experimental reactions of amphibolite with boron bearing aqueous fluids at 200 mpa implications for tourmaline stability and partial melting in mafic rocks reactions between hornblende plagioclase amphibolite and acidic and alkaline b bearing aqueous fluids have been investigated by experiments at 475 600 c and 200 mpa at 600 c hornblende calcic plagioclase react to form tourmaline danburite clinopyroxene quartz in acidic fluids containing 0 5 1 0 wt b2o3 tourmaline is precipitated directly from acidic fluids and the reaction is driven by neutralization of fluids by na ca derived from the breakdown of reactant solids the concentration of b2o3 in fluids needed to stabilize tourmaline increases as ph increases above approximately 6 0 and tourmaline is unstable in alkaline fluids ph approximately 6 5 7 0 regardless of b concentration in addition to acid base relations tourmaline stability is favored by comparatively higher activity coefficients for al species in acidic fluids the concentrations of al and si in fluid increase with alkalinity with the eventual production of felsic borosilicate melts through partial melting of the plagioclase component of the amphibolite in seeded experiments tourmaline also contributes components to melt partial melting is evident in the range 500 525 c at 200 mpa in experiments with 8wt b2o3 in fluid as na2b4o7 the experimental results are applied primarily to metasomatic reactions between mafic rocks and borate fluids derived from granitic magmas but tourmaline stability and partial melting in mafic regional metamorphic systems are also discussed briefly

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

boron and lithium in high grade rocks and minerals from the wawa kapuskasing region ontario there is no preferential partitioning of boron among the principal rock forming minerals in high grade rocks of the kapuskasing structural zone ksz and the wawa domal gneiss region wdg lithium is strongly concentrated in biotite and other ferromagnesian minerals but does not show consistent partitioning between these and the sialic minerals the distribution of b and li within a rock may be studied using an alpha track image which shows that the inconsistencies in partitioning may be largely attributed to disturbance of mineral equilibria by postmetamorphic low grade alteration that deposited b and li boron has similar concentrations in all the rock types studied although it is an incompatible element that elsewhere accumulates in pegmatites lithium concentrations are low in the anorthositic rocks but are otherwise very variable in some but not all rocks higher than usual b and li can be attributed to introduction during alteration boron occurs at low concentrations 2 3 ppm throughout both the k

modelling an infiltration driven geochemical front modelling of geochemical alteration profiles e g in 18o or 87sr 86sr resulting from fluid infiltration has provided important constraints on the volumes of fluid that move through the crust during metamorphism these models consider that alteration results from a combination of advection with diffusion and or kinetically limited solid fluid exchange models incorporating advection and one of the two broadening mechanisms have analytical solutions whilst the three parameter solution does not given a particular alteration profile it is therefore important from a computational point of view to determine whether use of the more comples three parameter model places tighter limits on the characteristics of the fluid infiltration event in this paper we address this problem through modelling of a measured oxygen isotope alteration profile from naxos greece for each end member model we calculate a set of best fit parameters emphasising which features of the data control the fit of each of the models we then consider numerical solutions which allow all three processes to operate and conduct a grid search in parameter space to map out the structure of the variance between the model and data while it is not possible to distinguish a single combination of the three processes that produces a strong global minimum in variance we can distinguish a family of solutions which are equally valid and we use this minimum variance family to place bounds on the time scales fluid velocity and porosity characteristic of the fluid alteration event

biodegradation of tar sand bitumens from the ardmore anadarko basins oklahoma ii correlation of oils tar sands and source rocks abstract in an earlier paper we reported the effects of biodegradation on tar sand bitumens from the southern part of the ardmore and anadarko basins in this paper we wish to describe geochemical correlations that have been made between the tar sand bitumens and oils produced from various formations in the pauls valley area 25 miles to the north it was determined that the tar sands were formed from a source similar to many of these oils whose reservoir ages ranged from ordovician to pennsylvanian the oils had been previously divided into two major groups on the basis of their biomarker distributions with one group 80 of the oils studied proposed to have been sourced from the woodford shale devonian and the other group from the viola limestone ordovician the tar sand bitumen oil correlation study based on hydrocarbon and porphyrin biomarker distributions and pyrolysis gas chromatography of asphaltenes has shown that the tar sand bitumen appears to be genetically related to the group of oils derived from the woodford shale and more specifically to those present in the oil creek formation ordovician of the anadarko basin

variations in the sterane carbon number distributions of marine source rock derived crude oils through geological time abstract the analysis of the sterane data of a large set of crude oils 414 derivedfrom marine carbonate 27 and siliciclastic source rocks 14 where influences of terrestrial or lacustrine derived organic matter can reasonably be excluded shows that there are increases in the relative content of c28 steranes and decreases in the relative content of c29 steranes through geological time there are no consistent variations in the relative content of c27 steranes through time with one major exception a proterozoic oil from oman palaeozolic and older crude oils are thus generally characterised by strong predominances of c29 steranes and low relative concentrations of c28 steranes significantly higher proportions of c28 steranes and lower proportions of c29 steranes occur in oils derived from jurassic and upper cretaceous source rocks these changes through time do not appear to reflect the chemical evolution of the sterols of one particular variety of marine organism the increase in c28 steranes may be related to the increased diversification of phytoplantonic assemblages in the jurassic and cretaceous possible sources of the c28 sterols necessary for the observed changes in crude oil steranes includes diatoms coccolithophores and dinoflagellates although the technique does not give an accurate means of determining the age of the source rock of a crude oil it is possible to distinguish younger crudes derived from the upper cretaceous and tertiary from palaeozoic and older crudes

garnet biotite geothermometry revised new margules parameters and a natural specimen data set from maine the garnet biotite geothermometer has been recalibrated using recently obtained margules parameters for iron magnesium calcium garnet mn interactions in garnet and al interactions in biotite as well as the fe oxidation state of both minerals fe mg and dwal margules parameters for biotite have been retrieved by combining experimental results on 6 al free and 6 al bearing biotite using statistical methods margules parameters per mole of biotite are bt w 5 40 719 2 30t j mole mgfe

oils and source rocks from pauls valley anadarko basin oklahoma u s a abstract thirty oils from the pauls valley area of the anadarko basin oklahoma have been analyzed for n alkane terpane and sterane distributions in an effort to classify genetically related oils ten rock samples from the area were also analyzed in an attempt to relate oil types to their possible source rocks the pauls valley area located near the southeast corner of the anadarko basin has producing formations ranging in age from middle ordovician to late pennsylvanian trapping mechanisms responsible for the accumulation of hydrocarbons vary from purely structural traps to fractured reservoirs to up dip truncations of reservoirs and up dip pinchouts of sandstones results show that 85 of oils in the area probably have a common source the woodford shale a group of oils reservoired in the viola group exhibit distinct geochemical characteristics and are thought to have a different source the differences between the oils from these two sources include enhanced c 24 tetracyclic terpane concentrations relative to c 26 tricyclic terpanes diminished c 28 30 tricyclic terpanes relative to t s and t m diminished c 30 steranes relative to their c 29 counterparts predominance of c 35 over c 34 extended hopanes and an even odd predominance of the normal alkane distribution extracts from the viola group generally exhibit the same qualities as the associated oils and the limestone is proposed as their probable source rock the predominance of c 29 steranes for oil samples which appear to have a marine source inferred by their n alkane distribution the presence of c 30 steranes and high levels of tricyclic terpanes suggests that caution be used in the interpretation of terrigenous sources based on the high abundance of c 29 steranes the deese group the springer formation the sylvan shale and the arbuckle group are not likely sources for the oils analyzed from the pauls valley area differences in api gravity and color previously used to classify oils in this region are not source related but are related to maturation and migration effects

