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

remobilization events involving cd and zn from intertidal flat sediments in the elbe estuary during the tidal cycle in laboratory experiments the effect of periodic alternations between aerobic and anaerobic conditions on the mobilization of zn and cd from the surface layers of an intertidal sand and mud flat sediment was studied a percolation technique was used to simulate submersion and exposure to the air by controlling the concentrations of oxygen and nitrate within undisturbed 2 cm sediment layers zn and cd released from the sediment were removed from the pore water under anerobic conditions and maintained in the percolating water when aerobic conditions were established zn was mobilized immediately after re oxidation whereas cd mobilization was observed after a retention time of 53 to 180 min and 25 72 h in sand and mud flat sediments respectively from 0 3 to 1 8 of the total cd was then lost from these sediments the rates of particulate organic matter degradation calculated from the production of co 2 under aerobic and anaerobic conditions were similar the ph values in sand flat sediments used in the experiments were significantly higher than in mud flat sediments neither the rates of organic matter mineralization nor the variations in ph controlled the observed trace metal mobility the results strongly indicate that trace metals were precipitated as sulphides under anaerobic conditions the release of trace metals under aerobic conditions was attributed to the oxidation of sulphides and the mineralization of organic matter in the surface layer of the mud flat the rate of zn mobilization reached 8 79 10 7 mol g 1 s 1 in summer but was only 1 82 10 7 mol g 1 s 1 in winter cd was released from the same layer during the whole year at a constant rate of 5 89 10 9 mol g 1 s 1 calculations based on the percolation experiments indicate that in mud flat sediments from the elbe estuary a loss of up to 50 of the total cd occurs within one month

three dimensional quantitative modeling of clinoform development abstract clinoform geometry pervades stratigraphic sequences across a variety of scales it is a composite surface which records the complex interplay between accommodation sediment supply physiography and hydrodynamics much of the sequence stratigraphic technique employs clinoform geometry to discriminate between the various systems tracts that constitute depositional sequences however many sequence stratigraphic models treat the generation of accommodation and the input of sediment supply as a two dimensional problem by assuming a line source of sediment entering a system impacted by relative sea level fluctuations one common attribute of clinoforms regardless of size and or shape is that their formation is inherently three dimensional therefore the clinoform geometry varies spatially and temporally throughout a region depending on the proximity to the sediment source and the character of the hydrodynamic regime we present a three dimensional stratigraphic model that combines both diffusion and advection to simulate across and along margin sediment transport and deposition this model allows us to examine how the morphology and internal clinoform geometry of deltas vary away from the sediment source in this application we simulate the development of a delta in a low energy environment to understand the importance of along shelf diffusion on clinoform geometry and the morphology of the delta we predict the three dimensional geometry and how it varies throughout a relative sea level cycle our model indicates that when the clinoform rollover is spatially coincident with the shoreline position the clinoform geometry changes dramatically along strike away from the sediment source region throughout a relative sea level cycle for example oblique clinoforms develop near the source region and evolve into an onlapping sequence along strike on the basis of stratal geometry and the technique of sequence stratigraphy this deposit would be interpreted as two different sequences with very different connotations for their formation we surmise that when the clinoform rollover and the shoreline position are separated e g a subaqueous delta the along strike variability of the clinoform geometry diminishes because of the hydrodynamic forces operative across the shelf consequently it is important to determine how clinoforms develop in three dimensions and to ensure that our window of observation is sufficient to discern between local and regional variability

styles of failure in late holocene highstand prodelta wedges on the adriatic shelf on the continental shelves of the northern mediterranean basin the late holocene highstand systems tract hst prograded un der the influence of major rivers after the attainment of the present sea level highstand about 5 5 cal kyr bp on the adriatic shelf the thickness distribution of the late holocene hst reflects the location of major deltas on the western side of the basin and the geostrophic cir culation which prevents a more uniform sediment dispersal toward the center of the basin very high sediment accumulation rates 1 to 10 cm year resulted in the construction of a hst depocenter up to 35 m thick this shore parallel depocenter is affected by failure of limited displacement over as much as 40 of its extent gas impregnation is common in the topset region and occurs at very shallow levels a few meters below the sea floor five areas are characterized by a variety of sea floor and subsurface crenulations although locally some of these crenulations have an intriguingly regular geometry sediment failure is the most plausible mechanism for their formation sediment failure better explains the large variety of geometries that characterizes the coastal mud prism of the late holocene hst furthermore we observe that these crenulations occur only where the downlap surface at the base of the hst is disrupted and affected by geometries that are con sistent with fluid escape processes this relationship suggests that the basal surface acts as a weak layer for sediment failure failure occurred in variable water depths from the northern slope of the modern po prodelta 10 20 m water depth to the narrow shelf offshore bari 40 110 m water depth in all these areas the proximal part of the hst prodelta wedge is intensely gas charged the thickness and age of the sediment sections affected by failure are slightly differ ent from place to place but appear everywhere younger than 5 5 cal kyr bp where failure affects the entire hst the detachment occurs on the downlap surface at its base failure geometries characterize the head region whereas compressional features such as pressure ridges and mud diapirs dominate in the toe region ranging in depth between 70 and 110 m where failure is limited to the upper few meters of the hst there is a clear lithologic change decrease in carbonate fraction and grain size across the basal surface this lithological change reflects a switch in sediment supply from local apennine rivers below to po derived mud this change occurred at the onset of the little ice age documenting the indirect control of short term climate change and hu man impact on sediment architecture the deformations affecting the late holocene hst in the various areas show differences in internal geometry but appear everywhere to be characterized by limited downward displacement and can be attri buted to shear dominated retrogressive failure it is suggested that some degree of consolidation occurred immediately after mobilization possibly induced by the escape of fluids nowhere has failure evolved into disintegration and flow likely because the type of cyclic loading that triggered it was not prolonged over a long enough interval short lived radionuclides in the uppermost stratigraphic layers which postdate the failure in the area offshore ortona allowed us to quantify systematic changes in sediment accumulation rates as a func tion of the underlying deformed sea floor in areas of wavy sea floor troughs show sediment accumulation rates of greater than 16 mm yr a figure that is fourfold the rate measured on the flanks of the troughs

clinoforms and clinoform systems review and dynamic classification scheme for shorelines subaqueous deltas shelf edges and continental margins abstract clinoforms are inclined and normally basinward dipping horizons developed over a range of spatial and temporal scales in both siliciclastic and carbonatic systems the study of clinoform successions underpins sequence stratigraphy and all efforts to reconstruct the relative partitioning of reservoir seal and source rocks along shoreline to basin floor profiles here we review clinoform research and propose a more systematic description and classification of clinoforms this is a crucial step to improve predictions of facies and lithology distribution within shoreline to continental shelf and abyssal plain successions together with the genesis drivers and dynamics of their constituent sedimentary units four basic clinoform types are here distinguished in delta shorelines lacustrine and marine environments on the basis of their overall spatial and temporal scale morphology outbuilding dynamic and geodynamic and depositional setting 1 2 delta scale clinoforms which in turns are sub divided into shoreline and delta scale subaqueous clinoforms 3 shelf edge clinoforms and 4 continental margin clinoforms delta scale clinoform sets are tens of metres high and typically represent 1 103 kyr with progradation rates ranging from 1 000 100 000 m kyr for shorelines and subaerial deltas to 100 20 000 m kyr for subaqueous deltas shelf edge clinoform sets are hundreds of metres high and are nucleated and accreted in 0 1 20 myr usual progradation rates of 1 100 m kyr by successive cross shelf transits of delta scale clinoforms continental margin clinoform sets are thousands of metres high hallmark key geodynamic crustal boundaries e g continent ocean transition and slowly prograde basinwards in ca 5 100 myr with typical rates of 0 1 10 m kyr as a consequence of the very different progradation rates and of the difficulty of large scale clinothems to backstep during transgressions shorelines are the most dynamic clinoforms with regards to position continental margins the least and shelf edges are intermediate shortly after a transgression therefore the four clinoform types may prograde synchronously along shoreline to abyssal plain transects forming compound clinoform systems during the subsequent regressive cycle however due to the dissimilarity in progradation rates different clinoform types will normally merge progressively with each other giving rise to hybrid clinoforms e g shelf edge deltas and fewer depositional breaks in slope are distinguished along a single shoreline to abyssal plain transect overall all clinoform systems are the result of the dynamic evolution of compound and hybrid clinoforms along a temporal and spatial continuum regulated by the cyclical backstepping of the smaller scale system within natural progradational retrogradational cycles of larger scale clinothem outbuilding all clinothem types may show either an accretionary active or draping passive style depending on the proximity to the sediment source draping clinothems are nearly always composed of condensed fine grained sediments while actively accreting clinothems can be composed of predominantly coarse grained i e reservoir forming or predominantly fine grained i e non reservoir lithotypes a novel hierarchical classification scheme for both recent and ancient clinoforms is here proposed consisting of 12 classes the four basic clinoform types delta scale shoreline delta scale subaqueous shelf edge and continental margin are sub divided into eight accretionary active and draping passive sub types 8 division each accretionary sub type is then sub divided into a sandstone prone and mudstone prone variant 12 division which can be at least tentatively predicted on the basis of the clinoform morphology even in the absence of direct stratigraphic logs

subaqueous delta of the ganges brahmaputra river system abstract the ganges brahmaputra is among the world s three largest river systems in terms of sediment load but until now no high resolution seismic data have been obtained to document the nature of the sediment deposit seaward of the rivers mouths the other two amazon huanghe discharge into energetic coastal environments and form subaqueous deltas with characteristic clinoform stratigraphy high resolution seismic reflection profiles of the bengal shelf reveal similar stratigraphy topset beds dip gently 0 036 and diverge offshore more steeply dipping foreset beds 0 190 converge farther seaward and relatively thin gently dipping bottomset beds 0 022 extend across the outer shelf overlying an erosional surface presumed to be of late pleistocene age sediment accumulation rates are highest in the foreset region 5 cm year and reduced in the bottomset region

did the rifting of the atlantic ocean cause the cretaceous thermal maximum the cretaceous thermal maximum was a major turning point in the history of earth s climate this interval of peak warmth in the turonian has been attributed to very high atmospheric pco2 resulting from rapid outgassing rates although crustal cycling rates peaked in the aptian albian interval on the basis of coupled ocean atmosphere model simulations of the middle cretaceous we hypothesize that the formation of an atlantic gateway could have contributed to the cretaceous thermal maximum differences between prerifting and postrifting climate experiments demonstrate substantial regional oceanographic changes in the north and south atlantic basins that are consistent with oxygen isotopic evidence used to infer a cretaceous thermal maximum the model results help reconcile the paleoclimate record inferred from foraminiferal d 18 o with our understanding of climate dynamics and cretaceous tectonism

