hydrocarbon generation migration alteration entrapment and mixing in the central and northern north sea abstract there is little doubt that sediments of upper jurassic to lowermost lower cretaceous age particularly those of the kimmeridge clay formation and its equivalents are the source of the vast bulk of the oil in the central and northern north sea this is true both of oil in conventional mesozoic plays and in tertiary clastic reservoirs the timing of oil generation and migration ranges from the late cretaceous through to the present the oil productivity of the kimmeridge clay formation in the central graben moray firth and south viking graben areas of the north sea is estimated to be in excess of 250 billion barrels of which about 25 is accounted for in accumulations discovered to date there is strong areal differentiation between oil trapped in mesozoic reservoirs as opposed to upper cretaceous chalk and tertiary reservoirs this paper is particularly concerned with hydrocarbons in tertiary reservoirs which have a wide range of compositions and appear to have complex accumulation and degradation histories migration to chalk and younger tertiary reservoirs occurs often through thick shale sequences the evidence for the timing and mechanism of this process is considered and a preferred model for the vertical migration and subsequent lateral migration mixing and degradation is proposed

copper lead zinc and cobalt mineralization in the english lake district classification conditions of formation and genesis the copper lead zinc and minor cobalt mineralization of the english lake district has been classified on the basis of mineralogy spatial distribution and geological setting of the veins and age of mineralization the two major types of mineralization are 1 chalcopyrite pyrite arsenopyrite of lower devonian caledonian age and 2 galena sphalerite of early carboniferous age when the former is closely associated with granite intrusions more complex mineral assemblages are found involving tungsten or molybdenum bearing phases also distinguished from these two major types are later assemblages which probably result from their alteration a later upper carboniferous permian baryte mineralization is also present minor graphite and stibnite deposits and the major haematite mineralization found in the area are incorporated into the classification but are not discussed since they have been dealt with by other authors using data from fluid inclusions and experimental data on particular mineral assemblages occurring in the major types of mineralization estimates have been made of the temperatures and compositions of the ore forming fluids the lower devonian veins formed at temperatures in the range of 350 200 c with typical a s 2 values of 10 10 l0 16 atm and a o 2 of 10 25 10 45 atm or even less the solutions were probably brines of low to moderate salinity 5 10 equiv wt nacl the lower carboniferous veins formed at temperatures in the region of 110 130 c from highly saline brines 23 equiv wt nacl theories regarding the origins of the mineralization are also discussed the distribution of lower devonian veins shows a clear relationship to the underlying composite granite batholith the lower carboniferous galena sphalerite veins show no such relationship but tensional tectonic activity in the early carboniferous may have provided a mechanism for the opening of fissures the source of the mineralizing fluids forming the lower devonian veins may have been the borrowdale volcanic group with contributions from fluids associated with the granites which are also likely to have provided a source of heat the high salinities of the fluids producing the lower carboniferous veins suggest that seawater may have been involved in leaching the metals from basement rocks

trace elements content of galenas and associated minerals in some miocene lead zinc deposits near red sea coast egypt the trace elements content of some m miocene egyptian galenas is given and the method is briefly described the relative enrichment in tl and cd together with the irregular distribution and low ag bi and sb content indicate low temperature conditions of formation the trace content of hemimorphites cerussites wulfenites and other minerals associated with galena shows that they are related to ascending exhalative solutions

geology and metallogenic evolution of the polymetallic deposits of the alcudia valley mineral field eastern sierra morena spain the alcudia valley is intensely mineralized with a large number of pb zn ag cu deposits hosted by neoproterozoic and paleozoic sedimentary rocks five distinct types of deposits have been recognized the most significant mineralizing events were related to the two major phases of deformation hd1 hd2 and granite emplacement during the hercynian orogeny stable isotope and lithogeochemical data demonstrate that the metals as well as sulfur and carbon were sourced from the local sedimentary rocks type a deposits are minor occurrences of strata bound mineralization with zn pb occurring as disseminations and small veins in late ordovician limestone a syndiagenetic origin is suggested by the limited stratigraphic distribution of the mineralization and anomalous base metal contents of late ordovician early silurian black shales overlying the mineralized limestone minor remobilization of disseminated sulfides into joints took place during late diagenesis or early hercynian deformation types b c and d are syntectonic deposits with zn pb type b deposits are strongly deformed veins in hd1 fractures in ordovician rocks a process involving local mobilization of metals by a surface derived fluid is indicated by depleted metal contents of host rocks adjacent to the veins the similarity of 34s values of ore sulfides with disseminated pyrite in the host rocks and the 18oh2o values type c deposits exhibit a greater variation in morphology and degree of deformation compared to other types and are found in both hd1 and hd2 fractures in late ordovician and silurian rocks the stratigraphic distribution and 34s values of sulfides are similar to type a deposits suggesting that localized hydrothermal systems either remobilized type a mineralization or derived metals and sulfur from the same source type d deposits occur in hd2 shear fractures in neoproterozoic rocks the 13c values of carbonate gangue and the similarity of 34s values of ore sulfides and disseminated pyrite in the host rocks indicate that black shales of the neoproterozoic sequence are the major source of sulfur and carbon mixing of a metamorphic fluid with a surface derived fluid is suggested by fluid inclusion and oxygen isotope data type e deposits the most abundant and economically most important type are post tectonic pb zn veins occupying hd2 fractures and are widely distributed through the district in rocks ranging from neoproterozoic to late ordovician mineral assemblages and ag contents of the veins show a zonal relationship with respect to monzogranite outcrops indicating that late hercynian magmatism was the source of heat driving fluid migration through the fracture system fluid inclusion and oxygen isotope data are typical of basinal brines reaction of the fluid with black shales of the neoproterozoic sequence is suggested by 34s values of sulfides and 13c values of carbonates of the main stages of the paragenetic sequence the final paragenetic stage consists of barite calcite and pyrite which may have been deposited during a later hydrothermal event probably in the early triassic

correlative geochemical study of crude oils from southeastern and southern parts of the pannonian basin abstract several crude oils from the southeastern yugoslav part of the pannonian basin are correlated for the first time on the basis of many bulk and specific parameters the investigations involved 15 oils from oil gas fields a and b and oil field c from the banat depression and oil field d from south backa depression and four oils from recently discovered oil shows e the kostolac depression on the basis of structural group analysis and other bulk parameters such as api gravity contents of asphaltenes and sulfur as well as content of n alkanes and pristane to phytane ratio the examined oils are classified into four groups however the distributions and relative abundances of n alkanes isoprenoids c19 c20 steranes tricyclic terpanes and pentacyclic triterpanes obtained by capillary gc and computerized gc ms analysis suggest classification of the examined oils into only two genetic types a d and e1 e4 the oils are of relatively high maturity they are not biodegraded except for both oils from field d and the oil a9

multi stage growth and fluid evolution of a hydrothermal sulphide chimney in the east pacific ridge 1 2 s hydrothermal field constraints from in situ sulphur isotopesx meng and othersin situ sulphur isotopes of hydrothermal sulphides sulphur isotopes can be used as a powerful tool to trace fluid evolution and explore the formation of chimneys to clarify the in situ s isotopic variations of sulphides at the micro scale we analyzed a sulphide chimney collected from the hydrothermal field in the east pacific rise 1 2 s using a sensitive high mass resolution ion micro probe for stable isotopes shrimp si three mineral zones can be identified in the chimney an external outer wall of porous anhydrite and colloform pyrite an internal middle zone of sub euhedral pyrite and massive chalcopyrite and an inner zone of massive pyrite the 34 s v cdt values of the sulphides fall within the range 1 83 7 51 avg 4 05 n 16 and s isotopic values increase from the core 3 09 n 3 to the middle 3 78 n 11 to the edge 6 99 n 2 these results illustrate mineral crystallization processes and the mixing between seawater derived s and magmatic hydrothermal fluids during the growth of the chimney the zones from the edge to the core are characterized by crystal morphologies of colloform anhedral pyrite to massive pyrite with decreasing 34 s values revealing multi stage mineral deposition and sulphur isotopic fractionation in contrast to the increase in 34 s values from the core to the edge in one profile profile a anomalously low 34 s values in fine grained pyrite relative to chalcopyrite in another profile profile b in the middle zone result from s isotopic exchange between seawater so 4 2 and fluid h 2 s due to different fluid seawater mixing possibly caused by variations in permeability and porosity across the chimney

source rock distribution model of the periadriatic region the periadriatic area is a mosaic of geological provinces comprised of spatially and temporally similar tectonic sedimentary cycles tectonic evolution progressed from a triassic early jurassic liassic continental rifting stage on the northern edge of the african craton through an early jurassic middle liassic late cretaceous eocene oceanic rifting stage and passive margin formation to a final continental collision and active margin deformation stage in the late cretaceous eocene to holocene this evolution occurred in a transtensional and transpressional framework resulting from the oblique separation and convergence of the african and european plates extensive shallow water carbonate platform deposits covered large parts of the periadriatic region in the late triassic platform breakup and development of a platform to basin carbonate shelf morphology began in the late triassic and extended through the cretaceous on the basis of this paleogeographic evolution the regional geology of the periadriatic region can be expressed in terms of three main upper triassic paleogene sedimentary sequences the platform sequence sequence a the platform to basin sequence sequence b and the basin sequence sequence c these sequences developed during the initial rifting and subsequent passive margin formation tectonic stages three distinct episodes of source bed deposition can be identified middle upper triassic to lower jurassic liassic organic rich oil prone and mature source beds generally are structurally controlled and are closely associated with transtensional intraplatform basins formed in the early continental rifting stage the principal triassic source basins and most of the surface hydrocarbon indications and economically important oil fields of the periadriatic region are associated with sequence b areas the second episode of organic rich rocks deposition includes both shallow and deeper water facies of jurassic cretaceous age thin immature deep water epioceanic organic rich marls and shales are generally bathymetrically controlled these units are related to basin wide anoxic events in the tethys ocean and its submerged continental margin and are associated with sequence b areas middle upper cretaceous shallow water oil prone facies occur in isolated anoxic basins within carbonate platforms these source sequences are generally thicker and are associated with sequence a areas no major hydrocarbon accumulation can be directly attributed to the jurassic cretaceous epioceanic and intraplatform source rock sequences the third episode of source bed deposition characterizes the final active margin deformation stage and is represented by upper tertiary organic rich terrigenous units mostly gas prone these are essentially associated with turbiditic and flysch sequences of foredeep basins and have generated the greater part of the commercial biogenic gases of the periadriatic region

the potential application of stable isotopes for distinguishing indigenous versus migrated hydrocarbons in a mature shale sandstone sequence abstract bitumens isolated from kokelsumer heide no 1 corehole ruhr area f r g are indicative of the problem of resolving contributions of indigenous versus migrated fluids within a depth interval of approximately 50 m thermally mature shales containing types ii and iii organic matter and a coal seam 1 2 r m are all encountered in addition to interbedded sands that are present in the upper portion of this interval presented here is an approach based on the unique isotopic compositions of indigenous bitumens kerogens and migrating fluids which appears to enable the evaluation of the proportion of extracts which migrated from a source rock stable carbon isotope values of kerogens and of saturate and aromatic fractions of residual bitumens isolated from kokelsumer heide no 1 and reckelsumer heide no 2 corehole samples are used to estimate the relative contributions of the various sources to the bitumens preliminary results indicate that from 10 shale sequences to 100 sandstone sequences of the extractable materials i e bitumens could be characterized as a migrating fluid also stable carbon and nitrogen isotope values for kerogens and coal samples from the kokelsumer heide corehole can be used to verify previous geochemical and microscopic evidence for the existence of distinct kerogen types i and ii in this corehole

origin of lead zinc mineralization in the southern benue trough nigeria fluid inclusion and trace element studies the epigenetic pb zn deposits of the southern benue valley nigeria are localized within cretaceous sediments of an intracontinental rift basin fluid inclusion studies of vein minerals from the abakaliki and ishiagu orebodies show that sphalerite and quartz were deposited at relatively low temperatures 102 175 c with ore fluid salinity mostly in the range of 17 25 equiv wt nacl trace element contents of sphalerite and galena are also consistent with the low temperature of formation and epigenetic origin on the basis of the geotectonic setting the mode of occurrence and fluid inclusion characteristics mineralization is attributed to connate brines set into motion by a high geothermal gradient accompanying continental rifting mineral deposition was caused principally by rapid cooling due either to reaction with wall rocks or mixing with meteoric or descending water of low salinity

