Search

Nineteen ichnotaxa, together with algal and invertebrate remains, and various pseudo-traces and sedimentary structures are described from the Torneträsk Formation exposed near Lake Torneträsk, Lapland, Sweden, representing a marked increase in the diversity of biotic traces recorded from this unit. The “lower siltstone” interval of the Torneträsk Formation contains mostly simple pascichnia, fodinichnia and domichnia burrows and trails of low-energy shoreface to intertidal settings. The assemblage has very few forms characteristic of high-energy, soft-sediment, foreshore or upper shoreface environments (representative of the Skolithos ichnofacies). Uranium-lead (U-Pb) LA-ICPMS analysis of zircon from a thin claystone layer within the “lower siltstone” interval yielded a maximum depositional age of 584 ± 13 Ma, mid-Ediacaran. Most of the zircon is represented by rounded detrital grains that yield dates between 3.3 and 1.0 Ga. Although the age of the basal sandstone-dominated interval of the Torneträsk Formation remains elusive owing to the absence of fossils, the ichnofossil suite from the overlying “lower siltstone” interval lacks deep arthropod trackways, such as Rusophycus and Cruziana, and is suggestive of a very early (Terreneuvian, possibly Fortunian) Cambrian age. The ichnofauna is otherwise similar to early Cambrian trace fossil assemblages from other parts of Baltica, regions further south in modern Europe, and from Greenland.

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) New studies on the geologic history of Earth are increasingly revealing the complex relationships among evolutionary patterns, diversification of major groups, and environmental changes. In the fossil record of the Ediacaran Period (635–541 Ma), the appearance of macroscopically complex organisms and animals resulted in major modifications in the environment, setting the stage for the subsequent “Cambrian explosion” and the development of Phanerozoic-style ecosystems. The Ediacaran biota can be found in several localities throughout the world, and researchers on this subject are able now to divide it in mainly three Assemblages: Avalon, White Sea and Nama. Compared to other deposits around the world, studies on South American Ediacaran fossils are still in their early stages, but already show a great potential to understand the evolution of early complex life. In this context, this work aimed to investigate the taxonomy, taphonomy and age of the poorly known fossils from the Itajaí Basin (Santa Catarina, southern Brazil), as well as its relationships to other coeval fossiliferous strata. For that, a multi-approach investigation was conducted, using diverse techniques, such as: stereomicroscopic investigation; petrography; U/Pb radiometric dating (SHRIMP); scanning electron microscopy (SEM) and dispersive energy spectroscopy (EDS); computerized microtomography (µCT); and Raman and infrared spectroscopy. The results of this work are presented here in three main published and/or submitted articles regarding: [I] the description of the Itajaí Biota and its age; [II] the taphonomic characteristics of the ‘Ediacaran-style’ preservation at the Itajaí Basin; and [III] the nature of microbial filaments. In Article 1, it is reported the presence of Ediacaran soft-bodied organisms, such as Palaeopascichnus, discoidal forms (Aspidella and Nimbia), as well as abundant microbial mat features (e.g., reticulated tufts, Arumberia, and wrinkles). Moreover, the age of the Itajaí Basin is further constrained by U/Pb radiometric dating of volcanic tuffs, giving a depositional age ca. 563 Ma and setting this Ediacaran biota as one of the oldest in Gondwana. In Article 2, it is presented a detailed investigation on the microbial filaments and their possible affinities with giant filamentous sulfide-oxidizing bacteria, such as the modern Beggiatoa. This has great implications for understanding the biotic and geochemical context during Ediacaran times. In Article 3, it is provided a model to the fossilization mechanisms of the Itajaí Basin, in which the micro and macrofossils would have been preserved by volcanic and microbial activity. This work shows for the first time robust evidences for the role of clay authigenesis in the early diagenesis of fossils. In sum, this thesis provides a comprehensive take on the paleobiology, taphonomy, and age of the Ediacaran Itajaí Biota, showing that these deposits are of key importance in studies on early macroscopic complex lifeforms of the fossil record. Novos estudos sobre a história geológica da Terra estão cada vez mais revelando as relações complexas que existem entre padrões evolutivos, diversificação dos principais