INTRODUCTORY OCEANOGRAPHY

Specific Reading Assignments for EXAM 1

Chapter 3	GLOBAL PLATE TECTONICS	ALL
Chapter 4	MARINE PROVINCES	ALL
Chapter 5	MARINE SEDIMENTS	ALL
Chapter 7	SEAWATER CHEMISTRY & ALKALINITY	ALL

Key Elements to Study

Chapter 3. Global Plate Tectonics

1. Definitions - define or describe

• crust/mantle/core of earth
• lithosphere
• asthenosphere
• geomagnetism and magnetites
• Isostasy
• subduction zone

2. Theory of Global Plate Tectonics

• Contrast and compare the concepts of continental drift and sea floor spreading. How are these concepts folded into the theory of global plate tectonics?
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• Describe the convective flow in the asthenosphere involved in this theory.
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  • Where is new oceanic lithosphere created?
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  • Where is old oceanic lithosphere destroyed?

3. Evidence Supporting the Theory of Continental Drift

• Fit of Continents - According to Sir Edward Bullard, how well does the fit of continents support the theory of continental drift? At what water depth contour below the sea does the best fit occur?
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• Continental Geology - the following categories of continental geology support the theory.
  • Fossils. How does a comparison of fossils of tropical flora and coral at the margins of continents (once thought to have been joined), and at tops of high mountain peaks, support the theory?
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  • Glaciation. It has been found that glaciers existed in Eastern S. America., Western S. Africa, Southern India, half of Antarctica and all of Australia, during the same time that tropical swamps (which have resulted in extensive coal deposits) existed in Eastern N. America and Western Europe. Why is this evidence of continental drift?
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  • Geomagnetism. There are at least three pieces of evidence due to the geomagnetism of continental rocks that support the theory:
    • How can the magnetic dip angle of magnetites in basaltic continental rocks be used to determine the latitude at which the rocks solidified? - Fig. 3.26.
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    • Continental rocks in India have a large dip angle. What does this say about their point of origin on the earth, and how does this support continental drift?
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    • How does the horizontal alignment (not the dip angle) of magnetites in rock of the same age explain the concept of apparent pole wandering, and how does this concept support the theory of Continental Drift?

4. Evidence Supporting Sea Floor Spreading and Plate Tectonics

This evidence comes primarily from the study of Marine Geology (e.g., the geology beneath the water).

• Geomagnetism. How do the alternating bands of magnetically oriented oceanic crust, which run roughly parallel to the mid-oceanic ridge line and show some symmetry on each side of the ridge, support the spreading theory? - Fig. 3.28 a&b.
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• Heat Distribution of Seafloor. What is the evidence that convection currents in the asthenosphere rise toward the surface and cause the formation of oceanic lithosphere at the oceanic ridges?.
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• Age of Rock and Thickness of Sediments. How do the age of the igneous rock and the thickness of oceanic sediments immediately above the crust lend support to the spreading theory? Fig. 3.29.
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• Subduction Zone. How does the subduction of an oceanic lithosphere plate beneath any other lithosphere plate give support to this theory:
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  • At what angle and to what depth does this subduction take place (what support do we get for this from the location of the earthquake foci in the subduction zone)? Fig. 3.21.
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  • Why is a trench usually associated with this subduction?
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  • By what process are andesite volcanoes formed during this subduction?

5. Plate Boundaries

There are three types of plate boundaries, each of which have two names. Fig. 3.17a.

• Divergent (Constructive). This boundary is found at mid-ocean ridges, where new oceanic lithosphere is created. Fig. 4.22.
• Transform Fault (Shear) - Fracture Zones and Transform faults are associated with lateral "cracks" in the crust that run perpendicular to the mid-oceanic ridge line. - Fig. 3.17a & Fig. 4.22.
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  • Along these "cracks", contrast and compare the transform faults and fracture zones.
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  • For each, how does the plate on one side of the crack move in relation to the plate on the other side?
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  • Why is the transform fault also considered a plate boundary?
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  • How are the movements of the plates on either side of fault, and on the ridge line itself, related to the theory of sea floor spreading?

    Note Fig. 3.25 for the best example of a Transform Fault - the San Andreas Fault.

