diagenetic and catagenetic products of isorenieratene molecular indicators for photic zone anoxia a wide range of novel diagenetic and catagenetic products of the diaromatic carotenoid isorenieratene a pigment of the photosynthetic green sulphur bacteria chlorobiaceae has been identified in a number of sedimentary rocks ranging from ordovician to miocene compound identification is based on nmr mass spectrometry the presence of atropisomers and stable carbon isotopes atropisomers contain an axially chiral centre which in combination with other chiral centres results in two or more diastereomers that can be separated on a normal gc column chlorobiaceae use the reverse tca cycle to fix carbon so that their biomass is enriched in 13c high 13c contents of isorenieratene derivatives therefore support their inferred origins isorenieratene derivatives include c 40 c 33 and c 32 diaryl isoprenoids and short chain aryl isoprenoids with additional aromatic and or s containing rings c 33 and c 32 compounds are diagenetic products of c 33 and c 32 carotenoids formed from isorenieratene during early diagenesis through expulsion of toluene and m xylene respectively cyclisation of the polyene acyclic isoprenoid chain can proceed via an intramolecular diels alder reaction followed by aromatisation of the newly formed ring sulphurisation is also an important process during early diagenesis competing with expulsion and cyclisation sulphur bound isorenieratane is released during progressive diagenesis due to cleavage of relatively weak ss and cs bonds cleavage of c c bonds during aromatisation of newly formed rings and during catagenesis yields short chain compounds the inherent presence of a conjugated double bond system in carotenoids implies that similar diagenetic and catagenetic reactions can occur with all carotenoids chlorobiaceae live at or below the oxic anoxic boundary layer and require both light and h 2s the presence of isorenieratene or its diagenetic and catagenetic products in ancient sedimentary rocks and crude oils is therefore an excellent indication for photic zone anoxia in the depositional environment diagenetic and catagenetic products of isorenieratene are expected to find applications in reconstruction of palaeoenvironments and in oil oil and oil source rock correlation studies their presence in several petroleum source rocks suggests that anoxia is an important environmental parameter for the preservation of organic matter

dolomitization a critical view of some current views the principal models in vogue today for dolomitization are the mixing zone and the sabkha models despite the wide acceptance of these models there has been little critical assessment of their validity such an assessment is the objective of the present paper a close look at the dorag mixing zone model badiozamani 1973 reveals several serious weaknesses 1 the range of freshwater seawater mixtures that meet the dorag requirement for dolomitization shrinks to a small window if the geologically more realistic disordered dolomite is used in the calculations instead of the ordered dolomite on which the model is based 2 in none of the known modern coastal mixing zones in limestone or lime sediments has replacement by dolomite been observed 3 in a number of dolomites interpreted to be of mixing zone origin dolomite has precipitated without dissolution of the calcite substrate evidence that negates the fundamental premise of the dorag model in addition to these weaknesses isotope and trace element data used to identify mixed water dolomite are inadmissible because 1 isotopic fractionation factors for dolomites remain unresolved 2 isotope values uncorrected for temperature for a host of dolomites interpreted to be of different origins overlap 3 nonisomorphous trace elements such as na in dolomite cannot on theoretical grounds be relied on to identify dolomitizing fluids similar overall objections can be brought against folk and land9s 1975 schizohaline version of mixing zone dolomitization in summary mixing zone models have such weak underpinnings that they should be questioned as viable explanations for massive dolomitization contemporaneous dolomite formation in modern sabkhas is well documented but the important question of whether the mechanism of dolomite formation is replacement or direct precipitation remains to be resolved in the well studied sabkha at abu dhabi brine chemistry changes have been used as evidence of a replacement origin for the dolomite but it is shown here that this evidence is far from unequivocal an alternative origin of direct precipitation of dolomite is offered an origin in keeping with dolomite precipitation known from other modern sabkhas and saline lakes and in line with our laboratory experience with dolomite synthesis moreover it is suggested here that in general contemporaneous dolomite will form at low temperatures only by direct precipitation a mechanism that requires special conditions of highly super saturated waters of high mg ca ratio and elevated co 3 hco 3 concentrations this may explain why modern dolomite is mainly restricted to evaporitic environments a bias not shared by ancient dolomites in contrast replacement dolomite appears to require at low temperatures long reaction times or 10 4 yr a requirement that is mainly to be met in large regional groundwater flow systems both marine and nonmarine a third dolomitization model considered here is that of baker and kastner 1981 based on the experimental finding that sulfate ions inhibit or retard dolomitization a number of modern sedimentary dolomites are not in accord with this model in that they are forming from brines with large sulfate concentrations 2 to 70 times that of seawater thus the baker kastner model should be held in abeyance until these serious contradictions are resolved the current emphasis on mixing zone and sabkha dolomitization has diverted attention from other promising avenues of approach to the dolomite problem four of these avenues each of which deemphasizes the special water approach are briefly addressed and are as follows 1 influence of temperature and time 2 mass transfer processes 3 burial diagenesis of epigenetic dolomites 4 fluid inclusion studies at elevated temperatures the dolomite problem essentially disappears ordered dolomite can be made in the laboratory in days at 100 degrees c what is more at temperatures above 60 degrees c ca rich waters become dolomitizing fluids which makes most natural subsurface waters capable of dolomitization at low temperatures time may be the key element so that seawater will become a major dolomitizing fluid only where stable circulation systems such as kohout convention can drive seawater through carbonate platforms for many thousands to millions of years this paper has tried to show that currently favored models of dolomitization carry serious uncertainties enough to warn us to look more critically at the validity of these models and also it is hoped enough to spur new efforts to find new solutions to the problems of dolomitization

classification of dolomite rock textures abstract dolomite rock textures can be classified according to crystal size distribution and crystal boundary shape the classification scheme presented here is largely descriptive but carries genetic implications because size distribution is controlled by both nucleation and growth kinetics and crystal boundary shape is controlled by growth kinetics size distributions are classified as unimodal or polymodal crystal boundary shapes are classified as planar or nonplanar if the evidence permits a complete classification includes a description of recognizable allochems matrix and void filling allochems and preexisting cements may be unreplaced partially replaced replaced mimically or replaced nonmimically allochems may be dissolved leaving molds matrix can be unreplace partially replaced or replaced by a unimodal or polymodal size dolomite unimodal size distributions generally indicated a single nucleation event on a unimodal substrate polymodal sizes can be formed by multiple nucleation events on a unimodal or polymodal substrate or differential nucleation on an originally polymodal substrate planar crystal boundaries develop when crystals undergo faceted growth and nonplanar boundaries develop when crystals undergo nonfaceted growth nonplanar boundaries are characteristic of growth at elevated temperature 50 c and or high supersaturation both planar and nonplanar dolomite can form as a cement replacement of caco3 or neomorphism of a precursor dolomite

geochemical constraints on the origin and volume of gas in the new albany shale devonian mississippian eastern illinois basin this study involved analyses of kerogen petrography gas desorption geochemistry microporosity and mesoporosity of the new albany shale devonian mississippian in the eastern part of the illinois basin specifically detailed core analysis from two locations one in owen county indiana and one in pike county indiana has been conducted the gas content in the locations studied was primarily dependent on total organic carbon content and the micropore volume of the shales gas origin was assessed using stable isotope geochemistry measured and modeled vitrinite reflectance values were compared depth of burial and formation water salinity dictated different dominant origins of the gas in place in the two locations studied in detail the shallower owen county location 415 433 m 1362 1421 ft deep contained significant additions of microbial methane whereas the pike county location 832 860 m 2730 2822 ft deep was characterized exclusively by thermogenic gas despite differences in the gas origin the total gas in both locations was similar reaching up to 2 1 cm3 g 66 scf ton lower thermogenic gas content in the shallower location lower maturity and higher loss of gas related to uplift and leakage via relaxed fractures was compensated for by the additional generation of microbial methane which was stimulated by an influx of glacial melt water inducing brine dilution and microbial inoculation the characteristics of the shale of the maquoketa group ordovician in the pike county location are briefly discussed to provide a comparison to the new albany shale

pore types and pore network evolution in upper devonian lower mississippian woodford and mississippian barnett mudstones insights from laboratory thermal maturation and organic petrology abstract pore evolution models from immature organic matter om rich barnett 0 42 r o and woodford 0 49 r o mudstones were compared with models previously developed from low maturity om lean boquillas eagle ford equivalent mudstones to investigate whether 1 different mineralogy siliceous vs calcareous exerts different catalytic and sorption effects and influences om pore origin and evolution and 2 different types of macerals show different om pore evolution history laboratory gold tube pyrolysis scanning electron microscopy sem and thin section petrography organic petrography and geochemical characterization were used to investigate the role of bulk mineralogy maceral type and thermal maturation on om pore evolution results suggest that mineralogy has little impact on om pore development and evolution macerals identified using both sem platy om particulate om organic mineral admixtures tasmanites and organic petrology vitrinite inertinite amorphous organic matter aom bituminite telalginite leiosphaeridia tasmanites do affect the origin and evolution of om pores owing to differences in chemical compositions generation kinetics and activation energy distributions between tasmanites matrix bituminite and other types of macerals leiosphaeridia and tasmanites in woodford mudstone samples exhibit a delay in onset and a shorter period of petroleum generation and pore development compared to the matrix bituminite in the barnett and woodford mudstone samples pre oil solid bitumen was observed to have migrated into initial primary mineral pore networks at the bitumen generation stage in both barnett and woodford samples at higher levels of thermal maturation the volume of primary mineral pores decreases and the pore volume composed of modified mineral pores and om pores becomes greater pore evolution and pore type heterogeneity in these mudstones is a function of the initial mineral pore network types of kerogen and macerals and generation kinetics of individual macerals upon thermal maturation

package fluids 1 computer programs for analysis of fluid inclusion data and for modelling bulk fluid properties the computer package fluids contains five sets of computer programs written in c for the calculation of fluid properties both model fluids and data from fluid inclusions can be analysed in the programs bulk density molar volume and composition of fluid inclusions are calculated with the program bulk which uses microthermometric data micro raman spectroscopic data cation ratios and volume fraction estimations as input the program offers a broad variety of equations of state which are selected according to the fluid system or the temperature and pressure conditions of interest the isochores that correspond to the output or test v x properties of fluid inclusions are calculated by the program isoc in calculating the isochores this program takes account of the compressibility and expansion of selected host minerals the program test allows different equations of state to be compared directly with experimental data thereby facilitating selection of the most adequate model in the programs bulk and isoc loner is a group of programs that handle individual equations of state eos for all fluid systems presented in the programs bulk and isoc aqso is a group of programs that allows purely empirical modelling of electrolyte bearing aqueous solutions henry s law for dilute gas bearing aqueous solutions and osmotic coefficients for dilute electrolyte bearing aqueous solutions the programs are available on the university of leoben web site at http www unileoben ac at buero62 minpet ronald

origin of dinantian zebra dolomites south of the brabant wales massif belgium zebra dolomites characterized by a repetition of dark grey a and light b coloured dolomite sheets building up abbabba sequences occur in dinantian strata from deep boreholes 2000 m south of the brabant wales massif in belgium these zebra dolomite sequences are several tens of metres thick the dark grey dolomite sheets a consist of non planar crystals 80 150 m in diameter these crystals display a mottled red orange luminescence and are interpreted to be replacive in origin the white dolomite sheets b consist of coarse crystalline nonplanar b1 dolomite which evolves outwards into transparent saddle shaped b2 dolomite the b1 dolomites possess a mottled red orange luminescence similar to the a dolomites while the saddle shaped b2 rims display red to dark brown luminescent zones the b1 dolomites are possibly partly replacive and partly cavity filling their b2 rims display criteria typical for a cement origin locally cavities exist between two succeeding white dolomite sheets these cavities make up 5 of the zebra rocks and are locally filled by saddle shaped ankerite and or xenomorphic ferroan calcite geochemical and fluid inclusion data th 120 c indicate a burial diagenetic origin for these zebra dolomites the a and b1 dolomites are characterized by similar geochemical compositions and fluid inclusion data pointing toward a related origin to explain the development of the zebra textures suprahydrostatic pressures in conjunction with late variscan tectonic compression are invoked a model involving dolomitizing fluids expelled during the variscan orogeny is proposed an overpressured system is also invoked to explain the important porosity development the creation of centimetre scale subvertical displacements of the zebra pattern and the microfractures affecting the b1 b2 dolomite crystals

impact of diagenesis and low grade metamorphosis on isotope δ26mg δ13c δ18o and 87sr 86sr and elemental ca mg mn fe and sr signatures of triassic sabkha dolomites abstract dolomite is a common rock forming mineral in the geological record but its value as archive of ancient seawater 26 mg signatures and their variations in time is at present underexplored unknown factors include the sensitivity of 26 mg ratio to processes in the diagenetic and low grade metamorphic domain this paper documents and discusses the first detailed 26 mg data set from early diagenetic and burial dolomites samples come from the upper triassic hauptdolomit dolomia principale the dolomites italy and include coeval dolomicrites that underwent differential burial diagenesis and low grade metamorphosis in a temperature range between about 100 and more than 350 c magnesium isotope data are complemented by dolomite 13 c 18 o and 87 sr 86 sr isotope ratios as well as ca mg mn fe and sr elemental abundances and data on the dolomite crystal structure as indicated by dolomicrite 87 sr 86 sr ratios and petrographic evidence sabkha calcian d1 dolomites precipitated from evaporated seawater and stabilized at an early marine pore water diagenetic stage to d2 dolomites analysed here with increasing burial temperature dolomite 26 mg ratio scatter in the data set decreases with increasing mg ca ratio and degree of order specifically 26 mg ratio variability is reduced from 0 36 2 at burial temperatures beneath 100 c to about 0 14 2 at temperatures in excess of 350 c respectively with mean 26 mg values ranging constantly near 1 9 this suggests that at least for the rock buffered system investigated here dolomicrite 26 mg proxy data are conservative and preserve near pristine values even at elevated burial temperatures at present the main element of uncertainty is the mg isotope fractionation factor between evaporated seawater and dolomite a possible solution to this problem includes the compilation of data from modern sabkha environments including pore water and calcian dolomite 26 mg isotope signatures

