Submarine levee

Depth of water

Shelf edge - Abyssal plain (120 - 5,000 m)

Circumstances

Levees around the submarine channels at the down stream of submarine canyons. Submarine channels and submarine levees are a part of Channel-Levee complexes which form submarine fan at the lower part of the continental slope. Sediments from the continental shelf flow as sediment gravity flows (Turbidity currents) in the submarine channels when an earthquake happens, and sediments flung up into seawater deposit on and outside of submarine levees. Turbidity currents pass intermittently, typically once every a few hundreds years. Levees formed at river banks are known as fluvial levees.

Sedimentary facies (Sediments)

Interbedded sandstones and mudstones, which called turbidite. A unit of turbidite (Bouma sequence) is composed of conglomerate, sandstone, and mudstone in order from the bottom. The ratio of fine sediments such as mud increases in proportion to the distance from submarine channels. Abyssal mudstone deposit between each turbidite unit.

Sedimentary facies (Structures)

Current marks on the basal plane of the conglomerate bed at the bottom of a turbidite unit. Graded bedding in the lower part, ripple marks in the middle part, and parallel foliations in the upper part of the sandstone bed at the middle of a turbidite unit.

Fossils

Shallow marine and terrestrial fossils carried by turbidity currents.