No description available.

On the basis of freezing and thawing tests of air-entrained concretes having poor quality cherts as course aggregates subjected to three different treatments for improving durability, the following conclusions have been derived: 1. Removal of cherts lighter than the BSSD specific gravity of 2.5 by heavy liquid definitely improved the durability of the concrete. 2. Combining 50 percent durable aggregate (1/2"-1/4" size) with 50 percent cherts (1"-1/2" size) did not show any significant improvement in durability over that containing 100 percent chert. 3. As much as 12 percent chert could be blended with durable aggregate without an appreciable reduction in durability. / Master of Science

The Lost River Groundwater Drainage Basin in Warren County, Kentucky, is a karst drainage system encompassing 55 square miles (143 square kilometers) developed within the Mississippian St. Louis and Ste. Genevieve Limestones. Near the contact between these two formations are two bedded chert units, the Lost River Chert Bed (Elrod, 1899) within the Ste. Genevieve and the Corydon Chert Member (Woodson, 1983) of the St. Louis, which appear to be perching layers to shallow karst groundwater flow. Groundwater may be seen flowing on top of these beds in various cave streams and at swallets and springs throughout the basin. In order to compare the vertical positions of these layers to shallow karst groundwater flow, geologic structure maps of the Lost River Chert Bed and the Corydon Chert Member were prepared for the basin, along with a contour map of the water table (at or near which shallow karst groundwater flow is assumed to take place) over the same area. These surfaces were digitized, then contoured and compared using SURFACE II and DISSPLA computer graphics systems. Correlation was accepted for points where the water table is either 20 feet (6.1 meters above or below the top of the two chert layers. The water table (at baseflow conditions) was found to correlate with the Lost River Chert Bed over 42.6% of the basin, as well as 40.7% for the Corydon Member. Shallow karst groundwater flow is found to correlated with bedded chert layers over 83.3% of the study area, and therefore it is concluded that chert layers have a dominant effect on the vertical position of groundwater flow within the Lost River Groundwater Drainage Basin.

