quantitative conodont based approaches for correlation of the late devonian kellwasser anoxic events we present the trends of absolute conodont abundance relative genera abundance and conodont morphometrics across the late devonian kellwasser horizons at three northern gondwanan epicontinental seaway locations at three contrasting depositional settings the kellwasser events are characterized by a decrease in conodont abundance high percentage of the conodont genus icriodus and morphological change of the conodont genus palmatolepis these changes can be identified in sections where the events are expressed as interbedded anoxic and oxic deposits as well as in settings characterized by continuous anoxic sediment accumulation hence these changes are interpreted as global and synchronous and can be thus used for event correlation the paradox of these results is that despite quite similar isotopic signals faunal change during the lower kellwasser event was less than during the upper kellwasser event we interpret that this discrepancy is due to an unconformity including topmost frasnian to earliest famennian at several f f sections which removed the record of peak paleoenvironmental change

patterns of deposition from experimental turbidity currents with reversing buoyancy turbidity currents are turbulent sediment laden gravity currents which can be generated in relatively shallow shelf settings and travel downslope before spreading out across deep water abyssal plains because of the natural stratification of the oceans and or fresh water river inputs to the source area the interstitial fluid within which the particles are suspended will often be less dense than the deep water ambient fluid consequently a turbidity current may initially be denser than the ambient sea water and propagate as a ground hugging flow but later reverse in buoyancy as its bulk density decreases through sedimentation to become lower than that of the ambient sea water when this occurs all or part of the turbidity current lofts to form a buoyant sediment laden cloud from which further deposition occurs deposition from such lofting turbidity currents containing a mixture of fine and coarse sediment suspended in light interstitial fluid is explored through analogue laboratory experiments complemented by theoretical analysis using a box and cloud model particular attention is paid to the overall deposit geometry and to the distributions of fine and coarse material within the deposit a range of beds can be deposited by bimodal lofting turbidity currents lofting may encourage the formation of tabular beds with a rapid pinch out rather than the gradually tapering beds more typical of waning turbidity currents lofting may also decouple the fates of the finer and coarser sediment depending on the initial flow composition the coarse fraction can be deposited prior to or during buoyancy reversal while the fine fraction can be swept upwards and away by the lofting cloud an important feature of the results is the non uniqueness of the deposit architecture different initial current compositions can generate deposits with very similar bed profiles and grading characteristics highlighting the difficulty of reconstructing the nature of the parent flow from field data it is proposed that deposit emplacement by lofting turbidity currents is common in the geological record and may explain a range of features observed in deep water massive sands thinly bedded turbidite sequences and linked debrites depending on the parent flow and its subsequent development for example a lofting flow may lead to a well sorted largely ungraded or weakly graded bed if the fines are transported away by the cloud however a poorly sorted largely ungraded region may form if during buoyancy reversal high local concentrations and associated hindered settling effects develop at the base of the cloud

identification of cyclone track regimes in the north atlantic a langrangian type climatology of north atlantic cyclones is established based on the high resolution european centre for medium range weather forecasts data set of the 1000 hpa height field first an algorithm is introduced to identify mid latitude cyclones and cyclone paths with as few constraints as possible cluster analysis of relative cyclone displacements yields three types of cyclone tracks characterizing stationary north eastward and zonally travelling storms the internal lagrangian statistics of these cyclone track types reveal representative life cycles for central pressure and geopotential height gradients and a power law scaling behaviour of cyclone displacements finally a basic climatology of north atlantic cyclone track regimes is deduced in terms of a time series and circulation statistics

systematic occurrences of malformed teratological acritarchs in the run up of early palaeozoic δ13c isotope excursions abstract the late ordovician and silurian are characterised by several strong global positive 13 c carb excursions some of them exceed 5 and thus belong to the strongest perturbations of the carbon cycle in the phanerozoic the onset of the excursions is characterised by extinction and or turnover events of several groups of marine invertebrates the causal mechanisms of the carbon cycle perturbations however are still unknown and currently a matter of vigorous scientific debate our own investigations in the hirnantian latest ordovician have shown that the onset of the major 13 c excursion hice is characterised by very high abundances of acritarchs showing abnormal teratological forms a critical review of published reports of abnormal acritarchs from the late ordovician to early devonian and a correlation of their occurrences with the global stable carbon isotope curve show that high abundances of teratological forms of acritarchs are often coeval to the run up of 13 c excursions high abundances of teratological forms in modern marine protists are commonly observed in environments with a high degree of environmental stress in the fossil record the challenge is to attribute abnormal forms of organisms to specific environmental circumstances our study implies that they are somehow related to the global carbon cycle i e to carbon isotopic composition of the ambient sea water and that they share a common extrinsic cause with the contemporaneous extinction and or turnover events in other fossil groups

southeast greenland high accumulation rates derived from firn cores and ground penetrating radar despite containing only 14 of the greenland ice sheet by area the southeastern sector has the highest accumulation rates and hence receives 30 of the total snow accumulation we present accumulation rates obtained during our 2010 arctic circle traverse derived from three 50 m firn cores dated using geochemical analysis we tracked continuous internal reflection horizons between the firn cores using a 400 mhz ground penetrating radar gpr gpr data combined with depth age scales from the firn cores provide accumulation rates along a 70 km transect we followed an elevation gradient from 2350 to 1830m to understand how progressive surface melt may affect the ability to chemically date the firn cores and trace the internal layers with gpr from the firn cores we find a 52 0 43 m w e a 1 increase in average snow accumulation and greater interannual variability at the lower site than the upper site the gpr profiling reveals that accumulation rates are influenced by topographic undulations on the surface with up to 23 variability over 7 km these measurements confirm the presence of high accumulation rates in the southeast as predicted by the calibrated regional climate model polar mm5

early holocene climate oscillations recorded in three greenland ice cores a new ice core chronology for the greenland dye 3 grip and ngrip ice cores has been constructed making it possible to compare the 18 o and accumulation signals recorded in the three cores on an almost annual scale throughout the holocene we here introduce the new time scale and investigate 18 o and accumulation anoma lies that are common to the three cores in the early holocene 7 9 11 7 ka before present three time periods with significant and synchronous anomalies in the 18 o and accumulation signals stand out the well known 8 2 ka event an event of shorter duration but of almost similar amplitude around 9 3 ka before present and the preboreal oscillation during the first centuries of the holocene for each of these sections we present a 18 o anomaly curve and a common accumulation signal that represents regional changes in the accumulation rate over the greenland ice cap

