evidence for episodic cementation and diagenetic recording of seismic pumping events north coles levee california u s a abstract bands of calcite and dolomite cements alternating with zones of nearly carbonate free sand occur in the stevens sandston aat north coles levee san joaquin valley california temperatures calculated from o isotopes suggest that the calcite cement bands were emplaced episodically as a result of repeated injections of hot water from deeper in the section burial analysis suggests that these cements precipitated from 7 ma to the present over the temperature range of 45 to 95 c carbon isotope data suggest that the c in the cements is a mixture derived from two sources detrital shell material 13c pdb and co2 liberated from maturing kerogen 13c 24 plots of 13c vs time and depth of crystallization show that the cementation sequence was 1 dolomite cements possibly concretionary precipitated at depths a log of 13c vs calculated depth of crystallization correlates with the stratigraphic column at north coles levee if the correlation is valid the light 13 in each cement sample can be tied to its source a model based on this interpretation suggests that the early light c was derived from maturing kerogen in the kreyenhagen formation eocene as it passed through the oil window between 4 and 5 ma the subsequent passage of younger sediments with less organic material produced correspondingly smaller amounts of light co2 which was reflected in the relatively heavier c isotopes in the later cements it is suggested that the epidsodic injections of hot water carried dissolved gases and minerals principally calcite upward from rocks as deep as 2 3 km below the stevens sandstone and reprecipitated the calcite in more permeable zones in the rock degassing of co2 from rising pore waters likely triggered the precipitation and accounts for the relatively large volumes of cement the sibson model for seismic pumping of pore fluids is considered a likely explanation for the observed cementation

lagrangian flow effects on phytoplankton abundance and composition along filament like structures abstract influence of frontal dynamics on phytoplankton distribution and composition was studied combining in situ observations and lagrangian computations from altimetry satellite derived currents four transects during the shebex cruise may 2015 over the western mediterranean were examined identifying a region with high spatial variability in the dynamical and biogeochemical properties the dynamical situation unraveled from the lagrangian analysis is dominated by filaments originated by an anticyclonic cyclonic eddy interaction that organize the transport modifying the biogeochemical properties of the water column and shaping the satellite derived surface chlorophyll a chla distribution the properties of the water column have been analyzed in relation to the dynamical properties of the filaments showing that local variation of the mixed layer and nutricline depths are correlated with the spatial variability of finite size lyapunov exponents furthermore the composition of phytoplankton community was studied regarding the path accumulated properties of the flow during the formation of the filaments in this regard new metrics accounting the lagrangian evolution of the turbulent and topological properties of the flow along fluid parcel trajectories have been developed here we provide observational evidence that fluid parcels associated with high lagrangian turbulent kinetic energy and lagrangian positive vorticity host higher presence of larger pennate diatoms i e pseudo nitzschia spp our findings indicate that the combination of these diagnostics provides an improved description of the turbulent dynamics showing that the lagrangian properties of the flow have important biological consequences for phytoplankton to high ecological levels

sandstone diagenesis and reservoir quality prediction models myths and reality models and concepts of sandstone diagenesis developed over the past two decades are currently employed with variable success to predict reservoir quality in hydrocarbon exploration not all of these are equally supported by quantitative data observations and rigorous hypothesis testing simple plots of sandstone porosity versus extrinsic parameters such as current subsurface depth or temperature are commonly extrapolated but rarely yield accurate predictions for lithified sandstones calibrated numerical models that simulate compaction and quartz cementation when linked to basin models have proven successful in predicting sandstone porosity and permeability where sufficient analog information regarding sandstone texture composition and quartz surface area is available analysis of global regional and local data sets indicates the following regarding contemporary diagenetic models used to predict reservoir quality 1 the effectiveness of grain coatings on quartz grains e g chlorite microquartz as an inhibitor of quartz cementation is supported by abundant empirical data and recent experimental results 2 vertical effective stress although a fundamental factor in compaction cannot be used alone as an accurate predictor of porosity for lithified sandstones 3 secondary porosity related to dissolution of framework grains and or cements is most commonly volumetrically minor 2 exceptions are rare and not easily predicted with current models 4 the hypothesis and widely held belief that hydrocarbon pore fluids suppress porosity loss due to quartz cementation is not supported by detailed data and does not represent a viable predictive model 5 heat flow perturbations associated with allochthonous salt bodies can result in suppressed thermal exposure thereby slowing the rate of quartz cementation in some subsalt sands

