sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

geochemical characteristics of deep sea sediments from the arabian sea a high resolution study abstract five deep sea cores from the arabian sea covering a time interval of 170 ky were sampled at high resolution and analysed for major and trace elements the stratigraphy of the cores was obtained by comparing the ba al ratio with the specmap data this method is based on the close correlation between ba concentrations or ba al ratios and oxygen isotope ratios 18o of foraminifera in arabian sea sediments ba al ratios used as a productivity proxy are variable but high in all deep sea cores of the arabian sea indicating a basin wide influence of nutrient rich water masses compared to glacial intervals the warmer periods are characterised by higher element al ratios of proxies which are directly ba ca sr p i e hard parts of organisms or indirectly u 230thex related to biological productivity 230thex provides evidence for intense boundary scavenging caused by high productivity due to enhanced upwelling and terrigenous input from the indus fan the mn distribution in a core from the western arabian sea shows enrichments during interglacial periods and may indicate mn export owing to the presence of a stronger oxygen minimum zone several processes limit the applicability of proxies intercalated turbidites in the deep sea cores can be identified by means of si al ti al and zr al ratios versus depth due to the enrichment of quartz ti minerals and zircon in the basal layer these elements are also important for the reconstruction of the history and extent of the eolian dust input diagenetic redistribution of redox sensitive elements occurs at the boundaries between turbidites and normal pelagic sedimentation and may mask or destroy primary signals

relationships between sulphur organic carbon and iron in the modern sediments of the black sea abstract the ratio of sedimentary s to organic c has been used as a diagnostic criterion for recognizing anoxic environments in the sedimentary record here we examine the relationship between pyrite s and organic c in the modern unit 1 sediments of the black sea to re evaluate this suggested relationship in box cores from shallow oxic or near oxic water pyrite s contents ranging from 0 1 and 2 5 by weight do not correlate with organic c contents in cores from the deep anoxic basin pyrite s concentrations range between 1 0 and 2 5 and are linearly related to organic c contents with an intercept that is not significantly different from zero the s c ratio is around 0 31 in these sediments which is somewhat lower than the ratio of 0 36 considered to be characteristic of normal marine oxic sediments thus the black sea anoxic sediments appear to be depleted in s relative to organic c the degree of pyritization dop of the sediments may be a better measure of anoxic conditions of sedimentation the dop values measured here show that pyrite formation is fe limited the correlation between organic c and pyrite s probably being induced by a positive correlation between fine grained sediment components the original fe source for pyrite formation in the sediments and organic matter such fe limitation is probably characteristic of anoxic basins where pyrite formation can take place in the water column and fe oxyhydroxides do not accumulate in the surface sediments the results on the sample set examined here are at variance with earlier data and interpretations for the black sea in particular the suggested s enrichment of anoxic black sea sediments was not found because of fe limitation

geochemistry of peruvian near surface sediments sixteen short sediment cores were recovered from the upper edge ueo within wo and below bo the oxygen minimum zone omz off peru during cruise 147 of r v sonne solids were analyzed for major trace elements total organic carbon total inorganic carbon total sulfur the stable sulfur isotope composition 34 s of pyrite and sulfate reduction rates srr pore waters were analyzed for dissolved sulfate sulfide and 34 s of sulfate in all cores highest srr were observed in the top 5 cm where pore water sulfate concentrations varied little due to resupply of sulfate by sulfide oxidation and or diffusion of sulfate from bottom water 34 s of dissolved sulfate showed only minor downcore increases strong 32 s enrichments in sedimentary pyrite to 48 vs v cdt are due to processes in the oxidative part of the sulfur cycle in addition to sulfate reduction manganese and co are significantly depleted in peruvian upwelling sediments most likely due to mobilization from particles settling through the omz whereas release of both elements from reducing sediments only seems to occur in near coastal sites cadmium mo and re are exceptionally enriched in wo sediments 600 m water depth high re and moderate cd and mo enrichments are seen in bo sediments 600 m water depth re mo ratios indicate anoxic and suboxic conditions for wo and bo sediments respectively cadmium and mo downcore profiles suggest considerable contribution to ueo wo sediments by a biodetrital phase whereas re presumably accumulates via diffusion across the sediment water interface to precipitation depth uranium is distinctly enriched in wo sediments due to sulfidic conditions and in some bo sediments due to phosphorites silver transfer to suboxic bo sediments is likely governed by diatomaceous matter input whereas in anoxic wo sediments ag is presumably trapped due to sulfide precipitation cadmium cu zn ni cr ag and t1 predominantly accumulate via biogenic pre concentration in plankton remains rhenium sb as v u and mo are enriched in accordance with seawater te availability lead and bi enrichment in ueo surface sediments is likely contributed by anthropogenic activity mining accumulation rates of toc cd mo u and v from peruvian and namibian sediments exceed those from the oman margin and gulf of california due to enhanced preservation off peru and namibia copyright 2004 elsevier ltd

oxygen minimum zone controlled mn redistribution in arabian sea sediments during the late quaternary 1 accumulation of labile mn is related to bottom water oxygen concentrations in this study we investigate the relation between oxygen minimum zone omz intensity and mn burial in arabian sea during the late quaternary mn carbonates in sediments of the deep arabian basin indicate that this part of the basin remained oxygenated for at least the last 185 kyr sequential leaching showed manganese carbonate enrichments with concentrations up to 3750 ppm in deep basin sediments these mn spikes must have formed diagenetically during periods of increased mn oxide fluxes to the deep basin associated with vertical extension of the omz this extension caused remobilization of mn oxides from a previously oxic slope resulting in increased mn accumulation in the deep basin mn relocation is evidenced by synchronous mn depletions in organic rich intervals in slope sediments mn records from the deep basin can thus be used as a qualitative proxy to reconstruct intermediate water oxygenation

organic matter composition and sulfate reduction intensity in oman margin sediments abstract petrographical and geochemical studies of neogene marine sediments from the oman sea leg 117 sites 720 724 726 and 730 show a close relationship between the nature and amount of the organic matter and the degree of degradation of organic matter by sulfate reduction i e pyritization petrographically three major pyritization types were observed 1 finely dispersed pyrite framboids in sediments from oman margin and indus fan enriched in autochthonous marine organic matter 2 infilling of pores by massive pyrite crystals in oman margin sediments with a low toc and a high microfossil content 3 pyrite mineralization of lignaceous fragments in organic depleted sediments from the indus fan leading to more massive pyrite geochemically we can define a sulfate reduction index sri as the percentage of initial organic carbon versus that of residual organic carbon finely laminated pliocene pleistocene sediments from the oman margin exclusively contain organic matter deriving from organic phytoplankton for which the quantity toc positively correlates with the geochemical quality hydrogen index we think that the occurrence of this residual organic matter is linked mainly to a high primary paleo productivity the intensity of sulfate reduction is constant for sediments with toc up to 2 and becomes more important when organic input decreases this degradation process can destroy up to 50 of the initial organic matter but is not sufficient to explain some of the encountered very low toc values it can be seen that sharp increases of certain plankton species with mineral skeletons are responsible for a pronounced degradation of organic matter due to increased sulfate reduction in that case the organic matter may be strongly degraded high sri although deposited in an oxygen depleted environment conversely miocene pliocene sediments contain an autochthonous organic matter that is typical of both low productivity and oxic processes their very low sulfate reduction index indicates that very little metabolizable organic matter was initially present

lack of enhanced preservation of organic matter in sediments under the oxygen minimum on the oman margin the impingement of oxygen minima on continental margins is widely thought to promote the accumulation of sedimentary facies enriched in well preserved organic matter it is shown here however that such a relationship does not clearly apply to the productive oman margin in the arabian sea which hosts one of the most severe oxygen minima in the oceans measurements made on the 0 1 cm depth interval from fourteen box cores collected from the outer shelf upper continental slope area off oman show that 1 1 deposited organic matter is overwhelmingly of marine origin 2 2 there is no significant correlation between the abundance of sedimentary organic carbon corg and the bottom water o2 concentration 3 3 there is no relation between the sedimentary corg n ratio and bottom water o2 4 4 there is no correlation between the hydrogen index hi of the organic matter and bottom water oxygen there are however significant correlations between the corg n ratio and the i corg cr al and zr al ratios as well as between the corg n ratio and the hydrogen index these relationships are interpreted as being the result of winnowing and attendant reworking which produce a progressive increase in the corg n ratio and a decrease in the hi and the i corg ratio as organic matter becomes progressively degraded commensurate rises in the cr al and zr al ratios result from the increased proportion of heavy minerals associated with winnowed lag deposits overall these data suggest that the bottom water oxygen concentration has little effect in governing either the distribution or the degree of preservation of organic matter on this margin thus the generally high but spatially variable corg content of the sediments on the oman margin may not reflect the occurrence of an oxygen minimum but instead be the result of a high settling flux of organic matter supported by monsoon driven upwelling and post depositional redistribution of the organic material by hydrodynamic influences

earthquake locations and three dimensional crustal structure in the coyote lake area central california previous work on the simultaneous inversion method has been improved and extended to incorporate iterative solution for earthquake locations and laterally heterogeneous structure approximate ray tracing and parameter separation are important elements of the improved method application of the method to p wave arrival time data recorded by stations of the u s geological survey central california network yields a three dimensional model for the velocity structure of the upper crust in an area encompassing the rupture zone of the coyote lake earthquake of august 1979 very strong correlations between the velocity model and the geology and gravity and magnetic anomalies are observed improved estimates of the locations of earthquakes in the study area are also determined the relocation of explosions indicates epicentral accuracies of the order of a kilometer or better based on the revised hypocentral locations it is concluded that the san andreas fault is vertical in this area with no actual offset between the epicenters and the fault trace in contrast the calaveras has two or more active fault surfaces one nearly vertical and another dipping 75 to the northeast

