Sequence Stratigraphic Unit
Sequence stratigraphy is a branch of lithostratigraphy. The basic unit of lithostratigraphy is the bed, but the basic unit of sequence stratigraphy is the sequence. A sequence comprises a set of relatively continuous and formation-related rock strata, the top and bottom of which are unconformities or correlative conformities. Sequence stratigraphic units can be subdivided into megasequences, supersequences, sequences, systems tracts and parasequences. Sequence boundaries are the results of geologic events or sea level changes.