18o 16o mapping and hydrogeology of a short lived 10 years fumarolic 500 c meteoric hydrothermal event in the upper part of the 0 76 ma bishop tuff outflow sheet california 18 o 16 o data from the 200 m thick 0 76 ma bishop tuff outflow sheet provide evidence for a vigorous short lived 10 years high temperature fumarolic meteoric hydrothermal event this is proved by 1 the juxtaposition in the upper partially welded bishop tuff of low 18 o groundmass glass 18 o 5 to 3 with coexisting quartz and feldspar phenocrysts having magmatic 18 o values 8 7 0 3 7 5 0 3 and 2 the fact that these kinds of 18 o 16 o signatures correlate very well with morphological features and mapped zones of fumarolic activity profiles of 18 o with depth in the bishop tuff within the fumarole area define a 40 to 50 m thick low 18 o stratigraphic zone that is sandwiched between the essentially unwelded near surface portion of the tuff and an underlying densely welded black tuff that displays magmatic 18 o 16 o values shallow dipping columnar joints and other fumarolic features i e subhorizontal tubular conduits and steep fissures correlate very well with these pervasively devitrified low 18 o zones the base of the low 18 o zone is extremely sharp 3 per meter and is located directly above the transition from partially welded tuff to densely welded black tuff the observed average whole rock 18 o depletions within this low 18 o zone are about 6 7 requiring meteoric water rock ratios in excess of 0 24 in mass units rainfall on the surface of the tuff would not have been high enough to supply this much h 2o in the short lifetime of fumarolic activity suggesting that some recharge must have been from groundwater flow through the upper part of the tuff above the sloping 1 5 top of the impermeable lower zone this is compatible with the observation that the fumarolic areas roughly correlate with the preeruptive regional drainage pattern some of this recharge may in part have been from the lake that filled long valley caldera which was dammed by the bishop tuff up to the level of this boundary between the partially and densely welded zones 7000 ft the elevation of the highest long valley lake shorelines gazis et al had previously shown that the 2 8 ma intracaldera chegem tuff from the caucasus mountains exhibits exactly the same kind of 18 o signature that we have correlated with fossil fumaroles in the bishop tuff outflow sheet although not recognized as such by mcconnell et al 18 o 16 o data from drill hole samples from the intracaldera bishop tuff in long valley also display this characteristic 18o signature i e analogous 18 o depth profiles as well as low 18 o groundmass coexisting with high 18 o feldspar phenocrysts this fumarolic 18 o 16 o signature is observed to much greater depths 650 750 m in the intracaldera tuffs 1500 m thick than it is in the 200 m thick bishop tuff outflow sheet 80 m depth

changes in antarctic bottom water properties in the western south atlantic in the late 1980s data collected in 1988 1989 as part of the south atlantic ventilation experiment have been combined with the historical database to study the circulation and water mass variability of the abyssal water in the argentine basin a map of potential temperature at 4000 m used as an indication of geostrophic shear defines a south and western intensified crescent shaped abyssal recirculation within this recirculation and its northward extension to the brazil basin antarctic bottom water aabw properties have undergone two modifications during the 1980s 1 the water mass cooled 0 05 c and freshened 0 008 in salinity ratio on surfaces of constant density 2 the densest layer of aabw was altered to less dense water through mixing or advection out of the study area this water mass change does not appear to have affected the flow pattern data collected in 1983 and 1988 to the north in the brazil basin show penetration of the freshwater mass in the deep western boundary current to between 18 s and 10 s indicating very rapid propagation of the anomaly from the argentine basin into the brazil basin as a deep western boundary current it is suggested that open ocean convective events within the weddell sea contributed to the change in aabw documented here

the microstructures of perthitic alkali feldspars revealed by hydrofluoric acid etching etching of alkali feldspar cleavage fragments with hydrofluoric acid vapor followed by study of the surfaces by scanning electron microscopy sem is a simple and rapid technique for characterizing the microtextures of crypto and microperthites this technique has a number of advantages over conventional transmission electron microscopy tem including ease of sample preparation and the large areas of crystals which can be imaged alkali feldspars studied by the method can yield important information on the cooling history of igneous and metamorphic rocks fluid feldspar interactions and the morphology and microstructures of albite exsolution lamellae some of these applications are illustrated by examples of etched crypto and micro perthites from the klokken layered syenite south greenland and the shap granite north west england

paleobotanical evidence for near present day levels of atmospheric co2 during part of the tertiary understanding the link between the greenhouse gas carbon dioxide co 2 and earth9s temperature underpins much of paleoclimatology and our predictions of future global warming here we use the inverse relationship between leaf stomatal indices and the partial pressure of co 2 in modern ginkgo biloba and metasequoia glyptostroboides to develop a co 2 reconstruction based on fossil ginkgo and metasequoia cuticles for the middle paleocene to early eocene and middle miocene our reconstruction indicates that co 2 remained between 300 and 450 parts per million by volume for these intervals with the exception of a single high estimate near the paleocene eocene boundary these results suggest that factors in addition to co 2 are required to explain these past intervals of global warmth

palaeoecology of macroneuropteris scheuchzeri and its implications for resolving the paradox of xeromorphic plants in pennsylvanian wetlands abstract the medullosan pteridosperm macroneuropteris scheuchzeri hoffmann cleal shute zodrow was widespread and abundant in the middle to late pennsylvanian forests of tropical pangaea on the basis of its thick cuticles few adaxial stomata sunken stomata and dense trichomes it has been inferred to be a xeromorphic plant here we test that hypothesis by analyzing its facies distribution especially in relation to coals at 273 site collections from 45 stratigraphic horizons accessioned in the smithsonian national museum of natural history washington d c u s a the collections represent mostly par autochthonous assemblages and cover the taxon s complete known temporal range west of the appalachians in west central pangaea chi square analysis of facies occurrence data indicates that m scheuchzeri had a strong preference for mineral enriched wetlands that immediately preceded and followed the development of peat swamps and mires coals particularly during the late middle pennsylvanian late moscovian times coincident with a period of reduced polar ice volume in the late pennsylvanian following an interval of global warming and tropical wetland reorganization palaeoequatorial climate shifted to an overall drier mode this was accompanied by the disappearance of m scheuchzeri from europe and its limitation west of the appalachians to the wettest available habitats on the landscape thus our data falsify the hypothesis that m scheuchzeri was a conventional xerophyte but highlight the paradox of a plant with apparent xeromorphic features confined to a wetland habitat we consider several possible explanations for this association 1 response to nutrient deficiency 2 response to substrate salinity due to growth in coastal mangrove habitats 3 response to the composition of the palaeozoic atmosphere 4 return on investment long leaf lifespan and 5 phylogenetic constraint reflecting ancestral conditions our findings have broader implications for interpreting a wide variety of other pennsylvanian wetland plants which similarly show xermorphic features

