GEOS 100           EXAM 2     FRIDAY, OCT 17th 2003                11-11:50 am

ANSWER KEY

 Correct answers are highlighted in blue.

1 point each

 

  1. [T        F]         Clay and mud sediments lithify to shales and mudstones.
  2. [T        F]         Detrital sedimentary rocks have clastic textures.
  3. [T        F]         Clastic particles in a sedimentary breccia are rounded and are about the same size as fine-grained sand.
  4. [T        F]         Peat is thought to be the original material from which coal forms.
  5. Detrital sediments are classified on what basis?

a.       color of the cementing material 

b.      compositions of the precipitated mineral 

c.       grain sizes of the clastic particles

d.      degree of lithification

  1. Sedimentary rocks account for about what percentage of Earth’s outermost 10 kilometers of rock?  a. 5%  b. 35%  c. 65%   d. 85%
  2. Which original sediment would eventually undergo most compaction?

..... a. marine mud b. desert dune sand      c. reef limestone  d. coarse gravel

  1. Which sedimentary feature would be found in shales but not in sandstones?  a. mud cracks  b. cross-bedding  c. ripple marks  d. bedding  e. fossilized tattoo
  2. Which chemical sedimentary rock is also likely to be biochemical in origin?

..... a. limestone      b. sandstone     c. coquina        d. rock salt

  1. [T        F]         Partial malting is an important process in the formation of migmatites.
  2. [T        F]         Slate and schist are both derived by metamorphism of shales and mudstones.
  3. [T        F]         Calcite is the main mineral constituent of the sedimentary rock limestone and of the metamorphic rock marble.
  4. [T        F]         Three major factors in involved in metamorphism are elevated temperature, elevated pressure, and the chemical action of hot fluids.
  5. Which textural term denotes a strong, parallel alignment of coarse mica flakes and /or of different mineral bands in a metamorphic rock?

..... a. rock cleavage  b. foliation  c. stress streaking  d. marbleizing  e. rock glazing

  1. A metamorphic aureole is a zone of:      a. contact metamorphic rock  b. movie theater in a volcano  c. contact metamorphism  d. intrusive body of rock
  2. What response best represents the condition of contact metamorphism? 

a.       pressure are very high, the rock is deeply buried, and the temperature is raised by Earth’s internal heat 

b.      pressure are fairly low, the rock is in the upper part of the crust, and the heat is supplied from a nearby magma body

c.       heat is generated by shearing and mechanical movements along fault zones

d.      depths are fairly shallow, but the temperatures and pressures are so high that the rocks begin to partially melt.

  1. Which rock forms through metamorphism of limestone?  a. calcite  b. migmatite  c. marble  d. sandstone  e. metaconglomerate
  2. What is the name of the metamorphic rock that is foliated and is composed of predominantly of platy minerals like mica?  a. slate  b. chalk  c. schist  d. karst  e. gneiss
  3. [T        F]         Impact metamorphism is the result of an impact between two rocks.
  4. [T        F]         Foliation results when minerals under pressure orients in a direction parallel to the direction of applied force.
  5. Which two metamorphic rocks are composed predominantly of single minerals? a. schist and granitic gneiss  b. fault breccia and graphite schist  c. garnet schist and mica schist  d. marble and quartzite
  6. [T        F]         Most sedimentary rocks are readily dated by radiometric dating.
  7. [T        F]         Geologic time scale is totally based on relative dating of sedimentary rocks found exposed on Earth.
  8. The rare element iridium has been implicated in which “ancient health” crisis? 

a.       poisoning of primitive turtles which transformed them to ninja turtles

b.      extinction of wooly mammoth in late Pleistocene time

c.       disappearance of Neandarthal man during early Cenozoic time

d.      extinction of dinosaurs at the end of the Cretaceous Period

  1. Which radioactive daughter of U238 decay series is a gas that can accumulate to unhealthful levels in poorly ventilated uranium mines and home basements?

a.       lead232  b. carbon14  c. radon222  d. argon40  e. oxygen16

  1. The law of superposition states that:

a.       any geological feature cross-cutting another feature is younger than the feature it is cutting across

b.      in terms of position younger layer is in front and older in the back

c.       in a sequence of thin to thick beds, thick beds are older and thin beds are younger

d.      in an undisturbed geologic sequence, as you go upwards starting from the bottom, the beds become younger and younger

e.       in an undisturbed geologic sequence, the beds at the bottom are younger than the beds at top

  1. The half-life for a radioactive isotope is:
    1. the time it takes for the isotope to travel one half distance around the globe

b.      the time it takes for the isotope to go up into the atmosphere and come back to the surface

c.       the time it takes for the isotope to become half of what was before

d.      the time for an isotope to get reduced by half in terms of quality

 

Use figure 1 (attached with the test) to answer Q 28 and 29.

