HISTORICAL GEOLOGY
Term Project: Geologic History of Rainbow Quadrangle
INTRODUCTION
Look at the attached map of a place called "Rainbow Quadrangle". (A "quadrangle" is a rectangular
map, and the term is often used to refer to topographic maps published by the U.S. Geological Survey. For
instance, the USGS "Mt. Vernon Quadrangle" includes Mt. Vernon, Lisbon, the Palisades, and surrounding
countryside.)
Rainbow Quadrangle is not a real place, but it is an adaptation of the geology of several areas. There
are some ways in which Rainbow Quadrangle resembles the Mt. Vernon Quadrangle. For instance, like the
Cedar River at the Palisades, Prism River in the Rainbow Quadrangle flows through rolling countryside and
is lined with bluffs made of native rock (a geologist would call these bluffs "bedrock"). In most places,
bedrock is covered by unconsolidated sediment (what you might just call "dirt").
Here are some questions we might ask about Rainbow Quadrangle:
What kinds of materials (rocks and sediments) does it contain?
Where are these materials found: along the rivers, deep underground, etc.?
What sequence of events produced these rocks and sediments?
How long ago did each event occur?
What environmental conditions existed at various times in the past?
What geologic processes caused changes in environmental conditions?
In your labs you will learn techniques used by geologists to gather data that can be used to describe
the geologic history of an area. By the end of the block you will have learned:
How to interpret geologic maps and cross sections,
How to identify fossils and use them in studying past events,
How to use specific features of sediments and rocks as clues to how and when these materials formed.
LOGISTICS
In the term project you will apply techniques learned at the beginning of each lab to the questions we
have asked about Rainbow Quadrangle. You will grade yourself on the preliminary exercises (which in most
labs take less than half the lab period), then spend the rest of the lab time working on reconstruction of the
geologic history of "Rainbow Quadrangle".
The class will be divided into several teams. Most of your lab grade will be based on work you turn
in individually, but there will also be a few assignments in which you will be graded as a team. We will
spend part of most lab periods sharing data since not every team will be working on exactly the same aspects
of the Rainbow study. Each team will be responsible for gathering and analyzing data on different Rainbow
area rock units and sediment units. At the end of the block, each team will report their findings to the rest of
the group and we will put together a comprehensive history of the Rainbow Quadrangle.
Although you will concentrate on the rock and sediment units assigned to your team, in some labs
you will also look at some of the other units since not all the units will show certain characteristics equally
well.
HISTORICAL GEOLOGY
SEDIMENTS AND ROCKS OF RAINBOW QUADRANGLE
Today you will look at some sediments collected in a stream near Mt. Vernon, and at sediments and
sedimentary rocks from Rainbow Quadrangle.
Refer to your Lab Manual p. 41 (Textural Terms) and p. 55 (Simplified Rock Classification)
PART ONE: MOUNT VERNON SEDIMENTS
These samples are in the box labeled "Sediment Reference Samples." Observe the small bottles or boxes of
sediment labeled with terms such as "coarse sand" and with phi numbers (e.g., Φ +2). Use your observations
and information in your manual to attach one of these terms to each of the definitions given below: clay,
gravel, mud, sand, silt.
_____________ Too small to be seen with naked eye, but visible with microscope, <0.0039
mm. in diameter
_____________ Barely visible with naked eye, 0.0039 to 0.06 mm.
_____________ Everything larger than silt and smaller than gravel
_____________ >2.0 mm. in diameter (~1/8 inch)
_____________ General term for undifferentiated silt and clay
_____________ Coarsest grained sediment
_____________ Fine-grained and feels smooth and powdery
_____________ Fine-grained and feels slightly gritty
Be sure you understand these terms before continuing. Check key.
PART TWO: OVERVIEW OF RAINBOW QUADRANGLE SEDIMENTS
All the Rainbow sediments have abbreviations that begin with the letter Q. We will be analyzing some of
these samples in more detail later in the course. For today, you will observe what size particles they contain.
A. Use the samples of Qd, Qao and Qap (box labeled “Observation Samples”) and your Mt. Vernon
reference samples.
1. Which sample best fits each description below:
a. Mixture of very fine sand and silt _____
b. Mixture of medium to coarse sand and gravel _____
c. The most homogeneous sample is _____, which consists of mainly ______________
sized particles.
B. Observe the single samples of Ql, Qow, Qt and Qv available up front. QT AND QV ARE FRAGILE;
PLEASE DO NOT MOVE THEM.
1. What size (gravel, etc.) are most of the particles in sample Ql? ______________________
2. What is the size of the largest particles you see in Qt (observe the big sample and material in
jar)?_______________
...and the size of the smallest? (Hint: does the loose material feel powdery plus gritty or only gritty)
____________________
3. Look carefully at the Qv sample and feel of the Qv sediment in the plastic jar. How does Qv differ from
Qt?
4. Observe Qow.
a. Which of the Part A samples does it most resemble (Qd, Qao or Qap)?______
b. What might such a resemblance indicate about its origins?
5. Which of these four sediments (Ql, Qow, Qt or Qv) is most homogeneous? ______
At this point do you have any theories to account for differences between the Q sediments?
CHECK KEY BEFORE CONTINUING.
Name__________________________
Hand in
SEDIMENTS AND ROCKS OF RAINBOW QUADRANGLE
PART THREE: ROCK NAMES
Geologists give rock units two names: (1) a rock type name such as shale or limestone, and (2) a
geographic name that refers to the specific locality in which the best example of a particular rock unit is
found. Map scale rock units named in this way are called "formations". For example, two distinctive
formations in eastern Iowa are the Maquoketa Shale (named for exposures found along the Maquoketa River)
and the St. Peter Sandstone (found throughout the Midwest, but named for a locality in St. Peter, Minnesota).
1. In Mt. Vernon, some of our water comes from a well drilled into a unit called the Jordan Sandstone. Do
you suppose this rock is named after the country of Jordan (located near Israel)? Why or why not?
Today you will see samples of all the rock units in Rainbow Quadrangle and name each formation.
Examples of rock units are on back counter and are given general labels (for example, "Fine-grained detrital
sedimentary rocks"). You may bring the samples back to your work area. Working in teams, answer the
questions for that table's samples. Use the simplified rock classification chart (p. 55) in your lab manual to
determine rock types. You may work on the specimens in any order. If you need to wait until another table
becomes free, begin work with your team on your sedimentary structure experiment. Use hydrochloric acid
only on the small samples in the egg carton on back counter.
IGNEOUS ROCKS
1. Compare Deer Mountain and Coyote Pass: Which is finer grained (individual crystals usually not visible)?
_______________________
2. Add rock types to these formation names:
Coyote Pass ________________ Deer Mountain _______________
FINE-GRAINED DETRITAL SEDIMENTARY ROCKS
1. In which one are sedimentary particles most obvious (largest)? ________________________
What size would you estimate the particles are (gravel, etc.)? ___________________
2. Compare the remaining two Rainbow rocks. What differences are there between them?
3. Using the information on energy levels found in your lab manual p. 41 "Textural Terms and
Interpretations", in what energy level environment were all these rocks deposited? _________
4. Which of the three rocks might have been deposited under somewhat variable energy conditions?
___________________ because
5. Add rock types to these formation names:
Avocado Valley __________________
Green Pond _____________________
Orange Brook ____________________
Name__________________________
Hand in
MEDIUM TO COARSE-GRAINED DETRITAL SEDIMENTARY ROCKS
1. Which rock contains mostly sand with some gravel? (Use the percent estimation chart and Mt. Vernon
Reference Samples.) ___________________
2. Which rock contains just sand? ________________________
3. Add the rock type to each formation name:
Purple Cliff _______________________ Red Ridge _________________________
4. Compare Red Ridge and Purple Cliff with the Rainbow Sediments Qap, Qao and Qd. Based on similarities
in textures, which ones might have formed in similar environments even though there may be millions of
years difference in their ages?