grupos de organismos, e mudanças ambientais. No registro fóssil do Período Ediacarano (635–541 Ma), o aparecimento de organismos macroscópicos complexos e animais resultaram em grandes modificações no ambiente, preparando o palco para a subsequente “explosão Cambriana” e o desenvolvimento de ecossistemas típicos do Fanerozoico. A biota ediacarana pode ser encontrada em várias localidades globalmente, e agora os pesquisadores do tema são capazes de dividi-la em três principais assembleias: Avalon, White Sea e Nama. Mesmo assim, comparado com outros depósitos globalmente, estudos sobre fósseis ediacaranos na América do Sul ainda estão em suas fases iniciais, mas já mostram um grande potencial para a compreensão da evolução inicial de organismos complexos. Este trabalho teve como objetivo investigar a taxonomia, tafonomia e idade dos fósseis da Bacia de Itajaí (Santa Catarina, Brasil), assim como suas possíveis relações com outros estratos fossilíferos contemporâneos. Para tanto, uma investigação de abordagem múltipla foi conduzida, usando diversas técnicas, como: estereomicroscopia; petrografia; datação radiométrica por U/Pb (SHRIMP); microscopia eletrônica de varredura (MEV) e espectroscopia de energia dispersiva (EDS); microtomografia computadorizada (µCT); e espectroscopia Raman e de infravermelho. Os resultados deste trabalho estão apresentados aqui em três artigos publicados e/ou submetidos, considerando: [I] a descrição e idade da biota de Itajaí; [II] os processos tafonômicos da preservação do ‘tipo Ediacarana’ na Bacia de Itajaí; e [III] a natureza dos filamentos micrométricos. No Artigo 1, é reportada a presença de organismos de corpo mole, como Palaeopascichnus, formas discoides (Aspidella e Nimbia), assim como abundantes texturas de esteiras microbianas (e.g., tufts reticulados, Arumberia e wrinkles). Além disso, a idade da Bacia de Itajaí é melhor restringida por datação radiométrica U/Pb de tufos vulcânicos, resultando numa idade de deposição de ca. 563 Ma e definindo esta biota ediacarana como uma das mais antigas do Gondwana. No Artigo 2, é apresentada uma detalhada investigação sobre os filamentos microbianos encontrados e suas possíveis afinidades com bactérias filamentosas gigantes oxidantes de enxofre, como o moderno gênero Beggiatoa. Estes resultados trazem implicações para a compreensão do contexto biótico e geoquímico durante o Ediacarano. No Artigo 3, é fornecido um modelo sobre os mecanismos de fossilização na Bacia de Itajaí, no qual micro e macrofósseis teriam sido preservados por meio de atividade vulcânica e microbiana. Este trabalho mostra pela primeira vez evidências robustas para o papel da autigênese de argilominerais na diagênese inicial de fósseis. Em resumo, esta tese fornece uma visão ampla sobre a paleobiologia, tafonomia e idade da bacia ediacarana de Itajaí, mostrando que estes depósitos são de importância chave para estudos sobre as primeiras formas de vida macroscópicas e complexas do registro fóssil. FAPESP: 2016/01827-4 FAPESP: 2018/21886-0

Crucial to our understanding of life on Earth is the ability to judge the validity of claims of very ancient ‘fossils’. Martin Brasier's most important contribution to this debate was to establish a framework within which to discuss claims of the ‘oldest’ life. In particular, he made it clear that the burden of proof must fall on those making the claim of ancient life, not those refuting it. This led to his formulation of the concept of the continuum of morphologies produced by life and non-life and the considerable challenges of differentiating biogenesis from abiogenesis. Martin Brasier developed a set of criteria for distinguishing life from non-life and extended the use of many new high-resolution analytical techniques to palaeontological research. He was also renowned for his work on the Cambrian explosion and the origin of animals. Although he had spent much of his early career working on the geological context of these events, it was not until he returned to studying the Ediacaran and Cambrian periods in his later years that he began to apply this null hypothesis way of thinking to these other major transitions in the history of life. This led to him becoming involved in the development of a series of nested null hypotheses, his ‘cone of contention’, to analyse enigmatic fossils more generally. In short, Martin Brasier taught us how to formulate biological hypotheses in deep time, established the rules for how those hypotheses should be tested and championed a host of novel analytical techniques to gather the data required. As a consequence, future discussions of enigmatic specimens and very old fossils will be greatly enriched by his contributions.

