Organic matter in anoxic sediments off Central Peru: Relations of porosity, microbial decomposition and deformation properties

Abstract

Microstructure of Central Peru continental margin sediments suggests that in environments of rapid hemipelagic sedimentation organic matter decomposition has a significant effect on geotechnical properties. In highly porous surface sediments particles resembling the remains of fecal pellets appear to be coated by bacterial "sheaths", but after burial sheaths disappear as an increasingly uniform and closed structure of organo-mineral aggregates develops. Interstitial water nutrient and solid phase C, N and P profiles support the interpretation that this progression corresponds to decomposition and metabolite regeneration from labile organic matter by microbial sulfate reduction. It is proposed that early aggregation has a strengthening effect and that this combined with the low density of near-surface sediments results in an effective overburden pressure lower than experimentally determined preconsolidation pressures. More basic knowledge of the "lifetime" of organo-mineral aggregates and the influence of gross and local microstructure on the rates and products of diagenetic reactions is needed in order to verify the relationship between organic matter accumulation and sediment stability in continental margin environments. © 1982.