petrography and microanalysis of pennsylvanian coal ball concretions herrin coal illinois basin usa bearing on fossil plant preservation and coal ball origins abstract petrographic analyses of 25 coal balls from well studied paleobotanical profiles in the middle pennsylvanian herrin coal westphalian d illinois basin and five select coal balls from university collections indicate that herrin coal ball peats were permineralized by fibrous and non fibrous carbonates fibrous carbonates occur in fan like to spherulitic arrays in many intracellular within tissue pores and are best developed in relatively open extracellular between plant pore spaces acid etched fibrous carbonates appear white under reflected light and possess a microcrystalline texture attributable to abundant microdolomite scanning electron microscopy x ray diffraction and electron microprobe analysis demonstrate that individual fibers have a distinct trigonal prism morphology and are notable for their magnesium content 9 15 mol mgco 3 non fibrous carbonates fill intercrystalline spaces among fibers and pores within the peat as primary precipitates and neomorphic replacements in the immediate vicinity of plant cell walls non fibrous carbonates cut across fibrous carbonates as a secondary neomorphic phase attributed to coalification of plant cell walls dolomite occurs as diagenetic microdolomite associated with the fibrous carbonate phase as sparite replacements and as void filling cement maximum dolomite 50 59 wt is in the top of seam coal ball zone at the sahara mine which is overlain by the marine anna shale coal ball formation in the herrin coal began with the precipitation of fibrous high magnesium calcite the trigonal prism morphology of the carbonate fibers suggests rapid precipitation from super saturated meteoric pore waters carbonate precipitation from marine waters is discounted on the basis of stratigraphic paleobotanical and stable isotopic evidence most non fibrous carbonate is attributable to later diagenetic events including void fill replacements recrystallization and post depositional fracture fills evidence suggests that co 2 degassing was important in coal ball formation in the herrin coal which mainly occurred sequentially upward with peat accumulation in the sites studied

model uncertainty quantification in seismic tomography method and applications uncertainty is inherent in every stage of the oil and gas exploration and production e p business and understanding uncertainty enables mitigation of e p risks therefore quantification of uncertainty is beneficial for decision making and uncertainty should be managed along with other aspects of business for example decisions on well positioning should take into account the structural uncertainty related to the non uniqueness of a velocity model used to create a seismic depth image moreover recent advances in seismic acquisition technology such as full azimuth long offset techniques combined with high accuracy migration algorithms such as reverse time migration can greatly enhance images even in highly complex structural settings provided that an earth velocity model with sufficient resolution is available modern practices often use non seismic observation to better constrain velocity model building however even with additional information there is still ambiguity in our velocity models caused by the inherent non uniqueness of the seismic experiment many different earth velocity models exist that match the observed seismic and well data and this ambiguity grows rapidly away from well controls the result is uncertainty in the seismic velocity model and the true positions of events in our images tracking these uncertainties can lead to significant improvement in the quantification of exploration risk e g trap failure when well logging data are not representative drilling risk e g dry wells and abnormal pore pressure and volumetric uncertainties whilst the underlying ambiguity can never be fully eradicated a quantified measure of these uncertainties provides a valuable tool for understanding and evaluating the risks and for development of better risk mitigation plans and decision making strategies

building tilted transversely isotropic depth models using localized anisotropic tomography with well information tilted transverse isotropytti is increasingly recognized as a more geologically plausible description of anisotropy in sedimentary formations than vertical transverse isotropy vti a lthough model building approaches for vti media are well understood similar approaches for tti media are in their infancy even when the symmetry axis direction is assumed known we describe a tomographic approach that builds localized anisotropic models by jointly inverting surface seismic and well data we present a synthetic data example of anisotropic tomography applied to a layered tti model with a symmetry axis tilt of 45 degrees we demonstrate three scenarios for constraining the solution in the first scenario velocity along the symmetry axis is known and tomography inverts for thomsen s and parameters in the second scenario tomography inverts for and velocity using surface seismic data and vertical check shot traveltimes in contrast to the vti case both these inversions are nonunique to combat nonuniqueness in the third scenario we supplement check shot and seismic data with the profile from an offset well this allows recovery of the correct profiles for velocity along the symmetry axis and we conclude that tti is more ambiguous than vti for model building additional well data or rock physics assumptions may be required to constrain the tomography and arrive at geologically plausible tti models furthermore we demonstrate that vti models with atypical thomsen parameters can also fit the same joint seismic and check shot data set in this case although imaging with vti models can focus the tti data and match vertical event depths it leads to substantial lateral mispositioning of the reflections

