observations of near surface currents and hydrography in the connecticut river plume with the surface current and density array it has been well established that the connecticut river forms a large plume in the vicinity of its mouth during periods of high river discharge the plume is bounded on the offshore side by a distinct front where the water color and turbidity changes rapidly and foam and detritus accumulate though there have been many observations of similar fronts throughout the world the details of the density and velocity structure in the vicinity of a plume front and the propagation velocity of the feature have not been adequately resolved to better observe the properties of these phenomena we have constructed a ship mounted array of instruments to measure the near surface currents and density scud distribution in plumes and fronts scud provides current velocity components at four levels and conductivity and temperature at five levels in the upper 3 m of the water column by using the global positioning system in differential mode to obtain position the system has a horizontal resolution of 5 m at a ship speed of 1 2 ms 1 estimates of the ground referenced water velocity components have an uncertainty of approximately 0 1 ms 1 to demonstrate the performance of the scud array we report the preliminary results of an observation program to examine the variability of the front of the connecticut river plume in the spring of 1994 several 200 m across front scud transects separated by 200 m were obtained during the mid ebb in long island sound during this period the front advanced to the west with a velocity of the order of 0 1 ms 1 in opposition to an eastward tidal current of 1 0 ms 1 a practical salinity increase of 20 in less than 10 m was observed at the front on crossing into the plume in concert the front normal velocity component decreased by 0 5 0 1 ms 1 over 10 m and the vertical shear in the front parallel component decreased dramatically the performance and potential of the instrumentation and the implication of the observations for the development theories of river plume fronts are discussed

episodic petroleum fluid migration in fault zones of the northwestern junggar basin northwest china evidence from hydrocarbon bearing zoned calcite cement hydrocarbon bearing zoned calcite cements occur widely in jurassic cretaceous fault zone cores and sandstone outcrops of the northwestern junggar basin northwest china hydrocarbon bearing bands alternate with nearly hydrocarbon free bands at a micron scale analytical results from biomarker organic geochemistry fourier transform infrared microspectroscopy and trace element geochemistry on these zoned cements suggest that at least three different types of fluids have participated in their formation the first fluid type is probably primary unmodified lacustrine formation water from which the hydrocarbon poor bands are formed and are characterized by mg rich calcite the other two types of fluids include basinal fluids e g hot hydrocarbon bearing fluids and meteoric water the hydrocarbon rich bands in which the hydrocarbons have been biodegraded and the mn content is relatively high suggest a mixture of hydrocarbon bearing basinal fluid and meteoric water the alternating growth of hydrocarbon bearing and hydrocarbon free bands of calcite cements implies that the cement formation is episodic it is related to alternating episodes of mixed petroleum bearing fluid and unmodified primary formation waters respectively the fault appears to have been a mixing zone where seismic pumping during the movement of associated regional faults occurred thus in the northwestern junggar basin the micron scale hydrocarbon bearing zoned structure of the calcite cements is likely a reflection of episodic petroleum fluid migration in fault zones

role of pore structure in the percolation and storage capacities of deeply buried sandstone reservoirs a case study of the junggar basin china abstract deeply buried sandstone reservoirs are characterized by their wide pore throat distributions and varied storage and percolation capacities an integrated analysis comprising casting thin section scanning electron microscopy x ray computed tomography micro ct high pressure mercury intrusion hpmi and constant rate mercury intrusion crmi is performed on thirteen samples from the jurassic sangonghe formation in the junggar basin to investigate the pore structures and their influence on the storage and percolation capacities hpmi crmi and micro ct are combined to determine the full range pore size distributions fpsds which have multimodal distributions between 2 77 nm and 500 m with three broad peaks the right peak ranging from 100 to 500 m is associated with residual and dissolution intergranular pores the middle peak is mainly composed of dissolution intergranular and intragranular pores with radii between 10 and 100 m the left peak exhibited fluctuations and is characterized by dissolution intragranular and intercrystalline pores with radii of 37 nm 10 m according to the pore types sizes and proportions in the fpsd the pores are classified as intercrystalline nanopores 100 m a storage capacity evaluation combining the classifications and fpsd indicates that the macropores and nanopores primarily contribute to porosity albeit with contrasting influences on the storage capacity the contents of macropores determine the storage capacity of a deeply buried sandstone reservoir while the negative effects of nanopores become predominant with decreasing porosity a percolation capacity evaluation on the basis of crmi results suggests that the permeability contribution is dominated by nanopores in tight sandstone controlled by micro small pores in low permeability sandstone and dominated by mesopores in conventional sandstone mesopores always play a favorable role in percolation however the negative impacts of nanopores should be considered in low permeability and tight sandstone micro small pores have a negative influence on the permeability of conventional sandstone but are favorable for the fluid percolation of most low permeability and tight sandstone reservoirs a new empirical equation indicates that r10 of the fpsd is the suitable as the proper pore throat radius for the permeability estimation of deeply buried sandstone reservoirs

constraints on the development of secondary porosity in the subsurface re evaluation of processes abstract secondary porosity formed by the dissolution of grains and cements is of great economic importance in both clastic and carbonate reservoirs a review of the commonly proposed mechanisms for the production of secondary porosity indicates that meteoric water penetration and mixing corrosion may be able to create significant volumes of secondary porosity in the shallow subsurface leaching by acidic fluids generated by solution of co 2 or monocarboxylic acids both derived during the thermal maturation of organic matter or by acidic fluids created by clay mineral reactions in shales are the most commonly proposed mechanisms by which secondary porosity is said to form in the deep subsurface however these mechanisms suffer from great difficulties in producing significant volumes of secondary porosity once mass balance and fluid migration problems are taken into account it is highly likely that the correct mechanism for the creation of economically significant amounts of secondary porosity in the deep subsurface is yet to be found

diagenetic controls on evolution of porosity and permeability in lower tertiary wilcox sandstones from shallow to ultradeep 200 6700 m burial gulf of mexico basin u s a abstract reservoir quality is a critical risk factor in deep to ultradeep reservoirs at depths 4 5 km analysis of paleogene wilcox sandstones on the upper texas gulf coast provides insight into the evolution of reservoir quality during shallow to ultradeep burial diagenesis reduction of porosity and permeability with burial in wilcox sandstones was evaluated using subsurface samples from 200 to 6700 m at temperatures of 25 230 c diagenesis and petrophysical properties were interpreted from petrographic data and core analyses wilcox sandstones are mostly lithic arkoses and feldspathic litharenites having an average composition of q59f22r19 provenance did not change significantly during wilcox deposition in this area nor does average sandstone composition vary among lower middle and upper wilcox sandstones however composition does vary with sequence stratigraphic position lowstand slope fan deposits contain more rock fragments than do deposits from highstand or transgressive systems tracts given observations from this onshore dataset wilcox sandstones deposited in deepwater environments in the gulf of mexico are likely to contain more rock fragments than their linked highstand equivalents pore types in wilcox sandstones change from a mix of primary and secondary pores and micropores at shallower depths to predominantly secondary pores and micropores in deeper sandstones wilcox sandstones show steady porosity reduction from an average of 33 at 38 c to 12 at 132 c with little additional loss at higher temperatures by 132 c most primary pores have been lost by mechanical compaction or occluded by quartz cementation volume of secondary pores remains nearly constant despite dissolution of 3 5 average potassium feldspar during deep burial volume of this late dissolution of potassium feldspar is offset by precipitation of ankerite albite illite and minor quartz in secondary pores the proportion of microporosity which occurs in authigenic clays altered grains and matrix increases in the deepest sandstones change in proportion of pore types and reduction in total porosity with increasing temperature changes porosity permeability transforms because most deep to ultradeep wilcox sandstones are dominated by secondary pores and micropores porosity permeability transforms have lower slopes than those for shallower sandstones

a simplified energy and mixing budget for a small river plume discharge 1 the formation and evolution of a tidally modulated river plume that spreads and mixes into english channel waters is investigated by combining results from two observational studies remote sensing imagery showed a near semicircular plume expansion as its diameter increased linearly during the ebb tide subsequent ship surveys made repeated transects across the plume front and showed that regions of mixing and instability froude numbers 1 were confined to horizontal length scales 1 suggesting that a plume cannot form

calibration of stable oxygen isotopes in siderastrea radians cnidaria scleractinia implications for slow growing corals geochemical proxies in the skeletons of corals used for the purpose of reconstructing environmental records have typically been obtained from relatively fast growing corals usually 8 mm yr 1 and from only a few key genera most commonly porites and montastraea in many areas however there are no suitable fast growing corals available for such reconstructions here we investigate the potential of siderastrea radians a slow growing atlantic and caribbean zooxanthellate coral as an archive of sea surface temperature sst and salinity over the period from 1891 to 2002 sampling the skeleton of three corals from the cape verde islands we were able to reproduce a clear seasonal signal but with limited correlation to monthly sst arising from inadequate chronologic constraint of the individual samples the sst 18o calibration slopes for different sampling scales on several cores can range from about 9 c 1 to 2 c 1 compared to other published values of around 5 to 4 c 1 careful treatment produced a 18o sst calibration equation where sst c 12 56 1 20 3 86 0 39 c w the recognition of the limitations of calibration at such small growth rates due to skeletal complexity and suspicion of environmental interferences suggests the need for careful consideration in the interpretation of climate proxy results from s radians and other slow growing corals

composition porosity and reservoir potential of the middle jurassic kashafrud formation northeast iran abstract in the kopet dagh basin of iran deep sea sandstones and shales of the middle jurassic kashafrud formation are disconformably overlain by hydrocarbon bearing carbonates of upper jurassic and cretaceous age to explore the reservoir potential of the sandstones we studied their burial history using more than 500 thin sections supplemented by heavy mineral analysis microprobe analysis porosity and permeability determination and vitrinite reflectance the sandstones are arkosic and lithic arenites rich in sedimentary and volcanic rock fragments quartz overgrowths and pore filling carbonate cements calcite dolomite siderite and ankerite occluded most of the porosity during early to deep burial assisted by early compaction that improved packing and fractured quartz grains iron oxides are prominent as alteration products of framework grains probably reflecting source area weathering prior to deposition and locally as pore fills minor cements include pore filling clays pyrite authigenic albite and k feldspar and barite existing porosity is secondary resulting largely from dissolution of feldspars micas and rock fragments with some fracture porosity porosity and permeability of six samples averages 3 2 and 0 0023 md respectively and 150 thin section point counts averaged 2 7 porosity reflectance of vitrinite in eight sandstone samples yielded values of 0 64 0 83 in the early mature to mature stage of hydrocarbon generation within the oil window kashafrud formation petrographic trends were compared with trends from first cycle basins elsewhere in the world inferred burial conditions accord with the maturation data suggesting only a moderate thermal regime during burial some fractures iron oxide cements and dissolution may reflect cenozoic tectonism and uplift that created the kopet dagh mountains the low porosity and permeability levels of kashafrud formation sandstones suggest only a modest reservoir potential for such tight sandstones fractures may enhance the reservoir potential

evolution of freely propagating two dimensional surface gravity current fronts this work addresses the two dimensional propagation and shape evolution of surface gravity current fronts with a surface density outcrop frontal line the problem is formulated using the reduced gravity shallow water equations and the gravity currents are assumed to advance into a fluid at rest we formulate a nonlinear analytical model for the gravity current plume front morphology by applying the shock tube theory of compressible fluids which casts the problem in the form of an initial value calculation to be solved numerically the simulations are initiated by assuming three different plan forms for the initial plume front and their subsequent evolutions followed in time the paper is concerned exclusively with gravity current fronts having initially a uniform frontal propagation speed locally normal to the plume front and a number of interesting results emerge we find that an initially concave region of the front can lead to a nonlinear focusing that results in an energetic bulge in the frontal plan view these bulges form sharp angles or kinks where they are joined to the front at their edges on either side as they evolve these angles increase toward 180 a straight line and the front becomes smoother in time the orientation of the bulge and kink features predicted by the model is in agreement with visual and radar imagery observations the kinks are always oriented toward the lighter plume material when a plume has two or more such concave regions the resulting energetic bulges can interact at a later time the issue of determining plume speeds by tracking these features on sequential images of gravity currents is also dealt with

high resolution measurements made across a tidal intrusion front high spatial resolution current and hydrographic measurements have been made across a tidal intrusion front in the james river estuary virginia during the first few hours of flood the current measurements were made with a surface towed acoustic doppler current profiler which was used in both profile and side scan configurations the profile data show a 30 50 cm s 1 inflow of water from the chesapeake bay a time evolving across front density gradient and downward velocity beneath the front of about 15 cm s 1 the side scan observations directly measure the across front change in current and provide a view of the three dimensional character of the frontal interface the near surface horizontal strain rate a critical parameter for understanding the modulation of surface waves across the front is estimated to be about 0 04 s 1 using phillips 1984 theory as a guide fronts with such large strain rates as these should be discernible in imagery from the ers 1 c band synthetic aperture radar for wind speeds of 4 m s 1

