geochemical evidence for a catastrophic biotic event at the frasnian famennian boundary in south china a strong delta sup 13 c anomaly coincides with a weak ir anomaly at the frasnian famennian f f boundary exposed at xiangtian guangxi south china the maximum whole rock ir abundance is 0 23 ppb 0 35 ppb on a carbonate free basis compared with averages of 0 016 and 0 044 ppb above and below the boundary interval the delta sup 13 c in carbonate abruptly shifts from a late frasnian level of about 1 per thousand to minus 2 49 per thousand in the boundary interval and then abruptly returns to pre boundary levels suggesting a temporary reduction of surface water biomass a widely distributed over at least several hundred kilometers limestone breccia unit of possible wave deposit origin is present directly below the boundary in south china enrichments of al v cr as and u and a dip in the mn abundance in the boundary interval indicate that reducing conditions might have been associated with the element enrichment however an alternative hypothesis is that oceanic impact s at the f f boundary near south china provided the excess ir and caused the biotic crisis and the formation of breccia deposits observed in the late devonian south china sea

the micrometeorite flux to earth during the frasnian famennian transition reconstructed in the coumiac gssp section france abstract we have reconstructed the distribution of extraterrestrial chrome spinels in a marine limestone section across the frasnian famennian stratotype section at coumiac in southern france providing the first insights on the types of micrometeorites and meteorites that fell on earth at this time the data can test whether the small cluster of roughly coeval large impact structures is related to an asteroid breakup and shower with possible bearings also on the late devonian biodiversity crisis a total of 180 extraterrestrial spinel grains 32 m were recovered from 957 kg of rock noble gas measurements of individual grains show high solar wind content implying an origin from decomposed micrometeorites element analyses indicate a marked dominance of ordinary chondritic over achondritic grains similar to the recent flux the relation between h l and ll meteorites is 29 58 13 similar to the late silurian flux 31 63 6 but different from the distribution 45 45 10 in the recent and the cretaceous flux our data show no indication of a generally enhanced late devonian micrometeorite flux that would accompany an asteroid shower however in a single limestone bed that formed immediately before the upper kellwasser horizon that represents the main end frasnian species turnover event we found an enrichment of 10 ordinary chondritic grains 63 m per 100 kg of rock compared to the 1 3 grains per 100 kg that characterise background the anomalously abundant grains are of mixed h l and ll types and may be related to an enhanced flux of extraterrestrial dust during postulated minima in both the 405 ka and 2 4 ma earth orbit eccentricity cycles at the onset of the upper kellwasser event in the present solar system the dust accretion at earth is the highest at eccentricity minima because of the spatial distribution of dust bands of the zodiacal cloud besides this small grain anomaly the data here and in previous studies support a stable meteorite flux through the late silurian and devonian in contrast to the mid ordovician when achondritic meteorites that are rare on earth today were common followed by the influx of a flood of debris related to the breakup of the l chondrite parent body our accumulated data for six time windows through the phanerozoic indicate that the ordinary chondrites make up a major fraction in the meteorite flux since at least the mid ordovician we note that the sources in the asteroid belt of the h and l meteorites the two most common types of meteorites today and through much of the phanerozoic remain elusive

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

the stratigraphic distribution of ni rich spinels in cretaceous tertiary boundary rocks at el kef tunisia caravaca spain and hole 761c leg 122 abstract ni rich spinels have been found throughhout the world at the cretaceous tertiary boundary these minerals have no counterparts in terrestrial rocks but have been observed in meteoroid ablation material and impact debris suggesting that the cretaceous tertiary boundary spinels result from an extraterrestrial event their stratigraphic distribution which has been observed at the cretaceous tertiary boundary sites of el kef tunisia caravaca spain and hole 761c odp leg 122 indian ocean are markedly different from site to site and are all much less extended than the ir anomalies regional differences in ni rich spinel distibution are entirely explained by a brief event recorded under different bioturbation conditions the wider stratigraphic dispersion of ir is attributed to postdepositional chemical processes at el kef the site which appears to be the least affected by bioturbation and which has the highest sedimentation rate the 1 2 mm thick ni rich spinel spike indicates that the deposition time did not exceed an upper limit of 100 years this upper limit is consistent only with the collision of an asteroid or a comet at the close of the cretaceous

microtektites and mass extinctions evidence for a late devonian asteroid impact glass spherules similar to microtektites have been found near the frasnian famennian boundary f f upper devonian at senzeilles belgium contemporaneous with one of the largest marine mass extinctions of the phanerozoic these spherules exhibit a wide range of compositions and display teardrop dumbbell and compound morphologies analogous to microtektites in addition they lack crystallites have few or no vesicles and have a low content of volatile material these characteristics are supportive of an impact origin the siljan ring sweden and charlevoix structure quebec canada are candidate craters of this age the presence of microtektites near the f f boundary supports the hypothesis that an impact caused the upper devonian worldwide benthic mass extinctions

