laboratory study of hydraulic fracturing laboratory tests on teton dam soil were performed by increasing the water pressure in model bore holes and in simulated rock joints the water pressure required to cause hydraulic fracturing was found to depend on soil density water content confining stress and test duration on the basis of the test results it was hypothesized that 1 hydraulic fracturing is a weak link phenomenon in that fracturing will occur in the least resistant soil subjected to increased water pressure and 2 hydraulic fracturing can probably occur only in the presence of a discontinuity within which the water pressure can act to create a wedging mechanism thus creating tensile stresses in the soil

nd isotopic variations of phanerozoic paleoceans abstract the size of various phanerozoic paleoceans determined from paleogeographic maps provides a framework for assigningend measurements of primary authigenic marine minerals to individual paleoceans and for establishing theirend versus age curves we report newend data in the range from 80 to 750 ma for the largest phanerozoic and late precambrian paleocean the pacific panthalassa ocean ppo and limited data on some small paleozoic paleoceans these new data and all other published data on paleoceanend values are used to determine the trends through time ofend in seven phanerozoic paleoceans the variations in paleoceanend curves are due to changes in the rate of crustal additions and in paleoceanic geometry from these data we can calculate a meanend curve and a mean nd model age curve for phanerozoic seawater these curves show large variations with age and reflect the variations ofend in erosion products from the continents as a function of age the high erosion rates of young uplifted areas enhanceend and nd model age variations of phanerozoic seawater this makes it difficult to quantitatively recover crustal addition rates from these curves however it makes the episodic nature of continental additions more evident

a far field record of the end ordovician glaciation the ellis bay formation anticosti island eastern canada abstract the end ordovician was a critical period in earth history it was a time of global climatic change with large scale continental glaciations a wealth of recent work has documented the stratigraphical records from the near field areas i e from various gondwanan continental relics where glaciation was more severely felt there is an urgent need to re examine the stratigraphic record from the far field areas at greater levels of resolution than it has been hitherto possible in order to understand the timing duration and character at the glaciation centred around the ordovician silurian o s boundary one of the best exposed and most complete stratigraphic records from paleotropical areas near the boundary is on anticosti island in eastern canada the east west trending 200 km long ellis bay hirnantian outcrop belt with superb coastal exposures at both ends of anticosti island is slightly oblique to the paleoshoreline with near shore siliciclastic dominated facies restricted to the eastern part of the island and more offshore carbonate dominated facies present along the central and western parts these mixed carbonate siliciclastic facies accumulated along a storm dominated beach to offshore profile they are organized into a stacked set of shallowing upward offshore to shoreline facies successions typically coarsening upward separated by deepening upward facies successions typically fining upward formed during intervening transgressions high frequency glacio eustatic fluctuations were the dominant control on the development of tr sequences observed in the ellis bay succession of anticosti island although tectonic subsidence had a substantial secondary effect on thickness five tr sequences are recognized allowing for precise correlation along the ellis bay outcrop belt in the eastern sections relatively thin tr sequences are locally bounded by unconformities a typical sequence begins with thin transgressive limestone overlain by a maximum flooding calcareous shale grading up into regressive storm influenced proximal to transitional zone fine sandstone grainstone and shale which are sharply overlain by shoreface to foreshore sandstone grainstone in the central and western sections the thicker tr sequences have more symmetrical transgressive regressive components reflecting greater subsidence compensated by a higher carbonate sediment supply two discrete glacial periods are recognized during the deposition of the hirnantian ellis bay succession with the younger one recording large sea level changes 50 m in magnitude caused by the development of very large ice sheets over western gondwana abundant ice conditions on the globe during the end ordovician and the resulting high amplitude eustasy appear to have left distinctive stratigraphical imprints on mixed paleotropical siliciclastic carbonate ramps

the assessment of ree patterns and 143nd 144nd ratios in fish remains abstract the ree content and isotopic composition of sr and nd have been determined in fish teeth ranging in age from the trias to the present and from various localities mostly around the atlantic these measurements have been carried out on selachian and teleost remains from the same locality in togo and show no appreciable difference which suggests with the help of a mass balance calculation of the ce anomaly that diagenetic effects are not responsible for the ree enrichment of biogenic phosphates one group of fossil teeth has about 3 times the ree abundances of shale and a shale normalized pattern with a minimum at sm it is thought to reflect deposition in the open sea environment a second group has ree concentration about 10 times higher than the first group with either a regular light ree enrichment or more frequently a maximum in the middle ree both being probably indicative of deposition in estuarine or near shore conditions the shape of the ree spectra and the size of the ce anomaly can be used semi quantitatively to determine the depth of deposition the results presented here on late cretaceous eocene fish teeth samples from morocco reflect an increasing influx of deep waters with a lowla yb ratio and strong negative ce anomaly which agrees well with the evolution of sediment chemistry and microfauna associations in contrast nd is typical of the water mass in which the fish debris decayed examples of nearly isolated basins identified with nd isotopes include the south atlantic prior to the lutetian nd 13 5 the miocene persian gulf nd 3 1 and bolivia during the late cretaceous nd 12 8 togo and guinea bissau results suggest that in the south atlantic the meridional oceanic circulation had not started before 45 ma ago combination of ree and nd data suggests that the assignment of jurassic cretaceous samples measured so far to open sea water masses is still ambiguous

sequence stratigraphy of a carbonate clastic ramp the cincinnatian series upper ordovician in its type area the cincinnatian series consists of five depositional sequences each is composed of a thin transgressive systems tract and a much thicker shallowing upward highstand systems tract whereas the highstand systems tracts are relatively poor in micrite but rich in terrigenous shale the transgressive systems tracts are composed of cleaner carbonate facies ranging from coarse grained calcarenites to micrite rich wackestones and micstones this alternation of carbonate and terrigenousfacies types resulted from the trapping of clastic sediment near its presumed source in the appalachians during a relative sea level rise and it may be a feature common to sequences in other mixed carbonate clastic settings these depositional sequences were produced by eustatic fluctuations as shown by the limited extent to which the sequences can be traced into more proximal portions of the appalachian basin the recognition of depositional sequences clarifies the regional paleogeography and simplifies regional lithostratigraphic nomenclature within current biostratigraphic resolution sequences in the cincinnatian series appear to have chronostratigraphic significance and thereby offer an additional means of intrabasinal correlation in the upper ordovician

high resolution carbon isotope stratigraphy of the basal silurian stratotype dob s linn scotland and its global correlation since its designation as the global stratotype section and point gssp for the base of the silurian system the choice of dob9s linn southern scotland has received criticism due to the difficulties of relating its well constrained graptolite biostratigraphy to shallow water sequences elsewhere kerogen samples from across the ordovician silurian boundary interval at dob9s linn have yielded carbon stable isotope signatures consistent with those recorded elsewhere in particular showing a clear positive 13 c excursion in the terminal ordovician the architecture of the 13 c curve from dob9s linn enables very high resolution stratigraphic subdivision and direct correlation between the deep water dob9s linn section and time equivalent carbonate shelf deposits an integrated stratigraphic scheme using isotope stratigraphy and biostratigraphy of graptolites conodonts and shelly faunas has been constructed this direct correlation shows that the shallow water successions including the former stratotype candidate at anticosti island are generally incomplete with hiatuses related to the rapid sea level changes during the hirnantian stage this confirms and greatly increases the global utility of dob9s linn as a boundary stratotype

submarine groundwater discharge is an important net source of light and middle rees to coastal waters of the indian river lagoon florida usa abstract porewater i e groundwater samples were collected from multi level piezometers across the freshwater saltwater seepage face within the indian river lagoon subterranean estuary along florida s usa atlantic coast for analysis of the rare earth elements ree surface water samples for ree analysis were also collected from the water column of the indian river lagoon as well as two local rivers eau gallie river crane creek that flow into the lagoon within the study area concentrations of rees in porewaters from the subterranean estuary are 10 100 times higher than typical seawater values e g nd ranges from 217 to 2409 pmol kg 1 with submarine groundwater discharge sgd at the freshwater saltwater seepage face exhibiting the highest ree concentrations the elevated ree concentrations for sgd at the seepage face are too high to be the result of simple binary mixing between a seawater end member and local terrestrial sgd instead the high ree concentrations indicate that geochemical reactions occurring within the subterranean estuary contribute substantially to the ree cycle a simple mass balance model is used to investigate the cycling of rees in the indian river lagoon and its underlying subterranean estuary mass balance modeling reveals that the indian river lagoon is approximately at steady state with respect to the ree fluxes into and out of the lagoon however the subterranean estuary is not at steady state with respect to the ree fluxes specifically the model suggests that the sgd nd flux for example exported from the subterranean estuary to the overlying lagoon waters exceeds the combined input to the subterranean estuary from terrestrial sgd and recirculating marine sgd by on average 100 mmol day 1 the mass balance model also reveals that the subterranean estuary is a net source of light rees lree and middle rees mree to the overlying lagoon waters but acts as a sink for the heavy rees hree geochemical modeling and statistical analysis further suggests that this fractionation occurs in part due to the coupling between ree cycling and iron redox cycling within the indian river lagoon subterranean estuary the net sgd flux of nd to the indian river lagoon is 7 fold larger than the local effective river flux to these coastal waters this previously unrecognized source of nd to the coastal ocean could conceivably be important to the global oceanic nd budget and help to resolve the oceanic nd paradox by accounting for a substantial fraction of the hypothesized missing nd flux to the ocean