diagenetic evolution of the upper devonian phosphorites alborz mountain range northern iran abstract the upper devonian mixed siliciclastic carbonate stratigraphic succession of the geirud formation in the alborz mountain range north of iran hosts numerous phosphorites and phosphatic rocks these phosphorites which represent one of the most globally important deposits in the devonian have gained little attention regarding their genesis and diagenetic evolution this study focuses mainly on the post depositional changes that occurred during shallow to deep burial diagenetic evolution and subaerial weathering of the geirud phosphorites the phosphorites consist of phosphatic massive mudclasts detritus rich lithoclasts bioclasts and bones formed by several stages of phosphogenesis and erosion reworking winnowing and condensation associated with famennian sea level changes the phosphatic clasts consist of early diagenetic poorly crystalline carbonate fluorapatite cfa and pyrite cementing detrital quartz illite muscovite rutile and zircon phosphatic clasts are intensely compacted with sutured grain contacts along which dissolution and reprecipitation of chemically refined well crystalline cfa with a bright blue cathodoluminescence and illite occurred during deep burial diagenesis similarly quartz shows deformation planar features overgrowth cement was developed as a result of pressure dissolution in phosphatic sandstones followed by precipitation of ferroan dolomite ankerite and chlorite in secondary porosity subaerial weathering led to oxidation of pyrite and generation of acidic ph condition under which ca and p from phosphates fe and s from pyrite fe ca mg and mn from ferroan carbonates and al and si from aluminosilicates were released to form goethite psilomelane calcite gypsum and crandallite the paas normalized rare earth elements rees show bell shaped patterns with middle rees enrichment positive eu anomaly and a weak negative ce anomaly this implies recrystallization of cfa in phosphorites and phosphatic rocks during deep burial diagenesis deviating from the modern seawater like ree patterns in this regard deep burial diagenesis affecting the upper devonian geirud phosphorites is possibly a common process in the proterozoic paleozoic phosphorites in northern iran and elsewhere in the world

the submarine delta of the ganges brahmaputra cyclone dominated sedimentation patterns the ganges brahmaputra belongs to the world s largest rivers in terms of sediment discharge but little is known yet about the processes controlling sediment distribution on the shelf and the documentation of these processes in large and small scale sedimentary structures for this study the submarine delta of the river system was investigated by high resolution seismic reflection profiles and piston and gravity coring logged physical properties of the cores were combined with visual core description grain size analysis and radiography sedimentation rates were estimated by 210pb and 137cs gamma spectrometry and cross checked with evaluation of seismic profiles the data reveal that the broad delta topset 20 m waterdepth is formed by a thick layer of sand silt highest sedimentation rates about 10 cm a 1 occur at the centre of clinoform delta foreset beds where about 20 of the total riverine sediment load is deposited and thus cause an annual progradation of the subaqueous delta front by about 15 m the foreset beds consist of graded sand silt layers which are thought to be deposited by sediment laden flows generated during the surge of tropical cyclones tempestites interbedded with silty clay layers the head of a canyon the swatch of no ground that deeply incises into the shelf forms a sediment trap along the westward cyclonic transport path where sedimentation rate increases to about 50 cm a 1 episodically earthquakes or storms destabilize especially the rapidly accumulated foreset beds in the eastern delta creating up to 8 m thick mass flows on the outer shelf in water depth beyond 80 m no holocene sediment is deposited

the late holocene gargano subaqueous delta adriatic shelf sediment pathways and supply fluctuations the gargano subaqueous delta formed on the eastern and southeastern sides of the gargano promontory in the western adriatic this subaqueous deposit represents the southernmost portion of the late holocene highstand systems tract hst growing along the western side of the adriatic as an extensive wedge of deltaic and shallow marine mud the late holocene hst rests above a regional downlap surface that marks the time of maximum landward shift of the shoreline attained around 5 5 cal kyr bp at the end of the late pleistocene holocene sea level rise high resolution seismic stratigraphic and tephra correlation indicate the presence of a thin basal unit recording condensed deposition between 5 5 and 3 7 cal kyr bp over much of the basin above this unit sediment accumulation rates increased to high values as much as 1 5 cm yr 1 reflecting the stabilisation of relative sea level and the forcing from high frequency climatic or anthropogenic changes affecting river dynamics the late holocene mud wedge of which the gargano subaqueous delta is a significant component reaches up to 35 m in thickness and has a volume of ca 180 km3 the shore parallel thickness distribution of the mud wedge reflects the dominant oceanographic regime of the basin and the asymmetric location of the mostly western sediment sources with a combined modern delivery of 51 7 106 t yr 1 of mean suspended load in sections perpendicular to the coast the late holocene mud wedge appears composed of forestepping clinoforms with gently dipping foresets typically 0 5 the gargano subaqueous delta is characterised by a submarine topset in water depths shallower than 25 28 m and accounts for about 1 7th of the total volume of the late holocene mud wedge despite the absence of direct river supply to the gargano area in the area of maximum interaction between shore parallel currents and basin morphology progradation occurs onto a flat and barren bedrock outcrop in about 50 80 m water depth the rapid transition from a thickness of 30 m of late holocene mud to nil is a good indication of the role of southward flowing bottom hugging shelf currents in causing the redistribution of sediment along the adriatic inner shelf additional evidence of this regime comes from 1 the most recent sigmoid defined at seismic stratigraphic scale deposited since the onset of the little ice age showing a shore parallel thickness distribution and a main depocentre to the southeast of the gargano promontory 2 the maximum values of sediment accumulation rates over the last century documented by 210pb measurements defining a narrow shore parallel belt immediately seaward of the depocentre of the most recent sigmoid the gargano subaqueous delta grows from the outbuilding of progressively younger progradational sigmoids that tend to parallel the previous ones the gargano subaqueous delta differs from other documented late holocene subaqueous deltas because its growth reflects 1 sediment transport dominated by bottom currents sub parallel to the strike of the composing clinoforms 2 a complex supply regime including the po delta 350 km to the north and several coalescing apennine rivers acting as line source 3 several alternating intervals of enhanced outbuilding and condensed deposition and 4 an in phase growth of the most recent sigmoid with the major progradation of the po delta during the little ice age

application of the ce anomaly as a paleoredox indicator the ground rules much attention has been paid in recent years to the potential application of the ce anomaly measured in various marine phases as a paleoceanographic indicator of widespread marine anoxia in this paper we present and discuss results from recent studies of present day rare earth element ree distributions and hence ce anomaly distributions in the marine environment which are particularly pertinent to paleoceanography subsequently we review and discuss the validity of the recent literature in which ce anomalies have been employed as paleoredox indicators

human impact in the holocene fluvial and coastal evolution of the marche region central italy abstract today the coasts of the marche region are represented by almost continuous rectilinea sand beaches except in the north at the border with the romagna region and in the central part around the conero ridge where there are active rock cliffs the sandy coasts are protected almost everywhere by artificial barriers built up as a protection against the general tendency to retreat along some tracts the coastal erosion started at the beginning of this century but became generalized after 1940 1950 this was mainly due first to the reduction in sediment supply following the improvement in agricultural techniques after the italian unification and later to the widespread extraction of gravels from the thalwegs related to the rapid increase in urban population in the 1950s however in the same period along the rivers there was a widespread creation of artificial levees to prevent lateral erosion or flooding and to extend areas suitable for agriculture following these practices the lower middle tracts of the rivers underwent a strong vertical downcutting which increased as a result of the creation of checkdams downvalley of many bridges which contributed to the store of the sediments in the upper part of the valleys at present most of the rivers have an irregular course and are deeply entrenched in the bedrock or inside their own sediments up to the beginning of the century most of the lower tracts of the valleys were characterized by strong aggradation in a braidplain system this aggradation started as early as the middle ages 1100 ad but increased after the renaissance as a consequence of a generalized deforestation of the periadriatic basin and the following severe soil erosion in the mean time the coast underwent a very fast progradation in some places more than 500 m small deltas were created at the mouths of the rivers and longshore bars and sandy beaches began to occupy the base of the active cliffs which previously extended between one river and another however in the mountain parts of the river basins a meander course existed and in many cases still exists expecially where the human interventions were of limited extent before 1000 1100 ad all the rivers had a meander pattern and at the junction with the sea entered lagoons and swamps in most cases protected by littoral barrier beaches these conditions were established earlier than the third century bc and have been attributed to the first systematic land clearance and the following soil erosion during the bronze and iron ages at that time the regional coastline became almost rectilinear but with many active cliffs between one river and another before being affected by a major human impact earlier than 4000 years bp the natural coastal environment was represented by active rock cliffs which alternated with pocket beaches corresponding to a river mouth in some rivers embayments and beaches were located up to 4 5 km inland from the present day position after the flandrian transgression the evidence presented reveals major changes that can be attributed to human impact

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

late cretaceous upwelling system along the southern tethys margin israel interrelationship between productivity bottom water environments and organic matter preservation organic rich upper cretaceous sequences in israel were deposited in an extensive highly productive upwelling linked system which prevailed along the southern tethys margin and lasted for 19 m y santonian to late maastrichtian an understanding of the spatial and temporal characteristics of this system was gained through detailed paleontological and geochemical analyses of subsurface sequences in two basins in israel representing an outer shefela and an inner zin facies belt the nature of the upwelling system and its effect on the sedimentary record is related to two basic environmental parameters namely paleoproductivity intensity and oxygen levels at the bottom the assessment of these parameters and their interrelationship has been performed through the development of paleontological foraminiferal criteria which are independent of the organic matter content following the establishment of these criteria it is concluded that the productivity reached its maximum intensity during the late campanian which was also the time of most notable differentiation between the center of the upwelling system in the inner belt and the less intense conditions in the outer basin this distribution is expressed in varied lithology organic rich carbonates phosphorites and siliceous rocks at the core of upwelling and a uniform lithology organic rich carbonates at the margin of this system the uniform lithology of the maastrichtian in both basins composed of organic rich carbonates is ascribed to a gradual weakening of productivity the bottom conditions in the inner belt during the late campanian the time of maximum surface productivity were near anoxic changing to more aerated dysaerobic conditions during the early maastrichtian in the outer belt a more aerated bottom dysaerobic prevailed throughout the late campanian to late maastrichtian the elevated organic matter content in both basins reflects the overall environment of high productivity its actual variations however seem to be unrelated to changes in surface productivity and bottom oxygen levels

late cretaceous ca 84 ma compressive deformation of the stable platform of northeast africa egypt far field stress effects of the santonian event and origin of the syrian arc deformation belt large scale northeast trending asymmetric folds and associated contractional faults seismically induced slump structures and strike slip and extensional faults of santonian age occur within the eastern desert of egypt 150 km south of the syrian arc mobile belt the region also displays a locally developed angular unconformity at the base of the flat lying campanian limestone these features demonstrate that the deformation event responsible for the syrian arc also led to northwest southeast shortening in central egypt ca 84 ma the late santonian shortening corresponds precisely with a brief period of compression that swept across the entire african plate coeval with a significant change in the poles of opening of the north atlantic this santonian event is a prominent example of the role that far field compressional stresses can play in stable intraplate settings