the relationship between aromaticity vitrinite reflectance and maceral composition of coals implications for the use of vitrinite reflectance as a maturation parameter abstract previous studies on the aromaticity f a of coals have either limited themselves to the effects of rank or to differences between the macerals and generally conclude that f a and rank increase simultaneously although not necessarily linearly this study contains 13 c cp mas nmr analysis data of more than 70 coals obtained from different coal basins these are combined with published data to produce a data base with more than 130 analyses the aim is to determine the influence of rank and maceral composition on the measured f a of coals a plot of f a vs r o vitrinite reflectance shows a non linear relationship that can be described by a polynomial equation the shape of the curve produced by this equation is determined by the processes that occur during maturation only approx 50 of the coals in the data base have f a values that are accurately predicted by the vitrinite reflectance this is an indication of the large spread of values observed in the plot of f a vs r o as a result of the processes that occur during maturation the influence of the maceral composition on the f a was restricted to coals with r omax values 0 70 r o the equation generated shows that more than 80 of the coals tested with this level of rank have f a values that can be accurately predicted by an equation containing the r omax value the total vitrinite content and the contents of fusinite semifusinite and macrinite in the coals comparison of the f a values obtained from vitrinitic type iii kerogen with the f a values obtained from liptinitic sporinites and type ii kerogens reveals a pattern which illustrates the structural changes that occur during maturation both vintrinites and liptinites show a change in the slope in an f a vs r o plot although the reflectance level at which the change in slope occurs differs between the two kerogen types the changes in molecular structure that occur within the two kerogen types during maturation are discussed the implications of the f a r o relationship of vitrinites on the use of vitrinite reflectance as a maturation parameter are also discussed

experimental controls on d h and 13c 12c ratios of kerogen bitumen and oil during hydrous pyrolysis abstract large isotopic transfers between water derived hydrogen and organic hydrogen occurred during hydrous pyrolysis experiments of immature source rocks in spite of only small changes in organic 13 c 12 c experiments at 330 c over 72 h using chips or powder containing kerogen types i and iii identify the rock water ratio as a main factor affecting d for water and organic hydrogen our data suggest that larger rock permeability and smaller rock grain size increase the h isotopic transfer between water derived hydrogen and thermally maturing organic matter increasing hydrostatic pressure may have a similar effect but the evidence remains inconclusive

distinct evolution trends of nanometer scale pores displayed by the pyrolysis of organic matter rich lacustrine shales implications for the pore development mechanisms abstract organic matter om compositions greatly affect hydrocarbon generation and expulsion processes which are critical for the organic porosity development in shale lacustrine shale samples of low thermal maturity were pyrolyzed using two pyrolysis systems closed and semi closed systems pore development was measured by low pressure gas adsorption and field emission scanning electron microscopy fe sem and bulk porosity was modeled utilizing organic geochemical data the gas adsorption analysis indicated that shale samples of different om compositions differed in pore volume evolution with thermal maturity mainly related to the different amounts of hydrocarbon generated and expelled residual bitumen significantly reduced the pore volume of om rich oil generative shale samples and restricted the micro meso and macro pore volumes to different extents calculations and experiments both showed that om rich and oil generative shale experienced a greater increase in pore volume after the oil peak in addition it was observed that variations in the main pore types were associated both with shale compositions and with exerted overburden pressure increase in overburden pressure were found to greatly facilitate the development of nanometer size spongy and complex om pores in shales containing type kerogens possibly as a result of the expulsion of gaseous hydrocarbons by contrast the shale with abundant type kerogen tended mainly to develop relatively large pores following oil expulsion regardless of overburden pressure the modeled organic porosity of pyrolyzed samples of type iii om was similar to the porosity of geological shale but the porosity of om rich oil generative shale samples with high expulsion efficiency at the oil generation stage was two to three times the measured porosity of the geological shale in some cases the higher modeled shale porosity might be related to the higher expulsion efficiency for geological shales of expulsion efficiency comparable to the pyrolyzed samples geological processes e g compaction and cementation may have greatly reduced the om associated pore volume

spatial patterns of diagenesis during geothermal circulation in carbonate platforms geothermal convection of seawater deep in carbonate platforms could provide the necessary supply of magnesium for dolomitization at temperatures high enough to overcome kinetic limitations we used reactive transport simulations to predict the rates and spatial patterns of dolomitization during geothermal convection in a platform that was 40 km across and 2 km thick in the simulations porosity and permeability decrease with depth to account for sediment compaction dolomitization of a platform consisting of medium grained 0 0 5 mm sediments occurred in a broad band ranging from 2 5 km depth near the margin to 1 5 km depth near the platform center the area of dolomitization is deep enough that temperatures exceed 50 c but not so deep that low permeabilities restrict mass transport complete dolomitization in the center of this zone is estimated to require at least 60 my incorporation of permeability contrasts permeable beds and reactive beds focused dolomitization strongly and reduced the estimated time required for dolomitization by as much as 50 percent dolomitization created magnesium depleted calcium rich fluids in less than 10 ky and results support a link between dolomitization and anhydrite precipitation where adequate sulfate is available

origin and characterization of eagle ford pore networks in the south texas upper cretaceous shelf abstract recent studies have shown that the loss of primary pores and the development of secondary pores in mudrocks are primarily controlled by burial diagenesis of the mineral matrix and thermal maturation of organic matter om however the lack of quantitative data on nanometer to micrometer scale rock properties has limited the ability to define and predict petrophysical properties and fluid flow in these fine grained rocks to upscale these rock properties quantitative data are needed at multiple scales representative eagle ford group samples were collected from continuous cores taken from two adjacent oil producing wells in karnes county texas to investigate small scale variations in mineralogy diagenesis and pore type point count and pore tracing methods were used to systematically quantify pore types and determine the size and shape of the identified pores the two cores from the eagle ford are dominated by modified mineral pores although secondary om pores in migrated petroleum bitumen are also important the mineral pore network includes 1 primary mineral pores originally saturated with formation water and 2 modified mineral pores containing migrated petroleum bitumen and or residual oil the om pore network includes 1 primary om pores and 2 secondary om pores including relatively large less abundant om bubble pores and relatively small more abundant om spongy pores the abundance of om spongy pores correlates positively with total organic carbon toc content and that of mineral pores weakly correlates with the volume of quartz plus feldspar studied samples have similar thermal maturities although samples from one deeper core are slightly more mature than the other except for thermal maturation the strong micrometer scale heterogeneity of rock components and properties texture fabric mineralogy and toc impacts the abundance distribution and type of pores this micrometer scale heterogeneity in porosity and pore networks would in turn significantly impact matrix permeability

influence of maceral content on δ13c and δ15n in a middle pennsylvanian coal abstract using density gradient centrifugation within sample heterogeneity in c n 13c and 15n was determined for a sample of the blue gem coal bed middle pennsylvanian duckmantian westphalian b breathitt formation and related to maceral petrographically identifiable organic component composition relatively pure macerals were separated by density with purities up to 99 in the case of vitrinite in fractions around 1 3 g ml lower density fractions 1 2 g ml contain predominantly liptinite 75 but also significant amounts of vitrinite 20 denser fractions contain increasing amounts of inertinite with several fractions between 1 37 and 1 44 g ml containing 98 total inertinite within these denser fractions semifusinite concentrated at lower densities than did fusinite the separation of macerals by density allowed a more detailed evaluation of the isotopic composition of relatively pure macerals within a single coal 13c becomes increasingly heavy across the density gradient with 13c values being lightest in the liptinites followed by vitrinite and then semifusinite and fusinite by contrast 15n becomes lighter across the same density range c h increases with density reflecting a general decrease in aliphatic components and increase in aromatic components c n follows a similar pattern ranging from 1 32 the point at which inertinite macerals begin to predominate over vitrinite the isotopic composition of macerals reflects chemical composition which in turn reflects 1 the original composition of plant tissues from which the macerals originated 2 early diagenetic changes and 3 changes during coalification macerals derived from lipid rich precursor materials liptinites have more depleted 13c values 2 relative to those derived from woody tissues vitrinite fusinized material derived from fossil charcoal has 13c values enriched by 0 5 compared with the vitrinite consistent with the results from combustion experiments using modern plant tissues vitrinite fractions have enriched 15n values relative to inertinite fractions which may reflect early diagenetic changes in woody tissues involving preferential loss of 14n possibly due to bacterial activity during the peat forming stage due to the within sample variability in carbon isotopic composition reported here it is suggested that chemostratigraphic studies based on type iii kerogen including both dispersed organic matter and coals carefully consider the associated effects of variability in maceral composition

application of organic petrography in north american shale petroleum systems a review abstract organic petrography via incident light microscopy has broad application to shale petroleum systems including delineation of thermal maturity windows and determination of organo facies incident light microscopy allows practitioners the ability to identify various types of organic components and demonstrates that solid bitumen is the dominant organic matter occurring in shale plays of peak oil and gas window thermal maturity whereas oil prone type i ii kerogens have converted to hydrocarbons and are not present high magnification sem observation of an interconnected organic porosity occurring in the solid bitumen of thermally mature shale reservoirs has enabled major advances in our understanding of hydrocarbon migration and storage in shale but suffers from inability to confirm the type of organic matter present herein we review organic petrography applications in the north american shale plays through discussion of incident light photographic examples in the first part of the manuscript we provide basic practical information on the measurement of organic reflectance and outline fluorescence microscopy and other petrographic approaches to the determination of thermal maturity in the second half of the paper we discuss applications of organic petrography and sem in all of the major shale petroleum systems in north america including tight oil plays such as the bakken eagle ford and niobrara and shale gas and condensate plays including the barnett duvernay haynesville bossier marcellus utica and woodford among others our review suggests systematic research employing correlative high resolution imaging techniques and in situ geochemical probing is needed to better document hydrocarbon storage migration and wettability properties of solid bitumen at the pressure and temperature conditions of shale reservoirs

stable carbon isotopes of wood a clue to palaeoclimate abstract detailed stable carbon isotope and molecular investigations were undertaken on a number of archaeological and fossil wood specimens to provide insights into their use as rigorous independent palaeoclimatic and palaeoenvironmental parameters the isotope data revealed large differences amongst the material with the oldest specimens being least depleted in 13 c although natural variation could account for some of the observed differences the isotope values of the archaeological and tertiary specimens are most probably related to the absolute abundance of polysaccharides present and the degree of lignin alteration the molecular data based on pyrolysis of the antarctic cretaceous conifer specimens revealed only transformed lignin with virtually no intact lignin building blocks 2 methoxyphenols preserved and no evidence of polysaccharides this degree of chemical alteration is suggested here to be one of the main causes for the 13 c enriched values of these conifer specimens these results show the importance of combining detailed molecular information on individual wood components with stable carbon isotope data for palaeoclimatic and palaeoenvironmental studies

epigenetic dolomitization and the origin of xenotopic dolomite texture abstract xenotopic texture which is commonly observed in pre cenozoic rocks is defined here as a mosaic of anhedral crystals with irregular or curved intercrystalline boundaries and usually undulatory extinction xenotopic dolomite texture is similar in appearance to neomorphic limestone textures idiotopic dolomite texture euhedral to subhedral crystals with straight intercrystalline boundaries contrasts with xenotopic texture and is commonly observed in both cenozoic and more ancient dolomites texture may be controlled by the temperature at which crystals grow crystal growth theory predicts that at low temperature a smooth crystal surface is energetically favored and atoms are added to crystal faces layer by layer with dislocations acting as nucleation sites this results in faceted crystals and euhedral to subhedral crystal mosaics above a critical roughening temperature crt a rough surface is energetically favored surface nucleation does not require dislocations and atoms are randomly added to the crystal surface resulting in nonfaceted growth and an anhedral crystal mosaic it is hypothesized that a critical roughening temperature exists for dolomite above 50 c xenotopic dolomites are produced by dolomitization of limestone and or neomorphic recrystallization of dolomite at elevated temperature above the crt after burial idiotopic dolomites are produced below the crt by near surface processes and are occasionally produced above crt if growth inhibiting effects of the solution or impurities stabilize crystal faces calcite has a crt below 25 c and therefore develops anhedral crystal mosaics characteristic of neomorphic texture both at near surface and at elevated temperatures synthetic xenotopic dolomite was produced in the laboratory at 250 c and 300 c by dolomitization of aragonite and calcite skeletal fragments and by recrystallization neomorphism of nonstoichiometric cenozoic dolomites xenotopic dolomite resulted from the metamorphic recrystallization of the idiotopic hueco dolomite permian texas near the marble canyon intrusion at temperatures between 350 c and 600 c hydrothermal dolomitization of periclase calcite marble near the intrusion also resulted in a xenotopic texture xenotopic dolomite in the galena group ordovician wisconsin was produced by neomorphism of a preexisting dolomite during the emplacement of lead zinc sulfides at temperatures between 80 c and 227 c in the trenton limestone ordovician michig n xenotopic dolomite replaced limestone during the migration of hot 50 c fluids along fracture systems xenotopic dolomite was not observed in cenozoic dolomites that were subjected to temperatures near surface values only

