complex fault fold interactions during the growth of the jabal qusaybah anticline at the western tip of the salakh arch oman the jabal qusaybah anticline is located at the western end of the salakh arch a major salient in the foothills of the oman mountains we performed a structural and petrographical geochemical study of vein sets and fault zones associated with the development of this anticline our data illustrate a complex deformation pattern both in space and time characterized by the unusual presence of widespread ne sw left lateral strike slip fault zones trending oblique to the e w fold axial strike and of abundant and well developed n s fold perpendicular extensional fault zones associated with axial bulging and dilation well developed in the central region of the anticlinal crest we propose a three stage evolution for the jabal qusaybah anticline starting with prefolding jointing in the foreland of the late cretaceous oman mountains and followed by development of extensional faulting in campanian times positive inversion of the qusaybah fault possibly in miocene times caused development of a layer parallel shortening fabric and amplification the jabal qusaybah anticline in concomitance with the activity of ne sw left lateral strike slip fault zones that triggered n s fold perpendicular extensional faulting particularly in the axial bump of the anticline the final evolutionary stage was characterized by further amplification of the axial bump and related n s extensional fracturing and by uplift and exhumation to explain the complex noncylindrical fault fold interactions in the study anticline we tentatively propose that they were triggered by near foredeep parallel tapering of the sedimentary tectonic overburden of the ara evaporites

diagenesis and formation water chemistry of triassic reservoir sandstones from southern tunisia the fluvial triassic reservoir subarkoses and arkoses 2409 5 2519 45 m of the el borma oilfield southern tunisia were subjected to cementation by haematite anatase infiltrated clays kaolinite and k feldspar at shallow burial depths from meteoric waters subsequently basinal brines controlled the diagenetic evolution of the sandstones and resulted initially in the precipitation of quartz overgrowths magnesian siderite minor ferroan magnesite and anhydrite the enrichment of siderite in 12c isotope 13cpdb 14 5 to 9 results from derivation of carbon from the thermal decarboxylation of organic matter during further burial the precipitation of dickite and pervasive transformation of kaolinite into dickite occurred followed by the formation of microcrystalline k feldspar and quartz chlorite and illite prior to the emplacement of oil present day formation waters are na ca cl brines evolved by the evaporation of seawater and water mineral interaction and are in equilibrium with the deep burial 3 1 km minerals these waters are suggested to be derived from the underlying silurian and devonian dolomitic mudstones

paleofluid evolution in fault damage zones evidence from fault fold interaction events in the jabal qusaybah anticline adam foothills north oman abstract fault zones are known to play a key role in controlling fluid migration including hydrocarbons at local and regional scales in this contribution physicochemical data from veins are used to document the extent and maintenance of fluid conductivity associated with fault damage zones in an anticlinal structure occurring in the frontal part of a foreland fold and thrust belt migration of fluids during major deformational events has been recorded by several generations of calcite and localized dolomite cementation in veins in marine cretaceous carbonates of the jabal qusaybah anticline north oman applying detailed petrographic and paragenetic relations geochemical analysis stable carbon and oxygen isotopes strontium isotopes and trace elements and microthermometry coupled with structural studies of fault zones and associated calcite veins made it possible to link fluid circulation to the structural evolution of the jabal qusaybah anticline based on the structural framework and fault systems three groups of veins were distinguished group 1 veins are interpreted to be linked to burial and early tectonic deformation in association with e w extensional fault zones calcite cementation in this group occurred in a closed to semiclosed fluid system which originated as a result of intraformational fluid movement along a low connectivity fracture network the 13c values of these veins range from 3 to 3 5 and 18o values vary from 10 3 to 8 1 v pdb group 2 veins are related to syntectonic deformation along ne sw strike slip and incipient n s extensional faults linked to culmination of the jabal qusaybah anticline from this stage onward fluids correspond to progressive fault connectivity and dilation related to interaction of fault folding systems the cements precipitated during this stage have more variable 13c values ranging from 0 9 to 3 2 and possess a wide range of 18o values varying between 11 2 and 0 3 v pdb the cements in group 2 veins originated from fluids characterized by a relatively broad range of precipitation temperature 75 107 c and salinities evolving from seawater to moderately saline fluids 3 4 12 8 eq wt nacl with h2o nacl composition the source of salinity is inferred to be evaporitic brines that originated from the ara group and the large range of salinity is interpreted as the result of mixing between those brines and modified seawater group 3 veins are considered to be related to late tectonic deformation corresponding to late fold amplification of the anticline hinge transition from ne sw left lateral strike slip to n s extensional faulting progressive regional and local uplift and exhumation stable isotope data support the occurrence of bacterial methanogenesis or co2 degassing at the end of this stage their associated cements are characterized by higher 13c and 18o values compared to other groups of veins ranging from 0 6 to 8 0 and 3 6 to 1 5 v pdb respectively fluids responsible for calcite precipitation in this group evolved from a moderate saline to a more saline 8 5 16 eq wt nacl h2o nacl cacl2 brine the progressive 18o enrichment relative to seawater and preceding cements and its covariation with fluid salinity in the later stage suggest the higher contribution of the evaporitic brines this hypothesis is further supported by the increase in their 87sr 86sr ratios compared to both middle to upper cretaceous marine carbonates and other groups of veins although during this episode calcite cementation occurred at temperatures below 50 c their geochemical signatures reveal that the faults were sufficiently conductive to transfer extraformational fluids late in the deformation history of this structure the interference between strike slip and extensional fault systems and their interaction with fold amplification is invoked to be responsible for enhanced conductivity in fault damage zones

