phosphogenesis and weathering of shelf sediments from the southeastern united states implications for miocene δ13c excursions and global cooling the enormous phosphorite deposits of the southeastern united states indicate intense upwelling but contain small amounts of organic carbon the authors propose that deposition of organic rich sediment on continental shelves in the southeastern united states and elsewhere during marine transgressions in the late oligocene and early to middle miocene resulted in global positive delta sup 13 c shifts and the formation of early diagenetic phosphorite multiple reworking and supergene weathering from subaerial exposure during miocene marine regressions oxidized most of the organic carbon and resulted in the return of delta sup 13 c to its preexcursion value the estimated phosphorite content of the southeastern united states requires sufficient organic carbon burial 10 sup 15 kg carbon to support a 1 per thousand delta sup 13 c excursions sea level fluctuations organic carbon burial phosphogenic episodes and possibly global cooling during the cenozoic

the oceanic phosphorus cycle and continental weathering during the neogene little is known about the history of dissolved phosphorus p input to the ocean during the cenozoic an important factor in reconstructing global change because of the role of p in controlling net oceanic productivity and organic carbon burial we present p accumulation rates from the eastern neogene and western cenozoic equatorial pacific a region chosen to reflect oceanic p input trends because of its importance in global models of new production and biogenic sedimentation p accumulation rates range from 5 to 60 mol p cm 2 kyr 1 and exhibit a positive correlation with mass sediment accumulation rates calcium carbonate being the major sediment component the influences of surface productivity patterns site migration through time relative to equatorial upwelling and water depth are observed in the p accumulation rate records these site specific effects are relatively minor however compared to synchronous significant trends in p accumulation rates in these equatorial pacific sites the most notable event occurred in the late miocene when mean p accumulation rates exhibited a strong peak at 5 6 ma to the highest mean value of the neogene 37 mol p cm 2 kyr 1 followed by a sharp decrease to 1 2 ma 14 mol p cm 2 kyr 1 after which values increased slightly to the present these changes in p accumulation rates in the equatorial pacific translate into substantial changes in p burial the decrease from 5 6 to 1 2 ma signified a 62 decrease in p burial in the equatorial pacific and the difference is equivalent to 14 of the estimated modern p input rate to the oceans some of the late neogene change in the equatorial pacific p accumulation rate record may have been due to redistribution of p burial to high latitude regions however on the basis of p mass balance considerations redistribution alone cannot account for the bulk of the change in p accumulation and burial in the equatorial pacific the p accumulation rate record is markedly different from the unidirectional increases in continental weathering rates over the last 40 m y interpreted from the sr isotope record suggesting a decoupling of nutrient input fluxes from input fluxes of other dissolved constituents

the impact of hydrodynamics authigenesis and basin morphology on sediment accumulation in an upwelling environment the miocene monterey formation at shell beach and mussel rock pismo and santa maria basins central california u s a abstract in the sections at shell beach pismo basin and mussel rock santa maria basin both along the central california coast the miocene monterey formation is composed of laminated biosiliceous organic rich and phosphate rich sediments which are intercalated with carbonates and volcanogenic deposits the presence of small and large scale scours conglomerates gravity flow deposits slumps and condensed intervals reveals the importance of sediment reworking which is related to the presence of bottom currents the general morphology of the basins and recurrent high energy events of likely seismic origin the lithologies reflect strong upwelling enhanced primary productivity and the presence of an oxygen minimum zone which is indicated by ubiquitous lamination a general absence of bioturbation with the rare exception of traces related to the gravity flow displacement of trace makers high pyrite mo and u concentrations and molar ratios of total organic carbon and organic phosphorus toc p org of up to 2000 oxygen depletion was particularly severe during the early langhian and the late serravallian and early tortonian and favored the preservation of organic matter episodes of deposition of organic rich sediment were followed by longer phases of subdued sediment accumulation and early diagenetic phosphogenesis which resulted in the formation of a low porosity less permeable lid in the near surface sediments that assisted in preserving organic matter phosphogenesis occurred throughout the time interval considered approximately 17 5 6 5 ma and phosphate rich sediments formed especially during periods of sedimentary condensation in the langhian and earliest serravallian and the latest tortonian and early messinian a comparison of temporal trends in the type and quantity of deposited sediments between the two sections at shell beach and mussel rock and three sections of the santa barbara basin el capitan state beach naples beach and haskell beach confirms that towards the top of the monterey formation sediments become enriched in biosilica in all three basins the transition into this lithology occurred diachronously during the serravallian in the pismo and santa maria basins and tortonian in the santa barbara basin and was probably related to a diachronous shift to more intense upwelling in all three basins a phase of important condensation and phosphogenesis terminated monterey type sedimentation during the latest tortonian and early messinian in both the santa maria and santa barbara basins the uniform expression of this phase is interpreted as the result of improved connections between the two basins

