landform regolith mapping in the west african context abstract in this paper we present an integrated landform regolith mapping protocol chart for west africa developed using a case from central burkina faso the chart accounts for i the specificities of the ubiquitous duricrust capped remnants of the regional paleolandsurfaces particularly the residual or detrital character of the fe duricrusts and ii the diversity of the remaining non duricrusted portions of the landscape with an emphasis on the pitfalls encountered in determining the in situ or transported character of the regolith the paper also provides field identification criteria and illustrations of the typical west african landform regolith associations the landform regolith mapping chart is integrated into a prospectivity chart which is used to define exploration guides i defining sampling strategies ii interpreting potential geochemical anomalies and iii targeting lateral extensions of known bedrock mineralizations the mapping protocol further allows for the definition of a class of landform regolith association propitious to supergene mineral concentrations the mapping protocol is shown to be transposable to wetter contexts and more generally to other tropical shield provinces

phosphorus cycling in sediments of the bohai and yellow seas using a box sampler surface and core sediment samples were collected from the bohai and yellow seas in 1998 1999 the sediments were sequentially extracted to determine six phosphorus fractions and non sequentially extracted for total p tp and inorganic p ip where the difference between tp and ip was assumed to be organic p op it was found that more than 70 of the total p is inorganic p the concentrations of phosphorus were high near the river mouth reflecting the influence from the huanghe and changjiang sediment loads the phosphorus levels in the bohai sea are higher than those in the yellow sea which is related to the sediment sources and distribution of chlorophyll a in these areas concentrations of tp in the bohai and yellow seas are comparable to the other worldwide coastal areas among the six forms of phosphorus phosphorus distribution ranges were 0 8 2 for loosely sorbed p 3 10 for iron bound inorganic p 4 19 for leachable organic p 3 15 for authigenic apatite 35 66 for detrital apatite and 14 36 for refractory organic p potentially bioavailable phosphorus accounts for a small amount of tp while phosphorus load associated with eroded soil may be larger than the anthropogenic load the regeneration of dissolved p from sediments is a slow process which could play a role in maintaining low phosphate levels in the seas most of the phosphorus was regenerated in a water column and almost all of the remaining phosphorus was buried in the sediments after its accumulation the high values of p burial efficiencies in the study areas were related to low benthic phosphate flux which is due to the high percent of detrital apatite that is not bioavailable and the high sediment accumulation rate

element concentration and formation of ore deposits by weathering abstract most important supergene ore or mineral deposits are those of al fe mn cu ni co and residual minerals au pge ree nb w sn cr ti minerals phosphates diamond during earth history directed trends of weathering are observed which depend on the following parameters tectogenesis and morphogenesis and evolution of the atmosphere and the biosphere several at least three cycles of weathering can be distinguished during early precambrian late precambrian paleozoic and meso cenozoic times the weathering cycle of the mesozoic cenozoic times is described here each weathering cycle starts under special world wide conditions which are marked by monotonous and flat relief by greenhouse effect and by an initial lateritic sequence followed by increasing differentiation of the weathering sequences the initial lateritic weathering provokes the main process of rock decomposition developing profiles with a thickness of several tens of metres the vertical and lateral variations of the profiles and therewith the quality pattern of ore deposits mainly depend on 1 morphology and drainage during the initial weathering low drainage activity which causes very thick saprolites with a lower smectitic and an upper kaolinitic zone optimal drainage restricts saprolite evolution favouring the formation of thick box horizons 2 lateritic cementation by chemical displacement and neoformation of textures during a progressive stage of lateritisation 3 mid tertiary to quaternary changes of climate and morphology produce a laterite degradation followed by erosion and or resedimentation accompanied by mainly lateral mechanical and or chemical displacement of element or mineral concentrations the evolution of laterites on parent rocks with preconcentration of certain elements leads to their destruction and reorganisation of geochemical provinces in new supergene element associations by relative or absolute enrichment creating special supergene geochemical provinces

roles of sorption and tube dwelling benthos in the cycling of phosphorus in bering sea sediments adsorption of dissolved phosphate onto iron hydroxides has been shown to be one of the primary regulators of phosphorus cycling in sediments bioturbation and bioirrigation by benthic infauna modify this cycling by accelerating the transport of dissolved and particulate phosphorus and by changing rates of reactions that occur in the sediment such as the adsorption of phosphate by amorphous iron hydroxides hydrographic processes vary regionally in the bering sea and nutrient exchange between the sediments of the broad shallow shelf and overlying water may influence water column productivity these characteristics make the bering sea a good study site for examining the processes that influence sedimentary cycling of phosphorus to examine these processes we collected samples in four domains southern middle shelf southern outer shelf southern off shelf consisting of the continental slope and bering sea basin and northern bering shelf based on hydrographic regime at each station we directly measured phosphate flux and sediment oxygen consumption using whole core incubations we also measured infaunal burrow abundances amorphous iron hydroxide concen trations and phosphate sorption we found that three out of the four domains had a high affinity for trapping phosphate in the sediment as indicated by their adsorption coefficients 6 59 81 81 however the measured phosphate fluxes could not be explained by the adsorption capacity of the sediment alone the results indicated that on the middle shelf the phosphate flux positively co varied with infaunal burrow abundances the high number of organisms in this domain 10 32 burrows per 50 cm

geomorphic and stratigraphic analysis of fire island new york abstract barrier islands along the east coast of the united states are believed to be migrating landward in response to sea level rise modes and rates of displacement of fire island along the south shore of long island n y were investigated through geomorphic and stratigraphic analyses inlet processes are principally responsible for bayshore sediment accretion and hence landward displacement while overwash has contributed to increasing the island s elevation portions of marsh areas covered by washover deposits were often raised above the tidal level permitting colonization by barrier flat vegetation photographic analysis showed that only the 1938 hurricane resulted in bayshore accretion by washover a small amount at one locality most of the bayside marshes formed on relict flood tidal delta shoals former inlet sites are characterized by typical geomorphic features including relict inlet ridges indentation of the bay shoreline wide marsh plains and relict flood tidal delta islands in the bay historical records and relict inlet features indicate that as much as 85 of the area has been affected by inlet activity the geomorphic and vegetative data supported by the stratigraphic interpretations showed that the western section of fire island n y is migrating landward more slowly than the eastern section of the barrier chain this trend is probably due to hurricane tracks and to an increased sediment supply to the western part barrier migration is occurring continuously over geologic time but considered on a short term basis displacement is sporadic and related to inlet processes over the past 1000 years fire island has experienced shoreface erosion as well as bayshore erosion and submergence

petrologie du gisement lateritique manganesifere d azul bresil at azul state of para brazil the lateritic weathering of organic shales with rhodochrosite and phyllosilicates mainly muscovite has led to one of the largest maganese deposits of brazil 45 mt of reserves with 42 65 mn