massive hydrothermal dolomites in the southwestern cantabrian zone spain and their relation to the late variscan evolution abstract large scale massive burial dolomitization affected upper carboniferous carbonates of the southwestern variscan cantabrian zone spain replacive and void filling dolomites formed and were post dated by calcite cementation the process of dolomitization was due to the circulation of hypersaline and hydrothermal marine derived brines controlled by rock anisotropies the dolomites probably formed in early permian time during post thrusting orocline formation in an extensional setting lithospheric delamination induced increased heat flow and allowed thermal convection of the fluids the dolomites from the cantabrian zone are excellently exposed and represent an interesting outcrop analogue for hydrocarbon reservoirs elsewhere in comparable geotectonic settings of the european variscan orogen large masses of similar dolomites could have formed if mg rich brines were available

chemical study of tectonically controlled hydrothermal dolomitization an example from the lessini mountains italy in the central southern alps feltre verona italy a 750 m thick interval of jurassic and cretaceous pelagic limestones shows post depositional partial brecciation and dolomitization the overlying 500 m thick tertiary sedimentary sequence is unaffected through the paleogene mostly submarine mafic volcanism has been documented in the area small scale extensional features were observed in the limestone near the contact with the dolomitized breccias their orientations measured in the field correspond to the tectonic framework of the area and give evidence for the contemporaneousness of the volcanic activity and the brecciation the distribution and petrologic characteristics of the basalts combined with the orientation of the extensional features observed in the field allow a paleotectonic reconstruction this tectonic scenario can be viewed as a back arc extension an eastward prolongation of the spreading that divided southern france from the sardinia corsica calabria block generating the ligurian balearic basin in the late oligocene

correlation between global lightning and whistlers observed at tihany hungary although the generation and propagation mechanisms for whistlers are fairly well understood the location and extent of the lightning source region for the whistlers observed at a given station are

petrographic and geochemical characteristics of dolomite types and the origin of ferroan dolomite in the trenton formation ordovician michigan basin u s a three major types of dolomite occur in the trenton formation mid ordovician of the michigan basin these are 1 regional dolomite which is confined to the extreme western edge of the basin 2 cap dolomite which occurs in the upper portion of the trenton and is confined to the basin s southern margin and 3 fracture related dolomite which occurs in association with both large and small scale faults and fractures these three dolomite types can be distinguished from one another by their major element chemistry oxygen isotope ratios and rock texture the regional dolomite is fine grained has 0 34 mol feco3 and mean 18o of 6 8 opbd the cap dolomite is texturally similar to regional dolomite but contains 3 13 0 mol feco3 and has a mean 18o of 7 7 fracture related dolomites are coarse grained low in iron and have the most depleted 18o ratios x 9 0 pdb petrographic relationships imply that the regional dolomite formed prior to the cap dolomite probably during early diagenesis the cap dolomite formed at relatively shallow depths as a result of the interaction of the overlying utica shale and the trenton limestone fracture related dolomites post date the cap dolomite and formed during deeper burial a temperature of precipitation of approximately 80 c was calculated for fracture related dolomites using oxygen isotope data the distribution of the cap dolomite was controlled by the availability of fe2 which was in turn controlled by the availability of s2 in the centre of the basin trenton utica deposition was continuous the upper trenton contained relatively high concentrations of organic matter which was used by sulphate reducing bacteria to produce h2s from seawater sulphate the precipitation of iron sulphides pyrite iron monosulphide followed and used up most of the available fe2 as a result only small amounts of ferroan dolomite formed on the periphery of the basin subaerial exposure resulted in the oxidation of most of the available organic matter sulphate reducing bacteria were therefore limited and produced limited amounts of h2s as a result only a minor amount of iron sulphide iron monosulphide formed the remaining fe2 was then available for the formation of the ferroan cap dolomite this model is supported by the following 1 in the southern margin of the basin the contact between trenton cap dolomite and the overlying utica shale is sharp and probably unconformable in the centre of the basin the contact is gradational 2 in the centre of the basin the total organic carbon content in the upper trenton is an order of magnitude higher than in the cap dolomite 3 the whole rock concentration of iron is high in both the cap dolomite and in slightly dolomitized equivalent beds in the basin centre 4 iron sulphides are abundant in the centre of the basin and mostly in the form of pyrite in the cap dolomite iron sulphide is minor and primarily in the form of iron monosulphide

poleward displaced electron precipitation from lightning generated oblique whistlers new simulation results show that obliquely propagating lightning generated whistlers which fill vast volumes of the magnetosphere readily induce significant energetic electron precipitation over large regions of the ionosphere depositing appreciable energy flux to the upper atmosphere at locations substantially poleward of the lightning source these results provide a new interpretation for the observed spatial relationships between lightning discharges and subsequently disturbed ionospheric regions inferred from subionospheric signal perturbations i e trimpi events reported in several lightning induced electron precipitation lep studies

the importance of shale composition and pore structure upon gas storage potential of shale gas reservoirs abstract the effect of shale composition and fabric upon pore structure and ch 4 sorption is investigated for potential shale gas reservoirs in the western canadian sedimentary basin wcsb devonian mississippian d m and jurassic shales have complex heterogeneous pore volume distributions as identified by low pressure co 2 and n 2 sorption and high pressure hg porosimetry thermally mature d m shales 1 6 2 5 vro have dubinin radushkevich d r co 2 micropore volumes ranging between 0 3 and 1 2 cc 100 g and n 2 bet surface areas of 5 31 m 2 g jurassic shales which are invariably of lower thermal maturity ranging from 0 9 to 1 3 vro than d m shales have smaller d r co 2 micropore volumes and n 2 bet surface areas typically in the range of 0 23 0 63 cc 100 g co 2 and 1 9 m 2 g n 2 high pressure ch 4 isotherms on dried and moisture equilibrated shales show a general increase of gas sorption with total organic carbon toc content methane sorption in d m shales increases with increasing toc and micropore volume indicating that microporosity associated with the organic fraction is a primary control upon ch 4 sorption sorption capacities for jurassic shales however can be in part unrelated to micropore volume the large sorbed gas capacities of organic rich jurassic shales independent of surface area imply a portion of ch 4 is stored by solution in matrix bituminite solute ch 4 is not an important contributor to gas storage in d m shales structural transformation of d m organic matter has occurred during thermal diagenesis creating and or opening up microporosity onto which gas can sorb as such d m shales sorb more ch 4 per weight percent wt toc than jurassic shales inorganic material influences modal pore size total porosity and sorption characteristics of shales clay minerals are capable of sorbing gas to their internal structure the amount of which is dependent on clay type illite and montmorillonite have co 2 micropore volumes of 0 78 and 0 79 cc 100 g n 2 bet surface areas of 25 and 30 m 2 g and sorb 2 9 and 2 1 cc g of ch 4 respectively dry basis a reflection of microporosity between irregular surfaces of clay platelets and possibly related to the size of the clay crystals themselves mercury porosimetry analyses show that total porosities are larger in clay rich shales compared to silica rich shales due to open porosity associated with the aluminosilicate fraction clay rich sediments low si al ratios have unimodal pore size distributions

formation of dolomite in recent island arc sediments due to gas seawater sediment interaction dolomite occurs as a primary precipitate that cements re cent volcaniclastic sands in the shallow marine environment of luise harbor lihir island papua new guinea field observations and geo chemical data suggest that dolomite precipitates through complex min eral reactions in response to discharge of gas 90 co2 and heated seawater from hydrothermal vents in the seafloor gas discharge caus es the formation of shallow circulation cells and cold seawater is drawn into the sediment where it is heated to approximately 100 8c reaction between hydrothermal co 2 g primary sediment grains and heated seawater causes the precipitation of primary dolomite once temperatures are above 70 8c the mg ca ratio in seawater increases because caso 4 precipitates while at the same time the dissolution of iron oxide minerals increases the ph both reactions favor dolomite precipitation ferrous iron reacts with h 2s to form co precipitated fe sulfide minerals the dolomite is nearly stoichiometric and occurs as zoned inclusion rich and inclusion poor spherulitic cements many of which are present as coalesced composite spherules oxygen isotope values for dolomite of 28 8 to 210 2 vpdb constrain the temper ature of precipitation to be between about 77 to 1108c strontium iso tope ratios for dolomite average 0 70886 are close to those of modern seawater their slightly less radiogenic compositions implicate minor addition of magmatic strontium hydrothermal dolomite may develop in shallow near surface sediments in active tectonic settings

metamorphic fluids and transtension in the cantabrian mountains of northern spain an application of the conodont colour alteration index conodont colour alteration index cai values from upper paleozoic rocks in the cantabrian zone of northern spain show that temperatures during hercynian metamorphism locally exceeded 300 c various temperature domains have been defined which are generally separated by fundamental structures these domains do not correspond with the tripartite subdivision based on stratigraphic analysis the observed cai values of conodonts are in general agreement with the mineral paragenesis areas with high cai values display extensive alteration and mineralization and where cai values exceed 4 4 5 200 c slaty cleavage has developed the cantabrian zone is an area of very low grade metamorphism where peak conditions were reached in upper carboniferous to lower permian times the characteristics of the metamorphism and its spatial relationship with major faults suggest that fluids were the main source for regional heating and that fluid transport was focussed along crustal scale structural features the overall deformation regime in this part of the variscan orogen of western europe is interpreted to be large scale transtension this is in agreement with earlier proposed models for the formation of upper palaeozoic basins in this area

strontium isotopic compositions and potassium and rubidium contents of formation waters in sedimentary basins clues to the origin of the solutes abstract strontium isotopic compositions of formation waters in sedimentary basins relate primarily to sr from dissolution replacement of alkali feldspar minerals dissolution recrystallization precipitation of marine carbonate and sulfate minerals and illitization formation waters in sedimentary basins are often depleted in k but enriched in rb relative to evaporated seawater and have k rb ratios commonly between 200 and 2000 the k and rb characteristics of formation waters suggest that deep burial conversion of smectite to illite has a major influence on the evolutionary history of these solutes

carbonate sedimentation and diagenesis associated with mg ca chloride brines the permian san andres formation in the texas panhandle abstract the san andres evaporitic sequence in the palo duro basin includes several thick carbonate units in its lower part and many thin units in its upper part evaporites are concentrated in the northern part of the northern shelf of the midland basin and carbonates predominate to the south within the palo duro basin the carbonates in the lower part of the sequence differ from those in the upper part in containing skeletal lithofacies and in having lower mn fe and terrestrial organic content the br content in halite in the lower part of the sequence is consistently high whereas halite in the upper part is commonly br depleted the sr content in dolomite calcite and anhydrite and 18o values are about the same in the en ire san andres sequence in the palo duro basin depleted 13c values in dolomite and low pristane phytane ratios occur toward the south na cl and k cl ratios attributed to liquid inclusions in almost all carbonates are characteristic of marine brines evaporated beyond halite saturation na in the dolomite lattice is generally low and increases from north to south at the same stratigraphic levels the lower part of the formation was deposited in a broad shelf basin or lagoon sufficiently deep to maintain long periods of steady state circulation during which little halite dissolution and no potash magnesia mineral precipitation occurred the upper part of the formation was deposited in smaller water bodies sensitive to fluctuations in inflow of marine water as well as meteoric water diagenesis of the carbonates occurred in contact with saline mg ca chloride brines evolved through anhydrite and halite precipitation skeletal mold formation anhydrite cementation dolomitization and high sr calcite cementation associated with celestite are all cogenetic products of such a brine rock interaction 18o of dolomite calcite and chert indicates apparent equilibrium relationships with the same solution temperatures have never exceeded 40 to 45 c and imply the 18o of such a solution to be about 3 the somewhat depleted 18 up o composition of the proposed halite saturated brine resulted from the reversal in the dependence of 18o on increased evaporation in highly saline brines the proposed diagenetic model implies that following early diagenetic processes the rock sequence remained as a closed but compacting system unchanged by later fluid introduction low sr values in dolomite are indicative of recrystallization and not fresh water diagenesis

characterization of dolomitizing fluids in the carboniferous of the cantabrian zone nw spain a fluid inclusion study with cryo raman spectroscopy abstract a late diagenetic dolomitization pervasively affected carboniferous carbonates of the variscan cantabrian zone nw spain the process generated replacive and void filling dolomite phases spatially related with various calcite cements the nature of the diagenetic fluids has been investigated by cryo raman spectroscopy i e a combination of raman spectroscopy and low temperature microthermometry which reveals in great accuracy the salinity and the major types of dissolved cations and anions in single fluid inclusions fluid properties obtained only from microthermometry are distinctively different the study demonstrates that this improved analytical method of fluid inclusions is a valuable contribution for the interpretation of fluids in dolomite research in primary fluid inclusions of the cantabrian dolomites hydrohalite and two unknown salt hydrates one of which resembles mgcl2 12h2o were detected by cryo raman spectroscopy whereas only hydrohalite appeared in the calcite primary inclusions the presence of cacl2 hydrates is suspected only from low eutectic temperatures dolomite formed from an evolving fluid as reflected by the highly variable equivalent na ca ratios calculated at high and nearly constant total salinities the approximately constant na ca ratio in the first calcite cement reflects a homogeneous source for the salts cryo raman spectroscopy reveals that different cooling procedures may induce the formation of different phase assemblages within the same fluid inclusion in both dolomite and calcite consequently fluid inclusions display different melting behaviors corresponding to different values of calculated salinities salinity calculation only from microthermometry may lead to an underestimation of true salinities according to an assumed hydrostatic geothermal gradient maximum formation conditions for the dolomites are 150 30 c and 40 10 mpa corresponding to a depth of 3 9 1 0 km the first calcite formed at 130 20 c and 35 5 mpa corresponding to a depth of 3 4 0 6 km the minimum t p of formation is defined by the homogenization conditions

