the vredefort structure estimates of energy for some internal sources and processes abstract the conspicuous features of the vredefort structure are the concentric arrangement of gneissose core steeply dipping metasediments and metavolcanics and a peripheral rim syncline the alkali intrusive suite and its metamorphic aureole the indicators of fracturing and high pressure shatter cones coesite and stishovite and microscopic deformation textures and the predominance of co 2 over h 2 o in fluid inclusions in the gneissose core the cause of the vredefort structure lies in either external or internal agencies possible internal agencies and sources of energy are discussed here in reviewing possibilities a continuum is recognized between two extremes at one extreme the major sources of energy are taken to be the density inversion metasediments overlying granitic gneiss and the alkali intrusions whereas at the other extreme the major source of energy is taken to have a deep seated and explosive character most of the energy being liberated in one or two short but very great bursts between the extremes lie scenarios in which violent energy releases form substantial but not overwhelming contributions to the total attention is focused initially on the less explosive end of the range the hypothesis explored is that the gneiss rose because of buoyancy while being disturbed and accelerated by the alkali intrusions the aspect selected for emphasis is the energy budget quantities of energy are estimated as follows 1 gravitational energy available from the density inversion 10 21 j 2 thermal energy associated with the alkali intrusions 10 21 j and 3 energy consumed in forming shatter cones 10 15 j by comparison for mount st helens in april may 1980 the estimates are thermal energy associated with magma 10 18 j and energy released in four major seismic events 10 13 j in addition to the energy budget aspects requiring attention are the apparent compressive stress intensities 8 10 gpa to form stishovite and the form and distribution of the shatter cones possibilities are 1 for stishovite that sufficient compressive stress developed locally at asperities on fracture surfaces and 2 for the cones that they formed by quasi static mohr coulomb fracture in radially symmetrical local stress fields produced by seismic pulses of magmatic origin imposed on rocks already prestressed during gravity doming with regard to the role of compressed volatiles they may have been important in affecting fracture behavior preserving stishovite by quenching and promoting development of certain microdeformations at low stress levels their relative importance as a source of energy in comparison with the other sources mentioned is not brought out by the calculations nothing in the above is intended to exclude other possible reconstructions from consideration the method of multiple working hypotheses being upheld

stromatolites near the permian triassic boundary in chongyang hubei province south china a geobiological window into palaeo oceanic fluctuations following the end permian extinction abstract stromatolites just after the end permian extinction are exceptionally well developed in the chongyang area of hubei province south china the stromatolites include endolithic coccoidal microbes and exhibit three growth forms columnar layered pseudo columnar and columnar each located in different stratigraphic horizons the columnar type is the most conspicuous and provides key information on the mode of their construction in this paper we describe the mega to microscopic features of these stromatolites together with interpretations of their construction the columnar type typically comprises alternations of lighter and darker laminae with intercalations of dense micritic laminae the lighter laminae are composed of fine to coarse calcite cement and fine dolomite whereas the darker laminae are composed of micrite and microspar endolithic coccoids are sporadic in these laminae in contrast the dense micritic laminae consist of micrite with abundant endolithic coccoids accentuating the laminae of stromatolites the columnar stromatolites were formed under deteriorating conditions after the end permian mass extinction as follows 1 the alternating development of lighter and darker laminae due to the colonization of different microbial communities in lower energy shallow to deep subtidal settings 2 carbonate precipitation within each microbial community through microbial metabolic activity and degradation of extracellular polymeric substances eps leading to the alternations of lighter and darker laminae 3 episodic interruption of the growth of the lighter and darker laminae by endolithic coccoidal activity and 4 high levels of endolithic activity accompanied by the precipitation of carbonate within boreholes to produce the dense micritic laminae in contrast the columnar layered and pseudo columnar types comprise alternations of lighter and darker laminae composed mainly of fine to coarse calcite cement fine dolomite micrite peloids and microspar with sporadic endolithic coccoids the dense micritic laminae are absent or rare in these stromatolites these types were essentially produced by the repetition of processes 1 and 2 documented in the columnar type the finely alternating laminae of these stromatolites are therefore the product of the repeated initiation and cessation of growth of relevant microbial communities in response to changing environmental conditions the stromatolites were formed immediately after the end permian extinction and persisted intermittently throughout the early triassic the chongyang stromatolites are undoubtedly some of the best developed stromatolites near the permian triassic boundary and retain a high resolution record of microbial successions and palaeo oceanic perturbations immediately following the end permian extinction

erosional truncation of uppermost permian shallow marine carbonates and implications for permian triassic boundary events replyreply to comment by paul wignall et al

griesbachian earliest triassic palaeoenvironmental changes in the salt range pakistan and southeast china and their bearing on the permo triassic mass extinction abstract facies and faunal analysis from pakistan and china show that the permo triassic mass extinction of marine invertebrate faunas was associated with a spectacularly rapid griesbachian transgression which lead to the widespread establishment of deep water anoxic and dysoxic conditions the extinction event was thus caused by habitat loss due to the extensive development of inhospitable conditions the initial griesbachian transgression in pakistan produced extensive shallow normal marine conditions in which permian holdover taxa were able to survive until the development of dysaerobic facies in the late griesbachian the exceptionally complete sections of china show a three phased deepening and extinction event beginning in the latest permia by the late griesbachian a variety of dysaerobic and anaerobic facies were developed in all the regions studied several of these contain evidence for minimal sulphate reducing activity suggesting that marine productivity and thus organic matter flux to the sediments was very low in early triassic seas

composition and structure of microbialite ecosystems following the end permian mass extinction in south china after the end permian mass extinction microbialites were widespread in the shallow marine environments in south china diverse microbialites are characteristic of the early triassic carbonate sequences their stratigraphic range is rather short just across the permian triassic p tr boundary and defined by conodonts n meishanensis h changxingensis and h parvus zones thus the p tr microbialites grew immediately after the first episode of the end permian mass extinction coinciding with the beginning of the conodont n meishanensis zone and ceased their growth at the beginning of the conodont i staeschei zone which occurred just before the second episode of the end permian crisis at meishan they include three main types stromatolites thrombolites and dendrites in south china the presence of abundant microbial remains of coccoid type and renalcis like microbes strengthens the previous view that the p tr microbialites are biogenic both cyanobacteria and other microbes have participated to construct the microbial ecosystems the thrombolite communities are dominated by the renalcis like microbes and foraminifers and also contain ostracods microgastropods and microconchids the stromatolite communities are dominated by coccoidal microbes with minor constituents of other undetermined microbes metazoans are rare the dendrolite assemblage contains few identifiable microfossils most of microbialite communities have a high abundance low diversity community structure characteristic of marine communities after the end permian mass extinction some metazoans of either opportunists or disaster forms dwelled in this special ecosystem the microbialite builders formed the primary producer communities and constructed the lowest level ecosystem structure the lower level ecosystem proliferated due to the collapse of the higher level of ecosystem structure characterized by benthic shelly and predator communities in the end permian crisis

early middle triassic stromatolites from the luoping area yunnan province southwest china geobiologic features and environmental implications abstract an early middle triassic stromatolite deposit is documented from the guanling formation of the luoping area yunnan sw china the luoping stromatolite shows five types of constructional microbial forms in various magnifications 1 typical stratified columnar structures up to 20 cm high with crinkled laminae dark coloured laminae 1 mm thick are composed of upright filamentous tubes averagely 29 4 m in diameter showing a vertical growth fabric 2 laminoid fenestrae 0 5 1 mm wide and 3 prostrate filaments which are reflected by strong fluorescence in sharp contrast to dolomite cement in fluorescent images 4 rod like aggregates 4 6 18 m in diameter composed of minute dolomite rhombs are very common in stromatolitic laminae they resemble present day cyanobacterial trichome and thus may represent putative fossilized cyanobacteria 5 moreover small pits coccoid like spheroids calcified biofilms and fibrous structures are also common in stromatolitic laminae the last two may represent calcified extracellular polymeric substances eps that contributed to the development and lithification of stromatolites authigenic quartz grains are common and may also have involved biological processes in stromatolite formation of these microbial functional groups driving accretion and lithification processes of stromatolite documented in literature both lithified cyanobacteria oxygenic phototrophs and possible sulfate reducing bacteria srb which induced microbial formation of dolomite and contributed to the accretion of the luoping stromatolite are suggestive of biogenic origin the luoping stromatolite differs from the permian triassic boundary microbialites ptbms in having abundant filamentous structures and growing in an oxic marine environment both sedimentary facies analysis and abundant fossilized cyanobacteria may indicate proliferation of oxygenic phototrophs in a normal oxic habitat during the middle anisian early middle triassic a period when hospitable environments coupled with biotic diversification prevailed in south china and set an agenda for the full recovery of marine ecosystems in middle late anisian however the post extinction stromatolites and other anachronistic facies are not necessarily indicative of anoxic or oxic conditions and their environmental settings are much more complex than previously thought

