sedimentation organic maturity and petroleum potential of the oligocene miocene oil shale deposits yayu basin southwestern ethiopia studies initiated in the search for domestic energy supplies for ethiopia have confirmed the presence of oil shales in the yayu basin this article presents some of the characteristics of these shales the basin is located in the southwest of ethiopia and consists of precambrian basement and cenozoic volcanic and sedimentary rocks three sedimentary successions reach a cumulative maximum thickness of 165 m 541 ft two oil shale horizons have been identified in the upper and lower sedimentary successions and reach a maximum thickness of 35 and 20 m 115 and 65 ft respectively sedimentation in the basin occurred in fluvial and lacustrine depositional environments the sandstone facies was deposited in a fluvial environment whereas the oil shale bearing sediments were deposited in a lacustrine environment algal amorphous materials and minor amounts of woody materials characterize the studied oil shales with botryococcus and pediastrum indicating a lacustrine environment the studied oil shales are characterized by high total organic carbon values up to 61 2 and s2 hydrocarbon generating potential values ranging from 10 78 to 119 07 hc g kg indicating excellent source rocks most of the oil shales are at the immature to early mature stage for hydrocarbon generation vitrinite reflectance measurements on the oil shale samples are less reliable because of the presence of abundant algal materials gas chromatogram results also indicate source rocks the yayu basin is estimated to have up to 1 billion metric tons of oil shale reserves

stagnant layers at the bottom of convecting magma chambers the evolution and crystallization of igneous complexes has received much attention from petrologists1 3 and more recently from physicists4 10 current models emphasize the role of compositional effects we present here a different viewpoint because compositional effects are due to crystallization they depend on the thermal structure and regime of cold boundary layers in convecting magma chambers particularly of the bottom layer where the thickest rock sequences form we have studied purely thermal convection in a large aspect ratio magma chamber which is cooled through both its upper and lower boundaries we made laboratory fluid dynamical experiments in turbulent and transient conditions and show that a stagnant layer develops at the bottom isolated from the convective part of the chamber the essential features of this layer are that it is not affected by mixing and that a significant thermal gradient is maintained across it these imply peculiar crystallization conditions

carbon isotope and magnetic polarity evidence for non depositional events within the cambrian ordovician boundary section near dayangcha jilin province china carbon isotope and magnetic polarity stratigraphic results from the cambrian ordovician boundary section at xiaoyangqiao near dayangcha jilin province china in comparison to a contemporaneous section at black mountain australia indicate strata equivalent to major portions of the australian sequence are either absent or are restricted to highly condensed intervals these intervals are correlative with regressive sea level events identified in australia and western north america suggesting regional or eustatic sea level changes strongly influenced deposition of the xiaoyangqiao sequence these results also suggest the xiaoyangqiao section is unfavourable as the site of the cambrian ordovician boundary global stratotype section and point

redox conditions across the g l boundary in south china evidence from pyrite morphology and sulfur isotopic compositions abstract the end guadalupian middle permian mass extinction recorded the disappearance of shelf faunas such as fusulinids small foraminifers brachiopods rugose corals which flourished in the warm shallow marine habitats after the late pennsylvanian early permian glaciation the causes for this mass extinction are still unclear marine anoxia often as a cause for other mass extinctions has been paid less attention in this extinction here we present a comprehensive study including pyrite morphology and sulfur isotopic compositions of pyrite across the guadalupian lopingian middle upper permian g l boundary at tianfengping in northern yangtze platform and at penglaitan in southern yangtze platform in south china our results show that the sulfur isotope ratios of pyrite mainly track the framboid size distributions in these two sections anoxia and intermittent euxinia occur at the g l boundary evidenced by the coincidence between reduction of framboid size and the extremely negative sulfur isotope values of pyrite involving disproportionation and corresponds to the main mass extinction of the end guadalupian suggesting a causal link between them long term dysoxic conditions during the middle capitanian are evidenced by the relative small framboid size and lower sulfur isotope ratios of pyrite and coincide with the first pulse of the end guadalupian mass extinction also suggesting a causal link between them the oxygen depletion conditions in the capitanian during the global sea level falling may be the main cause for the end guadalupian mass extinction

thermal equilibration of the earth following a giant impact b the earth is found to equilibrate thermally after a giant impact melts a significant portion of the planet on a time scale of a few million years a simple thermal evolution model for the cooling of a terrestrial planet a prescribed fraction of which is melted during a giant impact is presented two model geometries are considered the first has a laterally inhomogeneous distribution of melt and solid through a mega crater geometry and the second has a global magma ocean the model assumes convective heat transfer in the melt and in the case of the mega crater geometry convection in the solid part of the planet in the magma ocean case the solid interior is not convecting the melt region may cool due to heat transfer to the planet s surface and to the solid region and due to melting of solid the solid region cools by heat transfer to the planet s surface in the mega crater model the viscosities of the melt and the solid are assumed to be dependent on the exponential of the inverse absolute temperature convective heat transfer is parametrized by using semi empirical boundary layer thickness scaling laws most model parameters including planetary size are absorbed into a cooling time scale of the remaining parameters of the scaled model the rate of change of melt viscosity with temperature the surface temperature and for small melt fractions the melt region geometry are most important in determining the cooling time the initial melt temperature the heat capacities of the solid and the melt and the stefan number a measure of the latent heat of melting determine the proportion of the solid that is melted during cooling of the impact melt it is found that almost the whole planet may melt if the impact originally melted half of the planet and if the initial melt temperature was twice a representative planet melting temperature for reasonable choices of parameter values it is found that thermal equilibration of the earth occurs on a time scale of 1 to 10 million years

