palaeoenvironments and faunal recovery after the end permian mass extinction abstract strata of the lower triassic werfen formation dolomites northern italy record deposition in a wide range of palaeoenvironments from peritidal to outer ramp settings this enables accurate assessment of faunal recovery following the end permian mass extinction by eliminating facies related effects extinction of the shelly taxa appears to be rapid and occurs in the latest permian tesero oolite horizon disappearance of the various trace fossil taxa appears to be more gradual following the extinction the lower and middle griesbachian are characterised by laminated sediments containing low diversity bedding plane assemblages ichnological geochemical and sedimentological data show evidence of widespread low oxygen conditions normally oxygenated waters return in the late griesbachian and there is a moderate increase in tiering above and below the surface macrofaunal and ichnofossil diversity decrease markedly during the smithian with the appearance of more terrigenous strata possibly reflecting an increased run off and more brackish conditions complete recovery begins in the basal spathian with an increase in tiering above and below the substrate crinoids and ammonoids appear for the first time in the werfen formation and the ichnogenus rhizocorallium re appears global correlation is hindered by poor biostratigraphy in the dolomites region however on a broad scale it appears as though many of the palaeoenvironmental changes are repeated worldwide current available data suggest that the re appearance of some trace fossil taxa e g diplocraterion rhizocorallium may be globally synchronous

a newly discovered earliest triassic chert at gaimao section guizhou southwestern china abstract the permian triassic ptb boundary section at gaimao huaxi district guiyang guizhou province records a unique lithological transition between the permian and triassic in south china thus bioclastic limestones of the changxing formation are overlain by radiolarian bearing siliceous rocks of the dalong formation and ultimately limestone mudstone alternations of the shabaowan formation conodont sampling of the section revealed well preserved elements that enabled a conodont biostratigraphy to be established the occurrences of hindeodus julfensis and hindeodus typicalis in changxing formation bioclastic limestone indicate a late permian age four conodont zones have been established in dalong and shabaowan formations in ascending order those are the isarcicella isarcica zone neogondolella or clarkina planata zone neogondolella krystyni zone and neospathodus dieneri zone the presence of typical griesbachian conodonts i isarcica and isarcicella staeschei in upper dalong formation indicates that this formation s radiolarian bearing siliceous mudrocks are of earliest triassic age and not restricted to the permian as previously thought thin section analysis reveals that the upper dalong formation contains spheroidal radiolarians but not a diverse assemblage of permian holdover taxa the new data proves that following the end permian mass extinction of radiolarian the abundance of these siliceous planktons was maintained at least locally enabling chert deposition to persist thus the gaimao section provides an exception to the early triassic chert gap the first of its kind in palaeo tethys and indicates that the end of chert deposition does not always mark the end permian mass extinction

anomalously diverse early triassic ichnofossil assemblages in northwest pangea a case for a shallow marine habitable zone early triassic trace fossil assemblages from the northwest margin of pangea record a diverse suite of postextinction infauna these ichnofossil assemblages occurred within well oxygenated shallow marine refuges in a panthalassa ocean otherwise characterized by widespread anoxia we propose an environmentally controlled model for their distribution in which wave aeration enhanced by frequent storms gave rise to an optimal zone for benthic colonization within this habitable zone extinction pressures were ameliorated and postextinction recovery duration was minimized

trace fossil evidence for restoration of marine ecosystems following the end permian mass extinction in the lower yangtze region south china abstract unlike the high abundance low diversity macrofaunas that characterize many early triassic benthic palaeocommunities ichnofossils were relatively common in the aftermath of the end permian mass extinction worldwide ichnofossils therefore are a good proxy for ecosystem recovery after the end permian biotic crisis this paper documents 14 ichnogenera and one problematic form from lower triassic successions exposed in the lower yangtze region south china post extinction ichnodiversity remained rather low throughout the griesbachian early smithian period and abruptly increased in the late smithian however several lines of evidence including extent of bioturbation burrow size trace fossil complexity and tiering levels indicate that diversification of ichnotaxa in the late smithian did not signal full marine ecosystem recovery from the permian triassic p tr mass extinction marine ichnocoenoses did not recover until the late spathian in south china the marginal sea provided hospitable habitats for tracemakers to proliferate in the aftermath of the end permian mass extinction

