can biomass burning produce a globally significant carbon isotope excursion in the sedimentary record negative carbon isotope excursions have been comprehensively studied in the stratigraphic record but the discussion of causal mechanisms has largely overlooked the potential role of biomass burning the carbon isotopic ratios 13 c of vegetation soil organic matter and peat are significantly lower than atmospheric carbon dioxide co2 and thereby provide a source of low 13 c co2 when combusted in this study the potential role of biomass burning to generate negative carbon isotope excursions associated with greenhouse climates is modeled results indicate that major peat combustion sustained for 1000 yr increases atmospheric co2 from 2 5 present atmospheric levels pal to 4 6 pal and yields a pronounced negative 13 c excursion in the atmosphere 2 4 vegetation 2 4 and the surface ocean 1 2 but not for the deep ocean 0 9 release of co2 initiates a short term warming of the atmosphere up to 14 4 c with a duration of 1628 yr which is consistent with the magnitude and length of an observed toarcian excursion event these results indicate that peat combustion is a plausible mechanism for driving negative 13 c excursions in the rock record even during times of elevated pco2

sulfur isotope evidence for widespread euxinia and a fluctuating oxycline in early to middle ordovician greenhouse oceans article i nfo despite marine geochemical records indicating widespread oxygenation of the biosphere in the terminal neoproterozoic era late cambrian records point to the persistence of deep water anoxia and potential for development of euxinic conditions the late cambrian spice steptoean positive carbon isotope excursion event however is a globally recognized chemostratigraphic marker that likely represents significant organic carbon burial and subsequent liberation of oxygen to the biosphere here we present high resolution carbon and sulfur isotope profiles from early to middle ordovician carbonate rocks from the argentine precordillera and western newfoundland to constrain oceanic redox conditions in the post spice world marine c isotope profiles record relatively stable behavior excursions b3 that is characteristic of greenhouse climates ma rine s isotope profiles record short term b10 6 yr rhythmic variation superimposed over a longer term

isotopic evidence for a sizeable seawater sulfate reservoir at 2 1 ga abstract the 2 1 ga tulomozero formation deposited on the fennoscandian shield consists of shallow marine carbonate and siliciclastic rocks dissolution breccias and widespread syndepositional marine evaporites now mostly present as pseudomorphs after ca sulfates this study investigates sulfates hosted in three different proxies to constrain the sulfur isotopic composition of seawater sulfate acknowledging the presence of different types of sulfates carbonate associated sulfate cas breccia associated sulfate bas and sulfate relicts rs in a variety of lithologies of the tulomozero formation a widely used and accepted proxy for the ambient seawater sulfate sulfur isotopic composition is carbonate associated sulfate which was extracted from carbonate samples across the entire tulomozero formation in addition sulfate was extracted from a siliciclastic dissolution breccia which is suggested to have formed after dissolution of sulfate evaporites the sulfate sulfur isotopic composition from both lithologies was measured ex situ 34 s cas 10 9 2 7 34 s bas 9 0 1 1 ubiquitous pseudomorphs after ca sulfates occur in the tulomozero formation and contain m size anhydrite and barite relicts their sulfur isotopic composition was measured in situ by secondary ion mass spectroscopy sims 34 s anhydrite 9 6 1 0 34 s barite 11 0 3 1 sulfur isotope data from carbonate rocks breccias and the sulfate relicts match the existing 34 s record of seawater sulfate during that time and show no distinct stratigraphic variations indicating that the seawater sulfate sulfur isotopic composition remained unaffected from environmental changes during the time of deposition of the tulomozero formation physical evidence for widespread precipitation of sulfate rather than abundant chloride suggests a modern style evaporite sequence with carbonates followed by sulfate and then chlorides however this requires a minimum sulfate concentration of 2 5 mm in the ambient seawater consequently the evidence for persistent evaporitic sulfate deposition in the tulomozero formation implies a substantial seawater sulfate reservoir at 2 1 ga according to the estimated minimum depositional time from the thickness of the carbonate rocks of the formation the residence time of seawater sulfate is expected to have been at least 5 ma the available data support the existence of a sizeable seawater sulfate reservoir in the mid paleoproterozoic ocean in fact more than 10 of the modern sulfate reservoir

wildfires in the late palaeozoic of central europe an overview of the rotliegend upper carboniferous lower permian of the saar nahe basin sw germany abstract fossil charcoal from a number of different sedimentary settings e g lakes floodplains tuffs tuffites is reported from the rotliegend late carboniferous early permian of the saar nahe basin in sw germany it is one of the largest carboniferous permian basins which developed during the late variscan in europe the sedimentary deposits encompass the carboniferous permian boundary thus enabling us to examine the development of fire regimes parallel to the reconstructed drop in atmospheric o 2 across this boundary the majority of the identified macroscopical charcoal remains belongs to the conifers or other gymnosperms maybe pointing to a more fire prone vegetation in the drier hinterland preferentially inhabited by these plants most wildfires especially those which took place during the deposition of the lower rotliegend late carboniferous have probably been ignited by lightning whereas in the upper rotliegend early permian an intense volcanism may have also acted as an important additional source of ignition in the lower rotliegend charcoals occur in nearly all sedimentary facies types whereas in the upper rotliegend charcoal has so far only been found in some volcanically influenced deposits the absence of charcoal in most sediments from the upper rotliegend may be explained by i low atmospheric oxygen levels leading to reduced fire frequencies ii a generally sparse vegetation cover iii the mechanical breakdown of macroscopic charcoal under the prevailing semiarid conditions

burial of organic carbon and pyrite sulfur in sediments over phanerozoic time a new theory in present day marine sediments almost all of which are deposited in normal oxygenated seawater rates of burial of organic carbon c and pyrite sulfur s correlate positively and bear a constant ratio to one another c s 3 on a weight basis by contrast calculations based on the isotopic model of garrels and lerman 1981 indicate that at various times during the phanerozoic the worldwide burial ratio must have been considerably different than the present day value this ratio change is caused by the requirement that increases in the worldwide mass of organic carbon must be accompanied by equivalent decreases in the mass of sedimentary pyrite sulfur in order to maintain a roughly constant level of o2 in the atmosphere such apparently contradictory behavior can be explained if the locus of major organic carbon burial has shifted over time from normal marine environments as at present to non marine freshwater or to euxinic environments in the geologic past a shift to predominantly freshwater burial can help explain predicted high c s ratios in permo carboniferous sediments and a shift to euxinic environments can help explain predicted low c s ratios during the early paleozoic it is demonstrated that the three environments today exhibit distinguishably different average c s ratios

coal weathering and the geochemical carbon cycle abstract the weathering rate of sedimentary organic matter in the continental surficial environment is poorly constrained despite its importance to the geochemical carbon cycle during this weathering complete oxidation to carbon dioxide is normally assumed but there is little proof that this actually occurs knowledge of the rate and mechanisms of sedimentary organic matter weathering is important because it is one of the major controls on atmospheric oxygen level through geologic time we have determined the aqueous oxidation rates of pyrite free bituminous coal at 24 and 50 c by using a dual cell flow through method coal was used as an example of sedimentary organic matter because of the difficulty in obtaining pyrite free kerogen for laboratory study the aqueous oxidation rate obtained in the present study for air saturated water 270 m o2 was found to be on the order of 2 10 12 mol o2 m2 s at 25 c which is fast compared to other geologic processes such as tectonic uplift and exposure through erosion the reaction order with respect to oxygen level is 0 5 on a several thousand hour time scale for both 24 and 50 c experiments activation energies determined under 24 and 50 c conditions were 40 kj mol o2 indicating that the oxidation reaction is surface reaction controlled the oxygen consumption rate obtained in this study is two to three orders of magnitude smaller than that for pyrite oxidation in water but still rapid on a geologic time scale aqueous coal oxidation results in the formation of dissolved co2 dissolved organic carbon doc and solid oxidation products which are all quantitatively significant reaction products

