The dirty truth…about sediments Sediment is particles of organic or inorganic matter that accumulate in a loose, unconsolidated form. Most of the ocean floor is continuously being “dusted” by a continuous rain of sediment from many sources Accumulation rates range from a few centimeters per year to the thickness of a dime every thousand years!

There are few sediments near the mid-Atlantic Ridge because the ocean floor is fairly “new” here…

Brittle Stars (a type of starfish Brittle Stars (a type of starfish!) leave tracks in the sediment on the continental slope off of New England at a depth of 4,852 feet.

Ripples in the ocean floor sediment caused by the Antarctic Circumpolar Current (depth is 13,153 feet!)

Web link for total sediment thickness

Sediments can be classified by Size or by Source. A size classification also tells us something about how quickly a sediment particle will sink due to gravity, and thus it’s time to fall to the bottom. *Clay particles may lump together and fall more quickly

Erosion – breaking up of materials (usually above sea level) into smaller particles by physical and chemical processes. Transportation – the movement of eroded particles in a current of sufficient velocity to keep them suspended. The required velocity will depend on the size of the particles. Deposition – particles falling out of the transporting current and sinking to the ocean floor. Also called “Sedimentation”

The Challenger Expedition resulted in a sediment classification system based on the source of the sediments…

Terrigenous Sediments are the most abundant by volume Terrigenous Sediments are the most abundant by volume. They derive from eroded from erosion of continents and islands. Quartz, the primary mineral in granite, is the most common type of material. Estimates are that about 16.5 billion tons of material are transported by rivers into the sea each year. 1,650,000,000 x 2000 lbs!

Biogenous Sediments are the next most common, and found in the highest percentage of area in the deep ocean area. They are also abundant near coasts where more nutrients are available. They are either Silicon or calcium based. The silicon or calcium was extracted from the sea water to make shells and skeletons for small ocean plants and animals (phyto-plankton and zoo-plankton).

Hydrogenous Sediments are minerals that have precipitated (“fallen out of”) directly out of seawater due to changes in water temperature, salinity or pressure. The most common examples are manganese nodules found in some deep seabeds, and phosphorite nodules found near some coasts.

Cosmogenous Sediments are extra-terrestrial Cosmogenous Sediments are extra-terrestrial! They make up a very small percentage of total sediments, are are usually well-mixed with other, more abundant sediments. They arise from “interplanetary dust”, which is silt and sand-sized micrometeorites that come from asteroids and comets or from collisions between asteroids. The silt sized particles settle slowly, but the larger ones may heat due to atmospheric friction and be the “shooting stars” that people see. About 30,000 tons falls to Earth each year!

Terrigenous Sediments being transported into the Gulf of Mexico by the Mississippi River

Volcanic ash being thrown into the atmosphere in the 1991 eruption of Mt. Pinatubo in the Philippines. Other images

Dust from the Sahara Desert being blown across the Atlantic towards Florida. NASA article

Microtektites, very rare particles that began a long journey when a large body impacted the Earth and ejected material from Earth’s crust. Some of this traveled through space, re-entered the atmosphere, and melted. Size is about 0.8 mm. Other image

Distribution of Sediments

Sediments of the Deep Ocean Basins Turbidites – mixtures of sediment and water periodically rush down the continental slope (cutting submarine canyons!) and then eventually slow down and deposit the sediments. Link to web Clays are the finest terrigenous sediments. Accumulatiojn may be as small as 1/8 inch every 1000 years! Oozes – biogenous sediment are the most common in the deep oceans, but only because few terrigenous sediments get this far. A deep ocean sediment with at least 30% biogenmous is termed an “ooze”…There are siliceous oozes (silicon-based!) and calcareous oozes (calcium- based!). They dissolve below about 14,800 feet.

Organisms that contribute to calcareous oozes… Foraminifera Hastigerina - 2” wide! Much smaller planktonic Rosalina Coccolithophores, a form of planktonic algae

Calcium carbonate (CaCO3) compensation depth

Organisms that contribute to siliceous oozes… Amoeba-like radiolarians, found in warm waters A Diatom, a single-cell alga, found in cold waters Other images

Poop Pictures…. A fecal pellet of a small planktonic animal – this will sink in about 2 weeks A 2,000 times enlargement showing the indigestible organisms it ate..these alone would take months to sink if they were by themselves…

Hydrogenous Sediments Manganese nodules… Cross section of a 4 ½ nodule Lemon-sized nodules on pacific floor

General Distribution of Deep Ocean Sediments

Studying Sediments A “Clamshell” Sampler

A Piston Corer

Studying an ocean sediment core sample

Storage for core samples JOIDES Resolution, a deep-sea drilling ship. It can drill to a depth of 30,000 feet below sea level!

Seismic Analysis of ocean sediments

And some sample data!

Ages of Pacific Ocean Sediments

Marine Sediments on Mars??