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

ocean chemistry during glacial time abstract measurements of co2 to air ratios in the gas trapped in bubbles in ice of glacial age suggest that the co2 content of the atmosphere was considerably lower during peak glacial time than during holocene time the purpose of this paper is to show that such a change must in all likelihood be the result of alterations in the nutrient element chemistry of sea water two possible scenarios are presented one involves alternate storage and erosion of phosphorous leaving residues from shelf sediments the other involves changes in the c p ratio in the organic debris falling to the deep sea means of verifying the nutrient cycle hypothesis are also given it is shown that the 13c record as we know it in planktonic and benthic foraminifera the oxygen record as inferred from benthic foraminifera species distributions and the early post glacial caco3 preservation event as recorded by aragonitic pteropods are consistent with both of the hypotheses presented only if an early post glacial spike in the 13c record for planktonic shells could be found would it be possible to eliminate one of these hypotheses i e that involving shelf storage the implications of these nutrient hypotheses to climate theory are as follows if shelf storage is responsible for the glacial to interglacial co2 increase then the co2 change must be considered an amplifier of some primary cause the reason is that sea level changes are needed to drive deposition on and erosion from the shelves on the other hand if changes in the c p ratio for falling debris are responsible then the co2 change could either be an amplifier or a primary cause for the major glacial to interglacial climatic cycle the latter is possible as self sustained oscillations in ocean chemistry might be driven by interactions between ocean ecology and ocean nutrient chemistry

formation of fe mn crusts within a continental margin environment abstract this study examines fe mn crusts that form on seamounts along the california continental margin ccm within the united states 200 nautical mile exclusive economic zone the study area extends from approximately 30 to 38 north latitudes and from 117 to 126 west longitudes the area of study is a tectonically active northeast pacific plate boundary region and is also part of the north pacific subtropical gyre with currents dominated by the california current system upwelling of nutrient rich water results in high primary productivity that produces a pronounced oxygen minimum zone hydrogenetic fe mn crusts forming along the ccm show distinct chemical and mineral compositions compared to open ocean crusts on average ccm crusts contain more fe relative to mn than open ocean pacific crusts the continental shelf and slope release both fe and mn under low oxygen conditions silica is also enriched relative to al compared to open ocean crusts this is due to the north pacific silica plume and enrichment of si along the path of deep water circulation resulting in si enrichment in bottom and intermediate waters of the eastern pacific the ccm fe mn crusts have a higher percentage of birnessite than open ocean crusts reflecting lower dissolved seawater oxygen that results from the intense coastal upwelling and proximity to zones of continental slope pore water anoxia carbonate fluorapatite cfa is not present and ccm crusts do not show evidence of phosphatization even in the older sections the mineralogy indicates a suboxic environment under which birnessite forms but in which ph is not high enough to facilitate cfa deposition growth rates of ccm crusts generally increase with increasing water depth likely due to deep water fe sources mobilized from reduced shelf and slope sediments many elements of economic interest including mn co ni cu w and te have slightly or significantly lower concentrations in ccm crusts relative to crusts from the pacific prime crust zone and other open ocean basins however concentrations of total rare earth elements and yttrium average only slightly lower contents and in the future may be a strategic resource for the u s

carbon and phosphorus cycling in anoxic sediments of the saanich inlet british columbia abstract uncertainty currently exists about the removal of carbon c and phosphorus p from the oceanic reservoir especially in low oxygen settings in this paper the cycling of c and p is examined in sediments from the anoxic saanich inlet cored by ocean drilling program odp leg 169s in 1996 at two sites although c org p org ratios are high and increase with depth in the saanich inlet this effect is due largely to a remobilization of p from an organic matter sink to an authigenic sink reducible sedimentary components act as temporary shuttles in this process even in this anoxic setting with the ultimate burial sink for the remobilized p being carbonate fluorapatite the effective c org p reactive molar ratio appears to be about 150 200 indicating some preferential loss of p compared to c during organic matter degradation but not approaching previously reported values of over 3000 in black shales reactive p accumulation rates in this basin range from 10 000 60 000 mol cm 2 kyr greatly exceeding the range of 500 8000 mol cm 2 kyr found in most continental margin settings including regions of modern phosphogenesis the initiation of marine sedimentation in the saanich inlet occurred after deglaciation and the high rates of p burial seen here may provide an end member example of the effects of sea level and margin sedimentation on the distribution of p within the marine p cycle

