methane fluxes and carbonate deposits at a cold seep area of the central nile deep sea fan eastern mediterranean sea abstract high acoustic seafloor backscatter signals characterize hundreds of patches of methane derived authigenic carbonates and chemosynthetic communities associated with hydrocarbon seepage on the nile deep sea fan ndsf in the eastern mediterranean sea during a high resolution ship based multibeam survey covering a 225 km2 large seafloor area in the central province of the ndsf we identified 163 high backscatter patches at water depths between 1500 and 1800 m and investigated the source composition turnover flux and fate of emitted hydrocarbons systematic parasound single beam echosounder surveys of the water column showed hydroacoustic anomalies flares indicative of gas bubble streams above 8 of the high backscatter patches in echosounder records flares disappeared in the water column close to the upper limit of the gas hydrate stability zone located at about 1350 m water depth due to decomposition of gas hydrate skins and subsequent gas dissolution visual inspection of three high backscatter patches demonstrated that sediment cementation has led to the formation of continuous flat pavements of authigenic carbonates typically 100 to 300 m in diameter volume estimates considering results from high resolution autonomous underwater vehicle auv based multibeam mapping were used to calculate the amount of carbonate bound carbon stored in these slabs additionally the flux of methane bubbles emitted at one high backscatter patch was estimated 0 23 to 2 3 106 mol a 1 by combined auv flare mapping with visual observations by remotely operated vehicle rov another high backscatter patch characterized by single carbonate pieces which were widely distributed and interspaced with sediments inhabited by thiotrophic chemosynthetic organisms was investigated using in situ measurements with a benthic chamber and ex situ sediment core incubation and allowed for estimates of the methane consumption 0 1 to 1 106 mol a 1 and dissolved methane flux 2 to 48 106 mol a 1 our comparison of dissolved and gaseous methane fluxes as well as methane derived carbonate reservoirs demonstrates the need for quantitative assessment of these different methane escape routes and their interaction with the geo bio and hydrosphere at cold seeps

dense water formation in the aegean sea numerical simulations during the eastern mediterranean transient 1 dense water formation processes in the aegean sea eastern mediterranean are studied using a three dimensional numerical ocean model the simulations cover the period 1979 1994 during which major changes that affected the thermohaline circulation of the whole mediterranean sea were recorded sensitivity studies that focus on the role of freshwater budget are presented and the results are evaluated against available hydrological data of the same period the very cold winters of 1987 1992 and 1993 and the extended dry period 1989 1993 that affected the whole eastern mediterranean sea are the main driving mechanisms corresponding to 50 and 32 respectively of the excessive deepwater volume formed in the aegean after 1987 the reduced black sea water outflow during the same dry period was another important forcing mechanism contributing 18 to the total formation while the increased inflow of saline waters from the levantine sea after 1992 was an additional preconditioning factor the locations and mechanisms of water formation processes are identified with combined analysis of data from the march 1987 oceanographic cruise in the aegean sea and the respective model results for that period deep water is found to be formed mainly through open ocean convection in the central and north aegean sea while the contribution of shelf areas is limited intermediate water is also formed through open ocean convection in the southern aegean sea during cold winters as well as in the central and northern aegean during mild winters the total volume of dense water formed during 1979 1994 corresponds to an annual formation rate of 0 24 sv for deep water and 0 34 sv for intermediate water

how are diagenesis and reservoir quality linked to depositional facies a deltaic succession edgeoya svalbard abstract middle to late triassic strata exposed at edgeoya eastern svalbard represents an uplifted part of the northwestern corner of the barents sea this interval is characterized by a predominantly mud dominated deltaic depositional system where rocks with petroleum reservoir potential are expected both in delta front and channelized sandstone deposits recent drilling campaigns into time equivalent rocks in the barents sea have however been disappointing with porosity and permeability below expectation this study improves the current understanding of reservoir potential within depositional systems of this kind by examining the link between different depositional facies diagenesis and their impact on reservoir quality five depositional facies were mapped and correlated channel floodplain shallow marine prodelta and offshore our study suggests that diagenetic signatures that control the quality of reservoir rocks vary systematically with these depositional facies mechanical compaction was the main cause of porosity destruction in the channel shallow marine and floodplain samples while early carbonate cementation occludes the intergranular volume in the prodelta samples moreover quartz cement reduced the porosity in the shallow marine depositional facies the estimated maximum burial temperature of 124 c indicates burial to several km depths depositional settings within a deltaic to shallow marine system do not exert a strong control on the abundance of chlorite but it does impact whether the chlorite is pore filling or grain coating and porosity preserving efficient chlorite coating have aided in preserving porosities up to 32 in the very well well sorted medium to fine grained sandstones deposited by fluvial dominated channels

estimation of deep and intermediate water mass formation rates in the mediterranean sea abstract using a simple diagnostic model and climatological surface temperature salinity and air sea fluxes the deep and intermediate water formation sites of the mediterranean sea are determined as well as the annual formation rates for each of them with the same model the t and s characteristics of the water masses are estimated four distinct formation sites are formed one in the western gulf of lions and three in the eastern adriatic northern ionian rhodes gyre area southern aegean basin respectively with well defined water types being produced at each formation site the computed annual production rates compare quite well with other independent estimations found in literature

the effect of wind stress over the eastern mediterranean on deep water formation in the adriatic sea abstract we investigate the effect of interannual variability of the wind stress over the eastern mediterranean on adriatic deep water adw formation using an oceanic general circulation model of the mediterranean sea driven by monthly era interim wind stress of the years 1979 2014 this is done by using climatological annual cycle of the surface temperature and freshwater flux but interannually varying wind stress a connection between the wind stress magnitude over the rhodes gyre region and adw outflow is found in association with the formation of levantine intermediate water liw 720 years artificially generated wind stress fields were constructed based on the first 50 empirical orthogonal functions eofs of the wind stress monthly anomalies this simulation strengthen the connection that was found and also reveal a centennial internal variability of both the liw and the adw outflow it is also found that the intensity of the rhodes gyre is almost linearly related to the wind stress amplitude however the adw outflow is non monotonically related to the wind stress amplitude there is an optimal wind stress amplitude for which the adw formation is maximal when the wind stress amplitude is more than 50 the climatological mean wind stress amplitude the adw outflow is weakened this implies a different balance between the saline liw and the fresh atlantic water entering the eastern mediterranean from sicily strait under stronger than present wind stress amplitude

evaluating the mechanical compaction of quartzarenites the importance of sorting llanos foreland basin colombia abstract mechanical compaction is the main porosity reducing process in sandstones including high reservoir quality rigid grain sandstones for such sandstones the extrapolation of theoretical or experimental compaction algorithms needs calibration with rocks having well constrained burial histories evaluating the compaction of these rocks is achieved by comparing current intergranular volume igv with depositional igv which is strongly dependent on sorting however because sandstone sorting is difficult to measure accurately its impact on depositional porosity and compaction state is largely underestimated we use the quartzarenites of the oligocene carbonera formation in the subsurface of the hydrostatically pressured llanos basin to illustrate the importance of sorting when evaluating the compaction of rigid grain sandstones igv and sorting were measured in core samples using a combination of transmitted light and cathodoluminescence images resulting in improved accuracy over standard procedures the compaction state of clean quartzarenites at given depths is best described using igv versus sorting plots which are used to derive compaction curves for specified sorting values the igv versus sorting trends are displaced to lower igv values with increasing burial depth the differences in igv caused by differences in sorting exceed the differences in igv resulting from 1000 m of burial illustrating the high impact of sorting when evaluating compaction contrasting with published experimental results the compaction of the llanos basin ductile grain poor quartzarenites is independent of grain size and grain rearrangement is the main compaction mechanism during the first 1 6 km of burial based on the llanos data we have generated igv versus depth curves for clean pure quartzarenites of specific sorting which can be used to predict their maximum primary porosity up to moderate burial depths differences with other published burial curves are probably related to unaccounted variations in sorting ductile grain content and framework strengthening cements however the llanos basin quartzarenites contain virtually no cements explaining their high degree of compaction relative to other rigid grain sandstones and making them ideal to isolate the effects of compaction on the igv of quartzarenites the llanos basin data suggest that below 2 5 km of depth clean well to moderately well sorted quartzarenites continue reducing their igv by mechanical compaction below the 26 limit which should apply only to extremely well sorted rigid grain uncemented sandstones

solar forcing of nile discharge and sapropel s1 formation in the early to middle holocene eastern mediterranean we present high resolution records for oxygen isotopes of the planktic foraminifer globigerinoides ruber 18oruber and bulk sediment inorganic geochemistry for holocene age sediments from the southeast mediterranean our 18oruber record appears to be dominated by nile discharge rather than basin scale salinity temperature changes nile discharge was enhanced in the early to middle holocene relative to today the timing of the long term maximum in nile discharge during the early holocene corresponds to the timing of maximum intensity of the indian ocean influenced southwest indian summer monsoon sim this coincidence suggests a major influence of an indian ocean moisture source on nile discharge in the early to middle holocene while presently the atlantic ocean is the main moisture source nile discharge was highly variable on multicentennial time scale during the early to middle holocene being strongly influenced by variable solar activity this solar driven variability is also recorded in contemporaneous sim records however not observed in an atlantic ocean derived west african summer monsoon record from the holocene this supports the hypothesis that the indian ocean moisture source predominantly controlled nile discharge at that time solar driven variability in nile discharge also influenced paleoenvironmental conditions in the eastern mediterranean bulk sediment ba al and v al used as indicators for export productivity and redox conditions respectively varied both in response to solar forcing on multicentennial time scales we suggest that changes in nile discharge on these time scales have been concordant with nutrient inputs to and shallow ventilation of the eastern mediterranean

the levantine intermediate water experiment liwex group levantine basin a laboratory for multiple water mass formation processes 1 in winter 1995 the last major field work of the physical oceanography of the eastern mediterranean poem program was carried out the levantine intermediate water experiment liwex in this study a thorough analysis is presented of the data set collected during three successive surveys in january february and march april 1995 the major overall result is that the levantine basin is shown to be the site for multiple and different water mass formation processes levantine deep water ldw was formed in the rhodes gyre with the preconditioning phase starting in december 1994 in late january the chimney was ventilating to the atmosphere in february the strong mixing phase is documented by the convective cell vertically homogeneous to 900 m depth in march april recapping has occurred in the upper 200 m ldw remained confined inside the rhodes gyre cyclonic circulation levantine intermediate water liw is instead deeply affected by the upper thermocline circulation shallow ventilating chimneys with the liw thermostads were found in the january survey inside the cyclonic region of the northern levantine the formation process of liw does not involve deep penetrative convection winter surface cooling and evaporation are sufficient to produce a surface mixed layer 100 m deep with liw characteristics at the mixed layer basis liw subducts and spreads along isopycnal surfaces along pathways determined by the cyclonic anticyclonic structures of the upper thermocline circulation

a mixed layer study of the formation of levantine intermediate water a mixed layer model is used to investigate the formation of levantine intermediate water liw over the eastern mediterranean the one dimensional model is initialized with climatological hydrography and integrated over the levantine basin with forcing by climatological surface fluxes realistic and repeated seasonal mixed layer cycles are obtained if the annual surface heat input and water loss are offset by a parameterized horizontal advection the model integrations show that liw is formed during winter in the mixed layer of the northwestern levantine the preferred formation region for liw is found through idealized experiments to be controlled by the preconditioning of the hydrography especially that of the cold cyclonic rhodes gyre rather than by the pattern of the climatological fluxes the annual mean formation rate of liw is estimated to be 1 0 sv using the climatological surface fluxes the magnitude of the annual surface fluxes alters the formation rate and modifies the formation region an additional annual heat flux reduces the formation rate of liw whereas an extra cooling enhances it as well as forming waters denser than liw in the center of the rhodes gyre

reappraisal of strain estimations and measurement methods in the hammamat group sediments comparison of primary and secondary grain fabrics with new data from wadi zeidun and wadi arak basins ced egypt abstract in this study pebble and sand grain shape and orientation data from undeformed and deformed conglomerates and sandstones in the egyptian central eastern desert ced wadi zeidun and wadi arak basins were collected with the aim of providing more accurate tectonic strain estimations for deformed hammamat sediments by comparing their primary and secondary sedimentary fabrics common assumptions about primary pebble fabrics and pebble deformation behaviour in previous strain studies of the region are shown to be invalid this raises doubts about the accuracy of earlier reported strain estimates for the hammamat that were based on such assumptions for low strains in the hammamat sediments the best strain measurement method is normalized fry nfry analysis of sand grain centre to centre distance data an alternative is conventional fry analysis of pebble ellipse centre to centre distance data provided that large numbers of pebbles 300 are used and the pebbles form closely packed aggregates with high degrees of anticlustering this study also provides systematic guidelines for pebble axial length and orientation measurements in the field the progressive changes in the mechanical behaviour of pebbles with increasing bulk strain are discussed

