clay mineral evolution changes in the mechanisms of formation and global distribution of phyllosilicate clay minerals through 4 567 ga of planetary evolution in our solar system reflect evolving tectonic geochemical and biological processes clay minerals were absent prior to planetesimal formation 4 6 billion years ago but today are abundant in all near surface earth environments new clay mineral species and modes of clay mineral paragenesis occurred as a consequence of major events in earth s evolution notably the formation of a mafic crust and oceans the emergence of granite rooted continents the initiation of plate tectonics and subduction the great oxidation event and the rise of the terrestrial biosphere the changing character of clay minerals through time is thus an important part of earth s mineralogical history and exemplifies the principles of mineral evolution

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

double averaging concept for rough bed open channel and overland flows theoretical background the goal of this paper is to discuss the spatial averaging concept in environmental hydraulics and develop it further by considering transport equations for fluid momentum passive substances and suspended sediments the averaging theorems the double averaged in time and in space fluid momentum equation and advection diffusion equations for a passive substance and suspended sediments are introduced and their limitations and applications for modeling rough bed flows experimental design and data interpretation are discussed the suggested equations differ from those considered in terrestrial canopy aerodynamics and porous media hydrodynamics by accounting for roughness mobility change in roughness density in space and time and particle settling effects for the case of suspended sediments we show that the form of the double averaged equations may depend on the type of decomposition of flow variables and that this difference may have important implications for modeling we also show that the suggested methodology offers better definitions for hydraulic characteristics variables and parameters such as flow uniformity flow two dimensionality and bed shear stress

was atmospheric co2 capped at 1000 ppm over the past 300 million years abstract atmospheric carbon dioxide concentration has shifted dynamically over the phanerozoic according to mass balance models and the majority of proxy estimates a new paleo co 2 proxy method underpinned by mechanistic understanding of plant stomatal isotopic and photosynthetic responses to co 2 has provocatively claimed that maximum paleoatmospheric co 2 was capped at 1000 ppm for the majority of the past 300 million years here we evaluate the robustness of the new paleo proxy co 2 model by testing its sensitivity to initial parameterization and to scaling factors employed to estimate paleophysiological function from anatomical and morphological traits a series of sensitivity analyses find that the model is robust to modification in some of the constants employed such as co 2 compensation point and mesophyll conductance resulting in variability in paleo co 2 estimates which are already accounted for in the error propagation of the model we demonstrate high sensitivity in the model to key input parameters such as initial fossil plant assimilation rate termed a 0 and scaling factors used to estimate stomatal conductance from measurements of fossil stomata incorrect parameterization of a 0 has resulted in under estimation of p co 2 by as much as 600 ppm despite these uncertainties our analysis highlights that the new mechanistic paleo co 2 proxy of franks et al 2014 has significant potential to derive robust and more accurate co 2 estimates from fossil plant stomata as long as parameterization of a 0 is strongly justified with species appropriate morphological and anatomical data we highlight methods that can be used to improve current estimates of fossil plant assimilation rates reduce uncertainty associated with implementation of the franks et al 2014 model and importantly add to understanding of patterns of plant productivity over the phanerozoic for which there currently is no consensus

influence of dissolved oxygen on secular patterns of marine microbial carbonate abundance during the past 490 myr abstract shallow marine benthic microbial carbonate sediments declined episodically during the phanerozoic they were relatively abundant during the cambrian mid ordovician late devonian mississippian mid permian mid late triassic and to a lesser degree in the late jurassic early cretaceous they were least abundant when invertebrate especially reef diversity was relatively high in the mid ordovician late devonian early mid permian late triassic mid late jurassic and early cretaceous to present day these intervals of microbial carbonate abundance and invertebrate diversity generally alternate transitionally with one another but lows and periods of overlap also occur lows when benthic microbial carbonate abundance and invertebrate diversity both declined are apparent during the pennsylvanian and early mid jurassic overlaps when microbial carbonates and invertebrates were both relatively common occur in the early cambrian and late jurassic overall these patterns broadly support suggestions that microbial carbonate abundance declined as calcified invertebrates increased to further explore these relationships we compared microbial carbonate abundance and invertebrate diversity with estimates of changes in sea surface temperature and marine dissolved oxygen for the past 490 myr this analysis suggests that invertebrate diversity varied directly with oxygen availability invertebrate diversity was low when dissolved oxygen was low in the early ordovician late devonian early triassic and early mid jurassic it appears that by reducing invertebrate diversity low oxygen levels favored microbial carbonates at the same time low oxygen levels likely stimulated anaerobic metabolisms favoring carbonate precipitation this study suggests that dissolved oxygen was a major control on secular patterns of marine microbial carbonate abundance during the phanerozoic together with marine temperature and carbonate saturation state

flood plain and main channel flow interaction experimental results are presented concerning the discharge characteristics the boundary shear stress and boundary shear force distributions in a compound section comprising of one rectangular main channel and two symmetrically disposed flood plains equations are presented giving the shear force on the flood plains as a percentage of the total shear force in terms of two dimensionless parameters the experimental shear force results are used to derive ancillary equations for the lateral and vertical transfer of momentum within the cross section the apparent shear force acting on the vertical interface between one flood plain and the main channel is shown to increase rapidly for low relative depths and high flood plain widths equations are also presented giving the proportion of the total flow which occurs in the various sub areas the division of flow based on linear proportion of the areas is shown to be inadequate on account of the interaction between the flood plain and main channel flows

ordovician cyanobacterial calcification a marine fossil proxy for atmospheric co2 abstract ordovician atmospheric co2 level was an important influence on climate and life however modelled estimates of ordovician co2 differ widely and in contrast to much of the subsequent phanerozoic they lack fossil proxy constraints in vivo cyanobacterial sheath calcification promoted by carbon dioxide concentrating mechanisms ccms creates distinctive microfossils these provide a direct ecophysiological link to ambient concentrations of co2 and to a lesser extent o2 cyanobacteria do not calcify at high co2 concentrations experiments show that ccms can be induced in present day cyanobacteria at co2 levels below 10 times present atmospheric level pal and that this promotes sheath calcification we compiled a global database of cyanobacterial calcification in marine environments throughout the ordovician 485 443 myr ago and compared it with modelled estimates of atmospheric co2 and o2 these data show that many genera of marine calcified cyanobacteria reappeared from cambrian series 2 or first appeared globally during the late middle to late upper ordovician late darriwilian to late katian in carbonate platform facies resulting in a previously unrecognized ten fold increase in global diversity such a large increase in calcification suggests widespread induction of ccm expression in cyanobacteria consistent with sustained decline in external co2 concentrations below 10 pal together with increase in dissolved o2 level during the late darriwilian sandbian and katian stages 460 445 myr ago these cyanobacterial calcification fossil proxy data provide a first order constraint on modelled estimates of atmospheric co2 for the ordovician estimated co2 outputs from copse and recent geocarb based models are broadly consistent with this cyanobacterial calcification proxy for the ordovician in view of the long history of cyanobacteria the calcified cyanobacterial proxy offers potential to assist interpretation of co2 deeper into geological time