pore water evolution during sediment burial from isotopic and mineral chemistry of calcite dolomite and siderite concretions abstract coal measures often contain concretions segregations of diagenetic minerals originally formed within unconsolidated sediments three different types calcite pyrite dolomite pyrite and siderite occurring spatially quite close together in the central pennine region of england vary widely in carbon isotope composition 10 35 13c 21 49 and in major cation chemistry ca mg fe mn within some siderite concretions very high mn fe ratios were found in central subsamples these were also most enriched in 13c the fe mg ratio decreases systematically from centre to edge early shallow to deeper later precipitation the calcite pyrite and dolomite pyrite concretions developed completely prior to significant burial both have high mn fe ratios but negative 13c values calcite 21 49 dolomite 8 67 to 10 48 all of these patterns can be equated precisely with theories of pore water evolution developed on the basis of geochemical investigations of modem sediments microbial processes sulphate reduction methanogenesis contributed significantly as did thermal decarboxylation to siderite precipitated at considerable burial depth mn iv and fe iii acted differentially as oxidants producing co2 and increasing alkalinity the interplay of fresh and marine depositional waters is seen most obviously in the presence or absence of sulphate reduction this controlled mineral type iron sulphide or carbonate as well as isotopic and mineral chemistry

the pedogenic formation of coal balls by co2 degassing through the rootlets of arborescent lycopsids coal balls are calcium carbonate accumulations that permineralized peat in paleotropical permo carboniferous 320 250 ma mires the formation of coal balls has been debated for over a century yet a widely applicable model is lacking two observations have been particularly challenging to explain 1 the narrow temporal occurrence of coal balls and 2 their typical elemental high mg and isotopic low 18o composition that paradoxically indicate marine and freshwater origins respectively we evaluate a new model in which coal balls formed as co2 escaped from the peat by diffusion through unusual air filled spaces in the rootlets of lycopsid trees critically these trees were very common in paleotropical mires and their evolutionary range matches the temporal range of coal balls the episodic delivery of seawater and marine carbonate sediment to coastal mires is the first step in our model although other pathways for the delivery of divalent cations are permissible subsequent dilution by freshwater and dissolution of these carbonates at the elevated co2 of the mire subsurface is followed by the transport of co2 through the rootlet airspaces and into the overlying water and atmosphere which drives carbonate mineral precipitation in the sediment we show that dilution by freshwater because it minimally affects mg ca ratios can result in relatively low pore water 18o values while allowing high mg calcite formation this model thus explains the restriction of coal balls to the permo carboniferous and resolves the discrepancy between elemental and isotopic compositions of coal ball carbonate minerals furthermore we show with a 3d reactive transport model that co2 could escape rapidly enough through the rootlets to fill 25 percent of the peat pore spaces with calcite before substantial burial top decimeter of peat explaining the exceptional preservation of coal swamp flora therefore we suggest that coal balls are pedogenic in origin and that the disappearance of these pedogenically permineralized histosols represents the first documented decrease in soil diversity on a vegetated planet the rock record may thus provide important context for the modern loss and degradation of soils

analysis origin and significance of mineral matter in coal an updated review abstract the material classed as mineral matter in coal embraces crystalline mineral materials as well as a range of inorganic elements that occur in non crystalline form this review outlines the methods that may be used to evaluate the percentage of mineral matter for a coal sample as opposed to the ash yield and to identify the minerals their individual percentages and their modes of occurrence within the coal the principal techniques include low temperature oxygen plasma ashing quantitative evaluation of x ray diffraction data observation using optical microscopy and a combination of observation chemical analysis and in some cases mapping based on scanning electron microscopy and related methods a range of other techniques may also be used to provide additional information on particular mineral matter components processes responsible for mineral matter formation include detrital input biogenic activity and authigenic precipitation at different stages of the coal s depositional and post depositional history differential migration of non mineral inorganic elements may also occur in lower rank coals and expulsion of non mineral inorganics may take place with rank advance knowledge of the mineral matter may be of assistance in understanding the modes of trace element occurrence with implications for assessing possible environmental impacts and also the potential for recovery of economic products from coal the behaviour of different mineral matter components at high temperatures is also discussed as well as methods for mineralogical analysis of ashes and other coal utilization products information from mineral matter studies may provide an improved basis for understanding coal formation and for evaluating the response of particular coals to different combustion gasification and coking processes

