the road river group of northern yukon canada early paleozoic deep water sedimentation within the great american carbonate bank cambrian devonian sedimentary rocks of the northern canadian cordillera record both the establishment and demise of the great american carbonate bank a widespread carbonate platform system that fr

ordovician and silurian global geography presidential address delivered 3 may 2000 the main palaeocontinents during the early ordovician were gondwana laurentia baltica and siberia and a brief survey is made of their limits in the ordovician and silurian in particular gondwana by far the largest continent is analysed as including a core of south america antarctica africa australia and peninsular india and also the marginal terranes all of which show faunal links with but which may not have been attached to the core of avalonia ibero armorica and other european fragments turkey arabia and terranes from the far east including south china sibumasu and parts of australasia changes within the benthic faunas reveal that baltica whilst isolated in the early ordovician became united with avalonia by the end ordovician and the two with laurentia by the mid silurian to form the new supercontinent of laurussia island arcs had distinctive faunas during the ordovician in particular those in the iapetus between laurentia baltica and gondwana and the huge kipchak arc which ran from baltica to siberia as the period progressed the iapetus arcs became subducted beneath or accreted to their neighbouring cratons and the kipchak arc gradually collapsed to form the core of the new kazakhstania terrane gondwana drifted over the south pole and this movement is reflected in the cratonic benthic faunas particularly brachiopods and trilobites which in the early ordovician had formed a cline between the high latitude faunas of north africa and the equatorial faunas of the far east and australia but by the devonian lived in much warmer seas in southern europe and cooler waters in antarctica the faunas also reflect the global palaeoclimates which were warm in the early to mid ordovician and mid to late silurian but which were much colder in the half million year period of the late ordovician and early silurian particularly in the latest ordovician hirnantian ice age with its attendant widespread hirnantia brachiopod fauna the relative closeness of the chief palaeocontinents by the early silurian enabled brachiopod and trilobite larvae to cross the narrower oceans enabling a relatively cosmopolitan benthic fauna to be established over much of the globe apart from the cooler water higher latitude clarkeia fauna to the south and the tuvaella fauna to the north

integrated silurian conodont and carbonate carbon isotope stratigraphy of the east central appalachian basin abstract the eastern and southeastern margins of the appalachian basin contain extensive exposures of telychian through pridoli upper silurian strata litho and biostratigraphic analyses of these strata over the last century provided a general means for their chronostratigraphic correlation to global series and stage boundaries however a rarity of zonally diagnostic fauna limited precise correlation both within and beyond the appalachian basin recent conodont biostratigraphic studies substantially revised the chronostratigraphic position of these strata by more than a series in some cases much of the interval however remained biostratigraphically unzoned and the precise position of series and stage boundaries remained tentative to improve the chronostratigraphic correlation of these strata to global series and stage boundaries we provide new integrated conodont and high resolution 13ccarb chemostratigraphic analyses from two outcrops located in west virginia and virginia spanning the upper rose hill through tonoloway formations upper telychian through pridoli these new data show that the silurian carbon isotope record for this portion of the appalachian basin is shifted to more negative 13ccarb values than typical global data however the overall isotopic records appear correlative at least within the appalachian basin thereby providing a means for future correlation within the basin for intervals in which biostratigraphy is traditionally lacking these coupled data demonstrate that the ireviken and mulde excursions are contained within our sections the high amplitude lau excursion was however not observed and the present biostratigraphic data suggest that a majority of the ludlow series was either not recorded or was later removed by erosion these coupled analyses therefore indicate that the ludlow pridoli boundary resides within the wills creek formation and we propose that the overlying isotopic record presented here records the late ludlow carbon isotope excursion llcie and silale low previously identified only within the baltic basin

integrated sedimentary biotic and paleoredox dynamics from multiple localities in southern laurentia during the late silurian ludfordian extinction event abstract the silurian was a time of major climatic transition punctuated by multiple biotic crises and global carbon cycle perturbations the most severe of these biotic events was the late silurian ludfordian lau kozlowskii extinction event lke and the associated lau carbon isotope excursion cie although the extinction event and lau cie are globally documented the only records thus far of local and global marine paleoredox conditions through this interval are from a single region in scandinavia here we examine four sections along a bathymetric transect of mixed carbonate siliciclastic sediments from western tennessee usa a novel approach using a multi proxy dataset combining high resolution geochemical data and microfacies analyses from multiple localities explores the possibilities of local regional scale redox heterogeneities during a time of widespread environmental upheaval on a global scale paired positive excursions recorded in carbonate carbon isotopes and carbonate associated sulfate sulfur isotopes support recent work from carbonate and siliciclastic successions from scandinavia suggesting a global enhancement of organic carbon and pyrite burial driven by an expansion of euxinic anoxic and sulfidic water column conditions in the oceans during the mid ludfordian furthermore positive excursions in organic carbon isotopes and pyrite sulfur isotopes reflect the global changes in redox stratigraphic trends in i ca ratios imply a local expansion of low oxygen conditions with low but non zero values during the rising limb and peak of the cie the fossil assemblages vary across the shelf and through the cie interval stratigraphic changes in fossil assemblages and i ca are closely associated with local and global changes in oxygenation and sea level during the mid ludfordian the collective data indicate significant biotic reorganization in response to changes in marine redox conditions and in conjunction with sea level variation during the lke interval but detailed macroscopic biodiversity is currently unconstrained for this region

carbon isotope excursion near the wenlock ludlow silurian boundary in the anglo welsh area oxygen and carbon isotope analyses have been performed at close sampling intervals on rocks from several exposures that show the boundary between the wenlock and ludlow series in the classic silurian areas of wales the welsh borderland and the west midlands of england our data indicate a monotonic decline in 13 c from positive to negative values across the boundary between the much wenlock limestone formation wenlock series and the lower elton formation ludlow series and correlatives in all sites investigated a slightly earlier negative excursion is also present in the upper wenlock strata of two of these localities both negative 13 c excursions appear to be contemporaneous with episodes of increased ocean ventilation and eustatic sea level lowstand postulated by kemp at least one and possibly both of the late wenlock carbon isotope depletions can also be related to the decline in pelagic graptolite diversity the distribution of the carbon isotope depletion in both carbonate platform and off shelf facies implies that this trend is unlikely to have been caused by local diagenetic alteration isotope chemostratigraphy may also provide an extra correlation tool that can be integrated with traditional biostratigraphic methods for silurian strata

