The Mackenzie Mountains of NW Canada contains a superb record of biotic evolution through the late Ediacaran-early Cambrian that is ideal for studying the biological, ecological, behavioural, and environmental innovations that occurred during the Ediacaran and basal Cambrian. Newly discovered Ediacara-type megafossils in the uppermost Blueflower Formation at Sekwi Brook include tubes possibly attributable to suspension-feeding annelids, the preserved top of a large frond holdfast, and several problematica. These fossils represent the youngest and shallowest Ediacaran fossils known from NW Canada, and differ significantly from the communities of deep-water rangeomorphs preserved lower in the succession. Behavioural evolution of the infauna through the Ediacaran and earliest Cambrian can be observed in the rich trace fossil records of the Blueflower and Ingta formations. Trace fossils in the lower part of the Blueflower Formation are characterized by millimeter-diameter, simple, horizontal burrows of microbial grazers and deposit feeders that demonstrated very primitive and inconsistent two-dimensional avoidance strategies. Upper Blueflower trace fossils additionally include three-dimensional avoidance burrows and oblique burrows of filter-feeders or predators, reflecting new behavioural innovations and increased three-dimensional use of the substrate. The Cambrian strata of the Ingta Formation further include probing, U-shaped, and radiating burrows, irregular networks, and arthropod trails. These new feeding strategies were accompanied by increasingly more systematic grazing burrows. The development of more diverse feeding styles upwards through the succession both caused and reflected the spatial and temporal disappearance of Proterozoic matgrounds and their replacement by Phanerozoic mixgrounds. Avoidance strategies among grazing burrows became more consistent and complicated upward throughout this succession, increasingly resembling the guided meanders of Phanerozoic trace fossils. This implies that, while the first avoidance burrows probably reflected the responses of individual burrowers to individual stimuli, genetically-coded programmed behaviour developed and became dominant in the earliest Cambrian. These observations imply that increases in sensory and neural capacity accompanied skeletonization as a major factor in the Cambrian explosion of animal life. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2014-01-27 12:37:17.741

Submitted by Israel Vieira Neto (israel.vieiraneto@ufpe.br) on 2015-03-04T18:57:34Z No. of bitstreams: 2 TESE Letícia Chinglino Mendizábal.pdf: 6158345 bytes, checksum: db330a328ce998d184840c64a1611c7d (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) / Made available in DSpace on 2015-03-04T18:57:34Z (GMT). No. of bitstreams: 2 TESE Letícia Chinglino Mendizábal.pdf: 6158345 bytes, checksum: db330a328ce998d184840c64a1611c7d (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Previous issue date: 2013-10-29 / CAPES / O Grupo Ubajara localiza-se no Domínio Médio Coreaú, nordeste da Província Borborema, constitui uma sequência de plataforma marinha rasa, conformada a base ao topo por arenitos da Formação Trapiá, pelitos da Formação Caiçaras, calcários e margas subordinadas da Formação Frecheirinha, e no topo arenitos e guarvacas da Formação Coreaú. Os carbonatos da Formação Frecheirinha apresenta valores negativos de (δ 13C -3.5 ‰ e +3.7 ‰) em direção ao topo, e razão de 87Sr/86Sr entre 0.7075 e 0.7080. Pela primeira vez, são descritos para uma sequência do nordeste do Brasil, micorfossies de parede orgânica que se caracterizam pela baixa diversidade, compreendendo espécimens de Leiosphaeridia e Bavlinella subordinada. Esses dados, combinados com restrições de idade mínima de 560 ± 19 Ma determinada para diques máficos que cortam a unidade, sugerem uma idade de deposição Ediacarana entre 635 e ca. 580 Ma, para a Formação Frecherinha. A diferença de outras unidades carbonáticas Ediacaranas no Brasil, a Formação Frecherinha não tem depósitos glaciais associados, ou características sedimentares típicas das capas carbonaticas pósglaciais. Os valores negativos de δ 13C refletem a bioprodutividade e as alterações do nível do mar no momento de deposição. Os carbonatos da Formação Frecheirinha são importantes para a compreensão da biota e as concomitantes mudanças na composição isotópica da água do mar, como também na reconstrução paleogeográfica entre os episódios de quebra do supercontiente Rodinia e a fusão do Gondwana.