shale gas potential of the lower permian gufeng formation in the western area of the lower yangtze platform china abstract china is beginning to explore unconventional gas resources in the lower yangtze platform in the last two years we conducted undiscovered hydrocarbon resource assessment to investigate the geological and geochemical characteristic of the lower permian gufeng formation which is considered as one potential exploration layers in this area four outcrops and one well were used to determine the stratigraphic correlation and 40 available samples were used for an analytical investigation because of continuous changes in the sedimentary environment the shale of the gufeng formation not only includes black shale but also calcareous mudstone silicalite siliceous mudstone and carbonaceous shale the thickness of the gufeng formation is between 0 m and 200 m and it has two small depositional centers with an sw ne strike on plane the shale in the gufeng formation shows a high average toc total organic carbon content of 3 41wt based on test of 40 samples but the tocs in different tract systems have significant differences ehst early highstand systems tract average 9 85wt lhst late highstand systems tract average 0 96wt cs condensed section average 2 61wt tst transgressive systems tract average 0 76wt the shale is in the post mature stage of thermal maturity tmax temperature of maximum pyrolysis output 339 518 c and is in the dry gas window of hydrocarbon generation mean random vitrinite reflectance value ro 1 24 1 99 clay minerals dominate the mineralogy followed by quartz minerals pyrite only is found in some samples of ehst which is consistent with the presence of less anoxic conditions and lower levels of sediment dilution during sediment deposition the ehst shale of the gufeng formation which has a high content of organic carbon tentatively could be regarded as a potential shale gas exploration target in this area however because the complex multistage tectonic background could have caused gas loss the tectonic background and the hydrocarbon preservation condition must also be considered

mineralogy and geochemistry of mississippian and lower pennsylvanian black shales at the northern margin of the variscan mountain belt germany and belgium abstract exploration of unconventional gas resources from paleozoic formations in northwestern germany is just getting started large potential gas reservoirs are presumed to be present north of the rhenish massif where mississippian and pennsylvanian marine black shales occur this paper comprises geochemical and mineralogical data and other important aspects of potentially economic black shale formations of the carboniferous additionally the burial and thermal history was reconstructed using 1d modeling software schlumberger these 1d models were calibrated with vitrinite reflectance data from outcrops and shallow wells in general all paleozoic black shales are at present highly mature between about 1 5 and 3 vitrinite reflectance the shales of the uppermost mississippian upper alum shale chokier formation have high contents of organic carbon are tens of meters thick and can be regarded as potential gas shale targets most other mississippian and pennsylvanian black shales are relatively thin adjacent carbonates are often stained black and rich in solid bitumen indicating former oil impregnation of these reservoirs

polar wander and the cambrian joseph l kirschvink et al 1 1 propose that true polar wander tpw occurred during the cambrian 520 to 535 ma this conclusion is based on i apparently high drift rates from gondwana laurentia ii an anomalous pole reading from siberia and iii reinterpretation of polarity from a

magnetic reversal frequency and apparent polar wander of the siberian platform in the earliest palaeozoic inferred from the khorbusuonka river section northeastern siberia summary marly limestones that crop out along the khorbusuonka river northeastern siberian platform define a well dated lower and middle cambrian sequence which was sampled for magnetostratigraphy in the upper part of the section from the uppermost lower cambrian toyonian stage to the middle cambrian amgan and mayan stages thermal demagnetization isolates two magnetic components carried either by magnetite haematite or both the first is parallel to the recent geomagnetic field at the site and is removed in the low to middle temperature range the second component is isolated at higher temperatures and has dual magnetic polarities this component yields a positive but partial since we consider only two sites fold test with other middle cambrian data previously obtained from the distant kulumbe river section and was probably acquired during sedimentation or at an early stage of diagenesis it records a very high magnetic reversal frequency of at least six to eight reversals per myr during the entire middle cambrian assuming a 10 myr duration for this epoch a much more complex palaeomagnetic behaviour is observed within the upper tommotian lower atdabanian lower cambrian part of the khorbusuonka section demagnetization diagrams show large overlaps between magnetic components which prevents the isolation of a clear magnetic component at high temperatures analysis of these overlaps is however consistent with the existence of an ill determined primary magnetic direction for the lower cambrian which is very different from that isolated in the middle cambrian although still in need of further confirmation the possibility that a large drift in siberian apparent polar wander occurred over a rather short time during the lower cambrian appears to be supported by our data

