resolution of the earliest metazoan record differential taphonomy of ediacaran and paleozoic fossil molds and casts abstract much of our knowledge of early metazoan evolution is derived from unmineralized death mask or endorelief mold and cast fossils in ediacaran clastic sedimentary rocks this record is often regarded as a unique ediacaran taphonomic window however the prevalence of soft bodied molds and casts in paleozoic clastic rocks has been increasing begging an extension or modification to our understanding of this preservational motif chief amongst such fossils are eldonids a non biomineralized group of stem deuterostomes because eldonids are also preserved as compressed or flattened fossils from deposits like the burgess shale chengjiang and kaili they offer a comparative case study for evaluating the taphonomic fidelity of mold cast style preservation during this interval eds and raman microspectroscopic analysis of ordovician and devonian eldonid molds and casts and comparison with burgess shale eldonids suggests the mold cast taphonomic style produces significantly lower fidelity of fossil preservation we propose that eldonid mold cast fossils are preserved by the adsorption of reduced iron ions onto tissues composed primarily of high molecular weight hmw biopolymers which require enzymatic degradation prior to decay nucleation and growth of aluminosilicates and or sulfides around these adsorbed ions forms a fossilizable surface veneer preserving a death mask mold more labile tissues could not be fossilized in this mold and cast style ediacaran mold and cast fossils from south australia the white sea region of russia namibia and newfoundland exhibit preservational characteristics consistent with this new proposed model analysis of their preservational mode suggests that the first metazoans which would have lacked hmw biopolymeric tissues could not have been fossilized in this particular style thus understanding the origin and earliest evolution of the metazoa requires a focus on alternative modes of fossilization

modular construction of early ediacaran complex life forms newly discovered exceptionally preserved soft bodied fossils near spaniard9s bay in eastern newfoundland exhibit features not previously described from ediacaran terminal neoproterozoic fossils all of the spaniard9s bay taxa were composed of similar architectural elements centimeter scale frondlets exhibiting three orders of fracticality in branching frondlets were combined as modules atop semi rigid organic skeletons to form a wide array of larger constructions including frondose and plumose structures this architecture and construction define the rangeomorphs a biological clade that dominated the mistaken point assemblage 575 to 560 million years ago but does not appear to be ancestral to any phanerozoic or modern organisms

stratigraphy palaeontology and geochemistry of the late neoproterozoic aar member southwest namibia reflecting environmental controls on ediacara fossil preservation during the terminal proterozoic in african gondwana abstract common ediacaran fossils are well preserved in a late neoproterozoic ca 545 ma shallow marine sequence described here as the aar member of the dabis formation kuibis subgroup nama group near aus in southwest namibia this 31 38 m thick shale dominant unit records the transition from fluvial shallow marine kliphoek sandstone to open marine limestone of the mooifontein member of the zaris formation deposited on a subsiding continental margin during a major regional transgression thin sandstone beds contain fossils at a number of levels throughout the aar member concentrations of pteridinium were mostly transported in flood derived sheets while some ernietta assemblages are preserved close to in situ rangea has also been transported and is mostly confined to thin sandstone lenses incised into mudstone limestone beds common throughout include at least two marker horizons that can be followed regionally and show local evidence of storm reworking systematic sampling and analyses of limestone reveals enrichment in both 13 c and 18 o higher in the section with negative 13 c near the base rising to moderate positive values near the top the negative to positive transition in 13 c values is more pronounced in the east with all of the lower aar member samples consistently depleted in 13 c while this may reflect greater degrees of alteration by meteoric or dewatering fluids the same carbonates are notably enriched in 18 o relative to those at the same stratigraphic position to the west the overall rise in 13 c is attributed to greater proportional burial of organic matter and release of oxygen to surface environments while the spatial variability is likely the result of a strong surface to deep carbon isotopic gradient in seawater a number of the fossils especially rangea are encrusted with jarosite an iron bearing sulphate mineral and common weathering product of pyrite this observation suggests that preservation of the fossils may have resulted from the rapid encrustation of pyrite on the surface of the organisms as they decomposed and were consumed by sulphate reducing bacteria within the sandy near shore sediments insofar as pyrite formation requires iron which is soluble and reactive in anoxic solutions it is likely that the deeper subtidal environments lacked oxygen in situ pyritized forms like ernietta may have developed the capacity to survive under episodically anoxic or sub oxic environmental conditions while pteridinium and rangea lived within an oxygenated estuarine or fluvial setting and were transported during storms to anoxic ferruginous environments where they were exquisitely preserved

