SEDIMENTS
Sediments
20 questions
9) You should know what the differences are between the bathymetry of the Mid-Atlantic Ridge and the East Pacific Rise and why
Ocean ridges- mountainous formations at spreading centers • average spreading rate for the Mid Atlantic Ridge is 3 cm per year • average spreading rate for the East Specific Rise is about 18 cm per year (slower spreading rate) • the rate of spreading determines the bathymetric features o In a fast spreading system will look smoother like the East Pacific rise because the features are spread over a greater distance. No pronounced central rift valley o Slower spreading rate of the Mid Atlantic Ridge concentrates the features in a smaller area, it also, has a more pronounced central rift valley. Looks smoother sue to the accumulation of sediments. Mid Atlantic ridge- sediment accumulation changes the surface expression of the ridge. There is greater sediment accumulation the farther you get away from the spreading center because the crust is older and has had more time to accumulate sediments. • Spreading at a divergent boundary does not happen in a straight line because the earth is not changing in size, as the spreading occurs, it must be broken by transform faults • Ridge system must occur in segment's offset by transform faults
14) You should know what a seamount and guyot are and how they are formed
Seamounts- volcanic projections that do not reach the ocean surface o Formed near spreading centers, the volcanic activity, the magma chamber with passages of magma coming up though the plates can form these volcanoes o As the plates move apart the seamount is carried away and is submerged and is no longer active because it is not loner near the active magma chamber o As the mountains move away from the spreading center if there's enough sediment accumulations it could become an abyssal hill → increased fish activities Guyots- former seamounts that have flat tops and may have reached the surface and been eroded
12) You should know how sediment accumulation affects the bathymetry of a spreading center
Sediment accumulation changes the surface expression of the ridge. There is greater sediment accumulation the farther you get away from the spreading center because the crust is older and has had more time to accumulate sediments.
20) You should know what stratigraphy and paleoceanography are
Stratigraphy- analysis of layered sedimentary deposits Paleoceanography- study of the oceans past o Important when looking at how the earth has changed due to past climatic histories • At the end of the cretaceous period a huge meteor impacted the Gulf of Mexico. Cores taken from this region, a distinct layer called the ejectolayer, this layer is the layer that was ejected directly from the impact of the crater and laid down within just a few days of the impact. o Fireball layer - as it concocts of dust and ash fallout from the impact o By dating the core we can get a precise time on when the event occurred.
13) You should know what turbidites are and how they are deposited
• A type of pelagic sediment • Deposits formed by the action of turbidity currents • Graded layers of terrigenous sand embedded with smaller particle sediments • Episodic events so we end up with different size particles
9) You should know where rates of sediment accumulation are high
• Amount of marine sediments does not always correspond to the size of the area of the ocean • Areas that may be small in size might have a lot of marine sediments • Continental slopes have the greatest accumulation of sediments about 41 percent and also the area where sediments are the THICKEST
4) You should know the four different sediment by source types and their basic characteristics
• Biogenesis o These are sediments that have an organic source such as the shells of marine organisms. ONE of the two most dominant sediment types o Oozes o Dominant in the deep ocean floor o Biological origin mostly plankton o Composed of silica and calcium compunds o Form natural gas deposits over time o More abundant in areas where there is high planktonic production in the water column -continental margins -upwelling areas • Hydrogenous o Sediments that are formed from the precipitation of dissolved minerals often due to the activity of bacteria o Not common and are found in smaller quantities along with the dominant sediment type in the given location o Formed from minerals precipitated from seawater o Sources include: -hydrothermal vents -leaching of minerals from rocks and fresh crust -Substances transported to the ocean by rivers o Authigenic sediments- formed