relationship between petroleum composition and depositional environment of petroleum source rocks crude oils of nonmarine source can be distinguished from those of marine shale source and from oils originating in marine carbonate sequences by using a battery of geochemical parameters as demonstrated with a sample suite of nearly 40 oils a novel parameter based on the presence of c30 steranes in the oil was found to be a definitive indication of a contribution to the source from marine derived organic matter a second novel parameter based on monoaromatized steroid distributions was effective in helping to distinguish nonmarine from marine crudes and can be used to gauge relative amounts of higher plant input to oils within a given basin sterane distributions were similarly useful for detecting higher plant input but were less effective than monoaromatize steroid distributions for making marine versus nonmarine distinctions concentrations of high molecular weight paraffin can also be effective nonmarine indicators but are influenced by maturation and biodegradation processes certain algal derived nonmarine oils may show little high molecular weight paraffin response oils from carbonate sources with a few exceptions can be distinguished by having low pristane phytane ratios low carbon preference indexes and high sulfur contents gammacerane indexes and carbon isotope ratios of the whole crude are not effective in distinguishing these types of environmental differences on a global basis

effects of source thermal maturity and biodegradation on the distribution and isomerization of homohopanes in petroleum abstract the distributions of c31 c35 17 21 h homohopanes in marine petroleums can be used to describe redox conditions in the source rock depositional environment for example high c35 homohopane indices c35 c31 c35 are typical of petroleums generated from source rocks deposited under anoxic marine conditions where the c35 backbone of the precursor bacteriohopanetetrol is preferentially preserved homohopane distributions have been used to distinguish petroleums from different organic facies of the same source rock homohopane distributions are altered by secondary processes for example the c35 homohopane index decreases with increasing api gravity and thermal maturity of related oils from the monterey formation offshore california similar decreases in the homohopane index are observed for expelled oils from monterey source rock during hydrous pyrolysis biodegradation can result in selective loss of high or low molecular weight homologs apparently depending on the bacterial population in the reservoir bacterial demethylation of homohopanes appears necessary to explain 25 norhopanes in at least one biodegraded oil hydrous pyrolysis studies of the phosphatic and siliceous members in the monterey formation show that identical heating conditions result in different homohopane c 22 epimer ratios furthermore a reversal in the trend of the epimer ratio at high experimental temperatures is observed for the phosphatic but not for the siliceous lithology this could be caused by the combined effects of isomerization and differential thermal destruction of epimers at high temperatures possibly mediated by rock mineralogy

geochemical evaluation of oil and gas samples from the upper devonian and mississippian reservoirs southern anadarko basin oklahoma and its implication for the woodford shale unconventional play abstract the woodford shale sycamore and goddard formations have become important liquid rich unconventional resource play targets most petroleum experts believe the mature woodford shale is responsible for much of the southern anadarko conventional and unconventional petroleum production with notable exceptions this paper will focus on the well head oil and gas samples from the south central oklahoma oil province scoop area woodford shale and the younger mississippian reservoirs the purpose of this paper is to characterize the scoop area unconventional resource play using the produced petroleum discrepancies between produced oil and gas geochemistry rock maturity and production characteristics presents an interesting conundrum the produced volatile oils contain lower boiling point compounds c6 c8 that indicate a high maturity product from the woodford shale source whereas the high molecular weight fraction c15 biomarkers suggests a middle mature product from the woodford shale source the produced gas chemistry suggests a low to middle mature product using published gas plots lastly the production gas oil ratio gor and well head fluid gravities are typical of a gas condensate there is no simple unified petroleum system process to explain all these observations there could be a combination of factors resulting in this conundrum such as mixing of multiple charges from both local and off structure sources phase separation as a result of production or well head sampling storage issues at present it may be difficult to fully explain the current results however we do believe the geochemistry and production results demonstrate a significant off structure contribution a simple petroleum systems model based on source rock organic matter type and maturity does not always correctly predict production or ultimate recovery

origin and history of the oils in the lawton oil field southwestern oklahoma the lawton oil field is located on the wichita mountain uplift in southwestern oklahoma this study focused on addressing three problems related to the lawton oil field a what is are the source s of the oils b have the oils been subjected to alteration since emplacement and c what is the filling history of the field eighteen oils and one seep sample were collected and characterized by a variety of geochemical techniques including bulk composition biomarkers and stable carbon isotopes in order to address these questions source rocks in this region are absent following the pennsylvanian age wichita orogeny but biomarkers and stable isotopic data suggest the source of these oils is probably the woodford shale despite the fact that all of these oils were recovered from reservoirs at depths between 125 and 1 000 ft 38 and 305 m none of them appeared to be extensively biodegraded as manifested by the abundance of the complete range of n alkanes however the presence of 25 norhopanes in all eighteen samples suggests that these oils are mixtures of various proportions of degraded and non degraded or slightly degraded oils the seep sample and some oils have a relatively high abundance of the c32 22r hopanoic acid relative to the c31 22r hopanoic acid with the presence of these 22r hopanoic acids suggesting the oils have been degraded aerobically at some point in their history it was also noted that the concentration of the c31 22r hopanoic acid is higher in the shallower reservoirs than in the deeper reservoirs possibly indicating slightly higher levels of degradation in the shallower reservoirs compared to the deeper reservoirs a hydrocarbon accumulation model has been proposed for this field based on two main reservoir charging periods the initial charge of crude oil was biodegraded probably under anaerobic conditions the second charging period took place after or together with the uplift of the wichita mountains and subsidence of the southern part of the anadarko basin leading to deeper burial of the source rock and production of higher maturity oil which subsequently filled the reservoirs containing the degraded oil and may still be recharging these shallow reservoirs today

pegmatite wallrock interactions black hills south dakota progressive boron metasomatism adjacent to the tip top pegmatite abstract interaction between country rock and fluids derived from the tip top pegmatite has resulted in a series of boron enriched assemblages between unaltered quartz mica schist to the pegmatite contact is a succession of four mineral assemblages 1 1 quartz biotite potassium feldspar assemblage q b k which consists essentially of the original metamorphic silicate assemblage plus anomalously high amounts of modal tourmaline 2 2 quartz biotite tourmaline assemblage q b t 3 3 tourmaline quartz muscovite assemblage t q m 4 4 tourmaline quartz assemblage t q alkali elements cs rb k li sio 2 and ba show a decrease from the q b k assemblage to the t q assemblage a1 2 o 3 ga b total fe and zn increase moderately from the q b k assemblage to the t q assemblage the mineral chemistries also change considerably the mg mg fe 2 ratios in biotites range from 0 54 to 0 50 in samples from the q b k assemblage to 0 39 in the q b t assemblage the range in tourmaline end member components from the q b k assemblage to the t q assemblage is as follows q b k dravite 63 schorl 23 elbaite 05 buergerite 09 t q dravite 23 schorl 37 elbaite 17 buergerite 23 observed variations in mineral assemblage and whole rock chemistry within the alteration zone appear to a first approximation to be a function of b 2 o 3 boron metasomatism and k 2 o alkali leaching the breakdown of feldspar and biotite may be approximated by reactions 2hcl 2 k na alsi 3 o 8 ai 2 k na cl al 2 sio 5 5sio 2 h 2 o and 2 annite sio 2 5al 2 sio 5 2nacl 6h 3 bo 3 ai 2 tourmaline 2kcl 7h 2 o the alteration zone may represent either a single episode b cs li rb enriched fluid or multiple episodes b zn mn fluid and cs li rb fluid of pegmatite fluid schist interactions in both situations b in the aqueous fluid from the pegmatite reacts with the schist breaking down sheet silicate traps for cs rb li and k and forming tourmaline rich assemblages

