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

frasnian famennian biotic crisis undervalued tectonic control the prime cause of the late devonian kellwasser crisis culminating in a mass extinction event near the frasnian famennian f f boundary remains conjectural nevertheless rapid sea level fluctuations of uncertain origin during tectono eustatic highstand paired with repeated oceanic anoxia and climatic changes are usually thought at present to be one of the main immediate triggers the cathles hallam model of stress induced changes in plate density accompanying rapid rift formation furnishes an alternative for understanding the enigmatic sudden eustatic variations in the non glacial time late devonian tectonic extension causing rifting and volcanicity appears to be strongly marked in several regions of eurasia particularly in kazakhstan and eastern laurussia all larger devonian continents were more or less tectonically affected a subtle record of this tectonic rearrangement is implied even for distant and apparently quiet carbonate platforms in local extensional block faulting and tilting hydrothermal mineralisation geochemical anomalies and localized blooms of siliceous biota interpreting the late frasnian regressive transgressive pattern in terms of the cathles hallam tectono eustatic model two major rifting events are hypothesized one at about the beginning of the rhenana zone and a second principal pulse in the late linguiformis zone that encompassed the f f transition developing the veimarn milanovsky scenario of the global extensional pulse it is assumed that the key endogenous factors were related to episodic super plume activity the tectonically triggered changes climaxed in thermal and nutrient pulses and induced the stepdown ecosystem destabilization observed in the f f bio crisis minor cometary strike s might have eventually participated in this prolonged multicausal environmental stress mainly due to additional thermal shocks but perhaps effective on a regional scale only

formation processes of framboidal pyrite abstract pyrite framboid formation may be the result of four consecutive processes 1 nucleation and growth of initial iron monosulfide microcrystals 2 reaction of the microcrystals to greigite fe 3 s 4 3 aggregation of uniformly sized greigite microcrystals i e framboid growth and 4 replacement of greigite framboids by pyrite the uniform morphology uniform size range and ordering of the microcrystals in individual framboids as well as the range of observed framboid structures from irregular aggregates to densely packed spherical aggregates and polyframboids are consequences of these processes using dlvo theory derjaguin landau verwey and overbeek we have evaluated the stability of colloidal iron monosulfide suspensions with ionic strengths typical of marine and lacustrine waters in addition to van der waals attractive and double layer repulsive forces a term is included to account for the ferrimagnetic properties of greigite numerical models predict that magnetically saturated greigite particles 0 1 m in diameter will rapidly aggregate in either marine or fresh water the aggregation model is in agreement with the sequence of greigite formation followed by pyrite framboid formation established in a previous experimental study sweeney and kaplan 1973 and is consistent with the occurrence of framboids composed of other magnetic minerals e g greigite magnetite and magnesioferrite based on the temperature dependent magnetic properties of greigite and aging experiments in hydrothermal solutions this mechanism for framboid formation via precursor greigite could operate to temperatures of 200 c consistent with the occasional occurrence of pyrite framboids in the paragenesis of metalliferous ore deposits

the early toarcian and cenomanian turonian anoxic events in europe comparisons and contrasts two intervals of mesozoic time are demonstrably of sufficient geological brevity to qualify readily for the term anoxic event the earlyfalciferum zone orexaratum subzone of the toarcian and thewhiteinella archaeocretacea interval zone that straddles the cenomanian turonian boundary both periods of time saw regional deposition of anomalously organic rich strata black shales accompanied by a positive 2 pdb carbon isotope excursion in coeval biogenic carbonates and significant faunal change the duration of both events was probably less than half a million years and both were preceded by regional erosion and possible upwelling coincident sea level rise and transgression is likely a european view of these events however spotlights some significant differences whereas thefalciferum zone organic matter is generally more concentrated and more hydrogen rich on the palaeo european shelf than on the tethyan continental margins the reverse holds true for the black shales formed during thewhiteinella archaeocretacea interval zone furthermore the carbon isotope composition offalciferum zone organic matter from both north european and tethyan sites is anomalously negative compared to that developed in thewhiteinella archaeocretacea interval zone differing planktonic organisms may have been involved and their possible diverse ecological requirements may go some way to explaining the nature and distribution of facies deposited during these two events

sulfur isotope anomaly associated with the frasnian famennian extinction medicine lake alberta canada a sharp positive 34s anomaly occurs in a 0 5 cm siltstone that contains syndepositional pyrite and was deposited below wave base as part of a basinal off reef succession at medicine lake alberta the bed rests on bioturbated oxygenated dolomitic siltstones that are positively correlated with biostromal banks containing the last frasnian shelly benthos over a wide region above laminated anoxic argillaceous lime mudstones grade upward into beds containing famennian conodonts and brachiopods geochemical and sedimentological data suggest flooding of the craton by basin derived anoxic water at the extinction horizon as a result of a sudden deep basin or ocean turnover comparable positive 34s values are found in sedimentary pyrite in frasnian black shales from a passive margin basin in the yukon to the north values decrease in the famennian

interpreting benthic oxygen levels in mudrocks a new approach quantified paleoecology and gamma ray spectrometry have been applied in the analysis of the kimmeridge clay a highly organic rich british jurassic mudrock decreasing benthic oxygen trends are reflected in decreasing species richness and dominance diversity values similarly the degree of fragmentation of the benthos reflects the benthic energy levels and covaries with benthic oxygen the calculation of authigenic uranium values from data gathered by gamma ray spectrometry shows enrichment in more oxygen deficient environments the good correlation between the independently derived paleoecological and authigenic u data indicates the importance of these techniques in environmental analysis of marine petroleum source rocks