petrology and major element geochemistry of peru margin phosphorites and associated diagenetic minerals authigenesis in modern organic rich sediments abstract new petrographic and major element geochemical data from modern peru margin upper slope outer shelf phosphorites are presented which provide insight into their origin and paragenetic relationship with other authigenic minerals glauconite pyrite and dolomite occurring in organic rich sediments glauconites are precipitated relatively early following the partial reduction of ferric iron and following this process phosphate pyrite and then dolomite precipitation take place at progressively deeper levels in the sediment in association with microbial reduction of sulfate as in many ancient economic phosphorite deposits the phosphatic facies here consist of nodules crusts coatings and strata composed of phosphatic pelletal grains ooids structureless grains intraclasts clumps and biogenic grains in association with organic rich biosiliceous sediments all are considered to have formed within a few centimeters or within a few tens of centimeters below the sediment water interface important factors that influence which morphology will tend to develop include the amount of available pore space the presence of suitable nucleation sites the amount and size of siliciclastic detritus incorporated as inclusions and the relative solution chemistries of the precipitating solutions bacterial mediation may play an important but as yet unspecified role in the precipitation process textural data and factor analysis of chemical data suggest that structureless pellets are relatively inclusion free na f mg co3 substituted pore water precipitates whereas ooids are inclusion rich pore water precipitates poor in lattice substituted components variations in nodular cement birefringence and crystallinity are suggested to have been produced by similar lattice substitutions that directly reflect pore water carbonate ion concentrations and thus relative degrees of organic matter degradation phosphate and dolomite are intimately mixed yet mineralogically distinct phases in phosphatized dolomicrites depth stratified threshold carbonate ion concentrations may control the lower limit at which phosphatic minerals may precipitate below depths of a few centimeters excessive carbonate ion concentrations and diminished reactive iron and sulfate concentrations favor the development of dolomite while precluding further development of phosphatic minerals and pyrite periodic sediment reorganization bioturbation current winnowing and erosion mass wasting etc plays an important role in both concentrating pelletal grains and maintaining nodules and crusts at critical depth levels in the sediment as well as mixing ordered mineral parageneses into complicated sequences

geochemistry and deposition of 7be in river estuarine and coastal waters the atmospheric flux of cosmogenic 7be 53 3 day half life and the mode of 7be deposition in river estuarine and coastal environments have been examined the atmospheric flux of 7be commonly supports inventories ranging from 1 0 to 2 0 pci cm2 1 pci 0 037 bq beryllium 7 concentrations in water phase samples collected across salinity gradients in several estuaries along the eastern coastline of the united states range from 0 03 to 0 53 pci l and primarily reflect variations in 7be supply and sorption kinetics the major process controlling the concentration of 7be on estuarine suspended particles appears to be the length of time that these particles remain in the water column field particle to water distribution coefficients for 7be have a median value of about 4 104 but range over an order of magnitude reflecting short term variations in 7be input particle dynamics and particulate iron content rather than equilibrium sorption desorption responses to changes in water salinity or particle type residence times of 7be in the water column range from a few days in estuarine areas of rapid fine particle deposition to several weeks in high energy environments where pronounced sediment resuspension reintroduces deposited 7be back into the water column inventories of 7be in sediments range from nondetectable to 3 3 pci cm2 with the highest inventories in areas where fine particles are accumulating rapidly such sites are also major repositories for other particle reactive substances a 7be budget for the james estuary indicates that less than 5 of the expected 7be input is in the water column and that the short term estuarine trapping efficiency for atmospherically derived 7be is somewhere between 50 and 100

sedimentary redox conditions in continental margin sediments n e pacific influence on the accumulation of redox sensitive trace metals redox conditions in near surface sediments from the continental margin off western canada were characterized to determine how they influence the accumulation of redox sensitive trace metals despite the development of suboxic conditions within millimeters of the sediment water interface there is little enrichment of re u cd or mo in the upper 10 to 15 cm of the sediment column this observation is consistent with the low extractible solid mn concentrations but high i corg ratios that imply that near surface sediment redox conditions are poised between mn and i reduction in contrast below 15 cm re and to a lesser extent cd and u are enriched e g up to 65 ng g re but only in those cores collected from within and below the oxygen minimum zone molybdenum concentrations remain low b1 5 g g in all cores indicating that these near surface sediments never became fully anoxic

diagenetic constraints on the use of cerium anomalies as palaeoseawater redox proxies an isotopic and ree study of cambrian phosphorites seawater rare earth element ree distributions show heavy ree enrichment and cerium depletion but these characteristics are only rarely found in ancient marine authigenic minerals such as carbonate fluorapatite and calcite this enigma may be due to changing ree distributions in seawater through time or to post depositional redistribution of ree differentiating between these two factors is however far from straightforward as their relative importance is likely to vary and evidence is often ambiguous in this article we present ree as well as strontium and sulphur isotope data for basal cambrian phosphorites of south china which confirm the emerging rule of thumb that granular phosphorites seldom reveal extreme departures from the seawater norm and tend to undergo therefore less diagenetic alteration of ree spectra than skeletal apatites and other phosphate types this study reveals stratigraphic trends in ce anomalies ce ce that could be taken to imply the preservation of a palaeoenvironmental signal however further investigation of our data shows that such trends in phosphorites can also be caused by post depositional alteration which tends to 1 increase ree contents 2 reverse ce depletion 3 alter eu anomalies and 4 concentrate preferentially the middle ree mree further alteration which may be due to weathering has led to hree depletion and positive la and y anomalies tetrad effect this is the first study where ceanom and phosphate bound sulphate s isotope values could be compared for one particular stratigraphic section which provides us with an additional tool for the interpretation of diagenetic redox conditions least altered phosphorites from meishucun that yield a strongly negative ceanom constrain early cambrian seawater 34s to about 33 we conclude that phosphorite ceanom primarily records variations in the local conditions of diagenesis while outlining some special cases in which diagenetic redox conditions may broadly reflect local bottom water redox conditions

distribution texture and composition of modern phosphate pellets in peru shelf muds abstract textural analysis including estimates of concentrations of authigenic phosphate pellets were made for eight sediment cores from the peru continental margin phosphatic pellets separated from these modern organic rich sediments are black spherical ovoidal in shape and in thin section often display a concentric structure around a nucleus consisting of inorganic mineral grains some pellets have a gray white exterior coating which appears to be secondary diagenetic calcite phosphatic pellets account for upwards of 80 of the sediment mass in some cores pellets concentrate in specific size classes generally between 125 and 500 m in diameter and occur within a poorly sorted sediment

modern accumulation rates and a sediment budget for the eel shelf a flood dominated depositional environment the northern california continental margin is periodically impacted by geologically significant storms which have a marked influence on terrigenous sediment supply flood deposition and long term accumulation of fine grained sediment on the eel shelf accumulation of eel river muds on the adjacent shelf was investigated using 210pb and 137cs geochronologies in order to understand the fate of sediment discharged by the eel river and to relate patterns of net sediment accumulation 100 yr time scale to sediment dynamics 210pb data demonstrate that modern accumulation of river mud occurs from the 50 m isobath seaward across shelf accumulation rates decrease from maximum mid shelf values of 0 6 1 7 g cm 2 yr 1 to values of 0 2 0 4 g cm 2 yr 1 at the shelf break with a spatially weighted mean of 0 5 g cm 2 yr 1 0 4 cm yr for the entire shelf 210pbxs sediment depth profiles from the region of highest accumulation rate are characterized by subsurface intervals of low and uniform activity which are produced by flood deposition in some cores particular 210pbxs activity intervals may be associated with major eel river floods of 1955 1964 and 1974 it is postulated that because of the coincidence of high river flow events and southerly winds during cyclonic winter storms net northward transport allows for preferential deposition of fine grained sediment north of the river mouth over the past 100 years fluvial sediment input combined with marine dispersal processes have produced a mid shelf depocenter evident by both the spatial distribution of 210pb accumulation rates and by clay rich flood layers partially preserved in shelf deposits a fine grained sediment budget for the dispersal system based on hydrological data and 210pb geochronologies demonstrates that a maximum of 20 3 109 kg yr of the mean annual supply of fluvial mud 14 109 kg yr is trapped on the shelf the results of this study demonstrate that 1 short term sedimentation processes associated with floods can influence sediment accumulation on longer time scales and 2 a major fraction of fine grained sediment supplied to tectonically active margins by flood prone mountainous rivers bypasses narrow continental shelves

source diagenesis and fluxes of particulate organic carbon along the western adriatic sea mediterranean sea article i nfo in this study we investigated the modern organic carbon oc cycling along the clinoform shaped deposit that developed after the attainment of the modern sea level in the adriatic sea 5 5 kyr cal bp newly acquired data were combined with published results to characterize the i origin ii diagenesis and iii fluxes of oc along the adriatic clinoform 13 c 14 c and lignin phenols were used to constrain the composition of oc accumulating in surface sediments sediment cores collected at different water depths were used to describe the early diagenesis during burial in different regions in addition on the basis of an extensive number of accumulation rates and oc data we assessed the flux of oc to the seabed and its burial our results showed that terrigenous oc is the dominant oc source in the po prodelta mainly in the form of pre aged soil derived oc and vascular plant fragments along the clinoform both 14c and the concentration of lignin derived phenols decreased with increasing distance from the po prodelta indicating the influence of an additional pool of aged oc that gradually becomes more important because of its selective preservation during the sediment transport as a result degradation rates k decreased along the clinoform as a function of the sediment oxidative history the calculated half life of reactive oc t1 2 was 14 6 yrs in the po prodelta whereas topset forest deposits south of this region exhibited higher values 100 yrs indicating the presence of refractory material in the distal bottomset region the t1 2 was particularly high ranging from 255 to 912 yrs because of the significant southward component of the sediment transport the oc deposition in the southern surface sediments exceeded the local oc input via rivers ratio deposition input 1 2 conversely the northern adriatic was characterized by a marked imbalance ratio deposition input 0 3 0 5 according to our calculations the oc flux to the seabed along the clinoform was 309 gg of c per year whereas the oc burial was 180 gg of c per year corresponding to an overall burial efficiency of 59

geomorphic tectonic control of sediment discharge to the ocean the importance of small mountainous rivers analysis of data from 280 rivers discharging to the ocean indicates that sediment loads yields are a log linear function of basin area and maximum elevation of the river basin other factors controlling sediment discharge e g climate runoff appear to have secondary importance a notable exception is the influence of human activity climate and geology on the rivers draining southern asia and oceania sediment fluxes from small mountainous rivers many of which discharge directly onto active margins e g western south and north america and most high standing oceanic islands have been greatly underestimated in previous global sediment budgets perhaps by as much as a factor of three in contrast sediment fluxes to the ocean from large rivers nearly all of which discharge onto passive margins or marginal seas have been overestimated as some of the sediment load is subaerially sequestered in subsiding deltas before the proliferation of dam construction in the latter half of this century rivers

fine sediment mass balance in the western adriatic continental shelf over a century time scale abstract to obtain a quantitative estimate of the sediment accumulating on the muddy belt extending along the western adriatic continental shelf a budget was calculated based on the mass accumulation rates measured from more than one hundred activity depth profiles of 210 pb 137 cs depth distributions were used when possible to support 210 pb results 210 pb profiles show quasi monotonic declines in the foreset region of the central adriatic clinoform in the prodelta of the rivers po and isonzo 210 pb profiles are characterized by intervals of low and uniform activity which are thought to be produced by flood deposition since the north adriatic is shallow and occasionally affected by storms from bora wind sediments are not in steady state and their accumulation is the net result of recurring deposition resuspension and winnowing events in the western adriatic mass accumulation rates range between 0 04 and 6 6 g cm 2 yr 1 peak values were recorded in the po and isonzo prodeltas and along a narrow belt between pescara and the gargano promontory furthermore the latter depocentre is located immediately seaward of the offlap break 40 50 m water depth and parallels that of the most recent sigmoid of the hst the integration of mass accumulation rates throughout the mud wedge of the north and central adriatic gave a value of 42 0 tg yr 1 of sediment accumulating along the italian coast the balance between sediment accumulation and riverine sediment supply 46 6 tg yr 1 suggests an export of 4 6 tg yr 1 to the south adriatic basin and or the mediterranean sea the along shore sediment transport is very effective and in particular 16 2 tg yr 1 of sedimentary material 35 of the riverine supply is transferred from north to central adriatic through the ancona section

