microbe clay mineral interactions clays and clay minerals are common components in soils sediments and sedimentary rocks and they play an important role in many environmental processes iron is ubiquitous in clays and clay minerals and its oxidation state in part controls the physical and chemical properties of these fine grained minerals the structural ferric iron in clay minerals can be reduced either chemically or biologically biological reductants include mesophilic and thermophilic microorganisms from diverse environments such as soils sediments sedimentary rocks and hydrothermal hot springs multiple clay minerals have been used for microbial reduction studies including dioctahedral smectiteillite series palygorskite chlorite and their various mixtures in natural soils and sediments all of these clay minerals are reducible by microorganisms under various conditions with smectite nontronite being the most reducible and illite the least the rate and extent of bioreduction depends on many experimental factors such as the type of microorganisms and clay minerals solution chemistry and temperature despite significant efforts current understanding of the mechanisms of microbial reduction of ferric iron in clay minerals is still limited whereas some studies have presented evidence for a solid state reduction mechanism others argue that the clay mineral structure partially dissolves when the extent of reduction is high this inconsistency may be related to several experimental conditions and their specific effects are discussed in this paper whereas past experiments have been largely conducted in well controlled laboratory systems recent efforts have attempted to transfer knowledge to the field to improve our understanding of more complex soil systems for better agricultural practices biologically reduced clay minerals are also important agents in remediating inorganic and organic contaminants in soil and groundwater systems this paper reviews the most recent developments and suggests some directions for future research

calcimicrobial stromatolites at the permian triassic boundary in a western tethyan section bukk mountains hungary basal triassic carbonates of the gerennavar formation bukk mountains northern hungary were studied the succession was deposited in an open marine deep ramp environment of the western tethys and can be divided into three parts on the basis of the dominant microfacies the lowermost 0 5 m thick interval is made up by thin bedded and bioturbated mudstones which contain ostracods and earlandia along with relict skeletal fragments the successive 8 m thick deposits consist of planar stromatolites with well preserved microfabrics the most characteristic microfabric elements are sphere clusters in a dense micrite groundmass bushy aggregates of micrite clots bundles of prostrate micrite threads and peloids the formation of the spheres and the surrounding dense micrite is attributed to calcification of a coccoid cyanobacteria dominated mat community the tufted micrite clot clusters crudely resemble angusticellularia a filamentous microbial origin is likely for the thread bundles the peloids are interpreted either as reworked pieces of calcified mat or rolled microbial clumps the reduced preservation of microfabric components in the upper unit refers to less favourable condition for mat development which is probable due to deepening of the depositional environment the overlying mudstone unit is very poor in fossils the preservation of microbial microfabrics in the stromatolites indicates that early lithification by carbonate precipitation was widespread and intense even in open marine environments following the end permian boundary events this supports the assumption that significant changes took place in geochemistry of seawater during the late permian early triassic time interval d 2006 elsevier b v all rights reserved

microbial carbonates the geological record of the calcified bacterial algal mats and biofilms summary deposits produced by microbial growth and metabolism have been important components of carbonate sediments since the archaean geologically best known in seas and lakes microbial carbonates are also important at the present day in fluviatile spring cave and soil environments the principal organisms involved are bacteria particularly cyanobacteria small algae and fungi that participate in the growth of microbial biofilms and mats grain trapping is locally important but the key process is precipitation producing reefal accumulations of calcified microbes and enhancing mat accretion and preservation various metabolic processes such as photosynthetic uptake of co2 and or hco3 by cyanobacteria and ammonification denitrification and sulphate reduction by other bacteria can increase alkalinity and stimulate carbonate precipitation extracellular polymeric substances widely produced by microbes for attachment and protection are important in providing nucleation sites and facilitating sediment trapping microbial carbonate microfabrics are heterogeneous they commonly incorporate trapped particles and in situ algae and invertebrates and crystals form around bacterial cells but the main component is dense clotted or peloidal micrite resulting from calcification of bacterial cells sheaths and biofilm and from phytoplankton stimulated whiting nucleation interpretation of these texturally convergent and often inscrutable fabrics is a challenge conspicuous accumulations are large domes and columns with laminated stromatolite clotted thrombolite and other macrofabrics which may be either agglutinated or mainly composed of calcified or spar encrusted microbes stromatolite lamination appears to be primary but clotted thrombolite fabrics can be primary or secondary microbial precipitation also contributes to hot spring travertine cold spring mound calcrete cave crust and coated grain deposits as well as influencing carbonate cementation recrystallization and replacement microbial carbonate is biologically stimulated but also requires favourable saturation state in ambient water and thus relies uniquely on a combination of biotic and abiotic factors this overriding environmental control is seen at the present day by the localization of microbial carbonates in calcareous streams and springs and in shallow tropical seas and in the past by temporal variation in abundance of marine microbial carbonates patterns of cyanobacterial calcification and microbial dome formation through time appear to reflect fluctuations in seawater chemistry stromatolites appeared at 3450 ma and were generally diverse and abundant from 2800 to 1000 ma inception of a proterozoic decline variously identified at 2000 1000 and 675 ma has been attributed to eukaryote competition and or reduced lithification thrombolites and dendrolites mainly formed by calcified cyanobacteria became important early in the palaeozoic and reappeared in the late devonian microbial carbonates retained importance through much of the mesozoic became scarcer in marine environments in the cenozoic but locally re emerged as large agglutinated domes possibly reflecting increased algal involvement and thick micritic reef crusts in the late neogene famous modern examples at shark bay and lee stocking island are composite coarse agglutinated domes and columns with complex bacterial algal mats occurring in environments that are both stressed and current swept products of mat evolution ecological refugia sites of enhanced early lithification or all three

