the influence of convective thermal forcing on the three dimensional circulation around squall lines abstract midlatitude squall lines are typically trailed by a large region of stratiform cloudiness and precipitation with significant mesoscale flow features including an ascending front to rear flow a descending rear inflow jet line end vortices and at later times mesoscale convective vortices the present study suggests that the mesoscale circulation in the trailing stratiform region is primarily determined by the time mean pattern of heating and cooling in the leading convective line analysis of the line normal circulation shows that it develops as thermally generated gravity waves spread away from the leading line midlevel line end vortices are the result of diabatically driven tilting of horizontal vorticity generated by the time mean thermal forcing in the presence of the coriolis force a symmetric thermal forcing generates an asymmetric stratiform circulation and a pattern of vertical displacement that resembles the comma shaped stratiform anvil observed in real systems this suggests tha

ediacaran δ13c chemostratigraphy of south china abstract we report new 13 c chemostratigraphic data of the ediacaran system in south china using litho and biostratigraphic markers as independent calibrators we combine new and previously published 13 c data to construct a composite 13 c profile for the ediacaran system in south china the composite curve shows in chronostratigraphic order 1 a negative 13 c excursion en1 in the doushantuo cap carbonate that overlies the ghaub age nantuo diamictite 2 a pronounced positive 13 c excursion ep1 in the lower doushantuo formation where doushantuo type acanthomorphic acritarchs red algae and animal embryos first appear 3 a mild negative 13 c excursion en2 in the middle doushantuo formation 4 a positive 13 c excursion ep2 in the upper doushantuo formation where doushantuo type acanthomorphic acritarchs micrometazoans and stem group florideophyte red algae become abundant and diverse 5 a pronounced negative 13 c excursion en3 near the uppermost doushantuo formation 6 a strongly positive 13 c excursion up to 6 3 pdb ep3 in the lower dengying formation 7 a stable 13 c plateau ca 2 5 pdb ei in the middle and upper dengying formation where abundant vendotaenid algae macroscopic ediacaran fossils biomineralized animal tubes and mostly horizontal animal traces occur and 8 a 10 negative 13 c excursion en4 immediately below the ediacaran cambrian boundary the general pattern of this composite 13 c curve is robust despite a considerable amount of variation among the 13 c profiles of different sections this composite 13 c curve provides a first order chemostratigraphic framework for the subdivision and correlation of the ediacaran system in south china

an investigation of the influence of latent heat release on cold frontal motion abstract the effects of condensational heating on cold frontal translation speed are explored through the use of potential vorticity pv diagnostics and model sensitivity experiments it is hypothesized that condensational heating can lead to faster frontal translation speeds in the presence of vertical shear because of the horizontal propagation of the positive pv anomaly associated with the front a case study of a cold front with an evolving precipitation structure is presented a positive correlation existed between the position of condensational heating relative to the frontal zone and frontal translation speed with faster frontal movement occurring when condensational heating was present in the prefrontal zone this front was numerically simulated to see if the hypothesized mechanism for frontal movement was active through the use of a pv budget it was confirmed that condensational heating did contribute to the forward propagation of the cold frontal pv band numerical experiments were performed

the evolution of an mcs over southern england part 1 observations observations are described of a mesoscale convective system mcs with a cold pool which propagated across southern england on 25 august 2005 the observations were made as part of the convective storm initiation project csip the observed mcs structure broadly followed well established theories including the presence of a weak rear inflow jet in detail however unsteady transitions occurred involving the formation of two distinct lines of showers ahead of the initial linear system in each case the cold pool merged with cold downdraughts from the new showers leading to a discontinuous propagation of the system one of these lines formed independently of the mcs very probably on a sea breeze convergence line the mechanism for formation of the other is unknown but it is possible that it was triggered by ascent associated with gravity waves generated by the mcs the merged cold pool was deeper and colder and propagated faster than the original system eventually forming a bow echo and arc cloud as it propagated across the english channel until completion of the merger the propagation velocity of the overall system had been controlled by a combination of the above mechanisms rather than simply by cold pool dynamics

the evolution of an mcs over southern england part 2 model simulations and sensitivity to microphysics simulations using the met office unified model at 1 km horizontal grid spacing of a mesoscale convective system mcs with a cold pool which propagated across southern england on 25 august 2005 are validated using detailed observations from the convective storm initiation project csip early organisation of the system is not especially well treated but the model goes on to form a system which developed qualitative and quantitative features remarkably similar to the observations a sensitivity study suggests that the initial linear system is driven by the position of a low level lid and upper level instability the linear organisation being promoted by a weak rear inflow jet forced by the upper level warm anomaly in the cloud anvil a weak cold pool develops in the absence of ice phase processes but this does not promote system propagation strengthening and descent of the rear inflow jet and acceleration of the system is promoted by the additional heating through glaciation and cooling through snow evaporation the surface cold pool and gust front are further strengthened by snow melting and rainfall evaporation with ice phase processes present the cold pool strengthens as a result of the system development and its strength is broadly correlated with system propagation speed during the middle phase of the system s lifetime propagation enables the convective band to sweep up any convective cells which trigger ahead of the system the differing scales of microphysical processes means that it is difficult to form a steady state system the observed transition phase corresponds to an increase in the slantwise nature of the flow in the storm and in the low level cooling by rainfall evaporation near the gust front combined with a change in ambient conditions advection over the sea which eventually enable the cold pool to propagate ahead of the system

the biostratigraphic succession of acanthomorphic acritarchs of the ediacaran doushantuo formation in the yangtze gorges area south china and its biostratigraphic correlation with australia abstract abundant large acanthomorphic acritarchs from the ediacaran doushantuo formation in the yangtze gorges area south china are becoming useful tools for biostratigraphic subdivision and correlation of the ediacaran system despite limitations caused by facies control taphonomic bias and taxonomic problems based on thin section examination of chert samples collected from six sections of the doushantuo formation a clear stratigraphic distribution of acritarchs has allowed two assemblages of acanthomorphic acritarchs lower tianzhushania spinosa assemblage and upper tanarium anozos tanarium conoideum assemblage to be established these two assemblages which are found in the lower member ii and the upper member iii doushantuo formation respectively are constrained stratigraphically to the first and the second positive 13c excursions ep1 and ep2 respectively and are separated by a second negative 13c excursion en2 the lower t spinosa assemblage is dominated by the taxon t spinosa by comparison with the lower assemblage the upper t anozos t conoideum assemblage preserves more acanthomorphic acritarchs both in terms of number of individuals and in the diversity of the forms fifteen forms eotylotopalla delicata knollisphaeridium maximum echinosphaeridium maximum meghystrichosphaeridium magnificum schizofusa zangwenlongii sinosphaera rupina t anozos t conoideum tanarium irregulare variomargosphaeridium litoschum as well as the unnamed b c d e f and g forms are the predominant species in upper t anozos t conoideum assemblage among them the taxa t anozos and t conoideum occur in most great number and throughout the assemblage whereas the species t spinosa is presumed to have become extinct the upper t anozos t conoideum assemblage shares a number of species with the ediacaran complex acritarch palynoflora ecap in south and central australia including ceratosphaeridium glaberosum gyalosphaeridium pulchrum s zangwenlongii t conoideum t irregulare and v litoschum in addition the species t spinosa is not present in the ecap of australia hence the upper t anozos t conoideum assemblage of the doushantuo formation can be correlated with the ecap of south and central australia while the lower tianzhushania assemblage appears to be missing in south and central australia