Red Ridge and ______.
Purple Cliff and ______.
CHEMICAL SEDIMENTARY ROCKS (CARBONATES)
1. What evidence do you see that White Peak was formed in an environment with different energy level than
Grey Ledge and Blue Mountain? (See lab manual p. 55 for information on energy levels.)
2. Use hydrochloric acid on the test samples to determine the major mineral present. If rock fizzes vigorously
immediately the mineral is calcite; if it fizzes vigorously only when scratched with a nail or perhaps weakly
without scratching, the mineral is dolomite. Refer to Section C of rock classification chart on p. 57 in manual
to name these rocks.
List the major mineral in each rock unit and tell whether the basic rock type is limestone or dolomite.
Blue Mountain contains __________________and is _____________________ rock type.
Grey Ledge contains ____________________ and is _____________________ rock type.
White Peak contains ____________________ and is _____________________ rock type.
3. Which rocks consist of micrite:
____________________________ and _________________________________.
4. Which rock has shiny sparite cement? _______________________________.
What other term from the classification chart also applies to the sparry rock (exclude fossils)?
_______________
About how large are these particles in mm.? ______
5. Consult readings in your textbook on carbonates (beginning on p. 272). Because of their chemistry and
their relation to living organisms, carbonates indicate specific environment conditions of water temperature
and depth. What are these conditions?
HISTORICAL GEOLOGY
TEXTURAL ANALYSIS OF RAINBOW QUADRANGLE UNITS
Today we will get a closer look at the sizes of material found in some of the Rainbow
Quadrangle sediments and rocks. We will look at specific textural qualities, such as sorting and
angularity, and begin to think about what they tell us about sediment “maturity” and conditions
under which sediments are deposited.
Refer to your lab manual, p. 41, Textural Terms and Interpretations and p. 45 Textural Analysis
by Sieving.
A “THOUGHT EXPERIMENT”
Look at the sediment in the box or jar in your Mt. Vernon Reference Sediments box
which is labeled “Thought Experiment Sediment”. Imagine what would take place in each of the
following situations. What sizes of sediments would be deposited where? Would the sediments
be sorted by size or would they still be all mixed up? Would some be removed and others left
behind?
a. Imagine adding water and freezing the sediment in an ice cube. Assume that the sediment
remains randomly sorted. Move the cube a few inches along the table surface and leave it to
melt.
b. Imagine piling the sediment on the table and blowing gently on it.
c. Imagine putting the sediment on an inclined surface and running a gentle stream of water on it.
Place a small bowl at the bottom of the incline to catch the water.
Repeat the experiment, replacing the bowl with a half-full bucket of water and running the
water very hard.
d. Imagine a mile long cement-lined chute filled with running water. Place a series of 1 inch
cubes of both soft limestone and hard quartzite at the top of the chute. Examine the cubes at ¼mile intervals. How will they change in shape and size? What could you do to get te harder cube
to have the same degree of roundness as the soft one?
What you have been thinking about are (1) differences between materials deposited by ice
(glaciers), wind, and water (both moving on the incline, and quiet in the bucket) and (2) how the
distance a particle travels may affect its shape and size. Use these insights as you look more
closely at Rainbow sediments and rocks.
Optional: See if your thought experiments help you chose the best words in the following
statements:
1. Material directly deposited by glacial ice will be (well, poorly) sorted and will contain the
(narrowest, widest) range of grain sizes.
2. Material deposited by running water will tend to sorted by (size, color) depending on the
velocity of the water. Faster flowing water can carry (smaller, larger) particles than slower
moving water. Material of a given size is deposited when the water (drops below, exceeds) some
critical velocity.
3. Material deposited quickly in standing water will tend to form layers which get (finer, coarser)
as you move upwards through the deposit.
4. Material initially carried by a glacier can be “reworked” by meltwater and winds to produce
(choose as many as apply: aeolian deposits, lake deposits, stream deposits).
5. Overall, wind has (less, more) power to move objects than water. Therefore, although aeolian
deposits are (well, poorly) sorted, they are made up of (very coarse, medium to fine) grained
particles.
6. The further a particle travels the (smaller, larger) it becomes and the (more, less) angular it
becomes.
Check optional questions against key.
Name ______________________
Hand in, Group
RAINBOW QUADRANGLE SIEVE ANALYSIS
INDIVIDUAL INTERPRETATIONS
Part One: Sieve Results
You will want to consult your lab manual for help in doing calculations, making graphs and
interpreting your results. Compare your graphs with those in the manual. Also, try to apply the results of
your thought experiments and material in the Textural Terms and Interpretations section of the manual.
1. On the attached page, make a histogram of your data, choosing a range of phi sizes appropriate to your
sample.
2. Plot cumulative percents on the second graph.
3. Use the cumulative curve to calculate coefficient of sorting using the formula:
Phi deviation = (Phi 84% value - Phi 16 % value) / 2
Phi 84 % value (read from your graph) = ________.
Phi 16% value = _________.
Phi deviation = ____________.
4. Sorting can be expressed in words by comparing your coefficient with the “standards” given in your
manual (p. 46, B. 3. d). Is sorting in your sample poor, moderate, good? __________________ If
moderate, is it closer to being poor or to being good? closer to _________________
5. Discuss (don’t just list) some of the possible sources of error in your sieving (assume you have
correctly graphed your data and done correct calculations)? (At least some sources should differ from
your team members.)
Would weighing the fractions be more or less accurate? State your reasons.
6. Sorting is only one textural attribute. Using the microscope, if necessary, and information in your
manual, where would the majority of particles in your sample fall on a continuum between extremely
well-rounded and extremely angular? ____________________________
7. a. What does your sorting and angularity suggest about the transport history of this material?
b. Would knowing the composition of particles in a sample be useful in answering this question?
Explain.
8. Using guidelines on maturity in your manual (p. 44), compare Red Ridge and Purple Cliff. Which is
more mature? ___________________
Name ______________________
Hand in, individual
Part Two: Q sediment interpretations
Return to your box of observation samples (Qap, Qao and Qd), to the samples on the back
counter (Ql, Qv, Qt, and Qow), and to additional sieve information. If you sieved one of these samples
you already have some of this information.
1. Examine Qap, Qd and Qow and place each on the maturity continuum shown below:
very mature -- mature -- submature -- immature -- very immature
____________________________________________________
2. Summarize what you know on the table below. Use results of your thought experiments to think about
modes of deposition.