a tracer study of the formation dispersal and renewal of levantine intermediate water the formation and dispersal of levantine intermediate water liw are examined using a series of tracer experiments based on an eddy permitting general circulation model of the mediterranean liw is formed in the region of the rhodes gyre and disperses via both the time mean and time varying circulation tracer released in the rhodes gyre is transferred westward by the time mean circulation but also southward and eastward by the time varying circulation off line tracer experiments suggest that the time varying circulation exhibits both advective and diffusive components where the advective component opposes downgradient transfer in some regions the rate of invasion of tracer into the main thermocline suggests that the renewal timescale is 10 20 years for liw and of order 100 years for eastern mediterranean deep water assuming advection dominates the transfer of tracer the implied annual subduction rate is 0 6 0 1 sv in the rhodes gyre and 0 2 0 1 sv in the adriatic sea the liw mode is found to become cooler and fresher as a result of mixing with the adriatic outflow while its potential vorticity appears well conserved

muddy and dolomitic rip up clasts in triassic fluvial sandstones origin and impact on potential reservoir properties argana basin morocco abstract the significance of rip up clasts as sandstone framework grains is frequently neglected in the literature being considered as accessory components in bulk sandstone composition however this study highlights the great value of muddy and dolomitic rip up clast occurrence as a information source about low preservation potential from floodplain deposits and b key element controlling host sandstone diagenetic evolution and thus ultimate reservoir quality high resolution petrographic analysis on triassic fluvial sandstones from argana basin t6 and t7 t8 units highlights the significance of different types of rip up clasts as intrabasinal framework components of continental sediments from arid climates on the basis of their composition and ductility three main types are distinguished a muddy rip up clasts b dolomitic muddy rip up clasts and c dolomite crystalline rip up clasts spatial distribution of different types is strongly facies related according to grain size origin of rip up clasts is related to erosion of coeval phreatic dolocretes in different development stages and associated muddy floodplain sediments cloudy cores with abundant inclusions and clear outer rims of dolomite crystals suggest a first replacive and a subsequent displacive growth respectively dolomite crystals are almost stoichiometric this composition is very similar to that of early sandstone dolomite cement supporting phreatic dolocretes as dolomite origin in both situations sandstone diagenesis is dominated by mechanical compaction and dolomite cementation a direct correlation exists between 1 muddy rip up clast abundance and early reduction of primary porosity by compaction with irreversible loss of intergranular volume igv and 2 occurrence of dolomitic rip up clasts and dolomite cement nucleation in host sandstone occluding adjacent pores but preserving igv both processes affect reservoir quality by generation of vertical and 3d fluid flow baffles and barriers that compartmentalize the reservoir these findings may provide quantitative useful data for the better understanding of reservoir quality in analogous hydrocarbon bearing basins such as the bay of fundy nova scotia canada

effects of sandstone provenance on reservoir quality preservation in the deep subsurface experimental modelling of deep water sand in the gulf of mexico deep water turbidite sandstone reservoirs in the gulf of mexico have been sourced from a variety of provenance terrains as a result the framework composition of each reservoir in the basin varies widely including volcanic rich litharenite oligocene vicksburg feldspathicrich lithic arkose oligocene frio metamorphic rich feldspathic litharenite palaeogene wilcox lithic poor quartzarenite miocene quartz rich sublitharenite cretaceous and quartzand feldspar rich subarkose norphlet provenance driven differences in composition have a complex but critical influence on how each of these reservoirs responds to burial induced changes in depth fluid pressure effective stress and temperature a combination of petromod and touchstone modelling programs are used in this study to simulate the influence of provenance on compaction and cementation of the main reservoir types in the gulf of mexico for example modelling results predict that at higher levels of thermal exposure some lithic rich sands although more ductile and highly compacted will experience less quartz cementation than less ductile quartz rich sands thereby preserving a higher range of porosity and permeability furthermore modelling results predict that temperature effective stress depth windows for optimal reservoir quality preservation vary widely depending on sandstone provenance the evaluation of sandstone grain composition and subsequent interpretation of sand provenance has proven to be a useful methodology for oil and gas exploration for many years specific applications of provenance studies are varied and have included the following assistance in the interpretation of basin evolution and tectonic setting dickinson 1985 help in discriminating sandstone petrofacies and source areas ingersoll 1990 interpretation of relief and climate of source areas folk 1980 help with the interpretation of palaeo drainage and sediment dispersal patterns lowe et al 2011 and help with improving stratigraphic correlation morton hurst 1995 recent workers have used provenance as a means of discriminating potential areas of basins with higher reservoir quality potential vincent et al 2010 2013 provenance reconstruction has also become a critical step in selecting the most appropriate analogues for predictive reservoir quality modelling using diagenetic modelling software such as exemplarw lander walderhaug 1999 and touchstone lander et al 2008 what has not been reported as yet is the degree to which provenance affects predictive modelling results with this in mind we pose a question could provenance related differences in sandstone composition within a single basin be large enough to significantly affect predictive modelling results this study is intended to address that question by comparing a variety of sandstone compositions across a wide range of simulated burial histories specifically sandstone compositions representing the mesozoic through tertiary gulf of mexico reservoirs of the deep water basin are used in a series of test cases this basin provides a natural laboratory for testing the effects of provenance on reservoir quality prediction and the findings from this study are intended to be used for global application provenance and reservoir quality modelling provenance transport distance climate and depositional setting all affect the initial detrital composition and to some extent the textural attributes of sandstone reservoirs at the onset of burial depositional texture and composition greatly control the rate and style of compaction and other diagenetic processes that occur during burial specific subsurface processes that are affected by initial sand composition include the following 1 mechanical compaction 2 chemical compaction 3 dissolution of unstable minerals 4 precipitation of quartz cement 5 precipitation of other cements e g carbonates zeolites sulphates from scott r a smyth h r morton a c richardson n eds 2014 sediment provenance studies in hydrocarbon exploration and production geological society london special publications 386 27 47 first published online september 12 2013 http dx doi org 10 1144 sp386 17 the geological society of london 2014 publishing disclaimer www geolsoc org uk pub ethics at conocophillips on august 28 2014 http sp lyellcollection org downloaded from

experimental mechanical compaction of reconstituted shale and mudstone aggregates investigation of petrophysical and acoustic properties of sw barents sea cap rock sequences abstract this study investigates petrophysical and acoustic properties of experimentally compacted reconstituted samples of seal sequences from the southwestern barents sea the aggregates were collected from drill cuttings of mudstone and shale formations of two exploration wells 7220 10 1 salina discovery and 7122 7 3 goliat field the washed and freeze dried samples were characterized for grain size distributions geochemical analyses and mineralogical compositions a total of 25 compaction tests 12 dry and 13 brine saturated were performed with a maximum effective vertical stress of 50 mpa the laboratory measurements demonstrated that petrophysical and acoustic properties of argillaceous sediments can change within a sedimentary basin and even within a given formation the results show that the collected aggregates from goliat field are compacted more compared to salina discovery the maximum and minimum compaction are measured in samples collected from snadd and fuglen formations respectively the final porosity of brine saturated specimens varies between 5 and 22 the ultrasonic velocity measurements depict that samples with the same porosity values can have a broad range of velocity values the resulting compaction trends in this study were compared to published compaction curves for synthetic mixtures of quartz and clay all compaction trends show higher porosity reduction than the silt fraction with 100 quartz comparison of experimental compaction result of each mudstone and shale aggregate with its corresponding acquired well log data helps to delineate the burial history and exhumation in the study area a net exhumation of 950 m and 800 m is estimated at salina and goliat wells respectively the outcomes of this study can provide insights for hydrocarbon prospect discovery in a pre mature sedimentary basin in terms of exploration and production and also for geological co2 storage sites the experimental results may provide information for well log and seismic interpretation basin modeling and seal integrity of investigated horizons

sensitivity of mediterranean thermohaline circulation to gateway depth a model investigation 1 the neogene sedimentary record of the mediterranean sea holds evidence for changes in water properties and circulation these paleoceanographic changes have been attributed to changes in the flow through the ocean gateway between the mediterranean sea and the atlantic ocean we use an oceanic general circulation model to achieve quantitative physics based understanding of the effect of changes in the depth of the gateway such as may result from tectonic activity or variation in sea level to isolate these effects we use idealized basin geometry and impose simplified atmospheric forcing a reference experiment with present day sill depth demonstrates that the model simulates reasonably well the main features of the present day mediterranean thermohaline circulation as inferred from observations and previous numerical studies subsequently a series of sensitivity simulations is performed with different sill depths the model results show that mediterranean temperature salinity and thermohaline circulation depend strongly on sill depth as the sill depth decreases the upper overturning cell is quasi linearly reduced in strength while contrary to what one would expect the deep cell intensifies and does so in a nonlinear way we find that a shoaling of the sill depth induces a blocking effect on the outflow waters which creates a strong recirculation in the deep layers strengthening the deep cell nevertheless deep water formation is reduced and as a consequence the ventilation of the deep layers diminishes we identify three different circulation modes of the mediterranean thermohaline circulation depending on the sill depth shallow sill moderate sill and deep sill modes coupled with strong weak and negligible blocking effects respectively our results are consistent with the pre messinian paleoceanographic record of the mediterranean sea and may be useful to understanding the behavior of other land locked basins both extant and from the geological past

inferring the subduction rate and period over the north atlantic abstract the annual rate at which mixed layer fluid is transferred into the permanent thermocline that is the annual subduction rate sann and the effective subduction period x1d4af eff is inferred from climatological data in the north atlantic from its kinematic definition sann is obtained by summing the vertical velocity at the base of the winter mixed layer with the lateral induction of fluid through the sloping base of the winter mixed layer geostrophic velocity fields computed from the levitus climatology assuming a level of no motion at 2 5 km are used the vertical velocity at the base of the mixed layer is deduced from observed surface ekman pumping velocities and linear vorticity balance a plausible pattern of sann is obtained with subduction rates over the subtropical gyre approaching 100 m yr twice the maximum rate of ekman pumping the subduction period x1d4af eff is found by viewing subduction as a transformation process converting mixed layer fluid into stratified thermocline fluid the effective

surface circulation of the eastern mediterranean levantine basin insights from analyzing 14 years of satellite altimetry data 1 the complex multiscale system circulation of the levantine eastern mediterranean em basin is analyzed by applying various spatiotemporal statistical methods on the aviso 14 years 1993 2006 data set of satellite altimetry sea level anomalies the rossby deformation radius at the em is at the order of 10 km which is also the horizontal satellite resolution therefore the geostrophic currents derived from the satellite altimetry measurements represent well the basin and the mesoscale circulations the long term averaged mean dynamic topography mdt is found to capture the different eddy activity regions in the em however these regions are highly turbulent the instantaneous currents in these regions can be different from the mdt derived currents by the same order of magnitude furthermore the turbulence intensity appears to be nonperiodic despite of the seasonal and long term steric periodic variability because these eddies interact with the basin circulation flow they modify it continuously the major exception of this sporadic behavior is the ierapetra eddy southeast of crete it appears to be forced by shear of the summer etesian winds created when the crete mountain ridges block these winds and cause a funneling effect it has a persistent seasonal signature that dominates the variance of the entire levantine basin