an indicator of water column anoxia resolution of biofacies variations in the kimmeridge clay upper jurassic u k abstract an indicator of anoxicity ia defined as the ratio pyrite fe oxide fe total fe can be used to recognize sediments deposited under an anoxic water column modern marine sediments deposited under oxygenated bottom waters mainly have ia values 0 5 ia values in the central kimmeridge clay upper jurassic uk for fissile organic rich shales indicate that deposition occurred principally from anoxic bottom waters with infrequent oxygenation events

late frasnian sedimentation cycles in the appalachian basin possible evidence for high frequency eustatic sea level changes abstract during the late frasnian 11 fourth order progradational retrogradational marine sedimentation cycles were deposited in the appalachian foreland basin mapping based primarily on subsurface data demonstrates the continuity of these cycles over a distance of 700 km cyclicity in distal facies occurs as alternations of organic rich and organic poor shales two of the organic shales can be correlated with the transgressive kellwasser beds of europe in more proximal facies recurring lobes of siltstone and sandstone were deposited based on lithologic indices the temporal pattern shows significant variation in the strength of relative facies change during deposition in particular two times of particularly pronounced progradation correspond to previously recognized eustatic sea level falls the correlation of portions of appalachian basin depositional cyclicity with global sea level events suggests that the entire sequence of 11 cycles with estimated average duration of around 100 150 ka were the result of high frequency eustatic sea level changes this in turn would be consistent with a brief period of late frasnian glaciation as others have previously suggested

imaging supershear rupture for the 2014 mw 6 9 northern aegean earthquake by backprojection of strong motion waveforms the seismic source spatiotemporal evolution of the mw 6 9 event on 24 may 2014 in northern aegean is imaged by backprojection of strong motion envelopes the results indicate that the event ruptured on two different fault segments in the first one rupture propagated from the hypocenter westward for 20 km in the second delayed segment to the east rupture propagated eastward for 65 km with a supershear velocity 5 5 km s at the end of this rupture the largest stacking amplitudes are imaged associated with possible stopping phases from the abrupt cessation of a fast slip low aftershock seismicity on the supershear segment implies a simple and linear fault geometry there this is the third large event in the northern aegean trough northern anatolian fault zones that has ruptured with supershear speed this characteristic should be taken into account in studying past events and estimating seismic hazard in this area

electromagnetic constraints on a melt region beneath the central mariana back arc spreading ridge 1 an electrical resistivity profile across the central mariana subduction system shows high resistivity in the upper mantle beneath the back arc spreading ridge where melt might be expected to exist although seismic data are equivocal on the extent of a possible melt region the question arises as to why a 2 d magnetotelluric mt survey apparently failed to image any melt we have run forward models and inversions that test possible 3 d melt geometries that are consistent with the mt data and results of other studies from the region and that we use to place upper bounds on the possible extent of 3 d melt region beneath the spreading center our study suggests that the largest melt region that was not directly imaged by the 2 d mt data but that is compatible with the observations as well as the likely effects of melt focusing has a 3 d shape on a ridge segment scale focused toward the spreading center and a resistivity of 100 m that corresponds to 0 1 1 interconnected silicate melt embedded in a background resistivity of 500 m in contrast to the superfast spreading southern east pacific rise the 3 d melt region suggests that buoyant mantle upwelling on a ridge segment scale is the dominant process beneath the slow spreading central mariana back arc a final test considers whether the inability to image a 3 d melt region was a result of the 2 d survey geometry the result reveals that the 2 d transect completed is useful to elucidate a broad range of 3 d melt bodies

microfacies sequence stratigraphy and clay mineralogy of a condensed deep water section around the frasnian famennian boundary steinbruch schmidt germany abstract a multidisciplinary analysis microfacies sequential stratigraphy and clay mineralogy was made on frasnian famennian f f boundary strata of the steinbruch schmidt section in western germany three major microfacies are recognised their succession records a shallowing upward evolution from deep quiet and poorly oxygenated environments below the storm wave base to environments influenced by current activities close to the storm wave base the kellwasser horizons correspond to the deepest microfacies the shallowest microfacies correspond to fine grained calcareous tempestites or turbidites coming from a distant shelf of northwest germany the sequential pattern through the f f boundary shows the succession of seven systems tracts two sequence boundaries are located just above the lower kellwasser horizon and at the f f boundary itself these are underlined by hardgrounds suggesting time gaps the kellwasser horizons correspond to sea level highstands and the overlying beds record a transition from lowstand to transgressive systems tracts illite and kaolinite are the dominant clay minerals associated with mixed layers and traces of chlorite illite abundance is maximal during kellwasser horizons illite and kaolinite were probably inherited from a highly weathered source area although part of the illite is diagenetic kaolinite is the second most abundant clay mineral and is particularly well represented up to 50 between the kellwasser horizons an unusual clay assemblage of illite and mixed layers is associated with a bentonite layer kaolinite increases during times when thin tempestites or turbiditic microbioclastic layers come from a distant shelf during sea level falls the kaolinite percentage reaches its maximum at the top of the lowstand systems tract the high percentage of kaolinite suggests a hot wet climate and could be related to global warming

anoxic events in the late frasnian causes of the frasnian famennian faunal crisis carbon isotope data collected from five frasnian famennian boundary sections in central europe show two positive 13 c excursions in the late frasnian 367 ma both anomalies coincided with the deposition of the bituminous lower and upper kellwasser horizons the carbon isotope patterns indicate two phases of enhanced burial and subsequent recycling of organic carbon a maximum formation of warm saline waters on the subtropical to tropical epicontinental shelves during late frasnian transgressive episodes may have induced oceanic oxygen deficits variations in the c org burial rates may have resulted in changes in the co 2 concentrations in the oceans and in the atmosphere culminating in global climatic changes we propose that the repeated co occurrences of sea level fluctuations anoxic conditions and global climatic changes during the late frasnian would affect especially the subtropical to tropical shallow water communities and reef ecosystems which were severely affected during the frasnian famennian faunal crisis