the unusual surface chlorophyll signatures of southern ocean eddies southern ocean mesoscale eddies play an important role in ocean circulation and biogeochemical cycling but their biological characteristics have not been well quantified at the basin scale to address this we combined a 15 year tracked eddy data set with satellite observations of ocean color sea surface temperature and autonomous profiling floats to quantify the surface and subsurface properties of eddies anomalies of surface temperature and chlorophyll were examined in eddy centric composite averages constructed from thousands of eddies normalized surface chlorophyll anomalies chlnorm vary seasonally and geographically cyclones typically show positive chlnorm while anticyclones have negative chlnorm the sign of chlnorm reverses during late summer and autumn for eddies between the subtropical and polar fronts the reversal is most obvious in the indian sector and we attribute this to a combination of eddy stirring deformation of surface gradients by the rotational velocity of an eddy and deeper winter mixing in anticyclones both chlnorm and sea surface temperature anomalies transition from dipole structures north of the subtropical front to monopole structures south of the subantarctic front sea surface temperature and chlnorm composites provide evidence for eddy trapping transporting of anomalies and eddy stirring this research provides a basin scale study of surface chlorophyll in southern ocean eddies and reveals counterintuitive biogeochemical signals

fluid flow compartmentalization in the sicilian fold and thrust belt implications for the regional aqueous fluid flow and oil migration history abstract the fluid flow history in the frontal part of the sicilian fold and thrust belt ftb has been reconstructed using an integrated structural petrographic geochemical and microthermometric approach the study focused on comparing fluid flow during progressive deformation along major thrust horizons and in pelagic sediments occurring in the associated thrust sheets foot and hanging wall a fluid flow model is constructed for the frontal part of the sicilian ftb syn deformational quartz and calcite have been precipitated along decollement horizons in the iudica scalpello study area the microthermometric analysis of fluid inclusions in the quartz and calcite indicated migration of low saline high temperature aqueous fluids 1 5 h the fluid flow history in the thrust sheets can be subdivided into two stages calcite of types 1 and 2 has identical light orange cathodoluminescence as the surrounding mudstone furthermore its isotope signature 2 13 c 18 o m h between 80 and 140 c type 3 calcite has less depleted 18 o values compared to calcite of types 1 and 2 and the 18 o from calcite in faults is even positive during the final stages of fluid flow with precipitation of calcite type 3 the fluid flow model invokes infiltration of overpressured fluids that migrated along the decollement zone these fluids only infiltrate the thrust sheet in the hanging wall of the thrust leading to a compartmentalized fluid flow pattern an identical fluid flow pattern with migration of low and hot saline fluids associated with hydrocarbons was observed in other parts of the sicilian fold and thrust belt with identical structural deformation and fluid flow patterns the study confirms the suitability of the frontal part of the sicilian fold and thrust belt as an outcrop analog for deeply submerged accretionary prisms the study thus offers unique insights in expected fluid flow patterns in thrust sheets of deeply submerged accretionary complexes

diagenesis compaction and fluid chemistry modeling of a sandstone near a pressure seal lower tuscaloosa formation gulf coast petrographic isotopic and fluid inclusion evidence from normally and overpressured sand stones of the lower tuscaloosa formation upper cretaceous in the gulf coast documents quartz overgrowth precipitation at 90 c or less calcite cement precipitation at approximately 100 and 135 c and prismatic quartz cement precipitation at about 125 c textural evidence suggests that carbonate cement dissolution occurred before the second phases of calcite and quartz precipitation and was followed by precipitation of grain rimming chlorite and pore filling kaolinite geochemical calculations demonstrate that present day lower tuscaloosa formation water from 5500 m depth could either dissolve or precipitate calcite cements in model simulations of upward water low calcite dissolution or precipitation depends on pco2 variability with depth i e whether there is one or two phase flow or on the rate of generation of co2 with depth calculations suggest that 105 106 rock volumes of water are required to flow through the section to precipitate 1 10 calcite cement compaction analysis suggests that late stage compaction occurred in normally pressured sandstones after dissolution of carbonate cements but was hindered in overpressured sandstones despite the presence of high porosity these results document the inhibition of compaction by overpressured fluids and constrain the timing of pressure seal formation modeling results demonstrate that the proposed paragenesis used to constrain timing of pressure seal formation is feasible and that most of the cement diagenesis occurred before the pressure seal became effective as a permeability barrier

