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

patterns and processes of shell fragmentation in modern and ancient marine environments shell fragments are important components of many recent and fossil marine benthic ecosystems and can provide crucial information on past and present environmental conditions interpreting such fragments requires integrated knowledge in various fields and the information potential is therefore rarely optimally utilized this paper uses the definition of a fragment as being a piece of shell having less than 90 of its original form it then outlines the potential characteristics pathways and fates that shells and their fragments can have fragmentation is a key factor shaping the shelly part of death assemblages but it is difficult to interpret because it can be broadly caused by ecological biostratinomic or diagenetic processes and also depends on shell strength strength in turn reflects multifunctionality during ontogeny and depends on a complex set of skeletal and taphonomic factors therefore no particular shell parameter clearly determines strength but thickness microstructure type and degree of organic matrix have the strongest influence on pre and post mortality strength size measurements are usually less important for shell strength than thickness although ecologically complex size refuges from predation do exist similarly shell shape sculptural features and specific aperture types in gastropods provide various defence strategies rather than increasing strength per se key ecological factors of fragmentation include predation due to crushing peeling along with mistaken predation selfinflicted damage during predation and burrowing and more physical aspects such as impacts by stones modern studies must consider damage by benthic commercial fisheries or dredging by scientific vessels key biostratinomic factors include transportinduced abrasion littoral zone of surf washed beaches bioerosion and dissolution mainly sublittoral environments diagenetically fragmentation during compaction mainly occurs when shells are in direct contact with one another or with coarser grains taphonomic features e g drillholes have only minor influence a key step in interpreting fragments is to categorize breakage into repaired versus unrepaired diagnostic versus nondiagnostic and severe versus localized damage quantifying the above categories can then provide useful information on breakage patterns and underlying processes understanding the many characteristics of shells and their fragments is a significant interpretive tool in maximizing the information gain in palaeoecological and taphofacies analyses d 2003 elsevier science b v all rights reserved

early diagenetic processes in deep labrador sea sediments reactive and nonreactive iron and phosphorus a sequential extraction procedure was applied to separate the oxides and lithogenous phases of iron and manganese and the organic and inorganic phosphorus phases in four box cores and one piston core from the slopes and rises of the labrador sea sedimentation rate rather than the location in the basin appears as a master variable of the diagenetic transformations of fe mn and p high sedimentation rate characteristic of two of the box cores led to the creation of zones near the redox boundary of partial reprecipitation of dissolved fe mn and p released in the deeper reducing portions of the sediments in contrast surficial sediments from box cores with 10 times lower sedimentation rate only have sufficient reductive capacity to remobilize mn hydroxides while leaving the fe oxyhydroxides intact under these conditions there is evidence for a redistribution of reactive inorganic p leading to the crystallization of carbonate fluorapatite in the top 30 cm of the cores gradual transformation of bur

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

a three dimensional model of the mean and seasonal circulation of the gulf of california 1 the mean and seasonal circulation of the gulf of california is simulated with a three dimensional numerical model forced by the pacific ocean through specifying the sea level the temperature and the salinity fields at its entrance at the sea surface the wind and the heat and freshwater fluxes are specified the model reproduces the observed mean and seasonal variability of sea level of heat and salt balances and the sea surface temperature sst climatology it also reproduces the general surface circulation of the northern gulf which consists of a seasonally reversing basin wide gyre it is found that tides and heat fluxes are both indispensable to reproduce the spatial structure and temporal evolution of the sst tides provide the mixing to upwell the cooler subsurface waters in the large islands area and the heating from the surface raises the sst the general circulation of the southern part of the gulf is due to the wind and the pacific forcing in the ekman layer two periods of anticyclonic circulation and one cyclonic per year occur below this layer two cyclonic periods develop in the northern part the tides play an important role in producing mean residual currents and both tides and winds compete against the pacific forcing to produce a cyclonic and anticyclonic circulation once a year contrary to conclusions of previous studies the thermohaline circulation is found to be unimportant in the gulf

sequence stratigraphy of a carbonate clastic ramp the cincinnatian series upper ordovician in its type area the cincinnatian series consists of five depositional sequences each is composed of a thin transgressive systems tract and a much thicker shallowing upward highstand systems tract whereas the highstand systems tracts are relatively poor in micrite but rich in terrigenous shale the transgressive systems tracts are composed of cleaner carbonate facies ranging from coarse grained calcarenites to micrite rich wackestones and micstones this alternation of carbonate and terrigenousfacies types resulted from the trapping of clastic sediment near its presumed source in the appalachians during a relative sea level rise and it may be a feature common to sequences in other mixed carbonate clastic settings these depositional sequences were produced by eustatic fluctuations as shown by the limited extent to which the sequences can be traced into more proximal portions of the appalachian basin the recognition of depositional sequences clarifies the regional paleogeography and simplifies regional lithostratigraphic nomenclature within current biostratigraphic resolution sequences in the cincinnatian series appear to have chronostratigraphic significance and thereby offer an additional means of intrabasinal correlation in the upper ordovician