Sample
Angularity
by eye or
microscope
Sorting by
eye or
sieving or
graph
Maturity
(Graph
available)
NA
(Graph
available)
NA
Possible modes of deposition (more
than one may apply: Wind, Direct Ice,
Moving Water, Quiet Water) *
Qap
Qao
Qd
Ql
Too small to
see
Qv
Too small to
see
Qt
Large
particles
only:
Qow
NA
(Graph
available)
NA
(Graph
available)
* We will see in later labs if our predictions are supported by further observations. These are just
preliminary results.
3. If, based on lecture and text and after class discussion in lab, you have any thoughts on specific
sedimentary environments (facies) in which any of these sediments might have formed note them below.
If you don’t that’s OK. List your ideas here:
Hand In, Group
1. Histogram
SAMPLE:__________________
90
80
70
P
E
R
C
E
N
T
60
50
40
30
20
10
0
–
1. Cumulative curve
0
GRAIN SIZE (Φ)
+
SAMPLE:__________________
100
90
C
U
M 80
P
E
R
C
E
N
T
70
60
50
40
30
20
10
0
–
0
GRAIN SIZE (Φ)
+
HISTORICAL GEOLOGY
ORDERING GEOLOGIC EVENTS: RELATIVE AND ABSOLUTE AGES
In this lab you will observe and construct geologic cross sections. For each cross section you will work
out the sequence of geologic events from oldest to youngest. You can then assign relative ages to the rocks shown
on the cross sections. You will learn to read radiometric decay graphs to obtain absolute ages for some rocks.
When you have completed the practice exercises, you will apply all these principles to interpretation of Rainbow
Quadrangle rocks.
Background information for this lab is found in your Lab Reference Manual: Absolute Age Dating (p. 4),
Interpreting Geologic Cross Sections (p. 33), and Constructing Geologic Cross Sections (p. 36).
PART I PROCEDURES:
1. For each cross section determine the sequence of events, numbering events with #1 being the oldest.
2. As you work out the sequence, mark each cross section as follows (using these conventions will help you check
your own work on the posted key):
a. Igneous rocks: Mark each unit A, B, C, etc., oldest to youngest.
b. Sedimentary rocks: Mark each unit 1, 2, 3, etc., oldest to youngest.
c. Metamorphic rocks: You will only see contact metamorphic rocks which will be of the same age as the igneous
intrusion causing the metamorphism, and thus they do not need marking separately.
d. Unconformities: Mark each unconformity surface U1, U2, U3, etc., oldest to youngest.
e. Faults:
1. Mark each fault with arrows showing relative motion.
2. Label faults F1, F2, F3, etc., from oldest to youngest.
SAMPLE:
Given:
Marked:
Described:
7. Unit 6 deposited (youngest event)
6. Unit 5 (sandstone) deposited
5. Erosion of unit 4 and part of 3 to produce
disconformity U1
4. Unit 4 deposited (note: include “missing”
units)
3. Unit 3 deposited
2. Unit 2 (limestone) deposited
1. Unit 1 deposited (oldest event)
PRACTICE EXERCISES:
Mark Cross Section:
Describe History:
Check your work with posted key. When you are confident you understand the concepts covered so far,
continue with the next part of the lab which will be handed in for grading.
PART II INSTRUCTIONS:
CONSTRUCTION AND INTERPRETATION OF RAINBOW QUADRANGLE CROSS SECTION
1. The next step in studying the geologic history of Rainbow Quadrangle will be interpreting a cross section. When
you look at the cross section which is inserted in this lab you will see that only half of it is drawn.
2. Complete the cross section:
a. Follow the procedure outlined in your Lab Reference Manual (p. 36) to construct the rest of the cross section.
b. Data from Holes 1-3 have been plotted on the west side of the profile. Use the well data given below to plot
data for Holes 4, 5 and 6.
c. Correlate between holes to complete your cross section.
3. Work out relative ages of events:
a. Separate sedimentary and igneous rock types as you did earlier in the lab, numbering sedimentary units and
using letters for igneous rocks. For now, ignore the unconsolidated sediments. Number only the units seen on
the section. Do not leave out numbers to represent missing units at unconformities.
b. Number the unconformities as you did in the lab. Treat the contact between bedrock and unconsolidated
materials as an unconformity.
c. If it helps you, write out the sequence of events, but this is not required.
WELL DATA FOR W-E CROSS SECTION, RAINBOW QUADRANGLE
HOLE 1:
0-21’
21-100’
100-180’
180-220’
220-260’
260-285’
285-320’
320-370’
370-390’
390-560’
Qt
Limestone
Dirty Shale
Clean Sandstone
Shale
Dirty Sandstone
Dark igneous
Dirty Sandstone
Limy Shale
Light igneous
PLOT HOLE 4
0-30’
Undifferentiated Qao,
Qap, Qd, and Qv
30-100’ Dirty Shale
100-160’ Clean Sandstone
(lower 5’ contains sparse
pebbles)
160-260’ Limy Shale
260-440’ Dolostone
440-480’ Light igneous
HOLE 2:
0-22’
22-100’
100-180
180-216’
216-236’
236-250’
250-300’
300-394’
394-464’
464-500’
500-560’
Qt
Limestone
Dirty Shale
Clean Sandstone
Dirty Sandstone
Dark igneous
Dirty Sandstone
Limy Shale
Light igneous
Dark igneous
Light igneous
PLOT HOLE 5:
0-22’
Ql
22-60’
Qt
60-120’ Limestone
120-200’ Dirty Shale
200-220’ Clean Sandstone
220-320’ Dirty Sandstone
320-470’ Limy Shale
470-580’ Dolostone
HOLE 3:
0-38’
38-120’
120-200’
200-216’
216-240’
240-410’
410-438’
438-580’
Qt
Limestone
Dirty Shale
Clean Sandstone
Dirty Sandstone
Limy Shale
Dolostone
Light igneous
PLOT HOLE 6:
0-20’
Qt
20-60’
Limestone
60-140’
Dirty Shale
140-175’
Clean Sandstone
175-220’
Shale
220-325’
Dirty Sandstone
325-480’
Limy Shale
480-520’
Dolostone
Hand In
Name ____________________
ORDERING GEOLOGIC EVENTS: RELATIVE AND ABSOLUTE AGES
A. INTERPRETATION OF RAINBOW QUADRANGLE CROSS SECTION
Answer the following questions about your cross section. Refer to your Lab Reference Manual (beginning
on p. 33) for some helpful hints and definitions.
1. Bedrock outcrops appear at the land surface only in the vicinity of Hole # ____. Elsewhere the land is
covered with undifferentiated ________________________.
2. Why is there no light-colored igneous rock in Hole 5?
3. Why does a shale occur between the clean and dirty sandstones in Hole 6, but not in Hole 5?
4. Why is there no dirty sandstone in Hole 4?
5. Which sedimentary rock units might have been contact metamorphosed by the light igneous rock?
# _______ and # ________.
6. The dark-colored igneous rock has caused contact metamorphism of the sandstone below it, but has not
affected the dirty sandstone above it. Does this suggest that it forms an intrusive sill or an extrusive lava
flow? Explain.
7. Is the dark igneous rock younger, older, or in part the same age as the dirty sandstone? Give evidence.
8. Why is there no dark igneous rock found in Holes 5 or 6?
9. In the sediments and Rocks of Rainbow Quadrangle lab you identified the two igneous rocks shown on
today’s cross section.