Modificações nas concentrações iônicas em substratos de água rasa provocadas por micro-orgnaismos vêm demonstrando valorosas relevâncias tanto em fossilizações quanto precipitações de calcita, aragonita, dolomita, pirita e minerais de sílica e fosfato. Dados micropaleontológicos, petrográficos e geoquímicos, comumente estudados separadamente, quando integrados, podem elucidar questões sobre a formação destes minerais. A Formação Assistência (Subgrupo Irati, Permiano da Bacia do Paraná, Brasil) apresenta células e estruturas normalmente associadas a atividades microbianas, como microesferas dolomíticas, quartzo microcristalino e pirita. Microfósseis foram reconhecidos e seus processos de fossilização reconstituídos. Sílex, dolomito e folhelho de diversos níveis e localidades foram estudados utilizando-se seções petrográficas normais e polidas; resíduos orgânicos extraídos por dissolução ácida (HF/HCl); superfícies corroídas com dissolução parcial com HF; microscopia petrográfica e eletrônica de varredura (MEV); espectroscopia Raman e de energia dispersiva de raio-X (Energy Dispersive X-ray-EDX) e florescência e difratometria de Raio-X. As prospecções iniciais revelaram alta variedade de microfósseis de parede orgânica (cianobactérias; grãos de pólen; clrófitas; acritarcos; fitoclástos; escolecodontes; palinoforaminíferos e raros grãos de esporos) e microesferas dolomíticas. Diferentemente das pesquisas tradicionais sobre palinoestratigrafia, que utilizam de resíduos de rochas siliciclásticas finas, a petrografia do sílex diagenético revelou uma microbiota fóssil composta principalmente por delicadas cianobactérias. Permitiu também o reconhecimento de estágios ontogenéticos e de feições tafonômicas tais como a morfologia tridimensional de vesículas orgânicas e agregações polínicas. Estas preservações excepcionais é resultado de silicificação extremamente eodiagenética. Todas as amostras examinadas por florescência e difratometria de Raio-X apresentaram predomínio de sílica e dolomita e menores quantidades de pirita. Ao contrário dos nódulos e lentes de sílex de outros níveis, conhecidos de outras posições estratigráficas, somente o sílex maciço da Camada de Brechas Evaporíticas (CBE) demonstrou abundantes células de parede orgânica e estruturas preenchidas (fenestras e fraturas) com bordas dolomíticas. A sílica deste nível, portanto, foi gerada por fluídos supersaturados que substituíram a dolomita pré-existente. Analises com MEV e EDX revelaram cianobactérias fossilizadas com invólucros orgânicos (paredes celulares e/ou bainhas extracelulares) e regiões protoplasmáticas preenchidas por quartzo microcristalino. Comparações com estudos laboratoriais e ambientais demonstraram, em primeiro lugra, como a interação entre moléculas nas superfícies das células e íons em solução retiveram os componentes dos invólucros celulares e mineralizaram as demais partes das células. Em segundo lugar, porque o sílex da CBE também concentra microesferas dolomíticas agregadas em grandes quantidades e associadas e materiais carbonosos. Camadas externas recobrem esferas individuais, pequenos conjuntos e superfícies arredondadas. Nem toda microesfera exibem interiores celulares preenchidos por dolomita. Além das afinidades biológicas, as análises permitiram deduzir como certas condições na interface água/biosedimento provocaram a precipitação deste tipo de dolomita. Tais condições são relacionadas a salinidade, oxido-redução, razões \'Mg POT 2+\'/\'Ca POT 2+\' e atividades biológicas pretéritas tais como acumulações de substâncias poliméricas extracelulares (EPS - extracelular polymeric substances) e processos microbianos anóxicos (e.g.redução de sulfato e metanogênese). Foi possível também se reconhecer a sequência de mineralização (dolomitização e silicificação) bem como certas etapas que levaram a preservação de bainhas e interiores celulares. Os dados obtidos lançam novas perspectivas às discussões globais sobre o \"problema da dolomita\". / Microbial modification on ionic concentrations of shallow=water substrates recently reached valuable results both on fossilization and precipitation of calcite, aragonite, dolomite, pyrite, and minerals of silica and phosphate. Data on micropaleontology, petrography, and geochemistry, which are often sudied separately, when treated together, improve the understanding of the formation of these minerals. The Permian Assistência Formation of the Irati Subgroup in the Brazilian Paraná Bassin bears preserved cells and structures commonly associated with microbial activities, such as dolomite microspheres, microcrystalline quartz and pyrite. Microfossils were recognized and their processes of fossilization reconstituted. Chert, dolostone and shale from many stratigraphic leves and locations were studied by the use of normal and polished petrographic section; estracted organic residues via HF/HCL attach, HF-etched surfaces; petrographic microscopy; scanning electron microscopy (SEM); Raman and Energy Dispersive X-ray (EDX) spectroscopy; fluorescence and diffraction of X-ray. The initial surveys revealed a large variety of organic-walled microfossils (cyanobacteria, pollen grains, chlorophytes, acritarchs, phytoclasts, scolecodonts, palynoroaminifers and rare spores) and dolomitic microspheres. Unlike traditional researhce on palynostratigraphy, which employ organic residues from fine siliciclastic rocks, the petropgraphy of diagenetic chert revealed abundant fossil microbiota composed principally of delicate cyanobacteria. This procedure allowed also the recognition of ontogenetic stages of micoorganisms and taphonomic features such as three-dimensional morphology of organic vesicles and the pollen aggregations. This excellent preservation results from extreme eodiagenetic silicification. Every chert sample examined by fluorescence and X-ray diffraction shows mostly silica and dolomite with a minor amounts of pyrite. Unlike the nodules and lens of chert from other levels,which are known in many stratigraphic sequence, only the massive chert from Brecciated Evaporite Beb (BEB) bears abundant organic-walled cells and filled structures (fenestrae and fractures) exhibiting dolomitic edges. Silica from this sequence, therefore, was generated from supersaturated fluid solutions replacing pre-existing dolomite, preserving the organic content. The SEM and EDX revealed fossilized cyanobacteria with organic involucres (cell walls and/or extracellular sheath) and protoplasmatic region filled by microcrystalline quartz. Comparison with laboratory and environmental studies show, firstly, how the interaction between molecules in the cell surfaces and ions in solution retained the organic components of cellular surfaces and mineralized portions at the other parts of cells, and secondly, why BEB chert is massive at the expense of others relatively smaller in size and the occurrence of chert in other sequences. The quartzitic matrix of the BEB chert also concentrate dolomitic microspheres, which are aggregated in large quantities and associated with carbonaceous material. Outer layers coat indivisual shperes, small clusters and rounded surfaces. Not every microsphere exhibit the filling of dolomite in the interior of cells. Beyond their biological affinity, this analysis allowed the evaluation of how certain conditions on water-biosediment interface led to the precipitation of this kind of dolomite. Such conditions are related to salinity, redox, \'Mg POT 2+\'/\'Ca POT 2+\' ratios, and ancient biological activities such as the accumulation of extracellular polymeric substances (EPS) and anoxic microbial processes (e.g. sulfate reduction, methanogenesis). It was also possible to recognize the mineralization sequence (dolomitization and silicification) as well as certain steps that led to the preservation of sheaths and some cell interiors. The acquired data launches a new prospect for global discussions on the \"dolomite problem\".

