FALL 1996
GLY609
Marine Geology Test #2
I. Tectonic Evolution of the Ocean Basins (40 Points). The following section concerns the northern North Atlantic, Norwegian Sea, & the Arctic Ocean (Figure 1) & the North Atlantic Ocean (Figure 2). A time scale is also provided at the back of the test. The light dashed line is the shelf edge.
A. Spreading Rates. Calculate the following spreading rates. Show your calculations. Remember: 1_ of latitude equals ~110 km. (13 pts.)
1. What is the current full spreading rate for the Mid-Ocean
Ridge (MAR) between the Lomonosov Ridge & the Siberian margin?
2. What is the current full spreading rate for the MAR between
northern Greenland & Norway?
3. What is the current full spreading rate for the MAR between
southern Greenland & Rockall Plateau?
4. What is the current full spreading rate for the MAR between
the Grand Banks & Iberia?
5. What is the current full spreading rate for the MAR between
Dakar & Savannah?
6. Why do the spreading rates vary along the MAR? (3 pts.)
B. Answer & do the following. (27 pts.)
1. Indicate on Figure 2 the location of the oldest seafloor
in the North Atlantic Ocean using shading. (3 pts.)
2. When did Laurasia begin to separate from Gondwana (anomaly
#, age & geologic period)?
3. a. When did Laurasia begin to break up (anomaly #, age &
geologic period)?
b. What do the bights formed by anomaly 34 off the Grand Banks
& Iberia imply about Iberia during the initial Laurasian breakup?
4. a. How old is the oldest seafloor adjacent to the margins of
Greenland (anomaly #, age & geologic period)?
b. When did Greenland & Eurasia begin to separate (anomaly
#, age & geologic period)?
c. What do the bights formed by anomalies 24-20 south of Greenland
& off the Rockall Plateau imply about Greenland during this
time period?
d. When did Greenland become part of North America (anomaly #,
age & geologic period)?
5. What kind of crust probably underlies Rockall Plateau, the
marginal plateau lying NW of Britain?
6. What is the probable origin of the Lomonosov Ridge?
7. What is the origin of Iceland, the Faeroe Islands & the
Iceland-Faeroe Ridge.
8. Briefly describe the tectonic history of the seafloor between
southern Norway & central Greenland (north of Iceland &
the Faeroe Islands). Include in your description the origin of
Jan Mayen Ridge & timing of MOR jumps. (4 pts.)
II. Oceanic Crust (15 Points). Answer the following questions concerning Figure 2.
1. What type of basalt occurs at point "X"? (2 pts.)
2. What type of basalt occurs at point "Y"? (2 pts.)
3. Do these basalts differ in chemical composition? (2 pts.)
4. If so, what are the MAJOR (SiO2
& Na2O+K20 contents)
differences? (4 pts.)
5. If so, why do they differ? Use sketches if you wish. (5 pts.)
III. Sea Level. (15 Points).
1. Sketch sea level for the last 85 million years based on the ridge volume calculations of Pitman (1978). Label the depth axis. (5 pts.)
2. Briefly describe how ridge volume changes result in sea level changes. (10 pts.)
IV. Nearshore Zone and Continental Shelf. (15 Points).
1. Give an explanation for the origin of the sand ridge at
"A" and a second explanation for the sand ridges at
"B" in terms of barrier island evolution and modern
shelf processes in the diagram below. Indicate which sand body/bodies
consist/s of relict sediment & which consist/s of palimpsest
sediments. Use sketches if you wish.
VI. Additonal Item for GLY609 Students. - If you are registered for GLY609, do one of the following items in the space provided below. (10 points).
1. Briefly discuss the reason that it is pure coincidence that
the oldest seafloor in both the Atlantic & Pacific Oceans
is ~190 my old. Use sketches if you wish.
2. Briefly describe the lithologies of Seismic Layers 2 &
3 of the ocean crust. Use sketches if you wish.
3. 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.
4. Explain the reasons that, in the diagram on the previous page,
the sand at "B" occurs as ridges, with lagoonal mud
in the troughs, while the sand at "C" is blanket-like.
BONUS: For 5 points of extra credit, make up your own question on material not covered in this test & answer it.