variations of sea surface temperature wind stress and rainfall over the tropical atlantic and south america abstract empirical orthogonal functions e0fs and composite analyses are used to investigate the development of sea surface temperature sst anomaly patterns over the tropical atlantic the evolution of large scale rainfall anomaly patterns over the equatorial atlantic and south america are also investigated the eof analyses revealed that a pattern of anomalous sst and wind stress asymmetric relative to the equator is the dominant mode of interannual and longer variability over the tropical atlantic the most important findings of this study are as follows atmospheric circulation anomalies precede the development of basinwide anomalous sst patterns over the tropical atlantic anomalous sst originate off the african coast simultaneously with atmospheric circulation anomalies and expand westward afterward the time lag between wind stress relaxation strengthening and maximum sst warming cooling is about two months anomalous atmospheric circulation patterns over northern tropical atlantic are phase

relationship between reservoir diagenetic evolution and petroleum emplacement in the ula field north sea abstract the diagenetic and petroleum filling histories of the ula field have been studied by analysing aqueous and petroleum inclusions occurring in authigenic cements this study shows that diagenesis continues actively after the arrival of petroleum in the sandstones although the reaction rates and petroleum saturation remain obscure microthermometric measurements of fluid inclusions in authigenic quartz suggest an onset of extensive quartz cementation at temperatures around 110 c i e 2 5 km and that this cementation has continued to the present day synchronously with quartz cementation authigenic albite was formed as inter and intragranular cements large amounts of petroleum inclusions locally occur in the albite and quartz cements these inclusions were trapped in the cements as the main charge of petroleum arrived at the structure diffusion through thin water layers between the petroleum and the mineral surface would probably have dominated mass transfer of solutes for the precipitation of authigenic quartz and albite it is evident from analysis of the petroleum inclusions in early formed k feldspar overgrowths that some secondary migrated petroleum probably arrived in the reservoir at a shallow burial depth before the rapid subsidence in the last 25 my compared with petroleum in the free porosity of the ula formation the petroleum in the k feldspar inclusions is evidently sourced from a different source facies and most maturity parameters testify to the latter being less mature later trapped petroleum inclusions in quartz and albite have characteristics found both in k feldspar and in the ula formation dst oil and thus is likely to reflect the progressive change in the ula field petroleum charge which occurred during the time period of quartz diagenesis

diagenesis and reservoir quality evolution of palaeocene deep water marine sandstones the shetland faroes basin british continental shelf abstract the palaeocene deep water marine sandstones recovered from six wells in the shetland faroes basin represent lowstand transgressive and highstand systems tract turbiditic sediments mineralogic petrographic and geochemical analyses of these siliciclastics are used to decipher and discuss the diagenetic alterations and subsequent reservoir quality evolution the middle upper palaeocene sandstones subarkoses to arkoses from the shetland faroes basin british continental shelf are submarine turbiditic deposits that are cemented predominantly by carbonates quartz and clay minerals carbonate cements intergranular and grain replacive calcite siderite ferroan dolomite and ankerite are of eogenetic and mesogenetic origins the eogenetic alterations have been mediated by marine meteoric and mixed marine meteoric porewaters and resulted mainly in the precipitation of calcite 18 o v pdb 10 9 and 3 8 trace amounts of non ferroan dolomite siderite 18 o v pdb 14 4 to 0 6 as well as smectite and kaolinite in the lowstand systems tract lst and highstand systems tract hst turbiditic sandstone below the sequence boundary minor eogenetic siderite has precipitated between expanded and kaolinitized micas primarily biotite the mesogenetic alterations are interpreted to have been mediated by evolved marine porewaters and resulted in the precipitation of calcite 18 o v pdb 12 9 to 7 8 and fe dolomite ankerite 18 o v pdb 12 1 to 6 3 at temperatures of 50 140 and 60 140 c respectively quartz overgrowths and outgrowth which post and pre date the mesogenetic carbonate cements is more common in the lst and tst of distal turbiditic sandstone discrete quartz cement which is closely associated with illite and chlorite is the final diagenetic phase the clay minerals include intergranular and grain replacive eogenetic kaolinite smectite and mesogenetic illite and chlorite kaolinite has been subjected to mesogenetic replacement by dickite the k feldspar and plagioclase grains have been albitized dissolution of calcite cement and of framework grain feldspar volcanic fragments and mud intraclasts has resulted in a considerable enhancement of reservoir quality

nonlinear internal waves and plumes generated in response to sea loch outflow auv and time lapse photography observations the tidally modulated outflow of brackish water from a sea loch forms a thin surface layer that propagates into the coastal ocean as a buoyant gravity current transporting nutrients and sediments as well as fresh water heat and momentum the fresh intrusion both propagates into and generates a strongly stratified environment which supports trains of nonlinear internal waves nliws nliws are shown to propagate ahead of this buoyancy input in response to propagation of the outflow water into the stratified environment generated by the previous release as well as in the opposing direction after the reflection from steep bathymetry oblique aerial photographs were taken and photogrammetric rectification led to the identification of the buoyant intrusion and the subsequent generation of nliws an autonomous underwater vehicle auv was deployed on repeated reciprocal transects in order to make simultaneous ctd adcp and microstructure shear measurements of the evolution of these phenomena in conjunction with conventional mooring measurements auv based temperature and salinity signals of nliws of depression were observed together with increased turbulent kinetic energy dissipation rates of over two orders of magnitude within and in the wake of the nliws repeated measurements allow a unique opportunity to investigate the horizontal structure of these phenomena simple metric scaling demonstrates that these these processes are likely to be feature of many fjordic systems located on the west coast of scotland but may also play a key role in the assimilation of the outflow from many tidally dominated fjordic systems throughout the world

on the dynamics of droughts in northeast brazil observations theory and numerical experiments with a general circulation model abstract it is proposed that a possible mechanism for the occurrence of severe droughts over northeast brazil is the establishment of a thermally direct local circulation which has its ascending branch at about 10 n and its descending branch over northeast brazil and the adjoining oceanic region the driving for this anomalous circulation is provided by warming due to enhanced moist convection associated with warmer sea surface temperature anomalies over the northern tropical atlantic and cooling associated with colder sea surface temperature anomalies in the southern tropical atlantic the combined effects of thermally forced subsidence and reduced evaporation and moisture flux convergence produces severe drought conditions over northeast brazil we have examined the monthly mean sea surface temperature anomalies over the tropical atlantic and rainfall anomalies over two selected stations fortaleza 3 46 s 38 31 w and quixeramobim 5 12 s 39 18 w for 25 years 1948 72 it is found that the most sever

spreading dynamics of small river plumes off the northeastern coast of the black sea observed by landsat 8 and sentinel 2 abstract we use near simultaneous ocean color satellite imagery from nasa s landsat 8 and esa s sentinel 2 missions to reconstruct surface currents along the northeastern shore of the black sea and study the spread of a small river plume formed in this area several times a year landsat 8 and sentinel 2 satellites both pass over the study area within a time interval of

dissolution and its impacts on reservoir formation in moderately to deeply buried strata of mixed siliciclastic carbonate sediments northwestern qaidam basin northwest china abstract petroleum exploration is increasingly extending from shallowly to moderately to deeply buried strata with reservoir quality being a key the formation mechanism of conventional clastic and carbonate reservoirs under such conditions has been widely investigated however the mechanism of mixed siliciclastic carbonate reservoirs has not been well studied in this paper we address this issue using a case study in the northwestern qaidam basin northwest china n1 e1 2 age 2500 4500 m dissolution pores and fractures dominate the reservoirs however only the fractures were the focus of previous studies thus here we investigate dissolution and its impacts on reservoir formation providing a complementary understanding of the reservoir formation in the basin using core observations and examining thin section it was discovered that dissolution was both random and followed bedding the dissolved components primarily included calcareous and gypsum minerals with fingerprints that are characteristic of burial dissolution further electron probe analysis on authigenic minerals revealed that the dissolution fluid might have originated from acidic formation fluids associated with hydrocarbon generation the fluids passed through faults and fractures dissolution pores were an important component of the reservoir providing approximately 60 of the porosity in addition segments of high porosity generally above 5 are associated with dissolution based on these observations a schematic model was established to explain the impacts of dissolution on reservoir formation specifically organic acidic formation fluids enter tectonic fractures resulting in dissolution as they pass through them this dissolution enhances the size of the pore space and the reservoir properties of the rocks eventually developing a fracture dissolution reservoir

fluorescent bands in massive corals record centuries of coastal rainfall massive coral colonies on the great barrier reef grow outwards at 5 25 mm yr 1 ref 1 skeletal density varies seasonally in all massive corals from the great barrier reef and an exact temporal record of growth can be obtained by x radiography of appropriately cut sections of the colony2 3 environmental influences on coral growth have been described from such analyses4 6 this is the first report from the skeletons of massive corals of yellow green fluorescent bands which appear under long wave uv light such fluorescence is confined to corals growing within 20 km of the shore and is not present in massive corals from mid and outer shelf reefs of the central great barrier reef region the timing width and intensity of the fluorescent bands correlate strongly with summer monsoonal rainfall and coastal runoff large colonies several centuries old can provide long records of the strength and periodicity of terrestrial runoff to the tropical nearshore environment such records are potentially important to climatology meteorology agriculture civil engineering and management of the great barrier reef

stable oxygen isotopic composition of corals from the gulf of guinea as indicators of periods of extreme precipitation conditions in the sub sahara stable oxygen isotopic analyses of scleractinian coral skeletons from the gulf of guinea in the eastern atlantic reveal that the corals from this region can be used to identify periods of severe drought and above average precipitation in sub sahara africa data presented in this paper show an inverse correlation between precipitation in the sahel and the 18 o values of a coral skeletons of the species siderastrea spp collected from the island of principe in the gulf of guinea this is opposite to the correlation expected as previous work has suggested that higher sea surface temperatures occur in the gulf of guinea during periods of low rainfall in the sahel such an association would lead to a positive correlation between sahel precipitation and skeletal 18 o the explanation for the observed inverse correlation is that the salinity of the gulf of guinea is strongly influenced by the outflow from the niger and congo rivers these periods of high freshwater input also correlate with periods of higher rainfall in the sub sahara and therefore affect the 18 o values of the coral skeleton the correlation between 18 o values of the coral skeleton and temperature in the northern subtropical atlantic ocean r 0 34 the magnitude of the dipole r 0 45 and the latitudinal position of the intertropical convergence zone r 0 37 illustrate that the 18 o values in the coral skeleton reflect climate dynamics of the region that affect the precipitation patterns in sub sahara africa

diagenetic gypsum related to sulfur deposits in evaporites libros gypsum miocene ne spain abstract the libros gypsum is the thickest evaporite unit of the miocene infill of the teruel basin in ne spain during the deposition of this unit intense bacterial sulfate reducing bsr activity in the lake depocenter generated a native sulfur deposit diagenetic gypsum resulted from subsequent sulfur oxidation the different processes involved in these transformations were first investigated by anadon et al 1992 the present paper is concerned with this diagenetic gypsum from the stratigraphic petrographic isotopic and genetic points of view diagenetic gypsum occurs mainly as continuous or discontinuous layers individual levels or lenses irregular masses nodules and micronodules and veins its main textures are coarse crystalline anhedral and fine grained alabastrine both of which can replace any former lithology carbonate gypsum and sulfur the following sequence of processes and mineral textural transformations is deduced primary gypsum deposition bsr and biodiagenetic carbonate h 2 s production growth of native sulfur growth of diagenetic gypsum partial recrystallization of the diagenetic gypsum textures the gypsification of the native sulfur generated two types of banded structures in the diagenetic gypsum 1 concentric structures of centripetal growth and 2 expansive roughly concentric structures in the first type the gypsification operated from the outer boundaries towards the inner parts in the second type part of the carbonate hosting the sulfur was also gypsified replaced cemented in the diagenetic gypsum the 34 s values are in agreement with a native sulfur and h 2 s provenance the 18 o sulfate values however enable us to differentiate two main groups of values one with positive values and the other with negative values in the group of positive values interstitial evaporated solutions participated in the sulfur oxidation this process presumably occurred in a first oxidation stage during shallow to deeper burial of the libros gypsum unit in the group of negative values however only meteoric waters participated in the oxidation which presumably occurred in a second oxidation stage during the final exhumation of the unit a third group of values is characterized by very high sulfur and oxygen values suggesting that bsr residual solutions also participated in the oxidation processes locally during the two oxidation stages both the textural characteristics and the isotopic composition of the diagenetic gypsum indicate that gypsification operated as a multistadic process

plagioclase dissolution related to oil residence time north coles levee field california diagenetic mineral zones characterize an originally homogeneous turbidite sandstone reservoir at north coles levee ncl the medium to coarse grained sands in the reservoir contain a 500 ft oil column with high water saturation extensive plagioclase porosity and associated diagenetic kaolinite occur in the lower third of the oil column plagioclase dissolution is greatest near the oil water contact kaolinite and plagioclase porosity are vary rare in the upper third of the oil column next to the gas cap previous work has sown that at ncl plagioclase dissolution occurred in the last several million years of the reservoir burial history nearly contemporaneous with oil emplacement clearly if plagioclase alteration was independent of the hydrocarbons a uniform alteration pattern would be expected the zonation pattern described here appears to be related to the presence of the oil thus diagenesis was most intense where the residence time of the hydrocarbon was greatest in the lower part whereas near the gas cap plagioclase diagenesis was minimal where the accumulation of gas effectively shut down feldspar dissolution these new results indicate that plagioclase porosity at ncl was an effect of oil emplacement perhaps due to acid components solubilized from the oil important implications of these findingsmore are 1 maximum porosity enhancement may be off structure away from the gas cap 2 tends to confirm the importance of acid components associated with hydrocarbons on feldspar dissolution and 3 diagenetic interpretations may differ if sample locations relative to gas oil water zones are not known less

