hydrographic conditions in the eastern pacific before during and after the 1982 83 el nino abstract between june 1981 and june 1984 a total of thirteen ctd sections were made across the equator along 85 w on some of these cruises additional sections were made along 5 s and 10 30 s between 85 w and the south american coast this sampling period covers the events that took place during the 1982 83 el nino these sections are used to describe the variability that took place before during and after this major event at the surface little evidence was found for a major southward flooding of warm low salinity water from north of the equator that has been observed during some previous el ninos major changes took place in the sub surface hydrographic structures the thermostad between 13 c and 16 c which is a prominent feature of the hydrography in this region disappeared early in 1983 and reappeared early in 1984 the vertical temperature gradient along the equator and along the coast which is usually quite variable with depth became much more uniform in early 1983 it regained its normal structure by early 1984 changes were not confined to the upper ocean but were evident over the whole depth interval sampled 1000m during november 1982 evidence was found for symmetric poleward spreading of the equatorial disturbance along the eastern boundary many of the changes that took place are consistent with linear models based on equatorial wave theory these observations presented a unique opportunity for observing the ocean response to a major interannual change in the wind forcing

the effects of thermochemical sulfate reduction upon formation water salinity and oxygen isotopes in carbonate gas reservoirs abstract thermochemical sulfate reduction tsr is a well known process that can lead to sour h2s rich petroleum accumulations most studies of tsr have concentrated upon gas chemistry in this study we have investigated palaeoformation water characteristics in a deep anhydrite bearing dolomite sour gas reservoir of permian age in abu dhabi using fluid inclusion stable isotope petrographic and gas chemical data the data show that low salinity isotopically distinct water was generated within the reservoir by reaction between anhydrite and methane the amount of water added to the reservoir from tsr indicated by reduced fluid inclusion salinity and water 18o values varied systematically with the extent of anhydrite reaction with methane water salinity and isotope data show that the original formation water was diluted by between four and five times by water from tsr thus we have shown that large volumes of very low salinity water were generated within the gas reservoirs during diagenesis following gas emplacement the salinity of formation water in evaporite lithologies is therefore not necessarily high modelling based upon a typical khuff gas reservoir rock volume suggests that initial formation water volumes can only be increased by about three times as a result of tsr the extreme local dilution shown by the water salinity and 18o data must therefore reflect transiently imperfect mixing between tsr water and original formation water the creation of large volumes of water has important implications for the mechanism and rate of thermochemical sulphate reduction and the interpretation of gas volumes using petrophysical logging tools

geochemical variations among eastern saudi arabian paleozoic condensates related to different source kitchen areas abstract large reserves of gas and condensate are found in paleozoic reservoirs khuff unayzah and jauf in the ghawar area of eastern saudi arabia the source rock for these hydrocarbons is the basal organic rich hot shale of the qusaiba member of the silurian qalibah formation this is the same prolific source rock that generated the sweet light crude oil and condensate found in the unayzah reservoirs in central saudi arabia thermal maturity modeling of the source rock identifies two kitchen areas to the east and west of the ghawar structure the west kitchen was well into the oil window by 210 ma while the east kitchen was just entering the oil window large areas of both kitchens were in the wet gas window by 125 ma and by 90 ma most of the area north of ghawar was generating dry gas in eastern saudi arabia paleozoic oil and condensate are found in early formed structures carboniferous and early triassic growth whereas late cretaceous and tertiary structures contain only dry gas the geochemistry of the oils and condensates indicates two groups each generated from a different hydrocarbon kitchen suggesting that the two kitchens differ slightly in organic facies within each group variations among hydrocarbons are related to the thermal maturity of the source rock during generation within the khuff reservoir gas souring is caused by thermochemical sulfate reduction

circulation and low frequency variability near the chilean coast remotely forced fluctuations during the 1991 92 el nino results are reported from the first long recording current meter observations over the slope off chile these observations at 308s during the 1991 92 el nino event are analyzed together with observations of currents at a local deep sea site local wind and sea level sea level from the peru and chile coasts and wind temperature and currents from the equatorial pacific mean poleward flow of 12 cm s21 was observed within the peru chile undercurrent over the slope mean flow in the depth range of antarctic intermediate water was not distinguishable from zero in the presence of strong low frequency lf variability which dominated slope currents at all depths the strongest lf fluctuations had periods of about 50 days but periods of 10 and about 5 days were also observed significant local wind forcing of slope currents was only found in the period band 6 10 days and may be related to coastal trapped waves in the atmosphere our analysis shows that free coastal trapped waves in the ocean arriving from the north dominated the lf variability over the shelf and slope off northern and central chile during the 1991 92 el nino event strong 50 day period fluctuations there started their journey about two months earlier and 15 000 km farther up the coastal equatorial waveguide near the date line in the equatorial pacific as equatorial kelvin waves forced by westerly wind events of similar period upon reaching the south american coast these waves forced coastal trapped waves which propagated along the peru coast into the study region likewise a scenario of equatorial trapped waves forcing coastal trapped waves may explain 10 day as well as 6 day and 4 5 day period coastal trapped waves off chile stemming from mixed rossby gravity and inertia gravity waves trapped at the equator since the large 50 day period coastal trapped waves may strongly modify coastal upwelling source water such remotely forced waves may have a significant influence on the pelagic ecosystem off chile at least during el nino events

