EXAMPLE!!!!!!!!

Name:_____________________________ March 31, 1997

EPS101, SECTION 001, SECOND HOURLY EXAMINATION

Please note that the format of this exam is very similar to that of the first hourly. There are four (4) parts to this examination, which is printed on both sides. The total number of points for each section is given in parentheses. In part IV., you are to answer only one of the total questions; if you have additional time, you may answer a second question in this section for a maximum of ten extra credit points. Should you require clarification on a particular question, please do not hesitate to ask! Total points 100 +10(extra credit). We will begin Geologic Time on Wednesday—this exam will be turned back no later than Friday.

Part I. Multiple choice. (There is only one correct answer; 30 points.)

1. The two features in a sediment or sedimentary rock most responsible for layering or stratification are

a. color and organic material abundance variations.

b. grain size (sorting) and grain composition variations.

c. shape and color variations.

d. fossil content and color variations.

2. Hot spots or mantle "plumes"

a. differ from mid-ocean ridges in that silicic magmas result from complete melting of the

deep mantle.

b. differ from mid-ocean ridges in that heat from deep in the Earth's mantle is transferred

toward the surface in a focused manner, often resulting in major accumulations of mafic

magma and products of whole scale crustal melting on the Earth's surface.

c. are restricted to the last few million years of Earth history.

d. are only related to continental lithosphere plates.

e. differ from mid-ocean ridges in that the products of magmatism on the Earth's surface

remain stationary with respect to the lithosphere plate that contains them.

3. You are mapping a large area in the western United States and discover laterally continuous (traced over considerable distances) , nearly constant thickness ( of several meters) layers of pure quartz sandstone alternating with layers of shale . What kind of depositional environment does this setting most likely represent?

a. alluvial fan

b. continental dune

c. glacial lake

d. beach/nearshore marine, moderate latitudes

e. none of the above

4. Metamorphic rocks usually have a "fabric", defined by the preferred orientation of one or more silicate minerals, because

a. pyroxene, the most abundant mineral in metamorphic rocks, is a sheet silicate.

b. most metamorphic processes occur under the influence of some directed pressure at elevated temperature, resulting in the squeezing, stretching, and/or shearing of rocks.

c. by volume, regional metamorphism is considerably less important than contact metamorphism.

d. most metamorphic processes occur at very shallow levels in the earth's crust, where lithostatic pressures are very high.

e. none of the above.

5. When all of the ions in a substance become dissociated at the surface of Earth, the substance has been

a. weathered mechanically

b. altered to clay

c. dissolved

d. converted to soil

e. oxidized

6. How do the probable depositional environments in which a lithic-arenite and a fine-grained, quartz-rich sandstone compare?

a. the source of the lithic arenite was a coarse-grained intrusive igneous rock, like a granite from a batholith in an eroded magmatic arc.

b. the quartz-rich sandstone was derived from a rugged, actively eroding terrane whose bedrock was

entirely amphibolite.

c. the lithic arenite was deposited close to a magmatic arc, where fine-grained volcanic rocks were actively being eroded and relatively rapidly transported.

d. the quartz-rich sandstone was deposited in an alluvial fan environment, at the front of an actively

eroding mountain range in a very arid climate.

7. You discover in the field a sedimentary rock consisting entirely of silicon dioxide, and close inspection of a thin section of the rock reveals that it consists of the remains of microscopic, single-celled organisms. The rock

a. is called a quartz arenite and the “grains” were deposited in a stream

b. is called chert, and most likely represents slow accumulation of skeletal remains in a deep oceanic

environment

c. is called chert and represents slow accumulation of calcite in a shallow, equatorial marine environment.

d. when metamorphosed becomes a slate

e. is referred to as a detrital sedimentary rock

8. The impressive/damaging flooding of the Mississippi River three years ago represented major transportation of sediment! If you were to go back to the majority of the flooded areas that are now drained, what kind of sediment would you most likely find?

a. cobbles and pebbles

b. quartz sand

c. mud and silt, deposited in what are referred to as “overbank” areas.

d. carbonate mud

e. pyroxene sand

9. In comparison to sedimentary rocks, igneous and metamorphic rocks are referred to as "crystalline" rocks because

a. they are all Precambrian in age and have thus inevitably been metamorphosed, to some degree.

b. unlike sedimentary rocks, igneous and metamorphic rocks consist of three-dimensionally interlocking mineral grains, this feature serving to hold the rock together.

c. igneous and metamorphic rocks contain crystals.

d. all of the above.

