carbon isotopes stratigraphy and environmental change the middle upper cambrian positive excursion spice in port au port group western newfoundland canada in many basins upper cambrian carbonate successions display intervals with a positive carbon isotope excursion cie of up to 5 in north america this marks the boundary between the sauk ii iii super sequences a steptoean positive carbon isotope excursion spice locality previously identified in the port au port peninsula western newfoundland has been revisited and an additional potential spice locality found in both locations a cie is found to be associated with a prominent bioherm and sandstone layer within a sequence of carbonate rocks at march point columnar stromatolites occur whereas at felix cove thrombolites can be seen in the latter the sandstone immediately overlies the thrombolites coincident with the cie whereas at march point a dolomitized grainstone occurs above the stromatolites the sandstone at this locality post dates the cie although lower than the spice in some localities a positive cie is present in both sections march point 1 1 and felix cove 1 8 additional

climatic control on the late permian main dolomite ca2 deposition in northern margin of the southern permian basin and implications to its internal cyclicity

hypersaline burial diagenesis delineated by component isotopic analysis late paleozoic limestones west texas abstract pennsylvanian to lower permian cyclic platform carbonates from the southwest andrews area of west texas are now 3 km below the land surface isolated samples of brachiopod shell zones of calcite cement and saddle dolomite from limestone cores of the southwest andrews oilfields have been analyzed isotopically to determine if 1 diagenesis is dominated by early meteoric processes as suggested by bulk rock isotopes 2 whether significant burial diagenesis occurred in hypersaline waters and 3 whether most burial cements are allochthonous or internally derived bulk isotopic analyses of limestones show systematic variation in 13c and 18o according to length of subaerial exposure and stratigraphic position chemically zoned calcite cements show four growth stages stage 1 and 2 cements have average 13c values of 4 6o oo and average 18o of 5 0o oo and most are interpreted to have precipitated during subaerial exposure in meteoric water a few stage 1 cements with average 13c values of 4 7o oo and 18o of 1 4o oo apparently precipitated below the sediment surface from modified seawater in a sulfate reduction zone stage 3 and 4 calcite cements precipitated after compaction and compose up to 25 of the total rock volume they have 13c values 0 2o oo to 4 4o oo that vary according to stratigraphic position and are similar to bulk rock samples of the host limestone the 13c values indicate local derivation by dissolution of adjacent rock the 18o values of stage 3 and 4 cement 5 5o oo to 3 5o oo are indistinguishable from stages 1 and 2 cements precipitated from meteoric water the decrease in 18o expected from elevated temperatures during burial present formation temperature of 55 c is negated by precipitation from a late permian brine with 18o values of 5o oo stages 3 and 4 calcite and saddle dolomite cements have 87sr 86sr values that are lower than 87sr 86sr values for contemporaneous marine carbonate 0 70830 this is probably due to incorporation of sr with low 87sr 86sr values 0 70672 to 0 70682 also from the late permian hypersaline brine the southwest andrews area has several diagenetic features that are probably more common in ancient limestone than previously recognized 1 burial cements have 18o values similar to meteoric cements when precipitated from hypersaline waters with 18o values 5o oo greater than contemporary seawater 2 deep burial cements have 13c values similar to the bulk rock because carbon is derived from pressure dissolution of nearby carbonate 3 bulk rock isotope values are characteristic of marine limestones subjected to meteoric diagenesis even though they have suffered substantial deep burial diagenesis this study clearly illustrates the value of analyzing diagenetic components to accurately understand porosity evolution in limestones

spatial variability of watermass conditions within the european epicontinental seaway during the early jurassic pliensbachian toarcian in order to constrain spatial variability in watermass conditions within the european epicontinental seaway prior to during and after the toarcian oceanic anoxic event carbon 13cbel 13ccarb and oxygen 18obel 18ocarb isotope records were obtained from three sections in the grands causses basin southern france these data were then compared with similar records along a north south transect across the european epicontinental seaway as the conclusions reached here strongly depend on the reliability of belemnite calcites as archives of palaeoceanographic changes an attempt was made to improve the understanding of isotope signals recorded in belemnite calcite intra rostral carbon and oxygen isotope data from six belemnite specimens belonging to the genus passaloteuthis were collected intra rostral carbon isotopes are influenced by vital effects whereas oxygen isotopes reflect relative changes in temperature and salinity palaeotemperatures calculated from 18obel isotope records from the grands causses basin confirm relatively low temperatures throughout the late pliensbachian similar cool water conditions have previously been shown in germany england spain and portugal a temperature increase of up to 6 c is observed across the pliensbachian toarcian boundary a pronounced negative shift of at least 3 vienna pee dee belemnite is recorded in bulk carbonate carbon during the lower harpoceras serpentinum zone typical of the toarcian oceanic anoxic event before and after the toarcian oceanic anoxic event a good correlation between 13ccarb and 13cbel exists indicating well ventilated bottom waters and normal marine conditions instead data for the toarcian oceanic anoxic event indicate the development of a strong north south gradient in salinity stratification and surface water productivity for the western tethyan realm this study thus lends further support to a pronounced regional overprint on carbon and oxygen isotope records in epicontinental seaways

δ13c stratigraphy of a turinian chatfieldian upper ordovician foreland succession ottawa embayment central canada resolving local and inter regional isotope excursions in a tectonically active basin abstract positive 13ccarb excursions are correlated through an upper turinian to lower chatfieldian carbonate platform succession along the axis of the ottawa embayment and into outliers of the northern ottawa bonnechere graben in central canada successive turinian excursions e1 and e2 are lithostratigraphically constrained by erosional surfaces and hosted within the watertown and overlying l orignal formations respectively the latter coeval with the selby formation in the adjacent northern appalachian basin the excursions coincide with periods of regional transgression but geographic patterns of 13c depletion versus enrichment coincide with structurally defined areas of stratigraphically condensed and preferentially thickened formation successions respectively differential subsidence is interpreted to have created bathymetric variation resulting in intrabasinal restriction of seawater exchange between these areas with preferential corg recycling with stratigraphic condensation by early chatfieldian time segmentation of the once regional carbonate platform l orignal formation produced a regional mosaic of low energy muddy carbonate banks rockland formation and a deeper water platform lower hull formation settings subject to fluctuating high to low energy current flow excursion e3 occurs in both successions but 13c enrichment is associated only with the bank top muddy facies this may identify preferential photosynthetic drawdown of 12c across the bank tops due to limited seawater exchange across the bank deeper platform boundaries excursions e1 to e3 and a younger excursion e4 in the hull formation are correlated with varying confidence with excursions across southern laurentia excursion e3 being the local expression of the guttenberg 13c excursion our study supports local modulation of regional if not global 13c excursions arising from structurally controlled changes in oceanography and productivity

is mid late paleozoic ocean water chemistry coupled with epeiric seawater isotope records isotopes of epeiric sea carbonates are used to construct seawater records for modeling global changes in paleozoic ocean chemistry climate and for intercontinental correlation we present for the first time geochemical results of paleozoic brachiopods biogenic low mg calcite blmc from open ocean permian carboniferous seamounts of japan situated in the tropical mid panthalassic ocean strontium isotope values of blmc from the panthalassic and paleotethys oceans are coupled with those of coeval specimens from epeiric seas of north america europe and russia p 0 393 but not with those of epeiric sea whole rocks matrix aragonite calcite mac p 0 029 and conodonts biogenic apatite ba p 0 031 oxygen isotope values of blmc from the panthalassic and paleotethys exhibit mixed results with studies of counterparts from epeiric seas p 0 596 reflecting overprinting of local environmental conditions on global trends carbon isotope values of blmc and mac from the panthalassic and paleotethys oceans are generally dissimilar to those of coeval material from epeiric seas of north america europe and russia p 0 001 and 0 002 respectively factors such as water mass stratification evaporation dilution depth temperature carbon burial and or oxidation variations and syndepositional diagenesis within the local environment probably influenced the chemistry of the fauna and accumulating sediments this decoupling of carbon and oxygen isotope values from the open ocean with those from epeiric seas makes questionable the use of isotope results from epeiric seas for international correlation constructing global seawater records determining fluxes in the global carbon cycle and for modeling climate changes and subsequently atmospheric carbon dioxide levels

