thermal histories of the core and mantle recognition that the cooling of the core is accomplished by conduction of heat into a thermal boundary layer d at the base of the mantle partly decouples calculations of the thermal histories of the core and mantle both are controlled by the temperature dependent rheology of the mantle but in different ways thermal parameters of the earth are more tightly constrained than hitherto by demanding that they satisfy both core and mantle histories we require evolution from an early state in which the temperatures of the top of the core and the base of the mantle were both very close to the mantle solidus to the present state in which a temperature increment estimated to be 800 k has developed across d the thermal history is not very dependent upon the assumption of newtonian or non newtonian mantle rheology the thermal boundary layer at the base of the mantle i e d developed within the first few hundred million years and the temperature increment across it is still increasing slowly in our preferred model the present temperature at the top of the core is 3800 k and the mantle temperature extrapolated to the core boundary without the thermal boundary layer is 3000 k the mantle solidus is 3860 k these temperatures could be varied within quite wide limits without seriously affecting our conclusions core gravitational energy release is found to have been remarkably constant at 3 1011 w nearly 20 of the core heat flux for the past 3 109 y although the total terrestrial heat flux has decreased by a factor of 2 or 3 in that time this gravitational energy can power the chemical dynamo in spite of a core heat flux that is less than that required by conduction down an adiabatic gradient in the outer core part of the gravitational energy is used to redistribute the excess heat back into the core leaving 1 8 1011 w to drive the dynamo at no time was the dynamo thermally driven and the present radioactive heating in the core is negligibly small the dynamo can persist indefinitely into the future available power 1010 y from now is estimated to be 0 3 1011 w if linear mantle rheology is assumed or more if mantle rheology is non linear the assumption that the gravitational constant decreases with time imposes an implausible rate of decrease in dynamo energy with conventional thermodynamics it also requires radiogenic heating of the mantle considerably in excess of the likely content of radioactive elements

40ar 39ar geochronological constraints on the age and evolution of the permo triassic emeishan volcanic province southwest china abstract the biostratigraphically constrained permo triassic emeishan volcanic province evp extending over wide areas in southwest china has been recently considered as a large igneous province contemporaneous with the siberian traps and the siliceous tuffs at the p t boundary in south china we report the first 40ar 39ar ages on this igneous province minimum ages have been obtained on phenocrystic plagioclase of the emeishan basalt which has undergone a pervasive metamorphism most likely during subsequent tectonization as a consequence of terrane amalgamation comparison between the ar release spectra obtained on clear vs cloudy plagioclase indicates a 40 30 ma sericite resetting time a minimum apparent age of 246 4 ma for plagioclase from a plagiogranite a late differentiate of the panzhihua layered complex and an age of 254 5 ma for phlogopite from a pyroxenite near lake erhai provide the first absolute age constraint on this igneous province additional ar ar age measurements on post emeishan alkaline and mafic magmatism yielded 104 2 and 100 2 ma for an alkaline complex near panzhihua and 42 1 ma for a gabbro sill emplaced near the ertan dam further study is still needed to determine the age of the emeishan volcanic emission accurately and to test the validity of the assumed short duration of the eruption

time dependence of mantle plumes some simple theory dynamical calculations indicate that plate tectonics are likely to have a major effect on the initiation of plumes from the basal boundary layer in the mantle and their subsequent evolution plume start because the boundary layer is hotter than the overlying mantle and hence unstable to perturbations the growth rate of perturbations is too weakly dependent on wavelength to control the geographic distribution of plumes instead the distribution of plumes is strongly influenced by the shape of large perturbations associated with slabs and surface plates plumes evolve because downward return flow is needed to replace the material tapped from the boundary layer this flow downwarps the top of the boundary layer several hundred kilometers from the plume and thus restricts further flow of hot material toward an active plume the geometry of this downwarp is strongly influenced by the initial relief of the top of the boundary layer and hence by plate processes the actual history of plates and slabs is thus needed in numerical models for comparison with real data on plume fluxes

the mathematics of early diagenesis from worms to waves the changes that sediments undergo after deposition are collectively known as diagenesis diagenesis is not widely recognized as a source for mathematical ideas however the myriad processes responsible for these changes lead to a wide variety of mathematical models in fact most of the classical models and methods of applied mathematics emerge naturally from quantification of diagenesis for example small scale sediment mixing by bottom dwelling animals can be described by the diffusion equation the dissolution of biogenic opal in sediments leads to sets of coupled nonlinear ordinary differential equations and modeling organisms that eat at depth in the sediment and defecate at the surface suggests the one dimensional wave equation while the effect of waves on pore waters is governed by the two or three dimensional wave equation diagenetic modeling however is not restricted to classical methods diagenetic problems of concern to modern mathematics exist in abundance these include free boundary problems that predict the depth of biological mixing or the penetration of o2 into sediments algebraic differential equations that result from the fast reversible reactions that regulate ph in pore waters inverse calculations of input functions histories and the determination of the optimum choice in a hierarchy of possible diagenetic models this review highlights and explores these topics with the hope of encouraging further modeling and analysis of diagenetic phenomena

