the present day formation of apatite in mexican continental margin sediments abstract results of pore water and sediment analyses from the western mexican continental margin strongly suggest the present day formation of apatite the interstitial water phosphate and fluoride profiles indicate chemical removal at a depth which corresponds to a large maximum in the phosphorus content of the sediments apatite is identified within this maximum via x ray diffraction but is elsewhere undetectable in the core radioisotopic thorium uranium and radium data support the conclusion that this deposit is modern the present day depositional environment is consistent with those reported by other workers for phosphorite formation with the exception that pore water magnesium is not depleted below its seawater value

high resolution reflection seismic imaging of the upper crust at laxemar southeastern sweden abstract a major cost in exploring the upper 1 2 km of crystalline crust with reflection seismics is the drilling required for explosive sources by reducing the charge size to a minimum shallow inexpensive shotholes can be drilled with handheld equipment here we present results from a full scale test using small charges for high resolution seismic surveying over a nuclear waste disposal study site not an actual site two 2 2 5 km long crossing profiles were acquired in december 1999 with 10 m shot and geophone spacing in the laxemar area near oskarshamn in southeastern sweden after standard processing including dip moveout dmo several subhorizontal to moderately dipping reflections are imaged many of the dipping ones can be correlated to fracture zones observed in a ca 1700 m deep borehole where the profiles cross and or to fracture zones mapped on the surface the imaged fracture zones form a complex 3d pattern illustrating the necessity of having 3d control before interpreting seismic reflection data analyses of sonic and density logs from the borehole show that greenstones have significantly higher impedances than the more dominant granite found in the borehole granite greenstone reflection coefficient is 0 065 these greenstones may contribute to the reflectivity when associated with fracture zones in some cases where they are present as larger subhorizontal lenses they may be the dominant source of reflectivity a set of north dipping 10 reflectors at 3 3 5 km depth can be correlated to a similar set observed below the island of avro about 3 km to the east

a model for microbial phosphorus cycling in bioturbated marine sediments significance for phosphorus burial in the early paleozoic abstract a diagenetic model is used to simulate the diagenesis and burial of particulate organic carbon c org and phosphorus p in marine sediments underlying anoxic versus oxic bottom waters the latter are physically mixed by animals moving through the surface sediment bioturbation and ventilated by burrowing tube dwelling organisms bioirrigation the model is constrained using an empirical database including burial ratios of c org with respect to organic p c org p org and total reactive p c org p reac burial efficiencies of c org and p org and inorganic carbon to phosphorus regeneration ratios if p org is preferentially mineralized relative to c org during aerobic respiration as many previous studies suggest then the simulated p org pool is found to be completely depleted a modified model that incorporates the redox dependent microbial synthesis of polyphosphates and p org termed the microbial p pump allows preferential mineralization of the bulk p org pool relative to c org during both aerobic and anaerobic respiration and is consistent with the database results with this model show that p burial is strongly enhanced in sediments hosting fauna animals mix highly labile p org away from the aerobic sediment layers where mineralization rates are highest thereby mitigating diffusive po 4 3 fluxes to the bottom water they also expand the redox niche where microbial p uptake occurs the model was applied to a hypothetical shelf setting in the early paleozoic a time of the first radiation of benthic fauna results show that even shallow bioturbation at that time may have had a significant impact on p burial our model provides support for a recent study that proposed that faunal radiation in ocean sediments led to enhanced p burial and possibly a stabilization of atmospheric o 2 levels the results also help to explain c org p org ratios in the geological record and the persistence of p org in ancient marine sediments

changes in lowland floodplain sedimentation processes pre disturbance to post rehabilitation cosumnes river ca during the late holocene sediment deposition on the lowland cosumnes river floodplain ca has depended on factors that varied temporally and spatially such as basin subsidence sea level rise flow and sediment supply from both the sacramento river system and from the cosumnes river system itself and anthropogenic changes through field investigations and analyses of historical maps bridge core logs and sediment size distributions we link hydrogeomorphic processes to three stages of floodplain sedimentation on the lowland cosumnes river stage i 1000 200 ybp combined late holocene pre disturbance flood basin overflow and anastomosing river processes deposited spatially variable sediment consisting of gray blue clay 87 clay interlayered with relatively thin coarser sediment pre disturbance holocene deposition rates of up to f3 0 mm year kept pace with sea level rise and tectonic basin subsidence stage ii 200 to f10 ybp anthropogenic disturbances caused a rapid increase in floodplain sedimentation rates up to 25 mm year between 1849 and f1920 and deposited a relatively coarser reddish brown sandy clay f40 clay layer that overlies the basin deposits between f1920 and 1990 ad sedimentation was greatly limited on the lower cosumnes floodplain because levees inhibited connectivity between both the sacramento and cosumnes river systems and the cosumnes floodplain during this stage the density of channel segments in the anastomosing river floodplain decreased by 30 as agricultural activities filled secondary channels and leveled floodplain topography during stage iii f10 ybp to the present post rehabilitation floodplain sand splay complex sediment deposited after 1998 ad resulted from intentionally breaching levees to promote habitat at the cosumnes river preserve the splay complex is dominated by medium to very coarse sand with finer intervening layers the post rehabilitation splay complex overlies the older basin deposits in a generally upward coarsening sequence that reflects depositional processes and land use changes that continue to affect the lowland cosumnes river floodplain d 2003 elsevier science b v all rights reserved

sources sinks and storage of river sediment in the atlantic drainage of the united states the history of sediment and its movement in the atlantic drainage demonstrate some of the difficulties of modeling sediment on a river basin scale soil erosion was accelerated by a factor of at least 10 when european settlers cleared forests and planted crops although increasing soil conservation practice and decreasing crop farming have since reduced the rates of erosion large quantities of eroded material are still stored on hillslopes and in stream valleys where they continue to augment the sediment loads of the rivers the sediment from this episode of erosion that is largely past can be expected to emerge from storage for many decades and perhaps even several centuries to come the reservoirs that have been built on many of the major rivers trap significant portions of the moving sediment which in some places may be remobilized by large floods essentially all the river sediment that reaches the atlantic coastal zone is trapped in estuaries and coastal marshlands probably less than 5 is deposi

3 d structure below avro island from high resolution reflection seismic studies southeastern sweden two 1 km long perpendicular seismic reflection lines were acquired on avro island southeast sweden in october 1996 in order to 1 test the seismic reflection method for future site investigations 2 map known fracture zones and 3 add to the swedish database of reflection seismic studies of the shallow crystalline crust an east west line was shot with 5 m geophone and shot point spacing and a north south line was shot with 10 m geophone and shotpoint spacing an explosive source with a charge size of 100 g was used along both lines the data clearly image three major dipping reflectors and one subhorizontal one in the upper 200 ms 600 m the dipping reflectors to the south east and north west intersect or project to the surface at or close to where surface mapped fracture zones exist the south dipping reflector correlates with the top of a heavily fractured interval observed in a borehole kav01 at about 400 m the subhorizontal zone at about 100 200 m correlates with a known fracture zone in the same borehole kav01 3 d effects are apparent in the data and only where the profiles cross can the true orientation of the reflecting events be determined to properly orient and locate all events observed on the lines requires acquisition of 3 d data

rates of formation of modern phosphorite off western mexico abstract phosphorite deposition represents a significant but poorly constrained sink in the marine p cycle this study establishes conclusively that phosphorite forms today throughout a widespread region along the upper continental slope off southern baja california mexico in this region o2 depleted 5 50 m bottomwater overlies the seafloor and a narrow range of suboxic to anoxic redox conditions prevail in the modern 0 18 000 yr old near surface 0 50 cm organic c rich 2 10 wt sediment interstitial gradients of total alkalinity ta and inferred effects of organic matter decay correlate directly with sedimentation rates calculated from 14c dating other porewater and solid phase data indicate that francolite currently precipitates authigenically at each of five study sites moderately high concentrations 20 100 m of dissolved inorganic phosphate dip produced in the upper 5 cm of sediment sustain francolite growth at slightly greater depths while the necessary f diffuses into the sediment from above neither organic matter decay nor fish bone dissolution seem capable of producing the steep near surface gradients of dip measured in this study at some sites dip production coincides spatially with the reversible production of dissolved fe2 but thorough evaluation of the possible link between these processes requires further study the mechanism responsible for the near surface enrichment of interstitial dip thus remains unidentified box cores from each site contain an unreworked sequence of up to six thin 1 3 cm discrete francolite rich horizons several of which qualify as true phosphorite 50 wt francolite estimated diffusional burial fluxes of inorganic p and f range respectively from 2 40 g cm 2 y 1 and 4 12 g cm 2 y 1 or the equivalent in francolite of 16 260 g cm 2 y 1 these present day accumulation rates lie within the range of those determined for several ancient phosphorite deposits and for the extensively studied region of modern phosphorite deposition off peru