carbon isotope evidence implying high o2 co2 ratios in the permo carboniferous atmosphere abstract theoretical models predict a marked increase in atmospheric o2 to 35 during the permo carboniferous 300 ma occurring against a low 0 03 co2 level an upper o2 value of 35 however remains disputed because ignition data indicate that excessive global forest fires would have ensued this uncertainty limits interpretation of the role played by atmospheric oxygen in late paleozoic biotic evolution here we describe new results from laboratory experiments with vascular land plants that establish that a rise in o2 to 35 increases isotopic fractionation 13c during growth relative to control plants grown at 21 o2 despite some effect of the background atmospheric co2 level on the magnitude of the increase we hypothesize that a substantial permo carboniferous rise in o2 could have imprinted a detectable geochemical signature in the plant fossil record over 50 carbon isotope measurements on intact carbon from four fossil plant clades with differing physiological ecologies and ranging in age from devonian to cretaceous reveal a substantial 13c anomaly 5 occurring between 300 and 250 ma the timing and direction of the 13c excursion is consistent with the effects of a high o2 atmosphere on plants as predicted from photosynthetic theory and observed in our experiments preliminary calibration of the fossil 13c record against experimental data yields a predicted o2 co2 mixing ratio of the ancient atmosphere consistent with that calculated from long term models of the global carbon and oxygen cycles we conclude that further work on the effects of o2 in the combustion of plant materials and the spread of wildfire is necessary before existing data can be used to reliably set the upper limit for paleo o2 levels

wildfires and seasonal aridity recorded in late cretaceous strata from south eastern arizona usa lithostratigraphic and organic chemostratigraphic studies of fluvial lacustrine sediments in the late cretaceous fort crittenden formation in south eastern arizona usa reveal changes in palaeoclimate and tectonics as well as associated fluctuations in lake level the lower fort crittenden is dominated by marginal wetland to deep water lake deposits whereas the upper fort crittenden is characterized by wetland to deltaic deposits abundance of polycyclic aromatic hydrocarbons pah and reflectance of fusinite substantiate the impact of wildfires within the watershed organic geochemical evidence of wildfires is linked with sedimentological indicators of seasonal aridity suggesting that wildfires were common occurrences sedimentological evidence for seasonal aridity includes mottles and pseudoslickensides on ped structures within wetland mudstones distinct variations in pah assemblages characterized by the number of aromatic rings indicate that there were variations in the intensities of wildfires assuming no variations in the types of fuel fusinite reflectance values are consistent with combustion temperatures from 470 to 550 c observed in modern wildfires

the evolution of respiratory systems in theropoda and paracrocodylomorpha the end triassic extinction and the role of late triassic atmospheric o2 and co2 abstract during the late triassic period 235 201 3 ma paracrocodylomorpha and theropoda switched predatory roles with the former filling the subsidiary predator niche and the latter filling the top predator niche at the end triassic extinction reasons for the transition in predator guilds remain unknown but atmospheric conditions during this time which involved high co2 and low o2 concentration levels may be associated with the event evidence of bird like pneumatic post crania present in both groups as foramina and fossae correlates with an avian like respiratory system this may have allowed organisms to cope with declining atmospheric o2 environments of the late triassic this study estimated po2 throughout the late triassic using organic carbon isotope measurements from newark hartford basin paleosols and examined the morphological change in skeletal remains of theropoda focusing on pneumatic bones compared with paracrocodylomorpha during the late triassic and across the triassic jurassic boundary with data compiled from the paleobiology database and published anatomical literature the change of pneumaticity in taxa is quantified by a pneumatic index pi in which the number of pneumatized units is divided by the total number of bones examined patterns of pneumaticity are individually scored for the presence or absence of pneumatic bones morphological data are compared to corresponding femur length estimated atmospheric o2 and co2 level reconstructions and an ancestral state reconstruction depicting how pi values change throughout various clades our results suggest that pi values in theropoda and paracrocodylomorpha correspond with the vacillating po2 and pco2 throughout the late triassic and into the jurassic high pi values are prevalent in advanced theropod taxa while paracrocodylomorpha pi values vary by clade with a generally negative trend throughout the triassic ancestral state reconstruction analysis highlights the increasing pi values within theropoda and clade dependent trends in paracrocodylomorpha this study is instrumental in reconstructing how theropoda became evolutionarily successful and perhaps how and why the avian like respiratory system originated

carbon isotope signatures of pedogenic carbonates from se china rapid atmospheric pco2 changes during middle late early cretaceous time lower cretaceous pedogenic carbonates exposed in se china have been dated by u pb isotope measurements on single zircons taken from intercalated volcanic rocks and the ages integrated with existing stratigraphy 13 c values of calcretes range from 7 0 to 3 0 and can be grouped into five episodes of increasing decreasing values the carbon isotope proxy derived from these palaeosol carbonates suggests p co 2 mostly in the range 1000 2000 parts per million by volume ppmv at s z co 2 contributed by soil respiration 2500 ppmv and 25 c during the hauterivian albian interval c 30 ma duration such atmospheric co 2 levels are 4 8 times pre industrial values almost double those estimated by geochemical modelling and much higher than those established from stomatal indices in fossil plants rapid rises in p co 2 are identified for early hauterivian middle barremian late aptian early albian and middle albian time and rapid falls for intervening periods these episodic cyclic changes in p co 2 are not attributed to local tectonism and volcanism but rather to global changes the relationship between reconstructed p co 2 and the development of large igneous provinces lips remains unclear although large scale extrusion of basalt may well be responsible for relatively high atmospheric levels of this greenhouse gas suggested levels of relatively low p co 2 correspond in timing to intervals of regional to global enrichment of marine carbon in sediments and negative carbon isotope 13 c excursions characteristic of the oceanic anoxic events oae1a selli event kilian and paquier events constituting part of the oae 1b cluster and oae1d short term episodes of high p co 2 coincide with negligible carbon isotope excursions associated with the faraoni event and the jacob event given that episodes of regional organic carbon burial would draw down co 2 and negative 13 c excursions indicate the addition of isotopically light carbon to the ocean atmosphere system controls on the carbon cycle in controlling p co 2 during early cretaceous time were clearly complex and made more so by atmospheric composition also being affected by changes in silicate weathering intensity

a modeling case for high atmospheric oxygen concentrations during the mesozoic and cenozoic changes in atmospheric oxygen concentration over earth history are commonly related to the evolution of animals and plants but there is no direct geochemical proxy for o2 levels meaning that estimations rely heavily on modeling approaches the results of such studies differ greatly to the extent that today s atmospheric mixing ratio of 21 might be either the highest or lowest level during the past 200 m y long term oxygen sources such as the burial in sediments of reduced carbon and sulfur species are calculated in models by representation of nutrient cycling and estimation of productivity or by isotope mass balance imb a technique in which burial rates are inferred in order to match known isotope records studies utilizing these different techniques produce conflicting estimates for paleoatmospheric o2 with nutrient weathering models estimating concentrations close to or above that of the present day and imb models estimating low o2 especially during the mesozoic here we re assess the imb technique using the copse biogeochemical model imb modelling is confirmed to be highly sensitive to assumed carbonate 13c and when this input is defined following recent compilations predicted o2 is significantly higher and in reasonable agreement with that of non imb techniques we conclude that there is no model based support for low atmospheric oxygen concentrations during the past 200 m y high mesozoic o2 is consistent with wildfire records and the development of plant fire adaptions but links between o2 and mammal evolution appear more tenuous

control of sulfate pore water profiles by sedimentary events and the significance of anaerobic oxidation of methane for the burial of sulfur in marine sediments abstract gravity driven mass flow deposits proven by sedimentary and digital echosounder data are indicative for prevailing dynamic sedimentary conditions along the continental margin of the western argentine basin in this study we present geochemical data from a total of 23 gravity cores pore water so 4 is generally depleted within a few meters below the sediment surface by anaerobic oxidation of methane aom the different shapes of so 4 profiles concave kink and s type can be consistently explained by sedimentary slides possibly in combination with changes in the ch 4 flux from below thus mostly representing transient pore water conditions since slides may keep their original sedimentary signature a combined analysis and numerical modeling of geochemical physical properties and hydro acoustic data could be applied in order to reconstruct the sedimentary history we present first order estimates of the dating of sedimentary events for an area where conventional stratigraphic methods failed to this day the results of the investigated sites suggest that present day conditions are the result of events that occurred decades to thousands of years ago and promote a persisting mass transport from the shelf into the deep sea depositing high amounts of reactive compounds the high abundance of reactive iron phases in this region maintains low hydrogen sulfide levels in the sediments by a nearly quantitative precipitation of all reduced sulfate by aom for the total region we estimate a so 4 or ch 4 flux of 6 6 10 10 moles per year into the zone of aom projected to the global continental slope and rise area this may sum up to about 2 6 10 12 moles per year provided that the sulfur is completely fixed in the sediments it is about twice the global value of the recent global sulfur burial in marine sediments of 1 2 10 12 moles per year as previously estimated thus aom obviously contributes very significantly to the regulation of global sulfur reservoirs which is hitherto not sufficiently recognized this finding may have implications for global geochemical models as sulfur burial is an important control factor in the development of atmospheric oxygen levels over time