spatial variation in carbonate carbon isotopes during the cambrian spice event across the eastern north china platform abstract the cambrian spice steptoean positive carbon isotope excursion event is widely reported from the late miaolingian to the early furongian but recent studies imply that the synchroneity and magnitude of the spice may be controversial in order to test the spatial variation of the spice here we present 367 carbonate 13c data from six outcrop sections across a 700 km transect along the eastern north china platform the spice is present in all the studied sections but showing different features regarding the duration and magnitude an abrupt increase in 13c from 1 5 to 3 5 occurs in three shandong sections with maximum value present only in a thin 0 5 1 2 m thick transgressive lag deposit crudely wave stratified bioclastic grainstone in contrast the 13c record of the baijiashan and shashan sections in the liaoning region displays a gradual increase 20 m thick from 1 5 to the maximum value of 4 7 both facies analysis and trilobite collections suggest that the spatial variation of the spice in the north china platform most likely resulted from missing of sedimentary record with high 13c values in the shandong sections as a result of erosion and non deposition during sea level lowstand a possible coeval hiatus prior to the sauk iii transgression in the laurentian basins further high resolution integrated studies of sedimentology biostratigraphy and sedimentary geochemistry on the spice event are required to better understand its nature

platform drowning leading to cool water carbonate deposition evolution of a late ordovician turinian chatfieldian mixed sediment platform within the taconic orogen long point group newfoundland appalachians late ordovician turinian chatfieldian drowning of a mixed carbonate siliciclastic platform within the taconic orogen newfoundland appalachians is recorded by net deepening of an initial warm shallow water platform succession lourdes formation culminating in a metre scale thick condensed interval that characterizes a drowning succession punctuated by storm deposits composition of transported material suggests that seaward drowning was coupled with back stepping of a high energy carbonate factory related to hinterland uplift and erosion that would eventually lead to drowning of the outer platform beneath marine transported siliciclastic sediments winterhouse formation in the new offshore shelf setting a sparse reciprocal stratigraphy of fine to very coarse grained phosphatic carbonate and mixed sediment is interpreted to document gravity flow deposition downgradient from either a sustained or episodically developed high energy cool water carbonate source along the inner shelf transported carbo

sea water circulation on an oolite dominated carbonate system in an epeiric sea middle jurassic switzerland the middle jurassic burgundy carbonate platform occupied a central part of the central european epeiric sea during the middle jurassic the facies architecture of the oolitic calcarenite bodies was affected by tidal currents on the platform and relative sea level changes the 13c values of inorganic carbonates sampled in biostratigraphic defined intervals do not match very well between closely spaced sections and hence are of restricted use for stratigraphic purposes it appears that the platform interior might have been decoupled from the global carbon pool although deposited in a rapidly accumulating setting the recorded isotope signatures might be affected by some local stratigraphic gaps nonetheless the carbon isotope data imply lateral changes of the platform waters these appear to be related to the position on the platform and to the sediment dispersal pattern as evidenced by clay minerals adjacent to the eastern margin of the platform detrital chlorite and illite occur in considerable proportions both ascribed to a boreal source to the east and the north east in contrast smectite rich mixed layer clay mineral content increases significantly towards the platform interior pointing to a delivery from the north west all these data are suggestive of an overall clockwise current pattern in the central european epeiric sea during the middle jurassic

deciphering the impact of diagenesis overprint on negative δ13c excursions using rock magnetism case study of ediacaran carbonates yangjiaping section south china rock magnetism is used here to investigate the genesis of one of the puzzling negative carbon isotopic excursions of the neoproterozoic in the yangtze platform south china a detailed characterization of the magnetic mineralogy which includes low temperature and high field magnetometry and classical magnetic measurement arm irm susceptibility was therefore performed along upper doushantuo and lower dengying formations outcropping in the yangjiaping section the derived magnetic parameters show variations that can be interpreted as variations in magnetic grains size and in oxide contents they show that the magnetic content is significantly reduced in samples presenting negative 13ccalcite values we interpret this as a result of magnetite dissolution and secondary carbonate precipitation during early diagenesis bacterial sulfate reduction combined with c and o isotopic data paleomagnetic techniques thus show that the upper doushantuo lower dengying negative excursion of the yangjiaping section is largely due to diagenesis although the preservation of a genuine 13c excursion of lower magnitude from 7 down to 0 instead of down to 9 as usually considered cannot be ruled out a corrected 13ccarbonate chemostratigraphic curve is therefore proposed the unambiguous identification of a strong diagenetic component for this excursion casts doubts on the primary nature of other potentially time equivalent negative excursions of the yangtze platform and thus to its correlation to negative excursions in other cratons i e shuram excursion more generally this study illustrates the potential of magnetic mineralogy characterization a low cost time efficient and non destructive technique as screening tool for diagenetic overprints of 13c and 18o

detailed 3 d depositional architecture of late jurassic carbonate anhydrite cycles brightling mine weald basin uk abstract quantifying the geometries of evaporite deposits at a 13 c and 18 o isotope analysis the stratigraphic interval contains five facies in stratigraphic order these include supratidal porphyritic nodular evaporite shallow subtidal peloidal packstone with evaporite and two overlying rhythmic sequences of intertidal microbial laminite subtidal shale and subtidal laminar marl capped by nodular anhydrite the interpreted environment of deposition is a supratidal sabkha subject to periodic flooding in which intertidal tidal flat facies and subtidal shallow marine facies laterally passed into the evaporative sabkha the cycles are interpreted as meter scale shoaling upward sequences likely controlled by localized high frequency changes in relative sea level and or sabkha hydrology spatial patterns in the geometries of key stratigraphic surfaces reveal a subtle depression towards the central western region of the mine seam the variation in stratal geometries is interpreted as paleotopography and is a function of individual or composite processes related to dissolution eolian processes and coastal erosion these observations indicate a similar mode of deposition to the modern day sabkha of the persian gulf we conclude that the dynamic process of evaporite deposition led to subtle stratigraphic heterogeneities and changes in bed thicknesses but largely continuous lateral bedding at an interwell scale

response of larger benthic foraminifera to the paleocene eocene thermal maximum and the position of the paleocene eocene boundary in the tethyan shallow benthic zones evidence from south tibet

carbon isotope records in a mesoproterozoic epicratonic sea carbon cycling in a low oxygen world abstract carbon isotope profiles of sedimentary strata are widely used as both a tool for stratigraphic correlation and as a mechanism for inferring important changes in earth s biogeochemical cycles chemostratigraphic interpretations however often rely on the assumption that the isotopic composition of dissolved inorganic carbon dic in the surface oceans is broadly homogeneous at times of globally high sea level when epicratonic epeiric environments dominate our sedimentary record carbon isotope records reveal substantial lateral variability here we investigate lateral variability in the marine carbon isotope record from pericratonic to epicratonic environments of the mesoproterozoic 1 1 ga atar el mreiti groups of the taoudeni basin west africa restricted marine epicratonic environments are consistently 2 4 lighter than open marine pericratonic environments suggesting input of an isotopically light carbon source that preferentially affected epicratonic environments in contrast to epicratonic environments in the paleozoic where input of isotopically light carbon is generally attributed to input of terrestrial organic matter we suggest that in situ remineralization of organic carbon via anaerobic microbial cycling drove observed isotopic variability within epicratonic el mreiti group strata the extent of organic matter remineralization and thus degree of 13 c depletion is correlated with water depth and associated with distinct differences in both total organic carbon toc and pyrite concentration suggesting a potential linkage to both the persistence of anoxia and the availability of sulfate within epicratonic environments in such settings the isotopic effects of organic carbon remineralization are potentially enhanced by either methane oxidation following methanogenic decomposition or the intermittent oxidation of an enhanced dissolved organic carbon doc pool