estimating paleoatmospheric pco2 during the early eocene climatic optimum from stomatal frequency of ginkgo okanagan highlands british columbia canada abstract estimates of p co 2 for the early paleogene vary widely from near modern day levels to an order of magnitude greater based on various proxy measures resolving the relationship between climate and p co 2 during this globally warm period is a key task in understanding climate dynamics in a warmer world here we use the stomatal frequency of fossil ginkgo adiantoides from the okanagan highlands of british columbia canada to estimate p co 2 during the early eocene climatic optimum eeco the interval of peak warmth in the cenozoic we also examine a dataset of modern ginkgo biloba leaves to critically assess the accuracy and precision of stomatal frequency as a proxy indicator of p co 2 early eocene fossil g adiantoides has significantly lower stomatal frequency than modern g biloba suggesting p co 2 levels 2 modern pre industrial values this result is in contrast to earlier studies using stomatal frequency of ginkgo that indicated near modern day levels of p co 2 in the early paleogene though not including samples from the eeco we also find that levels of p co 2 as indicated by stomatal frequency are correlated with trends in climate mean annual temperature over time at the falkland fossil locality suggesting that climate and p co 2 were coupled during the eeco hyperthermal

compaction profiles of ash flow tuffs modeling versus reality abstract density profiles of 4 ash flow deposits in oregon and idaho are simulated using the model of riehle et al 1995 to calculate heat flow degassing and compaction the deposits are all the rattlesnake tuff a more complex ignimbrite sheet was sampled at 3 distal sites near to one another a medial site and 4 proximal sites model results of distal profiles are similar despite more than twofold variation in thickness and comprise 3 early deposits having emplacement temperatures of 724 732 c followed by two hotter deposits 785 790 c and a cooler capping deposit of about 735 c one distal site has an inferred surge deposit at its base density reversals simulated as cooling intervals all range from 3 to 10 days correlated cooling intervals agree to within a factor of two however the duration of a cooling interval cannot be precisely hindcast owing to potential complications by rainfall or accumulation of chilled airfall ash thus the seemingly wide range of model results for the cooling intervals is perhaps not surprising proximal profiles have more density reversals implying more deposits than the distal profiles they also have greater overall compaction and consequential loss of detail in the density profiles some earlier deposits have model temperatures of 736 757 c and may correlate with the lower distal deposits at one site these are overlain by two hotter deposits 790 796 c and a cooler capping deposit 745 c that are almost surely correlatives of the upper distal deposits some sites have additional early hotter deposits and one site has an uppermost deposit that is the coolest of all model deposits thus a picture emerges of thermally stratified near source flows during early eruptive activity and more far travelled flows during later eruptions shards analyzed by streck and grunder 1997 show a compositional range and corresponding magma temperatures of 795 880 c which is permissive of thermally layered deposits and implies cooling during fallback and travel of 50 100 c rare textural evidence for internal flow boundaries as well as our consistent model results among multiple sites despite variation in deposit thickness support the assumption that density reversals represent partial cooling breaks if so then modeling of density profiles can provide important evidence for how large ignimbrites are constructed sheridan and wang 2004 also report stratigraphically consistent results by modeling density reversals in distal bishop tuff as cooling breaks our results contrast with those of wilson and hildreth 2003 who concluded that density reversals in the proximal bishop tuff do not represent cooling breaks but instead are evidence for thermally heterogeneous deposits it may be that the proximal bishop tuff is not amenable to modeling due to its great thickness 100 200 m and deposition on steeply dipping rugged terrain factors which would likely cause turbulent flow obscure subtle stratigraphic details of flow boundaries and complicate resulting compaction zonation

phanerozoic atmospheric co2 change evaluating geochemical and paleobiological approaches abstract the theory and use of geochemical modeling of the long term carbon cycle and four paleo pco 2 proxies are reviewed and discussed in order to discern the best applications for each method geochemical models provide pco 2 predictions for the entire phanerozoic but most existing models present 5 10 m y means and so often do not resolve short term excursions error estimates based on sensitivity analyses range from 75 200 ppmv for the tertiary to as much as 3000 ppmv during the early paleozoic the 13 c of pedogenic carbonates provide the best proxy based pco 2 estimates for the pre tertiary with error estimates ranging from 500 1000 ppmv pre devonian estimates should be treated cautiously error estimates for tertiary reconstructions via this proxy are higher than other proxies and models 400 500 ppmv and should not be solely relied upon we also show the importance of measuring the 13 c of coexisting organic matter instead of inferring its value from marine carbonates the 13 c of the organic remains of phytoplankton from sediment cores provide high temporal resolution up to 10 3 10 4 year high precision 25 100 ppmv for the tertiary to 150 200 ppmv for the cretaceous pco 2 estimates that can be near continuous for most of the tertiary its high temporal resolution and availability of continuous sequences is advantageous for studies aiming to discern short term excursions this method however must correct for changes in growth rate and oxygen level at elevated pco 2 750 1250 ppmv this proxy loses its sensitivity and is not useful the stomatal density and stomatal index of land plants also provide high temporal resolution 2 year high precision 10 40 ppmv for the tertiary and possibly cretaceous pco 2 estimates and so also is ideal for discerning short term excursions unfortunately this proxy also loses sensitivity at some level of pco 2 above 350 ppmv which currently is largely undetermined our analysis of the recently developed 11 b technique shows that it currently is not yet well constrained most importantly it requires the assumption that the boron isotopic composition of the ocean remains nearly constant through time in addition it assumes that there are no biological or temperature effects and that diagenetic alteration of the boron isotopic composition does not occur a fifth co 2 proxy based on the redox chemistry of marine cerium has several fundamental flaws and is not discussed in detail here

