model for the evolution of the avalonian cadomian belt the inception and termination of the ca 670 550 ma avalonian cadomian orogenic cycle are interpreted in terms of the amalgamation and breakup of a late precambrian supercontinent synorogenic arc related volcano sedimentary and granitoid rocks are attributed to oblique southward directed subduction along the margin of the supercontinent after its amalgamation breakup of the supercontinent and inception of the iapetus cycle led to termination of subduction and its replacement by transform activity the resulting closure of late precambrian arc related basins and the development of early cambrian platform successions with acado baltic fauna accompanied the formation of iapetus but took place on the active margin of a preexisting ocean and do not record the evolution of its rifted european flank

age of amphibolitic metamorphism in the ophiolitic unit of the morais allochthon portugal implications for early hercynian orogenesis in the iberian massif structurally lower portions of the allochthonous morais complex are comprised of an ophiolitic unit exposed in two contrasting structural units separated by a ductile thrust fault the lower unit is dominated by variably foliated amphibolite whereas the upper unit is largely comprised of metaperidotite and metagabbro most of the ophiolitic unit has recrystallized synkinematically under amphibolite facies metamorphic conditions c 500 c and 5 kbar amphiboles formed during this metamorphism are typically magnesio hornblende an amphibole concentrate from the lower structural unit records a 39 ar 40 ar plateau age of 397 3 4 ma an amphibole concentrate from the upper structural unit displays an internally discordant 39 ar 40 ar age spectrum corresponding to a total gas age of 431 1 27 3 ma gas fractions evolved from each amphibole concentrate at intermediate and high experimental temperatures are characterized by similar apparent k ca ratios and yield well defined 36 ar 40 ar v 39 ar 40 ar isotope correlations which result in similar ages of 384 2 5 2 and 392 4 7 3 ma these are considered to be more reliable than the plateau ages and are interpreted as dating the last cooling through those temperatures required for intracrystalline retention of argon within constituent amphibole grains the associated tectonothermal event represented a first stage of hercynian orogenesis in the iberian massif it was probably related to oceanic closure and associated obduction of granulitic eclogitic massifs which at present structurally overlie the ophiolitic unit

the cadomian orogeny in the north armorican massif a brief review the north armorican massif nam of nw france is the type locality of the late precambrian cadomian orogenic belt the nam largely escaped reworking during the upper palaeozoic variscan cycle with the result that earlier geological relationships are commonly preserved intact a large part of the cadomian belt of the nam comprises variably deformed and metamorphosed supracrustal rocks of the brioverian succession barrois 1895 1896 1908 graindor 1957 cogne 1962 le corre 1977 rabu et al 1982 1983 chantraine et al 1982 the cadomian orogeny which takes its name from cadomus caen in normandy was defined by bertrand 1921 as the late precambrian orogeny which in the nam resulted in the folding and uplift of the brioverian succession prior to the deposition of lower palaeozoic red bed sequences events which have been ascribed to the cadomian orogeny span the period c 700 425 ma during which time the brioverian was heterogeneously deformed and metamorphosed and intruded by calc alkaline igneous complexes the evolution of the belt has been interpreted in terms of the gradual cratonization of calc alkaline arc complexes and syn orogenic sediments in an andean type continental margin brown et al 1990 dupret et al 1990 this contribution reviews briefly the geology of the cadomian belt of the nam fig 1 and outlines some of the more controversial debates concerning the distribution and status of precadomian basement the stratigraphy of the brioverian succession the nature of cadomian magmatism the kinematic significance of major structures and the geotectonic setting of the component parts of the belt

39ar recoil artifacts in chloritized biotite biotite separates from the metamorphosed granitic rocks of eastern taiwan yield disturbed 40ar39ar age spectra their disturbed profiles become more pronounced with increasing degree of chloritization and are attributed to mixed release of argon from sub micron scale biotite and chlorite intercalations 39ar internal recoil best explains the discordance of the age spectra chlorite is randomly intercalated with biotite at scales ranging from 10 a to several tens of microns both 40ar and k were evidently lost during the chloritization reaction during the neutron irradiation 39ar atoms recoil into the chlorite from the adjacent biotite intercalations the recoil and chloritization combine to produce a variable 40ar39ar spatial distribution in the intercalated biotite chlorite during 40ar39ar step heating analyses argon in biotite is released in two pulses centered at 650 c and 950 1050 c which represent two stages of dehydroxylation of the biotite chlorite out gasses in two pulses centered at 550 c and 700 900 c during dehydroxylation and then decomposes this differential thermal release of argon from each mineral phase with variable 40ar39ar ratios yields discordant incremental heating age spectra

oceanic versus continental influences over the last 7 kyrs from a mid shelf record in the northern bay of biscay ne atlantic abstract we discuss paleoenvironments of north western france over the last 7 kyrs in terms of i long term changes relative sea level rise and boreal summer insolation ii rapid climate changes millennial scale bond events and multi decadal regimes of the north atlantic oscillation nao and iii growing human impacts in watersheds our study focuses on the cbt cs11 core retrieved in the northern bay of biscay with new high resolution 70 years palynological data dinoflagellate cysts and pollen combined with sedimentological and oxygen stable isotopic records this multiproxy approach enabled us to gain a better understanding of the influence of varying middle to late holocene climate regimes on marine coastal and terrestrial ecosystems as well as on human coastal societies we especially show that the slowdown of the relative sea level rise starting at around 5 9 ka bp led to the stabilization of tidal flats in estuarine environments subsequently increasing river flows to the ocean resulted in a progressive seasonal stratification of the shelf under increasing winter precipitations and establishment of the modern winter thermohaline front at 3 3 ka bp in addition within the 4 2 ka bp interval palynological and sedimentological evidence suggests increasing river discharges in north western france in a context of a weakened atlantic subpolar gyre and recurrent negative nao like conditions finally we identified a major transition at around 1 2 ka bp early middle ages that appears to be linked to a period of maximal anthropogenic landscape opening and soil erosion implying stronger primary productivity in coastal surface waters of the studied region

