Abstract: Microfabric, Physical Properties, and Biogeochemistry of Continental Slope Sediments and Marine Snow: California Margin

Richard H. Bennett, Dennis M. Lavoie, Michael W. Lambert, Patti J. Burkett, Roy J. Baerwald, Miriam Kastner, Barbara Ransom, Vernon Asper

California margin sediments (north and south of the Mendocino Fracture Zone (MFZ) and seaward of San Luis Obispo) are being studied in detail to understand the microfabric, physical properties changes, and biogeochemistry of the sediment as a function of early diagenetic processes and dewatering with depth of burial. Sediment trap samples containing marine snow, clay-organic complexes, and aggregate assemblages are being studied by Wet Cell TEM and SEM and high resolution TEM. Sediment geochemistry measurements are delineating detailed changes in the pore-water chemistry. Optical studies of the organic petrology and millimeter scale microfabric features complement the TEM microfabric observations.

The marine snow consists largely of plankton and organic material, and the greatest amounts of terrigenous components apparently are in the water column near the seafloor. Significant quantities of polymeric organic material and microfaunal assemblages (bacteria and eukaryotic cells) are present in the surficial sediments. The influence of microfabric and organic content generally results in the highest porosity surficial sediment south of the MFZ. Porosities are generally lower and sediments coarser grained north of the MFZ, and these sediments contain the highest components of terrigenous organic material. Upper slope surficial sediments have porosities that are somewhat lower than down slope deposits. Sediment dewatering is dramatic in the near surface despite extensive bioturbatio . TEM observations confirm models depicting the presence of organic material during early microfabric development and diagenesis of fine-grained marine sediment.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994