widespread coastal upwelling along the eastern paleo tethys margin south china during the middle permian guadalupian implications for organic matter accumulation abstract guadalupian organic rich depositions within the eastern paleo tethys margin have been attributed to coastal upwelling but the idea has not been tested here a suite of geochemical proxies from the gufeng formation of the lower yangtze region south china are used to investigate the formation mechanisms of organic matter accumulation a high organic carbon content and similar enrichments of bio redox sensitive trace metals show strong similarities to the geochemical characteristics of modern upwelling sediments the use of high cd mo ratios and low co x mn values characteristic of modern upwelling settings sweere et al 2016 is replicated in the gufeng strata implying that lower yangtze area was dominated by persistent upwelling that become less intense seasonal later in the guadalupian application of these new geochemical proxies shows that the characteristics of modern upwelling systems such as the formation of an intense oxygen minimum zone omz can be confirmed in the ancient calculation estimates show that primary productivity was sustained at moderate to high levels and was at comparable levels to those of the modern peru upwelling system omz related anoxic conditions with transient euxinic episodes dominated permanently during the deposition of the gufeng formation and then became more intense conditions euxinia later in the guadalupian the radiolarian chert siliceous mudstone rhythms that coincide with fluctuations in major elements organic carbon total sulfur and trace metal concentrations may reflect dilution by biogenic silica chert zr al ratios are also higher than in mudstone suggesting the cherts may record more winnowed deposition at the margin of an ancient omz compared with a location within the omz for the mudstone the organic matter accumulation of the middle permian gufeng formation may be mainly controlled by the upwelling driven primary productivity and also influenced by the changes of anoxic euxinic conditions and the dilution of biogenic silica

unconventional shale gas systems the mississippian barnett shale of north central texas as one model for thermogenic shale gas assessment shale gas resource plays can be distinguished by gas type and system characteristics the newark east gas field located in the fort worth basin texas is defined by thermogenic gas production from low porosity and low permeability barnett shale the barnett shale gas system a self contained source reservoir system has generated large amounts of gas in the key productive areas because of various characteristics and processes including 1 excellent original organic richness and generation potential 2 primary and secondary cracking of kerogen and retained oil respectively 3 retention of oil for cracking to gas by adsorption 4 porosity resulting from organic matter decomposition and 5 brittle mineralogical composition the calculated total gas in place gip based on estimated ultimate recovery that is based on production profiles and operator estimates is about 204 bcf section 5 78 10 9 m 3 1 73 10 4 m 3 we estimate that the barnett shale has a total generation potential of about 609 bbl of oil equivalent ac ft or the equivalent of 3657 mcf ac ft 84 0 m 3 m 3 assuming a thickness of 350 ft 107 m and only sufficient hydrogen for partial cracking of retained oil to gas a total generation potential of 820 bcf section is estimated of this potential approximately 60 was expelled and the balance was retained for secondary cracking of oil to gas if sufficient thermal maturity was reached gas storage capacity of the barnett shale at typical reservoir pressure volume and temperature conditions and 6 porosity shows a maximum storage capacity of 540 mcf ac ft or 159 scf ton

differential evolution and the influencing factors of low maturity terrestrial shale with different types of kerogen a case study of a jurassic shale from the northern margin of qaidam basin china abstract the jurassic terrestrial shale on the northern margin of qaidam basin is characterized by high contents of organic matter but low maturity resulting in a lack of further research on shale gas in this area to better understanding the shale gas potential of organic matter with different types we conducted thermal maturity experiment of hydrocarbon generation from different kerogen types of low mature shales under closed conditions the results show that type ii and type iii kerogen have experienced similar hydrocarbon generation stages but they differ in the hydrocarbon generation interval and evolution process between liquid hydrocarbon and gaseous hydrocarbon compared with type iii kerogen type ii kerogen is characterized by a low initial temperature at each evolutionary stage and wide temperature range which caused the overall evolution of type iii kerogen lagged behind that of type ii kerogen the differential evolutions mainly result from the differences in hydrocarbon generation mechanism hydrocarbon generation activation energy and kerogen macerals among different kerogen types we summarized the evolution model of type ii and type iii kerogen based on the characteristics of kerogen in hydrocarbon generation carbon isotope change pore development and other aspects this work can provide theoretical and data support for reconstructing the hydrocarbon generation process of terrestrial shale gas investigating the hydrocarbon generation mechanism and predicting the hydrocarbon resources of terrestrial shale oil and gas on the northern margin of qaidam basin and even china

parameterized convection and the thermal evolution of the earth abstract thermal convection is an efficient means of extracting heat from the interior of the earth heat lost from the earth s interior comes from the decay of radioactive isotopes and the cooling of the earth to determine the magnitude of each contribution detailed studies of the convective mechanism must be carried out one approach to this problem is to parameterize a nondimensional mantle temperature in terms of the mantle rayleigh number the time variation of the radioactive heat production and the transient cooling of the entire earth are included also included is the differentiation of radioactive isotopes into the continents important conclusions are 1 1 that between 25 and 30 of the surface heat flow can be attributed to the cooling of the earth this gives a mean concentration of uranium in the mantle close to 30 ppb 2 2 that two scales of mantle convection are occurring the first associated with convection of the surface plates and the second a turbulent convection beneath the surface plates 3 3 that the mean temperature of the mantle in archean times was 100 150 k hotter than at present but that the mean thickness of the lithosphere was about one half the present value 4 4 that 60 to 80 of the area of the continents was formed prior to 3 b y b p