multiparameter tti tomography of p wave reflection and vsp data abstracttransversely isotropic models with a tilted symmetry axis tti media are widely used in depth imaging of complex geologic structures here we present a modification of a previously developed 2d p wave tomographic algorithm for estimating heterogeneous tti velocity fields and apply it to synthetic and field data the symmetry direction velocity vp0 anisotropy parameters e and and symmetry axis tilt are defined on a rectangular grid to ensure stable reconstruction of the tti parameters reflection data are combined with walkaway vertical seismic profiling vsp traveltimes in joint tomographic inversion to improve the convergence of the algorithm we develop a three stage model updating procedure that gradually relaxes the constraints on the spatial variations of the anisotropy parameters while the symmetry axis is kept orthogonal to the reflectors only at the final stage of the inversion are the parameters vp0 e and updated on the same grid we also incorporate geologic constraints

a decade of tomography over the past 10 years ray based postmigration grid tomography has become the standard model building tool for seismic depth imaging while the basics of the method have remained unchanged since the late 1990s the problems it solves have changed dramatically this evolution has been driven by exploration demands and enabled by computer power there are three main areas of change first standard model resolution has increased from a few thousand meters to a few hundred meters this order of magnitude improvement may be attributed to both high quality complex residual moveout data picked as densely as 25 m to 50 m vertically and horizontally and to a strategy of working down from long wavelength to short wavelength solutions second more and more seismic data sets are being acquired along multiple azimuths for improved illumination and multiple suppression high resolution velocity tomography must solve for all azimuths simultaneously to prevent short wavelength velocity heterogeneity from being mistaken for azimuthal anisotropy third there has been a shift from predominantly isotropic to predominantly anisotropic models both vti and tti with four component data anisotropic grid tomography can be used to build models that tie pz and ps images in depth

ray based gridded tomography for tilted transversely isotropic media reflection tomography in the migrated domain can help reconstruct heterogeneous anisotropic velocity fields needed for accurate depth imaging of complex geologic structures the presence of anisotropy however increases the uncertainty in velocity analysis and typically requires a priori constraints on the model parameters here we develop a 2d p wave tomographic algorithm for heterogeneous transversely isotropic media with a tilted symmetry axis tti and investigate the conditions necessary for stable estimation of the symmetry direction velocity vp0 and the anisotropy parameters e and the model is divided into rectangular cells and the parameters vp0 e and the tilt of the symmetry axis are defined at the grid points to increase the stability of the inversion the symmetry axis is set orthogonal to the imaged reflectors with the tilt interpolated inside each layer the iterative migration velocity analysis involves efficient linearized parameter updating designed to minimize the residual moveout in image gathers for all available reflection events the moveout equation in the depth migrated domain includes a nonhyperbolic term that describes long offset data which are particularly sensitive to e synthetic tests for models with a quasi factorized tti syncline i e e and are constant inside the anisotropic layer and a tti thrust sheet demonstrate that stable parameter estimation requires either strong smoothness constraints or additional information from walkaway vsp vertical seismic profiling traveltimes if the model is quasifactorized with a linear spatial variation of vp0 it may be possible to obtain the interval tti parameters just from long spread reflection data

first description of phanerozoic radiaxial fibrous dolomite abstract the petrographic analysis and crystallographic analysis of concretionary carbonate cements coal balls from carboniferous paralic swamp deposits reveal the presence of length fast radiaxial fibrous dolomite rfd a fabric not previously reported from the phanerozoic this finding is of significance as earlier reports of phanerozoic radiaxial fibrous carbonates are exclusively of calcite mineralogy dolomite concretions described here formed beneath marine transgressive intervals within palustrine coal seams this is of significance as seawater was arguably the main source of mg2 ions for dolomite formation here data from optical microscopy cathodoluminescence electron backscattered diffraction x ray diffraction and geochemical analyses are presented to characterize three paragenetic dolomite phases and one calcite phase in these concretions the main focus is on the earliest diagenetic non stoichiometric degree of order 0 41 0 46 phase i characterized by botryoidal dolomite constructed of fibres up to 110 m wide with a systematic undulatory extinction and converging crystal axes petrographic and crystallographic evidence clearly qualifies phase i dolomite as radiaxial fibrous conversely fascicular optical fabrics were not found carbon isotope ratios 13c are depleted between 11 8 and 22 1 as expected for carbonate precipitation from marine pore fluids in organic matter rich paralic sediment oxygen isotope 18o ratios range between 1 3 and 6 0 the earliest diagenetic nature of these cements is documented by the presence of ubiquitous non compacted fossil plant remains encased in phase i dolomite as well as by the complex zoned luminescence patterns in the crystals and is supported by crystallographic and thermodynamic considerations it is argued that organic matter and specifically carboxyl groups reduced thermodynamic barriers for dolomite formation and facilitated mg caco3 precipitation the data shown here reveal a hitherto unknown level of complexity with respect to radiaxial fibrous carbonates and are of importance for those concerned with dolomite and carbonate petrography in general