a burial diagenesis origin for the ediacaran shuram wonoka carbon isotope anomaly marked negative 13c excursions in ediacaran age carbonate sediments have been identified in several sections globally but are not recognized in all sections of similar age the presence of 13ccarb values as low as 12 has been interpreted as recording fundamentally different processes in the global carbon cycle than those recognized today the 13ccarb anomalies are strongly correlated with 18ocarb values but are not represented in 13corg records while no primary depositional processes have been identified that can produce the correlated 18o 13c arrays simulations show that fluid rock interaction with high pco2 fluids is capable of producing such arrays at geologically reasonable pco2 and water rock ratios variations in the mg ca ratio and sulfate concentration of the altering fluid determine the extent of dolomite vs calcite and anhydrite in the resulting mineral assemblage incorporation of an initially aragonitic mineralogy demonstrates that high sr low mn sr and modest alteration of 87sr 86sr in ancient carbonates are all compatible with a burial diagenesis mechanism for generation of the 13c anomalies and do not necessarily imply preservation of primary values the profound ediacaran negative 13c anomalies can be adequately explained by well understood diagenetic processes conflated with the difficulty of correlating precambrian sections independently of chemostratigraphy they are not a record of primary seawater variations and need not have independent stratigraphic significance

a pronounced negative δ13c excursion in an ediacaran succession of western yangtze platform a possible equivalent to the shuram event and its implication for chemostratigraphic correlation in south china abstract a pronounced negative 13 c shift that can be potentially correlated with the shuram excursion has been reported from middle ediacaran strata in the yangtze gorges area of south china whether it represents a perturbation to the ocean carbon cycle or a record of post depositional alteration is still open to debate resolving this controversy will help clarify if 13 c variations can be used for chemostratigraphic correlation of ediacaran successions to further understand the regional pattern of ediacaran carbon isotopic excursions in the yangtze platform we carried out a detailed 13 c analysis of the lianghong section in the western part of the yangtze platform the ediacaran system at lianghong is overlain by the maidiping formation yielding early cambrian small shelly fossils and underlain by the cryogenian lieguliu formation diamictite and tuffaceous siltstones it comprises the guanyinya and hongchunping formations which have been traditionally correlated with the doushantuo and dengying formations respectively in the yangtze gorges area two negative 13 c excursions occur in the lianghong section the lower one at the uppermost guanyinya formation with a nadir at 8 6 may be correlated with the pronounced negative 13 c shift en3 in the uppermost doushantuo formation in the yangtze gorges area and possibly with the well known shuram event in oman the upper negative 13 c excursion occurs in the upper hongchunping formation and may be correlated with negative excursions en4 near the ediacaran cambrian boundary other negative 13 c excursions e g en1 and en2 are not expressed in the lianghong section because the lower guanyinya formation is dominated by siliciclastic rocks combined with previously published ediacaran 13 c profiles our results indicate that the en3 excursion likely a shuram equivalent may occur widely in south china and can be a useful chemostratigraphic feature for regional and global stratigraphic correlation

preliminary analysis of shuttle radar laboratory srl 1 data to study aeolian features and processes in april 1994 the shuttle radar laboratory srl 1 obtained quad polarization data in l band spl lambda 24 cm and c band spl lambda 5 6 cm and vv polarized data in x band spl lambda 3 cm preliminary analyses show that radar backscatter coefficients spl sigma sup 0 can be used to map the aerodynamic roughness parameter z sub 0 over large areas from orbit as demonstrated by comparisons with measurements of z sub 0 obtained in the field although all wavelengths and polarizations show fairly good correlations with z sub 0 r 0 78 l band hv shows the best relationship r 0 81 this result has potential use in regional studies of sand and dust transport modeling atmospheric circulation and general climate studies srl images of aeolian landforms were also studied including dunes sand sheets and wind streaks dunes in the stovepipe wells area of death valley were clearly visible on l band hv images but not detected on c band images in the same area l band penetrated a sand sheet to reveal a buried fault scarp l band images in namibia showed the classic linear dunes near gobabeb and also revealed previously undetected sets of cross dunes wind streaks were imaged in several areas including namibia where streaks are associated with the impact crater roter kamm these features enable mapping of near surface wind patterns

50 myr recovery from the largest negative δ13c excursion in the ediacaran ocean sedimentary rocks deposited during the ediacaran period 630 542 ma contain carbonates whose carbon isotopic ratios show a marked negative excursion consisting of a precipitous drop from 5 to 12 followed by a sub linear recovery to positive 13c values isotopic ages u pb and thermal subsidence modelling are combined to constrain the excursion in time and indicate an onset at 600 ma and duration of recovery of approximately 50 myr the excursion is widely recognized in oman and has potential correlatives in ediacaran strata elsewhere and may thus represent a characteristic feature of the ediacaran period the amplitude of this carbon isotope excursion far exceeds those of other neoproterozoic anomalies the isotopic trend of negative excursion and long term recovery spanned at least one short lived glacial episode at 580 ma but appears unrelated to glaciation which indicates that negative anomalies in the neoproterozoic marine carbon isotope record are not directly or uniquely linked to ice ages

trace fossil evidence for ediacaran bilaterian animals with complex behaviors abstract distinguishing ediacaran trace fossils from tubular body fossils can be a challenge and several ediacaran fossils previously interpreted as animal traces have been shown to be tubular body fossils nonetheless true ediacaran trace fossils are present but they are relatively few and morphologically simple dominated by horizontal trails and shallow burrows such simple morphologies have been taken as evidence for a modest behavioral complexity and limited geobiological impact of animal bioturbators before the cambrian explosion here we report three types of trace fossils horizontal tunnels surface tracks trails and vertical traces from the latest ediacaran dengying formation 551 541 ma in the yangtze gorges area of south china cross cutting tunnels and the presence of scratch marks indicate that these traces are unlikely tubular body fossils instead these three types of traces likely represent animal activities related to under mat feeding epibenthic locomotion and temporary dwelling respectively we show that these three types of traces were constructed by the same bilaterian animals that had moderately complex interactions with microbial mats to exploit nutrients and o 2 resources these animals heralded a new age in ecosystem engineering animal sediment interaction and biogeochemical cycling

