precipitation of dolomite using sulphate reducing bacteria from the coorong region south australia significance and implications dolomite was successfully precipitated in culture experiments that simulated microbiogeochemical conditions prevailing during late stages of evaporation in ephemeral hypersaline dolomitic lakes of the coorong region south australia analyses of lake and pore water samples document rapid geochemical changes with time and depth in both dolomitic and non dolomitic lakes extremely high sulphate and magnesium ion concentrations in lake waters decline rapidly with depth in pore waters throughout the sulphate reduction zone whereas carbonate concentrations in pore waters reach levels up to 100 times those of normal sea water ultimately sulphate is totally consumed and no solid sulphate is recorded in the dolomitic lake sediments most probable number calculations of lake sediment samples record the presence of large populations of sulphate reducing bacteria whereas sulphur isotope analyses of lake water samples indicate microbial fractionation in all the lakes studied viable populations of microbes from the lake sediments were cultured in anoxic conditions in the laboratory samples were then injected into vials containing sterilized clastic or carbonate grains or glass beads immersed in a solution that simulated the lake water falls in the levels of sulphate and rising ph in positive vials were interpreted as indicating active bacterial sulphate reduction accompanied by increased concentrations of carbonate within 2 months sub spherical sub micron size crystals of dolomite identical to those of lake sediments were precipitated it is concluded that bacterial sulphate reduction overcomes kinetic constraints on dolomite formation by removing sulphate and releasing magnesium and calcium ions from neutral ion pairs and by generating elevated carbonate concentrations in a hypersaline strongly electrolytic solution the results demonstrate that bacterial sulphate reduction controls dolomite precipitation in both the laboratory experiments and lake sediments it is proposed that dolomite formation through bacterial sulphate reduction provides a process analogue applicable to thick platformal dolostones of the past where benthic microbial communities were the sole or dominant colonizers of shallow marine environments

the impact of depositional events and burial rate on carbonate silica diagenesis in a middle jurassic stromatactis carbonate mud mound sainte baume massif se france abstract understanding the processes and conditions of chertification in carbonates is a challenging problem to assess the marine silica cycle this contribution highlights parameters of internal silica recycling processes from their biogenic source to quartz cementation by describing a unique case of carbonate silica diagenesis in a mesozoic mud mound stromatactis carbonate mud mounds exposed in the sainte baume massif basse provence france developed in an outer shelf environment during the late aalenian concavum ammonite zone middle jurassic they form part of a cherty succession punctuated by hardgrounds and stratigraphically condensed intervals interpreted to record deepening episodes these mud mounds rich in siliceous sponge spicules and stromatactis are similar to their widespread paleozoic counterparts but are particular in being extensively silicified carbonate silica paragenesis forms a polymud fabric including four microcrystalline carbonates m1 to m4 all low mg calcite lmc five spar cements c1 to c5 c1 with high mg calcite hmc precursor mineralogy and four silica phases s1 to s4 s1 to s3 replacive chalcedony after opal ct s4 euhedral quartz cement m1 assumedly related to the degradative calcification of siliceous sponges forms a labyrinthine network into which m2 to m4 were infiltrated spar cements c1 to c3 include a successive decrease of 18 o at fairly invariable 13 c interpreted to represent marine to shallow burial conditions suggesting burial and successive transformation of marine bottom waters temperature estimation based on the average 18o value of c4 18o 7 9 indicates a temperature of around 50 c at a maximum burial depth of about 1000 meters replacive chalcedony s1 to s3 occurs between calcite cementation c3 and c4 in combination with traces of corrosion on c3 mg calcite was preferably replaced particularly the precursor of cement c1 that surrounds peloids of m2 and preserved some ghost structures corrosion and substrate selectivity suggest that acidification mg hydroxyl complexes and surface area are the triggers for flocculation of a silica gel because dissolution of opaline sponge spicules started almost contemporaneously with c1 the dissolved silica was retained in a connate fluid as phases c1 to c3 were precipitated and stagnant conditions prevailed for around 1 ma bulk 18o d values s1 s3 below the marine chert line together with the range of s1 s3 18o 18o smow 28 3 1 0 suggest silica flocculation in a shallow burial environment at temperatures of 25 30 c the establishment of acidic conditions might have been favored by sulfide oxidizing micro organisms numerical simulation of early diagenetic silica flux in such marine sediments is consistent with the interpretation that small grain size changes and fluid barriers that create diffusion controlled conditions such as those induced by stratigraphic condensation are key parameters to retain pore water dissolved silica over geologic time inversely paleozoic stromatactis carbonate mud mounds typically form part of large scale coarsening and shallowing upward successions that correspond to rapid burial these conditions support convergent pore water flux and drainage of pore water dissolved silica in the shallow burial realm hence spicule rich mounds should tend to silicify if they form part of a condensed section

on suspended barite and the oxygen minimum in the southern ocean particulate ba profiles were measured in the indian sector of the southern ocean the largest fraction 80 of this barium is present as barite microcrystals the profiles of total barium are characterized by a subsurface maximum between 200 and 500 m depth in the vicinity of the oxygen minimum highest barium values are found just south of the polar front while lowest values occur close to the antarctic divergence between the divergence and the polar front a tight inverse relationship is observed between oxygen in the oxygen minimum and barium in the barium maximum this relationship disappears north of the polar front since suspended barite is known to be of biological origin the correlation of barite with oxygen suggests that the observed decrease of oxygen in the oxygen minimum between the divergence and the polar front is due to local consumption of oxygen it is proposed that deep low oxygen water is advected towards the divergence where upwelling occurs and where this water subsequently partly spreads out to the north north east as entrained by the antarctic circumpolar current oxidation of locally produced organic matter with which barite crystals are associated consumes oxygen and sets free individual discrete barites as a result oxygen decreases and barite increases away from the divergence with barite integrating former biological processes