echinoderm skeletal preservation calcite aragonite seas and the mg ca ratio of phanerozoic oceans abstract the alternation between abiotic calcite and aragonite precipitation in shallow seawater and the oscillation of seawater mg ca ratio throughout the phanerozoic are both popular hypotheses echinoderms with well preserved stereom provide new empirical evidence that supports both these hypotheses analyses are reported from 29 specimens cambrian to eocene age containing ossicles preserved either as mg calcite 3 3 to 8 mole mgco3 or as mixed calcite and dolomite 5 to 12 5 mole mgco3 echinoderms with high mole mgco3 occur in the early cambrian and late carboniferous to triassic low values come from the silurian and jurassic to cretaceous the average composition of echinoderms with preserved stereom does not fall below 3 5 mol mgco3 during the phanerozoic and reaches its highest mean value of 16 0 mol mgco3 today an empirical partition coefficient of 0 03182 for modern tropical echinoids is used to indicate the mg ca ratio of ancient seawater from the mg ca ratio of fossil stereom some assumptions are involved and a likely error is calculated from the mg2 variation of modern echinoids high mean seawater mg ca ratios are calculated for early cambrian 3 3 and the late carboniferous to triassic 2 3 but never reached today s value of 5 2 low mg ca ratios 1 1 are indicated from jurassic to cretaceous echinoderms the 29 echinoderm samples plot close to first order mg ca seawater oscillations derived from geochemical models and mg ca ratios determined from fluid inclusions but considerable discrepancies exist when shorter 106 myr time intervals are considered further data and improved understanding of mg partitioning is required before accurate secular variation in the mg ca of seawater can be determined from echinoderms however they are an underused resource in this context and provide an excellent seawater archive

fossil plants from the eocene london clay the use of pyrite textures to determine the mechanism of pyritization pyritized twigs and roots from the eocene london clay of se england were studied to gain a better understanding of the process of pyritization by investigating pyrite textures in relation to cell type and quality of preservation highly polished sections and fractured surfaces taken from 124 specimens were examined using optical microscope and sem the latter equipped to map pyrite and carbon pyrite textures include microcrystalline framboidal massive polycrystalline and subhedral or euhedral forms the highest fidelity of preservation is always associated with microcrystalline pyrite precipitation on wall surfaces with subsequent infilling of cells with framboids or polyhedra preventing compression during burial but contributing nothing to actual ultrastructural preservation ultrastructurally parenchymatous cell walls are coalified whereas microcrystalline pyrite plus coalified material were observed within lignified cell walls in all four stages of pyritization are documented observations are interpreted in the light of recent experiments on pyritization of living material and the chemistry of pyrite formation in anoxic environments involving an aqueous and hence mobile fes cluster complex as a precursor the complexity of the fossilization process is reflected in the presence of different textures in adjacent cells of the same tissue this demonstrates the development of isolated chemical microenvironments as ph and eh vary in response to decay and mineralization and pyrite overgrowths within a cell indicate local microenvironmental changes through time

x ray photoelectron emission spectromicroscopic analysis of arborescent lycopsid cell wall composition and carboniferous coal ball preservation abstract two alternative processes complicate understanding of the biochemical origins and geochemical alteration of organic matter over geologic time selective preservation of original biopolymers and in situ generation of new geopolymers one of the best constrained potential sources of bio and geochemical information about extinct fossil plants is frequently overlooked permineralized anatomically preserved plant fossils allow analysis of individual cell and tissue types that have an original biochemical composition already known from living plants the original composition of more enigmatic fossils can be constrained by geochemical comparisons to tissues of better understood fossils from the same locality this strategy is possible using synchrotron based techniques for submicron scale imaging with x rays over a range of frequencies in order to provide information concerning the relative abundance of different organic bonds with x ray absorption near edge spectroscopy in this study x ray photoelectron emission spectromicroscopy x peem was used to analyze the tissues of lepidodendron one of the lycopsid trees that were canopy dominants of many pennsylvanian coal swamp forests its periderm or bark the single greatest biomass contributor to many late paleozoic coals is found to have a greater aliphatic content and an overall greater density of organic matter than lignified wood because x peem allows simultaneous analysis of organic matter and matrix calcite in fully mineralized fossils this technique also has great potential for analysis of fossil preservation including documentation of significant traces of organic matter entrained in the calcite crystal fabric that fills the cell lumens

