u th ages obtained by mass spectrometry in corals from barbados sea level during the past 130 000 years the study of the sea level record during the last glacial cycle has primarily proceeded indirectly by means of oxygen isotope measurements on foraminifera from deep sea sediments1 2 the direct approach of dating sea level indicators stagnated during the past decade mainly because the samples required to complete our knowledge of the past glaciations are below the present day sea level3 7 using the 14c ages of acropora palmata samples collected by drilling offshore the island of barbados fairbanks8 presented the first detailed chronology for the last deglaciation this radiocarbon chronology is limited to the past 30 kyr because of the short half life of 14c 5 730 yr we must therefore rely on other dating methods to obtain information for the whole last glacial cycle during the past four years 230th 234u dating of corals by thermal ionization mass spectrometry has been shown to be significantly more precise and accurate than the classical counting method9 14 we have used this technique to measure u th ages in coral samples from the barbados collection and from subaerially exposed outcrops see also ref 15 here we present results bearing on the sea level record for the past 130 000 years we conclude that the last deglaciation started 3 000 years earlier than previously thought and confirm that there were two surges in melt water8 at about 11 kyr and 14 kyr bp before present

carbon isotope systematics of archean au ag vein deposits in the superior province abundant carbonate is a characteristic feature of most archean mesothermal au ag vein deposits but the source of the c is controversial for superior province deposits collectively the maximum variation of average 13c values is from 9 0 0 7 1 n 19 darius to 0 6 1 6 1 n 7 cochenour willians and limiting 13c values are 13 6 and 1 3 at the deposit scale fe dolomites in nongraphitic lithologies are for the most part isotopically uniform where 13c 3 4 0 4 1 hollinger 3 2 0 3 mcintyre 4 7 1 7 dome 2 8 0 6 buffalo ankerite 3 6 0 5 macassa 3 2 0 3 bousquet 5 4 0 9 lamaque and 5 3 0 5 hasaga the restricted individual ranges of 13c values imply a corresponding uniformity to the ambient temperature and 13c c of the ore forming fluids within individual deposits small systematic variations of 13c carbonate arise from i interaction of hydrothermal fluids with carbonaceous rocks ii immiscible separation of co2 ch4 or iii

botryococcus a planktonic green alga the source of petroleum through the ages transmission electron microscopical studies of oil shales and petroleum source rocks abstract the hydrocarbon secreting alga botryococcus has been identified in organic remains of sediments ranging from precambrian to recent and is believed to have been a major source material for petroleum generation throughout the geological time in some petroleum source rocks of lower palaeozoic and precambrian age identification of the alga is only possible by electron microscopy transmission electron microscopy tem has been used in the present study to identify microstructures of the algal remains in a range of oil shales and petroleum source rocks it has been established that botryococcus is the predominant alga in the kukersite oil shale of estonia similarly the alga has been shown to be a major contributor to petroleum source rocks in cambrian and precambrian sedimentary basins in australia tem has been applied to observations of botryococcus in torbanites and to products from simulated maturation experiments on torbanite a comparison with algal remains from cambrian and precambrian sediments ranging from undermature to overmature enabled the distinction of organic matter in various stages of oil generation maturation thermal effects on alginite have been established by reflectance and fluorescence and compared with experimental results

are time and temperature the only constraints to the simulation of organic matter maturation abstract confined pyrolysis hydrous pyrolysis and high pressure hydrous pyrolysis were performed with various samples toarcian shale and kerogen woodford shale and kerogen manakam coal and under different experimental conditions in order to test the effects of pyrolysis variables on the simulation of maturation of organic matter results show that i experimental time and temperature are not exchangeable parameters as suggested by first order kinetic law models ii increasing confining pressure 300 1300 bars in gold cell experiments performed on woodford samples has a limited influence on the reduction rate of the oil potential the tsom total soluble organic matter yield and the structure of the polars iii the presence of excess liquid water 0 100 weight in confined pyrolysis experiments does not significantly influence organic matter maturation however comparisons with classic hydrous pyrolysis 200 weight water could indicate major differences in timing and composition of the tsom bitumen expelled fraction as well as of the solid residue it appears that excess water is not necessary to simulate organic matter maturation when the system is sufficiently confined hydrous pyrolysis conditions low partial pressure of products delay woodford kerogen conversion in addition results concerning the mahakam coal suggest that the structure of the organic matter plays an important role concerning the water effect iv increasing water pressure in hydrous conditions 220 1300 bars drastically lowers and delays woodford kerogen maturation quantitative analysis of the water produced during confined pyrolysis and comparison of the extent of aromatization in hydrous and confined pyrolysis suggests that two competing hydrogen transfer mechanisms occur during organic matter pyrolysis this study shows that additional parameters must be defined when comparing the results of the experimental simulation of organic matter maturation

generation of gas and oil from coal and other terrestrial organic matter abstract late carboniferous permian sedimentary rocks contain the world s largest coal reserves which have generated and released gas but little if any oil in comparison organic matter deposited in lacustrine fluvial deltaic or brackish water sediments has sourced large quantities of waxy oils in countries such as china australia the u s a argentina venezuela and indonesia plus gas and condensate in deltas worldwide why is more oil coming from land derived organic matter disseminated in sediments than from the carboniferous permian coal beds which also are land deposits the answer appears to be in the hydrogen content and the ease of migration when organic matter and coals have high hydrogen contents relative to carbon they can form oil when the hydrogen is low mainly gas is formed most of the world s coal is low in hydrogen whereas much of the terrestrial organic matter disseminated in sediments is higher in hydrogen so it forms more oil also both gas and oil are adsorbed on coal more strongly than on the disseminated kerogen of sedimentary rocks this makes migration of oil out of the coal more difficult compared to migration from conventional shale source rocks

carbon dioxide generation from coals in taranaki basin new zealand implications for petroleum migration in southeast asian tertiary basins elevated co2 levels in gas accumulations within the onshore area of the taranaki basin can be quantitatively accounted for by decarboxylation of vitrinite rich tertiary coals over the lignite to early high volatile bituminous coal rank range the highest levels are found within sandstone reservoirs vertically adjacent to eocene coal seams that have realized approximately 50 of their co2 generative potential the gas exists as a supercritical fluid under reservoir conditions and appears to be generated in significant amounts comparable to liquid hydrocarbons co2 may aid oil expulsion from coals directly when intense co2 generation coincides with major oil generation or indirectly by creating pressure induced microfractures du ing the relatively rapid generation of large amounts of co2 prior to the main phase of oil generation for these effects to be realized the rate of co2 production relative to removal is considered critical and favorable conditions are probably restricted to basins that have experienced relatively rapid heating in this respect the taranaki basin provides a model for co2 evolution in many southeast asian tertiary basins

crustal outgassing and lile enrichment in major lithosphere structures archean abitibi greenstone belt evidence on the source reservoir from strontium and carbon isotope tracers major structural discontinuities in the abitibi greenstone belt acted as conduits for outgassing of the archean crust as reflected in fixation of a select group of lithophile elements including si c k rb ba li cs b and pb in metasomatized faults for two of the largest structures the destor porcupine dp and kirkland lake cadillac kc fault zones 6 1015 g si 3 1015 g co2 and 1015 g k were introduced into the faults during expulsion of an estimated 6 1018 g aqueous fluids strontium isotope ratios of tourmaline piemontite actinolite and scheelite mineral separates characterized by rb sr 0 02 are concordant with respect to 87sr 86sr initial ratios over local sectors of the faults the sr isotope data record geographic variations which from east to west on the kc fault is 0 7031 0 7041 val d or 0 7008 0 7022 bourlemaque 0 7017 0 7019 bousquet 0 7029 0 7031 noranda and 0 7013 to 0 7015 kirkland lake at timmins on the pd fault 87sr 86sr initial ratios cluster at 0 7010 to 0 7020 metasomatised fault zones are systematically more radiogenic than contiguous host lithologies and imply a source reservoir 0 7010 to 0 7041 generally more radiogenic than the upper mantle at 2690 ma 0 700 0 001 or contemporaneous volcanic rocks of mafic to ultramafic composition 0 700 to 0 7012 whereas certain minerals are concordant and retentive rb sr isochrons based on suites of rocks at progressive intensities of metasomatism have been systematically reset over an elpased time of 200 ma after termination of outgassing due to disturbance accompanying incremental displacements on structures

simulated thermal maturation of type i and iii kerogens in the presence and absence of calcite and montmorillonite abstract the effects of a mineral matrix on hydrocarbon generation from different types of kerogen were examined simulated thermal maturation of type i iii a and iii b kerogens alone and mixed with minerals was investigated using anhydrous pyrolysis both calcite and montmorillonite modified the products of simulated thermal maturation of the kerogens montmorillonite slightly reduced and calcite slightly enhanced the formation of oil like products from the coals type iii a and iii b kerogens at higher levels of maturation however the catalytic effect of calcite resulted in cracking of the pyrolysates for retention of the pyrolysis products of type i kerogen montmorillonite proved to be a very active matrix whereas the products were less affected by calcite the amount of soluble bitumen extracted from heated type i kerogen was higher in the presence of minerals than in their absence on the contrary the amount of soluble bitumen obtained from heated type iii a kerogen was smaller in the presence of minerals in the case of type iii b kerogens this effect of minerals changed as a function of the temperature of simulated thermal maturation

high temperature hydration of ultramafic granulites from the southern marginal zone of the limpopo belt by infiltration of co2 rich fluid abstract the peak metamorphic assemblage of olivine orthopyroxene calcic amphibole spinel is replaced by a variety of high temperature retrograde assemblages in ultramafic granulites from the southern marginal zone of the limpopo belt the observed replacement of olivine according to the reaction forsterite co2 enstatite magnesite is restricted to the zone of rehydration which bounds the granulite zone in the south this observation is consistent with the post peak metamorphic infiltration of an externally derived co2 rich fluid during the high temperature post peak metamorphic history of the limpopo belt this event established a retrograde orthoamphibole isograd conditions of the retrogression are estimated to be near 670 c 6 kbar and xco2 fluid 0 67 c isotopic compositions of co2 extracted from magnesite produced by the high temperature breakdown of olivine supports a deep seated mantle source for the co2 rich retrograde fluid

kinetic models of vitrinite kerogen and bitumen reflectance abstract vitrinite reflectance is perhaps the most widely used property to calibrate paleothermal histories and the most common model for that purpose is easy ro this paper reviews the origin of easy ro as a simplification of vitrimat weaknesses of the original versions are discussed as are historical attempts to improve them new versions of vitrimat and easy ro are presented that use substantially higher frequency factors and activation energies and variations of these versions are derived for vitrinite itself and hydrogen rich macerals and bitumen the vitrimat models are based on the original premise that reflectance correlates primarily with h c ratio and secondarily with o c ratio with this approach the reflectance of different types of organic matter is automatically calculated based on the initial composition of that organic matter this general approach may also serve as a pathway with appropriate cross reaction terms to calculate suppression of true vitrinite reflectance matured in oil prone rocks containing significant concentrations of liptinite