solid bitumen occurrences in the arruda sub basin lusitanian basin portugal petrographic features abstract the middle jurassic to cretaceous sedimentary record in the lusitanian basin portugal reveals the presence of disseminated solid bitumen the present work is focused on the petrographic characteristics of solid bitumen identified in the freixial 1 and benfeito 1 boreholes arruda sub basin lusitanian basin that display different thermal maturities microscopy techniques reflected and transmitted white light incident blue light and sem and organic geochemistry analyses total organic carbon total sulfur and insoluble residue were used to study these samples from the results obtained by optical microscopy fluorescence and reflectance it was possible to distinguish three types of solid bitumen they were labeled as solid bitumen a present in all the samples solid bitumen b and solid bitumen c these ones observed in some of them they correspond to allochthonous migrated bitumens in blue incident light some bitumen do not show fluorescence while others reveal fluorescence that range from yellow solid bitumen b to dark brown solid bitumen a all bitumens are optically isotropic bitumen reflectance varies between 0 70 and 2 60 r r and the vitrinite reflectance ranges from 1 11 to 1 48 r r based on the r r values the solid bitumen identified in these samples are classified as impsonite epi and cata or pyrobitumen no relation can be established with confidence for the reflectance of bitumens with the reflectance of vitrinite

identification and distribution of chrysene methylchrysenes and their isomers in crude oils and rock extracts abstract chrysene its methylated homologues and their structural isomers are important polyaromatic compounds in crudes oils coals and sediment extracts chrysene benzo a anthracene methylchrysenes and methylbenzo a anthracenes were unequivocally identified in mass chromatograms by comparison with authentic standards and by retention indices reported in the literature the response factors relating those of chrysene and methylchrysenes to internal standards perdeuterated chrysene chrysene d12 and pyrene pyrene d10 were obtained by gc ms analyses of mixture solutions with different concentration ratios the oil families of ordovician reservoirs in the cratonic region of the tarim basin nw china are distinguished by the distribution patterns of chrysene methylchrysenes and their isomers the majority of the oil accumulations and sediment extracts from the middle upper ordovician source rocks are characterized by low concentrations of benzo a anthracene and methylbenzo a anthracenes relative to chrysene and methylchrysenes respectively in contrast some oils with relatively high abundances of benzo a anthracene and methylbenzo a anthracenes were derived from cambrian and lower ordovician source rocks the effect of maturity on the distribution patterns of methylchrysenes in tertiary lacustrine shales from the liaohe basin east china was investigated the 2 1 methylchrysene ratio keeps a nearly constant value with increasing maturity at the low maturity stages and then it abruptly increases corresponding approximately to the onset of intense c 15 hydrocarbon generation this indicates that chrysene and its methylated homologues are useful molecular indicators in petroleum geochemistry

structure of axisymmetric mantle plumes results of high resolution numerical calculations of axisymmetric thermal plumes in an infinite prandtl number fluid with thermally activated viscosity are used to infer the structure of axisymmetric subsolidus thermal plumes in the earth s lower mantle we calculate the velocity and temperature distribution for axisymmetric convection above a heated disk in an incompressible fluid cylinder 2400 km in height and 1200 km in diameter initially at a uniform temperature t the lower boundary representing the plume source region near the core mantle boundary is stress free and maintained at temperature tc t the upper boundary is permeable allowing the plume to escape the cylinder we determine the sensitivity of plume structure to viscosity variations c ranging from 102 to more than 104 and temperature differences t tc t in the range 400 850 k starting plumes consist of a large leading diapir and a trailing conduit connected to the thermal boundary layer above the heated surface the leading diapir expands during ascent to about 400 km diameter at 2200 km height in steady state the plume consists of a narrow high velocity conduit imbedded within a broader thermal halo the width of both these structures is proportional to height above the heated boundary and inversely proportional to t and the viscosity ratio heat transport in the plume is nearly independent of viscosity variations a simplified boundary layer model yields a heat transfer law nu ra where nu is the plume nusselt number and ra is the rayleigh number based on t and the radius of the heated circular region feeding the plume calculated steady state plume heat transports fit this law to within a few percent we present several calculations of plumes with heat transport in the range 100 400 gw similar to the advective heat transport by the hawaiian hotspot at the top of the lower mantle plumes with large viscosity variations have high velocity conduits 50 60 km in diameter and 125 km diameter thermal halos a centerline temperature anomaly of about 500 k and a centerline velocity of about 75 cm yr 1 plumes with weak viscosity variations are approximately twice as broad and have centerline temperature anomalies less than 160 k at the same height and much smaller velocity large viscosity variations and a minimum heat transport are both