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

evidence for enhanced phosphorus regeneration from marine sediments overlain by oxygen depleted waters phosphorus regeneration and burial fluxes determined from in situ benthic flux chamber and solid phase measurements at sites on the californian continental margin peruvian continental slope north carolina continental slope and from the santa monica basin california are reported comparison of these sites indicates that o2 depleted bottomwaters enhance p regeneration from sediments diminishing overall phosphorus burial efficiency based on these observations a positive feedback linking ocean anoxia enhanced benthic phosphorus regeneration and marine productivity is proposed on shorter timescales these results also suggest that o2 depletion in coastal regions caused by eutrophication may enhance p regeneration from sediments thereby providing additional p necessary for increased biological productivity

the phosphorus cycle in coastal marine sediments the concentration of dissolved phosphate in sediment box cores from the laurentian trough in the gulf of st lawrence increased sharply across the sediment water interface from 2 0 mol po4 1 in the bottom water to 6 3 mot po4 1 in the top cm remained almost constant at this value down to 5 15 cm depth and then increased rapidly with further depth in the region of constant concentration phosphate is buffered by sorption equilibria with the sediment the production rate of phosphate the sorption capacity of the sediment and the thickness of the diffusive boundary layer at the sediment water interface appear to control the shape of the pore water profile even though the buffering places an upper limit on the concentration gradient across the sediment water interface and hence on the flux the phosphate flux to the overlying water is controlled by the production rate of phosphate within the sediment a model is proposed to relate sediment chemistry to phosphorus fluxes

controls on phosphorus regeneration and burial during formation of eastern mediterranean sapropels the carbon c and phosphorus p geochemistry of sapropels from four sites in the eastern mediterranean sea was determined to obtain more insight into the role of differences in sediment accumulation rates and bottom water anoxia on p regeneration and burial in sediments sediment corg porg with org organic ratios above redfield indicate enhanced regeneration of p relative to c from organic matter during formation of the most recent sapropel s1 and a pliocene sapropel odp site 969e i 282c release of p from fe oxides was relatively unimportant increased burial of ca p authigenic carbonate fluorapatite and or biogenic hydroxyapatite occurred but was of minor importance compared to the enhanced p release from organic matter for sapropel s1 corg porg and corg preac with reac reactive defined as the sum of organic fe bound authigenic and biogenic ca p ratios decreased with increasing sedimentation rate and oxygen exposure and decreasing water depth whether the water column in the deep basin was dysoxic semi euxinic s1 or euxinic pliocene does not appear to affect the estimated burial efficiencies of porg and preac enhanced corg burial under the euxinic water column explains the much higher corg porg and corg preac ratios in the pliocene sapropel on average 2860 and 760 respectively compared to sapropel s1 on average 530 and 160 respectively

nano mineralogy and geochemistry of high grade diasporic karst type bauxite from parnassos ghiona mines greece abstract in the present work a combination of various techniques is utilized for the study of nano mineralogy and geochemistry of high grade karst type bauxite al rich and fe depleted samples al2o3 ca 80 wt from the parnassos ghiona mines located in greece initial characterization using pxrd and electron microscopy in microscale and mesoscale sem eds including stem mode proved the presence of fe cr ti containing diaspore anatase and minor rutile the study by means of 57fe mossbauer spectroscopy in correlation with magnetic susceptibility measurements and complemented with synchrotron based spectroscopies at the microscale sr micro xrf and micro xanes exafs indicated that fe3 in contrast to 6 cr3 is not exclusively a component of the diaspore structure while cr3 substitutes al3 in octahedral sites of diaspore 6 cr3 6 al3 the electron microscopy in nanoscale tem eds eels revealed that fe exists in the form of peculiar fe3 bearing nanominerals most likely maghemite type phases between 25 and 45 nm in size in addition to the fe3 ions substituting al3 in the diaspore structure moreover it was proven that tio2 polymorph mineral nanoparticles particularly rounded anatase mesocrystals and nanocrystals and individual needle shaped rutiles are dispersed into the diaspore matrix thus diaspore in the studied bauxite concerns in fact a distinct fe3 cr3 alooh low t authigenic phase demonstrated for the first time in literature on the other hand the observed tio2 mineral nanoparticles formed together with diaspore during diagenesis and fe nanominerals formed during epigenesis were hitherto unknown not only for the allochthonous karst type bauxite deposits of greece but also for the overall bauxite deposits worldwide

miocene global change recorded in columbia river basalt hosted paleosols paleosols preserved between flows of the columbia river basalt province record hiatuses in basalt emplacement and provide detailed information about paleoclimatic and pedogenic conditions during pedogenesis the relatively long duration of pedogenesis 104 to 106 yr for these paleosols makes them unlikely to have been influenced by short duration climate fluctuations and allows them to accurately reflect long term climate trends related to global climate change ten paleosols hosted by the grande ronde and wanapum formations of the columbia river basalts were identified on the basis of pedogenic features such as horizon development root traces and saprolitization and they were studied as paleoclimatic indicators relationships between the ages of the paleosols and their clay mineral compositions suggest that pedogenic processes changed in the eastern columbia river basalt province at ca 15 8 ma analyses of mass balance trends and chemical alteration in a ca 16 0 ma paleosol indicate that it formed under warm humid climate conditions we suggest that the absence of similar warm humid paleosols and the presence of 2 1 clay rich paleosols that formed after ca 15 8 ma represent a cooling and drying climate change related to the termination of the middle miocene climate optimum a development not previously captured in paleosol studies in addition the well constrained dates of the basalts provide better resolution on the timing of this termination when combined with other middle miocene paleoclimate estimates from the columbia river basalt province our results suggest a geographic control on mean annual precipitation in the middle miocene columbia river basalt province leading to an increasing to the east precipitation gradient

