Dimeropygidae Hupé, 1953 is a family of highly vaulted and small trilobites from the paleotropics of the uppermost Cambrian through the Ordovician. Specimens are known from Laurentia, Baltica, Avalonia, Siberia, Australia, North China, and South China. Dimeropygids are difficult to recover because of their small size and vaulted, tuberculate, and often spiny exoskeletons. Thus, most of their diversity is known from secondarily silicified material which preserves remarkable amounts of detail on the sclerites. Such faunas, while often rare, are common in the Great Basin of the western USA. Trilobite research has been conducted in the Great Basin has been since the late 1800s. Recent high intensity sampling and collection of larger sample sized from silicified horizons has increased the known diversity of trilobites from Lower Early Ordovician. New collections from the Lower Ordovician are providing crucial new insight into the groups early evolutionary history (e.g., Adrain & Westrop, 2007, McAdams & Adrain, 2009, Adrain et al., 2014a). Skullrockicurus n. gen. is a new genus of dimeropygid trilobites including at least seven new species. Five of the new species are well known enough from silicified material to formally name: S. greeni (Garden City Formation, Idaho and House Formation, Utah), S. plummeri (House Formation, Utah), S. judyi (House Formation, Utah), S. massarellai (House Formation, Utah), and S. brocki (House Formation, Utah). Synapomorphies of the new genus include four pairs of tubercles on the glabella, a posteriorly bowed glabella, long preglabellar field, and semilunate pygidium with a corona of tubercles or spines at the fulcrum.

The Laurentian trilobite genus Clelandia Cossmann, 1902, is represented by 12 named species that range from the late Cambrian to Early Ordovician. Species of Clelandia have been described from many localities in the United States, Canada, Scotland, and Greenland and attempts have been made to employ them as tools in biostratigraphic correlation. Nevertheless, important questions persist regarding the taxonomy and phylogeny of the group. No species-level phylogenetic analysis has been attempted for the genus and its family affinity has been unclear. Previous work often has produced limited numbers of small photographs which tend to mask subtle, but critical, morphological details and confuse taxonomic identification. New collections from the Great Basin of the western United States have resulted in material representing five new species of Clelandia, three of which are formally named. Other species of Clelandia are illustrated and the type species is redescribed. C. aspina and C. bispina are reported from a new locality in east-central Nevada. The first articulated specimens from a species of Clelandia are illustrated and demonstrate multiple synapomorphies of the thorax and pygidium that strongly indicate a unique, low-diversity clade of trilobites which persisted from the late Cambrian into the Early Ordovician with similarities to the Kingstoniidae. Phylogenetic analysis shows Clelandia to contain two distinct components. One component is characterized by species with glabellar furrows, widely flared posterior projections, and exsagittal pits of the occipital furrow. A more derived component consists of species with long glabellar spines, relatively narrow posterior fixigenae, bacculae, and a unique glabellar-occipital spine structure.

Previously unreported silicified trilobite faunas occur in a narrow stratigraphic interval of the Upper Cambrian (Sunwaptan) St. Charles Formation in the Bear River Range of southeastern Idaho. The faunas occur in four closely spaced rudstones and trilobite packstones indicating deposition in a shallow subtidal setting above storm wave base. At least 23 species are represented, included two undescribed genera and several undescribed species. The faunas are notable for their high trilobite abundance and pervasive silicification. Most coeval faunas have been described on the basis of small numbers of "crack-out" specimens, and the new material reveals many details of anatomy, including knowledge of most exoskeletal sclerites. The four trilobite-yielding beds contain markedly different taxon-abundance profiles, yet most species are shared between them. This suggests multiple, taphonomically-controlled samples of a similar underlying distribution, though true ecological variation cannot be discounted.

Since the East Texas area has many minerals in the categories which yield semiprecious stones of commercial value--jasper, wood agate, wood opal, and silicified stone, the author undertook this study to determine: (1) the extent which these minerals could be utilized as sources for gems; (2) the equipment necessary for cutting and polishing the stones; and (3) the techniques for finishing the gems.

