Ocean sediments

Think about this Where does the sediment on the ocean floor come from?

Through studying the thickness and composition of sediments a scientist can learn about  Tectonic history  Marine life evolution  Past climates  Past flow patterns of water  Volcanism  Fluctuations of sea level  Meteorite impacts  Mass extinctions In other words you can learn a lot from a pile of dirt!

Sediment particles are classified by their source, size and composition

Water is always flowing down hill, eroding and transporting sediment, but it is not the only source

Lithogenous sediment =fine and course grains that are produced by weathering and erosion of rocks on land  Lithogenous or rock-derived sediments - primarily from soils on the continents and transported by rivers and winds (weathering and erosion). A second source of this sediment type is volcanoes, both terrestrial and undersea (tephra) ¾ of all marine sediment

Biogenic sediment = fine and course grains that are derived from the hard parts of sea life, shells and skeletons Covers ~ 55% seafloor Three major groups based on chemical composition. In order of abundance:  Siliceous muds = formed of silica (SiO 2 ) from come from plants called diatoms and animals called radiolarians  Calcareous muds = formed of calcium carbonate (CaCO 3 ) from plants called coccolithophores (phytoplankton) and animals (zooplankton) called foraminifera and pteropods. 

3. Phosphatic sediments - come from bones, teeth and scales of fishes and other marine vertebrates (fecal pellets)

Hydrogenous sediment Particles that are precipitated by chemical or biochemical reactions in the mud or directly from seawater.  Manganese and phosphate nodules (which are known to cover 20-50% of the Pacific Ocean bottom)  Overall covers less than 1% seafloor They form very slowly around nucleation centers such as pieces of bones or teeth.form

And yet more! Cosmogenous sediment = very tiny grains from outer space  Bits of meteorites ( About 10,000 to 100,000 tons of meteorites and cosmic dust fall on the earth's surface everyday - can be found everywhere)meteorites  Covers much less than 1% of ocean floors

Particle size- the most common classification strategy for eroded sediment, based on the diameter of the grains Particle size- the most common classification strategy for eroded sediment, based on the diameter of the grains a. gravel- sand- mud-colloid b. the smaller the sediment the easier it is to move, larger particles are harder to move c. larger particles tend to stay closer to shore smaller out farther in the ocean particles smaller than.004 mm can remain suspended for hundreds of years (silt)

Sorting of sediment – the organization of the sediment particles a. Well sorted sediment = sediment that has similar grain size throughout (homogenous) This happens where energy levels remain constant (deep sea) b. Poorly sorted sediment = random mix of grain size gravel – silt (Heterogeneous) this happens where energy levels fluctuate (base of a seashore cliff)

The finest particles take years to finally settle out and can be carried thousands of km from their entry point. They are found throughout the oceans, but as in the cases of river sediments, their accumulation rates (and their thickness) decrease as one gets further away from the continents.