Sedimentology & Stratigraphy
LECTURE TEST #1
February 15, 2007
(A sample test)

(Your test will, of course, be different!)

1. Siliciclastic grains in a sediment take on many shapes.  What are some primary controls on grain shape?  In other words, why do grains take the shapes that they do?  [5 points]

2. Please draw a cross-section of a current ripple, showing internal features and the current direction.  Label all the parts.  [10 points]

3. For the following questions, imagine a stream 5.0 meters wide, 2.0 meters deep and flowing at 30 centimeters per second.  Please show your work for each section.  (Please note the “useful equations” and charts on the last pages of this examination.)

a. You drop a grain of quartz approximately 0.05 mm in diameter into this moving stream.  Does the grain remain suspended or drop to the bottom?  (Show support for your answer.)  [5 points]

b. Is the stream flowing under laminar or turbulent conditions?  Why?  [5 points]

c. Is the flow subcritical or supercritical?  Why?  [5 points]

d. What is the stream flow (Q)?

4. What is the difference between progradation and regression?  [5 points]

5. Please describe a disconformity.  Labeled diagrams always help  [5 points]

6. Why do grains saltate?  Why will a quartz grain saltate much higher in air than in water?  [5 points]

7. Please describe Walther’s Law of Facies, giving an example of its application.  [10 points]

8. Delta deposits are great places to find petroleum.  Why?  Also, please name two places in the world where oil and gas are pumped out of ancient delta deposits.  [10 points]

9. How do you distinguish the deposit of an arid alluvial fan from a humid alluvial fan?  A familiar question!  [10 points]

10. Please draw a meandering stream (map-view) showing the cut banks, point bars, natural levees, floodplains, and a crevasse splay or two.  [10 points]

11. Define and/or describe any three of the following terms, using labeled diagrams where appropriate and clearly stating the significance of the term in sedimentology or stratigraphy.  [15 points total]

______________________________________________________________________________________
           desiccation cracks

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           braided stream

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           chronostratigraphic units

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           Witwaterstrand

 

Useful Equations (did not fully translate onto the webpage, but you see what is supplied) 

Stokes' Law of Settling:

where w = settling velocity
rs = particle density (quartz has a density of 2.6 gm/cm3)
r = fluid density (water is 1.0 gm/cm3)
d = grain diameter
g = gravitational constant (981 cm/sec2)
µ = fluid viscosity (water is 0.01 gm/cm.sec)

Reynold's Number (Re):

where U is flow velocity
L is a reference length, such as depth
r = fluid density (water is 1.0 gm/cm3)
µ = fluid viscosity (water is 0.01 gm/cm.sec)

Froude Number (Fr):

where g is gravitational acceleration (981 cm/sec2)
L is a reference length, such as depth
U is flow velocity
g = gravitational constant (981 cm/sec2)

Stream flow equation:

Q = wdv

where Q is stream flow
w is width of the channel
d is channel depth
v is velocity of flow