeneity in objects whose igneous textures suggest crystallization from a homogeneous melt implies that melting was incomplete allowing survival of relict phases a comparison of the essential characteristics of pois and cais suggests that the major processes leading to formation of pois including condensation dust gas fractionation aggregation of chemically and isotopically disparate materials and partial melting are common to most cais and chondrules we present a scenario for the formation of these objects and conclude that the homogeneity of the final assemblage cai poi or chondrule is primarily a reflection of the thermal history rather than the nature of precursor materials

provenance of holocene calcareous beach dune sediments western eyre peninsula great australian bight australia abstract much of western eyre peninsula adjacent to the great australian bight is veneered with siliceous and calcareous quaternary aeolian dunes the lengthy coastline adjacent to this cool water carbonate factory is a series of precambrian crystalline bedrock pleistocene aeolianite headlands that separate many long sweeping holocene carbonate sand beaches and their backbeach dunes incessant sw waves rolling swells and onshore winds have resulted in 350 km of semi continuous calcareous strandline aeolian sands the sediment is composed of quartz grains cenozoic limestone clasts and relict particles extraclasts but the deposits are overwhelmingly dominated by contemporaneous biofragments from offshore these skeletal grains are in order of relative abundance molluscs benthic foraminifers coralline algae bryozoans and echinoids benthic foraminifers are mostly small especially rotaliids and miliolids but the large relict symbiont bearing protist marginopora vertebralis which grew in the latter stages of mis 2 is present locally there are no significant onshore offshore trends within individual beach dune complexes there is however a prominent spatial partitioning with extraclast rich sediments in the north and biofragment rich deposits in the south this areal trend is interpreted to result from more active seafloor carbonate production in the south an area of conspicuous seasonal nutrient upwelling and profound nektic and benthic biological productivity the overall system is strikingly similar to holocene and pleistocene aeolianites along the inboard margin of the lacepede shelf and bonney coast some 500 km to the southeast implying a potential universality to the nature of cool water carbonate aeolianite deposition the composition of these cool water aeolianites is more multifaceted than those formed on warm water shallow flat topped platforms largely because of the comparatively deep temperate shelf the high energy wave and swell climate impacting the shoreline and thus the different geohistory during sea level change

short term changes in the morphodynamic states of beaches and surf zones an empirical predictive model a time series of 6 5 years of daily observations of beach states and wave characteristics from southeastern australia was analyzed with the aim of determining the degree to which time varying beach state can be explained and predicted the six commonly occurring beach states dissipative longshore bar trough rhythmic bar and beach transverse bar and rip low tide terrace and reflective discussed earlier were related by means of discrete discriminant analyses to the parameter hb wst where hb is breaker height ws is the fall velocity of the beach sand and t is peak breaker period using a total of 1545 cases two values were used in the analyses the immediate value occurring on the day the particular state was observed and a weighted mean value expressing recently antecedent conditions the immediate value made a negligible contribution to explaining day to day beach state observations however the antecedent conditions showed a strong relationship and provide a successful means of prediction by examining cases where the time derivatives of both state and were near zero it was possible to define the equilibrium conditions associated with each state directions of change erosional or accretionary are predicted in terms of departures of from the equilibrium value appropriate to the beach state prevailing at the time change begins

role of wave forcing storms and nao in outer bar dynamics on a high energy macro tidal beach abstract outer sand bar dynamics on a high energy macro tidal beach were investigated using long term multi year field datasets of intertidal morphology and offshore bathymetry utilising a 15 year time series of argus video images five distinct outer bar types were identified mega rip longshore crescentic crescentic attached and welded the most common classification was crescentic attached with the outer bar oscillations being out of phase with the inner bar oscillations as would be expected for the shore normal wave approach at this site the outer bar had a typical amplitude of 0 5 1 m and a longshore wavelength of 600 m changes in outer bar morphology were related to measured and modelled nearshore wave data however the outer bar morphology changed over a much longer timescale monthly to annual than the daily to weekly variations in wave height and period an extended duration of energetic wave action was required to bring about an upstate bar transition to the longshore or mega rip state where the bar then remained arrested for a significant amount of time requiring several months of low wave conditions to induce a down state transition through crescentic to welded this slow morphological response is explained by extended relaxation times attributed to the large tidal range at the study site where the outer bar morphology is only active for part of the tidal cycle several hours around low tide the configuration and position of the outer bar were related the more upstate downstate bar types being associated with a more offshore onshore bar position the detrended outer bar position was significantly related to a forcing term based on wave power and disequilibrium of the dimensionless fall velocity with offshore onshore bar migration occurring when wave conditions were more less energetic that the antecedent conditions the upstate end member longshore or mega rip was attained sometime during the winter months for 14 out of the 16 years of monitoring the outer bar remained attached to the low tide shoreline over the winter 2005 2006 and 2010 2011 these two winters with incomplete upstate cycles were characterised by the lowest winter wave conditions and negative winter north atlantic oscillation nao indices suggesting that the winter nao is correlated with both beach state and nearshore bar configuration

rip current type spacing and persistence narrabeen beach australia abstract long term daily rip observations on narrabeen beach australia were made together with daily measurements of wave height period direction surf zone width and beach state a total of 3513 rips were observed on 270 days over a 19 month period results show that rips accompany moderate to high waves and are associated with intermediate beach types rip spacing follows wave conditions increasing in spacing size and intensity as waves rise and conversely as they fall rips are a function of both the prevailing and antecedent wave conditions and the rate and direction of change in wave conditions rips are classified into three types erosion mega and accretion erosion rips are initiated by rising seas in the transverse bar and rip and higher beach states they accompany general beach erosion they are widely spaced narrabeen ys 300 500 m 100 200 m increasing in size and intensity with the waves until the fully dissipative ripless state is reached they are both temporally and spatially highly variable persisting in one location for only hours to a day or so except where topographically controlled they are a major mechanism for the seaward transport of sediment and under extreme conditions may extend over a kilometer seaward of the breaker zone mega rips are large scale 1 km topographically controlled erosion rips that persist when nearshore and or embayment topography prevents the development of the fully dissipative state by inducing wave refraction and persist longshore gradients in surf zone dynamics that in turn drive the rip circulation accretion rips prevail during stable or falling wave conditions usually following erosion rip formation they are associated with general beach accretion are more closely spaced narrabeen ys 170 250 m 100 m less intense and become increasingly topographically arrested by crescentic bars and rhythmic bar beach morphology of the longshore bar trough rhythmic bar and beach and transverse bar and rip beach states they are relatively stable both spatially and temporally and may persist in one location for days to weeks if wave conditions remain favorable they are fair weather rips which may disappear by infilling in the low tide terrace beach state or be destroyed by rising seas rips generally are absent from the reflective low tide terrace and fully dissipative beach states

infragravity waves over a natural barred profile measurements of cross shore flow were made across the surf zone during a storm as a nearshore bar became better developed and migrated offshore measured infragravity band spectra were compared to synthetic spectra calculated numerically over the natural barred profile assuming a white run up spectrum of leaky mode or high mode edge waves as in earlier studies the spectra compared closely however for some frequencies the energy of the measured spectrum exceeded the energy of the synthetic spectrum suggesting that the run up spectrum was not white but had dominating frequencies utilizing cross shore flow data and synthetic spectra from a number of cross shore locations an equivalent run up spectrum was calculated for each day on the first day of the storm the equivalent run up spectrum indicated a dominant wave that had a node in velocity reasonably close to the bar crest later during the storm when the bar had migrated farther offshore there was no evidence for a dominant motion having a velocity node at the bar crest the structure of the equivalent run up spectrum compared well with spectra of direct measurements of run up obtained several hundred meters away we have no clear evidence in support of the theory that infragravity waves might form or force the offshore migration of a bar to confirm this finding longer records obtained synoptically over a developing bar are required the dominant wave observed early in the storm was consistent with symond and bowen s 1984 theoretical prediction of resonant amplification of discrete frequencies over a barred profile

modelling infragravity motions on a rip channel beach a non linear shallow water wave model operating on the time scale of wave groups is compared with measurements of infragravity motions on a rip channel beach to verify the model concepts and assess the model performance the measurements were obtained during the rip current experiment ripex in concert with the steep beach experiment sbe performed at sand city monterey bay ca during the spring of 2001 the nearshore bathymetry was made up of shore connected shoals incised by relatively narrow rip channels spaced approximately 125 m apart the comparison considers a 20 day period during which significant changes in both the offshore wave climate and nearshore bathymetry occurred the temporal variation in infragravity conditions during the experiment is strong with computational results typically explaining 70 to 80 of the observed infragravity motions within the nearshore in contrast to the temporal variation the alongshore spatial variation in infragravity intensity during the experiment is generally weak even though the underlying bathymetry shows strong depth variations model computations suggest preferential coupling between the computed edge wave motions and the quasi periodic bathymetry is present a prerequisite for strong spatial variability however the infragravity field is dominated by cross shore infragravity motions which are only weakly coupled to the quasi periodic bathymetry resulting in a weak alongshore variability of the total infragravity motions