dynamics of metal silicate separation in a terrestrial magma ocean in a terrestrial magma ocean the metal silicate separation involved small metal droplets our goal is to better understand the dynamics of the metal droplet scenario the mechanism of sedimentation in a vigorously convecting and strongly rotating magma ocean may differ significantly from settling droplets in a still fluid in order to systematically study the parameter dependence on the style of motion we utilize two dimensional and three dimensional numerical convection models combined with a tracer based sedimentation method we investigate the characteristic flow patterns resulting from the competing effects of convection and droplet settling and find three styles of motion a temperature dominated style where most droplets remain suspended a droplet dominated style where the droplets separate from the fluid and a style of repetitive motion we find that the droplet dominated style is relevant to the magma ocean in this scenario the droplets settle and form a dense bottom layer one of the key findings of this work is that the formation of the dense bottom layer and therefore the separation of metal droplets from the liquid silicate occurs on a characteristic timescale which is identical with the stokes settling time finally we study the chemical interaction of settling metal droplets and liquid silicate and discuss how accurately a simple parameterized model can describe the chemical equilibration in the metal rain scenario of a terrestrial magma ocean we find agreement between the parameterized model and our two dimensional model our simulations which include thermal convection into the metal rain model confirm the fundamental observation that metal droplets are not permanently suspended in the convecting silicate melt but that they sink and rapidly form a dense layer at the base of the magma ocean

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

the characteristics and significance of conventional and unconventional sinian silurian gas systems in the sichuan basin central china abstract oil and gas discoveries within proterozoic cambrian strata and the majority of shale gas production occurs in relatively stable tectonic regions and characterised by moderate thermal maturity r o o 2 5 the system comprises two components namely a conventional sinian cambrian dolomite hosted gas resource and an unconventional cambrian silurian shale gas deposit both represent trillion cubic meter accumulations the migration accumulation type sinian cambrian gas system is a result of numerous processes including 1 paleo high trapping within a relatively stable tectonic setting 2 appropriate source materials located in a paleo rift trough 3 large scale dolomite grainstone reservoirs located near the paleo high 4 adequate gas produced from in situ crude oil cracking and 5 gypsum salt and shale cap rock preservation the self contained source reservoir cambrian silurian shale gas system is localized by deepwater organic rich shelf facies characterized by high silicon and calcium contents the recent discovery of these two massive gas fields in old and over matured sedimentary strata has effectively extended the upper maturity limit of r o over 3 0 which may indicate the efficacy of broadening current natural gas exploration areas thus potentially increasing global natural gas resources significantly furthermore the discovery may spark interest in natural gas exploration in widely distributed old strata thus encouraging co development of conventional and unconventional petroleum accumulations

pre cretaceous tectonic evolution of the pacific plate and extension of the geomagnetic polarity reversal time scale with implications for the origin of the jurassic quiet zone abstract linear magnetic anomalies resulting from seafloor spreading were mapped in the vicinity of the magnetic bight in the western pacific ocean new aeromagnetic data allowed the magnetic bight to be more accurately mapped from m21 to m28 and enabled the identification of low amplitude magnetic lineations in the jurassic quiet zone these lineations were formed by magnetic field reversals prior to m29 a revised jurassic geomagnetic polarity reversal time scale was constructed with nineteen reversals older than m29 numbered m30 m38 these reversals extend the record of geomagnetic polarity back in time by approximately 8 ma and are important constraints on the origin of the quiet zone in particular they imply that the jurassic was not a period of constant normal polarity an explanation offered by some authors further they cast doubt on a model of systematically decreasing geomagnetic field strength with increasing age during this period the early history of the northern pacific plate and pacific farallon izanagi p f i triple junction was traced by mapped magnetic isochrons the pacific plate seems to have evolved from a small plate that formed near the phoenix farallon izanagi triple junction about 180 188 m y ago at approximately 17 n 160 e in present coordinates until m21 time the evolution of the northern pacific plate was relatively simple and the p f i triple junction migrated north northwest with respect to the pacific

ordovician magnetostratigraphy a correlation of global data palaeomagnetic studies where primary magnetizations are established from well dated rocks have been compiled to construct a magnetostratigraphic time scale for the ordovician period an excellent correlation of magnetozones is observed between independent studies of the baltic and south siberian platform sequences supplemental datasets from other continents concur with the baltic and siberian polarity data early ordovician times were mainly characterized by a reverse field rapid reversals then occurred during llanvirn and llandeilo times late ordovician times were dominated by a normal polarity field some gaps remain in the polarity record notably for late caradoc early ashgill and mid tremadoc times

sedimentary environments of the middle permian phosphorite chert complex from the northeastern yangtze platform china the gufeng formation a continental shelf radiolarian chert abstract radiolarian chert deposited on a continental shelf occurs in the middle permian gufeng formation on the northeastern yangtze platform china the sedimentary environments of radiolarian cherts from accretionary complexes have been well studied however there are few studies about radiolarian chert deposited on continental shelves therefore we have completed a sedimentological and geochemical study of the gufeng formation the gufeng formation is subdivided into the phosphate nodule bearing mudstone member pnmm and the siliceous rock member srm in ascending order the basal pnmm consists of glauconite bearing mudstone which indicates deposition under aerobic shallow marine conditions whereas the upper pnmm is composed of mudstone including abundant phosphate nodules suggesting deposition near the outer shelf in suboxic conditions the srm consists mainly of alternating beds of black chert mudstone and siliceous mudstone with minor tuffaceous mudstone and porous chert beds the black chert contains abundant radiolarians sponge spicules and organic matter framboidal pyrite occurs in the black chert porous chert in the srm includes abundant rhombohedral cavities which are dolomite moulds surrounded by quartz suggesting dolomitization before silicification during early diagenesis the gufeng chert is characterized by high si mo ni cu and zn contents and extremely low mn content the gufeng chert has high normal paraffin concentrations with petroleum like markers these geochemical features suggest that the gufeng chert was deposited under sulfate reducing conditions and is not hydrothermal but rather biogenic in origin the sedimentological and geochemical data suggest that the gufeng formation was deposited mainly on the outer shelf in suboxic anoxic conditions caused by organic matter produced during upwelling the upwelling probably led to high radiolarian productivity abundant silica and organic matter were deposited in the gufeng basin compared with chert from other sites the gufeng chert shows many similarities with chert from platformal basins but not with chert from accretionary complexes especially with respect to age rock type stratigraphy and geochemical features the chert of the gufeng formation is similar to that of the phosphoria formation in the western u s a which is a world class phosphorite giant these similarities suggest that upwelling occurred around the eastern margins of panthalassa and the paleotethys concurrently during the middle permian in general shelf type radiolarian chert represented by the gufeng chert usually shows some of the following features dark color lack of rhythmical bedding association with phosphorite platformal limestone felsic tuff abundant organic matter and sulfides shelf type radiolarian chert is deposited in a poorly aerated restricted basin or in an oxygen minimum zone