smothering of microbial mats by macrobiota implications for the ediacara biota abstract recent advances in understanding the preservation of the soft bodied neoproterozoic ediacara biota have centred upon the role of microbes in casting the morphologies of static or dead macrobiota on the precambrian sea floor this experimental study explores the preservational effects brought about by the passive movement of dead macro organisms upon a pre established marine microbial mat under laboratory conditions this demonstrates the potential for making multiple impressions of body tissues on the surface of microbial mats by means of passive transport alone this throws doubt on the evidence for active feeding in ediacaran fossils such as dickinsonia and yorgia supplementary material methods are available at http www geolsoc org uk sup18375

taphonomic bias in exceptionally preserved biotas abstract exceptionally preserved fossil biotas provide crucial data on early animal evolution fossil anatomy allows for reconstruction of the animal stem lineages informing the stepwise process of crown group character acquisition however a confounding factor to these evolutionary analyses is information loss during fossil formation here we identify that the ordovician fezouata shale has a clear taphonomic difference when compared to the cambrian burgess shale and chengjiang biota in the fezouata shale soft cellular structures are most commonly associated with partially mineralized and sclerotized tissues which may be protecting the soft tissue also entirely soft non cuticularized organisms are absent from the fezouata shale conversely the cambrian sites commonly preserve entirely soft cellular bodies and a higher diversity of tissue types per genus the burgess and chengjiang biotas are remarkably similar preserving near identical proportions of average tissue types per genus however the burgess shale has almost double the proportion of genera that are entirely soft as compared to the chengjiang biota indicating that the classic burgess shale was the acme for soft tissue preservation constraining these biases aids the differentiation of evolutionary and taphonomic absences which is vital to incorporating anatomical data into a coherent framework of character acquisition during the earliest evolution of animals

metallic ion binding by bacillus subtilis implications for the fossilization of microorganisms the silicification of bacterial cells has been followed in a laboratory simulation by electron microscopy and energy dispersive x ray spectroscopy structural degradation of the bacteria was not influenced by silica availability but the remains of degraded cells did promote the precipitation of silica in contrast cells reacted with ferric iron before aging remained intact and structures conforming to the original morphology of the bacteria were preserved by silicification the binding of metallic ions by microbial cells in particular the retention of iron is therefore considered to be an important contributing factor to the fossilization of microorganisms

assemblage palaeoecology of the ediacara biota the unabridged edition fossils of the ediacara biota offer our earliest insight into diverse macroscopic life on this planet in particular given the diversity and range of exquisite soft bodied preservation the potential for unraveling aspects of the paleobiology and paleoecology is great clearly however there can be a taphonomic overprint that dictates how complete the assemblage is new diversity data including richness and evenness from south australia is compared to previously published data from newfoundland and the white sea and is within the range of values for both modern and phanerozoic assemblages however missing from our current understanding of ediacaran ecosystems is a full description and interpretation of the many problematica structures and organic surfaces

dodging snowballs geochronology of the gaskiers glaciation and the first appearance of the ediacaran biota the snowball earth hypothesis predicts that low latitude glaciation lasted millions of years while co2 built up to critical levels to culminate in catastrophic deglaciation in a supergreenhouse climate the gaskiers formation of eastern newfoundland canada has been attributed to a snowball glaciation event but the lack of robust paleomagnetic data and precise geochronological constraints has precluded tests of the hypothesis here we present high precision u pb zircon geochronology chemical abrasion isotope dilution thermal ionization mass spectrometry from eight tuffs from multiple distant stratigraphic sections that bracket glacial diamictites and the first appearance of large ediacaran fossils including internal error deposition of the gaskiers diamictite on the avalon peninsula is constrained to have been between 580 90 0 40 and 579 88 0 44 ma and the trinity diamictite on bonavista peninsula was deposited between 579 63 0 15 and 579 24 0 17 ma assuming approximately synchronous deglaciation these results imply a maximum duration for deposition of the trinity diamictite of 340 k y this is inconsistent with the multimillion year duration predicted by the snowball earth hypothesis our geochronologic data also constrain the first appearance datum of ediacaran fossils to 9 5 m y after the gaskiers glaciation thus despite existing paleomagnetic constraints that indicate that marine ice sheets extended to low to middle latitudes it appears that earth narrowly escaped a third neoproterozoic snowball glaciation just prior to the late ediacaran expansion of metazoan ecosystems

