Seafloor Sediments What Are the Different Types

Seafloor Sediments

What are the different types of seafloor sediments?

The three main types / categories of seafloor sediments are Terrigenous sediment, Biogenous sediment, and Hydrogenous sediments. Terrigenous sediment covers about 45% of the ocean floors, and originated from the erosion of land near the ocean's edge, from volcanic eruptions, and from dust that has blown from land to the oceans (Garrison, 2011).

Terrigenous sediments are composed of quartz sand, clays, and estuarine mud. Biogenous sediment results from the organic accumulation of materials broken down from some marine organisms. Biogenous sediment makes up about 55% of the ocean floor, and is composed of "…calcareous and siliceous oozes" (Garrison). In short, some Biogenous materials originate from corals, from the shells of mollusks (as they deteriorate their particles sink to the bottom of the oceans).

Meanwhile only about one percent of the sediment on the ocean floor is composed of hydrogenous materials, which are materials that dissolve by the actions of salt water. The hydrogenous sediments result from rocks under the surface of the ocean, materials that are thrust out of hydrothermal vents (Butterworth-Heinemann, 1998). Some typical hydrogenous sediment are "…manganese nodules…and phosphorite nodules" (Butterworth-Heinemann).

What factors control the distribution of each major sea sediment type? And where does each major seafloor sediment type tend to accumulate in greatest quantity?

There are larger particles that are part of the Terrigenous sediment (like gravel) that tend to settle near the shoreline because they are deposited (distributed) there by rivers and streams. But the smaller particles like clay and sand can be swept out to the ocean, even "thousands of kilometers by ocean currents" (Garrison). To get an idea of how long it takes clay to gather in substantial amounts on the ocean floor, it may take up to 50,000 years for a one-centimeter layer of clay to accumulate. On the other hand, near the mouths of large rivers, the Terrigenous sediments don't take long at all to accumulate on the ocean floor. But for the deeper ocean accumulations of Terrigenous sediments, they are part of a cycle that moves in a "slow and massive cycle" which includes mountains rising as the tectonic plates crash into each other, Garrison explains.

And as the mountains erode, the sediments from those eroding mountains are "…transported to the sea by wind and water…" and they collect on the seafloor. Garrison estimates that about 16.5 billion tons or Terrigenous sediment are transported to the sea by rivers, and about 100 million "metric tons" of Terrigenous sediment are transported from the land as "airborne dust and volcanic ash" (Garrison). Most Biogenous sediments are transported to the ocean from biological materials that are delivered from rivers. What happens is the siliceous and calcareous materials (once they are in the ocean) "…are extracted from the seawater by the normal activity of tiny plants and animals to build protective shells and skeletons" (Garrison). Most of the organisms that produce the Biogenous sediments "…drift free in the water as plankton"; most of the Biogenous sediments can be found where there is "high biological productivity" which tends to be near tectonic plates and "upwelling" (Garrison).