dynamics of a high energy dissipative surf zone vright l d guza r t and short a d 1982 dynamics of a high energy dissipative surf zone mar geol 45 41 62 pressure and horizontal current u v time series were measured at different positions across the inner 150 m of a wide 500 m surf zone of a microtidal high wave energy beach incident waves had average heights of 3 4 m with maxima of 5 m and periods of 12 to 15 sec bores of broken waves diminished in height at a nearly constant rate as they progressed across the surf zone the ratio of bore height h to local water depth h was everywhere less than 1 for even the highest bores and was on the order of 0 40 for the significant bores at incident wave frequencies rip circulation was weak or absent but a moderate longshore current was present shore normal flows were vertically segregated with strong net onshore flows prevailing just below the surface accompanied by weaker net seaward flows near the bed spectra of water surface oscillations as determined from pressure u and v reveal that most of the energy in the inner surf zone was at infragravity frequencies periods greater than 30 sec shoreward decay of wave energy at incident wave frequencies was accompanied by shoreward growth of infragravity energy near the beach the infragravity oscillations had heights on the order of 1 m cross spectra show that the infragravity oscillations were standing in the shore normal direction from the relative magnitudes of infragravity versus incident wave currents it is inferred that the surf beat may be an order of magnitude more important than incident waves to the transport of sediment in the inner surf zone

morphodynamics of a large scale rip current system at muriwai beach new zealand abstract field measurements of rip spacing nearshore morphology water surface elevation and eulerian and lagrangian flows were made in order to investigate the morphodynamics of a large scale rip current system at muriwai beach new zealand muriwai is a high energy meso tidal beach characterised by modal breaker wave heights of 2 5 m and incident wave periods of 10 15 s the monitored rip system was characterised by a 400 m long 75 m wide longshore feeder channel and a 150 m wide rip neck channel oriented obliquely to the shore and extending over a distance of almost 400 m during the experiment the beach evolved from a longshore bar trough and rip state to a transverse bar and rip configuration mean eulerian flow velocities obtained from ducted flowmeters deployed on the margin of the feeder channel and rip neck were on the order of 1 m s 1 and instantaneous flows were commonly in excess of 2 m s 1 mean lagrangian surface flow velocities extending from the base of the feeder through to the rip head were obtained by tracking rip floaters and were on the order of 0 7 m s 1 with maximums in the rip neck region of 1 4 m s 1 a distinct tidal modulation of rip current flow existed with maximum velocities occurring at low tide and minimum velocities at high tide comparison with other rip studies suggests that although the magnitude of the morphodynamic and hydrodynamic processes occurring within large scale rip systems is extreme the behaviour of these rip systems is very similar to low energy rips with much smaller spatial scales there is evidence to suggest that distinct morphodynamic scaling relationships exist between these environments

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

trends in research on beaches and dunes on sandy shores 1969 2019 abstract trends in research on morphologic changes on beaches and foredunes on sandy shores are identified from the 1960s to the present research during this period evolved from early descriptive explanation and classification of profile change to instrumented field investigations to modelling of landform change at larger scales research efforts have become increasingly more collaborative with increasing use of field instrumentation data acquisition systems and remote sensing rich datasets are resulting in more comprehensive computational models human altered systems are of increasing interest but knowledge of these systems lags far behind knowledge of natural systems research is becoming more relevant to societal needs as the vulnerability of coastal populations increases the need for investigation of understudied or unexplored environments including human altered ones is ongoing many basic research issues remain but future studies would profit from the development of new models rather than validating or reconfiguring old models collaboration between geomorphologists and engineers may open up research opportunities particularly in modifying beaches and dunes built for shore protection to provide natural values in restricted space application of models to enhance knowledge of effects of sea level rise and coastal storms would be useful to managers developing resiliency plans

vertical structure of the undertow outside the surf zone the vertical structure of the undertow in the shoaling region outside the surf zone is quite different from that inside the surf zone inside the surf zone the undertow typically has a large seaward directed velocity near the bottom and either a shoreward directed or a small seaward directed velocity at trough level measurements show that outside the surf zone the undertow has a small seaward directed velocity near the bed and a large seaward directed velocity at trough level in this paper we develop theoretical expressions for the undertow outside the surf zone and show that the steady streaming from the bottom boundary layer which was earlier found to have a negligible effect in the surf zone svendsen et al 1987 does have a significant influence on the vertical structure of the undertow in that region

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

high time resolution by use of the 26al chronometer in the multistage formation of a cai the allende calcium rich inclusion cai 5241 has been found to contain distinct initial 26 al 27 al in the three consecutive igneous zones that have been identified by extensive petrogenetic studies to have formed in three distinct crystallization events the zones in order of sequence of formation from the petrologic observations are 1 spinel free islands sfi included in 2 a pyroxene spinel rich core src which in turn is included in 3 a melilite mantle mm the initial 26 al 27 al values of these zones are respectively 4 6 5 0 10 5 4 3 10 5 and 3 3 10 5 it is argued that these distinct 26 al 27 al 0 values are not the result of metamorphism but reflect the relative times of formation by crystallization from melts relative to the canonical value of 26 al 27 al 0 5 10 5 we find the following chronology t sfi 0 t src 10 5 yr and t mm 4 10 5 yr the three layer cai is inferred to have sampled a reservoir with an initial uniform 26 al 27 al ratio that decreased in value due to radioactive decay from these observations we conclude that we have resolved time differences of a few hundred thousand years at the very early stages of formation of the solar system the sfi src and mm zones reflect sequential addition of molten cai material which crystallized rapidly without seriously metamorphosing the previously formed material these additions took place over a time of about 400 000 years we believe that these sequential events are not compatible with condensation in a hot region of the solar nebula it is proposed that a scenario involving stages of protoplanetary accretion and of melt generation in protoplanetary sites heated by 26 al might provide a possible source for cais and chondrules

ion microprobe studies of efremovka cais i magnesium isotope composition five coarse grained ca al rich refractory inclusions cais from the efremovka cv3 chondrite are analysed for their magnesium isotopic composition using an ion microprobe the analysed inclusions represent the three common cai types a b1 and b2 data for magnesium isotopic composition of the major mineral phases melilite spinel fassaite and anorthite in these inclusions are used to determine intrinsic magnesium isotopic fractionations and to identify nonlinear effect in 26mg due to the decay of extinct 26al the magnesium isotopic mass fractionation f mg generally favours the heavier isotopes as is expected in the case of coarse grained cais the f mg data for two of the inclusions however show contrasting trends sympathetic behaviour found in both isotopic and petrographic data in one type b1 inclusion suggests that the parent melt of this inclusion experienced a short duration volatilization event prior to crystallization the isotopic data also suggest possible presence of relict spinel in this inclusion that constrains the cooling rate of the parent melt to 70 c h during crystallization hot and dense nebular settings that allow for such fast cooling can only be localized in nature the pristine nature of the efremovka cais as evident from the lack of secondary alteration products in them is well supported by the isotopic data three of the five inclusions yield well behaved mg al isochrons with 26al27al 0 close to the canonical value of 5 10 5 the anorthite data for another inclusion suggest minor disturbance in the isotopic systematics and yield a nearly well behaved isochron with a slightly lower value of 26al27al 0 data for melilite and anorthite in the fifth inclusion define apparent isochrons that suggest partial re equilibration and exchange of magnesium isotopes between these two phases the efremovka data are suggestive of a relatively homogeneous distribution of 26al in the solar nebula

waves currents sediment flux and morphological response in a barred nearshore system abstract a shore normal array of seven bi directional electromagnetic flowmeters and nine surface piercing continuous resistance wave staffs were deployed across a multiple barred nearshore at wendake beach georgian bay canada and monitored for a complete storm cycle time integrated estimates of total itvf and net invf sediment volume flux together with bed elevation changes were determined using depth of activity rods the three bars ranging in height from 0 10 to 0 40 m accreted during the storm 0 03 m and the troughs were scoured 0 05 m sediment reactivation depths reached 0 14 m and 12 of the nearshore control volume was mobilized however the invf value for the storm was less than 1 of the control volume revealing a near balance in sediment volume in the bar system landward migration of the inner crescentic and second sinuous bars occurred in association with an alongshore migration of the bar form itself the outermost straight shore parallel bar remained fixed in location the surf zone was highly dissipative throughout the storm 3 8 10 2 192 10 2 and the wave spectrum was dominated by energy at the incident frequency spectral peaks at frequencies of the first harmonic and at one quarter that of the incident wave were associated with secondary wave generation just prior to breaking and a standing edge wave respectively the former spectral peak was within the 95 confidence band for the spectrum while the latter contributed not more than 10 to the total energy in the surface elevation spectrum even near the shoreline during the storm wave height exceeded 2 m h s and periods reached 5 s t p k orbital velocities exceeded 0 5 m s 1 u rm s and were above the threshold of motion for the medium to fine sands throughout the storm shore parallel flows in excess of 0 4 m s 1 were recorded with maxima in the troughs and minima just landward of the bar crest the rate and direction of sediment flux is best explained by the interaction of antecedent bed slopes with spatial gradients in the mean and asymmetry of the shore normal velocity field these hydrodynamic parameters represent steady flows superimposed on the dominantly oscillatory motion and assumed a characteristic spatial pattern from the storm peak through the decay period increases spatially in the magnitudes of both the mean flows and flow asymmetries cause an increasing net transport potential erosion decreases in these values spatially cause a decreasing net transport potential and thus deposition these transport potentials are increased or decreased through the gravity potential induced by the local bed slope shore parallel flow was important in explaining sediment flux and morphological change where orbital velocities mean flows and flow asymmetries were at a minimum

