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

cretaceous tertiary and permian triassic boundary events compared abstract the cretaceous tertiary k t and permian triassic p tr events differ in many more aspects than they are similar this alone makes it unlikely that they are parts of a common web of periodic mass extinction events mee unlike the k t most mee have no ir anomalies and where in the comparatively complete section of the p tr at gartnerkofel austria weak ir concentrations are found their ratios to siderophile elements co ni cr are far less than chondritic in contrast ratios to chalcophile elements as sb zn never approach chondritic even in k t peaks and locality differences suggest local depositional processes that may also affect the siderophiles profiles of isotopes 13ccarb 87 sr 86 sr and possibly 18ocarb across these boundaries also differ radically whereas the k t profile of surface ocean 18ocarb has been shown to be mainly a drop in primary productivity the p tr profile is interpreted at least in part to be a consequence of a large and accelerating oxidation of previously stored corg with greatly differing consequences for climate these and other differences of proximate forcings for these two mee lead us to a hypothesis that such external exigencies were ever intermittently and severally with us but were effective only when the biotic web had already internally unravelled in some crucially strained patch gaia became antigaia

carbon isotope excursions and sea level change implications for the frasnian famennian biotic crisis new carbon and oxygen isotope data from carbonates spanning the frasnian famennian f f boundary in the guilin area south china show a broad positive 13 c rise and fall with sharp short lived negative 13 c events this pattern is comparable to that in europe and north america the integration of the isotope stratigraphy with high resolution sequence stratigraphy corroborates the onset of the positive 13 c excursion during a third order sea level fall in the latest frasnian this can best be explained through increased burial of c org during the sea level fall brought about by increased organic productivity caused by increased continent derived nutrient flux to the ocean due to enhanced weathering through the proliferation of land plants in the devonian this scenario would have resulted in anoxic and eutrophic conditions over epicontinental seas and blooms of cyanobacteria creating a highly stressful and fragile ecosystem for oligotrophic normal marine benthic organisms and leading to their massive decline the global third order sea level fall near the end of the frasnian may have led to gas hydrate dissociation giving the negative 13 c events and caused wild climatic fluctuations the subsequent short term events of sea level rise anoxia and eutrophication in the latest part of the f f transition would have placed additional environmental stresses on the already weakened biota leading to their further demise

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

collisions with ice volatile objects geological implications a qualitative treatment abstract an aperiodic collision of the earth with extra terrestrial ice volatile bodies is proposed as a mechanism to produce rapid changes in the geologic record due to the volatile nature of these bodies evidence for their impacts particularly in the ocean might be subtle and best seen as spikes in the geochemical or fossil record against normal background differing effects would result depending on the site of the major break up of the object in the atmosphere on land or in the ocean this paper focuses on the effects of adding material to the seas oceans and atmosphere the treatment is largely qualitative however mass balance calculations were used to estimate the relative mass needed to affect changes in a variety of reservoirs although actual impactors probably have a variable composition the effects of water c n and s containing objects are discussed in the atmosphere effects could include increased rain acidity increased levels of nutrients and enhanced greenhouse warming cooling oceanic effects might include increased oceanic productivity nitrogen containing objects as a result of increased chemical weathering and or greenhouse effects increased temperatures coupled with enhanced productivity could result in wider spread oceanic anoxia or altered calcite aragonite stability possible examples of such impacts from the geologic record and potential biotic effects are given