exceptional vertebrate biotas from the triassic of china and the expansion of marine ecosystems after the permo triassic mass extinction abstract the triassic was a time of turmoil as life recovered from the most devastating of all mass extinctions the permo triassic event 252 million years ago the triassic marine rock succession of southwest china provides unique documentation of the recovery of marine life through a series of well dated exceptionally preserved fossil assemblages in the daye guanling zhuganpo and xiaowa formations new work shows the richness of the faunas of fishes and reptiles and that recovery of vertebrate faunas was delayed by harsh environmental conditions and then occurred rapidly in the anisian the key faunas of fishes and reptiles come from a limited area in eastern yunnan and western guizhou provinces and these may be dated relative to shared stratigraphic units and their palaeoenvironments reconstructed the luoping and panxian biotas both from the guanling formation are dated as anisian pelsonian on the basis of conodonts and radiometric dates the former being slightly older than the latter the xingyi biota is from the zhuganpo formation and is ladinian or early carnian while the guanling biota is from the overlying xiaowa formation dated as carnian the first three biotas include extensive benthos and burrowing in the sediments and they were located in restricted basins close to shore further even though the luoping and panxian biotas are of similar age their faunas differ significantly reflecting perhaps palaeogeographically isolated basins between the time of the xingyi and guanling biotas there was a major transgression and the guanling biota is entirely different in character from the other three being dominated by pelagic forms such as large floating crinoids attached to logs very large ichthyosaurs and thalattosaurs and pseudoplanktonic bivalves with no benthos and no burrowing phylogenetic study of the fishes and marine reptiles shows apparently explosive diversification among 20 actinopterygian lineages very early in the early triassic but a later expansion of marine reptile groups in the late olenekian and early anisian this offset in diversification patterns is matched by comparisons of feeding guild categories and body size data new research tools will shed considerable light on the phylogenetic and ecological implications of recovery of mairne vertebrates in the triassic

distribution of dissolved manganese in the peruvian upwelling and oxygen minimum zone abstract the geochemistry of manganese mn in seawater is dominated by its redox chemistry as mn ii is soluble and mn iv forms insoluble oxides and redox transformations are mediated by a variety of processes in the oceans dissolved mn dmn accumulates under reducing conditions and is depleted under oxidizing conditions thus the peruvian upwelling region characterized by highly reducing conditions over a broad continental shelf and a major oxygen minimum zone extending far offshore is potentially a large source of mn to the eastern tropical south pacific in this study dmn was determined on cruises in october 2005 and february 2010 in the peruvian upwelling and oxygen minimum zone to evaluate the relationship between mn oxygen and nitrogen cycle processes dmn concentrations were determined using simple dilution and matrix matched external standardization inductively coupled mass spectrometry surprisingly dmn was depleted under the most reducing conditions along the peruvian shelf concentrations of dissolved mn in surface waters increased offshore indicating that advection of mn offshore from the peruvian shelf is a minor source subsurface mn maxima were observed within the oxycline rather than within the oxygen minimum zone omz indicating they arise from remineralization of organic matter rather than reduction of mn oxides the distribution of dmn appears to be dominated by non redox processes and inputs from the atmosphere and from other regions associated with specific water masses lower than expected dmn concentrations on the shelf probably reflect limited fluvial inputs from the continent and efficient offshore transport this behavior is in stark contrast to fe reported in a companion study which is very high on the shelf and undergoes dynamic redox cycling

the ichnogenus rhizocorallium classification trace makers palaeoenvironments and evolution rhizocorallium is one of the oldest known trace fossils with wide distribution through the phanerozoic and all over the world originally introduced from the epicontinental triassic of central germany its high morphological lability gave reason for the subsequent erection of about twenty ichnospecies the study of newly collected material from the type area and many specimens from various collections permits the conclusion that rhizocorallium jenense and rhizocorallium commune are the only valid ichnospecies of rhizocorallium the type ichnospecies r jenense is a comparatively small inclined and heavily scratched firmground burrow with passive fill while r commune consists of extensive more or less horizontal burrows with occasionally scratched marginal tubes and an actively filled spreite between the tubes the faecal pellets coprulus oblongus are typically associated with r commune morphological variations of r commune are captured in ichnosubspecies and varieties of this ichnospecies and can aid a refined reconstruction of palaeoenvironments a review of more than 180 records from the literature reveals the common confusion of both ichnospecies which has consequences for the application of rhizocorallium in facies interpretations the end members of both ichnospecies may be linked by transitional forms which suggests the same kind of trace maker polychaetes are the most likely producers of marine rhizocorallium based on their long ranging occurrence morphological features appearance of faecal pellets associated soft body remains and modern analogues r commune occurs from early cambrian to holocene while r jenense just appears after the end permian mass extinction probably as a consequence of an adapted firmground burrowing lifestyle of its producer fluvial r jenense are probably produced by mayfly larvae in homology to marine polychaete burrows a consequent application of the newly established classification scheme allows for a more rigorous application of rhizocorallium in the reconstruction of palaeoenvironments thus palaeozoic and mesozoic r commune are restricted to the cruziana ichnofacies of shallow marine environments while in cenozoic time similar forms are also found in deep marine deposits r jenense on the other hand is a constituent of the widespread glossifungites ichnofacies and aside from continental environments occurs in peritidal to deep marine deposits several studies have demonstrated the value of rhizocorallium for interpreting sequence stratigraphical surfaces current directions and fluctuations in salinity and oxygen

