The series of transgressions and regressions that produce cyclothems were likely produced by

The series of transgressions and regressions that produce cyclothems were likely produced by Glaciation.

Explanation:

Glaciation is a movement of glacier which can be very intense sometimes. The plate tectonic theory suggests that the continental movement make the glacier to move. These movements cause the production of cyclothems. Cyclothemes are the sequences of "marine and non-marine sediments". The various types of 'sedimentary rock beds' occurred in the specific sequences in the interior regions of continents. These order sequence of rocks are called as the cyclothems. The cyclothems are used worldwide to explore the coal deposits.

It is c. naturally in the environment

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