new probable cnidarian fossils from the lower cambrian of the three gorges area south china and their ecological implications abstract lower cambrian assemblages of phosphatic and chitinous tubular fossils of probable cnidarian affinities were recovered from the yanjiahe shuijingtuo and shipai formations in the three gorges area south china terreneuvian cambrorhytium cf c major co occur with an unnamed taxon in the yanjiahe formation they can be compared with specimens from the ediacaran miaohe fauna in the three gorges area the most abundant and diversified cnidarian assemblages including cambrorhytium gracilis n sp cambrorhytium cf major cambrorhytium minor sphenothallus songlinensis sphenothallus taijiangensis sphenothallus kozaki sphenothallus sp byronia sp and mackenzia sp are reported from the overlying cambrian stage 3 4 shuijingtuo and shipai formations these new fossils show previously unknown evidence for cnidarian affinities such as an attachment disk clonal clusters and probable budding structures these diversified assemblages of probable cnidarian fossils further fill major gaps in the cambrian record of stem metazoans and document associated early evolutionary patterns in addition our discovery suggests that along with sponges these tubular fossils represent another important component of benthic ecosystems that colonized often dysoxic deep settings during the cambrian explosion the observed increases of average body size and biomineralization among these probable cnidarians are tentatively linked to oxygenation of deep oceanic settings and appearance of predatory pressure during the ediacaran cambrian transition respectively

demise of ediacaran dolomitic seas marks widespread biomineralization on the siberian platform the trigger for biomineralization of metazoans in the terminal ediacaran ca 550 ma has been suggested to be the rise of oxygenation or an increase in seawater ca concentration but geochemical and fossil data have not been fully integrated to demonstrate cause and effect here we combine the record of macrofossils with early marine carbonate cement distribution within a relative depth framework for terminal ediacaran to cambrian successions on the eastern siberian platform russia to interrogate the evolution of seawater chemistry and biotic response prior to ca 545 ma the presence of early marine ferroan dolomite cement suggests dominantly ferruginous anoxic aragonite dolomite seas with a very shallow oxic chemocline that supported mainly soft bodied macrobiota after ca 545 ma marine cements changed to aragonite and or high mg calcite and this coincides with the appearance of widespread aragonite and high mg calcite skeletal metazoans suggesting a profound change in seawater chemistry to aragonite seas with a deeper chemocline by early cambrian stage 3 the first marine low mg calcite cements appear coincident with the first low mg calcite metazoan skeletons suggesting a further shift to calcite seas we suggest that this evolution of seawater chemistry was caused by enhanced continental denudation that increased the input of ca into oceans so progressively lowering mg ca which combined with more widespread oxic conditions facilitated the rise of skeletal animals and in turn influenced the evolution of skeletal mineralogy

evolution of primary producers and productivity across the ediacaran cambrian transition abstract nearly all extant animal phyla first appeared during the ediacaran cambrian transition a revolution in primary producer ecology and marine productivity has been proposed as a bottom up ecological driver for this rapid diversification of metazoans however the control s driving the evolution of primary producers and primary productivity around the ediacaran cambrian transition and their potential relationship to the cambrian explosion are not fully understood in this study we measured the nitrogen content and the nitrogen isotopic composition of kerogen in the piyuancun and hetang formations using samples collected from the chunye 1 well on the lower yangtze block in western zhejiang our isotope results suggest that nitrate was the dominant n source fueling primary productivity during deposition of the entire piyuancun formation and lower hetang formation with only a minor contribution from n 2 fixation quantitative reconstructions of paleoproductivity based on organic carbon and pyrite content and sedimentation rate indicate that productivity either stayed the same or increased during the transition from the piyuancun formation to the overlying hetang formation thus fixed n availability was not the ultimate factor limiting primary productivity during the ediacaran cambrian transition combining our data with published nitrogen isotope records from the early middle ediacaran to cambrian stage 4 suggests that no 3 was the dominant n species fueling phytoplanktonic productivity during the broad cambrian explosion interval from its earliest roots in the ediacaran through the main episode in cambrian stage 3 eukaryotes lack the ability to fix nitrogen and preferentially assimilate nitrate the no 3 dominated euphotic zone from the early middle ediacaran to cambrian stage 3 may have promoted the radiation of relatively large eukaryote phytoplankton which may have been an important driver of early animal diversification