The nature of the Ediacaran macrobiota (c. 580-541 Ma) remains puzzling. These first assemblages of large, complex fossils may have included early animals; giant microbial forms; and organisms representing radically different body plans that went extinct. Discoidal impressions – some forming the base of Ediacaran fronds but most found as isolated discs – dominate the Ediacaran macrobiota. However round markings may also be formed in a variety of abiogenic ways. This study investigates the nature and biogenicity of discoidal impressions from two Ediacaran successions: the c. 560-Ma upper Burway Formation, Longmyndian Supergroup, Shropshire, UK; and several sites on the Bonavista and Avalon Peninsulas, Newfoundland, Canada, ranging in age from 565–c. 560 Ma. The investigation involved fieldwork, photography, serial grinding through cross-sections, and optical and scanning electron microscopy. It concludes that several Longmyndian discoidal forms are pseudofossils formed by sediment injection resulting from small-scale fluid escape inferred to be driven by microbial mat sealing. Turning to clearly biogenic impressions, comparison of the varied morphologies of holdfast discs associated with fronds preserved under ash and sand from several Newfoundland sites leads to a generic model of their architecture as consisting of enclosed chambers, a complex construction perhaps for strength or possibly symbiosis. Detailed observations of the rayed disc Hiemalora suggest that it may have had an amoeboid lifestyle. Finally, the key Ediacaran taxon Aspidella is separated from the discs Ediacaria and Spriggia, with which it has been synonymized, and interpreted as a possible polyp-like animal capable of limited movement. This thesis thus demonstrates that the earliest reported Ediacaran discoidal impressions are abiogenic, produced by mat-influenced processes particularly relevant to the Precambrian, and proposes models and interpretations for several key Ediacaran forms that have important implications for both the nature and diversity of the Ediacaran macrobiota, and early animal evolution.

The evolution of the Metazoa is among the greatest success stories in Earth history. From modest origins, probably in the Cryogenian (~720 - 635 Ma), metazoans had acquired hard parts, and a vast range of life strategies and body plans by the middle Cambrian (around 520 Ma). This leaves a long delay between the origin of the Metazoa and their rise to ecological dominance. A popular explanatory hypothesis for this delay is that atmospheric oxygen levels, low in the Proterozoic (< 0.001 % PAL), began to rise towards modern levels towards the end of the Neoproterozoic. Among the earliest known putative metazoans are Namacalathus, Namapoikia and Cloudina, calcified marine invertebrates abundant in the latest Ediacaran (~ 548-541 Ma) Nama Group, Namibia. Although they were pioneers of metazoan biomineralisation, little is known of their affinities or palaeocology. The Nama Group, a well-characterised, relatively undeformed mixed carbonate and siliciclastic succession, provides a rare opportunity to investigate the palaeoecology of these important organisms in their environmental context. New geochemical data from the Nama Group confirm the heterogeneity of Ediacaran redox conditions. These contextualise in situ fossil assemblages which reveal diverse ecological strategies among the calcified metazoans of the Nama Group, and offer constraints on their affinities. Based on its large size (< 1 m), modular body plan and internal structure of interlinked tubules, Namapoikia was a long-lived specialist and possible Poriferan. I show that Namapoikia colonised both lithified and living microbial substrates in oxic, mid-ramp reef crypts. By contrast, size and occurrence data show that Namacalathus was an environmental generalist, forming large, thick aggregations in persistently oxic, mid-ramp reef environments but opportunistically exploiting the transiently oxic, inner ramp setting. Bilaterally symmetrical, asexual budding and a microlamellar skeletal ultrastructure suggest that Namacalathus may have been an early lophophorate, and had flexible growth depending on environmental setting, showing a cup diameter of 2 – 35 mm, and size distributions varying with substrate type, redox and water depth. In oxic mid-ramp reefs, Cloudina constructed large (> 20 m) reefs showing mutual attachment and consistent orientation in life position, making it the earliest known reef-building metazoan and suggesting that it was a passive suspension feeder. I further present food webs based on fossil assemblages from Ediacaran to Cambrian Stage 4 carbonate successions and evaluate their usefulness in tracking metazoan trophic diversification in the early Cambrian. Ediacaran redox conditions were a major control on the ecologies of the earliest metazoans. A requirement for oxygen made persistently oxic conditions a prerequisite for complex and long-lived ecologies, while highly flexible life strategies were used to exploit changeable environments. Ediacaran metazoans represent a phylogenetic and ecological foreshadowing of the complexity of the Phanerozoic, but it was not until much later that the Metazoa would attain their evolutionary potential.