upper lower triassic stromatolite from anhui south china geobiologic features and paleoenvironmental implications abstract widespread stromatolites and other microbialite deposits characterize lower triassic marine successions worldwide this study documents a stromatolite deposit 1 1 m thick from the upper spathian lower triassic of the susong area south china the stromatolite comprises distinct laminated domes in the basal part and columns at the upper part dark laminae are loosely spaced and interlayered with thicker light colored laminae diffusive dark colored laminae are composed of peloidal micrite that grade locally into microclotted structures and yield copies of bacteria clump like and coccoid like spheroid aggregates the former are characterized by cloudy micrite nuclei rimmed by coarse grained euhedral sparry calcite crystals while the latter are comprised of solid calcite crystal nuclei coated with rather thin micrite envelopes the cloudy micrite nuclei resemble bacteria clump like structures observed in present day travertine both the coccoid like spheroids and bacteria clump like structures are surrounded by coarse grained euhedral calcite crystals suggesting a similar accretion mechanism both spherical structures therefore could be crucial in the accretion of the susong stromatolite the laminated microclotted structures are interpreted as the result of variation in timing of lithification relative to the timing of the decay of microbes micro analysis also unravels the common occurrence of authigenic micro quartz crystals in association with fe bearing illite clay minerals in the stromatolite columns their coalescing nature with each other together with the associated pyrite grains strongly support the formation of micro quartz crystals from microbial reduction of an fe bearing smectite precursor by sulfate reducing bacteria a comparison of the susong stromatolite with its counterparts from the upper lower triassic strata in dajiang south china reveals many similarities in stromatolite microstructures suggesting that a harsh euxinic anoxic environment resulting in the bloom of sulfate reducing bacteria most likely extended into the latest spathian in south china

initial assessment of the carbon emission rate and climatic consequences during the end permian mass extinction numerous lines of geochemical and stable isotopic evidence indicate that the end permian mass extinction was accompanied by abrupt climate change induced by co2 addition catastrophic end permian siberian volcanism may have released a large amount of co2 into the atmosphere and pushed the earth s system beyond a critical threshold causing the mass extinction however the injection rate total amount and source of co2 are largely unknown we conducted a suite of simulations using the recently published carbon isotope records and u pb ages from meishan section in zhejiang province china an earth system model of intermediate complexity cgenie http www genie ac uk was used to extract the pattern of co2 release needed to replicate the observed carbon isotope excursion across the permian triassic boundary this analysis leads us to suggest that the source of co2 must have been significantly heavier than typical biogenic or thermogenic methane to explain the significant warming that occurred during and after the extinction event nevertheless as with the paleocene eocene thermal maximum end permian rates of co2 addition were likely small compared with modern fossil fuel burning but considerably more protracted such that the likely total co2 emitted significantly exceeded the modern fossil fuel reserves peak emission rates corresponded to the onset of the maximum extinction interval consistent with carbon cycle disruption including volcanogenic co2 induced warming and perhaps ocean acidification as a trigger for the end permian mass extinction

depositional conditions and revised age of the permo triassic microbialites at gaohua section cili county hunan province south china abstract in many tropical shallow water regions the end permian mass extinction event occurs at the top fossiliferous packstone beds and is immediately followed by the development of microbialite facies both the age and redox conditions of the microbialite have been debated and both factors are addressed here in a study of the gaohua section cili county hunan province china specifically the size distribution of pyrite framboids and high resolution conodont biostratigraphy the framboids populations show a broad size range with examples up to 30 microns in diameter and indicating dysoxic but not anoxic depositional conditions more intense dysoxia is recorded in interbedded laminated micrites but not beds of giant ooids both the hindeodus parvus zone and isarcicella isarcica zones were established with the microbialite beds being confined to the h parvus zone therefore the formation of microbialite postdates the end permian main mass extinction and records oxygen poor conditions even in a shallow water setting such as gaohua section at cili

latest permian to middle triassic redox condition variations in ramp settings south china pyrite framboid evidence a detailed 10 m y redox history of changhsingian to anisian latest permian to middle triassic oceans in ramp settings is reconstructed based on framboidal pyrite analysis from south china the result shows that the well established phenomenon of intense ocean euxinia anoxia is faithfully recorded in pyrite framboid data three major euxinia anoxia episodes namely the end changhsingian to end smithian middle to late spathian and early to middle anisian have been recognized from the ramp successions the first reducing episode is subdivided into four subepisodes permian triassic boundary griesbachian dienerian boundary earliest smithian and end smithian redox variations broadly track other oceanographic proxies euxinia anoxia episodes coincide with positive excursions of conodont ce anomalies negative excursions of 34scas carbonate associated sulfate increases in sea surface temperature and negative excursions of 13c in most cases however euxinia anoxia near the dienerian smithian boundary coincided with positive excursions of 13c and a general cooling period this exception may be the result of locally developed water column anoxia the permian triassic boundary subepisode witnessed two ephemeral euxinia anoxia events separated by a dysoxic to oxic period the former together with a rapid increase in sea surface temperature up to 8 c may have been responsible for the biodiversity crisis while the latter anoxic event destroyed ecosystem trophic structures in addition to the permian triassic boundary euxinia anoxia event which spread over habitats in all oceans the spathian and anisian euxinia anoxia episodes also prevailed in global oceans variation of the oxygen minimum zone are suggested as the driving mechanism that facilitated the movement of oxygen poor water columns in various paleogeographic settings over this critical period

small microbialites from the basal triassic mudstone tieshikou jiangxi south china geobiologic features biogenicity and paleoenvironmental implications abstract we report small microbialites from the calcareous mudstone slightly above the permian triassic boundary ptb in the tieshikou section southern jiangxi province south china the newly found microbialite is a bowl like structure which contrasts with the surrounding calcareous mudstone the small microbialite is composed of columnar forms and fan shaped structures mini columnar structures resemble mini stromatolites in plane view most branches are patchy or strip shaped with clotted structures resembling that of a thrombolite fan shaped cement precipitates are comprised of multiple crystal fans that have a radiating texture and that show distinct growth laminae the radiating fabrics are represented by rod shaped filaments under sem which are interpreted as calcified trichomes filaments prominent micropores occur within the rods and they may be the plane views of multiple sheaths of the false branching zone of trichomes thus both the columnar forms and radiating fans are probably microbial in origin moreover three types of nano sized structures intraparticle micropores fibrous biofilms and filamentous sheaths are also pronounced in both the columnar structures and cement fans of the tieshikou microbialite all suggestive of biogenicity these well preserved fibrous biofilms probably represent calcified extracellular polymeric substances eps and linear sheaths are interpreted as the traces of bacterial activities during the precipitation of dolomite crystals the tieshikou microbialite therefore shares similar biogenetic mechanisms with other ptb microbialites the combination of the absence of pyrite framboids slightly negative carbon isotope values and an association with abundant ammonoids bivalves and gastropods indicates oxic conditions during the growth of the tieshikou microbialite moreover the nodular preservational state resembles widely distributed nodular mudstones or muddy limestones of the lower triassic successions worldwide this implies that nodular mudstone or argillaceous limestones may also have been deposited in microbe rich environments in which terrigenous supply was abundant

