microbe clay interactions as a mechanism for the preservation of organic matter and trace metal biosignatures in black shales abstract organic rich fine grained sedimentary rocks such as black shales are important geochemical archives providing information on the evolution of seawater composition and biological activity over the past 3 billion years while biological productivity and sedimentation rates greatly affect the organic matter content in these rocks mechanisms linking these two processes remain poorly resolved here we examine the interactions of clay minerals with the marine planktonic cyanobacterium synechococcus sp pcc 7002 we suggest that clays settling through the water column could influence carbon and trace metal burial in three ways 1 the interaction of reactive clay surfaces with the bacterial cells increases organic matter deposition via mass increase in a seawater growth medium by several orders of magnitude 2 reactive bacterial cells become completely encased within a clay shroud enhancing the preservation potential of this organic matter and 3 the trace metal content of the biomass buried along with metals sorbed to the clay particles contributes to the trace metal concentrations of the black shale precursor sediments significantly our findings imply that the chemical composition of ancient organic rich fine grained deposits are not only archives of ancient seawater composition and redox state but they also provide a record of the degree of biological activity in the water column through geological time

lithologic succession in the path fork coal bed breathitt formation middle pennsylvanian southeastern kentucky abstract the path fork coal bed breathitt formation middle pennsylvanian westphalian b on the pine mountain thrust sheet in southeastern kentucky and adjacent portions of virginia exhibits a lithologic succession which is traceable for about 25 km lateral continuity of lithotypes within the bed can be demonstrated using organic petrography palynology and ash geochemistry the lithologic continuity is a consequence of the initial levelling of the pre peat topography and the interaction of the peat with growing anticlines and synclines

chromium isotopes in carbonates a tracer for climate change and for reconstructing the redox state of ancient seawater abstract strontium and carbon isotopes of marine carbonates are routinely applied for chemostratigraphic cross correlations of time equivalent sedimentary sequences and for calibration of the compositional evolution of seawater throughout earth s history mainly for the purpose of reconstructing ancient climatic changes we here present results of a new isotopic tracer system stable chromium isotopes applied to a late ediacaran marine carbonate sequence exposed in the calera de recalde syncline arroyo del soldado group uruguay the aim was to compare cr isotope signatures directly to 13 c 87 sr 86 sr and 143 nd 144 nd fluctuations in a well defined stratigraphic profile comprising sediments that were deposited during cold warm periods accompanied by sea level changes in response to glaciation deglaciation at higher latitudes the studied section is characterized by a pronounced negative down to 3 3 13 c excursion in carbonates paralleled by a decrease of 87 sr 86 sr values chromium isotope signatures over this section also show a correlated decrease in 53 cr 53 cr 53 cr 52 cr sample 53 cr 52 cr srm979 1 1000 values from 0 29 to 0 17 which mirrors a decrease in positively fractioned seawater signatures to slightly negative values characteristic of high temperature magmatic sources linear correlations between 53 cr and end 570 ma 87 sr 86 sr and cr concentrations can be explained by mixing between two major input sources of cr nd and sr into the shallow seawater 1 a source characterized by negative 53 cr values of 0 2 low 87 sr 86 sr values of 0 707 and elevated 147 sm 144 nd values of 0 13 recognized as a subaqueous hydrothermal dominated input source and 2 a source characterized by positively fractionated 53 cr values of 0 2 higher 87 sr 86 sr values of 0 708 and lower 147 sm 144 nd values of 0 11 a source which is strongly affected by continentally derived input chromium isotopes provide a powerful tool for reconstructing the redox state of ancient seawater since positive values indicate that at least locally neoproterozoic shallow ocean waters were sufficiently oxidized to fractionate chromium and or that oxygen levels of the atmosphere were sufficient to transform cr iii into the more mobile hexavalent cr vi formed during weathering processes on land the fact that 87 sr 86 sr values despite 13 c fluctuations remain low indicative of a strong hydrothermal input into the basin at his time implies that co 2 limitation was the cause of negative 13 c and 53 cr excursions in otherwise nutrient rich late neoproterozoic basins and that glaciation is only one more consequence of a tectonically driven biologically mediated system in such a scenario glaciation acts as an amplifier of 53 cr signals these signals in marine carbonates are a sensitive tracer for redox processes in the ocean and or on land and have the potential to contribute significantly in combination with the other commonly used isotopic tracers to the reconstruction of climatic changes particularly those that are associated with major glaciation periods in earth s history

control of relative sea level and climate on coal character in the westphalian c atokan four corners formation central appalachian basin u s a abstract peat successions preserved as coal seams preserve high resolution records of ancient terrestrial water table base level fluctuations that are driven by changes in relative sea level and or paleoclimatic change the aim of this study is to establish the roles of relative sea level and climate in controlling water table fluctuations within coal seams from the fluviodeltaic westphalian c bolsovian atokan four corners formation of the central appalachian basin usa comparison of the characteristics of 10 coals in the four corners formation with accommodation trends identified from analysis of intra coal clastic strata indicates that their thickness and vitrinite inertinite ratio correlate readily with the accommodation setting of the depositional sequence in which they occur coals that accumulated in relatively high accommodation fourth order sequences are high in vitrinite thin and overlain by or intercalated with marine and lacustrine sediments the coals have simple internal organization suggesting that they span parts of single high resolution accommodation cycles coals that accumulated in lower accommodation fourth order sequences are high in inertinite thick and overlain by or intercalated with terrestrial sediments the coals have composite internal organizations typified by multiple high resolution accommodation cycles and characteristic abrupt discontinuities of coal facies representing periods of depositional hiatus the correlations between the composition and thickness of the coals and the magnitude of associated marine transgression imply that relative sea level change was the principal control governing bulk accommodation in these mires landward of the paleoshoreline high frequency accommodation cycles within the coals reflect water table fluctuations in the original mires and were driven by high frequency sea level and or climate change the results of this study provide considerable insight into the manner in which coal composition and stratigraphy at a single locality vary over time in response to changing accommodation and provide a means to predict coal seam quality in an established sequence stratigraphic framework

comparison of ground water flow model particle tracking results and isotopic data in the mojave river ground water basin southern california usa abstract flow path and time of travel results for the mojave river ground water basin southern california calculated using the ground water flow model modflow and particle tracking model modpath were similar to flow path and time of travel interpretations derived from delta deuterium and carbon 14 data model and isotopic data both show short flow paths and young ground water ages throughout the floodplain aquifer along most the mojave river longer flow paths and older ground water ages as great as 10 000 years before present were measured and simulated in the floodplain aquifer near the mojave valley model and isotopic data also show movement of water between the floodplain and regional aquifer and subsequent discharge of water from the river to dry lakes in some areas it was not possible to simulate the isotopic composition of ground water in the regional aquifer away from the front of the san gabriel and san bernardino mountains because recharge in these areas does not occur under the present day climatic conditions used for calibration of the model

chromium vi generation in vadose zone soils and alluvial sediments of the southwestern sacramento valley california a potential source of geogenic cr vi to groundwater abstract concentrations of geogenic cr vi in groundwater that exceed the world health organization s maximum contaminant level for drinking water 50 g l 1 occur in several locations globally the major mechanism for mobilization of this cr vi at these sites is the weathering of cr iii from ultramafic rocks and its subsequent oxidation on mn oxides this process may be occurring in the southern sacramento valley of california where cr vi concentrations in groundwater can approach or exceed 50 g l 1 to characterize cr geochemistry in the area samples from several soil auger cores approximately 4 m deep and drill cores approximately 25 m deep were analyzed for total concentrations of 44 major minor and trace elements cr associated with labile mn and fe oxides and cr vi total concentrations of cr in these samples ranged from 140 to 2220 mg per kg soil between 9 and 70 mg per kg soil was released by selective extractions that target fe oxides but essentially no cr was associated with the abundant reactive mn oxides up to 1000 mg hydroxylamine reducible mn per kg soil was present both borehole magnetic susceptibility surveys performed at some of the drill core sites and relative differences between cr released in a 4 acid digestion versus total cr lithium metaborate fusion digestion suggest that the majority of total cr in the samples is present in refractory chromite minerals transported from ultramafic exposures in the coast range mountains chromium vi in the samples studied ranged from 0 to 42 g kg 1 representing a minute fraction of total cr chromium vi content was typically below detection in surface soils top 10 cm where soil organic matter was high and increased with increasing depth in the soil auger cores as organic matter decreased maximum concentrations of cr vi were up to 3 times greater in the deeper drill core samples than the shallow auger cores although cr vi in these vadose zone soils and sediments was only a very small fraction of the total solid phase cr they are a potentially important source for cr vi to groundwater enhanced groundwater recharge through the vadose zone due to irrigation could carry cr vi from the vadose zone to the groundwater and may be the mechanism responsible for the correlation observed between elevated cr vi and no 3 concentrations in previously published data for valley groundwaters incubation of a valley subsoil showed a cr vi production rate of 24 g kg 1 a 1 suggesting that field cr vi concentrations could be regenerated annually increased cr vi production rates in h amended soil incubations indicate that soil acidification processes such as nitrification of ammonium in fertilizers could potentially increase the occurrence of geogenic cr vi in groundwater thus despite the natural origin of the cr cr vi generation in the sacramento valley soils and sediments has the potential to be influenced by human activities

previously unknown mineral nanomineral relationships with important environmental consequences the case of chromium release from dissolving silicate minerals risk assessments that take into account the formation of environmentally dangerous hexavalent chromium in cr containing mine tailings and associated soils and sediments require an understanding of the occurrence and speciation of cr in silicate minerals and glasses silicates are more soluble and generally more susceptible to weathering than the refractory mineral chromite the principal ore mineral of cr studies at the nanoscale using a combination of advanced sample preparation via microtoming and focused ion beam techniques in combination with state of the art analytical transmission electron microscopy and electron diffraction reveal the occurrence of chromite nanoparticles held within clinochlore and lizardite grains in chromitite ore an igneous cumulate consisting primarily of chromite from the black thor chromium deposit in northern ontario canada and the mistake mine fresno county california u s a respectively nanoscale examinations of altered chromitite ore samples from the black thor deposit after dissolution experiments in sulfuric acid bearing solutions of ph 2 5 show that clinochlore alters to amorphous silica depleted in chromite nanoparticles this observation suggests the release of chromite nanoparticles rather than cr 3 aqueous species during the weathering of chromite bearing silicate minerals this will in turn have an impact on the environmental behavior of cr 3 and its potential oxidation to cr 6 the formation of cr 6 aq species in this case will require either the initial dissolution of the nanoparticles or the oxidation of cr 3 species on the surface of the nanoparticles either process being a rate limiting step in the formation of cr 6 aq species

