u pb evidence for polymetamorphic history of huronian rocks within the grenville front tectonic zone east of sudbury ontario canada abstract this paper presents u pb geochronological data for zircon titanite monazite apatite allanite and rutile from street township east of sudbury that help unravel two main facets of the geology of the grenville front tectonic zone gftz they document the presence of extensive huronian supergroup magmatic ca 2480 2460 ma and sedimentary rocks inside the gftz and highlight the significance of bimodal magmatism in the genesis of the huronian supergroup the data also provide further insights into the complex orogenic evolution of the gftz showing in particular that amphibolite facies metamorphism migmatization and deformation during grenvillian compression at 995 980 ma overprinted but did not totally erase the memory of earlier metamorphic events at ca 1720 and 1470 ma from the point of view of u pb systematics the results emphasize the nearly ubiquitous state of isotopic disequilibrium in these rocks most of the minerals investigated comprise two or more generations and are generally in a state of partial resetting because of the superimposed effects of younger events the preservation of pre grenvillian ages in titanite and allanite demonstrates that processes related to final grenvillian collision and exhumation occurred at great speed only apatite and to some degree rutile yield ages that are clearly post tectonic thereby reflecting the final stages of exhumation and cooling of the region

reconstructing recent landslide activity in relation to rainfall in the llobregat river basin eastern pyrenees spain abstract a chronology of recent landslides in the upper basin of the llobregat river eastern pyrenees has been reconstructed from technical reports field reconnaissance and dendrogeomorphological analysis the precipitation conditions responsible for triggering and reactivating landslides have been deduced by analysis of rainfall records from two rain gauges located in the area two different rainfall patterns relate to landslide occurrence i without antecedent rainfall high intensity and short duration rains trigger mostly debris flows and shallow slides developed in colluvium and weathered rocks a rainfall threshold of around 190 mm in 24 h initiates failures whereas more than 300 mm in 24 48 h are needed to cause widespread shallow landsliding ii with antecedent rain moderate intensity precipitation of at least 40 mm in 24 h reactivates mudslides and both rotational and translational slides affecting clayey and silty clayey formations in this case several weeks and 200 mm of precipitation are needed to cause landslide reactivation dendrochronological analysis shows that landslide activity in the eastern pyrenees was relatively low between 1926 and 1959 but has since increased significantly with reactivation now occurring about every 3 years

sand ridges off sarasota florida a complex facies boundary on a low energy inner shelf environment abstract the innermost shelf off sarasota florida was mapped using sidescan sonar imagery seismic reflection profiles surface sediment samples and short cores to define the transition between an onshore siliciclastic sand province and an offshore carbonate province and to identify the processes controlling the distribution of these distinctive facies the transition between these facies is abrupt and closely tied to the morphology of the inner shelf a series of low relief nearly shore normal ridges characterize the inner shelf stratigraphically the ridges are separated from the underlying pleistocene and tertiary carbonate strata by the holocene ravinement surface while surficial sediment is fine to very fine siliciclastic sand on the southeastern sides of the ridges and shell hash covers their northwestern sides the cores of these holocene deposits are a mixture of both of these facies along the southeastern edges of the ridges the facies boundary coincides with the discontinuity that separates the ridge deposits from the underlying strata the transition from siliciclastic to carbonate sediment on the northwestern sides of the ridges is equally abrupt but it falls along the crests of the ridges rather than at their edges here the facies transition lies within the holocene deposit and appears to be the result of sediment reworking by modern processes this facies distribution primarily appears to result from south flowing currents generated during winter storms that winnow the fine siliciclastic sediment from the troughs and steeper northwestern sides of the ridges a coarse shell lag is left armoring the steeper northwestern sides of the ridges and the fine sediment is deposited on the gentler southeastern sides of the ridges this pronounced partitioning of the surficial sediment appears to be the result of the siliciclastic sand being winnowed and transported by these currents while the carbonate shell hash falls below the threshold of sediment movement and is left as a lag the resulting facies boundaries on this low energy sediment starved inner continental shelf are of two origins which both are tied to the remarkably subtle ridge morphology along the southeastern sides of the ridges the facies boundary coincides with a stratigraphic discontinuity that separates holocene from the older deposits while the transition along the northwestern sides of the ridges is within the holocene deposit and is the result of sediment redistribution by modern processes

devonian extension in northwestern newfoundland 40ar 39ar and u pb data from the ming s bight area baie verte peninsula abstract the ming s bight group of northwestern newfoundland an outlier of humber zone continental margin rocks is entirely surrounded by ophiolitic rocks of the dunnage zone structures in the ming s bight group and adjacent units record three main phases of deformation the earliest structures relate to silurian sinistral transpression previously documented in the region two later phases of extensional deformation produced a series of dextral oblique normal shear zones and faults that now separate the ming s bight group in the footwall from ophiolitic and granitoid rocks in the hangingwall 40ar 39ar and u pb data constrain the times of oblique normal shear and cooling metagabbro in the point rousse ophiolite complex which lies in the hangingwall preserves disturbed ordovician hornblende 40ar 39ar ages whereas adjacent shear zones record devonian ages hornblendes in pacquet harbour group amphibolites within extensional shear zones mainly record 40ar 39ar ages of 390 380 ma synkinematic titanite

volcaniclastic debris avalanche on motomachi area of izu oshima japan triggered by severe storm phenomenon and mechanisms abstract heavy rainfall and strong wind associated with typhoon wipha hit izu oshima island japan and triggered catastrophic landslides on the western slope of oshima volcano on 16 october 2013 these landslides were shallow but large in scale and the displaced landslide materials were characterized by rapid and long runout movement a massive landslide resulted in 36 people dead and 3 missing with 46 buildings being completely destroyed in the downstream area of motomachi district to understand the initiation and movement of these shallow landslides we surveyed the landslide area and found that in addition to heavy rainfall strong wind may also have played a key role in increasing the instability of the slopes we took samples from the source areas and examined their static and dynamic shear behaviors under naturally drained or undrained conditions test results showed that high pore water pressure can be built up and maintained within the displaced landslide material and increase landslide mobility even though the thickness of displaced landslide materials is 0 7 1 2 m this may then give a rational explanation on the fluidization process of the displaced landslide materials we also examined the windthrow features of trees subjected to different wind speed through monitoring the ground motion by seismometer and portable anemometer and then performed cyclic shear tests on the materials laying above the sliding surface the test results suggest that the windthrow may have promoted the buildup of excess pore water pressure within the saturated soil layer and thus favoured the occurrence of slope failure therefore it is suggested that in the prediction of shallow landslides on forested slopes subjected to heavy storm both the effects of rainfall and strong wind should be taken into account

magmatism and metamorphism in a grenvillian fragment u pb and 40ar 39ar ages from the blair river complex northern cape breton island nova scotia canada the blair river complex in northern cape breton island nova scotia is interpreted to be an exposure of grenvillian basement which formed the southeastern tip of a promontory on the proto atlantic continental margin of north america u pb zircon data reported here confirm grenvillian ages for the major components in the blair river complex the locally granulite facies sailor brook gneiss has a minimum protolith age of 1217 ma and was metamorphosed at 1035 12 10 ma the lowland brook syenite has an igneous crystallization age of 1080 5 3 ma and the otter brook granitic orthogneiss yielded an igneous crystallization age of 978 6 5 ma an igneous crystallization age could not be obtained for anorthositic rocks in the blair river complex but the red river anorthosite suite was metamorphosed at 996 6 5 ma silurian thermal activity is recorded in the blair river complex by granitic magmatism dated at 435 7 3 ma and a widespread amphibolite facies metamorphic overprint of similar age these events are corroborated by 206pb 238u ages of ca 423 ma for titanite from seven widely distributed samples from both silurian and proterozoic units interpreted to represent cooling from igneous or peak metamorphic conditions through temperatures of ca 550 600 c rutile in one sample gave a u pb age of 410 2 ma which may represent postmetamorphic cooling through 405 c the u pb cooling ages are supported by similar 40ar 39ar ages of ca 420 ma for phlogopite and muscovite from rare calc silicate lenses in the blair river complex and for hornblende from a silurian diorite intrusion the widespread silurian metamorphism of this inlier is similar in age to that in western newfoundland and indicates involvement of the blair river complex in silurian orogenesis our data support the interpretation that the blair river complex represents laurentian grenvillian basement analogous to basement exposures in the humber zone of western newfoundland