environmental controls on the post permian recovery of benthic tropical marine ecosystems in western palaeotethys aggtelek karst hungary climate warming during the late permian is associated with the most severe mass extinction event of the phanerozoic and the expansion of hypoxic and anoxic conditions in shallow shelf settings it has been hypothesised that wave aeration provided a habitable zone in the shallowest environments that allowed the survival and rapid recovery of benthic invertebrates during the early triassic we test this hypothesis by studying the rock and fossil records of the aggtelek karst hungary nearshore settings recorded in the bodvaszilas sandstone formation and units a and d of the szin marl formation are characterised by taxonomically homogenous fossil assemblages of low diversity and low evenness ecological and taxonomic recovery in this environmental setting was hampered by persistent environmental stress this stress is attributed to increased runoff related to climate warming during the early triassic that resulted in large salinity fluctuations increased sedimentation rates and eutrophication that led to seasonal hypoxia and an environment only favourable for opportunistic taxa in contrast shoal and mid ramp settings further offshore are characterised by high diversity faunas with a greater functional complexity prior to the late spathian tirolites carniolicus zone the shelly fossils and trace fossils are limited to settings aerated by wave activity which supports the habitable zone hypothesis in the tirolites carniolicus zone however the oxygen minimum zone retreats offshore and the habitable deeper shelf settings are rapidly colonised by shallow water taxa evidenced by the highest levels of diversity and bioturbation recorded in the study locally full recovery of marine ecosystems is not recorded until the illyrian with the establishment of a sponge reef complex

early triassic trace fossils from the three gorges area of south china implications for the recovery of benthic ecosystems following the permian triassic extinction abstract the lower triassic daye and jialingjiang formations of the three gorges area south china record the recovery interval of benthic tracemaking invertebrates following the p tr mass extinction a total of 17 ichnospecies in 14 ichnogenera are documented from smithian and spathian strata our trace fossil data in combination with previously published studies show that ichnodiversity in the middle yangtze region increased markedly in the early spathian trace fossils in the smithian are dominated by simple small horizontal burrows including didymaulichnus and planolites whereas spathian trace fossils are diverse and abundant with moderate high bioturbation levels and complex burrow networks such as thalassinoides both burrow sizes and penetration depths increased gradually from the early spathian to the middle late spathian implying a gradual recovery pattern for benthic ecosystems early triassic ichnofossils are characterised by aspects of opportunistic behaviour e g low to moderate ichnodiversity low to moderate bioturbation small burrow widths and shallow tiering suggesting stressed environmental conditions the recovery tempo and pattern of ichnocoenoses in south china is likely structured by temporal and spatial changes of the refuge zone in the early triassic