the pangean ice age studies with a coupled climate ice sheet model application of an ice sheet model developed for the pleistocene to the extensive carboniferous glaciation on gondwana yields an ice sheet which has several features consistent with observations while complete deglaciation is not achieved without co2 changes the milankovich induced fluctuations in ice sheet volume are comparable to pleistocene glacial interglacial signals this result is shown to hold for a large fraction of physically reasonable parameter space the model also exhibits multiple equilibria and sharp bifurcations as infinitesimal changes in the solar constant or precipitation can lead to a qualitatively different climate the success of the model in predicting ice location in an environment quite different from the pleistocene provides additional support for the robustness of the basic model physics and suggests that the model can be applied with some confidence to other pre pleistocene glaciations

thermal history of a bishop tuff section as determined from the width of cryptoperthite lamellae the lamellar spacings in the sanidine cryptoperthites bulk composition or 66 4 ab 32 3 an 1 3 from the bishop tuff near long valley california have been determined using transmission electron microscopy the lamellar spacings show a sharp maximum at about 43 m below the topographically highest sample and a weak minimum about 4 m above this this pattern indicates that two flows compose the section the gradational boundary between the flows is about 37 m below the highest sample heat flow calculations applied to the pattern of lamellar spacings indicate that these flows were emplaced within 1 5 yr of each other the result illustrates the power of this technique in deciphering the geologic history of igneous rocks

permian phytogeographic patterns and climate data model comparisons abstract the most recent global icehouse hothouse climate transition in earth history began during the permian warmer polar conditions relative to today then persisted through the mesozoic and into the cenozoic we focus here on two permian stages the sakmarian 285 280 ma and the wordian 267 264 ma also known as the kazanian integrating floral with lithological data to determine their climates globally these stages postdate the permo carboniferous glaciation but retain a moderately steep equator to pole gradient judging by the level of floral and faunal differentiation floral data provide a particularly useful means of interpreting terrestrial paleoclimates often revealing information about climate gradations between dry and wet end member lithological indicators such as evaporites and coals we applied multivariate statistical analyses to the permian floral data to calibrate the nature of floral and geographical transitions as an aid to climate interpretation we then classified sakma

cooling rates of plinian fall and pyroclastic flow deposits in the bishop tuff inferences from water speciation in quartz hosted glass inclusions cooling rates inferred from water speciation in rhyolitic glass inclusions in quartz phenocrysts from the bishop tuff california vary over more than 5 orders of magnitude from about 10 to 10 4 c s 1 many of the cooling rates are within the previously published experimentally calibrated range of this technique but the slowest rates 10 4 c s 1 are extrapolated such extrapolation suggests cooling rates as low as 10 8 c s 1 0 3 c year 1 for the interiors of thick pyroclastic flow deposits the temperatures at which oh and molecular h2o species would be in equilibrium range from 400 c for glass inclusions from plinian fall deposits to 250 c for the most slowly cooled glassy inclusions from pyroclastic flow deposits notwithstanding appreciable uncertainties cooling rates correlate with depositional process fall vs flow deposition and distance above the cold ground or below overlying hot pyroclastic flow deposits plinian inclusions within 2 5 m of the cold pre bishop ground cooled at 1 10 c s 1 consistent with thermal modeling of small pumice clasts falling through cold air very slow inferred cooling rates for pyroclastic flow deposits 10 6 to 10 8 c s 1 also agree with thermal conduction models faster cooling rates 10 1 to 10 4 c s 1 for inclusions in the lowermost 0 5 m of pyroclastic flow deposits reflect the effect of quenching against the cold ground at blind spring hill east of long valley caldera intermediate cooling rates 10 3 to 10 6 c s 1 are observed in plinian deposits overlain by and partially interbedded with pyroclastic flow deposits indicating that reheating of rapidly cooled plinian inclusions can reset water speciation melt inclusions in pyroclastic flow deposits are quenched to glass only if the deposit is relatively thin or has a relatively low emplacement temperature in relatively thick or hot deposits inclusions may be quenched to glass at the base of the deposit where it is more rapidly cooled by contact with the pre eruption ground

use of carbon isotopes in paleosols as an indicator of the p co2 of the paleoatmosphere measurements of carbon isotopic composition of coexisting paleosol organic matter and carbonate results in improved estimates of the paleo p co2 content of the paleoatmosphere measurements from tertiary paleosols indicate that the levels of co2 in the early eocene middle and late miocene and pliocene were less than 1000 ppmv early cretaceous levels of p co2 were significantly higher of the order of 1500 to 3000 ppmv

the spreading of lower circumpolar deep water in the atlantic ocean abstract a stommel arons model of the circulation of lower circumpolar deep water lcdw in the atlantic ocean is presented and compared with observations the lcdw is defined as a layer of uniform thickness over a flat bottom the lateral boundaries are given by the 4000 m isobath the drake passage and the throughflow between africa and antarctica are closed the model is forced by a concentrated source in the weddell sea representing the net atlantic gain of lcdw due to production in the weddell sea and inflow through drake passage this net gain is termed the lcdw formation rate it is compensated by upwelling over the rest of the atlantic best agreement with observed net transport rates in the western atlantic was found using a lcdw formation rate of about 8 sv sv 106 m3 s 1 in reality however a higher rate is required in order to establish the outflow to the indian ocean the interior transport the transport through topographic gaps and the transport rates of western boundary currants on t

investigating the record of permian climate change from argillaceous sedimentary rocks oman a standard method for the analysis of carbon isotope composition of bulk organic matter 13 c bulk in palaeoenvironmental and stratigraphic studies of sedimentary basins associated with hydrocarbons is suggested this method includes the removal of interstitial hydrocarbon within the sediments which is shown to have a negative effect on 13 c using the method a 13 c bulk trend c 21 to 24 was found within the lower permian al khlata and lower gharif formations of thuleilat 16 and 42 well sections south oman palaeontological and sedimentological evidence indicates considerable palaeoenvironmental change from a cold climate lowland fern flora and upland primitive conifer flora low in the sequence to a lowland cycad like and upland glossopterid or other gymnospermous flora higher in the sequence the lithologies range from glacial diamictite at the base to calcrete horizons and redbeds at the top it is therefore likely that the 13 c bulk trend is related to palaeoenvironmental change