an inland facies controlled eogenetic karst of the carbonate reservoir in the middle permian maokou formation southern sichuan basin sw china abstract carbonate karst is one of the research highlights in the field of carbonate reservoir geology here we report on a new type of karst formed in the middle permian maokou formation southern sichuan basin sw china i e inland facies controlled eogenetic karst which is different from the previously defined telogenetic karst this karst is eogenetic as the formation was buried at shallow depths prior to being subaerially exposed for a period of 7 8 myr in the paleo continental region of the upper yangtze uplift subaerial exposure may have been caused by a sea level regression during the tungwu orogeny which gave rise to a depositional hiatus over a broad area the top of the maokou formation is commonly marked by a weathered crust and an unconformable relationship with overlying layers below the surface the maokou formation contains sediments deposited by an underground drainage the geological setting can be inferred from an inland karst far from coastline the subsurface karst interval consists mainly of coarse grained limestone and micrite with the former occurring in shoal facies deposited in a high energy depositional environment and the latter in non shoal facies deposited in a low energy environment both of them were interbedded with in variable thicknesses the coarse grained limestone layers with high porosity and permeability acted as inception horizons more favourable for the development of karst than the micritic layers with low porosity and permeability therefore in places where both coarse grained limestone and micrite are present the karst is considered to be facies controlled the primary permeability of the coarse grained limestone combined with the permeability provided by faults and fractures provides sufficient channels for karst water formation of the karst system was characterized by contemporaneous development at multiple levels as controlled by the stratigraphic position of coarse grained shoal facies the karst reservoir therefore developed in both karst highland and karst transitional zone area between the karst highland and karst basin according to this model of karstification hydrocarbon exploration should focus on karst highlands located on palaeohighs and in synclines located far from fault zones

classification of buoyant river plumes from large aspect ratio channels abstractthe dynamics of the grand river plume a major tributary of lake michigan was studied in the vicinity of the grand haven coast on the east side of the lake the river spread laterally from the mouth and formed a thin surface buoyant plume with various shapes that have not been previously reported to understand the influence of different driving forces primarily wind buoyancy and ambient currents extensive field experiments were carried out over four periods in august and june 2006 and june and july 2007 they included aerial photography over the plume acoustic doppler current profiler adcp deployments meteorological buoys drifters sf6 and rhodamine wt tracer releases three dimensional 3d ctd profiling over the plume and ctd casts at the river mouth the results showed more flow classes than included in previous studies a modified classification scheme based on the relative magnitude of the plume crossflow length scale and a richardson number were devised that includes longshore c

glaciers dominate eustatic sea level rise in the 21st century ice loss to the sea currently accounts for virtually all of the sea level rise that is not attributable to ocean warming and about 60 of the ice loss is from glaciers and ice caps rather than from the two ice sheets the contribution of these smaller glaciers has accelerated over the past decade in part due to marked thinning and retreat of marine terminating glaciers associated with a dynamic instability that is generally not considered in mass balance and climate modeling this acceleration of glacier melt may cause 0 1 to 0 25 meter of additional sea level rise by 2100

mass transfer and problems of secondary porosity creation in deeply buried hydrocarbon reservoirs abstract secondary porosity created by the post depositional leaching of detrital grains and cements can be of great economic importance the term secondary porosity is only descriptive and does not give any information on whether the porosity of the rock has been enhanced in reality there are two end member volumetric outcomes to the leaching process firstly the mineral can be completely dissolved and its components transported out of the system in such an instance the porosity of the rock will be enhanced secondly it is possible that a mineral will decompose and by product minerals will be precipitated which will occupy approximately the same volume as the original mineral the latter case is more likely where the pore waters are close to equilibrium with the majority of the minerals of the rock this will occur at elevated temperatures and or where the pore waters have been in contact with the rock for a long time these conditions are commonly met during intermediate to deep burial many metastable minerals such as high temperature feldspars probably decompose in this way a consequence of the decomposition of such metastable minerals is that primary porosity will be swapped for secondary and that older and more deeply buried rocks will contain a higher proportion of secondary porosity the mass transport equation may be used to examine the physico chemical environment where enhanced porosities most likely occur during leaching by using a simple non equilibrium mass transport model based on the silica system it is possible to demonstrate the relative importance of flow rate reaction rates specific surfaces and temperature in controlling the areal extent of leaching wide leaching zones are related to high flow rates which in turn promote a high throughput of undersaturated fluid and dispersion leaching over a wide area is also favoured by low reaction rates which will occur at low temperatures although it is true to say that less of a given silicate mineral can be dissolved by an undersaturated pore water at low temperature than at high temperature it is probable that pore fluids from deeply buried sediments are more likely to be close to equilibrium with a given mineral than for instance meteoric water thus the most likely environment for the production of widespread enhanced porosity is in the shallow subsurface the lower flow rates and higher temperatures that are encountered during deep burial diagenesis will result in far narrower more intense leaching zones as a result providing sufficient reactive mineral is present any undersaturated pore water will approach equilibrium in a short distance in order to transport undersaturated pore waters appreciable distances in the deep subsurface it is necessary to minimize their interaction with the host rock this could occur if the pore fluid were to move through a fracture system where it would interact with a far smaller surface area of reactive mineral than if it moved through the pore network

secondary porosity generation during deep burial associated with overpressure leak off fulmar formation united kingdom central graben the overpressure history of a sandstone can be estimated using a numerical model if the burial curve and geological setting are known from the resulting effective stress the maximum potential porosity mpp can be calculated the mpp is the maximum porosity the rock could theoretically hold open at the modeled burial depth and pore pressure measured rock porosities should be at or below the mpp we have determined the mpp history for the fulmar formation sandstones upper jurassic of the central graben north sea and have compared the predictions to measured core data we conclude that for the majority of the fulmar formation sandstones the porosity evolution is a simple pattern of reduction during burial caused by compaction and cementation however in wells sited close to regional overpressure leak off points the porosity has been significantly increased from an end of oligocene low mean 21 to the present day values mean 31 this porosity increase occurred by feldspar dissolution with the reaction products being removed from the sandstones secondary porosity generation and the export of solute occurred while the sandstone was highly overpressured although still part of an open hydrogeological system the generation of porosity within deeply buried sandstones is of commercial importance and potentially can be predicted

reconstruction of historical sea surface temperatures using empirical orthogonal functions abstract studies of climate variability often rely on high quality sea surface temperature sst anomalies although the high resolution national centers for environmental prediction formerly the national meteorological center optimum interpolation oi sst analysis is satisfactory for these studies the oi resolution cannot be maintained before november 1931 due to the lack of satellite data longer periods of ssts have come from traditional analyses of in situ ship and buoy sst observations alone a new interpolation method is developed using spatial patterns from empirical orthogonal functions e0fs that is a principal component analysis to improve analyses of sst anomalies from 1950 to 1981 the method uses the more accurate oi analyses from 1982 to 1993 to produce the spatial eofs the dominant eof modes which correspond to the largest variance are used as basis functions and are fit in a least squares sense to the in situ data to determine the time dependence of each mode a complete field

oil charge preserves exceptional porosity in deeply buried overpressured sandstones central north sea uk abstract exceptionally high porosity sandstones are reported from oil provinces worldwide yet the mechanism of porosity preservation remains controversial we present strong evidence that the exceptional porosities in the jurassic fulmar formation within the north sea are the result of early oil charging preventing cementation and chemical compaction in sands with relatively low detrital clay contents although overpressure and grain coatings do have some effect the most dramatic evidence that reservoir quality is related to early oil charge is the spatial distribution of the porosity the maximum porosity of the fulmar formation is systematically highest immediately below the top seal and decreases below this despite uniform sedimentology hence porosity is preferentially preserved where oil first accumulated in these unusually homogeneous overpressured reservoir sandstones at the top oil charge prevents or significantly retards chemical compaction and cementation of a reservoir preserving porosity there is independent evidence for early oil charging of reservoirs within the central graben from fluid inclusion studies and k ar age dates of authigenic illite micro quartz grain coatings which have been proposed to preserve porosity during burial are associated with only 5 extra porosity in sands that exceed the worldwide average sandstone porosity by almost 20

major factors controlling fracture development in the middle permian lucaogou formation tight oil reservoir junggar basin nw china abstract natural fractures in seven wells from the middle permian lucaogou formation in the junggar basin were evaluated in light of regional structural evolution tight reservoir geochemistry including toc and mineral composition carbon and oxygen isotopes of calcite filled fractures and acoustic emission ae factors controlling the development of natural fractures were analyzed using qualitative and or semi quantitative techniques with results showing that tectonic factors are the primary control on fracture development in the middle permian lucaogou formation of the junggar basin analyses of calcite dolomite and toc show positive correlations with the number of fractures while deltaic lithofacies appear to be the most favorable for fracture development mineral content was found to be a major control on tectonic fracture development while toc content and sedimentary facies mainly control bedding fractures carbon and oxygen isotopes vary greatly in calcite filled fractures 13c ranges from 0 87 to 7 98 while 18o ranges from 12 63 to 5 65 indicating that fracture development increases with intensified tectonic activity or enhanced diagenetic alteration by analyzing the cross cutting relationships of fractures in core as well as four kaiser effect points in the acoustic emission curve we observed four stages of tectonic fracture development first stage fractures are extensional and were generated in the late triassic with calcite fracture fills formed between 36 51 c and 56 89 c second stage fractures are shear fractures caused by extrusion stress from the southwest to the northeast generated by the rapid uplift of the tianshan in the middle and late jurassic calcite fracture fills formed between 62 91 c and 69 88 c third stage fractures are nnw trending shear fractures that resulted from north south extrusion and thrusting in a foreland depression along the front of the early cretaceous bogda mountains calcite fracture fills formed between 81 74 c and 85 43 c fourth stage fractures inherited the tectonic framework of the third stage resulting in fractures with the same orientation but without calcite filling by differentiating the various stages of fracture development we were able to better understand the origin of fractures in tight oil reservoirs and their significance for exploration and development

multi stage primary and secondary hydrocarbon migration and accumulation in lacustrine jurassic petroleum systems in the northern qaidam basin nw china abstract to improve the understanding on lacustrine jurassic petroleum migration and accumulation in the northern qaidam basin nw china we conduct an integrated analysis of the petrography and geochemistry of oil bearing fluid inclusion including inclusion petrography homogenization temperature combined with reservoir burial and thermal history and reservoir sequential extraction results show that during the first stage of late oligocene to early miocene the deep paleogene reservoir was first charged by oils sourced from middle jurassic rocks petroleum inclusion this charge was accompanied by some oil alteration during the second stage of early to middle miocene the deep paleogene reservoir was charged by lower jurassic sourced oils intergranular free oil and this charging event is different from the first one in that it witnessed little hydrocarbon alteration during the third stage in the pliocene widespread gas sourced from lower and middle jurassic rocks occurred in both the deep paleogene and shallow neogene reservoirs and primary oil accumulations in deep paleogene reservoirs migrated vertically to shallow neogene reservoirs along faults and formed secondary accumulations little alteration took place favorable for the remigration thus the lacustrine lower and middle jurassic petroleum systems in the northern qaidam basin represent multi stage primary and secondary hydrocarbon accumulations and mixing of hydrocarbons was very common

reservoir quality variation on an eocene carbonate ramp el garia formation offshore tunisia structural control of burial corrosion and dolomitisation abstract study of four closely spaced el garia formation reservoirs offshore tunisia has identified diagenetic controls on variation in reservoir quality the ashtart didon and zarat fields have been affected by significant dissolution porosity which occurred during burial diagenesis with vuggy pores preferentially forming in micritic sediment however inter crystalline porosity due to dolomitisation is the principal control on reservoir quality in the hasdrubal field this spatial variation in porosity type reflects to some extent the structural and sedimentological isolation of hasdrubal within the facies trend surrounded by deep water embayments and unlike the other studied fields not directly underlain by salt diapirs burial corrosion appears to have formed where mid to outer ramp mud rich el garia formation facies directly overlie salt domes a consequence of the circulation of aggressive fluids related to increased heat flow above the salt inorganic co2 focused into the reservoir prior to hydrocarbon emplacement by faults related to salt movement is the most likely candidate responsible for the burial dissolution porosity observed in the ashtart didon and zarat fields a salt diapir does underlie the most basinward north east margin of hasdrubal and minor dissolution porosity is present but we conclude that the absence of significant dissolution in hasdrubal is due to its offset position away from the highly faulted roof zone immediately above the salt although we favour this model we cannot rule out that the absence of dissolution porosity in hasdrubal may reflect the early emplacement of hydrocarbons from an older non bou dabbous formation source or differences in the timing of salt movement and consequent fault creation below hasdrubal compared to the other fields local temperature and or acid concentration effects or a different source of co2 differences in the distribution of dissolution porosity in the ashtart didon and zarat fields may be related to the presence of intra reservoir permeability barriers due to increased nummulithoclastic fragmented nummulites content this may also explain the strata bound nature of the dolomite in hasdrubal which like the dissolution porosity in ashtart is overlain by sediments with an increased nummulithoclastic content although dolomite is present in variable quantities in all of the studied fields the significant volume of dolomite in hasdrubal may reflect a local plumbing effect with dolomitising fluids entering the reservoir via a fault network that does not affect the other fields