carbonate diagenesis during thermo convection application to secondary porosity generation in clastic reservoirs abstract carbonate mass transfer due to a slow convective circulation within a sedimentary layer is modeled to assess the geometry of dissolution and precipitation zones as well as the time constant necessary for a significant dissolution or precipitation of solid phases this study is focused on the effect of aluminosilicates and in particular kaolinite on the time constant and location of carbonate diagenetic reactions and thus on porosity redistribution when kaolinite albite and chlorite are present in a carbonate system dissolution and precipitation rates are increased by a factor up to 50 compared to the pure carbonates case moreover carbonates tend to dissolve with increasing temperature and secondary porosity occurs at the bottom of downwelling currents it should be emphasized however that the net carbonate dissolution may result from calcite precipitation associated with dolomite dissolution in several instances the whole chemical system is dominated by a single reaction such as cation exchange in carbonates or the acid base reaction between kaolinite and chlorite this generally implies that the dissolution of every solid phase is proportional to that of calcite moreover when the variance of the chemical system is sufficiently low absolute dissolutions can be analytically derived from the variation with temperature of the reaction equilibrium constants this implies that a sufficient knowledge of the chemical system behavior could avoid numerical computations it is shown that uncertainties in the thermodynamical properties of aluminosilicates minerals may result in variations of more than one order of magnitude in computed dissolution rates in some cases the dominant reaction in the system is changed and therefore the whole pattern of dissolution and precipitation zones is disrupted this points out the need of reliable thermodynamic data bases to model mass transfer induced by convective circulations in porous layers

the influence of nonlinear mesoscale eddies on near surface oceanic chlorophyll oceanic rossby waves have been widely invoked as a mechanism for large scale variability of chlorophyll chl observed from satellites high resolution satellite altimeter measurements have recently revealed that sea surface height ssh features previously interpreted as linear rossby waves are nonlinear mesoscale coherent structures referred to here as eddies we analyze 10 years of measurements of these ssh fields and concurrent satellite measurements of upper ocean chl to show that these eddies exert a strong influence on the chl field thus requiring reassessment of the mechanism for the observed covariability of ssh and chl on time scales longer than 2 to 3 weeks the dominant mechanism is shown to be eddy induced horizontal advection of chl by the rotational velocities of the eddies

global observations of submesoscale coherent vortices in the ocean abstract subsurface intensified anticyclones are ubiquitous in the ocean yet their impact on the large scale transport of heat salt and chemical tracers is poorly understood these submesoscale coherent vortices scvs can trap and advect waters thousands of kilometers away from the formation region providing a transport pathway that is unresolved by low resolution earth system models however knowledge of the importance of these eddies for the large scale circulation is hindered by the lack of systematic observations here we take advantage of the global network of argo floats to identify occurrences of these eddies which appear as weakly stratified anomalous water masses with gaussian shaped vertical structures we develop a general algorithm to detect subsurface eddies that have propagated away from their source region and apply it to the database of argo float profiles resulting in roughly 4000 detections from more than 20 years of observations we further group detections into regional populations to identify hot spots of generation and mechanisms of formation analysis of regional scv statistics reveals important sites of scv generation in eastern boundary upwelling systems marginal sea overflows and mode water formation regions along major open ocean fronts because of the heat and salt anomaly contained within their cores scv could leave a significant imprint on the hydrographic properties of water masses in regions of high scv density

inhibition of calcite crystal growth by mg2 at 100 c and 100 bars influence of growth regime follow ing shiraki and brantley 1995 who found different growth mechanisms for calcite crystal growth at 100 c and 100 bars total pressure we investigated the inhibition of calcite crystal growth by mg 2 under the same conditions of temperature pressure and composition the results showed that the mg 2 inhibition depends on the growth regime for growth in the exponential rate regime the growth of calcite is almost totally inhibited and aragonite grows instead for growth in the linear rate regime both aragonite and calcite precipitate on the other hand for experiments best described by a parabolic growth model mg inhibits the growth rate of calcite but no aragonite precipitates the study also showed that mg inserts into the calcite structure but not into the aragonite structure to any significant extent during growth the aragonite growth which is controlled by primary nucleation suggests that neither nucleation nor growth are inhibited by mg discrepant observations concerning mg inhibition documented in the literature may be explained by such differences in the growth mechanism copyright 1997 elsevier science ltd

