stable isotopes of lake and fluid inclusion brines dabusun lake qaidam basin western china hydrology and paleoclimatology in arid environments the qaidam basin underlain by salt is the largest 120 000 km2 on the qinghai tibet plateau western china numerous shallow to ephemeral saline lakes and dry saline pans are present on the qarhan salt plain dabusun lake the largest about 200 km2 contains high salinity na mg cl brines whereas it precipitates halite it is fringed by a potash salt flat the dominant inflow to dabusun lake the golmud river contains dilute na hco 3 rich meteoric waters dabusun lake brines fall on an evaporation trend given by d 3 3 18o 43 both d and 18o values increase with salinity which in turn varies considerably with flooding and evaporation the isotope compositions of the fluid inclusion brines from modern halite formed along the lake s edge are intermediate to those of dabusun lake brines and those from the salt flat shallow sediments beneath qarhan consist of interbedded salts and mud a short core section 1 3 1 7 m depth from the northern edge of dabusun lake was found to contain three dissolution surfaces and three mud partings the 18o values for fluid inclusions in 22 primary halite samples from this section show a record of episodic flooding lower 18o values followed by evaporation gradual increase in 18o values primary fluid inclusions in halite crystallized initially at the surface provide a geochemical record of surface brines their major element compositions varied through time more concentrated fluids indicate more arid conditions in the basin whereas wetter conditions prevailed during intervals of non salt deposition when laminated muds accumulated the isotope compositions together with the activity of h2o of fluid inclusions in primary halite were used to determine isotope variations in regional precipitation and hence paleoclimatic changes on the qinghai tibet plateau during the past 50 000 years

quantitative radiometric and biostratigraphic calibration of the pennsylvanian early permian cisuralian time scale and pan euramerican chronostratigraphic correlation a quantitative biostratigraphic and radiometric calibration is presented for the pennsylvanian through early permian global time scale based upon high precision isotope dilution thermal ionization mass spectrometer id tims u pb zircon ages for interstratified ash beds in the parastratotype sections of the southern urals of russia twenty four ash bed ages in three outer ramp and basinal sections of the pre uralian foredeep bracket the biotic definitions of global stages and regional substages from the base of the upper pennsylvanian kasimovian stage to the base of the lower permian artinskian stage four additional ash bed ages in two sections of the eastern slope of the urals constrain the global bashkirian and serpukhovian stages quantitative stratigraphic methods conop9 are applied to a compilation of over 2000 bioevents in 22 stratigraphic sections supplemented by our dated volcanic horizons to refine the pennsylvanian early permian global time scale significant shifts in the duration of several stages are demonstrated ranging from one to six million years compared with prior estimates the unprecedented density of radiometric calibration points for the pennsylvanian permian transition provides a high resolution 0 1 ma global chronostratigraphic standard for testing and improving biostratigraphic correlations across euramerica we integrate radiometric ages biostratigraphic correlation and cyclostratigraphic tuning of major cyclothems to the long period 404 ka eccentricity cycle to elucidate the tempo magnitude and forcing of eustatic changes and cyclothemic deposition associated with the waxing and waning of gondwanan ice sheets and establish a pan euramerican chronostratigraphic framework for most of pennsylvanian and early permian time

isotopic investigation of infiltration and unsaturated zone flow processes at carlsbad cavern new mexico abstract stable isotopes of hydrogen and oxygen together with tritium were used to investigate infiltration and unsaturated zone flow at carlsbad cavern water samples were collected from drips and pools every 4 months for a year seepage flow dominates infiltration at the cavern homogenizing the isotopic composition of individual and seasonal precipitation events early along the vertical flowpath within the relatively narrow range in the stable isotopic ratios of cave drip water d of 53 tc 44 18o of 8 3 to 85 isotopic changes on two different time scales were identified a longer term variation probably driven by changes in the relative amount of heavy isotope enriched summer precipitation is evident in the slight enrichment of drips collected at shallower depths in the cavern above 1100 m elevation this suggests vertical travel times to the main cave rooms of the order of decades consistent with observed tritium activities from less than 4 6 to 16 9 tritium units t u given these residence times and the narrow range in isotopic composition a seasonal trend in the isotopic composition of cave water coincident at all levels in the cavern is probably related to seasonal changes in the cave climate active air circulation driven by differences in air temperature between the cave and outside during the winter increases the evaporation rate from cave pools and causes enrichment in heavy isotopes this signal may be transmitted to infiltrating water via isotope exchange before the water drips into the cave consistent with the temporary storage of drip water in limited zones of saturation around the cave rooms these zones may develop in response to capillary driven surface tension before infiltrating water drips into the unsaturated flow barriers represented by the large air filled cave passages