The light-colored igneous rock is the _________________________________ (give full formation name),
and the dark one is __________________________________.
10. Which of the igneous rock formations forms a pluton? ______________________
Which forms a dike? _________________________
11. Would you be likely to find xenoliths of dolostone in the Coyote Pass formation? Explain
Hand In
Name ____________________
12. Which is older: A or U1? ___________; B or U2? ___________
What law enabled you to determine the relative ages of these igneous units and unconformities?
________________________________
13. How did you determine the relative ages of the sedimentary rock units?
Law of _____________________________
14. How many episodes of folding can you recognize? _____ (Note: the question does NOT ask how
many different units have been folded.)
In this case you used the Law of original __________________________.
15. A “contact” is a line on a cross section or map which separates two formations. Contacts can be
unconformities, regular sedimentary contacts, or contacts between igneous rocks and other rocks.
Thicknesses of sedimentary units are measured perpendicular to their contacts. Using the cross section:
a. What is the thickness of the dirty shale? _______feet
b. Why is it harder to estimate the thicknesses of the limestone and of the clean sandstone?
AGES OF IGNEOUS ROCKS:
Use the U-235 decay curve graph on p. 5 of your lab manual to determine the ages of these units. Read the
graph as accurately as you can. Assume an experimental error of +/- 2 m.y. (million years). Use the
geological time scale on p.3 to obtain period names
1. Circle the word “Upper”, “Middle”, or “Lower”, then write in the correct period:
Deer Mountain Basalt: 69.0% of original U-235 remains in sample.
Age = _______________ m.y. or (Upper, Middle, Lower) _______________ Period.
Coyote Pass Granite: 65.5% of original U-235 remains in sample.
Age = _______________ m.y. or (Upper, Middle, Lower) _______________ Period.
2. Which is the best reason for calling the ages of the igneous rocks “absolute” rather than “relative”?
a. The +/- 2 m.y. range of experimental error is lower than for relative ages.
b. Information obtained in the lab is usually better than field observations.
c. Igneous rocks solidify more quickly than sedimentary ones, so their ages are more reliable.
d. The dates involve actual numbers instead of phrases like “older than”.
Hand In
Name ____________________
Hand In
Name ____________________
HISTORICAL GEOLOGY
INTRODUCTION TO PALEONTOLOGY
I. Introduction
Today you will be looking at examples of some of the more important fossil phyla and classes,
and learning to use a key to identify them. You will see different types of preservation in these fossils.
You will also identify some “trace” fossils. At the end of the lab you will use fossil information to
determine the ages of some of the Rainbow Quadrangle rocks.
Background information in Lab Reference Manual: Representative Fossil Groups (. 22);
Assemblage Interpretation (p. 6); Fossil Morphology and Taxonomy (p. 9); Fossil Identification Key (p.
10); Fossil Preservation (p. 21); Interpreting Trace Fossils (p. 29).
II. Fossil Preservation
A. A Trip to the Museum
Complete table included with this lab to complete a mini-field trip to the museum. This table should be
handed in along with the rest of the lab.
B. Preservation of Fossils
Use only these fossils in your lab set: #3, 4, 13, 14, 15, 18.
Select any one of these samples as an example of each type of preservation (you may wish to return to the
museum to compare your samples with the exhibit examples):
1. Unaltered (or recrystallized) hard parts: # _______
2. Mold: # ________ is (specify internal or external) _______________ mold.
3. Carbonization: # ________
4. Replacement: # ________
(If you have previously studied minerals you may be able to identify the mineral replacing the
fossil material.)
Why might noting the type of preservation be useful?
III. Identification
1. Review the terms defined in the fossil key in your lab manual. There are examples illustrating some of
these terms up front. Look at your own samples as you do this: which might be colonial, which have radial
symmetry, etc.
2. For each numbered specimen, use the key beginning on p. 10 of your lab manual to make a tentative
identification. Then look at the illustrations in the key and in your text to verify your identification. Write
the name of each fossil you identify in the column on the next page marked “Specimen Name”.
Classification
Classification of organisms is based on a hierarchical scheme first developed by Linnaeus. On the list
below, use table on p. 9 in lab manual to fill in any blanks in the Phylum and Class columns. You may also
use Appendix I in your text.
FOSSIL IDENTIFICATION AND CLASSIFICATION TABLE
No.
Specimen Name
Phylum
Class
0.
You
Chordata
_______________________
1.
_______________________
Cnidaria (Coelenterata)
_______________________
2.
_______________________
(#2: Look for pentameral
symmetry.)
Echinodermata
_______________________
3.
_______________________
Mollusca
_______________________
4.
_______________________
5.
_______________________
Echinodermata
Not listed in your text.
6.
_______________________
______________________
_______________________
7.
_______________________
8.
_______________________
Cnidaria (Coelenterata)
_______________________
9.
_______________________
Arthropoda
Subphylum:
_______________________
10.
_______________________
Mollusca
Class: __________________
Subclass:
_______________________
11.
_______________________
12.
_______________________
Mollusca`
________________________
13.
_______________________
Echinodermata
________________________
14.
_______________________
(#15: 2nd unequal valve
probably not obvious.)
Mollusca
________________________
15.
_______________________
16.
_______________________
17.
_______________________
18.
19.
_______________________
Hemichordata
_______________________
Mollusca
CHECK KEY.
You might want to group together all the members of each phylum and see what, if any, obvious features
they share in common. NOW, GO ON TO NEXT SECTION.
IV. Trace Fossils
Review the lab manual (p. 29) for information on trace fossils. There is also a set of clay models showing
types of trace fossils on the back counter. Observe the models and then identify the accompanying
Rainbow trace fossils. We will explore the significance of these trace fossils in a later lab. Check key
when you are done.
Formation
Trace Fossil Identification
1. Green Pond
_______________________________
2. Orange Brook
_______________________________
3. Red Ridge
_______________________________
4. Blue Mountain
_______________________________
5. White Peak
_______________________________
V. Using Fossils to Date Rocks
1. Data sheet for this lab is found on the next page.
2. Put aside all the fossils used in previous parts of the lab. You will be using different specimens in
this section.
3. Review pages 78-80 in your text which tell you how to determine the age of a given assemblage of
fossils when you know the range of ages in which each individual genus of organisms lived. Your lab
manual also has more information about the idea of “assemblages”.
4. Each team will determine ages for two rock formations. Team assignments will be written on the board.
Based on what samples are available, do the formations in either order. Each formation has a box on the
back counter labeled “Fossil Age Assemblage”. Other teams will be using these materials, so be sure to
return them promptly when you are done.
5. Use the monographs illustrating the fossils found in each unit to identify these new fossil specimens to
the genus level. If your assemblage contains brachiopods or trilobites, also consult the labeled reference
samples on the back counter.
6. Still using the monographs, determine the time span during which each genus lived. You should have
four fossil ranges for each formation.
7. Record the fossil name and the age range of each genus on the data table on the hand-in page.
8. Answer further interpretative questions.
Hand In:
Name __________________
HISTORICAL GEOLOGY
A TRIP TO THE MUSEUM: FOSSIL PRESERVATION
There is a fossil preservation exhibit on Level 2. Use criteria in your Lab Reference Manual, p.