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

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

impact of eddies on surface chlorophyll in the south indian ocean a unique feature of the subtropical south indian ocean is the existence of anticyclonic eddies that have higher chlorophyll concentrations than cyclonic eddies off western australia this anomalous behavior is related to the seeding of anticyclonic eddies with shelf water enriched in phytoplankton biomass and nutrients further off shore two mechanisms have been suggested to explain the eddy chlorophyll relationship i eddies originating from the australian coast maintain their chlorophyll anomaly while propagating westward and ii eddy induced ekman upwelling downwelling enhances dampens nutrient supply in anticyclonic cyclonic eddies here we describe the relationship between eddies and surface chlorophyll within the south indian ocean and discuss possible mechanisms to explain the anomalous behavior in light of new analyses performed using satellite chlorophyll data we show that anticyclonic eddies exhibit higher surface chlorophyll concentration than cyclonic eddies across the entire south indian ocean basin from 20 to 28 s particularly in winter using self organizing maps we analyze the chlorophyll patterns within anticyclonic eddies and cyclonic eddies and highlight their complexity our analysis suggests that multiple mechanisms may underlie the observed eddy chlorophyll relationship based on argo float data we postulate the relationship may be partly related to seasonal adjustment of the mixed layer depth within eddies deeper mixing in anticyclonic eddies is expected to enhance nutrient supply to the mixed layer while shallower mixing in cyclonic eddies is expected to reduce it this could explain why the observed winter surface chlorophyll bloom is stronger in anticyclonic eddies than in cyclonic eddies

mineral water interaction fluid flow and frio sandstone diagenesis evidence from the rocks the spatial distribution of burial diagenetic cements in sandstones of the frio formation is related to permeability and fluid flow the relationship between sandstone diagenesis and fluid flow implies that the modification of the rocks is largely the outcome of reactions between the detrital and authigenic minerals and the formation water in the pores during burial formation water preferentially flowed through the most porous and permeable sandstones diagenetic alteration is more extensive in permeable sandstones because the minerals in those rocks were exposed to significantly more pore volumes of reactive water each of which accomplished a small amount of diagenetic work consequently porous and permeable units were also the preferred sites of diagenetic mineral p ecipitation the heterogeneous distribution of authigenic minerals in sandstones is a result of changing preferential flow paths due to diagenetic modification during burial sandstones that are not the most porous or permeable at the time of deposition commonly preserve the best reservoir quality at depth because they are less modified by diagenesis petrographic analyses indicate that the sio2 needed for the quartz overgrowths in the sandstones had an allochthonous source dgr18o values for diagenetic quartz imply that the mineral precipitated from rapidly ascending hot formation water quartz overgrowths are most abundant in distal shelf facies sandstones where the isolated nature of the sandstones in a predominately shaly section maximized preferential fluid flow mass balance calculations show that thousands of pore volumes of formation water are required to supply the sio2 needed for the quartz overgrowths in the sandstones the amount of water required to produce the diagenetic modification of the sandstones is much larger than the amount of water present in the entire frio formation impl ing that reuse of formation water is an important and necessary process during diagenesis