increasing maturity of kerogen type ii reflected by alkylbenzene distribution from pyrolysis gas chromatography mass spectrometry abstract a series of late devonian to early mississippian type ii kerogens with vitrinite reflectance values ro 0 29 2 41 were analyzed using py gc ms in addition a low maturity kerogen with ro 0 44 was separated into fractions via density gradient centrifugation followed by py gc ms of the alginite and amorphinite maceral concentrates alkylbenzenes and n alk 1 ene n alkane doublets represented the main compound classes identified in all pyrolysates the pyrolysate from alginite featured 1 2 4 trimethylbenzene and toluene as the two most prominent alkylbenzenes in contrast alkylbenzenes in pyrolysates from amorphinite and low maturity bulk kerogens with ro 0 29 0 63 were dominated by 1 2 3 4 tetramethylbenzene with increasing thermal maturity pyrolysates were increasingly dominated by i alkylbenzenes with fewer methyl groups namely by tri and dimethylbenzenes at medium maturity ro 0 69 1 19 and ii by toluene at higher maturity ro 1 30 2 41 with increasing maturity of kerogen type ii the decreasing abundance of highly methyl substituted alkylbenzenes and the parallel increase in less methyl substituted alkylbenzenes in flash pyrolysates suggest that demethylation is an important chemical process in the thermal maturation of kerogen type ii

low temperature behaviour of natural saline fluid inclusions in saddle dolomite paleozoic nw spain the origin of many dolomites is still a matter of debate because of many possible chemical and hydrological conditions of formation fluid inclusion studies have been applied in order to improve knowledge about paleofluids responsible for the precipitation of dolomite and used to define temperatures and salinities the combination of raman spectroscopy and microthermometry is tested here to improve the analytical method to identify the main ion species present in individual inclusions natural samples of saddle dolomite from the cambrian lancara fm cantabrian mountains nw spain contain zoned crystals with two phase aqueous fluid inclusions liquid rich the most stable phase assemblage in these inclusions at 150 c consists of ice hydrohalite and an unknown salt hydrate the latter melts between 47 and 41 c probably representing a eutectic temperature subsequently ice melts in the range of 32 5 to 29 c and finally hydrohalite melts between 9 and 3 5 c salinities can be calculated in the fluid system h2o nacl with addition of another salt either cacl2 or mgcl2 and result in 7 5 10 6 eq mass nacl and 17 0 21 0 eq mass cacl2 dependent on the rate of cooling runs three different types of metastability may occur i e the absence of hydrohalite the unknown salt hydrate is not formed and the nucleation of only ice salinity calculations from those melting temperatures differ substantially from equilibrium behaviour values the unknown salt hydrate needs to be further specified by comparison to standard solutions the method gives an opportunity to characterize the major compounds in complex fluid systems active during dolomitization thus contributing to a better understanding of the dolomite problem

organic geochemistry and petrology of posidonia shale lower toarcian western europe the evolution from immature oil prone to overmature dry gas producing kerogen abstract kerogen concentrates as well as whole rock samples of the lower jurassic posidonia shale representing a complete maturity series from immature to highly overmature were analyzed using organic petrography palynology bulk geochemical analysis ft ir and curie point pyrolysis gc ms cp py gc ms in order to investigate changes in kerogen composition with increasing maturation vitrinite reflectance vrr ranges from 0 5 to 3 hi values reflect the maturity trend very well with little scatter in contrast tmax oi and pi values show more scatter and greater differences between kerogen concentrates and whole rock samples ft ir spectra show a decrease in functional group bands with increasing maturation which has been quantified cp py gc ms analyses indicate an increase in hydrocarbons especially for short and medium length n alkanes with a strong predominance of short length alkanes at highest maturities about 3 vrr this effect however depends also on the applied pyrolysis temperature where higher temperatures 920 c as compared to 650 c favor generation of short length n alkanes especially for samples at high levels of maturation ratios of aromatic over aliphatic hydrocarbons or alkenes over alkanes show a non steady evolution depending also on the applied pyrolysis temperatures indicating that higher pyrolysis temperatures are needed for pyrolytic alkene formation with a maximum alkene formation for samples within early overmature maturities 1 4 vrr aromaticity first decreases but increases at high levels of maturation finally weathering of the highly overmature sample 3 vrr resulted in strong oxidation of organic matter with impact on rock eval ftir and curie point pyrolysis data

assessing the thermal maturity of black shales using vitrinite reflectance insights from devonian black shales in the eastern united states abstract thermal maturity of source rocks indicated by vitrinite reflectance ro is an important and reliable parameter to determine the petroleum potential of sedimentary basins originally ro was used to characterize the degree of coalification of coals and thus works well for coal seams but it has limitations when used to determine the thermal maturity of black shale successions a suite of six coal shale pairs from the upper devonian black shale formations in the eastern united states new albany shale ohio shale dunkirk shale and rhinestreet shale was selected to study the applicability of ro in assessing the thermal maturity of black shale successions the results show that vitrinite in the studied coal samples is dominated by collotelinite whereas vitrinite in black shales occurs as small dispersed particles 5 m in the mineral matrix when comparing the size and morphology of dispersed vitrinite particles in shales and collotelinite fragments in coals vitrinite in shales and adjacent coals should have the same origin the measured mean random ro of vitrinite in coals ranges from 0 51 0 68 and is 0 04 0 11 average 0 07 lower than that of dispersed vitrinite particles in enclosing shales this observation contrasts with previously reported ro suppression in liptinite rich black shales a high standard deviation of ro measurements indicates a highly heterogeneous nature of vitrinite in black shales three mechanisms can be envisioned to contribute to the higher ro of dispersed vitrinite particles in black shales relative to enclosed coals first small vitrinite particles may become more oxidized because small particles are more frequently suspended during transport to the site of deposition and reworking of bottom sediments after deposition than large pieces of driftwood that will turn into enclosed coal lenses during burial diagenesis second misidentification of zooclast e g chitinozoan fragments as vitrinite due to loss of diagnostic morphology third various macerals in the vitrinite group e g corpogelinite and collotelinite may have had different original reflectance values based on the petrographic characteristics of vitrinite and vitrinite like particles caution should be applied when using the ro values of dispersed vitrinite and vitrinite like particles in black shales as indicators of thermal maturity

isotopically exchangeable organic hydrogen in coal relates to thermal maturity and maceral composition hydrogen isotopic exchangeability hex and dn values of non exchangeable organic hydrogen were investigated in coal kerogens ranging in rank from lignite to graphite the relative abundance of hex is highest in lignite with about 18 of total hydrogen being exchangeable and decreases to around 2 5 in coals with ro of 1 7 to ca 5 7 at still higher rank ro 6 hex increases slightly although the abundance of total hydrogen decreases dn is influenced by original biochemical d h ratios and by thermal maturation in contact with water therefore dn does not show an overall consistent trend with maturity

tectono thermal evolution in a region with thin skinned tectonics the western nappes in the cantabrian zone variscan belt of nw spain the palaeotemperature distribution in the transition from diagenesis to metamorphism in the western nappes of the cantabrian zone somiedo la sobia and aramo units are analysed by conodont colour alteration index cai and illite crystallinity ic structural and stratigraphic control in distribution of cai and ic values is observed both cai and ic value distributions show that anchizonal conditions are reached in the lower part of the somiedo unit a disruption of the thermal trend by basal thrusts is evidenced by cai and ic values there is an apparent discrepancy between the ic and cai values in carboniferous rocks of the aramo unit the ic has mainly anchizonal values whereas the cai has diagenetic values discrepant ic values are explained as a feature inherited from the source area in the carboniferous rocks of the la sobia unit both ic and cai indicate diagenetic conditions the anchimetamorphism predated completion of emplacement of the major nappes it probably developed previously and or during the early stages of motion of the units temperature probably decreased when the metamorphosed zones of the sheets rose along ramps and were intensely eroded in the context of the iberian variscan belt influence of tectonic factors on the metamorphism is greater in the internal parts where the strain and cleavage are always present than in the external parts cantabrian zone where brittle deformation and rock translation are dominant with an increasing role of the burial on the metamorphism

coalification history of the stephanian cinera matallana pull apart basin nw spain combining anisotropy of vitrinite reflectance and thermal modelling the stephanian cinera matallana basin of nw spain comprises 1 500 m of alluvial to lacustrine coal bearing sediments which were deposited in a late variscan transtensional transpressional pull apart setting the relationship between coalification pattern and rock deformation was evaluated by measurements of the anisotropy of vitrinite reflectance avr the avr ellipsoids reveal both pre tectonic elements related to the bedding fabric and syn tectonic elements related to folding producing biaxial ellipsoid shapes with the maximum reflectance parallel to fold axes the mean coalification gradient for the stephanian succession is about 0 62 rr km calculations of the mean palaeo geothermal gradient are presented on the basis of three different empirical equations a palaeo geothermal gradient of 85 c km is considered the most realistic with an overburden of about 1 000 m 1 d numerical modelling of the burial history results in two possible scenarios the most preferable involving a palaeo heat flow of 150 mw m2 and an overburden of ca 1 050 m these results indicate that maximum coalification was related to a localised but high palaeo heat flow geothermal gradient the anisotropy of vitrinite reflectance highlights the interactive and transitional nature of sedimentary compaction and rock deformation on the maturation of organic material within strike slip fault zones

vlf observations of ionospheric disturbances in association with tles from the eurosprite 2007 campaign 1 two very low frequency vlf awesome remote sensing systems located at algiers algeria 36 45 n 3 28 e and sebha libya 27 02 n 14 26 e monitor vlf signal perturbations for evidence of ionospheric disturbances during the eurosprite 2007 campaign a number of transient luminous events tles were captured over the mediterranean sea by cameras at pic du midi 42 94 n 0 14 e and at centre de recherches atmospheriques cra in southwestern france 43 13 n 0 37 e the cameras observations are compared to collected vlf awesome data we consider early vlf perturbations observed on 12 13 17 18 october and 17 18 december 2007 the data from the two vlf receivers confirm the association between tles and early vlf signal perturbations with the perturbations amplitudes dependent on the observation configuration i e whether the tle is near the receiver near the transmitter or far from both and the scattering process the results also reveal that the early vlf perturbations can occur in the absence of a tle

new distribution coefficient for the incorporation of strontium into dolomite and its implications for the formation of ancient dolomites late tertiary dolomites form the bahamas exhibit a strong inverse correlation between sr and mol mgco sub 3 it is proposed that this relation is a result of a distribution coefficient dependent on the concentration of ca in dolomite because these dolomites precipitated from water with a sr sup 2 ca sup 2 ratio similar to that of seawater a distribution coefficient d sub sr sup dolomite of 0 0118 is calculated for sr in stoichiometric dolomite this coefficient increases by about 0 0039 for every additional mol caco sub 3 in nonstoichiometric dolomite these data have three important implication first the new d sub sr sup dolomite is substantially lower than previously suggested second a relation has been established among the sr sup 2 ca sup 2 ratio of dolomite forming waters the major element composition of dolomites and the sr content of dolomites allowing the determination of the sr sup 2 ca sup 2 ratio of fluids involved in the formation of ancient dolomites third some published data sets on dolomites show a similar relation between sr content and major element composition suggesting that these dolomites may also have formed from seawater other data sets deviate from the correlation defined by little bahama bank dolomites indicating either dolomitization in fluids other than seawater or changes ofmore the sr sup 2 ca sup 2 ratio of seawater through time less

chemistry and environments of dolomitization a reappraisal abstract dolomitization of calcium carbonate can best be expressed by mass transfer reactions that allow for volume gain preservation or loss during the replacement process experimental data as well as textures and porosities of natural dolomites indicate that these reactions must include co 3 2 and or hco 3 supplied by the solution to the reaction site since dolomite formation is thermodynamically favoured in solutions of a low ca 2 mg 2 ratios b low ca 2 co 3 2 or ca 2 hco 3 ratios and c high temperatures the thermodynamic stability for the system calcite dolomite water is best represented in a diagram with these three parameters as axes kinetic considerations favour dolomitization under the same conditions and additionally at low as well as at high salinities if thermodynamic and kinetic considerations are combined the following conditions and environments are considered chemically conducive to dolomitization 1 environments of any salinity above thermodynamic and kinetic saturation with respect to dolomite i e freshwater seawater mixing zones normal saline to hypersaline subtidal environments hypersaline supratidal environments schizohaline environments 2 alkaline environments i e those under the influence of bacterial reduction and or fermentation processes or with high input of alkaline continental groundwaters and 3 many environments with temperatures greater than about 50 c subsurface and hydrothermal environments whether or not massive replacive dolostones are formed in these environments depends on a sufficient supply of magnesium and thus on hydrologic parameters most massive dolostones particularly those consisting of shallowing upward cycles and capped by regional unconformities have been interpreted to be formed according to either the freshwater seawater mixing model or the sabkha with reflux model however close examination of natural mixing zones and exposed evaporitic environments reveals that the amounts of dolomite formed are small and texturally different from the massive replacive dolostones commonly inferred to have been formed in these environments many shallowing upward sequences are devoid of dolomite it is therefore suggested that massive replacive dolomitization during exposure is rare if not impossible rather only small quantities of dolomite cement or replacement are formed which may act as nuclei for later subsurface dolomitization alternatively large scale dolomitization may take place in shallow subtidal environments of moderate to strong hypersalinity the integration of stratigraphic petrographic geochemical and hydrological parameters suggests that the only environments capable of forming massive replacive dolostones on a large scale are shallow hypersaline subtidal environments and certain subsurface environments