biodegradation and possible source of silurian and carboniferous reservoir bitumens from the halahatang sub depression tarim basin nw china abstract five core samples comprising three silurian and two carboniferous bituminous sandstones from the halahatang sub depression tarim basin nw china were studied to determine the nature and extent of microbial alteration and possible source s of the reservoir bitumens a total of twelve ordovician crude oil samples from this sub depression were also examined for comparative purposes co occurrence of a series of 25 norhopanes nhs c 28 c 34 variable amounts of chromatographically unresolved complex mixture ucm and diminished concentrations of n alkanes below ca c 20 in saturated hydrocarbon fractions of the silurian and carboniferous bitumens indicates that they are mixtures of heavily biodegraded oil from a former charge and slightly biodegraded oil from a later charge the presence of c 28 c 34 25 nhs suggests a biodegradation level of at least pm 6 for these bitumen samples nevertheless minor differences in terpane and sterane distributions between the silurian and carboniferous bitumen samples were observed which can be attributed to small variations in biodegradation levels values for the 25 nh ratio peters et al 1996 gammacerane gammacerane c 30 hopane c 28 25 nh c 29 hopane and c 29 25 nh c 30 hopane ratios indicate slightly higher levels of microbial alteration for the silurian bitumens compared to the carboniferous bitumens although caution must be exercised when comparing the biodegradation intensities using molecular parameters the ordovician crude oil samples appear to be more severely biodegraded than the silurian and carboniferous bitumens as evidenced by higher concentrations of tricyclic terpanes relative to hopanes and pregnanes and diasteranes relative to the regular steranes although thermal maturity effects cannot be ruled out geochemical correlation studies were successfully applied based on carbon isotopes and biomarkers including tricyclic terpanes and triaromatic steroids which are highly resistant to severe biodegradation pm 6 bulk isotopic compositions distribution patterns and certain ratios of these biomarkers indicate that the ordovician crude oils and the silurian and carboniferous bitumens originated from a single source they were probably derived from middle upper ordovician source rocks

direct evidence of fluid mixing in the formation of stratabound pb zn ba f mineralisation in the alston block north pennine orefield england the north pennine orefield alston block has produced approximately 4 mt pb 0 3 mt zn 2 1 mt fluorite 1 5 mt barite 1 mt witherite plus a substantial amount of iron ore and copper ore from predominantly vein hosted mineralisation in carboniferous limestones however a significant proportion of this production ca 20 came from stratabound deposits though much is known about the vein mineralisation the relationship between the veins and the stratabound mineralisation is not well understood new petrographic isotopic and fluid inclusion data derived from samples of stratabound mineralisation allow us to present a unified model that addresses the genesis of both the vein and stratabound styles of mineralisation the mineralisation can be considered in terms of three episodes 1 dolomitisation and ankeritisation limestones in the vicinity of the stratabound mineralisation were pervasively dolomitised ankeritised and developed vuggy porosity in the presence of a high salinity brine consistent with fluids derived from adjacent mud and shale filled basins 2 main stage fluorite quartz sulphide mineralisation metasomatism of limestone was accompanied by brecciation dissolution and hydrothermal karstification with modification of the existing pore system the open space was filled with fluorite galena sphalerite quartz and barite formed in response to mixing of low salinity sodic groundwater with high salinity calcic brine with elevated metal contents particularly fe up to 7 000 ppm relative to normal high total dissolved solids sedimentary brines 3 late stage barite mineralisation paragenetically appears to represent either the waning stages or the distal portions of the main hydrothermal circulation system under cooler conditions

survey of hydrothermally generated petroleums from the guaymas basin spreading center abstract the guaymas basin spreading center and hydrothermal system are generating an assortment of petroleum like bitumens by pyrolysis of organic matter in the overlying uncosolidated sediments samples collected by d s v alvin from hydrothermal fields in the southern trough exhibit large variations in the quantities and character of the solvent soluble organic materials various pyrolytic regimes combined with fluctuating thermal gradients and migration velocities may impart a compositional fractionation possibly by differential gaseous solubilization and hydrodynamic alteration of the multi component fluids the data suggest that differential condensation solidification biodegradation and water washing cause selective removal of components at the seabed many hydrothermal oils are unlike normal reservoir petroleums because they contain significant concentrations of polar material due to their rapid genesis and transport and probable solubilization or advection of polar immature components the biomarker distributions confirm high temperature pyrolysis at depth with variable entrainment of less thermally mature bitumens during transport data for shallow core samples from the northern trough indicate that those locations experienced variable influx predominantly volatiles of a low temperature pyrolysate

origin and chemical evolution of formation waters from silurian devonian strata in the illinois basin usa abstract a suite of formation water samples from silurian devonian reservoirs in the illinois basin has been analyzed for major minor and trace element concentrations and for h o and sr isotopic compositions in order to interpret origin of salinity and geochemical evolution of brine compositions in this evaporite and shale poor cratonic basin although chloride concentrations range from 2000 to 137 000 mg l cl br ratios 291 18 are consistent with those of seawater or seawater evaporated short of halite saturation cl br 292 thus during silurian devonian time subaerially evaporated penesaline brine entered the subsurface where it was chemically modified through brine rock interactions cation br ratios and mineralogy of associated strata indicate that na and k were depleted through interaction with clay minerals ca was enriched and mg depleted by dolomitization and sr was enriched as a result of caco3 recrystallization and dolomitization although significant dilution of the modified brine with meteoric water is supported by d 18o covariance original marine waters have not been completely expelled from silurian devonian strata hydrogen and oxygen isotopes exhibit covariant relations with cation and anion concentrations implying that isotopic exchange between h2o and minerals has not greatly influenced the d 18o trend brine 87 sr 86 sr ratios range from 0 7092 to 0 7108 when these ratios are plotted versus 1 sr a two component mixing trend is suggested although sr concentrations have experienced local diagenetic modification a 87sr enriched fluid may have accompanied petroleum migration from new albany shales into adjacent silurian devonian carbonates where it mixed with remnant evaporated seawater this event probably preceded the influx of meteoric water as gdd and 18o are not correlated with sr isotopic compositions of formation waters

geochemical correlation of surface and subsurface oils western greece abstract biodegraded seep oils devoid of n alkanes and most isoprenoid hydrocarbons were successfully correlated with subsurface crude oils in western greece primarily using carbon isotopes and the more microbially resistant tricyclic terpane and aromatic steroid hydrocarbon distributions all the studied oils seem to fit into three major genetic groups which are consistent with the geologic tectonic and geographic settings and are presumably related to different source rock facies group i oils are typical of the abundant oil shows in the epirus province northwest greece minor but consistent biomarker differences necessitated subgrouping of the epirus oils implying derivation from slightly different sources group ii oils are located in the katakolon area northwestern peloponnese group iii oils which are clearly distinct from the other groups are centered in zakynthos island an oil seep at trifos west central greece and a subsurface oil from paxi island because of uncertain correlations are classed intermediate between group i and ii oils an aromatic steroid hydrocarbon measurement modified after mackenzie et al 1981 appears useful in determining the relative maturity of biodegraded and conventional oils and carbonate rock extracts

geochemistry and genesis of hydrothermal au ag pb zn deposits in the hwanggangri mineralized district republic of korea the hwanggangri mineralized district within the ogcheon metamorphic belt of the southern korean peninsula contains more than 60 w mo and cu pb zn au ag bearing metallic ore occurrences and lesser fluorite and talc occurrences related to intrusion of late cretaceous 83 90 ma i type and magnetite series granites fissure filling veins in the district differ in mineralogy with distance from the granites w mo vein deposits are located within or near 500 m the granites whereas cu pb zn vein deposits occur up to 5 km from the granites the geumsil and daehyun au ag pb zn mines are unique and represent the most distal deposits in the district they consist of quartz carbonate veins which contain economic concentrations of gold 3 g t and silver 250 g t in addition to abundant base metal sulfides 6 wt pb zn study of these au ag enriched mines provides a key to understanding ore forming processes in the outer portions of a very large batholith driven hydrothermal circulation system phase equilibria fluid inclusions and stable isotopes indicate that ore deposition was the result of interaction of progressively less evolved meteoric waters with earlier highly evolved meteoric waters early fe sulfide mineralization occurred at temperatures of 380 degrees to 310 degrees c from fluids delta 18 o 10 12ppm whose chemistry was controlled dominantly by reactions with granite and carbonate bearing host rocks main base metal au ag mineralization occurred at temperatures of 250 degrees to 210 degrees c from fluids delta 18 o 6 7ppm whose chemistry changed rapidly as a result of fluid unmixing and cooling late postore carbonates were deposited at temperatures of 250 degrees to 165 degrees c from fluids whose stable isotope compositions delta 18 o 1 4ppm delta d 89ppm and salinities 3 wt nacl reflect increasing meteoric water dominance the most intriguing result of our studies is that gold deposition occurred from fluids whose chemistries were controlled dominantly by granites and wall rocks at temperatures well below magmatic conditions 250 degrees c at great distances from the intrusion the occurrence of increased gold and silver grades in these distal areas bodes well for increased exploration for au ag pb zn deposits at relatively great distance from granite batholiths

s sr and pb isotopic systematics of hydrothermal chimney precipitates from the eastern manus basin western pacific evaluation of magmatic contribution to hydrothermal system 1 sulfur strontium and lead isotopic analyses were performed on chimneys from the hydrothermal vent fields the pacmanus and susu knolls in the eastern manus back arc basin lead isotope composition varies in a narrow range 206pb 204pb 18 75 18 78 207pb 204pb 15 51 15 54 and 208pb 204pb 38 31 38 40 strontium isotopic ratios 87sr 86sr of sulfate minerals vary from 0 7051 to 0 7077 falling between those of seawater 0 7090 and the hydrothermal fluid end member 0 7050 the 34s values of the chimneys are 8 0 to 3 9 for the susu knolls sulfide 1 0 to 4 3 for the pacmanus sulfides and 7 4 to 20 6 for sulfate the susu knolls sulfides have the lowest values so far reported for volcanic hosted massive sulfides from modern seafloor the low 34s values of sulfates and sulfides cannot be explained by a simple seawater circulation model without an additional source of light sulfur this is also supported by the presence of sulfate in hydrothermal end member fluid indicated by sulfur and strontium isotopic ratios in chimney sulfates biogenic sulfur and or oxidation of h2s after boiling are excluded from the possible sources of light sulfur because of the lack of sediment cover and nonequilibrium in isotopic fractionation by boiling at seafloor disproportionation of magmatic so2 introduced into hydrothermal system through preeruptive degassing is the most plausible mechanism for the observed low 34s values the lighter 34s values and more radiogenic lead isotope compositions of the susu knolls samples indicate that magmatic degassing was more vigorous at the susu knolls than pacmanus

origin of methane and light hydrocarbons in natural fluid emissions a key study from greece abstract greece a country characterised by intense seismic and volcanic activity has a complex geodynamic and geological setting that favours the occurrence of many gas manifestations in this study we address the origin of ch 4 and light hydrocarbons in cold and thermal emissions discharging along the hellenic territory also we investigate their possible relationship with the main geochemical composition of the gases and the different geological settings of the sampling sites for this purpose we collected 101 new samples that were analysed for their chemical o 2 n 2 ch 4 co 2 he ne ar h 2 h 2 s and c 2 c 6 hydrocarbons and isotopic r r a 13 c co 2 13 c ch 4 and 2 h ch 4 composition results show that ch 4 presents a wide range of concentrations from 13 c ch 4 from 79 8 to 45 0 vs v pdb 2 h ch 4 from 311 to 301 vs v smow greece was subdivided in four geologic units external eh and internal ih hellenides hellenic hinterland hh and active volcanic arc va and a decreasing ch 4 concentration from eh to hh was recognized whereas ch 4 showed intermediate concentrations in va the ch 4 c 2 h 6 c 3 h 8 ratios from 1 5 to 93 200 coupled with ch 4 isotopic features suggest that the light alkanes derive from different primary sources and are affected by secondary processes an almost exclusive biotic mainly microbial origin of ch 4 can be attributed to eh gases cold gases at ih have mainly a thermogenic origin although some gases connected to continental serpentinization may have an abiogenic origin methane in gases bubbling in thermal waters of ih hh and va and fumarolic gases of the va seem to have an abiogenic origin although their chemical and isotopic characteristics may have been produced by secondary oxidation of thermogenic ch 4 a process that in some of the sampled gases causes extremely positive isotopic values 13 c ch 4 up to 45 0 vs v pdb and 2 h ch 4 up to 301 vs v smow