deep water massive sands facies processes and channel geometry in the numidian flysch sicily abstract the sedimentology of the numidian flysch in northern sicily has been little studied in the last twenty years with most works concentrating on the structural complexities of the area rather than the facies characteristics the numidian basin was intensively deformed during its complex tectonic history and the basin deposits have become segmented into different structural units the oligo miocene aged flysch comprises predominantly quartzarenitic sandstones and interbedded mudstones both of turbiditic affinities and most likely derived from a nw african source the sediments are well exposed along the coast and in dry river valleys in northern sicily and provide excellent examples of deep water massive sands i e very thick 4 25 m units of structureless sandstone associated with turbidites and related facies the overall characteristics of the examined sections indicate that the sandstones were deposited within both isolated channels and larger channel complexes that fed across a mud dominated slope the more proximal sections e g ponte finale and pollina have a high proportion of pebble conglomerates shale clast conglomerates and very thick bedded structureless pebbly sandstones deposited by high density turbidity currents debris flows and slumping other sections either more distal or with a more uniform sand rich source e g contrada di romano are dominated by very thick bedded and amalgamated structureless sandstones with extensive zones of water escape structures the massive sands are thought to originate from the gradual aggradation of sediment beneath steady or near steady flows with rapid deposition from final stage modified grain flows forming the water escape features

accumulation over the greenland ice sheet from historical and recent records water accumulation defined as precipitation minus evaporation was estimated over all of greenland as part of a program to understand changes in ice sheet mass and elevation over 360 historical and recent point accumulation estimates on the greenland ice sheet were evaluated and 276 estimates that were judged to be high quality were used to develop the accumulation map the data set includes 99 points developed as part of four investigations of the past 5 15 years these are judged to have the greatest accuracy using kriging the average accumulation over greenland is estimated to be 30 g cm 2 yr 1 for the interior part of the ice sheet above 1800 m elevation where most of the data were acquired the average accumulation is also estimated to be 30 g cm 2 yr 1 there are still many areas on the ice sheet including northwest southeast and southern greenland where accumulation is highly uncertain exceeding the mean ice sheet uncertainty at a point of 20 25 in these regions further sampling will be required to reduce uncertainty in both regional and ice sheet wide accumulation

greenland ice sheet mass balance reconstruction part i net snow accumulation 1600 2009 ice core data are combined with regional atmospheric climate model version 2 racmo2 output 1958 2010 to develop a reconstruction of greenland ice sheet net snow accumulation rate at g spanning the years 1600 2009 regression parameters from regional climate model rcm output regressed on 86 ice cores are used with available cores in a given year resulting in the reconstructed values each core site s residual variance is used to inversely weight the cores respective contributions the interannual amplitude of the reconstructed accumulation rate is damped by the regressions and is thus calibrated to match that of the rcm data uncertainty and significance of changes is measured using statistical models a 12 or 86 gt yr 21 increase in ice sheet accumulation rate is found from the end of the little ice age in 1840 to the last decade of the reconstruction this 1840 1996 trend is 30 higher than that of 1600 2009 suggesting an accelerating accumulation rate the correlation of at g with the average surface air temperature in the northern hemisphere satnht remains positive through time while the correlation of at g with local near surface air temperatures or north atlantic sea surface temperatures is inconsistent suggestinga hemispheric scale climateconnection an annualsensitivityof at g to satnhtof 6 8 k 21 or 51 gt k 21 is found the reconstuction at g correlates consistently highly with the north atlantic oscillation index however at the 11 yr time scale the sign of this correlation flips four times in the 1870 2005 period

integrated biostratigraphy of the lower silurian of the kolka 54 core latvia integrated graptolite conodont and chitinozoan biostratigraphical data are presented from the llandovery and wenlock of the kolka 54 core latvia correlations between graptolite and chitinozoan biozones are consistent with those published from other east baltic sections and the welsh basin while most correlations between graptolite and conodont biozones agree with those presented in previous studies there are important exceptions significantly we report here the discovery of distomodus staurognathoides biozone conodonts in the lowest aeronian demirastrites triangulatus graptolite biozone the base of the d staurognathoides biozone was previously considered to lie much higher in the aeronian also it is shown that walliserodus survived the late wenlock mulde event during which it was considered previously to have become extinct

integrated sedimentary biotic and paleoredox dynamics from multiple localities in southern laurentia during the late silurian ludfordian extinction event abstract the silurian was a time of major climatic transition punctuated by multiple biotic crises and global carbon cycle perturbations the most severe of these biotic events was the late silurian ludfordian lau kozlowskii extinction event lke and the associated lau carbon isotope excursion cie although the extinction event and lau cie are globally documented the only records thus far of local and global marine paleoredox conditions through this interval are from a single region in scandinavia here we examine four sections along a bathymetric transect of mixed carbonate siliciclastic sediments from western tennessee usa a novel approach using a multi proxy dataset combining high resolution geochemical data and microfacies analyses from multiple localities explores the possibilities of local regional scale redox heterogeneities during a time of widespread environmental upheaval on a global scale paired positive excursions recorded in carbonate carbon isotopes and carbonate associated sulfate sulfur isotopes support recent work from carbonate and siliciclastic successions from scandinavia suggesting a global enhancement of organic carbon and pyrite burial driven by an expansion of euxinic anoxic and sulfidic water column conditions in the oceans during the mid ludfordian furthermore positive excursions in organic carbon isotopes and pyrite sulfur isotopes reflect the global changes in redox stratigraphic trends in i ca ratios imply a local expansion of low oxygen conditions with low but non zero values during the rising limb and peak of the cie the fossil assemblages vary across the shelf and through the cie interval stratigraphic changes in fossil assemblages and i ca are closely associated with local and global changes in oxygenation and sea level during the mid ludfordian the collective data indicate significant biotic reorganization in response to changes in marine redox conditions and in conjunction with sea level variation during the lke interval but detailed macroscopic biodiversity is currently unconstrained for this region

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

reconstructing climate variability from greenland ice sheet accumulation an era40 study 1 re analysis data covering the period 1958 2001 are used to investigate the relationship between regional inter annual snow accumulation variability over the greenland ice sheet gris and large scale circulation patterns cyclone frequency and strength four regions of the gris have been identified that are highly independent with respect to accumulation variability accumulation indices of three of these regions are associated with distinct large scale circulation patterns central western gris reveals an inverse relationship with a nao like pattern the south west a positive correlation with a high pressure bridge from central north atlantic to scandinavia and the south eastern gris a positive correlation with a high pressure anomaly over the greenland sea these large scale patterns also impact european climate in different ways accumulation variability in north eastern gris however is dominated by cyclones originating from the greenland sea thus greenland ice core accumulation records offer the potential to reconstruct various large scale circulation patterns and regional storm activity

high precision u pb zircon age constraints on the duration of rapid biogeochemical events during the ludlow epoch silurian period precise determinations of the rates and durations of palaeozoic biogeochemical events are largely unavailable here we present two new high precision u pb zircon dates from volcanic ash deposits from the ludlow series silurian system of podolia ukraine that yielded weighted mean 206 pb 238 u dates of 424 08 0 20 0 29 0 53 ma and 422 91 0 07 0 21 0 49 ma analytical tracer and total uncertainties these new dates bracket the largest post cambrian global carbon cycle perturbation lau excursion and constrain the ludlow rise in 87 sr 86 sr these chronostratigraphically well controlled dates improve the calibration of the silurian time scale and provide the first determinations of the rates of biogeochemical change during the ludlow epoch supplementary material u pb geochemical methods data and cl imagery are available at http www geolsoc org uk sup18798

