No description available.

The Precambrian-Cambrian transition is a period with enormous geological and biological changes. There is a wide distribution of black shale sequence in the Late Sinian and Early Cambrian strata along the passive southern margin of the Yangtze Platform in South China. The remarkable polymetallic sulfide extremely enriched ore layer is embedded at the bottom of the Lower Cambrian Niutitang Formation, but its genesis remains highly disputable. Known mechanisms can hardly explain the extreme enrichment and paragenesis of multimetal sulfides with regard to their highly variant properties. Here, a case study is performed about the polymetallic sulfide enriched ore layer and related strata from the black shale-dominated Niutitang Formation in Zunyi, Guizhou Province and Zhangjiajie, Hunan Province. A phosphorite-rich layer is situated near the bottom of the Niutitang Formation. A few meters above the phosphorite is the polymetallic sulfide enriched ore layer embedded in the carbonaceous black shale wall-rock. A Combination of different methodologies were used to examine the polymetallic enriched ore, the black shale wall-rock and the adjacent phosphorite samples, including optical microscopy, electron microscopy, Mössbauer spectroscopy, Raman spectroscopy, electron microprobe analysis, X-ray absorption spectroscopy, etc. Submicron-scale organic vesicles resembling green algae were noted in the polymetal sulfide enriched layer, indicating the key role of microbial activities during the mineralization of the polymetallic sulfide ores. Larger biogenic structures with possible hydrozoan and anthozoan (or algal) affinities were discovered from the polymetal sulfide ores and phosphorites, respectively, suggesting the participation of metazoan during the mineralization process. The ability of biomineralized molybdenite and apatite to preserve pseudomorphs is attributed to their fine crystal sizes, even if they were precipitated under drastically different geological conditions. The geochemical cycling of phosphorus and other nutrients probably involves multiple marine life-forms. Nickel and iron sulfides, on the contrary, were suggested to be incapable of preserving fine fossil structures because of high-degree recrystallization. In the polymetallic ores, pyrite was proved to be the predominant form of iron, and the uranium minerals were recognized as mainly coffinite and a small portion of uraninite. The uranium radioactive decay-caused carbonization effects were scrutinized in the micro-environment, suggesting the authigenecity of these uranium minerals. With these novel mineralogical, paleontological and geochemical evidence at the Precambrian-Cambrian boundary, new perspectives on the geobiology of the polymetallic sulfide ores are presented as follows. Both benthic and planktonic organisms might have actively participated in the early Cambrian metallogenesis. Polymetal biosorption by live and dead biomass, especially those from algal blooms, is hypothesized to be a major cause of the unusual polymetallic sulfide ore layer, followed by microbial reduction and immobilization in a stratified water column. This unique ore formation reflects the complicated mutual relationships between Cambrian biota and its paleoenvironment. These results may provide a better understanding of the role of biological activities in the problematic metallogenesis of the polymetal sulfide enriched ores and open a new window to the cognition of the hypothetic Cambrian Explosion. / published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

No description available.

Pyrite is a ubiquitous mineral in shales. It results from the bacterial reduction of seawater sulphate to sulphide and the reaction of that sulphide with iron to form iron sulphides and subsequently pyrite. Five Jurassic shales were examined. 1 The Upper Oxford Clay (Oxfordian) Warboys Cambridgeshire. 2 The Dunans Clay (Callovian-oxfordian) Isle of Skye. 3 The Lower Oxford Clay (Callovian) East midlands. 4 The Posidonia Shales (Lias ε) Southern Germany. 5 The Dunans Shale (Callovian) Isle of Skye. The five shale units are divisible into three major biofacies "Normal" (Units 1& 2), "Restricted" (3) and "Bituminous" (4 & 5), which show varying pyrite contents and isotopic compositions, that reflect the changing influence of the three limiting factors of pyrite formation (sulphate, organic carbon, and iron). Samples of shale were analysed for fine grained pyrite content and isotopic composition, organic and carbonate carbon, and hydrochloric acid soluble iron. The Normal shales showed low pyrite sulphur (<1.3%) and organic carbon (<2%), degree of pyritization (D. O. P. ) (<0.5) and negative (<-28%o) δ34S values. These are consistent with the formation of pyrite near the sediment surface, limited by organic carbon. In the Restricted shales higher pyrite sulphur (av. 1.4%) and organic carbon (av. 5%), degree of pyritization (0.5 to 0.7) and less negative (>-28%o, <-9%o) δ34S values indicate the continuation of pyrite formation deeper into the sediment, where it is limited by sulphate diffusion. High D. O. Ps in the Posidonia Shales (>0.8) suggest that pyrite formation is limited by the availability of iron in Bituminous shales. Heavier δ34S values (>-28%o) in the Posidonia Shale suggest limitation of sulphate reduction by sulphate diffusion, and lighter values in the Dunans Shale (<-28%o) suggest limitation by organic matter. Petrographic and isotopic studies of shell replacement and associated concretionary pyrite from the Lower Oxford Clay show types of replacement related to the differences between the porewaters within the shell and those of the shale, particularly as regards iron supply.

Thesis (Ph. D.)--Columbia University, 1927. / Vita. Bibliography: p. 35-36, 70-71.

Pyrolysis of a New Brunswick oil shale has been studied in a 12.8cm diameter spouted bed reactor. The aim of the project was to study the effect of pyrolysis temperature, shale particle size, feed rate and bed material on oil yield. Gas and spent shale yields were also determined. Shale of different particle size ranging from 0.5mm to 4mm was studied using an electrically heated reactor containing sand or spent shale which was spouted with nitrogen or nitrogen/carbon dioxide mixtures. For a given particle size and feed rate, there is a maximum in oil yield with temperature. For particles of 1-2mm at a feed rate of about 1.4kg/hr, the optimum temperature is at 475°C with an oil yield of 7.1% which represents 89.3% of the modified Fischer Assay yield. For the 2-4mm and the same feed rate, the optimum temperature is 505°C with an oil yield equal to 7.4% which is 94.3% of the modified Fischer Assay value. At a fixed temperature of about 500°C, the oil yield increases with increasing particle size. This trend is in agreement with the Fischer Assay values which showed oil yields increasing from 5.2% to about 8% as the particle size was increased. In the spouted bed, the oil yield decreases as the oil shale feed rate increases at a given temperature. The use of spent shales as the spouting solids in the bed also has a negative effect on oil yield. The gas yields which were low (less than 2.1%) and difficult to measure do not seem to be affected by particle sizes, feed rate and bed material. Hydrogen, methane and other hydrocarbons are produced in very small amounts. C0₂ and CO are not released in measurable yield in the experiments. The trend of the spent shale yield has not been successfully understood due to the unreliability of the particle collection results. Attrition of the spent shale appears to be a serious problem. Results of the experiments are rationalized with the aid of a kinetic model in which the kerogen in the oil shale decomposes to yield a bitumen and other by products and the bitumen undergoes further decomposition into oil. The spouted bed is treated as a backmixed reactor with respect to the solids. A heat transfer model is used to predict the temperature rise of the shale entering the pyrolyzer. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Thesis (M.S. - Hydrology and Water Resources)--University of Arizona, 1982. / Includes bibliographical references (leaves 120-124).

No description available.

Not available / text

Not available / text