pyrobitumen in south china organic petrology chemical composition and geological significance abstract pyrobitumen has been discovered in the dolostone reservoir of the central sichuan basin southwest china accumulates coevally with hydrothermal minerals in pores the pyrobitumen has strong anisotropy with an evolutionary sequence from mosaic to a fibrous texture a similar sequence of anisotropy has also been observed in mesophase pitch during the process of coking coal reflectance of the pyrobitumen shows a positive correlation with anisotropic evolution and increasing depth hopane and sterane biomarkers are abundant in extracts of highly anisotropic pyrobitumen with smooth rough hyperplastic surface and honeycomb micropores methylpyrene and methylchrysene maturity indicators and the reflectance values of pyrobitumen show a positive linear correlation in cambrian samples but show random correlation in sinian samples fluid inclusion microthermometry of hydrothermal minerals together with the burial and heat flow history of the reservoir indicate an abrupt thermal event that may have impacted the generation and evolution of pyrobitumen this appears to be confirmed by the reflectance values of pyrobitumen in the source rock and reservoir the pyrobitumen in source rock was less heated by the hydrothermal fluid due to its poor porosity and have lower reflectance values however the pyrobitumen in weathering crust reservoir was more heated by the hydrothermal fluid and have higher reflectance values because the reservoir rocks have higher porosity the occurrence and characteristics of pyrobitumen indicate an in situ pyrolysis of oil which was triggered by an abrupt thermal event in the reservoir the reconstruction of burial history and heat flow as well as the hydrothermal fluid minerals of the dolomite reservoir all indicate the thermal event of the sichuan basin might correlate with the emei mantle plume in late permian

an occurrence of coked bitumen raton formation purgatoire river valley colorado u s a abstract numerous examples of coke produced by igneous intrusion into coal have been reported in the spanish peaks region of south central colorado however in a recent study of an intruded section of the raton formation upper cretaceous paleocene along the purgatoire river near medina plaza co coked bitumen has been observed this material occurs in fingers hexagonally jointed bodies in a shaley xenolith within a lamprophyre sill and in carbonaceous type iii shale directly below the sill the coke fingers are characterized by a remarkable flow mosaic texture high vitrinite coke reflectance average random reflectance between 8 and 9 but with maximum readings around 14 15 high anisotropy abundant devolatilization vacuoles and an absence of inertinite inclusions within the underlying shales the coked bitumen occurs as pore void and fracture linings and fillings geochemically the coke in the fingers has low s1 and s2 values these observations suggest that the coke found in this study was not formed by the direct coking of coal but from a mobile phase bitumen or pitch that was subsequently coked by the intrusion this bitumen was either derived from the abundant coal within the section above the sill or from the organic matter contained within the type iii carbonaceous shales or both unaltered type iii shale sampled at this site has a hi of 350 mg hc g toc suggesting some albeit limited capacity to generate petroleum we suggest that bitumen was generated prior to or during the time of intrusion and was subsequently coked by the high temperatures of the emplaced sill as the bitumen pooled adjacent to the sill rapid heating led to the development of mesophase resulting in a highly anisotropic ribbon mosaic texture on cooling and vaporization of gases that subsequently condensed along pores vacuoles and fractures as pyrolytic carbon and spherulitic pyrolytic carbon bitumen within the underlying silty shales was also coked but to a lesser degree the texture of this coked bitumen looks very much like commercially produced petroleum coke this coked bitumen differs from other reports of coked bitumen in its mode of occurrence coke fingers in a xenolith ribbon mosaic structure and extremely high anisotropy and reflectance

the origin of 4 methyl steranes and pregnanes from tertiary strata in the qaidam basin china abstract a geochemical study of oils and source rocks in tertiary saline lake facies from the qaidam basin of china demonstrates that pregnanes are mainly derived from the thermal degradation of organic matter in source rocks synchronous with hydrocarbon genesis whereas 4 methyl steranes may principally be a product of microbial activity during diagenesis

determination of thermal maturity and organic matter type by principal components analysis of the distributions of polycyclic aromatic compounds abstract the thermal maturity and organofacies sensitivity of polycyclic aromatic compound pac distributions was explored by examination of the aromatic fractions of solvent extracts from a diverse set of 53 shales coals and kerogen macerals which have undergone either natural or artificial maturation and which represent all three principal sedimentary organic matter om types systematic changes with maturation were observed in the following groups of isomers tri and tetramethylnaphthalenes methyl and dimethylphenanthrenes methyl and dimethyldibenzothiophenes methylpyrenes and methylchrysenes the maturity differences were quantified by mathematical ratios of the relative concentrations of the more thermally stable isomers to the less stable on the basis of theoretical considerations and empirical observations the pac maturity parameters unlike those derived from saturated biomarker stereoisomers are typically effective across the entire oil generation window to compensate for the effects of om type on the maturity parameters they were combined using principal components analysis the resulting first principal component was in good agreement with independent indicators of maturity the relative distributions of c0 c3 alkylphenanthrenes dibenzothiophene methyldibenzothiophenes and methyldibenzofurans were evaluated by a separate principal components analysis the results permitted an independent grouping of the samples by om type and suggested additional simple molecular ratios that allow graphical recognition of om type including the ratio of dibenzothiophenes to dibenzofurans and a ratio using c2 alkylphenanthrene isomers