revised sequence stratigraphy of the upper katian stage cincinnatian strata in the cincinnati arch reference area geological and paleontological implications abstract the upper ordovician cincinnatian series is a critical upper katian reference succession previously six 3rd order depositional sequences c1 to c6 have been recognized and frequently used as regional time slices recent research however indicates a need for revision and additions including the recognition of additional 3rd and 4th order sequences we propose amendments based upon high resolution correlations using a combination of regional disconformities cycle stacking patterns bioevents marker beds and chemostratigraphy several disconformities including a large regionally angular mid richmondian unconformity are newly recognized or reinterpreted in addition distinctive depositional patterns aid in the recognition of systems tracts with a thick proximal laminated peritidal facies representing early transgressive systems tracts tsts or lowstands in part lsts b shell rich limestone packages representing later tsts and overlain by c more shale prone highstand systems tracts hsts themselves overlain locally by d siliciclastic dominated falling stage systems tract fsst deposits that are commonly removed beneath substantial unconformities sequence boundaries at present we recognize eight 3rd order cincinnatian sequences designated c1 through c8 and 16 4th order subdivisions and their component systems tracts a younger hirnantian sequence may be present at some localities as the enigmatic centerville formation and or basal belfast member of the brassfield formation the implications of these new correlations and sequence interpretations include a new standard for relative sea level changes and insights into basin dynamics this framework also permits a more nuanced history of biotic changes that include geologically brief pulses of immigration associated with the transgressions of the c1 lower kope formation c5c clarksville member of waynesville formation and c7a basal whitewater formation

sea floor phosphorites along the central california continental margin early to middle miocene phosphorites are patchily distributed along the continental margin of central california at water depths of 200 to 2 000 m between cape san martin and point reyes greater concentrations of phosphorites are present along the lower continental slope off pescadero point on sur knoll and on twin knolls at water depths of 1 000 to 1 400 m no phosphorites were found on cordell bank or in monterey bay nor along the walls of adjacent submarine canyons the dominant mineral of these miocene phosphorites is carbonate fluorapatite francolite associated minerals include glauconite dolomite detrital silicates and minor pyrite most of the central california margin phosphorites are conglomeratic and contain a multitude of microdiscontinuity surfaces implying repeated alternations of deposition erosion reworking and cementation both orthochemical and allochemical phosphorites are recognized petrographically samples from offshore pescadero are mostly oolitic phosphorites whereas those collected from sur and twin knolls are predominantly microsphorites many samples also contain volcanic glass shards as well as opaque organics they have been extensively silicified and are intensely bioturbated sem observations reveal micron size euhedral crystals of apatite that are distinctly hexagonal and commonly are intergrown or stacked indicating in situ precipitation and or recrystallization of an amorphous precursor bacterialike structures were also observed suggesting the possibility of microbially mediated precipitation of apatite geochemically the central california margin samples are typical phosphorites p 2 o 5 content ranges from 11 5 to 31 0 percent and averages 24 4 percent major element si al fe ca mg k c analyses are consistent with published values for phosphorites but do indicate slight relative enrichments trace element concentrations are also typical for marine phosphorites with the exception of mn which is significantly depleted and sr which is greatly enriched whereas uranium values range from 47 to 170 ppm averaging 90 ppm organic carbon values range from 0 45 to 2 65 percent with darker colored phosphorites enriched in organic carbon relative to lighter colored samples the miocene central california margin phosphorites originated primarily by direct physio and or biochemical precipitation of apatite within oxygen depleted near surface sediments although subsequent recrystallization during burial may also have occurred polytaxic paleoceanographic conditions appear to have dominated during phosphogenesis but may have been repeatedly interrupted by episodes of increased oceanic circulation during glacial events times of transition from interglacial to glacial modes are believed to have been critical to phosphogenesis diagenetic formation of these phosphorites occurred along impinging dysaerobic 0 1 1 0 ml l o 2 oxygen minimum zones where internal nutrient recycling may have provided sufficient in situ organic material phosphorous and sufficiently high ph values to allow apatite precipitation central california margin phosphorites are a potential natural resource however their patchy distribution and occurrence at relatively great water depths make them economically less attractive than well known on land accumulations in central california as well as submarine deposits off the southern california shore that occur at much shallower 330 m water depths and in higher concentrations

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

cycle anatomy and variability in the storm dominated type cincinnatian upper ordovician coming to grips with cycle delineation and genesis although parasequence and sequence are scale independent terms they are frequently applied only to specific scales of cycles for example meter scale cycles are commonly assumed to be parasequences or pacs in the upper ordovi cian kope and fairview formations of northern kentucky we examined a succession of 50 meter scale cycles that have been variously interpreted as deepening upward shallowing upward or showing no relationship with water depth our analysis shows that these cycles characterized by shifts in storm bed proximality are highly variable in their thickness and internal construction most cycles are best considered high frequency sequences because deepening upward intervals are common and many cycles contain evidence of abrupt basinward shifts in facies as expected at sequence boundaries a minority fit the parasequence model of shallowing upward cycles bounded by flooding surfaces larger 20 m scale cycles are defined by systematic thickening and thinning trends of meter scale cycl

