probable benthic macroalgae from the ediacara member south australia abstract the ediacara biota records the rise of morphologically complex macroscopic eukaryotes including animals and other heterotrophs eltonian ecology demands that ediacaran ecosystems must have been supported by primary producers e g cyanobacteria phytoplanktonic eukaryotes benthic macroalgae but the fossil record of ediacaran primary producers has not been fully documented particularly with respect to benthic macroalgae hampering a complete understanding of ediacaran ecosystems here we provide systematic description of probable benthic macroalgal fossils from the ediacara member of the rawnsley quartzite at the national heritage site nilpena in south australia these fossils include flabellophyton stupendum sp nov f typicum liulingitaenia irregularis sp nov and longifuniculum cf dissolutum previously informally referred to as bundles of filaments bof they are characterized by bundled filaments that can be twisted loosened or otherwise deformed although many are fragmented some specimens of flabellophyton stupendum sp nov f typicum and possibly longifuniculum cf dissolutum bear structures that resemble variants of pseudorhizostomites and mop but interpreted here as holdfasts suggesting that in life these were epibenthic organisms attached to the substrate atypical populations of relatively small ediacara type fossils are found on a bedding surface dominated by benthic macroalgae suggesting that together with microbial mats these primary producers were beneficial for juvenile settlement of ediacara type organisms potentially contributing both oxygen and nutrients although debates about animal affinity dominate ediacaran paleontology this study highlights the importance of benthic macroalgae in ediacaran ecosystems

environmental interpretation and a sequence stratigraphic framework for the terminal proterozoic ediacara member within the rawnsley quartzite south australia abstract fossils of the ediacara biota are confined to preservational windows in the ediacara member of the rawnsley quartzite pound subgroup from the flinders ranges south australia the base of the ediacara member is a type 1 sequence boundary incised into the partly lithified chace quartzite member of the rawnsley quartzite the ediacara member and the upper half of the rawnsley quartzite comprise the rawnsley depositional sequence bounded above by the early cambrian uratanna depositional sequence the rawnsley sequence developed over an erosional surface cut into the chace quartzite member with some 250 m of relief southeasterly directed palaeovalleys are filled with a sequence of massive sandstone and laminated siltstone passing up into well bedded sandstone at lowstand local channels were filled by massive sand the highstand systems tract consists of several parasequence sets of laminated siltstone and channelized amalgamated massive sandstone overlain by interbedded siltstone and sandstone grading up into well bedded clean sandstone impressions of soft bodied ediacaran organisms are preserved above the valley fill facies on sandstone partings within upward shoaling delta front environments between storm and fairweather wavebase the ediacara member is in places conformably overlain by up to 500 m of sandstone of the same lithofacies as those underlying the member distinctive microbial mat bound sand laminae described as petee structures are characteristic of the rawnsley quartzite above and below the ediacara member during deposition of the ediacara member colonization of the deeper substrates by microbial mat communities enabled preservation of the ediacara biota the erosional surface at the base of the ediacara member is one of at least four incision events recorded in the terminal proterozoic and early cambrian succession of the adelaide geosyncline the similarity of incision filling lithofacies of the rawnsley and uratanna sequences has in condensed sections led to confusion between the depositional sequences characteristic trace and body fossil assemblages provide the only clear distinction between depositional cycles spanning the proterozoic cambrian boundary

textured organic surfaces associated with the ediacara biota in south australia abstract the ediacaran period takes its name from the fossils of the ediacara biota which represent the first appearance of large and diverse assemblages of organisms in the fossil record although the global record of these distinctive body fossils is now well known a previously unrecognized megascopic organic record of textured organic surfaces tos occurs in the ediacara biota however tos is also a feature over a wider range of paleoenvironmental settings where body fossils are unknown in ediacaran siliciclastic successions that have been studied in australia namibia and western north america paleoecological analysis of successive bedding planes of strata from the late ediacaran rawnsley quartzite in the flinders ranges of south australia reveals that tos represent the most common organic features in bedding surface assemblages of the ediacara biota the tos consist of preserved patterned assemblages of textured organic mats fibers and simple tubular body fossils complex ediacara body fossils while striking for their distinctive body plans and dominating some of the beds are relatively minor components of combined overall surface area many elements of tos have previously been miss diagnosed as trace fossils which are in practice limited to two or at most three morphotypes that indicate the presence of bilateria although tos represent a simpler grade of organismic construction than discrete and more complex ediacara body fossils they were preserved in a similar manner marked variability in all components of the biota between successive surfaces suggests that ediacara ecologies fluctuated at short intervals despite an apparently consistent sedimentary regime