silurian conodont biostratigraphy and carbon δ13ccarb isotope stratigraphy of the victor mine v 03 270 ah core in the moose river basin the moose river basin in ontario canada contains nearly 1 km of silurian marine strata and although it has been studied for more than a century its precise correlation globally has not been constrained herein a core from the victor mine in the moose river basin was examined for conodont biostratigraphy and carbonate carbon 13ccarb isotope chemostratigraphy to provide a detailed chronostratigraphic framework for the silurian strata severn river ekwan river and attawapiskat formations in the moose river basin the recovery of aspelundia expansa aspelundia fluegeli fluegeli distomodus staurognathoides ozarkodina polinclinata estonica pterospathodus eopennatus and aulacognathus bullatus as well as the lower aeronian upper aeronian lower telychian valgu and ascending limb of the sheinwoodian ireviken positive carbonate carbon 13ccarb isotope excursions provide significantly improved chronostratigraphic correlation of llandovery strata in the moose river basin

rare earth elements in sedimentary phosphate deposits solution to the global ree crisis abstract the critical role of rare earth elements rees particularly heavy rees hrees in high tech industries has created a surge in demand that is quickly outstripping known global supply and has triggered a worldwide scramble to discover new sources the chemical analysis of 23 sedimentary phosphate deposits phosphorites in the united states demonstrates that they are significantly enriched in rees leaching experiments using dilute h2so4 and hcl extracted nearly 100 of their total ree content and show that the extraction of rees from phosphorites is not subject to the many technological and environmental challenges that vex the exploitation of many identified ree deposits our data suggest that phosphate rock currently mined in the united states has the potential to produce a significant proportion of the world s ree demand as a byproduct importantly the size and concentration of hrees in some unmined phosphorites dwarf the world s richest ree deposits secular variation in phosphate ree contents identifies geologic time periods favorable for the formation of currently unrecognized high ree phosphates the extraordinary endowment combined with the ease of ree extraction indicates that such phosphorites might be considered as a primary source of rees with the potential to resolve the global ree particularly for hree supply shortage

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

ultra high resolution multivariate record and multiscale causal analysis of pridoli late silurian implications for global stratigraphy turnover events and climate biota interactions abstract the upper silurian and especially pridoli epoch is a critical interval for the understanding the evolution of earth s biota since it witnessed series of powerful extinction events global reorganizations of paleocommunities and expansion of new clades which assumed dominance in the subsequent devonian period the stratigraphic record of the eastern part of the silurian baltic basin represents an excellent candidate for the fine scale analysis of paleoecological and paleoceanographic dynamics therefore we presenting here stratigraphic record of the milaiciai 103 core south western lithuania of conodonts brachiopods 13ccarb 18ocarb and a series of various geochemical and geophysical proxies most of which were sampled at a very high resolution 11 ka spanning uppermost ludlow pridoli and the lowermost devonian the analysis revealed that the pridoli was characterized by four distinct long term dynamic states here named i normal pridoli i ii silal negative carbon isotopic excursion and extinction event iii normal pridoli ii and iv klonk positive stable carbon isotopic event and excursion the most significant change in most variables is detected approximately in the middle of the pridoli at the beginning of the delotaxis detorta zone at the recovery after silal event of conodonts and at the onset of collapse of brachiopod communities the analysis of dynamic complexity revealed the strong evidence for the presence of 405 ka metronome milankovitch cycles in the record of 13ccarb which constrains the duration of the pridoli epoch to 4 3 0 2 ma the recurrence plot analyses revealed deterministic coordination between 13ccarband conodont paleocommunity dynamics at all scales finally lead lag analysis using conditional joint recurrence revealed that conodont dynamics as a rule were driven by perturbations in the carbon cycle although silal event interval shown opposite pattern thus confirming the unusual nature of this previously unrecognized coordinated climatic and biotic event

geochemical evidence of the renewal of volcanic activity inferred from co2 soil and so2 plume fluxes the 2007 stromboli eruption italy on 27 february 2007 a new eruption occurred on stromboli which lasted until 2 april it was characterized by effusive activity on the sciara del fuoco and by a paroxysmal event 15 march this crisis represented an opportunity for us to refine the model that had been developed previously 2002 2003 eruption and to improve our understanding of the relationship between the magmatic dynamics of the volcano and the geochemical variations in the fluids in particular the evaluation of the dynamic equilibrium between the volatiles co2 and so2 released from the magma and the corresponding fluids discharged from the summit area allowed us to evaluate the level of criticality of the volcanic activity one of the major accomplishments of this study is a 4 year database of summit soil co2 flux on the basis of which we define the thresholds low medium high for this parameter that are empirically based on the natural volcanological evolution of stromboli the so2 fluxes of the degassing plume and the co2 fluxes emitted from the soil at pizzo sopra la fossa are also presented it is noteworthy that geochemical signals of volcanic unrest have been clearly identified before during and after the effusive activity these signals were found almost simultaneously in the degassing plume so2 flux and in soil degassing co2 flux at the summit although the two degassing processes are shown to be clearly different the interpretation of the results will be useful for future volcanic surveillance at stromboli

first record of the hirnantian upper ordovician δ13c excursion in the north american midcontinent and its regional implications the most prominent of the two major global delta c 13 excursions in the ordovician the hirnantian delta c 13 excursion hice which is previously recorded from the uppermost ordovician in a few sections in nevada quebec arctic canada baltoscandia scotland and china is documented for the first time from the north american midcontinent samples through the girardeau limestone and leemon formation in missouri and illinois show elevated delta c 13 values of 4 parts per thousand to 5 parts per thousand although not determined precisely the beginning of the hice is likely to be in the upper part of the orchard creek shale and it ends in the upper leemon formation being extraordinarily useful chronostratigraphically the presence of the hice makes it possible to provide a firm dating of the study interval whose age has long been controversial comparison between the study sections and coeval hice sequences in north america and europe show striking similarities especially in sea level history indicating that major local lowstands reflect eustatic sea level changes a comparison with hirnantian diamictite successions in north and south africa and argentina suggests that these lowstands correspond to two major gondwanan glacial episodes less

reply to comment on paper morphology and composition of spinel in pu u o o lava 1996 1998 kilauea volcano hawaii enigmatic discrepancies between lava and gas based fo2 determinations of pu u o o lava