determining accurate temperature time paths from u pb thermochronology an example from the kaapvaal craton southern africa thermochronology has revolutionized our understanding of the establishment and evolution of lithospheric thermal structure however many potential benefits provided by the application of diffusion theory to thermochronology have yet to be fully exploited this study uses apatite tc 450 550 c and titanite tc 550 650 c u pb id tims thermochronology at the single to sub grain scale to separate the variable effects of volume diffusion of pb from metamorphic over growth above and below the tc of a mineral data are presented from two ca 3227 ma tonalite samples from north and south of the barberton greenstone belt bgb southern africa two distinct populations of apatite from a sample north of the bgb record fast cooling followed by metamorphic growth 10 myr later both apatite and titanite dates from south of the bgb show a strong correlation with the grain size and record 100 myr of post emplacement cooling complex core rim zoning observed in cathodoluminescence images of apatite is interpreted to reflect metamorphic overgrowth above the tc the age and topology of grain size versus date curves from titanite and apatite are used in combination with a finite difference numerical model to show that slow non linear cooling and not thermal resetting is responsible for the observed distribution the thermal histories from either side of the bgb are very different and provide unique insight into the bgb s tectonic evolution a 70 myr period of apparent stability after ca 3 2 ga terrane assembly was followed by fast exhumation south of the bgb that led to lower crustal melting and intrusion of granitic batholiths ca 3 14 3 10 ga

shoreface dynamics evidence from bathymetry and surficial sediments abstract a conceptual model for the maintenance of equilibrium shoreface textures is tested on the shoreface of long island new york by using empirical eigenfunction analysis on sediment grain size data a bluff composed of morainal material in the headland section is a possible external sediment source for the study area within the shoreface system a remnant terminal moraine lobe complex sediments associated with old tidal inlet outer channels and drowned outwash plain deposits are permanent irreversible internal sediment sources the present shoreface sediments are derived primarily from the drowned outwash plain sediments as a result of in situ reworking by the present shoreface hydrodynamic regime other temporary reversible internal sediment sources are storm deposits and modern shoreface depositional features such as nearshore bars sand ridges and active ebb tidal deltas as sea level rises the shoreface will continue to migrate landward subsequently the recessional shoreface will leave behind a sheet of relict transgressive sand composed of mainly medium sands as the result of the winnowing of fine grained sediments by hydrodynamic processes of the traversing shoreface

a new mg in plagioclase geospeedometer for the determination of cooling rates of mafic rocks abstract we present a new mg in plagioclase geospeedometer based on the diffusive exchange of mg between plagioclase and clinopyroxene that allows cooling rates of a wide range of mafic rocks to be determined the major element composition of plagioclase is shown to play an important role in driving the flux of mg as well as the partitioning of mg between plagioclase and clinopyroxene therefore commonly used analytical solutions to the diffusion equation are not applicable in this system and an alternate approach is developed practical aspects of the method such as the role of anorthite zoning patterns and influence of shapes of cooling paths and grain geometries in controlling the mg concentration profile shapes are discussed propagation of uncertainties in the knowledge of diffusion and partition coefficients shows that the method is capable of resolving small differences in cooling rates e g log d t d t c yr 1 3 0 3 in one example the approach is illustrated by application to two samples from the lower oceanic crust

interpreting zirconium in rutile thermometric results at first sight experimental results and observations on rocks suggest that the zr content in rutile where equilibrated with quartz and zircon should be a useful thermometer for metamorphic rocks however diffusion data for zr in rutile imply that thermometry should not for plausible rates of cooling give the high temperatures commonly observed in high grade metamorphic rocks it is suggested here that such observations can be accounted for by high t diffusive closure of si in rutile causing the interior of rutile grains to become insensitive to the thermometer equilibrium well above the temperature of zr diffusive closure paired with comparatively slow grain boundary diffusion and problematic zircon nucleation this allows for cases of zr retention in rutile through temperatures where zr is still diffusively mobile within rutile grains other observations that may be accounted for in this context are large inter grain ranges of rutile zr contents uncorrelated with rutile grain size and flat zr profiles across individual rutile grains counter to what would be expected from diffusive closure a consequence is that it is unlikely that zr in rutile thermometry will be useful for estimating rock cooling rates

surficial sedimentology of the middelkerke bank southern north sea detailed surficial investigations over the middelkerke bank a tidal sand bank in the southern north sea revealed the relationship between morphology surficial structures and grain size parameters data from 85 grab samples all over the bank show that on a bank normal profile the coarser caco3 rich and badly sorted sediments are generally located near the highest point of the bank seaward at the northern end and landward at the southern end sedimentary structures were studied from 239 boxcores sampled on all the morphological units of the bank crest flanks and adjacent channels in the shallower parts foreset beds are preserved while in the deeper zones intense bioturbation arises and destroys any structure the combination between these data and the virtual absence of wave induced structures indicates that the main agents responsible for the bank shaping are the tidal currents

nonlinear modelling of shoreface connected ridges impact of grain sorting and interventions abstract the evolution of shoreface connected sand ridges on micro tidal inner shelves and the variations in the mean grain size over these ridges are investigated with process based models a review of previous studies is presented as well as new results that concern the influence of grain sorting on the finite amplitude behaviour of the ridges the application of the model to la barrosa beach and the role of wave topography feedbacks the ridges initially form due to morphodynamic self organisation in which the presence of waves and a storm driven current are crucial predicted growth time scales migration speeds topography and spatial pattern of the mean grain size agree with field data collected on micro tidal shelves in the case that both bedload and suspended load sediment transport are accounted for together with spatially non uniform wave orbital motion the model can not successfully explain the presence of large scale ridges observed on la barrosa inner shelf because strong and complex behaving tidal currents occur in that area nonlinear model simulations show that on the long term the height of the ridges evolves towards a finite constant value whilst their migration speed hardly changes during the evolution in the saturated stage the ridges have asymmetrical profiles with steep slopes on the downstream sides the maximum variation in mean grain size also tends to a constant value and during the evolution the spatial lag between the patterns in the mean grain size and topography decreases the processes that cause these changes are identified and explained model results can be obtained for transverse bottom slopes up to 50 of their observed values on micro tidal shelves extrapolation of results to realistic values of the inner shelf slope yields in case of long island shelf a final height that agrees with observed ridge heights but the modelled variation in mean grain size is small compared to field data finally the response of ridges to large scale interventions is considered experiments reveal that extraction of sand on the inner shelf causes a decrease of the sand volume stored in the surf zone

zr and hf diffusion in rutile abstract chemical diffusion of zr and hf under anhydrous conditions has been measured in synthetic and natural rutile the sources of diffusant used were hafnon or zircon powders or a hafnon rutile mixture experiments were run in crimped pt capsules in air or in sealed silica glass capsules with solid buffers to buffer at nno or qfm rutherford backscattering spectrometry rbs was used to measure zr and hf diffusion profiles from these measurements the following arrhenius relations were obtained for zr diffusion parallel to c over the temperature range 750 1100 c d zr c 9 8 10 15 exp 170 30 kj mol 1 rt m 2 s 1 for hf diffusion parallel to c over the temperature range 800 1000 c d hf c 9 1 10 15 exp 169 36 kj mol 1 rt m 2 s 1 for hf diffusion normal to c over the temperature range 750 1050 c d hf c 2 5 10 12 exp 227 62 kj mol 1 rt m 2 s 1 diffusivities for experiments buffered at qfm and nno are similar to those run in air diffusivities in synthetic and natural rutile are likewise similar indicating that these findings can be applied directly in determining zr diffusivities in rutile in natural systems these data indicate that rutile should be moderately retentive of zr chemical signatures with zr diffusivities within an order of magnitude of those for pb in rutile over most geologic conditions when applied in evaluation of the relative robustness of the recently developed zr in rutile geothermometer t zack r moraes a kronz temperature dependence of zr in rutile empirical calibration of a rutile thermometer contributions to mineralogy and petrology 148 2004 471 488 e b watson d a wark j b thomas crystallization thermometers for zircon and rutile contributions to mineralogy and petrology 151 2006 413 433 these findings suggest that zr concentrations in rutile will be somewhat more likely to be affected by later thermal disturbance than the geothermometer based on zr concentrations in titanite l hayden e b watson d a wark a thermobarometer for sphene abstract 16th v m goldschmidt conference 2006 and much less resistant to diffusional alteration subsequent to crystallization than the ti in zircon geothermometer e b watson d a wark j b thomas crystallization thermometers for zircon and rutile contributions to mineralogy and petrology 151 2006 413 433 e b watson t m harrison zircon thermometer reveals minimum melting conditions on earliest earth science 308 2005 841 844