genetic and temporal relations between formation waters and biogenic methane upper devonian antrim shale michigan basin usa abstract controversy remains regarding how well geochemical criteria can distinguish microbial from thermogenic methane natural gas in most conventional deposits has migrated from a source rock to a reservoir rarely remaining associated with the original or cogenetic formation waters we investigated an unusual gas reservoir the late devonian antrim shale in which large volumes of variably saline water are coproduced with gas the antrim shale is organic rich of relatively low thermal maturity extensively fractured and is both source and reservoir for methane that is generated dominantly by microbial activity this hydrogeologic setting permits integration of chemical and isotopic compositions of coproduced water and gas providing a unique opportunity to characterize methane generating mechanisms the well developed fracture network provides a conduit for gas and water mass transport within the antrim shale and allows invasion of meteoric water from overlying aquifers in the glacial drift steep regional concentration gradients in chemical and isotopic data are observed for formation waters and gases dilute waters grade into dense brines 300 000 ppm over lateral distances of less than 30 km radiogenic 14c and 3h and stable isotope 18o and d analyses of shallow antrim shale formation waters and glacial drift groundwaters indicate recharge times from modern to 20 000 yr bp carbon isotope compositions of methane from antrim shale wells are typical of the established range for thermogenic or mixed gas 13c 47 to 56 however the unusually high 13c values of co2 coproduced with methane 22 and dissolved inorganic carbon dic in formation waters 28 require bacterial mediation the d values of methane and coproduced formation water provide the strongest evidence of bacterial methanogenesis methane ethane propane ratios and 13c values for ethane indicate 1 the presence of a thermogenic gas component that increases basinward and 2 progressive bacterial oxidation of ethane as the antrim shale subcrop is approached multiple episodes of pleistocene glaciation over northern michigan appear critical to the development of these gas deposits loading of thick ice sheets may have provided hydraulic head that enhanced dilation of preexisting fractures and influx of meteoric water the physical erosion cycle of repeated glacial advances and retreats exhumed the antrim shale around the northern margin of the michigan basin subjecting it to near surface physiochemical and biochemical processes the chemical and hydrologic relations demonstrated in the antrim shale reservoir suggest a dynamic connection between pleistocene glacial history of the midcontinent region and development of recoverable microbially generated natural gas reserves

the undrained equilibrium behaviour of gassy sediments gassy soils are defined as those soils which contain a relatively large amount of gas dissolved in the pore fluid examples include the alberta oil sands marine sediments from deep ocean locations

13c 18o isotope signatures and clumped isotope thermometry in foraminifera and coccoliths accurate constraints on past ocean temperatures and compositions are critical for documenting climate change and resolving its causes most proxies for temperature are not thermodynamically based appear to be subject to biological processes require regional calibrations and or are influenced by fluid composition as a result their interpretation becomes uncertain when they are applied in settings not necessarily resembling those in which they were empirically calibrated independent proxies for past temperature could provide an important means of testing and or expanding on existing reconstructions here we report measurements of abundances of stable isotopologues of calcitic and aragonitic benthic and planktic foraminifera and coccoliths relate those abundances to independently estimated growth temperatures and discuss the possible scope of equilibrium and kinetic isotope effects the proportions of 13c 18o bonds in these samples exhibits a temperature dependence that is generally similar to that previously been reported for inorganic calcite and other biologically precipitated carbonate containing minerals apatite from fish reptile and mammal teeth calcitic brachiopods and molluscs aragonitic coral and mollusks most species that exhibit non equilibrium 18o 16o 18o and 13c 12c 13c ratios are characterized by 13c 18o bond abundances that are similar to inorganic calcite and are generally indistinguishable from apparent equilibrium with possible exceptions among benthic foraminiferal samples from the arctic ocean where temperatures are near freezing observed isotope ratios in biogenic carbonates can be explained if carbonate minerals generally preserve a state of ordering that reflects the extent of isotopic equilibration of the dissolved inorganic carbon species

extraction of nd isotopes from bulk deep sea sediments for paleoceanographic studies on cenozoic time scales abstract nd isotopes preserved in fossil fish teeth and ferromanganese crusts have become a common tool for tracking variations in water mass composition and circulation through time studies of nd isotopes extracted from pleistocene to holocene bulk sediments using hydroxylamine hydrochloride hh solution yield high resolution records of nd isotopes that can be interpreted in terms of deep water circulation but concerns about diagenesis and potential contamination of the seawater signal limit application of this technique to geologically young samples in this study we demonstrate that nd extracted from the 63 m decarbonated fraction of older ocean drilling program odp sediments using a 0 02 m hh solution produces nd isotopic ratios that are within error of values from cleaned fossil fish teeth collected from the same samples indicating that the hh extractions are robust recorders of deep sea nd isotopes this excellent correlation was achieved for 94 paired fish teeth and hh extraction samples ranging in age from the miocene to cretaceous distributed throughout the north tropical and south atlantic and composed of a range of lithologies including carbonate rich oozes chalks and black shales the strong nd signal recovered from cretaceous anoxic black shale sequences is unlikely to be associated with ferromanganese oxide coatings but may be derived from abundant phosphatic fish teeth and debris or organic matter in these samples in contrast to the deep water nd isotopic signal sr isotopes from hh extractions are often offset from seawater values suggesting that evaluation of sr isotopes is a conservative test for the integrity of nd isotopes in the hh fraction however rare earth elements ree from the hh extractions and fish teeth produce distinctive middle ree bulge patterns that may prove useful for evaluating whether the nd isotopic signal represents uncontaminated seawater alternatively a few paired hh extraction and cleaned fish teeth samples from each site of interest can be used to verify the seawater composition of the hh extractions the similarity between isotopic values for the hh extraction and fish teeth illustrates that the extensive cleaning protocol applied to fish teeth samples is not necessary in typical carbonate rich deep sea sediments

did cooling oceans trigger ordovician biodiversification evidence from conodont thermometry the ordovician period long considered a supergreenhouse state saw one of the greatest radiations of life in earth9s history previous temperature estimates of up to 70 c have spawned controversial speculation that the oxygen isotopic composition of seawater must have evolved over geological time we present a very different global climate record determined by ion microprobe oxygen isotope analyses of early ordovician silurian conodonts this record shows a steady cooling trend through the early ordovician reaching modern equatorial temperatures that were sustained throughout the middle and late ordovician this favorable climate regime implies not only that the oxygen isotopic composition of ordovician seawater was similar to that of today but also that climate played an overarching role in promoting the unprecedented increases in biodiversity that characterized this period

hydraulic fracturing of soil during laboratory experiments part 1 methods and observations hydraulic fracturing appears to have useful environmental and geotechnical applications but the details of fracture morphology and propagation in soil are poorly known to identify those details

calcite dust and the atmospheric supply of nd to the japan sea abstract we report neodymium concentrations and isotope ratios e nd measured in the carbonate and silicate fractions of chinese loess the goal of the study is to investigate if the atmospheric supply of dissolved calcite dust to the oceans influences the cycling of nd in seawater we primarily focus on the japan sea because it receives large quantities of dust from eastern asia and it has a known nd isotope composition and a simple hydrologic budget a steady state atmospheric transport model is used to calculate the flux of soluble nd delivered to the japan sea surface by the wet deposition of dissolved calcite dust this information is then incorporated in a steady state two box model in order to evaluate controls on dissolved e nd values as well as to calculate the residence time of nd in seawater on average calcite in fresh chinese loess contains 150 nmol of nd g 1 with an e nd of 8 6 the atmospheric input of dissolved calcite to the japan sea surface is 7 4 10 12 g yr 1 which corresponds to a dissolved nd flux of 1 1 10 18 pmol yr 1 this flux represents the largest input of nd to the basin and it is required to produce the e nd composition of japan sea waters approximately 65 of the nd flowing from the japan sea surface into the western north pacific originates directly from the input of dissolved calcite dust downwelling surface water and the remineralization of settling particles containing nd scavenged from surface water contribute 77 of the nd in the japan sea deep which indicates that 50 of the deep nd originates from calcite dust the e nd composition of deep water is balanced by a benthic flux but the input is a factor of 10 lower than the calcite dust flux and accounts for only 23 of the deep nd surface and deep waters in the japan sea have nd residence times with respect to particle scavenging of 14 and 530 yr respectively these findings reveal that the atmospheric supply of dissolved calcite dust to the japan sea is a more important component of the marine nd cycle in this basin than previously recognized

katian upper ordovician delta c 13 chemostratigraphy and sequence stratigraphy in the united states and baltoscandia a regional comparison delta c 13 values of numerous limestone samples from katian upper ordovician successions in oklahoma and the upper mississippi valley document the presence of at least three of the four positive excursions that have been recognized in the lower middle katian interval in the cincinnati region in ohio kentucky and indiana a comparison with estonia reveals that five out of the six positive excursions now recorded through the katian succession in the cincinnati region are present in the coeval stratigraphic intervals in estonia which suggests that these represent global perturbations in the carbon cycle a study of the relations between flooding events and delta c 13 excursions shows that only some of the excursions occur in transgressive intervals whereas other excursions are in regressive strata and hence this is in conflict with the idea that positive carbon isotope excursions are forced by rises in sea level part of a previously published attempt to use upper ordovician sequence stratigraphy for trans atlantic correlation is shown to be seriously out of phase with the biostratigraphy and chemostratigraphy several of the sequences recognized in the cincinnati region do not appear to have counterparts in estonia which suggests that they do not reflect eustatic but local conditions c 2010 elsevier b v all rights reserved less

rare earth elements in foraminifera tests abstract the concentrations of nine rare earth elements ree la ce nd sm eu gd dy er and yb have been determined in mixed species assemblages of foraminifera tests taken from atlantic ocean sediment core tops reductive cleaning techniques have revealed that ree are present in three phases in foraminifera tests collected from sea floor sediments ree included in the foraminiferal calcite matrix termed lattice ree ree associated with an authigenic femn rich phase adsorbed onto the surface of the test following the death of the organism termed coating ree and ree associated with alumino silicate detritus termed detrital ree which commonly infills the test chambers after burial in the sediment the concentrations of ree in the nondetrital lattice plus coating and lattice phases have been measured in this study approximately 90 of the ree measured in the non detrital phase reside in the coating phase the remainder being present in the lattice phase these data have been used to investigate the relationship between the distribution of dissolved ree in the ocean and in the coating and lattice phases in addition to the ree the concentrations of mn fe cu al and po4 have been measured as an aid to characterisation of the various phases