response of carboniferous permian mid oceanic seamount capping buildup to global cooling and sea level change akiyoshi japan abstract we discuss the response of a carboniferous permian mid oceanic atoll type carbonate buildup to global cooling and sea level fluctuation during gondwana glaciation our examination focused upon the stratigraphic distribution of emergence indicative diagenetic features as a proxy for sea level falls and we correlated their timing with hiatuses indicated by fusuline biostratigraphic discontinuities and the demise of warm adapted metazoan reef builders we examined the pennsylvanian moscovian to lower permian asselian shallow marine limestone succession ca 500 m thick of the akiyoshi limestone group southwest japan reconstructed as a mid oceanic seamount capping buildup in the panthalassan ocean the examined succession is dominated by atoll lagoon facies with subordinate coral chaetetes patch reefs and calci microbial mounds we have recognized several stratigraphic intervals less than 60 m thick in the examined succession in which emergence indicative diagenetic facies are concentrated these facies include the microcodium structure pendant cements recrystallization and algal casts each of the intervals occurs immediately below a fusuline zone boundary and represents a sea level fall event which lasted presumably 1 ma or less possibly reflecting the sea level fluctuation of third order cycles the emergence event in late kasimovian is the most prominent in the series of moscovian through asselian emergence events and resulted in a dissolution unconformity indicated by a fusuline biostratigraphic discontinuity we infer that many intercalations of less freshwater altered limestone in these stratigraphic intervals resulted from short lived emergence resubmergence episodes possibly due to the high frequency glacio eustyaic sea level fluctuation we also showed that the demise of warm adapted metazoan reef builders of corals and chaetetes happened nearly synchronously with the culmination of gondwana glaciation we hypothesize that the demise of these warm adapted reef builders is a biotic response of the akiyoshi buildup to the severe and prolonged global cooling during the pennsylvanian to early permian icehouse period the akiyoshi metazoan reef builders were replaced by calci microbes phylloid algae and calci sponges that exhibit an increasing significance during the lower to middle permian our results reveal the distinct sedimentary and biotic responses of a panthalassan atoll to global cooling and sea level fluctuation during gondwana glaciation in the southern hemisphere we conclude that carboniferous permian mid oceanic atoll stratigraphy has significant archival potential for recognizing the global palaeoclimatic change

cooling and welding history of the bishop tuff in adobe valley and chidago canyon california abstract a numerical model for cooling and welding of ash flow tuffs was developed to obtain a quantitative understanding of the welding compaction that occurs during the cooling of ash flow sheets and to evaluate the relative effects of emplacement temperature thickness and emplacement histories on compaction zonation density profiles of large ash flow sheets this model includes a set of two phase compressible navier stokes equations for the transport of mass momentum and energy for a variable density volatile outfluxing through a porous media ash flow tuff with this model we calculated theoretical compaction profiles density vs elevation to match actual data measured in sections of bishop tuff compaction profiles from the adobe basin indicate that there were 3 periods of non deposition 5 10 and 40 days separating 4 distinct rapidly emplaced packets rep of pyroclastic flow deposition in contrast the 3 periods of quiescence 400 20 and 800 days between the 4 reps in chidago canyon were considerably longer these data constrain models of eruption for the bishop tuff by implying an eruption cycle that lasted longer than 3 years the average calculated deposition temperatures for all 4 reps in the adobe basin are fairly uniform at 667 33 c in chidago canyon two of the reps had a higher deposition temperature 660 c than the other two 534 c

co2 levels in the late palaeozoic and mesozoic atmosphere from soil carbonate and organic matter satpura basin central india abstract a number of calcic palaeosols have been identified within the fluvial deposits of the motur permian the denwa triassic the bagra jurassic and the lameta cretaceous formations of the satpura sedimentary succession central india these palaeosols show accumulation of pedogenic carbonates in rhizocretions and glaebules the carbon isotopic compositions of these carbonates and the coexisting soil organic matters are used to determine the isotopic composition and the partial pressure of atmospheric co 2 using the co 2 palaeobarometer developed by cerling am j sci 291 1991 377 it is seen that the atmospheric co 2 level increased by a factor of 8 from the permian to the jurassic and declined again during the cretaceous the nature of the changes agrees with the result of the co 2 evolution model of berner geocarb ii but the magnitude of the co 2 increase in the middle jurassic and the late cretaceous was higher than the predicted value degassing of earth s interior due to rapid break up of the gondwana landmass during the triassic and jurassic period could have caused the rapid co 2 increase

origin of cryptoperthites in the bishop tuff and their bearing in its thermal history the bishop tuff is a large rhyolitic ash flow which erupted from long valley caldera in eastern california and contains abundant sanidine cryptoperthite phenocrysts which can be used to constrain the time between the two major cooling units the cryptoperthites bulk composition or66ab33an1 have exsolved in two principal stages followed by a third minor stage the earliest exsolution which produced patches of relatively wide lamellae 100 800 nm without wedge shaped ends wse occurred by coherent nucleation and was probably related to a high flux of water associated with fumarolic activity in this area the spacing of these lamellae shows no correlation with depth or thermal history the second major stage of exsolution occurred by spinodal decomposition which produced lamellae with wse having spa ein g s of from 80 to 170 nm and the spacing of these lamellae varies with depth in a pattern consistent with the two known cooling units heat flow calculations indicate that this pattern of lamellar spacings is consistent with an interval of about 1 0 2 0 years between the eruption of these two cooling units

changing co2 conditions during the end triassic inferred from stomatal frequency analysis on lepidopteris ottonis goeppert schimper and ginkgoites taeniatus braun harris abstract end triassic fluctuations in atmospheric carbon dioxide co2 concentration were reconstructed by the use of stomatal frequency analysis on a single plant species the seedfern lepidopteris ottonis goeppert schimper stomatal index showed no distinct intra and interpinnule variation which makes it a suitable proxy for past relative co2 changes records of decreasing stomatal index and density from the bottom to the top of the rhaetian hettangian wustenwelsberg section bavaria germany indicate rising co2 levels during the triassic jurassic transition additionally stomatal frequency data of fossil ginkgoalean leaves ginkgoites taeniatus braun harris suggest a maximum palaeoatmospheric co2 concentration of 2750 ppmv for the latest triassic