the petroleum characteristics and filling history of the froy field and the rind discovery norwegian north sea abstract the brent group reservoirs of the froy field and the rind discovery norwegian north sea show complex distributions of petroleum and aqueous fluids multiple fluid contacts are present in the rind discovery and the fields show various extent of compartmentalisation due to faulting geochemistry data of core extracts indicate that the two fields have different petroleum sources bhullar karlsen holm backer owe tran 1998 late diagenetic modifications of the reservoir quality consist of quartz cementation followed by carbonate and kaolinite cementation and dissolution of k feldspar fluid inclusion results indicate that filling of the reservoirs occurred after the main phase of quartz cementation at pressure temperature conditions close to the present differences in fluid properties between fault compartments in both fields have been identified fluid inclusion data have proved especially valuable for evaluation of the sealing capacity of faults through time and given evidence for the fault lineament north of both fields to be a time integrated pressure seal except for a lower gas condensate zone in the 25 2 13 compartment of rind the present reservoir fluids are volatile oils close to gas saturation the previous presence of an oil in the lower reservoir zone of 25 2 13 has also been demonstrated the fluid inclusion data indicate that the condensate in 25 2 13 represents a second episode of migration filling rather than phase separation

nature and tectonic significance of co seismic structures associated with the mw 8 8 maule earthquake central southern chile forearc abstract the mw 8 8 maule earthquake on february 27 2010 affected the central southern chilean forearc of the central andes here we show the results of field investigations of surface deformation associated with this major earthquake observations were carried out within three weeks after the seismic event mostly in the central and northern part of the forearc overlying the rupture zone we provide a detailed field record of co seismic surface deformation and examine its implications on active andean tectonics surface rupture consisted primarily of extensional cracks push up structures fissures with minor lateral displacements and a few but impressive extensional geometries similar to those observed in analogical modeling of rift systems a major group of nw wnw striking fractures representing co seismic extensional deformation is found at all localities these appear to be spatially correlated to long lived basement fault zones the nw striking normal focal mechanism of the mw 6 9 aftershock occurred on march 11 demonstrates that the basement faults were reactivated by the mw 8 8 maule earthquake the co seismic surface ruptures show patterns of distributed deformation similar to those observed in mapped basement involved structures we propose that co seismic reactivation of basement structures play a fundamental role in stress release in the upper plate during large subduction earthquakes the fundamental mechanism that promotes stress relaxation is largely driven by elastic rebound of the upper plate located right above the main rupture zone

characteristics of fluid inclusions and implications for the timing of hydrocarbon accumulation in the cretaceous reservoirs kelasu thrust belt tarim basin china abstract the kelasu thrust belt is a key area for oil and gas exploration within the tarim basin of china an area containing abundant oil and gas resources but where the processes that controlled hydrocarbon accumulation remain unclear this study reconstructs the accumulation history of hydrocarbons within the kelasu thrust belt by studying multiple sets of fluid inclusions from the cretaceous reservoirs using laser raman infrared spectroscopy fluorescence spectroscopy total scanning fluorescence and ptv simulation analyses the resulting data yield the following results 1 three types of cretaceous hydrocarbon bearing fluid inclusions are present and they record three periods of hydrocarbon accumulation period i involved low maturity medium oil as recorded by the presence of yellow green fluorescent oil inclusions with this accumulation occurring between the neogene jidike and kangcun stages 20 5 ma period ii involved high maturity light oils or condensates that are recorded by the presence of blue white fluorescent oil inclusions with this accumulation occurring during the early kuche stage 5 2 5 ma period iii involved the significant accumulation of gas as recorded by non fluorescent gas inclusions during and after the late kuche stage 2 5 0 ma 2 inclusion pvt simulations indicate that the pressures during the trapping of oil inclusions within the west kelasu reservoirs increase with increasing capture temperature suggesting that west kelasu cretaceous oil reservoirs formed over a short period of time in contrast the trapping pressures of oil inclusions within the east kelasu area are invariant with increasing trapping temperature indicating that the formation of east kelasu cretaceous oil reservoirs was a relatively slow and gradual process this most likely relates to the fact that the east kelasu reservoirs are close to the hydrocarbon generation centre in an area with sufficient hydrocarbon supply with hydrocarbon accumulation processes involving all of the stages of hydrocarbon generation recorded by the source rocks in this area in comparison the west kelasu reservoirs are far from the hydrocarbon generation centre and as such record only one phase of oil filling 3 significant tectonism associated with the uplift of the south tianshan mountain during the late kuche stage caused widespread changes to cretaceous paleo oil reservoirs in this area this led to some cretaceous paleo oils being transported to shallower traps to form secondary oil reservoirs whereas others were transported to the surface and were lost with residual paleo oils were also changed to condensate gas as a result of gas washing after the addition of large amounts of late stage gas