analysis of gases in fossil amber fossilized tree resin commonly known as amber has long served as a robust source of paleobiologic information via the preservation of embalmed invertebrates another more radical idea is that gas bubbles enclosed in fossil amber may represent ancient air trapped at the time the original resin was exuded from its host tree alternatively gas trapped in ancient amber may instead represent contamination by modern air here we analyze gaseous inclusions from ambers sampled worldwide spanning the cretaceous eocene eocene oligocene eocene miocene u oligocene miocene and modern after careful consideration of a number of possible explanations we suggest the gas inclusions may represent at least in part ancient air

first report of cisuralian early permian charcoal layers within a coal bed from baode north china with reference to global wildfire distribution abstract fossil charcoal is reported for the first time from a cisuralian coal bed of the shanxi formation in the qiaotou section baode shanxi north china based on anatomical characteristics these charcoal fragments consist of coniferous or cordaitalean xylem unidentified primary xylem and cordaitalean and possible fern leaves these charcoal fragments represent the evidence of palaeowildfire taking place in tropical peat swamps during the cisuralian in cathaysia the palaeowildfire is most likely to be a surface fire and burning litter and shrubby vegetation fire frequency for this early permian peat swamp might have been on the order of 176 294 588 1429 years close to modern values compared with modern analogues the north china block during the cisuralian was probably wet in general but could be occasionally seasonally dry for short time intervals previous charcoal and inertinite records moreover indicate that palaeowildfires were globally common during the cisuralian overall more wildfire evidence was found in the artinskian kungurian than the asselian sakmarian except in the euramerican realm probably due to more suitable regional climate vegetation to fuel fires and taphonomic circumstances

early paleogene wildfires in peat forming environments at schoningen germany wildfire activity in early paleogene greenhouse conditions can be used as an analogue to gauge the effect of future warming trends on wildfire in the current climate system inertinite fossil charcoal in coal from 11 autochthonous early paleogene lignite seams from the schoningen mine germany was quantified using macerations in situ pillars and industry standard crushed samples a new three transect method was developed to quantify in situ charcoal the combination of in situ pillars and crushed samples accounts for temporal and spatial variation in charcoal through a stratigraphically oriented pillar whilst maintaining comparability with industry standards and previous work charcoal occurs as a range of randomly distributed particle sizes indicating that fires were burning locally in the schoningen peat forming environment and in the surrounding areas but according to petrological data not in an episodic or periodic pattern although charcoal abundance is low relative to previous high fire worlds such as the cretaceous three quantitative and semi quantitative methods show increased wildfire activity relative to the modern world in the warmest parts of the early paleogene as atmospheric oxygen levels stabilised to modern values and precipitation and humidity became the main control on wildfire increased rainfall followed by drier intervals would have created an environment rich in dry fuel in which wildfires could easily propagate if humidity was low enough in the later part of the early eocene ypresian charcoal abundance fell to levels similar to those found in modern peats this indicates that the transition to the modern low fire world occurred within the early eocene earlier than previous records suggest

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

glaciation aridification and carbon sequestration in the permo carboniferous the isotopic record from low latitudes to evaluate the isotopic record of climate change and carbon sequestration in the late paleozoic we have compiled new and published oxygen and carbon isotopic measurements of more than 2000 brachiopod shells from carboniferous through middle permian 359 260 ma strata we focus on the isotopic records from the u s midcontinent and the russian platform because these two regions provide well preserved marine fossils spanning a broad time interval both regions show a 18o increase at the mid carboniferous boundary ca 318 ma that roughly correlates with geologic evidence for an expansion of gondwanan glaciers only the russian platform record shows a 18o maximum during the glacial maximum in the asselian in contrast to a previous study korte c jasper t kozur h w and veizer j 2005 18o and 13c of permian brachiopods a record of seawater evolution and continental glaciation palaeogeogr palaeoclimatol palaeoecol 224 333 351 our data show no oxygen isotope evidence for glacial retreat in the early permian but instead show increasing 18o values related to aridification dissimilarity in the 18o trends for the epicontinental seas of north american and the russian platform suggests that at least one region experienced periodic restriction that altered regional salinities and seawater 18o values these results highlight the need for complementary proxies to identify restricted circulation in epicontinental seas carbon isotopic compositions of carbonates exhibit substantial regional variation with low values in western north america intermediate values in the midcontinent and high values in the sverdrup basin russian platform and northern spain nevertheless both u s midcontinent and russian platform records show a late serpukhovian minimum a sharp increase across the mid carboniferous boundary and a minimum centered on the kasimovian the correlative increase in brachiopod 13c and 18o values at the mid carboniferous boundary is our best isotopic evidence for a link between the carbon burial and glaciation in the permo carboniferous

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

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

recognition of diagenetic contribution to the formation of limestone marl alternations a case study from permian of south china abstract limestone marl alternations lmas have been extensively used in studies of sedimentology cyclostratigraphy and paleoclimatology however it has long been debated whether lmas are derived from primary sedimentation or from diagenetic alteration and the markers to distinguish one source from the other remain ambiguous in this study we investigate widespread permian lmas from various depositional settings in south china using traditional petrographic mineralogical and major element al2o3 vs tio2 methods as well as emerging trace and rare earth element ree analyses performed using solution based and in situ techniques the original depositional differences of the limestone and its coupled marl beds can be identified based on 1 the high volumes of siliciclastic minerals in the marls 2 unremarkable differential compaction 3 the recognizable signatures of the detrital admixture i e the al zr and th characteristics and 4 flattened shale normalized ree patterns diagenetic lmas are characterized by the compaction of fossils rare aragonite skeletons and abundant diagenetic clays sepiolite and talc preserved in the marl beds we also identified fully diagenetic lmas originating from primary carbonate sedimentation based on two almost completely consistent seawater like ree patterns with diagnostic positive la and negative ce anomalies la la sn 1 64 0 17 ce ce sn 0 73 0 05 superchondritic y ho 47 4 and depleted light rees relative to high rees pr yb sn 0 39 0 09 diagenesis also dominates the formation of lmas with limited terrigenous input in shallow water carbonate depositional environments it is likely that both the active metabolic processes in early diagenesis especially aerobic sulfide oxidation and the temporal palaeoceanographic conditions e g high levels of dissolved oxygen and sulfate play crucial roles in the genesis of the diagenetic lmas in the permian strata of south china

flow distribution in compound channels the performances of four of the most commonly used methods for discharge calculation in compound channels of varying roughness were assessed by comparison with laboratory data the four methods are based on splitting the section into main channel and floodplain subdivisions using either horizontal or vertical interfaces the accuracy of the four methods in calculating overall section discharge generally increases at greater floodplain depth and with smoother floodplains however the distribution of flow within the section is generally poorly modelled which leads to very erroneous values for momentum and kinetic energy flux