disseminated phosphorus in oceanic sediments a review abstract the content of disseminated phosphorus in sediments of the world oceans fluctuates between 0 01 and 4 36 terrigenous and hemipelagic sediments contain on average about 0 07 phosphorus higher concentrations are characteristic of sediments enriched in iron and manganese hydroxides or bone detritus and phosphoritic material the general features of the phosphorus distribution in surface sediments depend on the ratio of continental runoff area to basin area which diminishes from the atlantic to the indian and pacific areas the relative extent of the nearshore phosphorus rich zone contracts whereas that of the pelagic phosphorus rich zone widens in the transition from the atlantic through the indian to the pacific areas the distribution of phosphorus in vertical sections of sediments gives some evidence of the diagenetic mobilisation of phosphorus and its partial loss to bottom water the rate of phosphorus accumulation in oceanic sediments is evaluated as between 10 g cm 2 k y 1 the bulk mass of phosphorus is accumulated in marginal zones of the oceans

an apparent contradiction in the role of phosphorus in cenozoic chemical mass balances for the world ocean little is known about the fluxes to and from the ocean during the cenozoic of phosphorus p a limiting nutrient for oceanic primary productivity and organic carbon burial on geologic timescales previous studies have concluded that dissolved river fluxes increased worldwide during the cenozoic and that organic carbon burial decreased relative to calcium carbonate burial and perhaps in absolute terms as well to examine the apparent contradiction between increased river fluxes of p assuming p fluxes behave like the others expected to drive increased organic carbon burial and observations indicating decreased organic carbon burial we determined p accumulation rates for equatorial pacific sediments from ocean drilling program leg 138 sites in the eastern equatorial pacific and leg 130 sites on the ontong java plateau in the western equatorial pacific although there are site specific and depth dependent effects on p accumulation rates there are important features common to the records at all sites p accumulation rates declined from 50 to 20 ma showed some variability from 20 to 10 ma and had a substantial peak from 9 to 3 ma centered at 5 6 ma these changes in p accumulation rates for the equatorial pacific are equivalent to substantial changes in the p mass balance however the pattern resembles neither that of weathering flux indicators 87sr 86sr and ge si ratios nor that of the carbon isotope record reflecting changes in organic carbon burial rates although these p accumulation rate patterns need confirmation from other regions with sediment burial significant in global mass balances e g the north pacific and southern ocean it appears that p weathering inputs to the ocean are decoupled from those of other elements and that further exploration is needed of the relationship between p burial and net organic carbon burial

the influence of bacterial activity on phosphorite formation in the miocene monterey formation california abstract authigenic phosphorites from the miocene monterey formation california including an autochthonous phosphatic laminite were analyzed for molecular biomarkers element content and sulfur isotopic composition of associated pyrite and sulfate to evaluate the role of bacterial activity in the precipitation of phosphate minerals the phosphorites formed in a depositional environment typified by upwelling with dynamic bottom currents and hardground formation pyrite enclosed in the phosphorites shows 34 s values as low as 36 5 vcdt which is consistent with bacterial sulfate reduction in a three step extraction phosphorite dissolution extraction procedure molecular fossils of sulfate reducing bacteria di o alkyl glycerol ethers and short chain branched fatty acids i and ai c 15 0 i and ai c 17 0 and 10mec 16 0 were preferentially released from the mineral lattice this suggests that the molecular fossils were tightly bound to carbonate fluorapatite indicating that sulfate reducing bacteria were involved in mineral formation a close association of sulfate reducing bacteria with large sulfide oxidizing bacteria which was previously suggested to favor carbonate fluorapatite precipitation could neither be confirmed nor excluded for the miocene monterey formation phosphorites