sedimentology geochemistry and reservoir potential of the organic rich qusaiba shale tabuk basin nw saudi arabia abstract the qusaiba shale formation of the qalibah group is the most prolific source rock for the paleozoic petroleum system in saudi arabia and is recently considered as a potential unconventional shale gas reservoir detailed sedimentological petrographical and geochemical analyses were undertaken on an 31 m thick outcrop of this organic rich shale exposed in the northwest of tayma city nw of saudi arabia to provide a better understanding of the vertical and lateral lithofacies variations and the effects of such variations on reservoir properties x ray diffraction analysis reveals that clay minerals average 50 and quartz average 28 dominate the bulk mineralogical composition while k feldspar plagioclase and pyrite occur as common to minor components in the analyzed samples an integration of the sedimentological description petrography and mineralogical composition allows the subdivision of the investigated outcrop section into six lithofacies these are laminated organic rich shale graptolitic concretion massive organic rich shale organic lean shale siltstone shale interbedded and cross stratified siltstone sandstone lithofacies toc content in the laminated and massive organic rich shale lithofacies ranges between 0 5 and 6 1 wt average 2 52 wt then it decreases upward 0 04 0 35 wt average 0 18 wt in the overlying organic lean shale and siltstone lithofacies trace elements cu mo as ni co u and v show positive excursions in the lowermost 20 m of the organic rich dark grey shale interval and display abrupt depletions at the contact with overlying organic lean shale the enrichment factors of these trace elements are characterized by similar distribution patterns as their measured concentrations like the elements these factors also exhibit a significant depletion at the contact between the organic rich shale and the overlying organic lean shale out of all the redox indices v v cr v v ni th u and mo s toc were found to best distinguish between the organic rich and the overlying organic lean intervals the laminated organic rich shale lithofacies indicate deposition of hemipelagic sediments by a relatively low energy quiet anoxic bottom water most likely in a sulfidic conditions that were associated with a strongly restricted bottom water mass circulation at the time of its deposition this restricted hydrographic condition was likely enhanced in the study area due to the paleotopography that was created by the deglaciation of the early silurian time the toc richness common occurrence of pyrite and high enrichment of redox elements mo u and v in the organic rich shale intervals support the existence of anoxic bottom water at the time of deposition the abrupt decrease of the toc and the redox sensitive elements and their associated indices from the underlying organic rich lithofacies to the overlying organic lean shale lithofacies is likely due to a gradual increase in oxygen level this improved bottom water oxygenation condition might have led to a reduction in organic productivity and limited organic matter preservation in the organic lean shale lithofacies the graptolitic concretion lithofacies found in the sequence refers to an in situ syngenetic to early diagenetic origin formed close to the sediment water layer when there was little or no deposition or at periods characterized by low sedimentation rates the siltstone fine sandstone lithofacies in the topmost part of the studied section is interpreted to indicate the dominance of high energy and highly oxygenated shallow bottom water conditions during deposition probably in a middle to inner shelf depositional settings the kerogen in qs is a mixture of type iii gas prone and type iv inert kerogen tmax values with an average of 430 c and vro values average 0 58 calculated from the tmax assigned the studied section as immature qualitative evaluation of porosity allows the identification of three different types of porosity including inorganic porosity organic porosity and natural fracture porosity although the ductile clay minerals are the most abundant minerals in the lower part of the studied qs average 56 the brittle minerals quartz feldspar and pyrite form an average of 42 and exhibit a uniform distribution of brittleness in the organic rich interval

oil source rock correlation in the tempoku basin of northern hokkaido japan abstract geochemical correlation studies of seven oils and source rocks from the onshore tempoku basin of northern hokkaido were carried out low sulfur high wax and high pristane phytane ratios of the oils suggest that they were generated mainly from nonmarine source rocks source rock evaluation and hydrous pyrolysis data show that coals and coaly shales in the paleogene haboro formation and cretaceous hakobuchi group have oil generating potential these nonmarine source rocks are correlated as the major source of the tempoku oils using sterane and triterpane distributions and carbon isotope compositions correlation studies also suggest a minor contribution from marine source rocks of the neogene onishibetsu or paleogene magaribuchi formations to the oils of the yuchi and wakkanai fields located in the western part of the basin

hydrothermal mixing carbonate dissolution and sulfide precipitation in mississippi valley type deposits a large number of mississippi valley type mvt deposits are located within dissolution zones in carbonate host rocks some genetic models propose the existence of cavities generated by an earlier event such as a shallow karstification that were subsequently filled with hydrothermal minerals alternative models propose carbonate dissolution caused by the simultaneous precipitation of sulfides these models fail to explain either the deep geological setting of the cavities or the observational features which suggest that the dissolution of carbonates and the precipitation of minerals filling the cavities are not strictly coeval we present a genetic model inspired by the textural characteristics of mvt deposits that accounts for both the dissolution of carbonate and precipitation of sulfides and later carbonates in variable volumes the model is based on the mixing of two hydrothermal fluids with a different chemistry depending on the proportion of the end members the mixture dissolves and precipitates carbonates even though the two mixing solutions are both independently saturated in carbonates we perform reactive transport simulations of mixing of a regional groundwater and brine ascending through a fracture both saturated in calcite but with different overall chemistries ca and carbonate concentrations ph etc as a result of the intrinsic effects of chemical mixing a carbonate dissolution zone which is enhanced by acid brines appears above the fracture and another zone of calcite precipitation builds up between the cavity and the surrounding rock sulfide forms near the fracture and occupies a volume smaller than the cavity a decline of the fluid flux in the fracture would cause the precipitation of calcite within the previously formed cavities therefore dissolution of carbonate host rock sulfide precipitation within the forming cavity and later filling by carbonates may be part of the same overall process of mixing of fluids in the carbonate host rock

gallium germanium indium and other trace and minor elements in sphalerite as a function of deposit type a meta analysis abstract while a significant amount of analytical data on trace and minor element concentrations in sphalerite has been collected over the last six decades no meta analysis of this data has ever been conducted in this study the results of such an analysis are presented while the study focusses on ga ge and in data for six other elements ag cd co cu fe and mn was also included the results show that there are systematic statistically significant differences in the mean concentrations of fe ga ge in and mn in sphalerite from different deposit types while cd and cu concentrations show no such differences and ag and co concentrations are only significantly different for vein type deposits a principal component analysis demonstrates that the differences between deposit types are approximately one dimensional being expressible in terms of a single number this number correlates strongly with the homogenisation temperature of fluid inclusions r 2 0 82 p 16 it may be expressed as follows pc 1 ln c ga 0 22 c ge 0 22 c fe 0 37 c mn 0 20 c in 0 11 with ga ge in and mn concentrations in ppm and fe concentration in wt the relationship is sufficiently strong to be used as a geothermometer ggimfis the empirical relationship between pc 1 and the homogenisation temperature t is t c 54 4 7 3 pc 1 208 10 our results indicate a strong control of sphalerite chemistry by fluid temperature particularly for the concentrations of ga r 2 0 40 ge r 2 0 65 fe r 2 0 30 and mn r 2 0 60 and to a lesser degree in r 2 0 10 the concentrations of ag cd co and cu appear to be independent of temperature as a consequence of the strong temperature control on pc 1 metamorphic overprinting of pb zn deposits even by lower greenschist facies events may lead to significant changes in sphalerite composition namely a relative decrease in ga and ge concentrations and increase in fe mn and to a lesser degree in concentrations the closure temperature of sphalerite in regional metamorphic events appears to be around 310 50 c such that higher grade events will not be reflected in its composition factors other than temperature such as differences in fluid salinity or source rock composition do not appear to be responsible for differences between deposit types but rather appear to cause differences between individual deposits particularly the cu activity in ore forming systems appears to have a strong influence on in concentrations in sphalerite the observed trends in sphalerite compositions provide a useful tool for future studies of different types of pb zn deposits as well as for mineral exploration they should be particularly relevant for the identification of new resources of ga ge and in

geochemical effects of primary migration of petroleum in kimmeridge source rocks from brae field area north sea ii molecular composition of alkylated naphthalenes phenanthrenes benzo and dibenzothiophenes abstract variations with depth in the quantitative distributions of di and tricyclic alkylaromatic hydrocarbons and sulfur heterocycles determined for a total of thirty two core samples from two thick shale intervals and thirteen thin interbedded shale layers of the upper jurassic age kimmeridge clay formation brae field area north sea reveal in part the effects of depletion with hydrocarbon expulsion trends of increasing depletion with approach to the nearest shale sandstone contacts as documented by a decrease in carbon normalized yields are more distinctive for the alkylnaphthalenes as compared to the alkylphenanthrenes and alkyldibenzothiophenes but less drastic than previously observed for long chain alkanes cf part i leythaeuser et al 1988 lowest yields consistently were encountered at the outermost 1 2 metres of the thick shale intervals and for the thin shale layers where the relative expulsion efficiencies were much higher for c15 to c30n alkanes 80 95 than for c2 and c3 alkylnaphthalenes 30 40 in contrast c2 and c3 alkylbenzothiophene yields were higher in these shale portions than further inside the thick shale which is interpreted to result from a post expulsion selective replenishment from the adjacent oil accumulation expulsion was not associated with any detectable fractionation among c1 and c3 alkylnaphthalenes or c1 and c2 alkylphenanthrenes as evidenced by a mass balance approach and concentration ratios of individual alkylaromatic isomers commonly used as maturity indicators based on a reconstruction of the quantitative distributions of aromatic hydrocarbons and sulfur aromatics expelled from thin shale layers from early mature through to mature stages of thermal evolution it was verified that the methylphenanthrene index mpi 1 and methyldibenzothiophene ratio mdr of the expelled oil reflects the average of the maturity levels during which the source rock has expelled petroleum

characteristics and petroleum origin of the carboniferous volcanic rock reservoirs in the shixi bulge of junggar basin western china abstract shixi bulge of the central junggar basin in western china is a unique region that provides insight into the geological and geochemical characteristics of large scale petroleum reservoirs in volcanic rocks of the western central asian orogenic belt carboniferous volcanic rocks in the shixi bulge mainly consist of striped lava and agglomerate as well as breccia lava and tight tuff volcanic rocks differ in porosity and permeability striped lava exhibits the highest porosity average 14 2 but the lowest permeability average 0 67 10 15 m among the rock types primary gas pores are widely developed and mostly filled secondary dissolution pores and fractures are two major reservoir storage spaces capillary pressure curves suggest the existence of four pore structure types of reservoir rocks several factors namely lithology pore structure and various diagenesis govern the physical properties of volcanic rocks the oil is characterized by a high concentration of tricyclic terpane a terpane distribution of c 23 21 c 20 and sterane distributions of c 27 28 29 and c 27 c 28 29 oil and gas geochemistry revealed that the oil is a mixture derived primarily from p 2 w source rock and secondarily from p 1 j source rock in the sag west of pen 1 well the gases are likely gas mixtures of humic and sapropelic organic origins with the sapropelic gas type dominant in the mixture the gas mixture is most likely cracked from kerogen rather than oils the carboniferous volcanic reservoirs in shixi bulge share some unique characteristics that may provide useful insights into the various roles of different volcanic reservoir types in old volcanic provinces the presence of these reservoirs will undoubtedly encourage future petroleum exploration in volcanic rocks up to the deep parts of sedimentary basins

tide influenced acidic hydrothermal system offshore ne taiwan elemental sulfur and hydrogen sulfide emitted offshore of northeastern taiwan known to local fishermen for generations but never studied until recently are found to have originated from a cluster of shallow 92 with small amounts of h2s helium isotopic ratios 7 5 times that of air indicate that these gases originate from the mantle high temperature hydrothermal fluids have measured temperatures of 78 116 degrees c and ph 25 degrees c values as low as 1 52 likely the lowest to be found in world records low temperature vents 30 65 degrees c have higher ph values continuous temperature records from one vent show a close correlation with diumal tides suggesting rapid circulation of the hydrothermal fluids c 2005 elsevier b v all rights reserved