marine sediment acoustics new field and laboratory data indicate that the assumption of a constant q or equivalently an attenuation coefficient that depends on the first power of frequency is unacceptable in the case of nearly all marine sediments the fluid component of marine sediments causes various forms of viscous damping that are always frequency dependent in coarser sediments overall motion of the fluid field relative to the skeletal frame causes a strong frequency dependence that depends on permeability and the tortuosity of the intergranular pores in the finer sediments local viscous losses occur near the intergranular contacts producing a viscoelastic response similar to the squeeze film phenomenon that is well known in lubrication theory both kinds of viscous damping as well as frictional losses at the grain contacts can be included in the generalized biot model which has been used to describe the acoustical response of marine sediments in this paper we summarize recent field data which illustrate the wide spread of q values that are to be expected and present some new experimental data that demonstrate both kinds of viscous damping mentioned above finally we use the model to estimate the response of a p wave based on laboratory measurements of torsional vibrations a simple mathematical model is used to establish the connection between these two modes of motion

the tectonic evolution of the fennoscandian border zone in denmark abstract the fennoscandian border zone is a complex tectonic zone defining the border between the stable fennoscandian baltic shield and the metastable danish basin and polish trough it forms the northwestern part of the tornquist teisseyre lineament one of the major european tectonic sutures intricate tectonic movements took place within the fennoscandian border zone from early paleozoic to recent time it is postulated that its evolution was dominated during the early palaeozoic by tensional tectonics and during the late paleozoic by dextral wrench movements the latter led to the development of curvilinear faults and the subsidence of pull apart basins transtensional stresses governing the triassic to early cretaceous evolution of the fennoscandian border zone induced the differential subsidence of rift basins during the late cretaceous and early cenozoic dextral transpressional stresses induced the partial inversion of mesozoic basins associated with the fennoscandian border zone this is reflected by the uplift of a major anticlinorium over which cretaceous strata became progressively truncated whilst adjacent areas developed into late cretaceous early tertiary depocentres basin inversion diminishes to the northwest along the fennoscandian border zone and disappears in the skagerrak area

diagenesis of silica rich mound bedded chalk the coniacian arnager limestone denmark abstract the coniacian arnager limestone formation is exposed on the danish island of bornholm in the baltic sea it is composed of mound bedded siliceous chalk and x ray diffraction and scanning electron microscopy indicate a content of 30 70 insoluble minerals including authigenic opal ct quartz clinoptilolite feldspars calcite dolomite and barite opal ct and clinoptilolite are the most common and constitute 16 53 and 2 9 respectively the content of insoluble minerals varies laterally both within the mounds and in planar beds and the opal ct content varies by up to 10 vertically the mounds consist of two microfacies spiculitic wackestone and bioturbated spiculitic wackestone containing 10 22 and 7 12 moulds after spicules respectively subsequent to deposition and shallow burial dissolution of siliceous sponge spicules increased the silica activity of the pore water and initiated precipitation of opal ct the opal ct formed at temperatures around 17 c the precipitation lowered the silica activity and the si al ratio of the pore water resulting in precipitation of clinoptilolite feldspar and smectite calcite formed synchronously with the latest clinoptilolite minor amounts of quartz precipitated in pore water with low silica activity during maximum burial probably to depths of 200 250 m the dissolution of sponge spicules and decomposition of the sponge tissue also resulted in the release of ba2 sr2 mg2 ca2 and co32 facilitating precipitation of barite and dolomite precipitation of especially opal ct reduced the porosity to an average of 40 and cemented the limestone the study highlights the diagenetic pathways of bio siliceous chalk and the effects on preservation of porosity and permeability

the relation of a coastal environment to early diagenetic clinoptilolite zeolite formation new data from the late cretaceous european basin abstract clinoptilolite an authigenic mineral of the zeolite group is commonly considered as a product of rhyolitic volcanic glass transformation during diagenesis of carbonate pelagic hemipelagic sediments of cretaceous paleogene age another subordinate way of clinoptilolite formation that has been suggested in the literature is its precipitation during diagenetic transformation of carbonate sediments enriched with biogenic silica the observations concerning transformation of the latter into zeolite are scarce and mostly based on cretaceous pelagic hemipelagic and shallow marine deposits and post cretaceous sediments in which there was no volcanic material the mechanism of diagenetic clinoptilolite formation in volcanic free sediments as well as the role of the depositional setting in its precipitation is not well understood in carbonates of the nw part of the european basin west side of the ysogory dobrogea archipelago studied here the clinoptilolite is associated with opal ct from the dissolution of sponge spicules and a detrital clays are documented for the first time in a cretaceous coastal environment the carbonates were deposited in a coastal environment which was under the influence of weak currents delivering sponge spicules biogenic opal from the offshore zone and the terrestrial input was transported by rivers from a neighboring island the lush plant vegetation with numerous pteridophytes and conifers within a warm sub tropical or tropical and humid climate enhanced the terrestrial weathering of clays and feldspars this unique combination of elevated silica concentrations from sponge spicules dissolution and aluminum availability from terrestrial weathering of feldspars in a subtropical climate during the early diagenesis combined with alkalinity triggered by organic matter decomposition enhanced the clinoptilolite formation a few centimeters below the seabed the investigation demonstrates a novel route by which pore fluids enriched with silica and aluminum initiate clinoptilolite formation during the very early stage of diagenesis a few centimeters below the seafloor the clinoptilolite distribution in late cretaceous silica rich deposits with no volcanic input of the european basin is always associated with opal ct from sponge spicules and elevated terrestrial input clays taking into account the distinctive campanian maastrichtian sedimentation in the epicontinental european basin composed almost exclusively of pure pelagic carbonates the depositional settings in which the silica and aluminum were available in pore waters was restricted to the part of the basin influenced by terrestrial input this leads to the conclusion that clinoptilolite formation in volcanic free sediment is an indicator of not only enhanced sponge silica availability but also the close proximity of the source area