hydrothermal dolomites in sw sardinia italy evidence for a widespread late variscan fluid flow event abstract epigenetic replacive and saddle dolomite frequently forming zebra structures geodic dolomite affected cambrian limestones and early diagenetic dolomites across large areas of the iglesiente sulcis mining district sw sardinia italy the dolomite crops out in an area of more than 500 km 2 and reaches a thickness of up to 600 m or even more this rock represents one of the most extensive dolomites of epigenetic origin yet documented prior to dolomitization the cambrian carbonates underwent ductile deformation and greenschist facies metamorphism the same is true for the overlying tectonic nappes fluid inclusion analysis combined with o and sr isotope data indicate that the dolomitizing fluid can be categorized as a basinal brine the spread in homogenization temperatures shows a gradient with values decreasing from east to west the higher temperatures mean of around 100 c have been measured in eastern parts of the iglesiente area whereas the lowermost temperatures mean of about 85 c have been found along the western coast of iglesiente this fluid certainly can neither have come directly from the low grade metamorphic lithotypes undergoing dolomitization nor from the low temperature metamorphic rocks within the overlying nappes it is assumed that a late variscan hydrothermal event which coincided with extensional tectonics set brine circulation into motion dolomitization may have occurred within circulation cells which were driven by high heat flow fluids originated in the underlying rocks and circulated upward to affect the overlying cambrian carbonates an alternative model is that the dolomitization was caused by hydrothermal brines that originated within basinal areas of the variscan orogenic pile circulating deep within the crust and ascended in the external zone iglesiente sulcis whatever the origin these reducing saline fluids which carried radiogenic sr dolomitized a large volume of early paleozoic rocks the many subhorizontal open cavities within the geodic dolomite only partly filled with cement might indicate fluid overpressure at the time of dolomitization

emplacement of the cuera and picos de europa imbricate system at the core of the iberian armorican arc cantabrian zone north spain new precisions concerning the timing of arc closure the final stages of the variscan orogeny mostly carboniferous in the western european variscan belt involved the development of the iberian armorican arc which is cored by the cantabrian zone nw iberia the cantabrian zone is the foreland of the western european variscan belt and it is interpreted to record the waning stages of the closure of the rheic ocean the distalmost tectonic units within the cantabrian zone the cuera unit and the picos de europa province were the last tectonic units emplaced at the core of the western european variscan belt orocline together they form an imbricate system and associated wedge top basins that are key to understanding the development of the orocline the emplacement of the cuera unit and the picos de europa province occurred in the latest pennsylvanian between moscovian and gzhelian times new detailed mapping together with stratigraphic sedimentologic and biostratigraphic data analysis of syntectonic successions and structural information constrain the timing and evolution of this imbricate system our analysis indicates that the thrust sheets were emplaced roughly perpendicular to previous tectonic units of the cantabrian variscan foreland fold and thrust belt most probably during the oroclinal bending of the sw european variscan belt that formed the iberian armorican arc the n s directed imbricate system was characterized by a shallow dip of the topographic surface 150 15 km and complex structure of the orogenic wedge are thought to result from the progressive increase in the dip of the basal decollement during bending of the underlying gondwana lithosphere and may reflect the closure of the iberian armorican arc

radiation belt electron precipitation fluxes associated with lightning in this study we consider the dependence of precipitation fluxes arising from whistler induced radiation belt losses on the strength of the associated lightning s return stroke current as a result of this work it will be possible to use lightning activity data sets to estimate globally induced precipitation flux rates and thus determine the lightning induced effect on the radiation belts more accurately four study days were selected during which a high proportion of the lightning activity occurring near the east coast of north america produced observable trimpi effects on vlf transmitter signals propagating in the region of the antarctic peninsula similar tol 2 2 5 the lack of lightning in antarctica gives this location a unique advantage for this study the functional dependence of the relative scattered field amplitude with the return stroke peak current of the lightning discharge suggests that during these events diffusion conditions are occurring near the precipitating radiation belt particles loss cone due to strong whistler wave fields probably caused by ducted signals the range of observed trimpi scatter amplitude of 10 to 35 db was produced by precipitation bursts with energy fluxes estimated to range over 6 5 0 4 x 10 3 ergs cm 2 s 1 the largest fluxes were found to be driven by lightning currents of about 250 ka while the smallest detectable fluxes relate to lightning currents of 70 ka although 3 of the 4 study days showed a high degree of consistency between the levels of lightning return stroke peak current required to produce any given perturbation scatter amplitude value conditions were significantly different on 23 april 1994 on this day observed trimpi signatures were 6 7 db greater for any given lightning intensity than on the other study days these events are consistent with a significantly harder radiation belt precipitation spectra probably caused by geomagnetic storm time acceleration processes of radiation belt electrons

structurally controlled hydrothermal alteration of carbonate reservoirs introduction langhorne taury smith heads the reservoir characterization group at the new york state museum he holds a b s degree from temple university a ph d from virginia tech and did postdoctoral work at the university of miami he also worked for chevron as a development geologist and current research interests are focused on carbonate reservoir characterization and hydrothermal alteration of carbonate reservoirs graham davies received his b sc honors degree and ph d from the university of western australia his doctoral thesis was on modern carbonates in shark bay western australia published in aapg memoir 13 after a postdoctoral fellowship with james lee wilson at rice university he joined the geological survey of canada gsc in calgary after 7 years with the gsc graham co founded and became principal owner of agat applied geoscience and technology consultants laboratories since 1983 he has operated through gdgc ltd he has published about 70 papers on the geology of australia and canada and has authored or coauthored more than 600 consulting reports graham received the cspg douglas medal in 2002 for his work on arctic paleozoic carbonates and evaporites and on the triassic and other aspects of western canadian geology his principal current interest is in hydrothermal dolomites this issue of the aapg bulletin is dedicated to structurally controlled hydrothermal alteration of carbonate rocks and reservoirs this type of alteration covers the spectrum of carbonate hosted sulfide ore deposits to hydrothermal dolomite to leached limestones and in many cases has a major impact on reservoir type geometry quality and distribution hydrothermal dolomite htd reservoirs have a long history of exploration and development in north america extending from the earliest discoveries in the ordovician lima indiana and other trends of the northeastern united states hurley and budros 1990 wickstrom et al 1992 and continuing today with the trenton black river play

zebra dolomitization as a result of focused fluid flow in the rocky mountains fold and thrust belt canada discordant zebra dolomite bodies occur locally in the middle cambrian cathedral and eldon formations of the main ranges of the canadian rocky mountains fold and thrust belt they are characterized by alternating dark grey a and white b bands forming an abba diagenetic cyclicity these bands developed parallel to both bedding and cleavage dark grey a bands consist of fine 300 m non planar crystalline impure dolomite the white b bands are composed of coarse up to several millimetres milky white pure saddle dolomites b1 which are often covered by pore lining zoned dolomite b2 the b phases often possess a saddle shaped morphology in contrast to the replacement origin of the a dolomite the zoned b2 dolomite rims are interpreted as a cement formed in open cavities the b1 dolomite is interpreted as the result of recrystallization with diagenetic leaching of non carbonate components all the zebra dolomites studied are nearly stoichiometric and are characterized by enriched na and depleted sr concentrations fe and mn concentrations in these dolomites differ depending on the sample locality fluid inclusion data indicate that the dolomites formed from relatively hot th 130 200 c saline 20 23 wt cacl2 eq fluids a diagenetic high temperature origin is also supported by depleted 18o values 20 to 14 vpdb a contribution of 87sr enriched fluids is reflected in the 87sr 86sr values 0 7091 0 7123 zebra dolomite development is explained by focused fluid flow which exploited areas of structural weaknesses e g basin platform rim areas faults etc expulsion of hot basinal brines in a tectonically active regime generated overpressures which explains the development of secondary porosity during zebra dolomitization as well as the intra zebra fracturing at decimetre to micrometre scale

association of uranium with macerals in marine black shales insights from the upper devonian new albany shale illinois basin abstract marine organic rich shales generally have high uranium content associated with sedimentary organic matter however organic matter in black shales is not homogeneous but instead a mixture of different macerals the uranium content and organic petrographic composition of 27 new albany shale samples indicate differential contributions of macerals to the uranium content in the upper devonian new albany shale of the illinois basin specifically uranium is mainly associated with amorphous organic matter microbially degraded phytoplankton zooplankton and bacterial biomass where an average uranium content of approximately 550 ppm has been estimated the amorphous organic matter s lack of structure as well as admixed with mineral grains

stable isotope geochemistry of coals humic kerogens and related natural gases isotope systematics are well defined for conventional sapropelic type i ii kerogens and their associated bacterial and thermogenic natural gas products these geochemical tools are used to estimate source type maturity and depositional environment and as a correlation technique in many cases the natural gas signatures in near surface samples and drill cuttings can be used to classify or predict a deeper lying source rock or reservoir corresponding interpretative schemes for coals type iii kerogens and their associated hydrocarbons are progressing quickly the shift in attention to humic sources is driven primarily by depletion of conventional oil and gas resources and the economic and societal requirements of coal and coal bed methane carbon hydrogen and nitrogen stable isotope variations can be large between different coals and humic kerogens these differences can often be recognized in their bulk 13corg dorg and 15norg values isotope signatures of coals can be diagnostic of several factors including deposit age type geographic location maturity and generation history however these characteristic isotopic variations are substantially better defined by the c h and n isotope ratios of the separate maceral groups such as vitrinite exinite and inertinite this new application of stable isotopes at the maceral and compound levels have great potential to improve the interpretative precision over conventional whole coal or bulk techniques hydrocarbon gases including coal gases derived from coals and humic kerogens can be distinguished from type i ii sources based on their molecular rations i e c1 c2 c3 and by comparing their stable isotope compositions especially 13cch4 and dch4 the 13cc2h6 can also be valuable but ethane is generally present in small amount 1 vol and requires

inferring paleotemperature from the d h ratio of lacustrine organic matter abstract linking the d h d records of the kerogen from bulk organic matter in lake sediments to known temperature d of precipitation relationships may offer new possibilities in paleoclimate studies here we examine the hydrogen isotope ratio obtained from a radiocarbon dated lake core from wisconsin situated in the midwestern part of the united states to infer paleo surface temperatures paleotemperatures were estimated by converting the d values of the organic fraction to the d values of the lake water and by implication to that of local precipitation the temperature estimates show that the middle holocene from 7000 to 5000 years before present bp was warmer by about 3 c in general agreement with speleothem data from the midwestern united states our study shows the usefulness of the d h rations of kerogen from bulk sediment as a climate proxy that can compliment compound specific hydrogen isotope studies

organic matter content and type variation in the sequence stratigraphic context of the upper devonian new albany shale illinois basin abstract organic matter quantity and type are important parameters in conventional source rock evaluation and unconventional shale oil gas reservoir characterization understanding the stratigraphic distribution of organic matter content and type in black shale successions is critical for identifying potentially productive intervals because organic matter can adsorb large amounts of oil and gas detailed examination of total organic carbon content organic petrographic composition and high resolution 8 cm spacing geochemical proxies in a sequence stratigraphic framework were conducted on an early mature 0 55 ro new albany shale core of the illinois basin to study the influence of relative sea level fluctuations on paleoproductivity clastic supply bottom water redox conditions and their combined control on total organic carbon distribution pattern and organic maceral variation marine organic matter including amorphous organic matter and alginite mainly derived from tasmanites cysts is the dominant organic matter in the new albany shale terrestrial organic matter accounts for stratigraphically amorphous organic matter content increases in transgressive systems tracts reaches a maximum near the maximum flooding surface and decreases in highstand systems tracts enrichment of broken tasmanites cysts and their detrital infills are an indicator of high energy environments and could possibly indicate lowstand systems tracts the stratigraphic distribution of organic matter content and type may result in cyclic stratigraphic variations of hydrocarbon generation potential and oil saturation and influence the development of secondary organic pores when the new albany shale is within the oil and gas windows

influence of geochemical organo petrographical and palynofacies assemblages on hydrocarbon generation a study from upper oligocene coal and shale of the makum coal basin assam india abstract the makum coal basin of northeast india comprises important coal and shale reserves of upper oligocene age a total of twenty samples were collected to evaluate the kerogen type hydrocarbon generation potential and thermal maturity through geochemically organo petrographically and palynofacies analyses the samples are characterized by high toc total organic carbon and large s2 remaining heavier hydrocarbons meet the required standards as good to excellent generation potential the coal and shale are marked by mixed type iii ii kerogen with minor occurrence of type i kerogen moderate to high hydrogen index hi values and are considered to generate thermogenic gas with some condensate oil the reflectance values indicate samples are mostly immature and close to the oil birth line the amount of vt60 grains also suggests that the samples can produce some condensate oil along with thermogenic gas the rock eval pyrolysis rep data stands with the interpretation through petrographic palynofacies and fourier transform infrared spectroscopy ftir in determining kerogen type and generation potential the generation potential is also controlled by the degree of organic matters reactivity the estimated reactivity indicates that besides vitrinite and liptinite up to 70 vol of the inertinite macerals have the potential to generate hydrocarbon the occurrence of a substantial amount of reactive macerals i e collotelinite vitrodetrinite collodetrinte corpogelinite alginite resinite and bituminite within the samples makes them more potential to generate hydrocarbons the diagram proposed based on our data of macerals and palynofacies assemblages may also be a convenient tool in detecting kerogen type s and nature of hydrocarbons