the early toarcian anoxic event in the westernmost tethys subbetic paleogeographic and paleobiogeographic significance a positive delta 13 c excursion reveals an oceanic anoxic event in the subbetic corresponding to the westernmost end of the tethys during the early jurassic this positive delta 13 c excursion exists in five stratigraphic sections consisting of lower and middle toarcian pelagic sediments the positive delta 13 c excursion in the subbetic is located in the upper part of the early toarcian serpentinus approx falciferum biozone while in other tethyan regions alps apennines and dinarides it has been found in the lower part of the same biozone the most significant positive delta 13 c excursion detected in the subbetic is therefore about half a million years younger although other relative peaks had been detected this isotopic anomaly can be correlated with a maximum transgression that occurred earlier in the regions closer to the open sea of the tethys ocean other features of the anoxic event faunal crises and black shale deposits appear at different ages related t

marine biodiversity through the late cenomanian early turonian palaeoceanographic controls and sequence stratigraphic biases changes in the marine macro and microfauna sedimentary geochemistry and surface water palaeoproductivity through the last 500 000 years of the cenomanian and first 300 000 years of the turonian are documented these are based on the succession at eastbourne the thickest and most complete section through the late cenomanian and early turonian in the anglo paris basin two levels of rapid faunal and geochemical change are identified one coincident with a significant increase in siliciclastic input at the base of the plenus marls member and the other with a marked drop in surface water productivity near the top of the same unit faunal change is demonstrated to be largely a pattern of immigration emigration rather than true extinction and our sequence stratigraphical analysis shows that it was coincident with major sea level changes no evidence is found to support the hypothesis that reduced bottom water oxygenation developed and was responsible for extinctions amongst the benthos in mid shelf environments the onset of pure chalk facies is interpreted to mark the breakdown of shelf break fronts and the spread of oligotrophic oceanic waters over much of the continental shelf initiated by rising sea level the cenomanian turonian event far from recording a mass extinction of shelf fauna is most probably an artifact caused by a significant switch in the nature of the surviving sedimentary record as a result of a major but perfectly ordinary oceanographic change

water column anoxia enhanced productivity and concomitant changes in δ13c and δ34s across the frasnian famennian boundary kowala holy cross mountains poland the investigation of the trace element and organic geochemistry of the frasnian famennian boundary section at kowala holy cross mountains poland shows that the lower water column was oxygen deficient during late frasnian and early famennian times the abundance and carbon isotopic composition of diaryl isoprenoids biomarkers indicative for green sulfur bacteria prove that euxinic waters reached into the photic zone at least episodically total organic carbon toc contents show two maxima that are time equivalent to the kellwasser horizons deposited in shallower water settings enhanced toc concentrations are explained by a higher primary productivity presumably as a consequence of an enhanced nutrient supply from the continent the increase in the abundance of hopanes and bituminite suggests that the bacterial contribution to toc increased at the frasnian famennian transition the sulfur isotopic composition of pyritic and organically bound sulfur shows a 27 excursion across the boundary the observation that the 34s values of organic bound sulfur closely resemble that of pyrite sulfur indicates a common sulfur source likely early diagenetic sulfide a change in the 13c of total dissolved inorganic carbon as a consequence of an enhanced burial of 12c enriched organic carbon is indicated by a 3 excursion measured for toc as well as for individual n alkanes and isoprenoids the burial of large amounts of organic carbon is expected to result in a decrease in pco2 and should affect the photosynthetic carbon isotope fractionation ep the fact that we observe no change in ep can be explained by the circumstance that ep was most probably at maximum values as a consequence of high atmospheric and oceanic dissolved co2 concentrations during the devonian

the frasnian famennian boundary interval in the south polish moravian shelf basins integrated event stratigraphical approach abstract the late devonian mass extinction event near the frasnian famennian f f boundary has been analysed using conodont biostratigraphy and biofacies sedimentology magnetic susceptibility and geochemistry in reference sections of the south polish moravian shelf holy cross mountains cracow and brno areas high resolution biostratigraphic study revealed difficulties in the precise recognition of this natural stage boundary but confirmed the occurrence of a major third order sequence boundary in the f f transition in an active synsedimentary tectonic setting marked by erosional discontinuities hardgrounds and brecciation or omission surfaces conclusive evidence of an extraterrestrial impact has not been found among earth bound factors the main devastating role in the shelf habitats is ascribed to fluctuating anoxia and or nutrient dynamics in a disturbed greenhouse climatic setting the long term facies changes were determined by a conspicuous break in carbonate production accompanied by replacement of mature stromatoporoid coral reefs by pioneer shelly crinoid banks microbial mounds and localised oolitic bars the key f f passage interval was marked by intermittent but generally accelerated periplatform ooze debris input and severe storm events as well as by probably highly fluctuating oxygenation and biological overproduction best manifested in radiolarian silicisponge and cephalopod acmes eutrophication phenomena at least partly stimulated by various hydrothermal and volcanic processes were one of the major biogeochemical processes during this climax of the late devonian biotic crisis however significant oceanographic perturbations were also linked with the onset of the transgressive hypoxic upper kellwasser event still within the latest frasnian linguiformis zone i e well before the f f conodont collapse implied variations in the redox state of seawater through the kellwasser timespan probably in regionally highly variable temporal scales are in agreement with recent palaeoecological and biogeochemical inferences in particular suggesting recovering oxygenation just prior to the f f boundary in the other laurussian intrashelf basins all the data support a long time multicausal earth bound crisis instead a worldwide cosmic catastrophe