the composition of a primary granite derived ore fluid from s w england determined by fluid inclusion analysis abstract electrolyte concentrations in aqueous fluid inclusions in quartz from a high temperature hydrothermal rock have been measured for 15 elements by an improved crush leach procedure the primary hydrothermal fluid was dominated by nacl and has been shown by previous studies to have been about 3 m with respect to cl on this basis the molar concentrations include fe 0 21 mn 0 06 and zn 0 02 and the fluid is interpreted as parental to some of the s w england ore bodies

fayalite rich rims veins and halos around and in forsteritic olivines in cais and chondrules in carbonaceous chondrites types compositional profiles and constraints of their formation abstract fayalite rich rims veins and halos around and in forsteritic olivines are a wide spread phenomenon in chondrules ca al rich inclusions cais and single grains in carbonaceous chondrites the presence of fayalite rod like crystals and laths in rims veins in wall of pores and as fluffy network bridging neighbouring olivines pyroxenes feldspars etc is strongly suggestive that the fayalitic olivine was formed by condensation presumably from the solar nebula gas the formation of the fayalitic olivine was probably caused by an increase in the h 2 o h 2 ratio to a ratio between 0 1 1 subsequent to condensation of forsterite at that stage feni inclusions in olivine were also oxidized and fayalitic halos around the metal were then formed by fe diffusion along with addition of sio 2 from the solar gas or loss of mgo to the solar gas the fa rich olivine rims and veins display a narrow compositional variation between fa 34 and fa 46 subsequent to condensation of fa rich olivine and oxidation of feni metal fe diffused in forsterite this diffusion was probably enhanced due to the presence of point defects in olivine or the formation of a nonstoichiometric phase analogous to laihunite enriched in al 2 o 3 and cr 2 o 3 however the presence of al 2 o 3 and cr 2 o 3 rich discrete domains cannot be excluded cooling rates calculated by modelling of the diffusion profiles are indicative of rapid cooling subsequent to the condensation of fayalitic olivines we obtain cooling rates ranging from 2000 c day and 10 c day at an initial temperature of 1200 c and 900 c respectively

co seismic riedel shear structures produced by the 2010 mw 6 9 yushu earthquake central tibetan plateau china abstract riedel shear structures are often developed within strike slip fault zones this study focuses on the riedel shear structures within the co seismic strike slip surface rupture zone produced by the 2010 mw 6 9 yushu earthquake in the central tibetan plateau china field surveys and structural analysis of the surface ruptures reveal that the co seismic riedel shear structures are characterized by i tension cracks t fractures ii compression structures mainly mole tracks p shears and iii discrete shear faults r and y shears developed in unconsolidated alluvial deposits along the pre existing left lateral strike slip ganzi yushu fault zone the t fractures generally show a right stepping en echelon pattern in contrast the p and r shears indicate a left stepping en echelon pattern the riedel shears are inclined to the general trend of the co seismic surface rupture zone at mean counterclockwise angles of 41 t fractures and 21 r shears and a mean clockwise angle of 35 for the p shears the present results show that i the co seismic riedel shear structures indicate a left lateral strike slip sense for the seismogenic fault and ii the t fractures and p and r shears are the primary riedel shear structures formed during the early stages of the evolution of a strike slip fault constrained by pre existing geologic structures

petroleum inclusions in sedimentary basins systematics analytical methods and applications abstract fluid dynamics in sedimentary basins is of tremendous interest both from a scientific and an economic point of view integration between fluid inclusion and present day fluid data provides the time aspect necessary for reconstruction of fluid flow paths and can be used for mapping fluid dynamics both on a regional basin scale or on the more local scale of petroleum reservoirs this paper presents a review of analytical and modelling methods for petroleum in fluid inclusions essentially four types of data for petroleum inclusions can be established through analysis and modelling 1 textures which give indirect information of the time aspect 2 fluid composition 3 fluid properties and 4 pressure temperature of trapping during the last decade development of analytical methods for determination of inclusion fluid compositions has taken place traditional correlation studies for characterisation of maturity and source facies may now therefore include fluid inclusion data the development has also been directed towards an improved understanding of the physical properties of petroleum inclusions although these methods are in their early stages concerning precision and accuracy data necessary for fluid flow modelling such as fluid densities viscosities pressure and temperature can be estimated