formation of 18o depleted dolomite within a marine evaporitic sequence triassic reichenhall formation austria dark grey bituminous dolostones interbedded with marine derived anhydrite horizons occur in the triassic reichenhall formation of western austria fossils are rare and indicate a hostile hypersaline depositional environment the dolomites are finely crystalline fairly stoichiometric well ordered and non ferroan closely spaced samples 94 in total of individual dolomite units have been analysed for their carbon and oxygen isotopic composition the data indicate surprisingly low 18o values 5 7 to 2 1 0 pdb whereas the 13c values are comparable to the contemporary triassic seawater 0 2 to 2 6 0 pdb sedimentological evidence including i lack of any evidence for extensive dissolution ii distinct oxygen and carbon isotope ratios of individual dolomite units iii covariance of carbon and oxygen isotopes within some dolomite layers and iv inclusions of celestite in dolomite indicates a nearly closed system after early diagenesis combining this information with water rock interaction calculations suggests that the lightest oxygen isotope compositions are the result of freshwater influx into the basin during very early dolomite formation a secondary factor may be dolomite recrystallization at elevated temperatures during burial

the upper thermal maturity limit of primary gas generated from marine organic matters abstract elemental composition and chemical structure of 16 kerogen samples concentrated from marine source rocks with maturity levels ranging from 0 65 ro to 3 3 ro were determined pyrolysis experiments of seven samples selected from the 16 kerogen samples were conducted in a gold tube system to clarify the process and determine the upper thermal maturity limit for primary gas generation from marine organic matter om the variation of the h c atomic ratio of the marine om appears to evolve through three phases with increasing maturity including a drastic decreasing phase before 1 3 ro a moderate decreasing phase from 1 3 to 2 0 ro and a gradual decreasing phase above 2 0 ro the evolution of the chemical structure measured by ftir indicates that most oxygen containing functional groups in marine om appear to be released prior to 0 8 ro aliphatic groups were still detected in the sample with a maturity of 3 0 ro but disappeared in the sample with a maturity of 3 3 ro the variation of aliphatic groups vs aromatic rings i1 displays a similar three stage pattern as the variation of h c atomic ratio with increasing maturity a step by step heating method in kerogen pyrolysis experiments was adopted to preclude secondary gas generation the pyrolysis experimental results for samples with different maturities proved that generally the maximum yield of primary gas generated by the marine om was not more than 140 ml per gram of total organic carbon toc only 1 16 ml g toc of hydrocarbon gas was generated by the sample with the maturity of 3 3 ro thus it can be rationally inferred that the upper thermal maturity limit for gas generation from the marine om may be around 3 5 ro nevertheless the main maturity range for the primary gas generation is suggested to be below 2 0 ro the yield of primary gas generated at the maturity range above 2 0 ro takes up 10 of maximum yield of the primary gas generated by the marine om

dolomite occurrence evolution and economically important associations abstract dolomite is not a simple mineral it can form as a primary precipitate a diagenetic replacement or as a hydrothermal metamorphic phase all that it requires is permeability a mechanism that facilitates fluid flow and a sufficient supply of magnesium dolomite can form in lakes on or beneath the shallow seafloor in zones of brine reflux and in early to late burial settings it may form from seawater from continental waters from the mixing of basinal brines the mixing of hypersaline brine with seawater or the mixing of seawater with meteoric water or via the cooling of basinal brines bacterial metabolism may aid the process of precipitation in settings where sulfate reducing species flourish and microbial action may control primary precipitation in some hypersaline anoxic lake settings dolomite is a metastable mineral early formed crystals can be replaced by later more stable phases with such replacements repeated a number of times during burial and metamorphism each new phase is formed by the partial or complete dissolution of an earlier dolomite this continual re equilibration during burial detracts from the ability of trace elements to indicate depositional conditions and resets the oxygen isotope signature of the dolomite at progressively higher temperatures because subsurface dolomite evolves via dissolution and reprecipitation a bed of dolomite can retain or create porosity and permeability to much greater burial depths and into higher temperature realms than a limestone counterpart dolomitization also creates new crystals with new rhomb growth following the dissolution of less stable precursors repetition of this process without complete pore cementation can generate intercrystalline porosity a number of times in the rock s burial history intercrystalline porosity is a highly interconnected style of porosity that gives dolomite reservoirs their good fluid storage capacity and efficient drainage the fact that many dolomite reservoirs formed via brine reflux means that they sit beneath an evaporite seal in both platform and basinwide evaporite settings the same association of evaporites sulfate source and entrained hydrocarbons means that burial conditions are also suitable for thermochemical sulfate reduction and the precipitation of base metals this tends to occur at higher temperatures 60 c 80 c and so the resulting dolomites tend to be ferroan and consist of saddle shaped crystals

upper cretaceous stable carbon isotope stratigraphy of terrestrial organic matter from sakhalin russian far east a proxy for the isotopic composition of paleoatmospheric co2 abstract time stratigraphic patterns of stable carbon isotopic ratios recorded in terrestrial organic matter from cenomanian maastrichtian successions for the russian far east can be correlated to those of carbonate carbon from well studied successions for other parts of the world age indicative biostratigraphy based on regional ammonoids and inoceramid bivalves are well established in japan and can be applied to the whole cretaceous succession except for the upper cenomanian lower turonian and the upper part of the maastrichtian zones lacking macrofossils globally correlative carbon isotopic events previously documented with carbonate carbon from europe and with carbonate carbon and marine organic matter from the u s western interior are recognized with similar magnitude through uppermost cenomanian lower campanian in ascending order these events are positive spike across the cenomanian turonian boundary step like leveled segment followed by negative shift lower middle turonian trough like negative excursion middle upper turonian positive rebound coupled with following broad peak coniacian and positive peak basal campanian followed by modest negative excursion the parallel fluctuation of the 13 c value between the terrestrial organic matter and carbonate suggests carbon isotopic equilibrium between surface seawater and atmospheric co 2 and demonstrates that the isotopic curve of terrestrial organic carbon can be used to monitor carbon isotopic fluctuations of co 2 in the ocean atmosphere system in the upper campanian and maastrichtian a negative 13 c excursion within chron 33r and a following rapid rebound can be correlated with the same distinctive carbon isotopic feature of carbonate observed in the deep sea cores from south and north atlantic the indian and the pacific oceans within this interval the 13 c value of terrestrial organic matter also reflects carbon isotopic fluctuation of the global co 2 reservoir with relatively minor regional local noise

the organic matter distribution and methane capacity of the lower cretaceous strata of northeastern british columbia canada abstract the methane sorption capacity of a succession of sandstone siltstone shale and coal from the lower cretaceous fort st john group of northeastern british columbia was investigated average organic matter om content for all formations is 2 3 wt with a minimum of 0 6 wt and maximum of 10 1 wt the methane sorption capacity ranges between 0 19 and 2 74 cm3 g at 6 mpa and at 30 c total gas capacity free and sorbed gas ranges between 2 2 and 16 6 cm3 g at 6 mpa micropore volumes range between 0 43 and 1 69 cm3 100 g a positive correlation exists between the om content micropore volume and the methane capacity of shales shales with high methane capacities have either high contents of inertodetrinite or vitrinite moisture content shows a positive relationship with om content micropore volume and methane capacity the negative relationship between moisture and surface area derived from n2 adsorption suggests the moisture is located within the microporosity of the om and also explains the positive relationship between methane capacity and moisture the high inertodetrinite and vitrinite contents correlate with sea level regressions that delivered terrestrial om from coastal plains located south of the study area into the basin

geochemical characterisation of organic matter in keg river formation elk point group middle devonian la crete basin western canada carbonates from the keg river formation la crete basin alberta western canada were examined in order to define a oil source rock potential b bulk maceral composition c extract yield and finally d facies variations using py gc ms thirty samples from 6 different wells were examined from the lower keg river member and 4 from the upper keg river member using conventional geochemical methods as maturity differences are absent within the sample set variations in toc tmax hydrogen index organic petrography and extract yields are caused by variability in organic matter input which is revealed by molecular characterisation using py gc ms lower keg river member bituminous wackestones are excellent potential source rocks containing types i ii and type ii organic matter types i ii organic matter contains large well preserved up to 200 m in diameter thick walled tasmanites 10 15 of sample and akinete algal cells indicative of algal blooms within an amorphous bituminite type ii organic matter contains a higher proportion of degraded alginites bituminite relative to well preserved alginites extract yields mg g toc were seen to increase from types i ii to type ii organic matter py gc ms revealed that 1 2 3 4 tetramethylbenzene was a major peak in most samples this is a pyrolysis product arising from cleavage of c40 diaromatic carotenoids incorporated within the kerogen during diagenesis the source of this compound is thought to be from an unknown diaromatic compound with a 2 3 6 3 4 5 trimethyl substitution pattern and isorenieratene which is specific to photosynthetic green sulphur bacteria chlorobiaceae suggesting that the photic zone was at least partially anoxic during deposition of these samples the relative abundance of this compound n c11 alkene and organic sulphur calculated from the thiophene ratio both increase from types i ii to type ii organic matter this trend was grossly similar to the trend seen in the variability of extract yield with hydrogen index a similar trend for hi and tmax indicates samples containing a higher proportion of degraded alginites bituminite relative to well preserved alginite are more labile than type i ii organic matter upper keg river member marls contain type ii organic matter which is characterised by heavily degraded algal material within a bituminous groundmass pyrolysates of two of the marl samples contain only low amounts of 1 2 3 4 tetramethylbenzene in contrast to the bituminous wackestones indicating that the depositional environment source input was different during deposition of the marl samples although both marls contain similar organic matter their pyrolysates were significantly different one marl 1141 9 m was highly paraffinic containing dominantly short chain alkene alkane doublets while the other marl 1137 6 m contained a bimodal n alkane alkene distribution and high amounts of alkylphenols which may be derived from preservation of resistant algal polyphenolic molecules or suggest a terrestrial input

algal bloom episodes and the formation of bituminite and micrinite in hydrocarbon source rocks evidence from the devonian and mississippian northern williston basin canada organic petrology incident light microscopy of middle devonian inter reef laminates and devonian mississippian epicontinental black shales williston basin canada indicates that algal bloom episodes and consequential bacterial activity played a significant role in the accumulation of amorphous bituminite iii rich organic microfacies corpohuminite like algal akinete cells produced by filamentous algae during algal bloom periods are persistent maceral inclusions within the potential hydrocarbon source rock intervals these cells ro mean range 0 24 0 90 are regarded as positive indicators of stressful palaeoenvironmental conditions unicellular tasmanites and leiosphaeridia marine alginite and variably degraded alginite remnants ghosts within the amorphous kerogen may be products of cell lysis photo oxidation and microbial alteration these processes are characteristic of algal bloom periods minute ca 1 m spheroidal and coccoidal bacteria like macerals are dispersed throughout the bituminite iii network attesting to the importance of microbial activity within the water column and sediment during and after organic matter accumulation dispersed granules laminations and replacement textures of micrinite like macerals within bituminite iii are interpreted as remnants of microbial alteration rather than a residual product of thermal maturation and hydrocarbon generation

subionospheric vlf signatures of oblique nonducted whistler induced precipitation subionospheric very low frequency vlf signal perturbations observed at multiple sites in association with individual lightning discharges exhibit onset delays which steadily increase with increasing l value the timing of the onsets and the inferred spatial extent 1000 km of the ionospheric disturbance are consistent with those expected for electron precipitation induced by obliquely propagating i e nonducted whistlers

palynological and bulk geochemical constraints on the paleoceanographic conditions across the frasnian famennian boundary new albany shale indiana abstract a down core record of stable isotope and geochemical results is integrated with palynofacies kerogen data from the new albany shale indiana to reconstruct environmental changes that occurred across the frasnian famennian boundary preliminary interpretations are focused on developing several multiproxy linkages that will potentially lead toward a more robust understanding of the occurrence and significance of phytoplankton assemblage variations during the late devonian a time of widespread black shale formation development of such linkages will potentially provide a more comprehensive assessment of the various controls on 1 primary production and 2 carbon sequestration in a large low paleolatitude intracratonic basin an abrupt change in the geochemical and biotic proxies for particulate organic matter across the frasnian famennian boundary coincides with a distinct lithological change characterized by laminated brownish black famennian mudstones unconformably overlying alternating bioturbated greenish gray and non bioturbated dark gray frasnian mudstones elemental and isotopic profiles reflect different patterns of production degradation and removal of organic carbon in the two shale facies a shift from acritarch to prasinophyte dominated waters across the boundary indicates the overall importance of bathymetric fluctuations chemico physical conditions and nutrient availability related to eustatic sea level change a positive 13 c v pdb shift of 1 1 across the boundary is interpreted to be correlative with the global upper kellwasser event a preliminary model is proposed to explain the sustainable primary production during times of maximum flooding thereby enhancing organic preservation during black shale formation