new high resolution age data from the ediacaran cambrian boundary indicate rapid ecologically driven onset of the cambrian explosion the replacement of the late precambrian ediacaran biota by morphologically disparate animals at the beginning of the phanerozoic was a key event in the history of life on earth the mechanisms and the time scales of which are not entirely understood a composite section in namibia providing biostratigraphic and chemostratigraphic data bracketed by radiometric dating constrains the ediacaran cambrian boundary to 538 6 538 8 ma more than 2 ma younger than previously assumed the u pb ca id tims zircon ages demonstrate an ultrashort time frame for the lad of the ediacaran biota to the fad of a complex burrowing phanerozoic biota represented by trace fossils to a 410 ka time window of 538 99 0 21 ma to 538 58 0 19 ma the extremely short duration of the faunal transition from ediacaran to cambrian biota within less than 410 ka supports models of ecological cascades that followed the evolutionary breakthrough of increased mobility at the beginning of the phanerozoic

skeletal faunas of the lower cambrian yu anshan formation eastern yunnan china metazoan diversity and community structure during the cambrian age 3 abstract the lower cambrian stage 3 yu anshan formation in yunnan province south china hosts the chengjiang lagerstatte an exceptional window on the cambrian explosion however skeletal microfossils from this formation have long been neglected owing to the dominance of siliciclastics over carbonates here we characterize a new assemblage of small shelly fossils from the maotianshan shale member of the yu anshan formation the assemblage consists of univalved mollusc hyolith and brachiopod shells trilobite and bradoriid carapaces chancelloriid sclerites sponge spicules and echinoderm ossicles combining this information with taxonomic data previously tabulated for fossil assemblages from three other facies we performed quantitative comparisons of the genus level taxonomic diversity and modes of life and nutrition of four mutually equivalent early cambrian age 3 paleocommunities 1 skeletal faunas of the inner shelf 2 predominantly soft bodied faunas of the intra shelf basin 3 archaeocyathan faunas of the carbonate shelf and 4 sponge dominated faunas of the slope to basin areas the taxonomic and paleoecological distinctness of these four paleocommunities indicate possible low levels of competition within the communities and rapid expansion of habitat ecospace ranges though with similarities in the taxonomic composition of poriferans and arthropods reflecting the rapid migration of these two groups into new habitats the present integrative study provides a more comprehensive portrait of metazoan diversification and paleocommunity evolution during the peak phase of the cambrian explosion than do investigations based on single communities

the terminal ediacaran tubular fossil cloudina in the yangtze gorges area of south china abstract the advent of biomineralizing metazoans in the terminal ediacaran age ca 550 539 ma represents a remarkable biological innovation in the history of life as a poster child of this evolutionary episode cloudina is widely regarded as a weakly biomineralizing tubular fossil with a global distribution therefore cloudina can both inform the evolution of animal biomineralization and facilitate terminal ediacaran stratigraphic correlation however this key taxon has not been fully described from the yangtze gorges area of south china where classical terminal ediacaran strata have been investigated extensively by paleontologists stratigraphers and geochemists here we document an assemblage of three dimensionally silicified tubular fossils from siliceous dolostone of the terminal ediacaran baimatuo member of the dengying formation in the yangtze gorges area western hubei province south china the baimatuo assemblage consists of sinotubulites which has been previously known in the baimatuo member as well as cloudina including c ningqiangensis c hartmannae c cf carinata and c sp indet and other unnamed tubular forms this discovery adds to the diversity of early biomineralizing metazoans in the yangtze gorges area and facilitates the biostratigraphic correlation of the cloudina sinotubulites co occurrence assemblage in terminal ediacaran strata

transitional ediacaran cambrian small skeletal fossil assemblages from south china and kazakhstan implications for chronostratigraphy and metazoan evolution abstract the ediacaran cambrian transition records distinct evolutionary changes of metazoans the ediacaran fossils i e ediacara type biota and tubular fossils are contrasting with the diverse small skeletal fossils ssfs from the early cambrian the apparent dissimilarities hindered studies deciphering their evolutionary relationships this also led to a popular assumption that there exists a mass extinction of the ediacara biota and cloudinids at the precambrian cambrian pc c boundary here we report for the first time a transitional fauna which consists of typical elements of ediacaran i e cloudinids and related tubicolous organisms together with cambrian ssfs including protoconodonts anabaritids and siphogonuchitids from south china and maly karatau kazakhstan the sediments yielding the transitional fauna are characterized by siliceous rocks in both regions and were previously considered to be unfossiliferous their chronostratigraphic assignment in south china has been debated for years based on the new fossil assemblage the siliceous strata of the daibu member northeast yunnan south china and the basal kuanchuanpu formation south shaanxi south china can be assigned to the earliest cambrian ssf biozone anabarites trisulcatus protohertzina anabarica assemblage zone and thus can be considered of early cambrian in age a new subzone of the earliest ssf zone in eastern yunnan south china is proposed herein defined as ganloudina symmetrica rugatotheca typica interval subzone the new fauna demonstrates that the cloudinids originally confined to the late ediacaran persisted into the cambrian fortunian and no major extinction event occurred at the pc c transition