silicon and chromium stable isotopic systematics during basalt weathering and lateritisation a comparison of variably weathered basalt profiles in the deccan traps india global biomass production is fundamentally affected by the hydrological cycling of elements at the earth s surface continental weathering processes are the major source for most bio essential elements in marine environments and therefore affect primary productivity in addition critical zone biomass depends on energy and chemical exchange reactions in weathering profiles the latter reservoirs are in turn influenced by different climatic conditions that control weathering and pore water parameters like ph and eh which regulate mineral break down rates and dictate the mobility and mass flux of elements two deccan traps basalt weathering profiles of contrasting age and alteration intensity provide a natural laboratory for investigating the effects of rock alteration on si and cr and their isotopic systematics the quaternary chhindwara profile has progressed to a moderate degree of alteration saprolite while the paleogene bidar example displays an extremely altered laterite the chhindwara saprolite profile shows a near uniform cr and si concentration and isotopic composition whereas the bidar laterite profile is characterised by an intense loss of si a large enrichment of cr within the most altered uppermost levels and a wide range of cr stable isotope ratios 0 85 to 0 36 parts per thousand delta cr 53 52 a co variation between si and cr isotopes as well as their co variation with iron content provides empirical evidence that iron redistribution within the profile has a large effect on cr mobility and si isotopic fractionation therefore it is concluded that iron oxides exert a primary control over the isotopic composition of both cr and si in pore waters of laterites since laterite formation is promoted by tropical climates the results of this study provide new evidence to suggest that the hydrological cr and si fluxes originating from continental weathering have changed in accordance with large scale deep time climate variation and continental plate configuration an increased flux of si and greater magnitude of cr mobility and isotopic fractionation are possibly amplified under co2 rich greenhouse episodes and or when large landmasses were tectonically arranged at near equatorial latitudes

the upper hance coal bed in southeastern kentucky palynologic geochemical and petrographic evidence for environmental succession the upper hance coal bed in bell county eastern kentucky exhibits considerable variation in depositional setting on a mine scale palynology and geochemistry of the coal are examined in order to supplement previous petrographic examinations the various depositional settings of the upper hance mire progress from the pioneer possibly partially allochthonous settings at the mire margins and base to the well developed planar to domed main body of the mire and finally to the terminal events of flooding clastic influx and temporary reestablishment of mires now seen as the thin rider coals palynologic diversity generally decreases upwards from the basal lithotype through the main body of the coal bed the cannel and rider lithologies represent distinct depositional events

petrology and palynology of the middle pennsylvanian leatherwood coal bed eastern kentucky indications for depositional environments abstract the eastern kentucky coal field is located in the central portion of the appalachian basin the pennsylvanian breathitt formation in this region is characterized by numerous sequences of bituminous coal bearing sedimentary rocks these coals have distinct maceral compositions due to variations in depositional environments coal characterization is an important method for determining conditions that influenced peat accumulation and overall depositional settings of mires this study focuses on the characterization of the maceral composition of the middle pennsylvanian age leatherwood coal bed it utilizes petrographical palynological and geochemical analyses to describe specific depositional environments and associated peat accumulation conditions petrographic analyses indicate that these coals have relatively high liptinite and varying inertinite content along with trace amounts of mineral matter vitrinite mainly in the form of collotelinite is the most dominant maceral group geochemical data reveals low ash and sulfur content ancillary palynological data shows the palynomorph assemblage to be dominated by tree fern and large lycopod tree spores with lesser amounts of small lycopod tree small fern and cordaites and calamites spores the petrographic geochemical and palynological data indicate that both domed ombrotrophic and planar rheotrophic mire conditions with limited local detrital influx contributed to the formation of the leatherwood coal

arsenic and lead concentrations in the pond creek and fire clay coal beds eastern kentucky coal field abstract the middle pennsylvanian breathitt formation westphalian b pond creek and fire clay coal beds are the 2 largest producing coal beds in eastern kentucky single channel samples from 22 localities in the pond creek coal bed were obtained from active coal mines in pike and martin countries kentucky and a total of 18 fire clay coal bed channel samples were collected from localities in the central portion of the coal field the overall objective of this study was to investigate the concentration and distribution of potentially hazardous elements in the fire clay and pond creek coal beds with particular emphasis on as and pb 2 elements that are included in the 1990 clean air act amendments as potential air toxics the 2 coals are discussed individually as the depositional histories are distinct the fire clay coal bed having more sites where relatively high s lithologies are encountered in an effort to characterize these coals 40 whole channel samples excluding 1 cm partings were analyzed for major minor and trace elements by x ray fluorescence and proton induced x ray emission spectroscopy previously analyzed samples were added to provide additional geographic coverage and lithotype samples from one site were analyzed in order to provide detail of vertical elemental trends the as and pb levels in the fire clay coal bed tend to be higher than in the pond creek coal bed one whole channel sample of the fire clay coal bed contains 1156 ppm as ash basis with a single lithotype containing 4000 ppm as ash basis most of the as and pb appears to be associated with pyrite which potentially can be removed in beneficiation particularly coarser pyrite disseminated finer pyrite may not be completely removable by cleaning in the examination of pyrite conducted in this study it does not appear that significant concentration of as or pb occurs in the finer pyrite forms the biggest potential problem of as or pb enriched pyrite is therefore one of refuse disposal

occurrence of hexavalent chromium in ground water in the western mojave desert california abstract about 200 samples from selected public supply domestic and observation wells completed in alluvial aquifers underlying the western mojave desert were analyzed for total dissolved cr and cr vi because cr vi is difficult to preserve samples were analyzed by 3 methods chromium vi was determined in the field using both a direct colorimetric method and epa method 218 6 and samples were speciated in the field for later analysis in the laboratory using a cation exchange method developed for the study described in this paper comparison of the direct colorimetric method and epa method 218 6 with the new cation exchange method yielded r 2 values of 0 9991 and 0 9992 respectively total dissolved cr concentrations ranged from less than the 0 1 g l detection limit to 60 g l and almost all the cr present was cr vi near recharge areas along the mountain front ph values were near neutral dissolved o 2 concentrations were near saturation and cr vi concentrations were less than the 0 1 g l detection limit chromium vi concentrations and ph values increased downgradient as long as dissolved o 2 was present however low cr vi concentrations were associated with low dissolved o 2 concentrations near ground water discharge areas along dry lakes chromium vi concentrations as high as 60 g l occurred in ground water from the sheep creek fan alluvial deposits weathered from mafic rock derived from the san gabriel mountains and cr vi concentrations as high as about 36 g l were present in ground water from alluvial deposits weathered from less mafic granitic metamorphic and volcanic rocks chromium iii was the predominant form of cr only in areas where dissolved o 2 concentrations were less than 1 mg l and was detected at a median concentration of 0 1 g l owing to its low solubility in water of near neutral ph depending on local hydrogeologic conditions and the distribution of dissolved o 2 cr vi concentrations may vary considerably with depth samples collected under pumping conditions from different depths within wells show that cr vi concentrations can range from less than the 0 1 g l detection limit to 36 g l in a single well and that dissolved o 2 concentrations likely control the concentration and redox speciation of cr in ground water

a chromate contaminated site in southern switzerland part 1 site characterization and the use of cr isotopes to delineate fate and transport abstract the risk of groundwater contamination by chromate at a former chromite ore processing industrial site in rivera switzerland was assessed by determining subsoil cr vi concentrations and tracking naturally occurring cr vi reduction with cr isotopes using a hot alkaline extraction procedure a total cr vi contamination of several 1000 kg was estimated jarosite kfe 3 so 4 x cro 4 1 x 2 oh 6 and chromatite cacro 4 were identified as cr vi bearing mineral phases using xrd both limiting groundwater cr vi concentrations to track assumed cr vi reduction at field scale 53 cr values of contaminated subsoil samples in addition to groundwater 53 cr data are used for the first time the measurements showed a fractionation of groundwater 53 cr values towards positive values and subsoil 53 cr towards negative values confirming reduction of soluble cr vi to insoluble cr iii using a rayleigh fractionation model a current cr vi reduction efficiency of approximately 31 along a 120 m long flow path was estimated at an average linear groundwater velocity of 3 3 m d groundwater and subsoil 53 cr values were compared with a site specific rayleigh fractionation model proposing that subsoil 53 cr values can possibly be used to track previous higher cr vi reduction efficiency during the period of industrial activity the findings strongly favor monitored natural attenuation to be part of the required site remediation measures

paleoecology of the fire clay coal bed in a portion of the eastern kentucky coal field vertically continuous increment samples of the fire clay coal bed mid middle pennsylvanian late westphalian b collected from a portion of the central appalachian basin were studied palynologically petrographically and geochemically in order to partially reconstruct the paleoecology and processes associated with peat formation in the ancient fire clay paleomire results indicate that four compositional groups can be identified they are 1 a lycospora vitrinite dominant group characterized by high percentages of lycospora and vitrinite macerals and generally low but variable ash yields and sulfur contents 2 a mixed palynoflora high vitrinite group that petrographically is similar to group 1 except that it contains a more diverse palynoflora 3 a mixed palynoflora moderate low vitrinite group characterized by various admixtures of lycopsid fern and calamite miospores increased percentages of liptinite and inertinite macerals and low ash yields and sulfur contents and 4 a mixed palynoflora high ash yield group characterized by high percentages of small lycopsid fern and occasionally calamite and cordaite miospores high liptinite and inertinite contents high ash yields and moderate to high sulfur contents the fire clay coal bed contains a distinctive flint clay parting of probable volcanic origin that naturally divides the bed into two benches these two benches upper and lower are highly disparte in occurrence appearance and composition in the study area the lower bench generally is thin 0 5 m laterally discontinuous and mainly composed of dull mainly durain coal lithotypes ash yields typically are high sulfur contents generally are moderate to high compositional group 4 the mixed palynoflora high ash yield group defines all of the increments examined from the lower bench in contrast the upper bench is thick 0 75 m laterally continous and mainly comprised of bright mainly clarain coal lithotypes overall ash yields and sulfur contents for this bench are generally low although vertical variation is apparent all of the compositional groups occur in the upper bench in some columns notably those that are thick and uninterrupted by clastic partings groups 1 and 4 often occupy basal coal layers and groups 2 and 3 occur in higher layers other columns especially those taken in areas of thin 0 5 m fire clay coal are dominated by groups 1 and 4

estimation of fracture parameters from reflection seismic data part iii fractured models with monoclinic symmetry existing geophysical and geological data indicate that orthorhombic media with a horizontal symmetry plane should be rather common for naturally fractured reservoirs here we consider two orthorhombic models one that contains parallel vertical fractures embedded in a transversely isotropic background with a vertical symmetry axis vti medium and the other formed by two orthogonal sets of rotationally invariant vertical fractures in a purely isotropic host rock using the linear slip theory we obtain simple analytic expressions for the anisotropic coefficients of effective orthorhombic media under the assumptions of weak anisotropy of the background medium for the first model and small compliances of the fractures all effective anisotropic parameters reduce to the sum of the background values and the parameters associated with each fracture set for the model with a single fracture system this result allows us to eliminate the influence of the vti background by evaluating the differences between t

seismic inversion for geologic fractures and fractured media abstractamplitude variation with offset avo inversion attempts to use the available surface seismic data to estimate the density p wave velocity and s wave velocity of the earth model under linear slip interface theory synthetic seismograms for models with fractures prove that fractures are also reflection generators consequently observed reflections are not necessarily due to lithologic variations only but they could be due in part to the effect of fractures to obtain approximate equations for avo inversion for fractured media denoted by avo with fracture avof we derived new equations for pp wave reflection and transmission coefficients that are based on nonwelded contact boundary conditions in particular along with the fracture compliances azimuth has also been taken into account in the equations because the fractures can have any orientation the new approximate avof equations for a horizontally fractured medium with impedance contrast are developed by simplifying the equations for the

