sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

organic carbon δ13c variations in sedimentary rocks as chemostratigraphic and paleoenvironmental tools abstract carbon isotopic variations in marine carbonate rocks and organic matter can provide important information on stratigraphic correlations and paleoenvironments in particular carbon isotopic variations in marine organic materials may yield information about the concentration of oceanic dissolved co 2 and or the physiology of the microalgal community this paper reviews evidence from laboratory experiments and oceanographic studies aimed at understanding controls on carbon isotopic fractionation by marine phytoplankton we also review factors affecting carbon isotopic compositions of bulk sedimentary organic matter and individual biomarker compounds guidelines for analysis of isotopic compositions of organic materials and interpretations of these results for use as chemostratigraphic and paleoenvironmental tools are presented we recommend caution in interpreting carbon isotopic variations of sedimentary organic matter because no environmental factor explains adequately variations in the carbon isotopic composition of modern phytoplankton studies of ancient materials should include compound specific isotopic analyses of known phytoplankton biomarkers or organism specific isotopic analyses with bulk isotopic results to assess the proportions of allochthonous organic materials the degree of reworking and the extent of thermal degradation to confirm any trends present in values of bulk sedimentary organic matter

carbon and oxygen isotope stratigraphy of the lower mississippian kinderhookian lower osagean western united states implications for seawater chemistry and glaciation a positive carbon isotope 1 3 c excursion has been recognized in upper kinderhookian and early osagean carbonates in three sections in southeast idaho and nevada the oldest 1 3 c peak 7 is dated to the isostichaconodont zone and a younger peak occurs in the typicus zone the shifts are recorded in a range of carbonate lithofacies representing various water depths along the shelf lithofacies sampled for 1 3 c and 1 8 o at the samaria mountain section in southeast idaho record the shallowest water conditions indicated by cross bedded skeletal and peloidal grainstones the deepest water conditions are present in the pahranagat range section in eastern nevada which consists mainly of bioturbated lime mudstone and skeletal wackestone the 1 3 c values from these widely separated sedimentary basins show a consistent trend that correlates with early mississippian curves generated from brachiopod calcite in western europe and the midcontinent of north america as well as dolomites in utah and wyoming 1 8 o values become more positive up section generally paralleling the positive trend in 1 3 c during the late kinderhookian no subaerial exposure surfaces are recognized in the sections examined in southeast idaho and nevada and at least the 1 3 c trends are interpreted as primary seawater fluctuations sea level changes occurred near the beginning of the late kinderhookian 1 3 c shift early to middle parts of the isosticha zone and within the peak of the 1 3 c excursion kinderhookian osagean boundary although tectonic changes associated with the antler orogeny have likely modified the eustatic signature

temperature limits for preservation of primary calcite clumped isotope paleotemperatures abstract solid state reordering of c o bonds in the calcite lattice can alter the clumped isotope composition of paleotemperature archives such as fossil brachiopod shells without inducing significant changes in shell microstructure and trace element concentrations metrics commonly used to gauge preservation quality to correctly interpret the paleoenvironmental significance of clumped isotope derived paleotemperatures it is necessary to understand the temperature time domain in which solid state c o bond reordering is important we address this question using a combination of laboratory and natural geological experiments on paleozoic brachiopod shells the laboratory experiments involve heating fossil brachiopod calcite at different temperatures and times to directly observe rates of 13 c 18 o bond reordering the resulting arrhenius parameters are indistinguishable from values previously determined for an optical calcite with similar trace element compositions we develop an alternative kinetic model for reordering that accounts for non first order reaction progress observed during the initial several hundred minutes of laboratory heating experiments and show that the simplified first order approximation model passey and henkes 2012 predicts reaction progress equally well for temperatures and timescales relevant to sedimentary basins we evaluate our laboratory based rate predictions by studying brachiopod calcite from several sedimentary basins with independently constrained burial temperature histories specifically we use the laboratory derived arrhenius parameters to predict the evolution of brachiopod calcite clumped isotope compositions during successive one million year time steps reflecting the burial and exhumation temperature paths of each basin while this exercise is limited by the relatively large uncertainties in the temperature histories of these basins we find general correspondence within error between predicted and observed clumped isotope values we present simplified temperature time diagrams for calcite showing domains where primary clumped isotope compositions will be preserved partially reordered and fully reordered in conclusion calcite samples dwelling at 100 c or lower for 10 6 10 8 year timescales should not be affected by solid state c o bond reordering

oxygen and carbon isotopes of early permian cold water carbonates tasmania australia abstract the permian carbonates of tasmania formed at a paleolatitude near 80 s during the gondwanan ice age contain abundant dropstones and are associated with glaciomarine sediments a shallow marine carbonate depositional model with floating icebergs calved from an adjacent ice shelf grading into an ice sheet has been proposed as the sea level rose during relatively warmer periods large volumes of melt waters mixed with marine waters retarding limestone deposition and causing deposition of shales siltstones these phases are preserved in the stratigraphic record as interbedded units australian permian brachiopods and molluscs are characterized by unusually light o18 pdb values and heavier c13 pdb values than those that occur in many modern cool temperate to subpolar cold water carbonates tasmanian permian whole rock o18 pdb values fall at the edge of the normal marine limestone field of keith and weber 1964 and range towards lighter values down to 16 9 pdb the o18 values of cements 7 6 to 25 6 pdb in the tasmanian early permian limestones partly overlap with those o18 values obtained for fresh water cements in the early permian continental tillites from antarctica and south africa gondwanaland indicating that the early permian sea was diluted by isotopically light melt waters during warming phases the o18 values of permian fauna if one assumes no diagenetic equilibration give unrealistic paleotemperatures because of this variable melt water dilution of the permian sea however calculated o18 values corresponding to marine c13 values of brachiopods and eurydesma and extrapolated from a model based on the linear trend of c13 o18 in modern and last glacial cold water carbonates give reasonable estimates of australian permian temperatures of up t 15 c with the coldest waters of less than 4 c around tasmania the sequential deviation lines of o18 c13 of both cements and the fauna associated with these cements indicate that the original o18 value of fauna was as high as 6 pdb this calculated original o18 value indicates an average seawater temperature for tasmania in the early permian of 1 8 c similar to the present average 1 9 c water temperature near ice shelves around antarctica the o18 values of ements suggest that the tasmanian limestones reacted with subfreezing melt waters during early diagenesis the o18 composition of the early permian sea is inferred to have been about 1 2 pdb similar to that observed during the pleistocene glaciations and was diluted by melt water as light as o18 smow 31 at 5 c 26 pdb in variable amounts it is unlikely that the o18 composition of the wellmixed open permian sea ever reached a value as light as o18 pdb 6 it is suggested that the permian sea c13 value was about 2 pdb heavier than that of modern and pleistocene seawater

echinoderm stabilization associated with a paleokarst surface at the mississippian pennsylvanian boundary in tennessee u s a abstract pennington formation limestone deposits in tennessee immediately underlie a paleokarst surface that straddles the mississippian pennsylvanian unconformity vertic paleosols with significant gleying and coal seams overlie the paleokarst surface this study quantifies the fe loss associated with paleosol gleying and subsequent incorporation of fe into echinoderm grains that underwent stabilization echinoderm grains immediately below the paleokarst surface have lower mg and 13c values and higher fe concentrations compared to echinoderm grains meters below the paleokarst surface additionally echinoderm grains have variable 13c and invariant 18o values characteristic of alteration in a meteoric setting paleosols draping the paleokarst surface and coal seams that were deposited immediately above the mississippian pennsylvanian unconformity provided ample organic matter that could have driven heterotrophic microbial activity additionally the paleosols were an ample source of oxidized fe that could have been used as a terminal electron acceptor by an anaerobic microbial community therefore we suggest that fe reduction transferred fe from the paleosol to the limestone during meteoric stabilization of echinoderm grains fluid rock modeling constrains the magnitude of fe transfer that occurred during echinoderm stabilization stabilization can account for only a fraction 8 to 14 of the total quantity of fe lost from the gleyed paleosol thus supporting the premise of continued transfer of fe from the paleosol to limestone during burial diagenesis additionally this study constrains the timescale associated with echinoderm stabilization which was likely 12 ky finally stabilization timescale is consistent with echinoderm alteration associated with organic diagenetic conditions with elevated dissolved inorganic carbon in stabilizing pore fluids that were localized immediately below the paleokarst surface

diagenesis and evolution of microporosity of middle upper devonian kee scarp reefs norman wells northwest territories canada petrographic and chemical evidence the middle upper devonian kee scarp reef complexes of norman wells northwest territories canada are oil producing stromatoporoid dominated carbonates episodic increases in the rate of sea level rise produced multiple cycles of reef growth that exhibit backstepping characteristics these carbonates composed of invariably altered limestones have original interskeletal intraskeletal and intergranular porosity mostly occluded by nonferroan dull luminescent cements secondary porosity represented by micropores of various types developed during diagenesis by aggrading neomorphism and dissolution the micropores represent the main reservoir porosity in the kee scarp limestone micropores in the kee scarp limestone can be classified into four categories based on thei shapes 1 stepwise rhombic about 1 m to 2 m in diameter developed mainly in stromatoporoids 2 intercrystalline rhombic about 1 m in diameter developed mainly in algal aggregates 3 microvugs 4 m to 10 m in diameter developed mainly in algal aggregates and 4 microchannels about 12 m in length and 0 5 m in width developed in algal aggregates and stromatoporoids the stepwise rhombic and microvugs are developed mainly at the kee scarp reef margin and constitute the best type of reservoir porosity petrographic chemical and isotopic studies of kee scarp reef components reveal a complex diagenetic history involving marine fluids modified by increasing water rock interaction and burial early diagenetic processes include marine cementation and micritization followed by neomorphic replacement of high mg calcite and aragonite reef components resulting in the creation of the first generation of microporosity via dissolution on a micron scale later diagenesis represented by microfracturing and cementation with two generations of equant calcite and stylolitization was responsible for the second generation of microporosity very minor silicification dolomitization and vertical fracturing occurred at variable depths portions of well preserved marine cements stromatoporoids an rare crinoids of postulated high mg calcite precursor mineralogy have escaped diagenetic alteration and preserve the original marine dgr18o and dgr13c signatures 4 7 0 3 pmil pdb for oxygen 1 0 0 4 pmil pdb for carbon minor and trace element data show less preservation of the postulated original marine composition neomorphic stabilization of skeletal components caused further depletion in dgr18o but very little change in dgr13c an argument for modification of the original marine fluids with increasing burial variations in magnitude of water rock interaction with depth facies changes and porosity modifications probably exerted some control on fractionation and distribution of stable isotopes and trace elements in ree components