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

chitinozoan bio event in the frasnian famennian boundary beds at la serre montagne noire southern france abstract chitinozoans and other palynomorphs have been investigated in frasnian famennian boundary beds from trench c at la serre montagne noire southern france this section is located some 30 km from the coumiac quarry containing the global stratotype section and point gssp for the base of the famennian at la serre the frasnian famennian f f boundary falls within interbedded anoxic dark shales and limestones this lithology proves to be more suitable for palynological investigations than the reddish nodular limestones of the f f stratotype in the coumiac section which are virtually devoid of organic matter at la serre the uppermost meter of frasnian deposits corresponding to the upper kellwasser event level contains only a few chitinozoans but other palynomorphs especially tasmanaceans maranhites proliferate in some horizons conversely the most basal famennian bed yields an exceptional number of chitinozoans up to 19 000 specimens per gram of rock a few tracheids but virtually no tasmanaceans the absence or the extremely low numbers of miospores and acritarchs in these f f boundary beds seems related to the distal position of the deposition site we have compared the fluctuation of the chitinozoan abundance both with the abundance of the other palynomorphs and with that of the conodonts present in the same samples these data collated with sedimentological and palaeoecological information document the relationships between the anomalous abundance of the chitinozoans and the latest frasnian earliest famennian mass extinction it is concluded that the exceptional chitinozoan concentration in the most basal famennian bed at la serre is not related to a sorting process generated by turbidity currents or by a temporary increase in the hydrodynamic energy at the water sediment interface it corresponds to the conjunction of a high production of chitinozoans a very low rate of destruction of the vesicles and minimal dilution of the deposit by terrestrial mineral input the environmental factors leading to such an exceptionally high record of chitinozoans are discussed with a particular attention to consequences of the late frasnian mass extinction

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

anoxia pre dates frasnian famennian boundary mass extinction horizon in the great basin usa abstract major and trace metal results from three great basin stratigraphic sections with strong conodont biostratigraphy identify a distinct anoxic interval that precedes but ends approximately 100 kyr before the frasnian famennian f f mid late devonian boundary mass extinction horizon this horizon corresponds to the final and most severe step of a more protracted extinction period these results are inconsistent with data reported by others from the upper kellwasser horizon in europe which show anoxia persisting up to the f f boundary in most sections conditions returned to fully oxygenated prior to the f f boundary in the study area these data indicate that the worst part of the f f extinction was not related directly to oceanic anoxia in this region and potentially globally

variations in ce anomalies of conodonts through the frasnian famennian boundary of poland kowala holy cross mountains implications for the redox state of seawater and biodiversity abstract rare earth element ree concentrations on upper devonian conodonts distinguished by very low color alteration index were measured by inductively coupled plasma mass spectrometry from a stratigraphic section across the frasnian famennian f f boundary in the holy cross mountains poland the present data show a hat shaped pattern of the ree spectra similarly to other devonian conodont spectra already documented however our sample composition suggests little to moderate alteration of the original oceanic pattern through the adsorption mechanism in a context of weak or early diagenesis all along the section the magnitude of the ce anomaly is always negative and there is an inverse correlation between the ce anomaly and the la sm sn ratio this has been interpreted as an la enrichment due to a terrestrial input a mathematical procedure was used in order to restore the original ce anomalies that would reflect the seawater environment not contaminated by terrestrial inputs no noticeable change is observed in the frasnian with homogeneous values of ce model but a sharp increase is initiated just below the f f boundary with maximum values in the lowermost famennian the measured la sm sn ratios co vary with the ce model in agreement with the hypothesis of a terrigenous input finally the inverse correlation between the values of ce model and the relative abundance of palmatolepis during the famennian constitutes the first evidence known of a redox control on the presence of a conodont genus that is an indicator of deep water environment

phanerozoic large igneous provinces lips heatt haline euxinic acidic thermal transgression episodes and mass extinctions abstract the phanerozoic consists of three mutually exclusive climate states icehouse greenhouse and hothouse the greenhouse is the default state representing 70 of the phanerozoic it is characterized by a weak thermal mode pole driven deep water formation with little or no continental sea ice and weakly oxic cool water sinking near the poles nitrogen limitation characterizes greenhouse oceans in which ammonium may be the dominant bioavailable form of nitrogen the steady state greenhouse default must be forced to produce either of the other two states continent continent collision produces the intense chemical weathering that draws down atmospheric co2 and results in the icehouse state that comprises 20 25 of the phanerozoic icehouses have ice caps in contact with the ocean that produce icebergs and foster sea ice formation sea ice formation fills the ocean with highly oxic phosphorus limited icewater except for a thin layer of warm surface water in the tropics of the 23 most conspicuous mass extinctions of the phanerozoic including the late ediacaran 4 are associated with ice volume related regressions and 3 are problematic we suggest that the other 16 mass extinctions occurred when greenhouse climate was forced to hothouse climate large igneous provinces lips can trigger the heatt haline euxinic acidic thermal transgression mechanism which can force greenhouse climate to a hothouse climate state the rapid voluminous co2 emissions of lips cause a series of events that result in very slow but pronounced haline mode circulation mid latitude driven deep water formation that produces warm saline bottom water at very dry hot subtropical and middle latitudes this water upwells at the poles causing warm and moist equable climate hothouse development promotes deep sea anoxia that is generated in concert with co2 buildup and warming the spread of anoxia favors reduced nitrogen over nitrate and limited iron dust curtails nitrogen fixation this leads to dominance of primary productivity by primitive green algae and or cyanobacteria progression to euxinia that reaches the photic zone severely curtails primary productivity via poisoning even as availability of usable nitrogen plummets the result is eukaryotic mass extinction we suggest that the 16 phanerozoic mass extinctions referred to above resulted at least in part from the heatt process evidence for this relationship at 11 of the most severe extinctions is convincing data sets for the other 5 are strongly suggestive of heatt related mass extinction but do not yet have enough documentation to reliably characterize them as heatt episodes

