snow megadune fields on the east antarctic plateau extreme atmosphere ice interaction large dune fields occupy more than 500 000 km 2 of the east antarctic plateau the megadunes or long wavelength surface ripples have amplitudes of only a few meters wavelengths of a few kilometers and parallel crests which can extend one hundred kilometers they occur in areas characterized by low accumulation extensively recrystallized snow and strong scattering of the microwave part of the spectrum dune crests are oriented perpendicular to the regional katabatic wind direction snow megadunes are unlikely to be formed by simple wind transport of snow particles

origin of minor limestone shale cycles climatically induced or diagenetic the opinion is widely held that each limestone bed in minor limestone shale cyclic sequences however modified subsequently by diagenesis reflects an environmental event on the assumption that this is true attempts have recently been made to relate limestone shale cycles to climatic variations affected by milankovitch orbital cycles a test is proposed and illustrated mainly with reference to the blue lias formation of dorset england that appears to indicate that many limestones can be produced solely by rhythmic unmixing of caco 3 during diagenesis unless such limestones can be clearly distinguished from those that record genuine environmental signals orbital cycle analysis based on such sequences will give meaningless results

reef development at the frasnian famennian mass extinction boundary a newly compiled global reef database indicates that the 5 6 myr long frasnian late devonian metazoan reef episode had relatively lowdiversity compared to middle devonian highs w ith over 200 genera of calcitic rugose and tabulate corals following an initial early rise after late givetian coral and stromatoporoid extinctions reefs expanded for the last time during mid frasnian sealevel highstands but declined markedly in the late frasnian rhenana linguiformis conodont zones belowthe frasnian famennian f f boundary globally metazoan reefs were wiped out by the end frasnian some famennian reefs while partly retaining the structure of the underlying carbonate platform were built by cyanobacterial consortia such as renalcis rothpletzella girvanella and epiphyton during the famennian foraminiferans with calcite walls became abundant for the first time in the phanerozoic adding a newdimension to carbonate platforms colonial rugose corals phaceloid cerioid and thamnasterioid modules were absent in the early post extinction phases up into the mid famennian and very rare and non reefbuilding later but solitary deep water lazarus corals survived locally coral sponge reefs are unknown from the 21 myr long famennian also a time of very lowplatform carbonate production rare small isolated stromatoporoid sponge and lithistid sponge patch reefs returned episodically during the famennian in north america western europe australia and china the aragonitic stromatoporoids became extinct at the end of the famennian during a late devonian tectonically very active collisional caledonian mountain building phase oceanic and atmospheric cooling accompanied by sealevel lowstand systems exposed most carbonate platforms accelerating coastal erosion and karsting this increased the amount of clastics in the shelf slope setting in the last 1 3 myr prior to the f f boundary often burying reefs immediately following there were protracted losses in nearly all major tropical shelf benthic marine invertebrates exceeded only by the end permian extinctions in severity there is no apparent link between black organic rich horizons and reef demise at or close to the f f boundary the f f boundary not also marks the largest change from widespread flooded early and mid paleozoic continental cratons to narrow distal shelves but also spikes the largest known global phanerozoic shift in atmospheric o2 enrichment and co2 drawdown this threshold matched the rise of the first tropical rainforests and expansion of terrestrial biomes on the tropical coastal lowlands formerly occupied by carbonate platforms 6 2002 elsevier science b v all rights reserved

upper devonian conodont zonation sea level changes and bio events in offshore carbonate facies lali section south china abstract the lali section guangxi province south china is composed of quiet water carbonates containing abundant conodonts which allowed recognition of 12 frasnian and 20 famennian biozones the kellwasser and annulata events are characterized by transgressive black carbonates while the hangenberg event is represented by black shale deposits other transgressive events recognized at lali include the middlesex nehden enkeberg and dasberg as well as the strunian transgression four regressive events were recognized on the basis of lithological and microfacies changes i e the linguiformis regression condroz event velifer regression and the derwer regression these sea level change events were of short duration and globally isochronous based on conodont correlations microfacies analyses and the abundance of palmatolepis indicate that the highest frasnian sea level lies in fz 12 13 upper rhenana zone whereas the highest famennian sea level was in the utahensis zone

the confluence zone of the intense katabatic winds at terra nova bay antarctica as derived from airborne sastrugi surveys and mesoscale numerical modeling the surface wind field inland of the intense coastal kataba c wind regime at terra nova bay antarctica has been studied both observationally and numerically airborne surveys of windinduced features on the snow surface have been used to construct the time averaged winter surface airflow pattern the surface motion field has also been simulated by a mesoscale primitive equation model using terrain slopes with a horizontal resolution of 32 km both methods of analys s demonstrate that the intense katabatic airstream at terra nova bay is forced by converging air currents in the continental interior the broadscale confluence zone becomes organized into two regions within about 180 km of the coast the primary route for katabatic mass transport into the terra nova bay area is reeves glacier valley but an important secondary source is provided by airflow down david glacier the former is generated by the coriolis induced concentration of mass transport on the left side looking downwind of the broadscale confluence zone as well as by the near coastal mountain deflection of airflow into the valley head the confluence zone feeding into david glacier valley stretches over 100 km into the interior and is forced by the broadscale terrain configuration of the ice sheet source areas for the two airstreams differ with reeves glacier valley being fed by cold air formed well into the interior whereas the airflow down david glacier is sustained by radiative cooling over lower parts of the ice sheet which are much closer to the ross sea evaluation of the observational and modeling results reveals both the strengths and weaknesses of each approach airborne surveys of sastrugi orientations are a highly successful method for establishing the detailed pattern of surface airflow however a systematic examination of sastrugi dimensions suggests that such work could also be carried out using spot type satellite observations which is a more cost effective approach than aircraft surveying the double jet structure of katabatic airflow into the terra nova bay area is well represented by the primitive equation modeling but much finer grids are needed to resolve the near coastal drainage details

simulation of the net snow accumulation along the wilkes land transect antarctica with a regional climate model regional climate modelling in conjunction with accumulation measurements collected on antarctic traverses of the international trans antarctic scientific expedition itase is presented as a tool for extending the spatial coverage of field measurements the modelling of part of east antarctica spanned the 7 year epoch 1980 86 where data covering the same period are available the agreement between simulation and observation is improved when a parameterization of the snow surface redistribution processes such as wind erosion is included in the regional climate model the modelled spatial distribution of the net snow mass transported in the boundary layer over coastal east antarctica indicates that this mass is a significant component of the surface mass balance