ultra high resolution multivariate record and multiscale causal analysis of pridoli late silurian implications for global stratigraphy turnover events and climate biota interactions abstract the upper silurian and especially pridoli epoch is a critical interval for the understanding the evolution of earth s biota since it witnessed series of powerful extinction events global reorganizations of paleocommunities and expansion of new clades which assumed dominance in the subsequent devonian period the stratigraphic record of the eastern part of the silurian baltic basin represents an excellent candidate for the fine scale analysis of paleoecological and paleoceanographic dynamics therefore we presenting here stratigraphic record of the milaiciai 103 core south western lithuania of conodonts brachiopods 13ccarb 18ocarb and a series of various geochemical and geophysical proxies most of which were sampled at a very high resolution 11 ka spanning uppermost ludlow pridoli and the lowermost devonian the analysis revealed that the pridoli was characterized by four distinct long term dynamic states here named i normal pridoli i ii silal negative carbon isotopic excursion and extinction event iii normal pridoli ii and iv klonk positive stable carbon isotopic event and excursion the most significant change in most variables is detected approximately in the middle of the pridoli at the beginning of the delotaxis detorta zone at the recovery after silal event of conodonts and at the onset of collapse of brachiopod communities the analysis of dynamic complexity revealed the strong evidence for the presence of 405 ka metronome milankovitch cycles in the record of 13ccarb which constrains the duration of the pridoli epoch to 4 3 0 2 ma the recurrence plot analyses revealed deterministic coordination between 13ccarband conodont paleocommunity dynamics at all scales finally lead lag analysis using conditional joint recurrence revealed that conodont dynamics as a rule were driven by perturbations in the carbon cycle although silal event interval shown opposite pattern thus confirming the unusual nature of this previously unrecognized coordinated climatic and biotic event

depositional versus ecological control on the conodont distribution in the lower frasnian fore reef facies holy cross mountains poland abstract lithofacies and conodont biofacies of reef slope deposits of the wietrznia beds lower frasnian palmatolepis transitans zone were studied in three measured sections at the wietrznia quarry holy cross mts poland the diverse reef derived grained deposits interrupted the background sedimentation that included lime mudstones deposited largely at 50 to 90 m depths in oxygen depleted middle slope to toe of slope settings the mainly storm controlled proximal gradient is laterally marked by gradual changes from coarse grained tempestites represented by flat pebble conglomerate fabric to diluted muddy tempestites the mostly sparse polygnathid and mesotaxid polygnathid biofacies characterize the hemipelagic facies whilst polygnathid ancyrodellid biofacies dominates in the event layers three step taphofacies scheme is proposed distinguishing settled parautochthonous residual winnowed and displaced settled from waning currents and or transported in sediment gravity flows conodont element accumulations the primary ecological signals are still partly preserved in most of the tempestite derived assemblages indicating scarcity of truly residual lag like taphofacies the hydraulic sorting was most effective in the middle slope setting affected by unidirectional and or oscillatory flows syndepositional mixing was strengthened upslope by an importation of off reef mesotaxid faunas due to storm surge onto the reef this reworking pattern as a key factor in biofacies interpretation may be applicable only on a local scale however similarly biased conodont signature is probably common in other hurricane affected carbonate complexes even if without a disrupting impact on major biofacies belts

dynamics of abundance of the mid to late pridoli conodonts from the eastern part of the silurian baltic basin multifractals state shifts and oscillations

north atlantic oscillation dynamics recorded in greenland ice cores carefully selected ice core data from greenland can be used to reconstruct an annual proxy north atlantic oscillation nao index this index for the past 350 years indicates that the nao is an intermittent climate oscillation with temporally active coherent and passive incoherent phases no indication for a single persistent multiannual nao frequency is found in active phases most of the energy is located in the frequency band with periods less than about 15 years in addition variability on time scales of 80 to 90 years has been observed since the mid 19th century

recurrence and cross recurrence plots reveal the onset of the mulde event silurian in the abundance data for baltic conodonts abstractone of the severest perturbations of the silurian marine environment is the mid homerian mulde bioevent this event proceeded in several temporal steps which according to some authors implies possible globally synchronous perturbation the dynamic pace and consequences of these perturbations as well as their effects on conodont community dynamics are largely unknown here i used so called recurrence and cross recurrence plots to test the hypothesis of common forcing of the mulde event on conodont abundance dynamics at the regional scale the results of the analysis of two lithuanian sections from the baltic basin revealed that in the uppermost part of the lundgreni graptolite biozone there was sharp transition in the recurrence patterns pre mulde homerian time was characterized by high amplitude fluctuations and a low recurrence rate on the other hand the mulde interval state was characterized by low abundance and a high recurrence rate with longer horizontal vertical and diagonal lines

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

vertebrate extinctions and reorganizations during the late silurian lau event during the silurian period as shown here by data from gotland sweden and other regions of the baltoscandian paleocontinent fish faunas were struck hard by extinctions caused by the late ludlow lau event also known for being associated with the largest positive stable carbon isotope excursion of the phanerozoic this event had a profound impact on the early evolutionary history of vertebrates wiping out two thirds of the fish taxa and causing significant ecological reorganizations over an estimated time span of similar to 200 ka our data show that immediately prior to the event jawed acanthodians dominated the fish faunas whereas the event led to a diverse fauna and a brief but marked dominance of the jawless thelodonts the stepwise changes observed mimic those of conodonts suggesting a similar mode of life and response to atmospheric oceanic perturbations for these clades less

annual accumulation over recent centuries at four sites in central greenland 1 accurate accumulation records are fundamental to understanding mass balance of the greenland ice sheet ice cores can provide multicentury high resolution ground based point estimates of water accumulation in 2003 and 2004 four new ice cores were collected in the central western d4 and d5 and summit sandy and katie regions of greenland annual layer counting based on multiple glaciochemical parameters primarily hydrogen peroxide sea salt and dust proxies was used to date the ice cores resulting in annual dating the bottom depth ages for d4 d5 sandy and katie were estimated at 1738 1673 1844 and 1934 a d with mean annual accumulation rates of 41 4 35 2 22 4 and 22 4 cmweq yr 1 respectively these new records were in good agreement with previous accumulation maps and four previously published records from nearby multicentury ice cores spatial variability was quantified through an analysis of variance thereby allowing for more meaningful comparisons to atmospheric processes more regionally representative accumulation records were constructed for the central western and summit regions spanning recent centuries using a principle component analysis of both the new and previously reported ice core measurements these regional records exhibited 6 7 interannual variability 1 standard deviation of the mean and had lower spatial variability uncertainties than individual accumulation records correlations indicate that 20 of the variance in the central western region was explained by the north atlantic oscillation nao and suggests that an array of more northern ice cores may correlate more closely with nao