forms of hydraulic fractures in shallow fine grained formations hydraulic fractures have been created in fine grained formations at depths of 2 10 m to improve the performance of environmental remediation projects at dozens of locations and in a wide range of geologic conditions the effectiveness of a hydraulic fracture during remediation will depend primarily on its form that is its shape thickness orientation length width and location with respect to the borehole the forms of many hydraulic fractures have been determined by mapping exposures in excavations and by compiling split spoon sampling data these observations indicate that a typical hydraulic fracture at shallow depths is gently dipping slightly elongate in plan and slightly asymmetric with respect to the parent borehole shallow hydraulic fractures lift the ground surface to produce gentle domes and the pattern of uplift reflects the location and thickness of the fracture at depth the forms of hydraulic fractures created over a narrow range of depths at the same site are similar but the forms

nd isotopic constraints on sediment sources of the ouachita marathon fold belt nd isotopes for the overthrust deep marine ouachita marathon sedimentary assemblage of arkansas oklahoma and west texas and associated paleozoic shelf and foreland deposits resolve into three distinct populations 1 lower to middle ordovician nd 13 to 16 average t dm 2 0 ga 2 upper ordovician to pennsylvanian nd 6 to 10 average t dm 1 6 ga and 3 mississippian tuffs nd 1 to 3 average t dm 1 1 ga a rapid shift in nd from 15 passive margin shales to 7 orogenic turbidites in the ouachita assemblage at ca 450 ma implies termination of craton dominated sources and the emergence of the appalachian orogen as the primary source of sediment for sea floor lying south of north america this connection is reinforced by nd isotopes in ordovician silurian turbidites from both the ouachita assemblage and the southern appalachian sevier martinsburg taconic foredeep which are identical nd 7 to 9 the post 450 ma ouachita assemblage falls along a single nd isotopic trend that significantly is not deflected by onset of carboniferous flysch nd 7 to 10 sedimentation nor by associated regional volcanism the less negative nd 2 of mississippian ash flow tuffs that erupted from arc s to the south probably resulted from isotopic mixing of old precambrian crust with young mantle derived components within a continental margin arc there is little isotopic trace element or petrographic evidence for any significant volcaniclastic detritus in the carboniferous turbidites indicating that volcanic arc sources were minimal nd isotopes in fluvio deltaic strata of the ouachita appalachian foreland and continental interior that is arkoma illinois and black warrior basins nd 7 to 10 imply that continental margin pathways and interior basins received the same detritus as the ouachita trough by pennsylvanian time these data are consistent with a composite carboniferous ouachita submarine fan complex built down the axis of a remnant ocean basin from varied mature immature delivery systems tapping dominantly appalachian fold thrust belt sources to the east graham et al 1975 carboniferous turbidites from the marathon fold belt west texas which are isotopically similar nd 8 to 11 to ouachita turbidites may have been ultimately derived from similar sources however they probably do not represent merely distal turbidites of a ouachita fan complex it is suggested that dominantly appalachian derived detritus augmented by uplifted plutonic and fold thrust belt sources south of the marathon basin was swept up into subduction complexes on the north side of the approaching arc and recycled along the collision zone

glacial interglacial variations in the neodymium isotope composition of seawater in the bay of bengal recorded by planktonic foraminifera this study presents neodymium isotope and elemental data for cleaned planktonic foraminifera from odp site 758 in the southernmost reaches of the bay of bengal in the north east indian ocean cleaning experiments using oxidative reductive techniques suggest that diagenetic fe mn oxyhydroxide coatings can be effectively removed and that the measured nd isotope composition reflects the composition of seawater from which the foraminiferal calcium carbonate was precipitated modern core top pulleniatina obliquiloculata and globorotalia menardii give end values of 10 12 0 16 and 10 28 0 16 respectively indistinguishable from recent direct measurements of surface seawater in this area a high resolution nd isotope record obtained from g menardii for the past 150 kyr shows systematic variations end 3 on glacial interglacial timescales the timing of those variations shows a remarkable correspondence with the global oxygen isotope record which suggests a process controlling the nd isotope composition that responds in phase with global climate cycles palaeoclimate reconstruction indicates that during the last glacial maximum changes in monsoon circulation resulted in a reduction in rainfall over the indian subcontinent and a decrease in the flux of river water delivered to the bay of bengal thus changes in the riverine input of nd a change in either flux or composition most likely caused the isotope variations although changes in dust source or local ocean circulation may have also played a role these results clearly establish a link between climate change and variations in radiogenic isotopes in the oceans and illustrate the potential of nd isotopes in foraminifera for high resolution palaeoceanographic reconstruction

revision of the position of the ordovician silurian boundary in southern ontario regional chronostratigraphic implications of δ13c chemostratigraphy of the manitoulin formation and associated strata delta c 13 values of 142 samples from the manitoulin formation and subjacent strata collected from 14 exposures and two drill cores on manitoulin island bruce peninsula and the region south of georgian bay suggest that the manitoulin formation is latest ordovician hirnantian rather than earliest silurian in age a delta c 13 excursion identified as the hirnantian isotope carbon excursion hice which has a magnitude of nearly 2 5 parts per thousand above baseline values is present in an interval from the upper queenston formation to the lower to middle part of the manitoulin formation in most of bruce peninsula and in the area south of georgian bay whereas on manitoulin island the rice appears to be absent this indicates that a significant part of the manitoulin formation is older on the bruce peninsula and in its adjacent region than on manitoulin island the chemostratigraphically based conclusions are consistent with biostratigraphic data from conodonts and brachiopods the hirnantian delta c 13 curve from anticosti island quebec is closely similar to those of southern ontario traditionally the ordovician silurian boundary has been placed at the base of the manitoulin formation but the new results suggest that it is more likely to be at or near the base of the overlying cabot head formation these new results have major implications for the interpretation of the geologic history and marine depositional patterns of the latest ordovician of a large part of the north american midcontinent

isotopic evidence for geochemical decoupling between ancient epeiric seas and bordering oceans implications for secular curves isotopic analysis of conodonts and their host limestones sampled between two regionally extensive altered volcanic ash layers in eastern laurentia shows that a 454 ma epeiric sea maintained large lateral differences in nd and c isotope compositions this is consistent with inferred temperature salinity defined epicontinental water masses and restricted circulation between epicontinental and oceanic environments because the majority of old marine fossils and sedimentary rocks are known from epeiric seas some isotope excursions in ancient marine strata may originate from expansion and contraction of geochemically distinct epicontinental water masses rather than global scale changes in the state of the earth ocean system

rare earth element and nd isotopic variations in regionally extensive dolomites from the burlington keokuk formation mississippian implications for ree mobility during carbonate diagenesis abstract marine carbonates of the burlington keokuk fm miss of the midcontinent region have been subject to two major episodes of regionally extensive 100 000 km2 dolomitization previous studies of the cathodoluminescent petrography sr c and o isotopic compositions and sr fe mn and ca concentrations of burlington keokuk dolostones outline a diagenetic history in which lime mud was pervasively dolomitized by a seawater dominated fluid at many localities this early dolomite generation dolomite i was recrystallized by nonmarine diagenetic fluids at shallow burial depths to produce dolomite ii dolomites i and ii have similar rare earth element ree patterns and abundances and a narrow range of initial 143nd 144nd isotope ratios of 0 511906 0 000025 1 this consistency in the nd isotope ratios and ree patterns along with the presence of anomalously low abundances of cerium in the dolomites cherts glauconite pellets fish apatite and crinoids suggests that 1 seawater derived ree dominated the system and 2 the extensive water rock interaction that produced profound textural and compositional changes during the formation of dolomite ii did not significantly alter the ree patterns or nd isotopic signatures of the dolomites the results of quantitative modeling of isotopic and trace lement exchange during water rock interaction in carbonate systems indicate that extremely large water rock ratios are required to alter the ree signatures of diagenetic carbonates such large water rock ratios can reflect either 1 large extents of fluid flow during carbonate recrystallization or 2 minimal interaction between diagenetic fluids and host rocks during carbonate cement crystallization late vug filling calcite and dolomite have low sm nd and high ce nd n ratios relative to the dolostones such distinct ree signatures probably reflect limited interaction between late diagenetic fluids and burlington keokuk host rocks penecontemporaneous clastic sediments have similar initial 143nd 144nd isotope ratios 0 511857 0 511877 and lower sm nd ratios compared to the dolomites suggesting 1 a common crustal source of ree for the clastics and carbonates and 2 ree fractionation during the formation of carbonate apatite glauconite and other authigenic phases in the marine environment

kinetics of weathering and diagenesis weathering and diagenesis are discussed from a kinetic standpoint such a discussion depends upon an intimate interplay between field measurements laboratory experiments and mathematical theory because of the accessibility of soils and sediments models based on laboratory measurements and theoretical calculations can be used along with field data to calculate rate parameters which are otherwise difficult to measure in the laboratory also theoretical models can be tested in the field ways in which chemical kinetics can be applied to geological problems in the surficial environment are discussed and the author recomends extensive future study of such problems jmt

reefs during the multiple crises towards the ordovician silurian boundary anticosti island eastern canada and worldwide multiple latest ordovician rawtheyan hirnantian glaciations in central africa with concomitant global sea level lowstands and cooler restricted equatorial carbonate shelves and ramps interrupted by warmer interstadial highstands had a dramatic global impact on the tropical shallow water reef ecosystem and carbonate production with the ordovician silurian boundary strata on anticosti island as a global standard for a carbonate shelf ramp setting the latest ordovician and earliest silurian reveal three reef phases ended by three extinctions the first extinction towards the end of the rawtheyan affected the last richmondian type reefs vaureal formation mill bay member the second extinction was less pronounced ending with reefs at the base of the prinsta member ellis bay formation interpreted as the top of the normalograptus extraordinarius graptolite subzone the third and most severe extinction phase capped the laframboise patch reef complex ellis bay formation at the top of the no