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

time richness and phosphatic microsteinkern accumulation in the cincinnatian katian ordovician usa an example of polycyclic phosphogenic condensation abstract millimeter scale phosphatic steinkern preservation is a feature of the taxonomically enigmatic early cambrian small shelly faunas but this style of preservation is not unique to the cambrian it is ubiquitous if infrequently reported from the phanerozoic record the polycyclic phosphogenic condensation ppc model envisions both the genesis and concentration of phosphatic microsteinkerns as natural outcomes of shell bed genesis through episodic sediment starvation this model predicts that more reworked and condensed shell bed limestones will contain more phosphatic microsteinkerns but that even the least reworked limestones may contain some phosphatic particles we test this model through examination of vertical thin sections densely collected through a 10 meter interval from the classic cincinnatian upper katian middle maysvillian north american stage upper fairview formation miamitown shale and lower grant lake formations at four localities near cincinnati ohio for each of approximately 50 distinguishable limestone depositional units in each locality a 2 2 cm square was selected for study each square was assigned a textural classification mud content of intergranular space and a breakage rank pristine to comminuted phosphatic particle distribution was quantified both by visual estimation and by particle counting with counts ranging from none detected to over 1000 per 4 cm2 our analyses show a strong positive relationship between phosphate content and both textural maturity and fragmentation this positive relationship is consistent with the ppc model and confirms that textural maturity can reflect the degree of condensation as well as depth related environmental energy this finding suggests that shell bed processes of repeated deposition and reworking make a significant contribution to the generation and accumulation of phosphatic particles if local scale sedimentary processes and conditions can control this accumulation temporal changes in phosphatic sediment deposition rates may be linked to earth changes more complexly than through changing ocean chemistry on a global scale

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

reactive surface area of skeletal carbonates during dissolution effect of grain size abstract major advances have recently been made in quantifying the chemical parameters which control carbonate mineral reaction kinetics in natural waters one of the primary factors influencing rates of reaction is the amount of surface area per unit mass available for reaction for relatively smooth nonporous carbonates the relationship between reactive and total surface area measured by gas adsorption has proven simple however the dominant carbonates in the marine environment are biogenic and exhibit complex microstructures we have performed experiments to determine dinghy what proportion of the total surface area of these biogenic carbonates is actually available for reaction during dissolution three biogenic carbonates having widely differing microstructures halimeda coral and echinoid were chosen for study and comparison with rhombic calcite the influence of grain size on the relation between total surface area determined from gas adsorption and reactive surface area determined relative to rhombic calcite during dissolution in constant composition solutions was of primary concern unlike rhombic calcites total surface area for texturally complex biogenic grains varied slightly or not at all with increasing grain size however both rhombic calcite and biogenic carbonate dissolution rates were inversely related to grain radius this implies that much of the total surface area of biogenic carbonates is unavailable for reaction with the aqueous solution dissolution rates were a function of both grain size and microstructure we have defined an empirical roughness factor which quantifies the difference in reactive surface area between rhombic calcite and a given biogenic grain of equivalent size the roughness factor increased with grain microstructural complexity but was independent of grain size over the grain size range 51 513 microns studied the maximum roughness factor value observed was 7 for halimeda relative to a value of 1 for rhombic calcite our findings indicate that both microstructure and grain size can play important roles in controlling reactivity of biogenic carbonates during diagenesis the relative significance of grain size versus microstructure for carbonate dissolution rates in natural systems is discus ed

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

the relationship between p fe and v fe ratios in hydrothermal precipitates and dissolved phosphate in seawater a strong positive relationship between the molar p fe ratio in fresh hydrothermal fe ferrihydrite precipitates and seawater dissolved phosphate has been demonstrated using samples from the atlantic and pacific oceans we ascribe this relationship to scavenging of dissolved phosphate from seawater during the formation of hydrothermal fe rich particles above hydrothermal vents in contrast molar v fe ratios in hydrothermal particles are inversely correlated with dissolved phosphate these results indicate that inter ocean variations in dissolved phosphate control the p fe and v fe ratios in hydrothermal fe precipitates one of the precursors of metalliferous sediment