reconstruction of sea level pressure fields over the eastern north atlantic and europe back to 1500 spatially and temporally high resolution estimates of past natural climate variability are important to assess recent significant climate trends the mid latitude atmospheric circulation is the dominant factor for regional changes in temperature rainfall and other climatic variables here we present reconstructions of gridded monthly sea level pressure slp fields back to 1659 and seasonal reconstructions from 1500 1658 for the eastern north atlantic european region 30 w to 40 e 30 n to 70 n these were developed using principal component regression analysis based on the combination of early instrumental station series pressure temperature and precipitation and documentary proxy data from eurasian sites the relationships were derived over the 1901 1960 calibration period and verified over 1961 1990 under the assumption of stationarity in the statistical relationships a transfer function derived over the 1901 1990 period was used to reconstruct the 500 year large scale slp fields systematic quality testing indicated reliable winter reconstructions throughout the entire period lower skill was obtained for the other seasons although meaningful monthly reconstructions were available from around 1700 onwards when station pressure series became available the quality and the reconstructed slp fields for two exceptionally cold years 1573 1740 are discussed and climatologically interpreted an eof analysis of the 1500 1999 winter slp revealed firstly a zonal flow pattern with pronounced decadal to centenial time scale variations secondly a monopole pattern over northwest europe and thirdly a pattern modulating the meridional flow component over europe these 500 year slp reconstructions should be useful for modelling studies particulary for analyses of low frequency atmospheric variability and for circulation dynamics

high resolution late silurian correlations between gotland sweden and the broken river region ne australia lithologies conodonts and isotopes high resolution correlations partly with a precision better than 10 ka are achieved between late ludfordian sequences on gotland sweden on baltica and a section cog through the coral gardens formation along the broken river northeastern australia on gondwana despite these sections having been on different palaeocontinents facing different oceans the interval is characterised by rapid very large faunal isotopic and lithologic changes lithologies are remarkably similar in the two areas consisting of in order from below marls with thin limestone beds flaggy limestones oncoidal crinoidal limestone oncoidal marls terrigenous clastics silty clay mudstone sandstone oolite and cliff gorge forming limestones further independent correlation dates several of the lithological changes as coeval the 813 c excursion in whole rock carbonates is one of the three largest ones known during the phanerozoic the increase in delta c 13 is very similar in the two areas from below 1 parts per thousand to c 9 parts per thousand vpdb though two gotland samples yielded 9 71 parts per thousand and 10 54 parts per thousand the corresponding cog interval included fewer carbonate layers than needed to definitely exclude that this difference is due to a lack of suitable rocks for sampling compared with the lithologies and the delta c 13 curves the conodont faunas display some divergence but key taxa permit precise correlations for much of the studied interval the conodont assemblages change stepwise from very diverse in the polygnathoides siluricus zone to a low diversity fauna dominated markedly by a single taxon upper icriodontid subzone returning abruptly to a comparatively diverse ozarkodina snajdri zone fauna a method resembling graphic correlation in some respects is used to propose a similarly high resolution correlation through a longer interval for future testing c 2006 elsevier b v all rights reserved less

a late silurian extinction event and anachronistic period resurgence of microbialites and anachronistic facies in the aftermath of phanerozoic extinction events has hitherto only been documented among the major five based on the classical silurian carbonate platform strata of gotland sweden a minor biotic event is herein for the first time related to a substantial increase in anachronistic facies strata deposited during and shortly after the lau event in the baltic paleobasin eke and burgsvik formations include evidence for reduced grazing and infaunal activity in contemporaneous shallow low latitude seas e g flat pebble conglomerates normal marine stromatolites mass occurrence of oncoids and subtidal wrinkle structures e g kinneyia and microripples the latter structures have recently been suggested to be restricted to proterozoic cambrian and early triassic time and therefore are regarded as anomalous for the phanerozoic the co occurrence of these facies and global extinctions among pentamerid brachiopods and conodonts suggests that minor extinction events also resulted in anachronistic periods less devastating but fully comparable to those in the aftermath of the end ordovician and end permian mass extinctions a global positive stable carbon isotope excursion and the last appearance datum of the conodont polygnathoides siluricus may facilitate identification of the late silurian anachronistic period elsewhere less

determinants of extinction in the fossil record the causes of mass extinctions and the nature of biological selectivity at extinction events are central questions in palaeobiology it has long been recognized however that the amount of sedimentary rock available for sampling may bias perceptions of biodiversity1 2 3 4 5 6 7 and estimates of taxonomic rates of evolution5 6 7 8 this problem has been particularly noted with respect to the principal mass extinctions5 6 7 8 9 10 11 12 here we use a new compilation of the amount of exposed marine sedimentary rock to predict how the observed fossil record of extinction would appear if the time series of true extinction rates were in fact smooth many features of the highly variable record of apparent extinction rates within marine animals can be predicted on the basis of temporal variation in the amount of exposed rock although this result is consistent with the possibility that a common geological cause determines both true extinction rates and the amount of exposed rock it also supports the hypothesis that much of the observed short term volatility in extinction rates is an artefact of variability in the stratigraphic record

quantifying the community turnover of the uppermost wenlock and ludlow silurian conodonts in the baltic basin abstract the homerian to ludfordian interval of the mid to late silurian period was a time of significant changes in conodont communities global climate oceanographic patterns and biogeochemical cycles the mulde and the lau events are preeminent examples of globally recognized conodont extinction episodes from this interval in earth s history the silurian baltic basin is the most suitable locality globally for studying these perturbations to the ocean atmosphere system since there is an extensive record of conodont taxa occurrences their communities and their environments spanning across shore face to open ocean settings in this study we present new conodont and 13c data from the upper homerian to ludlow interval from two core sections g luva 99 and g luva 118 representing shelfal environments and the numerical conodont data from the vidukl 61 section from deep water settings and compare them with patterns of conodont diversity change as revealed in the data rich milaiciai 103 core section for this purpose we explored the stratigraphically tied time series of conodont diversity changes employing recurrence and cross recurrence plots the binary similarity matrices that are used for deciphering complex spatial and temporal dynamic patterns the cross recurrence plots were used as a means of synchronizing the geological sections by applying dynamic time warping and the newly described moving window median recurrence point search algorithms the results revealed that the conodont community compositional data are sufficiently temporally and spatially coherent to be reasonably used for synchronizing geological records moreover the sudden state transitions detected in the cross recurrence plots suggest that the lau event was of great importance for conodont community evolution in the studied time slice