21, to find examples that fit each of the following observations:
Type of Preservation
Organisms Seen
Condition of Original
Material
Only carbon remains
Amount of Detail Preserved:
Excellent, Good, Fair, Poor
Excellent-Good
No noticeable changes
Excellent
Fossil looks like it is
made of metal
Fair-Poor
Only sediment remains
Outside: Good
Inside: No detail
Only sediment remains
Outside: No detail
Inside: Good
Hand In:
Name __________________
DATA SHEET: USING FOSSILS TO DATE ROCKS
EXAMPLE: A genus living from Middle Pennsylvanian through Lower Triassic periods.
GENUS
NAMES
|Ordovician | Silurian | Devonian | Miss.
| Penn.
| Permian | Triassic
L M U L M U L M U L M U L M U L M U L M U
Be sure you have 4 organisms for each formation.
FORMATION NAME: __________________________ AGE OF ASSEMBLAGE FROM CHART
BELOW: ___________________________
GENUS
NAMES
| Ord.
L M
U
| Silurian
| Devonian | Miss.
L M U L M U L M
U
| Penn.
L M
U
| Permian | Triassic
L M U L M U
FORMATION NAME: __________________________ AGE OF ASSEMBLAGE FROM CHART
BELOW: ___________________________
GENUS
NAMES
| Ord.
L M
U
| Silurian
| Devonian | Miss.
L M U L M U L M
U
| Penn.
L M
U
| Permian | Triassic
L M U L M U
Hand In:
Name __________________
VI. Interpretations
1. Fossils found in Q sediments have been dated using Carbon 14. Based on what you know about C-14
dating, which type of preservation would give the best results? Circle one:
Replacement, Internal Mold,
Unaltered Material,
Recrystallized Material
2. Gastropod fossils have been found in Qao. Based on fossil identity and type of preservation, which of
the fossils in the box on the back counter marked “Q Sediment Fossils” is the best specimen to use in
dating Qao:
A, B, C, or D? _________
3. Think about what different taxonomic levels (species, phylum, etc.) mean. In Part III of this lab we
identified most organisms to either phylum or class level. What are some other organisms that belong to
the same class as you?
Would you expect greater diversity in organisms within the same phylum or within the same class?
Explain.
4. Why did we need to identify fossils at the genus level for the age dating part of the lab?
How might identifying these fossils at the species level improve the precision of our age dates?
What might be a disadvantage of using species-level identification?
5. Is any fossil in either of your age assemblages a potential index fossil? First, define what you mean by
an index fossil, then explain your choice, if any.
6. Could the Pelecypod “Nuculana” be found in either of your formations? Explain.
HISTORICAL GEOLOGY
GEOLOGIC COLUMNS
I. Introduction
Another way of depicting geologic history is by drawing a geologic column. This topic is covered
beginning on p. 37 of your Lab Reference Manual. You will also need to consult the radiometric age graphs on
pages 4-5.
Use the Cross Section below to construct a column:
1. Label units and events on the cross section.
2. Briefly describe the sequence of events.
3. If 68% of the original Uranium 235 remains in the older igneous rock, how old is it?
______________ +/- 5 m.y. The younger igneous rock is 70 m.y. old or middle ____________.
4. Draw a geologic column, using the absolute age of the igneous rocks and assigning reasonable relative ages for
the other rocks. Use terms such as “Lower Permian” for ages. (See the example on p. 37)
CROSS SECTION
GEOLOGIC COLUMN
AGE SED. UNITS
Description of Events:
CHECK KEY.
IG. UNITS
II. Ages of Unconsolidated Sediments
In the lab on geologic cross sections we did not attempt to work out the ages of various sediments. Today,
we will determine ages of several sediments through Carbon 14 dating of organic material. We will also see why
we need to use care in applying the Law of Superposition.
1. Use the C-14 decay curve on p. 4 in your lab manual to determine the ages of the sediment units in the table
below. Assume a margin of error of +/- 330 years. Just for practice in reading the graph, ages for the last two
sediments have been given; you predict the percentage of C-14 they should contain.
Unit
Type of Fossil
Qv
Qap
Qao
Plant material near middle of unit
Bivalve (clam) near base of unit.
Gastropod (land snail) near base of
unit.
Mammal bones near top of unit.
Qd
Ql
Qt
Plant fragments near bottom of unit.
Gastropod (land snail) near top of
unit.
Wood fragments near base, assumed
to be somewhat older than Qt.
% C-14 Remaining in
Sample
20
29
27
20.5
Age in Years before
present (+/- 330 years)
Age range between:
19.5
12,900
14,500
2. Given the margin of error in the age dates, which unit is possibly of the same age as Qao? ________
3. Fill in the age dates from the table above on the Schematic Cross Section of the Prism River area shown below.
.
Hand In:
Name __________________
GEOLOGIC COLUMNS FOR RAINBOW QUADRANGLE
I. Interpretation of Q Sediments Cross Section
1. What is the possible age range for Qow deposits found in the Prism River valley? Use all available
evidence and narrow your range as much as you can.
2. Because it has the same symbol, you can assume that the Qt found at the east end of the cross section is
of a (similar, different) __________________ age from Qt in the valley. On the hilltop, the top of Qt
consists of “paleosol” (literally, “old soil”), which indicates that this unit was exposed at the earth’s surface
long enough for soil to form.
3. Based on the cross section, absolute ages, and the above information about Qt, does the age given for Ql
seem reasonable? Explain.
4. Review the meaning of the term facies in your text, p. 76-77. Which Q facies (excluding Qow and Qt)
form reasonable lateral facies tracts?
Qao and ___________.
Qv, ___________, and possibly ____________.
II. Construction of a Geologic Column for Q Sediments
1. Review the section on geologic columns in your lab manual (p. 37) and also note that on columns, facies,
which represent time-equivalent units, are often shown like this:
SANDSTONE
SHALE
2. In the space below draw a column for all the unconsolidated sediments (including Qow). Symbols for
different materials are shown on p. 34 of your lab manual. Choose symbols based on your actual
observations of the sediments in the lab Sediments and Rocks of Rainbow Quadrangle (or look again at the
actual samples). Place units in the valley and on the hill on the correct level relative to one another.
UNITS IN VALLEY
UNITS ON HILL
Youngest
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
Oldest
Qt
Qt
_______________________________________________________________________________
Hand In:
Name __________________
III. Geologic Column for the Rocks of Rainbow Quadrangle
1. If you haven’t already done so, neatly and in pencil add rock type symbols to your Rainbow Quadrangle
cross section.
2. Before constructing your column in the space on the next page, you need to synthesize the information
from two previous labs:
The Ordering Events lab gave you the rock types and their relative ages. For instance, the dirty
sandstone was #3 in the sequence of sedimentary rocks.
The Sediments and Rocks of Rainbow Quadrangle lab gave you rock types and their geographic
names. For instance, in this lab you learned that the dirty sandstone unit was called Purple Cliff.
On a piece of scrap paper you might want to make a list of the seven sedimentary units and two igneous
units found on the cross section and their formation names. Remember a formation name contains both
geographic and rock type information. Thus, formation #3 is called the Purple Cliff Dirty Sandstone.
3. You will actually have eight sedimentary units on your column, because in the Sediments and Rocks lab
we identified one rock that does not occur in the part of the quadrangle crossed by the cross section. The
eighth unit, Gray Ledge Micritic Limestone, is the (oldest, youngest) ________________ unit shown on
the column.