high precision u pb zircon age constraints on the duration of rapid biogeochemical events during the ludlow epoch silurian period precise determinations of the rates and durations of palaeozoic biogeochemical events are largely unavailable here we present two new high precision u pb zircon dates from volcanic ash deposits from the ludlow series silurian system of podolia ukraine that yielded weighted mean 206 pb 238 u dates of 424 08 0 20 0 29 0 53 ma and 422 91 0 07 0 21 0 49 ma analytical tracer and total uncertainties these new dates bracket the largest post cambrian global carbon cycle perturbation lau excursion and constrain the ludlow rise in 87 sr 86 sr these chronostratigraphically well controlled dates improve the calibration of the silurian time scale and provide the first determinations of the rates of biogeochemical change during the ludlow epoch supplementary material u pb geochemical methods data and cl imagery are available at http www geolsoc org uk sup18798

large scale hot water migration systems around salt diapirs in the danish central trough and their impact on diagenesis of chalk reservoirs abstract fracture filling calcite from the piercement fields of east rosa skjold rolf north arne nils and vagn directly underlain by salt diapirs and the dome field dan overlying a deep seated salt structure have been studied by fluorescence and cathodoluminiscence microscopy fluid inclusion microthermometry and carbon and oxygen isotopes the carbon and oxygen isotope compositions of the reservoir matrix chalk have also been measured the temperature estimates obtained from fluid inclusion data suggest that the fracture filling calcite of the piercement fields precipitated during hot water flushing of the reservoirs the flushing system only existed around the salt diapirs and was probably related to expulsion of overpressured fluid from the surrounding sediments the thermal anomaly and the faults associated with the diapirs probably were important factors in focusing the ascending water by combining fluid inclusion thermometry with o isotope data for the fracture filling calcites ranges of o isotopic values of the flushing water are deduced in skjold rolf north arne nils and vagn 18o 1 to 7 smow values typical of sedimentary porewater of sea water origin in east rosa 18o 4 and 4 smow which combined with data on fluid inclusion salinities suggest that the flushing waters were responsible for substantial salt dissolution lower 18o values with shallower depth of burial suggest that the porosity of chalk in the shallower fields was more severely reduced by calcite cementation during the flushing event than in the deeper fields in the case of north arne nils vagn and dan 13c values of the fracture filling calcites are similar to those of normal chalk 0 5 to 3 5 however calcites from rolf skjold and east rosa are depleted by 1 8 6 2 and 16 7 respectively only in east rosa is the matrix chalk itself depleted in 13c range 2 0 to 0 7 the low 13c values are interpreted as the result of biodegration sulphate originating from the underlying diapirs was flushed into the reservoir and used by bacteria to degrade present hydrocarbons this process produced 13c depleted bicarbonate which was incorporated into the fracture filling calcites

carbon isotope stratigraphy across the silurian devonian transition in podolia ukraine evidence for a global biogeochemical perturbation the carbon and oxygen isotope composition of marine carbonates 13 c and 18 o respectively are studied in the fossiliferous stratigraphically well constrained and remarkably expanded successions of podolia sw ukraine spanning the silurian devonian transition significant isotopic shifts are directly comparable to previously published global secular trends in well preserved brachiopod calcite isotopic ratios from this region and therefore may be taken as a reliable primary record of seawater 13 c changes the sections reveal a major positive 13 c excursion with an amplitude above 6 beginning in the upper pridoli and reaching peak values as heavy as 4 2 in the lowermost lochkovian this turnover in carbon cycling is followed by a general trend toward more negative 13 c values in the upper lochkovian the podolian isotopic signals provide strong support for the previously inferred global biogeochemical perturbation across the silurian devonian transition reflecting a complex combination of palaeogeographical biogeochemical and evolutionary processes in the late caledonian geodynamic setting with a likely undervalued role of the expanding vegetation in vast near coastal shallows and deltas