evolution of porewater composition through time in limestone aquifers salinity and d h of fluid inclusion water in authigenic minerals jurassic of the eastern paris basin france past water circulations can significantly reduce the porosity and permeability of marine limestones this is particularly the case in the middle bathonian bajocian to upper oxfordian jurassic limestones from the eastern border of the paris basin the knowledge of the timing the temperature and composition of paleowaters is essential to model the hydrological evolution in this area where the callovian oxfordian claystones are studied for the storage of nuclear wastes in this way fluid inclusions hosted in low temperature 60 c authigenic calcite quartz and celestite crystals were analyzed by raman spectroscopy and mass spectrometry to determine the chlorinity and d h ratios chlorinity measurements mmol cl per liter of water in fluid inclusions trapped in authigenic crystals during the late jurassic early cretaceous period revealed unexpected high values up to 3800 mmol l 1 indicating that brines were involved in some of the diagenetic crystallization processes by contrast fluid inclusions in calcite cements of cenozoic age within the oxfordian limestones have low cl concentration less than 150 mmol l 1 thus showing that a dilution event caused by water infiltrations during the cretaceous uplift of this part of the basin has flushed out the original saline porewater by coupling d of fluid inclusion with 18o of calcite crystals we estimate that calcite precipitation occurred at temperatures between 25 and 53 c the hydrogen isotope composition of calcite forming water is different between the middle jurassic d ranging from 20 to 35 8 v smow and the overlying oxfordian limestone d from 59 5 to 44 8 v smow present day groundwaters are also of distinct composition on both sides of the oxfordian claystones indicating that limestone aquifers underwent independent hydrologic evolutions since the early diagenetic jurassic cementation

tomographic inversion for sediment parameters in shallow water this article discusses inversions for bottom geoacoustic properties using broadband acoustic signals obtained from explosive sources the experimental data used for the inversions are sus charge explosions acquired on a vertical hydrophone array during the shelf break primer experiment conducted south of new england in the middle atlantic bight in august 1996 the sus signals were analyzed for their time frequency behavior using wavelets the group speed dispersion curves were obtained from the wavelet scalogram of the sus signals a genetic algorithm ga was used for the inversion of sound speeds in the water column and compressional wave speeds in the sediment layers the variations in the sound speeds in the water column were represented using empirical orthogonal functions eofs a range independent normal mode routine was used to construct the replica fields corresponding to the parameters comparison of group speeds for modes 1 to 9 and for a range of frequencies 8 to 200 hz was used to arrive at the best parameter fit an efficient hybrid optimization scheme using the ga and a levenberg marquardt algorithm is presented linear perturbation methods were also used to fine tune the inversions and to obtain resolution and variance estimates analysis was also done to compute the degree of convergence of each of the parameters by explicitly calculating the hessian matrices numerically a posteriori estimation of mean and covariance was also done to obtain error estimates group speeds for the inverted sound speed fields provide an excellent match to the experimental data the inverted sediment compressional speed profile compares well with in situ measurements

the structure of raylike arrivals in a shallow water waveguide acoustic remote sensing of the oceans requires a detailed understanding of the acoustic forward problem the results of a shallow water transmission experiment between a vertical array of sources and a vertical array of receivers are reported the source array is used to provide additional degrees of freedom to isolate and track raylike arrivals by beamforming over both source and receiver arrays the coordinated source receiver array processing procedure is presented and its effectiveness in an example of tracking raylike arrivals in a fluctuating ocean environment is shown many of these arrivals can be tracked over an hour or more and show slowly varying amplitude and phase the use of a double beamforming algorithm lays the foundation for shallow water acoustic remote sensing using travel time and source and receive angles of selected eigenrays

silica diagenesis i solubility controls abstract the diagenetic sequence of silica is examined in terms of several thermodynamic and kinetic concepts the relationship between solubility and surface area or particle size is sufficient to explain simple opal a opal ct quartz transformations suggesting that the role of temperature and other physical parameters may not be as critical as previously thought complexation and adsorption in an impure system when added to the model allow for possibilities of opal a transformation directly to quartz of clay and zeolite formation from an opaline silica source and of variations in silica transformation rates due to presence of impurities in the system

authigenic zeolites in late pleistocene sediments of the south atlantic angola basin two types of authigenic zeolites from late pleistocene hemipelagic sediments of the south atlantic were examined by xrd and sem analysis the xrd characteristics and the thermal behaviour of the zeolites suggest that type 1 is composed of clinoptilolite type 2 was identified as mordenite based on morphological features and qualitative elemental composition their authigenic nature is suggested from the shape of the crystals and their growth on and within foraminifera tests volcanic ash material acting as precursor minerals to zeolite formation could not be found nor were the zeolites directly related to siliceous remains an authigenesis from pore waters must be assumed mineral stabilities for amorphous sio2 and zeolites were calculated with the computer program solmineq88 interstitial waters proved to be oversaturated throughout the core in respect to all zeolites considered biogenic opal represents the limiting solid phase for si concentrations in pore waters therefore the dissolution of opal is regarded as the main source of si for interstitial waters below 9 m core depth where opal is only present in traces detrital feldspars and the zeolites themselves are affected by dissolution this may indicate the metastable nature of the zeolites also corroborated by the presence of two almost isochemical members of the same zeolite group

high resolution geoacoustic inversion in shallow water a joint time and frequency domain technique high resolution geoacoustic data are required for accurate predictions of acoustic propagation and scattering in shallow water since direct measurement of geoacoustic data is difficult time consuming and expensive inversion of acoustic data is a promising alternative however the main problem encountered in geoacoustic inversion is the problem of uniqueness i e many diverse geoacoustic models can be made to fit the same data set a key and perhaps unique aspect of this approach is the combination of data analysis in both the space time and the space frequency domains this combination attempts to ameliorate the uniqueness problem by exploiting as much independent data as possible in order to meet the stringent requirements of high spatial resolution and uniqueness an entire method has been developed including a new measurement technique processing analysis technique and inversion strategy these techniques are described and then illustrated with a shallow water data set sound speed gradients in the upper few meters of the sub bottom appear to be much higher one order of magnitude than generally assumed and although often ignored a large density gradient was observed in the top layer that played an acoustically significant role

