| The microfabric of fine-grained cohesive clay sediments from six diverse sites was examined using transmission electron microscopy (TEM) and physical properties analyses. These marine sediments were analyzed for signatures indicative of the depositional and post-depositional processes which determine their mechanical and dynamic behavior. The following types of marine deposits were examined and include (1) red clays (2) turbidites, (3) glaciomarine, (4) channelized hemipelagics, (5) deltaic, and (6) calcareous-rich accretionary wedge sediments. In prelude to TEM imaging sediments were prepared using techniques including pore fluid exchange, critical-point drying, low viscosity resin impregnation, ultra-thin sectioning, and carbon coating. Image analysis of digitized data from TEM micrographs quantified spatial features of the sediment microfabric. Observations include grain size, arrangement, and sorting; trends in orientation of particles; morphology of fluid flow micro-channels and cross channels; and pore characteristics (geometry, size, connectiveness, and intra/intergranular porosity). A feature common to the sediments analyzed is that the particle size and mineralogy of the sediment matrix exerts primary control over three-dimensional patterns of the mineral grains and micro-channels controlling fluid movement and small particle transport through the sediments. In general, the microfabric and associated physical properties of the sediments were heterogeneous at the micron-sized scale. The fabric analysis show porosity variability is a complex process and relates to the tectonic state of stress regime, changes in matrix composition, and porometry of the sediment. As a consequence, a particular sediment possesses a unique suite of microfabric signatures resulting from depositional and diagenetic processes. Recognizable signatures include preserved biologically-produced grains, mineral assemblages, particle-to-particle associations resulting from forcing agents (i.e. turbidity currents and wind), and degradation, transformation, and neoformation (authigenesis) indicative of early clay diagenesis. Diagenetic processes occur at the submicron-size scale and are resolvable using TEM. |