geochemical diagenetic trends during phosphorite formation economic implications the case of the negev campanian phosphorites southern israel research on the upper campanian upper cretaceous negev phosphorites mishash formation based on microprobe analyses fourier transform infrared spectroscopy wet chemistry microtextural scanning electron microscopy studies and mineralogical analyses together with quantified rates of sedimentation and p accumulation enables the chemistry of these rocks to be better constrained across the negev area and allows their suitability for the manufacture of p fertilizers to be better determined two phosphorite facies are differentiated i a pristine phosphorite facies of low p content more typical of basinal sections and ii a reworked granular phosphorite facies commonly enriched in p found predominantly near palaeo highs and forming most of the economic phosphates the distribution of f p2o5 co2 f u iv cd zn and other trace metals mo ni cr cu v and y rare earth elements concentration ce and eu anomalies and heavy rare earth elements enrichment are controlled by these two facies f p2o5 in carbonate fluorapatite is much lower 0 090 to 0 107 in the pristine than in the reworked facies 0 107 to 0 120 in addition the lower f p2o5 in the pristine facies is coupled with i higher cd zn mo ni cr cu and v concentrations ii a considerably reduced 10 u iv fraction of total u iii lower rare earth elements p2o5 and y p2o5 ratios iv less negative ce and eu anomalies and lower heavy rare earth elements lu la enrichment v an increase in fe rich smectites in the clay fraction and vi presence of oh in the carbonate fluorapatite structure sedimentary reworking of previously formed pristine phosphate together with its redeposition near structural highs in more oxic bottom conditions results in considerable diagenetic changes in the chemistry of the phosphorites making them more suitable for economic exploitation the results presented here provide geochemical criteria for identifying pristine phosphate in other phosphorite sequences and may help to better locate phosphate strata chemically suitable for the phosphate industry elsewhere

spatial and temporal arctic ocean depositional regimes a key to the evolution of ice drift and current patterns sediment physical properties measured in cores from all the major ridges and plateaus in the central arctic ocean were studied in order to analyze the spatial and temporal consistency of sediment d

the geochemistry of uranium and thorium in coastal marine sediments and sediment pore waters pore water profiles of uranium and thorium isotopes in the muddy sediments of buzzards bay ma permit an assessment of the effect of diagenetic redox reactions on the geochemical behavior of these elements uranium shows a pronounced minimum pore water concentration 1 2 dpm kg near the sediment water interface 0 3 cm which coincides with the pore water fe maximum u concentrations increase with depth to a broad maximum which is greater than the overlying seawater value then decrease laboratory sediment tank experiments maintained without macrofauna also show the near interface minimum and increase and sediment incubation experiments show removal of u from the pore water to a constant value by about 40 days the 234u238u activity ratio is equal to the seawater value in all samples oxidation state separations of pore water u in hcl solution using anion exchange demonstrate that u is present in the pore water as u vi the coincidence of the pore water uranium and fe maximum is consistent with the hypothesis of reduction of u vi to u iv and removal from solution at about the same depth or pe as fe is reduced increases in pore water u with depth appear to be related to release of authigenic seawater u vi to solution possibly as alkalinity and ph increase and organic matter with which the u is associated is oxidized lower concentrations at depth in the sediment column may be linked to increases of effective u reducing agents like hydrogen sulfide in the pore water or to the activities of macrofauna in contrast pore water profiles of the long lived th isotopes 232th and 230th show low activities 02 dpm kg and relatively little change with depth although values are greater than those in the overlying water solid phase activities are similarly constant with depth and the distribution may be controlled by a sorption equilibrium between pore water and the solid phase the short lived isotope 234th shows greatest pore water activities in the upper 5 cm and is present at virtually zero activities elsewhere in the sediment column the upper few centimeters of the sediment generally contain excess 234th scavenged from the overlying water column and distributed by bioturbation as well as pore water fe and mn profiles which show maxima indicating reduction and dissolution of fe and mn oxyhydroxides the pore water 234th profile can be explained by release of 234th from the solid phase as femn oxide surface coatings are reduced and dissolved

geochemistry of a tertiary sedimentary phosphate deposit baja california sur mexico abstract the san gregorio formation in baja california sur a phosphate enriched sedimentary unit of late oligocene to early miocene age has been analyzed in two areas la purisima and san hilario for its chemical composition major oxides cu cd cr co v and rare earth elements ree and isotopic composition 18 o and 13 c a detrital and a marine component were determined from major oxides the detrital component consists of an unaltered volcanic ash fraction and a terrigenous clay silt fraction the marine component which accumulated initially as biogenic and hydrogenous material is now present as opal a opal ct caco 3 organic matter and an authigenic phosphate fraction mostly pelletal and composed of the carbonate fluorapatite mineral francolite the minor elements have been partitioned into these components by assuming a constant composition for the two detrital fractions the composition of the marine component of minor elements can then be interpreted by assuming that the stoichiometry of the original accumulating organic matter was equal to that of modern plankton the cu and cd contents in the marine component of all rocks require that the seawater derived fractions of these two metals were supplied to the seafloor solely by organic matter enrichments of cr and v at both sites required an additional marine input on the basis of their geochemistry in the modern ocean cr and v could have precipitated or been adsorbed onto settling particles from an o 2 minimum zone in which the o 2 content was low enough to promote denitrification rather than oxygen respiration an enrichment of the ree now within the apatite fraction resulted from their adsorption onto particulates also in the o 2 minimum zone and to the dissolution and alteration of biogenic phases predominantly silica within the sediment co and fe 2 o 3 show no enrichment above a detrital contribution the 18 o values of apatites from the la purisima site are heavier than those of apatites from the san hilario site whereas the 13 c values show the opposite trend one possible interpretation of these variations is that 18 o reflects seawater values and 13 c sediment pore water values this interpretation suggests that upwelling rates and primary productivity within the water column were greater at la purisima an interpretation that is corroborated by a greater abundance of apatite measured in outcrop at la purisima the ce anomalies of the phosphate enriched samples also differ between the two sites indicating that they also recorded water masses similar to the 18 o values

rare earth elements in the phosphatic enriched sediment of the peru shelf abstract apatite enriched materials from the peru shelf have been analyzed for their major oxide and rare earth element ree concentrations the samples consist of 1 the fine fraction of sediment mostly clay material 2 phosphatic pellets and fish debris which are dispersed throughout the fine grained sediment 3 tabular shaped phosphatic crusts which occur within the uppermost few centimeters of sediment and 4 phosphatic nodules which occur on the seafloor the bulk ree concentrations of the concretions suggest that these elements are partitioned between the enclosed detrital material and the apatite fraction analysis of the fine grained sediment with which the samples are associated suggested that this detrital fraction in the concretions should have shale ree values the analysis of the fish debris suggested that the apatite fraction might have seawater values the seawater contribution of ree s is negligible in the nodules and crust in which the apatite occurs as a fine grained interstitial cement that is the concentration of ree s and the ree patterns are predominantly a function of the amount of enclosed fine grained sediment by contrast the ree pattern of the pelletal apatite suggests a seawater source and the absolute ree concentrations are relatively high the ree p 2 o 5 ratios of the apatite fraction of these samples thus vary from approximately zero in the case of the crust and nodules to as much as approximately 1 2 10 3 in the case of the pellets the range of this ratio suggests that rather subtle variations in the depositional environment might cause a significant variation in the ree content of this authigenic fraction of the sediment pelletal glauconite was also recovered from one sediment core its ree concentrations closely resemble those of the fish debris

the role of saltwater and waves in continental shelf formation with seaward migrating clinoform continental shelves have generally been interpreted as drowned coastal plains associated with the allogenic effect of sea level variation here without disputing this mechanism we describe an alternative autogenic mechanism for subaqueous shelf formation driven by the presence of dissolved salt in seawater and surface waves we use a numerical model describing flow hydrodynamics sediment transport and morphodynamics in order to do this more specifically we focus on two major aspects 1 the role of saltwater in the subaqueous construction of continental shelves and 2 the transformation of these shelves into seaward migrating clinoforms under the condition of repeated pulses of water and sediment input and steady wave effects but no allogenic forcing such as sea level change in the case for which the receiving basin contains fresh water of the same density as the sediment laden river water the hyperpycnal river water plunges to form a turbidity current that can run out to deep water in the case for which the receiving basin contains sea water but the river contains sediment laden fresh water the hypopycnal river water forms a surface plume that deposits sediment proximally this proximate proto shelf can then grow to wave base after which wave supported turbidity currents can extend it seaward the feature we refer to is synonymous with near shore mud belts

microbial pathways and palaeoenvironmental conditions involved in the formation of phosphorite grains safaga district egypt abstract phosphatic grains of the shallow marine phosphorite deposits of egypt are classified as either phosphatic bioclasts preserving biological structure e g skeletal fragments such as fish bones and teeth or phosphatic peloids and intraclasts this study describes the destructive and constructive microbial pathways represented by bioerosion of bones by endolithic cyanobacteria and accretion of phosphatic peloids by bacteria the palaeoenvironmental conditions and post depositional diagenetic history of these grains have also been considered scanning and transmission electron microscopy showed that the phosphatic peloids under transmitted light microscopy are composed mainly of microspheres 0 5 to 2 5 m similar in shape and size to coccoid like bacteria chemical mapping showed that these microspheres are composed of carbonate fluorapatite cfa and surrounded by degraded carbonaceous matrix these grains are suggested to be reworked from pre existing microbial mats during transgressive regressive cycles affecting the southern tethyan campanian maastrichtian shallow continental shelf the bioerosion of phosphatic bones is characterized by a network of meandering microborings that penetrated inward from the bone surface by endolithic cyanobacteria the bioerosion of bones resulted in a gradual centripetal digestion and conversion of bones into micritic phosphate peloids the bioerosion mechanism is probably started in the acidic sheath surrounding cyanobacteria followed by supersaturation of po 4 and reprecipitation of crystalline cfa as electron dense remineralized rims electron microprobe microanalyses showed that the remineralized microbored areas are higher in cao p 2 o 5 and f and depleted in cl relative to unaltered bones a gradual demineralization of remineralized rims followed by dissolution of cyanobacterial cells is probably occurred during diagenesis and meteoric water alteration leaving behind empty microborings bone exposed to meteoric water alteration is lower in cao and p 2 o 5 and higher in f and cl than the unaltered bones understanding bone bioerosion has significant implications for palaeoenvironmental and taphonomic reconstruction archaeological applications and a regional correlation of the late cretaceous to palaeogene phosphogenic province extending from middle east to north africa

the formation of sedimentary strata in an allochthonous shelf environment the washington continental shelf nittrouer c a and sternberg r w 1981 the formation of sedimentary strata in an allochthonous shelf environment the washington continental shelf mar geol 42 201 232 models of fine scale 120 m shelf regions the inner shelf sand and mid shelf sandy silt are the predominant accretionary deposits on the shelf important sedimento logical observations obtained by boxcoring the upper 1 2 m of these deposits are a progressive decrease in grain size with distance from the columbia b downward coarsening within the seabed c loss of distinct sedimentary structure homogenization of sediment with distance from the columbia non dimensional parameters based on sediment transport and benthic biological studies can be used to relate rates of sediment mixing re working to rates of accumulation these parameters have the potential for quantitative prediction of strata formation from measurements of active processes physical and biological mixing can be assumed to remain relatively constant in an alongshelf direction on the washington shelf and accumulation rate is known from pb 210 geochronology to decrease away from the columbia together these factors tend to increase the ratio of mixing to accumulation with distance from the columbia and predict the sedimentological observations listed above