structure and evolution of the northern red sea combined analyses of new geophysical data in the northern red sea with data from the gulf of suez and the gulf of aqaba dead sea rift strongly suggest that the development of the red sea took place in three stages 1 a gulf of suez stage in the oligocene accompanied by thinning of the continental lithosphere and the formation of an early red sea gulf of suez graben 2 an early dead sea stage with slow seafloor spreading from 25 to 15 myr accompanied by 62km of shear along the aqaba dead sea transform and 3 a recent dead sea stage with slow seafloor spreading from 4 5 to 0 myr accompanied by 45km of shear along the aqaba dead sea transform

sr nd and pb isotope constraints on the formation of the metalliferous sediments in the nereus deep red sea previous chemical analyses of sediments from nereus deep core 412 located in the northern part of the red sea at about 23 20 n have demonstrated the occurrence of v rich authigenic magnetites associated with fe zn and cu sulphides mostly located at the bottom of the core the evolutionary stage of nereus deep is intermediate between that of the immature shaban deep and the more evolved atlantis ii deep previous studies have proposed either morb basalts by analogy with east pacific rise sulphide deposits or sediments as possible sources of the metals in the red sea metalliferous sediments sr nd and pb isotope systematics observed at ten levels in nereus core 412 lead us to distinguish three types of sediments 1 with predominantly basaltic fragments associated with loose titanomagnetite crystals 0 70413 87sr86sr 0 70622 0 51271 143nd144nd 0 51300 18 618 206pb204pb 18 673 2 detrital or biogenic sediments with a continental isotopic imprint 0 70938 87sr86sr 0 71323 0 51242 143nd144nd 0 51262 18 848 206pb204pb 18 890 and 3 v rich metalliferous sediments 0 70872 87sr86sr 0 70895 0 51260 143nd144nd 0 51274 18 717 206pb204pb 18 851 on sr nd and pb pb isotope diagrams this last group of sediments defines a field located between the fields of the first two groups our data suggest that the sr nd and pb in the studied metalliferous sediments were derived from overlying sedimentary beds in which the two main constituent detrital components show very distinct origins red sea morb and continental arabo nubian shield these data clearly support a model of convective circulation within the nereus deep sedimentary pile this model involves leaching two main components from the upper sedimentary layers of the core and a downward circulation of a hot fluid promoting the growth of v rich magnetites and fe zn and cu sulphides when the fluid cooled by mixing with the pore water of sediments from the lower part of the core a driving force represented by magmatic activity located near the 412 core in the nereus deep is required to explain the presence of hot convective fluids these data also suggest that for sedimented ridges the isotopic imprint of a basaltic source in metalliferous sediments or a hydrothermal ore deposit may result by interaction of a hot fluid with detrital sediments that are enriched in basaltic clasts and loose magmatic crystals

metamorphic origin of the coeur d alene base and precious metal veins in the belt basin idaho and montana fluid inclusions geochronology and field studies show that the world class base and precious metal veins of the coeur d alene district idaho and montana are the product of deformation coupled with regional metamorphism of the belt basin around 850 ma fluid inclusion data show that the mineralizing solutions were complex co2 ch4 cnhm n2 h2o nacl fluids that changed in composition from ch4 cnhm rich fluids in the older zn rich veins to co2 rich fluids in the younger ag rich veins ore deposition occurred at about 250 to 350 c and at pressures in excess of 1 kbar

evolution and source of ore fluids in the stringer system hellyer vhms deposit tasmania australia evidence from fluid inclusion microthermometry and geochemistry the hellyer deposit is a classic large tonnage high grade mound style volcanic hosted massive sulphide vhms deposit in the cambrian mt read volcanic belt of western tasmania in the footwall directly underlying the deposit there is an extensively altered pipe which cootains a well developed and preserved stringer zone the vein paragenesis at hellyer indicates that premineralization stage i veins consist entirely of quartz and occur throughout the alteration pipe the synmineralization stage 2 veins are the most abundant veins in the stringer zone and consist of three sub stages stage 2a veins of crustiform quartz pyrite and carbonate with minor amounts of chalcopyrite sphalerite and galena stage 2b veins with abundant base metal sulphides minor quartz carbonate and barite gangue and stage 2c veins of coarsely crystalline barite with variable amounts of pyrite sphalerite galena and carbonate stages 3 6 veins are postmineralization veins and are related to the devonian tabberabberan orogeny textural petrographic and microthermometric investigations of fluid inclusions in the hellyer stringer system indicate that type i primary liquid vapour inclusions occur along growth planes of crustiform quartz crystals or within colour banding of zoned sphalerite these inclusions are 10 15 m in size and yielded homnogenisation temperatures of 170 220 c in early 2a veins 165 322 c in main stage 2b veins and 190 256 c io late stage 2c veins these data suggest a waxing and waning thermal history however the average salinity remained between 8 11 naci equiv wt in all stage 2 veins chalcopyrite bearing primary fluid inclusions have been recognised in the base metal rich stage 28 veins no evidence for presence of co2 e g formation of clathrates was recorded by rnicrothermometry however laser raman spectroscopic lrs analysis indicates the presence of co2 1 mole in the stage 2b veins and no detectable co2 in 2a and 2c vein stages semi quantitative sem wds microprobe analyses of fluid inclusion decrepitates indicate that the hellyer ore fluid was enriched in potassium and calcium but depleted in magnesium relative to seawater pixe microanalysis of fluid inclusions in quartz indicates that the stage 2b ore fluids have a significantly higher base metal concentration compared to the stage 2a veins the postmineralization stage 4 veins have a variable but lower base metal content in this study there was no fluid inclusion evidence of boiling cation composition higher salinities relative to seawater and the presence of co2 suggest that recycled seawater alone cannot be the sole source of the ore fluids this interpretation is in agreement with previous isotopic studies in the hellyer stringer system although direct input of bulk ore constituents from a magma chamber cannot be demonstrated from the present fluid inclusion data such a contribution of ore fluids from a magmatic source cannot be ruled out the possible input from the magmatic source may have occurred during the base metal rich stage 2b vein formation characterised by the intensifying temperature of deposition higher base metals and co2 contents

geological features and origin of the huize carbonate hosted zn pb ag district yunnan south china abstract the huize zn pb ag district in the sichuan yunnan guizhou zn pb ag metallogenic region contains significant high grade zn pb ag deposits the total metal reserve of zn and pb exceeds 5 mt the district has the following geological characteristics 1 high ore grade zn pb 25 wt 2 enrichment in ag and a range of other trace elements ge in ga cd and tl with galena sphalerite and pyrite being the major carriers of ag ge cd and tl 3 ore distribution controlled by both structural and lithological features 4 simple and limited wall rock alteration 5 mineral zonation within the orebodies and 6 the presence of evaporite layers in the ore hosting wall rocks of the early carboniferous baizuo formation and the underlying basement fluid inclusion and isotope geochemical data indicate that the ore fluid has homogenisation temperatures of 165 220 c and salinities of 6 6 12 wt nacl equiv and that the ore forming fluids and metals were predominantly derived from the kunyang group basement rocks and the evaporite bearing rocks of the cover strata ores were deposited along favourable specific ore controlling structures the new laboratory and field studies indicate that the huize zn pb ag district is not a carbonate replacement deposit containing massive sulphides but rather the deposits can be designated as deformed carbonate hosted mvt type deposits detailed study of the deposits has provided new clues to the localisation of concealed orebodies in the huize zn pb ag district and of the potential for similar carbonate hosted sulphide deposits elsewhere in ne yunnan province as well as the sichuan yunnan guizhou zn pb ag metallogenic region

composition and evolution of ore fluids in a magmatic hydrothermal skarn deposit the chemistry of brine vapor and low salinity fluid inclusions measured by proton induced x ray emission from the bismark skarn deposit mexico is consistent with an evolving magmatic hydrothermal system with no evidence for external fluid inputs the results support a model that invokes early phase separation of magmatic fluids into brine and vapor two phase field at high temperature and lithostatic pressure followed by the entrapment of a low salinity magmatic fluid one phase field at lower temperature and hydrostatic pressure the early brine and vapor inclusions contain high pb and zn concentrations and low cu however the vapor contains significantly more cu than the brine and was likely transported as a sulfur complex the fluid phase changes observed and behavior of cu are comparable to those of porphyry cu systems the later low salinity fluid at bismark represents a distinct pulse of magmatic fluid with a high k ca ratio in which base metals including cu were transported by chloride complexes paragenetic relationships and variations in the relative concentrations of cu pb and zn suggest that this fluid was primarily responsible for ore deposition the relative cu pb and zn concentrations in fluid inclusions at bismark are consistent with those measured from base metal ores in high temperature carbonate replacement deposits throughout mexico and suggest that the bulk metal budget of these deposits is primarily controlled by magmatic hydrothermal fluids deficient in cu

origin and secondary processes in petroleum in the eastern part of the polish outer carpathians a geochemical study of crude oil and natural gas from producing wells and seeps within the lower cretaceous oligocene sandstone reservoirs of the most eastern part of the polish outer carpathians was conducted for the evaluation of their origin migration pathways and the effects of secondary processes biodegradation water washing and evaporative fractionation the petroleum was generated from mixed marine terrigenous organic matter type ii iii kerogen occurring mostly in oligocene menilite beds in the silesian and skole nappes shales within upper cretaceous palaeocene istebna and lower cretaceous ve ovice lgota and spas beds are considered as an additional source of hydrocarbons mainly gaseous biodegradation processes were recorded in numerous oils especially occurring in seeps but the extent of these processes is not severe because steranes and terpanes were not affected all oils are more or less water washed while the evaporative fractionation processes are developed only on a minimal scale the natural gases are primarily of thermogenic origin usually co genetic with oil and often contain components of secondary microbial degradation of both oil and natural gas 13c enriched co2 and 13c depleted ch4 gases with the highest microbial methane contribution have been recorded in petroleum accumulated in dwernik and odyna fields

salt formation associated with sub surface boiling and supercritical water abstract laboratory experiments have demonstrated that supercritical water has extremely low solubility for normal sea salts this fact opens up the possibility for the precipitation of salt from seawater that circulates in faults and fractures close to a heat source in tectonically active basins typically extensional pre rifts and rift settings seawater attains supercritical conditions at depths exceeding 2800 m corresponding to a pressure of 300 bars and temperatures above 405 c salts may also precipitate by the boiling of seawater in sub surface or submarine settings this is demonstrated by a simple laboratory experiment the theoretical basis for the precipitation of salts from seawater attaining supercritical condition has been examined by molecular modelling these processes of salt precipitation constitute a new approach to the geological understanding of salt deposits and two regions are selected to examine whether salt may have deposited under such hydrothermal conditions today the atlantis ii deep in the red sea marine setting and lake asale dallol ethiopia continental setting

the movement of hydrocarbons in shales oil and gas hydrocarbons are formed at temperatures above 100 c by the chemical breakdown of the organic remains of dead organisms preserved in fine grained rocks called source rocks the organic remains are known as kerogen if enough hydrocarbons are formed some are expelled from the source rocks we have analysed kimmeridge clay upper jurassic shales from the north sea which are currently expelling hydrocarbons into adjacent sandstones the results could be explained if most expulsion occurs by the pressure driven flow of a discrete hydrocarbon phase through the pores of shales and into the pores of the sandstones as suggested previously1 in addition capillary forces seem to increase the efficiency of expulsion close to the interfaces between the shales and interbedded sandstones it appears that molecular diffusion of hydrocarbons with less than about ten carbon atoms alters the composition of the hydrocarbon fluids remaining in and expelled from the shales

hydrothermal fluid migration and brine pool formation in the red sea the atlantis ii deep numerical heat and fluid flow simulations of the atlantis ii deep in the red sea were conducted to investigate the development migration and discharge of hydrothermal fluids into a submarine depression and determine the conditions necessary to form a brine pool high salinity fluids are predicted to form by leaching miocene evaporates migrate and convect within young oceanic crust and discharge onto the seafloor predicted fluid discharge temperatures t max 301 c discharge fluid velocities v max 0 09 m s and salinities s max 21 wt increase over time and reach values comparable to modern seafloor observations established convection patterns and discharge behavior are robust and are not greatly affected by geometry of rock property changes modeling results were used to calculate the minimum conditions for hydrothermal fluids from a developing hydrothermal system to mix with seawater reverse buoyancy and begin to form a brine pool in a submarine depression under conditions encountered on the seafloor t 25 300 c s 5 25 wt fluid mixtures predicted to pond on the seafloor range from late in the mixing process 99 at low temperatures t 26 c to much earlier 36 mixing at higher temperatures t 94 c a model of brine pool evolution is proposed that describes the processes and conditions necessary to initiate brine pool formation and compares formation conditions with accumulated ore material in the atlantis ii deep and other locations