epigenetic sulfide mineralization associated with pennsylvanian paleokarst in eastern iowa u s a abstract paleokarst associated sulfide bearing mineral deposits are wide spread in the paleozoic carbonate rocks of eastern iowa minerals occur in nodules enclosed in karst filling mudstones as sandstone cements and as surface coatings on and fracture fillings in foundered carbonate rock clasts mineralogy and paragenetic sequence vary among the occurrences sulfur isotopic compositions exhibit wide variations within and among deposits 34 s 33 8 to 35 1 oxygen isotopic compositions of fracture filling calcite spars 18 o 8 41 to 3 60 are similar to the isotopic compositions of their carbonate rock hosts calcite spars are somewhat depleted in 13 c relative to host rock 13 c spars 5 66 to 0 24 vs 1 54 to 1 21 host rock results of mineralogic paragenetic and isotopic investigations suggest that 1 minerals are products of multiple events operating on a local rather than a regional scale 2 spatially disjunct fracture filling mineral deposits exposed in the same quarries are probably not cogenetic with paleokarst associated deposits 3 paleokarst filling calcite spars formed at near surface temperatures and 4 paleokarst associated deposits are probably not cogenetic with upper mississippi valley zn pb pitch flat deposits

geochemistry of campanian maastrichtian brachiopods from the rordal 1 core denmark differential responses to environmental change and diagenesis abstract past marine environmental conditions can be reconstructed from geochemical signatures of both benthic and planktic organisms and particularly brachiopods have been extensively used for this purpose however it is seldom possible to investigate the links between environmental conditions and shell geochemistry in monospecific records over extended periods of time here we present geochemical data from the 100 m thick brachiopod rich upper campanian upper maastrichtian chalk 73 8 68 6 ma of the rordal 1 drill core northern denmark two species that lived attached to small substrate argyrotheca bronnii roemer and gisilina jasmundi steinich and one secondarily free living species magas chitoniformis schlotheim have been studied for element concentrations as well as c and o isotope signatures each species has a unique chemical signature with m chitoniformis showing lowest mg and mn concentrations a bronnii the highest mn concentrations and g jasmundi the highest sr concentrations all three species display decreasing mg ca ratios throughout the studied interval and distinct mn enrichments in the campanian maastrichtian boundary cmb interval in the campanian part of the succession the three species are slightly enriched in 13 c median 13 c values of 0 0 to 0 5 and 18 o median 18 o values of 0 3 to 0 6 with respect to coeval chalk in the course of the maastrichtian the two attached species acquire progressively lighter isotopic compositions with a bronnii reaching 13 c and 18 o values 1 0 lower than coeval chalk the secondarily free living species m chitoniformis on the other hand becomes isotopically heavier and reaches 13 c and 18 o enrichments of 1 0 at the top of the core the observed differences between the species illustrate species specific signatures of biomineralisation diagenesis and response to environmental change this geochemical complexity illustrates that a comprehensive geochemistry based picture of the late cretaceous chalk sea can only be painted using detailed multi species and multi proxy datasets

genesis of mg fe carbonates from the sierra menera magnesite siderite deposits northeast spain evidence from fluid inclusions trace elements rare earth elements and stable isotope data the mg fe carbonate deposits of sierra menera underneath exploited goethite gossan are located in the iberian range of northeasten spain within the late ordovician dolomitic formation of the sierra menera unit mgo and feo contents of the carbonates range between 13 74 and 44 02 and 5 52 and 41 73 wt percent respectively corresponding to the breunnerite and pistomesite members the morphology petrographic mineralogical and geochemical characteristics of the mg fe carbonates are consistent with a metasomatic hydrothermal origin by replacement of a dolomitic protolith as the result of the influx of hot fe mg rich fluids under acid and reducing conditions these deposits have similarities to alpine type magnesite deposits austria slovakia western carpathian mountains pyrenees and mississippi valley type fe deposits basque cantabrian basin northern spain the mg fe carbonates have normalized rare earth element ree patterns characterized by low light ree heavy ree ratios and positive eu anomalies dolomite rocks that host mg fe occurrences have been recrystallized to saddle dolomite crystals and have less fractionated normalized ree patterns but are also characterized by positive eu anomalies these patterns are distinct from the pristine host dolomite which has ree distribution typical of marine carbonates based on ree fluid inclusion and stable isotope data the mg fe carbonates are interpreted to have been formed by interaction between hot 100 150 c 18o enriched and saline 20 wt nacl equiv iron rich hydrothermal fluids and marine carbonates recrystallization of the host dolomite resulted from moderate to low fluid rock ratios 10 the mg fe carbonates were partially replaced by late dolomite redolomitization due to the action of more dilute solutions although this event resulted in 18o depletion ree patterns and 13c values of the precursors were preserved

δ 18 o of carbonate quartz and phosphate from belemnite guards implications for the isotopic record of old fossils and the isotopic composition of ancient seawater belemnite guards of cretaceous and jurassic age were found to contain varying amounts of quartz deposited both on the external surface and inside the rostrum the oxygen isotopic composition of coexisting carbonate quartz and phosphate from the same rostrum was measured according to well established techniques none of these compounds showed isotopic values in equilibrium with one another assuming 18o values of the diagenetic water within the range of meteoric waters the 18o sio2 yield temperatures in agreement with the apparent secondary origin of this phase the 18o co32 range with a certain continuity between 10 8 and 0 97 pdb 1 with most of the intermediate values being within the range of the carbonate isotopic values of mesozoic fossils the most positive isotopic results obtained from phosphate are close to 23 24 v smow they can hardly be related to a secondary origin of the phosphate or to the presence of diagenetic effects since these results are among the most positive ever measured on phosphate as far as we know there is no widespread diagenetic process determining an 18o enrichment of phosphate the very low concentration of phosphate did not allow the determination of its mineralogical composition all the available 18o po43 values from belemnite and non belemnite fossils of marine origin of tertiary and mesozoic age are reported along with the newly measured belemnites the following conclusions may be drawn from the data reported 1 the pristine oxygen isotope composition of fossil marine organisms either carbonate or phosphate may easily undergo fairly large changes because of oxygen isotope exchange processes with diagenetic water this process is apparent even in the case of geologically recent fossils 2 the 18o po43 of belemnite rostra seems to be at least in the case of the most positive results in isotopic equilibrium with environmental water because of the similarity between the results from cretaceous belemnites and the results from cretaceous and lower tertiary pelecypods and fish teeth 3 if so the only feasible interpretation that can be suggested for the 18o enriched data is the possibility of a relatively large variation of the oxygen isotopic composition of ocean paleowater from jurassic to recent time

δ18o values 87sr86sr and sr mg ratios of late devonian abiotic marine calcite implications for the composition of ancient seawater abstract late devonian frasnian abiotic marine calcite has been microsampled and analyzed for 87 sr 86 sr ratios 18o and 13c values and minor element concentrations portions of marine cement crystals from the alberta and canning basins have escaped diagenetic alteration and preserve original marine 18o values 4 8 0 5 pdb 13c values 2 0 to 3 0 pdb 87 sr 86 sr ratios 0 70805 3 and sr mg weight ratios 0 04 to 0 05 marine 87 sr 86 sr ratios are globally consistent and can be correlated within the alberta basin and among the alberta canning and williston basins correlation of isotopic and chemical data strengthen the conclusion that marine cements from the leduc formation preserve original marine 18o values which are 3 to 4 lower than those of modern marine cements these low 18o values are best explained by precipitation from 18o depleted seawater and not by elevated seawater temperature or diagenetic alteration for comparison with devonian data analogous data were collected from holocene mg calcite and aragonite marine cements from enewetak atoll marshall islands mg calcite and aragonite marine cements are in isotopic equilibrium with ambient seawater and mg calcite cements are homogeneous with respect to sr and mg contents empirically derived homogeneous distribution coefficients for mg and sr in modern abiotic mg calcite from enewetak atoll are 0 034 and 0 15 respectively an equation describing the dependence of dsr on mg content was based on a compilation of sr and mg data from holocene abiotic marine calcite dsr 3 52 10 6 ppm mg 6 20 10 3 unlike that derived from experimental data this sr mg relation is consistent over a range of 4 to 20 mol mgco3 and may represent precipitation phenomena which are minimally controlled by kinetic effects comparison of sr and mg contents of analogous devonian and holocene marine cements suggests that the mg ca ratio of late devonian seawater was significantly lower and that the sr ca ratio was significantly higher than that of modern seawater

the stable isotopic records of fossils from the peterborough member oxford clay formation jurassic uk palaeoenvironmental implications carbon and oxygen isotopic compositions of calcareous nekton aragonite kosmoceras and calcite belemnites and benthos aragonite nuculacean bivalves and calcite gryphaea from the peterborough member of the oxford clay formation vary considerably at any one horizon but show no obvious trend with time this suggests that the temperature and isotopic composition of ambient seawater may have varied considerably over short time intervals but did not change systematically during deposition of the unit thus short term fluctuations were superimposed on longer term 9stability9 in this shallow shelf environment the overlap in carbon isotopic compositions between calcareous nekton and benthos suggest a well mixed water column oxygen isotopic palaeotemperatures suggest thermal stratification provided that kosmoceras 16 28 c inhabited near surface waters and belemnites 12 19 c indistinguishable from the range for benthic bivalves were nektobenthic oxygen isotopic compositions of phosphate from both shallow and possible deeper dwelling vertebrates reptiles bony fish and sharks yield the same range of palaeotemperatures 20 29 c suggesting that all vertebrate taxa may have lived predominantly in warm shallow waters