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

shallow marine sedimentary processes in the late devonian catskill sea new york state shallow marine strata of the upper devonian west falls group in south central new york comprise centimetre to decimetre thick sheetlike to lenticular beds of sandstone and siltstone interbedded with mudstone unidirectional current scour marks and tool marks occur on the basal erosion surfaces of the sandstones their internal structures are hummocky cross strata of various styles planar laminae and wave ripple cross laminae with characteristic vertical and lateral transitions among them vertical burrows of the skolithos ichnofacies dominate upper portions of sandstone beds whereas mudstones and silt stones contain mainly horizontal burrows of the cruziana ichnofacies transported and in situ shelly fossils occur throughout in places concentrated in coquinite lenses large scale 15 to 30 in bedding sequences are characterized by upward thickening and coarsening of sandstone beds increase in amalgamated hummocky cross strata coquinites plant debris and bivalves followed by abrupt fining and thinning of beds the depositional environment is interpreted as a shallow marine shelf episodically influenced by intense tropical storms hurricanes individual sandstone beds were deposited by spatially decelerating combined flows where an initially strong offshore directed flow component decreased in time relative to the oscillatory flow component large scale bedding sequences reflect changes in storm combined current intensity and deposition rate strong eustatic control is unlikely and there is no evidence of changing wave climate instead these sequences may be associated with delta lobe progradation and or offshore bar development

determination of inorganic sulphur speciation with polarographic techniques some preliminary results for recent hypersaline anoxic sediments abstract polarographic techniques have been used to determine reduced inorganic sulphur speciation in recent anoxic marine sediments from two hypersaline basins the tyro and the bannock basins in the eastern mediterranean the following phases were determined acid volatile sulphur avs pyritic sulphur and zerovalent sulphur the determination of avs and pyrite was based respectively on the acidification and cr ii reduction of these sulphur components to h2s h2s was collected in base and the sulphide concentration was measured by polarography standard na2s and pyrite gave recoveries of 99 6 3 9 and 97 12 respectively total zerovalent sulphur in a sediment sample was measured by the reaction of sulphite with thiosulphate thiosulphate was measured directly by polarography pyrite is the main phase of inorganic reduced sulphur in the sediments from the tyro and the bannock basins and it has about the same average level 125 moles per gramme dry weight in the cores recovered from the two areas however the distribution of pyrite in the top 100 cm of the two cores differs significantly in the bannock basin a sharp increase is observed with depth whereas in the tyro basin there is a small decrease with depth the total amount of reduced inorganic sulphur is less than the total amount of sulphur in the sediments this indicates that there must be additional sulphur bearing phases one of these phases may be gypsum and indeed gypsum crystals have been observed in the bannock basin in neither basin is there a significant correlation between reduced sulphur and organic carbon the pyrite that occurs in these basins may have been formed syngenetically at the interface of the anoxic brine and oxic seawater diagenetic pyrite may have been formed within the sediments of the basins avs and total zerovalent sulphur are still observed at depth we therefore suggest that this may be due to the incomplete transformation of avs and zerovalent sulphur into pyrite

late frasnian sedimentation cycles in the appalachian basin possible evidence for high frequency eustatic sea level changes abstract during the late frasnian 11 fourth order progradational retrogradational marine sedimentation cycles were deposited in the appalachian foreland basin mapping based primarily on subsurface data demonstrates the continuity of these cycles over a distance of 700 km cyclicity in distal facies occurs as alternations of organic rich and organic poor shales two of the organic shales can be correlated with the transgressive kellwasser beds of europe in more proximal facies recurring lobes of siltstone and sandstone were deposited based on lithologic indices the temporal pattern shows significant variation in the strength of relative facies change during deposition in particular two times of particularly pronounced progradation correspond to previously recognized eustatic sea level falls the correlation of portions of appalachian basin depositional cyclicity with global sea level events suggests that the entire sequence of 11 cycles with estimated average duration of around 100 150 ka were the result of high frequency eustatic sea level changes this in turn would be consistent with a brief period of late frasnian glaciation as others have previously suggested

controls on rare earth element distributions in ancient organic rich sedimentary sequences role of post depositional diagenesis of phosphorus phases abstract the processes that dictate the formation and preservation of rare earth element ree signatures in ancient marine black shales are incompletely understood thus potentially limiting the utility of the rees as geochemical tracers here we report on whole rock ree analyses of six black shale formations from different ages and depositional settings which fall within three general groupings group 1 is characterized by low whole rock ree content ree n la n n la n n la n 2 yb n la n 250 g g and moderately middle ree enriched patterns gd n la n 1 5 2 5 yb n la n 1 representative samples from these groups were selected from the marcellus and hushpuckney shales and subjected to a multi step leaching procedure to isolate four extractable p phases reducible authigenic carbonate associated detrital apatite organic in group 1 samples with low carbonate content 3 rees were hosted mainly in the organic 50 of ree and siliciclastic fractions 37 whereas in samples with greater carbonate content 25 caco 3 rees were hosted mainly in carbonate associated phases 53 in group 2 rees were hosted mainly in the carbonate associated 64 and organic fractions 30 and in group 3 rees were hosted mainly in the carbonate associated 60 detrital apatite 23 and siliciclastic fractions 16 authigenic phases include minerals such as carbonate fluorapatite and authigenic calcite that if present tend to dominate the whole rock ree inventory in the absence of carbonate whole rock ree content depends on the relative ree contributions of the organic and siliciclastic fractions

ichnology of a glacially influenced continental shelf and slope the late cenozoic gulf of alaska yakataga formation abstract the study of trace fossils in glaciomarine strata is important because of the low preservation potential of fauna but glaciomarine settings have received little attention from ichnologists widespread biological activity is recorded by ichnofossil assemblages in glaciomarine strata of the late cenozoic 6 ma to present yakataga formation alaska glacial sedimentation began in the gulf of alaska in the miocene along a deep water active margin basin dominated by turbidity currents and debris flows later strata record progradation of the continental slope by mass flow processes and the establishment of a broad shelf influenced by repeated glaciation ice rafting of coarse debris changes in water depth and salinity storms earthquakes and high sedimentation rates yakataga formation strata show overall a limited ichnological diversity and low degree of bioturbation in relation to comparable non glacial settings although certain beds are highly bioturbated twenty four ichnotaxa are identified and grouped into nine assemblages characteristic of different depositional settings and substrate types ichnogenera and body fossil evidence shows that polychaetes arthropods molluscs and echinoderms were the dominant infaunal benthic organisms with deposit feeding being the predominant feeding strategy poorly consolidated muddy sediments excluded suspension feeders and limited the development of the skolithos ichnofacies typical of non glacial shelves characterized by clean shifting sand substrates evidence of rapid sedimentation is given by escape structures fugichnia the presence of diplocraterion and by the mass mortality of bivalves firm ground burrows typical of the glossifungites ichnofacies are associated with erosional surfaces boulder pavements and coquinas diminutive feeding traces may reflect salinities lowered by glacial meltwater inputs the downslope transport of food by turbidity currents and mass flows may explain the development of a diverse cruziana ichnofacies in water depths where in non glacial settings the nereites ichnofacies is found an ichnological summary is presented for the late cenozoic gulf of alaska continental margin similar ecological conditions obtain in the modern setting and provide valuable supportive data ichnofacies identified from the yakataga formation are probably widespread in late paleozoic and late cenozoic glacially influenced marine strata

sulfur enrichment of humic substances in a delaware salt marsh sediment core abstract humic sulfur operationally defined as the sulfur extracted with humic substances in 0 l n naoh solution comprises up to 51 of the total sulfur inventory in a sediment core taken from a delaware spartina alterniflora marsh pyrite sulfur is the next largest fraction except at the near surface sediments where zerovalent sulfur concentrations are significant x ray photoelectron spectroscopy indicates that the humic sulfur consists of sulfoxides or sulfones and in a more reduced state organic sulfides and or organic polysulfides a subsurface decrease in the humic acid c s atomic ratio to 56 2 suggests that the upper 4 cm of marsh sediment is the locus for humic sulfur formation s alterniflora detritus and microbial biomass cannot fully account for observed sulfur enrichment of humic c s atomic ratios therefore the enrichment of humic substances by sulfur is probably via reaction of reduced sulfur compounds with organic matter a humic sulfur formation rate of 10 6 mol s cm 3 a 1 is calculated for the surface sediments and leads to an areal production of 18 mol s cm 2 a 1 of humic sulfur humic sulfur formation and preservation is enhanced by the limited availability of iron for the rapid precipitation of iron sulfide minerals and the apparent resistance of organic sulfur compounds towards reoxidation to sulfate especially in the upper 9 cm of marsh sediment where inorganic sulfur compounds are rapidly oxidized

eustatically controlled sedimentation in the hettangian sinemurian early jurassic of poland and sweden in earliest jurassic times terrigenous continental and marginal marine deposition occurred in a large epeiric basin along the tornquist line in europe detailed sedimentological studies allow recognition of palaeoenvironmental fluctuations in space and time the main earliest jurassic transgressions occurred in the early hettangian early sinemurian mid sinemurian and latest sinemurian and formed bounding discontinuities transgressive surfaces of considerable correlative significance there is a step wise trend of increasing marine extension and influence during the early hettangian early sinemurian mid sinemurian and latest sinemurian earliest pliensbachian transgressions four sequences four transgressive systems tracts three highstand systems tracts and three levels regarded as equivalents of maximum flooding surfaces are distinguished in the case of type 2 sequences when incised valley fill deposits are not developed and regional erosion is less common it may be rather difficult to define the sequence boundaries which are often concealed within the amalgamated fluvial deposits occurring in the neighbouring parts of two adjacent sequences fluvial deltaic sediments terminate the highstand systems tracts and in this setting the transgressive systems tracts start with continental deposits prior to the transgressive surfaces generally an exact correlation can be achieved between the sequence stratigraphy of the northeast and northwest european lower jurassic and the eustatic curve proposed by epr assuming some changes proposed by a hallam the establishment of this correlation hopefully will stimulate future studies of the sequence stratigraphy of poorly dated siliciclastic deposits of marginal basins in this setting even minor changes in sea level may cause major changes in facies development over large areas

geochemistry of inorganic and organic sulphur in organic rich sediments from the peru margin abstract we have determined 1 the abundance and isotopic composition of pyrite monosulphide elemental sulphur organically bound sulphur and dissolved sulphide 2 the partition of ferric and ferrous iron 3 the organic carbon contents of sediments recovered at two sites drilled on the peru margin during leg 112 of the ocean drilling program sediments at both sites are characterised by high levels of organically bound sulphur obs obs comprises up to 50 of total sedimentary sulphur and up to 1 of bulk sediment the weight ratio of s to c in organic matter varies from 0 03 to 0 15 mean 0 10 such ratios are like those measured in lithologically similar but more deeply buried petroleum source rocks of the monterey and sisquoc formations in california the sulphur content of organic matter is not limited by the availability of porewater sulphide isotopic data suggest that sulphur is incorporated into organic matter within a metre of the sediment surface at least partly by reaction with polysulphides most inorganic sulphur occurs as pyrite pyrite formation occurred within surface sediments and was limited by the availability of reactive iron but despite highly reducing sulphidic conditions only 35 65 of the total iron was converted to sulphide 10 30 of the total iron still occurs as fe iii in surface sediments the isotopic composition of pyrite is similar to that of both iron monosulphide and dissolved sulphide either pyrite like monosulphide formed by direct reaction between dissolved sulphide and detrital iron and or the sulphur species responsible for converting fes to fes2 is isotopically similar to dissolved sulphide likely stoichiometries for the reaction between ferric iron and excess sulphide imply a maximum resulting fes2 fes ratio of 1 1 where pyrite dominates the pool of iron sulphides at least some pyrite must have formed by reaction between monosulphide and elemental sulphur and or polysulphide elemental sulphur s0 is most abundant in surface sediments and probably formed by oxidation of sulphide diffusing across the sediment water interface in surface sediments s0 is isotopically heavier than dissolved sulphide fes and fes2 and is unlikely to have been involved in the conversion of fes to fes2 polysulphides are thus implicated as the link between fes and fes2