sedimentary iron phosphorus cycling under contrasting redox conditions in a eutrophic estuary abstract phosphorus p is often a limiting nutrient within freshwater and estuarine systems thus excess inputs of p from anthropogenic activities dominantly agriculture can induce eutrophication in receiving water bodies the sequestration of p within estuarine sediments is controlled by sorption and precipitation processes which are impacted by local redox conditions and burial environment despite the global spread of oxygen depletion in coastal marine systems p burial under reducing conditions remains poorly understood we investigated p cycling in relation to iron fe redox chemistry in sediments from the eutrophic peel harvey estuary in western australia using a combination of porewater analysis sequential chemical p extractions synchrotron based micro scale x ray fluorescence mapping and fe k edge x ray absorption spectroscopy and po43 sorption experiments the sediments represented redox regimes varying from strongly reducing organic rich sediments with little or no reactive fe iii oxyhydr oxides to oxygenated sediments that were enriched in reactive fe iii phases organic p and fe associated p were the main p burial phases and the latter was quantitatively important even in sediments with an overall strongly reducing character we attribute this to adsorption of p onto micro scale fe iii oxyhydroxide enrichments and or fe bearing clay minerals the organic rich sediments showed a strong decline in p contents with depth p was released from organic matter and fe phases but apatite precipitation was apparently inhibited in these sediments despite greater and stronger po43 sorption capacity the oxic sediments contained relatively little p due to a lack of the primary p source in marine sediments organic matter our results provide detailed insight into p burial in dynamic estuarine sediments and show that micro scale spectroscopic analyses greatly advance our understanding of p sequestration processes

west african lateritic pediments landform regolith evolution processes and mineral exploration pitfalls this paper is a contribution to the understanding of surface dynamics of tropical shields over geological timescales emphasis is put on the fundamental and applied implications of regolith production and dispersion processes through the formation dissection and preservation of landforms it is based on the case study of sub saharan west africa which recorded neogene 24 3 ma stepwise dissection of its topography through the emplacement of three lateritic pediment systems which still occupy most of its surface pediments are erosional transportation slopes having been weathered and duricrusted pediment regolith associations therefore depend on the parent rock transport dynamics and preservation of the material having transited on their surface as well as on the intensity of their weathering duricrusting iron oxy hydroxide cemented clastic sediments detrital ferricretes and unconsolidated clastic sediments are the dominant outcropping material and as such represent a challenge for mineral exploration that relies on surface geochemical sampling to detect metal concentration in the bedrock landform regolith mapping beyond the scale of modern interfluves combined with paleolandscape reconstitution are relevant to provide exploration guides for i interpreting geochemical anomalies on pediments ii tracing their potential source when they have been transported on pediments and iii targeting suspected ore bodies concealed beneath pediment s past and present latitudinal climatic zonation of pedimentation and weathering patterns suggests a gradation of pedimentation process across the intertropical zone and explains why pediments may have been overlooked in equatorial environments with implications for mineral exploration successive pediment systems adapted to uneven knickzone bearing river networks producing a spatially consistent and reduced 80 m stepping pattern of pediments independent from elevation or distance to base level pediments pediplains are therefore not proxies of uplift and their preservation over geological timescales typifies regions submitted to 10 m my erosion rates the identification and study of lateritic pediments bear important implications on shield sediment routing systems and a better access to the bedrock and its resources which may still be underestimated in the tropics

phosphorus diagenesis in sediment of the thau lagoon we describe the depth distribution of phosphorus in relation to the distribution of major redox species dissolved o2 n o 3 n h 4 mn and fe and particulate s organic c reactive mn and fe oxides in modern sediments of two stations in the thau lagoon sediments close to the oyster bank zone are enriched in organic carbon and are highly bioturbated while those outside the bank are less bioturbated and organic carbon levels are lower in all sites early diagenesis follows the well accepted depth sequence of redox reactions of organic matter mineralization the upper sediments of the station enriched in organic carbon contain high amounts of reactive particulate organic phosphorus that arrives at the sediment surface through biodeposition only a part of this phosphorus is released to the bottom water after mineralization since more than 50 of total p is buried as an authigenic phosphate mineral in the middle of the lagoon outside the oyster bank zone organic matter seems to be much more refractory but the distribution of the major redox compounds indicates that this organic matter is partially mineralized a portion of the phosphate and ammonium released during mineralization does not escape the sediment since the concentration gradient is close to zero between 1 and 25 cm depth below the sedimentewater interface pore water n and p are likely fixed by biological uptake the characterisation and magnitude of this process require further study 2006 elsevier ltd all rights reserved

a comparative study of manganese dynamics in the water column and sediments of intertidal systems of the north sea abstract the dynamics of the redox sensitive trace metal manganese mn and its response to biological activity were investigated in the water column and shallow pore waters of the german wadden sea southern north sea in 2008 and 2009 two systems one from the southern backbarrier area of spiekeroog island and one from the eastern part sylt romo wadden sea of the german bight were compared the major aim was to examine to which extent biogeochemical findings are specific for a particular tidal basin or transferable to other basins of the german wadden sea although both study areas reveal hydrodynamical sedimentological and ecological differences qualitatively pronounced similarities in mn dynamics are observed thus complex cycling of dissolved mn with increasing values in spring and late summer due to elevated biological activity as well as a depletion period in early summer were observed in both study areas this finding suggests a seasonal behaviour of mn being generally representative for the tidal basins of the southern north sea quantitative differences are significant as the backbarrier area of spiekeroog island shows much higher concentrations of dissolved mn in the water column especially during spring we suggest that this difference is due to a larger sediment area water volume ratio in the spiekeroog backbarrier area combined with a higher release of dissolved mn from the tidal flat sediments as seen in pore water profiles from surface sediments site specific differences are also seen in further tidal systems of the north frisian wadden sea which are characterised by individual hydrodynamical and sedimentological conditions several transects leading from offshore locations towards the coast also revealed a highly variable mn level overall the north frisian wadden sea most likely represents a less important source for dissolved mn than the east frisian wadden sea furthermore our data suggest that site specific properties of the different tidal basins have to be considered in budget calculations for the entire wadden sea

analysis of barrier island surface sediments by scanning electron microscopy abstract the analysis of quartz grain surface microtextures from a sedimentary environment where grain transport and depositional pathways were closely interconnected allowed insight into subtle microfeature alteration during movement between subenvironments four fire island new york and one montauk point beach sample were analysed principally through use of a checklist approach using 36 common surface features beach overwash floodtidal delta dune and inlet grains displayed similar surface features only the latter two samples displaying distinctive microtextural patterns the pattern of development of inlet grains was related to the application of higher shear stresses on the grains during transport in the shallow channel the results from dune grains testify to the effectiveness of aeolian transport mechanisms in rapidly altering existing features glacially derived microtextures altered by subsequent subaqueous action were prevalent but whether these glacial microfeatures are derived from the headland region montauk point or from a closer offshore glacial lobe source is not determined comparison of offshore lobe and adjacent sediments revealed contrasting surface and morphological differences statistical treatment of checklist data in binary form 1 0 using stepwise discriminant analysis proved workable but more rigorous testing is required to prove its relevance and use in deciphering raw textural data

