Turbidite is a conventional in the geology term for a from a turbulent flowing slurry or suspension flow (English " turbidity current" ) arisen rock that goes back to a short-term, avalanche-like transport and deposition process in the sea or in a lake. Most turbidites occur not individually, but often several 100 meters thick layer packets, which consist predominantly of fine sand and clay.

The name derives from the turbulence of the starting material of Turbidits transporting liquid. From the transport mechanism related sediments of other depositional environments, which go back to turbulent flow of other media, are, for example, avalanches, lahars and pyroclastic flows. The causative turbulent suspension currents are demarcated as deposition mechanism of turbidites from other geologic mass movements such as mudflow, landslide, debris flow, grain flow or Laminiten.

The importance of turbidites and their role in the formation of deep-sea sediments is understood only since the beginning of the Turbiditforschung from about 1960. Before the occurrence of apparently resulting in shallow sea rock sequences and shallow sea fossils in the midst of demonstrated in the deep sea sediments has been a difficult problem of geology.


A turbidite is deposited by suspension currents. These are formed from deposits on submarine slopes, for example on continental slopes that are unstable due to strong water saturation currents or vibrations about by earthquakes and slip off. By landslide and the resulting turbulence originally contiguous starting material can segregate into its individual components and in limbo ( suspension ) are kept so that it can travel long distances by flowing to the sea floor water, partially over several 100 km. Because of the beginning of the flow usually abrasive effect of a suspension flow deeply incised submarine underwater canyons are formed in continental shelf about before estuaries. At the output of the canyons, the current on the seabed depending on the flow of energy spreads from initially linearly concentrated to spread like a tongue at the end of the flow path. During the flow, the floating elements are sorted according to their buoyancy in suspension flow, fragile components such as shells are hardly broken, large foreign components experienced a considerable boost, which depends mainly on their surface. The turbulent flow finally starts to wane, the floating ingredients settle.

Rock formation

Characteristic of turbidites is the graded bedding within a layer or rock bank and the occurrence of a broad range of grain sizes within a bank, which are poorly sorted. The base area of ​​the Turbidits is always very sharply demarcated from the underlying layer and often curled weitspannig. The base of the rock bank usually consists of the coarsest represented material, such as gravel or sand. Towards the top, the grain size becomes increasingly fine and often turns into silt or clay. This grading is sometimes only at the rock - to identify thin section under the microscope. As a top layer of a fully formed Turbidits a resulting from the deposition of fine-grained suspended between suspension flow events capable of deep-sea sediments is usually adapted to the often traces can still be seen from ground-dwelling marine life. Turbidites occur in a layer stack as many consecutive Einzelturbidite in most cases.

The characteristic sequence of coarse grains at the base to fine-grained sediment in the upper part of a Turbidits is divided into five sections and named after the scientist Arnold H. Bouma as Bouma sequence. A distinction is made from the bottom up with letters designated five typical sections of a Turbiditschicht:

  • E: pelagic location, often with trace fossils ( Ichnofauna )
  • D: upper horizontally stratified layer ( silt, clay )
  • C: Location of current ripples, convolute bedding occur often (fine sand, silt )
  • B: lower horizontally stratified layer ( sand, fine sand )
  • A: graded position, with the coarsest grain at the base (gravel, sand )

Subordinately in turbidites on further characteristic features, which go back to the mode of origin. Often the base of the rock bench is littered with the negative molds of footprints in the subjacent rock layer, which go back to bouncing, rolling and grinding movement of larger components of the suspension flow. This impression, grinding and rolling marks are the German-speaking often with their English names used ( "bounce mark", "drag mark", "roll mark" ). In addition to these marks at the base of Turbidits are often structures such as ripple mark, plate structures, flow marks ( "flute cast" ) or Kolkmarken to see, caused by the flow of the suspension flow over the ocean or the sea bed. All these features may give a clue to the direction of flow.

By solving of already slightly solidified layers from the substrate in the flow path of the suspension flow and its windup during transport a winding stratification occurs ( " convolute bedding "). Sometimes largely solidified layers of the substrate are moved from the suspension flow, so that large, still partially coherent or broken fragments of foreign rocks ( Olistholith ) are expanded or added embedded in the normal consequence of a Turbidits.

Turbidites may have very different manifestations due to their formation. The rock reflects at first glance, especially the precursor sediment involved in its creation, such as clay slurry, lime mud or sand deposits. In addition, the rock -building sediment particles can differ greatly in grain size. In addition, the suspension causing currents transport in many cases, in addition to clay, silt and sand fragments of fossils such as shells or plant residues, which clearly salient size and shape determine the appearance of the rock in part by their.

Except for these layers of far transported, usually the flat sea entstamme ligand shell or plant residues are turbidites poor in fossils. In the rock can often determine microfossils, which are allocated to the deep sea.

Individual turbidites can often be traced over long distances. The rock body is designed as a more or less elongated, tongue-shaped body, which can form a large body of rock along with numerous other, overlapping turbidites. Based on the deposition location that can often be derived from the formation of the Turbidits and the layering sequence, turbidites are divided into two end members:

  • Proximal turbidite: rock from a suspension flow at the output of an underwater canyons or near the beginning of the deposition. Due to the high flow rate, the individual components are relatively large, Einzelturbidite usually have an erosive base and are not formed until the occurrence of fine-grained material. Frequently an inverse gradation on the basis.
  • Distal turbidite: rock transported far suspension currents with low energy without graduation, with sharp base contacts and layered fine debris or fine sand layers.


Rocks, which consist of turbidites, occur in the world and in rocks of nearly every age. Because of its origins, they occur more frequently in regions such as river deltas have a high sediment supply. Also at the edge of the continental shelves or in deep-sea trenches, which have a large height difference between the position of the output sediment and the ocean floor, turbidites are deposited preferentially in recurrent episode. The Turbiditfolgen be brought mainly with sediment deposits in mountain building in conjunction. For rock sequences of turbidites with intercalated deep-sea sediments of the flysch term has come to be in geology.

Turbidites also occur in non-marine waters. One finds, for example, turbidites at the mouths of rivers into ponds or lakes.