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Bouma sequence Idealized sequence of sedimentary structures observed in turbidity-current deposits. It is named after the geologist, A. H. Bouma, who first emphasized its generality (Sedimentology of Some Flysch Deposits, Elsevier, Amsterdam, 1962). The lowest unit, A, a massive or graded sand, is overlain progressively by the B (lower division of parallel lamination), C (ripple or convolute laminations), D (upper division of plane parallel laminations), and E (pelagic shale) units. Examples showing the entire sequence are not common. The sequence can be interpreted in terms of deposition under waning current conditions.