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

ether lipids from the lower and middle triassic at qingyan guizhou province southern china abstract ether lipids such as non isoprenoid mono and dialkyl glycerol ethers mages and dages and archaeol have been found in carbonate rocks and mud rocks deposited during the early and middle triassic 250 240 ma the oldest previous discovery of ether lipids is from cretaceous black shale deposited during the albian 112 ma paleoenvironmental reconstruction using ether lipids has therefore not been conducted on pre cretaceous sediments archaeol derives from archaea e g methanogenic methanotrophic halophilic and thermophilic archaea the non isoprenoid dages and mages likely derive from sulfate reducing bacteria srb which are restricted to anaerobic environments the presence of ether lipids thus indicates that anoxic conditions expanded in the depositional and or water column environment in the qingyan area during the early middle triassic these ether lipids may be useful for the reconstruction of paleoredox conditions and paleoecosystems in the area furthermore their occurrence suggests that paleoenvironmental reconstruction using ether lipids may be possible throughout the mesozoic and cenozoic

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

calcium carbonate seafloor precipitates from the outer shelf to slope facies of the lower triassic smithian spathian union wash formation california usa sedimentology and palaeobiologic significance abstract formerly aragonite seafloor fans from the lower triassic smithian spathian union wash formation of east central california were examined to determine the processes active during their growth the seafloor fans were deposited in an outer shelf to slope environment along the western margin of pangaea and are contained within two stratigraphic intervals the lower precipitate bearing interval is 130 m thick comprised of micritic limestone and contains precipitates that fall into 2 end member morphologies 1 laminated precipitate masses that contain distinct hemispheres or fans and 2 precipitate masses that are composed of a complex interlocking mosaic of hemispheres or fans precipitates found in the bedded lower half of the interval are typically 2 3 cm tall and 10 20 cm wide and are commonly undercut disturbed and in the case of the interlocking mosaics of hemispheres show evidence of entrainment and transport by density currents precipitates are larger in the upper massive portion of the lower precipitate bearing interval and occur only as interlocking hemisphere fan mosaics fans and hemispheres attain heights as tall as 30 cm and precipitate bodies made of interlocking mosaics of hemispheres and fans attain thicknesses of up to 50 cm and widths of 1 2 m chaotic bedding broken precipitates and brecciation of precipitate bodies imply an unstable and mobile substrate the upper precipitate bearing interval is 30 m thick comprised of bivalve ammonoid and microgastropod bearing wackestone and is separated from lower precipitate bearing strata by 23 m of interbedded shale and calcareous siltstone much of the upper precipitate bearing unit was deposited by subaqueous debris flows as suggested by multiple breccias contained within the interval seafloor cements are found in undisturbed units and rarely within breccia clasts suggesting that precipitates formed locally as well as higher on the shelf precipitate growth was likely the result of an increase in the saturation state of calcium carbonate in early triassic oceans related to widespread oceanic anoxia the presence of unusual carbonates during the period and their correlation with depauperate faunas in the equivalent shallow facies of the virgin limestone suggest that the remarkable oceanographic conditions associated with precipitate growth likely dampened the biotic recovery in the region until those conditions disappeared in the middle triassic