siberian glaciation as a constraint on permian carboniferous co2 levels reconstructions of phanerozoic co2 levels have generally relied on geochemical modeling or proxy data because the uncertainty inherent in such reconstructions is large enough to be climatically significant inverse climate modeling may help to constrain paleo co2 estimates in particular we test the plausibility of this technique by focusing on the climate from 360 to 260 ma a time in which the siberian landmass was in middle to high latitudes yet had little or no permanent land ice our climate model simulations predict a lower limit for co2 the value beneath which siberia acquires excess ice simulations provide little new information for the period in which siberia was at a relatively low paleoaltitude 360 340 ma but model results imply that paleo co2 levels had to be greater than 2 4 modern values to be consistent with an apparently ice free siberia in the late permian these results for the later period in general agree with soil co2 proxies and the timing of gondwanan deglaciation thus providing support for a significant co2 increase before the end permian boundary event our technique may be applicable to other time intervals of unipolar glaciation

modeling late paleozoic glaciation late paleozoic glaciation on gondwana is associated with changes in geography solar luminosity and estimated co sub 2 levels to assess the relative importance of these boundary conditions the authors conducted a suite of climate model simulations for the periods before during and after peak mid carboniferous approximately 300 ma glaciation 340 300 and 255 and 225 ma respectively orbital insolation values favorable for glaciation and interglaciation were used for each time interval results indicate that changes in geography cause significant changes in snow area but the temporal trend is not consistent with the geologic record for glaciation combined co sub 2 plus geography changes yield the best agreement with observations in addition interglacial orbital configurations result in almost ice free conditions for the glacial interval at 300 ma at a time of low co sub 2 the large simulated glacial interglacial snowline fluctuations for permian carboniferous time may explain cyclothem fluctuations at these times overall results support the importance of the co sub 2 paradigm but also indicate that a fuller understanding of past climate change requires consideration of paleogeographic luminosity and orbital insolation changes

geologic constraints on the glacial amplification of phanerozoic climate sensitivity the long term carbon cycle depends on many feedbacks silicate weathering consumes atmospheric co2 but is also enhanced by the increased temperatures brought about by this important greenhouse gas the long term sensitivity t2x of climate to co2 doubling modulates the strength of this negative feedback we update the model experiment of royer and others 2007 by estimating an empirical probability density function pdf of t2x for the phanerozoic by using an improved geocarbsulf carbon cycle model to predict a larger recalibrated set of proxy co2 measurements from the present day to 420 ma the new geocarbsulf parameterizes the rapid weathering of volcanic rocks relative to plutonic rocks updates to the carbon cycle model and the proxy co2 data set induce opposing model responses as a result our experiment maintains an agreement with t2x estimates based on numerical climate models and late cenozoic paleoclimate for a climate sensitivity t2x that is uniform throughout the phanerozoic the most probable value is 3 to 4 c geocarbsulf fits the proxy co2 data equally well and with far more parameter choices if t2x is amplified by at least a factor of two during the glacial intervals of the paleozoic 260 340 ma and cenozoic 0 40 ma relative to non glacial intervals of earth history for glacial amplification of two the empirical pdfs for glacial climate sensitivity predict t2x g 2 0 c with 99 percent probability t2x g 3 4 c with 95 percent probability and t2x g 4 4 c with 90 percent probability the most probable values are t2x g 6 to 8 c this result supports the notion that the response of earth9s present day surface temperature will be amplified by the millennial and longer term waxing and waning of ice sheets

alkali feldspar microtextures as provenance indicators in siliciclastic rocks and their role in feldspar dissolution during transport and diagenesis abstract alkali feldspars usually exhibit optical or sub optical intergrowths of albite and k feldspar known generically as perthite which have morphologies and crystallographic characteristics that are distinctive of the igneous or metamorphic environment in which they grew and cooled to surface temperatures we review the current terminology and understanding of how the microtextures form and discuss their role in feldspar dissolution during weathering transport and diagenesis we show how microtextures can be used as provenance indicators in arkosic siliciclastic rocks using examples from the fulmar formation a reservoir rock in the upper jurassic humber group in the central north sea in which feldspar dissolution is a major source of secondary porosity we describe the most effective techniques for routine characterization of which the most practical is back scattered electron imaging in a scanning electron microscope often coupled with cathodoluminescence we provide an atlas of the main types of perthitic intergrowth likely to be encountered in igneous and metamorphic rocks worldwide and show how many of the microtextures can be matched in clastic grains in the fulmar formation grains which are preferentially preserved have microtextures that make them relatively unreactive in aqueous fluids at low temperatures and we conclude that provenance has a major impact on reservoir quality detrital grains in the fulmar exhibit authigenic albitization k feldspar overgrowths and replacement and we discuss how diagenetic features can be distinguished from replacive features developed in the protolith

atmospheric co2 from the late oligocene to early miocene based on photosynthesis data and fossil leaf characteristics abstract the late oligocene represents a comparatively cool phase followed by a warming event the so called late oligocene warming that predates the mi 1 glacial event at the oligocene miocene transition there is evidence that these climate events were linked to level changes in atmospheric co2 in this study atmospheric co2 from the late oligocene to the early miocene is reconstructed by a terrestrial proxy stomatal parameters of angiosperm leaves fossil leaves of six plant species were considered laurophyllum pseudoprinceps l acutimontanum both lauraceae platanus neptuni platanaceae eotrigonobalanus furcinervis quercus rhenana and q praerhenana all fagaceae the plant material originates from various sites in germany late oligocene to the early miocene and austria early miocene a mechanistic theoretical approach based on stomatal data photosynthesis and gas exchange control was used since this approach also requires climate data as input parameters for calculating assimilation and transpiration rates palaeoclimate of these sites were also derived in detail considerable differences were found between results obtained by the two lauraceae taxa and all other taxa with the lauraceae indicating a high co2 level if lauraceae are included a co2 level of about 700 ppm for the late and latest oligocene is obtained and about 500 ppm for the early miocene all non lauraceae taxa belonging to different families indicate a consistently lower level of co2 of about 400 ppm for all considered sites and time slices a value of 400 ppm is also consistent with other proxy data that are available for that time period a steady level of 400 ppm would indicate a decoupling of co2 and cooling warming events from the late oligocene to the early miocene more data provided by different proxies are desirable to unravel the interactions between atmosphere and climate for the late oligocene and the early miocene