late archaean tectonics in the faeringehavn tre brodre area south of buksefjorden southern west greenland the faeringehavn tre brodre area consists of three distinct terranes tectonically jux taposed by a previously unrecognized event contacts between the terranes are mylonitic shear zones truncating lithological units in adjacent terranes the terrenes are 1 faeringehavn terrane largely composed of early archaean amitsoq gneiss cut by younger archaean granitic gneiss defined here as the satut gneiss 2 tre brodre terrane comprising mid archaean malene supracrustal rocks anorthosite complex and polyphase nuk gneisses 3 tasiusarsuaq terrane largely comprising mid archaean nuk gneisses affected by c 2800 ma granulite facies metamorphism the tasiusarsuaq terrane is structurally above both the faeringehavn and tre brodre terranes which at c 2800 ma experienced a lower grade of metamorphism juxtaposition of the terranes took place between 2800 and 2500 ma and involved thrusting and crustal thickening subsequent re equilibration involved folding steeply inclined shear belts intrusion of synkinematic granitoids under amphibolite facies conditions and retrogression of granulite facies assemblages this thrusting post dates the 2800 ma granulite facies metamorphism it is younger and distinct from the thrusting postulated to explain the intercalation of the early archaean amitsoq gneisses and the mid archaean malene supracrustal rocks associated with intrusion of the nuk gneiss precursors described from godthabsfjord the tectonic breaks provide for the first time marker horizons which can be used to assess the amount and type of late archaean deformation in the southern godthabsfjord region

silurian k bentonites of the dnestr basin podolia ukraine the dnestr basin of podolia ukraine is an epicratonic basin consisting of neritic carbonate and calcareous mudstone facies including a nearly complete silurian sequence ranging from late llandovery to late pridoli in age the silurian section has served as a standard for regional and interregional studies as a consequence of its well documented macro and microfaunal assemblages approximately 24 mid to late silurian k bentonites are present in this succession and their lateral persistence has aided in establishing regional correlations the k bentonites range from 1 to 40 cm in thickness and occur in the bagovitsa late wenlock malinovtsy ludlow and skala pridoli formations discrimination diagrams based on immobile trace elements together with rare earth element data suggest the k bentonites had a volcanic origin in a collision margin setting related to subduction thickness and stratigraphic distribution considerations are consistent with a source area in the rheic ocean

biogeology how old are bacteria from the permian age hazen and roedder touch on several geological issues raised by our limited description of the permian salado formation in our study we sampled coarse halite in dissolution pipes for testing for viable permian age bacteria

synsedimentary dissolution pipes and the isolation of ancient bacteria and cellulose coarse clear halite from synsedimentary dissolution pipes in the permian salado formation in southeastern new mexico usa yielded viable halotolerant bacteria and well preserved cellulose believed to be permian in age here we show that geologic and hydrologic conditions have isolated these rocks since permian time pipes were dissolved most likely along cracks created by thermal contraction or desiccation and the boundaries of salt polygons saucers on exposed salado formation salt pan surfaces down to the level of the water brine table macropores developed at the brine level in some horizons as the water level rose coarse halite cemented the open space fluid inclusions millimeter scale trapped bacteria which were probably in a spore state as well as cellulose inclusion water from pipes in some cycles may have isotopic values reflecting permian meteoric water while other cycles may show evaporated permian seawater exposure surfaces are more prominent in the upper part of salado formation depositional cycles due to basin desiccation as indicated by cracks and dish shaped laminae clays were concentrated on many exposure surfaces by floods wind and dissolution dissolution pipes formed from these surfaces and a synsedimentary age is confirmed by undisturbed overlying halite beds salado formation halite has very low permeability 10 22 m 2 effectively preventing significant fluid flow and passage of fluids through the formation either to recrystallize salt or to introduce modern bacteria stratigraphic relationships halite textures fluid inclusion chemistry and hydraulic properties are all consistent with a synsedimentary origin of the dissolution pipes their crystals and the bacteria and cellulose recovered from the salado formation