the diagenesis of the late dinantian derbyshire east midland carbonate shelf central england carbonate cements in late dinantian asbian and brigantian limestones of the derbyshire carbonate platform record a diagenetic history starting with early vadose meteoric cementation and finishing with burial and localized mineral and oil emplacement the sequence is documented using cement petrography cathodoluminescence trace element geochemistry and c and o isotopes the earliest cements pre zone 1 are locally developed non luminescent brown sparry calcite below intrastratal palaeokarsts and calcretes they contain negligible fe mn and sr but up to 1000 ppm mg their isotopic compositions centre around 18o 8 5 13c 5 0 calcretes contain less 13c subsequent cements are widespread as inclusion free low mg low fe crinoid overgrowths and are described as having a dead bright dull cathodoluminescence the dead cements zone 1 are mostly non luminescent but contain dissolution hiatuses overlain by finely detailed bright subzones that correlate over several kilometres across dead bright subzones there is a clear trend in mg 500 900 ppm mn 100 450 ppm and fe 80 230 ppm zone 1 cements have isotopic compositions centred around 18o 8 0 and 13c 2 5 zone 2 cement is bright thin and complexly subzoned it is geochemically similar to bright subzones of zone 1 cements dull zone 3 cement pre dates pressure dissolution and fills 70 or more of the pore space it generally contains little mn fe and sr but can have more than 1000 ppm mg increasing stratigraphically upwards the 18o compositions range from 5 5 to 15 and the 13c range is 1 to 3 20 00 zone 4 fills veins and stylolite seams in addition to pores it is synchronous with pb ba f ore mineralization and oil migration zone 4 is ferroan with around 500 ppm fe up to 2500 ppm mg and up to 1500 ppm mn isotopic compositions range widely 15o 2 7 to 9 and 13c 3 8 to 2 50 unaltered marine brachiopods suggest a dinantian seawater composition around 15o 0 smow but vital isotopic effects probably mask the original 13c pdb value pre zone 1 calcites are meteoric vadose cements with light soil derived 13c and light meteoric 18o an unusually fractionated pluvial 15o smow value of around 6 is indicated for local dinantian meteoric water calcrete 18o values are heavier through evaporation zone 1 textures and geochemistry indicate a meteoric phreatic environment fe and mn trends in the bright subzones indicate stagnation and precipitation occurred in increments from widespread cyclically developed shallow meteoric water bodies meteoric alteration of the rock body was pervasive by the end of zone 1 with a general resetting of isotopic values zone 3 is volumetrically important and external sources of water and carbonate are required emplacement was during the namurian early westphalian by meteoric water sourced at a karst landscape on the uplifted eastern edge of the derbyshire east midland shelf the light 18o values mainly reflect burial temperatures and an unusually high local heat flow but an input of highly fractionated hinterland derived meteoric water at the unconformity is also likely relatively heavy 13c values reflect the less altered state of the source carbonate and aquifer zone 4 is partly vein fed and spans burial down to 2000 m and the onset of tectonism light organic matter derived 13c and heavy 18o values suggest basin derived formation water combined with textural evidence of geopressures this relates to local high temperature ore mineralization and oil migration low water to rock ratios with host rock buffering probably affected the final isotopic compositions of zone 4 masking extremes both of temperature and organic matter derived co2

strontium isotopic signatures of oil field waters applications for reservoir characterization the 87sr 86sr compositions of formation waters that were collected from 71 wells producing from a pennsylvanian carbonate reservoir in new mexico display a well defined distribution with radiogenic waters up to 0 710129 at the updip western part of the reservoir grading downdip to less radiogenic waters as low as 0 708903 to the east salinity 2800 50 000 mg l displays a parallel trend saline waters to the west pass downdip to brackish waters elemental and isotopic data indicate that the waters originated as meteoric precipitation and acquired their salinity and radiogenic 87sr through dissolution of upper permian evaporites these meteoric derived waters descended perhaps along deeply penetrating faults driven by gravity and density to depths of more than 7000 ft 2100 m the 87sr 86sr and salinity trends record influx of these waters along the western field margin and downdip flow across the field consistent with the strong water drive potentiometric gradient and tilted gas oil water contacts the formation water 87sr 86sr composition can be useful to evaluate subsurface flow and reservoir behavior especially in immature fields with scarce pressure and production data in mature reservoirs sr isotopes can be used to differentiate original formation water from injected water for waterflood surveillance strontium isotopes thus provide a valuable tool for both static and dynamic reservoir characterization in conjunction with conventional studies using seismic log core engineering and production data roger barnaby has conducted stratigraphic studies of carbonates and siliciclastics in outcrop and subsurface for 15 years he holds a ph d from virginia polytechnic institute and a b s degree from east carolina university barnaby has worked on sedimentary successions of the gulf coast permian basin alaska north slope middle east and caspian region he maintains interests in carbonate diagenesis and geochemistry gregg oetting received an m a degree in geology in 1995 from the university of texas at austin he is the author of six publications concerning geochemical and strontium isotopic variations in edwards aquifer groundwaters for the past seven years oetting has traded energy futures for leading merchant energy concerns he works for an independent consulting business in houston texas guoqiu gao received his b s and m s degrees in geology from central south university hunan china and his ph d in geology from the university of texas at austin he works for a major oil company in houston texas his current interests lie in the field of geoscience computing

and ratios in skeletal calcite of mytilus trossulus covariation with metabolic rate salinity and carbon isotopic composition of seawater minor element and isotopic compositions of marine bivalve calcite are frequently used as proxy records of seawater temperature and salinity although molluscan calcite is secreted at or near oxygen isotope equilibrium the influence of metabolic activity i e vital effects on skeletal srca ratios and 13c values is not well known we present measurements of skeletal chemistry from a consecutive samples milled in chronological order from the organism s final year of growth and b adjacent samples within three separate growth bands of the marine mussel mytilus trossulus to investigate chemical disequilibrium effects among different parts of the shell seawater temperature and salinity were monitored for one year at squirrel cove british columbia at the end of the year a young rapidly growing mussel mussel a and an old slowly growing mussel mussel b were harvested from this site growth bands within the shells were sampled to provide a chronological record of shell carbonate chemistry results from consecutive samples show 1 a significantly higher average srca ratio in mussel a than that in mussel b and 2 13c values that correlate well with salinity in mussel a but not in mussel b results from time equivalent adjacent samples show 1 higher srca and 13c values near the ventral margin than at time equivalent regions on lateral margins of the shell and 2 little or no variation in 18o values these observations suggest that skeletal chemistry srca and 13c is primarily controlled by rate of mantle metabolic activity and secondarily modified by variation in seawater salinity because metabolic activity in the mantle at the site of carbonate precipitation varies with shell curvature the composition of calcite secreted along lateral margins is influenced to a greater extent by metabolic activity than calcite secreted coevally at the central margin of the shell hence the chemistry of calcite secreted at the ventral margin is precipitated in near equilibrium with seawater and allows accurate estimation of seawater srca ratios and carbon isotopic composition in contrast shell precipitation along lateral margins is dominantly controlled by metabolic activity and calcite chemistry is not in equilibrium with ambient seawater in this context we present a biomineralization model where variations in skeletal srca and 13c values are explained in the context of mantle metabolic activity and seawater salinity

carbon oxygen and strontium isotopes in paleozoic carbonate components an evaluation of original seawater chemistry proxies abstract brachiopods trilobites cements and whole rock matrix material were evaluated for their reliability as proxies of original seawater carbon oxygen and strontium isotope chemistry in this process coeval material was evaluated from individual horizons of formations spanning the permian to cambrian unaltered shells of low mg calcite articulated brachiopods retain original seawater oxygen carbon and strontium isotope compositions as old as late ordovician assessments of older specimens are hampered by a lack of suitable material coeval brachiopod whole rock sets a definitive assessment of cement marine chemistry is difficult due to the paucity of material but despite this caveat cements hold some promise for retaining original carbon and possibly strontium isotope seawater values in contrast the potential of whole rock material as a proxy of original seawater chemistry is quite complex in some but not all instances the carbon isotopic composition of whole rock after detailed scrutiny and evaluation appears to represent an original seawater chemistry signal in a few instances their oxygen isotope compositions reflect original seawater values unlike the stable isotope compositions the strontium isotopes of all studied whole rock material permian to upper cambrian appear not to reflect original seawater chemistry values thus the potential for retaining original seawater isotope chemistry and serving as specific proxies in order of decreasing reliability are 1 unaltered low mg calcite brachiopods c o and sr isotopes 2 pristine marine cements c and sr isotopes and 3 whole rock material c isotopes carbon oxygen and strontium isotope compositions of ordovician trilobites mirror those of coeval unaltered brachiopods cambrian trilobites hold significant promise as an important proxy of original seawater isotope chemistry but further studies are needed to ascertain their full potential the survey of isotopes in some ordovician and cambrian intermediate low mg calcite trilobites demonstrates their potential as an important proxy of original seawater chemistry

palaeoenvironmental and palaeoceanographic controls on black laminated mudrock deposition example from devonian carboniferous strata alberta canada abstract sedimentological palaeontological and ichnological analyses indicate that heightened episodes of equatorial upwelling in tandem with an expanded and intensified oxygen minimum zone promoted deposition of upper famennian to lower tournaisian laminated organic rich mud rocks of the exshaw formation on the alberta cratonic platform exshaw mud rocks represent the culmination of an upper devonian transgression that commenced with deposition of open marine carbonates of the big valley formation the transgression was abruptly halted at the devonian carboniferous boundary by a rapid eustatic sea level fall and the consequent deposition of near shore marine to shelfal bioturbated siltstones and sandstones of the exshaw formation the siltstones grade into laminated organic lean mud rocks to the north in more distal offshore shelf settings these mudrocks reflect a period of low primary production but continued anoxia of bottom waters continuation of anoxic conditions resulted from development of restricted circulation in the epicontinental sea due to the establishment of a westward located physical barrier following this event was a relative sea level rise that led to deposition of black laminated mudrocks of the banff formation

diagenesis of fossil ostracods implications for stable isotope based palaeoenvironmental reconstruction a protocol for assessing the diagenetic alteration of ostracod carapaces for use in palaeoenvironmental reconstruction is proposed based on comparison between fossil carboniferous and recent specimens recent ostracods have a carapace ultrastructure of fine 0 5 m diameter crystals of primary low magnesium calcite the degree of recrystallisation in fossil ostracods is assessed based on the carapace ultrastructure and geochemistry six diagenetic stages are identified 1 replacement of the original finely crystalline calcite carapace with neomorphic calcite 2 framboidal and euhedral pyrite growth 3 ferroan calcite carapace replacement and cavity void filling cement 4 ferroan dolomite carapace replacement and void fills 5 siderite growth and 6 sphalerite and barite mineralisation stage 1 occurs during early shallow burial stages 2 3 soon after and stages 4 6 during much later burial possibly hydrothermal alteration ostracods and macrofossils exhibiting diagenetic stages 1 5 were analysed for oxygen and carbon isotope ratios the oxygen isotope compositions clearly reflect the diagenetic stages the most negative oxygen isotopes 18o 12 9 represent the precipitation of ferroan dolomite stage 4 and the most positive values of the neomorphic calcite 18o 0 9 represent stage 1 and are within the predicted range of carboniferous seawater 18o 4 to 0 the diagenetic protocol established here is specific to palaeozoic fossil ostracods from carbonate and clastic sediments that were subject to shallow burial diagenesis and later hydrothermal alteration nevertheless the approach could be used to assess the utility of fossil ostracods for palaeoenvironmental interpretation from a wide range of geological settings