evidence for rapid environmental changes in low latitudes during the late silurian lau event the burgen 1 drillcore gotland sweden erosional outliers are an important component of the ludlow late silurian stratigraphy of gotland sweden however due to the poor degree of exposure outcrop studies have not revealed a detailed section from any of these outliers the first complete stratigraphy of such an erosional remnant the burgen outlier is presented here based on the recently recovered burgen 1 drillcore stratigraphical units encountered are from oldest to youngest the uppermost hemse group 35 m eke formation 0 4 m burgsvik formation 3 4 m and the basal hamra formation 12 in preserved based on carbon stable isotopes and lithological correlation to nearby outcrops that are zoned by conodonts it can be concluded that the most profound late ludlow sedimentary changes took place shortly after the onset of the globally recognized lau event delta 13 c values reach 8 7 parts per thousand in the lower hamra formation sedimentary changes include development of discontinuity surfaces widespread occurrence of an intraclastic conglomerate increased microbial activity rothpletzella and wetheredella and influx of clastics to the basin these changes are linked to substantial base level changes during the event a general comparison with the prague basin suggests contemporaneous sedimentary changes on baltica and on cratonic elements from peri gondwana during the event

carbon isotope event markers through the wenlock pridoli sequence at ohesaare estonia and priekule latvia abstract the ohesaare borehole in the northern part of the silurian baltic gulf penetrates shallow and deep shelf marlstones limestones and dolostones the priekule borehole in the deep shelf belt of the basin was drilled through marlstones and graptolitic mudstones most of the successions except the upper part are characterized by a high sr ca ratio close to marine calcites suggesting good preservation of carbonate material conodont alteration indices are low 1 2 carbon isotopes were measured using whole rock samples in the ohesaare core section two distinctive 13 c positive excursions were established one in the early wenlock riccartonensis and low rigidus ellesae standard graptolite zones 4 2 and the second in the late wenlock nassa zone 4 6 before and after the latter there are also intervals with low 13 c values the first just above the lundgreni zone 1 8 and another in the ludensis perhaps reaching into nilssoni zone 3 8 in the priekule section the early wenlock 13 c peak is well represented 3 1 but in the late wenlock early ludlow 13 c values show little variation from 2 0 to 1 in this section a high peak of 13 c values 5 9 was determined in the nova beds correlated with the topmost gorstian and lowermost ludfordian ludlow the carbon isotope positive excursions show good correlation with lows of the global sea level curve and with most of the biotic and supposed climatic events glaciation ocean state

middle palaeozoic extinction events faunal and isotopic data abstract at least 9 and possibly as many as 12 extinction events of global or near global impact can be discriminated in the mid palaeozoic earliest silurian to early carboniferous on the basis of brachiopod coral conodont and ammonoid data and the history of carbonate build ups isotopic data from whole rock samples are presented for three of these events based on australian carbonate sequences constrained by conodont data these data represent the initial phase of a more extensive investigation using c o s sr and nd isotopic signatures derived from conodonts articulate and inarticulate brachiopod shell and fish remains from numerous australian and european sequences the aim of the project is to identify isotopic responses to extinction events and address causes for these changes in limestone sections analysed so far variations in carbon isotope compositions on a whole rock scale are most marked at horizons that can be correlated with times of significant reduction in biomass and diversity this is despite the fact that the whole rocks are in fact multicomponent systems with respect to carbon in part arising from diagenetic rearrangements of carbon distribution within the scale of the whole rock thus the carbon isotope data do provide evidence on a whole rock scale for fundamental changes in the global carbon cycle that are correlative with extinction events it is however unlikely that the magnitude of the isotopic shift will be precisely documented from such whole rock analyses the oxygen isotope results are less obviously related to the times of carbon isotope excursion this contrast in apparent resilience to post depositional modification of pristine isotope compositions exemplifies the extreme caution needed in evaluating isotopic data from carbonates

graptoloid evolutionary rates track ordovician silurian global climate change graptoloid evolutionary dynamics show a marked contrast from the ordovician to the silurian subdued extinction and origination rates during the ordovician give way during the late katian to rates that were highly volatile and of higher mean value through the silurian reflecting the significantly shorter lifespan of silurian species these patterns are revealed in high resolution rate curves derived from the conop constrained optimization scaled and calibrated global composite sequence of 2094 graptoloid species the end ordovician mass depletion was driven primarily by an elevated extinction rate which lasted for c 1 2 ma with two main spikes during the hirnantian the early silurian recovery although initiated by a peak in origination rate was maintained by a complex interplay of origination and extinction rates with both rates rising and falling sharply the global 13 c curve echoes the graptoloid evolutionary rates pattern the prominent and well known positive isotope excursions during the late ordovician and silurian lie on or close to times of sharp decline in graptoloid species richness commonly associated with extinction rate spikes the graptoloid and isotope data point to a relatively steady marine environment in the ordovician with mainly background extinction rates changing during the katian to a more volatile climatic regime that prevailed through the silurian with several sharp extinction episodes triggered by environmental crises the correlation of graptoloid species diversity with isotopic ratios was positive in the ordovician and negative in the silurian suggesting different causal linkages throughout the history of the graptoloid clade all major depletions in species richness except for one were caused by elevated extinction rate rather than decreased origination rate

changes in greenland ice sheet elevation attributed primarily to snow accumulation variability the response of grounded ice sheets to a changing climate critically influences possible future changes in sea level recent satellite surveys over southern greenland show little overall elevation change at higher elevations but large spatial variability using satellite studies alone it is not possible to determine the geophysical processes responsible for the observed elevation changes and to decide if recent rates of change exceed the natural variability here we derive changes in ice sheet elevation in southern greenland for the years 1978 88 using a physically based model of firn densification and records of annual snow accumulation reconstructed from 12 ice cores at high elevation our patterns of accumulation driven elevation change agree closely with contemporaneous satellite measurements of ice sheet elevation change and we therefore attribute the changes observed in 1978 88 to variability in snow accumulation similar analyses of longer ice core records show that in this decade the greenland ice sheet exhibited typical variability at high elevations well within the long term natural variability our results indicate that a better understanding of ice sheet mass changes will require long term measurements of both surface elevation and snow accumulation

recurrent climate winter regimes in reconstructed and modelled 500 hpa geopotential height fields over the north atlantic european sector 1659 1990 recurrent climate winter regimes are examined from statistically reconstructed and modelled 500 hpa geopotential height fields over the north atlantic european sector for the period 1659 1990 we investigate the probability density function of the state space spanned by the first two empirical orthogonal functions of combined winter data regimes are detected as patterns that correspond to areas of the state space with an unexpected high recurrence probability using a monte carlo approach the reconstruction and the model reveal four recurrent climate regimes they correspond to the two phases of the north atlantic oscillation and two opposite blocking patterns complemented by the investigation of the temporal evolution of the climate regimes this leads to the conclusion that the reconstructed and the modelled data for this geographic sector reproduce low frequency atmospheric variability in the form of regime like behaviour the overall evidence for recurrent climate regimes is higher for the model than for the reconstruction however comparisons with independent data sources for the period 1659 1990 revealed a more realistic temporal evolution of the regimes for the reconstructed data

