EXAMPLE!!!!!!!!
Name:_____________________________ October 22, 1997
EPS101, SECTION 001, SECOND HOURLY EXAMINATION
I hope you had a good fall break. 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 (10) 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 Metamorphic Rocks on Friday--this exam will be
turned back no later than next Monday, maybe earlier.
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, 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. A purely residual soil on basaltic lava
flows, say in a moderately arid climate (use the Taos plateau as an example
will contain
a. lots of quartz and potassium feldspar grains
b. clay minerals, iron oxides, and probably some secondary
calcium carbonate
c. quartz and iron
oxides
d. this is a trivial
question, because basalts are very resistant to chemical weathering.
e. plagioclase
feldspar and potassium feldspar
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. What is the
difference between a dike and a sill?
a. the only
difference is thickness of each planar intrusion
b. the only difference is the composition of each planar
intrusion.
c. dikes are emplaced
along planes of weakness that cut across pre-existing fabrics in rocks, whereas
sills are concordant and are emplaced parallel to pre-existing fabrics.
d. dikes dilate or
expand the earth’s crust; sills do not.
e. dikes are
vertical, and are more resistant to erosion than surrounding rocks; sills are
not vertical.
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 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. 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
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. When marine
water evaporates in a closed basin, what is the logical material to form?
a. igneous rocks
b. salt (halite)
c. sandstones
d. coal
e. dolomite
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. annual lacustrine deposition
2. varves_______ b. detritus in a super-arid environment
3. partial
melting______ c. calcium
carbonate rich soil
4. porosity _______ d. more siliceous melts extracted from
mafic ones
5.
eustatic _______ e. limestone spheres, pptd in shallow
water
6. subduction
zone ______ f. rock salt, future home of low level
radioactive waste
7. continental
shelf_______ 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. batholith_______ k.
major environment for magmatism
12. alluvial fan _______ l. zone of leaching
13. A horizon _______ m. site
of major carbonate rock formation
14. clay _______ n. any sediment rich in organic material
15. dike _____ o. another word for a sandstone
16. source rock ________ p. world wide, as in sea level change
17. passive margin _______ q. methane
18. round feldspars ______ r. sheet
silicate, weathering product of feldspar
19. diamond arenite______ s. large,
irregular intrusion
20. ooid
______ t. planar, discordant intrusion
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 is a
batholith and why might these be of great importance in association with
unusual accumulations of base (Fe, Cu, Pb, Zn, etc.) and precious (Au, Ag)
metals (i.e. mineral deposits?)
__________________________________________________________________
___________________________________________________________________________.
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. _________________________
_____________________________________
_______ _______ _____________________________ _______________________ _____________
__________________________________________.
9. Why is the
basic categorization of sedimentary rocks between detrital and chemical
materials? __________________________________________________________
________________________________________________________________________.
10. Sketch a
pressure vs. temperature graph and indicate where the realm of sedimentation
and diagenesis "fits" with
respect to metamorphism. Also,
show examples of melting reaction for
dry earth materials and wet earth materials.
11. 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?
___________________________________________
___________________
____________________________________________________________________.
12. The rock
quartzite is the metamorphic equivalent of a sandstone. Suppose you start with a sandstone formed
in an environment where chemical weathering has been intense. What will the mineralogy of the sandstone
be?
_______________________________.
What do you (in an educated fashion) guess will happen to this rock as
progressive metamorphism occurs and why? _______________________________
___________________ ____________
_______ ____________________ _________________________
__________________________________________________.
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.
How would this differ if the “source” region consisted only
of limestones?
__________________________________________________________________________
____________________________________________________________________________.
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. Describe the
process of partial melting of geological materials, using sketches as
necessary. If you partially melted an
ultramafic rock, what would you anticipate producing? In addition, discuss the
difference between the melting of dry and “wet” geologic materials. Of what
importance is this difference for the generation of magmas?
2. With illustrations, describe how sedimentary 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,
Fall, 1997