the thermal and cementation histories of a sandstone petroleum reservoir elk hills california abstract recent developments in k feldspar 40 ar 39 ar thermochronometry have provided new tools to deal with interpretive impediments that previously limited its application to investigating sedimentary basin thermal histories these new methodologies were applied to detrital k feldspars recovered at various depths from a deep well drilled through a carbonate cemented sandstone petroleum reservoir in the southern san joaquin valley california thermal histories obtained from both thermochronological analysis and burial history constraints were used to constrain a conductive heat flow model of basin evolution the basin appears to have experienced a broadly linear heating history due to burial throughout the early and middle miocene followed by a significant increase in heating rate between 9 and 6 ma in a companion paper mahon k i harrison t m mckeegan k d 1998 the thermal and cementation histories of a sandstone petroleum reservoir elk hills california part 2 in situ oxygen and carbon isotopic results chem geol 152 257 271 we apply the thermal model to predict the temperature evolution of the much shallower late miocene stevens sands a prolific petroleum producer ratios of excess 40 ar to chlorine calculated from the differential release of radiogenic and nucleogenic argon during isothermal heating steps indicate a uniform value of 5 4 0 9 10 5 over the 2 5 km vertical distance separating the samples from well 934 29r suggesting that the basin receives a high basal flux of radiogenic argon

biomarker maturity parameters for high maturities calibration of the working range up to the oil condensate threshold abstract in a study of oils and source rocks from the kimmeridge clay united kingdom and the hanifa qatar formations several biomarker maturity parameters with working ranges up to vr e vitrinite reflectance equivalent 1 0 oil condensate threshold have been identified and calibrated this represents a significant improvement compared to commonly used biomarker maturity tools sterane and hopane isomerisation with their maturity maximum of approximately vr e 0 7 early part of oil window these new parameters are 1 the absolute concentrations of steranes and hopanes decreasing gradually with increasing maturity 2 the ratio of tricyclic terpanes tricyclic terpanes hopanes increasing with maturity 3 the ratio of diasteranes 14 h 17 h steranes depending both on maturity and on source rock lithology and 4 the ratio of t s t m 22 29 30 trisnorneohopane 22 29 30 trisnorhopane increasing rapidly at very high maturities during artificial maturation experiments the biomarker maturities described in the natural samples were also known to be time temperature dependent up to rather severe laboratory heating conditions this corresponds with the working range up to high maturity levels as observed in the natural samples

biomarkers in fluid inclusions a new tool in constraining source regimes and its implications for the genesis of mississippi valley type deposits biomarkers in fluid inclusion s can constrain source regimes for hydrocarbons associated with mississippi valley type pb zn deposits significant amounts of hydrocarbons have been detected in fluid inclusions in sphalerite and dolomite intimately associated with pb zn sulfides in the canning basin western australia the hydrocarbons are more mature than those in the host rocks to the ore and are therefore derived from an external source furthermore there are differences between the biomarker components of hydrocarbonas in inclusions in pb zn prospects but they are all different from hydrocarbons in organic rich strata and also in oils from the canning basin yet the hydrocarbons are mature and oil like suggesting that mature organic rich strata deeper in the basin which are less significant as potential source rocks for petroleum generation in the canning basin have contributed to the ore forming fluids

petroleum accumulation in the deeply buried reservoirs in the northern dongying depression bohai bay basin china new insights from fluid inclusions natural gas geochemistry and 1 d basin modeling abstract the deeply buried reservoirs dbrs from the lijin shengtuo and minfeng areas in the northern dongying depression of the bohai bay basin china exhibit various petroleum types black oil gas condensates and pressure systems normal pressure overpressure with high reservoir temperatures 154 185 c the pressure volume temperature composition pvtx evolution of petroleum and the processes of petroleum accumulation were reconstructed using integrated data from fluid inclusions stable carbon isotope data of natural gas and one dimensional basin modeling to trace the petroleum accumulation histories the results suggest that 1 the gas condensates in the lijin area originated from the thermal cracking of highly mature kerogen in deeper formations two episodes of gas condensate charging which were evidenced by the trapping of non fluorescent gas condensate inclusions occurred between 29 25 5 ma and 8 6 5 0 ma with strong overpressure pressure coefficient pc 1 68 1 70 resulting in the greatest contribution to the present day gas condensate accumulation 2 the early yellow fluorescent oil charge was responsible for the present day black oil accumulation in well t764 while the late blue white oil charge together with the latest kerogen cracked gas injection resulted in the present day volatile oil accumulation in well t765 and 3 the various fluorescent colors yellow blue white and blue and the degree of bubble filling fv 2 3 72 5 of the oil inclusions in the minfeng area show a wide range of thermal maturity api gravity ranges from 30 to 50 representing the charging of black oil to gas condensates the presence of abundant blue white fluorescent oil inclusions with high grain obtaining oil inclusion goi values 35 8 usually 5 in oil reservoirs indicate that a paleo oil accumulation with an approximate api gravity of 39 40 could have occurred before 25 ma and gas from oil cracking in deeper formations was injected into the paleo oil reservoir from 2 8 ma to 0 ma resulting in the present day gas condensate oil accumulation this oil and gas accumulation model results in three oil and gas distribution zones 1 normal oil reservoirs at relatively shallow depth 2 gas condensate reservoirs that originated from the mixture of oil cracking gas with a paleo oil reservoir at intermediate depth and 3 oil cracked gas reservoirs at deeper depth the retardation of organic matter maturation and oil cracking by high overpressure could have played an important role in the distribution of different origins of gas condensate accumulations in the lijin and minfeng areas the application of oil and gas accumulation models in this study is not limited to the dongying depression and can be applied to other overpressured rift basins

hydrocarbon composition of authigenic inclusions application to elucidation of petroleum reservoir filling history abstract geochemical analysis of petroleum inclusions trapped in authigenic feldspar and quartz in the ula formation in the north sea ula oil field revealed a petroleum of markedly different composition than the oil presently in the reservoir using microthermometry and the burial history as a dating tools it is concluded that the petroleum in the k feldspar inclusions was present in the more porous and permeable parts of the ula formation as early as 45 75 my bp when the field was at a depth of about 1 0 1 5 km as compared with the current depth of 3 4 km this early petroleum which was trapped as inclusions in authigenic k feldspar shows a distinctly different distribution of tricyclic terpanes and pentacyclic triterpanes from that of the current petroleum charge in the ula formation which was derived from the mandal formation source rock in late neogene time molecular parameters show that the oil in the k feldspar inclusions is significantly less mature than the crude oil in the present reservoir the approximate 90 c temperature increase occurring after entrapment of the early petroleum in kfeldspar the field is currently at 143 c appears not to have reset the low maturity signature of the oil in the k feldspar inclusions this could suggest that the temperature in the inclusions is too low for isomerization selective thermal degradation to occur lack of catalysts or that there are other controls on the ratio of some of these parameters still parameters like the ratio of c21 to c28 triaromatic steroids and those based on dimethyl and trimethyl naphthalenes are comparatively similar in both the inclusions and in the reservoir crude the oil inclusions in authigenic quartz and albite formed from about 10 my bp burial depth 2 5 km until the present burial depth 3 4 km are interpreted as representing a palaeo petroleum charge having a composition intermediate between the oil found in k feldspar inclusions and the oil charge in the present reservoir our data suggest strongly that the petroleum trapped in the inclusions in quartz and plagioclase represents progressive dilution of the early reservoired oil now found only in k feldspar inclusions with oil from the mandal formation analysis of solution gas in these inclusions suggests that the first petroleum associated gas to arrive at the trap from the progressively maturing mandal formation had a much wetter composition than the current reservoir solution gas to explain the present comparatively drier and isotopically lighter reservoir solution gas composition the inference is made that there has been a recent during formation of k feldspar inclusions 45 75 my bp maturation of the upper jurassic mandal formation the main source rock in this region was limited possibly to the graben axis this suggests that the petroleum found in the k feldspar inclusions was most likely derived from a deeper post caledonian palaeozoic formation

late palaeozoic hydrocarbon migration through the clair field west of shetland uk atlantic margin geochemical analysis of bitumen and hydrocarbon bearing fluid inclusions from the devonian carboniferous clair field indicates that the reservoirs contain a mixture of oils from different marine and lacustrine sources reconstruction of the clair field oil charge history using fluid inclusion petrography show that oil charging occurred at times of k feldspar quartz and calcite cementation temperature composition time data yielded from the integration of fluid inclusion microthermometry with high resolution ar ar dating date hydrocarbon bearing k feldspar overgrowths at 247 3 3 ma these data show that in order for oil to be trapped within primary fluid inclusions in k feldspar overgrowths hydrocarbon migration throughout the uk atlantic margin must have been taking place during the late palaeozoic and as such current industry oil play models based solely on oil charging from jurassic cretaceous marine sources are clearly incomplete and need revision apatite fission track analysis and vitrinite reflectance data were used to reconstruct thermal burial histories and assess potential oil generation from middle devonian lacustrine source rocks thermal history data from wells along the rona ridge adjacent to the clair field show that the palaeozoic section was heated to greater than 100 c at some time between 270 and 230 ma confirming that devonian source rocks were mature and expelling oil during the late palaeozoic at the time that authigenic k feldspar overgrowths were growing in the clair field

early formation of k feldspar in shallow marine sediments at near surface temperatures southern israel evidence from k ar dating authigenic k feldspar was investigated in two albian to turonian sections in israel using k ar and ar ar dating x ray diffraction scanning electron microscopy and chemical analysis both sections comprise a similar succession of shallow marine limestones dolomites and marls with some sandstone and shale beds of continental origin the hcl insoluble residue fraction of the studied samples consists of clays quartz feldspars goethite and trace amounts of heavy minerals most of the insoluble residues have a relatively high k feldspar content that has an adularia habit and is concentrated in the 4 7 m size fraction the authigenic origin of the k feldspar in the fine silt fraction is indicated by its high content relative to quartz the uniform and idiomorphic shape of the crystals and its limited size range of the fine silt 4 7 or 4 10 m separates 40 have ages that are similar to stratigraphic ages within the analytical and biostratigraphic errors ar ar dating of a fine silt fraction with 94 k feldspar 4 10 m sample gyp 7 yields a plateau age identical to the total gas age and similar to the stratigraphic age these results indicate that the k ar age is not a mixture between detrital and late diagenetic k feldspar ages but is rather an age of formation within a few million years after deposition it is suggested that the early formation of the k feldspar was associated with dolomitization and was induced by residual brines as part of a reflux process

evidence for an early cretaceous mineralizing event above the basement sediment unconformity in the intracratonic paris basin paragenetic sequence and sm nd dating of the world class pierre perthuis stratabound fluorite deposit world class stratabound fluorite deposits are spatially associated with the basement sediment unconformity of the intracratonic paris basin and the morvan massif in burgundy france the reserves are estimated to be about 5 5 mt of fluorite within six fluorite deposits in this study we aim to determine the age of the major fluorite mineralization event of the pierre perthuis deposit 1 4 mt fluorite by a combined study of the paragenetic mineral sequence and sm nd dating on fluorite crystals fluorite occurs as isolated cubes or filling geodes in a triassic silicified dolomitic formation three fluorite stages associated with sphalerite pyrite galena barite and quartz have been distinguished using optical cathodoluminescence and scanning electron microscopes seven crystals of the geodic fluorite stage were analyzed for their rare earth element ree contents and their 147sm 144nd and 143nd 144nd isotopic compositions the normalized ree distribution displays homogeneous bell shaped patterns for all the geodic fluorite samples with a mid ree enrichment over the light ree and heavy ree the 147sm 144nd varies from 0 3108 to 0 5504 and the 143nd 144nd from 0 512313 to 0 512518 a six point sm nd isochron defines an age of 130 15 ma initial 143nd 144nd 0 512054 mswd 0 21 this sm nd isochron provides the first age for the stratabound fluorite sediment hosted deposit related to an unconformity in the paris basin and highlights a major early cretaceous fluid circulation event mainly above the basement sediment unconformity during a flexural deformation of the paris basin which relates to the rifting of the bay of biscay and the formation of the ligurian sea in the western europe domain

application of 40ar39ar laser probe and step heating techniques to the dating of diagenetic k feldspar overgrowths abstract the feasibility of determining the age of diagenetic k feldspar overgrowths utilizing 40 ar 39 ar step heating and laser probe dating techniques was tested on samples from the lower cretaceous arkoses of the angola offshore basin a previous study of these samples combining cathodoluminescence and k ar dating indicated that the k feldspar diagenetic overgrowths were 98 16 ma and the detrital cores were 516 26 ma conventional 40 ar 39 ar step heating of overgrown grains from the bulk k feldspar fraction failed to unambiguously distinguish detrital from diagenetic ages similarly step heating analysis of overgrowth concentrates 84 diagenetic did not yield any distinct plateau age attributable to the diagenetic k feldspar detrital and diagenetic k feldspars from the arkoses studied appear to release their ar over similar ranges of temperature partial laser fusion of individual overgrown grains using lowenergy short duration laser pulses carefully focussed on the overgrowth yielded mixed ages with ar contributed from both the overgrowth and the core heat conduction calculations indicate that conductive heating through the core overgrowth boundary is not responsible for partial degassing of the core rather beam scattering along intragrain structural defects and incipient melting of the core must occur a more successful approach involved total laser fusion of individual grains from the overgrowth concentrates which were physically separated from their detrital core one limitation of this approach was that because of the young age and the small size of the diagenetic feldspar simultaneous fusion of several grains was required for accurate age determination our results suggest that future investigations will greatly benefit from the use of on line cathodoluminescence capability to reduce the possibility of contamination by detrital material and the use of a laser beam whose wavelength is strongly absorbed by diagenetic k feldspar