variable variscan thermal rejuvenation in the st malo region cadomian orogen france evidence from 40ar 39ar mineral ages abstract the st malo region in north west france contains migmatites and anatectic granites derived by partial melting of metasedimentary protoliths during cadomian orogenesis at c 540 ma previously reported rb sr model ages for muscovite and biotite range from c 550 to c 300 ma and suggest variable resetting of mineral isotopic systems these rocks display microscopic evidence for variably intense cadomian intracrystalline plastic strain but record no obvious evidence of penetrative palaeozoic regional deformation 40ar 39ar mineral ages have been determined to evaluate better the extent timing and significance of palaeozoic overprinting eleven muscovite concentrates and one whole rock phyllite have been prepared from various units exposed in the st malo and adjacent mancellian regions in the mancellian region muscovite from two facies of the bonnemain granite complex record 40ar 39ar plateau ages of c 527 and 521 ma an internally discordant 40ar 39ar release spectrum characterizes muscovite from protomylonitic granite within the cadomian alexain deux evailles ize granite complex and probably records the effects of variscan displacement along the north armorican shear zone muscovite concentrates from anatectic granite and from cadomian mylonites along ductile shear zones within the north western sector of the st malo region exhibit internally discordant 40ar 39ar release spectra which suggest variable and partial late palaeozoic rejuvenation by contrast muscovite concentrates from samples of variably mylonitic brioverian metasedimentary rocks exposed within the south eastern sector of the st malo region display internally concordant apparent age spectra which define plateaux of 326 320 ma a whole rock phyllite sample from brioverian metasedimentary rocks exposed along the eastern boundary of the st malo region displays an internally discordant argon release pattern which is interpreted to reflect the effects of a partial late palaeozoic thermal overprint muscovite from the plelan granite part of the variscan plelan bobital granite complex yields a 40ar 39ar plateau age of c 307 ma the 40ar 39ar results indicate that cadomian rocks of the st malo region have undergone a widespread and variable palaeozoic carboniferous rejuvenation of intracrystalline argon systems which apparently did not affect the mancellian region this rejuvenation was not accompanied by penetrative regional deformation and was probably of a static thermal hydrothermal origin the heat source for rejuvenation was probably either the result of heating during variscan extension or advection from variscan granites which are argued to underlie the st malo region

development of the benethic nepheloid layer on the south texas continental shelf western gulf of mexico abstract a monitoring study of suspended sediment on the south texas continental shelf indicates that a turbid benthic nepheloid layer is regionally persistent a sequence of quasi synoptic measurements of the water column obtained during six cruises in an 18 month period indicates substantial spatial and temporal variability in nepheloidlayer characteristics regionally the thickness of the shelf nepheloid layer increases both seaward and in a convergent alongshelf direction greatest thicknesses occur over a muddy substrate indicating a causal relationship maximum observed local thickness is 35 m which occurs along the southern shelf break analyses of suspended particulate matter in shelf bottom waters indicate mean concentrations ranging from 49 10 4 to 111 10 4 particle counts cc concentrations persistently increase shoreward throughout the region bottom particulate matter is predominantly composed of inorganic detritus admixtures of organic skeletal particles primarily diatoms are generally present but average less than 10 of the total particulate composition texturally the particulate matter in bottom waters is predominantly poorly sorted sediment composed of very fine silt 3 9 7 8 m the variability in nepheloid layer characteristics indicates a highly dynamic shelf feature the relationship of nepheloid layer characteristics to hydrographic and substrate conditions suggests a conceptual model whereby nepheloid layer development and maintenance are the results of the resuspension of sea floor sediment bottom turbulence is attributed primarily to vertical shear and shoaling progressive internal waves generated by migrating shelf water masses especially oceanic frontal systems and secondarily to shoaling surface gravity waves

fine grained sediment budget on the continental margin of the bay of biscay abstract under present day conditions rivers are the main source of fine sediments dispersed to the bay of biscay they deliver about 2 5 10 6 t yr 1 of continental fine sediments 60 of which is derived from the gironde estuary of this flux 65 is believed stored on the shelf two kinds of mud fields can be found in the bay of biscay coastal mud and shelf mud belts the total mass of fine sediments stored during the past 2000 years is 3 2 10 9 t consequently about 0 9 10 6 t yr 1 could reach the shelf edge and eventually the open sea from this amount of displaced material and the deposition surface areas an evaluation of sediment fluxes across the margin during the late holocene period is discussed this evaluation is compared with results obtained from ecosysteme du canyon du cap ferret ecofer data from sediment traps and surficial box cores

short paper cadomian terrane tectonics and magmatism in the armorican massif the north armorican composite terrane nw france is a collage of displaced terranes which result from the amalgamation of cadomian continental arcs and marginal basin complexes by sinistral transpression along a continental margin above a subduction zone early cadomian arc activity occurred at c 700 650 ma but terrane accretion did not occur until c 540 ma and post tectonic magmatism persisted well into the palaeozoic cadomian events thus span a considerably greater period than previously supposed