molecular isotopic characterisation of hydrocarbon biomarkers in palaeocene eocene evaporitic lacustrine source rocks from the jianghan basin china immature organic matter in lacustrine source rocks from the jianghan basin eastern china was studied for distributions and stable carbon isotopic compositions 13 c of hydrocarbon biomarkers all of the bitumens contain isorenieratane 13 c ca 17 indicating the presence of chlorobiaceae and thus periods of euxinic conditions extended into the photic zone aliphatic hydrocarbon fractions are dominated by pristane and phytane and contain relatively low amounts of 4a and 4 methylsteranes c 30 13 c ca 16 believed to originate from 4 methylsterols in dinoflagellates 13 c values of gammacerane ca 24 and c 30 17 21 h hopane ca 23 are consistent with an origin from bacterivorous ciliates that fed on chlorobiaceae the bitumens contain low relative amounts of organo sulphur compounds one rock contains c 37 and c 38 n alkanes 13 c ca 36 derived from alkadienes and alkenones of prymnesiophytes the distributions of hydrocarbon biomarkers suggest that they were initially sulphurised during early diagenesis and later released during early thermal maturation

lower palaeozoic and precambrian petroleum source rocks and the coalification path of alginite organic rich samples derived from a middle cambrian formation in the georgina basin and from the middle proterozoic of the mcarthur basin in northern and central australia yielded alginite ranging from immature oil shale material to overmature residue a maturation scale has been developed based on the thermal evolution of alginite as determined from reflectance and fluorescence the coalification path of alginite is marked by jumps in contrast to the linear path of wood derived vitrinite six zones have been recognised ranging from undermature zone i through the mature zones ii iii followed by a stable stage of no change zone iv to the overmature zones v and vi the onset of oil generation in alginite as evident from the present study is at 0 3 ro alg and is expressed in a change of fluorescence from yellow to brown and a coalification jump from 0 3 to 0 6 ro of alg in many boreholes zone iii can be distinguished between 0 6 and 0 8 ro of alg where subsequent oil generation occurs zones ii and iii represent the oil window a zone of little or no change designated zone iv at 0 91 0 ro of alginite follows zones ii iii a marked coalification jump characterises zone v where a pronounced change in reflectance occurs to 1 0 ro alg signifying peak gas generation the border of oil preservation lies at the transition of zone v and vi at 1 6 ro alg in zone vi gas generation only occurs comparison of reflectance results with experimental and geochemical pyrolysis data supports high activation energies for hydrocarbon generation from alginite and therefore a later onset of oil generation than other liptinite macerals i e cutinite exinite resinite as well as a narrow oil window transmission electron microscopy tem confirms that alginite does not go through a distinct intermediate stage but that the percentage of unreacted organic matter decreases as maturation proceeds a clear distinction can be made in tem between immature alginite alginite after oil generation and alginite residue following gas generation alginite beyond 1 6 ro acquires very high densities and the appearance of inertinite in tem bitumens pyrobitumens make a pronounced contribution to the organic matter throughout the basins and have been shown to effect pyrolysis results by suppressing tmax the bitumens pyrobitumens have been divided into four groups based on their reflectance and morphology which in turn appears to be an expression of their genetic history their significance is in aiding the understanding of the basins thermal history and the timing of oil and gas generation

carbon isotope compositions of fluid inclusions in charnockites from southern india models for the formation of crustal granulites which include the metamorphism of anhydrous lithologies1 2 the extraction of hygroscopic granite melts3 4 and fluxing by co25 7 constrain the thermal and geochemical evolution of the lower crust and its interaction with mantle derived volatiles here we present abundances and carbon isotope compositions of co2 in fluid inclusions in quartz and garnet from gneiss granulite pairs from the incipient char nockite quarries of southern india determined by a stepped combustion thermal decrepitation carbon extraction technique which quantifies problematic sample contamination and allows precise lithological control the results show that the co2 in incipient charnockite is more abundant and isotopically heavier than the co2 in associated gneiss providing evidence for the influx of co2 rich fluids during their formation the inferred carbon isotope compositions of these fluids are consistent with a mantle source and at ponmudi the isotopic composition of coexisting graphite and co2 implies fluid rock volume ratios in excess of 0 15

geochemistry of precambrian carbonates i archean hydrothermal systems abstract carbonate rocks from the superior and slave provinces of canada kaapvaal craton of south africa and the pilbara block of australia considered of hydrothermal origin from field criteria have been characterized mineralogically isotopically sr o c and chemically major and trace elements in agreement with previous studies the bulk chemical composition suggests that the carbonate rocks originated by massive carbonatization silicification and k na metasomatism of intermediate to ultramafic silicate precursors the carbonate component itself defines two partially overlapping populations the ferroan dolomite breunnerite assemblage is confined mostly to shear zones conduits and stockworks while the calcite ferroan dolomite ankerite siderite mineral assemblage represents a wider regional halo this dichotomy may result from a multistory not necessarily coeval plumbing system of the volcanosedimentary piles with the regional halo population being a product of shallow circulation cells while the conduit assemblage probably formed from deeper focussed flows trace element chemistry of carbonates is consistent with their precipitation from relatively low salinity solutions 2 sea water and with derivation of solutes from the contemporaneous volcanosedimentary piles 87 sr 86 sr 0 7020 0 0008 the hydrothermal waters were derived either from metamorphic dewatering at the base of the piles or from a magmatic source with 18o of about 6 7 smow in contrast carbon dioxide in the regional and the conduit assemblages had dissimilar principal sources in the former it was derived from exogenic sources decarbonation of marine carbonates and thermal decomposition and oxidation of organic matter while in the latter the co2 was of mantle origin 13c of 2 to 10 and 4 2 pdb respectively

carbon and hydrogen stable isotope variations in kerogen during laboratory simulated thermal maturation carbon and hydrogen stable isotope measurements on sapropelic and humic kerogen isolated from laboratory heated sediments reveal several isotopic trends an initial depletion of 13c and d 2h or deuterium in kerogen isolated from the heated sapropelic sediment appears to be the result of isotopic heterogeneity interaction with soluble organic matter and or volatilization of a heat labile fraction of the protokerogen during the main isotopic trend the sapropelic kerogen becomes enriched in 13c and d by about 5 and 50 ppt parts per thousand respectively theoretical calculations based on a rayleigh fractionation process suggest that this trend is largely controlled by the generation of isotopically light methane directly from the ker gen this argument also applies to the main hydrogen isotopic trend for the humic kerogen which becomes enriched in d by about 90 ppt the main 13c trend for the humic kerogen however results in a maximum enrichment in 13c of only about 1 6 ppt and appears to be largely controlled by factors other than methane a final depletion trend in 13c and d occurs for the sapropelic kerogen at very high temperatures this may be due to a reduced isotopic fractionation at higher temperatures or to the indirect generation of methane from kerogen through a liquid intermediate which is subsequently coked to pyrobitumen

differentiation of late archean crust in the eastern dharwar craton krishnagiri salem area south india the late archean crust south of krishnagiri tamil nadu consists of tonalitic trondhjemitic granodioritic ttg gneisses with mafic and sedimentary enclaves formed between 2 7 and 2 5 ga and metamorphosed at amphibolite facies in the north to granulite facies in the south close to 2 5 ga migmatization occurred at all grades and numerous small granite bodies were emplaced near the amphibolite to granulite facies horizon this nearly syn accretion meta morphism affected the entire crust and left a chemically differentiated section later exposed by uplift and erosion detailed chemical and petrographic study of 60 samples across a 90 km traverse provides evidence for an essentially unbroken crustal cross section paleopressures range from 4 kbar corresponding to 12 14 km paleodepth in the north to 8 kbar corresponding to 24 28 km paleodepth to the south corresponding paleotemperatures vary between 650 and 800 c across the section mineralogic grade monitors particularly increasing tio 2 con

in situ and laboratory investigation of the alteration of boom clay oligocene at the air geological barrier interface within the mol underground facility belgium consequences on kerogen and bitumen compositions abstract the boom clay formation oligocene is studied as a reference host rock for methodological studies on deep geological disposal of radioactive waste during excavation of galleries within the clay formation hades underground research facility mol belgium the physico chemical conditions are significantly modified as an air clay interface is created in order to study the long term impact of the air clay contact on the organic matter contained in the boom clay two types of samples were studied 1 a reference series of clay samples having been in contact with the atmosphere of the hades gallery for increasing times up to several years and 2 unaltered clay samples submitted to artificial oxidation in a ventilated oven at 80 c the evolution of geochemical data of the two series was compared using rock eval pyrolysis gc ms and size exclusion chromatography the organic matter of the unaltered clays sampled in the hades galleries is dominated by type iii kerogen terrestrial with some contribution of type ii marine and is thermally immature the evolution of geochemical parameters during air alteration for the two series are very similar they show progressive oxidation of kerogen accompanied by the release of bitumen enriched in low molecular weight constituents molecular analysis evidences the presence of a complex mixture of aliphatic and aromatic o bearing compounds inherited from the degradation of kerogen as well as from the clay catalyzed oxidation of the bitumen these results show that 1 air oxidation is a major process in the in situ alteration of the organic matter of boom clay within the hades galleries 2 laboratory oxidation experiments at 80 c yield similar results as in situ air alteration of boom clay and 3 artificial air oxidation may be used to assess the long term exposure of the organic matter to air

evidence and effects of fluid circulation on organic matter in intramontane coalfields massif central france abstract recent evidence for a late carboniferous hydrothermal event responsible for au as mineralization within the variscan belt of the french massif central adds a supplementary episode to the already rather complex thermal history of this area to better understand this history 45 coal samples from various sites in the massif central were studied petrographically reflectance analysis and geochemically rock eval pyrolysis the results of this study suggest that the studied coal was buried to 1500 m and that the coalification took place within 25 ma probably ending at the boundary between the early and late permian marked by the saalic orogeny two thermal end members basins were identified i the carboniferous of bosmoreau les mines limousin and west graissessac montagne noire showing geothermal paleoflow values between 150 and 180 mw m 2 and ii the stephanian of argentat and detroit de rodez sw massif central with values estimated at between 100 and 120 mw m 2 by plotting the t max and r o values on a diagram the samples were grouped into two populations the first showing a positive correlation between r o and t max and the second with higher t max values than expected after r o values selected samples of the second group are also characterized by a high oxygen index oi that increases with t max these divergence between r o and t max associated with a high oi may be the result of the circulation of slightly oxidizing hot fluids subsequent to coalification the other kind of r o t max divergence seems to be linked to local particularly high thermal activity especially in graissessac and bosmoreau basins it is interpreted as being due to a difference in response of these two maturity indicators respectively to the intensity and duration of the thermal events e g short lived hydrothermal circulation and thermal domes of regional extent

simulated petroleum generation studies by hydrous pyrolysis of a tertiary coal from northern cambay basin in india in the northern cambay basin ahmedabad mehsana block abundant coal seams occur at depths of 1000 1700 m the role such coals can play in hydrocarbon hc generation has not been determined hydrocarbon generation from a core sample with a hydrogen index hi 268 mg hc g total organic carbon toc oxygen index oi 19 mg co2 g toc and vitrinite reflectance in oil vro 0 38 has been simulated by hydrous pyrolysis at a temperature of 325 c for 2 10 50 and 100 h it has been observed that generation is in accordance with the model kerogen asphaltenes hydrocarbons the peak oil generation stage is reached at 0 89 vro the peak oil expulsion stage occurs at 0 91 vro although hydrocarbons are generated from 0 75 vro onwards the results indicate that these coals have not contributed towards hydrocarbon reserves of northern cambay basin