Research carried out in the Ediacaran of eastern Newfoundland focused on two projects: sedimentology of the Conception and St. John’s groups exposed on the Bonavista Peninsula; and taxonomic descriptions of the small, stemmed frondose fossils at Mistaken Point on the Avalon Peninsula. Sedimentological study of the upper Conception and lower St. John's groups at Catalina Dome on Bonavista Peninsula extends our understanding of the Conception Basin, in which the oldest known complex, deep marine organisms lived, by a factor of two. Mudstone-rich turbidites dominate the succession, and a lack of wave-generated structures or other shallow-water indicators support the interpretation that the depositional environment was deep-marine. The basal part of the succession contains seismoturbidites that show no evidence of horizontal translation, implying that deposition occurred on a flat basin plain. Strata higher in the succession exhibit horizontally slumped beds, implying a transition into slope deposition. Turbidite ripple marks show a change in paleocurrent direction from eastward to southward in the Trepassey Formation, consistent with a change from convergent to strike-slip tectonics that occurred diachronously across the basin. Volcanic ash beds are more common in the Catalina Dome succession than on the Avalon Peninsula, reflecting deposition closer to the volcanic source. These volcanic beds are associated with diverse fossil assemblages rich in rangeomorphs that locally persist into the Fermeuse Formation, in contrast with the Avalon Peninsula where the Fermeuse Formation contains only simple discoid fossils. This taphonomic window lends support to the hypothesis that the form genus Aspidella represents the holdfasts of Ediacaran fronds. Stemmed small frond fossils from Mistaken Point, Avalon Peninsula, have often been informally referred to as “featherdusters”, but due to their small size and consequent poor preservation, they have not until now been formally described. The small, stemmed fronds are more diverse than previously realized, and include representatives of taxa described from elsewhere in Newfoundland, juveniles of other Mistaken Point fronds, and two new monospecific genera. This biodiversity suggests that the basal elevated tier that the small fronds occupied was competitive, with convergent evolution of frondose taxa showing distinct architecture and constructions, but broadly similar size and shape. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2013-10-30 12:12:23.297

Rangeomorphs are a distinct group of millimeter- to meter-scale soft-bodied macrofossils that are restricted to the latter half of the late Neoproterozoic Ediacaran Period (635Ma- 542Ma). These fossils represent an extinct higher level taxon characterized by a modular construction based on a single architectural unit: the centimeter-scale, chevron-shaped rangeomorph element which displays several orders of self-similar branching. These elements could be arranged in a variety of different ways, constituting the wide array of gross morphologies found within the Group Rangeomorpha. The largest and most diverse assemblage of rangeomorph fossils in the world is found at Mistaken Point, on the Avalon Peninsula of Newfoundland, Canada, where these organisms are preserved within their original, in situ paleocommunities. Multibranched rangeomorphs are typified by bush-, comb- and network-shaped fossils which display multiple rangeomorph-bearing structures attached to an untethered basal stolon or central attachment point. Multibranched, comb-shaped rangeomorphs are endemic to Mistaken Point, and are represented by fossils displaying multiple parallel struts emerging along one side of an elongate, curved pedicle rod. Morphological and taphonomic evidence suggests that, in life, this organism had two rows of struts, each bearing a rangeomorph frondlet, arranged in an alternating pattern along the curved, tubular pedicle rod. Biometric analyses imply that the struts were added to both ends of the pedicle rod throughout the organism’s lifetime, with later inflation of the rangeomorph frondlets. Each comb-shaped rangeomorph locality likely represents a different age cohort within the organism’s lifecycle, providing rare evidence for spatfall reproduction in Ediacarans, which is similar to that found in modern macrobenthic organisms with pelagic larvae. Network-shaped multibranched rangeomorphs, represented by symmetrical to asymmetrical net-like fossils, are also endemic to Mistaken Point. This genus is reconstructed as having a symmetrical arrangement of flexible, rangeomorph-bearing leaflets that were, in part, neutrally buoyant with respect to the seawater. This flexible leaflet structure is unique, and shared only with a rare, previously undescribed, Ediacaran frond-like organism. It is suggested that the enigmatic leaflet structures shared by these two morphologically distinct taxa represent a new type of rangeomorph branching architecture, and therefore constitute a new type of rangeomorph. / Thesis (Master, Geological Sciences & Geological Engineering) -- Queen's University, 2008-07-25 11:01:43.469

No description available.