genetic mechanism of high quality reservoirs in permian tight fan delta conglomerates at the northwestern margin of the junggar basin northwestern china fan delta conglomerate reservoirs in the permian jiamuhe formation in the zhongguai area at the northwestern margin of the junggar basin northwestern china are reservoirs for large accumulations of natural tight gas the tight conglomerates and sandstones are mainly litharenites with a large amount of texturally and compositionally immature volcanic clastic materials core porosities demonstrate the development of anomalously high porosities at depths of 3200 4200 m 10 500 13 800 ft and 4500 4900 m 14 800 16 100 ft the permian reservoirs experienced initial rapid subsidence uplift and further subsidence and diagenetic reactions occurred in these reservoirs involving compaction precipitation of chlorite clays calcites zeolites iron oxides kaolinite and quartz cements and dissolution of unstable minerals including analcite laumontite feldspars and rock fragments low porosity reservoirs with extensive compaction and or cementation of calcite and heulandite ca consist of only few visible secondary pores formed by dissolution of feldspars and rock fragments reservoirs with anomalously high porosity however experienced relatively weak compaction and contain significant amounts of secondary pores formed by dissolution of mainly laumontites some feldspars and rock fragments comprehensive studies of sedimentary features and diagenesis of the reservoirs indicate that these anomalously high porosities originate from chronological coupling of four important geological processes 1 sedimentary facies and detrital compositions controlled distribution of various zeolites in reservoirs with abundant laumonites developed in reservoirs in the fan delta front subfacies 2 early precipitation of the laumontites inhibited compaction during deep burial however they provided unstable minerals for secondary porosity development 3 the permian reservoirs experienced subaerial exposure erosion during the uplift stage and meteoric freshwater leached laumontite cements and aluminosilicate grains to form secondary pores in reservoirs beneath the unconformity 4 hydrocarbon emplacement at relative shallow depth during a second subsidence period preserved the secondary pores in reservoirs by retarding late carbonate cementation

an oceanic general circulation model ogcm investigation of the red sea circulation 2 three dimensional circulation in the red sea 1 the three dimensional circulation of the red sea is studied using a set of miami isopycnic coordinate ocean model micom simulations the model performance is tested against the few available observations in the basin and shows generally good agreement with the main observed features of the circulation the main findings of this analysis include an intensification of the along axis flow toward the coasts with a transition from western intensified boundary flow in the south to eastern intensified flow in the north and a series of strong seasonal or permanent eddy like features model experiments conducted with different forcing fields wind stress forcing only surface buoyancy forcing only or both forcings combined showed that the circulation produced by the buoyancy forcing is stronger overall and dominates the wind driven part of the circulation the main circulation pattern is related to the seasonal buoyancy flux mostly due to the evaporation which causes the density to increase northward in the basin and produces a northward surface pressure gradient associated with the downward sloping of the sea surface the response of the eastern boundary to the associated mean crossbasin geostrophic current depends on the stratification and b effect in the northern part of the basin this results in an eastward intensification of the northward surface flow associated with the presence of kelvin waves while in the south the traditional westward intensification due to rossby waves takes place the most prominent gyre circulation pattern occurs in the north where a permanent cyclonic gyre is present that is involved in the formation of red sea outflow water rsow beneath the surface boundary currents are similarly intensified southward undercurrents that carry the rsow to the sill to flow out of the basin into the indian ocean index terms 4243 oceanography general marginal and semienclosed seas 4255 oceanography general numerical modeling 4532 oceanography physical general circulation keywords red sea marginal sea oceanic general circulation model water mass formation

variability of rhodes and ierapetra gyres during levantine intermediate water experiment observations and model results 1 this work is aimed at studying the variability of rhodes and ierapetra gyres during the levantine intermediate water experiment sea surface temperature maps derived from global area coverage advanced very high resolution radiometer avhrr data in the framework of the pathfinder project and sea level anomalies derived from topex poseidon altimeter were used to track the evolution both in terms of dimension and position of the cyclonic rhode gyre and ierapetra anticyclone the analysis was performed for the period from october 1994 to the end of april 1995 i e from the preconditioning to the spreading phase of levantine intermediate water the description of the surface fields was complemented by a temporal evolution study of the rhodes and ierapetra gyres hydrological vertical structure european centre for medium range weather forecasts avhrr derived fluxes have been used as forcing for a numerical model to study the variability of the mixed layer in both gyres the simulated upper layer dynamics remarkably matched remotely sensed and in situ observations this work shows that using a combined analysis of observational data and model simulations we were able to propose a dynamical scenario for the winter of 1995 where the levantine basin was characterized by short intense heat loss events occurring during at the beginning of december the intense air sea interaction contributed to deep instead of intermediate mixing as confirmed by remote sensing in situ data and model experiments a hypothesis on the role of the lateral contribution on the water column buoyancy content in the rhodes gyre was formulated

recent changes in deep water formation and spreading in the eastern mediterranean sea a review abstract observations of the last decade testify that the characteristics of the deep thermohaline circulation in the eastern mediterranean sea have changed thoroughly the source of the most dense waters of the basin has moved from the adriatic to the aegean sea this new source has proved to be very efficient since the estimated formation rate for the period 1989 95 was more than 1 sv about three times more than the dense water formation rate of the adriatic sea these new waters with hydrological characteristics that are warmer and more saline have replaced almost 20 of the older deep waters of the basin and have uplifted the deep isopycnals by about 500 m this major event can be attributed to important meteorological anomalies in the eastern mediterranean and to changes of circulation patterns the extended dry period of 1988 93 and the exceptionally cold winters of 1987 and 1992 93 created favorable conditions for increased formation of dense water in the aegean furthermore changes in the circulation patterns in the intermediate water range levantine intermediate water liw and cretan intermediate water themselves possibly linked to meteorological anomalies appear to have played an important role in the redistribution of salt as a result of an interruption to exchanges between the ionian and levantine basin the salinities in the latter started to rise high salinity waters were diverted into the aegean malanotte rizzoli p manca b b ribera dacala m theocharis a 1998 the eastern mediterranean in the 80s and in the 90s the big transition emerged from the poem bc observational evidence rapport du commission international de la mer medittanee 35 174 175 and the westward transport of liw was reduced an additional effect of the deep water discharge from the aegean and the resulting uplifting of mid depth waters was to lower salinities in the liw layer this effect is most strongly felt in the ionian sea a 3 d primitive equation numerical model for the eastern mediterranean with a 20 km grid size is used to simulate the observed changes and understand the basic mechanisms which caused them under appropriate atmospheric forcing the model successfully reproduces the main characteristics of the transient these results indicate that the observed changes can be at least partially explained as a response of the eastern mediterranean and more specifically of the aegean to atmospheric forcing variability

relationship of temperature to reservoir quality for feldspathic sandstones of southern california abstract the diagenetic alteration of a sandstone results from the combined effects of many factors in order to ascertain the role played by a particular diagenetic factor the remaining diagenetic factors must be held constant for the sandstones of the basins of southern california we have found that the effects of almost all of the principal diagenetic factors are essentially uniform the notable exception is thermal history because of this we have been able to evaluate the diagenetic imprint of temperature upon the sandstones measured reservoir property data taken on core samples of reservoir sandstones from 16 fields in the los angeles ventura and san joaquin basins were used to determine the average rate of porosity and permeability loss with depth for each field a s raight line appears to be the proper representation for the porosity versus depth profiles for the interval of interest the slope of this line is defined here as the porosity gradient porosity gradients for the fields investigated range from 1 1 to 5 8 per 1 000 ft a direct relationship exists between the porosity gradient and the present geothermal gradient for the 16 fields that have been examined as geothermal gradient increases porosity gradient increases the correlation coefficient between these variables is 0 916 for geothermal gradients between 1 6 f and 2 2 f 100 ft a similar relationship also exists between the rate of permeability loss with depth and the geothermal gradient but the average deviation from the mean permeability value is so great the relations ip has little practical significance end of article last page 250

diagenesis of a tight gas sand reservoir upper cretaceous mesaverde group piceance basin colorado abstract the upper cretaceous mesaverde group in the piceance basin western colorado contains thick sections of low porosity low permeability sandstones that are reservoirs for large accumulations of hydrocarbon gas the mesaverde sandstones are lithic arkoses and feldspathic litharenites containing quartz plagioclase variable k feldspar chert and volcanic rock fragments important diagenetic processes that have affected the sandstones include compaction dissolution of feldspar and or alteration to clay precipitation of carbonate and quartz cements precipitation of illite and alteration of detrital clays mixed layer illite smectite porosity is relatively constant a decrease in primary porosity downward is approximately balanced by an increase in secondary porosity with significant microporosity in authigenic and diagenetic clays k feldspar is almost completely absent below 5500 feet 1675 m fibrous illite is relatively abundant above this depth and variable in abundance below the k ar ages of the clays increase with depth from 40 m y at the top of the sampled section to 55 m y at the base indicating illitization of a precursor smectite at approximately the 100 c isotherm samples with abundant fibrous illite have relatively smaller age values mass balance calculations indicate that dissolution of k feldspar illitization of smectite and precipitation of fibrous illite were coupled these reactions suggest the transport of dissolved potassium upward hundreds of feet 100 300 m in the section possibly associated with water driven vertically by the migration of gas

modification of ocean eddies by air sea interaction a mixed layer model is developed for seasonal time scales and used to investigate the modification of ocean eddies by air sea interaction an eddy is modified by the air sea interaction for the local envionment and the feedback from its surface temperature signal which alters the surface heat and water fluxes this buoyancy forcing tends to decrease the eddy temperature anomaly and seasonal changes in mixed layer depth lead to the surface signal being removed in summer and reappearing in winter the dynamical adjustment of the eddy is assessed by coupling the mixed layer model to a quasi geostrophic model the buoyancy forcing alters the eddy velocity profile and over several seasons may lead to the formation of a subsurface velocity maximum after the spring decrease in mixed layer depth the eddy potential vorticity anomaly is reduced and lateral mixing may subsequently play a role in further eroding the eddy these modelling predictions are supported by the observations of a cold core eddy in the seasonal boundary layer of the northeast atlantic

circulation and hydrography of the levantine basin results of poem coordinated experiments 1985 1986 abstract a brief review of the meteorological setting hydrography and the circulation in the levantine basin of the eastern mediterranean is given the recent high resolution data obtained in poem coordinated experiments of 1985 1986 are then used to optimally estimate the circulation in the basin in two different seasons and to describe the water mass distributions some of the features observed during the experiments support the historical knowledge on the locations of sub basin scale gyres and the general circulation in addition to which some new features are established details of the circulation such as the intensity the multiple scales and the three dimensional structure of the various vortices and the central levantine basin current are displayed extensively a variety of sub basin meso and sub mesoscale vortices occur with highly assymmetric baroclinic vertical structures some eddies split into multiple centres with depth interpreted as indicating possible coalescences a number of long lived eddies were persistent in both surveys the sub surface atlantic water aw is advected by and entrapped within the eddy field the levantine intermediate water liw at intermediate depths is shown to be maintained throughout the year in the northeastern sector of the levantine basin and along the periphery of the rhodes gyre the levantine intermediate water also has a patchy distribution owing to the advection and trapping by the eddy field which it helps to generate through adjustment processes

mediterranean sea large scale low frequency ocean variability and water mass formation rates from 1987 to 2007 a retrospective analysis abstract we describe a synthesis of the mediterranean sea circulation structure and dynamics from a 23 year long reanalysis of the ocean circulation carried out by adani et al 2011 this mesoscale permitting dynamical reconstruction of past ocean variability in the mediterranean sea allows the study of the time mean circulation and its low frequency decadal components it is found that the time mean circulation is composed of boundary and open ocean intensified jets at the border of cyclonic and anticyclonic gyres the large scale basin circulation is generally characterized in the northern regions by cyclonic gyres and in its southern parts by anticyclonic gyres and eddy dominated flow fields with the exception of the tyrrhenian and the northern ionian sea the time mean tyrrhenian sea circulation is dominated by cyclonic gyres of different intensity and intermittency the northern ionian sea circulation however reverses in sign in two ten year periods the first in 1987 1996 and the second in 1997 2006 which is here called the northern ionian reversal phenomenon this reversal is provoked by the excursion of the atlantic ionian stream from the middle to the northern parts of the basin the decadal variability of other parts of the basin is characterized by changes in strength of the basin scale structures the water mass formation rates and variability are dominated by event like periods where the intermediate and deep waters are formed for 2 3 years at higher rates the largest deep water formation events of the past 23 years occurred separately in the western and eastern mediterranean basin the first coincided with the eastern mediterranean transient roether et al 1996 and the second with the western mediterranean deep water formation event in 2005 2006 smith et al 2008 a new schematic of the basin scale circulation is formulated and commented