genetic aspects of gold mineralization in the southern granulite terrain india abstract gold mineralization in southern granulite terrain sgt of india has close spatial relationship with the shear zones moyar bhavani present in cauvery suture zone gold is found to be associated with primary quartz veins placers and laterites the gold prospects in sgt can be broadly grouped into three provinces i wynad nilgiri ii malappuram and iii attappadi the auriferous quartz veins are within the deformed biotite hornblende bearing gneisses and amphibolite wall rock alteration is conspicuous around the mineralized veins and gives an assemblage of muscovite calcite ankerite chlorite biotite pyrite related to fluid rock interaction at the time of vein formation fluid inclusion studies of vein quartz gives an idea of the nature of the ore forming fluids the fluid involved in gold mineralization is of low saline and aqueous carbonic in composition and quite similar to the orogenic lode gold deposits reported world wide micro thermometric data indicates fluid immiscibility phase separation during trapping of fluid inclusions and this must have played an important role in gold deposition geochronological studies of mineral separates from wynad nilgiri province using rb sr and sm nd isochron methods of the auriferous quartz veins gave an age of approximately 450 ma for the vein formation the present studies on sgt gold mineralization indicate 1 during the pan african orogeny extensive fluid influx from mantle and metamorphism extracted gold from a mafic source and were focused along major structural discontinuities of moyar bhavani shear zone 2 the aqueous carbonic ore fluid interacted with rocks of the upper crust and triggered a set of metasomatic changes responsible for the dissolved components such as ca si and fe and finally precipitating in the veins and 3 the mineralizing fluid with dissolved gold in sulphide complex got destabilized due to fluid immiscibility and wall rock alteration leading to the deposition of gold with associated sulphide minerals in the vein system

coal as a source rock for oil a review the geological debate about whether and to what extent humic coals have sourced oil is likely to continue for some time despite some important advances in our knowledge of the processes involved it is clear that not only liptinites but also perhydrous vitrinites have the potential to generate hydrocarbon liquids in the course of natural coalification some liptinites especially alginite cutinite and suberinite contain a higher proportion of aliphatic moieties in their structure than other liptinites such as sporinite and resinite and are therefore more oil prone it is of potential value to be able to predict the several environments of deposition in which coals with high liptinite contents or containing perhydrous vitrinites may have been formed review of the distribution of oil prone coals in time and space reveals that most are jurassic tertiary with key examples from australia new zealand and indonesia methods based both on experimental simulations and the examination of naturally matured samples have been used to determine the order of generation of hydrocarbons from different macerals results are not entirely consistent among the different approaches and there is much overlap in the ranges of degradation but it seems probable that in the natural environment vitrinites begin to generate early followed by labile liptinites such as suberinite then cutinite sporinite and finally alginite petroleum potential may be determined by experimental simulation of natural coalification or inferred through various micro techniques especially fluorescence and infrared ir spectroscopy or bulk techniques such as elemental analysis and 13c nmr spectroscopy the latter three techniques enable a measure of the polymethylene component of the coal which now appears to be one of the best available approaches for determining petroleum potential no method of experimental simulation of petroleum generation from coals is without criticism and comparative results are highly variable however hydrous pyrolysis confined pyrolysis and forms of open system hydrous pyrolysis approach acceptable simulations whether and to what degree generated liquid hydrocarbons are expelled has long been the central problem in oil from coal studies the structure of vitrinite was believed until recently to contain an interconnected microporous network in which generated oil would be contained until an expulsion threshold was attained recent studies show the pores are not interconnected combined with a dynamic model of pore generation it now seems that expulsion of hydrocarbons is best explained by activated diffusion of molecules to maceral boundaries and ultimately by cleats and fractures to coal seam boundaries the main reason for poor expulsion is the adsorption of oil on the organic macromolecule which may be overcome 1 if coals are thin and interbedded with clastic sediments or 2 if the coals are very hydrogen rich and generate large quantities of oil the existence of oil in vitrinite is attested to by solvent extractions fluorescence properties and by microscopic observations of oil and bitumen experimental simulation of expulsion of oil from coals has only recently been attempted the relative timing of release of generated co2 and ch4 could have considerable importance in promoting the expulsion of liquid hydrocarbons but the mechanism is unclear as it is universally agreed that dispersed organic matter dom in some shales readily generates and expels petroleum it is curious that few consistent geochemical differences have been found between coal macerals and dom in interbedded shales unambiguous evidence of expulsion from coals is limited and in particular only a few commercial oil discoveries can be confidently correlated to coals these include upper cretaceous fruitland formation coals in the usa from which oil is produced new zealand tertiary coals and middle jurassic coals from the danish north sea it is likely that coals have at least contributed to significant oil discoveries in the gippsland basin australia in the turpan basin china and in the kutei and ardjuna basins in indonesia but this remains unproven early reports that early jurassic coals in mid norway were a major source of the reservoired oils have been shown to be inaccurate none of the proposed rules of thumb for generation or expulsion of petroleum from coals seem particularly robust decisions on whether a particular coal is likely to have been an active source for oil should consider all available geological and geochemical information the assumptions made in computational models should be well understood as it is likely with new understandings of processes involved that some of these assumptions will be difficult to sustain

hydrocarbon generating potential of humic coals from dry pyrolysis for comparing the oil and gas generation potential of humic coals two immature subbituminous coals australia gippsland an oil prone eocene coal ro 0 37 hi 237 5 and a gas prone rocky mountain upper cretaceous coal ro 0 45 hi 110 5 as well as an exinite poor vitrinite dominant gulf coast wilcox lignite ro 0 32 hi 183 7 were selected for dry pyrolysis at 300 degrees c from 2 to 1000 hr the results indicate that australia gippsland eocene coal gec generated four times as much liquid hydrocarbon i e c 12 saturated and aromatic hydrocarbons as the rocky mountain coal rmc whereas both coals have the same potential for generation of gaseous hydrocarbons wilcox lignite wl generated as much liquid hydrocarbon as gec the two coals ge and rmc and lignite wl exhibit similar h c ratios have high pristane phytane ratios of 5 0 4 5 and 5 1 respectively and sigma 13 c values of 25 7 24 9 and 25 5 parts per mil in rmc gec and wl respectively the study suggests that the relative abundances of various macerals exinite vitrinite and inertinite are not critical to the hydrocarbon generating potential rather the amount of dispersed algae and bacterial material unidentified in the coal probably is more significant depositional environment of the source organic material also may be important because it could control preservation of organic constituents because of the small stable isotope variations in c h n in the original coal kerogen as well as residual kerogen after pyrolysis of the three coals it seems unlikely that isotopic composition can characterize coal depositional environments

petroleum generation simulation over six years of hydrocarbon formation from torbanite and brown coal in a subsiding basin abstract dry samples of torbanite and soft brown coal from which mineral matter and material soluble in chloroform have been removed have been artificially matured in an attempt to simulate conditions in a subsiding sedimentary basin with a constant geothermal gradient sealed tubes were increased in temperature by 1 c per week beginning at 100 c a tube containing each source material was opened and analysed at yearly intervals for six years olefins and carbon monoxide were not significant products at any stage at less than 300 c torbanite generated a paraffinic crude oil in 35 yield while the brown coal gave a wet co2 rich natural gas in most respects these experiments which are possibly as slow as can be realistically planned within a human time scale appear to have duplicated geochemical hydrocarbon generation

co2 rich fluid inclusions in staurolite and associated minerals in a high pressure ultrahigh temperature granulite from the gondwana suture in southern india abstract we report the first detailed fluid inclusion study on mg al rocks from the gondwana suture zone along the palghat cauvery shear zone system in southern india these rocks underwent high pressure p 12 kbar and ultrahigh temperature t 990 c metamorphism during the late neoproterozoic associated with the collisional assembly of the gondwana supercontinent fluid inclusions of texturally primary and pseudosecondary categories occur in plagioclase staurolite and kyanite in these rocks inclusions of secondary nature are found in garnet and apatite all the trapped fluids show melting temperatures in the range of 58 6 to 56 6 c suggesting a dominantly pure co 2 composition the secondary inclusions show high homogenization temperatures t h of 12 9 to 30 0 c indicating low density of 0 59 0 83 g cm 3 although most of the primary and pseudosecondary inclusions also contain moderate to low density fluids 0 67 0 95 g cm 3 t h 3 5 to 27 4 c rare high density inclusions 1 00 1 06 g cm 3 t h 26 1 to 14 1 c were discovered in matrix plagioclase and porphyroblastic staurolite the estimated co 2 isochores for the high density primary and pseudosecondary inclusions intersect the clockwise p t trajectory of the rocks at around 8 3 9 0 kbar at 1000 c which broadly coincide with the peak metamorphic conditions of the area since these fluid inclusions show textural evidence for entrapment during the growth of the host high grade minerals we interpret the high density co 2 fluids to be traces of a co 2 rich synmetamorphic fluid that was present during the peak ultrahigh temperature metamorphism despite the preservation of high density co 2 inclusions in staurolite and plagioclase the primary and pseudosecondary inclusions in most of the other minerals show wide density variation which suggests the fluids in these inclusions underwent significant density reversal density decrease during decompression of the rocks from high pressure through the peak ultrahigh temperature stage along a clockwise p t trajectory the finding of pure co 2 inclusions in these mg al granulites conforms with similar observations from many other granulite facies terrains with the carbonic fluids probably derived from mantle reservoirs and transferred through deep seated shear zones that characterize this gondwana suture

structural anatomy of a dismembered ophiolite suite from gondwana the manamedu complex cauvery suture zone southern india abstract detailed geological and structural mapping of the manamedu ophiolite complex moc from the south eastern part of the cauvery suture zone csz within the gondwana collisional suture in southern india reveals the anatomy of a dismembered ophiolite succession comprising pyroxenite actinolite hornblendite hornblendite gabbro norite gabbro anorthosite amphibolite plagiogranite mafic dykes and associated pelagic sediments such as chert magnetite bands and carbonate horizons the magmatic foliation trajectory map shows inward dipping foliations and a variety of fold structures structural cross sections of the moc reveal gentle inward dips with repetition and omission of different lithologies often marked by curvilinear hinge lines the succession displays imbricate thrust sheets and slices of dismembered ophiolite suites distributed along several localities within the csz the moc can be interpreted as a deformed large duplex structure associated with south verging back thrust system consistent with crustal scale flower structure the nature and distribution of ophiolitic rocks in the csz suggest supra subduction zone setting associated with the lithospheric subduction of the neoproterozoic mozambique ocean followed by collision and obduction during the final stage of amalgamation of the gondwana supercontinent in the end precambrian

source rock evaluation by pyrolysis gas chromatography a pyrolysis gas chromatography system has been developed for the rapid evaluation of potential source rocks for the determination of organic richness and maturation this system uses the pyrolysis methods previously described however the determination of hydrocarbon production type and the identification of contamination by migrated hydrocarbons or drilling additives are accomplished by gas chromatographic gc analysis of the thermal extracts and pyrolysis products of rock samples or isolated kerogens the production type is recognized either qualitatively by gc fingerprint traces or quantitatively by hydrocarbon composition c1 to c6 c6 to c11 c11 from the kerogen peak ii pyrolysate oil prone erogens are recognized by gc traces with a full spectrum of c1 to c28 hydrocarbons or by high concentrations of c11 compounds in contrast gas prone kerogens are characterized by the predominance of light hydrocarbons from c1 to c4 and higher contributions of aromatic compounds mixed type production is intermediate in character between the two contaminants are identified from the gc analysis of the thermally extractable material in peak i possible mineral organic matter reactions during sample heating make interpreting data from whole rock samples more difficult