dolomite formation in anoxic sediments of kau bay indonesia authigenic dolomite layers occur in the organic matter rich sediments of kau bay indonesia dolomite formation is related to the anaerobic decomposition of organic matter which causes depletion of pore water sulfate and increase in interstitial water alkalinity x ray diffractograms of kau bay dolomites show sharply defined peaks including the superstructure reflections carbon isotopes indicate that a significant portion of the carbon is derived from the degradation of organic matter the pore waters are highly supersaturated with dolomite but at greater depths pore waters are undersaturated or are near saturation with calcite and aragonite dolomite seems to have formed by direct precipitation from solution the formation of dolomite is believed to be initiated by the high alkalinity levels found in the zone of anoxic methane oxidation the rate of dolomite formation is controlled by the supply of calcium and is on the order of a few centimetres per 1 ka

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

the origin of sulfide rimmed metal grains in ordinary chondrites abstract we report results from an experimental study of sulfide chemistry during metamorphism on ordinary chondrite parent bodies artificial ll chondrite material composed of silicate iron metal and sulfide grains was placed in sealed evacuated silica tubes and heated to either 500 c or 900 c these temperatures are representative peak metamorphic temperatures experienced by type 3 and type 6 ordinary chondrites respectively rapid sulfur mobilization occurs during heating and results in the formation of sulfide rims around the metal grains and sulfur loss from the original sulfide crystals the newly formed sulfide rims have two distinct layers that incorporate nearby silicate grains we also observe narrow sulfide trails that follow silicate grain boundaries and connect separate sulfide rimmed metal grains the morphologies of the sulfide rims suggest that vapor transport is the main mechanism for sulfur mobilization sulfur loss is observed along cracks and crystal boundaries of the initial sulfide grains after extensive reaction patches of iron metal appear at the outer edges of the sulfide crystals and large pore spaces form throughout the original sulfides the experimental metal sulfide assemblages resemble those found in low metamorphic grade ordinary chondrites this suggests metamorphism is mainly responsible for the observed metal sulfide textures in these chondrites

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

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

ultimate use of prestack seismic data integration of rock physics amplitude preserved processing and elastic inversion abstract elastic information carries important data about subsurface lithology and fluid it is highly valued by the seismic exploration industry compared with other methodologies e g 9c vsp and 3d 3c prestack p wave methods are used extensively to address reservoir and fluid prediction because of their wide availability of data however many traditional technologies can hardly extract accurate p wave and s wave information from conventional prestack pp data because of lacking systematic studies on how to properly handle prestack amplitudes a new concept prestack elastic integration pei emphasizes comprehensive interactions among rock physics amplitude preserved processing and inversion algorithm the influences of the three aspects are examined and discussed with real examples moreover achievements of pei are demonstrated through its application on a complex lithologic reservoir in eastern china in which pei characterizes target reservoir properties much better than traditional methods do

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

the phosphorus cycle phosphogenesis and marine phosphate rich deposits abstract phosphorus in the form of phosphate is an essential nutrient and energy carrier on many different levels of life and a key element in mediating between living and lifeless parts of the biosphere one of the most important aspects of the phosphorus cycle is its vital role in governing productivity thereby interacting with the exogenic part of the carbon cycle which in turn is important in regulating earth s climate phosphorus is a prime element to be traced in earth s history because it allows for the reconstruction of long term feedback mechanisms between climate environment and ecology and of global change as such marine sedimentary phosphate deposits are particularly suited to study aspects of the phosphorus cycle because in the case of ubiquity their origin may result from a general acceleration of the global phosphorus cycle sources of sedimentary phosphate are microbial breakdown of buried organic matter and redox driven phosphate desorption from iron and manganese oxyhydroxides dissolved sea water phosphate represents an additional source which may become important in the formation of phosphatic hardgrounds the main locus of phosphogenesis is near the sediment water interface but phosphogenesis also occurs at greater sediment depths current induced winnowing and transport processes along the sea floor concentrate phosphate precipitates into deposits which exhibit internal stratification patterns typical for the prevailing hydraulic energy regime in a sequence stratigraphic context phosphate deposits preferentially occur along marine or maximum flooding surfaces consequent sedimentary reworking may result in the transfer of phosphates to highstand or lowstand deposits bio chemical weathering on continents represents the most significant source of bioavailable phosphorus this implies that long term changes in marine phosphorus levels and with these changes in marine ecology productivity rates and ratios of exported carbonate carbon and organic carbon are a response to changes in continental weathering rates a compilation of marine sedimentary phosphorus burial rates for the last 160 myr suggests that natural variations have occurred that span one order of magnitude for the late jurassic cretaceous and most of the paleogene the phosphorus cycle appears to have been accelerated in times of climate warming which was most likely due to the spreading of zones of humid climate and more intense continental weathering in the neogene the phosphorus cycle appears to have responded to changes in glacially induced weathering this suggests that uniform interpretations with respect to the emplacement of major phosphorite deposits should be treated with caution integrated analyses of the sedimentary and biogeochemical context of phosphorite occurrences may help to identify paleoenvironmental conditions as well as to improve our understanding of periods of enhanced phosphate accumulation periods which were usually characterized by steep gradients in the development of climate and environment with regard to the complexity of feedback mechanisms between the phosphorus cycle and the biosphere the present day input rates of phosphate into the world s oceans should be of great concern they are more than doubled by anthropogenic means and affect ecological systems on a rapidly increasing scale