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

the pedogenic formation of coal balls by co2 degassing through the rootlets of arborescent lycopsids coal balls are calcium carbonate accumulations that permineralized peat in paleotropical permo carboniferous 320 250 ma mires the formation of coal balls has been debated for over a century yet a widely applicable model is lacking two observations have been particularly challenging to explain 1 the narrow temporal occurrence of coal balls and 2 their typical elemental high mg and isotopic low 18o composition that paradoxically indicate marine and freshwater origins respectively we evaluate a new model in which coal balls formed as co2 escaped from the peat by diffusion through unusual air filled spaces in the rootlets of lycopsid trees critically these trees were very common in paleotropical mires and their evolutionary range matches the temporal range of coal balls the episodic delivery of seawater and marine carbonate sediment to coastal mires is the first step in our model although other pathways for the delivery of divalent cations are permissible subsequent dilution by freshwater and dissolution of these carbonates at the elevated co2 of the mire subsurface is followed by the transport of co2 through the rootlet airspaces and into the overlying water and atmosphere which drives carbonate mineral precipitation in the sediment we show that dilution by freshwater because it minimally affects mg ca ratios can result in relatively low pore water 18o values while allowing high mg calcite formation this model thus explains the restriction of coal balls to the permo carboniferous and resolves the discrepancy between elemental and isotopic compositions of coal ball carbonate minerals furthermore we show with a 3d reactive transport model that co2 could escape rapidly enough through the rootlets to fill 25 percent of the peat pore spaces with calcite before substantial burial top decimeter of peat explaining the exceptional preservation of coal swamp flora therefore we suggest that coal balls are pedogenic in origin and that the disappearance of these pedogenically permineralized histosols represents the first documented decrease in soil diversity on a vegetated planet the rock record may thus provide important context for the modern loss and degradation of soils

phanerozoic atmospheric oxygen new results using the geocarbsulf model modifications of the geocarbsulf model for phanerozoic atmospheric oxygen have been made to account for new carbon isotopic data reconsideration of the fractionation of carbon isotopes between carbonate and organic matter deposited in sediments and different rates of weathering of volcanic rocks versus granitic rocks results indicate distinctly higher o2 values than geocarbsulf for the mesozoic and cenozoic lack of an appreciable drop in o2 below 15 percent at any time and a small late cenozoic decline of o2 to the present

the impact of single natural vegetation elements on flow characteristics in this experimental study measurements were conducted to explore the impacts of different forms of individual natural vegetative elements within the flow domain on velocity and turbulence characteristics all the experiments were performed in a flume measuring 26 m in length 0 98 m in width and 0 85 m in depth and real tree saplings were utilized to represent the vegetation element in order to analyse this commonly observed nature phenomenon in floodplains trees with wide trunks were classified into three groups on the basis of their volume versus height relation throughout the velocity measurements three acoustic doppler velocimeters were employed time averaged velocity streamwise and vertical turbulence intensities and turbulent kinetic energy parameters were examined additionally a formulation that gives the velocity profile at a certain distance downstream of vegetation was introduced and the validity of the proposed formulation was checked with experimental data it is seen that despite their porous structures the presence of vegetation considerably disturbs the flow field and dissipates a remarkable amount of energy by turbulence copyright 2008 john wiley sons ltd

constraints on carbon accumulation rate and net primary production in the lopingian late permian tropical peatland in sw china article i nfo during the permian peatland as represented in extensive coal deposits was a major component of the global carbon cycle carbon storage in peatland is a balance between decay and net primary production npp which in turn are sensitive to variations in the concentration of atmospheric co2 and o2 to evaluate peatland carbon storage and npp during the lopingian a period thought to be characterised by higher atmospheric o2 and co2 than modern levels spectral analyses of geophysical data from a 15 1 m thick lopingian upper permian coal in southwestern china were conducted to define the time frame of temporal carbon accumulation in tropical peatland the result shows that the mineral matter content ash yield of the coal was possibly influenced by 123 ka eccentricity 35 6 ka obliquity and 21 2 ka precession milankovitch periodicities using this timeframe and an understanding of carbon loss during coalification the lopingian tropical peatland carbon accumulation rate is calculated to be 61 1 73 0 g c m 2 yr which is expected to correspond to a npp of 611 1460 g c m 2 yr respectively a comparison between the predicted pennsylvanian late carboniferous npp and modern values indicates that the permian npp calculated is consistent with geochemical and paleobotanical models supporting a proposal that productivity was mainly controlled by temporal atmospheric o2 and co2 levels

biogeochemical effects of atmospheric oxygen concentration phosphorus weathering and sea level stand on oceanic redox chemistry implications for greenhouse climates abstract understanding the key factors influencing the global oceanic redox system is crucial to fully explaining the variations in oceanic chemical dynamics that have occurred throughout the earth s history in order to elucidate the mechanisms behind these variations on geological timescales numerical sensitivity experiments were conducted with respect to the partial pressure of atmospheric molecular oxygen p o 2 the continental shelf area a cs and the riverine input rate of reactive phosphorus to the oceans r p the sensitivity experiment for atmospheric p o 2 indicates that pervasive oceanic anoxia and euxinia appear when p o 2 p o 2 are higher than a previous estimate of 50 pal present atmospheric level due to redox dependent phosphorus cycling the sensitivity experiment regarding the shelf area demonstrates that changes in the shelf area during the phanerozoic significantly affected oceanic oxygenation states by changing marine biogeochemical cycling a large continental shelf acts as an efficient buffer against oceanic eutrophication and prevents the appearance of ocean anoxia euxinia we also found that an enhanced r p is an important mechanism for generation of widespread anoxia euxinia via expansion of both the oxygen minimum zone and coastal deoxygenation although the critical r p value depends significantly on p o 2 a cs and the redox dependent burial efficiency of phosphorus at the sediment water interface our systematic examination of the oceanic redox state under cretaceous greenhouse climatic conditions also supports the above results