iron sulfur phosphorus cycling in the sediments of a shallow coastal bay implications for sediment nutrient release and benthic macroalgal blooms we conducted a study to determine the seasonal relationship between iron sulfur and phosphorus in the upper sediments and pore waters of a shallow intercoastal bay from april 1999 to september 2000 sediment cores were collected from rehoboth bay delaware analyses of the sediments in the upper 4 cm revealed that redox conditions controlled fe s p concentrations in the sediments pore waters and overlying water monthly sampling showed a marked decrease in the reactive solid phase p pool ascorbate leachable fraction asc p and sharp increases in soluble p measured as po in pore waters and overlying waters as the conditions became more reducing through32 4 out the summer months these changes were paralleled by decreases in the amorphous fe iii ascorbate leachable fraction asc fe and total fe iii oxyhydroxide pools dithionite extracted fraction fe iii oxide and increases in solid fes fes2 the release of soluble p from sulfidic sediments to oxygenated overlying waters only occurred during periods of solid fes fes2 production which indicates that fe iii oxides act as a barrier to diffusive p flux during these anoxic conditions the regenerative p appears to induce secondary benthic algal blooms and promotes eutrophication in these inland bays through late summer by the late fall and into early spring sulfide production diminished and oxic conditions were reestablished as indicated by increases in solid amorphous and crystalline fe iii oxides and decreases in fes fes2 concentrations during this period increasing asc fe concentrations correlated with increases in asc p concentrations and decreases in pore water po the seasonal correlations 32 4 between fe s p indicate that fe redox chemistry controls sediment p flux to the overlying water column

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

the interrelation and distinction between flood tidal delta and washover deposits in a transgressive barrier island abstract the distinction and interrelation between flood tidal delta and washover deposits is described by comparing back barrier sands associated with an active and a relict tidal inlet system on the south shore of long island guidelines for comparison include three dimensional morphology sedimentary structures sediment texture and facies sequences the active modern flood tidal delta is covered by reversing small scale ripples represented by bidirectional small scale cross bedding in the subsurface large scale flood oriented cross beds are associated with non reversing sand waves on the flood ramp the relict flood tidal delta is represented by medium to fine grained sands characterized by small scale cross bedding or massive bedding relict flood tidal delta deposits are overlain by distinct washover deposits separated by thin units of salt marsh peat dominant washover structures are parallel laminations well preserved roots are commonly found in washover sands but are largely absent in flood tidal delta sands facies sequences of the relict inlet system indicate that flood tidal delta deposits extend the width of the barrier island overwashing serves to infill abandoned channels of the delta and contributes to vertical buildup

les mineralisations manganesiferes volcano sedimentaires du blafo gueto cote d ivoire parageneses alteration climatique les indices manganesiferes des collines blafo et gueto sont rencontres dans les quartzites et les schistes sericiteux associes aux epanchements rhyolitiques d une serie volcano sedimentaire birrimienne la mineralisation epigenetique est une impregnation d oxydes de fer goethite et de manganese essentiellement mno2 cryptomelane et nsutite surimposee a une paragenese initiale a magnetite pyrophanite et localement ottrelite et grenat l alteration meteorique n a provoque de transformations notables que dans les materiaux associes a deux surfaces d aplanissement l une est conservee sous forme de petits temoins bauxitises au sommet des collines et des minerais enrichis sont associes a la gibbsite et la kaolinite l autre est un glacis de piemont et le manganese s y disperse dans une cuirasse ferrugineuse

characteristics and origin of coarse gold in late pleistocene sediments of the cariboo placer mining district british columbia canada the cariboo placer mining district 1000 km2 sited in the interior plateau of central british columbia canada is the premier placer gold mining district of the province gold is recovered from three late pleistocene sedimentary facies postglacial fluvial gravels 25 ka this study reports the morphology size roundness sphericity of 1636 gold grains ranging in size from 0 25 to 17 mm recovered from 19 placer mines older gravels contain the smallest gold grains mean grani size 1 53 mm grains of intermediate size occur in till 2 23 mm and the coarsest gold occurs in postglacial gravels 2 34 mm with a mean of 1 93 mm for the mining district as a whole the most common grain shapes are sub rounded discoidal 14 73 of the grain population sub angular discoidal 10 88 and sub rounded sub discoidal 9 59 the most angular grains occur in postglacial gravels in situ growth of coarse angular grains is indicated by a composite grain structure consisting of aggregates of gold particles welded together by high grade ag 2 filamentous gold in situ coarsening may be reliant on organic complexing agents produced below a dense forest cover an evolutionary sequence of grain form from angular aggregates to rounded pumpkin seed grains is suggested rounded grains commonly show a crystalline structure which may result from the cold hammering of gold during transport fracturing along crystal boundaries is common gold grains may undergo cycles of coarsening rounding diagenesis and breakup in response to repeated recycling through pleistocene sedimentary environments

the role of adsorption in sediment water exchange of phosphate in north sea continental margin sediments the effect of adsorption on the sediment water exchange of po was investj gated in sediments from four different types of sedimentary environments in the southern and eastern north sea in august 1991 and february 1992 nonlinear adsorption isotherms for oxidized sediment from eight stations indicate that north sea sediments differ widely in their capacity to adsorb po a good correlation between the value of the adsorption coefficient and nh oxalate extractable fe was observed a combination of the adsorption data with porewater po profiles solid phase results and measured and calculated rates of sediment water exchange of po for 15 stations in both august and february indicates that adsorption plays an important role in controlling sediment water exchange of po during at least a part of the year in three of the four north sea environments at most stations po adsorption constrains the flux of po to the overlying water at one station in the depositional environment of the skagcrrak however desorption is responsible for the maintenance of a flux of po to the overlying water a one dimensional reactiondiffusion model describing porewater po and solid phase p profiles was de deloped and applied to results for two stations the model results show that both enhanced retention and enhanced release of po can be adequately described when simultaneous equilibrium and first order kinetic reversible adsorptive reactions are assumed