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

miocene phosphate accumulation in the cuyama basin southern california abstract middle and upper miocene phosphatic strata in the cuyama basin of southern california contain approximately 6 4 10 9 metric tons 2 1 10 14 mol of phosphorus p that accumulated in slope and shelf strata at rates between 0 9 and 3 8 mol p cm 2 year 1 from 15 5 to 10 8 ma an estimated 63 of all phosphorus lies in a single third order sequence deposited between 14 8 and 13 ma the main impetus for this brief phosphogenic event was a 200 m relative sea level rise that resulted from strike slip faulting immediately east of the basin minor element and petrologic analyses suggest the overall increase in phosphorus accumulation correlates with less reducing conditions in the shallowly buried marine sediments on the slope and the expansion of phosphogenesis to the outer shelf both events were probably related to landward shifts of the pacific oxygen minimum zone and coastal upwelling centers during the relative sea level rise whereas these tectonic events were apparently local the phosphatic deposits of the cuyama basin clearly demonstrate that tectonism can strongly influence phosphate accumulation rates in marginal marine environments

paleoceanographic model of neogene phosphorite deposition u s atlantic continental margin the neogene stratigraphic section of the southeastern u s continental shelf coastal plain system is characterized by i a series of major regional phosphogenic episodes ii a strong spatial relationship between the structural or topographic framework and phosphate deposition and iii distinct cyclical and regional patterns of deposition of the terrigenous carbonate and phosphate lithofacies the complex depositional patterns are explained by a paleoceanographic model based upon the interaction of glacial eustatic sea level fluctuations associated changes in climate and the dynamics of the gulf stream in response to the bathymetric configurations of the continental margin during the past 20 million years

formation of large metal nodules in ordinary chondrites literature data show that many large 2 30 mm metallic fe ni nodules in ordinary chondrites are depleted in refractory siderophiles e g re os ir ru pt and rh and cu relative to fine grained metal but are not depleted in normally refractory w and mo common siderophiles e g ni and co and volatile siderophiles e g au as and sb it was recently proposed that metamorphic diffusion could form the metal nodules and that partitioning of siderophile elements between kamacite and taenite could account for the nodules unusual compositions however the nodules have the same compositional trends as metal nodules and veins in shocked meteorites that clearly formed by impact related processes if large metal nodules formed during metamorphism type 6 chondrites should contain abundant large nodules instead the mean metal grain size in h6 chondrites is 0 12 0 15 mm far smaller than any of the nodules it seems likely that the metal nodules formed by impact vaporization oxidation of w and mo to form volatile oxides concomitant partial oxidation of re and os rapid fractional condensation of refractory siderophiles transport of the residual vapor condensation of cu s and se into vugs and fractures to form sulfide and condensation of the remaining siderophiles to form metal nodules and veins during vapor cooling and condensation or during subsequent parent body annealing w mo re and os oxides were reduced