chromium fluxes and speciation in ultramafic catchments and global rivers abstract the role of ultramafic rock weathering in global chromium cr budgets and how these may be linked to changes in earth s climate over geological time was investigated by compiling dissolved cr speciation and fluxes in i 73 of the worlds large rivers representing 35 of global river discharge to oceans and in ii an ultramafic catchment putah creek watershed in the california coast range mountains usa weathering of ultramafic rocks creates ideal conditions for cr release and redox cycling alkaline river water draining ultramafic catchments is naturally enriched in cr up to 582 nmol l chromium concentrations increase with the extent of rock water interaction as indicated by correlations with mg and hco3 concentrations and ph whereas cr cycling depends on the availability of electron donors and acceptors e g fe ii organics mn iii iv oxides thus dissolved cr is exported from ultramafic watersheds as both the soluble hexavalent cr vi species mgcro4 cro42 and also as trivalent cr iii species croh co3 22 cr oh 3 the latter cr iii species were previously thought to have low solubility ultramafic catchments have higher area normalized cr and major ion fluxes for a given runoff when compared to global rivers and may thus have a disproportional impact on global cr budgets long term carbon cycling and moderation of the earth s climate over million year timescales riverine export fluxes of cr are linearly correlated with fluxes of ca mg and alkalinity in both ultramafic catchments and global rivers this suggests that silicate weathering is a key control on cr fluxes and that major element weathering fluxes may be a useful proxy for estimating cr and other trace element fluxes globally present day riverine dissolved cr fluxes to oceans are spatially variable and estimated to be 1 7 109 mol yr three times higher than previously reported however when geochemical reactions in estuaries are considered riverine cr fluxes may be lower throughout earth history cr weathering fluxes also may have varied with changes in the global distribution of ultramafic rocks cr concentrations in continental rocks or climactic conditions e g atmospheric co2 levels or runoff such variation should be considered when interpreting both modern and past cr seawater isotopic compositions and residence times

frequency dependent anisotropy due to meso scale fractures in the presence of equant porosity fractured rock is often modelled under the assumption of perfect fluid pressure equalization between the fractures and equant porosity this is consistent with laboratory estimates of the characteristic squirt flow frequency however these laboratory measurements are carried out on rock samples which do not contain large fractures we consider coupled fluid motion on two scales the grain scale which controls behaviour in laboratory experiments and the fracture scale our approach reproduces generally accepted results in the low and high frequency limits even under the assumption of a high squirt flow frequency we find that frequency dependent anisotropy can occur in the seismic frequency band when larger fractures are present shear wave splitting becomes dependent on frequency with the size of the fractures playing a controlling role in the relationship strong anisotropic attenuation can occur in the seismic frequency band the magnitude of the frequency dependence is influenced strongly by the extent of equant porosity with these results it becomes possible in principle to distinguish between fracture and microcrack induced anisotropy or more ambitiously to measure a characteristic fracture length from seismic data

comparison of δ 53 cr cr vi values of contaminated groundwater at two industrial sites in the eastern u s with contrasting availability of reducing agents abstract natural attenuation of groundwater contaminated by toxic hexavalent chromium cr vi was studied at two industrial sites in the eastern u s concentration and isotope composition of the residual cr vi were determined at site a in connecticut whose aquifer was polluted by electroplating solutions between 1930 and 1995 and at site b in new jersey whose aquifer was polluted by soluble chromium processing wastes between 1911 and 1963 site a was characterized by lower mean cr vi concentrations 2 mg l 1 and lower mean 53crcr vi values 1 84 in groundwater than site b 200 mg l 1 and 2 89 respectively 53crcr vi values were strongly positively correlated with dissolved organic carbon doc p 0 002 but not with dissolved ferrous iron fe ii or divalent manganese mn ii indicating that doc may have played a major role in spontaneous reduction of the mobile carcinogenic cr vi to immobile non toxic cr iii at site b the supply of doc may be nearly unlimited due to the presence of a buried organic meadow mat at a depth of six meters below the ground surface at site a contaminated groundwater has been extracted and treated since 1995 the mean 53crcr vi values of the residual aqueous contamination at site a significantly decreased over the past 15 years p

stratigraphic and regional variation of the petrographic and chemical properties of the tradewater formation coals and surrounding rocks in western kentucky abstract the stratigraphic and regional variation of petrographic and chemical properties within the coals of the upper carboniferous tradewater formation and surrounding rocks in the western kentucky coal field were analyzed with the intent of constructing a depositional model for the occurrence of these low sulfur coals cores were megascopically described and coal samples were analyzed for maceral ash and sulfur contents these data were then analyzed to determine regional variation within the study area as well as vertical variation within single coal columns sedimentological data from core logs indicate that the majority of the tradewater rocks consist of irregularly distributed coarsening upward fine grained detrital material that was deposited in shallow bodies of water fossiliferous shales and limestones indicate a marine influence less common coarse grained fining upward sequences appear to represent deposits of meandering or braided channels like the detrital rocks the coal seams are irregularly distributed and exhibit substantial variation in petrographic and chemical properties which reflect changes in the eh and ph of the coal swamp waters these individual swamps were relatively limited in extent and probably occupied a low lying coastal area the relatively high vitrinite content of most of the coals suggests a reasonable degree of preservation of decaying plant materials the study of benched samples from surface mines suggests a distinct dichotomy between swamps that were in more or less continuous contact with sulfate rich marine or brackish water and those in which peat accumulated in a dominantly fresh water setting most of the latter show a pattern of upward increasing sulfur content and decreasing vitrinite content indicating increasing influences of oxygenated water that would encourage microbial action and which would degrade the peat and increase the tendency for sulfide precipitation the high sulfur coals do not display this variability the high rates of lateral variability encountered in the data suggest that future study should concentrate on smaller areas where variation can be completely documented

coal rank trends in the central appalachian coalfield virginia west virginia and kentucky abstract coal rank determined from vitrinite maximum reflectance and from chemical rank parameters increases from high volatile c bituminous in portions of the eastern kentucky coalfield to low volatile bituminous in buchanan county virginia and mcdowell county west virginia and then decreases significantly to the dry fork anticline 20 km to the southeast the latter rank decrease as noted when rank data from individual coals is used across the fold 400 500 m structural relief can be accounted for by post tectonic coalification at a paleogeothermal gradient of about 40 45 c km reflectance gradients decrease from about 0 09 rmax 100 m in central buchanan county virginia to 0 06 rmax 100 min southeastern pike county kentucky to 0 03 max 100 m and less among the high volatile a and b coals to the nortwest of pike county the reflectance gradients are likely an indication of a decrease in paleogeothermal gradient to the northwest depth of burial may have also decreased to the northwest northward trending rank anomalies superimposed on the regional trend in kentucky may have been caused by subtle changes in the geothermal gradients associated with basement discontinuities or alternately by a depth of burial not accounted for at present perhaps under now eroded thrust sheets

geochemistry petrology and palynology of the pond creek coal bed northern pike and southern martin counties kentucky abstract the geochemistry petrology and palynology of the duckmantian age pond creek coal bed were investigated in northern pike and southern martin counties eastern kentucky the coal bed exhibits significant vertical variation in the investigated geochemical parameters with many diagenetic overprints of the original geochemistry included in the range of geochemical signatures are the presence of elements particularly tio 2 and zr suggesting the detrital influences at the time of deposition of a low vitrinite durain a high cao zone with elevated b be both suggesting marine influence in a lithotype in the middle of the coal bed and the postdepositional emplacement of pyrite in the uppermost lithotype individual lithotypes each representing distinct depositional environments all complicated to some degree by diagentic overprints comprise the complex history of the coal bed

weighted stacking for rock property estimation and detection of gas amplitude versus offset concepts can be used to generate weighted stacking schemes here called geo stack which can be used in an otherwise standard seismic data processing sequence to display information about rock properties the zoeppritz equations can be simplified and several different approximations appear in the literature they describe the variation of p wave reflection coefficients with the angle of incidence of a p wave as a function of the p wave velocities the s wave velocities and the densities above and below an interface using a smooth representative interval velocity model from boreholes or velocity analyses and assuming no dip the angle of incidence can be found as a function of time and offset by iterative ray tracing in particular the angle of incidence can be computed for each sample in a normal moveout corrected cmp gather the approximated zoeppritz equation can then be fitted to the amplitudes of all the traces at each time sample of the gather and certain rock properties can be estimated the estimation of the rock properties is achieved by the application of time and offset variant weights to the data samples before stacking the properties which can be displayed by geo stack are p wave reflectivity or true zero offset reflectivity s wave reflectivity and the reflectivity of p wave velocity divided by s wave velocity or pseudo poisson s ratio reflectivity if assumptions are made about the relation between p wave velocity and s wave velocity for water bearing clastic silicate rocks then it is possible to create a display which highlights the presence of gas

geochemistry of the pond creek coal bed eastern kentucky coalfield the pond creek coal bed middle pennsylvanian breathitt formation is an important low sulfur resource in pike and martin countries in the eastern kentucky coalfield the mined area is crossed by the n20 e trending belfry anticline the pond creek coal bed has a higher sulfur content on the west side of the anticline the vertical trends in the ash geochemistry also vary across the anticline the sites to the east of the anticline represent deposition of peat through periods of relative stability with slow deposition bright lithotypes interspersed with periods of relatively rapid clastic deposition dull lithotypes both generally removed from marine influence comparison of elemental trends between the lowest bright lithotype and the second bright lithotype suggest that the swamp became less acidic with time an upward decrease in minor element concentration may be related to the influx of clays and other silicates present in the bone lithotype this bone may have acted as a relatively low nutrient soil for the growth of the plants which contributed to the overlying bright lithotype the sites to the west of the anticline were subjected to a greater marine influence than the eastern sites high k2o al2o3 ratios at the bottom and top of the coal bed and a high tio2 zr dull clarain near the bottom of the coal point to clastic influences on the geochemistry the relatively high cao percentages in the middle third of the coal bed suggest deposition at near neutral ph the upper third of the coal bed was dominated by syngenetic and epigenetic pyrite emplacement

fluctuations in late neoproterozoic atmospheric oxidation cr isotope chemostratigraphy and iron speciation of the late ediacaran lower arroyo del soldado group uruguay oxygenation of the earth s atmosphere occurred in two major steps near the beginning and near the end of the proterozoic eon 2500 to 542 ma ago but the details of this history are unclear chromium isotopes in iron rich chemical sediments offer a potential to highlight fine scale fluctuations in the oxygenation of the oceans and atmosphere and to add a further dimension in the use of redox sensitive tracers to solve the question regarding fluctuations of atmospheric oxygen levels and their consequences for earth s climate we observe strong positive fractionations in cr isotopes 53 cr up to 5 0 in iron rich cherts and banded iron formation horizons within the arroyo del soldado group ediacaran uruguay that can be explained by rapid effective oxidation of fe ii rich surface waters these fluctuations are correlated with variations in ratios of highly reactive iron fe hr to total iron fe tot which indicate a predominance of anoxic water columns fe hr fe tot 0 38 during the onset of oxidation pulses we favor the scenario by which isotopically heavy cr vi entered the basin after pulses of oxidative weathering on land and in which fe ii accumulated in the water column neodymium isotopes reveal that these oxygenation pulses were followed by increased influxes to the basin of continental crust derived detrital components of paleoproterozoic nd t dm model ages 2 1 2 2 ga provenance typical of the rio de la plata craton the association of positive 53 cr ferruginous fe hr fe tot 0 38 stratigraphic intervals with low diversity acritarch assemblages dominated by bavlinella faveolata strongly support models postulating a stratified eutrophic neoproterozoic ocean thus even within a few million years of the precambrian cambrian boundary paleoceanographic conditions resembled more those of paleoproterozoic oceans than phanerozoic and present oceans this highlights the sheer magnitude of ecological changes at the precambrian cambrian transition changes which ultimately led to the demise of the precambrian world and the birth of the metazoan dominated phanerozoic