world wide delivery of river sediment to the oceans new data and new estimates from old data show that rivers with large sediment loads annual discharges greater than about 15 times 10 6 tons contribute about 7 times 10 9 tons of suspended sediment to the ocean yearly extrapolating available data for all drainage basins the total suspended sediment delivered by all rivers to the oceans is about 13 5 times 10 9 tons annually bedload and flood discharges may account for an additional 1 2 times 10 9 tons about 70 of this total is derived from southern asia and the larger islands in the pacific and indian oceans where sediment yields are much greater than for other drainage basins

tectonothermal chronology of early cadomian arc development in guernsey and sark channel islands the cadomian orogen exposed in nw france and the channel islands comprises a collage of variably displaced terranes which record the late proterozoic evolution of a continental margin within a complex subduction zone on the islands of guernsey and sark calc alkaline quartz diorite stocks were emplaced during early stages of the cadomian orogeny zircons from two stocks of deformed quartz diorite display evidence of inheritance in larger and more magnetic fractions upper intercept ages for these discordant concentrates are c 1300 ma sm nd whole rock model ages t dm suggest older ages of c 2000 ma conversely the smallest and least magnetic zircons exhibit a distinct lead loss pattern suggesting that the 207 pb 206 pb dates of c 700 ma correspond to the time of crystallization of the stocks and provide a lower age constraint for initiation of subduction related magmatism in the cadomian orogen hornblende concentrates from deformed quartz diorite stocks exposed on guernsey and sark display discordant 40 ar 39 ar age spectra five samples record well defined isotope correlation ages ranging between 596 ma and 606 ma a hornblende concentrate from host orthogneiss sark yields a plateau age of 608 ma the hornblende ages are interpreted as dating post metamorphic cooling following late proterozoic deformation and metamorphism within the arc system both magmatic and cooling ages from this early cadomian arc contrast with those of younger initial tectonothermal activity c 570 ma and c 540 ma in other cadomian terrane elements and suggest palinspastic separation until very late stages of the orogeny the polyphase nature of this late proterozoic activity is similar to that of related orogens which probably occupied similar tectonic settings along the margin of gondwana e g sw iberia west africa

reconstructing and understanding the impacts of storms and surges southern north sea coastal barriers are ubiquitous globally and provide a vital protective role to valuable landforms habitats and communities located to landward they are however vulnerable to extreme water levels and storm wave impacts a detailed record of sub annual to annual decadal and centennial rates of shoreline retreat in frontages characterised by both high 3 m and low 1 m dunes is established for a barrier island on the uk east coast for four storms 2006 2013 we match still water levels and peak significant wave heights against shoreline change at high levels of spatial densification the results suggest that at least in the short term shoreline retreat of typically 5 8 m is primarily driven by individual events separated by varying periods of barrier stasis over decadal timescales significant inter decadal changes can be seen in both barrier onshore retreat rates and in barrier extension rates alongshore whilst the alongshore variability in barrier migration seen in the short term remains at the decadal scale shoreline change at the centennial stage shows little alongshore variability between a region of barrier retreat at 1 15 m a 1 and one of barrier extension a data mining approach synchronising all the variables that drive shoreline change still water level timing of high spring tides and peak significant wave heights is an essential requirement for validating models that predict future shoreline responses under changing sea level and storminess

late holocene record from a loire river incised paleovalley french inner continental shelf insights into regional and global forcing factors abstract sediment core kv14bis was retrieved from the fosse du croisic a loire river incised paleovalley located in the inner shelf of the bay of biscay this core 5 4 m length covers the past 2 6 cal kyr bp with high sedimentation rate a multiproxy approach x ray imagery xrf data grain size analyses and benthic foraminiferal assemblages was applied in order to reconstruct the hydrological regime of the loire river during the late holocene this hydrological regime was further linked to climate forcing e g solar activity north atlantic oscillation nao and human activity our data describe a succession of several dry humid periods the humid periods are centered on 2 2 1 3 and 0 5 cal kyr bp and are characterized by high terrigenous flux fine silty sedimentation relatively high organic carbon content and high proportions of the epiphytic foraminiferal species planorbulina mediterranensis this species was probably brought to the study site by the loire river plume attached on floating algae the dry periods are centered on 2 5 1 5 1 2 cal kyr bp and 1900 ce and are characterized by low terrigenous input and high carbonate content due to abundant shell debris during periods of low river runoff deposition of a sand particle population grain size 200 m could indicate increased storminess this latter may have remobilized sediments from shallower depths during these generally dry periods on the continent the overall coherence of our results with several european continental records supports a pluri centennial scale regional climate control of humidity and storminess resembling that of the nao spectral analyses emphasized a possible additional control of solar activity through deforestation and soil erosion early human impact was also probably superimposed on this climatic forcing

behaviour of rb sr whole rock and u pb zircon systems during partial melting as shown in migmatitic gneisses from the st malo massif ne brittany france the age of regional metamorphism and partial melting in the late proterozoic succession of the st malo area has been established at around 540 ma whole rock homogenization of the sr isotope systems has been achieved only in the anatectic granites whereas the associated metatexitic and diatexitic gneisses remain highly heterogeneous at lower grade than the sillimanite isograd metasedimentary gneisses contain detrital zircons which record the regional metamorphic event as a u pb lower intercept age 536 14 ma in the sillimanite zone u pb zircon lower intercept ages are around 500 10 ma and suggest a recent loss of radiogenic pb from the observed overgrowths zircons from the anatectic granites do not yield u pb intercept ages due to the presence of inherited radiogenic pb but the finer fractions define a discordant array whose upper intercept on concordia yields 555 13 ma an age significantly older than the partial melting event indicated by the lower grade zircon ages the lower intercept defined by the fine grained anatectic zircons yields a date in the future negative ordinate value in their regional context the st malo migmatites can be considered as resulting from late stage crustal melting in the cadomian orogenic belt following genesis of calc alkaline magma at an active margin around 600 ma ago an age of 540 ma for partial melting in the st malo migmatites places the end of the cadomian orogeny near the precambrian cambrian boundary

