Hydrothermal Sediment Alteration at Oceanic Spreading Centers: A Comparison of Thermogenic Organic Reactions in Laboratory and Natural Systems

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Hydrothermal alteration of organic matter in sediments overlying oceanic spreading centers such as the Guaymas Basin (Gulf of California), Escanaba Trough (Gorda Ridge), and Middle Valley (northern Juan de Fuca ridge) results in the generation of significant organically derived alteration products. Hydothermal experiments will be conducted in the laboratory at 200-400oC and 300 bars to constrain better factors that regulate the generation and stability of organic compounds and the extent and nature of organic-inorganic interactions. Experiments containing natural sediments and seawater type fluids or varying composition will allow detailed quantitative characterization of organic alteration products as a function of time, temperature, and sediment and fluid composition, and identity sources and sinks for these species in natural hydrothermal systems. The sediment alteration experiments will be used to calibrate paleogeothermometers based on the relative abundance and distribution of thermally altered organic species for use in ridge crest hydrothermal systems. The results of this study will be applied to natural environments to evaluate geochemical conditions during hydrothermal sediment alteration and to constrain the time-temperature history of sediment-covered spreading centers.