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

cometary impacts into ocean their recognition and the threshold constraint for biological extinctions the montagnais impact crater is presently the only site in the ocean where the effect of a meteorite fall on marine organisms has been studied the impact crater is 45 km in diameter and was formed at 50 8 ma by a fall of probably an old cometary nucleus 3 4 km in diameter into shallow 600 m ocean comparison of the impact structure and related deposits with those on land shows several major differences of which the most significant is the absence of an elevated crater rim instead the crater perimeter is bevelled and eroded as a consequence of impact induced bottom currents and turbulent return water flow into the excavating cavity by this process most of the fall out breccia is reworked back into the crater cavity where it accumulates in much larger thickness than in impact craters on land at a microscopic scale the shock metamorphism features are about the same as those for land impacts geochemically impacts of comet nucleii may not leave a recognizable signature at the impact horizon except for a minor increase in iridium thus stratigraphic horizons associated with extinctions and or major changes in biota have to be closely examined for other impact indicators like the presence of tectites glass spherules and quartz grains with shock features occurrence of megatsunami wave deposits extensive erosion on continental margins margin failures and faunal mixing above erosional unconformities are other potential impact indicators there is no single indicator that can provide sufficient proof of an impact event such interpretations have to be based on multiparameter studies of global extent since many of the impact indicators are only of regional extent the lack of extinction of any marine plankton genera or of bottom dwellers at the montagnais impact site allows us to place a lower limit for biological extinctions caused by cometary impacts on those with nucleus 4 km in diameter the calculated frequency for a cometary impact which could result in a 10 extinction of marine genera is about 6 10 7 yr 1 and for the k t boundary type of extinctions about 2 10 8 yr 1 even allowing for a large degree of uncertainty in these estimates it is unlikely that the biological extinction events for the last 250 ma identified by sepkoski 1990 could have been all caused by meteorite impacts

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

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

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

carbon isotope geochemistry of the frasnian famennian transition abstract carbon isotope records for inorganic and total organic carbon toc as well as for individual organic biomarkers show two positive excursions in the late frasnian with comparable shape and amplitude in 13c the positive shifts in 13c can be correlated with the deposition of the kellwasser horizons the inorganic carbon isotope excursions are explained by an enhanced organic carbon burial that is expected to lower the concentration of oceanic dissolved co2 toc 13c values do not exhibit a larger shift than that recorded by inorganic carbon 13c values this is unexpected since a decrease in the dissolved co2 concentration should result in lower carbon isotope fractionation during photosynthesis ep 13c values of presumed algal biomarkers low molecular weight n alkanes pristane phytane although offset by 2 5 exhibit essentially identical records as toc and confirm this unexpected result it is proposed that high atmospheric and oceanic co2 concentrations during the devonian resulted in maximum photosynthetic fractionation any change in the co2 concentration would thus not affect ep as such 13c of primary organic carbon and 13ccarb will exhibit parallel excursions the data imply that carbon isotopes and the relationship between ep and co2 will not be effective to study changes in pco2 levels during the devonian since co2 concentrations were too high

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

carbon and oxygen isotope event markers near the frasnian famennian boundary luoxiu section south china abstract anomalous values of 13c and 18o suddenly appear in a bed below the top of the frasnian stage at the luoxiu section in south china the 13c values are characterized by a multi negative peak reaching a maximum of 6 6 the complex peak occurs in a 20 cm thick bed suggesting that the event which produced the carbon isotope anomaly was of relatively short duration the critical bed unit e is referred to as an extinction layer as it contains no fossils probably due to hostile depositional conditions moreover 13o values within unit e display a positive excursion suggesting that the depositional environment experienced an estimated decrease in temperature of several degrees centigrade strata above unit e are again fossiliferous indicating a rapid revival of normal organic activity the 13c and 18o anomalies represent strong geochemical evidence for a major global catastrophe at the frasnian famennian boundary

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 great latest ordovician extinction on the south china plate chemostratigraphic studies of the ordovician silurian boundary interval on the yangtze platform continuous samples from four ordovician silurian boundary sections of graptolitic shales and mudstones in the yangtze basin yangtze platform on the south china plate spanning the latest ordovician mass extinction of many unrelated groups of organisms were chemically analyzed for the abundances of about 40 common and trace elements and iridium it is observed that the abundances of ir and other siderophile and chalcophile elements e g co cr as mo sb and v show elevated values in the extinction horizon at the base of the graptolite persculptus zone which corresponds to the stratigraphic level for the local systematic boundary in china between the ordovician and silurian iridium abundances show maxima at this extinction level in three of the four sections analyzed with varying strength 230 ppt at yichang 92 ppt at jinxian and 88 ppt at youyang but 50 ppt at xiushan these geochemical patterns appear to be of global significance since similar geochemical anomalies including weak ir anomaly were also recorded at about the same stratigraphic level in many other sections previously studied in quebec yukon arctic and northwest territories canada and scotland although impact by a comet with low platinum group element abundances could have been responsible for the geochemical anomalies we find it is most plausible to attribute the geochemical signal to the effects of a lower sedimentation rate and reducing water conditions at this horizon the beginning of a rapid transgression induced by rapid melting of the ice caps on gondwana carbon isotope excursions in organic material at yichang together with other carbon isotope data from central sweden northwestern canada latvia quebec and wisconsin suggest that after a period of decreasing atmospheric and marine pco2 in the latest ordovician the hirnantian a sudden large pco2 increase in the ocean and atmosphere may have occurred at the extinction horizon at the base of the persculptus zone a greenhouse effect might have existed for a short time what triggered such a sudden pco2 increase is uncertain but a rapid co2 degassing caused by volcanism tectonics and or extraterrestrial impact could have been responsible

