the upper ordovician black shales of southern quebec canada and their significance for naturally occurring hydrocarbons in shallow groundwater abstract shale gas exploration in the st lawrence platform of southern quebec eastern canada focussed on the upper ordovician utica shale from 2006 to 2010 during which 28 wells were drilled 18 of which were fracked the st lawrence platform is thus considered as a pristine geological domain where potential environmental effects of fracking can be evaluated relative to the natural baseline conditions of the shallow aquifers in the saint edouard area southwest of quebec city it has been shown that groundwater carries variable and locally high levels of naturally occurring dissolved hydrocarbons in which thermogenic ethane and propane can be found fifteen shallow 30 147 m wells were drilled into bedrock and sampled cores and cuttings with the purpose of characterizing the shallow bedrock in a shale gas pre development context the shallow bedrock geology is made of three upper ordovician clastic formations the lotbiniere and les fonds formations are time and facies correlative with the utica shale present at a depth of 1 5 to 2 km in this area they are dominated by calcareous black shales with minor siltstone and micrite beds the nicolet formation is the youngest unit of the area and consists of gray to dark gray shales with locally abundant thick siltstone and fine grained sandstone beds the organic matter in the lotbiniere and les fonds formations is represented by solid bitumen with subordinate liptinite algae graptolites and chitinozoans representing normal marine type ii kerogen both formations are at the post peak hydrocarbon generation as indicated by the equivalent random vitrinite reflectance of 0 94 to 1 04 rock eval data support the type ii nature of the kerogen and the late oil window maturation level hydrocarbon extracts from the three formations have yielded high to low concentrations of c1 to c6 for all units an upward decrease in total volatiles c1 c2 c3 together with an increase in the gas dryness ratio c1 c2 c3 is recorded the transitions occurring at depths shallower than 50 m where the shales are more fractured the upward increase in the gas dryness ratio results from the more significant reduction of ethane and propane concentrations compared to that of methane consistent with the dryness ratio trend the 13 c vpdb values of methane change from thermogenic values 50 for deeper samples to more biogenic negative values 2 h vsmow trend of more negative values at shallower depths is noted the 13 c vpdb and 2 h vsmow values of rock hosted methane indicate that samples at shallow depth recorded a microbial influence it is proposed that diffusion and some microbial degradation of hydrocarbons are responsible for the decrease of rock volatiles and the in situ generation of biogenic methane in the shales at shallow depths to mix with the in situ thermogenic methane the utica shale is a very good source rock with high generation potential however thermogenic volatiles can also originate from shallower units with much shorter migration pathways the mixed thermogenic and biogenic methane in the groundwater results from fracture enhanced diffusion and biodegradation of volatiles at shallow depths

geochemistry of groundwater in the saint edouard area quebec canada and its influence on the distribution of methane in shallow aquifers abstract shale gas and tight oil production has undergone a tremendous increase in the last decade in north america which was accompanied by animated scientific debate and local public uproar concerning environmental issues especially the risks of contamination for shallow groundwater resources in quebec eastern canada public concerns led to a de facto moratorium on hydraulic fracturing in 2010 for the st lawrence lowlands where the underlying utica shale is known to contain significant gas resources as only a few exploration gas wells have been drilled this vast area may still be considered virgin in 2012 a 4 year project was initiated by the geological survey of canada which aimed at characterizing aquifer vulnerability to deep industrial activities in the saint edouard region located close to quebec city in the st lawrence lowlands as part of this project a baseline study of hydrocarbons and other geochemical parameters was conducted in shallow aquifers this paper presents groundwater geochemical characteristics in the region and assesses the geological hydrogeological and geochemical controls on methane distribution results show that methane is present in 96 of the 48 sampling points over the 500 km2 study area and that concentrations are highly variable from undetected

late paleoproterozoic extension and a paleostress field reconstruction of the north china craton abstract mafic dyke swarms and aulacogens are major anorogenic extensional events in the late paleoproterozoic north china craton ncc the n nnw mafic dyke swarms are widespread in the ncc whose ages span between 1 83 and 1 77 ga the similar ages and orientations of 1 8 ga dyke swarms in the ncc demonstrate that the amalgamated ncc experienced widespread extension at this time based on the width statistics of dyke swarms on ten survey lines an average crustal extension ratio of 0 35 was found for the ncc the small magnitude of overall extension suggests that the mafic dyke swarms were emplaced into the elastic fractures and indicates that the ncc had become a brittle plate prior to the emplacement of the mafic dyke swarms precisely dated mafic dyke swarms when used as paleostress indicators can be employed in the paleostress field reconstruction of precambrian cratons two dimensional finite element modeling 2 d fem of the ncc in which the various blocks were assigned densities and elastic constants shows that north south compression favors dyke intrusion along generally n nw lines and that deviations in dyke trends can be explained by the effects of boundary constraints and the physical properties of the crust the best fitting model can be considered a plausible representation of the tectonic force acting on the ncc that produces the intraplate stress field that is most consistent with the observed orientation of dyke swarms the results of modeling of the late paleoproterozoic stress field suggest a common tectonic setting for the emplacement of mafic dyke swarms in the central orogenic zone western and east blocks of the ncc the results also show that the north south tectonic forces play an important role in determining the paleostress field in the ncc the widespread extension of the ncc resulted from the north south tectonic forces which may be related to the break up of the late paleoproterozoic supercontinent the paleostress field modeling provides a possible approach to consider the supercontinent paleostress reconstruction and to reveal the mechanisms of the supercontinent break up

chitinozoan graptolite and scolecodont reflectance as an alternative to vitrinite and pyrobitumen reflectance in ordovician and silurian strata anticosti island quebec canada because of the absence of vitrinite in lower paleozoic sediments the reflectance of pyrobitumen is used as an indicator of thermal maturation a new technique of preparing organic matter permits discrimination among types of zooclasts and solid bitumen including pyrobitumen and leads to more precise reflectance histograms studies of organic matter from ordovician silurian strata of anticosti island show that reflectance of zooclasts is different from that of solid bitumen and that each group of the following zooclasts chitinozoans graptolites and scolecodonts has a specific reflectance evolution path with increasing depth on a logarithmic scale the paths of the three groups of zooclasts are linear highly correlated and converging however reflectance of solid bitumen is not linear throughout the range studied solid bitumen becomes linear only where the reflectance is greater than 0 75 comparing the relations between zooclasts and solid bitumen with the vitrinite solid bitumen correlation in the literature suggests that a hypothetical vitrinite evolution line in the anticosti island basin should be subparallel with that of chitinozoans and graptolites but 0 4 0 8 lower in the 1 2 range however scolecodonts and vitrinite should have the same reflectance at 1 but scolecodont reflectance should be slightly 0 2 higher for a vitrinite reflectance of 2

stress directions in eastern north america determined to 4 5 km from borehole elongation measurements stress directions have been determined to depths of 4 5 km in eastern north america from borehole elongation measured by dipmeter calipers in 47 wells the average maximum horizontal stress directions are eastern canada n54 e 7 appalachian basin n58 e 8 and the illinois basin n89 w 5 stress directions determined for the illinois and appalachian basins are in agreement with published interpretations from hydraulic fractures and earthquake fault plane solutions new results from eastern canada and the appalachian basin show that stress directions are everywhere consistent with the midcontinent stress province these data suggest that the maximum horizontal stress does not rotate from the ene midcontinent trend to nw near the atlantic coast a directional analysis of hydraulic fractures petal centerline fractures and natural fractures from the appalachian basin shows that borehole elongation is systematically aligned perpendicular to the directions of hydraulic fractures centerline fractures and northeast striking natural fractures but is not systematically aligned with northwest striking natural fractures these observations indicate that borehole elongations provide reliable stress orientations

geochemical evidence for possible natural migration of marcellus formation brine to shallow aquifers in pennsylvania the debate surrounding the safety of shale gas development in the appalachian basin has generated increased awareness of drinking water quality in rural communities concerns include the potential for migration of stray gas metal rich formation brines and hydraulic fracturing and or flowback fluids to drinking water aquifers a critical question common to these environmental risks is the hydraulic connectivity between the shale gas formations and the overlying shallow drinking water aquifers we present geochemical evidence from northeastern pennsylvania showing that pathways unrelated to recent drilling activities exist in some locations between deep underlying formations and shallow drinking water aquifers integration of chemical data br cl na ba sr and li and isotopic ratios 87sr 86sr 2h h 18o 16o and 228ra 226ra from this and previous studies in 426 shallow groundwater samples and 83 northern appalachian brine samples suggest that mixing relationships between shallow ground water and a deep formation brine causes groundwater salinization in some locations the strong geochemical fingerprint in the salinized cl 20 mg l groundwater sampled from the alluvium catskill and lock haven aquifers suggests possible migration of marcellus brine through naturally occurring pathways the occurrences of saline water do not correlate with the location of shale gas wells and are consistent with reported data before rapid shale gas development in the region however the presence of these fluids suggests conductive pathways and specific geostructural and or hydrodynamic regimes in northeastern pennsylvania that are at increased risk for contamination of shallow drinking water resources particularly by fugitive gases because of natural hydraulic connections to deeper formations

graptolites as indicators of the temperature histories of rocks a pilot study of the optical properties of graptolite skeletal materials shows progressive changes of reflectance bireflectance refractive index and absorptive index produced by temperature changes related to depth of burial samples of lower ordovician to upper silurian graptolites were selected from across canada from locations where the conodont alteration indices of adjacent conodont collections provide a control index of temperature the reaction to temperature of graptolite skeletal material appears to be similar to that of bitumen but somewhat different to that of the vitrinite and liptinite maceral components of coal maximum reflectance in oil and bireflectance appear to be the characteristics most diagnostic of maximum temperature and both show progressively higher rates of increase at higher temperatures these factors show potential for more sensitive discrimination of temperatures at high levels of conodont alteration indices the optical properties of graptolites may perhaps provide a useful tool for unravelling the post depositional histories of lower palaeozoic rocks in deformed belts

stability metastability and elastic properties of a dense silica polymorph seifertite 1 dense silica polymorphs with sixfold coordinated si have been found in snc and lunar meteorites and may be important minerals for silica rich components in the lower mantle however the stable crystal structure in the lower mantle and properties of dense silica remain controversial under stable heating and quasi hydrostatic stress conditions we found that the cacl2 type undergoes a phase transition to the pbo2type seifertite at 130 140 gpa and 2500 k our data suggest that this phase transition occurs at a greater depth than the perovskite postperovskite transition in the lowermost mantle the molar volume measured at 1 bar is the smallest among the reported silica polymorphs therefore having the highest calculated density and in excellent agreement with recent first principles calculations the greater molar volume of seifertite found in the shergottite meteorite and previous experiments supports a metastable synthesis of the phase outside its stability field our data combined with the hugoniots of silica polymorphs also rule out the possibility of the formation of seifertite in the meteorite within its stability field we found very little change in bulk sound speed across the cacl2 type seifertite transition if shear wave velocity decreases at the transition to seifertite as suggested by some computational studies this silica transition may provide an alternative explanation for the discontinuities with a shear wave velocity decrease found at depths greater than the d discontinuity