review of the evolution of geochemical monitoring networks and methodologies applied to the volcanoes of the aeolian arc italy abstract fluids discharged from volcanic systems are the direct surface manifestation of magma degassing at depth and provide primary insights for evaluating the state of volcanic activity we review the geochemical best practice in volcanic surveillance based to a huge amount of monitoring data collected at different active volcanoes using both continuous and discontinuous approaches the targeted volcanoes belong to the aeolian arc located in the tyrrhenian sea italy and they have exhibited different activity states during the monitoring activities reported here la fossa cone on vulcano island has been in an uninterrupted quiescent stage characterized by variable solfataric activity in contrast stromboli island has shown a persistent mild explosive activity episodically interrupted by effusive eruptions in 1985 2002 2007 and 2014 panarea island which is the summit of a seamount rising from the seafloor of the southern tyrrhenian sea showed only undersea fluid release the only observable clues of active volcanism at panarea island have been impulsive changes in the undersea fluid release with the last submarine gas burst event being observed in november 2002 the geochemical monitoring and observations at each of these volcanoes has directly involved the volcanic plume and or the fumarole vents thermal waters and diffuse soil degassing depending on the type of manifestations and the level of activity encountered through direct access to the magmatic samples when possible and the collection of as much observable data related to the fluid release as possible the aim has been i to verify the thermodynamic equilibrium condition ii to discern among the possible hydrothermal magmatic marine and meteoric sources in the fluid mixtures iii to develop models of the fluid circulation supported by data iv to follow the evolution of these natural systems by long term monitoring and v to support surveillance actions related to defining the volcanic risk and the evaluation and possible mitigation of related hazards the examples provided in this review article show the close relationships among data analysis interpretation and modeling we particularly focus on describing the fieldwork procedures since any theoretical approach must always be verified and supported by field data rather than just by experiments controlled in laboratory indeed the natural systems involve many variables producing effects that cannot be neglected the monitored volcanic systems have been regarded as natural laboratories and all of the activities have focused on both volcanological research and surveillance purposes in order to ensure that these two goals have overlapped an appendix is also included that explains the scientific approach to the systematic activities regarding geochemical monitoring of volcanic activity

testing the limits of paleozoic chronostratigraphic correlation via high resolution 500 k y integrated conodont graptolite and carbon isotope δ13ccarb biochemostratigraphy across the llandovery wenlock silurian boundary is a unified phanerozoic time scale achievable the resolution and fidelity of global chronostratigraphic correlation are direct functions of the time period under consideration by virtue of deep ocean cores and astrochronology the cenozoic and mesozoic time scales carry error bars of a few thousand years k y to a few hundred k y in contrast most of the paleozoic time scale carries error bars of plus or minus a few million years m y and chronostratigraphic control better than 1 m y is considered high resolution the general lack of paleozoic abyssal sediments and paucity of orbitally tuned paleozoic data series combined with the relative incompleteness of the paleozoic stratigraphic record have proven historically to be such an obstacle to intercontinental chronostratigraphic correlation that resolving the paleozoic time scale to the level achieved during the mesozoic and cenozoic was viewed as impractical impossible or both here we utilize integrated graptolite conodont and carbonate carbon isotope delta c 13 carb data from three paleocontinents baltica avalonia and laurentia to demonstrate chronostratigraphic control for upper llandovery through middle wenlock telychiansheinwoodian similar to 436 426 ma strata with a resolution of a few hundred k y the interval surrounding the base of the wenlock series can now be correlated globally with precision approaching 100 k y but some intervals e g uppermost telychian and upper shein woodian are either yet to be studied in sufficient detail or do not show sufficient biologic speciation and or extinction or carbon isotopic features to delineate such small time slices although producing such resolution during the paleozoic presents an array of challenges unique to the era we have begun to demonstrate that erecting a paleozoic time scale comparable to that of younger eras is achievable less

magma supply and storage at kilauea volcano hawaii 1956 1983 abstract shallow crustal magma reservoirs beneath the summit of kilauea volcano and within its rift zones are linked in such a way that the magma supply to each can be estimated from the rate of ground deformation at the volcano s summit our model builds on the well documented pattern of summit inflation as magma accumulates in a shallow summit reservoir followed by deflation as magma is discharged to the surface or into the rift zones magma supply to the summit reservoir is thus proportional to summit uplift and supply to the rift zones is proportional to summit subsidence the average proportionality constant is 0 33 10 6 m 3 rad this model yields minimum supply estimates because it does not account for magma which escapes detection by moving passively through the summit reservoir or directly into the rift zones calculations suggest that magma was supplied to kilauea during july 1956 april 1983 at a minimum average rate of 7 2 10 6 m3 month roughly 35 of the net supply was extruded the rest remains stored within the volcano s east rift zone 55 and southwest rift zone 10 periods of relatively rapid supply were associated with the large kapoho eruption in 1960 and the sustained mauna ulu eruptions in 1969 1971 and 1972 1974 bursts of harmonic tremor from the mantle beneath kilauea were also unusually energetic during 1968 1975 suggesting a close link between kilauea s deep magma supply region and shallow storage reservoirs it remains unclear whether pulses in magma supply from depth give rise to corresponding increases in shallow supply or if instead unloading of a delicately balanced magma transport system during large eruptions or intrusions triggers more rapid ascent from a relatively constant mantle source

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

continental island from the upper silurian ludfordian stage of inner mongolia implications for eustasy and paleogeography an unconformity between the silurian xibiehe formation and ordovician igneous rocks marks the perimeter of a small paleoisland near bater obo in north central inner mongolia 180 km northwest of the provincial capital of hohhot the stratigraphic position of the lower part of the xibiehe formation is correlated by means of conodonts with the upper part of the ancoradella ploeckensis zone in the basal ludfordian stage corresponds to mid ludlovian epoch ca 421 ma elongate in plan 610 m 200 m the exhumed diorite core rises 30 m above the lowest elevations of surrounding silurian strata paleoshores along the principal axis of the inlier delineate contrasting facies robust stromatoporoids are in growth position within silty limestones some directly encrusting the unconformity surface of the sheltered southeast margin a basal conglomerate of diorite cobbles and boulders characterizes the high energy northwest margin the depositional constraints and timing of transgressive facies associated with this continental paleoisland have implications for the eustatic and paleogeographic history of the parent sino korean plate burial of the island corresponds to the beginning of a global rise in sea level that peaked in late ludlovian time our interpretation of windward and leeward facies requires an approximate 90 clockwise rotation of the parent plate to accommodate the dominant pattern of low latitude trade winds and storms

