calcic amphibole equilibria and a new amphibole plagioclase geothermometer there is currently a dearth of reliable thermobarometers for many hornblende and plagioclase bearing rocks such as granitoids and amphibolites a semi empirical thermodynamic evaluation of the available experimental data on amphibole plagioclase assemblages leads to a new thermometer based on the aliv content of amphibole coexisting with plagioclase in silica saturated rocks the principal exchange vector in amphiboles as a function of temperature in both the natural and experimental studies is left na square 1 right a left alsi 1 right t1 we have analysed the data using 3 different amphibole activity models to calibrate the thermometer reactions 1 edenite 4 quartz tremolite albite 1 2 pargasite 4 quartz hornblende albite 2 the equilibrium relation for both 1 and 2 leads to the proposed new thermometer t frac 0 677p 48 98 y 0 0429 0 008314 ln k and k left frac si 4 8 si right x ab plag where si is the number of atoms per formula unit in amphiboles with p in kbar and t in k the term y represents plagioclase non ideality rtln ab from darken s quadratic formalism dqf with y 0 for xab 0 5 and y 8 06 25 5 1 xab 2 for xab 0 5 the best fits to the data were obtained by assuming complete coupling between al on the t1 site and na in the a site of amphibole and the standard deviation of residuals in the fit is 38 c the thermometer is robust to ferric iron recalculation procedures from electron probe data and should yield temperatures of equilibration for hornblende plagioclase assemblages with uncertainties of around 75 c for rocks equilibrated at temperatures in the range 500 1100 c the thermometer should only be used in this temperature range and for assemblages with plagioclase less calcic than an92 and with amphiboles containing less than 7 8 si atoms pfu good results have been attained on natural examples from greenschist to granulite facies metamorphic rocks as well as from a variety of mafic to acid intrusive and extrusive igneous rocks our analysis shows that the pressure dependence is poorly constrained and the equilibria are not suitable for barometry

numerical modelling of the hydro mechanical behaviour of fractured rock masses abstract results are presented from an investigation into the hydro mechanical response of a rock mass to changes in effective stress associated with fluid extraction numerical models of regularly and randomly fractured reservoirs have been created using udec the distinct element code relationships between permeability and stress state have been established in regions immediately adjacent to simulated wellbores and more generally throughout the fractured reservoirs the effects of in situ stress state hydraulic boundary conditions and scale have been investigated the results demonstrate that numerical modelling combined with analytical solutions can be employed to investigate coupled flow deformation analysis realistically for simple geological situations the relationships presented here relating fracture pemeability to stress field changes will be helpful in understanding the behaviour of naturally fractured reservoirs during pressure depletion

experimental calibration of the aluminum in hornblende geobarometer with application to long valley caldera california volcanic rocks a new geobarometer based on the al content of igneous hornblendes in equilibrium with melt fluid biotite quartz sanidine plagioclase sphene and magnetite or ilmenite has been calibrated experimentally the calibration was performed by equilibrating the required phase assemblage over the pressure range 2 8 kbar at 740 780c and then analyzing euhedral hornblendes in equilibrium with glass melt experiments were performed on natural samples of both volcanic and plutonic rocks earlier empirical calibrations of this geobarometer relied on analyzing natural hornblendes from plutons with the required phase assemblage and inferring pressure from nearby metamorphic country rocks the experimental calibration differs from the empirical calibrations especially above 5 kbar and shows that the al content of hornblendes in equilibrium with the required phase assemblage is greater for a given total pressure than previously thought the geobarometers uncertainty is dramatically reduced the derived equation is p plus minus 0 5 kbar 3 minus 3 46 plus minus 0 24 4 23 plus minus 0 13 al sup t the geobarometer is applied to post bishop tuff volcanic rocks from long valley caldera california and reveals that most rhyodacites in this complex erupted from depths of about 6 km these eruptions occurred over 500 000 yr suggesting that the rhyodacitic magma reservoir beneath longmore valley had reached a steady p depth t state less

the origin of rapakivi texture by sub isothermal decompression abstract the rapakivi texture plagioclase mantled k feldspar ovoids rounded quartz megacrysts and euhedral plagioclase megacrysts in a more fine grained granitic matrix has been studied in five proterozoic 1 64 1 55 ga anorogenic rapakivi granite batholiths in the fennoscandian shield with emphasis on mineral stability and inherited cores k feldspar ovoids and rounded quartz megacrysts with deep embayments consist principally of a core zone and an outer melted and recrystallized zone when the k feldspar ovoids are mantled by plagioclase the outermost part of the mantle is homogeneous but towards the k feldspar a skeletal texture develops intensive parameters obtained from different textural positions show that mineral inclusions in cores of the k feldspar ovoids and quartz megacrysts were formed at low t 680 720 c and high p 5 6 kbar conditions while inclusions in the periphery of ovoids and the plagioclase mantles display high t 780 c and intermediate to low p 3 5 1 kbar the lowest p is comparable to that during solidification of the matrix the total water equivalent of the volatile content in the magma has been calculated as 2 5 the amount of solids in the magma at 1 kbar has been estimated as 40 theoretical calculations and experimental data for mineral stabilities in granitic systems suggest that the texture formed when a crystal saturated kfsp qtz pl 60 and volatile undersaturated a type granite magma was transported under approximately constant temperature 760 780 c from the lower middle crust 5 6 kbar to upper crustal levels according to phase stabilities in the eutectoid granite system quartz and k feldspar were resorbed but plagioclase remained stable and precipitated during this sub isothermal rise of magma textural presence of disequilibrium textures and mineralogical presence of different mineral assemblages including relics evidence of a sub isothermal rise of the rapakivi magmas is better preserved in subvolcanic and contact varieties of rapakivi granites than in the more deep seated rapakivi granites formed by slow cooling

organic geochemical and petrographic characteristics of the miocene salif organic rich shales in the tihama basin red sea of yemen implications for paleoenvironmental conditions and oil generation potential abstract this study is the first investigation which provides information regarding the organic geochemical and petrographic characteristics of miocene salif organic rich shales from tihama basin in the red sea yemen we evaluate organic matter content type maturity and oil generation potential as well as depositional environmental conditions the total organic carbon toc contents of the miocene salif shales vary between 0 59 and 5 40 indicating fair to very good source rock potential the salif shales have hydrogen index values in the range of 64 576 mg hc g toc the organic matter in the salif shales are dominated by type ii kerogen and mixed ii iii kerogens with a minor contribution of type iii kerogen as supported by kerogen microscopy this is also confirmed by their biomarker and carbon isotope results which indicate that the salif shales were deposited in highly reducing marine conditions and received high contributions of aquatic organic matter e g algal and microbial and terrigenous organic matter consequently the salif formation is likely to be an oil source rock maturity indicators such as vitrinite reflectance and pyrolysis data i e tmax and pi indicate that most of the salif shale samples are generally thermally mature at the early mature to peak oil window stage the new data presented in this paper suggest that early mature oil has been generated from miocene salif organic rich shales so exploration strategies should focus on the known location of miocene salif organic rich shales for predicting the location of the source kitchen

deformation resulting from regional extension during pluton ascent and emplacement central sierra nevada california solid state foliation lineation small scale folds and domainal shear zones have developed in preexisting granitic and minor metasedimentary wallrock during a combined deformation involving a regional extensional strain and ascent and emplacement of the mt givens pluton mgp mylonite is common throughout much of the 1 2 km wide 10 km long shear zone with ultramylonite best developed near the contact with the mgp which itself lacks significant solid state deformation migmatization accompanies ultramylonite formation in the northern half of the zone but both these features are poorly developed or absent in its southern half where the shear zone is distributed over a wider area strain estimates across the shear zone using microgranitic enclaves as markers show a positive gradient and an increasing ratio of simple shear pure shear towards the mgp microprobe analyses on hornblende and plagioclase yield pressure and temperature estimates of 3 5 kb and 680 c respectively during shear zone formation at least at its late stages of development zircon pb u and 40 ar 39 ar ages constrain timing of the high temperature movement on the shear zone to 90 ma essentially the age of the mgp although movement immediately prior to that time appears likely we speculate that a regional extensional shear zone was developing prior to the emplacement of the mgp which as it ascended heated the wallrock facilitating both further strain in the zone as well as buoyant rise of the pluton along the zone the mgp was near its critical melt fraction during the last several kilometers of its ascent and could have possessed sufficient viscosity strength to impose a weak shear strain on the shear zone rocks although most of the foliation and extensional features in the zone are probably related to the regional strain field late stage folding of the foliation is attributed to shouldering aside of the wallrock by the mgp during the last increment of its ascent and final emplacement