the nature of mineralizing fluids of the kipushi zn cu deposit katanga democratic repubic of congo quantitative fluid inclusion analysis using laser ablation icp ms and bulk crush leach methods fluid inclusions from the epigenetic zn cu deposit of kipushi central african copper belt katanga democratic republic of congo have been subjected to an integrated microthermometric bulk crush leach and laser ablation inductively coupled plasma mass spectrometric la icp ms study to elucidate the physicochemical conditions of ore formation and the origin of the mineralizing fluids the kipushi deposit is hosted in carbonates and partly in siliciclastic rocks that have undergone regional low grade greenschist facies metamorphism and which were strongly deformed during the lufilian orogeny main deformation phase 550 ma investigation of host rock gangue and ore samples enabled reconstruction of the paragenesis of ore deposition the main zn cu ge pb sulfide mineralization was accompanied by three generations of hydrothermal dolomite and a generation of coarse grained quartz primary and pseudosecondary fluid inclusions in these minerals contain predominantly halite saturated aqueous brines 30 43 wt nacl equiv with locally unidentified trapped solids these inclusions mostly decrepitate upon heating before total homogenization which could suggest that they also trapped excess carbonic vapor they show petrographic and microthermometric evidence for postentrapment reequilibration prohibiting their use as accurate geothermometers and geobarometers previous studies on chlorite and sphalerite geothermometry framed the formation temperature of the kipushi cu zn deposit between 290 to 380 c younger fluids are present as secondary inclusions in the gangue minerals and as primary fluid inclusions in sphalerite from a minor secondary mineralization phase these two phase aqueous inclusions have a slightly lower salinity 23 31 wt nacl equiv and have homogenization temperatures ranging from 170 to 80 c in successive fluid inclusion assemblages sporadically some mixed aqueous carbonic and gaseous co2 ch4 inclusions are present but their genetic position is un clear and they are insignificant with regard to the mineralization process as a whole crush leach bulk analysis of the fluid inclusions show that the mineralizing fluids had a molar cl br ratio close to or somewhat higher than the seawater value which rules out a major contribution from bittern brines and suggests that the fluids gained their salinity primarily by the dissolution of evaporites younger fluids that circulated through the deposit after the main phase of ore formation have cl br and na br signatures indicative of a greater involvement of halite dissolution brines values much higher than that of seawater la icp ms analyses of the mineralizing fluids reveal that they have molar li na ca na mg na mn na and sr na in the range of natural high salinity fluids in metamorphic environments worldwide however they have relatively high molar fe na zn na pb na and especially very high ba na ratios their molar k na is also somewhat higher than for other low grade metamorphic fluids but is nevertheless in agreement with the values predicted by the k na geothermometer at the conditions of ore formation this suggests that the major element composition of the fluids was buffered by fluid mineral equilibria their relatively high metal contents ba zn fe and pb suggest that they interacted with and leached these elements from felsic basement rocks at higher temperatures whatever the origin of the fluids their salinity and the metals their uniformly high ba and ore metal content together with the absence of barite and the occurrence of ba silicates at kipushi indicates that sulfide mineralization occurred when the metal bearing fluids encountered a reducing h2s rich reservoir the ubiquitous presence of preexisting metamorphosed carbonic material shungite in the sulfides and host rock and a sulfur isotope signature of the ores in agreement with thermogenic sulfate reduction suggests that this condition was likely created due to the high initial reduced carbon content of the host rocks at kipushi which seems to be exceptional in the copper belt therefore we postulate that a critical factor in the formation of major vein type zn cu mineralization was the presence of a hydrocarbon rich facies of the lower nguba carbonates at kipushi

multiple generations of high salinity formation water in the triassic sherwood sandstone wytch farm oilfield onshore uk abstract the origin and heterogeneity of oilfield formation water in the lower triassic sherwood sandstone at wytch farm in the wessex basin uk have been investigated using production data detailed water geochemistry and o s and h stable isotope data the formation waters are highly saline nacl type brines with tds values of up to 230 000 mg l there is a general decrease in salinity from the flanks of the field to the crest with cl decreasing from about 136 000 to 109 000 mg l the cl br ratio of the water shows that salinity was largely derived from the dissolution of upper triassic continental evaporites found off structure to the west and north of the field the water in the field had a meteoric source although variation in 2h values suggests that there may be meteoric waters of different ages in the oilfield reflecting recharge under different palaeoclimatic conditions at the crest of the field aqueous so 4 2 resulted from dissolution of anhydrite in the reservoir in contrast in other parts of the field there is an indication that some of the dissolved so 4 2 was derived from oxidation of pyrite at some point on the recharge path of meteoric water to the field there were two meteoric influx events bringing different cl concentrations and different 2h values the first was probably before the eocene oil influx and could have occurred in the lower cretaceous or early tertiary the second meteoric influx event probably occurred after or during oil migration into the wytch farm structure since the second meteoric water is found at the flanks of the field adjacent to the regions where salt is found in the stratigraphy the preservation of heterogeneities in oilfield formation water compositions suggests that there has been little aqueous fluid movement or diffusive flux for over 40 million years mass flux has been restricted by density stratification within the aquifer and the very low effective permeability for the aqueous phase in the oil filled reservoir

propagation and forcing of high frequency sea level variability along the west coast of south america tide and wind data from coastal and island stations from buenaventura colombia 4 n to callao peru 12 s have been analyzed for the 1979 1984 time period to determine the propagation and forcing characteristics of coastal sea level variability at periods of days to weeks as well as how they vary either with season or between the 1982 1983 el nino southern oscillation enso period and non enso years during four non enso years the ensemble averaged cross spectra between coastal sea level height slh and local winds show weak evidence of local forcing during the whole year without significant differences between the austral summer and winter seasons other than a greater energy in the wind fluctuations at talara during summer cross spectra between slh series from neighboring stations show evidence of poleward phase propagation during winter seasons at speeds of about 2 0 m s 1 between la libertad and talara at periods of a week or more and about 2 7 m s 1 between talara and callao at periods of 5 11 days but no propagation is found during summers during the 1982 1983 enso there is a large increase in slh energy at most frequencies at all coastal stations but especially in the 8 to 11 day band where energies are enhanced by as much as an order of magnitude above non enso levels the cross spectra between adjacent slh stations indicate a nondispersive poleward propagation of events during the 1982 1983 enso with phase speeds of 2 2 3 5 m s 1 from la libertad to talara periods of a week or more and 3 4 3 6 m s 1 from talara to callao 3 5 days or more as with the slh energy the coherence and phase propagation were much stronger along the peru coast in 1982 1983 than during non enso periods especially in the 8 to 11 day band the one third increase in phase speeds during the enso over the non enso speeds is found to be consistent with the anomalous depression of the density structure during el nino comparisons between coastal slh and the local alongshore wind suggest that locally forced slh variability was obscured during the 1982 1983 enso by the noncoastally forced but energetic propagating fluctuations which probably originated in the equatorial waveguide

geochemical and carbon isotopic studies of crude oil destruction bitumen precipitation and sulfate reduction in the deep smackover formation abstract crude oil generated by the lower smackover source facies migrated to upper smackover reservoirs where slow thermal cracking of crude oil resulted in the formation of gas condensate and late solid bitumen ultimately only pyrobitumen methane and nonhydrocarbon gases including hydrogen sulfide persist in the deepest smackover reservoirs the carbon isotopic compositions of crude oils became heavier during crude oil destruction the carbon isotopic compositions of asphaltenes nso compounds and saturated hydrocarbons in late solid bitumen and the lower smackover source facies became isotopically lighter during crude oil destruction it is suggested that some isotopically light components from crude oils were incorporated in late solid bitumen by reactions involving thermochemical sulfate reduction thermochemical sulfate reduction and crude oil destruction occurred over a long span of geologic time at temperatures in the 120 150 c range