early triassic stromatolites as post mass extinction disaster forms aftermaths of mass extinctions have been thought to be characterized by relaxation of ecological constraints accompanied by increased prominence of opportunistic generalists such taxa termed disaster forms have been shown to increase dramatically in range and abundance after several mass extinction events the cambrian ordovician stromatolite decline in normal marine level bottom environments has been explained as a direct or indirect consequence of increases in ecological constraints such as greater levels of predation and or bioturbation of microbial communities caused by early paleozoic benthic invertebrate evolution and diversification thus one would predict that in post ordovician strata stromatolites might appear in normal marine level bottom environments as disaster forms in the aftermaths of mass extinction particularly devastating to the benthic biota such as during early triassic time mounded stromatolites are present in two beds up to 1 5 m thick of the lower triassic spathian virgin limestone member moenkopi formation in the southwestern spring mountains of nevada stromatolites from level bottom normal marine subtidal environments have also been described from other lower triassic strata in north america europe and asia these stromatolites unusual in level bottom normal marine settings may have developed locally during the long aftermath 4 5 m y of the permian triassic mass extinction because of partial relaxation of the ecological constraintsmore that typically restricted them from unstressed subtidal normal marine level bottom environments less

the north atlantic oscillation and its imprint on precipitation and ice accumulation in greenland interannual to decadal fluctuations in net precipitation and ice accumulation are examined over greenland it is shown that in western greenland these fluctuations are correlated with the north atlantic oscillation the analysis is based on two complementary data sources a highly resolved net precipitation and accumulation history over 15 years derived form the reanalysis data of the european centre for medium range weather forecasts and a composite ice accumulation record representative for the western part of central greenland it is suggested that western greenland snow accumulation is a good proxy for the nao index with the potential for the reconstruction of a long time series

first u pb detrital zircon ages from numidian sandstones in southern apennines italy evidences of african provenance abstract two samples of quartz rich sandstones collected in the numidian flysch of southern apennines italy have been studied to highlight the provenance of detritus using radiometric dating by la icp ms of detrital zircons and to compare the obtained ages with those of the betic and maghrebian chains the provenance of quartzose detritus from european or african plates is still debated in these chains accordingly the ages of the detrital zircons can contribute significantly to discriminate the origin of the quartzose supply the u pb zircon ages n 47 vary from 3047 13 ma mesoarchean to 516 19 ma cambrian the predominance of paleo proteozoic ages 2500 1600 ma and the lack of hercynian and alpine ones suggest a provenance of the numidian supply from north african cratonic areas during the early middle langhian when the numidian successions of southern apennines were deposited in addition a cluster of ages at 773 24 ma and 668 12 ma in one sample and at 664 17 ma in the other sample calculated on zircon domains with magmatic zoning testify to an important contribution from neo proterozoic granitic rocks widely outcropping in the north african craton the age data on detrital zircons from numidian sandstones in southern apennines overlap those found in the numidian sandstones widespread in the betic cordillera and in the maghrebian chain from south spain to sicily this suggests that the entire depositional zone in which numidian flysch deposited was fed from a southerly source represented by the african craton where archean proterozoic and cambrian rocks widely crop out from the atlantic coast to the hoggar and tibesti massifs finally it must be outlined that a meso archean zircon age 3047 ma has been found in the numidian flysch of the southern apennines whereas in the numidian flysch of the maghrebian chain zircons older than paleo proterozoic 1840 ma have not yet been found

retrieving a common accumulation record from greenland ice cores for the past 1800 years 1 in the accumulation zone of the greenland ice sheet the annual accumulation rate may be determined through identification of the annual cycle in the isotopic climate signal and other parameters that exhibit seasonal variations on an annual basis the accumulation rate in different greenland ice cores is highly variable and the degree of correlation between accumulation series from different ice cores is low however when using multiyear averages of the different accumulation records the correlation increases significantly a statistical model has been developed to estimate the common climate signal in the different accumulation records through optimization of the ratio between the variance of the common signal and of the residual using this model a common greenland accumulation record for the past 1800 years has been extracted the record shows significant 11 9 years periodicity a sharp transition to very dry conditions is found just before a d 1200 and very dry conditions during the 13th century together with dry and cold spells during the 14th century may have put extra strain on the norse population in greenland and may have contributed to their extinction accumulation rates gradually decrease from a distinct maximum in a d 1394 to very dry conditions in the late 17th century and thus reflect the little ice age

delineation of carbonate dust aluminous dust and sea salt deposition in a greenland glaciochemical array using positive matrix factorization 1 high resolution trace element records from polar ice cores are fundamental to identifying spatial and temporal variability in dust and sea salt aerosols here we developed high temporal resolution glaciochemical records over recent centuries from an array of seven recently collected greenland ice cores positive matrix factorization pmf was used to assess apportionment of trace elements between three unique sources which were identified as proxies of carbonate dust aluminous dust and sea salt the three pmf factors agree well with literature values and represent the first time carbonate and aluminous dust sources have been quantifiably differentiated using high resolution glaciochemistry the concentrations of all three sources varied with ice core site however the large array of ice cores provided a regional scale understanding of the sources and magnitude of dust and sea salt impurities deposited on the greenland ice sheet at the regional level all three sources varied on seasonal annual and multiyear timescales the seasonal deposition of sea salt impurities reached a maximum in the winter followed by spring peaks of carbonate and aluminous dust over the 331 year composite record only aluminous dust exhibited a long term increasing trend that peaked in the 1930s and was followed by a 20 decline in recent decades

interannual variations of snow accumulation on the greenland ice sheet 1985 1996 new observations versus model predictions newly measured time series of net water equivalent accumulation from ice cores are reported for 11 sites located near the 2000 m contour of the greenland ice sheet many of these sites are located in regions where accumulation has not been previously measured we compared these new time series of annual accumulation with previously reported modeled precipitation covering the same time range because ice core accumulation records include both regional and local accumulation components we used adjacent ice core records at six multiple core sites to estimate the local component and extrapolated these results to the five single core sites we investigated the impact of this short scale spatial variability in accumulation on statistical comparisons between the observed accumulation and model precipitation although sealers were required to match the 12 year mean modeled precipitation to the mean observed accumulation a high degree of correspondence between observed interannual accumulation and scaled modeled precipitation was found at 7 of 11 locations the need for scaling and the low correspondence between model simulations and observations at some sites clearly indicate that model improvements are needed although very encouraging a more spatially distributed array of ice core accumulation measurements spanning the same time period as the precipitation modeling is necessary for continued model improvement and validation in agreement with earlier studies the large temporal variability in snow accumulation predicted by modeling and confirmed by ice cores indicates that the ice sheet elevation varies by tens of centimeters from year to year simply because of changing accumulation