cryptoperthites and cooling rate in a layered syenite pluton a chemical and tem study alkali feldspars in the klokken layered syenite south greenland are optically either coarse turbid deuteric patch perthites or clear unaltered fine braid microor cryptoperthites irregular clear volumes can be found in most turbid grains electron microscopy shows that all clear crystals or volumes are cryptoperthites in which the periodicity of the exsolution lamellae increases systematically with distance from the roof of the intrusion from 40 nm to 300nm they are composed of low albite and diagonally associated maximum microcline a secondary coarsening is responsible for optically visible braid microperthites the layered series consists of interleaved granular syenites and coarser grained laminated syenites with mineral layering microprobe analyses show a downward decrease in ca and ba in the granular syenite feldspars consistent with chilling from the roof inwards most laminated syenite feldspars contain 1 an increasing to 5 in mafic layers the periodicity of the exsolution lamellae in the laminated syenite feldspars is consistently up to twice that in adjacent granular syenites periodicity is not influenced by ab or or an content but high an feldspars have continuous zig zag intergrowths while others are more lozengeshaped lamellar periodicities largely reflect cooling rate in the pluton cooling times in the exsolution interval were probably about 103 104 years at the top of the series whereas existing experimental data suggest that the periodicities would be reached in a few days or years the periodicities at the top of the granular series are only slightly greater than experimentally determined initial wavelengths for spinodal decomposition suggesting that little or no coarsening occurred despite the long cooling times coarsening did occur lower in the pile framework ordering and twinning must slow or stop coarsening the difference in periodicity between the granular and laminated syenite series may be caused by differences in amount of water incorporated in the feldspar structure from the magma the exsolution of this water at low temperatures could be the cause of the deuteric unmixed patch perthites small volumes of cryptoperthite which have escaped deuteric unmixing may be common in igneous rocks in general and may be useful relative indicators of cooling rate

palaeoenvironmental implication of resedimented limestones shed from mississippian permian mid oceanic atoll type buildup into slope to basin facies akiyoshi japan abstract for better understanding of long term environmental changes in a mid oceanic atoll type buildup akiyoshi limestone group we examined the atoll derived carbonate sediments that were contemporaneously shed into the spicular chert of slope to basin facies ota group in the akiyoshi area southwest japan both of these two units are dated as upper visean to capitanian and interpreted as having laterally passed into each other on and around a mid oceanic seamount the resedimented limestone occurs as slab like bodies and isolated and laterally discrete smaller pods and thin beds and laminae in the spicular chert of the ota group the composite succession ca 105 m thick measured in slab like bodies is divided into the lower and upper units each of which consists of the sharp based calcarenite siliceous lime mud siltstone and spicular chert with blocks beds and laminae of calcarenite and siliceous limestone in ascending order the calcarenite forming slabs and smaller blocks are massive and dominantly comprises densely packed coarse crinoid debris and subordinate bryozoan fragments with no or sparse matrix the siliceous lime mud siltstone consists of siliceous sponges spicules minute calcitic skeletal debris and peloidal particles with the matrix of a mixture of lime mud and microcrystalline quartz the calcarenite and siliceous lime mud siltstone beds and laminae in the spicular chert occasionally contain graded and parallel laminae the massive calcarenite and graded calcarenite and siliceous limestone were formed by redeposition mainly of skeletal sands presumably by grain flows with minor debris flows and by mixing of sponge spicule rich siliceous sediments and redeposited lime mud and skeletal debris by muddy turbidites of distal facies respectively these redeposited carbonate sediments were exported from the akiyoshi limestone group onto the spicular sediments of slope to basin facies conodonts fusulinids and smaller foraminifers from the resedimented limestone indicate that the redeposition of the carbonate sediments took place dominantly in late visean to late bashkirian and subordinately in sakmarian to capitanian time the absence of the moscovian to asselian resedimented limestone implies much reduced carbonate shedding during this period the correlation with the interpreted palaeoenvironmental episodes in the akiyoshi buildup shows that late visean to late bashkirian and sakmarian to capitanian carbonate shedding events correspond to the times of generally warm climate and high sea levels in the akiyoshi buildup moscovian to asselian time which lacks records of carbonate shedding nearly corresponds to the moscovian to gzhelian cooling and sea level lowering in the akiyoshi buildup we consider that the shedding of carbonate sediments from the akiyoshi atoll is its depositional response to the warm climate and elevated sea levels and is compared with a sedimentary system of the highstand shedding of carbonates atoll type carbonates equivalent to the akiyoshi limestone group in the akiyoshi terrane also show comparable responses of carbonate shedding into slope and slope to basin facies

strontium and carbon isotopic evidence for decoupling of pco2 from continental weathering at the apex of the late paleozoic glaciation

low atmospheric co 2 levels during the permo carboniferous glaciation inferred from fossil lycopsids earth history was punctuated during the permo carboniferous 300 250 million years myr ago by the longest and most severe glaciation of the entire phanerozoic eon but significant uncertainty surrounds the concentration of co2 in the atmosphere through this time interval and therefore its role in the evolution of this major prepleistocene glaciation here i derive 24 late paleozoic co2 estimates from the fossil cuticle record of arborsecent lycopsids of the equatorial carboniferous and permian swamp communities quantitative calibration of late carboniferous 330 300 myr ago and permian 270 260 myr ago lycopsid stomatal indices yield average atmospheric co2 concentrations of 344 ppm and 313 ppm respectively the reconstructions show a high degree of self consistency and a degree of precision an order of magnitude greater than other approaches low co2 levels during the permo carboniferous glaciation are in agreement with glaciological evidence for the presence of continental ice and coupled models of climate and ice sheet growth on pangea moreover the permian data indicate atmospheric co2 levels were low 260 myr ago by which time continental deglaciation was already underway positive biotic feedbacks on climate and geotectonic events therefore are implicated as mechanisms underlying deglaciation

a guide to phanerozoic cold polar climates from high latitude ice rafting in the cretaceous the high latitude extent of warm climate indicators at certain times in earth history has been considered as evidence that the globe was ice free for long intervals despite theoretical considerations and results from numerical modelling experiments1 2 indicating that this was unlikely one of the warmest periods the cretaceous displays faunal and floral evidence for cool temperate to sub tropical conditions very near to the poles however our studies of lower cretaceous mudstones of central australia that contain outsized exotic blocks have led to the conclusion that the blocks were emplaced by ice rafting implying that high latitude ice was present at sea level strata of a similar origin of mid jurassic to mid cretaceous age occur on other continents that were positioned between 65 and 78 palaeolatitude indeed there is a record of high latitude ice rafting throughout the phanerozoic suggesting that ice was present on earth for much of its history and that ice free conditions could have been at most only episodic over the past 600 myr

