ocean since quotations
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modified_lecture_notes_chapter_4.pptxChapter 4 Marine Sediments The Key to the Ocean’s History!
http://scienceblogs.com/startswithabang/2009/05/could_an_asteroid_have_wiped_o.php
K-T Boundary
Sediment = solid particles of organic or inorganic matter that accumulate in a loose, unconsolidated form.
Examples include sand, gravel, shell fragments, bones…
Sedimentary rock = the rock formed by consolidation (lithification) of sediments.
Examples include sandstone, conglomerate, and limestone…
The type of sediment deposited in any area depends on the geography of that area.
latitude,
climate,
environment…
For example, there will be different sediments near the coast than at the bottom of the deep sea floor.
| Particle Name | General Size | Size Range (mm) | Energy of Environment of Deposition | Settling Rate | Time to sink 4 km (2.5 miles) | Example |
| Boulder | Arm sized (Coarse) | >256 | High Energy | Rivers and beaches | ||
| Cobble | Fist sized | 64 - 256 | ||||
| Pebble | Pea sized | 4 - 64 | ||||
| Granule | Rice sized | 2 - 4 | ||||
| Sand | Just visible w/o magnification | 1/16 - 2 | 2.5 cm/sec (1 in/sec) | 1.8 days | Beaches | |
| Silt | Feels gritty | 1/256 – 1/16 | 0.025 cm/sec (1/100 in/sec) | 6 months | Outer continental shelf | |
| Clay | Feels smooth (Fine) | 1/4096 – 1/256 | Low Energy | 0.00025 cm/sec ( 1/1000 in/sec) | 50 years | Deep sea floor |
Marine snow = clumps or aggregates of fine grained sediments, fish scales, fecal matter, and dead micro-organisms.
bigger/heavier = sinks faster – weeks instead of years.
This “rain” of organic matter is an efficient mechanism for storing carbon on the deep sea floor (less global warming).
http://www.waterencyclopedia.com/Mi-Oc/Ocean-Biogeochemistry.html
http://www.whoi.edu/oceanus/viewImage.do?id=4950&aid=2387
Sediments can also be categorized by origin or source:
Lithogenous (terrigenous) sediments originate from eroding rocks on land and through volcanic eruption.
Biogenous sediments consist of the remains of once living things.
Hydrogenous sediments form directly from seawater.
Cosmogenous sediments originate from space.
Lithogenous Sediments come from land
most abundant in the ocean by volume
covers the 2nd largest area of the seafloor!
Eroded by water, wind, ice, and waves.
transported to the ocean by rivers, glaciers, landslides, and wind.
The thickest and most extensive deposits of lithogenous sediments are found on the continental margin.
Ice - Lithogenous sediments traveling to the sea trapped in a glacier
http://www.gettyimages.com/detail/200542371-001/Stone
Streams - Lithogenous sediments pour from the mouth of the Mississippi River into the Gulf of Mexico Garrison, 2012, Essentials of Oceanography
Gravity - Waves have undercut this cliff in Norfolk, England causing a landslide that will quickly wash into the ocean. http://commons.wikimedia.org/wiki/File:Coastal_Erosion_Hunstanton_Cliffs.jpg
Storm - Barrier Island breached and eroded by Hurricane Katrina http://rst.gsfc.nasa.gov/Sect14/Sect14_10a.html
Waves - Erosion of Banda Aceh, Indonesia by the “Christmas” Tsunami of 2004 http://www.msnbc.msn.com/id/6776380/ns/technology_and_science-science/
Lithogenous sediments:
Are the primary sediment of the continental margin.
Sediment size shrinks with distance from land
Transported seaward in the ocean by turbidity flows
Deposited as many thin horizontal layers
Layers may be hundreds or thousands of feet thick
Example: How much sediment will be deposited on a portion of the continental shelf after 1,000,000 years if the deposition rate is 30 cm/1000 years?
30 cm/1000 yr x 1,000,000 yr = 30,000 cm
given there are 2.54 cm/in
30,000 cm ÷ 2.54 cm/in = 12,00 in = 1000 feet (almost 1/5 mile)
Sedimentation rates average 10 – 40 cm/1000 years on the continental margin
Abyssal clay = Lithogenous sediments of the deep sea floor:
Mainly fine grained sediments deposited in thin layers Accumulation rates average 0.5 – 1 cm/1000 yr
http://www.noc.soton.ac.uk/gg/SEDCORAL/SEDCoral_sedtrans.html
Stream - Plume of suspended sediment makes its way far out to sea before settling to the deep sea floor
http://academic.emporia.edu/aberjame/wetland/mississippi/miss_delta.htm
Gravity - Turbidity currents suspend fine-grained sediments that travel far out over the deep seafloor before being deposited.
Duxbury and Duxbury, 2002, Oceanography
Wind - False color image of a dust storm in the Sahara Desert
http://jwocky.gsfc.nasa.gov/aerosols/africa/canary.html
Ash and cinders released during volcanic eruptions. This is transported to the ocean by the wind. Mt. Pinatubo, the Philippines
Icebergs can carry fine sediments and very large rocks (erratics) far out into the open ocean, where they are deposited as the ice melts. http://meteorite-recovery.tripod.com/2006/mar06.htm
http://meteorite-recovery.tripod.com/2006/mar06.htm
Biogenous Sediments are primarily but not exlusively composed of the remains of once-living things:
Biogenous Oozes contain >30% biological remains.
The 2nd most abundant by volume, and
Cover the greatest area of seafloor
Biogenous oozes are most plentiful under upwelling zones = areas where nutrient rich water rise from the deep seafloor to the surface, providing nutrients for life.