the surface accumulation and ablation of a coastal blue ice area near cap prudhomme terre adelie antarctica a record of accumulation and ablation from a network of 47 stakes at a coastal blue ice area in terre adelie antarctica is presented and analyzed the record covers early 2004 to early 2006 from 25 field surveys including some in austral winter the two years are very different with a virtually null surface mass balance during the 2004 winter but large accumulation during the 2005 winter a snow ice energy and mass balance model is used to reproduce the accumulation and ablation record a parameterization for snow erosion by wind is included input meteorology is from the european centre for medium range weather forecasts ecmwf analyses and forecasts corrected using 1 year of local meteorological observations from an automatic weather station model results agree reasonably well with the observations wind erosion is the largest contributor to ablation removing much of the precipitation sublimation and to a lesser extent melt runoff together account for 60 cm w e of ablation in 2 years mainly in summer although the record is short it confirms high interannual variability and thus high sensitivity to meteorology and climate monitoring and understanding the mass balance of such coastal blue ice areas may help monitor and detect climate change in the antarctic coastal regions

on the extraordinary katabatic winds of adelie land the winds observed in adelie land eastern antarctica are the strongest observed anywhere on earth close to sea level e g cape denison measured a mean annual wind speed of about 20 m s 1 some historic data from the area are available however such measurements were carried out at different places for different time periods hence in december 1992 we placed four automatic weather stations along the coast of adelie land two in the maximum wind jet port martin and cape denison and one on each side of this jet d 10 close to dumont d urville and penguin point respectively we obtained about three months of good data as on march 25 1993 a strong storm destroyed three of the four wind sensors wind velocities are discussed as a function of other meteorological parameters further the interrelationships between the stations are described some of the findings are 1 the very high wind speeds reported earlier this century are in agreement with our measurements the wind directional constancy is high 2 historic measurements reported cape denison to be the windiest station not only for antarctica but also close to sea level for planet earth again our measurements are in agreement 3 very strong wind speeds have a more down slope direction than weaker ones 4 the general atmospheric pressure gradient enhanced or inhibited the gravity flow this is especially well pronounced in summer and 5 in summer above normal pressure is correlated with above normal temperatures in fall the opposite holds true

spatial and temporal variability of surface mass balance near talos dome east antarctica 1 predictions concerning antarctica s contribution to sea level change have been hampered by poor knowledge of surface mass balance snow accumulation is the most direct climate indicator and has important implications for paleoclimatic reconstruction from ice cores snow accumulation measurements stake core snow radar taken along a 500 km transect crossing talos dome east antarctica have been used to assess accumulation signals and the representativeness of ice core records stake readings show that accumulation hiatuses can occur at sites with accumulation rates below 120 kg m 2 yr 1 differences between cores and stakes can lead to statistical misidentification of annual layers determined from seasonal signals at sites with accumulation rates below 200 kg m 2 yr 1 because of nondetection of higher and lower values achieving 10 accuracy in the reconstruction of snow accumulation from single cores requires high accumulation 750 kg m 2 yr 1 low accumulation sites are representative if cumulative rates computed over several years are used to reach the 750 kg m 2 yr 1 threshold temporal variability of accumulation over the last two centuries shows no significant increase in accumulation wind driven processes are a fundamental component of surface mass balance spatial variations in accumulation are well correlated with surface slope changes along the wind direction and may exceed 200 kg m 2 yr 1 within 1 km wind driven sublimation rates are less than 50 kg m 2 yr 1 in plateau areas and up to 260 kg m 2 yr 1 in slope areas and account for 20 75 of precipitation whereas depositional features are negligible in surface mass balance

secondary flow shear stress and sediment transport a mathematical modeling and computational technique is presented which is capable of treating and dealing with interactions among hydraulic variables is open channel flows such as the distribution of primary flow velocity channel cross section discharge rate secondary flow shear stress and sediment concentration a shear stress formula is presented that can include the effect of secondary flow the formula gives peak values of boundary shear that occur on the channel bottom near the corners and on the side walls such peak values of boundary shear are owing to the momentum transfer to the region by secondary flow the simulation technique can be used as a decision making tool in selecting engineering designs and controls for channel protections the main role of secondary flow in sediment transport seems to be to transport sediments in the transverse direction whereas the gravity brings sediments downward and the diffusion brings sediment particles upward the vertical component of secondary flow seems to help gravity bring sediment down in most of the area in a transverse cross section of a channel

the late devonian frasnian famennian f f biotic crisis insights from δ13ccarb δ13corg and 87sr 86sr isotopic systematics a severe biotic crisis occurred during the late devonian frasnian famennian f f transition f367 myr here we present d 13 ccarb d 13 corg and 87 sr 86 sr isotopic systematics from identical samples of two sections across f f boundary in south china which directly demonstrate large and frequent climatic fluctuations 200 kyr from warming to cooling during the f f transition these climate fluctuations are interpreted to have been induced initially by increased volcanic outgassing and subsequent enhanced chemical weathering linked to the rapid expansion of vascular plants on land which would have increased riverine delivery to oceans and primary bioproductivity and subsequent burial of organic matter thereby resulting in climate cooling such large and frequent climatic fluctuations together with volcanic induced increases in nutrient e g biolimiting fe toxin sulfide and anoxic water supply and subsequent enhanced riverine fluxes and microbial bloom were likely responsible for the stepwise faunal demise of f f biotic crisis d 2005 elsevier b v all rights reserved

timing and patterns of the frasnian famennian event evidences from high resolution conodont biostratigraphy and event stratigraphy at the yangdi section guangxi south china abstract continuous centimeter scale sampling for conodonts with microfacies and carbon isotope analysis has been carried out across the frasnian famennian f f transition at the yangdi section guangxi south china the newly revised conodont biostratigraphy reveals a succession of six zones ranging from the upper palmatolepis rhenana zone to lower palmatolepis crepida zone in ascending order based on a detailed analysis of conodont abundance and diversity changes through the section two intervals involving significant conodont faunal changes were recognized in the uppermost palmatolepis linguiformis zone at the yangdi section the first conodont change occurred at the transition between the lower and upper pa linguiformis zone and is marked by the disappearance of pa linguiformis accompanied by the successive disappearances of pa eureka pa rhenana pa nasuta pa gigas ad ioides and ad nodosa the second conodont change appeared in a horizon equivalent to the uppermost upper kellwasser horizon ukh and is indicated by the elimination of nearly all frasnian palmatolepids ancyrodellids and polygnathids furthermore the second conodont change is coincident with the decimation of ostracods and tentaculitids and is synchronous with the turnovers of conodont biofacies in addition the onset of the 13 c carb perturbation is a little earlier than the second conodont change with the maximum amplitude of excursion right at the start of the famennian therefore we conclude that the second conodont change represents the f f mass extinction based on the temporal correlation among 13 c carb excursions pelagic faunal changes and conodont biofacies turnovers during the f f boundary interval according to the high resolution conodont biostratigraphy together with cyclostratigraphy the uppermost ukh and whole ukh contain 1 and 12 bundle cycles respectively thus the time span of the mass extinction and the entire upper kellwasser crisis lasted 16 18 kyr and 200 kyr respectively