hydrodynamic behavior of partly vegetated open channels the hydrodynamic response of turbulent flow in a compound wide rectangular open channel with a vegetated domain at the channel bank in a channel corner and in a floodplain to the vegetation density and diameter is discussed to this end a phenomenological model was imbedded in an algebraic stress model with the vegetation modeled as an internal resistance that exerts drag force produces energy of turbulence and interferes with its anisotropy and length scale simple suggestions for some modeling problems associated with the presence of wide vegetated domains are used to yield the three dimensional flow vorticity sources relaxation was implemented to smooth periodic behavior and dissipation correction was introduced as a coordinate invariant damping with these the results represent fully developed flow

flow patterns in compound channels with vegetated floodplains understanding the hydraulics of flow in a compound channel with vegetated floodplains is very important for determining the stage discharge curve and for supporting the management of fluvial processes in this paper the flow patterns over different types of vegetation such as tree shrub and grass are described based on an experimental study for vegetation on the floodplain the authors choose plastic grass duck feathers and plastic straws as model grass shrubs and trees respectively a 3d acoustic doppler velocimeter was used to measure the local flow velocities for different types of vegetation on the floodplain and the total discharge and flume slope were measured independently in the cases of nonvegetated floodplains all measured streamwise velocity distributions followed the logarithmic distribution but for vegetated floodplains they followed an s shaped profile exhibiting three zones for all cases the fluctuating velocity followed a normal distribution the influence of different types of vegetation on the distributions of the secondary currents turbulence intensities and reynolds shear stresses were also analyzed

overbank flow with vegetatively roughened flood plains an experimental and theoretical investigation into the flow characteristics of channels with complex cross sections was undertaken in this study particular attention was given to the problem of non submerged flood plain roughnesses this differs from previous studies in which compound channel flow was primarily investigated for more or less uniform boundary roughnesses in order to achieve more conformity with natural rivers the flood plain and the main channel were separated in the model by a sloping bank two cross sections with varying aspect ratios and flood plain roughnesses were investigated the necessary measurements were carried out by applying ldv and preston tube techniques on the basis of simple turbulence assumptions methods are presented by which the flow resistance in vegetatively roughened flood plains and main channels can be properly predicted as a function of independent and directly determinable basic flow parameters a first verification of this model was accomplished using field

the climatic significance of late ordovician early silurian black shales the ordovician silurian transition approximate to 455 430ma is characterized by repeated climatic perturbations concomitant with major changes in the global oceanic redox state best exemplified by the periodic deposition of black shales the relationship between the climatic evolution and the oceanic redox cycles however remains largely debated here using an ocean atmosphere general circulation model accounting for ocean biogeochemistry mitgcm we investigate the mechanisms responsible for the burial of organic carbon immediately before during and right after the latest ordovician hirnantian 445 444ma glacial peak our results are compared with recent sedimentological and geochemical data we show that the late katian time slice approximate to 445ma typified by the deposition of black shales at tropical latitudes represents an unperturbed oceanic state with regional organic carbon burial driven by the surface primary productivity during the hirnantian our experiments predict a global oxygenation event in agreement with the disappearance of the black shales in the sedimentary record this suggests that deep water burial of organic matter may not be a tenable triggering factor for the positive carbon excursion reported at that time our simulations indicate that the perturbation of the ocean circulation induced by the release of freshwater in the context of the post hirnantian deglaciation does not sustain over sufficiently long geological periods to cause the rhuddanian approximate to 444ma oceanic anoxic event input of nutrients to the ocean through increased continental weathering and the leaching of newly exposed glaciogenic sediments may instead constitute the dominant control on the spread of anoxia in the early silurian

impacts of global warming on permo triassic terrestrial ecosystems geologists and palaeontologists have expressed mixed views about the effects of the end permian mass extinction on continental habitats and on terrestrial life current work suggests that the effects on land were substantial with massive erosion following the stripping of vegetation associated with long term aridification and short term bursts of warming and acid rain wildfires at the permo triassic boundary contributed to the removal of forests and the prolonged absence of forests from the earth s surface for up to 10 myr these physical crises on land impinged on the oceans suggesting tight interlocking of terrestrial and marine crises levels of extinction on land may well have been as high as in the sea and this is certainly the case for tetrapods the mass extinction seems to have been less profound for plants and insects but it is hard at present to disentangle issues of data quality from reductions in abundance and diversity several killing agents have been proposed and of these tetrapods may have succumbed primarily to acid rain mass wasting and aridification plants may have been more affected by the sudden effects of heating and wildfires and the crisis for insects has yet to be explored

severe selenium depletion in the phanerozoic oceans as a factor in three global mass extinction events abstract selenium se is one of the key trace elements required by all animal and most plant life and se deficiencies in the food chain cause pathologies or death here we show from new geochemical analyses of trace elements in phanerozoic marine pyrite that sustained periods of severe se depletion in the past oceans correlate closely with three major mass extinction events at the end of the ordovician devonian and triassic periods these represent periods of se depletion 1 5 2 orders of magnitude lower than current ocean abundances being within the range to cause severe pathological damage in extant se reliant organisms se depletion may have been one of several factors in these complex extinction scenarios recovery from the depletion extinction events is likely part of a natural marine cycle although rapid rises in global oxygen from sudden major increases in marine productivity and plant biomass after each extinction event may also have played a crucial role

from greenhouse to icehouse nitrogen biogeochemistry of an epeiric sea in the context of the oxygenation of the late devonian atmosphere ocean system abstract the late devonian emergence of extensive arborescent terrestrial ecosystems produced changes in the earth s atmosphere and climate that resulted in substantial changes to the biogeochemistry of marine ecosystems the biogeochemistry of nitrogen in epeiric seas was particularly susceptible to alteration because of its dependence upon the series of redox mediated reactions that comprise the marine n cycle in order to explore the impact of climate change on n biogeochemistry in a late devonian epeiric sea we sampled a core from the appalachian basin that spans the interval from the greenhouse climate at the base of the famennian period to glacial conditions near its conclusion based upon stable isotope analysis of n c and s as well as elemental analysis of n c p s and fe we contend that two distinct biogeochemical regimes obtained during the contrasting climates the greenhouse regime featured low seawater o2 and ph that served to significantly curtail the oxidation of ammonia i e nitrification resulting in an ammonium dominated water column and low sediment 15n values the greenhouse also featured more extensive recycling of c n and p in contrast the higher seawater o2 and ph of the icehouse regime permitted nitrification in the water column resulting in a nitrate dominated system and higher sediment 15n values we conclude that nitrification was the key component of the n cycle that differentiated the two climate biogeochemical regimes

