Cyclothems

In geology, cyclothems are alternating stratigraphic sequences of marine and non-marine sediments, sometimes interbedded with coal seams.

The cyclothems consist of repeated sequences, each typically several meters thick, of sandstone resting upon an erosion surface, passing upwards to pelites (finer-grained than sandstone) and topped by coal.

Depositional sequences have been thoroughly studied by oil geologists using geophysical profiles of continental and marine basins.

A general theory of basin-scale deposition has been formalized under the name of sequence stratigraphy.

[3] Some cyclothems may have formed as a result of marine regressions and transgressions related to growth and decay of ice sheets, respectively, as the Carboniferous was a time of widespread glaciation in the southern hemisphere.