comment on k ar evidence from illitic clays of a late devonian age for the 120 km diameter woodleigh impact structure southern carnarvon basin western australia by i t uysal s d golding a y glikson a j mory and m glikson earth planet sci lett 192 2001 218 289 abstract k ar isotopic ages presented by uysal et al for illitic clay minerals from drill core samples were interpreted to date the woodleigh impact event at 359 4 ma allegedly implicating woodleigh in the late devonian mass extinction however only very equivocal evidence is presented by uysal et al to support a link between clay mineral paragenesis and impact related features and the k ar ages reveal a distribution that is essentially a continuum between 308 and 364 ma the age computed by uysal et al is based on an average of the five oldest ages within this group which has no geological or statistical basis the stratigraphic age constraints considered by uysal et al to be consistent with this age are much weaker than acknowledged and the impact could have been much older than mid devonian the size of the woodleigh crater is poorly constrained and the subject of an ongoing controversy uysal et al s suggestion of 120 km diameter is probably overestimated by a factor of two in which case a link to any mass extinction is unlikely

reply to comment on orbital cyclostratigraphy of the devonian frasnian famennian transition in south china abstract although we cannot entirely exclude possible subjective factors under the condition of less then ideal outcrop exposure in the course of grouping laminae or beds classification of hierarchical boundaries is objectively based mainly on the lateral clarity continuity and stability of boundaries and cyclothems a highly ranked sedimentary boundary is usually the surface above and below which apparent variations of the stratigraphical architecture pattern take place the thickness and lithology of grouped beds laminae are also important criteria in the classification of hierarchical cyclothems and boundaries in similar sedimentary facies and environments we suggest that hierarchical changes of cyclothems boundaries and lithology in stratigraphical sequences are common indicators of episodic sedimentation which correspond ultimately to cyclic or periodic climate and sea level fluctuations related in some degree to milankovitch cycles in tectonically relatively stable regions and periods therefore hierarchical cyclothems boundaries and lithology can reasonably be selected as proxies of tracing milankovitch cycles in contrast to proxies of chemical elements and isotopes recorded in strata hierarchical cyclothems boundaries and lithology are not easily influenced by diagenesis and epidiagenesis even lower graded metamorphism which is especially truthful for the pre cenozoic sedimentary records it is difficult to conclusively reply whether a possible bolide impact could have modified orbital parameters and climatic oscillation periods but if our deduction that the bundle bundleset and superbundleset cycles must have been controlled by orbital forcing is considered to be supported by data the assumption that impact event s could have altered long eccentricity periodicity of the early famennian may be a more suitable useful and inspirational working hypothesis than the synsedimentary tectonism our recent works indicate that of the 15 frasnian superbundlesets studied in the du an and yangdi sections 14 show a 1 4 ratio with bundlesets that is the ratio of the frasnian from the conodont falsiovalis zone to linguiformis zone and early famennian from the conodont lower triangularis zone to upper triangularis zone long eccentricity to eccentricity is 1 4 and 1 3 respectively

