Sediment gravity flow

This turbidite from the Devonian Becke-Oese Sandstone of Germany is an example of a deposit from a sediment gravity flow. Note the complete Bouma sequence.

A sediment gravity flow is one of several types of sediment transport mechanisms, of which most geologists recognize four principal processes. These flows are differentiated by their dominant sediment support mechanisms,[1][2] which can be difficult to distinguish as flows can be in transition from one type to the next as they evolve downslope.[3]

Sediment support mechanisms

Sediment gravity flows are represented by four different mechanisms of keeping grains within the flow in suspension.

Resulting deposits

Diagram showing debris flow, turbidity current and traction processes in a single sediment gravity flow. The resulting deposit, which some geologists call a linked debrite, exhibits features of all three processes.

Description

Although the deposits of all four types of sediment support mechanisms are found in nature, pure grain flows are largely restricted to aeolian settings, whereas subaqueous environments are characterized by a spectrum of flow types with debris flows and mud flows on one end of the spectrum, and high-density and low-density turbidity currents on the other end. It is also useful in subaqueous environments to recognize transitional flows that are in between turbidity currents and mud flows. The deposits of these transitional flows are referred to by a variety of names, some of the more popular being "hybrid-event beds (HEB)", linked debrites" and "surry beds".[7] Powder snow avalanches and glowing avalanches (gas-charged flows of super heated volcanic ash) are examples of turbidity currents in non-marine settings.

Modern and ancient examples

Modern and ancient (outcrop) examples of deposits resulting from different types of sediment gravity flows.

Significance

Sediment gravity flows, primarily turbidity currents, but to a lesser extent debris flows and mud flows, are thought to be the primary processes responsible for depositing sand on the deep ocean floor. Because anoxic conditions at depth in the deep oceans are conducive to the preservation of organic matter, which with deep burial and subsequent maturation through the absorption of heat can generate oil and gas, the deposition of sand in deep ocean settings can ultimately juxtapose petroleum reservoirs and source rocks. In fact, a significant portion of the oil and gas produced in the world today is found in deposits (reservoirs) originating from sediment gravity flows.[9]

References

  1. 1 2 3 4 Middleton, G.V. and Hampton, M.A. (1973). "Sediment gravity flows: mechanics of flow and deposition". Turbidites and deep-water sedimentation. Pacific Section of the Society of Economic Paleontologists and Mineralogists. Short Course Lecture Notes, p. 1–38.
  2. Postma, G. (1986). "Classification for sediment gravity-flow deposits based on flow conditions during sedimentation" (PDF). Geology (Geological Society of America) 14: 291–294. doi:10.1130/0091-7613(1986)14<291:cfsgdb>2.0.co;2. Retrieved 6 December 2011.
  3. Visher, G.S. (1999). Stratigraphic systems: origin and application 1. Academic Press. 521. ISBN 978-0-12-722360-5. Retrieved 28 December 2011.
  4. 1 2 3 4 5 Lowe, D.R. (1982). "Sediment gravity flows: II. Depositional models with special reference to the deposits of high-density turbidity currents". Journal of Sedimentology (Society of Economic Paleonotlogists and Mineralogists) 52: 279–297. doi:10.1306/212f7f31-2b24-11d7-8648000102c1865d.
  5. Lowe, D.R. (2006). "Subaqueous liquefied and fluidized sediment flows and their deposits". Sedimentology 23: 285–308. doi:10.1111/j.1365-3091.1976.tb00051.x.
  6. 1 2 Gani, M.R. (2004). "From turbid to lucid: a straightforward approach to sediment gravity flows and their deposits". The Sedimentary Record (A publication of the SEPM Society for Sedimentary Geology) 2 (3 (Sept.)): 4–8.
  7. 1 2 Haughton, P., Davis, C., McCaffrey, W., and Barker, S. (2009). "Hybrid sediment gravity flow deposits - classification, origin and significance". Marine ad Petroleum Geology (Elsevier) 26: 1900–1918. doi:10.1016/j.marpetgeo.2009.02.012.
  8. Hampton, M.A. (1972). "The role of subaqueous debris flows in generating turbidity currents". Journal of Sedimentary Petrology 42: 775–793. doi:10.1306/74d7262b-2b21-11d7-8648000102c1865d.
  9. Weimer, P. and Link, M.H., eds. (1991). Seismic facies and sedimentary processes of submarine fans and turbidite systems. Springer-Verlag. 447 p.

See also

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