geomagnetic polarity reversal model of deep tow profiles from the pacific jurassic quiet zone the jurassic magnetic quiet zone jqz contains magnetic lineations but their low amplitudes make correlation and interpretation difficult part of the problem is the separation of source and sensor for old deep ocean crust we increased anomaly amplitudes by collecting magnetic data along two deep tow profiles over western pacific jqz lineations a magnetic polarity reversal timescale was constructed by matching deep tow anomalies with a simple rectangular block magnetization model for oceanic crust the polarity sequence covers 11 m y 156 167 5 ma and contains 88 pre m29 polarity chrons extending to chron m41 a limitation of this model is its poor representation of the oldest anomalies upward continued to sea level on deep tow profiles these anomalies have both long and short wavelength components but only the latter are easily modeled on a datum close to the source an alternative polarity model was constructed to match the anomalies upward continued to sea level this model retains only 44 of the deep tow model polarity chrons because of short wavelength attenuation by upward continuation because of the inferred periods and magnetization contrasts we think many of the short wavelength anomalies represent paleofield intensity fluctuations in contrast polarity reversals have been documented by prior magnetostratigraphic work for the younger part of the timescale covered by our model thus our data may show a transition from a geomagnetic field behavior dominated by intensity fluctuations to one dominated by reversals

viscosity of partial melts in the upper mantle the viscosity and density of melts of composition close to primary olivine tholeiite and alkali olivine basalt have been measured at pressures between 0 7 and 1 5 gpa and at temperatures between 1300 and 1475 c using the falling floating sphere method the viscosity of the olivine tholeiite melts decreases only slightly from 1 atm to 1 0 gpa whereas that of the alkali olivine basalt melts decreases by a factor of about 2 in the same pressure range and they become very close to one another about 2 0 pa s at 1 0 1 25 gpa at 1400 c the activation energy for viscous flow of the olivine tholeiite melt is about 250 kj mol at 1 0 gpa the viscosity of partial melts melts formed by partial melting in the upper mantle can be estimated based on the viscosities of the melts and the activation energy for viscous flow obtained by the present experiments the viscosity of the partial melts along the anhydrous solidus of peridotite decreases from about 2 5 pa s at 0 8 gpa 1220 c to only about 0 2 pa s at 3 5 gpa 1580 c thus the partial melts must be extremely fluid at depths greater than 100 km even under anhydrous conditions such partial melts might not ascend because of their high density and play an important role in the movement of the lithosphere the viscosities of the partial melts in the upper mantle may decrease with increasing depth until completion of the transformation of si to six fold coordination the viscosities of magmas and the diffusivity of oxygen in them have an inverse relation which is approximated by the eyring s equation the diffusivity of oxygen in the partial melts estimated from this relation and the viscosity increases from 10 7 cm2 s at 0 8 gpa to 10 5 cm2 s at 3 5 gpa along the anhydrous solidus of peridotite homogenization of partial melts or magmas would be greatly enhanced with increasing depth down to the viscosity minimum

petrologic and geochemical evidence for the formation of organic rich siliceous rocks of the late permian dalong formation lower yangtze region southern china abstract black shales are economically and scientifically important because they are commonly associated with high quality hydrocarbon source rocks and metal accumulations formed during periods of abrupt environmental change organic rich siliceous rocks of the late permian dalong formation developed extensively within middle upper yangtze region western yangtze platform however the formation mechanism of its formation in the lower yangtze region eastern yangtze platform remains a subject of debate due to a lack of outcrop exposure petrologic mineralogic and geochemical data are presented for three sections of the dalong formation within the lower yangtze region geochemical ratios including v v ni v cr ni co u th and v sc suggest that the dalong formation was deposited in an oxygen poor environment the elevated concentration of mo 100 ppm further suggests that free h2s existed in the bottom water which was favorable for the accumulation of large amounts of organic matter mo toc ratios reveal that water flow in the lower yangtze basin was moderately to strongly restricted during deposition of the dalong formation flow within the upper middle parts of the yangtze basin was also restricted suggesting that northern marginal basins on the yangtze platform formed part of a single ocean during the late permian i e changhsingian cherts of the dalong formation reflect high primary productivity similar to that of modern day upwelling zones which increased the amount of organic matter these results combined with previous work suggest that the long term oxygen poor conditions during deposition of the dalong formation were caused by restricted water circulation in a unique paleogeographic environment characterized by low latitude and submarine paleo highlands such settings of low latitude characterized by tropical climate favored the growth of siliceous zooplankton in the zones with submarine paleo highlands having created topographic barriers to water circulation restricted bottom water flow and oceanic anoxia during the late permian were likely the main controls on the accumulation of organic rich rocks elevated nutrient levels caused by frequent oceanic upwelling along the western margin of the south china craton and global volcanism at this time facilitated siliceous organism productivity