Ediacaran phosphorites provide a principal record of the paleoenvironmental and paleoecological conditions of the oceans during Earth's second major oxygenation and the evolution of complex life. Although the fidelity of this record is high, diagenesis and metamorphism frequently alter or overprint primary minerals and structures, necessitating validation of results from mineralogical and geochemical analyses and determinations of fossil affinities. Therefore, it is imperative to unravel the complications of post-depositional alteration, and thus provide a strong foundation for environmental and biological interpretations, via an integrated sedimentological, stratigraphic, petrographic, and geochemical approach. Transmitted light, cathodoluminescence, and scanning electron microscope petrography in conjunction with Raman spectroscopic and X-ray diffraction analyses were employed to determine the origin of phosphorites from the early Ediacaran (632 – 614 Ma) Doushantuo Formation at the Wanjiagou section, near Zhangcunping, Hubei Province in South China. Results suggest granular phosphorites were deposited during one to two episodes of reworking of pristine phosphorite hardgrounds, which originated during redox-controlled and/or microbially-mediated phosphogenesis. Granular laminae were then cemented by a ferric iron-phosphate mineral, phosphosiderite. As a product of oxidative weathering and/or thermal stabilization of ferrous iron-phosphates (e.g., vivianite), this cement is suggestive of precipitation from ferruginous porewaters. This is the first direct evidence for iron-phosphate minerals in Ediacaran phosphorites and substantiates previous hypotheses of P burial beyond primary calcium phosphate. If accumulation and burial of phosphorites during this interval was rapid enough to have limited P availability and thus primary productivity, their formation may have governed oxygen production prior to the Neoproterozoic Oxygenation Event (NOE). Oxygenation of the oceans during the NOE and the appearance of complex, multicellular life are suspected to be causally linked within the Ediacaran. However, a fragmented fossil record with insufficient analogues and varied taphonomic modes leaves much of the Ediacaran fauna with uncertain taxonomic and phylogenetic affinities, leading to ambiguity regarding their life modes and environmental associations. Furthermore, demonstrating biogenicity is an often overlooked, yet fundamental component of Ediacaran fossil identification and interpretation, something that has particularly affected the morphologically simple discoidal group of fossils known colloquially as Aspidella. Petrographic observations supported by Raman and energy dispersive spectroscopy provide evidence that discoidal concretions from the Ediacaran Miaohe Member near Maxi, Hubei Province in South China are diagenetic in origin but superficially resemble Aspidella's morphology. Erosion of these syn-compactional concretions produced concentric rings on bedding planes caused by internally deformed laminae resulting in Aspidella pseudofossils. These results highlight the necessity for critical evaluation of the origin of discoidal structures observed in Ediacaran sedimentary successions. / Master of Science / Contemporary and ancient phosphorus-rich sedimentary deposits, known as phosphorites, precipitate within the oceans as a result of intricate chemical and biological interactions. The Ediacaran Period (635 – 539 million years ago) contains the first truly extensive occurrences of phosphorites in addition to a fossil record of the earliest animal organisms. Deposited after the end of Earth's last global glaciation, the origins of Ediacaran phosphorites are affiliated with these dramatic climatic and evolutionary transitions as well as the rise of atmospheric and oceanic oxygen concentrations to near modern levels. Deposition of phosphorites often occurs in low-oxygen oceanic environments and their formation constitutes the dominant mechanism by which phosphorus is removed from the phosphorus cycle on time scales greater than 1000 years. Therefore, phosphorite occurrences provide a record of phosphorus cycling, oxygen availability, and biological productivity. However, microscopic and chemical analyses of phosphorites from the Ediacaran Doushantuo Formation in South China demonstrate they are partially composed of phosphorus minerals that likely formed in non-oxygenated environments. The presence of these atypical phosphorus minerals has been previously hypothesized, with the implication that they further limited the availability of phosphorus for use by photosynthetic organisms. Such a limitation on photosynthesis would have resulted in decreased oxygen production and thus the formation of these phosphorites may explain the rate and trend of the change in oxygen concentrations observed during the Ediacaran. Ediacaran fossils also act as a proxy for environmental conditions of the ancient oceans through inferences about the preserved organisms' requirements for life. Although most fossils of this age are the first of their kind in terms of biological complexity, they are typically simple in terms of their morphology, making identification difficult. Furthermore, providing evidence that such simple structures actually represent a fossilized organism is often problematic due to the inability to compare them with modern organisms. Microscopic and chemical analyses of disc-shaped structures from the Ediacaran Miaohe Member in South China reveal that they are concretions that were not created by an organism, even though their morphology very closely resembles the Ediacaran fossil Aspidella. Identification of these concretions as pseudofossils suggests that close examination of fossils from Ediacaran rocks is necessary.