structure and magnitude of the carbon isotope excursion during the paleocene eocene thermal maximum abstract the paleocene eocene thermal maximum petm was a geologically rapid and transient warming event that occurred ca 56 million years ago ma it was associated with a pronounced negative carbon isotope excursion cie and with profound changes in the atmosphere hydrosphere and biosphere this event reflects injections of large amounts of carbon into the atmosphere ocean system but whether single or multiple episodes of carbon release caused this event is uncertain here we present carbon isotope data of bulk carbonate from two parallel limestone sections at tingri south tibet where the limestone was deposited on a tropical carbonate ramp during the petm carbon isotope data of bulk carbonate from both sections are almost identical displaying an expanded stepped cie profile with large magnitude the stepped cie profile consists of three discrete intervals of decreasing carbon isotope values which can be correlated on an inter regional scale between sections from different depositional environments lake carbonate ramp continental slope and open ocean the consistency of these correlations implies occurrence of at least three carbon releases within the cie and indicates complex processes of carbon injection during the petm moreover the cie magnitude of 7 recorded at tingri is tentatively interpreted to reflect carbon isotope changes in the atmosphere and the surface ocean which is larger than the generally accepted value of 4 but is still within the range of some previous records

upper ordovician mohawkian carbon isotope δ13c stratigraphy in eastern and central north america regional expression of a perturbation of the global carbon cycle abstract the guttenberg carbon isotope excursion gice documented from eastern north america demonstrates the effects that regional geochemically distinct water masses upwelling and ocean circulation have on the carbon isotope record from carbonate platforms late turinian chatfieldian carbonates from oklahoma kentucky virginia and west virginia record a positive carbon isotope excursion 3 0 the gice excursion the gice excursion has relations to established biostratigraphy beginning in the north american midcontinent phragmodus undatus conodont zone and continuing through the plectodina tenuis zone sequence and event stratigraphy previously established models for positive carbon isotope shifts on carbonate platforms have been tested during the gice excursion where geochemically distinct water masses are defined for the upper ordovician a major eustatic sea level rise before the gice promoted a greater exchange of open ocean waters onto the carbonate platform of laurentia however restricted or sluggish circulation and exchange between water masses within the epeiric seas and the adjacent iapetus ocean were still apparent local variations documented in the gice excursion are directly related to upwelling of nutrient rich isotopically light waters increased primary productivity and the subsequent organic carbon production and burial

carbon and oxygen isotope stratigraphy of the early cretaceous carbonate platform of pădurea craiului apuseni mountains romania a chemostratigraphic correlation and paleoenvironmental tool abstract stable c and o isotope records were obtained from carbonate rocks spanning the hauterivian to cenomanian interval collected in several sections from the carbonate platform of p durea craiului apuseni mountains romania in the absence of some key biostratigraphic marker species stable isotopes were applied as a tool for stratigraphic correlation and dating the composite 13c and 18o curves for the early cretaceous shows variable conditions with large positive and negative excursions and provide information on past environmental changes the hauterivian and the barremian limestones blid formation display lower 13c values 2 8 to 2 9 relative to the aptian albian deposits 2 6 to 5 4 ecleja valea m gurii and v rciorog formations the red detrital formation albian cenomanian is characterized by a highly variable distribution of the 13c values 3 5 to 3 9 based on the similarities between the c isotope curve established in p durea craiului and from other sections in the tethyan and the pacific regions two major oceanic anoxic events characterized by 13c positive excursions were clearly recognized the first is the oae1a event early aptian in the upper part of the ecleja formation and the valea m gurii formation the second is the oae1b event late aptian albian in the upper part of the v rciorog formation and in the subpiatr member the position of the aptian albian boundary is estimated to be at the upper part of the v rciorog formation immediately after the beginning of the 13c positive excursion the 13c data show major negative excursions during the barremian blid formation early aptian ecleja formation and late aptian v rciorog formation the o isotope variation pattern 10 2 to 2 1 is consistent with progressively warming temperatures during the early barremian followed by a cooling period a subsequent warming period culminated in the early aptian a significant cooling phase corresponds to the late aptian and early albian and the climate cooled again during the late albian and into the early cenomanian stage the data provide a better understanding of the early cretaceous sedimentation cycles in p durea craiului and create a more reliable framework for regional correlations

transvaal supergroup carbonates implications for paleoproterozoic δ18o and δ13c records abstract the paleoproterozoic interval is characterized by the first evidence for incontrovertibly free oxygen in the ocean atmosphere system in this study carbonates from the transvaal group the silverton lucknow rooinekke and particularly the duitschland formations were analyzed for isotopes of carbon oxygen and strontium in order to constrain models dealing with the patterns of seawater evolution although the trace element data showed variable alteration of the carbonate samples selected samples with a lesser degree of alteration yielded interpretable results the best measured 87sr 86sr isotope value of 0 7031 at 2 35 ga ago fits well with the published curve for precambrian seawater confirming that paleoproterozoic budget of sr was dominated by input from continental sources during the paleoproterozoic times carbonates with 13c values of about 10 are known to have been present worldwide and they have been studied also during this research the observation that in the duitschland formation such high isotope values and normal marine values were both present within a single formation indeed within its single beds suggested that the large spread of 13c values reflects local or regional rather than global phenomena the oxygen isotope data show a large spread of values from 3 to 16 while their corresponding 13c signals are almost unchanged over this entire range with the lucknow and silverton formations clustering around 10 and the rooinekke formation around 2 the duitschland formation has a bimodal distribution with both 13c populations present the last formation also contains samples with 18o as low as 20 particularly in the vicinity of the bushveld intrusive body these highly 18o depleted samples show homogenization of 13c values towards 5 modelling suggests that the trends could have resulted from post depositional alteration by basinal fluids at near surface to about 50 c temperatures in a rock buffered system the duitschland formation samples particularly at duitschland farm the locality closest to the bushveld complex were then further altered at temperatures up to about 80 c in response to this intrusion

a critical assessment of mollusk 18 o 16 o mg ca and 44 ca 40 ca ratios as proxies for cretaceous seawater temperature seasonality seasonal temperature fluctuations of tethyan coastal water are recorded in a pristine 80 my old rudist shell from turkey in order to critically assess factors other than seawater temperature that might have influenced the shell geochemical record three different paleo temperature proxies 18o mg ca and 44ca were applied in a qualitative manner all three proxies reflect the same cyclical trends and thus yield robust evidence for seasonal fluctuations in late cretaceous surficial seawater temperature this suggests the successful application of the new 44ca temperature proxy to fossil mollusk calcite the direct comparison of the three data sets however demonstrates that all proxies are fraught with problems similar to other studies 18o 16o ratios point to warmer summer temperature maxima than those in comparable costal settings today nevertheless the 18o 16o proxy is subject to environmental factors that might lead to an overestimation of peak temperatures moreover mg ca molar ratios are less sensitive to environmental factors but were strongly affected by the ion regulating capability of the rudist bivalve that responded to the low mg ca ratio of cretaceous seawater similarly uncertainties of the 44ca composition of cretaceous seawater and the complex bio calcification of mollusks presently limit the interpretation of 44ca values in terms of absolute seawater temperature the multiproxy approach applied here however documents that these limitations do not obscure the dominant patterns of seasonal sea surface temperature variations recorded in the biogeochemical rudist archive

ca and mg isotope constraints on the origin of earth s deepest δ13c excursion abstract understanding the extreme carbon isotope excursions found in carbonate rocks of the ediacaran period 635 541 ma where 13 c of marine carbonates 13 c carb reach their minimum 12 for earth history is one of the most vexing problems in precambrian geology known colloquially as the shuram excursion the event has been interpreted by many as a product of a profoundly different ediacaran carbon cycle more recently diagenetic processes have been invoked with the very negative 13 c values of ediacaran carbonates explained via meteoric alteration late stage burial diagenesis or growth of authigenic carbonates in the sediment column thus challenging models which rely upon a dramatically changing redox state of the ediacaran oceans here we present 257 44 40 ca and 131 26 mg measurements along with mg mn and sr data from carbonates of the ediacaran aged wonoka formation fm of south australia to bring new isotope systems to bear on understanding the shuram excursion data from four measured sections spanning the basin reveal stratigraphically coherent trends with variability of 1 5 in 26 mg and 1 2 in 44 40 ca this ca isotope variability dwarfs the 0 2 0 3 change seen coeval with the permian triassic mass extinction the largest recorded in the rock record and is on par with putative changes in the 44 40 ca value of seawater seen over the phanerozoic eon changes in both isotopic systems are too large to explain with changes in the isotopic composition of ca and mg in global seawater given modern budgets and residence times and thus must be products of alternative processes relationships between 44 40 ca and sr and 26 mg and mg are consistent with mineralogical control e g aragonite vs calcite limestone vs dolostone on calcium and magnesium isotope variability the most pristine samples in the wonoka dataset preserving sr concentrations in the 1000s of ppm range and 44 40 ca values inherited from an originally aragonitic polymorph have 13 c carb of 8 to 7 thereby providing strong geochemical evidence that extremely negative 13 c carb values are primary products of the ediacaran surface environment