disseminated jigsaw piece dolomite in upper jurassic shelf sandstones central north sea an example of cement growth during bioturbation unusual textural and chemical characteristics of disseminated dolomite in upper jurassic shelf sediments of the north sea have provided the basis for a proposed new interpretation of early diagenetic dolomite authigenesis in highly bioturbated marine sandstones the dolomite is present throughout the franklin sandstone formation of the franklin and elgin fields as discrete non ferroan generally unzoned subhedral to highly anhedral jigsaw piece crystals these are of a similar size to the detrital silicate grains and typically account for 5 of the rock volume the dolomite crystals are never seen to form polycrystalline aggregates or concretions or ever to envelop the adjacent silicate grains they are uniformly dispersed throughout the sandstones irrespective of detrital grain size or clay content dolomite authigenesis predated all the other significant diagenetic events visible in thin section the dolomite is overgrown by late diagenetic ankerite and bulk samples display stable isotope compositions that lie on a mixing trend between these components extrapolation of this trend suggests that the dolomite has near marine delta18o values and low positive delta13c values the unusual textural and chemical characteristics of this dolomite can all be reconciled if it formed in the near surface zone of active bioturbation sea water provided a plentiful reservoir of mg and a pore fluid of regionally consistent delta18o labile bioclastic debris e g aragonite mg calcite supplied isotopically positive carbon to the pore fluids during shallow burial dissolution such dissolution took place in response to the ambient calcite sea conditions but may have been catalysed by organic matter oxidation reactions bioturbation not only ensured that the dissolving carbonate was dispersed throughout the sandstones but also prohibited coalescence of the dolomite crystals and consequent cementation of the grain framework continued exchange of mg2 and ca2 with the sea water reservoir maintained a sufficient mg ca ratio for dolomite rather than calcite to form irregular crystal shapes resulted from dissolution of both the dolomite and the enclosed fine calcitic shell debris before ankerite precipitation during deep burial diagenesis

satellite observations of mesoscale eddy induced ekman pumping abstractthree mechanisms for self induced ekman pumping in the interiors of mesoscale ocean eddies are investigated the first arises from the surface stress that occurs because of differences between surface wind and ocean velocities resulting in ekman upwelling and downwelling in the cores of anticyclones and cyclones respectively the second mechanism arises from the interaction of the surface stress with the surface current vorticity gradient resulting in dipoles of ekman upwelling and downwelling the third mechanism arises from eddy induced spatial variability of sea surface temperature sst which generates a curl of the stress and therefore ekman pumping in regions of crosswind sst gradients the spatial structures and relative magnitudes of the three contributions to eddy induced ekman pumping are investigated by collocating satellite based measurements of sst geostrophic velocity and surface winds to the interiors of eddies identified from their sea surface height signatures on average e

the influence of calcite dissolution on reservoir porosity in miocene sandstones picaroon field offshore texas gulf coast abstract middle miocene sandstones occur in picaroon field corsair trend offshore texas gulf coast at depths of approximately 4 9 to 5 2 km 16 17 000 ft these deltaic sandstones contain evidence of the following sequence of diagenetic events 1 formation of chlorite coatings on detrital grains 2 partial dissolution of detrital feldspar 3 quartz cementation 4 calcite cementation 5 dissolution of calcite cement and grains 6 ankerite cementation the reservoir quality of the sandstones is largely a function of porosity enhancement by calcite dissolution calcite cement was emplaced at depths of approximately 1 8 to 2 6 kin the calcite has 87 86sr values of 0 7083 0 7086 eliminating coeval 15 myr seawater and marine carbonate 0 70873 0 70885 as the primary source of strontium the 87 86sr composition of calcite cement implies that mass transfer of calcite from older marine sources to younger sediments has occurred fluid inclusion measurements indicate that ankerite cement formed at minimum temperatures of 120 188 c 3 0 5 1 km oxygen isotope modeling predicts that at these depths shales would expel waters with 18osmow of 5 to 9 during smectite illite conversion ankerite 18opdb 7 8 would be in isotopic equilibrium with these waters at temperatures similar to those derived from fluid inclusions ankerite cements have relatively radiogenic 87 86sr ratios 0 7097 which are consistent with their formation from shale derived fluids calcite dissolution occurs between the precipitation of calcite and ankerite it is therefore concluded that calcite cement dissolution occurred at burial depths of 2 6 to 3 0 km 107 120 c

wintertime convection in warm core rings thermocline ventilation and the formation of mesoscale lenses large heat losses from warm core ring 82b during february march and april 1982 formed a 400 m thick thermostad in the center of the ring two different models were constructed to simulate the formation of the thermostad water mass properties a one dimensional vertical model forced with a meteorological time series and a volumetric mixing model with climatological input both models indicate that a flux of slope water into the ring is necessary to yield the observed thermostad salinities the subsequent slow decay of the ring core in the slope water suggests that such winter convected rings can easily maintain the warm band water identified by wright and parker 1976 the large loss of core water during interactions with the gulf stream suggests that the reabsorption of such winter cooled warm rings is an important source of high salinity high oxygen anomalies in the main thermocline of the sargasso sea the volume of water in a typical ring reabsorption is sufficient to generate many 20 intrathermocline eddies with t s properties close to those of recently reported lenses this suggests that many of these small eddies are much more local in origin and may be more highly dissipative than has previously been suggested an estimate of the flux of high salinity high oxygen water into the main thermocline by this mechanism leads to ventilation at a rate that is a significant fraction of the ekman pumping at these density levels thus the reabsorption of winter cooled warm core rings by the gulf stream is an important eddy ventilation mechanism for the sargasso sea