geochemical constraints on the sources of cr vi contamination in waters of messapia central evia basin the present study aims to define geochemical constraints on contamination source s by cr vi in central evia through a compilation of new and literature data on an integrated set of approaches including mineralogy and isotope geochemistry leach experiments on rocks soils and ni laterites and comparison with literature data on groundwater the concentrations of cr vi in leachates from various geological materials decrease in the following order ni laterites from kastoria soils altered ultramafic rocks ni laterites from evia a salient feature is the diversity in the cr vi concentrations and 53cr values in a groundwater ranging from 2 to 850 g l cr vi and 0 60 1 99 53cr and b leachates from ni laterites ranging from 0 6 to 2 0 g l and 1 01 in evia samples and from 750 to 1200 g l and negative to slightly positive 0 21 to 0 03 53cr in kastoria samples a positive correlation r2 0 514 between the 53cr values and depth of the aquifers potentially reflects the decrease in soluble o2 with increasing depth the relatively high cr mn and the abundance of fine grained mn hydr oxides in the kastoria laterite ore may be major controlling factors for the existence of high cr vi concentrations in the water leachates in contrast the low cr vi concentrations and positively fractionated cr isotopes in the ni laterite leachates from evia are potentially related to redox and multistage transportation redeposition processes the positive correlation between cr concentrations and ca mg ratios r2 0 647 for rock leachates and the negative correlation r2 0 694 for soil leachates suggest that cr in groundwater may be released mainly from cr bearing mg silicates in altered ultramafic rocks and soils the plot of 53cr values versus cr vi concentrations for the contaminated waters from central evia and assopos basin fall within both fields defined from a global database for natural waters and waters contaminated by human activities

petrology of the pond creek coal bed in eastern kentucky abstract the middle pennsylvanian breathitt formation pond creek coal bed was examined along two cross sections in pike and martin countries in the eastern kentucky coal field along the north south profile the sulfur content increased markedly to the top of the bed in the eastern portion of the east west profile the coal bed is marked by a high vitrinite high ash bone shaley coal lithotype within the top half of the bed and by a thin clarodurite vitrinertoliptite rich durain at the top of the bed a northeastward plunging anticline termed here the belfry anticline marks the boundary between the high sulfur coal beds in the west and the appearance of the bony horizon on the east the coal and the interval between the rider and the coal bed both thin across the anticline which was active at the time of deposition

weathering and transport of chromium and nickel from serpentinite in the coast range ophiolite to the sacramento valley california usa abstract a soil geochemical study in northern california was done to investigate the role that weathering and transport play in the regional distribution and mobility of geogenic cr and ni which are both potentially toxic and carcinogenic these elements are enriched in ultramafic rocks primarily serpentinite and the soils derived from them 1700 10 000 mg cr per kg soil and 1300 3900 mg ni per kg soil in the coast range ophiolite chromium and ni have been transported eastward from the coast range into the western sacramento valley and as a result valley soil is enriched in cr 80 1420 mg kg 1 and ni 65 224 mg kg 1 compared to median values of u s soils of 50 and 15 mg kg 1 respectively nickel in ultramafic source rocks and soils is present in serpentine minerals lizardite antigorite and chrysotile and is more easily weathered compared to cr which primarily resides in highly refractory chromite mg fe2 cr3 al fe3 2o4 although the majority of cr and ni in soils are in refractory chromite and serpentine minerals the etching and dissolution of these minerals presence of cr and ni enriched clay minerals and development of nanocrystalline fe hydr oxides is evidence that a significant fractions of these elements have been transferred to potentially more labile phases

geochemical processes and petrogenetic evolution of rodingite dykes in the ophiolite complex of othrys central greece rodingite dykes occur in serpentinised harzburgites in the othrys ophiolite hydrogrossular and diopside along with chlorite appeared first and mark the initiation of rodingitisation of the dolerite protolith subsequently calcite formed after diopside and consequently reacted with chlorite to enrich the rodingites in diopside and garnet apatite also forms at the late stages of alteration several geochemical exchanges were triggered by variably alkaline and continuously evolving fluids passing through the serpentinising peridotites a possible t xco2 path along with a reaction series are proposed for the development of the rodingitic assemblages that entail a fluid phase leaching of the peridotite was triggered by fluids very rich in co2 and carbonate complexes are thought to be responsible for mobilization of cr and ni under such conditions ree also were mobile and the presence of co32 and po43 ions that complexed them further assisted their transportation zr mobilised at increased ph conditions with the aid of the oh and po43 during the late stage of alteration and due to the incorporation of more saline fluids after formation of calcite and apatite in the two metasomatic stages respectively the ree complexes were destabilised due to reduced activity of co32 and po43 and free rees were able to precipitate onto garnet cr and ni hydroxides were precipitated after formation of calcite in the rodingite the saline fluids were also reducing hence eu remained in its divalent state and was highly absorbed on garnet surfaces the rodingitisation at othrys ophiolite occurred in a subduction regime as it is implicated by the very rich in co2 fluid phase which is readily explained by involvement of subducted carbonate sediments and is favoured by the development of structural zones that acted as conduits to the metasomatising fluid phase

stable isotope records across the cretaceous paleogene transition stevns klint denmark new insights from the chromium isotope system abstract late cretaceous to early paleogene time represents a critical transitional period in earth history global events include short term instability in climate and ocean circulation large igneous province emplacement and catastrophic extinction of marine and terrestrial fauna due at least in part to a bolide impact event the response of the ocean system to cretaceous paleogene k pg global events has been the subject of much research yet fundamental questions remain regarding carbon cycling climate ocean mixing and redox conditions to help elucidate paleoceanographic changes across the k pg transition we revisit the classic maastrichtian to danian chalk limestone succession at stevns klint denmark with a suite of new geochemical data including insights from the redox sensitive chromium isotope system we use carbon and oxygen isotope trends to form a well constrained framework for the succession before presenting strontium isotope chromium isotope and rare earth element data for the units deposited both before and after the k pg event carbon isotopes show only minor perturbation across the k pg boundary and oxygen isotopes record a prominent positive excursion with both of these trends standing in contrast to many k pg boundary sections worldwide strontium isotopes record a spike towards more radiogenic values which is consistent with a globally observed short term weathering pulse the chromium isotope profile of maastrichtian chalk begins with strongly positive values followed by a sharp negative excursion associated with a facies shift and initiation of bottom currents in the chalk sea 53 cr values then recover before falling steadily across the k pg boundary and into the danian limestone chromium isotope trends do not correspond to changes in hydrothermal input or basin redox conditions instead we propose that mixing of water masses with distinct chromium isotope signatures controlled temporal chromium isotope variability the local mixing event inferred from our maastrichtian chromium isotope data could be related to a temporary inflow of tethyan bottom waters or the shift from end maastrichtian greenhouse warming associated with deccan volcanism to the worldwide cooling phase that immediately preceded the k pg boundary no immediate change in chromium isotopes is recorded across the k pg boundary indicating that the bolide impactor did not substantially perturb the marine chromium cycle at least at the scale resolvable by our data instead chromium isotope trends continued to be controlled by local oceanographic processes highlighting the potential of the chromium isotope system to record isotopic heterogeneity and mixing events in ancient oceans

isotopic evidence for the cretaceous tertiary impactor and its type high precision mass spectrometric analysis of chromium in sediment samples from the cretaceous tertiary k t boundary coincident with the extinction of numerous organisms on earth confirms the cosmic origin of the k t phenomenon the isotopic composition of chromium in k t boundary samples from stevns klint denmark and caravaca spain is different from that of earth and indicates its extraterrestrial source the chromium isotopic signature is consistent with a carbonaceous chondrite type impactor the observed differences in the chromium isotopic composition among various meteorite classes can serve as a diagnostic tool for deciphering the nature of impactors that have collided with earth during its history

the chromium isotopic composition of seawater and marine carbonates article history chromium isotopes are fractionated during redox reactions and have the potential to provide a record of changes in the oxygenation levels of the oceans in the geological past however cr is a trace metal in seawater and its low concentrations make isotopic measurements challenging here we report the first determinations of 53 cr for seawater from open ocean argentine basin and coastal southampton water settings using a double spike technique the total chromium concentration in seawater from southampton water is 1 85 nm whereas the cr content of argentine basin samples is 5 8 6 6 nm the 53cr value of seawater from the argentine basin is 0 491 0 556 in intermediate and deep waters and varies between 0 412 and 0 664 in surface waters 150 m the 53

a review of least squares inversion and its application to geophysical problems geophysical inversion involves the estimation of the parameters of a postulated earth model from a set of observations since the associated model responses can be nonlinear functions of the model parameters nonlinear least squares techniques prove to be useful for performing the inversion a common type of inversion applies iterative damped linear least squares through use of the marquardt levenberg method traditionally this method has been implemented by solving the associated normal equations in conventional ways however singular value decomposition svd produces significant improvements in computational precision when applied to the same system of normal equations iterative least squares modeling finds application in a wide variety of geophysical problems two examples illustrate the approach 1 seismic wavelet deconvolution and 2 the location of a buried wedge from surface gravity data more generally nonlinear least squares inversion can be used to estimate earth models for any set of geophysical observations for which an appropriate mathematical description is available

cr vi occurrence and geochemistry in water from public supply wells in california hexavalent chromium cr vi in 918 wells sampled throughout california between 2004 and 2012 by the groundwater ambient monitoring and assessment priority basin project gama pbp ranged from less than the study reporting limit of 1 microgram per liter g l to 32 g l statewide cr vi was reported in 31 percent of wells and equaled or exceeded the recently established 2014 california maximum contaminant level mcl for cr vi of 10 g l in 4 percent of wells cr vi data collected for regulatory purposes overestimated cr vi occurrence compared to spatially distributed gama pbp data ninety percent of chromium was present as cr vi which was detected more frequently and at higher concentrations in alkaline ph 8 oxic water and more frequently in agricultural and urban land uses compared to native land uses chemical isotopic tritium and carbon 14 and noble gas data show high cr vi in water from wells in alluvial aquifers in the southern california deserts result from long groundwater residence times and geochemical reactions such as silicate weathering that increase ph while oxic conditions persist high cr vi in water from wells in alluvial aquifers along the west side of the central valley results from high chromium in source rock eroded to form those aquifers and areal recharge processes including irrigation return that can mobilize chromium from the unsaturated zone cr vi co occurred with oxyanions having similar chemistry including vanadium selenium and uranium cr vi was positively correlated with nitrate consistent with increased concentrations in areas of agricultural land use and mobilization of chromium from the unsaturated zone by irrigation return