sea level reconstructions from the peri vocontian zone south east france point to valanginian glacio eustasy the valanginian is a period of global environmental change as illustrated by sedimentary palaeontological geochemical and climatic perturbations a production crisis in most of the carbonate platforms suggests important changes in palaeoenvironmental conditions during the same time interval a major positive excursion in 13c the weissert event suggests perturbations of the carbon cycle from the latest early valanginian to the early hauterivian in order to better understand the link between these changes sea level fluctuations have been reconstructed in detail from the middle berriasian to the earliest hauterivian sections from the peri vocontian zone south east france have been investigated because of the good quality of outcrops on the carbonate platforms their margins and in the vocontian basin sections ranging from the most proximal zone swiss jura to the basin were interpreted in terms of sequence stratigraphy and cyclostratigraphy and correlated at high resolutions using the identified small medium and large scale sequences as well as depositional geometries sea level fluctuations were reconstructed two main trends are evidenced during the studied interval i the peak amplitude magnitude of the sea level fluctuations increased gradually from the middle berriasian to the early valanginian and reached a maximum more than 50 m from the middle early valanginian to the valanginian hauterivian boundary and ii sea level variations were quite symmetrical during the late berriasian slightly asymmetrical during the early valanginian and strongly asymmetrical fast sea level rise slow fall from the latest early valanginian to the earliest hauterivian moreover three orders of sea level fluctuations were recognized in the sedimentary rocks of the peri vocontian zone platform basin correlations and cyclostratigraphic interpretations of the basinal sections evidence an astronomical control on the sea level variations mainly by the two eccentricity cycles of 100 and 400 kyr the increase in the amplitude of the sea level fluctuations and their change from symmetrical to asymmetrical can be related to the onset of a major cooling event in the early valanginian fast transgressions followed by slower regressions would correspond to waxing and waning of high latitudinal ice during most of the valanginian especially from the latest early valanginian to the latest late valanginian glacio eustatic sea level fluctuations in tune with the 100 and 400 kyr eccentricity cycles are in agreement with glaciations during the valanginian

microtektite like impact glass associated with the frasnian famennian boundary mass extinction abstract glass spherules of probable impact origin occur in the late devonian hony section in belgium they are found at the stratigraphic level of the frasnian famennian boundary which is marked by one of the largest mass extinctions in the phanerozoic the hony glass spherules are chemically identical to those previously described from the stratigraphically equivalent senzeille section located 90 km to the west southwest in contrast to the senzeille layer the age of the hony spherule layer is well constrained by conodont biostratigraphy the spherules have morphological and chemical characteristics similar to tektites and microtektites they have a broad range of chemical composition with generally high k2o na2o and al2o3 na2o k2o their water content is in the range measured for tektites and impact glasses small inclusions of lechatelierite may be present in the spherules these glass spherules are likely to be the product of an impact event that occurred at or very near the frasnian famennian boundary the target rock was probably a clay rich pelitic sediment intermixed with carbonates the 368 1 ma siljan ring crater sweden is the most likely impact site candidate the hony and senzeille glass spherules represent the first substantial evidence that an impact event may be linked to the frasnian famennian mass extinction

astronomical tuning of the aptian stage from italian reference sections a high resolution grayscale series of the pelagic fucoid marls piobbico core central italy shows strong pervasive lithological rhythms throughout the aptian interval a hierarchy of centimeter to meter scale cycles characterizes the rhythms when calibrating 1 m cycles to earth s 405 k y orbital eccentricity cycle these rhythms correspond to the periods of the eccentricity obliquity and precession index tuning to orbital eccentricity cycles provides a high resolution time scale for the aptian correlation to the cismon core northern italy extends the tuning to the aptian barremian boundary the tuning indicates a minimum duration of 13 42 m y for the aptian stage where previous estimates range from 6 4 to 13 8 m y the combined aptian albian astronomical tuning of the entire 77 m long piobbico core and part of the cismon core provides a 25 85 m y long astronomically calibrated time scale for earth history

search for impact remains at the frasnian famennian boundary in the stratotype area southern france abstract in order to detect whether the end frasnian worldwide biotic crisis is related to an extraterrestrial impact the global stratotype section of the frasnian famennian boundary and auxiliary sections within the stratotype area have been examined for impact indicators iridium ni rich spinel bearing spherules and glassy microtektites this area is particularly well suited to the search for discrete events because it exhibits biostratigraphically continuous sections of sedimentologically homogenous off shore deposits different environmental settings on oxygenated deep water seamounts such as the stratotype section at coumiac and in oxygen depleted depressions la serre section are available the latter is investigated in more detail because it is the least condensed across the boundary which is determined by the first occurrence of the typical morphotype of palmatolepis triangularis the indicator of the first famennian conodont biozone samples from the biostratigraphically defined boundary and adjacent levels failed to provide significantly high ir values and no ni rich spinel or microtektite has been recovered this is in contradiction with the results of earlier investigations carried out by h geldsetzer on the same section in contrast the values of ir concentrations that we measured are always very low or not detectable the small overabundances observed in some samples which are about two orders of magnitude lower than what is currently observed at the cretaceous tertiary boundary are probably due to the accumulation of the normal flux of cosmic dust during periods of relatively low depositional rates or to a terrestrial origin at present we have no evidence that an extraterrestrial impact occurred at the f f transition