the abundance and distribution of diamondoids in biodegraded oils from the san joaquin valley implications for biodegradation of diamondoids in petroleum reservoirs abstract the biodegradability of diamondoids was investigated using a collection of crude oil samples from the san joaquin valley california that had been biodegraded to varying extent in the reservoir our results show that diamondoids are subjected to biodegradation which is selective as well as stepwise adamantanes are generally more susceptible to biodegradation than other diamondoids such as diamantanes and triamantanes we report a possible pathway for the microbial degradation of adamantane this cage hydrocarbon possibly breaks down to a metabolic intermediate through the action of microbes at higher levels of biodegradation in petroleum reservoirs microbial alteration has only a minor effect on diamondoid abundance in oil at low levels of biodegradation our results suggest that most diamondoids with the exception of adamantane are resistant to biodegradation like the polycyclic terpanes e g c19 c24 tricyclic terpanes hopanes gammacerane oleananes ts tm c29 ts steranes and diasteranes microbial alteration of diamondoids has a negligible impact on the quantification of oil cracking achieved using the diamondoid biomarker method

geochemical characterization of the upper mississippian goddard formation noble ranch group and related oils in the anadarko basin of oklahoma the woodford shale is anecdotally assumed to be the major source of oil for plays in the anadarko basin including the stacked oil and condensate play in the southcentral oklahoma oil province scoop however there is little published geochemical work to confirm this assumption this study set out to identify a characteristic geochemical fingerprint for the goddard formation another potential source rock in the scoop to determine if the goddard is contributing to oil accumulations within the scoop the upper mississippian goddard formation has been a target for unconventional production in scoop since 2012 published geochemical interpretations for the goddard formation are still limited and this study represents the first detailed oil source rock correlation for the goddard in the scoop area the most characteristic geochemical signature of the goddard extracts is a predominance of tricyclic terpanes relative to the hopanes in the mass to charge ratio 191 chromatogram possibly related to enrichment via thermal stress or a unique source signature additional distinctive signatures were also identified for the triaromatic steroid hydrocarbons sesquiterpenoids and steranes the biomarker fingerprints of scoop oils are nearly identical with those of the goddard extracts in this study oils in the scoop therefore appear to originate from a mississippian source such as the goddard rather than the woodford this observation demonstrates the value of oil source rock correlation studies and suggests that there may be effective source rocks in the anadarko basin that have been overlooked in the past and should be re evaluated in detail

biodegradation of oil in uplifted basins prevented by deep burial sterilization biodegradation of crude oil by bacterial activity which has occurred in the majority of the earth s oil reserves is known to reduce greatly the quality of petroleum in reservoirs for economically successful prospecting for oil it is therefore important to understand the processes and conditions in geological formations that lead to oil biodegradation although recent studies speculate that bacterial activity can potentially occur up to temperatures as high as 150 degrees c refs 3 4 it is generally accepted that effective petroleum biodegradation over geological timescales generally occurs in reservoirs with temperatures below 80 degrees c ref 2 this appears however to be at odds with the observation that non degraded oils can still be found in reservoirs below this temperature here we compile data regarding the extent of oil biodegradation in several oil reservoirs and find that the extensive occurrence of non biodegraded oil in shallow cool basins is restricted to those that have been uplifted from deeper hotter regions of the earth we suggest that these petroleum reservoirs were sterilized by heating to a temperature around 80 90 degrees c during deep burial inactivating hydrocarbon degrading organisms that occur in the deep biosphere even when such reservoirs are subsequently uplifted to much cooler regions and filled with oil degradation does not occur implying that the sterilized sediments are not recolonized by hydrocarbon degrading bacteria

two dimensional synthetic seismogram modeling of wide angle seismic data from the wichita uplift oklahoma abstract in conjunction with the 1979 cocorp wichita uplift survey wide angle reflection refraction data were recorded on a fixed array the object of the present study is to model and interpret these wide angle data to add independent constraints on the deep structure of the wichita uplift three common receiver profiles were extracted from the data recording apertures were 3 2 to 23 4 km to the north of the array 4 2 to 14 9 km to the east and 4 2 to 12 6 km to the west these profiles are modeled by iterative fitting of high frequency synthetic seismograms computed by asymptotic ray theory the model derived contains low velocity 2 0 to 2 16 km sec surficial sediments that vary in thickness these account for strong local travel time variations of 0 05 sec and for a small but persistent ghost arrival that follows all the main branches with a delay of 0 2 sec the basement granites rhyolites and gabbros are very near the surface throughout the study area both granite and gabbro outcrops are seen basement p wave velocities are therefore relatively high representative velocities are 4 7 km sec at 0 8 km depth 6 2 at 1 8 6 4 at 2 8 and 6 5 at 4 0 local velocities as high as 7 4 km sec may be present the basement is fairly transparent beneath the wichita uplift with only a few local reflectors present this is consistent with the cocorp results

tourmaline occurrences within the penamacor monsanto granitic pluton and host rocks central portugal genetic implications of crystal chemical and isotopic features tourmalinization associated with peraluminous granitic intrusions in metapelitic host rocks has been widely recorded in the iberian peninsula given the importance of tourmaline as a tracer of granite magma evolution and potential indicator of sn w mineralizations in the penamacor monsanto granite pluton central eastern portugal central iberian zone tourmaline occurs 1 as accessory phase in two mica granitic rocks muscovite granites and aplites 2 in quartz mica tourmaline rocks tourmalinites in several exocontact locations and 3 as a rare detrital phase in contact zone hornfels and metapelitic host rocks electron microprobe and stable isotope 18o d 11b data provide clear distinctions between tourmaline populations from these different settings a schorl oxyschorl tourmalines from granitic rocks have variable foititic component x 17 57 and mg mg fe ratios 0 19 0 50 in two mica granitic rocks and 0 05 0 19 in the more differentiated muscovite granite and aplites granitic tourmalines have constant 18o values 12 1 0 1 with wider ranging d 78 2 4 7 and 11b 10 7 to 9 0 values b vein breccia oxyschorl mg mg fe 0 31 0 44 results from late b and fe enriched magma derived fluids and is characterized by 18o 12 4 d 29 5 and 11b 9 3 while replacement tourmalines have more dravitic compositions mg mg fe 0 26 0 64 close to that of detrital tourmaline in the surrounding metapelitic rocks and yield relatively constant 18o values 13 1 13 3 though wider ranging d 58 5 to 36 5 and 11b 10 2 to 8 8 values and c detrital tourmaline in contact rocks and regional host metasediments is mainly dravite mg mg fe 0 35 0 78 and oxydravite mg mg fe 0 51 0 58 respectively boron contents of the granitic rocks are low 650 ppm compared to the minimum b contents normally required for tourmaline saturation in granitic melts implying loss of b and other volatiles to the surrounding host rocks during the late magmatic stages this process was responsible for tourmalinization at the exocontact of the penamacor monsanto pluton either as direct tourmaline precipitation in cavities and fractures crossing the pluton margin vein breccia tourmalinites or as replacement of mafic minerals chlorite or biotite in the host rocks replacement tourmalinites along the exocontact of the granite thermometry based on 18o equilibrium fractionation between tourmaline and fluid indicates that a late b enriched magmatic aqueous fluid av 18o 12 1 at 600 c precipitated the vein breccia tourmaline 18o 12 4 at 500 550 c and later interacted with the cooler surrounding host rocks to produce tourmaline at lower temperatures 400 450 c and an average 18o 13 2 closer to the values for the host rock although b metasomatism associated with some granitic plutons in the iberian peninsula seems to be relatively confined in space extending integrated studies such as this to a larger number of granitic plutons may afford us a better understanding of variscan magmatism and related mineralizations