chemical and isotopic evidence for secondary alteration of natural gases in the hetianhe field bachu uplift of the tarim basin h2s and co2 are found in elevated concentrations in the reservoirs near the carboniferous ordovician unconformity in the hetianhe field of the tarim basin nw china chemical and isotopic analyses have been performed on produced gases formation waters and reservoir rocks to determine the origin of co2 and h2s and to explain the heterogeneous distribution of isotopic and geochemical characteristics of petroleum fluids it is unlikely that h2s and co2 had a mantle component since associated helium has an isotope ratio totally uncharacteristic of this source instead h2s and co2 are probably the result of sulphate reduction of the light hydrocarbon gases lhg increasing h2s concentrations and co2 co2 c1 4 values to the west of the hetianhe field occur commensurately with increasingly heavy hydrocarbon gas 13c values however thermochemical sulphate reduction is unlikely because the temperatures of the reservoirs are too low no h2s or rare pyrite was detected in deeper reservoirs where more tsr should have occurred and inferred 34s values of h2s from late stage pyrite in the carboniferous and ordovician reservoirs are as low as 24 9 such low 34s values discount the decomposition of organic matter as a major source of h2s and co2 bacterial sulphate reduction of the light hydrocarbon gases in the reservoir possibly coupled indirectly with the consumption of organic acids and anions is most likely the result is the preferential oxidation of 12c rich alkanes due to the kinetic isotope effect and decreasing concentration of organic acids and anions modern formation water stable isotope data reveal that it is possible that sulphate reducing bacteria were introduced into the reservoir by an influx of meteoric water from the west by way of an inversion related unconformity this may account for the apparently stronger influence of bacterial sulphate reduction to the west of the hetianhe field and the consequent greatest decrease of the 13c co2 values and the greatest increase in 13c values of the alkane gases

spectral characteristics of sea level variability along the west coast of north america during the 1982 83 and 1997 98 el nino events abstract we use hourly sea level records from southern california to the aleutian islands to examine low frequency variability in the northeast pacific during the 1982 83 and 1997 98 el nino events comparison between events is facilitated by long term records for yakutat tofino neah bay and san francisco which appear to be representative of distinct coastal oceanic regimes residual tide removed time series reveal that the anomalously high sea levels of the 1997 98 el nino persisted from the spring of 1997 to the spring of 1998 and this event was more protracted than the 1982 83 el nino during both major events the annual sa semiannual ssa and synoptic scale sea level constituents were amplified relative to non el nino years with synoptic fluctuations in sea level height and sea level pressure for mid latitude sites tofino and neah bay strongly correlated through the inverted barometer response the spectral anomaly coefficient sjr rj 1 rj 1 where r j s j s j is the spectral ratio between the el nino spectrum sj and the time averaged non el nino spectrum s j for tide gauge site j indicates that both events gave rise to enhanced sea level variability at periods of days to weeks because of passing atmospheric systems however the 1982 83 el nino generated greater signal variance at seasonal scales periods of months while the 1997 98 el nino generated greater variance at synoptic scales periods of days findings further indicate that poleward oceanic propagation of the 1982 83 and 1997 98 events terminated near central california and that much of the enhanced sea level variability observed at mid to high latitudes was associated with atmospheric teleconnection responses that gave rise to amplified variations in coastal sea level pressure and or surface wind stress

a lumped parameter model of groundwater influx to a mine adit in mountainous terrain 1 acidic and metal laden drainage from the portals of abandoned mines is a serious environmental problem in wet mountainous regions where steep hydraulic gradients ensure that fresh recharge waters are continuously flushed through the workings hydrogeological characterization of these sites is hampered by their geological complexity and their frequent inaccessibility this paper presents a material balance model for the groundwater capture zone associated with influx to a mountainside adit the model can be used to estimate bulk hydraulic properties of the rock surrounding an adit from hydrograph data commonly recorded at its portal this application is illustrated using data from the myra falls mining camp vancouver island british columbia by simultaneously fitting base flow recession slopes for hydrographs of discharge water table elevation and head in an underground borehole the model yields plausible and well constrained estimates of hydraulic conductivity porosity skin factor and hydraulic gradient

multidisciplinary thermal maturity studies using vitrinite reflectance and fluid inclusion microthermometry a new calibration of old techniques a critical component of petroleum exploration risk assessment involves quantifying the risks associated with the presence of a viable hydrocarbon system this requires an accurate estimate of thermal maturity and thermal history however in some sedimentary basins traditional organic based maturity tools such as vitrinite reflectance cannot be used because of various geologic and sampling limitations this article establishes fluid inclusion microthermometry as a new inorganic thermal maturity tool that can be used to help fill the void in these situations this tool uses an empirical calibration of fluid inclusion data and vitrinite reflectance data to estimate thermal maturity our empirical approach uses rigorous sample selection criteria that improve the statistical chance of analyzing aqueous fluid inclusions that have been thermally reequilibrated stretched this empirical calibration is based on a worldwide set of data that yield a logarithmic correlation having r2 0 96 for an ideal sample set and r2 0 81 for a nonideal sample set the amount of data scatter absolute deviation of measured vitrinite reflectance in ro from the logarithmic correlation line is minimal 0 12 ro for the ideal data set this new calibration along with the sample selection and data analysis procedures described in this study forms the basis for a new thermal maturity technique

the complexity secondary geochemical process genetic mechanism and distribution prediction of deep marine oil and gas in the tarim basin china abstract most paleozoic marine craton basins in china are rich in natural gas except the tarim basin where both oil and gas are prolific various hydrocarbon types have been found in this basin including deep ultra heavy oil heavy oil normal oil volatile oil condensate and natural gas petroleums with diverse types even coexist within a single reservoir generally the ordovician and cambrian reservoirs are deeply buried 5500 8000 m and intensively altered after initial oil and gas accumulations bringing challenges to physical property prediction before drilling and evaluation of exploration targets based on recent exploration discoveries and experimental data we systematically analyzed the origin of oil and gas demonstrated the mechanisms and processes of secondary geochemical alteration e g biodegradation gas washing fractionation tsr and high temperature cracking moreover the preservation mechanism of ultra deep normal oil was also clarified and the distribution patterns of oil and gas were predicted tarim basin has been uplifted and shallowly buried in the early accumulation stage then rapidly and deeply buried in the late stage resulting in various geochemical alteration processes at different burial stages through the reconstruction of complex deep strata oil and gas accumulation histories the spatial distribution of deep petroleum types were predicted this review has provided detailed assessment with case studies in the tarim basin and shed light on the preservation mechanisms and the alteration processes of deep liquid petroleums in addition to massive gas accumulations liquid oils still have great exploration potential in strata deeper than 8000 m in the tarim basin

further evidence for coastal trapped waves along the peru coast abstract time series of coastal sea level during 1976 77 from 2 12 s to 17 s along the west coast of south america show that low frequency 0 25 cycles per day cpd fluctuations propagate poleward with the phase speed of baroclinic kelvin waves 2 3 m s 1 the alongshore coherence is highest in the frequency band 0 1 0 2 cpd computing the frequency domain empirical orthogonal functions eof for alongshore current from an army of current meters extending from 5 s to 15 s during march may 1977 gives 70 of the variance in the 0 1 0 2 cpd frequency band to an eof mode with poleward phase propagation at 2 75 m s 1 the vertical structure of the alongshore current fluctuations 0 1 0 2 cpd over the continental slope at 5 s and 15 s is consistent with a first mode baroclinic kelvin wave the current and sea level fluctuations are coherent and propagate poleward through latitudes where their frequency equals the local inertial frequency the fluctuations are not significantly coherent with coastal