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

p and s wave travel time inversions for subducting slab under the island arcs of the northwest pacific we have observed slablike high p and s velocity anomalies around the wadati benioff zone under island arcs of the northwest pacific through travel time tomographic inversions nineteen years of international seismological centre travel time residuals for events and stations in this large region are used analyses of resolution and noise show that the images are generally well resolved the images illustrate that slab anomalies are continuous along strike in most parts of the upper mantle of the region and become contorted and generally broadened with depth near the bottom of the upper mantle fingering of the slabs including segmenting and spreading is indicated the fast anomalies associated with the japan izu bonin and mariana subduction zones tend to flatten to subhorizontal at depth while downward spreading may occur under parts of the mariana and kurile arcs the fast anomalies below 700 km are not in the shape of a single coherent sheet the principal compressional axes of focal mechanisms in the region consistently follow the downdip direction of the high velocity slab even when it bends to subhorizontal at depth the depth at which compression begins to dominate the downdip stress regime in the slab apparently depends on bending of the slab and its dip slab fingering and intense deep seismicity probably are the consequence of the slab encountering a barrier of some form around the 670 km discontinuity

whole mantle p wave travel time tomography abstract a method of tomographic inversion to obtain three dimensional velocity perturbations in the earth s whole mantle has been developed and applied to more than two million p wave arrival time data reported by international seismology center isc the model is parameterized with 32 768 blocks the divisions in latitude longitude and radius are 32 64 and 16 respectively horizontal cell size is 5 6 5 6 the layer thicknesses vary with depth 29 km just below the surface and 334 km just above the core mantle boundary starting from a spherically symmetric earth model we obtained a three dimensional model using the following iterative procedures first we relocated all the events second we backprojected the residual into the whole mantle third we refined the spherically symmetric earth model the solutions have been converged in five iterations we adopted the following techniques in the backprojection procedure the first order smoothness was introduced as a damping which makes the solution independent of the starting model and its apparent fluctuation minimal the basic equations for delay times and smoothness are solved using the conjugate gradient method an iterative method which guarantees the convergence of solution into the exact least squares solution the weight on the smoothness i e the damping factor was objectively determined by a simplified cross validation technique the final solution was obtained as an average of the ten solutions each of which was derived from one tenth of the total data set the reliability of the solution is examined in two ways 1 mapping the resolution given by the reconstruction of checkerboard patterns and 2 mapping the variance given from the gaussian noise input this is the first result which delineates the whole mantle structure with its reliability mapping the longest wavelength anomalies of the lower mantle are similar to those of previous studies by dziewonski 1984 and hager and clayton 1989 however the shorter wavelength patterns have many discrepancies the fast anomalies of the uppermost mantle beneath the shield and the slow anomalies beneath the active tectonic regions are clearly seen we also revealed the l 2 pattern at the transition zone reported by the previous surface wave and free oscillation studies the most striking feature is that of the fast anomalies lying along the extension of the large subducting plate up to depths of about 1000 km or more the resolving powers in these regions are generally good

hummocky cross stratification like structures and combined flow ripples in the punta negra formation lower middle devonian argentine precordillera a turbiditic deep water or storm dominated prodelta inner shelf system abstract turbidity current and storm induced deposits may exhibit similarities in particularly when the latter is laid down by a combination of oscillatory and unidirectional flows recent progress in facies analysis helps to discriminate the sedimentary effects of oscillatory from unidirectional components of the flow on the basis of detailed analysis of sedimentary facies strata geometry and palaeocurrent data the present study reinterprets the punta negra formation pnf lower middle devonian argentine precordillera previously considered as a depositional system of deep water as a storm dominated prodeltaic shelf depositional system in the sandstone beds of the pnf planar low angle and undulating laminations with weakly asymmetric hummocky and swaley bedforms combined flow ripples accretionary hummocky cross stratification like hcs like and anisotropic hcs like suggest the action of oscillatory currents combined with unidirectional currents in forming the deposits different hypotheses on the origin of the oscillatory currents have been examined the most convincing interpretation is that the oscillatory component of the velocity is attributed to storm induced waves the palaeocurrent data indicate offshore current directions suggesting that the unidirectional flow was a gravity induced bottom current inverse grading at the base and overlying normally graded divisions of the sandstone beds testify to waxing waning behaviour of the depositional flows interbedding of sedimentary structures undulating laminations low angle and parallel laminations and combined flow ripples in the lower and intermediate divisions of the beds indicate fluctuations of flow velocity this organisation of the sedimentary structures permits association of the unidirectional component with hyperpycnal bottom currents the terrestrial origin of the hyperpycnal flows is suggested by the abundance of terrestrial plant remains the mineralogical and textural immaturity of the sandstone composition and the relative scarcity of bioturbation which was likely controlled by fresh water input and a high rate of sedimentation storm influenced hyperpycnal flows generated subaqueous channelised forms at the mouth of the river deltas which later filled with sand at the distal end of the channelised forms lobe shaped sandstone beds were deposited evolving distally into thin sandstone beds alternating with sandy mudstone

early cretaceous strata of the nepal himalayas conjugate margins and rift volcanism during gondwanan breakup early cretaceous sandstones shales and marlstones chukh tangbe and muding formations at least 625 m thick crop out north of the main central thrust in central nepal they were strongly deformed during himalayan collision with telescoping of facies transitions as a result of crustal shortening the sediments show northerly palaeoflow and were deposited on the steadily subsiding northern tethyan margin of gondwana berriasian deltaic deposits pass upward into valanginian albian storm dominated shelf deposits and into latest albian pelagic slope carbonates an unconformity probably of valanginian age separates the chukh and tangbe formations locally and is overlain by volcanic conglomerates the gondwanan margin succession matches well with that observed on the formerly conjugate margin of nw australia which separated from greater india during the valanginian to hauterivian volcanic detritus where suitable for analysis shows within plate geochemical affinity and reflects gondwanan fragmentation abundant volcanic detritus in aptian strata may have been derived from extensions of the rajmahal traps of northeast india however volcanism was active near central nepal in the valanginian and volcanic detritus possibly far travelled reached the area during the berriasian early cretaceous strata1 successions and relative sea level changes show a first order relationship to tectonism associated with gondwanan break up

the latest cretaceous early paleogene rapid growth of accretionary complex and exhumation of high pressure series metamorphic rocks in northwestern pacific margin episodic growth of accretionary complexes along the northwestern pacific margin is well documented from detailed biostratigraphy and radiometric dating of metamorphic rocks the latest cretaceous to early paleogene rapid growth of the accretionary complexes observed in hokkaido and sakhalin islands was caused by the supply of a large amount of terrigenous sediments from an intracontinent collision zone the mongolia okhotsk zone in the northern asian continent rapid growth of the accretionary prism resulted in episodic tectonic events in the forearc and magmatic arc rapid underplating caused uplift and exhumation of previously accreted complexes along with high pressure series metamorphic rocks now exposed as the kamuikotan complex in hokkaido and the susunai complex in sakhalin the forearc basin shallowed as a result of the uplift the uplift collapsed the old accretionary complex and supplied olistoliths onto the forearc region magmatic activity along the continental margin was also active at the same time subduction of a large amount of terrigenous sediments into the mantle may have contributed to active magmatism at that time a large supply of water trapped in the subducted sediments entered the mantle and increased partial melting of the mantle wedge

a simple three dimensional model of diffusion with precipitation applied to localised pyrite formation in framboids fossils and detrital iron minerals a three dimensional diffusion with precipitation model is constructed to estimate radial variations in the amounts of pyrite which precipitate where a spherical mass of organic matter producing h2s by sulphate reduction is enveloped in a dissolved iron bearing porewater the model indicates that higher rates of sulphate reduction more readily metabolisable organic matter and larger organic masses require increasingly high dissolved iron concentrations in order to confine pyrite or iron sulphide precipitation to the decay site the maximum size sphere of exceedingly metabolisable organic matter equivalent to fresh planktonic material which can be pyritised is about 50 m radius where decay occurs in porewaters with typical dissolved iron levels this radius is close to the maximum radius of framboidal pyrite the formation of which could involve model type processes fossil carcases although mainly composed of less readily metabolisable organic matter may be orders of magnitude larger and the model demonstrates that their pyritisation requires unusually high porewater dissolved iron concentrations these inferred chemical conditions are consistent with sedimentological observations of pyritisation in beecher s trilobite bed new york state at greater depths within the sediment pyritisation is controlled by the kinetics of iron mineral reactivity towards h2s sediments vary widely in their exposure times to h2s which can range at least from 50 to 106 years at low exposure times only iron oxides are pyritised whereas at high exposure times even the most refractory iron silicates can become pyritised

paleogene history of the kula plate offshore evidence and onshore implications paleocene to middle eocene magnetic anomalies were mapped over oceanic crust that accreted at the kula pacific spreading center and is now obliquely entering the western aleutian trench between 179 e and 168 e the strike of anomalies and the pattern of abyssal hills and fracture zones changed abruptly during 56 55 ma when north south spreading veered to northwest southeast 310 130 kula pacific spreading ceased in 43 ma a 75 km long section of the fossil kula rift axis has avoided subduction although it now intersects the trench axis almost orthogonally near 171 5 e a narrow remnant of the former kula plate northwest of this fossil spreading center is bounded by a fossil kula pacific transform with a high transverse ridge alongside a sediment filled transform valley anomalies on this remnant show that eocene kula pacific spreading was highly asymmetric 2 1 the 56 55 ma change in kula plate rotation inferred from the change in spreading direction coincided with birth of the aleutian subduction zone and was probably a consequence of the resulting change in slab pull stresses on the oceanic lithosphere the change in direction of kula north american motion is a plausible explanation for the detachment of continental terranes from the pacific northwest and their migration around the gulf of alaska and for the early eocene demise of alaska range are volcanism the cessation of kula pacific spreading coincides with a major change in pacific plate rotation and the subsequent direction of convergence of the pacific plate with the aleutian arc was similar to the 55 43 ma direction of kula plate convergence

the bude formation lower westphalian sw england siliciclastic shelf sedimentation in a large equatorial lake the 1300 m thick turbiditic bude formation was deposited in a lake lake bude but disagreement persists over whether the environment was a deltaic or deep water fan the tectonic setting of the lake was the northern flank of a northerly advancing variscan foreland basin close to the westphalian palaeo equator palaeocurrents indicate sediment sourcing from all quadrants except the south there is a dm m scale cyclicity whereby sandstone bodies comprising amalgamated event beds alternate with mudstone intervals containing non amalgamated event beds the ideal cycle is a symmetrical coarsening up fining up cycle consisting of three facies i 2 and 3 arranged in 12321 order facies 3 in the middle of the cycle is an amalgamated sandstone body up to 10 m thick which interfingers laterally with thin cm mudstone layers the sandstone body comprises amalgamated beds of very fine sandstone which are largely massive and up to 0 4 m thick channels are absent except for scours up to 0 2 m deep which truncate the interfingering mudstone layers sandstone bodies are inferred to be tongue shaped in three dimensions facies 1 and 2 completing the 12321 cycle are respectively dark grey fine and light grey coarse varved mudstone containing thin 0 4 m sandstone event beds fossils and burrows indicate that facies 1 and 2 were deposited respectively in brackish rarely marine and fresh water hence the ideal cycle 12321 reflects an upward decrease then increase in salinity brackish fresh brackish this is attributed to the lake sill being periodically overtopped by the sea due to glacio euitatic sea level oscillations the resulting oscillations in lake depth produced the coarsening up fining up regressivetransgressive cyclicity the central sandstone body representing the regressive maximum event beds are interpreted as river fed turbidites deposited during catastrophic storm floods combinedflow ripples and other wave influenced structures occur in event beds throughout the ideal cycle suggesting deposition of the entire bude formation above storm wave base the proposed environment is a shelf of continental shelf dimensions but lacustrine instead of marine sandstone bodies are interpreted to be river connected tongues or lobes the absence of cycles containing nearshore or emergent facies is attributed to i the lake sill preventing the water level from falling below sill level thereby insulating the lake floor from eustatically forced emergence and ii relatively distal deposition beyond the reach of shoreline progradations the lack of palaeoflow from the south is attributed to a now eroded deep water trough lying to the south in front of the northerly advancing orogen some facies 2 laminated mudstone beds grade laterally into massive and or contorted beds interpreted as in situ seismites facies 4 consistent with an active foreland basin setting development of seismites was possibly facilitated by gas bubbles and or weak cohesion in the fresh water bottom mud the late quaternary black sea with its broad northwestern shelf is probably a good physiographical analogue of lake bude and was likewise fresh at times