determination of offset across the northern margin of the wichita uplift southwest oklahoma the wichita uplift represents a tectonic element within the ancestral rocky mountains a series of basement involved uplifts and associated basins within the foreland of the ouachita orogen contrasting tectonic models for the evolution of the wichita uplift are evaluated by i analyzing the suite of structures within the frontal fault zone which separates the uplift from the adjoining anadarko basin and ii undertaking a palinspastic restoration of houton group late ordovician devonian thickness trends between the basin and the frontal fault zone to estimate the magnitude and sense of offset across the principal uplift bounding faults cross sections from uplift to basin show basement involved thrusts and folds similar to those recognized within the laramide late cretaceous tertiary foreland of the rocky mountains structural patterns in map view possess elements that have been previously interpreted as resulting from reverse slip and or left slip on the uplift bounding faults palinspastic restoration of isopach patterns between the frontal fault zone and anadarko basin indicates that offset across the frontal faults may be explained by oblique slip left reverse slip on the uplift bounding faults the component of left slip is nearly an order off magnitude less than proposed in some previous models of carboniferous tectonism within the foreland of the ouachita orogen

guidelines for evaluating petroleum source rock using programmed pyrolysis rock eval pyrolysis is used to rapidly evaluate the petroleum generative potential and thermal maturity of rocks accurate conclusions require programs every 30 60 ft 9 18 m understanding of interpretive pitfalls and supporting data such as visual kerogen vitrinite reflectance and elemental analyses the generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography most coals show high s2 s3 5 and low hi values 300 mg hc g toc migrated oil and mud additives which alter rock eval data can sometimes be removed by special processing for immature rocks bimodal s2 peaks and pi values over 0 2 indicate contamination pyrolysis downgrades organic poor clay rich rocks which show lower hi and higher tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays tmax values for small s2 peaks 0 2 mg hc g toc are unreliable tmax is affected by maturation organic matter type contamination and the mineral matrix s3 is sensitive to inorganic and adsorbed carbon dioxide and to instrumentation problems acidification of carbonate rich samples and proper maintenance improves s3 measurement constant sample weights 100 mg are recommended below a threshold weight tmax increases by up to 10 c and other parameters decrease organic rich samples which overload the detector can be diluted with carbonate detector linearity is determined by pyrolyzing various weights of an organic rich rock

biodegradation of tar sand bitumens from the ardmore and anadarko basins carter county oklahoma abstract a series of tar sand bitumens collected from a single shallow well in the ardmore basin carter county oklahoma has been characterized by various geochemical techniques particular emphasis has been placed on determination of variations in biomarker distributions both hydrocarbons and porphyrins as a function of biodegradation the tar sand bitumens have been severely biodegraded and most of the n alkanes low molecular weight cycloalkanes isoprenoid alkanes c27 c29 steranes light aromatics and sulfur compounds have been removed in addition the hopane distributions have been altered to differing degress with the pseudohomolugoues above c30decreasing in concentration prior to the c20 21 the triaromatic steroid hydrocarbons were also altered with preferential removal of 20r epimers c20 21 and c27 28 diasterane and c30 sterane distributions appear to be relatively unaffected by biodegradation the high resistance of tricyclic terpanes the c24 tetracyclic terpane and monoaromatic steroid hydrocarbons to biodegradation indicate that the distributions of these compounds are well suited to serve as correlation parameters in heavily altered samples it was also observed in this study that the main ring structure of the porphyrin molecule was not affected by these very high levels of biodegradation previously hypothesized changes in porphyrin structure due to biodegradation have included n alkyl side chain cleavage and possible conversion from dpep to etio type porphyrins an investigation has also been made with an active seep collected from sulphur in the anadarko basin oklahoma and the results show that the relative rate of biodegradation of various classes of biomarkers differs between these two locations although it was proposed that the original oil responsible for these two seeps is derived from the same source rock formation

classification and thermal history of petroleum based on light hydrocarbons abstract classifications of oils and kerogens are described two indices are employed termed the heptane and isoheptane values based on analyses of gasoline range hydrocarbons the indices assess degree of paraffinicity and allow the definition of four types of oil normal mature supermature and biodegraded the values of these indices measured in sediment extracts are a function of maximum attained temperature and of kerogen type aliphatic and aromatic kerogens are definable only the extracts of sediments bearing aliphatic kerogens having a specific thermal history are identical to the normal oils which form the largest group 41 in the sample set this group was evidently generated at subsurface temperatures of the order of 138 149 c 280 300 f defined under specific conditions of burial history it is suggested that all other petroleums are transformation products of normal oils

contrasting scales of element mobility in metamorphic rocks near harney peak granite black hills south dakota outcrop scale and regional dispersion patterns of rare elements help establish origins of fluid components mechanisms of fluid flow and the scale of element mobility in metamorphic rocks near the harney peak granite enrichment of granite derived elements sn b w li cu f p adjacent to a quartz vein 3 5 km north of the granite indicates that fracture controlled flow was one mechanism for movement of magmatic fluids graphitization of wall rocks and co2 ch4 fluid inclusions in vein quartz show that c was also transported by the vein forming fluid mixing of h2o rich magmatic fluid and co2 ch4 bearing metamorphic fluid within a concealed intrusive below the vein is proposed based on the observation of late stage graphite in several exposed pegmatite bodies in the area other wall rock alteration includes small relative gains of rb k and al toward the vein and relative losses of na sr ca si fe mg mn and possibly ti changes in p k al and si and reequilibration of whole rock 18o are confined to a 50 cm wide zone next to the vein additions of c sn w and cu and depletion of ca na and sr reach 100 150 cm from the vein boron reaches a maximum 25 150 cm from the vein and drops to background levels between 150 and 250 cm in contrast to these elements li is three times the regional background level throughout the outcrop at least 600 cm from any known veins and f and rb remain at elevated levels comparing these results with a regional geochemical profile away from the harney peak granite and published results on dispersion around rare element pegmatites documents the extent of element redistribution on a broader scale for example rb and f can be affected up to 100 m from local fluid sources whereas li appears to record interaction with granite derived fluids in rocks that are 500 m or more from map scale fluid sources thus regional dispersion patterns of li and other rare elements provide a minimum estimate of the volume of mid crustal rock that interacted with granite derived fluids in the harney peak area