on the nature of the frontal zone of the choctawhatchee bay plume in the gulf of mexico river plumes often feature turbulent processes in the frontal zone and interfacial region at base of the plume which ultimately impact spreading and mixing rates with the ambient coastal ocean the degree to which these processes govern overall plume mixing is yet to be quantified with microstructure observations a field campaign was conducted in a river plume in the northeast gulf of mexico in december 2013 in order to assess mixing processes that could potentially impact transport and dispersion of surface material near coastal regions current velocity density and turbulent kinetic energy values e were obtained using an acoustic doppler current profiler adcp a conductivity temperature depth ctd profiler a vertical microstructure profiler vmp and two acoustic doppler velocimeters advs the frontal region contained e values on the order of 10 5 m2 s 3 which were markedly larger than in the ambient water beneath o 10 9 m2 s 3 an energetic wake of moderate e values o 10 6 m2 s 3 was observed trailing the frontal edge the interfacial region of an interior section of the plume featured opposing horizontal velocities and a e value on the order of 10 6 m2 s 3 a simplified mixing budget was used under significant assumptions to compare contributions from wind tides and frontal regions of the plume the results from this order of magnitude analysis indicated that frontal processes 59 dominated in overall mixing this emphasizes the importance of adequate parameterization of river plume frontal processes in coastal predictive models

convergence and downwelling at a river plume front abstract the small scale structure of the circulation and hydrography at the frontal boundary of the connecticut river plume in long island sound has been resolved using a novel combination of instruments a towed acoustic doppler current profiler adcp and a rigid array of current meters and conductivity temperature sensors observations were made during the latter half of the eastward ebb tide when the river plume was well established and the front was moving to the west at approximately 0 3 m s 1 two across front transects revealed a horizontal convergence rate in the across front velocity components at 0 6 m of 0 05 0 1 s 1 this was associated with a salt induced horizontal density gradient of 10 2 kg m4 observations obtained during a period in which the towed adcp was caught in the zone of maximum surface convergence showed significant downwelling with a near surface maximum of 0 2 m s 1 vertical velocities of this magnitude are consistent with observed magnitudes of the convergence rate at 0 6

reservoir characterization and hydrocarbon accumulation in late cenozoic lacustrine mixed carbonate siliciclastic fine grained deposits of the northwestern qaidam basin nw china abstract late cenozoic lacustrine mixed carbonate siliciclastic sequences in the northwestern qaidam basin nw china are mainly composed of high porosity and low permeability fine grained rocks but have big potentials of oil gas commercial production however how these fine grained rocks generate high quality reservoirs and accumulate hydrocarbons remains poorly known this study focuses on shallow buried shang youshashan formation middle late miocene n22 and shizigou formation late miocene pliocene n23 reservoirs and hydrocarbons in xiaoliangshan area of the northwestern qaidam basin we conduct mineralogy petrography and porosity and permeability analysis for reservoir rocks and biomarker analysis for hydrocarbons and potential source rocks the results indicate that the n22 high quality reservoirs are dominated by fractured marlstones and lime mudstones and constitute structural traps whereas the n23 hydrocarbon reservoirs are mainly composed of siliciclastic dominantly rocks and form stratigraphic lithologic traps similar biomarker ratios between crude oil samples and paleogene organic matter rich rocks reveal that hydrocarbons in the shallow system were likely derived from deep buried source rocks rather than late cenozoic lacustrine fine grained rocks themselves in this case large scale vertical fractures created by kink band structures in the northwestern qaidam basin are supposed to facilitate hydrocarbon migration and accumulation preliminary production data and exploration well oil gas test results demonstrate highest yields and thus large hydrocarbon potentials in the n22 marlstone and lime mudstone reservoirs collectively we suggest that relatively high permeability fractured and carbonate rich reservoirs on structural highs are favorable targets for future oil gas exploration in the northwestern qaidam basin this petroleum system provides a typical and significant example for hydrocarbon exploration and development in mixed carbonate siliciclastic fine grained rocks of nonmarine petroliferous basins

identification and composition of secondary meniscus calcite in fossil coral and the effect on predicted sea surface temperature this study uses electron backscatter diffraction ebsd and atomic force microscopy afm to identify secondary calcite in coral skeletons secondary calcite appears to have nucleated on the original aragonite dissepiments producing horizontal structures that mimic the morphology of the original coral aragonite forming dissepiment like meniscus structures the sr ca and 18o of the pristine aragonite and secondary calcite were analysed by secondary ion mass spectrometry sims the effect of calcite inclusion on the mean geochemistry of the coral carbonate and subsequent sea surface temperature sst calculations were determined for both sr ca and 18o inclusion of as little as 1 secondary calcite within the primary coral aragonite elevates the sr ca derived sst by 1 2 c and could markedly offset estimates of past tropical climate conversely inclusion of 10 secondary calcite has little effect on the sst estimated from 18o 0 6 c indicating that this proxy is relatively robust to even large amounts of calcite the different extents to which the two proxies would be influenced by inadvertent inclusion of such meniscus calcite demonstrate the importance of a multi proxy approach

anomalously high porosity and permeability in deeply buried sandstone reservoirs origin and predictability porosity and permeability generally decrease with increasing depth thermal exposure and effective pressure however a significant number of deep 4 km approximately 13 000 ft sandstone reservoirs worldwide are characterized by anomalously high porosity and permeability anomalous porosity and permeability can be defined as being statistically higher than the porosity and permeability values occurring in typical sandstone reservoirs of a given lithology composition and texture age and burial temperature history in sandstones containing anomalously high porosities such porosities exceed the maximum porosity of the typical sandstone subpopulation major causes of anomalous porosity and permeability were identified decades ago however quantification of the effect of processes responsible for anomalous porosity and permeability and the assessment of the predictability of anomalous porosity and permeability occurrence in subsurface sandstones have rarely been addressed in published literature the focus of this article is on quantification and predictability of three major causes of anomalously high porosity 1 grain coats and grain rims 2 early emplacement of hydrocarbons and 3 shallow development of fluid overpressure grain coats and grain rims retard quartz cementation and concomitant porosity and permeability reduction by inhibiting precipitation of quartz overgrowths on detrital quartz grains currently prediction of anomalous porosity associated with grain coats and grain rims is dependent on the availability of empirical data sets in the absence of adequate empirical data sedimentologic and diagenetic models can be helpful in assessing risk due to reservoir quality such models provide a means to evaluate the effect of geologic constraints on coating occurrence and coating completeness required to preserve economically viable porosity and permeability begin page 302 in a given play or prospect these constraints include thermal history and sandstone grain size and composition the overall effect of hydrocarbon emplacement on reservoir quality is controversial it appears that at least some cements quartz and illite may continue to precipitate following emplacement of hydrocarbons into the reservoir our work indicates that integration of basin modeling with reservoir quality modeling can be used to quantify prior to drilling the potential impact of hydrocarbon emplacement on porosity and permeability the best case scenario for significant reservoir quality preservation due to fluid overpressure development is in rapidly deposited tertiary or quaternary sandstones our models suggest that significant porosity can be preserved in sandstones that have experienced continuous high fluid overpressures from shallow burial depths the models also indicate that the potential for porosity preservation is greatest in ductile grain rich sandstones because compaction tends to be the dominant control on reservoir quality in such rocks the case for significant porosity preservation associated with fluid overpressures in pre tertiary basins however is more problematic because of the complexities in the history of fluid overpressure and the greater significance of quartz cementation as a potential mechanism of porosity loss

coastal river plumes collisions and coalescence abstract plumes of buoyant river water spread in the ocean from river mouths and these plumes influence water quality sediment dispersal primary productivity and circulation along the world s coasts most investigations of river plumes have focused on large rivers in a coastal region for which the physical spreading of the plume is assumed to be independent from the influence of other buoyant plumes here we provide new understanding of the spreading patterns of multiple plumes interacting along simplified coastal settings by investigating i the relative likelihood of plume to plume interactions at different settings using geophysical scaling ii the diversity of plume frontal collision types and the effects of these collisions on spreading patterns of plume waters using a two dimensional hydrodynamic model and iii the fundamental differences in plume spreading patterns between coasts with single and multiple rivers using a three dimensional hydrodynamic model geophysical scaling suggests that coastal margins with numerous small rivers watershed areas 2 such as found along most active geologic coastal margins were much more likely to have river plumes that collide and interact than coastal settings with large rivers watershed areas 100 000 km 2 when two plume fronts meet several types of collision attributes were found including refection subduction and occlusion we found that the relative differences in pre collision plume densities and thicknesses strongly influenced the resulting collision types the three dimensional spreading of buoyant plumes was found to be influenced by the presence of additional rivers for all modeled scenarios including those with and without coriolis and wind combined these results suggest that plume to plume interactions are common phenomena for coastal regions offshore of the world s smaller rivers and for coastal settings with multiple river mouths in close proximity and that the spreading and fate of river waters in these settings will be strongly influenced by these interactions we conclude that new investigations are needed to characterize how plumes interact offshore of river mouths to better understand the transport and fate of terrestrial sources of pollution nutrients and other materials in the ocean

burial diagenesis and porosity evolution upper jurassic smackover arkansas and louisiana the jurassic upper smackover ooid lime grainstone of the central gulf coast has been a major hydrocarbon exploration target for nearly half a century study of the geologic and sedimentologic framework petrography two phase fluid inclusions and trace element and stable isotope chemistry indicates the following diagenetic history the upper smackover is a blanket ooid grainstone ranging in thickness from 300 to 400 ft 91 to 122 m and covering at least 4 000 sq mi 10 400 sq km in the northern part of the arkansas shelf a regional meteoric water system was established in the grainstone shortly after deposition and prior to significant burial this meteoric water system gave way to conditions which were increasingly more marine toward the south near the louisiana arkansas state line the fresh to marine hydrologic gradient is responsible for the strong precompaction regional diagenetic overprint that eventually controlled available diagenetic pathways for the unit during burial three diagenetic zones are present 1 a northern zone dominated by oomoldic porosity and preburial spar cementation 2 a sou hern zone characterized by compaction effects late subsurface cement primary porosity preservation and late secondary subsurface porosity generation and 3 a transitional zone having characteristics common to both the northern and southern zones during the shallow burial phase compaction became increasingly more important to the south in zones dominated by marine connate fluid whereas rock integrity and a secondary oomoldic porosity system had already been established in the northern zone as burial increased brine originating in the underlying louann salt reached the shelf grainstone and began to displace the original connate fluid the brine triggered the inversion to calcite of remaining grains and cement composed of unstable mineralogy when the louann brine had displaced the original connate fluid caso4 replacement as gypsum and anhydrite was common across all three diagenetic zones also precompaction fine cement associated with oomoldic porosity was recrystallized and reequilibrated with the concentrate brine localized replacement dolomitization may well have developed throughout the burial history of the sequence but was most commonly postcompactional postcompaction poikilitic calcite cement and baroque dolomite were precipitated from the louann brine under conditions of elevated temperature and pressure as subsidence continued organic material from the basinward equivalents of the upper smackover lime grainstone arrived on the shelf and catalyzed so4 reduction resulting in pyrite and galena replacement in the southern and transitional zones as hydrocarbon maturation continued in the fine grained equivalents of the upper smackover h2s and co2 by products of these processes began to increase in the brine of the southern and transitional zones ultimately causing regional dissolution of existing carbonate and significantly enhancing preserved porosity porosity in the northern zone was established early and preserved through moderate burial although porosity is well developed permeability has been largely destroyed by recrystallization dolomitization is a prerequisite for economic reservoir development in the northern zone porosity in the southern zone is solution enhanced preserved primary intergranular porosity compaction is the most important porosity destruction process compaction in the absence of an early diagenetic overprint is affected primarily by grain type and secondarily by size and sorting pellets and oncolites compact easily yet destroy porosity during burial ooids and rhodolites resist compaction during burial therefore are related to porosity preservation grain type distribution as well as size and sorting are controlled by depositional environment processes with the most favorable areas for porosity development concentrations of ooids and rhodolites associated with early salt related structural movement porosity distribution in the southern zone therefore can be outli ed with the aid of geophysical end page 597 techniques porosity in the transitional zone is early secondary or preserved primary intergranular or a combination porosity in this zone therefore is highly unpredictable and a strong potential exists for diagenetic traps unrelated to structure or original depositional environment documentation of significant deep subsurface secondary porosity possibly associated with hydrocarbon maturation opens the potential for hydrocarbon exploration in deeply buried carbonate dominated basins this would include carbonate rocks heretofore thought to be well below the depth of carbonate porosity maintenance because of lithostatic load