taphonomy and depositional dynamics of devonian shell rich mudstones abstract fossil preservation e g articulation of multi element skeletons provides important insights into depositional dynamics detailed taphonomic analysis of marine mudstones and associated shell beds from the middle devonian of western new york indicates that these beds record primarily episodic sediment deposition of short duration we propose a storm winnowing mud blanketing model to explain the variety of shell and mudstone beds observed and to explain apparent onshore offshore gradients of shell bed characteristics shell beds themselves appear to have accumulated during relatively long spans of time ranging up to perhaps thousands of years most are internally complex and exhibit evidence for multiple events of burial and exhumation by winnowing shell accumulation facilitated colonization of the seafloor by hard substrate encrusting organisms these contributed to increasingly complex communities that were ultimately destroyed and permanently blanketed by thick mud layers the sparsely fossiliferous mudstones which compose up to 85 of the hamilton stratigraphic section mainly record very abrupt inputs of sediment in some instances taphonomy of enclosed fossils indicates deposition of layers up to several centimeters thick prior to compaction within hours to a few days in turn some sequences of shell and mudstone beds were deposited within the life span of single colonial organisms and thus also record only relatively short spans of time overall this reinforces our conclusions that most time in mudstone sequences must be represented by discontinuities at sharp surfaces or thin condensed beds that bound more or less continuous bundles of shell and mudstone beds again these often subtle discontinuities can be recognized on the basis of taphonomic criteria many complex shell beds as well as simple shell beds can be traced along depositional strike for tens of kilometers condensed shell beds only a few centimeters thick can commonly be correlated for 100 to 200 km along and across depositional strike the correlatable nature of shell beds apparently reflects the temporal contrast between these beds and enclosing muds on a regional scale shell beds represent integrated accumulations that were deposited over spans of tens to thousands of years conversely the mud layers that blanketed and terminated shell bed accumulations may represent very rapid depositional events spanning hours to days which are locally isochronous thus the study of taphonomy of shell beds reveals a good deal of detail about their depositional history these studies imply that the stratigraphic record is even more episodic and discotinuous than commonly recognized episodic deposition implies that while the stratigraphic record of epeiric seas may be adequate for examining details of community succession and paleontology it probably can not generally be used for microevolutionary studies other than examination of patterns of stasis

tomographic imaging of the p wave velocity structure beneath the kamchatka peninsula summary a total of 5270 shallow and intermediate depth earthquakes recorded by the 32 stations of the regional seismic network of the geophysical service of russia are used to assess the p wave velocity structure beneath the kamchatka peninsula in the western pacific the tomographic inversion is carried out in three steps first a 1 d tomographic problem is solved in order to obtain an initial velocity model based on the 1 d velocity model 3 d tomographic inversions with homogeneous and heterogeneous starting models are obtained the conrad 15 km depth and moho 35 km depth discontinuities determined from the 1 d tomographic inversion and the upper boundary of the subducting slab are taken into account in the heterogeneous starting model for the traveltimes and ray path determinations both velocity structure and hypocentral locations are determined simultaneously in the inversion the spacing of the grid nodes is a half degree in the horizontal direction and 20 50 km in the vertical direction a detailed p wave tomographic image is determined down to a depth of 200 km the resulting tomographic image has a prominent low velocity anomaly that shows a maximum decrease in p wave velocity of approximately 6 per cent at 30 km depth beneath a chain of active volcanoes at depth low velocity anomalies are also observed in the mantle wedge extending down to a depth of approximately 150 km these anomalies are apparently associated with the volcanic activity the sedimentary basin of the central kamchatsky graben to the west of the volcanic front and the accretionary prism at the trench correlate with shallow low velocity anomalies highvelocity anomalies observed at a depth of 10 km may be associated with the location of metamorphic basements in the ganalsky valaginskoe uplift and upper crust of shipunsky cape the results also suggest that the subducted pacific plate has p wave velocities approximately 2 7 per cent higher than those of the surrounding mantle and a thickness of approximately 70 km

tomographic inversion of p and pp data for aspherical mantle structure below the northwest pacific region summary to investigate the morphology of subducted slab in the mantle below northwest pacific island arcs we inverted traveltime residuals for aspherical variations in p wave propagation velocity relative to the radially symmetric iasp91 reference model the tomographic method used is based on a step wise linearization of the inversion problem first we relocated isc international seismological centre hypocentres with re identified p and pp phase data using the iasp91 traveltime tables the variance of p residuals relative to iasp91 traveltimes was 17 per cent less than the variance of p data reported by the isc relative to the jeffreys bullen j b traveltime tables second we performed a linearized lsqr inversion for earth structure and source relocation with the p and pp residuals obtained from the first step using iasp91 as the reference model for seismic velocities the incorporation of the depth phase pp in the tomographic inversions has two major advantages 1 the pp data provide constraints on focal depth and thus reduce the trade off between source relocation and structure and 2 the pp ray paths improve the sampling of earth structure in the shallow mantle and transition zone we used more than 2 times 106 and about 1 times 105p and pp wave traveltime residuals respectively from about 40 000 earthquakes with epicentres in the study region that were recorded at one or more of the 2300 globally distributed seismological stations considered in this study we assessed the spatial resolution in the tomographic images with checker board type sensitivity tests these tests reveal high resolution of upper mantle and transition zone structure particularly below the central part of our study region structure with wavelengths of the order of 100 km is resolved below japan whereas structure with wavelengths of the order of 300 km is well resolved below the kuril izu bonin and ryukyu arcs small scale structure is poorly resolved in depth below the northern part of the kuril kamchatka arc and below the izu bonin and mariana arcs this limits the interpretation of slab structure and mantle flow from tomographic images alone with this limitation in mind we conclude from the tomographic images that subducted slab deflects in the mantle transition zone below the geographical area encompassed by the kuril basin the japan sea and the northern part of the philippine sea this is in good agreement with the results of other recently published tomographic studies the occurrence of earthquakes several hundred kilometres off the inclined wadati benioff seismic zones and inferences about 660 km discontinuity topography in contrast slab like structures of high p wave velocity are imaged in the lower mantle below the deepest earthquakes of the northern kuril kamchatka and mariana seismic zones this is indicative of local slab penetration of the lower mantle from tomographic images we cannot discern between compositionally or thermally induced variations in seismic velocity however with regard to the nature of the boundary between upper and lower mantle our observations argue against either compositional mantle layering with large contrasts in intrinsic density or phase changes with steep clapeyron slopes

early diagenesis and sulphur speciation in sediments of the oman margin northwestern arabian sea the pore waters from two boxcores from the oman margin from sites niop484 and niop487 respectively in and below the oxygen minimum zone in the water column were analysed for concentrations of iodide sulphide thiosulphate phosphate silica ammonia nitrate nitrite dissolved iron dissolved manganese and dissolved sulphur in addition the solid phase of samples from the same cores was analysed for organic carbon pyritic sulphur acid volatile sulphide elemental sulphur organic polysulphides humic sulphur reactive iron phases and reactive manganese phases pore water profiles show that post oxic diagenesis dominates in these holocene sediments only minor amounts of reduced sulphur species were found in pore waters despite the low oxygen concentration of the bottom water and the relatively high organic matter content of the sediments significant amounts of solid phase reduced sulphur were only found in the lower half of the boxcore at station niop484 consequently sulphate reduction is not as significant in these sediments relative to sediments from other upwelling areas and thus more sedimentary organic matter is preserved

signature of remnant slabs in the north pacific from p wave tomography summary a 3 d ray tracing technique was used in a global tomographic inversion in order to obtaintomographicimagesofthenorthpacific thedatareportedbythegeophysical surveyofrussia 1955 1997 wereusedtogetherwiththecataloguesoftheinternational seismologicalcenter 1964 1991 andtheusgeologicalsurveynationalearthquake information center 1991 1998 and the recompiled catalogue was reprocessed the final data set used for following the inversion contained 523430 summary ray paths the whole of the earth s mantle was parametrized by cells of 2 2 and 19 layers the large and sparse system of observation equations was solved using an iterative lsqr algorithm asubhorizontalhigh velocityanomalyisrevealedjustabovethe660kmdiscontinuity beneaththealeutiansubductionzone thishigh velocityfeatureisobservedatlatitudes of up to 70 n and is interpreted as a remnant of the subducted kula plate which disappeared through ridge subduction at about 48ma a further positive velocity perturbation feature can be identified beneath the chukotka peninsula and okhotsk sea extending from 300 to 660km depth and then either extending further down to 800km chukotka or deflecting along the 660km discontinuity okhotsk sea this high velocity anomaly is interpreted as a remnant slab of the okhotsk plate accreted to siberia at 55ma

degree of pyritization of iron as a paleoenvironmental indicator of bottom water oxygenation abstract a new method is presented for recognizing the degree of bottom water oxygenation in organic carbon bearing rock the method uses the parameter degree of pyritization dop which is the ratio of pyritic fe to pyritic fe acid soluble fe sediments with ages ranging from devonian to cretaceous have been classified on paleoecological and sedimentological criteria as having been deposited in aerobic conditions deposited in fully oxygenated bottom waters restricted marine conditions deposited in waters with low oxygen concentrations or inhospitable bottom conditions where little or no oxygen is present and h2s may be continually or intermittently present aerobic dop

distribution of organic carbon in surface sediments along the eastern arabian sea a revisit abstract one hundred twelve surface sediment samples along the western continental margin of india were analyzed for organic carbon oc elevated oc concentrations are associated with sediments deposited in areas where productivity is moderate to high very high oc concentrations as reported in earlier studies even for regions where productivity is comparatively low could not be confirmed the re analysis of selected samples by coulometry shows that oc concentrations determined previously by the wet oxidation method may be too high by up to more than a factor of two a broad similarity in the distribution of oc and bioproductivity is observed which is in accordance with other productivity proxies such as the abundance of planktonic foraminiferal species g bulloides and hydrogen indices hi our results indicate the importance of bioproductivity for oc accumulation along the western continental margin of india even though low dissolved oxygen concentrations in the water column sedimentation rate sediment texture clay mineral content dilution by quartz and carbonate as well as topography are considered responsible for the general oc distribution in this area