40ar 39ar and k ar geochronology of the dykes from the south indian granulite terrain abstract 40ar 39ar and conventional k ar data on mafic dykes and a felsic dyke together with previous data have been used to constrain the ages of the dyke magmatism in the south indian granulite terrain the age of the mainly ene wsw trending agali anaikatti swarm is estimated to be 1980 25 ma with a very limited occurrence of upper cretaceous 80 90 ma dykes in the area the nw se dharmapuri swarm is dated as at least 1800 ma possibly 1855 9 ma both the nw se and the ne sw dyke swarms of tiruvannamalai are dated at 1650 10 ma only a few dykes in north kerala are of middle proterozoic ca 1700 1650 ma age furthermore the 40ar 39ar results of dharmapuri dykes exhibit age spectrum characteristic of partial degassing they provide strong evidence of latest proterozoic overprinting by a thermal event probably related to the pan african orogeny most of the phanerozoic dykes are confined to the coastal region in kerala province the dolerites of central kerala and the majority of north kerala dolerites intruded during the 70 65 ma period whereas a large gabbro and a felsic dyke in central and north kerala respectively are of upper cretaceous age ca 85 ma and the mean 81 1 5 ma age from these dykes may represent cooling age the oldest phanerozoic upper jurassic 144 6 ma dyke intrusions have a restricted occurrence in south kerala very close to the southern tip of india the proterozoic dykes are interpreted as being lateral intrusions from under plating igneous bodies beneath the eastern shield region the geological record of the terrain does not show indications of significant pre magmatic extension and rifting but dyke magmatism may have led to extension rifting and the consequent development of the india antarctica sri lanka proterozoic high grade terrain the data are also interpreted to suggest that the south indian granulite terrain is an early proterozoic tectono metamorphic terrane with strong thermal imprints of neoproterozoic early palaeozoic age it is difficult to reconcile its extensions into proterozoic sri lanka or antarctica where tectono metamorphism is dated to be of neoproterozoic age the late phanerozoic dykes are predominantly related to the deccan trap event and are associated with mantle plume decompressional tectonics that gave rise to ocean floor spreading between the seychelles and the indian continent the few older ca 145 ma dykes in south kerala may be related to the rift tectonics that preceded the separation of australia antarctica and india

the utica shale and gas play in southern quebec geological and hydrogeological syntheses and methodological approaches to groundwater risk evaluation abstract the risk of groundwater contamination from shale gas exploration and development is a major societal concern especially in populated areas where groundwater is an essential source of drinking water and for agricultural or industrial use since groundwater decontamination is difficult or nearly impossible it is essential to evaluate exploration and production conditions that would prevent or at least minimize risks of groundwater contamination the current consensus in recent literature is that these risks are primarily related to engineering issues including casing integrity and surface activities such as truck traffic equipment and fluid haulage waste management mainly drill cuttings and water storage and treatment when hydraulic fracturing is utilized concerns have also been raised with respect to groundwater contamination that could result from potential fracture or fault interconnections between the shale unit and surficial aquifers which would allow fracturing fluids and methane to reach the surface away from the wellbore despite the fact that groundwater resources are relatively well characterized in some regions there is currently no recognized method to evaluate the vulnerability or risks to aquifers resulting from hydrocarbon industry operations carried out at great depths this paper focuses on the utica shale of the st lawrence platform quebec where an environmental study aiming to evaluate potential risks for aquifers related to shale gas development has been initiated to provide the context of these research efforts this paper describes the regional tectono stratigraphic evolution and current stress regime of the cambrian ordovician st lawrence platform as well as the utica shale internal stratigraphy mineralogy and thermal maturation then the hydrogeological context of the st lawrence platform is discussed finally the methodology for this environmental study based on geological geophysical geomechanical hydrogeological and geochemical data is presented

optical characteristics of graptolite bearing sediments and its implication for thermal maturity assessment abstract graptolite reflectance was thought to be one of the most useful thermal maturity indicators for graptolite bearing sediments however the relationship between graptolite reflectance and vitrinite reflectance is not well established graptolites especially in the wufeng longmaxi formations from the ordovician to silurian of south china have been mistaken for vitrinite like particles or solid bitumen which results in inconsistent data on the thermal maturity in this paper we have employed optical microscope techniques to describe the detailed optical characteristics of graptolites and solid bitumen in the wufeng longmaxi formations laboratory simulation of maturation was used to determine the relationship between graptolite reflectance and vitrinite reflectance the organic constituents in the wufeng longmaxi formations are mainly composed of graptolites and solid bitumen granular and non granular graptolites were observed in the wufeng longmaxi formations with non granular as the most common texture solid bitumen can be distinguished from non granular graptolites by its coarse surface weaker anisotropy and lower random reflectance the combination of non polarized and polarized light is very helpful to distinguish solid bitumen from graptolite for comparison organic material from the early ordovician alum shale formation of sweden and estonia was also studied the macerals of the alum shales are mainly composed of lamalginites mineral bituminous groundmasses graptolites and solid bitumen the major textures of the graptolites in the sweden and estonia sediments are non granular and granular respectively both non granular graptolite and vitrinite reflectances display a systematic increase with the increase of heating temperature and time the granular graptolites in the estonian sample were gradually changed to non granular graptolites following laboratory simulated maturation indicating that granular graptolites can transform into non granular graptolites with maturation solid bitumen in the wufeng longmaxi formations was derived from the solid residue of kerogen and or post oil bitumen the graptolite random reflectance is a better thermal maturity indicator than graptolite maximum reflectance and is more precise due to the smaller standard deviation several equations are proposed to determine the thermal maturity of the graptolite bearing sediments based on graptolite random reflectance graptolite maximum reflectance and solid bitumen random reflectance

post stishovite phase boundary in sio2 determined by in situ x ray observations a laser heating diamond anvil cell experiment with an angle dispersive x ray diffraction using synchrotron radiation source at the spring 8 has been developed to observe the phase transition in silica sio2 between the p42 mnm rutile type and pnnm cacl2 type up to pressures of 100 gpa and at temperatures up to 2200 k the transition was observed in the vicinity of 55 gpa at room temperature and showed a positive temperature dependence of the transition pressure the phase boundary was determined to follow the equation p gpa 51 2 0 012 0 005 t k our result gives a transition pressure of near 80 gpa and a depth of 1900 km at an expected lower mantle temperature of 2000 2500 k therefore this sio2 transition is not the cause of recent observations of seismic anomalies between 800 and 1600 km depth in the mid lower mantle

diachronous tectonic collapse of the ordovician continental margin eastern canada comparison between the quebec reentrant and st lawrence promontory the upper ordovician trenton group of southern quebec represents the last taconian foreland basin carbonate unit in the quebec reentrant prior to final collapse of laurentia s continental margin and its burial under synorogenic flysch the trenton group either conformably or unconformably overlies the black river group and is in turn conformably overlain by the utica shales the tripartite trenton carbonate unit records progressive deepening 1 very shallow to shallow subtidal 2 shallow to deep carbonate ramp and 3 shallow to deep outer shelf regional facies distribution lithotectonic elements and thickness variations indicate that the trenton shelf was dissected by extensional faults delineating blocks subsiding at various rates this scenario compares favourably with taconian foreland basin development in the middle ordovician table head group at the st lawrence promontory newfoundland a similar stratigraphic succession and tectono sedimentary history occurring 10 15 ma earlier at the s

evidence for 1 8 ga extension of the eastern block of the north china craton from shrimp u pb dating of mafic dyke swarms in shandong province abstract a large mafic dyke from the nnw trending dyke swarms in the eastern block of the north china craton was dated by shrimp u pb age analysis this dyke occurs near mt taishan in shandong province it cuts neoarchean tonalite adamellite and diorite plutons two types of zircons were found in the dyke type 1 zircons were inherited from the host rocks and gave a shrimp u pb age of 2544 24 ma with a weighted mean 207pb 206pb age of 2523 18 ma type 2 zircons were crystallized from the dyke magma and yielded a concordant shrimp u pb age of 1830 17 ma with a weighted mean 207pb 206pb age of 1837 18 ma indicating that the large dyke at taishan was emplaced at 1830 ma the mafic dyke swarm provides evidence of a phase of extension in the eastern block of the north china craton at 1 8 ga this dyke has a similar age to dyke swarms in the western block and in the central orogen belt of the north china craton this lithospheric extension led to the opening of the yanliao and zhongtiao aulacogens the similar ages and orientations of 1 8 ga dyke swarms throughout the north china craton demonstrate that at that time the eastern and western blocks were united and that the amalgamated craton experienced widespread extension

1891 1883 ma southern bastar cuddapah mafic igneous events india a newly recognized large igneous province abstract a newly recognized remnant of a paleoproterozoic large igneous province has been identified in the southern bastar craton and nearby cuddapah basin from the adjacent dharwar craton india high precision u pb dates of 1891 1 0 9 ma baddeleyite and 1883 0 1 4 ma baddeleyite and zircon for two se trending mafic dykes from the bd2 dyke swarm southern bastar craton and 1885 4 3 1 ma baddeleyite for a mafic sill from the cuddapah basin indicate the existence of 1891 1883 ma mafic magmatism that spans an area of at least 90 000 km2 in the south indian shield this record of 1 9 ga mafic ultramafic magmatism associated with concomitant intracontinental rifting and basin development preserved along much of the south eastern margin of the south indian shield is a widespread geologic phenomenon on earth similar periods of intraplate mafic ultramafic magmatism occur along the margin of the superior craton in north america 1 88 ga molson large igneous province and in southern africa along the northern margin of the kaapvaal craton 1 88 1 87 ga dolerite sills intruding the waterberg group existing paleomagnetic data for the molson and waterberg 1 88 ga large igneous provinces indicate that the superior and kalahari cratons were at similar paleolatitudes at 1 88 ga but a paleocontinental reconstruction at this time involving these cratons is impeded by the lack of a robust geological pin such as a limpopo like 2 0 ga deformation zone in the superior province the widespread occurrence of 1 88 ga intraplate and plate margin mafic magmatism and basin development in numerous archean cratons worldwide likely reflects a period of global scale mantle upwelling or enhanced mantle plume activity at this time

genese du gaz naturel de la region de trois rivieres basses terres du saint laurent et de saint flavien appalaches quebec canada isotopic analyses of 13c and 2h concentrations in methane and determinations of the total gas molecular composition were completed on five samples collected in the pleistocene sediments of the trois rivieres area st lawrence lowlands and of the saint flavien area in the appalachians where accumulations of natural gas occur the results indicate that i the gas at yamachiche is biogenic and formed in situ within the pleistocene deposits ii the gas at saint flavien is thermogenic and iii the gas at pointe du lac and at the vieilles forges is likely a mixture of both the petrogenic study of the organic matter of the beekmantown group middle ordovician age suggests that the gas at saint flavien migrated into the present reservoir after the thermal peak journal translation

mineral assemblages of basalt in the lower mantle high pressure x ray diffraction and analytical transmission electron microscopy of laser heated diamond cell samples show temperature dependent phase assemblages in mid ocean ridge basalt morb at lower mantle pressures the assemblage observed below 2250 k consists of only stishovite plus an orthorhombic perovskite phase space group pbnm or cmcm having a composition close to that of morb but slightly depleted in sio2 with increasing temperature the assemblage transforms to orthorhombic and cubic perovskites plus stishovite and then at 3250 k to orthorhombic and cubic perovskites plus stishovite and the cafe2o4 phase all of these assemblages could be present in slabs that have penetrated deep into the mantle and can therefore contribute to the seismological heterogeneity of the lower mantle

mineral chemistry and density of subducted basaltic crust at lower mantle pressures subducted slabs are less dense than the surrounding mantle near the base of the transition zone 660 km depth because of the survival of garnet in former basaltic crust by this depth mantle peridotite has transformed to denser perovskitite1 2 the buoyancy of the former basaltic crust may contribute to the observed accu mulation or horizontal displacement of many slabs at the base of the transition zone3 here we report experimental confirmation of the widely held belief that the basaltic crust of slabs eventually transforms to a dense perovskititic lithology stable in the lower mantle synthetic mid ocean ridge basalt more glass subjected to pressures of 45 80 and 100 gpa in a laser heated diamond anvil cell transforms to an assemblage of aluminous mg fe silicate perovskite non quenchable casio3 perovskite stishovite and a sodic aluminous phase with the ca ferrite structure fig 1 per ovskititic more is about 0 06 g cm 3 more dense than a model lower mantle prem derived from seismological data thus even thermally equilibrated perovskititic slabs should encounter no sig nificant hindrance to subduction and convection in the lower mantle

assessing thermal maturity of palaeozoic rocks from reflectance of chitinozoa as constrained by geochemical indicators an example from southern ontario canada the reflectance of chitinozoa chr0 was investigated as an alternative technique of determining the level of thermal maturity of organic rich palaeozoic rocks in southern ontario these sedimentary strata which include the ordovician collingwood member and the blue mountain formation as well as the devonian marcellus formation lack vitrinite precluding the application of a standard vitrinite reflectance vr0 technique chr0 shows a proportional increase at marginal to moderate maturities being on average 20 to 25 higher than expected vitrinite reflectance the reflectance data fall into a very narrow range showing a high degree of consistency for each lithostratigraphic unit the average chr0 are as follows collingwood mbr 0 63 georgian bay area and 0 88 toronto area blue mountain fm 0 92 marcellus fm 0 68 correlation with more conventional optical and geochemical maturity parameters obtained from the same set of samples fluorescence of tasmanites leiosphaeridia and gloeocapsomorpha alginite rock eval tmax extract data distribution of terpanes and steranes in extracts indicates that within the area of study the beginning of the catagenetic stage corresponds to chr0 0 65 equivalent vr 0 50 whereas the threshold of significant oil generation is reached at chr0 0 9 equivalent vr 0 70 therefore the blue mountain formation is thermally mature with respect to hydrocarbon generation throughout the whole area of study the collingwood shales are mature only in the toronto area while those occurring in the georgian bay area as well as the marcellus shales have yet to enter the main stage of hydrocarbon generation this integrated approach of assessing thermal maturity shows that chr0 when constrained with other maturity parameters is a very reliable indicator of thermal maturity in lower to middle palaeozoic sedimentary rocks