confidence limits on kinetic models of primary cracking and implications for the modelling of hydrocarbon generation abstract kinetic models of primary cracking for use in hydrocarbon modelling are obtained through empirical calibration against laboratory measurements this paper utilizes least squares variance analysis to evaluate the uncertainty in the calibrated kinetic parameters and discusses some consequences for the prediction of hydrocarbon generation it is substantiated that the sensitivity of the average kinetic parameters e a and log e a to micropyrolysis errors can be parameterized by errors in pyrolysis tmax the absolute and relative errors in tmax are modelled by normal gaussian random variables and the variance analysis yields the joint normal probability density distribution of variability in e a and log e a it is found that tmax errors reduce the ability to resolve independently the values of e a and log e a the estimation errors are highly positively correlated and repeated measurements on identical kerogens will produce values of e a and log e a which tend to fall close to and along the line log e a e a irt p constant where tp is an average pyrolysis temperature this correlation is consistent with observations and hence it is suggested that it is mainly an artifact which originates in the experimental errors of laboratory pyrolysis when values of e a and log e a are confined to the region of the confidence ellipsoid the pyrolysis data are satisfied within their error bounds however the variability in predictions of hydrocarbon generation may be large depending on the particular geological temperature history the uncertainties in the depth to the oil window may be several hundreds of metres and the timing of peak hydrocarbon generation rate may vary considerably the inclusion of basin geochemical data in the calibration drastically reduces the ambiguity in e a and log e a and emphasizes the need to validate the laboratory calibrated kinetic models against basin observations

isotopic evidence for involvement of c0 2 bearing magmas in granulite formation it has been suggested1 2 that co2 bearing magmas play an important part in the formation of granulites these magmas crystallize directly into granulites and also expel fluids which promote the development of granulite facies mineral assemblages in adjacent country rocks direct evidence for carbonic fluids remains elusive however as granulite facies aureoles adjacent to charnockitic intrusives1 may result either from the influx of carbonic fluids derived from the intrusives or simply from extraction of water into a vapour absent melt here we report results of a detailed study of carbon isotope compositions of graphite associated with a charnockite dyke from the ponmudi quarry of south india higher graphite abundances and an anomalously heavy carbon isotopic composition 13cgr 8 1 0 at the dyke margins indicate that externally derived co2 rich fluids were transported into the ponmudi paragneisses by the intrusive and precipitated nearly quantitatively as graphite on encountering reducing country rocks the occurrence of large orthopyroxene crystals along the dyke margins suggests that these fluids also served to dehydrate the country rocks this dyke may thus be representative of the widespread transport of carbonic fluids in this terrain by felsic magmas

detection of a collision zone in south indian shield region from magnetotelluric studies magnetotelluric mt investigations were carried out along a profile in the greenschist granulite transition zone within the south indian shield region sisr the profile runs over a length of 110 km from kuppam in the north to bommidi in the south it covers the transition zone with 12 mt stations using a wide band 1 khz 1 ks data acquisition system the mettur shear zone mtsz forms the ne extension of moyar bhavani shear zonethattraverses alongthetransitionzone theregionalgeoelectric strikedirectionofn40 eidentifiedfromthepresent studyisconsistentwiththe strike direction of the mtsz in the center of the profile the 2 d conductivity model derived from the data display distinct high electrical resistivity character 10 000 m below the archaean dharwar craton and less resistive b3000 m under the southern granulite terrain located south of the mtsz the mtsz separating the two regions is characterized by steep anomalous high conductive feature at lower crustal depths the deep seismic sounding dss study carried out along the profile shows dipping signatures on either side of the shear zone the variation of deep electrical resistivity together with the dipping signature of reflectors indicate two distinct terrains namely the archaean dharwar craton in the north and the proterozoic granulite terrain towards south they got accreted along the mtsz which could represent a possible collision boundary 2006 international association for gondwana research published by elsevier b v all rights reserved

the petroleum potential of some tertiary lignites from northern greece as determined using pyrolysis and organic petrological techniques abstract oil condensate and gas have recently been discovered in the thermaikos gulf area of northern greece the source of these hydrocarbons is not known although there is a possibility that more mature equivalents of certain tertiary brown coals and lignites may be responsible a contribution from tertiary terrestrial organic matter to the epanomi oil is supported by its biomarker distributions especially the predominance of triterpenoid compounds other than hopanes in the m z 191 mass fragmentogram in this study the hydrocarbon potential of a suite of greek tertiary lignites is first examined using rock eval analysis three samples are then further investigated using organic petrography and gas chromatography gc and gas chromatography mass spectrometry gc ms of the extracted hydrocarbon fractions as well as by hydrous pyrolysis an intermontane lignite 6og 5 contains fluorescing huminite together with resinite on extraction this resinite is found to be of predominantly diterpenoid origin rock eval and hydrous pyrolysis support previous proposals that diterpenoid resinite needs a lower activation energy to generate hydrocarbons than most other types of organic matter a sample of a lignite deposited in a deltaic environment mm 3 contains a more diverse collection of liptinite macerals with resinite again predominating the resinite appears to be mostly of triterpenoid and sesterterpenoid origin the best hydrocarbon potential is shown by a sample deposited in a lagoonal environment kas 3 little discrete resinite is observed in this sample but it does contain abundant fluorescing huminite although it has a low s 1 s 1 s 2 ratio it gives a high yield on solvent extraction during which a significant fraction of the s2 is removed the fluorescence of the huminite after extraction is greatly reduced the hydrocarbons of the extract are believed to be predominantly derived from triterpenoid resinite unlike the pyrolysates of the other two lignites but in common with the epanomi oil the triterpenoids in the kas 3 pyrolysate are dominated by resin derived compounds rather than hopanes this and other similarities between the composition of the pyrolysates of kas 3 and the oil support the possibility that a more mature equivalent of this lignite could be the source of the epanomi oil

expulsion of oil from petroleum source rocks inferences from pyrolysis of samples of unconventional grain size oil expulsion efficiencies from different lithologies have been investigated and compared employing pyrolyses of samples of unconventional grain size from 300 mg hc g corg show that liquid range hydrocarbons are expelled from coal when the generated oil exceeds the coal sorption capacity this suggests that expulsion of oil from liptinite poor or in general h poor humic coals is primarily limited by the release of generated liquid hydrocarbons from kerogen because such coals generally do not generate sufficient amounts of liquid hydrocarbons to overcome the coal sorption capacity

reaction mechanism for the replacement of calcite by dolomite and siderite implications for geochemistry microstructure and porosity evolution during hydrothermal mineralisation carbonate reactions are common in mineral deposits due to co2 rich mineralising fluids this study presents the first in depth integrated analysis of microstructure and microchemistry of fluid mediated carbonate reaction textures at hydrothermal conditions in doing so we describe the mechanisms by which carbonate phases replace one another and the implications for the evolution of geochemistry rock microstructures and porosity the sample from the 1 95 moz junction gold deposit western australia contains calcite derived from carbonation of a metamorphic amphibole plagioclase assemblage that has further altered to siderite and dolomite the calcite is porous and contains iron rich calcite blebs interpreted to have resulted from fluid mediated replacement of compositionally heterogeneous amphiboles the siderite is polycrystalline but nucleates topotactically on the calcite as a result the boundaries between adjacent grains are low angle boundaries 10 which are geometrically similar to those formed by crystal plastic deformation and recovery growth zoning within individual siderite grains shows that the low angle boundaries are growth features and not due to deformation low angle boundaries develop due to the propagation of defects at grain faces and zone boundaries and by impingement of grains that nucleated with small misorientations relative to each other during grain growth the cores of siderite grains are aligned with the twin planes in the parent calcite crystal showing that the reactant fe entered the crystal along the twin boundaries dolomite grains many of which appear to in fill space generated by the siderite replacement also show alignment of cores along the calcite twin planes suggesting that they did not grow into space but replaced the calcite where dolomite is seen directly replacing calcite it nucleates on the fe rich calcite due to the increased compatibility of the fe bearing calcite lattice relative to the pure calcite both reactions are interpreted as fluid mediated replacement reactions which use the crystallography and elemental chemistry of the calcite experiments of fluid mediated replacement reactions show that they proceed much faster than diffusion based reactions this is important when considering the rates of reactions relative to fluid flow in mineralising systems

comparison of generative capacities for bitumen and gas between carboniferous coals from donets basin ukraine and a cretaceous coal from sabinas piedras negras basin mexico during artificial maturation in confined pyrolysis system abstract the goal of this work is to study the ability of two immature carboniferous coals from donets basin ukraine to act as source for oil heating experiments in confined medium were performed to compare the thermal behavior of these coals 1l1 dim r r 0 55 h c at 0 79 and 2c10yd r r 0 65 h c at 0 80 relative to a mature cretaceous coal from sabinas basin olmos r r 0 92 h c at 0 77 macerals analysis carried out on starting materials showed that olmos is exhausted in liptinite contrary to 2c10yd 20 vol and 1l1dim 6 vol the vitrinite content is lower for 2c10yd 59 vol than for olmos 84 vol and 1l1dim 80 vol solid bitumen occurs often dispersed in the raw coals both petrographic and geochemical analyses on starting materials revealed that the selected carboniferous donets coals have better potentialities for bitumen generation than the cretaceous sabinas coal the presence of long chain n alkanes n c 8 in the pyrolysis gc chromatograms indicates that the two raw carboniferous coals from donets basin can yield non volatile hydrocarbons under further thermal maturation it is speculated that some vitrinite macerals present in hydrogen rich carboniferous coals from donets basin can act as source rocks for oil as a matter of fact results showed that the oil window occurs between 1 0 r r and 2 0 r r for both cretaceous sabinas and carboniferous donets coals during confined pyrolysis as expected from geochemical and petrographic analyses of starting samples the carboniferous donets coals yielded more bitumen and hydrocarbons than cretaceous sabinas coal during artificial maturation low proportions of solid bitumen r r and 1 5 r r during confined pyrolysis of coals two solid bitumen groups have been identified which correspond to distinct phases of neo formation the drop in the solid bitumen content at higher ranks indicates that it contributes to generation of gas during experimental simulation moreover their morphology and porosity change with the level of maturity the porosity of the vitrinite matrix increases as well as the pore size with increasing maturity a relationship has been observed between the porosity and the weight loss the higher pore content of carboniferous donets coals is correlated with a higher generation of gas compared to cretaceous sabinas coal