excess argon in k ar and ar ar geochronology the k ar and ar ar dating techniques occasionally produce anomalously old ages attributed to excess argon and such data is often rejected as not offering any insight into the age thermal history or geochemistry of the rock however improvements in the quantification of argon geochemistry now provide a framework to model excess argon in both open and closed systems solubility data for argon in hydrous fluids melts and emerging data for minerals can be used to understand the behaviour of excess argon and provide valuable insights into the environment in which the samples cooled to their argon retention or closure temperature treating excess argon as a trace element also throws light on its behaviour in minerals above the closure temperature in deeply buried dry systems such as eclogites blueschists granulites and even in the lithospheric mantle extremely low partition coefficients between k feldspar and hydrous fluid phases predict lower excess argon susceptibility than micas and this is observed in fluid poor systems variation of partition coefficients can lead to excess argon in fluids being introduced into minerals or removed from minerals as grain boundary fluids change during flow through a rock however excess argon can also be introduced or removed from minerals by varying temperature without the need for fluid flow high mineral melt and mineral fluid partition coefficients are also the reason why excess argon is often concentrated in inclusions within minerals partition coefficients between minerals and hydrous fluids as low as 10 6 lead fluid inclusions to dominate the radiogenic argon budget particularly in low potassium minerals melt inclusions are less dominant but become critical in dating younger samples

origin of groundwater salinity in the fasa plain southern iran hydrogeochemical and isotopic approaches the study area the fasa plain is situated in the semiarid region of fars province in the south of iran the salloo diapir is a salt dome that crops out in the northwest of the study area isotopic and hydrochemical analyses were used to examine the water and how the origin of salinity and the diapir affect the quality of the groundwater quality in the study area groundwater was sampled from 31 representative pumping wells in alluvial aquifer and five springs in order to measure their stable isotope compositions bromide ion concentration and physical and chemical parameters the alluvial aquifer was organized into two main groups based on the chemistry with group 1 consisting of low salinity well samples 544 1744 s cm with water type ca mg hco3 so4 which were taken in the center and north of the area and group 2 consisting of high salinity samples 2550 4620 s cm with water type ca mg cl so4 which were taken from the wells in the south and southwest of the area a saline spring near the salt dome with an ec of 10 280 s cm has water type na cl while the compositions of the water in the other karstic springs is comparable to the fresh groundwater samples all groundwater samples are undersaturated with respect to gypsum anhydrite and halite and are supersaturated with respect to calcite and dolomite stable isotopes 18o and 2h differentiated four water types saline springs freshwater spring fresh groundwater and saline groundwater the results indicate that meteoric water is the main origin of these water resources halite dissolution from the salt dome was identified as the origin of salinity the na cl and cl br ratios confirmed the results groundwater compositions in the southwestern part of the area are affected by the intrusion of saltwater from the salt dome the average saltwater fraction in the some water wells is about 0 2 in the south and southwestern part of the area the saltwater fraction is positive in mixed freshwater saltwater group 2 different processes interact together to change the hydrochemical properties of fasa s alluvial aquifer the main processes that occur in the aquifer are mixing gypsum dissolution and calcite precipitation

tectono thermal evolution of the palaeoproterozoic granites tanami orogen north australian craton implications from hornblende and biotite 40ar 39ar geochronology abstract the palaeoproterozoic granites tanami orogen gto hosts a number of gold deposits located in the southern margin of the north australian craton the major stratigraphic succession is the palaeoproterozoic tanami group which is subdivided into the dead bullock formation and conformably overlying killi killi formation new geochemical data for the ca 1864 coora and groundrush dolerite sills in the dead bullock formation suggests that they have the same characteristics with the enriched back arc basin basaltic rocks from the former stubbins formation such as tholeiitic affinity high tio 2 contents 0 94 to 1 24 wt and low mg 41 45 slightly enriched lile rb th u and k weakly depleted hfse nb ta and relatively flat ree patterns their magma was generated by high degree decompressional melting 5 15 of the asthenosphere source with an input of 3 4 subduction related material the petrological and geochemical similarities of igneous rocks provide new evidence for the assignment of the ca 1864 ma former stubbins formation and the mount charles formations in the dead bullock formation of the tanami group these conclusions confirmed that the extensive palaeoproterozoic tanami group was deposited in a back arc basin environment hornblende and biotite 40 ar 39 ar geochronological study identified three major tectono thermal events in the gto since the deposition of the dead bullock formation the ca 1840 ma 40 ar 39 ar cooling age of metamorphic hornblende from the coora and groundrush dolerite sills in the dead bullock formation provided precise age constraint for the first palaeoproterozoic tectono thermal event during the evolution of the granites tanami back arc basin this age is highly consistent with the ca 1850 1840 ma subduction and peak metamorphism events in the north australian craton nac associated with the halls creek orogeny in the halls creek orogen and the tennant orogeny in the tennant creek inlier the 40 ar 39 ar age of 1753 8 ma for the early biotite bi b from the dead bullock formation is a cooling age record of the peak greenschist facies metamorphism during the ca 1795 ma tanami orogeny which is interpreted as the continental continental collisional event between the gto and the arunta orogen in the central australian craton to the south the approximately 40 million year slow cooling is a combined result of exhumation heat released from the upwelling asthenospheric mantle regional magmatism and long term crustal residence this tectono thermal event was associated with gold mineralisation in the gto and the proterozoic nac was finally cratonised during this period the late biotite bi g is a recrystallization product of hydrothermal alteration its 40 ar 39 ar age of 1718 8 ma revealed the last tectono thermal overprint to the gto and arunta orogen this age reflected the distal thermal influence by the ca 1723 ma strangways event in the arunta orogen

a fluid inclusion study of quartz cemented sandstones from offshore mid norway possible evidence for continued quartz cementation during oil emplacement abstract jurassic sandstones from the oil zone in a well from the haltenbanken area offshore mid norway contain both aqueous and hydrocarbon fluid inclusions within quartz overgrowths homogenization temperatures for the inclusions range from 92 c up to the present formation temperature of approximately 118 c since the inclusions mostly are located at the boundaries between quartz clasts and quartz overgrowths the homogenization temperatures indicate that quartz cementation started at temperatures slightly below 92 c poikilotopic ferroan calcite cement usually predates formation of quartz overgrowths and most calcite cement must be precipitated at temperatures below 90 c although in one calcite cemented zone ferroan calcite encloses quartz overgrowths with inclusions trapped at temperatures of up to 105 c none of the examined hydrocarbon inclusions homogenized below 102 c and this suggests that oil started entering the reservoir at temperatures of around 100 c the burial history of the examined sandstones indicates that temperatures of 100 c were not reached before the late pliocene and that filling of the reservoir has taken place during the last few million years homogenization temperatures approximately equal to present formation temperature suggest that quartz cementation may still be in progress and that emplacement of oil did not necessarily stop precipitation of quartz cement possible continued quartz cementation after oil filled the reservoir could be explained by dissolution of quartz at stylolites and grain contacts as transport of dissolved quartz from these sources might possibly take place by diffusion through irreducible water

application of aromatic compounds as maturity indicators in source rocks and crude oils concentration ratios of aromatic compounds such as naphthalenes phenanthrenes and dibenzothiophenes are at present attracting increasing attention as maturity indicators in sedimentary rocks and crude oils generally these indicators rely either on an increase with maturity in the degree of alkylation of a given parent compound or a shift in the isomer distribution of alkyl aromatic homologues towards thermally more stable isomers a combination of both concepts in the methylphenanthrene index mpi resulted in an excellent maturity parameter as demonstrated for rock extracts by an improved correlation with mean vitrinite reflectance rm between 0 65 and 1 4 i e in the zone of oil formation in cases that rm measurements were ambiguous this empirical relationship has proved useful in the calculation of theoretical vitrinite reflectance rc values from the mpi on the other hand for potential petroleum source rocks reaching maturity at relatively low temperatures the influence of the organic matter type on the aromatic distributions cannot be neglected consequently organic facies effects should be taken into account in the interpretation of aromatic distributions of such source rocks and related crude oils since the impact of the organic facies is strongly reduced with increasing maturity aromatic maturity parameters are particularly useful in the maturity evaluation of post mature crude oils and condensates in contrast to biological markers substantially higher concentrations of the key alkyl aromatics persist at elevated maturation levels thus aromatic maturity parameters should be considered as versatile tools in organic maturation studies and can complement established maturity indicators based on steranes and terpanes

hydrothermal fluid origins in a fluorite rich mississippi valley type district combined noble gas he ar kr and halogen cl br i analysis of fluid inclusions from the south pennine ore field united kingdom the south pennine peak district ore field united kingdom is host to several fluorite rich mississippi valley type deposits and was chosen for study as an analogue to the illinois kentucky fluorspar district united states the study was undertaken to test the idea that the large scale carbonate dissolution and fluorite rich mineralogy characteristic of both districts may require a magmatic source of hf the data also provide constraints for water rock interactions and potential fluid sources relevant to the local geology of the south pennine ore field samples were studied from two of the largest and most economically important deposits within the south pennine ore field the hucklow edge and dirtlow rakes in vacuo crushing of irradiated calcite samples released inclusion fluids that were analyzed for noble gas isotopes ar ar kr and the halogens cl br i this was achieved simultaneously by noble gas mass spectrometry ar ar methodology and was combined with fluid inclusion thermometric salinity data to determine noble gas concentrations in addition he isotope analyses were obtained from unirradiated fluorite the he he ratio of the pennine ore fluids 0 1 ra where ra atmospheric he he ratio of 1 4 10 is significantly lower than the maximum value recorded in the illinois kentucky fluorspar district 0 35 ra kendrick et al 2002 this volume indicating a crustal fluid source and supporting existing basinal brine models the low ar ar ratios with most 50 to 60 percent halite dissolution water br cl mol ratio 0 57 0 92 10 the salinity of fluids included in the main stage of the hucklow edge mineralization avg of 22 wt nacl equiv places an upper limit on the extent of meteoric recharge at 15 vol percent a secondary vein present at hucklow edge has a lower salinity of 40 m y a time scale compatible with models in which fluids were derived from small local basins such as the widmerpool and edale gulfs

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

ar ar dating of authigenic k feldspar quantitative modelling of radiogenic argon loss through subgrain boundary networks we have analysed two distinct generations of authigenic k feldspar in fucoid bed sandstones from an t sron and skiag bridge nw highlands scotland which have experienced post growth heating to levels in excess of the predicted ar closure temperature authigenic k feldspars show microtextural similarities to patch perthites that is subgrains separated by dislocation rich boundary networks that potentially act as fast diffusion pathways for radiogenic argon the two generations of authigenic k feldspar in the fucoid bed sandstones can be distinguished by different microtextural zones bulk mineral compositions fluid inclusion populations and inferred temperatures and chemistries of parent fluids ar ar age data obtained using high resolution ultraviolet laser ablation show that the first cementing generation is ordovician and the second cementing generation is silurian modelling of ar diffusion using subgrain size as the effective diffusion dimension and a simplified tectono thermal thrust model assuming transient heating of the fucoid beds is inconsistent with observed data removal of heat from the thrust zone through rapid flushing of heated fluids rather than transient heating can be invoked to explain the observed ar ar ages for both generations of cement alternatively ar diffusion modelling using overgrowth thickness as the effective diffusion dimension instead of subgrain size also yields models that are consistent with both the fucoid bed palaeothermal maxima and determined ar ar age ages for the two generations of k feldspar cement based on this alternate explanation we propose a theoretical microtextural model that highlights fundamental differences between the microtextures of deuterically formed patch perthites and authigenic k feldspars explaining the apparent robustness of authigenic k feldspar with respect to ar retention

