ABSTRACT
Sedimentary deposits are those formed at the Earth's surface by the action of water, wind and ice, and encompass the full range of environments, from land to ocean. Oceans and seas have large-scale accumulation of sediment in all marine settings, from shallow shelf to abyssal plain, as unconsolidated particles that cover the bedrock of the underlying crust. However, it seems that plate tectonic action has been necessary to maintain both a source for erosion of sediment (by mountain building), and accommodation space for sediment carried to the sea (by removal of ocean crust with its sediment veneer in subduction zones). Otherwise, global estimates indicate that the oceans would fill up with sediment in 100 Ma and the mountains would erode flat in 50 Ma (Holland, 1978). The average marine deposit is 0.5 km thick, being thinnest at the youngest ocean crust of mid-ocean ridges, and thickest at continental margins, due to both a higher sedimentation rate at the margins (nearer the sources of supply from land), and the greater age of underlying ocean crust due to seafloor spreading (more time for sediment to accumulate). Marine sediments are important reservoirs in the crust-ocean system, as discussed in the previous chapter.
