The nearshore sediments are thus younger than those on the outer shelf (Flemming and Hay 1988), typically being produced by deposition of sand, silt, and clay from rivers, with subsequent redistribution by longshore currents (Flemming and Hay 1988). 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 and/or clastic sediment production.