40ar 39ar dating of oil generation and migration at complex continental margins oil bearing fluid inclusions trapped within authigenic k feldspar in late jurassic reservoirs throughout the uk atlantic margin are evidence for an early oil migration event from late jurassic source rocks in the faeroe shetland basin previous compound specific isotope studies confirm the hydrocarbon provenance temperature composition time data show that the late jurassic source rocks were oil mature 113 3 5 ma 2 this new 40ar 39ar authigenic k feldspar age shows that the late jurassic source rocks were oil mature 30 40 m y prior to current estimates

stewart field finney county kansas seismic definition of thin channel reservoirs fluvial channel sandstones of early pennsylvanian morrowan age comprise regional reservoirs in parts of colorado kansas texas and oklahoma in southwestern kansas these reservoirs commonly exist at depths of 4000 5000 ft 1200 1500 m and have reserves of 150 000 200 000 bbl of oil per well making them highly economical reservoir sandstones form part of transgressive valley fill sequences deposited within channels incised into underlying mississippian carbonates thickness of the fill varies up to 60 ft 18 m is commonly 10 30 ft 3 9 m and displays rapid changes along channel length as a result detailed mapping of channel trends is difficult stewart field located in finney county kansas is a good example of this type of reservoir maximum reservoir qual ty exists in very fine to fine grained fluvial sandstones reworked by tidal action early attempts to extend the field to the east failed because existing two dimensional seismic and well data did not help workers properly resolve channel orientation a three dimensional 3 d seismic survey shot prior to initiation of waterflood operations helped 1 locate the channel between existing dry holes and 2 identify prospective locations that were then successfully drilled further extrapolation of the 3 d data resulted in a dry hole that established the limits of interpretation in this area stewart field thus provides an important case study regarding the capabilities and limitations of 3 d data in exploring the interwell frontier

evaluating re os systematics in organic rich sedimentary rocks in response to petroleum generation using hydrous pyrolysis experiments abstract successful application of the 187re 187os geochronometer has enabled the determination of accurate and precise depositional ages for organic rich sedimentary rocks ors as well as establishing timing constraints of petroleum generation however we do not fully understand the systematics and transfer behaviour of re and os between ors and petroleum products e g bitumen and oil to more fully understand the behaviour of re os systematics in both source rocks and petroleum products we apply hydrous pyrolysis to two immature hydrocarbon source rocks the permian phosphoria formation toc 17 4 type ii s kerogen and the jurassic staffin formation toc 2 5 type iii kerogen the laboratory based hydrous pyrolysis experiments were carried out for 72 h at 250 300 325 and 350 c these experiments provided us with whole rock extracted rock and bitumen and in some cases expelled oil and asphaltene for evaluation of re os isotopic and elemental abundance the data from these experiments demonstrate that the majority 95 of re and os are housed within extracted rock and that thermal maturation does not result in significant transfer of re or os from the extracted rock into organic phases based on existing thermodynamic data our findings suggest that organic chelating sites have a greater affinity for the quadravalent states of re and os than sulphides across the temperature range of the hydrous pyrolysis experiments both whole rock and extracted rock 187re 188os ratios show small variations 3 3 and 4 7 for staffin respectively and 6 3 and 4 9 for phosphoria respectively similarly the 187os 188os ratios show only minor variations for the staffin and phosphoria whole rock and extracted rock samples 0 6 and 1 4 and 1 3 and 2 2 these isotopic data strongly suggest that crude oil generation through hydrous pyrolysis experiments does not disturb the re os systematics in ors as supported by various studies on natural systems the elemental abundance data reveal limited transfer of re and os into the bitumen from a type iii kerogen in comparison to type ii s kerogen 0 02 vs 3 7 suggesting that these metals are very tightly bound in type iii kerogen structure the 187os 188os data from the pyrolysis generated phosphoria bitumens display minor variation 4 across the experimental temperatures with values similar to that of the source rock this indicates that the isotopic composition of the bitumen reflects the isotopic composition of the source rock at the time of petroleum generation these data further support the premise that the os isotopic composition of oils and bitumens can be used to fingerprint petroleum deposits to specific source rocks oil generated through the hydrous pyrolysis experiments does not contain appreciable quantities of re or os 120 and 3 ppt respectively in contrast to natural oils 2 50 ppb and 34 288 ppt for re and os respectively which may suggest that kinetic parameters are fundamental to the transfer of re and os from source rocks to oils from this we hypothesise that at the temperatures employed in hydrous pyrolysis re and os are assimilated into the extracted rock as a result of cross linking reactions

evolution of late triassic rift basin evaporites passaic formation newark basin eastern north america the passaic formation of the late triassic newark supergroup is 2700 m thick and was deposited in series of wide deep to shallow lacustrine environments in the newark rift basin eastern north america the passaic formation can be divided into lower middle and upper sections based on depositional structures composition and the distribution and morphology of its evaporites evaporites formed as a result of syndiagenetic cementation and or displacive processes evaporitive minerals now include gypsum and anhydrite although other mineral species such as glauberite may have originally existed most of the evaporites of the passaic formation occur within massive red mudstone and siltstone lithologies in the form of diffuse cements void fillings euhedral crystals crystal clusters and nodules these evaporites grew displacively within the fine siliciclastic matrix as a result of changes in the hydrochemical regimes of the rift basin a well developed upward increase in the amount of evaporite material is present in the passaic formation this resulted from 1 long term progressive increase in aridity and 2 significant increase in evaporation surface area of the basin during its tectonic evolution a nonmarine source for the evaporites is evident from the isotopic data sulphate 34s ranges from 11 to 3 3 cdt while 18o ranges from 15 1 to 20 9 smow indicating derivation from early diagenetic oxidation of organic sulphur and pyrite within the organic rich lacustrine deposits the 87sr 86sr ratios in sulphate are radiogenic average 0 71211 showing the interaction of basin waters with detrital components and that the newark basin was isolated from the world ocean most of the original evaporites show evidence of diagenetic change to polycrystalline and polymineralic pseudomorphs now filled with recrystallized coarse grained anhydrite 1 3 mm size and low temperature albite homogenization temperatures of fluid inclusions within the coarse grained anhydrite indicate crystallization temperatures for anhydrite in the range of 150 to 280 c such elevated temperatures resulted from circulation of hot water in the basin later exhumation of these rocks caused partial to total replacement of anhydrite by gypsum in the upper part of the section the resulting increase in volume due to hydration of anhydrite at shallow depths also emplaced non evaporative satin spar veins fibrous gypsum along bedding planes and in fractures while the local geology of the newark rift basin controlled the distribution of facies the sedimentological development of the passaic formation evaporites resulted from the world wide climatic aridity that prevailed during the late triassic because the newark basin sequence was only covered with about 3 km of sedimentary overburden that correspond to about 100 c and hence suggests that evaporites have experienced alteration by hot fluids 5 as the triassic marks the greatest evaporite formation world wide and profound sense of parched continentality throughout the world existed before the final break up of the pangea the passaic formation evaporites are an example of the influence of these palaeoclimatic conditions at the eastern margin of north america

diffusion and fluid interaction in itrongay pegmatite madagascar evidence from in situ 40ar 39ar dating of gem quality alkali feldspar and u pb dating of protogenetic apatite inclusions alkali feldspar 40ar 39ar and apatite upb geochronological studies have typically invoked two mechanisms to account for apparent loss of radiogenic 40ar and 206 208pb some studies have suggested that the radiogenic isotopes were lost by volume diffusion and used these dates to constrain temporal variations of rock temperatures others have argued that the radiogenic isotopes were lost due to interaction with fluids and related these dates to chemical alteration these two end member interpretations have fundamentally different implications for tectonic models derived from geochronological data and therefore it is important to reliably identify the principal mechanism for loss of radiogenic isotopes here we revisit the mechanisms of 40ar loss in the famous gem quality alkali feldspar from the itrongay pegmatite in madagascar previous studies have suggested that volume diffusion is the dominant mechanism of 40ar loss providing key evidence to support the use of 40ar 39ar dating of alkali feldspar for thermochronology we attempted to verify these results by obtaining time temperature paths from petrologically characterised cogenetic feldspar and apatite from the itrongay pegmatite and comparing them with each other however our results suggest that only a minor component in the variability of 40ar 39ar dates of itrongay feldspar is related to the diffusive loss of 40ar and that this loss was not compatible with the majority of previously proposed models which hinders quantitative interpretations the crystal studied here grew in five episodes related to the influx initially of co existing dense sio2 rich solution and co2 dominated fluid the first and supposedly the following two episodes and subsequently of h2o rich fluid supposedly the final two episodes much greater component in the variability of the acquired 40ar 39ar dates is interpreted to reflect the differences in the ages of these growth episodes which we estimate to span from 477 ma to 176 ma the first four episodes apatite inclusions in this crystal are interpreted to be xenocrysts derived from the country rocks of the itrongay pegmatite these yield older upb dates than the estimated age of their host feldspar and have apparently experienced diffusive loss of 206 207pb prior to entrapment our 40ar 39ar results indicate that there is a lack of unambiguous evidence for diffusive loss of 40ar from alkali feldspar that can be readily interpreted for thermochronological purposes however in situ 40ar 39ar dating of alkali feldspar appears to be a promising tool for tracking fluid flow events in the earth s crust whose applicability is not restricted to sedimentary rocks our upb results corroborate previous suggestions that upb dating of apatite can be used for thermochronology

how subaerial salt extrusions influence water quality in adjacent aquifers summary brines supplied from salt extrusions cause significant groundwater salinization in arid and semi arid regions where salt rock is exposed to dissolution by episodic rainfalls here we focus on 62 of the 122 diapirs of hormuz salt emergent in the southern iran to consider managing the degradation effect that salt extrusions have on the quality of adjoining aquifers it is first necessary to understand how they influence adjacent water resources we evaluate here the impacts that these diapirs have on adjacent aquifers based on investigating their geomorphologies geologies hydrologies and hydrogeologies the results indicate that 28 62 45 of our sample of salt diapirs have no significant impact on the quality of groundwater in adjoining aquifers namely type n while the remaining 34 62 55 degrade nearby groundwater quality we offer simple conceptual models that account for how brines flowing from each of these types of salt extrusions contaminate adjacent aquifers we identify three main mechanisms that lead to contamination surface impact type a subsurface intrusion type b and indirect infiltration type c a combination of all these mechanisms degrades the water quality in nearby aquifers in 19 62 31 of the salt diapirs studied having characterized the mechanism s by which each diapir affects the adjacent aquifer we suggest a few possible remediation strategies to be considered for instance engineering the surface runoff of diapirs types a and c into nearby evaporation basins would improve groundwater quality

geothermometry and geochemistry of aqueous and oil bearing fluid inclusions from fateh field dubai abstract the production of oil from fateh field dubai is principally from the cretaceous mishrif formation porosity in the reservoir facies is partly occluded by late coarse grained calcite cement this cement contains both aqueous and oil bearing fluid inclusions fluid inclusion geothermometry was used to determine the temperature of that cement precipitation and calculate its timing relative to basin burial history these data were related to source rock maturation and from that the timing of oil migration was inferred to be oligocene to mid miocene which is geologically contemporaneous with early petroleum generation r 0 0 5 0 6 in the khatiyah source rock the fluid inclusions were analyzed by a thermal decrepitation gas chromatography technique benzene and low molecular weight paraffins were present and a series of normal alkenes was tentatively identified in the aqueous inclusions fresh oil inclusions consisted of c 1 n c 25 compounds whose light hydrocarbon composition was consistent with derivation from an early mature source rock altered petroleum residues detected in many mishrif samples are contained either in inclusions or along crystal cleavages these materials are the subject of an ongoing geochemical study of fateh field

direct dating of authigenic k feldspar overgrowths from the kilombero rift of tanzania k feldspars form important detrital and authigenic components in sediments but may be difficult to separate by conventional means for isotope analysis particularly geochronology uv lasers are being increasing applied to in situ analysis since they are strongly absorbed by clear minerals such as k feldspar and can achieve a spatial resolution of better than 20 m for individual ar ar analyses here we demonstrate separation of detrital k feldspar with a mean age of 423 14 ma and authigenic overgrowths with a mean age of 138 5 ma in clastic sediments from the msolwa group of the kilombero rift of tanzania the young age obtained for authigenic k feldspar overgrowth demonstrates that precipitation occurred more than 160 ma after sedimentation during the period of deepest burial and synchronous with the initial extensional phases of the intracontinental anza and sudan rifts as well as the initial stages in the break up and separation of south america and africa

hydrocarbon evolution of the over mature sinian dengying reservoir of the neoproterozoic sichuan basin china insights from re os geochronology abstract rhenium osmium re os geochronology is a robust technique for constraining the accurate timing of hydrocarbon evolution but its effectiveness in over mature petroleum systems has not been well constrained here we conduct a case study in the neoproterozoic sichuan basin china i e the sinian dengying sequence 635 542 ma re os isotopic data from this highly mature hydrocarbon reservoir yield a re os isochron ages of 414 44 ma with an initial 187os 188os osi of 1 36 0 19 for bitumen and a 78 37 ma age with an osi of 3 21 0 17 for pyrobitumen coupled with thermal evolution of possible source rocks and fluid inclusion homogenization temperatures the 414 ma age marks the timing of oil generation and the 78 ma age indicates the timing of gas generation associated with the thermal cracking of oil and the formation of pyrobitumen in the reservoir a comparison of the osi of the 414 ma bitumen and that of possible source rocks at the time of bitumen formation reveal that it was primarily sourced from shale of the lower cambrian qiongzhusi formation the results of this study provide new insights to better understand the over mature oil gas system in the sinian sichuan basin and show that dengying formation reservoirs in the depocenter areas of the basin are potentially favorable for oil and gas exploration the results further highlight the utility of the re os geochronometer to constrain the accurate age and source of hydrocarbon evolution

new time constraints on dyke swarms related to the parana etendeka magmatic province and subsequent south atlantic opening southeastern brazil abstract 40 ar 39 ar incremental heating analyses were carried out on tholeiitic dyke swarms of santa catalina florianopolis and rio de janeiro and alkaline dykes from the proximity of rio de janeiro city southeastern brazil most of the plagioclases from the tholeiitic dykes display disturbed age spectra with younger apparent ages most often clearly correlated with alteration phases however a calculated weighted mean age from the less disturbed released fractions of the ne oriented santa catarina dyke swarm gives an age of 129 4 0 3 ma which is contemporaneous with the ponta grossa dyke swarm pgds and at least the northern parana continental flood basalts cfb the rio de janeiro tholeiitic dykes display age spectra affected by alteration and probably excess argon but with low temperature mini plateau ages between 130 6 and 129 8 ma which are concordant with previous data obtained on the pgds and rio de janeiro dyke swarms by renne et al 1996a and turner et al 1994 these new geochronological data when added to the previous ones show that the initiation of gondwana s breakup in the region was characterized by a volcano tectonic system with a geometry more complicated than the rift rift rift system suggested by many authors the different rift arms of this structural feature were operating during a brief time period mainly from 131 5 to 129 ma and were contemporaneous at least with the northern part of the parana etendeka province pep single grain and bulk sample biotite from the alkaline mainly coast parallel dyke swarm near rio de janeiro city display plateau ages around 80 ma 81 8 1 8 and 78 8 2 8 ma and 70 ma 72 5 0 5 and 69 7 0 2 ma these magmatic intrusions refer to late cretaceous flexuring and vertical movements and rift basin formations almeida 1976 due the northward progressing rifting motions separating south america and africa during south atlantic ocean formation

