ORGANIC-MATTER PRESERVATION ON CONTINENTAL SLOPES - IMPORTANCE OF MINERALOGY AND SURFACE-AREA

Theoretical considerations, calculations, and data reported by Keil et al. (1994a) were used to assess the recent hypotheses that mineral su rface roughness controls the specific surface area of continental marg in sediments and that the matrix-linked organic carbon content of cont inental margin sediments occurs as a monolayer or 'monolayer-equivalen t' coating of organic compounds on the surfaces of detrital minerals a nd other detrital nonorganic grains (Mayer, 1994). Results of our anal ysis indicate that it is not the surface roughness of the terrigenous detrital framework grains that controls the specific surface area of m ost continental margin sediments, even in the sand and silt fractions, but rather the presence of nonspherical, high surface area-to-volume particles, primarily clays but also oxy-hydroxides and ultra-structure d nonorganic bioclasts such as diatom frustules. Analysis of the miner alogy, organic carbon content, surface area, and in situ microfabric o f continental margin sediments off California in the Mendocino and San Luis Obispo areas and off the state of Washington indicate a strong c orrelation between the amount of matrix linked organic matter present and the suite of clay minerals. Data indicate that organic carbon appe ars to be preferentially sequestered in smectite-rich sediments compar ed to those whose clay fractions are dominated by chlorite. We suggest that this association is a function of differences in the site densit y and chemistry of the clays and differences in their flocculation beh avior. Our data also indicate that organic carbon preservation on the three California transects, all of which have a suboxic oxygen minimum zone that impinges on the sea floor, is not significantly influenced by differences in bottom water oxygen concentration; and carbon stable isotope data suggest no preferential preservation of continental orga nic matter over that of marine origin. Copyright (C) 1998 Elseiver Sci ence Ltd.