a smithian early triassic ichnoassemblage from lichuan hubei province south china implications for biotic recovery after the latest permian mass extinction abstract a late smithian ichnoassemblage is reported from the lower triassic succession from the lichuan section western hubei province south china this ichnoassemblage comprises 13 ichnogenera which include simple horizontal traces cochlichnus cosmorhaphe didymaulichnus gordia circulichnis and planolites vertical traces arenicolites laevicyclus oblique or horizontal branching traces palaeophycus slightly complex burrow networks thalassinoides and treptichnus and grazing traces cosmorhaphe and gyrochorte these traces are also categorized into fodinichnia domichnia pascichnia and repichnia ethologic types suggesting a fairly high degree of behavioral complexity of these the fodinichnia traces are most abundant the ichnoassemblage horizons usually have rather high ichnofabric indices ii reaching ii 4 5 bedding plane coverage is up to 70 90 resulting in high bedding plane bioturbation index as well bpbi 4 5 the lichuan ichnoassemblage traces have mean and maximum diameters of 4 8 mm and 9 mm respectively n 342 the traces penetrate to a depth of up to 30 mm into the sediment with an average depth of penetration of 15 mm indicating third to fourth tiering levels 3 4 overall the lichuan ichnofauna shows an abrupt increase in ichnodiversity burrow width behavioral complexity and ecologic tiering level which are indicative of recovery stages of 2 3 in the late smithian when compared to five coeval ichnoassemblages from other sections in south china yashan susong daxiakou gaimao and tianshengqiao and coeval ichnoassemblages from elsewhere northern italy western australia western us the lichuan trace fossil assemblage reaches similar level of diversity during this time interval paleoenvironmental analysis indicates that the late smithian recovery pulse is typically confined to the offshore transition setting whereas more distal zones record much lower levels of recovery therefore time and environmental conditions were the two crucial factors controlling the rate and degree of recovery of trace making organisms in the aftermath of the latest permian mass extinction

trace fossils and the aftermath of the permo triassic mass extinction evidence from northern italy abstract the duration of early triassic anoxia in the carbonate ramp settings of the werfen formation dolomites northern italy has been constrained using ichnofabric and sedimentological data this includes fine lamination and abundant pyrite framboids commonly reworked into lags by storm events the anoxic event spanned the entire griesbachian stage and extended from deep waters into extraordinarily shallow water settings evidence for oxygen deficiency can be found in mid and inner ramp facies the extent and duration of this event may at least partially explain the magnitude of the permo triassic mass extinction normal benthic conditions returned rapidly in the dienerian stage and pervasively bioturbated distal ramp facies testify to the ventilation of the deeper water areas of the region in post griesbachian times a post mass extinction radiation is not particularly well displayed in either trace fossil or body fossil diversity compilations from the dolomites moderate low levels of trace fossil diversity are maintained throughout the post griesbachian werfen formation whilst the body fossil data shows a moderate increase from the mid smithian stage there is thus a curious lag period spanning the dienerian to mid smithian when environmental conditions were apparently normal but the marine fauna failed to show any recovery

bacterial and algal markers in sedimentary organic matter deposited under natural sulphurization conditions lorca basin murcia spain abstract free lipids sulphur bound lipids present in macromolecular fractions and kerogen pyrolysis products have been studied in shales and early diagenetic carbonates replacing gypsum from a messinian sequence of lorca basin the high abundance of phytane 2 3 dimethyl 5 2 6 10 trimethylundecyl thiophene mid chain c 20 isoprenoid thiophenes and bithiophenes and bis o phytanyl and o phytanyl o sesterterpanyl glycerol ethers indicates that the organic matter in all these samples was deposited under hypersaline conditions the isopranyl glycerol ethers are essentially found in the sulphur bound macromolecular matter which contrasts with the low concentrations of these compounds as free lipids however the distributions of these isopranyl glycerols is paralleled by the occurrence of free phytanic acid shales and laminated carbonate and 3 7 11 15 19 pentamethyleicosanoic acid only in the laminated carbonate the bacterial inputs are represented by 2 hydroxytetracosanoic acid n octadec 11 enoic acid hopanoic acids and the distributions of iso and anteiso c 15 and c 17 homologues and minor amounts of iso c 16 and anteiso c 14 these branched fatty acids are characteristic of sulphate reducing bacteria the relative proportions of the iso and anteiso compounds in the total fatty acid distributions are correlated with the proportion of reduced sulphur in the sediments

conodont zonation across the permian triassic boundary at the xiakou section yichang city hubei province and its correlation with the global stratotype section and point of the ptb xiakou section is situated north of the central yangtze platform with successive late permian to early triassic strata thicker than the global stratotype section and point gssp of the permian triassic boundary ptb we recognized three conodont zones across the ptb in this section by high precision biostratigraphy they are the hindeodus latidentatus clarkina meishanensis zone hindeodus parvus zone and isarcicella isarcica zone in ascending order which correspond well with the gssp the present biostratigraphic work on xiakou section certainly confirmed the conodont zonation through the ptb at the gssp and also testified to the correctness of the ptb demarcation in xiakou section based on this precise demarcation of the ptb the appearance of a clay layer bed zsji266 just beneath the ptb should be an important advantage over the gssp because this clay layer approaches to the ptb much in contrast with those two clay layers bed 26 and bed 28 in the gssp therefore the radiometric isotopic da