zinc and strontium isotope evidence for climate cooling and constraints on the frasnian famennian 372 ma mass extinction abstract the frasnian famennian f f mass extinction is one of the big five biotic crises during the phanerozoic whereas the cause of this catastrophic event still remains debated here we present for the first time high resolution zn and sr isotope data obtained by a sequential leaching procedure for carbonate rocks across the f f boundary from the fuhe section in south china both 66zn and 87sr 86sr values rapidly increase in the lower and upper kellwasser horizons and palmatolepis delicatula platys to p minuta minuta conodont zones and the positive isotope shifts are exactly located in the same horizons characterized by low 13c values equivalent to low atmospheric pco2 level reflecting climate cooling and sea level fall stages the strong temporal coupling of 66zn values raise with elevated 87sr 86sr ratios is most likely to have been caused by input of isotopically heavy zn and radiogenic sr from carbonate dominated weathering and or uptake of isotopically light zn into primary producers during climate cooling climate cooling could cause relative sea level falls resulting in widespread exposure of carbonate platform enhance carbonate influx proportion through differential weathering of carbonate and silicate rocks and cause greater productivity by promoting oceanic thermohaline circulation and enhancing upwelling of bio limiting nutrients all of these processes would have contributed to the positive shifts of 66zn as observed this proposed scenario is in accordance with the fact that the f f mass extinction was almost limited to the shallow water tropical stenothermal faunas whereas the high latitude and deep water faunas were less affected our data support and represent the composite effect of a series of events linked to climate cooling which may have induced this catastrophic event

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

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

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

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

laser argon dating of melt breccias from the siljan impact structure sweden implications for a possible relationship to late devonian extinction events in earlier studies the 6575 km diameter siljan impact structure in sweden has been linked to the late devonian mass extinction event the siljan impact event has previously been dated by kar and ar ar chronology at 342368 ma with the commonly quoted age being 362 7 2 2 ma 2 recalculated using currently accepted decay constants until recently the accepted age for the frasnian famennian boundary and associated extinction event was 364 ma which is within error limits of this earlier siljan age here we report new ar ar ages extracted by laser spot and laser step heating techniques for several melt breccia samples from siljan interpreted to be impact melt breccia the analytical results show some scatter which is greater in samples with more extensive alteration these samples generally yield younger ages the two samples with the least alteration yield the most reproducible weighted mean ages one yielded a laser spot age of 377 2 2 5 ma 95 confidence limits and the other yielded both a laser spot age of 376 1 2 8 ma 95 confidence limits and a laser stepped heating plateau age over 70 6 39ar release of 377 5 2 4 ma 2 our conservative estimate for the age of siljan is 377 2 ma 95 confidence limits which is significantly different from both the previously accepted age for the frasnian famennian f f boundary and the previously quoted age of siljan however the age of the f f boundary has recently been revised to 374 5 2 6 ma by the international commission for stratigraphy which is within error the same as our new age however the currently available age data are not proof that there was a connection between the siljan impact event and the f f boundary extinction this new result highlights the dual problems of dating meteorite impacts where fine grained melt rocks are often all that can be isotopically dated and constraining the absolute age of biostratigraphic boundaries which can only be constrained by age extrapolation further work is required to develop and improve the terrestrial impact age record and test whether or not the terrestrial impact flux increased significantly at certain times perhaps resulting in major extinction events in earths biostratigraphic record

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

carbon and sulfur isotope anomalies across the frasnian famennian extinction boundary alberta canada stable isotopes of carbonate and organic carbon from two upper devonian sections in alberta canada indicate a heavy carbon event across the frasnian famennian f f boundary and a negative 13 c shift at the boundary at cinquefoil mountain 13 c values in carbonate are anomalously high 3 5 to 4 5 pdb peedee belemnite within an interval 10 m below to 23 m above the f f boundary representing about 1 m y two standard conodont zones compared to background values of 1 above and below this interval superimposed on this positive excursion is a marked 13 c decrease of about 1 at precisely the f f boundary at medicine lake a similar 13 c excursion in organic carbon from a background of 29 to a high of 26 5 is recorded across the f f boundary the 34 s data for iron sulfide in these sections show unusually high values as much as 15 to 20 cdt canon diablo troilite in the f f boundary interval these data together with those from other areas indicate a period of major global changes e g greenhouse and marine anoxia that took place well before and after the sudden biomass killing event at the f f boundary existing evidence suggests that the f f mass extinction was probably caused by a large extraterrestrial impact on earth at a time when the global ecosystem was already severely stressed

