FALL 1996
GLY609
Marine Geology Final Exam
GROUND RULES: You may use the textbook & your notes in answering the questions on this test. I expect clear & concise answers.
I. Drill Sequence (55 Points) - The sedimentary & igneous sequence on the right was drilled at a sea-floor depth of 6000 m east of Japan in the Pacific on crust of Late Jurassic (~150 Ma) age. Assume the CCD everywhere in the Pacific except along the Equator has been at a depth of 4500 meters since the Late Jurassic (which is not true), that 30 Ma old ocean crust is 4500 m deep (which is true) & that 80 Ma old ocean crust is 5500 m deep (which is also true). Answer the following questions concerning this sequence.
A. Deep Sea Sediments (20 Points). Answer the following questions concerning the origin the sedimentary portion of this sequence to the right . As part of your answer to each question, discuss the seafloor depth range during deposition of each lithology & the relationship of seafloor depth to the depth of the CCD, & calculate the sedimentation rate for each lithology. Use diagrams if you wish.
1. What is the origin of the limestone in the interval from 375 m to 750 m? What microfossils would you find? (5 pts)
2. What is the origin of the clay in the intervals from 125 to 175 m & from 325 to 375 m? What is the probable color of the clay? Why? How does the sedimentation rate of the clay compare to that of the underlying limestone? Why is there a difference? (5 pts.)
3. What is the origin of the chalk in the interval from 175 m to 325 m? What microfossils would you find in the chalk? Was the CCD depth different during chalk compared to during clay deposition? Why? Why is there chert at the top & bottom of the chalk interval? What microfossils would you find in the chert? What morphologic province did the seafloor comprise during chalk deposition? How does the sedimentation rate of the chalk compare to that of the underlying limestone? To that of the under- & overlying clay ? (7.5 pts.)
4. Why is there 125 m of volcanic ash at the top of the sequence? (2.5 pts.)
B. Active Margins (10 Points) Draw a schematic structure section across the (Japanese) continental margin to the west of the drill site diagram on page 1.Extend the section into the Sea of Japan. Show lithospheric & crustal thickness, sites of sediment accumulation, & the accretionary wedge.
C. Sea Level (5 Points) - To the right side of the drill sequence diagram on page 1, indicate when eustatic sealevel was at its maximum elevation above present with an arrow (<-). How much further above present sealevel was eustatic sealevel at its maximum?
D. Oceanic Crust (5 Points) - What is the specific major type of basalt encountered at the base of the drill sequence in the diagram on page 1? How does this major type of basalt differ from the other major type?
E. Tectonic Evolution of the Ocean Basins (5 Points) - Indicate on Figure 1 (the map of the Pacific Ocean) at the back of this test the approximate path traversed by the seafloor from the Late Jurassic to the present. What marine magnetic anomaly would be identified with the drill site?
F. Morphology (5 Points). Answer the following questions concerning the morphologic province of the drill site above during deposition of each lithology. Use diagrams if you wish.
1. What morphologic province did the seafloor comprise during limestone deposition?
2. What morphologic province did the seafloor comprise during clay deposition?
3. What morphologic province did the seafloor comprise during chalk deposition?
4. Which of the seismic profiles in Figure 2 at the back of this test would most likely have been obtained during the site survey prior to drilling the sequence in the diagram on page 1? Why?
G. Instruments & Techniques (5 Points) - How was the drill sequence in the diagram on page 1 obtained?
II. Deep Sea Sediments (10 Points) - Compare & contrast turbidites & contourites in terms of their origin, sediment structures, & their geographic distribution.
III. Active Margins (5 Points) - Briefly discuss the variation of K2O across an active continental margin in terms of what the variation is & why it occurs. Use sketches if you wish.
IV. Passive Continental Margins (30 Points)
A. Figure 3 at the back of this test is a cross-section across the northern Bay of Biscay passive continental margin. Answer & do the following. (10 pts.)
1. Sketch in the oceanic, transitional & continental crustal boundaries, & label each crustal type.
2. What type of fault occurs at "X"?
3. At what depth does the dashed boundary at "Y" occur 100 kilometers to the northeast?
4. How has the crust above the dashed boundary at "Y" responded to tensional forces?
5. How has the crust below the dashed boundary at "Y" responded to tensional forces?
6. Why does the fault at "X" sole out at the dashed boundary at "Y"?
7. What kind of sediments would you expect to find at "Z"?
8. What rifting process is best explained by this cross-section?
B. Draw a schematic cross-section to 40 km depth across the passive margin off Georgia, showing crustal thickness, boundaries between oceanic, continental & transitional crust, sediment thickness, sediment type, approximate sediment age & correct topography. Label the depth axis. (10 pts)
C. Briefly explain the reasons that the thick sediments at passive continental margins must result from both of passive sediment loading & active tectonic subsidence. Use sketches if you wish. (10 pts.)
V. Coastal Zone (10 Points) - Discuss the relationship between tidal range & coastal morphology. Give examples of coasts from different parts of the world that illustrate particular kinds of coastal morphology. In particular, discuss the nature of Georgia's coastal morphology. Use sketches if you wish.