origin and evolution of high salinity zn pb mineralising fluids in the variscides of belgium high salinity na ca cl rich fluids 20 wt salts in inclusions in gangue and ore minerals from mesozoic mississippi valley type mvt deposits in the verviers synclinorium eastern belgium and in cretaceous vein calcites at the variscan front were investigated by microthermometric and crush leach analysis the mvt deposits formed at temperatures of 110 c while the cretaceous vein calcites were precipitated at temperatures 50 c their cl br content cl br ratio between 246 and 458 suggests that the fluids probably originated by the evaporation of seawater during basin development at the southern margin of the caledonian brabant massif in the late palaeozoic the na ca k content na 29 700 49 600 ppm ca 25 700 46 200 ppm k 1 000 5 620 ppm is similar to that of the mineralising fluids in other pb zn districts interpreted to be of evaporative origin e g newfoundland east tennessee polaris furthermore comparison of the na ca k content of the fluids with that of an evolved evaporitic brine enables the recognition of major water rock interactions that modified the fluid composition it indicates that the ambient fluids participated in the early diagenetic dolomitisation of upper palaeozoic carbonates and also in the albitisation of plagioclase in lower palaeozoic siliciclastics of the caledonian basement illitisation of smectites or dissolution of k feldspar probably controlled the k content of the fluids a model is proposed where the bittern brines migrated down into the deep subsurface because of their density during extension after the variscan orogeny these fluids were finally expelled along extensional faults resulting in the formation of zn pb deposits

geochemical constraints on the origin of the kicking horse and monarch mississippi valley type lead zinc ore deposits southeast british columbia canada two mississippi valley type mvt ore deposits kicking horse and monarch have been studied with the aim of comparing the ores at the two localities and to characterize the origin of the mineralizing fluids and the ore formation process es both deposits are hosted by the middle cambrian cathedral formation carbonate host rocks kicking horse on the north and monarch on the south flank of the kicking horse valley near field se british columbia the ore bodies are situated at the transition of western basinal to eastern shallow water strata of the paleo pacific passive margin succession in the cordilleran foreland province of the western canada sedimentary basin both deposits are related spatially to normal faults in both localities the ore minerals are dominated by pyrite sphalerite and galena dolomite minor quartz and calcite are also present in close association with the ores the salinity 21 30 wt nacl eq and homogenization temperatures 63 182 c measured in fluid inclusions in carbonate quartz and sphalerite lie within the typical range of mvt fluid conditions the good stoichiometry 50 53 mol caco3 low 18o values 21 to 14 vienna peedee belemnite and relatively high homogenization temperatures 95 c of the dolomite suggest the dolomites were formed under burial diagenesis the ore forming fluids probably interacted with siliciclastic units based on elevated li contents and 87sr 86sr ratios which are highest in the dolomite type after the main ore stage we propose that the ores formed from the mixing of a downward infiltrating sulfur bearing halite dissolution fluid with an upward migrating metal rich evaporated seawater fluid which had already undergone minor mixing with a dilute fluid

origin of the saline paleofluids in fault damage zones of the jabal qusaybah anticline adam foothills oman constraints from fluid inclusions geochemistry abstract the jabal qusaybah anticline in north oman is affected by syn folding strike slip and extensional fault zones developed during foreland deformation ahead of the northern oman mountains thrust wedge in cenozoic times migration of fluids in fault damage zones is recorded in complex calcite vein networks by employing the microthermometric and compositional microanalysis of the fluid inclusions crush leach two distinct generations of veins have been studied the aim was to determine the source of elevated salinity in fluids involved in their cementation and explain their compositional evolution through fluid rock interactions the ionic ratios na br and cl br obtained from crush leach analysis give supporting evidence that the elevated salinity of fluid inclusions in both vein groups originated from an evaporated seawater beyond the onset of halite precipitation residual brines the results reveal a gradual increase in salinity of the fluids f cl molar ratios as well as li cl molar ratios these results imply the progressively increasing contribution of evaporitic residual brines and fluids that interacted with or were derived from siliciclastic rocks we suggest that the most likely origin of the former fluids is provided by residual brines associated with precipitation of the ara evaporites cambrian the regional driving mechanism for such a significant fluid migration is believed to be compaction driven upward flow that was channeled into faults and fractures during major deformational events

origin characteristics and distribution of fault related and fracture related dolomitization insights from mississippian carbonates isle of man abstract the southwest davis zinc field sdzf is among the westernmost mvt districts associated with the allegheny ouachita orogeny in the midcontinent u s it consists of a series of small zinc sulfide deposits and associated dolomitization covering an area of 16 km2 6 mi2 adjacent to the arbuckle anticline in southern oklahoma mineralization occurs within the royer dolomite upper cambrian and the butterly dolomite lower ordovician of the arbuckle group and is associated with faults and breccia bodies that parallel the trend of the anticline mining activity in the sdzf was restricted to the early part of the 20th century ore mineralization consists chiefly of sphalerite and subordinate smithsonite with minor galena chalcopyrite and pyrite as well as supergene alterations of these minerals homogenization temperatures th of fluid inclusions in gangue dolomite cement range from 88 to 101 c and have salinities of 6 5 to 20 9 wt nacl equivalent rarer fluid inclusions in sphalerite have an average th value of 105 c and average salinity of 19 2 wt nacl equivalent gangue dolomite cements have 18o values of 6 9 to 9 1 vpdb and 13c values of 0 2 to 1 1 vpdb the 87sr 86sr ratios for these dolomites range from 0 7088 to 0 7105 mineralization likely occurred from a flow system in which basement influenced brines entered the host formations through faults and circulated through the brecciated zones as the ore hydrothermal system waned the relative importance of local brines within the carbonate section increased and resulted in precipitation of late dolomite cements