microbial primary dolomite from a norian carbonate platform northern calabria southern italy the origin of fine grained dolomite in peritidal rocks has been the subject of much debate recently and evidence is presented here for a microbial origin of this dolomite type in the norian dolomia principale of northern calabria southern italy microbial carbonates there consist of stromatolites thrombolites and aphanitic dolomites high relief thrombolites and stromatolites characterize sub tidal facies and low relief and planar stromatolites with local oncoids typify the inter supratidal facies skeletal remains are very rare in the latter whereas a relatively rich biota of skeletal cyanophycea red algae and foraminifera is present in the sub tidal facies some 75 of the succession consists of fabric preserving dolomite especially within the microbial facies whereas the rest is composed of coarse dolomite with little fabric preservation three end members of dolomite replacement fabric are distinguished type 1 and type 2 fabric retentive with crystal size 5 and 5 60 m respectively and type 3 fabric destructive with larger crystals from 60 to several hundred microns in addition there are dolomite cements precipitated in the central parts of primary cavities during later diagenesis microbialite textures in stromatolites are generally composed of thin dark micritic laminae of type 1 dolomite alternating with thicker lighter coloured laminae of the coarser type 2 dolomite thrombolites are composed of dark micritic clotted fabrics with peloids composed of type 1 dolomite surrounded by coarser type 2 dolomite marine fibrous cement crusts are also present now composed of type 2 dolomite scanning electron microscope observations of the organic rich micritic laminae and clots of the inter supratidal microbialites reveal the presence of spherical structures which are interpreted as mineralized bacterial remains these probably derived from the fossilization of micron sized coccoid bacteria and spheroidal ovoidal nanometre scale dwarf type bacterial forms furthermore there are traces of degraded organic matter probably also of bacterial origin the microbial dolomites were precipitated in a hypersaline environment most likely through evaporative dolomitization as suggested by the excess ca in the dolomites the small crystal size and the positive 18o values the occurrence of fossilized bacteria and organic matter in the fabric preserving dolomite of the microbialites could indicate an involvement of bacteria and organic matter degradation in the precipitation of syn sedimentary dolomite

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

microbially induced sedimentary structures misss from the lower triassic kockatea formation northern perth basin western australia palaeoenvironmental implications abstract like microbialites microbially induced sedimentary structures misss are commonly observed in siliciclastic and mixed carbonate siliciclastic settings in the lower triassic and are represented by several morphological types including wrinkle structures however their origin and their role in the early triassic ecosystem recovery is currently a hot topic of debate herein we report and describe abundant wrinkle structures from the smithian kockatea shale formation of northampton area in the perth basin western australia on the basis of detailed field observations as well as petrographic and sem examinations of rock thin sections the surficial morphologies of wrinkles are characterized by closely spaced crests and ridges on the upper bedding surfaces together with other forms such as pitted bulges and reticulated ridges detailed petrologic analysis revealed that the smithian wrinkle structures from the northern perth basin possess a distinct vertical profile 1 cross stratified lamianted sandstone 2 alternating laminated layers and sandstone 3 laminated layers and 4 wrinkled layers in an ascending order the wrinkled layers are overlain by thin shale laminated layers beneath wrinkled surfaces comprise densely packed pronounced wavy laminae mica flakes in laminations show a preferred alignment parallel to bedding under sem imaging suggesting the binding and trapping of the former presence of a microbial matground these evidences support that the early triassic wrinkle structures from the smithian kockatea formation are biogenic in origin close association of both trace and body fossils with the wrinkle structure bearing layers is interpreted to indicate the presence of a matground ecosystem in which some small gastropods and various trace making animals lived possibly taking the habitat as a refuge the global temporal and spatial occurrences of early triassic miss were tabulated and analyzed revealing a wide range of palaeoenvironmental distributions and the seemingly selected association between metazoans and certain miss as to why only some misss have been found together with metazoans remains as an open question it will require further investigation especially with regard to the specific type of microbes that had built the microbial matground ecosystems and their interplay with the hosted metazoans in the aftermath of the end permian mass extinction

facies changes and diagenetic processes across the permian triassic boundary event horizon great bank of guizhou south china a controversy of erosion and dissolution the permian triassic boundary interval in shallow shelf seas of south china shows upper permian limestones overlain by lowermost triassic microbialites global sea level rose across the permian triassic boundary but an irregular top permian erosion surface across a 10 km north south transect of the great bank of guizhou contains evidence of sea level fluctuation the surface represents the event horizon of mass extinction below the biostratigraphic permian triassic boundary defined by first appearance datum of conodont hindeodus parvus an upper permian foraminiferal grainstone beneath this surface contains geopetal sediments etched grains and pendent and meniscus cements interpreted here as vadose however these latter diagenetic processes occurred before the event horizon and were followed by erosion of the final permian surface this erosion cuts previous fabrics but lacks evidence of weathering or bioerosion a few centimetres below is an earlier grainstone that was also eroded but lacks proof of sub aerial processes samples therefore reveal one or possibly two small scale relative sea level changes before the triassic transgression in this area and these may relate to local tectonics the final permian surface is subject to at least four interpretations i sub aerial physical erosion and dissolution by carbon dioxide enriched fresh water or carbon dioxide enriched mixed water prior to triassic transgression ii sub aerial physical erosion overprinted by dissolution related to carbon dioxide enriched sea water in the early triassic transgression iii submarine dissolution affected by acidified sea water due to rapid increase in volcanically derived carbon dioxide and oxidized methane released from marine clathrates iv submarine dissolution due to acid anoxic waters rising across the continental shelf unrelated to atmospheric carbon dioxide or oxidized methane field and petrographic evidence suggests that i is the simplest option and it is possible that ii and iii occurred but none are proved option iv is unlikely given the evidence and modelling of supersaturation of upwelled waters with respect to bicarbonate

origins of microspherules from the permian triassic boundary event layers in south china abstract volcanism and impact scenarios are two of the most plausible ways of interpreting the causes of the largest biological mass extinction at the end permian microspherules have previously been widely reported from tens of different permian triassic boundary ptb sections in south china and some other regions these microspherules have been interpreted as either the product of volcanic eruptions or an impact event in order to test these scenarios we collected 60 samples from 12 intensively studied ptb sections in south china in addition four soil samples close to these ptb layers were also collected for comparison our investigation indicates that abundant microspherules with mosaic or dot shape crystals on rounded surface are present in the surface samples in the ptb layers at meishan meili and shatian sections and most soil background samples in south china those microspherules consist of four different types based on their main chemical composition surface features and internal structure including iron magnetite silicate glassy pyrite microspherules and framboids in contrast microspherules have not been found in a few sections in remote areas such as the selong xishan section in tibet and the dalongkou section in xinjiang northwest china in the deeply excavated samples at the shangsi section and the hard tuff layers around the ptb at the xiaochehe section in guiyang microspherules decrease in abundance with depth in ptb clay beds all these microspherules except the pyrite microspherules and framboids are found in both the ptb layers and the nearby soil background samples the iron microspherules are pure iron oxides such as magnetite hematite or maghemite and contain low concentrations of nickel and chromium and lack an ni fe core and general extraterrestrial mineral wustite all these external and chemical characteristics suggest that most of iron microspherules previously reported from ptb sections in south china are modern industrial fly ashes a low ratio of fe 3 fe total in crystals of magnetite silicate microspherules and high zno contents can identify them as industrial contaminants the pyrite microspherules and framboidal pyrite found from bed 24e and bed 26 at the meishan sections are of depositional or and diagenetic origins and only the rounded quartz and the fragments containing extremely high sio 2 and tio 2 are possibly of volcanic origin

calcium isotope constraints on the end permian mass extinction the end permian mass extinction horizon is marked by an abrupt shift in style of carbonate sedimentation and a negative excursion in the carbon isotope 13c composition of carbonate minerals several extinction scenarios consistent with these observations have been put forward secular variation in the calcium isotope 44 40ca composition of marine sediments provides a tool for distinguishing among these possibilities and thereby constraining the causes of mass extinction here we report 44 40ca across the permian triassic boundary from marine limestone in south china the 44 40ca exhibits a transient negative excursion of 0 3 over a few hundred thousand years or less which we interpret to reflect a change in the global 44 40ca composition of seawater co2 driven ocean acidification best explains the coincidence of the 44 40ca excursion with negative excursions in the 13c of carbonates and organic matter and the preferential extinction of heavily calcified marine animals calcium isotope constraints on carbon cycle calculations suggest that the average 13c of co2 released was heavier than 28 and more likely near 15 these values indicate a source containing substantial amounts of mantle or carbonate derived carbon collectively the results point toward siberian trap volcanism as the trigger of mass extinction