extreme euxinia just prior to the middle triassic biotic recovery from the latest permian mass extinction abstract the greatest mass extinction on earth occurred 252 million years ago during the latest permian complete biotic recovery characterized by a return to pre extinction diversity levels took an extraordinarily long time ca 5 10 6 yr probably because harsh conditions developed repeatedly during the early triassic here we show the recurrence of euxinic conditions during the early triassic and the development of especially severe such conditions during the late early triassic just prior to full biotic recovery from the mass extinction dibenzothiophenes and carotenoids accumulated in upper lower triassic sediments from south china located on the western margin of the paleotethys ocean among these chlorobactane a biomarker for green pigmented green sulfur bacteria and okenane a biomarker for purple sulfur photosynthetic bacteria were identified in upper early triassic samples both compounds were detected in limestone micrite and we therefore infer that planktonic green and purple sulfur bacteria were the sources of these carotenoids and that their presence indicates photic zone euxinia at the time of deposition concentrations of redox sensitive elements m v and u relative to that of al and the u th ratio progressively increased during the late early triassic the euxinic conditions represented by the carotenoids and the elements were likely caused by a combination of locally shallow restricted conditions and global environmental oscillations such as those related to global warming during the late early triassic the presence of these biomarkers together with the increase in the abundance of redox sensitive elements relative to al and the u th suggests that euxinic conditions could be one of the causes for the delayed recovery of marine communities in the paleotethys ocean after the latest permian mass extinction event

predominance of archaea derived hydrocarbons in an early triassic microbialite abstract we investigated the distribution of lipids in lower triassic sedimentary rocks 252 247 myr from south china including a shallow water microbialite in the uppermost section of the outcrop archaeal derived hydrocarbons were the major constituents of the microbialite from the latest early triassic among these we detected i abundant c 40 acyclic and monocyclic biphytanes possibly derived from glycerol dialkyl glycerol tetraether lipids and their degradation products c 30 39 pseudohomologues and ii a c 25 head to tail linked regular isoprenoid hydrocarbon possibly derived from dialkyl glycerol diether lipids dgds and its degradation products c 21 24 pseudohomologues and abundant pristane and phytane through combination of compound specific stable carbon isotope analysis of isoprenoid hydrocarbons which had average 13 c values of 35 to 30 and their molecular distribution it was not possible to unambiguously define the archaeal source for the biphytanes in the microbialite the 13 c values for pristane and phytane were similar to those for head to tail linked c 21 25 isoprenoids potential source organisms for these compounds were halophilic archaea except for methane seep microbialites no other ancient or recent phototrophic microbialites have been reported to contain predominantly archaeal isoprenoid hydrocarbons our findings suggest the presence of a new type of microbialite

earliest triassic microbialites in curuk dag southern turkey composition sequences and controls on formation the permian triassic boundary sequence at curuk dag near antalya turkey begins with a major erosion surface interpreted as being the late permian lowstand on which lies ca 0 4 m of grainstone packstone composed of ooids peloids and bioclasts most ooids are superficial coats on fragments of calcite crystals presumed to be eroded from crystal fans which are no longer present the erosion surface is smooth and shows no evidence of dissolution the grainstone packstone contains intraclasts of the underlying wackestone proving erosion next are 15 m of microbialite comprised of interbedded stromatolites thrombolites plus beds of planar limestones with small scale erosion the latter comprise a complex interlayering of stromatolitic thrombolitic and peloidal fabrics and precipitated crystal fans which form a hybrid of microbialite and inorganic carbonate together with bioclastic debris and micrite the curuk dag microbialite sequence is repetitious the lower part is more complex with abundant stromatolites and hybrid microbialites some of the stromatolites are themselves hybrids composed of peloids and crystal fans in the upper part of the sequence stromatolites are missing and the rock is composed mostly of recrystallized thrombolites that develop upwards from tabular to domal form the domes form directly below small breaks in microbialite growth where very thin shelly micrites and grainstones packstones are deposited repetition of facies may be controlled by sea level change a deepening up model is consistent with the evidence stromatolites with abundant crystal fans dominate in shallower water deepening through hybrid microbialite and interlayered sediments to thrombolite probably no more than a few tens of metres deep followed by breaks and renewal of microbialite growth an interpretation of open marine fully oxygenated waters for microbialite growth is consistent with ongoing parallel work that has identified bairdioid ostracods in the microbialite a group known to be open marine however other researchers have proposed low oxygen conditions for permian triassic boundary facies globally so work continues to confirm whether the curuk dag microbialite grew in dysoxic or normally oxygenated conditions the principal stimulus for post extinction microbialites is likely to be carbonate supersaturation of the oceans the microbialite sequence is overlain by a further 25 m of grainstone packstone without microbialite followed by early triassic shales overall microbialites form a thin aggradational sequence during an overall relative sea level rise consistent with global eustatic rise following the late permian lowstand

transient metazoan reefs in the aftermath of the end permian mass extinction microbes were thought to be the dominant reef constructors following the end permian mass extinction sponge microbe reef deposits formed in the early triassic from the western united states suggest that instead metazoan reef building continued immediately following the extinction wherever marine conditions allowed