the end permian mass extinction and its aftermath on an equatorial carbonate platform insights from ichnology terra nova 22 195 202 2010 abstract a semi quantitative analysis of the endobenthic activity across the permo triassic boundary ptb was carried out on a 445 m thick well core interval from the persian gulf by logging the degree of bioturbation trace fossil distribution and ichnodiversity id this analysis enables for the first time the evaluation of recovery of endobenthic organisms after the end permian mass extinction by direct comparison of post extinction lower triassic with pre extinction upper permian units the results indicate that the studied shallow marine carbonate platform within an equatorial setting acted as oxygenated refugee for the biotic recovery traces of suspension and deposit feeders reappear simultaneously shortly after the extinction event but are reduced in size macroborings so far unknown from the lower triassic occur where suitable firm or hard substrate was available recovery took place in two phases early induan 50 pre extinction id and 20 30 bioturbation and late induan 75 id and almost 90 bioturbation re established

new trace fossil evidence for an early recovery signal in the aftermath of the end permian mass extinction abstract new ichnological data from the lower triassic werfen formation dolomites italy revealed an unexpectedly diverse and complex ichnofauna in mixed siliclastic carbonate shelf sediments of the western tropical tethys shortly after the end permian mass extinction event common elements are thalassinoides palaeophycus and planolites other associated ichnogenera include spongeliomorpha rhizocorallium lockeia catenichnus helminthopsis and taenidium one structure is tentatively determined as curvolithus biostratigraphic data conodonts and bivalves of the trace fossil interval lower seis siusi member suggest a late griesbachian age less than 1 ma after the end permian mass extinction event similarly diverse ichnofossil communities from this time interval have recently been described from the boreal realm but this is the first record of a diverse griesbachian ichnoassemblage from the tropics indicating that the early recovery of trace fossil producers was not latitudinally restricted as previously proposed accordingly relatively advanced recovery stages were reached on a global scale much earlier than the spathian as is commonly acknowledged the early and interregional peak in ichnofaunal recovery implies subsequent ecological setbacks in post griesbachian times that explain the overall delay of benthic recovery until the spathian rather than persistent catastrophic conditions during the griesbachian a global and synchronous succession of crises and relaxation phases after the griesbachian is proposed as an explanatory model for the recovery pattern of benthic ecosystems

early triassic trace fossils from gondwana interior sea implication for ecosystem recovery following the end permian mass extinction in south high latitude region abstract the kockatea shale formation is one of few marine early triassic successions recorded in the gondwana this formation is exposed at the northampton area of the northern perth basin western australia and was deposited in the gondwana interior sea during the permian and early triassic trace fossils identified within the kockatea shale formation are extremely abundant and contain 16 ichnogenera including a problematic ichnogenus the gondwanan ichnoassemblage is constrained as late smithian in age and is the most diverse among coeval ichnofaunas around the world several types of grazing traces are also reported for the first time in the lower triassic several proxies such as bioturbation level ichnodiversity burrow size trace fossil complexity and tiring level suggest that tracemakers diversified in the gondwana interior sea during the late smithian the gondwanan ichnofauna dominated ecosystem may have reached the ecologic recovery stage 3 of twitchett s model in late smithian the rebound of ichnoassemblages in the aftermath of the end permian mass extinction was not controlled by particular environmental settings all of which however were characterized by oxygenated substrata

ichnological analysis of the cretaceous palaeogene boundary interval at the caravaca section se spain abstract ichnological analysis of the cretaceous palaeogene k pg boundary at caravaca betic cordillera southeast spain reveals significant data for the interpretation of the k pg boundary event the uppermost maastrichtian marls below the cretaceous palaeogene k pg boundary at caravaca contains the dark coloured trace fossils chondrites targionii planolites thalassinoides zoophycos and alcyonidiopsis the composition of trace fossil associations in the upper maastrichtian and lower danian marls is generally the same yet much more poorly preserved in the latter showing in general no ichnological evidence of a severe macroinfaunal crisis at the k pg boundary the dark coloured trace fossils penetrate from two bioturbated horizons in the dark boundary layer separated by two horizons with primary lamination the ichnofauna rapidly recovered after the k pg event following deposition of the lower parallel laminated bed 14 mm thick that occurs in the dark boundary layer above the k pg boundary zoophycos is the deepest trace fossil penetrating as far as 90 cm below the k pg boundary probably in stiff or partly firm substrate which was dewatered to some extent during the slow accumulation of the danian dark boundary layer the firmness probably prevented the chondrites trace maker from deeper burrowing the maastrichtian sediments may be contaminated with danian microfossils due to bioturbation