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

hydromechanical behavior of a deformable rock fracture subject to normal stress lbl 12297 preprint to be published in the journal of geophysical research hydromechanical behavior of a deformable rock fracture subject to normal stress y w tsang and p a witherspoon january 1981 two week loan copy this is a library circulating copy which may be borrowed for two weeks for a personal retention copy call tech info diu is ion ext 6782 prepared for the u s department of energy under contract w 7405 eng 48

plagioclase stability at elevated temperatures and water pressures the breakdown of plagioclase to zoisite kyanite quartz and a more sodic plagioclase in the system naalsi sub 3 o sub 8 caal sub 2 si sub 2 o sub 8 h sub 2 o has been investigated with reversed reactions at 8 9 and 10 kbar at these pressures all plagioclase compositions from approx an sub 40 to an sub 100 break down along the same p t curve as pure anorthite which can be described by the equation p 4590 20 4t p bars t sup 0 c the isobaric curves in the t x section are thus represented by a horizontal line constant temperature between approx an sub 40 and an sub 100 at compositions more sodic than approx an sub 40 the curves dip rather sharply to lower temperatures in the regions beneath the curves the composition of sodic plagioclase along the down dipping limb is in equilibrium with zo ky qz the remarkable behavior in the an sub 40 an sub 100 region suggests that under the hydrothermal conditions of this study regions of ordered anorthite develop in the plagioclase and subsequently react with water as would independent crystals of an partial melting of pure an in the presence of water begins at 10 2 kbar and 725 sup 0 c at 10 8 kbar a region of partial melt extends atmore nearly the same temperature from an sub 30 to an sub 100 jmt less

source rock characterization and oil generating potential of the jurassic madbi formation onshore east shabowah oilfields republic of yemen abstract the hydrocarbon source rock potential of shales from the jurassic madbi formation was evaluated using organic geochemistry rock eval pyrolysis toc and bitumen extraction and organic petrology very good source rock potential is suggested by high values of total organic carbon content toc 2 0 wt and high extractable organic matter content and hydrocarbon yields 11 000 and 6000 ppm respectively the madbi formation samples have high hydrogen index hi and low oxygen index oi values most of the samples in the study area are thermally mature and contain oil prone type i and type ii kerogen vitrinite reflectance ro values for the madbi shale samples were measured from 0 74 to 0 89 tmax values range from 430 to 438 c which are in reasonably good agreement with vitrinite reflectance data reveal that the madbi shales are at the early to peak mature stage on the basis of biomarker maturity parameters these shales are thermally mature shales of the madbi formation contain abundant hydrogen rich kerogen liptinite up to 55 and therefore good oil generating potential is anticipated this is supported by high hydrogen indices hi of up to 400 mg hc g toc and early to peak mature oil window range

the genesis of coal from the viewpoint of coal petrology abstract the genesis of the microscopic constituents of coal macerals and of maceral associations microlithotypes representing various coal facies is discussed in the light of recent advances that have been made in the study of coals and modern peats peat microscopy especially promoted the understanding of humification and biological gelification both of which are decisive for the genesis of huminites vitrinites in brown coals and hard coals respectively microbial activity during peatification has been documented by chemists microbiologists and petrologists and recently by electron microscopical observations in coals this activity leads to the incorporation of lipid substances into the humic matter and later influences the chemical physical and technological properties of vitrinites geochemical gelification transforms the huminites of brown coals into the vitrinites of bituminous coals and is probably caused by the onset of bitumen generation in coal in this process the hydrogel brown coal is transformed to the bitumogel bituminous coal coal as a source rock for oil has become an important research subject for coal petrologists and oil exploration the formation of more or less liquid bitumen and its later cracking to gaseous hydrocarbons leads to the coalification jumps of the macerals especially liptinites and vitrinites and to the generation of secondary macerals like exsudatinite bitumen and micrinite dead carbon bituminization in coal has been revealed by the use of fluorescence microscopy which also found the presence of new liptinite macerals bituminite fluorinite and exsudatinite and suggests a higher proportion of algal material in coals than was thought earlier the genesis of various types of inertinite macerals will probably become an increasingly important subject of research especially with regard to rank inertinites that seem to attain their high inertinitic reflectance initially during coalification besides the origin of macerals the origin of various coal facies in terms of maceral associations is considered in relation to the palaeogeographic depositional milieu the peat forming vegetation palaeoclimate water and nutrient supply acidity marine and calcareous influence and fire with examples from euramerican carboniferous coals gondwana coals and tertiary brown coals vegetation water and oxygen supply eh conditions are most important for the generation of coal facies vegetation has been reconstructed with the help of palaeobotany including palynology cuticular analysis and wood anatomy in brown coals and with the study of petrified permineralized peats preserved in coal balls the microscopical investigations of botanically recognizable plant remains isolated from coals or accompanying rocks has been especially informative however the results of palynological and cuticular analyses should be evaluated with caution considering the varying resistance of palynomorphs and cuticles and in the case of palynomorphs their possible extrapaludal origin microscopical studies of modern peats that were derived from different types of vegetation growing in different hydrological environments have been very helpful in interpreting coal facies especially in brown coals the much disputed origin of brown coal lithotypes is considered in detail for hard coals there seems to be agreement that coal layers rich in vitrites and liptinite poor clarite were deposited in wet forest swamps that microlayered liptinite rich clarites are sub aquatic humic muds and that inertinite rich durites represent oxidized peats the origin of liptinite rich durites is controversial either subaquatic muds or oxidized peats the latter perhaps from raised bogs a recent trend in the literature is the assumption that many if not all mineable coal seams have been deposited in raised bogs under ombrogenous oligotrophic conditions although raised bogs with a dense arborescent vegetation are known from borneo it seems not probable that most seams which were deposited in foredeeps or steadily sinking graben zones are of ombrogenous origin although a succession from relatively wet and eutrophic to relatively dry and oligotrophic conditions may be true for occasional seams but as in modern peats striking changes of coal facies are commonly caused by hydrological events e g inundations as a consequences of crevasses or of fires that burned the peat the origin of the inertinite rich gondwana coals is discussed in relation to their specific climatic conditions and a comparison with sub arctic peats is recommended coals influenced by marine and calcareous conditions are characterized by high contents of sulfur and pyrite as well as by hydrogen rich vitrinites with a relatively low reflectance and high fluorescence all due to a strong bacterial activity in peats of low acidity proposals for further research are made in the conclusions

tertiary stratigraphy and basin evolution southern sabah malaysian borneo abstract new mapping and dating of strata in the southern part of the central sabah basin in northern borneo has made it possible to revise the lithostratigraphy and chronostratigraphy of the area the recognition in the field of an early miocene regional unconformity which may be equivalent to the deep regional unconformity recognised offshore has allowed the development of a stratigraphic framework of groups and formations which correspond to stages in the sedimentary basin development of the area below the early miocene unconformity lies ophiolitic basement which is overlain by an accretionary complex of eocene age and a late paleogene deep water succession which formed in a fore arc basin the late paleogene deposits underwent syn depositional deformation including the development of extensive melanges all of which can be demonstrated to lie below the unconformity in this area some localised limestone deposition occurred during a period of uplift and erosion in the early miocene following which there was an influx of clastic sediments deposited in delta and pro deltaic environments in the middle miocene these deltaic to shallow marine deposits are now recognised as forming two coarsening upward successions mapped as the tanjong and kapilit formations the total thickness of these two formations in the central sabah basin amounts to 6000 m only half of the previous estimates although the total stratigraphic thickness of cenozoic clastic strata in sabah may be more than 20 000 m