valanginian weissert oceanic anoxic event biotic changes in nannofossils and radiolarians associated with the valanginian 1 3 c anomaly are documented at ocean drilling program hole 1149b in the pacific ocean they are coeval and similar to those previously documented in the tethys suggesting a global perturbation of marine ecosystems a marked increase in abundance of diazomatolithus absence of nannoconids and a pantanellium peak characterize the valanginian 1 3 c excursion such changes are interpreted as being due to global enhanced fertility and a biocalcification crisis under conditions of excess co 2 the occurrence of organic c rich black shales in the southern alps and in the pacific in the interval corresponding to the 1 3 c excursion suggests a valanginian oceanic anoxic event oae volcanism of the parana etendeka large igneous province ca 132 ma was presumably responsible for an increase of co 2 triggering a climate change and accelerated hydrological cycling possibly causing an indirect fertilization of the oceans widespread nutrification via introduction of biolimiting metals at spreading ridges could have significantly increased during the gondwana breakup and simultaneous tectonic events in three separate oceans there is no paleontological or 1 8 o evidence of warming during the valanginian oae on the contrary both nannofossils and oxygen isotopes record a cooling event at the climax of the 1 3 c excursion weathering of basalts and burial of organic c rich black shales were presumably responsible for co 2 drawdown and establishment of reversed greenhouse conditions

orbital calibration of the early kimmeridgian southeastern france implications for geochronology and sequence stratigraphy classic stratigraphic methods rarely provide high resolution correlations between intrabasinal sedimentary sequences which are important to understand the origin of sedimentation process and its environmental change in this study we investigate high resolution cyclostratigraphic correlation from magnetic susceptibility in two early kimmeridgian pelagic marl limestone successions at la meouge and chateauneuf d oze southeastern france spectral analysis reveals the complete suite of orbital frequencies precession obliquity and eccen tricity with the marl limestone couplets being primarily pre cession driven frequencies detected by the spectral analysis are similar between the sections but their relative amplitudes are somewhat different linked to the palaeoenvironmental position and the completeness of the sections high resolution correlation reveals two significant hiatuses at chateauneuf d oze early kimmeridgian platynota hypselocyclum and div isum ammonite zones were orbitally calibrated for an ultra high resolution assessment of geological time finally strong 405 kyr eccentricity cycles are recorded as third order depositional sequences

high resolution cyclostratigraphic analysis from magnetic susceptibility in a lower kimmeridgian upper jurassic marl limestone succession la meouge vocontian basin france abstract high resolution magnetic susceptibility ms analysis was carried out on a lower kimmeridgian alternating marl limestone succession of pelagic origin that crops out at la meouge vocontian basin southeastern france the aim of the study was to characterize the strong dm scale sedimentary cyclicity of the succession at a very high resolution and to analyze the cycles for evidence of astronomical forcing from marl to limestone ms varies progressively and closely tracks the highest frequency cyclicity corresponding to the basic marl limestone couplets long term wavelength cycling modulates the high frequency cyclicity couplets and appears to be controlled by clay content spectral analysis of the ms record reveals the presence of the complete suite of orbital frequencies in the precession obliquity and eccentricity 95 128 ka and 405 ka bands with very high amplitude of the precession index cycles originating from dm scale couplets 405 ka eccentricity cycles are very pronounced in the ms maxima of the marl members of the couplets suggesting eccentricity driven detrital input to the basin 405 ka orbital tuning of the ms maxima further sharpens all of the orbital frequencies present in the succession these results are similar to those of previous studies at la meouge that used carbonate content observed in field our results are also in accordance with cyclostratigraphic studies in spain and canada that report dominant precession index forcing by contrast in the kimmeridge clay dorset uk obliquity forcing dominates cyclic sedimentation with weaker influence from the precession index ammonite zone duration estimates are made by counting the interpreted precession cycles and provide an ultra high resolution assessment of geologic time in sum this study demonstrates the power of the ms as a proxy in characterizing the high resolution cyclostratigraphy of mesozoic sections particularly in alternating marl limestone successions and for high resolution correlation and astronomical calibration of the geologic time scale

astrochronology of the valanginian stage from reference sections vocontian basin france and palaeoenvironmental implications for the weissert event abstract high resolution gamma ray measurements performed on five biostratigraphically well dated reference sections from the vocontian basin south eastern france are used to develop a new astrochronology of the valanginian stage and its subdivisions i e ammonite and calcareous nannofossil zones and subzones spectral analyses show a pervasive dominance of 405 kyr eccentricity cycles with the expression of 100 kyr eccentricity obliquity and precession previous rough estimates of valanginian stage duration ranged from 3 9 to 6 5 myr but were generally based on less reliable or indirect methods this study provides a precise duration of 5 08 myr tuning the series to the 405 kyr eccentricity cycle thus further enhancing the accuracy of the geologic time scale new durations of magnetochrons are proposed based on intercalibration between ammonite and calcareous nannofossil biozones cyclostratigraphy and carbon isotope stratigraphy after integrating orbitally calibrated durations and available radio isotopic ages for the berriasian hauterivian interval a link between the weissert event and the emplacement of the parana etendeka traps now appears unlikely strontium carbon and oxygen isotope stratigraphy sedimentological and palaeontological features clay mineralogy and the orbital record during the upper valanginian all suggest that a transient cool arid climate occurred after the carbon isotope event possibly associated with limited polar ice