temporal spatial reconstruction of the early frasnian late devonian anoxia in nw africa new field data from the ahnet basin algeria anoxic conditions were widespread in nw africa during the early frasnian late devonian that resulted in deposition of organic rich shales and limestones with total organic carbon toc values of up to 14 organic richness and thickness of these sediments vary laterally and organic rich vs organic poor facies boundaries are likely to have been diachronous a precise temporal spatial reconstruction of this anoxic phase in nw africa is complicated because the organic matter in outcrops is largely oxidised and biostratigraphic resolution in boreholes is generally low due to the lack of recoverable conodonts this contribution is based on eight outcrop sections at the margin of the central algerian ahnet basin where detailed spectral gammaray measurements were carried out using a handheld instrument the pre weathering organic richness in frasnian outcrop sections is approximated using the characteristic uranium enrichment in the anoxic facies that based on well studies is positively correlated with the total organic carbon content conodont biostratigraphic results from these sections suggest that the uraniumenriched interval the anoxic interval at the basin margin is most common in the basal frasnian conodont biozones 1 2 confirming previous results from the anti atlas in morocco in three of the eight localities studied the basal frasnian has not been deposited and the frasnian here commences with distinctly younger uranium enriched intervals including zones 4 11 well data from the eastern algerian berkine basin is interpreted to indicate a significantly longer anoxic phase there million yearscale diachroneities of the frasnian anoxia therefore clearly exist across the north africa shelf it is assumed that the palaeorelief might have been a major factor in controlling the onset duration and intensity of anoxia in the region d 2003 elsevier b v all rights reserved

greenhouse to icehouse a biostratigraphic review of latest devonian mississippian glaciations and their global effects the latest devonian mississippian interval records the long term transition from devonian greenhouse conditions into the late palaeozoic ice age lpia this transition was punctuated by three short glaciation events in the latest famennian mid tournaisian and visean stages respectively primary evidence for glaciation is based on diamictite deposits and striated pavements in south america appalachia and africa the aim of this review is to assess the primary biostratigraphic and sedimentological data constraining diamictite deposits through this transition these data are then compared to the wider record of eustasy mass extinction and isotope stratigraphy in the lower palaeolatitudes precise age determinations are vital to integrate high and low palaeolatitude datasets and to understand the glacial control on wider global changes palynological techniques currently provide the best biostratigraphic tool to date these glacial deposits and to correlate the effects of glaciation globally this review highlights a high degree of uncertainty in the known history of early lpia glaciation as much of the primary stratigraphic data are limited and or unpublished future high resolution stratigraphic studies are needed to constrain the history of glaciation both spatially and temporally through the latest devonian and mississippian

devonian carboniferous boundary glacioeustatic fluctuations in a platform to basin direction a geochemical approach of sequence stratigraphy in pelagic settings abstract we investigated high resolution stratigraphic distribution of selected major and trace elements and gamma ray spectra of fourteen devonian carboniferous d c boundary sections of europe located in the late palaeozoic laurussia and gondwana the aim was to trace the geochemical signature of a marked forced and normal regressive interval which was associated with rapid progradation of siliciclastics into the marine carbonate systems rhenish massif and a prominent hiatus in shallow water ramp settings namur dinant basin this interval represents the late devonian hangenberg event hbe sensu lato middle praesulcata conodont zone as defined by previous authors this regressive interval fsst to lst correlates with thin shale layers hbe shale sandwiched between monotonous nodular calcilutite calcisiltite successions at five pelagic sections of moravia carnic alps montagne noire and pyrenees in all sections with continuous d c sedimentation i e except those of the namur dinant basin the hbe s l interval is accompanied by elevated percentages of detrital proxies al k rb zr and changes in their ratios zr rb k al rb k which are normally interpreted as indicators of increased siliciclastic input provenance and grain size zr rb and other proxies are traceable even without apparent lithological evidence and can therefore facilitate stratigraphic correlation paleoredox and productivity proxies u th and ni rb enrichment factors only rarely show elevated values in the hangenberg black shale interval indicating that the associated water dysoxia anoxia was a local rather than global phenomenon global correlations based on the hbe black shales should therefore be dropped in favor of the hbe s l interval moreover analysis of sedimentation rates in the upper expansa to kockeli zone interval using the published radiometric ages suggests that the hbe s l was a time of significant increase in the rate of siliciclastic supply into the ocean even in the most distal pelagic sections consequently the previous interpretation of the hbe black shale as a condensed succession deposited during rapid sea level rise seems unlikely we interpret the hbe s l i e including the hbe black shale as a marine record of glacioeustatic sea level drop and increased aeolian transport in connection with late devonian climatic cooling and glaciation the set of geochemical markers related to the late devonian sea level fluctuation can be used for super regional to global correlations from platform to basin settings moreover they can facilitate current efforts to determine a new d c boundary definition

on the formation of blue ice on byrd glacier antarctica blue ice areas bias cover 1 of the east antarctic ice sheet and are visual evidence of persistent ablation in these regions more snow is sublimated and or eroded than is accumulated the physical processes driving the formation of bias are poorly understood here we combine a firndensification model with high resolution 5 5 km maps of surface mass balance and ice velocity to simulate the build up and removal of a firn layer along an ice flowline passing byrd glacier a bia is formed once the complete firn layer is removed feedback processes which enhance blue ice formation through the difference in surface characteristics of snow and ice are examined using sensitivity simulations the presence of blue ice on byrd glacier is found to be mainly determined by 1 ice velocity 2 surface mass balance and 3 the characteristics thickness mass of the firn layer prior to entering the ablation area with a moderate decrease of the surface mass balance the location and extent of the simulated bia on byrd glacier is found to be in good qualitative agreement with modis optical imagery