origin evolution and distribution of shoreface sand ridges atlantic inner shelf u s a abstract a computer mapping system was employed to document the location of 259 shoreface attached and detached sand ridges in water although shoreface attached sand ridges appear to have several different modes of formation a two step process for the development of most shoreface attached and detached sand ridges along u s atlantic barrier island and cape coastlines is proposed 1 sand is deposited as ebb tidal deltas or river deltas along the lower shoreface and or inner continental shelf prior to or during transgression followed by 2 further transgression which reworks the deltaic sand bodies into linear sand ridges at the base of the shoreface by shelf processes the best developed shoreface sand ridge fields along the u s atlantic shelf lie adjacent to shorelines characterized by all of the following 1 transgression 2 mixed energy wave dominated barrier islands and 3 laterally migrating tidal inlet systems tidal inlet systems are natural sediment sinks that capture sand carried by longshore sediment transport ebb tidal delta deposits associated with these migrating tidal inlets provide the initial sand body for the development of shoreface attached sand ridges the oblique orientation and linear form of shoreface attached sand ridges appear to be a function of shoreline transgression lateral inlet migration and wave reworking of ebb tidal delta deposits concentrated along an ebb tidal delta retreat path shelf processes act as modifying agents in the evolution of sand ridges during and after ebb tidal delta deposition in general shoreface attached sand ridges are poorly developed or absent along eroding headlands spits and barrier island shorelines characterized by naturally stabilized tidal inlets these latter inlets and shoreline types are dominated or influenced by one or all of the following 1 antecedent topography 2 higher tidal ranges 3 larger tidal prisms 4 lower wave energies or 5 finer grain sizes the coupling of shoreline and shallow marine sedimentary processes during a transgression is critical to the origin evolution and distribution of shoreface sand ridges in the study area modern shoreface attached sand ridges are also known to occur in different coastal and shelf settings where large amounts of sediment were supplied to the shoreface and inner shelf during or immediately before transgression commonly observed vertical and lateral interrelationships of holocene shoreface attached sand ridges and tidal inlets or distributary channels have important ramifications for the development of shelf sandstone facies models in addition the geometric relationship documented in this study provides predictive petroleum and hard mineral exploration models of the spatial and temporal distribution of shoreface and shelf sand ridges

evolution of a classic sand ridge field maryland sector north american inner shelf the ridge and swale topography of the middle atlantic bight is best developed on the delaware maryland inner shelf here sand ridges can be seen in all stages of formation several aspects of the ridge field are pertinent to the problem of ridge genesis the first is ridge morphology there is a systematic morphologic change from shoreface ridges through nearshore ridges to offshore ridges which reflects the changing hydraulic regime as successively more seaward ridges are examined maximum side slope decreases the ratio of maximum seaward slope to maximum landward slope decreases and the cross sectional area increases these changes in ridge morphology with depth and distance from shore appear to be equivalent to the morphologic changes experienced by a single ridge during the course of the holocene transgression a second aspect is the change in bottom sediment characteristics that accompanies these large scale morphologic changes megaripples sand waves and mud lenses appear in the troughs between nearshore and offshore ridges these changes indicate that the storm flows which maintain ridges are less frequently experienced in the deeper sector and that the role of high frequency wave surge becomes less important relative to the role of the mean flow component in shaping the sea floor a third aspect is the systematic relationship of grain size to topography grain size is 90 out of phase with topography so that the coarsest sand lies between the axis of the landward trough and the ridge crest while the finest sand lies between the ridge crest and the axis of the seaward trough this relationship is characteristic of large scale bedforms finally flow was measured and transport calculated on the same ridge during a one month period november 1976 threshold was exceeded only during storm events mean transport was southerly and a little seaward with respect to both the ridge crest and the shoreline these flow measurements are in conformity with the pattern of smaller bedforms a 43 year time series of bathymetric change for this ridge reveals a systematic pattern of landward flank erosion seaward flank deposition and seaward crest migration sand ridges are considered the consequence of constructive feedback between an initial topography and the resulting distribution of bottom shear stress the relationship between grain size and topography supports this model but does not account directly for the oblique angle of the ridge with respect to the coastline this feature may be due to a more rapid alongshore migration rate of the inshore edge of the ridge than the offshore edge and the relationship between this migration rate and the rate of shoreface retreat

long term changes in morphology and textural sediment characteristics in response to energy variation on shoreface connected ridges off the east frisian barrier island coast southern north sea abstract patterns of surficial sediment distribution across shoreface connected sand ridges located along the barrier island coast of the southern north sea generally show a strong affinity between textural parameters and ridge morphology comparable to that observed in other parts of the world thus the sediment of the upper shoreface and the inner ridge crest consists of fine sand water depths 12 m in order to assess the mobility of the sediments and the consistency of the observed textural patterns two high resolution multi beam bathymetric surveys were carried out along selected corridors across a ridge and trough system off spiekeroog island located along the southern north sea coast of germany one in 2003 the other in 2007 the bathymetric data of the two surveys show only small scale topographic changes these were produced mainly by local changes in the bedform patterns on the inner ridge the bathymetric surveys therefore document a remarkable morphological stability of the ridges over time periods of several years spatial and temporal variations in the distribution of standard textural parameters were assessed on the basis of 95 sediment samples recovered on the same grid in 1989 and 2005 these data show that for example the distribution of coarse sand 0 1 phi became enhanced along the axis of the outer trough while expanding onto the lower ridge flanks current measurements in fair weather demonstrate that the coarse sediments cannot be moved by the local tidal currents the observed changes in the distribution of coarse sand and in particular its expansion onto the adjacent ridge flanks must therefore be associated with wave action probably in combination with tidal currents this is supported by an assessment of the entrainment potential of coarse sand d 1 mm by typical waves during storms t 8 s h 2 5 m and fair weather t 4 s h 0 7 m the results demonstrate that the effective wave base for coarse sand during fair weather conditions is limited to a water depth of 4 8 m whereas during storms it exceeds a depth of 26 4 m the mobility of the coarse sands in the outer trough at water depths 16 m and with it the morphodynamics of the ridges as a whole is thus clearly controlled by the superimposition of storm waves on the tidal current regime

an exhumation history of continents over billion year time scales the continental lithosphere contains the oldest and most stable structures on earth where fragments of ancient material have eluded destruction by tectonic and surface processes operating over billions of years although present day erosion of these remnants is slow a record of how they have uplifted eroded and cooled over earth s history can provide insight into the physical properties of the continents and the forces operating to exhume them over geologic time we constructed a continuous record of ancient lithosphere cooling with the use of uranium lead u pb thermochronology on volcanically exhumed lower crustal fragments combining these measurements with thermal and pb diffusion models constrains the range of possible erosion histories measured u pb data are consistent with extremely low erosion rates persisting over time scales approaching the age of the continents themselves

solving the production diffusion equation for finite diffusion domains of various shapes part i implications for low temperature u th he thermochronology abstract we propose an accurate fast and easy to use method to derive numerical solutions for production diffusion equations for finite diffusion domains of various shapes and arbitrary cooling histories previous studies provide solutions for spheres infinite cylinders and infinite sheets we extend this range and provide solutions for finite bodies i e finite cylinders and rectangular blocks of any aspect ratio this approach is important as recently it has become clear that for example the physical grain is the diffusion domain for he diffusion in apatite and titanite j geophys res 105 2000 2903 geochim cosmochim acta 63 1999 3845 we discuss the use of the new approach for forward modelling u th he production diffusion in apatite taking results with finite cylinders as a good approximation for apatite crystals it is found that approximating instead with spheres or infinite cylinders having the same radius yields differences in calculated ages that can easily be as large as 20 35 the relative differences are most pronounced in thermal histories that spend significant time at or near the closure temperature on the other hand reasonable agreement is found with spheres having the same surface to volume ratio

modes of cross shore sediment transport on the shoreface of the middle atlantic bight the mechanisms responsible for onshore and offshore sediment fluxes across the shoreface zone seaward of the surf zone were examined in a 3 year field study the study was conducted in the southern part of the middle atlantic bight in the depth region 7 17 m using instrumented tripods supporting electromagnetic current meters pressure sensors suspended sediment concentration sensors and sonar altimeters the observations embraced fairweather moderate energy swell dominated and storm conditions cross shore mean flows ranged from near zero during fairweather to 20 cm s 1 during the storm oscillatory flows were on the order of 10 cm s 1 during fairweather and 100 cm s 1 during the storm suspended sediment concentrations at about 10 cm above the bed were 5 kg m 3 during the storm three methods were applied to evaluate the relative importance of incident waves long period oscillations mean flows and gravity in effecting shoreward or seaward sediment flux 1 an energetics transport model was applied to instantaneous near bottom velocity data 2 higher moments of near bottom flows were estimated and compared and 3 suspended sediment fluxes were estimated directly from the instantaneous products of cross shore velocity and suspended sediment concentration the results show that measurable contributions were made by all four of the processes most significantly mean flows were seen to dominate and cause offshore fluxes during the storm and to contribute significantly to onshore and offshore flux during fairweather and moderate energy incident waves were in all cases the major source of bed shear stress but also caused shoreward as well as seaward net sediment advection low frequency effects involving wave groups and long period waves made secondary contributions to cross shore sediment flux contrary to expectations low frequency fluxes were just as often shoreward as seaward whereas cross correlations between suspended sediment concentration and the instantaneous near bottom current speed were high and in phase under storm conditions they were weak and out of phase during fairweather conditions this suggests that simple energetics models are probably inadequate for predicting fairweather transport of suspended sediment