surface deformation and tectonic background of the 2019 ms 6 0 changning earthquake sichuan basin sw china abstract the june 17 2019 ms 6 0 changning earthquake at a depth of 3 5 km struck the changning anticline fold system no active faults have been observed in the region some studies have attributed the earthquake to the regional shale gas exploitation following the earthquake we conducted a field survey to investigate co seismic surface deformation in the area and observed many surface fractures and uplifted areas our work indicated that the deformation followed a riedel shear pattern the fractures and uplifted areas represent t fractures and s extrusions respectively the observed riedel shear pattern is indicative of left lateral strike slip motion to ascertain the relationship between the riedel shear pattern and regional tectonics we investigated the trends in layer striations and fault scratches the results indicated that there were two stages in the evolution of the anticline in the first stage the principal compressive stress that dominated the original formation of the anticline trended ne sw in the second stage the regional principal compressive stress shifted to the current e w trend generating oblique motion that included reverse and left lateral components we propose that the tectonic stress field in this region had a strong bearing on the focal mechanism of the mainshock and the co seismic surface deformation both the eastward expansion of the xianshuihe area and southeastward expansion of the longmen shan have affected the current changning anticline fold system

geochemistry and origin of formation brines from the paris basin france 2 saline solutions associated with oil fields abstract oil fields from the paris basin are located in three geological levels dogger middle jurassic rhaetian and keuper upper triassic the origin of water and dissolved salts in saline solutions associated with oil is investigated using the hypothesis that cl and br are conservative in solution in a diagram of cl br ratios vs cl the points of the dogger and the keuper aquifers lie in the zone of primary brines whereas those of the rhaetian are located in the zone of secondary brines the na cl ratio is very high in all of the saline solutions suggesting either a relatively poorly evolved brine at the beginning of halite deposition or some halite dissolution all of the saline solutions especially those from the dogger aquifer are clearly diluted dilution by meteoric waters would not alter the cl br ratio high concentrations of lithium rubidium and boron are attributed to the presence of an extremely evolved brine of marine origin in mixtures of secondary brines formed by dissolution of halite and small amounts of sylvite and ca sulphate mass balance calculations of the excess of cl with respect to na k allows the fraction x of water derived from the primary brine to be calculated assumptions are that all na and k is derived from the secondary brine and that the cl content of the primary brine is constrained by bischofite saturation at 11 000 mmol kg 1 the typical proportion of water from the primary brine waters is 0 7 in the dogger formation and 2 4 in the keuper values of the concentration factor cf expressed as the ratio of the molal concentration of a conservative ion in the evolved brine to its concentration in seawater have been calculated for lithium solutions from the dogger and keuper aquifers have cfli values of 1 8 103 and of 7 7 103 respectively in the rhaetian aquifer the linear relationship between heavy isotope contents of the brine 2h and 18o and the cl content indicates a mixture of two water sources the first one is meteoric water as defined by the intersection of the formation water line with the global meteoric water line 2 h 65 18 o 9 3 the other end member is enriched in heavy isotopes and in cl and is attributed to seawater that has dissolved evaporites mainly halite however the presence of small amounts of an extremely evolved brine is required to account for the bromide lithium rubidium and boron contents of the formation brine from the rhaetian aquifer as this contribution is very limited in amount it cannot affect the heavy isotope content of the formation water mass balance equations are solved for ternary mixtures of meteoric water seawater and brine the same constraints as above no na and k supplied by the primary brine and clbrine 11 000 mmol kg 1 are applied it is also assumed that the seawater component has the same ionic contents as modern seawater and that the salt content of the meteoric component is negligible the fraction of primary brines is x 1 4 according to the cl balance this estimate agrees with that obtained from the lithium balance assuming that the primary brine component was the same as that of the keuper formation water mass balance calculations also indicate that the so42 content of the rhaetian formation water is exclusively due to the secondary brine component in the three saline solutions the very high ca2 contents and high ca 2 mg 2 ratios may be attributed to reaction of the very evolved brine free of so2 4 with gypsum or anhydrite the result is an exchange of mg2 for ca2 which causes a release of ca2 to the solution and a precipitation of secondary mg sulphate this process can also account for the high strontium contents of the analysed samples values of the ratio 87 sr 86 sr are very high in the keuper formation water due to close contact of the solutions with the granitic basement or with granite derived detrital deposits values in the rhaetian and dogger aquifers equal those of upper triassic marine deposits the stable isotope 34s and 18o content of the dissolved aqueous so2 4 indicates a triassic origin for the bulk of sulphate involved in the evolution of formation waters from the rhaetian and from the dogger all geochemical indicators thus show a vertical migration of triassic brines however aqueous so2 4 from the keuper has a permian isotopic signature suggesting a reworking in solution of salts from this period