jurassic magnetostratigraphy 3 bathonian bajocian of carcabuey sierra harana and campillo de arenas subbetic cordillera southern spain abstract four sections in majocian bathonian middle jurassic pelagic limestone with standard ammonite zonation have yielded magnetic polarity sequences magnetic directions in these red to white limestones were obtained by thermal demagnetization and were stable from about 300 c to in excess of 450 c the polarity patterns indicate that the majority of the bajocian and bathonian is characterized by quite frequent reversals of the magnetic field lengthy periods of constant polarity particularly constant normal polarity were not observed the average frequency of reversals is about 6 per ammonite zone which roughly may be interpreted as a frequency of a reversal every 260 000 years a rate comparable to that of the miocene pliocene paleolatitudes of these sites 25 28 are about 10 south of their present positions variable clockwise block rotations within the subbectic region have rotated these sites relative to stable iberia

geological and geochemical characterization of the lower cretaceous pearsall formation maverick basin south texas a future shale gas resource as part of an assessment of undiscovered hydrocarbon resources in the northern gulf of mexico onshore mesozoic section the u s geological survey usgs evaluated the lower cretaceous pearsall formation of the maverick basin south texas as a potential shale gas resource wireline logs were used to determine the stratigraphic distribution of the pearsall formation and to select available core and cuttings samples for analytical investigation samples used for this study spanned updip to downdip environments in the maverick basin including several from the current shale gas producing area of the pearsall formation the term shale does not adequately describe any of the pearsall samples evaluated for this study which included argillaceous lime wackestones from more proximal marine depositional environments in maverick county and argillaceous lime mudstones from the distal lower cretaceous shelf edge in western bee county most facies in the pearsall formation were deposited in oxygenated environments as evidenced by the presence of biota preserved as shell fragments and the near absence of sediment laminae which is probably caused by bioturbation organic material is poorly preserved and primarily consists of type iii kerogen terrestrial and type iv kerogen inert solid bitumen with a minor contribution from type ii kerogen marine based on petrographic analysis and pyrolysis carbonate dominates the mineralogy followed by clays and quartz the low abundance and broad size distribution of pyrite are consistent with the presence of oxic conditions during sediment deposition the pearsall formation is in the dry gas window of hydrocarbon generation mean random vitrinite reflectance values ro 1 2 2 2 and contains moderate levels of total organic carbon average 0 86 wt which primarily resides in the inert solid bitumen solid bitumen is interpreted to result from in situ thermal cracking of liquid hydrocarbon generated from original type ii kerogen that was prevented from expulsion and migration by low permeability the temperature of maximum pyrolysis output tmax is a poor predictor of thermal maturity because the pyrolysis s2 peaks from rock eval analysis are ill defined vitrinite reflectance values are consistent with the dry gas window and are the preferred thermal maturity parameter a maverick basin pearsall shale gas assessment unit was defined using political and geologic boundaries to denote its spatial extent and was evaluated following established usgs hydrocarbon assessment methodology the assessment estimated a mean undiscovered technically recoverable natural gas resource of 8 8 tcf of gas and 3 4 and 17 8 tcf of gas at the f95 and f5 fractile confidence levels respectively significant engineering challenges will likely need to be met in determining the correct stimulation and completion combination for the successful future development of undiscovered natural gas resources in the pearsall formation

origin and deposition of organic matter in continental chert of the middle permian gufeng formation in the northeastern yangtze platform abstract the middle permian gufeng formation in the northeastern yangtze platform china contains radiolarian chert that is characterized by black color high content of fe mo ni cu and zn based on the inorganic geochemical features previous work concluded that the cherts were deposited under sulfate reducing conditions in this study organic carbon c org n and s contents of the cherts and h c and o c ratios of kerogen were examined to explore the origin of the organic matter the concentration of c org in the black chert is extremely high relative to other cherts in accretionary complexes and continental platforms the average c n ratio of organic matter is 35 indicating that the organic matter originates from land plants the kerogen from the chert is classed as type iv based on the h c and o c ratios suggesting that oxidized or reworked organic matter was supplied to the gufeng basin therefore the organic matter is considered to originate from terrestrial plants or reworked material from land due to the depositional setting on a continental platform nutrient supplied with organic matter from land probably played an important role in abundant biogenic productivity and sedimentation of the radiolarian chert on the continental platform