the petrogenesis of a type magmas from the amram massif southern israel the 550 530ma alkaline magmatic suite of the amram massif southern israel was emplaced during the transition from an orogenic to an intra plate tectonic setting in the northeastern arabian nubian shield ans the suite ranges from 45 6t o 788 wt sio2 and consists of rhyolites alkali quartz syenites quartz syenites monzonites and co magmatic mafic to felsic alkaline dikes these rocks define a continuous chemical evolutionary trend and reveal a correlation between decreasing stratigraphic age and increasing silica content the felsic members of the suite display a type characteristics and are genetically linked through fractionation to the more mafic ones moderately positive initial end values a2 05 low initial 87 sr 86 sr values 07036 2 high mgo and fe2o3 concentrations 410 895 and 100 125 wt respectively and relatively flat rare earth element patterns la yb na 64 09 in the amram mafic dikes 456 495 wt sio2 suggest their derivation from the sub continental lithospheric mantle above the garnet stability zone the melts program was used to quantitatively model the chemical evolution of the suite extensive anhydrous fractionation 490 of plagioclase alkali feldspar clinopyroxene olivine and minor timagnetite and apatite from parental mafic magmas represented by the amram mafic dikes produced the rhyolitic compositions as well as the intermediate members of the suite this suggests the presence of a large unexposed body of cumulate rocks at depth as well as fusion of a large source region equivalent to an 5km layer in the lithospheric mantle regarded as a representative example for similar a type outcrops in this region this petrogenetic model further suggests that neoproterozoic early cambrian a type magmatism in the northeastern ans represents a significant post orogenic addition of mantlederived material to the juvenile crust this magmatic episode was of a similar magnitude to that of the cenozoic extensionrelated alkaline volcanism of the arabian plate

quantifying subsidence and isostatic readjustment using sedimentary paleomarkers example from the gulf of lion passive margins are characterised by an important tectonic and thermal subsidence which favours a good preservation of sedimentary sequences this sedimentation in turn enhances the subsidence because of loading effects we present here a direct method based on sedimentary markers seen on seismic data to evaluate total subsidence rates from the coast to the outer shelf and to the deep basin in the gulf of lion from the beginning of massive salt deposition up to present day the last circa 6 ma with minimal theoretical assumptions on the shelf the pliocene quaternary subsidence shows a seaward tilt reaching a rate of 240 m ma 15 m ma at the shelf break 70 km from the present day coastline i e a total angle of rotation of 0 88 0 16 ma we were also able to measure and quantify for the first time the isostatic rebound of the outer shelf due to the messinian salinity crisis msc this value is very high and reaches up to 1 3 km of uplift during the crisis around the herault sete canyon heads around 1 8 km ma on the slope we also find a seaward tilting subsidence from km 90 to km 180 with a measured angle of 1 41 from 180 km to the deepest part of the basin the total subsidence is then almost vertical and reaches 960 m ma 40 m ma during the last 5 7 ma 0 25 ma in the deepest part of the basin the subsidence is organised in three compartments that seem related to the very deep structure of the margin during the opening of the liguro provencal basin these very high total subsidence rates enable high sedimentation rates along the margin with sediments provided by the rhone river flowing from the alps which in turn enable the detailed record of climate evolution during pliocene quaternary that make of the gulf of lion a unique archive

corrigendum to paleo sea levels reconsidered from direct observation of paleoshoreline position during glacial maxima for the last 500 000 years earth planet sci lett 252 2006 119 137

deposition and flux of sediment from the po river italy an idealized and wintertime numerical modeling study abstract recent studies of sediment dynamics and clinoform development in the northern adriatic sea focused on winter 2002 2003 and provided the data and motivation for development of a detailed sediment transport model for the area near the po river delta we used both idealized test cases and more realistic simulations to improve our understanding of seasonal sediment dynamics there we also investigated the relationship between physical processes and the observed depositional products e g the accumulation of sediment very near the po river distributary mouths sediment transport near the po river was evaluated using a three dimensional ocean model coupled to sediment transport calculations that included wave and current induced resuspension suspended sediment transport multiple grain classes and fluvial input from the po river high resolution estimates from available meteorological and wave models were used to specify wind wave and meteorological forcing model results indicated that more than half of the discharged sediment remained within 15 km of the po river distributary mouths even after two months of intensive reworking by winter storms during floods of the po river transport in the middle to upper water column dominated sediment fluxes otherwise sediment fluxes from the subaqueous portion of the delta were confined to the bottom few meters of the water column and correlated with increases in current speed and wave energy spatial and temporal variation in wind velocities determined depositional patterns and the directions of sediment transport northeasterly bora winds produced relatively more eastward transport while southwesterly sirocco winds generated fluxes towards both the north and the south eastward transport accounted for the majority of the sediment exported from the subaqueous delta most likely due to the frequent occurrence of bora conditions progradation of the po river delta into the adriatic sea may restrict the formation of the western adriatic coastal current increasing sediment retention at the po delta and reducing the supply of sediment to the apennine margin a positive morphodynamic feedback may therefore be present whereby the extension of the delta into the adriatic increases sediment accumulation at the delta and facilitates further progradation

oxygen isotope composition of diagenetic calcite in organic rich rocks evidence for 18o depletion in marine anaerobic pore water upper cretaceous organic rich carbonates in israel contain benthonic foraminifera and varying amounts of early diagenetic infilling of sparry calcite the sparry calcite has oxygen isotope values down to 9 5 pdb that are significantly lower than those of the coexisting skeletal calcite averaging 2 pdb low 18o values are very common in carbonates that are associated with organic matter these occurrences are conventionally explained as being due to carbonate formation under conditions of low salinity and or elevated temperature on the basis of petrographic data and local geologic evidence however none of the conventional explanations can be applied in this case we advance an alternative model that relates the light oxygen compositions of the diagenetic calcite to depletion of 18o in pore water of normal salinity the proposed operating mechanism is a direct consequence of organic matter decomposition in the sulfate reducing zone being inherent to reducing marine environments this model can be applied to many organic rich rock associations

event driven deltaic sedimentation on a low gradient low energy shelf the brazos river subaqueous delta northwestern gulf of mexico abstract the brazos river delta is located in the northwestern gulf of mexico sedimentation on the brazos river subaqueous delta has been largely understudied swath bathymetry data collected across the subaqueous delta reveals a noticeable asymmetry with much deeper water depths and greater cross shelf slopes along the eastern up drift side of the delta than along the western down drift side end member sampling reveals that brazos river derived sediment is red red brown or brown in color exhibits increased bulk density and is enriched in calcium a function of carbonate rich areas of the watershed whereas the gulf of mexico inner shelf muds are gray to black and have a relatively lower calcium content analyses of a series of 33 submersible vibra cores collected across the subaqueous delta reveal alternating beds of brazos river derived sediment and gulf of mexico shelf dominated sediment excess 210pb geochronologies of select cores reveal that sediment accumulation has been a combination of fluvial flood event deposition and deposition of remobilized sediment from the proximal shelf and older portions of the delta rather than steady state accumulation because the brazos river is susceptible to local climatic cycles fluvial flood events that create the event layers are intermittent between prolonged periods where marine processes drive accumulation results also show that the primary depocenter of the subaqueous delta has migrated southwestward over time and the erosion of earlier depocenters and proximal shelf sediment has contributed to accumulation on the delta over the past 50 years the subaqueous delta has reached an equilibrium where flood event beds can be completely remobilized within a year and net accumulation approximates relative sea level rise this study highlights relatively rapid clinoform migration due to natural and anthropogenic changes to the system and demonstrates subaqueous delta growth through a combination of direct fluvial and marine derived sediment input

the adriatic sea general circulation part ii baroclinic circulation structure abstract in the second part of the paper dedicated to the adriatic sea general circulation the horizontal structure of the hydrographic parameters and dissolved oxygen fields is described on a seasonal timescale maps of temperature and salinity climatological fields reveal the enhanced seasonal variability of the adriatic sea which at the surface is associated with the major dilution effects of river runoff the density and derived dynamic height fields show for the first time the baroclinic geostrophic structure of the general circulation winter is dominated by compensation effects between temperature and salinity fronts along the western coastline the resulting baroclinic circulation is weak and suggests the presence of barotropic current components not accessible by the dataset spring and summer seasons have the smallest spatial scales in the temperature and salinity fields and stronger subbasin scale gyres and current systems which have been classified in a schematic representation of the circu

uranium oxidation state and related variations in geochemistry of phosphorites from the negev southern israel abstract study of the u iv fraction in mishash phosphorites of the negev reveals an apparently paradoxical trend the u iv fraction is very low less than 10 in the pristine organic rich laminated phosphorites while this proportion considerably increases up to 60 in the recycled mechanically reworked granular phosphorites which deposited under more oxidizing conditions this u iv trend seems to differ from that reported in other phosphate sequences elsewhere and is also quite unexpected in view of the sediment patterns and the specific formational conditions of the two phosphorite facies in addition a lower u iv in the analyzed granular phosphorites is coupled with a lower rare earth elements ree p 2 o 5 and y p 2 o 5 ratio a higher cd and zn concentration less negative ce ce ce and eu eu eu anomalies a lower hree dy er enrichment and a lower f p 2 o 5 and higher co 2 f ratio in francolites this u iv trend in the two negev phosphorite facies may be explained by varying time spans of apatite growth changes in sediment burial rates and principally different residence times of the phosphate fraction in the suboxic apatite forming diagenetic zone near the sediment water interface the associated varying concentrations of rees y cd and zn in phosphorites and of f and co 2 in francolites in the two granular phosphorite facies are apparently collectively regulated by the same sedimentary dynamics during phosphate deposition it is presumed that the u iv trend observed in the negev phosphorites could be detected in other phosphate sequences as well if pristine phosphorites are carefully identified and selectively analyzed

modern rates of glacial sediment accumulation along a 15 s n transect in fjords from the antarctic peninsula to southern chile 1 rates of glacial erosion in temperate climates rank among the highest worldwide and the sedimentary products of such erosion record climatic and tectonic signals in many glaciated settings as well as temporal changes in glacier behavior glacial sediment yields are expected to decrease with increasing latitude because decreased temperature and meltwater production reduce glacial sliding erosion and sediment transfer however this expectation lacks a solid supportive database herein we present modern 210pb derived sediment accumulation rates on decadal to century time scales for 12 fjords spanning 15 of latitude from the antarctic peninsula to southern chile and interpret the results in light of glacimarine sediment accumulation worldwide 210pb records from the antarctic peninsula show surprisingly steady sediment accumulation throughout the past century at rates of 1 7 mm yr 1 despite rapid warming and glacial retreat cores from the south shetland islands reveal accelerated sediment accumulation over the past few decades likely due to changes in the thermal state of the glaciers in this region which straddles the boundary between subpolar and temperate conditions in patagonia and tierra del fuego sediment accumulates faster 11 24 mm yr 1 and previously collected seismic profiles show that rates reach meters per year close to the glacier termini this increase in sediment accumulation rates with decreasing latitude reflects the gradient from subpolar to temperate climates and is consistent with glacial erosion being much faster in the temperate climate of southern chile than in the polar climate of the antarctic peninsula