channelling versus inversion origin of condensed upper cretaceous chalks eastern isle of wight uk evidence from regional stratigraphical patterns in santonian campanian chalk is used to infer the presence of a very broad channel system 5 km across with a depth of at least 50 m running nnw sse across the eastern isle of wight only the western part of the channel wall and fill is exposed within this channel were smaller erosional structures

modeling ocean bottom reflection loss measurements with the plane wave reflection coefficient ocean bottom reflection loss has been measured at an abyssal plain site in the northeast pacific ocean the layer of unconsolidated sediment at this site is thin less than 200 m and the near surface sediments are composed of strongly reflecting sandy turbidites in consequence the surficial sediments and the relatively shallow substrate must be accounted for in describing the bottom loss measurements the bottom loss has been modeled in this paper using the plane wave reflection coefficient calculated for a geoacoustic model of the bottom developed from seismic profiling experiments carried out at the site in the model the sediment column is described by fluid layers with a relatively small value of attenuation and a large value of sound speed gradient in the surficial layer and the substrate is assumed to be a solid the bottom loss measurements are presented in 1 3 octave bands at 40 80 and 160 hz the results are well modeled at small grazing angles 20 where the interaction is confined to the surficial sediments at larger grazing angles the importance of including a solid substrate is demonstrated

turning point filters analysis of sound propagation on a gyre scale acoustic transmissions from pioneer seamount off california to a vertical array near hawaii are analyzed using a technique which we call a turning point filter the observables travel time and axial inclination are interpreted in terms of the ocean sound speed field the method permits a uniform treatment of the arrival pattern from the early ray like arrivals to the late mode like arrivals including peak arrivals which cannot be identified as either rays or modes an adiabatic range dependence is assumed and wentzel kramers brillouin jeffreys formalism is applied

barium peaks at glacial terminations in sediments of the equatorial atlantic ocean relicts of deglacial productivity pulses in sediment cores recovered from oligotrophic settings of the western and eastern north equatorial atlantic ocean ceara rise and sierra leone rise distinct peaks of excess barium were detected at glacial interglacial transitions these ba maxima are unrelated to any other potential productivity proxy e g organic carbon carbonate or opal moreover they coincide with minima in organic carbon contents despite the lack of correlation between excess barium and organic carbon we ascribe these ba spikes to pulses of productivity that occurred during glacial interglacial transitions the discrepancy between barium and organic carbon in these transitional sediment intervals is attributed to the action of downward progressing oxidation fronts during deglacial nonsteady state depositional conditions the oxidation fronts were initiated due to the overall low sedimentation rates prevailing in the study areas and an increase in bottom water oxygen concentrations at the onset of enhanced nadw production during interglacial periods the fronts led to a very efficient oxidation of the organic carbon initially present leaving peaks in solid phase barium as relicts of these short time productivity events this assumption is supported by the depth arrangement of the solid phase peaks of ba fe and mn along the 6 5 oxygen isotope stage boundary in sediments of the ceara rise which show striking similarities to the distribution of these elements in oxidized sapropel intervals in eastern mediterranean sediments it remains unclear whether productivity was proportional to the magnitude of the baexcess maxima possibly higher dissolved ba concentrations in intermediate and deep waters during glacial interglacial transitions caused the precipitation of barite to increase out of proportion of the postulated deglacial productivity pulses

clinoptilolite as a new proxy of enhanced biogenic silica productivity in lower miocene carbonate sediments of the bahamas platform isotopic and thermodynamic evidence abstract massive clinoptilolite authigenesis was observed at about 1105 meters below sea floor mbsf in lower miocene well compacted carbonate periplatform sediments from the great bahama bank ocean drilling program odp leg 166 site 1007 the diagenetic assemblage comprises abundant zeolite crystallized within foraminifer tests and sedimentary matrix as well as mg smectites in carbonate rich deposits the formation of the zeolite requires a supply of silica thus the objective of the study is to determine the origin of the silica supply its diagenetic evolution and consequently the related implications on interpretation of the sedimentary record in terms of local or global paleoceanographic change for lack of evidence for any volcaniclastic input or traces of si enriched deep fluids circulation an in situ biogenic source of silica is validated by isotopic data and chemical modeling for the formation of such secondary minerals in shallow water carbonate sequences geochemical and strontium isotopic data clearly establish the marine signature of the diagenetic zeolite as well as its contemporaneous formation with the carbonate deposition sr model ages of 19 6 23 2 ma the test of saturation for the pore fluids specifies the equilibrium state of the present mineralogical assemblage seawater rock modeling specifies that clinoptilolite precipitates from the dissolution of biogenic silica which reacts with clay minerals the amount of silica opal a involved in the reaction has to be significant enough at least 10 wt to account for the observed content of clinoptilolite occurring at the most zeolite rich level modeling also shows that the observed amount of clinoptilolite 19 reflects an in situ and short term reaction due to the high reactivity of primary biogenic silica opal a until its complete depletion the episodic occurrence of these well lithified zeolite rich levels is consistent with the occurrence of seismic reflectors particularly the p2 seismic sequence boundary located at 1115 mbsf depth and dated as 23 2 ma the age range of most zeolitic sedimentary levels biostratigraphic ages of 21 5 22 ma correlates well with that of the early miocene glaciation mi 1 and mi 1a global events thus the clinoptilolite occurrence in the shallow carbonate platform environment far from volcanogenic supply or in other sensitive marine areas is potentially a significant new proxy for paleoproductivity and oceanic global events such as the miocene events which are usually recognized in deep sea pelagic sediments and high latitude deposits