4. From earlier labs, we know the period in which many Rainbow rock units formed.
For the sedimentary rocks these periods were determined in the Introduction to Paleontology lab and are
based on the Principle of ___________________________________. (Principles are found on p. 33 in the
lab manual).
Are these ages absolute or relative? _________________
Ages of igneous rocks are found at the end of the Ordering Events lab and are based on radiometric
dating; they are thus (absolute, relative) __________________.
5. Make a note of the known ages of Rainbow rocks. In the Ordering Events lab you found that one of the
igneous rock units overlaps in age with one of the sedimentary units. Which formations are involved?
___________________________ and ________________________. How will you show this overlap on
your column?
6. We have no fossil age for the Avocado Valley Shale. How will you go about predicting its likely age?
7. On the column on the next page, draw symbols for the eight sedimentary and two igneous units and label
them with their formation names, placing them carefully so that relative ages between sedimentary and
igneous rocks are clear. Add ages, such as “Upper Triassic”, to both the sedimentary and igneous rocks.
8. Show unconformities U1 and U2 on the column with wavy lines. Label them. You do not have to show
timing of folding.
9. Which formations have an unconformity at their bases? ______________________________ and
__________________________.
10. The top of which of these formations has been eroded to form an unconformity? (Circle one):
Blue Mountain, Orange Brook, Red Ridge,
Green Pond
Hand In:
Name __________________
RAINBOW QUADRANGLE GEOLOGIC COLUMN FOR ROCK UNITS
AGE
SEDIMENTARY ROCKS
(youngest)
Middle
Miss.
Gray Ledge Micritic Limestone
________________ Oolitic
Limestone
(oldest)
AGE
IGNEOUS ROCKS
HISTORICAL GEOLOGY
GEOLOGIC MAPS
I. INTRODUCTION
In this lab you will review what folds and faults look like in cross sections and learn to recognize
and interpret folds, faults and unconformities on geologic maps. A geologic map shows the rock units
which are found at the earth’s surface. Geologists draw maps based on field work in which they locate and
identify rocks exposed at various localities. They may also use aerial photographs in areas of sparse
vegetation. When rocks are poorly exposed, data from wells is also helpful in predicting where rocks may
occur.
A. Introduction to fold geometry
1. To help you visualize structures in three dimensions, we will look at a series of “block diagrams” (which
consist of two cross sections and a map view) and clay models.
Domes and basins will appear as concentric circles on a map. Which is which in the block
diagrams shown below?
This is a: _ ___________
This is a: _____ ____________
2. Place representative strike and dip symbols on map views only. (Strike and dip are not used on cross
sections). Strike lines are parallel to the contacts between units. The shorter dip mark points in the
direction the layers are tilted. What is the symbol for horizontal beds?
3. Linear folds (anticlines and synclines) will appear as repeating bands of rock units. Which is which in
the block diagrams below?
This is a (an):
This is a (an): __ ___
4. Place representative strike and dip symbols on the linear fold diagrams.
5. Unless overturned, rocks dip towards the (older, younger) ____________________ units.
B. Unconformities review -- Class discussion
You are now experienced in recognizing unconformities in cross sections. We will look at one
type of unconformity on a block diagram. This will show you what some unconformities look like on
maps.
1. On the block diagram, fill in the missing numbers. Refer to the geologic column for help.
2. What type of unconformity is shown on the front of the cross section?
____________________________
3. Which of the map views below best matches the geologic features that might be seen on the top of the
block diagram? Letter _______ (If you are not sure which is correct, try to number the units on the map so
they correspond with those on the cross section.)
II. INTERPRETATION OF GEOLOGIC MAPS
In this section of the lab we will look at geologic maps of real places. These maps are found in
Hamblin and Howard, Physical Geology Lab Manual (various editions). Please do not remove lab
manuals from the lab.
On the maps each group of rocks of a particular age has a distinctive color and pattern as well as
an abbreviated symbol, such as “Su”, meaning Upper Silurian age rocks. A few very distinctive rock units
are separated out and abbreviated on the basis of their age and formation name, such as “Osp”, Ordovican
age St. Peter Formation.
A. Geologic Map of the Black Hills
Use the map and geological column labeled ”Wyoming Area”. The Black Hills occur in the
northeastern part of the map. Ignore the rest of the map as you answer the following:
1. As and Ai are the oldest rocks found in the Black Hills. Which is older? _______
2. The schematic cross section below was drawn from Newcastle, WY to Rapid City, SD.
a. What direction does unit Kc dip in the vicinity of Newcastle:
N, NE, E, SE, S, SW, W, NW ____
b. What geologic structure is responsible for the Black Hills:
anticline, syncline, dome, basin, thrust fault ___________________________
c. Note that beds on the Rapid City side of the structure dip (more, less) ____________ steeply
than those on the Newcastle side. How does the width of unit Cm shown on the geologic map reflect
changes in dip? The exposure is wider where the dip is (more, less) _________ steep.
3. If you continued the cross section southwest from Newcastle, which unit would be in the center of the
next basin? Km, El Efu, Ews, Kmn, AR __________
4. Locate the white River Group (φw) in the southwest part of the Black Hills. How do we know that φw
is younger than the structure you named in question 2?
5. Arrange these events in order from oldest (#1) to youngest. When you list rock units be sure to list only
those found in the Black Hills.
_____
_____
_____
_____
_____
_____
_____
a. Period of erosion or non-deposition followed by deposition of Co age formations. Type of
unconformity: _________________________
b. Metamorphism of As and intrusion by Ai (order uncertain).
c. Deformation shown by map pattern (see question 2) or intrusion by Ti.
d. Period of erosion or non-deposition followed by deposition of Pennsylvanian or Permian age
rocks. Type of unconformity unknown. List rock units deposited: ____________________
e. Period of erosion or non-deposition followed by deposition of Oligocene age rocks. Type of
unconformity: _________________________.
List rock units deposited: ______________________
f. Deposition of Triassic-Cretaceous age rocks; list units: _______________________
g. Deposition of sediments that became As.
B. Geologic Map of Michigan and Surrounding Area
In this section you will be looking again at evidence of folds and unconformities on a geologic
map. Use the Michigan map and accompanying geologic column.
1. The oldest rocks are found in the NW corner of the map (Upper Peninsula of Michigan). What is the
name or symbol for these rocks? ______________________
2. The youngest unit (light blue) is found in two locations: in the center of Michigan, and in the extreme
SW corner of the map. What is the name or symbol of this unit? _________________________
3. Most of Michigan is part of what feature? (circle one) anticline, syncline, dome, basin
4. Since all the rocks on the map have been deformed by this feature, the age of deformation must be
younger than Upper _____________________ period.
5. As you go from Napoleon to Bucyrus, Ohio (SE corner of the map), note the repeats of units Du and Su
and maybe others. What structural feature (basin, dome, anticline, syncline) have you crossed?