post collisional sediment budget history of the alps tectonic versus climatic control based on the sediment budget of the eastern swiss and western alps since the oligocene the regional tectonic evolution has been identified as the dominant factor it is superimposed on the influence of both regional and global climate change and global sea level change during late pliocene and pleistocene times climate became the dominant factor because of cyclic glaciations the early post collisional history of the alps is characterized by a doubling of sediment discharge rates around the rupelian chattian boundary this increase is attributed to isostatic re adjustment either after large scale thermal reorganization of the lithosphere related to slab break off or to crustal thickening as continental crust became subducted from middle oligocene to late miocene times the overall trend of sediment discharge rates in the entire alps was modified only during relatively short lived phases these are characterized by an increase in aquitanian ca 23 21 ma and late burdigalian times ca 18 16 4 ma and a decrease in early to middle burdigalian 21 19 ma and langhian to serravalian times 16 4 12 ma an important still ongoing period of uplift reflected by rapidly increasing sediment discharge rates started in latest miocene times in the swiss and western alps and affected the eastern alps some 2 million years later the reason for this uplift is not clear but deep seated lithospheric processes appear to be likely

mechanical compaction of deeply buried sandstones of the north sea abstract sandstones experience mechanical compaction when the overburden load exceeds the compressive strength petrographic evidence is rarely sufficient to determine the timing of mechanical compaction it is often assumed from indirect evidence such as regional porosity depth trends that mechanical compaction is a process that occurs exclusively during shallow or intermediate burial mechanical compaction without grain fracturing may occur at depth following pervasive framework grain dissolution and or if anomalously high porosity has been preserved due to the presence of small amounts of cement we describe examples from the fulmar sandstone formation of the central graben north sea that experienced late stage mechanical compaction following sponge spicule dissolution and microcrystalline quartz cementation deep burial mechanical compaction involving grain crushing may occur if the rate of grain contact quartz dissolution and or quartz overgrowth development cannot compete with the rate of stress increase at grain contacts some rotliegendes sandstones of the southern north sea that have been buried to 4 5 km offer a good example where the suppression of chemical compaction due to the presence of grain coating clays resulted in pervasive grain fracturing mineral veins are frequently associated with sandstones that have experienced pervasive mechanical compaction during deep burial these may reflect the sudden development of overpressure resulting from the transfer of load to the fluid during collapse of the sandstone framework

impact of regional variation in detrital mineral composition on reservoir quality in deep to ultradeep lower miocene sandstones western gulf of mexico abstract future exploration in lower miocene sandstones in the gulf of mexico will focus increasingly at depths greater than 4 5 km and reservoir quality will be a critical risk factor in these deep to ultradeep reservoirs the goal of this study was to understand the variation in reservoir quality of lower miocene sandstones across the western gulf of mexico to do this we examined regional variation in detrital mineral composition diagenesis and reservoir quality in five areas 1 louisiana 2 upper texas coast 3 lower texas coast 4 burgos basin mexico and 5 veracruz basin mexico using petrographic and petrophysical data from depths of 0 9 7 2 km there are strong variations in mineralogical composition within the study area lower miocene sandstones from offshore louisiana have an average composition of quartz 86 feldspar 12 and rock fragments 2 q 86 f 12 r 2 feldspar and rock fragment content increase southward as source areas shifted to include volcanic and carbonate rocks composition of samples from offshore texas ranges from q 67 f 24 r 9 in the upper texas coast to q 58 f 24 r 19 in the lower texas coast lower miocene sandstones from the onshore burgos basin northern mexico have an average composition of q 54 f 22 r 23 whereas sandstones from the veracruz basin southern mexico contain the highest proportion of rock fragments q 33 f 12 r 55 main diagenetic events in quartz rich lower miocene sandstones in louisiana were mechanical compaction and precipitation of quartz cement compactional porosity loss increased to the south with increasing rock fragment content calcite is the most abundant cement in the south and is strongly related to reservoir quality loss at moderate burial depths the best reservoir quality occurs in quartz rich sandstones in louisiana and decreases with increasing lithic content in texas and mexico porosity is higher in louisiana and upper texas than in lower texas and mexico at all depths and temperatures but at depths 5 km and temperatures 175 c porosity differences are lessened the lower miocene sandstone trend in the western gulf of mexico from louisiana to mexico is an example of the importance of variation in detrital mineralogy as a control on diagenesis and reservoir quality

abiotic interactions of natural dissolved organic matter and carbonate aquifer rock abstract abiotic interactions between natural dissolved organic matter ndom and carbonate aquifer rock may be controlling factors of biogeochemical processes and contaminant fate in carbonate aquifer systems the importance and effects of these interactions were examined using batch adsorption experiments of soil ndom and representative carbonate sorbents from the floridan aquifer adsorption of ndom carbon to aquifer rocks was well described using a modified linear model and was mostly reversible significant adsorption was observed at higher ndom concentrations while the release of indigenous organic matter from the rocks occurred at lower concentrations longer interaction periods led to more adsorption indicating that adsorption equilibrium was not achieved for relatively pure carbonate rock samples sorbent surface area was found to be the most important controlling factor of adsorption whereas the presence of indigenous organic matter and subdominant mineral phases were more important when they occurred preferential adsorption of a high over low molecular weight and humic over fulvic components of ndom onto carbonate sorbents was detected using liquid size exclusion chromatography and excitation emission fluorometry respectively the presence of ndom inhibited mineral dissolution though this inhibition was not proportional to ndom concentration as surface area and mineralogy of carbonate sorbents played additional roles though the ndom carbonate rock adsorption mechanism could not be completely determined due to the heterogeneity and complexity of ndom and sorbent surfaces it is speculated that both rapid and weak outer sphere bonding and stronger but slower hydrophobic interaction occur these results have important implications for groundwater quality and hydrogeologic projects such as aquifer storage and recovery

controls on reservoir quality in exhumed basins an example from the ordovician sandstone illizi basin algeria abstract petroleum exploration in many north african intracratonic basins targets early paleozoic sandstones as the primary reservoir objective these sandstones are often characterized by highly variable reservoir quality 0 0001 1000 md and the ability to predict and selectively target areas of enhanced porosity and permeability is crucial to unlock the hydrocarbon potential the objective of this study is to characterize the primary controls on reservoir quality in an ordovician field in the illizi basin of algeria through detailed core and petrographic analysis and establish if variations in thermal history across the field have a material impact on reservoir quality the best reservoir quality is observed in facies where primary intergranular porosity has been preserved in fine to coarse grained quartzarenites with less than 1 fibrous illite these lithologies are most commonly found within the high energy tidally reworked post glacial facies sandstones of the uppermost ordovician succession observed differences in quartz cement volume within compositionally and texturally similar samples from the southern and northern parts of the field are interpreted to reflect variations in thermal exposure due to deeper burial this interpretation is supported by field wide numerical modelling of sandstone diagenesis this study indicates that subtle variations in thermal history can have a material impact on the spatial trends in reservoir permeability thermal history therefore is an important consideration in reservoir quality studies in exhumed basins where variations in present day burial depth will be a poor guide for evaluating reservoir quality risk across a basin or play

contourite distribution and bottom currents in the nw mediterranean sea coupling seafloor geomorphology and hydrodynamic modelling abstract contourites are common morphological features along continental margins where currents encounter the seafloor they can provide long term archives of palaeoceanography may be prone to sediment instability and can have a great potential for hydrocarbon exploration despite their importance and increasingly recognised ubiquitous occurrence worldwide the link between oceanographic processes and contourite features is poorly constrained in particular it is unclear under which specific conditions sediments are mobilised modified and deposited by bottom currents here we aim to determine key bottom current characteristics velocity and bottom shear stress affecting contourite deposition by assuming that recent oceanographic regimes may be extended back in time over the past glacial interglacial cycles with strong winter circulation assumed similar to glacial conditions and weak summer circulation to interglacials we present an integrated study from the nw mediterranean sea that couples results of the mars3d hydrodynamic model with high resolution sedimentological and geophysical data piston cores multibeam bathymetry and high resolution seismic data near bottom circulation was modelled during winter and summer 2013 as representative of past periods of high and low current intensity respectively model results match well with the extent of contourite depositional systems and their different localised morphologic elements we deduce that higher intensity events control the formation of erosional features such as moats and abraded surfaces the heterogeneous distribution of bottom current intensity on slopes explains the development of different types of contourite drifts plastered drifts form in zones of low bottom current velocities constrained upslope and downslope by higher current velocities separated elongated mounded drifts develop where fast bottom currents decelerate at foot of the slope in contrast no mounded contourite morphologies develop when the current velocity is homogeneous across the slope especially in margins prone to downslope sediment transport processes in confined basins gyres may transport sediment in suspension from a margin with a high sediment supply to an adjacent starved margin favouring the development of fine grained contourites in the latter our results provide new insights into how detailed bottom circulation modelling and seafloor geomorphological analyses can improve the understanding of palaeoflow regimes at least over time spans when the overall paleogeography and the distribution of contourite drifts is comparable to present day conditions the approach of coupled hydrodynamic models and geomorphological interpretations proposed here for depositional erosional and mixed contourite features may be used to understand other areas affected by bottom currents and for a better conceptual understanding of bottom current processes and their interactions with the seafloor

rheological and tectonic modeling of salt provinces abstract technological improvements and a more rigorous research approach have led the petroleum industry to renew and expand its interest in physical modeling of faulting associated with halokinesis salt tectonics and the formation of structural hydrocarbon traps can be reproduced in models using viscous polymers for the substratum and frictional plastic granular materials for the overburden the fault patterns simulated in these dynamically scaled models are remarkably similar to those in depth converted seismic sections scale models are therefore useful for generating new concepts and for reconstructing the structural evolution of hydrocarbon traps although even unsealed models may help generating ideas the full transfer of quantitative data requires that models be dynamically scaled to their natural prototypes previously published scaling theory for salt tectonics has erroneously assumed fluid behaviour of the overburden this paper provides a sound scaling approach for geological deformations involving brittle overburdens on ductile substrata rheological data from overburden rocks and salt are compiled and compared to model rheologies using dimensions of laboratory analogs and other intrinsic material properties scaling approaches are compared and rules are formulated for achieving dynamic similarity in models of salt tectonics including those with synkinematic sedimentation

the effect of ductile lithic sand grains and quartz cement on porosity and permeability in oligocene and lower miocene clastics south china sea prediction of reservoir quality ductile clay rich sand grains control porosity and permeability in the fluvio deltaic oligocene and lower miocene sandstones of the south china sea ductile grains account for between approximately 5 and 50 of the original sand grain population there is a pronounced loss of porosity with increasing burial depth in the basin at depths of less than 3000 m this is due solely to ductile grain compaction where the rate of porosity loss with depth increases with increasing ductile grain content at depths greater than 3000 m the steep porosity loss with depth is due to combined ductile grain compaction and quartz cementation the amount of quartz cement increases with increasing burial depth however cleaner sandstones tend to have greater amounts of quartz cement at any given depth below 3000 m this leads to convergence of porosity evolution for the clean and ductile rich sandstones below 3000 m there is a rapid loss of permeability with decreasing porosity because compaction of ductile grains smears them between rigid quartzose grains leading to blocked pore throats a consequence of this process is that the lowest permeabilities are found in sandstones with the highest ductile grain contents quartz cement does not have a clear and discernible control on permeability the pronounced loss of porosity with increasing depth and permeability with decreasing porosity leads to low permeability at relatively shallow burial depths reservoir quality is thus controlled by the nature of the primary sand and depth of burial the sediment supply system led to systematic changes in ductile grain content across the basin with ductile content increasing into the more distal part of the sediment system the consequence is that depth of economic basement in terms of porosity or permeability can be predicted as a function of ductile grain content and burial depth for prospects across the basin

diagenesis and provenance of silurian quartz arenites in south eastern new york state abstract combined scanning electron microscopy cathodoluminescence and optical microscopy sem cl om of single quartz grains was used to determine the diagenetic history and provenance of framework grains in quartz arenites of the silurian shawangunk conglomerate and binnewater sandstone in south eastern new york state most sand sized sedimentary rocks of these two units experienced compaction and quartz cementation after deposition except for those with high matrix or pseudomatrix content no primary porosity is left today and secondary porosity is insignificant leaving the shawangunk conglomerate and binnewater sandstone with poor reservoir qualities the medium to coarse sand fraction of the shawangunk conglomerate and binnewater sandstone is dominated by quartz of plutonic origin of these usually sub rounded to rounded grains 10 15 carry remnants of inherited quartz cement indicating recycling from a sedimentary source such as quartz rich sedimentary rocks of the former iapetus passive margin in contrast polycrystalline vein quartz pebbles in the shawangunk conglomerate were most likely derived from a proximal crystalline source in the taconic orogen to the east formation of the shawangunk conglomerate and binnewater sandstone quartz arenites was likely supported by subtropical climatic conditions given the latitudinal position of eastern north america during the silurian with relatively high mean annual temperatures and high precipitation rates which accelerated the breakdown of unstable grains