geochemistry of autochthonous and hypautochthonous siderite dolomite coal balls foord seam bolsovian upper carboniferous nova scotia canada abstract the 11 13 m thick foord seam in the fault bounded stellarton basin nova scotia is the thickest seam from the euramerican floral province known to contain coal balls in addition to the first discovery of autochthonous coal balls in the foord seam nova scotia its shale parting also contains hypautochthonous coal balls with histologically preserved plant structures the coal ball discovery helps fill a stratigraphic gap in coal ball occurrences in the upper carboniferous bolsovian of euramerica the autochthonous and hypautochthonous coal balls have a similar mineralogical composition and are composed of siderite 81 100 dolomite ankerite 0 19 minor quartz and illite and trace amounts of calcite similar is also their permineralizing mineralogy which consists of dolomite ankerite and siderite their low pyrite content and carbonate mineralogy and nonmarine origin differentiates the foord seam coal balls from other euramerican coal ball occurrences a preliminary geochemical model which is based on oxygen and carbon isotopic data indicates that siderite in both the autochthonous and hypautochthonous coal balls is of very early diagenetic nonmarine origin from 13 c enriched bicarbonate derived from bacterial methanogenesis of organic matter

are coal balls rare a cyclostratigraphic analysis of coal ball occurrence in north america abstract from the perspective of phanerozoic time coal balls are rare apparently limited to a 24 m y interval 323 299 ma in the pennsylvanian and earliest permian yet within this interval coal balls occur in many coals approximately 82 transgressive regressive sedimentary cycles have been described for the midcontinent illinois and appalachian basins of north america during the mid to late pennsylvanian one third 27 82 have coal balls including 57 of major cycles 36 of intermediate cycles and 16 of minor cycles coal ball occurrence in the donets basin is similar over an interval of about 4 m y 315 311 ma latest bashkirian to mid moscovian 39 11 28 of transgressive regressive cycles have coal balls as north american paleoclimate became drier tree ferns replaced lycopsids as the dominant plant in peat swamps at the desmoinesian missourian boundary and coal ball occurrence declined overall 47 of cycles 19 40 with lycopsid or cordaitean dominance have coal balls whereas 19 8 42 of cycles with tree fern dominance have coal balls p this pattern may reflect the relative abundance of coal in the late pennsylvanian with drier paleotropical climates in the missourian virgilian leading to less paleotropical coal fewer mines and a lower probability of discovering missourian and virgilian coal balls however average cycle duration decreased from 150 kyr in the desmoinesian to 100 kyr in the missourian and virgilian and faster rates of relative sea level rise could have affected coal ball abundance particularly if coal balls formed in marine swamps with more rapid transgression leading to thinner coals or to freshwater coals directly overlain by marine sediments rygel et al 2008 suggested that missourian virgilian cycles recorded more erosional relief than desmoinesian cycles consistent with increased amplitude and rates of sea level rise during each glacial eustatic cycle changes in missourian virgilian cycles may have been augmented by stratigraphic attenuation as sediment filled the antecedent topography

carbonate petrology and geochemistry of pennsylvanian coal balls from the kalo formation of iowa abstract coal balls are carbonate and pyrite concretions enclosing uncompressed peat primarily found in pennsylvanian and earliest permian paleotropical coals petrographic and microprobe analysis of coal balls from the mid moscovian latest atokan or earliest desmoinesian williamson no 3 mine kalo formation from lucas county iowa indicates that pyrite was the earliest mineral to form followed by high mg calcite average 13 9 mol mgco 3 which is also high in sr 700 1500 ppm suggesting that the kalo formation coal balls formed in response to the incursion of marine water into the mire the high mg calcite has an unusual growth habit radiating arrays of bladed polycrystals which look like distorted triangles with elongated apices when cut parallel to the basal plane these high mg calcite polycrystals have low mg non ferroan calcite rims consistent with diagenesis in meteoric water the presence of early high mg and low mg non ferroan calcite in the williamson no 3 coal balls suggests that these coal balls formed in a hydrologically dynamic environment most of the remaining cements in the kalo formation coal balls are low mg ferroan calcite consistent with burial diagenesis these cements retain regions of low mg and high mg calcite suggesting that they are neomorphs of the early high mg calcite cement fibers in the vascular bundle supports of cordaites principalis leaves have narrow rims of dolomite that appear unique to this species the presence of high mg calcite in the williamson no 3 coal balls supports the stopes and watson phil trans roy soc london b 1909 200 167 218 model of coal ball formation as a result of incursions of marine water into coastal mires it conflicts with stable isotopic data which suggests that most coal ball cements formed in meteoric water however in our samples the most common cement is diagenetically altered low mg ferroan calcite which might yield meteoric oxygen isotopic values excellent preservation of plant fossils in coal balls is not necessarily correlated with the presence of original cement