petrographic and sims pyrite sulfur isotope analyses of ediacaran chert nodules implications for microbial processes in pyrite rim formation silicification and exceptional fossil preservation abstract the lower ediacaran doushantuo formation in the yangtze gorges area contains exceptionally preserved microfossils including the earliest known animal resting eggs and embryos these fossils are preserved in cm sized chert nodules which typically have a microbial mat fragment in the center a silica cortex a pyrite rim and an outer rim of blocky calcite petrographic analysis indicates that the formation of the blocky calcite rim postdates that of the pyrite rim and silica cortex the pyrite rim grew centripetally during early diagenesis representing a reaction front that was determined by the dynamics between ambient fe2 and h2s the latter of which was derived from bacterial sulfate reduction bsr of mat fragment in nodule center the silica cortex was formed pervasively through replacement of carbonate sediments prior to compaction secondary ion mass spectroscopy sims sulfur isotopes of individual pyrite crystals 34spy sims in pyrite rims and matrices show highly positive values 15 2 39 8 the pyrite rims do not show an isotopic gradient between small crystals formed in outer rim during early diagenesis and large crystals formed in inner rim during subsequent overgrowth although rim pyrite in the same chert nodule has consistent 34spy sims values there are significant spatial and stratigraphic variations in 34spy sims values of both matrix and rim pyrite overall isotopic fractionation between pyrite and carbonate associated sulfate cas is small

ubiquitous burgess shale style clay templates in low grade metamorphic mudrocks despite the burgess shale s british columbia canada paleobiological importance there is little consensus regarding its taphonomy its organic fossils are preserved as compressions associated with phyllosilicate fi lms clay templates debate focuses on whether these templates were fundamental in exceptional preservation or if they formed in metamorphism meaning that it is important to establish the timing of their formation relative to decay an early diagenetic origin has been proposed based on anatomy specifi c variations in their composition purportedly refl ecting contrasts in decay however we demonstrate that these films bear a remarkable similarity to those that occur on organic fossils in graptolitic mudrocks and form as a normal product of low grade metamorphism such phyllosilicates may also occur within voids created by volume loss in maturation a process that may have aided their formation in bedding plane assemblages from graptolitic mudrocks different taxa are associated with distinct phyllosilicates this likely refl ects stepwise maturation of their constituent kerogens in an evolving hydrothermal fl uid with different hyllosilicates forming as each taxon progressively underwent maturation these observations provide an analogue for the distribution and composition of phyllosilicates on burgess shale fossils which we interpret as refl ecting variations in the maturation of their constituent tissues thus their clay templates seem unremarkable forming too late to account for exceptional preservation

wrinkle structures microbially mediated sedimentary structures common in subtidal siliciclastic settings at the proterozoic phanerozoic transition sedimentary structures produced by microbial activity are well known from ancient carbonate facies but little is known about equivalent microbial structures in ancient siliciclastic facies wrinkle marks and kinneyia ripples are closely related sedimentary structures that are commonly found in ancient siliciclastics and they may represent microbial activity to evaluate this possibility these structures were studied in vendian cambrian strata of north america and compared to structures formed by modern microbial mat communities in redfish bay texas striking similarities in sedimentologic petrographic and morphologic characteristics of modern and ancient occurrences suggest that the enigmatic but widespread ancient structures could have been formed by microbial processes the relative abundance of these structures in siliciclastic facies of this interval further suggests that prior to the onset of relatively intense bioturbation in the ordovician microbial mats could have played a significant role in the evolution and diversification of early life in a broad variety of sea floor environments

ediacara type fossils in cambrian sediments fossil assemblages that preserve soft bodied organisms are essential for our understanding of the composition and diversity of past life the worldwide terminal proterozoic ediacara type fossils from 600 544 myr bp are unique in consisting of soft bodied animals which are typically preserved as impressions in coarse grained sediments1 2 3 4 these lagerstatten are also special because they pre date the major burst of skeletonization which occurred near the start of the cambrian period3 most ediacara type fossils are interpreted to be cnidarians but higher metazoans such as annelids and molluscs may also be represented1 2 3 4 however the unique style of preservation and difficulties in finding convincing morphological homologies with definite animals have led some specialists to prefer non metazoan interpretations such as vendobionta5 in addition the rarity of ediacara type fossils in younger sediments has led to suggestions of a terminal proterozoic mass extinction6 here we report typical ediarcara type frond shaped fossils that occur together with an assemblage of cambrian type trace fossils in unequivocally cambrian aged sediments of the uratanna formation south australia this occurrence bridges the apparent divide between the terminal proterozoic and cambrian fossil assemblages and also suggests that closure of a taphonomic window an interval of time with unique preservational conditions was as important as extinction in the disappearance of ediacara type organisms

paleobiology of a three dimensionally preserved paropsonemid from the devonian of new york abstract a three dimensionally preserved stellate fossil from the middle upper devonian of new york is described although it shares gross similarities with oral cones of anomalocaridids we interpret it as the mold of the dorsal portion of the segmented alimentary canal of the rare soft bodied animal paropsonema cryptophya together with two other dorsally preserved p cryptophya specimens such fossils strengthen the hypothesized link between two primitive deuterostome stem groups the paropsonemids and the eldonids although the taxonomic affinities of these groups remain uncertain it is important to illustrate fossils like these because they provide paleontologists with a search image for more material that may elucidate patterns in early animal evolution or may help revise taxonomic interpretations the new specimen of paropsonema is also the youngest described occurrence of the paropsonemids and its sediment filled gut is consistent with an epibenthic lifestyle for that group