modification of the quaternary stratigraphic framework of the inner continental shelf by holocene marine transgression an example offshore of fire island new york abstract the inner continental shelf off fire island new york was mapped in 2011 using interferometric sonar and high resolution chirp seismic reflection systems the area mapped is approximately 50 km long by 8 km wide extending from moriches inlet to fire island inlet in water depths ranging from 8 to 32 m the morphology of this inner continental shelf region and modern sediment distribution patterns are determined by erosion of pleistocene glaciofluvial sediments during the ongoing holocene marine transgression much of the shelf is thus an actively forming ravinement surface remnants of a pleistocene outwash lobe define a submerged headland offshore of central fire island east of the submerged headland relatively older pleistocene outwash is exposed over much of the inner continental shelf and covered by asymmetric sorted bedforms interpreted to indicate erosion and westward transport of reworked sediment erosion of the eastern flank of the submerged pleistocene headland over the last 8000 years yielded an abundance of modern sand that was transported westward and reworked into a field of shoreface attached ridges offshore of western fire island west of the submerged headland erosion of pleistocene outwash continues in troughs between the sand ridges resulting in modification of the lower shoreface comparison of the modern sand ridge morphology with the morphology of the underlying ravinement surface suggests that the sand ridges have moved a minimum of 1000 m westward since formation comparison of modern sediment thickness mapped in 1996 1997 and 2011 allows speculation that the nearshore shoreface sedimentary deposit has gained sediment at the expense of deflation of the sand ridges

multistage exhumation and juxtaposition of lower continental crust in the western canadian shield linking high resolution u pb and 40ar 39ar thermochronometry with pressure temperature deformation paths 1 new u pb titanite apatite rutile and 40ar 39ar hornblende muscovite biotite data are linked with existing pressure temperature deformation paths to impose detailed temporal constraints on the juxtaposition and unroofing of domains in an extensive 20 000 km2 region of exhumed lower crust in the east lake athabasca region of the western canadian shield in the 200 m y between circa 1 9 ga high pressure granulite facies metamorphism and circa 1 7 ga unconformable deposition of athabasca basin sediments on the exhumed rocks our analysis reveals at least three distinct phases of unroofing at different rates specifically we distinguish 1 an early phase of extensional unroofing in the chipman domain at rates of 1 5 2 0 km m y from 1 0 gpa to 0 8 gpa associated with mafic magmatism and metamorphism 2 an episode of regional contractional uplift and associated unroofing along the legs lake shear zone at circa 1850 ma from 0 7 0 8 gpa to 0 4 0 5 gpa and 3 a final period of extensional unroofing at rates of 0 2 0 3 km m y from 0 4 to 0 5 gpa that culminated in transport of current exposures to near surface conditions the cooling patterns and retrograde assemblages are consistent with pauses between exhumational phases the apparent convergence of disparate higher temperature histories in several deep crustal domains at circa 1 89 1 88 ga implies their juxtaposition at 0 7 0 8 gpa conditions regional east directed thrusting of the deep crustal domains as a coherent unit at 1 85 ga juxtaposed the granulites with middle crustal hearne domain rocks at 0 4 0 5 gpa conditions the detailed exhumational history allows correlation with changing regional tectonic regimes associated with the amalgamation of laurentia the temporal and spatial heterogeneity of exhumation patterns in the east lake athabasca region may be a common feature of the unroofing histories of lower crustal rocks

hydrodynamics and sedimentation in wave dominated coastal environmentsshoreface morphodynamics on wave dominated coasts an open ocean shoreface typical of long wave dominated sandy coasts has been examined through a combination of extensive field measurements of wave and current patterns with computations of marine bedload transport and sedimentation sand transport on the upper shoreface is dominantly controlled by waves with only secondary transport by currents sand on the middle and lower shoreface as well as the inner continental shelf is entrained by storm waves and transported by a complex pattern of bottom boundary layer currents storm events have been studied and modeled for the shoreface off tiana beach long island the dominant effect of coastal frontal storms is to cause significant shore parallel bedload transport with important shore normal secondary components these storms tend to result in net offshore transport of sand removed from the beach and surf zone systems the bedload transport during a storm is convergent on the shoreface leading to accretion most accretion occurs on the upper shoreface with lesser deposits covering the middle and lower shoreface as well as the inner continental shelf longer term equilibrium can be maintained by slow return of sand up the shoreface during non storm conditions annual and geologic time scale budgets of shoreface sand transport and sedimentation yield equilibrium net accretion or net deposition the annual balance results from an integration of the event scale bedload transport patterns and morphologic responses these processes and responses have feedback mechanisms which stabilize the system over longer but not geologic time scales geologic time scale balances are controlled by relative sea level changes and relative availability of sediment supply with the event scale shoreface and transporting processes providing the mechanism to produce the changes in long term morphology and sedimentation patterns in the area of study the long term pattern is one of net shoreface erosion and the permanent loss of sand to the shelf floor

zirconium in rutile speedometry new constraints on lower crustal cooling rates and residence temperatures abstract the incorporation of zirconium into the mineral rutile tio2 has been both empirically and experimentally calibrated as a measure of rutile crystallization temperatures watson et al 2006 this temperature sensitive system has been employed as a geothermometer with applications to a number of different geologic settings and rock types experimentally measured kinetics for zr diffusion in rutile cherniak et al 2007 indicate that zr can be lost to temperature dependent diffusion warranting further investigation of the geologic significance of calculated temperatures coupling diffusion kinetics with numerical solutions to the diffusion equation provides a means to forward model the time and temperature dependency of the system modeled results indicate a strong dependency of zr concentration in rutile on both 1 initial cooling rate following high temperature metamorphism crystallization and 2 temperature and duration of long term geologic residence zr concentrations measured in rutile from lower crustal xenoliths that resided at 25 45 km depths for 2000 my reveal zr concentrations in the approximate grain center that are consistent with temperatures measured by independent thermometers forward models for zr diffusion show that preserving a zr record of these initial temperatures in the center of a rutile crystal with a 50 m radius requires rapid cooling 300 c ma from magmatic metamorphic temperatures followed by a long term residence 2000 my at temperatures

shoreface morphodynamics on wave dominated coasts abstract an open ocean shoreface typical of long wave dominated sandy coasts has been examined through a combination of extensive field measurements of wave and current patterns with computations of marine bedload transport and sedimentation sand transport on the upper shoreface is dominantly controlled by waves with only secondary transport by currents sand on the middle and lower shoreface as well as the inner continental shelf is entrained by storm waves and transported by a complex pattern of bottom boundary layer currents storm events have been studied and modeled for the shoreface off tiana beach long island the dominant effect of coastal frontal storms is to cause significant shore parallel bedload transport with important shore normal secondary components these storms tend to result in net offshore transport of sand removed from the beach and surf zone systems the bedload transport during a storm is convergent on the shoreface leading to accretion most accretion occurs on the upper shoreface with lesser deposits covering the middle and lower shoreface as well as the inner continental shelf longer term equilibrium can be maintained by slow return of sand up the shoreface during non storm conditions annual and geologic time scale budgets of shoreface sand transport and sedimentation yield equilibrium net accretion or net deposition the annual balance results from an integration of the event scale bedload transport patterns and morphologic responses these processes and responses have feedback mechanisms which stabilize the system over longer but not geologic time scales geologic time scale balances are controlled by relative sea level changes and relative availability of sediment supply with the event scale shoreface and transporting processes providing the mechanism to produce the changes in long term morphology and sedimentation patterns in the area of study the long term pattern is one of net shoreface erosion and the permanent loss of sand to the shelf floor

a view on some hydrological triggering systems in landslides abstract in this paper different types of hydrological triggering systems for debris flows shallow and deeper landslides are described the generation of surface run off and high peak discharges in first order alpine catchments is an important triggering mechanism for debris flows failure conditions in shallow landslides can occur when at a critical depth which is determined by the cohesion of the soil and the slope angle the moisture content in the soil becomes close to saturation resulting in a considerable reduction of soil strength deeper landslides 5 20 m depth are in most cases triggered by positive pore pressures on the slip plane induced by a rising ground water level the assessment of meteorological threshold conditions for shallow landslides 1 2 m needs more detailed meteorological information than for deeper landslides in the analyses of the hydrological triggering systems of deeper landslides the presence of a permeable top layer and fissures has to be taken into consideration