upper kellwasser carbon isotope excursion pre dates the f f boundary in the upper devonian lennard shelf carbonate system canning basin western australia abstract here we report four high resolution carbon isotope records in addition to trace element data for the frasnian famennian f f boundary interval in the lennard shelf carbonate system of the canning basin western australia this region lacks the characteristic black shale horizons associated with the global late devonian kellwasser extinction events yet still exhibits a trend in carbon isotope character similar to what has been reported from elsewhere in the world two positive 13c excursions with 3 4 amplitudes enrichments in select trace element ratios suggest that both excursions are related to periods of oxygen deprivation and perhaps increased biological productivity given the continuous and stratigraphically expanded nature of lennard shelf sections together with high density sampling constrained by both conodont biostratigraphy and magnetostratigraphy we observe that the upper kellwasser isotope excursion maximum 13c values and associated trace element enrichments occur distinctly lower than the f f boundary level these results have implications for the paleoenvironmental conditions leading up to the late devonian mass extinction in terms of ocean chemistry and circulation patterns this data set allows for a rare detailed look at the temporal relationship between the kellwasser events and the f f boundary and constrains the pattern of carbon isotope perturbations at the intra zonal scale

late devonian rugose corals and the frasnian famennian crsis all well dated occurrences of upper devonian septate corals subclass rugosa are analyzed at species and higher taxonomic levels platform dwelling corals are differentiated from the less numerous basin dwelling corals through early and middle frasnian time evolution outpaced the extinction of rugose corals so that late frasnian faunas were more diverse than the earliest frasnian faunas this gradual increase of genera was terminated abruptly by an almost complete extinction of late frasnian platform dwelling rugosa in uppermost gigas to lower palmatolepis triangularis zone time none of the 151 species and probably as few as two or three at most five of the 47 genera of late frasnian shallow water corals survived this event the loss of coral biomass was equally devasting very few early famennian platform dwelling corals are known although platform carbonates of this age were deposited in several regions platform faunas comprising 66 species and 27 genera reappeared in late famennian time the

magnetostratigraphy susceptibility of the frasnian famennian boundary magnetosusceptibility event and cyclostratigraphy msec is used to establish a non polarity based magnetostratigraphy susceptibility mss between the stratotype region for the frasnian famennian f f boundary sequence in the montagne noire of southern france the eastern rheinisches schiefergebirge of germany belgium the eastern anti atlas of morocco and the arbuckle mountains of southern oklahoma usa despite differences of depositional environment the mss is remarkably consistent and can be described in the context of a hierarchy of magnetozones that allow the extension of correlation away from the montagne noire reference section the nature of the controls on the influx of iron into the marine system produces a natural hierarchy of at least seven orders or magnetozones designated msz1 msz2 msz3 msz4 msz5 msz6 and msz7 these are characterized in terms of the magnitude of their duration the mss reference section of choice for the f f boundary is the well known trench c at la serre lsc in the northeastern montagne noire of southern france the f f boundary is located at the lower boundary of magnetozone la serre i 3b at la serre as well as in all other sections studied msz4 and msz5 magnetozones are used to establish intra and inter regional correlation between the reference sequence and the other regions the base of the upper kellwasser event is as variable within the mss zonation as it is within the biostratigraphic zonation as is the position of the lower kellwasser event

shallow marine dysoxia across the permian triassic boundary evidence from pyrite framboids in the microbialite in south china abstract the end permian mass extinction resulted in the collapse of reef ecosystems and the subsequent formation of microbialites in shallow carbonate platforms in south china large quantities of pyrite framboids are preserved in the microbialites but absent in the underlying skeletal limestone indicating an abrupt shift in water column redox conditions in association with the shallow marine faunal mass extinction detailed study of size distributions of 1374 pyrite framboids found in 9 horizons in laolongdong section in chongqing municipality south china were performed to evaluate this shift in paleo redox condition of the shallow marine environment pyrite framboids in the microbialite average 8 41 m in size comparable with those from modern sediments underlying dysoxic water columns this infers that dysoxic waters in the latest permian might have expanded to reach the shallow marine environments in south china mean diameters of pyrite framboids from mudstones overlying the microbialite are 7 63 m 7 68 m likely indicating continuing intensification of oxygen deficiency in the bottom waters microgastropods ostracods and some foraminifers which survived and flourished in the microbialite almost disappeared during the mudstone deposition possibly reflecting a consequence of oxygen depletion

