The diffusion model is potentially useful for quantifying the effect of
down-slope gravity transport on sedimentation rate variations, which
are commonly found between DSDP and ODP sites. If appropriate,
the model and stratigraphy could be used, for example, to constrain
the amount and timing of fault block rotation. Deep Tow profiler
records from the FAMOUS area of the Mid-Atlantic Ridge are
examined to determine whether they are consistent with a diffusion
model. Sedimentary contacts with basement show that a variety of
processes may be operating, some of which are inconsistent with the
diffusion model. For example, there are moats around some contacts
which are typical of scouring or non-deposition due to high current
velocities. More than half of the contacts, however, show onlapping,
which is qualitatively consistent with the diffusion model. Sediments
generally fill low areas of the topography and have smooth surfaces,
as expected from a diffusive process. Where the fluxes of sediment
entering a basin are constant, the diffusion model predicts that the
sediment surface should evolve to a parabola (the steady-state
solution). Some 20 curved surfaces in the profiler data were digitized
and least-squares parabolas fitted to them with r.ms. errors of less
than 1 m. The slopes of the model parabolas provide values for the
ratio of sediment flux to diffusivity at the edges of the basins (steep
surfaces are produced by low diffusivity or high fluxes). This ratio is
combined with estimates of the fluxes to determine the apparent
sediment diffusivity, Kapp, for each basin. Flux is estimated by
assuming the abyssal hill topography acts as a simple sediment trap,
so that the lateral flux equals the width of a basin's pelagic catchment
area times the area's mean sedimentation rate S. Using this method,
median Kapp is 0.04-0.11 m2/yr (assuming S=10-30 m/m.y.).
Variations in Kapp and the assumptions behind the diffusion model
are discussed, and alternative causes of sediment surface tilts are
considered, in particular differential compaction which is modelled
using a simple porosity-depth function.
Mitchell, N. C., "Diffusion transport model of pelagic sediments on the Mid-
Atlantic Ridge", J. Geophys. Res., 100, 19,991-20,009, 1995.