extinction of cloudina and namacalathus at the precambrian cambrian boundary in oman biostratigraphic carbon isotope and u pb zircon geochronological data from the ara group of oman indicate an abrupt last appearance of cloudina and namacalathus coincident with a large magnitude but short lived negative excursion in the carbon isotope composition of seawater that is globally coincident with the precambrian cambrian boundary u pb zircon age data from an intercalated ash bed directly define this negative excursion to be at 542 0 0 3 ma consistent with previous age constraints from siberia and namibia combined with the global biostratigraphic record these new data strengthen hypotheses invoking mass extinction within terminal proterozoic ecosystems at or near the precambrian cambrian boundary

nitrogen cycle perturbations linked to metazoan diversification during the early cambrian abstract the rapid diversification of metazoans during the late ediacaran early cambrian is one of the most remarkable evolutionary events in earth history however the triggering mechanism remains highly contentious particularly concerning the relationship of this biological event to contemporaneous changes in ocean redox and nutrient cycling in this study we report new bulk nitrogen isotope 15n and organic carbon isotope 13corg data from the lower cambrian niutitang formation in two deep water sections in south china to provide a better understanding of the relationship of the nitrogen cycle ocean redox and biological evolution during this key period the 15n data from two study sections are characterized by consistently low values 1 to 2 throughout the niutitang formation despite large variations in 13corg we interpret these low 15n values to have resulted from assimilation of recycled ammonium nh4 and n2 fixation compilation of available 15n data reveals large temporal and spatial 15n variations from 1 to 7 in time equivalent strata in south china such 15n variations imply the co existence of aerobic and anaerobic n cycles and highly heterogeneous ocean redox conditions during the early cambrian in south china which is consistent with inferences from other geochemical proxies temporal fluctuations and spatial heterogeneity in ocean redox conditions may have controlled the distribution and evolution of metazoans during the early cambrian

neoproterozoic to early cambrian small shelly fossil assemblages and a revised biostratigraphic correlation of the yangtze platform china abstract small shelly fossils ssfs occur widely on the yangtze platform and have great potential for biostratigraphic subdivision of pre trilobitic early cambrian strata based on the ssf record of the shallow water realm five biozones can be recognized for the meishucunian stage in ascending order the biozones are anabarites trisulcatus protohertzina anabarica assemblage zone paragloborilus subglobosus purella squamulosa assemblage zone watsonella crosbyi assemblage zone formerly heraultipegma yunnanensis zone poorly fossiliferous interzone sinosachites flabelliformis tannuolina zhangwentangi assemblage zone in addition one ssf biozone is recognized for the overlying qiongzhusian stage pelagiella subangulata taxon range zone the formerly used siphogonuchites triangularis paragloborilus subglobosus zone and heraultipegma yunnanensis zone are discussed and redefined approximately 80 species of ssfs were screened for their spatial and temporal distribution on the yangtze platform variations in lithofacies and biofacies can be recognized throughout the yangtze platform extending over an area of 2000 900 km in a deeper water shelf setting the first zone is represented by the protohertzina anabarica kaiyangites novilis assemblage zone while younger zones are not recognized in the southern region at the northern platform margin the qiongzhusian is represented by the ninella tarimensis cambroclavus fangxianensis assemblage zone and the rhombocorniculum cancellatum taxon range zone the southeastern shaanxi western hubei region followed a slightly different lithological and faunal development than the rest of yangtze platform indicating a stronger similarity with parts of east gondwana some taxa such as w crosbyi p subangulata r cancellatum microdictyon effusum a trisulcatus protohertzina unguliformis and p anabarica occur nearly worldwide and support an international correlation of early cambrian sequences between the yangtze platform and smaller west gondwanan blocks siberia newfoundland and australia the six investigated zones of the yangtze platform comprise an interval spanning the early nemakit daldynian to the late atdabanian early botoman stage on the siberian platform palaeobiogeographic analysis revealed a strong taxic similarity between the yangtze platform and the tarim platform a smaller number of species are shared with other west gondwanan platform fragments such as india and iran palaeobiogeographic results do not support the previously reported position of the south china block between australia and siberia during the early cambrian