initial 26al 27al in carbonaceous chondrite chondrules too little 26al to melt asteroids we report 26mg excesses correlated with al mg ratios in five chondrules from the primitive co3 0 chondrite yamato 81020 that yield a mean initial 26al 27al ratio of only 3 8 0 7 10 6 about half that of ordinary chondrite oc chondrules even if asteroids formed immediately after chondrule formation this ratio and the mean al content of co chondrites is only capable of raising the temperature of a well insulated co asteroid to 940 k which is more than 560 k too low to produce differentiation the same ratio combined with the higher al content of cv chondrites results in a cv asteroid temperature of 1100 k we calculate that the mean initial 26al 27al ratio of about 7 4 10 6 found in ll chondrules is only able to produce small amounts of melting too little to produce differentiation these results cast serious doubt on the viability of 26al as the heat source responsible for asteroid differentiation inclusion of 60fe raises temperatures about 160 k but this increment is not enough to cause differentiation even of an ll chondrite asteroid

dynamics of multiple intertidal bars over semi diurnal and lunar tidal cycles north lincolnshire england multiple intertidal bars are common features of wave dominated sandy beaches yet their short term 1 month and small scale 1 km morphology and dynamics remain poorly understood this study describes the morphodynamics of multiple intertidal bars in north lincolnshire england during single and lunar tidal cycles under two contrasting conditions first when significant wave height was 0 5 m and second when significant wave height frequently exceeded 1 m the relative importance of swash surf and shoaling processes in determining morphological change was examined using detailed field observations and a numerical model the beach featured four intertidal bars and both cross shore and longshore bar morphology evolved during the field investigation particularly under medium to high wave energy conditions numerical modelling suggests shoaling processes are most common on the seaward two bars under calm wave conditions hs 0 5 m and that surf zone processes become more common during neap tides and under more energetic hs 0 5 m conditions surf processes dominate the inner two bars though swash influence increases in a landward direction the numerical modelling results combined with low tide survey data and high resolution morphological measurements strongly suggest changes in the intertidal bar morphology are accomplished by surf zone processes rather than by shoaling wave or swash processes this is because shoaling waves do not induce significant sediment transport to have any morphological effect whereas swash action generally does not have enough scope to act as the swash zone is much narrower than the surf zone it was found however that the absolute rate of morphological change under swash action and surfzone processes are of similar magnitudes and that swash action may induce a significant amount of local morphological change when the high tide mark is located on the upper bar making this process important for bar morphodynamics copyright 2007 john wiley sons ltd

magnitude and cross shore distribution of bed return flow measured on natural beaches abstract field measurements of cross shore currents 0 25 m from the bed were made on two natural beaches under a range of incident wave conditions the results indicated the presence of a relatively strong offshore directed mean current both within and seaward of the surf zone typical velocities within the surf zone were of the order of 0 2 0 3 m s this bed return flow or undertow represents a mass conservation response returning water seaward that was initially transported onshore in the upper water column primarily above the trough of the incident waves the measurements demonstrated that the bed return flow velocity increases with the incident wave height in addition the crossshore distribution of the bed return flow is characterised by a mid surf zone maximum which exhibits a strong decrease in velocity towards the shoreline and a more gradual decay in the offshore direction several bed return flow models based on mass continuity were formulated to predict the cross shore distribution of the bed return flow under an irregular wave field and were compared with the field data best agreement was obtained using shallow water linear wave theory after including the mass transport associated with unbroken waves the contribution of the unbroken waves enables net offshore directed bottom currents to persist outside the region of breaking waves providing a mechanism other than rip currents to transport sediment offshore beyond the surf zone

flow characteristics at the rip current neck under low energy conditions abstract this paper presents the flow signature of the rip current neck as determined by fourteen near bottom velocity records with a comparison made to 63 recordings in the surf zone the field experiments including wave monitoring and morphological mapping were conducted under relatively calm dissipative wave conditions tsig 3 6 s hsig 0 3 1 1 m at herzliya beach israel on the mediterranean shore the current data were analysed for shore normal and resultant components the processing of the time series in the form of instantaneous and smoothed velocities provided spectral energy orbital and current velocity specific current discharge and directional distribution data the unique characteristic of the neck environment was found to be its continuous unidirectional seaward flow due to the channeling effect this steady offshore drift constituted the fastest flow in the surf zone with a typically narrow 35 94 directional range through spectral analysis of the unidirectional return flow the morphodynamic process signature at the rip neck was defined by the relative contribution from the incident waves 78 the subharmonic edge waves 14 and the infragravity oscillations 8 the pulsatory jet like rip model with concentration of energy at low frequencies is not corroborated by this study the studied environment of the rip and bar pattern represented an inherited beach morphology at an initial accretional although not yet reflective stage

characteristics and dynamics of multiple intertidal bars north lincolnshire england multiple intertidal bars and troughs often referred to as ridges and runnels are significant features on many macrotidal sandy beaches along the coastline of england and wales they are particularly prevalent in the vicinity of estuaries where the nearshore gradient is gentle and a large surplus of sediment is generally present this paper examines the dynamics of such bar systems along the north lincolnshire coast a digital elevation model of the intertidal morphology obtained using lidar demonstrates that three to five intertidal bars are consistently present with a spacing of approximately 100 m the largest and most pronounced bars height 0 5 0 8 m are found around mean sea level whereas the least developed bars height 0 2 0 5 m occur in the lower intertidal zone annual aerial photographs of the intertidal bar morphology were inspected to try to track individual bars from year to year to derive bar migration rates however there is little resemblance between concurrent photographs and resetting of the intertidal profile occurs on an annual basis three dimensional beach surveys were conducted monthly at three locations along the north lincolnshire coast over a one year period the intertidal bar morphology responds strongly to the seasonal variation in the forcing conditions and bars are least numerous and flattest during the more energetic winter months morphological changes over the monthly time scale are strongly affected by longshore sediment transport processes and the intertidal bar morphology can migrate along the beach at rates of up to 30 m per month the behaviour of intertidal bars is complex and varies over a range of spatial and temporal scales in response to a combination of forcing factors e g incident wave energy different types of wave processes longshore and cross shore sediment transport relaxation time and morphodynamic feedback copyright 2005 john wiley sons ltd

hibonite bearing microspherules a new type of refractory inclusions with large isotopic anomalies reported are petrographic descriptions major and trace element chemistry and mg ca and ti isotopic compositions of a new class of refractory inclusions that consist of spherules composed of hibonite and a silicate glass the distinctive features of these inclusions are excesses in 48ca and 50ti in both glass and hibonite and 26mg depletions relative to terrestrial isotopic compositions three spherules have been examined and analyzed one from the lance co3 meteorite and two from the murchison cm2 meteorite lance 3413 1 31 la3413 1 31 and murchison 7 228 mur7 228 have euhedral to subhedral hibonite crystals enclosed within glass murchison 7 753 mur7 753 has a rounded hibonite core with several small inclusions of perovskite a small fragment of glass is attached to the hibonite and an fe silicate rim is imperfectly preserved around the grain la3413 1 31 has a group ii ree pattern mur7 228 a refractory pattern with depletions in the relatively volatile elements sr ba nb v and eu and mur7 753 a pattern characterized by the prior removal of an ultrarefractory component and overall fractionation of all rees the partitioning of the lrees between hibonite and glass in mur7 228 is consistent with equilibrium hibonite liquid partition coefficients previously determined la3413 1 31 shows much less partitioning while mur7 753 shows no evidence for partitioning and preserves an unequilibrated refractory component highly enriched in gd all spherules have initial magnesium depleted in 26mg by around 3 relative to terrestrial mg but only mur7 228 shows evidence for in situ decay of 26al with an initial 26al27al of 1 7 0 7 10 5 both hibonite and glass in all three spherules show excesses of 48ca and 50ti ranging up to 40 and 20 respectively relative to terrestrial ca and ti spherules such as these are rare and the only other occurrence is in the unique chondrite alh85085 the hibonite in the spherules shows similarities to isotopically anomalous hibonite crystal fragments placs but it is unlikely that the spherules formed by remelting of placs the precursors include isotopically anomalous ca ti carriers but also isotopically normal refractory components that probably formed as condensates the spherules formed by melting of these precursors under disequilibrium conditions and rapid cooling after hibonite crystallization these inclusions must have formed early prior to the dilution of isotopic anomalies by mixing processes and in an area characterized by excesses of 48ca and 50ti depletions of 26mg and lack of 26al