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

smithian shoreline migrations and depositional settings in timpoweap canyon early triassic utah usa in timpoweap canyon near hurricane utah usa spectacular outcrop conditions of early triassic rocks document the geometric relationships between a massive smithian fenestral microbial unit and underlying lateral and overlying sedimentary units this allows us to reconstruct the evolution of depositional environments and high frequency relative sea level fluctuations in the studied area depositional environments evolved from a coastal plain with continental deposits to peritidal settings with fenestral microbial limestones which are overlain by intertidal to shallow subtidal marine bioclastic limestones this transgressive trend of a large scale depositional sequencemarks a long term sea level rise that is identified worldwide after the permian triassic boundary the fenestral microbial sediments were deposited at the transition between continental settings with terrigenous deposits and shallow subtidal marine environments with bioturbated and bioclastic limestones such a lateral zonation questions the interpretation of microbial deposits as anachronistic and disaster facies in the western usa basin the depositional setting may have triggered the distribution of microbial deposits and contemporaneous marine biota the fenestral microbial unit is truncated by an erosional surface reflecting a drop in relative sea level at the scale of a medium depositional sequence the local inherited topography allowed the recording of small scale sequences characterized by clinoforms and short distance lateral facies changes stratal stacking pattern and surface geometries allow the reconstruction of relative sea level fluctuations and tracking of shoreline migrations the stacking pattern of these small scale sequences and the amplitude of corresponding high frequency sea level fluctuations are consistent with climatic control large andmedium scale sequences suggest a regional tectonic control

stromatolites of the lower triassic union wash formation ca evidence for continued post extinction environmental stress in western north america through the spathian abstract recent studies have documented the complexity of biotic recovery from the permian triassic mass extinction by revealing that recovery began quickly in some regions while the biota in other areas continued to suffer as the result of widespread harsh environmental conditions throughout much of the early triassic period examination of lower triassic rocks from the southwestern u s has produced a variety of sedimentologic and biotic evidence that point to persistent environmental stress following the extinction specifically anoxic alkaline waters in the deep ocean and possible high carbon dioxide levels in the surface ocean and have also documented trends in the long suffering biota present in that region the shoaling facies of the upper member of the union wash formation at the cerro gordo ca usa locality contain stratiform stromatolites that suggest harsh environmental conditions in the area may have lingered until the late spathian latest early triassic the stromatolites are laterally extensive some layers persist for at least 1 km and typically exhibit planar to wavy laminations with some development of small domes up to 10 cm in height a shallow subtidal depositional environment is suggested by evidence of eroded or planed surfaces within the stromatolites as well as channelization of the stromatolites and the occurrence of ooids and coated grains within the interval the stromatolites documented here occur stratigraphically higher than previously documented inorganic calcium carbonate precipitates from the union wash formation e g woods a d bottjer d j corsetti f a 2007 calcium carbonate seafloor precipitates from the outer shelf to slope facies of the lower triassic smithian spathian union wash formation california u s a sedimentology and palaeobiologic significance palaeogeography palaeoclimatology palaeoecology 252 281 290 woods a d bottjer d j mutti m morrison j 1999 lower triassic large seafloor carbonate cements their origin and a mechanism for the prolonged biotic recovery from the end permian mass extinction geology 27 645 648 and microbialites from the virgin limestone e g schubert j k bottjer d j 1992 early triassic stromatolites as post mass extinction disaster forms geology 20 883 886 pruss s b bottjer d j 2004 late early triassic microbial reefs of the western united states a description and model for their deposition in the aftermath of the end permian mass extinction palaeogeography palaeoclimatology palaeoecology 211 127 137 therefore these stromatolites may represent the last known occurrence of anachronistic facies and associated unusual palaeoceanographic conditions in eastern panthalassa following the permian triassic mass extinction

origins of microbial microstructures in the neoproterozoic beck spring dolomite variations in microbial community and timing of lithification abstract microbialite microstructures form at the scale of microbial processes and can preserve evidence of growth degradation and lithification in microbial communities understanding how these processes are preserved in microstructures will provide insights into microbial ecosystems and how microbial communities have evolved through time microbialites in the neoproterozoic beck spring dolomite southern california u s a contain microstructures that record variations in the morphology of microbial communities as well as the timing of degradation versus lithification in the communities these processes are represented by five end member microbial microstructures 1 distinct laminated microstructure 2 diffuse laminated microstructure 3 distinct clotted microstructure 4 diffuse and regular clotted microstructure and 5 diffuse and irregular clotted microstructure these microstructures are distinguished by fabrics defined by organic inclusions in distinct microstructures organic inclusions sharply define microbial features such as laminae that are laterally continuous for millimeters or 50 200 micron diameter microdots the contacts between distinct microstructures are always sharp in diffuse microstructures zones of organic inclusions lack distinct boundaries neighboring laminae and clots grade into each other within tens of microns and boundaries between microbial structures and encasing cements are indistinct diffuse microstructures grade into each other and into distinct microstructures in a systematic way that suggests that differences are due to variations in the timing of mineralization relative to growth and degradation of microbial communities sharply defined textures in distinct microstructures suggest that lithification started during growth of the microbial community and the close spatial association but lack of intergrading between distinct laminated and distinct clotted microstructures suggests that they formed from two distinct microbial communities that lived in the same environment by contrast diffuse microstructures formed where lithification occurred after the onset of decay and degradation of the primary growth structure the continuum from distinct microbial textures through more diffuse and irregular textures documents variations in the timing of lithification relative to growth and decay of the microbial community thus where petrographic preservation is extremely good such as in the beck spring dolomite sub millimeter scale microbial microstructures record a gradation between growth and degraded microbial structures depending on the relative timing of lithification and heterotrophic decay