The archaeological and technical questions about ancient stone tools lead to various research activities such as chemical and petrographical analysis. Considering research areas and publications it can be suggested that mineralogical studies of stone samples of ancient stone tools have disclosed useful information concerning identification of the stone. Within this context, aim of this study is to determine the chemical, mineralogical and petrographical identities of the stone samples of Karain Cave (Antalya). Most paleolithic caves show one specific time interval layer but Karain Cave shows lower-upper and middle layers which give information about the migration ways between Near East and Europe. Stone tools excavated from Karain Cave are not only first human remainings in Anatolia but also first artworks of Anatolian people.Most of the stone tools excavated from Karain Cave are cherts. These cherts were analysed for archeological aspects but mineralogical, petrographical, and chemical contents have not been analysed yet. During the excavations at the Karain Cave in Antalya many stone pieces in different sizes and colors had been found. In this study ten samples were examined. The methods used consists of thin section, X- ray powder diffraction , scanning - electron microscopy coupled with energy dispersive X-ray analysis , differential thermal analyses and inductively coupled plasma mass spectrometry to determine material characteristics of the samples. Petrographically the nine of the samples are chert with some including radiolarian fossils. Microcrystalline &aacute / - quartz is the major mineral in the chert. Only one sample is composed calcite and is identified as micritic limestone. Chemical analysis reflect the typical composition of chert with the average values of / 40.9% Si and 1 sample is limestone, which is composed of 35.7% Ca . Minor elements are Fe, Al, K, and Ti in the samples. Thermal analysis is also supported the thin section studies.Further research is suggested for provenance analysis of stone tools from the Karain Cave.

Thesis (M.A.)--Rutgers University, 2009. / "Graduate Program in Anthropology." Includes bibliographical references (p. 435-461).

No description available.

Les cherts archéens permettent de contraindre les environnements primitifs qui ont vu l'apparition de la vie sur Terre. Ces roches siliceuses se forment selon trois processus : les C-cherts (cherts primaires) se forment par précipitation chimique de silice océanique sur le plancher, sous la forme d'une boue siliceuse ou en tant que ciment dans les sédiments de surface; les F-cherts (cherts de fracture) précipitent dans les fractures de la crôute depuis les fluides circulant; les S-cherts (cherts secondaires) sont issus de la silicification de roches préexistantes lors de la percolation de fluides enrichis en silice. Ces processus sont largement acceptés mais des questions majeures subsistent : comment reconnaître ces différents types de chert ? Quelle est l'origine de la silice et sous quelle forme a-t-elle précipité ? Quel signal chimique est porté par les cherts et comment s'en servir pour les reconstructions paléo-environnementales ? Ces questions sont abordées à travers trois sites de la ceinture de roches vertes de Barberton, en Afrique du Sud. L'approche adoptée combine l'analyse des structures sédimentaires et de déformation, de la pétrologie et de la composition chimique et isotopique de ces unités. Dans ces sites, la formation des cherts est étroitement liée à l'environnement de mise en place. La sédimentation clastique (turbidites) est à l'origine des C-cherts de Komati River, déposés sous la forme d'une boue siliceuse par adsorption de silice sur les particules argileuses en suspension. En absence de contribution continentale, les alternances de cherts noirs et blancs de Buck Reef sont interprétées comme issues de variations climatiques à l'échelle saisonnières (chert noir), voire glaciaires/inter-glaciaires (chert blanc). Les cherts de fracture de Barite Valley sont liés à la précipitation de silice depuis une suspension colloïdale thixotrope remontant à travers la croûte. La composition chimique des cherts est contrôlée par leur environnement de mise en place, et représente un mélange entre une phase siliceuse et une phase contaminante, indépendamment des processus qui ont précipité la silice. Les cherts de Komati River et de Barite Valley sont enrichis en Al, K, Ti, HFSE et en REE, ce qui est attribué à la contamination de la matrice siliceuse par la présence de phyllosilicate. Une telle contribution clastique peut expliquer les larges gammes de δ30Si dans les cherts de Komati River (-0.69‰à +3.89‰), et la majorité des valeurs positives est probablement liée à la contribution de l'eau de mer. Dans les dykes de Barite Valley, les δ30Si très négatifs (-4.5‰ à +0.22‰) sont cohérents avec l'origine hydrothermale basse température des fluides initiaux. A Buck Reef, l'absence de contribution continentale s'exprime dans les cherts blancs par une minéralogie exclusivement microquartzitique et par des concentrations extrêmement faibles en éléments traces (i.e. ΣHFSE et ΣREE<1ppm). 2% de carbonates et 3-4% de matériel continental (e.g. argiles) suffisent à masquer le signal siliceux dans ces cherts purs. Nous ne pouvons conclure sur la présence d'un signal océanique dans ces cherts par manque de fiabilité des proxys océaniques modernes (appauvrissement en LREE, enrichissement en La et Y). Reconnus à la fois dans des quartz océaniques, hydrothermaux, magmatiques et pegmatitiques, ils ne permettent pas d'identifier un signal d'eau de mer dans les cherts archéens. Les δ 18O de ces cherts indiquent la présence de circulations fluides secondaires à moins de 100°C, et leurs δ 30Si négatifs ou positifs (-2.23‰ et +1.13‰ en moyenne) montrent la contribution de fluides différents au moment de leur formation. Le couplage des observations pétrologiques et de terrain est la seule approche fiable pour reconnaître le mode de mise en place des cherts. Leur composition chimique dépend plus des conditions environnementales que des caractéristiques du fluide initial.