compaction of lithic sands experimental results and applications compaction experiments showed that the degree of physical compaction of a lithic sand is related to the amount and type of lithic material present these experiments produced a product that is texturally indistinguishable from natural lithic sandstones generally sedimentary lithic fragments are more ductile than metamorphic lithic fragments volcanic lithic fragments when altered to phyllosilicate minerals by weathering or diagenesis are extremely ductile mineralogy and intragranular microporosity influence ductility ratios based on weight percent of soft ductile minerals clay and micas to hard brittle minerals quartz and feldspar within the lithic fragments provides a good indication of ductility a ratio greater than 1 indicates the lithic material will be h ghly ductile microporous lithic fragments are more ductile than dense lithic fragments physical compaction models were developed based on experimental data from well sorted lithic sandstones for which the percentage of preserved porosities were functions of the effective stress the type of lithic material and the quantity of lithic material these models are derived from laboratory sandstones with at least 25 lithic grains in the following categories moderately ductile metamorphic lithic fragments highly ductile shale lithic fragments and extremely ductile altered volcanic lithic fragments application of the compaction models of the experimental compaction techniques to modern subsurface sand samples or outcrop equivalents can provide valuable estimates of the preserved porosities i e reservoir potential for lithic sandstones that may be exploratory objecti es in frontier basins examples using the models and experimental compaction techniques for exploration are given experimental data showed that precompaction cement and overpressure may be beneficial to porosity preservation an early formed partial cement can retard compaction and preserve porosity by stabilizing the sand pack a later cement does not have this beneficial effect overpressure when developed early retards compaction by reducing the effective stress of course a late developing overpressure is not effective at preserving porosity because compaction is an irreversible process

the role of detrital composition and climate on the diagenetic evolution of continental molasses evidence from the cambro ordovician guaritas sequence southern brazil abstract the cambro ordovician molassic guaritas sequence camaqua basin southern brazil comprises alluvial fan and braided fluvial sandstones and conglomerates with intercalated aeolian and lacustrine deltaic deposits and andesitic lava flows the sediments display a complex detrital composition derived from plutonic gneissic acidic volcanic and low grade metamorphic source rocks this detrital assemblage was strongly modified by semi arid continental near surface diagenesis early cementation by hematite smectite quartz and calcite and the relatively limited burial prevented strong compaction and preserved some primary macroporosity in most of the sandstones whereas the absence of early cements and or abundance of ductile grains promoted substantial porosity destruction by compaction and the inhibition of further diagenetic modifications the diagenetic dissolution and replacement of volcanic rock fragments and detrital feldspars by clays and albite changed the original framework composition as well as the tectonic provenance classification of the sandstones detailed quantitative petrographic study allowed the reconstruction of the original detrital compositions and the distinction of six different pathways of diagenetic evolution of the sandstones attesting to the efficiency of this method for diagenetic modelling and provenance analyses of ancient sandstones

experimental diagenesis exploratory results we conducted experiments in which a granular mixture of quartz and labradorite was deformed in compression at elevated temperatures 200 350 c and pressures 100 mpa in the presence of deionized water following initial consolidation of the material by application of the loads at room temperature a second hydrothermal phase of consolidation was observed when the temperature was increased with the loads fixed the strain rate during this hydrothermal consolidation decayed approximately exponentially with time and was accompanied by only minor porosity reduction the sample permeability decreased rapidly during the hydrothermal consolidation and continued to decrease following cessation of the deformation the rate of this self sealing process was a complex function of temperature scanning electron microscopy and microprobe analysis of the indurated post experimental material showed albitization of the feldspar especially in highly deformed regions analysis of post experimental fluids show that si in solution increased with increasing flow and temperature fluid rock equilibrium was not achieved within the short durations of the experiments 50 60 hours our interpretation is that deformation occured by grain boundary sliding aided by solution and reaction at high stress contacts and sealing occurred by precipitation in low stress regions in the throats of pores

sem petrography of eastern mediterranean sapropels analogue data for assessing organic matter in oil and gas shales abstract examination of organic matter hosted pore systems in unconventional reservoir rocks has drawn attention to the appearance of sedimentary organic matter om as seen in high resolution sem images field emission sem imaging of eastern mediterranean sapropels pliocene pleistocene age from ocean drilling program drill sites was performed on samples prepared by ar ion cross section polishing the immaturity of marine kerogen in these rocks allows inspection of petrographic textures without overprints related to thermal maturation hydrocarbon generation kerogen in these samples includes discrete particles that in some cases contain primary intragranular pores the most abundant organic matter is in the form of microns thick flaky or stringy material largely nonporous and internally amorphous and lacking the well defined shapes of discrete particles this dominant om has behaved in a highly ductile manner in compaction and is now highly pervaded into intergranular spaces between silt and clay size grains a portion of the larger mineral hosted pores remain open unfilled by ductile om minor nanometer scale pores of uncertain origin occur in the dominant om silt and clay size mineral crystals are distributed in organic matter of most types and it is difficult to fully ascertain if the om mineral mixing has occurred during compaction versus during aggregation during gravity settling marine snow sedimentation or through sediment accumulation in om rich microbial mats results indicate that sediments rich in marine kerogen are subject to substantial compactional porosity loss in early burial these observations of marine detrital organic matter in its early diagenetic state provide a useful baseline for interpretation of petrographic features in more mature om rich mudrocks it is clear that petrographic discrimination of diagenetically generated organic matter bitumen and related om types from ductile dispersed amorphous detrital om kerogen using sem data will be challenging in the absence of compositional information

impacts of sedimentology and diagenesis on pore structure and reservoir quality in tight oil sandstone reservoirs implications for macroscopic and microscopic heterogeneities abstract integrated analysis of reservoir quality pore structure depositional and petrologic characteristics and types and degree of diagenetic alterations was done in this study by employing petrophysical evaluation thin section observation stable isotope analysis scanning electron microscopy combined with eds x ray computed tomography and high pressure mercury intrusion the purpose was to investigate the macroscopic and microscopic heterogeneities and the effects of depositional factors and diagenetic alterations responsible for them the results indicate that the chang 8 tight oil sandstone of the longdong area in the ordos basin can be divided into three categories namely the type i reservoir with porosity greater than 10 and permeability greater than 1 0 md having sparse lenticular distributions in the mouth bar of the braided delta front the type ii reservoir with porosity of 6 10 and permeability of 0 1 1 0 md mainly distributing in the distributary channel and the type iii reservoir with porosity less than 6 and permeability less than 0 1 md having a reticular distribution in the distributary bay the type i reservoir has an intergranular pore inter p dominant pore system with a greater pore throat radius 1 10 m a larger pore volume and better connectivity the type ii reservoir has a mixed system consisting of intragranular pores intra p and inter p with a pore throat radius of 0 1 1 m smaller pore volume and worse connectivity the type iii reservoir is characterized by an intra p dominated system with a radius between 10 and 500 nm smallest pore volume and worst connectivity the wide range of porosity permeability and pore structure parameters can be attributed to the frequent variations in depositional facies and diagenetic alterations larger grain size higher content of quartz and feldspar and moderate grain coating chlorite content less than 8 are favorable for the preservation of intergranular pores and dominate the formation of the type i reservoir the mesogenetic calcite and ferrocalcite cementation and pore filling kaolinite precipitation obstruct the intergranular space and are the predominant factors tightening the reservoirs in the distributary channel and distributary bay leading to multi scale heterogeneities secondary porosity from dissolution plays a much more important role in contributing to the porosity and permeability of the type ii and iii reservoirs than of the type i reservoir the study provide a comprehensive understanding for the multi scale heterogeneities and can be used to predict the potential high quality zones in tight oil sandstone reservoirs

what classic greywacke litharenite can reveal about feldspar diagenesis an example from permian rotliegend sandstone in hessen germany abstract rotliegend siliciclastic sediments in southern hessen germany are a good example of dissolution of detrital feldspars which is a common feature in many sandstones dissolution occurred after mechanical compaction of the lithic rich sandstone which experienced framework collapse with pores and pore connections filled and obstructed by deformed ductile lithic grains pseudomatrix thereby reducing pore space to microporosity the advanced degree of compaction and reduced porosity caused low permeability and low hydraulic conductivity of the rock mass this is further reduced by the presence of wackes and shales that occur intercalated with the sandstones feldspar dissolution thus took place in low permeable sediments when large scale flow of meteoric or acidic fluids is ruled out as a cause of feldspar dissolution mineral precipitation illite kaolinite and albite took place within pseudomatrix and detrital matrix as well as in secondary pores created by feldspar dissolution feldspar was the source for the authigenesis the system was thus closed during burial after framework collapse and diagenetic reactants in the form of detrital components were already present within the system the original mass was preserved but redistributed and diagenetic minerals were the local sinks for the dissolved reactants precipitating within the system this also suggests that burial diagenesis in general might be more mass conservative than usually assumed rotliegend sandstones thus form a case where despite of the lack of external exchange of mass by fluid flow major diagenetic processes did take place and significantly modified the original mineralogy and texture feldspar diagenesis can take place from other processes than mere large scale flushing of open systems as often supposed it implies that the volumes of rock affected by feldspar diagenesis may be much larger than anticipated based upon the common hold believe that feldspar diagenesis is linked to unconformities and surface weathering or dissolution in near surface aquifers

currents water masses eddies and jets in the mediterranean levantine basin abstract hydrographic measurements in the southeastern levantine basin are analyzed and the climatological water masses of the region and their seasonal variations are identified we observe the formation of the salty and warm levantine surface water layer lsw we characterize the subsurface atlantic water layer aw and we describe the properties of the thermocline waters called levantine intermediate waters liw the baroclinic dynamical modes are computed for the climatological stratification parameters the empirical orthogonal function eof analysis of the vertical shear profiles shows that considerable energy is contained in the second eof at the thermocline and deep levels maps of the baroclinic streamfunction field referred to 700 meters are displayed 16 instantaneous flow field realizations show an intense mesoscale eddy file never revealed before in the region the space scales of the eddies are about 100 km and a smaller scale 60 70 km variability is also evident the eddies are pres

variability of the large scale general circulation of the mediterranean sea from observations and modelling a review abstract in this paper we present an overview of the most recent findings about the mediterranean sea present day circulation structure both historical observations and numerical model simulations are presented outlining the differences and agreement the model simulations are presented for both an eddy resolving and a coarse resolution numerical model and the results are intercompared the importance of the mesoscales in modifying the large scale flow field is elucidated the critical point is the discovery of the large amplitude interannual variability of the circulation and water mass structure associated with the anomalies of atmospheric forcing over the basin the seasonal variability can be strictly related to changes in heat and momentum fluxes while the interannual variability has a component which is related to the mesoscale field the latter is very intense in the algerian current region and levantine basin but different in structure in the two regions results are shown which confirm the importance of wind driving in establishing the kinetic energy of the flow field by comparing the current transport at the strait of corsica with observations in conclusion the essential characteristics of the present day circulation are associated with the atmospheric forcing and the basin topographic structure results from palaeoceanographic simulations for the last 20 000 years show that changing the atmospheric forcing can cause large changes in the circulation structure which may have affected sapropel formation

open ocean convection observations theory and models we review what is known about the convective process in the open ocean in which the properties of large volumes of water are changed by intermittent deep reaching convection triggered by winter storms observational laboratory and modeling studies reveal a fascinating and complex interplay of convective and geostrophic scales the large scale circulation of the ocean and the prevailing meteorology two aspects make ocean convection interesting from a theoretical point of view first the timescales of the convective process in the ocean are sufficiently long that it may be modified by the earth s rotation second the convective process is localized in space so that vertical buoyancy transfer by upright convection can give way to slantwise transfer by baroclinic instability moreover the convective and geostrophic scales are not very disparate from one another detailed observations of the process in the labrador greenland and mediterranean seas are described which were made possible by new observing technology when interpreted in terms of underlying dynamics and theory and the context provided by laboratory and numerical experiments of rotating convection great progress in our description and understanding of the processes at work is being made