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

estimation of the equivalent rayleigh friction in mesosphere lower thermosphere region from the migrating diurnal tides observed by timed 1 we use thermosphere ionosphere mesosphere energetics and dynamics timed global temperature and wind data from 2002 to 2007 to investigate the damping of the diurnal tide horizontal winds are measured by tidi and are calculated from saber temperature measurements the determination of tidal winds from saber temperature depends on the damping and therefore the discrepancy between tidi and saber determinations of the wind tides can be used to calculate the tidal damping this damping is approximated here by an equivalent rayleigh friction erf and it is adjusted to minimize the difference in winds derived from saber and tidi data the results show that during some periods the erf coefficient can be very large over narrow vertical regions of about 5 km 10 5 s 1 in low latitudes and about 10 4 s 1 in midlatitudes the magnitude and shape of the vertical profiles change with latitude and season the peak in the vertical profile of erf is larger and located at a higher altitude in summer than in winter and the erf coefficients at 40 are stronger than at 20 in both hemispheres the erf deduced in this study without a priori assumption about the mechanism of the damping shows a seasonal variation that is clearly consistent with the seasonal variation of the zonal mean wind the maximum erf generally coincides with the altitudes of strongest wind reversal in the mesopause region

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

geochemical evidence from bio apatite for multiple oceanic anoxic events during permian triassic transition and the link with end permian extinction and recovery abstract a detailed 20 myr redox history of permian to triassic oceans changhsingian to carnian stages has been constructed using ce anomaly ce and th u ratios from conodont albid crown apatite material the results show that the well established phenomenon of intense ocean anoxia coincident with the end permian mass extinction is faithfully recorded in conodont ce and th u data extending this conodont redox record shows that end permian anoxia persisted possibly into the earliest dienerian stage and that two intense oceanic anoxic events also occurred later in the early triassic earliest smithian earliest spathian and middle spathian followed by a weaker manifestation of anoxia in the anisian stage seen in ce data marine benthic radiation following the end permian mass extinction began after the smithian earliest spathian anoxic event suggesting a suppression of evolution prior to this due to these inimical conditions the failure of the middle spathian anoxic event to retard the evolutionary rebound implies shallow shelf seas remained well ventilated at this time even if the oceans did not other attributes of the early triassic record also closely coincide with redox fluctuations phases of anoxia intensification saw the proliferation of microbial carbonates and major negative carbon isotope swings that can be attributed to chemocline shallowing causing alkalinity pulses and enrichment in light remineralised carbon and or indicate a trigger meachnaims related to increased fluxes of light c from siberian volcanic sources

lower triassic conodont sequence in chaohu anhui province china and its global correlation abstract the early triassic paleogeographical setting of the chaohu section in china was in a deep part of the yangtze platform and this has resulted in a rather complete lower triassic sequence with rich ammonoid and conodont successions three lower triassic sections west pingdingshan north pingdingshan and south majiashan have been sampled in detail for a systematic conodont study eight conodont zones are recognized in ascending order these are the zones of hindeodus typicalis neogondolella krystyni neospathodus kummeli neospathodus dieneri neospathodus waageni neospathodus pingdingshanensis neospathodus homeri and neospathodus anhuinensis these are correlated with the sequences in north america and other areas of the world the succession provides a good basis for the definition of the global stratotype of the induan olenekian boundary gssp which has been proposed at the base of the neospathodus waageni zone in west pingdingshan seven new species are introduced neospathodus chaohuensis n chii n concavus n eotriangularis n pingdingshanensis n posterolongatus n tongi a new subspecies n waageni eowaageni and three morphotypes of n dieneri

