1. n. [Reservoir Characterization]

A succession of strata deposited during a single cycle of deposition. These sedimentary successions usually occur repeatedly, one above the other. The two main varieties are the cyclic units that are symmetrical cyclothems, and the rhythmic units that are asymmetrical cyclothems. Cyclic groupings of cyclothems are called megacyclothems, and cyclic groupings of megacyclothems are called hypercyclothems. Cyclothems are thought to be due to natural cycles, such as changes in sea levels related to changes in the volume of polar ice caps.