storm deposited sandstones tempestites and related ichnofossils of the late ordovician georgian bay formation southern ontario canada the late ordovician geogian bay formation of southern ontario canada comprises up to 250 m of grey to blue grey shales interbedded with highly fossiliferous calcareous sandstones these strata were deposited in equatorial paleolatitudes after 448 ma in a shallow foreland basin created by overthrusting along the eastern margin of north america the taconic orogeny the georgian bay formation comprises the middle part of an upward shallowing progradational sequence from deep water transgressive shales of the underlying whitby formation to muddy tidal flat sequences of the overlying queenston formation exposures in brickyard and river cuts near toronto and northwards along a narrow outcrop belt along the foot of the niagara escarpment show laterally extensive 100 m sharp based sheets of sandstone up to 1 m thick with gutter casts and washed out hypichnial trace fossils dominantly planolites and paleophycus on their lower bedding surfaces detailed examination of sandstone beds in outcrop and i

tectonic and eustatic signals in the sequence stratigraphy of the upper devonian canadaway group new york state we have refined the late frasnian to early famennian relative sea level curve based on detailed stratigraphic data from more than 1200 outcrops in the appalachian basin of western new york this curve is constructed from considerations of lithologies bedforms and ichnofacies we document 3 sequences and 48 parasequences in the canadaway group part of the marine component of the catskill delta complex several apparent lowstands and one transgression are localized along the syndepositionally active clarendon linden fault system we infer that these systems tracts are forced and result from interaction between fault block motion and eustatic sea level changes this detailed study thus demonstrates that sea level curves inferred from local foreland basins may have a stronger tectonic signal than formerly perceived

recognition of facies bounding surfaces and stratigraphic patterns in foreland ramp successions an example from the upper devonian appalachian basin u s a abstract a detailed stratigraphic study of the upper devonian lock haven formation in the appalachian basin provides new interpretations applicable to understanding sedimentation and stratigraphic architecture in the foreland ramp setting the common occurrence of graded beds hummocky cross stratification and shell lags indicates that storm processes played an important role in deposition gradational based coarsening upward shoreface sequences of interbedded sandstone and mudstone formed during gradual fall in relative sea level in contrast sharp based regressive sequences consist of laminated sandstone facies overlying a submarine erosion surface that developed in response to more rapid fall in relative sea level transgressive sequences become finer grained upward from conglomerate lag which was deposited on a basal transgressive surface to heterolithic facies and mudstone facies a combination of eustasy and tectonic subsidence of the foreland ramp produced changes of relative sea level these fluctuations provided a means for transporting sand onto the ramp and for producing repetition of stratigraphic patterns in the lock haven formation the upper devonian clastic succession which includes both the lock haven formation and the catskill formation represents northwestward progradation of shoreline to nonmarine environments as sediment supply to the foreland ramp exceeded the rate of formation of accommodation compared to passive margin shelves thick fine grained successions such as the lock haven formation are more likely to form in foreland basins where tectonic subsidence provides a mechanism for creating accommodation sediment influx from uplifted areas and absence of a slope break on the foreland ramp results in a higher rate of fine grained clastic sedimentation than occurs on shelves of passive margins

simultaneous travel time inversion for earthquake location and subduction zone structure in the central aleutian islands a combined location and velocity inversion technique is applied to travel time data from 151 well recorded central aleutian earthquakes the data include p and s wave arrivals at stations of a local network and p pp and sp wave arrivals at teleseismic stations after correction for crustal structure at the reflection points the depth phases pp and sp provide important constraints on subduction zone structure not ordinarily resolved by other types of data the structure is assumed to vary only across the arc and in depth it is parameterized with cubic splines by specifying the velocity at each point of a gridded arc cross section to avoid ray tracing it is assumed that the velocity part of the problem is linear preliminary results show that deep earthquakes apparently occur within a narrow downdip zone near the upper surface of the descending slab in contrast with previous studies which have located them within the presumably stronger and colder inner core of the slab a slab thickness of 80 100 km and a downdip length of about 400 km well below the deepest seismic activity are indicated the slab is characterized by seismic velocities as much as 11 higher than the surrounding mantle in its upper portions and 4 6 higher at depth a sharp velocity gradient and lower velocities occur directly beneath the volcanic arc near the top of the slab the slab anomaly appears to spread out and fall off very slowly with depth these are probably not real effects but consequences of the omission of three dimensional ray tracing

sharp based tide dominated deltas of the sego sandstone book cliffs utah usa the lower part of the cretaceous sego sandstone member of the mancos shale in east central utah contains three 10 to 20 m thick layers of tide deposited sandstone arranged in a forward and then backward stepping stacking pattern each layer of tidal sandstone formed during an episode of shoreline regression and transgression and offshore wave influenced marine deposits separating these layers formed after subsequent shoreline transgression and marine ravinement detailed facies architecture studies of these deposits suggest sandstone layers formed on broad tide influenced river deltas during a time of fluctuating relative sea level shale dominated offshore marine deposits gradually shoal and become more sandstone rich upward to the base of a tidal sandstone layer the tidal sandstones have sharp erosional bases that formed as falling relative sea level allowed tides to scour offshore marine deposits the tidal sandstones were deposited as ebb migrating tidal bars aggraded on delta fronts most delta top deposits were stripped during transgression where the distal edge of a deltaic sandstone is exposed a sharp based stack of tidal bar deposits successively fines upward recording a landward shift in deposition after maximum lowstand where more proximal parts of a deltaic sandstone are exposed a sharp based upward coarsening succession of late highstand tidal bar deposits is locally cut by fluvial valleys or tide eroded estuaries formed during relative sea level lowstand or early stages of a subsequent transgression estuary fills are highly variable reflecting local depositional processes and variable rates of sediment supply along the coastline lateral juxtaposition of regressive deltaic deposits and incised transgressive estuarine fills produced marked facies changes in sandstone layers along strike estuarine fills cut into the forward stepped deltaic sandstone tend to be more deeply incised and richer in sandstone than those cut into the backward stepped deltaic sandstone tidal currents strongly influenced deposition during both forced regression and subsequent transgression of shorelines this contrasts with sandstones in similar basinal settings elsewhere which have been interpreted as tidally influenced only in transgressive parts of depositional successions

closing the gap between regional and global travel time tomography recent global travel time tomography studies by zhou 1996 and van der hilst et al 1997 have been performed with cell parameterizations of the order of those frequently used in regional tomography studies i e with cell sizes of 1 2 these new global models constitute a considerable improvement over previous results that were obtained with rather coarse parameterizations 5 cells the inferred structures are however of larger scale than is usually obtained in regional models and it is not clear where and if individual cells are actually resolved this study aims at resolving lateral heterogeneity on scales as small as 0 6 in the upper mantle and 1 2 3 in the lower mantle this allows for the adequate mapping of expected small scale structures induced by for example lithosphere subduction deep mantle upwellings and mid ocean ridges there are three major contributions that allow for this advancement first we employ an irregular grid of nonoverlapping cells adapted to the heterogeneous sampling of the earth s mantle by seismic waves spakman and bijwaard 1998 second we exploit the global data set of engdahl et al 1998 which is a reprocessed version of the global data set of the international seismological centre their reprocessing included hypocenter redetermination and phase reidentification finally we combine all data used p pp and pwp phases into nearly 5 million ray bundles with a limited spatial extent such that averaging over large mantle volumes is prevented while the signal to noise ratio is improved in the approximate solution of the huge inverse problem we obtain a variance reduction of 57 1 synthetic sensitivity tests indicate horizontal resolution on the scale of the smallest cells 0 6 or 1 2 in the shallow parts of subduction zones decreasing to approximately 2 3 resolution in well sampled regions in the lower mantle vertical resolution can be worse up to several hundreds of kilometers in subduction zones with rays predominantly pointing along dip important features of the solution are as follows 100 200 km thick high velocity slabs beneath all major subduction zones sometimes flattening in the transition zone and sometimes directly penetrating into the lower mantle large high velocity anomalies in the lower mantle that have been attributed to subduction of the tethys ocean and the farallon plate and low velocity anomalies continuing across the 660 km discontinuity to hotspots at the surface under iceland east africa the canary islands yellowstone and the society islands our findings corroborate that the 660 km boundary may resist but not prevent present day large scale mass transfer from upper to lower mantle or vice versa this observation confirms the results of previous global mantle studies that employed coarser parameterizations

anoxia vs productivity what controls the formation of organic carbon rich sediments and sedimentary rocks discussion the prevailing explanation for the origin of organic rich sediments and rocks invokes deposition under conditions of anoxia however recent research suggests that high primary production and not water column anoxia provides the first order control on the accumulation of organic rich facies in the modern oceans oxygen minima do not appear to have any direct effect on carbon accumulation in continental margin or marginal sea environments sediments accumulating in the modern black sea the type euxinic basin are not particularly enriched in organic matter despite the presence of an anoxic water column although a sapropel containing extremely high carbon concentrations was deposited during the holocene at a time when the basin was oxic results of a recently published co pled ocean atmosphere model indicate that during the cretaceous thermohaline and surface circulation in the oceans was similar to or more intense than modern conditions despite the overall equable climate such conditions confound the idea that circulation in the cretaceous atlantic for example was punctuated by oceanic anoxic events brought about by more sluggish circulation sporadic temporal and spatial increases in primary production reflecting changes in the behavior and or state of the ocean atmosphere system constitute a more tenable explanation for the occurrence of modern and quaternary carbon rich sediments and cretaceous black shales consequently the fundamental control on the accumulation of carbon rich facies in the oceans and marginal seas is not the presence or absence of anoxia

subduction triggered magmatic pulses a new class of plumes article i nfo a variety of atypical plume like structures and focused upwellings that are not rooted in the lower mantle have recently been discussed and seismological imaging has shown ubiquitous small scale convection in the uppermost mantle in regions such as the mediterranean region the western us and around the western pacific we argue that the three dimensional return flow and slab fragmentation associated with complex oceanic subduction trajectories within the upper mantle can generate focused upwellings and that these may play a significant role in regional tectonics the testable surface expressions of this process are the outside arc alkaline volcanism topographic swell and low velocity seismic anomalies associated with partial melt using three dimensional simplified numerical subduction models we show that focused upwellings can be generated both ahead of the slab in the back arc region though five times further inward from the trench than arc volcanism and around the lateral edges of the slab in the order of 100 km away from slab edges vertical mass transport and by inference the associated decompression melting in these regions appears strongly correlated with the interplay between relative trench motion and subduction velocities the upward flux of material from the depths is expected to be most pronounced during the first phase of slab descent into the upper mantle or during slab fragmentation we discuss representative case histories from the pacific and the mediterranean where we find possible evidence for such slab related volcanism