an analytic model for a mantle plume fed by a boundary layer summary an approximate analytical solution for flow in a mantle plume of constant radius viscosity and density contrast is obtained in cylindrical coordinates the differential equations for vertical velocity of the mantle surrounding the plume and for topography are homologous to the equation for flexure of an elastic plate although the model is too simple to be fully applicable to the earth one can conclude that the vertical velocity in the mantle changes significantly away from plumes that the viscosity of the plume is important for controlling flow rate and that the long wavelength geoid anomalies are sensitive to the viscosity of the surrounding mantle the first induced upwelling away from a plume is quite weak and unlikely to control the spacing of plumes

application of aromatic compounds as maturity indicators in source rocks and crude oils concentration ratios of aromatic compounds such as naphthalenes phenanthrenes and dibenzothiophenes are at present attracting increasing attention as maturity indicators in sedimentary rocks and crude oils generally these indicators rely either on an increase with maturity in the degree of alkylation of a given parent compound or a shift in the isomer distribution of alkyl aromatic homologues towards thermally more stable isomers a combination of both concepts in the methylphenanthrene index mpi resulted in an excellent maturity parameter as demonstrated for rock extracts by an improved correlation with mean vitrinite reflectance rm between 0 65 and 1 4 i e in the zone of oil formation in cases that rm measurements were ambiguous this empirical relationship has proved useful in the calculation of theoretical vitrinite reflectance rc values from the mpi on the other hand for potential petroleum source rocks reaching maturity at relatively low temperatures the influence of the organic matter type on the aromatic distributions cannot be neglected consequently organic facies effects should be taken into account in the interpretation of aromatic distributions of such source rocks and related crude oils since the impact of the organic facies is strongly reduced with increasing maturity aromatic maturity parameters are particularly useful in the maturity evaluation of post mature crude oils and condensates in contrast to biological markers substantially higher concentrations of the key alkyl aromatics persist at elevated maturation levels thus aromatic maturity parameters should be considered as versatile tools in organic maturation studies and can complement established maturity indicators based on steranes and terpanes

recognition of vitrinite with non uniaxial negative reflectance characteristics non uniaxial negative reflectance characteristics are being reported for coals from around the world with increasing frequency these data have traditionally been collected from oriented sections cut from a block of coal to determine the magnitudes of the principal reflectance axes to make data collection less time consuming a method of determining the principal reflectance axes from a standard crushed coal sample has been developed the method requires measurement of the maximum and minimum apparent reflectances from a series of randomly oriented vitrinite particles the reflectance crossplot displays these two reflectance values against their difference or bireflectance the paper describes the method of interpreting the resultant pattern to determine the values of the three principal reflectance axes analysis of coals from the british columbia rocky mountains and foothills revealed biaxial and uniaxial positive as well as uniaxial negative reflectance characteristics a new measure of maturation rev is proposed which is based purely on the lengths of the three principal reflectance axes rm approximates this value but is influence by any eccentricity of the reflectance indicating surface ris vitrinite with a non uniaxial reflectance characteristics cannot be adequately described by a single measure such as rmaxorrm but requires reference to both the size and shape of the ris a reflectance determination such as rev or rm provides rank astm information whereas the new measures rst and ram describe a reflectance indicating surface shape which is the result of maturation and tectonic histories vitrinites with non uniaxial negative reflectance characteristics are abundant in the coalfields of the rocky mountains and foothills of british columbia rmax does not fully describe the reflectance character of these coals and does not describe the potentially useful ris shape

a simple model of whole mantle convection isotopic evidence of the chemical variability of basalts implies the existence of distinct long lived chemical reservoirs in the mantle this has commonly been interpreted as evidence that mantle convection is layered since known models of whole mantle convection have too much shearing to allow preservation of these reservoirs however the geochemical evidence requires at least three reservoirs and models of layered convection have dynamical difficulties casting serious doubt on the viability of these models this difficulty has been resolved in the present paper by the development of a simple model of whole mantle convection which allows the preservation of chemically distinct reservoirs in this model heating of the mantle from below produces axisymmetric plumes which carry heat upward through the mantle without causing overturning hence the lower mantle is much less sheared than in the usual two dimensional model mantle convection is driven by the penetration of cold lithospheric slabs from above it is argued that the pattern of convection is governed primarily by the dependence of viscosity on temperature and this dependence drives the mantle toward an isoviscous state these ideas are quantified in a simple one dimensional model of mantle convection in which the slab mass flux as a function of radius is governed by the requirement that the temperature profile remains isoviscous the resulting convection cycles material through the upper mantle more rapidly than through the lower mantle this provides a mechanism for an initially homogeneous mantle to become chemically stratified with a depleted upper mantle and primitive lower mantle

magnetotelluric imaging of the society islands hotspot in april june 1989 seafloor magnetotelluric data across and along the leading edge of the tahiti hotspot were obtained the magnetotelluric response functions were found to be strongly influenced by bathymetric and island effects and a new procedure for modeling and removing this distortion using a thin sheet approach combined with the measured water depths is introduced the corrected response functions are consistent with a two dimensional structure inversion of the data shows a slightly higher conductivity relative to a reference site located away from the hotspot down to 130 km depth beneath the active area southeast of tahiti underlain by a more resistive structure there is a suggestion for a change in conductivity in the 400 450 km depth range which is consistent with elevated temperatures this result is consistent with a mantle plume of limited extent less than 150 km radius located near the leading edge of the tahiti hotspot the magnetotelluric data provide no evidence for lithospheric thinning or for a strong thermal influence over a large area as would be required by a superswell model

