Marine Sediments
Sources of Biogenous Sediments
- Calcereous organisms (CaCO3): foraminifera (zooplankton); coccolithophores (phytoplankton) - siliceous organisms (SiO2): radiolaria (zooplankton); diatoms (phytoplankton)
Cosmogenous Sediments
- derive mostly from interplanetary dust, and impacts by large asteroids and comets - interplanetary dust consists of silt and sand sized micrometeoroids that come from asteroids and comets or from collisions between asteroids - impacts of large meteors or small asteroids on teh crust of the earth form translucent oblong particles of glass called microtektites
Evaporites (Hydrogenous Sediments)
- form when there is restricted open ocean circulation and evaporation is high - as evaporation and water salinity increase, carbonates are formed, then gypsum, then sodium chloride
Biogenous Sediments
- formed biologically in the ocean(e.g. seashells, whole or fragments) - particles produced directly by marine organisms - most common made of calcium carbonate (CaCO3) or silica (SiO2) - production is highest on continental shelves (but terrigenous sediments still tend to be dominant except in mid-depth ocean "oozes")
Inorganic Carbonates (Hydrogenous Sediments)
- hydrothermal vents, or black smokers are hot springs discovered on oceanic ridges - water descends in the ridge floor until it comes into contact with very hot rocks - the superheated, chemically active water dissolves minerals and gases and escapes upward through the vents by convection
Rivers (sources of terrigenous sediments)
- lots of water moving to the oceans from rivers - around mountains there are rivers and lots of exposed rock
Marine Sediments
- particles of various sizes derived from a variety of sources that are deposited on the ocean floor - a vast "library" recording geologic, oceanographic, and climatic conditions - remarkably complete compared to land (oceans are young though, only ~280mya vs 3bya for continents)
Distribution of Biogenous Sediments
- production in surface waters: nutrients (nitrogen and phosphorus) are the ultimate factor controlling biological productivity - dilution to the sea floor: biogenous oozes do not occur where influx of terrigeous sediment is high - dissolution into deep waters
Where marine sediments come from
- rivers - winds - surface waters - volcanoes (both on land and submarine) - deep ocean water - outer space
Manganese and Phosphorite Nodules (Hydrogenous Sediments)
- rounded, hard lumps of Mn, Fe, and other metals - found on top of the ocean floor sediments - they have a layered structure formed by precipitation around a central nucleation object - phosphorite nodules occur at the depth of <1000m, mainly on the continental shelf, and they indicate abundant biological activity in the surface water - form very slowly, can't get very large
Volcanoes (sources of terrigenous sediments)
- volcanic ash and other volcanic debris come straight from a volcano and is transported by wind (at first) - sometimes water will move ash after the wind deposits it
Wind (sources of terrigenous sediments)
Can carry sediment very far distances in very large amounts - can cross oceans and seas
Terrigenous Sediments
Erosion of continents, volcanic ash (volcagenic) - consist of fragment (clasts) produced by: weathering (breakdown of pre-existing rocks: physical-reducing rocks to smaller fragments, and chemical-dissolving the minerals in rocks); erosion; transport and deposition by physical processes (running water, glaciers, wind, and gravity) - most common marine sediment by mass - mainly quartz and clay minerals - sources: rivers, winds (eolian), glaciers (ice-rafted debris), turbidity currents, volcanic eruptions - used to be more sediments, and more moved by wind (dryer, more loose sediment, less vegetation)
Red Clays
Fine-grained, reddish-brown terrigenous sediments that accumulate very slowly and cover the deepest abyssal basins - produced by chemical weathering
Glaciers (sources of terrigenous sediments)
Ice-rafted Debris - when a glacier reaches the sea, it breaks off into hunks of ice (icebergs) - icebergs float out to sea, gradually melting, and dumping the sediments trapped in the ice (ice rafting)
Hydrogenous Sediments
Precipitate (crystallize) from seawater - form in specific environments and they have many different compositions
Sediment Distribution
Two regions of sediment accumulation: - continental shelf (neritic sediments): influences of past sea level (relict sediments) - deep ocean floor (pelagic sediments): influences of latitude, distance from landmasses, calcium carbonate compensation depth (CCD); mostly red clay and biogenous oozes (fine grained material that accumulates slowly)