storm effects on siliciclastic and carbonate shelf sediments in the medial silurian succession of pennsylvania abstract upper llandoverian through wenlockian strata in the pennsylvania part of the northern appalachian basin formed on a gentle epeiric ramp that extended from marginal tidal flats through coarser grained mid shelf shoals to a muddy basin center over approximately 10 million years the composition of the accumulating sediment evolved from siliciclastic to carbonate while the ramp maintained a relatively similar configuration and position below sea level and while storm generated processes continued as the major producers of sediment characteristics in both siliciclastic and carbonate parts of the succession sedimentary structures and their sequences are generally similar with only a small number of dissimilar features resulting from the differences in composition small scale coarsening and shallowing upward sequences are present in both mid shelf bar and basin transition deposits although specific sequence characteristics are different in siliciclastic and carbonate parts such sequences record cyclic fluctuations of relative sea level while the composition of the sediment evolved over this extended period the gentle ramp gradient was maintained largely by the processes generated by storms such processes were more effective because of the fluctuations of relative sea level

a numerical study of sediment transport and event bed genesis during tropical storm delia some event beds tempestites are thought to be emplaced on shallow marine shelves by the combined action of strong coastal currents and high waves during fairly short lived storms to test this hypothesis a storm sedimentation system has been constructed from six numerical models describing a cyclonic wind field three dimensional coastal circulation wind waves generated over the continental shelf the combined effect of steady and oscillatory currents within the benthic boundary layer suspended and bed load transport of sediment and conservation of the seafloor this model system is used to hindcast winds currents waves and resulting sedimentation during tropical storm delia which passed over the texas louisiana shelf on september 3 4 1973 sensitivity to the initial substrate is investigated in four experiments using uniform silt uniform sand a mud line at the 20 m isobath and a simplified modern sediment distribution modeled coastal currents are vertically uniform and do not reveal the structure predicted by the mid latitude geostrophic storm circulation model because the predicted depth of the wind mixed layer is greater than the water depth over the shelf shelf currents in excess of 2 m s flow predominantly along the coast to the southwest during most of the storm driven by the wind stress and the trapped coastal wave which peaks at 180 cm near galveston significant wave heights reach 8 m on the outer shelf but are less than 4 m over the inner shelf these waves combine with steady currents to produce bed shear velocities which locally exceed 20 cm s the region of highest stresses always lies to the right of the storm track viewed down the path and moves across the shelf with the eye of the storm three general sediment transport paths are evident 1 onshore transport of finer sediment over the outer shelf to the right of the storm track 2 westward directed along shelf transport of predominantly fine sediment between approximately 40 m and 20 m water depths and 3 minor offshore transport of sand from the shoreface to depths less than 30m the resulting event bed has a ragged appearance with a maximum thickness of about 20 cm in region 1 and covers an area of approximately 3 104 km2 to the right of the storm track aside from local transport associated with finer sediments these results are relatively insensitive to initial sediment type comparison of model results to observed data from buccaneer platform shows that the different models performed adequately during the peak of the storm except for a significant underprediction of the significant wave height by the wind sea model the estimated uncertainty in the calculated combined shear stresses u based on errors produced by the individual model components is most dependent on the wave bottom orbital amplitude the total uncertainty in u is estimated to be approximately 7

processes controlling the distribution and cycling of manganese in the oxygen minimum zone of the arabian sea abstract vertical and horizontal distributions of dissolved and particulate manganese were investigated in the arabian sea northwestern indian ocean during the 1995 spring intermonsoon period march april us jgofs process cruise 2 tn045 the region is characterized by an intense basin wide oxygen minimum zone omz that strongly influences the manganese distribution in the omz two distinct dissolved mn d mn maxima were observed at depths of 200 300 m and 600 m respectively the latter peak displayed concentration maxima of approximately 6 nanomolar and was largely confined to stations north of 19 n latitude stations n2 n7 this mid depth maximum was associated with the low oxygen core of the omz o 2 saager et al 1989 geochimica et cosmochimica acta 53 2259 2267 this signal was largely absent at stations along the southern transect likely due to oxidative scavenging of d mn to the suspended particulate phase mid depth particulate mn maxima at some southern stations stations s4 s11 appear to be remnants of this feature the upper d mn maximum 200 300 m depth was more widely distributed than the 600 m peak with d mn concentrations of 3 to as high as 8 nm at most stations east of about 62 e longitude the signal was everywhere correlated with the secondary nitrite maximum at stations within the main denitrification zone delineated by naqvi 1991 nepheloid layers presumably bacterial also were associated with this depth interval particulate mn profiles displayed corresponding concentration minima and low mn al and reactive refractory mn ratios for this same depth interval suggesting reductive dissolution of mn oxyhydroxides these observations imply that in situ microbially mediated processes may be the predominant source of d mn in the upper omz while horizontal advection is more important deeper in the water column

stable sulfur isotopes indicate net sulfate reduction in near surface sediments of the deep arabian sea depth profiles of the stable sulfur isotopic composition of dissolved sulfate in near surface sediments were measured at five stations of the deep arabian sea between 1918 and 4426 m water depth wast wast top cast sast nast sampled in april 1997 the results clearly indicate that net microbial sulfate reduction took place in the sediments at stations wast and nast below about 12 cm depth sulfate reduction at wast was more pronounced compared to station nast most likely due to higher organic carbon content in turbiditic sediments no net sulfate reduction took place within the upper 10 cm of the surface sediments at all stations and no significant isotopic indication for sulfate reduction was found down to 30 cm bsf at station sast results are in accordance with accumulation of reduced isotopically light sulfur species below about 6 cm bsf at station wast it is concluded that the sulfur isotopic composition of remaining sulfate is more sensitive to net sulfate reduction than the so4 cl ratio the sulfur isotopic composition of a vertical profile for dissolved sulfate through the water column at station wast was essentially constant 250 4047 m full size image 1 k vs v cdt n 8 a similar constancy 20 4565 m water depth full size image 1 k vs v cdt n 15 was found for the station biotrans in the northeastern atlantic 47 11 19 33w indicating that the oxygen minimum zone in the arabian sea has no influence on the sulfur isotopic composition of dissolved sulfate

sulfur speciation in the upper black sea sediments abstract we report solid phase sulfur speciation of six cores from sediments underlying oxic suboxic and anoxic sulfidic waters of the black sea our dataset includes the five sulfur species pyrite sulfur acid volatile sulfides avs zerovalent sulfur s 0 organic polysulfides rsx humic sulfur together with reactive iron and manganese as quantified by dithionite extraction and total organic carbon pyrite sulfur was the major phase in all cores 200 400 mol g dry wt 1 except for the suboxic core however zerovalent sulfur and humic sulfur also reached very significant levels up to about 109 and 80 mol g dry wt 1 respectively humic sulfur enrichment was observed in the surface fluff layers of the eastern central basin sediments where unit 1 type depositional conditions prevail elemental sulfur accumulated as a result of porewater sulfide oxidation by reactive iron oxides in turbidities from the anoxic basin margin and western central basin sediments the accumulation of elemental sulfur to a level close to that of pyrite s in any part of central black sea sediments has never been reported before and our finding indicates deep basin turbidites prevent the build up of dissolved sulfide in the sediment this process also contributes to diagenetic pyrite formation whereas in the non turbiditic parts of the deep basin water column formed syngenetic pyrite dominates the sulfur inventory in slope sediments under suboxic waters organic sulfur humic sulfur organic polysulfides account for 33 42 of total solid phase s indicating that the suboxic conditions favor organosulfur formation our study shows that the interactions between depositional patterns unit 1 vs turbidite redox state of overlying waters oxic suboxic sulfidic and organic matter content determine sulfur speciation and enable the accumulation of elemental sulfur and organic sulfur species close to a level of pyrite s

early diagenesis of sulfur in a tropical upwelling system cabo frio southeastern brazil the early diagenesis of sulfur was assessed in four short sediment cores on the continental shelf off southeastern brazil that were deposited under the influence of an upwelling tropical system this tropical upwelling area allows a direct focus on the coupled roles of hydrodynamic and bioturbation driven influences on sulfate reduction sulfide re oxidation and corresponding stable sulfur isotope signal formation under the depositional conditions of cabo frio the degree of reactive iron pyritization was limited by both dissolved sulfide availability and pyrite oxidation events textural analyses of pyrite framboids provide evidence of re oxidation processes reflecting dynamic redox conditions in the sediments the isotope composition of pore water sulfate remained close to the modern seawater value but very light stable sulfur isotope ratios 34 s 32 s of chromium reducible sulfur essentially pyrite are found that reflect intense bioturbation induced sulfur re cycling the sulfur isotope signatures developing in these tropical upwelling sites are similar to those of modern euxinic systems although they are caused by a superimposition of sulfate reduction and an intense oxidative sulfur cycle

barium accumulation in the arabian sea controls on barite preservation in marine sediments in this study a new sequential extraction technique is used to investigate the particulate barium ba phases in sediments from the arabian sea to determine the processes controlling ba accumulation in marine sediments the total solid phase ba concentration in arabian sea surface sediments increases with water depth from 200 ppm at 500 meters below sea surface mbss to 1000 ppm at 3000 mbss the sedimentary ba composition consists of three major fractions barite ba incorporated in aluminosilicates and ba associated with mn fe oxides accumulation of barite which is the most important ba fraction in sediments located below 2000 mbss increases gradually with water depth the ba al ratio of the terrigenous fraction varies significantly across the arabian basin as the result of differences in grain size and provenance of the terrigenous sediment ba associated with mn oxides is a relatively minor fraction compared with bulk ba concentrations and it only accumulates in well oxygenated sediments below the present day oxygen minimum zone the water depth dependent accumulation of barite in the arabian sea is not related to the continuous formation of barite in settling organic particles or ba scavenging by mn oxyhydroxides but is primarily controlled by differences in ba preservation upon deposition a good correlation between the barite saturation index and the barite accumulation rate in the upper 2000 m of the water column may indicate that the degree of barite saturation of the bottom water is the main environmental factor regulating the burial efficiency of barite organic matter degradation bioturbation diagenetic mn cycling and the crystallinity of the accumulating barite may play additional roles copyright 2001 elsevier science ltd

cenozoic global plate motions cenozoic global plate motions relative to the hot spots are investigated and compared to plate motions in a mean lithosphere reference frame plate motions were analyzed over six time intervals divided by ages 10 25 43 48 and 56 ma chosen as much as possible to coincide with key plate reorganizations alternative motion circuits and rotational parameters were considered and evaluated with paleomagnetic data from the pacific and north american plates the circuit found to be in best agreement with the paleomagnetic data is one in which the hot spots in the atlantic region are assumed to be fixed relative to the hot spots in the pacific region throughout the cenozoic the hot spot and mean lithosphere reference frames have been in continual slow relative motion the rate of motion is nonuniform however most of the motion having occurred during the middle cenozoic the net cenozoic rotation of the lithosphere relative to the hot spots is described by a right handed rotation of 7 about a euler pole at 46 s 87 e which yields a 5 displacement of the north poles of the two reference frames this motion is small enough that inferences drawn about plate speeds in one reference frame should be valid in the other analysis of the global motions resulting from our preferred model showed that many characteristics of current plate motions have persisted throughout the cenozoic plate speeds correlate with latitude plates moving faster near the equator than near the poles throughout the cenozoic as at present continental plates except for the indian plate moved slower than oceanic plates throughout the cenozoic even the structure of the velocity fields as revealed in a contour of root mean square velocities in equatorial bands persists throughout the cenozoic the migration of the paleomagnetic axis over time is also compared to the hot spot and mean lithosphere reference frames the paleomagnetic axis has shifted 5 10 relative to the hot spot frame and a lesser amount relative to the mean lithosphere frame