the stratigraphic expression of a large negative carbon isotope excursion from the ediacaran johnnie formation death valley the rainstorm member of the ediacaran johnnie formation of the southern basin and range us records a large negative excursion in carbon isotope ratios of carbonate strata 13 c vpdb 6 the character of the excursion raises fundamental questions about whether this isotopic pattern is accurately capturing the time series behavior of marine dissolved inorganic carbon dic or is a product of diagenesis to explore this issue we examined the expression of this isotopic excursion within the johnnie oolite a 2 m thick marker bed which records the highest rate of change in 13 c sedimentologically the oolite unit is thought to be time transgressive if the isotopic excursion reflects time series behavior of the carbon cycle its expression in the oolite across the basin should systematically align the sections according to their slight diachroneity detailed carbon and oxygen isotopic stratigraphy of the oolite at seven different locations indicates the magnitude of the excursion at the base of the oolite is spatially variable such that after a palinspastic reconstruction the sections align along a systematic north to south gradient in the isotopic data the oolite preserved in the old dad mountains the most southerly section measured is an outlier to this trend and the most difficult to ordinate accurately in the reconstruction showing the largest isotopic range between the onset of carbonate deposition and top of the oolite several hypotheses are congruent with these data but the sum of observations is best explained by a scenario wherein the oolite is time transgressive and deposited in a north to south manner throughout the onset of the isotopic excursion if correct this implies that the stratigraphic 13 c pattern reflects time series behavior of marine dic

isotope stratigraphy of the ediacarian neoproterozoic iii of the adelaide rift complex australia and the overprint of water column stratification abstract this study establishes a high resolution 13c chemostratigraphic framework for the type ediacarian terminal proterozoic section in the adelaide rift complex a framework that contributes to the emerging global chronostratigraphic synthesis of a period that saw momentous changes in the earth s surface environment only 15 m of the 3 5 km thick type section consists of shallow water carbonates of the kind that have formed the basis of most previous studies of neoproterozoic chemostratigraphy however the organic 13corg record reveals a surprising richness of information and shows excellent utility in correlation between sections in the adelaide rift complex lateral variations in 13corg profiles correspond to expected diachronous patterns of basin fill with the addition of 87sr 86sr data correlation can also be made to the officer and amadeus basins consistent with known lithostratigraphic and sequence stratigraphic constraints sublittoral micritic carbonates of the upper nuccaleena formation cap dolostone and lower and middle wonoka formation show strong basinwide 13c depletion 13ccarb 3 to 10 despite compelling evidence for preservation of depositional 13ccarb such as good textural preservation evidence for sea floor lithification and in the wonoka formation pristine 87sr 86sr and low mn sr associated with the depleted carbonates are rare subaqueous evaporite relatively heavy 13corg and anomalously 13c depleted organic carbon of benthic microbial mat origin and a common cause salinity stratification of the water column is postulated the indicated palaeogeographic setting an evaporative mediterranean like basin tenuously connected to the world ocean is entirely consistent with previous suggestions of one or more messinian type desiccation events to explain very deep 1 km incised valleys or canyons in the adelaide rift complex and officer basin at horizons within the wonoka formation and correlates positive excursions in 13corg during basin stratification may in part be due to 12c depletion of surface waters by photosynthetic carbon fixation despite the proposed semi isolation of australian ediacarian basins from the world ocean major 13c excursions which can to some extent be differentiated by the monotonic rise in ediacarian marine 87sr 86sr appear to be correlatable to the upper windermere supergroup northwest canada

eight armed ediacara fossil preserved in contrasting taphonomic windows from china and australia we report the preservation of the eight armed ediacara fossil eoandromeda octobrachiata as carbonaceous compressions in the doushantuo black shale of south china and as casts and molds in the rawnsley quartzite in south australia the contrasting preservational styles in two taphonomic windows indicate that e octobrachiata may have had a relatively recalcitrant organic integument which rules out its close comparison with giant agglutinated foraminifers such as xenophyophores its octaradial symmetry and dextrally spiraling arms suggest that it may be a diploblastic grade animal sharing some features with cnidarians and ctenophores although its phylogenetic affinity remains open it is the first and only unambiguously identified ediacaran macrofossil that occurs in two drastically different taphonomic windows thus bridging the conventional biological and taxonomic gaps between the ediacara and miaohe biotas which collectively record the earliest known macroscopic and complex life

redox architecture of an ediacaran ocean margin integrated chemostratigraphic δ13c δ34s 87sr 86sr ce ce correlation of the doushantuo formation south china abstract early diagenetic silicification and phosphatization of the ediacaran doushantuo formation ca 635 to 551 ma in south china offer extraordinary taphonomic windows into the early evolution of multicellular eukaryotes including various algal groups and potentially animals in order to understand how the ecological and taphonomic distribution of these ediacaran eukaryotes was controlled by oceanic redox conditions it is critical to reconstruct the redox architecture of the sedimentary basin recently two alternative redox models have been proposed to account for the geochemical and sedimentary features of the doushantuo formation one argues that the unit was deposited on a continental margin where a metastable sulfidic wedge was dynamically maintained by a sulfate concentration gradient between shelf and basinal environments the other contends that the sulfidic water mass was largely restricted to the intra shelf basin behind a rimmed margin these two models make different predictions about the stratigraphic completeness and correlation of the doushantuo formation to test these predictions we generated high resolution time series trends of multiple isotopic and elemental tracers including 34s 87sr 86sr and ce ce to facilitate an integrated chemostratigraphic correlation between inner shelf xiaofenghe intra shelf jiulongwan and outer shelf yangjiaping and zhongling sections our correlations suggest that both the inner and outer shelf sections are stratigraphically incomplete relative to the intra shelf section the euxinic wedge model should be reconsidered insofar as it is based on a miscorrelation between sections viewed from our revised chemostratigraphic framework euxinic conditions on the platform appear to have been largely restricted to the intra shelf basin carbonates in the upper doushantuo formation at jiulongwan and their stratigraphic equivalents are characterized by a profound negative carbon isotope anomaly i e the shuram excursion coincident with a drop in pyrite sulfur isotope values and a significant rise in 87sr 86sr from 0 7080 to 0 7090 the integrated stratigraphic data from south china suggest that the onset of the shuram excursion is associated with enhanced oxidative continental weathering that delivered radiogenic strontium as well as sulfate to the ediacaran basin

