The formation of carbonate minerals in laboratory and environmental settings
Microbial sulfate reduction, couple to organic matter oxidation or methane oxidation, is one of the key processes driving the formation of sedimentary carbonate minerals. While some work has been done exploring the formation of carbonate minerals via microbial sulfate reduction, less attention has been given to the detailed processes involved in this microbially induced carbonate mineral formation and how the carbonate minerals form may transform and change over time. In this thesis, I investigated the role that microbial sulfate reduction has on the types of calcium carbonate polymorphs precipitated. For this, I grew sulfate-reducing bacteria (Desulfovibrio bizertensis) in media with varying Mg/Ca and different types of seeding materials. My results suggest that sulfate-reducing bacteria induce carbonate precipitation and serve as a nucleation for the growing carbonate minerals. In media where the Mg/Ca is greater than 2, a crystalline monohydrocalcite is the primary carbonate mineral produced. In addition, I examine the role of different seeding materials such as calcite and kaolinite have on the generation of alkalinity and microbial growth in the incubation experiments. My results show higher alkalinity production and rates of sulfate reduction in samples with kaolinite seeds. I suggest this is due to the fact that bacteria grow better in the presence of clay minerals that have a higher surface area. In the final chapter of my thesis, I extend my research from the laboratory setting to the field, in the Norfolk saltmarshes. Using an incubation approach of the saltmarsh sediment allows high-resolution monitoring of the evolution of pore fluid chemistry and thus the stability of siderite in conditions that mimic the saltmarsh. My incubation results suggest that the formation of siderite nodule can be very rapid (within weeks) after burial when there is a substantial iron source. My research thus explores the mineralisation of carbonate through microbial processes and how the diversity of carbonate minerals may be explained and examined in the geological record.
Alkalinity, calcium carbonate minerals, microbial sulfate reduction, seeding materials
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