the influence of solid reservoir bitumen on reservoir quality 1 reservoir bitumen precipitates in pore systems from the alteration of trapped or migrating oil in carbonate and siliciclastic reservoirs reservoir bitumen is not readily identified on typical log suites where it is read as open porosity which has hampered its broad recognition as a reservoir altering cement when present as a solid it can be as influential on reservoir quality as carbonate silica or authigenic clay cements and should therefore be evaluated as part of the diagenetic evolution of any pore system whenever encountered five morphotypes of reservoir bitumen have been identified and named droplets carpets peanut brittle vesicular and digitate data from east texas gulf coast and west african examples indicate that reservoir bitumen can significantly reduce total effective porosity permeability can be significantly reduced by restricted or closed pore throats and by fines migration even when bitumen occurs in only moderate amounts the occurrence and distribution of bitumen on well field and regional scales can range from uniform and predictable to irregular and unpredictable but mappable through examination of core and cuttings within a trap bitumen can cause heterogeneity and form permeability barriers not related to depositional facies or pre bitumen diagenesis and reservoir quality it economic importance must be recognized when reservoir parameters are adversely affected impacting reserves calculations recovery factors and secondary recovery programs on a regional scale predictive models can be developed to determine the areas of a trend or portions of a stratigraphic section that are most likely to be affected and these models can be incorporated with other data for evaluating expected reservoir quality in regional play assessments

mineralisation of organic matter in coastal sediments at different frequency and duration of resuspension coastal sediments represent sites of major importance for many biogeochemical processes including organic matter mineralisation these sediments are frequently subjected to intermittent physical f

solid bitumen in calcite veins from the natih formation in the oman mountains multiple phases of petroleum migration in a changing stress field abstract solid bitumen in calcite veins in natih limestone on the southern flank of the jebel akhdar anticline provide evidence for at least two previously unrecognized petroleum migration events in the oman mountains we present field observation of bituminous calcite veins combined with microscopy using highly polished thin sections this allows imaging of solid bitumen in reflected light and study of its microstructural context in transmitted light straight and en echelon black impregnated bedding normal natih a calcite veins strike 110 they formed as one of the earliest structures in an extensional stress regime at the end of cretaceous turonian santonian either by flexure of the arabian plate wasia aruma break or by subsidence during subduction the veins always contain planar arrays of small during the first migration event microfracturing during obduction of the semail ophiolite and emplacement of the hawasina thrust sheets in santonian campanian times formed pathways for oil into the veins mosaic type solid bitumen formed during further vein growth it has a higher solid bitumen reflectance br r 3 40 3 76 combined with a high optical anisotropy compared to the underlaying thermally overmature natih b source rock br r 3 10 3 14 the higher reflectance of mosaic type solid bitumen is interpreted to result from deformation and does not reflect maximum burial temperatures which are inferred to have been about 225 c the second migration event is indicated by low reflective homogeneous type solid bitumen with palaeotemperatures br r 0 86 0 92 about 145 c lower than maximum burial it occurs along pressure solution seams which cross cut the veins showing that this is the latest event in the paragenetic sequence interpreted to have formed after lateral intraformational oil migration from the active natih oil kitchen located approximately 40 km sw of the study area during doming and uplift of the oman mountains in oligocene to pliocene times

tomography the geoid and plate motions the dynamics of the earth s mantle and its relationship to mantle structure as revealed by seismic tomography the geoid and plate motions are discussed in a critical review of u s research from the period 1987 1990 sections are devoted to plates and mantle convection seismic anomalies flow and the geoid subducted slabs and the 670 km discontinuity the physical properties of the mantle plumes and computational and experimental modeling efforts also included is a comprehensive bibliography for the period 248 refs

microstructures and microtextures of natural cokes a case study of heat affected coking coals from the jharia coalfield india abstract in jharia coalfield nearly 1250 mt of coking coal has been devolatilized due to igneous intrusives and 1900 mt due to mine fires this paper is an effort to investigate the effect of carbonization in two intrusive affected coal seams of ena seam xiii and alkusa seam xiv collieries of this coalfield through petrographic studies by microscopy characterization of normal and heat affected coals was carried out the microstructures and microtextures produced due to extraneous heat have been related to nature and extent of heat location of heating source and quality and quantity of natural coke produced based on the results of this study and earlier studies an effort has been made to study the classification scheme for microtextures of natural cokes generated through in situ carbonization of the coal seams it has been observed that in case of such heat effects under overburden pressure the anisotropy is much more pronounced as compared to laboratory carbonized cokes in the mildly carbonized coals pre plastic phase 500 c the identified microtextures were mesophase spheres different shapes and sizes of natural cokes graphitic sphaeroliths pyrolytic carbons inerts with morpho structural changes and slightly higher reflectance values and altered and unaltered mineral matters a gradual change in the heat affected coals with increasing temperature was observed with respect to location of intrusive body it has been concluded that barring the effect of pressure the changes due to heat effect on coking coals whether in situ or laboratory carbonization are almost similar organic and inorganic constituents undergoing changes at a particular temperature are nearly similar in both conditions in case of pronounced overburden pressure flow structures develop in the natural coke groundmass higher reflectance and very strong anisotropy as evidenced in completely baked coking coals with fine to very coarse mosaic structures may be a good criterion to explore these heat altered coals for the carbon artifact industry and further efforts are required to be made in this line