origin of shallow burial cements in the late visean of the campine basin belgium abstract the diagenesis of late visean buildup and shelf carbonates from three boreholes in the campine basin northern belgium has been studied to determine the early diagenetic pore fluid evolution in the basin the earliest cementation occurred by isopachous fibrous and radiaxial fibrous calcites which precipitated in a marine environment under oxidizing conditions neomorphism during subsequent diagenesis altered these cements extensively precipitation of these first stage cements was followed by an episode of dissolution of carbonate components gastropods pelecypods and echinoderms after this episode non bright and dull luminescent stages successively developed in the shelf carbonates in response to the pore waters becoming progressively more anaerobic fluid inclusions and oxygen stable isotopes in the dull luminescent stage indicate that this cement formed in a meteoric fluid at relatively low temperatures 30 c and thus under burial conditions of a few hundred metres buildup carbonates from the shelf margin show a similar diagenetic evolution but dull luminescent cements appear to have precipitated at higher temperatures 45 c than in the shelf carbonates the meteoric waters responsible for the cementation are interpreted to have been sourced from near the brabant massif where dissolution of visean limestones could have taken place when the limestones to the north were already buried underneath namurian strata lateral gravity driven groundwater flow may be a very important type of fluid flow causing the cementation of shelf carbonates fracturing of the late visean strata started before the precipitation of the meteoric cements but was most intense just before and during the precipitation of the dull luminescent calcites this fracturing probably took place during the sudetic phase at the end of the visean and early namurian times

an evaporated seawater origin for the ore forming brines in unconformity related uranium deposits athabasca basin canada cl br and δ37cl analysis of fluid inclusions abstract analyses of halogen concentration and stable chlorine isotope composition of fluid inclusions from hydrothermal quartz and carbonate veins spatially and temporally associated with giant unconformity related uranium deposits from the paleoproterozoic athabasca basin canada were performed in order to determine the origin of chloride in the ore forming brines microthermometric analyses show that samples contain variable amounts of a nacl rich brine cl concentration between 120 000 and 180 000 ppm and a cacl2 rich brine cl concentration between 160 000 and 220 000 ppm molar cl br ratios of fluid inclusion leachates range from 100 to 900 with most values between 150 and 350 cl br ratios below 650 seawater value indicate that the high salinities were acquired by evaporation of seawater most 37cl values are between 0 6 and 0 seawater value which is also compatible with a common evaporated seawater origin for both nacl and cacl2 rich brines slight discrepancies between the cl concentration cl br 37cl data and seawater evaporation trends indicate that the evaporated seawater underwent secondary minor modification of its composition by i mixing with a minor amount of halite dissolution brine or re equilibration with halite during burial ii dilution in a maximum of 30 of connate and or formation waters during its migration towards the base of the athabasca sandstones iii leaching of chloride from biotites within basement rocks and iv water loss by hydration reactions in alteration haloes linked to uranium deposition the chloride in uranium ore forming brines of the athabasca basin has an unambiguous dominantly marine origin and has required large scale seawater evaporation and evaporite deposition although the direct evidence for evaporative environments in the athabasca basin are lacking due to the erosion of 80 of the sedimentary pile cl br ratios and 37cl values of brines have behaved conservatively at the basin scale and throughout basin history

individual characterization of petroleum fluid inclusions composition and p t trapping conditions by microthermometry and confocal laser scanning microscopy inferences from applied thermodynamics of oils abstract this paper proposes a new method to characterize individual oil bearing fluid inclusions it uses both the homogenisation temperatures measured by microthermometry and the degree of gas bubble filling measured by confocal laser scanning microscopy in conjunction with thermodynamic modelling for describing liquid gas phase transitions and the volumetric behaviour of hydrocarbon mixtures it is associated with a two parameter compositional model that describes the wide range of compositions of petroleums we show that this method can give 1 useful estimations of the compositions and pressure temperature entrapment conditions of oils in fluid inclusions and 2 insights into the various processes that have affected these fluids either before entrapment liquid gas unmixing gas leaching mixing etc or after leakage etc