intraseasonal oscillations in sea level along the west coast of the americas abstract hourly observations of coastal sea level at stations from peru to british columbia are analyzed for low frequency content a space time contour plot of sea level from four years of data during the 1971 75 period shows the meridional structure of the seasonal cycle and interannual variability associated with the 1972 73 el nino oscillations with intraseasonal periods of 36 73 days are also evident coherent over alongshore distances of several thousand kilometers further investigation using spectral methods and empirical orthogonal function analysis in the frequency domain reveals in particular that intraseasonal sea level variability has a peak in spectral density along the coasts of south america central america and mexico with high coherence from near the equator tumaco 2 n north to central california 34 n and south to at least callao 12 s phase propagation north of the equator is poleward at 150 200 kilometers day atmospheric pressure alongshore wind stress and wind stress cu

unconfined groundwater flow calculation into a tunnel abstract unconfined flow of groundwater into a tunnel is analyzed by a numerical model the model is based on the finite element method for the solution of nonsteady groundwater flow with a free surface the numerical results are compared with those obtained from analytical approximations to be in the same order of magnitude these results are used to estimate the rate of water inflows during tunnel construction

modes of covariability between sea surface temperature and wind stress intraseasonal anomalies along the coast of peru from satellite observations 2000 2008 1 the tropical rainfall measuring mission microwave imager sea surface temperature sst and quikscat wind stress satellite data are used to investigate the intraseasonal upwelling variability along the coat of peru over the period 2000 2008 two regions of peak variance correspond to the central peru region pisco region 15 s and the northern peru region piura region 5 s a covariance analysis reveals a significant coherency between winds and sst anomalies off pisco consistent with ekman pumping and transport dynamics the upwelling cell consists in a meridionally extended fringe of colder warmer water extending as far as 250 km from the coast at 15 s in the piura region the intraseasonal covariability pattern is represented by two modes one relevant to the direct ekman dynamics and the other one associated with the remote forcing of intraseasonal oceanic kelvin wave two regimes of variability are evidenced a low period regime 10 25 days is the signature of ekman transport pumping dynamics and is remotely forced by the migratory atmospheric disturbances across the southeastern pacific anticyclone a high period regime 35 60 day band is associated with the combined forcing of oceanic equatorial kelvin waves and migratory atmospheric disturbances in the midlatitudes in particular the modes of covariability exhibit a prominent 50 day period energy peak it is shown that this period arises from the impact of the first two baroclinic modes kelvin wave with the second baroclinic mode kelvin wave being more influential on the piura region

reequilibration of fluid inclusions in low temperature calcium carbonate cement calcium carbonate cements precipitated in low temperature near surface vadose environments contain fluid inclusions of variable vapor to liquid ratios that yield variable homogenization temperatures cements precipitated in low temperature phreatic environments contain one phase all liquid fluid inclusions neomorphism of unstable calcium carbonate phases may cause reequilibration of fluid inclusions stable calcium carbonate cements of low temperature origin which have been deeply buried contain fluid inclusions of variable homogenization temperature and variable salt composition most inclusion fluids are not representative of the fluids present during cement growth and are more indicative of burial pore fluids therefore low temperature fluid inclusions probably reequilibrate with burial fluids during progressive burial reequilibration is likely caused by high internal pressures in inclusions which result in hydrofracturing the resulting fluid inclusions population could contain a nearly complete record of burial fluids in which a particular rock has been bathed

formation of diagenetic dolomite in coastal sabkha along arabian persian gulf aragonitic intertidal sediments are being dolomitized in the subsurface supratidal environment of a sabkha along the south shore of the arabian persian gulf as a result of the percolation of wind driven marine derived brines the development of abundant diagenetic dolomite results from an optimum combination of high mmg mca ratio fluids a rapid flow rate which is related to the flooding frequency and sediment permeability and a shoreline configuration that maintains the proper conditions for a sufficient length of time strongly dolomitized areas are localized along the flanks of remnant channels and in the lee of islands that have been engulfed by the prograding sabkha the dolomitizing process takes about 1 000 to 1 500 years most diagenetic dolomite forms at the expense of primary aragonite according to the reaction mg 2caco3 arag rarr camg co3 2 ca dolomite forms under the following conditions a chloride concentration between 3 25 and 3 75 mcl kg b mmg mca greater than about 6 c ph between 6 3 and 6 9 d minimum pco2 of 10 2 to 10 3 atm e temperature between 25 and 40 c f saturation with respect to gypsum and g reducing environment in association with hydrogen sulfide other recent dolomite occurrences in the bahamas florida and bonaire are significantly different in terms of stratigraphy degree of lithification and evaporite mineral association from those in the arabian gulf

local and remote forcing of sea surface temperature in the coastal upwelling system off chile an analysis is presented of records of sea surface temperature sst sea level and winds collected during the period 1991 1995 along the coast of northern and central chile sea level also from the peru coast in 1991 1994 and of sst from remote sensing during the austral summers of 1991 and 1992 off northern chile large interannual fluctuations of sst and sea level off northern chile are linked to vertical displacements of the equatorial thermocline during el nino la nina events in the intraseasonal 50 day band sst and sea level are intimately related all along the coast whereby sst anomalies lag sea level perturbations by about 12 days such sea level fluctuations are due to free coastal trapped waves ultimately forced via equatorial kelvin waves by 50 day wind events in the western and central tropical pacific these results and those of the remote sensing analysis suggest significant remote forcing of sst fluctuations in the coastal zone off chile by the action of the coastal trapped waves off central chile sst is also related to local wind stress in the intraseasonal band simulations with a simple local wind driven upwelling entrainment model capture rather well observed synoptic and intraseasonal oscillations of sst there off northern chile however this simple model is not successful in simulating observed sst an attempt to include effects of coastal trapped waves into this simple one dimensional model did not improve model fit to data at either location an explanation for the apparent strong influence of these waves on sst along this coast should therefore be sought in other effects not considered by this model such as cross shelf and alongshore advection

thermochemical sulphate reduction can improve carbonate petroleum reservoir quality abstract interest in the creation of secondary pore spaces in petroleum reservoirs has increased because of a need to understand deeper and more complex reservoirs the creation of new secondary porosity that enhances overall reservoir quality in deeply buried carbonate reservoirs is controversial and some recent studies have concluded it is not an important phenomenon here we present petrography geochemistry fluid inclusion data and fluid rock interaction reaction modeling results from triassic feixianguan formation sichuan basin china core samples and explore the relative importance of secondary porosity due to thermochemical sulphate reduction tsr during deep burial diagenesis we find that new secondary pores result from the dissolution of anhydrite and possibly from dissolution of the matrix dolomite assuming porosity before tsr was 16 and the percentage of anhydrite was 6 modelling shows that due to tsr 1 6 additional porosity was created that led to permeability increasing from 110 md range 72 168 md within a 95 confidence interval to 264 md range 162 432 md within a 95 confidence interval secondary porosity results from the density differences between reactant anhydrite and product calcite the addition of new water during tsr and the generation of acidity during the reaction of new h2s with the siderite component in pre existing dolomite in the reservoir fluid pressure was high during tsr and approached lithostatic pressure in some samples this transient overpressure may have led to the maintenance of porosity due to the inhibition of compactional processes an additional 1 6 porosity is significant for reserve calculations especially considering that it occurs in conjunction with elevated permeability that results in faster flow rates to the production wells