redox dependent distribution of early macro organisms evidence from the terminal ediacaran khatyspyt formation in arctic siberia abstract the ediacaran period witnessed the first appearance of macroscopic animal life in earth s history however the biogeochemical context for the stratigraphic occurrence of early metazoans is largely uncertain in part due to the dearth of integrated paleobiological and chemostratigraphic datasets in this study a comprehensive geochemical analysis was conducted on the fossiliferous khatyspyt formation in arctic siberia in order to gain insights into the ediacaran paleoenvironments this study was designed to specifically address the relationship between paleoredox conditions and ediacaran fossil occurrences in the khatyspyt formation our data reveal a dramatic shift in pyrite sulfur isotope compositions 34 s pyrite from ca 20 to ca 55 and this shift is intriguingly associated with the first occurrence of ediacara type macrofossils at the studied section suggesting a possible link between seawater redox conditions and distribution of early macroscopic organisms based on multiple lines of sedimentological and geochemical evidence we propose that the development of oceanic euxinia which may be widespread in the continental margins due to enhanced oxidative weathering in the terminal ediacaran period may have locally prohibited the colonization of ediacara type organisms and resulted in low 34 s pyrite values in the lower khatyspyt formation in the middle and upper khatyspyt formation progressive secular transition from euxinic to non euxinic and more habitable conditions may have allowed for the colonization of ediacara type and other macro organisms

reconstruction of paleoceanic redox conditions of the lower cambrian niutitang shales in northern guizhou upper yangtze region abstract the paleoceanic redox conditions and the vertical and spatial distribution of organic matter rich lower cambrian niutitang shales are varied in the upper yangtze region china an integrated approach including organic geochemistry major and trace elemental geochemistry and x ray diffraction xrd mineralogy was used to characterize changes in redox conditions and to determine key controls on organic matter accumulation during deposition of the lower cambrian niutitang shales a 202 m long cored well located in kaiyang county in northern guizhou china was thoroughly characterized by the integrated approach in this study vertically total organic carbon toc rich siliceous and argillaceous black shales were developed in the lower and middle niutitang formation and toc lean silty shales were found in the upper niutitang formation the toc content in the lower and middle niutitang shales ranges from 0 27 to 6 7 with an average value of 2 1 and it decreases from 0 30 to 0 11 in the upper niutitang formation shales the toc rich siliceous shales in the lower niutitang formation were characterized by high total sulfur content enrichment in redox sensitive trace elements high corg p ratios and high authigenic mo u covariation indicating they were deposited under persistent anoxic conditions most organic rich shales from the middle niutitang formation were deposited under anoxic conditions whereas a few intervals having low toc contents were deposited in a predominantly oxic depositional environment in contrast the upper niutitang formation were deposited under fully oxic conditions a combination of high primary productivity and enhanced organic preservation under euxinic water column conditions is the key control on organic matter accumulation in the lower niutitang formation shales however a coupling of redox depositional environment and terrestrial mineral dilution plays an important role in organic matter accumulation and preservation in the middle niutitang formation similar organic matter abundance distribution and carbon isotope excursion of organic matter in the sediments deposited at different depositional facies on the yangtze platform suggest regional isotopically homogenous organic carbon input due to the widespread transgressive event with deep basinal waters being transported into the shallow shelf environments at the base of the lower cambrian as a result 13corg distribution patterns can be used as a stratigraphic correlation marker in the upper yangtze region

detrital zircon age and biostratigraphic and chemostratigraphic constraints on the ediacaran cambrian transitional interval in the irkutsk cis sayans uplift southwestern siberian platform

precambrian cambrian boundary global stratotype ratified and a new perspective of cambrian time the precambrian cambrian boundary global stratotype is the base of the phycodes pedum zone at fortune head southeastern newfoundland the initial two stage radiation of the phanerozoic fauna the appearance of phanerozoic aspect trace producers and subsequent origin of diverse skeletalized metazoans was earliest cambrian fossil assemblages with deep complex burrows or originally mineralized skeletal fossils with exception of cloudina are early cambrian or younger correlation into avalon indicates that strata once referred to the proterozoic e g manykaian or nemakit daldynian and rovno stages are lowest cambrian and that the siberian tommotian stage is middle lower cambrian the thick sequence and complex epeirogenic history of the placentian series as compared with the trilobite bearing branchian series suggest that most early cambrian time is represented by the subtrilobitic lower cambrian