feldspar microtextures and multistage thermal history of syenites from the coldwell complex ontario optical and tem transmission electron microscopy observations of perthites from augite syenites in the coldwell complex ontario reveal a complex set of microtextures that outline a multistage thermal history regular microtextures linear or braid texture straincontrolled coherent intergrowths show a progressive evolution from the margin of the intrusion inwards with lamellar spacings in the range 40 100 nm the textures evolve in a manner similar to those for the klokken intrusion and reflect differences in cooling rates and bulk composition superimposed upon the regular microtexture are 10 m scale compositional fluctuations which we call ripples the boundary relationships and bulk composition of ripples which are themselves ab rich and or rich linear coherent cryptoperthites suggest that they formed by coarsening during a phase of high temperature 530 c fluid feldspar interaction this was followed by a return to coherent exsolution in which fluid was not involved coarse irregular patch microperthite cross cuts all other microtextures these final deuteric intergrowths are believed to result from a further low temperature 380 c fluid feldspar interaction and are associated with subgrain formation and the presence of micropores the outermost syenite sample against a gabbro ring structure has distinctive modified microtextures indicating that the gabbro is at least in part a later intrusion our findings show that tem work on alkali feldspar microtextures can identify discrete thermal events in the cooling history of igneous plutons and illustrates the potential of such microtextures for establishing the relative ages of intrusive rocks

effects of chemical preparation protocols on δ13c values of plant fossil samples abstract for over a half century studies of the stable carbon isotope compositions of plant fossils have provided noteworthy conclusions about the evolution of earth climate however different preparation protocols were used prior to carbon isotope analysis of plant fossils and the accuracy of measured 13c 12c ratios may strongly depend on them we have applied the most frequently used chemical preparation protocols to frenelopsis leaves from four cretaceous localities of western europe our results indicate that procedures to extract plant fossils from sediments are not adequate to retrieve the original plant 13c values the use of schulze s reagent to bleach cuticles in paleobotany allows misleading 13c values of specimens from a same locality with positive shifts of up to 13 6 and increases intra specimen and inter specimen variances sample treatment involving hcl or hcl hf gives consistent 13c mean values for a same leaf and for leaves from a same sedimentary bed however although hf does not provide any advantage in removing potential contamination sources it alters plant fossil tissues slightly increasing the intra and inter leaf variances of 13c values our results indicate that processing plant fossils with hcl only is the most accurate and conservative way to retrieve original 13c values

the land plant δ13c record and plant evolution in the late palaeozoic abstract based on the evaluation of 1323 carbon isotope values for silurian to permian terrestrial organic carbon measured on plant fossils cuticules humic coals and bulk terrestrial organic matter tom we conclude that the temporal trend in 13ctom records variations in the global carbon cycle notably an increase in the fractional burial of light terrestrial organic matter in late palaeozoic sediments 13ctom values suggest that the late palaeozoic po2 peak could have been restricted to a time frame of 40 ma carbon isotope data from four taxonomic groups reveal small differences that could be a consequence of habitat conditions no significant differences in organic carbon isotopic composition in relation to variable climatic conditions are discernible the carbon isotopic composition solely reflects c3 plant metabolism

mineralization of biogenic materials in the water masses of the south atlantic ocean i assessment and results of an optimum multiparameter analysis abstract this is the first of two manuscripts dealing with the circulation mixing ventilation and organic matter mineralization of the south atlantic ocean sao the present work quantifies the complex mixing of water masses in the sao using a constrained least squares regression optimum multiparameter omp analysis the omp based on temperature salinity silicate and the conservative parameter no was applied on two world ocean circulation woce lines a17 and a14 in the western and eastern sao respectively the constrained omp sensitivity to sources of error in the end member characteristics measured parameters equation weights and oxygen to nitrogen mineralization ratio rn was carefully assessed using perturbation tests perturbation of rn was the only test that changed significantly the mixing proportions although by less than 5 the constrained omp method allowed defining the realm and identifying the core of flow of each water mass to study its circulation the evolution of its chemical composition and eventually to separate the contribution of physical and biogeochemical processes relevant specific outputs of this first manuscript are 1 north of the south equatorial current the silicate maximum is primarily composed of antarctic intermediate water aaiw rather than circumpolar deep water cdw 2 the two degree discontinuity tdd experiences a dramatic meridional change of water masses composition being dominated by north atlantic deep water nadw north of the vema channel and by cdw southwards 3 the 50 proportion horizon of weddell sea deep water wdsw with a of 0 3 c at the entry of the sao defines the upper limit of the wsdw realm more properly than the classical isopycnals of 46 04 or 46 06 4 where the proportion of wsdw is around 75

