The Bouma Sequence (after Arnold H. Bouma, 1962-2011) describes a classic set of sedimentary beds (turbidites) deposited by a sediment-water turbidity current. The Bouma Sequence specifically describes the medium grained variety, which are usually found in the continental slope or rise setting.
The Bouma Sequence is divided into 5 distinct beds labelled A through E, with A being at the bottom and E being at the top; each bed is described by Bouma as having a specific lithology (see below). In a real Bouma sequence, some beds may be missing - Bouma describes the ideal sequence.
The beds are:
- E: Muds, ungraded, often bioturbated...
- D: Parallel laminated silts.
- C: Cross laminated sands.
- B: Parallel laminated sands.
- A: Sands and any larger grains the turbidity current was carrying at the time of deposition.
The base of the sandstone, below A, is scoured.