phanerozoic concentrations of atmospheric oxygen reconstructed from sedimentary charcoal varying concentrations of atmospheric oxygen have affected the development of animals and the role of wildfire in ecosystems reconstructions of past oxygen concentrations from fossil charcoal constrain atmospheric oxygenation over the past 400 million years variations of the earth s atmospheric oxygen concentration po2 are thought to be closely tied to the evolution of life with strong feedbacks between uni and multicellular life and oxygen1 2 on the geologic timescale po2 is regulated by the burial of organic carbon and sulphur as well as by weathering3 reconstructions of atmospheric o2 for the past 400 million years have therefore been based on geochemical models of carbon and sulphur cycling4 5 6 however these reconstructions vary widely4 5 6 7 8 9 10 particularly for the mesozoic and early cenozoic eras here we show that the abundance of charcoal in mire settings is controlled by po2 and use this proxy to reconstruct the concentration of atmospheric oxygen for the past 400 million years we estimate that po2 was continuously above 26 during the carboniferous and permian periods and that it declined abruptly around the time of the permian triassic mass extinction during the triassic and jurassic periods po2 fluctuated cyclically with amplitudes up to 10 and a frequency of 20 30 million years atmospheric oxygen concentrations have declined steadily from the middle of the cretaceous period to present day values of about 21 we conclude however that variation in po2 was not the main driver of the loss of faunal diversity during the permo triassic and triassic jurassic mass extinction events

relations between geomorphic form and sedimentologic stratigraphic variability holocene ooid sand shoal lily bank bahamas although the linkages among surface sediments geomorphic forms and hydrodynamics in holocene ooid tidal sand shoals have been evaluated recently how these factors are reflected in the geomorphic evolution and stratigraphic record of shoals is less constrained yet such understanding is essential to developing meaningful predictive conceptual models of three dimensional architecture of ancient reservoir analogs integrating remote sensing imagery high frequency seismic data and core characterization from lily bank a modern tidally dominated bahamian ooid shoal in which sedimentologic processes are well documented reveals the stratigraphic record of geomorphic change an irregular gently dipping rocky surface interpreted as the top pleistocene with no pronounced topographic high underlies the holocene oolitic succession a 6 m 20 ft thick poorly sorted gravelly muddy sand with few ooids overlies this basal surface this lower interval is overlain by sand with an upward increase in proportion of ooids sorting and grain size the uppermost unit present only under active bar forms is well sorted oolitic medium sand with accretionary foresets sediments vary stratigraphically and geomorphically the lower unit is finer and less well sorted than the upper units and in the oolitic upper unit sediment size and sorting on bar crests are distinct from bar flanks collectively these results suggest that a marked antecedent bump is not necessary for occurrence of ooid shoals and that the stratigraphic record of analogous ooid shoal systems may preserve clues of geomorphic position as well as geobody size and orientation

discharge assessment in compound channel flow a series of laboratory tests were performed to measure the boundary shear stresses in a compound channel consisting of a main channel and associated shallow floodplains four different floodplain roughnesses were used from these results apparent shear stresses across three different assumed main channel floodplain interface planes vertical horizontal and diagonal were calculated the data was used with data from previous studies to derive a statistical relationship between the apparent shear stress on the vertical interface and several easily calculated parameters of the channel geometry and hydraulic characteristics the accuracies of different methods of discharge calculation were shown to be dependent upon the assumptions they make regarding the magnitude of the apparent shear stress on the particular interface chosen an apparent shear stress ratio was proposed which was found to be a useful yardstick in selecting the best method of discharge calculation for particular channel and flow conditions generally it was found that at low floodplain depths using the horizontal or diagonal interfaces gave better discharge results than the vertical

addendum to inclusion of the weathering of volcanic rocks in the geocarbsulf model r a berner 2006 v 306 p 295 302 in the paper by berner 2006a 1 the compiled data presented by dessert and others 2001 2 for different values of the relative weathering rates of basalts versus granites was missed the term granite is used here to refer to all granitoid rocks including gneisses it is the primary

late cenozoic fire enhancement response to aridification in mid latitude asia evidence from microcharcoal records fire provides an important indicator of paleoclimatic change however little information relating to late cenozoic fire history has been gathered in mid latitude asia including inner asia and east asia a key region for understanding the development of the arid monsoon climate system as well as the driving forces behind it here we first report the records of microcharcoal concentrations mc covering the holocene 10 0 ica and late pleistocene 0 8 0 ma which we use to analyze the fire activity patterns at an orbital time scale then we compile the late cenozoic mc record to investigate the long term fire history by analyzing four cores from the yangtze river delta yrd area east asia representing 8 0 ma and three sites in inner asia representing 18 2 ma the results show that the i mc remained higher during the relatively dry late holocene glacial stages than that during the humid middle holocene interglacial stages at individual sites ii mc increased with time in both inner asia and east asia after 18 and 8 ma respectively and iii mc always remained higher in the dry inner asia than in the contemporaneous wet east asia all these characteristics imply that late cenozoic fire occurrence in mid latitude asia experienced a gradual increasing trend along with the global temperature ice volume change and indicates a continuous aridification trend across mid latitude asia the global cooling rather than the tibetan plateau uplift might have played a key role in this observed trend c 2016 elsevier ltd all rights reserved

secular distribution of highly metalliferous black shales corresponds with peaks in past atmosphere oxygenation highly metalliferous black shales hmbs are enriched in organic carbon and a suite of metals including ni se mo ag au zn cu pb v as sb se p cr and u pge compared to common black shales and are distributed at particular times through earth history they constitute an important future source of metals hmbs are relatively thin units within thicker packages of regionally extensive continental margin or intra continental marine shales that are rich in organic matter and bio essential trace elements accumulation and preservation of black shales and the metals contained within them usually require low oxygen or euxinic bottom waters however whole rock redox proxies particularly mo suggest that hmbs may have formed during periods of elevated atmosphere po2 this interpretation is supported by high levels of nutrient trace elements within these rocks and secular patterns of se and se co ratios in sedimentary pyrite through earth history with peaks occurring in the middle paleoproterozoic early cambrian to early ordovician middle devonian middle to late carboniferous middle permian and middle to late cretaceous all corresponding with time periods of hmbs deposition this counter intuitive relationship of strongly anoxic to euxinic localized seafloor conditions forming under an atmosphere of peak oxygen concentrations is proposed as key to the genesis of hmbs the secular peaks and shoulders of enriched se in sedimentary pyrite through time correlate with periods of tectonic plate collision which resulted in high nutrient supply to the oceans and consequently maximum productivity accompanying severe drawdown into seafloor muds of c s p and nutrient trace metals the focused burial of c and s over extensive areas of the seafloor during these anoxic to euxinic periods likely resulted in an o2 increase in the atmosphere causing short lived peaks in po2 that coincide with the deposition of hmbs as metals become scarce particularly mo ni se ag and u the geological times of these narrow hmbs horizons will become a future focus for exploration