high fo2 during sillimanite zone metamorphism of part of the barrovian type locality glen clova scotland introduction the redox state of sillimanite zone 650 700 c 5 6 kbar metasediments of the barrovian type area scotland was investigated the chemical and mineralogical evolution of the crust using estimates of metamorphic oxygen fugacity fo2 sulfur fugacity during orogenesis is critically dependent upon the redox fs2 and fluid chemistry based on new determinations of mineral state of metamorphic fluids james 1955 chinner 1960 and rock compositions from 33 samples a total of 94 of the buddington lindsley 1964 miyashiro 1964 french samples lack graphite contain both ilmenite hematite solid solutions 1966 eugster skippen 1967 thompson 1970 harte rhomox and magnetite and had metamorphic fo2 about 2 1975 ohmoto kerrick 1977 rumble 1978 lamb log10 units above the quartz fayalite magnetite qfm buffer the valley 1985 frost 1991a 1991b brenan et al 1995 regional variation in metamorphic fo2 for these rocks was minimal harlov et al 1997 ague 1998 the classical barrovian about 0 3 log10 units reflecting either a protolith that was type locality in glen clova angus scotland is a superb homogeneous with respect to redox state or an initially variable example of redox controls on metamorphism chinner protolith whose redox state was homogenized by metamorphic 1960 based on field relations petrography and the fluid rock interaction rhomox inclusions in garnet porchemical systematics of minerals and bulk rocks chinner phyroblasts that become richer in ilmenite from the interior to the 1960 showed that large differences in bulk rock oxedge of the host porphyroblast suggest that at least some synidation ratio or existed at local and regional scales metamorphic reduction of rock occurred significant variations in between metasediments during amphibolite facies metabulk rock oxidation ratio or that are probably inherited from morphism in glen clova or molecular 2fe2o3 sedimentary protoliths are found from one layer to the next or 100 2fe2o3 feo these differences were attributed ranges mostly between 20 and 50 or molecular 2fe2o3 to chemical contrasts inherited at least in part from the 100 2fe2o3 feo these or variations are uncorrelated sedimentary protoliths and were taken as evidence that with fo2 and do not indicate that large order of magnitude gradients significant differences in fo2 and fluid composition existed in fo2 and redox state existed or were preserved between layers during between layers during metamorphism chinner 1960 metamorphism the other 6 of the samples contain ilmenite lack rock oxidation ratio variations in glen clova have magnetite and had low fo2 0 1 order of magnitude below qfm been unequivocally established but important questions in the stability field of graphite they are characterized by comremain regarding the metamorphic fluids for example binations of the following large fluid hf h2o metasomatic what were the quantitative variations in the fugacities of tourmaline bearing veins absence or rarity of primary organic o2 and sulfur species such as s2 in the region did large matter and crosscutting late metamorphic shear zones rich in variations in fo2 and fluid composition exist between carbonaceous material such observations suggest that locally low intercalated metasedimentary layers could metafo2 conditions may have been related to the influx of reducing fluids morphic fluid rock interaction between layers have overfrom elsewhere in the area come characteristic buffer capacities inherited from

tourmaline rich pseudomorphs in sillimanite zone metapelites demarcation of an infiltration front textural features combined with mineral chemistry preserved in metamorphic rocks provide insights into metamorphic reaction mechanisms as well as open vs closed system processes prograde tourmaline rich muscovite pseudomorphs after staurolite develop in sillimanite zone metapelites adjacent to peraluminous granitoid intrusives in nw maine tourmalines occur in discrete domains restricted to central regions of muscovite rich quartz poor pseudomorphs with biotite rich margins these tourmaline grains are relatively large 1 0 mm lack detrital cores and exhibit only minor compositional zoning in sharp contrast to matrix tourmaline from other samples these features suggest fluid infiltration as the causative mechanism for the formation of these tourmaline rich mica pseudomorphs after staurolite irreversible thermodynamic models of local reactions and material transport in combination with mineral chemistry allow evaluation of reaction mechanisms that produced these pseudomorphs thermodynamic models in the nkcmtfashob system mimic the observed textural features if a threestage process is used stage 1 staurolite replacement is initiated by infiltration of an aqueous phase that adds k na h2o to the rock with the concomitant removal of al fe because the system is initially undersaturated with respect to tourmaline a pseudomorph containing muscovite with minor biotite develops at the expense of staurolite stage 2 with continued infiltration concentration of b increases tourmaline saturation is exceeded tourmaline nucleates and grows local material transport constraints mandate that tourmaline precipitation be spatially restricted to regions of staurolite dissolution consequently tourmaline forms in clusters at sites containing the last vestiges of staurolite in the pseudomorph core also evidenced by staurolite inclusions within several tourmaline grains resultant domains of staurolite replacement during this stage contain about equal amounts of muscovite and tourmaline typical staurolite poikiloblast pseudomorphing reactions require silica transport matrix quartz dissolves from the surrounding host resulting in a local enrichment of biotite and plagioclase at the pseudomorph margin stage 3 small amounts of sillimanite nucleate and grow throughout the rock late stage aqueous fluids from the adjacent monzonitic intrusive are likely to be the primary b source theoretical textural and compositional modeling combined with observational data indicate that boron must have been derived externally from the rock that the modal amount of tourmaline is very sensitive to the b content of the fluid that tourmaline is stable throughout the sillimanite zone depending on other cation activities and ph of the fluid and that these pseudomorphs provide insight into b contents of metamorphic fluids and the timing of the b influx the outer geographic extent of the tourmaline bearing pseudomorphs marks the boundary of a reactive geochemical front and thus defines an advective isograd interpretation of subtle textural features preserved in the rock in conjunction with irreversible textural modeling provides a powerful tool with which to understand the chemical evolution of metamorphic rocks and the fluids involved

oxygen isotope constraints on metamorphic fluid flow townshend dam vermont u s a fluid rock interaction during amphibolite facies metamorphism has been investigated for rocks exposed in a single 400 m long lithologically heterogeneous outcrop near townshend vermont usa oxygen isotopic compositions have been measured in profiles across single garnet crystals from thirteen samples and from hornblende and garnet separates from thirty three fine grained samples this outcrop was previously studied who measured large oxygen isotope gradients 3 per thousand in garnets from one sample and inferred large amounts of pervasive fluid flow all of the garnets that we have analyzed show less isotopic zonation le 1 per thousand twelve of them have zonation 0 5 per thousand and the mineral separate data imply both a strong correlation of isotopic composition with rock type and large gradients in peak metamorphic fluid isotopic compositions although devolatilization reactions in these rocks must have produced metamorphic fluids the data preclude cross foliation time integrated fluid fluxes greater than 300 600 cm sup 3 cm sup 2 during prograde amphibolite facies metamorphism the isotopic trends can all be interpreted in terms of closed system behavior channeled fluid flow or diffusive exchange of oxygen in an interconnected grain boundary fluid and within uncertainty cross strike advective fluxes could have been zero any significant flow at this locality was dominantly either layer parallel or channeled out of the system in veins more if all fluid flow occurred in veins then their spacing must have been less than 300 600 m the data are inconsistent with massive and pervasive metamorphic fluid flow across strike but do not address layer parallel flow less

aromatic hydrocarbon biomarkers in terrestrial organic matter of devonian to permian age abstract this paper presents the results of a detailed study on the occurrence and distribution of alkylnaphthalenes and alkylphenanthrenes in 39 coal and sediment samples from the late palaeozoic containing predominantly terrestrial organic matter most of the samples represent the euramerian flora realm and originate from locations beyond the variscan front in eastern northern and central europe i e especially england and the moscow basin the samples are of relatively low maturity 0 32 to 1 80 rr and consist mainly of mixtures of type iii and ii kerogen quantification of the c0 to c4 naphthalenes and the c0 to c4 phenanthrenes showed that these compound classes were highly abundant in all samples aromatic hydrocarbon maturity parameters in general are in good agreement with measured vitrinite reflectance values 1 2 7 trimethylnaphthalene an assumed diagenetic product of oleanane type biomarkers was present in all investigated samples this observation provides evidence that oleanane type lipids were biosynthesised by organisms predating the evolution of angiosperms or that assumed formation pathways for 1 2 7 trimethylnaphthalene are insecure 1 2 8 trimethylphenanthrene was significantly enriched in samples from the permian and the one sample from the devonian investigated in this study the precursor s of 1 2 8 trimethylphenanthrene therefore may have been produced by organisms which were least abundant in the carboniferous depositional environments represented by our samples