vendobionta and psammocorallia lost constructions of precambrian evolution the non availability of biomineralized skeletons and low levels of predation led vendian evolution along strange avenues the ediacara type vendobionta appear to represent a kingdom in which foliate shapes large sizes and the necessary compartmentalization were achieved by quilting of the skin rather than by multicellularity psammocorallia in contrast are interpreted as coelenterates that constructed an internal sand skeleton both were immobile soft bottom dwellers that had high population densities and both became preserved by obrutional accidents thus they render fossil snap shots in which the original distributional patterns age structures and standing biomasses of populations are accurately recorded

preservation of early cambrian animals of the chengjiang biota the chengjiang biota of yunnan china documents the earliest extensive radiation of the metazoa recorded in the fossil record gauging preservational bias is crucial in providing an assessment of the completeness of this biota and thereby elucidating whether it represents a comprehensive depiction of early cambrian life we here present a model to explain the nature of the exceptional preservation of the chengjiang biota and details of the decay process this study indicates that chengjiang fossils were preserved through two taphonomic pathways that may have captured tissues of distinct compositions and this finding should provide a foundation for the interpretation of chengjiang fossils many chengjiang fossils are preserved by pyrite later pseudomorphed by iron oxides the clay rich host sediment was deficient in organic carbon but replete in available fe and this composition ensured that a decaying carcass acted as a local substrate for fe and s reducing bacteria pyrite morphology probably reflects contrasts in the decay rate and hence the h 2 s production rate of different tissues in a carcass reactive rapidly decaying tissues would have quickly supplied h 2 s producing many pyrite nuclei resulting in framboidal habits more recalcitrant tissues would have produced h 2 s more slowly so that crystal growth operated on fewer nuclei resulting in larger euhedral pyrite crystals reflective films especially common on chengjiang arthropods represent the remains of degraded carbon

explaining the exceptional preservation of ediacaran rangeomorphs from spaniard s bay newfoundland a hydraulic model exceptional 3 d preservation of ediacaran rangeomorph fossils is found on a single bedding plane at upper island cove spaniard s bay newfoundland this high quality preservation has previously been explained by entrainment of organisms within the td e mudstone division of a distal turbidite followed by encasement within concretions our sedimentological and taphonomic analysis reveals a clear association between these fossils and evidence for erosive unidirectional flows including scours marks tool marks ridge and groove marks parting lineations and current crescents we suggest an alternative sequence of events that runs broadly as follows i rangeomorph discs were anchored to the seafloor during deposition of planar laminated silts our unit 2 10 mm thick td now bearing pyrite framboids and pyritized organic matter ii rangeomorph fronds were then felled and entrained by high velocity unidirectional currents to lie within their own erosional scours at the top of unit 2 or to form tool marks iii this topography was then draped and cast by soft weathering sand unit 3 tc associated with the growth of early diagenetic pyrite around sand grains pyrite grains also appear to have replaced clumps of organic matter fossil impressions have since been exposed by differential weathering of the ferruginous sands with respect to the silts this new context now provides a parsimonious explanation for a range of hitherto paradoxical structures features previously regarded as microbial mats bubble trains that formed in the lee of sinuous ripples on the top of unit 2 may be explained as load casts or by localised gas escape within areas of lowered hydraulic pressure rangeomorph fronds remarkably preserved in positive rather than the more usual negative epirelief are explained by means of sediment casting of branches that became ruptured in the high velocity current paradoxical structures previously thought to be enclosing biological sheaths around rangeomorph fronds are reinterpreted as scour marks whereas imbricate overlaps of first order branches in beothukis trepassia and avalofractus are explained by hydraulic shear driven by overlying currents across ruptured and deflated fronds we find that rangeomorph bodies could be deflated imbricated folded over inverted and infilled with fine sediment our hydraulic model provides a null hypothesis against which future observations of rangeomorph fronds can now be tested it removes some significant anomalies in our understanding of rangeomorph architecture and provides a better understanding of the physical properties of their body tissues permitting the possibility of a reasoned consideration of their puzzling biological affinities

