Nanocomposites as Models of Mineral Surface - Organic Matter Relationships and Their Application to Organic Carbon Preservation

Derkowski, Arkadiusz¹, Martin Kennedy², Thomas F. Bristow¹ (1) University of California, Riverside, Riverside, CA (2) University of California Riverside, Riverside, CA

Several factors can control the pathway of preservation and absolute concentration of organic mater in marine sediments including: primary productivity, concentration of oxidants, dilution by mineral material, rates of sinking and burial, the association with mineral surfaces, and the availability of abiogenic reductants. In recent years, increasing data has pointed to a strong correlation between clay mineral dominated mineral surface area and TOC, though the physical mechanism that facilitates organic carbon preservation by mineral surfaces remains unresolved. Strong interactions between organic matter (OM) and clays as well as their spatial relationships, can protect OM from both biogenic and abiogenic oxidation. The advanced techniques from nanocomposite studies can be successfully applied to test different models of clays / OM interactions. 1. Microcomposite is common relationship between OM and clays with OM occurring in mesopores and macropores of sediment as large (micrometric scale) OM particles. 2. Exfoliated nanocomposite – clays occur as fundamental particles dispersed in OM, interacting with OM with strong physicochemical reactions; one of the most efficient mechanism of OM protection. 3. Thin film - OM covers external surfaces of minerals (including clays). This model can be applied only to explain small quantities of TOC (up to several % OM). 4. Polar molecules intercalated nanocomposite – polar OM molecules substitute water layers in interlayer space, preserving crystallite structure. 5. Charged molecules intercalated nanocomposites. Charged OM molecules can substitute inorganic exchangeable ions on all sites showing electric charge. That is also the first step for adsorption of other non-polar or hydrophobic OM molecules, which can not be adsorbed directly on clays without agents.