widespread bedding parallel veins of fibrous calcite beef in a mature source rock vaca muerta fm neuquen basin argentina evidence for overpressure and horizontal compression in the neuquen basin of argentina beef bedding parallel veins of fibrous calcite is widespread within late jurassic black mudstones a typical vein consists of two grey inner zones and two white outer zones the inner zones contain inclusions of wall rock and hydrocarbons calcite fibres are perpendicular to the margins in the outer zones the angle between fibre and margin varies from about 45 at the vein tips to 90 in the centre imprints of fossils are offset proving that the fibres have grown antitaxially we infer that the veins opened in two phases during phase 1 the opening was vertical against gravity during phase 2 the veins resisted tectonic shortening so that shear stresses acted at the margins the senses of shear account for the fibre angles at outcrop igneous intrusive rocks have cut and metamorphosed the veins from burial curves maturity calculations growth strata and ages of igneous intrusions we estimate that the inner zones of the beef formed in the oil window during the aptian to albian and that the outer zones formed in the gas window during the cenomanian to campanian we infer that the beef is evidence for fluid overpressure during hydrocarbon generation

graptolites as fossil geo thermometers and source material of hydrocarbons an overview of four decades of progress abstract the thermal maturity of lower paleozoic graptolite bearing marine sediments which host many hydrocarbon deposits worldwide has long been difficult to determine due to the absence of wood derived vitrinite particles for conventional vitrinite reflectance in 1976 graptolite reflectance was introduced as a new indicator for organic maturity of these deposits and has been used since in many regional studies the majority of these studies however were done on a limited sample set and a limited range of thermal maturity which resulted in a number of controversial views concerning the usefulness of graptolite reflectance as an alternative paleothermal indicator and its correlation with vitrinite reflectance through various proxies in this paper we review previous studies and combine those analyses with new data to assess the physical and chemical characteristics of graptolite periderm with increasing thermal maturity we conclude that graptolite random reflectance gror is a better parameter for the thermal maturity assessment than graptolite maximum reflectance gromax due to the better quality of available data combining published data with results of our study of both natural and heat treated graptolites and vitrinite we present a new correlation between gror and equivalent vitrinite reflectance eqvro as eqvro 0 99gror 0 08 chemical composition of graptolite periderm is similar to vitrinite graptolites are mainly kerogen type ii iii are gas prone and have a substantial hydrocarbon potential lower paleozoic graptolite bearing organic rich sediments are important shale gas source rocks and reservoirs globally and make a significant contribution to worldwide petroleum reserves

sequence stratigraphy and plate tectonic significance of the transvaal succession of southern africa and its equivalent in western australia the transvaal succession in the northeastern part of the kaapvaal province of southern africa is the erosional remnant of four 2 7 to 2 1 ga unconformity bounded stratigraphic units or sequences each of which is 102 to 103 m thick and spans 107 to 108 years three of these phanerozoic like cratonic sequences occur in the western part of the kaapvaal province and in the pilbara province of western australia thus the two provinces once were part of the same continent vaalbara the stratigraphically lowest sequence historically assigned to the transvaal succession is part of the ventersdorp supergroup in kaapvaal and the upper part of the fortesque group in pilbara it consists predominantly of arkosic sandstone and basaltic andesite it probably is 2687 2 ma the second sequence contains the quartz arenites dolomites and banded iron formations of the transvaal and griqualand west successions in the kaapvaal and the hamersley group in the pilbara the span of ages 2684 6 to 2432 31 ma lithologies and geographic extent of this sequence imply that the limpopo orogeny which welded the zimbabwe province to vaalbara is 2 47 ga not 2 67 0 05 ga the third sequence the pretoria and postmasburg groups in the kaapvaal and the lower part of the wyloo group in the pilbara probably is the clastic wedge generated by the limpopo orogeny the fourth sequence dominated by the felsites of the rooiberg group is restricted to northeastern kaapvaal sequence stratigraphy lithostratigraphy and lithofacies indicate that the pilbara rifted from the southern edge of western kaapvaal the penge iron formation in northeastern kaapvaal the asbesheuwels iron formation in southwestern kaapvaal and the brockman iron formation in the pilbara are the same formation in which cyclothemic units 0 6 to 15 0 m thick extended 1200 km

upper ordovician facies in the lac saint jean outlier quebec eastern canada palaeoenvironmental significance for late ordovician oceanography upper ordovician caradocian carbonates of eastern north america were deposited along the iapetus continental margin and record a transition from warm to cool water settings despite this margin having been within the southern hemisphere tropical belt this event has been documented from virginia usa to southern quebec canada although not previously from areas close to the palaeoequator field petrographic and major element geochemistry data have been gathered from the poorly known upper ordovician carbonate succession outcropping in the lac saint jean outlier in central quebec the succession consists of a lower siliciclastic formation tremblay overlain by three limestone formations simard shipshaw and galets and capped by shales pointe bleue shale from macro and microfaunal evidence carbonate sedimentation occurred during the late caradoc and is younger than the early to mid caradoc carbonate succession present farther south relative sea level fluctuations recorded in the sediments suggest an overall sea level rise briefly halted by a minor end caradocian sea level fall the lower limestone formation simard consists of muddy sediments with algal coral stromatoporoid boundstones green algae are abundant this unit reflects low energy sedimentation on a shallow warm water carbonate ramp colonized by a diverse chlorozoan fauna the upper limestone formation galets is typified by coarse grained bioclastic sediments punctuated by numerous phosphate rich hardgrounds with evidence for high energy shallow marine conditions faunas were dominated by crinoids and bryozoans this unit represents high energy sedimentation on a cool shallow water carbonate ramp colonized by a brynoderm faunal association between both units a deeper marine outer shelf limestone formation shipshaw was developed in the lac saint jean area a transition from warm to cool water carbonate ramps occurred in latest caradoc times and is litho and biofacies wise similar to what is documented for lower caradocian limestones present farther south upwelling of nutrient rich cool bottom oceanic waters was a probable cause for this transition

paleomagnetism anisotropy of magnetic susceptibility and argon argon geochronology of the clearwater anorthosite saskatchewan canada abstract the clearwater anorthosite in saskatchewan is a major gabbro anorthosite layered intrusion lying within the archean rae province along the northwestern hinterland of the paleoproterozoic trans hudson orogen tho the intrusion which could be at least 2 4 ga old carries a well defined remanent magnetization with a direction of declination 112 and inclination 38 k 316 95 3 1 n 8 the corresponding paleomagnetic pole plat 6 5 n plong 48 2 w dp 2 2 dm 3 7 is the first one obtained from the archean western granulite domain of the rae province field observations supplemented by anisotropy of magnetic susceptibility data show that the magnetization post dates ductile deformation of the anorthosite argon argon plateau dates of 1917 7 ma for hornblende and 1839 5 ma for biotite are interpreted as cooling ages with the hornblende age approximating the time of remanence the pole position and others of comparable age from the northwestern margin of the tho form a loose cluster the mean of which is about 90 of arc away from that of a broadly contemporaneous group of poles from the superior province this relation supports previous interpretations of paleomagnetic data that prior to the tho at about 1 9 ga ago a major ocean the manikewan ocean at least 5000 km across separated the superior and rae hearne provinces

discovery of sapphirine bearing mg al granulites in the north china craton implications for paleoproterozoic ultrahigh temperature metamorphism abstract we report here for the first time the occurrence of mg al granulites within the khondalite belt of the north china craton and provide robust evidence for extreme crustal metamorphism at ultrahigh temperature uht conditions in this region the uht indicator assemblages in these rocks include equilibrium sapphirine quartz high alumina orthopyroxene sillimanite quartz and high temperature perthites the surrounding khondalites also carry spinel quartz equilibrium assemblage the sapphirines occurring in various microstructural associations are markedly magnesian x mg 0 69 0 77 with a composition varying from 7 9 3 to 2 2 1 end members spinel is a solid solution of mg spinel and hercynite x mg 0 41 0 54 with zno content varying from 0 48 to 1 79 wt garnet shows a compositional range between pyrope and almandine x mg 0 39 0 48 with minor grossular 2 6 3 8 mol and spessartine 0 5 1 8 mol the orthopyroxenes display marked compositional variations in terms of al 2 o 3 content with the core of the medium grained orthopyroxene adjacent to sillimanite in the matrix showing the highest al 2 o 3 content 8 4 wt the history of prograde to peak metamorphism of these rocks is indicated by inclusions of sapphirine spinel quartz and sillimanite within garnet sapphirine formed during the peak stage through the reaction spl qtz sil spr occurrence of sapphirine and quartz inclusions trapped in sillimanite suggests the reaction spr qtz grt opx sil a series of retrograde reactions are observed in these rocks as corona and symplectite textures around early coarse grained minerals such as opx sil qtz crd grt sil qtz crd grt qtz crd opx grt o 2 crd qtz fe 2 o 3 in mag or ilm and finally opx kfs h 2 o bt qtz whereas the stability of sapphirine quartz and orthopyroxene sillimanite quartz in the matrix assemblage suggests t 1000 c and p 10 kbar peak metamorphism conventional geothermobarometric estimates confirm the ultrahigh temperature nature and also trace the retrograde conditions 930 970 c at p 10 kbar al in opx 900 1000 c perthite 930 990 c grt opx and 910 940 c sapphirine spinel electron microprobe dating of monazites in textural association with the uht assemblages yield a sharply defined isochron age of 1917 48 ma which correlates with the 1927 11 ma obtained in a previous study from monazites in the surrounding khondalites carrying spinel quartz assemblage an evaluation of the assemblages and textures using appropriate petrogenetic grids indicate that following peak ultrahigh temperature conditions the rocks underwent initial isobaric cooling and subsequent isothermal decompression and we interpret these trajectories to be part of an overall anti clockwise p t evolution the study area located within the northern margin of the north china craton defines a collisional orogenic belt where continental collision and deep subduction was possibly followed by extensional collapse of the orogen evidence for the extensional phase is provided by the several mafic magmatic intrusives of paleoproterozoic age occurring in the region which suggest a possible link between the thermal anomaly associated with extreme crustal metamorphism in this region with mantle derived magmas the uht metamorphism in north china craton coincided with the assembly of the paleoproterozoic supercontinent columbia

hydrocarbon evaporative loss from shale core samples as revealed by rock eval and thermal desorption gas chromatography analysis its geochemical and geological implications abstract the s1 peak generated by rock eval analysis of source rock and reservoir interval core and cuttings samples has been routinely employed for in place hydrocarbon resources assessment by petroleum geochemists geologists and even engineers significant evaporative loss of gaseous and light hydrocarbons up to c10 can occur during core and cuttings collection and storage and subsequent sample preparation in the laboratory before instrumental analysis consequently a correction to the s1 values is needed in order to obtain a more accurate estimate of the resources to investigate the effect of evaporative loss on both the amount and the composition of the hydrocarbons retained in shale a time series of rock eval and thermal desorption gas chromatography td gc analyses have been carried out on an organic rich devonian duvernay formation shale core sample from the western canada sedimentary basin wcsb and an organic lean ordovician lotbiniere formation shale core sample from quebec canada the results suggest that the content of total organic carbon toc may play an important role in retaining and preserving light hydrocarbons in sedimentary rocks a total loss of gaseous and light liquid hydrocarbons up to c9 is shown to take place within 21 h of sample preparation for the low toc 11 devonian duvernay shale core sample after 360 h of exposure to the open air the powdered duvernay shale sample shows only 15 decline in its rock eval s1 peak and still contains high relative concentrations of c7 c9 hydrocarbons in addition the evaporative loss of some isomers of c5 c7 hydrocarbons from the organic rich shale is not fully in agreement with their gc retention elution behavior but appears to be partially controlled by their adsorption desorption on the organic matter and mineral matrix this suggests that the c5 c8 gasoline range hydrocarbon parameters should be used with caution for oil oil correlation for unconventional shale and tight petroleum systems while the findings in this study validate the current industrial practice that targets organic rich and mature shale intervals for unconventional shale gas and oil exploration because of their large hydrocarbon storage capacity the results also have an important implication that high toc content may adversely affect the production efficiency of shale and tight hydrocarbon reservoirs due to the strong adsorption of hydrocarbons by the high maturity organic matter