carbonate hosted avalon type fossils in arctic siberia avalon type fossils are crucial to understanding the origin of phanerozoic ecosystems but their usual occurrence in volcaniclastic and siliciclastic facies greatly limits their paleobiological resolution the unique carbonate hosted assemblage of the khatyspyt formation on the olenek uplift of north central siberia promises a much enhanced anatomical and paleo ecological view of these enigmatic organisms avalon type fossils are preserved by authigenic carbonate cementation in intervals of finely laminated nodular limestones khatyspyt type taphonomic window interbedded silicified calcareous mudstones yield diverse carbonaceous compressions occasionally with taphonomic phantoms of avalon type taxa miaohe type taphonomic window styles of moldic preservation do not appear to be taxon selective and therefore cannot alone be responsible for the morphological distinctiveness of ediacaran macrofossils and the profound disparity in the taxonomic composition between fossil assemblages on the other hand the exclusion of avalon type fossils from carbonaceous compressions miaohe type preservational window is a real taphonomic signal that provides an important constraint on the properties of certain ediacaran tissues

taphonomic study of ediacaran organic walled fossils confirms the importance of clay minerals and pyrite in burgess shale type preservation burgess shale type bst macrofossils and organic walled microfossils are preserved as carbonaceous compressions and may share similar taphonomic processes previous taphonomic investigations of carbonaceous compressions have primarily focused on the microchemistry of cambrian bst fossils but comparative data from organic walled microfossils were not available to address these issues we analyzed two organic walled taxa from the yangtze gorges area of the south china block chuaria an acritarch and vendotaenia a ribbon shaped fossil their abundance offers the opportunity for destructive microanalysis including petrography electron microscopy and elemental mapping on both bedding planes and in cross sections our data suggest that chuaria preservation is remarkably similar to bst fossils in that its vesicle walls are closely associated with clay minerals in addition like many bst macrofossils chuaria and vendotaenia are also closely associated with pyrite chuaria vesicles are often filled with framboidal pyrite and vendotaenia fossils are associated with sulfate partly derived from pyrite oxidation the comparative taphonomy of chuaria and vendotaenia and bst macrofossils indicates that the preservation of organic walled acritarchs may be aided by clay and pyrite mineralization and that these abundant microfossils may serve as proxies for uncovering in more detail the taphonomic histories of bst preservation

upper ordovician planktic and benthic graptolites and a possible hydroid from the tafilalt biota southeastern morocco

formation of fe silicates and fe oxides on bacterial surfaces in samples collected near hydrothermal vents on the southern explorer ridge in the northeast pacific ocean samples collected in low temperature 2 50 degrees c waters near hydrothermal vents of the southern explorer ridge in the northeast pacific ocean contained fine 500 nm fe and mn oxide and fe silicate particles coating bacterial surfaces partially to totally mineralized bacteria along with bacterial exopolymers were covered with a mixture of poorly ordered si rich fe oxides possibly ferrihydrite mn oxides and fe silicates possibly nontronite minerals occur as very fine 2 20 nm granular material fine 20 100 nm needles and sheets small 200 500 nm nodules and filaments i e mineralized exopolymers under saturation conditions we infer that bacterial surfaces provided nucleation sites for poorly ordered oxides and silicates the formation of fe and mn oxides was likely initiated by the direct binding of soluble fe and mn species to reactive sites like carboxyl phosphate and hydroxyl groups present within the bacterial cell wall and the exopolymers fe silicate formation involved a more complex binding mechanism whereas metal ions such as fe possibly bridged reactive sites within the cell walls to silicate anions to initiate silicate nucleation

a re examination of the nama type vendian organism rangea schneiderhoehni the need to re examine rangea has been motivated by two factors first by the recent progress in the understanding of three dimensional mouldic preservation of vendian fossils and second by discoveries of this taxon outside gondwana albeit in the same sedimentary environment as seen in namibia several important features are revealed including the in situ posture in the sediment the double layered quilted structure the tripartite stemless body and the mucous supported sheath in the sediment it is suggested that rangea represents an infaunal organism and that the similarity with other members of the nama type biota reflects convergence in functional and fabricational constraints in relation to infaunal life habit

eight armed ediacara fossil preserved in contrasting taphonomic windows from china and australia we report the preservation of the eight armed ediacara fossil eoandromeda octobrachiata as carbonaceous compressions in the doushantuo black shale of south china and as casts and molds in the rawnsley quartzite in south australia the contrasting preservational styles in two taphonomic windows indicate that e octobrachiata may have had a relatively recalcitrant organic integument which rules out its close comparison with giant agglutinated foraminifers such as xenophyophores its octaradial symmetry and dextrally spiraling arms suggest that it may be a diploblastic grade animal sharing some features with cnidarians and ctenophores although its phylogenetic affinity remains open it is the first and only unambiguously identified ediacaran macrofossil that occurs in two drastically different taphonomic windows thus bridging the conventional biological and taxonomic gaps between the ediacara and miaohe biotas which collectively record the earliest known macroscopic and complex life