the record of triassic charcoal and other evidence for palaeo wildfires signal for atmospheric oxygen levels taphonomic biases or lack of fuel abstract as wildfires are today important sources of disturbance in many terrestrial ecosystems it is of great interest to understand how different environmental parameters and fire activity interacted during past periods of the earth history fossil charcoal inertinites and pyrogenic polycyclic aromatic hydrocarbons pahs represent the only direct evidence for the occurrence of such palaeo wildfires in the present study a review of published data together with new data on the occurrence of fossil charcoal for the permian and the triassic is presented for a long time it has been speculated that an assumed lack of evidence for palaeo wildfires during the triassic should be explained by a large drop in atmospheric oxygen concentration following or during the end permian mass extinction event preventing the occurrence of wildfires however evidence for palaeo wildfires is relatively common in many middle and late triassic strata whereas such evidence is almost totally lacking from early triassic sediments the interpretation of this charcoal gap or depression is difficult as many factors e g atmospheric oxygen concentration taphonomical biases lack of sediments suitable for the preservation of macroscopic charcoal lack of fuel and ignorance of scientists may have influenced not only the production but also the preservation and recovery of evidence for palaeo wildfires during this period thus it is not clear whether this early triassic charcoal gap can also be seen as evidence for an assumed wildfire gap or not without any doubt further investigations on the early triassic record of charcoal and other evidence for palaeo wildfires will be necessary before this problem can be solved in fact it can be expected that the number of published records of early triassic evidence for palaeo wildfires will increase in the future as more and more scientist working on sediments of this age may become aware of the interest in fires from this time this will certainly make it possible to give a much better picture of the temporal and regional distribution of wildfires during this period in the future

geologic history of seawater a magic approach to carbon chemistry and ocean ventilation abstract we explore the relationship between atmospheric o 2 and co 2 evolution and seawater chemistry with particular focus on the co 2 carbonic acid system and ocean ventilation over the phanerozoic eon using a coupled biogeochemical earth system model magic this model describes the biogeochemical cycles involving the major components of seawater ca mg na k cl so 4 co 2 hco 3 co 3 as well as components o 2 fe p organic c reduced s central to long term ecosystem productivity the magic calculations show that the first order input fluxes from weathering of continental rocks of ca mg and dissolved inorganic carbon dic to the ocean varied in a cyclical manner over the phanerozoic the cyclicity is mainly the result of the impact of changing atmospheric co 2 levels and hence temperature and runoff on these fluxes reflecting the nature of hothouse greenhouse high co 2 and warm versus icehouse low co 2 cool and continental glaciation conditions during the phanerozoic uptake of dic by seafloor basalt seawater reactions also varied in a corresponding fashion to the weathering fluxes the fluxes of ca mg dic and other seawater constituents removed in oceanic sinks were also calculated and hence with calculated inputs and outputs of seawater constituents the changes in seawater chemistry through phanerozoic time could be obtained seawater ph increased irregularly during the phanerozoic from just above 7 in the cambrian period approaching modern average values in the most recent several millions of years calcite saturation state also increased with decreasing age both ph and calcite saturation state trends exhibited a cyclic overprint of hothouse and icehouse environmental conditions dissolved sulfate changed in a cyclical manner reflecting mainly variations in weathering and accretion rates and redox conditions whereas dissolved potassium exhibited little variation in concentration using our standard model results for the chemistry of seawater and changes in atmospheric co 2 and o 2 as the basis for a series of sensitivity experiments we vary the ventilation rate of the global ocean and quantify the resulting changes in terms of processes such as net primary production organic carbon burial and oxidation pyrite weathering and sulfate reduction we use these preliminary results to discuss how changes in ocean ventilation affect atmospheric co 2 and o 2 and in turn exert changes in the sulfur organic carbon and inorganic carbon systems we postulate that periods of slow plate accretion rates associated with lower atmospheric co 2 vigorous deep water formation cooler drier climatic conditions and greater poleward temperature gradients are more likely to be associated with a strong thermohaline circulation and thus enhanced global ocean mixing conversely periods of higher accretion rates higher co 2 higher average global temperatures with more equable poleward gradients and higher sea levels resulting in extensive continental inundation would be more likely to be coincident with times of reduced mixing of the global ocean it is important to recognize that the scale of these changes depends on how major tectonic cycles controlling chemical weathering co 2 and temperature in turn affect nutrient supply global ocean productivity and global ocean thermohaline circulation the key to elucidating these changes lies in an understanding of the relationship between long term tectonic evolution which leads to changes in climate sea level and the global distribution of continental landmasses and the sedimentary environments they host and the circulation of the global ocean

a model for calcium magnesium and sulfate in seawater over phanerozoic time a theoretical model has been constructed for calculating the concentrations of dissolved calcium magnesium and sulfate in seawater over the past 550 million years phanerozoic time it is demonstrated that the weathering of ca carbonates and silicates by carbonic acid can be generally ignored in the modeling a previous model of the carbon cycle is used to guide input to the oceans of mg from carbonate and silicate weathering by h 2 co 3 similarly a previous model of the sulfur cycle is used to guide input fluxes to the ocean by calcium sulfate weathering and the weathering of ca and mg carbonates and silicates by sulfuric acid the sulfuric acid is derived from the oxidation of pyrite during weathering plus the oxidation of sulfur gases derived from the metamorphic volcanic decomposition of pyrite and caso 4 calcium is removed from seawater as sedimentary carbonates and sulfates so 4 is removed as sedimentary pyrite and caso 4 and mg is removed by exchange for ca via basalt seawater reaction and or dolomitization plus minor burial in sediments with pyrite as anoxic dolomite by adjusting starting conditions modeling results can be found that agree well with results of studies of salt fluid inclusions for variations of ca and so 4 this is especially true of the timing when ca was more abundant in seawater than so 4 and vice versa general agreement was also found with fluid inclusion results for changes in the mg ca ratio thereby distinguishing calcite seas from aragonite seas because of this overall agreement the modeling offers a new perspective on why oceanic ca mg and so 4 have varied over phanerozoic time

the carbon and sulfur cycles and atmospheric oxygen from middle permian to middle triassic the results of a theoretical isotope mass balance model are presented for the time dependence of burial and weathering plus degassing fluxes within the combined long term carbon and sulfur cycles averaged data for oceanic 13c and 34s were entered for every million years from 270 to 240 ma middle permian to middle triassic to study general trends across the permian triassic boundary results show a drop in the rate of global organic matter burial during the late permian and a predominance of low values during the early to middle triassic this overall decrease with time is ascribed mainly to epochs of conversion of high biomass forests to low biomass herbaceous vegetation resulting in a decrease in the production of terrestrially derived organic debris additional contributions to lessened terrestrial carbon burial were increased aridity and a drop in sea level during the late permian which led to smaller areas of low lying coastal wetlands suitable for coal and peat deposition mirroring the drop in organic matter deposition was an increase in the burial of sedimentary pyrite and a dramatic increase in the calculated global mean ratio of pyrite s to organic c high s c values resulted from an increase of deposition in marine euxinic basins combined with a decrease in the burial of low pyrite associated terrestrial organic matter the prediction of increased oceanic anoxia during the late permian and early triassic agrees with independent studies of the composition of sedimentary rocks weathering plus burial fluxes for organic carbon and pyrite sulfur were used to calculate changes in atmospheric oxygen the striking result is a continuous drop in o2 concentration from 30 to 13 over a twenty million year period this drop was brought about mainly by a decrease in the burial of terrestrially derived organic matter but with a possible contribution from the weathering of older organic matter on land it must have exerted a considerable influence on animal evolution because of the role of o2 in respiration some examples are the extinction of many vertebrates loss of giant insects and amphibians and the restriction of animals to low elevations it is concluded that the extinction of plants may have contributed to the extinction of animals