high resolution late silurian correlations between gotland sweden and the broken river region ne australia lithologies conodonts and isotopes high resolution correlations partly with a precision better than 10 ka are achieved between late ludfordian sequences on gotland sweden on baltica and a section cog through the coral gardens formation along the broken river northeastern australia on gondwana despite these sections having been on different palaeocontinents facing different oceans the interval is characterised by rapid very large faunal isotopic and lithologic changes lithologies are remarkably similar in the two areas consisting of in order from below marls with thin limestone beds flaggy limestones oncoidal crinoidal limestone oncoidal marls terrigenous clastics silty clay mudstone sandstone oolite and cliff gorge forming limestones further independent correlation dates several of the lithological changes as coeval the 813 c excursion in whole rock carbonates is one of the three largest ones known during the phanerozoic the increase in delta c 13 is very similar in the two areas from below 1 parts per thousand to c 9 parts per thousand vpdb though two gotland samples yielded 9 71 parts per thousand and 10 54 parts per thousand the corresponding cog interval included fewer carbonate layers than needed to definitely exclude that this difference is due to a lack of suitable rocks for sampling compared with the lithologies and the delta c 13 curves the conodont faunas display some divergence but key taxa permit precise correlations for much of the studied interval the conodont assemblages change stepwise from very diverse in the polygnathoides siluricus zone to a low diversity fauna dominated markedly by a single taxon upper icriodontid subzone returning abruptly to a comparatively diverse ozarkodina snajdri zone fauna a method resembling graphic correlation in some respects is used to propose a similarly high resolution correlation through a longer interval for future testing c 2006 elsevier b v all rights reserved less

origin and geochemistry of formation waters from the lower eagle ford group gulf coast basin south central texas abstract the lower eagle ford group lefg is one of the most productive continuous hydrocarbon plays in the united states but few associated produced waters data and minimal interpretation have been published this effort focuses on results from compositional and isotopic data from 39 produced water samples collected from horizontal wells producing from the lefg in south central texas the depth of the lefg increases by approximately 1 km across the study area from northwest 2 9 km to southeast 3 9 km associated increases in calculated reservoir temperature 125 165 c development of reservoir over pressuring 400 800 bars total pressure and increased thermal maturity heavy oil to gas condensate also occur along this trend produced water salinity starts at nearly 100 g l in the shallowest samples and decreases linearly with depth to

the origin of fluids in the salt beds of the delaware basin new mexico and texas abstract oxygen and hydrogen isotope analyses have been made of 1 brines from several wells in the salt deposits of the delaware basin 2 inclusion fluids in halite crystals from the erda no 9 site and 3 local ground waters of meteoric origin the isotopic compositions indicate that the brines are genetically related and that they probably originated from the evaporation of paleo ocean waters although highly variable in solute contents the brines have rather uniform isotopic compositions the stable isotope compositions of brine from the erda no 6 site 826 3 m depth and fluid inclusions from the erda no 9 site are variable but remarkably regular and show that 1 mixing with old or modern meteoric waters has occurred the extent of mixing apparently decreasing with depth and 2 water in the erda no 6 brine may have originated from the dehydration of gypsum alternatively the data may reflect simple evaporation of meteoric water on a previously dry marine flat stable isotope compositions of all the waters analyzed indicate that there has been fairly extensive mixing with ground water throughout the area but that no significant circulation has occurred the conclusions bear importantly on the suitability of these salt beds and others as repositories for nuclear waste

graptoloid evolutionary rates track ordovician silurian global climate change graptoloid evolutionary dynamics show a marked contrast from the ordovician to the silurian subdued extinction and origination rates during the ordovician give way during the late katian to rates that were highly volatile and of higher mean value through the silurian reflecting the significantly shorter lifespan of silurian species these patterns are revealed in high resolution rate curves derived from the conop constrained optimization scaled and calibrated global composite sequence of 2094 graptoloid species the end ordovician mass depletion was driven primarily by an elevated extinction rate which lasted for c 1 2 ma with two main spikes during the hirnantian the early silurian recovery although initiated by a peak in origination rate was maintained by a complex interplay of origination and extinction rates with both rates rising and falling sharply the global 13 c curve echoes the graptoloid evolutionary rates pattern the prominent and well known positive isotope excursions during the late ordovician and silurian lie on or close to times of sharp decline in graptoloid species richness commonly associated with extinction rate spikes the graptoloid and isotope data point to a relatively steady marine environment in the ordovician with mainly background extinction rates changing during the katian to a more volatile climatic regime that prevailed through the silurian with several sharp extinction episodes triggered by environmental crises the correlation of graptoloid species diversity with isotopic ratios was positive in the ordovician and negative in the silurian suggesting different causal linkages throughout the history of the graptoloid clade all major depletions in species richness except for one were caused by elevated extinction rate rather than decreased origination rate