calibrating the devonian time scale a synthesis of u pb id tims ages and conodont stratigraphy the recalibrated devonian time scale represents an important improvement of devonian chronology regarding two aspects firstly a data set of 13 biostratigraphically well bracketed u pb id tims zircon and monazite ages constitutes the framework of the scale secondly approximately time linear biostratigraphic scales have been used for the interpolation between the isotopic ages the new construction thus represents a biochronometric time scale which allows the assignment of numeric ages not only to stage boundaries but also to each biozone boundary the method of interpolation applied also enables the projection of the geochronological error onto the time scale according to the newly calibrated scale the devonian lasted 57 4 5 7 ma from 418 1 3 0 to 360 7 2 7 ma this is compared to previously published time scales the longest time span ever calculated for this period the age interpolations for the eight stage boundaries are famennian tournaisian devonian carboniferous 360 7 2 7 ma frasnian famennian 376 1 3 6 ma givetian frasnian 383 7 3 1 ma eifelian givetian 388 1 2 6 ma emsian eifelian 391 9 3 4 ma pragian emsian 409 1 3 8 ma lochkovian pragian 412 3 3 5 ma pridolian lochkovian silurian devonian 418 1 3 0 ma full size table table options view in workspace download as csv the duration of the middle devonian is calibrated here as quite short with 8 2 ma and the emsian and the famennian are the longest stages with interpolated durations of 17 2 and 15 4 ma respectively together all devonian stages contain 57 conodont zones including subzones according to the standard conodont zonation giving a mean duration of about 1 ma in the highly resolved part of the time scale mid eifelian to the devonian carboniferous boundary zonal resolution averages 0 6 ma in contrast the lowest resolution is shown in the early emsian to mid eifelian interval with zonal durations of up to 5 5 ma serotinus zone

increased flow speed on a large east antarctic outlet glacier caused by subglacial floods large ice streams and outlet glaciers drain greenland and antarctica an observed acceleration of ice velocity in one of these outlet glaciers byrd glacier east antarctica coincides with a large water discharge from two subglacial lakes allowing direct attribution of the change in glacier dynamics to the water drainage network beneath the ice

devonian climate sea level and evolutionary events an introduction the face of planet earth has changed significantly through geological time dynamic processes active today such as plate tectonics and climate change have shaped the earth s surface and impacted biodiversity patterns from the beginning organisms on the other hand have the capacity to significantly alter earth s hydrological and geochemical cycles its atmosphere and climate sediments and even hard rocks deep down under the surface abiotic biotic interactions characterize earth s system history and together with biotic competition and food webs were the main trigger of evolutionary change innovations and biodiversity fluctuations within the palaeozoic the devonian was an especially interesting time interval as it was characterized by the mid paleozoic predator revolution signor brett 1984 brett 2003 and the related nekton revolution klug et al 2010 characterized by the blooms of free swimming cephalopods including the oldest ammonoids and fish groups e g toothed sharks and giant placoderms the rise of more advanced vertebrates including the oldest tetrapods e g blieck et al 2007 2010 niedzwiedzki et al 2010 the most extensive reef complexes of the phanerozoic e g kiessling 2008 and the greening of land by the diversification and spread of land plants including the oldest forests e g stein et al 2012 giesen berry 2013 which resulted in new soil types and changing weathering these major evolutionary trends did not unfold in a long interval of environmental stability but in times of numerous and repeated geologically brief global events that punctuated prolonged periods up to several million years in duration of relative stability termed ecological evolutionary subunits ee subunits boucot 1990 brett baird 1995 brett et al 2009 the bounding events even those of lesser intensity produced major re structuring in local to global ecosystems and are seen as critical drivers of long term evolutionary patterns brett 2012 these linked abiotic and biotic events and extinctions of different magnitude have been summarized by house 1983 1985 2002 walliser 1984 1996 and more recently by becker et al 2012 the devonian event succession is summarized in figure 1 two first order mass extinctions at the frasnian famennian boundary kellwasser crisis and at the end of the devonian hangenberg crisis characterized by the loss of major fossil groups classes and orders and complete ecosystems e g metazoan reefs early forests have to be viewed in the context of a complex global event sequence there are important similarities between discrete pulses phases of the major biotic crises and individual smaller scale events in our understanding second order global events are characterized by sudden extinctions in many groups and ecosystems including the complete disappearance of several widespread and diverse organism groups orders and families examples are the basal emsian atopus event where the planktonic graptolites finally died out the taghanic crisis frasnes events and lower kellwasser event third order global events show globally elevated extinction rates often at lower taxonomic level genera and species but within many clades and in several ecosystems examples are the silurian devonian boundary klonk event and the daleje chot c kacak condroz and annulata events fourth order global extinctions refer to the sudden disappearance of relatively fewer but widespread groups which implies a global not regional trigger this category may include the lochkovian pragian boundary

size reduction of conodonts indicates high ecological stress during the late frasnian under greenhouse climate conditions in south china abstract the late frasnian mass extinction lfme during extreme greenhouse conditions had a serious impact on biotic evolution herein based on detailed size measurements of 1783 elements of the conodont genera polygnathus and palmatolepis at the lali and duan sections in south china conodont animals underwent significant size reduction at the genus level during the late frasnian the bergmann s rule controlled the evolution of frasnian conodont animals and their size reduction during the late frasnian may have resulted from long term global warming and indicated high ecological stress before the frasnian famennian boundary ffb this phenomenon can explain why the decline of benthic faunas such as corals brachiopods or metazoan reefs predated the extinction of pelagic faunas such as conodonts in the upper kellwasser ukw event and at the ffb

palaeoenvironmental changes at col des tribes montagne noire france a reference section for the famennian of north gondwana related areas we present detailed biostratigraphy based on conodonts and palaeoenvironmental trends deduced from microfacies and conodont abundance through the famennian late devonian at col des tribes montagne noire france the succession is characterized by micritic limestones deposited in settings oscillating between mid to outer ramp facies contain poor fauna widely dominated by nektonic organisms this section is complete and one of the most conodont rich for the famennian of the north gondwana related area the upper kellwasser event frasnian famennian boundary and the hangenberg devonian carboniferous boundary have been lithologically identified they are characterized by decimetre thick black dysoxic to anoxic argillaceous sediments the condroz and annulata events although not materialized by lithological changes have been positioned due to the precise stratigraphy the first event occurred during the deposition of condensed ferruginous facies griotte limestones and the second event during the deposition of micrites barren of benthic fauna the combination of information from both facies and conodont biofacies changes allows a general sea level curve through the entire famennian for north gondwana to be proposed for the first time at col des tribes the general trend is a slight deepening upwards from triangularis to trachytera zones then a pronounced shallowing upwards trend from upper trachytera to praesulcata zones this curve correlates with the well known reference curve from euramerica concerning the late famennian trachytera to praesulcata zones there are some discrepancies in minor cycles which can be explained by tectonical phenomena at the onset of the edification of the variscan belt in europe