proliferation of early triassic wrinkle structures implications for environmental stress following the end permian mass extinction lower triassic strata in the western united states and northern italy have yielded the first reported occurrence of microbially mediated wrinkle structures in shallow subtidal siliciclastic paleoenvironments since the cambrian we hypothesize that wrinkle structures formed under reduced infaunalization conditions during the aftermath of the end permian mass extinction these wrinkle structures occur in siliciclastic sedimentary rocks in association with hummocky cross stratification and in some cases trace fossils such as asteriacites rhizocorallium planolites and gyrochorte that indicate a subtidal paleoenvironment wrinkle structures were found in the campil member in the werfen formation of northern italy and in the virgin limestone member of the moenkopi formation and the upper member of the thaynes formation exposed in the western united states the presence of wrinkle structures is likely related to a unique taphonomic window that allowed for the preservation of these delicate features on storm dominated siliciclastic shelves wrinkle structures commonly formed in a variety of subtidal paleoenvironments during the proterozoic cambrian but thereafter became restricted to intertidal supratidal and deep sea environments this restriction has been attributed to the increase in infaunalization of metazoans following the cambrian radiation the proliferation of wrinkle structures in subtidal settings during the early triassic suggests that infaunal bioturbation was reduced after the end permian mass extinction and that this reduction lasted for millions of years

high resolution local earthquake tomography of the southern dead sea area summary local earthquake data from a dense temporary seismological network in the southern dead sea area have been analysed within the project desire dead sea integrated research project local earthquakes are used for the first precise image of the distribution of the p wave velocity and the vp vs ratios 65 stations registered 655 local events within 18 months of observation time a subset of 530 well locatable events with 26 730 p and s arrival times was used to calculate a tomographic model for the vp and vp vs distribution since the study area is at first order 2 d a gradual approach was chosen which compromised a 2 d inversion followed by a 3 d inversion the sedimentary basin fill is clearly imaged through high vp vs ratios and low vp the basin fill shows an asymmetric structure with average depth of 7 km at the western boundary and depth between 10 and 14 km at the eastern boundary this asymmetry is reflected by the vertical strike slip eastern border fault and the normal faulting at the western boundary caused by the transtensional deformation within the last 5 myr within the basin fill the lisan salt diapir is imaged through low vp vs ratios reflecting its low fluid content the extensions were determined to 12 km in e w and 17 km in n s direction while its depth is 5 6 km the thickness of the pre basin sediments below the basin fill cannot be derived from the tomography data it is estimated to less than 3 km from former investigations below the basin down to 18 km depth very low p wave velocities and low vp vs ratios are observed most likely caused by fluids from the surrounding crust or the upper mantle

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

microbial dissolution of clay minerals as a source of iron and silica in marine sediments interactions between microbes and minerals have the potential to contribute significantly to the global cycles of various elements and serve as a link between the geosphere and life in particular the microbially mediated cycle of iron within marine sediments is closely tied to the carbon cycle the dissolved iron that serves as a nutrient is thought to be primarily drawn from well known pools of highly reactive bioavailable iron and iron complexes iron contained within the crystal lattice of clay minerals the most abundant materials found at the earth s surface is not thought to be part of this pool here we analyse the mineral composition of middle cambrian aged mudstones from the western united states we find intergrown mineral aggregates of quartz pyrite and calcite on the basis of mineral phase relationships and temperatures of crystallization derived from stable isotopes of oxygen we infer that mineral dissolution driven by microbes released iron and silica to the surrounding sediment pore waters and led to the subsequent precipitation of the observed minerals the microbial extraction of structurally coordinated fe3 from clay minerals after their deposition in marine sediments may liberate a fraction of iron previously considered unavailable and may be important in iron and silica cycling in marine sediments interactions between microbes and minerals are evident in modern global elemental cycles relationships between minerals in cambrian mudstones indicate that such interactions may have released otherwise unavailable mineral bound iron and silica into the ancient oceans

early triassic stromatolites as post mass extinction disaster forms aftermaths of mass extinctions have been thought to be characterized by relaxation of ecological constraints accompanied by increased prominence of opportunistic generalists such taxa termed disaster forms have been shown to increase dramatically in range and abundance after several mass extinction events the cambrian ordovician stromatolite decline in normal marine level bottom environments has been explained as a direct or indirect consequence of increases in ecological constraints such as greater levels of predation and or bioturbation of microbial communities caused by early paleozoic benthic invertebrate evolution and diversification thus one would predict that in post ordovician strata stromatolites might appear in normal marine level bottom environments as disaster forms in the aftermaths of mass extinction particularly devastating to the benthic biota such as during early triassic time mounded stromatolites are present in two beds up to 1 5 m thick of the lower triassic spathian virgin limestone member moenkopi formation in the southwestern spring mountains of nevada stromatolites from level bottom normal marine subtidal environments have also been described from other lower triassic strata in north america europe and asia these stromatolites unusual in level bottom normal marine settings may have developed locally during the long aftermath 4 5 m y of the permian triassic mass extinction because of partial relaxation of the ecological constraintsmore that typically restricted them from unstressed subtidal normal marine level bottom environments less