the frasnian famennian mid late devonian boundary in the type section of the long rapids formation james bay lowlands northern ontario canada utilizing a combination of conodont based biostratigraphy and geochemistry the frasnian famennian f f mid late devonian boundary was located in the long rapids formation northern ontario it is present in a black shale sequence 21 46 m above the base of the long rapids formation just above a carbonate bed that has similarities to the upper kellwasser limestone recognized as a lithological marker for the f f boundary in germany belgium and france there is no evidence of an impact event and sedimentation across the boundary is continuous although there is a discontinuity layer just below the boundary and the early part of the linguiformis zone of the standard late devonian conodont zonation is missing strong positive 13 c organic and carbonate values were identified and are interpreted as evidence of mass mortality in anoxic waters at the f f extinction positive 18 o values suggest the extinction was also accompanied by a temperature drop negative 34 s values also indicate anoxia and negative 15 n values provide evidence of reduced surface water productivity no iridium anomaly was found at the boundary although higher than usual values were found about 85 cm below the f f boundary sedimentological and biological evidence in the long rapids formation indicates that the f f extinction was coincident with major sea level fluctuations in the late frasnian including a transgression beginning at the end of the linguiformis zone and continuing through the early triangularis zone and beyond marine oscillations were accompanied by anoxia which appears to be the killing mechanism for the conodont and other end frasnian extinctions

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

platinum group element enrichments and possible chondritic ru ir across the frasnian famennian boundary western new york state the frasnian famennian boundary is recognized as the culmination of a global mass extinction in the late devonian in western new york state the boundary is a distinct horizon within a pyritic black shale bed of the upper hanover shale defined by the first occurrence of palmatolepis triangularis in the absence of frasnian conodonts the boundary is characterized by a minor disconformity marked by a lag concentration of conodonts iridium at the boundary is 0 11 0 24 ng g two to five times background levels of 0 05 ng g other ir enrichments of 0 38 ng g and 0 49 ng g occur within 50 cm of the conodont constrained boundary numerous ir enrichments in the boundary interval suggest extraterrestrial accretion and platinum group element pge concentration at disconformities or mobilization and concentration in organic rich pyritic rich laminations from cosmic or terrestrial sources pge ratios of pt pd and ru ir at the boundary horizon approximate chondritic ratios and are suggestive of an unaltered extraterrestrial source these values do not conclusively establish a single extraterrestrial impact as the ultimate cause of the frasnian famennian mass extinction especially given the presence of similar ir enrichments elsewhere in the section and the absence at the boundary of microtektites and shocked mineral grains

magnetostratigraphy late devonian iridium anomaly and impact hypotheses paleomagnetism sedimentology and fine scale stratigraphy have been integrated to explain the origin of an iridium anomaly in the late devonian of western australia thermal demagnetization experiments were carried out on 93 specimens of marginal slope limestone form the northern canning basin samples are from a condensed sequence of deep water 100 m frutexites microstromatolites frutexites is a shrublike cyanobacterial organism that probably precipitated hematite or a metastable precursor from sea water when plotted within the microstratigraphic framework for the study area the observed characteristic directions from the sampled interval 14 5 cm thick are in five discrete layer parallel normal and reversed polarity zones the measured northeast southwest declinations and shallow inclinations probably record late devonian magnetostratigraphy on a centimetre scale the frutexites bed studied there occurs close to the frasnian famennian late devonian boundary a time of mass extinction of a wide variety of marine organisms throughout the world anomalously high iridium concentrations observed in the frutexites bed have suggested to some authors that the mass extinction was caused by meteorite impact this study concludes that iridium which is present over the span of five layer parallel magnetic reversals was concentrated over a long period of time by biologic processes thus the canning basin iridium anomalymore may be unrelated to meteorite impact less

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

palaeoenvironmental changes at the frasnian famennian boundary in key european sections chemostratigraphic constraints abstract the study aims to put constraints on global environmental changes which took place during the frasnian famennian f f transition by using a geochemical multiproxy approach for this several key european f f boundary sections deposited in different palaeogeographic settings were selected including in addition to the stratotype and parastratotype sections of coumiac montagne noire france and steinbruch schmidt branau germany respectively also some other sections thoroughly characterized by other authors the drilling budesheimer bach prumer mulde germany kowala section holy cross mountains poland la serre france changes in the detrital flux along the sections were evaluated on the basis of both variations in mineral composition and in some diagnostic element ratios like ti al the biogenic flux was assessed as a function of the corg content the input of nutrients or the palaeoproductivity was determined by the p2o5 and ba in excess the degree of anoxia during deposition was constrained by determining the concentration of redox sensitive metals e g fe mn in the bulk sediment of specific element ratios e g v cr as well as the size of pyrite grains together with the degree of pyritization dop in the budesheimer bach core the hydrothermal and volcanic influence in the sedimentary record was detected using e g the al al fe mn and zr al2o3 ratios the kellwasser horizons are characterized by a general decrease in the detrital input together with the increase of al normalized concentration of some of the transition metals these changes are interpreted as reflecting a relative sea level rise and a higher hydrothermal influence in contrast to these the establishment of dysoxic anoxic conditions in the depositional environment as well as the increase of organic matter burial are not always restricted to the kellwasser horizons kwh moreover the hydrothermal influence can lead to misinterpretation with respect to redox conditions and productivity due to the additional input of some specific elements our results indicate the coincidence of sea level rise with hydrothermalism and volcanism during the deposition of the kwh in the area of south laurussia and north gondwana the resulting enrichment in metals and nutrients is coupled in several f f boundary sections with a higher microbial activity as already observed by some authors these effects coupled with a general lowering of the degree of oxygenation of the water bodies could have played a significant role in the demise of the biota