uranium and molybdenum isotope evidence for an episode of widespread ocean oxygenation during the late ediacaran period abstract to improve estimates of the extent of ocean oxygenation during the late ediacaran period we measured the u and mo isotope compositions of euxinic anoxic and sulfidic organic rich mudrocks orm of member iv upper doushantuo formation south china the average 238 u of most samples is 0 24 0 16 2sd relative to standard crm145 which is slightly higher than the average 238 u of 0 02 0 12 for restricted black sea deep water unit i euxinic sediments and is similar to a modeled 238 u value of 0 2 for open ocean euxinic sediments in the modern well oxygenated oceans because 238 u is preferentially removed to euxinic sediments compared to 235 u expanded ocean anoxia will deplete seawater of 238 u relative to 235 u ultimately leading to deposition of orm with low 238 u hence the high 238 u of member iv orm points to a common occurrence of extensive ocean oxygenation ca 560 to 551 myr ago the mo isotope composition of sediments deposited from strongly euxinic bottom waters h 2 s aq 11 m either directly records the global seawater mo isotope composition if mo removal from deep waters is quantitative or represents a minimum value for seawater if mo removal is not quantitative near the top of member iv 98 mo approaches the modern seawater value of 2 34 0 10 high 98 mo points to widespread ocean oxygenation because the preferential removal of isotopically light mo to sediments occurs to a greater extent in o 2 rich compared to o 2 deficient marine environments however the 98 mo value for most member iv orm is near 0 relative to standard nist srm 3134 0 25 suggesting extensive anoxia the low 98 mo is at odds with the high mo concentrations of member iv orm which suggest a large seawater mo inventory in well oxygenated oceans and the high 238 u hence we propose that the low 98 mo of most member iv orm was fractionated from contemporaneous seawater possible mechanisms driving this isotope fractionation include 1 inadequate dissolved sulfide for quantitative thiomolybdate formation and capture of a seawater like 98 mo signature in sediments or 2 delivery of isotopically light mo to sediments via a particulate fe mn oxyhydroxide shuttle a compilation of mo isotope data from euxinic orm suggests that there were transient episodes of extensive ocean oxygenation that break up intervals of less oxygenated oceans during late neoproterozoic and early paleozoic time hence member iv does not capture irreversible deep ocean oxygenation instead complex ocean redox variations likely marked the transition from o 2 deficient proterozoic oceans to widely oxygenated later phanerozoic oceans

evaluation of the seasat wind scatterometer surface wind velocities have been derived from backscatter measurements of the ocean surface made by a satellite borne microwave sensor comparisons with high quality surface based measurements obtained during the joint air sea interaction experiment are described the accuracy of the scatterometer winds at this mid latitude site or 1 6 m s in speed and or 18 deg in direction for winds between 3 and 16 m s is within the design specification

interactions between ediacaran animals and microbial mats insights from lamonte trevallis a new trace fossil from the dengying formation of south china abstract a new ichnogenus and ichnospecies lamonte trevallis is formally described from the shibantan member limestone of the upper ediacaran dengying formation yangtze gorges area south china it is characterized by horizontal tunnels connected with short vertical burrows and surface trails the horizontal burrows are elliptical or bilobed in transverse cross section preserved in full relief and filled with carbonate intraclasts micrites as well as calcite and silica cements they occur exclusively in silty crinkled and microlaminated layers that are interpreted as amalgamated cyanobacterial microbial mats no burrows have been found in intraclastic layers adjacent to the microlaminated layers the vertical traces are filled with the same material as the burrows but they typically project through the crinkled microlaminae and are exposed on the bedding surface the surface tracks are always preserved in negative epirelief or positive hyporelief and consist of two parallel series of either sharp scratch marks or small knobs the burrow infill has 18ocarb and 13ccarb values distinct from but intermediate between microlaminated and intraclastic layers consistent with petrographic observation that burrow infill consists of a mixture of early carbonate cements intraclasts and micrites bedding plane bioturbation intensity 20 40 measured as percentage of bedding plane area covered by l trevallis traces is comparable to similar measurements in pre trilobite cambrian carbonates the exclusive occurrence of l trevallis within microbial mats may have both taphonomic and ecological significance these mats may have provided firm substrates and localized geochemical conditions that contributed to the structural integrity of the burrows and they may have also facilitated early diagenetic cementation of burrow infill thus facilitating burrow preservation the close association of these burrows with microbial mats implies that the trace producers actively mined cyanobacterial mats to exploit oxygen or nutrient resources the trace makers of l trevallis were better able to utilize the resources around them than many other ediacaran trace makers and provide an ichnological record of a flourishing benthic ecology in late ediacaran oceans at the dawn of the agronomic revolution

the interactions of gravity waves with mesocyclones preliminary observations and theory abstract apparent interactions between ducted gravity waves and preexisting mesocyclones are investigated preliminary analyses of weather surveillance radar 1988 doppler wsr 88d observations from several cases reveal that the intersection of fine lines whose propagation speed is consistent with that of gravity waves and existing mesocyclones leads to an increase in the rotational velocity of the mesocyclone utilizing simplified ducted wave kinematics and the vorticity equation changes in vorticity associated with convergence divergence and perturbation wind shear within the gravity wave are examined convergence ahead of wave ridges may be significant causing mesocyclone intensification through vorticity stretching it will also be shown that a wave may significantly change the vertical wind shear and streamwise vorticity in storm inflow a simple one dimensional model is presented which shows that vorticity decreases temporarily ahead of the wave ridge then increases rapidly behind the ridge as

nested model simulation of moist convection the impact of coarse grid parameterized convection on fine grid resolved convection future generation operational weather prediction systems will likely include storm scale limited area models that will explicitly resolve convective precipitation however the high resolution convection resolving grids will need to be embedded or nested within coarser resolution grids that will provide lateral boundary conditions it is the purpose of this study to illustrate how the convective environment on a convection resolving stormscale model grid and therefore the convection itself can be significantly influenced by the treatment of convection on the coarser grids within which the fine grid is embedded it was confirmed that as in the actual atmosphere mass field adjustments resulting from convection in one area the outer grids in this case affect the convection in other areas the inner convection resolving grid that is the errors in precipitation timing precipitation intensity and the vertical distribution of latent heating associated with the treatment of convection on the outer grids greatly affect the explicit convection on the inner grid in this case the different precipitation parameterizations on the outer two grids produce up to a factor of 3 difference in the 24 h amount of explicit rainfall simulated on the inner grid even when the parameterization is limited to only the outer grid with explicit precipitation on both the middle and inner grids over a factor of 2 difference in 24 h total explicit rainfall is produced on the inner grid the different precipitation parameterizations on the outer grids appear to differently modulate the intensity and the timing of the explicit convection on the inner grid through induced subsidence

