Sediments In the Sea Chapter 12

The Study of Sediments Tools and Techniques: Clamshell sampler (Grab Sampler) Used when large sample of top sediment is needed.

Grab Sampler Set of jaws (like cranes) Descends to the bottom, jaws are open during descent. When it hits sediment they close and scoop up a sample of sediment. Brings up a lot of material but destroys layering. (Bedding)

Box or Piston Corers Penetrate sediment and bring up samples but leave bedding intact to study layers. Piston corer is able to bring up samples from deeper in sediment. Vacuum inside hollow metal tube drives it down into the sediment. To dig deeper JOIDES resolution (drilling ship) holes deeper than 2000m.

Seismic reflection Air gun transmits sound waves into water which penetrate into seafloor. Some reflect back due to density changes. Wave’s return speed depends on density (faster means denser, slower means less dense) Can also help determine slope of layers, fracture, discontinuities ect.

Stratigraphy and Paleoceanography https://www.youtube.com/watch?v=FXhMx37bOwk https://www.youtube.com/watch?v=eUwXJBsGYBM https://www.youtube.com/watch?v=cmpY5BpLLMc https://www.youtube.com/watch?v=LVBgkFa1UK4 https://www.youtube.com/watch?v=NnB8Qzhv26g

Stratigraphy and Paleoceanography Sedimentation from various sources is constantly ongoing and settle at the bottom. Scientists thought that sediment layers through basins would be very thick, and would tell them about the earliest days of Earth’s history. After plate tectonic theory was formulated it was found that sediment layers at ridges are almost non- existent. New crust being formed, therefore little sediment has had a chance to fall into it. Thickness increases with distance from the ridge, until it reaches trenches.

Stratigraphy and Paleoceanography Stratigraphy: study of sediment layers ( stratum=layers, graph=drawing) Rock composition, microfossils, deposit patterns are analyzed. Estimate age of rock and make conclusions about past Previous circulation patterns, sea levels, an trends in biological productivity. Paleoceanography: the study of prehistoric oceans (Paleo=ancient)

Stratigraphy and Paleoceanography Paleoceanographers study: Chemical ratios Radioactive isotopes Microfossils Used to estimate prehistoric conditions such as ocean temperature, and climatic conditions. Siliceous and calcareous oozes Core samples from glaciers and other formations (Grand Canyon)

Types of Sediment Sediment origins: Lithogenous Biogenous Hydrogenous Cosmogenous

Lithogenous Sediments Come from land Lithos=stone, generare=to produce Aka terrigenous sediments Result from erosion (wind, water, ice) Landslides, volcanic eruptions Make up the majority of sediments near shore Quartz (most common mineral in granite) Most common mineral in lithogenous sediment because it is very hard and resistant to weathering

Lithogenous Continued Feldspar is also found in granite (most abundant mineral in continental crust) Breaks down to form clay Clay is common in lithongenous sediment Found further from shore since they are carried further (because they are smaller and lighter) before being deposited. 15 billion tons of lithogenous are deposited into the ocean annually by rivers and streams. 100 million more as fine dust and volcanic ash

Biogenous Sediment Originate from organism Shells and hard skeletons Lithogenous are greater in volume, biogenic cover largest area Come from plankton with siliceous and calcareous tests which later settle as sediment Some may settle as shells and hard corals Other deepwater sediments may form oozes

Biogenous Sediments Plentiful in areas of high productivity (high in Antarctic ocean, low in the tropics) Productivity is high in coastal areas, but influx of lithogenous sediment is much higher. Most common sediment in pelagic (open ocean) zone. May accumulate over time (in the right conditions) to form crude oil and natural gas.

Hydrogenous Sediments Minerals precipitate out of solution and form particles that deposit at the bottom Sources of minerals include: Dissolved rocks Dissolved sediments Minerals from new crust formation Hydrothermal vents Minerals dissolved in river runoff.

Hydrogenous Sediments <1% of seafloor sediments Produces important mineral deposits: Ferromanganese nodules Phosphorite nodules Usually form slowly, but can form quickly under specific conditions and are found among other sediments as well.

Cosmogenous Sediment Kosmos=space, sediment from outer space Small particles the size of, or smaller than, sand (cosmic dust) Thought to form from collision of asteroids and comets Continually settle through the atmosphere. A meteor that strikes ground is called meteorite Between cosmic dust and meteors ~15,000-30,000 metric tons of cosmogenous sediments reach the surface each year.

Cosmogenous Sediment Microtektites: glass particles that form when large meteors impact Earth. Impact results in enough energy to melt crust and send some of it into space. Crust particles melt again as the enter the atmosphere and then cooling back into tear-shaped glass “drops” Least common sediment

Sediment sizes

Sediment Size Classified by size because scientists study the effects of on sediment. (diameter of individual particle) Mud= silt and clay Smaller particles are moved more easily by water (therefore deposited further from shore) Coarse grain sizes (larges particles) closer to shore with increasingly finer as you move away Exceptions: clay particles have a “charge” and therefore attract each other making them cohesive, so they may clump together forming larger particles and settle more quickly Upwelling can delay settling as well

Sediment size Sediment size + current velocity affect deposition and erosion Large particles require more energy to erode but particles smaller than sand also require more energy Again because they are cohesive Sand is the smaller non-cohesive particle and easiest to erode.