a compositional classification for grain assemblages in fine grained sediments and sedimentary rocks reply abstract a tripartite compositional classification is proposed for sediments and sedimentary rocks that have grain assemblages with greater than 50 percent of a weight or volume of particles smaller than 62 5 m 4 phi tarl terrigenous argillaceous contains a grain assemblage dominated by more than 75 percent of particles of extrabasinal derivation including grains derived from continental weathering and also volcanogenic debris carl calcareous argillaceous contains less than 75 percent of particles of extrabasinal derivation debris and among its intrabasinal grains contains a preponderance of biogenic carbonate particles including carbonate aggregates sarl siliceous argillaceous contains less than 75 percent of particles of extrabasinal derivation and contains a preponderance of biogenic siliceous particles over carbonate grains these three classes of fine grained particulate sediments and rocks effectively separate materials that have distinct depositional settings and systematic contrasts in organic matter content and minor grain types in the subsurface the grain assemblages that define these classes follow contrasting and predictable diagenetic pathways that have significant implications for the evolution of bulk rock properties and thus assigning a fine grained rock to one of these classes is an important first step for predicting its economic and engineering qualities for purposes of description these three class names can be joined to modifier terms denoting rock texture more precise compositional divisions specific grain types of notable importance and diagenetic features

the effect of grain coating microquartz on preservation of reservoir porosity clay coatings have been widely accepted by many workers as an explanation for preserving high porosity in deeply buried sandstones but few workers have realized that similar effects can be produced by microcrystalline quartz coatings this phenomenon can be expected only under special circumstances but in such cases it can have profound consequences for exploration in the central graben area of the southern north sea unusually high porosity 20 27 and permeability 100 1000 md are found in certain zones in upper jurassic sandstones at depths of 3 4 4 4 km the porosity in these zones is 5 15 higher than expected based on average porosity depth trends from brent and haltenbanken sandstones we propose that the high porosity is due to continuous grain coatings of euhedral microcrystalline quartz crystals that are 0 1 2 m thick the distribution of microcrystalline quartz coatings is controlled by the presence of siliceous sponge spicules rhaxella which implies a sedimentological control on the reservoir quality we present a thermodynamic model showing how continuous microcrystalline quartz coatings inhibit development of no mal macrocrystalline quartz overgrowths sourced mainly from stylolites high porosities in parts of various upper jurassic oil fields ula and gyda have previously been explained by inhibition of quartz cementation by early hydrocarbon charge we suggest that the microcrystalline quartz coatings provide a more plausible explanation

porosity reduction during diagenesis of diatomaceous rocks with lithification and burial diatomaceous rock transforms from opal a to opal ct and then quartz this study documents two different patterns of porosity reduction and their associated mineralogical and density changes using samples from the monterey formation california samples that have one set of properties are called group 1 and those showing other trends are assigned to group 2

a dolomitized diatomite in an oligocene miocene deep sea fan succession gonfolite lombarda group northern italy abstract an unique 5 10 cm thick layer of a dolomitized diatomite which contains traces of volcanic material occurs intercalated between terrigenous mudstones thin bedded turbidites and pebbly mudstones of the montana member burdigalian of the oligocene miocene gonfolite lombarda group south alpine molasse dolomite formation took place during early diagenesis under conditions of sulfate reduction as suggested by the strongly negative 13 c values 13 pdb stereoscan electron microscope observations show that the dolomite grew as a pore filling cement enveloping deeply corroded diatom frustules the dolomitized diatomite can be correlated with coeval occurrences of biosiliceous tripoli and cineritic deposits in the northern apennines and the southern alps its preservation as a unique and distinct layer in the deep sea fan facies of the gonfolite lombarda group appears to reflect a particular event and suggests that it was deposited rapidly rather than during a longer time interval of slow pelagic sedimentation

geoacoustic inversion with two source receiver arrays in shallow water a geoacoustic inversion scheme based on a double beamforming algorithm in shallow water is proposed and tested double beamforming allows identification of multi reverberated eigenrays propagating between two vertical transducer arrays according to their emission and reception angles and arrival times analysis of eigenray intensities yields the bottom reflection coefficient as a function of angle of incidence by fitting the experimental reflection coefficient with a theoretical prediction values of the acoustic parameters of the waveguide bottom can be extracted the procedure was initially tested in a small scale tank experiment for a waveguide with a plexiglas bottom inversion results for the speed of shear waves in plexiglas are in good agreement with the table values a similar analysis was applied to data collected during an at sea experiment in shallow coastal waters of the mediterranean bottom reflection coefficient was fitted with the theory in which bottom sediments are modeled as a multi layered system retrieved bottom parameters are in quantitative agreement with those determined from a prior inversion scheme performed in the same area the present study confirms the interest in processing source receiver array data through the double beamforming algorithm and indicates the potential for application of eigenray intensity analysis to geoacoustic inversion problems

a comparison between excess barium and barite as indicators of carbon export 1 since dymond et al 1992 proposed the paleoproductivity algorithm based on bio ba which relies on a strong correlation between ba and organic carbon fluxes in sediment traps this proxy has been applied in many paleoproductivity studies barite the main carrier of particulate barium in the water column and the phase associated with carbon export has also been suggested as a reliable paleoproductivity proxy in some locations we demonstrate that baexcess total barium minus the fraction associated with terrigenous material frequently overestimates babarite barium associated with the mineral barite most likely due to the inclusion of barium from phases other than barite and terrigenous silicates e g carbonate organic matter opal fe mn oxides and hydroxides a comparison between overlying oceanic carbon export and carbon export derived from baexcess shows that the dymond et al 1992 algorithm frequently underestimates carbon export but is still a useful carbon export indicator if all caveats are considered before the algorithm is applied babarite accumulation rates from a wide range of core top sediments from different oceanic settings are highly correlated to surface ocean 14 c and chlorophyll a measurements of primary production this relationship varies by ocean basin but with the application of the appropriate f ratio to 14 c and chlorophyll a primary production estimates the plot of babarite accumulation and carbon export for the equatorial pacific atlantic and southern ocean converges to a global relationship that can be used to reconstruct paleo carbon export index terms 3022 marine geology and geophysics marine sediments processes and transport 4267 oceanography general paleoceanography 4825 oceanography biological and chemical geochemistry keywords paleoproductivity barite export production excess barium marine sediments citation eagle m a paytan k r arrigo g van dijken and r w murray a comparison between excess barium and barite as indicators of carbon export paleoceanography 18 1 1021 doi 10 1029 2002pa000793 2003