factors controlling the abundance of organic sulfur in flash pyrolyzates of upper cretaceous kerogens from sergipe basin brazil the molecular and elemental composition of immature kerogens isolated from upper cretaceous marine carbonates from sergipe basin brazil were investigated using combined pyrolysis gas chromatography mass spectrometry and organic petrographic techniques the kerogens are predominantly composed of reddish fluorescing amorphous organic matter aom and variable amounts of yellow fluorescing alginite and liptodetrinite the abundance of organic sulfur in the kerogens inferred from the ratio 2 ethyl 5 methylthiophene 1 2 dimethylbenzene dec 1 ene in the pyrolyzates is variable and may be related to changes in the type of primary organic input and or to variations in rates of bacterial sulfate reduction a concomitant increase in s c and o c ratios determined in situ using the electron microprobe is observed in aom and alginites and may be related to a progressive oxidation of the organic matter during sulfurization the s c ratio of the aom is systematically higher than the s c ratio of the alginites combined with a thiophene distribution characteristic of pyrolyzates of type ii organic matter the higher s c of aom in sergipe kerogens suggests that sulfurization and incorporation of low molecular weight lipids derived from normal marine organic matter into the kerogen structure predominated over direct sulfurization of highly aliphatic algal biomacromolecules

variation of organic matter density with thermal maturity an estimate or measurement of organic matter density is required for converting between the weight percent of total organic carbon toc and the volume percent of organic matter for wireline log calibration it is therefore important to recognize when significant changes in organic matter density occur a method is presented for calculating organic matter density from measurements of crushed rock dry grain density and soxhlet extracted toc i have investigated the thermal evolution of organic matter by tracking changes in the intrinsic density of organic matter as a function of thermal maturity organic matter density shows two step increases that correspond to the generation of liquid hydrocarbons in the oil window up to 1 2 vitrinite reflectance ro and the conversion of organic matter to graphitelike carbon more correctly turbostratic carbon at high thermal maturity 4 ro profound structural changes of organic matter may in part determine the maturity limits of source rock tight liquids and shale gas plays particularly at high thermal maturity where gas is hosted within the organic matter hosted pore system

sources of alkylbenzenes in lower cretaceous lacustrine source rocks west african rift basins abstract we conducted molecular biomarker and compound specific carbon isotope analyses of off line pyrolyzates from lacustrine samples recovered by onez 1 well the kissenda formation in the gabon basin and well a the maculungo formation in the kwanza basin in west africa pyrolyzates from onez 1 well contain isotopically depleted 1 2 3 4 tetramethylbenzene 1 2 3 4 tetramb 26 1 to 29 4 and 1 2 4 trimethylbenzene 1 2 4 trimb 26 4 to 29 7 which are isotopically similar to aryl isoprenoids 29 9 and 31 2 and carotane 28 5 to 31 3 identified in the bitumen fractions pyrolyzates from 3 samples in the lower sections of well a contain isotopically enriched 1 2 3 4 tetramb ca 16 and 1 2 4 trimb ca 14 consistent with an origin from diagenetic products of isorenieratene chlorobactene biosynthesized by green sulfur bacteria chlorobiaceae pyrolyzates from five samples in the upper sections of well a are characterized by the presence of intermediate carbon isotope values of 1 2 3 4 tetramb 20 7 to 22 8 and 1 2 4 trimb 19 3 to 21 2 and isotopically enriched isorenieratane ca 14 5 off line pyrolyzates from these lacustrine source rocks represent two distinct end members 13 c depleted diagenetic products of carotene derived from a lacustrine algal source and 13 c enriched diagenetic products of isorenieratene chlorobactene derived from green sulfur bacteria organic matter om from onez 1 well shows a significant proportion of algal biomass with a 13 c depleted composition the presence of 13 c enriched biomarkers derived from carotenoids of chlorobiaceae from samples in the lower part of well a indicates the development of photic zone euxinia and a significant biogeochemical role of sulfur in the upper section of well a the 1 2 3 4 tetramb and 1 2 4 trimb have 13 c values indicative of contributions from both chlorobiaceae and algae to the om

geochemistry of the alginite and amorphous organic matter from type ii s kerogens abstract maceral fractions of the type ii s kerogens from the monterey formation miocene california u s a and duwi formation campanian maastrichtian egypt were separated by density gradient centrifugation the monterey fm kerogen sample was comprised chiefly of light red fluorescing amorphous organic matter aom the flash pyrolyzate of which was characterized by a predominance of alkylbenzenes alkylthiophenes and alkylpyrroles in contrast the pyrolyzates of its alginite concentrate showed a highly aliphatic character typical of this maceral with the series of n alkenes and n alkanes c6 c26 predominating the pyrolyzate of the dominant light brown fluorescing aom of the duwi fm kerogen had a relatively high concentration of alkylbenzenes and alkylthiophenes while its alginite concentrate showed a more aliphatic character upon pyrolysis there was a marked enrichment of thiophenic sulfur in the light colored aom of both samples and also pyrrolic nitrogen in the case of the monterey relative to the alginite the results support a bacterially mediated degradative origin for type ii s amorphous organic matter with algal remains as the primary source of the kerogen

alternative biological sources for 1 2 3 4 tetramethylbenzene in flash pyrolysates of kerogen pyrolysates of kerogens isolated from indian ocean surface sediments and from black sea unit ii contain abundant 1 2 3 4 tetramethylbenzene 1 2 3 4 tmb suggesting the presence of macromolecularly bound isorenieratane skeletons derived from isorenieratene biosynthesized by green sulphur bacteria cf hartgers et al 1994c however the 13c content of 1 2 3 4 tmb is identical to that of algal lipids excluding an origin from green sulphur bacteria the presence of 1 2 3 4 tmb in pyrolysates of stable residues of several marine algae indicates that it can also have an algal origin therefore the assessment of photic zone anoxia on the basis of the abundant presence of 1 2 3 4 tmb in the pyrolysate is not possible without determination of its stable carbon isotopic composition and comparison with those of algal lipids

post oil solid bitumen network in the woodford shale usa a potential primary migration pathway abstract an important if not predominant component of porosity in many gas shales has been identified in organic matter an organic network in shales has been described in the literature as organic matter generalized term kerogen primary or bitumen secondary recognition of the type and origin of an organic network in shales has relevance in establishing the origin and timing of porosity and fracture development the pervasive nature of the organic network adopting the shape of pores in type ii kerogen rich woodford shale suggests it is the residue of primary oil migration we use the term post oil solid bitumen to distinguish this bitumen occurrence from pre oil solid bitumen defined as a precursor of oil three forms of this post oil solid bitumen network are recognized in reflected white light at 500 magnification and confirmed in backscattered scanning electron microscope images at 2500 magnification namely speckled 1 2 m wispy 2 5 m and connected 5 m the post oil solid bitumen network demonstrates the prior occurrence of oil generation and migration within this hydrocarbon source rock provides porosity for hydrocarbon storage sites and forms hydrocarbon migration pathways

a tem microstructural study of dolomite with curved faces saddle dolomite electron diffraction analytical electron microscopy and high voltage high resolution electron microscopy have been used to investigate crystal defects in calcium rich saddle dolomites having pronounced curvature of the faces results show that branching ribbon like defects in these so called saddle dolomites are thin coherent laths of calcitic material the ribbons are profuse and explain the characteristic calcium excess found in most saddle dolomites because the lattice spacings of calcite are between 3 8 and 6 7 larger than the corresponding lattice spacings of dolomite a calcitic ribbon causes local distortion of the host dolomite the branching ribbons have a predominant 10 14 orientation and are generally present in high density they may represent the source of crystal distortion that ultimately manifests itself on the macroscopic scale the calcitic ribbons form during growth from aqueous solution although they have features in common with similar defects found in carbonatite carbonates this fine scale intergrowth microstructure may be a variant of even finer scale modulated structures found in other sedimentary calcian dolomites

hydrothermal dolomitization in a complex geodynamic setting lower palaeozoic northern spain burial hydrothermal dolomitization is a common diagenetic modification in sedimentary basins with implications for oil and gas reservoir performance outcrop analogues represent an easily accessible source of data to refine the genetic models and assess risk in hydrocarbon exploration and production the palaeozoic succession of northern spain contains numerous excellent exposures of epigenetically dolomitized limestones particularly in the carboniferous and cambrian the epigenetic dolomites in the cambrian carbonates of the lancara formation are volumetrically small but have a large aerial distribution across different tectonic units of the variscan fold and thrust belt coarse crystals abundant saddle dolomite cement negative 18o and fluid inclusion homogenization temperatures between 80 c and 120 c characterize these dolomites which are petrographically and geochemically similar to the tens of kilometre sized hydrothermal dolomites replacing the upper carboniferous succession in the same area in both cases the dolomitizing fluids are derived from highly evaporated sea water modified to a limited degree through fluid rock interaction the dolomitization events affecting both cambrian and carboniferous strata are probably related to the same post orogenic hydrothermal fluid flow the formation of the post collisional latest carboniferous cantabrian arc fostered dolomitization the extension related to bending of the arc generated deep reaching faults and strike slip movements which favoured the circulation of hot dolomitizing fluids in the outer parts of this orocline a similar dolomitization process affected other areas of europe after the main stages of the variscan orogeny dolomitization was a continuous uninterrupted isochemical process limestone replacement resulted in a major porosity redistribution and focused the fluid flow into the newly created porous zones replacement was followed immediately by partial to complete cementation of the pores including zebra fabrics and vugs with saddle dolomite the amount of porosity left depends on the volume of cement and therefore on the volume of fluids available

fault development and stress evolution of the post hercynian asturian basin asturias and cantabria northwestern spain abstract the asturian basin an emerged part of the north iberian continental margin has been investigated in terms of fault development and stress evolution the mesozoic history of this domain is mainly linked to the extensional faulting processes which preceded the opening of the bay of biscay preserved jurassic faulted blocks and associated half graben structures bounded by wnw ese to nw se faults are related to a late jurassic kimmeridgian rifting stage this fault system seems to have played a major role during the mesozoic structuring of the basin suggesting an extension oriented approximately ne sw the cenozoic evolution is related to the iberia eurasia convergence and collision leading to compressional and subsequent extensional structures the direction of compression documented in various sites was nnw sse during an initial early middle eocene stage reoriented probably in the oligocene to ne sw this succession of stress regimes was applied to the same three major fault systems ne sw nw se and e w which were inherited from the variscan orogeny some of them having already been involved in the latest stephanian early permian rifting episode during the tertiary compressional phase the nw se trend which is believed to have controlled the late jurassic tectonic development was rejuvenated into dextral strike slip faults whereas the ne sw system moved in a sinistral sense the e w system was reactivated as reverse faults giving rise to a partial inversion of the basin

dolomitization of a carbonate platform during late burial lower to middle cambrian shady dolomite virginia appalachians abstract outer platform carbonates of the lower to middle cambrian shady dolomite virginia appalachians record a lengthy and complex diagenetic history ranging from marine cementation to burial diagenesis during late paleozoic overthrusting analysis of petrographically well preserved marine cements has provided an estimate of the isotopic composition of lower cambrian marine carbonate 18o 7 5 to 6 1 pdb 13c 0 2 to 0 8 pdb 87sr 86sr 0 70869 to 0 70975 establishing a base line with which to assess later diagenetic carbonate meteoric dissolution and early calcite cement postdate marine cementation and formed during subaerial exposure the platform margin carbonates were extensively dolomitized dolomitization postdates calcite cementation and the initial development of stylolites and tectonic fractures several episodes of dolomite replacement and cementation are evident zone 1 dolomite consists of rare relict dolomite cores which were replaced and overgrown by zone 2a dolomite the dominant replacement phase zone 2a dolomite is depleted in 18o 18o 10 2 to 7 0 and enriched in 13c 13c 1 0 to 1 6 relative to marine carbonate reflecting precipitation from warm formation fluids buffered by the host carbonate uniformly low sr contents 25 to 65 ppm and nonradiogenic 87sr 86sr 0 70900 to 0 70971 also attest to pore water equilibration with the host rock replacement dolomitization was followed by widespread carbonate dissolution which formed vuggy porosity and local solution breccias the host dolomite locally is encrusted by mississippi valley type mvt occurrences of ore mineralization consisting of sphalerite galena and pyrite this major generation of ore minerals is overgrown by three generations of dolomite cement the first dolomite cement zone 2b has similar 18o composition 13o 10 3 to 7 4 but slightly depleted 13c values 13c 0 4 to 1 1 relative to zone 2a dolomite and has similar sr contents 30 to 45 ppm and 87sr 86sr ratios 0 70933 to 0 70966 zone 2b dolomite cement exhibits petrographic isotopic and geochemical affinities with zone 2a replacement dolomite implying that the two dolomite types formed from fluids of similar composition and temperature primary fluid inclusions in zone 2b dolomite indicate precipitation from warm minimum 120 to 150 c brines 23 26 wt nacl equiv these temperatures imply that the dolomitizing fluid was enriched in 18o due to extensive water rock interaction with host carbonate which also buffered the fluid 13c sr and 87sr 86sr content zones 3 and 4 dolomite cement are depleted in 18o 13o 13 8 to 11 3 relative to the previous dolomites implying a temperature increase to 150 to 210 c the late dolomite cements have 13c compositions 13c 0 7 to 0 9 ranging from those similar to the earlier dolomites to more depleted values zones 3 and 4 dolomite cement are enriched in sr 60 to 135 ppm which is radiogenic 87sr 86sr 0 71025 to 0 71445 these later cements thus record fluids that were no longer buffered by the host carbonate dolomite cements locally were overgrown by sphalerite followed by authigenic quartz and calcite cement secondary three phase fluid inclusions in quartz and calcite indicate hot 175 to 225 c saline 30 to 33 wt nacl equiv fluids temperatures and pressures interpreted from the fluid inclusions are compatible with estimated burial depths in excess of 5 km the dolomites formed during deep burial coeval with late paleozoic alleghanian age thrusting the mg required for burial dolomitization was derived from pressure solution of structurally lower platform interior dolomites that were overridden by the shady dolomite thrust sheet tectonic uplift and deformation resulted in regional fluid flow which transported this mg to the shady dolomite outer platform during burial dolomitization