δ18o and δ13c variability in brachiopods from modern shelf sediments and its utility for understanding complex oceanography southern australian shelf abstract the 18o and 13c values of brachiopod shell calcite are commonly used as proxies for ancient environmental marine conditions and secular changes in ancient ocean chemistry the variability of 18o and 13c across modern shelf settings is however not well documented this study presents 18o and 13c data from 407 holocene 5000 yr bp and living brachiopods collected from 220 sites across 3000 km along australia s southern shelf the largest cool water carbonate shelf in the modern world significant isotopic variability is present in separate specimens at individual sites and across the entire region individual specimens analyzed at multiple shell positions have an isotopic range of values up to 1 3 and 1 9 for 18o and 13c respectively multiple brachiopods at a single site have values that vary as much as 2 1 for 18o and 1 8 for 13c regional variability ranges on the order of 3 6 and 3 4 for 18o and 13c respectively the distribution of intrasite variability can be divided into areas of high and low variability areas characterized by low variability occur in zones of relatively consistent shelf water conditions high variability zones usually correspond to areas of seasonal upwelling onto the shelf and this aspect is interpreted to be the main cause of isotopic variability upwelling waters are cold leading to higher 18o values and are commonly rich in respired dissolved inorganic carbon dic and nutrients promoting active phytoplankton growth and leading to variable 13c values the extensive spatial coverage across this vast latitude parallel region provides a valuable baseline illustrating the isotopic range that could occur in a single layer in the rock record furthermore changes in isotopic signatures measured across stratigraphy might not necessarily reflect secular changes in ocean chemistry but instead could be recording local changes in shelf circulation and upwelling intensity

early aptian paleoenvironmental evolution of the bab basin at the southern neo tethys margin response to global carbon cycle perturbations across ocean anoxic event 1a 1 lower aptian carbonates in the bab basin at the southern neo tethys margin record significant environmental changes across oceanic anoxic event 1a oae1a a long lasting negative shift of carbon isotope ratios 13c associated with a distinct decrease in oxygen isotope ratios 18o in orbitolinid rich carbonates characterizes the onset of oae1a livello selli supporting a hypothesis that a long lasting volcanic co2 emission is the main cause of oae1a inducing global warming a bloom of microencrusters lithocodium and bacinella across the proto bab basin occurred synchronously at the beginning of the subsequent positive 13c excursion responding to the global carbon cycle perturbations the carbonates formed during the oae1a show higher strontium isotope ratios 87sr 86sr compared with those of global seawater this was likely caused by a local influx of isotopically heavier strontium along with nutrients into the proto bab basin these biotic proliferations were triggered by an increased nutrient supply induced by intensified continental weathering due to the global warming suggested by the increase in 18o values spatial variations in the 13c values among sites in the bab basin and its surrounding platform are related to local environmental factors such as the degree of mixing of basin water with ocean water and local removal of 12c by metabolic activity at the platform top the 13c profile of the studied core indicates global removal of organic carbon of oae1a began during the early stage of the second order transgression and lasted until the early stage of the highstand after the oae1a the livello selli corresponds to the early stage of this transgression

87sr 86sr and sr ca investigation of jurassic mollusks from scotland implications for paleosalinities and the sr ca ratio of seawater measurements of 87 sr 86 sr sr ca 18 o and 13 c were performed on molluskan fos sils from the great estuarine group scot land to deduce paleosalinity patterns and hydrodynamic environments in this classic jurassic marginal marine succession fos sils are found as winnowed accumulations in shell beds that bear low diversity assem blages consistent with deposition in a la goonal paleoenvironment previous studies have concluded that estuarine mixing of seawater and freshwater took place based on correlated trends in 18 o and 13 c most notably in the mussel praemytilus strathair densis from the kildonnan member this interpretation is shown to be incorrect based on 87 sr o 13 c and the sr ca ratio this is consistent with a lagoonal hydrology controlled more by seasonal changes in evaporation precipitation and flooding than by direct inputs of seawater or river ine water transported over large distances lagoons containing the oyster praeexogyra in the duntulm formation have similar in ferred o and c isotope characteristics but based on their 87 sr 86 sr ratios they have a higher proportion of seawater than the praemytilus lagoons of the kildonnan member the data thus far suggest that many of the lagoonal environments in the great es tuarine group were nearly hydrologically closed at least over the interval represent ing the molluskan invasion of these habi tats rendering o and c isotopes unreliable proxies of paleosalinity because strontium isotopes are not directly affected by evap oration of the lagoons knowledge of marine and freshwater 87 sr 86 sr ratios along with estimates of sr concentration are used to calculate the proportion of seawater in the brackish water mixture unio is nearly al ways the most radiogenic taxon compared to other genera in closely adjacent sedimen tary strata confirming its freshwater affin ity the purported marine brackish bivalve tancredia yields a low paleosalinity of 4 only slightly more saline than unio and praemytilus at 1 3 the oyster praeexo gyra hebridica yields paleosalinities between 2 and 26 attesting to the wide salinity tolerance of this species thus far only neomiodon from the dun tulm and staffin bay formations show co variant relationships between 87 sr 86 sr and ca sr ratio that can be reconciled with a dynamic response to seawater freshwater mixing the slopes of these trends converge at 0 7068 which is close to the early cal lovian seawater composition of 0 7069 us ing values of dsr from modern aragonite se creting mollusks the sr ca ratio of middle jurassic seawater is constrained from the best correlated mixing line to be 5 4 0 6 millimoles mole in contrast sr ca ratios in the great estuarine group lagoons and continental watershed range from 5 4 to 19 0 these are much higher than the av erage value of 2 3 for modern rivers but typical of sr ca ratios in rivers draining arid climate regions the semirestricted hy drodynamic regime inferred from the high seawater like 18 o values and high but uni form sr ca ratios in many of the great es tuarine group mollusks is consistent with a seasonally dry mediterranean style climate for the middle jurassic of britain

paired isotope records of carbonate and organic matter from the middle ordovician of argentina intrabasinal variation and effects of the marine chemocline abstract we investigate the expression of the middle darriwilian isotope carbon excursion mdice across marine shelf environments in the argentine precordillera previous work identified the mdice in the las chacritas formation in argentina but did not recognize the expression of the mdice in time equivalent strata of the deeper water las aguaditas formation albanesi et al 2013 palaeogeography palaeoclimatology palaeoecology v 398 p 48 66 recent biostratigraphic investigations of these units have for the first time provided the opportunity for high resolution correlation which suggest that the mdice or at least the initiation of the mdice should be observed in both the las chacritas and las aguaditas formations here we present new paired carbon isotope data of carbonate and organic carbon from the las chacritas and las aguaditas formations we identify a 2 positive shift in the isotopic composition of marine carbonate in the las chacritas formation whereas values abruptly fall to