Kladno-Rakovník Basin and especially its western part is well known for its abundant silicified wood, so-called as "araukarity". The occurrence of these fossils is described since the 19th century, however, modern systematic classification is lacking. Araukarity, linked mainly to the Týnec and Líně Formations, are found almost exclusively on the fields, therefore it was difficult to implement any detailed sedimentological conclusions. The Master Thesis is focused on the western part of the Kladno-Rakovník Basin, where large amount of material was discovered. After a detailed xylotomical study of thin sections and polished cross sections, two different types of wood were discerned. First related to the coniferous and cordaite wood, attributable to the of the morphogenus Araucarioxylon and the second one, rather rare and unknown in the western part of the Kladno-Rakovník Basin represents a calamite wood and it is assigned to the morphogenus Arthropitys. I was able to partially confirm Skoček's (1970) theory, that so-called black araukarity are linked to the grey (Kladno and Slaný) formations.

<p> A series of shallow intrusive and extrusive silicic volcanic rocks near Mamainse Point, Ontario, were sampled and analyzed for major and trace elements. The rocks are mainly fine grained, silicified rhyolites grading to dacites containing phenocrysts of quartz and feldspar. The analyses performed (XRF, AAS) indicate that many of these rocks have been altered from the normal igneous spectrum of rocks to potassic keratophyres. An enrichment in potash from potash metasomatism has accompanied low grade, burial metamorphism to produce a secondary mineral assemblage including chlorite, carbonate, and sericite. Local intense alteration of some rocks involved the depletion of mobile alkalis and addition of water and co2 to form calcite and kaolin. The overall field and chemical evidence suggest a single magmatic source for these rocks. </p> / Thesis / Bachelor of Arts (BA)

The late Paleozoic deposits of the Czech Republic are famous for their rich occurence of silicified stems. Despite the fact they have been often described and are well-known among scientists and collectors, their modern evaluation is lacking. This work summarizes results of recent anatomical and paleoenvironmental studies of silicified stems of the Intra Sudetic and Krkonoše Piedmont basins, where are these fossils found very frequently. Based on field research and review of public and private collections, the presence of silicified remnants was proved in several stratigraphic units. Firstly, this work deals with silicified stems of calamitaleans, which are known from the Ploužnice Horizon of the Krkonoše Piedmont Basin, and some gymnosperms. Based on anatomical studies of the secondary xylem and other related features there were found two species of calamitaleans: Arthropitys cf. bistriata and Calamitea striata. Secondly, the more abundant Agathoxylon - type of wood was divided into two groups, which are assigned to cordaitaleans, and conifers. The palaeoenvironmental conditions were partly reconstructed according to sedimentary structures and also according to cordaitaleans - conifers ratio in each wood-bearing layer. Powered by TCPDF (www.tcpdf.org)

A Formação Sete Lagoas, base do Grupo Bambuí, tem sido alvo de constantes discussões sobre o contexto temporal e ambiental sob a qual esta unidade foi depositada. Sua idade tem sido atribuída a dois momentos distintos do Neoproterozoico, e ambas têm implicações evolutivas significativas. A primeira proposta, baseadas em dados geoquímicos e litoestratigráficos,relaciona a deposição da Formação Sete Lagoas após o fim da glaciação Marinoana (do modelo paleoclimático Snowball Earth), há cerca de 635 Ma, quando mudanças paleogeográficas e geoquímicas levaram a mudanças climáticas de escala global, o quepode ter impactado significativamente na bioprodutividade do Edicarano. O segundo modelo deposicional baseia-se na ocorrência de Cloudina sp., um fóssil-guia do Ediacarano final, em níveis estratigráficos próximos à base da Formação Sete Lagoas, apontando, portanto, para uma idade mais nova que a primeira hipótese. No entanto, ambos os modelos preveem um cenário de mudanças, ocorridas no Neoproterozoico tardio, enquanto a Formação Sete Lagoas estava sendo depositada. Tais mudanças foram de natureza climática, paleogeográfica e geoquímica, que influenciaram a composição da atmosfera e da hidrosfera, e culminaram em profundas mudanças na biosfera. Propôs-se aqui uma análise pormenorizada de microbialitos e microfósseis da Formação Sete Lagoas, visando compreender como os produtores, base dos ecossistemas, teriam respondido a tantas transformações ambientais e ecológicas, além de estabelecer a abrangência estratigráfica dos microbialitos e microfósseis desta unidade. Foram analisadas tramas de microbialitos