published_or_final_version / English / Doctoral / Doctor of Philosophy

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

Racialization, Representation, and Resistance: Black Visual Artists and the Production of Alterity queries the relationship between Black visual representation and Black social and cultural politics. For the past two centuries Black visual artists throughout the African Diaspora have painted, sculpted, and filmed images of blackness inspired, funded, and otherwise supported by progressive patrons and institutions. Largely produced outside of mainstream art worlds, these visual representations focused on Black social and cultural politics and Black alterity more than mainstream tastes or stereotypes. As the coherence of Black social and political movements and resources declined in the late twentieth century, however, commercialization and the mainstream art world had increasing influence on Black visual culture. These changes created intense resistance and debate about the politics of visual representation throughout the Black Atlantic, particularly in the United States, Cuba, and the United Kingdom. Ethnographic observations, interviews, and gallery talks with artists in these three nations, including John Yancey, Vicky Meek, Marcus Akinlana, Kara Walker, Michael Ray Charles, Gloria Rolando, Anissa Cockings, and Andrew Sinclair, along with cultural and historical comparisons, provide fresh insight into the relationship between Black visual representation and contemporary Black social and cultural politics. / text

SA 's first black film scorer, Zethu Mashika (29) talk us through his journey to a unique profession

Multiple-brooding (raising more than one brood of young in quick succession) occurs infrequently in raptors and is generally restricted to either smaller species with shorter nesting periods, co-operative breeders or species capable of capitalizing on conditions of prolonged food abundance whenever they occur. This paper presents the first recorded cases of multiplebrooding in the Black Sparrowhawk Accipiter melanoleucus from two distinct locales in South Africa. In the Western Cape (Cape Peninsula), four attempts to multiple-brood were recorded in four different years, involving three distinct pairs of birds, and in KwaZulu–Natal (Eshowe), three distinct pairs of Sparrowhawks successfully multiple-brooded on several occasions over a 5-year study period. These results establish the Black Sparrowhawk as one of only two relatively large, monogamous raptor species, and the only specialist bird-eating raptor, in which multiple-brooding has been recorded with any frequency. The species’ capacity to thrive in human-modified environments (i.e. alien plantations) and particularly to exploit associated foraging opportunities (e.g. high densities of doves and pigeons in suburban areas) may, at least partly, account for the instances of multiple-brooding reported here. We suggest that biologists be more vigilant for cases of multiple-brooding in raptors, as it is possible that this trait is more common than originally thought and has previously been overlooked.

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