crystal chemical controls on rare earth element concentrations in fossil biogenic apatites and implications for paleoenvironmental reconstructions abstract fossil biogenic apatites display rare earth element ree patterns which have been proposed to reflect environmental and biological controls on past seawater composition these patterns can be separated in two groups 1 patterns that are similar to those of open ocean and epicontinental waters and 2 patterns that exhibit a strong enrichment in intermediate ree bell shaped patterns because ree trapping in biogenic apatites occurs mostly post mortem it is essential to understand the crystal chemical inorganic factors that can influence the fractionation of ree between apatite and water a model is proposed by which partition coefficients of ree between apatite and water for a substitution mechanism can be extrapolated from mineral melt partition data to seawater or sedimentary basin conditions these are compared with available experimental partition coefficients for ree adsorption mechanism and used to discuss ree patterns in fossil biogenic apatites calculations of ree patterns for apatites at equilibrium with water show that the bell shaped patterns in fossil apatites can be explained by fractionation with seawater or continental fluids at low temperature under crystal chemical control involving a substitution mechanism and in the context of extensive or late diagenesis in that case the equilibrium composition of the fluid cannot be unequivocally determined from observed ree concentrations in fossil apatites this type of sample is inappropriate to discuss the past environmental or biological controls on ree concentrations in the ocean other sample compositions suggest little to moderate alteration of the original oceanic to freshwater pattern through the adsorption mechanism in the context of weak or early diagenesis and may be used with caution for that purpose

physico chemical mechanisms of weathering processes and corresponding models of dynamics of mineral zonality evolution abstract the peculiarities of weathering processes involving duration slow change of ambient conditions isothermality as well as proceeding in open systems permit to study these processes in a steady state approach d c i d t 0 where ci is concentration of intermediates and t is time the most typical quasi stationary processes for a water rock system are 1 non equilibrium step surface reaction of primary mineral dissolution and 2 non equilibrium step secondary mineral precipitation these respectively determine two extreme mechanisms of mineral formation 1 pseudomorphous replacement and 2 dissolution transfer crystallization besides non stationary weathering processes are known it is the case when a process is controlled by diffusion through a layer of secondary minerals which have been deposited on the surface of the primary mineral a mathematical model of weathering dynamics of feldspar with its metasomatic replacement by clay minerals is presented numerical simulation led to the prediction of mineral zonality development along the weathering profile at any time

neodymium and strontium isotopic dating of diagenesis and low grade metamorphism of argillaceous sediments the behaviour of the rb sr and sm nd isotopic systems with increasing degree of hercynian metamorphic overprint was studied along a transect in cambrian shales of northwestern morocco clay fractions of 0 2 to 2 6 m size from five samples were investigated representing a range from nonmetamorphic to epizonal metamorphic conditions the samples were washed in cold l n hc1 prior to digestion to separate soluble exchangeable rb sr sm and nd from amounts of these elements fixed in the crystallographic sites of the minerals and to analyze both components separately the results reveal that the rb sr isotopic system is dominated by sr hosted by clay mineral phases both detrital and authigenic illite and chlorite and carbonate hosted soluble sr isotopic homogenization of sr occurred during hercynian metamorphism yielding ages between 309 and 349 ma the sm nd isotopic system on the other hand is dominated by cogenetic apatite and fe oxide hydroxide both having high contents of leachable rees the leachates yield a sm nd isochron age of 523 72 ma indicating diagenetic equilibrium between apatite and fe oxide hydroxide fine grained clay fractions of 0 2 m show inheritance of a detrital nd component the study demonstrates that the diagenesis of the investigated argillaceous sediments can be dated by the sm nd chronometer in authigenic cement phases the isotopic system of these minerals apatite fe hydroxide oxide was homogenized during authigenic mineral growth in a sediment that was flushed by diagenetic fluids and had abundant primary or secondary interconnected pore space the hercynian metamorphic overprint caused partial isotopic rehomogenization of the adsorbed and clay hosted portion of the sr as well as of the carbonate hosted sr the sm nd system in the cement phases survived this metamorphism this results in decoupling of the two isotopic systems and allows the dating of diagenesis on the one hand sm nd and metamorphism on the other hand rb sr

nd isotope records of late ordovician sea level change implications for glaciation frequency and global stratigraphic correlation abstract detailed records of ice sheet advances and retreats are reconstructed for the hirnantian and katian ages of the late ordovician using nd isotopes e nd as a sea level proxy in three study sections from the western margin of laurentia two shallow water platform sections located south and north of the paleo equator and one deep water section located in a continental slope rise setting when sea level was high and paleo shorelines had migrated eastward the e nd value of seawater in the vicinity of each of the study sections shifted toward the e nd value of the eastern panthalassa ocean 4 0 by contrast when sea level was low and paleo shorelines had migrated westward the e nd value of seawater shifted toward the e nd value of the continental weathering flux from laurentia 8 5 0 2 2 mean these stratigraphic patterns of changing e nd values are interpreted to reflect the eustatic sea level fluctuations that previous studies have documented in response to gondwanan ice sheet advances and retreats thus linking the e nd sea level proxy to late ordovician global scale climate changes the e nd profiles for the two platform sections yielded similar proxy sea level curves with five cycles of oscillation recorded during the latest katian and hirnantian three additional cycles of late katian sea level change are recognized in the e nd profile of the deep water continental slope rise section the combination of e nd 13 c and graptolite biostratigraphic data facilitates a precise interregional correlation of the hirnantian age and the paleoclimate changes that took place during this interval the new correlations support previous findings that the hirnantian ice age comprised two major glacial periods separated by a minor interglacial during the early part of the metabolograptus persculptus biozone the younger glacial confined to mid m persculptus biozone time led to more extensive sea surface cooling than did the earlier one and resulted in extensive eustatic sea level drawdown and c cycle changes it records the strata most often recognized as hice the hirnantian carbon isotope excursion in sedimentary successions worldwide such as anticosti island scotland estonia siberia and south china the results of this study support and strengthen the view that glaciation predated the hirnantian age in the late ordovician and that the records of small positive 13 c excursions in katian successions from baltica and eastern north america are themselves proxy indicators of glaciation frequency and eustatic sea level changes

high resolution stable isotope stratigraphy of upper ordovician sequences constraints on the timing of bioevents and environmental changes associated with mass extinction and glaciation the two phases of the late ordovician mass extinction are approximately coeval with the periods of rapid climate change associated with the onset and demise of the gondwanan glaciation in this paper we argue that the distinctive late ordovician carbon isotope profile provides a chronostratigraphic ruler against which a sequence of environmental and biotic events may be located the ruler also allows regional and global high resolution correlation of successions representing very different environments cores from the upper ordovician succession of estonia and latvia record a large 1 3 c c a r b o n a t e excursion up to 6 with a similar profile shape the consistent relationship between the chemostratigraphy and biostratigraphy in the baltic region suggests that the isotope profile has a regional chronostratigraphic value the presence of similar profiles in nevada united states suggests that the excursion is a global chronostratigraphic signal this interpretation enables a detailed correlation to be made between upper ordovician shallow marine and basinal sequences that have wholly different faunas successions in the baltic area and in canada that do not display the model profile are interpreted as incomplete reinter pretation of these important successions significantly modifies the global database used to assess the pattern of diversity change during the mass extinction key levels of environmental change have been located against the carbon isotope profile new oxygen isotope data from brachiopod and ostracode calcite set tight limits on the start of the glacial events cooling and sea level fall started at the same stratigraphic level as the start of the carbon isotope excursion the later rise in sea level and fall in oxygen isotope values record the end of the glaciation these restrict the duration of the main glaciation to only 1 5 graptolite zones we propose that models of the carbon cycle should be adapted to be consistent with the temporal relationships between carbon cycling sea level fall and temperature change documented here the chronostratigraphic ruler provided by the carbon isotope profiles is used as a scale to determine the sequence of biotic changes and to allow high resolution correlation of biotic events at different locations this approach identifies regional similarities and differences in the patterns of extinction the main phase of graptolite extinction in the monitor range nevada for example is synchronous with the chitinozoan extinction in the baltic region but chitinozoan taxa survive to higher levels in nevada the benthic faunas in the baltic region demonstrate that the main extinction event corresponded with the beginning of the isotope excursion at the start of the hirnantian the level at which the marine environment started to change rapidly but that there were further extinctions of species within the early hirnantian the cold adapted hirnantia fauna did not appear immediately after the extinction in this area the relationship between the second phase of extinction and the carbon isotope excursion is less clear but the available data suggest that the extinction coincides with a time of rapid environmental change but not at the inception of environmental change as happened in the first phase

rare earth elements in limestone marlstone couplets from the albian cenomanian cismon section venetian region northern italy assessing ree sensitivity to environmental changes abstract we have studied the ree distribution through the albian cenomanian interval of a stratigraphic succession cismon section scaglia variegata formation venetian prealps consisting of rhythmically alternating carbonate rich and carbonate poor strata which are the sedimentary expression of systematic variations of surface fertility and bottom water redox conditions in the depositional basin limestone semicouplets show seawater like shale normalized patterns hree enriched with negative ce anomalies and high er nd ratios indicating a clear dependence on the ree chemistry of surface seawaters marlstones and shales exhibit flatter patterns more moderate ce anomalies and low er nd good correlations between er nd ce ce and mn suggest that superimposed on ree signatures imparted by detrital and biogenic phases the ree composition shows evidence of their sensitivity to palaeoredox conditions resulting in ree fractionation and ce cycling ree data are consistent with results from previous stratigraphic and geochemical major and trace elements investigations in reflecting palaeoenvironmental conditions rhythmically varying from efficiently mixed seawater during the limestone deposition to oxygen depleted bottom waters at the time of marlstone deposition