carbonáticos e precocemente silicificados, amostras de mão para comparação e dados de afloramentos. Uma avaliação de materiais reportados em meados e na segunda metade do século passado também foi necessária, tendo em vista os avanços recentes no campo da Paleobiologia do Pré-Cambriano. Os dados demonstraram que a Formação Sete Lagoas conta com uma riqueza treze formasmicrobialíticas, sendo onze detalhadas neste trabalho e encontradas ao longo de toda a formação, tanto sobre o Cráton do São Francisco, quanto sobre a Faixa Brasília, porém em baixa quantidade. Estas formas são compostas por onze tipos de tramas, cujo conteúdo biogênico em última análise, remete, mesmo que de forma reliquiar, à formas cianobacterianas recentes reconhecidas como formadoras de estromatólitos. Por outro lado, microfósseis silicificados não são comuns, e foram observados apenas em três localidades, onde já tinham sido reportados. Porém, a re-análise deste material permitiu refinar os dados e identificar cinco táxons, quatro cianobacterianos - os gêneros Siphonophycus, Oscillatoriopsis e Eosynechococcus- e um Incertae sedis - o gêneroArchaeotrichion. A baixa diversidade de microfósseis, ou seja, baixa riqueza e baixa abundância, somada à baixa abundância e densidade de microbialitos nos afloramentos analisados foi interpretada como resultados de eventos diagenéticos e tectônicos que resultaram na perda de material. Outra vertente do  presente trabalho foi a re-avaliação de estruturas reportadas como fósseis há cerca de 50 anos, cuja interpretação à luz dos conhecimentos atuais, permitiram a identificação de alguns como pseudofósseis, a reclassificação deuma espécie de acritarco esferomórfico (Leiosphaeridia jacutica[Timofeev 1966]) e de outro espécime como provável Nemiana simplexPalij 1976. De um modo geral, pode-se perceber que, embora poucos espécimes tenham sido preservados, o registro fóssil da Formação Sete Lagoas é variado e inclui microbialitos, microfósseisbentônicos e planctônicos, identificados neste trabalho, além de icnofósseis, biomarcadores e metazoários reportados em trabalhos anteriores, mas que ainda demandam novas considerações. A ocorrência vertical de microbialitos ao longo de toda a unidade e a diversidade de tramas que os compõem demonstram que a bioprodutividade não sofreu declínio com as mudanças paleoambientais, seja por conta de mudanças climáticas, se considerarmos a Formação Sete Lagoas como capa carbonática, seja pelo estabelecimento de metazoários nos ecossistemas, se a considerarmos uma unidade depositada a partir do Ediacarano tardio. / The Sete Lagoas Formation, base of BambuíGroup, has been under constant discussion about the temporal and environmental context under it was deposited. Its age has been attributed to two different moments ofNeoproterozoic, each one comprising significative evolutionay changes. The first one, based on geochemical and lithostratigraphic data, related the deposition of Sete Lagoas Formation to the end of Marinoan glacial episode (the Snowball Earthpaleoclimatic model), ca. 635 Ma, when pelogeographic and geochemical changes resulted in global climatic changes, that could result in significative impacts over the Ediacaran bioprodutivity. The second age model is based on the occurrence of Cloudinasp., an index fossil of Terminal Neoproterozoic, in stratigraphic levels near the base ofthe formation, pointing for a younger age that previously proposed. However, both modelspredict a scenario of environmental changes, occurred during the Late Ediacaran, while the Sete Lagoas Formation deposited. Such changes include climatic, paleogeographic and geochemical, that influenced the composition of atmosphere and hydrosphere, what resulted in profound changes in the biosphere. Here it was proposed a detailed study of microbialites and silicified microfossils of Sete Lagoas Formation, aiming to understand the responses of producers, the framework of any ecosystem, would reacted to suchpaleoenvironmental and ecological changes, as well also establish the stratigraphic occurrence of Sete Lagoas Formatiom microbialites and microfossils. Fabrics of carbonate and early silicified microbialites were analyzed, aswell hand samples for comparison and data acquired in the outcrops. Previous reported material, collect in the past half century was also re-evaluated due to new knowledge concerning the Paleobiology of Precambrian. The data showed that the Sete Lagoas Formation has a richness of thirteen microbialite forms, which eleven were detailed in this paper and found throughout the unit, on the São Francisco Craton, as well on the Brasília Fold Belt, but in low abundance. These forms are composed of eleven types of fabrics, which biogenic content ultimately refers, even if reliquiar preservation, to Recent cyanobacteria recognized as mat formers. Moreover, silicified microfossils are not