Cyclic sedimentation

Cyclic sedimentation: A term applied to a sequence of sediments which change their character progressively from one (extreme) type to another followed by a return to the original type. A typical example would be:

• Decreasing salinity (Fresh water deposits, Brackish water deposits)
• Increasing salinity (Marine deposits, Brackish water deposits, Fresh water deposits)

representing a marine incursion into an otherwise freshwater environment. The essential features of the cyclic unit is the steady sequence of changes, starting and finishing with similar types. This may be symbolically expressed: a b c d c b a - Cyclic units tend to be large in thickness and extent.