emerald mineralisation in colombia fluid chemistry and the role of brine mixing emerald mineralisation in colombia is located in two distinct zones along the borders of the eastern cordillera some 80 km apart mineralisation in the western zone has been dated at ca 35 ma whereas in the eastern zone it is 30 ma older crush leach analysis of the electrolyte chemistry of fluid inclusions contained in emerald quartz calcite dolomite and fluorite from both zones demonstrates that in each region brines associated with emerald mineralisation range between two extremes with many samples yielding intermediate compositions fluid 1 found mainly in emerald hosted fluid inclusions is dominated by nacl with high cl br ratios indicating that the salinity was derived by dissolution of halite most probably from the local salt beds fluid 2 found notably in quartz hosted fluid inclusions is of similar salinity but contains less na and significant concentrations of ca k fe cl and other cations it has lower cl br ratios more comparable with formation waters but is inferred to have obtained part of its salinity by halite dissolution bivariate plots of almost all cations have linear or sublinear trends regardless of the mineral hosting the inclusions or the locality from which the samples originated demonstrating that mixing of the two saline fluids has occurred because the same two fluids occur in both eastern and western zones despite the difference in space and time it is inferred that fluid compositions were rock controlled by similar interactions with evaporites and black shales in both instances it is proposed that beryllium was transported as be f complexes in the nacl fluid and was precipitated as emerald after mixing with the calcic brine caused precipitation of fluorite and parisite

stratigraphic organization of carbonate ramps and organic rich intrashelf basins natih formation middle cretaceous of northern oman the middle cretaceous carbonate deposits in the middle east are among the most productive oil bearing stratigraphic intervals in the world containing numerous giant fields in for instance the united arab emirates mauddud and mishrif formations iran sarvak formation and oman natih formation one of the main reasons for this concentration of hydrocarbons is a geological factor the coexistence of both reservoir facies and source rocks in the same depositional sequences due to the repeated creation of organic rich intrashelf basins this is demonstrated in a high resolution sequence stratigraphic study of the natih formation in oman which shows distinct and predictive patterns in the distribution and geometries of reservoir source rock and seal facies the sequence stratigraphic model presented here may serve as a reference for time equivalent deposits in the middle east the sedimentological analysis showed that the natih formation was formed by the alternation of two types of depositional systems 1 a flat bedded mixed carbonate clay ramp dominated by benthic foraminifera and 2 a carbonate dominated ramp bordering an intrashelf basin with abundant rudists in the mid ramp environment and organic rich basinal facies three fully developed third order sequences are distinguished showing a similar evolution of the depositional system with a mixed carbonate clay ramp system at the base followed by a carbonate dominated ramp system in the upper part variations occur on this pattern however depending on the relative influence of eustasy environmental factors and tectonism the late albiannearly cenomanian sequence i shows an evolution from a mixed flat ramp to a carbonate dominated ramp and organic rich intrashelf begin page 22 basin and sedimentation is predominantly controlled by eustatic sea level in the middle cenomanian sequence ii the evolution from a mixed ramp to a carbonate ramp is also observed but no intrashelf basin topography was developed in the studied area this may be due to the high influx of clay that influenced the environment in this sequence inhibiting the carbonate production probably in combination with the lack of sufficient creation of accommodation space the late cenomaniannearly turonian transgressive part of sequence iii shows a similar evolution to that observed in sequence i with the development of an organic rich intrashelf basin during highstand however a tectonically controlled sedimentation pattern is observed with the development of forced regressive wedges due to the flexural bulge of the foreland basin intrashelf basin formation occurred twice in the transgressive part of the third order depositional sequences of the natih formation our study shows that this is mainly the result of differential sedimentation rates that is the dynamics of the carbonate sedimentary system itself in response to rapid rises in relative sea level probably of eustatic origin tectonism was only a minor factor in the creation of the basin topography possibly through the creation of small initial relief the accumulation of the organic matter is not only a result of the creation of a sufficiently deep water column to guarantee dysaerobic conditions for its preservation the late albian and late cenomaniannearly turonian were also periods of generally favorable conditions worldwide for high organic matter productivity the time lines and stratigraphic architecture of the third order sequences presented here have an application potential at the scale of the arabian plate the general sedimentation pattern is predicted by our model but modifications due to different local conditions are likely to occur

constraints on the origins of fluids forming irish zn pb ba deposits evidence from the composition of fluid inclusions the numerous zn pb deposits in the irish midlands together with the quantity and grade of the ore make this a world class base metal province despite significant exploration and research there is still disagreement on the origin of the mineralizing fluids in this study we have measured the composition of fluid inclusions using a crush leach technique these data constrain the possible sources of the fluids both during and after mineralization chloride and br concentrations indicate that the main ore fluid at tynagh and silvermines was seawater that had evaporated until the salinity was between 12 and 18 wt percent however na k and li data show that water rock interactions have resulted in the depletion of na and the enrichment of k and li relative to the concentrations expected for evaporated seawater the fluids that produced postore dolomitization were also derived from seawater that had evaporated to higher salinities and had precipitated halite the concentrations of na k and li are what would be expected for seawater at this degree of evaporation and show that these fluids did not interact with the same lithologies as the ore fluids the major change to their fluid composition was exchange of mg for ca during dolomitization we suggest that the ore fluids could only have reached their high salinity by evaporation of seawater on the extensive shallow water shelf regions that existed over much of the irish midlands