metal sorption and mineral precipitation by bacteria in two amazonian river systems rio solimoes and rio negro brazil the surfaces of epiphytic and episammic bacteria from the solute rich waters of the rio solimoes brazil interacted with available cations in solution and provided major sites for iron deposition once bound to the bacteria the iron served as nucleation sites for the formation and growth of fine grained authigenic mineral phases because of progressive mineralization the precipitates exhibited a wide range of morphologies from amorphous gel like to crystalline structures complete encrustation of some bacterial cells was observed the most abundant mineral phase associated with the bacteria was a complex fe al silicate with a variable composition energy dispersive x ray spectroscopy suggested that the gel like structures were similar in composition to a chamositic clay whereas the crystalline phases were increasingly kaolinitic bacteria collected from the solute deficient waters of the rio negro remained conspicuously unmineralized suggesting that metal sorption and biomineralization largely reflect the availability of dissolved metals in the water column in a solute rich river system the fate of the metal loaded bacteria has profound implications for the transfer of metals from the hydrosphere to the sediment through diagenesis the bound metals may either be recycled to the overlying water column or become immobilized as stable mineral phases if the latter occurs microorganisms will have played an important role in metal deposition low temperature clay formation and invariably mudstone diagenesis this implies that in the geologic record microorganisms may have been instrumental in the genesis of many sedimentary rocks of fluvial origin

a biota of ediacaran aspect from lower cambrian strata on the digermul peninsula arctic norway three elements of the ediacara fauna are described from lower cambrian strata on the digermul peninsula norway nimbia occlusa fedonkin 1980 and tirasiana sp occur approximately 80 m above the base of the lower breivik member which approximately coincides with the neoproterozoic cambrian boundary a specimen of cyclomedusa sp has also been found in the lower duolbasgaissa member about 600 m above the boundary in rocks of trilobite bearing age these discoveries add to a growing body of evidence that some elements of the dominantly neoproterozoic ediacara fauna continue into the phanerozoic thereby diminishing the scope of a possible late neoproterozoic mass extinction event the taxa described here particularly nimbia and cyclomedusa also occur at many other localities within neoproterozoic strata and in common with other elements of the ediacara fauna display remarkable morphological variation some of this diversity in form is probably caused by environmental and preservational factors the possibility that it may at least in part reflect an inability of these early life forms to replicate faithfully their genes during reproduction should however not be overlooked

evidence of organic structures in ediacara type fossils and associated microbial mats ediacara type fossils represent a group of soft bodied organisms mainly known from imprints in proterozoic coarse grained siliciclastic sedimentary rocks circular compressions of beltanelliformis brunsae and remains related to ediacara type fossils such as cucullus fraudulentus and mucuplagum primitivum are reported here in an organic mode of preservation from the neoproterozoic doushantuo and liulaobei formations of china they can be interpreted as prokaryotic colonies a charnid fossil with circular attachment disc and stalk but torn off frond is documented in a three dimensional and partly organic mode of preservation from the neoproterozoic ust pinega formation white sea coast russia according to their morphology and structure the charniidae are not regarded by us as pennatulaceans modern myxobacteria illustrate that macroscopic size complexity and even compartmentalization can also be developed by prokaryotic colonies part of the ediacara type fossils may therefore represent prokaryotic colonies or symbiotic organisms involving prokaryotes finally direct evidence indicates that biofilms with associated prokaryotic sheaths preserved in both organic and pyritic fashion form the wrinkled surfaces elephant skin that were preferentially colonized by ediacara type fossils this finding supports previous interpretations based on comparative morphological and sedimentological approaches that ancient wrinkle structures were microbial mats

preservational modes in the ediacaran gaojiashan lagerstatte pyritization aluminosilicification and carbonaceous compression abstract burgess shale type bst fossils often are preserved as two dimensional carbonaceous compressions sometimes aided by two mineralization processes pyritization and aluminosilicification defined by a thin and sometimes localized coating of authigenic pyrite or aluminosilicate minerals on the carbonaceous materials here we report similar mineralization modes within the late ediacaran gaojiashan lagerstatte of southern shaanxi province south china examination of two common gaojiashan fossils conotubus hemiannulatus and gaojiashania cyclus hereafter referred by generic names only indicates that pervasive pyritization is the primary taphonomic pathway in this deposit responsible for the preservation of 80 of the collected fossils pervasive pyritization of gaojiashan fossils results in their three dimensional preservation as opposed to two dimensional carbonaceous compression with thin pyrite coatings seen in some bst lagerstatte however microscale investigation using environmental scanning electron microscopy esem and energy dispersive x ray spectroscopy eds shows that some flattened specimens of conotubus and gaojiashania are preserved as carbonaceous compressions which are in some cases associated with aluminosilicate minerals rare compressed specimens of conotubus are replicated by greenish clay minerals which are interpreted as diagenetic products of aluminosilicate precursors our taphonomic analysis shows that pervasive authigenic pyritization tends to replicate more labile tissues than aluminosilicate aided carbonaceous compression but both pyritization and aluminosilicification processes can facilitate the replication and preservation of soft bodied organisms in siliciclastic sediments building upon this conclusion we propose that multiple taphonomic processes including kerogenization or polymerization of organic molecules pyritization and aluminosilicification can contribute to the mode of bst preservation viewed in this light various siliciclastic hosted lagerstatten that are facilitated by kerogenization pyritization and aluminosilicification can be plotted on a ternary diagram based on the relative importance of these taphonomic processes