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

resolving miss conceptions and misconceptions a geological approach to sedimentary surface textures generated by microbial and abiotic processes the rock record contains a rich variety of sedimentary surface textures on siliciclastic sandstone siltstone and mudstone bedding planes in recent years an increasing number of these textures have been attributed to surficial microbial mats at the time of deposition resulting in their classification as microbially induced sedimentary structures or miss research into miss has developed at a rapid rate resulting in a number of misconceptions in the literature here we attempt to rectify these miss misunderstandings the first part of this paper surveys the stratigraphic and environmental range of reported miss revealing that contrary to popular belief there are more reported miss bearing rock units of phanerozoic than precambrian age furthermore miss exhibit a pan environmental and almost continuous record since the archean claims for the stratigraphic restriction of miss to intervals prior to the evolution of grazing organisms or after mass extinction events as well as claims for the environmental restriction of miss appear to result from sampling bias in the second part of the paper we suggest that raised awareness of miss has come at the cost of a decreasing appreciation of abiotic processes that may create morphologically similar features by introducing the umbrella term sedimentary surface textures of which miss are one subset we suggest a practical methodology for classifying such structures in the geological record we illustrate how elucidating the formative mechanisms of ancient sedimentary surface textures usually requires consideration of a suite of sedimentological evidence from surrounding strata resultant interpretations microbial or non microbial should be couched within a reasonable degree of uncertainty this approach recognizes that morphological similarity alone does not constitute scientific proof of a common origin and reinstates a passive descriptive terminology for sedimentary surface textures that cannot be achieved with the current miss lexicon it is hoped that this new terminology will reduce the number of overly sensational and misleading claims of miss occurrence and permit the means to practically separate initial observation from interpretation furthermore this methodology offers a scientific approach that appreciates the low likelihood of conclusively identifying microbial structures from visual appearance alone informing the search for true miss in earth s geological record and potentially on other planetary bodies such as mars

microbial origin of early animal trace fossils abstract elongate surface trails that abound in late ediacaran and early paleozoic sandstone and siltstone are often attributed to early animals these trails commonly exist on the same beds as wrinkle structures millimeter to centimeter size ridges and pits that are interpreted as evidence of the former presence of microbial mats here we show that interactions between oscillatory flow and centimetric microbial aggregates produce elongate trails on the surface of a sediment bed trails left by moving microbial aggregates share a number of characteristics with some presumed trace fossils of the earliest animals elevated edges zig zag patterns smooth curves reversals intersections with other trails series of pits and paths that terminate abruptly and restart nearby under the same flow conditions millimetric microbial aggregates generate wrinkle structures thus the interaction between flow and microbial aggregates on a sediment bed can produce a number of structures that are commonly interpreted as evidence of early animal locomotion

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

principles of thermal expansion in the feldspar system following the recent thermal expansion work of hovis et al 2008 on alsi 3 feldspars we have investigated the thermal expansion of plagioclase ba k and ca k feldspar crystalline solutions x ray powder diffraction data were collected between room temperature and 925 c on six natural plagioclase specimens ranging in composition from anorthite to oligoclase and as well on their k exchanged equivalents and five synthetic ba k feldspars with compositions from 25 to 99 mol baal 2 si 2 o 8 the resulting thermal expansion coefficients for volume v have been combined with earlier results for end member na and k feldspars unlike alsi 3 feldspars al 2 si 2 feldspars including anorthite and celsian from the present study and sr and pb feldspar from other workers show essentially constant and relatively limited thermal expansion in the context of structures where the lowenstein rule requires al and si to alternate among tetrahedra the proximity of bridging al o si o atoms to divalent neighbors ranging from 0 to 2 results in ca o or ba o bonds that are especially short it is suggested that short bonds such as these have a partly covalent character resulting from the requirement for local charge balance this in turn stiffens the structure for feldspar series with coupled substitution the change away from a purely divalent m site occupant gives the substituting less strongly bonded monovalent cations increasingly greater influence on thermal expansion overall thermal expansion in the feldspar system is well represented on a plot of v against room temperature volume v rt where one sees a quadrilateral bounded by data for 1 alsi 3 feldspars whose expansion behavior is governed largely by the size of the monovalent alkali site occupant 2 al 2 si 2 feldspars whose expansion is uniformly limited by divalent cations having stronger partially covalent bonds to bridging al o si o atoms and 3 4 plagioclase and ba k feldspars where expansion behavior across the series transitions from one control to the other overall the coefficient of thermal expansion in any binary feldspar series is a linear function of v rt between the pertinent end members this makes it possible to predict the thermal expansion behavior of any feldspar simply from knowledge of its chemical system and room temperature volume