the fabrics and origins of peloids immediately after the end permian extinction guizhou province south china abstract peloids are major contributors to modern and ancient limestones although their origins are not yet comprehensively understood upper permian to lower triassic carbonate successions are well preserved at the bangeng area in guizhou province south china where microbialites thrombolites coccoidal microbes and peloids are preserved together these peloids are classified into three types peloid a b c that typically occur together along with coccoidal microbes and restricted bioclasts in a variety of microenvironments peloid a is most common and exhibits close relationship with coccoidal microbes peloid a1 has spherical grain and a size range typical for coccoidal microbes 10 60 m in diameter whereas peloid a2 is marked by larger spherical and subrounded grains with diffuse margins ranging from 70 to 200 m in diameter peloid a1 is in part produced by the complete micritic filling in coccoidal microbes by their metabolic activities whereas peloid a2 is related to the calcification of a colony of coccoidal microbes by their metabolic activities or simply to the aggregation of individual peloids and coccoidal microbes peloids of this type might also originate from other carbonate precipitation processes peloid b is derived merely by micrite filling in ostracodes and gastropods skeletons whereas peloid c is of micritized bioclast origin these peloidal origins do not explain those of all environments and ages peloids are polygenetic in origin irrespective of the presence of coccoidal microbes however it is emphasized that the peloids formed after the end permian extinction are dominated by microbes related ones those kinds of peloids might have occurred repeatedly and predominantly especially in severely deteriorated environments such as those after the end permian mass extinction

high resolution carbon isotope changes in the permian triassic boundary interval chongqing south china implications for control and growth of earliest triassic microbialites abstract high resolution 13 c carb analysis of the permian triassic boundary ptb interval at the laolongdong section beibei near the city of chongqing south china encompasses the latest permian and earliest triassic major facies changes in the south china block scb microbialites form a distinctive unit in the lowermost 190 cm above the top of the changhsing formation latest permian at laolongdong comparable to a range of earliest triassic sites in low latitudes in the tethyan area the data show that declining values of 13 c carb well known globally began at the base of the microbialite high positive values 3 to 4 ppt of 13 c carb in the late permian are interpreted to indicate storage of 12 c in the deep waters of a stratified ocean that was released during ocean overturn in the earliest triassic contributing to the distinctive fall in isotope values this interpretation has been stated by other authors and is followed here the 13 c carb curve shows fluctuations within the microbialite unit which are not reflected in the microbialite structure comparisons between microbialite branches and adjacent micritic sediment show little difference in 13 c carb demonstrating that the microbialite grew in equilibrium with surrounding seawater the early triassic microbialites are interpreted to be a response to upwelling of bicarbonate rich poorly oxygenated water in low latitudes of tethys ocean consistent with current ocean models for the ptb interval however the decline of 13 c carb may be due to a combination of processes including productivity collapse resulting from mass extinction return of deep water to ocean surface oxidation of methane released from methane hydrate destabilisation and atmospheric deterioration nevertheless build up of bicarbonate rich anoxic deep waters may be expected as a result of the partial isolation of tethys due to continental geography release of bicarbonate rich deep water by ocean upwelling in the earliest triassic may have been an inevitable consequence of this combination of circumstances

shallow water redox conditions from the permian triassic boundary microbialite the rare earth element and iodine geochemistry of carbonates from turkey and south china redox sensitive elements serve as useful proxies of the oxygenation state of ancient environments but their interpretation may not always be straightforward to evaluate the inherent complexities rare earths and yttrium rey iodine and major element concentrations are determined in two carbonate sections spanning the permian triassic p tr transition in demirtas turkey and cili south china we use major oxides to identify non seawater rey sources such as siliciclastics fe oxides phosphates and diagenetic fluids additionally we employ y ho ratio la anomaly and light rare earth element depletion to identify which samples preserve a seawater like reysn distribution in contrast to past interpretations we find that the p tr boundary microbialites in both sections contain rey signatures indicative of deposition in an oxic environment these boundary microbialites have their base at the extinction horizon and are widespread within the tethyan region in the cili section the underlying permian limestone also preserves a seawater like rey signature with a negative ce anomaly this indicates that the water column was oxygenated both before and after the extinction event the permian limestone in the demirtas section does not preserve a seawater like reysn distribution so the absence of a ce anomaly cannot be used to distinguish prevailing redox conditions during deposition however in these samples we find the presence of a diverse permian benthic community sufficient to identify deposition in an oxic environment the geochemical evidence for a continuously oxic environment during the deposition of the boundary microbialite presented in this study strongly supports work done using ostracods as redox indicators within the boundary microbialite in south china the microbialite has been proposed as a disaster facies in part resulting from the exclusion of grazers although anoxia is one of the suggested mechanisms for the exclusion of grazers we find that it is not supported by geochemical and biotic evidence

a microbialite carbonate crust at the permian triassic boundary in south china and its palaeoenvironmental significance a 1 m thick carbonate crust layered and commonly domal caps crinoidal limestones on reef complexes of the top permian changxing formation in the huaying mountains eastern sichuan china the crust s stratigraphic level lies at a sharp change in facies and is overlain by poorly fossiliferous laminated micrites and shales of the lower triassic feixianguan formation the crust therefore appears to coincide with the end permian extinction event although the dating of the strata is currently imprecise the crust is composed mostly of digitate carbonate locally thrombolitic with remnant lobate fabric and resembles microbialites but is mostly recrystallised and a microbial origin is unconfirmed it is enclosed in micrite with pyrite crystals ostracode and other shell debris the crust is absent from interreef areas previous interpretations of karstification and calcrete formation are not upheld and the facies were deposited under water overlying sediments are low energy with abundant ferroan calcite and pyrite reflecting anoxia associated with rising sea level various interpretations of the crust are possible 1 it was organic and microbia grew preferentially on topographic highs of reef tops 2 microbia were a disaster biota in the absence of grazers 3 microbia took advantage of favourable conditions for calcification associated with a rapidly rising environmental co2 content during the late permian 4 the crust was an inorganic precipitate associated with co2 rich water microbial crusts are rare after the cambrian but whether this crust is organic or not its presence in these strata reinforces the view that oceanic atmospheric conditions in the permian triassic boundary interval were unusual

co 2 rich fluid inclusions along planar elements of quartz in basement rocks of the vredefort dome south africa along a nw se profile through the basement core starting below the sedimentary unconformity and ending in the center of the nearly circular structure the constituent quartz grains and their fluid inclusions exhibit the following characteristics

