page_title: Turbidite
section_title: Formation
hierarchical_section_title: Turbidite / Formation
context_page_description: A turbidite is the geologic deposit of a turbidity current, which is a type of sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean.
context_section_description: Turbidites are sediments which are transported and deposited by density flow, not by tractional or frictional flow.
  The distinction is that, in a normal river or stream bed, particles of rock are carried along by frictional drag of water on the particle (known as tractional flow). The water must be travelling at a certain velocity in order to suspend the particle in the water and push it along. The greater the size or density of the particle relative to the fluid in which it is travelling, the higher the water velocity required to suspend it and transport it.
  Density-based flow, however, occurs when liquefaction of sediment during transport causes a change to the density of the fluid. This is usually achieved by highly turbulent liquids which have a suspended load of fine grained particles forming a slurry. In this case, larger fragments of rock can be transported at water velocities too low to otherwise do so because of the lower density contrast (that is, the water plus sediment has a higher density than the water and is therefore closer to the density of the rock).
  This condition occurs in many environments aside from simply the deep ocean, where turbidites are particularly well represented. Lahars on the side of volcanoes, mudslides and pyroclastic flows all create density-based flow situations and, especially in the latter, can create sequences which are strikingly similar to turbidites.
  Turbidites in sediments can occur in carbonate as well as siliciclastic sequences.
  Classic, low-density turbidites are characterized by graded bedding, current ripple marks, climbing ripple laminations, alternating sequences with pelagic sediments, distinct fauna changes between the turbidite and native pelagic sediments, sole markings, thick sediment sequences, regular bedding, and an absence of shallow-water features. A different vertical progression of sedimentary structures characterize high-density turbidites.
  Massive accumulations of turbidites and other deep-water deposits may result in the formation of submarine fans. Sedimentary models of such fan systems typically are subdivided into upper, mid, and lower fan sequences each with distinct sand-body geometries, sediment distributions, and lithologic characteristics.
  Turbidite deposits typically occur in foreland basins.
caption: Gorgoglione Flysch, Miocene, South Italy
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