the use of modeling and suspended sediment concentration measurements for quantifying net suspended sediment transport through a large tidally dominated inlet abstract sediment exchange at large energetic inlets is often difficult to quantify due complex flows massive amounts of water and sediment exchange and environmental conditions limiting long term data collection in an effort to better quantify such exchange this study investigated the use of suspended sediment concentrations ssc measured at an offsite location as a surrogate for sediment exchange at the tidally dominated golden gate inlet in san francisco ca a numerical model was calibrated and validated against water and suspended sediment flux measured during a spring neap tide cycle across the golden gate the model was then run for five months and net exchange was calculated on a tidal time scale and compared to ssc measurements at the alcatraz monitoring site located in central san francisco bay 5 km from the golden gate numerically modeled tide averaged flux across the golden gate compared well r 2 0 86 p value mckee et al 2013 this issue there was little variation from year to year exports were computed to be greatest during the wettest water year analyzed but only marginally so

rare earth elements in the permian phosphoria formation paleo proxies of ocean geochemistry abstract the geochemistry of deposition of the meade peak member of the phosphoria formation mpm in southeast idaho usa a world class sedimentary phosphate deposit of permian age that extends over 300 000 km2 is ascertained from its rare earth element ree composition ratios of ree al2o3 suggest two sources seawater and terrigenous debris the seawater derived marine fraction identifies bottom water in the phosphoria sea as o2 depleted denitrifying suboxic most of the time and seldom sulfate reducing anoxic this interpretation is supported by earlier research that showed progressively greater ratios in the marine sediment fraction of cr ni v ni mo ni relative to their ratios in seawater for which marine cr v and mo can have a dominantly o2 depleted bottom water source and ni a photic zone largely algal source the water chemistry was maintained by a balance between bacterial oxidation of organic matter settling through the water column determined largely by primary productivity in the photic zone and the flux of oxidants into the bottom water via advection of seawater from the open ocean samples strongly enriched in carbonate fluorapatite the dominant ree host mineral have variable er sm tm sm and yb sm ratios their distribution may represent greater advection of seawater between the phosphoria sea and open ocean during deposition of two ore zones than a center waste and greater upwelling of nutrient enriched water into the photic zone however the mean rate of deposition of marine ni a trace nutrient of algae and po43 a limiting nutrient indicate that primary productivity was probably high throughout the depositional history an alternative interpretation of the variable enrichments of er tm and yb relative to sm is that they may reflect temporally variable carbonate alkalinity of open ocean seawater in permian time a more strongly negative ce anomaly for all phosphatic units than the ce anomaly of modern pelletal phosphate is further indicative of an elevated o2 concentration in the permo carboniferous open ocean as proposed by others in contrast to the depletion of o2 in the bottom water of the phosphoria sea itself the oceanographic conditions under which the deposit accumulated were likely similar to conditions under which many sedimentary phosphate deposits have accumulated and to conditions under which many black shales that are commonly phosphate poor have accumulated a shortcoming of several earlier studies of these deposits has resulted from a failure to examine the marine fraction of elements separate from the terrigenous fraction

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

similar phosphorus fluxes in ancient phosphorite deposits and a modern phosphogenic environment phosphogenesis is major sink for phosphorus p in the modern ocean and the deposition of ancient phosphorites appears to have been an important sink for p in past oceans to evaluate the importance of p burial we combined published estimates along with our data for one section of the monterey formation california of p inventories areal extents and time intervals of deposition for three well studied major phosphorite deposits to calculate p accumulation and burial rates phosphorus accumulation and burial rates of major phosphorite deposits are comparable to those of the modern peru margin though phosphorite deposition probably requires favorable sedimentological tectonic and or oceanographic conditions it does not appear to be a geochemically anomalous phenomenon when compared to modern oceanic conditions

early diagenetic reactions in interbedded pelagic and turbiditic sediments in the nares abyssal plain western north atlantic consequences for the composition of sediment and interstitial water abstract measured pore water concentrations of iron in interbedded pelagic and turbiditic sediments from the nares abyssal plain are in excellent agreement with sediment colour and measured redox potential the organic carbon content of these sediments appears to define the redox conditions and consequently the porewater and solid phase concentration of constituents that are involved in early diagenetic reactions in the turbiditic sediments the concentration of no 3 generally goes to zero within a sediment depth of 1 m whereas at 8 m in a pelagic core from the same area the concentration of no 3 is still higher than it is in the bottom water the pore water concentration of mn 2 in the turbiditic sediments increases sharply down to a depth of approximately 3 m and from thereon remains nearly constant due to saturation with respect to mn ca co 3 the pore water of the turbiditic sediments is also saturated with respect to calcite the few diagenetic spikes in the pore water concentration of no 3 and mn 2 and the concentration depth profile of dissolved iron h 4 sio 4 and phosphate all clearly demonstrate the inhomogeneous nature of interbedded pelagic and turbiditic sediments the simultaneous occurrence of peaks of dissolved iron silica and of sediment intervals with a relatively high organic carbon content is attributed to enhanced early diagenetic reactions associated with the decomposition of organic matter in these specific intervals linked with these reactions is the irregular pore water concentration of phosphate which is shown to originate partly from the oxidation of organic matter but mainly from the desorption of phosphate from iron oxide potential concentrations of phosphate are calculated from the stoichiometric early diagenetic reactions and compared with measured concentrations due to the unique combination of low porosity and relatively high sedimentation rates the sediments from the nares abyssal plain are an ideal basis for the study of such interbedded sequences of pelagic and turbiditic deposits

catchment clearing accelerates the infilling of a shallow subtropical bay in east coast australia abstract understanding processes that govern the transport and distribution of terrestrial sediments to and within bays is critical for interpreting the drivers of long term changes in these ecosystems on the east coast of australia increased soil erosion and sediment delivery following extensive land clearing in the contributing catchments associated with european settlement is highlighted as a key driver of the decline of numerous nearshore habitats including seagrass meadows and in shore coral reefs here we use optical radiocarbon and radionuclide dating to estimate mass accumulation rates and type of terrestrial sedimentation in central moreton bay during the holocene we compare the long term rates of infilling within the central basin with the recent past and show a 3 9 fold increase in sediment accretion over the last 100 years compared to the long term last 1500 to 3000 yrs average infilling during the holocene is not spatially uniform with preferential deposition occurring within the now submerged palaeochannels of the brisbane and pine rivers we suggest that modern turbidity regimes in moreton bay are the result of the compounded effect of both a historical increase in fine sediment supply and a rapid decline in the effective storage capacity of the basin

geologic site characterization for deep nuclear waste disposal in fractured rock based on 3d data visualization abstract three dimensional 3d visualization of data is an essential step in the development of descriptive hydrologic and rock mechanical models of fractured rock systems data includes geological properties rock mechanical properties and hydraulic responses the 3d visualization approach is applied to characterizing a hypothetical site for a high level nuclear waste repository located at 500 m depth in granitoids of the trans scandinavian igneous belt 1 6 1 8 ga old the study is based on site specific data at the aspo hard rock laboratory hrl on the southeastern coast of sweden the data are extensive and spatially complex and are based on surface information as well as a large number of boreholes penetrating up to 1000 m at this site fractures and fracture zones control both groundwater flow and mechanical stability structures are found within a 2 2 1 km deep model block representing the site 3d locations of fractures and fracture zones are hypothesized based on surface and subsurface geological and geophysical information including borehole radar this results in a 3d geological model structure of the site

comparison of sediment supply to san francisco bay from watersheds draining the bay area and the central valley of california article i nfo quantifying suspended sediment loads is important for managing the world s estuaries in the context of nav igation pollutant transport wetland restoration and coastal erosion to address these needs a comprehen sive analysis was completed on sediment supply to san francisco bay from fluvial sources suspended sediment optical backscatter velocity data near the head of the estuary and discharge data obtained from the output of a water balance model were used to generate continuous suspended sediment concentration records and compute loads to the bay from the large central valley watershed sediment loads from small tributary watersheds around the bay were determined using 235 station years of suspended sediment data from 38 watershed locations regression analysis and simple modeling over 16 years net annual suspended sediment load to the head of the estuary from its 154 000 km 2 central valley watershed varied from 0 13 to

environmental control on concretion forming processes examples from paleozoic terrigenous sediments of the north gondwana margin armorican massif middle ordovician and middle devonian and sw sardinia late ordovician abstract concretions of various compositions are common in the paleozoic terrigenous successions of the north gondwana margin this study focuses on phosphatic p and siliceous si concretions present in some successions of the armorican massif nw france and sw sardinia w italy it shows that they consist of mudstones fine to very fine grained sandstones or shellbeds with a more or less abundant p cement and form a continuum between a phosphatic end member and a siliceous biogenic end member the p 2 o 5 contents are ranging from 0 26 to 21 5 and are related to apatite the sio 2 contents vary from 25 to 82 and are linked both to a terrigenous phase and to a biogenic silica phase concretions showing the lower p contents p 2 o 5 2 al 2 o 3 5 comparison with the surrounding sediments shows that all the concretions are enriched in chlorite and in middle rare earth elements la s gd s 0 12 0 72 and some of them in y up to 974 ppm rare earth elements more than 300 ppm and sr 260 880 ppm the concretions with highest biogenic silica concentrations are contained in the outer shelf sediments whereas the other concretions are present from the proximal part of the inner shelf to the outer shelf a genetic model in two stages is proposed during early diagenesis the dissolution of shells and degradation of organic matter progressively enrich the pore water in dissolved si ca and p when the suboxic zone is reached p precipitation begins leading to the formation of protoconcretions in shallow environments the relative permeability of sediments and the winnowing or reworking of the upper few centimetres by bottom currents allow for suboxic conditions to be maintained leading to p rich concretion formation in deeper environments the anoxic zone is reached more rapidly thereby preventing extensive phosphogenesis nevertheless in the protoconcretions the early p cement preserves pore spaces from compaction in the presence of biogenic siliceous particles the fluids are enriched in dissolved silica and diffuse towards the protoconcretions silica precipitation can thus occur later in the intergranular spaces