paleoproterozoic amphibolite facies retrogression and exhumation of archean metapelitic granulites in the southern marginal zone of the limpopo belt south africa abstract granulite facies terrains that have undergone extensive retrogression provide insights into the recycling of volatiles in the crust during orogenesis the timing of retrogression is key to understanding the geodynamic circumstances of such events this study has investigated amphibolite facies retrogression of melt depleted granulite facies metapelites from the south marginal zone smz of the limpopo belt the granulites formed via incongruent partial melting reactions that consumed biotite and produced garnet and rutile as prominent peritectic products at 2 7 ga under conditions of 11 kbar and 875 c peak metamorphic garnet is replaced by cordierite orthopyroxene symplectites with cordierite subsequently partially replaced by fine grained intergrowths of amphibolite facies assemblages including rutile zr in rutile thermometry yielded a temperature range of 731 846 c for the granulite facies rutiles and 629 690 c for rutile in the retrograde assemblage all rutile generations yielded a youngest u pb age of 2 1 ga some granulite facies rutiles record older dates 2 55 2 25 ga which are non systematic with regard to crystal size and represent non reset relicts of metamorphic recrystallization during a potentially complex history of amphibolite facies metamorphism between 2 7 and 2 2 ga the youngest 2 1 ga rutile u pb age represents the time of final exhumation related cooling of the rocks following a discrete paleoproterozoic amphibolite facies retrograde event coexisting orthoamphiboles in the peak metamorphic assemblage indicate a maximum peak temperature of 625 c the lack of age size correlation and intragrain age zoning in rutile suggest fast cooling following the amphibolite facies retrograde event which is inferred to be not much older u pb dating of zircon from the same rocks confirms that the metapelites underwent granulite facies metamorphism at 2695 35 ma thus the metapelites of the smz record both an archean granulite facies event and a polymetamorphic paleoproterozoic amphibolite facies history that culminated in a mid amphibolite facies peak inducing partial retrogression of the granulites the paleoproterozoic amphibolite facies event is tentatively correlated with mantle melting documented between 2 3 and 2 1 ga to produce mafic and intermediate volcanic rocks in the pretoria group on the kaapvaal craton

sediment transport under wave and current combined flows on a tide dominated shoreface northern coast of france abstract hydrodynamic circulation and sediment transport patterns were investigated on a macrotidal shoreface off the southern north sea coast of france from in situ directional wave and current measurements and through numerical modeling of sediment flux current meters equipped with wave gauges were deployed at two sites on the mid upper shoreface in approximately 5 6 m water depth during 6 and 15 days sediment flux was estimated using the sedtrans96 numerical model li m z amos c l 2001 sedtrans96 the upgraded and better calibrated sediment transport model for continental shelves comp geosc 27 619 645 based on grant and madsen s grant w d madsen o s 1986 the continental shelf bottom boundary layer ann rev fluid mech 18 265 305 combined flow boundary layer theory the hydrodynamic measurements and modeling results show that sediment on the shoreface is essentially transported alongshore in response to shore parallel tidal currents the direction of the net sediment transport is largely determined by the asymmetry of the tidal flows which can be flood or ebb dominated but during important wind speed events winds blowing in the same direction as tidal flow can significantly reinforce tidal currents or conversely can limit tidal current speeds when acting in the opposite direction although sediment transport on this macrotidal shoreface is strongly controlled by tidal processes waves can significantly enhance bed shear stresses resulting in increased sediment remobilization and hence higher sediment flux wave induced onshore sediment transport may occasionally occur but is several orders of magnitude lower than longshore transport this macrotidal shoreface is thus characterized by a hydraulic regime strongly dominated by shore parallel tidal flows that favour longshore sediment dispersal rather than shore normal transport our results imply that the water depths from which sediment may be transported shoreward to beaches is certainly much more restricted on a macrotidal shoreface such as the one bordering the northern coast of france than on micro and mesotidal shoreface environments where weaker tidal currents do not significantly limit cross shore sediment movements

mechanisms for linear sandbank formation and maintenance in relation to dynamical oceanographic observations abstract theories associated with flow in the vicinity of headlands and sandbanks together with proposed mechanisms for sandbank formation and maintenance are reviewed to exemplify water and sand movement around a sandbank on a tidally dominated shelf tidal currents in the vicinity of a headland associated linear sandbank are described these data are integrated with sedimentological information on bedforms and grain size distributions the sandbank under detailed investigation the scarweather sands is located along the northern coastline of the bristol channel uk which is an area susceptible to high energy inputs the maximum spring tidal range here is around 10m and a 6000km fetch is available for storm wave approach from the atlantic ocean but the area is 460km from the shelf break detailed observations are presented from 11 long term current meter stations located within 10km of the sandbank currents are described in terms of residual water circulation shallow water harmonics and tidal ellipse characteristics bedload transport paths are inferred from the distribution of bedforms grain size and m2 m4 tidal current interactions transport vectors are predicted from near bed current meter observations combined with empirically derived formulae it is demonstrated that water circulation and sand transport paths form part of a clockwise eddy system around the sandbank mechanisms controlling the location and the characteristics of this particular sandbank are shown to be explicable in terms of a combination of models for sandbank formation and maintenance the results of the present study are thought to be applicable directly to headland associated sandbanks elsewhere it is shown on the basis of theoretical considerations that the pattern of residual water movement and possibly sand transport around this sandbank could be extended to continental shelves on a global basis

relationship between rain and or meltwater pore water pressure and displacement of a reactivated landslide abstract in order to clarify the relationship between rain and or meltwater mr pore water pressure and landslide displacement continuous monitorings were conducted at a reactivated landslide comprised mainly of weathered mudstone of tertiary in age an exponential relationship was found between the total amount of mr at each event and the amount of pore water pressure increment integrated by time impulse of pore water pressure in addition as the total mr increased the difference between the minimum and maximum values of pore water pressure for each event fluctuation range of pore water pressure also increased but the intensity of mr had little effect on the fluctuation range of pore water pressure the correlation coefficient for the fluctuation range of pore water pressure and cumulative landslide displacement and that for the impulse of pore water pressure and cumulative displacement were similar but were only 0 57 to 0 66 on the other hand the correlation coefficient for the total mr and cumulative landslide displacement was large 0 65 0 69 cumulative landslide displacement was very highly correlated with effective mr which shows the estimated water content in the ground for a half life period of 4 days and correlation coefficients were 0 89 0 92 thus the displacement characteristics of this reactivated landslide which has a long history of landsliding can be explained using the hydrological factor of water content rather than the hydraulic characteristics of pore water pressure

trace element systematics in granulite facies rutile implications for zr geothermometry and provenance studies metamorphic rutile from granulite facies metapelitic rocks of the archean pikwitonei granulite domain pgd manitoba canada provides constraints on the systematics of trace elements in rutile during high temperature conditions and subsequent slow cooling compositional profiles and maps of the zr concentrations in rutile grains 120 600 m from three metapelitic gneisses were acquired by electron probe micro analysis using a spatial resolution of down to 2 m simultaneously profiles were analysed for nb cr and v which have significantly different diffusion characteristics in rutile the profiles of all elements show relatively homogeneous concentrations within most grains but significant inter grain differences even within a single thin section some rutile grains display a slight concentration decrease from a neighbouring garnet towards the matrix for all measured elements the lack of diffusion profiles for all analysed elements shows that these are highly immobile in rutile and that distributions of these elements are primary and preserve prograde information the nb and cr concentrations overlap with ranges that are ascribed to different provenances indicating that source discrimination based on these elements is not possible in all cases high retentiveness for zr implies that the zr in rutile geothermometer is highly robust to diffusive re equilibration even during very slow cooling 2 c ma 1 from granulite facies conditions most grains have high zr contents 3000 4600 ppm differences between high zr contents suggest that during growth under vapour absent conditions there may not be saturation of zr in rutile even if zircon is present therefore several rutile grains need to be analysed in a sample to obtain a useful minimum peak temperature the highest zr concentrations correspond to 900 c this is significantly higher than previous peak temperature estimates of 820 c based on two feldspar thermometry on a regional scale this implies that part of the pgd was affected by ultra high temperature uht metamorphism it also implies that rutile is able to preserve primary compositions even to uht conditions this study shows that if combined with textural information zr in rutile has the potential to be a very useful tool for estimating rutile crystallization temperatures and peak metamorphic conditions for granulite facies rocks zr in rutile yields more reliable peak metamorphic temperatures than most other exchange geothermometers which tend to partially re equilibrate by diffusion during cooling

identification of flysch landslide triggers using conventional and nearly real time monitoring methods an example from the carpathian mountains poland abstract this paper presents a study of active landslides in the carpathian flysch in poland site investigation of 15 landslides was conducted during the reconstruction of the szymbark szalowa road the landslides selected for analysis are located in slopes with inclination from 9o to 18o of the oligocene age characterized by shallow groundwater levels these slopes are made of soft clays and claystones interbedded by sandstones that allow seepage processes the flysch mixtures of weak soils and stiff rocks typically pose some difficulties for in situ and laboratory tests therefore methods for the recognition of landslide size depth and activity need to be applied site investigations and laboratory tests started in 2006 with conventional inclinometer and piezometer monitoring measurements however significant time lags between the measurements made it difficult to quantify landslide triggers therefore a more comprehensive nearly real time landslide monitoring network was deployed on may 2010 the first of this type in poland this system consisted of a weather station and three monitoring field stations with continuous recording of 3d inclinometers in place tilt sensors and pore pressure transducers at depths of 11 15 m the online measured displacement reached 33 500 mm heavy rainfalls and water infiltration led to pore pressure changes ranging from 50 to 100 kpa in june 2010 an acceleration of ground movements occurred after the highest monthly rainfall of 225 303 mm during a major flood in southern poland and again in july 2011 slope saturation was found to be the primary cause of landslide activation and groundwater pore pressure variations of 100 were found critical as a trigger for landslide accelerations in the polish carpathian flysch the appearance of high pore pressures variations could be used as an initial warning signal before the significant movements