obliquity forcing of organic matter accumulation during oceanic anoxic event 2 1 an analysis of orbitally influenced climate sensitive sedimentation is conducted across a meridional transect of the proto north atlantic to reconstruct the behavior of the carbon cycle and climate during oceanic anoxic event 2 oae 2 94 ma midlatitude to near equatorial sites spanning deep ocean to shelf environments are evaluated using a new inverse method for the identification and calibration of orbital influence in ancient strata the results yield consistent independent astrochronologies at each location compatible with the recently published radioisotopic astrochronologic time scale at the cenomanian turonian gssp and thus provide a unified high resolution temporal context for evaluation of the event the proto north atlantic astrochronologies document an amplification of obliquity power during oae 2 indicating that obliquity was the dominant pacemaker of organic matter accumulation by the latter portion of the event the strong obliquity signal suggests an influence of high latitude climate processes across midlatitude deep ocean to tropical shelf environments changes in oceanic circulation during oae 2 represent a likely mechanism for the propagation of a high latitude signal and proxy data from demerara rise reveal the development of a new intermediate water mass source synchronous with the record of obliquity amplification we hypothesize that a dense high latitude water mass displaced a pre existing nutrient rich anoxic deep water layer in the proto north atlantic augmented by enhanced volcanism driving an episode of high productivity that lasted 700 800 ka the development and intensification of the new intermediate deep water source was potentially driven by eustatic sea level rise which created expansive seaways in mid to high latitudes

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

iridium anomaly in the upper devonian of the canning basin western australia a moderate iridium anomaly about 20 times the local background has been found in upper devonian rocks in the canning basin it occurs at or near the frasnian famennian boundary which is known to be associated with a major massextinction event of global extent the anomaly occurs in an extremely condensed limestone sequence laid down under quiet deepwater conditions its occurrence suggests a causal link with some form of meteoroid impact moreover carbon isotope data indicate that a large reduction in biomass could have occurred at this level however the anomaly coincides with a stromatolite bed containing the fossil cyanobacterium frutexites iridium platinum iron manganese cobalt arsenic antimony and cerium are preferentially concentrated in filaments of this organism with concentrations ranging from two to five times that of the matrix it is possible that frutexites extracted these elements directly from seawater without the need for their derivation from an extraterrestrial source

on the duration of magnetochrons c24r and c25n and the timing of early eocene global warming events implications from the ocean drilling program leg 208 walvis ridge depth transect 1 five sections drilled in multiple holes over a depth transect of more than 2200 m at the walvis ridge se atlantic during ocean drilling program odp leg 208 resulted in the first complete early paleogene deep sea record here we present high resolution stratigraphic records spanning a 4 3 million yearlong interval of the late paleocene to early eocene this interval includes the paleocene eocene thermal maximum petm as well as the eocene thermal maximum etm 2 event a detailed chronology was developed with nondestructive x ray fluorescence xrf core scanning records and shipboard color data these records were used to refine the shipboard derived spliced composite depth for each site and with a record from odp site 1051 were then used to establish a continuous time series over this interval extensive spectral analysis reveals that the early paleogene sedimentary cyclicity is dominated by precession modulated by the short 100 kyr and long 405 kyr eccentricity cycles counting of precession related cycles at multiple sites results in revised estimates for the duration of magnetochrons c24r and c25n direct comparison between the amplitude modulation of the precession component derived from xrf data and recent models of earth s orbital eccentricity suggests that the onset of the petm and etm2 are related to a 100 kyr eccentricity maximum both events are approximately a quarter of a period offset from a maximum in the 405 kyr eccentricity cycle with the major difference that the petm is lagging and etm2 is leading a 405 kyr eccentricity maximum absolute age estimates for the petm etm2 and the magnetochron boundaries that are consistent with recalibrated radiometric ages and recent models of earth s orbital eccentricity cannot be precisely determined at present because of too large uncertainties in these methods nevertheless we provide two possible tuning options which demonstrate the potential for the development of a cyclostratigraphic framework based on the stable 405 kyr eccentricity cycle for the entire paleogene