a novel microbial hydrocarbon degradation pathway revealed by hopane demethylation in a petroleum reservoir abstract the origin of 25 norhopanes is controversial despite their abundance in many biodegraded oils in a biodegraded oil reservoir we found concomitant and directionally opposite changes with depth in the concentrations of certain 17 hopanes and their 17 25 norhopane counterparts demonstrating microbially induced demethylation of hopanes these observations suggest a hitherto unknown biodegradation mechanism and provide insight into the poorly understood process of natural petroleum biodegradation

novel cyclised and aromatised diagenetic products of β carotene in the green river shale abstract a suite of novel diagenetic products of carotene has been identified in an extract of a sample from the green river shale identification is mainly based on comparison of mass spectra with those of diagenetic products of another carotenoid isorenieratene these compounds were formed by i cyclisation and aromatisation of the polyene isoprenoid chain ii explusion of toluene and m xylene from the polyene isoprenoid chain and iii aromatisation of the 1 1 5 trimethylcyclohex 5 enyl moieties resulting in 1 2 dimethylbenzene end groups reduction of the double bonds of carotene is the most important diagenetic process however as judged from the high relative amount of carotane 63 of quantified diagenetic products of carotene these results indicate that the fossilisation potential of carotenoids is greater than previously thought

a forest fire and soil erosion event during the late devonian mass extinction abstract the late devonian mass extinction occurred in a stepwise manner and culminated close to the frasnian famennian f f boundary 372 million years ago organic molecular indices from marine sedimentary rocks at the sinsin section belgium indicate that the sequence of combustion of land vegetation soil erosion and anoxia euxinia occurred close to this boundary the increased concentrations of biomarkers indicating forest fire and soil erosion measured in the sinsin section suggest that fire became widespread at this time leading to various damaging consequences increased runoff and oceanic anoxia that caused marine extinctions magnetic susceptibility data in the sinsin section indicate a relatively dry climate spanning the f f boundary which would have encouraged forest fires the study of organic biomarkers presents several lines of evidence to link forest fire and soil erosion to the late devonian mass extinction

secular episodic changes in stable carbon isotope composition of crude oils abstract stable carbon isotopic compositions of c15 saturate and aromatic hydrocarbon fractions from 514 crude oils from known source rocks were examined for secular episodic variations the oils have been correlated by means of biomarker analyses and or geological inferences to their respective source rocks and were further categorized into seven source rock types based on geochemical and petrologic indicators of depositional environments thus these oil samples represent a wide range of source paleoenvironments from thirteen age divisions riphean to neogene the stable carbon isotopic compositions of both fractions become enriched in 13 c with decreasing geologic age three major abrupt shifts toward 13 c enrichment occurred at the precambrian cambrian ordovician triassic jurassic and paleogene neogene boundaries analysis of smaller scale isotopic shifts reveals four distinct groups of oils generally independent of organic facies and secondary alteration processes comparison of evolutionary changes in the biosphere to episodic changes in stable carbon isotopic compositions throughout the phanerozoic indicates that isotopic shifts of crude oils may generally be related to the diversity of preserved phytoplankton

migration of reaction and isotopic fronts in infiltration zones assessments of fluid flux in metamorphic terrains abstract criteria are presented for recognising fluid infiltration driven reactions in metamorphic rocks and quantifying the associated fractionations of oxygen and carbon isotopic compositions in medium or high grade metamorphic rocks with local equilibrium between fluid and solid phases reactions or isotopic changes driven by infiltrating fluid are expected to migrate as relatively sharp fronts with limited diffusive broadening fluid leaving such reaction fronts is compositionally buffered by the reacting phases in suitably reactive rocks a series of reaction fronts will develop each driven by infiltration of fluid buffered by the upstream reaction knowledge of the spatial arrangement of such fronts allows calculation of the time integrated fluid fluxes total fluid volume per unit area distinctive stable isotope fractionations are predicted adjacent to infiltration driven reactions with the distribution and magnitude of the fractionation effects dependent upon the relative velocities of the reaction and isotopic fronts the various possibilities are illustrated by reference to a hypothetical infiltration driven decarbonation reaction the calculated isotopic fractionations do not in general resemble those predicted by the open or closed system water rock ratio calculations

the ratios of dibenzothiophene to phenanthrene and pristane to phytane as indicators of depositional environment and lithology of petroleum source rocks abstract the ratio of dibenzothiophene to phenanthrene and the ratio of pristane to phytane when coupled together provide a novel and convenient way to infer crude oil source rock depositional environments and lithologies such knowledge can significantly assist in identifying the source formation s in a basin thereby providing valuable guidance for further exploration the ability to infer this information from analysis of a crude oil is especially valuable as frequently the earliest samples in a new area may be shows and or drill stem test samples from exploratory wells which are characteristically drilled on structural highs stratigraphically remote from the source formation s a cross plot of dibenzothiophene phenanthrene versus the pristane phytane ratios measured on seventy five crude oils from forty one known source rocks ranging in age from ordovician to miocene consistently classified the oils into the following environment lithology groups marine carbonate marine carbonate mixed and lacustrine sulfate rich lacustrine sulfate poor marine and lacustrine shale and fluvial deltaic carbonaceous shale and coal the dibenzothiophene phenanthrene ratio alone is an excellent indicator of source rock lithology with carbonates having ratios 1 and shales having ratios the dibenzothiophene to phenanthrene and the pristane to phytane ratios can also be used to classify source rock paleodepositional environments the classification scheme is based on the premise that these ratios reflect the different eh ph regimes resulting from the significant microbiological and chemical processes occurring during deposition and early diagenesis of sediments the dibenzothiophene phenanthrene ratio assesses the availability of reduced sulfur for incorporation into organic matter and the pristane phytane ratio assesses the redox conditions within the depositional environment interpretation of these ratios has been aided by quantitative biomarker analysis and by carbon isotope data for pristane and phytane obtained by gas chromatography isotope ratio mass spectrometry

polymetamorphism in medium to high grade pelitic metamorphic rocks west central maine a regional petrologic study of pelitic metamorphic rocks has been undertaken with emphasis on the area bounded by the cities of augusta lewiston norway rangeley kingfield and madison this report involves a regional isograd map interpretation of the nature of the various reactions and discussion of petrologic problems of polymetamorphism isograd distribution and widespread occurrence of muscovite in the k feldspar sillimanite zone a future contribution will deal more specifically with mineral chemistry geotherrnometry and geobarometry of much of the area after a low grade metamorphism m 1 the region suffered a higher grade early metamorphism m 2 which in many places produced andalusite and cordierite as well as staurolite this was followed by a somewhat higher pressure metamorphism m 3 involving staurolite chlorite and sillimanite in some areas m 3 has produced extensive retrograde effects with increasing grade in ms the major mineral reactions are 1 formation of staurolite from reaction of garnet chlorite and muscovite 2 formation of sillimanite from staurolite chlorite and muscovite 3 reaction of staurolite to form sillimanite biotite and in many rocks garnet and 4 formation of k feldspar from the partial reaction of muscovite quartz and plagioclase a possible fourth metamorphism m 4 produced narrow aureoles with andalusite and staurolite around the three latest plutons analysis of the isograd pattern demonstrates that the pressure was rather uniform throughout the area at a given time but increased about 0 5 kbar or more between m 2 and m 3 metamorphism the more regional distribution of isograds to the south is consistent with higher initial temperatures and more closely spaced magmatic heat sources but not necessarily with increasing pressure to the south the pressure increase between m 2 and m 3 might have been produced by intrusion of magma above the present level and or extrusion of rhyolitic volcanics

