The diffusion model is potentially useful for quantifying the effect of downslope gravity transport on sedimentation rate variations, which are commonly found between Deep Sea Drilling Project and Ocean Drilling Program 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 French-American Mid-Ocean Undersea Study 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 nondeposition due to high current velocities. More than half of the contacts, however, show onlapping, which is qualitatively consistent with the 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 nondeposition 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 diffusion model. 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 rms 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-1 (assuming S=10--30 m m.y.-1). 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. ¿ American Geophysical Union 1995.