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

organic geochemistry and palynofacies of the early middle frasnian transition late devonian of the holy cross mountains southern poland abstract geochemical and palynological investigation of the lower to middle frasnian reef to basin succession at the well known kowala quarry holy cross mountains demonstrates the variable character of organic matter om deposited in different oxidative reductive conditions during sedimentation of the basinal deposits anoxic conditions in the water column prevailed in the organic rich sediments deposited during the palmatolepis punctata zone set d anoxia occurred in the photic zone as inferred from the presence of isorenieratane aryl isoprenoids and gammacerane in the same kind of deposits but occurring during the palmatolepis hassi zone set f anoxia apparently occurred mainly in the deeper parts of the basin and only sporadically reached the photic zone this interpretation is based on the lack of isorenieratane traces of aryl isoprenoids and the presence of gammacerane in the investigated samples the basinal clay enriched sediments of sets d and f are divided by an organic poor set e typical for the carbonate platform fore reef environment characterized by oxic conditions a palynostratigraphical study of the frasnian section from the kowala quarry allowed recognition of two miospore zones geminospora semilucensa perotrilites donensis sd and archaeoperisaccus ovalis verrucosisporites grumosus og relatively small quantitative and qualitative changes of the organic particles miospores tracheids prasinophytes and acritarchs are interpreted primarily in terms of sea level fluctuations and enhanced productivity in particular the appearance of abundant abnormally large mature leiospheres in set d can be the result of progressive eutrophication related to environmental changes recorded in the recently detected major positive carbon isotope anomaly as during the frasnian famennian mass extinction interval this eutrophication could have been stimulated by a rapid increase in primary production and subsequently expanding anoxic conditions but it is evident only in the early phase of the middle frasnian 13 c excursion the processes of the secondary hydrothermal fluid migration taking place after the lithification of the sediments caused partial om oxidation the products of these processes are such phenyl derivatives of aromatic hydrocarbons as phenylphenanthrenes terphenyls phenyldibenzothiophenes and phenyldibenzofurans moreover an oxygen compound rarely described from sedimentary om dibenzo p dioxin and its methyl and dimethyl derivatives seems to be the additional product of hydrothermal om oxidation

thermal structure of the low velocity zone derived from laboratory and seismic investigations laboratory measurements of seismic velocities in upper mantle peridotite can be used to constrain the thermal state in the low velocity zone the measurements carried out at high temperature and high confining pressure can be extrapolated to upper mantle conditions we compare laboratory velocities with seismic observations and estimate temperatures and partial melt fractions in the low velocity zone the comparison gives 1310 c and 7 vol partial melt at 45 km depth in 0 5 my asthenosphere beneath the iceland plateau and 1450 c and 3 vol partial melt at 85 km depth in 0 20 my asthenosphere beneath the pacific ocean the laboratory results show that up to a 6 velocity drop in the low velocity zone relative to the lithospheric velocity does not necessarily require the existence of partial melt this implies that partial melt may not exist in the low velocity zone older than 5 my and 50 my in the iceland plateau and the pacific ocean respectively

molecular and petrographic indicators of redox conditions and bacterial communities after the f f mass extinction kowala holy cross mountains poland abstract pyrite framboid diameter analysis and organic geochemistry of the triangularis crepida boundary section at kowala holy cross mountains poland imply suboxic to oxic and sporadically euxinic bottom waters during the lower famennian in addition morphological web like structures typical for microbial mats as well as the recognition of 2 methylhopanes and monomethyl alkane cyanobacteria biomarkers is evidenced of microbial activity after the global frasnian famennian f f extinction event the presence of cyanobacterial mats also suggests suboxic to oxic environments and at the same time photic bottom water conditions however isorenieratane and its derivatives were detected in almost all samples the presence of this well known biomarker of green sulfur bacteria implies that euxinic conditions were present in the upper part of the water column at least intermittently or that temporal euxinia occurred in the water column presence of euxinic conditions is confirmed by the occurrence of small sized pyrite framboids which were particularly dominant in the lower part of the section the shift towards low 13 c values in both micritic limestones and in sedimentary organic matter seen at the beginning of the period of diminished photic zone might reflect an influx of newly respired co 2 to surface waters caused by enhanced respiration at depth after the f f transition in the checiny zbrza basin

seismic anisotropy in the mantle beneath an oceanic spreading centre beneath an active mid ocean ridge the mantle upwells in response to the divergence of the newly formed plates leading to high temperatures and pressure release melting below the ridge axis the width of the upwelling region and the amount of melting depend on mantle rheology1 5 but all models predict a maximum decrease in seismic velocity at the ridge axis it has also been suggested however that the alignment of anisotropic minerals by shear in the upwelling mantle will increase seismic velocity for rays travelling subvertically through the upwelling zone6 7 here we report the observation of a consistent pattern of anomalously early p wave arrival times at an array of ocean bottom seismographs deployed across the axis of the southern mid atlantic ridge p waves from distant earthquakes arrive earlier at stations near the axis than at those further away our results are consistent with a model of anisotropy in which the degree of mineral alignment is greatest directly beneath the ridge axis and significant anisotropy extends tens of kilometres from the axis

the expression of the hangenberg event latest devonian in a relatively shallow marine succession pomeranian basin poland the results of a multi proxy investigation the uppermost famennian lowermost tournaisian interval has been analysed in detail using biostratigraphy sedimentology magnetic susceptibility and geochemistry in a reference section of the relatively shallow carbonate ramp environment within the pomeranian basin high resolution biostratigraphic study based on miospores allows recognition of the standard western european lepidophyta nitidus ln and verrucosus incohatus vi zones as well as the convolutispora major zone a local pomeranian equivalent of the european standard hibernicus distinctus hd zone the sedimentary succession and specific phenomena recognized close to the devonian carboniferous boundary such as fluctuations in water column euxinia wildfire evidence relative sea level changes and perturbations of the carbon cycle reflected by positive carbon excursions display a pattern partly similar to that observed in many areas in europe during the hangenberg event although the hangenberg black shale horizon is not developed here these important microscale environmental perturbations were observed not only within the famennian ln miospore zone but in a wide interval between the ln and the lowermost local convolutispora major miospore zones lower part of hd standard miospore zone it is still uncertain whether the recognized event s were connected solely with the hangenberg event which was possibly complex and multi phased as is sometimes suggested or whether they represent a succession of regionally limited post hangenberg events this question needs to be further investigated on broader stratigraphic and geographical scales