trace elements and isotope geochemistry c o fe cr of the caue iron formation quadrilatero ferrifero brazil evidence for widespread microbial dissimilatory iron reduction at the archean paleoproterozoic transition abstract the banded iron formation bifs of the caue formation quadrilatero ferrifero brazil are part of the great volume of bifs deposited worldwide around 2 45 ga samples of carbonate ankerite dolomite bif from this unit were collected from a drill core ca 600 m deep in the alegria region geochemical data suggest low clastic contamination y ho 37 7 and seawater like signatures with positive la and y anomalies no true ce anomalies and mean eu eu 1 62 u th shows a sharp increasing downwards pattern up to ca 15 below the 535 m mark values of 13c and 18o are all negative reaching a minimum of 10 0 and 24 6 respectively in the 540 560 m interval values of 56fe are mostly positive between 0 5 and 1 3 the higher values are attained in the same interval values of authigenic 53cr range between 0 01 and 0 26 with an increasing downwards pattern which mirrors the u th variation a possible explanation for both the low 13c and the high 56fe is the activity of microorganisms in the dissimilatory iron reduction dir of the precursor ferric oxides thus we put forward a model for deposition of the caue bifs that starts with the generation of fe ii aq through hydrothermal input to the deeper basin which upon reaching a chemocline in the platform border oxidizes to fe iii and settles as iron oxy hydroxides to the basin floor when reaching the sediment layer fe iii is then reduced by microbial activity to generate magnetite and iron rich carbonates with negative 13c and positive 56fe an important issue is how u vi and cr vi were mobilized to the basin to form the positive u th and 53cr excursions these could reflect oxidative continental weathering but an alternative possibility is that those elements became available through local oxygenation in continental microenvironments which would better explain the lack of ce redox cycling in either case our results together with a growing body of data for bif sequences of similar age around the world e g kuruman south africa and hamersley australia suggest that microbial mediated dir was a common and widespread mechanism for the genesis of bifs at the archean paleoproterozoic transition

alpha emitting isotopes and chromium in a coastal california aquifer abstract the unadjusted 72 h gross alpha activities in water from two wells completed in marine and alluvial deposits in a coastal southern california aquifer 40 km north of san diego were 15 and 25 picocuries per liter pci l although activities were below the maximum contaminant level mcl of 15 pci l when adjusted for uranium activity there is concern that new wells in the area may exceed mcls or that future regulations may limit water use from the wells coupled well bore flow and depth dependent water quality data collected from the wells in 2011 with analyses for isotopes within the uranium actinium and thorium decay chains show gross alpha activity in marine deposits is associated with decay of naturally occurring 238 u and its daughter 234 u radon activities in marine deposits were as high as 2230 pci l in contrast gross alpha activities in overlying alluvium within the piedra de lumbre watershed eroded from the nearby san onofre hills were associated with decay of 232 th including its daughter 224 ra radon activities in alluvium from piedra de lumbre of 450 pci l were lower than in marine deposits chromium vi concentrations in marine deposits were less than the california mcl of 10 g l effective july 1 2014 but 53 cr compositions were near zero and within reported ranges for anthropogenic chromium alluvial deposits from the nearby las flores watershed which drains a larger area having diverse geology has low alpha activities and chromium as a result of geologic and geochemical conditions and may be more promising for future water supply development

climate change and tectonic uplift triggered the formation of the atacama desert s giant nitrate deposits the giant nitrate deposits of the hyperarid atacama desert chile are one of the most extraordinary yet enigmatic mineral occurrences on earth these deposits are complex assemblages of highly soluble nitrates chlorides sulfates perchlorates iodates and chromates and their preservation is the result of prevalent hyperarid climate conditions in the atacama desert since the late miocene with average rainfall rates of 10 mm yr in the past 3 m y although several hypotheses have been proposed since the mid 1800s the formation of these extensive deposits still remains highly controversial despite the fact that recent studies have argued toward an atmospheric source for the nitrate sulfate and perchlorate components in this report we focus on the often overlooked and poorly studied iodine and chromium components of atacama s nitrates we present the fi rst cosmogenic iodine 129 i and stable chromium 53 52 cr isotope data of nitrates showing that groundwater has played an unforeseen role in the formation of these massive deposits the isotopic signature of i in the nitrates 129 i i 150 600 10 15 share similarities with deep sedimentary marine pore waters and shales deviating signifi cantly from atmospheric iodine 129 i i 1500 10 15 while the positive and highly fractionated 53 52 cr srm979 values 0 7 to 3 are indicative of intense cr redox cycling due to groundwater transport our evidence points toward a multi source genetic model for the atacama desert nitrate deposits where these extensive accumulations were the result of long lived near surface mineral precipitation driven by groundwater i e chromates iodates coupled with dry atmospheric deposition i e nitrates perchlorates and sea spray inputs i e sulfates chlorides triggered by increasing aridity and tectonic uplift

the isotopic composition of authigenic chromium in anoxic marine sediments a case study from the cariaco basin chromium cr isotopes are an emerging proxy for tracking redox processes at the earth s surface however there has been limited exploration of the cr isotope record of modern and recent marine sediments the basic inorganic chemistry of cr suggests that anoxic marine basins should factor prominently in the global cr cycle and that sediments deposited within anoxic basins may offer a valuable cr isotope archive throughout earth s history here we present 53 cr data from sediments of the cariaco basin venezuela a type environment for large perennially anoxic basins with a relatively strong hydrological connection to the global oceans we document a marked positive shift in bulk 53 cr values following the termination of the last glacial maximum followed by relative stasis based on a suite of independent redox proxies this transition marks a switch from oxic to persistently anoxic and sulfidic euxinic depositional conditions within the basin we find good agreement between two independent approaches toward estimating the 53 cr composition of authigenic cr in euxinic cariaco basin sediments and that these estimates are very similar to the 53 cr composition of modern open atlantic ocean seawater these data together with considerations of reaction kinetics and mass balance within the cariaco basin are consistent with the hypothesis that anoxic marine settings can serve as a chemical archive of first order trends in seawater 53 cr composition additionally the cariaco basin data suggest that there has been secular stability in the average 53 cr value of atlantic seawater over the last 15 kyr

redox fluctuations in the early ordovician oceans an insight from chromium stable isotopes abstract chromium cr stable isotopes are a useful tracer of changes in redox conditions because changes in its oxidation state are accompanied by an isotopic fractionation recent co precipitation experiments have shown that cr vi is incorporated into the calcite lattice suggesting that carbonates are a potential sink for dissolved cr in the ocean and could effectively capture the cr isotope composition of ambient seawater thus the cr isotopic composition 53cr of carbonates has the potential to record changes in the oxygenation state of ancient oceans to test the potential of this system we measured 53cr values of limestones and dolostones from an early ordovician marine carbonate platform cerro la silla section of the precordillera san juan argentina an increasing number of studies support the hypothesis that the early ordovician oceans were stratified with respect to oxygen and that the global ocean experienced multiple episodes of anoxic expansion and contraction making this time period ideal for testing the usefulness of the cr isotope system the most prominent feature of the cerro la silla cr isotope profile is a positive excursion of 0 5 during the late tremadocian accompanied by exceptionally low cr concentrations

oxidative release of chromium from archean ultramafic rocks its transport and environmental impact a cr isotope perspective on the sukinda valley ore district orissa india abstract this study investigates cr isotope fractionation during soil formation from archean 3 1 3 3 ga ultramafic rocks in a chromite mining area in the southern singhbhum craton orissa india the cr isotope signatures of two studied weathering profiles range from non fractionated mantle values to negatively fractionated values as low as 53 cr 1 29 0 04 local surface waters are isotopically heavy relative to the soils this supports the hypothesis that during oxidative weathering isotopically heavy cr vi is leached from the soils to runoff the impact of mining pollution is observed downstream from the mine where surface water cr concentrations are significantly increased accompanied by a shift to less positive 53 cr values relative to upstream unpolluted surface water a microbial mat sample indicates that microbes have the potential to reduce and immobilize cr vi which could be a factor in controlling the hazardous impact of cr vi on health and environment the positive cr isotope signatures of the brahmani estuary and coastal seawater collected from the bay of bengal further indicate that the positively fractionated cr isotope signal from the catchment area is preserved during its transport to the sea isotopically lighter cr vi downstream from the mine is probably back reduced to cr iii during riverine transport leading to similar cr isotope values in the estuary as observed upstream from the mine

the cr isotope signature of surface seawater a global perspective abstract this study presents chromium isotope data expressed as 53 cr and chromium concentrations cr of surface seawater 0 2 m depth from a variety of locations worldwide in addition to samples from the open ocean arctic southern pacific and atlantic oceans samples were analysed from areas with more restricted water exchange rates the mediterranean sea oresund and baltic sea the data indicate a heterogeneous distribution of 53 cr in seawater with a total range from 0 13 to 1 24 the data are in agreement with a previous study which focused on depth profiles suggesting that seawater heterogeneity in 53 cr and cr concentration can be explained using a single fractionation factor for cr reduction e 0 79 0 06 2sd in basins with limited water exchange with the open ocean however local factors seem to control the cr isotope composition

elastic wave propagation in media with parallel fractures and aligned cracks a model of parallel slip interfaces simulates the behaviour of a fracture system composed of large closely spaced aligned joints the model admits any fracture system anisotropy triclinic the most general monoclinic orthorhombic or transversely isotropic and this is specified by the form of the 3 3 fracture system compliance matrix the fracture system may be embedded in an anisotropic elastic background with no restrictions on the type of anisotropy to compute the long wavelength equivalent moduli of the fractured medium requires at most the inversion of two 3 3 matrices when the fractures are assumed on average to have rotational symmetry transversely isotropic fracture system behaviour and the background is assumed isotropic the resulting equivalent medium is transversely isotropic and the effect of the additional compliance of the fracture system may be specified by two parameters in addition to the two isotropic parameters of the isotropic background dilute systems of flat aligned microcracks in an isotropic background yield an equivalent medium of the same form as that of the isotropic medium with large joints i e there are two additional parameters due to the presence of the microcracks which play roles in the stress strain relations of the equivalent medium identical to those played by the parameters due to the presence of large joints thus knowledge of the total of four parameters describing the anisotropy of such a fractured medium tells nothing of the size or concentration of the aligned fractures but does contain information as to the overall excess compliance due to the fracture system and its orientation as the aligned microcracks which were assumed to be ellipsoidal with very small aspect ratio are allowed to become non fiat i e have a growing aspect ratio the moduli of the equivalent medium begin to diverge from the standard form of the moduli for flat cracks the divergence is faster for higher crack densities but only becomes significant for microcracks of aspect ratios approaching 0 3

geochemistry of the blue gem coal bed knox county kentucky abstract the blue gem coal bed middle pennsylvanian westphalian b breathitt formation has low ash with some sample sites having less than 1 ash and low sulfur contents through parts of knox county kentucky most collection sites exhibit similar vertical elemental trends in ash geochemistry the relatively high ash 1 ash lower part of the bed displays enrichment in tio2 zr cr v and ni co zn rb and mn show enrichment at some sites a low ash 1 ash and a relative enrichment in sio2 k2o and rb and a relative decrease in cu ni co ba and mn when compared to the middle part of the bed principal components analysis indicates that the samples with an ash content 0 63 1 0 show associations for ni cu cr and co samples with between 1 01 2 0 ash display strong element associations that suggest increased clastic sediment contributions tio2 zr k2o rb sio2 the low ash content and the upwards decrease in trace concentrations both suggest that the blue gem peat swamp was ombrotrophic through at least a part of its geologic history