There are two classes of biogenous sediments
Calcareous oozes are composed of calcium carbonate-rich remains (similar to limestone or marble)
Siliceous Oozes consists mainly of silica-rich remains (glass-like)
Neritic Calcareous Biogenous Deposits:
Coral Reef Communities (e.g. Great Barrier Reef, Florida Keys)
warm, shallow water environments
Stromatolites
mats of single-celled algae trap fine calcareous sediments and/or produce calcareous fibers
prefer warm, shallow, high salinity water
similar to the first, simplest fossils every found
Pelagic (and rarely neritic) Calcareous Biogenous Oozes:
Most common in low and mid-latitudes
Can contain species of two common microscopic organism families
Coccolithophores
Foraminifera
Calcareous Biogenous Oozes:
Deposited at rates averaging 10-20 cm/1000 years below upwelling zone, 1-6 cm/1000 year elsewhere
Deposition rates ≠ accumulation rates as the slightly acidic waters near the deep seafloor dissolve the calcareous sediments.
CCD = the calcium carbonate compensation depth
= the depth at which the rate of calcareous sediment deposition equals the rate of calcareous sediment dissolution.
=>Below this depth no new calcareous sediments will accumulate.
=>The depth of the CCD varies from place to place depending on sedimentation rate and water chemistry.
Note that the old carbonate sediments, deposited above the CCD, do not dissolve once the seafloor sinks below the CCD!
Dating these sediments can give us information about when the seafloor was shallower than the CCD.
Figure 4.16, p. 113
Modern distribution of calcareous sediments.
Siliceous Biogenous Oozes are primarily pelagic:
Most common at the equator and near the poles.
Can contain species of two common microscopic organism families
Diatoms (cold water)
Radiolarians (warm water)
Garrison, 2007, Oceanography
Siliceous Biogenous Oozes:
Deposited at rates averaging 10-20 cm/1000 years below upwelling zone, 1-6 cm/1000 year elsewhere
Deposition rates ≠ accumulation rates as these also dissolve near the deep sea floor, but much more slowly
The thickest deposits of siliceous deposits are below areas of high productivity of siliceous organisms
Hydrogenous Sediments form by precipitating (falling out of) oversaturated seawater due to changes in temperature, pressure, or seawater chemistry.
Deposited at all depths from continental shelves to the deep sea floor
Rate of deposition is very slow, about 1 – 10 mm/1 my
Important components of the seafloor sediments only where lithogenous and biogenous sediments are missing
Examples of hydrogenous sediments include:
Phosphate deposits on the continental shelves below areas with lots of biological activity http ://www.teara.govt.nz/en/marine-minerals/2/2
Oolitic Sands – calcite “beads” formed in warm, shallow water areas with high biological activity. http ://www3.ncc.edu/faculty/bio/fanellis/biosci119/SEDIMENTS.htm
Hydrothermal deposits are also hydrogenous sediments.
Manganese Nodules scattered over wide areas of the deep sea floor are also hydrogenous sediments http://sgyq8pm.edu.glogster.com/ http://www.whoi.edu/science/B/people/sbeaulieu/H2O_new/H2O_images/mn_nodule.html
Salt deposits = evaporites formed naturally along arid (dry) climate coasts are also hydrogenous sediments
Cosmogenous Sediments originate in outer space and plummet through our atmosphere to fall into the ocean (some fall on land too).
Up to 300,000 tons splash into the ocean every year
Most are metallic, and rapidly rust away in the ocean.
Accumulation rates are very, very slow
Tektites, micrometeorites, and cosmic dust are the main examples.
http://blogs.nature.com/news/blog/2009/07/apolloplus40_-_the_mystery_of.html
http://fuse.ithaca.edu/4003/
http://www.uni.edu/morgans/astro/course/Notes/section4/new22.html
Of course, different types of sediment often get mixed together as they sink to the sea floor.
Biogenous sediments often contain a mixture of calcareous and siliceous sediments and almost always contain at least a little clay (lithogenous sedimnets)
Lithogenous sediments usually contain a little bit of biogenous material
Different types of hydrogenous sediments are found in different regions of the seafloor
Pelagic deposits are dominated by biogenous oozes above the ccd and below areas of high siliceous productivity, abyssal clay dominate in areas with sparse biogenous oozes (the deepest part of the seafloor).
Neritic deposits are dominated by lithogenous sediments (with some biogenous and hydrogenous mixed in).
Resources from marine sediments:
Petroleum – oil and gas, form in sediments with high content of biologic materials.
Gas hydrates – ices of carbon dioxide, hydrogen sulfate, and methane hydrate.
These stay frozen at the cold depths of the seafloor, but melt when brought to the surface.
Form through bacterial decomposition of organic matter in sediments
Construction materials – sand and gravel used in concrete and fill
Evaporites – salt and gypsum, deposited as water evaporates nearshore
Phosphate – used for fertilizers, formed in warm, shallow areas with lots of biological material
Manganese Nodules – precipitate directly out of water on the deep sea floor
Rare-earth elements – from hydrothermal vents, deposited in abyssal muds
Paleo-oceanography = the study of marine sediments to determine the past history of that section of the ocean basin.
Scientists compare seafloor rock type, fossils present, and sediment thickness to what we see happening today
They can then infer the changes in location, tectonic activity, and seafloor depth experienced by that section of the seafloor over time.
These studies can also tell us about regional and global climatic variations, changes in ocean circulation patterns, and the movement of the continents through time
These studies can be thought of as giant 3-dimensional jigsaw puzzles with many pieces missing.
50 million years ago
http://www.valdostamuseum.org/hamsmith/location.html
Today
http://www.kidsgeo.com/geography-for-kids/0145-ocean-currents.php
