Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Bacteria constitute one of the most interesting and least studied potential metal-accumulating agents in sediments due to their widespread occurrence, large biomass and generally high affinity for metals. Model diagenesis experiments were carried out to ascertain the relative stability of organically-complexed metals (U('+6), Fe('+2), Cu('+2) and Zn('+2)) as a function of Eh and pH up to 100(DEGREES)C in equilibrium with water. Metal-loaded cells of the ubiquitous bacterium, Bacillus subtilis, artificially aged in a variety of synthetic sediments under confined, anoxygenic conditions at 100(DEGREES)C for up to 200 days, gave rise to mixed assemblages of crystalline metal phosphates, metal sulphides and metal-complexed, polymeric organic residues (kerogen). The influence of Eh, pH and the nature of the complexed metal on thermal degradation of cellular matter and authigenic phosphate and sulphide formation as a consequence of thermal maturation of sedimentary organic matter is discussed.;The association of microfossils, complex organic residues and graphite with Precambrian sedimentary metal deposits has often been cited as evidence for the probable interaction of microorganisms in metal accumulation and mineralization. Recent biological/biochemical, geological/geochemical and micropaleontological/organic chemical data challenge the current wisdom that the marine biomass throughout the Archean and early Proterozoic eras consisted solely of anaerobic bacteria adapted to life in an anoxygenic hydrosphere in equilibrium wth an atmosphere devoid of free oxygen. Major evolutionary events within the lithosphere, atmosphere, hydrosphere and biosphere might be resolved ultimately in terms of thermal decay of an early planetary system. Horizontal expansion of an oxygen minimum as a consequence of temperature-modulated rates of oxygen supply and thermocline circulation within the Precambrian hydrosphere may account for the preponderance of reduced sediments. The concept of gradual oxygenation of the photic zone as a consequence of decreasing water temperature and increasing oxygen solubility is consistent with the progression of biospheric evolutionary events leading up to and including the development of the eukaryotic cell. Micropaleontological studies provide at least circumstantial evidence that oxygenation of the photic zone was locally realized as early as 3.4 By BP.



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