the strontium isotopic composition of ordovician and silurian brachiopods and conodonts relationships to geological events and implications for coeval seawater utilized for strontium isotope measurements the results document a gradual decrease in 87 sr 86 sr from 0 7091 to 0 7087 from tremadoc to llandeilo a sharp decline to 0 7078 during the late llandeilo early caradoc little change during caradoc and the ashgil and a steady rise to 0 7087 through the silurian these long term 10 7 yr variations with magnitudes in the range of 10 23 are interpreted to be controlled primarily by continental collisional tectonics and its associated erosion and weathering the gradual decrease in 87 sr 86 sr ratio during the early ordovician may record the reduction in uplift and weathering rates due to waning of the pan african orogenies the rapid decline near the llandeilo caradoc boundary suggests a strong hydrothermal flux likely due to increased sea floor spreading and a possible superplume event the latter may have caused the prominent transgressive phase the largest in the phanerozoic which would have muted continental flux input although the caradoc was the main interval for the taconic orogeny its impact on the sr continental flux may have been delayed until the early llandovery this effect complemented by reworking of glacial deposits near the ordovician silurian boundary and enhanced by phases of the silurian salinic orogeny may have combined to give the progressive increase in the strontium isotope ratio through the silurian the scale and directionality of these changes makes the strontium isotope curve valuable for dating and correlation purposes copyright 1998 elsevier science ltd

fluctuations in epeiric sea carbonate production during silurian positive carbon isotope excursions a review of proposed paleoceanographic models positive excursions in the carbon isotopic ratio of marine carbonates 13ccarb are commonly attributed to an increase in the burial ratio of organic versus carbonate carbon in the global oceans regardless of whether this increased deposition of organic carbon was oceanographically or biologically induced the fact that high carbon isotope values are most often attributed to the sequestration and burial of organic carbon remains the notion that high 13ccarb values should be the result of organic rich deposition in epeiric sea settings is not surprising considering that the overwhelming majority of organic carbon burial in the modern oceans occurs in continental shelf and margin settings what is surprising is that major positive carbon isotope excursions during the silurian are recorded in clean carbonate successions with little to no appreciable black shale deposition in epeiric seas in fact silurian 13ccarb excursions occurred during intervals of prolific reef development and an overall expansion of carbonate platform environments globally this discrepancy has sparked considerable debate among silurian carbon isotope specialists but has offered a valuable opportunity to re examine the intricate connections among nutrients primary productivity carbonate sedimentology and the global carbon cycle in the lower paleozoic here we consider several sedimentological and geochemical features of one of these silurian positive carbon isotope 13ccarb excursions and discuss the broader implications of current silurian 13ccarb models to the interpretation of lower paleozoic carbonate sequences

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

a revised 87sr 86sr curve for the silurian implications for global ocean chemistry and the silurian timescale abstractrecent recalibration of the silurian timescale and improved global chronostratigraphic correlation of silurian strata significantly altered the silurian 87sr 86sr curve and the temporal extent of available data whereas previous silurian 87sr 86sr composites showed a generally monotonic increase throughout the silurian revisions to the silurian timescale now require a major increase in the rate of change in 87sr 86sr at or near the onset of the gorstian age of the ludlow epoch similarly improved chronostratigraphic correlations between silurian outcrops on anticosti island canada and gotland sweden indicate that the middle part of the telychian age which is roughly 10 15 of the total duration of the silurian period is undersampled and underrepresented in silurian 87sr 86sr composites a revised silurian 87sr 86sr curve based on 241 new and published analyses confirms the significant increase in the rate of change of 87sr 86sr toward more radiogenic values near the base of the ludlow ser

u pb zircon age constraints on the timing and duration of wenlock silurian paleocommunity collapse and recovery during the big crisis high precision isotope dilution u pb zircon dating was conducted on three volcanic ash fall bentonite samples from the swedish island of gotland and on a fourth bentonite from the west midlands england zircons from the ireviken grotlingbo djupvik gotland and wren s nest hill 15 west midlands bentonites yielded weighted mean pb 206 u 238 ages of 431 83 0 23 0 67 ma 428 45 035 0 73 ma 428 06 0 2110 66 ma and 427 86 032 0 71 ma respectively analytical total uncertainties these biostratigraphically well controlled age dates effectively bracket the wenlock epoch of the silurian period and provide control for the duration of one of the major paleozoic biotic events and associated perturbations to the global carbon cycle the big crisis or lundgreni event graptolites the niulde event conodonts the mulde excursion carbon isotopes these new data suggest an older and shorter duration for the recalibration of the wenlock series and demonstrate that the cascade of biological and chemical events that took place during the big crisis happened on time scales of tens to hundreds of thousands of years less