observations of the response of a buoyant estuarine plume to upwelling favorable winds 1 the response of the buoyant plume from the chesapeake bay to upwelling favorable winds and during conditions of low freshwater discharge is examined using an offshore array of bottom deployed acoustic doppler current profilers adcps as well as ancillary data during periods of northward upwelling favorable winds the observed response is strong offshore flow u 0 2 m s in a shallow layer of plume water and a rapid reversal of the near surface flow from the usual southward flow associated with inertial turning of the plume the offshore migration of the plume front is deduced from sequential arrivals at the various mooring locations the orientation of the plume front is approximately alongshore north south suggesting that the upwelling response is two dimensional a plume thickness calculated from the adcp data is relatively constant at about 4 m as the plume moves across the moorings the offshore propagation speed of the plume front of about 0 20 m s matched the advection speed predicted by ekman theory using the calculated plume layer thickness the mooring velocity profiles provide a view of the across plume structure in a reference frame fixed to the front this reveals a pattern of circulatory motion with sinking of plume and ambient water at the front and an ascending motion occurring inshore suggesting a recirculation between the seaward and inshore portions of the plume these results are consistent with recent model simulations of the response of a river plume during upwelling favorable winds

meteoric like fabrics forming in marine waters implications for the use of petrography to identify diagenetic environments petrographic fabrics have long been used to identify meteoric diagenesis of carbonate sediments however on the basis of oxygen isotopic data we document similar fabrics forming in marine pore fluids in the shallow subsurface of great bahama bank therefore petrographic fabrics alone are not reliable indicators of diagenetic environments even for shallow water sediments in our study skeletal grainstones show two distinct diagenetic assemblages either dissolution of aragonitic grains and minimal cementation high permeability intervals or abundant blocky spar cement and neomorphism of aragonitic skeletal grains low permeability intervals these marine burial fabrics are present as shallow as 110 m below sea level well above the aragonite compensation depth a feature that must be considered for models of diagenesis in ancient carbonate sediments marine burial diagenesis may be important in ancient carbonate sediments deposited in moderate water depths or in shallow water during rising sea level where meteoric diagenesis is suppressed

a unique lacustrine mixed dolomitic clastic sequence for tight oil reservoir within the middle permian lucaogou formation of the junggar basin nw china reservoir characteristics and origin abstract the middle permian lucaogou formation in the jimusaer sag of the southeastern junggar basin nw china was the site of a recent discovery of a giant tight oil reservoir this reservoir is unusual as it is hosted by lacustrine mixed dolomitic clastic rocks significantly differing from other tight reservoirs that are generally hosted by marine lacustrine siliciclastic calcitic sequences here we improve our understanding of this relatively new type of tight oil reservoir by presenting the results of a preliminarily investigation into the basic characteristics and origin of this reservoir using field petrological geophysical including seismic and logging and geochemical data field and well core observations indicate that the lucaogou formation is a sequence of mixed carbonate mainly dolomites and terrigenous clastic mainly feldspars sediments that were deposited in a highly saline environment the formation is divided into upper and lower cycles based on lithological variations between coarse and fine grained rocks in particular dolomites and siltstones are interbedded with organic rich mudstones in the lower part of each cycle whereas the upper part of each cycle contains few dolomites and siltstones tight oil accumulations are generally present in the lower part of each cycle and dolomites and dolomite bearing rocks are the main reservoir rocks in these cycles including sandy dolomite dolarenite dolomicrite and a few dolomitic siltstones optical microscope back scattered electron and scanning electron microscope imaging indicate that the main oil reservoir spaces are secondary pores that were generated by the dissolution of clastics and dolomite by highly acidic and corrosive hydrocarbon related fluids

massive recrystallization of low mg calcite at high temperatures in hydrocarbon source rocks implications for organic acids as factors in diagenesis we document massive recrystallization of low mg calcite lime mudstone source rocks at moderately high temperatures in the smackover formation of mississippi this process was driven by organic acids produced during kerogen maturation and holds the implications for studies of primary migration of hydrocarbons secondary porosity generation in reservoirs and global environmental change this interpretation is based on contrasting the following petrographic and bulk rock geochemical characteristics of organic poor vs organic rich lime mudstones

characteristics of a surface buoyant jet tidal outflow from leschenault estuary in winter forms an unsteady surface buoyant jet in koombana bay on each outgoing tide as the water moves away from the exit channel and spreads radially over the bay it assumes a plumelike nature the mean features of this buoyant outflow such as the plume shape frontal celerity internal circulation and the bulk entrainment were measured in an intensive field program these features are shown to compare favorably with results from previous laboratory investigations and predictions from a simple inertia buoyancy force balance which includes entrainment at the front the stability of the plume frontal region was examined and it is shown that subfronts were present but their behavior cannot be explained by reference to previous work

radial spreading of buoyant surface plumes in coastal waters shallow buoyant surface plumes in coastal waters sometimes develop by nearly radial spreading from a continuous source such as at a river mouth such plumes often display a ring structure where buoyant water is concentrated between fronts at both the leading and trailing edges of the expanding ring these rings often occur in multiple concentric forms a model of the radial time dependent spreading of a shallow buoyant layer over a motionless deep ambient layer is developed it includes fronts as discontinuities and treats the remainder of the plume flow as inviscid gravitational spreading controlled by nonlinear internal waves calculations by the method of characteristics are presented that show the evolution of a clear ring structure the combination of rapid spreading in the radial geometry together with reflection of internal waves off the frontal boundary at the plume leading edge is shown to be necessary for ring formation a mechanism is suggested for the formation of multiple rings through the shear flow instability inherent in radial spreading

carbonate replacement of lacustrine gypsum deposits in two neogene continental basins eastern spain abstract bedded nonmarine gypsum deposits in the miocene teruel and cabriel basins eastern spain are partly replaced by carbonate the libros gypsum teruel graben is associated with fossiliferous carbonate wackestones and finely laminated organic matter rich mudstones which accumulated under anoxic conditions in a meromictic permanent lake the gypsum is locally pseudomorphed by aragonite or less commonly replaced by calcite low 13c values indicate that sulphate replacement resulted from bacterial sulphate reduction processes that were favoured by anacrobic conditions and abundant labile organic matter in the sediments petrographic evidence and oxygen isotopic composition suggest that gypsum replacement by aragonite occurred soon after deposition a subsequent return to oxidising conditions caused some aragonite to be replaced by diagenetic gypsum native sulphur is associated with some of these secondary gypsum occurrences the los ruices sulphate deposits cabriel basin contain beds of clastic and selenitic gypsum which are associated with limestones and red beds indicating accumulation in a shallow lake calcite is the principal replacement mineral bacterial sulphate reduction was insignificant in this basin because of a scarcity of organic matter stable isotope composition of diagenetic carbonate indicates that gypsum replacement occurred at shallow burial depths due to contact with dilute groundwaters of meteoric origin depositional environment evidently has a major influence upon the diagenetic history of primary sulphate deposits the quantity of preserved organic matter degradable by sulphate reducing bacteria is of particular importance and along with groundwater composition is the main factor controlling the mechanism of gypsum replacement by carbonate

fluorescent bands in massive corals result from terrestrial fulvic acid inputs to nearshore zone the discovery of yellow green fluorescent bands in the skeletons of massive corals from inshore waters of the great barrier reef and the temporal and spatial correlations of these bands with adjacent river flow1 prompted an investigation into the substances responsible for the phenomenon we have determined that all regions of the coral skeleton contain fulvic acids2 3 which impart a blue background fluorescence the yellow green fluorescent bands found only in inshore coral appear to result from enhanced concentrations of low relative molecular mass 10 000 fulvic acids from adjacent river input these compounds are ubiquitous and the yellow green banding phenomenon can be expected to occur in massive corals located near to significant river systems in the widely distributed genus porites4 the great age of the largest colonies1 means that extremely long highly resolvable records of coastal runoff exist throughout tropical nearshore seas

major factors controlling lamina induced fractures in the upper triassic yanchang formation tight oil reservoir ordos basin china abstract lamina induced fractures lf are abundant in lacustrine formations playing an important role for the tight oil resource exploration studies of controlling factors of the lf are still lacking especially for the heterogeneous formations characterized with complex combinations of the lamina and surrounding rock therefore 28 long column samples for triaxial compression tests 37 short column samples for brazil split tests and 12 powder samples for mineral component analysis and isotopes analysis carbon and oxygen are made from 6 cores in 4 petrophysical faces the experiments are designed to study the lf propagation process considering the controlling factors in terms of mineral component the lamina angle and the petrophysical faces our results show that clay content and dolomite cement degree more significantly control the lf propagation than the other minerals the lf propagation is not only dependent on the mineral component in the lamina but even more on the mineral component difference between the lamina and the surrounding rock i e the l s values where l represents the lamina and s represents the surrounding rock adjacent to the lamina the lf tended to propagate in a middle lamina angle range approximately 10 60 in shear properties and characterized with lower compression strength values all the lf observed in the thin sections were associated with oil although there was no obvious oil shown in the study cores the 13c and 18o values of lamina samples varied with the lamina mineral component for the complex organic matter oxidation and degradation reactions additionally the hydrocarbon flow parameter phf has been proposed on the carbon and oxidation isotope trace lines to indicate the oil rock reactions during the lf open period

burial dissolution of micrite in middle east carbonate reservoirs jurassic cretaceous keys for recognition and timing abstract this paper discusses burial diagenesis and especially a burial dissolution phase and its effects on micrite microtexture in reservoirs in the middle east three microporous reservoirs were selected the cenomanian mishrif formation in iraq the kimmeridgian tithonian arab d and the barremian kharaib formations both in abu dhabi staining cathodoluminescence and scanning electron microscopy were used for petrographic observations in the selected reservoirs three typical micrite microtextures are distinguished micro rhombic compact anhedral and rounded the chronology of diagenesis based on petrographic observations shows that mineralogical stabilisation through high magnesian calcite replacement by low magnesian calcite led to the formation of micro rhombic micrites non reservoir facies such as seals present compact anhedral micrites correlation between these micrites and high aluminium content suggests alumino silicate minerals clays as a catalyst for pressure dissolution and thus for reservoir degradation through cementation micrites from the upper part of oil reservoirs are dissolved during burial diagenesis dissolution is responsible for rounded shape and for reduction of crystal size it also implies pore diameter and pore throat size enlargement comparison of porosity and permeability with scanning electron microscope data confirms that rounded micrites are better reservoirs than micro rhombic micrites

a review of modern coral δ18o and δ14c proxy records abstract this paper is a review of published modern coral 18 o and 14 c isotopic records that are at least 30 and 20 years long respectively the data are presented to show basin scale trends in both of these proxy records on decadal to centennial timescales the goal was to qualitatively integrate the general inter annual to centennial timescale variability revealed in these data as well as the statistical and modeling output results that have been produced using these coral records while many review papers typically include a representative subset of the data available this review aims to include as much of the available data as possible in general coral 18 o records show a long term warming and or freshening throughout the tropical oceans and agree with the noaa extended reconstruction sea surface temperature 2 ersst on decadal timescales in the western pacific it is most likely a freshening of the seawater 18 o that dominates the signal el nino southern oscillation enso variability dominates most 18 o records either by varying local seawater temperature or salinity depending on the regional oceanography climatology outside of the pacific enso affects seawater temperature and salinity via atmospheric or oceanic teleconnections post bomb coral 14 c records collectively show that the uptake of 14 c has been greatest in gyre water fed sites followed in descending order by western boundary current areas equatorial upwelling regions and eastern tropical pacific upwelling sites these surface water 14 c values indicate the proportion of surface water and or the residence time of water at the surface at a given location and can be used to model water mass mixing rates such models have only begun to be run and show that the amount of eastern pacific water entering the central south pacific increases during el ninos and that the indonesian throughflow is supplied year round by the north pacific comparing ocean circulation models with coral 14 c modelled circulation enables researchers to explore the mechanisms that drive seawater 14 c variability and fine tune their models in addition our comparison between the rate of coral 14 c increase between 1960 and 1970 and total anthropogenic co 2 uptake rates show general agreement demonstrating the value of coral records in understanding past carbon fluxes overall coral 18 o and 14 c proxy records represent natural archives of seawater conditions and are critical for studying the natural variability in local and regional patterns within and teleconnection patterns between the tropics extra tropics temperate and polar regions on intra annual to centennial timescales

