There are four basic types of marine sediments, all of which are grouped and ordered by the origin of their particles, the grain sizes, and where they are deposited. These four kinds include lithogenous, biogenous, hydrogenous, and cosmogenous. All of these are different from one another in some way but all share in common the tendency to collect along the floor of the oceans as a testament to many natural processes such as weathering, erosion, and collision.

          Lithogenous sediments are formed by the weathering process and are made up of small particles of weathered rocks and oceanic volcanoes. They are often formed together when metal and silicate ions bond. There are two types of lithogenous sediments; terrigenous and “red clay” and they are different because of the process behind their existences. For instance, terrigenous sediments are produced as a result of the weathering process of rocks above the water. These eroded particles are carried by the wind and other natural means to the oceans and are deposited at the bottom. Although it can be easily found in river beds, not much of this finds its way to the deep ocean. Red clay lithogenous sediment, on the other hand, is plentiful in the ocean. It is reddish-brown (hence the name) and is a combination of terrigenous material and volcanic ash. It is transported to the oceans by currents and wind and it settles in deep places along the ocean floor.

          Biogenous sediments are formed from the insoluble remains of past life forms and parts such as bones and teeth. In many areas where the water is shallow, a majority of these sediments are the remains of shells or fragments from shelled sea creatures as well as corals. In the deep sea where there is no such a high concentration of these life forms, biogenous sediment is made from the microscopic shells that are deposited by tiny plants, animals, and plankton that live on the water’s surface and eventually make their way down to the ocean floor.

          Hydrogenous sediments are formed by precipitation of minerals from the ocean’s water or can be formed as a new mineral as a result of chemical reactions between the water of the ocean and sediments that already exist on the ocean floor. Chemically speaking, this is an interesting sedimentary process because of the reactions that take place. For instance, the water of earth’s oceans contains ions that have already been dissolved. When evaporation occurs and large amounts of these ions remain the area can become saturated with the leftovers from this process, salt.

Cosmogenous sediments are extraterrestrial in nature and are generally like miniature meteorites. These sediments are the remains of impacts of large bodies of space material (such as comets and asteroids). They are comprised of silicates and mixtures of different metals and, as one might imagine, they are not incredibly common to find. This is rather surprising because there is a constant “rain of these materials that falls to earth daily.  The amounts of such sediments also leads researchers to wonder if these space-driven events might have been responsible for mass extinction and thus these sediments hold several possible keys to future understanding of ancient life on earth.

Other essays and articles in the Main Archives related to this topic include : The Contributions of the United States to Global Warming & Climate Change   •   An Argument Against Drilling in the Arctic National Wildlife Refuge (ANWR)  •  Wetlands : The Ecological Effect of Loss