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

orbital cyclostratigraphy of the devonian frasnian famennian transition in south china abstract superbundlesets bundlesets bundles and laminae were formed in the carbonate successions of the devonian frasnian famennian transition in guangxi south china their hierarchical structures ratio relationships and arrangement order within conodont zones are lasting and stable in the stratigraphical sequences and can be traced across the different facies belts and sedimentary basins the hierarchically organized superbundlesets bundlesets bundles and laminae correspond to a long eccentricity eccentricity obliquity and precession and sub milankovitch cyclothem respectively the ratio of long eccentricity to eccentricity is 1 4 below the boundary between frasnian famennian and 1 3 above the boundary between frasnian famennian eccentricity to obliquity is 1 3 and eccentricity to precession is 1 6 in the devonian since the eccentricity periodicity of 100 000 years remains essentially steady through geological time the periodicity of the long eccentricity obliquity precession and sub milankovitch cycle was 400 000 33 333 16 667 and 8000 or 17 000 years these ratios are different from those of the permian cretaceous and quaternary and coincide well with those calculated theoretically by berger et al science 255 1992 560 this reinforces the hypothesis of the slowing of the earth s rotation and the lengthening of precession and obliquity periods since at least the devonian time on the basis of the hierarchical milankovitch cyclothems the chronostratigraphical subdivision and correlation of the frasnian famennian transition can be made at the resolution of 100 000s and 10 000s of years the duration of the upper rhenana zone linguiformis zone and lower middle and upper triangularis zone is 0 6 0 8 0 3 0 3 and 0 3 ma respectively

a forest fire and soil erosion event during the late devonian mass extinction abstract the late devonian mass extinction occurred in a stepwise manner and culminated close to the frasnian famennian f f boundary 372 million years ago organic molecular indices from marine sedimentary rocks at the sinsin section belgium indicate that the sequence of combustion of land vegetation soil erosion and anoxia euxinia occurred close to this boundary the increased concentrations of biomarkers indicating forest fire and soil erosion measured in the sinsin section suggest that fire became widespread at this time leading to various damaging consequences increased runoff and oceanic anoxia that caused marine extinctions magnetic susceptibility data in the sinsin section indicate a relatively dry climate spanning the f f boundary which would have encouraged forest fires the study of organic biomarkers presents several lines of evidence to link forest fire and soil erosion to the late devonian mass extinction

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

frasnian famennian crisis in the malaguide complex betic cordillera spain devonian sediments of the malaguide complex potentially could include the frasnian famennian boundary one of the five greatest phanerozoic biotic crises conodont biofacies and microfacies of carbonate clasts from a pebbly mudstone underlying tournaisian radiolarites allows identification for the first time in the malaguide complex of devonian shallow marine environments laterally grading to deeper realms the clasts yielded frasnian conodont associations of the falsiovalis to rhenana biozones with six biofacies that reveal different environmental conditions in their source areas source sediments were dismantled and redeposited within the pebbly mudstone whose origin is tentatively related to one of the events that are associated worldwide with the frasnian famennian crisis the latter is recorded in two equivalent malaguide pelagic successions by stratigraphic discontinuities and it was probably tectonically and or eustatically controlled as in other alpine mediterranean paleotethyan margins

sequence stratigraphy of the frasnian famennian transitional strata a comparison between south china and southern belgium the sedimentological evolution of the frasnian famennian transitional strata in south china and southern belgium has been investigated a similar trend in the deepening and shallowing of the sedimentation environment occurs in the two palaeogeographically distinct areas the stratigraphic succession has been subdivided into depositional sequences a general deepening occurs in the palmatolepis rhenana conodont zone during the most rapid rise in sea level a transgressive systems tract formed this transgressive systems tract is followed by a highstand systems tract in the late p rhenana zone a major sequence boundary within the latter zone is indicated by an unconformity in intraplatform and platform areas and by a conformity in the basinal area the uppermost sediments within the late rhenana zone correspond to a lowstand systems tract a rapid flooding took place near the base of the palmatolepis linguiformis zone and dark shales and limestones formed a second sequence boundary coincides with or is very close to the frasnian famennian boundary base p triangularis zone the global extinction event at the frasnian famennian boundary coincides with an important eustatic fall in sea level the proposed stratigraphic subdivision should allow worldwide correlations of shallow and deep water deposits