the global frasnian famennian kellwasser event during the uppermostp gigas conodont zone p linguiformis zone the stepwise frasnian extinction culminates in the global transgressive regressive frasnian famennian kellwasser event most pelagic organisms of the tropical marine environment are more or less affected by this mass extinction during the early upper devonian extinction rates are clearly related to the deposition of black shales and the storage of a great amount of organic carbon in the shelf sediments contemporaneous positive excursions of the 13c recorded from pelagic limestones of europe and australia prove a worldwide change in the co2 content of the oceans surface water which is in balance with the atmosphere if the climate is controlled by the co2 content of the atmosphere a cyclic operation process might have developed with the succession transgression high organic production deposition of organic carbon lowering of co2 in the atmosphere icehouse effect polar glaciation regression erosion of organic carbon and re supply of co2 to the ocean and atmosphere greenhouse effect deglaciation transgression during the change from a greenhouse to an icehouse effect an overturn of the anoxic oceans probably was one of the causes for the mass killing of low latitude marine organisms

seismic attenuation tomography of the mariana subduction system implications for thermal structure volatile distribution and slow spreading dynamics 1 the anelastic structure of a subduction zone can place first order constraints on variations in temperature and volatile content we investigate seismic attenuation across the western pacific mariana subduction system using data from the 2003 2004 mariana subduction factory imaging experiment this 11 month experiment consisted of 20 broadband stations deployed on the arc islands and 58 semibroadband ocean bottom seismographs deployed across the fore arc island arc and back arc spreading center we compute amplitude spectra for p and s arrivals from local earthquakes and invert for the path averaged attenuation for each waveform along with the seismic moment and corner frequency for each earthquake additionally we investigate earthquake source parameter assumptions and frequency dependent exponents ranging from 0 to 0 6 tomographic inversion of nearly 3000 t estimates at 0 27 for 2 d qp 1 and qp qs structure shows a 75 km wide columnar shaped high attenuation anomaly with qp 43 60 beneath the spreading center that extends from the uppermost mantle to 100 km depth a weaker high attenuation region qp 56 70 occurs at depths of 50 100 km beneath the volcanic arc and the high attenuation regions are connected at depths of 75 125 km the subducting pacific plate is characterized by low attenuation at depths greater than 100 km but high attenuation is found in the plate between 50 and 100 km depth the fore arc shows high attenuation near the volcanic arc and beneath the serpentinite seamounts in the outer fore arc qs structure is less well resolved than qp because of a smaller data set but qp qs ratios are significantly less than 2 throughout the study region as temperatures estimated from qs 1 are unusually high we interpret the arc and wedge core anomalies as regions of high temperature with enhanced q 1 due to hydration and or melt the slab and fore arc anomalies as indicative of slab derived fluids and or large scale serpentinization and the columnar shaped high qp 1 anomaly directly beneath the back arc spreading center as indicative of a narrow region of dynamic upwelling and melt production beneath the slow spreading ridge axis

frasnian upper devonian integrated facies analysis magnetic susceptibility and sea level fluctuations in the nw algerian sahara changes in the palaeoenvironment are investigated in two representative frasnian sections of the nw algerian sahara integrating sedimentology and magnetic susceptibility ms the ben zireg section is characterized by condensed and ferruginous calcareous deposits in the south marhouma section the sedimentation rate is high dominated by muddy nodular limestones with several hypoxic shale intervals in both sections sediments were mostly emplaced on pelagic outer ramps below the limit of storm wave base evolving through time from proximal to distal setting investigations of the temporal evolution of facies and ms data permit a first estimate of the local sea level trends in nw algeria these trends match the overall long term rise of sea level recognized worldwide from frasnian zone 5 upwards noteable positive excursions of the sea level curve related to the semichatovae transgression as well as to the late frasnian transgression prior to the late kellwasser event can be established in this area although the sharp regression of sea level at the upper kellwasser level can be confirmed from our data no particular trend is depicted at the transition of conodont zones frasnian zones 12 13 where the presence of the lower kellwasser level has not yet been clearly recognized

the early toarcian jurassic anoxic event stratigraphic sedimentary and geochemical evidence detailed paleogeographic studies in the southern alps suggest that an oxygen minimum model is appropriate for interpreting conditions on tethyan continental margins advection of manganese in this low oxygen layer may explain the local occurrence of carbonate ores of this element carbon sulfur and iron sulfur ratios although showing considerable scatter suggest that bottom waters at this time were locally euxinic containing free hydrogen sulfide this oceanic anoxic event was preceded by significant faunal turnover of ammonites in tethys and accompanied by widespread extinction of benthos in northern europe in response to the lateral spread of anoxic bottom waters during transgression similar changes may be recognized in other parts of the world other anoxic events may have taken place during the jurassic but documentation is as yet meagre furthermore models for such phenomena remain largely speculative although upwelling and increased planktonic productivity commencing in pre toarcian time are favored for the falciferum zone event documented here from author

gravity anomalies and crustal thickness variations along the mid atlantic ridge between 33 n and 40 n multibeam bathymetry and gravity data have been obtained along an 800 km long section of the mid atlantic ridge from just south of the hayes fracture zone at 33 n to the northern edge of the azores platform near 40 n a three dimensional analysis of these gravity and topography data combined with results from earlier seismic refraction studies in this area reveal two different scales of crustal heterogeneity a systematic along axis segment scale 8 9 km near the middle of spreading segments and the thinnest crust 3 4 km near segment offsets the magnitude of this along axis variation in crustal thickness is proportional to the length of the spreading segment and the size of the adjacent ridge offset there also is a distinct asymmetry in crustal structure across the rift valley near large segment offsets with gravity highs inferred to be thinner crust beneath the inside corner highs adjacent to these offsets this segment scale crustal heterogeneity is similar to that reported from the kane to atlantis section of the mid atlantic ridge and from parts of the intermediate spreading southern mid atlantic ridge it is superimposed on a second longer wavelength variation in gravity and crustal thickness associated with the azores hot spot the most pronounced effect of the azores hot spot on the mid atlantic ridge occurs between 38 n and 40 n where the ridge axis rapidly shoals by more than 1000 m the crust thickens by over 2 km and the rift valley largely disappears the absence of a deep axial rift valley on the azores platform and near the midpoints of some ridge segments along the mid atlantic ridge to the south agrees well with the predictions of recent ridge crest thermal and rheological models that suggest a dependence of axial morphology on both crustal thickness and spreading rate the transition from a rift valley to an axial high morphology at these spreading rates 11 mm yr half rate occurs at a crustal thickness of about 9 1km

