Early diagenesis: impact of organic matter on mass physical properties and processes, California continental margin

High-resolution (scales of 2.5 mm to submicrometer), interdisciplinary studies of California continental slope sediments (0-80 cm) reveal the importance of marine organic material and mineralogy on mass physical properties in fine-grained sediments during very early diagenesis. The combination of organic material (greater than or equal to 2 wt.%) with smectite (greater than or equal to 5%) is associated with high depositional porosities, low effective stresses, low porosity reduction and dewatering, and the impedance of interstitial fluid flow. Living (microbiota) and nonliving (mucopolysaccharides) organic matter, affecting the physical properties, was revealed by transmission electron microscopy and carbon isotope studies. Calculations using the Redfield ratio show that sediments containing high organic carbon (greater than or equal to 5 wt.%) have 'hydrated' organic material in the pore spaces that can occupy a volume that is up to 20% of the total sediment porosity. Pore-water chemistry and X-ray diffraction show evidence of early diagenetic processes that may significantly influence sediment fabric. An important geochemical process near the sediment-water interface that affects sediment fabric is the rapid dissolution of biogenic opal. (C) 1999 Elsevier Science B.V. All rights reserved.