initial expansion of the columbia river tidal plume theory and remote sensing observations 1 analysis of the columbia river tidal plume using lagrangian frontal equations provides a concise description of the evolution of frontal depth h velocity u reduced gravity g and frontal internal froude number fr because the estuary mouth is narrow the initial radial plume motion is supercritical fr 1 for up to 12 hours understanding this supercritical phase is vital because plume properties change rapidly with strong ecosystem impacts to analyze this expansion analytical and numerical models the latter with three mixing formulations were tested model results are compared to synthetic aperture radar images to verify that the predicted frontal properties are realistic lagrangian theory provides especially simple constraints independent of the mixing model on spatial variations in fr and ug h for parameters representative of the columbia river plume the plume spreads 10 35 km and thins to 25 60 of its initial depth before becoming subcritical after liftoff fr increases as the front accelerates and thins it then decreases to unity g decreases but more slowly than h and u h controlled by a balance between spreading and mixing first decreases then increases the strength of vertical mixing and the mixing efficiency ef ratio of buoyancy flux to dissipation both play a significant role in determining plume properties and it is important to include both the horizontal gradient in g and surface slope component of the pressure gradient a model with an ellison turner type entrainment scheme predicts the plume trajectory better than one that assumes a constant interfacial gradient richardson number

decadal cyclicity of regional mid holocene precipitation evidence from dominican coral proxies 1 the stable carbon 13c and oxygen 18o isotopic compositions of four holocene specimens of montastraea sp and siderastrea sp coral skeletons from the dominican republic were analyzed to examine decadal scale fluctuations in regional precipitation the specimens range in length from 47 to 197 years individually and range in age from 7 2 to 5 2 kyr oscillations in the 13c and 18o of coral skeletons from the holocene enriquillo valley occur with a seemingly consistent frequency of 15 20 years for one coral 6 ka this decadal to multidecadal mode of variability is statistically significant the decadal to multidecadal mode of stable isotopic variability may represent cyclic fluctuations in mid holocene migration of the intertropical convergence zone itcz or in the hydrogeology of the region as governed by fluctuations in the passage of tropical storms and hurricanes regional temperature is believed to act as only a secondary control on the 18o values of these corals however itcz migration and or oscillations in storm frequency at this site may ultimately reflect decadal scale patterns in greater tropical north atlantic sea surface temperatures the length and resolution of climate variability represented in this study indicate a persistent decadal to multidecadal mode of atlantic climate fluctuation throughout the mid holocene that is indistinguishable from observed historical climate

frontogenesis in a fluid with horizontal density gradients the adjustment under gravity of a fluid containing a horizontal density gradient is described the fluid is initially at rest and the resulting motion is calculated as the flow accelerates driven by the baroclinic density field two forms of the initial density distribution are considered in the first the initial horizontal gradient is constant a purely horizontal motion develops as the isopycnals rotate towards the horizontal the vertical density gradient increases continually with time but the horizontal density gradient remains unchanged the horizontal velocity has a uniform vertical shear and the gradient richardson number is constant in space and decreases monotonically with time to the second density distribution consists of a piecewise constant gradient with a jump in the gradient along a vertical isopycnal the density is continuous in this case frontogenesis is predicted to occur on the isopycnal between the two constant density gradient regions and the timescale for the formation of a front is determined laboratory experiments are reported which confirm the results of these calculations in addition lock exchange experiments have been carried out in which the horizontal mean gradient is represented by a series of step density differences separated by vertical gates

mesogenetic dissolution of the middle ordovician limestone in the tahe oilfield of tarim basin nw china abstract the mesogenetic dissolution is well developed in the middle ordovician yijianfang formation o2yj limestone and the dissolution pores are very important for petroleum accumulation in the south slope area of the tahe oilfield which lies in the north of the tarim basin northwestern china mottled dotted or laminar dissolution can be observed in the o2yj limestone under microscope the grains lime matrix and all stages of calcite cements including oil inclusion bearing blocky calcite cements can all be found dissolved ubiquitously the stylolites in the limestone were enlarged and rounded because of dissolution some dolomite rhombs precipitated along stylolites in burial environment were found dissolved as well the dissolution of the blocky calcite cements and dolomite rhombs and the enlarging of stylolites demonstrate that the dissolution took place in the mesogenetic environment concentration of trace elements including rees of the eroded part of the o2yj limestone is intermediate between that of the uneroded part and that of the underlying lower ordovician limestone hydrocarbon source rocks both 13cpdb and 18opdb values of the eroded part are less than those of the uneroded part respectively the geochemical characteristics indicate that the eroding fluids are hydrocarbon bearing fluids coming from the underlying hydrocarbon source rocks

decadal variability of the tropical atlantic ocean surface temperature in shipboard measurements and in a global ocean atmosphere model abstract numerous analyses of relatively short 25 30 years in length time series of the observed surface temperature of the tropical atlantic ocean have indicated the possible existence of decadal timescale variability it was decided to search for such variability in 100 yr time series of sea surface temperature sst measured aboard ships and available in the recently published global ocean surface temperature atlas gosta fourier and singular spectrum analyses of the gosta sst time series averaged over 11 subregions each approximately 1 106 km2 in area show that pronounced quasi oscillatory decadal 8 20 yr and multidecadal 30 40 yr timescale variability exists in the gosta dataset over the tropical atlantic motivated by the above results sst variability was investigated in a 200 yr integration of a global model of the coupled oceanic and atmospheric general circulations developed at the geophysical fluid dynamics laboratory gfdl the second 100 yr of sst in the coupled model s tropical

impact of sequence stratigraphy depositional facies and diagenesis on reservoir quality a case study on the pennsylvanian taiyuan sandstones northeastern ordos basin china abstract the pennsylvanian taiyuan formation of the shenmu field in the northeastern ordos basin of china contains tight sandstone reservoirs that have recently been commercially produced an evaluation of the reservoir quality of the taiyuan sandstones will play a critical role in the development of the field an investigation was conducted to explore possible effects of the sequence stratigraphy depositional facies and diagenetic alterations on the reservoir quality of the taiyuan sandstones based on core descriptions the examination of thin sections and core plug and scanning electron microscope analyses the taiyuan formation consists of lowstand system tracts lst transgressive system tracts tst and highstand system tracts hst the lst sandstones are principally medium to coarse grained and are interpreted to have been deposited in the dominant distributary channels of a delta plain the early tst fine to coarse grained sandstones were largely deposited in the underwater distributary channel and mouth bar of a delta front and the middle tst fine to medium grained sandstones were deposited in the shoreface to foreshore environment the hst silt to medium grained sandstones were mostly deposited in the mouth bar of a delta front and shoreface to foreshore the taiyuan sandstones which are composed of sublitharenites quartzarenites and litharenites suffered from extensive compaction that resulted in a large loss of intergranular porosity before the sandstones were further cemented severely the sandstone cements are mostly composed of illite ankerite calcite and quartz the taiyuan sandstones have a particularly low average core plug porosity of 7 41 and horizontal permeability of 0 916 md which results from that most of the pores of the sandstones are micropores and secondary pores with poor connectivity the lst dominant distributary channel early tst underwater distributary channel and proximal mouth bar and hst shoreface to foreshore sandstones with relatively coarser grain sizes mostly medium to coarse grained have relatively higher porosities and permeabilities than the sandstones with relatively finer grain size which is ascribed to a widespread early dissolution by meteor water leaching and lower content of cements within the coarser grained sandstones however the lst dominant distributary channel sandstones had undergone a more effectively early dissolution and less carbonate cementation than the tst underwater distributary channel and proximal mouth bar and hst shoreface and foreshore sandstones had which lead to the relatively best reservoir quality of the lst dominant distributary channel sandstones among the taiyuan sandstones the study revealed that the reservoir quality of the tight taiyuan sandstones was controlled by sequence stratigraphy framework depositional facies grain size and diagenetic alterations together the sequence stratigraphy framework played a key role in controlling the reservoir quality of the taiyuan sandstones by governing the depositional facies and corresponding diagenetic products while the grain size affected the reservoir quality of the sandstones by controlling the content of cement within the sandstones

the influence of tide and wind on the propagation of fronts in a shallow river plume in this study we used field data and radar images to investigate the influence of winds and tides on the propagation of tidal plume fronts the measurements were collected in a shallow shelf region off the dutch coast 10 km north of the rhine river mouth and they clearly show the passage of distinct freshwater lenses and associated fronts at the surface that propagate all the way to the coastline these fronts are observed as a sudden drop in near surface salinity accompanied by high cross shore shear with onshore velocities at the surface we determined the arrival time to our measurement site frontal propagation speed and structure of the fronts by combining the in situ data and radar images frontal froude numbers show a wide range of values with an average of 0 44 our results show that fronts during spring tides are thinner more mixed and move faster relative to the ground during calm spring tides when compared to calm neap tides downwelling winds during spring tides result in thicker and faster fronts however the intrinsic frontal propagation speed indicates that the wind and tide control the frontal propagation mainly due to advection rather than by changing the frontal structure strong return currents in the near bed layer resulting from fast and thick fronts increase near bed turbulence and bed stresses these high stresses suggest that the passage of fronts in shallow coastal areas can initiate sediment resuspension and contribute to transport processes

the influence of organic matter on the boron isotope geochemistry of the gulf coast sedimentary basin usa large variations in the boron isotopic composition of sedimentary environments make boron an attractive monitor of fluid rock interactions during diagenesis studies of b in marine sediments have shown that preferential adsorption of 10b on clay minerals leaves pore waters enriched in 11b during diagenesis clay minerals recrystallize and incorporate 10b into the mineral structure spivack a j palmer m r edmond j m 1987 the sedimentary cycle of the boron isotopes geochim cosmochim acta 51 1939 1949 this process should cause a depletion of b in the pore water with an increase in the 11b in the gulf coast sedimentary basin usa however there is a general increase in b content of formation waters land l s macpherson g l 1992 origin of saline formation waters cenozoic section gulf of mexico sedimentary basin geochim cosmochim acta 76 1344 1362 moldovanyi e p walter l m 1992 regional trends in water chemistry smackover formation southwest arkansas geochemical and physical controls aapg bull 76 864 894 and a decrease in 11b with depth this suggests that another source of 10b exists in deep basinal environments we know that oil reservoir brines are commonly enriched in boron collins a g 1975 geochemistry of oilfield waters elsevier new york p 496 therefore this study examines organic matter as a possible source of boron during thermal maturation samples of water oil and cored sediments were collected from three stacked hydrocarbon reservoirs in the gulf of mexico sedimentary basin at a depth of 3500 4350 m extraction of boron from organic matter oil and kerogen was done by parr bomb volatilization with mannitol used as a b complexing agent the isotope ratios were measured using negative thermal ionization and compared to in situ analyses using secondary ion mass spectrometry the 11b values of pore filling clays in sandstone reservoirs is 2 2 the b content of the clay averages 144 ppm oil field waters show a range in b content from 8 85 ppm and 11b values from 28 to 37 increasing from the lowest to the uppermost reservoir there is an apparent 11b enrichment of fluids with progressive migration through clay rich sediments very little b ppb was found in the oil but kerogen extracted from the oil source rock sassen r 1990 lower tertiary and upper cretaceous source rocks in lousiana and mississippi implications to gulf of mexico crude oil aapg bull 74 857 878 contains significant b 140 ppm with a 11b of 2 2 similar to the pore filling clay minerals in the sandstones while kerogen comprises only 2 of the sedimentary basin its influence can be significant if b with distinctly low 11b is released over a specific temperature interval during thermal maturation the release of b from organic compounds could cause the observed regional 10b enrichment in waters deep in the gulf coast basin

characteristics of the great whale river plume observations of the motion field and dilution effects associated with the plume of great whale river in hudson bay are presented for both open water and ice covered conditions in the summer months a distinct plume of about 100 km2 in area is formed offshore which is characterized by a 1 2 m thickness and large velocities directed away from the river mouth in contrast to slower currents parallel to the shore in the ambient waters underneath surface drifter results suggest that the outer boundary of plume may be a zone of frontal convergence under ice covered conditions the plume was significantly thicker and extended much farther offshore in spite of a marked reduction in river runoff at this time

evolution of diagenetic system and its controls on the reservoir quality of pre salt dolostone the case of the lower ordovician majiagou formation in the central ordos basin china abstract the evolution of diagenetic system and its impact on the carbonate reservoir quality are of paramount importance new investigation of the lower ordovician majiagou formation central ordos basin china has revealed that the diagenesis and quality of pre salt dolostone reservoirs were controlled by the evolution of diagenetic system three different reservoir types grain crystalline and algal dolostone and five kinds of reservoir space intergranular pore intragranular pore intercrystalline pore dissolution pore and vug in karst system and parallel dissolution pore of laminar algae are identified in the majiagou formation pre salt dolostone of the central ordos basin based on the petrographic characteristic the diagenetic process of pre salt dolostone can be divided into four stages the penecontemporaneous diagenesis the early diagenesis the epidiagenesis and the mesodiagenesis late diagenesis petrographic and geochemical analyses of the studied dolostone reservoir indicated that the diagenetic system was open during the penecontemporaneous diagenesis and became closed during the early diagenesis open and closed diagenetic system existed in the west and east of the central ordos basin during the epidiagenesis respectively after that the western and eastern pre salt dolostone reservoirs both evolved into a closed diagenetic system during the mesodiagenesis late diagenesis subaerial meteoric dissolution in an open diagenetic system secondary pore formation and subsequent pore preservation in a closed diagenetic system are the critical factors in the improvement of pre salt dolostone reservoir quality although two cycles from open to closed diagenetic system developed in the western dolostone reservoir the pore space there was filled with overlying weathering mud in the second open diagenetic system during the epidiagenesis which reduced the reservoir quality the eastern dolostone reservoir experienced just one cycle from open to closed diagenetic system the reservoir quality was improved and then preserved thus only a good match among the diagenetic systems during different diagenetic stages will be good for the reservoir formation and preservation therefore the potential high quality reservoirs in the pre salt dolostones mainly located in the eastern part of the central ordos basin