an early diagenetic deglacial origin for basal ediacaran cap dolostones abstract the beginning of the ediacaran period 635 ma is marked by conspicuous dolostone units that cap marinoan glacial deposits worldwide the extent and sedimentary characteristics of the cap dolostones indicate that anomalous carbonate over saturation coincided with deglacial sea level rise and ocean warming however the geochemical variability within cap dolostones both between continents across single continental margins and within individual stratigraphic sections has been difficult to reconcile with depositional models using a compilation of new calcium and magnesium isotope measurements in marinoan cap dolostone successions worldwide we show that the geochemical variability can be explained by early diagenetic dolomitization of aragonite along a spectrum of fluid and sediment buffered conditions dolostones from the outer platform formed under fluid buffered conditions whereas dolostones on the inner platform and foreslope environment formed under sediment buffered conditions this spatial pattern of dolomitizing conditions is consistent with buoyant recirculation of glacial seawater within carbonate platforms driven by the deglacial sea level rise and development of a meltwater surface ocean using a numerical diagenetic model to evaluate the geochemical differences between sediment and fluid buffered cap dolostone units we constrain the chemical and isotopic composition of both the dolomitizing fluid glacial seawater 13 c 0 2 the meltwater lens 13 c 11 and the primary aragonite sediment 13 c 6 to 3 these model end members do not imply that primary geochemical variability did not exist but demonstrates that it is not necessary to change the chemistry of seawater to explain the global stratigraphic variability in the geochemistry of basal ediacaran cap dolostones our results provide a novel framework for understanding the geochemical variability of cap dolostone units including large excursions in carbon isotopes and how this variability is the product of local diagenetic processes expressed globally in continental margin environments following the last snowball earth

arctic reappraisal of global carbon cycle dynamics across the jurassic cretaceous boundary and valanginian weissert event abstract late jurassic early cretaceous global carbon cycle dynamics have mainly been inferred from tethyan atlantic and pacific carbon isotope 13c records these records indicate a steady deceleration of the carbon cycle in late jurassic and jurassic cretaceous j k boundary times followed by a major mid valanginian carbon cycle perturbation demarcated by the well documented positive excursion named the weissert event however this model remains to be confirmed in boreal records which are rare and typically difficult to correlate with the global 13c signal in this study the first continuous and biostratigraphically calibrated organic carbon isotope 13corg stratigraphy is established for the bathonian lower barremian representing 30 myr of the boreal realm based on high resolution sampling of bulk rock marine shale from four time equivalent sections in arctic svalbard supplemented by existing 13corg data the 13corg stratigraphy displays several distinctive trends notably i a kimmeridgian positive excursion followed by a large negative excursion 6 4 in the upper kimmeridgian middle volgian consistent with existing boreal 13c records ii an upper volgian ryazanian overall positive recovery across the j k boundary and iii a prominent positive excursion 5 5 in the valanginian interpreted to represent the weissert event followed by steady high values into the lower barremian with no apparent excursion decay time calibrated correlation of the observed trends with existing 13c records representative of the entire exchangeable carbon reservoir reflects major global carbon cycle adjustments including i boreal decoupling from the global carbon reservoir during late jurassic and j k boundary times due to basinal isolation and ii global carbon cycle recoupling at the onset of the weissert event coinciding with incipient oceanographic connectivity boreal carbon cycling was inherently controlled by the basin configuration the new 13corg stratigraphy provides a well calibrated tool for boreal and boreal tethyan correlations and confirms that the weissert event represents an important perturbation of the global carbon cycle

the stable oxygen and carbon isotopic record from a coral growing in florida bay a 160 year record of climatic and anthropogenic influence abstract a 160 year record of skeletal 13 c and 18 o was examined in a specimen of the coral solenastrea bournoni growing in florida bay variations in the 18 o of the skeleton can be correlated to changes in salinity while changes in the 13 c reflect cycling of organic material within the bay based on the correlation between salinity and skeletal 18 o we have concluded that there has been no long term increase in salinity in this area of florida bay over the past 160 years using salinity correlations between the various basins obtained from instrumental data we have been able to extend our interpretations to other parts of florida bay reaching similar conclusions in contrast to current ideas which have focused on changes in florida bay water quality over the past 20 yr history of the bay as causative in its decline we have determined that changes in water quality in this basin were already set in motion between 1905 and 1912 by the construction of the florida east coast railway from miami to key west the construction of the railway resulted in the restriction of the exchange of water between the florida reef tract and the gulf of mexico causing florida bay to become more eutrophic evidence of this process is observed in the sudden shift to relatively lower 13 c values coincident with railway construction natural events also appear to have influenced the water in the bay between 1912 and 1948 frequent hurricanes had the effect of increasing exchange of water between the bay and reef tract and removing large quantities of organic rich sediments however since 1948 the number of hurricanes affecting the area has decreased and the products of the oxidation of organic material have been increasingly retained within the basin promoting the initiation of eutrophic conditions

the response of two tethyan carbonate platforms to the early toarcian jurassic oceanic anoxic event environmental change and differential subsidence chemostratigraphic analyses 87 sr 86 sr d 13 ccarb of limestones from two jurassic platform carbonate sequences in italy trento and campania lucania platforms illustrate previously established trends found in pelagic sediments and skeletal carbonates from biostratigraphically well calibrated sections elsewhere in europe chemostratigraphic correlations between the platform carbonate successions and appropriate intervals from well dated reference sections allow the application of high resolution stratigraphy to these shallow water peritidal carbonates and furthermore elucidate the facies response to the early toarcian oceanic anoxic event oae lower jurassic toarcian levels of the western trento platform southern alps northern italy contain spiculitic cherts that appear where rising carbon isotope values characterize the onset of the oae a palaeoceanographic phenomenon interpreted as driven by increased nutrient levels in near surface waters there is a facies change to more clay rich facies at the level of the abrupt negative carbon isotope excursion also characteristic of the oae higher in the section the campania lucania platform southern apennines southern italy records a change to more clay rich facies where carbon isotope values begin to rise at the beginning of the oae but the negative excursion higher in the section occurs within oolitic facies although in both examples the early toarcian oae can be recognized by a change to more clay rich lithologies this facies development is diachronous and in neither case did the platform drown although the trento platform in the south west sector studied here was adversely affected by the oae it did not drown definitively until late aalenian time the campania lucania platform persisted throughout the jurassic and cretaceous differential subsidence rates which can be calculated using comparative chemostratigraphy are identified as a crucial factor in the divergent behaviour of these two carbonate platforms relatively fast in the case of the trento platform relatively slow in the case of the campania lucania platform it is proposed that where water depths remained as shallow as a few metres during the oae campania lucania platform dissolved oxygen levels remained high nutrient levels relatively low and conditions for carbonate secretion and precipitation remained relatively favourable whereas more poorly ventilated and or more nutrient rich waters trento platform adversely

migration of acidic pore waters at the waite amulet tailings site near rouyn noranda quebec canada pore waters found in the unsaturated zone of the waite amulet tailings have been modified by sulphide mineral oxidation resulting in acidic ph near 4 and high concentrations of dissolved iron an

carbon isotope record of late cambrian to early ordovician carbonates of the argentine precordillera a more than 2000 m thick cambrian ordovician carbonate platform succession developed on the exotic argentine precordillera terrane during rifting from laurentia and drifting towards gondwana on base of these carbonates a carbon isotope curve could be developed for the cambrian ordovician we measured 13ccarb and 13corg values on bulk rocks selected components and diagenetic cements whereas the carbon isotope signals of intertidal and supratidal rocks are altered by diagenesis most subtidal carbonates exhibit primary marine values we can report reliable curves for the middle late cambrian transition and for the latest cambrian to earliest middle ordovician the 13c curve matches well with the published data from global cambrian ordovician boundary sections excursions and shifts in the carbon isotope curve correspond to events in sequence stratigraphy this indicates the interdependence on sea level which rules the productivity and or preservation of organic carbon and therefore the partition between corg and ccarb burial