calcic amphibole equilibria and a new amphibole plagioclase geothermometer reply to the comment of poli and schmidt although only aliv appears in our thermometer expression this in no way infers that we believe tschermakite or katophorite kaersutite and other substitutions to be unimportant a careful reading of our earlier papers makes it clear that the reverse is true e g holland and richardson 1979 will et al 1990a b guiraud et al 1990 indeed in b and h p 211 we state that natural and synthetic amphiboles are dominated by a combination of edenite pargasite hornblende and hastingsite substitutions what we endeavoured to point out was that because of the nature of reaction 1 and the use of mixing on sites activity models the extent of al substitutions on m2 or na on m4 do not materially influence our expression for k1 and consequently our thermometer certainly any sophisticated activity model for amphibole explicitly should account for all cross site interactions between m tl and a site cations as alluded to by p and s in reference to docka et al 1987 as well as o3 site anions however such a day currently is well away and mixing on sites with modifications as outlined above and to be detailed in t j b holland and j d blundy in preparation seems rather promising for the purposes of amphibole thermometry we do not share the rather negative and pessimistic outlook on activity models and thermobarometry implicit in p and s comments

rock eval tmax suppression documentation and amelioration the rock eval thermal maturation parameter tmax may occasionally be suppressed relative to surrounding rock units this is commonly assumed to result from either a bitumen contribution to the s2 peak or the presence of sulfur rich and hence thermally labile kerogen the phenomenon is frequently coincident with a high natural gamma ray signature and elevated rock eval hydrogen index hi and total organic carbon toc contents determination of thermal maturity of such units relies either on the interpolation of tmax from surrounding units or the direct estimation of the extent of suppression on a given sample the latter may be required if the available samples are restricted to conventional or sidewall core material representative of imited stratigraphic intervals the second white speckled shale part of the cretaceous colorado group in the alberta basin displays tmax suppression over part of its thickness a consistent relationship emerges from calculating a linear regression of tmax as a function of either toc or hi for several wells at different levels of thermal maturity below values of about 453 c late oil window tmax is suppressed by about 1 c for every increase in hi of 50 mg hydrocarbon g toc thus tmax suppression in the second white speckled shale can be corrected by extrapolating all tmax values to a constant hi of 100 to 150 mg hydrocarbon g toc values typical of type iii kerogen

pressure temperature and time indicators in mafic schist their application to reconstructing the polymetamorphic history of vermont mineral chemistry and overgrowth relationships in mafic schist from vermont are shown to be sensitive indicators of pressure temperature and relative time and to be good chronicles of the paleozoic history of this polymetamorphic terrane within the common assemblage amphibole chlorite epidote plagioclase quartz ti phase carbonate k mica fe 3 oxide electron microprobe analyses show that increasing metamorphic grade as defined by intercalated pelitic schist is recorded by an increase in the edenite glaucophane and tschermakite contents of amphibole in the anorthite content of plagioclase and in the substitution of al vi f 2 ti al iv for fe 2 mg mn si in biotite chlorite and muscovite with increasing pressure the glaucophane component of amphibole increases for medium pressure metamorphism the albite oligoclase gap is in the garnet zone where amphibole has between 1 2 and 1 8 formula proportion al iv and al vi fe 3 ti cr this gap is below the garnet isograd in low pressure mafic schist where al iv and al vi fe 3 ti cr in the amphibole are both less than 0 6 mineral growth periods observed are characterized by metamorphic grade and facies series and are assigned to two ordovician taconic and two devonian acadian events silurian devonian mafic schist in northeastern vermont records two periods of low pressure devonian metamorphism these events are expressed by medium pressure and low pressure metamorphism in the cambrian and ordovician rocks to the west and south in the pre silurian rocks high pressure and medium pressure metamorphism is assigned to the ordovician the observed high pressure metamorphism is confined to a 110 by 40 km area along the green mountain anticlinorium axis in north central vermont

petrological and geochemical characterization of candiota coal seams brazil implication for coal facies interpretations and coal rank abstract seven coal seams from cores of the borehole m iv c 101 candiota coalfield located in rio grande do sul state southern part of the parana basin were analyzed by coal petrographical and organic geochemical methods the seams occur in the rio bonito formation guata group tubarao supergroup of the parana basin and are of permian artinskian kungurian age the composition rank coal facies and depositional environment characterization were made based on lithotype maceral and microlithotype analyses the data were then used in the definition of different types of facies critical petrographical indices and were displayed in diagrams of coal facies in addition coal seams samples from candiota mine were analyzed by proximate total moisture and gross calorific values and were classified using the united nations economic commission for europe un ece classification in addition rock eval pyrolysis liquid chromatography gc and gc ms analyses were made to obtain independent parameters on coal rank and organic matter composition and environment of deposition the results suggest deposition in open mires with elevated contents of detrital macerals and clay minerals and also limno telmatic coal facies coal bearing sequence of coal seams represent a back barrier setting according to the international classification un ece candiota coals are in the subbituminous or low rank coal a stage results from geochemical analyses showed that terrestrial organic matter is predominant as indicated by hydrogen and oxygen indices carbon preference indices and the sterane distribution geochemical maturity parameters such as the 20 s 20 s 20 r and ratios for c 29 regular steranes support the low level of rank maturity as indicated by the vitrinite reflectance measurements 0 41 0 45 and gross calorific values

variations in the geochemistry of closely interbedded oil prone coals and shales paralic and deltaic environments frequently contain closely interbedded oil prone coals and carbonaceous shales of similar organic facies however differences in depositional and diagenetic conditions can result in significant variations in geochemistry between these coals and shales these variations are observed in sediments from a range of ages and areas including australia new zealand and indonesia for example pristane phytane and pristane n c sub 17 ratios are frequently higher in coals than in associated shales although n alkane distributions are similar the c sub 27 ts tm ratios are frequently much lower in coals although most other biomarker ratios are generally the same for coals and shales however absolute biomarker concentrations particularly of c sub 27 tm hopane can be two to four times higher in coals significantly many coals contain high concentrations of diasteranes equivalent to those observed in shales differences in other parameters such as the c sub 30 diahopane c sub 30 hopane ratios and pyrolysate compositions are also evident data indicate that rocks begin to become more coal like at tocs of approximately 25 the variations in these parameters are probably the result of variability in early depositional and diagenetic conditions such as eh ph and microbial action in addition these parameters are probably influenced by the effectsmore of an organic vs an inorganic matrix the impact of this variability must be considered when conducting oil source correlation studies and when assessing the relative contributions of coals and shales to the generation of oil in a basin less

organic geochemical characteristics and depositional environment of the tertiary tanjong formation coals in the pinangah area onshore sabah malaysia article i nfo article history the tertiary tanjong formation coals exposed in the west middle block of the pinangah coalfield central part of southern sabah were analyzed and their depositional environments were interpreted the tertiary tanjong coals are humic and generally dominated by vitrinite with significant amounts of liptinite and low amounts of inertinite macerals total organic carbon contents toc of the coals range from 51 2 to 77 7 wt and yield of bitumen values ranging from 57 300 to 140 000 ppm which meet the standard as a source rock with good hydrocarbon generative potential in support good liquid hydrocarbons generation potential can be expected from the tanjong coals based on significant liptinitic content 15 this is supported by their high hydrogen index up to 300 mg hc g toc consistent with type ii and mixed type ii iii kerogens and py gc s2 pyrograms with n alkane alkene doublets extending beyond c30 the coal samples have vitrinite reflectance values in the range of 0 42 0 66 ro indicating immature to early mature stage for hydrocarbon generation these vitrinite reflectance values also indicated that the tanjong coals are with sub bituminous b a and high volatile bituminous c rank tmax values ranging from 419 to 451 c are good agreement with the vitrinite reflectance data this is supported by biomarker maturity parameters as suggested by the c32 homohopane the saturated fraction of the tanjong coals are characterized by dominant odd carbon numbered n alkanes n c23 to n c33 high pr ph ratios 8 18 high tm ts ratios 6 28 and pre dominant of regular sterane c29 all biomarker parameters clearly indicate that the organic matter was de rived from terrestrial inputs and deposited under oxic condition