  1. A hypothetical radioactive isotope has a half-life of 20,000 years. The ratio of radioactive parent to stable daughter product is 1.3. How old is the rock? 

..... a. 1,000  b. 10,000  c. 20,000  d. 30,000  e. 40,000

  1. How many half-lives have elapsed for the radioactive isotope in question 28 to come to the ratio of 1:3?  a. 0  b. 1  c. 2  d. 3  e. 4

 

Use figure 2 (attached with the test) to answer Q 30 and 31.

 

  1. What will be the proper sequence of beds as oldest to youngest between layers E & C? 

a.      E, H, C 

b.      E, H, C, F, A, B  

c.       A, E, H, C, I 

d.      E, H, C, A, F

  1. A is an intrusion. What is the relative age of intrusion A? 

a.       younger than C but older than D 

b.      older than H but younger than B 

c.       younger than B but older than E 

d.      younger than D

e.       none of the above

  1. Which best describes the unconformity? 

a.      buried, erosional surface with younger strata above and older rocks below 

b.      the lower contact of an intrusive sill with sedimentary strata

c.       a fault with younger, sedimentary rocks above older, igneous rocks

d.      contact between a cross-cutting intrusive igneous body and sedimentary rocks

  1. Which one denotes an angular unconformity? 

a.       when the beds separated by an unconformity is parallel 

b.      when the beds at the bottom is horizontal and the beds at top is vertical

c.       when both the beds are inclined at each other

d.      when older beds at the bottom is at an angle with the younger beds on top

  1. [T        F]         Disconformity is that type of unconformity where the contact is between a sedimentary and igneous or metamorphic rock.
  2. [T        F]         Slump describes the very slow, downhill movement of soil and regolith.
  3. [T        F]         Bedding planes and foliations can both act as slip surfaces for rockslides.
  4. [T        F]         The very destructive, mass wasting event that wiped out Yungay and Ranrahirca, Peru was caused by hot, volcanic ash falling on deep snow in the summit region of a volcano.
  5. Of the following which one do you think is always triggered by earth shaking?  a. slump  b. rock avalanche  c. soil creep  d. mud flow
  6. [T        F]         Mass wasting is an independent process that shapes our earth continually.
  7. [T        F]         Wind and water are essential controls of mass wasting process besides gravity.
  8. [T        F]         Mass wasting is only a surficial (external) process that operates only on surface.
  9. [T        F]         Debris fall and rock fall is same type of mass wasting event. The difference is that in debris fall, the debris slides down the slope while in rock fall, the rock literally falls through air.
  10. [T        F]         A scarp is the exposed portion of the rupture surface beneath a slump block.
  11. Which mass wasting process has the fastest movement?   a. slump  b. fall  c. avalanche  d. slide  e. flow
  12. What affect does water have on the cohesion of clay bearing formation? 

a.       it enhances the cohesion by adding an adhesive effect to clay 

b.      when clay becomes wet it will start to move as mudflow

c.       clay becomes stickier and holds the slope

d.      a little water increases the cohesion but excessive water reduces the strength and clay becomes fluid

 

Use figure 3 to answer Q 46 to 48

 

  1. [T        F]         The bedding plane shown in slope A in the figure will not destabilize the slope.
  2. [T        F]         The slope B in the figure will be a stable slope because of orientation of rock layers.
  3. [T        F]         Rock bolting could be a method to stabilize the slope A
  4. [T        F]         As the discharge of a stream increases, the velocity decreases as a result of heavy load carried by the river.
  5. [T        F]         Gradient does not have anything to do with the velocity of a stream because the velocity increases as more water comes into the river and contributes to the flow.
  6. [T        F]         As groundwater and surface water are not connected there is no possibility of groundwater contamination from surface or vice versa.
  7. [T        F]         The precipitation over the land totally returns to sea as surface runoff. The sea water is a big source of groundwater recharge.
  8. [T        F]         A losing stream is a stream which recharges the groundwater.