hydrothermal petroleum in mineralized mounds at the seabed of guaymas basin petroleum has been dredged from an active hydrothermal mound area in the southern rift of guaymas basin gulf of california this organic matter is composed of gasoline range aliphatic and aromatic hydrocarbons and predominantly residual polar asphaltic material the aliphatic hydrocarbons of two bitumen samples have very different boiling range and composition both samples contain polynuclear aromatic hydrocarbons and olefins which indicate formation at pyrolytic temperatures the overall compositional data indicate an origin from biological detritus by thermal alteration and rapid quenching by hydrothermal removal followed by condensation at the seabed

constraints on origin and evolution of red sea brines from helium and argon isotopes brines from three depressions along the axis of the red sea the atlantis ii the discovery and the kebrit deep were sampled and analyzed for helium and argon isotopes we identified two principally different geochemical fingerprints that reflect the geological setting of the deeps the atlantis ii and the discovery brines originating from locations in the central red sea show 4 he concentrations up to 1 2u10 35 cm 3 stp g 31 and a 3 he 4 he ratio of 1 27u10 35 the morb like 3 he 4 he ratio is typical of an active hydrothermal vent system and clearly indicates a mantle origin of the helium component within the brines 40 ar 36 ar ratios are as high as 305 implying that mantle derived 40 ar excesses of up to 3 of the total argon concentration are present in the brines and transported along with the mantle helium signal the mean 4 he 40 ar excess ratio of 2 1 is in agreement with the theoretical mantle production ratio in the kebrit deep located in the northern red sea we found a helium excess of 5 7u10 37 cm 3 stp g 31 the low 3 he 4 he ratio of 1u10 36 points to a predominantly radiogenic source of the helium excess with only a minor mantle contribution of approximately 9 we propose a new scenario assuming that the kebrit brine accumulates a diffusive helium flux that migrates from deeper sedimentary or crustal horizons in contrast to the atlantis ii and discovery deep the kebrit brine shows no sign of an active hydrothermal input fl 2001 elsevier science b v all rights reserved

thermobarometry of the bleikvassli zn pb cu deposit nordland norway the bleikvassli massive sulfide ore deposit is hosted by proterozoic pelitic quartzofeldspathic and amphibolitic rocks of the uppermost allochthon of the scandinavian caledonides staurolite garnet biotite and kyanite staurolite biotite assemblages indicate that metamorphism reached the kyanite zone of the amphibolite facies geothermobarometry was conducted on rocks in and around the deposit using a variety of silicate and sulfide calibrations temperature determinations are most reliant on the garnet biotite exchange reaction with analyses obtained from 259 garnet rims and adjacent biotite results from nine calibrations of the garnet biotite geothermometer are considered but compositional limitations of many calibrations involving high ca and mn contents in garnet and alvi and ti in biotite make many of the coexisting mineral pairs unsuitable average temperatures calculated from the two calibrations that most closely address the garnet biotite compositions observed at bleikvassli are 584 c 49 c and 570 c 40 c the application of two calibrations of the garnet staurolite geothermometer on a limited number of samples yields 581 c 2 c and 589 c 12 c assuming a h2o 0 84 based upon calculations of the modal proportions of gaseous species pressure determinations are less constrained phengite and plagioclase biotite garnet muscovite geobarometers give average pressures of approximately 5 0 kbar and 8 5 1 2 kbar respectively pressures obtained from the sphalerite hexagonal pyrrhotite pyrite barometer average 7 7 1 0 kbar in consideration of these results the peak metamorphic conditions at the bleikvassli deposit are estimated to be 580 c and 8 kbar

volcanism and metallogenesis of axial and off axial structures on the east pacific rise near 13 degrees n a fast spreading segment 12 cm yr super 1 of the east pacific rise near 12 degrees 50 n explored in detail by surface ship and manned submersible displays intense hydrothermal activity the rise crest about 1 500 m in width with a regional depth of 2 600 m is occupied at its center by an axial graben 1 3 titania alkali enriched olivine ti k basalts with high tio 2 1 4 and high alkali content na 2 o 3 0 k 2 o 0 3 occur on the southeastern seamount the fractionated tholeiites are believed to have been derived from primitive melts during differentiation which took place within a magma reservoir asymmetrical with respect to the axis of the graben which supplied both axial and off axial lava flows the ti k enriched basalts are believed to have been produced from an alkali enriched magmatic source

sea floor massive sulfide deposits from 21 degrees n east pacific rise juan de fuca ridge and galapagos rift bulk chemical composition and economic implications

characteristics and origin of carbon isotopes of n alkanes in crude oils from the western pearl river mouth basin south china sea abstract the quantitative characterization of carbon isotopes of n alkanes is commonly carried out in organic geochemical studies possible controls on carbon isotopes include source organic matter maturity fractionation during oil expulsion and migration and the mixing of different oils in this study of the origin of crude oils in the western pearl river mouth basin the influences of all of these factors have been considered in reaching a conclusion carbon isotopes of n alkanes in the crude oils and the extracts of the two effective source rocks the wenchang and enping formations in the basin exhibit clear differences the wenchang source rocks have heavy 13 c values that remain almost constant or become slightly heavier with increasing carbon number the enping source rocks have light 13 c values that become lighter with increasing carbon number two groups of oils in this area were identified based on the carbon isotopes of the n alkanes groupioils are similar to extracts of the wenchang source rocks however the groupiioils are different from both the wenchang and enping source rocks and the carbon isotopic profiles of their n alkanes exhibit a v feature with increasing carbon number the results of artificial thermal maturation experiments indicate that from the early stage to the peak stage of oil generation with easyro between 0 64 and 1 02 the 13 c values of n alkanes in the pyrolysis oils become heavier by about 3 with increasing thermal maturity but the shape of the carbon isotopic profiles are not significantly changed calculated 13 c values of n alkanes in mixed artificial pyrolysis oils indicate that the mixture of oils generated from the same source rocks with different maturities could not change the carbon isotopic profile of the n alkanes however a mixing of the wenchang and enping oils could give the v feature in the profiles similar to the groupiioils in this area the groupiioils appear to be mixed wenchang and enping oils the latter being the dominant component in the mixture we conclude that the source organic matter and the degree of mixing are the main factors controlling the carbon isotopic characteristics of n alkanes in crude oils in the western pearl river mouth basin

the impact of severe biodegradation on the molecular and stable c h n s isotopic compositions of oils in the alberta basin canada abstract although the effects of biodegradation on the composition and physical properties of crude oil have been well studied effects of in reservoir petroleum biodegradation on molecular and isotopic compositions of crude oils are not yet clearly understood the alberta basin in western canada is one of the world s largest petroleum accumulations and constitutes an ideal example of a natural suite of sequentially biodegraded oils the basin hosts moderately to severely biodegraded petroleum regionally distributed and in single more or less continuous oil columns in this study a series of oil samples from the alberta heavy oil and oil sands provinces with varying degrees of biodegradation were analyzed to assess the impact of progressive biodegradation on the molecular and c h n and s isotopic compositions of oils the results of the molecular characterization of the hydrocarbon fraction of the studied oils show that the oils have suffered biodegradation levels from 2 to 10 toward the alberta saskatchewan border on the peters and moldowan scale of biodegradation abbreviated pm 2 to pm 10 and from tens to hundreds on the manco scale within single reservoirs increasing biodegradation was observed from top to bottom of the oil columns at all sites studied the whole oil stable isotopic compositions of the samples varied in the ranges 13 c 31 2 to 29 0 2 h 147 to 133 15 n 0 3 4 7 and 34 s 0 4 6 4 the maximum differences between values of samples within single oil columns were 13 c 1 4 2 h 7 15 n 1 7 and 34 s 1 0 regional variations in the isotopic compositions of oil samples from different wells averaged values from top to bottom were 1 2 for 13 c 12 for 2 h 4 1 for 15 n and 5 5 for 34 s and hence generally significantly larger variations were seen than variations observed within single oil columns especially for n and s it appears that even severe levels of biodegradation do not cause observable systematic variations in carbon nitrogen or sulfur isotope composition of whole oils this indicates that sulfur and nitrogen isotopic compositions may be used in very degraded oils as indicators for oil charge from different source rock facies

sedimentary hosted polymetallic massive sulfide deposits of the kebrit and shaban deeps red sea massive sulfides recovered from the kebrit deep carbonaceous sedimentary succession represent black smoker fragments novel to any red sea brine pool deposit chimneys which were also observed in situ near the seawater brine interface of the kebrit deep pool are primarily comprised of fe zn and pb bearing phases and are often tar and asphalt impregnated cu sulfides are virtually absent from parageneses contrasting rift related smoker and red sea metalliferous sediment deposits concentration of nickel in discrete bravoite points to a basalt seawater leaching process as a source for most metals the sedimentary package which probably hosts cu mineralization in lower stockworks of the smoker deposit is considered the major source of lead prevention of boiling of hydrothermal fluids passing through a succession of organic rich carbonate and clay horizons prior to discharge is essential for smoker formation shaban deep sedimentary hosted massive sulfides are less frequent with pyrite being the dominant ore mineral sulfur isotope data indicate both high temperature inorganic as well as biogenic sulfate seawater and or evaporite reduction in sulfide forming processes cogenetic sulfates formed from residual bacteriogenically reduced seawater sulfate rather low sulfide sulfate precipitation temperatures of 110 130 c for the kebrit brine pool and 100 c for shaban deep massive sulfides are evident

geology isotopes and geochronology of the caijiaping pb zn deposit in the north wuyi area south china implications for petrogenesis and metallogenesis abstract the caijiaping pb zn deposit is a recently discovered subvolcanic hydrothermal deposit in the north wuyi area its mineralization is generally distributed at the contact of rhyolite porphyry and sandstone and in the interlayer crushed zone of early jurassic sandstone sulfide minerals in this deposit mainly consist of abundant sphalerite galena pyrite and chalcopyrite silicification chloritization and sericitization are widely developed and closely related to the pb zn mineralization the 34s values of early dark brown sphalerite marmatite main stage sphalerite and galena 1 1 2 5 average 0 83 suggest that the sulfur was mainly sourced from a magmatic system lead isotope ratios in the sulfide minerals rhyolite porphyry and sandstone are relatively homogeneous 206pb 204pb 17 786 18 612 207pb 204pb 15 504 15 635 208pb 204pb 38 115 38 798 and are compatible with metamorphic rocks of mesoproterozoic zhoutan group wuyi metamorphosed basement early jurassic sandstone deposited in an active continental margin or continental arc setting exhibits low textural maturity and displays geochemical similarities to the zhoutan group the rhyolite porphyry with features of volcanic arc granite also shows an affinity with the zhoutan group sims zircon u pb dating shows that the rhyolite porphyry was emplaced at 156 0 1 2 ma indicating that caijiaping mineralization formed later than 156 ma hf isotope compositions of the rhyolite porphyry ehf t 14 3 to 8 5 average 10 6 imply that it was mainly derived from reworking of ancient crust potassium feldspar selected from felsic veins within the ore cutting f4 fault yields a 40ar 39ar age of 120 0 4 0 ma indicating that the pb zn mineralization formed before 120 ma therefore the age of mineralization is bracketed between 156 and 120 ma combined with regional geological information we propose that the caijiaping mineralization mainly formed from magmatic hydrothermal processes in a regionally extensional setting and the wuyi metamorphosed basement significantly contributed to diagenetic and metallogenic processes in this deposit

punctiform initiation of seafloor spreading in the red sea during transition from a continental to an oceanic rift transition from a continental to an oceanic rift occurs in the red sea by initial emplacement of oceanic crust in regularly spaced hot points which serve as nuclei for axial propagation into segments of oceanic crust accretion and for initiation of seafloor spreading hot points develop above upwelling mantle diapirs caused by density viscosity inversion beneath continental and oceanic rifts