evolution of rodingites along stratigraphic depth in the iti and kallidromon ophiolites central greece abstract rodingitised rocks were collected from the neighbouring iti and kallidromon ophiolites they comprise metasomatic assemblages after serpentinised lherzolite and harzburgite gabbro and dolerite dykes the main mineral phases in the metasomatised mantle and gabbroic rocks include grossularitic garnet chlorite and diopside whereas epidote group minerals were mainly developed at the expense of the dolerite dykes the fluid phase involved in the metasomatic reactions was highly alkaline in the metasomatising peridotites and less alkaline in the altered gabbro and dolerite under such conditions ti is assumed to have remained immobile in the whole process while zr remained constant in the stratigraphically upper rodingitised gabbro and dolerite transportation of rare earth elements zr cr and ni from the altered mantle segment to the upper gabbro level was assisted by the presence of carbonate and hydroxyl ligands after consequent breakdown of the carbonate complexes these elements were deposited in the rodingitised gabbro and dolerite rare earths were mainly integrated in the neoblastic diopside whereas cr and ni likely formed insoluble hydroxides in that less reducing environment the metasomatic event happened in the mantle wedge close to the subduction of the pelagonian carbonates that strongly enriched the fluid phase in co 2 the entrance of an externally derived hydrothermal fluid was responsible for the reduction of ph at the higher levels and the calculated influx of si in the system

chromium chromium isotopes and selected trace elements western mojave desert usa abstract chromium vi concentrations in excess of the california maximum contaminant level mcl of 50 g l occur naturally in alkaline oxic ground water in alluvial aquifers in the western mojave desert southern california the highest concentrations were measured in aquifers eroded from mafic rock but cr vi as high as 27 g l was measured in aquifers eroded from granitic rock chromium vi concentrations did not exceed 5 g l at ph

coal facies studies in the eastern united states coals in the eastern united states east of the mississippi river have been the subject of a number of coal facies studies going back to the 19th century such studies would not necessarily fall within a strict modern classification of coal facies studies but if a study encompassed some aspects of paleobotany palynology petrology geochemistry or sedimentology we assumed that some data and interpretations may be of use in evaluations of the facies references are presented as a guide for further research with annotation in the tables

temporal changes in cr fluxes and δ53cr values in runoff from a small serpentinite catchment slavkov forest czech republic abstract headwater catchments underlain by ultramafic bedrock may release toxic amounts of hexavalent chromium cr vi into runoff redox cycling of cr during weathering pedogenesis and runoff generation can be constrained by studying 53cr 52cr isotope systematics we report a 12 month time series of 53cr values of runoff from a small serpentinite dominated catchment in central europe complemented with a 5 year monitoring of cr and doc concentrations 53cr values of bulk bedrock rock forming minerals and bulk soil were also determined cr vi concentrations in runoff exceeded the 10 ppb maximum contaminant level by 70 concentrations of cr vi in runoff were positively correlated with water discharge and doc concentrations chromium export flux in winter was significantly higher than in summer runoff 53cr exhibited a temporal trend with negative values 0 6 in winter and positive values 0 5 in summer on an annual basis the mass weighted 53cr value of runoff was 0 4 dissolved cr exported in winter was isotopically lighter than the within site cr sources 53cr of bulk bedrock ranged from 0 2 to 0 0 and 53cr of soil ranged from 0 2 to 0 3 chromium isotope analysis of seven rock forming minerals separated from serpentinites tremolite actinolite schists and amphibolites revealed a much wider range of 53cr values from 0 4 hornblende to 1 7 albite most of the variability in runoff 53cr can be explained by incongruent oxidative weathering with a contribution of isotope selective processes related to pedogenesis isotopically light cr was preferentially mobilized from weathered bedrock and soil in cold water rich periods and exported via stream water in these periods precipitation water more rapidly penetrates into the soil than in summer months characterized by lower rainfall and larger evapotranspiration and more efficiently leaches the accumulated cr vi

whole coal versus ash basis in coal geochemistry a mathematical approach to consistent interpretations abstract several standard methods require coal to be ashed prior to geochemical analysis researchers however are commonly interested in the compositional nature of the whole coal not its ash coal geochemical data for any given sample can therefore be reported in the ash basis on which it is analyzed or the whole coal basis to which the ash basis data are back calculated basic univariate mean variance distribution etc and bivariate correlation coefficients etc measures of the same suite of samples can be very different depending which reporting basis the researcher uses these differences are not real but an artifact resulting from the compositional nature of most geochemical data the technical term for this artifact is subcompositional incoherence since compositional data are forced to a constant sum such as 100 or 1 000 000 ppm they possess curvilinear properties which make the euclidean principles on which most statistical tests rely inappropriate leading to erroneous results applying the isometric logratio ilr transformation to compositional data allows them to be represented in euclidean space and evaluated using traditional tests without fear of producing mathematically inconsistent results when applied to coal geochemical data the issues related to differences between the two reporting bases are resolved as demonstrated in this paper using major oxide and trace metal data from the pennsylvanian age pond creek coal of eastern kentucky usa following ilr transformation univariate statistics such as mean and variance still differ between the ash basis and whole coal basis but in predictable and calculated manners further the stability between two different components a bivariate measure is identical regardless of the reporting basis the application of ilr transformations addresses both the erroneous results of euclidean based measurements on compositional data as well as the inconsistencies observed on coal geochemical data reported on different bases

weathering on land and transport of chromium to the ocean in a subtropical region misiones nw argentina a chromium stable isotope perspective abstract we have investigated the pathway of chromium from its mobilization on land and along its riverine transport in a subtropical region of south america misiones province argentina in an attempt to link cr stable isotope compositions recently measured in seawater with signals prevailing in rivers and ultimately with cr isotope effects observed during oxidative surface weathering in subtropical red soils cr concentrations and stable cr isotopic compositions expressed as 53cr values in two typical and representative surface profiles of weathered basalt show significant depletion of cr in the soils of up to 50 together with pronounced negatively fractionated 53cr values which are indicative of oxidative mobilization of heavy cr vi into the run off the behavior of cr in the studied weathering profiles is not correlated with that of other redox sensitive elements such as ce and u this is essentially due to the affinity of ree and u but not cr with secondary phosphates which form during weathering processes smaller tributaries in nw argentina to the parana river second largest river in south america carry dissolved cr in the order of 0 7 1 4 ppb 13 27 nm with 53cr values of 0 2 to 0 4 balancing the negatively fractionated weathering products the isotope composition and concentration of dissolved cr in the ca 1200 km long parana river from misiones to its estuary and discharge area into the south atlantic ocean remains relatively constant with an average cr concentration around 2 4 ppb 46 nm and an average 53cr value of 0 32 the cr concentration in the estuary itself drops by ca 50 but with only minor change in its cr isotope composition results from the parana estuary are identical with recently analyzed surface seawater from the argentine basin with cr contents of 0 3 ppb 6 nm and 53cr values 0 4 bonnand et al 2013 and indicate that there is only a minimal cr isotopic variability during riverine transport even during long transport distances as shown in our example of the parana river simple cr input flux calculations reveal that the parana river accounts for 5 of the total yearly cr flux to the world s oceans today and that its isotopic signature seems to be at least locally imparted to the surface seawater of the argentine basin whether or not this cr isotope signature is generally exhibited by the world s oceans needs further investigations particularly the characterization of seawater around the globe

use of avoa data to estimate fluid indicator in a vertically fractured medium microstructural attributes of cracks and fractures such as crack density aspect ratio and fluid infill determine the elastic properties of a medium containing a set of parallel vertical fractures although the tangential weakness t of the fractures does not vary with the fluid content the normal weakness n exhibits significant dependence on fluid infill based on linear slip theory we used the ratio g n t termed the fluid indicator as a quantitative measure of the fluid content in the fractures with g representing the square of the ratio of s and p wave velocity in the unfractured medium we used a born formalism to derive the sensitivity to fracture weakness of pp and ps reflection coefficients for an interface separating an unfractured medium from a vertically fractured medium our formulae reveal that the pp reflection coefficient does not depend on the 2d microcorrugation surface roughness with ridges and valleys parallel to the fracture strike whereas the ps reflection coefficien

application of chromium stable isotopes to the evaluation of cr vi contamination in groundwater and rock leachates from central euboea and the assopos basin greece abstract major and trace elements a in groundwater ultramafic rocks from natural outcrops and soil samples from cultivated sites of central euboea and assopos basin and b in experimentally produced laboratory water leachates of rocks and soils were investigated by sem eds xrd and icp ms in addition stable chromium isotopes expressed as 53cr values were measured in groundwater and leachates in order to identify potential sources for cr contamination the higher cr vi concentrations in soil leachates compared to those in the rock pulp leachates potentially can be explained by the presence of larger amounts of fe fe ii and mn mn oxides acting as oxidizing catalysts assuming that redox processes produce significant cr isotope fractionation groundwater 53cr values range between 0 8 and 1 98 the compilation of the obtained analytical data suggests that the dominant cause of cr isotope fractionation is post mobilization reduction of cr vi however the lack of a very good negative relationship between cr vi concentrations and 53cr values may reflect that sorption precipitation and biological processes fractionation during uptake by plants complicate the interpretation of the cr isotope signatures the variation in 53cr values 0 84 to 1 98 in groundwater from euboea and from 0 98 to 1 03 in samples from the assopos basin imply initial oxidative mobilization of cr vi from the ultramafic host rocks followed by reductive processes that lead to immobilization of portions of cr iii using a rayleigh distillation model and different fractionation factors of cr vi reduction valid for aqueous fe ii and fe ii bearing minerals we calculate that more than 53 but maximum 94 of the originally mobile cr vi pool was reduced to immobile cr iii in the waters investigated this indicates that efficient processes in the aquifers may facilitate natural attenuation of the toxic cr vi to less harmful cr iii

geochemistry and cr stable isotopes of cr contaminated groundwater in leon valley guanajuato mexico abstract leon valley located in the mexican state of guanajuato has a long history 35 a of cr contamination of groundwater and surface water here data are presented for cr major ion and trace element concentrations and cr stable isotope measurements of groundwater in a heavily contaminated aquifer in buenavista where cr ore processing residue piles coprps located in a chromate production factory are the main source of cr the aquifer directly beneath the factory still retains very high cr vi concentrations 121 mg l ongoing pump and treat remediation is keeping the high concentration plume confined to the factory area and immediate vicinity though cr is also detected at some distance away chromium isotope data of the aquifer directly under the factory show only a small increase in 53 cr 0 33 to 0 81 and indicates minimal reduction of cr vi to cr iii very high cr vi concentrations have possibly overwhelmed natural reductants and furthermore fresh cr vi was being leached into the groundwater from the coprp from just one year of cr isotope data it is clear that more aggressive remediation techniques will be necessary to reduce or eliminate the contamination the fringes of the cr plume have substantially lower concentrations and can be partially explained by transport of the main plume or mixing between waters from the nearby landfill and highly contaminated waters from qc while the source of cr at the fringes of the plume could be attributed to a source from the nearby landfill instead of the main plume from the factory the cr stable isotope data show enrichment in the heavier isotopes and point to varying amounts of reduction isotopic enrichment seen between 2007 and 2008 along the fringe may indicate either reduction or less unreacted cr vi is being transported to the fringes in either case some potential for natural attenuation of cr vi exists at the western margin of the plume with the landfill playing a role