micromorphology and differential preservation of upper permian brachiopod low mg calcite abstract calcareous shells of rhynchonelliform brachiopods from the nesen formation late permian of iran were studied by scanning electron microscope cathodoluminescence and trace element chemistry to define their microstructure and state of preservation in the strophomenata shell succession the secondary layer consists of cross bladed laminar calcite and in a few species there is a tertiary layer of prisms in the rhynchonellata shell succession the secondary layer consists of elongated fibers and the tertiary layer of prisms all specimens were classified into six micromorphological types based on the fabric of the layer and the morphology of their microstructural units laminae fibres and prisms shell micromorphology and enclosing whole rock were further analyzed by cathodoluminescence and trace chemistry to assess preservation of brachiopod low mg calcite and specifically of their layers and microstructural units relative color frequencies were determined for each morphological type and degree of luminescence based on the lithology of the host rocks to evaluate the main factors that affect shell preservation results suggest that diagenetic alteration may depend on shell fabric and taxonomy as well as lithology of the host rock but it appears that the first and the second features are the most important factors in determining the degree of brachiopod low mg calcite preservation in general the fibrous secondary layer is likely more often and better preserved than its laminar counterpart irrespective of host rock lithology furthermore tertiary layers tend to be better preserved than secondary ones in rhynchonellata low mg calcite shells whereas no preferential preservation of either layer over the other was observed in the shells of strophomenata this information is important when selecting fossil brachiopod low mg calcite shells as geochemical proxies for paleoclimatic paleoecologic paleoenvironmental and other studies

δ13c values from the cenomanian turonian passage beds of southern tibet a group of bituminous sediments of mid cretaceous late cenomanian early turonian age are well exposed in the tingri gamba basin of southern tibet the characteristics of microfossils and geochemistry in the strata show that paleoceanographic environmental changes took place in the tethys himalayan sea the 13c profiles of southern tibet are characterized by a low high low cycle the maximum positive excursion of 2 0 occurs at the position just above the cenomanian and turonian boundary in tingri and 2 74 occurs underneath the cenomanian and turonian boundary in gamba the mid cretaceous in southern tibet is a short period of expansion of the tethys himalayan sea which brought about local sea level rise the positive excursion of 13c coincides with both global and local sea level rises the correlation of the 13c spike and well dated occurrence of layers rich in organic carbon indicate that intense orgc burial took place during the latest cenomanian to earliest turonian the positive 13c excursion reflects the burial of total dissolved carbon the positive excursion and excess carbon burial in southern tibet are coincident with the oceanic anoxic event during the time

87sr86sr isotopic evolution of lower carboniferous seawater dinantian of western europe abstract the chemical and isotopic evolution of ocean water mirrors the dynamics of the earth system the original seawater signature can be measured only indirectly for the palaeozoic samples with the greatest utility for such an approach are the secondary layers of articulate brachiopods for a correct interpretation of isotope data samples that have suffered alteration by diagenetic processes must be avoided trace element analysis is frequently utilized as an analytical tool the present study deals with the delineation of a detailed 87 sr 86 sr curve for the dinantian this in turn enables us to search for causative factors of the observed isotopic oscillations a total of 175 lower carboniferous dinantian brachiopod shells from a variety of western european locations have been analysed for their 87 sr 86 sr ratios for 152 of these shells quantitative geochemical tests on diagenetic alteration based on trace element repartitioning during recrystallisation have been performed the concentrations of ca mg sr mn and fe were routinely measured by inductively coupled plasma atomic emission spectroscopy icp aes analysing the diluted phosphoric acid that remained after carbonate dissolution for stable isotope gas preparation in addition 71 samples have been analysed by proton induced x ray emission spectroscopy micro pixe despite large differences in the analysed masses 3 6 mg for icp aes as low as 10 ng for pixe both methods yield comparable data for the sr and mn contents any discrepancies can be related to inhomogeneities of the shells e g punctae of these shells 73 have sr and mn contents of 600 ppm and the sr isotope record of the dinantian seawater is characterised by a decline in 87 sr 86 sr ratio from 0 7082 at the devonian carboniferous transition to 0 7076 in the mid visean superimposed on this trend are higher order fluctuations with a periodicity in the ma range the dinantian seawater curve may potentially serve as a geochronological and correlation tool particularly for the hastarian to lower chadian interval where the attainable resolution is 1 ma this is better than the resolution available by biostratigraphy the higher order wiggles for the most part can be generated by changing the riverine flux of sr or its isotopic ratio within reasonable geological scenarios some spikes however are too large and too short to be explained by the above phenomena these apparent spikes may reflect instead the fact that their duration has been underestimated due to unreliable geochronology and or the presence of unrecognised hiatuses

deciphering kinetic metabolic and environmental controls on stable isotope fractionations between seawater and the shell of terebratalia transversa brachiopoda this study presents carbon and oxygen stable isotope data obtained from high resolution sampling 500 m of the brachiopod terebratalia transversa from the san juan islands washington state usa the aim of this study is to unravel the respective effects of physiological and environmental controls on the stable isotopic composition of brachiopod shell calcite based on an sem study of the shell a three dimensional sampling was performed in order to investigate carbon and oxygen isotope variations along isochrons and ontogenetic transects the primary as well as the outer part of the secondary shell layer display large and variable isotopic offsets as high as 7 for 13c and 6 for 18o relative to expected equilibrium values the significant positive correlations between 18o and 13c values indicate that the isotopic compositions of these shell domains are mainly controlled by kinetic isotope fractionation effects the ontogenetic 13c and 18o variations can be used to establish a growth curve of the studied specimen whose age is estimated close to 8 years the extent of apparent o 18 disequilibrium observed in this study is about as large as any yet measured in any organism which makes this brachiopod an interesting and important case the carbon and oxygen isotope compositions increase from the outer towards the inner part of the secondary layer where they reach values of 0 0 8 and 0 8 to 0 2 respectively corresponding calculated temperatures are between 12 and 13 8 c and fall in the range of seawater temperatures recorded off the san juan islands 7 13 c these results suggest that the calcite fibres were secreted more and more slowly during the thickening of the shell throughout the animal s life finally approximating isotopic equilibrium this study illustrates that the stable isotopic composition of the modern brachiopod t transversa is predominantly influenced by kinetic fractionation and to a minor degree by metabolic effects except for the innermost part of the shell the measured isotope ratios do not reflect environmental conditions during shell precipitation it remains to be tested by comparable studies whether other modern brachiopod species or even fossil brachiopods reflect comparable fractionation effects these results point out the need for re examination of paleozoic oceanographic conditions

geochemistry of cambro ordovician arbuckle limestone oklahoma implications for diagenetic δ18o alteration and secular δ13c and variation abstract isotopic analyses of 227 limestone samples from the cambro ordovician arbuckle group oklahoma document slow secular changes in the chemistry of the limestones from late cambrian to early ordovician the 18o values of the limestones increase from 10 to 7 pdb 13c values decrease from 0 to 2 pdb and 87 sr 86 sr ratios decrease from 0 7091 to 0 7088 the light 18o values suggest that all arbuckle limestones underwent diagenetic alteration probably caused by meteoric water recharged during the development of the overlying pre middle ordovician unconformity the gradual 18o increase from late cambrian to early ordovician reflects reduced 18o depletion with decreasing burial temperature during alteration although the presence of additional primary secular 18o variation cannot be ruled out the 13c and 87 sr 86 sr variations in accord with 13c and 87 sr 86 sr variations in the literature represent primary secular variations the variations indicate that the 13c value and 87 sr 86 sr ratio of early paleozoic surface seawater decreased from late cambrian to early ordovician the 13c variation during this time period seems to correlate with sea level variation specifically during sea level fall an increase in the rate of oxidation of organic matter caused 13c depletion of inorganic bicarbonate in seawater as a result early ordovician carbonates probably deposited during the regression stage of the latest precambrian to latest early ordovician cycle became 13c depleted relative to late cambrian carbonates the decrease of seawater 87 sr 86 sr ratio from late cambrian to early ordovician may have resulted from decreased riverine sr input caused by decreased rate of continental weathering

stable isotope variations in modern articulate brachiopods abstract carbon and oxygen isotopic analyses were performed on several species of holocene articulate brachiopods from various locations in the caribbean sea and in the atlantic and pacific oceans from salinities ranging between 30 and 38 pmil and over a temperature range from 4 to 28 c 39 to 82 f the dgr18o of articulate brachiopods are systematically related to the dgr18o and temperatures of the ambient waters lowenstam in 1961 concluded that articulate brachiopods secrete calcium carbonate low magnesium calcite in isotopic equilibrium with the surrounding waters the data compiled in this study along with that of lowenstam closely approximate the equilibrium calcite water end page 500 line deviation from apparent equilibrium was most evident for samples from a few cold water sites intraspecific isotopic variations in several warmer water assemblages were up to 2 pmil and isotopic variation within individual specimens as high as 1 5 pmil were noted articulate brachiopods were not separable at any taxonomic level on the basis of ranges in isotopic values the two extant orders of brachiopods the terebratulida and the rhynchonellida as well as the suborder thecideidina had essentially equivalent isotopic ranges at any given locality thus there is no evidence for significant taxonomic control of oxygen isotope fractionation among articulate brachiopods no correlation appears to exist between dgr18o and dgr13c values our results suggest strongly that isotopic data from small populations or communities of well preserved articulate brachiopods can be used in paleogeographic and paleo oceanographic reconstructions end of article last page 501

a high resolution middle to late permian paleotemperature curve reconstructed using oxygen isotopes of well preserved brachiopod shells abstract climatic warming has been widely cited as a driver for many mass extinction events in earth history including the middle late permian guadalupian lopingian boundary glb mass extinction and end permian mass extinction epme investigated in this study however the role of warming in driving the epme event is under debate because current paleotemperature studies indicate the rapid increase in sea surface temperature postdate the onset of the epme event and a reliable paleotemperature record across the glb event is lacking here we present a high resolution and successive 18 o record using low mg calcite shells of brachiopods blmcs from a single stratigraphic section in central china to reconstruct paleotemperature changes from the middle to the latest permian after a rigorous screening for diagenesis our data show a 1 0 decrease in 18 ocalcite and thus climatic warming during the middle capitanian followed by a gradual 2 0 increase climatic cooling during the late wuchiapingian from the latest wuchiapingian to the early changhsingian 18 o decreased gradually and reached the lowest values of 4 0 and thus rapid climatic warming immediately before the permian triassic boundary the two warming events are coeval with the onset of the emeishan large igneous province and the siberian traps large igneous province respectively suggesting the two volcanic events are the plausible drivers of these climatic warming events a close comparison of paleontological and geochemical records indicates that the warming events occurred predate the glb and epme events this is in contrast with conodont 18 oapatite data which document the rapid climatic warming lagged the onset of the extinction event the comparison between 18 o of blmcs and 18 o of conodonts from the same section shows that the long term trends are similar but at higher temporal resolution discrepancies are present entailing further investigation in the near future our study confirms that 18 o of the brachiopod shells underwent important changes during the end of paleozoic highlighting that sea surface temperature is a key factor to understand the biosphere history since it changes simultaneously with the biological crises and that blmcs are invaluable archive for tracking physical and chemical conditions of past oceans