chemical and isotopic tracers of the contribution of microbial gas in devonian organic rich shales and reservoir sandstones northern appalachian basin in this study the geochemistry and origin of natural gas and formation waters in devonian age organic rich shales and reservoir sandstones across the northern appalachian basin margin western new york eastern ohio northwestern pennsylvania and eastern kentucky were investigated additional samples were collected from mississippian berea sandstone silurian medina sandstone and ordovician trenton black river group oil and gas wells for comparison dissolved gases in shallow groundwaters in devonian organic rich shales along lake erie contain detectable ch4 0 01 50 55 mol with low 13c ch4 values 74 68 to 57 86 and no higher chain hydrocarbons characteristics typical of microbial gas nevertheless these groundwaters have only moderate alkalinity 1 14 8 72 meq kg and relatively low 13c values of dissolved inorganic c dic 24 8 to 0 6 suggesting that microbial methanogenesis is limited the majority of natural gases in devonian organic rich shales and sandstones at depth 168 m in the northern appalachian basin have a low ch4 to ethane and propane ratios 3 35 mol c1 c2 c3 and high 13c and d values of ch4 53 35 to 40 24 and 315 0 to 174 6 respectively which increase in depth reservoir age and thermal maturity the molecular and isotopic signature of these gases show that ch4 was generated via thermogenic processes despite this the geochemistry of co produced brines shows evidence for microbial activity high 13c values of dic 10 slightly elevated alkalinity up to 12 01 meq kg and low so4 values 1 mmole l in select devonian organic rich shale and sandstone formation water samples suggest the presence of methanogenesis while low 13c dic values 22 and relatively high so4 concentrations up to 12 31 mmole l in many brine samples point to so4 reduction which likely limits microbial ch4 generation in the appalachian basin together the formation water and gas results suggest that the vast majority of ch4 in the devonian organic rich shales and sandstones across the northern appalachian basin margin is thermogenic in origin small accumulations of microbial ch4 are present at shallow depths along lake erie and in western ny

do all fractions of organic matter contribute equally in shale porosity a case study from upper ordovician utica shale southern quebec canada abstract in many unconventional hydrocarbon systems organic matter om substantially contributes to total porosity of the rock that led to a positive correlation between total organic carbon toc and porosity while organic porosity is an important reservoir property of unconventional hydrocarbon systems toc of these rocks consists of different macerals or petrographic fractions these toc fractions can be geochemically divided and quantified by the revised extended slow heating esh rock eval analysis this study discusses the contribution of different fractions of om on porosity variation in the mature to overmature utica shale in southern quebec using esh rock eval analysis helium pycnometery scanning electron microscopy sem and x ray diffraction xrd mineralogy selected samples from three wells at depths of 400 700 and 2000 m covering a range of thermal maturity from late peak oil window vroeqv 1 to dry gas zone vroeqv 2 1 were analyzed in this study the predominant om constituents are solid bitumen chitinozoans and minor graptolites with mean toc of 1 1 0 4 wt the mean porosity for oil and gas window samples decreases with depth from 3 9 0 9 to 2 6 0 5 respectively the sem images reveal that organic porosity is limited to pores developed in solid bitumen while regardless of thermal maturity chitinozoans have a non porous structure throughout the oil to dry gas window this observation suggests that the impact of thermal maturity on porosity is different for different om fractions i e macerals leading to different contribution of om fractions to total porosity the latter conclusion is further supported by the improved correlation observed between the solid bitumen fraction and porosity compared to toc porosity correlation for oil window samples our entire data set suggests that om i e bitumen fraction especially in the dry gas window is not the major controlling factor on the total porosity in the utica shale whereas intergranular porosity has the dominant control on total porosity this observation suggests that the hydrocarbon storage potential may largely reside in inorganic pores rather than organic pores in the analyzed intervals of the utica shale the decrease in total porosity observed from shallower samples i e oil window to deeper samples i e dry gas window also suggests that intergranular porosity is the dominant porosity component which decreases with burial

maturation thermique des roches meres dans les bassins des basses terres du saint laurent et dans quelques buttes temoins au sud est du bouclier canadien caradocian source rocks belonging to the utica group occur around and overlay the southeastern part of the canadian shield from the ottawa embayment in the southwestern part of st lawrence lowlands to the anticosti island basin the kerogen of the source rocks is mainly made up of amorphous organic matter transmitted light resembling a solid bitumen framework in reflected light and contains a small portion of zooclasts graptolites and chitinozoans the kerogen is often too mature to have preserved the structure of the original constituents except those of graptolites and chitinozoans otherwise uv fluorescent colonial alga and tasmanites are observed in the eastern half of the st lawrence lowlands stratigraphic and tectonic burial is the main control of source rock thermal maturation from an area located 50 km west of quebec city the estimated vitrinite reflectance ro std of the source rock increases in both northeastern montmorency falls and southwestern st maurice river directions from ro std of 1 2 to 1 5 and 1 7 respectively the source rocks of the ottawa embayment and montreal area western half of the basin are overmature due to hydrothermal and igneous activities 2 3 ro std 2 8 in chicoutimi and lac saint jean outliers the source rocks show reflectances between 0 9 and 1 2 slightly less than reflectance values in the quebec city area ro std between 1 2 and 1 5 on anticosti island the thermal maturation is related to burial only and increases downdip of the inclined platform from the northeast toward the southwest ro std between 0 9 and 2 1 these observations suggest that the st lawrence platform and the southeastern canadian shield were buried by at least 3 5 km of paleozoic strata prior to erosion to grenville basement this implies that most potential hydrocarbon fields are presumably also lost by erosion

tracking low temperature tectonism of the st lawrence platform and humber zone southern quebec appalachians through apatite and zircon u th he thermochronology the st lawrence platform slp and humber zone hz of the southern quebec appalachians have been the subject of extensive studies to resolve the degree of thermal maturation yet the timing of the thermal maximum is not well understood we have employed apatite ahe and zircon zhe u th he thermochronometry across a network of late cambrian to late ordovician siliciclastic and grenvillian basement outcrops to resolve the thermal history below 200 c single crystal dates from individual samples exhibit age dispersion by as much as 300 million years with a strong positive to negative correlation with increasing effective uranium eu concentration the data in the southwestern portion of the basin allow for thermal maxima of up to 200 c during the late ordovician or early devonian regional burial trends combined with local estimates of paleogeothermal gradients indicate that if sedimentation continued after the late ordovician there was no significant increase in burial in southwestern portions

mesozoic fault reactivation along the st lawrence rift system eastern canada thermochronologic evidence from apatite fission track dating the st lawrence rift system is an active fault zone where reactivation of late proterozoic iapetus related faults is believed to occur it forms both a ne sw trending half graben and nw se trending grabens that link and include the ottawa bonnechere and saguenay river grabens both interpreted as aulacogens the rift faults locally preserve kinematic evidence for normal sense displacement the lack of isotopic chronological constraints and the absence of strata younger than the ordovician make it difficult to determine the timing of fault increments field relations in the quebec city charlevoix and saguenay river regions suggest faulting event s younger than the devonian age charlevoix crater we determined apatite fission track aft ages for grenvillian basement rocks from the hanging wall and footwall of typical rift faults at different locations of the st lawrence and saguenay river fault systems along the st lawrence rift system the footwall rocks of major faults yielded late triassic early jurassic aft ages ranging from 235 28 ma to 184 22 ma the hanging wall samples yielded older ages between 443 44 ma and 279 28 ma along the nw trending saguenay river fault system that are consistent with triassic early jurassic normal faulting at ca 250 200 ma based on hefty inverse models of fission track length distributions younger late jurassic aft ages ranging from 152 17 ma to 149 14 ma in the hanging wall of the ne sw trending st lawrence fault system suggest the occurrence of localized faulting increments during the late jurassic the latter aft age discontinuities are interpreted as the result of normal faulting at ca 250 200 ma followed by tectonic inversion evidence for the reactivation and inversion of preexisting normal faults during or after jurassic time is also found in the mesozoic rift related basins of the atlantic coast the nw se trending compressive stress field currently documented along the st lawrence river is consistent with tectonic inversion along the st lawrence rift system this study provides geochronological support for atlantic rift related extensional deformation followed by compressional deformation in the interior of the canadian shield more than 500 km west of the axis of the mesozoic atlantic rift basins

present day stress analysis of the st lawrence lowlands sedimentary basin canada and implications for caprock integrity during co2 injection operations abstract a geomechanical analysis of the st lawrence lowlands sedimentary basin is important to reliably estimate the maximum sustainable fluid pressures for co 2 injection that will not reactivate pre existing faults in the caprock thereby inducing a breeched co 2 reservoir this requires the determination of prevailing stresses orientations and magnitudes fault and fractures geometries and rock strengths the average maximum horizontal stress orientation s hmax is estimated n59 e 20 in the st lawrence lowlands the stress orientations were obtained from stress induced wellbore breakouts inferred from four arm dipmeter caliper data in 17 wells these wellbore failure features are confined to paleozoic lithological units of the st lawrence platform succession and frontal thrusts of the quebec appalachians at depths from 250 m to 4 km our results are consistent with the regional ne sw s hmax stress orientation trend that is generally observed in eastern canada and the u s the stresses pressure gradients estimated for the st lawrence lowlands depths hmin 20 5 3 kpa m s v 25 6 kpa m s hmax 40 7 5 kpa m pore pressure p p 9 8 kpa m indicating a strike slip stress regime s hmin v hmax the high angle ne sw regional faults and fractures in the paleozoic sedimentary succession and the grenvillian basement are oblique to the s hmax stress orientations 10 to 36 and could be reactivated slip tendency 0 34 to 0 58 under the present day stress field if fluid pressures exceeded the critical threshold further refinement of regional geomechanical model is required to estimate the maximum sustainable injection pressure necessary for shear reactivation along the regional faults the regional pore pressure stress coupling ratio under assumed parameters is about 0 5 0 65 and may contribute to reduce the risk of shear reactivation of faults and fractures the maximum sustainable p p that would not cause opening of vertical tensile fractures during co 2 operations is about 18 5 20 mpa for the depth of 1 km

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

bedding parallel fibrous veins beef and cone in cone worldwide occurrence and possible significance in terms of fluid overpressure hydrocarbon generation and mineralization abstract bedding parallel fibrous veins are common worldwide in sedimentary basins especially within strata of low permeability the term beef refers to bedding parallel veins of fibrous minerals where the fibres are mutually parallel and have formed quasi vertically more complex on a smaller scale are cone in cone structures yet these are also common within bedding parallel veins for both beef and cone in cone we have compiled a worldwide catalogue 157 localities typically the veins consist mainly of white gangue minerals for example calcite gypsum or quartz but may also contain accessory minerals of economic interest for example bitumen sulphides emerald pitchblende or gold fluid inclusions may contain oil or gas calcite beef 110 localities is common in organic rich shale of marine carbonate origin especially of 1 cambrian ordovician 2 devonian carboniferous 3 early jurassic or 4 cretaceous to palaeogene ages gypsum beef 30 localities is common in evaporitic or lacustrine strata of continental origin especially of triassic or neogene ages quartz beef 17 localities is common within meta turbidite sequences especially of ordovician or proterozoic ages because these modal ages seem to reflect climatic controls we infer that the fibre forming mineral species have not travelled far vertically the same conclusion holds for accessory minerals typical temperatures of formation are 1 up to 60 c for gypsum beef 2 70 c to 120 c for calcite beef and 3 200 c to 350 c for quartz beef hydrocarbon bearing calcite beef may be a good indicator of a petroleum system in which oil or gas migrate together with aqueous solutions we argue that beef and cone in cone layers result from tensile fracturing and vertical dilation coeval with fibre growth possible causes are either 1 force of crystallization or 2 seepage forces due to fluid overpressure for layers that form at depths of several km fluid overpressure is the more likely cause

review and update of the applications of organic petrology part 1 geological applications abstract organic petrology developed as coal petrology at the beginning of the 20th century dedicated mainly to the study of coals because of their utilization in industry coal petrology was then considered a branch of coal science later with the development of specialized nomenclature classification of coal components and the standardization and improvement of analytical microscopical methods this discipline expanded in interests and name becoming organic petrology organic petrology carries a broader context being as well a tool applied in the study of dispersed organic matter in sedimentary rocks due to its importance in exploration for fossil fuel resources at present organic petrology is a discipline widely recognized for its role in fundamental and applied research with respect to both coal utilization and in geosciences throughout the 20th century several important monographs have been published on the discipline of organic petrology including stach s textbook of coal petrology 1st edition 1935 2nd 1975 3rd 1982 updated as the more general organic petrology by taylor et al 1998 more recently the text applied coal petrology the role of petrology in coal utilization was published by suarez ruiz and crelling 2008 this review is the first in a two part review series that describes and updates the role of organic petrology in geosciences a second part complementing this one and focused on the applications of organic petrology to other scientific fields will follow

surface and subsurface signatures of gas seepage in the st lawrence estuary canada significance to hydrocarbon exploration abstract the seabed of the st lawrence estuary is characterized by many fluid releasing features on multibeam bathymetric images these features correspond to crater like depression pockmarks predominantly found on the northwestern shoulder of the 300 m deep laurentian channel as well as on the channel floor aligned pockmarks which define segments up to 12 km long are frequent in the laurentian channel whereas they are preferentially associated with submarine landslides on the northwestern shoulder of the channel on high resolution seismic profiles pockmarks found in the laurentian channel are characterized by seismic chimneys that may be traced down to the autochthonous paleozoic rocks st lawrence platform suggesting a thermogenic origin for the gas on the northwest shoulder of the laurentian channel the seismic signature of pockmarks does not extend downward to the reflector that corresponds to bedrock st lawrence platform and or grenvillian province suggesting together with high sedimentation rate a biogenic origin for the gas these results are discussed in the light of the data collected in the onshore parts of the st lawrence platform and suggest the presence of a mature hydrocarbon source the conclusions are supportive arguments for the hydrocarbon prospectivity of both the onshore and offshore segments of the paleozoic autochthonous domain st lawrence platform

