A muddy river is an indication that the river is carrying a large load of sediment. Sand bars on inner banks formed when flow velocity decreased and larger sediment was deposited. Clastic sediments are deposited when the velocity of the transporting medium drops. Delta of the Ebro river, Spain, which deposits sediment into the western Mediterranean Sea. Image courtesy of NASA .
Deposition concentrates sediments of the same size together.
As the pile of sediment grows, sediment at the base of the pile becomes compacted , squeezing out water and forcing the grains closer together. Fluids circulating through the pile precipitate minerals to cement the grains together, converting the sediment into a cohesive aggregate, i.e. a rock. The processes of compaction and cementation that convert sediment into sedimentary rock are termed lithification . Shale, Mudstone Silt 0.0039 to 0.0625 mm Siltstone Sand 0.0625 to 2 mm Sandstone Gravel more than 2 mm Conglomerate Chemical sedimentary rocks Chemical sedimentary rocks are precipitated from a solution as a result of changing physical conditions. The most common solution is seawater.