organic matter apatite pyrite relationships in the botneheia formation middle triassic of eastern svalbard relevance to the formation of petroleum source rocks in the nw barents sea shelf abstract the middle triassic botneheia formation of eastern svalbard edgeoya and barentsoya comprises an organic carbon rich fine grained clastic succession 100 m thick that makes the best petroleum source rock horizon in the nw barents sea shelf the succession records a transgressive regressive interplay between the prodelta depositional system sourced in the southern barents sea shelf black shale facies of the lower and middle parts of the muen member and the open shelf phosphogenic system related to upwelling and nutrient supply from the panthalassic ocean phosphogenic black shale facies of the upper part of the muen member and the blanknuten member the relationships between organic matter authigenic apatite and pyrite in these facies allow to characterize the relative roles of redox conditions and oceanic productivity in the organic carbon preservation the accumulation of terrestrial and autochthonous marine organic matter in the black shale facies occurred under dominating oxic conditions and increasing upward productivity related to early transgressive phase and retrogradation of the prodelta system the phosphogenic black shale facies deposited in an oxygen minimum zone omz of the open shelf environment during the late transgressive to regressive phases under conditions of high biological productivity suppressed sedimentation rates and changing bottom redox the phosphatic black shales occurring in the lower and upper parts of the phosphogenic succession reveal depositional conditions indicative of the shallower part of omz including high input of autochthonous organic matter into sediment oxic to dysoxic episodically suboxic and or anoxic conditions intense phosphogenesis and recurrent reworking of the seabed the massive phosphatic mudstone occurring in the middle of the phosphogenic succession reflects the development of euxinia in the deeper part of omz during high stand of the sea high input of autochthonous organic matter in this environment was coupled with mineral starvation and intermittent phosphogenesis in mature sections in eastern svalbard the petroleum potential of the botneheia formation rises from moderate to good in the black shale facies and from good to very good in the phosphogenic black shale facies attaining maximum in the massive phosphatic mudstone

seismic reflections from subvertical diabase dikes in an archean terrane a 20 km seismic reflection profile in the superior province of northwestern ontario imaged polydeformed archean terrane including the manitouwadge greenstone belt and the adjacent wawa quetico subprovince boundary in addition to reflectivity from archean lithostructural elements we recognize discrete reflections that correlate with undeformed subvertical proterozoic dikes moderately to steeply inclined linear events in the stacked section are related to matachewan dikes that intersect the seismic profile at 50 75 the reflections project to the surface at points corresponding to dike profile intersections and have apparent dips in the seismic section consistent with the intersection angles in map view subhorizontal linear to curvilinear reflections originate from marathon dikes that are subparallel to the seismic line on the basis of forward modeling studies the events occur at two way traveltimes for horizontally propagating waves we conclude that a number of dipping and subhorizontal events represent refracted waves propagated along horizontal ray paths near the surface and reflected from subvertical dikes in many other seismic profiles in crystalline crust reflections originating from subvertical dikes have likely been overlooked or misinterpreted either because the presence of dikes was not recognized or because their seismic response was not evaluated

imaging of fracture zones in the finnsjon area central sweden using the seismic reflection method in 1987 the swedish nuclear fuel and waste management co skb funded the shooting of a 1 7 km long high resolution seismic profile over the finnsjon study site using a 60 channel acquisition system with a shotpoint and geophone spacing of 10 m the site is located about 140 km north of stockholm and the host rocks are mainly granodioritic the main objective of the profile was to image a known fracture zone with high hydraulic conductivity dipping gently to the west at depths of 100 to 400 m the initial processing of the data failed to image this fracture zone however a steeply dipping reflector was imaged indicating the field data were of adequate quality and that the problem lay in the processing these data have now been reprocessed and a clear image of the gently dipping zone has been obtained in addition several other reflectors were imaged in the reprocessed section both gently and steeply dipping ones correlations with borehole data indicate that the origin of these reflections are also fracture zones the improvement over the previous processing is caused mainly by 1 refraction statics 2 choice of frequency band 3 f k filtering and 4 velocity analyses in addition to reprocessing the data some further analyses were done including simulation of acquisition using only the near offset channels channels 1 30 and the far offset channels channels 31 60 and determining the damping factor q in the upper few hundred meters based upon the amplitude decay of the first arrivals the data acquisition simulation shows the far offset contribution to be significant even for shallow reflectors in this area contrary to what may be expected a q value of 10 determined from observed amplitude decay rates agrees well with theoretical ones assuming plane wave propagation in an attenuating medium

a modern vs permian black shale the hydrography primary productivity and water column chemistry of deposition the sediment currently accumulating in the cariaco basin on the continental shelf of venezuela has an elevated organic carbon content of approximately 5 is accumulating under o2 depleted bottom water conditions so42 reduction is composed dominantly of foraminiferal calcite diatomaceous silica clay and silt and is dark greenish gray in color upon lithification it will become a black shale recent studies have established the hydrography of the basin and the level of primary productivity and bottom water redox conditions these properties are used to model accumulation rates of cd cr cu mo ni v and zn on the seafloor the model rates agree closely with measured rates for the uppermost surface sediment the model is applied to the meade peak phosphatic shale member of the phosphoria formation a phosphate deposit of permian age in the northwest united states it too has all of the requisite properties of a black shale although the deposit is a world class phosphorite it is composed mostly of phosphatic mudstone and siltstone chert limestone and dolomite it has organic carbon concentrations of up to 15 is strongly enriched in several trace elements above a terrigenous contribution and is black the trace element accumulation defines a mean primary productivity in the photic zone of the phosphoria basin as moderate at 500 g m 2 year 1 organic carbon comparable to primary productivity in the cariaco basin the source of nutrient enriched water that was imported into the phosphoria basin upwelled into the photic zone and supported primary productivity was an o2 minimum zone of the open ocean the depth range over which the water was imported would have been between approximately 100 and 600 m the mean residence time of bottom water in the basin was approximately 4 years vs 100 years in the cariaco basin the bottom water was o2 depleted but it was denitrifying or no3 reducing rather than so42 reducing

high resolution seismic characterization in an urban area subway tunnel construction in barcelona spain traveltime seismic tomography used to aid subway tunnel drilling in barcelona spain provides a detailed characterization of the shallow subsurface including a complex network of faults and dikes we encountered many difficulties while working in this urban setting such as cultural noise and the inability to deploy instruments along much of the tunnel trace because of the street layout furthermore the shallow subsurface is highly heterogeneous because of gas and water lines building foundations and the sewage system obscuring deeper structures we acquired seismic data using a 10 s vibroseis sweep that provided relatively good signal to noise s n ratio first arrival traveltime tomography proved to be a key tool to differentiate rock vol umes characterized by different physical properties in particular the contact between the weathered upper layer and the more competent rock below we interpreted the seismic results using surface geologic observations and borehole cores low seismic velocit

organic carbon cycling and modern phosphorite formation on the east australian continental margin an overview during 1987 the australian bureau of mineral resources conducted a multidisciplinary investigation of the modern phosphorites on the continental margin of southeastern australia between 28 and 32 s the objectives of the work were to examine the processes controlling the cycling of organic carbon and bioactive elements nitrogen phosphorus sulphur and iron in the sediments and to investigate the roles which these processes played in the formation of the modern phosphorites bacterial productivities sulphate reduction rates sedimentary oxygen and pore water concentrations of nitrate ammonia phosphate iron sulphate and fluoride were measured at sea the highest rates of microbial productivity were found in the surficial 0 20 mm sediments of the modern phosphorite zone in 350 460 m water depth these rates were about double those in shallower shelf 300 m sediments and 3 4 fold those rates in mid slope 600 1000 m sediments aerobic and anaerobic oxidation rates of organic matter calculated from sediment oxygen profiles and sulphate reduction rates were highest in the surface sediments in the modern phosphorite zone the recycling of sedimentary iron via reductive dissolution of iron oxyhydroxides and reprecipitation at the oxic anoxic boundary results in a near surface sedimentary trap for iron in the phosphorite zone sediments phosphate released from organic matter in the interfacial sediments and fluoride from seawater are scavenged by iron oxyhydroxides in the top few centimetres of sediment phosphorus in this way is decoupled from organic carbon in the near surface sediments and linked to the redox cycling of iron phosphate and fluoride scavenged onto iron oxyhydroxides and concentrated in the surficial sediments are subsequently released to pore waters in the anoxic sediments when iron oxyhydroxides are buried and dissolve the recycling process releases phosphate and fluoride for incorporation into apatite fluoride is depleted from pore waters at depths 18 cm phosphorite nodules form within anoxic sediments at depths 18 cm and continue to accumulate iron and phosphorus while resident in the mixed layer combinations of rapid sediment mixing rates a slow sedimentation rate and a mixed layer to about 18 cm result in an average particle residence time in the phosphorite zone sediments which is about ten fold that of the mid slope sediments long residence times and rapid mixing promote the oxidation of organic carbon and release of phosphate while the continuous recycling of iron and phosphate concentrates the phosphorus for apatite precipitation and accumulation into phosphorite nodules phosphorite nodules are not found in mid slope sediments probably because of combinations of relatively rapid sedimentation rates ineffective iron phosphorus and fluoride recycling and trapping mechanisms plus dilution and dissemination of any incipient apatite