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

microbially induced sedimentary structures a new category within the classification of primary sedimentary structures abstract cyanobacterial films and mats syndepositonally influence erosion deposition and deformation of sediments the biomass levels surface morphologies and microbial mats stabilize depositional surfaces and shelter the sediment against erosion or degassing growing microbial mats dredge grains from their substrate upwards whereas cyanobacterial filaments that are oriented perpendicular to the mat surface reach into the supernatant water and baffle trap and bind suspended particles these and similar biotic physical interactions are reflected in syndepositional formation of microbially induced sedimentary structures we distinguish structures on bedding planes leveled bedding surfaces wrinkle structures microbial mat chips erosional remnants and pockets multidirectional ripple marks and mat curls and internal bedding structures sponge pore fabrics gas domes fenestrae structures sinoidal laminae oriented grains benthic ooids biolaminites mat layer bound grain sizes we propose to place this group of microbially mediated structures as a fifth category bedding modified by microbial mats and biofilms in pettijohn and potter s 1964 existing classification of primary sedimentary structures

discussion were the ediacaran siliciclastics of south australia coastal or deep marine by retallack et al sedimentology 59 1208 1236 richard h t callow martin d brasier and duncan mcilroy department of geology and petroleum geology university of aberdeen meston building aberdeen ab24 3ue uk e mail r callow abdn ac uk department of earth sciences university of oxford south parks road oxford ox1 3an uk department of earth sciences memorial university of newfoundland 300 prince philip drive st john s nl a1b 3x5 canadaintroductionthe late ediacaran period is a critical interval inthe history of life on earth and its poorly under stood fossils have potential to shape our under standing of early biosphere evolution critical tothis process is an accurate assessment of theenvironments in which these organisms our ished prior to the radiation of animal life duringthe cambrian explosion few successions can bemore historically important for this than theediacara member of the rawnsley quarzite inthe flinders ranges south australia glaessner 1984 the depositional settings for these rockshave hitherto been established and widelyaccepted as being below fair weather wave base delta front prodelta shoreface to intertidal gehling 2000 the new interpretation advancedby retallack 2012 is thought provoking andincludes a diverse dataset which is used to arguefor deposition of the ediacara member within ashallow marine coastal and subaerial suite ofenvironments this discussion examines a num berofthe conclusions insupportofthatclaim andconsiders that the established marine depositionalsetting of the ediacara member remains valid deep marine context of theediacara memberthe title of the paper implies that gehling 2000 interpreted the ediacara member to be a deepmarine unit see also mount 1989 the term deep marine is rarely used in a strict sense bygeologists it has been used variously to refereither to environments situated beyond the shelfbreak e g pickering et al 1989 or to environ ments affected by processes that are typical ofslope and basin oor environments i e sedimentgravity ows the depositional environmentsrecognized by gehling 2000 include sandstonedeposition below fair weather wave base inincised valley lls palaeovalleys delta front topro delta palaeoenvironments delta top sandsheets braid deltas and intertidal ats it is clearfrom this list of palaeoenvironmental interpreta tions that gehling 2000 did not consider theediacara member as deep marine for example intertidal environments were identi ed from theinference of ancient microbial mats and sandgypsum crystals gehling 2000 gehling dro ser 2009 most importantly the fossiliferousbeds were interpreted as tempestites that formedin delta front palaeoenvironments between stormand fair weather wave base gehling 2000 sediment gravity ows including but not lim ited to turbidites were identi ed as componentsof the succession by gehling 2000 as parts offacies associations c d and e however it wasstated explicitly that the massive channelizedsands 0ae5 to 8 m thick beds were not depositedin a basinal setting but rather in sub wave basesubmarine channels similarly the micro turbi dites facies association e were interpreted aspart of a distal pro delta environment suchshelfal prodelta turbidites are common in depo sitional systems with high sediment supply andhigh rates of accommodation generation e g mcilroy et al 2005 we concur with gehling 2000 that the thick bedded massive and dewa tered channelized sandstones are not readilycompatible with uvial facies models and aremore consistent with deposition from submarine ows e g kneller branney 1995 the pres ence of hummocky cross strati ed beds gehling 2000 g 10d has been con rmed by manyauthors such bedforms were not observed bysedimentology 2013 60 624 627

