The mechanics of high velocity deposition of fine-grained sediment from suspension
- Univ. of Montana, Missoula, MT (United States). Dept. of Geology
Sequences of fine-grained sediments are commonly assigned to low energy depositional environments. This assignment is based on the conventional model for deposition from suspension which requires only that the settling velocity of the grains be greater than the shear velocity of the flow. This paper reports a major flaw in the conventional model for deposition from suspension. The flaw is shown by discrepancy that exists between a flow's velocity as predicted by bedform phase diagrams using the sedimentary structures and a flow's velocity as predicted by the grain's settling velocity. Explanations for this discrepancy all assume the conventional model for deposition from suspension is correct and the velocities indicated by the bedform phase diagrams are incorrect. Two conditions must be satisfied to maintain sediment in suspension. The first, called the velocity requirement, states that the upward velocity of the turbulence must be greater than the settling velocity of the particles in the suspension. The second, called the stress requirement, states that the upward directed stress produced by the turbulence must be greater than or equal to the stress produced by the immersed weight of the sediment in the suspension. In other words, the velocity requirement, by itself, is not sufficient to maintain sediment in suspension. Evidence for high velocity deposition from suspension in turbidites, tempestites and tidalites include the following primary sedimentary structures: planar parallel lamination; long, very low angle cross-lamination; hummocky cross-stratification, and thick intervals of climbing ripple cross-lamination.
- OSTI ID:
- 5807476
- Report Number(s):
- CONF-921058--
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Journal Name: Geological Society of America, Abstracts with Programs; (United States) Vol. 24:7; ISSN GAAPBC; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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