the burning of gondwana permian fires on the southern continent a palaeobotanical approach abstract fossil charcoal has widely been accepted as a direct indicator for the occurrence of palaeo wildfires in upper palaeozoic sediments of euramerica and cathaysia records of these remains are relatively common and regionally and stratigraphically more or less homogeneously distributed in terrestrial sequences on the other hand just a few records have been published for the permian of gondwana and only recently has it been demonstrated that macroscopic charcoals are also common here most permian macroscopic charcoal from gondwana is gymnospermous and has been reported from coal bearing strata macroscopic charcoal occurrences are spread out in different sequences and also in distinct stratigraphic intervals in the permian e g parana basin sakmarian artinskian of brazil karoo basin artinskian of south africa damodar basin lopingian of india and dead sea area changhsingian of jordan they range from peri glacial post glacial to warm temperate climatic systems throughout the permian macro and micro charcoal occurrences are compared to inertinite incidences to support the pyrogenic origin for these coal macerals and to provide an up to date overview on the known evidences of permian wildfires on gondwana in space and time

uranium isotopes distinguish two geochemically distinct stages during the later cambrian spice event a b s t r a c t anoxic marine zones were common in early paleozoic oceans 542 400 ma and present a potential link to atmospheric po2 via feedbacks linking global marine phosphorous recycling primary production and organic carbon burial uranium u isotopes in carbonate rocks track the extent of ocean anoxia whereas carbon c and sulfur s isotopes track the burial of organic carbon and pyrite sulfur primary long term sources of atmospheric oxygen in combination these proxies therefore reveal the comparative dynamics of ocean anoxia and oxygen liberation to the atmosphere over million year time scales here we report high precision uranium isotopic data in marine carbonates deposited during the late cambrian spice event at ca 499 ma documenting a well defined 0 18 negative 238 u excursion that occurs at the onset of the spice event s positive 13

unstable patterns in partly vegetated channels unstable patterns are identified in the results of numerical simulations of two cases of partly vegetated open channels at the free unobstructed flow side of the shear layer that separates the unobstructed channel from the vegetated zones a time dependent pattern was identified in a rectangular open channel compound with a vegetated bank and cellular structure was found in a wide ractangular open channel spanning over a vegetated thin layer at the channel bed distinction between three modes of algebraic stress models a prompt algebraic stress model a delayed algebraic stress model and an algebraic stress model with longitudinal vorticity sources relaxation and the modeling of time dependent turbulence is made and discussed in the present context

magnitude and significance of carbon burial in lakes reservoirs and peatlands globally lakes are currently accumulating organic carbon oc at an estimated annual rate of about 42 tg yr 1 most of the oc in all but the most oligotrophic of these lakes is autochthonous produced by primary production in the lakes the sediments of reservoirs accumulate an additional 160 tg annually and peatlands contribute 96 tg annually these three carbon pools collectively cover less than 2 of the earth9s surface and constitute a carbon sink of about 300 tg yr 1 although the oceans cover 71 of the earth9s surface they accumulate oc at a rate of only about 100 tg yr 1

turbulence modeling of flood plain flows a numerical model capable of predicting flow characteristics in a compound channel is described the model solves the continuity and momentum equations along with the transport equations of kinetic energy of turbulence and the dissipation rate closure is achieved with the aid of algebraic relations for turbulence stresses the model is capable of treating compound channels formed by regular geometrical sections of main channel and flood plain segments the width of the main channel the width of the total section the depth of flow in flood plain the total depth channel slope and boundary roughness of main channel section and flood plain section can all be varied the model predictions of total flow rate shear stress distributions around the wetted perimeter and the percentage of flow and shear force carried by the different sections were compared with published experimental data reasonable agreement between data and predictions was obtained

organic matter from the callovian middle jurassic deposits of lithuania compositions sources and depositional environments abstract this study presents the first organic geochemical and petrographical investigation of the callovian deposits of the eastern part of the central european basin it is shown that in both the terrigenous papil formation lower callovian and shallow to deeper marine facies of the papartin and skinija formations middle and upper callovian respectively terrestrial organic matter predominates this is reflected by the carbon preference index values higher than 1 2 for all samples and in some cases higher than 2 as well as the occurrence of characteristic higher plant biomarkers like cadalene dehydroabietane simonellite and retene moreover in the case of the papil formation sugiol a natural product terpenoid produced by distinct conifer families has been detected in clay sediments the occurrence of such a biomolecule in the middle jurassic clays is reported for the first time its occurrence is probably connected with the presence of small wood debris in the clay sediments in samples of the papil formation charcoal fragments co occurring with unsubstituted polycyclic aromatic hydrocarbons were detected indicating that wildfires took place during the early callovian of lithuania and or neighbouring areas in the middle and upper marine callovian sediments of lithuania there is no evidence of anoxic conditions occurring in the water column however periodic anoxic or strongly dysoxic episodes may have occurred most probably below the photic zone during the deepest phase of the late callovian transgression as is evidenced from pyrite framboid diameter distribution and general impoverishment of benthic fauna huminite reflectance r r values for the investigated area are in the range of 0 21 0 31 suggesting the occurrence of immature organic matter such values indicate that these investigated deposits were close to the surface during their whole diagenetic history and the thickness of younger cover did not exceed ca 500 m this is also supported by a biomarker analysis in which less thermally stable hopanes and hopenes significantly dominated

study of the west gondwana floras during the late paleozoic a paleogeographic approach in the parana basin brazil abstract the late paleozoic in west gondwana was a period of significant climatic changes ranging from a glacial climate in the late carboniferous to a semi arid climate in the late permian the floristic province of gondwana in the parana basin was directly affected by such changes and underwent a transformation regarding composition and geographic distribution thus the climatic phases were divided into three intervals phase a containing interglacially developed flora phase b containing floras of immediate post glacial temperate climates and phase c identified with floras related to the decline of dryness regarding their geographical distribution the floras were concentrated in the far northern and far southern portions of the basin during the glacial interval and with a gradual increase in temperature went on to occupy the entire basin finally we can see that the floras located in the argentinean portion of west gondwana are older and have greater species diversity than those present in the parana basin and africa during phase a in phase b there is a decline of argentinean flora species a large increase in the parana basin floras and an average increase in african floras in the final stage the floristic province no longer exists in argentina the flora of the parana basin also suffers a decrease of specimens and the african flora undergoes its moment of greatest development such diversity change also reflects a west to east migration throughout the late carboniferous