middle palaeozoic extinction events faunal and isotopic data abstract at least 9 and possibly as many as 12 extinction events of global or near global impact can be discriminated in the mid palaeozoic earliest silurian to early carboniferous on the basis of brachiopod coral conodont and ammonoid data and the history of carbonate build ups isotopic data from whole rock samples are presented for three of these events based on australian carbonate sequences constrained by conodont data these data represent the initial phase of a more extensive investigation using c o s sr and nd isotopic signatures derived from conodonts articulate and inarticulate brachiopod shell and fish remains from numerous australian and european sequences the aim of the project is to identify isotopic responses to extinction events and address causes for these changes in limestone sections analysed so far variations in carbon isotope compositions on a whole rock scale are most marked at horizons that can be correlated with times of significant reduction in biomass and diversity this is despite the fact that the whole rocks are in fact multicomponent systems with respect to carbon in part arising from diagenetic rearrangements of carbon distribution within the scale of the whole rock thus the carbon isotope data do provide evidence on a whole rock scale for fundamental changes in the global carbon cycle that are correlative with extinction events it is however unlikely that the magnitude of the isotopic shift will be precisely documented from such whole rock analyses the oxygen isotope results are less obviously related to the times of carbon isotope excursion this contrast in apparent resilience to post depositional modification of pristine isotope compositions exemplifies the extreme caution needed in evaluating isotopic data from carbonates

karst controlled diagenesis and reservoir development example from the ordovician main reservoir carbonate rocks on the eastern margin of the ordos basin china the ordovician majiagou formation contains the main reservoir of the ordos central gas field in the ordos basin the producing zone at the top of member 5 consists of carbonate rocks modified during a long period of subaerial exposure and karstification from the late ordovician to the middle carboniferous on the eastern margin of the ordos basin the porosity of the exposed carbonate rocks of this unit ranges from 0 5 to 15 1 and permeability ranges from 8 and permeability ranges from 0 1 to 5 md the main reservoir porosity is a dissolution enhanced vuggy porosity associated with dolomite the carbonate rocks show great heterogeneity reflecting the varying effects of karstification in creating and modifying porosity petrographic and geochemical analyses of various components in these carbonates provided evidence for depositional and diagenetic processes the reservoir carbonates were deposited in shallow and restricted hypersaline environments and were later modified by karstification and burial diagenesis dolomitization appears to have resulted from mixing of marine and meteoric waters and probably occurred in both shallow and deep burial settings cementation by calcite also occurred in both shallow and deep environments under different hydrodynamic conditions both depositional settings and diagenetic processes such as leaching by meteoric water paleokarstification dolomitization and cementation controlled reservoir development the outcrop and subsurface samples show similar petrographic features porosity types and geochemical characteristics but the exposed section of the formation shows evidence of more alteration by meteoric water

meteoric modification of early dolomite and late dolomitization by basinal fluids upper arbuckle group slick hills southwestern oklahoma 1 thick massive dolomite units from the upper arbuckle lower ordovician peritidal carbonate sequence slick hills southwestern oklahoma provide insight into two important problems 1 modification of early dolomite and 2 late dolomitization early dolomite volumetrically dominant is nonluminescent to dully luminescent 87 sr 86 sr ratios of most early dolomite samples are similar to both early ordovician seawater and associated limestones consistent with an early origin from coeval seawater all early dolomite samples are characterized by low delta 18 o values 5 1 to 10 0 o oo pdb indicating postdepositional modification meteoric water buffered by younger carbonates with lower 87 sr 86 sr ratios was probably responsible for modification because lower sr concentrations delta 18 o values and 87 sr 86 sr ratios characterize the more intensively modified early dolomite samples meteoric modification probably occurred during emergence of the carbonate platform in the ordovician late dolomite volumetrically minor is brightly luminescent and occurs mainly in transition zones between early dolomite and associated limestone late dolomite has high 87 sr 86 sr ratios delta 18 o values 5 9 to 2 5 o oo pdb and fe and mn concentrations relative to early dolomite and associated limestone 87 sr 18 o fe and mn enriched fluids derived from the anadarko basin during the late paleozoic are proposed to have formed the late dolomite the fluids migrated through preexisting early dolomite aquifers and dolomitized limestones near the early dolomite limestone contacts which existed at that time although early dolomite remained more porous than limestone during early burial burial alteration by solution compaction and cementation by late dolomite have reduced porosity considerably better reservoir quality is expected to be associated with late dolomite in the arbuckle group

oxygen isotope fluctuations in a modern north sea oyster crassostrea gigas compared with annual variations in seawater temperature implications for palaeoclimate studies abstract a total of 181 oxygen isotope values from sequential samples of the left shell of a modern pacific oyster crassostrea gigas that lived on a sub tidal oyster bank in the list basin north sea germany shows periodically varying values between 1 3 and 2 5 in order to test whether these 18 o fluctuations reflect seawater temperature changes the isotope values of the shell were compared to actual seawater temperature variations from the region c gigas serves as an excellent proxy for temperature of palaeoseawater and the results show that the examined oyster precipitated its shell in 18 o equilibrium with the ambient seawater a cessation of the oyster shell calcification starts at water temperatures below 6 c at lower temperatures than previously thought for crassostrea for palaeoclimate investigations the termination of shell production is important because the lowest temperatures might not be represented in the shell higher water temperatures are therefore potentially over represented in time spans when the shell grows faster and mean oxygen isotope values may potentially bias the mean seawater temperatures of annual variations towards higher temperatures

brachiopods as indicators of original isotopic compositions in some paleozoic limestones the original stable isotopic composition of paleozoic marine carbonate rocks is important to establish a baseline for evaluating diagenetic alteration and providing a reliable data base for modeling exogenic geochemical cycles of the elements we have compared the 18 o and 13 c values in the nonluminescent portions of brachiopods with similar published data of whole brachiopods other whole fossils and estimates of original isotopic composition of marine cements the oxygen and carbon isotopic records for each of these paleozoic components show generally good internal consistency significant discrepancies however were noted between results on the different components isotopic and trace element data presented in this study suggest that permo carboniferous whole brachiopods are little altered chemically nonetheless a more reliable but not fool proof approach for obtaining pristine isotopic values is microsampling of least altered regions based on cathodoluminescence in conjunction with staining techniques and elemental analyses the carbon and oxygen isotopic compositions of all components decrease in 18 o and 13 c in geologically older material neither temporal trend is monotonic however oxygen isotopic results suggest an important positive shift in 18 o of about 2 during the early carboniferous whereas the carbon isotope trend shows a major positive shift 2 3 during the mid carboniferous

palaeotemperatures indicated by upper jurassic kimmeridgian tithonian fossils from mallorca determined by oxygen isotope composition abstract the oxygen and carbon composition of calcite has been determined for belemnites ammonite aptychi and the matrix surrounding these fossils from the kimmeridgian tithonian of mallorca petrography cathodoluminescence and trace element analyses indicate that both ammonite aptychi and matrix has been diagenetically altered whereas the belemnites have been undergone minimal or no modification the belemnites give the heaviest oxygen isotope values of 0 04 to 0 99 pdb and lighter values of 0 71 to 3 98 pdb come from the ammonite aptychi and matrix the carbon isotopic compositions obtained from all the fossils are positive and are similar to those derived from modern marine shallow water skeletons palaeotemperatures calculated on the basis of the oxygen isotopic composition of the belemnites give a range of values from 13 6 to 16 c these results agree with late jurassic palaeotemperatures from similar palaeolatitudes

geochemistry of brachiopods oxygen and carbon isotopic records of paleozoic oceans abstract combined trace element and isotope studies of 319 brachiopods covering the ordovician to permian time span show that 13c and 18o in well preserved specimens varied during the paleozoic the overall 13c secular trend is in accord with the previously published observations but its details are obscured by vital isotopic fractionation effects at generic level nonetheless the results suggest that the negative correlation between marine 13ccarbonate and 34ssulphate deteriorates at time scales of 106 years due to the long residence time and thus slow response of so42 in the ocean for oxygen isotopes all devonian and older specimens have 18o of 4 while the well preserved permian samples have near present day 18o of about 1 pdb this isotopic dichotomy is probably not due to post depositional phenomena salinity or biogenic fractionation effects this leaves open the perennial arguments for a change in 18 o 16 o of sea water versus warmer ancient oceans the present data are difficult to explain solely by the temperature alternative the coincidence of the proposed shift in 18o with the large late paleozoic changes in marine 87 sr 86 sr 13 c 12 c 34 s 32 s and sea level stands argues for a tectonic cause and for a change in 18 o 16 o of sea water although such explanation is difficult to reconcile with global balance considerations and with isotopic patterns observed in alteration products of ancient basalts and ophiolites whatever the precise cause or combination of causes the implications for tectonism and or paleoclimatology are of first order significance