anatomy and origin of a cretaceous phosphorite greensand giant egypt late cretaceous epicontinental phosphorites porcelanites cherts dark coloured shales glauconitic sandstones and bioclastic and fine grained carbonate rocks in egypt are examined in terms of their overall depositional and diagenetic framework and stable isotopic and organic geochemical characteristics two main depositional realms are interpreted and correlated through sequence stratigraphic analysis 1 a shallow hemipelagic environment accompanying initial stages of marine transgression and conducive to the formation of organic carbon rich shales biosiliceous sediments and thick phosphorites and 2 a relatively high energy depositional regime accompanying sea level fall during which deltas advanced glauconites were reworked seaward and prograding oyster banks became periodically exposed to episodes of fresh water diagenesis thereby promoting solution collapse phenomena in associated cherts lenticular to massive phosphorites are viewed as the result of current winnowing and concentration of authigenic grains initially precipitated in associated reducing shales and biosiliceous sediments in eastern egypt the phosphorites form winnowed lag layers some of which may have been redeposited down slope in structural lows in the west these sands were concentrated into giant phosphorite sand waves built by reworking of penecontemporaneously deposited phosphatic muds during marine transgression carbon isotopic results substantiate interpretations from modern deposits for limitation of phosphate mineral precipitation with depth in sediments as a result of lattice poisoning however direct desorption of phosphorus to pore waters from detrital iron oxyhydroxide phases also may have been important in the cretaceous setting the iron reduced in this process being available for incorporation in glauconites the main locus for authigenic glauconite precipitation appears to be where iron fluxes from regions of lateritic weathering were highest and near the boundary between oxygenated and reduced waters this study suggests a model for the common coexistence of glauconites and phosphorites in the geological record although upwelling is often advocated as the origin of nearly all giant phosphorite deposits we suggest that some of these may have been strongly influenced by fluvially derived phosphorus borne on particulates and desorbed from these compounds upon flocculation and or reduction in bottom waters or pore waters

trace elements as palaeoenvironmental markers in strongly mature hydrocarbon source rocks the cretaceous la luna formation of venezuela abstract the late cretaceous la luna formation is the main hydrocarbon source rock formation in venezuela in the lake maracaibo area the formation shows a steep maturation gradient affecting sedimentary organic matter om and clay minerals related to local burial history and thrusting events the influence of the gradient is examined through geochemical organic and inorganic and mineralogical investigations carried out on samples from five cored boreholes in the maracaibo basin the analytical procedure comprises rock eval pyrolysis vitrinite reflectance measurement palynofacies observation major and trace element content determination performed on bulk rock samples or after a sequential leach protocol dop calculation and the examination and analysis of clay mineral assemblages the maturation gradient seems to have had no effect upon the distribution of the trace elements referred to as proxy indicators for palaeodepositional conditions of om rich sediments ba p v mo ni co cu cd cr and mn consequently trace elements appear to be reliable palaeoenvironmental markers they indicate that during the la luna fm deposition the water column must have had variable conditions with high primary production near the surface and the correlative development of euxinic conditions at the bottom this provides further arguments for an upwelling system affecting the northern platform of south america during late cretaceous time the relative scarcity of reactive iron in the depositional environment must have taken an active part in a process involving sulphur and acting on the environmental conditions as well as on om vulcanisation this process favours aliphatic om storage and may be relevant for many other om rich facies or hydrocarbon source rocks

processes controlling forms of phosphorus in surficial sediments from the eastern arabian sea impinged by varying bottom water oxygenation conditions abstract the surficial sediments from the upper continental slope of the eastern arabian sea impinged by the oxygen minimum zone omz 150 1200 m water depth show varying concentrations of the biogenic element phosphorus p 0 1 0 2 in the northern and southern areas even though total organic carbon concentrations are relatively constant toc 2 5 prakash babu et al 1999 to understand this discordance 17 surface sediment samples from shelf slope and deep sea of the eastern arabian sea were investigated using a five step sequential extraction scheme to delineate the process responsible for p enrichment in omz high fractions of organic phosphorus porg 10 26 biogenic phosphorus pbio 36 48 relatively low molar corg porg ratios 322 447 and corg preactive ratios close to redfield ratio in omz sediments of the se arabian sea suggest accumulation under high surface production and low residence time of labile forms of p due to high sedimentation rates despite higher productivity in surface waters low fractions of porg 8 13 less than deep sea sediments of the study area 12 13 pbio 25 33 relatively high molar corg porg ratios 341 508 and corg preactive ratios less than redfield ratio in omz sediments from the ne arabian sea may indicate a higher degree of regeneration and diagenetic transformation of labile forms of p to other phases authigenic phosphorus paut fraction varies by a factor of 2 8 in sediments from the omz when compared to well oxygenated deep sea sediments of the study area while the ptotal remains constant significant p transformation seems to occur in ne arabian sea which is suggested by high paut fraction 50 compared to low paut fraction 10 39 in the se arabian sea sediments supply rates of phosphorus variable rates of p dissolution under varying dissolved oxygen contents in the bottom waters and early diagenetic transformation of p within the sediments seem to influence p geochemistry in sediments overlain by the omz in the eastern arabian sea

