The Role of Organic Matter-Clay Mineral Assemblages on the Transportation and Sequestration of Organic Matter

Amelia C. Robinson 
Department of Geology, University of California-Davis
Davis, CA
[email protected]

Ocean anoxia events have been attributed to abrupt conditions that lead to burial of organic-and clay-rich sediments underlying anoxic water columns. This, however, may not be the only environmental parameter required for preservation. Recent studies document the role clay minerals play in sequestration and long-term stability of organic matter. If organic matter partitions preferentially onto fine-grained sediments, then interfaces between organic and inorganic phases are critical for net burial of organic matter. Sorption mechanisms, distinguished by relative bond strengths, factor into the reactivity, partitioning and stability of organic matter-clay mineral assemblages. Nanoscale surface area relationships may control the availability of organic compounds for microbial degradation, timing of desorption of organic matter from clay surfaces, reaction kinetics and diagenetic transformations in the subsurface.

A three-fold empirical and experimental approach addresses the importance of different surface characteristics and loading conditions conducive to sorption in continental margins. Deep sea sediments, representing a range in mineral surface reactivity, are used to characterize natural organic matter-clay mineral assemblages. Sorption-desorption experiments, using amino acids, lignin and natural organic matter with clay mineral mixtures, provide insight into the surface coverage, loading capacity and specifically the distribution of clay reactive sites responsible for sequestering amino-, phenyl- and carboxyl group-bearing organic compounds over a range of ambient fluid conditions. Results from these sorption studies at the nano-scale can be scaled up to issues of organic matter sequestration in continental margin deposits, and should ultimately provide constraints on the fate and transport of organic carbon from source to sink.

AAPG Search and Discovery Article #90033©2004 AAPG Foundation Grants-in-Aid