implications for organic maturation studies of evidence for a geologically rapid increase and stabilization of vitrinite reflectance at peak temperature cerro prieto geothermal system mexico discussion a short term rapid heating and cooling of the rock in well m 94 below 1300 m was caused by a pulse of hot water passing through the edge of the cerro prieto mexico geothermal system below 1300 m the peak paleotemperatures were about 225 250 degrees c but equilibrium well log temperatures indicate a decrease to 150 210 degrees c at present this hot water pulse sharply increased vitrinite reflectance to levels comparable to those measured in the central part of the system even though studies of apatite fission track annealing indicate that the duration of heating was only 10 0 10 1 yr in m 94 in contrast to 10 3 10 4 yr in the central part of the system these data indicate that sedimentary organic matter chemically reacts quickly to temperature increases of about 125 degrees c above ambient even when the higher temperature existed for only 10 0 10 1 yr the quick change of the vitrinite reflectance geothermometer indicates that thermal maturation reactions can stabilize after a geologically short period of heating to a level consistent with peak temperature under moderate to high temperature diagenesis in open fluid rich geothermal systems cerro prieto is one of the most intensively studied and well known geothermal systems in the world thus data from cerro prieto are a benchmark to compare with the predictions of published thermal maturation models such as those formulated by j karweil n v lopatin and a k burnham and j j sweeney these thermal maturation models inaccurately predict duration of heating at cerro prieto the kinetic equations used in these models explicitly allow thermal maturation to continue indefinitely at peak temperature which does not seem to be the case at cerro prieto

precambrian continental crust of india and its evolution the indian precambrian continental crust exhibits a variety of geological features fashioned at different times by different geotectonic processes the bulk of this crust was formed prior to 2600 m y ago and remobilized at least twice between 2600 2000 m y ago early proterozoic mobile belt epmb and 2000 1500 m y ago middle proterozoic mobile belt mpmb three early precambrian nucleii karnataka kn jeypore bastar jbn and singhbhum sn appear to have survived in the craton and are characterized by low grade supracrustals and tonalitic trondhjemite gneisses formed 3800 2600 m y ago the epmb event involved sedimentation amphibolite granulite facies metamorphism and co 2 k metasomatism and produced amphibolite facies rocks and k granites in the north and charnockite and other granulite facies rocks in the south gold sporadically distributed in the supracrustal rocks of the craton was remobilized during the epmb event k granites form a garland around the central dharwar craton sugg

influence of in situ bitumen on the generation of gas and oil in new zealand coals new zealand coals of peat to high volatile bituminous rank have been studied in order to assess the effect of in situ bitumen soluble in a methanol acetone chloroform azeotrope on petroleum potential during progressive maturation both non extracted and extracted coals as well as the extracted bitumen itself were analyzed using rock eval and pyrolysis gas chromatography the difference in yields between non extracted and extracted coals attributable to the influence of bitumen were compared with direct measurements made on the bitumen itself major compositional changes in pyrolysis products were seen when the bitumen was finely dispersed throughout the kerogen matrix notably second order reactions between kerogen and bitumen during pyrolysis reduce primary gas yield and enhance both oil yield and potential secondary gas yield the stabilization of free radicals and prevention of recombination repolymerization processes have been attributed to the presence of the dispersed in situ bitumen these results demonstrate that petroleum formation in coals likely proceeds via intermolecular interactions and not simply first order cracking the common procedure of employing solvent extraction prior to pyrolysis is clearly not appropriate when assessing the petroleum potential of coal

ductile shearing in attur shear zone and its relation with moyar shear zone south india abstract in the eastern part of southern peninsular india the charnockitic hills of the madras block are cut across by the e w trending attur shear zone asz which is characterised by a thick 1 to 1 5 km phyllonite zone showing intense mylonitisation due to ductile shearing steeply plunging 70 80 stretching lineation on steeply dipping mylonitic foliation within this zone indicates a relative vertical upliftment of the adjacent blocks a dextral shearing event from west to east is envisaged from the kinematic analysis of shear sense indicators such as s c fabric asymmetric folds asymmetric augens and asymmetric porphyroclasts simultaneous development of these features related to vertical and horizontal movements may be explained by the mechanism of transpressional deformation the attur shear zone may be correlated with the moyar shear zone based on distinct lithological and structural similarities

hydrocarbon habitat in main producing areas saudi arabia discussion most petroleum geologists have wondered why the persian arabian gulf area contained such enormous volumes of petroleum saudi arabia alone has produced 44 1 billion barrels of oil and remaining reserves are estimated at 177 2 billion bbl previous studies concluded the jurassic callovian to oxforidan organic rich carbonates were the only rocks considered rich enough to be the likely source for saudi arabia s vast reserves these authors believed the unique size of the accumulations reflected the scale of the system with large volumes of petroleum generating rocks coupled efficiently to large traps it was argued that the type of organic matter generally associated with carbonates was algal rich oil prone and a more efficient generator compared with the organic matter in clastics it was concluded that the previously identified source rocks only partly answer the question of the unique size of oil accumulations in the part of the middle east

ore fluids associated with the wynad gold mineralization southern india evidence from fluid inclusion microthermometry and gas analysis abstract in southern india major gold deposits occur in the archean granite greenstone terrain of kolar hutti ramagiri and within proterozoic granulite terrain in wynad the wynad gold field wgf which is located within the moyar bhavani lineament a proterozoic transcrustal shear zone hosts gold within quartz veins which are emplaced along the mesoscopic faults and shears in the region the quartz veins cut the regional fabric of the country rocks suggesting that the veins were formed in post tectonic and post metamorphic episode of crustal shearing gold as visible specks or interstitial grains and veinlets are seen within quartz and associated sulfide minerals indicative of multiple mineralizing events fluid inclusion studies carried out on gold quartz veins showed the frequent occurrence of bi phase primary inclusions of h 2 o co 2 pseudosecondary inclusions of h 2 o co 2 and aqueous secondary inclusions microthermometric studies of different samples revealed a near pure co 2 composition associated with the aqueous phase with melting temperatures close to 56 6 c clathrate melting temperatures of primary and pseudosecondary inclusions show that the fluids were low to moderately saline 2 14 wt nacl equiv homogenization temperatures of primary and pseudosecondary inclusions range between 250 330 c and 230 300 c respectively the secondary aqueous inclusions have much lower homogenization temperatures between 130 and 220 c fluid densities calculated from the microthermometric data were between 0 8 and 1 0 g cm 3 the isochores pertaining to these fluid densities intercept the trapping temperatures within pressure ranges of 0 5 and 2 9 kbars fluid inclusion gas analyses were carried out on selected samples using a quadrupole mass spectrometer the analysis shows that the fluid inclusions were mainly of h 2 o and co 2 with minor quantities of n 2 and ch 4 which was in close correlation with our visual analytical data we envisage that the fluids responsible for the wynad gold mineralization evolved from an h 2 o co 2 fluid and precipitated gold at temperatures of 300 350 c due to the sudden pressure and temperature decrease as the fluids entered the shear zone

regional carbonate alteration of the crust by mantle derived magmatic fluids tamil nadu south india regional carbonate alteration of the crust associated with major shear zones provides direct evidence for co 2 rich fluid mobility a good example occurs within the attur lineament one of numerous proterozoic shear zones which crosscut charnockitic gneisses and other lithologies of the southern indian craton at this locality widespread carbonate alteration of silicate rocks has involved growth of ankerite and other carbonate minerals which replace preexisting silicates some of the ankerite was subsequently recrystallized to fine grained calcite and iron oxide accompanied by sericitization of feldspar carbon oxygen and strontium isotope analyses of samples of ankerite and calcite together with some of the coexisting silicate minerals have been used to constrain the conditions of formation of the carbonate alteration and the origin of the fluids involved delta 13 c values of ankerite are relatively homogeneous ranging between 6 5 and 3 9 with a mean of 5 3 delta 18 o is also

microbial remains in some earliest earth rocks comparison with a potential modern analogue abstract carbonaceous matter cm from ca 3 5 ga hydrothermal black cherts of the pilbara craton of western australia and the barberton greenstone belt of south africa yielded transmission electron microscopy tem images that are suggestive of microbial remains and possible remnants of microbial cell walls these are compared to a potential modern analogue the hyperthermophilic methanocaldococcus jannaschii derived from an active seafloor hydrothermal environment and cultured under similar conditions a striking resemblance to the early archaean forms was evident in wall structure and thermal degradation mode cell disintegration of the cultures occurred at 100 c marking the limits of life complete disintegration deformation and shrinkage occurred at 132 c a multidisciplinary approach to the characterisation of the cm was undertaken using organic petrology tem coupled with electron dispersive spectral analysis eds high resolution tem hrtem to determine molecular ordering and elemental and carbon isotope geochemistry reflectance measurements of the cm to determine thermal stress yielded a range of values corresponding to several populations and pointing to different sources and processes the 13c values of dresser formation cm 36 5 to 32 1 are negatively correlated with toc 0 13 0 75 and positively correlated with c n ratio 134 569 which is interpreted to reflect the relative abundance of high ro oxidised recycled cm and preferential loss of 12c and n during thermal maturation tem observations inferred carbon isotopic heterogeneity and isotope fractionations of 27 to 32 are consistent with the activity of chemosynthetic microbes in a seafloor hydrothermal system where rapid silicification at relatively low temperature preserved the cm

the effect of igneous intrusive bodies on sedimentary thermal maturity abstract the high temperatures of igneous intrusives cause localized thermal maturity of sediments far in excess of the regional variation previous studies have shown that igneous bodies cool in less than about a million years for all but the most exceptional geological conditions two case studies are provided which show how the increase in thermal maturity around an igneous body can be used to assess the temperature of the intrusive at emplacement and also the time of intrusion corollorative implications for localized hydrocarbons generation migration and accumulation are also discussed briefly

simple kinetic models of petroleum formation part i oil and gas generation from kerogen modern basin analysis uses kinetic models to predict the extent of petroleum generation within potential source rocks the global kinetic model presented here assigns kinetic parameters based on gross depositional environment and stratigraphic age this is useful in areas of low geochemical knowledge including exploration frontiers five kerogen kinetic organofacies each characterized by a specific organic matter input and early diagenetic overprint can broadly be related to sedimentary facies age associations even using seismic sequence stratigraphy alone a aquatic marine siliceous or carbonate evaporite any age b aquatic marine siliciclastic any age c aquatic non marine lacustrine phanerozoic d e terrigenous non marine ever wet coastal mesozoic and younger and f terrigenous non marine coastal late palaeozoic and younger routine pyrolysis data allow partitioning of organic carbon in the immature source rock into four initial components oil oil generative gas generative and inert separate kinetic parameters for the oil and gas generative fractions allow computation of the evolving concentration and composition of the products it was assumed that the activation energy distributions for each fraction were normally distributed non linear regression of large combined laboratory and field data sets varying by up to 12 orders of magnitude in heating rate established optimum values for the required ten 5 2 kinetic parameter sets a emean e differences in kinetic parameters can be reconciled with known chemical properties although our knowledge base is still inadequate to construct kinetic models from first principles mean activation energies governing oil generation increase systematically in the order a f causing a corresponding increase in generation temperature at a reference heating rate 2 c ma 1 the oil generation window 10 90 oil generative kerogen degraded increases from ca 95 135 c to 145 175 c organofacies c has the tightest energy distribution and narrowest oil generation window the gas generation window ranges from ca 105 155 c to 175 220 c thermal stress results from a combination of temperature and time an order of magnitude increase decrease in heating rate elevates depresses reaction temperatures by ca 15 c heating rates in subsiding sedimentary basins can vary by two orders of magnitude dramatic differences in generation temperature can result if the heating rate and organofacies effects compound thus global oil and gas generation temperature thresholds constitute blunt instruments with which to screen the petroleum potential of sedimentary basins because unexpelled oil provides a potential feedstock for oil to gas cracking in the source rock quantitative models of petroleum generation become really useful only when coupled with models of oil gas cracking and expulsion for example the frequently observed association between gas provinces and coals cannot be explained solely by their generation behaviour

