Sedimentation of particles in the ocean leads to inhomogeneous horizontal distributions over the seafloor. We study this phenomenon considering a horizontal sheet of falling particles immersed in an oceanic flow, and determine how they spatially distribute when the particles sediment on the seabed (or are collected at a given depth by sediment traps).This is performed from a Lagrangian viewpoint attending to the oceanic flow properties and the physical characteristics (size and density) of typical biogenic sinking particles (for which we have previously discussed the proper equation describing their falling dynamics). Two main processes determine the distribution, the stretching of the sheet caused by the flow and its projection on the surface where particles accumulate. These mechanisms are checked, besides an analysis of their relative importance to produce inhomogeneities, with numerical experiments in the Benguela region. Faster (heavier or larger) sinking particles distribute more homogeneously than slower ones.