problems in predicting the mobility of slow moving landslides abstract this paper discusses problems in predicting the mobility of slow moving landslides three case studies are presented here where research has been carried out by the utrecht university the la valette landslide complex in the french alps the la mure landslide in the french pre alps near grenoble and the hau landslide in switzerland to predict field velocities of these slow moving landslides the viscosity parameters of the material of these landslides were determined by strain controlled tests in a ring shear apparatus based on bishop s design at utrecht university the viscosity parameters from the laboratory proved to be 10 to 1000 times lower than viscosities obtained from back analyses on the observed velocities in the field this discrepancy may be explained by the development of negative pore pressures when the plastic material slides over a rigid wavy slip surface and or by convergent flow effects the associated gain in strength results in a higher apparent viscosity a more detailed analysis is made for the movements of the la valette landslide observed velocities at the la valette landslide are difficult to describe by one parameter set as the response to a change in groundwater level is not the same during a rise or fall in the piezometric level this deviation may be explained by rapid changes in total stresses and consequently changes in pore pressure under partly undrained conditions the emerging hysteresis with local and temporal variations in pore pressure makes it difficult to predict in detail the moving pattern of landslides

prograde and near peak zircon growth in a migmatitic pelitic schist of the southeastern canadian cordillera abstract u pb dates and trace elements acquired simultaneously on zircon from a migmatitic pelitic schist from the southeastern canadian cordillera are linked with results of phase equilibria modeling the first of three phases of zircon growth occurred between 77 and 72 ma along a prograde path in the kyanite melt field between the wet melting and muscovite dehydration melting reactions 675 775 c this protracted phase of prograde growth is characterized by a shallow positive slope in heavy rare earth elements hree the second phase occurred at c 69 ma after significant garnet growth by biotite dehydration melting at 775 875 c which produced zircon depleted in hree the last phase occurred at c 63 ma on the retrograde path as garnet and rutile were consumed at 780 c as indicated by enrichments in hree and nb but prior to feldspar crystallization in the melt as suggested by the moderate eu anomaly this path is consistent with rutile and monazite petrogenesis documented herein and in a previous study respectively in contrast with the high temperatures at which zircon grew 675 875 c ti in zircon thermometry yields unrealistically low estimates 470 739 c with 80 below the wet solidus there are no uncertainties in the buffering assemblage as rutile and quartz were present throughout and no effect of pressure because a pressure dependent calibration was used this study demonstrates that zircon growth along a prograde path is possible and warrants further investigation on factors controlling the ti content of zircon thermometry in metamorphic rocks

eclogites of the snowbird tectonic zone petrological and u pb geochronological evidence for paleoproterozoic high pressure metamorphism in the western canadian shield eclogite occurs within the southern domain of the east athabasca mylonite triangle in northern saskatchewan situated at the boundary between the archean rae and hearne provinces of the western canadian shield the east athabasca mylonite triangle is a fundamental exposure of the 3 000 km long snowbird tectonic zone the eclogite occurs in association with a variety of lower crustal high pressure granulites that record a complex metamorphic history from 2 6 to 1 9 ga temperatures of the eclogite facies metamorphism are constrained by garnet clinopyroxene exchange thermometry at 920 1 000 c minimum pressure conditions are recorded by the jadeite quartz albite geobarometer at 1 8 2 0 gpa a near isothermal decompression path to granulite facies conditions is inferred from retrograde reaction textures involving the formation of granulite facies assemblages such as orthopyroxene plagioclase and pargasite plagioclase u pb idtims zircon geochronology of the eclogite yields a weighted mean 207pb 206pb date of 1 904 0 0 3 ma which we interpret as the time of peak eclogite facies metamorphism shrimp in situ analyses of metamorphic zircons included within omphacitic clinopyroxene support this interpretation with a weighted mean 207pb 206pb date of 1 905 19 ma inclusion suites of high pressure phases and the petrographic setting of zircon are a direct link between zircon growth and eclogite facies metamorphism zircon from one eclogite sample has older cores that are 2 54 ga which is a minimum age for the emplacement or earliest metamorphism of the gabbroic protolith u pb rutile data indicate slow cooling at 1 c ma below 500 c from 1 88 to 1 85 ga the formation and exhumation of the eclogites at ca 1 9 ga has important implications for the tectonic significance of the snowbird tectonic zone during the paleoproterozoic the eclogites described here are consistent with transport of continental crust to mantle depths during the paleoproterozoic followed by rapid buoyancy driven exhumation to normal lower crustal depths

bedforms of the canadian eastern seaboard a comparison with global occurrences this paper presents a compilation of sedimentary bedforms identified from acoustic and seismic records collected over the southeastern canadian continental shelf in order to make the compilation it was found necessary to firstly review and synthesise the various terminologies used to describe the bedforms found and thereafter to relate the subsequent terminology to any diagnostic generic characteristic identifiable from the records sand waves are considered to be those forms that are composite in nature and are generated solely by the action of superimposed megaripples these latter features are identifiable adopting the classification of dalrymple et al 1978 which proves adequate for the acoustic differentiation of 2 d and 3 d types though we observed a greater coherence in bedform spacing of the 2 d types than reported hitherto sand ridges were adequately defined and recognised using the description of swift et al 1978 with respect to storm generated ridges and that of off 1963 and others with respect to tidal current ridges such ridges appear not to be uniquely described by ratios of their metrics the bedforms on the southeastern canadian continental shelf are abundant and wide spread virtually all types of bedforms recognisable on the u s shelf are present to the north the majority of these bedforms appear to be storm generated and are considered intermittently active many of the sand waves s s have no measureable relief though retaining their distinctive spatial geometry both active and moribund sand ridges were found of these ridges both tidal and storm generated types were identified the storm generated ridges were further broken down into shoreface connected ridges and offshore ridges a metrical analysis of the various bedforms show that a differentiation into stable bed phases can be made using height length ratios provided the bedforms are active and fully developed there is some overlap between megaripples and small sand waves and indeed between 2 d and 3 d megaripples yet the distinction is good between sand waves and sand ridges even moribund types sand ribbons in general can be confused with moribund sand waves and megaripples a detailed morphological examination is required to distinguish each feature data from sand ridges of the eastern canadian shelf combined with data from similar features found globally shows that ridge heights tend to cluster into three distinctive modes these modes are at heights of 7 13 and 27 m the first mode is correlated with storm generated ridges the second with tidal current ridges and the third possibly with submerged barrier islands

boundary layer dynamics and sediment transport under storm and non storm conditions on the scotian shelf abstract near bed measurements of waves currents seabed responses and ripple migration rates were obtained using an instrumented tripod at a water depth of 39 m on the scotian shelf during the winter of 1992 93 these data and the grant and madsen s 1986 grant w d madsen o s 1986 the continental shelf bottom boundary layer annu rev fluid mech 18 265 305 combined flow boundary layer model are used to examine wave current interaction various sediment dynamic thresholds and sediment transport on an exposed high energy continental shelf the seabed was found to be rippled for most time of the deployment and thus the ripple enhanced combined skin friction shear velocity had to be used to determine the initiation of bedload transport under combined flows this indirectly indicates adequate predictions of the skin friction shear velocities inside the wave boundary layer by the grant and madsen model at high transport stages bedload roughness must be added to the grain size roughness to obtain a transportrelated combined shear velocity in order to predict correctly the onsets of saltation suspension and sheet flow transports otherwise the initiation of suspended load transport and the total sediment transport rates will be severely under estimated the comparison between the prediction by the grant and madsen 1986 model and the calculation of a quadratic stress law suggests that the total current shear velocity was enhanced by a factor of 2 3 due to the wave current interaction during storms while the apparent bottom roughness was increased by more than an order of magnitude the non linear coupling between waves and currents also causes a 20 increase of the combined skinfriction shear velocity inside the wave boundary layer this non linear coupling is most important when waves and currents are roughly equal in magnitude and the angles between them are less than 30 four sediment transport formulae were tested while the engelund hansen total load and yalin bedload methods did not perform well the einstein brown and bagnold formulae were found to respectively give reasonable predictions of the bedload and total load sediment transport rates under the observed combined flow conditions the predicted sediment transport direction is also in good agreement with the observed ripple migration direction the gsc sediment transport model sedtrans92 predicts that the net daily transport rates during the storms reached 822 kg m 1 day 1 and were 2 3 orders of magnitude higher than the non storm transport suggesting the dominance of storm processes in sediment transport on the scotian shelf these values are in good agreement with the results from sand tracer experiments conducted in this region we thus conclude that sedtrans92 can properly simulate boundary layer dynamics and sediment transport on continental shelves