impact of model resolution on simulated wind drifting snow and surface mass balance in terre adelie east antarctica this paper presents the impact of model resolution on the simulated wind speed drifting snow climate and surface mass balance smb of terre ad elie and its surroundings east antarctica we compare regional climate model simulations at 27 and 5 5 km resolution for the year 2009 the wind speed maxima in terre ad elie and the narrow glacial valleys of victoria land are better represented at 5 5 km resolution because the topography is better resolved drifting snow sublimation is 100mma 1 in regions with high wind speeds our results indicate a strong feedback between topography wind gradients and drifting snow erosion as a result smb shows much more local spatial variability at 5 5 km resolution that is controlled by drifting snow erosion whereas the large scale smb gradient is largely determined by precipitation drifting snow processes lead to ablation in the narrow glacial valleys of victoria land the integrated smb equals 86gt although wind climate drifting snow processes and smb variability are better represented at 5 5 km the area integrated smb is not significantly different between the simulations at 27 and 5 5km a horizontal resolution of 27 km is sufficient to realistically simulate ice sheet wide smb

river width adjustment i processes and mechanisms in 1993 a task committee tc of the asce was established to study the hydraulics bank mechanics and modeling of width adjustment in alluvial channels the work of the tc in reviewing width adjustment processes and mechanisms is reported in this paper a companion paper presents the findings of the tc with regard to width adjustment modeling this paper first establishes the geomorphic context within which width adjustments occur and it demonstrates that width adjustment may take place over a wide range of scales in time and space in the past engineering analyses of channel width have tended to concentrate on prediction of the equilibrium width for stable channels most commonly the regime extremal hypothesis and rational mechanistic approaches are used and these are reviewed herein more recently attention has switched to channels that are adjusting their morphology either due to natural instability or in response to changes in watershed land use river regulation or channel engineering chara

event stratigraphic markers within the kellwasser crisis near the frasnian famennian boundary upper devonian in germany abstract short time intervals of anomalous conditions often referred to as global events yield excellent tools for detailed stratigraphic correlations in addition to pronounced effects minor features may be applied for fine scale comparisons of rock sequences these include alternations within a given portion of rock or distinct layers at exactly the same position such marker horizons are often traceable over long distances recognition of these specific markers allows for a more detailed search for possible causes of anomalous events

a new ecological severity ranking of major phanerozoic biodiversity crises a new ecological severity ranking of the major phanerozoic biodiversity crises is proposed in which the capitanian crisis is ranked lesser than the frasnian late devonian but greater than the serpukhovian end mississippian and the famennian end devonian crisis is ranked as equal in ecological impact to the hirnantian end ordovician two new decouplings between taxonomic severity and ecological severity are revealed in these analyses the capitanian and famennian crises in which the ecological impact of the biodiversity loss was markedly different from the magnitude of the biodiversity loss these analyses also reveal that the great devonian interchange gdi invasive species event in the givetian biodiversity crisis may provide an important palaeoecological analog for the study of present day extinction and homogenization in ecosystems produced by modern invasive species

the biostratigraphical and palaeogeographical framework of the earliest diversification of tetrapods late devonian the biostratigraphical and palaeogeographical framework of the earliest diversification of tetrapods late devonian

snow megadunes in antarctica sedimentary structure and genesis 1 megadune fields occupy large areas in the interior of the east antarctic ice sheet and are the result of unusual snow accumulation and redistribution processes they therefore are important to surface mass balance and ice core interpretation field observations gps gpr and surface measurements have provided a detailed description of megadune sedimentation and morphology over a 70 km2 area located 200 km east of dome c a combination of remote sensing analysis using landsat and satellite radar altimetry and field measurements indicate that slope in the prevailing wind direction spwd and climatic conditions play a crucial role in megadune genesis the megadune areas tend to be characterized by slightly steeper regional slope and the presence of highly persistent katabatic winds the megadunes represent 2 to 4 m amplitude waves of 2 to 5 km wavelength formed by variable net accumulation ranging between 25 leeward faces to 120 windward faces of the accumulation in adjacent nonmegadune areas leeward faces are characterized by glazed sastrugi free surfaces and extensive depth hoar formation windward faces are covered by large rough sastrugi up to 1 5 m in height

observations of blowing snow at the south pole 1 observations of blowing snow from visual observers records as well as ground based infrared and lidar measurements at south pole station are analyzed to obtain the first climatology of blowing snow over the antarctic plateau occurrence frequencies of blowing snow wind direction and speed during blowing snow events typical snow layer heights as well as optical depths are determined blowing snow is recorded in roughly one third of the visual observations and occurs under a narrow range of wind directions blowing snow layers are usually less than 400 m in thickness but can exceed 1000 m during blowing snow conditions these near surface layers are apparent in lidar backscatter profiles these layers emit radiances similar to those from optically thin clouds frequently seen over the antarctic plateau because the near surface blowing snow layers are frequently present they are a factor in space borne laser altimetry and other satellite remote sensing

the influence of the late devonian kellwasser events on deep water ecosystems evidence from palaeontological and geochemical records from south china abstract the late devonian frasnian famennian f f event consisting of the lower and upper kellwasser events had a severe impact on shallow water ecosystems while the effect on deep water ecosystems is ambiguous in order to recognize the kellwasser events and to evaluate their influences on the deep water ecosystems a newly refined conodont biostratigraphic framework spanning the lower palmatolepis rhenana zone to the pa delicatula platys zone has been established in the nandong section basinal facies guangxi south china the upper devonian lower and upper kellwasser horizons lkh and ukh have been recognized in the deep water facies on the basis of lithological variations biological turnovers and positive carbon isotope 13ccarb excursions the lkh is characterized by the enrichment of marine nektonic communities e g conodonts homoctenids and entomozoacean ostracods whereas the top of the ukh is barren of fossil organisms suggesting that the upper kellwasser event had a more severe effect on nekton than the lower kellwasser event the upper kellwasser uk 13ccarb positive excursion lags behind the enrichment of cu ni mo and v indicating that the uk 13ccarb positive excursion was probably related to elevated primary productivity which induced oxygen depletion in the water column the uk 13ccarb positive excursion peak prior to the f f boundary indicates a more limited effect of riverine influx on the deep water setting which suggests that the regional palaeogeographic configuration played an important role in the carbon cycle