The Precambrian-Cambrian Athel Silicilyte is an enigmatic chert unit of up to 390 m thick found as slabs (each slab typically 2 × 6 km across) entrapped within salt domes at a depth of 4-5 km in the South Oman Salt Basin. This formation is a prolific self-charged reservoir with high porosity (up to 34 %) and high oil saturation (80 %). Despite its economic value, the origin and the variability of this formation are not fully understood. This study therefore aims to investigate the variability and the origin (silica source and precipitation mechanism) of the Athel Silicilyte. Data obtained from core, wireline log and petrographical analysis were employed to establish the vertical and the lateral variability and, with the assistance of geochemical data, the likely source and precipitation mechanism of silica was determined.The Athel Silicilyte is only present in the deepest parts of the South Oman Salt Basin within the fault-bounded Athel Basin, bounded by two silt-rich mudstone units. Six lithofacies were recognised in the Athel Silicilyte that reflect variability in detrital material contents (three silica-rich facies), sediment remobilisation (slumped and brecciated lithofacies) and diagenetic modification (carbonate-bearing lithofacies), with the silica-rich facies being the most abundant (> 97 % of the total thickness). The Athel Silicilyte exhibits wavy discontinuous lamination and it is predominately (silica-rich facies average = 80 wt. %) composed of connected-networks of microcrystalline quartz (1-5 µm). Other constituent components are detrital quartz (3 wt. %), illite (10 wt. %), pyrite (4 wt. %) and organic carbon (TOC = 3 wt. %). The detrital contents increase towards the Upper Athel Silicilyte and towards the basin margins (ranging from 3 to 30 wt. %). The wavy laminations are interpreted to have a microbial origin. The homogeneity, loose packing of detrital grains and preservation of 390 m thick laminated fabric suggest that the Athel Silicilyte precipitated syndepositionally in microbial layers during low detrital input. The intense detrital input during bounding mudstones sedimentation inhibited Athel Silicilyte precipitation as a result of the rapid burial of microbial layers. The Athel Silicilyte shows strong enrichments of redox-sensitive elements (U, V and Mo), Mn-depletion, positive Ce anomalies, and small framboidal pyrites (3.6-4.0 µm), suggesting that the water column was euxinic during precipitation.Based on the petrographical evidence for the Athel Silicilyte forming as a syndepositional precipitate alongside seawater-like rare earth element (REE) characteristics, silica is interpreted to have been sourced directly from seawater. Mass balance calculations support this interpretation, indicating that silica-rich Precambrian seawater provided the significant silica mass in the Athel Silicilyte. The ability of dissolved silica to form hydrogen bonds with the functional groups (e.g. carboxyl and hydroxyl) in microbial layers was the key for Athel Silicilyte precipitation. The formation of hydrogen bonds was made possible under euxinic conditions, where the pH values were probably lower (< 7) than for the normal seawater as a result of HS- and H+ production by sulphate reducing bacteria and HS- oxidation at the redox boundary by sulphur oxidising bacteria. Consequently, dissolved silica was concentrated in microbial layer microenvironemnts, resulting in silica nucleation and polymerisation.

No description available.