Week Three - Week Three(Jan 29 31 Marine Sediments 11:03:00...

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Week Three (Jan 29 & 31) 29/01/2008 13:03:00 January 29, 2008 Marine Sediments Sediments: Particles that accumulate in a loose unconsolidated form May be biological or inorganic Usually classified by size and origin  Sediments are sampled using various coring devices Grab Sampler: Surface sediments (disturbed) Box Corer: surface sediments (undisturbed) Multicorer: Surface sediments (very undisturbed) Gravity Core: Record several meters long Piston Core: record tens of meters long Ocean Drilling: Records to ~2km long; also dill into crust Paleocenography: K-T boundary (65 ma) Sediment size determines  Boulder >51.2 cm Cobble 6.4-51.2 cm Pebble 4mm-6.4cm Granule 2-4mm Sand 63 micrometers-2mm Silt 4-63micrometers
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Clay <4micrometers settling rate and transport  The main factor controlling sinking rate of mineral grains in still water is  particle size (larger=faster) Smaller particles have greater surface area to volume ratio and therefore  greater frictional resistance to sinking  Smaller particles are therefore transported more easily because they settle  out of waters more slowly Fine sediments may be resuspended by bottom currents Ultrafine sediments (clay to fine silt) behave cohesively due to electrostatic  attraction  Stokes Law o Theoretical sinking rate of a spherical particle through a still fluid  o Variables: particle size, density of the particle or the fluid o Fluid viscosity (resistance to flow) o Typical settling time through ocean (~4km) Sand: Few Days Silt: few months Clay: few decades  Particle Aggregation: Packaging   Biogenic sediments are predominately either calcareous or liliaceous Produced by organisms 
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