______________________ How do you know?
6. All the rocks Cambrian and younger are sedimentary.
a. What kind of unconformity occurs in central Michigan? __________________________
b. What unit is missing? ___________________________
7. What kind of unconformity occurs in the NW part of the map between Pre-Cambrian units and Cu?
____________________________________
8. What kind of unconformity occurs in the SW part of the map between Ordovician and Carboniferous
(Mississippian) age rocks? ________________________
9. There is a fault east of Lansing, Michigan. How is it shown on the map?
10. Sketch a geologic cross section from L. Sable Pt. through Mt. Pleasant and east to Lake Huron.
Procedure is outlined below.
a. Line up folded paper on map.
b. Mark contacts between units and label with initials for each unit. The first two units on the west side
of the section have been done for you.
c. Connect the units from one side of the structure to the other based on your answer to question 3. Use
shallow dips of less than 20 degrees.
A shallow dip:
CHECK KEY, THEN CONTINUE WITH LAB
A steep dip:
Hand in
Name
III. BEDROCK GEOLOGIC MAP OF RAINBOW QUADRANGLE
You will need to refer to your Rainbow Quadrangle cross-section from Ordering Events lab
and your column from Geologic Columns lab. You may also wish to compare the geologic map to the
topographic map handed out in the first lab. In today’s lab you will interpret the attached geologic map
and second cross section. The geologic map shows only the bedrock in Rainbow Quadrangle, as though all
the unconsolidated material had been scraped away.
Rock formations are abbreviated on the map and cross section as they were on the geologic maps
you just used; for instance, Devonian age Avocado Valley Shale is “Dav”.
A. COMPLETE THE SECOND CROSS SECTION (N-S CROSS SECTION)
The second cross section is drawn north to south along the eastern edge of the geologic map.
(There is a model to help you visualize this.) On the cross section, fill in the remaining units as follows:
1. Locate the fault on the N-S cross section. Unit Dav is shown on both sides of the fault. Place arrows on
the fault (on cross section) to show relative movement. Label hanging wall and foot wall (see lab manual
p. 35 for definitions).
2. On the N-S section, the rocks older than Dav are only drawn south of the fault. You will use the original
cross section from the Ordering Events lab to add rocks younger than Dav to your second cross section.
The point marked “Your W-E profile” on the N-S section corresponds with the eastern edge of the earlier
W-E cross section. Measure the thicknesses of the youngest units along the east edge of your first cross
section and plot them above Dav on the N-S profile. (If confused, look at model.)
3. Since the youngest units are horizontal, you can draw in layers based on the points you just plotted.
Label the layers with symbols like “Dav”.
4. Only Dav and older units are found north of the fault on the N-S cross section. Using thicknesses
derived from the southern part of the cross section for units older than Dav, complete the section north of
the fault.
a. Why is there a question mark in the lower part of the section? __________________________
b. Estimating the thickness of Sbm is affected by the question mark. How do we know that Sbm is much
thicker than 50 feet?
c. Use a dashed line to show the minimum thickness of Sbm.
B. COMPLETE THE BEDROCK MAP
1. On the map, place a “U” on the upthrown side of the fault, and a “D” on the downthrown side. Place
“ticks”
along the fault line to show which way it dips.
2. There is an unconformity shown at two locations on the geologic map. Decide whether it is U1, U2 or
U3: _______ Mark both locations on your map (note: not on cross section).
Hand in
Name
C. INTERPRETATIVE QUESTIONS
1. What type of unconformity is the one you just added to your map? ____________________________
2. What type of fault is found in Rainbow Quadrangle? _______________________
3. Does this fault indicate conditions of extension or compression? __________________
4. What type of fold is exposed in the northern half of the quadrangle? _________________
5. What is the age of the fault relative to the age of the fold? (Which cuts which?)
____________________ is younger than _____________________.
6. Turtle Rock is a prominent hill in the northwest part of the quadrangle (see topographic map). Your
geologic map shows it is made of granite. Based on both cross sections and the geologic map, could this
granite be Coyote Pass granite? Explain.
7. In what parts of the quadrangle is the Gray Ledge Limestone (Mgl) exposed?
Looking at the geologic map and the two cross sections (also the topographic map if you are used to using
one), why do you think Gray Ledge was not found in the first week’s W-E cross section:
(a) because it has been eroded from there, or (b) because it was never deposited there?
Explain.
8. Based on information in questions 1-7, why can’t you tell for sure the relative ages of the fault and Gray
Ledge?
9. Where the same fault is exposed west of Rainbow Quadrangle, it cuts a Lower Triassic age granite. The
fault must be (younger, older) ________________ than ~235 m.y.
Could the same event that produced the granite at Turtle Rock have also created this granite? Explain.
10. Add this granite to your Rainbow Quadrangle geologic column.
We have now worked out the ambiguities in the chronology of events in Rainbow Quadrangle and will be
ready to summarize these events in our last lab.
Optional--test yourself:
Folding occurred after deposition of ____ but before the period of erosion that produced U ____.
Faulting occurred after the intrusion of ________ but before U ______.
Hand in
Name
Hand in
Name
HISTORICAL GEOLOGY
PALEOENVIRONMENTAL INTERPRETATION
The purpose of this lab is to get as accurate a picture as we can of the different environments in
which specific Rainbow Quadrangle rocks formed. Using information in your lab manual, you will try to
determine the salinity, turbidity, and depth of water on the basis of fossils and trace fossils. Textural
information from earlier labs indicates the overall energy conditions under which the rocks formed. Using
information about how specific sedimentary structures form, we can further refine estimates of energy
levels and determine other conditions, such as whether the rock was deposited by wind or water, if wet and
dry conditions alternated, whether there were waves or currents present, etc. All this information will lead
to identification of the most likely facies (sedimentary environment) in which each rock unit was deposited.
Here is a “warm up” exercise to demonstrate how the data you will use were derived and to give
you practice in interpreting environmental conditions.
PART ONE: PRACTICE EXERCISE
1. We will be working with two organisms and one trace fossil. The organisms are a gastropod and a fossil
you have not seen, a calcisponge. Look at the gastropods in your fossil collection, just to remind yourself
what they are. There is a model of a trace fossil, a unidirectional crawling track, on the back counter.
2. You will be using the Environmental Interpretation of Fossils section of your lab manual This
information was gathered by observing living organisms. What principle allows us to apply this
information to fossils? ____________________________
3. Look at the tables in the Environmental Interpretation of Fossils section of the manual (begins on p. 22).
The wider the bar on each table, the more living species are found under the environmental conditions
indicated at the top of the table. For purposes of an introductory-level lab, we assume that species
distributions in various environments were similar in the past. We also have to make assumptions about
taxa that are now extinct. We will interpret our results in terms of likely environments (wide bar, many
species), possible environments (tapering or dashed bar), and unlikely environments (no modern species
found in that environment).
4. What is meant by turbidity?
5. How about salinity?
6. The section on Depth Terms gives you terms and useful background on important characteristics of
water depth. You will need to know the meaning of terms like “intertidal”, “wave base” and “transitional”
to do today’s lab.
7. The data table for you to use is on the white insert sheet. Some information for the calcisponge has been
plotted for you. Compare it with the tables in your manual, completing the depth section.
8. Plot the information for the gastropod in the same way, then use the manual to find the depths at which
unidirectional crawling tracks are typically found. Be careful in indicating intertidal and supratidal
environments.
9. Using the same reasoning about assemblages as in your fossil age dating, find the more restricted
environments in which a calcisponge, a gastropod, and the organism responsible for the tracks could have
coexisted. Use solid bars for the likely conditions of turbidity, salinity and depth, and dashed lines for
possible conditions.