10. Diagenesis

a. involves the sum of processes by which sediment is converted or lithified to sedimentary rock at relatively low temperatures and pressures near the surface of our planet.

b. is the process by which sediment grains are cemented together to form a detrital sedimentary rock.

c. refers to the breakdown of organic material in sediments, beginning at temperatures greater than 300^oC.

d. refers to the formation of micas from clay minerals in mudstones at temperatures exceeding 300^oC.

e. none of the above.

11. Primary sedimentary "structures" are important in determining the "up direction" in sequences of sedimentary rocks. Which of the following is correct?

a. In a shale-sandstone-limestone sequence, the limestone bed is always the oldest.

b. Crossbeds in sandstones deposited in any environment are convex upwards.

c. Burrowing organisms enter the moist, juicy, organic rich sediment from the bottom of the beds and work their way to the top.

d. In graded beds, the coarsest sediment is usually at the base of the bed, resulting in a fining upward sequence.

e. The law of superposition states that older strata are deposited on younger strata

f. All other factors remaining constant, the greater sediment is transported from the source, the more angular the grains.

12. What is the principal origin of sodium in seawater?

a. weathering of quartz arenites

b. deposition of limestones

c. a combination of processes, including weathering of mafic and intermediate composition igneous

rocks, weathering of salt beds, volcanic exhalations at mid ocean ridges as well as in continental

environments.

d. biologic activity

e. chemical weathering of coal

13. What would you expect to find deposited in a continental shelf environment at low latitudes?

a. inorganic and organic limestones

b. arkoses

c. coal

d. chert, consisting of shell fragments of radiolaria

e. glacial varves

f. none of the above.

14. Dehydration reactions in progressive or prograde metamorphism

a. involve the conversion of hydrous minerals to anhydrous minerals and fluids, principally as a result of increasing pressure.

b. facilitate the melting of geologic materials because in the presence of fluids rocks melt at considerably lower temperatures than in the dry state.

c. are not of great importance in metamorphism because there are few hydrous silicate minerals in nature.

d. involve the conversion of low density minerals to high density minerals as a function of increasing temperature.

e. none of the above

15. When solid rock is exposed at the earth's surface, it is subjected to which of the following processes which will result in sedimentary material.

a. metamorphism

b. lithification

c. subduction

d. weathering

e. cementation

Part II. Matching. (20 points total)

1. pedocal_______ a. parent to a metamorphic rock

2. foliation _______ b. detritus in a super-arid environment

3. transgression ______ c. calcium carbonate rich soil

4. porosity _______ d. relative or absolute increase in sea level

5. eustatic _______ e. limestone spheres, pptd in shallow water

6. subduction zone ______ f. rock salt, future home of low level rad waste

7. protolith _______ g. most voluminous sedimentary rock

8. halite _______ h. “stable” edge of a continent, high sedimentation

9. natural gas _______ i. build up of detritus, mountain front

10. shale/mudstone _____ j. amount of void space

11. schist _______ k. major environment for magmatism

12. alluvial fan _______ l. zone of leaching

13. A horizon _______ m. planar fabric in metamorphic rocks

14. clay _______ n. any sediment rich in organic material

15. quartzite _____ o. changes in pressure and temperature with time

16. source rock ________ p. world wide, as in sea level change

17. passive margin _______ q. methane

18. rounded feldspar grains ______ r. sheet silicate, weathering product of feldspar

19. metamorphic path or trip ______ s. metamorphosed sandstone

20. ooid ______ t. mica-rich metamorphosed mudstone

Part III. (Relatively) short answer questions. (35 points, therefore each question is worth two or three points!).

1. What is the term given to particle sizes of about a mm to at most a few mm for detrital sedimentary material?_________________________________________ _____________________________ .

2. You find a fine-grained sedimentary rock consisting of extremely fine (i.e. mud size) “grains” of calcium carbonate, and nothing else. What is the rock? Where would it most likely have formed and why? _____________ ___________________________________________________________________ __________________________________________________________________________________ _________________________________________________________________________________.

3. What are metamorphic rocks and how do they form?________________________________________ ______________________________________________ ____________________________________.