plume front and suspended sediment dispersal off the yangtze changjiang river mouth china during non flood season abstract a sea survey was conducted in may 2001 using ctd together with direct reading current meter and water sampling to investigate the sediment dynamics off the yangtze river mouth data obtained from five observational sites reveal density flows characterized by the halocline thermocline and associated sharp current velocity gradients that prevail in the study area especially at the freshwater plume front the interaction of the yangtze freshwater plume littoral current and tidal current has generated these density flows particularly the anomalous high speed 140 cm s 1 current recorded at the freshwater plume front during the early flood stage leads to the resuspension of the sediment ssc reaching 0 5 g l 1 off the river mouth during that time period the suspended sediment flux measured at b2 the ideal site for recording frontal processes in the estuary indicates the main trend of southward transport of fine grained sediment up to 60 kg m 2 s 1 at early flood stage and 1 32 kg m 2 s 1 as net flux during two tidal periods it is inferred that the density flow at the plume front plays key roles in dispersing the yangtze fine suspended sediments southward during the non flood season

slope transport of suspended particulate matter on the aquitanian margin of the bay of biscay abstract spatial and temporal characteristics of the water masses and the dispersion of the suspended particulate matter were investigated using current meter hydrographic and nephelometric observations gathered during the ecofer experiment 1989 1991 in the cap ferret canyon on the aquitanian margin of the bay of biscay while characteristics of the deep water masses were stable from one year to another large hydrographic change in the upper 500 m related to winter renewal induced by poleward advection of warm and saline water along the continental slope the slope circulation and seasonal eddy activity appear as important dynamical mechanisms that control the entrainment and the dispersion of the suspended particulate matter from the neritic domain to the deep ocean a predominantly northward along slope current with occasional reversal characterizes this circulation the nephelometric structures also showed seasonal changes in the overall suspended particulate matter content but recurrent features such as the presence of intermediate nepheloid layers at the shelf break depth and various depths along the slope 500 1000 and 2000 m were observed these nepheloid layers extended off the slope to about 10 30 km but especially laterally along the slope their presence indicated that suspended particulate matter exchanges between the shelf and the slope occurred mainly in the head of the canyon and along the southern open slope the intermediate nepheloid layers around 500 m depth detached from the slope particularly in regions where the bottom slope is close to critical for the m2 internal tide

dynamics of mercury species in surface sediments of a macrotidal estuarine coastal system adour river bay of biscay estuarine and coastal surface sediments from the adour estuary and adjacent coastal area south bay of biscay have been investigated to establish mercury species variability in a macrotidal system submitted to contrasted seasonal river discharges and downstream urbanisation surface sediments were sampled during three campaigns in the major sediment deposits of the adour estuary and at selected discharge points concentrations of hg2 and mehg in adour estuarine sediments average 1600 and 1 3 pmol g 1 and range from 2 to 7300 pmol g 1 and from 0 5 to 8 0 pmol g 1 respectively the concentrations of inorganic ionic mercury hg2 and monomethylmercury mehg in the surface sediments display large seasonal variation being one order of magnitude higher in june 2001 for hg2 and in october 2000 for mehg the results show that hg2 can be accumulated in the estuarine sediments after seasonal river inputs and both remobilised and methylated during dry period mercury species concentrations in coastal sediments collected in june 2001 assessed the impact of estuarine inputs on the nearby coastal area except direct anthropogenic discharge points the variability and transfer of hg2 and mehg in surface sediments of the whole estuarine coastal macrotidal system can be depicted by simple geochemical parameters of the bulk sediments such as grain size distribution organic carbon and total sulphur

polyphase late paleozoic tectonothermal evolution of the southwestern meguma terrane nova scotia evidence from 40ar 39ar mineral ages 40ar 39ar incremental release ages of hornblende muscovite and biotite from a variety of granitic stocks and host metamorphic rocks suggest a complex late paleozoic tectonothermal evolution for the southwestern meguma terrane regional d1 folding with cleavage formation under greenschist lower amphibolite facies m1 metamorphic conditions occurred at ca 400 410 ma and was followed by emplacement of a series of granitic stocks ranging in age between ca 375 and 315 ma these were emplaced at relatively shallow crustal levels and developed contact metamorphic aureoles of variable grade these are locally superposed on m1 regional metamorphic assemblages and result in a complex isograd pattern 40ar 39ar mineral ages suggest episodes of contact metamorphism occurred at 1 360 375 ma possibly related to emplacement of the south mountain batholith or temporal equivalents 2 350 356 ma around the port mouton pluton and northeastern shelburne pluton 3 ca 315 325 ma near the wedgeport pluton and in