comments on the petrology of tambora volcano indonesia a model for the 1815 eruption by j foden foden 1986 presents an account of the petrology of tambora volcano with emphasis on the great explosive eruption of 1815 a comprehensive volcanological and petrologic study of tambora is long overdue and in this regard we welcome foden s paper however there are several points of the work that we wish to bring to the reader s attention especially foden s conclusion that the 1815 magma body was overpressured by 4 kbar prior to eruption our discussion here will concentrate on 3 major points a the validity of field data and its interpretation supportive of a large pre eruption overpressure b the nature of the samples of 1815 material presented by foden c the petrological treatment

microcodium an extensive review and a proposed non rhizogenic biologically induced origin for its formation abstract microcodium has been previously described as a mainly cenozoic calcification pattern ascribed to various organisms a review of the available literature and our data reveal two peaks in microcodium abundance the moscovian early permian and the latest cretaceous paleogene a detailed analysis of late paleozoic and cenozoic examples leads to the following new conclusions typical microcodium forming unilayered corn cob aggregates of elongated grains and thick multilayered palisade replacing structures cannot be linked to smaller grained intracellular root calcifications as became widely accepted after the work of klappa klappa c f 1979 calcified filaments in quaternary calcretes organo mineral interactions in the subaerial vadose environment j sediment petrol 49 955 968 typical microcodium is recognized from the early carboniferous with doubtful devonian reports to quaternary as a biologically induced mineralization formed via dissolution precipitation processes in various aerobic ca rich soil and subsoil terrestrial environments morphology and 13c signatures of microcodium suggest that neither plants algae or roots and root associated mycorrhiza regulate the formation of these fossil structures non recrystallized microcodium grains basically consist of slender 1 5 4 m curved radiating monocrystalline prisms with occasionally preserved hyphae like morphology thin 0 5 3 m hypha like canals can also be observed these supposed hyphae may belong to actinobacteria however thin fungal mycelia cannot be excluded we propose a model of microcodium formation involving a mycelial saprotrophic organism responsible for substrate corrosion and associated bacteria capable of consuming acidic metabolites and caco3 reprecipitation into the microcodium structures

external ballistic of volcanic explosions in order to determine the kinetic energy of an explosion it is necessary to know the initial velocities of ejected fragments calculations of initial velocities made earlier with few exceptions did not take into account the resistance of the air and therefore greatly underestimated the initial velocities and consequently the energy of the explosions a solution of the inverse problem of ballistics which takes into account air resistance makes it possible to find precise values of initial velocities of ejection determined from the distance of ejected fragments and their ballistic coefficients the method makes it possible to determine the kinetic energy of explosions for eruptions which were not directly observed it is shown that the velocity field in volcanic explosions is not spherical i e the velocities of ejection of fragments differ markedly in different directions accordingly the maximum distance of ejection of fragments depends not only on the initial angle of ejection but also on the character of distribution of initial velocities and the ballistic coefficients of the fragments for fragments with diameters of 40 cm to 2 m the maximum distance of ejection is realized in the case of angles of ejection of 30 36 for smaller fragments the optimal angles of ejection are still smaller the ballistics of explosive eruptions of the volcanoes asama arenal and shiveluch are considered

the oxygen geochemical cycle dynamics and stability abstract the first and possibly only major rise of atmospheric oxygen from p o 2 0 1 pal the present atmospheric level to p o 2 10 pal appears to have occurred sometime before 2 ga ago although the exact time of and the cause s for the rise have been hotly debated equally important questions on the atmospheric oxygen concern its stability especially the mechanisms regulating the atmospheric p o 2 level and the causes and magnitude of p o 2 variations since the first major rise of atmospheric oxygen previous efforts to model the p o 2 variation during the phanerozoic time have typically relied on secondary information such as the carbon and sulfur isotopic records of sedimentary rocks and on simple dynamics of the geochemical cycles of o c s and p based on box type models as a result many kinetic questions about the variation and stability of atmospheric oxygen could not have been answered here we quantitatively evaluate the dynamics and stability of atmospheric o 2 and co 2 using recent experimental data field observations and a new model for the c o coupled geochemical cycles we examine the change with time in the fluxes of various compounds o 2 co 2 phosphate organic c carbonate c c bearing reduced volcanic gases and c free reduced volcanic gases among the various reservoirs atmosphere soil surface ocean deep ocean the lower crust and mantle and upper crust under a variety of scenarios our model does not assume steady state fluxes for any of the reservoirs rather the model incorporates the kinetic experimental data on oxidation of coal a proxy for kerogen the dynamics of soil formation and erosion the kinetics of decomposition of organic matter in the oceans by aerobic and anaerobic bacteria the equilibrium ocean atmosphere carbonate model the observed relationships among the organic burial flux dissolved o 2 content of deep ocean and sedimentation rates and the three box model ocean the important parameters that strongly influence the dynamics of atmospheric o 2 are found to be a the total area of soil formation on earth b the average soil depth c the average rate of physical erosion of soils which is linked to the average rate of accumulation of clastic sediments in the oceans d the composition and flux of volcanic gas and e the level of atmospheric co 2 we develop kinetic equations linking these parameters to the production and consumption fluxes of atmospheric oxygen and also to stable p o 2 values considering the likely ranges of variations in these parameters in geologic history we suggest that the atmospheric p o 2 level is likely to have stayed within a very narrow range of 0 6 2 pal and that the entire ocean except for local euxinic basins is likely to have been basically oxygenated since the first major rise of atmospheric oxygen more than 2 ga ago

ediacaran growth of the marine sulfate reservoir abstract the sulfur isotope record as preserved in sedimentary sulfate and sulfide minerals reflects the progressive oxidation of earth s surface environment the latest proterozoic to early paleozoic marine sulfur isotope record is distinguished by unusually high 34 s values in marine sulfates and sulfides geological considerations and sulfur isotopic data indicate that the 34 s enrichment of the marine sulfate reservoir was the result of a rapid increase in the net fractionation between sedimentary sulfate and pyrite 34 s without a compensatory decline in the fractional burial rate of pyrite f pyr a simple one box model in which 34 s is linked non linearly to marine so 4 is used to explore the response in sedimentary sulfur isotope records 34 s sulf and 34 s pyr to an increasing marine sulfate reservoir the model results when compared with a compilation of existing 34 s sulf and 34 s pyr data suggest that the marine sulfate reservoir grew rapidly to roughly phanerozoic levels in the middle ediacaran period before the gaskiers glaciation and prior to the onset of the shuram wonoka negative 13 c anomaly it is further hypothesized that p o 2 levels rose prior to the onset of this extreme perturbation to the global carbon cycle permitting the oxidation of a previously euxinic deep ocean and appearance of the first ediacaran fauna by ca 575 ma despite the enormous demand on oxidants implied by this large magnitude and long duration carbon isotope anomaly

volcanological study of the great tambora eruption of 1815 the 1815 eruption of tambora is one of the largest explosive volcanic events of the past 10 000 yr by a conservative estimate 175 km3 of nepheline normative trachyandesitic pyroclastic material equivalent to about 50 km3 of dense rock was erupted in 24 h major activity began with a brief plinian phase followed by pyroclastic flows much of the ignimbrite that was produced shows evidence of deposition by turbulent flows a 6 7 km caldera about 1 km deep formed at the end of the pyroclastic flow phase caldera volume closely matches that of magma ejected plinian and co ignimbrite ash fall 1 cm thick covered 500 000 km2 of the java sea and surrounding islands accounting for more than two thirds of the magma volume erupted this distal tephra is known only from 1815 reports indicating that some great eruptions especially those from island volcanoes may be virtually undetectable in the geologic record without supporting information such as deep sea core data land based volume estimates may be insufficient to characterize eruption magnitude in many cases

geological nitrogen cycle and atmospheric n2 over phanerozoic time using the average nitrogen carbon ratio n c of sedimentary organic matter coal and volcanic metamorphic gases existing models of the carbon cycle have been used to calculate the fluxes of nitrogen to and from the atmosphere via the weathering burial and metamorphic volcanic decomposition of organic matter results indicate no appreciable change less than one percent of that present in the mass of atmospheric n 2 over phanerozoic time this is in sharp contrast to atmospheric o 2 which shows notable variations variation of the mass of o 2 but not that of n 2 must have led to variation in total atmospheric pressure with time results are not altered by considering n c ratios ten times higher than the average for sedimentary rocks nor by considering nitrogen release from silicate weathering the residence time of n 2 in the atmosphere relative to exchange with and storage in crustal rocks is estimated to be about one billion years