Submitted by LUCAS INGLEZ DOS REIS (lucas.inglez@hotmail.com) on 2018-06-06T18:02:34Z No. of bitstreams: 1 DISSERTAÇÃO -Lucas Inglez- autoarquivamento - FINAL.pdf: 12760735 bytes, checksum: 9847c1cd1dde8ad58cb47401261d84e6 (MD5) Approved for entry into archive by Ana Paula Santulo Custódio de Medeiros null (asantulo@rc.unesp.br) on 2018-06-06T19:12:52Z (GMT) No. of bitstreams: 1 inglez_l_me_rcla_par.pdf: 916449 bytes, checksum: 6c11d33d56869825ce4c8e71ffaa31dd (MD5) Made available in DSpace on 2018-06-06T19:12:52Z (GMT). No. of bitstreams: 1 inglez_l_me_rcla_par.pdf: 916449 bytes, checksum: 6c11d33d56869825ce4c8e71ffaa31dd (MD5) Previous issue date: 2018-04-12 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) A Formação Cerro Negro, Grupo La Providencia (Região das cidades de Olavarría e Barker, Argentina), compreende uma sucessão siliciclástica marinha com idade ediacarana. A unidade é composta por uma intercalação de pelitos e arenitos ricos em estruturas microbialmente induzidas (MISS), depositada sob influência de tempestades em ambiente de inter- a inframaré. Nesse contexto, camadas de evento de arenitos finos a muito finos, ricos em estruturas de deformação por sobrecarga apresentam em seu topo centenas de estruturas discoides preservadas como relevo completo (epirelevo positivo + endorelevo + epirelevo negativo). Os discos densamente distribuídos no acamamento ocorrem como protuberâncias centimétricas (5 – 140 mm) de epirelevo liso em oposição a sua superfície inferior radialmente enrugada e marcada por uma depressão central. Tais feições, juntamente com a distribuição de frequências de tamanho e presença de deformação mútua de indivíduos em contato lateral levaram a interpretação dos discos como tafomorfos do plexus Aspidella. Entretanto, os contextos sedimentares e tafonômicos das estruturas discoides ornamentadas (EDO) argentinas, bem como sua morfologia interna complexa, impedem sua associação direta com o registro de macrobiotas em outras unidades ediacaranas. Assim, de modo a elucidar a gênese e preservação das ED em termos de sua natureza biótica ou abiótica, foi proposta a aplicação de uma série de técnicas analíticas, tais como: 1) contagem e medições sistemáticas das estruturas em campo, observando a distribuição de classes de tamanho em distintas populações de discos, 2) secção e escaneamento de slabs de rocha, de modo a acessar suas feições internas, 3) análise secções delgadas ao microscópio óptico e eletrônico de varredura (MEV), 4) análise por microtomografia computadorizada (Micro-CT), compondo modelos tridimensionais das estruturas. Assim, o uso combinado de diferentes técnicas permitiu discutir as EDO diante de duas hipóteses alternativas, HA-I e II, as quais compreendem: I- Uma origem biológica, de acordo com a qual, perturbações em subsuperfície seriam produzidas por uma comunidade infaunal produzindo tubos verticais simples (icnofósseis tipo-Skolithos), que podem ou não culminar em discos horizontalmente radiados (icnofósseis tipo-Asterosoma). II – Uma natureza abiótica, implicando nos discos como produtos da ascensão de sedimento fluidificado interagindo com o substrato microbialmente estabilizado. Tal hipótese explica a correlação entre os discos e as feições de liquidificação observadas, o que lhe confere maior poder de síntese. Além do mais, a HA-II independe do rompimento de paradigmas biológicos e paleontológicos, sendo compatível com a interpretação presente na literatura para ocorrências semelhantes. Dessa forma, conclui-se que as EDO sejam estruturas problemáticas, com gênese provavelmente associada a processos de fluidificação e injeção de sedimentos em interação com substratos bioestabilizados, caracterizando assim um pseudofóssil. The Cerro Negro Formation, La Providencia Group (Olavarría and Barker municipalities Argentina) comprises a marine siliciclastic succession of ediacaran ages. The unit is composed of intercalated mudstones and sandstones rich in microbially induced structures (MISS) and deposited under the influence of storms in inter- to subtidal settings. In this context, event beds of fine to very fine sandstones are rich in overload deformation features (liquidization processes). They also commonly exhibit on its upper surface hundreds of discoidal strucutures preserved in full relief. The densely distributed discs occur as centimetric protuberances (5 to 140 mm) with a smooth upper surface and a radially symmetric wrinkled underside, which is marked by a central depression. These characters, along with their size frequency distribution and the occurrence of mutually deformed individuals, led to the interpretation of the discs as probable taphomorphs of the plexus Aspidella. However, the sedimentary and taphonomic context of the Argentinian Ornamented Discs (OD), as well as their complex internal morphology, prevent direct association with macrofossils from other Ediacaran units. Thus, in order to elucidate the genesis and preservation of the discs in terms of their biotic or abiotic nature, I proposed the application