integrated ediacaran sinian chronostratigraphy of south china abstract the ediacaran period was a critical time in the history of life and earth understanding the complex interactions between geological and biological events during this interval requires high resolution chronostratigraphy thanks to its uniquely favorable palaeogeographic setting south china is an ideal region for constructing a framework for global chronostratigraphic correlation of ediacaran strata here continuous ediacaran successions contain both siliciclastic and carbonate rocks that range from shallow to deep marine and contain rich fossil assemblages showing a variety of preservation styles as part of the present study 62 reference sections distributed throughout the yangtze platform were investigated analyses of the sedimentary facies and sequence stratigraphy of more than 40 sections revealed four major sequences in the shallow marine facies three major sequence boundaries occur respectively in the middle and upper parts of the doushantuo formation and in the middle part of the dengying formation subdivision and correlation of the ediacaran successions of the yangtze platform based on sequence stratigraphy is congruent with the carbon isotope chemostratigraphy of 12 reference sections 1075 samples the sequence boundary sb2 in the middle part of the doushantuo formation is suggested here as the lower xiadongian upper yangtzean series boundary of the ediacaran which coincides with several globally recognizable events namely 1 the end of the neoproterozoic glaciations 2 the first appearance of animals 3 the sudden increase in the diversity of acanthomorphic acritarchs and 4 a negative 13 c excursion the ediacaran system of south china may be subdivided into five stages furthermore the criteria for defining these stages may be applicable throughout the world also the composite carbon isotope profile of the ediacaran of south china can be used as a global reference for chronostratigraphic subdivision and correlation in addition to the globally recognizable negative 13 c excursion in the cap carbonate at the base of the ediacaran the negative 13 c excursion in the uppermost doushantuo wonoka shuram interval represents another globally correlatable major excursion the positive 13 c excursion immediately following the uppermost doushantuo excursion and ending at 548 ma is also useful for global correlation current ediacaran chronostratigraphy and global correlations indicate that the upper doushantuo wonoka shuram negative 13 c excursion ranges from ca 560 ma to 551 ma and therefore coincides with the evolutionary renovation of life feedback between evolutionary innovation and geochemical cycling was the key mechanism for this unique and most strongly negative 13 c excursion in earth history our chronostratigraphic correlations also imply that the earliest known metazoan biotas namely the weng an and characteristic ediacaran biotas do not constitute two temporally separate evolutionary lineages as proposed previously but represent two parallel evolutionary pathways preceding the cambrian explosion of animal life

atmospheric origin of the devastating coupled air sea event in the east adriatic enhanced sea level oscillations with devastating effects occurred on 26 27 june 2003 in the east adriatic the phenomenon was recognized as a resonantly coupled air sea interaction where the sea wave is forced by the propagating atmospheric pressure disturbance this study examines the dynamics and predictability of the atmospheric component of the coupled system first the initiation amplification and maintenance of the system are examined the source of the perturbation is traced back to the alpine region where the potentially unstable air in the westerly current lifts over the alps resulting in convection and wave development the wave and convective activity apparently couple in a wave cisk manner and propagate southeastward down the eastern adriatic coast due to the potentially unstable air above the adriatic the system additionally amplifies along its track the dissipation of the system occurs after the landfall second the performance of the numerical model at the resolution that is similar to operational nwp model resolution is examined this severe event is highly susceptible to the details of the model configuration presumably due to the sensitivity in coupling of the wave and mcs thus although the model is able to reproduce and forecast this kind of event at a fairly coarse resolution the details of the spatial structure as well as the time of onset are questionable in this case the greatest sensitivity is primarily in the treatment of moist and convective processes

integrated chemostratigraphy of the doushantuo formation at the northern xiaofenghe section yangtze gorges south china and its implication for ediacaran stratigraphic correlation and ocean redox models abstract the ediacaran doushantuo formation in the yangtze gorges of south china plays an important role in our understanding of biological evolution global correlation and ocean redox conditions because of the availability of high resolution paleontological and geochemical data and numerous radiometric dates however integrated study has been focused on the jiulongwan section that was largely deposited below wave base in a restricted shelf lagoon jiang et al 2011 zhu et al 2011 studies of shallower water successions are lacking and this presents a challenge to test ediacaran stratigraphic correlation and ocean redox models to fill this knowledge gap we conducted a high resolution integrated study of the doushantuo formation at the northern xiaofenghe nxf section approximately 35 km to the northeast and paleogeographically updip of the jiulongwan section with the exception of the basal 20 m nxf sediments were deposited above normal wave base integrated biostratigraphic and chemostratigraphic data indicate that the 140 m thick nxf section correlates with the lower doushantuo formation member i and much of member ii i e the lower ca 70 m of the formation at jiulongwan geochemical data from nxf and other doushantuo sections indicate that euxinic conditions may have been limited to a shelf lagoon represented by the jiulongwan section that was restricted between the proximal inner shelf and a distal shelf margin shoal complex at least during early doushantuo time following the deposition of the doushantuo cap dolostone further integrated studies are necessary to test whether euxinic conditions existed in open marine shelves in south china and elsewhere during the ediacaran period

the shuram wonoka event recorded in a high grade metamorphic terrane insight from the scandinavian caledonides an approximately 250 m thick polydeformed and polymetamorphosed isotopically unusual variegated marble locally termed the leivset marble shows a great lateral extent in the scandinavian caledonides its extremely 13c depleted primary nature 7 9 1 2 on average n 93 makes the leivset marble unique this together with a high sr content up to 8740 ppm that buffered 87sr 86sr ratios between 0 70802 and 0 70872 suggests correlation with the worldwide shuram wonoka isotopic event occurring within the 600 550 ma time interval during the ediacaran vendian period despite a high grade deformation and metamorphism the leivset marble has retained its original carbon and strontium isotope ratios a combination of the variegated colour with unusually low 13ccarb can potentially be used for stratigraphic correlations in high grade non fossiliferous marble dominated terranes across the caledonian orogenic belt in baltica and laurentia isotope chemostratigraphy has identified a prominent cryptic stratigraphic discontinuity and suggests that the ediacaran leivset marble was tectonically juxtaposed above low grade llandovery age fossiliferous marbles during the scandian orogeny

dynamic changes in sulfate sulfur isotopes preceding the ediacaran shuram excursion large excursions in 13 c and 34 s are found in sedimentary rocks from the ediacaran period that may provide detailed mechanistic information about oxidation of earth s surface however poor stratigraphic resolution and diagenetic concerns have thus far limited the interpretation of these records here we present a high resolution record of carbon and sulfur isotopes from the khufai formation leading up to and including the onset of the shuram carbon isotope excursion we document large coherent excursions in the sulfur isotope composition and concentration of carbonate associated sulfate cas that occur both independently and synchronously with the carbon isotope excursion isotopic changes appear decoupled from major stratigraphic surfaces and facies changes suggesting regional or global processes rather than local controls our data suggest that very low marine sulfate concentrations are maintained at least through the middle khufai formation and require that the burial fraction of pyrite and the fractionation factor between sulfate and pyrite necessarily change through deposition reconciliation of simultaneous up section increases in marine sulfate concentration and 34 s cas requires the introduction of strongly 34 s enriched sulfate possibly from weathering of cryogenian and earlier ediacaran 34 s enriched pyrite our analysis of the onset of the shuram carbon isotope excursion observed in stratigraphic and lithologic context is not consistent with diagenetic or authigenic formation mechanisms instead we observe a contemporaneous negative excursion in sulfate 34 s suggesting linked primary perturbations to the carbon and sulfur isotope systems this work further constrains the size isotopic composition and potential input fluxes of the ediacaran marine sulfate reservoir placing mechanistic constraints on possible drivers of extreme isotopic perturbations during this critical period in earth history