two episodes of evolution of trace fossils during the early triassic in the guiyang area guizhou province south china abstract the lower triassic of the guiyang area of southern china contains abundant and well preserved trace fossils which are useful in the reconstruction of ecological conditions following the end permian mass extinction a total of 16 ichnogenera and 22 ichnospecies were identified their vertical distribution and evolution indicate that benthic ecosystems experienced two periods of episodic recovery after the p t event episode 1 occurs in the daye formation during the dienerian when trace makers first appear in the upper portion of member d1 member d2 exhibits the first abrupt increase in ichnodiversity and trace makers shift from simple to complex and undergo a substantial increase in size these trends indicate a strong capability to rework sediments and an improvement of feeding strategies of trace makers and points to the development of an early initial benthic ecosystem despite the emergence of complex trace fossils in d2 such as phycodes and phycosiphon most of the trace fossils are small horizontal burrows that are not fully developed in three dimensions by the end of dienerian the regional environment deteriorated and the benthic ecosystem was destroyed as evidenced by the disappearance of trace fossils from upper d3 to lower a1 which also corresponds to a marked negative shift of 13 c carb as a result this newly established benthic ecosystem was vulnerable episode 2 occurs from the late smithian to the spathian trace fossils reappear in the lower anshun formation the trace fossils from this stage are larger more complex and are fully three dimensional trace maker diversity increases from single polychaeta followed by the appearance of crustaceans as represented by rhizocorallium in member a3 of the anshun formation during this period the marine environment improved and benthic organisms gradually established a basis for a new benthic ecosystem the marine benthic communities had a transformative effect on the ecological environment of the ocean bottom and played an essential role in paving the way for the recovery of other organisms two episodes of evolution of trace fossils reflect that initial restoration of benthic ecosystems was apparently reset at least once during the early triassic recovery was not delayed because of persistent environmental stress but short episodes of deleterious conditions marine benthic ecosystems had a full and lasting recovery occurred at the global scale during the spathian when oceanographic conditions ameliorated and allowed the recovery of ecosystems worldwide

paleoethologic interpretation of complex thalassinoides in shallow marine limestones lower ordovician southern sweden abstract lower ordovician thalassinoides t bacae isp nov from oland sweden is characterized by irregularly anastomosing horizontal tunnel mazes with highly variable branching angles accompanied by numerous closely spaced short vertical shafts that must have provided a large number of burrow openings to the sea floor these complex trace fossils appear to be agrichnial burrow systems that represent chemosymbiotic feeding behavior by infaunal animals they occur profusely in thin bedded fossiliferous lime mudstone and wackestone that were deposited on a shallow marine carbonate platform

loss of the sedimentary mixed layer as a result of the end permian extinction abstract the end permian mass extinction resulted in the most dramatic degradation of marine bottom communities during the phanerozoic one result of this extinction was the long recognized extreme reduction in bioturbation of the early triassic seafloor several lines of evidence i e preferential preservation of epifaunal and very shallow tier infaunal trace fossils paucity of mid and deep tier trace fossils absence of mottled bioturbation textures dominance of cohesive substrates widespread occurrence of microbially induced sedimentary structures in open marine environments ecological composition of early triassic communities show that the reduction in bioturbation was so extreme that the sedimentary mixed layer was eradicated at an interregional scale for the only time since it was established in the early palaeozoic the consequences of this for ecosystem function and geochemical cycling must have been profound and yet they have received little consideration biogenic mixing of sediments is fundamental to geochemical cycling in extant marine ecosystems and it also governs ecologically limiting factors such as nutrient fluxes benthic primary production and availability of ecospace the collapse of biogenic sediment mixing during the early triassic must have affected geochemical properties of sediments and the seawater as reflected in the geologic record of the sulphur cycle additionally many of the proxies traditionally used to infer early triassic seawater anoxia may rather reflect poor sediment oxygenation arising from the extinction of bioturbators because of its impact on seawater and sediment chemistry the loss of the mixed layer may have been an important but hitherto little considered constraint on the recovery from the end permian mass extinction