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

enhanced regeneration of phosphorus during formation of the most recent eastern mediterranean sapropel s1 phosphorus regeneration and burial fluxes during and after formation of the most recent sapropel s1 were determined for two deep basin low sedimentation sites in the eastern mediterranean sea organic c p ratios and burial fluxes indicate enhanced regeneration of p relative to c during deposition of sapropel s1 this is largely due to the enhanced release of p from organic matter during sulfate reduction release of p from fe bound p also increased but this was only a relatively minor source of dissolved p pore water hpo4 concentrations remained too low for carbonate fluorapatite formation an increased burial of biogenic ca p i e fish debris was observed for one site estimated benthic fluxes of p during sapropel formation were elevated relative to the present day 900 to 2800 vs 70 to 120 mol m 2 yr 1 the present day sedimentary p cycle in the deep basin sediments is characterized by two major zones of reaction 1 the zone near the sediment water interface where substantial release of hpo4 from organic matter takes place and 2 the oxidation front at the top of the s1 where upward diffusing hpo4 from below the sapropel is sorbed to fe oxides the efficiency of aerobic organisms in retaining p is reflected in the low organic c p ratios in the oxidized part of the sapropel burial efficiencies for reactive p were significantly lower during s1 times compared with the present day 7 to 15 vs 64 to 77 budget calculations for the eastern mediterranean sea demonstrate that the weakening of the antiestuarine circulation and the enhanced regeneration of p both contributed to a significant increase in deep water hpo 4 concentrations during sapropel s1 times provided that sufficient vertical mixing occurred enhanced regeneration of p at the seafloor may have played a key role in maintaining increased productivity during sapropel s1 formation copyright 2002 elsevier science ltd

paleogene evolution of the burmese forearc basin and implications for the history of india asia convergence the geological history of the burmese subduction margin where india obliquely subducts below indochina remains poorly documented although it is key to deciphering geodynamic models for the evolution of the broader tibetan himalayan orogen various scenarios for the evolution of the orogen have been proposed including a collision of india with myanmar in the paleogene a significant extrusion of myanmar and indochina from the india asia collision zone or very little change in paleogeography and subduction regime since the india asia collision this article examines the history of the burmese forearc basin with a particular focus on eocene oligocene times to reconstruct the evolution of the burmese margin during the early stages of the india asia collision we report on sedimentological geochemical petrographical and geochronological data from the chindwin basin the northern part of the burmese forearc and integrate these results with previous data from other basins in central myanmar our results show that the burmese margin acted as a regular andean type subduction margin until the late middle eocene with a forearc basin open to the trench and fed by the denudation of the andean volcanic arc to the east we show that the modern tectonic configuration of central myanmar was formed 39 37 million years ago when the burmese margin shifted from an andean type margin to a hyper oblique margin the forearc basin was quickly partitioned into individual pull apart basins bounded to the west by a quickly emerged accretionary prism and to the east by synchronously exhumed basement rocks including coeval high grade metamorphics we interpret this shift as resulting from the onset of strike slip deformation on the subduction margin leading to the formation of a paleo sliver plate with a paleo fault system in the accretionary prism pull apart basins in the forearc and another paleo fault system in the backarc this evolution implies that hyper oblique convergence below the burmese margin is at least twice older than previously thought our results reject any india asia convergence scenario involving an early paleogene collision of india with myanmar in contrast our results validate conservative geodynamic models arguing for a close to modern precollisional paleogeography for the indochina peninsula and indicate that any postcollisional rotation of indochina if it occurred at all must have been achieved by the late middle eocene

sedimentary evidence of hurricane strikes in western long island new york 1 evidence of historical landfalling hurricanes and prehistoric storms has been recovered from backbarrier environments in the new york city area overwash deposits correlate with landfalls of the most intense documented hurricanes in the area including the hurricanes of 1893 1821 1788 and 1693 a d there is little evidence of intense hurricane landfalls in the region for several hundred years prior to the late 17th century a d the apparent increase in intense hurricane landfalls around 300 years ago occurs during the latter half of the little ice age a time of lower tropical sea surface temperatures multiple washovers laid down between 2200 and 900 cal yr b p suggest an interval of frequent intense hurricane landfalls in the region our results provide preliminary evidence that fluctuations in intense hurricane landfall in the northeastern united states were roughly synchronous with hurricane landfall fluctuations observed for the caribbean and gulf coast suggesting north atlantic wide changes in hurricane activity

phosphorus speciation in the sediment and mass balance for the central region of the great barrier reef continental shelf australia abstract solid phase p speciation has been determined in sediments from a transect across the central section of the continental shelf and slope of the great barrier reef gbr lagoon this region is characterized by a gradient of riverine aluminosilicate clay and silt nearshore seawards of which biogenic carbonate sediment predominates phosphorus speciation results show large variations along this transect organic p and authigenic apatite p are the major chemical forms of phosphorus in the central gbr continental shelf sediments post depositional reorganization of p was also observed converting organic p and iron bound p fe p to authigenic apatite p phosphorus burial rate was estimated from measurements of total p concentration and excess 210pb sediment mass accumulation rates burial efficiency varies significantly over the shelf inshore areas showed significant p remobilization from sediments to the water column up to 50 the mid and the outer shelf showed little evidence for remobilization except for coral reef platform sediments with more of the sediment p being in the less reactive authigenic apatite phases an appreciable fraction of this non labile authigenic apatite phase was identified as fish bone p sources and sinks over the central part of the gbr shelf were quantified using a mass balance approach this showed that coral sea shelf edge upwelling events are essential to satisfy the large p nutrient demand of the whole gbr lagoon p inputs due to upwelling events were greater than those contributed by local rivers over an average year

the distribution and chemical speciation of dissolved and particulate phosphorus in the bering sea and the chukchi beaufort seas abstract water samples were collected from the bering sea and the chukchi beaufort seas during the 4th chinese arctic research expedition in summer 2010 to examine the abundance spatial distribution and phase partitioning of phosphorus p between dissolved and particulate inorganic and organic phases measurements of p species included dissolved inorganic p dip dissolved organic p dop and five particulate p species operationally defined by sequential extraction techniques inorganic p was generally the predominant form of both dissolved and particulate p comprising on average up to 91 13 of the dissolved phase and 72 23 of the particulate phase in the study area concentrations of dip in the water column of the chukchi sea and bering sea were considerably higher than those in the beaufort sea 3 m vs 1 m showing a strong influence of north pacific inflow waters the percentage of dop in the dissolved p pool was generally higher in surface waters than deeper waters and higher in the chukchi sea than in the bering sea consistent with their difference in primary productivity and reflecting sources of dop from the surface waters within the particulate p pool the labile p and ferric bound p were the two predominant species especially in the upper water column

phosphorus recycling and burial in baltic sea sediments with contrasting redox conditions in this study redox dependent phosphorus p recycling and burial at 6 sites in the baltic sea is investigated using a combination of porewater and sediment analyses and sediment age dating pb 21