clinoform development by advection diffusion of suspended sediment modeling and comparison to natural systems clinoforms are the building blocks of prograding stratigraphic sequences these sig moid shaped surfaces can be found forming today on modem deltas sedimentation rate profiles over the clinoform surface of these deltas show low rates of sediment accumulation on both topset and bottomset regions with a maximum accumulation rate on the upper foreset region we pres ent a model for the formation of clinoforms that relies on the interpretation of modem clinoform sedimentation as a result of the distribution of shear stresses at the mouth of a river model clino form surfaces are generated using an equation for the conservation of suspended sediment concentration together with a conservation of fluid equation for simple time averaged flow velocity fields in the model suspended sediment is advected horizontally into a basin and gravitational settling of sediment particles is counteracted by vertical turbulent diffusion in shallow water shear stresses are too large to allow deposition and sediment bypasses the topset region with increasing water depth near bed shear stresses decrease and sediment is allowed to deposit at the foreset region with gradually decreasing rates toward deeper water this sedimentation pattern leads to progradation of the clinoform surfaces through time the clinoform surfaces produced by the model capture the fundamental morphological characteristics of natural clinoforms these include the gradual slope rollover at the topset and bottomset steeper foreset slopes with increased grain size and an increase in foreset slope through time as clinoforms prograde into deeper water because the parameters controlling the model clinoforms have a direct relation to physical quantities that can be measured in natural systems the model is an important step toward unraveling the physical processes associated with these deposits

the deltaic nature of amazon shelf sedimentation despite the annual discharge of more than a billion tons of sediment by the amazon river the sedimentary environment near the river mouth has little subaerial expression and thus does not meet the classic definition of a delta the river mouth however is not an estuary either these observations raise a major question as to what type of sedimentary environment the amazon river mouth represents seismic stratigraphy has been examined on the continental shelf at the mouth of the amazon river using high frequency 3 5 khz seismic records from about 6 000 km of ship track these records demonstrate three regions 1 the amazon river has built a subaqueous feature which stretches for hundreds of kilometres offshore and alongshore from its mouth the feature is prograding seaward and accreting upward and it contains fine scale stratification typical of classic deltas the feature forming at the mouth of the amazon is a subaqueous delta it differs from classic deltas primarily in its lack of subaerial expression subaqueous deltas such as the amazon represent the general case of a major river entering an energetic oceanic regime

the moroccan high atlas phosphate rich sediments unraveling the accumulation and differentiation processes the phosphate series of the moroccan high atlas accumulated during the upper cretaceous paleogene phosphogenic period on a biologically productive shallow water platform these phosphate rich sediments were deposited during a relative sea level cycle generating major stratigraphic surfaces five different types of phosphatic lithofacies are recognized based on their petrographic and sedimentologic features the pristine phosphate lithofacies corresponds to phosphatic marls formed by francolite authigenesis within the outer platform domain below the storm wave base primary phosphogenesis zone this primary phosphatic lithofacies can be differentiated as a result of the interaction between hydrodynamic autocyclic processes and allocyclic forcing accordingly the granular phosphate lithofacies was formed by in situ storm and bottom currents that winnowed the pristine phosphate this winnowed lithofacies composed of densely packed peloids shows relatively high p2o5 concentrations the turbiditic phosphate resulted from the basinward transport and deposition of other phosphate types by gravity flows leading to normally graded phosphatic sediment the phosphatic lags were formed by wave reworking and transporting of pristine and associated granular facies within the inner platform the karst filling phosphate corresponds to former phosphate types transported by early transgressive currents and trapped within karstic pockets as phospharudites the distribution of the different phosphate types across the margin and within the depositional sequences is controlled by the effects of relative sea level changes the pristine phosphate and associated winnowed facies are found above the major maximum flooding surface which is dated by nannoflora to the selandian thanetian transition the phosphatic turbidites occurred during periods of high sea level the karst related phosphatic facies accumulated during early transgressive stages the phosphatic lags accumulated mainly during the regressive phases of third and fourth order sequences the accumulation processes of the different phosphatic lithofacies control the ore grade of the phosphatic sediments repeated storm induced winnowing of pristine phosphate contributes to the enrichment of the phosphate ore grade

clinoform sedimentation along the apennine shelf adriatic sea abstract sedimentation along the central adriatic coastline of italy results from a series of small distributed fluvial sources i e a line source draining the apennine mountains these rivers deliver 3 107 t y 1 of sediment contributing to the formation of a shore parallel shelf clinoform that has developed throughout the holocene across shelf sediment accumulation rates calculated from 210pb half life 22 3 years measurements are greatest on the clinoform foreset 1 cm y 1 which is characterized by seafloor crenulations in a few areas however for some cross sections of the clinoform accumulation rates are not significantly higher on the foreset than on the topset and bottomset indicating that the clinoform may not be actively prograding in those areas today accumulation rates increase southward along the shelf and are greatest near the gargano peninsula 1 7 cm y 1 between ravenna and the gargano peninsula 3 1 107 t y 1 of sediment accumulate on the apennine shelf although the amounts of sediment supply and accumulation are about the same additional po river sediment is thought to enter the system from the north and some sediment is transported beyond the gargano peninsula to the south anthropogenic activities particularly dam construction following world war ii have significantly impacted sedimentation in this region changes in 210pb profiles document reduction in sediment accumulation however observations during winter 2002 2003 using the short lived radioisotope 7be half life 53 3 d have indicated that some new sediment is delivered to the shelf during periods of elevated discharge so dam entrapment is not complete

fluvial dynamics in the castel di sangro plain morphological changes and human impact from 1875 to 1992 abstract in recent years morphology and hydrogeology of the castel di sangro plain have undergone significant man made changes the plain is located in a very complex geological area where the latium abruzzi carbonate platform the morrone rotella pizzone carbonate platform and the molise nappe meet hydrology hydrogeology morphology and neotectonics of the area are conditioned by interlocking and overlapping of such palaeogeographic units some of them can be clearly recognised in the upper and middle sangro area after outlining the geological structural and geomorphological features of the area the authors discuss the morphological changes which occurred in the sangro river pattern and its alluvial plain from 1875 to 1992 as a result of construction of major hydraulic structures dams river bed cementation urbanisation of flood plain and spring areas wells elements inferred from comparison of maps and aerial photographs were also considered the study provides a concise description of objective observations on both natural and man induced fluvial processes and groundwater flows

uranium geochemistry and dating of pacific island apatite abstract uranium series disequilibrium dating of island phosphate deposits is evaluated in terms of known associated coral ages uranium geochemistry and stratigraphic sequences as well as the concordance between the geochronometers 234 u 238 u 230 th 234 u and 226 ra 238 u u vi is the predominant oxidation state of uranium in island phosphorites and by analogy to the youngest surficial deposits most of the uranium initially bound is in the form of u vi sorbed by surfaces from seawater insular deposits contain more organic matter than even very young ocean floor samples and this leads to a greater probability of reduction of available recoil uranium than occurs in marine deposits as a consequence r vi r t r vi where r represents the 234 u 238 u activity ratio this situation is completely opposite from that observed for marine origin phosphorites we determined that a fraction of u vi in ancient insular phosphorites is very labile and lost to alkaline carbonate solutions with a uranium activity ratio even more depleted in 234 u than the bulk r vi most younger samples appear to have no more discordance between 234 u 238 u 230 th 234 u and 226 ra 238 u than marine phosphorites of similar apparent age young surficial atoll rim apatite cements and unconsolidated phosphorites date in the range of 1500 8000 years b p consistent with the concept of partial submergence of low lying coral islands prior to 2000 years b p sub surficial samples in the same environment date older at about 20 000 years b p violation of the closed system assumption occurs in at least 6 out of 13 ancient 800 000 year samples uranium series disequilibrium dating of insular apatite shows some promise as a recorder of climatic sea level events but the assumptions necessary for valid ages must be carefully evaluated for each occurrence

sedimentology geochemistry and origin of phosphatic chalks the upper cretaceous deposits of nw europe santonian lower campanian and lower maastrichtian phosphatic chalks in northern france southern england and belgium are europe s largest sedimentary phosphatc deposits the stratigraphy sediment ology petrography mineralogy and geochemistry of the lithofacies are reviewed and new data presented depositional and diagenetic models for phosphatic chalk deposits are developed using published experimental work and from observations of modern high and low productivity phosphogenic systems it is concluded that phosphatic chalks were deposited in well oxygenated current swept environments phosphatization required a delicate balance to be maintained between moderate organic carbon and carbonate sedimentation rates reduced bulk sediment accumulation rate and an enhanced rate of bioturbation precipitation of carbonate fluorapatite francolite accompanied the bacterially mediated decomposition of organic matter occurring within centimetres of the sediment seawater interface and taking place preferentially within microbial bodies and coatings in addition to the organically derived component pore water phosphate levels were enhanced by phosphate absorbed on ferric oxyhydroxides which was liberated during iron reduction mineralization was probably a dominantly post oxic process but occurred in a thick sediment mixed layer in which marine organic matter was undergoing intense mixed aerobic and anaerobic microbial degradation phosphogenesis occurred predominantly on the ne margins of the anglo paris basin where shallower sea floors and suitable palaeoceanographic conditions prevailed phosphogenic episodes were limited by sea level fluctuations which controlled the effectiveness of the erosional currents that formed and maintained the phosphatic basins and may have stimulated local productivity

sediment accumulation in a modern epicontinental shelf setting the yellow sea sediment accumulation in the yellow sea epicontinental shelf environment is investigated on 100 yr and 1000 yr time scales using 210pb and 14c geochronologies the distribution of modern 210pb accumulation rates in the yellow sea reveals that the loci of modern huanghe sediment accumulation are the topset 1 2 mm yr foreset 4 9 mm yr and proximal bottomset deposits 2 4 mm yr of the shandong subaqueous delta which extends south from the shandong peninsula 210pb rates in the distal bottomset deposits of the subaqueous delta in the central and southern yellow sea are generally low 0 3 0 9 mm yr a sediment budget demonstrates that between 9 15 of the annual huanghe discharge is accumulating in the yellow sea about two thirds of this sediment is accumulating in the topset foreset and proximal bottomset deposits of the shandong subaqueous delta with the remaining third accumulating as widespread distal bottomset deposits 14c age dates of subaqueous delta sediments indicate that the thick 40m clinoform structure formed predominantly between 6200 and 4060 yrs b p at rates approaching 20 mm yr observations in the yellow sea as well as on the amazon and ganges brahmaputra shelves demonstrate that subaqueous deltaic stratigraphy is the general rule where major rivers enter energetic shelves whether epicontinental or pericontinental the development of extensive bottomset deposits may be restricted to epicontinental shelf environments and may be diagnostic of sedimentation in this type of setting