time span of plutonism fabric development and cooling in a neoproterozoic magmatic arc segment u pb age constraints from syn tectonic plutons sark channel islands uk abstract new u pb zircon and titanite dates from syn tectonic plutons on the british channel island of sark constrain the time span of plutonism fabric development and cooling in this part of the neoproterozoic cadomian magmatic arc the tintageu leucogneiss is a mylonitic unit that was dated previously at 615 6 4 2 2 3 ma the port du moulin quartz diorite which intruded the tintageu unit contains a high strain solid state deformation fabric that is less intense than but parallel to fabrics in the leucogneiss and yields a u pb zircon date of 613 5 2 3 1 5 ma the little sark quartz diorite also displays solid state deformation fabrics in addition to relict magmatic textures and yields a u pb zircon date of 611 4 2 1 1 3 ma the north sark granodiorite is largely penetratively undeformed exhibits mainly magmatic fabrics and textures and has a u pb zircon date of 608 7 1 1 1 0 ma two fractions of titanite from each intrusion are essentially concordant and are identical within error with mean dates of 606 5 0 4 ma port du moulin quartz diorite 606 2 0 6 ma little sark quartz diorite 606 4 0 6 ma north sark granodiorite the new u pb data in combination with previous u pb and 40 ar 39 ar data and previous field studies confirm the syn tectonic nature of the sark plutons and quantify the time span ca 7 m y required for intrusion and sufficient crystallization of each body to record incremental strain during waning deformation titanite u pb and hornblende 40 ar 39 ar dates mark final cooling about 2 m y after intrusion of the last pluton

significance of a hiatus in down temperature fabric development within syn tectonic quartz diorite complexes channel islands uk detailed fabric development histories have been deduced for neoproterozoic foliated quartz diorite complexes of the channel islands uk the plutons were emplaced during regional d2 deformation magmatic fabrics formed at low crystal contents pre rheologically critical melt percent are only locally preserved due to overprinting by solid state deformation which occurred at moderate temperatures 400 550 c this is demonstrated by brittle microcracking of plagioclase and amphibole with only local ductile bending and dynamic recrystallization marginal recrystallization and myrmekite development on alkali feldspar ductile deformation of quartz to form types 2 3 ribbons quartz recrystallization by sub grain rotation associated with a slip but not c slip biotite recrystallization within micro shears and variable amphibole recrystallization the deformation histories display a distinct division between magmatic state and moderate temperature solid state deformation features with little evidence for intervening high temperature solid state fabrics this contrasts with criteria widely considered diagnostic of syn tectonic plutons which envisage development of a continuum of magmatic through high temperature solid state deformation fabrics however we consider the plutons syn tectonic and attribute the hiatus to contrasting strain and pluton cooling rates length and nature of deformation events and host rock ambient temperatures intermediate magmas emplaced at moderate to shallow levels in the crust may be more prone to develop such apparently punctuated deformation histories than sio 2 richer granitoids

relationship between hydrology and seasonal distribution of suspended sediments on the continental shelf of the bay of biscay abstract numerous oceanographic cruises with hydrology water sampling drift current measurements carried out since 1980 on the continental shelf of the bay of biscay together with available noaa avhrr infra red images form the basis of a proposed explanation for the processes responsible for the distribution of suspended sediments on the shelf the seasonal hydrographic structure of continental shelf waters is of paramount importance in sediment distribution in summer there is an horizontal stratification of water masses and suspended sediment distribution is closely related to the thermo haline structure a fresher water mass with less suspended material lies on a thicker and more turbid homogeneous layer during winter when sediment discharge from the rivers often reaches its annual maximum an oceanic thermo haline wedge occurs on the shelf at around 100 m as a result winter turbidity values on the outer continental shelf are low comparable to summer values and a permanent nepheloid layer is never observed the wedge which lasts for several months may act as a filter preventing transport to the slope high turbidities on the external shelf and the continental slope are only measured in spring when the thermo haline wedge disappears it seems possible that during winter time suspended materials brought by rivers are deposited in the grande vasiere the large mud patch it is postulated that the position of this mud patch is linked to the long term stable location of the thermo haline front that separates oceanic waters from the colder and less salty coastal waters

millennial scale holocene hydrological changes in the northeast atlantic new insights from la grande vasiere mid shelf mud belt a mid to late holocene paleohydrological reconstruction from the northeast atlantic is proposed through the study of a high resolution sedimentary record from the northern continental shelf of the

the columbia river plume study subtidal variability in the velocity and salinity fields a comprehensive study of the strongly wind driven midlatitude buoyant plume from the columbia river located on the u s west coast demonstrates that the plume has two basic structures during the fall winter season namely a thin 5 15 m strongly stratified plume tending west to northwestward during periods of southward or light northward wind stress and a thicker 10 40 m weakly stratified plume tending northward and hugging the coast during periods of stronger northward stress the plume and its velocity field respond nearly instantaneously to changes in wind speed or direction and the wind fluctuations have timescales of 2 10 days frictional wind driven currents cause the primarily unidirectional flow down the plume axis to veer to the right or left of the axis for northward or southward winds respectively farther downstream currents turn to parallel rather than cross salinity contours consistent with a geostrophic balance in particular during periods when the plume is separated from the coast currents tend to flow around the mound of fresher water at distances exceeding about 20 km from the river mouth the along shelf depth averaged flow over the inner to midshelf is linear and depth averaged acceleration is governed to lowest order by the difference between surface and bottom stress alone in this region along shelf geostrophic buoyancy driven currents at 5 m calculated from surface density and along shelf geostrophic wind driven currents computed from a depth averaged linear model are comparable in magnitude 10 25 cm s 1