the marine phosphorus cycle phosphorus introduced to the ocean must ultimately be removed if a steady state is to be maintained over geologic time aeolian input is insignificant and there is evidently no hydrothermal contribution rivers dominate p input to the ocean the fluvial p flux is poorly quantified due to the interactions of two factors 1 man s influence on river nutrient fluxes and 2 inherent complexities in understanding the biological and inorganic associations of p in estuarine and coastal waters our best estimate of the natural or pre man p input flux is about 10 x 10 sup 9 moles p cm sup 2 ocean surface year of the identified flux of phosphorus to the sediments about 90 percent is in the form of biogenic debris or its regeneration products the burial of phosphatic fish debris is negligible p removal by direct reaction of phosphate in seawater with sea floor basalts during mid ocean ridge hydrothermal circulation is insignificant p removal by processes such as sorption on clay surfaces or formation of authigenic fe and al phosphate phases is presently unquantified and remains a serious uncertainty in the phosphorus cycle the identified sources and sinks approximately balance yielding a residence time for p in the oceans of about 10 sup 5 yrs

elemental geochemistry of lower cambrian phosphate nodules in guizhou province south china an integrated study by la icp ms mapping and solution icp ms abstract the late ediacaran to early cambrian transition was a critical interval in earth history during which both the environment and life experienced dramatic change relationships between these events however are widely debated this time interval also witnessed the occurrence of massive phosphate deposits studies on the characteristics origins and depositional context of this geochemical archive may provide important insights into not only the ore forming process but also the coevolution of the earth surface system here phosphate nodules from two sections jinsha and songtao are investigated using in situ la icp ms mapping and solution icp ms methods elemental images and factor analyses of the la icp ms dataset show that ca p and sr are evenly distributed and co enriched within the nodule whereas iron related elements fe as and mo are roughly present as concentric layers the paas normalized ree patterns of the jinsha samples exhibit moderately negative ce anomalies and pronounced mree enrichments possibly related to uptake of ree released by iron oxyhydroxides during early diagenesis in contrast the songtao samples are characterized by more seawater like signals with significantly lower ce ce and higher eu eu values these positive eu anomalies are ascribed to active submarine hydrothermal vents along the yangtze platform margin based on a compilation of published ce ce data we suggest that the prominent negative ce anomalies during the ediacaran cambrian phosphogenesis give evidence of possible link between p dynamics and ocean oxygenation

phosphate regeneration from sediments of the peru continental margin by dissolution of fish debris generally oxidative regeneration of phosphate from anoxic sediments is by microbially mediated sulfate reduction processes stoichiometric modelling of such reactions takes into consideration varying proportions of decomposable organically bound p to account for the ratios among nutrients in depth concentration profiles of near surface sediments new results of interstitial water composition from sediments underlying the water masses influenced by coastal upwelling of the eastern boundary current system off peru indicate that dissolution of phosphatic fish debris represents a mechanism for remineralization of phosphate comparable to or larger in magnitude than that by oxidative regeneration of organically bound p dissolved interstitial phosphate from fish debris is revealed by an excess amount of phosphate over that predicted from a simple stoichiometric oxidative regeneration model and by anomalously high dissolved interstitial fluoride concentrations phosphate flux estimates based on diffusion from the sediment suggest that this mechanism may generate up to 10 of the nutrient pool in the waters of the peru undercurrent partitioning of p among the two sources reveals further that fish debris phosphate is about four times more important than organically bound p in nutrient generation from sediments of the peru continental margin not only does this mechanism of regeneration affect the nutrient cycling but may also control widespread phosphorite formation in this area

phosphogenesis and organic carbon preservation in the miocene monterey formation at naples beach california the monterey hypothesis revisited the middle part of the miocene monterey formation at naples beach west of santa barbara california is predominantly composed of organic rich mudstone interstratified with phosphatic laminae minor lithologies include volcanic ash dolomite porcelanite and chert and condensed phosphatic beds sediments dated as 14 3 13 5 ma have average total organic carbon toc values around 8 5 wt and organic carbon oc accumulation rates are around 565 mg cm2 k y sediments dated as 13 5 13 ma are characterized by average toc values of 12 6 wt and oc accumulation rates of around 1130 mg cm2 k y the interval between 13 and 10 6 ma is marked by condensation average toc values are around 8 6 wt and oc accumulation rates diminished to around 55 mg cm2 k y the last interval studied is dated as 10 6 9 4 ma and average toc values are around 6 wt whereas oc accumulation rates rose again to 320 mg cm2 k y the presence of erosional surfaces angular unconformities and reworked clasts and nodules suggests that bottom current activity and gravity flow deposition have been instrumental in sediment accumulation the phosphatic laminae were precipitated at a very early stage of diagenesis during periods of nonsedimentation they formed less permeable sedimentary lids and may as such have contributed to enhanced oc preservation between 13 and 10 6 ma the thus formed phosphatic laminae were frequently subjected to subsequent sediment winnowing and reworking resulting in the formation of condensed phosphatic beds calculated p c molar ratios suggest that 1 the measured section is highly enriched in phosphorus p relative to oc 2 regeneration of organic p from organic matter decomposition was negligible and 3 the source of p was external likely upwelled bottom water rich in inorganic p in spite of good preservation conditions and correspondingly high toc contents the overall oc accumulation rates are moderate in comparison to those of actual high productivity areas which is mainly due to the episodic character of depositional processes and the intervening long periods of nondeposition and sediment reworking they preclude this section and by extrapolation the monterey formation in general from being an important oc sink during the middle miocene alternatively large oc sinks were probably created on the continent lignite deposits and in sedimentary depocenters which received increasing amounts of detrital sediments due to a combination of climate change spreading of grasslands and the increasing importance of mountain chains such as the himalaya the associated high nutrient fluxes may have been involved in the backstepping and drowning of carbonate platforms and in the generation of widespread phosphat rich deposits during the late early and early middle miocene

sediment transport in the san francisco bay coastal system an overview abstract the papers in this special issue feature state of the art approaches to understanding the physical processes related to sediment transport and geomorphology of complex coastal estuarine systems here we focus on the san francisco bay coastal system extending from the lower san joaquin sacramento delta through the bay and along the adjacent outer pacific coast san francisco bay is an urbanized estuary that is impacted by numerous anthropogenic activities common to many large estuaries including a mining legacy channel dredging aggregate mining reservoirs freshwater diversion watershed modifications urban run off ship traffic exotic species introductions land reclamation and wetland restoration the golden gate strait is the sole inlet connecting the bay to the pacific ocean and serves as the conduit for a tidal flow of 8 10 9 m 3 day in addition to the transport of mud sand biogenic material nutrients and pollutants despite this physical biological and chemical connection resource management and prior research have often treated the delta bay and adjacent ocean as separate entities compartmentalized by artificial geographic or political boundaries the body of work herein presents a comprehensive analysis of system wide behavior extending a rich heritage of sediment transport research that dates back to the groundbreaking hydraulic mining impact research of g k gilbert in the early 20th century