anachronistic facies from a drowned lower triassic carbonate platform lower member of the alwa formation ba id exotic oman mountains abstract the lower member of the alwa formation lower olenekian found within the ba id exotic in the oman mountains sultanate of oman consists of ammonoid bearing pelagic limestones that were deposited on an isolated drowned carbonate platform on the neotethyan gondwana margin the strata contain a variety of unusual carbonate textures and features including thrombolites frutexites bearing microbialites that contain synsedimentary cements matrix free breccias surrounded by isopachous calcite cement and fissures and cavities filled with large botryoidal cements thrombolites are found throughout the study interval and occur as 0 5 1 0 m thick lenses or beds that contain laterally laterally linked stromatactis cavities the frutexites bearing microbialites occur less frequently and also form lenses or beds up to 30 cm thick the microbialites may be laminated and often developed on hardgrounds in addition the frutexites bearing microbialites also contain synsedimentary calcite cement crusts and botryoids typically frutexites bearing microbialites low level of calcium carbonate supersaturation associated with anoxic conditions and deposition below a stable chemocline formed the results of this study point to continued environmental stress in the region during the early triassic that likely contributed to the uneven recovery from the permian triassic mass extinction

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

terrestrial marine teleconnections in the collapse and rebuilding of early triassic marine ecosystems abstract the latest permian mass extinction lpe just prior to the permian triassic boundary at 252 ma resulted in the disappearance of 90 of skeletonized marine taxa and the replacement of the paleozoic fauna by the modern fauna in the immediate aftermath of the extinction shallow marine ecosystems were dominated by microbial communities and diminutive disaster taxa lilliput faunas and the post crisis period in general was characterized by high abundance low diversity marine communities occupying a reduced ecological space the recovery of marine ecosystems was a protracted process lasting throughout the 5 myr long early triassic some clades failed to recover and subsequently went extinct dead clades walking while others recovered only to suffer secondary crises during the early triassic profound environmental changes accompanied these biotic developments deep oceans experienced sustained hypoxia or anoxia for at least several million years following the boundary event anoxia was also widespread in shallow marine areas especially at the time of the lpe but it was more episodic and abated more rapidly than in the deep ocean making it an unlikely factor in the delayed recovery of early triassic marine ecosystems the development of anoxia was due at least in part to a sharp temperature rise following the lpe but may have been stimulated by changes in marine nutrient inventories and productivity rates as well these conditions may have been the result of a concurrent increase in subaerial weathering rates that was sustained into the early triassic in addition to increasing nutrient fluxes to marine areas rapid weathering caused a massive influx of sediment to shallow marine systems subjecting marine biotas to siltation stress this scenario implies close teleconnections between terrestrial and marine environments during the permian triassic boundary crisis with perturbations of the terrestrial realm contributing to the marine crisis

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

microbial carbonate abundance compared with fluctuations in metazoan diversity over geological time abstract secular variation in microbial carbonate abundance may be reflected by stromatolite morphotype diversity and reefal microbial carbonate abundance these datasets reveal long term changes over the past 3000 myr that include a peak of abundance 1250 myr ago late proterozoic decline cambrian resurgence and fluctuating decline during the remainder of the phanerozoic it is conceivable that proterozoic metazoan diversification coincided with inception of stromatolite decline 1250 myr ago but microbial carbonate increase during cambrian metazoan radiation together with failure of microbial carbonates to increase in the aftermaths of the end ordovician end triassic and end cretaceous mass extinctions suggest that factors in addition to metazoan competition significantly influenced long term changes in microbial carbonate abundance

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

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

the lower triassic of south china abstract the permian triassic boundary of south china has been well known and well studied for decades but what is relatively less noticed is that there are also many excellent marine lower triassic sequences in the region covering various paleogeographic lithofacies this paper presents an outline of the various lower triassic stratigraphic sequences in south china and provides a reference to the application of the lower triassic subdivision and stages the early triassic marine basin of south china is subdivided into five sedimentary provinces cathaysia lower yangtze upper yangtze youjiang and lijiang provinces each province has an interrelated distribution of lithofacies and stratigraphy the lower triassic biostratigraphic sequences of bivalves ammonoids and conodonts are summarized in the various sedimentary facies and provinces of south china the chinese twofold subdivision of the lower triassic is primarily demonstrated as well in this paper