an approach to reduce exploration risk using spectral decomposition prestack inversion and seismic facies classification petroleum companies have invested heavily in the exploration of frontier offshore basins in brazil uncertainties associated with geologic complexity lithostratigraphy fluid content and seismic resolution in these basins are the most common challenges many methods have been used to circumvent these issues such as assessing seismic attributes seismic inversion spectral decomposition and the integration of these methodologies to accomplish an optimal approach because of the complex geology of these areas it is very difficult to identify potential reservoirs within one specific geologic formation hence applying spectral decomposition to frontier basins of high geologic complexity can help overcome the challenges because in the frequency domain it is possible to better define variability and lateral discontinuities the correct choice of the spectral decomposition optimization approach is critical for accurate target zone representation as well as selection of the appropriate transform prestack inversion spectral decomposition and attribute seismic facies classification were applied to evaluate the extent of a reservoir and analyze whether an appraisal well has been sited at a good location the results showed that the new appraisal well was planned at a good location but that its facies were not as good as those of the first discovery well as confirmed after drilling

cordaiteans in paleotropical wetlands an ecological re evaluation abstract cordaiteans in cordaite dominated permineralized peat from pennsylvanian coals in iowa have been reconstructed as mangroves using root anatomy peat taphonomy and geochemical data macrofloral palynofloral and conodont biostratigraphy indicate that these peats come from the latest atokan blackoak coal and earliest desmoinesian cliffland coal mid moscovian both in the kalo formation thus their depositional setting can be used to evaluate the mangrove hypothesis in recent mires thick mangrove peats have accumulated in tropical to subtropical carbonate systems in contrast thick tropical freshwater peats have accumulated in siliclastic systems kalo formation coals which we interpret as freshwater deposits formed in siliciclastic depositional settings similar to those of modern tropical freshwater peat and to other pennsylvanian coals in north america interpreted as freshwater deposits in the late atokan and earliest desmoinesian mid moscovian cordaiteans and tree ferns predominated in the western interior and illinois basins lycopsids and cordaiteans predominated in the appalachian and donets basins the scarcity of lycopsid only mires in north america during the late atokan earliest desmoinesian mid moscovian suggests drier climates than during the mid to late desmoinesian late moscovian rather than indicating mangrove swamps cordaite dominated peat may indicate climates with a low rain season although most plants in cordaite dominated peat probably grew in freshwater coastal mires in climate zones with seasons of low rain may harbor mangrove taxa the changuinola swamp of panama a modern peat accumulating wetland that has a low rain season is a possible analog of ancient cordaite dominated mires in changuinola most plants require freshwater however mangroves sustained by salt water influx into the swamp grow along the seaward edge and along blackwater creeks the low rain season hypothesis has implications for understanding rainfall amount and continuity during pennsylvanian cyclothem deposition the floral succession in diverse cordaite coals from cordaiteans to tree ferns to lycopsids suggests increasingly wet climate during coal accumulation the position of these coals immediately above the sequence boundary suggests humid climate during early glacial melting for these cyclothems

migration velocity analysis for ti media in the presence of quadratic lateral velocity variation abstractone of the most serious problems in anisotropic velocity analysis is the trade off between anisotropy and lateral heterogeneity especially if velocity varies on a scale smaller than the maximum offset we have developed a p wave mva migration velocity analysis algorithm for transversely isotropic ti models that include layers with small scale lateral heterogeneity each layer is described by constant thomsen parameters e and and the symmetry direction velocity v0 that varies as a quadratic function of the distance along the layer boundaries for tilted ti media tti the symmetry axis is taken orthogonal to the reflectors we analyzed the influence of lateral heterogeneity on image gathers obtained after prestack depth migration and found that quadratic lateral velocity variation in the overburden can significantly distort the moveout of the target reflection consequently medium parameters beneath the heterogeneous layer s are estimated with substantial error even when borehole informa

moveout inversion of wide azimuth p wave data for tilted ti media currently tti transversely isotropic with a tilted symmetry axis models are widely used for velocity analysis and imaging in many exploration areas we develop a 3d parameter estimation algorithm for tti media composed of homogeneous layers separated by plane dipping interfaces the input data include p wave nmo ellipses and time slopes horizontal slownesses of the zero offset rays combined with borehole information if the symmetry axis is perpendicular to the bottom of each layer it is possible to estimate the interval symmetry direction velocity vp0 anisotropy parameter d and the reflector orientation using a single constraint the reflector depth the algorithm can tolerate small 5 deviation of the symmetry axis from the reflector normal however as is the case for the 2d problem the parameter e can seldom be obtained without nonhyperbolic moveout inversion if the symmetry axis deviates from the reflector normal but is confined to the dip plane stable parameter estimation requires specifying a relationship between the tilt and dip in each layer when the tilt represents a free parameter the input data have to be supplemented by wide azimuth vsp traveltimes with the offset reaching at least 1 4 of the maximum reflector depth moreover the additional angle coverage provided by vsp data may help resolve the parameter e in the upper part of the model the developed methodology can be used to build an accurate initial anisotropic velocity model for processing of wide azimuth surveys