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

time and the persistence of alluvium river engineering fluvial geomorphology and mining sediment in california abstract river managers need to understand fluvial systems as they change through time many river systems are presently in a state of flux as a result of substantial anthropogenic changes to water and sediment regimes and channel hydraulics yet historical approaches to understanding river systems rarely receive adequate attention because historical methodologies are not conducive to the application of quantitative analysis while there is limited precision in most historical reconstructions the information derived from these studies constrains other interpretations and is essential to a full understanding of the behavior of fluvial systems geomorphology provides a perspective on river systems in which time at various scales is interwoven into practical and theoretical aspects of scientific inquiry thus geomorphology is important to our understanding of not only physical systems but also fundamental concepts of time this study examines channel morphological changes in the bear and american basins brought about by two episodes of sedimentation from hydraulic gold mining the primary event was the production of more than 1 billion m3 of sediment throughout the northern sierra nevada from 1853 to 1884 which caused aggradation in many channels across the sierra foothills and sacramento valley assumptions by both engineers and geomorphologists that morphologic responses to this event were ephemeral that sediment loads have returned to previous levels and that deposits have stabilized are not borne out by field and historical data in the sacramento valley a secondary sedimentation event not previously studied was the production of at least 24 million m3 of sediment during a period of licensed mining from 1893 to 1953 this episode of sedimentation has been largely overlooked as a geomorphic hydrologic or water quality event yet channel morphologic responses in phase with mining during this period are demonstrated systematic changes in stage discharge relationships reflect channel morphological changes that are relevant to flood risk assessments stability of engineering structures on floodplains and geomorphic interpretations

tectonic and metallogenic implications of regional seismic profiles in the timmins mining camp four regional seismic reflection profiles totalling 153 line km were acquired near timmins ontario within the southern abitibi greenstone belt five additional high resolution lines targeted specific metallogenically important features such as the porcupine destor deformation zone interpretation of these profiles individually and in a composite north south transect reveals a number of prominent bands of reflectors within the upper 15 km of the crust that define a series of folds or antiformal stacks of thrust nappes structures and stratigraphy mapped at the surface confirm structural culminations in these locations at depths greater than 10 km the reflectors have generally shallower dips implying broad folding major ore deposits such as those at the kidd creek hollinger mcintyre and dome mines are located on the northern steeply dipping limbs of these antiformal stacks implying that the fold structures focused post tectonic mineralizing fluids within the upper crust into the near surface the porcupine destor deformation zone is proximal to the large gold deposits near timmins and is revealed by the new seismic data to be a composite of early fold structures and late transpressive fault arrays

the effect of hydrothermal processes on midwater phosphorus distributions in the northeast pacific abstract the distributions of dissolved particulate and sedimentary phosphorus were measured in the region of the juan de fuca ridge to determine the impacts of hydrothermal processes on the phosphorus cycle in the oceans significant negative dissolved phosphate anomalies ranging from 0 to 60 nmol l were observed in the water column at depths between 1900 and 2300 db the largest anomalies

the diagenesis of phosphorus in a nearshore marine sediment abstract chemical analyses have been made for total inorganic phosphorus total organic phosphorus and organic carbon in plankton and in anoxic sediments from long island sound u s a when combined with laboratory experiments the measurements of other studies on the same sediments and mathematical modelling the results indicate that 1 1 a large proportion of dissolved phosphate in the upper 10 cm of sediment zone of bioturbation is provided by the release of adsorbed phosphate during the reduction of ferric oxyhydroxides 2 2 below the zone of bioturbation phosphate is liberated to solution solely via organic matter decomposition and the release is stoichiometrically coupled to bacterial sulfate reduction and ammonia formation 3 3 a steady state diagenetic model can be used to predict the profile of organic phosphorus from that of dissolved phosphate at depths below the zone of bioturbation 4 4 the flux of dissolved phosphate out of the sediment must arise largely from phosphate liberation occurring very close 5 5 there is a large preferential loss of phosphorus relative to carbon from organic matter at the time of or prior to burial whereas after burial phosphorus is not lost preferentially at this location

dams and geomorphology research progress and future directions dams impose changes of flow and sediment transfer that drive changes of channel form along the downstream regulated river these changes have been described for more than 50 years but process form relationships have only been advanced with the establishment of a conceptual framework during the 1970s and then the extension of monitoring data and advancement of remote sensing technologies particularly over the past 20 years this paper reviews these developments and identifies three influential themes i channel dynamics ii the role of riparian vegetation and iii channel change as the driver of ecological change changes can be rapid in semi arid regions but elsewhere relaxation periods may extend to millenia in these latter cases regime or steady state models should be replaced by models of transient states applied to the reach scale in order to respond to the needs of river managers over decadal timescales

pore water fluoride in peru continental margin sediments uptake from seawater abstract fluoride analyses display downward decreasing pore water gradients in peru shelf phosphatic muds that require diffusion from the overlying seawater into the sediment column and removal by reaction within the upper few tens of centimeters presumably by incorporation into carbonate fluorapatite the profiles can be modeled as first order f removal with rate constants of 3 yr 1 and asymptotic f concentrations deep in the cores of 35 45 m almost one half the seawater value the integrated flux of fluoride from seawater into organic rich shelf sediments in coastal upwelling zones phosphatic muds yields a contemporaneous global f burial of 0 54 10 10 mol f yr 1 about one fifth the burial in other sinks mostly carbonates and opal the associated burial flux of phosphorus in shelf phosphorites is about 1 6 10 10 mol p yr 1 comparable to p burial in the deep sea with organic matter 1 4 10 10 mol yr 1 and biogenic carbonates 1 4 10 10 mol yr 1 thus phosphorite formation on the peru shelf is a significant contemporaneous process

relation between sedimentation rate and burial of organic phosphorus and organic carbon in marine sediments organic carbon and organic phosphorus concentrations in marine sediment cores with known sedimentation rates were determined and collected from the literature with the exception of organic rich sediments from upwelling areas organic phosphorus concentrations in marine sediments do not correlate linearly with organic carbon concentrations the c p ratios of organic matter buried in marine sediments vary systematically with sedimentation rate over the range studied 0 0001 to 2 5 cm y low c p ratios 200 atomic occur in sediments with sedimentation rates both less than 0 002 cm y and greater than 1 cm y higher c p ratios up to 600 are found at intermediate sedimentation rates a simple steady state model is developed for the early diagenesis of organic carbon and organic phosphorus in marine sediments the processes included are sediment burial pore water diffusion and bacterial decomposition of organic matter by oxic respiration and sulfate reduction preferential regeneration of phosphorus relative to carbon is assumed to take place during oxic respiration the modeling shows that both organic matter preservation and the degree of elemental fractionation between phosphorus and carbon depend strongly on the overall sedimentation rate very high sedimentation rates coastal deltaic environment result in a good preservation of deposited organic matter with an initial c p ratio close to the redfield value at very slow sedimentation rates pelagic environment the oxidation of the sedimentary organic matter is nearly complete and produces a low c p residual organic material this residual organic matter may represent either refractory detrital organic compounds enriched in phosphorus or in situ synthesized low c p bacterial remains the high c p ratios at intermediate sedimentation rates slope and shelf environment reflect the preferential regeneration of phosphorus during the incomplete decomposition of the metabolizable organic matter

impact of historic land use change on sediment delivery to a chesapeake bay subestuarine delta historic land use in the chesapeake bay drainage basin induced large fluxes of fluvial sediment to subestuarine tributaries stratigraphic and palaeoecologic analyses of deltaic deposits may be used to infer changes on the landscape but are not sufficient to quantify past sediment supply when viewed as an inverse boundary value problem reconstruction of the sediment supply function may be achieved by combining deltaic sedimentation chronologies with an equation governing delta progradation we propose that the diffusion equation is appropriate for simulating delta progradation and obtaining the sediment supply function provided a suitable diffusion constant d can be determined three new methods for estimating d are presented for the case of estuarine deltas when the inverse boundary value technique was applied to otter point creek a tidal freshwater delta at the head of bush river in upper chesapeake bay d values ranged from 3763 to 6199 m2 a 1 delta growth simulations showed a 1740 1760 initial pulse a 1760 1780 erosive redistributive interval a 1780 1920 growth period and a 1920 present erosive redistributive era coupling of simulated delta elevations with an empirical plant habitat predictive equation allowed for comparison of predicted versus actual relative habitat areas also the model yielded reconstructed watershed erosion rates and stream suspended sediment concentrations that could be useful for development of water quality regulations copyright 2001 john wiley sons ltd

the initial gradient of sulfate in gulf of california sediments abstract results of pore waters sulfate analysis from 26 cores from the gulf of california were used to calculate initial gradients of sulfate the values range from 0 05 to 0 72 mm cm 1 the highest values are from the continental shelf the intermediate and lowest values are from deep basins regression analysis between sedimentation rates and sulfate gradients gives an equation of the form w b c x o with an empirical constant b 1 49 this constant differs from that obtained for marine sediments from other areas this difference may be due to the fact that gulf of california sediments apparently contain less reactive organic matter than do other marine sed ments with similar sedimentation rates

early diagenetic redistribution and burial of phosphorus in the sediments of the southwestern east sea japan sea this study was carried out in order to understand the early diagenetic redistribution of phosphorus and relevant mass balance in the sediments of the east sea in two cruises during may 1993 and october 1995 11 box cores were collected in the southwestern part of the east sea dissolved phosphorus and iron were analyzed in the porewater from the cores sediment samples were analyzed for solid phase p species and solid phase fe oxyhydroxide by sequential extraction phosphorus speciation results show that organic p is the major chemical form of phosphorus in young sediments within the upper 50 cm of sediment however the authigenic fraction of total p increases with depth indicating the precipitation of carbonate fluorapatite cfa in the sediments the authigenic cfa ca5 po4 2 6 co3 0 4f was formed and buried at rates of 11 110 mol cm 2 kyr 1 the main source of dissolved phosphorus for the precipitation of cfa is organic p dissolved phosphorus released from the decomposition of organic p diffuses upward to return to bottom water or is sorbed to iron oxides in the oxidized sediments as sedimentation proceeds the iron oxide bound p is released in the reduced layer and enters the dissolved phase which contributes p to the formation of cfa in addition to that contributed by the organic p the burial flux of reactive p iron oxide bound p authigenic p organic p is 0 09 0 53 g p m 2 yr 1 that accounts for 18 58 of the reactive p arriving at the sediment water interface the burial flux of reactive p is high in the upper and lower continental margin sediment the burial flux of reactive p in the ulleung basin sediment is less than those in the continental margin sites by a factor of 6 indicating that the reactive p burial flux is mainly dependent on sedimentation rate