the late devonian frasnian famennian event in south china patterns and causes of extinctions sea level changes and isotope variations abstract the frasnian famennian f f event may be recognized in various facies areas in south china in the pelagic cherty basin facies both lower and upper kellwasser events can seemingly be recognized in the deeper water carbonate facies the f f event level is well controlled in light of conodont biostratigraphy in the shallow water carbonate and mixed carbonate shale facies the f f boundary may be defined by clear taxonomic distinction in benthic fossils articulate brachiopods and corals as well as evidence from minor pelagic fossils post extinction recovery rate of benthic organisms differs in different facies settings and different taxonomic groups in open shallow water platform to inter platform depression areas brachiopods seem to recover quickly probably in the middle pa triangularis zone benthic ostracodes seem to recover at a later stage recovery of rugose corals did not happen until the uppermost famennian three steps of the f f mass extinction are postulated 1 extinction of diverse brachiopods including most atrypids 2 extinction of pelagic conodonts 3 extinction of both benthic faunas very abundant and diverse rugose corals and ostracodes and pelagic conodonts evidence of an end frasnian regression in south china is clear particularly in shallow water settings however in deeper water settings the picture is complicated with evidence of both sea level rise and fall in the latest frasnian it may be assumed from overall data so far known that crustal evolution itself and associated multiple volcanic hydrothermal activities may have mainly caused frequent and rapid climatically warming cooling alterations and sea level changes as well as marine ecologic collapse eutrophication microbial blooming seawater acidification and anoxia which may explain the f f extinction pattern in south china

cyclostratigraphy and astrochronology case studies from china abstract a high precision geologic time scale is the essential key for understanding the earth s evolutionary history and geologic processes astronomical tuning of orbitally forced stratigraphic records to construct high resolution astronomical time scales ats has led to a progressive refinement of the geologic time scale over the past two decades in turn these studies provide new insights regarding the durations and rates of major earth events evolutionary processes and climate changes all of which provide a scientific basis for contextualizing and predicting future global change trends south china hosts some of the best exposed and well dated neoproterozoic through mesozoic stratigraphic sections in the world many of which are suitable for cyclostratigraphy and calibrating the geologic time scale in north china several cenozoic oil bearing basins have deep boreholes with continuous sampling and or well logging that enable derivation of astronomically tuned time scales for an improved understanding of basin evolution and hydrocarbon generation this special issue focuses on case studies of astrochronology and applied cyclostratigraphy research using reference sections within china in this introductory overview we 1 summarize all existing astrochronology studies of the neoproterozoic through cenozoic sections within china that have been used to enhance the international geologic time scale 2 examine briefly the astronomically forced paleoclimate information recorded in various depositional systems and the modern techniques employed to analyze the periodicity of these signals encoded within the sedimentary record and 3 summarize the 20 contributions to this special issue of palaeogeography palaeoclimatology palaeoecology on cyclostratigraphy and astrochronology case studies from china

conodonts across the devonian carboniferous boundary a review and implication for the redefinition of the boundary and a proposal for an updated conodont zonation this paper is a contribution to the redefinition of the base of carboniferous system at present the criterion for the definition of the devonian carboniferous boundary is the first occurrence of a conodont species in order to evaluate the stratigraphic potential for new criteria for the definition of the devonian carboniferous boundary the distribution of conodont species of bispathodus branmehla palmatolepis polygnathus protognathodus pseudopolygnathus and siphonodella across the boundary is presented and discussed an updated biozonation scheme across the boundary based on the first appearance of bispathodus ac aculeatus bispathodus costatus bispathodus ultimus protognathodus kockeli siphonodella bransoni and siphonodella duplicata is proposed and it is suggested that the new criterion for the definition of the base of the carboniferous system be the first appearance datum of pr kockeli or si bransoni

the role of sea level change and marine anoxia in the frasnian famennian late devonian mass extinction johnson et al johnson j g klapper g sandberg c a 1985 devonian eustatic fluctuations in euramerica geological society of america bulletin 96 567 587 proposed one of the first explicit links between marine anoxia transgression and mass extinction for the frasnian famennian f f late devonian mass extinction this cause and effect nexus has been accepted by many but others prefer sea level fall and cooling as an extinction mechanism new facies analysis of sections in the usa and europe france germany poland and comparison with sections known from the literature in canada australia and china reveal several high frequency relative sea level changes in the late frasnian to earliest famennian extinction interval a clear signal of major transgression is seen within the early rhenana zone e g drowning of the carbonate platform in the western united states this is the base of transgressive regressive cycle iid of the johnson et al johnson j g klapper g sandberg c a 1985 devonian eustatic fluctuations in euramerica geological society of america bulletin 96 567 587 eustatic curve this was curtailed by regression and sequence boundary generation within the early linguiformis zone recorded by hardground and karstification surfaces in sections from canada to australia this major eustatic fall probably terminated platform carbonate deposition over wide areas especially in western north america the subsequent transgression in the later linguiformis zone recorded by the widespread development of organic rich shale facies is also significant because it is associated with the expansion of anoxic deposition known as the upper kellwasser event johnson et al s johnson j g klapper g sandberg c a 1985 devonian eustatic fluctuations in euramerica geological society of america bulletin 96 567 587 original transgression anoxia extinction link is thus supported although some extinction losses of platform carbonate biota during the preceeding regression cannot be ruled out conodont faunas suffered major losses during the upper kellwasser event with deep water taxa notably affected this renders unreliable any eustatic analyses utilising changes in conodont biofacies claims for a latest frasnian regression are not supported and probably reflect poor biostratigraphic dating of the early linguiformis zone sequence boundary

climate controlled mass extinctions facies and sea level changes around the devonian carboniferous boundary in the eastern anti atlas se morocco abstract detailed sedimentological and biostratigraphical studies of successions in the eastern anti atlas se morocco focused on changing depositional environments and reconstructions of sea level changes during the late famennian to middle tournaisian the investigations cover a transect from the central maider to the easternmost and southern tafilalt regions near the moroccan algerian border the moroccan data are compared with the standard succession of the german rhenish massif and with the regional and global stratigraphic record the results testify to high frequency sea level changes including two global transgressive and anoxic events the main hangenberg event hangenberg black shale level at the top of the wocklumeria zone upper devonian vi e and the lower alum shale event at the lower middle tournaisian lower carboniferous i ii boundary regionally both anoxic intervals coincided with mass extinctions followed by rapid radiation especially of pelagic biota a significant shallowing and regression occurred just below the devonian carboniferous boundary at the northern margin of gondwana and caused the sudden n nw progradation of a large deltaic complex over 300 500 km thick siliciclastic successions filled fast subsiding synsedimentary troughs of the maider and amessoui syncline southern tafilalt correlation with the glacial phases of southern gondwana south america south africa indicates a glacial eustatic origin of sea level changes and a major sea level fall in the scale of 100 m or more coinciding with the main regressive phase of the extended hangenberg crisis interval the new results are in accord with the hypothesis of an episode of cool humid climate at the end of the devonian that allowed contemporaneous glacial buildup in high latitudes and extensive clastic discharge in the middle latitudes of nw africa