multi sensor observations of a wave beneath an impacting rear inflow jet in an elevated mesoscale convective system observations of a wave generated below and propagating with an elevated mesoscale convective system mcs are presented the mcs and the wave tracked directly across the 90 km extent of the observational network deployed for the convective storm initiation project csip and maintained a coherent structure and velocity during this 1 5 hour period the rear inflow jet of the mcs was observed to impact upon but not penetrate the stable undercurrent that was located beneath the mcs apparently constricting the depth of the undercurrent which did not participate in the main convective updraught the wave crest was located approximately 15 km ahead of this constriction the overall wave led to between 200 and 1000 m of ascent and approximately 1500 m of descent however undulations were superimposed on the overall wave with a wavelength of approximately 7 km and a crest totrough amplitude of approximately 1000 m these undulations were associated with double maxima in surface pressure and the elevation of the observed low level wind anomaly where low level winds were backed by more than 90 t hese winds were never at rest relative to the system and the wave was therefore a gravity wave without stagnation the hydrostatic effect expected from the observed lifting in the wave was broadly consistent with the observed surface pressure perturbation of 2 hpa no cold pool outflow was ever observed instead the observed surface cooling of approximately 4 c was shown to be consistent with reduced solar insolation the generation of the observed wave structure and its implications for the maintenance of the mcs and numerical modelling of the system are discussed copyright c

mesoscale convective systems 1 mesoscale convective systems mcss have regions of both convective and stratiform precipitation and they develop mesoscale circulations as they mature the upward motion takes the form of a deep layer ascent drawn into the mcs in response to the latent heating and cooling in the convective region the ascending layer overturns as it rises but overall retains a coherent layer structure a middle level layer of inflow enters the stratiform region of the mcs from a direction determined by the large scale flow and descends in response to diabatic cooling at middle to low levels a middle level mesoscale convective vortex mcv develops in the stratiform region prolongs the mcs and may contribute to tropical cyclone development the propagation of an mcs may have a discrete component but may further be influenced by waves and disturbances generated both in response to the mcs and external to the mcs waves of a larger scale may affect the propagation velocity by phase locking with the mcs in a cooperative mode the horizontal scale of an mcs may be limited either by a balance between the formation rate of convective precipitation and dissipation of stratiform precipitation or by the rossby radius of the mcv the vertical redistribution of momentum by an mcs depends on the size of the stratiform region while the net vertical profile of heating of the large scale environment depends on the amount of stratiform rain regional variability of the stratiform rain from mcss affects the large scale circulation s response to mcs heating

anomalous wind estimates from the seasat scatterometer the seasat a satellite scatterometer sass measured the radar backscatter intensity from the sea surface using a four beam microwave antenna1 3 estimates of wind speed and direction derived from these data agree well with surface measurements made during the joint air sea interaction jasin experiment4 6 but there are occasions 3 out of 23 satellite passes when the results are anomalous we have now studied one such occasion when the satellite measurements differed substantially from those at the surface of the sea and conclude that the interpretation of the sass measurements may have been vitiated by a mid level convective system deep enough to produce thunderstorms and lightning

palaeoenvironment and carbon isotope stratigraphy of upper proterozoic carbonates of the yangtze platform the 13c values for phanerozoic marine carbonates display secular trends mainly in the range 1 to 2 1 these have been interpreted as primary features reflecting changes in the carbon isotope composition of dissolved bicarbonate in seawater brought about largely by variations in the proportions of carbon being sequestered in the oxidized and reduced carbon reservoirs1 2 carbon isotope trends are not as well established for the precambrian but there are indications that upper proterozoic sequences contain carbonates with unusually high 13c values3 9 here we present the results of the first carbon isotopic study of the upper proterozoic carbonate strata from the type locality of the sinian system in the yangtze gorges sections near yichang south china and discuss their implications for accumulation of organic matter we also compare the results for these chinese strata with 13c trends in other upper proterozoic cambrian sequences and assess the extent to which such isotopic data can be used to make stratigraphic correlations between widely spaced sequences

high resolution biostratigraphic and chemostratigraphic data from the chenjiayuanzi section of the doushantuo formation in the yangtze gorges area south china implication for subdivision and global correlation of the ediacaran system intensive investigations on the doushantuo formation of south china have greatly advanced our understanding of the evolution of multicellular life and the atmospheric oceanic system during the ediacaran period particularly the well established carbon isotope profile and rich acritarch microfossils from the composite carbonate and shale successions of the yangtze gorges area provide potential for chronostratigraphic subdivision and global correlation of the ediacaran system here we present high resolution biostratigraphic and carbon isotope data from a well exposed section the chenjiayuanzi section in the yangtze gorges area the bio and chemostratigraphic data confirm the presence of three distinct negative and two positive 13c excursions and two characteristic assemblages of acanthomorphic acritarchs the lower tianzhushania spinosa assemblage and upper hocosphaeridium scaberfacium hocosphaeridium anozos tanarium conoideum tanarium anozos in liu et al 2013 assemblage within the doushantuo formation the results demonstrate the clear stratigraphic relationship between the acritarch assemblages and carbon isotope excursions of the doushantuo formation and that the last occurrence of acanthomorphic acritarchs in the chenjiayuanzi section represents the last occurrence datum found so far in the yangtze gorges of south china four stratigraphic markers are suggested here for defining chronostratigraphic boundaries of the ediacaran system based on bio and chemostratigraphy combined with intra and interbasinal correlation in particular the base of the most significant and distinctive carbon isotope excursion dounce at the top of the doushantuo formation which is equivalent to the shuram wonoka event elsewhere shows potential to be a marker to define the series lower and upper boundary of the ediacaran system because it also marks the extinction of the ediacaran acanthomorphic acritarchs

numerical simulation and analysis of a prefrontal squall line part ii propagation of the squall line as an internal gravity wave abstract a numerical study of the squall line that occurred on 17 18 june 1978 was described in part i of this paper the squall line was collocated with a surface front during its initial development at 0000 utc 18 june 1978 but then propagated faster than the front resulting in a separation of approximately 200 km by 0300 utc and 300 400 km by 0600 utc in this paper part ii the movement of the squall line in the model is shown to be due to the propagation of a deep tropospheric internal gravity wave in a wave cisk like conditional instability of the second kind process the thermal and dynamic perturbations associated with the hypothesized wave are shown to be consistent with internal gravity wave theory and the characteristics of the wave are compared to similar results from other wave cisk studies the current literature favors the mechanism of gust front convergence to explain squall line propagation although there are other modeling studies that show specific instances of squall line pro

origin evolution and finescale structure of the st valentine s day mesoscale gravity wave observed during storm fest part iii gravity wave genesis and the role of evaporation abstract on 14 february 1992 a long lived moderate amplitude mesoscale gravity wave formed in kansas during the storm scale operational and research meteorology fronts experiment systems test storm fest wave formation was evident in correlated surface pressure and wind fields the wave of depression accompanied by a weak rainband tracked across the state a wealth of data was collected on the mature wave as it passed over the storm fest dual doppler domain however the mechanism of genesis remained difficult to ascertain since wave formation occurred in a region of less comprehensive observations the genesis of the storm fest gravity wave is successfully simulated using the fifth generation pennsylvania state university national center for atmospheric research penn state ncar mesoscale model mm5 which was run at 6 km grid spacing in the innermost domain the lee cyclone movement dry airmass development and gravity wave formation over kansas were successfully captured by the model results