VI. Sea Level (10 Points).
A. Briefly describe the evidence indicating that addition of juvenile water from the mantle probably has not resulted in significant sea level changes during the Phanerozoic. Use sketches if you wish. (5 pts.).
B. Sketch sea level during the last 150,000 years based on d18O of benthic forams. Label the depth axis. (5 pts.).
VII. Oceanic Crust (5 Points) - Briefly summarize the distribution of Layers 2A, 2B, & 2C in the upper oceanic crust as a function of age, & explain the reason for this distribution.
VIII. Tectonic Evolution of the Ocean Basins (40 Points). The following section concerns the tectonic evolution of the Pacific Ocean (the map is at the back of the test). A time scale is also provided at the back of the test. The light dashed line is the shelf edge.
1. a. Where is the oldest seafloor in the Pacific located? (2 pts.)
b. How old is this seafloor? (3 pts.)
c. How do you know this? (3 pts.)
2. The Mesozoic sequence in the western Pacific shows two bights. In the space below, sketch a cartoon showing the implications of this in terms of: 1) plate boundary types, 2) number of plate boundaries, and 3) number of plates. Label all plates. (10 pts.)
3. a. Why did the East Pacific Rise change oriention? (3 pts.)
b. How do we know that it changed orientation? (3 pts.)
c. When did it change orientation? (3 pts.)
4. Why is there a bend in the Hawaiian-Emperor Seamount Chain? (3 pts.)
5. Why do magnetic anomaly #'s increase to the south away from the Aleutian Trench? Use sketches to illustrate the sequence of events leading to the present situation. (10 pts.)
IX. Plate Tectonics (15 Points) - Use the map of the Pacific Ocean at the back of this test to answer & do the following:
1. Draw focal mechanisms for earthquakes that would be generated at locations (1), (2), & (3) in the circles provided below. Darken compressional quadrants. (6 pts.)
2. At location 1, the ______________________ plate is being subducted under the _______________________ plate. (2 pts.)
3. Indicate 2 of the 3 active mantle hotspots in the Pacific Ocean on the map with blue triangles. (2 pts.)
4. Indicate the zone of andesitic/island arc volcanoes in the Pacific Ocean on the map with red triangles. (5 pts.)
X. Seafloor Spreading (7.5 Points) - Describe briefly how the fact that the earth's magnetic field reversed was shown & how the timing of the reversals was determined. Why was the magnetic polarity time scale derived by this work carried back only to 4 million years.
XI. Continental Drift (7.5 Points) - What four kinds of data did Alfred Wegener cite as evidence supporting continental drift? Give examples of each. Use sketches if you wish. Why was the general geologic community not convinced of the validity of continental drift as espoused by Wegener?
XII. Structure of the Earth (5 Points). Sketch a cross-section of the upper 800 kilometers of the earth showing the structure of the earth based both on composition & rigidity, & label each layer.
XIII. Morphology. (5 Points)
A. What morphologic province does the topography shown in Figure 2 (both profiles) typify?
2. What ocean is the profile in Figure 2 that you did not pick in the drill sequence question on page 3 probably found in? Why?
XIV. Important Names (5 Points). Briefly describe the role each of the persons or ships listed below had in the development of marine geology, continental drift, seafloor spreading, or plate tectonics.
1. Maurice Ewing -
2. Harry Hess -
3. Sir James Ross -
4. J. Tuzo Wilson -
5. H. M. S. Challenger -
XV. Additonal Item for GLY609 Students. - If you are registered for GLY609, do two of the following items in the space provided below. (20 points).
1. What kind of crust is associated with positive isostatic gravity anomalies? Why? What kind of crust is associated with positive free air gravity anomalies? Why? (10 pts.)
2. Compare & contrast the evolution of the New Jersey continental margin with that of the Georgia continental margin. (10 pts.)
3. Give approximate full spreading rates for the following. (10 pts.)
a. Mid-Ocean Ridge in the south Atlantic -
b. East Pacific Rise in the south Pacific -
c. Mid-Ocean Ridge in the Arctic Ocean -
d. Mid-Ocean Ridge south of Australia -
e. Juan de Fuca Ridge in the north Pacific -
& given the following information, calculate half spreading rates. Show your calculations. A time scale is provided at the back of this test.
a. MOR crest to Brunhes-Matayama boundary is 140 km.
b. MOR crest to Gauss-Gilbert boundary is 330 km.
c. MOR crest to anomaly 5 is 100 km.
d. Width of seafloor from anomaly 32 on the west side of the MOR to anomaly 32 on the east side of the MOR is 2850 km.
e. Width of seafloor from anomaly M-25 to anomaly M-16 on the west side of the MOR is 600 km.
4. What contribution did Authur Holmes make to the continental drift argument? (10 pts.)
5. Discuss briefly the range of depths that characterize shelf breaks & the reasons shelf breaks vary in depth. (10 pts.)
6. Compare & contrast the morphology of the MOR between India & Madgascar with that of the MOR south of Australia. Use sketches if you wish. (10 pts.)