observations and a model of undertow over the inner continental shelf abstract onshore volume transport stokes drift due to surface gravity waves propagating toward the beach can result in a compensating eulerian offshore flow in the surf zone referred to as undertow observed offshore flows indicate that wave driven undertow extends well offshore of the surf zone over the inner shelves of martha s vineyard massachusetts and north carolina theoretical estimates of the wave driven offshore transport from linear wave theory and observed wave characteristics account for 50 or more of the observed offshore transport variance in water depths between 5 and 12 m and reproduce the observed dependence on wave height and water depth during weak winds wave driven cross shelf velocity profiles over the inner shelf have maximum offshore flow 1 6 cm s 1 and vertical shear near the surface and weak flow and shear in the lower half of the water column the observed offshore flow profiles do not resemble the parabolic profiles with maximum flow at middepth observed within the su

aluminum 26 in calcium aluminum rich inclusions and chondrules from unequilibrated ordinary chondrites in order to investigate the distribution of 26 a1 in chondrites we measured aluminum magnesium systematics in four calcium aluminum rich inclusions cais and eleven aluminum rich chondrules from unequilibrated ordinary chondrites uocs all four cais were found to contain radiogenic 26 mg 26 mg from the decay of 26 a1 the inferred initial 26 al 27 al ratios for these objects 26 al 27 al 0 5 10 5 are indistinguishable from the 26 al 27 al 0 ratios found in most cais from carbonaceous chondrites these observations together with the similarities in mineralogy and oxygen isotopic compositions of the two sets of cais imply that cais in uocs and carbonaceous chondrites formed by similar processes from similar or the same isotopic reservoirs or perhaps in a single location in the solar system we also found 26 mg in two of eleven aluminum rich chondrules the 26 al 27 al 0 ratio inferred for both of these chondrules is 1 10 5 clearly distinct from most cais but consistent with the values found in chondrules from type 3 0 3 1 uocs and for aluminum rich chondrules from lightly metamorphosed carbonaceous chondrites 0 5 10 5 to 2 10 5 the consistency of the 26 al 27 al 0 ratios for cais and chondrules in primitive chondrites independent of meteorite class implies broad scale nebular homogeneity with respect to 26 al and indicates that the differences in initial ratios can be interpreted in terms of formation time a timeline based on 26 al indicates that chondrules began to form 1 to 2 ma after most cais formed that accretion of meteorite parent bodies was essentially complete by 4 ma after cais and that metamorphism was essentially over in type 4 chondrite parent bodies by 5 to 6 ma after cais formed type 6 chondrites apparently did not cool until more than 7 ma after cais formed this timeline is consistent with 26 al as a principal heat source for melting and metamorphism

field experiment on secondary wave generation on a barred beach and the consequent evolution of energy dissipation on the beach face a field experiment conducted on a sandy barred beach situated on the southern part of the french atlantic coastline allowed us to investigate the formation of secondary waves when a moderate significant wave height of about 0 8 m in 3 7 m water depth long 11 14 s narrowband swell propagated over an intertidal ridge and runnel system in both breaking and nonbreaking conditions field evidence using higher spectral analysis is given for the sum interactions between pairs of waves at the primary spectral peak and the consequent energy transfer to nearly harmonic wave components although wave breaking appears to weaken the strength of nonlinear couplings the generation of high frequency energy is hardly affected by wave breaking the phenomenon of harmonic decoupling which takes place behind the bar cannot be completely ascribed to the increase in water depth and the so called deshoaling effect indeed the variation in the values of the maximum bicoherence was very moderate when no breaking occurred finally the doubling in the number of wave crests and the consequent decrease in the significant wave period delay the energy dissipation on the beach face d 2002 elsevier science b v all rights reserved

wave transformation across the inner surf zone sea and swell wave heights observed on transects crossing the mid and inner surf zone on three beaches a steep concave up beach a gently sloped approximately planar beach and a beach with an approximately flat terrace adjacent to a steep foreshore were depth limited i e approximately independent of the offshore wave height consistent with previous observations the wave evolution is well predicted by a numerical model based on the one dimensional nonlinear shallow water equations with bore dissipation the model is initialized with the time series of sea surface elevation and cross shore current observed at the most offshore sensors located about 50 to 120 m from the mean shoreline in mean water depths 0 80 to 2 10 m the model accurately predicts the cross shore variation of energy at both infragravity nominally 0 004 f 0 05 hz and sea swell here 0 05 f 0 18 hz frequencies in models of surf zone hydrodynamics wave energy dissipation is frequently parameterized in terms of s the ratio of the sea swell significant wave height to the local mean water depth the observed and predicted values of s increase with increasing beach slope and decreasing normalized by a characteristic wavenumber k water depth kh and are well correlated with kh a measure of the fractional change in water depth over a wavelength errors in the predicted individual values of s are typically less than 20 it has been suggested that infragravity motions affect waves in the sea swell band and hence s but this speculation is difficult to test with field observations numerical simulations suggest that for the range of conditions considered here s is insensitive to infragravity energy levels

beach and nearshore facies southeast australia abstract the morphology texture and facies sequence on seven sand beaches located in low moderate and high wave energy microtidal environments in southern australia were investigated using box coring and scuba observations systematic variation in facies occur both within and between the beaches low energy reflective beaches are limited in lateral and vertical extent and in facies to beach laminations separated by coarse step deposits from finer nearshore cross lamination facies moderate energy intermediate beaches characterised by rip circulation possess increasingly wider surfzones with ridge and runnel and bar trough facies separating the beach and step facies from the more extensive nearshore sequence high energy dissipative beaches may have 500 m wide surfzones containing multiple bar trough topography fine beach laminations with backwash structures grade into 4 5 m thick bar trough sequences then the extensive nearshore facies as wave energy increases from low h b h b 2 5 m the vertical extent of the beach to nearshore sequence increases from

surficial sediments on the continental shelf of tasmania australia abstract the continental shelf around the island of tasmania and in adjacent bass strait is veneered with quaternary palimpsest sediment composed of quartzose sand relict pleistocene carbonate particles and abundant holocene biogenic carbonate neritic deposits to water depths of 200 m are predominantly coarse grained ranging from gravels to sands to muddy sands the only true carbonate muds lie in the centre of bass strait this pattern reflects the overall high energy sea state and winnowing action of southward flowing currents along the outer shelf sediments can be resolved into three megafacies dominated either by quartzose sand inner shelf and around islands in bass strait relict carbonate particles mid shelf and near islands in bass strait or holocene biogenic carbonate inner to outer shelf facies can be distinguished depending upon whether bryozoans molluscs or other biofragments are dominant relict particles on the mid shelf are only present in large numbers on the western margin and around islands in bass strait they are a minor component of deposits on the eastern shelf this situation is interpreted to reflect higher overall carbonate production on the eastern shelf promoted by increased trophic resources via upwelling of subantarctic waters holocene molluscs especially infaunal bivalves are most prominent on the inner shelf holocene bryozoans are the most numerous particles overall and most abundant on the western shelf reflecting preferential conditions for growth probably promoted by episodic mid shelf upwelling bryozoan fragments can be separated into associations dominated by either 1 shallow water erect flexible articulated branching or articulated zooidal growth forms or 2 mid to outer shelf erect rigid fenestrate or flat robust branching types less abundant vagrant growth forms are limited to shallow waters whereas delicate branching forms are localized to deep waters nodular arborescent growth forms mainly celleporaria sp occur in both shallow and deep waters but are unusual on most of the shelf superimposed on this depth related distribution is a north to south cool to cold trend the whole spectrum of bryozoans is present on the shelf in the north whereas in the south bryozoan biofragments are mostly erect flexible with delicate branching forms restricted to the outer shelf and upper slope the change coincides with the furthest northward extent the subtropical convergence zone during winter surficial sediments in bass strait are most comparable to those on the extensive continental shelf to the west off southern continental australia where inboard sediment production takes place in environments populated by macroalgae but dominated by seagrasses where water depth is

a petrographic chemical and isotopic study of calcium aluminum rich inclusions and aluminum rich chondrules from the axtell cv3 chondrite petrographic compositional and isotopic characteristics were studied for three calcium aluminum rich inclusions cais and four plagioclase bearing chondrules three of them al rich from the axtell cv3 chondrite all seven objects have analogues in allende cv3 and other primitive chondrites yet axtell like most other chondrites contains a distinctive suite of cais and chondrules in common with allende cais cais in axtell exhibit initial 26 al 27 al ratios 26 al 27 al 0 ranging from 5 10 5 to 2 ma after the first cais as in other cv3 chondrites some objects in axtell show evidence of isotopic disturbance axtell has experienced only mild thermal metamorphism 600 c probably not enough to disturb the al mg systematics its cais and chondrules have suffered extensive metasomatism probably prior to final accretion these data indicate that cais and chondrules in axtell and other meteorites had an extended history of several million years before their incorporation into the axtell parent body these long time periods appear to require a mechanism in the early solar system to prevent cais and chondrules from falling into the sun via gas drag for several million years before final accretion we also examined the compositional relationships among the four plagioclase bearing chondrules two with large anorthite laths and two barred olivine chondrules and between the chondrules and cais three processes were examined 1 igneous differentiation 2 assimilation of a cai by average nebular material and 3 evaporation of volatile elements from average nebular material we find no evidence that igneous differentiation played a role in producing the chondrule compositions although the barred olivine compositions can be related by addition or subtraction of olivine methods 2 and 3 could have produced the composition of one chondrule axch 1471 but neither process explains the other compositions our study indicates that plagioclase bearing objects originated through a variety of processes