environmental correlates of hermatypic coral montastrea annularis growth on the east flower gardens bank northwest gulf of mexico time series of annual linear growth increments from 12 montastrea annularis e and s collected at the east flower gardens bank reef in the northwestern gulf of mexico have a common pattern this is best expressed in an index master chronology average by year of the annual percentage deviations from the mean of each coral comparisons with time series of environmental data indicate that coral extension rates vary positively with seasonal february through may4 months surface water temperature and negatively with annual discharge of the atchafalaya river we propose that secular variations of water temperature and other parameters are the major long term controls of coral growth in the area our data do not support the view that sinking of the flower gardens reef caused by catastrophic collapse of the underlying substrate has been a prime influence on the corals

hydraulically controlled front trapping on a tidal flat 1 we report observations of baroclinic surface fronts in skagit bay the fronts formed repeatedly in very shallow 0 7 m deep water along the edge of a tidal channel shortly after the incoming tide flooded the adjacent tidal flat and eventually departed from channel edge as the flood tide progressed the fronts were surface convergence zones trapping gps drifters and other flotsam across front salinity temperature jumps were a few practical salinity units a few degrees with freshwater on the channel side across front transects of velocity from mobile and fixed acoustic doppler current profilers and density from mobile and fixed conductivity temperature depth profilers are presented composite froude numbers indicate that supercritical flow over the flats initially held fronts near the channel edge as flood tide progressed depth averaged flow speeds decreased while internal wave speeds increased owing to increasing depths and density gradients flow over the flats eventually became subcritical at which point fronts departed from the channel edge the front then formed the leading edge of a shallow around 0 3 m thick freshwater plume which propagated across the flats against the incoming tidal flow water was then exchanged between the channel and flats with a channel edge composite froude number near 0 5 consistent with mixing induced reduction in channel flats exchange the across channel velocity shear was correlated with the across channel wind consistent with a simple eddy viscosity model strong winds prevented plume propagation

proxy interpretation of coral recorded seawater δ18o using 1 d model forced by isotope incorporated gcm in tropical oceanic regions the oxygen isotopic ratio in the seawater 18osw recorded in 18o of coral skeleton for several centuries in tropical regions is an important variable for reconstructing the past climate however the relationship between 18osw and hydrological balance has not been clearly uncovered yet in this study a one dimensional ocean budget model forced by the global quasi reanalysis isotope data which is the output of an isotope incorporated global spectral model is employed to simulate 18osw the results from the simulations are compared with 31 coral records in tropical oceanic regions the 1 d model successfully reproduces 18osw in 21 coral records indicating these corals have the potential to reconstruct the local hydrological budget the results also confirm that the reproducibility of the 1 d model generally increases with the annual precipitation variability however in the regions where the precipitation variability is less it is more difficult to reconstruct climatic information from the 18osw since the nonlocal physical processes unaccounted for in the 1 d model may affect 18osw the sensitivity analysis of the 1 d model shows that in tropical oceanic regions the large scale precipitation is the dominant factor for 18osw confirming that 18osw recorded in the coral records is a proxy for the precipitation anomaly this study implies that 18osw is more closely associated with precipitation and local water isotope budget in tropical oceanic regions than elsewhere and that the 1 d model is a useful approach for the proxy interpretation in tropical oceanic regions

the 13c suess effect in scleractinian corals mirror changes in the anthropogenic co2 inventory of the surface oceans 1 new 13 c data are presented from 10 coral skeletons collected from florida and elsewhere in the caribbean dominica dominican republic puerto rico and belize these corals range from 96 to 200 years in age and were collected between 1976 and 2002 the change in the 13 c of the skeletons from these corals between 1900 and 1990 has been compared with 27 other published coral records from the atlantic pacific and indian oceans the new data presented here make possible for the first time a global comparison of rates of change in the 13 c value of coral skeletons of these records 64 show a statistically significant p 0 05 decrease in 13 c towards the modem day 23 out of 37 this decrease is attributable to the addition of anthropogenically derived co 2 13 c suess effect to the atmosphere between 1900 and 1990 the average rate of change of the 13 c in all the coral skeletons living under open oceanic conditions is approximately 0 01 o yr 1 in the atlantic ocean the magnitude of the decrease since 1960 0 019 yr 1 0 015 is essentially the same as the decrease in the 13 c of atmospheric co 2 and the 13 c of the oceanic dissolved inorganic carbon 0 023 to 0 029 yr 1 while in the pacific and indian oceans the rate is more variable and significantly reduced 0 007 yr 1 0 013 these data strongly support the notion that i the 13 c of the atmosphere controls ambient 13 c of the dissolved inorganic carbon which in turn is reflected in the coral skeletons ii the rate of decline in the coral skeletons is higher in oceans with a greater anthropogenic co 2 inventory in the surface oceans iii the rate of 13 c decline is accelerating superimposed on these secular variations are controls on the 13 c in the skeleton governed by growth rate insolation and local water masses

burial dolomitization and dissolution of upper jurassic abenaki platform carbonates deep panuke reservoir nova scotia canada a large gas reservoir was discovered in the previously unproductive jurassic aged abenaki carbonate margin in 1998 most of the reservoir porosity is developed in dolostones these dolostones replaced preexisting wackestones packstones and grainstones associated with reefal and adjacent depositional environments many dolomites were subsequently recrystallized or dissolved accounting for much of the preserved secondary porosity subsequent fracturing helped enhance reservoir permeabilities enhanced petrographic techniques established that dissolution of previously dolomitized fabrics generated much of the secondary porosity in these dolostones diffused plane polarized light revealed relict grains and textures invisible with standard microscopic observations petrographic and geochemical observations also confirmed that dissolution occurred under deep burial conditions after incipient pressure solution dissolution was not confined to the centers of dolomitized grains as is commonly seen when remnant calcitic grains dissolve out during the advanced stages of replacement dolomitization instead dissolution was random within relict grains as isolated dolomite crystals were also variably dissolved the geochemistry of these dolomites and associated late stage calcites implied precipitation from basinal hot fluids as well as hydrothermal fluids later diagenetic fluids either acidic or calcium rich or perhaps both at different times based on associated mineralization seemingly promoted dolomite dissolution the presence of tectonic fractures and stylolites helium gas and faults observed in seismic data implied that dolomitization and subsequent dissolution along the abenaki platform margin were controlled by reactivated wrench faults tied to basement on a finer scale diagenetic fluids moved through fractures and pressure solution seams the data collected to date support our contention that the dolomitization and dissolution process which has created most of the porosity in the abenaki reservoir was poststylotization and deeper burial in origin given the timing of tectonic activity in the area and its inferred connection to diagenesis it is probable that at least a part of the diagenetic fluids were hydrothermal in nature

cenozoic deformation history of the qaidam basin nw china results from cross section restoration and implications for qinghai tibet plateau tectonics abstract the deformation and uplifting history of the qinghai tibet plateau is a controversial issue and so far there has been insufficient evidence for interpretation investigations of the cenozoic deformation in the northeastern edge of this plateau may provide some relevant information in this paper the cenozoic deformation history of the qaidam basin has been studied based on results from the balanced cross section restoration of six geological sections they indicate that 1 the qaidam basin has been undergoing continuous shortening since the beginning of cenozoic with two relatively fast shortening phases the first during 42 8 40 5 ma and the second during 2 8 ma present 2 the shortening rate of the qaidam basin reached its maximum value since 2 8 ma and approximately 32 of the average total cenozoic shortening took place in this period and 3 the shortening of all sections reached approximately 50 of their respective total shortening by miocene the cenozoic deformation history of the qaidam basin shows good synchroneity with uplifting history of the qinghai tibet plateau it is therefore proposed that the deformation and uplifting in the south and north edges of the qinghai tibet plateau was almost synchronous with the altyn tagh fault formed at the beginning of india asia collision accordingly it is postulated that since the india asia collision at the beginning of cenozoic the indian plate moved northward continuously with two relatively fast phases the first during 42 8 40 5 ma and the second during 2 8 ma present approximately 50 of the total cenozoic northward displacement of the indian plate of the total amount of crustal shortening and uplifting of the qinghai tibet plateau and of the total cenozoic strike slip displacement of the altyn tagh fault were probably reached by the early miocene moreover another 30 40 might have taken place during 2 8 ma present the periods during 42 8 40 5 ma and during 2 8 ma present may also be the two fast phases for crustal shortening and uplifting of the qinghai tibet plateau and strike slip displacement of the altyn tagh fault

characteristics of low frequency sea surface temperature fluctuations in the tropical atlantic abstract sea surface temperature anomalies in the tropical atlantic ocean are reexamined to investigate an apparent low frequency oscillation that has been described as a fluctuating dipole structure with poles north and south of the equator and a node near the itcz using principal components rotated by the varimax method and simple correlations of area averaged temperatures we show that during the 1964 88 interval sst anomalies north and south of the itcz are not significantly correlated therefore the low frequency variation with an apparent decadal period observed in the sst gradient across the itcz during 1964 88 does not arise from temporally coherent and out of phase fluctuations in each hemisphere and cannot be characterized as a dipole

types of mixing and heterogeneities in siliciclastic carbonate sediments abstract mixed siliciclastic carbonate deposits consist of a suite of different types of mixing between the two components from bed core plug to stratigraphic seismic scales producing a high vertical and lateral lithological variability mixed deposits results from the interaction of siliciclastic input and coeval carbonate production controlled by temporal and or spatial factors although mixed deposits are very diffuse in the geological record studies about these deposits are scrappy and not well encoded accordingly mixed deposits represent a labyrinth for researchers who want to investigate them for the first time in this paper different types of mixing compositional versus strata controlled by different allocyclic e g sea level climate and or autocyclic e g depositional processes factors that operate at different scale are documented mixing is recognized and described at three main scales of observation bed core plug scale lithofacies well log scale and stratigraphic seismic scale i compositional mixing reflects the contemporaneous accumulation of the two heterolithic fraction in space and time this type of mixing is observable at lamina to bed scale locally producing depositional structures diagnostic for particular depositional environments ii strata mixing results from the alternation of the two heterolithic fraction in time this type of mixing is observable at lithofacies to stratigraphic scale and can be related to depositional processes climatic variations and or relative sea level changes a correct identification of these different types of mixing and the scale of their occurrence is crucial in revealing i physical processes that control the sedimentation ii environmental factors that influence the carbonate factory related to the siliciclastic dispersal mechanisms and iii internal heterogeneity of the resulting sedimentary deposit furthermore the petroleum industry is interested to unravel new insights about internal properties of mixed siliciclastic carbonate systems e g porosity permeability and to reconstruct predictive 3d models for the related reservoirs the correct prediction of internal heterogeneity and the recognition of lateral and vertical compartmentalization have an important impact on hydrocarbon exploration and exploitation

tropical atlantic sea surface temperature variability and its relation to el nino southern oscillation past analyses of tropical atlantic sea surface temperature variability have suggested a dipole behavior between the northern and southern tropics across the intertropical convergence zone itcz by analyzing an improved 43 year 1950 1992 record of sst smith et al 1996 and other data derived from the comprehensive ocean atmosphere data set coads it is shown that the regions north and south of the itcz are statistically independent of each other at the seasonal to interannual timescales dominating the data confirming the conclusions of houghton and tourre 1992 some dipole behavior does develop weakly during the boreal spring season when there is a tendency for sst anomaly west of angola to be opposite of that in the tropical north atlantic it is further shown that tropical atlantic sst variability is corre lated with pacific e1 nifio southern oscillation enso variability in several regions the ma jor region affected is the north atlantic area of ne trades west of 40ow along 10on 20on and extending into the caribbean there about 50 80 of the anomalous sst variability is associ ated with the pacific enso with atlantic warmings occurring 4 5 months after the mature phases of pacific warm events an analysis of local surface flux fields derived from coads data shows that the enso related atlantic warmings occur as a result of reductions in the surface ne trade wind speeds which in turn reduce latent and sensible heat losses over the region in ques tion as well as cooling due to entrainment this enso connection is best developed during the boreal spring following the most frequent season of maximum enso anomalies in the pacific a region of secondary covariability with enso occurs along the northern edge of the mean itcz position and appears to be associated with northward migrations of the itcz when the north at lantic warmings occur although easterly winds are intensified in the western equatorial atlantic in response to pacific warm events they do not produce strong local changes in sst contrary to expectations from studies based on equatorial dynamics these teleconnected wind anomalies do not give rise to significant correlations of sst in the gulf of guinea with the pacific enso as the teleconnection sequence matures strong se trades at low southern latitudes follow the de velopment of the north atlantic sst anomaly and precede by several months the appearance of weak negative sst anomalies off angola and stronger positive anomalies extending eastward from southern brazil along 15o 30os