short range travel time geoacoustic inversion with vertical line array this paper presents travel time geoacoustic inversion of broadband data collected on a vertical line array at short range of 230 m during the shallow water 2006 experiments a ray tracing method combined with a hybrid optimization algorithm that utilizes differential evolution and downhill simplex was used for the inversion of sediment properties the ocean sound speed profile and geometric parameters were inverted prior to the sea bottom properties to account for the temporally variable ocean environment the sediment sound speed and thickness estimates are consistent with in situ measurements and matched field inversion results of longer range data from the experiment

mathematical approach to hydrocarbon generation history and source rock potential in the thrace basin turkey abstract a mathematical approach is presented to hydrocarbon generation history and source rock potential in the thrace basin which is one of the most important hydrocarbon provinces in turkey the basin formed by extension in late middle eocene to latest oligocene times and contains thousands of metres of thick marine clastic sediments deposited as turbiditic sequences over a metamorphic and crystalline basement among these sequences the so ucak and ceylan formations upper eocene lower oligocene mezardere formation lower oligocene upper oligocene and dani men and osmancik formations upper oligocene lower miocene contain potential source rocks four wells were selected to assess the thermal history of the basin and estimate the source rock potential and the timing of hydrocarbon generation cohen s method was used for the computations and the time temperature indices were calculated with and without the cooling effect of the uplift the results indicate that of the potential source rocks the ceylan and the mezardere formations are found to have probable source rock potential in the thrace basin and that the timing of hydrocarbon generation varies between 22 and 4 5 ma for these formations in different wells

activity diagrams for clinoptilolite susceptibility of this zeolite to further diagenetic reactions clinoptilolite is the predominant zeolite in diagenetically altered volcanic rocks at yucca mountain nevada having formed by posteruptive reactions of ground water with vitric tuffs in the pyroclastic deposits compositional variations of clinoptilolites in the fractured and zeolitized tuffs not presently in contact with ground water and the vulnerability of zeolites to burial diagenesis raise questions about the long term stability of clinoptilolite equilibrium activity diagrams were calculated for clinoptilolite solid solutions in the seven component system ca na k mg fe al si plus h sub 2 o employing available thermodynamic data for related minerals aqueous species and water stability fields are portrayed graphically assuming the presence of potassium feldspar saponite and hematite and using ranges of activities for sio sub 2 and al sup 3 defined by the saturation limits for several silica polymorphs gibbsite kaolinite and pyrophyllite the clinoptilolite stability field broadens with increasing atomic substitution of ca for na and k for ca reaches a maximum for intermediate activities of dissolved al and decreases with increasing temperature the thermodynamic calculations show that ground water of the sodium bicarbonate type is approximately in equilibrium at 25c with calcite and several zeolites including heulandite and calcic clinoptilolite mg rich clinoptilolites are stabilized in ground water depleted in ca sup 2 the activity diagramsmore indicate that prolonged diagenetic reactions with ground water depleted in al enriched in na or ca and heated by the thermal envelope surrounding buried nuclear waste may eliminate sorptive calcic clinoptilolites in fractured tuffs and underlying basal vitrophyre less

the impact of sediment provenance on barium based productivity estimates abstract biogenic barium in marine sediments has been suggested to be a reliable proxy of export productivity from the surface ocean and algorithms have been developed to link these properties however problems arise when the proposed algorithms are applied to predominantly terrigenous sediments a major source of error is incorrect estimates of the terrigenous ba al ratio in normative calculations of the amount of biogenic barium in the sediment compared to an often used global average ba al ratio much better results can be obtained by estimating the terrigenous ba al ratio from exponential regression of the ba al ratios of surface sediments obtained from continental slope transects this method has been applied to surface sediments from the chilean continental slope the calculated regional terrigenous ba al ratios could be verified with purely terrigenous samples from chilean rivers the resulting accumulation rates of biogenic barium on the chilean continental slope reliably reproduce the regional pattern of primary productivity in the southern peru chile current indicating the potential of biogenic barium as a useful paleo productivity proxy

stratigraphically controlled silicification in danian chalk and its implications for reservoir properties southern danish central graben abstract the effect of silica on reservoir quality in chalk is subject to continuing debate in particular the stratigraphic variations in silica content within the chalk matrix have not been addressed sufficiently in this study a new approach is applied to constrain silica variability in reservoir chalk utilizing hand held x ray fluorescence hh xrf on samples from four maastrichtian danian cores from hydrocarbon producing fields in the southern danish central graben the results indicate a significant lateral and stratigraphic variability in silica concentrations across the study area data display a common stratigraphic signature in all wells however with maximum silica concentrations and minimum porosities occurring in the lower part of the danian ekofisk formation correlation between hh xrf quantified silica concentrations and biostratigraphic data indicates the synchronous onset of an at least semi regional silica event during the mid danian nannofossil zones nntp2f g to nntp4a d whereas the upper boundary of the peak silica unit is poorly constrained generally stratigraphic trends in silica concentrations appear to be negatively correlated with porosity trends however comparison between the hh xrf quantified silica content and reservoir data porosity permeability estimated pore radius and calculated specific surface area shows poor correlation indicating that silica content within the ekofisk reservoir is not the only factor controlling the reservoir quality unknown complex diagenetic interactions between calcite silica and clay probably influence the reservoir properties by promoting calcite cementation in stratigraphically controlled zones making the ekofisk reservoir much less predictable than the underlying maastrichtian tor formation