an isotopic and petrologic study of calcium aluminum rich inclusions from co3 meteorites we have studied the mineralogy and petrology of 229 calcium aluminum rich inclusions cais from ten co3 meteorites of petrologic types 3 0 3 7 subsets of these inclusions were measured by ion probe for magnesium calcium and titanium isotopes and ree abundances most cais from co3 meteorites fall into three major types 1 melilite rich inclusions which also contain spinel hercynite perovskite and occasionally hibonite 2 spinel pyroxene inclusions and 3 hibonite hercynite inclusions in addition several isolated hibonite grains two grossite caal 4o 7 bearing cais two hibonite fassaite microspherules and one anorthite spinel pyroxene inclusion were found cais from co3 meteorites exhibit all of the ree patterns commonly seen in inclusions from cv3 and cm2 chondrites most exhibit evidence of 26 ai and many have inferred 26 ai 27 ai o 5 10 5 the relative abundances of different types of cais in co3 chondrites differ from those in cv3 and cm2 chondrites cais in co3 chondrites have experienced considerable secondary alteration both before and after accretion signatures of nebular alteration include wark lovering rims and the high fe contents in spinels from all hibonite hercynite inclusions occasionally melilite and anorthite show evidence of nebular alteration to feldspathoids and pyroxene the magnesium aluminum systematics of some melilite rich inclusions were apparently disturbed prior to final accretion of the parent body parent body alteration is indicated by correlations between cai characteristics and the petrologic type of the host meteorite spinel in melilite rich and coarse grained spinel pyroxene inclusions becomes more fe rich with the development of relatively homogeneous hercynitic spinel 50 60 mol in cais from metamorphic grades 3 4 perovskite has been converted to ilmenite in types 3 4 melilite rich inclusions are abundant in co3 0 3 3 meteorites rare in 3 4 meteorites and absent meteorites of types 3 5 3 7 melilite rich cais are probably replaced by inclusions rich in feldspathoids pyroxene and fe rich spinel isotopic disturbance of the magnesium aluminum systematics may be more severe in higher petrologic types hibonite seems to be unaffected by this level of metamorphism three isotopically unusual inclusions were found one single crystal hibonite isna sp16 has a ree pattern strongly depleted in ce and y 26 ai 27 ai o 2 4 0 3 10 5 and mass fractionated calcium f ca 12 2 amu but no resolvable nuclear anomalies in neutron rich calcium isotopes the ree pattern which is thought to reflect nebular conditions and mass fractionated calcium indicative of evaporation are similar to those of the fun inclusion hal and related hibonites indicating similar formation conditions the absence in isna sp16 of the nuclear anomalies observed in hal and the difference in 26 ai 27 ai o between hal and isna sp16 indicate that the processes that produced hal type hibonites operated on diverse materials two hibonite bearing microspherules colony sp1 and alh82101 sp15 exhibit nearly flat ree patterns with negative europium anomalies and slightly negative 26 mg alh82101 sp15 has resolved excesses of 48 ca and 50 ti these characteristics are similar to those of previously described microspherules from murchison and lance implying that the microspherules formed via a single process from related but not identical source materials

correlated study of initial sr 87 sr 86 and al mg isotopic systematics and petrologic properties in a suite of refractory inclusions from the allende meteorite we have studied a suite of six coarse grained ca al rich inclusions cais from the allende meteorite applying in concert detailed petrographic and chemical characterization ion probe mass spectrometric analyses of the al mg isotopic system to determine the abundance and distribution of 26a1 and thermal emission mass spectrometric analyses of the rb sr system to determine initial 87sr86sr ratios the simplest inclusion is a type bl usnm 3529 z that shows evidence of minor alteration and recrystallization since solidification from a melt droplet e g some of the coarse grained anorthite in the inclusion especially near the inclusion rim apparently formed by recrystallization or melting of fine grained secondary anorthite that had replaced melilite four other type bs contain evidence of more widespread recrystallization in addition to evidence of local replacement of melilite by coarse anorthite e g melilite zoning is complex and not igneous in origin and in one inclusion usnm 3529 21 melilite and pyroxene crystals enclose relicts of an earlier generation of the same phases the sixth inclusion usnm 3898 is a type a whose properties appear to be largely metamorphic in origin all six inclusions show variations in mg isotopic compositions indicating that they incorporated 26a1 in 3529 z the relative abundance of 26a1 26al27al 4 0 0 1 10 5 is close to the canonical value 26al27al 5 10 5 for cais but both anorthite and melilite show minor departures from a strict isochron relationship between mg and al in particular the coarse anorthite near the inclusion rim has initial 26al27al ratios of 1 2 10 5 implying formation at least 1 5 million years after the first generation anorthite the other four type bs exhibit larger disturbances of the al mg system that can be understood in terms of local recrystallization and isotopic exchange primarily between anorthite and melilite only 3898 is consistent with a strict al mg isochron relationship but this cai lacks primary anorthite and the small range of al mg among the phases analyzed may preclude resolution of any small isotopic disturbances the rb sr isotopic system also typically indicates some level of disturbance some of which must have been relatively recent nevertheless phases characterized by very low rb sr permit precise identification of initial 87sr86sr our al mg and sr data are largely consistent with a simple chronological interpretation of both systems i e the 26al results suggest that all the initial 87sr86sr ratios should have the same value and with one exception our initial 87sr86sr ratios are consistent with a single value this value is somewhat higher than the primitive value all reported by gray et al 1973 however also with one exception the very low rb sr cai data reported by gray et al 1973 are consistent with the same value the exception is the same inclusion in both studies our analysis of usnm 3898 yields an initial 87sr86srhigher than that of the other cais while gray et al 1973 obtained an initial 87sr86srlower than that of the other cais for the same inclusion labeled as d7 on which all is based neither result can be readily explained as a chronological aberration since 3898 has nearly canonical 26al27al the present data are the first which establish a firm association between primitive 26al27al and primitive 87sr86sr by analysis of both isotopic systems in the same inclusions the comparison of both isotopic systems interpreted as simple nebular chronometers does not reveal any chronological inconsistencies that demand resolution in terms of a grossly heterogeneous distribution of 26al

a field study of wave reflections from an exposed dissipative beach abstract this paper describes a field study of wave reflections from an exposed dissipative beach using only water surface elevation data from five wave height sensors many insights were gained into beach reflections and their detection a technique normally reserved for laboratory use was successfully applied to surf zone data to separate incident and reflected infragravity wave energy spectra the reflected wave energy was found to be significant for all wave periods greater than 20 seconds and often total for wave periods greater than 30 seconds the evidence was heavily weighted towards the observed reflected wave activity being essentially two dimensional with the influence of three dimensional edge waves being minimal other findings relate to the value of wave energy spectra computed from a single surf zone sensor the relevance of single slope approximations of beach profiles and the relationship between incident infragravity wave activity and the longer period swash excursions on a beach face

the morphodynamics of shore platforms in a micro tidal setting interactions between waves and morphology abstract the interactions between waves and morphology on shore platforms were investigated at four platforms located at kaikoura peninsula new zealand and the otway coast victoria australia waves were measured over six tidal peaks of a spring tidal sequence at each site during a six month period february 2007 july 2007 this paper reports the results of an investigation into the research question how are waves modified by platform morphology in a micro tidal setting through the investigation of wave interactions on shore platforms it was found that complex hydrodynamic patterns formed on the shore platforms studied through direct measurement of waves on the platforms it was found that wave attenuation was not dependent on platform width but rather influenced by platform gradient and depth of water on the platform spectral analysis was used to assess how wave energy was transformed across the platforms at three of the four platforms investigated energy gradients formed across the platform with wave energy recorded within the infragravity range

modern u pb chronometry of meteorites advancing to higher time resolution reveals new problems in this paper we evaluate the factors that influence the accuracy of lead pb isotopic ages of meteorites and may possibly be responsible for inconsistencies between pb isotopic and extinct nuclide timescales of the early solar system instrumental mass fractionation and other possible analytical sources of error presence of more than one component of non radiogenic pb migration of ancient radiogenic pb by diffusion and other mechanisms possible heterogeneity of the isotopic composition of uranium u uncertainties in the decay constants of uranium isotopes possible presence of freshly synthesized actinides with short half life e g 234u in the early solar system possible initial disequilibrium in the uranium decay chains and potential fractionation of radiogenic pb isotopes and u isotopes caused by alpha recoil and subsequent laboratory treatment we review the use of 232th 238u values to assist in making accurate interpretations of the u pb ages of meteorite components we discuss recently published u pb dates of calcium aluminum rich inclusions cais and their apparent disagreement with the extinct nuclide dates in the context of capability and common pitfalls in modern meteorite chronology finally we discuss the requirements of meteorites that are intended to be used as the reference points in building a consistent time scale of the early solar system based on the combined use of the u pb system and extinct nuclide chronometers

