Pelagic sediments are deposited at such low rates that they tend to be overwhelmed near shore by terrigenous deposits from land. So, pelagic sediments are normally associated with deep sea regions.
Unlike terrigenous sediments, pelagic sediments are classified by composition, not size. The size of pelagic sediments is uniformly pretty small, so their widely varying compositions are more interesting. There are four main compositional groups for marine sediments: Lithogenous: This is sediment that is derived from rocks. Remember, it's pelagic, so it has to settle out of the water column and will be most prevalent far from land. So, lithogenous pelagic sediment can be wind-blown dust (this is called eolian sediment), volcanic ash, or other fine particles that were originally rocks. Lithogenous sediment dominates in deep areas such as the Pacific Ocean away from the East Pacific Rise. Biogenous: Biogenous sediment is derived from living organisms, normally planktonic organisms because they're the most abundant. Planktonic life comes in a variety of forms and species, but the kinds that form biogenous sediment are the kinds that have shells that are resistant to dissolution or destruction. The most common shell materials for plankton are calcite (CaCO3 or calcium carbonate) and opal (SiO2 or silica), and most biogenic marine sediment comes from four species. Guilford Geology Department