Ocean Floor Sediments 20.3

Seafloor sediments Ocean floor is mantled with sediment Sources Turbidity currents Sediment that slowly settles to the bottom from above Thickness varies Thickest in trenches – accumulations may approach 10 kilometers

Seafloor sediments Thickness varies Pacific Ocean – about 600 meters or less Atlantic Ocean – from 500 to 1000 meters thick Mud is the most common sediment on the deep-ocean floor

Inorganic Sediments Some of the ocean-basin sediments consist of rock particles that have been carried from the land to the oceans by rivers. Most of these sediments are deposited along the shore and on the continental shelf. Great quantities of these sediments slide down continental slopes to the ocean floor. The tremendous force of the slide creates powerful turbidity currents that spread the sediments over the deep ocean basin.

Some deep ocean-basin sediments consist of fine particles of rock, including volcanic dust. Icebergs provide sediments by carrying material from the land into the ocean. Meteorites contribute to ocean-basin sediments as cosmic dust un vaporized by earth's atmosphere falls to earth.

Seafloor sediments Types of seafloor sediments Organic sediments Shells and skeletons of marine animals and plants Most common are calcareous oozes produced from microscopic organisms that inhabit warm surface waters Siliceous oozes composed of skeletons of diatoms and radiolarians Phosphate rich materials derived from the bones, teeth, and scales of fish and other marine organisms

The two most common substances in organic sediments are silica and calcium carbonate. Silica comes from microscopic organisms. Calcium Carbonate come mostly from the skeletons of tiny organisms called foraminifera.

Chemical Deposits Many chemical reactions take place in the ocean in which solid material is formed. Nodules are lumps of minerals that form on abyssal plains. They are mostly formed of oxides, manganese, nickel, and iron.

Physical Classification of Sediments Two general types of sediments are found on the ocean floor. Muds are very fine silt and clay sized particles. Red clay is common on abyssal plains. About 40% of the ocean floor is covered with a soft organic sediment called ooze.

Two types of ooze: Calcareous ooze mostly calcium carbonate and is never found below 4,500 m. Siliceous ooze mostly silicon dioxide and found in cool, nutrient rich ocean waters around Antarctica.