enhanced effects of large scale co 2 transportation on oil accumulation in oil gas bearing basins implications from supercritical co 2 extraction of source rocks and a typical case study abstract large scale mantle derived co2 emplacement and co accumulation of co2 and crude oil have been discovered in oil gas bearing basins in eastern china and many other areas worldwide to investigate the effect of the natural supercritical co2 on the migration of crude oil as well as on the formation of oil reservoirs experiments on supercritical co2 extraction sce and traditional chloroform extraction ce of hydrocarbon source rocks were carried out and the geochemical characteristics of the huangqiao co2 oil reservoir in the subei basin eastern china were investigated the sce yielded a large proportion of the hydrocarbons in the permian mudstone source rocks at 110 c under 30 mpa compared with the traditional chloroform extraction ce the sce retrieved organic compounds are dominated by saturated hydrocarbons and contain a relatively higher concentration of small molecular mass compounds many wells in the huangqiao reservoir yielded large amounts of co2 from several formations such as the triassic qinglong formation t1q and the permian longtang formation p2l accompanying the co2 flow a certain amount of oil is commonly recovered the oil is mainly light oil or condensate oil with a relative density of 0 7933 0 8308 and it contains 90 06 97 37 saturated hydrocarbons compared with hydrocarbons in the permian source rocks the oil accompanying the co2 in the huangqiao reservoir contains more c20 hydrocarbons and less c21 hydrocarbons the oil accompanying the co2 has a similar composition to the sce extracts from the source rocks namely both contain a relatively high concentration of low molecular mass hydrocarbons therefore it can be concluded that in the huangqiao area during movement upward along deep faults and fractures or flow through source rocks the deep supercritical co2 naturally extracted hydrocarbons especially small molecular hydrocarbons from the source rocks and then brought them to the shallow strata to form the co2 oil coupling reservoirs

upper cambrian to middle ordovician magnetostratigraphy from the kulumbe river section northwestern siberia abstract we present the magnetostratigraphy of an upper cambrian to middle ordovician sedimentary section sampled along the kulumbe river in northwestern siberia thermal demagnetization yields the determination of two magnetic components a component of steep inclination is interpreted as a remagnetization acquired during the emplacement of the siberian traps at the permian triassic boundary another component with a moderate inclination essentially carried by hematite and sometimes by magnetite likely represents a syndepositional or nearly syndepositional magnetization of the studied deposits a sequence of 17 magnetic intervals is observed between the upper part of the upper cambrian and the tremadoc three of them being poorly defined by single samples we also find that the llanvirn magnetostratigraphic sequence contains only one reversed polarity interval together with magnetostratigraphic results previously obtained from the moyero river section from siberia our data suggest the occurrence of a 25 30 myr long period during the lower and the middle ordovician characterized by a very low magnetic reversal frequency possibly containing a superchron and dominated by reversed polarity this geomagnetic feature would be compatible with a time constant of about 150 myr in the reversal process through the whole phanerozoic

mechanisms of shale gas storage implications for shale gas exploration in china this article reviews the mechanisms of shale gas storage and discusses the major risks or uncertainties for shale gas exploration in china at a given temperature and pressure the gas sorption capacities of organic rich shales are primarily controlled by the organic matter richness but may be significantly influenced by the type and maturity of the organic matter mineral composition especially clay content moisture content pore volume and structure resulting in different ratios of gas sorption capacity gsc to total organic carbon content for different shales in laboratory experiments the gsc of organic rich shales increases with increasing pressure and decreases with increasing temperature under geologic conditions assuming hydrostatic pressure gradient and constant thermal gradient the gsc increases initially with depth due to the predominating effect of pressure passes through a maximum and then decreases because of the influence of increasing temperature at greater depth this pattern of variation is quite similar to that observed for coals and is of great significance for understanding the changes in gsc of organic rich shales over geologic time as a function of burial history at an elevated temperature and pressure and with the presence of moisture the gas sorption capacities of organic rich shales are quite low as a result adsorption alone cannot protect sufficient gas for high maturity organic rich shales to be commercial gas reservoirs two models are proposed to predict the variation of gsc and total gas content over geologic time as a function of burial history high contents of free gas in organic rich shales can be preserved in relatively closed systems loss of free gas during postgeneration uplift and erosion may result in undersaturation the total gas contents lower than the sorption capacity and is the major risk for gas exploration in marine organic rich shales in china

melt segregation from partially molten source regions the importance of melt density and source region size the compressibility of basic melt at 1 atmosphere is about an order of magnitude higher than that of mantle minerals consequently the density contrast between melt and the principal residual crystals in mantle source regions is expected to decrease with increasing source region depth the increasingly olivine normative character of primary melts produced at greater depths is also expected to result in a decrease in this density contrast with increasing source region depth once vertical permeability is established by melt generated during partial melting buoyancy driven melt percolation can under some circumstances segregate melt from the residual crystals in its source region on a geologically rapid time scale limits to this process are provided by cooling of the source region freezing melt in and rigidity of the crystalline matrix mechanically trapping melt source region size influences these limits strongly consequently small partially molten diapirs km in diameter may be able to trap large melt fractions 30 but larger source regions would be unable to do so the reduction in density contrast with pressure reduces the buoyant force driving melt percolation and provides another limit to melt segregation diapirs at depth may thus stably contain large fractions of melt but may decompress and unload their melt during ascent this effect would be enhanced in small diapirs and may be relevant to the genesis of komatiitic magma melt compression may also be a factor in explaining why the very different maximum depths inferred for typical basic melt segregation from source regions on different planets 500 km on the moon 250 km on mars 100 km on earth correspond to similar pressures 25 35 kbar at greater pressures melt may no longer be capable under ordinary conditions of segregating upwards by buoyancy this may also help to explain why depleted peridotites overlie more fertile peridotites and how deep regions of the mantle are able to remain fertile over geologic time