the korudag anticlinorium in the south thrace basin northwest turkey a super giant petroleum trap complex the sedimentary sequence of the south thrace basin northwest turkey comprises upper cretaceous holocene sediments in this basin the korudag anticlinorium which is the subject of this study is located between the aegean sea in the west and the sea of marmara to the east the anticlinorium which is approximately 300 km 186 mi long and 40 km 25 mi wide was formed by effects of the neotethys subduction accretion complex and istranca massif collision during the late early miocene the korudag anticlinorium was deformed to its present day structure by the oldest splay of the north anatolian fault upper middle miocene and the northern branch of the north anatolian fault naf n not earlier than 200 ka organic geochemical analysis oil and gas to source rock correlation and basin modeling studies suggest that the korudag anticlinorium should be charged by hydrocarbons generated from the karaagac ceylan regionally and mezardere formations gas and oil are being produced from the korudag anticlinorium and its subparallel anticlines in the north marmara degirmenkoy seymen cayirdere karacali yulafli tekirdag sevindik and vakiflar gas plus oil fields mapping done as part of this study indicates that the korudag anticlinorium has not yet been tested and explored comprehensively

joint time frequency domain inversion of reflection data for seabed geoacoustic profiles and uncertainties this paper develops a joint time frequency domain inversion for high resolution single bounce reflection data with the potential to resolve fine scale profiles of sediment velocity density and attenuation over small seafloor footprints approximately 100 m the approach utilizes sequential bayesian inversion of time and frequency domain reflection data employing ray tracing inversion for reflection travel times and a layer packet stripping method for spherical wave reflection coefficient inversion posterior credibility intervals from the travel time inversion are passed on as prior information to the reflection coefficient inversion within the reflection coefficient inversion parameter information is passed from one layer packet inversion to the next in terms of marginal probability distributions rotated into principal components providing an efficient approach to partially account for multi dimensional parameter correlations with one dimensional numerical distributions quantitative geoacoustic parameter uncertainties are provided by a nonlinear gibbs sampling approach employing full data error covariance estimation including nonstationary effects and accounting for possible biases in travel time picks posterior examination of data residuals shows the importance of including data covariance estimates in the inversion the joint inversion is applied to data collected on the malta plateau during the scarab98 experiment

inversion for sediment geoacoustic properties at the new england bight this article discusses inversions for bottom geoacoustic properties using broadband acoustic signals obtained from explosive sources two different inversion schemes for estimating the compressional wave speeds and attenuation are presented in this paper in addition to these sediment parameters source receiver range is also estimated using the arrival time data the experimental data used for the inversions are sus charge explosions acquired on a vertical hydrophone array during the shelf break primer experiment conducted south of new england in the middle atlantic bight in august 1996 the modal arrival times are extracted using a wavelet analysis in the first inversion scheme arrival times corresponding to various modes and frequencies from 10 to 200 hz are used for the inversion of compressional wave speeds a hybrid inversion scheme based on a genetic algorithm ga is used for the inversion in an earlier study potty et al j acoust soc am 108 3 973 986 2000 have used this hybrid scheme in a range independent environment in the present study results of range dependent inversions are presented the sound speeds in the water column and bathymetry are assumed range dependent whereas the sediment compressional wave speeds are assumed range independent the variations in the sound speeds in the water column are represented using empirical orthogonal functions eofs the replica fields corresponding to the unknown parameters were constructed using adiabatic theory in the second inversion scheme modal attenuation coefficients are calculated using modal amplitude ratios the ratios of the modal amplitudes are also calculated using time frequency diagrams a ga based inversion scheme is used for this search finally as a cross check the computed compressional wave speeds along with the modal arrival times were used to estimate the source receiver range the inverted sediment properties and ranges are seen to compare well with in situ measurements and historical data

acoustic travel time perturbations due to shallow water internal waves and internal tides in the barents sea polar front theory and experiment during august 1992 a combined acoustics physical oceanography experiment was performed to study both the acoustical properties and the ocean dynamics of the barents sea polar front in the region near bear island oceanographic observations from shipboard hydrography and moored sensors allowed the construction of the internal wave frequency spectrum for the area a rapidly sampled tomographic section from a 224 hz 16 hz bandwidth acoustic source to a 16 element vertical receiving array enabled the monitoring of travel time fluctuations over the internal wave frequency band to describe the measured acoustic fluctuations theoretical expressions have been developed for the travel time variances which are functions of the internal wave oceanographic field the local acoustic propagation characteristics and the acoustical system s properties both ray and mode theory expressions are generated as the experiment was performed in shallow water and both ray and mode arrivals were resolvable comparison of the

geoacoustic inversion of ambient noise a simple method the vertical directionality of ambient noise is strongly influenced by seabed reflections therefore potentially geoacoustic parameters can be inferred by inversion of the noise in this approach using vertical array measurements the reflection loss is found directly by comparing the upward with the downward going noise theory suggests that this simple ratio is in fact the power reflection coefficient potentially a function of angle and frequency modeling and parameter searching are minimized and the method does not require a detailed knowledge of the noise source distribution the approach can handle stratified environments and is believed to tolerate range dependence experimental data from five sites four in the mediterranean one on the new jersey shelf are described most of the mediterranean sites had temporally varying noise directionality yet yielded the same reflection properties as one would hope one site was visited in conditions of very low surface noise this paper concentrates on an experimental demonstration of the feasibility of the method and data quality issues rather than automatic search techniques for geoacoustic parameters