organic geochemical characteristics and depositional environments of the jurassic coals in the eastern taurus of southern turkey abstract in this study organic matter content type and maturity as well as some petrographic and physical characteristics of the jurassic coals exposed in the eastern taurus were investigated and their depositional environments were interpreted the total organic carbon toc contents of coals in the feke akkaya kozan gedikli and kozan kizilinc areas are 24 54 66 78 and 49 15 respectively the feke akkaya and kozan kizilinc coals have low hydrogen index hi values while the kozan gedikli coals show moderate hi values all coal samples display very low oxygen index oi values the kozan gedikli coals contain type ii organic matter om the feke akkaya coals contain a mixture of type ii and type iii om and the kozan kizilinc coals are composed of type iii om sterane distribution was calculated as c27 c29 c28 from the m z 217 mass chromatogram for all coal samples tmax values for the feke akkaya kozan gedikli and kozan kizilinc coals are 439 412 and 427 c vitrinite reflectance values ro for the feke akkaya and kozan kizilinc coal samples were measured as 0 65 and 0 51 and these values reveal that the feke akkaya and kozan kizilinc coals are at subbituminous a or high volatile c bituminous coal stage on the basis of biomarker maturity parameters these coals have a low maturity the pristane phytane pr ph ratios for the feke akkaya kozan gedikli and kozan kizilinc coals are 1 53 1 13 and 1 25 respectively in addition all coals show a homohopane distribution which is dominated by low carbon numbers and c35 homohopane index is very low for all coal samples all these features may indicate that these coals were deposited in a suboxic environment the high sterane hopane ratios with high concentrations of steranes low pr ph ratios and c25 c26 tricyclic ratios 1 may indicate that these coals formed in a swamp environment were temporarily influenced by marine conditions

generation and expulsion of oils from permian coals of the sydney basin australia abstract organic geochemical and petrological assessment of coals coaly shales and fine grained sediments coupled with organic geochemical analyses of oil samples all from permo triassic sections of the southern sydney basin australia have enabled identification of the source for the widely distributed oil shows and oil seeps in this region the permian coals have higher hydrogen indices higher liptinite contents and much higher total organic matter extract yields than the fine grained sediments a variety of source specific parameters obtained from n alkanes regular isoprenoids terpanes steranes and diasteranes indicate that the oil shows and seeps were generated and expelled predominantly from higher plant derived organic matter deposited in oxic environments the source and maturity related biomarkers and aromatic hydrocarbon distributions of the oils are similar to those of the coals the oil coal relationship also is demonstrated by similarities in the carbon isotopic composition of the total oils coal extracts and their individual n alkanes extracts from the permo triassic fine grained sediments on the other hand have organic geochemical signatures indicative of mixed terrestrial and prokaryotic organic matter deposited in suboxic environments which are significantly different from both the oils and coal extracts the molecular signatures indicating the presence of prokaryotic organic matter in some of the coal extracts and oils may be due to thin sections of possibly calcareous lithologies interbedded within the coal measures the genetic relationship between the oils and coals provides new evidence for the generation and expulsion of oils from the permian coals and raises the possibility for commercial oil accumulations in the permian and early triassic sandstones potentially in the deeper offshore part of the sydney basin

calcic amphibole equilibria and a new amphibole plagioclase geothermometer reply to the comments of hammarstrom and zen and rutherford and johnson we reaffirm the barometric potential of our amphibole plagioclase thermometer for rocks where and only where the final equilibration temperature is very well constrained in the advantageous case of granitoids with simple thermal histories this temperature may be the wet granitoid solidus at the pressure of interest we emphasise the need for careful petrographic assessment of equilibrium between plagioclase and amphibole before attempting total al barometry and recommend that a relatively large number of pairs are analysed for each sample in rocks with complex post consolidation or fluid flow histories such barometry requires an independent means of determining amphibole equilibration temperature

organic facies and depositional palaeoenvironment of lignites from rio maior basin portugal abstract the rio maior basin portugal is a tectonic depression filled by a pliocene sequence that comprises from floor to roof i kaoliniferous fine sands ii diatomites and lignites iii recent deposits of sandstone and clay the diatomites and lignites form a small dissimetric syncline with alternating seams ten lignite seams were identified and named from floor to roof as f e d c 2 c 1 c b a a and a seams a d e and f are considered to be the main seams the organic fraction consists mainly of macerals of the huminite group with small percentages of inertinite and liptinite groups however the petrographic composition of each seam is distinct particularly with regards to macerals of the huminite and liptinite groups calculation of petrographic indices permitted to plot the coals in facies and palaeoenvironment diagrams five facies have been defined i aquatic ii herbaceous swamp iii mixed swamp with forest and herbaceous vegetation vi forest swamp wetter and v forest swamp drier these lignites are humic coals formed from organic matter of terrestrial origin the peat biomass at the origin of these coals formed from a very diverse vegetation comprising gymnosperms and angiosperms in seams f and occasionally in seams e and d botryococcus algae have also contributed to the biomass peat deposition corresponded to a rheotrophic hydrological regime the water level always remained above the topographic surface of the basin nevertheless during the deposition of seam a in the northern part of the basin the water level was slightly below the topographic surface the organic matter was preserved in anaeorobic conditions

organic facies and maturation of jurassic cretaceous rocks and possible oil source rock correlation based on pyrolysis of asphaltenes scotian basin canada abstract this paper establishes source rock characterization and oil oil and oil source rock correlations of selected organic rich shale source rocks and selected light oils and condensates from jurassic and cretaceous formations of the scotian basin multiple source rocks of kerogen types iia oil prone iia iib oil and condensate prone iib condensate and gas prone iii gas prone and iv nonsource are identified in various stratigraphic horizons vitrinite reflectance and t inmax data indicate variable maturation histories in different parts of the basin which are related to differences in lithology related heat conductivity and the presence of older sediments closer to areas of rifting multiple linear regression and cluster analyses of aromatic hydrocarbon ratios reveal two oil families some kerogen type iib rock extracts match many of the light oil and condensates in terms of the aromatic hydrocarbon distributions a second family of oils could not be correlated with any of the analyzed source rock extracts pyrolysis gas chromatography of asphaltenes from the cohasset a 52 and sable island 3h 58 wells are significantly different in n alkane aromatics and phenol content the asphaltene pyrolyzates of samples from venture b 52 and s desbarres o 76 have a high aromatic content low content of n alkanes and high phenol values s desbarres which is typical of a terrestial source they correlate well with one another and also with sable island light oil the n triumph g 43 whole rock and extract asphaltene pyrolyzates are dominated by normal hydrocarbons with aromatic phenolic and thiophenic compounds in low concentrations suggesting an algal source algal type organic matter may have made a contribution to the cohasset petroleum as its asphaltene pyrolyzate is also dominated by normal hydrocarbons

fluid rock interactions in the lower oceanic crust thermodynamic models of hydrothermal alteration rocks from the lower oceanic crust show both petrologic and isotopic evidence for extensive alteration by circulating hydrothermal fluids derived from seawater deeply circulating fluids may have a substantial but as yet largely undetermined impact on the thermal regime of spreading centers magmatic processes at mid ocean ridges and elemental fluxes at ridge hydrothermal systems in the present study the consequences of water rock interactions during the penetration of seawater into hot lower oceanic crust were investigated using thermodynamic reaction path models alteration assemblages predicted for reaction of an evolving seawater with olivine gabbro gabbronorite and troctolite during heating from 300 to 900 c closely resemble alteration assemblages observed in rock samples from the lower oceanic crust these assemblages include sodic plagioclase actinolite diopsidic clinopyroxene epidote chlorite prehnite analcime quartz at lower temperatures 300 500 c and plagioclase hornblende diopside chlorite trace magnetite at intermediate temperatures 500 700 c the relative abundances of these alteration products show much greater variation with temperature than with water rock w r ratio indicating that variations in the amounts of hydrated minerals such as amphiboles may not be an accurate indication of the w r ratio experienced by rocks in the lower crust since the same amount of fluid may produce widely differing amounts of amphibole at slightly different temperatures depending on the temperature of interaction some rocks in the lower oceanic crust may have experienced much higher w r ratios than has previously been proposed based on the amount of amphibole present at higher temperatures 750 900 c the models predict that very little alteration occurs before the fluid equilibrates with the rock producing only trace amounts of amphibole as an alteration phase with the remainder of the rock retaining its igneous mineral composition essentially unchanged this result suggests that extensive penetration of rocks by aqueous fluids may occur in the lower ocean crust at temperatures 700 c and leave very little conspicuous petrologic evidence for their presence such cryptic alteration is consistent with isotopic evidence for hydrothermal alteration of oxygen and sr isotopes by seawater in lower ocean crust rock samples which otherwise retain their igneous compositions and textures taken together the model results allow for much more extensive circulation of fluids in the lower oceanic crust and at much higher temperatures than has been proposed by previous studies based on petrologic interpretations