chemostratigraphy of the mid carboniferous boundary global stratotype section and point gssp bird spring formation arrow canyon nevada usa abstract the iugs in 1998 decided that the mid carboniferous mississippian pennsylvanian global boundary stratotype section and point gssp be assigned to a sequence of sedimentary units within the lower bird spring formation in arrow canyon nevada usa with the boundary defined by the first appearance of declinognathodus noduliferus this study represents the geochemical work on brachiopods matrix and cement covering a 35 m interval of the gssp about the mid carboniferous boundary samples were collected wherever brachiopods were noted in the sequence interval and their stratigraphic position was carefully measured using the a markers left by amoco geologists from their detailed biostratigraphic work the mean chemostratigraphic 1000 sr ca value of unaltered brachiopods from the mississippian side of the boundary 1 928 0 575 are similar to their pennsylvanian counterparts 2 141 0 427 and both are within the range of values obtained for recent low latitude brachiopods 1 50 to 5 50 manganese concentrations are similar with mean values of 33 mg kg and 27 mg kg for mississippian and pennsylvanian boundary brachiopods respectively and fall well within the manganese range of recent low latitude representatives 4 to 58 mg kg in contrast mississippian unaltered boundary brachiopods 244 125 mg kg contain significantly more fe p 0 001 than pennsylvanian ones 141 97 mg kg although both of these averages are above there is some overlap in their ranges with that recorded for fe in recent counterparts 10 to 127 mg kg oxygen isotope values of unaltered brachiopods from the mississippian side of the boundary 2 38 0 82 pdb are similar to the pennsylvanian ones 2 19 0 72 pdb and well within the range recorded in recent low latitude specimens 3 04 to 0 40 pdb carbon isotope values for the mississippian boundary brachiopods 2 01 0 81 pdb are dissimilar to those from the pennsylvanian 2 42 0 83 pdb but both are within the range observed in recent low latitude brachiopods 0 94 to 3 11 pdb the 1000 sr ca mn fe 13c and 18o values contents of the unaltered brachiopods reflect oceanographic conditions of the arrow canyon sea and as such are valuable proxies for local and possibly regional basin correlation at this time the 87sr 86sr values of unaltered brachiopods provide the most useful geochemical tool in recognizing and correlating the mid carboniferous boundary on a global scale the frequency and variations of the mississippian 87sr 86sr trend 0 708 082 0 000 040 are pronounced and significantly different p 0 045 from the essentially invariant trend for the post boundary pennsylvanian 0 708 123 0 000 031 brachiopods from the gssp the mid carboniferous boundary 87sr 86sr value based on unaltered brachiopod samples from within 1 m of the boundary is 0 708 056 0 000 021

deciphering processes controlling mid jurassic coccolith turnover the middle jurassic is characterized by major changes within the fossil coccolithophorid community with a transition from lotharingius dominated to watznaueria dominated assemblages concomitant with a significant increase in the pelagic carbonate production the mechanisms that triggered this overturn remain poorly understood here we present a compilation new and previously published data of lotharingius and watznaueria abundances through the early middle jurassic transition alongside this trends in newly acquired and literature derived carbon and oxygen isotope data were used to represent paleoceanographic indicators such as nutrient and temperature changes the nannofossil data show a rapid around 1 5 myr turnover around the aalenian bajocian transition across the aalenian bajocian boundary assemblages dominated by lotharingius spp give way to assemblages dominated by watznaueria spp coinciding with a peak in a particular morphological group of watznaueria species with a cross in the central area the proliferation of this morphogroup occurred during a time of oceanic opening and rearrangement of ocean circulation this led on to the evolution of pioneering coccolithophorid taxa but also to extinctions in several marine groups in the early bajocian the proliferation of two other morphogroups watznaueria without a central area structure and watznaueria with a bar corresponds to the major diversification of watznaueria and the beginning of its meso zoic dominance the watznaueria diversification and dominance are associated with radiation in other marine groups and these biotic changes occurred during a time of putative enhanced oceanic fertility and relatively low temperatures this study suggests that restructuring of fossil coccolithophorid communities may be favored during short turnover intervals related to major paleoceanographic change

paleoenvironmental changes in the silurian indicated by stable isotopes in brachiopod shells from gotland sweden ratios of stable carbon and oxygen isotopes in brachiopod shells more than 370 specimens esp atrypa reticularis from the silurian of gotland sweden have been analysed preservation of biological skeletal ultrastructures observed in sem micrographs and cathodoluminescence analyses indicate that usually no diagenetical alteration occurs the silurian of gotland consists of 440 m carbonate deposits spanning the late llandovery to late ludlow epochs 431 411 m y repeatedly uniform sequences of micritic limestones and marks are interrupted by complex structured reefs and adjacent platform sediments previously the alteration of facies is interpreted as the result of sea level fluctuations caused by a gradual regression with superimposed minor transgressive pulses the silurian sequence of gotland exhibits principally parallel carbon and oxygen isotope records corresponding closely to the topostratigraphic units lower values occur in periods dominated by deposition of marly sequences higher values are observed in periods dominated by reefs and extended carbonate platforms the isotope ratios are influenced by local as well as global factors the oxygen isotope ratios are interpreted to reflect paleosalinity changes due to varying freshwater input rather than changes in paleotemperature consequently the facies distribution of gotland is interpreted as resulting from changes in terrigenous input caused by different rates of continental weathering and freshwater runoff rather than by sea level fluctuations periods of arid climate and therefore anti estuarine downwelling of oxygenated surface water appear as short episodes of reef growing 1 5 m y in an epoche characterized by a tropic humid climate which causes an estuarine circulation and the upwelling of co2 rich deep water carbon isotope ratios are obviously connected to these changes in circulation by the advection of 13c rich surface water arid episodes or upwelling of 13c depleted deep water humid episodes of a silurian ocean which itself reveals generally euxinic deep water conditions due to the burial of organic carbon in black shales

palaeoatmospheres in the phanerozoic except in the recent geological past palaeoatmospheric composition cannot be measured but only inferred from palaeontological or geochemical observations the likely controls on atmospheric composition are reviewed and the role of organisms stressed as monitors recorders motors and moderators of palaeoatmospheric changes whereas there is a good general case for changes in po 2 and pco 2 during phanerozoic time proposals for timing and mechanism in the earlier phanerozoic are speculative at present it seems probable that the late palaeozoic spread of land plants raised o 2 and reduced co 2 levels in the atmosphere the end cretaceous crisis had a transient impact on the atmosphere whose general constancy through geological time is one of the most remarkable features of earth history

the silurian of gotland sweden facies interpretation based on stable isotopes in brachiopod shells the silurian of gotland sweden consists of 440 m of carbonate deposits repeatedly uniform sequences of micritic limestones and marls are interrupted by complex structured reefs and by adjacent platform sediments generally the alteration of facies is interpreted as the result of sea level fluctuations caused by a gradual regression with superimposed minor transgressive pulses the purpose of this study is a facies interpretation based on both field observations and stable isotope measurements of brachiopod shells approximately 700 samples from stratigraphically arranged localities in different facies areas have been investigated the carbon and oxygen isotopes show principally parallel curves and a close relationship to the stratigraphic sequence lower values occur in periods dominated by deposition of marly sequences higher values are observed in periods dominated by reefs and extended carbonate platforms the oxygen isotope ratios are interpreted to reflect paleosalinity changes due to varying freshwater input rather than to paleotemperature carbon isotope ratios are believed to have been connected to global changes in the burial of organic carbon in black shales during periods of euxinic deep water conditions consequently the facies succession on gotland results from global paleoclimatic conditions changes in terrigenous input due to different rates of weathering and freshwater runoff rather than sea level fluctuations control the carbonate formation of the silurian on gotland

changes in marine isotopic composition and the late ordovician glaciation well preserved brachiopod shells and marine cements from limestone coquinas which cap carbonate mudmounds in the siljan area of central sweden have the heaviest stable oxygen and carbon isotope values yet reported for lower palaeozoic marine sediments the coquinas formed during the eustatic regression at the onset of the late ordovician glaciation the isotopic compositions reflect simultaneous shifts in both carbon and oxygen more than 5 13 c and up to 2o 18 o away from more normal lower palaeozoic values in similar carbonates from within the mounds oxygen isotope data are consistent with a change in the isotopic composition of the sea water probably accompanied by a decrease in temperature the changes in carbon values suggest enhanced deposition of organic carbon a process which would have decreased p co 2 in the ocean and the atmosphere and thus contributed to rapid global cooling

salina margin tepees pisoliths and aragonite cements lake macleod western australia their significance in interpreting ancient analogs tepee structures banded aragonite cements and pisoliths are currently forming in lake macleod a carbonate evaporite salina in western australia although lake macleod is separated from the indian ocean by a barrier it lies 3 4 m below sea level which promotes the seepage of seawater through the barrier and its discharge from vents and seepage mounds around the margin of the salina discharging waters have precipitated and diagenetically altered carbonate sediments within these seepage mounds to form tepee structures of lithified protodolomite overlying cavities that are lined with banded aragonite cement and floored by both cement and pisoliths significant variations in 18o 5 1 pdb and 13c 5 5 pdb of the aragonite cements were documented and are thought to record shifts in the isotopic composition of the water brought about by the effects of evaporation influx of meteoric water and oxidation of organic water carbon 14 dating of cements indicates that cementation began about 3400 b p and has proceeded at a rate of about 0 2 to 0 4 mm 100 yr the highest rate occurring during evaporative episodes by analogy with lake macleod and other australian salinas peritidal tepee structures and associated diagenetic carbonates in the permian capitan reef complex may owe their origin to speleanlike diagenesis operative in a marine groundwater discharge zone

radiaxial fibrous calcite as early burial open system cement isotopic evidence from permian of china abstract the nanpanjiang basin of south china occupies about 100 000 km2 in southern guizhou and eastern yunnan provinces and northwestern guangxi autonomous region the basin contains a thick paleozoic carbonate sequence overlain by about 3 000 m of triassic basinal deposits permian carbonate rocks comprise a large portion of the paleozoic strata and form several platforms separated by basins containing dark thin bedded limestones siliceous shales and cherts the platform margins are rimmed by sponge or algal reefs radiaxial fibrous calcite rfc is the most abundant cement in very coarse sponge or algal debris of upper permian reef and fore reef sediments exposed along the western margin of the nanpanjiang basin small volumes of syndepositional cements interpreted to have been fibrous magnesian calcites and botryoidal aragonite predate rfc coarse blocky burial calcite postdates rfc evidence that rfc was precipitated during sediment deposition was not found rfc occurs as isopach layers up to 15 mm thick and exhibits white gray and black bands about 1 mm wide the presence of microdolomite inclusions in these cements indicates that they were originally magnesian calcites dgr18o of rfc cements are more positive than any of the earlier or later components of the reef and fore eef facies analyses of successive bands reveals the most positive dgr18o near the center of the isopach layers dgr13c of successive bands reveals generally more negative values toward the centers of layers rfc layers are interpreted to have precipitated during early burial of the platform margin while reef and fore reef sediments were in communication with seawater cement layers recorded isotopic characteristics of seawater as platform edge sediments subsided through the water column at the basin margin dgr18o of successive bands records cooler water at depth in the basin followed by geothermal warming dgr13c records increased incorporation of light carbon as the platform subsided through the oxygen minimum zone followed by a return to normal values at depth these data and interpretations suggest rfc layers precipitated very slowly during time spans commensurate with those of subsiding platforms millions of years isotopic characteristics of rfc may not reflect shallow seawater rather they may reflect burial environments where dgr18o is affected by cooler water and dgr13c is affected by biologic activity end of article last page 261