the role played by carbonate cementation in controlling reservoir quality of the triassic skagerrak formation norway anomalously high porosities up to 30 at burial depth of 3000 m along with varying amounts and types of carbonate cements occur in the fluvial channel sandstone facies of the triassic skagerrak formation central graben norway however porosities of the skagerrak formation are lower in the norwegian sector than in the uk sector in this study petrographic analysis core examination scanning electron microscopy elemental mapping carbon and oxygen isotope fluid inclusion and microgeometry analysis are performed to determine the diagenesis and direct influence on reservoir quality with particular focus on the role played by carbonate cementation the sandstones are mainly fine grained lithic arkosic to sub arkosic arenites and display a wide range of intergranular volumes 2 3 43 7 with an average of 23 6 porosity loss is mainly due to compaction av 26 6 with minor contribution from cementation av 12 1 the carbonate cements are patchy in distribution from trace to 20 7 and appear as various types e g calcretes i e calcareous concreted gravels poikilitic sparite and sparry ferroan dolomite and euhedral or and aggregated ankerite ferroan dolomite crystals this study highlights the association of carbonate precipitation with the remobilisation of carbonate from intra skagerrak calcretes during early burial stage i e 500 m during deeper burial compaction is inhibited by carbonate cements resulting high intergranular volume of up to 32 and 29 for fine and medium grained sandstones respectively carbonate cement dissolution probably results from both meteoric water flow with co2 during shallow burial and organic co2 and carboxylic acid during deep burial the maximum intergranular volume enhanced by dissolution of early carbonate cements is calculated to 8 and 5 for fine and medium grained sandstones respectively compaction continues to exert influence after dissolution of carbonate cements which results in a loss of 6 intergranular volume for fine and medium grained sandstones reservoir quality of the norwegian sector is poorer than that of the uk sector due to a lower coverage of clay mineral coats e g chlorite later and deeper onset of pore fluid overpressure lower solubility of carbonate compared to halite and a higher matrix content

satellite observations of chlorophyll phytoplankton biomass and ekman pumping in nonlinear mesoscale eddies nonlinear mesoscale eddies can influence biogeochemical cycles in the upper ocean through vertical and horizontal advection of nutrients and marine organisms the relative importance of these two processes depends on the polarity of an eddy cyclones versus anticyclones and the initial biological conditions of the fluid trapped in the core of the eddy at the time of formation eddies originating in the eastern south indian ocean are unique in that anticyclones typically associated with downwelling contain elevated levels of chlorophyll a enhanced primary production and phytoplankton communities generally associated with nutrient replete environments from analysis of 9 years of concurrent satellite measurements of sea surface height chlorophyll phytoplankton carbon and surface stress we present observations that suggest eddy induced ekman upwelling as a mechanism that is at least partly responsible for sustaining positive phytoplankton anomalies in anticyclones of the south indian ocean the biological response to this eddyinduced ekman upwelling is evident only during the austral winter during the austral summer the biological response to eddy induced ekman pumping occurs deep in the euphotic zone beyond the reach of satellite observations of ocean color

aftershock decay of three recent strong earthquakes in the levant aftershock sequences are studied from three recent strong earthquakes in the levant the mw 7 1 earthquake of 22 november 1995 and the ml 5 8 earthquake of 3 august 1993 both in the gulf of aqaba and the mw 6 8 earthquake of 9 october 1996 off the southwest coast of cyprus the modified omori s law provides a good fit to the decay of aftershock activity for both events the two sequences from the gulf of aqaba have rather low p values 0 90 in 1993 and 0 75 in 1995 reflecting slow decay of the aftershock activity this may be attributed to low heat flow close to the epicenters for the cyprus sequence the p value is 1 09 similar to that of many other sequences around the globe

