EPS101, SECTION 001, SECOND HOURLY EXAMINATION
Please note that the format of this exam is somewhat different from the first hour examination. There are three parts to this examination, which is printed on both sides. The total number of points for each section is given in parentheses. Should you require clarification on a particular question, please do not hesitate to ask! In Part IV, there are several extra credit questions at the end. The exam will be returned no later than next Monday.
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.
e. none of the above
2. Quartzites are metamorphic rocks consisting essentially of quartz. What
is the most logical protolith (parent rock)?
a. rhyolite
b. halite (rock salt)
c. limestone
d. basalt
e. peridotite
f. none of the above
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. The geologic eras of the Phanerozoic eon are, from youngest to oldest.
a. Paleozoic, Cenozoic, Mesozoic
b. Paleozoic, Mesozoic, Cenozoic
c. Cenozoic, Mesozoic, Paleozoic
d. Proterozoic, Mesozoic, Cenozoic
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. A nonconformity is identified when there is a significant break in time
between overlying sedimentary rocks and underlying crystalline rocks. Which
of the following probably occurred to produce a nonconformity.
a. strata were exposed for a period of time, without disruption, prior to deposition
of younger strata.
b. strata were tipped upside down prior to deposition of younger strata.
c. the crystalline rocks below the unconformity must have been somehow exposed
at the Earth’s surface prior to sedimentation.
d. pre-existing strata must have been deeply incised prior to deposition of
younger strata.
e. the beds above the nonconformity were deformed after their deposition.
8. Before it was turned into an irrigation in central New Mexico, the Rio Grande
overflowed its banks on almost a regular basis. If you were to go back to most
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 and very good for developing a thick, relatively fertile soil.
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 been metamorphosed, to some
degree.
b. unlike sedimentary rocks, igneous and metamorphic rocks consist of three-dimensionally
interlocking mineral grains, this feature serves to hold the rock together.
c. igneous and metamorphic rocks contain crystals.
d. all of the above.
10. Lithification
a. involves the sum of processes by which sediment is converted to sedimentary
rock at relatively low temperatures and pressures near the surface of our planet.
b. is only the process where sediment grains are cemented to form a chemical
sedimentary rock.
c. refers to the breakdown of organic material in sediments, beginning at temperatures
greater than 300oC.
d. refers to the formation of micas from clay minerals in mudstones at temperatures
exceeding 300oC.
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. Regional metamorphism occurs
a. when rocks are heated due to the local effects of magma injection
b. when rocks are buried to sufficiently great depths, usually in response to
tensional stresses.
c. when rocks are buried to sufficiently great depths, typically in association
with mountain building and contractional processes, which facilitate crustal
thickening.
d. when rocks are buried to temperature and pressure conditions above the liquidus.
13. What would you 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. Soils
a. Form on unstable surfaces where erosion rates are rapid.
b. Form In environments were precipitation is nonexistent
c. Include an uppermost horizon devoid of decaying plant material
d. May include both residual and transported components.
e. Lack clay minerals
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. melting
Part II. Relative Geologic Time
The sketch on the ATTACHED colored sheet is a vertical cross-section through
a part of Earth's continental crust with an interesting (depends on your point
of view) geologic history. All important geologic materials, or sequences of
rock types are labeled. Below, please place in succinct outline form the events
producing this section of crust. NOTE: I=intrusive igneous rocks; V = volcanic
rocks; M=metamorphic rocks; S=sedimentary rocks; U = unconformities, marked
by bold, squiggly lines!!! Also, answer the questions on the next page related
to the materials in the cross section.
Chronology, Youngest Event (10 points)
Oldest Event
PLEASE NOTE THAT I GIVE PARTIAL CREDIT (LOTS) FOR THIS QUESTION, SO IF YOU CANNOT
DETERMINE THE RELATIVE HISTORY OF ALL MATERIALS, AT LEAST DO SO FOR AS MANY
AS YOU ARE CONFIDENT!
Questions: (10 points)
1. Rocks S1,S2,S3, and S4 are respectively conglomerate, coarse-grained arkose, thin shales, fine-grained quartz-rich sandstone, additional thin shales, and limestone. From a standpoint of depositional environments, what took place in this area during the time of deposition of these rocks ?___________________________ _______________________ __________________ ____________________________________________________________________________How might this have occurred? _______________________________________________.
2. In the right part of your cross-section, sedimentary rocks S15 to S19 have been tilted and are now overlain by sedimentary rocks S1 to S4. What kind of unconformity is this? __________ _______________________________ Why must sedimentary rocks S1 to S4 be younger than sedimentary rocks S15 to S19? ________________________________________________.