ordovician and silurian sea water chemistry sea level and climate a synopsis following the cambrian explosion and the appearance in the fossil record of most animal phyla associated with a range of new body plans the ordovician and silurian periods witnessed three subsequent major biotic events the great ordovician biodiversification event the end ordovician extinction the first animal extinction and second largest of the five mass extinctions of the phanerozoic and the early silurian postextinction recovery there are currently no simple explanations for these three major events combined extrinsic geological and intrinsic biological factors probably drove the biodiversifications and radiations and the appearance and disappearance of marine habitats have to be analysed in the frame of changing palaeogeography palaeoclimate and sea water chemistry the present paper reviews the relationships of the three biotic events to chemical and physical processes occurring in the ocean and atmosphere during the ordovician and silurian including sea level changes geochemical proxies 13c 18o 87sr 86sr of the ocean waters and the evolution of the atmosphere oxygen and carbon dioxide content less

interpreting carbon isotope excursions carbonates and organic matter abstract variations in the carbon isotopic compositions of marine carbonate and organic carbon provide a record of changes in the fraction of organic carbon buried through time and may provide clues to changes in rates of weathering and sources of organic carbon paired carbonate and organic carbon isotope determinations provide a possibility of interpreting not only changes in the global carbon cycle through time but changes in atmospheric pco2 as well interpretations of these types of data are typically rather qualitative a quantitative basis is required to develop a better understanding of changes in the carbon cycle for this purpose we employ a simple model of the global carbon cycle which is subjected to a number of different perturbations each lasting 500 ky i e much longer than the residence times of carbon and phosphorus in the ocean atmosphere system in addition to standard considerations of carbon mass and isotopic fluxes to the ocean atmosphere system from weathering and volcanism and fluxes of organic carbon and carbonate carbon to sediments the model incorporates sensitivity of the photosynthetic carbon isotope effect to changes in pco2 the inclusion of this parameter leads to unexpected carbon isotope responses to forcing that causes increased rates of organic carbon burial a series of simple to more complex simulations illustrates the significant effects of varying differences between the carbon isotopic composition of sedimented carbonate and organic carbon b with constant b a 50 increase in organic carbon burial produces a parallel increase in carbonate and organic carbon isotopic compositions however the same simulation with b responsive to pco2 changes produces an initial parallel 13 c increase but this is followed by an even greater 13 c enrichment in organic carbon because pco2 falls in response to increased organic carbon burial the counterintuitive overall result of the enhanced organic carbon burial event is that the carbonate carbon isotopic composition actually decreases because of the more substantial increase in 13 c org in addition we illustrate the effects on carbon isotopic compositions of the oceanic inorganic carbon reservoir and buried organic matter of a 50 increase in volcanic co2 outgassing a 50 increase in weathering rate with coupled phosphate and riverine carbon flux responses a 50 decrease in shale associated organic carbon weathering a 50 decrease in silicate weathering rate and the possible effects of the rise in abundance of c4 plants in the late miocene to recent we compare the model simulated carbon isotopic responses for some of these experiments to paired carbonate and organic carbon records to illustrate how these records might be interpreted in light of the model response

origin and evolution of formation waters from oil fields on the norwegian shelf abstract stable isotopes of h and o and chemical analyses of formation waters from upper triassic jurassic clastic reservoirs and cretaceous carbonate reservoirs offshore norway are employed to interpret the origin and evolution of these waters in both types of reservoir the formation waters become progressively enriched in total dissolved solids and the heavy isotope of o with increasing depth whereas deuterium varies erratically between 20 and 40 smow bromine analyses and stable isotope data indicate that the formation waters are mixtures of a brine end member formed by evaporation of sea water beyond the point of halite saturation and meteoric water the chemical and isotopic composition of the formation waters and general geological considerations suggest that the brines originated as connate waters in permian evaporites and were later expelled into overlying strata there is a disequilibrium stable isotope distribution between the bulk chalk formations and the formation waters and only minor diagenetic modification of the formation waters appears to have taken place in these reservoirs the formation waters from the clastic reservoirs on the other hand are modified by diagenetic reactions