determining azimuthal variations in frontal froude number from sar imagery 1 river plume fronts are the locus of strong mixing between plume and ambient coastal waters contribute to coastal productivity and exert a major impact on coastal ecosystems the frontal froude number fr is an important parameter characterizing the frontal status with respect to both propagation and vertical mixing in this study we examine azimuthal variations in fr using a new remote sensing method we derive fr from sar image data on the basis of the sar imaging theory and the mechanism of internal wave fission at front this method is applied to a sar image showing a front off the columbia river cr mouth taken on 31 may 2003 at 14 33 19 utc under weak wind conditions fr increases from south to north along the front this variation is consistent with potential vorticity conservation and the influence of tidal currents on the plume this calculation confirms arguments based on vessel observations by jay et al 2009

characteristics and formation mechanism of multi source mixed sedimentary rocks in a saline lake a case study of the permian lucaogou formation in the jimusaer sag northwest china abstract the permian lucaogou formation in the jimusaer sag of the southeastern junggar basin in china is an uncommon set of mixed sedimentary rocks the mixed sediment content of the lucaogou formation is unusual due to the large amounts of tuffaceous material which makes the system more complex than the commonly mixed siliciclastic carbonate rocks in this study the volcanic material acts as a third end member component in a multi source mixed sedimentary system therefore a new type of mixed siliciclastic carbonate tuffaceous rocks has been introduced methods including core observations thin section analysis grain size measurements and x ray diffraction are used to investigate the characteristics of mineral components sedimentary structures and lithological assemblages in upper and lower sections of the formation these analyses are then used to determine the lateral distribution area of mixed sedimentation sedimentary mixing processes originally described for siliciclastic carbonate systems are used and expanded here for the multi source mixed rocks in a saline lacustrine basin controlling factors on mixed sedimentation included climate change lake level fluctuation tectonic activity and sediment supply rate mentioned in previous studies as well as variations of energy levels in different parts of the lake mixed depositional models for the lower and upper sections of the lucaogou formation in saline lacustrine basin have been established respectively

effects of natural gas acidic components on local porosity generation in a carbonate reservoir insights from reactive transport modeling to investigate the mechanism of local porosity modification in a carbonate reservoir caused by the acidic components associated with natural gas generation a numerical model for the charging of natural gas rich in acidic components co2 was developed the acidic components are originated from maturation of organic matter in the source rock the model includes coupled gas water rock interactions multiphase flow and spatial heterogeneities of the geochemical reactions the simulation results indicate the following 1 when regional groundwater travels through the gas water contact gwc it is acidified by the co2 g in the gas zone and will dissolve carbonate minerals to form local secondary porosity the generated local secondary porosity is approximately 0 04 volume fraction with a maximum value of approximately 0 27 and is located mainly in the vicinity of the gwc 2 under reservoir conditions the solubility of calcite is much higher than dolomite the higher solubility and common ion effect of ca results in calcite being the primary reactive mineral in pure carbonate reservoirs having both calcite and dolomite the presence of anhydrite in the system does not change this situation 3 the groundwater flow field causes gwc evolution to be s shaped the inflection and gentle sloping parts at both ends of the gwc have different angles with the groundwater stream lines resulting in different amounts of mineral dissolution and precipitation and porosity increase 4 the limited amount of co2 from the source rock and groundwater flow in the subsurface seems to be sufficient to support local secondary porosity generation

diagenesis porosity evolution and petroleum emplacement in tight gas reservoirs taranaki basin new zealand abstract tight gas reservoirs have become popular targets in petroleum exploration in recent years due largely to the increasing market demand for gas and also to technology advances used in extraction reservoir quality is typically poor due to deep burial diagenesis resulting in significant compaction cementation and illitization however analysis of tight reservoirs using integrated techniques can improve our understanding about the controls on reservoir quality and these results can potentially be used to help predict reservoir quality at other sites the use of integrated analysis of diagenetic and burial history is here shown for the eocene k3e kapuni group reservoir in cardiff 1 taranaki basin new zealand the k3e belongs to a deep gas play that was considered uncommercial in the early 1990 s due to poor reservoir quality associated with extensive authigenic illite potassium argon dating has shown that destruction of the reservoir through illitization occurred in the pliocene associated with a late stage heating and or fluid flow event timing of illite authigenesis in the k3e reservoir postdates the likely circulation of co2 rich fluids that caused reaction of feldspar to form kaolinite and quartz homogenization temperatures from two phase aqueous fluid inclusions within quartz cements together with 1d basin models of co2 expulsion from coaly source rocks indicate that feldspar reactions may have started in the mid miocene the co2 rich fluids are thought to have been generated by thermal decarboxylation of intraformational paleocene eocene coals at the same time oil was being expelled from older cretaceous coals and migrated into the mid late eocene reservoirs evidence for oil migration is demonstrated by the presence of residual oil and by the local occurrence of abundant oil bearing fluid inclusions the products of feldspar dissolution appear to be in reasonable balance with the amount of dissolved feldspar suggesting a relatively closed diagenetic system with little improvement in reservoir quality despite the large volume of feldspar dissolved petrographic evidence of reservoir sandstones at cardiff 1 demonstrates the presence of some illite free secondary macropores lined by residual oil this local preservation of porosity may be replicating the original distribution of oil saturated pores in the pliocene at the time when authigenic kaolinite underwent reaction to form illite remobilization of the oil probably occurred by gas flushing after the main phase of illitization at c 5 ma the data presented in this study are consistent with redistributed liquid petroleum into up dip traps and represent the potential for a new exploration play the eocene reservoir at cardiff 1 is currently gas charged with the pore system composed of approximately one third large macropores connected by a tortuous microporous network however it is possible that with the currently buoyant gas market and modern hydraulic fracturing techniques it may now be economic to flow gas from the locally large pores identified in the k3e reservoir

potential relation between equatorial sea surface temperatures and historic water level variability for lake turkana kenya summary water level in lake turkana kenya in the past ca 150 years is controlled primarily from the biannual passage of the east and west african monsoon with rainfall volume related partially to sea surface temperatures ssts in the western indian and east atlantic oceans empirical orthogonal function analyses show significant correlation between eastern atlantic or western indian ssts and lake level anomalies with the first mode accounting for 66 and 55 of the variability the primary geographic loadings are consistent with a gulf of guinea moisture source and positive indian ocean dipole iod state the second mode explains 10 of variability and reflects the westward extension of an indian ocean cool pool potentially indicative of a normal to a negative iod state there is significant spatial correlation between basin rainfall anomalies associated with eastern atlantic ssts and a low in the continental divide between the kenyan and the ethiopian highlands which is a passage for moisture from the congo basin linear regression analysis with bootstrap sampling and monte carlo simulations define numeric relations between western indian and eastern atlantic ssts and lake level change for ad 1992 2013 the monthly and yearly lake level reconstructions based on this numeric analysis capture the decadal scale variability and the 15 m drop in water level in the early 20th century meter scale variability in lake level since ca ad 1930 is associated with precipitation sourced from the western indian ocean with iod variability whereas the 15 m drop in water level in the early 20th century may reflect a profound decrease in moisture from atlantic congo basin source these numerical solutions are poised to reconstruct water level variations in the past ca 300 years for lake turkana with new proxy records of ssts from the western indian ocean and the gulf of guinea

improved understanding of petroleum migration history in the hongche fault zone northwestern junggar basin northwest china constrained by vein calcite fluid inclusions and trace elements calcite veins and cements occur widely in carboniferous and permian reservoirs of the hongche fault zone northwestern junggar basin in northwest china the calcites were investigated by fluid inclusion and trace element analyses providing an improved understanding of the petroleum migration history it is indicated that the hongche fault behaved as a migration pathway before the early cretaceous allowing two oil charges to migrate into the hanging wall fault core and footwall reservoirs across the fault since the late cretaceous the hongche fault has been sealed as a consequence meteoric water flowed down only into the hanging wall and fault core reservoirs the meteoric water incursion is likely an important cause for degradation of reservoir oils in contrast the footwall reservoirs received gas charge the third hydrocarbon event following the late cretaceous this helps explain the distribution of petroleum across the fault this study provides an example of how a fault may evolve as pathway and seal over time and how reservoir diagenetic minerals can provide clues to complex petroleum migration histories

seawater normalized ree patterns of dolomites in geshan and panlongdong sections china implications for tracing dolomitization and diagenetic fluids abstract in conventional studies of tracing dolomitization and diagenetic fluids rees of dolomites were widely used as been normalized by paas nasc or chondrite however most dolomites are formed in seawater or seawater derived fluids thus we conduct a new attempt to normalize the rees of dolomite using seawater standard based on case studies on 36 triassic limestone dolomite samples from the geshan section of southeast china and 26 permian triassic dolomite samples from the panlongdong section of northeastern sichuan basin southwest china the geshan seawater normalized sn ree patterns are characterized by notable positive ce sn average ce sn ce 6 823 sd 0 192 and negative pr sn anomalies average pr sn pr 0 310 sd 0 010 and slightly negative gd sn anomalis average gd sn gd 0 864 sd 0 053 with no obvious eu sn anomaly average eu sn eu 1 036 sd 0 094 the signatures of ree patterns barely changed during the dolomitization process for the ree compositions of the panlongdong dolomite it can be found that 1 the recrystallization process can result in varied total ree concentrations between 7 16 ppm and 37 87 ppm but do not alter the ree patterns including consistent positive ce sn anomalies average 4 074 sd 0 27 and lree enrichment average nd sn yb sn 3 164 sd 0 787 2 meteoric incursion can reverse ce anomaly from the strong positive ce anomalies ce sn ce 5 059 to slightly positive ce sn ce 2 459 or even negative ce anomalies and 3 hydrothermal fluid altered ree pattern is complicated by fluctuated distribution curve negative ce anomaly and positive eu anomaly eu sn eu 1 862 these results suggest that the seawater normalized ree patterns of dolomite can serve as an index to study the source of the dolomitization fluids and distinguish complex diagenetic processes providing a complement to previous works

mesogenetic dissolution its role in porosity development in carbonate reservoirs models of porosity formation in carbonate rocks have stressed subaerial exposure and attendant shallow meteoric diagenesis porosity formation also occurs in deep burial or mesogenetic settings as a result of dissolution enlargement of preexisting pores porosity enhancement and creation of new pore systems brines charged with organic acids carbon dioxide and or hydrogen sulfide derived from organic matter diagenesis and thermochemical sulfate reduction are the likely fluids causing significant mesogenetic dissolution enhanced and newly created mesogenetic pore types can mimic pore types formed in shallow meteoric environments and therefore the mesogenetic origin of some porosity may go unrecognized

compaction microstructures in quartz grains and quartz cement in deeply buried reservoir sandstones using combined petrography and ebsd analysis abstract sandstone diagenesis involves porosity loss by mechanical and chemical compaction in this study we have examined relations of diagenesis and microstructures in quartz grains and quartz cement in sandstones from relatively deep burial depths offshore mid norway electron backscatter diffraction analysis ebsd has been combined with optical and cathodoluminescence petrography study of samples with different degrees of compaction and quartz cementation quartz cement is shown to be syntaxial to the nearest host domain grain or subgrain both for monogranular polygranular undeformed and deformed quartz the quartz cement growth may have been initiated at different subgrain surfaces and preserving pre depositional deformation structures ebsd inverse pole figure imaging shows dauphine twins to be common in all samples both in quartz grains and quartz cement the dauphine twins appear in grain grain contacts and in cement crystal boundaries and commonly crossing grain cement boundaries on basis of twin distributions we suggest that both inherited twins from the source area and twins formed by compaction induced grain boundary deformation are present a general problem in sedimentary rocks is to distinguish inherited from sedimentary compaction induced intra grain deformation structures this study shows that the role of ductile deformation mechanisms e g twinning in sediment compaction can be clarified by more comprehensive following up studies using ebsd analysis in combination with other techniques

instability and mixing in a small estuarine plume front detailed field observations at the front of a small tidally modulated radial river plume have been carried out to study the localized internal instabilities thought responsible for mixing a novel ship borne instrument array was used to resolve internal features inside the spreading plume down to horizontal length scales of less than 0 25 m within the top 4 m of the water column results from this study that applied stringent correctional and filtering procedures to the field data identify the presence of multiple internal hydraulic jumps on the plume interface some 30 40 m behind the main plume frontal discontinuity this region of instability fri 1 corresponds to the rear of a gravity head current bulk mixing characteristics in the frontal region of the plume were quantified through methods originally applied to laboratory models of gravity current mixing and also used to represent the extent of turbulent mass and momentum exchange in frontal boundary conditions of numerical models results from field experiments suggested that mixing in the plume front was modulated by the tidal outflow from the estuary and across frontal velocity the ebb tidal mean magnitude of the bulk frontal mixing coefficient was more than double 0 37 that computed from previous analogous laboratory experiments but of the same order of magnitude as recent small scale river plume frontal studies