hydrothermal petroleum generation in red sea sediments from the kebrit and shaban deeps abstract petroleum impregnated sediments and massive sulfides have been found in two deeps of the northerns red sea biological marker distributions in extracts and polar fraction degradation products were analyzed in order to elucidate the source of the petroliferous material two organic phases could be distinguished according to their source and maturity the amounts of n alkanes show a marked decrease with depth whereas the concentrations of various branched and cyclic hydrocarbons increase resulting in a humpof unresolvable compounds in a depth as shallow as 300 cm changes in concentrations and distributions of hopanoids in the kebrit deep sediments indicate a rapid increase of maturity with depth the deepest core section 300 cm and the masive sulfide reveal comparable maturation indices typical for mature oils by chemical degradation of the polar fractions a series of c 40 isoprenoids was obtained which reveals a considerable contribution from methanogenic and thermophilic archapbacteria to the immature organic matter the data suggest that petroliferous material ofthermogenic origin migrates through the younger sequences superimposes the autochthonous organic substances in the sediments and furthermore forms asphaltic impregnations in the massive sulfides

origin and migration of oil and natural gas in the western part of the ukrainian outer carpathians geochemical and geological approach abstract we established the generation and migration processes as well as the influence of secondary processes of oil and natural gas accumulated in lower cretaceous oligocene strata of the western part of the ukrainian outer carpathians based on the results of organic geochemical analyses of oil and natural gas related to the geological setting and source organic matter the oligocene menilite beds from the boryslav pokuttya nappe are the main source rock for oil and natural gas accumulated in the fields of the boryslav pokuttya and skiba nappes co sourcing of oils and natural gas accumulated in the skiba nappe in the study area by both menilite and spas beds of this nappe cannot be excluded in some cases e g novoshidnytsya field oil and natural gas originated within the oligocene menilite beds of the boryslav pokuttya nappe migrated through thrusts and fissure zones and accumulated in the lower cretaceous reservoirs of the skiba nappe oil from small vovche field and pohar seep of the krosno nappe was generated by menilite source rocks of this tectonic unit and migrated to the traps sporadically oils underwent secondary processes mainly biodegradation and occasionally water washing hydrocarbon gases and carbon dioxide were generated mainly during low temperature thermogenic processes from type ii kerogen and partly during the microbial co2 reduction process only natural gas from the mala volosyanka oil and gas seep of the krosno nappe was documented to have undergone biodegradation

the geology and genesis of the proterozoic massive sulfide deposit at garpenberg central sweden the garpenberg deposit of central sweden is a metamorphosed strata bound zn pb cu ag sulfide deposit intercalated in an early proterozoic supracrustal sequence of felsic metavolcanics and subordinate metasedimentary rocks which have been folded metamorphosed and intruded by synorogenic granitoids the magmatism is calc alkaline and most of the volcanic activity occurred as explosive submarine volcanism the garpenberg deposit is emplaced at the contact between metasedimentary and metavolcanic rocks and consists of 32 lens shaped orebodies stratiform zn pb cu mineralization is underlain by cu bearing stockwork ore with an extensive alteration zone of quartz phlogopite rocks with minor chlorite cordierite garnet staurolite and andalusite chemically the altered zone is enriched in magnesium iron ore metals manganese and volatiles and is depleted in sodium and calcium the proposed volcanogenic origin related to calc alkaline magmatism is supported by the morphology wall rock alteration and ore mineralogy the similarity of the garpenberg deposit to the archean massive sulfide deposits of canada and the kuroko deposits of japan supports this theory but also reveals possible differences between the compositions of precambrian and phanerozoic seawater dissimilarities in the metal ratios cu pb zn of the different deposits and their associated lithologies suggest differences in their tectonic setting the garpenberg deposit is thought to have formed in an active continental margin setting rather than in an island arc

fe mn hydr oxide carbonate crusts from the kebrit deep red sea precipitation at the seawater brine redoxcline lithified crusts located within the sediment and recovered from the kebrit deep red sea are composed of fe and mn hydr oxides carbonates and sulfides mineralogical and geochemical features of these crusts suggest that they are metalliferous layers lithified by carbonates and formed in the narrow band where the transition zone between the anoxic brine and deep seawater crossed the seafloor carbonates cementing the fe mn hydr oxides precipitated from normal saline seawater at t 20 30 degrees c precipitation of fe mn hydr oxides was superimposed the carbonate precipitation in the transition zone a pumping mechanism involving cyclic fe and mn hydr oxide precipitation redissolution operated through the transition zone and produced an enrichment of a number of elements in the crusts the microbiota played an important role in the geochemical cycle of the elements through the redoxcline and in the mineralogy of the sediments underlying the redoxcline waters diagenetic processes led to formation of bi and ternary carbonates and disulfides c 2006 elsevier b v all rights reserved

phase relations and adiabats in boiling seafloor geothermal systems abstract observations of large salinity variations and vent temperatures in the range of 380 400 c suggest that boiling or two phase separation may be occurring in some seafloor geothermal systems consideration of flow rates and the relatively small differences in density between vapors and liquids at the supercritical pressures at depth in these systems suggests that boiling is occurring under closed system conditions salinity and temperature of boiling vents can be used to estimate the pressure temperature point in the subsurface at which liquid seawater first reached the two phase boundary data are reviewed to construct phase diagrams of coexisting brines and vapors in the two phase region at pressures corresponding to those of the seafloor geothermal systems a method is developed for calculating the enthalpy and entropy of the coexisting mixtures and results are used to construct adiabats from the seafloor to the p t two phase boundary results for seafloor vents discharging at 2300 m below sea level indicate that a 385 c vent is composed of a brine 7 nacl equivalent in equilibrium with a vapor 0 1 nacl brine constitutes 45 by weight of the mixture and the fluid first boiled at approximately 1 km below the seafloor at 415 c 330 bar a 400 c vent is primarily vapor 88 wt 0 044 nacl with a small amount of brine 26 nacl and first boiled at 2 9 km below the seafloor at 500 c 520 bar these results show that adiabatic decompression in the two phase region results in dramatic cooling of the fluid mixture when there is a large fraction of vapor

effects of weathering on biological marker and aromatic hydrocarbon composition of organic matter in phosphoria shale outcrop gc ms analyses were performed on core samples collected from a shale outcrop of the permian phosphoria formation in utah u s a to study effects of weathering on selected biological marker and aromatic phenanthrene hydrocarbon compounds among the biological markers the most important weathering effects are a decrease in 20s 20r diastereomer ratio of the c sub 29 steranes and loss of low molecular weight triaromatic steroids a decrease in the c sub 19 through c sub 22 tricylcic terpanes occurs relative to the total c sub 19 c sub 26 tricyclic fraction pronounced loss of methyl substituted phenanthrenes occurs relative to phenanthrene no major effect on the overall distribution of pentacyclic terpanes is evident

trace elements of indium bearing sphalerite from tin polymetallic deposits in bolivia china and japan a femto second la icpms study abstract indium bearing tin polymetallic base metal deposits in japan toyoha ashio and akenobe china dulong and dachang and bolivia potosi huari huari bolivar and porco were studied using femto second laser ablation icpms fsla icpms and epma analyses for major and minor elements in sphalerite paying special attention to in concentrations sphalerite is a principal mineral in these tin polymetallic deposits and a broad range of in concentration is measured in the ores there are distinct differences in mode of occurrence of the sphalerite and the distribution of in the highest in concentration up to 18 wt occur as a zn in mineral within black sphalerite zones in an oscillatory zoned sphalerite from the huari huari deposits additionally jamesonite from the huari huari deposit also contains anomalous in values ranging from several hundreds to thousands g g sphalerite from the toyoha and the other bolivian deposits are characterized by oscillatory and chemical zoning whereas those from akenobe and the chinese deposits are represented by homogeneous distribution of in the 1000in zn values of sphalerite are in good agreement with those of the ore grade for each of the selected tin polymetallic deposits indicating that sphalerite is the principal host of in the in bearing sphalerite principally involves the combined coupled substitutions 2zn2 cu in3 3zn2 cu ag sn4 and 3zn2 2cu sn4 the first of these is apparent in sphalerite from huari huari and bolivar whereas the second is prominent in sphalerite from toyoha ashio potosi porco and dachang akenobe and dulong sphalerite features the dominant coupled substitution of 2zn2 cu or ag in3 owing to their poor sn content occasionally sub micron inclusions of minerals such as stannite and pb sb bearing sulfides can occur in sphalerite contributing to high cu sn and high ag contents respectively the observed correlations of each element in the in cu ag sn bearing sphalerite can be proposed as a fundamental reason for the indium enrichment related to sulfur rich oxidized magmatism in addition the ag content in sphalerite is considered a possible indicator of formation depth which ranges from plutonic to subvolcanic environments

multistage supercritical fluid extraction of petroleum source rocks application to samples from kimmeridge clay and posidonia shale formations abstract a study to determine whether supercritical fluid extraction can replace liquid extraction of source rocks has been initiated the extractions have been performed with plain carbon dioxide with small amounts of 2 propanol mixed with carbon dioxide and with carbon disulfide and tetrahydrofuran added to carbon dioxide to increase extraction yields multistage extractions were performed in order to obtain a compromise between rapid extraction and selective extraction the extracts were collected either in a solvent or on a sorbent cartridge in a stream of water the yields were similar to or higher than those obtained by liquid extraction with a 3 stage extraction the first extract was dominated by saturates the second by aromatics and the third by nso compounds in preliminary results obtained with 1 2 g samples of posidonia shale 0 8 soluble organic matter was extracted with multistage sfe and each stage was completed in 30 min the extracts could be used for the determination of biomakers

novel side chain methylated and hexacyclic hopanes identification by synthesis distribution in a worldwide set of coals and crude oils and use as markers for oxic depositional environments abstract novel side chain methylated and hexacyclic hopanes have been identified in coals and oils from around the world extended hopanes c 32 with an additional methyl in the side chain isohopanes were identified by comparison with synthetic standards the major c 33 c 35 isohopanes are 31 methylbishomohopanes 32 methyltrishomohopanes and 33 methyltetrakishomohopanes extended hopanes methylated at c 29 were not detected the 17 h 21 h 31 methyltrishomohopanes show four peaks on gas chromatography because of the extra asymmetric carbon at c 31 like regular hopanes the isohopanes extend beyond c 35 low concentrations of novel hexacyclic hopanes having 35 or more carbons were also detected in oils and coal extracts the c 35 hexacyclic hopanes were identified as 29 cyclopentylhopanes isohopanes are released from the kerogen by hydrous pyrolysis and hydropyrolysis the 22s 22s 22r ratio for 31 methylbishomohopanes and other isohopanes is around 0 60 at equilibrium in geological samples they isomerize slightly more slowly than regular c 33 hopanes isohop 17 21 enes 2 methylisohopanes and two series of rearranged isohopanes were tentatively identified isohopanes can be biodegraded to form the corresponding 25 norhopanes when 25 norhopanes are not formed the isohopanes are much more resistant to biodegradation than regular hopanes in biodegraded oil seeps from greece 30 norisohopanes were tentatively assigned the composition and relative abundance of c 33 and c 34 isohopanes in a worldwide set of coals and crude oils was determined isohopanes are abundant in coal and coal generated oils where they can account for more than 5 of all extended hopanes and low in abundance in oils from source rocks deposited under anoxic conditions

the source rock horizons of the ionian basin nw greece abstract the organic geochemical study of six geological sections and two wells in the ionian zone nw greece allows us to distinguish five horizons of possible source rocks the vigla shales cenomanian turonian the upper posidonia beds callovian tithonian the lower posidonia beds toarcian aalenian the marls at the base of the ammonitico rosso early toarcian and shale fragments incorporated within the triassic breccias these horizons have good hydrocarbon potential and an organic matter type i to ii in the deeper parts of the botsara sub basin the oil window is located in the interval between 3700 5800 m depth consequently the triassic shales have already entered the gas window the lower and upper posidonia beds and the marls at the base of the ammonitico rosso are mature in terms of oil generation the vigla shales maturity corresponds to the early maturation stage the timing of the principal oil source horizons maturation is the late jurassic for the triassic shale beds and the serravalian for the lower posidonia beds the preservation of the organic matter in the lower and upper posidonia beds through toarcian to tithonian and in the marls at the base of the ammonitico rosso during early toarcian are directly related to the geometry of the syn rift period of the ionian basin the organic matter preservation in the vigla shales is related to the sub basins that were preserved by the continuation of halokinetic movements during the post rift period the geometry of the restricted sub basins that were formed during the syn rift and post rift period of the ionian basin evolution favored water stagnation and the development of local euxinic conditions in the bottom waters these conditions were accentuated during the anoxic events that are known to have affected the tethys ocean during the early toarcian and late cenomanian the organic rich shale fragments within the triassic breccias were initially deposited as stratigraphic layers in sub basins of the evaporitic basin the establishment of evaporitic sedimentation in the entire basin favored the preservation of the organic matter the processes that resulted in the formation of the evaporite dissolution collapse breccias caused also the fragmentation of the organic rich layers which are present actually as organic rich shale fragments within the triassic breccias

