Interactions between Microorganisms and Clay-Rich Sediments during Early Burial and Diagenesis

Abstract

The purpose of this dissertation was to understand interactions between microorganisms and fine-grained sediments during the early stages of burial and diagenesis. Despite the abundance of research on sediment diagenesis, there remain many overlooked and understudied relationships between microorganisms and sediments. We investigated interactions between (1) clay minerals and sediment pore fluids, (2) microorganisms and fine-grained sediments, and (3) microorganisms, clay transformations, and carbonate precipitation. We employed an integrated program of numerical modeling as well as experimental and analytical techniques using natural marine sediments and iron-reducing bacteria to study these interactions. We found that clay minerals modulate sediment pore fluid pH and carbonate mineral saturation, that the effectiveness of microorganisms at altering permeability and compression properties is dependent on burial depth (porosity as a function of vertical effective stress) and the grain size, pore and pore throat size, and specific surface area of a sediment, and that microorganisms can induce clay mineral transformations (smectite to illite) and carbonate precipitation during the early stages of diagenesis. These results are of importance for carbon and elemental cycling throughout Earth history, fluid flow and overpressure generation in the subsurface, friction properties on faults, and oil and gas exploration.