paleoenvironmental changes in the silurian indicated by stable isotopes in brachiopod shells from gotland sweden ratios of stable carbon and oxygen isotopes in brachiopod shells more than 370 specimens esp atrypa reticularis from the silurian of gotland sweden have been analysed preservation of biological skeletal ultrastructures observed in sem micrographs and cathodoluminescence analyses indicate that usually no diagenetical alteration occurs the silurian of gotland consists of 440 m carbonate deposits spanning the late llandovery to late ludlow epochs 431 411 m y repeatedly uniform sequences of micritic limestones and marks are interrupted by complex structured reefs and adjacent platform sediments previously the alteration of facies is interpreted as the result of sea level fluctuations caused by a gradual regression with superimposed minor transgressive pulses the silurian sequence of gotland exhibits principally parallel carbon and oxygen isotope records corresponding closely to the topostratigraphic units lower values occur in periods dominated by deposition of marly sequences higher values are observed in periods dominated by reefs and extended carbonate platforms the isotope ratios are influenced by local as well as global factors the oxygen isotope ratios are interpreted to reflect paleosalinity changes due to varying freshwater input rather than changes in paleotemperature consequently the facies distribution of gotland is interpreted as resulting from changes in terrigenous input caused by different rates of continental weathering and freshwater runoff rather than by sea level fluctuations periods of arid climate and therefore anti estuarine downwelling of oxygenated surface water appear as short episodes of reef growing 1 5 m y in an epoche characterized by a tropic humid climate which causes an estuarine circulation and the upwelling of co2 rich deep water carbon isotope ratios are obviously connected to these changes in circulation by the advection of 13c rich surface water arid episodes or upwelling of 13c depleted deep water humid episodes of a silurian ocean which itself reveals generally euxinic deep water conditions due to the burial of organic carbon in black shales

the silurian of gotland sweden facies interpretation based on stable isotopes in brachiopod shells the silurian of gotland sweden consists of 440 m of carbonate deposits repeatedly uniform sequences of micritic limestones and marls are interrupted by complex structured reefs and by adjacent platform sediments generally the alteration of facies is interpreted as the result of sea level fluctuations caused by a gradual regression with superimposed minor transgressive pulses the purpose of this study is a facies interpretation based on both field observations and stable isotope measurements of brachiopod shells approximately 700 samples from stratigraphically arranged localities in different facies areas have been investigated the carbon and oxygen isotopes show principally parallel curves and a close relationship to the stratigraphic sequence lower values occur in periods dominated by deposition of marly sequences higher values are observed in periods dominated by reefs and extended carbonate platforms the oxygen isotope ratios are interpreted to reflect paleosalinity changes due to varying freshwater input rather than to paleotemperature carbon isotope ratios are believed to have been connected to global changes in the burial of organic carbon in black shales during periods of euxinic deep water conditions consequently the facies succession on gotland results from global paleoclimatic conditions changes in terrigenous input due to different rates of weathering and freshwater runoff rather than sea level fluctuations control the carbonate formation of the silurian on gotland

observed and modeled greenland ice sheet snow accumulation 1958 2003 and links with regional climate forcing abstract annual and monthly snow accumulation for the greenland ice sheet was derived from ecmwf forecasts mainly 40 yr ecmwr re analysis era 40 and further meteorological modeling modeled accumulation was validated using 58 ice core accumulation datasets across the ice sheet and was found to be 95 of the observed accumulation on average with a mean correlation of 0 53 between modeled and observed many of the ice core datasets are new and are presented here for the first time central and northern interior parts of the ice sheet were found to be 10 30 too dry in era 40 in line with earlier ecmwf analysis although too much 50 locally snow accumulation was modeled for interior southern parts of greenland nevertheless 47 of 58 sites show significant correlation in temporal variability of modeled with observed accumulation the model also captures the absolute amount of snow accumulation at several sites most notably das1 and das2 in southeast greenland mean modeled accumulation over the

discussion on ludlow late silurian oceanic episodes and events journal vol 157 2000 1137 1148 scientific editing by alistair crame d k loydell writes in their recent paper jeppsson aldridge 2000 p 1137 expressed reservations about the method behind the generation of my loydell 1998 sea level curve for the early silurian llandovery to earliest ludlow as the method used was based upon decades of consistent observations of graptolite distribution i am rather surprised that jeppsson aldridge could not accept the scientific basis of the sea level curve s construction simply stated graptolite diversity increases from low usually 1 3 species in nearshore environments to a maximum in outer shelf environments thus a significant rise in relative sea level can be inferred in a section where a diverse graptolite assemblage is recovered from above an unconformity or above strata with features indicative of deposition in very shallow water where such a deepening pattern can be demonstrated to occur at the same stratigraphical level on a number of different palaeocontinents a eustatic sea level rise is the logical explanation clearly it is necessary for me to cite here some of the decades of consistent observations that i refer to above which contrast low diversity inshore graptolite assemblages with diverse outer shelf assemblages i should also state here that there are no known exceptions to this pattern the examples selected below have been chosen for their wide palaeogeographical as well as stratigraphical coverage the list is by no means exhaustive berry boucot 1972 watkins berry 1977 kaljo 1978 paskevicius 1979 chen 1990 cooper et al 1991 lenz et al 1993 finney berry 1997 storch 1998 goldman et al 1999 jeppsson aldridge also note that my sea level curve loydell 1998 differs significantly from those published previously based on other criteria this is

northern hemisphere midlatitude cyclone variability in gcm simulations with different ocean representations the impact of different ocean models or sea surface temperature sst and sea ice concentrations on cyclone tracks in the northern hemisphere midlatitudes is determined within a hierarchy of model simulations a reference simulation with the coupled atmosphere ocean circulation model echam hope is compared with simulations using echam and three simplified ocean and sea ice representations 1 a variable depth mixed layer ml ocean 2 forcing by varying sst and sea ice and 3 with climatological sst and sea ice the latter two are from the coupled echam hope integration the reference simulation reproduces the observed cyclone tracks the cyclones are tracked automatically by a standard routine and the variability of individual cyclone trajectories within the storm tracks is determined by a cluster approach in the forced simulation with varying sst the geographical distribution and the statistics of the cyclones are not altered compared to the coupled reference simulation in the ml and the climatological simulation deviations of the mean cyclone distribution are found which occur mainly in the north pacific and can partially be traced back to missing el nino southern oscillation enso variability the climatological experiment is superior to the ml experiment the variability of the individual cyclone trajectories as determined by the cluster analysis reveals the same types and frequencies of propagation directions for all four representations of the lower boundary the largest discrepancies for the cluster occupations are found for the climatological and the ml simulation