impact of long term climate change and sea level fluctuation on mississippian to permian mid oceanic atoll sedimentation akiyoshi limestone group japan abstract to understand the impacts of long term climatic episodes and sea level changes on mid oceanic atoll sedimentation the stratigraphic changes of litho and bio facies and stratigraphic levels of freshwater diagenetic alteration and biostratigraphic discontinuity of the akiyoshi limestone group upper visean to upper capitanian were reviewed this group records approximately 70 million years of atoll sedimentation in a mid oceanic realm of the panthalassa ocean which developed nearly synchronously with the late paleozoic gondwana glaciation the entire succession of the akiyoshi limestone group was divided into four facies associations skeletal oolitic grainstone muddy limestone muddy limestone skeletal grainstone and reefal limestone associations skeletal oolitic grainstone and reefal limestone associations upper visean to bashkirian are characterized by an abundance of oolite and crinoidal grainstone and reef facies of warm adapted metazoan reef builders corals chaetetes and bryozoans respectively characteristics of skeletal oolitic grainstone and reefal limestone associations indicate their deposition in a warm climate with elevated sea level muddy limestone association moscovian to kasimovian records the demise of the warm adapted metazoan reef builders and frequent emergence events of the buildup many geochemical data support the significant drop in temperature during moscovian through kasimovian time these depositional and biotic events of muddy limestone association indicate that its sedimentation was strongly affected by cool climate and generally low sea level muddy limestone skeletal grainstone association is characterized by an upward increasing significance of calcimicrobes calcareous algae and calcisponges the succession records less frequent emergence events than that of muddy limestone association ii these characters reflect a warming climate and sea level rise in gzhelian to capitanian time the climate episodes and sea level changes interpreted from the akiyoshi limestone group generally correspond to the global trend of mississippian to permian long term climatic change and sea level fluctuation related to the major glacial events of gondwana glaciation the late visean to bashkirian warm climate and elevated sea levels moscovian to kasimovian cooling and sea level lowering and gzhelian to capitanian warming and sea level rise recorded in the akiyoshi buildup are comparable to the global climate model and sea level fluctuation which contain early to middle mississippian pre glacial warm climate and highstands middle to late pennsylvanian cooling and related glacio eustatic sea level fluctuation at the culmination of gondwana glaciation and early to middle permian global warming and sea level rise due to the retreat of gondwana ice sheets akiyoshi atoll sedimentation was most significantly affected pennsylvanian global cooling and related sea level lowering but their impact was short lived the onset of the cooling and frequent emergence events in the akiyoshi buildup occurred delayed approximately 10 millions years later than that of comparable episodes on the pangean shelves the post glacial warming in the akiyoshi buildup started at least several millions of years earlier than in epicontinental seas of the pangea this phenomenon may be due to the palaeoposition of the akiyoshi buildup in a mid oceanic realm of the panthalassa ocean

the paleozoic to mesozoic carbon cycle revisited the carbon isotopic composition of terrestrial organic matter 1 two thousand one hundred forty eight carbon isotope values for terrestrial organic matter plant fossils coal bulk terrestrial organic matter provide a proxy record for temporal changes in the global carbon cycle 13ctom 13ccarb and 13cco2 allow a full evaluation of carbon transfer in the atmosphere ocean system as well as between the marine and the terrestrial realm the temporal evolution of 13ctom parallels respective data sets from marine carbonate carbon thus reflecting the linkage between both reservoirs via atmospheric carbon dioxide on the basis of a comparison between measured and predicted isotope records for 13ctom changes in the carbon isotopic fractionation associated with plant metabolism are discernible this contradicts the notion of an invariable carbon isotopic fractionation associated with c3 plant metabolism in light of results from current plant growth experiments these changes are viewed as dependent on the atmospheric o2 co2 hence 13ctom might serve as a proxy signal for atmospheric composition

coarsening kinetics of coexisting peristerite and film microperthite over 104 to 105 years alkali feldspar crystals from the klokken syenite pluton south greenland have a coarse patch perthite exsolution texture on the scale of hundreds of micrometers produced by dissolution reprecipitation reactions at 500 c we have discovered that ab rich patches ab92an7or1 subsequently exsolved by spinodal decomposition to give peristerite with a periodicity of 17 nm this is the first time a peristerite has been characterized by tem within a perthite and the first peristerite to be found outside regional metamorphic rocks and pegmatites the coexisting or rich patches ab16or84 an0 3 unmixed over the same temperature interval to yield coherent film microperthite with periodicities 1 m because the peristerite and film perthite from a single hand specimen from the klokken intrusion have shared exactly the same cooling history they provide a novel opportunity to test the utility of diffusion coefficients obtained in the laboratory for prediction of coarsening rates over 105 yr time scales in the light of a calculated cooling trajectory for the pluton we find good agreement between observed and predicted periodicities for the film perthite which began to exsolve by coherent nucleation at the coherent solvus for ordered feldspars at 420 c 32 000 yr after crystal growth and took a further 13 000 39 000 yr to coarsen to a periodicity of 1 m peristerite exsolution began at the conditional spinodal at 450 c but on the basis of the best existing experimental data would have taken 520 000 4 600 000 yr to coarsen incompatible with the cooling history we speculate on changes to these best parameter values to describe nasi caal interdiffusion that would lead to peristerite coarsening rates compatible with the cooling history of the klokken intrusion we find that an interdiffusion expression batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document mathit d nasi caal 9 times 10 12 exp 220 000 mathit rt end document where d and the pre exponential term a are in units of m2 s and the activation energy e a is in j mol leads to coarsening rates compatible with the experimental data the cooling path of the klokken intrusion and the coarsening rate of the coexisting film perthite the new interdiffusion parameters are consistent with fine scale peristerite intergrowths in low grade metamorphic rocks and with the existence of the coarsest known peristerite in the light of our discovery it seems likely that peristerite is commonplace in albitic plagioclase in granitic rocks

the deep waters from the southern ocean at the entry to the argentine basin hydrographic data from the world ocean circulation experiment woce and south atlantic ventilation experiment save in the region of transition between the scotia sea and the argentine basin are examined to determine the composition of the deep water from the southern ocean that enters the atlantic and to describe the pathways of its constituents the deep current that flows westward against the falkland escarpment is formed of several superposed velocity cores that convey waters of different origins lower circumpolar deep water lcdw southeast pacific deep water spdw and weddell sea deep water wsdw different routes followed by the wsdw upstream of and through the georgia basin lead to distinctions between the lower wsdw 4 46 09 and the upper wsdw 46 04 4 46 09 the lower wsdw flows along the south sandwich trench then cyclonically in the main trough of the georgia basin although a fraction escapes northward to the argentine basin a comparison of the woce data with those from previous programmes shows that this component had disappeared from the southwestern argentine basin in 1993 1994 this corroborates previous results using save and pre save data a part of the upper wsdw recognizable from different s characteristics flows through the scotia sea then in the georgia basin along the southern front of the antarctic circumpolar current northward leakage at this front is expected to feed the argentine basin through the northern georgia basin the spdw is originally found to the south of the polar front pf in drake passage the northward veering of this front allows this water to cross the north scotia ridge at shag rocks passage it proceeds northward to the argentine basin around the maurice ewing bank the lcdw at the falkland escarpment is itself subdivided in two cores of which only the denser one eventually underrides the north atlantic deep water nadw in the atlantic ocean this fraction is from the poleward side of the pf in drake passage it also crosses the north scotia ridge at shag rocks passage then flows over the falkland plateau into the atlantic the lighter variety from the northern side of the pf is thought to cross the north scotia ridge at a passage around 55 w it enters the argentine basin in the density range of the nadw