biosedimentological features of major microbe metazoan transitions mmts from precambrian to cenozoic abstract biotic activities are involved in almost all sedimentation processes throughout the evolutionary history of life on our planet however deep time organism induced sedimentation and biosedimentary records remain unclear in terms of lithologic types strata stacking patterns and possible controlling factors we document biosedimentary features of major transitions from microbe dominated switching to metazoan dominated biosedimentary systems based on the global distributions of both microbial and metazoan carbonates through precambrian to phanerozoic times with emphasis on sedimentary records from china the compilation of 150 and 180 well documented metazoan and microbial reefs respectively from china reveals that metazoan reefs proliferated during the middle ordovician middle devonian and middle permian whereas microbial reefs were well developed during the cambrian late devonian and early middle triassic plus a moderate development during the early silurian these stratigraphic abundances of metazoan and microbial carbonates of china generally match the global patterns the updated variation trends of microbial and metazoan carbonates throughout the late precambrian and phanerozoic reveal that there were five major microbe metazoan transitions mmts the late ediacaran the cambrian and the aftermaths of the mass extinctions of the end ordovician late devonian and end permian the late ediacaran mmt began with microbe dominated oceans with occasional occurrences of metazoans the presence of cloudina dominated reefs in the latest ediacaran marks the completion of the switching of this microbe dominated depositional system into a metazoan dominated system the cambrian saw the expansion of skeletal microbes i e epiphyton renalcis in the oceans and the stratigraphic successions yield the most diverse biosedimentary deposits and or structures of the entire phanerozoic the cambrian mmt was the longest microbial metazoan alternation period and is marked by two metazoan occurrence peaks marked by dominance of abundant archaeocyath buildups during its epoch 2 and by maceriate and lithistid sponge reefs during the late furongian epoch the early silurian in china saw the deposition of a thick suite of organic rich black shales followed by alternations of microbe rich sediments oil shales and metazoan bearing deposits which are replaced by microbial and metazoan reefs during the late early silurian the late devonian mmt started during the late frasnian and persisted into the early mississippian and thus extended slightly longer than the aftermath of the frasnian famennian extinction interval alternating occurrences of microbial and metazoan reefs characterize this late devonian mmt almost all microbe mediated sediments structures observed in the cambrian mmt reoccurred in the aftermath of the end permian mass extinction during the early middle triassic mmt suggesting high similarities between those two mmts cambrian and early middle triassic mmts also share comparable carbon and sulfur isotopic perturbations warming regimes and generally oxygen deficient seawaters some of these environmental and climatic extremes may also occur during other mmts but they usually did not occur synchronously most mmts seem to have undergone four developmental stages they initiated as microbe dominated successions stage a and then were characterized by alternations of microbe dominated and of metazoan bearing or bioturbated successions stage b both microbial and metazoan reefs co occurred during stage c and a dominance of metazoan reefs marks the development of stage d ediacaran and cambrian mmts seem to have undergone the first three development stages whereas the three post extinction mmts experienced the full set of stages a d corresponding to metazoan survival initial recovery and full recovery the majority of volatile rich large igneous provinces lips coupled with intensive acidification events anoxia and global warming regimes took place during the mesozoic cenozoic however microbe dominated sediments were only widely deposited during the early triassic and greatly declined after that time therefore it seems that microbial abundance in mmts may not be directly related to these extreme lip events this is probably because a primary source of food for the metazoans might have shifted to phytoplankton e g coccoliths dinoflagellates and radiolarians in the marine waters since the triassic certainly the pre mesozoic oceans were not dominated by phytoplankton perturbations in the carbon isotope record characterize all mmts and thus may be reliable proxies indicating mmt biosedimentary systems

oxygen deficiency in lake sihetun formation of the lower cretaceous liaoning fossillagerstatte china the redox state of lake sihetun represented by the lower cretaceous yixian formation western liaoning china is evaluated to understand the formation of this konservat lagerstatte lake evolution is subdivided into four phases of which phases 2 and 3 exhibit excellent fossil preservation exceptional preservation and mass mortality events within phase 2 were previously attributed to synsedimentary volcanism and oxygen deficiency however the volcanic trigger for mass mortality events remains enigmatic and distinction between anoxia and dysoxia has not been put forward so far to resolve the redox state of the lake during phase 2 5394 diameters of pyrite framboid pseudomorphs in 29 thin sections from three localities have been measured framboid size distributions reveal that lake sihetun was governed by dysoxic bottom waters with spells of anoxia recording pronounced environmental stress hence holomictic eutrophic conditions were episodically replaced by meromictic interludes spatial variations in redox state were common and oxic conditions were detected in two of the three studied localities concentrated iron sulphide layers resulted from biofilms at the lake floor or the development of microenvironments around organic remains which preserved highly reactive organic compounds in contrast sediments of phase 3 record oxic conditions and an entirely holomictic lake

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

shock metamorphism in the vredefort collar evidence for internal shock sources shock metamorphic microstructures in the vredefort collar include planar features crystallographically controlled cleavage crystallographically controlled faults and mosaic extinction in addition several recrystallization textures are developed in the quartzites of the collar and quartz c axis distributions for both primary and recrystallized quartz grains are random the degree of recrystallization decreases away from the core collar contact two events of shock deformation have been identified in the collar and using planar feature orientations shock pressures have been estimated using the technique of robertson 1975 the first shock d1 subjected the lowermost witwatersrand rocks to shock pressures of about 150 kbar and the uppermost beds to pressures of about 60 kbar following a period of extensive recrystallization of the quartzites came the second shock event d2 which was weaker than the first and subjected the lowermost strata in the collar to pressures of between 75 and 100 kbar the d2 event has been shown to be separated in time from the d1 event the results are used to show that the shock sources were probably within the earth and that the vredefort ring structure has formed as a result of endogenous processes rather than hypervelocity meteorite impact

ostracod fauna from the permian triassic boundary interval of south china huaying mountains eastern sichuan province palaeoenvironmental significance thirteen species of ostracods in a sample of 400 specimens were extracted by hot acetolysis from three samples within the earliest triassic hindeodus parvus zone in the permian triassic boundary interval in the huaying mountains eastern sichuan province south china one new species langdaia laolongdongensis n sp was found ostracod preservation is good this study provides ostracod data that demonstrate a confirmation of palaeozoic holdovers in the earliest triassic in south china b consistency between the palaeoecological interpretation of ostracod faunas and previous environmental and oceanic interpretations that suggest poorly oxygenated waters invaded the shelf in the earliest triassic and demonstrate the value of ostracods in the analysis of these rocks and c evidence of palaeobiogeographical links are between south china and turkey and confirm that south china iran and turkey remain close from middle permian until at least the earliest triassic d 2004 elsevier b v all rights reserved

a permian triassic boundary microbialite deposit from the eastern yangtze platform jiangxi province south china geobiologic features ecosystem composition and redox conditions abstract a permian triassic p tr boundary microbialite ptb microbialite deposit occurs near xiushui on the southern margin of the eastern yangtze platform south china this 2 m thick microbialite overlies uppermost permian bioclastic limestone with a 5 cm thick oolite like grainstone layer at the contact this ptb microbialite consists of lower thrombolite 1 5 m thick and an upper dendrolite 0 5 m thick the thrombolite interval is characterized by a clotted texture of reddish sparitic patches embedded in a gray micritic matrix whereas the dendrolite texture consists of brownish sparitic patches embedded within a yellow micritic matrix abundant calcified microbes occur in both the thrombolite and the dendrolite including 1 columnar and clustered fabrics which are especially rich in the thrombolite assigned as products of gakhumella or related microorganisms and 2 microspheroids 40 60 m in diameter with different interior structures these calcimicrobes are considered to have played an important role in constructing the xiushui ptb microbialite the demise of the microbialite was likely due to a sea level fall during the early griesbachian lowermost triassic which resulted in a lowering of the wave base thereby destroying the microbialite frameworks and facilitating the deposition of winnowed skeletal grainstone metazoan community structures within the microbialite changed sharply across the end permian extinction horizon which is placed at a sharp negative shift in 13 c carb quantitative analyses show that the xiushui microbialite community is similar to that of chongyang and cili microbialites this is probably because all of these microbialites grew along the margins of the lower yangtze region during the p tr transition however unlike other ptb microbialites the xiushui ecosystem contains fairly abundant metazoans which are dominated by ostracods with minor occurrences of foraminifers microgastropods and microconchids both the ostracod assemblage and the pyrite framboid analyses indicate an upper dysoxic zone to a well oxygenated condition for the xiushui microbialite this implies that some ptb microbialite ecosystems developed in conditions that were not always harsh instead some were hospitable for some metazoans to survive immediately after the end permian crisis considering that the redox conditions indicated by ptb microbialites are quite variable we infer that oxygen levels probably were not the crucial factor affecting the growth of the ptb microbialites