common, and were only observed in three localities, where they had already been reported. However, re-analysis of this material allowed to refine the data and identify five taxa, four cyanobacteria - Siphonophycus, Oscillatoriopsis, Eosynechococcus- and one Incertae sedis - Archaeotrichion. The low diversity of microfossils, including low richness and low abundance, coupled with the low abundance and density of microbialites in outcrops were interpreted as a result of diagenetic and tectonic events that resulted in the loss of material. Another aspect of this work was the re-evaluation of structures reported as fossils for about 50 years, whose interpretation in the light of updated knowledge, allowed the identification of some pseudofossils as the reclassification ofa species of sphaeromorphic acritarch (Leiosphaeridia jacutica [Timofeev 1966]) and putative Nemiana simplexPalij 1976. In general, it can be seen that, although a few specimens have been preserved, the fossil record of the Sete Lagoas Formation is varied and includes microbialites, benthic and planktonic microfossils, identified in this work, as well as trace fossils, biomarkers and metazoan reported in previous works, which require new considerations. The vertical occurrence of microbialites throughout the unit and the variety of frames that make up demonstrate that bioproductivity did not declined due to paleoenvironmental changes, either due to climate change, considering the formation Sete Lagoas Formation as cap carbonate, or by establishment ofmetazoan ecosystems, if we consider a unit deposited during the Late Ediacaran.

Basée sur un vaste corpus d’œuvres en quartzite, axé sur la statuaire mais prenant aussi en compte d’autres types de monuments, l’étude vise à examiner l’utilisation de cette pierre dure par les anciens Égyptiens au Nouvel Empire, sous les XVIIIe et XIXe dynasties. Correspondant à du grès silicifié, le quartzite a été extrait du Gebel el-Ahmar au nord et des carrières d’Assouan au sud. Après avoir évoqué les caractéristiques géologiques du quartzite et sa désignation dans les anciens textes égyptiens, l’étude traite du travail dans les carrières du point de vue de son organisation et de ses aspects techniques (méthodes d’extraction, outils employés, ébauches in situ), avant d’envisager la question du transport et de la finition dans les ateliers de sculpteurs. La seconde partie, introduite par un chapitre sur l’usage du quartzite avant le Nouvel Empire, est consacrée à l’examen des œuvres du corpus replacées dans leur contexte : il permet de mettre en évidence l’essor de ce matériau au cours de la XVIIIe dynastie, avec une utilisation majeure sous les règnes d’Amenhotep III et d’Akhénaton, fortement marqués par les conceptions solaires, et un nouveau regain sous Séthi Ier, notamment à Héliopolis, et sous Ramsès II qui a cherché à imiter son prédécesseur Amenhotep III. La symbolique solaire du quartzite, due à sa couleur rouge et à l’origine mythique du Gebel el-Ahmar, explique en grande partie son emploi dans les monuments royaux et divins et en fait une pierre de prestige, presque exclusivement réservée à l’élite. Les résultats d’analyses scientifiques menées sur des objets en quartzite du musée du Louvre sont annexés au travail. / Based on a large corpus of works made of quartzite, centred on statuary but also taking into account other types of monuments, the present study is a review of this hard stone use by the ancient Egyptians during New Kingdom, mainly 18th and 19th dynasties. Quartzite or silicified sandstone was extracted from Gebel el-Ahmar quarries in the North and from Aswan quarries in the South. Having mentioned the geologic characteristics of quartzite and its name in the ancient Egyptian texts, the study deals with the work in the quarries (organization and technical aspects like extraction technologies, tools, rough or unfinished pieces found in situ) and the transport of the stone from the quarry to the workshop. The second part of the research, introduced by a chapter on quartzite use before New Kingdom, is dedicated to the monuments of the catalogue put in their context : their examination reveals the significant development of this material during the 18th dynasty, with a peak under the reigns of Amenhotep III and Akhenaton, heavily influenced by solar beliefs, and a revival under Seti Ist (especially in Heliopolis) and Ramesses II, who wanted to emulate his predecessor Amenhotep III. The use of quartzite in royal and divine monuments might be explained by its solar symbolism, due to the red colour of the stone and the mythical origin of the Gebel el-Ahmar : it is the reason why this high-value stone is almost exclusively reserved for the Egyptian elite. An appendix containing the results from scientific analysis conducted on some quartzite objects kept in the Louvre Museum completes the study.