factors controlling reservoir properties and hydrocarbon accumulation of lacustrine deep water turbidites in the huimin depression bohai bay basin east china abstract lacustrine deep water turbidite plays are a novel area for exploration in the huimin depression bohai bay basin turbidites in the shang 847 block a typical turbidite play in the huimin depression provide an opportunity to study the factors controlling the reservoir properties and hydrocarbon accumulation in lacustrine turbidite sandstones the reservoir quality of turbidite sandstones very fine grained moderately to well sorted mainly lithic arkose in this study area are mainly controlled by the distribution patterns of carbonate cements and pseudomatrix significant inverse relationships exist between the volume of carbonate cement and both porosity and permeability of the turbidite sandstones carbonate cement is located preferentially near the margins of the sandstone bodies sandstones with distance from the sandstone mudstone contact surface less than 0 7 m or with thickness less than 1 2 m are commonly tightly cemented carbonate cement 15 with low porosity and permeability lower than 10 and 0 1 md respectively the source of carbonate cement was most likely external probably derived from the surrounding mudstone most pore filling carbonate cements occurred during late diagenesis at burial depths greater than 2200 m the petrophysical properties of turbidites have a positive relationship with the content of kaolinite and chlorite but have a negative relationship with the content of illite 2 d and 3 d reconstructions of non oil bearing and oil bearing layers indicate that dissolution of carbonate cement feldspars and unstable rock fragments was more developed in oil bearing layers than in non oil bearing layers and hance oil bearing layers have higher porosity and larger pore sizes petrophysical property appears to have a significant effect on the hydrocarbon accumulation in the turbidite sandstones sandstones with porosities lower than 9 and or permeabilities lower than 0 78 md are not prone to contain oil

dolomite diagenesis and porosity preservation in lithic reservoirs carmopolis member sergipe alagoas basin northeastern brazil the lithic sandstones and conglomerates of the carmopolis member of the muribeca formation aptian were deposited bp fan deltas alluvial fans and braid deltas that prograded from low grade metamorphic terrains into the sergipe alagoas rift basin during

insights from petrography mineralogy and u pb zircon geochronology into the provenance and reservoir potential of cenozoic siliciclastic depositional systems supplying the northern margin of the eastern black sea the eastern black sea is one of the few remaining underexplored hydrocarbon basins in europe reservoir quality is a key risk factor in the basin the analysis of up dip portions of oligocene to pliocene depositional systems exposed around its northern and eastern margins enable the composition and provenance of sandstones within the basin to be predicted two major sources of quartz rich sandstone are present the russian western greater caucasus which became a subaerial sediment source in the oligocene and the east european craton scythian platform these are predicted to form better quality reservoirs at shallow and moderate burial depths than their rock fragment rich counterparts due to lesser amounts of compactional porosity loss oligo miocene sandstones from the russian western greater caucasus were deposited as turbidites in the tuapse trough sandstones from the east european craton scythian platform were largely trapped within the indolo kuban basin north of the greater caucasus they only entered the eastern black sea in large volumes from latest miocene or pliocene time in the region of the kerch taman shelf at the western tip of the greater caucasus however it is possible that a precursor to this system supplied the oligocene to early miocene reservoir sandstones within the subbotina field the dziruli massif in western georgia also generated quartz rich sandstones but these are not thought to have entered the black sea

variations in eastern mediterranean hydrology during the last climatic cycle as inferred from neodymium isotopes in foraminifera abstract the nd isotopic compositions end of mixed planktonic foraminifera have been analyzed in two sediment cores collected in the nile deep sea fan in order to reconstruct past end of the eastern mediterranean deep water emdw and to assess the relative contributions of nile discharge and modified atlantic water maw inflow to the eastern mediterranean sea hydrology as well as their potential control on anoxic events over the last climatic cycle the two foraminiferal end records are similar and display an increase in end values during the african humid periods superimposed on this precession forced variability insolation received by the earth at low latitudes the record of variations in foraminiferal end indicates a 2 unit decrease in end during the interglacial marine isotope stages mis 5 and 1 compared to glacial mis6 4 3 and 2 the end results suggest that the long term glacial to interglacial changes in nd isotopic composition of emdw were not entirely induced by variations in nile river discharge and saharan dust inputs decreases in end during mis5 and mis1 interglacials indicate an increase in the contribution of unradiogenic maw to the eastern mediterranean sea related to high sea level stands and greater seawater exchange between the north atlantic and mediterranean basins in addition radiogenic seawater end values observed during african humid periods and sapropel events are associated with an intensification of nile discharge and an increase in residence time of deep water masses in the eastern mediterranean sea which induces an increase in the interaction between deep water masses and radiogenic sediments along the margin of the eastern mediterranean sea results confirm that an intensification of the hydrological exchanges between the western and eastern mediterranean basins during high sea level stand and the subsequent higher proportion of atlantic water in the levantine basin may have preconditioned the eastern mediterranean sea to sapropel depositions during the last climatic cycle

depositional environment of the lower cretaceous upper albian winton formation at isisford central west queensland australia inferred from sandstone concretions abstract numerous vertebrate and plant fossils have been found in ex situ sandstone concretions near isisford in central west queensland since the mid 1990s these concretions are found in the lower cretaceous portion upper albian 100 5 102 2 ma of the winton formation the lower most winton formation is thought to have formed in a fluvial channel or flood basin setting proximal to the eromanga sea but due to the scarcity of good exposures the local depositional environment at isisford has not been ascertained minimal compression of vertebrate and plant fossils a lack of grain suturing predominantly cement supported fabric and fractures running through calcite cement as well as fossil bone and framework grains indicates that concretions formed during early diagenesis pre compactional or syndepositional calcite stable isotope 18ovpdb values range from 12 25 to 4 indicating mixed marine and meteoric pore waters and 13cvpdb values range from 5 3 to 4 1 indicative of both sulfate reduction and methanogenesis of organic material including decaying vertebrate soft tissues in the burial environment the mixed marine and freshwater signature suggests a marginal marine setting possibly deltaic or estuarine connected to the regressive epicontinental eromanga seaway at around 102 100 ma this is not inconsistent with the lithology from nearby cores coupled with isisford fossil vertebrate ecology personal observation our research demonstrates the utility of investigating ex situ concretions to refine paleoenvironments at localities where little or no outcrop is available and traditional facies analysis is impractical

role of pressure solution in the formation of bedding parallel calcite veins in an immature shale cretaceous southern uk bedding parallel fibrous calcite veins in black shales cretaceous southern uk were investigated using a combined field stable isotopic geochemistry petrographic and crystallographic method to examine their formation mechanism calcite veins occur in all shale beds and are most abundant in the bituminous shales of the chief beef beds the calcite fibres in these veins exhibit either an antitaxial fibre growth with curvy stylolites as the median zone or a predominantly syntaxial upwards growth the calcite veins range from 0 49 to 1 78 of 13c values and 6 53 to 0 03 of 18o values which are both similar to those of their host shales our petrographic observations demonstrate that subhorizontal and interconnecting microstylolite networks commonly occur within the calcite veins equant calcite grains in the median zones exhibit indenting truncating and also interpenetrating grain contacts it is interpreted that the fibrous calcite veins were sourced by neomorphic calcite from their host shales with evidence from the 13c signatures pressure solution features stylolites microstylolites and grain contact styles and embedded fossil ghosts within the veins the diagenetic fluids from which calcite was precipitated were a mixing of the original seawaters and 18o depleted meteoric waters development of bedding parallel calcite veins is considered to have been enhanced by pressure solution as a positive feedback mechanism which was facilitated by the overburden pressure as the maximum principal stress calcite fibres with a predominant subvertical c axis orientation exhibit a displacive growth in porous shales and a replacive growth at vein limestone contacts this study highlights the critical role of pressure solution in the formation of bedding parallel calcite veins during burial and diagenesis of immature black shales

a sedimentological process based approach to depositional reservoir quality of deep marine sandstones an example from the springar formation northwestern voring basin norwegian sea reservoir properties of deep marine sandstones deposited by various sediment gravity flow types in the northwestern voring basin norwegian sea are characterized using detailed sedimentological and petrographic analyses the sandstones are quartz arenites and subarkoses having similar mineralogical compositions a low degree of diagenetic modification and low to moderate volumes of quartz cement up to 6 however significant textural variability is observed for the various sandstone types which were subdivided based upon their interpreted processes of deposition in the studied wells there is a predominance of turbidites deposited by high density turbidity currents hdts and a range of hybrid event beds hebs hdts are coarser grained and contain less detrital clay than the various hebs in addition the dominant grain size of hebs decreases down the depositional profile whilst the content of detrital clay increases porosities of the various bed types span the same interval but overall the hdts and proximal hebs have a higher proportion of samples with porosities higher than 20 compared to distal hebs permeabilities in contrast are significantly different with the hdts having permeabilities approximately two orders of magnitude higher than clay rich hebs a comparison of the observed variability in composition and textural parameters with porosity and permeability indicates that sedimentological flow processes control the depositional reservoir quality of deep marine sandstones understanding these processes therefore enhances our ability to predict distribution of reservoir quality in deep marine systems

geometric models of porosity reduction by ductile grain compaction and cementation pore volume reduction of sediments by plastic deformation during compaction and by cementation of grains has been evaluated for different proportions of ductile and hard grains we represent the compaction behavior of grains with a purely geometric model which uses the cooperative rearrangement algorithm to produce dense random packings of partly interpenetrating spheres we varied the fraction of grains assumed to be ductile and the radius of the rigid core of the ductile grains the predicted relationship between the fraction of ductile grains in the sediment and the porosity after compaction agrees well with previously published experimental data in the literature the radius of the rigid core of the ductile grains is an effective way to represent different kinds of ductile material ranging from brittle rigid radius 0 9 to extremely ductile rigid radius 0 7 we simulated quartz cementation in our compacted rock by adding isopachous cement cement thickness was reduced on the smaller grains and increased on the larger grains to account for presumed export of pressure dissolved material from finer grained regions and the import of material into coarser grained regions these simulations yield descriptions of pore scale geometry resulting from processes common in sandstones modeled pore geometry provides insight into transport properties of such rocks for example the models predict to within a factor of five the permeability of samples of tight gas sandstones having little intragranular porosity

quantifying tectonic versus erosive denudation by the sediment budget the miocene core complexes of the alps abstract the denudation budget of the alps is quantified for the main period of lateral extrusion between 22 and 12 ma the relative importance of tectonic denudation increases from w to e from 70 in the lepontine window in the swiss alps to 80 in the tauern window and to more than 95 in the rechnitz window the driving mechanism of tectonic denudation was eastward extrusion due to an unconstrained orogenic margin in the pannonian basin tectonic denudation in the alps was responsible for about 30 of the total exhumation between 22 and 12 ma

structural controls on mechanical compaction within sandstones an example from the apsheron peninsula azerbaijan abstract mechanical compaction of sand rich reservoirs usually occurs during shallow burial and involves the rearrangement of framework grains and the ductile deformation of soft lithoclasts the reservoir quality porosity and permeability of some neogene sandstones of the south caspian basin has however been dramatically reduced by mechanical compaction involving extensive grain fracturing i e porosity collapse these sandstones were probably susceptible to pervasive grain fracturing because they were buried rapidly and experienced compressional deformation prior to reaching 80 c consequently they did not undergo quartz cementation and were therefore exposed to high stresses while they were extremely weak grain size and structural position are also important controls on the distribution of grain fracturing in the onshore analogue in the apsheron peninsula microstructural analysis confirms that susceptibility to distributed grain fracturing increases with increasing grain size structural position has also an important impact on the distribution of porosity collapse in particular sandstones within the hinges of folded sections have undergone much more extensive grain fracturing than within the surrounding area the increased stresses in this structural position have enhanced distributed grain fracturing and subsequent deformation band development

late holocene productivity and hydrographic variability in the eastern mediterranean inferred from benthic foraminiferal stable isotopes 1 the paleoproductivity paleo oxygenation and paleohydrographic configuration of the southeastern mediterranean during the late holocene was reconstructed on the basis of the isotopic composition of the epibenthic heterolepa floridana shallow endobenthic uvigerina mediterranea and the deeper endobenthic bulimina inflata from two high resolution cores ga 112 470 m and ga 110 670 m the 13c between h floridana and u mediterranea reveals four intervals of enhanced productivity from 3 3 2 6 2 3 1 9 1 5 1 1 and 0 8 0 4 kyr bp coinciding with increased nutrient supply by the nile river the entire basin was well aerated with oxygen consumption varying between 1 0 and 3 5 ml o2 l oxygen consumption increases toward present day probably because of higher accumulation of total organic carbon at 1 7 kyr bp coinciding with the appearance of the mesotropic benthic species the hydrographic configuration of the basin has changed during the course of the last 3 75 kyr the levantine intermediate water liw deepens below 470 m between 3 3 and 2 0 kyr and especially between 2 5 and 2 0 kyr during the last 1 5 kyr the liw becomes shallower than 470 m similar to the present day the change in the hydrographic configuration reflects changes in evaporation precipitation ratio and in temperature