carbonate carbon isotope chemostratigraphy and u pb zircon geochronology of the liuchapo formation in south china constraints on the ediacaran cambrian boundary in deep water sequences abstract the ediacaran cambrian transition was one of the most significant intervals in geological history witnessing the origin of the metazoans and major environmental changes establishing a precise chronostratigraphic framework for the ediacaran cambrian transition has great significance for understanding the geological and evolutionary processes during this transition an integrated study on carbonate carbon isotopes and u pb zircon dating was conducted within the liuchapo formation in the sifangjing section in northeastern guizhou province south china to recognize the ediacaran cambrian boundary in slope facies of the yangtze block a substantial negative carbonate carbon isotope excursion was recognized within the lower part of the liuchapo formation moreover a weighted mean u pb zircon age of 540 7 3 8 6 6 ma was obtained from a tuffaceous interlayer approximately 2 m above the interval of the negative carbon isotope excursion the carbon isotope and age dating results indicate that the ediacaran cambrian boundary within the sifangjing section should be placed in the lower part of the liuchapo formation additionally in the sifangjing section a distribution of horodyskia minor extends up to the basal cambrian while the last appearance datum lad of palaeopascichnus jiumenensis correlates to the large negative carbon isotope excursion within the liuchapo formation this relationship indicates that the lad of the palaeopascichnus jiumenensis is a potential tool for the stratigraphic correlation of the ediacaran cambrian boundary successions in slope and deep water basin settings of the yangtze block

a horodyskia nenoxites dominated fossil assemblage from the ediacaran cambrian transition liuchapo formation hunan province its paleontological implications and stratigraphic potential abstract because of the scarcity of fossil data life evolution in deep water settings through the ediacaran cambrian transitional interval is still poorly understood this study describes a horodyskia nenoxites dominated fossil assemblage from the chert of the liuchapo formation in liujiata village western hunan province which was deposited in a slope to basinal setting at the terminal ediacaran and earliest cambrian in this assemblage horodyskia covers the longest range possibly from the upper part of the lower ediacaran to the base of the cambrian other members including three types of nenoxites helanoichnus shaanxilithes and two affinity undetermined forms appear in the upper part of the liuchapo formation the whole assemblage exhibits an upward increasing complexity and fossil abundance which reaches its acme at a few meters below the cambrian xiaoyanxi formation regardless of the lithology of the host rock these fossils are exclusively preserved with clay minerals and devoid of any detectable concentration of carbon such a preservation mode is dominant among the known records of these fossils worldwide and possibly related to an unknown biological commonality of these organisms microscope observations support a body fossil origin of nenoxites and contradict the trace fossil interpretation meanwhile some large horodyskia show features implying a close relation to testate amoebae however despite some resemblances the differences between these fossils and any suggested relatives are considerable taking all the information together we tentatively interpret this fossil assemblage as a diverse and complex deep water community of protist grade organisms the worldwide occurrence of some members in this assemblage endows them with a biostratigraphic potential nevertheless to establish such a tool more quality data of fossil occurrences and referential radiometric ages and a better understanding of the interplay between these organisms and sedimentary environments are required

geochronological constraint on the cambrian chengjiang biota south china the cambrian chengjiang biota of south china provides compelling fossil evidence for the rapid appearance of metazoan phyla in earth history the cambrian explosion however the timing of the chengjiang biota is poorly constrained owing to lack of datable rock materials within the maotianshan shale that yields the fossils here we integrate secondary ion mass spectrometry sims and chemical ablation isotope dilution thermal ionization mass spectrometry ca id tims u pb analyses of detrital zircons from the maotianshan shale to provide high precision geochronological constraint on the chengjiang biota the youngest group of sims u pb detrital zircon dates yields an age peak at 520 ma six zircons from this group are further dated by the ca id tims u pb technique but suggesting that they were not formed from a single zircon growth event thereby neither the age peak nor the weighted mean age defined by the youngest sims u pb dates could represent the maximum depositional age of the maotianshan shale instead the youngest ca id tims u pb date 518 03 0 69 0 71 ma 2 analytical uncertainty incorporates u pb tracer calibration uncertainty provides the first robust maximum age of the chengjiang biota this new geochronological constraint on the chengjiang biota indicates that the cambrian explosion reached its major phase around 518 03 0 69 0 71 ma demonstrating a protracted process 22 myr for the cambrian explosion supplementary material sims and ca id tims zircon u pb data are available at https doi org 10 6084 m9 figshare c 4024849

marine redox stratification on the earliest cambrian ca 542 529 ma yangtze platform abstract in order to explore the marine redox structure on the earliest cambrian ca 542 529 ma yangtze platform south china new fe mo c s geochemical data from the slope xugongping section for the liuchapo and the base of niutitang formation are reported here integrated fe speciation and mo abundance data from the xugongping section in combination with previously published data from slope basinal longbizui section and others suggest oxic surface waters and ferruginous deep waters coexisting with occasional mid depth euxinic waters during the fortunian stage and with widespread euxinic waters during the early stage 2 marine transgression a compilation of new and published sulfur isotope data of pyrite for the liuchapo and the base of niutitang formations presents high isotopic values mostly 10 and distinctly different spatiotemporal gradient characteristics during the fortunian stage and the beginning of the stage 2 we propose that redox stratification developed in the earliest cambrian protected basin and eustatic change and the connectivity of the protected basin with the open ocean controlled the materials supply from riverine input and open ocean reservoir and thus spatiotemporal variability of ocean chemistry