record of microendoliths in different facies of the upper ordovician in the cincinnati arch region usa the early history of light related microendolithic zonation abstract this study provides the first documentation of microendolithic borings made by cyanobacteria algae and fungi in invertebrate skeletons from the late ordovician of eastern north america samples from the upper mohawkian to cincinnatian series katian stage caradoc to lower ashgill of traditional usage limestones and calcareous shales of ohio indiana and kentucky were selected for study because of the excellent preservation of fossil shell material the substrates mostly are brachiopods and corals strata of the mohawkian lexington limestone and cincinnatian kope formation maysville and richmond groups have been recently studied in terms of facies sequence stratigraphy and paleoenvironments which facilitates a reliable comparison of the distribution of microborings and inferred environmental settings especially relative paleobathymetry this paper reports the first occurrence of 10 ichnospecies plus various conchocelis traces in late ordovician cincinnatian marine shells these traces have been previously observed in shells from younger geological periods their modern counterparts are produced by species of cyanobacteria green algae red algae and heterotrophic microendoliths considering the bathymetric index ichnocoenoses of microendoliths defined for the later phanerozoic it appears that only one or two light related bathymetric zones can be recognized in a few samples from the upper ordovician cincinnatian of ohio and kentucky but not in all deposits where they might have been expected the shallow euphotic zone iii and with less certainty the deep euphotic zone on the contrary our samples from the underlying lexington formation contain only borings of worms macrotubular form and some forms with unknown producers although they were collected in facies realms comparable to the younger samples given the present state of knowledge the best explanation for the appearance of these 10 ichnospecies and the first bathymetric index ichnocoenoses within the late ordovician is that they represent the early evolution of microendolithic ichnospecies and early emplacement of ichnocoenoses

models for circulation patterns in epicontinental seas applied to paleozoic facies of north america craton circulation in epicontinental seas develops in response to thermohaline wind driven and tidal motions in various climatic geographic and bathymetric settings mass balance relations in a seaway are established by the relative rates of outflow inflow freshwater and ocean water and evaporation which constrain two contrasting styles of epicontinental circulation quasietuarine circulation qec is established where rates of freshwater influx exceeds evaporation surface outflow from a seaway with qec typically is balanced by inflow of oceanic water at depth a density stratification can be established below the limits of vertical mixing a bottom layer of oxygen poor or anoxic water may develop in a seaway with or without an entrance sill if the bottom waters are derived from the oxygen minimum zone of the open ocean or if organic productivity exceeds the limits of aerobic respiration upwelling may be promoted in specific epicontinental settings with qec antiestuarine circulation aec is developed in arid climates where evaporation exceeds freshwater influx evaporative concentration in the surface layer causes oxygenated water to sink bottom outflow of denser more saline water is balanced by surface inflow from the open ocean a sill or barrier may inhibit bottom circulation in seas with aec permitting development of a basal brine layer stagnation in the brine layer may lead to oxygen depletion seas with aec commonly are characterized by extensive carbonate evaporite facies geographic and stratigraphic syntheses of lithofacies and biofacies provide the empirical basis for interpretations of seaway dynamics in ancient epicontinental settings examples from the upper ordovician maquoketa formation and upper devonian lime creek sweetland creek formations of cratonic north america are interpreted in the context of stratified qec patterns in each case oxygen poor to anoxic waters appear to have impinged along the basin slope below the margin of an oxygenated carbonate shelf upwelling along the shelf margin in the maquoketa example helps explain the distribution of phosphatic sediments a stratified aec pattern is interpreted for the gower formation silurian of eastern iowa a barrier to bottom circulation at the mouth of an embayment in the epicontinental sea resulted in a basal layer of hypersaline water devoid of shelly benthos surface water salinities increased progresively shoreward within the embayment but benthic organisms flourished where carbonate mounds built upward into the oxygenated layer

middle upper ordovician darriwilian sandbian paired carbon and sulfur isotope stratigraphy from the appalachian basin usa implications for dynamic redox conditions spanning the peak of the great ordovician biodiversification event abstract the evans ferry section from the appalachian basin of eastern north america has been analyzed for chemostratigraphic trends to elucidate possible causal mechanisms facilitating the great ordovician biodiversification event gobe paired stable isotope 13c and 34s analyses were used in this carbonate dominated locality from the appalachian basin to reconstruct the marine redox states during this key period of rapid biodiversification this succession is one of the most expanded sandbian stage upper ordovician deposits known from north america and it allows new high resolution reconstructions of long term global carbon and sulfur cycle fluctuations the integrated geochemical and sequence stratigraphic investigation presented here from the laurentian epeiric seaway allows for possible identification of the contraction and expansion of reducing water masses during the middle late ordovician that may have been linked to global marine paleoredox dynamics utilizing new conodont based 87sr 86sr isotope stratigraphy along with previous conodont biostratigraphy we can confidently correlate our stable isotope profiles to other carbonate successions globally carbonate facies indicate that this area experienced partial restriction from open marine conditions during certain intervals in the sandbian these semi restricted environments record carbon 13ccarb isotope trends that are secular in nature as they can be correlated to other successions across laurentia and baltica we identify several intervals when 13ccarb and 34scas carbonate associated sulfate trends are decoupled these inverse stratigraphic trends are at times followed by parallel positive shifts in 13ccarb and 34scas causal mechanisms for the observed decoupled 13c and 34s trends may include a wide variety of factors such as more closed system local biogeochemical processes associated in part with diagenesis or they could instead reflect variations in the global fluxes of organic matter and pyrite burial linked to changing marine paleoredox conditions the positive covariation in trends presented here likely represents transient increases in organic carbon and pyrite burial in response to expansion of reducing marine environments