the evaporation path of seawater and the coprecipitation of br and k with halite brines and salt were sampled at the morton bahamas solar salt production facility on great inagua island in the bahamas the brines were analyzed by ion chromatography to define more precisely than heretofore the evaporation path of seawater to the end of the halite facies at inagua calcium carbonate begins to precipitate at a brine concentration factor of 1 8 times that of seawater gypsum begins to precipitate at a brine concentration of 3 8 times seawater and halite at a concentration factor of 10 6 three of the most concentrated brines from inagua 40 times seawater were evaporated further in the laboratory magnesium sulfate first precipitated at brine concentrations about 70 times those of seawater and potassium bearing phases began to precipitate for these brines at concentrations greater than 90 times those of seawater the distribution of coefficients of br and k between brines and halite were determined by combining analytical data for the inagua brines with measurements of the br and k content of halites from inagua and of halite which had precipitated from inagua brines during storage the observed average value of dbr is 0 032 in good agreement with some of the previous measurements the measured values of dk are highly variable 0 001 to 0 021 dk for halite precipitated early in the halite facies is in the vicinity of 0 015

the 2001 bhuj earthquake tomographic evidence for fluids at the hypocenter and its implications for rupture nucleation 1 the january 26 2001 bhuj earthquake mw 7 6 is one of the most catastrophic indian earthquakes we have investigated the 3 d seismic velocity and poisson s ratio structures of the bhuj source area to understand the probable cause of triggering the earthquake we used 1948 p and 1865 s wave high quality arrival times from 331 aftershocks recorded at a temporary seismic network significant variations up to 5 in velocity and 10 in poisson s ratio are revealed in the aftershock area the mainshock is located in a distinctive zone characterized by high vp low vs and high poisson s ratio in the depth range of 20 to 30 km and extending 15 to 30 km laterally this feature is very similar to that of the 1995 kobe earthquake zhao et al 1996 the anomaly may be due to a fluid filled fractured rock matrix which might have contributed to the initiation of the bhuj earthquake

chemical osmosis reverse chemical osmosis and the origin of subsurface brines abstract calculations using recently tabulated values of density and osmotic coefficient for nacl h2o indicate that overpressuring is more than adequate to overcome chemical osmosis and drive reverse chemical osmosis in sedimentary sequences the best demonstrated overpressuring mechanism is the rapid deposition of fine grained sediments the dehydration of gypsum contributes to overpressuring for brief time intervals at shallow depths whereas water evolved during the protracted conversion of smectite to illite is probably a subordinate but continuing contributor to overpressuring at greater depth occurrences of overpressuring in sedimentary sections older than cretaceous indicate that post depositional mechanisms such as tectonic compression and aquathermal pressuring must also operate the latter may be of major importance in geothermal areas with adequate low permeability seals and a nontrivial contributor in areas of normal geothermal gradient because of shales that sharply decrease normal fluid flow the strongest arguments for the importance to present day brine compositions of membrane concentration of sea water solutes are 1 1 the correlation of d values of water molecules of pore fluid with those of local meteoric water 2 2 the need for major sources of mg2 and cl in apparently evaporite free basins even where dissolution of halite is a major contributor of solute reverse chemical osmosis still operates to leak relatively dilute water of the associated diagenetic chemical reactions that of mg2 with limestone to form dolomite is particularly effective in generating concentrated cl brines rich in ca2 it decreases the concentration of mg2 increases that of ca2 and decreases those of both so42 and co32 by precipitating caco3 and caso4 because of the ca2 common ion effect

combined use of confocal laser scanning microscopyand pvt simulation for estimating the composition andphysical properties of petroleum in fluid inclusions we present a method to determine the composition and pvt properties of petroleum inindividual petroleum fluid inclusions confocal laser scanning microscopy is used to generatethree dimensional images of single petroleum inclusions because liquid petroleum fluorescesunder the laser the images readily distinguish the liquid and vapour within the inclusion and canbe used to determine the inclusions volumetric liquid vapour ratio using pvt modellingsoftware the liquid vapour ratio is used along with the homogenisation temperature to determinethe bulk composition phase envelope isochore and a range of physical properties of the includedpetroleum this is done using an iterative series of pvt calculations which match twoparameters 1 the molar volume of the petroleum at room and homogenisation temperatures 2 the liquid vapour ratio of the inclusion at room temperature key uncertainties in the methodare explored including the accuracy with which the liquid vapour ratio can be determined thecomposition of the titrant gas used in the iterative procedure and the composition of thepetroleum chosen to model the physical properties of the included petroleum data from coevalinclusions suggest that the saturation pressure gas oil ratio viscosity molar volume densityand surface tension of included petroleum are determined with a precision of a few percent confirmation of the accuracy of the method awaits tests using inclusions grown in the laboratoryunder carefully controlled pvtx conditions however it is likely that the physical properties ofincluded petroleums are more accurately modelled by fluids which are genetically related tothem if proven to be accurate the method will provide a routine method for determiningpalaeopressure in petroleum systems finally we present data from a central north sea examplewhich are geologically realistic and which for the first time record the evolution of fluid pressureand petroleum composition in a petroleum reservoir