complete biotic and sedimentary records of the permian triassic transition from meishan section south china ecologically assessing mass extinction and its aftermath abstract the meishan section south china is the global stratotype section and point gssp for the permian triassic boundary ptb and is also well known for the best record demonstrating the permian triassic mass extinction ptme all over the world this section has also been studied using multidisciplinary approaches to reveal the possible causes for the greatest phanerozoic biocrisis of life on earth many important scenarios interpreting the great dying have been proposed on the basis of data from meishan nevertheless debates on biotic extinction patterns and possible killers still continue this paper reviews all fossil and sedimentary records from the permo triassic p tr transition based on previously published data and our newly obtained data from meishan and assesses ecologically the ptme and its aftermath to determine the biotic response to climatic and environmental extremes associated with the biocrisis eight updated conodont zones clarkina yini clarkina meishanensis hindeodus changxingensis clarkina taylorae hindeodus parvus isarcicella staeschei isarcicella isarcica and clarkina planata zones are proposed for the ptb beds at meishan major turnover in fossil fragment contents and ichnodiversity occurs across the boundary between bed 24e 5 and bed 24e 6 suggesting an extinction horizon in a thin stratigraphic interval the irregular surface in the middle of bed 27 is re interpreted as a firmground of glossifungites ichnofacies rather than the previously proposed submarine dissolution surface or hardground surface both fossil fragment contents and ichnodiversity underwent dramatic declines in beds 25 26a coinciding with metazoan mass extinction fossil fragment content ichnodiversity and all ichnofabric proxies including burrow size tiering level bioturbation level indicate that the p tr ecologic crisis comprises two discrete stages coinciding with the first and second phases of the ptme in meishan ecologic crisis lagged behind biodiversity decline during the ptme pyrite framboid size variations suggest that depositional redox condition was anoxic to euxinic in the latest changhsingian became euxinic in beds 25 26a turned dysoxic in bed 27 then varied from euxinic to anoxic through most of the griesbachian the 9 c increase in seawater surface temperature from bed 24e to bed 27 at meishan seems to result in dramatic declines in biodiversity and fossil fragment contents in beds 25 26a but had little effect on all ecologic proxies both metazoans and infauna seem not to have been affected by the pre extinction anoxic euxinic condition the anoxic event associated with the ptme may have occurred in a much shorter period than previously thought and is only recorded in beds 25 26a at meishan fossil fragment contents ichnofaunas ichnofabrics and pyrite framboid size all show that no signs of oceanic acidification and anoxia existed in bed 27 the early griesbachian anoxia may have resulted in rarity of ichnofauna and metazoans in the lower yinkeng formation in which the ichnofauna is characterized by small simple horizontal burrows of planolites and metazoan faunas are characterized by low diversity high abundance opportunist dominated communities the rapid increase of 9 c in sea surface temperature and a short anoxia or acidification coincided with the first pulse biocrisis while a prolonged and widespread anoxia probably due to a long period of high seawater temperate condition may be crucial in mortality of most organisms in the second pulse ptme marine ecosystems started to recover coupled with environmental amelioration in the late griesbachian

lower middle triassic conodont biostratigraphy of the qingyan section guizhou province southwest china abstract the middle triassic qingyan formation at its type section the qingyan section of guizhou southwest china yields more than 300 species belonging to 17 fossil groups which mark the radiation of benthic organisms following the end permian mass extinction this study intends to establish a primary conodont biostratigraphical succession through the lower and middle triassic sequence at qingyan to provide a time framework for the understanding of the recovery and radiation process from the mass extinction a total of 30 species in 8 conodont genera are stratigraphically significant and assigned to the neospathodus dieneri neospathodus cristagalli neospathodus waageni neospathodus homeri chiosella timorensis and neogondolella cf bulgarica zones in ascending order most conodont zones correlate well with their counterparts recognized from elsewhere in china and even worldwide the first appearance of ns waageni marks the induan olenekian boundary which is placed at the lower middle part of the luolou formation 121 47 m above the permian triassic boundary the olenekian anisian early middle triassic boundary is here defined by the first occurrence of chiosella timorensis at the base of the qingyan formation although no conodonts retrieved from the upper qingyan formation containing the extraordinarily diverse biota i e the qingyan biota stratigraphical correlation with the neighbouring conodont bearing sections in guizhou and the ammonoid zones suggest that the qingyan biota has an age of early late anisian early middle triassic