middle tertiary contractile deformation uplift extension and rotation in the san emigdio range southern california new data from the san emigdio range of southern california provide evidence of major tectonism during the middle tertiary including uplift of the adjacent mojave region disruption of marine basins and rotation of the southern tail of the sierra nevada the san emigdio range was the site of the southernmost marine deposition in the san joaquin basin from the earliest through the middle eocene overlapping deeply eroded midcrustal granitic rocks these marine rocks were associated with a northtrending west facing shoreline to the north the coast probably was embayed to the east as far as the goler basin of southeastern california this marine embayment was disrupted and the record of stratigraphic continuity between san joaquin and goler basins was destroyed as the result of uplift in the latest eocene and oligocene conglomerates of the uppermost eocene and oligocene nonmarine tecuya formation of the san emigdios comprise an unroofing sequence whose provenance suggests marked uplift and erosion of the mojave region geohistory analysis of the coeval marine pleito fm suggests that the uplift and unroofing was related to contractile deformation by about 22 ma extension replaced contractile deformation in the san emigdios as indicated by normal faulting and basaltic volcanism and synchronousmore extension reported for the adjacent mojave region the authors paleomagnetic data from five sites from tecuya creek to pleito creek reveal that basalts are rotated 44 degree clockwise this rotation occurred prior to 16 ma and perhaps between 18 20 ma if comparison with the mojave region is valid this episode of rotation accounts for most or all of the southwesterly trend of the southern tail of sierra nevada basement rocks less

lagrangian surface circulation in the gulf of california from a 3d numerical model the surface circulation of the gulf of california was studied from a lagrangian point of view using the results of a 3d numerical model the advection of particles whose depth is fixed was carried out for annual and monthly periods with 710 particles homogeneously distributed over the gulf an anticyclonic circulation was found at the northern region from october to may and in the central and southern regions during may and from october to november cyclonic circulation was found in the entire gulf from july to august this circulation pattern agrees with direct measurements of drifters in the northern region during the cyclonic period the particles from the central and southern regions travel to the northern basin where they are trapped by a gyre for more than a month on the other hand during the anticyclonic period the particles flow to the southern part of the gulf some particles escape to the pacific ocean and others remain in the gulf and return to the northern part during the cyclonic period the principal gyre that appears on the center of the northern gulf in both cyclonic and anticyclonic periods traps particles for more than 30 days in a radius of 50 km in the central and southern regions a trapping zone was found in the peninsula side where the particles travel less than 100 km in 30 days on the other hand over the continental coast there is a rapid transit zone the particles escape only during the anticyclonic period

compositional maturity of limestones a review abstract compositional maturity as defined for carbonates is the extent to which a sediment approaches the constituent end member intraclasts ooids fossils peloids micrite matrix and terrigenous minerals to which it is driven by the environmental processes operating upon it an immature lime sediment is produced in an environment where many biological physical and chemical processes are operating simultaneously the resulting sediment is a mixture of several of the six major constituents as the number of competing processes decreases in an environment the sediment progresses through advanced stages of compositional maturity a supermature sediment is produced in an environment where a single formative process has operated to completion consequently only one constituent dominates the sediment the index of compositional maturity provides a clue to the complexity of the depositional setting reflecting the number of environmental processes their interactions and rates of sediment production there is a natural tendency for many different carbonate constituents to be produced on the shallow water shelf and most lime sediments of this deposystem are mature and immature on the other hand the number of environmental processes is generally low and the compositional maturity high on mobile oolite shoals beaches tidal flats and sabkhas and in deep water basins application of compositional maturity in carbonate facies analysis therefore focuses attention on sedimentary processes in the depositional environment

wind influence on water exchange between the ria of ferrol nw spain and the shelf abstract the wind induced water exchange between the ria of ferrol nw spain and the adjacent shelf is analyzed by means of a three dimensional hydrodynamic model mohid2000 since thermohaline measurements indicate that the estuary can be considered vertically homogeneous a barotropic version of the model has been used real in situ wind measurements have been used for model calibration and further analysis the approach to study the wind effect on water exchange through the ria strait consisted in subtracting the signal calculated with only tidal forcing t s from the one with wind and tidal forcing wt s this shows the existence of a residual circulation with water flowing in wind direction along surfaces layers and a counter current flowing in the opposite direction at bottom layers the flux across the strait of ferrol has shown to increase linearly on wind strength with a correlation larger than 96 and reaching values close to 20 m 3 s 1 under real wind forcing