comment on the combined analysis of remagnetization circles and direct observations in paleomagnetism by p l mcfadden and m w mcelhinny

methane sorption capacities and geochemical characterization of paleozoic shale formations from western peninsula malaysia implication of shale gas potential abstract thick sequences of overmatured paleozoic black shales formation were deposited in the western peninsula wp malaysia which can be considered as the potential shale gas reservoir therefore to study the shale gas potential of the paleozoic silurian permian shale formations 146 samples from seven formations were collected from wp malaysia a combination of methane sorption capacities geochemical and trace element studies have been performed on the shale samples the results indicate that the high pressure up to 15 mpa methane sorption capacity of the silurian devonian devonian carboniferous and permian shales are between 0 079 and 0 154 0 056 and 0 113 0 052 and 0 094 and 0 085 and 0 169 mmol g rock respectively at 30 c methane sorption capacities of the wp malaysia shale were found to be greatly similar to sorption values of hot shales from posidonia germany barnett usa and longmaxi china shales the measured total organic carbon toc generally exceeded 2 wt average of 4 wt except for carboniferous shales 1 wt the biomarker analysis and tmax values revealed that the kerogen has evolved into the metagenesis stage the organic matter is likely comprises hydrogen rich kerogen deposited under marine conditions in dysoxic to anoxic environment after a comprehensive analysis the silurian devonian devonian and permian shales in western peninsula malaysia can be classified as potential gas shales based on their high toc contents presence of type iii kerogen high thermal maturity and significant methane sorption capacities

modes of mantle convection and the removal of heat from the earth s interior earth thermal histories based on two layer and whole mantle parameterized convection models have been explored to determine the influence of the mode of mantle convection on the content and distribution of mantle radioactive heat sources and on the temperatures and heat transfer properties of the mantle two layer mantle convection thermally insulates the lower mantle and is less efficient at heat removal than whole mantle convection consequently two layer mantle convection requires a lower mantle depleted of radioactive heat sources contrary to the undepleted lower mantles of recent geochemical models whole mantle convection removes 3 times more primordial heat from the earth s interior and 6 times more heat from the core in 4 5 billion years than does two layer convection the average mantle volumetric heat generation rates for both modes of convection are comparable to that of a potassium depleted chondrite thus no potassium is necessary in the core to balance the observed present day surface heat flux however most of the radioactives are concentrated in the upper mantle for two layer convection model geotherms for whole mantle convection compare well with independent estimates of temperature at various depths including the core mantle boundary while the lower mantle is too hot for two layer convection models thermal histories of the upper mantle in two layer models are similar to those of whole mantle models thermal histories for the lower mantle in two layer models are similar to those of the core in whole mantle convection models this is because the lower mantle is thermally insulated by the upper mantle if it convects separately just as the core is thermally insulated by the whole mantle the differences between whole and two layer mantle convection are mostly due to the thermal insulation of the lower mantle and the smaller efficiency of heat removal of the upper mantle compared to that of the whole mantle which is much larger in volume a whole mantle convection model reconciling the need for distinct geochemical reservoirs with the physics of mantle convection is presented

guadalupian middle permian ocean redox evolution in south china and its implications for mass extinction abstract the guadalupian mass extinction was a long term biocrisis that started in the early guadalupian epoch permian period many studies of the causes of the extinction have focused on the late guadalupian although the entire guadalupian should be studied to address its origins the selective nature of the species removed during the guadalupian extinction also remains a puzzle here we present pyrite framboid size distributions pyrite sulfur isotopic compositions and c n s profiles for the entire guadalupian from south china to develop a record of ocean redox evolution to help understand the selective extinction our results indicate that euxinia was mostly persistent in the deep water platform basin throughout the guadalupian which triggered long term early and middle guadalupian shallow water dysoxia and frequent episodic late guadalupian euxinia events that resulted in a gradual long term early and middle guadalupian diversity decrease and selective late guadalupian extinction the combined effect of euxinia and global regression led to selective extinction of taxa that had weakly buffered respiratory physiology and high growth efficiency such as brachiopods large fusulinids and giant bivalves

reservoir evaluation of the lower silurian longmaxi formation shale gas in the southern sichuan basin of china abstract the lower silurian longmaxi formation the palaeozoic is organic rich black shale in the southern sichuan basin the yangtze plate of china this study analyses the lateral extent and thickness burial depth total organic carbon content and thermal maturity of the longmaxi formation black shale as the key features of the shale gas reservoir the thickness of the black shale ranges from 10 to 170 m the thickest reservoir is located in changning naxi yongchuan region the toc of the shale at the bottom of the formation 50 m thickness is above 2 0 the lateral distribution of toc varies with the lateral distribution of thickness with the maximum toc in the gongxian luzhou yongchuan region the burial depth ranges from 2000 to 4500 m the shale is thermally over mature the evaluation of reservoir characteristics indicates that the longmaxi formation has conditions appropriate for shale gas accumulation and thus resource potential in the southern sichuan basin of china the objective of this preliminary evaluation of the reservoir characteristics is to locate potential areas favourable for exploration the most favourable areas are defined here as those where the thickness of black shale is more than 100 m and the burial depth is less than 3000 m these cover approximately 12 600 km 2 the most favourable areas which cover an area of approximately 5100 km 2 are located in the northeast luzhou region