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

evidence for wildfire in the meishan section and implications for permian triassic events polynuclear aromatic hydrocarbons pahs and black carbon bc in sediments are powerful tools in the identification of the combustion process throughout geologic history in this study combustion derived pahs and bc were carefully investigated in sediments from the global stratotype section and point of the permian triassic p tr boundary in meishan china quantitative analyses of combustion derived pahs and bc demonstrate anomalously high concentrations in the boundary event beds that coincide with the mass extinction horizon the prevalence of parent polynuclear aromatics e g phenanthrene in pahs together with non metric multidimensional scaling analysis confirms that the pahs are mainly derived from vegetation burning instead of having a coal and or oil origin bc detected in sediment occurs in various forms from large irregular charcoal particles to fine aciniform soot with an equivalent reflectance of up to 3 5 the results strongly suggest that a wildfire occurred during the p tr boundary which served as one of the possible triggers of mass extinction on land the wildfire occurrence indicates that the o2 concentration of the atmosphere during or before the p tr mass extinction was probably 17 the temporal coincidence of the mass extinction with intensive volcanic eruption marine anoxia and wildfire events in the region of the meishan section provides new insight into the mechanisms of the p tr biotic crisis our results show that wildfires could have played an important role in the collapse of the ecosystem in the meishan p tr events

protracted development of bioturbation through the early palaeozoic era mobile organisms first appeared in the fossil record prior to the precambrian cambrian transition sediment textures indicate that the degree of sediment mixing by animal activity remained low for 120 million years following the transition

evidence of widespread wildfires in coal seams from the middle jurassic of northwest china and its impact on paleoclimate abstract today wildfire is an important disturbance in many continental ecosystems and it is assumed that with ongoing climate changes the frequencies and impacts of wildfires will increase in many regions one way to obtain information about the potential long term influences of wildfires on ecosystems and the climate system itself is to study palaeo wildfires a total of 140 jurassic samples including 122 coal samples and 18 rock samples from roof and floor of coal seams were collected from 4 coalfields in northwestern china the samples were analyzed by macropetrography microscopy scanning electron microscopy gas chromatography and gas chromatography mass spectrometry to study the evidences of wildfires and their impact on the paleoclimate high contents of pyrogenic inertinites charcoal natural char and natural coke particles observed in the samples which indicate that widespread wildfire events occurred in the early middle jurassic in all over northwestern china additionally high molecular weight polycyclic aromatic hydrocarbons were detected in the coal samples these aromatic compounds were formed under high temperature and provide further evidence of wildfires according to a carbon emission model for modern forest fires the total carbon and gas emissions from wildfires in peat swamps of the middle jurassic in northwest china were calculated by the data from 21 575 coal samples of number of 1567 drill core samples the total carbon released from peat swamp forest wildfires was at least 1207 gt corresponding to emissions of co2 co and ch4 of 1926 gt 163 gt and 8 8 gt respectively the huge amount of co2 released by forest fires in the peat swamp systems of the middle jurassic in northwestern china alone was equivalent to 64 20 of the total co2 in the atmosphere at present 3000gt the large amounts of greenhouse gases released by wildfires must have led to long term changes in the atmospheric composition and have caused global warming which could have the reason of affected the paleoclimate

inclusion of the weathering of volcanic rocks in the geocarbsulf model the carbon cycle model geocarbsulf is extended by dividing the weathering of silicates into volcanic and non volcanic rocks the proportion of volcanic weathering is calculated as a function of time from the oceanic record of 87sr 86sr the volcanic proportion is then used to modify the equations for calculating atmospheric co2 by the addition of a new non dimensional volcanic weathering factor the effect of uplift and physical erosion on weathering is also modified by using only the distribution over time of the abundance of sandstones and shales and not sr isotopic data that had been used previously results indicate moderate change from geocarbsulf in the distribution of atmospheric co2 over phanerozoic time this includes an increased minimum in co2 during the late ordovician in agreement with the presence of a continental glaciation at that time and a shift of maximum mesozoic values from the jurassic to the early cretaceous

coal more than a resource critical data for understanding a variety of earth science concepts abstract coal is one of the world s primary energy sources and it is critical for making coke used in steel making and is used for a multitude of chemical products aside from its significance as a fuel or product however coal and data derived from the exploration or mining of coal have also provided the foundation and testing ground for diverse geologic concepts because of coal s economic importance and common variability in thickness distribution and quality it has been critical to collect and correlate a wide variety of surface and subsurface data sets at relatively high spatial frequency which varies from the mine to basinal scale also because many coal beds occur in most coal basins the collection of coal data from multiple beds creates relatively high temporal frequency data sets at scales from laminae to bed to larger unit scale these data have been important for the development and expansion of many earth science concepts including aspects of basin analyses paleogeography paleoclimatology paleontology stratigraphy sedimentology structural geology and tectonics

terrestrial sedimentation and the carbon cycle coupling weathering and erosion to carbon burial this paper examines the linkages between the carbon cycle and sedimentary processes on land available data suggest that sedimentation on land can bury vast quantities of organic carbon roughly 1015 g c yr 1 to evaluate the relative roles of various classes of processes in the burial of carbon on land terrestrial sedimentation was modeled as a series of 864 scenarios each scenario represents a unique choice of intensities for seven classes of processes and two different global wetland distributions comparison was made with presumed preagricultural conditions the classes of processes were divided into two major component parts clastic sedimentation of soil derived carbon and organic sedimentation of autochthonous carbon for clastic sedimentation masses of sediment were considered for burial as reservoir sediment lake sediment and combined colluvium alluvium and aeolian deposits when the ensemble of models is examined the human induced burial of 0 6 1 5 1015 g yr 1 of carbon on land is entirely plausible this sink reaches its maximum strength between 30 and 50 n paddy lands stand out as a type of land use that warrants future study but the many faces of rice agriculture limit generalization in an extreme scenario paddy lands alone could be made to bury about 1 1015 g c yr 1 arguing that terrestrial sedimentation processes could be much of the sink for the so called missing carbon is reasonable such a hypothesis however requires major redesign of how the carbon cycle is modeled unlike ecosystem processes that are amenable to satellite monitoring and parallel modeling many aspects of terrestrial sedimentation are hidden from space

vegetative impacts on hydraulics and sediment processes across the fluvial system summary vegetation creates a complicated system of feedbacks and linkages across the fluvial system that is realized through river planform shape interactions occur among flow hydraulics sediment deposition and erosion and plant morphology density and biomechanics interest in the interactions and feedback loops between vegetation and the fluvial system has grown extensively in the past few years this interest is partially driven by the popularity of stream restoration activities worldwide that include re vegetation of stream banks and formation of an ecosystem that is intended to encourage the growth of aquatic macrophytes we present a review of the research into the interactions and dependencies between vegetation and the fluvial system to identify hydraulic and sediment dynamics that are consistent around vegetation located in the channel on channel banks and over the floodplain we illustrate process commonalities operating across spatial locations within the fluvial system and highlight some of the current research opportunities and challenges to encourage research collaborations between those working in areas of the fluvial system traditionally viewed as disparate