carboxylic acids as indicators of oil migration ii case of the mahakam delta indonesia the acid distributions of oils and coals from a wide depth range in the mahakam delta indonesia were studied in order to determine the effects of oil migration the crude oils of the mahakam delta indonesia are particularly well suited for such a study since the depth of the reservoir can be directly related to the migration distance of the oil two processes seem to control the changes in the acidic biomarker distributions during oil migration solubilization of immature organic matter during migration and to a much lesser extent geochromatography both processes are reflected differently in the acid distributions of the oils the solubilization process is most clearly reflected in variations taking place with increasing degree of migration increasing shift towards long chain acids with a higher even predominance and increase in cyclic acids typical of immature zones a geochromatographic effect may be seen in the depletion of short vs long chain acids with increasing vertical migration distance

paleoenvironmental implications of novel c30 steranes in precambrian to cenozoic age petroleum and bitumen petroleums and bitumens from early proterozoic 1800 ma to miocene 15 ma age marine strata contain 24 isopropylcholestanes a novel group of c30 steroids the abundance of these compounds relative to 24 n propylcholestanes varies with source rock age late proterozoic vendian and early cambrian oils and or bitumens from siberia the urals oman australia and india have a high ratio of 24 isopropylcholestanes to 24 n propylcholestanes 1 while younger and older samples have a lower ratio 0 4 temporal changes in this parameter may reflect the relative abundance of certain porifera sponges and certain marine algae through time geochemical indicators such as this which can constrain the source rock age of a migrated oil are useful in source rock identification during petroleum exploration

oil generation in the michigan basin a biological marker and carbon isotope approach abstract palaeozoic strata in the michigan basin produced crude oils which despite their rather small volume and economic value are interesting because of the considerable age of the basin and because of the opportunity to study generation and migration of oils within a relatively simple but ancient geological setting based on n alkane profiles biological marker distributions and carbon isotope ratios the oils belong to three main families of different genetic origin and a few less important mixed types silurian oils from salina and niagara limestones have broad n alkane distributions and abundant isoprenoid hydrocarbons a strong phytane over pristane predominance and the lack of diasteranes indicate a carbonate source for these oils chemical maturity parameters show that they are more mature than the oils from the other main families from which they are also clearly distinguished by carbon isotope ratios of hydrocarbon fractions and single n alkanes oils found in the calcareous ordovician trenton formation contain n alkane cyclohexylalkane and alkyl phenanthrene distributions typical of immature oils many oils from the devonian dundee reservoirs are very similar in overall composition to the trenton oils devonian traverse oils are considered to be mainly from a devonian source with some contribution of ordovician type oil and are of intermediate maturity based on calculations using kinetic parameters of biological marker reactions considerably deeper subsidence of the devonian source rock in the past is implied

multistage boron metasomatism in the alamo complex central iberian zone spain evidence from field relations petrography and 40ar 39ar tourmaline dating the alamo complex consists of structural metamorphic domes surrounded by low grade metasedimentary rocks of upper proterozoic to lower cambrian age that form part of the schist graywacke complex central iberian zone spain tourmaline is ubiquitous throughout the domes in which it occurs in tourmalinites psammo pelitic schists quartzites gneisses migmatites leucogranites aplo pegmatites and quartz veins overall tourmaline compositions can be described within the four component system schorl dravite foitite magnesiofoitite with k2o 0 23 low ca contents mg mg fe 0 25 0 71 and x x na 0 18 0 43 where x vacancies in the x site field relations and petrographic observations combined with tourmaline 40ar 39ar data provide evidence of intense boron metasomatism affecting this region tourmaline 40ar 39ar step heating spectra for cambrian ordovician orthogneisses are complex yielding a pseudo plateau age of 370 ma that is interpreted to reflect variscan rejuvenation of older tourmaline tourmaline 40ar 39ar data for mylonitized and folded tourmalinites yield disturbed spectra with pseudo plateau ages of 355 342 ma that are unsuitable for precise age determination these ages however are consistent with published ages 340 350 ma for the second variscan deformation d2 tourmaline from fine layered tourmalinite and metasedimentary rocks yield well defined plateau ages of 317 and 315 ma respectively recording an additional metasomatic event concomitant with anatexis and evolution of b bearing granites pegmatites and hydrothermal fluids the different tourmaline forming stages reflect significant boron cycling within the continental crust of the central iberian zone driven by deformation metamorphism and magmatism during the variscan orogeny boron rich aqueous fluids related to cambro ordovician magmatism are considered to be the primary source of boron

evolution of compositional polarity and zoning in tourmaline during prograde metamorphism of sedimentary rocks in the swiss central alps the compositional evolution of tourmaline from diagenetic to lower amphibolite facies conditions was investigated in two metasedimentary units redbed and black shale formations along a traverse across the central alps with increasing metamorphism three distinct rim zones grew around detrital tourmaline cores simultaneously with the development of prismatic neoblasts detrital cores and all successive rim zones are preserved in the amphibolite facies rocks as indicated by whole rock data the b required for tourmaline growth was released from illite and muscovite and was not introduced from external sources the studied samples of tourmaline exhibit compositional polarity i e their compositions are different at the opposite ends of the c axis the compositional difference between the two poles can be expressed by the substitutions na mg 0 al and 2al ti mg with the positive pole always richer in al and having more x site vacancies both chemical and optical polar effects are most pronounced in the internal rim zones and become less prominent toward the external zones the systematic prograde compositional trends are depicted in a vector space for li poor tourmaline at low grade conditions the tourmaline composition is clearly controlled by the host rock composition but with increasing metamorphic grade the compositions of tourmaline from a variety of rocks converge the data show that in the central alps increasing metamorphic grade is reflected by increases in ca ca na and mg mg feh a decrease in fe3 and an increase in the occupancy of the x site of tourmaline

trimethylnaphthalenes in crude oils and sediments effects of source and maturity abstract three sedimentary sequences and a number of crude oils have been analysed for trimethylnaphthalenes tmns using gas chromatography the sediments were found to contain enhanced relative abundances of 1 2 5 tmn and 1 2 7 tmn in samples of cretaceous age and younger this was especially pronounced in lower maturity sediments containing type iii organic matter older samples containing type iii organic matter were found to contain enhanced relative abundances of 1 2 5 tmn and lower relative abundances of 1 2 7 tmn 1 2 7 tmn appears to be derived directly from the structural degradation of oleanane type triterpenoids present in angiosperms and as such is proposed as a marker for this class of plant and indirectly therefore also for samples deposited since the early cretaceous the crude oils have been classified according to their trimethylnaphthalene compositions this classification enables crudes of higher plant origin to be identified and to be further classified according to whether the organic matter pre dated or post dated the evolution of angiosperms

organic geochemistry of the woodford shale southeastern oklahoma how variable can shales be woodford shale samples obtained from a cored outcrop in southeastern oklahoma were geochemically analyzed to determine vertical variations of organic facies thermal maturity and an evaluation of their depositional environments total organic carbon values ranged from 5 01 to 14 81 indicating a good source rock potential in this area the woodford shale is marginally mature as indicated by vitrinite reflectance values rock eval data revealed that the samples are dominated by type ii kerogen biomarker ratios based on pristane phytane steranes and hopanes show a mix of marine and terrigenous organic matter high salinity conditions and water density stratification also prevailed during deposition of this formation as indicated by the presence of gammacerane the woodford shale was subdivided into lower middle and upper members based on the integration of geochemical and geologic data moreover the presence and extent of photic zone anoxia pza were determined by the presence of aryl isoprenoids the lower and upper woodford shale members were deposited under dysoxic to suboxic conditions and episodic periods of pza the middle member was deposited under anoxic conditions and persistent pza in addition aryl isoprenoids helped infer the position of the chemocline during deposition of the different members the relative hydrocarbon potential parameter was used in determining transgressive and regressive cycles within the woodford shale this study undoubtedly demonstrates the significant lithologic and chemical variability that occurs within shales the application of this workflow to regional studies can have a direct influence on exploration and production activities in shale gas systems