estimation of emplacement temperatures of pyroclastic flows using h c ratios of carbonized wood abstract laboratory experiments aimed at allowing estimation of emplacement temperatures of pyroclastic deposits flows using h c ratios of entrained carbonized wood were carried by simulating the thermal conditions in pyroclastic flows live wood cuttings of four tree genera cryptomeria pinus quercus and gonystylus were implanted in volcanic ash heated in an electric furnace in one group of experiments wood samples were inserted into the ash in separate runs at temperatures ranging from 238 to 714 c and then slowly cooled in a second group samples were held at temperatures between 241 and 743 c for one three or five days h c ratios of the carbonized woods produced were then determined by combustion analysis no systematic differences in h c ratios were observed between genera at given temperatures h c ratios from the first group of experiments show a strong correlation with temperature yielding the equation log t c 2 50 0 530 log h c where h c ratios are 300 c similar relations are also shown by the second group although the equations produced differ with time of maximum heating the relations between h c ratios and temperature from the experiments were tested by analysis of natural carbonized wood fragments from holocene pyroclastic flow deposits coupled with independent emplacement temperature estimation from paleomagnetic blocking temperatures of clasts within the flows the two methods produced comparable results suggesting that the h c thermometer is a simple and reliable method for estimating maximum emplacement temperatures of pyroclastic flows cooling rates can also be approximated when combined with paleomagnetic studies

nature of source material for hydrocarbons in cooper basin australia the cooper basin which produces a large proportion of australia s natural gas also includes small oil fields source rocks for the hydrocarbons are believed to be the terrestrial coal measure sediments of the permian gidgealpa group dispersed organic matter in the sediments of the gidgealpa group in the patchawarra trough cooper basin ranges between 1 and 5 by volume through seven formations less than 10 of the dispersed organic matter is exinite and less than 30 is vitrinite if these two macerals only are considered as source material for the liquid hydrocarbons none of the formations contains the 0 5 organic carbon currently deemed necessary for a sediment to be classified as a source rock if inertinite is regarded to have generating potential then most of the formations rate as good to excellent source rocks recent studies on vitrinites and inertinites from a variety of coal seams suggest that if vitrinite is accepted as a possible source of liquid hydrocarbons then inertinite is equally prospective consequently dispersed inertinite in the gidgealpa group sediments is proposed as one of the sources for the liquid hydrocarbons in the cooper basin

age of younger tonalitic magmatism and granulitic metamorphism in the south indian transition zone krishnagiri area comparison with older peninsular gneisses from the gorur hassan area abstract a major episode of continental crust formation associated with granulite facies metamorphism occurred at 2 55 2 51 ga and was related to accretional processes of juvenile crust dating of tonalitic trondhjemitic granitic gneisses and charnockites from the krishnagiri area of south india indicates that magmatic protoliths are 2550 2530 5 ma as shown by both u pb and 207pb 206pb single zircon methods monazite ages indicate high temperatures of cooling corresponding to conditions close to granulite facies metamorphism at 2510 10 ma these data provide precise time constraints and sr nd isotopes confirm the existence of late tonalitic granodioritic juvenile gneisses at 2550 ma pb single zircon ages from the older peninsular gneisses gorur hassan area are in agreement with some previous sr ages and range between 3200 20 and 3328 10 ma these gneisses were derived from a 3 3 3 5 ga mantle source as indicated from nd isotopes they did not participate significantly in the genesis of the 2 55 ga juvenile magmas all these data together with previous work suggest that the 2 51 ga granulite facies metamorphism occurred near the contact of the ancient peninsular gneisses and the 2 55 2 52 ga juvenile tonalitic trondhjemitic terranes during synaccretional processes subduction mantle plume rb sr biotite ages between 2060 and 2340 ma indicate late cooling probably related to the dextral major east west shearing which displaced the 2 5 ga juvenile terranes toward the west

pan african charnockite formation in kerala south india sm nd mineral ages of gneisses and associated granulites from the ponmudi incipient charnockite locality south india indicate that granulite metamorphism occurred at or shortly after 558 ma proterozoic ages recorded by garnet separates reflect a detrital age or an earlier metamorphic event preserved by inclusions within garnet the age of post metamorphic uplift 440 460 ma is constrained by sr isotope equilibration between biotite and plagioclase since charnockite formation and subsequent uplift north of the palghat cauvery shear zone had terminated by earliest proterozoic time these results confirm two distinct periods of granulite formation in south india and suggest that the palghat cauvery shear zone represents the boundary between two blocks of strongly contrasting geological histories both incipient charnockite formation and subsequent uplift at ponmudi may be correlated with the tectonothermal evolution of the highlands group in sri lanka the similarity between nd and sr model ages for charnockites and gneisses from ponmudi indicates that no significant rb sr fractionation has occurred during the crustal history of these incipient charnockites pb isotopic ratios suggest that th u ratios were fractionated during charnockite formation at about 500 ma in contrast to charnockites found north of the palghat cauvery shear zone fractionation of u pb during the archaean did not occur in the ponmudi granulites

geochemical and stable isotope studies of the no 4 lode kalgoorlie western australia the no 4 lode is a silicified pyritic shear zone with gold telluride mineralization which is located in the golden mile dolerite along the western limb of the kalgoorlie syncline wallrocks in this zone have undergone a series of metamorphic and metasomatic events this alteration is characterized by an increase in the ko nao ratio introduction of co and s and significant enrichment of au ag te and other ore forming constituents major and trace element and isotopic data are presented 40 chemical analyses ore mineralization is thought to have formed by reaction of chloritic host rocks with a moderately reduced near neutral hydrothermal fluid at t 250 or 50oc isotope and geochemical data suggest that these ore fluids were of metamorphic derivation and may have incorporated magmatic c s and possibly precious metals at deeper levels in the crust j e s

crustal architecture and tectonic evolution of the cauvery suture zone southern india abstract the cauvery suture zone csz in southern india has witnessed multiple deformations associated with multiple subduction collision history with incorporation of the related accretionary belts sequentially into the southern continental margin of the archaean dharwar craton since neoarchean to neoproterozoic the accreted tectonic elements include suprasubduction complexes of arc magmatic sequences high grade supracrustals thrust duplexes ophiolites and younger intrusions that are dispersed along the suture the intra oceanic neoarchean neoproterozoic arc assemblages are well exposed in the form of tectonic melanges dominantly towards the eastern sector of the csz and are typically subjected to complex and multiple deformation events multi scale analysis of structural elements with detailed geological mapping of the sub regions and their structural cross sections geochemical and geochronological data and integrated geophysical observations suggest that the csz is an important zone that preserves the imprints of multiple cycles of precambrian plate tectonic regimes

paleosalinity from trace metals in fossil ostracodes compared with observational records at devils lake north dakota usa abstract the chemistry of closed basin lakes responds directly to the hydrologic budget through evaporative concentration of dissolved salts and the sediments of these basins contain several excellent fossil and geochemical proxies for past changes in water chemistry and salinity the trace metal content of ostracode shells among the most promising of these paleosalinity methods is further explored in this study of mg and sr partitioning in candona rawsoni a widespread ostracode of the north american great plains the molar distribution coefficients kd mg and kd sr for this species k d mg ca caco 3 0 004 mg 2 ca 2 h 2 o 9 68 10 5 t c k d sr sr ca caco 3 sr 2 ca 2 h 2 oz 0 406 are determined from laboratory experiments in which c rawsoni are cultured under controlled temperatures and salinities our formulation of kd mg contains a correction term for excess mg that is incorporated into the shell during early calcification the accuracy of the distribution coefficients is tested against field collections of live ostracodes from a suite of 12 dakota lakes the kd inferred values for mg2 ca2 h2o and sr2 ca2 h2o are in close accord with the same ratios measured in the lakes a comparison of ostracode reconstructed and historically measured salinities for devils lake north dakota shows good agreement within the salinity range preferred by c rawsoni 1 10 0 although salinity excursions beyond this optimum are poorly represented in the sedimentary record in most lakes salinity is more readily inferred from mg ca h2o than sr ca h2o because sr solubility is a complex function of several carbonate phases as shown for devils lake sr ca h2o may not vary systematically with the salinity of some brines

hydrothermal petroleums from yellowstone national park wyoming u s a abstract in yellowstone national park oil is actively discharging with thermal waters at several widely separated thermal areas samples from two locations were studied petroleum from calcite springs occurs as vapor condensates in steam vents detailed geochemical analyses show a complex origin for the petroleum fluid deeply buried hydrothermally altered sedimentary rocks are believed to have contributed a high temperature pyrolysate consisting largely of polynuclear aromatic hydrocarbons and heterocyclic compounds shallow sedimentary rocks which are also hydrothermally altered have contributed large amounts of aromatic and polar compounds as well as minor amounts of hydrocarbons the permian phosphoria formation is suggested as a likely source rock for the bulk of the oils autochthonous pyrolysates and lipids from thermally altered surface and near surface bacterial and land plant debris have also been introduced to the vents the latter may have been introduced by downward percolating meteoric water the oil from rainbow springs is a highly paraffinic low s crude oil depleted in light hydrocarbons unlike the calcite springs samples the oil from rainbow springs is believed to have originated from a single sedimentary source rock with little or no hydrocarbon contributions from surface biota the oil contains a unique molecular marker assemblage that suggests both gymnosperm and angiosperm input and places the age of the source unit in the tertiary consideration of the local stratigraphy and water temperatures limits the probable source zone to the eocene aycross formation an intra volcanic lacustrine mudstone calculation of deep water temperatures indicates that this unit is exposed to thermal waters in an extensive near surface aquifer such conditions are consistent with the widespread surface manifestations and biomarker kinetic models consideration of the petroleum chemistry and regional hydrodynamics indicates that the yellowstone park oils did not migrate into the park from distant sources the chemical data are also inconsistent with the oils being generated and trapped prior to tertiary volcanism at both calcite springs and rainbow springs oil generation appears to be contemporaneous and is attributed to thermal alteration of relatively shallow sedimentary rocks by hydrothermal fluids

vitrinite recycling diagnostic criteria and reflectance changes during weathering and reburial abstract the aim of this study was first to review or even identify reliable diagnostic criteria to distinguish recycled and autochthonous vitrinite particles and second to examine and try to explain the impact of weathering and reburial on optical changes reflectance of recycled material the work was based on indigenous and recycled particles of two sample sets from two wells drilled in the senegalese margin basin and the ardeche paleomargin se france respectively in addition to reflectance measurements the studied samples have also been analysed by rock eval pyrolysis for both sample sets hydrogen index hi and oxygen index oi values suggest a type iii organic matter of dominant terrestrial origin two main diagnostic criteria appear particularly useful to identify indigenous and recycled vitrinite particles the first is the clear genetic relationship between telinite and collotelinite the second is the presence of pyrite framboid inclusions in indigenous vitrinite the pyrite vitrinite association illustrates the relationship between sulphate reduction pyritisation and in situ organic matter transformation through gelification process however application of both diagnostic criteria requires some additional information about depositional conditions i e anoxicity and thermal maturity of the studied samples weathering has no or only very limited effect on vitrinite reflectance during their new burial history recycled vitrinites follow a reflectance evolution path close to that of inertinites and thus appear as transitional materials between vitrinite and inertinite macerals consistently this behaviour implies that recycled vitrinite reflectance changes during burial diagenesis do not solely depend on their chemical composition but most probably too on combined chemical and structural changes inherited from their past burial history and from the impact of weathering during their recycling stage