localized anisotropic tomography with well information in vti media we develop a concept of localized seismic grid tomography constrainedbywellinformationandapplyittobuildingvertically transversely isotropic vti velocity models in depth the goal is to use a highly automated migration velocity analysis to build anisotropic models that combine optimal image focusing withaccuratedepthpositioninginonestep welocalizetomographytoalimitedvolumearoundthewellandjointlyinvertthesurface seismic and well data well information is propagated into thelocalvolumebyusingthemethodofpreconditioning whereby model updates are shaped to follow geologic layers with spatial smoothing constraints we analyze our concept with a synthetic data example of anisotropic tomography applied to a 1d vti model we demonstrate four cases of introducing additional information in the first case vertical velocity is assumed to be known and the tomography inverts only for thomsen s and profiles using surface seismic data alone in the second case tomography simultaneously inverts for all three vti parameters including vertical velocity using a joint data set that consists of surface seismic data and vertical check shot traveltimes in the thirdandfourthcases sparsedepthmarkersandwalkawayverticalseismicprofilingvspareused respectively tosupplement the seismic data for all four examples tomography reliably recovers the anisotropic velocity field up to a vertical resolution comparable to that of the well data even though walkawayvsp hastheadditionaldimensionofangleoroffset itoffersnofurther increase in this resolution limit anisotropic tomography with well constraints has multiple advantages over other approaches anddeservesaplaceintheportfolioofmodel buildingtools

maastrichtian north atlantic warming increasing stratification and foraminiferal paleobiology at three timescales 1 analysis of 944 single specimens of three species of late maastrichtian planktonic foraminifera racemiguembelina fructicosa contusotruncana contusa and rugoglobigerina rugosa from 38 samples spanning the last 3 myr of the cretaceous shows consistent isotopic trends through time consistent isotopic differences among taxa and high within sample isotopic variability throughout within sample variability does not change systematically through time for any taxon but average 18o values decrease by 1 5 and average 13c values diverge up section comparing taxa average 18o values are similar within most samples but average 13c values generally decrease from r fructicosa to r rugosa to c contusa in addition the within sample variability of individual 13c measurements is larger for r fructicosa than for either c contusa or r rugosa an observation which is consistent with a photosymbiotic habitat for r fructicosa in terms of maastrichtian paleoceanography the negative 18o trend of 1 5 corresponds to a temperature increase of 6 c and the divergence of 13c values up section suggests an increasingly stratified water column in the western atlantic through the late maastrichtian we suggest that these trends are best explained by increasing import of south atlantic waters into the north atlantic and an intensification of the northern hemisphere polar front

anatomically preserved plants in siderite concretions in the shale split of the foord seam mineralogy geochemistry genesis upper carboniferous canada abstract a shale split in the well studied foord seam upper carboniferous stellarton basin nova scotia provides a rare opportunity to study little known siderite concretions with anatomically preserved plants from a limnic basin siderite concretions occur throughout the split commonly as sheet like inter connected lepidodendrid logs or less frequently as spherical masses they are typically vuggy a sample of 14 stratigraphically oriented concretions in the split shows that primary siderite varies from 45 to 80 wt due to selective replacement by 5 to 40 ferroan dolomite or ankerite in plant tissues these two minerals show large mg fe and mg ca variability and are fezoned clay content ranges from trace to 20 and quartz from 5 to 10 partial cell wall destruction by erosion and changeable oxic anoxic conditions prior to siderite permineralization resulted in preservation mainly of the more resistant plant tissues on average carbon from siderite is isotopically heavier 4 8 1 9 0 00 than that from dolomite 7 2 1 1 0 00 the distribution of and the positive correlation between 13 c and 18 o probably reflects the two fractionation processes associated with methanogenesis and dolomitization respectively in the genetic history of the siderite concretions in the split siderite concretions formed diagenetically early from bicarbonate under reducing conditions in a slightly alkaline freshwater environment that precluded calcite deposition