observations of turbulence within a natural surf zone abstract here the reynolds stresses u w and w where u and w are the cross shore alongshore and vertical turbulence velocities respectively and the angle brackets represent time averaging are used to diagnose turbulence dynamics beneath natural breaking surf zone waves the data were collected at truc vert beach france during a 12 day period in 1 3 m water depth with strong cross shore and alongshore currents under high energy wave conditions offshore significant wave heights ranged between 2 and 8 m the u w term is predominantly negative increases with the ratio of wave height hs to water depth h degree of wave breaking and decreases in magnitude toward the bed this supports the view that the cross shore shear stress is due to breaking induced vortices that transport high speed cross shore flow downward and disintegrate close to the bed the occasional positive sign of u w within the lower 15 20 of the water column indicates that sometimes surface generated turbule

salinity reflux and dolomitization of southern australian slope sediments the importance of low carbonate saturation levels anomalously saline waters in ocean drilling program holes 1127 1129 1130 1131 and 1132 which penetrate southern australian slope sediments and isotopic analyses of large benthic foraminifera from southern australian continental shelf sediments indicate that pleistocene holocene meso haline salinity reflux is occurring along the southern australian margin ongoing dolomite formation is observed in slope sediments associated with marine waters commonly exceeding 50 salinity a well flushed zone at the top of all holes contains pore waters with normal marine trace element contents alkalinities and ph values dolomite precipitation occurs directly below the well flushed zone in two phases phase 1 is a nucleation stage associated with waters of relatively low ph ca 7 caused by oxidation of h2s diffusing upward from below this dolomite precipitates in sediments 80 m below the sea floor phase 2 dolomite grows on dolomite cores precipitated during phase 1 phase 2 dolomite has d 13 c values similar to those of the surrounding bulk carbonate and high sr values relative to phase 1 dolomite consistent with having formed in waters affected by aragonite and calcite dissolution the nucleation stage in this model phase 1 challenges the more commonly accepted paradigm that inhibition of dolomitization by sea water is overcome by effectively increasing the saturation state of dolomite in sea water

petrology and mineralogy of the ningqiang carbonaceous chondrite we report detailed chemical petrological and mineralogical studies on the ningqiang carbonaceous chondrite ningqiang is a unique ungrouped type 3 carbonaceous chondrite its bulk composition is similar to that of cv and ck chondrites but refractory lithophile elements 1 01 x ci are distinctly depleted relative to cv 1 29 x ci and ck 1 20 x ci chondrites ningqiang consists of 47 5 vol chondrules 2 0 vol ca al rich inclusions cals 4 5 vol amoeboid olivine aggregates aoas and 46 0 vol matrix most chondrules 95 in ningqiang are mg rich the abundances of fe rich and al rich chondrules are very low al rich chondrules arcs in ningqiang are composed mainly of olivine plagioclase spinel and pyroxenes in arcs spinel and plagioclase are enriched in moderately volatile elements cr mn and na and low ca pyroxenes are enriched in refractory elements al and ti the petrology and mineralogy of arcs in ningqiang indicate that they were formed from hybrid precursors of ferromagnesian chondrules mixed with refractory materials during chondrule formation processes we found 294 cals 55 0 type a 39 5 spinel pyroxene rich 4 4 hibonite rich and several type c and anorthite spinel rich inclusions and 73 aoas in 15 ningqiang sections equivalent to 20 cm 2 surface area this is the first report of hibonite rich inclusions in ningqiang they are texturally similar to those in cm ch and cb chondrites and exhibit three textural forms aggregates of euhedral hibonite single crystals fine grained aggregates of subhedral hibonite with minor spinel and hibonite al ti diopside spinel spherules evidence of secondary alteration is ubiquitous in ningqiang opaque assemblages formed by secondary alteration of pre existing alloys on the parent body are widespread in chondrules and matrix on the other hand nepheline and socialite existing in all chondritic components formed by alkali halogen metasomatism in the solar nebula

spectral signatures for swash on reflective intermediate and dissipative beaches in this paper we synthesise a large data set gathered from a wide variety of field deployments and integrate it with previously published results to identify the spectral signatures of swash from contrasting beach types the field data set includes the full range of micro tidal beach types reflective intermediate and dissipative with beach gradients ranging from approximately 1 6 to 1 60 exposed to offshore significant wave heights of 0 5 3 0 m the ratio of swash energy in the short wave f 0 05 hz to long wave f 0 05 hz frequency bands is found to be significantly different between the three beach types swash energy at short wave frequencies is dominant on reflective and intermediate beaches and swash at long wave frequencies is dominant on dissipative beaches consistent with previously reported spectral signatures for the surf zone on these beach types the available swash spectra were classified using an automated algorithm clara into five different classes the ordered classes represent an evolution in the spectrum shape described by a frequency downshifting of the energy peak from the short wave into the long wave frequency band and an increase in the long wave swash energy level compared to a relatively minor variation in the short wave swash energy level a universally common feature of spectra from all beach states was an f 4energy roll off in the short wave frequency band in contrast to the broadly uniform appearance of the short wave frequency band the appearance of the long wave frequency band was highly variable across the beach states we incorporate the results presented here and previously published observations into the morphodynamic beach state model and propose an ordered sequence of swash spectra under increasing and decreasing incident wave energy level this extension of the beach state model to include the swash zone leads to the following propositions for morphodynamic controls on the nature of the swash spectrum 1 the short wave part of the swash spectrum is relatively constant in form across all beach states f 4 energy roll off and the energy density per unit frequency is controlled by the beach face gradient alone 2 the spectral bandwidth of the energy roll off varies directly with offshore wave energy level and inversely with beach face gradient or beach state in a manner consistent with the non linear wave breaking criterion 3 the infragravity part of the swash spectrum is highly variable in form across all beach states and the energy level is related to the offshore wave energy level and surf zone morphology

ripex observations of a rip current system rip current kinematics and beach morphodynamics were measured for 44 days at sand city monterey bay ca using 15 instruments composed of co located velocity and pressure sensors acoustic doppler current profilers and kinematic gps surveys the morphology consisted of a low tide terrace with incised quasi periodic rip channels representative of transverse bars offshore 17 m depth significant wave height and peak period ranged 0 20 3 0 m and 5 20 s the mean wave direction was consistently near 08 resulting in rip channel morphology which evolved in response to the changing wave characteristics an inverse relationship between sediment accreting on the transverse bar and eroding in the rip channel was found the spatial distribution of sediment is reflected in the background rip current flow field the mean velocity magnitudes within the rip channel transverse bars increased offshore onshore with decreasing tidal elevations and increased with increasing sea swell energy eulerian averaged flows were predominantly shoreward on the transverse bars and seaward within the rip channel throughout the experiment resulting in a persistent cellular circulation except during low wave energy the rip current spacing to the rip channel width was less than or equal to two which suggests that the rip currents are influenced by each other and that no two dimensional bar return flow should be present the vertical velocity profile on the bar indicated that the flow was predominantly shoreward the flow field within the surf zone was depth uniform except for significant shear occurring near the surface owing to stokes drift the wave induced transport hypothesis is evaluated d 2005 elsevier b v all rights reserved

long wave forcing on a barred beach we present new laboratory data on long wave forcing over a barred beach profile under random wave breaking conditions the data include incident and radiated wave amplitudes wave set up and detailed measurements of the cross shore variation in long wave amplitude including shoreline swash amplitudes the total surf zone width was varied via changes in both wave height and the water level over the bar crest the data obtained from the barred beach are also compared with previous data obtained from a plane beach under essentially identical short wave forcing conditions the presence of the bar induces a frequency downshift in the spectral peak of the radiated long waves a consequence of the increased surf zone width on the barred beach and a clear signature of long wave forcing by a time varying breakpoint further comparisons of the two data sets suggest that the bar leads to resonant trapping and amplification or suppression of the shoreline motion at discrete long wave frequencies well defined standing long wave motion occurs at discrete frequencies inside the bar and the resonant response is consistent with a simple seiche between the bar crest and shoreline in agreement with previous numerical model studies the long wave structure offshore of the breakpoint depends on the relative positions of the bar shoreline and breakpoint and is inconsistent with a numerical solution for a free standing long wave over the barred beach profile

suspended sediment transport and the role of infragravity waves in a barred surf zone abstract collocated optical backscatterance suspended solids sensors and electromagnetic flowmeters were deployed at stanhope lane beach p e i canada to assess the contributions of wind waves infragravity waves and mean currents to the cross shore flux of suspended sediment across a barred surf zone the local net transport of suspended sediment magnitude and direction was highly variable both spatially and temporally with respect to the relative magnitudes of the suspended sediment transport 1 that induced by quasi steady mean currents and oscillatory currents at both incident and infragravity frequencies were almost equal in magnitude when the total surf zone was averaged over the storm event 2 waves in the near infragravity band were quantitatively more important during the waning of the storm especially where when surf persisted well after the initial decay of the offshore wave field 3 incident waves were important where when the waves were not saturated i e during the early stages of the storm at all locations and persistently throughout the storm on the seaward slope of the bar where wave saturation was limited to a very short period with respect to the direction of net sediment transport 1 that attributable to mean currents was directed offshore in the inner surf zone probably reflecting the presence of an undertow while further seaward an onshore transport occurred probably resulting from mass transport induced by surf bores or drift velocities induced by the infragravity wave boundary layer 2 that induced by oscillatory currents at incident wave frequencies was generally onshore at any one location throughout the storm event in contrast oscillatory transport at low frequencies changed direction and also varied in magnitude at any given location in part these changes reflect the existence of significant oscillatory sediment transport at discrete infragravity frequencies the standing infragravity waves consistently transported suspended sediment towards antinodes in the water surface elevation