ultra fine structures and genesis of the campanian negev high grade phosphorites southern israel ultra fine structures of the negev high grade phosphorites provide valuable clues to unravelling the genesis of these rocks the question of their differential areal distribution and the biosedimentary mechanisms involved in their considerable enrichment peculiar to these phosphorites is an intergranular phosphate matrix for the most part constituted by a variety of phosphatic microbial tubules displaying a range of spatial micro organizations the phosphate particles fixed by this filamentous meshwork also consists of internally organized and non organized packed microbial remains of different types analogies between the fabrics of the matrix and the corpuscles lead to conception of a two stage depositional scheme for these phosphorites based on rhythmical repetition of two sedimentary mini events in a slightly oscillating very shallow marine system 1 a low energy event of microbial colonization of the mishash bottoms followed by early phosphatization of the organic structures mainly in marginal situations and 2 a higher energy event which broke up the phosphatic mats into debris redepositing them as clastic layers in nearby basinward sites while becoming bound by a new meshwork of filamentous microphytes the differential phosphatization of the intergranular microbial binder again occurring mostly in marginal localities produced highly enriched phosphorites minor truncations and redepositions leading to amalgamation of the successive layers account for the massive fabric now displayed by most of these rocks examining the structural and textural features the validity of the sedimentary mechanisms of recent phosphorite formation for the campanian negev rocks is discussed

the use of 7be to identify event and seasonal sedimentation near the po river delta adriatic sea in october 2000 a major flood event of the po river occurred the resulting seabed deposit was initially sampled in december 2000 and most sites were reoccupied on subsequent cruises over a 3 yr period using the maximum penetration depth of the short lived radioisotope 7be half life 53 3 d the flood deposit was found to be up to 15 cm thick individual depocenters of thick strata were located immediately adjacent to the distributaries at the river mouth in relatively shallow water 30 m these flood deposit thicknesses are minimum estimates because the depth of 234th half life 24 1 d exceeds that of 7be in physically stratified flood sediment indicating that the first sediment deposited during the flood event likely originated from the river channel 30 55 of the estimated sediment load delivered to the shelf during the flood event can be accounted for using 7be penetration depths seasonal deposition also can be quantified using 7be after removing the effects of biological mixing seasonal deposition rates are a maximum of 6 cm yr 1 near the pila distributary decreasing to 2 cm yr 1 in the southern portions of the dispersal system

stratigraphic simulations of the shelf of the gulf of lions testing subsidence rates and sea level curves during the pliocene and quaternary determining the relative importance of factors interacting to control stratigraphic organization is a key issue in sedimentology the pliocene quaternary chronostratigraphy on the gulf of lions platform is still poorly constrained giving rise to different interpretations of the evolution of its subsidence through time this paper examines the pliocene quaternary sedimentary filling of the gulf of lion s shelf with dionisos a numerical stratigraphic model our results show that a constant subsidence rate accurately reproduces the observed geometries whereas a varying subsidence rate reproduces them only if the acceleration of subsidence is limited at this time scale a third order eustatic curve is also reappraised a higher resolution curve built using d 18 o measurements gives a more realistic restitution of our stratigraphic markers finally the constant subsidence rate and sediment fluxes implied in these modellings are discussed relative to climate and local factors of sedimentation

sedimentary response to climate and sea level changes during the past 400 ka from borehole prad1 2 adriatic margin 1 borehole prad1 2 was drilled in 186 m water depth on the upper slope of the central adriatic in the frame of profiles across mediterranean sedimentary systems promess1 european union funded project the borehole penetrated 71 2 m through a stratigraphic interval characterized by subparallel seismic reflections and uniform seismic units according to an age depth model based on several independent proxies including foraminifera and nannoplankton stratigraphy 18o curves and magnetostratigraphy the cored interval records marine isotope stages and substages mis from mis1 to the top of mis11 thus encompassing the past 370 ka prad1 2 therefore represents an unprecedented continuous record through the last four glacial interglacial cycles from a proximal continental margin setting where depositional sequences are typically composed of progradational units these progradational units record dominantly interglacial intervals mis5 mis7 and mis9 and appear composed of thicker highstand deposits hst formed during interstadials and thinner forced regression units fsst deposited during stadials above distinctive downward shift surfaces the development of thicker highstand deposits with a distinctively thicker bottomset reflects enhanced shore parallel advection any time sea level rise leads to the drowning of the adriatic shelf triggering the formation of dense water and vigorous cyclonic circulation this advection mechanism persisted in each cycle throughout the early phases of the sea level fall but progressively decreased as sea level fall proceeded approaching the maximum lowstand position when most of the shelf became exposed relative sea level falls punctuating interglacials within each 100 ka cycle were thus accompanied by a dearth in sediment flux on the outer shelf the alternation of hst and fsst progradational wedges with markedly different thickness and downlap geometry of their bottomsets is the most evident stratigraphic signature within each 100 ka depositional cycle of the impact on the shelf of higher frequency 20 ka sea level cycles and concomitant supply fluctuations

sediment dispersal in the northwestern adriatic sea 1 sediment dispersal in the adriatic sea was evaluated using coupled three dimensional circulation and sediment transport models representing conditions from autumn 2002 through spring 2003 the calculations accounted for fluvial sources resuspension by waves and currents and suspended transport sediment fluxes peaked during southwestward bora wind conditions that produced energetic waves and strengthened the western adriatic coastal current transport along the western adriatic continental shelf was nearly always to the south except during brief periods when northward sirocco winds reduced the coastal current much of the modeled fluvial sediment deposition was near river mouths such as the po subaqueous delta nearly all po sediment remained in the northern adriatic material from rivers that drain the apennine mountains traveled farther before deposition than po sediment because it was modeled with a lower settling velocity fluvial sediment delivered to areas with high average bed shear stress was more highly dispersed than material delivered to more quiescent areas modeled depositional patterns were similar to observed patterns that have developed over longer timescales specifically modeled po sediment accumulation was thickest near the river mouth with a very thin deposit extending to the northeast consistent with patterns of modern sediment texture in the northern adriatic sediment resuspended from the bed and delivered by apennine rivers was preferentially deposited on the northern side of the gargano peninsula in the location of thick holocene accumulation deposition here was highest during bora winds when convergences in current velocities and off shelf flux enhanced delivery of material to the midshelf

organic matter origin and distribution in suspended particulate materials and surficial sediments from the western adriatic sea italy abstract in this study organic carbon oc total nitrogen tn stable carbon isotopic 13 c oc and cuo reaction product compositions were used to identify the sources of organic matter om and to quantify the relative importance of allochthonous and autochthonous contributions to the western adriatic sea italy suspended particulate material 195 samples and surficial sediments 0 1 cm 70 samples from shallow cross shelf transects were collected in february and may 2003 respectively vertical water column profiles were acquired along the same transects data include depth potential temperature salinity density and chlorophyll fluorimetry along the western adriatic shelf in the near shore region the phytoplankton growth was influenced by dynamics of the buoyant plumes from the po and appennine rivers a small amount of very fine terrigenous material remained suspended within the coastal current and was exported southward along the shelf to the slope high variability in the bulk composition was detected in the po prodelta surficial sediments whereas the western adriatic shelf although a larger area exhibited a narrower range of values a significant decoupling was observed between suspended particles in the water column and surficial deposits the organic material collected in the water column was compositionally heterogeneous with contributions from marine phytoplankton riverine estuarine phytoplankton and soil derived om frequent physical reworking of surficial sediments likely leads to the efficient oxidation of marine oc resulting in the observed accumulation and preservation of refractory soil derived oc delivered by the po and appennine rivers

paleoenvironmental reconstruction of late quaternary succession by foraminiferal assemblages of three cores from the san benedetto del tronto coast central adriatic sea italy new shelf records based on benthic foraminiferal assemblages allowed reconstruction of the paleoenvironmental evolution of the central adriatic sea during the late quaternary four distinct assemblages related to four different environments were identified based on multivariate analyses cluster analysis and principal component analysis circalittoral shallow water with vegetation deltaic and shallow marine with riverine influence two main phases were recognized by comparing the study area with the northern and southern portion of the adriatic basin the first phase was characterized by the last glacial lowstand or the beginning of the last pleistocene transgression the foraminiferal assemblage distribution was controlled by sea level changes and by the location of the ancient po river delta likely placed at the northern margin of the mid adriatic deep a subsequent deepening from a deltaic to normal marine shallow water environment occurred river supply decreases consistently from the bottom to the top of the cores due to the northern migration of the po delta the second phase which occurred during the holocene was characterized by sea level stabilization and modern water circulation pattern circalittoral foraminiferal assemblage typical of the outer mud belt developed during this second phase

evolution of tethyan phosphogenesis along the northern edges of the arabian african shield during the cretaceous eocene as deduced from temporal variations of ca and nd isotopes and rates of p accumulation abstract the evolution of tethyan phosphogenesis during the cretaceous eocene is examined to try to explain fluctuations of phosphogenesis through time and whether or not they reflect long term changes in ocean circulation or in continental weathering twenty seven time stratigraphic phosphate levels in various tethyan sites covering a time span of about 90 myr from the hauterivian to the eocene were analyzed for 44 ca 42 ca and 143 nd 144 nd in their carbonate fluorapatite cfa fraction p and ca accumulation rates and bulk sedimentation rates were quantified throughout the cretaceous eocene negev sequence to examine how changes in 44 ca 42 ca and 143 nd 144 nd are reflected in the intensity of phosphogenesis a clear cut change occurs in e nd t and 44 ca and in the rates of p and ca accumulation and bulk sedimentation through the time analyzed e nd t is much lower in the hauterivian lower cenomanian 12 8 to 10 9 than in the upper cenomanian eocene 7 8 to 5 9 much lower 44 ca values occur in the hauterivian turonian 0 22 to 0 02 than in the coniacian eocene 0 23 to 0 40 p accumulation rates in the negev steeply increase from 2 k yr 1 in the albian coniacian to 1500 mol cm 2 k yr 1 in the campanian whereas a strong decrease is concomitantly recorded in the rates of ca accumulation and bulk sedimentation in addition distinct e nd t values are shown by the phosphorites of the negev 6 7 to 6 4 and egypt 9 1 to 7 6 during the campanian and by those of the negev 7 8 to 6 3 and north africa 10 1 to 8 9 during the maastrichtian eocene the culmination of p accumulation rates in the negev during the campanian occurring with a high in e nd t and 44 ca and a low in sedimentation rates indicates that paleoceanographic and paleogeographical factors mostly governed phosphorite accumulation in this area the abrupt e nd t rise after the cenomanian is attributed to increased incursion of pacific radiogenic water masses into the tethys driven by the late cretaceous global sea level rise the connection between north and south atlantic the global post santonian cooling and the progressive widening of the caribbean threshold all acting in combination to significantly intensify the tethyan circumglobal current tcc it also reflects a weakening of the continental nd signal due to a reduction of exposed landmasses caused by increased flooding of continental shelves high 44 ca values at those times also point to a decrease in weathering ca 2 fluxes and expansion of carbonate sedimentation in shelves both enriching seawater with isotopically heavy ca 2 deep ocean circulation intensified by the post santonian cooling of high latitudes increased p inventory in the tethys basin whereas the strengthened tcc and the folded shelf likely resulted in coastal and topographically induced upwelling supplying p rich intermediate waters to southeastern tethys shelves only in the paleocene eocene following major changes in global circulation produced by narrowing of tethys and widening of the atlantic did phosphogenesis shifts its locus of high intensity to the western atlantic tethys and west african atlantic coasts this change in paleocirculation is expressed by distinctly differing e nd t in the middle east and the north and west african phosphorites suggesting different oceanic p sources and current systems for these two major groups of phosphorites our nd isotope results further suggest a weaker tcc during the mid cretaceous becoming more intense in late cretaceous times they also point to the north pacific ocean as major source of deep water formation for the intermediate deep waters in the tethys basin during the late cretaceous

