Anaerobic methane oxidation and the formation of dolomite

Author(s): Moore, Tommy S.
Source: 37p. Institution: Boston University, Boston, MA, United States
Note: In English. Master's thesis
Summary: We examine the link between organic matter degradation, anaerobic methane oxidation (AMO), and sulfate depletion, and explore how these processes potentially influence dolomitization. We determined rates and depths of AMO and dolomite formation for a variety of organic rich sites along the West African Margin using data from Ocean Drilling Program Leg 175. Rates of AMO are calculated from the diffusive fluxes of CH4, and SO4 rates of dolomite formation are calculated from the diffusive flux of Mg. We find that the rates of dolomite formation are relatively constant regardless of the depth at which it is forming, indicating that the diffusive fluxes of Mg and Ca are not limiting. Based upon the calculated log I AP values, log Ksp values for dolomite were found to narrowly range between 16.1 and 16.2. Dolomite formation is controlled in part by competition between AMO and methanogenesis, which controls the speciation of dissolved CO2. AMO increases the concentration of CO32- through sulfate reduction, favoring dolomite formation, while methanogenesis increases the pCO2 of the pore waters, inhibiting dolomite formation. In addition to providing a mechanistic link between AMO and dolomite formation, our findings provide a method by which the stability constant of dolomite can be calculated in modern sediments, and allows prediction of regions and depth domains in which dolomite may be forming.
Year of Publication: 2003
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 06 Petrology, Sedimentary; Aliphatic hydrocarbons; Alkanes; Anaerobic environment; Atlantic Ocean; C-13/C-12; Carbon; Carbon dioxide; Carbonate rocks; Carbonatization; Dolomitization; Dolostone; Hydrocarbons; Isotope ratios; Isotopes; Leg 175; Methane; ODP Site 1081; ODP Site 1082; ODP Site 1084; Ocean Drilling Program; Organic compounds; Oxidation; Sedimentary rocks; South Atlantic; Southeast Atlantic; Stable isotopes; Sulfate ion
Coordinates: S193712 S193712 E0111910 E0111910
S210539 S210539 E0114914 E0114914
S253049 S253049 E0130140 E0130140
Record ID: 2004067366
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