permian strontium isotope stratigraphy cvu acknowledges funding from the leopoldina german national academy of sciences grant no lpds 2014 08

oxygen isotope and mg ca composition of late visean mississippian brachiopod shells from sw iberia palaeoclimatic and palaeogeographic implications in northern gondwana abstract latest visean brachiopod shells gigantoproductus sp from the pedroches basin of sw spain were sampled in order to obtain chemical and isotopic evidence that may help first to assess if primary geochemical and isotopical signals are preserved in these shells and second to reconstruct temporal variations in palaeoceanographic and palaeoclimatic conditions in northern gondwana during this time span microtexture cathodoluminescence cl and ultrastructure under sem of the brachiopods were examined to avoid sampling of shell portions altered after deposition shell portions classified as non luminescent nl and non luminescent to slightly luminescent nl sl present geochemical signatures within the ranges considered normal for recent brachiopods that have not undergone significant diagenetic modification these include low to undetectable fe and mn contents high sr values and 18o values similar to those of carbonates in equilibrium with seawater on the other hand valve areas that are luminescent l or moderately luminescent with luminescent portions ml l present higher fe and mn contents lower sr concentrations and lower 18o values than those corresponding to nl and nl sl shells this suggests a greater diagenetic alteration of these portions and that they acted as microzones of reaction with the diagenetic fluids temporal trends through the studied interval show a spread in 13c values much lower than that observed for contemporaneous samples up to 1 6 thus obscuring the 13c global signal at the time scale resolution of this study in contrast the 18o record of brachiopod calcite 18oc shows an overall increase of 1 relative to v pdb from the oldest to the youngest samples this is accompanied by a 30 decrease in mg ca ratios of the brachiopod calcites confirming that at least part of this shift in 18oc was related to cooling combination of mg ca and 18oc proxies established in this paper although not full proof for brachiopods yet allowed for the calculation of a temperature drop of 3 3 c and a change in seawater 18ow that becomes 0 4 more positive during this interval the data are consistent with regional seawater cooling that accompanied an increase in continental ice volume over a relatively short time period of

within shell variations in carbon and oxygen isotope compositions of two modern brachiopods from a subtropical shelf environment off amami o shima southwestern japan 1 this study examines the fidelity of carbon 13c and oxygen 18o isotope compositions of two modern brachiopod species kikaithyris hanzawai and basiliola lucida to use as proxies of 13c values of total dissolved inorganic carbon and temperature and or 18o values of seawater respectively well preserved shells of k hanzawai and living individuals of b lucida were collected from a subtropical shelf environment off amami o shima southwestern japan some portions of the shells are in isotopic equilibrium with the ambient seawater while other portions are not the degree of disequilibrium differs between the two species and between different portions of each shell statistically significant positive correlations are recognized between the 13c and 18o values of these samples which can be ascribed to a kinetic fractionation effect far from the posterior shell edge and along the axis of shell growth the 18o values of the secondary shell layer of k hanzawai mostly fall within the expected range of equilibrium calcite the 13c values from the inner surface of the secondary shell layer in both species are relatively constant and are equivalent to or very close to equilibrium calcite therefore these portions of the shells are most suitable for collecting reliable environmental proxy data although the 13c and 18o values of modern brachiopod shells are predominantly controlled by a kinetic fractionation effect the appropriate selection of species and shell portions that reflect the isotopic composition of ambient seawater can facilitate the reconstruction of secular variations in oceanic 13c or 18o values

pre ore burial dolomitization adjacent to the carbonate hosted gays river zn pb deposit nova scotia the gays river formation of the lower windsor group in the vicinity of the gays river zn pb deposit was completely dolomitized via a volume for volume transformation prior to mineralization premineralization porosity was the precursor limestone porosity comprising fenestrae dissolution molds and intercrystalline intraskeletal and growth pores which remained essentially unchanged through dolomitization regionally the dolomites one replacement and one cement overlapped with sediment compaction and dissolution of aragonite the dolomites are characterized by low 18opdb values 14 to 4 average 8 slightly radiogenic 87sr 86sr ratios 0 70778 0 70900 and locally high percentages of feco3 and mnco3 up to 13 5 and 9 5 mol respectively the presented petrographic and geochemical data compiled with existing fluid inclusion microthermometry data suggest dolomitization by hot brines in a burial setting high fe and mn concentrations south of the studied area with progressive depletion toward

correlation of the askyn river section southern urals russia with the mid carboniferous boundary gssp bird spring formation arrow canyon nevada usa implications for global paleoceanography abstract isotopic data of unaltered low mg calcite brachiopods from type bashkirian strata of the askyn river section southern urals russia are correlated with those from the mid carboniferous boundary global stratotype section and point gssp at arrow canyon southern nevada usa strontium isotope and conodont data of precisely located samples from the sub to tropical locations spanning the mid carboniferous boundary facilitate the correlation of the two sequences and support the discontinuous nature of the sequence at askyn carbon isotopic trends of the two sites are generally divergent and demonstrate the influence overprinting of local oceanographic conditions on global parameters oxygen isotopes show a similar divergence for the latest mississippian time period with concurrence of values for the earliest pennsylvanian at the two sites in both instances differences variations in water temperature currents salinity and burial rate amount of organic matter or combinations of these factors may have played roles of influencing water chemistry at the local level it is possible to achieve global correlations at a finer scale than biozones with precisely located material from stratotype and ancillary sections especially if a global stratotype point has been identified and selected according to universally accepted biostratigraphic criteria consequently it is possible to resolve oceanographic influences at the local level and reconcile them with truly global oceanographic conditions and ultimately define global causes effects such as cryospheric and tectonic events seawater chemistry at arrow canyon probably represents panthalassan global mid carboniferous oceanic conditions supported by its similarity with data from other locations and modern global oceanographic parameters askyn represents paleotethys and global oceanographic conditions but in part overprinted by local influences the mid carboniferous seems to be a time of expansion of the cryosphere as documented by a positive shift in seawater oxygen isotope composition of about 0 5 smow from the latest mississippian 1 2 to earliest pennsylvanian 0 7

paleoceanographic conditions at approximately 20 and 70 ka recorded in kikaithyris hanzawai brachiopoda shells abstract the 13c and 18o values of fossil brachiopod shells have been widely used as paleoenvironmental proxies in this study we investigated intrashell and intraspecific variations in the isotopic and minor element concentrations of well preserved shells of the brachiopod kikaithyris hanzawai yabe from the last glacial period 20 ka last glacial maximum lgm and 70 ka marine isotope stage 4 mis4 collected in the central ryukyus and used these data to estimate the paleoceanographic conditions seawater temperature concentration of dissolved inorganic carbon dic and 13c value of dic 13cdic the 13c and 18o profiles along the maximum growth axis obtained from the inner shell surface show three distinct intervals corresponding to changes in shell morphology these results suggest that the bulk isotopic compositions of brachiopods with complex shell morphologies are unsuitable for paleoenvironmental reconstructions nevertheless there exists a specific shell portion with relatively small intrashell and intraspecific variations the past seawater temperatures derived from the 18o values of this portion are consistent with the alkenone and planktic foraminiferal mg ca based past seawater temperatures reported in previous studies the past 13cdic values estimated from the 13c values of the specific shell portion are within the range of the past 13cdic values calculated from known atmospheric and oceanographic parameters the past dic concentrations reconstructed from the brachiopod based 13cdic values are lower than the present concentrations in the east china sea which can be explained by low partial pressure of co2 during the last glacial period these results indicate that the 13c and 18o values obtained from k hanzawai shells are potential paleoenvironmental indicators the intrashell and intraspecific variations in the k hanzawai shells are different for each minor element some anomalously high mn and fe concentrations in the shells are probably caused by metabolic factor s not by meteoric diagenesis this suggests that the minor element concentrations are useful but not perfect for distinguishing diagenetically altered and unaltered portions of the shells of k hanzawai in the studied succession

the parent body controls on cosmic spherule texture evidence from the oxygen isotopic compositions of large micrometeorites high precision oxygen isotopic compositions of eighteen large cosmic spherules 500 mu m diameter from the atacama desert chile were determined using ir laser fluorination isotope ratio mass spectrometry the four discrete isotopic groups defined in a previous study on cosmic spherules from the transantarctic mountains suavet et al 2010 were identified confirming their global distribution approximately 50 of the studied cosmic spherules are related to carbonaceous chondrites 38 to ordinary chondrites and 12 to unknown parent bodies approximately 90 of barred olivine bo cosmic spherules show oxygen isotopic compositions suggesting they are related to carbonaceous chondrites similarly similar to 90 porphyritic olivine po cosmic spherules are related to ordinary chondrites and none can be unambiguously related to carbonaceous chondrites other textures are related to all potential parent bodies the data suggests that the textures of cosmic spherules are mainly controlled by the nature of the precursor rather than by the atmospheric entry parameters we propose that the po texture may essentially be formed from a coarse grained precursor having an ordinary chondritic mineralogy and chemistry coarse grained precursors related to carbonaceous chondrites i e chondrules are likely to either survive atmospheric entry heating or form v type cosmic spherules due to the limited number of submicron nucleation sites after total melting ordinary chondrite related coarse grained precursors that suffer higher peak temperatures will preferentially form cryptocrystalline cc textures instead of bo textures conversely the bo textures would be mostly related to the fine grained matrices of carbonaceous chondrites due to the wide range of melting temperatures of their constituent mineral phases allowing the preservation of submicron nucleation sites independently of the nature of the precursors increasing peak temperatures form glassy textures

geocarbsulf a combined model for phanerozoic atmospheric o2 and co2 abstract a model for the combined long term cycles of carbon and sulfur has been constructed which combines all the factors modifying weathering and degassing of the geocarb iii model berner r a kothavala z 2001 geocarb iii a revised model of atmospheric co2 over phanerozoic time am j sci 301 182 204 for co2 with rapid recycling and oxygen dependent carbon and sulfur isotope fractionation of an isotope mass balance model for o2 berner r a 2001 modeling atmospheric o2 over phanerozoic time geochim cosmochim acta 65 685 694 new isotopic data for both carbon and sulfur are used and new feedbacks are created by combining the models sensitivity analysis is done by determining 1 the effect on weathering rates of using rapid recycling rapid recycling treats carbon and sulfur weathering in terms of young rapidly weathering rocks and older more slowly weathering rocks 2 the effect on o2 of using different initial starting conditions 3 the effect on o2 of using different data for carbon isotope fractionation during photosynthesis and alternative values of oceanic 13c for the past 200 million years 4 the effect on sulfur isotope fractionation and on o2 of varying the size of o2 feedback during sedimentary pyrite formation 5 the effect on o2 of varying the dependence of organic matter and pyrite weathering on tectonic uplift plus erosion and the degree of exposure of coastal lands by sea level change 6 the effect on co2 of adding the variability of volcanic rock weathering over time berner r a 2006 inclusion of the weathering of volcanic rocks in the geocarbsulf model am j sci 306 in press results show a similar trend of atmospheric co2 over the phanerozoic to the results of geocarb iii but with some differences during the early paleozoic and for variable volcanic rock weathering lower co2 values during the mesozoic atmospheric oxygen shows a major broad late paleozoic peak with a maximum value of about 30 o2 in the permian a secondary less broad peak centered near the silurian devonian boundary variation between 15 and 20 o2 during the cambrian and ordovician a very sharp drop from 30 to 15 o2 at the permo triassic boundary and a more or less continuous rise in o2 from the late triassic to the present

