Sediment transports to the ocean floors by rivers, ice and wind.
The thickest deposits of sediment on Earth are on the ocean floor where it piles up to 5½ miles thick, with the thickest buildup found on continental rises and slopes. The ocean floor is comprised of material that contains differing amounts of two classifications of marine sediments. The amount of each classification is due to the location of the area on the ocean floor.
Main Classifications
The two main classifications of marine sediments, terrigenous and pelagic, are characterized either by size of material and composition, such as terrigenous, or by composition only, such as the pelagic. The terrigenous marine sediment is typically classified by size of the grains commonly found in the sediment. Examples are boulder, cobble, pebble, gravel, coarse sand, medium sand, fine sand, silt and clay. The development of these sediment grain sizes results from the energy of the environment where it is found. In environments where the water flows quickly, such as in steep mountain streams, the larger sizes develop. Whereas slower currents, such as in a river bed, form sand or silt. Less active water offshore produces clay-sized particles or silt. Terrigenous marine sediment comes from river discharge and more than 1/3 of this discharge comes from 10 rivers, with the Amazon and Ganges rivers accounting for 20 percent of the world's total. Compositions such as lithic fragments, limestone, feldspar and quartz can classify terrigenous sediment.
Pelagic marine sediments are those found out in the open ocean away from land. These sediments are classified according to composition, as all the grain-size of these sediments is basically the same out in the slow moving ocean water which is silt. Pelagic marine sediment has four categories.
Lithogenous
One of the pelagic marine sediment compositions derives from rock such as volcanic ash (consisting of tiny bits of glass), wind-blown dust (called "eolian sediment") and other fine particles that were once rock. Feldspar grains are found in lithogenous marine sediment as well as lithogenous clay. Lithogenous clay is termed pelagic clay if more than 70 percent of it has lithogenous sediment in its dry mass. Ocean floors in deep areas in the Pacific Ocean are predominately composed of lithogenous sediment, and in central ocean basins the largest component of lithogenous sediment is clay.
Cosmogenous
Another type of pelagic marine sediment is composed of matter that has come into the ocean from macroscopic meteor debris and microscopic cosmic dust. This type of sediment only accounts for a tiny fraction of the sediment on the ocean floor.
Hydrogenous
Hydrogenous sediment is usually found near hydrothermal vents where metal ions release into the water and combine with silica to become dark, metal-rich sediment. Other forms of hydrogenous sediments are manganese nodules, phosphates, carbonates and evaporite salts and ammonia.
Biogenous
Biogenous marine sediment is a pelagic marine sediment that contains remnants of living organisms, mostly plankton. The plankton that forms this sediment comes from species that have shells made of calcite and opal. For phytoplankton, the plant-like photosynthesizers, coccoliths have calcite shells and diatoms have siliceous or opal shells. Zooplankton, the animal element, produce foraminifera that have calcite shells and radiolaria composed of siliceous or opal shells.
Tags: marine sediment, ocean floor, comes from, lithogenous sediment, marine sediments