evolution of the southern san joaquin basin and mid tertiary transitional tectonics central california a cenozoic tectonic and sedimentary history is proposed for the southern san joaquin basin ssjb and tehachapi mountains that evolved adjacent to the plate margin off central california seismic reflection borehole field biostratigraphic and paleomagnetic data are integrated into geologic and fault structure maps cross sections and geohistory plots and are analyzed with previous work in the region to develop a model relating the sequence timing and distribution of complex tectonically linked events the largely buried structures and strata in the ssjb preserve an unusually complete record of the mid tertiary transition from convergent to transform plate boundary as well as the regional transition to contraction during the pliocene significant structural relief existing across both extensional and contractile features is preserved in the subsurface and an active fold thrust belt propagates basinward along the margin of the u shaped tejon embayment the cenozoic evolution of the ssjb reflects the regional deformation of central california as different tectonic events followed each other along the adjacent north american plate margin five oligocene miocene basin phases are identified in the ssjb 1 late oligocene early miocene extensional subsidence with high and low angle normal faulting accompanied by volcanism and deposition of coarse syntectonic conglomerates 2 middle miocene uplift 3 later mid miocene transtensional subsidence to lower bathyal depths 4 alternating subsidence and uplift until the late miocene and 5 flexural subsidence due to pliocene to recent contraction reconstructions of mid tertiary california place the southern san joaquin tehachapi extensional terrane as a paleotectonic block located between the western mojave terrane then to the east and the western california terrane then to the south and west regional extension occurred during a long transition period between convergent and transform boundaries along the north american plate margin significant slip along the san andreas transform postdates this extensional event its origin apparently coincided with a regional middle miocene uplift event indicating that the san andreas fault is younger than previously supposed the tertiary ssjb has subsided due to extension transtension crustal tilting and thrust related loading the maricopa subbasin floor is likely composed of ensimatic and mafic rocks like those along the west side of the sierra nevada and locally has subsided beyond 12 km in contrast the relatively stable tejon embayment underlain by sierran crystalline crust achieved its maximum subsidence in the miocene since pliocene time the ssjb has filled and continued to deepen after the basin was tectonically shut off from the pacific ocean

provenance and stratigraphy of the eocene tejon formation western tehachapi mountains san emigdio mountains and southern san joaquin basin california abstract the eocene tejon formation of the western tehachapi and san emigdio mountains of california provides a unique east west trending outcrop belt of otherwise deeply buried strata that underlie the san joaquin basin to the north its stratigraphy and framework mineralogy have been used to define offsets along the san andreas fault a major neogene plate boundary transform fault that has translated coastal california northward more than 300 km by right slip the tejon formation was deposited directly on crystalline basement rocks as a result of an eastward transgression of at least 45 km from the early to the late middle eocene followed by a major regression in the late middle eocene the basal uvas conglomerate member consists entirely of coarse grained transgressive system tract tst deposits characterized by abundant current formed sedimentary structures it is overlain by offshore marine shales of the liveoak shale member which consist of lower tst deposits overlain by highstand system tract hst deposits the overlying regressive metralla sandstone member consists mostly of highly bioturbated fine grained shallow marine hst sandstones with local thin bedded turbidites present in some western exposures the quartzofeldspathic sandstones grand mean qm51 12f42 12lt7 4 of the tejon formation suggest a provenance consisting of plutonic metamorphic and volcanic rocks such as those present in the basement of the san emigdio and techachapi mountains northwestern mojave desert and southern sierra nevada petrologic parameters however suggest variable contributions from these source areas through time three distinctive petrofacies coincide with the three principal lithostratigraphic subdivisions the shallow marine tst sandstones from the uvas conglomerate member are more quartzose than those of the hst metralla sandstone member possibly because higher energy deposition preferentially preserved quartz thin bedded turbidites in the western exposures of the metralla sandstone in contrast have more abundant feldspar and volcanic lithic fragments than the uvas and liveoak members the composition of the tejon formation suggests derivation from a basement uplift provenance with progressive upsection changes from qm60 f33 lt8 uvas to qm46 f44 lt10 liveoak and qm 43 f52 lt5 metralla the composition and provenance of the tejon formation is different from that of the coeval butano sandstone and point of rocks sandstone submarine fan deposits to the north and west

phosphorus sources for phosphatic cambrian carbonates the fossilization of organic remains and shell material by calcium phosphate minerals provides an illuminating but time bounded window into ediacaran cambrian animal evolution for reasons that remain unknown phosphatic fossil preservation declined significantly through cambrian series 2 here we investigate the phosphorus p sources for phosphatic cambrian carbonates presenting sedimentological petrographic and geochemical data from the cambrian series 2 3 thorntonia limestone australia some of the youngest cambrian strata to display exceptional phosphatic preservation of small shelly fossils we find that within thorntonia sediments phosphate was remobilized by organic decay and bacterial iron reduction with subsequent reprecipitation largely as apatite within the interiors of small shelly fossils we discuss the merits of bioclastic derived organic matter bound or iron bound p as potential sources to these strata petrographic observations suggest that the dissolution of phosphatic skeletal material did not provide the p for fossil preservation in contrast high organic carbon contents imply significant organic fluxes of p to thorntonia sediments sedimentology and iron speciation data indicate that phosphorus enrichment occurred during times of expanded anoxic ferruginous conditions in subsurface water masses suggesting that phosphorus adsorption to iron minerals precipitating from the water column provided a second significant p source to thorntonia sediments simple stoichiometric models suggest that by themselves neither organic carbon burial nor an iron shuttle can account for the observed phosphorus enrichment thus we infer that both processes were necessary for the observed phosphorus enrichment and subsequent fossil preservation in the thorntonia limestone