early permian to middle jurassic rifting and sedimentation in east africa and madagascar pre drift sediments of madagascar early permian middle jurassic have been studied palynologically these studies resulted in a more precise dating of individual stratigraphic units and the recognition of minor and major breaks in the succession palynostratigraphic and physical evidence of unconformities have been used to subdivide the pre drift sediments into depositional cycles and to infer rifting events a comparison with equivalent strata of mozambique tanzania kenya ethiopia and somalia shows a general correspondence and provides additional information for the construction of a generalized framework for the east african madagascan region which demonstrates the relationships between rifting and sedimentation and elucidates the prehistory of the break up of gondwana into a western and eastern fragment during the middle jurassic the predrift succession of east africa madagascar can be subdivided into two major sequences a karoo sequence cycles 1 5 asselian early smithian and a transitional sequence cycles 6 9 ladinian early bajocian the two sequences are separeted by a late scythian to anisian hiatus which indicates extensive uplift and erosion before a major rifting event initiated the resumption of sedimentation in the ladinian this middle triassic event marks the transition from the intracratonic rift stage to the pericratonic basin stage and correlates with a significant event in the pangaean history the transition from final coalescence to initial dispersal the onset of the southward drift of madagascar is believed to have occurred about 60 ma later near the aalenian bajocian boundary contemporaneous with or immediately after the deposition of syntectonic sediments of cycle 9

a high precision 40ar 39ar age for hydrated impact glass from the dellen impact sweden the dating of terrestrial impact craters and impact glasses that exhibit high degrees of mineralogical complexity can be problematic however if the maximum potential of the terrestrial impact crater record is to be realized accurate and precise ages for crater forming events are critical here we report a high precision 40ar 39ar age for the dellen impact structure sweden previous radio isotopic constraints show a wide variation in age as a result of poor sample characterization and analytical approach a detailed petrographical and mineralogical study provides a solid foundation for interpretation of step heating 40ar 39ar data culminating in a statistically robust age of 140 82 0 51 ma 2 full external precision for the dellen impact event for which data disfavour an inherited argon component primary hydration of the impact melt during cooling quenching and entrapment of molecular water promoted rapid loss of inherited 40ar from the impact melt of rhyolitic composition duplicate analyses of the water content and d of the glass give similar values for the former 1 9 0 1 mol mg 1 but unexpectedly low values for the latter 159 8 with scatter beyond the expected analytical reproducibility due to isotopic heterogeneity this study highlights that the 40ar 39ar technique is unrivalled in its ability to precisely and accurately date the products of hypervelocity collisional events less

a high resolution record of multiple diagenetic events ultraviolet laser microprobe ar ar analysis of zoned k feldspar overgrowths abstract high spatial resolution uv laser ar ar analyses were performed in situ on k feldspar overgrowths from sandstone hosted pb zn bodies from central sweden two different populations of ages were detected precambrian cambrian 528 10 to 567 8 ma and late silurian 403 6 to 453 8 ma these were both detected in single pore spaces with the older population adjacent to the detrital feldspar whilst the younger population was always distal to the detrital grain this younging of authigenic k feldspar ages with distance from the detrital grain margin is discussed in terms of disturbance to the argon system within an authigenic overgrowth that is of a single age a the overgrowths are precambrian cambrian in age and the late silurian population might be an artefact of argon loss due to partial resetting b the overgrowths are late silurian and the precambrian cambrian population might have resulted from excess argon uptake and c the overgrowths are late silurian but the precambrian cambrian population is an experimental artefact arising from the analysis of overlapping detrital authigenic feldspars diffusion modelling shows that the partial resetting scenario is a very unlikely cause for the observed age variation because it requires a very particular arrangement of sub grain sizes excess argon was not detected in either the k feldspar or quartz the data are best interpreted as the ages of two discrete diagenetic events an early burial diagenesis and a later tectonically induced fluid flow event relating to the collapse of the caledonian orogen further the use of 38arcl 39ark as a proxy for cl k ratio highlights the physical boundaries between feldspar populations where all other petrographic sem and cl analyses have failed to do so this study shows that high spatial resolution uv laserprobe ar ar analysis is a powerful tool for extracting age information from complex hydrothermal minerals as a means to investigating fluid flow events

the impact of salt diapirs on the quality of carbonate karst waters bastak iran the gavbast karstic aquifer located in southern iran is in direct contact with an exposed salt diapir to assess the influence of the diapir on the quality of groundwater in the karstic aquifer electrical conductivity total dissolved solids flow rate temperature and major ion concentrations were measured at 57 sampling sites including springs surface waters and wells a conceptual model of groundwater flow is proposed for the gavbast karstic aquifer based on the geological setting water budget local base of erosion and hydrochemistry of the sampling sites the model suggests two subbasins in the gavbast anticline draining into two distinct discharging alluvial sections unexpectedly groundwater discharging from the carbonate gavbast aquifer is saline or brackish and water is of chloride type the study indicates that the source of salinity of the gavbast aquifers is infiltration of surface diapir derived brine into the aquifer the contribution of the diapir brine in the gavbast karst aquifer is calculated about 4 l s using chloride mass balance construction of salt basins to evaporate brine discharging from the diapir springs is proposed to reduce the salinity of karst water a row of strategically placed wells in the gavbast karst aquifer would potentially exploit large volumes of fresh groundwater before it is contaminated by the salt such low cost remediation should allow the agricultural exploitation of 40 km2 of currently barren land

some aspects of the organic geochemistry of petroleum fluids the most important influences on the compositions of petroleum fluids are in many cases the composition of a petroleum sample may allow the depositional environment of its source rock and its temperature history before and after expulsion to be determined this information assists the search for more petroleum in a region we suggest that this approach should be used more frequently to validate models of petroleum generation and migration in the second part of the paper we discuss the origin and nature of the differences in petroleum composition which are frequently found within individual petroleum reservoirs petroleum accumulations in permeable reservoirs are normally found to be inmechanical equilibrium and verticalchemical equilibrium this is manifested by constant subsurface fluid density at any given depth across the accumulation and increases in subsurface density with depth known as gravitational segregation however even in permeable reservoirs lateral differences in composition inherited from the reservoir filling process are not totally eliminated by mixing processes such as diffusion and convection thus lateral chemical equilibrium is often not achieved and lateral compositional variations are observed in present day oil and gas reservoirs these observations are justified in terms of order of magnitude estimates for the rates at which reservoirwide mixing occurs a case history is presented

diagenetic k feldspar textures a tem study and model for diagenetic feldspar growth abstract diagenetic k feldspar overgrowths from the permo triassic continental clastic sediments of the elgin area in scotland were examined using conventional petrographic techniques and transmission electron microscopy to investigate the mechanisms of feldspar authigenesis the detrital k feldspar in these rocks is tartan twinned whereas the diagenetic k feldspar is untwinned the overgrowths are optically homogeneous but are not in optical continuity with the detrital grains overgrowths are up to 50 m thick and comprise numerous rhombs indicating that nucleation was a relatively easy process most overgrowths consist of a mosaic of micron sized rhombs nucleation on different twin planes on the detrital grain surface resulted in different orientations of the diagenetic nuclei the different orientations were propagated into the overgrowth as new nuclei formed on the surface of pre existing diagenetic crystals the detrital k feldspar is triclinic maximum microcline diagenetic k feldspar deviates only slightly from monoclinic orthoclase even though the triclinic polymorph is the stable k feldspar under the low temperature conditions of growth disordered crystals involve a simpler nucleation growth mechanism than ordered crystals consequently disordered crystals grow faster than ordered crystals monoclinic feldspar has disordered al si and triclinic feldspar has ordered al si diagenetic feldspar has metastable low triclinicity because this crystal structure could grow faster than the stable feldspar nanometer scale growth zones occur within individual rhomb representing variations in al si disorder such variations probably result from subtle variations in the state of supersaturation of the pore fluids and therefore in the rate of growth the interface between the detrital grain and the overgrowth represents no profound break in the feldspar crystal lattice despite the change in crystallography but is marked by the termination of twin planes in the detrital grain and the presence of dislocations in the overgrowth the termination of twins resulted in strain in the overgrowth which was relieved by the formation of dislocations small pores representing fluid inclusions and rare clay grains also occur at the interface

40ar 39ar dating of hydrothermal activity biota and gold mineralization in the rhynie hot spring system aberdeenshire scotland this study presents a new high precision 40ar 39ar age for the devonian hot spring system at rhynie hydrothermal k feldspar sampled from two veins that represent feeder conduits and a hydrothermally altered andesite wall rock date the hydrothermal activity the fossilised biota and syn k feldspar gold mineralization at 403 9 2 1 ma 2 oxygen isotope data for the parent fluid 4 to 2 show that the k feldspar was precipitated from a dominantly meteoric fluid which mixed with magmatic fluids from a degassing magma chamber the 40ar 39ar age 403 9 2 1 ma 2 when recalculated 407 1 2 2 ma 2 with respect to the astronomically tuned age for fish canyon sanidine 28 201 0 023 ma 1 also provides a robust marker for the polygonalis emsiensis spore assemblage biozone within the pragian earliest emsian furthermore the age identifies the devonian pull apart volcano sedimentary basins of the british and irish caledonides and their root zones as specific targets for future gold exploration

classification of offshore gulf of mexico oils and gas condensates five groups of petroleums can be recognized in the offshore gulf of mexico on the basis of carbon isotope and sulfur isotope ratios sulfur content and relative abundances of nickel and vanadium of 355 oils analyzed 341 96 1 are evidently closely related and cannot be subdivided on the basis of carbon or sulfur isotopes we suggest that these oils represent a single broad superfamily however two subgroups within this set are distinguishable on the basis of sulfur content and relative abundances of nickel and vanadium group 1a sigma 13 c 26 5 0 4 parts per mil sigma 34 s 5 6 2 4 parts per mil s 0 25 0 15 v ni v 0 27 0 10 and group 1b sigma 13 c 26 5 0 3 parts per mil sigma 34 s 5 9 1 2 parts per mil s 0 73 0 43 v ni v 0 67 0 07 group 1a oils are broadly distributed across the louisiana and adjacent texas continental shelf whereas group 1b oils are found along the louisiana shelf edge and continental slope group 1b oils have substantial genetic affinities to those from the campeche shelf offshore mexico of mesozoic origin the remaining 14 analyzed petroleums include supermature condensates from offshore texas and oils from offshore southern florida believed to be cogenetic with those from the jurassic smackover formation a three dimensional appraisal of geohistory suggests that petroleum generation began in the eocene in the region of the rio grande delta progressed coastwise to the mississippi delta area by the miocene and then occurred in regions of progres ively deeper water during the pliocene pleistocene

flow unit modeling and fine scale predicted permeability validation in atokan sandstones norcan east field kansas characterizing the reservoir interval into flow units is an effective way to subdivide the net pay zone into layers for reservoir simulation commonly used flow unit identification techniques require a reliable estimate of permeability in the net pay on a foot by foot basis most of the wells do not have cores and the literature is replete with different kinds of correlations transforms and prediction methods for profiling permeability in pay however for robust flow unit determination predicted permeability at noncored wells requires validation and if necessary refinement this study outlines the use of a spreadsheet based permeability validation technique to characterize flow units in wells from the norcan east field clark county kansas that produce from atokan aged fine to very fine grained quartzarenite sandstones interpreted to have been deposited in brackish water tidally dominated restricted tidal flat tidal channel tidal bar and estuary bay environments within a small incised valley fill system the methodology outlined enables the identification of fieldwide free water level and validates and refines predicted permeability at 0 5 ft 0 15 m intervals by iteratively reconciling differences in water saturation calculated from wire line log and a capillary pressure formulation that models fine to very fine grained sandstone with diagenetic clay and silt or shale laminae the effectiveness of this methodology was confirmed by successfully matching primary and secondary production histories using a flow unit based reservoir model of the norcan east field without permeability modifications the methodologies discussed should prove useful for robust flow unit characterization of different kinds of reservoirs

petroleum generation and migration in the cambro ordovician laurentian margin succession of nw scotland fluid inclusion and organic biomarker data show that there was formerly a hydrocarbon system in the cambro ordovician laurentian margin rocks of nw scotland oil fluid inclusions occur in stylolitized eriboll formation sandstone in k feldspar cements with an 40 ar 39 ar age of 415 5 5 5 8 ma 2 analytical precision full external precision organic extracts from durness group black limestones yield biomarker ratios characteristic of high thermal maturity organic maturation to yield oil probably occurred during orogenic deformation along the moine thrust zone the recognition of a hydrocarbon system in scotland adds to a huge hydrocarbon province in laurentian rocks including north america and greenland supplementary material technical data for ar ar dating are available at https doi org 10 6084 m9 figshare c 3879616