the end of the ediacaran two new exceptionally preserved body fossil assemblages from mount dunfee nevada usa evaluation of hypotheses that relate environmental to evolutionary change across the ediacaran cambrian transition has been hampered by a dearth of sections that preserve both the last appearance of ediacaran body fossils and the first appearance of treptichnus pedum within carbonate rich strata suitable for chemostratigraphic studies here we report two new exceptionally preserved latest ediacaran fossil assemblages from the deep spring formation at mount dunfee nevada usa further we report these occurrences in a high resolution carbon isotope chemostratigraphic framework permitting correlation on a regional and global scale the lower of the two horizons at the base of the deep spring formation hosts a body fossil assemblage that includes gaojiashania other vermiform body fossils and possible wutubus annularis interbedded with cloudina shell beds the upper of the two fossil horizons in the esmeralda member of the deep spring formation contains conotubus and occurs within the basal cambrian negative carbon isotope excursion establishing it as the youngest ediacaran fossil assemblage discovered to date this is the first report of gaojiashania conotubus and wutubus in laurentia extending the known stratigraphic ranges and biogeographic distributions of these taxa to a global scale these data refine the relative ages of defining characteristics of the ediacaran cambrian boundary and confirm that a large perturbation to the carbon cycle and surface ocean conditions coincided with the extinction of ediacaran organisms

observations of gas hydrates in marine sediments offshore northern california biogenic gas hydrates were recovered in shallow cores 6 m deep from the eel river basin in offshore northern california between 40 38 and 40 56 n the gas hydrates contained primarily methane 13c 57 6 to 69 1 and occurred as dispersed crystals small 2 20 mm nodules and layered bands within the sediment these hydrates recovered in sediment at water depths between 510 and 642 m coincide nearly but not exactly with areas showing bottom simulating reflectors bsrs on seismic reflection records this study confirms indirect geophysical and geologic observations that gas hydrates are present north of the mendocino fracture zone in sediment of the eel river basin but probably are absent to the south in the point arena basin this discovery extends the confirmed sites of gas hydrates in the eastern pacific region beyond the peruvian and central american margins to the northern california margin

the neoproterozoic huttenberg δ13c anomaly genesis and global implications abstract the neoproterozoic huttenberg formation in northeastern namibia records a remarkable 13 c carb positive excursion with a sustained plateau of values up to 12 i e the huttenberg anomaly high resolution chemostratigraphic analyses of drill core samples spanning the upper elandshoek and huttenberg formations reveal multiple new observations 1 overall high but oscillatory 13 c carb values 2 18 o carb values ranging from 8 to 2 3 significant enrichment of 13 c in organic carbon and a broad co variation between 13 c carb and 13 c org 4 a profound negative excursion in 34 s pyrite from 30 to 10 5 an overall inverse 13 c 34 s relationship and 6 87 sr 86 sr values down to 0 7074 in limestone samples the new data suggest that the huttenberg anomaly records dynamic fluctuations in marine redox conditions which may include an oxygenation event during the height of the 13 c carb positive excursion and a deoxygenation event at its termination the 34 s pyrite negative excursion suggests the buildup of the marine sulfate reservoir likely due to enhanced pyrite oxidation during the oxygenation event the 34 s pyrite increase at the end of the huttenberg anomaly may result from a seawater sulfate concentration drawdown towards pre anomaly conditions on one hand the huttenberg anomaly may reflect restricted basin signals that are deviated from the ediacaran open ocean on the other hand the ediacaran huttenberg anomaly together with the cryogenian 13 c carb positive excursions suggests a stepwise pattern of the neoproterozoic oxygenation event both local and global environmental factors may have contributed to the huttenberg anomaly the huttenberg anomaly therefore represents a local enhancement of global oxygenation signals our data support the emerging view that the neoproterozoic oxygenation event may have facilitated the evolution of early life at that time