detection of gas in sandstone reservoirs using avo analysis a 3 d seismic case history using the geostack technique the geostack technique is a method of analyzing seismic amplitude variation with offset avo information one of the outputs of the analysis is a set of direct hydrocarbon indicator traces called fluid factor traces the fluid factor trace is designed to be low amplitude for all reflectors in a clastic sedimentary sequence except for rocks that lie off the mudrock line the mudrock line is the line on a crossplot of p wave velocity against s wave velocity on which water saturated sandstones shales and siltstones lie some of the rock types that lie off the mudrock line are gas saturated sandstones carbonates and igneous rocks in the absence of carbonates and igneous rocks high amplitude reflections on fluid factor traces would be expected to represent gas saturated sandstones of course this relationship does not apply exactly in nature and the extent to which the mudrock line model applies varies from area to area however it is a useful model in many basins of the world including the one

geochemistry of natural chromium occurrence in a sandstone aquifer in bauru basin sao paulo state brazil abstract anomalous concentrations of cr vi occur in groundwaters of the adamantina aquifer in a large region in the western state of sao paulo sometimes exceeding the potability limit 0 05 mg l 1 to identify the possible geochemical reactions responsible for the occurrence of cr in groundwater in ur nia borehole rock samples were collected in order to carry out mineralogical and chemical analyses in addition multilevel monitoring wells were installed and groundwater samples were analyzed analyses of the borehole rock samples show the occurrence of a geochemical anomaly of cr in the quartzose sandstones average concentrations of 221 ppm chrome diopside is one of the main minerals contributing to this anomaly having an average cr content of 1505 ppm sequential extraction experiments indicated weakly adsorbed cr in the order of 0 54 ppm and this quantity is enough to provide the cr concentrations observed in groundwater groundwaters from the monitoring wells proved to be stratified with the highest concentrations of cr vi 0 13 mg l 1 being associated with high redox and ph values over 10 and high concentrations of na geochemical reactions that may explain the release of cr from the solid phase to groundwater involve the release of cr iii from minerals like chrome diopside and cr fe hydroxide followed by oxidation of cr iii to cr vi probably related to the reduction of mn oxides present in the aquifer then cation exchange occurs and dissolution of carbonates which increases the ph of groundwater resulting in the desorption and mobilization of cr vi into groundwater

late cenozoic tectonics of the northwestern san bernardino mountains southern california the late cenozoic structural and stratigraphic history of the northwestern san bernardino mountains supports two distinct episodes of uplift in late miocene to earliest pliocene and quaternary time that we hypothesize are related to movements on low angle structures beneath the range in this paper we document the nature distribution and timing of late cenozoic deformation and deposition in the northwestern san bernardino mountains and we illustrate the neotectonic evolution of the area in a series of interpretive paleotectonic block diagrams in the first episode of deformation late miocene to earliest pliocene motion on the south southwest directed squaw peak thrust system disrupted drainage in pre existing miocene nonmarine basins and uplifted the western third of the present range to form the ancestral san bernardino mountains crystalline rocks of the san bernardino mountains were thrust southward across the present site of the san andreas fault between 9 5 and 4 1 ma at a time when the san gabriel fault was the active strand of the san andreas transform system we speculate that the liebre mountain crystalline block at the northern margin of the ridge basin may be the missing upper plate of the squaw peak thrust now offset along the san andreas fault the second episode of deformation began with uplift of the northern plateau of the modern san bernardino mountains on north directed range front thrusts in early pleistocene time between 2 0 and 1 5 ma synchronous uplift of the northern plateau recorded in early pleistocene fanglomerates on the northwestern margin of the range is interpreted to be the result of movement of a relatively coherent crustal block northward up a south dipping detachment ramp beneath the central range in middle pleistocene time activity on the northern range front began to wane and the locus of uplift shifted to a narrow zone of arching and northward tilting adjacent to the san andreas fault which subsequently migrated rapidly northwestward along the san andreas fault from the western san bernardino mountains into the northeastern san gabriel mountains we attribute this pattern of deformation to the passage of a bulge or strike slip ramp attached to the southwest side of the san andreas fault at depth

platinum group element and gold enrichment in soils monitored by chromium stable isotopes during weathering of ultramafic rocks abstract weathering of ultramafic rocks can lead to the formation of soil profiles with high contents of fe ni co platinum group elements pge and gold traditionally these metal rich soils are known as laterites and are formed under tropical climates and stable tectonic conditions however little is known about their possible development in cold humid regions and the factors governing pge and gold mobility and enrichment under these weathering conditions are poorly constrained in this study five soil profiles developed on serpentinized chromite bearing ultramafic rocks at la cabana located in the coastal range of south central chile 38 s were studied by combining major and trace element geochemistry with chromium stable isotope data the results show that the soils developed at la cabana have higher pge and au contents than the parent serpentinite rock with pge and au reaching up to 160 ppb and 29 ppb in a limonitic soil horizon and clay saprolite respectively most soil samples have slightly negative 53 52crsrm979 values within a range of 0 089 0 012 to 0 320 0 013 average of 0 178 and are in agreement with previous data reported for modern soils a noteworthy relation between 53 52cr data and pge au contents is observed in the studied soil horizons where isotopically lighter values of 53 52cr match the higher contents of pge and gold these results show that pedogenetic processes operating at the cold and humid la cabana area are capable of increasing the total pge and au contents of certain soil horizons such processes are complex and multivariate but are primarily modulated by chromite dissolution and the formation of secondary phases such as clay minerals and oxy hydroxide phases in the soil these findings provide evidence that important weathering and pge au supergene accumulation are not only restricted to tropical latitudes and that the chromium isotope system is a useful proxy to track surface redox process and noble metal enrichment during pedogenesis

palynologic and petrographic variation in the pond creek coal bed pike county kentucky abstract recent studies of the petrology and ash geochemistry of the pond creek coal bed middle pennsylvanian breathitt formation in pike and martin countries kentucky have defined vertical and lateral trends that are related to the development of the northeast trending belfry anticline contemporaneous with the deposition of the pond creek peat to the northwest of the anticline the coal bed has a high caco3 middle zone and a high fe2o3 high sulfur upper zone to the east of the anticline particularly in the lick creek and jamboree 7 1 2 quadrangles the coal bed exhibits a distinctive petrographic zonation in the latter area the usual megascopic sequence is a basal durain followed by a bright clarain durain dull the palynology of the pond creek coal bed was investigated in six sets of bench lithotype samples from the lick creek and jamboree 7 1 2 quadrangles the low vitrinite basal durain zone 1 has a palynomorph assemblage which reflects the importance of tree ferns and herbaceous lycopods the easternmost site has a bright clarain below the durain the latter lithotype has a fair diversity of palynormph groups and also has the highest percentage of arborescent lycopod forms of any bench below the bone zone 5 the bright zone 2 above the durain has the greatest maceral group range and the greatest floral diversity of any of the lithotypes the zone 3 dull lithotype has increased amounts of herbaceous lycopods and decreased amounts of arborescent lycopods sphenopsids and tree ferns the zone 4 bright lithotypes are generally over 80 vitrinite and in general exhibit a dominance of arborescent lycopods although sphenopsid tree fern and small fern forms exhibit varying importance the high ash bone zone 5 has 71 6 77 0 vitrinite this lithotype is marked by a dominance of herbaceous lycopods at the expense of arborescent lycopods and sphenopsids the zone 6 bright clarian is marked by an increase in arborescent lycopods and a large decrease in herbaceous lycopods the low vitrinite terminal durain has an assemblage with high percentages of herbaceous lycopods and low percentages of arborescent lycopods as well as increase in tree fern spores over zone 6 in general the petrology and palynology trends are predictable dull lithotypes have abundant herbaceous lycopod representation and bright lithotypes have abundant arborescent lycopod representation the greatest deviation from this simple pattern is within the zone 4 bright lithotypes where diverse palynomorph assemblages occur among the high vitrinite benches overall the greatest floral diversity appears to have occurred near the base of the coal bed

multiple bench architecture and interpretations of original mire phases examples from the middle pennsylvanian of the central appalachian basin usa abstract coal seams often exhibit lateral and vertical variability in composition when sampled as a whole seam this variability is masked but if a seam is subdivided into correlateable components this variability can be tested and better understood herein an architectural approach is used to divide seams into intra seam components clastic splits and mineral partings as well as persistent fusain and durain layers can be used as intra seam bounding units to subdivide a seam into subdivisions called benches regional examination of lower and middle pennsylvanian age coal seams shows that many contain laterally persistent bounding surfaces that can be used to define multiple benches of coal within each seam inter bench analyses from some of the most extensively mined seams in the central appalachian basin show that individual benches often have different spatial and quality trends hence some component of whole seam variability is a function of changes in the relative contribution of these different benches to the seam as a whole many coal benches also exhibit intra bench variation in coal parameters intra bench variation can be analyzed in terms of parameters such as sulfur content and ash yield in order to address changes in coal quality for regional resource evaluation intra bench variation can also be analyzed in terms of a combination of palynologic petrographic and geochemical parameters termed compositional groups in order to better understand the development of the original mire systems compositional groups are defined by ranges of multiple criteria which are inferred to owe their origin to the mire type in which they formed vertical changes in compositional groups within coal benches can be used to infer paleo edaphic conditions during peat accumulation if seam thickness is a product of bench configuration and trends in compositional groups occur in benches then trends in quality can be marginally predicted based upon seam thickness and inferred bench architecture additionally changes in inter bench and intra bench thickness and compositional profiles can be used to infer original depositional controls such as paleotopography syndepositional structural movement and syndepositional clastic influx for more accurate reserve estimates

chromium isotope variations δ53 52cr in mantle derived sources and their weathering products implications for environmental studies and the evolution of δ53 52cr in the earth s mantle over geologic time here we report chromium isotope compositions expressed as delta cr 53 52 in per mil relative to nist 979 measured in selected cr rich minerals and rocks formed by the primary magmatic as well as the secondary metamorphic and weathering processes the main objectives of this study were i to further constrain the isotope composition of the earth s mantle cr inventory and its possible variation during geological history based on the analysis of globally distributed and stratigraphically constrained mantle derived chromites and ii to investigate the magnitude and systematics of cr isotope fractionation during oxidative weathering and secondary alteration i e hydration serpentinization of the magmatic cr sources specifically we analyzed delta cr 53 52 in a set of globally distributed mantle derived chromites femgcr2o4 n 30 collected from various locations in europe asia africa and south america and our results confirm that a chromite hosted earth s mantle cr inventory is uniform at 0 079 0 129 2sd which we named here as a canonical mantle d 53 52 cr signature furthermore our dataset of stratigraphically constrained chromites whose crystallization ages cover most of the earth s geological history indicate that the bulk cr isotope composition of the chromite hosted mantle inventory has remained uniform within about 0 100 since at least the early archean times similar to 3500 million years ago ma to investigate the systematics of cr isotope fractionation associated with alteration processes we analyzed a number of secondary cr rich minerals and variably altered ultramafic rocks i e serpentinized harzburgites lherzolites that revealed large positive delta cr 53 52 anomalies that are systematically shifted to higher values with an increasing degree of alteration and serpentinization the degree of aqueous alteration and serpentinization was quantified by the abundances of fluid mobile rb k elements and by the loss on ignition loi parameter which determines the amount of structurally bound water oh h2o present in secondary hydrated minerals like serpentine overall we observed that altered ultramafic rocks that yielded the highest loi values and the lowest amounts of fluid mobile elements also yielded the heaviest delta cr 53 52 signatures therefore we conclude that secondary alteration i e hydration serpentinization of ultramafic rocks in near surface oxidative environments tend to shift the bulk cr isotope composition of the weathered products to isotopically heavier values pointing to a dynamic redox cycling of cr in the earth s crustal and near surface environments hence if validated by future

