The deposition of sediment is the natural process by which particles of solid material are transported by wind, water and ice and deposited in a new place.
The term deposition can also apply to minerals and salts dissolved in water and carried to places they were not previously present or towards sites where they do not naturally occur.
The coarser materials get deposited first and finer ones later. By deposition depressions get filled up. The same erosional agents viz., running water, glaciers, wind, waves and groundwater act as a gradational or depositional agents also.
Deposition occurs when the forces responsible for sediment transportation are no longer sufficient to overcome the forces of gravity and friction, creating a resistance to motion; this is known as the null-point hypothesis.
Deposition can also refer to the buildup of 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.