hydraulic fracturing of soil during laboratory experiments part 2 propagation the propagation of hydraulic fractures in soil was studied in the laboratory by glycerine injected at a constant rate into rectangular samples of silty clay confined in a triaxial cell during propagation the trace of a hydraulic fracture appeared on the side of the cell as a nearly straight narrow line that tapered from 0 05 mm to negligible aperture at the tip pressure of the glycerine was recorded as a function of time and is characterized by a period of nearly linear increase a break in slope followed by a period of increasing pressure but decreasing slope a maximum and then a period of decreasing pressure tests terminated early in that sequence of events indicated that the break in slope marks the onset of hydraulic fracturing the pressure at the onset of fracturing was predicted from a determination of the fracture toughness of the silty clay the forms of the pressure records were markedly affected by the water content of the soil increasing water content decreased the pressure required to

glaciation and deglaciation of the libyan desert the late ordovician record detailed outcrop studies at the flanks of al kufrah basin libya reveal the nature of glacially related sedimentation and post depositional deformation styles produced in association with the late ordovician glaciation during which ice sheets expanded northward over north africa to deposit the mamuniyat formation at the se basin flank jabal azbah the mamuniyat formation is sand dominated and incises interfingering braidplain and shallow marine deposits of the hawaz formation the glacially related sediments include intercalations of mud chip bearing tabular sandstones and intraformational conglomerates which are interpreted as turbidite and debrite facies respectively these record aggradation of an extensive sediment wedge in front of a stable former ice margin an increase in mudstone content northward is accompanied by the occurrence of more evolved turbidites a widespread surface bearing streamlined nw se striking ridges and grooves punctuates this succession the structures on the surface are interpreted to have formed during a regional north westward ice advance above siltstones bearing arthrophycus burrows and orthocone bearing sandstones beneath tidal bars testify to glaciomarine conditions for deposition of the underflow deposits beneath by contrast the northern basin margin jabal az zalmah is appreciably different in recording shallower water paralic sedimentation styles and major glaciotectonic deformation features although facies analysis also reveals northward deepening here a siltstone wedging from 8 to 50 m toward the north was deposited lower delta plain succeeded by climbing ripple cross laminated sandstones up to 60 m in thickness distal through proximal delta mouth bar deposits with occasional diamictite interbeds these rocks are deformed by thrusts and 50 m amplitude fault propagation folds the deformation locally sealed by a diamictite then overlain by conglomeratic lag during ultimate deglaciation integrating observations from both basin margins a model of fluvial dominated delta systems feeding a pulsed debrite and turbidite fan system in a shallow proglacial shelf is proposed

middle and upper ordovician carbon isotope chemostratigraphy in baltoscandia a correlation standard and clues to environmental history abstract the baltoscandian epeiric sea was characterised by relatively slow but continuous carbonate deposition from the middle ordovician up to the silurian relatively good preservation of ordovician and silurian carbonate rocks in baltoscandia makes this region unique for chemostratigraphical and palaeoenvironmental studies previous palaeozoic carbon isotope studies have revealed isotopic events in different lithologies over the baltoscandian palaeobasin and some of them on different palaeocontinents we propose a composite carbon isotope curve for the baltoscandian region a new subdivision of the middle and upper ordovician succession into seventeen chemostratigraphic zones and an improved nomenclature of isotopic excursions based on analyses of 13 c carb data from 25 drillcore and outcrop sections of estonia latvia and sweden the composite carbon isotope curve is compared with biostratigraphical data on conodont and chitinozoan distribution the katian hirnantian interval with highly fluctuating isotopic values shows climatic cyclicity of about two million years in baltoscandia no abrupt changes occur in the dapingian sandbian part of the baltoscandian isotope curve but the mid darriwilian excursion nearly coincides with the onset of cooler temperatures similar to modern like equatorial sea surface temperatures and related global biodiversification increase suggesting a climatic background for this event

neodymium isotopic variations in north pacific modern silicate sediment and the insignificance of detrital ree contributions to seawater the neodymium isotopic composition of the silicate fraction of holocene pelagic sediments from the north pacific define two provinces a central north pacific province characterized by unradiogenic and remarkably homogeneous end 10 2 0 5 and a narrow circum pacific marginal province characterized by more radiogenic and variable end 4 2 3 8 the silicate fraction in the central north pacific is exclusively eolian based on prevailing wind patterns meteorological data and neodymium isotopic data the only significant sediment source is chinese loess leaching experiments on chinese loess confirm that leachable nd is isotopically indistinguishable from bulk and residual silicate nd silicates in the circum north pacific marginal province comprise eolian loess volcanic ash and hemipelagic sediments derived from volcanic arcs a compilation of pacific seawater and mn nodule end data shows no clear spatial variation except for a general decrease from surface to deep waters from 3 to 4 and slightly lower end in bottom waters along the western north pacific due to the incursion of antarctic bottom water the relative homogeneity of bottom water end which contrasts sharply with the distinctive variation in sediment end plus the large difference between the average end of bottom waters and the central north pacific eolian silicates 4 vs 10 suggests that any contribution of ree to seawater from eolian materials is insignificant furthermore leaching of ree from eolian particles as they sink though the water column must be insignificant because nd in shallow waters is more radiogenic than nd in deeper waters that there is no contrast in the nd isotopic composition of bottom waters that overlie the central and marginal sediment provinces suggests that the ash and hemipelagic sediments derived from pacific rim volcanic arcs also contribute minimal ree to seawater the elimination of eolian ash and hemipelagic sediments leaves only near shore riverine particulates as a possibly significant particulate source of ree to seawater

tightly coupled records of ca and c isotope changes during the hirnantian glaciation event in an epeiric sea setting abstract a 44 40 ca excursion of 0 5 is recorded during the hirnantian glaciation event in carbonate rocks of the monitor range section in nevada the timeframe for the glaciation is 1 03 0 2 ma the 44 40 ca changes are synchronous with lithofacies and biofacies indicators of sea level change and co vary negatively with a large positive 13 c excursion of 7 that was previously interpreted to reflect local c cycling effects in circulation restricted waters of the epeiric martin ridge basin the synchronousness of the ca and c isotope excursions is inconsistent with what we know of ca and c geochemical cycles in the modern ocean because the residence time of ca is longer than that of c a box model is used to illustrate that the negative 44 40 ca excursion would take longer to recover than the positive 13 c excursion if the relative timescales of the hirnantian ca and c cycles were scaled similarly to those in the ocean today one way to speed up the timescale of the ca isotope response is to decrease the size of the ca reservoir this is what is accomplished when seawater circulation is restricted between oceans and epeiric seas approximately 30 of the 0 5 shift in hirnantian 44 40 ca values may be attributed to lower sea surface temperatures in the tropics during glaciation the remainder is attributed to local ca cycling effects in the martin ridge basin which include an increase in isotopically light ca inputs by submarine groundwater discharge sgd and a larger kinetic isotope fractionation effect due to increased carbonate precipitation rate the hypothesized increase in carbonate precipitation rate may have been caused by high photosynthesis rates maintained by high nutrient fluxes from sgd which increased the local carbonate saturation state of the waters additionally the conditions in this setting may have fostered a suite of organisms employing a calcification mechanism that involved microenvironments bacterial or algal surfaces biofilms or sedimentary pore fluids where biological activity could effectively alter the carbonate chemistry in very small c reservoirs a similar scenario was presented by laporte et al 2009 to explain the bulk of the anomalously large 7 positive 13 c excursion in the same section the strong negative coupling between the stratigraphic records of ca and c isotope changes in the martin ridge basin may serve as a tool to identify other epeiric sea settings in the rock record where similar physical and ecological attributes developed during periods of restricted circulation brought on by low sea level

rare earth elements in old biogenic apatites abstract the ree distributions in individual upper devonian conodonts have been measured by ion probe the patterns of all analyzed conodonts are enriched in middle ree eu gd and have a weak or no ce anomaly concentrations and la yb or la sm ratios vary very little within or among individuals from the same zone which suggests that uptake of labile ree from sediments was essentially quantitative therefore the ree signature of the primary carriers probably organic and oxyhydroxides particulates from marine suspensions was efficiently transferred to biogenic apatites and survived late diagenetic processes ree patterns of conodonts do not resemble those of present day seawater and post cretaceous biogenic phosphates which are typically depleted in nd and sm with a negative ce anomaly since ree distributions in the modern water column mimic those of nutrients we assume that in pre cretaceous seawater they were not controlled by surface biological activity we assume instead that ree in pre cretaceous seawater can be explained by mechanism of desorption adsorption on particle surfaces progressive extraction of lree from river water by oxyhydroxides leads to precipitates enriched in middle ree a simple quantitative model was calculated in order to illustrate the proposed mechanism

late ordovician early silurian ashgillian llandovery sea level curve derived from conodont community analysis anticosti island quebec abstract earlier workers have established sea level curves for the ashgillian llandovery sequence on anticosti island quebec canada based on sedimentology and on brachiopod and reef communities the complete anticosti sequence has been collected for conodonts to provide a database of over 77 600 conodonts derived from 272 samples through the 800 1100 m sequence this paper uses a statistical analysis of the database to establish the pattern of conodont communities and their interpreted water depths this allows the establishment of a eustatic sea level curve for the sequence this curve is in general agreement with those of the earlier workers but is more detailed and better constrained stratigraphically given the large sampling program the curve reflects more oscillating sea level changes for the whole sequence than those constructed earlier and different water depths for certain intervals from those established earlier the curve is valuable given that the anticosti sequence is one of the most complete in the world for this interval and its divergence from global eustatic curves for this interval is noted

a weathering hypothesis for glaciation at high atmospheric pco2 during the late ordovician new paired carbonate and organic carbon isotope analyses from nevada usa together with a consideration of the effects of mountain building and ice sheet coverage of the continents on atmospheric pco2 lead to a new hypothesis for the cause of the late ordovician glaciation we suggest that the taconic orogeny which commenced in the late middle ordovician caused a long term decline in atmospheric pco2 through increased weatherability of silicate rocks ice sheet growth was triggered when pco2 decreased to a threshold of 10 present atmospheric level and proceeded by positive ice albedo feedback in the midst of glaciation atmospheric pco2 began to rise as continental silicate weathering rates declined in response to coverage of weathering terrains by ice sheets at first this enhanced greenhouse effect was overcompensated for by ice albedo effects ultimately however atmospheric pco2 reached a level which overwhelmed the cooling effects of ice albedo and the glaciation ended the isotope results can be interpreted to indicate that atmospheric pco2 rose during the glaciation consistent with other proxy information although alternative interpretations are possible the large positive carbonate isotope excursion observed in late ordovician rocks around the world is explained as the expected response to increased carbonate platform weathering during glacioeustatic sea level lowstand rather than as a response to increased organic carbon burial