in the place they now occupy. o Ex: manganese nodules - precipitate onto a sediment grain on hard objects. Over time the accumulation grows. First discovered on the challenger expedition. o Form due to chemical reactions occurring on particles of the dominant sediment • Evaporites o Different salt compounds that from at different points during the evaporative process (as salinity increases) • Ooliite sands o Formed by precipitation of calcium carbonate o In shallow, warm waters with high productivity o Autotrophs (plants) use up carbon dioxide and make seawater less acidic o Found in the Bahamas • Cosmogenous o Derived from dust from space and debris from meteorites o Rare but clearly distinguished by their extraterrestrial materials o Extraterrestrial origin -interplanetary dust -impacts by comets and meteors -micro tektites o Ex: tektite spheres 5) You should know how terrigenous sediments are transported • Derived primarily from erosion of the land or continents. The dominate type in the continental margins but are also a large component of sediments in the abyssal plains As their transported their off the continental slope • Transported: o Sediments are eroded from the continent by wind and rain and are carried via rain water to rivers and streams and then into the ocean where they are deposited on the continental shelf. THEN are transported to the continental slope and the abyssal plain. At convergent plate boundaries the sediments are subducted and recycled as their melted into the mantle and can return to the continent through volcanic activity. o Transported by RIVERS (most common) ex: Mississippi delta o Transported by wind (Sahara desert) transported by wind and then deposited into the ocean • ONE of the two most dominant sediment types
14) You should know what oozes are, the different types, and what they are composed of and where they are found
• Biogenous sediments • Composed of the rigid remains of organisms (primarily plankton) • If a sediment contains at least 30 % biogenous material, it is termed an OOZE • Accumulation rates of 1-6 cm every 1000 years o Depends on the balance between abundance of the organisms that contribute to oozes and the rate of accumulation of terrigenous material. 1. Calcareous Oozes : EXAMPLE: white cliffs of Dover in the United Kingdom formed by thick deposits of calcareous oozes hat went under lithification and were lifted by plate tectonics o Primarily found in pelagic deep sea areas o Form primarily from foraminifera and coccoliths o 48% of the surface of the deep seabed is covered by calcareous oozes. o Shells containing calcium dissolve at greater depths due to - increased ocean acidity by a greater amount of carbon dioxide being dissolved at depth -increased solubility of calcium carbonate under pressure and in cold water o CCD determines pattern of accumulation of calcareous oozes o Example is near Antarctic an arctic ocean: - At depths above the CCD calcium carbonate sediments can accumulate and the rate of accumulation is GREATER than the rate of dissolution - Below the CCD no calcareous oozes will be found because the rate of dissolution is equal to the rate of accumulation - Shallower at the poles because the water here is colder and because the water is more acidic because cold water can absorb more carbon dioxide. 2. Silicious oozes • Dominate in highly productive ocean areas such as the southern ocean, the equator, and the upwelling areas such as off the coast of south America • Formed from radiolarians and diatoms • 14 % of the surface of the deep seabed is covered by silicious oozes • Predominate at greater depths and polar regions • Silicia does not dissolve as quickly as calcium carbonate • Diatom oozes are found in areas where there is high diatom production (Southern Ocean near Antarctica) • Radiolarian oozes more common in equatorial upwelling regions this region while production has generally lower nutrient levels that the Southern Ocean • Transport to the seafloor o Compaction into fecal pellets speeds the sinking rate of these particles to the seabed
17) You should know what seismic surveys are and what they can tell us about sediments
• Conducted frequently in the Gulf of Mexico a ship tows a seismic array. The array has an instrument on it that sends out an explosive burst of air and sends out a loud noise, the rest of the array has a serious of hydrophones that detect the returning echo from the sound pulse - by noting the time difference between different echoes we can make a map of the layers of sediments below this is how potential petroleum deposits are detected.