modeling the three dimensional structure of macroscopic magma transport systems application to kilauea volcano hawaii we report the results of modeling the three dimensional internal structure of kilauea s magmatic passageways the approach uses a clear plexiglass model containing equally spaced levels upon which well located seismic hypocenters are plotted application of constraining geologic and geophysical criteria to this distributed volume of earthquakes permits the interpretation of seismic structures produced by fracturing in response to locally high fluid pressures four magma transport and storage structures have been identified within and beneath kilauea 1 primary conduit the conduit transporting magma into kilauea s summit storage reservoir rises from the model base 14 6 km to the 6 5 km depth level it is a zone of intense fracturing and inferred intrusion whose horizontal sections are elliptical in planform over its height the average major axis of the component horizontal sections is 3 3 km with an average minor axis of 1 7 km this yields an aspect ratio of 0 52 at the 14 6 km level the strike of the major axis is n67 e during passage from the upper mantle through the oceanic crust this axis rotates in a right handed sense until the strike is n41 w at the 6 5 km level 2 magma chamber complex floor the interval from 6 5 to 5 7 km immediately over the primary conduit is aseismic this suggests differentially high fluid to rock ratios and relatively weak pathways for further vertical transport into higher levels of the storage complex as well as lateral leakage eastward into the mauna ulu staging area for later vertical ascent beneath the upper east rift zone seismicity within the immediately subjacent rocks that form the top of the primary conduit at 6 5 km suggests that this inferred magma rich horizon forms the effective floor of the summit storage complex 3 magma chamber crown intense seismicity over the 1 1 1 9 km depth interval defines an elliptical region in plan view the top of this region has a broad apex with an average major axis of 1 5 km and an average minor axis of 1 1 km producing an aspect ratio of 0 73 this region coincides with the epicentral position of summit vertical displacement maxima during inflationary deformation and is interpreted as a region of intense diking crowning the summit storage complex 4 upper east rift zone pipe from a depth of 5 7 km a cylindrical region of seismicity rises beneath the upper east rift zone to the 1 9 km level where it merges with the subhorizontal upper east rift zone duct this pipe like zone has a mean diameter of 1 4 km and a vertical axis that pierces the surface of the volcano at the intersection of the koae fracture system and the upper east rift zone we suggest this pipe forms a principal connection between the base of the summit storage reservoir and near surface storage compartments and ducts in the upper east rift zone in this role the pipe is suggested to have contributed heavily to mauna ulu s magma supply during 1969 1974 the model of magma transport and storage thus constructed provides a context in which other types of data e g ground deformation and electrical conductivity may be interpreted as well as a means of refining petrological inferences based on lava chemistry

linked silurian carbon cycle perturbations bursts of pinnacle reef growth extreme sea level oscillations and evaporite deposition michigan basin usa abstract integration of sedimentologic chemostratigraphic biostratigraphic and geochronologic data identifies the profound influence that sudden bursts of carbonate sedimentation sea level oscillation and hypersalinity associated with ireviken and mulde carbon cycle perturbations had on the evolution of the michigan basin during the silurian conodonts and carbon isotope 13ccarb stratigraphy of the lockport and engadine dolomites constrain the rapid build up and progradation of a thick biohermal wedge along the basin margins to the sheinwoodian age ireviken excursion a recently identified period of global reef growth this event significantly changed the hydrologic architecture of the basin ultimately resulting in restricted seawater exchange that drove evaporite deposition zircon u pb ages of 428 ma from bentonites near the base of the evaporite bearing salina group together with 13ccarb profiles transecting the basin constrain the onset of hypersalinity to initiation of the late homerian mulde excursion importantly the double 13ccarb peak of this event parallels a complex pattern of dramatic sea level oscillations on the order of 100 m recorded within the a 0 to a 2 evaporites and associated pinnacle reefs ascending 13ccarb values were accompanied by sea level fall karstification and the formation of evaporites in the basin center intra excursion sea level rebounds triggered exceptionally rapid upward pinnacle reef growth subsequent sea level fall again exposed the ramp and pinnacle reefs resulting in basin wide restriction and massive salt deposition that ultimately encased the reefs in salt the return to baseline 13ccarb values was accompanied by flooding and carbonate sedimentation our integrated approach with high resolution 13ccarb stratigraphy from closely spaced intra basinal sections as a central component enables finely tuned chronostratigraphic correlation recognition of unconformity bound facies packages i e systems tracts and constrains variations in sea level and sedimentation rates these findings have immediate applications to predictive static reservoir models for the evaluation of the reefs as repositories for anthropogenic co2 sequestration gas storage reservoirs and hydrocarbon exploration ultimately our findings demonstrate that a cascade of rapid environmental changes including pulses of carbonate sedimentation high amplitude sea level oscillations and evaporite deposition were associated with the ireviken and mulde perturbations of the silurian carbon cycle

carbonate platform evolution and conodont stratigraphy during the middle silurian mulde event gotland sweden evidence from sedimentology and conodont biostratigraphy is used to reinterpret the mid homerian late wenlock succession on gotland sweden a new conodont zonation includes from below the ozarkodina bohemica longa zone including five subzones the kockelella ortus absidata zone and the ctenognathodus murchisoni zone two taxa are named ozarkodina bohemica longa and pseudooneotodus linguicornis these new zones are integrated with facies in order to correlate strata and infer the major depositional environments and the controls on deposition during the mid homerian mulde event reef associated and skeletal carbonate deposition predominated before and after the event i e during the uppermost o s sagitta zone and again in the c murchisoni zone these periods are characterized by the expansion of reefs and shoal facies across marls in the topmost slite group on eastern gotland and in the lower parts of the klinteberg formation on western gotland respectively the intervening o b longa and k o absidata zones are initially characterized by rapid facies changes including siliciclastic deposition and later stabilisation of a carbonate depositional system the composition of sediments and depositional rates are closely related to the creation and destruction of accommodation space and reflects a classical case of depositional bias of the carbonate and siliciclastic depositional systems based on coastline migration stratal boundaries and the stratigraphic position of major reef belts several facies associations can be fitted into a sequence stratigraphic model for platform evolution a highstand systems tract hst situation prevailed prior to and during the early part of the event the upper slite group including the lower frjel formation this hst was characterized by prolific skeletal production and regional reef development except for during the latest stage when carbonate production declined at the onset of the mulde event platform growth was inhibited during a following regressive systems tract rst when regional siliciclastic deposition predominated the gannarve member the subsequent lowstand resulted in regional emersion and karstification i e a complete termination of the platform the post extinction transgressive systems tract tst is exclusively composed of non skeletal carbonates the bara member of the halla formation re occurrence of reefs and a prolific skeletal production marks platform recovery during a second hst the remaining halla and the lower klinteberg formations integration of high resolution biostratigraphy and sequence stratigraphy reveals that the major physical control on platform evolution was a 5th order eustatic sea level change during an early part of the mulde event and that the bulk of the strata accumulated when the platform aggraded and prograded during the highstand systems tracts thus silurian oceanic events and associated sea level changes had profound impact on the neritic carbonate system the gotland based middle and late homerian sea level curve shows two rapid regressions both leading to truncation of highstand systems tracts the first lowstand occurred at the very end of the c lundgreni chron and the second at the end of the co ludensis chron the intervening interval was characterized by stillstand or possibly slow transgression