chemical variation in pennsylvanian brachiopod shells diagenetic taxonomic microstructural and seasonal effects abstract to improve our ability to use minor and trace element mte variation in biotic carbonates as diagenetic and paleoenvironmental indicators we performed electron probe microanalysis on more than 100 late pennsylvanian brachiopod shells from texas kansas missouri and new mexico texturally preserved specimens of the genera crurithyris composita and neospirifer from all three regions were analyzed as were eridmatus specimens from texas twenty measurements were made in two transects across each shell shell microstructure and cathodoluminescence were described for each spot analyzed three modern shells were analyzed for comparison diagenesis as indicated by cathodoluminescence and or absence of microstructure tends to enrich shells in fe and mn x ca 0 7 mmol mol and deplete shells in na and s mg content shows no consistent trend with diagenesis in fabric retentive nonluminescent shell areas mg na and s contents vary twofold to sevenfold depending on taxonomy microstructure and season overall taxonomy is the dominant factor controlling mte composition na and s concentrations are consistently highest in crurithyris and eridmatus intermediate in neospirifer and lowest in composita in taxa with mixed microstructure composita neospirifer secondary fibrous layer calcite contains 1 5 to 2 times more na than does interlayer prismatic calcite thus whole shell na contents of these taxa depend on the proportion of fibrous and prismatic shell seasonal cycles are revealed in mte transects across growth lines mg na and s contents commonly vary by more than a factor of two between maxima presumably summer and minima winter within the same shell retention of taxonomic microstructural and seasonal effects in shell chemistry argues for preservation of original chemistry in fabric retentive nonluminescent paleozoic brachiopod shells

late ordovician mass extinction a new perspective from stratigraphic sections in central nevada integrated sequence stratigraphic biostratigraphic and chemostratigraphic analyses of three stratigraphic sections in central nevada indicate that late ordovician glaciation induced sea level fall produced diachronous stepwise faunal turnover in graptolites conodonts chitinozoans and radiolarians and also triggered a strong but transient positive 13c excursion this pattern is very different from that described for most mass extinction events

the sources and transport of sr and nd isotopes in the baltic sea we have determined the concentration and isotopic composition of sr and nd in waters from the baltic sea the baltic sea is an intracontinental stratified brackish water estuarine like system and the rivers emptying into it drain a suite of terranes ranging from proterozoic archean in the north to phanerozoic in the south the sampled brackish waters range in salinity from seawater sw at 35 289 to a minimum of 2 460 at the surface in the innermost part of the gulf of bothnia the sr concentrations show generally conservative behavior indicating a simple two component mixing however small deviations 3 70 from a perfect mixing line reveal that the imprints from rivers with different sr concentrations are preserved in the blending strontium concentrations from a depth profile across the redoxcline in the baltic proper indicate that vertical particle transport alters the sr concentration in the water our estimated concentration of sr in the average freshwater input to the baltic is 0 03 ppm which is only about 0 4 of the sw concentration the sr isotopic data range from e sr sw 0 in seawater to e sr bw sw 7 8 in the least saline baltic water bw sample in the gulf of bothnia the isotopic composition of sr versus 1 sr in the baltic sea follows an almost perfect mixing line which shows that seawater sr is mixed with much more radiogenic components calculated end member values of e sr sw for each sample show that the riverine input into the gulf of bothnia has e sr sw 120 200 and 10 50 e units in the baltic proper these values are in general agreement with direct measurements of river waters in each region however the calculated values in the gulf of bothnia are lower than the measured river water input in this region which indicates the presence of less radiogenic sr presumably originating from the river waters draining the southern part of the basin which are partially transported northward and mixed with sr from the gulf of bothnia rivers the nd concentration in the baltic sea is not conservative varying between 5 and 45 ppt with the highest concentrations in the bottom waters due to vertical particulate transport a plot of e nd o in baltic water yields a good correlation with the calculated freshwater end member e sr sw the data show that it is possible to unravel the different freshwater sources into the baltic and to identify the zones of particulate removal of both non conservative species such as the ree and of quasi conservative species such as sr the use of isotopic tracers in this estuarine environment may provide a much better insight into mixing and element transport it should also be possible to trace lateral movements of freshwater inputs

the ree and end of 40 70 ma old fish debris from the west african platform ree concentrations and nd isotopic compositions have been determined in late cretaceous early cenozoic fish debris from west african and israeli platform sediments and show a strong regional control independent of time except for those from the northern morocco it is suggested that although diagenetic fluids do not contribute ree s directly to the phosphatic debris they may significantly change the ce anomaly and the end t value of the epicontinental seas which in turn control the ree in marine phosphates it is shown that over the investigated period the north moroccan shelf seawater was progressively flushed by deep north atlantic water

upper ordovician sequences of western estonia abstract the upper ordovician uppermost caradoc ashgill section of western estonia consists of a series of seven open shelf carbonate sequences depositional facies grade laterally through a series of shelf to basin facies belts grain supported facies shallow shelf mixed facies middle shelf mud supported facies deep shelf and slope and black shale facies basin locally a stromatactis mud mound occurs in a middle to deep shelf position shallow to deep shelf facies occur widely across the estonian shelf and grade laterally through a transitional slope belt into the basinal deposits of the livonian basin each sequence consists of a shallowing upward prograding facies succession sequences 1 upper nabala stage and 2 vormsi stage record step wise drowning of underlying shelf units lower nabala that culminated in the deposition of the most basinal facies fjacka shale in the livonian basin sequences 3 6 comprise the overlying pirgu stage and record the gradual expansion of shallow and middle shelf facies across the estonian shelf the porkuni stage sequence 7 is bracketed by erosional surfaces and contains the shallowest water facies of the preserved strata the uppermost part of the section normalograptus persculptus biozone is restricted to the livonian basin and includes redeposited carbonate and siliciclastic grains it is the lowstand systems tract of the lowest silurian sequence 8 sequence 7 and the overlying basinal redeposited material i e the lowstand of sequence 8 correspond to the latest ordovician hirnantian glacial interval and the bracketing unconformities are interpreted as the widely recognized early and late hirnantian glacial maximums the sequences appear correlative to upper ordovician sequences in laurentia graptolite biozones indicated that the estonian sequences are equivalent to carbonate ramp sequences in the western united states great basin and mixed carbonate siliciclastic sequences in the eastern united states appalachian basin cincinnati arch region these correlations indicate a strong eustatic control over sequence development despite the contrasting tectonic settings of these basins

rare earth elements and neodymium isotopes in ferromanganese oxide coatings of cenozoic foraminifera from the atlantic ocean abstract an evaluation has been made of the method of establishing the ree contents and patterns and nd isotopic compositions of sea water over cenozoic time from their record in the femn oxide coatings of foraminiferal calcite using 0 60 ma samples from the rio grande rise dsdp site 357 it has been established that the ree contents of the coatings are generally similar to those of recent samples however in the cenozoic samples the surface coatings have been diagenetically modified under suboxic conditions resulting in a distinctly different ree pattern although the original 143 nd 144 nd ratios appear to have been preserved the nd isotopic curve for cenozoic sea water in the s atlantic shows clear temporal trends although these are not so extreme as to show 143 nd 144 nd ratios outside the range observed in modem sea water with the principal exception of the oldest samples there is an approximate inverse relationship between the nd and sr isotopic compositions of the foraminifera it is suggested that the changes reflect both global changes in the relative proportions of nd and sr derived from continental input and from the weathering of volcanic debris together with short term and local variations to which the sr curve is insensitive reflecting the different response times of the two elements to changes in oceanic input functions the nd isotope curve appears to be a potentially useful tracer of ocean palaeochemistry

nd isotopic composition of water masses and dilution of the mediterranean outflow along the southwest european margin nd isotopic compositions epsilon nd of seawater profiles and deep sea corals collected off the coast of iberia and from the bay of biscay were measured 1 to constrain the nd isotopic composition of water masses along the southwest european margin 2 to track the mediterranean outflow water mow during its northward propagation and 3 to establish hydrological changes during the last 1500 years the eastern north atlantic central water enacw is characterized by nd isotopic composition of around 12 0 mediterranean sea water msw is collected from 800 and 1200 m depth and is characterized by epsilon nd values ranging from 10 9 off the coast of iberia to 11 6 in the bay of biscay these epsilon nd results suggest a strong dilution of the pure mow at the strait of gibraltar epsilon nd 9 4 of approximately 40 and 30 along its northward circulation pathway essentially with a contribution from enacw at around 2000 m depth epsilon nd water profiles display the occurrence of a nonradiogenic water mass epsilon nd 13 originating from the labrador sea labrador sea water fossil deep sea corals dated between 84 and 1500 years display nd isotopic compositions that vary moderately from present day seawater values suggesting a weaker influence of mow in the formation of msw during the dark ages and the little ice age these recent cold events seem to be associated with a reduction in the northward penetration of msw which may result from a greater eastward extension of the middepth subpolar gyre and or a reduction of msw formation likely tied to a variation in deep mediterranean water production