stable isotope profiles ca o c through modern brachiopod shells of t septentrionalis and g vitreus implications for calcium isotope paleo ocean chemistry brachiopod shells are widely used as an archive to reconstruct elemental and isotopic composition of seawater studies focused on oxygen and carbon isotopes over the last decades are increasingly extending to the emerging calcium isotope system to date only little attention has been paid to test the reliability of fossil brachiopods on their modern counterparts in this context the present study investigates two modern brachiopods terebratulina septentrionalis eastern canada 5 30 m depth 7 1 c seasonal temperature variation two layer shell and gryphus vitreus northern mediterranean 200 m depth constant all year round temperature three layer shell both species were sampled along the ontogenetic growth direction and calcium oxygen and carbon isotopes as well as elemental concentration were measured calcium isotopes were analyzed on tims the elemental composition was analyzed by la icp ms and icp aes the results indicate an intra specimen 44 40ca variation ranging from 0 16 to 0 33 pointing to a fairly homogenous distribution of calcium isotopes in brachiopod shells however in the light of the suggested 0 7 increase in calcium isotopes over the phanerozoic such intra specimen variations constrain ocean reconstruction 44 40ca values of t septentrionalis do not seem to be affected by growth rate calcium isotopic values of g vitreus are heavy in the central part of the shell and trend towards lighter values in peripheral areas approaching the maximum isotopic composition of t septentrionalis the maximum inter species 44 40ca difference of 0 62 between t septentrionalis and g vitreus indicates that care should be taken when using different taxa species with different strontium content or brachiopods with specialized shell structure such as g vitreus for ocean water reconstruction in terms of ca isotopic composition t septentrionalis may record ca isotopic fractionation related to seasonal seawater temperature variations in its shell but this is difficult to resolve at the current analytical precision average 18o derived temperatures of the two investigated species are close to on site measured temperatures

no vital effect on δ18o and δ13c values of fossil brachiopod shells middle devonian of china biogenic fractionation vital effect of carbon and oxygen isotopes during metabolism is ubiquitous among marine organisms whether there is vital effect on the isotopic compositions of fossil brachiopods represents one of the most controversial issues in the carbonate stable isotope geochemistry furthermore the problem involves not only the feasibility of the utilization of fossil brachiopod shells as analysis samples for obtaining the original carbon and oxygen isotopic compositions of carbonates but also the credibility of the data and conclusions already achieved in the study field with fossil brachiopods from middle devonian of china this study investigates the vital effect by comparisons of 18o and 13c between the fossils of the same original living environment and the shell s preservation at levels of species genus and family no systematic differences of 18o and 13c between fossils were found which led to the conclusion that no detectable vital effect occurred in the fossil brachiopod shells the argument that the fossil brachiopod possibly has biogenic fractionation with the stable isotopes of carbon and oxygen resulted likely from studies of fossils that are different in the original living environment or the state of preservation

isotope geochemistry of oxygen and carbon in phosphate and carbonate of phosphorite francolite oxygen isotope ratios in phosphate delta sup 18 o sub p were determined in 219 samples of phosphoritic rocks from all major phosphogenic provinces of the world ranging in age from lower proterozoic to recent in 58 samples oxygen was analyzed in the two oxygen lattice sites of francolite both in phosphate and in structural carbonate delta sup 18 o sub c delta sup 13 c was also analyzed in the latter and in coexisting calcite for 10 of them both delta sup 18 o sub p and delta sup 18 o sub c decrease sharply from the recent to the cretaceous and decrease with a gentler slope to the precambrian the nature of the time variation is elucidated by means of a delta sup 18 o sub p vs delta sup 18 o sub c plot which suggests that a the main cause of the time trends is the increase in temperature between recent and the cretaceous b the pre cretaceous trend is overprinted by both low temperature nonequilibrium exchange between sup 18 o depleted water and the rocks and higher temperature exchange between phosphate and carbonate c the observed trend cannot be explained by sup 18 o depleted cretaceous and paleozoic oceans the calcite coexisting with apatite in phosphatic rocks is similar in both delta sup 18 o and delta sup 13 c to the structural carbonatemore of the apatite even though phosphate may exchange its oxygen with environmental water to a greater extent than the authors originally claimed it is probably still a very good isotopic recorder of sedimentary environments less

clusters of cyclones encircling jupiter s poles the familiar axisymmetric zones and belts that characterize jupiter s weather system at lower latitudes give way to pervasive cyclonic activity at higher latitudes two dimensional turbulence in combination with the coriolis effect that is the large meridionally varying coriolis force on the giant planets of the solar system produces alternating zonal flows the zonal flows weaken with rising latitude so that a transition between equatorial jets and polar turbulence on jupiter can occur simulations with shallow water models of giant planets support this transition by producing both alternating flows near the equator and circumpolar cyclones near the poles jovian polar regions are not visible from earth owing to jupiter s low axial tilt and were poorly characterized by previous missions because the trajectories of these missions did not venture far from jupiter s equatorial plane here we report that visible and infrared images obtained from above each pole by the juno spacecraft during its first five orbits reveal persistent polygonal patterns of large cyclones in the north eight circumpolar cyclones are observed about a single polar cyclone in the south one polar cyclone is encircled by five circumpolar cyclones cyclonic circulation is established via time lapse imagery obtained over intervals ranging from 20 minutes to 4 hours although migration of cyclones towards the pole might be expected as a consequence of the coriolis effect by which cyclonic vortices naturally drift towards the rotational pole the configuration of the cyclones is without precedent on other planets including saturn s polar hexagonal features the manner in which the cyclones persist without merging and the process by which they evolve to their current configuration are unknown

18o16o and 13c12c in lower paleozoic articulate brachiopods implications for the isotopic composition of seawater three hundred and eleven articulate brachiopods with extensive geographic coverage spanning the cambrian to silurian stratigraphic interval were analyzed for oxygen and carbon isotopic composition cambrian samples have 18o 7 ordovician samples 2 4 and silurian samples 1 9 confirming the previously established trend towards lighter isotopic compositions with increasing age throughout the lower paleozoic forty nine best preserved ordovician and silurian samples were identified based on scanning electron microscopy and trace element analysis they were found to bracket the isotopic compositions of over 85 of specimens from these stratigraphic intervals supporting widespread preservation of the isotopic signal some latest ordovician and lower ludlovian samples associated with shale sequences are apparently enriched in 18o these are interpreted as an environmental phenomenon perhaps related to water temperature and glaciation a number of silurian samples of varying genera and stratigraphic levels are highly enriched in 13c up to 6 some are shale related but some are associated with carbonate bearing basins these are also thought to represent near original compositions but a single environmental cause is unknown the present data show that luminescence is not a decisive criterion for evaluating the degree of brachiopod preservation whole shell values were isotopically similar to their nonluminescent portions for both oxygen and carbon

gradients in seasonality and seawater oxygen isotopic composition along the early permian gondwanan coast se australia abstract oxygen isotope compositions of marine carbonates are commonly employed for understanding ancient temperatures but this approach is complicated in the very distant past due to uncertainties about the effects of diagenesis and the isotopic composition of seawater both locally and globally microsampled accretionary calcite from two species of the fossil bivalve eurydesma sowerby and morris 1845 collected from sediments of cisuralian age in high latitude marine sediments along the se coast of australia records cyclic seasonal fluctuations in shell 18 o values during growth demonstrating the primary nature of the isotope signal and thus allowing investigation of early permian seawater isotopic composition and water temperature in the high southern latitudes the mean and seasonal range of 18 o carb decreases poleward across about 10 of paleolatitude 67 s 77 s the presence of co occurring dropstones and stratigraphically associated glendonites constrains winter temperatures across the region to near freezing thus permitting calculation of realistic estimates of water composition and summer temperatures summer 18 o carb values indicate water temperatures between 5 c and 12 c with warmer values at lower latitudes the decrease in both mean sea surface temperature and seasonal amplitude with increasing latitude on the gondwanan coast is much like that observed along high latitude coastlines today calculated 18 o water decreases toward the pole likely associated with an increasing contribution of isotopically light fresh water derived from summer snow melt the gradient in 18 o water is similar to that documented over a similar span of latitude on the modern se greenland coast we infer the presence of a north flowing coastal current of cold o 18 depleted water that entrains progressively greater amounts of more typical seawater as it moves away from the pole 18 o values in se australia however are about 3 lower than those off greenland suggesting comparatively lower salinity water or more o 18 depleted glacial ice runoff in the permian gondwanan high latitudes perhaps augmented by more depleted negative global average seawater conditions in southeastern australia during the largest of the permian deglaciations were warmer than present day antarctica at similar latitudes but may approximate those of early mid miocene antarctica with frozen winters but summers closer to 10 c

oxygen and carbon stable isotope records of the lochkovian pragian boundary interval from the prague basin lower devonian czech republic abstract climate changes close to the lochkovian pragian event are still widely discussed carbonate 18o and 13c and conodont apatite 18o from medial to distal carbonate ramp sediments were analysed to provide further stable isotope data from the stratotype area in the prague basin the uppermost silurian to lower emsian 18o trends are put into an updated conodont biostratigraphy framework carbonate 18o and 13c are discussed in the context of facies dependent diagenesis the 13c pattern measured from different sections enables the correlation of intervals with development of different facies inside the prague basin positive 13c shifts are often coupled with trends of decreasing computed gamma ray cgr values interpreted as regressions whereas negative 13c shifts commonly coincide with opposite trends in cgr the lochkovian pragian boundary interval coincided with an increase in carbonate 13c and an increase in the 18o of conodont apatite and carbonate which we interpret as consequence of climate cooling generally the lochkovian was warmer than the pragian and earliest emsian