neoarchean to paleoproterozoic continental evolution and tectonic history of the north china craton a review rocks of archean age are widely distributed in the north china craton ncc and can be divided into high grade regions and granite greenstone belts even though most underwent amphibolite to granulite facies metamorphism quartzo feldspathic gneisses occupy 70 to 85 of the total exposure of archean rocks in the craton supracrustal rocks commonly consist of intercalated volcano sedimentary rocks including metabasites meta intermediate to acid rocks banded iron formations metapelites and minor marbles the oldest rocks outcrop over a small area of 4 km2 and are a quartzite amphibolite sequence that yield 3 8 3 5 ga isotopic ages chemical and geochronological data constrain the earliest main crust forming episode at ca 2 9 2 7 ga when most rocks were metamorphosed to upper amphibolite or granulite facies at moderate pressures mafic granulites can be classified into two textural types referred to as near isobaric cooling ibc and near isothermal decompression itd types high pressure granulites and retrograded eclogites occur mainly near the junction of the provinces of hebei shanxi and inner mongolia in the central ncc and in eastern shandong province of the eastern ncc as well as locally in henan province in the southern ncc these high pressure rocks show clockwise p t paths indicating decompression from 14 kb to 5 6 kb an exposed section interpreted as representing precambrian continental lower crust has also been identified in the northern part of the craton although some mafic ultramafic metamorphic rocks have been interpreted as remnants of ancient oceanic crust and mantle by a number of geologists geochemical and petrological evidence demonstrates that many supracrustal orthogneiss associations have island arc affinities therefore several tectonic models have been proposed including continent continent collision and island arc terrain accretion achieved by arc arc or arc microcontinent collision the ncc underwent multiple high grade metamorphic events of which the two most important took place during the intervals 2600 2450 ma and 1950 1750 ma which are considered to be related to early precambrian supercontinental cycles

recent advances in the study of mantle phase transitions we review recent advances in the study of phase transitions of minerals in the earth s mantle including unsolved problems regarding these processes the phase boundaries of mg fe 2sio4 in the mantle transition zone are modified under the wet conditions by changes in thermodynamic properties of its polymorphs because of differences in the water solubilities of these minerals the shift of phase boundaries has significant implications for the topography of the 410 km and 660 km seismic discontinuities the post perovskite phase with cairo3 structure exists at pressures above 110 gpa and at high temperature the effects of al and fe on phase transition are under debate several post stishovite phases have been reported but equilibrium boundaries and existence in the real lower mantle are also still debatable spin transition occurs in magnesiowustite perovskite and post perovskite phases at high pressures of the lower mantle and core the pressure interval in the spin transition can be large at high temperature and so the transition might not cause a discrete change in physical properties under real earth conditions 2008 elsevier b v all rights reserved

microbial production and modification of gases in sedimentary basins a geochemical case study from a devonian shale gas play michigan basin an expanded data set for gases produced from the antrim shale a devonian black shale in the michigan basin united states has allowed for a detailed examination of the related chemical and isotopic compositional changes in the solid gas liquid systems that discriminate between microbial and thermogenic gas origin in the antrim shale economic microbial gas deposits are located near the basin margins where the shale has a relatively low thermal maturity and fresh water infiltrates the permeable fracture network the most compelling evidence for microbial generation is the correlation between deuterium in methane and coproduced water along the basin margins there is also a systematic enrichment in 13c of ethane and propane with decreasing concentrations that suggests microbial oxidation of these thermogenic gas components microbial oxidation accounts not only for the shift in 13c values for ethane but also in part for the geographic trend in gas composition as ethane and higher chain hydrocarbons are preferentially removed this oxidation is likely an anaerobic process involving a syntrophic relationship between methanogens and sulfate reducing bacteria the results of this study are integrated into a predictive model for microbial gas exploration based on key geochemical indicators that are present in both gas and coproduced water one unequivocal signature of microbial methanogenesis is the extremely positive carbon isotope values for both the dissolved inorganic carbon in the water and the coproduced co2 gas in contrast the 13c value of methane is of limited use in these reservoirs as the values typically fall between the commonly accepted fields for thermogenic and microbial gas in addition the confounding isotopic and compositional overprint of microbial oxidation increasing the values to typically thermogenic values may obscure the distinction between methanogenic and thermogenic gas

x ray diffraction study of phase stability in sio2 at deep mantle conditions the stability of sio2 phases were examined by x ray diffraction at pressure up to 131 gpa and temperature n1300 k corresponding to earth s deep lower mantle conditions three materials stishovite cristobalite and silica glass were used as starting materials and an argon pressure transmitting medium was loaded with the sample for five out of six sets of laser heated diamond cell experiments x ray fluorescent crystals were loaded with the sample to ensure alignment of x ray beam and heating laser our results from three different staring materials indicate that the cacl2 type phase is the stable phase throughout our studied p t range we observe the a pbo2 type phase for cristobalite starting material at pressures greater than 48 gpa at room temperature however this transforms to the cacl2 type structure upon heating between 72 113 gpa transition kinetics and metastability may be important in explaining differences in results reported above 75 gpa and key experimental variables are discussed d 2005 elsevier b v all rights reserved

late precambrian keweenawan asymmetric reversals palaeopoles from the keweenawan 1 200 1 000 myr rocks of the lake superior region form the western and eastern arms of the great logan palaeomagnetic loop 1 5 fig 1a this is defined by both normal n and reversed r poles which are the consequence of at least two geomagnetic reversals4 6 7 the younger one r n has been detected throughout the lake superior region from various rock types 1 6 the older reversal n r is only recorded in the lowermost keweenawan lavas in the southern part of the lake 8 wherever found the reversals depart from the 180 symmetry fig 1a 2 6 due to these asymmetries the logan loop has large segments that are devoid of data and thus the geophysical interpretations of the loop or hairpin critically depend on the cause of the reversal asymmetry 4 four models11 secondary component6 apparent polar wander1 5 wilson s dipole offset5 7 9 and non dipole field configuration1 3 10 have been put forward to explain the asymmetries here we demonstrate that the two dipole field configuration model can explain the reversal asymmetries and discuss the global effects of this model in the light of worldwide late precambrian palaeomagnetic data

proterozoic palaeomagnetism of the mafic dyke swarms in the high grade region of southern india abstract palaeomagnetic investigations have been carried out on four major dyke swarms 38 sites in the high grade metamorphic region of the south indian shield a total of 37 sites 243 samples in four dyke swarms have yielded precambrian palaeomagnetic vectors after progressive ac and thermal demagnetisation 1 the agali anaikatti swarm bordering the nilgiri massif to the south 2 the tiruvannamalai swarm to the interior of the pondicherry coast 3 the dharmapuri swarm towards the west of tiruvannamalai in the interior of tamil nadu and 4 a few dykes from a swarm in north kerala on the west coast ages of the palaeomagnetic vectors are estimated from available k ar isotope dates on samples from a number of sites from all swarms and rb sr isotope results from the older agali anaikatti dykes the vectors and their corresponding ages are as follows d 13 9 i 27 94 95 26 pole 75 7 n 153 2 e for the 2000 ma agali anaikatti swarm n 2 sites d 359 8 i 9 2 51 95 10 pole 79 7 n 101 1 w for the 1800 1750 ma dharmapuri swarm n 5 sites d 217 2 i 50 103 95 24 pole 51 n 130 e for the 1700 1650 ma northern kerala dykes n 2 sites and d 106 9 i 77 6 42 95 9 4 pole 18 8 s 125 2 w for the 1650 ma tiruvannamalai swarm n 7 sites these results in conjunction with other available good quality data have been used to compile an apparent polar wander curve of india for the proterozoic eon the palaeolatitudes derived from the data show that the indian indian landmass was situated at mid latitudes of the northern hemisphere during 2000 ma at a low latitude near the equator 10 n during 1800 1750 ma close to the south pole region 60 s by 1650 ma again near the equator 1000 ma near the north pole 80 n region at 850 800 ma and moved to 10 30 n by 750 ma

regional hydrostratigraphy and insights into fluid flow through a clay aquitard from shallow seismic reflection data in the monteregie region east of montreal quebec canada high resolution compressional p and shear s wave reflection sections were obtained using a vibratory source and three component 3c landstreamer data acquisition system during field programs carried out in 2009 and 2010 the work was part of a strategy to improve the knowledge and understanding of groundwater resources within the glacial and postglacial sediments in the region the 100 line km of seismic profiling is an excellent example of hydrogeophysics providing detailed information on the depth to bedrock the architecture and stratigraphy and physical properties of the overlying sediments on both the regional and local scales hydrostratigraphic mapping as well as insights into fluid water and or gas transport through the surface aquitard correlations of porosity and shear wave velocity in the region also allow some estimation of the variation in subsurface porosities for hydrogeological modeling

characterization of a high pressure phase of silica from the martian meteorite shergotty recently there has been substantial interest in post stishovite high pressure polymorphs of sio 2 discovered as extraterrestrial minerals or synthesized in the laboratory previous investigators reported the presence of pbo 2 like and baddeleyite like sio 2 in the martian meteorite shergotty and also the synthesis of an pbo 2 like phase at pressures of 60 80 gpa in a laser heated diamond anvil cell to provide definitive information about the nature of the natural pbo 2 phase we recovered a small sample from the shergotty meteorite obtained powder x ray diffraction patterns and performed a rietveld refinement of the structure the resulting cell parameters and space group are a 4 097 1 a b 5 0462 9 a c 4 4946 8 a and pbcn the structure refinement confirms that this sample does have the pbo 2 structure

structural and u pb geochronological evidence for 1 47 ga rifting in the belt basin western montana structural mapping and u pb dates from mafic sills in the perma culmination of west central montana constrain the timing of a major rifting event in the early history of the belt basin magmatic zircon from the plains and paradise mafic sills within the prichard formation yielded u pb ages of 1469 2 5 and 1457 2 ma respectively the older sill invaded unconsolidated wet sediments at a depth of less than 1 6 km and its emplacement is coeval with widespread soft sediment folding mud diapirism and bathymetric collapse of the basin between members e and f of the prichard formation the youngest sill intruded near the base of the exposed section after significant accumulation of sediment had occurred in the basin correlation of these data with recent geochronologic results from the moyie sills in british columbia and purcell lava in montana suggests that the rifting and subsidence event was basin wide and that at least two thirds of the deposition of the belt supergroup occurred between 1470 and 14

reflected light microscopy of chitinozoan fragments abstract certain optical properties of some silurian ordovician chitinozoans have been measured and their morphology described using polished block mounted samples and polished thin sections the chitinozoans were found to be optically isotropic and many fine details of their morphology were observed using reflected light microscopy it has also proved possible to recognize chitinozoan fragments in sections made from kerogen concentrates and whole rock samples from early palaeozoic sediments using reflected light microscopy reflectance studies indicate their potential use as maturity indicators

some key issues in reconstructions of proterozoic supercontinents abstract supercontinents containing most of the earth s continental crust are considered to have existed at least twice in proterozoic time the younger one rodinia formed at 1 0 ga by accretion and collision of fragments produced by breakup of the older supercontinent columbia which was assembled by global scale 2 0 1 8 ga collisional events little consensus has been reached regarding configurations of these supercontinents because of some unresolved issues concerning continental fits one of these issues concerns how siberia was related to laurentia previous reconstructions that consider the aldan shield of siberia as a continuation of the wyoming province of laurentia have been largely abandoned in favor of models connecting siberia to northern laurentia but it remains controversial which part of siberia is contiguous with northern laurentia also at issue is the western laurentia australia east antarctica connection most rodinia reconstructions place australia together with east antarctica adjacent to either western canada the sweat hypothesis or the western united states the auswus hypothesis however recent studies combining paleomagnetic and isotopic age data have called into question the validity of sweat auswus and other variants another issue is the position of north china in rodinia columbia limited paleomagnetic data seem to be consistent with the paleo mesoproterozoic north china siberia baltica connection whereas geological data support the recently proposed archean to mesoproterozoic north china india connection controversial issues have also been raised about the timing and history of the amalgamation and fragmentation of south america and west africa both geological and paleomagnetic data suggest that south america sao francisco and amazonia cratons and west africa congo and west african cratons coalesced into a single landmass along the 2 1 2 0 ga transamazonian eburnean orogens however whether they were divorced and then re married to form part of gondwana or remained largely coherent from their amalgamation at 2 1 2 0 ga until their incorporation into gondwana is unclear also little known is the position of amazonia west africa in the proposed supercontinents with some workers believing that they existed as a separate landmass whereas others place amazonia west africa adjacent to baltica in summary although geological and paleomagnetic data are supportive of the existence of proterozoic supercontinents rodinia and columbia they are insufficient to determine their exact geometries