diagenesis and compositional partitioning of quaternary cool water carbonate aeolianites southeastern australia abstract middle to late pleistocene stranded carbonate sea beaches adjacent aeolian dunes and pleistocene aeolianites together with holocene marginal marine calcareous sediments across southeastern australia contain the longest record of such deposition in the modern world stretching back to at least 900 ky mis 23 the grains are were derived from a suite of cool water heterozoan carbonate sediments produced on the adjacent offshore shelf most modern shelf carbonate sediments in the region today are aragonite rich but the aragonite is presently slowly being dissolved on or just below the seafloor before the deposits enter the rock record beach dune sediments are derived mainly from the shallow 30 meters deep adjacent seafloor they are mollusk rich but with most bryozoan particles having been destroyed in the surf zone the mollusks are dominantly aragonite these nearshore sediments are swept onshore before any significant seafloor diagenesis can take place and so are compositionally different from the eventual aragonite poor open shelf sediments aragonite skeletal fragments in the dunes progressively dissolve with time under a semi arid climate and produce diagenetic low magnesium calcite meteoric cements a well known process common in tropical aragonitic pleistocene aeolianites the loss of metastable minerals with time is matched by a progressive and well understood change in stable isotopes such alteration in this environment however seems to take longer than in tropical carbonates with lithification herein not beginning until 200 ka and complete cementation being achieved in 450 ky thus neither aeolianites nor offshore marine carbonates record the composition of the original sediment aeolianites lack the important bryozoan constituents whereas neritic deposits lack the prolific mollusks this partitioning revealed for the first time answers the conundrum as to why some cool water neritic shelf and coastal sediments in the rock record are compositionally different

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

equilibrium slopes and cross shore velocity asymmetries in a storm dominated barred nearshore system abstract the near bed 0 10 m elevation horizontal velocities were measured across a two barred lacustrine shoreface during a storm and reveal a spatially coherent but temporally variable pattern in the low order moments of the velocity field large cross shore velocity asymmetries indicated 1 1 spatially extensive and temporally persistent offshore mean flows up to 0 18 m s 1 across the landward slope of the linear outer bar reflecting an undertow driven by a wave induced setup 2 2 an onshore directed skewness opposing the mean flow of wind wave origin and persistent under propagating bores in the inner bar system long after this asymmetry had disappeared from the outer bar extensive sediment reactivation with near zero net sediment flux over the whole of the upper shoreface indicated a sediment prism in a steady state volumetrically over the storm cycle uniform depths of sediment reactivation with zero bed elevation change over the storm cycle revealed local slopes in a steady state in the outer linear bar however time integration of the near bed velocity field at this location indicated an offshore net flux of water while sedimentary structures indicated bedform migration and thus at least bedload almost uniformly onshore when ripples and megaripples were present the sediment transport giving rise to the local equilibrium cannot be explained therefore on the basis of the mean properties of the near bed velocity vector but requires knowledge of the time varying instantaneous sediment transport vector onshore migration of the inner bar correlated well with the large and persistent onshore skewness of the velocity distribution in the inner surf zone associated with translatory surf bores throughout the storm decay period low frequency oscillations were only significant close to the shoreline but may have influenced the development of a sinuous three dimensional inner bar form as it migrated onshore

cross shore suspended sediment transport in the surf zone a field based parameterization existing cross shore sediment transport models for two dimensional surf zone bathymetries almost invariably predict offshore directed sand transports and bar migrations during storm conditions however onshore directed suspended sediment fluxes and associated nearshore bar migration were observed during recent field experiments on a gently sloping beach on the danish north sea coast field measurements of suspended sediment flux obtained during three experiments on two different beaches are used to parameterize the observed fluxes this parameterization predicts suspended sediment transport due to incident waves and undertow across bars in two dimensional surf zones first a non dimensional sediment flux index is formulated which describes the tendency towards net onshore or offshore transport and the strength of that tendency the non dimensional formulation circumvents the problem of measurement inconsistencies due to varying elevations of sediment concentration sensors relative to the bed the index is found to depend upon the undertow velocity the incident wave skewness and the cross correlation between orbital velocity and sediment concentration however some of these parameters are difficult to predict particularly in barred surf zones and therefore the independent variables are recast in terms of a set of more easily obtainable parameters the sediment flux index depends on a combination of the following non dimensional bed shear stress the shields parameter relative water depth wave orbital velocity relative wave height and bed slope finally a formulation of suspended sediment transport across bars is obtained by linking the flux index with a parameterization of the sediment concentration distribution in the water column these concentrations are found to depend on non dimensional bed shear stress relative wave height and water depth the formulation predicts a tendency for onshore directed sediment transport due to incident waves on gently sloping beaches and or with large bed shear stresses on steeply sloping beaches and or in the inner part of the surf zone there is a tendency towards offshore sediment transports due to the undertow

al mg systematics of hibonite bearing ca al rich inclusions from ningqiang hibonite bearing ca al rich inclusions cais usually occur in cm and ch chondrites and possess petrographic and isotopic characteristics distinctive from other typical cais despite their highly refractory nature most hibonite bearing cais have little or no 26mg excess the decay product of 26al but do show wide variations of ca and ti isotopic anomalies a few spinel hibonite spherules preserve evidence of live 26al with an inferred 26al 27al close to the canonical value the bimodal distribution of 26al abundances in hibonite bearing cais has inspired several interpretations regarding the origin of short lived nuclides and the evolution of the solar nebula herein we show that hibonite bearing cais from ningqiang an ungrouped carbonaceous chondrite also provide evidence for a bimodal distribution of 26al two hibonite aggregates and two hibonite pyroxene spherules show no 26mg excesses corresponding to inferred 26al 27al 8 x 10 6 two hibonite melilite spherules are indistinguishable from each other in terms of chemistry and mineralogy but have different mg isotopic compositions hibonite and melilite in one of them display positive 26mg excesses up to 25 parts per thousand that are correlated with al mg with an inferred 26al 27al of 5 5 0 6 x 10 5 the other one contains normal mg isotopes with an inferred 26al 27al 3 4 x 10 6 hibonite in a hibonite spinel fragment displays large 26mg excesses up to 38 parts per thousand that correlate with al mg with an inferred 26al 27al of 4 5 0 8 x 10 5 prolonged formation duration and thermal alteration of hibonite bearing cais seem to be inconsistent with petrological and isotopic observations of ningqiang our results support the theory of formation of 26al free poor hibonite bearing cais prior to the injection of 26al into the solar nebula from a nearby stellar source

surf zone eddies coupled with rip current morphology 1 energetic very low frequency vlf frequencies 0 004 hz surf zone eddies szes were observed on a beach composed of shore connected shoals with quasi periodic 125 m incised rip channels at sand city monterey bay california incident waves consisted of predominantly shore normal narrow banded swell waves szes were located outside the gravity region in alongshore wave number ky spaced within the vlf band and did not appear to exist in higher frequency bands the szes were significant urms vlf 0 25 m s and constant in intensity within the surf zone shore connected shoals and rip channels and rapidly decreased offshore the alongshore and cross shore sze velocity variances were similar in magnitude vlf sze velocities were not forced by vlf surface elevations and were not well correlated with rip current flows r2 0 18 there is an indication that the szes were related to wave forcing with the szes statistically correlated with incoming sea swell wave height r2 0 49 f ky spectral estimates illustrate a strong relationship between rip channel spacing and sze cross shore velocities ky 0 008 m 1 and minimal sze alongshore velocity variation ky 0 m 1 data analysis suggests that the szes are not simply instabilities of an unstable rip current jet a simple conceptual model suggests that sze f ky spectra can be explained by the entire rip current circulation cells oscillating predominantly in the cross shore and slightly in the alongshore