a quantitative study of lower cretaceous cyclic sequences from the atlantic ocean and the vocontian basin se france milankovitch type periodicity was identified within lower cretaceous cyclic sequences from the western central atlantic ocean and the vocontian basin southeast france through application of the walsh spectral method to detailed stratigraphic sections the repetitious bedding in these sequences appears to be the product of cyclic climatic changes controlled by the orbital forcing obliquity seems to be the most important and persistent orbital element responsible for cyclic sedimentation whereas precession is less important upper berriasian and valanginian strata from the atlantic ocean contain indications of eccentricity induced periodicity and of a nonlinear response of the climatic system variations in orbitally tuned pelagic sedimentation rates in the atlantic ocean correlate with the changes in the character of cycles and with the occurrence of calcareous turbidites therefore this suite of sedimentary features are responding to evolving paleoceanographic conditions and possible relative sea level fluctuations the orbitally tuned durations of the valanginian and hauterivian stages in the vocontian basin are a minimum of 5 9 and 5 3 m y respectively

evaluation of the astronomical time scale for the paleocene and earliest eocene abstract the astronomical tuned time scale is rapidly extended into the paleogene but due to the existence of an eocene gap different tuning options had to be presented for the paleocene these options differ both in number and tuning of 405 kyr eccentricity related cycles and are only partially consistent with recalculated 40 ar 39 ar constraints for the cretaceous paleogene k pg and paleocene eocene p e boundaries in this paper we evaluate the cyclostratigraphic interpretation of records from odp leg 198 and 208 sites and the zumaia section to solve the problem of the different tuning options we found that the interval between the k pg boundary and the early late paleocene biotic event elpe comprises 17 instead of 16 405 kyr eccentricity related cycles as previously proposed while the entire paleocene contains 25 405 kyr cycles starting from 40 ar 39 ar age constraints for the k pg boundary a new tuning to 405 kyr eccentricity is presented for the paleocene and earliest eocene which results in ages of 66 0 and 56 0 ma for the k pg and p e boundaries respectively this tuning introduces considerable differences in age for a number of nannofossil events at odp sites 1209 and 1262 in the interval between 61 and 63 ma but eliminates large and abrupt changes in the seafloor spreading rate the tuning seems further consistent with recalculated 40 ar 39 ar ages for ash layer 17 of early eocene age however despite this apparent consistency with existing radio isotopic constraints an alternative 405 kyr younger or less likely older tuning cannot be excluded at this stage

age constraint for an earliest famennian forest and its implications for frasnian famennian boundary in west junggar northwest china abstract as one of the five major extinction events in earth history the frasnian famennian boundary ffb crisis caused dramatic reductions in marine and terrestrial diversity the effects of this event on terrestrial ecosystems are not well understood due to the limited preservation of terrestrial sedimentary rocks and the relative scarcity of plant fossils this study generates a robust zircon u pb age 371 5 0 9 ma earliest famennian for a new fossil assemblage containing lycopsida archaeopteridales and cladoxylopsida from the upper zhulumute formation of the west junggar basin nw china these taxa are typical arborescent plants of the late devonian and represent the oldest known forest in china documenting afforestation in west junggar coevally with or just after the upper kellwasser event 372 ma the new u pb ages generated in this study refine the placement of the ffb in west junggar to within the zhulumute formation instead of the hongguleleng formation as previously thought

osmium isotopic evidence against an impact at the frasnian famennian boundary two sections across the frasnian famennian boundary were analyzed for re and os concentrations and 187os 188os ratios to evaluate evidence for a meteoritic input coincident with this boundary and its associated mass extinction these sections are from a siltstone and shale sequence at irish gulf in new york us and a calcareous shale and ferromanganese oxide sequence at la serre in france the irish gulf section with an initial 187os 188os of about 0 49 does not show the characteristic meteoritic os imprint with an 187os 188os of about 0 13 the integrity of the section with regard to re and os retention is indicated by the construction of an isochron with an age of 388 41 ma consistent with independently determined ages for the frasnian famennian boundary although the la serre section with os concentrations as high as 33 ppb and re concentrations ranging from 1 4 to 7 4 ppb might be expected to show excellent evidence for a meteoritic contribution the highly radiogenic isotopic composition 187os 188os 2 42 3 61 instead suggests recent massive re loss or addition of radiogenic os these possibilities prevent the reconstruction of an initial 187os 188os value for the boundary for this site assuming reasonable re concentrations prior to loss the os isotopic composition is inconsistent with a large meteoritic component this inconsistency emphasizes that platinum group element pge concentrations are not reliable indicators of extraterrestrial addition