geochemistry of meteoric calcite cements in some pleistocene limestones in this study the stable isotope and trace element geochemistries of meteoric cements in pleistocene limestones from enewetak atoll western pacific ocean cat island bahamas and yucatan were characterized to help interpret similar cements in ancient rocks meteoric calcite cements have a narrow range of 18o values and a broad range of 13c values in each geographical province these pleistocene cements were precipitated from water with stable oxygen isotopic compositions similar to modern rainwater in each location enewetak calcite cements have a mean 18o composition of 6 5 0 pdb and 13c values ranging from 9 6 to 0 4 0 pdb sparry calcite cements from cat island have a mean 18o composition of 4 1 0 and 13c values ranging from 6 3 to 1 1 0 sparry cements from yucatan have a mean 18o composition of 5 7 0 and 13c values of 8 0 to 2 7 0 the mean 18o values of these pleistocene meteoric calcite cements vary by 2 4 0 due to climatic variations not related directly to latitude the 13c compositions of meteoric cements are distinctly lower than those of the depositional sediments variations in 13c are not simply a function of distance below an exposure surface meteoric phreatic cements often have 13c compositions of less than 4 0 0 which suggests that soil derived co2 and organic material were washed into the water table penecontemporaneous with precipitation of phreatic cements concentrations of strontium and magnesium are quite variable within and between the three geographical provinces mean strontium concentrations for sparry calcite cements are for enewetak atoll 620 ppm 510 ppm for cat island 1200 ppm 980 ppm and for yucatan 700 ppm 390 ppm equant cements intraskeletal cements and bahamian cements have higher mean strontium concentrations than other cements equant and intraskeletal cements probably precipitated in more closed or stagnant aqueous environments bahamian depositional sediments had higher strontium concentrations which probably caused high strontium concentrations in their cements magnesium concentrations in pleistocene meteoric cements are similar in samples from enewetak atoll mean 1 00 mol mgco3 0 60 mol mgco3 and cat island mean 0 84 mol mgco3 0 52mol mgco3 but yucatan samples have higher magnesium concentrations mean 2 20 mol mgco3 0 84mol mgco3 higher magnesium concentrations in some yucatan cements probably reflect precipitation in environments where sea water mixed with fresh water

formation and distribution of coal balls in the herrin coal pennsylvanian franklin county illinois basin usa large areas of concentrated coal balls permineralized peat up to 4 m thick obstructed longwall mining in the herrin coal at the old ben no 24 mine the largest coal ball area mapped contained 1500 m 3 several areas contained 400 m 3 of coal balls in mine mapping established that there were two types of roof freshwater and marine and that the coal balls were spatially correlated with the marine roof units regional studies and local data revealed that the younger freshwater energy shale mud originally covered all of the peat deposited at the mine but the mud was locally removed during a period of erosion the great majority of coal balls are found within the coal seam where they were permineralized in situ by carbonates some coal balls are found exposed on the eroded coal surface and others are within the channel fill associated with the erosion which predates any marine sedimentation thus the mineralization of the coal balls was synchronous with the erosion of the energy shale mud data from c and o isotope geochemical and mineralogical analyses of coal balls and associated materials were used to refine a depositional model of coal ball formation the concentrated coal ball areas were created by the triggered degassing of co 2 from partially decomposed peat in the presence of cations from fresh waters 13 c 12 c ratios in these coal balls average 23 9 13 c 12 c ratios as low as 34 occurring in the most concentrated coal balls are consistent with co 2 produced by anaerobic oxidation of methane top of seam coal balls were formed later and show slight to strong marine influence their 13 c 12 c ratios average 10 8

wave equation migration velocity analysis for vti models abstractanisotropic models are needed for wave simulation and inversion where a complex geologic environment exists we extended the theory of wave equation migration velocity analysis to build vertical transverse isotropic models because of the ambiguity between depth and in the acoustic regime we assumed can be accurately obtained from other sources of information and inverted for the nmo slowness and the anellipticity parameter we combined the differential semblance optimization objective function with the stacking power maximization to evaluate the focusing of the prestack image in the subsurface offset domain to regularize the multiparameter inversion we built a framework to adapt the geologic and the rock physics information to guide the updates in nmo slowness and this regularization step was crucial to stabilize the inversion and to produce geologically meaningful results we tested the proposed approach on a synthetic data set and a 2d gulf of mexico data set starting with a fairly

anisotropic migration velocity analysis using reverse time migration abstractseismic anisotropy if not accounted for can cause significant mispositioning of the reflectors in depth migrated images accounting for anisotropy in depth migration requires velocity analysis tools that can estimate the anisotropic background velocity field we extended wave equation migration velocity analysis to deal with 2d tilted transverse isotropic media the velocities were obtained automatically by nonlinear optimization of the focusing and stack power of common image point gathers constructed using an extended imaging condition we used the elastic two way wave equation to reconstruct the wavefields needed for the image and gradient computations this led to an anisotropic migration velocity analysis algorithm based on reverse time migration we illustrated the method with synthetic and field data examples based on marine surface seismic acquisition the results showed that the method significantly improves the quality of the depth migrated image however as is common in the case of v