kinetic modelling thermal maturation and hydrocarbon generation in the united arab emirates abstract kinetic basin modelling by computer is applied to subsurface data from the united arab emirates during evaluation of the thermal maturation the geothermal gradient used here was assumed to be invariant during the subsidence history of the basin the diversity of composition of organic material kerogen type was considered in the computer modelling by using various values of the kinetic e and a parameters activation energy and frequency factor respectively in arrhenius s equation the kinetic method used in this study calculates the multiple parallel reactions that occur as organic matter undergoes degradation to hydrocarbons the thermal maturation history of the source rocks in abu dhabi have been evaluated using time temperature indices tti based on arrhenius s equation in conjunction with kinetic modelling techniques the thermal modelling of well data shows that the major source rocks shilaif formation middle cretaceous thamama group bab member lower cretaceous and diyab dukhan formation upper jurassic have attained thermal maturity to post maturity with respect to the generation of liquid hydrocarbons over much of the united arab emirates the shilaif formation lies within the oil window in the bab field and is immature in the shah field the thamama group is within the oil window over most of the area and the diyab dukhan formation is past the liquid hydrocarbon generation stage over most of the abu dhabi area hydrocarbon generation from the diyab dukhan source rock began in campanian time 85 80 ma the thamama group reached the oil generation threshold in the early middle eocene 55 44 ma the shilaif formation began oil generation in the late miocene 10 ma geochemical correlation between the source rocks and the crude oils indicates that thermal alteration of the organic matter in the diyab dukhan shilaif formations and possibly the thamama group has led to the generation of the hydrocarbons that charged most of the oil fields in the united arab emirates

the equatorial source of propagating variability along the peru coast during the 1982 1983 el nino using data obtained from tide gages in south america current meters along the equator and the peru coast and an array of pressure gages and inverted echo sounders within and around the galapagos archipelago we have analyzed the equatorial origin of coastal trapped waves observed by cornejo rodriquez and enfield this issue along the peru coast during the intense 1982 1983 el nino the propagating fluctuations along the coast were much stronger at that time than either before or after the el nino and the variability was not locally forced by coastal winds we find that the coastal variability was also more energetic during previous el nino occurrences at periods of 1 2 weeks the meridional component of currents on the equator is up to an order of magnitude more energetic than the zonal fluctuations and is consistently associated with sea level that fluctuates antisymmetrically between hemispheres at periods longer than 2 weeks the zonal velocity component is more energetic and the cross equatorial sea level variability is symmetric the meridional and zonal phase structures of cross spectra involving the currents and sea level establish the 1 to 2 week equatorial fluctuations as mixed rossby gravity yanai waves of low wave number with infinite phase speed standing oscillations in the middle of the band 10 days the corresponding structures for longer periods are consistent with nondispersive kelvin waves frequency domain eof modes of the sea level and current data establish the mixed rossby gravity waves as the principal source of the strong trapped wave variability in the 1 to 2 week band along the ecuador peru coast during the 1982 1983 el nino episode

contrasting diagenetic evolution patterns of platform margin limestones and dolostones in the lower triassic feixianguan formation sichuan basin china abstract deeply buried carbonate reservoirs from the lower triassic feixianguan formation in the sichuan basin of china host extensive natural gas resources these reservoirs are predominantly found in oolitic shoals with the reservoir quality of dolomitized zones being higher than that of undolomitized limestone counterparts here we present a combination of petrographic isotopic fluid inclusion and quantitative porosity data in order to understand and predict the diagenetic processes that have impacted the reservoir quality of dolostones and limestones the porosity of limestones has been reduced to 7 5 due to calcite cementation whereas the porosity in oolitic dolostones is not cemented with calcite and typically has 23 5 porosity dolomitization and concurrent early diagenetic gypsum growth played crucial roles on the development and preservation of high porosity in the oolitic dolostone first by stabilizing the rock fabric to inhibit loss of porosity during burial and secondly through the generation of new porosity by dissolution of carbonate and anhydrite a negative shift of 18 o and salinity values 13 c values 20 vpdb and 18 o 10 vpdb together with elevated calcite precipitation temperatures 110 c it is likely that tsr was responsible for the formation of enlarged dissolution vugs that increased porosity by 2 in dolostones due to i anhydrite dissolution ii production of significant amounts of water resulting in formation water undersaturated with respect to calcite and dolomite iii generation of h 2 s and co 2 and the consequent reaction of h 2 s with the siderite feco 3 component in calcite and dolomite this study demonstrates the importance of diagenesis in the formation of deeply buried high quality reservoirs in ooid dominated grainstones influenced by the presence of evaporites our results should be useful for guiding future exploration and reservoir developments in similar paleogeographic and diagenetic settings

hydrogeological impact assessment by tunnelling at sites of high sensitivity abstract a tunnel for the high speed train hst was constructed in barcelona with an earth pressure balance epb tunnel boring machine tbm the tunnel crosses barcelona and passes under some famous landmarks such as the sagrada familia and the casa mila both monuments are unesco world heritage sites and a committee appointed by the unesco acted as external observers during the construction concerns about soil settlements and the hydrogeological impacts of the construction were raised these concerns were addressed during the design stage to forestall any unexpected events the methodology consisted of 1 characterising the geology in detail 2 predicting the impacts caused in the aquifer 3 predicting the soil displacements due to water table oscillations produced by the construction and 4 monitoring the evolution of groundwater and soil settlements the main estimated impact on groundwater was a moderate barrier effect the barrier effect the magnitude of which matched the predictions was detected during construction the monitoring of soil settlements revealed short and long term movements the latter movements matched the analytical predictions of soil displacements caused by the groundwater oscillations this paper proposes a realistic procedure to estimate impacts on groundwater during tunnel construction with an epb our methodology will considerably improve the construction of tunnels in urban areas

experimental stretching of fluid inclusions in calcite implications for diagenetic studies homogenization temperatures of fluid inclusions trapped in calcite crystals may change with increased heating beyond the homogenization temperature fluid inclusions trapped in calcite during basin subsidence will tend to yield homogenization temperatures approaching maximum burial temperatures diagenetic studies that depend on these data will be biased coarse crystalline calcite containing saline fluid inclusions was used to examine the influence of increased temperatures and pressures on measured homogenization temperatures stepped heating experiments were conducted at 1 atm over a temperature range of 90 to 245 c along with hydrothermal experiments at confining pressures of 173 and 691 bar and temperatures of 160 250 and 350 c in all cases significant increases in the homogenization temperatures of the inclusion population were recorded presumably stresses generated during heating of the fluid inclusions exceeded the combined strength of the calcite crystal and the external pore pressure and thus caused fluid inclusion stretching size is a secondary factor that controls fluid inclusion reequilibration