subhorizontal fractures in a granitic pluton their detection and implications for radioactive waste disposal several countries are actively investigating the feasibility of using crystalline rock bodies for the ultimate disposal of radioactive nuclear waste as part of the concept assessment phase in the canadian nuclear fuel waste management program a multidisciplinary research investigation is being conducted across the lac du bonnet batholith in southeastern manitoba no radioactive materials other than sealed sources or tracers are to be emplaced within this rock body the results of a high resolution seismic reflection survey together with information from a number of deep boreholes demonstrates that major subhorizontal fractures occur at depths of up to 800 m within the batholith an integrated interpretation of the seismic data with selected borehole logs shows that warm water is flowing up the major fractures from depth a natural corollary of these results is that a three dimensional seismic reflection survey combined with an appropriate exploratory drilling program has the potential for delineatin

geochemical characteristics of phosphorite and carbonate nodules from the miocene funakawa formation western margin of the yokote basin northeast japan abstract phosphorite nodules were discovered in diatomite and diatomaceous mudstones of the late miocene funakawa formation in dewa height on the western margin of the yokote basin northeast japan they occur as small nodules cemented burrows and small trace fossils in diatom rich sediment that was deposited just above the contact between underlying siliceous shales the underlying shales are essentially devoid of fossils and the overlying bioturbated diatomaceous mudstones are fossil rich the underlying shale is rich in manganese mn calcite nodules and the overlying mudstone is rich in magnesian mg calcite nodules some phosphorite nodules exhibit a zonal structure caused by two phases of mg calcite cementation with or without mn calcite within the pore space of the nodule the phosphorus p content of these nodules exceeded 25 wt in p2o5 the principle phosphate mineral composing the nodules is fluor f carbonate apatite crystals which are a few m in length and cocoon shaped their aggregate includes a small amount of silica aluminum and water si al and h2o respectively the rare earth element ree composition of the phosphorite nodules is characterized by a positive europium eu anomaly and no cerium ce anomaly the biomarker distribution of the phosphorite nodules is characterized by low cpi low carbon number n alkane and high hopenes type hopane and isoprenoid ketone phosphorite nodules originate from the phosphate contained in diatoms the mineralization occurs in the bacterial sulphate reduction zone and bacteria appear to have played an important role in the concentration of p and precipitation of apatite

enhancing base metal exploration with seismic imaging commencing in 1988 and continuing for 5 years lithoprobe acquired a series of high resolution seismic experiments within and near base metal mining camps in canada including the abitibi subprovince of quebec and ontario the world class sudbury ni cu mining district the buchans mine in newfoundland and the thompson ni belt in manitoba this work undertaken in close cooperation with the geological survey of canada and major canadian mining companies stimulated an intensive and broadened series of followup studies with the common objective of assessing potential applications of multichannel seismic mcs imaging for deep mineral exploration and mine development this research was motivated by a widely recognized disparity between the depths from which ores can be profitably mined up to 2 km or more and the resolving depths typically 500 m of commonly used geophysical methods for mineral exploration initial rock property studies established that the expected contrast in acoustic impedance between

2d 3c high resolution seismic data from the abitibi greenstone belt canada abstract one high resolution seismic profile acquired as part of a 3 component three orthogonal seismometers regional seismic reflection survey within the southern abitibi greenstone belt was investigated in more detail using tomography and by processing all three components several high resolution lines had targeted the porcupine destor deformation zone a zone proximal to the large gold deposits of the timmins mining camp and revealed by the new seismic data to be a composite of early fold structures and late transpressive fault arrays that host quartz vein gold processing of the horizontal component data assumed that seismic waves were converted from p waves to s waves between vibrator source and receivers s wave static corrections proved especially important radial component sections showed most features observed previously on vertical component sections but some amplitudes became enhanced others reduced the transverse component stack demonstrated that a few structures are 3 d or contain significant seismic anisotropy two dimensional p and s wave travel time tomography analysis using data from the 10 km long linear receiver array revealed low resolution 200 m physical property variations possibly related to mineralization in near surface structures of the porcupine destor deformation zone these variations were especially apparent using poisson s ratio

phosphorus speciation and its bioavailability in sediments of the jiaozhou bay abstract phosphorus p is an important macronutrient that can limit primary productivity in coastal marine ecosystems in this study four sediment cores were collected in the jiaozhou bay to study the phosphorus forms and their bioavailability including exchangeable or loosely sorbed p ex p iron bound p fe p authigenic p ca p detrital p de p and organic p op which were separated and quantified using a sequential extraction method sedex the results showed that the concentration of total p tp in core sediments ranged from 6 23 to 10 46 mol g and inorganic p ip was the dominated p form fe p and de p were the main chemical forms of ip in core sediments the profile variation of op presented the most significant among the phosphorus forms whereas the concentrations of ex p fe p and ca p varied slightly with depth indicating that the transformation of ex p fe p ca p and op could occur during sedimentary p burial moreover the distribution of p species was influenced by many factors including terrigenous input biological processes organic matter degradation and increasing human activities high total organic carbon toc op ratio occurred in the jiaozhou bay ranging from 73 to 472 average 180 81 in core sediments which was caused by the increasing terrestrial organic matter the ratio of toc p reactive ranged from 24 to 101 average 46 15 in core sediments lower than the redfield ratio implying a surplus of sedimentary reactive p compared with toc potential bioavailable p bap accounted for about 28 2 60 8 average 47 1 7 4 of tp in core sediments and presented an increasing trend since 1980s which might be responsible for the shift of phytoplankton community composition during these decades

pre and poststack migration of glimpce reflection data abstract glimpce deep seismic reflection profiles across the midcontinent rift system beneath lake superior reveal a central asymmetric rift with an enormous thickness of volcanic and sedimentary rocks true amplitude cmp processing poststack and prestack migration and forward modelling are used to improve images of steeply dipping faults unconformities and other discontinuities in the deep seismic data with prestack migration important steeply dipping structural features of the lake superior data set are revealed for the first time improved images of high angle normal faults later reactivated as reverse faults provide key structural information for understanding the evolution of the rift system results illustrate that structural interpretations of complex deep reflection records such as those recorded by glimpce should always be based on migrated data furthermore depth migrated sections provide useful starting models for forward velocity modelling of seismic data

particulate iron and manganese in the santa barbara basin california abstract particulate fe and mn may be important trace metal scavengers in the water column as well as being probable indicators of biologically mediated redox processes a study has been made of suspended particulate composition in the santa barbara basin a shallow near shore basin off southern california with sub oxic conditions below sill depth observations have revealed several interesting phenomena relating to the geochemistry of fe and mn most striking is a profound enrichment of particulate fe in samples from the bottom two hundred meters these particulates have a constant fe p mole ratio of about three and may originate at the sediment water interface or may be transported to the basin from local marshes for particulate mn enrichments are observed both in the sub sill waters and near the base of the euphotic zone a consideration of particle removal rates suggests that the sub photic zone enrichment has a biogenic origin in the sub sill waters enrichment in mn is apparently due to the precipitation of dissolved mn diffusing from the anoxic basin sediments a simple mass balance suggests that most of the mn lost from the sediments is transported from the santa barbara basin in dissolved form

channel incision on the lower american river california from streamflow gage records channel incision along the lower american river from 1905 to 1995 is investigated using channel cross section plots and statistical analysis of stage discharge data from two streamflow gages located at three sites channel incision lowered thalweg elevations at rates of up to 8 2 cm yr 1 and flow stages decreased at rates of up to 4 3 cm yr 1 for periods lasting several decades at a critical flood risk location in sacramento flow stages lowered 2 m from 1924 to 1970 channel incision was the result of channel recovery from aggradation due to hydraulic gold mining sediment and was exacerbated by sediment storage behind dams prolonged erosion and transport of historical alluvium in this river suggest that g k gilbert s symmetrical sediment wave model is inappropriate for the lower american river and may not adequately allow for the importance of sediment storage and remobilization in fluvial systems