shipboard routine and pressure filtration system for pore water extraction from suboxic sediments abstract a shipboard working procedure for the handling and porewater extraction of suboxic sediments is outlined in addition a detailed description is given of the shipboard pressure filtration system that has been used to extract porewater this procedure in combination with the pressure filtration system has been demonstrated to produce reliable porewater from suboxic sediments

extraction of pore water from marine sediments a review of possible artifacts with pertinent examples from the north atlantic abstract great care must be taken in extracting pore water if results are to be reliable errors can arise by inadequate storage conditions prior to pore water extraction by a difference between extraction temperature and the in situ temperature by oxygen contamination and possibly by high squeezing pressures three different extraction methods have been applied to samples from 30 m long piston cores collected in two abyssal plains in the north atlantic ocean the results demonstrate that all of the above mentioned errors have occurred these errors are discussed ad examples are shown

geochemical processes governing the performance of a constructed wetland treating acid mine drainage central scotland abstract constructed wetland systems often represent a low cost means for the remediation of dissolved metal and so4 rich acid mine drainage the surface water sediment and porewater geochemistry of one such wetland were investigated to determine the active geochemical processes that govern wetland performance the influent drainage has a ph of 2 6 200 250 mg l of dissolved fe and al mg and mn concentrations of 30 100 mg l sulphate concentrations are also high ranging from 500 1000 mg l sediment cores show high levels of amorphous fe oxyhydroxides near the surface and some amorphous reduced inorganic sulphur ris in deeper layers taken together with a decline in porewater so4 with depth the data suggest that bacterial so4 reduction is occurring all sediment cores display an increase in porewater so4 with depth in their top sections often forming a subsurface peak which could be attributed to oxidative dissolution of ris at the redox boundary however the increase in so4 is also accompanied by a rise in porewater ph desorption experiments yielded up to 8 wt so4 in these top layers suggesting that ph dependant sorption is an active so4 removal mechanism along with the precipitation of fe oxyhydroxysulphates which also removes dissolved fe the maximum treatment efficiency of the wetland is 25 for the removal of dissolved fe and the retention of other species is equally poor comparison with other wetland systems suggests that poor performance is due to the low ph and high dissolved metal concentration of the drainage together with deterioration in the wetland over time as a result of reduced active surface area and retention time

evaluation of high frequency paleoenvironmental variation using an optimized cyclostratigraphic framework example for c s fe analysis of devonian mississippian black shales central appalachian basin u s a abstract stratigraphic successions are rarely sampled at sufficiently dense spacing to permit evaluation of paleoenvironmental variation at the shortest fundamental frequency operative in the depositional system of interest often because that frequency remains undetermined here we provide an example of a sampling strategy optimized for recovery of high frequency paleoenvironmental signals based on 1 full core analysis using a continuous survey tool such as x radiography followed by 2 fine sampling of selected small scale cycles that record significant short term paleoenvironmental variation we show that this strategy results in recovery of high frequency paleoenvironmental signals that are completely missed by low density sampling protocols permitting key insights into depositional and early diagenetic processes that may otherwise by overlooked the present case study is based on c s fe systematics of the cleveland and sunbury shales which belong to the upper devonian lowermost carboniferous black shale succession of the central appalachian basin in eastern north america in these units the fundamental scale of paleoenvironmental variation is recorded by pervasive decimeter scale 5 to 20 cm thick compositional cycles that are readily visible in outcrop in which high organic layers weather out as resistant ledges we identified these cycles in drillcores using x radiography which proved to be an effective proxy for compositional variation owing to control of bulk density primarily by total organic carbon toc content we then sampled selected dm scale cycles n 21 at a centimeter spacing generating short high resolution multiproxy chemostratigraphic records including toc sulfur and fe concentrations fepy fehr a redox proxy 34spyrite and organic maceral content this analysis yielded the novel insight that all proxies related to authigenic iron sulfides e g stotal and spyrite fetotal and fepyrite fepy fehr and 34spyrite covary negatively with toc within the dm scale cycles we interpret the unusual pattern of negative toc pyrite covariation in the cleveland and sunbury shales to have resulted from differential distributions of labile organic matter om which drove h2s production via microbial sulfate reduction msr and reactive fe which controlled pyrite formation labile om was concentrated in high toc layers whereas reactive fe was concentrated in low toc layers possibly as fe oxyhydroxide coatings on silt grains as a consequence of which part of the h2s generated in the high toc layers diffused upward into the low toc layers before becoming fixed as pyrite this process is evidenced by several contrasts between high toc and low toc layers 1 higher spyrite concentrations and fepy fehr values in the latter 2 concentration of pyrite in the lower part of low toc layers immediately above high toc layers and 3 higher 34spyrite values in the latter reflecting late diagenetic formation of the h2s that diffused upward into the low toc layers to our knowledge this process has not been documented previously in ancient marine shales probably owing to insufficiently high resolution analysis in earlier studies

diagenetic pyritisation under eastern mediterranean sapropels caused by downward sulphide diffusion recurrent organic rich layers sapropels in eastern mediterranean sediments are enriched in corg fe and s sulphur and fe are enriched in a zone immediately below the sapropels whereas corg is not 34s values of bulk sediments and simple mass balance calculations indicate that so42 reduction has taken place in an open system with all hs formed at or close to the sediment surface formation of pyrite in the sapropel was fe limited and consequently excess hs was able to migrate downwards downward sulphidisation this resulted in the formation of pyrite below the sapropel by reaction of this hs with solid phase ferric iron and fe2 diffusing upwards from underlying sediments the fe2 source probably includes fe hydr oxide layers formed at former oxidation fronts above previously deposited and buried sapropels this downward sulphidisation mechanism allows accumulation of twice as much s in alternating organic rich anoxic organic poor suboxic sediments compared to what is preserved in organic rich anoxic sediments

storm features of siliciclastic shelf sedimentation in the mid cretaceous epeiric seaway of northern australia abstract late aptian to early cenomanian strata were deposited in a large epeiric seaway which covered much of the northern australian landmass during mid cretaceous time the seaway stretched from the carpentaria basin in the north to the eromanga basin in the south during this period siliciclastic sediments accumulated on a gently sloping epeiric shelf which formed the western margin of the carpentaria basin the shelf maintained a relatively similar configuration throughout the mid cretaceous with water depths rarely exceeding 50 m and the seafloor was apparently within the influence of storm waves over much of the area the shelf was storm and wave dominated and most early formed or fair weather sedimentary structures were destroyed or extensively modified during episodic storms storm features include hummocky cross stratification shelly lags erosional conglomeratic lags gutter casts lenticular micro hummocky sand beds megaripples characteristic low diversity and opportunistic ichnofacies various styles of wave ripple lamination and poorly preserved event beds most storm influenced units are preserved as coarsening and shallowing upwards facies successions which aggraded during high relative sea level and prograded during falling relative sea level some of these successions were subsequently eroded during further cyclic fluctuations of relative sea level

subducting slabs stagnant in the mantle transition zone the p wave velocity structure beneath the western pacific is found from the international seismological center first arrival data special attention was paid to the deep structure beneath the wadati benioff zone we discretized the whole mantle into blocks with finer blocks in the region of interest to obtain the velocities of all the blocks this way of discretization minimizes a problem with tomographic studies of regional scale difficulty in making corrections for the effects outside the region of interest our solution is iterative with the alternate step of the relocation of earthquakes using the whole mantle model of inoue et al 1990 as a starting model a first order smoothness constraint was imposed to suppress the possible fluctuation of the solution around the initial model the essential result depends little on whether the reference spherical model is smooth or discontinuous near 400 and 670 km depths we examined the resolution by calculating the resolving kernels for selected blocks and by reconstructing the checkerboard test patterns of velocity perturbation and the test structures of subducting lithosphere the resolution is depth dependent but in general good enough to see the slab configuration beneath the southern kurile japan izu bonin arcs and the java arc it is relatively poor beneath the northern kurile and mariana arcs the seismic image of subducting slab beneath the southern kurile to bonin arcs bends to subhorizontal near the leading edge of the wadati benioff zone and extends continentward over a distance of more than 1000 km the subhorizontal portion of the slab connects a high velocity blob to the bottom that reaches a depth of at least 800 km across the 670 km discontinuity under the japan arc although the image of the java slab directly penetrates the 670 km discontinuity it then bends to a shallow dip with a considerable spread reaching a depth of about 1200 km these results suggest that descending slabs of lithosphere in the western pacific tend to be stagnant in the transition zone under a subtle control of the 670 km discontinuity although stagnant slab materials eventually descend into the lower mantle they no longer maintain their original configuration below the 670 km discontinuity

manganese iron and sulphur cycling on the pakistan margin abstract benthic biogeochemical processes in the oceans oxygen minimum zones omzs are of global significance yet they remain poorly defined here sedimentary manganese iron and sulphur cycling are studied at sites above within and below the omz on the pakistan margin of the arabian sea before and immediately after the southwest monsoon mechanisms and rates of sedimentary mn fe and s cycling demonstrated down slope variation according to the position of the omz no significant seasonal change was evident except at one station on the upper margin where bottom waters became hypoxic during the late to post monsoon sampling due to the shoaling of the upper omz boundary within the omz mn 4 reduction within the water column limited supply of reactive mn to the underlying sediments the majority of reactive mn reaching the sedimentary environment is reduced abiotically via reaction with fe 2 sediments within the omz act as a source of mn 2 to the overlying water below the omz mn 2 is re oxidised within the water column and is deposited on the surface of the underlying sediments manganese is then reduced microbially and re oxidised within the oxygenated surface sediments uniform surface sediment fe al ratios across the margin suggest that fe 3 reduction is lacking within the water column omz in contrast fe is actively cycled within the sediments with fe 3 reduction occurring via dissimilatory pathways an absence of potential fe 2 oxidants within the omz results in an efflux of fe 2 from the sediments to the water column below the omz greater oxidant availability ensures that fe is retained within the sediments measured sulphate reduction rates at all sites across the margin were surprisingly low 0 0 45 mmol m 2 d 1 relative to rates observed on other omz margins the abundance of fe oxides in the sedimentary environment appears to suppress sulphate reduction

a study of sulphur enrichment in the humic fraction of marine sediments during early diagenesis abstract the evolution of the sulphur content of humic acids extracted from a near shore sediment core was investigated special attention was taken to avoid s contamination of the humic materials during extraction the s c ratios increased continuously with depth to values which strongly suggest s addition to the humic matrix during early diagenesis by reactions between organic matter and h2s or its oxidation products their light isotopic composition supports this view however subsequent isotopic exchange has obscured the mechanism initially involved since a large fraction of the enrichment occurred above the sulphidic zone redox boundaries such as the interface of anoxic microniches within more oxidized zones or the sulphidic suboxic boundary of the sediment column must have been important sites for s addition bioturbation by increasing the contact between sedimentary zones of a different redox regime will likely enhance such processes