the aurora volcanic field california nevada oxygen fugacity constraints on the development of andesitic magma the aurora volcanic field located along the northeastern margin of mono lake in the western great basin has erupted a diverse suite of high k and shoshonitic lava types with 48 to 76 wt sio2 o ver the last 3 6 million years there is no correlation between the age and composition of the lavas three quarters of the volcanic field consists of evolved 4 wt mgo basaltic andesite and andesite lava cones and flows the majority of which contain sparse euhedral phenocrysts that are normally zoned there is no evidence of mixed hybrid magmas the average eruption rate over this time period was 200 m 3 ykm 2 yyear which is typical of con tinental arcs and an order of magnitude lower than that for the slow spreading mid atlantic ridge all of the au rora lavas display a trace element signature common to subduction related magmas as exemplified by baynb ratios between 52 and 151 pre eruptive water contents ranged from 1 5 wt in plagioclase rich two pyroxene andesites to 6 wt in a single hornblende lamprophyre and several biotite hornblende andesites calculated oxygen fugacities fall within 0 4 and 12 4 log units of the ni nio buffer the aurora potassic suite follows a classic calc alkaline trend in a plot of feo t ymgo vs sio 2 and displays linear decreasing trends in feo t and tio2 with sio2 content suggesting a prominent role for fe ti oxides during differentiation however develop ment of the calc alkaline trend through fractional crys tallization of titanomagnetite would have caused the residual liquid to become so depleted in ferric iron that its oxygen fugacity would have fallen several log units below that of the ni nio buffer nor can fractionation of hornblende be invoked since it has the same effect as titanomagnetite in depleting the residual liquid in ferric iron together with a thermal stability limit that is lower than the eruption temperatures of several andesites 1040 10808c derived from two pyroxene ther mometry unless some progressive oxidation process occurs fractionation of titanomagnetite or hornblende cannot explain a calc alkaline trend in which all erupted lavas have oxygen fugacites the ni nio buffer in con trast to fractional crystallization closed system equi librium crystallization will produce residual liquids with an oxygen fugacity that is similar to that of the initial melt however the eruption of nearly aphryic lavas ar gues against tapping from a magma chamber during equilibrium crystallization a process that requires crys tals to remain in contact with the liquid a preferred model involves the accumulation of basaltic magmas at the mantle crust interface which solidify and are later remelted during repeated intrusion of basalt as an end member case closed system equilibrium crystallization of a basalt followed by equilibrium partial melting of the gabbro will produce a calc alkaline evolved liquid namely high sio 2 and low feo t ymgo with a relative fo2 corrected for the effect of changing temperature that is similar to that of the initial basalt differentiation of the aurora magmas by repeated partial melting of previous underplates in the lower crust rather than by crystal fractionation in large stable magma chambers is consistent with the low eruption rate at the aurora vol canic field

carbon isotope event markers through the wenlock pridoli sequence at ohesaare estonia and priekule latvia abstract the ohesaare borehole in the northern part of the silurian baltic gulf penetrates shallow and deep shelf marlstones limestones and dolostones the priekule borehole in the deep shelf belt of the basin was drilled through marlstones and graptolitic mudstones most of the successions except the upper part are characterized by a high sr ca ratio close to marine calcites suggesting good preservation of carbonate material conodont alteration indices are low 1 2 carbon isotopes were measured using whole rock samples in the ohesaare core section two distinctive 13 c positive excursions were established one in the early wenlock riccartonensis and low rigidus ellesae standard graptolite zones 4 2 and the second in the late wenlock nassa zone 4 6 before and after the latter there are also intervals with low 13 c values the first just above the lundgreni zone 1 8 and another in the ludensis perhaps reaching into nilssoni zone 3 8 in the priekule section the early wenlock 13 c peak is well represented 3 1 but in the late wenlock early ludlow 13 c values show little variation from 2 0 to 1 in this section a high peak of 13 c values 5 9 was determined in the nova beds correlated with the topmost gorstian and lowermost ludfordian ludlow the carbon isotope positive excursions show good correlation with lows of the global sea level curve and with most of the biotic and supposed climatic events glaciation ocean state

gas composition of the january 1983 eruption of kilauea volcano hawaii abstract gas collections were made from a 900 c vent both by conventional evacuated bottle wet chemical techniques and by manual pumping of flowthrough bottles the complete analyses suggest an equilibrium assemblage quenched at 1 010 c about midway between fountain and vent temperatures i suggest that the very low c s ratio is due to degassing of co2 during storage of the magma in a shallow reservoir before eruption the two sampling techniques yielded analytical data in mutual agreement

high resolution event stratigraphy hires and the quantification of stratigraphic uncertainty silurian examples of the quest for precision in stratigraphy abstract the ability to resolve the stratigraphic record of earth history is critical to understanding past global change events and the range of natural variability within the global paleoclimate the geosphere hydrosphere atmosphere biosphere system operates on geologically very short time scales and we must be able to resolve the stratigraphic record of past events on similar time scales if we are to understand the cause and effect relationships operating within the system global resolution 100 kyr is commonly available when evaluating events from the cenozoic era but such resolution is less common for older portions of earth history the introduction of high resolution event stratigraphy hires more than two decades ago revolutionized the ability to resolve the mesozoic and cenozoic stratigraphic records of global change and a similar revolution is currently underway for the paleozoic as well here we review the application of the principles of hires to the paleozoic stratigraphic record with examples from the silurian system discuss the quantification of chronostratigraphic uncertainty and highlight the current deep time earth history revolution that has the potential to open the entire phanerozoic record to the evaluation of short time scale global climate dynamics

h2s fluxes from mt etna stromboli and vulcano italy and implications for the sulfur budget at volcanoes abstract we present here new measurements of sulfur dioxide and hydrogen sulfide emissions from vulcano etna and stromboli italy made by direct sampling at vents and by filter pack and ultraviolet spectroscopy in downwind plumes measurements at the f0 and fa fumaroles on vulcano yielded so 2 h 2 s molar ratios of 0 38 and 1 4 respectively from which we estimate an h 2 s flux of 6 to 9 t d 1 for the summit crater for mt etna and stromboli we found so 2 h 2 s molar ratios of 20 and 15 respectively which combined with so 2 flux measurements suggest h 2 s emission rates of 50 to 113 t d 1 and 4 to 8 t d 1 respectively we observe that source and plume so 2 h 2 s ratios at vulcano are similar suggesting that hydrogen sulfide is essentially inert on timescales of seconds to minutes this finding has important implications for estimates of volcanic total sulfur budget at volcanoes since most existing measurements do not account for h 2 s emission