• Convergent (Destructive). There are three possible types of plate collisions: (oceanic-oceanic, oceanic-continental, continental-continental); each results in a different plate boundary system. In each case, the leading edge (or edge of a plate that contacts another plate in the subduction zone) determines how we classify this collision (e.g., an oceanic-oceanic collision is between two plates whose leading edges are oceanic, even though one or both may also contain a continent).
  • Oceanic-oceanic plate collisions result in an Island Arc System. Fig. 3.22 a
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    • What are island arcs, and how are they formed?
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    • If the plate also contains a continent, what kind of sea often lies between the island arc and the continent?
  • Oceanic-continental plate collisions result in a Continental Arc System.
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    • In place of an island arc, what topographic features do andesite volcanoes produce?
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    • Where is the trench located in relation to these volcanoes ?
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    • What was the major consequence of the subduction of the JUAN DE FUCA Plate under the NORTH AMERICAN Plate? - Fig. 3.20.
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  • Continental-continental plate collisions result in a Continental Mountain System. Fig. 3.23.
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    • What happens to the sedimentary rock (once a part of seafloor) that is caught between the converging continents?
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    • Under what conditions does the sedimentary rock usually not subduct?
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    • In the Indian Ocean, what major effect did the movement of the INDO-AUSTRALIAN Plate have on Asia?

Chapter 4. Marine Provinces

1. Hypsographic Curve

• What percent of the earth's surface is beneath the ocean surface? - Fig. 4.7.

2. Marine Provinces

• Continental Margin Fig. 4.11
  • What are the differences between Active and Passive margins?
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  • By what processes are continental shelves formed?
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  • Through which parts of the continental margin are Submarine Canyons cut? Fig. 4.16
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    • Why are they prominent on the slope, with secondary tributaries on the shelf?
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    • Most are thought to have been cut by what process?
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    • In what way did the trans-Atlantic cable breaks off Newfoundland in 1929 provide evidence for the mechanism that is thought to have cut these canyons?.
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    • Why are they not likely the result of rivers that flow into the sea?
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  • How are continental rises formed, and are they found on active continental margins?
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• Deep Ocean Basin
  • Describe an abyssal plain, a mid-ocean ridge (or rise) and a trench. Fig. 4.21.
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  • In what ocean are the most trenches found?
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  • Subduction Zones are at the base of what kind of continental margins?
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  • Seamounts and tablemounts (Guyots) - what are their differences and how may their formation support the theory of sea floor spreading? - Fig. 4.28.
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  • Coral Atolls - what is the difference between fringing and barrier reefs; what part may sea floor spreading play in the formation of atolls? - Fig. 12.27.
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  • Hot spots - what are they and how do the islands formed by them provide evidence for sea floor spreading? Describe the age and volcanic activity of the islands formed by these hot spots as you move away from the hot spot. - Fig. 3.32 & Fig. 3.33.
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Chapter 7. Seawater Chemistry and Alkalinity

1. Definitions - define or describe

• element
• Bohr model of atom
• molecule
• chemical reaction
• atomic number
• atomic mass number
• acid/alkaline-base and pH
• cations, anions
• noble gas

2. Chemical Bonds - contrast and compare

• covalent bonds
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• ionic bonds

3. Acidity and Alkalinity of Seawater

• Explain the self-buffering process by which pH of ocean water is maintained at 8.1. What role does the H⁺ ion play?
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• Is the pH of seawater acidic or alkaline, and what is its narrow range?

Chapter 5. Marine Sediments

1. Sorting of Sediment

• What is the concept of sediment maturity as particles are carried from the source to the point of deposition.
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• Why does the clay content decrease as sediments mature?

2. Transport of Sediments

• What is the relationship between grain size, current velocity, and the transport and deposition of sediments?
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• How does this relationship change for the erosion of sediments? - Fig. 5.5.
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• Why, even for higher current velocities, are some clay particles less likely to erode than medium grain sand?
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• By what two means are particles, with sizes finer than silt, carried far out to sea?