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

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

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

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

a global marine sedimentary response to the end permian mass extinction examples from southern turkey and the western united states the end permian mass extinction greatly diminished marine diversity and brought about a whole scale restructuring of marine ecosystems these ecosystem changes also profoundly affected the sedimentary record data presented here attained through facies analyses of strata deposited during the immediate aftermath of the end permian mass extinction southern turkey and at the close of the early triassic southwestern united states in combination with a literature review show that sedimentary systems were profoundly affected by 1 a reduction in biotic diversity and abundance and 2 long term environmental fluctuations that resulted from the end permian crisis lower triassic strata display widespread microbialite and carbonate seafloor fan development and contain indicators of suppressed infaunal bioturbation such as flat pebble conglomerates and wrinkle structures facies considered unusual in post cambrian subtidal deposits our observations suggest that depositional systems too respond to biotic crises and that certain facies may act as barometers of ecologic and environmental change independent of fossil assemblage analyses close investigation of facies changes during other critical times in earth history may serve as an important tool in interpreting the ecology of metazoans and their environment

the paleoenvironmental distribution of phanerozoic wrinkle structures abstract wrinkle structures are microbially induced sedimentary structures that are known to have formed in ancient marine siliciclastic environments this study reviews the sedimentary context and paleoenvironmental distribution of these sedimentary structures throughout three distinct intervals of the phanerozoic the cambrian the post cambrian paleozoic and the lower triassic during these times wrinkle structures are found primarily within two sedimentary environments storm dominated subtidal environments and the intertidal zone subtidal occurrences of wrinkle structures during the post ordovician phanerozoic only appear to occur during intervals of environmental stress while earlier examples from the cambrian and lowermost ordovician likely formed prior to significant increases in extent and depth of bioturbation that hallmark most of the phanerozoic intertidal examples occur regardless of severe environmental stress and may have formed under low levels of bioturbation due to inherent vagaries of a marginal marine setting these environmental preferences appear to be conservative throughout the phanerozoic and may very well extend throughout earth s history

geobiology of microbial carbonates metazoan and seawater saturation state influences on secular trends during the phanerozoic abstract microbial carbonates are long ranging essentially bacterial aquatic sediments their calcification is dependent on ambient water chemistry and their growth is influenced by competition with other organisms such as metazoans in this paper these relationships are examined by comparing the geological record of microbial carbonates with metazoan history and secular variations in caco3 saturation state of seawater marine abundance data show that microbial carbonates episodically declined during the phanerozoic eon past 545 myr from a peak 500 myr ago this abundance trend is generally inverse to that of marine metazoan taxonomic diversity supporting the view that metazoan competition has progressively limited the formation of microbial carbonates lack of empirical values concerning variables such as seawater ionic composition atmospheric partial pressure of co2 and ph currently restricts calculation of caco3 saturation state for the phanerozoic as a whole to the use of modeled values these data together with palaeotemperature data from oxygen isotope analyses allow calculation of seawater caco3 saturation trends microbial carbonate abundance shows broad positive correspondence with calculated seawater saturation state for caco3 minerals during the interval 150 545 myr ago consistent with the likelihood that seawater chemistry has influenced the calcification and therefore accretion and preservation of microbial carbonates these comparisons suggest that both metazoan influence and seawater saturation state have combined to determine the broad pattern of marine microbial carbonate abundance throughout much of the phanerozoic in contrast for the major part of the precambrian it would seem reasonable to expect that seawater saturation state together with microbial evolution was the principal factor determining microbial carbonate development interrelationships such as these with feedbacks influencing organisms sediments and the environment are central to geobiology

assessing early triassic paleoceanographic conditions via unusual sedimentary fabrics and features article i nfo analysis of the lower triassic sedimentary rock record has revealed a variety of unusual sedimentary fabrics and features many of which were more common in the proterozoic than the phanerozoic these so called anachro nistic facies developed across lower triassic carbonate platforms from shallow subtidal environments to deep basinal environments and include features associated with the enhanced precipitation of calcium carbonate e g synsedimentary seafloor cements microbialites and fabrics that formed due to a reduction in the intensity and depth of bioturbation e g vermicular limestones three interacting factors controlled the development of anachronistic facies during the early triassic including 1 environmental conditions i e the unusual chemistry of early triassic oceans 2 biotic factors e g bioturbation and grazing pressures and 3 actualistic sedimen tologic processes e g waves and currents sedimentation because these three factors typically acted in concert with each other it is important to consider the role of each when using anachronistic facies to reconstruct early triassic paleoceanographic conditions overall anachronistic facies are indicative of enhanced calcium carbonate precipitation during the early triassic but do not necessarily indicate the former presence of anoxic or suboxic conditions where they were deposited the influence of seawater chemistry on the deposition of anachronistic facies was most pronounced in deeper water environments where anomalous paleoceanographic conditions heightened calcium carbonate precipitation and caused a decrease in bioturbation and grazing pressures via the upwelling of anoxic alkaline waters the degree of environmental influence lessened shorewards where biotic factors and actualistic processes were more important and slight modification of seawater by microbial activity shallow burial or co2 degassing was necessary for calcium carbonate precipitation to occur anachronistic facies are a useful tool for reconstructing paleoceanographic conditions and examining shifts in the distribution of environmental stress during the recovery from the permian triassic mass extinction but only when the biologic sedimentologic and geochemical factors that led to their growth are carefully considered