on the origin of cenozoic and mesozoic third order eustatic sequences abstract the origin of third order eustatic sequences is reviewed by comparing recent sequence stratigraphic data to the latest best constrained astronomical model middle eocene to holocene icehouse sequences correspond to 1 2 myr obliquity cycles constraints from oxygen isotope records highlight the link between icehouse sea level lowerings sequence boundaries and 1 2 myr obliquity nodes mesozoic greenhouse sequences show some relation with the 2 4 myr eccentricity cycles suggesting that orbital forcing contribute to sea level change we suggest that during the icehouse large ice sheets associated with significant glacioeustatic changes 25 m up to 120 m changes were mainly governed by obliquity forcing during icehouse worlds obliquity forcing was the stongest control on global sea level and depositional sequences additionally during the middle eocene third order sequences were glacioeustatically driven in tune with 1 2 myr obliquity cycle suggesting that the presence of significant ice sheets is earlier than previously supposed i e early eocene in contrast during greenhouse worlds e g ephemeral small to medium sized or no ice sheets 0 25 m glacioeustatic changes the expression of obliquity in the sedimentary record is weak and intermittent instead the eccentricity signature which is the modulator of climatic precession is documented moreover we presume that greenhouse sequences on the myr scale are global and hence cannot be caused by regional tectonism e g intraplate stress or mantle hot blobs instead the eccentricity link implies a weaker glacioeustatic control because thermoeustasy is too small to explain the sea level changes stratigraphically well documented fourth order sequences may be linked to the astronomically stable strongest amplitude 405 kyr eccentricity cycle and possibly to 160 200 kyr obliquity modulation cycles fifth order sequences to the short 100 kyr eccentricity cycles and finally sixth order sequences to the fundamental obliquity 40 kyr and climatic precession 20 kyr cycles these astronomical cycles could be preserved in the sedimentary record and have been demonstrated to control sea level changes accordingly by placing depositional sequence orders into a high resolution temporal framework i e orbital periodicities standardization of eustatic sequence hierarchy may be possible

late devonian kellwasser event mass extinction horizon in germany no geochemical evidence for a large body impact the hypothesis that the late devonian frasnian famennian mass extinction was triggered by an asteroidal impact has received renewed attention with the discovery of a late devonian ir anomaly in australia in europe the mass extinction event corresponds stratigraphically to the geographically widespread kellwasser black shale and bituminous limestone units and the biological crisis itself has been alternatively designated the kellwasser event the authors report here the results of an extensive geochemical analysis of the kellwasser stratigraphic interval in a section with exceptional conodont zonal control in the federal republic of germany no ir anomaly was found neither at the biological crisis horizon recognized in europe nor at the conodont horizon that corresponds to the ir anomaly zone reported in australia no shock metamorphosed quartz sanidine spherules or siderophile rich magnetic spherules were found which might have been indicative of a cometary impact oxygen isotope ratios show little variation across the mass extinction horizon though carbon isotope data suggest a sudden increase in phytoplankton activity they further note that the australian ir anomaly 1 is most likely not associated with a large body impact because no equivalent ir signature occurs in europe and 2 is stratigraphically above the european biological crisis horizon thus postdating the kellwasser mass extinction event

restriction of convective depth in the weddell sea 1 the depth open ocean convection can reach around maud rise in the weddell sea is estimated based on the entrainment assumption using hydrographic data obtained in winter 1986 during which no distinct polynya was observed while the water column is stable at all ctd stations when observed additional cooling makes the mixed layer water heavier than the underlying water at any depth in an adiabatic sense however convective plume cannot reach the ocean bottom since it loses positive density anomaly due to thermobaricity by entraining the warm deep water wdw on its downward way the deeper convection is located over maud rise where the maximum temperature of the wdw max is about 0 5 c while the shallower one in the warm water cell region where max is more than 1 0 c the mean convective depth is much shallower than the ocean depth and the ventilated depth during the weddell polynya years 3 4 km

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

climatic precession is the main driver of early cretaceous sedimentation in the vocontian basin france evidence from the valanginian orpierre succession the valanginian sediments outcropping in the vocontian basin se france exhibit striking marl limestone alternations which were formed under the influence of orbital forcing and which have served for geochronological and paleoenvironmental studies previous studies have suggested an obliquity forcing during the late valanginian interval reflecting specific environmental conditions such as polar ice using a cyclostratigraphic correlation of previously studied sections and performing time series analysis on the most complete late valanginian interval we argue that the climatic precession cycle is the primary driver of these marl limestone alternations in addition we highlight the modulation of the precession by the 100 and 405 kyr eccentricity cycles we suggest that the cyclostratigraphic misinterpretation i e obliquity forcing hypothesis results mainly from poorly preserved 405 kyr eccentricity cycles due to local hiatuses and or missed beats this study shows the potential of cyclostratigraphic correlations for the detection and quantification of differential hiatuses and or missed beats within intrabasinal sequences hence providing constraints on cyclostratigraphic interpretations the recorded 405 kyr eccentricity cycle is of prominent amplitude and controlled the fourth order sea level sequences these latter are faithfully detected through cyclostratigraphically inferred sedimentation rate finally we show that the well known pronounced lithostratigraphic markers intervals in the basin were orbitally paced by the 405 kyr eccentricity extrema this is a good argument for the strong impact of this cyclicity on the sedimentary processes especially during greenhouse periods