dynamic redox conditions control late ediacaran metazoan ecosystems in the nama group namibia the first appearance of skeletal metazoans in the late ediacaran 550 million years ago ma has been linked to the widespread development of oxygenated oceanic conditions but a precise spatial and temporal reconstruction of their evolution has not been resolved here we consider the evolution of ocean chemistry from 550 to 541 ma across shelf to basin transects in the zaris and witputs sub basins of the nama group namibia new carbon isotope data capture the final stages of the shuram wonoka deep negative c isotope excursion and these are complemented with a reconstruction of water column redox dynamics utilising fe s c systematics and the distribution of skeletal and soft bodied metazoans combined these inter basinal datasets provide insight into the potential role of ocean redox chemistry during this pivotal interval of major biological innovation the strongly negative 13c values in the lower parts of the sections reflect both a secular global change in the c isotopic composition of ediacaran seawater as well as the influence of local basinal effects as shown by the most negative 13c values occurring in the transition from distal to proximal ramp settings critical though is that the transition to positive 13c values postdates the appearance of calcified metazoans indicating that the onset of biomineralization did not occur under post excursion conditions significantly we find that anoxic and ferruginous deeper water column conditions were prevalent during and after the transition to positive 13c that marks the end of the shuram wonoka excursion thus if the c isotope trend reflects the transition to global scale oxygenation in the aftermath of the oxidation of a large scale isotopically light organic carbon pool it was not sufficient to fully oxygenate the deep ocean both sub basins reveal highly dynamic redox structures where shallow inner ramp settings experienced transient oxygenation anoxic conditions were caused either by episodic upwelling of deeper anoxic waters or higher rates of productivity these settings supported short lived and monospecific skeletal metazoan communities by contrast microbial thrombolite reefs found in deeper inner and mid ramp settings supported more biodiverse communities with complex ecologies and large skeletal metazoans these long lived reef communities as well as ediacaran soft bodied biotas are found particularly within transgressive systems where oxygenation was persistent we suggest that a mid ramp position enabled physical ventilation mechanisms for shallow water column oxygenation to operate during flooding and transgressive sea level rise our data support a prominent role for oxygen and for stable oxygenated conditions in particular in controlling both the distribution and ecology of ediacaran skeletal metazoan communities

chemostratigraphic and sedimentological framework of the largest negative carbon isotopic excursion in earth history the neoproterozoic shuram formation nafun group oman abstract oman records in its neoproterozoic nafun group huqf supergroup an essentially complete carbonate rich ediacaran succession the nafun group overlies the presumed marinoan rift related fiq member ca 635 ma and ends just below the precambrian cambrian boundary 542 ma tectonic subsidence caused by thermal contraction following fiq aged rifting allowed the preservation of about 1 km of postrift stratigraphy with no major stratigraphic breaks the nafun group above the marinoan cap carbonate hadash formation represents two siliciclastic to carbonate grand cycles both initiated by significant transgressions these cycles comprise the masirah bay khufai formations and the shuram buah formations the khufai shuram boundary is associated with the start of a major carbon isotope perturbation the uppermost ramp carbonates of the khufai formation record a smooth decrease in 13c from about 4 to values around 0 followed by two descending steps across which values plunge to a nadir of 12 in the overlying red siltstones and shales interbedded with thin limestones of the shuram formation this fall in isotopic values is temporally rapid and coincident in both shallow and deep water sections in the time span of a single parasequence the 13c nadir is then followed by 50 million years of monotonic recovery the shuram shift represents the largest 13c inorganic carbon negative excursion in earth history although the snowball earth theory links periods of depleted carbon isotopic ratios with periods of global glaciation the non glaciated context of the shuram formation suggests that the causal relationship between global glaciation and negative carbon isotopic excursions is non unique although the precise mechanism driving this major perturbation of the carbon cycle remains enigmatic the long term remineralization of an isotopically depleted organic carbon reservoir in ocean water is a promising candidate

two day disturbances in the equatorial western pacific from november 1992 to february 1993 westward propagating disturbances with scales of 1000 1500 km frequented the equatorial western pacific they propagated at about 16 m s 1 and their passage was accompanied by a two day oscillation in high cloudiness their convection was most intense when the lower troposphere was cool and the level of free convection was relatively low the disturbances propagated westward at about 18 m s 1 faster than the lower tropospheric flow this rapid propagation may have been the result of a coupling between the disturbance s convection and the 20 m s 1 vertical mode the signal of this mode was apparent in vertical profiles of temperature and wind and the most intense convection began when the mode dynamically cooled the lower troposphere lowering the level of free convection

carbon isotope chemostratigraphy and sedimentary facies evolution of the ediacaran doushantuo formation in western hubei south china abstract the doushantuo formation of south china consisting of intercalated siliciclastic and carbonate rocks which exhibit considerable variation in thickness and sedimentary facies is one of the key sedimentary units in the world for understanding ediacaran geobiological processes however stratigraphic correlation and sedimentary facies evolution of the doushantuo formation remain controversial sedimentary facies analysis of the well known sections of the yangtze gorges area and new sections in northern yichang western hubei indicate that the doushantuo succession in the yangtze gorges area was deposited in an offshore intra shelf basin within the yangtze platform in contrast the doushantuo formation in the northern yichang area which is characterized by one or a few phosphate rich horizons represents deposition on the subtidal or intertidal shelf and so is similar to the succession in the weng an area central guizhou province the carbon isotope profiles of the different sections exhibit significant variation which is interpreted to result from facies differences sequence and high resolution carbon isotope stratigraphy have clarified problematic correlations and the temporal relationship between fossil assemblages of the doushantuo formation on the yangtze platform the results confirm that a prominent negative 13ccarb excursion baince nadir down to 5 in the middle portion of the second sequence of the doushantuo formation is a widely traceable event baince together with three other 13ccarb excursions namely cance at the base wance near the first sequence boundary near the middle and dounce at the top of the doushantuo formation constitute a complete carbon isotope profile for the doushantuo formation that reflects contemporaneous seawater and so serves as a reference chemostratigraphic profile for global stratigraphic correlation and for evaluating the chemical evolution of seawater during the ediacaran period