earth s oldest jellyfish strandings a unique taphonomic window or just another day at the beach discoidal macrofossils reported herein from the lower cambrian zabriskie quartzite great basin western united states record the oldest phanerozoic medusozoan body fossils as well as the oldest medusozoan stranding event on record moreover these fossils provide evidence of a significant shift in the taphonomic mode characteristic of preservation of nonmineralized taxa in coarse grained siliciclastic successions near the onset of the phanerozoic taphonomic and sedimentological evidence recorded by these and younger examples of stranded cambrian medusae is consistent in suggesting that several of the requirements for preservation of these fossils were holdovers from the ediacaran period including the presence of microbial mats and a lack of carcass disturbance by scavenging and or bioturbating taxa to shed further light upon the taphonomic factors necessary for the preservation of cambrian medusae we compared the biostratinomy and sedimentology of cambrian medusa strandings to those of ediacara biota assemblages from lithologically similar successions we find key secular disparities in the taphonomic histories of these two types of fossil assemblage inconsistencies between the preservational styles characteristic of fossil assemblages preserved in sandstone lithofacies on each side of the precambrian cambrian boundary are explained by a considerable change in the preferred depositional setting in which these macrofossil assemblages are preserved thus rather than documenting a single taphonomic continuum through the precambrian cambrian transition the zabriskie and younger medusozoan body fossil assemblages record the advent of an entirely new yet still very rarely exploited taphonomic window exclusive to the cambrian period

microbial shaping of sedimentary wrinkle structures wrinkle structures in ancient sedimentary environments are enigmatic wave tank experiments suggest that wrinkle structures are shaped by microbial mat fragments that are moved by waves over sandy bed surfaces and thus are morphological biosignatures

the problems and potential of using animal fossils and trace fossils in terminal proterozoic biostratigraphy abstract despite the discovery of soft bodied megascopic fossils of late neoproterozoic age at numerous localities world wide there has been slow acceptance of their potential for intercontinental correlation the stratigraphic thickness of sediments separating individual occurrences of such fossils from the base of the cambrian is very varied basic questions have also been posed as to the classification of the organisms represented and hence their likely time significance recent geochronological studies support notions of a narrow time distribution well studied neoproterozoic sequences in eurasia eastern and western north america and southern australia show strikingly similar patterns of increase in the numbers and diversity of trace fossils and soft bodied megascopic remains up section though strata immediately preceding the cambrian are relatively barren other than for a sparse palynoflora and compressions of primitive plants trace fossils from australian sections relating to an early part of the ediacaran apparently overlap a time of abundance of large process bearing acritarchs and big leiosphaerids this overlap of early animal traces and distinctive acritarchs may prove to be of significant biostratigraphic importance rare discoveries of forms resembling rangea gurich in the flinders ranges of south australia precede the classical ediacara assemblage and may provide a possible correlation with occurrences of this genus in namibia the distinctive remains and trace fossils at this level constituting the rangeid hiemalora assemblage zone resemble a biota from the podolia region of the ukraine and show a similarity to finds in parts of the windermere supergroup of the northwest territories canada similarly the offshore frondose assemblage of newfoundland is comparable with the biota of charnwood forest england the type ediacara assemblage of the flinders ranges characterizing the dickinsonia costata assemblage zone is a climax biota with diverse taxa and large individual species as well as some 20 ichnogenera it closely correlates with a late redkinian or early kotlinian assemblage in the upper part of the section on the zimny gory coast of the white sea northern russia the trace fossils of these levels show that significant diversification began before the cambrian