effects of momentum transfer in compound channels different methods of considering the shear stresses between a main channel and its flood plains are discussed the methods considered include the simplistic method of considering the entire hydraulic cross section as one dividing the cross section into independent sections assuming limited shear stresses between main channel and the flood plain trying to find an interface with zero shear stress or allowing for the shear stresses from a momentum balance based on evaluation of alternative steady state models it is concluded that the area method is the most promising for computation of discharge and that the prinos townsend equation gives accurate results for apparent shear stresses at the main channel flood plain interface the results of the theoretical study are used in an unsteady flow model prepared based on hydrodynamic principles the model facilitates the investigation of the significance of the momentum transfer phenomenon between the main channel and its floodplains the analysis demonstrate

the diversification of paleozoic fire systems and fluctuations in atmospheric oxygen concentration by comparing silurian through end permian 250 million years myr charcoal abundance with contemporaneous macroecological changes in vegetation and climate we aim to demonstrate that long term variations in fire occurrence and fire system diversification are related to fluctuations in late paleozoic atmospheric oxygen concentration charcoal a proxy for fire occurs in the fossil record from the late silurian 420 myr to the present its presence at any interval in the fossil record is already taken to constrain atmospheric oxygen within the range of 13 to 35 the fire window herein we observe that as predicted atmospheric oxygen levels rise from 13 in the late devonian to 30 in the late permian so too fires progressively occur in an increasing diversity of ecosystems sequentially data of note include the occurrence of charcoal in the late silurian early devonian indicating the burning of a diminutive dominantly rhyniophytoid vegetation an apparent paucity of charcoal in the middle to late devonian that coincides with a predicted atmospheric oxygen low and the subsequent diversification of fire systems throughout the remainder of the late paleozoic first fires become widespread during the early mississippian they then become commonplace in mire systems in the middle mississippian in the pennsylvanian they are first recorded in upland settings and finally based on coal petrology become extremely important in many permian mire settings these trends conform well to changes in atmospheric oxygen concentration as predicted by modeling and indicate oxygen levels are a significant control on long term fire occurrence

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

oxygenation as a driver of the great ordovician biodiversification event the largest radiation of phanerozoic marine animal life quadrupled genus level diversity towards the end of the ordovician period about 450 million years ago a leading hypothesis for this great ordovician biodiversification event is that cooling of the ordovician climate lowered sea surface temperatures into the thermal tolerance window of many animal groups such as corals a complementary role for oxygenation of subsurface environments has been inferred based on the increasing abundance of skeletal carbonate but direct constraints on atmospheric o2 levels remain elusive here we use high resolution paired bulk carbonate and organic carbon isotope records to determine the changes in isotopic fractionation between these phases throughout the ordovician radiation these results can be used to reconstruct atmospheric o2 levels based on the o2 dependent fractionation of carbon isotopes by photosynthesis we find a strong temporal link between the great ordovician biodiversification event and rising o2 concentrations a pattern that is corroborated by o2 models that use traditional carbon sulfur mass balance we conclude that that oxygen levels probably played an important role in regulating early palaeozoic biodiversity levels even after the cambrian explosion an increase in biodiversity 450 million years ago coincided with a rise in atmospheric oxygen concentrations suggests a geochemical analysis oxygen availability may have thus helped spur the radiation alongside climatic cooling

evidence of wildfires and elevated atmospheric oxygen at the frasnian famennian boundary in new york usa implications for the late devonian mass extinction the devonian period experienced significant fluctuations of atmospheric oxygen o2 levels 25 13 for which the extent and timing are debated also characteristic of the devonian period at the frasnian famennian f f boundary is one of the big five mass extinction events of the phanerozoic fossilized charcoal inertinite provides a record of wildfire events which in turn can provide insight into the evolution of terrestrial ecosystems and the atmospheric composition here we report organic petrology programmed pyrolysis analysis major and trace element analyses and initial osmium isotope osi stratigraphy from five sections of upper devonian f f interval from western new york usa these data are discussed to infer evidence of a wildfire event at the f f boundary based on the evidence for a wildfire at the f f boundary we also provide an estimate of atmospheric o2 levels of 23 25 at this interval which is in agreement with the models that predict elevated po2 levels during the late devonian this coupled with our os isotope records support the currently published osi data that lacks any evidence for an extra terrestrial impact or volcanic event at the f f interval and therefore to act as a trigger for the f f mass extinction the elevated o2 level at the f f interval inferred from this study supports the hypothesis that pco2 drawdown and associated climate cooling may have acted as a driving mechanism of the f f mass extinction

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

oxygen escape from the earth during geomagnetic reversals implications to mass extinction abstract the evolution of life is affected by variations of atmospheric oxygen level and geomagnetic field intensity oxygen can escape into interplanetary space as ions after gaining momentum from solar wind but earth s strong dipole field reduces the momentum transfer efficiency and the ion outflow rate except for the time of geomagnetic polarity reversals when the field is significantly weakened in strength and becomes mars like in morphology the newest databases available for the phanerozoic era illustrate that the reversal rate increased and the atmospheric oxygen level decreased when the marine diversity showed a gradual pattern of mass extinctions lasting millions of years we propose that accumulated oxygen escape during an interval of increased reversal rate could have led to the catastrophic drop of oxygen level which is known to be a cause of mass extinction we simulated the oxygen ion escape rate for the triassic jurassic event using a modified martian ion escape model with an input of quiet solar wind inferred from sun like stars the results show that geomagnetic reversal could enhance the oxygen escape rate by 3 4 orders only if the magnetic field was extremely weak even without consideration of space weather effects this suggests that our hypothesis could be a possible explanation of a correlation between geomagnetic reversals and mass extinction therefore if this causal relation indeed exists it should be a many to one scenario rather the previously considered one to one and planetary magnetic field should be much more important than previously thought for planetary habitability

structure of turbulence in compound channel flows the structure of turbulence in compound channel flows is examined in a laboratory study shear stresses and turbulence intensities are measured in a channel comprised of a deep central section flanked on either side by wide shallow berms flood plains the study concerns the nature of turbulence in the mixing regions separating the deep and shallow zones also studied is the mixing region s effect on the compound flow field for both wide and narrow channel conditions under narrow channel conditions the mixing process extends to the center of the main channel flow field however under wide channel conditions the central region is not affected and observed turbulence levels at the center of the main channel are in close agreement with theoretical values for a two dimensional flow field apparent shear stress at the vertical main channel flood plain interface was measured directly and compared favorably with estimated values based on momentum considerations