natural and human induced dissolution and subsidence processes in the salt outcrop of the cardona diapir ne spain the cardona diapir in ne spain with a salt outcrop about 0 9 km2 in area has a well developed endokarstic system that used to discharge into the cardener river underground mining for potassium salt carried out from 1930 to 1990 caused significant changes in the topography and hydrology of the diapir the accumulation of two halite slag heaps totalling around 10 million tons locally dammed the surface drainage creating closed depressions and preferential zones of water recharge the waters that infiltrated in one of these depressions largely derived from uncontrolled sewage disposal led to the generation of a 335 m long human induced cave excavated in one of the slag heaps moreover the inflow of freshwater from the surrounding sandstone aquifer caused by the excavation of a ventilation gallery resulted in the generation of a 280 m long cave in march 1998 the interception of a phreatic conduit by a halite mine gallery 50 m deep caused dramatic changes in the hydrology and geomorphology of the diapir including a a sudden decline in the piezometric level of the karstic aquifer b the inflow of freshwater and debris from the cardener river into the endokarstic system and the mine galleries a tunnel had to be constructed to divert the river flow from the salt outcrop c massive dissolution of salt creating new cavities and enlarging the pre existing ones including both mine galleries or cave passages the 4 300 m long salt meanders cave was largely generated by the inrush of water from the cardener river into the mine galleries and d the generation of a large number of sinkholes in the vicinity of the cardener river an inventory of 178 sinkholes has allowed us to estimate minimum probability values of 4 7 and 8 sinkholes km2 year for time intervals previous and subsequent to the 1998 mine flood event respectively

synthetic saline aqueous and hydrocarbon fluid inclusions trapped in calcite at temperatures and pressures relevant to hydrocarbon basins a reconnaissance study abstract we conducted reconnaissance experiments to synthesize aqueous and hydrocarbon inclusions trapped in calcite at conditions relevant to petroleum basins and characterize the microthermometric properties of such inclusions fluid inclusions fis were synthesized in a system of saline aqueous solution 5 or 20 wt nacl coexisting with either heavy crude oil or gasoline under gas undersaturated conditions from 90 to 210 c and 200 550 bar the synthetic inclusions are not representative of gas bearing systems and methane ch 4 was not detected in any aqueous inclusions the fis are mainly distributed along planar healed cracks indicating that the inclusions formed by fracture healing in the calcite crystal microthermometric measurements were conducted on coeval aqueous and hydrocarbon inclusions and raman spectroscopic analyses were done on aqueous inclusions to determine the properties of fis trapped at these conditions homogenization temperatures of synthetic fis are mostly lower than the experimental trapping temperature although the fis show high variability in measured homogenization temperature results allow comparison of t h values for each sample with the expected t h isochores and pressure corrections calculated for the system h 2 o nacl the latter parameters are broadly consistent with the known pvtx properties of h 2 o nacl fluids suggesting little effect of hydrocarbons on the homogenization behavior although the low precision of the t h data limits this assessment nevertheless this result is not unexpected considering that light hydrocarbons gas is not present in the experiments as corroborated by raman spectroscopy a consequence of using dead oil in the experiments simulation of gas bearing petroleum basins will require additional protocols for producing gas either by in situ cracking of the starting hydrocarbon material or by other means the reconnaissance experiments documented here provide a basis for such future experiments

evidence for late paleozoic brine migration in cambrian carbonate rocks of the central and southern appalachians implications for mississippi valley type sulfide mineralization abstract many lower paleozoic limestones and dolostones in the valley and ridge province of the central and southern appalachians contain 10 to 25 weight percent authigenic potassium feldspar this was considered to be a product of early diagenesis however 40 ar 39 ar analyses of overgrowths on detrital k feldspar in cambrian carbonate rocks from pennsylvania maryland virginia and tennessee yield late carboniferous early permian ages 278 322 ma simple mass balance calculations suggest that the feldspar could not have formed isochemically but required the flux of multiple pore volumes of fluid through the rocks reflecting regional fluid migration events during the late paleozoic alleghanian orogeny microthermometric measurements of fluid inclusions in overgrowths on detrital k feldspar and quartz grains from unmineralized rocks throughout the study area indicate homogenization temperatures from 100 to 200 c and freezing point depressions of 14 to 18 5 c 18 21 wt nacl equiv the apparent similarity of these fluids to fluid inclusions in ore and gangue minerals of nearby mississippi valley type mvt deposits suggests that the regional occurrences of authigenic k feldspar and mvt mineralization may be genetically related this hypothesis is supported by the discovery of authigenic k feldspar intergrown with sphalerite in several mines of the mascot jefferson city district e tennessee regional potassic alteration in unmineralized carbonate rocks and localized occurrences of mvt mineralization are both explainable by a gravity driven flow model in which deep brines migrate towards the basin margin under a hydraulic gradient established during the alleghanian orogeny the authigenic k feldspar may reflect the loss of k during disequilibrium cooling of the ascending brines mvt deposits are probably localized manifestations of the same migrating fluids occurring where the necessary physical and chemical traps are present

microtextures of authigenic or rich feldspar in the upper jurassic humber group uk north sea detrital alkali feldspars currently at burial depths of 3 2 3 5 km in the upper jurassic humber group of the fulmar oilfield uk north sea are overgrown and have been partially replaced by authigenic or rich feldspar intracrystal microtextures suggest several different provenances for the detrital grains the overgrowths are uniformly non cathodoluminescent and have occasional celsian rich zones transmission electron microscopy shows that they are composed of a microporous mosaic of sub m to m sized sub grains associated with barite illite and pyrite the subgrains are somewhat rounded but have an approximate 110 adularia habit and display a faint modulated microtexture on the nanometre scale they have triclinic symmetry but the lattice angles depart only slightly from monoclinic symmetry these features are characteristic of k feldspar precipitated relatively rapidly and at low temperature authigenic or rich feldspar has also partially replaced microcline and perthitic albite within the detrital grains often at a suboptical scale although like diagenetic albitization replacement by k feldspar is probably a very common diagenetic reaction it has rarely been reported owing to difficulties in imaging the diagnostic textures with the scanning electron microscopy techniques used by most workers the permeability of the subgrain microtexture may significantly hinder the use of feldspar overgrowths for k ar and 4 0 ar 3 9 ar dating of diagenesis and the existence of suboptical replacive authigenic k feldspar within detrital grains may significantly modify the apparent ar ages of detrital grains similar subgrain microtextures in optically featureless quartz overgrowths are also illustrated

modeling petroleum expulsion in sedimentary basins the importance of igneous intrusion timing and basement composition we thank siccar point energy ltd for permission to publish this study thanks also to robert holdsworth simon holford and christian huag eide for their insightful feedback which has greatly improved the manuscript 1gsa data repository item 2019328 supplementary data geochemical summary rationale and data tables is available online at http www geosociety org datarepository 2019 or on request from editing geosociety org

karst development on a mobile substrate konarsiah salt extrusion iran most karst terranes develop slowly on static limestone substrates as part of the global hydrological cycle here we introduce the novel concept of a karst morphology developing very rapidly on a more soluble substrate of salt nacl that is moving through its own global cycle we open with a reminder of karst features and processes in limestone we then illustrate the global salt cycle using the 180 or so extrusions of hormoz salt in the zagros mountains of iran after describing the geology of an example we consider how it fits into the evolution of salt extrusions this example konarsiah was chosen for its simple hydrology konarsiah is covered by residual soils of the insoluble components that remain in place as the hormoz salt is dissolved dolines in the surface of these soils enlarge and the soils thicken as the moving salt dissolves the long term rate of salt dissolution and soil production on konarsiah are estimated using traditional methods the calculated age of the thickest most distal soil is used to constrain the average rate at which the underlying salt flows downslope after extruding from two vents the average velocities constrained for salt flow are lower than rates of displacement of markers near the summit of konarsiah measured at irregular intervals over five years salt extruding from recently truncated diapirs near the arid south coast of iran exhibit all the features seen in classical karst terranes in the more humid mountains inland vegetated soils protect salt extrusions like konarsiah from erosion and limit their salt karst features soil covers also probably even out salt flow velocities salt extrusions advance when such protective covers grow and thicken in humid conditions they retreat when such protection is lost to erosion in drier conditions these external signs complement internal recumbent folds in extruded salt that signal intervals of faster salt flow when wet than dry they also add to the features that render salt extrusions records of climate change

stratigraphy and morphotectonics of karoo deposits of the northern selous basin tanzania late permian karoo deposits of the northern selous basin in south central tanzania comprise conglomerates and diamictitic boulder beds of alluvial and scarp foot fan origin these merge with grey to greenish sandstones siltstones and black shales of deltaic and lacustrine environments microflora assemblages indicate a late permian age lateral changes and interfingering of various lithofacies units are common depositional development was controlled by syndepositional faulting and variations of gradients resulting from fault movements the position of the fault scarp separating the basin area from the elevated basement horst to the west roughly corresponded with the present boundary between the selous basin and the precambrian metamorphics of the uluguru mountains the late permian karoo succession of this part of the selous basin apparently overlaps older karoo deposits contained in the north northeast trending narrow graben structures it is therefore regarded as a new depositional event which was initiated by renewed tensional tectonism in late permian time during this tectonic episode the narrow early karoo graben structures were expanded into much broader rift basins material eroded from the rift shoulders and associated highlands was literally dumped across the fault scarps forming debris aprons and scarp foot fans rivers emanating from the highlands formed large alluvial fans and further afield deltas issued into freshwater lakes some of these late permian faults were rejuvenated by late cretaceous to early tertiary tectonism thermal waters circulating along fractures converted feldspars biotites and hornblendes to prehnite further tectonic adjustments in mid tertiary time led to the present day morphology

dating of anatase forming diagenetic reactions in rotliegend sandstones of the north german basin diagenetic conditions controlling authigenic formation of anatase and in situ la icp ms u pb isotope dating of this phase are studied in upper rotliegend ii sandstones from two wells in nw germany anatase grew after breakdown of detrital ti phases e g ilmenite although local scale ti transport and mobilization from detrital clay hematite coats or condensed hydrocarbons cannot be ruled out the anatase forming reaction marks the change from a regime of reducing conditions imposed by first hydrocarbon generation to oxidizing conditions probably caused by influx of a fluid from evaporitic zechstein rocks this change in fluid influx is interpreted as response to enhanced normal faulting and halokinesis during accelerated burial in triassic times isotope data of u and pb indicate incorporation of crustal common pb from mesozoic pore fluids but precisely mark diagenetic growth of anatase at 224 3 5 1 5 6 ma in a tera wasserburg plot locally u pb isotope signatures are consistent with either additional incorporation of u and pb from detrital precursor phases or with uptake of uranogenic pb from hydrocarbons generated prior to 224 ma anatase is shown to be a valuable authigenic phase suitable for u pb chronometry of diagenetic events which appears to be unaffected by protracted burial and temperatures exceeding temperatures of crystallization

steps toward dating early diagenetic k feldspar by the 40ar 39ar method abstract authigenic sedimentary low temperature k feldspar separated from albian turonian carbonates in israel was dated by the step heating 40ar 39ar method in contrast to high temperature k feldspars ca 90 of the radiogenic ar was released at temperatures lower than 600 c and fusion mostly occurred below 750 c though formed under low temperature ar loss in all but one sample is estimated to be less than 2 nevertheless the effect of 39ar recoil is evident in some separates probably due to their very fine size 4 10 m the plateau age of one sample with the highest content of authigenic k feldspar 93 96 ma is slightly younger than the assumed stratigraphic age and thus defines the timing of an early diagenetic event within a few million years after deposition other samples where a plateau age could be determined yield ages slightly older strong acid etching 7 n hno3 85 c of the k feldspar enriched fraction may have improved the 39ar 40ar spectra but did not eliminate the presence of minute quantities of detrital k bearing minerals though the present set of data is insufficient for a clear cut conclusion the activation energy of the authigenic k feldspar is in the range of 14 26 kcal mol 1 s 1 much lower than that of magmatic and hydrothermal k feldspars and can probably be attributed to the heating schedule and the small crystal size it is not clear whether the formation at low temperatures

resolution of regional fluid flow related to successive orogenic events on the laurentian margin seven localities distributed along a 180 km long outcrop within the uk sector of the laurentian margin were sampled and all showed two phases of authigenic k feldspar the first phase was precipitated from a cool fluid of moderate salinity and the second phase was precipitated from a hotter more saline fluid ar ar ages for the two episodes of authigenesis are ca 470 ma and ca 432 ma the data can be interpreted to represent two phases of regional scale fluid migration related to ordovician arc accretion and silurian continent continent convergence corresponding to the grampian and scandian episodes of the caledonian orogeny respectively