fossil charcoal as an indicator of palaeoatmospheric oxygen level charcoal results from incomplete combustion of plant material it is produced naturally by wildfire and being relatively tough and unbiodegradable it may be transported and incorporated into a variety of sedimentary environments wildfire requires adequate atmospheric oxygen for the combustion of plant fuel wood leaf litter fossil charcoal from the devonian onwards suggests that the oxygen level in the atmosphere has not fallen below 13 in this interval further the extreme flammability of even wet plant fuel at oxygen levels above 35 makes this the highest figure compatible with the occurrence of terrestrial vegetation

evaluating the use of amber in palaeoatmospheric reconstructions the carbon isotope variability of modern and cretaceous conifer resins abstract stable carbon isotope geochemistry of fossilized tree resin amber potentially could be a very useful tool to infer the composition of past atmospheres to test the reliability of amber as a proxy for the atmosphere we studied the variability of modern resin 13 c at both local and global scales an amber 13 c curve was then built for the cretaceous a period of abundant resin production and interpreted in light of data from modern resins our data show that hardening changes the pristine 13 c value by causing a 13 c depletion in solid resin when compared to fresh liquid viscous resin probably due to the loss of 13 c enriched volatiles modern resin 13 c values vary as a function of physiological and environmental parameters in ways that are similar to those described for leaves and wood resin 13 c varies between plant species and localities within the same tree and between different plant tissues by up to 6 and in general increases with increasing altitudes of the plant growing site we show that as is the case with modern resin cretaceous amber 13 c has a high variability generally higher than that of other fossil material despite the high natural variability amber shows a negative 2 5 3 13 c trend from the middle early cretaceous to the maastrichtian that parallels published terrestrial 13 c records this trend mirrors changes in the atmospheric 13 c calculated from the 13 c and 18 o of benthic foraminiferal tests although the magnitude of the shift is larger in plant material than in the atmosphere increasing mean annual precipitation and p o 2 could have enhanced plant carbon isotope fractionation during the late cretaceous whereas changing p co 2 levels seem to have had no effect on plant carbon isotope fractionation the results of this study suggest that amber is a powerful fossil plant material for palaeoenvironmental and palaeoclimatic reconstructions improvement of the resolution of the existing data coupled with more detailed information about botanical source and environmental growing conditions of the fossil plant material will probably allow a more faithful interpretation of amber 13 c records and a wider understanding of the composition of the past atmosphere

a new model for atmospheric oxygen over phanerozoic time a mathematical model has been constructed that enables calculation of the level of atmospheric o2 over the past 570 my from rates of burial and weathering of organic carbon c and pyrite sulfur s burial rates as a function of time are calculated from an assumed constant worldwide clastic sedimentation rate and the relative abundance and c and s contents of the three rock types marine sandstones and shales coal basin sediments and other non marine clastics red beds arkoses by our model values of o2 versus time using a constant total sedimentation rate agree with those for variable sedimentation derived from present day rock abundances and estimates of erosional losses since deposition this agreement is the result of our reliance on the idea that any increase in total worldwide sediment burial with consequently faster burial of c and s and greater o2 production must be accompanied by a corresponding increase in erosion and increased exposure of c and s on the continents to o2 consumption via weathering it is the redistribution of sediment between the three different rock types and not total sedimentation rate that is important in o2 control to add stability to the system negative feedback against excessive o2 fluctuation was provided in the modeling by the geologically reasonable assignment of higher weathering rates to younger rocks resulting in rapid recycling of c and s we did not use direct o2 negative feedback on either weathering of c and s or burial of c because weathering rates are assumed to be limited by uplift and erosion and the burial rate of c limited by the rate of sediment deposition the latter assumption is the result of modern sediment studies which show that marine organic matter burial occurs mainly in oxygenated shallow water and is limited by the rate of supply of nutrients to the oceans by rivers results of the modeling indicate that atmospheric o2 probably has varied appreciably over phanerozoic time during the late carboniferous and permian periods o2 was higher than previously because of the rise of vascular land plants and the widespread burial of organic matter in vast coal swamps a large decrease in o2 during the late permian was due probably to the drying up of the coal swamps and deposition of a large proportion of total sediment in c and s free continental red beds sensitivity study shows that major parameters affecting results are the mean c concentration in coal basins and the relative sizes of the reservoirs of young rapidly recycled versus old rocks less sensitivity was found for changes over time in total land area undergoing weathering and the use of direct o2 negative feedback on marine carbon burial good agreement for rates of c burial calculated via our model and via independent models which are based on the use of stable carbon isotopes indicates that the dominant factor that has brought about changes in atmospheric o2 level and the isotopic composition of dissolved inorganic carbon in seawater over phanerozoic time is sedimentation and not weathering or higher temperature phenomena such as basalt seawater reaction

glacial and glaciofluvial deposits in the interlobate areas of the scandinavian ice sheet abstract rapid flow within ice streams took place in a broad marginal zone of the scandinavian ice sheet during deglaciation ice streams and interlobate zones have been characterised by analysis of glacial flow patterns and examination of sedimentary features of interlobate glacial and glaciofluvial deposits reconstructed glaciodynamic systems are compared with ice streams of modem ice sheets wide interstream areas of inactive ice were left between some adjacent ice streams where they separated during the retreat of the margin these areas are characterised by morainic hummocks composed of both till and glaciofluvial sediment and sections show indications of subglacial deformation observations from fennoscandia suggest that these interstream areas were sites of net accumulation of glacial and glaciofluvial sediment during deglaciation glaciofluvial sediment was deposited in subglacial tunnels or cavities simultaneously with till deformation and deposition resulting from subglacial melting substantial glaciofluvial complexes were formed in narrow interlobate joints where adjacent ice lobes coalesced a case study made in southern finland shows converging flow patterns of two ice lobes and intervening glaciofluvial deposits concentration of meltwater in interlobate zones was a consequence of ice sheet configuration thinner ice in interlobate zones caused convergence of supraglacial and subglacial drainage the crevassed and strain softened ice may also have allowed surface meltwater to penetrate down to the ice bed interface close to the ice margin steep ice velocity gradients in interlobate zones would have increased subglacial melting rates and this environment was favourable for establishment of a subglacial drainage network and deposition of glaciofluvial sediment

medullosalean fusain trunk from the roof rocks of a coal seam insight from ftir and nmr pennsylvanian sydney coalfield canada abstract reported for the first time from the sydney coalfield canada is a fragmentary fusain r o 2 51 specimen 41 cm long of a medullosalean trunk or massive petiole that originated from the roof rocks of the banded bituminous hub seam r o 0 65 megascopic characteristics of the flat preserved specimen include an irregular cracked fusain surface with secretinite rodlet structures and sclerenchymatous strands some of which still embedded in the shaly matrix and locally preserved vitrain r o 0 69 co occurrence with a compression flora composed virtually of only the seed fern taxon macroneuropteris scheuchzeri hoffmann is noted the goal of this study is to provide a framework for the phytophysicochemical taphonomic history which includes the perspective on vitrinite fusinite relationship formation of fusinite and on the significance the only fusinized identifiable plant fossil specimen in the sydney coalfield we use state of the art solid state ftir 13 c 1 h nmr cp mas techniques and standard reflected light microscopy and sem methods as investigative tools results indicate that the fusinite is characterized by long and narrow xylem fibers without fungal signals and cell structures infilled with pyrite and carbonate ftir spectra of the fusinite and secretinite are similar particularly in respect to high absorbance of aromatic and low absorbance of aliphatic compounds and absorbance of si o functionalities relating to kaolinite 13 c nmr experiments with direct carbon excitation quantify the aromatic to aliphatic ratio as being 20 3 1 as part of the taphonomic history the evidence favors a hot 400 c directional surface fueled flame palaeofire of local extent that charred trunks of growing arborescent seed ferns on only one side and that these trunks were transported to comprise part of the roof rocks of the hub seam