stylolites porosity depositional texture and silicates in chalk facies sediments ontong java plateau gorm and tyra fields north sea comparison of chalk on the ontong java plateau and chalk in the central north sea indicates that whereas pressure dissolution is controlled by effective burial stress pore filling cementation is controlled by temperature effective burial stress is caused by the weight of all overlying water and sediments as counteracted by the pressure in the pore fluid so the regional overpressure in the central north sea is one reason why the two localities have different relationships between temperature and effective burial stress in the chalk of the ontong java plateau the onset of calcite silicate pressure dissolution around 490 m below sea floor bsf corresponds to an interval of waning porosity decline and even the occurrence of proper stylolites from 830 m bsf is accompanied by only minor porosity reduction because opal is present the pore water is relatively rich in si which through the formation of ca silica complexes causes an apparent super saturation of ca and retards cementation the onset of massive pore filling cementation at 1100 m bsf may be controlled by the temperature dependent transition from opal ct to quartz in the stylolite bearing chalk of two wells in the gorm and tyra fields the nannofossil matrix shows recrystallization but only minor pore filling cement whereas microfossils are cemented cementation in gorm and tyra is thus partial and has apparently not been retarded by opal controlled pore water a possible explanation is that due to the relatively high temperature silica has equilibrated to quartz before the onset of pressure dissolution and thus in this case dissolution and precipitation of calcite have no lag this temperature versus effective burial stress induced difference in diagenetic history is of particular relevance when exploring for hydrocarbons in normally pressured chalk while most experience has been accumulated in the over pressured chalk of the central north sea

diagenetic clinoptilolite and opal ct from the middle eocene wittering formation isle of wight u k abstract thinly interbedded estuarine sandstones and mudstones in the middle eocene wittering formation bracklesham group isle of wight contain authigenic clinoptilolite opal ct and possibly authigenic smectite over a thickness of 8 5 m the clinoptilolite and opal ct cements have resulted in these beds being the only ones tightly cemented in the wittering formation the rest being soft sands and muds the unit contains abundant siliceous sponge spicules many of which are preserved as voids and were the likely source of the opal ct the presence of an organic rich rooted paleosol histosol immediately overlying the unit is believed to have contributed significantly to the early diagenetic history of the estuarine sediments in particular the formation of zeolite although the ph and dissolved silica of unmodified seawater are too low for zeolite formation high concentrations of dissolved silica are believed to have resulted from dissolution of siliceous sponge spicules opal a and formation of silica organic acid complexes organic acid dissolution of feldspars absent from the zeolite bearing interval is the most probable source of alumina and cations for zeolite formation ree data show that volcanic ash was never present and cannot therefore have been the source of the zeolite this investigation therefore demonstrates a novel route by which the pore fluid chemistry required for zeolite formation can be achieved

remote sensing of sediment density and velocity gradients in the transition layer the geoacoustic properties of marine sediments e g bulk density and compressional velocity commonly exhibit large variations in depth near the water sediment interface this layer termed the transition layer is typically of o 10 1 100 m in thickness depth variations within the transition layer may have important implications for understanding and modeling acoustic interaction with the seabed including propagation and reverberation in addition the variations may contain significant clues about the underlying depositional or erosional processes characteristics of the transition layer can be measured directly e g coring or remotely remote measurements have the advantage of sampling without disturbing the sediment properties they also have the potential to be orders of magnitude faster and less expensive than direct methods it is shown that broadband seabed reflection data can be exploited to remotely obtain the depth dependent density and velocity profiles in the transition layer to high ac

effect of ocean sound speed uncertainty on matched field geoacoustic inversion the effect of ocean sound speed uncertainty on matched field geoacoustic inversion is investigated using data from the sw06 experiment along a nearly range independent bathymetric track significant sound speed differences were observed at the source and receiving array and several environmental parameterizations were investigated for the inversion including representing the ocean sound speed at both source and receivers with empirical orthogonal function eof coefficients a genetic algorithm based global optimization method was applied to the candidate environmental models then a bayesian inversion technique was used to quantify uncertainty in the environmental parameters for the best environmental model which included an eof description of the ocean sound speed

gas source rock correlation in thrace basin turkey abstract the tertiary thrace basin is the most productive gas province of turkey since exploration in the basin started almost 40 years before many elements of the petroleum system are now known however a gas source rock correlation is still not available as modern methods of correlation have still not been utilized yet a recent study on molecular and isotopic composition of gases could only show that gas accumulations have different origins accordingly a mature source rock with a mixed type of organic matter an early mature source rock with a mainly marine organic matter and a biogenic source have contributed in varying combinations to the formations of gas fields in the basin all of the three potential source rocks namely the lower eocene hamitabat formation upper eocene lower oligocene ceylan formation and the oligocene mezardere formation can fulfill the required maturity and organic matter type requirements in different parts of the basin furthermore the basin wide variation of these parameters is not known due to insufficient subsurface data and non representative distribution of data points therefore a new approach which considers the temporal development of maturation and gas generation in different source rocks within the drainage area of the gas fields and the presence of traps during this critical period was necessary in this study maturation and gas generation history of these three potential source rocks in the drainage areas of gas fields were determined by basin modelling comparing the presence of traps for a given gas field at these critical time periods of maturation and gas generation the most probable source rock could be determined the evaluation of the respective petroleum system in the drainage areas of the gas fields indicated that the hamitabat formation was the source for the pure thermogenic mature gases in the kuzey marmara hamitabat and karacaoglan fields it also contributed to the gas accumulations in several reservoir horizons in the degirmenkoy field the mezardere formation was the source rock for mature thermogenic gas in the karacali hayrabolu and tekirdag fields in these fields mixing with a biogenic gas also took place the mezardere formation was also the source of early mature thermogenic gas in the degirmenkoy field

silica activity and the smectite illite reaction early silicate diagenesis is characterized by the precipitation of minerals with high silica activity such as opaline silica smectite and clinoptilolite and by pore water silica activities exceeding quartz saturation with burial this early high silica activity diagenesic facies is succeeded by a low silica activity facies distinguished by quartz precipitation and progressive development of illite as the nonexpandable component of mixed layer clays we suggest that the smectite illite reaction occurs as a consequence of the reduction of silica activity at the onset of quartz precipitation data from oceanic and sedimentary basins confirm that the smectite illite reaction does not control aqueous silica activities where the smectite illite reaction occurs at higher temperatures aqueous silica activities likewise reach quartz saturation at higher temperatures