ES 10 Geologic Principles;	Final;		December 16, 1994;	Alfred Hochstaedter

1) (5 pts)The mastodons (those big, hairy, elephant-like creatures with big tusks) lived from the
beginning of the Miocene to the end of the Pleistocene. Dinosaurs lived during the Mesozoic.
During which Periods did the mastodons live? During which Periods did the dinosaurs live? Did
dinosaurs and mastodons ever fight over food or territory? Were hominoids (defined here as
creatures more like us than chimps) more likely to kill a dinosaur, a mastodon, or both for dinner? 

Mastodons lived during the Tertiary and Quaternary.
Dinosaurs lived during the Triassic, Jurassic, and Cretaceous.
Dinosaurs and mastodons never faught; they lived during different times.
Hominoids more likely to kill mastodons for dinner becuase they lived during same
time.


2) a. (5 pts) Rocks may try to hide deep down there in the earth, but we can always tell where they
have been when they come back to the surface. Draw a pressure-temperature diagram of the
various metamorphic-rock facies. Remember to label the axes and give an indication of their
values and units (i.e., I want to see numbers on the axes, and what their units are).

Figure 5.17 direct from book.

b. (3 pts) What is the difference between a greenschist and a greenschist-facies metamorphic rock,
or, what is the difference between an amphibolite and an amphibolite-facies metamorphic rock? 

Greenschist and amphibolite are specific rock names with specific mineralogies. 
Greenschist- and amphibolite-facies metamorphic rocks refer to any metamorphic
assemblage that equilibrated during specific P-T conditions.


c. (3 pts) Three things determine the metamorphic mineral assemblage that will develop in a given
rock. Temperature is one of them. What are the other two?

Pressure and Protolith.


d. (5 pts) For the following three facies examples, please explain 1) how the geotherm differed
from ÒnormalÓ (if at all) during metamorphism, and 2) what type of tectonic or geologic setting is
implied.

i) Blueschist
Geotherm cooler than normal -- subduction.

ii) Greenschist or Amphibolite
Geotherm normal -- burial or crustal thickening through mountain building.


iii) Hornfels
Geotherm hotter than normal -- igneous intrusion / contact metamorphism.


e. (4 pts) In general, how do rocks that were once presumably at the surface get to regions where
they undergo metamorphism, and how do they get back up to the surface?

Get there: burial or crustal thickening through compressional deformation.
Get back: erosion + isostasy or normal faulting. (only one of each needed for full
credit).

3. a. (3 pts) Rivers supply sediments to the oceans. Deltas and lagoons form where they empty
into the ocean. Using a delta or lagoon as an example, explain what a Òtransgressive sequenceÓ
(sea level rising relative to land) would look like.(You can include lagoonal deposits (muds), beach
deposits, offshore shelf deposits, and continental slope deposits in your answer; IÕm more
interested in their relationship to each other than what they actually look like).


Deeper-water deposits overlying shallower-water deposits; beach deposits overlying
lagoonal deposits.


b. (5 pts) Again using your transgressive deltaic or lagoonal sequence as an example, explain why
rock-stratigraphic units do not represent time units. For full credit use the term Òsedimentary
faciesÓ in English sentences in your answer (a mere definition will not garner full credit). If
formations are used to correlate rock-stratigraphic units, what are used to correlate time units?


Sedimentary facies suggests that different, but related, sediments can be deposited at
the same time, i.e., in any sedimentary system, different sediments will be deposited in
different areas. Those that were deposited adjacent to one another, will wind up
directly over- or under-lying one another. As sea level rises, the same sediments are
deposited, but their actual position changes. Thus, rocks are not time correlative,
because the same rock could have been deposited at different times in different places
as the sea level changed. Fossils are used to correlate time units.