A Formação Sete Lagoas, base do Grupo Bambuí, tem sido alvo de constantes discussões sobre o contexto temporal e ambiental sob a qual esta unidade foi depositada. Sua idade tem sido atribuída a dois momentos distintos do Neoproterozoico, e ambas têm implicações evolutivas significativas. A primeira proposta, baseadas em dados geoquímicos e litoestratigráficos,relaciona a deposição da Formação Sete Lagoas após o fim da glaciação Marinoana (do modelo paleoclimático Snowball Earth), há cerca de 635 Ma, quando mudanças paleogeográficas e geoquímicas levaram a mudanças climáticas de escala global, o quepode ter impactado significativamente na bioprodutividade do Edicarano. O segundo modelo deposicional baseia-se na ocorrência de Cloudina sp., um fóssil-guia do Ediacarano final, em níveis estratigráficos próximos à base da Formação Sete Lagoas, apontando, portanto, para uma idade mais nova que a primeira hipótese. No entanto, ambos os modelos preveem um cenário de mudanças, ocorridas no Neoproterozoico tardio, enquanto a Formação Sete Lagoas estava sendo depositada. Tais mudanças foram de natureza climática, paleogeográfica e geoquímica, que influenciaram a composição da atmosfera e da hidrosfera, e culminaram em profundas mudanças na biosfera. Propôs-se aqui uma análise pormenorizada de microbialitos e microfósseis da Formação Sete Lagoas, visando compreender como os produtores, base dos ecossistemas, teriam respondido a tantas transformações ambientais e ecológicas, além de estabelecer a abrangência estratigráfica dos microbialitos e microfósseis desta unidade. Foram analisadas tramas de microbialitos carbonáticos e precocemente silicificados, amostras de mão para comparação e dados de afloramentos. Uma avaliação de materiais reportados em meados e na segunda metade do século passado também foi necessária, tendo em vista os avanços recentes no campo da Paleobiologia do Pré-Cambriano. Os dados demonstraram que a Formação Sete Lagoas conta com uma riqueza treze formasmicrobialíticas, sendo onze detalhadas neste trabalho e encontradas ao longo de toda a formação, tanto sobre o Cráton do São Francisco, quanto sobre a Faixa Brasília, porém em baixa quantidade. Estas formas são compostas por onze tipos de tramas, cujo conteúdo biogênico em última análise, remete, mesmo que de forma reliquiar, à formas cianobacterianas recentes reconhecidas como formadoras de estromatólitos. Por outro lado, microfósseis silicificados não são comuns, e foram observados apenas em três localidades, onde já tinham sido reportados. Porém, a re-análise deste material permitiu refinar os dados e identificar cinco táxons, quatro cianobacterianos - os gêneros Siphonophycus, Oscillatoriopsis e Eosynechococcus- e um Incertae sedis - o gêneroArchaeotrichion. A baixa diversidade de microfósseis, ou seja, baixa riqueza e baixa abundância, somada à baixa abundância e densidade de microbialitos nos afloramentos analisados foi interpretada como resultados de eventos diagenéticos e tectônicos que resultaram na perda de material. Outra vertente do  presente trabalho foi a re-avaliação de estruturas reportadas como fósseis há cerca de 50 anos, cuja interpretação à luz dos conhecimentos atuais, permitiram a identificação de alguns como pseudofósseis, a reclassificação deuma espécie de acritarco esferomórfico (Leiosphaeridia jacutica[Timofeev 1966]) e de outro espécime como provável Nemiana simplexPalij 1976. De um modo geral, pode-se perceber que, embora poucos espécimes tenham sido preservados, o registro fóssil da Formação Sete Lagoas é variado e inclui microbialitos, microfósseisbentônicos e planctônicos, identificados neste trabalho, além de icnofósseis, biomarcadores e metazoários reportados em trabalhos anteriores, mas que ainda demandam novas considerações. A ocorrência vertical de microbialitos ao longo de toda a unidade e a diversidade de tramas que os compõem demonstram que a bioprodutividade não sofreu declínio com as mudanças paleoambientais, seja por conta de mudanças climáticas, se considerarmos a Formação Sete Lagoas como capa