adjustment of the san francisco estuary and watershed to decreasing sediment supply in the 20th century abstract the general progression of human land use is an initial disturbance e g deforestation mining agricultural expansion overgrazing and urbanization that creates a sediment pulse to an estuary followed by dams that reduce sediment supply we present a conceptual model of the effects of increasing followed by decreasing sediment supply that includes four sequential regimes which propagate downstream a stationary natural regime transient increasing sediment supply transient decreasing sediment supply and a stationary altered regime the model features characteristic lines that separate the four regimes previous studies of the san francisco estuary and watershed are synthesized in the context of this conceptual model hydraulic mining for gold in the watershed increased sediment supply to the estuary in the late 1800s adjustment to decreasing sediment supply began in the watershed and upper estuary around 1900 and in the lower estuary in the 1950s large freshwater flow in the late 1990s caused a step adjustment throughout the estuary and watershed it is likely that the estuary and watershed are still capable of adjusting but further adjustment will be as steps that occur only during greater floods than previously experienced during the adjustment period humans are actively managing the system to try to prevent greater floods if this hypothesis of step changes occurring for larger flows is true then the return interval of step changes will increase or if humans successfully control floods in perpetuity there will be no more step changes

a step decrease in sediment concentration in a highly modified tidal river delta following the 1983 el nino floods abstract anthropogenic activities in watersheds can have profound effects on sediment transport through river systems to estuaries disturbance in a watershed combined with alterations to the hydro climatologic regime may result in changes to the sediment flux and exacerbate the impacts of extreme events such as large magnitude floods on sediment transport in the san francisco estuary suspended sediment has been declining over the past 30 years as a result of declining sediment supply contributing to dramatic changes in the ecology and geomorphology of the estuary however the decline has not been gradual recent observations of an abrupt decrease in suspended sediments in the san francisco bay have been explained by a model that suggests that the step change has occurred due to exceedance of a sediment regulation threshold that triggered the change from a sediment transport regime to a supply limited system we investigated structural changes in the historical record of total suspended solids tss concentration measured in the upper estuary to verify the model predictions tss in the upper estuary exhibited an abrupt step decrease in 1983 corresponding to the record high winter and summer flows from the 1982 to 1983 el nino event after this step change tss concentrations had a significant declining trend despite subsequent near record high flows the abrupt change in tss followed by the declining trend provides evidence for the hypothesis of sediment supply limitation in the san francisco estuary

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

role of a strong oxygen deficient zone in the preservation and degradation of organic matter a carbon budget for the continental margins of northwest mexico and washington state rates of organic carbon oxidation in marine sediments were determined for the continental margins of northwest mexico and washington state with the goal of assessing the role of oxygen in the preservation of organic matter on a margin with a strong oxygen deficient zone and on a typical western continental margin total carbon oxidation rates including rates for individual electron acceptors o2 no3 and so4 were determined at depths ranging from 100 to 3000 m on both margins carbon oxidation rates were generally higher on the washington margin than on the mexican margin the relative importance of the different electron acceptors varied across the two margins and was related primarily to the availability of o2 and no3 from the overlying water the relative contribution of o2 consumption increased in deeper sediments 2000 m as aerobic processes began to dominate the total carbon oxidation rate denitrification rates were highest in washington sediments however denitrification represented a larger fraction of the total carbon oxidation rate in the mexican sediments 40 for mexico vs 30 for washington sulfate reduction accounted for as much as 79 of the total carbon oxidation rate in shallow sediments and less than 20 in deep sediments on both margins the offshore trends in carbon oxidation rate appeared to be related to the organic carbon input rate pore water o2 and no3 penetration depths were shallowest in nearshore stations and increased offshore regeneration ratios of c n p reveal non redfield behavior on both margins carbon budgets for the two margins demonstrate that off mexico a much greater percentage of the organic matter produced in the surface ocean reached the sediments 15 vs 8 for mexico and washington respectively on the mexican margin 8 of the primary production escaped oxidation in the surface sediments to be permanently buried as compared with only 1 2 of the primary production on the washington margin this suggests that oxygen deficient conditions on mexican margin are linked to enhanced carbon preservation

crustal structure of the kapuskasing uplift from lithoprobe near vertical wide angle seismic reflection data reprocessing of one lithoprobe kapuskasing deep seismic reflection profile discloses significant new information on the structure of the kapuskasing uplift ku the shallow structure of the ivanhoe lake fault zone ilfz along which the high grade granulites of the ku were thrust to the surface is conspicuously imaged on a seismic section as a series of prominent northwest dipping reflections with listric geometry the new images show that the ilfz is a steep fault 50 near the surface which quickly flattens out at shallow depths these reflections coincide with bright positive aeromagnetic anomalies over the fault zone direct correlation with geological observations indicates that the high reflectivity and high magnetism associated with the fault zone likely originate from mylonites the reprocessing also reveals a pronounced midcrustal reflector within the abitibi greenstone belt agb dipping northwest and plunging under the ku the existence of such a reflector is independently confirmed by wide angle reflection data acquired from a cross profile this reflector is apparently also detected on two other reflection profiles crossing the ilfz about 80 km to the southwest its concave down shape and broad lateral extent suggest that it represents underthrusting of the agb beneath the ku with these new results a more complete structural cross section can be constructed it shows that on the northwest side the ku was overthrust along the northwest dipping ilfz and on the southeast side the agb was underthrust northwesterly it seems evident that the ku is a product of intraplate collision during the early proterozoic and the underthrusting of the agb is primarily responsible for the emplacement of the ku

phosphorus accumulation in marine sediments and the oceanic phosphorus cycle ideas about key factors in the oceanic mass balance of dissolved reactive phosphate have changed substantially i present an integrated overview of these here with an emphasis on evaluating the burial sinks for p and defining areas needing further research the major source of reactive p to the ocean is river input reactive p is delivered to the oceanic sediment water interface primarily in particulate organic matter p scavenged by hydrothermal iron rich oxyhydroxide particles with uptake in proportion to deep water phosphate concentrations represents a substantially smaller flux to the sediment water interface diagenetic transformations are important influences on the form of reactive p burial in marine sediments p burial occurs with organic carbon burial and as p associated with iron rich oxyhydroxide particles and coatings formation of authigenic p rich phases presumably apatite at the expense of organic p and oxide associated p is significant in open ocean marine sediments the authigenic p sink may represent a substantially larger portion of the sedimentary burial than indicated by previous estimates focused on p burial in organic rich continental margin sediments

anthropogenic influences on shoreline and nearshore evolution in the san francisco bay coastal system abstract analysis of four historical bathymetric surveys over a 132 year period has revealed significant changes to the morphology of the san francisco bar an ebb tidal delta at the mouth of san francisco bay estuary from 1873 to 2005 the san francisco bar vertically eroded an average of 80 cm over a 125 km 2 area which equates to a total volume loss of 100 52 million m 3 of fine to coarse grained sand comparison of the surveys indicates the entire ebb tidal delta contracted radially with the crest moving landward an average of 1 km long term erosion of the ebb tidal delta is hypothesized to be due to a reduction in the tidal prism of san francisco bay and a decrease in coastal sediment supply both as a result of anthropogenic activities prior research indicates that the tidal prism of the estuary was reduced by 9 from filling diking and sedimentation compilation of historical records dating back to 1900 reveals that a minimum of 200 million m 3 of sediment has been permanently removed from the san francisco bay coastal system through dredging aggregate mining and borrow pit mining of this total 54 million m 3 of sand sized or coarser sediment was removed from central san francisco bay with grain sizes comparable to the ebb tidal delta and its direct connection to the bay mouth removal of sediments from central san francisco bay may limit the sand supply to the delta and open coast beaches swan wave modeling illustrates that changes to the morphology of the san francisco bar have altered the alongshore wave energy distribution at adjacent ocean beach and thus may be a significant factor in a persistent beach erosion hot spot occurring in the area shoreline change analyses show that the sandy shoreline in the shadow of the ebb tidal delta experienced long term 1850s 1890s to 2002 and short term 1960s 1980s to 2002 accretion while the adjacent sandy shoreline exposed to open ocean waves experienced long term and short term erosion therefore the recently observed accelerating rates of bay sediment removal ebb tidal delta erosion and open coast beach erosion are all correlated temporally

shallow 3d seismic reflection imaging of fracture zones in crystalline rock a limited 3d seismic reflection data set was used to map fracture zones in crystalline rock for a nuclear waste disposal site study seismic reflection data simultaneously recorded along two roughly perpendicular profiles 1850 and 1060 m long and with a 400 x 400 m receiver array centered at the intersection of the lines sampled a 680 x 960 m 2 area in three dimensions high levels of source generated noise required a processing sequence involving surface consistent deconvolution which effectively increased the strength of reflected signals and a linear tau p filtering scheme to suppress any remaining direct sv wave energy a flexible binning scheme significantly balanced and increased the cmp fold but the offset and azimuth distributions remain irregular a wide azimuth range and offsets 800 m are only found at the edges of the site three dimensional dip moveout and 3d poststack migration were necessary to image events with conflicting dips up to about 40 degrees despite the irregular acquisition geometry and the high level of source generated noise we obtained images rich in structural detail seven continuous to semicontinuous reflection events were traced through the final data volume to a maximum depth of around 750 m previous 2d seismic reflection studies and borehole data indicate that fracture zones are the most likely cause of the reflections

