READING QUESTIONS: Sedimentary Rocks
NAME________________________
GEOL 131
Fall 2015
DUE: Tuesday, September 22nd
50 pts
All answers should be in your own words.
The Importance of Sedimentary Rocks (p. 68)
1. What sedimentary rock is used as an energy source? ______________
Origins of Sedimentary Rock (p. 69-70)
2. What is the first step in the formation of sedimentary rock? ______________________
3. Give two examples of Earth surface features that transport sediment. (2 pts)
a. __________________________
b. __________________________
4. Which of the following is not a sediment deposit? (Circle one answer.)
a. Mud suspended in a river current
b. A river delta
c. A sand dune
d. A pile of gravel at the front of a glacier
5. For each description below, give the name of the sedimentary rock category that matches it. (3 pts)
a. Carbon-rich remains of organisms: ____________________
b. Solid sediment (e.g. sand, mud): __________________
c. Sediment formed when ions precipitate from a solution: __________________
Detrital Sedimentary Rocks (p. 70-74)
6. What two minerals are the main components of detrital rocks? ____________________________ (2 pts)
7. If a body of the igneous rock granite were weathered into sediment, and the feldspar crystals from the
granite were preserved in the resulting sedimentary rock, what would this indicate about the speed of
erosion and deposition of the sediment, and why? (3 pts)
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
8. Detrital rocks are mainly distinguished on what basis? ___________________________________
9. Describe the relationship between sediment particle size in detrital rocks and the amount of energy
needed to transport the particles. (2 pts) _______________________________________________
_______________________________________________________________________________
10. What is the difference between the detrital rocks conglomerate and breccia? __________________
_______________________________________________________________________________
11. Why does the detrital rock shale often form barriers to the movement of groundwater? __________
________________________________________________________________________________
12. Sand that undergoes long periods of transport are most likely to form which of the following sandstones?
(Circle one.)
a. A graywacke with well-rounded, poorly-sorted grains
b. A quartz sandstone with well-rounded, well-sorted grains
c. An arkose with angular, poorly-sorted grains
d. A quartz sandstone with angular, poorly-sorted grains
13. Match each type of sandstone with the correct description: (3 pts)
a. graywacke
made mostly or entirely of quartz grains
_____
b. quartz sandstone
contains significant feldspar
_____
c. arkose
contains significant rock fragments and clay matrix
_____
14. Which detrital rock, conglomerate or breccia, has sediment that likely underwent less transport, and
how can you tell? (2 pts) _____________________________________________________________
__________________________________________________________________________________
Chemical Sedimentary Rocks (p. 74-78)
15. What is the difference between how inorganic and biochemical rocks form? (2 pts) _______________
__________________________________________________________________________________
__________________________________________________________________________________
16. What chemical sedimentary rock is made mostly of the mineral calcite? ________________________
17. Match each chemical sedimentary rock to the correct description: (2 pts)
a. Travertine
biochemical; formed of shell fragments
_____
b. Oolitic limestone
biochemical; formed of microscopic plankton
_____
c. Coquina
inorganic; precipitated in caves
_____
d. Chalk
inorganic; forms around “seed particles” in shallow oceans _____
18. EXTRA CREDIT: Oolitic limestone and sandstone can look very similar. What is one easy test you
could perform to tell them apart? (1 pt) ______________________
19. The chemical rock chert often forms in the same way as chalk, by compaction of millions of plankton
skeletons on the ocean bottom. But their physical properties are very different. Name one important
difference in their physical properties, and explain the cause of this difference. (2 pts)
__________________________________________________________________________________
__________________________________________________________________________________
Coal: An Organic Sedimentary Rock (p. 78-79)
20. What has to accumulate in large quantities in order for coal to eventually form? __________________
21. What special condition is required for the accumulation referred to in the last question to occur?
__________________________________________________________________________________
22. What characteristic of coal determines its energy ranking? ________________________________
Turning Sediment into Sedimentary Rock: Diagenesis and Lithification (p. 80-81)
23. Define the term diagenesis. (2 pts) ______________________________________________________
__________________________________________________________________________________
__________________________________________________________________________________
24. One diagenetic process is recrystallization. Give an example of one mineral that recrystallizes into
another within sediment that is undergoing burial (name both minerals, and indicate which one changes
into which.) (2 pts) __________________________________________________________________
__________________________________________________________________________________
25. Fill in the blanks in the following sentences using words from the list below. Not all words will be used.
During ________________, new ___________________ crystals form between existing sediment grains.
These crystals precipitate from ions dissolved in __________________, and fill in the ___________ spaces
between grains. (2 pts)
GROUNDWATER, SEDIMENT, ACIDIC, PORE, CEMENTATION, MINERAL
26. EXTRA CREDIT: Name two tests you could use to tell whether a rock is cemented with calcite or silica.
a. __________________________
b. __________________________
Classification of Sedimentary Rocks (p. 81-82)
27. Sediment particle size is the main basis for classifying detrital rocks. What two characteristics are used
to classify chemical rocks? (1 pt)
a. _____________________________________
b. _____________________________________
28. A chemical sedimentary rock consisting of fine-crystalline quartz and having a dark color would be
called _________________.
Sedimentary Rocks Represent Past Environments (p. 82-88)
29. Define sedimentary environment. (2 pts) _________________________________________________
__________________________________________________________________________________
30. A set of sedimentary rocks whose characteristics reflect a particular depositional environment is called a
a. Strata
b. Structure
c. Facies
d. Cross-section
31. For each rock listed below, name one sedimentary environment in which it could have formed. (2 pts)
Well-sorted sandstone:
__________________________________
Fossil-rich limestone:
__________________________________
Shale:
__________________________________
Coquina:
__________________________________
32. Match each sedimentary structure to the correct description (continues on next page). (3 pts)
a. Ripple marks
Any trace of past life preserved in rock
______
b. Graded bed
c. Cross-bedding
Inclined layers of sediment associated with sand dunes
Formed when fine-grained sediment dries out
______
______
d. Strata
Ridges formed at right angles to direction of current flow
______
e. Mud cracks
Layers of sediment or sedimentary rock
______
f. Fossils
Grain size decreases upward within a single layer
______
33. EXTRA CREDIT: The figure below shows a cross-section of a ripple mark. In which direction was the
current flowing that created this structure (left or right)? (1 pt)