sr and nd isotopic evidence for punctuated clay diagenesis texas gulf coast we report rb sr sm nd and mineralogical data for leached whole rock 1200 m independent of the duration of burial the exchangeable sr in the clay has remained an open system and has undergone isotopic exchange since that time minimum fluid rock ratios of 0 2 to 2 are modeled from sr isotopic data consistent with rock dominated open system diagenesis leachates and residues of the 0 1 zm fraction below the smectite illite transition appear to have achieved nd isotopic equilibrium during clay diagenesis and show no signs of subsequent exchange the clay residues have low 147sm 144nd 0 085 indicating that authigenic illite has a lower sm nd ratio than its bulk rock protolith conversely the coexisting exchangeable ree inventory has elevated sm nd as reflected by leachate 14vsm 144nd as high as 0 188 this sm nd fractionation in conjunction with the preserved isotopic equilibrium may be useful for dating diagenesis and associated fluid rock interaction in older rocks

influence of exsolved gases on slope performance at the sarnia approach cut to the st clair tunnel in 1993 over 100 years after the completion of the original st clair tunnel and its approach cuts work com menced on the new st clair tunnel the new tunnel used the existing approaches but required additional excavation to widen and deepen the original cuts in sarnia the new work initiated unusual deep seated deformations on the south slope of the approach effective stress finite element analysis fea using an elliptical cap soil model coupled with biot consol idation theory was used to model the 1993 construction but initial predictions were unable to capture the trend of defor mations noted in the field naturally occurring gases are frequently encountered near the base of the overburden in the sarnia area and this phenomenon was observed during drilling investigations in the sarnia approach cut including the ef fects of the presence of exsolved natural gases in fine grained soils subjected to unloading in the fea results in substan tially better predictions in the trend of deformations on the slopes of the approach cut

effect of gassy sand lenses on a deep excavation in a clayey soil abstract gas venting mainly methane was encountered during a deep excavation in a 40 m thick clayey deposit with silty sand lenses overlying a shale layer believed to be the source of biogenic gas the upward diffusion of methane and chloride from the bedrock aquifer through the clay till is modeled and the potential for chloride migration contributing to the exsolution of methane due to a reduction in methane solubility is discussed two approaches to modeling the lenses are examined where gas exsolution either occurs prior to the excavation or during the excavation both approaches lead to similar conclusions although sand lenses were more prone to liquefaction if the methane was present in its gaseous state prior to unloading the results suggest that while liquefaction of a sand lens near the base of the excavation may have contributed to the formation of the seeps and vents the gassy response of sand lenses due to the exsolution of gas during unloading cannot explain the level of venting that was observed in the field

local and global perspectives on carbon and nitrogen cycling during the hirnantian glaciation abstract the impact of climate and ocean circulation changes on marine carbon and nitrogen cycling was investigated for a period covering the late ordovician hirnantian glaciation three sections were studied two from nevada one proximal and one distal and one from the yukon the opportunity to compare 13 c carb 13 c org and 13 c grap profiles between ocean and epeiric platform settings enabled a more thorough assessment of environmental and diagenetic factors influencing the preservation of seawater 13 c values at each stratigraphic section using the best preserved sedimentary components from the two nevada sections a lowstand sedimentary gradient of 4 was found between platform and ocean settings during the hirnantian glaciation gradients of similar magnitude have been reported from hirnantian platforms in the canadian arctic and baltic basins taking the outboard sections as the most representative of the ocean carbon pool a mean positive 13 c shift of just 2 7 0 4 is calculated which is significantly smaller than the 5 7 positive shifts recorded in epeiric platform settings the discrepancy is attributed to the effects of local carbon cycling in tropical and subtropical epeiric seas it is hypothesized that increased carbonate weathering caused 13 c values of local carbon weathering fluxes to increase which in turn caused seawater 13 c values to increase in basin proximal settings in addition nutrient dust fluxes may have contributed to increased levels of photosynthetic activity in proximal settings driving sedimentary 13 c values even higher much higher than sediment deposited in outboard settings where carbon exchanges with the surface ocean were less restrictive a 15 n profile reconstructed from deposits of the distal vinini creek section records a 1 5 positive shift through the hirnantian glacial interval interpreted as a major late ordovician upwelling zone high organic carbon 1 wt and high hydrogen indices 400 600 make the vinini creek section a suitable candidate for the preservation of original sedimentary 15 n records to explain the results a conceptual model of ocean nitrogen cycling under greenhouse climate conditions is presented that highlights the role of cyanobacteria as both primary producers and nitrogen fixers it is hypothesized that in greenhouse climates the fixed nitrogen inventory of the abyssal ocean was low due to efficient denitrification in the ocean s expansive oxygen minimum zones this caused algal productivity to become strongly dependent on continuous supplies of fixed nitrogen from cyanobacteria in the photic zone yielding sedimentary 15 n values between 0 and 2 by contrast the cooler icehouse climate of the hirnantian led to increased ocean ventilation greater partitioning of atmospheric oxygen into downwelling surface waters and oxygen minimum zone shrinkage as a result fixed nitrogen levels climbed in the ocean s abyssal depths due to the lower denitrification rates this in turn allowed nitrogen with high 15 n values to recycle back into the photic zone driving sedimentary 15 n values higher during the hirnantian glaciation

forensic numerical analysis of gas venting in southwestern ontario abstract a forensic modeling study examines the potential causes of gas and water venting observed during the excavation of a landfill in a 40 m thick clayey till deposit in southwestern ontario canada the clayey till is known to be underlain by permeable natural gas bearing rock and gas has been diffusing through the clayey deposit over about the last 13 000 15 000 years attention is focused on 2d modeling of hydrofracturing as well as gassy soil behavior the model examines the predicted location of venting with and without the presence of gassy sand lenses and a discontinuous layer of basal till between the bedrock and the low permeability till the modeling shows that hydrofracturing alone can explain the occurrence and location of the observed venting in one of the sub cells in the other sub cell hydrofracturing explains the occurrence but not the location of the observed venting or the presence of the sand in the venting water at this location modeling of appropriately placed gassy sand lenses is shown to explain the occurrence and location of the observed venting as well as the presence of both waters with different geochemistry from the bedrock and the till in the venting waters

terminal ordovician carbon isotope stratigraphy and glacioeustatic sea level change across anticosti island quebec canada globally documented carbon isotope excursions provide time varying signals that can be used for high resolution stratigraphic correlation we report detailed inorganic and organic carbon isotope curves from carbonate rocks of the ellis bay and becscie formations spanning the ordovician silurian boundary on anticosti island quebec canada strata of the anticosti basin record the development of a storm dominated tropical carbonate ramp these strata host the well known hirnantian positive carbon isotope excursion which attains maximum values of 4 5 in carbonate carbon of the laframboise member or the fox point member of the becscie formation the excursion also occurs in organic carbon and 13 c carb and 13 c org values covary such that no reproducible 13 c 13 c carb 13 c org excursion is observed the most complete stratigraphic section at laframboise point in the west shows the characteristic shape of the hirnantian stage excursion at the global stratotype section and point gssp for the hirnantian stage in china and the silurian system in scotland we therefore suggest that the entire hirnantian stage on anticosti island is confined to the laframboise and lower fox point members by documenting discontinuities in the architecture of the carbon isotope curve at multiple stratigraphic sections spanning a proximal to distal transect across the sedimentary basin we are able to reconstruct glacioeustatic sea level fluctuations corresponding to maximum glacial conditions associated with the end ordovician ice age the combined litho and chemostratigraphic approach provides evidence for the diachroneity of the oncolite bed and becscie limestones the former transgresses from west to east and the latter progrades from east to west the sea level curve consistent with our sequence stratigraphic model indicates that glacioeustatic sea level changes and the positive carbon isotope excursion were not perfectly coupled although the start of the isotope excursion and the initial sea level drawdown were coincident the peak of the isotope excursion did not occur until after sea level had begun to rise carbon isotope values did not return to baseline until well after the anticosti ramp was reflooded the sea level 13ccarb relationship proposed here is consistent with the weathering hypothesis for the origin of the hirnantian 13 c carb excursion

preservation of seawater sr and nd isotopes in fossil fish teeth bad news and good news abstract we analyzed 87sr 86sr ratios in foraminifera pore fluids and fish teeth for samples ranging in age from eocene to pleistocene from four ocean drilling program sites distributed around the globe site 1090 in the cape basin of the southern ocean site 757 on the ninetyeast ridge in the indian ocean site 807 on the ontong java plateau in the western equatorial pacific and site 689 on the maud rise in the southern ocean sr isotopic ratios for dated foraminifera consistently plot on the global seawater sr isotope curve for sites 1090 757 and 807 sr isotopic values of the pore fluids are generally less radiogenic than contemporaneous seawater values as are values for fossil fish teeth in contrast pore fluid 87sr 86sr values at site 689 are more radiogenic than contemporaneous seawater and the corresponding fish teeth also record more radiogenic values thus sr isotopic values preserved in fossil fish teeth are consistently altered in the direction of the pore fluid values furthermore there is a correlation between the magnitude of the offset between the pore fluids and the seawater curve and the associated offset between the fish teeth and the seawater curve these data suggest that the hydroxyfluorapatite of the fossil fish teeth continues to recrystallize and exchange sr with its surroundings during burial and diagenesis therefore sr chemostratigraphy can be used to determine rough ages for fossil fish teeth in these cores but cannot be used to fine tune age models in contrast to the sr isotopic system our nd concentration data combined with published isotopic and rare earth element data suggest that fish teeth acquire nd during early diagenesis while they are still in direct contact with seawater the concentrations of nd acquired at this stage are extremely high relative to the concentrations in surrounding pore fluids as a result nd isotopes are not altered during burial and later diagenesis therefore fossil fish teeth from a variety of marine environments preserve a reliable and robust record of deep seawater nd isotopic compositions from the time of deposition