authigenic apatite formation and burial in sediments from non upwelling continental margin environments abstract evidence for precipitation of authigenic carbonate fluorapatite cfa in long island sound and mississippi delta sediments suggests that formation of cfa is not restricted to environments of active coastal upwelling we present porewater data suggestive of cfa formation in both these areas application of a sequential leaching procedure designed specifically to separate authigenic carbonate fluorapatite from other phosphorus containing phases including detrital apatite of igneous or metamorphic origin provides strong supporting evidence for authigenic apatite formation in these sediments the size of the authigenic apatite reservoir increases with depth indicating continued formation of cfa during early diagenesis this depth increase is mirrored by a decrease in solid phase organic p at both sites suggesting that cfa is forming at the expense of organic p mass balance considerations application of diagenetic models to interstitial water nutrient data and the saturation state of the interstitial water are consistent with this interpretation diagenetic redistribution of phosphorus among the different solid phase reservoirs is observed at both sites and results in near perfect retention of p by these sediments over the depth intervals sampled formation of cfa in continental margins which do not conform to the classically defined regions of phosphorite formation renders cfa a quantitatively more important sink than has previously been recognized including this reservoir as a newly identified sink for reactive p in the ocean the residence time of p in the modern ocean must be revised downward the implication for ancient oceans of cfa formation in continental margin sediments other than phosphorites is that phosphorite formation may be less a representation of episodicity in removal of reactive p from the oceans than of localized concentration of cfa in phosphatic sediments by secondary physical processes

geology of microtidal coastal lagoons rhode island abstract the coastal lagoons of rhode island are contained behind narrow 200 300 m wide barrier spits in a microtidal wave dominated environment the major depositional environments within the lagoons are 1 flood tidal deltas 2 subtidal storm surge platforms and 3 back lagoon low energy basins the pathways of sediment influx into the coastal lagoons are 1 tidal inlets breachways 2 temporary storm surge channels cut through the barrier spits and 3 overwash transport of sand that crosses the spits and builds into the lagoons sediment transport in the lagoons is caused by currents generated by windshear within the lagoon basins and by storm surge generated flow both of which may be additive to tidal currents lagoonal sedimentation was initiated in ninigret pond approximately 4100 b p based on radiocarbon dating as low energy basins developed on an uneven pleistocene glaciofluvial surface tidal delta sedimentation began approximately 2500 b p the continued existence of the lagoons is dependent on rate of infill and barrier retreat versus rate of sea level rise based on long term sea level rise past 2500 years calculations indicate that the lagoons will decrease in size as sediment influx exceeds the rate of inundation

the applicability of the gibbs equation for grain settling velocities to conditions other than quartz grains in water abstract gibbs et al 1971 have derived empirical equations that yield settling velocities in water for spherical grains of approximately quartz density the present investigation examines the applicability of their relationships to other grain densities fluids and to gravity fields other than earth s the comparison is with data generated from a standard drag coefficient versus reynolds number curve that is applicable to the settling of spheres in any newtonian fluid this comparison shows that the gibbs et al relationships cannot be used for gravity fields other than earth s or for fluids other than water in each case the errors being extreme their relationships do yield good results over the range of grain densities represented by the common heavy minerals settling in water as the density progressively departs from that of quartz the amount of error increases reaching 8 5 percent for densities as high as magnetite a correction factor is introduced which is a function of grain density the use of which greatly improves the estimated settling velocities of the common heavy minerals and of low density materials such as foraminifera shells

phosphogenesis and active phosphorite formation in sediments from the arabian sea oxygen minimum zone in this study porewater chemistry solid phase analysis and microscopic observations were combined to evaluate phosphogenesis in three boxcores located within the intensive oxygen minimum zone of the arabian sea three parameters namely a decrease of the dissolved phosphate and fluoride concentrations with depth saturation with respect to carbonate fluorapatite and the presence of a solid phase ca phosphate mineral all indicate that phosphogenesis is currently taking place at all three sites authigenic apatite precipitation rates vary between 0 076 and 1 04 molp cm 2 yr 1 and are of the same order of magnitude as reported for other high productivity areas precipitation of an intermediate precursor precedes francolite formation in the continental slope sediments on the karachi margin results of a diagenetic p model indicate that phosphogenesis is induced by high rates of organic matter degradation dissolution of fish debris is likely to provide a substantial additional source of phosphate redox iron cycling does not influence phosphogenesis in these environments model results suggest that sediment mixing is essential in promoting early diagenetic phosphogenesis the highest rate of francolite formation was observed in a boxcore taken on the oman margin where it contributes to the formation of a holocene phosphorite deposit this observation contrasts with previous reports of only old phosphorites in this area phosphorites are presently forming on the oman margin as a result of a deposition of older reworked material from the continental shelf which has undergone an earlier phase of phosphogenesis b a high input of reactive p fish debris and degradable organic matter c a relatively low sediment accumulation rate and d the absence of winnowing on this location holocene phosphorite deposits may be less common on the oman margin than in other coastal upwelling areas because of the narrowness of the shelf and the steepness of the slope which limit the area where phosphorite formation may occur

washover fans a modern geomorphologic analysis and proposed classification scheme to improve reservoir models abstract washover fan deposits are part of a much larger system of highly heterolithic barrier and shoreline margin deposits which form notoriously hard to produce hydrocarbon reservoirs this survey of modern fan morphologies identifies common fan geometries considers the preservation potential and range of probable geometries of fan facies in subsurface datasets and outcrops and aims to improve hydrocarbon recovery in barrier island reservoir systems we use satellite imagery to conduct a spatial analysis of 118 modern fans to quantify attributes of fans including throat width intrusion length fan area and barrier island width a new classification scheme for fans is proposed that refines the current fan model in this classification fans are initially divided into channelized and non channelized fans channelized fans are subdivided according to the location of primary deposition barrier depocenter or lagoonal depocenter non channelized fans are subdivided based on morphology dissipative lobate or apron sourced quantitative cross plots of morphologic parameters are analyzed to define geometric relations in fan morphologies the probability of identifying fans in the subsurface is discussed our results indicate that the most commonly used model for a washover fan the 52 km2 st joseph island fan is anomalous and does not reflect the most common sizes or geometries of washover fans we suggest that our classification be used instead to capture the range of fan morphologies although our study encountered non channelized line sourced lobate washover fans with an area of less than 1 km2 more frequently than any other types of fans washover fans exhibit diverse morphologies therefore the entire range of washover fan morphologies should be considered when interpreting exploration data and looking to identify washover fans in the subsurface

lateritic bauxite in central germany and implications for miocene palaeoclimate intense chemical weathering during middle miocene times led to the formation of deep ferralitic weathering profiles on the vogelsberg basaltic massif saprolite more than 50 m thick was formed and in its higher parts bauxite concretions developed by absolute accumulation of aluminium the tops of the profiles consist mostly of allochthonous lateritic bauxite which has been mined intensively in the past similar high latitude bauxites occur on the paleogene basalts of ireland these formed during a phase of recognized greenhouse conditions with a climatic optimum near the paleocene eocene boundary while during the miocene the climate was already changing toward quaternary icehouse conditions however the occurrence of deep weathering profiles with lateritic bauxite at the high palaeolatitude of 45 n may be interpreted as pointing to extreme climatic conditions also during the middle miocene the associated laterites and bauxites on middle miocene basalts 17 15 ma provide evidence for a global climatic optimum around 17 14 5 ma reduced uplift rates of the himalayan tibetan plateau and associated reduced co2 consumption coupled with additional volcanogenic co2 production could have induced high atmospheric co2 and an intensification of the global greenhouse effect this may be reflected in accelerated chemical weathering and bauxite formation basalt volcanism has thus provided both a source eruption and a sink via weathering of co2