influence of rock particle size on the artificial thermal evolution of kerogen a petrographic and geochemical study abstract two series of samples grain series gs and block series bs with different particle size between 0 5 1 0 mm and 1 5 1 5 5 0 cm and rock geometry irregular and prismatic respectively were obtained from an oil shale with type ii kerogen from cantabria northern spain both series were pyrolyzed at different temperatures between 50 and 500 c by the open medium pyrolysis system petrological and geochemical analyses were carried out to determine the organic transformation level to characterize the resulting products and to establish a relation of maturation between the two series results show that the main processes of organic diagenesis occurred at a temperature interval ranging from 250 to 450 c in both series however differences in evolution parameters show that the diagenetic processes do not occur in the same way in both series as they depend on the physico morphological characteristics of the rock that is being pyrolyzed this is reflected in the greater level of oil production and expulsion during the pyrolysis process that is more important in bs than in gs expulsion seems to be favoured by the fissure system developed during the thermal evolution in bs which does not occur in samples with smaller particle size at the same time in bs a greater retention of some polar components asphaltenes leading to a differential impregnation of vitrinites is produced this explains the differences in reflectance found between both series after the primary cracking the results of this study confirm and supplement previous work about the importance of confinement in pyrolysis experiments aiming to reproduce sedimentary organic diagenesis in addition to qualitative and quantitative variations in kerogen degradation products the present study conducted on rock samples shows that the confinement also enhances oil expulsion through cracks and fissures developed in the rock in the course of heating although these results are probably not directly applicable to natural series they help to interpret the origin of discrepancies between evolution parameters which appear to be primarily related to confinement

oxygen isotope fractionation in quartz albite anorthite and calcite laboratory measurements of equilibrium oxygen isotope fractionation in quartz albite anorthite and calcite have been carried out by anhydrous exchange between silicates and calcite at temperatures of 600 c and above exchange in these systems is as rapid as exchange between silicates and water fractionation factors can be summarized in the following equations qc 0 38 106t 2 abc 0 57 106t 2 anc 1 59 106t 2 from which the silicate pair fractionations are readily obtained these results are compared with published theoretical estimates as well as data derived from hydrothermal experiments some significant differences are found in particular it is difficult to reconcile all of the hydrothermal data either with theoretical calculations or with the present experimental data the new experiments provide an internally consistent set of fractionation factors suitable for isotopic thermometry and for test of disequilibrium in natural systems

the micro scale simulation of maturation outline of a new technique and its potential applications a micro analytical technique has been developed for artifically maturing sedimentary organic matter and then quantifying the major components generated during this process in a single analytical step such a capability is well suited for examining the compositional relationships between kerogens and petroleums determining reaction kinetics and making precursor product mass balances according to this technique simulations are made using sealed glass capillary tubes heated here for three days at 300 c 330 c and 350 c pyrolysis products are then released directly into a combined thermovaporisation pyrolysis gc instrument and the major components of the entire c1 yto c35 range can be quantified in a single step using gas chromatography alkene yields are very low and pyrolysates are oil like this is exemplified by the fact that then c9 c19 alkane distribution range of simulated whole petroleum chromatograms from originally immaturegloeocapsamorpha typz alginite a resembles that seen in crude oils generated from this same kerogen type in nature sealed tube experiments usingbotryococcus type alginite a generated a high wax pyrolysate the relative abundance ofn alkanes in the c2 c32 range of many kerogen pyrolysates does not appear to change significantly despite an approximately fifteen fold difference inn alkane yield between the 300 c and 350 c experiments kerogens which are paraffinic oil prone and whose pyrolysates are very rich inn alkanes might therefore generate petroleums in nature with a fixed wet gas c2 c4 to oil c5 ratio alginite b in a greenland shale is much more thermally labile than eitherbotryococcus type alginite a orgloeocapsamorpha type alginite a the mass balance capabilities of the technique have been tested using alum shale kerogen two gas chromatograms were obtained one for the free compounds generated during simulation and one for the high temperature pyrolysate of the kerogen residue for each heating experiment precursor product relationships were qualitatively assessed and dead carbon formation was quantified in this exercise

microbial remains and other carbonaceous forms from the 3 24 ga sulphur springs black smoker deposit western australia well preserved carbonaceous materials including filamentous microbial remains have been isolated from an archaean sedimentary package overlying the sulphur springs volcanic hosted massive sulphide vhms deposit in the pilbara of western australia one of the oldest best preserved vhms deposits on earth the isotopically light carbonaceous material 13 c values of 26 8 to 34 0 v pdb occurs as finely striated lenticular to banded organic matter om within fine grained epiclastic sediments and silicified materials that overlie the deposit the predominant banded lenticular carbonaceous material occurs parallel to original sedimentary bedding planes and is distinctly visible in light microscopy transmission electron microscopy tem reveals this om as bundles of filamentous and tubular structure closely resembling both modern day and more ancient microbial forms documented from sea floor hydrothermal environments total organic carbon toc has a range of 1 0 to 2 3 while the thermal maturity of the filamentous microbial bundles indicated by reflectance ro points to maximum temperatures since deposition ca 3 24 ga of around 90 100 c a factor that has enabled the preservation of their morphology these results and the intimate association of sulphides with the om are suggestive of a well developed archaean sediment hosted microbial community situated within a basinal environment associated with an active centre of seafloor hydrothermal activity 2007 elsevier b v all rights reserved

recent advances in petroleum geochemistry applied to hydrocarbon exploration this paper presents a critical review of recent advances in the study of generation maturation and migration of petroleum the different source potentials for generating hydrocarbons depend on the type of kerogen in addition to the classic types i ii and iii a residual oxidized organic matter is also observed which has no potential for hydrocarbon generation coal is widely considered as a potential source for gas but some coals may generate sizeable amounts of oil as well the development of routine analytical tools particularly pyrolysis makes possible the preparation of geochemical logs that are the basis for screening samples and for interpreting other analyses among optical techniques the major subjects of discussion concern the nature of amorphous organ c matter which may encompass different chemical types of kerogen and the applicability of vitrinite reflectance techniques to type i and ii kerogens following important advances in identification of biological markers in sediments and crude oils these markers are used for oil source rock correlation and proposed for reconstruction of depositional environment and subsequent thermal evolution migration of hydrocarbons is now better understood and the importance of a hydrocarbon phase migration is widely recognized overpressuring of pore fluids is mainly responsible for expulsion of petroleum geologic models of basin evolution subsidence compaction thermal history and geochemical models hydrocarbon generation and migration become progressively available their integration int a comprehensive model should be one of the major developments in future petroleum exploration

coal and coal macerals as source rocks for oil and gas abstract the role of coals in the generation and migration of hydrocarbons is discussed from the viewpoints of chemistry and petrology extract data and considerations of volatile matter and maturity suggests that under geochemical conditions most coals can give rise to oil as well as gas a distinction is drawn between release of absorbed oil and formation of hydrocarbons by thermal breakdown of the coal matrix itself the generation and preservation of oil require not only that suitable lipidic structures be present but that the product oil can escape before being cracked to gas exinite preferably in large discrete particles is the most oil prone maceral vitrinite can form oil but subsequent migration depends on the availability of cracks and fissures in the coal matrix the most highly reflecting forms of inertinite e g fusinite have no inherent capacity to generate oil low reflectance inertinite such as is common in many australian coals may have minor source potential a speculative attempt is made to quantify the oil generating capacity of coal macerals and mixtures as a general broad rule on a weight basis exinite can produce ten times more oil than vitrinite and a hundred times more than inertinite approximate calculations suggest that thermal maturation of coals can account for all the known oil and gas reserves in the gippsland and cooper basins of australia even if only 1 of generated hydrocarbons is trapped

microfacies and petroleum properties of coals as revealed by a study of north sea jurassic coals abstract the influence of the composition and microstructural aspects of coal microfacies on petroleum properties were investigated in light of petrographic and geochemical studies the first study concerns a collection of north sea jurassic coals of various maceral compositions the second study is a pyrolysis gas chromatography study on pure microlithotypes from a similar french jurassic coal the results show that hydrocarbon potential is logically increased by a high content in liptinite but more often in hydrogen rich vitrinite in the same way the hydrocarbon potential is reduced by a high inertinite content mainly due to pre sedimentary oxidation of the original biomass but also due to early diagenetic processes that lead especially to the formation of micrinite or to post sedimentary alterations these trends indicate that total hydrocarbon potential is increased by an autochthonous origin of the organic matter that was deposited in a relatively closed paleoenvironment and thus protected from detrital and organo detrital inputs finally the oil potential of humic coals as determined by open pyrolysis gas chromatographic studies as related to the weight of rock is similar to classical source rocks the structural aspects of the coal microfacies which probably play a role in the release of oil from coal seams in natural conditions are also discussed

archean gold relation to granulite formation and redox zoning in the crust the archean was the principal period for gold mineralization these rocks compose 12 of the exposed crust but have produced more than half of the world9s gold most major lode deposits formed at 2 7 0 2 ga this corresponds to the principal time of crustal thickening and stabilization an essential part of which was formation of granulite the anhydrous refractory base for the crust upward streaming of mantle co 2 along shear zones in the lower crust is one means for dehydrating amphibolite to form granulite and is accompanied by removal of large ion lithophile lil elements to higher crustal levels archean lode gold deposits were formed along major shear zones at intermediate crustal depths they are enclosed by zones of co 2 metasomatism many of them kilometres in extent 13 c data indicate that the co 2 is juvenile some major archean deposits have been shown to have formed from relatively oxidized hydrothermal fluids co 2 streaming with lil element depletion could only have occurred under relatively oxidized conditions that permitted a free co 2 vapor to exist in the lower crust such conditions would also have favored dissolution of gold and associated sulfide and their transfer to the mid crust in a co 2 h 2 o fluid the h 2 o coming from dehydration of amphibolite

reflections on cohmap cohmap cooperative holocene mapping project had its start in the 1970s with the intent to compare atmospheric general circulation models with quantitative palaeoclimatic reconstructions based on stratigraphic pollen analysis as the sophistication of the models increased and as additional palaeoclimatic indicators lake levels marine microfossils were incorporated in the reconstructions the programme expanded to global coverage through the participation of numerous collaborators the carefully nurtured dual approach of modelling and data analysis was strengthened by continued testing of one against the other with emphasis on interdisciplinary understanding fostered by workshops with the development of new computer models that have higher spatial resolution and improved boundary conditions and with diversification and enlargement of the geographic and temporal coverage of field and analytical data substantial refinements can be anticipated in the understanding of global climatic changes since the