archean geodynamics in the central zone north china craton constraints from geochemistry of two contrasting series of granitoids in the fuping and wutai complexes abstract the archean to paleoproterozoic central zone of the north china craton is situated between the eastern and western archean continental blocks and contains two contrasting series of neoarchean granitoids the 2523 2486 ma tonalite trondhjemite granodiorite ttg gneisses in the fuping complex and the 2555 2525 ma calc alkaline granitoids tonalite granodiorite granite and monzogranite in the wutai complex the fuping ttg gneisses most likely formed from partial melting of 2 7 ga basalts at 50 km with an involvement of 3 0 ga crustal material the wutai granitoids have higher k 2 o lile and rb sr but lower sr y and la n yb n than the fuping ttg gneisses are characterized by nd t dm from 2 5 to 2 8 ga and e nd t from 0 49 to 3 34 and are derived from partial melting of a juvenile source at the geochemistry of these two contrasting series of neoarchean granitoids provides further evidence that the wutai complex originated and evolved separately from the fuping complex the wutai complex most likely formed as an oceanic island arc with volcanism and synvolcanic granitoid intrusions at 2555 2525 ma the wutai complex was subsequently accreted onto the eastern archean continental block and was probably responsible for crustal thickening and ttg magmatism at 2523 2486 ma in the fuping complex as part of the taihangshan hengshan block at the western margin of the eastern archean continental block

short lived 1 9 ga continental margin and its destruction wopmay orogen northwest canada a 1 9 ga continental margin in the northwest of the canadian shield evolved in less than 15 m y from a zone of crustal stretching through a phase of passive margin subsidence to attempted subduction beneath an exotic microcontinent reversal of subduction polarity and generation of a major episutural magmatic arc occurred within 15 m y following microcontinental accretion terminal collision occurred 90 m y at most after initial rifting certain differences in detail between this collided margin and those of phanerozoic age may be related to subduction of newly rifted lithosphere rapid evolution of the orogen the contracted passive margin phase in particular is consistent with but does not prove more rapid recycling of oceanic plates at that time

reflectance measurements of zooclasts and solid bitumen in lower paleozoic shales southern scandinavia correlation to vitrinite reflectance abstract reflectance measurements have been carried out on zooclasts graptolites chitinozoans and vase shaped microfossils and other organic particles vitrinite like particles porous granular vitrinite like particles and solid bitumen in middle cambrian to upper silurian shales from central and southern sweden and the danish island of bornholm baltic sea the most abundant organic components in all the shales are fragments of graptolites and vitrinite like particles the reflectance distribution of these two types of components is largely identical and it is suggested that the vitrinite like particles are fragments of graptolites without any recognizable morphology reflectance measurements of graptolites and vitrinite like particles yield well defined reflectance populations in samples with average r graptolite and average r vitrinite like of 0 75 r o the reflectance distributions are bimodal because of increasing bireflectance and the average reflectance value of the well defined lower reflecting population is arbitrarily used as maturity indicator our results suggest that with increasing thermal maturity the reflectance of graptolites increases faster than the predicted vitrinite reflectance the relationship between graptolite reflectance and equivalent vitrinite reflectance can be expressed by the equation vr eqv 0 73 r graptolite vitrinite like low 0 16 the gas generation window which normally is considered to begin at a vitrinite reflectance of 1 3 r o in post lower paleozoic rocks containing vitrinite starts accordingly at 1 56 r o graptolite reflectance porous granular vitrinite like particles occur in minor amounts and they may represent graptolite fragments with a non smooth surface they generally yield slightly higher reflectance than non granular vitrinite like particles and graptolite fragments the middle cambrian to furongian upper cambrian shales may contain sparse fragments of vase shaped microfossils vsm that seem to follow the maturation trend of chitinozoans in the present sample set the reflectance of chitinozoans and vsm is comparable to that of graptolites at the same level of maturity reflectance measurements of solid bitumen are a poor maturity indicator probably because bitumen can have various origins and morphologies and it may not be indigenous to the host rock

the cuddapah salient a tectonic model for the cuddapah basin india based on landsat image interpretation abstract analysis of geologic geophysical data and lineaments derived from landsat image interpretation has revealed a pattern of tectonic inheritance of archean structural elements by the folded and thrusted eastern margin of the middle late proterozoic cuddapah basin in india a structural pattern set by deep crustal faults in the archean and intracratonic basin fabric is apparent in both sedimentary and tectonic trends in the basin the lineaments represent broad zones of en echelon and parallel alignments that appear to have nucleated on deep crustal faults which were reactivated as structural uplifts lateral and frontal ramps and transverse tear faults the major zones recognized are the northeast trending veldruti guntur lateral ramp to the north and the northwest trending cuddapah nellore transverse tear fault to the south east west directed compression during the eastern ghats latest proterozoic orogeny was apparently confined within these converging lineament zones that effectively buttressed the west verging thrust fronts block uplift along the ne trending veldruti guntur lateral ramp acted as a boundary to east to west thrust translation the northeastern ends of folds and thrusts were pinned down with relative displacement being clockwise and greater increasing to the southwest the lack of a lateral ramp or basement buttress to the south resulted in the development of the left lateral cuddapah nellore transverse tear fault steep imbricate thrust ramps in the foreland resisted further movement westward the resulting convex to the west arcuate nallamalai and vellikonda thrust fronts broadly paralleled by the east coast gravity high anomaly kaila and bhatia 1981 is herein named the cuddapah salient

effects of nanoporosity and surface imperfections on solid bitumen reflectance bro measurements in unconventional reservoirs abstract bitumen reflectance bro is an alternative maturity indicator to vitrinite reflectance vro in lower paleozoic and marine rocks where few higher plant macerals can be found in unconventional petroleum rocks locally exuded and or migrated oil are retained in the tight rocks and thermally and diagenetically consolidated into solid bitumen and pyrobitumen finding suitable bitumen macerals for bro measurements pose a challenge in indicating the proper thermal maturity this study reports the effects of surface imperfections caused by nanoporosity surface granularities and impurities on measuring bro in core samples from the jurassic nordegg shale shale oil and the triassic montney siltstone tight gas in the western canada sedimentary basin the degree that bitumen s surface imperfections influence any given reflectance measurement was controlled by changing the probe size area the larger the measuring probe the higher the degree of surface imperfections is included in bro readings the effect is quantified in this paper showing up to 27 diminishment of mean bro values when the probe size increased from 0 31 to 5 85 m2 the mode in which bitumen accumulates within the rock has a strong influence on the degree of surface imperfections bitumen which is disseminated within clay matrix introduces a high degree of nanoporosity and mineral interference and hence will result in lowest bro in contrast inclusions of high reflecting micrinite or diagenetic minerals such as pyrite result in higher bro these effects can vary at the microscopic scale leading to multiple populations of reflectance readings and difficult interpretations of thermal maturity

a palaeomagnetic investigation of the mashonaland dolerites north east zimbabwe summary earlier palaeomagnetic work on the mashonaland dolerite sills and dykes 1830 230 ma showed that they record a geomagnetic field reversal 28 new sites have been sampled in sills 26 and dykes 2 in north east zimbabwe detailed alternating field demagnetization afd is more effective in removing secondary components of remanence than thermal demagnetization td and enables an assumed primary remanence to be isolated at 16 sill sites combined with earlier results there are 11 sill sites with a positive inclination p d 287 i 53 k 40 and 18 with a negative inclination n d 114 i 47 k 35 the data lead to a positive class b reversal test field tests suggest that the n remanence is the younger and that the period of mashonaland igneous activity spanned a reversal of the earth s magnetic field from p to n the areal distribution of polarity is not random sills with only p remanence are found in the more elevated central region of the mashonaland igneous province whilst predominantly n bearing sills occupy the lower surrounding terrain

correlations among the reflectances of vitrinite chitinozoans graptolites and scolecodonts abstract paleozoic marine sequences sampled in outcrops and wells of northeastern gaspe peninsula quebec appalachians yield kerogen composed in part of vitrinite and zooclasts chitinozoans scolecodonts and graptolites on which reflectance measurements were made the comparison between means of random measurements show that reflectance of chitinozoans is similar to that of telinite vitrinite with a cellular texture and that the reflectance of scolecodonts is significantly lower than that of telinite in the lower range of studied values at higher reflectivities differences decrease but at the end of the condensate gas zone reflectancea are not yet identical as shown by previous studies reflectance of graptolites is slightly less than that of telinite pyrobitumen reflectance is related to the lithology of the host rock and no generalized correlation can be established between the reflectance of pyrobitumen and that of vitrinite

calcite cemented concretions in cretaceous sandstone wyoming and utah u s a abstract spheroidal cannon ball calcite cemented concretions some of gigantic size were studied from three cretaceous shelf sandstone units ferron frontier and second frontier the concretions have diameters between 2 cm and 6 m those larger than 40 cm in diameter in the ferron and frontier have septarian structure rare concretions in the second frontier with cone in cone also have septaria the pattern of carbon and oxygen isotopic data and intergranular volume igv data across concretions indicate that concretion growth was complex not all concretions grew progressively from their centers toward their edges in many concretions displacive fascicular optic high mg calcite foc precipitated simultaneously throughout the concretions pervasive growth pattern although the earliest cementation was concentrated in and near their centers remaining pores were subsequently filled by poikilotopic calcite of lower mg content displacive foc cement in the bodies of concretions and in cone in cone structure and the large igv values indicate that these carbonate phases formed at burial depths no greater than tens of meters igv values indicate that spar cement continued to depths of at least 50 m and possibly deeper the association of organic matter and microbial structures or microbial byproducts with displacive foc and cone in cone calcite raises the possibility that biogenic processes were responsible for the apparently rapid growth of the displacive calcite the oxygen isotope composition of pore waters was fairly uniform in the range of 18o of 4 to 6 smow during 80 of concretion growth but became even more depleted in 18o during the last stage of growth and during septarian fracture filling ranging into values as depleted as 14 smow 13c in calcite is negative 4 to 18 v pdb but variable reflecting a range of microbial processes under both oxidizing and reducing conditions earlier calcites fall mostly in the range of 10 to 16 v pdb relatively later calcite in veins and on concretion margins is more enriched in 13c fe and mn concentrations in calcites have a rough positive correlation with higher 13c values the concentration of mg derived from seawater and altered volcanic rock fragments covaries positively with the degree of meteoric influence lower mg contents correlate positively with relatively depleted 18o values 87sr 86sr values are typical of sr derived from coeval seawater or marine skeletal debris growth of concretions 4 to 6 m in diameter apparently in 5 my requires some spatial localization of growth sites by a self organization process and probably a large supply of carbonate shells in the original sediment elongation of larger concretions in the plane of bedding suggests that advective rather than diffusive supply of cement components dominated late in concretion growth history concretions formed close to the tops of parasequence boundaries

a late archean foreland fold and thrust belt in the north china craton implications for early collisional tectonics abstract the archean north china craton is divided into the western and eastern blocks along the central orogenic belt a 1600 km long archean foreland basin and thrust belt fringes the eastern side of the central orogenic belt rocks in the orogen form tectonically stacked east vergent fold and thrust sheets including foreland basin sediments 2 50 ga ophiolitic melange and an island arc complex foreland basin sediments overlie a passive margin sequence and include a 2 50 ga deep water turbidite sequence that grades upward and westward into shallow water molasse now disposed in structurally imbricated east verging thrusts and asymmetric folds that gradually migrated craton ward with deformation uplift and erosion of the orogen there is a strong linked relationship of the formation of the foreland basin to collision of the east and west blocks of the north china craton along the central orogenic belt at 2 50 ga the qinglong foreland basin and central orogenic belt of the north china craton represents one of the best preserved archean orogen to craton transitions in the world its classic internal to external zonation and flexural response to loading demonstrate that convergent tectonics in the archean were broadly similar to phanerozoic convergent margin processes

the hypothetical mesoproterozoic supercontinent columbia implications of the siberian west laurentian connection abstract the siberian west laurentian connection is a postulated reconstruction of a proterozoic craton that formed between 1800 ma and 1500 ma correlation of geological trends and of rift facies between the siberian platform and western laurentia indicates that although the two cratons underwent significant intracontinental rifting in mesoproterozoic and neoproterozoic times they did not undergo complete separation until early cambrian ca 530 ma although this interpretation does not support the hypothetical columbia supercontinent model of rogers 2000 and rogers and santosh 2002 some elements of it are compatible with that model