high resolution iridium δ13c δ18o foraminifera and nannofossil profiles across the latest paleocene benthic extinction event at zumaya spain in the expanded upper paleocene lower eocene section 30 m of zone p5 sediments at zumaya northern spain the highest occurrence of many late paleocene deep sea benthic foraminifera species 40 extinction coincides with a transition from marl to calcite free clay our high resolution studies chemical elements 613c 6180 calcareous nannofossils planktic and benthic foraminifera show that below the marl clay transition there is a 40 50 cm thick interval corresponding to 10 20 kyr containing a detailed record of a gradual succession of faunal and geochemical events culminating in the benthic extinctions planktic foraminiferal and nannofossil changes e g the onset of demise in fasciculithus genus occur a few meters below the marl clay transition in the limestone 50 cm below the base of the clay a prominent glauconite maximum indicates that sea floor oxygenation suddenly decreased glauconite continues to be common until the onset of clay deposition a whole rock negative 613c shift 1 6 0 most likely reflecting an original sea water trend is gradually developed over the 40 cm of greenish brown marls immediately below the clay at the base of these marls there is a small significant iridium anomaly of 133 ppt ir compared with an average background of 38 ppt in the marls the demise of the fasciculithus species accelerates gavelinella beccariiformis becomes extinct and the abundance of acarinina species begins to increase the superjacent 4 m of clay is devoid of original calcite in its lower part and has a low calcareous content higher up at calcareous levels in the clay an unusual planktic foraminifera fauna occurs dominated by acarinina species when marl deposition returns 613c gradually increases and then stabilizes at values about 0 5 o lower than before the isotopic excursion the 613c excursion spans in total 5 m probably corresponding to 200 400 kyr the fasciculiths disappear shortly after the stabilization of 613c here we also present a whole rock 6 3c profile through the entire paleocene section at zumaya the profile is very similar to previous profiles registered in well preserved deep sea material suggesting that whole rock 613c at zumaya can be used for correlation

geochemistry of the 1984 mauna loa eruption implications for magma storage and supply the 1984 eruption of mauna loa volcano hawaii produced about 220 106 m3 of lava of remarkably homogeneous composition no significant compositional changes occurred during the 22 day eruption and along the 20 km vent system even though crystallinity increased substantially accompanying a decline in the eruption rate such homogeneity in lava composition is typical of many historic mauna loa eruptions the 1984 lava along with most other homogeneous mauna loa lavas is multiply saturated crystallizing olivine clinopyroxene and plagioclase bulk compositions are perched at the intersection of an olivine control trend with a trend for more differentiated lavas there is no evidence to indicate that the 1984 lava is a differentiate of the 1975 magma or that it results from mixing a new batch of magma with differentiated melt remaining in the magmatic plumbing system after the 1975 eruption it is proposed that these lavas are erupted directly from a small continuously replenished magma reservoir located about 3 4 km beneath the summit caldera successive eruptions therefore provide a sampling of magma chamber processes and small but discernible changes in lava composition reflect the competing processes of magma supply differentiation and eruption

geochemical analysis through the transitional zone of conodont faunal turnover in the ordovician silurian boundary interval anticosti island quebec geochemical analysis of the ordovocian silurian boundary interval on anticosti island quebec has revealed low ir abundances for the lower becscie formation 0 005 0 039 ppb comparable to those reported for the upper ellis bay formation 0 005 0 058 ppb when normalized as caco3 free values and ratioed to al a small amount of excess ir over background ir levels was observed in and on the upper surface of an oncolite platform bed in member 7 laframboise of the ellis bay formation except for this bed the abundances of ir and other elements are relatively uniform throughout the section but small enrichments are apparent in a few clay layers as in other areas previously studied south china northwestern canada scotland the ir maxima on anticosti island occur near the base of the graptolite persculptus zone and are attributable to condensation and slower sedimentation rates associated with the hardgrounds found within and on the upper surface of the oncolite platform bed although we cannot p

biological depositional microspherule and geochemical records of the frasnian famennian boundary beds south china abstract the investigation of shallow subtidal inter reef depression and inter reef platform sections from central hunan of china shows that a transgression regression cycle occurred in the late frasnian linguiformis zone the lowest triangularis zone to middle triangularis zone deposits are either very thin or variously missing in some shallow water sections of hunan the uppermost frasnian upper linguiformis zone black shale interval including black shale and carbonates was not ubiquitously developed and probably formed in a regressive shallower water and anoxic to dysoxic conditions suggested from higher ce la ratios penecontemporaneous dolomitization of carbonates and low faunal diversity two steps of the frasnian famennian f f mass extinction are postulated the first is the extinction of the benthos near the end of the frasnian which was probably caused by the sudden onset of anoxic environments shallow water rugose corals and ostracods experienced sudden biomass loss right at the deposition of the black shale the second is the extinction of pelagic fauna at the end of the frasnian microspherules of probable impact origin are found in several layers in the xikuangshan f f boundary section including two major peaks respectively at the upper rhenana zone and upper linguiformis zone and two minor peaks respectively near the top of the linguiformis zone and lower triangularis zone the microtektites are white or brownish in color characterized by high contents of si al and intermediate cao mno and feo and minor k2o and na2o occurrences of these microtektites do not seem to be directly related to the f f mass extinction from the lower rhenana zone through the upper crepida zone there are four elemental anomalous layers these elemental anomalies are interpreted to have resulted from the contemporaneous active rifting process and hydrothermal activities in south china