sediment entrainment on a wave graded shelf roussillon france abstract the sands of the inner shelf off the roussillon coast of the microtidal golfe du lion display a seaward fining texture and merge in water deeper than 20 30 m with midshelf muds there is a qualitative correspondence between the textural gradient and the seaward attenuating annual surface gravity wave power expended by tangential stress on the shelf surface various equations used to quantify the relation of sediment texture to fluid energy predict the trend of the observed textural gradient but overestimate its value an empirical threshold equation komar and miller 1975a b and a theoretical null point equation johnson and eagleson 1966 give comparable results implying that both may be describing the same state there is a disparity between the predictions of an incipient motion equation johnson and eagleson 1966 and the threshold equation probably because static instability of grains occurs prior to dynamic instability of grains in an increasing fluid velocity field theory forecasts that in water shallower than 30 m the sands are frequently entrained by shoaling waves particularly during the winter months the threshold of movement of sands in 5 m of water is exceeded for more than 40 of the year hence the grain size of the shallow water sands does not reflect the maximum energy level of the environment

chronology of cadomian tectonothermal activity in the baie de saint brieuc north brittany france evidence from 40ar 39ar mineral ages the late precambrian cadomian orogen exposed in the north armorican massif northwest france is a collage of displaced terranes that in part developed during amalgamation of continental arc and marginal basin complexes 40ar 39ar mineral ages reported here place new constraints on the timing of cadomian tectonothermal activity in the southern part of the st brieuc terrane in the baie de saint brieuc area brioverian supracrustal units were deformed metamorphosed and intruded by calc alkaline plutonic complexes metamorphic hornblende from a metabasic amphibolite sheet within brioverian rocks records an isotope correlation age of 568 4 2 6 ma interpreted to date postmetamorphic cooling through appropriate argon closure temperatures similar isotope correlation cooling ages are recorded by metamorphic hornblende within both an amphibolite sheet intrusive into the penthievre complex 567 5 1 2 ma and the la croix gibat amphibolite 574 8 2 1 ma igneous hornblende from the late tectonic to pos

intermittent stability and frontogenesis in an area influenced by land runoff a frontal structure in liverpool bay was studied using conductivity temperature depth ctd and current meter data at times of weak vertical mixing by wind and tides a density driven gravity flow induced by river discharge distorts the thermohaline field so that an expanding stratified region develops bounded offshore by a surface front expansion of this frontal structure is increasingly curbed by rotation as a near geostrophic balance is attained owing to friction the space scale and time scale of frontogenesis are somewhat greater than two internal rossby radii and an inertial period respectively at times of increased mixing the frontal structure is destroyed and the enhanced friction between layers inhibits gravity flow hampering the frontogenesis mechanism large variability in mixing conditions results in an intermittent frontal structure

neoproterozoic shear zone tectonics within the icartian basement of guernsey and sark channel islands the channel islands of guernsey and sark are amongst the few localities within the neoproterozoic cadomian orogenic belt where palaeoproterozoic basement is exposed basement units collectively referred to as icartian comprise orthogneisses e g the c 2000 ma icart granite gneiss metasediments and amphibolites on guernsey the protolith to the icart granite gneiss was intruded into metasediments already deformed during a d 1 deformation event both were variably deformed during a d 2 event within an approximately north south trending steeply dipping oblique dextral shear zone on sark metasediments and amphibolites carry a d 1 fabric not necessarily correlatable with that on guernsey which was deformed during d 2 to form recumbent gently inclined folds and tectonic fabrics which locally carry top to the south kinematic indicators early cadomian quartz diorites which intruded the icartian basement carry variably developed magmatic and moderate temperature 400 550 c ls solid state fabrics which are similarly oriented to d 2 basement structures this indicates that the quartz diorites were emplaced and deformed during a protracted d 2 event published 40 ar 39 ar amphibole cooling ages of c 600 ma from guernsey and sark quartz diorites and a host icartian amphibolite are consistent with reworking of basement units during the cadomian orogeny the contrasting kinematic pattern during cadomian deformation implies that a flat lying shear zone on sark may have accommodated oblique dextral strike slip movement on guernsey with an overall southerly direction of tectonic transport deformation most likely occurred in the hanging wall of a major south dipping neoproterozoic subduction zone

benthic foraminiferal thanatocoenoses from the cap ferret canyon area ne atlantic a complex interplay between hydro sedimentary and biological processes abstract benthic foraminiferal thanatocoenoses from the cap ferret canyon area were studied in the 150 m fraction of 4 5 cm deep sediment levels at 13 stations the shallowest station 151 m depth is located at the shelf break close to the canyon head all other stations are located along two bathymetric transects seven stations along the canyon axis between 300 and 3000 m depth and five stations from 300 m to 2000 m depth along the southern flank of the canyon the comparison between the live rose bengal stained and dead assemblages shows that biological i e population dynamic and taphonomic processes i e test destruction transport generate important discrepancies between live and dead assemblages an important question is to what degree post mortem transport and redeposition of foraminiferal tests contribute to the difference between living and dead assemblages the composition of the thanatocoenoses 150 m from the inner continental shelf to the cap ferret canyon axis however transport of tests from outer shelf or upper canyon axis towards deeper sites occurs as indicated by an increase of diversity indices of the dead fauna along the canyon axis moreover some species e g cassidulina carinata are observed in the living fauna restricted to the shallow sites but occur in important amounts in the dead fauna at deeper stations suggesting that these taxa have been transported from upper canyon stations toward deeper sites since cap ferret canyon is inactive in terms of massive sediment transport i e gravity events downslope transport of foraminiferal tests probably takes place in nepheloid layers downslope transports of foraminiferal tests may create important biases for the utilisation of paleoceanographic proxies using the assemblage characteristics and or the geochemical composition of selected species however the study of dead assemblages along a canyon axis can give important clues about the sedimentary dynamics especially an idea of the quantity of reworked foraminifera transported through the canyon axis along the adjacent flank such evidence of downslope transport was not observed despite taphonomic test destruction and biological processes population dynamics the live fauna closely resembles the distribution and the composition of the dead assemblage therefore ecological information obtained from the fossil flank samples can be more reliably used to reconstruct paleoenvironmental conditions