k ar and ar ar dating the aim of this chapter is to present the k ar and ar ar dating techniques in the context of noble gas studies since there are already several recent texts on k ar and ar ar dating dickin 1995 mcdougall and harrison 1999 the focus of this section will be aspects of argon transport and storage in the crust which affect k ar and ar ar dating including ar loss from minerals by diffusion and ar gain by minerals or excess argon the k ar dating technique was one of the earliest isotope dating techniques developed soon after the discovery of radioactive potassium and provided an important adjunct to u pb and u he dating techniques the ease of measurement and ideal half life 1250 million years see table 2 below for dating geological events has made this the most popular of isotopic dating techniques aldrich and nier 1948 first demonstrated that 40ar was the product of the decay of 40k and soon after k ar ages were being measured in several laboratories most often using an absolute method such as a mcleod gauge to measure argon concentrations the first published k ar results by such a technique were those of smits and gentner 1950 who analyzed sylvite from the buggingen oligocene evaporite deposits obtaining an age of 20 million years mass spectrometers which simultaneously measured very small amounts of gas and the isotope ratios necessary to make corrections for atmospheric contamination quickly replaced manometric techniques crucially the use of static vacuum techniques pioneered by john reynolds at the university of california berkeley meant that mass spectrometers were sufficiently sensitive to analyse the small amounts of gas released from common rocks and minerals although the earliest mass spectrometers were built in house the introduction of the commercially available ms10 farrar et al 1964 a small 180 metal mass spectrometer built for

gas condensate migration and oil fractionation in deltaic systems abstract the term evaporative fractionation is proposed to describe several phenomena involved in the secondary alteration of reservoired oil firstly it is suggested that oil is frequently partially vaporized in the reservoir secondly that gas bearing substantial portions of the oil in solution is conducted along faults to form independent gas condensate accumulations thirdly that residual oils formed in this fashion bear internal evidence of fractionation in addition to the conspicuous loss of light ends there is an increase in the content of light aromatic and naphthenic hydrocarbons relative to paraffins in the residual oil evaporative fractionation effects are recognized for the first time in the distillation and physical property data of us bureau of mines routine method oil analyses fractionation effects are postulated to be the cause of sigmoid as opposed to normal curvilinear aromatic profiles the effects of evaporative fractionation are widespread in oils throughout the united states they are evident in approximately 75 of oils in the gulf coast region and in a large proportion of the gas condensate accumulations the process is a major and apparently unrecognized means of petroleum alteration and of generation of gas condensates experimental evidence shows that partial vaporization results in enhanced levels of light aromatic hydrocarbons in residual oils oil samples were partially vaporized in excess methane at elevated pressure and temperature followed by removal of the vapour the gas chromatographic features of many gulf coast oils were reproduced various levels of light end depletion and enhancement of aromaticity were brought about

petroleum source rock identification of united kingdom atlantic margin oil fields and the western canadian oil sands using platinum palladium osmium and rhenium implications for global petroleum systems this study demonstrates that petroleum and source rocks are enriched in pt and pd to the ppb level and that the 187os 188os composition coupled with the pt pd value permits the fingerprinting of petroleum to its source oils from the united kingdom atlantic margin sourced from the upper jurassic kimmeridge clay fm as well as source rock samples have been analysed for pt and pd when the pt pd value is compared with 187os 188os calculated at the time of oil generation osg the values from both the known source and the oils are similar demonstrating that they can be used as an oil to source fingerprinting tool this inorganic petroleum fingerprinting tool is particularly important in heavily biodegraded petroleum systems where traditional fingerprinting techniques e g biomarkers are severely hampered e g the world s largest oil sand deposit the west canadian oil sands wcos this has caused the source of the wcos to be hotly debated with no present day consensus between inputs from potential source units e g exshaw and gordondale fms 187os 188os and pt pd fingerprinting of the oil sands shows that the majority of the petroleum have similar 187os 188os and pt pd values supporting the hypothesis of one principal source analysis of the potential source rocks establishes that the principal source of the oil sands to be from the jurassic gordondale fm with a minor exshaw fm input thus the combination of previously pioneered re os petroleum geochronology with 187os 188os and pt pd values of petroleum permits both a temporal and spatial understanding of petroleum systems

identifying sources of salinization using hydrochemical and isotopic techniques konarsiah iran konarsiah salt diapir is situated in the simply folded zone of the zagros mountain south iran eight small permanent brine springs emerge from the konarsiah salt body with average total dissolved solids of 326 7 g l there are numerous brackish to saline springs emerging from the alluvial and karst aquifers adjacent to the diapir concerning emergence of konarsiah diapir in the study area halite dissolution is the most probable source of salinity in the adjacent aquifers however other sources including evaporation and deep brines through deep mangerak fault are possible the water samples of the study area were classified based on their water type salinity and the trend of the ions concentration curves the result of this classification is in agreement with the hydrogeological setting of the study area the hydrochemical and isotopic evaluations show that the groundwater samples are the result of mixing of four end members gachsaran sulfate water sarvak and asmari carbonate fresh waters and diapir brine the molar ratios of na cl li cl br cl and so4 cl and isotopic signature of the mixed samples justify a groundwater mixing model for the aquifers adjacent to the salt diapir the share of brine in each adjacent aquifer was calculated using cl mass balance in addition concentrations of 34 trace elements were determined to characterize the diapir brine and to identify the possible tracers of salinity sources in the mixed water samples b mn rb sr cs tl and te were identified as trace elements evidencing contact of groundwater with the salt diapir

the influence of diapir brine on groundwater quality of surrounding aquifers larestan iran hormuz salt breaches the surface in 122 diapirs in southern iran that source brines that generally degrade the groundwater quality in adjacent aquifers the karmustadj salt diapir larestan iran is surrounded by one karstic and two alluvial aquifers we use hydrochemical and hydrogeological measurements of brine springs and exploitation wells to investigate the impact of the karmustadj salt diapir on water quality in its surrounding aquifers our study indicates that the karmustadj salt diapir does not degrade the quality of the adjacent karstic aquifer because impermeable geological formations interrupt the potential hydraulic connectivity between them by contrast the diapir does significantly degrade water quality in part of the western alluvial aquifer and all of the eastern alluvial aquifer infiltration of surface brines draining from the diapir and discharge from perennial brine springs account for the high salinity of groundwater in the surrounding aquifers

degradation and maturity controls on oil field petroleum column heterogeneity in the gullfaks field norwegian north sea abstract a geochemical mapping of the gullfaks reservoir petroleum column based on 226 reservoir core extracts and 23 drill stem test dst and repeat formation test rft oil samples indicates the presence of statistically testable lateral compositional heterogeneities in the petroleum column these different petroleum populations can be related to lateral filling of the field from two source basins and a more pervasive subsequent episode in reservoir biodegradation petroleum maturity gradients within the field were detected using conventional biomarker gc ms methods on saturated hydrocarbon fractions the degree of biodegradation was monitored by quantitative gc of n alkanes in whole oil samples using a squalane internal standard the observed compositional differences in the gullfaks petroleum column are consistent with diffusion being the primary mixing process thermal convection being eliminated on both compositional and modeling grounds compositional differences between core extracts and dst samples from the same intervals suggest that fractionation of petroleum might occur during testing and that interpretation of reservoir petroleum columns from mixed sample sets should be treated cautiously

analysis of petroleum fractions by tlc fid applications to petroleum reservoir description abstract thin layer chromatography and flame ionization detection iatroscan tlc fid offers a rapid and accurate method for quantifying saturated and aromatic hydrocarbons and resin asphaltene fractions in solvent extracts of petroleum source rocks reservoir rocks and crude oils while the instrument is superficially simple special precautions need to be taken in calibration and parameter setting due to complexities arising from the operational characteristics of the detector system nevertheless the technique offers superior speed and precision to conventional mplc analysis of petroleum fractions this paper describes the choice of operational parameters provides comparison with the traditional group type analysis technique mplc and presents some geochemical applications

diagenetic k feldspar pseudomorphs in the triassic buntsandstein sandstones of the iberian range spain early diagenetic k feldspar in the triassic buntsandstein of the iberian range spain occurs as pseudomorphs after detrital k feldspar or 99 untwinned commonly heavily clouded by vacuoles and tiny inclusions dark luminescing and are composed of numerous fine euhedral crystals of k feldspar the latter property suggests that the pseudomorphs form via dissolution of detrital k feldspar and plagioclase and precipitation of authigenic k feldspar x ray diffraction analysis shows that the authigenic k feldspar is intermediate microcline

fluid inclusions in sedimentary and diagenetic systems abstract some of the major problems in sedimentary geology can be solved by using fluid inclusions in sedimentary and diagenetic minerals important fluids in the sedimentary realm include atmospheric gases fresh water of meteoric origin lake water seawater mixed water evaporated water formation waters deep in basins oil and natural gas preserving a record of the distribution and composition of these fluids from the past should contribute significantly to studies of paleoclimate and global change research is essential for improving understanding of diagenetic systems and provides useful information in petroleum geology applications of fluid inclusions to sedimentary systems are not without their complexities some fluid inclusions exposed to natural conditions of increasing temperature may be altered by thermal reequilibration which results in stretching or leakage and refilling of some fluid inclusions similarly overheating in the laboratory can also cause reequilibration of fluid inclusions so fluid inclusions from the sedimentary realm must be handled carefully and protected from overheating natural overheating of fluid inclusions must be evaluated through analysis of the most finely discriminated events of fluid inclusion entrapment fluid inclusion assemblages fia consistency in homogenization temperatures within a fluid inclusion assemblage consisting of variably sized and shaped inclusions is the hallmark of a data set that has not been altered through thermal reequilibration in contrast fluid inclusion assemblages yielding variable data may have been altered through thermal reequilibration if a fluid inclusion assemblage has not been altered by thermal reequilibration its fluid inclusions may be useful as geothermometers for low and high temperature systems or useful as geobarometers applicable throughout the sedimentary realm if a fluid inclusion assemblage has been altered partially by thermal reequilibration techniques for distinguishing between altered and unaltered fluid inclusions may be applied in studies of global change fluid inclusions can be used as sensitive indicators of paleotemperature of surface environments fluid inclusions also preserve microsamples of ancient seawater and atmosphere the analysis of which could figure prominently into discussions of past changes in chemistry of the atmosphere and oceans in petroleum geology fluid inclusions have proven to be useful indicators of migration pathways of hydrocarbons they can delineate the evolution of the chemistry of hydrocarbons and they remain important in understanding the thermal history of basins and relating fluid migration events to evolution of reservoir systems in studies of diagenesis fluid inclusions can be the most definitive record most diagenetic systems are closely linked to temperature and salinity of the fluid thus fluid inclusions are sensitive indicators of diagenetic environments

the application of fluid inclusions to migration of oil and diagenesis in petroleum reservoirs abstract fluid inclusions can be used to interpret thermal history and petroleum maturation and migration relative to burial history temperature pressure and composition data collected from fluid inclusions are used to determine the environment of diagenesis and the timing of cementation and migration cements in petroleum reservoirs contain both oil and aqueous fluid inclusions fluorescence spectroscopy is used to identify oil inclusions and to determine the maturity of entrapped oil the lifetime of fluorescence induced by a pulsed laser is related to the api gravity of entrapped oil interpretation of fluid inclusion data depends on knowing the origin of fluid inclusions and the probability that they survive in the burial environment those aspects of fluid inclusion study are investigated by synthesizing oil and aqueous inclusions in calcite crystals in laboratory experiments examples of how fluid inclusions are used to determine the physico chemical environments of diagenesis in petroleum reservoirs and the timing of cementation and migration are given for the wealden basin england the mishrif formation dubai the smackover formation gulf coast u s a and jurassic sandstones offshore norway in the wealden basin temperature data from fluid inclusions are used to determine that oil migration occurred in the cretaceous and that the reservoir rocks have been uplifted to varying degrees at a time after migration distribution of oil inclusions indicates that generation and migration of oil was principally in the western part of the basin the geochemistry of oil inclusions in calcite cements from the mishrif formation dubai are used to determine the type and maturity of entrapped oil temperature data from oil and water inclusions are used to relate reservoir diagenesis to burial history and the migration of oil in deep smackover reservoirs oil contains h 2 s the origin of the h 2 s is examined by study of fluid inclusions containing h 2 s in jurassic sandstones offshore norway fluid inclusion studies show that silica cementation is related to burial depth whereas a later calcite cementation originated from invasion of a hot fluid

age and geologic setting of quartz vein hosted gold mineralization at curraghinalt northern ireland implications for genesis and classification acknowledgments we are grateful to dalradian gold ltd for providing the sections for petrographic analysis geochemical data and general support we would also like to thank the following john still alison sandison and jenny johnston of the school of geosciences university of aberdeen for assistance with the sem studies js and with preparing figures as and jj nerc for ongoing funding of the argon isotope facility at suerc jim imlach and ross dymock at suerc for technical assistance and martin lee at the school of geographical and earth sciences at the university of glasgow for use of the sem cl equipment the paper has benefitted significantly from comments by the official reviewers and unofficial reviews by garth earls jamie wilkinson mark cooper and adrian boyce and detailed conversations with ian alsop structural geology of the sperrins and nyree hill and gawen jenkin gold mineralization in the caledonides the authors are entirely responsible for the conclusions expressed

hydrocarbon generation and migration from jurassic source rocks in the e shetland basin and viking graben of the northern north sea in the e shetland basin oil generation began 65 ma ago peak oil generation maturity occurs today at 3250 m 0 7 r 0 and was first reached 40 50 ma ago the oil generation threshold is at 2500 m highest oil saturations in the kimmeridge clay occur at 0 8 r 0 oil expulsion efficiencies are 20 30 oil phase migration has probably occurred through oil wet kerogen laminae and through interconnected large pores aided by low oil water interfacial tensions oil migrated along strong lateral fluid pressure gradients from overpressured source rocks in half grabens to jurassic reservoirs in tilted fault blocks in the viking graben the kimmeridge clay is at oil floor maturity below 4500 m oil and peak oil generation began 7c 80 and 55 65 ma ago respectively 40 ma ago the kimmeridge clay passed through peak generation and gas generation by cracking of oil had begun peak dry gas generation from brent coals occurs today below 5000 m and began 40 ma ago the frigg field gas probably generated from late jurassic source rocks migrated through microfractures in overpressured mudstones below 3500 m above 3500 m methane probably migrated in aqueous solution and was exsolved in the early tertiary aquifer