identification of aryl isoprenoids in source rocks and crude oils biological markers for the green sulphur bacteria abstract a series of c13 to c31 aryl isoprenoids 1 alkyl 2 3 6 trimethylbenzenes have been identified in reef hosted oils and their source rocks from the middle and upper silurian of the michigan basin and middle devonian of the alberta basin canada their structure has been confirmed by unambiguous synthesis of the c14 member of the series their structure and isotopic composition indicate that they are derived from isorenieratene from the chlorobiaceae family of sulphur bacteria these results are consistent with geological and geochemical studies that show that the source rocks were deposited under metahaline to hypersaline sulphate and sulphide rich water columns the distribution of other biomarkers in these oils and source rocks indicates that a diverse biota contributed organic matter to the source environment in conjunction with the aryl isoprenoids they show that there is a remarkable similarity in composition between the two sets of oils and source rocks despite their great temporal and geographic separation this reflects the similarity of their environments and emphasizes the importance of sedimentary facies in controlling the composition of organic matter in source rocks and their derived oils

hydrogen isotope values in lacustrine kerogen abstract kerogen derived from plankton and sedge cattail that accumulated in sediment during two distinct phases of swan lake s development was extracted from segments of radiocarbon dated cores carbon c hydrogen h and nitrogen n amounts and the d values of kerogen extracts were determined kerogen extracts younger than 3900 ybp contained higher average h c and n c atom ratios than older kerogen 5000 to 3900 ybp the more recent kerogen extracts were derived primarily from plankton in open water sediment and are characterized by significantly higher lipid and protein fractions than those from the sedge cattail that formed the marsh layer plankton derived kerogen was more depleted in d averaging 20 per mil lighter than that from older extracts 5000 to 3900 ybp which according to pollen analysis were dominated by sedge cattail derived kerogen in the sediment profiles differences in the d values appear more related to kerogen source than to postdepositional hydrogen loss or temperature

self subduction of the pangaean global plate one of the most striking and rare occurrences in the earth s history is the amalgamation of most of the continental lithosphere into one supercontinent the most recent supercontinent pangaea lasted from 320 to 200 million years ago here we show that after the continental collisions that led to the formation of pangaea plate convergence continued in a large wedge shaped oceanic tract we suggest that plate strain at the periphery of the supercontinent eventually resulted in self subduction of the pangaean global plate when the ocean margin of the continent subducted beneath the continental edge at the other end of the same plate our scenario results in a stress regime within pangaea that explains the development of a large fold structure near the apex of the palaeotethys ocean extensive lower crustal heating and continental magmatism at the core of the continent as well as the development of radially arranged continental rifts in more peripheral regions of the plate

ftir absorption indices for thermal maturity in comparison with vitrinite reflectance r0 in type ii kerogens from devonian black shales abstract ftir absorbance signals in kerogens and macerals were evaluated as indices for thermal maturity two sets of naturally matured type ii kerogens from the new albany shale illinois basin and the exshaw formation western canada sedimentary basin and kerogens from hydrous pyrolysis artificial maturation of the new albany shale were characterized by ftir good correlation was observed between the aromatic aliphatic absorption ratio and vitrinite reflectance r 0 ftir parameters are especially valuable for determining the degree of maturity of marine source rocks lacking vitrinite with increasing maturity ftir spectra express four trends i an increase in the absorption of aromatic bands ii a decrease in the absorption of aliphatic bands iii a loss of oxygenated groups carbonyl and carboxyl and iv an initial decrease in the ch 2 ch 3 ratio that is not apparent at higher maturity in naturally matured samples but is observed throughout increasing r 0 in artificially matured samples the difference in the ch 2 ch 3 ratio in samples from natural and artificial maturation at higher maturity indicates that short term artificial maturation at high temperatures is not fully equivalent to slow geologic maturation at lower temperatures with increasing r 0 the carboxyl carbonyl aromatic carbon ratio generally decreases except that kerogens from the exshaw formation and from hydrous pyrolysis experiments express an intermittent slight increase at medium maturity ftir derived aromaticities correlate well with r 0 although some uncertainty is due to the dependence of ftir parameters on the maceral composition of kerogen whereas r 0 is solely dependent on vitrinite

a strontium isotopic study of formation waters from the illinois basin u s a abstract the isotopic composition of sr has been measured in 73 formation water samples from paleozoic strata in the illinois basin 87sr 86sr ratios range from 0 7079 to 0 7108 with the exception of four samples the waters are more radiogenic than corresponding paleozoic sea water values the relatively narrow range of slightly elevated 87sr 86sr rations is uniformly distributed in waters throughout the stratigraphic column and in silurian waters across the basin isotopic analyses of core samples from reservoir rocks show an absence of water rock sr isotopic equilibration basin lithology and analyses of detrital rock units indicate that clay minerals in shales and in quartz sandstone matrices represent the only significant source of radiogenic sr for the waters silurian and devonian water show a two component mixing relation which suggests that they comprise a single hydrogeological system that evolved when radiogenic water from new albany shales entered silurian devonian carbonate rocks and mixed with marine interstitial water regional migration of the waters and associated petroleum within the silurian devonian strata proposed in other studies is consistent with the sr isotopic data under favorable circumstances subsurface waters are capable of retaining a sr isotopic recor of their evolution

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

influence of provenance and preservation on the carbon isotope variations of dispersed organic matter in ancient floodplain sediments 1 carbon isotope ratios of bulk organic matter in sedimentary rocks 13cdom are a potential source of paleoenvironmental information in terrestrial stratigraphic sequences however insufficient understanding of the range of depositional and post depositional controls on 13cdom values makes interpretations of these data difficult here we evaluate the effects of organic matter om provenance and preservation on 13cdom using records spanning the paleocene eocene thermal maximum petm in the bighorn basin wyoming usa as a case study we sampled sedimentary rocks spanning the petm in two well studied locations polecat bench pb and highway 16 hw16 in the bighorn basin independent carbon isotope records from biomarkers and pedogenic carbonates at these sites suggest that local shifts in plant and soil 13c values associated with the petm cie were broadly similar and were characterized by an abrupt 5 decrease followed by a plateau and a eventual return to pre petm 13c values the 13cdom records from both sites differ significantly from these reference curves in both amplitude of change and in preserving high frequency isotopic fluctuations and large isotopic anomalies superimposed on the general pattern of isotopic change through the cie for each location we separated organo mineral fractions mom concentrated macerals from 20 stratigraphic levels and analyzed the carbon isotope ratio 13c of each fraction at both sites the 13c of the fine and coarse mom differ significantly from each other and from 13cdom concentration weighted mixing of these isotopically distinct om fractions explains high resolution 13cdom fluctuations but does not explain the large isotopic anomalies observed at both sites at hw16 we identified two thermally and isotopically distinct populations of macerals interpreted as being indigenous and recycled om at this site one over total organic carbon 1 toc values correlate with 13cdom for pre petm and petm strata and both relationships converge toward the 13c of recycled om for low toc at pb macerals display homogeneous thermal maturity but the proportion of isotopically distinct vitrinite and liptinite varies between facies relationships between 1 toc and 13cdom are also present within specific stratigraphic intervals at pb but values do not converge on a single isotopic value across the sampled interval these observations are consistent with variable mixing of om fractions having different provenance mixing of exotic recycled om at hw16 and locally reworked om at pb with indigenous fresh om at both sites and explain the large anomalies observed in the 13cdom records at both sites our findings raise questions about the assumption that om in ancient sediments is indigenous and dominantly records 13c variations of local plants

influence of maceral composition on geochemical characteristics of immature shale kerogen insight from density fraction analysis abstract variations in the relative proportions of individual macerals in shales can significantly influence the geochemical characteristics of bulk organic matter density fractions of kerogen from the thermally immature new albany shale devonian and mississippian with contrasting maceral compositions exhibit strong geochemical differences the parental shale is characterized by a vitrinite reflectance ro of 0 45 a total organic carbon content of 13 wt and a sulfur content of 6 2 wt organic matter is dominated by amorphinite and alginite with vitrinite and inertinite accounting only for 1 by volume alginite dominated density fractions density ca 1 0 1 15 g cm3 contain significantly more aliphatic hydrogen a stronger carboxyl carbonyl contribution and reduced fourier transform infrared spectroscopy absorbance in the 1000 to 1100 cm 1 region assigned to ether bonds c o c as compared to the amorphinite dominated density fraction density ca 1 2 1 6 g cm3 aromaticity generally increases from alginite dominated to amorphinite dominated fractions density fractions dominated by amorphinite are more deuterium depleted dn values of nonexchangeable hydrogen up to 105 than alginite rich density fraction dn values reach 90 in contrast changes in relative proportions of alginite and amorphinite in the new albany shale do not significantly affect the amount of isotopically exchangeable hydrogen in total hydrogen i e hydrogen exchangeability alginite is relatively 13c enriched whereas density fractions having a high content of amorphinite are relatively 13c depleted our results suggest that even small bulk geochemical and isotopic differences can gain relevance after deconvolution from maceral related variability the masking influence of maceral abundance patterns must be considered when interpreting bulk geochemical data as paleoenvironmental proxies the findings of this study on shale and type ii kerogen are relevant for all types of kerogens in sediments and rocks

origin properties and implications of solid bitumen in source rock reservoirs a review abstract this paper reviews the significance of solid bitumen with emphasis on source rock reservoirs we discuss difficulties and discrepancies with terminology especially those terms related to the origin of solid bitumen and its physical and chemical properties various definitions of solid bitumen have their own justifications and can be used provided there is clarity about which defining criteria are being considered difficulties in conforming to chemical solubility or origin related definitions lead us to suggest adapting the reflectance of solid hydrocarbon as a practical choice for placing the boundary between solid bitumen and pyrobitumen and 1 50 is proposed as the boundary value it has to be noted that this boundary may be shifted down to 1 3 for sulfur rich kerogen recently much progress has been made by combining imaging and physical adsorption techniques in porosity studies and so the porosity of solid bitumen is given special emphasis comparing pore characteristics obtained from sem versus those generated by gas adsorption mercury intrusion or neutron scattering techniques indicates that the sem pore inventory fails to account for the smallest pores we review the implications of the abundance of solid bitumen on reservoir quality porosity permeability and producibility based on examples of selected sequences one of the difficulties in predicting the influence of solid bitumen bearing horizons on reservoir quality arises from the problems with detecting organic phases using various logging techniques the use of specialized techniques such as nmr logging that allows two dimensional t1 and t2 measurements should be expanded and other potential techniques need to be further researched and tested certain aspects of the properties of solid bitumen that are not as well understood such as its hydrocarbon generation potential or its role in hydrocarbon migration are also discussed with the aim of identifying further research that could lead to a better understanding of the role that solid bitumen plays in unconventional reservoirs

structurally controlled hydrothermal dolomite reservoir facies an overview structurally controlled hydrothermal dolomite htd reservoir facies and associated productive leached limestones are major hydrocarbon producers in north america and are receiving increased exploration attention globally they include multiple trends in the ordovician locally silurian and devonian of the michigan appalachian and other basins of eastern canada and the united states and in the devonian and mississippian of the western canada sedimentary basin they also occur in jurassic hosts along rifted atlantic margins in the jurassic cretaceous of the arabian gulf region and elsewhere hydrothermal dolomitization is defined as dolomitization occurring under burial conditions commonly at shallow depths by fluids typically very saline with temperature and pressure t and p higher than the ambient t and p of the host formation the latter commonly is limestone proof of a hydrothermal origin for htd reservoir facies requires integration of burial thermal history plots fluid inclusion temperature data and constraints on timing of emplacement hydrothermal dolomite reservoir facies are part of a spectrum of hydrothermal mineral deposits that include sedimentary exhalative lead zinc ore bodies and htd hosted mississippi valley type sulfide deposits all three hydrothermal deposits show a strong structural control by extensional and or strike slip wrench faults with fluid flow typically focused at transtensional and dilational structural sites and in the hanging wall transtensional sags above negative flower structures on wrench faults are favored drilling sites for htd reservoir facies saddle dolomite in both replacive and void filling modes is characteristic of htd facies for many reservoirs matrix replacive dolomite and saddle dolomite appear to have formed near contemporaneously and from the same fluid and temperature conditions the original host facies exerts a major influence on the lateral extent of dolomitization resultant textures pore type and pore volume breccias zebra fabrics shear microfractures and other rock characteristics record short term shear stress and pore fluid pressure transients particularly proximal to active faults high temperature hydrothermal pulses may alter kerogen in host limestones a process designated forced maturation basement highs underlying sandstone and or carbonate aquifers probably overpressured and overlying and internal shale seals and aquitards also may constrain or influence htd emplacement although many questions and uncertainties remain particularly in terms of mg and brine source and mass balance recognition and active exploration of the htd play continues to expand increasing use of three dimensional seismic imagery and seismic anomaly mapping combined with horizontal drilling oblique to linear trends defined by structural sags helps to reduce risk