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

carbon isotope stratigraphy of the upper telychian and lower sheinwoodian llandovery wenlock silurian of the banwy river section wales 13 corg and toc data are presented from the upper spiralis biozone telychian llandovery silurian through to the upper sheinwoodian wenlock silurian of the banwy river section wales in laminated hemipelagites from the telychian 13 corg values rise through the upper lapworthi biozone to a maximum in the lower insectus biozone after which they decline slightly the most conspicuous feature of the 13 corg curve is the prolonged positive excursion in the sheinwoodian commencing in the upper murchisoni biozone and ending in strata yielding monograptus flexilis this sheinwoodian positive 13 c excursion in the banwy river section correlates precisely with that recognized in the east baltic the interval with the highest 13 corg values also records the highest toc values suggesting that for the sheinwoodian at least burial of carbon may have contributed to the positive 13 c excursion bioturbated strata yield very low toc values whether the 13 corg values from these beds reflect a primary signal or the result of biostratinomic or diagenetic modification is uncertain

oxygen buffering of kilauea volcanic gases and the oxygen fugacity of kilauea basalt volcanic gases collected during episode 1 of the puu oo eruption along the east rift zone of kilauea volcano hawaii have uniform c o h s cl f compositions that are sharply depleted in co2 the co2 poor gases are typical of type ii volcanic gases gerlach and graeber 1985 and were emitted from evolved magma stored for a prolonged period of time in the east rift zone after releasing co2 rich gases during an earlier period of temporary residence in the summit magma chamber the samples are remarkably free of contamination by atmospheric gases and meteoric water thermodynamic evaluation of the analytical data shows that the episode 1 gases have equilibrium compositions appropriate for temperatures between 935 and 1032 c open and closed system equilibrium models of species distributions for the episode 1 gases show unequivocally that coexisting lavas buffered the gas oxygen fugacities during cooling these models indicate that the fo2 buffering process occurs by transfer of oxygen from the major species in the gas phase h2o co2 so2 to the lava during cooling and that the transfer of oxygen also controls the fugacities of several minor and trace species h2 co h2s s2 cl2 f2 in addition to o2 during cooling gas lava exchanges of other components are apparently insignificant and exert little influence compared to oxygen exchange during cooling oxygen transfer during cooling is variable presumably reflecting short term fluctuations in gas flow rates higher flow rates restrict the time available for gas lava oxygen transfer and result in gases with higher equilibrium temperatures lower flow rates favor fo2 constrained equilibration by oxygen transfer down to lower temperatures thus the chemical equilibrium preserved in these gases is a heterogeneous equilibrium constrained by oxygen fugacity and the equilibrium temperatures implied by the compositions of the gases reflect the temperatures at which gas lava oxygen exchange ceased this conclusion challenges the common assumption that volcanic gases are released from lava in a state of chemical equilibrium and then continue equilibrating homogeneously with falling temperature until reaction rates are unable to keep pace with cooling no evidence is found moreover that certain gas species are kinetically more responsive and able to equilibrate down to lower temperatures than those of the last gas lava oxygen exchange homogeneous reaction rates in the gas phase are apparently slow compared to the time it took for the gases to move from the last site of gas lava equilibration to the site of collection an earlier set of data for higher temperature co2 rich type i volcanic gases which come from sustained summit lava lake eruptions supplied by magma that experienced substantially shorter periods of crustal storage shows fo2 buffering by oxygen transfer up to 1185 c oxygen fugacity measurements in drill holes into ponded lava flows suggest that buffering by oxygen transfer may control the fo2 of residual gases down to several hundred degrees below the solidus in the early stages of cooling although the details of the fo2 buffering mechanisms for oxygen transfer are unknown the fact that fo2 buffering is effective from molten to subsolidus conditions suggests that the reaction mechanisms must change with cooling as the reactants change from predominantly melt to melt plus crystals to glass plus crystals mass balance calculations suggest that redox reactions between the gas and ferrous ferric iron in the lava are plausible mechanisms for the oxygen transfer and that the fo2 of the gases is buffered by sliding ferrous ferric equilibria in the erupting lavas contrary to expectations based on models predicting the oxidation of basalt by h2 and co escape during crustal storage co2 rich type i gases and co2 poor type ii gases have identical oxygen fugacities despite greatly different crustal storage and degassing histories volcanic gas data give a tightly constrained log fo2 of nno 0 5 0 05 for subaerially erupted kilauea basalt from liquidus to solidus temperatures consistent with recent fo2 determinations for the mantle source regions of ocean island basalts because the oxygen fugacities of volcanic gases emitted by subaerial lavas imply that the fo2 of kilauea basalt is unchanged during crustal storage kilauea basalt either arrives in the crust with an oxygen fugacity between nno and fmq or it develops an oxygen fugacity in this range immediately upon arrival in the summit chamber

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

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

alunite and the role of magmatic fluids in the tambo high sulfidation deposit el indio pascua belt chile the tambo high sulfidation deposit located within the el indio pascua belt in chile produced almost 25 t 0 8 m oz of gold from altered tertiary rhyodacitic volcanic rocks episodic magmatic hydrothermal activity in the district occurred over at least 4 my and is characterized by several stages of acid sulfate alteration including magmatic hydrothermal magmatic steam steam heated and apparent supergene assemblages two stages of aufag mineralization are recognized and are hosted in barite and alunite within hydrothermal breccias and veins isotopic compositions of fluid in alunite show a dominant magmatic signature with only a variable 18 o enriched meteoric water component throughout the entire hydrothermal process alunite 40 ar 39 ar ages constrain the timing of alteration and the duration of the hydrothermal system pre ore alteration occurred at about 10 to 11 ma and was contemporaneous with the volcanism of the tambo formation alunite from this stage of alteration occurs in the matrix of barren breccias and as fine intergrowths of alunite quartzfclays that selectively replaced feldspars and pumice fragments the textural relationships combined with stable isotope systematics suggest a magmatic hydrothermal origin for the alunite with a local magmatic steam overprint early ore stage alunite 8 7f0 2 ma occurs with barite and goldfwalthierite within open spaces of the breccia matrix and has d 34 s values 24 27x typical of magmatic hydrothermal alunite reflecting equilibrium between aqueous h2s and so4 fluid inclusion ratios of h2s so2 approximately 6 are consistent with ratios determined from stable isotope data and indicate reduced fluid conditions during ore deposition vaporphase transport of au and deposition from condensed magmatic vapor rising from the brittle ductile transition is inferred late gold coprecipitated with a third stage of alunite 8 2f0 2 ma that is characterized by nearly uniform chemical compositions and d 34 s values 1x similar to those for associated enargite reflecting disequilibrium between h2s and so4 this third stage of alunite is isotopically and chemically similar to that of post ore coarse banded alunitefhematite quartz veins that crosscut the breccias in the tambo area analyses of fluid inclusion gas from alunite in these veins indicate high so2 and disequilibrium co2 co ch4 h2 species consistent with a magmatic steam origin the gases are also depleted in he and the late goldbearing alunite was probably precipitated from rapidly ascending so2 rich vapors that were flashed from condensed magmatic