applications of 3d seismic attribute analysis in hydrocarbon prospect identification and evaluation verification and validation based on fluvial palaeochannel cross sectional geometry and sinuosity ness county kansas usa abstract due to their high resolution and established success rates the analysis of geometrical and stratigraphic 3d seismic reflection data attributes have become one of the most important tools in many hydrocarbon exploration and development programs in areas with high drilling risk as a result of the lack of spatial continuity and lithological variation of potential prospects analysis of relevant seismic attributes is essential to successful placement of wells this study of the york field ness county kansas presents a corroborative finding based on the analysis of a set of 3d seismic attributes revealing a meandering fluvial channel system incised on the mississippian stratigraphic unconformity north east of a previously interpreted weirman field palaeoshoreline and submarine channels the york field prospect identification and appraisal program targeted the cherokee sands where reservoir properties are favorable and where it was thought that thick cherokee sands correlate with structural mississippian highs we produce evidence that cherokee sand prone fluvial facies is mappable based on synergistic analysis of seismic arrival time amplitude spectral decomposition acoustic impedance and waveform attributes seismic amplitude highs and relative acoustic impedance lows showed moderate conformance with mississippian horizon time lows controls exerted by channel post confluence water and sediments supply provide corroborating hydraulic geometry aspects for the interpreted fluvial system time structural maps in addition to time and horizon slices of several 3d seismic attributes including amplitude spectral decomposition components and relative acoustic impedance all seem to indicate that five previously drilled dry wells within the study area were outside the boundary of a meandering cherokee fluvial system of potential reservoir quality additionally comparisons of the results of this research to previous studies conducted in the south west of ness county have provided an opportunity to support and contribute to interpreted paleodepositional setting established by raef et al 2015 where a palaeoshorline was interpreted the results of this study support a broadly ne sw trending meandering channel system with se flow direction

rb sr and k ar dating of clay diagenesis in jurassic sandstone oil reservoir north sea rb sr and k ar isotopic determinations were combined with scanning electron microscopy sem observations and x ray diffractometry xrd controls to date the diagenetic formation of clay minerals from oil bearing sandstones of the middle jurassic brent sandstone in the north sea the separated clay fractions often contain detrital components especially k feldspars which are reduced to sizes smaller than 0 4 m either by intense in situ alteration or by destructive sample preparation direct rb sr and k ar isotopic dating of diagenetic illite therefore was not possible isotopic data obtained on mixtures of detrital and newly formed components showed however that illite formed about 40 to 45 ma this value also was obtained directly on clay fractions separated by a gentle method of disaggregation illitization is related to emplacement of hydrocarbons and associated waters into the formation aqueous and hydrocarbon fluids simultaneously trapped in quartz overgrowth inclusions indicate late silicification contemporaneous with this fluid migration minimum trapping temperatures of at least 110 c for these fluid inclusions are too high for the present burial depth hot fluids are assumed to have originated in deep source rocks beneath the brent reservoirs and migrated upward during the middle eocene

re os geochronology and fingerprinting of united kingdom atlantic margin oil temporal implications for regional petroleum systems we demonstrate that the re os system can be used to understand the temporal evolution of a petroleum system as well as aid in the identification of source units traditional geochemical methods high performance liquid chromatography carbon isotope gas chromatography and biomarker analysis indicate that the main source of 18 oils analyzed for re os geochronology from the united kingdom atlantic margin clair schiehallion cuillin and foinaven fields is late jurassic marine shales this is supported by the os isotopic composition 187 os 188 os of the late jurassic source 0 9 2 4 at the timing of oil generation being similar to that of the oil 68 ma 0 92 1 12 indicating that the re os system can potentially be used to fingerprint the source of an oil the re os data for the 18 oils yield an age 68 13 ma that agrees with both the relative basin models and absolute ar ar geochronology timing of oil generation indicating that that re os oil geochronology records oil generation events

hydrochemical characteristics and groundwater quality assessment in bushehr province sw iran the chemical quality of groundwater of bushehr southwest of iran was assessed for its suitability for drinking purposes hydro geochemical studies were carried out in this area to identify the geochemical processes and their relation to groundwater quality a total of 19 water samples were collected from the aquifer the samples were then analyzed for different physicochemical properties such as ph total dissolved solids tds total hardness th calcium magnesium carbonate bicarbonate sulfate and chloride concentrations in this study the average tds content was in the range of 4419 10 066 mg l l and other important parameters of water such as th 1200 3500 mg l 1 and chloride 1046 3855 mg l 1 were also higher than the maximum permissible limits specified by who on the basis of concentrations of major elements studies of the study area showed that the total samples collected are unsuitable for drinking linear increase in sodium and chloride of the total dissolved ion indicated a dissolution of halite in the study area salinity of the aquifer is mainly a result of the dalaki river recharge dissolution of evaporated minerals intraformation and also agricultural returned water the dissolution of evaporite minerals such as halite and gypsum has increased the concentration of total dissolved solids and of sulfate in the shahpour river and also groundwater entering the study area has caused salinity in this river

geochemical and biological marker assessment of depositional environments using brazilian offshore oils abstract a combined geochemical and molecular characterization of a wide selection of oils from the major brazilian offshore basins has been undertaken the elemental sulphur nickel and vanadium and bulk oapi and 13c properties of each sample been considered together with its molecular composition determined using liquid and gas chromatography and quantitative biological marker investigations using gas chromatography mass spectrometry for alkanes the results reveal significant differences in the chemical features of the various oils which enable them to be divided into five groups the distinction of the groups appears to reflect differences in the depositional environment of the source rocks of the oils each group is correlated tentatively with source rocks laid down in a specific depositional regime namely lacustrine freshwater lacustrine saline water marine evaporitic marine carbonate or marine deltaic the diagnostic features that allow this classification are the relative abundance and carbon number distributions of n alkanes pristane phytane ratios sulphur nickel and vanadium contents carbon isotope data the absolute concentrations of hopanes and steranes and their abundance relative to 4 methylsteranes and also the occurrence and abundance of several specific biological markers including 18 h oleanane gammacerane carotane tricyclic terpanes higher acyclic isoprenoids 28 30 bisnorhopane and 25 28 30 trisnorhopane this investigation shows the value of a combined geochemical and molecular approach in the assessment of the palaeoenvironment of deposition of the source rocks which gave rise to the oils

strengthening the link between geochronology textures and petrology time must be integrated with other geologic parameters such as pressure temperature p t composition or structural textural information in order to quantify the dynamics of geologic processes like mountain building faulting metamorphism or magmatism in the past this connection was weak due to large sample sizes required in geochronology however recent developments open up exciting new possibilities texturally controlled in situ dating of minerals utilizing uv laser ablation 40ar 39ar or rb sr microsampling facilitates the crucial link between ages and textures at high spatial resolution in situ u pb ages of accessory minerals can now be linked to the corresponding p t evolution via their characteristic trace elemental signatures indicative of mineral reactions in rocks garnet dating by sm nd and more recently lu hf can greatly benefit from both laser ablation inductively coupled plasma mass spectrometry icpms screening and improved leaching strategies improving the link between time and p t such integrated approaches can yield the duration and rates of deformation in shear zones the rates of burial and exhumation of subducted rocks or the duration of entire metamorphic loops to name a few potential for further development is identified in diverse areas dating of carbonate minerals related to brittle faulting using u pb could provide previously unavailable constraints on rates and duration of brittle deformation in the earth s upper crust in situ rb sr dating applicable to micas could become available using either laser ablation dynamic reaction cell icpms or microbeam accelerator mass spectrometry other future developments and trends and their limitations are discussed briefly

natural fracture propping and earthquake induced oil migration in fractured basement reservoirs the geological processes that create fluid storage capacity and connectivity in global fractured basement reservoirs are poorly understood compared to conventional hydrocarbon plays hosting potentially multibillion barrels of oil the upfaulted precambrian basement of the rona ridge offshore west of shetland uk gives key insights into how such reservoirs form oil presence is everywhere associated with sub millimeter to meterthickness mineralized fracture systems cutting both basement and local preseal cover sequences mineral textures and fluid inclusion geothermometry suggest a low temperature 90 220 c near surface hydrothermal system as does the preservation of clastic sediments in the same fractures these fills act as permanent props holding fractures open forming long term fissures in the basement that permit oil ingress and storage calcite fill u pb dating constrains the onset of mineralization and contemporaneous oil charge to the late cretaceous the additional preservation of oil stained injected sediment slurries and silica gels along basement faults suggests that rift related seismogenic faulting initiated lateral oil migration from jurassic source rocks into the adjacent upfaulted ridge subsidence below sea level in the latest cretaceous sealed the ridge with shales and buoyancy driven migration of oil into the preexisting propped fracture systems continued long after the cessation of rifting these new observations provide an explanation for the viability of sub unconformity fractured basement reservoirs worldwide and have wider implications for subsurface fluid migration processes generally

k ar dating of time of gas emplacement in rotliegendes sandstone netherlands the time of emplacement of gas into each of two reservoirs in the rotliegendes sandstone one in the groningen field and one in the broad fourteens basin was estimated from potassium argon k ar ages of diagenetic illitic clays and careful petrographic observations of the rocks in which the clays occurred in each reservoir the intensity of diagenetic alteration increased downward within a relatively thin 15 to 175 m or 50 to 580 ft interval apparently reflecting a longer period of alteration for deeper samples this is expected in cases where a gradually accumulating gas column expels pore water from progressively deeper parts of the reservoir rock illite is a common diagenetic phase in the rotliegendes because detrital contamination in these rocks has been infer ed to be minimal k ar ages of very fine grained illite should indicate the time the illite forming process ceases in each case reported here the age of the deeper sample is younger than that of the shallower we interpret the age of the finest illite fraction in the gas zone of each reservoir to indicate the time at which illite formation ceased as the result of gas emplacement and pore fluid displacement in the rock our results indicate that gas emplacement in the groningen field commenced prior to 150 ma and that the growth of diagenetic illite continued in the present day water zone from that time until at least 120 ma

comparative 40ar 39ar and k ar dating of illite type clay minerals a tentative explanation for age identities and differences abstract the 40 k 40 ar k ar and 40 ar 39 ar dating methods are applied here to the same very small micrometric illite type particles that crystallized under low temperature 5 9 ma the same size fractions dated by the 40 ar 39 ar method give total gas ages ranging from 173 3 2 0 to 228 8 1 6 ma nearly all 40 ar 39 ar total gas ages are slightly older which cannot be explained by the recoil effect only the impact of which being amplified by the inhomogeneous shape of the clay minerals and their crystallographic characteristics with varied crystallinity indices and a particle width about 10 times large than thickness the 40 ar 39 ar data outline some advantages such as the plateaus obtained by incremental step heating of the various size fractions even if not translatable straight as ages of the illite populations they allow identification of two generations of authigenic illite that formed at about 200 and 175 ma and one detrital generation however 40 ar 39 ar dating of clay minerals remains challenging as technical factors such as the non standardized encapsulation may have potential unexpected effects both dating methods have their limitations 1 k ar dating requires relatively large samples ca 10 20 mg incurring potential sample homogeneity problems with two aliquots required for k and ar analysis for an age determination also inducing a higher analytical uncertainty 2 an identified drawback of 40 ar 39 ar dating is ar recoil and therefore potential loss that occurs during neutronic creation of 39 ar from 39 k mostly in the finer mineral particles if all the recoiled 39 ar is redistributed into adjacent grains minerals the final 40 ar 39 ar age of the analyzed size fraction remains theoretically identical but it is not systematic in clay type material the finest grain sizes e g 39 ar recoil and are therefore only datable by the 40 ar 39 ar method using an encapsulation technique that still needs to be technically evaluated in this study 39 ar recoil during irradiation was quantified by encapsulation it ranged from about 20 of the total 39 ar for the 39 ar recoil confirms that grain size increasing minimizes the recoil effect but how it proceeds has still to be explained despite recent developments in 40 ar 39 ar dating the conventional k ar method is still a valuable tool for clay dating due to a convenient and straightforward use supported by a standardized and well controlled technical approach the present comparison of the two ar dating methods as applied to clay material shows that neither method is presently outdated and that they are even of reciprocal use both methods have distinct application fields in clay geochronology and complementary application fields in clay crystallography

petroleum evolution within the tarim basin northwestern china insights from organic geochemistry fluid inclusions and rhenium osmium geochronology of the halahatang oil field the newly discovered halahatang oil field in the northern tarim basin has a potential resource of more than 70 billion bbl of oil oil organic geochemical data from the halahatang oil field indicate that the oils are of moderate maturity biodegraded and represent one oil family derived from the same paleozoic marine source modeling of coeval aqueous and hydrocarbon bearing inclusion data provide fluid trapping temperatures and pressures of 100 c to 110 c and approximately 39 to 59 mpa 5656 8557 psi respectively the fluid inclusion data coupled with the previous basin model studies suggest a single prolonged oil migration event during the permian the re os isotope data of the oil yields an early permian re os age of 285 48 ma the age agrees with the timing of maturation of the paleozoic source via burial history modeling but is slightly older 5 55 m y than the oil migration and accumulation timing implied by the basin modeling coupled with fluid inclusion analysis and the published reservoir illite k ar dates thus the oil re os date suggests that oil generation in the halahatang depression of the tarim basin occurred during the early permian rather than the silurian as previously proposed with subsequent oil migration and accumulation occurring during the middle late permian as recorded by basin modeling coupled with fluid inclusion analysis and illite k ar dating in addition to promoting petroleum exploration in the tarim basin this study which combines crude oil re os isotope dating and traditional analytical methods organic geochemistry and fluid inclusion analysis to constrain petroleum evolution is applicable to hydrocarbon systems worldwide