erosional truncation of uppermost permian shallow marine carbonates and implications for permian triassic boundary events on shallow marine carbonate buildups in south china turkey and japan uppermost permian skeletal limestones are truncated by an erosional surface that exhibits as much as 10 cm of topography including overhanging relief sedimentary facies microfabrics carbon isotopes and cements together suggest that erosion occurred in a submarine setting moreover biostratigraphic data from south china demonstrate that the surface postdates the uppermost permian sequence boundary at the global stratotype section and truncates strata within the youngest known permian conodont zone the occurrences of similar truncation surfaces at the mass extinction horizon on carbonate platforms across the global tropics each overlain by microbial buildups and their association with a large negative excursion in 13 c further suggest a causal link between erosion of shallow marine carbonates and mass extinction previously proposed to account for marine extinctions the hypothesis of rapid carbon release from sedimentary reservoirs or the deep ocean can also explain the petrographic observations rapid unbuffered carbon release would cause submarine carbonate dissolution accounting for erosion of uppermost permian skeletal carbonates and would be followed by a pulse of high carbonate saturation explaining the precipitation of microbial limestones containing upwardgrowing carbonate crystal fans models for other carbon release events suggest that at least 5 10 18 g of carbon released in 100 k y would be required of previously hypothesized permian triassic boundary scenarios thermogenic methane production from heating of coals during siberian traps emplacement best accounts for petrographic characteristics and depositional environment of the truncation surface and overlying microbial limestone as well as an associated carbon isotope excursion and physiologically selective extinction in the marine realm

bacterial fossils and microbial dolomite in triassic stromatolites triassic stromatolitic dolomite from italy preserves mineralized bacterial remains one of the first unequivocal identifications of such structures in the geological record they consist of empty spheroids 1 0 m diameter resembling coccoid bacteria and smaller 150 400 nm objects interpreted as dwarf bacterial forms occurring within and between syn sedimentary dolomite crystals moreover gently folded sheets 100 200 nm thick and several micrometers long form a sub polygonal network reminiscent of eps extracellular polymeric substance their granular textured surfaces suggest bacterial degradation of original organic matter these features confirm a biological origin for the stromatolites as in modern microbial mats and the preserved original geochemical signatures indicate early precipitation of mg carbonates induced through microbial sulfate reducing metabolic activities

volcanism redox conditions and microbialite growth linked with the end permian mass extinction evidence from the xiajiacao section western hubei province south china we thank both anonymous reviewers and editor thomas algeo for critical comments and constructive suggestions which have greatly improved the quality of the paper this study is partly supported by the 111 program of china b08030 two nsfc grants 41572091 41402089 and one research grant from the state key laboratory of biogeology and environmental geology bgeg china university of geosciences gbl11206 it is a contribution to the igcp 630 permian triassic climatic and environmental extremes and biotic response

evidence for end permian ocean acidification from calcium isotopes in biogenic apatite c record of carbonate rocks 13 c carb for the selective extinction of heavily calcifi ed marine animals and for the abrupt transition in carbonate facies across the extinction horizon an additional proxy is necessary to distinguish among these options calcium isotopes hold promise for differentiating between suggested scenarios for change in seawater carbonate chemistry linked with the end permian extinction the calcium cycle is linked to the carbon cycle through the weathering of limestone and the deposition of calcium carbonate sediments calcium isotopes fractionate by 0 6 and 1 3 in calcite and aragonite respectively during the precipitation of modern carbonate minerals meaning carbonate sediments are enriched in the lighter isotope relative to the seawater from which they precipitated skulan et al 1997 tang et al 2008 imbalances between calcium delivery and burial fl uxes and changes in the magnitude of fractionation during carbonate deposition will result in changes in the 44 40 ca of seawater and will be recorded in marine sediments depaolo 2004 farkao et al 2007 therefore variation in the

early triassic calcimicrobial mounds and biostromes of the nanpanjiang basin south china stanley s model 1988 proposed that a permiantype reef fauna survived the early triassic reefless period in yet undiscovered refuges in the ancestral pacific ocean and then reappeared as the builders of middle triassic reefs flugel 1994 in contrast suggested that the middle triassic reefbuilding fauna are not holdovers from the permian but bear only a superficial resemblance to permian fossils recent publications reflect a consensus that the early triassic lacked reefs and reef mounds although some authors acknowledged the possibility that reef like structures may have existed in poorly explored areas such as south china and russia senowbari daryan et al 1993 flugel 1994 it is shown herein that calcimicrobial framework mounds and biostromes existed in the early triassic in the nanpanjiang basin of south china organic framework in this paper refers to a three dimensional biologically constructed network of calcified fossils that forms a rigid mass and supports an interconnected network of internal cavities that were open during accumulation although the calcimicrobial frameworks discussed herein are much smaller than frameworks of modern metazoan reefs the term framestone is more appropriate for these fabrics than other reef rock terms such as bindstone or bafflestone embry and klovan 1971 these calcimicrobial mounds and biostromes are important as the first organic framestones documented from the early triassic

pattern of marine mass extinction near the permian triassic boundary in south china the meishan section across the permian triassic boundary in south china is the most thoroughly investigated in the world a statistical analysis of the occurrences of 162 genera and 333 species confirms a sudden extinction event at 251 4 million years ago coincident with a dramatic depletion of 13ccarbonate and an increase in microspherules

the end permian regression in south china and its implication on mass extinction abstract records of more than 20 permian triassic boundary ptb sections from south china show that widespread end permian regression took place in whole south china timing of the low ebb of this regression was pinpointed to the clarkina meishanensis and hindeodus changxingensis zones biostratigraphic and paleogeographic studies at conodont zonation level reveal that the yangtze carbonate platform and isolated small carbonate platforms in the hunan guizhou guangxi hgg basin experienced sedimentary hiatus during these two zones which lasted about 50 100 kya meanwhile the basinal areas namely the northern marginal basin of yangtze platform and the hunan guizhou guangxi basin have continuous conodont zonation with silicious and ashbed deposits the basinal areas show two negative 13c shifts during the ptb interval from clarkina yini zone to isarcicella isarcica zone while on the platforms there is usually only one negative shift because the early shift at c meishanensis zone was lost during hiatus the end permian regression and successive rapid transgression taking place at the ptb casted important effects to the pattern and process of the ptb mass extinction the depositional hiatus hitherto underestimated will necessitate reassessment of some interpretations on the causes and results of that extinction

do peatland microforms move through time examining the developmental history of a patterned peatland using ground penetrating radar using ground penetrating radar gpr to map subsurface patterns in peat physical properties we investigated the developmental history of meso scale surface patterning of microforms within a raised bog common offset gpr measurements were obtained along a 45 m transect at frequencies ranging from 100 to 900 mhz we found that low frequency central frequency 240 mhz showed a striking pattern of subsurface reflections that dip consistently in a northerly direction the angle of these dipping reflectors is calculated using a semblance algorithm and was shown to average 3 9 degrees between a depth of 1 0 and 2 5 m these dipping reflectors may indicate downslope migration of surface microforms during the development of the peatland based on the estimated angle and the rate of peat accumulation the average rate of downslope propagation of these surface microforms is calculated at 9 8 mm per year further survey work is required to establish whether the downslope migration is common across the peatland

megascopic planar shock fractures in the vredefort structure a potential time marker abstract megascopic planar shock response fractures densely spaced s surfaces hitherto ignored in the vredefort structure by geoscientists reveal a systematic and symmetrical geometric pattern in the vredefort collar rocks the s surfaces where occurring as a conjugate system display an intimate geometrical relationship to the shatter cones suggesting a common origin for these features the master cone is enveloped by two sets of s surfaces and occupies the obtuse angle of the conjugate system in such a manner that its axis bisects the angle between these surfaces and is approximately perpendicular to their line of intersection the angle between the two sets of s surfaces and their respective angular relationships to the bedding vary little around the structure this is concluded from structural data recorded at 41 study areas spaced at regular intervals around the circumference of the vredefort structure a pre overturning age for the s surfaces is postulated from their geometrical relationship to the shatter cones and their low variance angular relationship to bedding we suggest that the occurrence of these planar shock fractures provides a potential geological time marker