widespread delayed mixing in early to middle cambrian marine shelfal settings abstract the radiation of burrowing metazoans in the early phanerozoic dramatically altered the properties of marine sediment an event commonly referred to as the cambrian substrate revolution or agronomic revolution the advent of infaunalization and especially biogenically mediated sediment mixing profoundly impacted the development of phanerozoic biogeochemical cycling including nutrient fluxes organic carbon burial seafloor oxygenation and sediment ecology however the timing of the development of mixed seafloor sediment has historically not been well constrained mixing has been assumed in the absence of data to occur at the precambrian cambrian boundary with the appearance of the index fossil and three dimensional burrow treptichnus pedum herein we present new ichnological stratigraphic and taphonomic data suggesting that although significant developments in infaunalization paleobiologically complex animal substrate interactions particularly burrow construction occurred during the early and middle cambrian mixing remained suppressed throughout this interval we demonstrate using a novel multi proxy approach that shelfal sediment in the earliest cambrian was essentially unmixed moreover our findings indicate that even as late as the middle cambrian 30 million years after the precambrian cambrian transition and well after the appearance of supposedly deposit feeding trilobites seafloor heterolithic shelfal sediment remained largely unmixed on a global scale these findings challenge the current assumption that mixing occurred with the first appearance of three dimensional burrows and hold important implications for the advent and development of modern style biogeochemical cycling

a field guide to finding fossils on mars the martian surface is cold dry exposed to biologically harmful radiation and apparently barren today nevertheless there is clear geological evidence for warmer wetter intervals in the past that could have supported life at or near the surface this evidence has motivated national aeronautics and space administration and european space agency to prioritize the search for any remains or traces of organisms from early mars in forthcoming missions informed by 1 stratigraphic mineralogical and geochemical data collected by previous and current missions 2 earth s fossil record and 3 experimental studies of organic decay and preservation we here consider whether how and where fossils and isotopic biosignatures could have been preserved in the depositional environments and mineralizing media thought to have been present in habitable settings on early mars we conclude that noachian hesperian fe bearing clay rich fluvio lacustrine siliciclastic deposits especially where enriched in silica currently represent the most promising and best understood astropaleontological targets siliceous sinters would also be an excellent target but their presence on mars awaits confirmation more work is needed to improve our understanding of fossil preservation in the context of other environments specific to mars particularly within evaporative salts and pore fracture filling subsurface minerals

the early paleozoic development of bioturbation evolutionary and geobiological consequences abstract bioturbation the physical and chemical mixing of sediments by burrowing animals is a critical engineering process in modern seafloor environments and exerts an important control on not only benthic ecology and sediment properties but also ocean wide biogeochemical cycling well mixed sediments have long been assumed to appear at the precambrian cambrian boundary with the first occurrence of the index fossil and three dimensional burrow treptichnus pedum however field based analyses synthesizing ichnological stratigraphic sedimentological and taphonomic data collected from lower paleozoic successions worldwide indicate that sediment mixing in marine shelf environments remained limited until at least the late silurian 120 million years after the precambrian cambrian transition in spite of early advances in complex modes of infaunalization mixed layer development had a much more gradual trajectory and did not occur in step with the first appearance of three dimensional burrows the delayed appearance of modern style intensities of sediment reworking postdating both the cambrian explosion and the great ordovician biodiversification event may be due to the late stage radiation of mobile infaunal deposit feeders biological bulldozers the organisms which are in modern marine settings the most efficient bioturbators the protracted development of the sediment mixed layer holds important implications for contemporaneous biogeochemical cycling and oxygenation of the ocean atmosphere system the delayed development of intensive sediment mixing may have also mediated exceptional preservation of both fossilized soft tissues and shallow tier trace fossils and may therefore have contributed to the anomalous preponderance of konservat lagerstatten and exceptionally preserved shallow tier trace fossils and bioglyphs characteristic of the lower paleozoic stratigraphic record