geochemical evidence for triassic rifting in southwestern florida abstract mesozoic rhyolites and basalts from three drillholes penetrating the pre cretaceous basement of southwestern florida were analyzed for their trace element and sr and nd isotopic compositions major and trace element abundances suggest the suite was erupted in an extensional environment and isotopic data indicate derivation primarily from aged enriched precambrian continental lithosphere combined to varying degrees with an asthenospheric component nd model ages show no significant difference in the age of the lithosphere from which these rocks and volcanic rocks of paleozoic age from north florida were derived arguing against major displacement across the peninsula including along proposed extensions of the jay fault and or bahamas fracture zone we suggest that the geophysically inferred boundary across the peninsula if a fault may have had a strong normal component consistent with the greater depth to basement south of the boundary in this view the southwestern florida mesozoic volcanic province sfmv may represent a part of a major triassic rift basin associated with the breakup of pangaea

sediment budget and transfer of suspended sediment from the gironde estuary to cap ferret canyon abstract a study of the particulate organic carbon content the grain size of suspended sediment and turbidity in a transect between the gironde estuary and cap ferret canyon indicates that particles from the gironde river are transferred to near the bottom of the canyon the separation of turbid estuarine water into bottom and surface nepheloid layers takes place in the gironde itself and in the nearshore zone the development of these two separate turbid layers is due to vertical a turbid surface plume and horizontal bottom layer salinity gradients the bottom nepheloid layer is caused primary by a horizontal supply of suspended sediment from the gironde rather than from resuspension or vertical sedimentation as suggested by other workers on the median and outer shelf the distribution of particles in the water column is influenced by thermal stratification the thickness of the bottom nepheloid layer increases from the estuary towards cap ferret canyon as a function of the thickness of the bottom waters detached nepheloid layers are observed at the shelf break coinciding with isopycnal surfaces due to the presence of cold waters in the cap ferret canyon superimposed advective inputs from the northern part of the shelf and resuspension of particles from mud patches contribute to the supply of particles towards the canyon suspended sediment in transit over the shelf break represents 2 3 of the total discharge from the gironde estuary this is a considerable amount as 50 of the suspended sediment is trapped in the west gironde mud patch and another undefined portion of the gironde sediment load is transported along the coast by tidal currents

tidal influence on suspended sediment distribution and dispersal in the northern andaman sea and gulf of martaban abstract surface and water column profiles of suspended matter collected during april may 2002 and satellite images were used to study factors influencing suspended sediment concentrations sscs and dispersal in the northern andaman sea and gulf of martaban one of the largest highly turbid areas of the world s oceans perennial high ssc in the gulf of martaban is due to a combination of factors including resuspension of sediments by strong tidal currents shallow bathymetry and seasonal sediment influx from rivers from satellite images it was observed that in the central portion of the gulf of martaban the turbidity front oscillates about 150 km in phase with spring neap tidal cycles and the area covered by the turbid zone ssc 15 mg l 1 increases from less than 15 000 km2 during neap tide to more than 45 000 km2 during spring tide the sediment discharged by the ayeyarwady river is transported mainly eastward along the coast into the gulf of martaban occasionally during the winter monsoon period sediment plumes are seen heading westward into the bay of bengal turbidity profiles show that bottom nepheloid layers are actively transporting some of the sediments into the deep andaman sea via the martaban canyon

sediment transport off the huanghe yellow river delta and in the adjacent bohai sea in winter and seasonal comparison abstract based on the data on the current velocity water temperature salinity turbidity and concentration of suspended sediment collected in november 2006 along three survey transects at three time series ship based stations off the huanghe yellow river delta and at twenty four grid survey stations in the adjacent bohai sea sediment transport off the huanghe delta and in the adjacent bohai sea under winter regime were studied and compared with those from the summer season the homogeneous distribution of salinity temperature and sediment in the water column indicated a well mixed body of water a zone of high suspended sediment concentrations ssc 100 mg l 1 with a width of 35 km was identified along the delta coast two highest ssc centers were found in the surface and middle water layers around the abandoned diaokou huanghe river mouth and the present huanghe river mouth and the third one in the bottom layer around the abandoned qingshuigou huanghe river mouth these three highest ssc centers become major sediment source areas in winter based on the location of the high bottom shear stress zone the prevailing wave directions and the protuberant topography of the river mouths we identified the resuspension origin of the three highest ssc centers caused mostly by the winter storm waves partially by tidal currents suspended sediment flux ssf along the three coastal transects indicated that the sediment in the northwest part of the delta was transported northeastward and southeastward along the coast of the recent delta lobe the ssc and ssf were higher in winter than summer by 1 7 27 1 and 2 122 5 times respectively except around the present river mouth this indicates that the intensity of sediment transport in winter is much stronger than in summer due to the powerful effect of winter storms although the river water and sediment discharges to the sea were much greater in summer the massive huanghe sediment to the sea was accumulated in a narrow coastal area due to weak hydrodynamics in summer and then strongly resuspended mostly by storm waves in winter and transported to the offshore area the coastal area off the huanghe delta acts as a sediment sink in summer and converted to be a sediment source in winter in response to the seasonal variation of the east asian monsoon in this region the erosion accumulation pattern of the huanghe subaqueous delta from 1976 to 2003 illustrates that river laden sediment is deposited mainly in the southern part off the coastal area and it is also the result of intensive southward sediment transport in winter