iridium and other platinum group elements as geochemical markers in sedimentary environments iridium anomalies are commonly used as indicators of extraterrestrial processes which caused global extinctions however platinum group element pge anomalies may result from several different processes both syn and postdepositional acting separately or jointly the sources and processes of enrichment involved are extraterrestrial asteroid comet cosmic dust impact ejecta volcanogenic pge rich condensates precipitation from seawater low sedimentation rate anoxic conditions microbial concentration dissolution reprecipitation exhalative hydrothermal leaching transport and precipitation at a redox boundary geochemical characteristics of pge and accompanying elements in sediments can be used to identify the contributions of some specific sources and processes 1 extraterrestrial chondritic ru ir and os ir ratios low 187os 186os ratio high ir compared to pt pd and au 2 volcanogenic high iridium and se as sb and in contents 3 exhalative hydrothermal high au pd and pt relatively low ir contents 4 precipitation from seawater high pt and low pd contents also high cd and ag contents under anoxic conditions and 5 reduction from intermediate and low temperature solutions high pge and cu or mo u ni contents

conodont sr ca and δ18o record seawater changes at the frasnian famennian boundary abstract the oxygen isotopic composition 18 o p and strontium calcium sr ca p ratios have been measured in late devonian conodonts palmatolepis sp from contemporaneous sections at coumiac france and m rirt morocco the sequences encompass two anoxic horizons the lower kellwasser lkw and upper kellwasser ukw events with the top of the ukw coinciding with the mass extinction at the frasnian famennian boundary the genus palmatolepis survived the faunal crisis but exhibited plastic responses to the environmental changes which are recorded in the evolution of shape during the anoxic events the present study demonstrates that shape 18 o p and sr ca p values of conodonts are correlated in both localities excluding diagenesis as the driving process for the measured 18 o p and sr ca p values the conodonts 18 o p and sr ca p values are correlated in both localities and distributed into either a pre crisis and crisis group using the relationships between the 18 o p and sr ca p values we estimate that the variation of the seawater sr ca ratio during the frasnian famennian mass extinction was of about 20 its initial value this drastic decrease of the seawater sr ca ratio is discussed in the light of the reef demise that occurred during the faunal crisis

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

upper devonian iridium anomalies conodont zonation and the frasnian famennian boundary in the canning basin western australia abstract two iridium anomalies have been identified near the frasnian famennian boundary upper devonian in the canning basin of western australia both anomalies are associated with the cyanobacterium frutexites and are located in marginal slope facies the first was identified in the virgin hills formation on the west flank of mcwhae ridge near the southeastern end of the devonian outcrop belt this anomaly initially identified as being from the famennian upper palmatolepis triangularis zone is now known to be from the early palmatolepis crepida zone on the basis of the presence of palmatolepsis crepida in the bed the second anomaly found in drill core from the napier formation just south of the napier range is older than the first and is from the frasnian montagne noire conodont zone 12 or 13 of klapper 1989 the palmatolepis rhenana zone of ziegler and sandberg 1990 these two iridium anomalies are thus significantly below and above the frasnian famennian boundary and are not associated with the extinction event in the palmatolepis linguiformis zone in the canning basin the association of two iridium anomalies with beds containing abundant frutexites microstromatolites indicates that the concentrations of iridium are probably associated with a process of organic concentration there is no evidence that either example is directly associated with an impact event