splint coals of the central appalachians petrographic and geochemical facies of the peach orchard no 3 split coal bed southern magoffin county kentucky the bolsovian middle pennsylvanian peach orchard coal bed is one of the splint coals of the central appalachians splint coal is a name for the dull inertinite rich lithologies typical of coals of the region the no 3 split was sampled at five locations in magoffin county kentucky and analyzed for petrography and major and minor elements the no 3 split coals contain semifusinite rich lithologies up to 48 mineral free basis in one case the nature of the semifusinite varies with position in the coal bed containing more mineral matter of detrital origin in the uppermost durain the maceral assemblage of these terminal durains is dominated by detrital fusinite and semifusinite suggesting reworking of the maceral assemblage coincident with the deposition of the detrital minerals however a durain in the middle of the coal bed while lithologically similar to the uppermost durains has a degraded macrinite rich texture the inertinite macerals in the middle durain have less distinct edges than semifusinites in the uppermost terminal durains suggesting degradation as a possible path to inertinite formation the uppermost durain has higher ash and semifusinite contents at the eastern sites than at the western sites the difference in the microscopic petrology indicates that megascopic petrology alone can be a deceptive indicator of depositional environments and that close attention must be paid to the individual macerals and their implications for the depositional setting especially within the inertinite group

evolution of some depositional models in late carboniferous rocks of the appalachian coal fields abstract models for carboniferous coal bearing strata developed early in this century and consisted of vertical columns that described commonly occurring sequences of coal beds and associated rocks these were followed by other models that expressed patterns of both vertical and lateral variation but in those as well as earlier models depositional interpretation did not extend much beyond a basic marine nonmarine dichotomy subsequently depositional processes were linked to lithic components and showed that the areal distribution of these components formed a lateral geomorphically controlled continuum ranging from alluvial plains seaward to barrier islands evaluation of this model within a tectonic setting of rapid and differential subsidence produced by growth faulting in the southern part of the appalachian coal fields has shown that while depositional processes are substantially the same as those suggested by the model the form and spatial distribution of resulting lithic components are profoundly affected by movements on contemporaneously active subsurface structures this leads to the conclusion that previous models are a product of depositional processes strongly controlled by their tectonic setting and that further attempts at model generation will require careful assessment of the relationships of lithic distribution to subsurface structures and amounts of data necessary to recognize them

chromium isotope stratigraphy of ediacaran cap dolostones doushantuo formation south china abstract the yangtze platform in south china is considered a key site for studying neoproterozoic ocean oxygenation comprehensive cr concentration and isotopic signatures are presented from cap dolostones of the doushantuo formation from a deep water and a shallow marine carbonate section that have previously been used to constrain the redox evolution of ediacaran seawater in space and time employing major and trace element abundances as well as sr o and c isotope compositions the majority of the studied samples yield elevated cr concentrations and negatively fractionated 53 cr signals due to i detrital contamination consistent with cr signatures of other post marinoan cap dolostones ii diagenetic carbonate alteration and post depositional remobilization of cr al concentrations were used as indicator of detrital contamination and to calculate authigenic cr concentration and isotope signatures when the detrital contribution of cr was 18 o carb signals that correlate with low cr concentrations and negatively fractionated 53 cr values post depositional remobilization of cr results in the loss of heavy cr isotopes and consequently light cr isotopes are retained during precipitation of secondary carbonates however some samples might still show pristine ediacaran seawater signals two samples pertaining to the deep water cap dolostone section at yanwutan and one sample pertaining to the shallow water section at jijiawan yield slightly positively fractionated 53 cr signals particularly when corrected to presumably authigenic signals 53 cr auth these values are consistent with those from other neoproterozoic carbonate sections deposited in an oxygenated environment this short sequence of positively fractionated 53 cr auth is concurrent with a cap dolostone 87 sr 86 sr signal close to ediacaran seawater values with relatively high sr and cr concentrations with decreased detrital contamination and with a pronounced negative ce anomaly they indicate either light pulses of enhanced oxidative weathering or inferred from a few least altered samples prevailing oxic conditions during cap dolostone deposition the cr isotopic composition of ediacaran cap dolostones pertaining to the doushantuo formation reveals fine scale fluctuations in post glacial detrital contamination and diagenesis balanced against a clear signal of oxidative weathering cr isotopes have the potential to further enhance our understanding of neoproterozoic weathering regimes and past ocean oxygenation however before the cr isotope system can be faithfully applied to delineate changes in redox conditions recorded in ancient marine carbonates possible diagenetic alteration of the cr signal as well as cr contribution from detrital contamination need to be taken into consideration

mining geology of the pond creek seam pikeville formation middle pennsylvanian in part of the eastern kentucky coal field usa abstract the pond creek seam is one of the leading producers of coal in the eastern kentucky coal field the geologic factors that affect mining were investigated in several underground mines and categorized in terms of coal thickness coal quality and roof control the limits of mining and thick coal are defined by splitting along the margin of the coal body within the coal body local thickness variation occurs because of 1 leader coal benches filling narrow elongated depressions 2 rider coal benches coming near to or merging with the main bench 3 overthrust coal benches being included along paleochannel margins 4 cutouts occurring beneath paleochannels and 5 very hard and unusual rock partings occurring along narrow elongated trends in the study area the coal is mostly mined as a compliance product sulfur contents are less than 1 and ash yields are less than 10 local increases in sulfur occur beneath sandstones and are inferred to represent post depositional migration of fluids through porous sands into the coal run of mine quality is also affected by several mine roof conditions and trends of densely concentrated rock partings which lead to increased in and out of seam dilution and overall ash content of the mined coal roof control is largely a function of a heterolithic facies mosaic of coastal estuarine origin regional fracture trends and unloading stress related to varying mine depth beneath the surface lateral variability of roof facies is the rule in most mines the largest falls occur beneath modern valleys and parallel fractures along paleochannel margins within tidally affected stackrock and beneath rider coals shale spalling kettlebottoms and falls within other more isolated facies also occur many of the lithofacies and falls related to bedding weaknesses within or between lithofacies occur along northeast southwest trends which can be projected in advance of mining fracture related falls occur independently of lithofacies trends along northwest southeast trends especially beneath modern valleys where overburden thickness decreases sharply differentiating roof falls related to these trends can aid in predicting roof quality in advance of mining

geochronology and paleoenvironment of pluvial harper lake mojave desert california usa abstract accurate reconstruction of the paleo mojave river and pluvial lake harper manix cronese and mojave system of southern california is critical to understanding paleoclimate and the north american polar jet stream position over the last 500 ka previous studies inferred a polar jet stream south of 35 n at 18 ka and at 40 n at 17 14 ka highstand sediments of harper lake the upstream most pluvial lake along the mojave river have yielded uncalibrated radiocarbon ages ranging from 24 000 to 30 000 14 c yr bp based on geologic mapping radiocarbon and optically stimulated luminescence dating we infer a 45 40 ka age for the harper lake highstand sediments combining the harper lake highstand with other great basin pluvial lake spring and marine climate records we infer that the north american polar jet stream was south of 35 n about 45 40 ka but shifted to 40 n by 35 ka ostracodes limnocythere ceriotuberosa from harper lake highstand sediments are consistent with an alkaline lake environment that received seasonal inflow from the mojave river thus confirming the lake was fed by the mojave river the 45 40 ka highstand at harper lake coincides with a shallowing interval at downstream lake manix

influence of regional structure on the development and quality of the upper elkhorn no 2 coal bed eastern kentucky abstract the upper elkhorn no 2 coal bed middle pennsylvanian breathitt formation in eastern kentucky exhibits thickness and coal quality trends which suggest that peat deposition was contemporaneous with tectonism the coal thickens and has high vitrinite and low ash and sulfur content the belfry anticline in pike country t in the vicinity of the floyd country channel a basement trough in both cases other pennsylvanian coals exhibit similar trends suggesting that the penecontemporaneous tectonism persisted at least through a portion of the carboniferous

fractionation behavior of chromium isotopes during coprecipitation with calcium carbonate implications for their use as paleoclimatic proxy interest in chromium cr isotope incorporation into carbonates arises from the observation that cr isotopic composition of carbonates could be used as a paleoclimate proxy to elucidate past fluctuations of oxygen contents in atmosphere and hydrosphere the use of cr isotopes to track paleoenvironmental changes for example related to the rise of oxygen during the archaean and protoerozoic needs careful assessment of the signal robustness and necessitates a thorough understanding of the cr cycle in earth system processes we conducted experiments testing the incorporation of chromate into the calcite lattice to investigate isotopic changes facilitated by the coprecipitation process our experiments indicate enrichment in cr concentration in the precipitates compared to the solutions consistent with previous reports of cr enrichment in chemical sediments compared to ambient seawater the fractionation of cr isotopes during calcium carbonate coprecipitation was assumed to be small based on previously published data of modern seawater and modern non skeletal marine carbonates however results from this study for rapidly precipitated calcium carbonate in the presence of chromate show a tendency for preferential incorporation of heavy cr isotopes in the precipitates resulting in increasing relative isotope difference between precipitate and initial solution 53cr p is from 0 06 to 0 18 with increasing initial cr concentration of the solution sample precipitation in the presence of chromate also showed the presence of vaterite calcium carbonate crystals were also precipitated in a double diffusion silica hydrogel over a longer period of time resulting in samples consisting of micrometric millimetric calcite crystals which were again significantly enriched in heavy cr isotopes compared to the initial solutions they average irrespective of the initial cr concentration a relative isotope difference 53cr p is of 0 29 0 08 2 whereas silica hydrogel samples show a preferential retention of light cr isotopes these results imply that in previous studies the 53cr seawater signals inferred from carbonates may be too positive or at lower cr concentrations typical for seawater marginal to no cr isotope fractionation can be expected this might have implications for the use of cr isotopic signals recorded in ancient marine carbonates in relation to ambient seawater and pave the way for future work to enable a reliable application of the cr isotope proxy

delta chromium 53 52 isotopic composition of native and contaminated groundwater mojave desert usa abstract chromium vi concentrations in groundwater sampled from three contaminant plumes in aquifers in the mojave desert near hinkley topock and el mirage california usa were as high as 2600 5800 and 330 g l respectively 53 52cr compositions from more than 50 samples collected within these plumes ranged from near 0 to almost 4 near the plume margins assuming only reductive fractionation of cr vi to cr iii within the plume apparent fractionation factors for 53 52cr isotopes ranged from eapp 0 3 to 0 4 within the hinkley and topock plumes respectively and only the el mirage plume had a fractionation factor similar to the laboratory derived value of e 3 5 one possible explanation for the difference between field and laboratory fractionation factors at the hinkley and topock sites is localized reductive fractionation of cr vi to cr iii with subsequent advective mixing of native and contaminated water near the plume margin chromium vi concentrations and 53 52cr isotopic compositions did not uniquely define the source of cr near the plume margin or the extent of reductive fractionation within the plume however cr vi and 53 52cr data contribute to understanding of the interaction between reductive and mixing processes that occur within and near the margins of cr contamination plumes reductive fractionation of cr vi predominates in plumes having higher eapp these plumes may be suitable for monitored natural attenuation in contrast advective mixing predominates in plumes having lower eapp the highly dispersed margins of these plumes may be difficult to define and manage