heterogeneity of oil composition within a reservoir as a reflection of accumulation history abstract the unaltered petroleums of a small oil field in the f r germany reveal pronounced spatial heterogeneities in bulk and molecular composition over most of the field area the oil in high porosity high permeability sand intervals bears a higher proportion of saturated hydrocarbons and has a higher maturity chemical signature as compared to oils occupying lower porosity lower permeability zones for all sands with less than about 13 porosity a regular relationship was observed between oil composition and porosity permeability with a decrease of the latter petrophysical properties increasingly lower chemical maturities and increasingly different bulk chemical compositions lower proportions of saturated hydrocarbons and higher proportions of nso compounds were recorded maximum contrasts measured for chemical maturities are e g 0 63 versus 0 82 vitrinite reflectance equivalents rc values calculated on the basis of the methylphenanthrene index according to radke and welte 1983 0 31 versus 0 84 for the ratio of triaromatic to mono plus triaromatic steroid hydrocarbons and 0 38 versus 0 47 for the 20s 20s 20r ratio of c29 5 h 14 h 17 h steranes these spatial heterogeneities in the composition of the oils are interpreted to reflect 1 i successive stages of trap filling due to episodes of increasing burial and maturation of the relevant source rocks in combination with 2 ii low rates of in reservoir mixing of these individual oil charges by convection or diffusion recognition of compositional heterogeneities within the oil column of individual fields may not only provide a basis for the reconstruction of reservoir filling history but may also have important implications for improving petroleum production

dating of multistage fluid flow in sandstones through ultraviolet laser argon argon dating of potassium feldspar cements containing fluid inclusions we determined temperature composition time data for paleofluids in a sedimentary basin including data for an evolving episode of fluid flow recorded in distinct phases of cement the fluid evolved from mixed aqueous oil 83 million years ago to purely aqueous by 76 million years ago thus dating the time of oil charge in this reservoir

magmatism and continental break up in the south atlantic high precision40ar 39ar geochronology abstract a detailed ar ar study of the parana etendeka continental flood basalts cfb has been undertaken using laser spot analysis data provide information not only on the age of the samples but also on the variability of the non radiogenic ar component and state of alteration the results indicate the parana etendeka cfb were erupted over 10 million years between 137 and 127 ma providing a minimum overall eruption rate of 0 1 km3 yr 1 this is an order of magnitude less than that previously proposed for this the deccan and siberian cfb provinces but it is similar to estimates for hawaii iceland and the columbia river cfb in detail the new ar ar analyses indicate that magmatism within the parana etendeka province migrated from nw to se prior to and during the opening of the south atlantic providing an explanation for the asymmetry of the cfb lavas about the south atlantic moreover chemically defined magma types were erupted at different times in different places and so within the paranathey may not be used as reliable chronostratigraphic units rather such magmatic units may reflect the extent of compositionally distinct source regions in the uppermost mantle and indicate that partial melting took place over a wide area under the paranabasin the nw se migration of the onset of magmatism might be interpreted as a plume trace but the inferred rate of movement is 3 times faster than that inferred from subsequent magmatism on the rio grande rise it is argued that the onset of magmatism reflected extensional tectonics normal to the ponta grossa dyke swarm given that magmatism preceded the main phase of rifting and that extension across the ponta grossa was moderate current plume models have difficulty in predicting sufficient melting within the asthenosphere

genetic characterization of natural gases natural gases can be characterized genetically using four properties c2 concentration carbon and hydrogen isotope variations in methane and carbon isotope variation in ethane three diagrams for genetic characterization of gases have been designed in which the carbon isotopic composition of methane is correlated with the other parameters in these diagrams compositional fields have been defined for primary gases biogenic thermogenic associated and thermogenic nonassociated and for gases which result from mixing of these gases these fields are strictly empirical and comprise compositional variations found in about 500 natural gases the isotopic and compositional variations in natural gases can be described in terms of 1 processes during formation of the gases such as bacterial fermentation or maturation of organic matter and 2 processes during secondary migration mixing of primary gases is an important and common process migration of gases predominantly affects the c2 concentration whereas the isotopic properties of gaseous hydrocarbons primarily remain unchanged allowing an assessment of the origin of migrated gases and properties of their source rocks the formation of gas from humic organic matter and coals is not yet clear from published data the diagrams use data from various basins and areas interstitial gases from the gulf of california are entirely of bacterial origin traces of thermogenic gases are formed only in the vicinity of dolerite sills gases in the south german molasse basin and in the vienna basin are of bacterial mixed and thermogenic origins data from the north italian po basin provide examples for genetic characterization of migrated gases

3 d 40ar39ar geochronology in the parana continental flood basalt province new 40ar39ar analyses of borehole samples from the parana etendeka continental flood basalt province provide critical evidence of eruption rates in unexposed regions when combined with surface samples the new data clarify the duration of this major volcanic province new ages from both surface and borehole samples confirm a 10 12 million year duration of magmatism which post dates the tithonian mass extinction and provide a unique 3 dimensional picture of the spatial and temporal eruption of the lava pile chemically defined magma types are diachronous and the onset of magmatism occurred 500 1000 km inland migrating southeast towards the incipient south atlantic ocean calculated eruption rates increased from 0 03 km3 yr 1 between 138 and 135 ma through 0 13 km3 yr 1 between 135 and 133 ma to 0 21 km3 yr 1 between 133 and 131 ma supporting the notion that the rate of magmatism increased with time and proximity to the developing south atlantic after 131 ma the continental eruption rates dropped dramatically to 0 01 km3 yr 1 presumably because rifting had occurred and eruption centred in the oceanic rio grande rise with eruption rates of around 0 3 0 5 km3 yr 1 given the available constraints on the potential temperature of the plume thickness of the continental lithosphere and degrees of extension through time predicted melt production rates within the plume seriously underestimate the calculated eruption rates on the continent however the eruption rates can be reconciled if melting occurred by conductive heating of volatile enriched mantle the diachronous nature of the magma types supports the idea that melting occurred over a wide area and that the different magma types reflect different source regions rather than the temporal evolution of magmas from a single source given that 10 million years is appropriate to the timescales for conductive heating above the mantle plume it is suggested that these distinct source regions were located within the lithospheric mantle consistent with geochemical studies

seismic stratigraphy of early pennsylvanian morrowan sandstones minneola complex ford and clark counties kansas the oil fields of the minneola complex in southwest kansas produce from northwest southeast trending marine sandstones of morrowan age reservoir quality stratigraphic traps developed at the intersection of sandstone trends and topographic lows or channels on the underlying eroded mississippian surface the discovery well ladd 1 8 norton was drilled in sec 8 t30s r25w clark county kansas on a seismic anomaly recognized on 12 fold vibroseis data eleven feet 3 m of productive morrowan sandstone at 5 280 ft 1 609 m was completed for 157 bopd electric logs in the discovery well revealed that an expanded up to 100 ft or 30 m morrow section consisting of sandstone and shale had been deposited in lows on the underlying eroded mississippian surface modeling indicated that the addition of this low velocity clastic material within these channels caused a variety of seismic anomalies the distribution of which guided subsequent exploration and development drilling these seismic anomalies are associated with topographic lows on the mississippian unconformity surface rather than the productive sandstones the anomalies vary in character and consist of 1 diffractions 2 high amplitude bright spots 3 breaks in seismic continuity of the mississippian reflector polarity reversals 4 sagging of the marmaton reflector and 5 possible faulting of viola arbuckle reflectors these anomalies vary according to the thickness of sediment deposited within the erosionally low areas the varying geometry and lithologies of these deposits variations in overlying sediments and the angle at which the seismic line is shot across the lows subsurface control and seismic data can be used to trace the paleodrainage pattern and to interpret the distribution of the overlying productive morrowan sandstones

rhenium osmium geochronology and oil source correlation of the duvernay petroleum system western canada sedimentary basin implications for the application of the rhenium osmium geochronometer to petroleum systems the re os geochronometer has been applied to many petroleum systems worldwide however it is debated if the re os systematics in petroleum actually record the timing of oil generation here we investigate the re os isotope systematics of the duvernay petroleum system in the western canada sedimentary basin which has been shown to be a relatively simple petroleum system that is associated with oil generated during the late cretaceous early eocene laramide orogeny from a single source the organic geochemistry of the duvernay oils pristane phytane ratios of 1 5 smooth homohopane profile c29 c27 c28 regular sterane distribution and predominance of diasteranes over regular steranes strongly suggests the oil source to be that of type i ii marine organic matter of the upper devonian duvernay formation the asphaltene fraction re os isotope data of the duvernay oil yield an age of 66 31 ma which is in excellent agreement with the timing of the main stage hydrocarbon generation of the duvernay formation based on basin models further the similarity between the 187os 188os compositions of the duvernay formation source rock 0 46 1 48 and the oil 0 55 1 06 at the time of oil generation supports the hypothesis that the 187os 188os composition of an oil is inherited from the source unit at the time of oil generation and therefore shows no or limited influence from interaction with basin fluids this study supports that the re os isotope systematics of an oil can yield the timing of oil generation and be used to trace its source

mineralogy of the volcanic influenced great northern coal seam in the sydney basin australia abstract the mineralogy of the individual coal plies and intra seam claystone bands in the great northern seam of the sydney basin has been evaluated using optical and scanning electron microscopy and quantitative x ray diffraction techniques the uppermost two claystone bands are tonsteins consisting mainly of well ordered kaolinite with graupen to vermicular textures idiomorphic crystals of k feldspar within these tonsteins may represent members of the anorthoclase sanidine series or a sodic sanidine and indicate an acid to intermediate volcanic ash input in contrast the lowermost parting was largely derived from epiclastic sediment admixed with minor volcanic material such as high temperature quartz and a different type of k feldspar component the mineral fraction of the coals especially in the middle and upper parts of the seam is dominated by authigenic kaolinite with a very low abundance of quartz apart from the tonsteins authigenic processes therefore appear to be the dominant mechanism of mineral matter formation authigenic k feldspar also occurs in the lower few metres of the seam with a variety of modes of occurrence including cell and cleat infillings cross cutting veins and thin laminae parallel to the organic matter and detrital clay bands a late syngenetic low temperature hydrothermal fluid injection process is suggested for formation of the feldspar veins the origin of the fluid is uncertain but is most likely associated with contemporaneous volcanic activity

occurrence and resource evaluation of the subsurface high k brines in the pingluoba brine bearing structure in western sichuan basin in the western sichuan basin of china occurs an anticline in which high k brines are found in the carbonate rocks of the middle triassic leikoupo group the brine bearing formation is at depth ranging from 4 465 to 4 565 m and the brines are enriched in a fault zone in the anticline the pl4 well tapping the brine bearing formation flows brines having tds of 348 392 377 27 g l k contents of 48 95 53 267 g l and b contents of 4 994 g l the tds of the brines are close to those of the yellow sea water and the south china sea water when evaporated to the stage of epsomite precipitation the hydraulic head of the high k brines in the pl4 well tapping the brine bearing formation is calculated as high as 7 564 m and is 3 049 m above the land surface a 3d numerical model is used to simulate the flow of the brines under the condition of exploitation and prediction calculation of the exploitation of the pl4 well is also performed when the hydraulic head of the brines in the pl4 well is dropped to the land surface and to a depth of about 1 000 m below the land surface the exploitable brine resources of the well are estimated as approximately 1 1 106 and 3 8 106 m3 respectively

tectonic controls on rift basin morphology evolution of the northern malawi nyasa rift radiometric k ar and ar 40 ar 39 age determinations of volcanic and volcaniclastic rocks combined with structural gravity and seismic reflection data are used to constrain the age of sedimentary strata contained within the seismically and volcanically active northern malawi nyasa rift and to characterize changes in basin and flank morphologies with time faulting and volcanism within the tukuyu karonga basin began at approximately 8 6 ma when sediments were deposited in abroad initially asymmetric lake basin bounded on its northeastern side by a border fault system with minor topographic relief extensions primarily by a slip along the border fault and subsequent regional isostatic compensation led to the development of a 5 km deep basin bounded by broad uplifted flanks along the low relief basin margin opposite border fault younger stratigraphic sequences commonly onlap older wedge shaped sequences although their internal geometry is often progradational intrabasinal faulting flankuplift and basaltic and felsic volcanism from centers at the northern end of the basin became more important at about 2 5 ma when cross rift transfer faults developed to link the tukuyu karonga basin to the rukwa basin local uplift and volcanic construction at the northern end of the basin led to a southeastward shift in the basin s depocenter sequence boundaries are commonly erosional along this low relief hanging wall margin and conformable in the deep lake basin the geometry of stratigraphic sequences and the distribution of the erosion indicate that horizontal and vertical crustal movements both across and along the length of the rift basin led to changes in levels of the lake irrespective of paleoclimatic fluctuations