of a series of analytical techniques, including: 1) Systematic counting and measuring the discs in the field, understanding the size distribution of different disc populations; 2) sectioning and scanning rock slabs in order to observe internal features; 3) analyses of thin sections under optical and electron scanning microscopes (MEV); 4) scanning with Micro-computorized Tomography (Micro-CT) to observe the tridimensional distribution of internal features. The combined use of these techniques allowed the discussion of the OD under the light of two main alternative hypothesis, AH-I and AH-II, that comprise: AH-I) A biogenic genesis, in which subsurface perturbations were originated by an infaunal community producing simple vertical tubes (Skolithos-like traces), that may or may not culminate in horizontal radiated discs (Asterosoma-like traces). AH-II) An abiotic origin, in which the discs arethe product of the ascension of fluidized sediments interacting with a microbially bounded substrate. This hypothesis explains the observed correlation between discs and the liquidization features, thereby providing it greater synthesizing power. The AH-II is also independent of the breaking of biological and paleontological paradigms and it is compatible with the interpretation of similar occurrences in the literature. As such, I consider the OD as a problematic structure probably associated to migrating fluidized sediments, trapped under a biostabilized substrate. In this interpretation, therefore, they are considered pseudofossils. FAPESP: 15/24608-3

International audience; Titanite-bearing microtubes in metabasalts have been interpreted as evidence for early microbial life thriving in the oceanic crust up to 3.5 Ga ago based on similarities with microtubular pitting occurring in modern volcanic glass. An alternative abiogenic origin as ambient inclusions trails (AITs) has been debated but textural evidence such as the absence of diagnostic terminal inclusions was used to discard this possibility. Here, we describe a variety of microtubes occurring in pyroclastic tuff of the 2.72 Ga Tumbiana Formation, Western Australia, some of which resemble titanite-filled microtubes reported in metamorphosed Archean pillow basalts. To assess the origin of the Tumbiana microtubes, we investigated their structure and chemistry and their root zone down to the sub-micrometer scale using a combination of Raman microspectroscopy, scanning electron microscopy (SEM), focused ion beam (FIB) milling and scanning transmission electron microscopy (STEM) coupled with energy dispersive X-ray spectrometry (EDXS). We report four types of microtubes. Type 1 comprises calcite microtubes. Type 2 comprises AITs showing terminal pyrite and trails with negative crystal shapes. Type 3 comprises titanite microtubes in chlorite displaying morphologies similar to those reported in ~3.5 Ga old Archean lavas. At the sub-micrometer scale, they display a dendritic structure. Depending on their localization, Type 3 microtubes have been divided in three main sub-types: i) Type 3A extends in pores filled by chloritized cement, ii) Type 3B occurs in pyroclasts, and iii) Type 3C overgrows and thus post-dates Type 2 AITs. Type 4 comprises titanite microtubes confined to quartz and calcite rims. Types 3 and 4 microtubes are terminated by sub-micrometric carbonaceous and/or mineral inclusions. Altogether, these features suggest that the Tumbiana titanite microtubes have formed as dendritic AITs associated with displacement of mineral and/or organic inclusions in pyroclasts and in surrounding void-filling cements during recrystallization. They are therefore unlikely to represent relics of the activity of early microbial life, rather abiotic features formed in the presence of organic matter during burial metamorphism. In that sense, they may represent some sort of indirect evidence for life.

Sedimentary features in eolian sandstones with plane-parallel lamination of the Botucatu Formation, situated in a quarry in Novo Hamburgo (RS), southern Brazil, were preciously interpreted as possible plant imprints. They show very variable shapes, comprising: a) small, isolated, lenticular or lamellar molds with oblique borders; b) aggregated molds, comprising divergent or intercepting, rarely radiated geometry; c) large, lenticular or lamellar molds with small molds transversally to their margins; d) rounded or oval-shaped molds, some with small molds along their margins. The shapes and distribution of these imprints indicate their origin from the dissolution isolated and aggregated gypsum (CaSO42H2O) crystals, an evaporitic mineral common in desertic environments. The gypsum was precipitated as large crystals (“selenitic gypsum”) within eolian sheet sands shortly after their deposition. Gypsum dissolution was promoted by the later percolation of meteoric groundwaters throughout the sandstones, leaving molds delineated by iron and manganese oxides. Therefore, the studied imprints represent pseudofossils, without any relationship with plants.