postaccumulation sandstone porosity evolution by mechanical compaction and the effect on gas saturation case study of the lower shihezi formation in the bayan aobao area ordos basin china abstract porosity evolution and reservoir quality are strongly affected by mechanical compaction however the compaction induced porosity reduction process in sandstone reservoirs during the postaccumulation period and its effect on gas saturation remain poorly understood by studying the sandstones in the bayan aobao area we were able to quantify the porosity evolution and gas saturation variations caused by mechanical compaction during the postaccumulation period through fluid inclusion analysis and mathematical modeling moreover we verified our findings by compaction experiments and geological statistics fluid inclusion microthermometry was employed to determine the hydrocarbon accumulation periods and the highest homogenization temperature of the two phase aqueous fluid inclusions coexisting with natural gas fluid inclusions i e 115 c with a corresponding geological age of 140 ma was regarded as the beginning of the postaccumulation stages with these data we constructed an inversion evolution model based on the geologic statistical model of sandstone mechanical compaction for the postaccumulation period and determined the gas saturation changes based on compaction porosity evolution the modeling results indicate that the sandstone porosity decreased greatly during postaccumulation subsidence and increased slightly during late stage uplift while the gas saturation increased with both the porosity decrease during the postaccumulation subsidence and the porosity increases during the later uplift the modeling results of subsidence are concordant with the compaction experiments which also show that the larger the initial porosity the greater the porosity reduction the uplift modeling results demonstrate that an erosion induced decrease in burial depth allowed the sandstone porosity to increase which is supported by some scholars findings e g neuzil and pollock 1983 jiang et al 2004 zhang 2013 and by the positive correlation between sandstone porosities and restored geologic unit thicknesses in the study area however the inversion modeling indicates that the reason for the porosity rebound in litharenites is that the increase in elastic porosity slightly exceeds the decrease in viscoplastic porosity which would have been different if the uplift induced erosion rate had been distinctly lower gas production test data and restored geologic unit thicknesses indicate that uplift and erosion may be able to enrich sandstone gas reservoirs to a certain extent consistent with the calculated gas saturation variation results but a full understanding of gas saturation evolution awaits further studies the inversion model can provide a powerful tool for quantitative analysis of the sandstone compaction process during the postaccumulation period which could be used for reference in other similar regions

paleoenvironmental conditions at core kc01b ionian sea through mis 13 9 evidence from calcareous nannofossil assemblages quantitative analyses on calcareous nannofossil assemblages on high temporal resolution 600e800 years have been carried out from core kc01b in the ionian sea eastern mediterranean throughout marine isotope stage mis 13e9 between 500 and 300 ka this is an interval of considerable climate changes known as the mid brunhes event which includes mis 11 considered as a possible analogue for future interglacial conditions in the mediterranean core the interval is characterized by the dominance of gephyrocapsaspp as also known fromocean records calcareous nannofossil abundance fluctuations have been interpreted in terms of modification of sea surface primary productivity water stratification and temperature specifically the increase in abundance of gephyrocapsa caribbeanica and small gephyrocapsa coupled with decreases of florisphaera profunda syracosphaera spp and rhabdosphaera spp suggests enhanced primary productivity mixed surface waters during interglacial stages and at the terminations which can be interpreted in terms of interaction between climate changes and mesoscale oceanographic circulation on the other hand distributions of calciosolenia spp oolithotus spp and umbilicosphaera sibogae which are inphase with d 18 o curve showing higher abundances at the lighter values of the marine

a review of the physical oceanography of the mediterranean outflow abstract the physical oceanography of the mediterranean sea is reviewed with particular emphasis on the mediterranean outflow in the gulf of cadiz in this region the dense mediterranean water forms a high velocity bottom current that interacts strongly with the sea floor the major energy source for the plume comes from the release of potential energy as the plume descends the continental slope and the major energy sink is work against bottom stress which is as large as 4 pa where the plume begins to descend the continental slope in this region the current makes a nearly inertial turn that would otherwise appear to be steered by the underlying topography the mediterranean plume entrains the overlying north atlantic central water and thereby loses much of its density anomaly the mixed mediterranean water becomes neutrally buoyant in the lower portion of the north atlantic thermocline near cape st vincent there are then two preferred transport modes having somewhat different temperature and salinity whose distinct characteristics can be found far into the open north atlantic the temperature salinity and volume of the mediterranean water in the strait of gibraltar and in the gulf of cadiz appear to be roughly constant since modern measurements have been made the estimated westward transport of mediterranean water has gone down considerably as direct measurement techniques have been applied a recent estimate is that the westward transport of pure mediterranean water is only about a half a sv 1 sv 106 m3 s 1 the transport of mixed mediterranean water in the western gulf of cadiz is larger by about a factor of three or four because of the entrainment of north atlantic water

the valle di manche section calabria southern italy a high resolution record of the early middle pleistocene transition mis 21 mis 19 in the central mediterranean abstract the on land marine valle di manche section crotone basin calabria southern italy one of the candidates to host the gssp of the middle pleistocene ionian stage preserves a manifold record of independent chronological paleoclimatic and stratigraphic proxies that permit a straightforward correlation with marine and terrestrial reference records at the global scale in particular the section holds an excellent record of the matuyama brunhes magnetic reversal which occurs in the midst of marine isotope stage mis 19 we report on a complete revision of the section that improves dramatically the available dataset especially in the stratigraphic interval straddling the lower middle pleistocene boundary our benthic 18o record provides evidence that the matuyama brunhes transition the stratigraphic position of which is marked by a prominent tephra the pitagora ash occurred during full mis 19 in agreement with many records worldwide we obtained an age of 786 9 5 ka for the matuyama brunhes magnetic reversal and pinpointed the paleomagnetic transition of to a 3 cm thick interval indicating that the event was very fast since the section fulfills all the requirements to host the gssp of the ionian stage we propose that the boundary should be placed at the base of the pitagora ash ca 12 5 cm below the midpoint of the matuyama brunhes reversal

impact of diagenesis on reservoir quality and heterogeneity of the upper triassic chang 8 tight oil sandstones in the zhenjing area ordos basin china abstract reservoir quality and heterogeneity are critical risk factors in tight oil exploration the integrated analysis of the petrographic characteristics and the types and distribution of diagenetic alterations in the chang 8 sandstones from the zhenjing area using core log thin section sem petrophysical and stable isotopic data provides insight into the factors responsible for variations in porosity and permeability in tight sandstones the results indicate that the chang 8 sandstones mainly from subaqueous distributary channel facies are mostly moderately well to well sorted fine grained feldspathic litharenites and lithic arkose the sandstones have ultra low permeabilities that are commonly less than 1 md a wide range of porosities from 0 3 to 18 1 and two distinct porosity permeability trends with a boundary of approximately 10 porosity these petrophysical features are closely related to the types and distribution of the diagenetic alterations compaction is a regional porosity reducing process that was responsible for a loss of more than half of the original porosity in nearly all of the samples the wide range of porosity is attributed to variations in calcite cementation and chlorite coatings the relatively high porosity reservoirs formed due to preservation of the primary intergranular pores by chlorite coatings rather than burial dissolution however the chlorites also obstruct pore throats which lead to the development of reservoirs with high porosity but low permeability in contrast calcite cementation is the dominant factor in the formation of low porosity ultra low permeability reservoirs by filling both the primary pores and the pore throats in the sandstones the eogenetic calcites are commonly concentrated in tightly cemented concretions or layers adjacent to sandstone mudstone contacts while the mesogenetic calcites were deposited in all of the intervals and led to further heterogeneity this study can be used as an analogue to understand the variations in the pathways of diagenetic evolution and their impacts on the reservoir quality and heterogeneity of sandstones and is useful for predicting the distribution of potential high quality reservoirs in similar geological settings

the diagenetic controls of the reservoir heterogeneity in the tight sand gas reservoirs of the zizhou area in china s east ordos basin implications for reservoir quality predictions abstract the shan 23 sandstone formations are important exploratory targets for tight gas resources in the zizhou area of the ordos basin in this study we investigated the effects of diagenesis on the heterogeneity of tight sandstone deposits in similar sedimentary facies and identified the main controlling factors of reservoir quality a total of 169 samples were collected from 50 wells for a series of analyses the heterogeneity of the sandstones is mainly controlled by cement and pore throat characteristics which showed regional differences in the study area consistent with the regional variations in the detrital components these results indicate that the diagenesis influenced by the sediment composition is the main controlling factor of the reservoir heterogeneity the compaction dominated by ductile grains is the major cause of the primary porosity losses in the sandstones followed by the quartz and clay kaolinite and illite cementation residual intergranular pores rarely occur in the sandstones with a ductile lithic grain content greater than 2 altered kaolinite and recrystallized illite commonly occur in the sandstones with high ductile grain content residual intergranular pores quartz overgrowths and authigenic kaolinite are the most common phases in the sandstones rich in detrital quartz the dissolution formed secondary pores and provided a minor contribution to reservoirs permeability secondary pores predominantly occur in the quartz arenite due to the preservation of the primary pores the main controlling factor for the quality of the sandstones is the pore type which has pronounced effects on both the pore structure and the pore throat size distribution the residual intergranular pores preserved in sandstones will lead to larger radii and better sorting characteristics of the pore throats which subsequently contribute to the higher permeability therefore the sandstones with the higher content of primary intergranular pores are considered high quality reservoirs they are characterized by quartz richness and mainly located in the zizhou mizhi area the inter crystalline micropores occur in the clay mineral resulting in small sized and poor sorted pore throats they give subordinate contributions to the reservoir quality and are the key factor of the extremely low permeability in sandstones the dry layers of the study area are mainly composed of sandstones dominated by inter crystalline micropores these sandstones are characterized by the high content of ductile grains and are mainly located in the qingjian area

surface water conditions in the mediterranean basin during earliest pliocene as revealed by calcareous nannofossil assemblages comparison between western and eastern sectors abstract the abundant and diverse calcareous nannofossil assemblages found in the sediments of two odp cores from the western site 975b south balearic basin and eastern site 969b mediterranean ridge mediterranean sea have been taken into account for the paleoenvironmental reconstruction of the surface water conditions during the first 490 kyrs immediately following the end of the messinian salinity crisis chronostratigraphically settled at 5 332 ma the areal distribution of the calcareous nannofossils is closely linked to their ecological and environmental affinities mostly driven by temperature salinity nutrients or other chemical parameters of the water masses hence taxa or groups of taxa showing well known ecological behaviors were considered and different environmental evolutions were recognized for the two sectors of the mediterranean basin during the early zanclean early pliocene specifically in the western mediterranean a switching from a warm and oligotrophic water environment showing normal open marine conditions to a colder and eutrophic one characterized by a decrease in salinity rates and the development of a more restricted environment can be recorded conversely in the eastern mediterranean the environmental setting immediately following the msc is indicative of temperate waters and normal open marine conditions which evolves in the younger layers to a warmer environment characterized by high salinity rates and typical of a restricted marine context the timing of the environmental transitions recognized at the two sites has been set through the principal component analysis taxa and groups of taxa reflecting precise ecological affinities have been handled together and a transition interval have been defined between 5 20 5 15 ma and 5 06 4 98 ma and between 5 10 ma and 4 92 ma in the western and eastern mediterranean respectively

diagenetic modeling to assess the relative timing of quartz cementation and brittle grain processes during compaction this study describes porosity reduction by brittle deformation and the application of touchstone sandstone diagenesis modeling software to assess the relative timing and interactions between grain fracturing and cement formation during burial compaction two examples from a previous study of compactional fracturing are used the oligocene frio formation gulf of mexico basin and the cambrian mount simon formation illinois basin united states grain fracturing during compaction creates intragranular fracture surfaces that are favorable sites for quartz nucleation compared to external grain surfaces that may bear coatings that inhibit the nucleation and growth of quartz cement thus the progress of brittle fracture processes during diagenesis affects quartz cementation in turn modeling of the quartz cementation process can serve to place fracturing into its proper context in burial history in the mount simon formation the extent of brittle deformation of quartz grains correlates with reconstructed effective stress at the onset of quartz cementation for frio formation samples however the extent of brittle deformation does not correlate well with reconstructed effective stress obtained using a one dimensional basin model that uses compaction disequilibrium as the dominant mechanism for overpressure generation judging from the observed degree of grain fracturing significant fluid overpressures in the frio may not have developed at the shallow depths indicated by our basin models the degree of compactional fracturing in sandstones constitutes observable evidence that can be used to decipher the complexities of pressure history