gas souring by thermochemical sulfate reduction at 140 c discussion 814 the subject of the article gas souring by thermochemical sulfate reduction at 140 c by worden et al 1995 is closely related to our recent research we examined the origin of h2s and other organic sulfur compounds osc in produced gas from gas condensate filled stari gradac field in the drava depression in croatia based on results of numerous conventional and specific analyses of reservoir rocks gas condensate and formation water and data from fluid composition monitoring over a long period of time we concluded that sulfur compounds in the stari gradac reservoir permian triassic depths greater than 3700 m were formed by thermochemical reduction mechanism of sulfate rock anhydrite in the presence of

origin and carbon isotope fractionation of co2 in marine sour gas reservoirs in the eastern sichuan basin abstract according to gas chemical and carbon isotopic compositions for 75 gas samples from the eastern sichuan basin c 1 c 3 gaseous hydrocarbons are dominant with high dryness coefficient c 1 c 1 3 0 99 1 0 despite the presence of various contents of h 2 s and co 2 a reasonably good positive correlation is exhibited when both contents are 5 the carbon dioxide in the natural gas in the eastern sichuan basin mainly originated from carbonate dissolution by acid gases and thermochemical sulfate reduction tsr the content of co 2 produced at the early stage of acid gas dissolution is commonly 13 c co2 value 2 content exceeds 5 the 13 c co2 values range from 8 to 2 and the co 2 and h 2 s contents demonstrated a positive correlation the majority of co 2 is generated via tsr as well as acid gas dissolution during the late uplift of the basin particularly the co 2 with 13 c co2 value 2 generated via the tsr after it was partially precipitated to form calcite while the co 2 with 13 c co2 value 3 is a mixture of the co 2 produced early via tsr and the co 2 produced by the subsequent carbonate rock dissolution by acid gases

chemical and carbon isotopic fractionations of gaseous hydrocarbons during abiogenic oxidation abstract the variations of chemical and carbon isotopic compositions in gaseous hydrocarbons upon abiogenic oxidation by sulfates hematite and both in laboratory studies were clearly demonstrated through a unique two step experimental approach in the first step a large number of small gold capsules containing gaseous hydrocarbons were prepared by kerogen pyrolysis experiments which were conducted under the same condition 450 c and 50 mpa for 72 h using the same kerogen the analytical results demonstrated that the chemical and carbon isotopic compositions of gases were almost identical among the capsules in the second step each of these gaseous hydrocarbon bearing capsules along with mineral oxidant hematite or magnesium sulfate heptahydrate or both and deionized water 15 of the amount of the oxidant was placed into a large gold capsule after welding sealing the small gaseous hydrocarbon bearing capsule was forced to leak while the large capsule remained undamaged by compressing the large capsule from the outside at the position where this small capsule was located then these large capsules containing gas and mineral reactants were heated isothermally at 350 c and 50 mpa for 72 144 216 and 288 h respectively the results of the oxidation experiments with increasing heating time can be outlined as follows 1 the amount of methane remained almost unchanged in the experiments using hematite and the mixed oxidants hematite mgso4 while it increased substantially in the experiment using mgso4 after 72 h indicating methane was one of the final products of c2 oxidation 2 the amounts of c2 c5 hydrocarbons decreased consistently and more rapidly in the experiment using mgso4 than that using hematite and the mixed oxidants 3 the oxidation rates of gas hydrocarbons increased with increasing carbon number of hydrocarbons 4 the oxidation rates of i butane and i pentane were substantially higher than those of the corresponding n butane and n pentane 5 the amount of h2s increased substantially in the experiment using mgso4 whereas it was below the detection level in the experiments using hematite and the mixed oxidants 6 the 13c values of c1 c5 hydrocarbons became less negative and the isotopic fractionation extent increased with increasing carbon number of hydrocarbons and oxidation extent 7 carbon isotopic fractionation factor k12 k13 decreased with increasing oxidation rate of gas hydrocarbons and 8 the rate of thermochemical sulfate reduction tsr was strongly dependent upon the presence and concentrations of h2s

the generation and propagation of sea level variability along the pacific coast of mexico abstract case history analysis cross spectra and multiple regression analysis have been used in a study of low pass filtered sea level records from the pacific mainland coast of mexico in 1971 and 1973 75 during the summer fall season may october sea level variability is characterized by strong alongshore coherence and nondispersive poleward phase propagation over a wide frequency range 0 02 0 37 cpd the strength and clarity of the propagating signals seem to be related primarily to large amplitude events of elevation 10 30 cm that are generated off the southern coast of mexico by tropical storms these events are typically forced by the alongshore poleward movements of the storms to as far north as 20 n and thereafter continue to propagate freely at least as far as guyamas 28 n large variable phase speeds 250 500 km day 1 are observed in the southern region consistent with the alongshore speeds of the forcing a multiple input statistical forcing model in which adjusted sea level is r

steady flow to a horizontal drain in an unconfined aquifer with variable thickness summary in this study we have used an analytical element method together with genetic algorithm ga optimization to determine the steady state flow rate to an infinite horizontal drain with a finite radius in an unconfined aquifer with a variable thickness in this study we first determine the water table position by using the ga optimization method which is carried out by satisfying the zero pressure and the perpendicularity of iso potential and iso pressure gradients on the water table then we illustrate that one has to use a weighting factor in implementing the above mentioned two conditions simultaneously to optimize the objective function better here we propose two methods to calculate the flow rate to the drain the first method determines the flow rate based on the water table elevation using the dupuit forchheimer assumption the second method determines the flow rate by differentiating the hydraulic head the flow rates calculated by these two methods agree with each other especially in the regions that are more than 1 8 dimensionless distance from the drain where the dimensionless distance is defined as the ratio of distance over the drain elevation the functionality of the flow rate with respect to the drain radius the drain elevation and the distance to the constant head boundary is also studied

saddle dolomite as a by product of chemical compaction and thermochemical sulfate reduction petrographic stable and radiogenic isotope trace element and fluid inclusion data from the devonian nisku reef trend in the subsurface of alberta canada suggest that saddle dolomite was a by product of chemical compaction and thermochemical sulfate reduction in subsiding dolomitized rocks furthermore thermochemical sulfate reduction may be representative of other processes that increase the amount of saddle dolomite via an increase in carbonate alkalinity the data also confirm that saddle dolomite is most likely to form at elevated temperatures from hypersaline brines