microbial and animal evolution in relation to redox fluctuations in a deep water setting of south china during the ediacaran cambrian transition ca 551 523 ma abstract the ediacaran cambrian e c transition witnessed significant ecosystem perturbations of the oceanic environment e g oxygen concentrations of seawater and biological evolution however in spite of abundant ediacara type megafossils trace fossils small shelly fossils ssfs macroscopic algae and metazoans recovered from shallow water e c transition strata throughout south china the manifestation of geological events in deep water settings remains elusive here we present new paleontological and geochemical evidence from the 38 m thick deep water liuchapo formation ca 551 523 ma of the yangtou section northeastern guizhou province china which consists mainly of chert through the e c transition the liuchapo formation can be divided into two members based on biostratigraphy and redox proxies the lower member 0 32 m is characterized by low mo al 0 15 1 82 ppm and u al 0 47 2 51 ppm values that suggest deposition under suboxic conditions these deposits are dominated by horodyskia minor paleopascichnus jiumenensis spherical cyanobacteria myxococcoides and random acritarchs the upper member 32 38 m records a transition to anoxic non sulfidic conditions as suggested by marked increases in mo al 5 47 ppm and u al 8 810 ppm the upper member contains ssfs sponge spicules filamentous cyanobacteria multicellular algae and sheet like fossils the survival of diverse organisms under strongly reducing conditions reflected in the upper member suggests that marine redox fluctuations may limit the growth of late ediacaran organisms and provide the living space and elevated nutrients for early cambrian biota

cambrian evolutionary radiation context correlation and chronostratigraphy overcoming deficiencies of the first appearance datum fad concept abstract use of the first appearance datum fad of a fossil to define a global chronostratigraphic unit s base can lead to intractable correlation and stability problems fads are diachronous they reflect species evolutionary history dispersal biofacies preservation collection and taxonomy the cambrian evolutionary radiation is characterised by diachronous fads biofacies controls and provincialism of taxa and ecological communities that confound a stable lower cambrian chronostratigraphy cambrian series and stage definitions require greater attention to assemblage zone successions and non biostratigraphic particularly carbon isotope correlation techniques such as those that define the ediacaran system base a redefined basal cambrian trichophycus pedum assemblage zone lies above the highest ediacaran type biotas vendobionts putative metazoans and calcareous problematica such as cloudina and the basal asteridium tornatum comasphaeridium velvetum zone acritarchs this definition and the likely close correspondence of evolutionary origin and local fad of t pedum preserves the fortune head newfoundland gssp of the cambrian base and allows the presence of sub cambrian branched ichnofossils the sub tommotian equivalent base of stage 2 a suggested laolinian stage should be defined by the i l4 zhuce 13 c positive peak bracketed by the lower ranges of watsonella crosbyi and aldanella attleborensis molluscs and the skiagia ornata fimbrioglomerella membranacea zone acritarchs the w crosbyi and a attleborensis fads cannot define a stage 2 base as they are diachronous even in the newfoundland type w crosbyi zone the series 2 base cannot be based on a species fad owing to the provincialism of skeletalised metazoans in the terreneuvian series 2 boundary interval and global heterochrony of the oldest trilobites a series 2 and stage 3 a suggested lenaldanian series and zhurinskyan stage new gssp base is proposed at the siberian lower atdabanian 13 c iv peak which correlates into south china avalonia and morocco and assigns the oldest trilobites to the terminal terreneuvian series

a deep root for the cambrian explosion implications of new bio and chemostratigraphy from the siberian platform much uncertainty remains as to the temporal relationship between the ediacaran and cambrian biotas yet this is critical to our understanding of the rise of metazoans here we present new high resolution carbon isotope chemostratigraphy and biostratigraphy for a terminal ediacaran to cambrian succession on the eastern siberian platform russia which shows the presence of a succession of diverse fossil assemblages before the start of the basal cambrian negative carbon isotope excursion bace soft bodied ediacaran biota beltanelliformis occur before the start of the late ediacaran positive carbon isotope plateau epip a mixed ediacaran and cambrian skeletal biota cloudina anabarites cambrotubulus appears within the epip and diverse cambrian type small shelly fossils including protohertzina and other protocondonts halkieriids chancelloriids hyoliths hyolithelminthes and the burrowing trace fossil diplocraterion appear at the beginning of the bace these integrated data show that taxa attributed to so called ediacaran and earliest cambrian skeletal biotas in fact overlap without notable biotic turnover and thus refute the presence of a large isotope excursion coincident with mass extinction of all ediacaran biota we propose a new biozone the cloudina namacalathus sinotubulites assemblage zone to precede the known small shelly fossil ssf zones these observations raise doubts as to whether there is any true separation between the ediacaran and cambrian skeletal biotas and suggest that there is a deep root for the cambrian explosion of metazoans

deep water dissolved iron cycling and reservoir size across the ediacaran cambrian transition abstract the majority of the deep ocean was likely under ferruginous conditions during the first four billion years of earth s history as the atmosphere was gradually oxygenated the sources sinks redox cycling and reservoir size of dissolved iron in the deep ocean are likely to have changed dramatically whether deep water was thoroughly oxygenated by the time of the ediacaran cambrian transition and the relationship of this oxygenation to the cambrian explosion remains debated to explore the degree of oceanic oxygenation and its effect on cambrian explosion we measured the iron isotopic composition 56fe of bulk rock i e cherts and mudstones shales through the piyuancun and hetang formations using samples collected from the chunye 1 core on the lower yangtze block in western zhejiang the limited variation in 56fe values 0 55 during the end ediacaran and cambrian stages 1 3 to