the influence of multiple stage oil emplacement on deeply buried marine sandstone diagenesis a case study on the devonian donghe sandstones tabei uplift tarim basin nw china abstract understanding the oil emplacement influence on diagenesis is one of the most key factors of reservoir quality prediction the devonian donghe sandstones are deeply buried to 5700 6000 m and they are important exploration target in the tarim basin additional the reservoirs experienced multi phase hydrocarbon accumulation and destruction the donghe sandstones contain various diagenetic minerals which are mainly composed of calcite cement a small amount of quartz overgrowth and pyrite trace ankerite and ferrocalctie the current study investigates the influence of multiple stage oil emplacement on the diagenesis with particular attention to calcite and quartz cementation of marine clastic reservoir interval of the donghe sandstones in the tarim basin the samples in the oil leg and water leg have been collected and a series of studies were performed including thin section petrography scanning electron microscopy sem carbon and oxygen isotopes and cathodoluminescence cl analysis the 13cv pdb values of calcite cement from the oil leg and water leg between 4 73 and 1 21 and 3 81 to 0 86 respectively the 18ov pdb values of calcite cement from the oil leg and water leg range from 15 59 to 6 61 and 14 97 to 7 76 respectively both of them display no obviously different in the oil leg and water leg all of the 13cv pdb values in the whole interval of the donghe sandstones show lightly depletion was explained mixing from marine carbon and carbon produced from bacterial sulfate reduction bsr that happens during petroleum degradation associated with sulfate reduced by hydrocarbons bacterially two dull luminescence zones trace fe and mn content and high fe accompanied by low mn content and orange red and bright orange yellow luminescence zones in oil leg indicate four generations of calcite occurred whereas two generations of calcite occurs in water leg which are dull and orange red luminescence zones two origins of calcite cement were clearly identified marine biogenic carbonates and hydrocarbon related from palaeo reservoir bsr during uplift the first generation of calcite cement originated from biogenic carbonate the second and third generations of calcite cement were mixing from predate carbonate cement dissolved and re precipitated and calcite precipitated by bsr directly some quartz grains and k feldspars were dissolved by residual organic acids that remained in the irreducible water and following replaced by the fourth generation of calcite cement some calcite cement in the oil leg precipitated in a temperature higher than the homogeneous temperature of fluid inclusion which indicates oil emplacement has no influence on calcite cementation the quartz overgrowth postdate the first hydrocarbon accumulation and predate the second hydrocarbon accumulation which originated from quartz grains dissolved by organic acids that produced from bsr and re precipitated at a low temperature the current study can promote the understanding of the influence of multiple stage hydrocarbon accumulation on diagenesis and it can also inspire the diagenesis process of other paleozoic hydrocarbon reservoirs in the tarim basin

an argo mixed layer climatology and database a global climatology and database of mixed layer properties are computed from nearly 1 250 000 argo profiles the climatology is calculated with both a hybrid algorithm for detecting the mixed layer depth mld and a standard threshold method the climatology provides accurate information about the depth properties extent and seasonal patterns of global mixed layers the individual profile results in the database can be used to construct time series of mixed layer properties in specific regions of interest the climatology and database are available online at http mixedlayer ucsd edu the mlds calculated by the hybrid algorithm are shallower and generally more accurate than those of the threshold method particularly in regions of deep winter mixed layers the new climatology differs the most from existing mixed layer climatologies in these regions examples are presented from the labrador and irminger seas the southern ocean and the north atlantic ocean near the gulf stream in these regions the threshold method tends to overestimate winter mlds by approximately 10 compared to the algorithm

thermogenetic degradation of early zeolite cement an important process for generating anomalously high porosity and permeability in deeply buried sandstone reservoirs abstract diagenetic explanations to anomalously high porosities and permeabilities in deeply buried sandstones have been presented for many reservoirs for example grain coatings of microquartz or chlorite can preserve porosity by preventing succeeding quartz overgrowths and dissolution of grains or cement can generate secondary porosity anomalously high porosity and permeability up to 25 and 500 md respectively characterize the deeply buried 5 km upper jurassic shoreface sandstones of the gert member heno formation in the hejre field in the danish central graben optical cathodoluminescence and scanning electron microscopy were used to characterize the petrography and diagenetic changes that resulted in this high pressure and high temperature hpht reservoir this was supplemented by chemical analyses icp oes and icp ms mineralogical composition xrd and oxygen isotope composition of quartz and calcite cement sims the petrographic investigation shows that none of the known explanations for anomalously high porosity and permeability can be applied hence a new hypothesis for deeply buried sandstones in contact with lavas and volcaniclastic lithologies is proposed the new hypothesis includes reducing mechanical compaction due to early patchy zeolite cement which was sourced from adjacent lavas and volcaniclastic rocks locally stylolites developed where zeolite cement was less effective hence the present overpressure formed at a later stage increased temperatures during burial resulted in thermal instability of the zeolite cement which was dissolved and authigenic k feldspar and quartz precipitated instead this resulted in a reduction of the cement volume of up to 70 if the zeolite was k heulandite and a corresponding relative porosity increase thus a reduction in cement volume was generated by replacing zeolite of an open crystal structure with mineral phases k feldspar and quartz of denser crystal structures the thermogenetic breakdown of zeolite was forced by increased temperatures during burial this process may explain previously enigmatic highly porous and permeable deeply buried sandstone reservoirs