carbon and oxygen isotopic composition of silurian brachiopods gotland sweden palaeoceanographic implications abstract one hundred and seventy two non luminescent brachiopod shells from the silurian sequence of gotland were investigated for their carbon and oxygen isotopic composition diagenetic alteration of the shell calcite was excluded by means of petrographic trace element and cathodoluminescence analysis oxygen and carbon isotopic signals vary considerably within the uppermost llandovery to the ludlow average 18o and 13c values of well defined stratigraphic units range from 2 4 to 5 9 and 1 to 8 respectively we observed parallel trends in the carbon and oxygen isotope curves with the most prominent shifts occurring in the lower wenlock upper wenlock and middle ludlow average 18o values 2 4 to 2 9 recorded in the middle ludlow are among the highest 18o values reported for the early palaeozoic the recorded 18o variations cannot solely be explained by changes in sea surface temperature and salinity the variations in the isotopic signals correlate negatively with changes in sea level heavy carbon and oxygen signals coincide with sea level lowstands whereas light signals are recorded during sea level highstands sea level highstands were probably characterized by the formation of warm saline waters on subtropical epicontinental shelves inducing oxygen deficiency in the basins alumshale facies the low 18o values are attributed to 18o depletion in surface waters owing to the storage of 18o enriched saline waters in the basins low 13c values are explained by a low surface water productivity since nutrients were not supplied to the photic zone but rather stored in the deeper ocean during sea level lowstands colder waters that formed in higher latitudes may have represented the main intermediate water source a better ventilation of the basins is documented by the deposition of well aerated sediments whereas the high 18o values are explained by the change in oceanic circulation the high 13c values are attributed to an enhanced primary productivity and possibly to an enhanced burial of corg the model discussed here may provide an attractive scenario for accounting for the recorded short term variations in the isotopic signals without the necessity of introducing an isotopic correction factor for silurian sea water

equilibrium temperature and redox state of volcanic gas at unzen volcano japan abstract high temperature volcanic gases were collected from a growing dacitic dome of unzen volcano japan apparent equilibrium temperatures aet were calculated for the following two reactions so2 3h2 h2s 2h2o and co2 h2 co h2o both the aet s are higher than the outlet temperature to two hypotheses are examined as a cause of this disagreement one is a partial advancement in the reaction so2 3h2 h2s 2h2o the other is an addition of external water after a final equilibrium attainment based on these hypotheses the equilibrium compositions temperatures and redox potentials were estimated resulting in similar values the estimated temperatures range from 850 to 911 c which is consistent with a petrological estimation made with the lava however the estimated redox potential is one unit less in logfo2 scale than the petrological estimation

summer atmospheric bridging between europe and east asia influences on drought and wetness on the tibetan plateau abstract based on the era 40 reanalysis data dryness and wetness over the tibetan plateau are categorized according to the monthly standardized precipitation index the atmospheric features associated with severe and extreme dryness and wetness reveal two cross eurasia wave trains the scandinavia east asia wave train and the mediterranean east asia wave train severe and extreme dryness is associated with an anomalous cyclone over south and southeast asia which directs the moisture supply from the arabian sea the bay of bengal and the south china sea directly eastward towards the western pacific thus bypassing the tibetan plateau this cyclone anomaly constitutes part of the scandinavia east asia wave train which is sustained by the divergence and convergence of the anomalous transient eddy heat transport associated with a more southwest northeast oriented north atlantic storm track and a northward shift of the polar front jet in the north atlantic in contrast severe and extreme wetness over the tibetan plateau is associated with a more zonally elongated north atlantic storm track wave trains excited from there have a high probability to reach the mediterranean region and to propagate eastward following the subtropical westerly jet this mediterranean east asia wave train generates anticyclonic anomalies around the tibetan plateau and east china which bring more moisture supply from the arabian sea the south china sea and the western pacific towards the tibetan plateau and enhance the moisture convergence there this paper demonstrates how atmospheric bridging processes affect regional climate variability under present day climatic conditions which are also relevant for understanding past climates

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

degassing of halogens from basaltic volcanism insights from volcanic gas observations abstract the currently available data set of s cl f abundances in volcanic gas plumes and high temperature fumarolic gas samples from basaltic volcanism is reviewed here in the attempt to derive constraints on the modes of halogen degassing from mafic silicate melts apart from large volcano to volcano variations reflecting remarkable differences in volatile abundances in the source magmas each of the explored volcanoes displays large changes of so2 hcl and so2 hf ratios with the style of volcanic activity with hcl hf staying fairly constant halogen abundances are low and so2 hcl and so2 hf are high when fresh volatile rich magmas sustain degassing as during explosive eruptions at the onset of eruptive cycles or shortly before paroxysmal events low so2 hcl and so2 hf ratios are instead characteristic of late stages of volcanic degassing typically being observed in the concluding stages of basaltic eruptions or during periods of reduced magma supply at persistently degassing volcanoes these observations are taken as evidence of halogens being less keen to enter the gas phase relative to s during degassing of basaltic magmas and quantitatively interpreted in light of a rayleigh type open system degassing model the model though simple quantitatively reproduces the range of volcanic gas compositions observed at basaltic volcanoes worldwide and allows prediction of vapour melt partitioning contrasts of factors 9 and 36 for the volatile couples s cl and s f respectively these predictions require validation from appropriately designed experiments of halogen partitioning between magmatic vapours and silicate melts over a range of p t x conditions