11) You should know where the thickest sediments are found within the continental margin and which ocean has the thickest sediments and why
• Continental slopes have the thickest sediments • Near the mount of the Mississippi river in the gulf of Mexico and the mouth of the Ganges river in the Indian Ocean • Makes sense because rivers are the most important mode of transport for terrigenous sediments • Thinnest sediment accumulation is near spreading centers like near the Mid Atlantic Ridge
16) You should know what the CCD is and what controls the deposition of calcium carbonate in the oceans
• Depth at which the rate of calcareous sediments supplied to the seabed equals the rate at which they dissolve. • Affects it: increased acidity , pressure, temperature
16) You should know how much of the Earth the abyssal plains cover and where in the ocean basins they are located
• Exists between the spreading center and the continental margins • Cover about ¼ of the earth's surface (abyssal plains and hills) • Flat, featureless areas • More common in the Atlantic Ocean • Smooth, even surface due to accumulation of terrestrial sediments o Abyssal hills -small, sediment covered mountains (extinct volcanoes) that have moved away from a spreading center
18) You should know at what type of plate boundary are island arcs formed
• Features of ocean basins also occurring on the edge of the abyssal plains near continental margins • Convergent pate boundaries where trenches form where one plate is subducted under the other • On the coast of south America where we have a trench there is a Collison of an ocean and continent plate so the oceanic plate dives underneath and we get a trench • Island arcs are formed in areas only when TWO ocean plates converge an done plate subducted beneath the other o Islands of japan were formed in this way
8) You should know what authigenic sediments are
• Formed in the same place they now occupy • Minerals expelled at hydrothermal vents that are also found at the same vent site
18) You should know two types of samplers for sediments and what types of samples you can collect with them
• Grab o Grab or clamshell sampler o The instrument is lowered to the bottom in the open position when it hits the bottom it closes and takes a sample of the surface sediments o Used to extensively sample sediments from the bottom • Corer o The instrument is lowered to the bottom (piston corer) it is then drilled into the sediment it then closes and the samples are retrieved bringing back with it stratified core sediments that allows scientist to look at the different sediment layers. • Joint ocean drilling project was formed this project is a global collaboration to obtain cores and then to house them in core libraries. The cores are openly available to any scientist who wants to conduct research on them. The cores can be analyzed at the library of shipped out for analysis.
1) You should know how sediments are classified
• Grand Canyon is the southwest United States - many layers of rock in this cross-section, although, at one point all of these layers were sediments that were laid down and compacted and became rock through the process called lithification. o Each layer has characteristics that can tell us about the conditions at the time the sediments were deposited. Many of the rocks at the Grand Canyon were derived from marine sediments because this area was once a shallow sea in the past. o As the Colorado River cut through these layers and formed the Grand Canyon, the different layers were exposed and we could essentially go back in time by examining the increasingly older layers as we move deeper into the Canyon. • Definition of sediments o Particles of organic and inorganic matter that are accumulated in a loose, unconsolidated form o Particles are derived from erosion of rocks, living organisms, volcanic eruptions, and chemical processes o Rates of accumulation vary greatly • Different levels of accumulation o Low sediment accumulation- rocks protruding and a sea anomie is on top of one of the rocks. Near the Mid Atlantic Ridge spreading Center. The crust here is relatively young and there has been little time for sediment to accumulate o High sediment accumulation- adjacent abyssal plain there has been much more time for the sediment to accumulate and smooth out the features. • Current patterns Shape sediment surface o Can be shaped by currents
15) You should know what controls the rate of deposition of oozes
• Higher rates of deposition on the continental shelf than the deep ocean • Higher rates near river mouths (1m every 1000 years) -Estuaries trap sediments and can reduce this rate - Big factor in Louisiana's costal land loss
10) You should know where the Mid-Atlantic ridge intersect land and the characteristics of this area
• Iceland • The Mid-Atlantic Ridge "comes ashore" • Large amounts of thermal and volcanic activity
15) You should know what is significant about the Trieste
• In 1959, Jaques Piccard and US navy Lieutenant Don Walsh became the only humans to descend to the bottom of the Mariana trench • It has been visited twice since that time with ROVs • March 25, 2015 is the only person to solo dive into the Mariana trench o Dive lasted about 7 hours o He collected a lot of interesting footage
11) You should know the lead scientist who discovered hydrothermal vents
• Jack Corliss, a marine geologist noticed that rocks he was analyzing from the Mid Atlantic Ridge had chemical signatures that indicated that they had been exposed to hot maybe even boiling water. o He then realized that water had to be circulating at these spreading centers and he and fellow scientist Dr. Jack Diamond both postulated the theory that water must be circulating through rocks at spreading centers and the cold ocean water that went in was emerging as heated water around the spreading center. o The theory was good enough to be funded by the national science foundation or NSF o This lead to a cruise, with the research submersfal Alvin to the East Pacific rise. o At the East Pacific rise they found the circulating water that they had expected and also found areas teaming with life around the vents that they had never expected or seen before.