the evolution of microbialite forms during the early triassic transgression a case study in chongyang of hubei province south china abstract the widespread development of microbialites in shallow areas of the tethys ocean at the start of the early triassic reflects the deterioration of marine ecosystems in the aftermath of the extinction that marked the demise of the majority of palaeozoic marine faunas here we present a study of the evolving microbialite forms and associated biotic assemblages of this pioneering microbialite interval from exposures at chongyang hubei province china this research provides a perspective on the effects of eustatic transgression on marine ecosystems as water depths increased at the beginning of mesozoic through the study of the changing forms microfacies and distribution of microbialites microbialite forms evolved from stratiform stromatolites to a sequence of tabular thrombolites with an intercalated layer of columnar stromatolites followed by domical thrombolites that were overlain in turn by oolites the stratiform stromatolites contain poorly preserved remains of calcified cyanobacteria but microfossils with chambered structure can also be seen metazoan fossils increased from the base of the overlying tabular thrombolite reflecting increasing biodiversity with deepening of seawater the occurrence of columnar stromatolites within the tabular thrombolite may indicate a temporary sea level shallowing foraminiferans and other metazoans are absent within the columnar stromatolites but spherical cyanobacterial remains are extremely abundant well preserved calcified cyanobacteria may reflect an absence of metazoan predation and or carbonate supersaturation of seawater as water deepened domical thrombolites developed and the more complex seafloor relief created varied niches between and within the domes that harboured more ecologically diverse communities during the process of transgression within the microbialite interval carbon isotopes exhibit a negative relationship with biodiversity implying that upwelling of anoxic deep ocean water if associated with the negative excursion of carbon isotope values did not inhibit the diversification of benthic organisms at least on shallow carbonate platforms in the period immediately after the end permian mass extinction

marine peloids a product of bacterially induced precipitation of calcite high magnesian calcite peloids are a common constituent of cemented marine carbonate accumulations they are abundant and well developed within both isolated microcavities and surface crusts the nuclei of marine peloids are composed of fossil bacterial clumps encased within anhedral submicron to micron sized high magnesian calcite crystals the marine peloids are similar to silt sized particles found in travertine deposits that also are composed of fossil bacterial clumps and their surrounding calcite coronas these similarities include size 20 60 mu m a cloudy brown nucleus and rims of clear euhedral crystals in addition previous studies have established the presence of fatty acids of bacterial origin within peloidal deposits and enriched stable isotopic signatures have been interpreted as recording organic fractionation concomitant with calcite precipitation these characteristics all indicate that the nuclei of many peloids originate as calcite precipitates within and around clumps of bacteria and that this precipitation was induced by the vital activity of bacterial colonies

erosional truncation of uppermost permian shallow marine carbonates and implications for permian triassic boundary events comment payne et al 2007 1 suggest that there is widespread evidence for a carbonate dissolution surface at the level of the end permian mass extinction and that this crisis was at least partly due to ocean acidification that preferentially affected heavily calcified marine invertebrates these ideas

pyrite framboid study of marine permian triassic boundary sections a complex anoxic event and its relationship to contemporaneous mass extinction size analysis of pyrite framboids has been undertaken on epicontinental permian triassic boundary sections throughout the world in order to evaluate the intensity and duration of anoxia mid paleolatitude sections from the margins of the boreal spitsbergen greenland and neotethyan oceans western australia reveal intense anoxia throughout the permian triassic boundary interval with euxinic conditions frequently developing and dysoxia encountered even in relatively shallow water settings above storm wave base at equatorial paleolatitudes weakly oxygenated dysoxic conditions are widely developed in a broad range of water depths including those shallow enough to produce oolite deposition although euxinia was rare western and eastern tethyan locations re veal a complex and unstable redox history anoxia in the hindeodus praeparvus zone was replaced by oxygenated facies in the permian triassic boundary interval h changxingensis to h parvus zones oxygen poor deposition returned during the succeeding isarcicella isarcica zone the more persistent and intense development of oxygen restriction in cooler water mid paleolatitude sections argues against warming and dissolved oxygen decline as the key cause of permian triassic bound ary anoxia in higher paleolatitudes the ben thic invertebrate extinctions occurred during a prolonged phase of oxygen poor deposition while in equatorial tethyan locations benthic losses occurred at the end of the fi rst anoxic phase in the late h praeparvus zone

occurrence and orientation of shatter cones in pretoria group quartzites in the collar of the vredefort dome impact origin precluded shatter cones have been found cutting completely indurated fault breccia associated with the down faulting of previously overturned pretoria group quartzites around the vredefort structure the evidence indicates that the shatter cones formed later than the overturning hence they cannot be considered to have been formed by an impact generated shock wave which penetrated the strata just before overturning

travertines depositional morphology and the bacterially constructed constituents abstract investigation of travertine accumulations throughout central italy and the west central u s has shown that the carbonate is precipitated in response to both inorganic and organic processes individual deposits range up to 85 m thick and hundreds of square kilometers in areal extent all of the carbonate is low magnesian calcite water chemistry temperature and morphology of the accumulation greatly influence the constituents comprising these deposits harsh environmental situations favor inorganic deposits while increasingly more moderate conditions result in the formation of a greater abundance of organically precipitated material morphological variations of travertine deposits recognized include 1 waterfall or cascade 2 lake fill 3 sloping mound fan or cone 4 terraced ound and 5 fissure ridge gross morphology internal stratification and constituents comprising these deposits vary systematically depending upon the type of accumulation and chemistry of the waters bacterially precipitated calcite forms a large percentage of the carbonate in many travertine accumulations exceeding 90 of the framework grains comprising some of the lake fill deposits bacteria are among the first taxa to inhabit and reproduce in harsh spring environments and produce a variety of fascinating constituents the bacteria are primarily rods generally 0 2 m in diameter and less than 1 0 m in length the rods readily decay resulting in calcite crystals loaded with micropores the basic building block of bacterially constructed travertine is a clump of bacteria averaging 20 m in diameter enclosed in a single crystal of calcite aggregates of these crystals produce a variety of deposits including 1 crudely laminated carbonate mud 2 finely laminat d layers of mud 3 intraclasts 4 foam rock and 5 shrubs the shrubs are most striking commonly forming layers 1 3 cm thick but also producing bacterial pisoids at some locales bacterial stromatolites composed of layers of shrubs alternating with finely laminated layers of bacterial mud comprise essentially the entire deposit the shrub layers are the result of flourishing summer growth of bacteria and furthermore show remarkable daily laminae 0 1 0 5 mm thick the importance of bacteria in the formation of travertine and their universally recognized abundance in modern sediments provides an impetus for a reexamination of the role of bacteria in the origin of other types of ancient deposits

stable carbon isotope stratigraphy across the permian triassic boundary in shallow marine carbonate platforms nanpanjiang basin south china a distinct negative 13c excursion is documented in two permian triassic sections heping and taiping in shallow marine carbonate platform deposits in the nanpanjiang basin south china these sections span from the changhsingian to the dienerian and are characterized by a distinct marine boundary facies change from massive skeletal lime packstone in the changhsingian to distinctive calcimicrobial framestone in the griesbachian hindeodus parvus zone the 13corg and 13ccarb excursions occur directly after the onset of the calcimicrobial framestone herein termed the permian triassic boundary event and before the first occurrence of h parvus the isotope shifts are associated with a sharp drop in species abundance and diversity and coincide with a decrease in total organic carbon toc content the shift towards depleted values in 13corg and 13ccarb at the permian triassic boundary event together with low toc contents persists throughout the griesbachian h parvus zone these data document a corresponding negative shift of 13corg and 13ccarb values and low toc contents with the onset of growth of calcified microbial framestones a postextinction disaster facies immediately below the base of the griesbachian h parvus zone based on paleontological evidence the first occurrence of the disaster facies follows the extinction event which implies that the 13c depleted values above this facies postdate the event this suggests that two separate events had to account for the initiation of the extinction and the 13c excursion however the consequences that led to the negative isotopic shift might be linked to the intriguing recovery lag of early triassic ecosystems based on data from ptb sections worldwide of a greater 13c offset in high compared with low latitudes we propose that methane eruptions from thermal destabilization of high latitude clathrate deposits may have led to the negative 13c shift and may have caused long term adverse ecological conditions