dynamic redox conditions control late ediacaran metazoan ecosystems in the nama group namibia the first appearance of skeletal metazoans in the late ediacaran 550 million years ago ma has been linked to the widespread development of oxygenated oceanic conditions but a precise spatial and temporal reconstruction of their evolution has not been resolved here we consider the evolution of ocean chemistry from 550 to 541 ma across shelf to basin transects in the zaris and witputs sub basins of the nama group namibia new carbon isotope data capture the final stages of the shuram wonoka deep negative c isotope excursion and these are complemented with a reconstruction of water column redox dynamics utilising fe s c systematics and the distribution of skeletal and soft bodied metazoans combined these inter basinal datasets provide insight into the potential role of ocean redox chemistry during this pivotal interval of major biological innovation the strongly negative 13c values in the lower parts of the sections reflect both a secular global change in the c isotopic composition of ediacaran seawater as well as the influence of local basinal effects as shown by the most negative 13c values occurring in the transition from distal to proximal ramp settings critical though is that the transition to positive 13c values postdates the appearance of calcified metazoans indicating that the onset of biomineralization did not occur under post excursion conditions significantly we find that anoxic and ferruginous deeper water column conditions were prevalent during and after the transition to positive 13c that marks the end of the shuram wonoka excursion thus if the c isotope trend reflects the transition to global scale oxygenation in the aftermath of the oxidation of a large scale isotopically light organic carbon pool it was not sufficient to fully oxygenate the deep ocean both sub basins reveal highly dynamic redox structures where shallow inner ramp settings experienced transient oxygenation anoxic conditions were caused either by episodic upwelling of deeper anoxic waters or higher rates of productivity these settings supported short lived and monospecific skeletal metazoan communities by contrast microbial thrombolite reefs found in deeper inner and mid ramp settings supported more biodiverse communities with complex ecologies and large skeletal metazoans these long lived reef communities as well as ediacaran soft bodied biotas are found particularly within transgressive systems where oxygenation was persistent we suggest that a mid ramp position enabled physical ventilation mechanisms for shallow water column oxygenation to operate during flooding and transgressive sea level rise our data support a prominent role for oxygen and for stable oxygenated conditions in particular in controlling both the distribution and ecology of ediacaran skeletal metazoan communities

namacalathus cloudina assemblage in neoproterozoic miette group byng formation british columbia canada s oldest shelly fossils the uppermost part of the miette group windermere supergroup in eastern british columbia has yielded shelly macrofossils in cliff forming biostromal carbonates byng formation the biostromes are made up of two principal elements intergrowths of complex sinuous plate like stromatolites cf platella and intervening planar to curviplanar pockets filled with packstone and wackestone crowded with namacalathus and cloudina presumed calcified metazoans of uncertain biological affinities preservation is best in limestone and the shells are mostly obliterated where the carbonate is dolomitized this assemblage was previously known only from the nama sequence in namibia the new find in the antipodal miette group in the canadian rocky mountains greatly extends its geographic range and suggests a more widespread distribution in similar facies in intermediate areas both assemblages constitute the earliest occurrences of shelly fossils in their respective regions

first finds of problematic ediacaran fossil gaojiashania in siberia and its origin we describe the first occurrence of the problematic fossil gaojiashania outside china in the ediacaran yudoma group of the siberian platform in both areas gaojiashania characterizes the lower upper ediacaran strata and precedes the appearance of cloudina and other skeletal fossils which highlights its significance for the ediacaran subdivision and correlation features of this fossil such as indeterminate length the absence of a distinct growth pattern and self avoiding behaviour indicate its trace fossil origin but do not necessarily imply metazoan affinities for its producers several organisms including stem group social amoebozoans and unicellular protists may have been proterozoic trace fossil producers

predicting oil quality from sidewall cores using pfid tec and nir analytical techniques in sandstone reservoirs rio del rey basin cameroon abstract the expense and uncertainty of obtaining fluid samples from mdt tools provide a strong incentive for an alternative method for assessing oil character sidewall cores which are inexpensive and easy to obtain contain sufficient oil for microanalyses that can provide indications of oil quality degree of degradation api gravity and numerous additional characteristics including sulfur content acid number and viscosity the present study is concerned with the application of the micro techniques pfid pyrolysis flame ionization detection tec thermal extraction chromatography and nir near infra red spectroscopy for the characterization of oil from sidewall cores taken from two exploration wells in the rio del rey basin of cameroon in 1993