carbon isotope lateral variability in a middle frasnian carbonate platform belgium significance of facies diagenesis and sea level history abstract carbon isotopic variations of frasnian shallow water carbonates from belgium are related to facies and major sea level trends the influence of the diagenetic overprint was assessed in order to determine the primary signal of the frasnian carbonates shallow water microfacies are characterized by biostromes with stromatoporoids and lagoonal deposits dominated by carbonate mud and calcareous algae with subaerial exposure surfaces the diagenetic history was controlled by three main events early meteoric diagenesis short term subaerial exposure during deposition late meteoric diagenesis major famennian regression and burial diagenesis the oxygen isotopic values are almost constant with respect to facies original material carbonate mud and cement and sedimentological units no differences before or after the main regression this homogeneity is related to resetting during late meteoric diagenesis the carbon isotopic values are related to facies with the more negative values for the shallowest facies and to major sea level variations most negative values after the main regression this pattern is interpreted as being related to primary signals this trend was enhanced by early meteoric diagenesis and the influence of more negative values from paleosols the carbon isotope patterns reflect the influence of sea level and water circulation on shallow water deposits and this influence implies that shallow water carbonates are not necessarily good material for assessing the primary isotopic values of the ocean because of the influence of long residence time aging of the platform top water and because of early diagenesis

depletion of 13c in seawater σc02 on modern carbonate platforms significance for the carbon isotopic record of carbonates seawater co2 from modern carbonate platforms bahama banks and florida is depleted in 13c by as much as 4 relative to open ocean water depletion in 13c is caused by isotopically light co2 input from respiration of marine and terrestrial organic matter during water mass residence on the bank as such depletion in 13c is related to changes in water chemistry driven by evaporation freshwater discharge and caco3 withdrawal deviation of modern platform seawater 13c values away from those of surface seawater suggests that 13c values of ancient cratonic carbonate must be cautiously interpreted initial depositional environment as well as alteration during diagenesis must be considered in extracting valid secular trends for oceanic 13c variation

geochemical decoupling of water masses in the variscan oceanic system during late devonian times abstract neodymium isotope data obtained from conodonts collected in morocco and poland attest a geochemical decoupling of seawater in the variscan realm during the late devonian the water masses on the shelves were characterized by unradiogenic e nd values from about 7 to 12 the surface water in the bordering oceans the rheic ocean and the variscan sea yielded more radiogenic e nd values ranging from about 1 to 6 a compilation of nd and c isotope signatures from the moroccan meseta suggests that the shelf and the surface oceanic water differed also in their carbon isotope evolution the geochemical decoupling constrains a restricted water exchange between shelves and the ocean oceanic waters entered far into the shelf areas only during the semichatovae transgression in the frasnian zone 11 sea level fluctuations constituted the major force that modified circulation and thus controlled the mixing of shelf and surface oceanic seawater the nd conodont data reveal that the surface water of the variscan oceanic water resembled the seawater of the modern pacific ocean rather than those of the atlantic and indian oceans the geochemical character of the variscan oceanic water is consistent with the geotectonic regime of the variscan realm in late devonian and carboniferous times

petrography and geochemistry of the permian triassic boundary interval yangou section south china implications for early griesbachian seawater δ 13 c dic gradient with depth abstract the carbon isotopic composition 13 c carb recorded in shelf carbonates has been widely used as a proxy for the isotopic composition 13 c dic of surface ocean water to establish paleocean chemistry and circulation patterns however 13 c carb values do not necessarily preserve the 13 c dic due to post depositional diagenetic alteration in order to examine the early griesbachian surface to deep 13 c dic gradient with depth the diagenetic features of the permian triassic boundary interval beds 18 to 35 from yangou section located in the yangtze carbonate platform interior south china are delineated to compare with those of the slope gssp meishan section the petrographic and geochemical observations show that the early griesbachian carbonates in the yangou section underwent pervasive dolomitization in its early diagenetic history three types of early replacement dolomites and one type of dolomite cement are present the dolomite crystals display internal zonation with high ca calcian dolomite hcd core being encased successively by calcite and an outermost fe rich hcd cortex the initial dolomitization took place in anoxic seawater and underwent subsequent diagenetic system involved with meteoric water the two most negative 13 c values in claystones of beds 21 3 and 35 are probably related to meteoric diagenesis above and or below the meteorically influenced beds the dolomite and calcite have uniformly positive 13 c values the primary carbon isotopic compositions are probably preserved in the early griesbachian carbonate from the platform yangou section which could probably be related to the poor formation of the outermost fe rich hcd cortex compared to the slope carbonate from the meishan section the platform carbonate from the yangou section has lower primary 13 c carb values it is estimated that the 13 c dic gradient with depth between yangou and meishan is less than the previously suggested the results highlight the need for evaluation of local 13 c carb as record of 13 c dic in paleoseawater and carry important implications for understanding the permian triassic carbonate successions throughout the world

carbon isotope stratigraphy and carbonate production during the early middle jurassic examples from the umbria marche sabina apennines central italy abstract the carbon isotopic signature of carbonates depends on secular variations of organic carbon and carbonate carbon production burial rates a decrease in carbonate productivity makes the organic carbonate carbon ratio unstable up to the point that even minor variations in the organic carbon reservoirs can provoke carbon isotopic shifts the 13c positive shifts of the middle carixian early pliensbachian and the early bajocian recorded in the umbria marche sabina domain represent a good example of this mechanism both sedimentology and lithostratigraphy of pelagic platform basin carbonate systems in this area show that important changes in the source of carbonates correspond to the observed isotopic shifts the middle carixian event is in fact well correlatable to the drastic reduction of benthic carbonate production on rift related intrabasinal highs which then became pelagic carbonate platforms the early bajocian event is concomitant with the beginning of a long hiatus on the pelagic carbonate platforms and with a drop of the biodiversity of calcareous organisms followed by the onset of biosiliceous sedimentation in basins

imprint of the late palaeozoic ice age on stratigraphic and carbon isotopic patterns in marine carbonates of the orogrande basin new mexico usa the permian records one of the most extreme climate transitions of the phanerozoic yet the climatic and environmental dynamics of this interval and their effects on neritic carbonate systems remain poorly constrained new stratigraphic and carbon isotope records from uppermost pennsylvanian to lower permian strata of the orogrande basin in south central new mexico usa provide fresh insights into the response of palaeotropical carbonate systems to the growth and demise of ice sheets on gondwana the earliest permian acme of glaciation is recorded in the orogrande basin as a series of subaerial exposure surfaces marked by highly variable 13c values that tend toward values as low as 6 these stratigraphic and isotopic patterns are interpreted to reflect the retreat of the sea from the basin during glacial expansion younger lower sakmarian to kungurian strata deposited during the long decline of the late paleozoic ice age are characterized overall by higher and more uniform 13c values 2 to 5 and show no evidence of long term subaerial exposure however these strata record two short lived excursions toward more negative 13c values these excursions occur through intervals that record shifts toward shallower and more restricted conditions in the orogrande basin the timing of these shifts corresponds to two periods of glacial expansion across eastern australia during late sakmarian to early artinskian and kungurian time these relationships suggest that pulses of glacial expansion in eastern gondwana were of sufficient magnitude to have caused relative sea level fall and possibly environmental change in the orogrande basin the results from this study suggest that marine chemistry depositional environments and sea level in the orogrande basin were profoundly influenced by epochs of gondwanan glaciation these inferences help improve the understanding of how palaeotropical carbonate systems responded to the effects of cryospheric changes during the acme and waning stages of the late palaeozoic ice age

response of early cretaceous carbonate platforms to changes in atmospheric carbon dioxide levels during the late barremian and early aptian about 120 million years ago intense volcanic degassing and extremely rapid release of methane hydrates contained in marine sediments added high amounts of carbon to the ocean and atmosphere and resulted most probably in rising atmospheric carbon dioxide pressure in order to document the response of the shallow water carbonate producing communities to this pronounced disturbance of the carbon cycle we studied a late barremian to early aptian neritic carbonate succession deposited on the northern tethyan shelf swiss alps the sedimentological and stable carbon and oxygen isotope records of two sections located along a n s transect from proximal to more distal shelf environments were investigated the sediments correspond to outer mid and inner ramp deposits of a homoclinal carbonate ramp vertical facies variations within the two studied sections feature three progradation phases of the platform a highly resolved correlation of the shelf sediments with a pelagic succession from the southern alps northern italy is based on both 13c stratigraphy and biostratigraphy and indicates that the drowning of the helvetic carbonate platform coincided with a pronounced calcification crisis of calcareous nannofossils the biocalcification crisis started before but culminated during the aptian methane event recorded in a negative carbon isotope spike we propose that increased carbon dioxide concentrations in oceans and atmosphere related to volcanic activity and to sudden methane release reduced the marine calcium carbonate oversaturation and the calcification potential of benthic and planktonic organisms carbonate producing shallow water communities on platforms and ramps suffering from additional environmental stress such as extreme temperatures or high nutrient levels could not survive during times of rising sea level and as a consequence carbonate platforms drowned