stress dilatancy behaviour of bubbled fine grained sediments abstract although the strength and stiffness of fine grained gassy soil have been relatively well characterised its dilatancy remains poorly understood this study aimed to understand and formulate the stress dilatancy behaviour of fine grained gassy soil through a series of triaxial tests 19 in total conducted on fine grained gassy specimens where different initial gas volume fractions 0 and initial pore water pressures uw0 were considered compared to the stress dilatancy relation of saturated fine grained soil the addition of gas bubbles was found to result in more contractive or dilative soil behaviour depending on the combination of 0 and uw0 these distinct features cannot be captured by the existing stress dilatancy functions for fine grained saturated soils which solely depend on the stress ratio therefore a new stress dilatancy function is proposed within the framework of critical state soil mechanics to quantify the distinct modification effects of bubbles which either suppress or enhance dilatancy on the dilatancy of gassy soils with different 0 and uw0 values in a unified manner this new function has been validated and can be readily implemented in critical state based constitutive models for predicting the shear behaviour of fine grained gassy soil and therefore the response of various offshore structures i e foundations and pipelines founded on a gas bearing seabed

sm nd in marine carbonates and phosphates implications for nd isotopes in seawater and crustal ages this study explores the possibility of establishing nd isotopic variations in seawater over geologic time calcite aragonite and apatite are examined as possible phases recording seawater values of nd modern biogenic and inorganically precipitated calcite and aragonite from marine environments were found to have nd concentrations of from 0 2 to 70 ppb showing that primary marine caco 3 contains little ree and that nd ca is not greatly enhanced relative to seawater during carbonate precipitation very young marine limestone and dolomite containing no continental detritus have 200 ppb nd all the carbonates are lree enriched 0 16 sm nd 0 45 modern and very young atlantic and pacific carbonates have nd in the range of shallow atlantic and pacific seawater respectively implying that they derive their ree from local seawater the nd in well preserved carbonate fossils is 4 10 4 ppb much greater than in their modern counterparts but like the high values found for carbonates in other studies we believe the high ree contents at the 500 ppb level in some detritusfree carbonates are due to ree rich fe hydroxide in on the carbonate in favorable cases such material may record seawater nd values however introduction of extraneous ree may obscure the original isotopic composition of pure caco 3 because of its very low intrinsic primary ree abundance modern biogenic apatite is also shown to have very low ree content 150 ppb nd but appears to quickly scavenge ree from seawater inorganically precipitated apatite from phosphorites has high concentrations of seawater derived ree young phosphorite apatite from the atlantic and pacific oceans has nd in the range of the seawater from these oceans older apatite samples of similar age from different localities bordering common oceans record similar values of nd t sedimentary apatite has sr t values in good agreement with the curves for 87 sr 86 sr of seawater as a function of time individual conodonts from a single formation yield the same sr t and nd t other workers have shown that sedimentary apatite preserves seawater ree patterns these characteristics suggest that sedimentary apatite can be used to determine nd t in ancient seawater the seawater values so inferred range between 1 7 and 8 9 over the last 700 my and lie in the range of modern seawater showing no evidence for drastic changes high values of seawater nd t in the triassic and latest precambrian may correlate with the breakup of large continental landmasses the initial nd t 15 0 of a 2 ae old phosphorite implies the presence of 1 5 ae old continental crust at 2 ae ago the approach outlined here can be used to constrain the age of the exposed crust as a function of time

cosmogenic 3he in igneous and fossil tooth enamel fluorapatite igneous fluorapatite samples from a suite of six granitic rocks from the transantarctic mountains have high 3he concentrations to 5 10 9 atoms g 1 and high 3he 4he ratios to 9 10 7 these values are far higher than those found in several hundred igneous apatites from elsewhere around the world and are higher than can be attributed to nuclear reactions on 6li this 3he is almost certainly derived from cosmic ray reactions in rocks with high exposure ages at high latitude and elevation several samples of fossil tooth enamel fluorapatite from the turkana basin of kenya are similarly rich in 3he with up to 1 10 7 atoms 3he g 1 and 3he 4he ratios up to 4 10 6 again this 3he is most logically attributed to cosmic ray reactions provided that cosmogenic 3he like radiogenic 4he is quantitatively retained in fluorapatite under earth surface conditions routine 3he exposure dating of this common phase may be possible based on its chemical composition the 3he production rate in fluorapatite is about 100 atoms g 1 yr 1 at sea level and high latitude using this rate the apatites from the transantarctic mountains have apparent exposure ages of 0 5 6 2 myr in agreement with values elsewhere in the range the fossil tooth enamel samples have apparent exposure ages ranging from a few up to 130 kyr such high exposure ages suggest some of these fossils may be lag deposits with a very long residence time at or near the earth s surface 3he exposure ages can provide insights to the depositional and reworking history of enamel bearing fossils at present the major limitations to 3he exposure dating of fluorapatite are purification of sufficient amounts of material and measurement of small amounts of 3he in the presence of large quantities of 4he in addition further work is necessary to establish the nucleogenic 3he background in fluorapatite

geochronology and mass transfer in gulf coast mudrocks south central texas u s a rbsr smnd and ree systematics whole rock shale and 0 5 m sized clay separates from a well spanning 3500 m of burial in south central texas have been analyzed for there ree sm nd and rb sr contents clay rb sr and sm nd hcl leachate residue pairs yield ages which decrease with depth implying that these samples have not experienced a punctuated diagenetic event rb sr ages from the most deeply buried clay samples are younger than their depositional ages but sm nd leachate residue ages are always equal to or greater than depositional age leachate sr appears to be in isotopic equilibrium with present day sandstone formation waters implying that pore fluids readily pass between the two lithologies during and after diagenesis the ree are redistributed and fractionated on a local mineral grain scale during burial diagenesis the hcl soluble ree reservoirs decrease from 20 to 8 in whole rock and from 35 to 7 in 0 5 m clay and become progressively enriched in the middle ree relative to the light and heavy ree conversely the hcl insoluble silicate reservoirs become progressively enriched in the light and heavy ree relative to the middle ree this fractionation which is more pronounced in the clay than in the whole rock appears to be a result of authigenic illite and phosphate formation during burial diagenesis although the ree are redistributed on a local scale there is little evidence that the ree are gained or lost by the mudrocks during diagenetic redistribution combined nd and sr isotopic data show that the whole rock shale system may be modelled as a three component system composed of young volcanic derived and old craton derived detritus and a seawater derived component these three components are partially homogenized during diagenesis and as a result the sr nd provenance information originally held in the silicate fraction of whole rock shale becomes obscured

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

did the late ordovician african ice sheet reach europe abstractpaleovalleys and their in lling successions are described from outcrops and drill cores of the cantabrian range northern spain a hirnantia fauna and associated diamictites with striated lonestones indicate that the paleovalleys are related to the hirnantian latest ordovician glacial event based on overall geometry depositional facies and associated deformation structures the paleovalleys are interpreted as subglacial tunnel valleys they were most likely related to the north gondwana ice sheet the ice sheet therefore reached the ibero armorican domain that was still attached to the gondwana landmass at least until the latest ordovician introduction the hirnantian glacial record documents one or several ice sheets throughout africa arabia and south america the extents of which are still controversial ghienne et al 2007 schonian and egenhoff 2007 although glaciomarine strata are widespread in european peri gondwa nan terranes robardet and dore 1988 brenchley et al 1991 they do not precisely indicate the presence of glaciers at those localities because a number of these terranes would have been attached to the gondwana land mass during the late ordovician e g robardet 2003 the gondwanan ice sheet may have reached some of them the hirnantian paleovalleys of the cantabrian range northwest spain are the rst glacial valleys to be recognized outside the gondwana landmass they may be related to a gondwanan ice sheet lobe or to a peri gondwana satellite ice cap

cosmogenic and nucleogenic 3he in apatite titanite and zircon cosmogenic 3he was measured in apatite titanite and zircon and cosmogenic 21 ne in quartz at 13 depth intervals in a 2 7 m long drill core in a miocene ignimbrite from the altiplano of bolivia all three 3he depth profiles as well as the 21 ne profile attenuate exponentially with depth indicating that both of these isotopes are cosmogenic in origin with no significant contribution from other sources the attenuation lengthscale for 3he production of 180 11 g cm 2 is consistent with expectations for neutron spallation and is identical to that found for the cosmogenic 21 ne in quartz by normalizing the measured 3he concentrations to 21 ne and using the independently known cosmogenic 21 ne production rate the apparent cosmogenic 3he production rates in apatite titanite and zircon were respectively found to be 112 97 and 87 atoms g yr at sea level and high latitude the formal uncertainty on these estimates is 20 2 and arises in equal parts from uncertainties in the measured 3he 21 ne ratios and the uncertainty in the 21 ne production rate however an additional factor affecting the apparent 3he production rate in these phases arises from the long stopping range of spalled 3he and tritium which decays to 3he because all three accessory phases have higher mean atomic number than major rock forming minerals they will have lower 3he production rates than their surroundings as a consequence the long stopping ranges will cause a net implantation of 3he and therefore higher apparent production rates than would apply for purely in situ production thus these apparent production rates apply only to the specific grain sizes analyzed analysis of sieved zircon aliquots suggests that a factor of 2 increase in grain size from 50 to 100 m cross section yields a 10 decrease in apparent production rate while this effect warrants further study the grain sizes analyzed here are typical of the accessory phases commonly encountered so the apparent rates provide an appropriate starting place for surface exposure dating using 3he in these minerals

tectonically driven changes in the indian ocean circulation over the last 25 ma neodymium isotope evidence abstract changes in ancient oceanic current patterns have been strongly influenced by plate tectonics particularly by the opening or closing of gateways between different oceans such modifications of oceanic circulation have important consequences on climate we studied the nd seawater isotopic composition of indian and pacific ocean cores using nd isotopes which are good paleo oceanographic tracers we focused on the past 25 ma which are marked by the closure of the indonesian gateway as well as the mediterranean connection we show that a strong westerly oceanic surface current which we refer to the miocene indian ocean equatorial jet miojet linked the eastern and western indian ocean from 14 ma to 3 ma and infer that this major change in oceanic circulation probably induced important variations of global climate

graptolites in british stratigraphy 697 taxa of planktonic graptolites are recorded and their stratigraphical ranges are given through 60 biozones and subzones in the ordovician and silurian strata of england wales and scotland in the first such stratigraphical compilation for great britain since the synthesis of elles wood 1901 1918