model for transgressive black shales many black shales in thick epicontinental basinal successions formed beneath an oxygen restricted puddle of deep water other black shales formed during rapid transgression when basinal deposition expanded to cover basin margin areas normally characterized by shallow water deposition an expanding puddle model is developed from the early jurassic of england wherein rapid sea level rise leads to marine sediment starvation due to sediment entrapment in flooded river valleys subsidence sea level rise and decreased sediment supply during early transgression are suggested to lead to rapid deepening and therefore the expansion of the are of the puddle such that in previously shallow water areas black shales rest on condensed basal transgressive lags or unconformities that in turn rest on shallow water facies reestablishment of sediment influx and aggradation in excess of any continued sea level rise cause shallowing throughout the basin and the cessation of black shale formation

on the glaciological meteorological and climatological significance of antarctic blue ice areas this paper presents the current state of our knowledge about antarctic blue ice areas scattered widely over the antarctic continent yet covering only approximately 1 of its surface area blue ice areas have some peculiar characteristics that make them of particular interest for planetary geologists glaciologists meteorologists and climatologists for instance blue ice areas are subject to net ablation mainly by sublimation since any accumulation is easily swept off their smooth surfaces by winds moreover they are significantly warmer than their surroundings and the wind over them is generally more gusty an important feature of blue ice is its relatively low albedo 0 56 compared with that of snow 0 80 blue ice is probably considerably smoother than snow in the aerodynamic sense with roughness lengths as low as 3 10 6 m which indicates that blue ice is probably the only permanent natural surface over which the air flow is mainly in the aerodynamic smooth regime further since it is likely that very old ice is exposed at the surface of some blue ice areas this ice would be of great interest for paleoclimatic studies it has also been suggested that blue ice areas are sensitive to climate change this would make them useful as antarctic climate indicators because they can easily be monitored by satellite finally this paper addresses several gaps in our knowledge about blue ice areas and gives suggestions for future blue ice area research

dynamics and mass balance of four large east antarctic outlet glaciers this is the publisher s version also available electronically from http www ingentaconnect com

dynamics of cyclic carbonate deposition and biotic recovery on platforms during the famennian of late devonian in guangxi south china constraints from high resolution cycle and sequence stratigraphy to better understand the dynamics of platform carbonate deposition evolution and biotic recovery during the famennian high resolution cycle and sequence stratigraphic analyses were carried out upon three platform sections one in ramp and two in rimmed platforms along with a biostratigraphically well constrained basinal section in guangxi south china four main facies and fourteen lithofacies are identified in the three isolated platforms these are vertically arranged into decimetre to metre scale shallowing upward peritidal and subtidal cycles or parasequces in which the peritidal cycles predominate over the lower middle famennian six third order sequences s1 to s6 are identified based on the cycle stacking patterns as illustrated by fischer plots and vertical facies changes these sequences are temporally calibrated through correlation with basinal sequences constrained with conodont zonation and match well the six main famennian transgressive regressive cycles t1 to t6 in euramerica and elsewhere indicating a eustatic control however an opposite longer term trend in accommodation change s3 to s4 between platform interior and deeper open shelf to basin settings during the middle famennian suggests a differential subsidence across the platform basin section likely driven by block tilting thus both eustatic fluctuations and local tectonism had played an important role in platform development and evolution after the frasnian famennian biotic crisis main marine benthos preferentially recovered in the normal marine niches on the nearshore open shelves and radiated gradually into offshore restricted platforms brachiopods notably rhychonellides were the taxa recovering the earliest s1 in the normal or near normal marine conditions then echinoderms s3 stromatoporoids upper s3 and corals s5 stepped in episodically however these benthos generally appeared later in the restricted platform interiors only as if the ecological conditions were improved well enough for their colonization therefore the biotic recovery processes were diachronous both taxonomically and ecologically specified

conodont and carbon isotope stratigraphy near the frasnian famennian devonian boundary at wulankeshun junggar basin nw china abstract conodont faunas from the wulankeshun section in the northwestern junggar basin of xinjiang nw china are characterized by shallow water assemblages with many endemic taxa this study presents separate local icriodid and polygnathid conodont zonations for the lower member of the hongguleleng formation which can only roughly be correlated with the pelagic standard zonation the basal beds of the hongguleleng formation are assigned to a low diverse icriodus praealternatus ferus n ssp zone which possibly includes latest frasnian strata but it continues into the basal famennian at present the frasnian famennian boundary cannot be defined unequivocally by conodonts and there are no obvious upper kellwasser equivalents however the carbon isotope data are comparable with the bulongguor reservoir stratotype where the top frasnian lies within the basal hongguleleng formation in the early famennian partly endemic icriodid lineages provide successive icriodus cornutus i stenoancylus junggarensis n ssp and i plurinodosus n sp sub zones the basal famennian is possibly marked by the oldest endemic species of neopolygnathus neo huijunae n sp it is followed by local neo communis communis polygnathus pomeranicus po cf szulczewskii and po pseudocommunis n sp zones the new local conodont zonations provide a high biostratigraphic resolution for further future studies the wulankeshun shallow water conodont faunas show restricted similarities with contemporaneous faunas from eastern europe kazakhstan and iran there are a few taxa that were originally described from other distant regions such as nw canada and eastern australia the local high number of endemic taxa 17 sub species 46 points to a significant plate tectonic isolation of the junggar basin in the early famennian