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

negligible microbial matground influence on pre vegetation river functioning evidence from the ediacaran lower cambrian series rouge france supported by shell international exploration and production b v under research framework agreement pt38181

possible evidence of primary succession in a juvenile dominated ediacara fossil surface from the flinders ranges south australia abstract ediacara fossil surfaces from the flinders ranges south australia commonly record excellent preservation quality and can provide a palaeoecological window into some of the oldest communities on earth ca 555 ma an excavated semi contiguous sandstone bed of 6 5 m 2 from a fossil locality at crisp gorge in the central flinders ranges records an abundance of taxa and structures characteristic of white sea assemblage communities stratigraphic analysis places the fossil surface within the oscillation rippled sandstone facies of the ediacara member at crisp gorge the community appears to be predominantly juvenile forms with dickinsonia costata parvancorina minchami and tribrachidium heraldicum present only within interpreted juvenile size ranges the textured organic surface contains structures including low relief ridges and round bosses but overall records a smooth bed surface and is interpreted as representing a surface with only an immature microbial mat developed before burial no effaced or decayed organisms were identified community analysis describes an intermediate shannon diversity 1 27 and an uneven community dominated by the population of d costata which comprises more than 50 of the individuals the examined parameters when combined with the presence of small juvenile taxa and an immature organic mat suggests that the community inhabiting this surface prior to its catastrophic burial may have been comparable to a modern early stage primary successional community the crisp gorge bed emphasizes that ediacara fossil surfaces from south australia span a range of developmental stages and offer a window into ediacaran sea floor communities at various stages of maturity

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

dickinsonia liftoff evidence of current derived morphologies abstract dickinsonia an iconic member of the ediacara biota is abundant in the ediacaran deposits found at the nilpena field site south australia despite exquisite fossil preservation at this site many specimens of dickinsonia appear to be incomplete with an apparently missing piece on the periphery orientation measurements from specimens on three fossil beds suggest that these so called missing pieces are aligned irrespective of the axial orientation of dickinsonia the nonrandom orientation of incomplete specimens matches that of other aligned structures found on two of these beds the preferred directionality of this feature suggests the molding of incomplete specimens under the influence of current activity prior to or during burial we propose that this feature originates where part of a dickinsonia was lifted off of the substrate during a storm event and that sand was deposited beneath this lifted portion this model suggests that dickinsonia was easily separated from the sea floor and was not attached to the substrate on which it lived this is consistent with the data from dickinsonia footprints suggesting that dickinsonia was mobile

exceptional preservation of soft bodied ediacara biota promoted by silica rich oceans reply the ediacara biota earth s earliest fossilized ecosystem of complex macroscopic multicellular organisms occurs in terminal ediacaran strata worldwide yet how the fossils are preserved remains controversial ediacara assemblages consist of exceptionally preserved soft bodied forms of enigmatic morphology and phylogenetic affinity many of these fossil assemblages are anactualistically preserved as casts and molds in sandstones ediacara style preservation here we present evidence from the ediacara member of south australia that ediacara style preservation was due to rapid early stage precipitation of silica cements facilitated by the high silica saturation state of the oceans prior to the appearance of prolific silica biomineralizers an early silicification model provides a coherent mechanistic and empirically supported explanation for the widespread preservation of soft bodied organisms of ediacaran early paleozoic age as sandstone casts and molds the prevalence of early silicification confirms that ediacara style fossil assemblages can provide an accurate window into life on the ediacaran seafloor that can be used to reconstruct critical steps in the development and diversification of early animal ecosystems

problematic fossils in the late neoproterozoic wonoka formation south australia abstract complex biogenic structures are described from the upper wonoka formation late neoproterozoic of the adelaide geosyncline south australia the structures are preserved within silty limestones and calcareous siltstones as dark bedding plane markings defining branching arrays of parallel elongate curved elements the fossils bear at least a superficial resemblance to the putative trace fossil palaeopascichnus normally preserved in siliciclastic sediments and reported from a number of late neoproterozoic sections worldwide the material from the wonoka formation is not a trace fossil and seems most likely to represent a surface encrusting alga the nature of palaeopascichnus needs to be carefully reassessed in the light of the possibility that the wonoka fossils represent a different preservational window into the same phenomenon the thin ca 2 m but widespread nature of the fossil horizon makes it a useful stratigraphic marker within the wonoka formation with the potential to aid in regional correlation within the adelaide geosyncline