Sorting Sorting results from the nature of water movement in the region. When water movement is steady, sediment is well sorted (sediments of one grain size) When water movement changes frequently, sediment is poorly sorted (mix of grain sizes) Unprotected shoreline

Continental Shelf Sediments: Sedimentation Processes Affected by tides, waves, and currents. Turbulence prevents deposition Surf and waves carry clay and silt out to sea (Ideal Deposition): Sand 0-20 km Muddy sand 20-30 km Sandy mud 30-60 km Mud 60 km on

Continental-Shelf Sediment: Recent and Relic Sediments Sea level changes affect the deposition of sediments because the affect the location of the shoreline with respect to the continental shelf Ideal shelf patterns are therefore not commonly found in the natural world Instead there is a pattern of coarse to fine sediment which may repeat itself a number of times along the continental shelf. Recent (accumulated since sea level stabilized) Relict (accumulated and were left stranded when sea level was lower)

Continental-Shelf Sediment: Sedimentation Rates Rates vary with region, coastal rates are faster than Pelagic, and regions of river influx (without estuaries) have the highest rates of sedimentation. Estuaries trap sediment rather than letting it flow directly into the ocean.

Continental-Shelf Sediment: Sedimentation Rates Continental shelf can only accumulate so much sediment until it slides down the continental slope. These large movements of sediment are called turbidity currents Carry sediment down to abysmal plains Deposits are called turbidites Consist of lithogenous sand and deep sea sediments (clay and silt)

Continental-Shelf Sediment: Sedimentation Rates High productivity results in high biogenic sediment deposition. Productivity is higher in coastal areas due to upwelling Highest in the Antarctic because of the lack of a pycnocline and the circumpolar current Lowest in the Tropics due to year round pycnocline. Calcareous biogenous sediments dominate

Deep-Ocean Sediments: Sedimentation Processes Vary depending on location due to productivity High in biogenous material 30% or more consists of siliceous or calcareous oozes (more specific names depending on dominant plankton remains) Accumulate slowly (1-6 cm every 1000 years) Still 10X faster than deep ocean lithogenous sediment

Deep-Ocean Sediments: Sedimentation Processes Ooze accumulation is affected by: 1. abundance of organisms, 2. rate of lithogenous sedimentation, 3. rate CaCO3 dissolves at the bottom (CCD) Clays = ~38% of deep ocean floor, combined with wind blown dust and volcanic ash Result in fine brown, olive, and reddish clays (accumulate ~2 mm every 1000 years).

Deep-Ocean Sediments: Sedimentation Processes Average sediment thickness in the Pacific is ~1/2 the thickness of sediment in the Atlantic. Atlantic must have…….? Rivers flowing into the Atlantic drain more continental area Rivers flowing into the Pacific drain less Therefore they accumulate less …….? Pacific ocean also has a lot of large trenches which ________ sediment reducing accumulation everywhere else.

Deep-Ocean Sediments: Sedimentation Processes Thickness is also affected by topography: Largest in abyssal plains Almost non-existent in Ridges and sea mounts. Due to seafloor spreading and tectonic processes.

Deep-Ocean Sediments: Carbonate Compensation Depth (CCD) Calcareous phytoplankton live everywhere in the ocean surface, but below a certain depth (~3,000m) so CaCO3 is completely dissolved (deposits cannot form) This results from higher concentrations of CO2 which make the water more acidic. Above CCD carbonate oozes dominate, below it siliceous oozes do.

Deep-Ocean Sediments: Carbonate Compensation Depth (CCD) Siliceous oozes consist mostly of diatoms (most productive phytoplankton) and radiolarians Silicate shells dissolve more slowly than calcareous at all depths Siliceous oozes are most common in Antarctica due to strong ocean currents, constant upwelling (no pynocline). Can also be found in equatorial regions near South America.

Deep-Ocean Sediments: Fecal Pellets Clay particles take 20-50 years to sink to the bottom (affected by water motion like currents and gyres) Copepods and other large plankton consume same organism that produce ooze, but release waste in dense fecal pellets which sink much quicker 2 weeks versus 20-50 years.

Deep-Ocean Sediments: Mineral Nodules Possible commercial potential 4,000-6,000 m deep Discovered in 1803, then studied by the HMS Challenger Irregular lumps the size of potatoes some up to a meter across Ferromanganese= iron + manganese (some cobalt nickel, chromium, Molybdenum, and zinc) Phosphorite are mostly pure with some trace minerals.

Deep-Ocean Sediments: Mineral Nodules Hydrogenous sediments (slowest deposition rates 1- 200mm every 1,000,000 years) Form around a nucleus (i.e. shark’s tooth, rock fragment) Three theories, two involve the presence of organic material Mineral they contain are used for various purposes but these deposits cost more to recover than the minerals are worth because of the pressures at those depths.

Sediments as Economy Resources Petroleum and Natural Gas Many geological oceanographers work in the gas and petroleum industry (that’s where the $$’s at) More than a third of the worlds crude petroleum and 1/4th its natural gas comes from the continental shelf (Gulf of Mexico) Sedimentary deposits account for 1/3 or more of world’s oil and gas reserves.

Sediments as Economy Resources Sediments as Economy Resources Other Sediments with Economic Importance Metal sulfides from hydrothermal vents Evaporites (salts left behind) provide sources of: CaCO3, CaS, CaSO4*2H2O (gypsum used in production of concrete),NaCl Oolithic sands and gravel (500M$ a year) Diatomaceous Earth (used in water filters, paints, car polish and toothpaste).