a high resolution multiproxy stratigraphic analysis of the devonian carboniferous boundary sections in the moravian karst czech republic and a correlation with the carnic alps austria a multidisciplinary correlation of the devonian carboniferous d c boundary sections from the moravian karst czech republic and the carnic alps austria based on conodont and foraminifer biostratigraphy microfacies analysis field gamma ray spectroscopy grs carbon isotopes and element geochemistry is presented in this paper the study is focused on the interval from the middle palmatolepis gracilis expansa zone late famennian to the siphonodella sandbergi zone early tournaisian in lesni lom moravian karst a positive 13 c excursion in the bisphatodus costatus protognathodus kockeli interregnum from a distinct laminated carbonate horizon is correlated with a carbon isotope excursion from the grune schneid section of the carnic alps and is interpreted as the equivalent of the hangenberg black shales and a local expression of the global hangenberg event sensu stricto higher up at both sections a significant increase in the terrigenous input which is inferred from the grs signal and elevated concentrations of terrigenous elements si ti zr rb al etc provides another correlation tieline and is interpreted as the equivalent of the hangenberg sandstone both horizons are discussed in terms of relative sea level fluctuations and palaeoceanographic changes recent studies show that conodont biostratigraphy is facing serious problems associated with the taxonomy of the first siphonodellids their dependence on facies and discontinuous occurrences of protognathodids at the d c boundary therefore the correlative potential of geochemical and petrophysical signatures is high and offers an alternative for the refining of the problematic biostratigraphic division of the d c boundary

identification of antarctic ablation areas using a regional atmospheric climate model the occurrence of antarctic ablation areas in dronning maud land the lambert glacier basin victoria land the transantarctic mountains and the antarctic peninsula is realistically predicted by the regional atmospheric climate model racmo2 ant with snowdrift related processes calculated offline antarctic ablation areas are characterized by a low solid precipitation flux in combination with strong sublimation snowdrift erosion and or melt the strong interaction between atmospheric circulation and topography plays a decisive role in the precipitation distribution and hence that of ablation areas three types of antarctic ablation areas can be distinguished all occurring in dry regions type 1 is the erosion driven ablation area caused by 1 d and or 2 d divergence in the katabatic wind field at high elevations 2000 3200 m asl type 2 is the sublimation driven ablation area this type occurs at lower elevations

cellular secondary currents in straight conduit an investigation of cellular secondary currents i e three dimensional flow patterns is very important in hydraulic engineering because these currents might cause three dimensional sediment distributions and bed configurations such as sand ribbons in straight rivers it is however fairly difficult to measure secondary currents of water flows even by making use of hot film anemometers because the velocity of secondary currents is within 5 of the mainstream velocity thus on the basis of the hypothesis that the existence of free surface may not be an essential cause of secondary currents the present study has investigated experimentally the turbulent structure of their currents in air conduit considering an essential interaction between secondary currents and bedform longitudinal ridge elements were attached onto both lower and upper bottoms of the conduit which simulated the longitudinal ridges and troughs of river bedform i e sand ribbons all three components of the velocity were measured accurately by hotwire anemometers the structure of secondary currents was examined through the equations of mean flow vorticity and mean flow energy

antarctic precipitation and climate change predictions horizontal resolution and margin vs plateau issues all climate models participating in the fourth assessment report of the intergovernmental panel on climate change as made available by the program for climate model diagnosis and intercomparison pcmdi as the coupled model intercomparison project 3 cmip3 archive predict a significant surface warming of antarctica by the end of the 21st century under a moderate sresa1b greenhouse gas scenario all models but one predict a concurrent precipitation increase but with a large scatter of results the models with finer horizontal resolution tend to predict a larger precipitation increase because modeled antarctic surface mass balance is known to be sensitive to horizontal resolution extrapolating predictions from the different models with respect to model resolution may provide simple yet better multi model estimates of antarctic precipitation change than mere averaging or even more complex approaches using such extrapolation a conservative estimate of the predicted precipitation increase at the end of the 21st century is 30 kg m 2 a 1 on the grounded ice sheet corresponding to a 1 mm a 1 sea level rise about three quarters of this rise originates from the marginal regions of the antarctic ice sheet with surface elevation below 2250 m this is where field programs are most urgently needed to better understand and monitor accumulation at the surface of antarctica and to improve and verify prediction models

the surface windfield over the antarctic ice sheets the intense radiative cooling of air over the ice slopes of antarctica generates a surface wind regime that is strongly controlled by topography and plays a key role in determining the behaviour of the atmosphere and ocean in high southern latitudes1 7 resultant surface winds are intimately linked to the orientation of the ice terrain fig 1 and display the highest degree of persistence found on earth the close coupling between wind and topography allows estimation of the former if the latter is known with some precision here we report on time averaged near surface airflow over the antarctic continent during winter diagnosed from a recent accurate synthesis of terrain slopes and from estimates of the lower atmospheric temperature structure the simulated drainage pat tern exhibits strong spatial variability with the airflow concentrated into several zones near the coastal margin these confluence regions are responsible for strong persistent katabatic winds over downstream coastal stretches and are indicative of zones of greatest katabatic potential

facies and geochemistry across the early middle frasnian transition late devonian on south china carbonate shelf comparison with the polish reference succession abstract dongcun and longmen are two important reference sections for the study of the frasnian carbonate platform of guangxi southern south china at the dongcun section conodonts recovered in the present study provide a robust biostratigraphic framework for the lower middle frasnian interval the studied interval uppermost givetian to middle frasnian basal palmatolepis hassi zone is characterized by repeated shallower and deeper water deposits but the cyclic depositional trend was mainly deepening upward carbon isotopic investigation of bulk samples recognizes a major four step perturbation across the lower middle frasnian boundary which is also evident in the holy cross mountains poland the pattern is reinforced by correlative organic carbon isotopic secular trends from the reference polish sections a prominent long lasting increase in 13ccarb up to 4 5 event iii is evident in the palmatolepis punctata zone but is preceded and followed by rapid negative shifts events ii and iv respectively to ca 0 a weak incipient positive excursion event i is recognized in carbonate carbon only in the upper part of the palmatolepis transitans zone in chinese sections different background isotopic values indicate decoupled isotopically dissimilar hydrothermally affected and mostly oxygenated water masses over the carbonate shelf as shown by trace and rare earth elements the shallower water upslope diagenetically unaltered dongcun succession reveals lighter carbon isotopic ratios on the order of 2 while the less densely sampled and less certainly dated mostly muddy siliceous longmen downslope succession shows 13ccarb levels similar to those recorded worldwide the onset of the bipartite event iii is marked by 13c enrichment of 4 3 at dongcun event iv a light carbon excursion is especially well recorded in the shallow water facies by a 2 5 negative shift the event i excursion in the transitans zone is obscured as in some polish successions but is probably recorded in organic carbon trends slight differences in timing and magnitude of the 13ccarb oscillations may originate from geochemical decoupling between the open ocean and the tectonically active morphologically differentiated epeiric basins nevertheless a global extent for this major punctata event is clear from the similar biogeochemical signals recorded on the distantly separated south laurussian and south china shelves