new constraints on carbonate diagenesis from integrated sr and s isotopic and rare earth element data jurassic smackover formation u s gulf coast a reply isotopic sr s o c and trace element including rare earth element ree compositions of calcite cements metal sulfides and sulfate minerals from oolitic carbonate grainstones of the smackover formation jurassic southwest arkansas shelf constrain the mechanism of sulfate reduction and establish temporal relations between sulfur and carbonate diagenesis strontium isotopic values of calcite cements range from near jurassic age sea water values 0 7068 up to values of 0 7096 this evidence coupled with variation in o and c isotopic compositions and in cement zoning under cathodoluminescence suggests that calcite cement precipitated over the course of burial diagenesis strontium isotopic compositions of pyrite marcasite and native s range up to maximum values observed for calcite cements but galena and sphalerite are less radiogenic the sr contents of sulfides and native s are 30ppm but the rb content is sufficiently low that in situ growth of87sr would not dramatically alter the initial sr isotope ratio diagenetic sulfate minerals also exhibit a range of sr isotopic compositions anhydrites range from 0 7071 to 0 7081 while celestites are more radiogenic 0 7096 the ree patterns of early and late calcite cements and framework grains differ using sm yb ratios as an indicator of heavy vs light ree enrichment early calcites have sm yb ratios 1 whereas late calcite cements have ratios of 1 8 3 2 importantly both cement signatures differ from framework grain ratios 1 3 1 7 indicating lack of rock buffering in fluids from which the cements precipitated furthermore the sympathetic increase in sm yb and sr isotopic ratios from early to late calcites is consistent with input of light ree from siliciclastic sources sulfur isotopic compositions of metal sulfide minerals range from 32 to 8 cdt native s and anhydrite values 18 are near jurassic age sulfate values while celestites are heavier 28 although thermochemical sulfate reduction has been proposed to explain h2s in deeply buried carbonate units associated with evaporite s lack of s isotopic homogenization between sulfate and sulfide minerals lack of s isotopic equilibration of oil with reservoir so4 and the limited distribution of h2s rich brines in southwest arkansas demand a more complex origin

gas souring by thermochemical sulfate reduction at 140 c reply natural gas in the permian triassic khuff formation of abu dhabi contains variable amounts of h2s gas souring occurred through thermochemical sulfate reduction of anhydrite by hydrocarbon gases sour gas is observed only in reservoirs hotter than a critical reaction temperature 140 c petrographic examination of core from a wide depth range showed that the anhydrite reactant has been replaced by calcite reaction product only in samples deeper than 4300 m gas composition data show that only reservoirs deeper than 4300 m contain large quantities of h2s i e 10 at present day geothermal gradients 4300 m is equivalent to 140 c fluid inclusion analysis of calcite reaction product has shown that calcite growth only became significan at temperatures greater than 140 c thus three independent indicators all show that 140 c is the critical temperature above which gas souring by thermochemical sulfate reduction begins the previously suggested lower temperature thresholds for other sour gas provinces 80 130 c derive from gas composition data that may not allow adequately either for the reservoir temperature history or for the migration of gas generated at higher temperatures into present traps conversely published proposals for higher threshold temperature 180 200 c derive from short duration experimental data that are not easily extrapolated to geologically realistic temperatures and time scales therefore the temperature of 140 c derived from our study of the khuff formation may be th best estimate of temperature required for in situ thermochemical sulfate reduction to produce the high h2s concentrations encountered in deep carbonate gas reservoirs

the annual cycle of sea level in the eastern tropical pacific abstract the long period response of sea level on the eastern boundary of the pacific separates for linear dynamics into a remotely forced part mainly due to zonal winds along the equator to the west and a locally driven part where sea level slopes to balance the alongshore wind examination of the annual component of sea level on the eastern boundary indicates that the locally forced part dominates whereas the remotely forced part plays a major role at semiannual and interannual periods

geochemical characteristics of the zhaolanzhuang sour gas accumulation and thermochemical sulfate reduction in the jixian sag of bohai bay basin abstract natural gas from the zhaolanzhuang field of the jizhong superdepression bohai bay basin contains the highest proportions of h 2 s 40 92 among the sour gases encountered in china the gas payzones include the eocene oligocene kongdian formation ek and the es4 member of the shahejie formation the sedimentary sequence consists of halite anhydrite carbonate sandstone and shale interbeds deposited in the evaporative brackish water lacustrine salt lake setting in the deepest part of the jinxian sag the total thickness of evaporites is more than 1000 m of which halite accounts for over 40 various organic rich mudstones intercalated with the evaporites are currently within the conventional hydrocarbon window with a depth of 2500 3500 m and likely the source for the oil and sour gas in the zhaolanzhuang field the temperatures of the gas reservoirs range from 75 to 100 c too low for significant thermochemical sulfate reduction the co occurrence of abundant elemental sulfur with the sour gas and the 34 s values of the various sulfur containing compounds indicate that the h 2 s gases were most likely derived from much deeper source kitchens where significant thermochemical sulfate reduction has occurred

a comparison of long coastal trapped wave theory with observations off peru abstract the agreement between coastal trapped wave theory and observation is studied for the case of observations made off peru during the 1977 cuea joint ii experiment wave properties are calculated using a numerical model with realistic horizontally uniform stratification and realistic bottom topography these properties are then explored as a function of the ratio of the first internal rossby radius of deformation to the shelf slope width the agreement of observed and calculated first mode free wave phase speeds 230 cm s 1 is excellent while modal structures agree more poorly a forced wave calculation using observed winds and currents as input is used to hindcast alongshore currents and sea level in the frequency band where smith 1978 observed free coastal trapped waves during 1977 the model suggests that most of the observed sea level and alongshore velocity fluctuations in the 5 10 day period band are due to free waves originating equatorward of 5 deg s while winds between 5 deg s and

facies and sedimentary environment of the permian carbonates khuff formation in the united arab emirates abstract the late permian to early triassic khuff formation of the united arab emirates is a 625 970 m thick sequence of shallow water carbonates dolomites limestones and dolomitic limestones with subordinate anhydrite it can be subdivided into ten facies units distinguished on the basis of their depositional textures that represent an overall regressive carbonate evaporite sequence based on the paleoecology sedimentary structures and lithology four distinct depositional settings can be recognized supratidal sabkha lagoon shoal and shallow shelf the khuff formation has both primary interparticle and secondary dissolution vugs and intercrystalline porosities

origin of deep sour natural gas in the ordovician carbonate reservoir of the tazhong uplift tarim basin northwest china insights from gas geochemistry and formation water abstract deep sour gases are found in the ordovician carbonate reservoir of the tazhong uplift in the tarim basin northwest china all sour gases in this field are dominated by gas hydrocarbons c1 c4 with varying amounts of h2s most of the gases in the eastern tazhong are characterized by high gas dryness coefficients 0 95 13c enriched methane 13c1 ranging from 44 6 to 35 8 and small difference between values of the 13c2 and 13c1 13c2 1 in contrast the gases in the western tazhong are characterized by relatively low gas dryness coefficients mostly