This thesis makes several contributions to improve our understanding of Proterozoic-Cambrian evolution of eukaryote life. Chapter 1 provides, for the first time, a quantitative characterization of the evolutionary trends of Proterozoic macroalgae. The analysis reveals that morphological disparity of Paleoproterozoic macroalgae was low but increased in the Mesoproterozoic and Ediacaran, with a plateau in between. There was also a significant increase in thallus surface/volume ratio and maximum canopy height of the Ediacaran macroalgal communities. The prolonged plateau between the Mesoproterozoic and Ediacaran may be related to either nutrient stress or the absence of animal grazing pressure. The Ediacaran increase in surface/volume ratio and morphological complexity may have been driven by decreasing pCO₂ levels and increasing animal grazing pressure. Chapter 2 presents a systematic re-examination of the carbonaceous compression fossils Protoarenicola baiguashanensis Wang, 1982, Pararenicola huaiyuanensis Wang, 1982, and Sinosabellidites huainanensis Zheng, 1980, from the early Neoproterozoic Liulaobei and Jiuliqiao formations in northern Anhui, North China. These fossils were previously interpreted as worm-like metazoans. Our study reveals new morphological features that weaken the metazoan interpretation. Instead, the new data indicate that these fossils can be alternatively interpreted as erect epibenthic organisms, possibly coenocytic algae. Chapter 3 examines two important eukaryote fossils: Horodyskia Yochelson and Fedonkin, 2000, and Palaeopascichnus Palij, 1976, from the upper Ediacaran chert of the Liuchapo Formation in central Guizhou, South China. These exceptionally preserved fossils offer us a unique opportunity to investigate their body constructions and affinities. The morphologies of Horodyskia and Palaeopascichnus support a phylogenetic relationship with agglutinated foraminifers, shedding new light on the divergence of bikont eukaryotes, the rise of rhizarians, and the ecological importance of heterotrophic eukaryotes in Proterozoic ecosystems. Chapter 4 focuses on Cambrian microfossils that represent the primary producers' cyanobacteria and eukaryotic phytoplankton (acritarchs). Careful investigation of the basal Cambrian Yanjiahe Formation in the Yangtze Gorges area and the Yurtus Formation in the Aksu area revealed abundant acanthomorphic acritarchs, clustered coccoidal microfossils, filamentous cyanobacteria, and tubular microfossils. This study confirms previous stratigraphic correlation between the Yanjiahe and Yurtus formations and suggests that animals and phytoplankton radiated in tandem during the Cambrian explosion. / Ph. D.

The Ediacaran Period (635-542 Ma) just preceded the radiation of animals, yet witnessed profound changes in biological innovation, including the first appearance of large spiny acritarchs called the acanthomorphic acritarch, followed by the radiation of the Ediacara biota (575-542 Ma), and earliest recognizable bilaterally symmetrical animals (~550 Ma). It has been proposed that key environmental events, such as the termination of the Cryogenian glaciations, the Neoproterozoic Acraman impact event, and oxygenation of the deep oceans may have played an integral role in the evolution of Ediacara organisms and early animals. However, the extent to which these events shaped biological evolution remains elusive. The Doushantuo Formation in South China, radiometrically constrained between 635.2±0.6 and 551.1±0.7 Ma, is ideal for high-resolution interdisciplinary research, and has the potential to clarify the relationship between environmental and biological events. Research in this dissertation aims to address the following questions: (1) was the Doushantuo Formation deposited in an open marine or a (partially) restricted basin; (2) are Doushantuo paleoenvironmental and biostratigraphic proxies consistent with an Ediacaran oxidation event; and (3) can the Doushantuo acanthomorphic acritarchs be useful biostratigraphic tools for the Ediacaran Period? Detailed (sub-meter) sampling of six sections in the Doushantuo Formation in the Yangtze Gorges area of South China reveal a complex depositional history. Eight broad lithostratigraphic facies and 6 cycles packaged into 3 sequences can be identified and potentially traced into basinal sections. It is likely that the deposition of the Doushantuo Formation occurred under open marine conditions and became increasingly restricted with the development of thick carbonate accumulations at the platform margin. Geochemical analysis shows extreme isotopic variability in the Doushantuo Formation that may be the result of pulsed oxidation of a deep oceanic organic carbon reservoir. Oxidation events may have had further implications on the radiation of early animals. Distinct assemblage biozonation of the Doushantuo acanthomorphic acritarchs is concurrent with isotopic variability, suggesting an ecological and/or evolutionary response during the early Ediacaran. Further efforts in refining the internal geochronology of the Doushantuo Formation is needed in order to test competing hypotheses on the radiation of important taxonomic groups. / Ph. D.