Deposition is the geological process by which material is added to a landform or land mass. Fluids such as wind and water, as well as sediment gravity flows, transport previously eroded sediment, which, at the loss of enough kinetic energy in the fluid, is deposited, building up layers of sediment.
Deposition occurs when the forces responsible for sediment transportation are no longer sufficient to overcome the forces of particle weight and friction, which resist motion. Deposition can also refer to the build up of a sediment from organically derived matter or chemical processes. For example, chalk is made up partly of the microscopic calcium carbonate skeletons of marine plankton, the deposition of which has induced chemical processes (diagenesis) to deposit further calcium carbonate. Similarly, the formation of coal begins with the deposition of organic material, mainly from plants, in anaerobic conditions.
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