Bouma sequence

The Bouma Sequence (after Arnold H. Bouma, 1932–2011) describes a classic set of sedimentary structures in turbidite beds deposited by turbidity currents at the bottoms of lakes, oceans and rivers.Bouma A interval of a turbidite showing dish structures with pillar structures between the dishes. Northern California.Cretaceous turbidite showing Bouma A-D layers. Pigeon Point Formation, Pescadero Beach, California.Bouma B and convolute-laminated Bouma C layers in a sandy turbidite. Cozy Dell Fm, Topatopa Mountains, Calif.Bouma C-D layers of distal turbidites deposited in a levee crevasse splay. Venado Fm, Lake Berryessa, Calif. The Bouma Sequence (after Arnold H. Bouma, 1932–2011) describes a classic set of sedimentary structures in turbidite beds deposited by turbidity currents at the bottoms of lakes, oceans and rivers. The Bouma sequence specifically describes the ideal vertical succession of structures deposited by low-density (i.e., low sand concentration, fine-grained) turbidity currents. An alternate classification scheme that is generally called the Lowe sequence exists for the ideal vertical sequence of structures deposited by high-density flows. The Bouma sequence is divided into 5 distinct layers labelled A through E, with A being at the bottom and E being at the top. Each layer described by Bouma has a specific set of sedimentary structures and a specific lithology (see below), with the layers overall getting finer-grained from bottom to top. Most turbidites found in nature have incomplete sequences - Bouma describes the ideal sequence where all layers are present.