dynamically supported geoid highs over hotspots observation and theory hotspots are associated with long wavelength geoid highs an association that is even stronger when the geoid highs associated with subduction zones are removed we quantify these associations by expanding the hotspot distribution in spherical harmonics and calculating correlation coefficients as a function of harmonic degree the hotspot distribution spectrum is nearly white except for peaks at degrees 2 and 6 it is correlated positively with the slab residual geoid for degrees 2 6 with low seismic velocity in the lower mantle at degree 2 and with low seismic velocity in the upper mantle at degree 6 we test fluid mechanical models for hotspots including lithospheric delamination and hot plumes by calculating their predicted dynamic geoid responses and comparing them to the observations these models include the effects of temperature dependent rheology our preferred hotspot model based on observations of the geoid and seismic tomography has plumes preferentially occurring in regions of large scale background temperature highs in a mantle which has a substantial viscosity increase with depth although other models are possible alternatively strong plumes in the lower mantle may neck down and attenuate in the upper mantle due to changes in plume viscosity the major low density anomalies causing the geoid highs associated with plumes appear to be in the lower mantle we hypothesize that cold lower mantle underlying the complementary geoid lows is due to deeply subducted oceanic lithosphere and that hotspot plumes tend to be excluded from these cold regions of the mantle

thermal alteration of gilsonite due to bushfire an example from southwest iran abstract heat affected fragments of bitumen with distinctive properties which can be interpreted as being produced by local heating were found in gilsonite deposits in the vicinity of an asphaltic pool southwest iran the coke fragments consist of multi phase isotropic to anisotropic thermally altered fragments the morphology of the coke fragments is described and an attempt is made to correlate these fragments with laboratory carbonized products of natural bitumen the presence of natural coke in bitumen deposits suggests redeposition of coke following its initial production the formation of natural bitumen coke probably resulted from heat generated by bushfire s in the area in recent times

remineralization of organic carbon in eastern canadian continental margin sediments abstract undisturbed sediment samples were collected for chemical analyses at six sites during winter and summer cruises to the eastern canadian continental margin micro electrode oxygen profiles were obtained in freshly collected multicorer samples and replicate cores were incubated at in situ temperature for 48 h to monitor changes in the concentrations of dissolved oxygen and nitrate in addition box cores were subsampled vertically for porewater chemistry porosity and particulate carbon the data obtained are combined with estimates of sedimentation rate based on sediment trap measurements 210 pb dating and historical data to evaluate the role of benthic processes in the carbon cycle on the eastern canadian continental margin with one exception oxygen uptake rates determined from incubations and calculated from micro profiles were very similar indicating that exchange of oxygen across the sediment water interface was dominated by molecular diffusion on the basis of this observation transport by diffusion is assumed for the calculation of the flux rates for other solutes from their respective porewater gradients the fluxes of oxygen into the sediments were low but generally comparable to other continental margins at comparable depths they varied from 1 4 to 1 8 mmol m2 d in december 1993 and from 2 8 to 4 5 mmol m2 d in june 1994 uptake of nitrate by the sediment occurred at all sites except for the continental slope off nova scotia both oxygen and nitrate uptake were higher in summer than in winter indicative of a lingering response to the input of organic matter associated with the early spring bloom at one of the sampling sites miscou channel the measured oxygen uptake rate far exceeded the flux calculated from the oxygen gradient the difference suggests biologically enhanced exchange with the overlying waters at this site consistent with the greater abundance of benthic organisms the rate of organic carbon mineralization at the seafloor 1 6 4 2 mmol m2 d was estimated as the sum of the sediment oxygen and nitrate uptake rates the contribution of other electron acceptors to the mineralization of organic carbon is assumed to be accounted for by the oxidation of most of their reduced by products by o2 and no3 the return fluxes of dissolved inorganic carbon co2 efflux corrected for carbonate dissolution were generally comparable to the carbon oxidation rates a detailed carbon budget was established at one of the sampled stations for which a complete set of measurements is available the vertical flux of total particulate carbon through the water column measured with a sediment trap at 150 m depth accounts for approximately 9 of the annual primary production pp in the sediment about 6 of the pp is remineralized and total carbon equivalent to 4 5 pp is buried the self consistency of the flux data at this station is used to justify similar budget calculations at the other stations where a limited data set was gathered sequestration of organic carbon via burial with the accumulating sediments on average 0 5 mol m2 yr is partially offset by the release of co2 associated with carbonate precipitation and burial about 0 2 mol m2 yr