sulfur isotope composition of carbonate associated sulfate from the mesoproterozoic jixian group north china implications for the marine sulfur cycle abstract the mesoproterozoic has been traditionally viewed as a period of prolonged stability in terms of environmental and biological evolution yet growing body of evidence suggests subtle yet dynamic changes in marine biogeochemical cycles in this study we present a high resolution analysis of carbonate associated sulfate cas from the mesoproterozoic jixian group 1 6 1 4 ga north china combined with previously reported carbon isotopes from the same sections sulfur isotope data provide insight into both oceanic chemistry and biospheric evolution during this period the sulfur isotopic composition of cas in the jixian group displays high amplitude variations with a total range from 3 7 to 51 9 stratigraphic variation in 34scas is most noted in the wumishan formation and records shifts of 10 over stratigraphic thickness of 100 200 m indicating a short residence time resulting from a limited oceanic sulfate reservoir differences in the pattern of isotopic variability between the gaoyuzhuang and wumishan formations suggest complex behavior of the marine sulfur cycle based on proximity of depositional environments to a local or regional chemocline and the degree of mixing between adjacent environments deposition under predominantly oxic conditions favored a stable sulfate reservoir whose isotopic composition was controlled primarily by pyrite burial by contrast depositional environments proximal to euxinic waters were subject to rapid changes in both sulfate reservoir size and isotopic composition resulting from growth and subsequent oxidation of a reactive hydrogen sulfide reservoir together these units demonstrate the difficulty of interpreting marine sulfur cycling in a low oxygen low sulfate world subject to a range of environmental controls data also reveal a long term positive trend in average 34scas and 13ccarb from approximately 10 to 20 and 0 5 to 0 5 respectively which is interpreted as reflecting prolonged organic carbon and pyrite burial burial of reduced carbon and sulfur may have resulted in a slow but steady release of oxygen to the biosphere ultimately driving a gradual increase in oceanic sulfate levels our study combined with previous contributions from the late mesoproterozoic supports hypotheses of protracted biospheric oxygenation marked by a modest increase in oceanic sulfate concentrations through the mesoproterozoic

sulfur and carbon isotope records from 1700 to 800 ma carbonates of the jixian section northern china implications for secular isotope variations in proterozoic seawater and relationships to global supercontinental events abstract this study is a comprehensive stable isotope survey of the marine carbonate dominated upper paleo to lower neoproterozoic stratigraphy of jixian county china carbonate associated sulfate cas was extracted and measured for 34 s cas using the same samples analyzed for 13 c carbonate this integrated proxy approach is a step towards a more comprehensive picture of secular variation in the composition of proterozoic seawater we specifically sampled marine carbonate intervals from the lower section of the chuanlinggou formation changcheng group ca 1700 ma to the top of the jingeryu formation qingbaikou group ca 800 ma 13 c carbonate values are mostly negative in the upper paleoproterozoic changcheng group with an ascending trend from 3 to 0 we observed variation of approximately 0 1 in the mesoproterozoic jixian group and positive values of 2 2 characterize the lower neoproterozoic qingbaikou group stratigraphic variations in 34 s cas are more remarkable in their ranges and magnitudes including conspicuously high values exceeding 30 in the three intervals at ca 1700 ma 1300 1100 ma and 1000 900 ma in the changcheng group 34 s cas values are typically higher than 25 with only a few values of less than 15 in contrast most of the data spanning from the mesoproterozoic tieling formation of the jixian group to the lower neoproterozoic jingeryu formation of the qingbaikou group are highly variable between 10 and 25 with some values exceeding 25 in the late paleoproterozoic 1700 1600 ma a 10 decrease in 34 s cas and 3 increase in 13 c carbonate are coincident with and likely related to the breakup of columbia a supercontinent that predated rodinia carbon and sulfur isotope data from the mesoproterozoic when global tectonic activity was comparatively weaker fall mostly in the ranges of 15 10 and 0 1 respectively but fluctuations of 20 for 34 s cas and 3 for the 13 c carbonate at ca 1450 1400 ma may reflect subduction and large scale magmatic activity in island arcs marking the end of columbia breakup from the late mesoproterozoic ca 1300 1100 ma to the early neoproterozoic ca 800 ma the 13 c and 34 s of seawater increased gradually with increasing variability most impressive are 34 s cas values that exceed 30 in two intervals at ca 1300 1100 ma and ca 1000 900 ma which may reflect the assembly and early breakup of rodinia although gaps in the record remain and studies of even higher resolution are warranted our results suggest that changes in paleoceanographic conditions linked to global tectonics strongly influenced the biogeochemical cycles of c and s furthermore periods of the proterozoic previously noted for their isotopic invariability show clear isotopic expressions of this tectonic activity

early atmospheric oxygen levels constraints from archaean photoautotrophy various independent lines of evidence suggest that photoautotrophic carbon fixation is a very ancient process that had attained control of the terrestrial carbon cycle from at least 3 5 ga if not 3 8 ga since it is generally accepted that only biological processes could substantially increase the negligible oxygen pressures sustained on the early earth by inorganic photochemistry probably between 10 8 and 10 14 present atmospheric level pal the advent of photoautotrophy would provide a limiting condition for the oxygenation of terrestrial near surface environments however as the size of the free oxygen reservoir is determined by the kinetics of the geochemically relevant oxygen consuming reactions we may assume that the start of photosynthetic oxygen production did not result in an instantaneous buildup of modern p o 2 levels low atmospheric oxygen pressures generally inferred for the archaean and lower proterozoic earth would therefore indicate extremely rapid processes of oxygen consumption in certain compartments of the ancient exogenic system notably the hydrosphere rather than the non existence of photosynthetic oxygen production at this time

a numerical model of the evolution of ocean sulfate and sedimentary sulfur during the last 800 million years abstract a reservoir model describing the time evolution of the sedimentary cycle of sulfur over the past 800 my has been developed as a first approximation the ocean sulfate concentration is assumed to be time independent with this assumption the model is integrated backward in time and a new initialization procedure is derived in order to calculate the present state of the system which must be compatible with both observational data and model equations the effects of a variation of the present state of the cycle on its past evolution are investigated it is found that when the present gypsum reservoir content is too low or when the weathering rate constants are too high no acceptable solution can be obtained for the evolution of the cycle since one reservoir is forced to depletion the sensitivity of the model to the mean isotopic composition of the sedimentary system and to the fractionation factor during pyrite formation is also studied moreover a model with time dependent ocean sulfate concentration was developed the existence of an acceptable solution appears to be linked to the steady state hypothesis for ocean sulfate since a model with no acceptable steady state solution may be integrated until t 800 my without any problem of reservoir depletion when the time dependent equations are used a tentative evolution of the ocean sulfate concentration is calculated it is shown that this concentration is negatively correlated to the 34s of seawater sulfate the carbon cycle is modelled in order to compare the calculated 13c of carbonate deposits to the observational data

silurian records of carbon and sulfur cycling from estonia the importance of depositional environment on isotopic trends abstract the llandovery wenlock carbonate marl succession of the baltoscandian basin has been analyzed in the viki drill core western estonia for carbonate carbon 13 c carb organic carbon 13 c org carbonate associated sulfate 34 s cas and pyrite 34 s pyr isotopes along with trace element concentrations following the end ordovician glaciation and the hirnantian carbon isotope excursion 13 c carb values rise to an early llandovery carbon isotope maximum 2 subsequently 13 c carb and coeval 13 c org record a large 4 5 excursion in the early wenlock associated with a regression and biotic turnover known as the ireviken bioevent ibe overall 34 s cas values generally fall within a range 25 to 35 similar to that reported in other sections of comparable age two distinct trends are observed low and stable 34 s cas values are associated with deep water facies while 34 s cas becomes higher and more variable in the shallow water facies similarly 34 s pyr values are low and invariant 15 in deep water facies but become higher and more variable ranging between 35 and 16 in shallow water deposits despite abundant recrystallization no obvious evidence for large scale alteration of proxies is apparent in concentrations of fe sr mn and mg or in isotopic correlations although increased variability and lower values of 34 s cas are observed where cas abundance is low a large well resolved positive excursion in 34 s cas observed during the ibe from a time correlative section on gotland sweden is absent in the data presented here this difference demonstrates that counter to general understanding local environmental variations can give rise to divergent 34 s cas profiles in coeval sections the s isotope fluctuations in cas and pyrite in the viki drill core can be explained by local processes involving facies changes early diagenetic processes and associated open vs closed system behavior that can overprint and potentially mask basin or global signals