4. What are the three most important environments for magma production within the upper few hundred kilometers of the earth’s surface? _____________________________________________________ _________________________________________________________________________________.

5. Why is hydrocarbon formation considered part of sedimentary diagenesis? ___________________________________________________________________________________ _________________________________________________________________ __________________.

6. In introducing the concept of beds of sedimentary rock, we discussed the notion of "breaks" in the record of sedimentary deposition. What is meant by this? _______________________________________________________________________________ __________________________________________________________________________________.

7. What is the difference between chemical and physical weathering? _________________________ _______________________________________________________________________________ _______________________________________________________________________________.

8. Using the West Mesa of Albuquerque an example, briefly explain how topography is influenced by differences in resistance to erosion of different geologic materials. _________________________ _____________________________________ ___________________________________________

______________________________________________________________________________

11. Starting with a shale, what metamorphic rocks would be produced by increasing heat and pressure?__________________________________________________________________________ _______________________________________________________________________.

12. Where does contact metamorphism occur? Would you expect pronounced deformation fabrics (like a foliation) to develop in contact metamorphosed rocks? Why or why not? __________________ ______________________________ _________________________________________________

13. Sketch a pressure vs. temperature graph and indicate where the realm of metamorphism "fits" with respect to sedimentation and diagenesis and melting. Also, show an example of a dehydration reaction.

14. What is the difference between a residual and a transported soil? ___________________ ________ __________________________________________________________________________________

Are transported soils important in tropical climates? _____________ Why? __________________

______________________________________________ Are they important in arid environments?

_____________________________ Why? ___________________________________________ ____________________________________________________________________________.

15. The rock quartzite is the metamorphic equivalent of a sandstone. If you start with a sandstone formed in an environment where chemical weathering has been intense, what will happen to this rock as progressive metamorphism occurs? __________________________________________________ ___________________________________________________________________________________

16. In recent years, geoscientists have been exceedingly interested in learning about past changes in Earth's climate, for a range of reasons. To investigate such changes in climate, what kind of sedimentary rocks might you choose to study, and why? ___________________________________ _________ __________________________________________________________________________________.

17. Sketch the likely distribution of sediment types surrounding a relatively small, circular to sub-circular rapidly uplifting mountainous region consisting principally of granites and gneisses.

PART IV. Long Answer Questions. Answer only one (1), (15 points total). NOTE: YOU MAY ANSWER A SECOND QUESTION FOR UP TO 5 POINTS EXTRA CREDIT.

1. Name the three PRINCIAL FACTORS of metamorphism and explain how each contributes to metamorphsim.

2. With illustrations, describe how metamorphic rocks fit into the rock cycle.

3. What are hydrocarbons? How are they produced? What are the essential general requirements for the production and retention of hydrocarbons in the earth's crust?

4. List and discuss three factors that significantly affect the rate of chemical weathering. Indicate how the rate is affected by each factor.

5. Compare and contrast the depositional environments, types of sedimentary material deposited, rate of deposition, and nature of the sedimentary produced for an alluvial fan in a relatively arid, tectonically active (active uplift) environment with that of a glacial lake which freezes during the winter.

6. Six sedimentary rocks are found in stratigraphic succession. From top to bottom, they are: coarse arkose, quartz arenite (poorly sorted), quartz arenite (well sorted, frosty grains), siltstone, limestone, and coal. The section has not been turned upside down. Describe logical depositional environments for the sequence of sedimentary rocks. How might, overall, the sequence be interpreted in terms of changes in depositional environments?

7. How does mechanical weathering differ from chemical weathering? What is the role of climate in dictating whether one type of weathering will predominate in a particular area? What conditions of climate, weathering rate, and erosion rate could lead to a feldspar-rich sandstone? What type of weathering predominates in New Mexico? How does transportation of sediment differ from weathering?

8. Describe the formation of a soil from pristine bedrock. Sketch and label a soil profile typical of central New Mexico. Do the same for a soil profile typical of Central America or the Brazilian rain forest.

9. Using the theory of plate tectonics as a basis, describe the three principal environments for the formation of magmas. Use sketches for each environment to help illustrate where the magmas are generated. Indicate the approximate composition of the magmas produced.

Please place your answer(s) to part IV on this page and the following page. ADDITIONAL PAPER, IF REQUIRED, IS AVAILABLE AT THE FRONT OF THE ROOM.

Second Hourly Examination, EPS 101