evolution of gas and aqueous fluid in low permeability argillaceous rocks during uplift and exhumation of the central swiss alps abstract fluid chemistry and the hydraulic regime in a marl formation of the swiss alps were studied by a number of techniques fluid inclusions record the conditions of maximum burial and regional low temperature metamorphism whereas fluid samples and hydraulic tests derived from deep boreholes reflect present day near surface conditions the characterization of the different types of fluids places constraints on the geochemical and hydraulic evolution of low permeability argillaceous rocks during uplift and exhumation fluid inclusions were studied by microthermometry and sampled directly by decrepitation techniques they contain a two phase system consisting of an aqueous fluid and a coexisting ch4 rich gas t 190 250 c plith 2500 bar bulk and isotopic compositions of aqueous fluid inclusions are consistent with a mixture of connate seawater and water derived from the dehydration of clay minerals methane was generated in situ by thermal cracking of kerogen textural evidence and stable isotopic signatures of carbonates in veins and in the rock matrix indicate local buffering of fluid compositions and very low water rock ratios free fluids residing in the present day fracture and matrix porosity consist of ch4 saturated na cl groundwater with minute amounts of free ch4 gas which occurs in druses their chemical and isotopic compositions are very similar to those of the fluid inclusions suggesting a common origin post metamorphic admixtures of externally derived waters cannot be identified and it is suggested that present day na cl groundwaters that occur in the central parts of the marl have resided in the formation since the time of metamorphism some 20 ma b p the only major change in the fluid composition has been the outgassing of ch4 from the formation most probably by diffusion the hydraulic regime during metamorphism was characterized by localized fluid underpressures in open veins because widely scattered sub hydrostatic pressures were often identified in fluid inclusions the central part of the argillaceous rock body approximately coinciding with the region where na cl groundwaters occur has sub hydrostatic pressures today as indicated by hydraulic tests in deep boreholes both the closed system behavior derived from the chemical and isotopic characteristics of the fluids and the recurrent or continuous existence of hydraulic underpressures suggest very low permeabilities of argillaceous rocks during metamorphism and throughout subsequent uplift and exhumation all fluids present in the central parts of the formation are either connate or produced in situ even though major events of brittle faulting and unloading due to uplift occurred since the peak of metamorphism fluid flow through the formation has been negligible

discovery of a large brine deep in the northern red sea the red sea is formed of marginal areas shallower than 1 000 m which are separated by a deeper axial zone the axial zone can be subdivided into three main segments the southern segment is a relatively simple trough which north of 16 n corresponds to an oceanic rift1 the middle segment from 19 30 n to 23 50 n is characterized by the presence of about 15 closed depressions or axial deeps ranging from several kilometres to less than a kilometre in length and containing hot of cold brines underlain by their associated deposits of soft and fine grained metalliferous muds1 3 the northern segment of the axial zone is shallower with depths rarely exceeding 1 500 m and has a smoother relief than the southern and central segments in the northern segments south of the al wajh depression at 25 25 n the axis strikes north south fig 1 north of the depression towards the approaches of the gulf of suez the strike is nnw sse the small circular 1 km diameter oceanographer deep is located4 along the western border of the axial zone of this northernmost segment the jean charcot deep which we discovered on 3 december 1983 during a cruise of the rv jean charcot lies near 25 15 n 35 22 e close to the axis of maximum depth of the same segment in contrast with the magnetically quiet neighbourhood a strong dipolar magnetic anomaly typifies this deep which in spite of intensive international surveys is the first brine deep to have been discovered in the red sea in the past 10 years

correlation of homogenization temperatures of accessory minerals from sphalerite bearing deposits and ga ge model temperatures abstract the ga ge ratio in sphalerite can be related to the temperature of the initial fluids from which the sphalerite grew after mixing with various amounts of fluids from different origins the extent of mixing of the two fluids can be qualitatively derived from the pressure corrected homogenization temperature which represents the temperature after mixing of the fluids and the ga ge temperatures of sphalerite which indicates the temperature of the hot metal bearing initial fluids different temperature information strongly indicate that mixing of fluids did occur prior to sulphide formation

the so called herodotus springs at keri lake in zakynthos island western greece a palaeoenvironmental and palaeoecological approach abstract in the present study the palaeoenvironmental setting of the coastal mire swamp zone called keri lake on zakynthos island west greece is presented the mire swamp area is famous for the asphalt pitch seepages named as herodotus springs in order to interpret the holocene evolution of the area samples from four 7 m long vibracores were analyzed for their total organic carbon total nitrogen and sulfur contents as well as for their micro and macro fauna the chronological framework of this study was based on three 14c ages while the age depth model and the sedimentation rate were estimated applying oxcal software the age depth model indicates that the cores cover the period from the middle holocene to present with a mean sedimentation rate of 1 mm yr before 4000 bp large part of the area inundated by the sea while after 4000 yrs bp the ecosystem changed to a high marsh and gradually to a fen environment where peat accumulated under telmatic to limnotelmatic conditions the trends and the ratios of the geochemical markers toc tn and ts clearly reflect the palaeoenvironmental change from terrestrial to fen depositional environments the results show that during the middle holocene the herodotus lake was influenced by sudden sea water inundation events possibly as a result of high waves or storm events while since the late holocene the setting is that of a brackish coastal fen where peat accumulates under the significant inflow of fresh water that originates from the karstic systems of the catchment area

ionian sea western greece its structural outline deduced from drilling and geophysical data abstract this paper outlines the preliminary structural results obtained by the compilation of geological drilling and geophysical data in western greece most external geotectonic zones of the hellenides are included in the geological setting of the marine and insular domain of western greece ionian pre apulian and apulian zones the gavrovo and pindus zones make a restricted contribution to the marine geological framework continental shelf of southwest peloponesus besides the geographical setting of the geotectonic units their general tectonic characteristics allow the following remarks to be made the main tectonic events younger than eocene are well marked in both ionian and pre apulian zones the detrital sequence shows a fast pinch out towards the apulian platform where the plio quaternary clastic layers overlap what are probably late mesozoic or early tertiary limestones taking into consideration general tectonic features we can distinguish a northern area and a southern one separated by a fault trending 30 n located on the western margin of kephallinia lefkas islands 1 a in the northern area we observe a strong tangential tectonism decreasing towards the apulian platform with transitional characteristics on the pre apulian zone paxos where asymmetrical folding occurs 2 b in the southern area from lefkas kephallinia islands to the s w cape of peloponesus the tangential tectomism is well masked by strong vertical faulting attributed to young plio quaternary deformations the fast subsidence induces huge diapiric structures in the ionian zone salt walls originating from triassic layers intersect a thick pleistocene sequence

simple kinetic models of petroleum formation part iii modelling an open system abstract the movement of petroleum from organic rich source beds to potential carrier beds is the net result of two processes expulsion the release of generated petroleum from kerogen within the source bed and primary migration flow of a petroleum phase through the inorganic void networks of the source bed and all other intervening fine grained rocks expulsion is by far the more important process within the source bed orgas a simple zero dimensional model of the source rock as an open system explicitly models expulsion concurrent with oil and gas generation and oi lgas cracking as a storage threshold problem oil and gas are retained adsorbed absorbed within kerogen until their concentrations exceed the respective sorptive capacity of the residual organic carbon 0 1 and 0 02 g g ck 1 the initial hydrogen index hl 0 controls the important balance between potential sorbate petroleum and sorbant residual carbon using simple geochemical measurements the initial organic carbon is divided into initial oil inert kerogen and oil and gas generative reactive kerogen components reactive kerogens are assigned to one of five global kinetic organofacies with pre determined kinetic parameter sets governing separately rates of oil and gas generation kinetic parameters governing the rates of oil cracking within the source rock are predicted from hl 0 the two most important determinants of source rock behaviour are organofacies and hl 0 at a reference constant heating rate of 2 c ma 1 the projected oil expulsion threshold for typical organofacies members increases in the order a de 100 110 120 135 c f typically expels no oil an order of magnitude increase decrease in heating rate increases decreases these thresholds by ca 15 c typical cumulative gas mass fractions in their ultimate expulsion products are a f 0 25 0 3 0 25 0 65 and 1 0 g g 1 a value of 200 mg hc g c 1 is an approximate minimum hl 0 prerequisite for oil expulsion irrespective of absolute petroleum potential p 0 as a family coals vary dramatically in their expulsion behaviour as their hl 0 ranges both above and velow this value primary migration is efficient for expulsive source rocks movement within the source bed is limited only at low p 0 a source rocks total genetic potential p 0 thickness becomes important during migration outside the source bed it potentially restricts the primary migration distance and the excess of petroleum available for secondary migration and entrapment we evaluate primary migration approximately using a small migration loss factor no more than about 10 saturation of porosity or 1 mg g 1 coupled with an understanding of fluid potential gradients which determine migration direction within the stratigraphic architecture ultimately kerogen degradation and oil to gas cracking in the source rock are the rate limiting processes in petroleum accumulation

principles of geochemical prospect appraisal our current understanding of the geochemical processes responsible for the creation of commercial accumulations of oil and gas can be reduced to simple rules and equations to allow the petroleum geologist to use geochemistry to estimate before drilling the likely volumes and compositions of oil and gas delivered to the trap in most sedimentary basins oil is expelled from source rocks between 120 and 150 c whereas most gas and gas condensate are released between 150 and 230 c when the initial potential of source rocks exceeds 10kg mt oil expulsion efficiencies are between 60 and 90 expelled oil and gas migrate as petroleum rich phases driven by fluid potential gradients most flow is laterally updip in beds with effective horizontal permeabilities greater than 1 md in lower permeability rocks the petroleum fluids move vertically up or down along the path of least resistance i e the most permeable or thinnest beds separating them from a high permeability lateral carrier bed the residual saturations of petroleum left behind along the migration pathway are of the order of a few percent of the porosity geochemical analysis of source rocks helps determine the yields and compositions of petroleum fluids expelled in the catchment area of a prospect these fluid masses are converted to volumes from knowledge of the phase relations and densities of petroleum fluids evaluation of the total volume of rock through which the petroleum potentially can migrate and the mean porosity of the rocks that constitute the migration pathway allow migration losses to be assessed these losses constrain both the range of migration of petroleum fluids away from the mature source rock and the volumes of petroleum remaining for entrapment in the prospect