geocarbsulf a combined model for phanerozoic atmospheric o2 and co2 abstract a model for the combined long term cycles of carbon and sulfur has been constructed which combines all the factors modifying weathering and degassing of the geocarb iii model berner r a kothavala z 2001 geocarb iii a revised model of atmospheric co2 over phanerozoic time am j sci 301 182 204 for co2 with rapid recycling and oxygen dependent carbon and sulfur isotope fractionation of an isotope mass balance model for o2 berner r a 2001 modeling atmospheric o2 over phanerozoic time geochim cosmochim acta 65 685 694 new isotopic data for both carbon and sulfur are used and new feedbacks are created by combining the models sensitivity analysis is done by determining 1 the effect on weathering rates of using rapid recycling rapid recycling treats carbon and sulfur weathering in terms of young rapidly weathering rocks and older more slowly weathering rocks 2 the effect on o2 of using different initial starting conditions 3 the effect on o2 of using different data for carbon isotope fractionation during photosynthesis and alternative values of oceanic 13c for the past 200 million years 4 the effect on sulfur isotope fractionation and on o2 of varying the size of o2 feedback during sedimentary pyrite formation 5 the effect on o2 of varying the dependence of organic matter and pyrite weathering on tectonic uplift plus erosion and the degree of exposure of coastal lands by sea level change 6 the effect on co2 of adding the variability of volcanic rock weathering over time berner r a 2006 inclusion of the weathering of volcanic rocks in the geocarbsulf model am j sci 306 in press results show a similar trend of atmospheric co2 over the phanerozoic to the results of geocarb iii but with some differences during the early paleozoic and for variable volcanic rock weathering lower co2 values during the mesozoic atmospheric oxygen shows a major broad late paleozoic peak with a maximum value of about 30 o2 in the permian a secondary less broad peak centered near the silurian devonian boundary variation between 15 and 20 o2 during the cambrian and ordovician a very sharp drop from 30 to 15 o2 at the permo triassic boundary and a more or less continuous rise in o2 from the late triassic to the present

modeling the carbon and sulfur isotope compositions of marine sediments climate evolution during the devonian abstract a model of global biogeochemical cycles coupled to an energy balance climatic model modified after the combine model godderis y joachimski m m 2004 global change in the late devonian modeling the frasnian famennian short term carbon isotope excursions palaeogeogr palaeoclimatol palaeoecol 202 309 329 is used to calculate the short term evolution of atmospheric p co 2 during the devonian the geochemical cycles for carbon alkalinity phosphorus sulfur and oxygen are included in this model with also 13 c and 34 s cycles high resolution records of 13 c of marine carbonates and 34 s of marine sulfates are used as forcing parameters of the geochemical cycles in an inverse modeling atmospheric p co 2 and p o 2 at the end of the silurian are calculated to have been 3000 ppmv and 0 165 bar 0 75 pal respectively a long term decrease in p co 2 is modeled for almost the entire devonian short term lowering of p co 2 to concentrations around 2000 ppmv is calculated for the silurian devonian transition and the pragian contents around 900 ppmv are modeled for the eifelian givetian givetian frasnian and frasnian famennian boundaries as a consequence of enhanced organic carbon burial during deposition of lochkovian eifelian and frasnian grey and black shales organic carbon burial is enhanced by the increase of phosphorus delivery to the ocean triggered by short term sea level falls the corresponding short term global climatic cooling at the silurian devonian boundary at the end of the pragian and the givetian frasnian as well as frasnian famennian boundaries reached 2 c at the equator the rapid colonization of continental surface by land plants during the middle and late devonian increasing chemical alteration of the continents and co 2 consumption by silicate weathering is assumed to have caused cooling of surface seawater as suggested by the 18 o values of biogenic apatites

brine pool deposition for the zn pb cu massive sulphide deposits of the bathurst mining camp new brunswick canada ii ocean anoxia during mineralisation abstract current models of massive sulphide ore genesis in the bathurst mining camp new brunswick involve settling of sulphide particles from a stagnating low salinity hydrothermal plume spreading laterally in an anoxic ocean layer with minimal sulphate content there is fragmentary evidence of ocean anoxia in the form of local fine lamination in the shales that host some of the deposits but the total organic carbon s fe u th ni co v ni and v cr relationships indicate deposition under oxic or dysoxic conditions vanadium and mn values range from oxic to anoxic and sulphate reducing to non sulphate reducing but mn may be anomalously low due to derivation by erosion of acidic volcanic rocks the somewhat equivocal physical and chemical data combined with the likely disturbing effects of penecontemporaneous volcanism considerably weaken the case for an anoxic bottom layer in a static ocean the presence of barite with ambient seawater 34 s values in brunswick no 12 ore and the abundance of sulphate in modern euxinic basin waters make a sulphate free layer unlikely even if anoxic sulphate bearing low salinity fluids mixing with seawater would lead to growth of barite bearing chimneys and baritic rubble mounds which are not observed a model involving brine pool deposition better explains the major features of the bathurst ores

discovery of agglutinated benthic foraminifera in devonian black shales and their relevance for the redox state of ancient seas abstract agglutinated foraminifera are benthic organisms that occur in marginal marine to bathyal environments though some taxa can live in oxygen deficient environments they require at least some oxygen in order to persist at the seafloor the discovery that they occur widely in late devonian black shales has a bearing on the boundary conditions required for episodes of extensive carbon sequestration in marine sediments and their connection to atmospheric composition and global climate devonian black shales of the eastern us have been studied extensively to determine the fundamental controls on carbon burial and a range of mechanisms has been proposed finding agglutinated benthic foraminifera in these black shales refocuses the debate about their origin and points to limitations of earlier models

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

causes and consequences of extreme permo triassic warming to globally equable climate and relation to the permo triassic extinction and recovery permian waning of the low latitude alleghenian variscan hercynian orogenesis led to a long collisional orogeny gap that cut down the availability of chemically weatherable fresh silicate rock resulting in a high co2 atmosphere and global warming the correspondingly reduced delivery of nutrients to the biosphere caused further increases in co2 and warming melting of polar ice curtailed sinking of o2 and nutrient rich cold brines while pole to equator thermal gradients weakened wind shear and associated wind driven upwelling lessened further diminishing productivity and carbon burial as the earth warmed dry climates expanded to mid latitudes causing latitudinal expansion of the ferrel circulation cell at the expense of the polar cell increased coastal evaporation generated o2 and nutrient deficient warm saline bottom water wsbw and delivered it to a weakly circulating deep ocean warm deep currents delivered ever more heat to high latitudes until polar sinking of cold water was replaced by upwelling wsbw with the loss of polar sinking the ocean was rapidly filled with wsbw that became increasingly anoxic and finally euxinic by the end of the permian rapid incursion of wsbw could have produced 20 m of thermal expansion of the oceans generating the well documented marine transgression that flooded embayments in dry hot pangaean mid latitudes the flooding further increased wsbw production and anoxia and brought that anoxic water onto the shelves release of co2 from the siberian traps and methane from clathrates below the warming ocean bottom sharply enhanced the already strong greenhouse increasingly frequent and powerful cyclonic storms mined upwelling high latitude heat and released it to the atmosphere that heat trapped by overlying clouds of its own making suggests complete breakdown of the dry polar cell resulting rapid and intense polar warming caused or contributed to extinction of the remaining latest permian coal forests that could not migrate any farther poleward because of light limitations loss of water stored by the forests led to aquifer drainage adding another 5 m to the transgression non peat forming vegetation survived at the newly moist poles climate feedback from the coal forest extinction further intensified warmth contributing to delayed biotic recovery that generally did not begin until mid triassic but appears to have resumed first at high latitudes late in the early triassic current quantitative models fail to generate high latitude warmth and so do not produce the chain of events we outline in this paper future quantitative modeling addressing factors such as polar cloudiness increased poleward heat transport by deep water and its upwelling by cyclonic storms and sustainable mid latitude sinking of warm brines to promote anoxia warming and thermal expansion of deep water may more closely simulate conditions indicated by geological and paleontological data