partial melting beneath a mid atlantic ridge segment detected by teleseismic pkp delays an array of six ocean bottom seismometers deployed across a segment of the mid atlantic ridge recorded pkp phases from four teleseismic earthquakes after correcting for normal moveout and elevation differences there is a systematic variation of anomalous travel time with distance from the ridge stations at the ridge axis are slowest the average anomaly at a station 16 km from the axis is 0 36 s relative to the axial stations most of this anomaly is probably caused by the presence of partial melt beneath the ridge axis perhaps concentrated primarily in the upper 30 km of the mantle the rapid variation across axis suggests that the melt is either associated with a narrow zone of buoyant upwelling or a region of veins and dikes forming a narrow transport zone connecting a deep melt production region to the crust

extent and duration of marine anoxia during the frasnian famennian late devonian mass extinction in poland germany austria and france the intensity and extent of anoxia during the two kellwasser anoxic events has been investigatedinarangeofeuropeanlocalitiesusingamultidisciplinaryapproach pyriteframboidassay gamma ray spectrometry and sediment fabric analysis the results reveal that the development of the lower kellwasser horizon in the early late rhenana zone frasnian stage in german type sections does not always coincide with anoxic events elsewhere in europe and in some locations seafloor oxygenation improves during this interval thus this anoxic event is not universally developed in contrast the upper kellwasser horizon developed in the late linguiformis zone frasnian stage in germany correlates with a european wide anoxic event that is manifest as an intensification of anoxia inbasinallocationstothepointthatstableeuxinicconditionsweredeveloped forexample inthebasins of the holy cross mountains poland the interval also saw the spread of dysoxic waters into very shallow water for instance reefal locations and it seems reasonable to link the contemporaneous demise of many marine taxa to this phase of intense and widespread anoxia in basinal locations euxinic conditions persisted into the earliest famennian with little change of depositional conditions only in the continental margin location of austria was anoxia not developed at any time in the late devonian consequently it appears that the upper kellwasser anoxic event was an epicontinental seaway phenomenon caused by the upward expansion of anoxia from deep basinal locales rather than an oceanic anoxic event that has spilled laterally into epicontinental settings

nannofossils and superplumes the early aptian nannoconid crisis a group of calcareous nannoplankton named nannoconids experienced a crisis in the early aptian and recovered only later in the late aptian after a period of virtual absence although no extinctions occurred the widespread nature of the nannoconid crisis suggests a global causal factor this crisis is recorded within the chiastozygus litterarius nannofossil and globigerinelloides blowi planktonic foraminiferal zones postdates magnetic chronozone m0 by approximately 300 kyr and precedes the oceanic anoxic subevent 1a and associated 13c anomaly by some 40 100 kyr selective dissolution and anoxia cannot explain the crisis because nannoconids are dissolution resistant forms and their crisis clearly precedes the deposition of anoxic sediments at least 1 m y prior to the nannoconid crisis the onset of a nannoplankton speciation event may be the response of nannofloras to a major rise in relative sea level the nannoconid crisis seems to be synchronous with the early aptian volcanic eruptions in the pacific ocean hence calcareous nannoplankton were severely affected by the superplume volcanic episode the coccolithophorid bloom nannoconid crisis was possibly induced by the excessive co2 levels in the atmosphere and or caused by changes in nutrient content of oceanic surface waters fertility was enhanced by rapid turnover of nutrients due to the abnormal volcanic activity and accelerated transfer of nutrients from the continents into the oceans under warm and humid conditions of the mid cretaceous greenhouse climate the nannoconid crisis may represent a competition between phytoplankton groups for nutrients or more likely competition between different calcareous nannoplankton the biologic affinity and mode of life of nannoconus are unknown because there is no modern analog of this genus however comparison of lower cretaceous nannofossil assemblages with modern nannoplankton cummunities suggests that nannoconids like extant florisphaera profunda possibly inhabited the lower photic zone concentrations of nutrients in the upper euphotic zone may have triggered blooms of coccolithophorids and nannoconid depletion this model implies that the nannoconid crisis is the result of an abrupt major change in the structure of surface waters caused directly or indirectly by the superplume the adjustments of the biosphere to the new paleoceanographic and climatic conditions required some 40 100 kyr before changing into abnormally high primary productivity and deposition of organic carbon rich sediments with dinoflagellates outcompeting nannoplankton

crustal thickness on the mid atlantic ridge bull s eye gravity anomalies and focused accretion spreading segments of the mid atlantic ridge show negative bull9s eye anomalies in the mantle bouguer gravity field seismic refraction results from 33 s indicate that these anomalies can be accounted for by variations in crustal thickness along a segment the crust is thicker in the center and thinner at the end of the spreading segment and these changes are attributable to variations in the thickness of layer 3 the results show that accretion is focused at a slow spreading ridge that axial valley depth reflects the thickness of the underlying crust and that along axis density variations should be considered in the interpretation of gravity data