Size sorting of fine sediment during transport and deposition: difficulties with mud

McCave, I. N. (2005) Size sorting of fine sediment during transport and deposition: difficulties with mud. In: From particle size to sediment dynamics, International workshop. Research Centre Terramare, Wilhelmshaven, pp. 117-119.

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Abstract

The transport and deposition of contourites, involving many cycles of erosion and deposition under intermittently strong deep-sea currents, produces fine sediments that show some sorting. Palaeocurrent reconstruction with high temporal resolution requires sensitive parameters from rapidly accumulating and continuously deposited fine sediments. As most structures are severely degraded by biological disturbance, grain-size parameters are needed and the mean size of medium to very coarse silt has proved to be a useful measure of the speed of the depositing flow. Because these sediments are cohesive, they pose several analytical problems not encountered in the study of sands and gravels. It is important to remember that for the finest sediments (but not for sands) the disaggregated state in which the samples are analysed is not the state in which they were deposited, because that involved varying degrees of particle aggregation. Therefore, dynamical inferences may not be made from the properties of the whole disaggregated size distribution. However, as particles increase in size, they become less prone to aggregation, and aggregates are more easily broken up by turbulent stresses. It was this fact that led McCave et al. (1995b) to propose the use of the 10–63 mm silt fraction, ‘‘Sortable silt’’ (mean size denoted by SS), as a flowspeed indicator, because the grains were more likely to have been deposited individually in response to fluid stresses. Because the particle size is not sensitive to the flow direction, but responds to the scalar flow speed, the latter term is used here rather than ‘‘f low velocity’’, which has vector connotations.

Item Type: Book Section
Uncontrolled Keywords: 2006 AREP 2005 P IA50
Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Volume: Report
Page Range: pp. 117-119
Depositing User: Sarah Humbert
Date Deposited: 16 Nov 2011 16:46
Last Modified: 23 Jul 2013 09:58
URI: http://eprints.esc.cam.ac.uk/id/eprint/1544

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