origin distribution and accumulation of organic carbon in the skagerrak abstract organic carbon contents have been determined in grain size fractions of sediments from the skagerrak southern slope and basin c org concentrations were generally inversely related to grain size the 62 63 m fraction in surface sediments from deeper waters had higher contents attributable to agglutination of fine material by tube forming benthic organisms especially in the clay and fine silt fractions c org increased with increasing fraction content presumably as a result of higher grazing pressure on fine material in coarse sediments a comparison of high resolution age 210 pb porosity and grain size composition profiles indicates that deviations in the 210 pb curves are due both to bioturbation and sedimentation events porosity profiles also show high regional variability on a small scale when primary production c org vertical fluxes and accumulation rates are compared an excess of organic carbon stored in skagerrak sediments becomes apparent potential sources for this carbon such as river input dumping or sea floor erosion are examined

coastal flooding and the 1861 2 california storm season abstract a series of large storms attributed to atmospheric river conditions struck the california coast in the winter of 1861 2 although historical accounts document inland flooding little is known about how the 1861 2 storms impacted the now heavily developed california coast here we show that the 1861 2 storms emplaced a deposit of beach sand up to 50 cm thick over 450 m inland within a southern california salt marsh this deposit is unprecedented in the post european sediments of the marsh and more extensive than that derived from any other historical event it is comparable in scale to hurricane and tsunami washover fans in back barrier environments along other coastlines the presence of overwash deposits in carpinteria suggests that the 1861 2 storm season was erosive enough to remove coastal barriers allowing for inundation of parts of the coastline currently developed efforts to prepare for a recurrence of an 1861 2 like storm season should address potential coastal impacts likewise interpretations of past washover deposits should consider these unusually prolonged stormy periods in addition to hurricane and tsunami inundation

phosphorus diagenesis in deep sea sediments sensitivity to water column conditions and global scale implications abstract the geological record bears evidence of various periods of wide scale oceanic anoxia that are associated with perturbations of the marine carbon and phosphorus p cycles in this study we examine the impact of changes in bottom water oxygen and organic matter om input on burial of p in deep sea sediments using a reactive transport model results show that the burial of key reactive p phases namely authigenic calcium associated p minerals ca p organic p org p and iron bound p fe p responds non linearly to both water column forcings namely water column oxygenation and om loading high organic matter om flux with either very low or high oxygen 180 m favor the formation of authigenic ca p while low oxygen and intermediate to high om fluxes promote org p burial iron bound p is only preserved in the sediment when oxygen levels are high and om fluxes low the conditions for maximum p recycling or minimum p burial are low bottom water oxygen concentrations and low om fluxes to the sediment water interface hypoxic oligotrophic deep sea settings the bivariate dependence of p burial on oxygen and om flux was implemented in an existing box model of the global marine p oxygen and organic carbon cycles replacing simple empirical redox functions for p burial the response of the original and new box model to decreased ocean mixing was then assessed in the context of a long term response in the new model org p instead of authigenic ca p is the dominant burial phase of p in deep sea environments during periods of oceanic anoxia nevertheless reduced ocean mixing leads to a similar response in total p burial and as a consequence to a similar increase in deep water anoxia and decrease in open ocean productivity whether an empirical or mechanistic description of phosphorus diagenesis is considered

evolution of the barrier islands of southern long island new york three lines of evidence based on data from more than 400 boreholes and vibrocores have been used to reconstruct the evolution of the barrier islands during the holocene transgression in southern long island new york 1 the holocene transgressive stratigraphic sequence behind the present barriers 2 the stratigraphic patterns of the inner shelf and 3 the morphology of the now buried late pleistocene coastal features the extensive preservation of backbarrier sediments radiocarbon dated between 7000 and 8000 yr bp on the inner shelf of southern long island suggests that the barriers have not retreated by continuous shoreface erosion alone but have also undergone discontinuous retreat by in place drowning of barriers and stepwise retreat of the surf zone such stepwise retreat of the surf zone has prevented the backbarrier sediments from being reworked based on the presence of submerged barrier sand bodies in seismic records it is inferred that about 9000 years ago when the sea stood about 24 m below the present sea level a chain of barriers developed on the present shelf about 7 km offshore of the present barriers with continued sea level rise the 24 m barrier built upward until the sea reached about 15 m msl just prior to 7000 yr bp the barriers were then submerged by the rapidly rising sea and the surf zone shifted rapidly landward to a position about 2 km from the present shoreline the surf zone overstepped to the landward margin of the old lagoon which had become fixed at the steep seaward face of mid wisconsinan or sangamonian coastal barriers during the past 5000 or 6000 years the shoreface has retreated continuously by about 2 km evidence from southern long island and elsewhere in regions of coastal submergence indicates that rapid sea level rise and low sand supply seem to favour the stepwise retreat of barriers whereas slow rates of submergence and a greater supply of sand generally favour continuous shoreface retreat stationary upbuilding or seaward progradation of barriers may occur when supply of sand is great and or submergence is slowed or reversed morphologic highs on the pretransgression surface such as old barrier ridges tend to fix the migrating barrier shoreline during either continuous retreat or stepwise retreat of barriers

trace and rare earth element geochemistry of phosphate nodules from the lower cambrian black shale sequence in the mufu mountain of nanjing jiangsu province china abstract phosphate nodules are abundant in the lowermost section of the lower cambrian black shale sequence along a ne trend belt in the yangtze platform south china in this study we examined the neoproterozoic cambrian mufu mountain section near nanjing of jiangsu province and conducted a detailed trace and rare earth element ree study on the phosphate nodules we employed a step leaching acid dissolution protocol of 1 m hac and 1 m hcl respectively to separate carbonate from phosphate mineral contributions in the nodules both the hac leached and hcl leached fractions of the phosphate nodules show similar symmetrical variations in trace and ree concentrations and ratios the total rees and a number of redox sensitive trace metals such as v cr mo ni abundances show a systematic increase from the core to rim whereas the u and mn abundances decrease from the core to rim in most of the nodules similar trends are also observed for the rb sr u th co ni and v ni ratios but these trends in the hac leached fractions are less pronounced than the hcl leached fractions all of the hcl leached fractions for the nodule cores show seawater like shale normalized ree patterns but the rims of the nodules display slightly mree enriched and hree depleted patterns we suggest that the phosphate nodules may have formed in a basinal setting beneath a stratified water column during early cambrian and the compositional variations of rees and redox sensitive trace elements from the core to rim may record a changing redox condition and fluid mixing during different stages of nodule growth the cores of the nodules preserve more pronounced negative ce anomalies and progressively hree enriched patterns which may retain primary early cambrian seawater chemistry whereas the nodule rims record chemistry consistent with changed redox conditions and or influences from pore fluids such as generated from degradation of organic matter