abrupt cooling of the mediterranean levantine intermediate water at the beginning of the 1980s observational evidence and model simulation abstract the levantine intermediate water liw is an important water mass for the overall hydrology of the mediterranean sea and there are open questions connected with the possible long term variability of its physical characteristics this paper is dedicated to the analysis and the interpretation of the liw long term variations over the last 50 years it is based on data analysis and model simulations on the one hand new temperature and salinity gridded data of interannual and decadal anomalies have been produced from existing historical datasets on the other hand a long term primitive equation model simulation has been generated to be compared to the observational reconstructions results indicate that the major feature of both datasets observations and model is an intense cooling of the liw 0 24 0 28 c at 200 m depth at the beginning of the 1980s winters 1981 and 1983 around the aegean sea and the cretan arc the amplitude of the cooling is as large as 0 4 c the model simulations force

imaging pores in sedimentary rocks foundation of porosity prediction abstract this review examines the history and current practice of technologies for imaging of pores in sedimentary rocks pores are that portion of the rock volume occupied by components of relative mobility such as water of various salinities microbial life petroleum liquids gases and supercritical fluids through a rock s history the contained pores evolve as the primary detrital assemblage responds chemically and mechanically to changing conditions in the subsurface description and classification of pores based upon their paragenesis depends upon inspection by imaging that allows the pores to be seen and interpreted in the context of historical processes responsible for formation of the pore walls since the late 1960s sample preparation and imaging methodologies that clarified our understanding of pores in their correct historical context have been at the root of important advances in prediction of porosity and related bulk properties in the subsurface these older approaches are now joined by new technologies that serve current efforts to extend predictive capabilities to nm scale pores in the fine grained low permeability rocks that dominate in the deeper parts of sedimentary basins and indeed in the sedimentary record as a whole placing the smallest pores into their proper paragenetic context presents a challenge in the quest to develop predictive models for porosity evolution in fine grained rocks

packing states of ideal reservoir sands insights from simulation of porosity reduction by grain rearrangement abstract the question being tackled in this study is to which extent grain rearrangement contributes to porosity reduction in very well sorted quartzose sands ideal reservoir sands a numerical model rampage an acronym of random packing generator has been developed to address this long standing problem rampage represents a synthesis of various algorithms designed to simulate packing of equal sized spheres which have been used to represent ideal solids liquids and gases as well as natural porous media the results of rampage simulations compare favourably to theoretical and experimental data from various disciplines and allow delineation of the field of gravitationally stable random packing of equal sized spheres in the 2 d state space of porosity p versus mean coordination number n three end member packing states have been identified random loose packing rlp p 45 4 n 5 2 random close packing rcp p 36 3 n 7 0 and bridged random close packing bridged rcp p 39 5 n 5 2 unlike previously proposed models rampage can simulate the transition from rlp to any other point in the stability field the rlp state is fully consistent with wet packed porosities of synthetic sands with lognormal mass size distributions reported in the literature the much higher in situ porosity values reported for modern air packed sands are unlikely to be preserved at depth on geological time scales data on the relation between intergranular volume and burial depth indicate that the observed intergranular volume reduction in the upper 800 m of the sediment column corresponds to the evolution of rlp to rcp and is thus fully explained by non destructive grain rearrangement

quantification of brittle deformation in burial compaction frio and mount simon formation sandstones abstract brittle deformation together with grain rearrangement and ductile grain deformation is a key mechanism of compaction in sandstones quartz cementation by virtue of its impact on sandstone mechanical properties is expected to affect the compaction progress by these various mechanisms sandstone samples of different ages and compositions taken from two basins with contrasting burial histories are used to quantify the relationship between brittle deformation and quartz cementation in the context of burial compaction exponential trends of increasing deformation by microfracturing are observed in both the lithic rich frio formation from the gulf of mexico basin r2 0 81 and in the quartz rich mount simon formation from the illinois basin r2 0 78 the two formations contrast in terms of the observed rate of grain fracture increase with depth a larger number of quartz grains in the mount simon formation undergo fracturing at shallow burial 3 km a larger number of quartz grains are fractured in the frio sandstones cathodoluminescence cl imaging conducted on an sem shows that grain fracturing and subsequent cementation of fractures by quartz can occur before during and after normal quartz overgrowth precipitation although fracturing is generally concurrent with cementation the intensity of brittle deformation for a single fractured grain is independent of depth as illustrated by plotting the ratio of the number of particles in fractured grains versus depth r2 0 21 for frio and 0 03 for mount simon suggesting that once fractured grains do not tend to become the locus of subsequent fracturing apparent fracture apertures in the frio grains are slightly wider average 5 m than in mount simon grains average measurable aperture width 4 m quartz grains in the frio have a variety of fracture morphologies including wedge shaped apertures intense comminution at grain contacts and grains with exploded fabrics apparent fracture apertures in mount simon grains are thinner and transect grains as straight uniform traces differences in fracture intensity and pattern are attributed to the fact that cementation in the frio began at greater depth than cementation in the mount simon combining information on the degree of brittle deformation and the amount of quartz cement localized within microfractures here referred to as cf or volume of intragranular cement allows calculation of the amount that brittle deformation influences compaction in the frio formation 0 12 to 8 37 of porosity loss due to compaction can be attributed to brittle deformation whereas the values for the mount simon formation lie between 0 25 to 2 16 the larger values within both formations are affiliated with deeper samples in which a majority of grains manifest fracturing

hydrography of the eastern mediterranean basin derived from argo floats profile data abstract as the eastern mediterranean integrates different sub basins with important hydrological features during recent decades it has often become a target of study by the oceanographic community the recent expansion of observational tools and methods in the marginal seas has allowed more enhanced studies of the oceanographic processes that dominate such areas in this work temperature and salinity profile data collected by argo floats in the eastern mediterranean are analysed for the period 2004 2017 the spatio temporal variability of the basin s physical properties together with the depicted changes in the different sub basins is investigated in an attempt to construct the latest hydrographic picture of the region the findings describe the dominant water masses and reveal a general positive trend in the basin s thermohaline properties the inter annual variability of the stored heat and salt and their distribution in the water column reveals strong climatic signals that are dominated by previously reported alternations of the general circulation and convection events in the area the latter are correlated with the surface temperature and salinity fields and are traced within the area s different sub basins in the early period 2004 2010 data from levantine and ionian depict inter annual variability of the upper layers salinity field that is correlated with previously reported alternations of the levantine s circulation and intermediate water production in the ionian during the latest period 2012 2017 when the data coverage is denser and more representative for the wider area of the eastern mediterranean the adriatic sub basin presents intense dense water production activity while the aegean sea undergoes a relaxation period with significant variability at intermediate layers due to water mass exchanges

diagenetic heterogeneity in sandstone at the outcrop scale breathitt formation pennsylvanian eastern kentucky twenty seven samples of feldspathic phyllarenite were obtained from three 1 m grids in a large homogeneous distributary bar sand stone body with the goal of elucidating bed scale diagenetic het erogeneity significant variability in the content of both detrital and diagenetic components is present in the sample set this variation is within the range of values predicted from comparison with a large regional data set from the same formation but nonetheless it is large enough to preclude successful prediction of diagenetic prop erties from consideration of average composition and thermal his tory alone grain size is one important local control on the overall abundances of cement and porosity grain size operates to control the overall degree of cementation in these particular rocks indi rectly through its influence on lithic grain content and hence on compaction relatively minor carbonate cement is an exception to this trend and appears to be distributed somewhat randomly with out regard to the size or composition of the detrital components diagenetic heterogeneity of the magnitude documented in this example is correlated to differences in porosity and permeability and therefore has implications for reservoir simulation and explo ration risk assessment prediction of rock properties through dia genetic modeling is more successful if the textural controls on dia genetic heterogeneity are considered

modeling the dispersal of levantine intermediate water and its role in mediterranean deep water formation this paper demonstrates the importance of levantine intermediate water liw in the deep water formation process in the mediterranean using the modular ocean general circulation model at 0 25 resolution 19 vertical levels over the entire mediterranean with an open gibraltar strait liw formation is strongly prescribed in the rhodes gyre region by haney 1971 relaxation while in other regions surface salinity relaxation is much reduced by applying the mixed thermohaline surface boundary conditions isopycnal diagnostics are used to trace water mass movements and volume fluxes are monitored at straits low viscosity and diffusion are used to permit baroclinic eddies to play a role in water mass dispersal the overall water budget is measured by an average flux at gibraltar of 0 8 sv of which 0 7 sv is exchanged with the eastern basin at sicily liw density around 28 95 spreads rapidly after formation throughout the entire levantine due to baroclinic eddies toward the west liw accumulates in the northern and central ionian with some entering the adriatic through otranto and some mixing southward in eddies and exiting to the western mediterranean through sicily liw is converted to deep water in the south adriatic at an average rate of 0 4 sv water exchange through the otranto strait appears to be buoyancy driven with a strong bias to the end of winter march april while at sicily the exchange has a strong symmetric seasonal cycle with maximum transport of 1 1 sv in december indicating the effects of wind driving liw pathways in the west are complex and variable in the tyrrhenian intermediate water becomes uniform on isopycnal surfaces due to eddy stirring west of sardinia two liw boundary currents are formed in the balearic basin one flows northward up the west coast of sardinia and corsica and one westward along the northern african coast the northward current is consistent with observations while the westward current is intermittent for the first 10 years often breaking up into eddies which enter the basin interior some observations of high salinity waters near the african coast may support this interpretation liw retains a subsurface salinity maximum of 38 4 38 5 practical salinity units psu when reaching the northwestern mediterranean contrasting with surface waters fresher than 38 0 psu west mediterranean deep water is formed below 1500 m depth with climatological characteristics when it is mixed and cooled during winter convection in lions gyre

impact of the spatial distribution of the atmospheric forcing on water mass formation in the mediterranean sea the impact of the atmospheric forcing on the winter ocean convection in the mediterranean sea was studied with a high resolution ocean general circulation model the major areas of focus are the levantine basin the aegean cretan sea the adriatic sea and the gulf of lion two companion simulations differing by the horizontal resolution of the atmospheric forcing were compared the first simulation med16 era40 was forced by air sea fields from era40 which is the ecmwf reanalysis the second simulation med16 ecmwf was forced by the ecmwf analyzed surface fields that have a horizontal resolution twice as high as those of era40 the analysis of the standard deviations of the atmospheric fields shows that increasing the resolution of the atmospheric forcing leads in all regions to a better channeling of the winds by mountains and to the generation of atmospheric mesoscale patterns comparing the companion ocean simulation results with available observations in the adriatic sea and in the gulf of lion shows that med16 ecmwf is more realistic than med16 era40 in the eastern mediterranean although deep water formation occurs in the two experiments the depth reached by the convection is deeper in med16 ecmwf in the gulf of lion deep water formation occurs only in med16 ecmwf this larger sensitivity of the western mediterranean convection to the forcing resolution is investigated by running a set of sensitivity experiments to analyze the impact of different time space resolutions of the forcing on the intense winter convection event in winter 1998 1999 the sensitivity to the forcing appears to be mainly related to the effect of wind channeling by the land orography which can only be reproduced in atmospheric models of sufficient resolution thus well positioned patterns of enhanced wind stress and ocean surface heat loss are able to maintain a vigorous gyre circulation favoring efficient preconditioning of the area at the beginning of winter and to drive realistic buoyancy loss and mixing responsible for strong convection at the end of winter

climatic changes in the aegean sea influence the eastern mediterranean thermohaline circulation 1986 1997 recent changes of water mass characteristics in the south aegean sea have considerably influenced the eastern mediterranean thermohaline circulation a combination of salinity increase 1987 92 and temperature drop 1992 94 caused massive dense water formation and strong outflow towards the deep and bottom parts of the eastern mediterranean this climatic shift the most important since the existence of observations in the basin is a combined effect of extreme meteorological events superimposed on large scale trends it has initiated a series of modifications in the hydrology and dynamics of the entire eastern mediterranean with possible influence on the mediterranean outflow in the north atlantic ocean