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

gently dipping fracture zones in paleoproterozoic metagranite sweden evidence from reflection seismic and cored borehole data and implications for the disposal of nuclear waste 1 the svecokarelian orogen in the coastal area north of stockholm central sweden is characterized by a complex deformation belt in this belt bedrock domains strike wnw nw dip steeply and are affected by high ductile strain these domains anastomose around tectonic lenses that are up to a few tens of kilometers in length and are a few kilometers wide the bedrock within the lenses is folded and in general affected by lower ductile strain site investigations for the disposal of highly radioactive nuclear waste are presently in progress within one of these lenses approximately 16 km of high resolution 10 m source and receiver spacing 100 channels seismic data were acquired in 2002 along five separate profiles 2 to 5 km in length within this lens in the southeast reflection orientations are well determined where profiles cross one another here there is a nearly one to one correlation of distinct reflections on the seismic sections with hydraulically conductive fracture zones in cored boreholes indicating that these fracture zones control the reflectivity however smaller lenses of amphibolite within the fracture zones may enhance the reflectivity the reflections dip gently to the sse and se and the zones in the boreholes are dominated by fractures that show the same dip direction or are subhorizontal a working hypothesis for the gently dipping fracture zones suggests that these structures formed as minor thrust faults during the later stages of the svecokarelian orogeny mineral fillings and coatings along fractures in these zones indicate later reactivation the current stress field a high intensity of fractures in the zones at a high angle to 3 high in situ stresses in the bedrock and rapid glacial unloading with the development of high differential stresses may explain the large volume of groundwater in these zones the reflection seismic data in combination with the verifying work presented in the cored borehole data have steered the subsequent focus in geoscientific studies to the northwestern part of the candidate area

relationship between phosphogenesis and sequence architecture sequence stratigraphy and biostratigraphy in the middle ordovician of the armorican massif nw france abstract in the armorican massif nw france the middle ordovician formations contain abundant phosphatic p beds associated with terrigenous sediments laid down on a storm dominated shelf facies analysis and sequence stratigraphy carried out on sections located in the crozon peninsula w armorican massif allow us to distinguish four p facies 1 beds with p nodules and crusts contained within sediments laid down on the distal and median parts of the inner shelf 2 amalgamated beds with p nodules and crusts and 3 beds with lingulid brachiopods heavy minerals and p clasts associated with retrogradation phases 4 p clast bearing conglomerates associated with progradation phases the genesis of these facies and their location in the depositional sequences are controlled by the fluctuation of terrigenous inputs during sea level changes sediment volume partitioning we propose a genetic model integrating the superposition of very high frequency vhf and high frequency hf eustatic signals in this model the amalgamated beds and beds with lingulid brachiopods heavy minerals and p clasts result from the superposition of several sea level rise episodes of vhf cycles occurring within the retrogradation phase of a hf cycle the lateral extension of p facies was investigated in the eastern part of the armorican massif benioc domfront les tanneries and st aubin du cormier sections several early darriwilian transgressive events associated with phosphogenesis episodes are dated through high resolution chitinozoan studies some of these transgressive events are at least of regional scale e g ornensis and protocalix transgressive events the topmost calix transgressive event is clearly identified over the northern gondwanan and avalonian domains and may reflect a global eustatic signature

speciation bioavailability and preservation of phosphorus in surface sediments of the changjiang estuary and adjacent east china sea inner shelf abstract the speciation potential bioavailability and preservation of phosphorus p in surface sediments of the changjiang yangtze river estuary and adjacent east china sea ecs inner shelf were investigated through the analyses of p fractions and sediment bulk properties a sequential extraction method sedex was used to separate and quantify the following six sedimentary p reservoirs exchangeable p ex p authigenic p au p detrital p de p organic p or p refractory p re p and fe bound p fe p total p tp in surface sediments ranged from 15 0 to 21 4 mol g 1 and was highest near the changjiang river mouth the average contribution of each form of p to tp was 55 6 de p 17 8 re p 16 1 or p 5 5 au p 2 5 ex p and 2 5 fe p respectively de p showed relatively higher concentrations in the river mouth and the ecs shelf region off the changjiang estuary high concentrations of or p were found mainly in mud areas showing a similar distribution pattern with silt sediment surface area ssa and total organic carbon toc re p was mainly distributed near the estuarine area and the zhe min coast bioavailable p bap accounted for 9 5 32 0 of tp with a mean of 21 2 and showed a similar distribution pattern to that of or p de p ssa and toc ssa loadings both decreased with increasing of ssa while or p ssa loadings varied little with ssa indicating that or p may have reached an adsorption desorption equilibrium on mineral surfaces toc to total organic p top sum of re p and or p ratios less than the redfield ratio 84 in average may have indicated efficient remineralization of organic matter in mobile muds of the changjiang estuary and adjacent ecs inner shelf furthermore the relatively high toc or p ratios 72 422 with a mean of 188 likely suggest a higher degree of preferential regeneration of labile or p over toc in sediments

diagenetic trends of fluorine concentration in negev phosphorites israel implications for carbonate fluorapatite composition during phosphogenesis an electron probe and chemical study of bulk phosphorite samples and separated constituents from various negev deposits was carried out together with xrd ftir spectroscopy and textural analysis the results allow a better understanding of the distribution of fluorine in these upper cretaceous phosphorite sequences and shed light on variations in the composition of the carbonate fluorapatite cfa phase during phosphogenesis two facies are recognized 1 a pristine microbially generated phosphorite facies 2 a recycled peloidal and biodetrital facies fluorine distribution in the negev phosphorites is facies controlled f p2o5 is much lower in the pristine facies 0 090 0 107 than in the recycled facies 0 107 0 120 in addition f p2o5 varies considerably between the various constituents of the phosphate fraction f poor francolites f p2o5 as low as 0 080 co exist with f rich francolites f p2o5 as high as 0 135 in the same phosphorite bulk sample a lower f p2o5 in francolite is associated with higher cd and zn concentrations in the phosphorite an increase in fe rich smectites in the clay fraction and the presence of structural oh in the francolite the lower f p2o5 ratios in the pristine facies are attributed to high organic deposition rates during the formation of these matted sediments leading to rapid burial of the in situ forming cfa this is possibly coupled with diffusion of f from sea water into bottom sediments being hampered by microbial mat coatings these conditions resulted in o2 depleted porefluids inducing the precipitation of cd rich zn sulphides and the formation of fe rich smectites f enrichment probably takes place when the earlier formed f poor primary cfa is relocated close to the sea floor and bathed with interstitial sea water solutions of higher f concentrations oxidation and removal of the sulphide bound cd and zn apparently occurred together with enrichment in f of the francolite combining chemical data with xrd and ftir results suggests a multistage growth for the negev phosphate constituents in shifting formational sites and porefluids of varying f concentrations this multiphase growth is reflected in the patchy distribution of f in the negev constituents and might explain the inverse correlation between mean co2 f and f p2o5 ratios of the analysed phosphorites in the two facies it also suggests that cfa or an amorphous precursor initially formed with some oh groups in the apatite structure which were subsequently substituted by f ions in recycled francolite through re equilibration with porefluids of higher f concentrations

early diagenesis of organic matter in peru continental margin sediments phosphorite precipitation abstract pore water chemistry total dissolved co 2 nh 4 no 3 no 2 po 4 si oh 4 ca mg fe mn so 4 h 2 s and f and titration alkalinity solid phase chemistry c org p org c tot n tot f si opal and s ii and sediment characteristics porosity dry bulk density and formation factors were determined on a centimeter scale spacing in the upper 20 40 cm of sediments under intense upwelling areas on the peru continental shelf these data demonstrate that carbonate fluorapatite cfa is precipitating from pore waters in the upper few centimeters of a gelatinous mud with high organic carbon content up to 20 c org very high porosity 0 96 ml cm 3 and very low dry bulk density 3 dissolved phosphate concentrations at the sediment water interface range from 20 to 100 m orders of magnitude higher than bottom water concentrations and much higher than predicted from regeneration of organic matter the mechanism of this interfacial phosphate release is unclear but is apparently uncoupled from carbon and nitrogen metabolism and thus may be linked either to dissolution of fish debris or to the presence of a microbial mat in surficial sediments fluoride is incorporated into cfa by diffusion from the overlying seawater and carbonate ions are provided from pore water alkalinity magnesium concentrations in this reaction zone are not significantly different from those of seawater suggesting that magnesium depletion is not a necessary prerequisite for cfa precipitation the environment of precipitation is interface linked rather than driven by organic diagenesis of phosphorus deeper in the sediment most of the cores display a wide range of diagenetic characteristics below the immediate interfacial region but almost all show the precipitation signature near the interface this interface linked early diagenetic porewater environment for the precipitation of cfa explains many of the geochemical characteristics of phosphorites and provides a testable model to compare the modern phosphogenic analog with ancient phosphorite deposits two of the cores display very high solid phase phosphorus and fluoride contents reflecting the presence of apparently modern pelletal apatites

deep onshore reflection seismic imaging of the chalk group strata using a 45 kg accelerated weight drop and combined recording systems with dense receiver spacing the chalk group forms important hydrocarbon reservoirs offshore and water aquifers onshore denmark within a day of fieldwork a 450 m long reflection seismic profile was acquired onshore in an are