orbitally forced climate and sea level changes in the paleoceanic tethyan domain marl limestone alternations lower kimmeridgian se france abstract high resolution analysis of multiple climatic proxies was carried out on a 8 5 m lower kimmeridgian interval of a pelagic marl limestone succession at ch teauneuf d oze vocontian basin southeastern france the aim of the study was to characterize the orbitally controlled sedimentary cyclicity and to decipher paleoclimatic and paleoceanographic changes all analysed proxies magnetic susceptibility carbonate content manganese content and bulk carbon and oxygen stable isotopes 13c and 18o respond in synchrony to orbitally forced climate change precession index cycles modulated by short 100 kyr eccentricity cycles are strongly expressed in magnetic susceptibility carbonate and mn contents but less so in 18o obliquity cycles are expressed in manganese and particularly in 13c the orbital forcing was conferred to these rhythmic pelagic sediments via paleoclimatic and paleoceanographic changes as follows detrital input and marine carbonate production are recorded by the magnetic susceptibility and carbonate signals with strong precession cyclicity calcareous nannofossil analysis shows the omnipresence of coccoliths and debris of coccoliths in the marls and limestones suggesting that the carbonate production was in largest part in situ precession index may exert oscillations in the antagonist marine surface productivity and detrital flux processes via solar radiation change oxygenation of the seafloor leading to redox cycles is detected in the manganese signal and supported by the 13c record with a strong expression of the obliquity finally paleotemperature variations were deduced from the 18o record although this latter has been in part perturbed by diagenesis in sum the variations in the studied proxies suggest a depositional model of combined climate and sea level cycles forced in concert by earth s orbital parameters in particular the limestones represent warmer climates and higher sea levels and the marls colder climates and lower sea levels this depositional model concurs with a previous depositional model of deep water carbonates of the german kimmeridgian while is in opposition to a previous one of the same section in the vocontian basin

glassy microspherules microtektites from an upper devonian limestone the properties of microspherules recovered from an upper devonian marine limestone immediately overlain by a geochemical anomaly of siderophile and chalcophile elements are similar to those of impact derived microtektites these microspherules are glass have splash form shapes contain spherical vesicles and lechatelierite inclusions and show oxide compositional variations similar to those in known microtektites these characteristics suggest that these upper devonian microspherules have an impact origin a bolide impact may have occurred about 365 million years ago on the south china plate and caused a faunal extinction on eastern gondwana

formation of spinels in cosmic objects during atmospheric entry a clue to the cretaceous tertiary boundary event abstract magnetic spinels produced by oxidation of extraterrestrial objects in the atmosphere have a composition distinct from terrestrial spinels they are characterized by a high iron oxidation state arising from crystallization under high oxygen fugacities and a high nickel concentration due to the relatively high abundance of this element in extraterrestrial material the iron oxidation state increases from micrometeorites to meteoroid ablation material and to impact generated products this reflects a progressive increase of the oxygen fugacity corresponding to decreasing altitudes of crystallization spinels found at the cretaceous tertiary boundary are similar to those that crystallized from meteoroid ablation material and impact generated products supporting the view that a collisional event did occur at the end of the cretaceous

the frasnian famennian biotic crisis how many if any bolide impacts the prime causation of the mid late devonian mass extinction near the frasnian famennian f f boundary remains uncertain nevertheless geochemical evidence has been presented recently as decisive evidence of a giant bolide impact occurring precisely at the f f boundary which promoted the global mortality episode palaeobiological data however imply a gradual global change which is otherwise seen as a record of either multiple extraterrestrial catastrophes or of impact triggered earth bound mechanisms sedimentological mega tsunami physical craters microtektites and geochemical records remain either elusive in many aspects or incompatible with the predicted impact crisis pattern biotic succession across the f f horizon is still poorly known especially in continental domains to evidence a synchronous bedding plane killing event at the close of the crisis instead the commonly documented stepwise loss of biomass and an unproved distinctive dead zone are hard to explain simply as sampling artifacts the assumed mass mortality precisely at the f f boundary may be limited mainly to the pelagic realm the underestimated role of early variscan tectonism and associated volcanic hydrothermal processes resulting in thermal and nutrient pulses as possible prime controls of the f f crisis is suggested as well as resemblances to the superplume conditioned eventful mid cretaceous interval exemplified in the cenomanian turonian mass extinction additional shocks generated by minor cometary strikes are not excluded but may have affected some f f biotas or areas

trace elements in conodont phosphates from the frasnian famennian boundary abstract rare earth elements ree and th concentrations on individual devonian conodonts were measured by icp ms from stratigraphic sections across the frasnian famennian f f boundary in the montagne noire southern france and morocco the present data confirm the reversed concavity of the ree spectra found by wright et al 1986 which is a characteristic although poorly understood feature of the ancient oceanic sediments within the layers corresponding to the upper kellwasser and the f f events the ce ce ratios show only minor changes with respect to younger and older sediments the magnitude of the ce anomaly is nevertheless consistently weak over all the sections if as in modern oceans the biologically mediated ce anomaly in particles and seawater originates in the uppermost water column the present observations suggest a global decrease in the biological productivity lower productivity is supported by the decreasing abundance of conodont elements during the upper kellwasser but continuing carbonate deposition through this period still makes evidence quite equivoqual as a proxy to th pa fractionation in modern sediments the th la fractionation is a potential tracer of the rate of horizontal exchange of seawater between deep sea and continental margins which may be correlated with eustatic sea level fluctuations during the upper kellwasser crisis the th la ratios fall significantly in all the sections this can reflect reduced exchanges between the deep sea and continental margins it is suggested that the f f extinction event was the result of the coincidence between a rather modest transgression event and global suboxia