A cyclothem is a series of repeating sediments representing the transgression and regression of wateror the submergence and emergence of land.
In coal-bearing strata, changes in depositional environment produced a cyclic repetition of beds. The cyclothem is defined as a series of beds deposited during a single sedimentary cycle.
The consist of shale, limestone, shale, coal, underclay, limestone, shale, and sandstone.
Sub-environments of a delta as for the Carboniferous and a graphic log of a typical sedimentary succession for a delta illustrating the different sediments from mudstones coarsening up into sandstones.
© Stuart Jones (2015)
https://dalesrocks.org.uk/swaledale/carboniferous-layers-of-the-landscape/deltas-and-big-trees/