19) You should know what the deepest trench is and how deep it is
• Mariana trench in the Pacific • 11,000 meters deep • Off the coat of guyuam
19) You should know where the oldest sediments are, how old they are, and why there are no older sediments
• Oldest sediments 180 million years old • This is because the oldest oceanic crust on earth is 180 million years old • While there have been continental and oceanic plates since the earth cooled and the lithosphere formed, due to tectonic plates the plates are constantly being moved at spreading centers and recycled at subduction zones. • Oldest oceanic crust is in the western pacific this is because the spreading center where this is formed, the East pacific rise in south America, is incredibly far away
10) You should know what pelagic and nertitic sediments are and where they are located
• Sediment distribution (see below) o Clay is the dominant sediment type in most of the open ocean -38 percent of the deep seabed is covered by clays - Average rate of accumulation is 2 mm every 1000 years (slows) -Terrigenous sediments • Neritic sediments o Overlay continental margins o Mostly terrigenous o There also biogenesis sediments as these are areas of high pelagic production o Larger particle size deposited nearshore (sand) o Smaller particle size deposited offshore (silts and clays) o Ice shelves and icebergs and turbidity currents can disrupt this sorting pattern. Ice shelves and ice bergs: sediments of larger particle size can be deposited on the ice. The ice can then extend out from the continent or float away. As the ice melts the sediment can be deposited this can lead to sediments with larger particles to be laid down offshore where they would not normally be transported o Historical changes in sea level are evident in these sediment records. -for example: if sea level was higher than present we may see sediments with a larger grain size • Pelagic sediments o Overlay the continental slope, rise, and deep-ocean basin o High proportion of biogenesis sediments than neritic sediments, but still the majority of the volume are terrigenous sediments o Sediments of the slope, rise, and deep-ocean floor o Thickness is highly variable -thickness on the abyssal plains and thinnest on the ridges o Average thickness in the Atlantic is greater than the Pacific -more rivers feed the Atlantic -The Atlantic is geographically smaller -Specific has more subduction zones
12) You should know what the process of lithification is
• Sediments are converted into sedimentary rock by pressure - induced compaction or cementation • These formations can be lifted above sea level through the action of plate tectonics o Mt. Everest o Colorado plateau
3) You should know how size affects settling rate
• The smaller the particle the smaller the settling rate and the longer it will take for the particles to sink to the bottom. Important because it dictates how sediments are deposited and re-suspended in the water column. • Decrease in steam velocity from larger to smaller particles • For any particles larger than sand the settling velocity is very fast and not reported • Stream velocity- how fast the water is moving. This erodes the particle and brings it out sediment and into the water column. The particle can then be transported as long as stream velocity remains above some minimal level • Increase from sand to clay because although clay particles are smaller, they can pack together more tightly and it requires more energy to initially erode them and bring them into the water column.
13) You should know the basic water circulation at hydrothermal vents
• Vents occur where there are fissures in the crust that allow seawater to seep in and be drawn down towards the spreading center. The heat from the magma rising in the spreading center heats the water and it moves back up with minerals dissolved in it from the crust. Specifically, different sulfur compounds. The sulfur compounds support life at these vent systems. • One of the dramatic geological features are black smokers o Chimneys that build up over time as Minerals in the hot water is rising from the bottom build up. Overtime chimneys are formed and the hot water full of minerals continues to escape from the top o Some chimneys can appear white due to different minerals being dissolved in them o Bacteria and organism are thriving
7) You should know how sediments are classified based on sorting and under what conditions we find these different classes of sediments
• Well sorted sediments o Sediments composed primarily of particles of one size o Found where energy fluctuation occurs in a narrow range • Poorly sorted sediments o Sediments composed of particles of a range of sizes o Found where energy fluctuations occur over a wide range
17) You should know the characteristics of the bathymetry of the abyssal plains
• between ridge systems and continental margins • They are generally smooth and featureless due to the accumulation of sediments