precise u pb zircon ages from alderney channel islands growing evidence for discrete neoproterozoic magmatic episodes in northern cadomia the northernmost exposures of rocks formed during the late neoproterozoic cadomian orogeny in the channel islands northern france region occur on alderney the island mainly comprises foliated quartz diorite once considered to be 2 ga pre cadomian basement and an undeformed basic to intermediate plutonic complex a precise age of 610 2 ma based on u pb analyses of single and small groups of zircons for the foliated fort tourgis quartz diorite demonstrates that the oldest rocks were emplaced and deformed during a cadomian magmatic event the age is virtually identical to ages from similar foliated syntectonic quartz diorite bodies on the islands of guernsey and sark and at la hague north normandy indicating that this magmatic and deformational event was regional in extent discordant zircon xenocrysts define an upper intercept age of c 2 ga indicating the presence of palaeoproterozoic basement at depth single zircons from the undeformed bibette head granodiorite give a precise u pb age of 572 1 ma this age is closely similar to that for the emplacement of the northern igneous complex of guernsey the emerging data indicate that cadomian magmatism in the northern channel islands region was not a protracted continuum but occurred during two distinct short lived events separated by c 30 40 my

origin and morphosedimentary evolution of fine grained modern continental shelf deposits the gironde mud fields bay of biscay france the gironde mud fields are thin blankets 4 m that extend from the inner to mid shelf over a restricted area 600 km 2 and overlie palimpsest sands and gravels seaward of the modern gironde estuary south western france the bulk of the mud has accumulated over the last two millennia and reflects the complex interactions of 1 an increasing estuarine supply of suspended particulate matter 2 resuspension of substrate material by storm events and 3 biological mixing the combination of these processes has produced various features within the deposits related to 1 the water depth and distance from source of the fine grained material which are manifested as a proximal distal cross shelf trend from an area of alternating mud sedimentation temporary after large river flows with resuspension by storm events to an area of mud accumulation in deeper water where bioturbation predominates 2 expansions of the mud depocentres over time such that they become more remote from sources of coarser shelf sediment resulting in an upward fining trend the lithofacies of the gironde shelf mud fields exhibit a number of similarities to those of larger scale modern muddy shelves and ancient shallow water mudrocks this work provides a detailed description of a facies model for fine grained shelf sediments deposited under relatively constant sea level

tectonomagmatism in continental arcs evidence from the sark arc complex abstract the island of sark channel islands uk exposes syntectonic plutons and country rock gneisses within a precambrian cadomian continental arc this sark arc complex records sequential pulses of magmatism over a period of 7 ma ca 616 609 ma the earliest intrusion ca 616 ma was a composite sill that shows an ultramafic base overlain by a magma mingled net vein complex subsequently deformed at near solidus temperatures into the amphibolitic and tonalitic tintageu banded gneisses the deformation was synchronous with d 2 deformation of the paragneissic envelope with both intrusion and country rock showing flat top to the south ls fabrics later plutonism injected three homogeneous quartz diorite granodiorite sheets the creux moulin pluton 150 250 m ca 614 ma the little sark pluton 700 m 611 ma and the northern pluton 500 m 609 ma similar but thinner sheets in the south derrible hogsback dixcart and west port es saies brecqhou are interpreted as offshoots from the creux moulin pluton and little sark pluton respectively all these plutons show the same ls fabric seen in the older gneisses with rare magmatic fabrics and common solid state fabrics recording syntectonic crystallisation and cooling the cooling rate increased rapidly with decreasing crystallisation age 9 ma for the oldest intrusion to cool to lower amphibolite conditions 7 8 ma for the creux moulin pluton 5 6 ma for the little sark pluton and 2 the initiation of the d 2 event is suggested to have been a response to the intrusion of the tintageu magma which promoted a rapid increase in strain rate 10 14 s 1 that focussed extensional deformation into the sark area the increased rates of extension allowed ingress of the subsequent quartz diorite granodiorite sheets although strain rate slowly declined as the whole complex cooled during exhumation the regional architecture of syntectonic cadomian arc complexes includes flat lying sark type and steep guernsey type domains produced synchronously in shear zone networks induced by oblique subduction a pattern seen in other continental arcs such as that running from alaska to california

grain size relationship between suspended matter originating in the gironde estuary and shelf mud patch deposits abstract the grain size variations of the elementary fraction without aggregates of gironde suspended matter during its transfer to the shelf were analyzed and compared with those of the surficial sediment of the west gironde mud patch located between water depths of 30 and 70 m which is considered as a preferential deposition area for estuarine suspended matter sm the results made it possible to show that two processes complicate the relationships between the estuary and the shelf a biogenic contribution identified as early as at the gironde outlet corresponding to a mode at 15 20 m in the sm of the turbid plume and an inorganic contribution of a fine grained fraction coming from sandy shelf deposits corresponding to micas with a mode at 50 60 m and settling on the inner part of the mud patch the nourishment of the western and deeper part of this mud patch by estuarine suspended matter is derived from the benthic nepheloid layer in terms of grain size distribution this supply is characterized by the 7 5 m mode which is typical of particulate matter originating in the gironde estuary