thermochemical sulfate reduction and fluid evolution of the lower triassic feixianguan formation sour gas reservoirs northeast sichuan basin china the dolomite hosted lower triassic feixianguan formation from the northeast sichuan basin china is an economically important reservoir that contains sour natural gas these reservoirs were initially filled with oil later replaced by gas during burial to 7000 m 22 965 ft followed by uplift to about 4000 m 13 123 ft we have studied the souring process thermochemical sulfate reduction tsr and diagenetic evolution of the feixianguan formation using detailed petrology fluid inclusion studies and stable isotope data from carbonate minerals pre tsr diagenesis included in time order the eodiagenetic main stage of dolomitization by a reflux mechanism fracture related calcite cementation barite quartz celestite and fluorite mineralization and a dolomite recrystallization stage thermochemical sulfate reduction resulted in anhydrite replacement by calcite petroleum destruction formation of sulfur rich pyrobitumen and elemental sulfur and generation of large volumes of and diagenesis during tsr can be subdivided into oil stage tsr and gas stage tsr with oil stage tsr defined by the presence of primary oil and bitumen inclusions in the tsr calcite based on aqueous inclusion homogenization temperatures oil stage tsr commenced at a temperature of 116 c with a mode between 130 c and 140 c gas stage tsr started at a temperature of 135 c and continued to maximum burial temperatures of about 220 c trace amounts of pyrite barite quartz and celestite grew during tsr post tsr diagenesis was dominated by fracture related calcite precipitation as well as celestite and anhydrite crystallization formation water salinity increased from depositional values 3 5 wt up to 24 wt during pre tsr dolomite recrystallization probably because of an influx of evaporite associated water from the overlying jialingjiang formation although pre tsr barite quartz celestite and fluorite mineralization was associated with a transient decrease in water salinity during tsr formation water salinity decreased from 26 wt to as low as 4 wt as a result of water being produced during tsr reactions

burial diagenesis and thermochemical sulfate reduction smackover formation southeastern mississippi salt basin the smackover formation in the southeastern mississippi salt basin has been buried from 3 03 to 6 06 km and subjected to temperatures of 100 to 200c pre hydrocarbon migration burial diagenesis is characterized by precipitation of calcite cement followed by saddle dolomite and late anhydrite these phases formed at temperatures of less than 100c the oxygen isotopic composition of calcite ranges from minus 5 to minus 8 4 pdb and carbon isotopic composition ranges from 3 5 to 6 0 pdb the sulfur isotopic composition of late anhydrites ranges from 18 1 to 19 1 cdt post hydrocarbon migration burial diagenesis is dominated by replacement of previously formed late anhydrite by calcite or calcite plus elemental sulfur and precipitation of post bitumen calcite cement these diagenetic phases formed at temperatures above 150c and are present only in the deep part of the basin the oxygen isotopic compositions of calcites that replace anhydrite range from minus 3 0 to minus 4 0 pdb and carbon isotopic compositions range from minus 2 0 to 4 2 pdb the oxygen isotopic compositions of post bitumen calcites range from minus 3 4 to minus 5 6 pdb and carbon isotopic compositions range from minus 1 6 to minus 16 3 pdb two samples of elemental sulfur have sulfur isotopic compositions of 15 8 and 16 1 cdt the high temperature replacement of anhydrite by calcite more the presence of post bitumen calcite cement the sulfur isotopic composition of sulfates and elemental sulfur and high concentration of hydrogen sulfide indicate that rapid thermochemical reduction of solid sulfates is taking place in the deep part of the mississippi salt basin at temperatures as low as 150c less

hydrographic conditions off northern chile during the 1996 1998 la nina and el nino events 1 the evolution of oceanographic conditions in the upwelling region off northern chile 18 24 s between 1996 and 1998 including the 1997 1998 el nino is presented using hydrographic measurements acquired on quarterly cruises of the chilean fisheries institute with sea surface temperature sst sea level and wind speeds from arica 18 5 s iquique 20 5 s and antofagasta 23 5 s and a time series of vertical temperature profiles off iquique spatial patterns of sea surface temperature and salinity from may 1996 to march 1997 followed a normal seasonal progression though conditions were anomalously cool and fresh starting in march 1997 positive anomalies in sea level and sea surface temperature propagated along the south american coast to 37 s maximum sea level anomalies occurred in two peaks in may july 1997 and october 1997 to february 1998 separated by a relaxation period maximum anomalies 2 c and 0 1 practical salinity units psu extended to 400 m in december 1997 within 50 km of the coast march 1998 presented the largest surface anomalies 4 c and 0 6 psu strong poleward flow 20 35 cm s 1 occurred to 400 m or deeper during both sea level maxima and weaker 10 cm s 1 equatorward flow followed each peak by may 1998 sst had returned to the climatological mean and flow was equatorward next to the coast however offshore salinity remained anomalously high owing to a tongue of subtropical water extending southeast along the peruvian coast conditions off northern chile returned to normal between august and december 1998 the timing of the anomalies suggests a connection to equatorial waves the progression of the 1997 1998 el nino was very similar to that of 1982 1983 though with different timing with respect to seasons

dolomitization of gas reservoirs the upper permian changxing and lower triassic feixianguan formations northeast sichuan basin china abstract the lower triassic feixianguan formation and to a lesser extent the upper permian changxing formation contain more than ten giant recently discovered dolomite gas fields on either side of a paleo embayment kaijiang liangping bay sichuan basin china this study documents the origin of the dolomite using a combination of petrology fluid inclusion trace element geochemistry and stable isotope and radiogenic isotope analysis of samples from outcrop and core samples from producing gas fields three stages of dolomitization are revealed dolomicrite from the lagoon facies in the feixianguan formation and minor fabric retentive dolomite from reef facies in the changxing formation on the northeast side of kaijiang liangping bay represent the initial dolomite phase caused by reflux of feixianguan brine with salinity close to gypsum saturation 18 wt salinity during the first stage of diagenesis at 30 c the second and dominant dolomite phase fabric retentive dolomite in both the feixianguan and changxing formations on the both sides of kaijiang liangping bay is the result of reflux of diagenetic fluids with salinity ranging from normal feixianguan seawater 3 5 salinity up to mesohaline water 6 5 salinity during early burial diagenesis at about 35 40 c as shown by the dominance of single phase aqueous inclusions shallow formed stylolites that cut the second phase of dolomite and the early triassic marine carbon oxygen and strontium isotope and rare earth element and yttrium ree y signals the subordinate third dolomite phase fabric obliterative dolomite and dolomite cement was due to burial diagenetic recrystallization between 80 and 140 c in the feixianguan and changxing formations on both sides of kaijiang liangping bay the third phase of dolomitization involved water expelled from the slightly younger lower triassic jialingjiang formation marine evaporites and carbonates on the northeast side of kaijiang liangping bay revealed by the high salinity of the aqueous inclusions that homogenize at 80 to 140 c and elevated strontium isotope data the carbon isotope and ree y signals of the third phase of dolomite are similar to earlier dolomite cements confirming the lack of exotic input future exploration should be focused on dolomitized high energy sediments e g reef and oolitic shoal and bank in similar triassic tethyan paleogeographic settings that are associated with restricted facies but underlying dolomitized high energy permian strata may also be good exploration targets