the frasnian famennian mass extinction insights from high resolution sequence stratigraphy and cyclostratigraphy in south china two sequences sfr sfa each 1 1 2 myr in duration are recognised in the strata across the frasnian famennian f f transition both in carbonate platform and interplatform basinal successions in south china the sequence boundary between the two sequences is placed a little below the top of the frasnian the sequences are basically composed of coarsening upward bed thickness increasing upward cycles and shallowing upward cycles parasequences in basinal and platform deposits respectively which stack into cycle sets typically six to eight cycles 10 and 12 cycle sets are identified in sequences sfr and sfa respectively these cycle sets can be further grouped into larger scale composite cycle sets herein termed mesocycle and megacycle sets with two and four cycle sets respectively this vertical cycle stacking pattern and the hierarchy of cyclicity suggest a milankovitch style of forcing such that the cycles and cycle sets were formed in response to the orbital perturbations of precession 16 18 kyr and eccentricity v100 kyr in duration respectively in the basinal cycles smaller scale rhythmic stratification beds typically six to eight beds in a cycle are extensive and were likely caused by millennial scale climatic forcing in the lower sequence sfr the latest highstand deposits consist of calciturbidites and debrites in deep water strata and fenestral limestones in shallow water strata representing a major third order sea level fall within these deposits four cycle sets are further identified in both coeval deep water and platform successions succeeding deeper water organic rich facies within which three cycles occur are the transgressive deposits of the overlying famennian sequence sfa these cycles represent three higher frequency 16 18 kyr sea level fluctuations and accompanying anoxia superimposed on a major third order sea level rise the f f boundary is placed at the top of the first cycle based on conodont data thus a major sea level fall and then a rise occurred in the f f transitional period faunal and sedimentological data reveal a massive biotic decline in concert with the major sea level fall and a further biotic demise coinciding with the major sea level rise and its three superimposed higher frequency sea level fluctuations and accompanying anoxia the f f biotic crisis was therefore characterised by two episodes of step down extinction on the basis of milankovitch orbital rhythms the first major biotic extinction took place over v400 kyr and the subsequent event was v50 kyr in duration i e v450 kyr for the entire event at the same time as the massive decline of normal marine fossils during the latest frasnian sea level fall there was widespread cyanobacterial growth and a thriving of planktonic calcispheres suggesting eutrophic conditions this situation could have caused a severe biotic loss as a result of the deterioration of surface water clarity and formation of anoxic bottom waters due to over

high resolution bio and chemostratigraphic framework at the frasnian famennian boundary implications for regional stratigraphic correlation between different sedimentary facies in south china abstract as one of the big five mass extinctions in phanerozoic the frasnian famennian f f boundary event records the extinction of 40 of marine invertebrate genera the f f boundary is defined by the first appearance of conodont palmatolepis subperlobata as well as the abundant occurrences of pa ultima at the base of the lower pa triangularis zone the f f boundary is also broadly coincident with a positive excursion in carbon isotopes suggesting the possible linkage between the perturbation of marine carbon cycle and the biotic crisis however the correlation between conodont biostratigraphy and carbon isotope chemostratigraphy has not been established yet preventing the high resolution regional stratigraphic correlation among different sedimentary facies in this study we studied the conodont biostratigraphy and analyzed carbonate carbon 13 c carb and organic carbon 13 c org isotopes of the baisha section in the guangxi province south china the first appearance of index conodont fossil pa subperlobata for the lower pa triangularis zone i e the f f boundary is coincident with the onset of a 3 positive excursion in 13 c carb while pa triangularis and pa subperlobata occur nearly simultaneously but predate the disappearances of pa linguiformis and other typical frasnian elements in addition a positive excursion in 13 c org is associated with the decline of 13 c carb near the base of the middle pa triangularis zone which is marked by the first appearance of pa delicatula another important famenian element pa minuta the index fossil for the upper pa triangularis zone first appears when 13 c org starts to decline the offset between 13 c org and 13 c carb excursions could be attributed to the oceanic anoxia the kellwasser event near the f f boundary followed by the mixing of surface and deep water in earliest famenian the high resolution bio and chemostratigraphic framework can be used as the standard for regional stratigraphic correlation and identification of the f f boundary in different depositional environments in south china we propose that the f f boundary can be identified from a conodont poor carbonate section by the onset of the positive excursion in 13 c carb whereas the f f boundary in a non fossiliferous siliciclastic section might be placed slightly below the positive excursion in 13 c org