carbonática, seja pelo estabelecimento de metazoários nos ecossistemas, se a considerarmos uma unidade depositada a partir do Ediacarano tardio. / The Sete Lagoas Formation, base of BambuíGroup, has been under constant discussion about the temporal and environmental context under it was deposited. Its age has been attributed to two different moments ofNeoproterozoic, each one comprising significative evolutionay changes. The first one, based on geochemical and lithostratigraphic data, related the deposition of Sete Lagoas Formation to the end of Marinoan glacial episode (the Snowball Earthpaleoclimatic model), ca. 635 Ma, when pelogeographic and geochemical changes resulted in global climatic changes, that could result in significative impacts over the Ediacaran bioprodutivity. The second age model is based on the occurrence of Cloudinasp., an index fossil of Terminal Neoproterozoic, in stratigraphic levels near the base ofthe formation, pointing for a younger age that previously proposed. However, both modelspredict a scenario of environmental changes, occurred during the Late Ediacaran, while the Sete Lagoas Formation deposited. Such changes include climatic, paleogeographic and geochemical, that influenced the composition of atmosphere and hydrosphere, what resulted in profound changes in the biosphere. Here it was proposed a detailed study of microbialites and silicified microfossils of Sete Lagoas Formation, aiming to understand the responses of producers, the framework of any ecosystem, would reacted to suchpaleoenvironmental and ecological changes, as well also establish the stratigraphic occurrence of Sete Lagoas Formatiom microbialites and microfossils. Fabrics of carbonate and early silicified microbialites were analyzed, aswell hand samples for comparison and data acquired in the outcrops. Previous reported material, collect in the past half century was also re-evaluated due to new knowledge concerning the Paleobiology of Precambrian. The data showed that the Sete Lagoas Formation has a richness of thirteen microbialite forms, which eleven were detailed in this paper and found throughout the unit, on the São Francisco Craton, as well on the Brasília Fold Belt, but in low abundance. These forms are composed of eleven types of fabrics, which biogenic content ultimately refers, even if reliquiar preservation, to Recent cyanobacteria recognized as mat formers. Moreover, silicified microfossils are not common, and were only observed in three localities, where they had already been reported. However, re-analysis of this material allowed to refine the data and identify five taxa, four cyanobacteria - Siphonophycus, Oscillatoriopsis, Eosynechococcus- and one Incertae sedis - Archaeotrichion. The low diversity of microfossils, including low richness and low abundance, coupled with the low abundance and density of microbialites in outcrops were interpreted as a result of diagenetic and tectonic events that resulted in the loss of material. Another aspect of this work was the re-evaluation of structures reported as fossils for about 50 years, whose interpretation in the light of updated knowledge, allowed the identification of some pseudofossils as the reclassification ofa species of sphaeromorphic acritarch (Leiosphaeridia jacutica [Timofeev 1966]) and putative Nemiana simplexPalij 1976. In general, it can be seen that, although a few specimens have been preserved, the fossil record of the Sete Lagoas Formation is varied and includes microbialites, benthic and planktonic microfossils, identified in this work, as well as trace fossils, biomarkers and metazoan reported in previous works, which require new considerations. The vertical occurrence of microbialites throughout the unit and the variety of frames that make up demonstrate that bioproductivity did not declined due to paleoenvironmental changes, either due to climate change, considering the formation Sete Lagoas Formation as cap carbonate, or by establishment ofmetazoan ecosystems, if we consider a unit deposited during the Late Ediacaran.