climate change and productivity variations recorded by sedimentary sulfur in lake edward uganda d r congo abstract we investigate changes in the sulfur geochemistry of sediment cores from lake edward uganda congo to constrain the effects of recent climate changes in the region on the partitioning and isotopic composition of reduced sedimentary sulfur we measured the concentration and isotopic composition of kerogen sulfur chromium reducible and acid volatile sulfides as well as the abundance and partitioning of sedimentary phosphorus and iron and the abundance and isotopic composition of organic carbon and nitrogen results indicate an approximately 150 increase in sulfur concentrations in sediments from lake edward over the past 200 years during which time rainfall in the basin increased and the salinity of the lake fell increased sulfur concentrations are largely accounted for by increasing concentrations of kerogen sulfur which is likely caused by environmentally driven changes in organic matter quality and concentration including increased anoxia and nutrient supply to the lake during wet intervals the isotopic compositions of sedimentary sulfur pools support our interpretation that organic sulfur is derived primarily from sulfurization reactions in the sediment rather than primary bio sulfur and gradual isotopic enrichment of the 34 s of sedimentary pyrite and kerogen sulfur could result from decreased lake salinity and sulfate availability during the past 200 years these results highlight the importance of understanding environmentally mediated changes in organic sulfur accumulation in interpreting the sulfur geochemistry of sediments and sedimentary rocks

sequence stratigraphic hierarchy of the upper devonian foreknobs formation central appalachian basin usa evidence for transitional greenhouse to icehouse conditions abstract the foreknobs formation upper devonian upper frasnian to basal famennian comprises the uppermost marine strata of the progradational catskill clastic wedge of the south central appalachian mountains virginia west virginia usa the foreknobs formation consists of 14 lithofacies arranged in four facies associations which record the following depositional settings 1 storm dominated distal to proximal offshore to shoreface facies association a 2 sharp based conglomeratic shoreface facies association b 3 fluvial redbed facies association c and 4 incised valley fill ivf facies association d vertical juxtaposition and stacking patterns of lithofacies and facies associations permit recognition of a hierarchy of three scales of cyclicity up to 70 short term 5th order cycles each averaging 65 kyr consist of coarsening upward parasequences of storm dominated offshore marine facies in the distal setting which correspond to high frequency unconformity bound sequences hfs of fluvial redbed strata overlain by offshore marine strata in the proximal setting these facies relationships are a consequence of 10 15 m of sea level fluctuations up to 12 intermediate term 4th order cycles each averaging 375 kyr consist of stacked 5th order cycles the 4th order cycles are bounded by regressive surfaces of marine erosion rsme at the base of sharp based conglomeratic shoreface sandstones in the distal setting that correspond with paleosols in the proximal setting in some cases the 5th order cycles within each 4th order cycle exhibit stacking patterns indicative of increasing or decreasing accommodation space these facies relationships are a consequence of 25 35 m of sea level fluctuations three complete and portions of two additional 3rd order cycles each averaging 1 12 myr consist of stacked 4th order cycles the 3rd order sea level trends reflected in the foreknobs formation are nearly identical to published eustatic sea level curves incised valley fills are present at one of the 3rd order cycle boundaries and are a consequence of a 35 45 m sea level fluctuation the amplitudes of the inferred sea level fluctuations are comparable to the expansion and contraction of ice volumes within the current greenland and antarctic ice sheets which suggests glacioeustasy was the primary control on sea level fluctuations and cyclicity within the foreknobs formation such an interpretation is consistent with knowledge of devonian climate transitioning from middle devonian greenhouse to late devonian icehouse as indicated by evidence of glaciation during parts of the late devonian in south america and the appalachians

speciation and stable isotopic compositions of humic sulfur in mud sediment of the east china sea constraints on origins and pathways of organic sulfur formation abstract humic sulfur is commonly the most important pool of organic sulfur os in marine sediments and also important for the budget of total sedimentary sulfur in this study contents and stable sulfur isotopic compositions of hydrolyzable organic sulfur hyos humic acid sulfur ha s and fulvic acid sulfur fa s in one core collected from the east china sea ecs inner shelf were determined to investigate the sources and pathways of os formation and to compare diagenetic geochemistry of ha s and fa s hyos in the core is essentially biological in origin and diagenetically refractory with a fairly low fraction of labile sulfur bearing biomolecules ha s in the core is largely terrigenous residual bio os while fa s is a mixture of marine bio and diagenetic os diag os with the diag os fractions between 44 and 71 both ha s and fa s contents in the core are at the lower ends of the corresponding values reported in the literature the ha in the sediments is diagenetically inert subject to neither significant diagenetic sulfurization nor bio os mineralization loss while the fa is reactive prone to both sulfurization and decomposition loss of diagenetically bound os low contents of humic s i e ha s fa s in the core may suggest that os burial has only minor contribution to the burial of total sulfur in the sediments due to generally low om sulfurization

porewater nutrient concentrations and benthic nutrient fluxes across the pakistan margin omz abstract porewater concentrations and benthic fluxes of phosphate silicate ammonia nitrate and nitrite were measured at five sites spanning the pakistan margin oxygen minimum zone omz in order to characterise the biogeochemical processes occurring and to assess whether oxygen concentration and a seasonal pulse of organic matter are controlling factors typical concentrations of 1 70 m 50 250 m 0 270 m 30 cm in the sediment these processes are all redox sensitive and their intensities varied across the margin suggesting that oxygen concentration exerts a strong influence over nutrient concentrations and cycling variation in nutrient concentrations and fluxes before and after the summer monsoon was limited to an oxygen driven change to the po43 profile at one site indicating that either nutrient profiles do not generally alter on seasonal timescales or that any impact of the monsoon had subsided before the post monsoon sampling period porewater profile modelling tended to underestimate the magnitude of fluxes but was in general agreement with the directions of measured fluxes and in situ and shipboard flux measurements also generally agreed phosphate and h4sio4 concentrations and benthic fluxes on the pakistan margin were similar to those reported at abyssal sites from around the world while nh4 and no3 concentrations and fluxes were comparable to shallower more productive and or hypoxic marine settings

ediacaran and cambrian paleosols from central australia abstract ediacaran to cambrian red sandstones of the northern territory including arumbera sandstone and grant bluff and central mount stuart formations have been reexamined and sampled in order to reconstruct paleoenvironments from sedimentary facies and paleosols sedimentary facies include green gray calcareous sandstone member iii of arumbera sandstone only red siltstone with calcareous nodules also only member iii and also non calcareous red green siltstone interbedded red siltstone and sandstone and trough bedded sandstone the green gray facies has diverse and distinctive cambrian marine trace fossils not found in the red beds which have instead an assemblage of problematic body fossils including arumberia noffkarkys hallidaya ernietta trepassia and dickinsonia the red facies are interpreted as fluvial paleochannels trough cross bedded fluvial levees interbedded siltstone and sandstone poorly drained floodplain red green siltstone and well drained floodplain or low terrace calcareous nodular the carbonate nodules have micritic replacive fabrics and a significant positive correlation of 13c and 18o characteristic of pedogenic carbonate of calcid soils other red beds have pseudomorphous sand crystals after gypsum like those of gypsid soils individual red beds show negative strain and mass transfer for cationic bases typical of soils as well as gradational alteration down from fossiliferous tops characteristic of soils their varied degree of pedogenic differentiation is identified as psamment aquent and ochrept paleosols phosphorus depletion in the paleosols is evidence that organisms lived in the paleosols and were not introduced by transient marine incursions the problematic quilted fossils arumberia noffkarkys and hallidaya formed a distinctive inland terrestrial polsterland during the ediacaran and early cambrian

mantle structure beneath indonesia inferred from high resolution tomographic imaging we investigated mantle structure beneath the indonesian region by means of tomographic inversions of traveltime residuals of direct p and the surface reflected depth phases pp and pwp the hypocentres and phase data used in the inversions were derived from the reprocessing of data reported to international data centres which include data from the australian skippy project we used more than 6 0 10 data from more than 50 000 globally distributed earthquakes recorded at a subset of nearly 3000 seismological stations worldwide the use of depth phases improved the sampling of the upper mantle structure in particular beneath the back arc regions the mapping of distant aspherical mantle structure into the study region was minimized by combining a high resolution regional with a low resolution global inversion the inversion was linearized around the ak135 reference velocity model and a combination of minimum norm and gradient damping was applied to constrain the solution inversion of different subsets of the data and test inversions of synthetic data indicate that resolution is sufficient to substantiate the conclusions pertinent to the complex large scale structure of the subducted slab beneath the indonesian archipelago the tomographic images confirm previous evidence for regional slab penetration into the upper part of the lower mantle but suggest a more complex trajectory of mantle flow beneath indonesia the implied lateral variation in the shape of the upper mantle slab is generally in good agreement with inferences from seismicity the data reveal a seismic anomaly beneath the sunda arc which is detected to at least 1500 km in depth and forms the eastern end of a deep anomaly associated with the past subduction of lithosphere of the mesozoic tethys ocean below java the lithospheric slab is probably continuous from the earth s surface to the lower mantle but beneath sumatra the deep slab seems to be detached from the seismogenic slab the high resolution images suggest that the subducted slab is deflected in the transition zone beneath the banda arc and that the descending slabs form a spoon shaped structure north of the banda sea we detect the two opposing subducted slabs of the molucca sea plate this is consistent with previous studies but our images suggest that the westward subduction has a significantly steeper dip than the eastward subduction slab structure beneath the banda and molucca seas is explained in the context of the continent arc collision between australia and the southeast indonesian island arc and the arc arc collision between sangihe and halmahera inversion of traveltime residuals of direct s phases a novelty for this region largely confirms the inferences from the p wave data even though less detail is resolved

hummocky cross stratification and post vortex ripples length scales and hydraulic analysis duke 1987 argues that the structure reported by greenwood sherman 1986 as hummocky cross stratification from a shallow lacustrine environment is instead bedding formed by simple post vortex oscillation ripples his primary concern is with the length scale of the structures identified in box cores however using measured flow data it is shown here that existing models of bedform generation based upon wave orbital velocity orbital diameter and grain diameter do not support a simple post vortex ripple interpretation in particular the relative steepness of the structure refutes such an origin the structural characteristics of the lacustrine cores most closely match those associated with classic hummocky cross stratification and were produced under a combined oscillatory quasi steady flow field

a molecular and stable carbon isotopic study of lipids in late quaternary sediments from the arabian sea the distribution of apolar and polar lipids and their stable carbon isotopic compositions were determined for a number of sediment samples from different sites in the arabian sea lipids are mainly derived from planktonic archaea and a range of algae including haptophytes eustigmatophytes and diatoms the stable carbon isotopic compositions of compounds from diatoms highly branched isoprenoids fall into distinct groups suggesting other sources beside the diatom species rhizosolenia setigera for these compounds high amounts of sterol ethers which may be derived from diatoms were also detected a recently identified triterpenoid malabaricatriene was also present in high abundance in these samples the terrestrial input of lipids consists of n alkanes and their carbon isotopic compositions show that they are derived from aeolian dust input from the arabian peninsula the isotopic compositions of c37 alkenones from two cores during the last 15 ka is relatively constant and suggests that growth conditions for haptophyte algae averaged over 500 years did not change significantly over this period

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