3. Classification of Marine Sediment by Origin

There are four different types of marine sediments classified by the origin of their particles: Lithogenous, Biogenous Hydrogenous and Cosmogenous. Table 5.2

• Cosmogenous sediments come from outer space. What is evidence that Spherules and Meteorites impact the earth?
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• Lithogenous sediments are formed by the weathering of continental rocks and oceanic volcanoes. These rocks are formed by combining ions of metal with silicate:
  • What very stable compound does weathering of rocks produce?
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  • How is clay produced by this weathering?
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  • What are the grain texture and color differences between extrusive and intrusive igneous rocks?
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  • What is the difference between sialic and simatic rocks?
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• Biogenous sediments are formed from insoluble remains of organisms (bones/teeth/protective coverings, etc.) called "tests".
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  • What percent insoluble remains must a sediment contain to be classed as an ooze?
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  • What are the chemical makeup's of calcareous ooze and siliceous ooze?
• Hydrogenous sediments are formed by precipitation of minerals from seawater. Manganese Nodules are a unique type of this sediment that lie on the seafloor itself. The most common hydrogenous sediment found in the ocean, however, is calcium carbonate (limestone - CaCO₃).
  • Because water is basically saturated with the calcium ion (Ca⁺⁺), it is the availability of the carbonate ion (CO₃^--) that governs whether precipitation of CaCO₃ from sea water occurs.
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  • How does CO₂ affect the availability of this CO₃^--?
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  • How does ocean water temperature, water pressure and photosynthesis affect the availability of CO₂, and at what relative depth in the ocean would you expect to find CaCO₃?
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  • Using the three factors given in (2) above, explain why CaCO₃ is precipitated on the Bahaman Banks when the cold Florida current flows up over the shallow banks.

4. Classification of Sediments by location

Sediments are distributed on the continental margins (as Neritic sediments) and in the deep ocean basins (as Oceanic sediments).

• Neritic Sediments - of Continental Margins
  • What is the primary source of sediments found on the continental margins?
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  • Relict Sediments, covering over 70% of the ocean's continental shelves, have ages between 3000-7000 yrs.
    • Explain why a falling sealevel, associated with the intensification of the last ice age (which peaked 10,000 yrs. ago), would remove all sediments from the continental shelf.
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    • Explain why a rising sealevel after the peak of the ice age would again begin depositing sediments on the continental shelf that were no older than 7000 yrs. old.
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    • If the present sealevel returned 3000 yrs. ago, explain why there are few sediments found on the shelf younger than 3000 yrs.
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  • What are turbidites and why are they found as a "layered-bedding" of sediments? Fig. 5.12.
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  • What is the average deposition rate for lithogenous sediments on the continental margin?
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• Oceanic Sediments - of Deep Ocean Basins
  • Abyssal ooze -
    • What is abyssal ooze and what are the chemical compositions of the tests that makeup this ooze?
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    • What is the range of deposition rates for abyssal oozes?
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    • In general the deposition rate of a biogenous ooze depends on three factors: The first two are Productivity and Dilution. Define and describe both factors.
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    • The third is the Destruction of skeletal remains (tests), which is dependent on the tests' chemical composition:
      • Silica skeleton destruction results because of the undersaturation of ocean waters with Silicon (Si), so SiO₂ tests are dissolved at any depth.
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      • How does the availability of carbon dioxide (CO₂) affect the destruction of calcium carbonate tests and the deposition of calcareous ooze, and what part does the Calcium Carbonate Compensation Depth (CCD) play in the distribution of calcareous ooze? Fig. 5.14.
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      • Explain the significance of the narrow band of radiolarian ooze just north of the equator in the equatorial Pacific. Hint: what relationship does it have to have to the depth of the North Pacific basin?
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      • What organism accounts for all the siliceous ooze found in the Antarctic?
  • Abyssal clay -
    • What is abyssal clay?
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    • Contrast and compare the average deposition rate of abyssal clay with that for abyssal ooze.
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    • Using the Dilution factor listed above for abyssal ooze, explain why abyssal clay is generally found only in the deepest parts of the ocean, and in the abyssal sediments of the Pacific Ocean?
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• Sedimentation and seafloor spreading - We learned earlier that the age and thickness of sediments increased with increasing distance from the mid-ocean ridges. As further evidence of sea floor spreading, what can be said about the types of sediments found in layers in the deep ocean basin, as distance from the ridge increases? Refer to Fig. 5.13 and the last figure in Part 3 of this Chapter Lesson.

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