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

marcasite in black shales a mineral proxy for oxygenated bottom waters and intermittent oxidation of carbonaceous muds abstract black shales in the geologic record have long been considered to reflect deposition under anoxic or even euxinic conditions although bottom water anoxia favors deposition of black shales certain biological indicators such as benthic fossils and bioturbation suggest that bottom water conditions may not have been as persistently anoxic as commonly presumed examination of twelve marine carbonaceous shale bearing units ranging in age from middle proterozoic to cretaceous suggests that in addition to paleontological clues early diagenetic marcasite formed in uncompacted surficial sediments is a reliable indicator of oxygen bearing bottom waters marcasite requires low ph values to form and oxidation of already existing sedimentary pyrite provides a plausible chemical scenario to achieve that condition in the studied examples degraded pyrite framboids and corrosion features on pyrite grains indicate partial pyrite destruction in surface sediments and suggest that intermittent reoxidation of earlier formed iron sulfides may indeed have generated the low ph values required for marcasite formation thus observations of textures spatially associated with secondary marcasite growth are consistent with a scenario whereby oxygen in overlying sea water drove downward migration of oxidation fronts pervasive marcasite in black shales from a wide range of occurrences suggests multiple reoxygenation events during the deposition of these shale units and calls for more dynamic ocean circulation than previously assumed the latter consideration may for example prove important for those instances where a black shale is associated with an oceanic anoxic event oae because these are commonly presumed to have been deposited under fully anoxic conditions

iron and sulphur isotopes from the carajas mining province para brazil implications for the oxidation of the ocean and the atmosphere across the archaean proterozoic transition abstract mineralogical analyses and major and trace element geochemistry combined with iron and sulfur isotopes were applied to banded iron formations bifs and pyrite bearing sandstones from the carajas mineral province brazil the bifs belong to the 2 7 ga old grao para group and show a rather simple mineralogy hematite and quartz or cryptocrystalline silica their ree y patterns suggest deposition under marine sub oxic conditions fe isotopes show highly positive values 57 fe irmm 14 2 06 0 34 in average which can be explained by the partial oxidation of fe 2 aq in the surface ocean subsequent to the upwelling of deep anoxic seawater the resulting iron oxy hydroxides likely formed in the shallow photic zone as a seasonal process and acquired highly positive iron isotope signature values consistent with a rayleigh distillation model the pyrite bearing sandstones belong to the aguas claras formation of palaeoproterozoic younger age and were cored at the base of the giant azul manganese deposit diagenetic pyrite is characterized by positive 57 fe irmm 14 1 02 0 2 and 34 s vctd 11 97 0 12 average values that are different from values of modern marine biogenic pyrite results likely indicate that dissolved sulfate was the limiting factor controlling biogenic pyrite formation at that time near zero 33 s values 0 013 0 003 indicate minimal mass independent sulfur isotope fractionation mif s consistent with the 2 1 ga age previously obtained from the aguas claras pyrites this result suggests deposition at a time when the oxygen partial pressure in the atmosphere was already high enough 10 5 to 10 2 pal or present atmospheric level to hinder mif s by photochemical reactions incidentally this also confirms that the giant mn deposit of carajas is in the same age range 2 1 0 2 ga as other mn ores in gabon and south africa pointing to the importance of mn precipitation in paleoproterozoic times

modeling atmospheric o2 over phanerozoic time a carbon and sulfur isotope mass balance model has been constructed for calculating the variation of atmospheric o2 over phanerozoic time in order to obtain realistic o2 levels rapid sediment recycling and o2 dependent isotope fractionation have been employed by the modelling the dependence of isotope fractionation on o2 is based for carbon on the results of laboratory photosynthesis experiments and for sulfur on the observed relation between oxidation reduction recycling and s isotope fractionation during early diagenetic pyrite formation the range of fractionations used in the modeling agree with measurements of phanerozoic sediments by others results derived from extensive sensitivity analysis suggest that there was a positive excursion of o2 to levels as high as 35 during the permo carboniferous high o2 at this time agrees with independent modeling based on the abundances of organic matter and pyrite in sediments and with the occurrence of giant insects during this period the cause of the excursion is believed to be the rise of vascular land plants and the consequent increased production of o2 by the burial in sediments of lignin rich organic matter that was resistant to biological decomposition

the effect of rising atmospheric oxygen on carbon and sulfur isotope anomalies in the neoproterozoic johnnie formation death valley usa abstract carbonates within the rainstorm member in the terminal neoproterozoic johnnie formation of death valley california record a remarkable negative carbon isotope anomaly to a nadir of near 11 that accompanies a dramatic rise in trace sulfate abundance and fall of carbonate associated sulfate 34 s values the carbonates including the laterally extensive johnnie oolite were deposited during marine flooding atop a sequence boundary best observed in cratonward sections the 12 c rich alkalinity delivered to the seawater pool was likely associated with a dramatic rise in atmospheric o 2 which resulted in 1 the oxidation of exposed continental shelf sediments rich in fossil organic matter and sulfides and 2 the ventilation of the oceans similar carbon isotope anomalies are recorded in broadly equivalent successions that post date known marinoan glacial deposits and pre date the precambrian cambrian boundary in oman india china australia and namibia supporting the view that the oxygenation event was global thus the biogeochemical anomaly post dates the last widely recognized neoproterozoic ice age but is nonetheless associated with sea level drawdown that is likely to be eustatic in origin the radiation of a high diversity microbiota and the first appearance of large metazoan fossils ediacaran animals follow this carbon isotope anomaly suggesting that a critical threshold with respect to atmospheric o 2 had been crossed by this time a negative excursion of similar magnitude occurs in overlying strata at the precambrian cambrian boundary which likely reflects similar processes

mass dependent fractionation of quadruple stable sulfur isotope system as a new tracer of sulfur biogeochemical cycles abstract sulfur isotope studies of post archean terrestrial materials have focused on the ratio 34s 32s because additional isotopes 33s and 36s were thought to carry little information beyond the well known mass dependent relationship among multiple isotope ratios we report high precision analyses of 33s and 36s values defined as deviations of 33s and 36s from ideal mass dependent relationships for international reference materials and sedimentary sulfides of phanerozoic age by using a fluorination technique with a dual inlet isotope ratio mass spectrometer measured variations in 33s and 36s are explained as resulting from processes involve branching reactions two or more reservoirs formed or mixing irreversible processes in closed systems rayleigh distillation amplify the isotope effect we outline how this new isotope proxy can be used to gain new insights into fundamental aspects of the sulfur biogeochemical cycle including additional constraints on seawater sulfate budget and processes in sedimentary sulfide formation the isotope systematics discussed here cannot explain the much larger variation of 33s and 36s observed in archean rock records furthermore phanerozoic samples we have studied show a characteristic 33s and 36s relationship that differs from those measured in archean rocks and laboratory photolysis experiments thus high precision analysis of 33s and 36s can be used to distinguish small non zero 33s and 36s produced by mass dependent processes from those produced by mass independent processes in archean rocks and extraterrestrial materials

the petrology of tambora volcano indonesia a model for the 1815 eruption abstract tambora is an active volcano in the east sunda arc and is well known for its catastrophic eruption in april 1815 its lavas are of unusual moderately undersaturated k2o rich types ranging from ne trachybasalt to ne trachyandesite they evolved under conditions of high oxygen fugacity about two log units below the m h buffer and crystallised leucite at low pressures the products of the 1815 eruption are black glassy biotite bearing ne trachyandesites together with scoria pumice and tuff of the same composition the parent trachybasalt liquid probably contained about 3 wt h2o and the trachyandesites nearly 6 wt the model presented here suggests that the 1815 eruption which is known to have followed a lengthy period of inactivity was the result of gradual cooling of a hydrous magma in a closed high level magma chamber emplaced at depths between 1 5 and 4 5 km eruption followed the exsolution of a high pressure aqueous fluid phase formed during cooling and crystallisation of the magma second boiling by the time eruption took place overpressures of about 4 5 kbar had been generated and temperatures in the magma chamber ranged from about 850 c to 700 c the catastrophic eruption took place after failure of the roof and the discharge of the vapour phase may have reached velocities of 650 m s 1 calculations indicate that the volume of magma involved in the eruption was of the order of 33 km3 and this may have evolved about 1 2 1027 ergs of energy during the eruption a blast equivalent to 30 000 megatons of tnt