halogens and trace metal emissions from the ongoing 2008 summit eruption of kīlauea volcano hawai i volcanic plume samples taken in 2008 and 2009 from the halema uma u eruption at k lauea provide new insights into k lauea s degassing behaviour the cl f and s gas systematics are consistent with syn eruptive east rift zone measurements suggesting that the new halema uma u activity is fed by a convecting magma reservoir shallower than the main summit storage area comparison with degassing models suggests that plume halogen and s composition is controlled by very shallow 77 as gaseous elemental mercury at the point of emission sulphate is an important aerosol component modal particle diameter 0 44 m aerosol halide ion concentrations are low compared to other systems consistent with the lower proportion of gaseous hydrogen halides plume concentrations of many metallic elements rb cs be b cr ni cu mo cd w re ge as in sn sb te tl pb mg sr sc ti v mn fe co y zr hf ta al p ga th u la ce pr nd sm eu gd tb dy er tm are elevated above background air there is considerable variability in metal to so2 ratios but our ratios generally at the lower end of the range previously measured at k lauea support assertions that k lauea s emissions are metal poor compared to other volcanic settings our aerosol re and cd measurements are complementary to degassing trends observed in hawaiian rock suites although measured aerosol metal s ratios are about an order of magnitude lower than those calculated from degassing trends determined from glass chemistry plume enrichment factors with respect to hawaiian lavas are in broad agreement with those from previous studies allowing similar element classification schemes to be followed i e lithophile elements having lower volatility and chalcophile elements having higher volatility the proportion of metal associated with the largest particle size mode collected 2 5 m and that bound to silicate is significantly higher for lithophiles than chalcophiles many metals show higher solubility in ph 7 buffer solution than deionised water suggesting that acidity is not the sole driver in terms of solubility nonetheless many metals are largely water soluble when compared with the other sequential leachates suggesting that they are delivered to the environment in a bioavailable form preliminary analyses of environmental samples show that concentrations of metals are elevated in rainwater affected by the volcanic plume and even more so in fog however metal levels in grass samples showed no clear enrichment downwind of the active vents

degassing of metals and metalloids from erupting seamount and mid ocean ridge volcanoes observations and predictions recently it has been reported that the element polonium degasses from mid ocean ridge and seamount volcanoes during eruptions published and new observations on other volatile metal and metalloid elements can also be interpreted as indicating significant degassing of magmatic vapors during submarine eruptions this process potentially plays an important role in the net transfer of chemical elements from erupting volcanoes to seawater in addition to that arising from sea floor hydrothermal systems in this paper a framework is constructed for predicting and assessing semiquantitatively the potential magnitude and chemical fingerprints in the water column of metal and metalloid degassing using 1 predictions from a summary of element volatilities during mafic subaerial volcanism worldwide and 2 limited data from submarine volcanic effusives the latter include analyses of polonium and trace metals in near volcano water masses sampled following a submarine eruption at loihi seamount hawaii 1000 m bsl in 1996 the element volatility predictions and observations show good agreement considering the limited dataset some of the highest volatility main group and transition element enrichments in seawater over loihi are predicted by the degassing mass transfer model i present when expanded to cover all submarine volcanic activity it is predicted that exit fluxes of these elements are up to 102 103 greater by degassing than by normal mor hydrothermalism in contrast mor exit fluxes of low volatility alkali and alkaline earth elements are likely 102 106 greater from hydrothermal inputs degassing inputs to the ocean are probably highly episodic occurring almost entirely during eruptions these are times of enhanced and abnormal hydrothermalism as well although major hydrothermal and degassing events may not be chemically recognizable in real water masses as wholly distinct entities it is nevertheless possible to predict to what extent each process flavors the effluents of the other degassing at mid ocean ridges may explain a variety of observations previously ascribed to complexities occurring during hydrothermal venting and or fluid ascent in the buoyant hydrothermal plumes above ridges

integrated δ13ccarb conodont and graptolite biochemostratigraphy of the silurian from the illinois basin and stratigraphic revision of the bainbridge group

paleobiogeography high resolution stratigraphy and the future of paleozoic biostratigraphy fine scale diachroneity of the wenlock silurian conodont kockelella walliseri the wenlock epoch of the silurian period has become one of the chronostratigraphically best constrained intervals of the paleozoic the integration of multiple chronostratigraphic tools such as conodont and graptolite biostratigraphy sequence stratigraphy and delta c 13 carb chemostratigraphy has greatly improved global chronostratigraphic correlation and portions of the wenlock can now be correlated with precision better than 100 kyr additionally such detailed and integrated chronostratigraphy provides an opportunity to evaluate the fidelity of individual chronostratigraphic tools here we use conodont biostratigraphy sequence stratigraphy and carbon isotope delta c 13 carb chemostratigraphy to demonstrate that the conodont kockelella walliseri an important guide fossil for middle and upper sheinwoodian strata lower stage of the wenlock series first appears at least one full stratigraphic sequence lower in laurentia than in baltica rather than serving as a demonstration of the unreliability of conodont biostratigraphy this example serves to demonstrate the promise of high resolution paleozoic stratigraphy the temporal difference between the two first occurrences was likely less than 1 million years and although it is conceptually understood that speciation and colonization must have been non instantaneous events paleozoic paleobiogeographic variability on such short timescales tens to hundreds of kyr traditionally has been ignored or considered to be of little practical importance the expansion of high resolution paleozoic stratigraphy in the future will require robust biostratigraphic zonations that embrace the integration of multiple chronostratigraphic tools as well as the paleobiogeographic variability in ranges that they will inevitably demonstrate in addition a better understanding of the paleobiogeographic migration histories of marine organisms will provide a unique tool for future paleozoic paleoceanography and paleobiology research c 2010 elsevier b v all rights reserved less

geochemical evidence for expansion of marine euxinia during an early silurian llandovery wenlock boundary mass extinction abstract repeated biotic crises have become the hallmark for the silurian with the three most significant marine turnover events being related to dramatic global environmental perturbations causal mechanisms linking these marine extinction events with positive carbon isotope 13 c excursions paleoceanographic change and climate remain poorly constrained here we examine the positive 13 c excursion across the llandovery wenlock boundary and the associated ireviken extinction event this positive 13 c excursion has been interpreted to reflect a major change in global oceanographic climate state and enhanced organic carbon burial new geochemical data from two paleocean basins have been analyzed to determine local and global redox conditions using carbon and sulfur isotopes 34 s and iodine i ca mg proxies the high resolution 13 c and 34 s data from both sections show positive excursions indicative of global perturbations to each of these elemental cycles with minimal temporal offsets between the two systems numerical box modeling of 13 c and 34 s data indicates that these isotopic shifts can be generated by significant increases in the burial of organic carbon and pyrite which are most likely due to enhanced burial under euxinic anoxic and sulfidic conditions independently i ca mg values point to locally anoxic bottom waters in the distal and deeper basinal setting in nevada before during and after the ireviken positive 13 c excursion i ca mg values in the proximal shelf setting in tennessee show relatively oxic waters during the onset of peak 13 c values after which bottom water oxygen concentrations dropped throughout the remainder of the excursion this multiproxy paleoredox dataset provides the first direct evidence for local and global expansion of reducing marine conditions coincident with the silurian biotic event and positive 13 c excursion integration of these geochemical data for local and global scale changes in marine redox conditions with the paleontological data and evidence for eustatic sea level rise points toward a shoaling of anoxic and or euxinic waters onto the shelf as a driver for the ireviken extinction event

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