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

aqueous alteration of opaque assemblages in the ningqiang carbonaceous chondrite evidence from oxygen isotopes chondrules and matrix of the ningqiang carbonaceous chondrite contain numerous opaque assemblages oas these oas are mainly composed of ni rich metal magnetite sulfides phosphates with minor amounts of silicates and trace amounts of pt metal grains their mineral assemblage is very similar to that of oas found in allende refractory inclusions in this study we performed in situ analyses of o isotopic compositions of magnetite and whitlockite in oas and of olivine adjacent to oas from ningqiang o isotopic compositions of magnetite vary by 16 parts per thousand in 618 0 and fall on a regression line with a slope of 0 51 and a mean delta 17o of 2 9 0 3 1 sigma parts per thousand in the three o isotope diagram magnetite grains have consistently higher delta o 17 values than their adjacent olivine grains the mineral chemistry and o isotopic compositions of oas in ningqiang chondrules and matrix are most consistent with the formation of magnetites and whitlockite by aqueous alteration of preexisting metal alloys within a planetary body formation of magnetites and phosphates in oas thus do not constrain processes in the early solar nebula but rather provide information on metamorphism in a planetary environment c 2006 elsevier b v all rights reserved

swash zone sediment transport modes abstract the result of field experiments designed to investigate the relative proportions of bedload and suspended load are described the ratio of bedload to suspended sediment load in the swash zone is examined in both swash and backwash on four beaches by measuring the amounts collected in a sediment trap bedload transport is found to dominate the backwash the relative proportions of bedload and suspended load change over the tidal cycle with increasing bedload dominance at low tide the total amount of sediment transported as swash and backwash is noticeably greater at high tide than at low tide more sediment is transported on the flood tide than on the ebb

petrology mineralogy and oxygen isotope compositions of aluminum rich chondrules from cv3 chondrites bulk major element composition petrography mineralogy and oxygen isotope compositions of twenty al rich chondrules arcs from five cv3 chondrites northwest africa nwa 989 nwa 2086 nwa 2140 nwa 2697 nwa 3118 and the ningqiang carbonaceous chondrite were studied and compared with those of ferromagnesian chondrules and refractory inclusions most arcs are marginally al richer than ferromagnesian chondrules with bulk al2o3 of 10 15 wt arcs are texturally similar to ferromagnesian chondrules composed primarily of olivine pyroxene plagioclase spinel al rich glass and metallic phases minerals in arcs have intermediate compositions low ca pyroxene fs0 6 8 8wo0 7 9 3 has much higher al2o3 and tio2 contents up to 12 5 and 2 3 wt respectively than that in ferromagnesian chondrules high ca pyroxene fs0 3 2 0wo33 54 contains less al2o3 and tio2 than that in ca al rich inclusions cais plagioclase an77 99ab1 23 is much more sodic than that in cais spinel is enriched in moderately volatile element cr up to 6 7 wt compared to that in cais al rich enstatite coexists with anorthite and spinel in a glass free chondrule implying that the formation of al enstatite was not due to kinetic reasons but is likely due to the high al2o3 cao ratio 7 4 of the bulk chondrule three arcs contain relict cais oxygen isotope compositions of arcs are also intermediate between those of ferromagnesian chondrules and cais they vary from 39 4 to 13 9 in 18o and yield a best fit line slope 0 88 close to the carbonaceous chondrite anhydrous mineral ccam line chondrules with 5 10 wt bulk al2o3 have a slightly more narrow range in 18o 32 5 to 5 9 along the ccam line except for the arcs with relict phases however most arcs have oxygen isotope compositions 20 in 18o similar to those of typical ferromagnesian chondrules arcs are genetically related to both ferromagnesian chondrules and cais but the relationship between arcs and ferromagnesian chondrules is closer most arcs were formed during flash heating and rapid cooling processes like normal chondrules only from chemically evolved precursors arcs extremely enriched in al and those with relict phases could have had a hybrid origin krot et al 2002 which incorporated refractory inclusions as part of the precursors in addition to ferromagnesian materials the occurrence of melilite in arcs indicates that melilite rich cais might be present in the precursor materials of arcs the absence of melilite in most arcs is possibly due to high temperature interactions between a chondrule melt and the solar nebula

the relative formation ages of ferromagnesian chondrules inferred from their initial aluminum 26 aluminum 27 ratios we performed a systematic high precision sims 26al 26mg isotopic study for 11 ferromagnesian chondrules from the highly unequilibrated ordinary chondrite bishunpur ll3 1 the chondrules are porphyritic and contain various amounts of olivine and pyroxene and interstitial plagioclase and or glass the chemical compositions of the chondrules vary from feo poor to feo rich eight chondrules show resolvable 26mg excesses with a maximum 26mg of 1 in two chondrules the initial 26al 27al ratios inferred for these chondrules range between 2 28 0 73 x 10 5 to 0 45 0 21 x 10 5 assuming a homogeneous distribution of al isotopes in the early solar system this range corresponds to ages relative to cais between 0 7 0 2 my and 2 4 0 4 0 7 my the inferred total span of the chondrule formation ages is at least 1 my which is too long to form chondrules by the x wind the initial 26al 27al ratios of the chondrules are found to correlate with the proportion of olivine to pyroxene suggesting that olivine rich chondrules formed earlier than pyroxene rich chondrules though we do not have a completely satisfactory explanation of this correlation we tentatively interpret it as a result of evaporative loss of si from earlier generations of chondrules followed by addition of si to the precursors of later generation chondrules

mg diffusion in anorthite implications for the formation of early solar system planetesimals we have measured the self diffusion coefficients of mg ca and sr in anorthitic plagioclase in order to assess the potential of mg isotopic heterogeneities in early solar system planetesimals to survive thermal metamorphism diffusion couples were constructed from polished single crystals of natural anorthite and synthetic isotopically enriched anorthite glass couples were annealed at atmospheric pressure and 1200 1400 c and isotopic concentration profiles were measured with an ion microprobe the results show that mg diffusion in anorthite is surprisingly fast with d mg being over 2 orders of magnitude greater than d sr this indicates that the diffusion coefficient of mg in anorthite cannot be approximated with that for sr mg diffusion in the c direction is also slightly faster than in the b direction while ca and sr diffusion appear to be isotropic the results provide important constraints on the thermochronological history of anorthite bearing mineral assemblages that preserve radiogenic 26 mg excesses in a planetesimal heated by the decay of 26 al the temperature at any point depends on the planetesimal size time of formation thermal conductivity and depth within the planetesimal given sufficient heating 26 mg heterogeneities produced by the in situ decay of 26 al in ca al rich inclusions cais and chondrules will be erased by diffusive equilibration using the self diffusion coefficient for mg in anorthite measured in this study we show that the common occurrence of 26 mg excesses in these inclusions requires that they must be stored in small 15 km bodies or the outermost rims of larger bodies for the first 1 2 million years of the solar system s history for early formed bodies larger than 15 km most of the mass will have been heated sufficiently for any radiogenic 26 mg to have been diffusively homogenized in the mg rich planetary environment

petrography and classification of ca al rich and olivine rich inclusions in the allende cv3 chondrite a detailed systematic petrographic survey of all 189 ca al rich and olivine rich inclusions larger than 0 2 mm in diameter in 17 thin sections of allende was performed by optical and scanning electron microscopy most of these inclusions are aggregates containing varying proportions of three distinct constituents termed concentric objects chaotic material and inclusion matrix a new classification system for allende inclusions is proposed olivine rich inclusions occur in two textural varieties unrimmed olivine aggregates type 1a inclusions and rimmed olivine aggregates type 1b inclusions we classify ca al rich inclusions cai s on the basis of the size and abundance of their constituent concentric objects rather than their grain size into unrimmed complex cai s type 2 inclusions rimmed complex cai s type 3 inclusions and simple cai s type 4 inclusions several of the inclusion classes grade into each other some fundamental relationships among various types of allende inclusions are discussed we suggest that the term coarse grained even if used only in a relative sense is too restrictive for some members of one class of inclusion simple cai s and is inappropriate for most members of another class melilite rich complex cai s

isotopic composition of a large photosymbiotic foraminifer evidence for hypersaline environments across the great australian bight during the late pleistocene abstract analysis of carbon and oxygen isotopic compositions of large benthic foraminifera tests marginopora vertebralis that lived in the great australian bight during the late pleistocene reveal that the tests are enriched by 1 to 3 in both 18o and 13c relative to modern specimens from the same region the intolerance of m vertebralis for cool waters negates lower ocean water temperature as an explanation for such high 18o values the oxygen isotopic compositions are thus interpreted to reflect tests secreted in hypersaline waters of up to 56 ppt salinity concentrated from seawater by evaporation m vertebralis thrives today in waters of similar salinity at shark bay western australia the pleistocene sedimentary assemblage supports an interpretation that environments broadly similar to those in outer modern day shark bay were wide spread across the great australian bight during portions of marine isotope stages 2 3 and 4 the high 13c values of the pleistocene m vertebralis are interpreted to reflect enhanced photosynthetic activity that depletes dissolved carbonate in 12c in such shallow saline settings these hypersaline environments formed during periods of lower sea level when shallow waters

rip currents as a geological tool this paper considers the nature and sedimentary significance of rip currents rip currents are the main factor responsible for the transport of coarse sediments from the littoral zone to greater depths such sediments deposited outside the zone of wave deformation may be identified as storm rip current increments within sediments deposited during fair weather composite beds deposited during a given wave cycle by storm rip currents are closely similar to turbidites and many so called fluxo turbidites described from flysch deposits using data gathered in studies conducted on the modern baltic coast supplemented by experimental work and theoretical considerations a sedimentary model is proposed the model may be used to interpret possible rip current deposits among shallow water turbidites and both modern storm sediments and ancient tempestites language en