controls on sedimentation in distal margin palaeovalleys in the early tertiary alpine foreland basin south eastern france the influence of palaeodrainage characteristics palaeogeography and tectonic setting are rarely considered as controls on stratigraphic organization in palaeovalley or incised valley systems this study is an examination of the influence of source region vs downstream base level controls on the sedimentary architecture of a set of bedrock confined palaeovalleys developed along the distal margin of the alpine foreland basin in south eastern france three distinct facies associations are observed within the palaeovalley fills fluvial facies association a is mainly dominated by poorly sorted highly disorganized clast to matrix supported cobble to boulder conglomerates that are interpreted as streamflood deposits facies association b comprises mainly yellow siltstones and is interpreted as recording deposition in an estuarine basin environment estuarine marine facies association c comprises interstratified estuarine siltstones and clean well sorted washover sandstones the sedimentary characteristics of the valley fill successions are related to the proximity of depositional sites to sediment source areas palaeovalleys located proximal to structurally controlled basement palaeohighs are entirely dominated by coarse fluvial streamflood deposits in contrast distal palaeovalley segments which are located several kilometres downstream contain successions showing upward transition from coarse fluvial facies into estuarine central basin fines and finally into estuarine marginal marine facies facies distributions suggest that the fluvial deposits form wedge shaped downstream thinning sediment bodies whereas the estuarine deposits form an upstream thinning wedge the vertical stacking of fluvial to estuarine to marginal marine depositional environments records the fluvial aggradation and subsequent transgression of relatively small bedrock confined river valleys which drained a rugged upland terrain facies geometries suggest that a fluvial sediment wedge initially prograded downvalley in response to high bed load sediment yields subsequently palaeovalleys became drowned during the passage of a marine transgression with the establishment of estuarine conditions initial fluvial aggradation and subsequent marine flooding of the palaeovalleys is a consequence of the interaction of high local rates of sediment supply and relative sea level rise driven by flexural subsidence of the basin

intense storm activity during the little ice age on the french mediterranean coast understanding long term variability in the frequency of intense storm activity is important for assessing whether changes are controlled by climate evolution understanding this variability is also important for predicting present and future community vulnerability and economic loss our ability to make these assessments has been limited by the short less than 50 years instrument record of storm activity storm induced deposits preserved in the sediments of coastal lagoons offer the opportunity to study the links between climatic conditions and storm activity on longer timescales in this study we present a record of these extreme climatic events that have occurred in the french mediterrannean coast over the past 1500 years the identification of these extreme events is based on the analysis of sediment cores from gulf of aigues mortes lagoons that contain a specific sedimentary and geochemical signature associated with intense storms overwash deposits do not show any evidence of intense storm landfalls in the region for several hundred years prior to the late 17th century a d the apparent increase in intense storms around 250 years ago occurs during the latter half of the little ice age a time of lower continental surface temperatures comparison of the sediment record with palaeoclimate records indicates that this variability was probably modulated by atmospheric dynamics the apparent increase of the superstorm activity during the latter half of the little ice age was probably due to the thermal gradient increase leading to enhanced lower tropospheric baroclinicity over a large central atlantic european domain and leading to a modification of the occurrence of extreme wind events along the french mediterranean coast a complete understanding of the relationship between climate fluctuations storm activity and the coastal response will be crucial to predicting the impacts of future climate change

assessing the suitability of holocene environments along the central belize coast central america for the reconstruction of hurricane records since the belize coast was repeatedly affected by hurricanes and the paleohurricane record for this region is poor sediment cores from coastal lagoon environments along the central belize coast have been examined in order to identify storm deposits the paleohurricane record presented in this study spans the past 8000 years and exhibits three periods with increased evidences of hurricane strikes occurring at 6000 4900 4200 3600 and 2200 1500 cal yr bp two earlier events around 7100 and 7900 cal yr bp and more recent events around 180 cal yr bp and during modern times have been detected sand layers redeposited corals and lagoon shell concentrations have been used as proxies for storm deposition additionally hiatuses and reversed ages may indicate storm influence while sand layers and corals represent overwash deposits the lagoon shell concentrations which mainly comprise the bivalve anomalocardia cuneimeris and cerithid gastropods have been deposited due to changes in lagoon salinity during and after storm landfalls comparison with other studies reveals similarities with one record from belize but hardly any matches with other published records the potential for paleotempestology reconstructions of the barrier lagoon complexes along the central belize coast differs depending on geomorphology and deposition of washovers in the lagoon basins is limited probably due to the interplay of biological geological and geomorphological processes

phosphorus forms related to sediment grain size and geochemical characteristics in french coastal areas abstract phosphorus forms with respect to sediment characteristics such as grain size and major chemical elements were studied in french coastal marine areas the bay of seine and the loire and gironde estuaries in the three areas fe al bound phosphate fe al p and exchangeable phosphate exch p were significantly related to the proportion of fine fraction calcium bound phosphate ca p was found in all grain size classes with comparable concentrations in the bay of seine where there was no correlation between ca p and ca this corresponded to the calcium s marine origin shells in the bay of seine in contrast the correlation of ca p with ca and the fine fraction of the sediment in the loire and gironde estuaries was characteristic of the predominant metamorphic origin of ca p in these areas useful information for interpretation of p forms can be obtained from major sediment characteristics thus for areas where specific relationships have previously been established good estimates of p forms could be predicted from sediment properties

mobility of gold and silver in lateritic weathering profiles some observations from western australia experimental evidence suggests that very acid chloride solutions generated in lateritic profiles by ferrolysis oxidation and hydrolysis of iron are responsible for the dissolution of gold and silver au is subsequently reprecipitated by reduction of the aucl 4 super ion with fe super 2 reduction of the agcl complex does not similarly occur because of the relative redox potentials of fe super 2 fe super 3 and ag agcl thus chemical refinement of gold occurs during lateritization the development of low ph and the redistribution of gold and silver in lateritic weathering profiles appear to be more common over granitic and gneissic basement and may be inhibited by the presence of carbonate in the weathering zone of basic rock sequences modified journal abstract