integrated record of ludlow upper silurian oceanic geobioevents coordination of changes in conodont and brachiopod faunas and stable isotopes abstract the ludlow epoch silurian was marked by several globally recognized but mechanistically poorly understood biotic events the most pronounced of them was the lau event which strongly decimated conodont graptolite and brachiopod faunas additionally this event coincides with the largest positive stable carbon isotopic anomaly in the whole phanerozoic as well as the resurgence of the so called anachronistic microbial facies that were frequently encountered during survival episodes of the major mass extinction events in this contribution based on the analysis of the outer shelf facies succession milaiciai 103 core from the lithuanian part of the silurian baltic basin as integrated quantitative record of conodont brachiopod and 13 c changes across most of the ludlow is presented the succession was subdivided into four conodont zones that served as a stratigraphic framework for analyzing the 13 c and palaeoecological trends the depth constrained cluster analysis revealed successions of three statistically distinct conodont and six statistically distinct brachiopod assemblages that replace each other near the change points in the stable carbon isotopic curve the application of a newly developed mathematical technique based on the analysis of recurrence patterns of the fossil assemblages revealed that both conodonts and brachiopods are represented by highly time specific assemblages in the aftermath of the lau event o snajdri interval zone the anomalous interval is confined to the transgressive and highstand phases of the 3rd order post lau transgression the discussed interval is coeval with the extensive development of stromatolitic communities in the nearshore environments around the world the results allow for the first time to quantify the profound ecosystem wide geobiological impact of the mid ludfordian event that lasted up to the latest ludfordian

biotic recovery after mass extinction the role of climate and ocean state in the post glacial late ordovician early silurian recovery of the conodonts

new precipitation and accumulation maps for greenland annual total precipitation and the annual accumulation on the greenland ice sheet are evaluated and presented in two maps the maps are based on accumulation measurements of 25 1 pits and cores obtained from the upper accumulation zone and precipitation measurements made at 35 meteorological stations in the coastal region to construct the accumulation map the annual precipitation was split into solid and liquid precipitation components annual total precipitation exceeding 2500 mm w e occurs on the southeastern tip of greenland while the minimum precipitation is estimated to occur on the northeastern slope of the ice sheet the mean annual precipitation for all of greenland is 340 mm w e the largest annual accumulation of about 1500 mm w e is found on the glaciers in the southeastern corner of greenland while the smallest accumulation is found on the northeastern slope of the ice sheet west of danmarkshavn the mean accumulation on the greenland ice sheet is estimated at 310 mm w e the regional difference in accumulation is examined with respect to the 850 hpa m bar level circulation the present surface topography is found to play an important role in determining regional accumulation on the ice sheet

the ireviken event in the lower silurian of gotland sweden relation to similar palaeozoic and proterozoic events abstract for a long time the silurian was thought to represent a time of stable environmental conditions in the greenhouse period that followed the late ordovician glaciation during the past decade knowledge about the silurian has increased markedly and today it is known that the conditions in the silurian were much more variable than previously assumed detailed isotopic investigations have revealed several distinct positive excursions in both carbon and oxygen isotope values in low latitudes these periods of high c and o isotope values are in many cases characterised by the growth of reefs and the formation of extended carbonate platforms the sediments deposited during these excursions contain impoverished fossil assemblages especially with respect to conodonts graptolites and trilobites a conspicuous isotope excursion coincident with facies changes and a marked mass extinction is observed near the llandovery wenlock boundary this event is called the ireviken event after its type locality on the island of gotland sweden jeppsson l 1987 in palaeobiology of conodonts ellis horwood ltd chichester pp 129 145 here isotope data from nine sections at the nw coast of gotland are presented that cover the time interval of the ireviken event the 13c mean values rise from 1 4 to 4 5 and the 18o values increase from 5 6 to 5 0 the relative timing of stable isotope development extinctions and facies development is discussed it is shown that first extinctions precede the isotope excursion this indicates that extinction events and stable isotope development are only indirectly connected but might reflect the same causes other events characterised by similar relationships between positive isotope excursions mass extinctions and facies development are found in younger parts of the silurian late wenlock and ludlow in the late ordovician the late cambrian and with some reservations in the proterozoic the similarities between these events indicate analogous controlling mechanisms for the silurian climatic changes between humid and arid conditions in low latitudes were postulated in an earlier study of the authors a palaeoceanographic climatic model was postulated which is consistent with most of the sedimentological palaeontological and geochemical data here we demonstrate that this model may be applicable also for the older events

mid ludfordian coeval carbon isotope natural gamma ray and magnetic susceptibility excursions in the mielnik ig 1 borehole eastern poland dustiness as a possible link between global climate and the silurian carbon isotope record abstract the graptolite bearing upper silurian succession of the mielnik ig 1 borehole eastern poland represents a periplatform setting on a neritic carbonate platform located on the palaeocontinent of baltica and records widely recorded positive mid ludfordian carbon isotope excursion cie the initial increase of 13 c values occurs in the uppermost part of the neocucullograptus kozlowskii zone whereas pronounced increase and maximal values 6 74 are noted in the n kozlowskii pseudomonoclimacis latilobus interzone pristiograptus dubius bloom interval the thickness time relation in the section indicates that the main initial shift in carbon isotope ratio of 2 7 occurred over a very short time estimated to be around 4000 years and is coeval with a rapid initiation of deposition of rock forming silt sized detrital dolomite and quartz the cie decline is interpreted as steeper than in inner shelf sections and is coincident with a flooding event in the ps latilobus slovinograptus balticus zone whereas the end of the excursion is coeval with the next flooding surface marked by the ps latilobus uncinatograptus acer graptolite assemblage combined sgr spectral gamma ray facies and faunal records during the cie suggest prolonged sea level lowstand conditions the abundant detrital material dolomite siltstone facies occurring exclusively in the cie interval is noted in microfacies as well as in the geophysics record as pronounced negative excursions in total natural gamma ray and magnetic susceptibility both resulting from dilution by diamagnetic and low radioactivity minerals the perfectly sorted vertically equally sized silt material contains unique constant and low diversified grain assemblage euhedral dolomite quartz minute ooids suggesting its provenance exclusively from the shallower and or emerged parts of the carbonate platform interior the spot findings of graptolites and nautiloids along with delicate parallel lamination of sediments indicates relatively deep environment with absence of traction processes these features along with the lack of dolomite detritus in accompanying redeposited carbonates suggest its derivation by wind with regard to the earlier noted presence of aeolian detritus in the middle ludfordian we suggest dustiness as a plausible driving force of the cie in the hypothesis proposed bioavailable fe bearing dust inflow in concert with antiestuarine circulation on shelfs caused nutrient n p ratio disturbances resulting in methanogenesis in surface layer of the seas the surface layer methanogenesis should resulting in bathymetric gradient of isotope fractionation what is consistent with the cie record coincidence of sea level lowstand low latitude aridity and gustiness of the global climate are in accordance with the hypothetical short lived glaciation in mid ludfordian time

graptolites in british stratigraphy 697 taxa of planktonic graptolites are recorded and their stratigraphical ranges are given through 60 biozones and subzones in the ordovician and silurian strata of england wales and scotland in the first such stratigraphical compilation for great britain since the synthesis of elles wood 1901 1918