recent and modern marine erosion on the new jersey outer shelf abstract recent chirp seismic reflection data combined with multibeam bathymetry backscatter and analysis of grab samples and short cores provide evidence of significant recent erosion on the outer new jersey shelf the timing of erosion is constrained by two factors 1 truncation at the seafloor of what is interpreted to be the transgressive ravinement surface at the base of the surficial sand sheet and 2 truncation of apparently moribund sand ridges along erosional swales oriented parallel to the primary direction of modern bottom flow and oblique to the strike of the sand ridges these observations place the erosion in a marine setting post dating the passage of the shoreface ravinement and the evolution of sand ridges that form initially in the near shore environment also truncated by marine erosion are shallowly buried fluvial channel systems formed during the last glacial maximum and filled during the transgression and a regional reflector r that is 40 kyr depths of erosion range from a few meters to 10 m the seafloor within eroded areas is often marked by ribbon morphology seen primarily in the backscatter data as areas of alternating high and low backscatter elongated in the direction of primary bottom flow ribbons are more occasionally observed in the bathymetry where observed crests exhibit low backscatter and troughs exhibit high backscatter sampling reveals that the high backscatter areas of the ribbons consist of a trimodal admixture of mud sand and shell hash with a bimodal distribution of abraded and unabraded sand grains and microfauna the shell hash is interpreted to be an erosional lag while the muds and unabraded grains are in this non depositional environment evidence of recent erosion at the seafloor of previously undisturbed strata the lower backscatter areas of the ribbon morphology were found to be a well sorted medium sand unit only a few 10 s of cm thick overlying the shelly muddy sandy material concentrations of well rounded gravels and cobbles were also found in eroded areas with very high backscatter and at least one of these appears to be derived from the base of an eroded fluvial channel seafloor reworking over the transgressive evolution of the shelf appears to have switched from sand ridge evolution which is documented to 40 m water depth to more strictly erosional modification at greater water depths we suggest that this change may be related to the reduction with water depth in the effectiveness of sediment resuspension by waves resuspension is a critical factor in the grain size sorting during transport by bottom currents over large bedforms like sand ridges otherwise we speculate displacement of sand by unidirectional currents will erode the seafloor

tracer test to assess flow and transport parameters of an earth slide the montecagno landslide case study italy abstract subsurface water processes are principle triggering and driving factors during slope movements however the hydraulic properties that drive groundwater flow along the slope remain poorly understood moreover landslide deposits are often characterized by layering and fissures that cause high heterogeneity in the distribution of hydraulic properties this heterogeneity leads to great uncertainty in the prediction of groundwater flow paths this study aimed to improve understanding of hydraulic and transport properties of deep earth slides and to identify preferential flow directions inside the landslide body a dye tracer test was used to estimate transport parameters and characterize groundwater flow paths the results indicate that in the studied landslide two groundwater flow types exist and are related to the presence of fissured rock blocks and debris horizons embedded in a fine matrix the estimated low groundwater flow velocity has rarely been estimated in other studies of this landslide type the groundwater flow direction appears to be mainly influenced by the failure surface shape and differs from the sliding direction our results differ from those in other landslide studies and improve our knowledge of groundwater flow properties in deep earth slides furthermore they offer a new contribution to slope stability analyses and formula and to the effective design of mitigation strategies

the significance of titanite and apatite u pb ages constraints for the post magmatic thermal hydrothermal evolution of a batholithic complex berens river area northwestern superior province canada abstract titanite apatite and in one case rutile from a suite of twenty seven samples representing the major phases of an extensive and well dated archean plutonic domain of the northwestern superior province have been dated by u pb to determine the temporal progress of thermal and hydrothermal events accompanying and following major plutonism and to assess the isotopic behaviour of these geochronometers most samples contain 1 dark brown titanite with 350 20 ppm u showing shapes and textural relationships indicative of a primary magmatic origin and yielding ages corresponding either to the time of magmatic crystallization or to that of secondary metamorphic or magmatic events known in the area 2 pale titanite with 30 2 ppm u showing textural evidence for a secondary origin by breakdown of biotite hornblende oxide or older titanite and yielding ages that in general post date the major plutonic and metamorphic events in the area 3 apatite containing 30 5 ppm u occasionally up to 150 ppm u showing igneous shapes and textural relationships but yielding post magmatic ages similar to those of coexisting pale titanite 4 rutile in one sample postdating the ages of coexisting titanite and apatite the common coexistence of two noncoeval titanite generations demonstrates that the often invoked mechanism of pb diffusion during slow cooling in this case has no general validity the distribution of primary dark titanite ages however could be explained by late closure to diffusion or alternatively as the result of resetting by the thermal or hydrothermal effects caused by younger plutonic activity the ages of the secondary pale titanites probably reflect crystallization during discrete retrogressive events promoted by moderate heating or enhanced fluid activity the correspondence between pale titanite and apatite ages suggests that the same processes also caused the isotopic resetting of apatite on a regional scale the data pattern permits the identification of domains characterized by differences in the length and intensity of the thermal and hydrothermal processes the most protracted activity is recorded in northern domains of the berens river area whereas the gold mineralized red lake area in the south underwent a very rapid decline of the thermal hydrothermal activity these data also highlight important differences between the red lake and other gold camps of the superior province such as hemlo and val d or where hydrothermal activity locally associated with mineralization occurred as much as 30 80 m y after the major orogenic developments

pb diffusion in rutile diffusion of pb was measured in natural and synthetic rutile under dry 1 atmosphere conditions using mixtures of pb titanate or pb sulfide and tio2 as the sources of diffusant pb depth profiles were then measured with rutherford backscattering spectrometry rbs over the temperature range 700 1100 c the following arrhenius relation was obtained for the synthetic rutile d 3 9 10 10exp 250 12 kj mol 1 rt m2s 1 results for diffusion in natural and synthetic rutile were quite similar despite significant differences in trace element compositions mean closure temperatures calculated from the diffusion parameters are around 600 c for rutile grains of 100 m size this is about 100 c higher than rutile closure temperature determinations from past field based studies suggesting that rutile is more resistant to pb loss through volume diffusion than previously thought

high pressure granulites formation recovery of peak conditions and implications for tectonics high pressure granulites are characterised by the key associations garnet clinopyroxene plagioclase quartz in basic rocks and kyanite k feldspar metapelites and felsic rocks and are typically orthopyroxene free in both basic and felsic bulk compositions in regional metamorphic areas two essential varieties exist a high to ultrahigh temperature group and a group representing overprinted eclogites the high to ultrahigh temperature type formerly contained high temperature ternary feldspar now mesoperthite coexisting with kyanite is associated with garnet peridotites and formed at conditions above 900 c and 1 5 gpa clinopyroxene in subordinate basic rocks is al rich and textural evidence points to a high pressure high temperature melting history the second variety contains symplectite like or poikilitic clinopyroxene plagioclase intergrowths indicating former plagioclase free i e eclogite facies assemblages this type of rock formed at conditions straddling the high pressure amphibolite high pressure granulite field at around 700 850 c 1 0 1 4 gpa importantly in the majority of high pressure granulites orthopyroxene is secondary and is a product of reactions at pressures lower than the peak recorded pressure in contrast to low and medium pressure granulites which form at conditions attainable in the mid to lower levels of normal continental crust high pressure granulites of nonxenolith origin mostly represent rocks formed as a result of short lived tectonic events that led to crustal thickening or subduction of the crust into the mantle short times at high temperature conditions are reflected in the preservation of prograde zoning in garnet and pyroxene high pressure granulites of both regional types although rare are known from both old and young metamorphic terranes e g c 45 ma namche barwa e himalaya 400 340 ma european variscides 1 8 ga hengshan china 1 9 ga snowbird saskatchewan and 2 5 ga jianping china this spread of ages supports proposals suggesting that thermal and tectonic processes in the lithosphere have not changed significantly since at least the end of the archean

the influence of grain size analysis methods and sediment mixing on curve shapes and textural parameters implications for sediment trend analysis abstract to this day deterministic physical models capable of explaining the evolution of grain size distributions in the course of transport are still lacking for this reason various attributes of particle frequency distributions in particular curve shapes and textural parameters have for many decades been investigated for potential information about transport behaviour and size sorting processes of sediments in numerous environments such approaches are essentially conceptual and hence rely heavily on the validity of the assumptions on which they are based a factor which has to date been largely ignored in this context is the fact that different methods of grain size analysis e g sieving laser absorption and diffraction settling velocity measurements when applied to the same sample material produce variable curve shapes and hence incongruous textural data this is illustrated by selected examples showing the differences between sieving and settling results conversion of settling velocities into equivalent settling diameters psi phi transformations and the influences of particle shape particle density and water temperature it is demonstrated that particle size distributions are not only method dependent but also dependent on the adopted post processing procedure as a result only frequency curves generated by the same method and subsequently processed by identical computational procedures can be meaningfully compared furthermore the computation of textural parameters from bi or multimodal size distributions produces spurious results which are unrelated to the processes leading to the mixing of different size populations frequently observed in nature in such cases only the decomposition of such distributions into individual populations and the spatial comparison of such populations makes any sense because a physical explanation for the generation of size distributions is lacking a particular curve shape of a grain size population has no meaning on its own only a systematic comparison of progressively changing curve shapes and associated textural parameters of sediments collected on a closely spaced grid can yield data suitable for sediment trend analysis