microbial proliferation coinciding with volcanism during the permian triassic transition new direct evidence from volcanic ashes south china abstract coupling with major biotic extinction both widespread microbially mediated deposits and ash beds characterize the permian triassic boundary ptb successions worldwide thus active volcanism through the ptb interval has been proposed to account for contemporary microbial bloom direct evidence however has long been scarce here we present several lines of evidence for microbial proliferation in the ptb ashes from south china petrographic analysis reveals annular granular and tubular bioalteration textures that formed during microbial dissolution of glass and subsequent precipitation annular textures appear as fresh glass shards connected with bands in different thicknesses showing rough and sharp interfaces and are bordered with fibrous textures granular textures are composed of clusters of near spherical bodies ranging in size from 0 05 to 2 m tubular textures occur as straight curved or spiral tunnels excavating into fresh glass their distinctive morphologies microbe analogous sizes and log normal size distributions all indicate a biogenic origin element mapping along alteration fronts shows enrichment of organic carbon and depletion in metabolically significant elements providing further support for their biogenicity besides textural relationships low n k and high c contents as well as pronounced microstructure density variations between different ash beds in same section all suggest that the bioalteration textures are syngenetic with volcanic glass relevant to microfossils rather than recent microbes we interpret the fossilized organic remains e g small coccoid like spheroids rods filaments and thin films as extracellular polymeric substances eps probably produced by microorganisms which might have served as templates for nucleation and played a crucial role in bio mineralization process the diversity of microstructure sizes shapes and organic remains may reflect a complex community of microbes in the ptb ashes we infer that microbial proliferation may contribute to negative c isotope excursions in the ptb ashes microbial blooms in ash beds directly triggered by large scale volcanism may reveal that extreme environmental stresses prevailed during the ptb crisis

characteristics of claystones across the terrestrial permian triassic boundary evidence from the chahe section western guizhou south china abstract x ray diffraction xrd scanning electronic microscopy sem and x ray fluorescence spectroscopy xfs studies were undertaken for claystones and or mudstones from the chahe section a terrestrial permian triassic boundary tptb section our results indicate that the compositions of claystones in the permian triassic boundary ptb interval beds 66f 68 outlined by biostratigraphy are different from claystones and or mudstones found either below or above the interval of the same section the clay minerals in the claystones of the ptb interval are mainly composed of illite montmorillonite interlayers with a few montmorillonites and chlorites the other claystones and or mudstones underlying and overlying the ptb consist of chlorites and or kaolinites some authigenic clastic minerals such as hexagonal dipyramid quartz and zircons are only found in claystones in the ptb interval from the chahe section and some marine ptb sections in western guizhou and eastern yunnan southwestern china in addition some elements are present in abnormal concentrations in the claystones of the ptb interval as well most important is that we found no spherules in all the claystones studied indicating no evidence of an extraterrestrial impact during the permian triassic transition the particular characteristics of the tptb claystones at the chahe section indicate their volcanic origin and thus provide a reliable auxiliary event marker for high resolution demarcation of the tptb in south china they are also indicative in the marine ptb claystones in south china thus the ptb claystones can be used as auxiliary markers for high resolution correlation of the ptb from marine facies to land in south china when direct fossil evidence in the ptb sequence is lacking

cyanobacterial blooms tied to volcanism during the 5 m y permo triassic biotic crisis widespread but episodic deposition of cyanobacterial mats occurred during the 5 m y permo triassic biotic crisis providing a critical record to decipher the long term stressful environmental conditions and thus a linkage with the killer here we document the timing and duration of these blooms indicated by lipid biomarkers and microbialites throughout south china and compare them to the timing of volcanic activity the initial cyanobacterial bloom has the longest duration and is associated with a prominent eu anomaly in southwestern china where the most intensive volcanism has been proposed to occur suggesting a causal relationship subsequent cyanobacterial blooms in the early triassic are associated with known volcanic events in south china and also with the most voluminous siberian flood basalts and with the largest negative carbon isotope excursions thus it appears that volcanic activity has had a significant impact on microbial development in south china south china volcanism around the permian triassic boundary ptb could have played a much larger role in biotic changes of both bacterial and calcified faunal ecosystems than previously thought the well known siberian volcanism is proposed herein on the basis of the current compilation of dating data to protract the early triassic faunal recovery rather than to cause the end permian extinction

cyanobacterially generated peloids in laminated organic matter rich limestones an unobtrusive presence the late kimmeridgian southern jura france is a carbonate platform where laminated limestones accumulated locally notably at orbagnoux the two types of laminations encountered result either from particle settling in a very quiet environment or from bacterial mat growth in the latter case as revealed by acid etching the dark coloured laminae result from filamentous cyanobacteria developments whereas the light coloured laminae appear surprisingly to comprise packed peloids these peloids are interpreted as originating from the in vivo or shortly post mortem calcification of sheaths of coccoid cyanobacteria in an environment loaded by temporary excess alkalinity and possible h2s emissions thus a simple etching treatment reveals the unsuspected albeit prominent role of cyanobacteria in the genesis of the limestones from orbagnoux as such facies are widespread in late jurassic records the role of cyanobacteria in their formation deserves re evaluation

the timing and pattern of biotic recovery following the end permian mass extinction the aftermath of the great end permian period mass extinction 252 myr ago shows how life can recover from the loss of 90 species globally the crisis was triggered by a number of physical environmental shocks global warming acid rain ocean acidification and ocean anoxia and some of these were repeated over the next 5 6 myr ammonoids and some other groups diversified rapidly within 1 3 myr but extinctions continued through the early triassic period triassic ecosystems were rebuilt stepwise from low to high trophic levels through the early to middle triassic and a stable complex ecosystem did not re emerge until the beginning of the middle triassic 8 9 myr after the crisis a positive aspect of the recovery was the emergence of entirely new groups such as marine reptiles and decapod crustaceans as well as new tetrapods on land including eventually dinosaurs the stepwise recovery of life in the triassic could have been delayed either by biotic drivers complex multispecies interactions or physical perturbations or a combination of both this is an example of the wider debate about the relative roles of intrinsic and extrinsic drivers of large scale evolution from a much more devastated planet and biota than the others with only some 10 of species surviving the epme was much harsher than the other mass extinctions during which global species diversity reduced to only about 50 of the pre extinction total 1 2 24 26 this means that the triassic recovery has two profound implications first it may show qualitative as well as quantitative differences from the other post extinction recoveries and second it can act as an exemplar of what to expect at its most extreme when global biodiversity is pushed to the brink there are obvious implications for current concerns about biodiversity loss and recovery resulting from human impacts 27 28 in the past ten years attention has focused on the sedimentary successions in south china these are enormously laterally extensive with some formations extending more than 2 000 km from the zhejiang to yunnan provinces the huge exposures length of the sections and improving dating open up the opportunity to explore physical environmental and biotic changes through the extinction and recovery times in varied marine habitats and compare these with patterns elsewhere in the world fig 1 a fine scale forensic analysis of this extraordinary time in earth s history now becomes possible the end permian mass extinction the epme killed 80 96 of marine animal species and 70 of terrestrial vertebrate species

analysis of seismic body waves excited by the mount st helens eruption of may 18 1980 seismic body waves which were excited by the may 18 1980 eruption of mount st helens and recorded by the global digital seismographic network stations are analyzed to determine the nature and the time sequence of the events associated with the eruption the polarity of teleseismic p waves period 20s is identical at six stations which are distributed over a wide azimuthal range this observation together with a very small s to p amplitude ratio at 20 s suggests that the source is a nearly vertical single force a simple model shows that for seismic radiation a volcanic eruption can be represented by a single force applied in the direction opposite to the blast direction the time history of the vertical force suggests two distinct groups of events about 2 min apart each consisting of several subevents with a duration of about 25 s the magnitude of the force is approximately 2 6 10 12 n this vertical force is in contrast with the long period 150 s southward horizontal single force which has been determined by a previous study and interpreted to be due to the massive landslide an m s 5 2 earthquake initiated the eruption sequence the direction of the p wave first motion of this event observed at two nearby stations is consistent with the radiation pattern expected for the landslide and suggests that it represents the onset of the landslide the ground motions observed at station lon 67 km are dominated by rayleigh waves i e lamb pulse and provide tight constraints on the time sequence of the events