the nearshore sediments are thus younger than those on the outer shelf flemming and hay typically being produced by deposition of sand silt and clay from rivers with subsequent redistribution by longshore currents flemming and hay however where these riverine clastic sediment inputs are small biogenic bioclastic sedimentation produced by erosion of the skeletal carbonate remains of marine organisms can dominate the type of sediment can thus change substantially along and across a shelf depending on the relative contributions from carbonate andor clastic sediment production