verification studies of seasat a satellite scatterometer sass measurements comparisons are made between the seasat a satellite scatterometer sass data and surface truth gathered from the gulf of alaska seasat experiment goasex and the joint air sea interaction jasin program one comparison attempts to evaluate the performance of sass irrespective of the algorithms employed to convert sass data to geophysical parameters this is accomplished by separating the backscatter measurements into small bins of incidence and azimuth angles and polarity and regressing against wind speed measurements the algorithms themselves are tested by comparing their predicted slopes and y intercepts with those derived from the regressions the algorithms are further tested by comparing each sass backscatter measurement with the backscatter derived from the algorithms given wind velocity from the observations results of the comparisons show that sass becomes insensitive to winds at high incidence angles for horizontal polarizations for other angles fairly high correlations exist between backscatter and wind speeds the algorithms are shown to function well at midranges of incidence angle and backscattering coefficient failure to predict accurately at the extremes may be attributed to saturation of the sensor at these values another study shows that averaging the backscatter from two orthogonal beams produces a result which is essentially independent of wind direction and correlates well with the observed wind speed results also fail to favor any particular parameterization of the surface wind

summary of the jasin 1978 field experiment jasin was designed to observe the physical processes causing mixing and to quantify aspects of the heat and momentum budgets in mid latitude oceanic and marine atmospheric boundary layers the multiplicity of processes to be sampled necessitated a large experiment and jasin involved 14 ships and 3 aircraft with more than 50 teams of investigators from 9 countries the experiment took place from july to september 1978 in the north rockall trough an area of deep water several hundred kilometres off the west coast of scotland hydrographic surveys revealed eddies 100 km across and intensive measurements on smaller scales revealed fronts in the confluence zones of the eddy field the development of the mixing layer and seasonal thermocline internal and inertial wave fields and the ekman response to winds are all complicated by the fronts and eddies the atmospheric boundary layer on scales of 200 km was non steady and inhomogeneous surface generated turbulence occupied the subcloud layer and transfers through the cloud layer occurred on scales greater than 50 km or intermittently possible driving factors were the variability in surface fluxes near the oceanic mesoscale eddies radiative processes in the cloud layer and condensation processes the lifting of warm sector boundary layer air from widely differing sources into the free atmosphere at a front resulted in well mixed moist layers that exhibited near thermal wind equilibrium

evolution of neoproterozoic wonoka shuram anomaly aged carbonates evidence from clumped isotope paleothermometry the wonoka shuram anomaly represents the largest negative carbon isotope excursion recognized in the geologic record and is associated with the emergence and diversification of metazoan life ca 580 million years ago ma the origin of the anomaly is highly debated with interpretations ranging from primary to diagenetic each having unique and potentially transformative implications for early life here we apply carbonate clumped isotope thermometry to three sections expressing the anomaly in order to constrain mineral formation temperatures and thus directly calculate water oxygen isotope compositions 18ow with which carbonate minerals equilibrated with 18ow known it is possible to address previous hypotheses for the origin of the anomaly in each section precipitation temperatures correlate positively with reconstructed 18ow previous hypotheses based on the covariance of 18ocarb vs 13ccarb uncorrected for temperature effects suggested a meteoric diagenetic origin for the anomaly however reconstructed 18ow values do not covary with carbon isotope compositions 13ccarb within anomaly facies rather the oxygen isotope and temperature data are consistent with carbonate recrystallization and equilibration under increasingly rock buffered conditions based on simple modeling and comparison to modern formation fluids recrystallization may have occurred in an environment far removed from the initial depositional or early diagenetic regime in addition although clumped isotope temperatures vary significantly and reach elevated values consistent with burial diagenesis it is unclear to what degree if at all carbon isotope values were reset during recrystallization ultimately these new data indicate that wonoka shuram aged carbonates experienced equilibration with fluids under increasingly closed system conditions the clumped isotope data do not provide a means to distinguish previous hypotheses outright but provide additional context for the evaluation of geochemical signatures within these ancient carbonate rocks

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

the shuram and subsequent ediacaran carbon isotope excursions from southwest laurentia and implications for environmental stability during the metazoan radiation current understanding of secular changes in the carbon isotopic composition of mid to late ediacaran carbonates suggests a relatively long steady recovery of the global ocean from the shuram negative excursion followed by a smaller negative excursion at the precambrian cambrian boundary new radiometric stratigraphic and carbon isotope data from thick exposures of the upper johnnie formation in the panamint range of eastern california combined with data from carbonate rich facies of the stirling quartzite in the funeral mountains confirm an ediacaran age for these strata and provide a more complete record of isotopic variations during this time interval than previously determined from sw laurentia and other key sections around the globe a siltstone in the lower part of the johnnie formation yielded a detrital zircon grain with an age of 640 33 0 09 ma lowering the maximum radiometric age constraint on the johnnie formation by 400 m y consistent with an ediacaran age based on chemo and biostratigraphic data in contrast to previous c isotope compilations from this region which were generally based on relatively thin portions of the cordilleran miogeocline near its depositional hinge the more basinward exposures exhibit a recovery from values near 12 to 0 within the upper part of the johnnie formation details in the shape of the chemostratigraphic profile through the upper johnnie formation closely match those in profiles through the wonoka formation in south australia which lies above the basal ediacaran global stratotype section and point and the shuram buah interval in oman confirming temporal correlation and suggesting genesis through changes in the isotopic composition of the global ocean the shuram excursion in sw laurentia is followed by at least three smaller ediacaran to earliest cambrian isotopic excursions recorded within from oldest to youngest the uppermost johnnie formation the middle stirling quartzite and the lower wood canyon formation these data indicate that the negative excursion associated with the base of the cambrian is not a unique post shuram event and that post shuram pre cambrian animal evolution occurred in an environment of repeated large magnitude fluctuations in the carbon isotopic composition of the global ocean

the stratigraphic complexity of the middle ediacaran carbon isotopic record in the yangtze gorges area south china and its implications for the age and chemostratigraphic significance of the shuram excursion abstract the middle ediacaran shuram excursion represents the most pronounced negative carbon isotopic shift in earth history and has been considered as evidence for a profound disturbance to the global carbon cycle and proposed as a key chemostratigraphic marker for ediacaran stratigraphic subdivision and global correlation previous study has revealed a pronounced negative 13c shift en3 in the upper doushantuo formation of south china which has been interpreted as an equivalent of the shuram excursion detailed 13c investigation of multiple sections of the ediacaran doushantuo formation around the huangling anticline western hubei province south china indicates that the 13c variation in the upper doushantuo formation is more complex than previously reported in the western region of the huangling anticline a moderately positive 13c excursion here termed the diaoyapo positive excursion bisects two strongly negative 13c excursions here termed the jiuqunao negative excursion and the younger miaohe negative excursion with a 551 ma ash bed capping the miaohe negative excursion in the central region there is only one negative 13c excursion whereas in the eastern region the negative 13c excursion is absent the variable stratigraphic expression of these 13c excursions is most parsimoniously interpreted as reflecting local facies variation diagenesis and or a cryptic unconformity the more complete but more complex 13c chemostratigraphic record in the western region of huangling anticline implies that depending on how this record is correlated with the shuram excursion the latter may be significantly older than 551 ma if it does represent a global chemostratigraphic marker