the nature of mesoproterozoic central indian tectonic zone with exhumed and reworked older granulites abstract the ese wnw trending central indian tectonic zone citz divides the indian subcontinent into southern and northern crustal provinces its narrow northern belt consists of closed early proterozoic mahakoshal rift zone which is presently confined between two moho reaching faults that characterize the son narmada sona lineament the mesoproterozoic sausar mobile belt smb the chhotanagpur granite gneiss complex cggc and the gneissic complex of northeast india represent the wider southern belt the mahakoshal rift belt has a thick pile of mafic ultramafic rocks and possibly oceanic components the basin closed due to a south directed subduction creating a magmatic arc that was sutured to its southern boundary during 1 8 1 7 ga a south dipping ductile shear zone known as the son narmada south fault affects both its supracrustals and intrusive granitoids the son narmada south fault generally delimits the northern boundary of the gondwana basins whereas the son narmada north fault delineates the northern boundary of the mahakoshal mobile belt and the southern boundary of the meso neoproterozoic vindhyan basin the smb representing the southern belt of the citz in the central sector comprises strongly folded and metamorphosed non volcanic and mn rich sausar sediments intermixed with reworked basement gneisses migmatites and granulites representing the pre sausar assemblage the sausar orogeny closed during terminal mesoproterozoic ca 1 0 ga on the other hand metamorphism in the basement gneiss migmatites and northern and southern granulite belts pre dates the sausar orogeny the earliest structure of the smb truncates and rotates the n s oriented structures of the southward located sakoli and the dongargarh belts of neoarchaean palaeoproterozoic age the northern granulite belt of the smb and the cggc and the high grade supracrustals from the sonapahar area in ne india all indicate very high p t conditions during 1 7 1 5 ga peak metamorphism which was followed by decompressional cooling the setting resembles continental collision which was followed by tectonic exhumation and denudation on the other hand the southern granulite belt from the smb documents a late archaean 2 6 ga event and a later 1 4 ga event the dalma volcanic belt located close to the southern tectonized boundary of the cggc belt and possibly the assemblage of copious mafic enclaves within the ca 550 ma granite plutons from ne india represent back arc like setting during 1 6 1 5 ga the setting is caused due to the southward subduction of the north indian block beneath the southern block leading to continental collision the metasedimentary belt located further to the south of the dalma volcanic belt and flanking the archaean singbhum craton to the north on the other hand is palaeoproterozoic in age but has been metamorphosed during ca 1 6 ga because of the northern collision related orogeny reworking and incorporation of basement gneisses and granulites from the mid crust level to the younger sausar cover sediments denote renewed spell of thrust tectonics that remobilized the collision zone rocks of the earlier orogeny the tectonic transport was from the north to the south with north dipping thrusts thus there was a reversal in the direction of convergence from the preceding orogeny the sausar orogeny closed during ca 1 0 ga it caused anatectic event producing granitoid plutons migmatites and charnockites in the cggc belt and migmatites in the gneissic complex in ne india

geochemical and petrographic characterization of the upper ordovician utica shale southern quebec canada abstract the utica shale is a potential unconventional tight gas reservoir from southern quebec the utica shale is a calcareous shale with intervals of fine grained siltstone with total organic content of 1 2 wt median n 408 the major organic matter constituents are migrabitumen and zooclasts chitinozoan and graptolite macerals the primary kerogen is characterized as marine due to the presence of chitinozoan and marine derived prasinophyte algae such as tasmanites a significant portion of the bulk organic matter is dominated by migrabitumen the present hydrocarbon potential s2 mg hc g rock of the utica shale is largely controlled by distribution of solid migrabitumen throughout the unit hydrogen index hi declines with increasing maturity which is controlled by greater burial from shallow to deep sections oxygen index oi remains low in most samples which is attributed to lack of terrestrial input however organic lean intervals show significantly inflated oi due to interference of mineral carbon possibly siderite random reflectance measurements on matrix solid bitumen and chitinozoans are robust indicators of thermal maturity the maturity ranges from the late oil window in the shallow utica to the wet and dry gas windows in the intermediate and deep utica respectively the results suggest that matrix bitumen formed during migration and dissemination of hydrocarbon into the clay fraction of the rock this is associated with significant bacterial sulfate reduction possibly in the early stages of generation and migration of oil it appears that the porous siltstone facies in the deeply buried section of the utica shale acts as a reservoir for the migrated bitumen from organic rich strata within the section and or possibly overlying source rock

archean blocks and their boundaries in the north china craton lithological geochemical structural and p t path constraints and tectonic evolution an examination of lithological geochemical geochronological structural and metamorphic p t path data suggests that the basement of the north china craton can be divided into eastern and western blocks separated by major crustal boundaries that roughly correspond with the limits of a 300 km wide zone called the trans north china orogen the eastern block consists predominantly of late archean domiform tonalitic trondhjemitic granodioritic ttg batholiths surrounded by anastomosing networks and linear belts of open to tight synforms of minor volcanic and sedimentary rocks metamorphosed from greenschist to granulite facies at 2 5 ga with anticlockwise p t paths some early to middle archean rocks are locally present in the eastern block but their tectonic history is unclear due to reworking by the 2 5 ga tectonothermal event the western block has a late archean assemblage structural style and metamorphic history similar to that of the eastern block but it differs in the absence of early to middle archean assemblages and in being overlain by and interleaved with paleoproterozoic khondalites which were affected by a 1 8 ga metamorphic event involving clockwise p t paths a mantle plume model is proposed for the formation and evolution of late archean basement rocks in the eastern and western blocks based on a combination of extensive exposure of ttg gneisses affinities of mafic rocks to continental tholeiitic basalts presence of voluminous komatiitic rocks dominant diaprism related domiform structures anticlockwise p t paths and a short time span from the primary emplacement of ttg and ultramafic to mafic rocks until the onset of regional metamorphism between the two blocks is the trans north china orogen which is bounded by two major fault systems and is composed of late archean to paleoproterozoic ttg gneisses and granitoids interleaved with abundant sedimentary and volcanic rocks that are geochemically interpreted as having developed in magmatic arc and intra arc basin environments these rocks underwent multiple phases of compressional deformation and peak high pressure metamorphism followed by rapid exhumation during the late paleoproterozoic at 1 8 ga as a result of collision between the eastern and western blocks resulting in the amalgamation of the north china craton

the paleoproterozoic north hebei orogen north china craton s collisional suture with the columbia supercontinent abstract understanding the geologic history and position of the north china craton in the paleoproterozoic columbia supercontinent has proven elusive paleoproterozoic orogenic episodes 2 00 1 85 ga are temporally associated with ultimate stabilization of the north china craton ncc followed by the development of extensive craton wide rift systems at 1 85 1 80 ga the age difference between the sedimentary cover and the metamorphic basement is up to 500 700 ma suggesting that uplift and doming of cratonic basement occurred in the latest paleoproterozoic mafic dike swarms 1 80 1 77 ga and anorogenic magmatism 1 80 1 70 ga record the extensional breakup and dispersal of the north china craton during this stage the late paleoproterozoic tectonic framework and geological events documented provide important constraints for reconstruction of the ncc within the late paleoproterozoic supercontinent of columbia an east west striking thousand kilometer long belt of khondalites granulite facies metapelites stretches along the northern margin of the north china craton on the cratonward side of the northern hebei orogenic belt this granulite belt includes mg al sapphirine bearing granulites that reached ultrahigh temperature peak metamorphic conditions of 1000 c at 10 kbars at 1927 11 ma following peak ultrahigh temperature conditions the rocks underwent initial isobaric cooling and subsequent isothermal decompression and these trajectories are interpreted to be part of an overall anti clockwise p t evolution indicating that the northern margin of the craton experienced continental collision at 1 93 1 92 ga the position of the khondalite belt south of the northern hebei orogenic belt makes it analogous to tibet a continental collision related plateau characterized by double crustal thicknesses and granulite facies metamorphism at depth we suggest that the tectonic evolution of the ncc during this period was closely related to the assembly and break up of the columbia supercontinent and that the ncc was adjacent to the baltic and amazonian cratons in the period 2 00 1 70 ga craton wide extension occurred within 100 150 ma of collision along the northern margin of the craton at 1 93 1 92 ga it is concluded that mantle upwellings are chiefly responsible for the breakup of the ncc from the paleoproterozoic supercontinent

coalification and graphitization of graptolites in the anchizone and lower epizone abstract in lower paleozoic sediments of the south alpine carnic alps carinthia austria fragments of graptolites were used to trace the process of coalification and graphitization in a continuous anchizonal to epizonal metamorphic section beginning with the onset of meta anthracitic coal ranks the process of graphitization produces graptolites with the structure of coke like transitional matter the path of coalification of graptolite fragments is explained by the model of a reflectance indicating surface ris this path resembles the coalification of vitrinite during the process of coalification the shape of the ris shows a non coaxial evolution starting with a primary biaxial negative geometry the oblate graptolite ris shapes of the carnic alps are indicative of a metamorphic event with only minor tectonic influence

emergence biodiversification and extinction of the chitinozoan group chitinozoans are considered as reproductive bodies of marine invertebrates called chitinozoophorans these chitinozoophorans were most likely to have been small pelagic or necto pelagic soft bodied probably wormlike animals and judging from the size of chitinozoans they probably measured from a few millimetres to a few centimetres in length the chitinozoophorans most likely survived by grazing on phytoplankton there is no evidence of a large colonization of the pelagic niche in the cambrian but from the early ordovician onward this niche was exploited chiefly by graptolites and chitinozoophorans both groups inhabited nearshore and offshore habitats but in contrast to the graptolites the chitinozoans displayed their highest diversity at high latitude in less distal that is upper and lower offshore environments the chitinozoan group evolved rapidly during the ordovician and reached its maximum ordovician diversity in the late darriwilian from the first occurrence of chitinozoans in early tremadocian times to the biodiversity crisis in latest ordovician times nearly 80 of the morphological innovations took place until their extinction in the latest devonian chitinozoans survived through several biodiversity crises in the early late ordovician late hirnantian late wenlock earliest emsian and in the latest frasnian kellwasser event during the melting of the hirnantian ice sheet most ordovician genera and species became extinct but some genera extended beyond the boundary e g spinachitina belonechitina cyathochitina ancyrochitina the hirnantian glaciation was not directly responsible for the dramatic extinction of organic walled microfossils but it certainly accelerated the extinction of lineages that had already been weakened since the early to mid katian the late wenlock and earliest emsian graptolite crises affected the chitinozoophorans to a lesser degree and the latest frasnian kellwasser event did not greatly affect chitinozoophorans the disappearance of the chitinozoan group at the end of the famennian resulted from a combination of factors for example the chitinozoophorans probably no longer had the genetic potential for successful adaptations to successive drastic environmental changes only one species is known from the latest famennian their usual niche was invaded by more efficient groups and their usual food supply disappeared or was no longer sufficient the latter factor is supported by the contemporaneous decline in phytoplankton

taconian melanges in the parautochthonous zone of the quebec appalachians revisited implications for foreland basin and thrust belt evolution in the quebec appalachians disruption imbrication and thrusting of the taconian foreland basin sequence are responsible for the development of chaotic units within the turbiditic sequence of the caradocian sainte rosalie group the main lithologic assemblage of the parautochthonous zone these chaotic units have been termed olistostromes or tectonosomes on the basis of field criteria and following pini s 1999 classification olistostromal units containing blocks of the middle mudstone utica shale and upper turbidite units ste rosalie group of the foreland basin and spanning the caradocian n gracilis c americanus o ruedemanni and c spiniferus graptolite zones were deposited and incorporated into the sainte rosalie group disruption of more competent beds of the flyschic sequence and fault stacking and slicing of older rock units occurred along major thrust faults and now form structurally aligned corridors or tectonosomes graptolites and new chitinozoan data from both olistostromes and tec

configuration of the late paleoproterozoic supercontinent columbia insights from radiating mafic dyke swarms abstract remnants of 2 1 1 8 ga orogens can be recognized in nearly every craton assembled within reconstructions of the rodinia supercontinent although no particular pattern of laterally extensive orogenic belts emerges these cratons may be the fragments of an older supercontinent formed in response to the collision and accretion of even older cratons during the early earth history paleomagnetic constraints have played a limited role in many previous reconstructions of the early precambrian supercontinent mainly because of the poor age control and a large scatter of the paleomagnetic poles the geometry of giant radiating dyke swarms and orogenic belts provide important constraints for the reconstruction of the pre rodinian supercontinent some early unmetamorphosed and undeformed mafic dyke swarms in north china southern peninsular india and north america share coeval age of 1 85 ga if these continents are assembled the overall pattern exhibited by the mafic dyke swarms appears to constitute a giant radiating swarm with a piercing point between the cuddapah rift in south india and the xiong er aulacogen in north china this suggests that the north china craton indian craton and canadian shield may be fragmented from the same landmass the reconstruction of 1 85 ga giant radiating dyke swarm attempted in this paper suggests that the north china craton india craton and canadian shield were united together to form a landmass within the columbia supercontinent before its extension and break up the 1 90 1 85 ga andean style north orogenic belt suggests that a subduction zone existed on the northern margin of the north china craton wopmay orogenic belt developed in a 1 88 1 84 ga continental volcano plutonic arc which is interpreted as the product of eastward subduction of oceanic lithosphere the transantarctica orogenic belt in east antarctica may be another candidate to be linked with the subduction zone the north orogenic wopmay orogenic and transantarctica orogenic belts could be connected to form a continuous subduction zone the orogenic comparison strengthens the configuration of the columbia supercontinent proposed by the reconstruction of the giant radiating dyke swarm the laurentia west australia and east antarctica were relatively stable from 1 85 ga to 1 20 ga as inferred from the data on dyke swarms magmatism and the paleomagnetism these continents constituted the core of the columbia supercontinent in the late paleoproterozoic time the north china craton and indian craton were however separated from the columbia supercontinent during the mesoproterozoic time