taxis behaviour of burrowing organisms recorded in an ediacaran trace fossil from ukraine abstract the trace fossil archaeonassa cf fossulata fenton and fenton is a bilobate slightly undulating corrugated ridge on upper bedding plains in the ediacaran shallow marine siltstones of ukraine which are no younger than 557 ma it was produced partly under microbial mats this trace fossil shows strong orientation within a sector of 20o 40 which is approximately perpendicular to the expected shoreline the orientation points to ability of some ediacaran burrowing organisms to taxis during early evolutional stages of bilaterians in response to physical or chemical stimuli probably according to direction of tides undulations of a cf fossulata can be regarded as a record of the in and out burrowing in response to diurnal cycles of oxygen production within microbial mats probably this is one of the oldest examples of such behaviour in general archaeonassa is considered as a relatively common trace fossil in upper ediacaran deposits worldwide especially in shallow marine deposits in the time interval from 560 to 550 ma

controls on the formation of microbially induced sedimentary structures and biotic recovery in the lower triassic of arctic canada microbially induced sedimentary structures miss are reportedly widespread in the early triassic and their occurrence is attributed to either the extinction of marine grazers allowing mat preservation during the permo triassic mass extinction or the suppression of grazing due to harsh oxygen poor conditions in its aftermath here we report on the abundant occurrence of miss in the lower triassic blind fiord formation of the sverdrup basin arctic canada sedimentological analysis shows that mid shelf settings were dominated by deposition from cohesive sand mud flows that produced heterolithic rippled sandstone facies that pass down dip into laminated siltstones and ultimately basinal mudrocks the absence of storm beds and any other event beds points to an unusual climatic regime of humid quiet conditions characterized by near continuous run off geochemical proxies for oxygenation mo al th u and pyrite framboid analysis indicate that lower dysoxic conditions prevailed in the basin for much of the early triassic the resultant lack of bioturbation allowed the development and preservation of miss including wrinkle structures and bubble textures the microbial mats responsible for these structures are envisaged to have thrived on sandy substrates within the photic zone in oxygen poor conditions the dysoxic history was punctuated by better oxygenated phases which coincide with the loss of miss thus permo triassic boundary and griesbachian mudrocks from the deepest water settings have common benthos and a well developed tiered burrow profile dominated by phycosiphon the presence of the intense burrowing in the earliest triassic contradicts the notion that bioturbation was severely suppressed at this time due to extinction losses at the end of the permian the notion that early triassic miss preservation was caused by the extinction of mat grazers is not tenable

proliferation of miss forming microbial mats after the late neoproterozoic glaciations evidence from the kimberley region nw australia abstract a total of 20 morphological types of microbially induced sedimentary structures miss are recognized from the late neoproterozoic tillite bearing successions of the kimberley northwestern australia which include alpha petees triradiate cracks multidirectional linear ridges millimeter ripples erosional remnants and pockets and so on of these triradiate cracks multidirectional linear ridges and millimeter ripples are reported for the first time from the neoproterozoic worldwide most kimberley miss are morphologically comparable with their ancient and present day counterparts whose biogenicity have been well demonstrated in the kimberley during the interglacial period miss have colonization preference to relatively coarse sandy substrates ranford formation and their abundance decreased towards the younger strata throssell shale in contrast miss abundance increased from the older strata yurabi formation towards the younger strata flat rock formation during the postglacial period however overall both miss abundance and bedding plane coverage percentage increased from the marinoan younger marinoan gaskiers interglacial successions to younger marinoan gaskiers postglacial successions indicating a proliferation of microbial mats after the younger marinoan gaskiers glaciation the increase of microbial mats could have ameliorated marine biogeochemical conditions and ecosystems and thus laid the foundation for the rise of ediacaran biota in australian basins