organic membranous skeleton of the precambrian metazoans from namibia unlike the celebrated ediacara fossils those from the roughly coeval localities of the kuibis quarzite of namibia are preserved not as imprints on the sandstone bedding plane but three dimensionally within the rock matrix the pattern of deformation and the presence of sand in lower parts of the bodies of ernietta the most common and typical of those organisms indicate that their three dimensional preservation is a result of a density controlled sinking of sand filled organic skeletons within hydrated mud layers specimens of ernietta have preserved various stages of migration across the mud beds their wall material as documented by the mode of deformation was not only flexible but also elastic which makes it unlike chitin the walls thus seem to be proteinaceous built probably of a collagenous fabric the ernietta skeleton was built of series of parallel chambers which excludes the possibility that these were external body covers the chambers apparently represent walls of hydraulic skeleton units resembling the basement membrane of chaetognaths or the notochord sheath of primitive chordates such chambers are widespread among the earliest fossil animals represented by fossils preserved in sandstone the rise and fall of the ediacaran faunas thus seem to be partially preservational artifacts the range of its occurrence is a result of two successive evolutionary events the origin of an internal hydraulic skeleton enclosed by a strong basement membrane and the appearance of decomposers with abilities to disintegrate such collagenous sheaths

depositional and preservational environments of the ediacara member rawnsley quartzite south australia assessment of paleoenvironmental proxies and the timing of ferruginization abstract the paleoenvironmental setting in which the ediacara biota lived died and was preserved in the eponymous ediacara member of the rawnsley quartzite of south australia is an issue of longstanding interest and recent debate over the past few decades interpretations have ranged from deep marine to shelfal to intertidal to terrestrial here we examine the evidence in support of and against various paleoenvironmental interpretations of the fossiliferous ediacara member as well as exploring in depth a range of paleoenvironmental proxies that have historically been employed in such studies we emphasize the importance of reconciling paleoenvironmental analysis with an understanding of sedimentological processes and outline which proxies are consistent with this approach a careful assessment of paleoenvironmental parameters is essential to the reconstruction of the depositional and early diagenetic history of the ediacara biota and thus the physical chemical and biological factors that shaped the development and the fossilization of these earliest examples of complex life we find no compelling evidence for a terrestrial setting for the ediacara member and strong support for a shallow marine depositional environment

formation of fine grained metal and silicate precipitates on a bacterial surface bacillus subtilis abstract the ability of the gram positive bacterium b subtilis to bind and nucleate precipitates from silicate anions has been studied over 24 weeks in the presence of fe and a1 at concentrations close to those levels in soils and at slightly acid 5 5 and basic 8 0 ph in all cases formation of silicate crystallites quasi crystalline precipitates on the bacterial surfaces was observed bacterially mediated minerals were more diverse in composition and morphology less crystalline smaller and sometimes more abundant than those that were abiotically formed fe pretreatment of the bacterial cells enhanced the binding of silicate at ph 8 0 walls which were not pretreated with fe bound silicate more favourably at acid values when heavy metals pb cd zn cr ni cu were added to the mixture at ph 4 5 silicate retention was greatly favoured giving greater retention of either si or metals than was seen in abiotic controls experiments with only heavy metals showed a high affinity of the bacterial walls for the metals even at low temperatures 4 c it is postulated that a cationic bridging mechanism is involved in the binding of silicate anions by bacterial cell walls

bacteria as nucleation sites for authigenic minerals in a metal contaminated lake sediment abstract sediment samples contaminated with metals arising from mine tailings drainage were obtained from lower moose lake in the onaping region near sudbury ontario canada the samples were examined by electron microscopy selected area electron diffraction and energy dispersive x ray spectroscopy individual bacterial cells and their remains were prominent as nucleation sites for both metal sulfides and a complex polymorphic fe al silicate the principal metal sulfide species associated with the bacteria were amorphous mackinawite fes 1 x and microcrystalline millerite nis trace amounts of cu and zu were also detected in some of the sulfide precipitates at least two structural forms of the fe al silicate were present and energy dispersive x ray spectroscopy point analyses revealed corresponding differences in chemical composition poorly ordered limonitic clay type phases had a granular morphology and contained less fe than well developed crystalline material which generated hexagonal diffraction patterns with reflections d 4 60 and 2 55 characteristic of an interstratified chamositic clay