the interaction of plume heads with compositional discontinuities in the earth s mantle the effects of compositional discontinuities of density and viscosity in the earth s mantle on the ascent of mantle plume heads is studied using a boundary integral numerical technique three specific problems are considered 1 a plume head rising away from a deformable interface 2 a plume head passing through an interface and 3 a plume head approaching the surface of the earth for the case of a plume attached to a free surface the calculated time dependent plume shapes are compared with experimental results two principal modes of plume head deformation are observed plume head elongation or the formation of a cavity inside the plume head the inferred structure of mantle plumes namely a large plume head with a long tail is characteristic of plumes attached to their source region and also of buoyant material moving away from an interface and of buoyant material moving through an interface from a high to low viscosity region as a rising plume head approaches the upper mantle most of the lower mantle will quickly drain from the gap between the plume head and the upper mantle if the plume head enters the upper mantle if the plume head moves from a high to low viscosity region the plume head becomes significantly elongated and for the viscosity contrasts thought to exist in the earth could extend from the 670 km discontinuity to the surface plume heads that are extended owing to a viscosity decrease in the upper mantle have a cylindrical geometry the dynamic surface topography induced by plume heads is bell shaped when the top of the plume head is at depths greater than about 0 1 plume head radii as the plume head approaches the surface and spreads the dynamic topography becomes plateau shaped the largest stresses are produced in the early stages of plume spreading when the plume head is still nearly spherical and the surface expression of these stresses is likely to be dominated by radial extension as the plume spreads compressional stresses on the surface are produced beyond the edges of the plume consequently extensional features will be produced above the plume head and may be surrounded by a ring of compressional features

benthic remineralization at the land ocean interface a case study of the rhone river nw mediterranean sea abstract biogeochemical processes in sediments under the influence of the rhone river plume were studied using both in situ microelectrodes and ex situ sediment core incubations organic carbon oc and total nitrogen tn content as well as stable carbon isotopic composition of oc 13 c oc were analysed in 19 surface sediments to determine the distribution and sources of organic matter in the rhone delta system large spatial variations were observed in both the total o 2 uptake 5 2 to 29 3 mmol m 2 d 1 and nh 4 release 0 1 to 3 5 mmol m 2 d 1 rates at the sediment water interface the highest fluxes were measured near the rhone river mouth where sedimentary oc and tn contents reached 1 81 and 0 23 respectively values of 13 c oc ranged from 26 83 to 23 88 with a significant seawards enrichment tracing the dispersal of terrestrial organic matter on the continental shelf the amount of terrestrial derived oc reaches 85 in sediments close to the rhone mouth decreasing down to 25 in continental shelf sediments on the prodelta high terrestrial oc accumulation rates support high oxygen uptake rates and thus indicating that a significant fraction of terrestrial oc is remineralized a particulate organic carbon poc mass balance indicates that only 3 of the deposited poc is remineralized in prodelta sediments while 96 is recycled on the continental shelf it was calculated that a large proportion of the rhone poc input is either buried 52 or remineralized 8 mostly on the prodelta area the remaining fraction 40 is either mineralized in the water or exported outside the rhone delta system in dissolved or particulate forms

the dynamical structures of d and deep plumes in a non newtonian mantle the dynamical structures of the d layer and deep mantle plumes have been determined for a mantle with a power law creep rheology generalising recent newtonian analyses the lateral scales of d and plumes are determined by a balance between thermal diffusive thickening and lateral inflow the non newtonian effect of concentrating shear in regions of high stress acts to thicken the region of rapid flow in both d and plumes this effect is nearly counterbalanced by the increased lateral inflow in the non newtonian case resulting in a modest broadening of the lateral scales of the regions of rapid flow these changes are structurally unimportant and the essential physics of core cooling via convective flow in a thin d layer and narrow plumes is remarkably independent of mantle rheology

coldspots and hotspots global tectonics and mantle dynamics of venus magellan radar images and altimetry data and pioneer venus gravity data of major highlands and lowlands on venus are examined with the objective of relating these tectonic and volcanic landforms to convection within venus mantle two roughly circular lowlands atalanta and lavinia planitiae are bowl shaped depressions which contain compressional tectonic features and lack hotspot related features such as coronae and shield volcanoes they are identified as surface expressions of young mantle coldspots or regions of mantle downwelling highlands can be divided into two distinct groups volcanic rises and plateau shaped highlands volcanic rises are domical circular to elongate regions characterized by volcanic construction extensional tectonism large positive gravity and geoid anomalies centered on the highlands and large apparent depths of compensation volcanic rises include beta bell atla and western eistla regiones and are identified as surface expressions of large mantle hotspots or plumes plateau shaped highlands are steep sided elevated regions that range from circular alpha regio to elongate or irregular ovda regio tellus regio in shape their surfaces are dominated by complex ridged terrain rather than the shield volcanoes and flows that dominate volcanic rises most plateau shaped highlands contain compressional structures some of which commonly lie along their margins and have small gravity and geoid anomalies and small apparent depths of compensation compared to volcanic rises plateau shaped highlands which include those mentioned above and western ishtar terra thetis regio and phoebe regio are identified as surface expressions of mantle coldspots or regions of downwelling the highland coldspot features are elevated as a consequence of crustal thickening crustal thickening is absent or minor at lowland coldspots the importance of mantle downwelling in the tectonic deformation of venus suggests that its mantle like the mantle of earth is strongly heated from within the major venusian hotspots attest to the existence of large mantle plumes carrying heat upward from the planet s core