the formation and potential importance of cemented layers in inactive sulfide mine tailings abstract investigations of inactive sulfide rich tailings impoundments at the heath steele new brunswick and waite amulet quebec minesites have revealed two distinct types of cemented layers or hardpans that at heath steele is 10 15 cm thick occurs 20 30 cm below the depth of active oxidation is continuous throughout the tailings impoundment and is characterized by cementation of tailings by gypsum and fe ii solid phases principally melanterite hardpan at the waite amulet site is only 1 5 cm thick is laterally discontinuous 10 100 cm occurs at the depth of active oxidation and is characterized by cementation of tailings by fe iii minerals principally goethite lepidocrocite ferrihydrite and jarosite at heath steele an accumulation of gas phase co2 of up to 60 of the pore gas occurs below the hardpan the calculated diffusivity of the hardpan layer is only about 1 100 that of the overlying uncemented tailings the pore water chemistry at heath steele has changed little over a 10 year period suggesting that the cemented layer restricts the movement of dissolved metals through the tailings and also acts as a zone of metal accumulation generation of a cemented layer therefore has significant environmental and economic implications it is likely that in sulfide rich tailings impoundments the addition of carbonate rich buffering material during the late stages of tailings deposition would enhance the formation of hardpan layers

carbon isotope stratigraphy of cenomanian turonian platform carbonates from the southern apennines italy a chemostratigraphic approach to the problem of correlation between shallow water and deep water successions the carbon isotope record of three sections of shallow water carbonates from the upper cretaceous sequences of the southern apennines italy shows a pronounced positive excursion of about 4 5 using the upper cenomanian cisalveolina fraasi level as a biostratigraphic tie point we correlate this excursion to the oae 2 isotopic event comparison with the standard reference 13 c curve of eastbourne england shows that the overall character of the excursion is clearly reproduced in the shallow water curves chemostratigraphic correlation allows definition of the age of some important shallow water biostratigraphic events to the precision of an ammonite zone using the well established bio chronostratigraphic framework defined in the eastbourne section the onset of the cenomanian turonian isotopic excursion coincides with a transgressive trend recorded by the occurrence of more open marine facies and culminating with an incipient drowning in one of the sections studied our data suggest that the open ocean isotopic signal is most faithfully recorded and preserved in shallow water platform carbonates during transgressive periods when the effects of meteoric diagenesis and seawater ageing are less severe

oyster shells as recorders of short term oscillations of salinity and temperature during deposition of coral bioherms and reefs in the miocene lorca basin se spain abstract we use 18 o and 13 c of oyster shells inferred seawater 18 o w and temperature tolerance ranges of modern zooxanthellate coral communities to constrain and model paleo salinities of marginal marine waters of the miocene lorca basin spain salinities ranged from 22 to 32 psu during growth of coral bioherms and carpets of the soriana and parrilla formations and from 35 to 39 psu during deposition of the hondo formation reef complex the periods with lower modeled salinities correspond with deltaic and alluvial fan sedimentation in the area the modeling is supported by 87 sr 86 sr data and provides new insights into the evolution of the local depositional settings departures of sr isotope values from the global oceanic curve occur within the intervals with the lowest modeled salinities and the non oceanic 87 sr 86 sr preserved in individual oyster shells was probably sourced from uplifted aquitanian burdigalian limestones 87 sr 86 sr values that plot along the global ocean sr isotope curve for the late miocene indicate a tortonian age for the upper part of the soriana formation and the parrilla formation and a messinian age for the hondo formation more generally we demonstrate how the chemical analyses of oyster shells provide additional information regarding short term oscillations of salinity and temperature of seawater beyond what can be obtained by traditional paleoecological methods

carbon cycle dynamics following the end triassic mass extinction constraints from paired δ13ccarb and δ13corg records 1 constraining the carbon isotopic changes associated with the end triassic mass extinction is key to understanding the causes of the extinction and dynamics of recovery from it yet the pattern and timing of 13c variation surrounding the extinction remain poorly constrained here we present close to 1000 new 13c measurements from six newly sampled sections in italy we observe a sharp negative excursion in 13ccarb coincident with the disappearance of the triassic fauna and two positive excursions above it the negative 13ccarb excursion in these sections does not occur in 13corg suggesting a possible diagenetic origin in contrast the interval of elevated 13c occurs in both carbonate and organic carbon suggesting that it is likely to be a primary feature the positive excursions in the lombardy basin southern alps and mt cefalo southern apennines appear to be time correlative on the basis of their position above the disappearance of characteristically triassic biota however it is less certain that they are time correlative with positive excursions in other sections worldwide as few options exist that honor both bio and chemostratigraphy nonetheless similarity to other events that are interpreted as global as well as carbon cycle considerations suggest that the isotopic enrichment is best interpreted to reflect a shift in the isotope composition of the global surface carbon reservoir our data indicate that perturbation of the global carbon cycle was not confined to the immediate vicinity of the extinction interval but rather persisted for substantial length of geologic time afterwards

characterization lateral variability and lateral extent of discontinuity surfaces on a carbonate platform barremian to lower aptian oman hiati of various duration in carbonates are commonly expressed as discontinuity surfaces the understanding of processes that form and affect these surfaces leads to an improved sequence stratigraphic interpretation a reliable outcrop correlation and better models for reservoir compartmentalization various intraformational discontinuities were analysed and interpreted in a well exposed study window 2 5 km in lateral length and 60 m in height comprising the barremian aptian qishn formation haushi huqf area central oman this study focuses on the lateral extent and morphology of the surfaces the petrography of the underlying rocks and the facies changes and geochemical trends across these discontinuities furthermore the lateral variability of discontinuity surfaces was documented three genetic types of discontinuities are differentiated i erosion surfaces ii omission surfaces hard and firmgrounds and iii composite surfaces with evidence for both subaerial exposure and submarine boring field observations combined with petrographic and geochemical data suggest that 17 surfaces are laterally extensive for at least 20 km and record relative sea level fluctuations of regional scale in contrast a large number of laterally limited surfaces 1 km are related to locally active processes such as waves and current erosion the lateral variability along extensive surfaces is the result of the depositional environment below the discontinuity the sea floor topography waves and currents and differential erosion the most pronounced lateral variability is present along six laterally extensive composite surfaces that record terrestrial exposure and subsequent flooding of a tidal flat environment this variability is caused by spatial variability in the tidal flat environment meteoric alteration and differential erosion this study emphasizes the spatial and temporal complexity of processes that form and modify discontinuity surfaces this variability must be kept in mind when interpretations and correlations are based on one dimensional sections or cores 2005 international association of sedimentologists

changes in sedimentary patterns of coastal and deep sea successions from the north atlantic portugal linked to early cretaceous environmental change coastal mixed carbonate siliciclastic and carbonate deposits of late barremian to early aptian age from the lusitanian basin portugal are compared with a deep sea succession odp 641 off the coast of portugal the coastal deposits show an abrupt cessation of rudist dominated carbonate deposition marked by an emersion horizon and followed by the deposition of orbitolinid rich marls during the early aptian the subsequent development of the carbonate platform during the late aptian is masked by a hiatus for this time interval shallow water debris deposits of the deep sea succession odp 641 indicate that carbonate production in shallow water areas resume in the early late aptian carbon isotope stratigraphy in combination with available biostratigraphic data is used for intrabasinal correlation and for the correlation of the portuguese with shallow water successions from switzerland france oman and the pacific the correlation reveals that during the early aptian similar changes in their sedimentary patterns occur at the beginning of a marked negative shift of carbon isotope values associated with the global deposition of organic rich black shales in the deep sea oae 1a in all compared sections rudist dominated carbonate deposition is stopped and followed either by orbitolinid rich deposits the deposition of microbial carbonates or by the drowning of the carbonate platform the comparison shows that the deterioration for carbonate platform growth conditions during the early aptian occurred essentially simultaneously at the various localities during this episode the ocean waters were in a preconditioned state of acidification stressing biocalcifying organisms sea level change combined with local effects like elevated nutrient levels and higher temperatures were probably determining the nature of sedimentary change in shallow water environments during the carbonate crisis in the sections studied in portugal the high abundance of orbitolinids overlying rudist limestones indicates that increased nutrient input may have played an important local role among the factors that caused an overall deterioration for carbonate producers during the late early aptian