4. (4 pts) The imaginary town of Angelou lies on the banks of the Mayan River and near the
Pulse-of-Morning Fault. Last year, Angelou experienced a 100-year flood and a large earthquake,
the like of which had not been felt in nearly 100 years. The inhabitants are bravely re-building, but
are wondering whether they are more likely to experience another large flood or another large
earthquake within the next five years. You know the answer. Which is it and why? The term
Òrecurrence intervalÓ is a bad term for either floods or earthquakes and a very good term for the
other. Which is which and why?

A large flood is more likely to happen in the next 5 years because 100-year flood
means a 1 in 100 chance of occurring in any given year. A large EQ in the few years
after a large EQ is extremely unlikely because most or all of the stress has been
releived. EQs happen because stress builds up, while floods occur because of the
weather. ÒRecurrence intervalÓ is a bad term for floods because large flood could
easily happen in two successive years. This is much less likely for EQs.

5. (4 pts) Rocks, however, do move. And paleomagnetism provides some of the most compelling
evidence. What is the property of the magnetite grains that we actually measure? And why does
this information tell us about paleo-latitude, but not about paleo-longitude? (Remember that lines
of latitude parallel the equator, while lines of longitude pass through the poles.) 

Paleomagnatists measure the inclination of magnetite. Because of the magnetic field,
this measures distance from the poles. There is no way to measure movement parallel
to the equator, because the magnetic field is exactly the same for any given latitude.


6. (4 pts) What is a terrane? What is a suspect terrane? How might terranes contribute to the
growth of the continents? Why are terranes such an attractive idea for explaining the geology of the
Western Cordillera?

A terrane is a distinct sequence of rocks that are completely bounded by faults (not 
necessarily active). The rocks within the terrane can have their own sedimentary,
diformational, metamorphic, and paleomagnetic history that may not be related to the
rocks on the other side of the fault. A suspect terrane is a terrane for which the origin is
unclear, i.e., we donÕt know where it came from. We cannot correlate them to any of the
rocks on the other sides of the faults. Terranes were attractive for the western
Cordillera because traditional geologic theory of being able to determine a local origin
for all of the rocks did not work well. The sequences of rocks observed (now called
terranes) are all apparently unrelated to each other.


7. (5 pts) Draw a cross-section of a mid-ocean ridge showing the crust, lithosphere and
asthenosphere. Use the concept of isostasy to explain why high elevation is the most distinctive
feature of spreading centers. Remember that mantle material gets denser and stronger as it cools.

Drawing is something like 16.13 -- the standard mid-ocean ridge diagram showing
thickening lithosphere with age. As lithosphere ages it cools. Asthenosphere cools too,
and ÒfreezesÓ against it from the bottom. As the lithosphere cools it gets denser.
Because of isostasy, the denser and thicker lithosphere floats deeper on the
asthenosphere. Becase it ÒfloatsÓ deeper, the depth increases with age.

8. a. (7 pts) California History: Below is a simplified diagram of the tectonics of western North
America. On this diagram, identify the two triple junctions. Draw in the motion of the San
Andreas Fault. Now, draw two additional plate-tectonic diagrams to show CaliforniaÕs transition
from a convergent margin to the present-day transform margin. In other words, use two diagrams
to explain how California tectonics got the way it is today. Draw one diagram to depict the
situation about 30 million years ago and the second diagram at about 10 million years ago.


Drawing straight from 16.25. SAF is right-lateral. Two triple junctions. 
Pacific Plate motion should be drawn in as west-northwest -- parallel to Hawaii (from d,
below).

b. (3 pts) Which way will the two triple junctions continue to move in the future?

Mendocino TJ moves north (2 pts). Other triple junction moves south (1 pt).

c. (4 pts) What are at least two pieces of geological evidence that the entire California coast was
once a convergent margin?

1. Sierra Nevada batholith -- roots of volcanic arc.
2. Franciscan Complex -- old accretionary wedge.
3. Great Valley Sequence -- old fore-arc basin.


d. (3 pts) The Hawaiian islands are located on the interior of the Pacific Plate and were formed by a
hot spot. They get progressively older to the west-northwest. On the present-day diagram, above,
draw the absolute plate motion of the Pacific Plate. Which way do you think is the absolute motion
of the North American Plate.