three dimensional modeling of plume lithosphere interaction in order to understand better the dynamics of hot spots such as hawaii we present a three dimensional numerical model for the interaction of a thermal plume with a moving lithosphere the model domain is a rectangular box filled with fluid whose viscosity depends upon temperature and pressure the lithosphere is represented by a layer of cold highly viscous fluid moving with an imposed horizontal velocity u in the x direction and a thermal plume is generated by a circular temperature anomaly on the bottom of the box the steady flow is determined numerically using a hybrid spectral finite difference technique the flow is characterized by a stagnation streamline of width y x1 5 that represents the edge of the spreading plume material we illustrate the detailed behavior of the model using the example of the hawaiian plume our best fitting hawaiian model is obtained by adjusting the plume buoyancy flux b until the predicted topography anomaly matches the observed hawaiian swell topography we find b 4100 kg s 1 which implies a plume radius of 90 km for an assumed plume mantle temperature contrast of 300 c the predicted topography is supported primarily by density anomalies beneath the lithosphere and cannot be explained by lithospheric erosion we therefore conclude that the classical lithospheric reheating model is unable to account for hotspot swells the horizontal flux of buoyancy associated with the swell exceeds b by up to 80 suggesting that current estimates of b for mantle plumes are too high empirically derived scaling laws for the width of the stagnation streamline and for the topography anomaly exhibit power law dependencies on b and u that agree well with those predicted by the refracted plume model of olson 1990 the principal weakness of the model is that the predicted geoid topography ratio of 0 010 for the hawaiian swell is about twice the observed value of 0 004 0 006

geoid anomalies in a dynamic earth in order to obtain a dynamically consistent relationship between the geoid and the earth s response to internal buoyancy forces we have calculated potential and surface deformation love numbers for internal loading these quantities depend on the depth and harmonic degree of loading they can be integrated as green functions to obtain the dynamic response due to an arbitrary distribution of internal density contrasts spherically symmetric self gravitating flow models are constructed for a variety of radial newtonian viscosity variations and flow configurations including both whole mantle and layered convection we demonstrate that boundary deformation due to internal loading reaches its equilibrium value on the same time scale as postglacial rebound much less than the time scale for significant change in the convective flow pattern by calculating relaxation times for a series of spherically symmetric viscous earth models for uniform mantle viscosity the geoid signature due to boundary deformations is larger than that due to internal loads resulting in net negative geoid anomalies for positive density contrasts geoid anomalies from intermediate wavelength density contrasts are amplified by up to an order of magnitude geoid anomalies are primarily the result of density contrasts in the interior of convecting layers density contrasts near layer boundaries are almost completely compensated layered mantle convection results in smaller geoid anomalies than mantle wide flow for a given density contrast viscosity stratification leads to more complicated spectral signatures because of the sensitivity of the dynamic response functions to model parameters forward models for the geoid can be used to combine several sources of geophysical data e g subducted slab locations seismic velocity anomalies surface topography to constrain better the structure and viscosity of the mantle

effect of oxygen on degradation rate of refractory and labile organic matter in continental margin sediments in order to study the effect of oxygen on degradation rate of bulk sedimentary organic matter we developed a new incubation method in contrast to most previous experiments 1 all of the sediment undergoing decomposition was maintained under oxygenated or oxygen free conditions and 2 organic matter of varying lability was studied the production of co2 during incubations of sediment in glass test tubes corrected for dissolution precipitation of calcium carbonates was used as a measure of degradation rates the laboratory experiments using surficial and buried continental shelf and slope sediment from the open skagerrak northeastern north sea demonstrated that the effect of oxygen on the degradation rate of sedimentary organic matter is a function of the lability of the decomposing material fresh material was degraded with little difference in rates in the presence or absence of oxygen whereas old material was decomposed significantly up to 3 6 times faster with oxygen than without oxygen an implication of these findings is that bioturbation by exposing old buried material to oxygen may enhance integrated organic carbon oxidation in marine sediments this constitutes a previously unexplored mechanism by which faunal reworking may stimulate carbon degradation the anoxic decomposition rates of organic material buried at 20 cm depth in sediment were the lowest measured we found however that the extent of oxidation of this buried old sediment was considerably larger than that of surficial sediment under oxygenated conditions which indicated that the oxic anoxic oxic redox transitions deposition under oxic conditions burial under anoxia and reexposure to oxygen promoted degradation our results therefore also suggest that the extent of long term decomposition of sedimentary organic material is smaller under oxygenated or anoxic conditions alone than when the material is exposed to the repeated activities of both oxic and anoxic microorganisms