reconstruction of jurassic bathonian palaeosalinity using stable isotopes and faunal associations abstract the bathonian is an interval from which salinity controlled benthic faunas are particularly well known this study examines late bathonian faunas from dorset uk from the wattonensis beds fuller9s earth of known marine origin the overlying elongata beds and the boueti bed marking the base of the forest marble 18 o values of belemnites belemnopsis from the wattonensis beds range from 1 4 to 0 7 and carbon isotope values range from 2 3 to 0 5 vpdb isotope values of well preserved rhynchonella from the wattonensis beds range from 2 4 to 1 3 for oxygen and 1 1 to 0 6 vpdb for carbon the 18 o data suggest high palaeotemperatures possibly up to 28 c a similar spread of data is derived from brachiopods goniorhynchia boueti from the boueti bed given the marine origin of the wattonensis beds and overlap of data the reduced faunal diversity of the boueti bed is considered unlikely to be the result of reduced salinity brachiopods therefore should not be regarded more sceptically as evidence for fully marine conditions as has been suggested the oysters praeexogyra hebridica elongata and brachiopods rhynchonella from the elongata beds have isotope values that also imply fully marine conditions and are interpreted as being indicative of slightly cooler conditions

flow and sediment dynamics in the vegetated secondary channels of an anabranching river the loire river france this study investigates the hydrological and sedimentological mechanisms occurring in the vegetated secondary channels of an anabranching river affected by incision the loire river france during and after flood events that occurred between 2000 and 2003 observations and measurements were performed on a vegetated secondary channel located in the study site of brehemont 790 km downstream the source morphological changes and sediment dynamics were analysed using low elevation airborne photographs topographic and bathymetric surveys and scour chains the hydraulic behaviour of the channel was also analysed by measurements performed on flow velocity and direction during different flood stages in order to quantify the influence of woody vegetation on flow resistance the roughness of bands of trees was determined from measurements performed on the field the impact of the disruption of armour layers on bedload pulses the variation of sedimentary processes during a single flood event and the fixation of bedforms by vegetation are all identified as key processes influencing the behaviour of the study channel topographic surveys demonstrate that sediment dynamics is substantial in the upstream part of the channel and that sediment budgets are different according to the temporal scale considered moreover an asymmetrical behaviour of the secondary channel is demonstrated reduced quantities of sediment deposited and preserved in the vegetated zones contrast with material by passing observed in the third order channels flow velocity and direction measurements indicate that these parameters vary according to the water level and to the morphological units of the channel pools riffles vegetated areas during low flows scouring and export of particles from the secondary channel are a consequence of reduced sediment supply from the main channel of the loire river for these water levels sedimentation occurs in pools where velocity and turbulence decrease whereas third order channels are subjected to erosion during high discharges large quantities of sediment available in the main channel feed the temporary stores formed by riffles and bars in the secondary channel the vegetated area located in the downstream part of the secondary channel deflects current trickles at low discharges and decreases flow velocity during high water levels the sedimentary accretion observed in this area exerts a feedback on flow and sedimentary processes d 2005 elsevier b v all rights reserved

stable carbon isotope record of shallow marine evaporative epicratonic basin carbonates ordovician williston basin north america secular variations in stable carbon isotope values of marine carbonates are used widely to correlate successions that lack high resolution index fossils various environmental processes however commonly may affect and alter the primary marine carbon isotope signal in shallow epicratonic basins this study focuses on the marine carbon isotope record from the carbonate evaporite succession of the upper katian upper ordovician red river formation of the shallow epicratonic williston basin usa it documents the carbon isotope signal between the two major ordovician positive shifts in 13c the early katian guttenberg and the hirnantian excursions eight 13c stages are identified based on positive excursions shifts from positive to negative values and relatively uniform 13ccarb values a correlation between carbon isotope trends and the relative sea level changes based on gross facies stacking patterns shows no clear relation based on the available biostratigraphy and 13c trends the studied williston basin curves are tied to the isotope curves from the north american midcontinent quebec anticosti island and estonia which confirm the late katian age aphelognathus divergens conodont zone of the upper red river formation the differences in the 13c overall trend and absolute values coupled with the petrographic and cathodoluminescence evidence suggest that the carbon isotope record has been affected by the syndepositional environmental processes in the shallow and periodically isolated williston basin and stabilized by later burial diagenesis under reducing conditions and the presence of isotopically more negative fluids

the pore water geochemistry and the mineralogy of the vadose zone of sulfide tailings waite amulet quebec canada low ph waters requiring treatment because of high concentrations of dissolved metals are being discharged from a decommissioned tailings impoundment at the former waite amulet zncu mine in northeastern quebec canada a detailed study of the vadose zone of the tailings comparing mineralogical and geochemical analyses of the tailings solids with geochemical analysis of the tailings pore water and pore gas indicates the presence of three zones within the tailings these zones include an upper sulfide depleted zone in which the sulfides have been extensively removed and oxidation is largely complete an intermediate zone where sulfide oxidation and acid neutralization reactions are occurring and an unoxidized zone below the depth of oxygen penetration where sulfides are unoxidized high aqueous concentrations of dissolved solids are being displaced downward from the sulfide depleted zone through the unoxidized zone toward the water table sulfide oxidation and acid neutralization reactions have generated concentrations of dissolved solids high enough to lead to the precipitation of a series of secondary solid phases precipitation dissolution reactions involving these solid phases control the concentrations of the major ions in the tailings pore water concentrations of dissolved metals are controlled by precipitation dissolution crystal structural replacement and adsorption coprecipitation reactions predictions based on the observed data and numerical simulations suggest that in the absence of an effective remedial program sulfide oxidation and h production will continue for several centuries

carbon cycling across the southern margin of laurentia during the late ordovician abstract the guttenberg isotope carbon excursion gice a positive carbon isotope excursion that occurs near the base of the katian stage is thought to be a global event possibly related to late ordovician cooling documenting how much regional and global variability exists in carbon isotopic trends prior to and during the gice is a critical aspect in understanding the implications of the excursion for interpreting changes in the global carbon cycle paleoclimate and chemostratigraphic correlation during the ordovician to investigate carbon isotopic trends along the southern margin of the laurentian carbonate platform during the late ordovician we measured bulk carbonate 13 c carb and 18 o carb as well as organic carbon 13 c org values from four locations in alabama these sections are excellent study sites because they are well exposed contain the regionally well correlated deicke and millbrig k bentonites and are in a region where 13 c trends have not been studied carbonate 13 c carb results from one section i e fort payne in northeastern alabama record a 1 5 positive excursion above the millbrig k bentonite we interpret the 1 5 positive excursion as a primary feature and identify it as the gice the characteristic gice excursion is absent in the other study sections and we attribute this absence to the presence of unconformities either non depositional or erosional in these sections we find neither evidence for sea level control on 13 c trends nor conclusive evidence for 13 c dic gradients along the southeast margin of laurentia s epeiric sea combined with the proximity to the iapetus ocean these results suggest that carbon isotopic trends in alabama are a reliable proxy for open ocean conditions therefore despite the absence of gice excursion in all but one of our study sections increasing 13 c values in alabama prior to the gice provides evidence for a steady 13 c enrichment of the global surficial carbon reservoir consistent with a drawdown of atmospheric co 2 during the early late ordovician