hydrocarbon potential of pennsylvanian coal in bohai gulf basin eastern china as revealed by hydrous pyrolysis abstract a hydrous pyrolysis experiment was performed using pennsylvanian brown coal with a vitrinite reflectance vr 0 of 0 56 from a coal mine at the southwest corner of the bohai gulf basin eastern china to evaluate the hydrocarbon potential of the coal the coal sample is vitrinite rich 74 5 and inertinite poor 16 7 with liptinite content of 8 8 much of the vitrinite in the sample consists of hydrogen rich vitrinite collodetrinite hydrous pyrolysis was performed at 200 c 230 c 260 c 290 c 320 c and 350 c for 72 h separately yields of both total liquid pyrolysates and expelled oil increased with temperature before reaching their maximum production of 17 27 kg t coal and 14 57 kg t coal at the same temperature of 320 c vr 0 1 18 and decreased afterwards gaseous products increased sharply at 320 c and tended to increase even at the highest experimental temperature 350 c vr 0 1 53 results show that the coal has not only a certain oil generation potential but also a large capacity for gas production and a high expulsion efficiency oil potential of the coal is attributed to its depositional environment which was transitional from shallow marine to coastal plain or swamp during middle to late pennsylvanian the coal was protected from oxidation under water after deposition experimental results indicate that this pennsylvanian coal could have contributed to oil gas accumulation in the bohai gulf basin

rank and petrographic composition of selected upper cretaceous and tertiary coals of southern nigeria abstract the rank and composition of upper cretaceous tertiary coals from five localities enugu orukpa okaba ihioma and azagba ogwashi in southern nigeria are described ranks determined by huminite reflectance measurements indicate a range from sub bituminous c to sub bituminous a coalification grade for the lower maastrichtian coals of the mamu formation whereas the oligocene miocene coals in the ogwashi asaba formation are predominantly of lignite rank the highest grade of sub bituminous a was attained in the enugu area onyeama mine in the south and this decreases towards the okaba mine where ranks are within the sub bituminous c coalification grade composition was determined by maceral analyses results indicate that the lower maastrichtian sub bituminous coals are characterized by moderate to high concentrations of huminites humodetrinites humocollinite and humotellinite and varied concentrations of inertinites and liptinites concentration of large amounts of liptinites especially resinite sporinite and cutinite at the bottom of the orukpa seam indicate the wet conditions of a reed swamp depositional environment whereas the large abundance of inertinites mainly fusinite on the top parts of the onyeama and okaba seams is interpreted as a shift to drier conditions possibly forest swamp facies the occurrence and predominance of humodetrinite attrinite and densinite in the tertiary lignites of ihioma and azagba ogwashi are interpreted as indications of reed swamp depositional environments we conclude that peat depositional environments for the lower maastrichtian coals was dominated by alternating high and low groundwater tables which resulted from recurrent subsidence forest and reed marsh swamps appear to have developed in delta plain environments lignites in the oligocene miocene stages accumulated in reed swamps of a less telmatic depositional environment

significance of coniferous rain forests and related organic matter in generating commercial quantities of oil gippsland basin australia contrary to the conventional belief that humic coal generates primarily gas 3 billion bbl of recoverable oil has been discovered in the humic coaly succession of the fluviodeltaic latrobe group upper cretaceous tertiary that serves as both the reservoir and the source for hydrocarbons in the offshore gippsland basin of southeastern australia evidence for generation of liquid hydrocarbons from the coaly succession includes 1 similarity of n alkane distribution in the oil and in the coal extracts 2 high wax content of oil up to 27 by weight 3 high ratio of pristane phytane in oil 5 6 and 4 dominance of c29 steranes in the oil in the gippsland basin coniferous rain forests dominated by kauri vegetation flourished in a raised bog setting present temperate climate and kauri vegetation of new zealand are considered to be the modern analog to the gippsland basin the coniferous vegetation provided large quantities of hydrogen rich exinite macerals such as cutinite and resinite with potential to generate oil high rainfall raised ground water level low oxygen high acidity and low nutrient conditions of a raised bog setting were suitable for preserving organic matter a comparison of gas chromatograms of oils in the gippsland basin with gas chromatograms of oils generated by hydrous pyrolysis in the laboratory from the immature source rocks suggests that the paraffinic fraction of the oil was derived from coal and the naphthenic fraction was derived chiefly from resin

a comment on calcic amphibole equilibria and a new amphibole plagioclase geothermometer by j d blundy and t j b holland contrib mineral petrol 1990 104 208 224 the calibration by blundy and holland is not a calibration of the reaction albite tremolite edenite 4quartz because the aliv content of amphiboles is a combined result of vec tk text vec ed text and vec pl substitutions

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

synthetic and natural tremolite in equilibrium with forsterite enstatite diopside and fluid the following equilibrium among tremolite forsterite diopside and orthorhombic enstatite has been investigated using either synthetic tremolite or natural amphibole in the starting materials ca2mg5si8o22 oh 2 mg2sio4 2 camgsi2o6 5mgsio3 h2o a significant increase in the stability of the reactants was observed with natural rather than synthetic tremolite for example in nearly pure h2o with the h2 content of the fluid buffered by nickel bunsenite at one kilobar 108 pascals the breakdown of the assemblage with synthetic amphibole occurs at 708 20 c the breakdown of the assemblage with natural amphibole ca2 16mg4 94fe0 03si7 92 al0 01o22 oh 2f0 03 occurs at 841 47 c the shift in the breakdown curve is attributed to variation in the properties of the amphiboles since all other factors were common in the experiments the reactions have also been investigated with hydrogen fugacity defined by the methane buffer and the nb oh xg coh buffer analysis of the experimental data by linear programming indicates that the enthalpy of reaction is tightly constrained when the calorimetrically determined entropy of 160 92 joules degree is used the resulting enthalpy of reaction is 113 96 1 82 kilojoules with the natural amphibole and 104 83 0 12 kilojoules with synthetic tremolite deviation of the natural amphibole from the ideal tremolite formula as well as a greater number of defects and dislocations in the synthetic amphibole may have contributed to the change in stability

hydrocarbon generation from deltaic and intermontane fluviodeltaic coal and coaly shale from the tertiary of texas and carboniferous of nova scotia abstract selected samples of coal and coaly shale from southeastern texas depositional environment deltaic age paleocene eocene ro 0 25 0 75 and nova scotia depositional environment intermontane swamp delta and lacustrine age carboniferous westphalian a d ro 0 67 0 70 were analyzed by fluorescence microscopy rock eval pyrolysis nmr anhydrous pyrolysis temperature programed and flash and hydrous pyrolysis to evaluate the hydrocarbon potential and hydrocarbon types based on maceral assemblages palynofacies and hydrocarbon potential these coal and coaly shale samples are classified as humic mixinitic mixed and sapropelic compared to humic and sapropelic as defined by stach et al coal petrology gebruder borntraeger berlin 1982 mixinitic or mixed coal and coaly shale containing mainly humodetrinite and lipodetrinite generated more than 10 pyrolysate expelled oil oil in wash fraction remaining coal extract and show a bimodal n alkane distribution derived from cutinite suberinite and alginite pyrolysis of humotelinite humocollinite rich and liptinite poor humic coals generated low amounts

the a type mount scott granite sheet importance of crystal magma traps the presence of rapakivi feldspar and of distinctive porphyritic texture of mount scott granite indicates a period of crystallization prior to final emplacement beneath an extensive penecontemporaneous rhyolite volcanic pile final crystallization conditions are interpreted to have been 50 mpa at depths 1 4 km based on stratigraphic constraints however geobarometry based on the al content of amphibole phenocrysts and comparison of granite compositions with phase relations in the sio2 naalsi3o8 kalsi3o8 ternary system both yield pressure estimates of 200 mpa these pressure estimates are interpreted as plumbing the depth of a temporary storage chamber at 7 8 km this depth coincides in this case both with the probable proterozoic basement cover contact and with the calculated brittle ductile transition at time of ascent of mount scott magma although rising magma that fed the preceeding voluminous carlton rhyolite apparently rose unimpeded past these horizontal anisotropies rising magma that formed mount scott granite temporarily paused at this depth based on magmastatic calculations we suggest that horizontal anisotropies e g brittle ductile transition become crustal magma traps where the magma driving pressure exceeds the lithostatic load when the anisotropy is encountered during rifting initial large influxes of magma may proceed passed crustal anisotropies but have the effect of increasing the relative magma driving pressure through reducing horizontal stress thus magma driving pressure may eventually exceed the lithostatic load at the depth of the brittle ductile transition thereby activating this crustal magma trap ponding of magma at the brittle ductile transition chokes the eruption such a pause in magma supply rate may permit a return to initial stress conditions and deactivate the crustal magma trap once again magma will rise to the surface initiating a new magmatic cycle