Pacific Plate moves west-northwest, parallel to Hawaii (2 pts). North American Plate
moves west ( 1 pt).


9. (5 pts) Gary Greene talked about the inter-relationship between groundwater flow, faulting, the
formation of Monterey Canyon, and underwater lifeforms that live off of freshwater seeps in
Monterey Canyon. He emphasized how all disciplines come together to study the oceans. Answer
only one of the following two questions.

A. What is the origin of the freshwater the emits from seeps in Monterey Canyon and supports
chemosynthetic (sp?) clams? What does the existence of these seeps tell us about saltwater
intrusion in the Pajaro Valley. Use DÕarcyÕs Law to explain.

OR

B. What role does groundwater play in the formation (i.e., erosion) of submarine canyons? What
other process is also important?

A. Seeps show that water is moving from Pajaro Valley sedimentary rocks out to sea.
The hydrologic gradient combined with the coefficient of ermeability in these rocks
allows ground-water to easily flow from on-land (i.e., high area) to off-shore locations.
Since g-water is moving from land out to sea, saltwater intrusion cannot occur. Water
flows downhill.

B. Freshwater seeps weaken the sedimentary formations of the canyon walls and
cause them to collapse. Bottom scouring of turbidity currents (undersea landslies) is
also important.

10. (3 pts) We are located on the Salinian Block. Where does the Salinian Block come from, or,
more importantly, how would we go about figuring out where it comes from?

The Salinian Block comes from somewhere to the south, perhaps the southern Sierras.
We could attempt to figure it out be trying to match the rocks up to some other rocks
down there, or measuring the paleomagmatism of Salinian rocks.


11. Slides: For all of these, IÕd like to know about Earth History. That means tell me what
happened first, second, third, and so on. Start at the beginning and tell me what observation causes
you to interpret a particular event as first, second, etc..DonÕt forget to mention the process that
made the present-day topography. In addition to history, answer the questions given for each slide.

a. (4 pts) These are cross-bedded sandstones. What is the depositional environment? What enables
these canyon walls to be so steep?

Deposition of sand. Lithification into rock. Uplift. Erosion by small river. Depo
environment is anywhere with clean, mature sand, like sand dunes or a beach. The
canyon walls are so steep because the rock is extremely strong and resistant to
weathering.


b. (4 pts) What was the depositional environment for these unsorted sediments?

Deposition of unsorted sediments. Uplift. Erosion of unsorted sediments. Depo
environment is anywhere high energy, like glacial morains, landslides, or mudflows.


c. (4 pts) Treat the layered rocks as one depositional unit and the ductile deformation as one event.
I will point out where a normal fault lies just out of view.

Eposition of sediments. Deformation of sediments. Uplift of deformed rocks along the
normal fault. Erosoion of mountain due to water.


d. (4 pts) The red rocks are meta-sediments and meta-volcanics. The white rock is granite.

Deposition of sediments. Burial to deep levels of sediments (tectonism or burial).
Intrusion of granites and formation of roof pendents. Uplift. Erosion of mountains due to
glaciers and rivers.e. (4 pts) This may be familiar to some of you.

Grand Canyon. Deposition of sediments. Uplift. Deformation -- tilting of beds. Erosion.
(Unconformity). Deposition of more sediments. Uplift. Erosion by Colorado River.


12. (5 pts) I sometimes go to grade schools to speak about geology. I enjoy it; kids ask the best
questions. Teach your children well, for they are our future. If you were able to take a group of 6th
graders on a field trip (no expense or limit) to a single locality to show them what you believe to be
some of the most important example(s) of Earth Science relationships, where would it be, what
would you see, and why is it so important? Points will be awarded here on the basis of style
(originality), technical ability  (i.e., ability to actually see a real geologic feature that you write
about), and presentation (how well you support what you say). Write only on the lower half of this
side of this page.


Anything reasonable.