depositional controls on mixed carbonate siliciclastic cycles and sequences on gently inclined shelf profiles the interplay between carbonate production and siliciclastic input produces mixed systems that typically contain a very high degree of lateral and vertical facies heterogeneity this heterogeneity complicates the sequence stratigraphic analysis of mixed systems outcrop studies facilitate the deciphering of controls and understanding of facies distributions within sedimentary successions the picun leufu anticline in the neuquen basin argentina offers the opportunity to integrate large scale depositional architecture with detailed facies descriptions of the shelf to basin successions of the upper jurassic lower cretaceous quintuco picun leufu vaca muerta system the strata in the system are mixed and range in depositional environments from shallow marine sandstones and limestones to deep basinal shales these environments are arranged in metre scale shallowing upward cycles and cycle sets with increasing carbonate proportions in regressive hemicycles increased input of siliciclastic material from the volcanic arc area occurred during phases of relative sea level rise and was controlled by the intensity of along shelf currents the shelf transport was driven by the available accommodation space on the shelf and therefore was a function of the eustatic sea level fluctuations within the studied section a pure carbonate depositional system developed because siliciclastic input was shut down either due to long lived highstand settings or a sudden climatic change to more arid conditions carbonate siliciclastic mixing in this setting is a function of siliciclastic dilution of the carbonate sedimentation and differs from the classical reciprocal sedimentation model which typically includes shut off of carbonate production during lowstand periods in the regional context the subsurface strata of time equivalent reservoirs in the eastern neuquen embayment display strong similarities of architecture indicating that similar mixing processes occurred along most of the neuquen basin

direct determination of7be in sediments cosmic ray produced7be 53 days half life is directly measurable in freshly collected samples of river and coastal zone sediments using a lithium drifted germanium detector calibration of the detector is discussed and an assessment of overall accuracy and sensitivity presented the detection limit for a 250 g dry weight sediment sample contained in a marinelli beaker and counted for 200 minutes is approximately 0 4 pci g applications toward locating zones of rapid sedimentation as well as in understanding shallow water sedimentation dynamics are suggested

phosphorus accumulation rates in a miocene low oxygen basin the monterey formation pismo basin california abstract phosphorus p limits oceanic productivity on long time scales and therefore determining changes in oceanic p accumulation through time is important for modeling oceanic paleoproductivity we determined p concentrations and accumulation rates at shell beach california a section of phosphatic rich marine sedimentary rocks which includes the widespread phosphatic and siliceous facies of the monterey formation phosphorus concentrations had wide ranges in the major lithologies found in these facies with values in phosphatic shales ranging from 0 36 to 3 9 wt compared to 0 02 to 0 42 wt in dolomitic and siliceous strata phosphorus accumulation rates in mol p cm 2 yr 1 for all values reported here showed significant variability with both sample lithology and position in the section phosphorus accumulation rates were much higher in phosphatic shale strata 1 5 29 than in dolomitic and siliceous strata 0 1 3 1 in both facies furthermore p accumulation rates were generally higher in phosphatic shale strata of the upper siliceous facies 3 1 29 compared to the lower phosphatic facies 1 5 14 mean p accumulation rates calculated using linear sedimentation rate models for each facies and observations of the relative amount of phosphatic shale dolomite and siliceous strata are comparable between the portions of phosphatic and siliceous facies studied this indicates that the two facies with their faunal and sedimentological characteristics considered to reflect major oceanic and climatic changes during the middle miocene are similar in terms of p burial total p accumulation rates are also comparable to other phosphogenic miocene and modern environments we modeled variable sedimentation rates to examine the sensitivity of mean p accumulation rates to the linear sedimentation rate assumption increasing shale sedimentation rates to values above those estimated by linear models yields higher mean p accumulation rates in both facies though they remain comparable in terms of net p burial modeling also revealed that for increased shale sedimentation rates in each facies siliceous sedimentation must be about three times faster than dolomitic strata sedimentation

the effect of sediment mixing on pb 210 accumulation rates for the washington continental shelf abstract nine cores from the washington continental shelf were examined by radiochemical techniques in order to evaluate the effect of mixing on the calculation of sediment accumulation rates from pb 210 profiles th 234 profiles indicate mixing coefficients of 140 cm 2 yr 1 for the seabed offshore from the columbia river and 47 cm 2 yr 1 for the seabed of the mid shelf silt deposit 75 km north of the columbia river these large mixing coefficients demonstrate that particles can penetrate to the base of the intensely mixed surface layer 10 cm within one year after emplacement at the seabed surface observed depths of cs 137 penetration within the seabed are compared with depths predicted from the surface mixed layer thickness and the pb 210 accumulation rate the observed and predicted depths agree well at all but one station at this station a combination of th 234 co 60 pb 210 and cs 137 profiles suggests that active mixing occurs below the intensely mixed surface layer the agreement of pb 210 and cs 137 data at the other stations however indicates a general absence of deep mixing on the washington shelf thus the apparent accumulation rates calculated from pb 210 profiles below the intensely mixed surface layer on the washington shelf generally reflect the true rates of sediment accumulation

upper cretaceous campanian phosphorites in jordan implications for the formation of a south tethyan phosphorite giant a record of sedimentary authigenic and biological processes are preserved within the upper cretaceous campanian alhisa phosphorite formation ap in central and northern jordan the ap formed near the eastern extremity of the south tethyan phosphorite province stpp a carbonate dominated upper cretaceous to eocene phosphorite giant that extends from colombia north africa to the middle east multidisciplinary research of the ap and associated cherts chalks and oyster buildups indicate that phosphatic strata formed on a highly productive storm dominated east west trending epeiric platform along the south tethyan margin the onset of phosphogenesis and the accumulation of economic phosphorite coincided with a rise in relative sea level that onlapped peritidal carbonates of the ajlun group pristine phosphates are associated with well developed micrite concretionary horizons and contain abundant non keeled spiral planktic foraminifera and a low diversity benthic assemblage of buliminacean foraminifera suggesting that pristine phosphates are a condensed facies and phosphogenesis was stimulated by the effects of a highly productive surface ocean and the suboxic diagenesis of sedimentary organic matter the bulk sediment composition and absence of fe bearing authigenic phases such as glauconite pyrite including pyrite molds siderite and goethite within pristine phosphates suggests that deposition and authigenesis occurred under conditions of detrital starvation and that iron pumping played a minimal role in phosphogenesis authigenic precipitation of phosphate occurred in a broad array of sedimentary environments herein termed a phosphorite nursery that spanned the entire platform this is a non uniformitarian phenomenon reflecting precipitation of sedimentary apatite across a wide depositional spectrum in a variety of depositional settings wherever the conditions were suitable for phosphogenesis sedimentologic data indicate that pristine phosphates were concentrated into phosphatic grainstones through storm wave winnowing and storm generated shelf parallel geostrophic currents economic phosphorites formed through the amalgamation of storm induced event beds stratigraphic packaging of phosphatic strata indicates that temporal variations in storm frequency were a prerequisite for the formation of economic phosphorite syndepositional phosphogenesis reworking and amalgamation to form phosphorites contrasts sharply with the principles of baturin cycling a transgressive systems tract coupled with high surface productivity created detritally starved settings favourable for phosphogenesis storm reworking of pristine

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 trace metals used as an indicator of past productivity changes in coastal sediments in sediments of kiel bight which differ significantly in their redox states and the rates of corg degradation depth profiles of both dissolved and solid phase fe mn cd cu ni and co were measured porewater fluxes of cd cu and ni were significantly higher at shallower more oxic stations as compared to highly reducing deeper subthermocline sediments while mn fluxes behaved the opposite way when normalized to fe for grain size correction the measured solid phase metal contents revealed that the high porewater flux has led to a near surface depletion of mn from more anoxic sediments and to a reduced rate of accumulation of anthropogenic cd in more oxic sediments this difference in early diagenetic behaviour suggests the use of these metals as a proxy for the redox state and the intensity of carbon recycling contrary to the recent sediment layers the normalized metal contents of preindustrially deposited sediment layers were similar for both metals at all stations thus at stations having highly anoxic sediments today the preindustrial benthic flux must have been lower for mn and higher for cd reflecting a shift from more oxic to more reducing conditions in subthermocline sediments during the last 100 years this change of the redox state in subthermocline sediments reflects an increase of primary production and of subsequent corg input to the sediment due to eutrophication which accompanied industrialization

geochemistry of cadmium in the negev phosphorites cadmium cd in the negev phosphorites as in many other phosphorites is the most enriched trace element relative to average shale nevertheless similar to many other phosphorites cd is either not correlated to p2o5 or has a slightly negative correlation with it there is a clear correlation between the cd content the textural and the compositional characteristics of the phosphorites and the structural position of the phosphate deposits well developed synclinal sections comprised of many thin strata of laminated non disturbed pelletal phosphorites have much higher cd concentrations than the condensed anticlinal sections which consist of a few amalgamated thick beds of massive reworked phosphorites cd is in general poorly related to the present organic matter content but has a good correlation with organic matter in unoxidized beds of the synclinal sections cd is strongly correlated to zn in the relatively undisturbed beds of the synclinal sections but shows no correlation in the highly reworked beds of anticlinal sections the source of cd is upwelled seawater that is enriched in both p and cd this is the basis of the relationship between phosphogenesis and cd concentration reducing conditions during decomposition of organic matter immobilize cd in the pore fluids of the bottom sediments precipitation of cd rich sphalerite and adsorption on organic matter appear to be the main processes for its initial speciation and concentration in the negev phosphorites cd is concentrated mainly in laminated non disturbed microbially generated phosphorites where authigenic apatites are also found cd does not as a rule replace ca in the structure of authigenic primary sedimentary apatites this finding has practical applications since it makes possible the production of a phosphate concentrate with a much lower cd concentration than the original phosphorite exposure to oxic conditions leads to mobilization of the sulfide bound cd scouring activity bioturbation and recycling and transportation of stirred up phosphate corpuscles in an oxidizing environment appear to be effectual for removing cd oxidation alone without fabric disruption and mobilization of the phosphate grains does not significantly lower cd concentrations since the released cd may be almost immediately readsorbed on the various components of the phosphorite such as iron oxyhydroxides organo clay fractions and apatites the cadmium concentration and the cdzn ratio of a phosphorite may help to determine whether a phosphorite is pristine or not and to unravel its diagenetic history

geomicrobiology its significance for geology abstract some microorganisms including various kinds of bacteria fungi algae and protozoa serve as geochemical agents in the uppermost lithosphere and in the hydrosphere some promote rock weathering by mobilizing mineral constituents with inorganic or organic acids or ligands that they excrete others promote rock weathering by redox attack of mineral constituents such as fe and mn still others cause active or passive mineral formation by precipitation and subsequent nucleation of crystal formation on or in the cell or in the bulk phase they play a role in some phases of fossil fuel formation and accumulation they modulate the terrestrial and marine cycles of c n s and p and some other elements and they influence the composition of the atmosphere in respect to o 2 co 2 and ch 4 some discriminate between stable isotopes of h c o n and s

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