chemical composition of rock forming minerals in gold related granitoid intrusions southwestern new brunswick canada implications for crystallization conditions volatile exsolution and fluorine chlorine activity chemical composition of rock forming miner als in appalachian siluro devonian granitoid intru sions southwestern new brunswick was systematically determined by electron microprobe the mineral chem ical data together with petrographic examination was used to test magmatic equilibration and to constrain crystallization conditions volatile exsolution and fluo rine chlorine activity of fluids associated with these intrusions mineralogical distinction between late silu rian to early devonian granodioritic to monzogranitic series gms and late devonian granitic series gs rocks is evident although both are subsolvus i type to evolved i type granitoids oxidized to reduced gms rocks consist of quartz plagioclase an 10 k feld spar biotite apatite titanite zircon monazite hornblende pyroxene magnetite ilmenite and sulfide gs rocks comprise quartz k feldspar pla gioclase an 10 mica group minerals zircon mon azite apatite sulfide ilmente magnetite topaz columbite and xenotime inter intrusion and intra intrusion variations in mineral chemistry are in terpreted to reflect petrogenetic processes e g assim ilation and fractional crystallization during granitoid evolution although magmatic equilibration among rock forming minerals are disturbed by subsolidus hy drothermal processes gms rocks appear to have higher magmatic temperatures variable levels of emplacement a range of fo2 i e reduced intrusions 10 16 7 10 13 4 and oxidized intrusions 10 14 0 10 10 5 bars and rela tively low fhf fhcl ratios 10 3 0 10 1 0 in exsolved fluids compared to gs rocks reduced gms intrusions bear higher gold potential and thus may be prospective targets for intrusion related gold systems

organic petrological and organic geochemical characterisation of the tertiary coal bearing sequence of batu arang selangor malaysia abstract the tertiary coal bearing sequence at batu arang in selangor peninsular malaysia consists of a sandstone coal oil shale facies assemblage a detailed organic petrological and organic geochemical study was carried out on several organic rich sediments from this sequence the oil shales are dominated by botryococcus derived telalginite and pediastrum derived lamalginite the coals hypautochthonous in origin are mainly duroclarite type although other minor microlithotypes also occur alginite is not observed in the coals but other liptinitic constituents are very common particularly thin walled cutinite and sporinite the oil shales and the coals are thermally immature this immaturity has a considerable influence on the biomarker distributions particularly so on the triterpanes which are dominated by c 31 22r and c 30 compounds interestingly for tertiary aged sediments of continental origin the diagnostic biomarker compounds such as 18 h oleanane and bicadinanes normally linked to the higher land plant group of angiosperms are not observed in the samples analysed tricyclic terpanes occur only in very low relative abundance or are virtually absent a clear distinction however in the biomarker distributions of the shales and the coals carbargilite can be made based upon the distribution of c 27 c 29 regular steranes the shales with a source input being predominantly planktonic algae are dominated by 5 h 14 h 17 h 20r cholestane while the coals carbargilites with a source input consisting mainly of higher plant material are dominated by 5 h 14 h 17 h 20r ethyl cholestane the depositional environment of the batu arang coal bearing sequence is interpreted as varying from an alluvial flood plain peat swamp to fluvio lacustrine depositional setting

hydrocarbon distribution in coals and in dispersed organic matter of different maceral compositions and maturities more than 60 samples from 5 coal seams and adjacent siltstones and sandstones were selected from a well through westphalian b sediments from northern germany in order to study bitumen generation and migration the cores were drilled between 1200 und 1530 metres depth in this interval vitrinite reflectance rr is increasing from 0 70 to 0 92 results reveal high hydrocarbon generation potentials for all coal samples but not for adjacent clastic rocks although maceral compositions of both are quite similar yields and compositions of thermal extracts from the coals depend on maceral compositions and rank however the bulk of the already generated bitumen has not been removed during natural coalification and is not easily releasable by thermovaporisation a mass balance based on elemental composition of dull coals indicates that in the rather narrow rank interval 0 70 0 92 rr a total mass loss of 20 may have occurred by migration this is evidenced by a loss of about 20 of the original hydrogen the rest being stored in the coals

empirical model for estimating groundwater flow into tunnel in discontinuous rock masses the high volume of water inflow into tunnel plays a significant role in the design of drainage systems and exerts bio environmental effects in engineering practice analytical and empirical methods that are commonly used to estimate water inflow in sedimentary rock masses lack sufficient accuracy the geostructural anisotropy in a fractured rock has a great impact on water inflow in discontinuous media anisotropy and heterogeneity of the fractured rock masses are highlited hence these methods are not efficient to calculate water inflow to tunnel in such media due to the assumed isotropic hydraulic coefficient in this regard an empirical formula is developed in this study for hydraulic conductivity in the fractured rock masses for analytical methods alternately used to predict water inflow to achieve this a discrete network flow model was performed the simulation resulted in a dataset that is helpful in developing hydraulic conductivity empirical formula for well known goodman equation the geostructural parameters such as the joint orientation aperture spacing and joint interconnectivity were included to determine this formula the acquired empirical equation was utilized in the evaluation of groundwater inflow to middle depth amirkabir tunnel in north of iran in comparison to the observerd flow analytical methods resulted in higher overestimation especially in the sites with high anisotropy however empirical model led to a better estimation of water inflow to tunnel

lithotype maceral composition and variation as correlated with paleo wetland environments gates formation northeastern british columbia canada abstract lithotype samples collected from mid albian gates formation coal seams in northeastern british columbia were analysed in order to gain a better understanding of coal facies variation compositional boundaries between lithotypes are gradational from bright to dull coals there is a progressive decrease in vitrinite and increase in inertinite liptinite is negligible

numerical methods in rock mechanics the purpose of this civilzone review paper is to present the techniques advances problems and likely future development directions in numerical modelling for rock mechanics and rock engineering

two new geobarometers for garnet amphibolites with applications to southeastern vermont two new geobarometers for the assemblage garnet hornblende plagioclase quartz have been calibrated on the basis of the equilibrium 6 anorthite 3 tremolite 2 grossular 1 pyrope 3 tschermakite 6 quartz and its fe end member equivalent data representing 37 natural samples that equilibrated at conditions of 2 5 to 13 kbar and 500 to 800 c were fitted to the general equation rt in keq a bt p i c by using a weighted least squares method multiple correlation coefficients are high 0 98 and 0 97 lines of constant keqhave extremely shallow slopes in p t space 2 to 8 bars per degree suggesting that pressures may be deduced precisely even where temperatures are only poorly constrained typical analytical errors and temperature imprecisions propagate to very small errors in pressure about 500 bars caution is advised in applying the barometers outside the range of calibrant mineral compositions application of the calibrations to samples from southeastern vermont near the strafford chester and athens domes documents relatively high pressure metamorphism 7 to 10 kbar for these structures

petrology palynology coal facies and depositional environments of an upper carboniferous coal seam minto coalfield new brunswick canada coal petrology and palynology of the minto coal seam enable depositional environments of the precursor mire to be established in terms of facies critical maceral ratios maceral assemblages and spore and pollen assemblages the overall petrographic composition indicates a vitrinite rich coal mean 67 followed by inertinite mean 27 and liptinite mean 7 pyrite is common to abundant maximum 15 lithotype logs demonstrate a dominance of dull lithotypes dull and banded dull petrographic composition at the lithotype and seam subsection level is highly variable vitrinite maceral assemblages are enriched in brighter lithotypes banded bright and bright whereas liptinite and inertinite maceral assemblages are enriched in dull and banded dull lithotypes the duller lithotypes are enriched by mineral matter based on spores the seam is assigned to the vestispora zone of atlantic canada with the basal torispora securis torispora laevigata sl zone of western europe and the lower torispora secur