extreme crustal metamorphism during columbia supercontinent assembly evidence from north china craton abstract a vast supracrustal belt of khondalites granulite facies metapelites occur along the northern margin of the north china craton we report here for the first time spinel quartz equilibrium assemblage from these rocks in two textural settings 1 high zno up to 14 47 wt spinel with quartz as inclusions within garnet porphyroblasts defining pressure above 12 kbar and temperature of 900 c and 2 low zno down to 1 2 wt spinel in association with quartz in the matrix assemblage formed during peak ultrahigh temperature conditions ca 975 c and 9 kbar we present a unique case of decompression where the metamorphic conditions of the rocks traversed mostly through the spinel quartz extended stability field monazite grains in textural association with both types of spinel quartz textures were analysed for age determination and the data define two age peaks at 1927 11 ma and 1819 11 ma since the peak thermal regime of the khondalites was close to or exceeded the theoretical closure temperature of pb in monazite we infer the 1819 11 ma age as the timing of ultrahigh temperature event in this craton our data lend support to the idea of ca 1 9 1 8 ga e w collisional orogen at the northern margin of the north china craton we correlate the extreme crustal metamorphism with tectonics associated with the assembly of the north china craton within the columbia supercontinent

organic petrography of graptolite fragments from turkey abstract the reflectance and bireflectance of graptolite fragments silurian ordovician from southeast turkey were examined and the morphology was described using reflected light microscopy the dispersion of maximum and minimum reflectance of graptolites sectioned parallel and perpendicular to the bedding was also determined the graptolites were anisotropic and the anisotropy was stronger for sections perpendicular to the bedding the graptolite fragments show two types of surface morphology granular and non granular the granular type had a rough surface and granular anisotropy the non granular fragments showed a smooth surface and basic anisotropy the fine internal structure of graptolite was evident under crossed polars the reflectance of graptolite increased with depth and was higher than other organic material e g bitumen found in the same sediment the present study indicates that the reflectance of graptolite in sediment can be used to determine the maturity of the dediment

the late archean record a puzzle in ca 35 pieces abstract the global archean record preserves ca 35 large cratonic fragments and a less well defined number of smaller slivers most archean cratons display rifted margins of proterozoic age and therefore are mere fragments of supercratons which are defined herein as large ancestral landmasses of archean age with a stabilized core that on break up spawned several independently drifting cratons the tectonic evolution of individual archean cratons such as the slave craton of north america or the kaapvaal craton of southern africa should therefore always be considered in the context of their ancestral supercratons this is particularly true for many of the smaller cratons which are too limited in size to preserve the complete tectonic systems that led to their formation these limitations not only apply to the crustal geology of archean cratons but also to their underlying lithospheric mantle keels if these keels are archean in age as their broad correlation with ancient surface rocks suggests they also are rifted and drifted remains of larger keels that initially formed below ancestral supercratons the study of archean cratons and their lithospheric keels should thus be global in scope in the search for late archean supercratons a craton like the slave with three to four rifted margins has a ca 10 maximum probability of correlating with any of the ca 35 remaining cratons around the globe assuming wholesale recycling of archean cratons has been limited since ca 2 0 ga alternatively if the original number of independently drifting cratons was significantly larger the probability of successful correlations is much less due to repeated cycles of break up and plate tectonic dispersal since ca 2 0 ga the probability of correlation is probably independent of present day proximity unless there is independent evidence that two neighbouring cratons were only separated by a narrow ocean nevertheless most previously proposed craton correlations rely erroneously on present day proximity implicitly extrapolating relatively recent paleogeography back to the archean considering the fundamental differences between some of the better known cratons such as the slave superior and kaapvaal it seems likely that these cratons originated from independent supercratons sclavia superia vaalbara with distinct amalgamation and break up histories this is contrary to widely held opinion based largely on an idealized view of the supercontinent cycle that all cratons shared a common history in a single late archean supercontinent in contrast to the superior and kaapvaal cratons which are radically different from the slave craton and each other the dharwar craton of peninsular india the zimbabwe craton of southern africa and the wyoming craton of north america all show significant similarities to the slave craton it thus seems likely that at least some of these were nearest neighbours to the slave craton in the ca 2 6 2 2 ga sclavia supercraton

assessing potential impacts of shale gas development on shallow aquifers through upward fluid migration a multi disciplinary approach applied to the utica shale in eastern canada abstract potential impacts of shale gas development on shallow aquifers has raised concerns especially regarding groundwater contamination the intermediate zone separating shallow aquifers from shale gas reservoirs plays a critical role in aquifer vulnerability to fluid upflow but the assessment of such vulnerability is challenging due to the general paucity of data in this intermediate zone the ultimate goal of the project reported here was to develop a holistic multi geoscience methodology to assess potential impacts of unconventional hydrocarbon development on fresh water aquifers related to upward migration through natural pathways the study area is located in the st lawrence lowlands southern quebec canada where limited oil and gas exploration and no shale gas production have taken place a large set of data was collected over a 500 km2 area near a horizontal shale gas exploration well completed and fracked into the utica shale at a depth of 2 km to investigate the intermediate zone integrity this project integrated research results from multiple sources in order to obtain a better understanding of the system hydrodynamics including geology hydrogeology deep and shallow geophysics soil rock and groundwater geochemistry and geomechanics the combined interpretation of the multi disciplinary dataset demonstrates that there is no evidence of and a very limited potential for upward fluid migration from the utica shale reservoir to the shallow aquifer microbial and thermogenic methane in groundwater of this region appear to come from the shallow organic rich fractured sedimentary rocks making up the regional aquifer nonetheless diluted brines present in a few shallow wells close to and downstream of a normal fault revealed that some upward groundwater migration occurs but only over a few hundred meters from the surface based on the isotopic signature of methane the methodology developed should help support regulations related to shale gas development aiming to protect groundwater

fractured shale gas systems the first commercial united states natural gas production 1821 came from an organic rich devonian shale in the appalachian basin understanding the geological and geochemical nature of organic shale formations and improving their gas producibility have subsequently been the challenge of millions of dollars worth of research since the 1970s shale gas systems essentially are continuous type biogenic predominant thermogenic or combined biogenic thermogenic gas accumulations characterized by widespread gas saturation subtle trapping mechanisms seals of variable lithology and relatively short hydrocarbon migration distances shale gas may be stored as free gas in natural fractures and intergranular porosity as gas sorbed onto kerogen and clay particle surfaces or as gas dissolved in kerogen and bitumen five united states shale formations that presently produce gas commercially exhibit an unexpectedly wide variation in the values of five key parameters thermal maturity expressed as vitrinite reflectance sorbed gas fraction reservoir thickness total organic carbon content and volume of gas in place the degree of natural fracture development in an otherwise low matrix permeability shale reservoir is a controlling factor in gas producibility to date unstimulated commercial production has been achievable in only a small proportion of shale wells those that intercept natural fracture networks in most other cases a successful shale gas well requires hydraulic stimulation together the devonian antrim shale of the michigan basin and devonian ohio shale of the appalachian basin accounted for about 84 of the total 380 bcf of shale gas produced in 1999 however annual gas production is steadily increasing from three other major organic shale formations that subsequently have been explored and developed the devonian new albany shale in the illinois basin the mississippian barnett shale in the fort worth basin and the cretaceous lewis shale in the san juan basin in the basins for which estimates have been made shale gas resources are substantial with in place volumes of 497 783 tcf the estimated technically recoverable resource exclusive of the lewis shale ranges from 31 to 76 tcf in both cases the ohio shale accounts for the largest share

geochronology and tectonic evolution of karimnagar and bhopalpatnam granulite belts central india abstract the karimnagar granulite belt kgb and the bhopalpatnam granulite belt bgb occur along both flanks of the pranhita godavari pg rift basin we present a state of the art overview on the geochronological and tectonic aspects of these belts and surrounding geologic domains and report new age data on zircon monazite and uraninite recovered from granulite facies assemblages from kgb and bgb based on electron microprobe analyses epma zircons from kgb charnockites show core ages of up to 3 1 ga mantled by rims of 2 6 ga zircons from bgb have 1 9 ga cores mantled by 1 7 ga rims zircons with core ages of 1 6 to 1 7 ga in bgb rocks suggest new growth at this time monazites and uranitite from kgb show clear peaks with well defined ages in the narrow range between 2 42 0 08 ga and 2 47 0 03 ga rims of monazite show mean age of 2 21 0 08 ga monazites from bgb define sharp linear trend in pbo vs tho2 diagram delineating a clear isochron with age of 1 59 0 03 ga age data from kgb and bgb presented in this report negate current models linking these terrains to godavari granulite belt and considering them as single and contemporaneous entity the mid archaean to early palaeoproterozoic signature recognized from kgb is totally missing in bgb on the other hand kgb rocks do not record any evidence for major mesoproterozoic thermal regime the two granulite belts shouldering the pg rift basin have therefore evolved in different times under distinct p t conditions and thermal regimes our results have important implications in evaluating models of supercontinent assemblies particularly the older assemblies of ur columbia and rodinia while tectonothermal events in kgb broadly match with those of east dharwar we propose that bgb represents a 1 6 ga collisional mobile belt between the bastar and the dharwar cratons the 1 6 ga collisional mobile belt at the southern margin of the bastar craton was superposed by rift activity along the pg basin at 1 5 ga this sequence of events goes against the existence of a 3 0 ga old contiguous assembly of ur but closely matches with the history of accretion and break up of the columbia further parts of the pg basin located away from the influence of the eastern ghats mobile belt neither recorded any grenville ages 1 0 ga corresponding to the rodinia accretion nor late pan african ages ca 550 ma relating to the gondwana amalgamation indicating that the region did not witness any of these younger tectonic events

vaalbara earth s oldest assembled continent a combined structural geochronological and palaeomagnetic test the only remaining areas of pristine 3 6 2 7 ga crust on earth are parts of the kaapvaal and pilbara cratons general similarities of their rock records especially of the overlying late archean sequences suggest that they were once part of a larger vaalbara supercontinent here we show that the present geochronological structural and palaeomagnetic data support such a vaalbara model at least as far back as 3 1 ga and possibly further back to 3 6 ga vaalbara fragmented prior to 2 1 ga and possibly as early as 2 7 ga suggesting supercontinent stability of at least 400 myr consistent with neoproterozoic and phanerozoic analogues

an overview of canadian shale gas production and environmental concerns abstract production of hydrocarbons from canadian shales started slowly in 2005 and has significantly increased since natural gas is mainly being produced from devonian shales in the horn river basin and from the triassic montney shales and siltstones both located in northeastern british columbia and to a lesser extent in the devonian duvernay formation in alberta western canada other shales with natural gas potential are currently being evaluated including the upper ordovician utica shale in southern quebec and the mississippian frederick brook shale in new brunswick eastern canada this paper describes the status of shale gas exploration and production in canada including discussions on geological contexts of the main shale formations containing natural gas water use for hydraulic fracturing the types of hydraulic fracturing public concerns and on going research efforts as the environmental debate concerning the shale gas industry is rather intense in quebec the utica shale context is presented in more detail

the paleomagnetic significance of new u pb age data from the molson dyke swarm cauchon lake area manitoba u pb geochronology paleomagnetism and petrography indicate that the molson dyke swarm along the western margin of the superior craton is a composite of at least two ages of intrusion the more extensive younger dyke set the molson swarm sensu stricto generally has a 030 trend is mainly pyroxenitic to noritic with subordinate diabase and has been related to rifting in a back arc environment during closure of the manikewan ocean at about 1920 1800 ma which culminated in the trans hudson orogen a u pb zircon age from one of these dykes located at cauchon lake indicates emplacement at 1877 7 150 4 similar to two previous u pb age determinations on molson dykes another dyke from cauchon lake yields a baddeleyite zircon u pb date of 2091 2 ma and appears to be part of an older mainly diabasic suite of east northeast trending dykes that may represent a continental rifting episode that preceded the opening of the manikewan ocean the new u pb age data require a revision to the interpretation of