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

eustatic and tectonic control on the distribution of marine seismites examples from the upper ordovician of kentucky usa abstract widespread zones of soft sediment deformation are not ubiquitous throughout the rock record rather they are associated with orogenic sediments and are concentrated in specific portions of depositional sequences characterized by deformation prone facies upper ordovician soft sediment deformation features exposed in kentucky are here interpreted as the result of seismically induced thixotropic fluidization of muds resulting in foundering of denser silts and carbonate sands and corresponding diapiric injection of muds severity of soft sediment deformation is associated with sediment density gradients bed thicknesses and varying magnitudes of triggering events the widespread nature 5000 km 2 of multiple deformation horizons argues for a seismic trigger resulting from reactivation of multiple basement faults eight large scale 3rd order depositional sequences were examined for the presence of specific deformation features and stratigraphic position of those intervals the regular distribution of deformation prone facies throughout the upper ordovician seems to have been regulated by eustatic fluctuations seismicity generated by far field tectonics provided the triggering mechanism to disrupt deformation prone strata the record of seismites and their co occurrence with k bentonites provides a meter of intensity and timing of tectophases of the taconic orogeny

cascading trend of early paleozoic marine radiations paused by late ordovician extinctions the greatest relative changes in marine biodiversity accumulation occurred during the early paleozoic the precision of temporal constraints on these changes is crude hampering our understanding of their timing duration and links to causal mechanisms we match fossil occurrence data to their lithostratigraphical ranges in the paleobiology database and correlate this inferred taxon range to a constructed set of biostratigraphically defined high resolution time slices in addition we apply capture recapture modeling approaches to calculate a biodiversity curve that also considers taphonomy and sampling biases with four times better resolution of previous estimates our method reveals a stepwise biodiversity increase with distinct cambrian and ordovician radiation events that are clearly separated by a 50 million year long period of slow biodiversity accumulation the ordovician radiation is confined to a 15 million year phase after which the late ordovician extinctions lowered generic richness and further delayed a biodiversity rebound by at least 35 million years based on a first differences approach on potential abiotic drivers controlling richness we find an overall correlation with oxygen levels with temperature also exhibiting a coordinated trend once equatorial sea surface temperatures fell to present day levels during the middle ordovician darriwilian age contrary to the traditional view of the late ordovician extinctions our study suggests a protracted crisis interval linked to intense volcanism during the middle late ordovician katian age as richness levels did not return to prior levels during the silurian a time of continental amalgamation we further argue that plate tectonics exerted an overarching control on biodiversity accumulation

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

long term accumulation of carbonate shells reflects a 100 fold drop in loss rate shells in modern seabeds can be thousands of years old far older than would be extrapolated from the rapid rates of shell loss detected in short term experiments an extensive shelldating program on the southern california usa shelf permits rigorous modeling of the dynamics of shell loss in the mixed layer discriminating the key rates of carbonate disintegration and sequestration for the first time we find that bivalve shells experience an initially high disintegration rate l 1 decadal half lives but shift abruptly within the first 500 yr postmortem to a 100 fold lower disintegration rate l 2 millennial half lives at sequestration rate t burial and or diagenetic stabilization this drop permits accrual of a long tail of very old shells even when sequestration is very slow and allows only a minority 1 of all shells to survive the first phase these high rates of disintegration and low rates of sequestration are consistent with independent measures of high carbonate loss and slow sedimentation on this shelf our two phase model thus reveals significant spatial and temporal partitioning of car bonate loss rates within the mixed layer and shows how shell age frequency distributions can yield rigorous and realistic estimates of carbonate recycling on geological time scales

significance of seismic reflections beneath a tilted exposure of deep continental crust tehachapi mountains california the focus of this article is a process whereby lower crustal crystalline and schistose rocks can rise to the surface with the tehachapi mountains in california being the case in point as a prime example of the lower crust these mountains expose cretaceous gneisses that formed 25 30 km down in the sierra nevada batholith and appear to be underlain by the ensimatic rand schist integrated geophysical and geological studies by the calcrust program have produced a cross section through this post mid cretaceous structure and suggest a general model for its development seismic reflection and refraction profiles show that the batholithic rocks dip northward as a tilted slab and extend beneath the southern end of the san joaquin basin s tejon embayment two south dipping reverse faults on the rim of the tejon embayment were discovered in the reflection data and verified in the field the faults have a combined separation of several kilometers and cut through an upper crustal reflection zone that projects to the surface outcrop of the rand schist the upper and lower crusts are separated by a zone of laterally discontinuous reflectors reflections from the lower crust form a wedge the base of which is a nearly flat moho at 33 km regional geological relations and gravity models both suggest that the reflective zone corresponds to the rand schist and the newly recognized faults account for its neogene exposure alternatively the reflective zone maybe part of the gneiss complex suggesting that the schist either lies deeper or is not present under the gneisses if the rand schist underlies the tehachapi mountains and mojave region to their south a model for their evolution can be constructed from regional geological relations it seems that during late cretaceous laramide subduction the protolith of the schist was thrust eastward beneath the mojave along this portion of the cordilleran batholithic belt the subduction was evidently at very low angles the bottom of the batholith was removed and replaced by a thick section of schist fluids from which weakened the overlying batholith this thickened crust collapsed by horizontal flow in the schist and faulting of the upper crust into flat lying slabs when emplacement of the schist ended in latest cretaceous earliest paleocene the underlying mantle rose compensating for the extension and providing material for magmatic underplating in the neogene transpression and rotation of the upper crust along the san andreas and garlock faults resulted in the exposure of the schist

