Sediments! ☺ January 19, 2009

Wentworth Scale of Grain Size Boulder Cobble Pebble Granule Sand Silt Clay

Benthic Sediments by the Numbers Cover 75% of seafloor Oozes = >30% biogenous material –Siliceous (14% of ocean surface area) –Calcareous (48% of ocean surface area) Abyssal clay (38% of ocean surface area)

Siliceous ooze SiO2 – opal Comes from diatoms & radiolarians deeper depths Less abundant han calcareous ooze b/c silica dissolves readily in ocean water Usu. <100 micrometers

Calcareous ooze CaCO3 Comes from coccolithophores & foraminiferans Dissolves under high pressure great depths) & in basic water, so only found in shallower water (<4500m)

Calcium carbonate Carbonate compensation depth: which CaCo3 same rate as replenished from above. Affected by CO2 concentrations, pressure, temperature, pH, productivity of calcareous-shelled organisms. Lysocline: which rate of CaCO3 dissolution significantly ↑

Types of Sediment Lithogenous (rocks, volcanoes, continents) Biogenous (remains of living organisms, usu. plankton) Cosmogenous (space) Hydrogenous (precip of ions dissolved in H2O)

Lithogenous: Examples Volcanic ash Ferromagnesian minerals (iron, silicate, magnesium compound) Igneous rocks –Extrusive = fine-grained –Intrusive = coarse-grained

Biogenous: Examples CaCO3 (foraminiferans, coccolithophores, coral reefs) Silica (SiO2) (diatoms, radiolarians)

Cosmogenous: Examples Nickel-iron spherules Tektites Silicate chondrules

Hydrogenous: Examples Manganese nodules (manganese dioxide, iron oxide) Phosphorite nodules (P2O5) (grow down into sediment) Calcium carbonate (not from coral)

Sediment Deposits Turbidites edge of continental margin (form continental rise) Phosphorite mined→phosphate (fertilizer) Glacial deposits = from continental shelf, many formed during Pleistocene Epoch Rafting = sediments carried from shore by icebergs & deposited when they melt Stromatolites = dome-shaped calcareous structures in shallow water that had been secreted in layers by ancient cyanobacteria

Miscellaneous Fecal pellets = detritus material from plankton; responsible for carrying particles from shallow depths to deep in ocean Sediment maturity = ↑ as move away from source→more sorting of particles, ↓ clay content, rounding of grains such as sand Huljstrom’s Diagram: relationship b/w current velocity & erosion/transportation/deposition of different-sized grains

Accretion Process by which material is added to a tectonic plate or landmass (could be sediment, volcanic arcs, seamounts, etc.) –Plate accretion (in subduction, sediment scraped off subducted plate attaches to top plate; island arcs & seamounts collide w/ continent, add to it.) W. Coast, E. Coast of Australia, New Zealand. –Landmass accretion (addit. of sediment to coastline/riverbank. Alluvium deposits!)

Random Landforms Seamount: elevation of sea floor 1000m or higher –Guyot: seamount w/ flat top –Seapeak: seamount w/ peak

Random Terms Bioturbation: disturbance of sediment near water interface by benthic organisms (burrowing worms)