climate variability during the last 1000 years inferred from andean ice cores a review of methodology and recent results abstract andean ice core investigations began approximately 30 years ago today 10 drilling sites from 0 to 52 s have been explored for paleoclimate reconstructions most of the ice cores reaching the bedrock cover the last 20 000 years with seasonal resolution over the last few centuries to the last 1000 years for the quelccaya site we discuss both the potential and the limitations of tropical ice cores as climate archives with regard to the collaborative effort to reconstruct past climate variations in south america over the last 1000 years we point out the uniqueness of south american ice cores due to their location at high altitude and also their two main limitations which are related to i the interpretation of certain proxies in terms of climate and ii the relatively poor dating when seasonal cycles are no longer resolved in addition we present an overview of the proxies that have been used so far to analyze tropical climate dynamics finally we discuss records of enso the little ice age and the 20th century decadal variability including the anthropogenic period which are all preserved in ice cores

insights into cyanobacterial fossilization in ediacaran siliciclastic environments ediacaran sedimentary successions are noted for the preservation of microbes and microbial textures on the surfaces of sandstones and siltstones although microorganisms have been preserved in coarse grained siliciclastic sand throughout geologic history the exceptional preservation of microbes in ediacaran sediments suggests the potential for a unique taphonomic window here we identify conditions conducive to the fossilization of filamentous cyanobacteria growing in the presence of siliciclastic sand and demonstrate that the sheaths of filamentous cyanobacteria can become coated by clay minerals within days under oxic conditions smooth extensive mineral coatings develop in the presence of 5 6 to 55 6 mg l of suspended clay and 0 1 mm or greater concentrations of dissolved silica thus elevated concentrations of seawater silica and the delivery of suspended clays promote microbial preservation on sandy and silty surfaces these factors likely facilitated microbial fossilization in coarse grained siliciclastic sand throughout the ediacaran period and may have also contributed to microbial fossilization in siliciclastic deposits at other times throughout earth s history

fire history and human activity revealed through poly cyclic aromatic hydrocarbon pah records at archaeological sites in the middle reaches of the yellow river drainage basin china abstract disentangling the role of natural and anthropogenic factors is a major challenge in paleofire studies here we introduce the molecular biomarkers of polycyclic aromatic hydrocarbon pahs combined with charcoal and black carbon in sediments of archaeological sites to identify anthropogenic signals of environmental change during the middle holocene in the prehistoric period an intensified fire regime period inferred on the basis of pahs char and macro charcoal levels has been attributed to intensified anthropogenic biomass burning from dry crop cultivation between 6500 and 5000 and 3900 3600 yr bp corresponding to the earliest chinese settlements during the miaodigou banpo iv culture and the development of the erlitou culture under drier climate conditions subsequently the fire frequency decreased notably between 4500 and 4000 yr bp as the climate became wetter and there were shifts in the frequency of high magnitude floods corresponding to the abandonment of late neolithic settlements in the floodplain changes in the pah fluxes in sediments are positively correlated with intensified fire regime periods consistent with the charcoal and black carbon fluxes during those periods principal component analysis of pah fluxes suggests that these intensified fire events have a pyrogenic signature implying that the pahs were derived from biomass burning of fuelwood and other woody plants in this study pahs in loess sediments have been used as the indicators of anthropogenic biomass burning through time meanwhile pahs also record the shift of modes of production and the evolution of human settlements as well as the choices made in response to limited natural resources to comprehensively analyze the paleofire records of pahs charcoal and black carbon combined with multiproxy evidence are needed to understand wildfire history as well as human land use and social and cultural development across the study regions in depth

stranded on a late cambrian shoreline medusae from central wisconsin fossilized impressions of soft bodied organisms are exceptionally rare in coarse grained strata fossilized mass stranding events of soft bodied organisms are even rarer the upper cambrian mt simon wonewoc sandstone in central wisconsin contains at least seven horizons characterized by hundreds of decimeter sized impressions of medusae these represent one of only two fossilized mass stranding deposits medusae exhibit features nearly identical to those observed in modern scyphozoan strandings including impressions of subumbrellar margins and gastrovascular cavities this deposit provides insights about soft tissue preservation in phanerozoic marginal marine sediments and suggests that large soft bodied pelagic organisms were abundant in cambrian seas