predicting ripple roughness and sand resuspension under combined flows in a shoreface environment ripple measurements and flow and sediment dynamical data obtained from the shoreface of the middle atlantic bight using instrumented tripods were analyzed to evaluate various predictors of ripple geometry and roughness ripple roughness controls on sand resuspension and suspended sediment concentration profiles under combined waves and currents were also evaluated the limited observation of sand ripples in the field indicates that the grant and madsen 1982 method overestimates ripple roughness while the nielsen 1981 method tends to under predict ripple roughness a modified ripple predictor is thus proposed based on the grant and madsen method and it is shown to give reasonable predictions under the present experiment conditions this modified ripple prediction along with wave current and suspended sediment concentration data recorded by the tripods were then brought into the combined flow bottom boundary layer model of grant and madsen 1986 and the modified rouse equation of glenn and grant 1987 to calculate sand resuspension coefficient 0 and to predict suspended sediment concentration profiles it was found that under low energy fair weather conditions sand ripples are in the equilibrium range and ripple roughness increases with the bed shear stress this causes strong vortex activity close to seabed and thus higher resuspension coefficient reference concentrations are moderate due to this high resuspension coefficient even though bed shear stresses are low under moderate storm conditions ripple break off occurs and ripple roughness will decrease with bed shear stress this reduces the vortex activity and hence sand resuspension coefficient 0 the combination of this moderately high bed shear stress and reduced but still moderate ripple roughness favours sand suspension and produces the highest reference concentration for the encountered experimental conditions as bed shear stress is further increased ripples are nearly washed out and sand resuspension coefficient is further decreased approaching the previously suggested constant value of 1 3 10 4 this corresponds with the lowest reference concentration despite the high bed shear stress suspended sediment concentrations predicted by the modified rouse equation using this time variable resuspension coefficient and properly calculated bottom boundary layer parameters are reasonable compared to the field measured concentration profiles

sediment starved sand ridges on a mixed carbonate siliciclastic inner shelf off west central florida high resolution side scan mosaics sediment analyses and physical process data have revealed that the mixed carbonate siliciclastic inner shelf of west central florida supports a highly complex field of active sand ridges mantled by a hierarchy of bedforms the sand ridges mostly oriented obliquely to the shoreline trend extend from 2 km to over 25 km offshore they show many similarities to their well known counterparts situated along the us atlantic margin in that both increase in relief with increasing water depth both are oriented obliquely to the coast and both respond to modern shelf dynamics there are significant differences in that the sand ridges on the west central florida shelf are smaller in all dimensions have a relatively high carbonate content and are separated by exposed rock surfaces they are also shoreface detached and are sediment starved thus stunting their development morphological details are highly distinctive and apparent in side scan imagery due to the high acoustic contrast the seafloor is active and not a relict system as indicated by 1 relatively young ams 14c dates 1600 yr bp from forams in the shallow subsurface 1 6 meters below seafloor 2 apparent shifts in sharply distinctive grayscale boundaries seen in time series side scan mosaics 3 maintenance of these sharp acoustic boundaries and development of small bedforms in an area of constant and extensive bioturbation 4 sediment textural asymmetry indicative of selective transport across bedform topography 5 morphological asymmetry of sand ridges and 2d dunes and 6 current meter data indicating that the critical threshold velocity for sediment transport is frequently exceeded although larger sand ridges are found along other portions of the west central florida inner shelf these smaller sand ridges are best developed seaward of a major coastal headland suggesting some genetic relationship the headland may focus and accelerate the n s reversing currents an elevated rock terrace extending from the headland supports these ridges in a shallower water environment than the surrounding shelf allowing them to be more easily influenced by currents and surface gravity waves tidal currents storm generated flows and seasonally developed flows are shore parallel and oriented obliquely to the nw se trending ridges indicating that they have developed as described by the huthnance model although inner shelf sand ridges have been extensively examined elsewhere this study is the first to describe them in a low energy sediment starved dominantly mixed siliciclastic carbonate sedimentary environment situated on a former limestone platform

combined rutile zircon thermometry and u pb geochronology new constraints on early paleozoic hp uht granulite in the south altyn tagh north tibet china abstract hp granulite and garnet peridotite constitute a hp metamorphic unit in the south altyn tagh northern tibet previous data suggest that hp granulites experienced high pressure ultrahigh temperature metamorphism 870 1050 c 19 25 kbar followed by a medium pressure granulite facies overprint 780 820 c 9 5 12 kbar previous zircon u pb geochronology of hp granulites gave an age of ca 500 ma but it is unclear if this age reflects the metamorphic peak or the post peak overprint in this contribution new shrimp analyses indicate that the zircons associated with the peak metamorphic assemblage in hp felsic granulite are characterized by flat heavy ree patterns and 30 62 ppm ti yielding a temperature of 892 1002 c by ti in zircon thermometry suggesting that the growth of the zircons occurred under or close to peak ultrahigh temperature conditions rather than under post peak conditions these zircons gave a shrimp u pb age of 495 4 ma representing the age of peak metamorphism in contrast oscillatory zoned zircon cores yield magmatic ree patterns ti in zircon temperatures of 720 820 c and neoproterozoic u pb ages 936 22 ma this indicates that the protoliths of the felsic granulites were formed in the early neoproterozoic and were taken to extreme temperatures and pressures during the early paleozoic orogenic event in situ la icpms and emp analyses indicate that rutiles are characterized by broad scatter and bimodal distribution in both zr concentration and u pb age which are interpreted as a result of recrystallization or growth rather than volume diffusion the first rutile u pb age cluster is at ca 485 ma with a zr concentration of ca 3000 ppm yielding ca 950 c at 20 kbar implying that they grew at or near the peak metamorphic conditions the second rutile u pb age cluster is at ca 450 ma with a zr concentration of ca 1000 ppm corresponding to a temperature around 780 c at 10 kbar which is related to post peak reheating under medium pressure medium temperature granulite facies conditions these results demonstrate that hp granulites in the south altyn tagh experienced a peak ultrahigh temperature and high pressure metamorphism at ca 495 ma followed by medium pressure medium temperature granulite facies overprint before ca 450 ma

sand suspension and transport on the middelkerke bank southern north sea by storms and tidal currents abstract estimates have been made of the suspended sand transport at two sites on the middelkerke bank in the southern north sea from suspended sand profiles and current meter measurements over a period of approximately 40 days sand resuspension was mainly due to waves while transport was dominated by a few hours when large waves coincided with peak flood currents soulsby s relationships for the stress under combined currents and waves were found to be poor predictors for the observed near bed concentrations the mean stress m predicting 45 of the variance while the maximum stress max predicted just 15 and overestimate the effects of the waves when the influence of the stress due to the waves is reduced the variance explained increases to 67 the sand transport rate on the steep slope of the bank was 10 times that of the southern end and was up slope at 25 to the bank axis in the direction of the major axis of the tidal ellipse the transport on the steep slope was mainly in the size range 100 140 m which did not occur in any significant proportion in samples of the sea bed at that site but was advected from deeper water to the southeast excluding this finer component the transport rates of coarser sand 200 m at the two sites were similar over the 40 day period the up slope transport during storms suggests that waves play an important part in the bank maintenance and are not simply the mechanism which prevents the continual growth of the sand bank due to asymmetrical transport by the tidal currents alone the transport rates are consistent with a time scale of 10 2 10 3 years for the formation of the middelkerke bank

characterization of the instability mechanisms affecting slopes on carbonatic flysch alicante se spain case study abstract the studied flysch sequence of alicante occupies a widely populated area crossed by main communication routes the slopes existing on this area usually suffer slope instabilities that cause substantial damage and a very high maintenance cost in order to assess the type of instability mechanisms affecting these heterogeneous carbonatic slopes in this paper a wide inventory of 194 flysch rock slopes has been performed reporting the existing lithologies their competence and their relative arrangement and the geometrical relationship between bedding and the slope and the associated instability mechanism all these data have been jointly used for performing an instability mechanisms characterization for systematically characterizing the wide type of complex rock exposures existing in the study area they are divided into basic units referred as lithological pattern columns to which the different observed instability mechanisms are associated inventoried instability mechanisms are diverse and sometimes are combined with each other rockfalls are a very common instability mechanism associated to the differential weathering and sapping of the marly lithologies which are present in a wide number of geometrical combinations the other instability mechanisms closely depend on the combination of the geometrical and lithological parameters therefore this work provides a new basic tool which can be easily used during preliminary project stages for knowing the instability mechanisms which can affect rock slopes excavated on carbonatic flysch heterogeneous geological formations