multi stage fluid incursion in the palaeozoic basement hosted saint salvy ore deposit nw montagne noire southern france abstract the saint salvy vein hosted zn ge deposit occurs in an e w fault system which flanks the southern margin of the late variscan sidobre granite and cross cuts cambrian black shales of the palaeozoic basement comprehensive mineralogical and geochemical studies of vein samples have revealed four mineralizing events m1 m4 related to late and post variscan tectonic events a further late stage event may be related to weathering m1 skarn deposits and m2 patchily mineralized quartz veinlets are associated with granite emplacement quartz contains low salinity h2o co2 nacl dominated fluids 6wt nacl equiv of relatively high temperature 300 580 c trapped under moderate to high pressure estimated m1 fluid d and calculated fluid 18o plot within the metamorphic water field there appears to be no involvement of magmatic fluids by contrast m3 barren quartz and m4 zinciferous economic mineralization stages have h2o co2 nacl cacl2 fluid inclusions with high salinities 23 25 wt nacl equiv and low temperatures 80 140 c which were trapped under low pressure conditions the high salinity and nacl cacl2 content of both m3 and m4 indicates that their parent fluids leached evaporitic salts m3 fluids are meteoric water dominated falling close to the meteoric water line d and 18o averaging 64 and 8 respectively m4 fluids have highly distinctive d averaging 101 and calculated fluid 18o varying from 1 2to 7 1 the unusually low d composition of m4 suggests the involvement of organic fluids in which h is derived directly or indirectly from organic matter the relatively high 18o of m4 fluids indicates that considerable isotopic exchange with sedimentary material took place displacing the 18o from the meteoric water line the data imply interaction of meteoric waters with evaporite and hydrocarbon bearing sedimentary sequences most probably the adjacent aquitain basin the main economic mineralization m4 stage took place during a tensional event probably coincident with the lias dogger transition calculated 34sh2s of m4 sulphide 5 4to 8 2 is almost identical to 34s of local cambrian sulphides 4 7to 9 4 suggesting a genetic link abundant siderite associated with m4 sphalerite has 13c ranging from 2 6to 4 4 indicating that carbon was sourced from sedimentary carbonate mobilized by or equilibrated with the hydrothermal fluid late stage sulphides exhibit extraordinary and highly distinctive 34s sphalerite has extremely low 34s 42 5to 50 5 whereas pyrite has an extraordinary large range from 33 2 to 74 3 closed system sulphate reduction is held to be responsible for the extremely high 34s whereas more open system reduction produces the very low values the coincidence of isotopically low 13c 7 6to 11 9 for co genetic calcite suggests the involvement of organic matter in the reduction process

sphalerite geobarometry in the cu fe zn s system phase relations have been determined among sphalerite pyrite pyrrhotite and intermediate solid solution iss from 439 degrees to 725 degrees c at 1 bar and 353 degrees to 760 degrees c at 5 kb the extents of solid solution in the four phase assemblage are described as functions of temperature in kelvins by the following equations log mole zns in iss 1 bar 2 795 1 632 t super 1 log mole zns in iss 5 kb 2 659 1 608 t super 1 log mole cus in pyrrhotite 1 bar 2 546 1 866 t super 1 log mole cus in sphalerite 1 bar 4 202 3 755 t super 1 and log mole cus in sphalerite 5 kb 4 084 3 791 t super 1 the pressure dependence in kb of the composition of sphalerite in equilibrium with pyrite and pyrrhotite with or without iss can be expressed for the temperature independent portion of the sphalerite geobarometer as p 42 30 32 10 log mole fes because of the low solubility of copper in sphalerite in the four phase assemblage below 650 degrees c the presence of chalcopyrite in natural ores should be of no consequence to sphalerite geobarometry over its temperature independent portion nevertheless sphalerites which are inhomogeneous in fes and which contain abundant blebs of chalcopyrite in excess of the amount that can be reasonably accounted for by an equilibrium process of solubility and subsequent exsolution are a common feature of many sulfide ores such sphalerite grains should be avoided in applying the geobarometer the chalcopyrite blebs may be a product of a premetamorphic sphalerite chalcopyrite intergrowth or represent true exsolution from sphalerite in any one of 1 a former sphalerite pyrrhotite iss equilibrium 2 a stable four phase assemblage at temperatures above the temperature independent portion of the geobarometer or 3 a metastable four phase assemblage in which pyrite was inert use of the sphalerite geobarometer requires a thorough understanding of the textural relationships and discrimination of equilibrium from disequilibrium or low temperature reequilibrated assemblages

organic rich sediments in brine filled shaban and kebrit deeps northern red sea the element compositions si ca and al of up to 2 1 1 ka old sediments in about 10 in long cores from the southern basin of the shaban and kebrit deeps in the northern red sea allowed a classification of major sediment types in carbonate sands and muds and siliceous oozes a feooh enriched sediment horizon and a few samples with high zn values in the kebrit core indicate a hydrothermal origin probably near the brine sea water interface with subsequent transport of hydrothermal compounds into the deep sediments high organic carbon contents up to 8 4 are positively correlated with the ba concentrations which suggests that high bioproductivity and rapid deposition c 14 dating suggests a sedimentation rate near 70 cm ka led to the formation of sapropelic sediments between 11 8 and 13 6 ka younger dryas organic petrological observations showed that the sediment organic material largely consists of 20 gm sized roundish fecal pellets intimate mixtures of organic matter and inorganic constituents and bituminite terrestrial organic matter pollens of land plants fusinite etc is very rare in the sediment cores from both deeps organic geochemical investigations of kerogens and organic extracts show that a significant hydrothermal hydrocarbon production did not occur in near surface sediments of the shaban and kebrit deeps rock eval pyrolysis of kerogens characterised the organic matter to be of type ii quality the delta c 13 values of the kerogens from the most prominent sapropel in the shaban deep indicate an enrichment of c 12 rich nutrients in the water column during postglacial sapropel formation in the younger dryas the n alkane spectra are dominated by short chain lengths between n c 15 and n c 25 prevailing n c 15 to n c 25 alkanes in low mature sediments are indicative of algal and microbial source pristane phytane ratios are generally low i to similar to 1 which suggests that anoxic conditions prevailed within the anaerobic brine filled deeps for the whole time covered by the sediments this again indicates that sapropel formation was caused by high bioproductivity in the northern red sea rather than episodic stagnation with better preservation of the organic matter long chain alkenones and sterols are the dominating compounds of the lipid fraction cholesterol contents in the sediment cores reflect phases of eukaryotes production in the water column whereas the positive correlations of dinosterol with toc and the amounts of total extract suggests that the major organic carbon source in the northern red sea during postglacial high productivity stages were dinoflagellates another important carbon source however is indicated by the occurrence of 22 29 30 trisnorhopan 21 one tnh although the formation of tnh from its precursors is not fully understood this compound probably results from microbial degradation of intact bacteriohopanepolyols bhp which can be used as indicators for bacterial abundances and phyla tnh is most likely produced at the brine sea water interface where sedimenting organic matter accumulates and if the redoxcline corresponds to the density gradient the organic matter is subjected to efficient aerobic bacterial degradation processes however during high bioproductivity stage younger dryas the redoxcline was probably higher in the water column and thus a significant tnh production at the brine sea water interface did not occur at times of sapropel formation in the northern red sea deeps c 2007 elsevier b v all rights reserved

western greece and ionian sea petroleum systems in western greece the ionian and pre apulian zones represent respectively the basin and the transitional zone slope to the apulian platform the apulian platform constitutes the weakly deformed foreland of the external hellenides the pre apulian zone appears in the ionian islands and the eastern ionian sea whereas the apulian platform is exclusively found in the ionian sea the ionian zone consists of triassic evaporites jurassic upper eocene mostly pelagic carbonates minor cherts and shales overlainbytheoligoceneflysch organic richsourcerocks occur within triassic evaporites and jurassic cretaceous pelagic argillaceous siliceous rocks the pre apulian zone consists of triassic to miocene deposits mainly mixed neritic pelagic carbonates hydrocarbon source rocks include pelagic and hemipelagic deposits rich in marine organic material although terrigenous organic matter is also found in siliciclastic layers apulian platformsourcerocksaremainlytheorganic richshaleswithinthe triassic burano evaporites western greece contains major petroleum systems which extend into the ionian sea ionian pre apulian and apulian petroleum systems contribute to the probable hydrocarbon accumulations within the big offshore ionian sea anticlines western greece contains important oil and gas shale reservoirs with a potential of unconventional exploration promising areas for hydrocarbons need systematic and detailed threedimensional seismic data exploration for conventional petroleum reservoirs through the interpretation of seismic profiles and the abundant surface geologic data will provide the subsurface geometric characteristics of the unconventional reservoirs their exploitation should follow that of conventional hydrocarbons to benefit from the anticipated technological advances eliminating environmental repercussions

tracing the source of ancient reworked organic matter delivered to the north atlantic ocean during heinrich events a major effort of the geochemical and paleoclimate community has been to identify the specific sources of the ice rafted debris ird in heinrich layers hls although the general consensus is that the majority of the ird originated from the hudson area of northern canada the specific sources are not well constrained here we compare the diagnostic organic geochemical signature of hls to that of a number of paleozoic outcrops across the former margin of the laurentide ice sheet we show that the biomarker signature of upper ordovician strata from southampton and baffin island is compatible with that found in hls in the labrador sea and north atlantic while the biomarker signature of other paleozoic formations from the former margin of the laurentide ice sheet is not in addition to the biomarker signature key inorganic characteristics 18o end and 87sr 86sr ratios of these formations from southampton and baffin island are consistent with those reported from hls the location of these formations in and around the hudson strait is compatible with palaeo ice flow regimes through the hudson strait allowing for easy entrainment and rapid transport to the ocean based on these results we propose that these specific upper ordovician formations form a main source of ird in hls and hence infer an active role of the hudson strait paleo ice flow in these events

organic geochemical study of the w oil gas field in the yugoslav part of the pannonian basin the naphthenic crude oil from the w oil gas field differs from almost all other paraffinic base oils discovered until now in the yugoslav part of the pannonian basin in order to explain this difference some geological and organic geochemical investigations were carried out on the basis of the bulk and biomarker parameters determined in oil samples taken from 13 producing wells located at different parts of the field it is concluded that the crude oil throughout the field has an almost uniform composition however some differences in alkane content due to biodegradation and or water washing were found in the northeast part of the field where a tilted oil water layers shows an active hydrodynamism and where the temperatures are the lowest and pressure gradients the highest the isoprenoids pristane and phytane were detected in trace amounts indicating the most intensive biodegradation in the central part where a hydrocarbon accumulation exists in a miocene reservoir somewhat lower biodegradation was observed the crude oil from this field has probably a mixed terrestrial marine origin and is derived from argillaceous source rocks sedimented in marine delta or brackish lakes specific maturation parameters confirmed that the w crude oil has reached a quite uniform and significant thermal maturation considering maturation parameters such as ratios c30 moretane hopane and c29 20s 20s 20r steranes as well as the presence of oleanane it could be proposed that the w oil originates from a pre tertiary source rock at least an upper cretaceous one unlike most pannonian basin oils which are tertiary in age

lead isotopes as tracers of crude oil migration within deep crustal fluid systems abstract although pb u and th may be fractionated between crude oil and formation waters pb isotopes are not this unique property makes pb isotopes a particularly useful marker of hydrocarbon generation and migration here we show that pb isotopes offer a new vision of long range secondary oil migration relevant to the formation of oil fields north sea oils are largely generated from jurassic black shales yet their pb isotopes are mixtures of cenozoic to proterozoic end members the same observation is made for crude oils from the paris basin the barents sea libya kuwait kazakhstan and australia bulk pb in crude oil therefore for the most part is foreign to its source rock s our high precision pb isotope data on 195 crude oils worldwide the first such data set in the published literature and 17 northern european black shales indicate that deep seated pb components originating beneath the source rocks are ubiquitous in crude oil this implies that oil fields are embedded in basinal convective systems of hydrous fluids heated from below plumes of hot fluids rise from the lower thermal boundary layer which pb isotopes require douse the basement into the core of the porous flow convective cell where they dissolve the newly formed hydrocarbons sequestered in the source rocks the fluids finally unload unmixed formation waters and crude oil at the base of the upper conductive boundary layer where they can be trapped in favorable sites based on these new insights we argue that pb isotopes in crude oil constitute a good tracer of oil migration

calculation of petroleum masses generated and expelled from source rocks abstract an algebraic scheme for calculating the masses of petroleum formed in mature source rocks has been constructed the scheme exploits routine geochemical measurements and a basic understanding of the behaviour of sedimentary organic matter at elevated temperatures under both laboratory and subsurface conditions application of these techniques to data from a wide range of source rock types has led to the following general conclusions 1 1 major oil and gas generation from kerogen occurs between 120 and 150 c in the subsurface gas generation continues to temperatures 160 c 2 2 oil prone source rocks with average initial potential 5 kgt 1 of rock and average organic carbon contents 1 5 expel 60 90 of the total oil generated 3 3 oil expulsion from leaner source rocks is less efficient most of the oil generated remains in the source rock it is subsequently converted to lighter components at higher temperatures and expelled in the vapour state 4 4 the major loss of organic carbon from rich oil prone source rocks during generation and expulsion means that the petroleum potential and organic carbon content of mature source rocks are much less than their initial immature values hence the algebraic scheme must be used to calculate the initial values before expelled petroleum masses can be determined