geochemistry of oil seeps and rock samples of the early tertiary section from the northandean flank of the venezuelan andes abstract an organic geochemical study of oil seeps and early to middle tertiary source rocks of the northandean flank naf of the venezuelan andes range was performed to establish the possible contribution of terrestrial source rocks to the oil accumulations in the unexplored southern part of the maracaibo basin source rocks were identified within the paleocene barco and los cuervos formations and the late eocene oligocene carbonera formation biomarker distributions indicate a terrigenous organic source for these units geochemical modeling performed by parnaud et al 1995 indicated plio pleistocene oil generation for the orocue group and middle miocene to plio pleistocene oil generation for the carbonera formation geochemical modeling also indicates that the quantity of crude oil expelled by the carbonera formation is four times that expelled by the orocue group barco and los cuervos formations a northeast to southwest variation from marine to terrestrial oil seeps was identified based on sterane and terpane distributions the marine oil seeps appear to be derived from the la luna source rocks the characteristics of the mixed oils suggest contributions from different sources la luna and a terrestrial source rock most likely the orocue group or carbonera formation coals source facies similar to those in the los cuervos and carbonera formations coals are most likely the main source rocks of terrestrial oil seeps in the naf

late quaternary glaciation of the cordillera real bolivia glacial geological studies in tropical mountain areas of the southern hemisphere can be used to address two issues of late pleistocene climate change the global synchroneity of deglaciation and the magnitude of temperature reduction in the tropics radiocarbon dates from the cordillera real and from other areas in peru and bolivia suggest that late pleistocene glaciation culminated between 14 000 and 12 000 yr bp followed by rapid deglaciation because deglaciation was apparently synchronous with that in northern hemisphere regions insolation change at high latitudes may not have been the only factor that produced global deglaciation at this time late pleistocene glaciation in the cordillera real culminated when precipitation was 200 mm yr 1 higher and temperatures were 3 5 1 6 c lower than today this produced an equilibrium line altitude depression of about 300 100 m on the western side of the cordillera prior to this conditions were drier and probably at least as cold however the lack of moraines in the cordillera real dated to the last glacial maximum ca 18000 yr bp precludes using the equilibrium line altitude method to quantitatively evaluate the discrepancy between warm sea surface temperatures and cold terrestrial conditions reconstructed with other proxies for this time period

strain pattern and deformational history in the eastern part of the cauvery shear zone southern india abstract regional structural mapping guided by remote sensing interpretation in the eastern part of the cauvery shear zone csz southern granulite terrain reveals a structural framework of two major boundary shear zones interlinked by a set of sigmoidal shear belts the strain pattern and deformational history are manifest in terms of two major episodes d1 and d2 while d1 structures are well preserved in low strain areas the d2 fabrics are well reflected in high strain belts enveloping the low strain domains our multiscale structural observations can be modelled in terms of a plan view duplex showing a cross sectional flower structure related to regional transpression resulting from late neoproterozoic collisional processes in the eastern gondwana

fluid assisted granulite metamorphism a continental journey abstract lower crustal granulites which constitute the base of all continents belong to two series high pressure granulites generated by crustal thickening subduction and ultra high temperature granulites associated with crustal extension fluid inclusions and metasomatic features indicate that the latter were metamorphosed in the presence of low water activity fluids high density co2 and brines which have invaded the lower crust at peak metamorphic conditions fluid assisted granulite metamorphism high pressure and ultra high temperature granulites commonly occur along elongated paired belts they were formed from the early proterozoic onwards during a small number of active periods lasting a few hundreds of m y these periods were separated from each other by longer periods of stability each period ended with the formation of a supercontinent whose amalgamation coincided with low to medium pressure ultra high temperature granulite metamorphism immediately before continental break up it is proposed that large quantities of mantle derived co2 stored in the lower crust at the final stage of supercontinent amalgamation are released into the hydro and atmosphere during breakup of the supercontinent fluid assisted granulite metamorphism therefore appears to be an important mechanism for transferring deep mantle fluids towards the earth s surface possible consequences were for example the sudden end of proterozoic glaciations as well as the post cambrian explosion of life

fluids in granulite facies metamorphism a comparative oxygen isotope study on the south india and adirondack high grade terrains oxygen isotope compositions have been determined for samples from the south india archean to pro terozoic and northwest adirondack late proterozoic high grade terrains delta 18 o values of charnockites and related orthogneiss protolith from the prograde amphibolite facies to granulite facies transition zone in south india range from 5 9 to 8 4 charnockites khondalites sillimanite gneisses and retrogressed gneisses from the interior of the granulite facies terrain average 2 higher than orthogneisses of the transition zone individual minerals in incipient charnockitic net veins as at kabbaldurga karnataka and ponmudi kerala have delta 18 o identical to minerals of their non charnockitic host rocks quartz delta 18 o values of the northwestern adirondack granites and gneisses average 3 4 higher than those from the indian rocks the two terrains are thus isotopically distinct which may reflect differences in premetamorphic history or different degrees of communication with external

thermal generation of carbon dioxide and organic acids from different source rocks carbon dioxide and organic acids are claimed to play an important role in sandstone diagenesis in the present work hydrous pyrolysis was used for a qualitative comparison of the relative potential of different source rocks to generate organic acids and carbon dioxide in addition the carbon isotopic composition of the generated carbon dioxide was determined experiments with three immature source rocks are described a miocene brown coal from germany a coal from the middle jurassic ness formation in the northern north sea and a rich marine type ii source from the late jurassic kimmeridge clay formation onshore u k both coal samples are typically humic a stepwise heating program from 150 to 365 c was used closed pyrex tubes containing immature coal rmm 0 37 were heated in order to measure vitrinite reflectance evolution the experimental results were related to vitrinite reflectance as a maturity reference parameter and to a kinetic model using kinetic parameters for carbon dioxide generation burnham a k and sweeney j j 1989 geochim cosmochim acta53 2649 2657 differences in the yiels and carbon isotopic composition were obtained between the marine type ii source rock and the coals organic acid generation converted between 1 and 3 of the organic carbon carbon dioxide was the major oxygen containing component with molar yields 5 10 times that of organic acids the experimental yields of organic acids and carbon dioxide were compared to a first order kinetic model for carbon dioxide generation and a reasonable correspondence in the transformation ratio curves was observed

pathways of calcrete development on weathered silicate rocks in tamil nadu india mineralogy chemistry and paleoenvironmental implications abstract poorly documented yet spectacularly thick and extensive outcrops of calcrete hardpan occur on gneiss in the semiarid region of coimbatore south india the hardpan caps a series of residual plateaux forming the present day continental divide and grades into large expanses of vertisols characteristic calcrete and vertisol profiles were logged along toposequences and sampled for macro and micromorphological study and for chemical and mineralogical composition strontium isotopic analyses revealed that the calcrete is derived from in situ weathering of ca bearing primary minerals of the saprolite which is rich in ankerite ca amphiboles and ca plagioclase the macroscale analysis revealed a range of facies developed within the gneiss saprolite but in terms of relative chronology the nodular hardpan has the longest history two evolutionary pathways leading to nodular hardpan formation have been established the first occurs entirely within a vadose environment whereas the second begins within a phreatic environment before continuing to develop in vadose conditions the ability to identify and map these generic categories of calcrete constitutes a potential tool for reconstructing paleotopography and paleogroundwater levels the bedrock weathering derived nodular hardpan is blanketed by a laminar facies that correlates with an eolian event with marine sr signatures this suggests influx of ca dust from the arabian sea continental shelf during a pleistocene sea level low stand it defines an important benchmark in the chronology of the area and highlights the potential antiquity of the thick calcrete profiles

effects of thermal maturation on stable organic carbon isotopes as determined by hydrous pyrolysis of woodford shale acquiring crude oils that have been expelled from the same rock unit at different levels of thermal maturation is currently not feasible in the natural system this prevents direct correlation of compositional changes between the organic matter retained in a source rock and its expelled crude oil at different levels of thermal maturation alleviation of this deficiency in studying the natural system requires the use of laboratory experiments natural generation of petroleum from amorphous type ii kerogen in the woodford shale may be simulated by hydrous pyrolysis which involves heating crushed rock in contact with water at subcritical temperatures 374 c four distinct stages of petroleum generation are observed from this type of pyrolysis 1 pre oil generation 2 incipient oil generation 3 primary oil generation and 4 post oil generation the effects of thermal maturation on the 13c values of kerogen bitumen and expelled oil like pyrolysate from the woodford shale have been studied through these four stages of petroleum generation similar to the natural system the kerogens isolated from the pyrolyzed rock showed no significant change in 13c this suggests that the 13c value of kerogens may be useful in kerogen typing and oil to source rock correlations 13c values of bitumens extracted from the pyrolyzed rock showed an initial decrease during the incipient oil generation stage followed by depletion during the primary and post oil generation stages this reversal is not favorable for geochemical correlation or maturity evaluation saturated and polar components of the bitumen show the greatest 13c variations with increasing thermal maturation the difference between the 13c of these two components gives a unidirectional trend that serves as a general indicator of thermal maturation and is referred to as the bitumen isotope index bii 13c values of the expelled pyrolysates show a unidirectional increase with increasing thermal maturation the constancy and similarity of 13c values of the aromatic components in the expelled pyrolysates and bitumens with increasing thermal maturation encourages their use in oil to oil and oil to source rock correlations isotopic type curves for expelled pyrolysates indicate that they may be useful in oil to oil correlations but have a limited use in oil to source rock correlations

a magnetotelluric study from over dharwar cratonic nucleus into billigiri rangan charnockitic massif india abstract the electrical resistivity structure of the crust beneath the dharwar craton in southern india was investigated by magnetotelluric method in the present study a northwest southeast oriented 220 km long profile of 18 stations with a station spacing of 10 15 km is used the profile extends from dharwar cratonic nucleus in the north to billigiri rangan charnockitic massifs in the south time series data are processed to get the apparent resistivity and phase the dominant geoelectric strike direction 75 was calculated in a period range of 0 01 1000 s the data are rotated to 75 strike direction two dimensional inversion is carried out by using the non linear conjugate gradient scheme for both apparent resistivity and phase our inversion results show a conductor in the northern side of the profile and two distinct prominent conductors in southern part of the profile the mid lower crust in southern part of the profile shows less resistive 2 flushed terranes regional scale carbonation occurred in late archaean is associated with chitradurga shear zone and in late proterozoic is associated with salem attur shear zone the co 2 rich fluids derived during that time might have exhausted in dehydration reactions later events such as the indian plate passing over several hotspots and the metasomatized fluids associated with the cretaceous tertiary magmatism in the region is the reason for observed low resistivity near billigiri rangan massif and surrounding regions in the south

fe ti oxide chronometry with application to granulite formation abstract ilmenites occurring in amphibolite and granulite facies orthogneisses in sri lanka yield precise u pb ages coexisting ilmenite magnetite in the granulite facies rocks indicate temperature conditions of 680 60 c and log o 2 17 0 1 2 the u pb age of 498 2 3 3 ma obtained for ilmenite is indistinguishable from the pb pb age of 501 5 ma derived for coexisting silicate minerals and suggests that oxide silicate equilibration has been preserved in contrast fe ti oxides in adjacent amphibolitefacies rocks indicate a temperature of 830 60 c and log o 2 12 7 0 8 and record u pb ages of 1093 7 7 6 ma and 1095 4 4 2 ma these ages are some 600 ma older than those obtained for coexisting silicate phases in the same sample or for both oxide and silicate minerals in the nearby charnockite and relate either to the time of emplacement of the granitic precursor or to some earlier metamorphic episode these results suggest that temperature o2 and fluid conditions estimated from fe ti oxides should be interpreted with extreme caution