3. Metamorphic rock M3 is a marble. What is one of the most abundant minerals in the rock? ______________ _____ What is a logical protolith (parent) for the rock and where would it have formed? _______________________________________________________.
4. Sedimentary rock S1 is a conglomerate, and contains cobbles of slate, phyllite, garnet schist, and mica-bearing gneisses. What kinds of rocks are these cobbles? _______ ____________ ____________ ___________________________________________. How would they have originated ? ______________ __________________________________.
5. Why is igneous rock I5 older than the unconformity? _________________________ ____________________________________________________________.
Part III. Surface Processes (15 points)
Draw a profile of a continent and its margin, from high elevation, high local relief mountainous terrane to low elevation, continental margin out into the deep marine environment. Describe processes affecting geologic materials (rocks) exposed at Earth’s surface, including what happens to the size and shape of materials removed from their point of origin with distance from it. Show different kinds of depositional environments.
Highest Topography: Lowest Topography/Relief:
Part IV. (Relatively) short answer questions. (25 points, therefore each question
is worth two or three points!). Note that there are extra credit questions at
the end of this section!
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. Name three kinds of sandstones _________________________________
4. What is the geologic time scale? ________________________________ _____________________________________________________________________________________________________________________.
5. What would round feldspar grains in a sandstone tell you? _____________________ _______________________________________________________________________.
6. Why is hydrocarbon formation considered part of sedimentary diagenesis? ___________________________________________________________________________________ _________________________________________________________________ ______________________________________________________________
7. Many fine grained detrital sediments are deposited at a rate of about 1 centimeter per 1000 years. At this rate, how long would it take to accumulate a stratigraphic sequence that is half a kilometer thick. (One kilometer equals a thousand meters. There are 100 centimeters in a meter.) ________________________________________________________________
8. How do clastic (detrital) sedimentary rocks differ from chemical and biochemical sedimentary rocks? __________________________________________________________ ________________________________________________________________________.
9. Sketch a pressure vs. temperature graph and indicate where the realm of sedimentation and diagenesis "fits" with respect to metamorphism and melting of geologic materials, in a “dry” and “wet” state.
10. Draw a vertical cross section showing flat lying sedimentary rocks cut by a vertical dike.
11. What is the most important kind of metamorphic reaction? ______________________________________. Of what importance is this kind of reaction in influencing the melting behavior of rocks? __________________________________ __________________________________________________________
12. What is the most abundant silicate mineral group in the crust of our Home? _______________________________. What takes place when these minerals are exposed to surface conditions (you do not need to write a balanced chemical reaction!!!) _________ _______________________________ __________________ ____________________ _________________________ __________________________________________________.
13. 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? ___________________________________ _________ _________________________ ________________________________________________________________________.
14. 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.
15. How can cross-cutting age relations be used to deduce or understand relative
geologic ages?__________________________________________________________________________
____________________.
Extra Credit Questions: (three points each) (note that you are not penalized for wrong answers)
16. In the context of geologic time,
why is the principle of uniformitarianism important to geologists?________________________
__________________________________
________________________________________________________________.
17. What is the difference between regional metamorphism and contact metamorphism? _______________ __________________________________________________.
18. What is the principle of components? ________________________________________ __________________________________________________________________________.
19. Draw a cross section of an angular unconformity and label the unconformity
and the different kinds of rocks involved.
20. At the crest of the Sandia Mountains,
upper Paleozoic sedimentary rocks rest on top of the Precambrian Sandia Granite.
The age of intrusion of the granite is about 1.4 billion years. What is this
relationship called?
______________ ____________________________________ __________________Explain,
succinctly, how it may have developed___________________________ ____ _____________
Part III. Matching. (20 points total)
1. sorting _______ a. annual lacustrine
deposition
2. varves_______ b. detritus in a super-arid environment
3. compaction______ c. decay of unstable nucleii in atoms
4. porosity _______ d. younger material deposited on older material
5. relative age_______ e. limestone spheres, pptd in shallow water
6. radioactivity______ f. rock salt, future home of low level radioactive waste
7. continental shelf_______ g. most voluminous sedimentary rock
8. halite _______ h. inert gas, able to move through a crystal at high T
9. natural gas _______ i. build up of detritus, mountain front
10. shale/mudstone _____ j. amount of void space
11. superposition _______ k. order of geologic events and rock formation
12. alluvial fan _______ l. zone of leaching
13. paleontology_______ m. site of major carbonate rock formation
14. clay _______ n. any sediment rich in organic material
15. Triassic_____ o. another word for a sandstone
16. source rock ________ p. period in the Mesozoic
17. argon_______ q. methane
18. round feldspars ______ r. study of ancient life and its evolution
19. arenite______ s. relatively uniform sediment grain size
20. ooid ______ t. decrease in void space, decrease in water