17 21 secohopanoic acids 25 norhopanoic acids and 28 norhopanoic acids in source rocks and crude oils the presence of three families of hopanoic acids 17 21 secohopanoic acids 25 norhopanoic acids and 28 norhopanoic acids is discussed oils from west siberia and tar balls from the seychelles islands were found to contain relatively high proportions of 17 21 secohopanoic acids these acids have not been previously reported in any oils or source rocks a heavily biodegraded west siberian oil was found to contain an homologous series of 25 norhopanoic acids co occurring with the 25 norhopanes as previously reported in only a small number of oils from campos basin brazil 28 norhopanoic acids have been reported in various sediments and extracts of the monterey shale but in this study their occurrence has been extended to oils degraded oils and tar balls sourced from the monterey shale the primary purpose herein is to report the occurrence of these acids and possible relationships between the acids and corresponding hydrocarbons

oil families and inferred source rocks of the woodford mississippian tight oil play in northcentral oklahoma twenty four oils produced from the woodford shale and overlying mississippian strata in central oklahoma were characterized geochemically to determine their possible source s the 168 core samples from the woodford and mississippian sections of 14 wells in central oklahoma were initially characterized by total organic carbon toc rock eval and vitrinite reflectance and select samples toc 1 0 wt were subjected to biomarker analyses to characterize source input depositional environment maturity and oil to source rock correlations thermal maturity parameters indicate the woodford shale is immature to marginally mature in payne county oklahoma and shows a progressive increase in maturity toward the southwest close to the nemaha uplift the woodford is in the main stage of oil generation it is proposed that the oils in this area have three possible origins 1 oils produced from the woodford and overlying mississippian strata have similar fingerprints suggesting the woodford shale and overlying mississippian strata are in communication 2 oils produced near the nemaha uplift logan and western payne counties were sourced from the woodford but had a significant mississippian source contribution based on source specific biomarkers 3 oils east of the cherokee platform eastcentral payne county share strong woodford source characteristics and they were not generated in situ from the immature woodford shale but probably migrated from the woodford shale in the deeper part of the anadarko basin in southern oklahoma these results are consistent with the findings that indicate abundant marine coarse grained biogenic silica radiolarian rich chert facies found in eastcentral payne county may contribute to good reservoir petrophysical properties suggesting the woodford shale may not be a source in this area but simply a tight reservoir

tourmaline bearing rocks in the singhbhum shear zone eastern india evidence of boron infiltration during regional metamorphism frozen in reaction textures combined with mineral chemistry of tourmaline bearing metamorphic assemblages provide valuable information about fluid rock interaction during orogenesis tourmaline occurs in four distinct mineralogical associations in the singhbhum shear zone ssz of the precambrian east indian craton the tourmaline bearing rocks are associated intimately with pelitic to psammopelitic and quartzofeldspasthic rocks including meta granite the rocks were affected by two sets of folding f1 and f2 and ductile shearing associated with f1 during ca 1 6 1 8 ga tectonic activity in this belt quantitative geothermobarometry and the stability relations of the metamorphic assemblages developed in the pelitic rocks establish the presence of two episodes of metamorphism a prograde m1 event that culminated at 480 40 c 6 4 0 4 kbar and an m2 event that caused retrogression of the m1 assemblages field and petrographic observations in combination with data on chemical composition of tourmaline indicate three stages of tourmaline growth the earliest stage is represented by pretectonic pre metamorphic greenish yellow tourmaline cores in the tourmalinite from the surda area association a the textural relations demonstrate that in the second stage greenish yellow cores of oscillatory zoned tourmaline in the metagranite albite quartz biotite chlorite muscovite apatite magnetite association c very fine tourmaline grains in muscovite schist muscovite quartz association b and greenish yellow cores of tourmaline in biotite muscovite schist biotite muscovite magnetite chlorite apatite quartz association d crystallized during the f1 m1 events post tectonic greenish blue tourmaline belonging to the third stage replaces the earlier tourmaline grains along their margins and cracks compositionally tourmalines of all four associations fall in the alkali group most of the data fall in the dravite field with a few analyses straddling the boundary between schorl and dravite an abrupt compositional change was noted across the different color zones in the tourmaline grains this change is explained by one or more of the coupled substitutions al nar 1 car naal 1 and mg fe 1 where r mg fe2 mn integrating the field petrographic and phase compositional data it has been demonstrated that tourmaline growth in the second and third stages was induced by infiltration driven b metasomatism during prograde metamorphism of the rocks deep seated magma was the source of the b bearing hydrothermal fluid

geochemical study of potential source rocks and crude oils in the anadarko basin oklahoma paleozoic source rocks and crude oils from the anadarko basin oklahoma have been characterized by means of a variety of organic geochemical techniques the potential source rocks investigated include the viola group sylvan shale lower mississippian limestone chester group springer formation and morrow group the woodford shale which is an important source rock in the basin and has been discussed extensively in the literature was used as a laboratory standard in this study the crude oils examined in this study were obtained from reservoir formations of various ages from throughout the basin the source rock screening analysis indicates that the lower and middle subfacies of the viola especially from the southeastern part of the basin have substantial oil generation potential the sylvan is not a source rock although the black shales in the springer and morrow have substantial oil and especially gas generation potential the results of this study support the proposal for multiple sources of oil and gas generation in the anadarko basin selected source rock and oil samples were characterized in more detail and the distributions and concentrations both relative and absolute concentrations of biomarkers in different source rocks and oils were determined the biomarker characteristics were combined with other geochemical and geological data to interpret the sources depositional environments diagenesis and catagenesis processes migration and weathering oil source rock correlations were made between source rocks and a number of crude oils based on quantitative and qualitative biomarker distributions petrographic descriptions and graptolite reflectance measurements were used to evaluate copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received november 1 1995 revised manuscript received april 8 1996 final acceptance september 13 1996 2arco international oil and gas company 2300 w plano parkway plano texas 75057 3school of geology and geophysics university of oklahoma norman oklahoma 73019

diamondoid hydrocarbon ratios as indicators of biodegradation in australian crude oils the effect of biodegradation on diamondoid distributions in petroleum has been investigated on a series of crude oils reservoired in two australian sedimentary basins the gippsland basin and the carnarvon basin the ratio of methyladamantanes to adamantane rises with increasing biodegradation significant changes in the ratio occur at extreme levels indicating that diamondoids can be indicators of petroleum biodegradation especially when most other hydrocarbons have been removed the methyladamantane adamantane ratio can also be used to assess the composition of crude oils that are comprised of a mixture of severely biodegraded and non biodegraded oil