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

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

carbonaceous and phosphate rich sediments of the miocene monterey formation at el capitan state beach california u s a abstract the organic and phosphate rich interval of the monterey formation at el capitan state beach west of santa barbara california u s a late early to early late miocene in age is composed of a carbonaceous marl toc contents between 1 2 and 23 2 wt with intercalated phosphate rich laminae lenses and layers subordinate lithologies include ash layers dolomitized horizons and siliceous beds we distinguished five lithological units 1 a gray marl unit lacking major phosphate accumulations 16 3 ma average toc content 2 by weight average sedimentation rate 75 m my average toc accumulation rate 0 19 mg cm2 yr 2 a black marl unit including light colored phosphatic laminae lenses and discrete particles 16 3 14 5 ma average toc content 7 5 by weight average sedimentation rate 20 m my average toc accumulation rate 0 19 mg cm2 yr 3 a red marl unit including light colored phosphatic laminae lenses and commonly reworked particles 14 5 12 7 ma average toc content 15 by weight average sedimentation rate 20 m my 14 5 13 3 ma and 2 m my 13 3 12 7 ma respectively average toc accumulation rate 0 39 mg cm2 yr 14 5 13 3 ma and 0 04 mg cm2 yr 13 3 12 7 ma respectively 4 a unit of complex and condensed phosphatic beds interbedded with red marl 12 7 10 8 ma average sedimentation rate 3 m my and 5 a black marl unit with intercalated phosphatic laminae and lenses 10 8 ma average sedimentation rate 9 m my average toc accumulation rate 0 09 mg cm2 yr phosphogenesis and accumulation of phosphate were dynamic processes which started with local phosphogenesis leading to the formation of phosphatized particles as well as stratigraphically bound phosphogenesis leading to the formation of phosphate laminae and lenses phases of subsequent sediment reworking resulted in the concentration of phosphate particles in phosphate rich layers and repeated phases of sediment reworking and phosphogenesis ultimately resulted in the formation of the complex phosphate condensed horizons preservation of organic matter was favored by high productivity rates and by the development of dysaerobic bottom water conditions the dynamic sedimentary environment likely led to the formation of early diagenetic phosphatic lids which may have sealed off subjacent organic rich layers as well as to the rapid deposition of entire layers in the form of mud flows thereby eventually enhancing the potential of organic matter preservation our new age data suggest that at the el capitan state beach section the intervals characterized by high toc values and maximum toc accumulation rates red marl as well as significant quantities of in situ phosphates appeared in the late middle miocene i e during and after the major cooling phase at around 14 5 ma this implies that deposition of phosphate and organic carbon continued well after this cooling phase thereby underlining the observation that preservation of organic carbon in the monterey formation is not only dependent on climate change during the mid miocene but also on regional conditions

pacific pelagic phosphorus accumulation during the last 10 m y as a limiting nutrient to marine life phosphorus p is an effective tracer of today s marine productivity the distribution of p in marine sediments likewise tracks the history of marine productivity because of its relative insolubility in seawater caco3 biogenic opal terrigenous sediment and total p have been measured in cores from nine pacific sites deep sea drilling project dsdp 65 66 310 77 62 572 463 586 and gpc 3 and one subantarctic dsdp 266 site these sites were specifically chosen to provide information on biota burial flux changes with time for sedimentary sinks that represent key oceanographic variables i e rate of upwelling water depth and carbonate dissolution gradient the accumulation rates of these components for the last 10 ma were then calculated from determined core age versus depth plots core bulk density and porosity data the accumulation of p weakly correlates with that of caco3 moderately with that of total sediment and very strongly with carbonate free accumulation two prominent peaks for all components occur at 2 3 ma and 5 6 ma and record the chemical loading of dissolved caco3 sio2 and p from glacially emergent continental shelves these results indicate that continental shelf phosphorites form during interglacially high sea levels and correspond to low deep sea p accumulation rates whereas glacially lowered sea levels allow for shelf bypassing and greater deep sea p accumulation rates

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