equilibration conditions of eclogite lenses from isla margarita venezuela implications for the tectonic evolution of the metasedimentary juan griego group abstract the constituent primary and secondary minerals in a suite of fifteen samples of eclogite amphibole eclogite and garnet amphibolite scattered as boudins and pods in metapelitic schists and gneisses on isla margarita venezuela have been analysed by electron microprobe to augment existing bulk rock chemical data the large sample population available allows spurious effects of stoichiometric fe3 calculation procedures and bulk rock influence to be recognised and eliminated all samples belong to one population with a relatively homogeneous character the equilibration temperatures are derived from fe 2 mg fractionation between garnet and clinopyroxene and range from 525 650 c jadeite contents of clinopyroxene and the persistence of minor stable albite constrain pressures to between 13 and 19 kbar combined with new evidence for high pressure metamorphism in the enclosing metapelites and with existing data on an eclogitic metabasic unit exposed in north eastern isla margarita la rinconada group these data show convincingly that the margarita crustal block is and has been a relatively coherent unit ever since the entire complex suffered high pressure metamorphism in late mesozoic times

amphibole plagioclase equilibria an empirical model for the relation albite tremolite edenite 4 quartz equilibria between plagioclase calcic amphibole and quartz can be described in part by the relation among mineral components naalsi3o8 ca2mg5si8o22 oh 2 naca2mg5alsi7o22 oh 2 4sio2 this relation governs the partitioning of na between plagioclase and the a site of coexisting amphibole data from natural amphibolites reveal that this partitioning is systematic and sensitive to metamorphic grade the ideal portion of the equilibrium constant kid xna a x a xab derived from natural samples is sensitive to bulk composition inasmuch as both plagioclase and amphibole are highly non ideal samples from a single outcrop have values ranging from 0 5 xab 0 74 to 4 1 xab 0 10 the continuous reaction naalsi3o8 ca2mg5si8o22 oh 2 naca2mg5alsi7o22 oh 2 4sio2 proceeds to the right with increasing grade of metamorphism and for a given bulk composition kid increases with increasing temperature two related discontinuous reactions actinolite albite hornblende oligoclase quartz and actinolite oligoclase hornblende anorthite quartz also proceed to the right with increasing metamorphic grade and result in changes in the topology of a phase diagram that describes the partitioning of na between plagioclase and amphibole a site a schreinemakers net is presented that is consistent with natural occurrences the results of this study should aid in the delineation of metamorphic facies within amphibolites

pristane phytane ratios in the mineralized kupferschiefer of the fore sudetic monocline southwest poland abstract the interaction of organic matter with fluids is important in geochemical processes in surface and diagenetic environments in the kupferschiefer copper deposits of southwestern poland organic fluid interactions are inferred to have been important in the genesis of the ore deposits previous organic geochemical studies of the kupferschiefer report evidence of a late diagenetic oxidation event that altered the organic geochemistry this study uses the saturated hydrocarbons as indicators of the biological input and the earliest diagenetic processes to affect the organic geochemistry of the kupferschiefer the normal alkane distributions are lithofacies controlled indicating that they reflect biological input the ratio of the saturated isoprenoids pristane phytane are potential indicators of the redox conditions during sedimentation and diagenesis very low pr ph ratios are associated with lithofacies that were deposited in hypersaline environments increases in the pr ph ratio within individual traverses are interpreted as indicating increasing oxidation of organic matter during deposition and early diagenesis trends of increasing pristane phytane ratios are observed at the base of the kupferschiefer and at the transition within the kupferschiefer from the clay rich to the carbonate rich kupferschiefer which corresponds approximately to the transition from cu zone to the pb zone early diagenetic copper depleted cu and cu fe sulfides have also been reported form the top of the weissliegendes and the cu zone pb zone transition and it is conceivable that both could be related to the same processes

correlation of different maturity parameters in the ahmedabad mehsana block of the cambay basin abstract the potential use of organic matter maturation parameters in assessing the diagenetic catagenetic transition zone with the help of various known molecular parameters has been investigated in the ahmedabad mehsana block of the cambay basin a set of 24 conventional cores from the eocene shales covering a depth regime of 922 2500 m has been studied the oil generation threshold i e the boundary between the diagenetic and catagenetic maturation regimes is assessed to be at 1800 m based on a combination of parameters including percent hydrocarbons in eom saturate aromatic hydrocarbon ratio in eom and the rock eval production index the pr n c17 ratio rock eval hi and oi were not suitable for reliable maturation profiling nor for independently indexing the stages of maturation the extent of the catagenetic regime is distinguished by ph n c18 ratios

a review of existing methods used to evaluate the hydraulic conductivity of a fractured rock mass we review the existing methods for evaluating the hydraulic conductivity of a rock mass rock mass permeability may be assessed using empirical analytical and numerical approaches empirical methods use data from in situ field tests to derive the relationship between depth and permeability by applying a curve fitting method and establishing the relationship between hydraulic conductivity and a geological index analytical methods rely on darcy and cubic laws to estimate the permeability of a rock mass by taking into account the geometrical characteristics of the joint sets analytical equations of the flow rate into underground excavations are also developed by solving the laplace equation for homogeneous and isotropic aquifers under various boundary conditions numerical modeling can evaluate the outcomes of both empirical and analytical approaches and vice versa and can provide a sensitivity analysis of the parameters that affect rock mass permeability the importance of stress and joint set characteristics is often investigated via numerical modeling as are the scale effect and directional permeability in this review paper we provide a comprehensive review of these approaches for studying rock mass permeability we summarize the advantages and disadvantages of existing methods and highlight potential future research directions

sensitivity of biomarker properties to depositional environment and or source input in the lower toarcian of sw germany abstract a sequence of lower toarcian sediments which are highly contrasting in their depositional environment over a 5 m depth interval has been investigated in detail for the variability of geochemical properties which are used for source characterization and oil to source correlation lower liassic marls are representative of a well aerated shallow water environment in contrast to the immediately overlying bituminous shales which are deposited under extremely reducing conditions various properties have been found to vary considerably within these two units amongst the most important are carbon isotopic composition of the kerogen the pristane phytane ratios nickel as opposed to vanadyl porphyrins and the c27 dia regular steranes although maturation within the profile does not change some of the maturation dependent biomarker properties such as the monoaromatic steroid side chain cracking and the tm ts ratio exhibit large changes which can be assigned to diagenetic processes another maturation dependent property the 20s 20r epimerization of c29 steranes exhibits smaller changes which could also be due to early diagenetic processes the study suggests that reducing and oxidizing conditions i e eh and ph in the sediment exert an influence on several biomarker precursor product pathways in maturation studies initial variations due to depositional conditions have therefore to be taken into account

oleananes in oils and sediments evidence of marine influence during early diagenesis abstract the oleananes as markers for the angiosperms provide valuable source and age information when present in an oil nevertheless they are not quantitatively related to the land plant input and indeed their presence reflects only a small leak in diagenetic processes leading primarily to aromatic oleanoids because they are minor products the abundance of oleananes in terrigenous oils and sediments may be highly sensitive to changes in early diagenetic conditions here we present evidence that contact of plant matter with seawater during early diagenesis enhances the expression of oleananes in a mature sediment or oil oleananes are absent or present at very low concentrations in samples from the base of an eocene coal seam affected by postdepositional seawater intrusion however their abundance increases toward the top of the seam in correlation with organic sulphur dibenzothiophene phenanthrene and the homohopane index similarly in deltaic sediments from the south sumatra basin oleanane hopane is strongly correlated with indicators of marine influence such as c 27 c 29 steranes and the homohopane index in each case increasing oleanane abundance is accompanied by a reduction in the extent of aromatisation and for the south sumatra basin the proportion of a ring contracted oleananes an angiosperm derived miocene coal from the philippines deposited under freshwater conditions shows abundant aromatic oleanoids but no oleananes these results show that oleananes need to be used with caution as age and source markers in fluvio deltaic and lacustrine petroleum systems on the other hand their sensitivity to early diagenetic conditions may make them useful in locating effective source rocks in such systems