a three dimensional model of tide and wind induced residual currents in the central strait of georgia canada a 3 dimensional baroclinic numerical model has been used to study residual i e mean and low frequency 0 5 cycles day 1 currents of the strait of georgia canada in the central part of the strait the observed mean circulation is characterized by cyclonic eddies of about 8 km diameter the observed low frequency currents account for approximately half of the total kinetic energy of the fluctuating currents the other half is associated with diurnal and semi diurnal tidal currents the low frequency currents have about one third of their energy at the fortnightly and monthly bands the mean and low frequency fluctuating components have similar amplitudes the model is forced with tides winds and runoff and produces energy levels that are smaller than but comparable to the observed mean and low frequency currents the spatial e g eddy formation and temporal structures are reasonably reproduced it is found that the residual currents in the model are produced by non linear interactions of the diurnal and semi diurnal tidal components and by wind forcing thereby supporting earlier suggestions based on observations about 50 of the variance in the model is contained in frequencies of tidal origin and the rest is spread over a broad energy band which is related to wind forcing a qualitatively good agreement between modelled and observed currents is found in the upper and middle parts of the water column

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

cyclic alteration of proximal and distal storm facies kope and fairview formations upper ordovician ohio and kentucky the upper ordovician kope and fairview formations and the bellevue tongue of the grant lake limestone exposed in the cincinnati ohio region represent storm dominated sedimentation on a prograding intracratonic ramp the upper kopelower fairview transition zone 25 m thick is an outer to intermediate ramp lithofacies and is composed of numerous 1 3 m thick shallowing upward subtidal cycles bedding cycles are composed of two depth controlled facies 1 a shale dominated distal facies and 2 a fossiliferous proximal facies the distal facies records low energy largely single storm events and consists of thin graded shale beds nearly in situ fragile fossil accumulations thin parautochthonous packstones and quartzose siltstone beds siltstones contain abundant storm depositional indicators tool marked soles gutter casts mud filled scours hummocky lamination and hummocky bedforms the proximal facies represents deposition in an energetic storm wave swept environment and consists of amalgamated sets of thick bedded fine to coarse grained skeletal grainstones and packstones with low angle cross lamination megaripples and shale lithoclasts sedimentary structures and paleocurrent patterns from both facies record deposition under a combined flow regime with the unidirectional current vector oriented in the offshore direction cycles are laterally continuous across the 35 km by 32 km study area cycle boundaries flooding surfaces are parallel to a unique storm generated marker bed implying that these surfaces are effective time lines their widespread character and relatively deep subtidal facies assemblage argues against autocyclic processes in cycle formation we propose that the alternation of proximal and distal facies was tied to fluctuations in storm wave base driven by short term glacio eustasy three scales or orders of sedimentary cyclicity are recognized in the study area meter scale bedding cycles are considered fifth order parasequences 20 100 ka duration and stack into genetically related parasequence sets these fourth order units have been previously described as member scale lithostratigraphic tongues analysis of fischer plots suggest that cycle thickness and subfacies composition was controlled by both accommodation and siliciclastic sediment supply these higher order stratal units are super imposed onto the highstand portion of the kope to bellevue depositional sequence and give insight into the high frequency controls on the progradation of the ramp complex

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

influence of water column anoxia on the elemental fractionation of carbon and phosphorus during sediment diagenesis abstract organic carbon oxidation and benthic total phosphorus flux measurements from sites covering a range of bottom water oxygen concentrations have been compiled the data show that p regeneration relative to carbon oxidation is much more extensive in sediments overlain by oxygen depleted waters these results are consistent with studies showing that low oxygen bottom water concentrations correlate with reduced total phosphorus burial efficiencies and enhanced organic carbon burial efficiencies based on these observations a positive feedback is proposed between water column anoxia enhanced benthic phosphorus regeneration and marine productivity this feedback may help explain the widespread accumulation of organic rich marine sediments from anoxic waters observed in the geologic record

growth rates of phosphate nodules from the continental margin off peru modern sea floor phosphorite nodules sampled from off the coast of peru are shown to grow at rates of millimeters per thousand years in spite of the fact that the measured accumulation rates of the underlying sediment are two to four orders of magnitude faster phosphate nodules grow downward into soft sediment and the rates of phosphorus accumulation into nodules are approximately equal to the upward diffusive flux of dissolved phosphate inferred from pore water profiles these results demonstrate that phosphorus in nodules originates from regeneration in sediments rather than as a result of direct precipitation from bottom waters