shear and richardson number in a mode water eddy abstract measurements of stratification and shear were carried out as part of the eddies tracer release experiment in mode water eddy a4 during the summer of 2005 these measurements were accomplished using both shipboard instrumentation and a drifting mooring a strong relationship between shear intensity and distance from the center of the eddy a4 was observed with the shipboard adcp diapycnal diffusivity at the sf6 tracer isopycnal prior to and during the release was estimated from the drifting mooring to be 2 9 10 6 m2 s 1 diffusivity increased by an order of magnitude to 3 2 10 5 m2 s 1 during the period of the final tracer survey in early september which was similar to the value estimated from the tracer analysis for the whole experiment 3 5 10 5 m2 s 1 ledwell j r mcgillicuddy jr d j anderson l a 2008 nutrient flux into an intense deep chlorophyll layer in a mode water eddy deep sea research ii this issue doi 10 1016 j dsr2 2008 02 005

depositional and diagenetic controls on the reservoir quality of lower cretaceous pendencia sandstones potiguar rift basin brazil the quality of the reservoirs of the lower cretaceous pendencia formation of the potiguar basin northeastern brazil is directly controlled by depositional facies related carbonate cementation and compaction the study of the interplay of these processes in the reservoirs offers an opportunity to unravel the diagenetic patterns of clastic sequences in interior rifts and in particular the role of carbonate cementation in poorly understood continental systems the pendencia formation is a thick sequence of fan deltaic fluvial deltaic turbiditic and lacustrine sandstones conglomerates and shales deposited during the rift stage of the basin the sandstones are predominantly arkoses average q49f40l11 with subordinate plutonic and volcaniclastic feldspathic litharenites compaction and cementation had similar importance in the destruction of porosity with a dominance of cementation in the turbidites and of compaction in the fluvial deposits carbonate cementation in pendencia reservoirs increases progressively with depth and is facies controlled eodiagenetic nonferroan calcite i d18opdb 10 7 to 4 0 d13cpdb 17 5 to 8 5 mesodiagenetic rhombohedral ferroan dolomite ankerite d18opdb 9 3 to 3 9 d13cpdb 1 7 to 1 1 and ferroan calcite ii d18opdb 17 2 to 6 8 d13cpdb 13 6 to 2 3 were precipitated at three distinct temperature intervals calculated from the d18o values 21 to 58 c 70 to 79 c and 85 to 150 c respectively according to the d13c values dissolved carbonate for calcite i was derived from oxidation and methanogenic fermentation of organic matter and from methane oxidation ferroan mesogenetic cements were derived from thermal decarboxylation of organic matter the shales were a major source of dissolved begin page 1720 carbonate as indicated by the isotopic similarity between their calcite d13cpdb 0 2 to 1 8 87sr 86sr 0 719 and most cements in the sandstones and by the peripheral cementation along the contacts of interbedded sandstones as a result of this cementation pattern thin turbiditic and deltaic sandstone beds are pervasively cemented the best reservoir quality potential is encountered in the partially cemented fluvial sandstones at moderate depths deltaic and turbiditic sandstones are more pervasively cemented by carbonate derived from the interbedded shales alluvial fan conglomerates and sandstones were flushed by telogenetic meteoric waters close to the borders of the basin and to the proximity to the postrift unconformity however porosity enhancement was very limited due to the precipitation of kaolinite and the intense compaction related to the compositionally immature detrital framework