microfacies and depositional environment of tertiary tanjung enim low rank coal south sumatra basin indonesia abstract the south sumatra basin is among the most important coal producing basins in indonesia results of an organic petrography study on coals from tanjung enim south sumatra basin are reported the studied low rank coals have a mean random huminite reflectance between 0 35 and 0 46 and are dominated by huminite 34 6 94 6 vol less abundant are liptinite 4 0 61 4 vol and inertinite 0 2 43 9 vol minerals are found only in small amounts 0 2 vol mostly as iron sulfide based on maceral assemblages the coals can be grouped into five classes 1 humotelinite rich group 2 humodetrinite rich group 3 humocollinite rich group 4 inertinite rich group and 5 humodetrinite liptinite rich group comparing the distribution of maceral assemblages to the maceral or pre maceral assemblages in modern tropical domed peat in indonesia reveals many similarities the basal section of the studied coal seams is represented typically by the humodetrinite liptinite rich group this section might be derived from sapric or fine hemic peat often occurring at the base of modern peats the middle section of the seams is characterized by humotelinite rich and humocollinite rich groups the precursors of these groups were hemic and fine hemic peats the top section of the coal seams is typically represented by the humodetrinite rich or inertinite rich group these groups are the counterparts of fibric peat at the top of the modern peats the sequence of maceral assemblages thus represents the change of topogenous to ombrogenous peat and the development of a raised peat bog a comparison between the result of detailed maceral assemblage analysis and the paleodepositional environment as established from coal maceral ratio calculation indicates that the use of coal maceral ratio diagrams developed for other coal deposits fails to deduce paleo peat development for these young tropical coals in particular mineral distribution and composition should not be neglected in coal facies interpretations

hydrocarbon potential of middle and upper devonian coals from melville island arctic canada abstract some of the oldest coals in the world are found within the middle to upper devonian clastic wedge of the canadian arctic archipelago the coals investigated here occur in the weatherall hecla bay and beverly inlet formations on western melville island and range in age from late givetian to middle frasnian many of these coals are rich in liptinite macerals particularly sporinite and hence can be termed canned coals both elemental and rock eval analysis indicate these coals have the potential to generate liquid hydrocarbons a good correlation between liptinite with both h c or hydrogen index is observed up to about 50 liptinite after which the latter two parameters level off the coals range in maturity from 0 61 to 0 87 r o and hence should be in the oil window the amounts of hydrocarbons that can be extracted from the coals when expressed in mg g organic carbon are very low suggesting that they are poor source rocks for oil all the extracts except for the most mature and vitrinite rich sample show high pr ph ratios and biomodal n alkane distributions a cannel coal from the beverley inlet formation has a very unusual triterpane distribution that includes regular ab ring desmethyl and ab ring methyl hopanes steranes are in very low concentrations compared to hopanes in all samples the relative abundance of c 28 and c 29 steranes appears to be influenced by maceral composition hydrous pyrolysis at 330 c for 72 h generated greater amounts of hydrocarbons from the coals suggesting they could be the source of liquid hydrocarbons at greater maturities the hydrous pyrolysis experiments also indicate that thin walled spores are more reactive than thick walled spores at lower temperatures the coals on melville island are not thought to be significant source rocks for the oil and gas occurrences in this area of the canadian arctic because they make up only a very small fraction of the total sedimentary package

oleanane parameter verification by quantitative study of the biomarker occurrence in sediments of the niger delta abstract the variation of the absolute concentration of oleananes in three selevted sedimentary columns of the tertiary niger delta is paralleled by the corresponding oleanane parameter op profile thereby confirming that the latter can be utilized for estimating the relative contribution of terrigenous organic matter it is shown that op features a dynamic range especially at the oil generative window ogw and can precisely delimit the top of the ogw which for the niger delta is shown to coincide approximately with the 80 c isotherm and ro 0 55 this study provides the first direct evidence of the inadequacy of vitrinite reflectance as a maturity parameter for type iii kerogen furthermore based on the new findings an alternative model for oleanene oleanane interconversions in the geosphere is proposed

liquid hydrocarbon generation potential from tertiary nyalau formation coals in the onshore sarawak eastern malaysia tertiary coals exposed in the north central part of onshore sarawak are evaluated and their depositional environments are interpreted total organic carbon contents toc of the coals range from 58 1 to 80 9 wt and yield hydrogen index values ranging from 282 to 510 mg hc g toc with low oxygen index values consistent with type ii and mixed type ii iii kerogens the coal samples have vitrinite reflectance values in the range of 0 47 0 67 ro indicating immature to early mature initial oil window t max values range from 428 to 436 c which are good in agreement with vitrinite reflectance data the tertiary coals are humic and generally dominated by vitrinite with significant amounts of liptinite and low amounts of inertinite macerals good liquid hydrocarbons generation potential can be expected from the coals with rich liptinitic content 35 this is supported by their high hydrogen index of up to 300 mg hc g toc and py gc s 2 pyrograms with n alkane alkene doublets extending beyond c30 the tertiary coals are characterised by dominant odd carbon numbered n alkanes n c23 to n c33 high pr ph ratio 6 8 high t m t s ratio 8 16 and predominant regular sterane c29 all biomarkers parameters clearly indicate that the organic matter was derived from terrestrial inputs and the deposited under oxic condition

organic geochemistry characterization of the paleogene to neogene source rocks in the sayhut subbasin gulf of aden basin with emphasis on organic matter input and petroleum generation potential paleogene umm er radhuma and ghaydah and neogene sarar source rocks from sayhut subbasin in the gulf of aden basin were studied to provide information such as organic matter types paleoenvironmental conditions and petroleum generation potential this study is based on whole rock organic geochemical analyses and organic petrology the total organic carbon toc contents of the paleogene to neogene source rocks range from 0 43 to 6 11 with an average toc value of 1 00 indicating fair to very good source rock potential the paleogene ghaydah and umm er radhuma source rocks are relatively higher in genetic petroleum potential than neogene sarar source rocks mainly oil and gas are anticipated from the ghaydah and umm er radhuma source rocks with hydrogen index hi values ranging from 95 to 715 mg hydrocarbon hc g toc this is supported by the presence of significant amounts of liptinite macerals in the ghaydah and umm er radhuma source rocks the sarar source rocks are dominated by vitrinitic type iii kerogen hi 200 mg hc g toc and are thus considered to be gas source rocks the paleogene to neogene source rocks have vitrinite reflectance r o values in the range between 0 30 and 0 77 r o and pyrolysis maximum temperature values range from 412 c to 444 c 774 f to 831 f consistent with the immature to early mature oil window therefore the present day kerogen type in the paleogene to neogene source rocks is original and should not have been altered by thermal maturity the biomarker of organic matter suggests that the paleogene to neogene source rocks were deposited in a marine environment under suboxic to anoxic conditions the biomarkers also indicate that the paleogene to neogene source rocks contain a mixture of aquatic organic matter planktonic and bacterial and terrigenous organic matter with increasing terrigenous influence to sarar source rock samples highly hypersaline reducing conditions are also evidenced in ghaydah and umm er radhuma source rocks as indicated by the presence of the gammacerane biomarker low pristane to phytane ratios and homohopane distribution patterns

the peristerite gap in low grade metamorphic rocks coexisting na plagioclases from greenschists both in the thermal aureole of the kasugamura granite japan and in the low p metamorphic zone of yap island western pacific were analyzed in great detail the peristerite solvus was determined for each suite the asymmetric solvus has steep albite rich and gentle oligoclase rich limbs that are similar to those for higher pressure series the present results together with those from vermont new zealand and the sanbagawa belt indicate that the peristerite solvus shifts toward the albite component and higher temperature with increasing pressure with increasing pressure albite co existing with oligoclase an 100 ca ca na 20 varies in composition from an 8 9 in kasugamura through an 3 in yap island and vermont to an 1 in new zealand and an less than 0 5 in the sanbagawa belt the consolute temperatures for the peristerite solvus estimated from available geothermometry are 420 c in kasugamura 450 550 c in vermont and 550 600 c in the sanbagawa belt the variation of plagioclase composition in progressive metamorphic zones is explained by intersection of a plagioclase forming reaction and the peristerite immiscibility gap in an isobaric t xan diagram the greenschist zone is characterized by albite the transition zone by occurrence of peristerite pairs and the amphibolite zone by plagioclase of an 20 50