TURBIDTY
SALINITY
Marine
20
30
40
50
60
Hypersaline
Hypersaline
Sl.
Hypersaline
Normal
Sl. Brackish
Brackish
Brackish
Fresh
Extreme
Very
Moderate
Slight
Clear
Fossil # and
Name
Calcisponge
(use plain
sponge info)
Gastropod
FOSSIL
ASSEMBL.
DEPTH
Dry
Fresh
0
Supratidal
Intertidal
FOSSIL
ASSEMBL.
20
V. Shallow
Unidirect.
Crawling
tracks
Shallow
TRACE
FOSSIL
200
Mod.
Shallow
Gastropod
Mod. Deep
Calcisponge
(use specific
info)
Deep
V. Deep
2000
10. Interpretation
Choose one or more phrases within the parentheses, or fill in the blanks in the following statements:
a. The entire assemblage most likely lived in (clear, moderately turbid) water, but could be found
in (slightly, extremely) turbid water.
b. Salinity information indicates either freshwater (_____ parts per thousand dissolved salt) or
normal marine (_____ to ______ ppt) conditions are most likely. But (slightly, somewhat, very
hypersaline) or any range of brackish conditions are possible.
c. We can revise our determination of salinity conditions because the depth table gives information
about three specific groups of sponges. Which salinity environment can we eliminate now?
_____________________
d. Calcisponges are usually found in very shallow to shallow water (slightly >0 to ______ m.) but
can be found in (moderately shallow, moderately deep) water.
e. Crawling tracks are found in many environments and so are (useful, not useful) in further
restricting possible environments.
f. Based on turbidity, did the assemblage live in an area of rapid sedimentation ? (Y, N, maybe)
g. Based on salinity/depth information, could this assemblage have lived in fresh water, or is it
exclusively marine? (F, M, either)
h. If marine, does this assemblage require constant submergence in water (below 0 m. at all times),
or can it tolerate tidal conditions? (S or T)
i. Use this information from fossil interpretation plus the lab manual information on p. 31-32 to
decide which of these sedimentary structures might be found with this fossil assemblage:
(desiccation cracks, oscillation ripples, graded beds).
PART TWO: PALEOENVIRONMENTS OF RAINBOW ROCKS
Rainbow rocks are arranged chronologically on tables in lab. With each rock sample you will find
a fossil assemblage and a group of sedimentary structures. Some rocks also have trace fossils. There are
diagrams at each table showing the conditions under which each fossil could have lived, and information
sheets about the sedimentary structures.
(1) Name the fossils at the level of phylum or class, not genus (no new procedures needed; simply look up
in your Introduction to Paleontology lab white sheet,).
(2) Use the same lab to review the identification of trace fossils (note that information from your lab
manual regarding the depths at which these trace fossils are found is already plotted for you ).
(3) Identify the sedimentary structures (use information on the table plus lab manual).
(4) Determine the Turbidity, Salinity and Depth requirements for your assemblage (including any trace
fossils) as you did in the warm up exercise.
(5) Required: answer questions 1-3 for each formation.
In addition, each team will answer more in-depth questions (numbers 4-6) about some of the rock
formations and identify the most likely sedimentary environments in which they formed. The formations
for each team will be posted on the board.
You may visit the rocks in any order you wish. We will be working on this lab over two lab
periods. In the second lab, we will take a brief look at the Q sediments as well.
Hand in
ENVIRONMENTAL INTERPRETATION WORKSHEET (Instructions on page 2 of lab.)
#1 BLUE MOUNTAIN DOLOSTONE
1. Identifications
Fossils and Trace Fossils
# / Letter
Name
1
6
8
11
Trace:
Sedimentary Structures
# / Letter
Name
19
77
UT 1-2
No more
No more
2. Use the turbidity, salinity and depth information posted with the rock to predict likely, possible and
unlikely conditions for the entire assemblage. Use solid and dashed lines on the summary tables below.
TURBIDTY
20
30
40
50
60
Hypersaline
Hypersaline
Sl.
Hypersaline
Normal
Sl. Brackish
Brackish
Brackish
Fresh
Extreme
Very
Moderate
Slight
Clear
SALINITY
Marine
DEPTH
Dry
Fresh
Supratidal
Intertidal
20
V. Shallow
Shallow
200
Mod.
Shallow
Mod. Deep
Deep
V. Deep
2000
0
3. Summarize information from the assemblage by answering Y, maybe or N:
Area of rapid sedimentation? _____
Fresh water? ______ Only normal marine salinity? ______
Dry land? ______
Intertidal _____ or supratidal zone? _________
4. What does the edgewise conglomerate indicate about energy levels in the facies represented by the Blue
Mountain Dolostone?
5. How do you account for the presence of organism #8 in a formation with oscillation ripples and
edgewise conglomerate? Which is the more reliable interpretation in this case, an environment of
deposition based on the fossil information or the sedimentary structures?
6. Best choice(s) for facies:
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ENVIRONMENTAL INTERPRETATION WORKSHEET
#2 ORANGE BROOK LIMY SHALE
1. Identification
Fossils and Trace Fossils
Sedimentary Structures
# / Letter
Name
# / Letter
Name
4
T42
6
No more
9
No more
18
No more
No sample:
No more
Hexactinellid Siliceous Sponge
Trace:
No more
2. Use the turbidity, salinity and depth information posted with the rock to predict likely, possible and
unlikely conditions for the entire assemblage. Use solid and dashed lines on the summary tables below.
TURBIDTY
20
30
40
50
60
Hypersaline
Hypersaline
Sl.
Hypersaline
Normal
Sl. Brackish
Brackish
Brackish
Fresh
Extreme
Very
Moderate
Slight
Clear
SALINITY
Marine
DEPTH
Dry
Fresh
Supratidal
Intertidal
20
V. Shallow
Shallow
200
Mod.
Shallow
Mod. Deep
Deep
V. Deep
2000
0
3. Summarize information from the assemblage by answering Y, maybe or N:
Area of rapid sedimentation? _____
Fresh water? ______ Only normal marine salinity? ______
Dry land? ______
Intertidal _____ or supratidal zone? _________
4. Depth information is especially useful in determining the sedimentary environment for this formation.
Which of the following was most useful in narrowing down the depth: a specific organism, trace fossil, or
sedimentary structure? Explain.
5. Since we have not seen any sponge fossils in lab, check your text. What kind of organisms are siliceous
sponges and what parts of their bodies would you expect to be preserved?
6. Best choice(s) for facies:
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ENVIRONMENTAL INTERPRETATION WORKSHEET
#3 PURPLE CLIFF DIRTY SANDSTONE
1. Identification
Fossils and Trace Fossils
# / Letter
Name
4
12
No Sample: Ostracode
No more
Trace: None
Sedimentary Structures
# / Letter
Name
109
UT 1-9
UT 3-2
UT 4-1
No more
2. Use the turbidity, salinity and depth information posted with the rock to predict likely, possible and
unlikely conditions for the entire assemblage. Use solid and dashed lines on the summary tables below.
TURBIDTY
20
30
40
50
60
Hypersaline
Hypersaline
Sl.
Hypersaline
Normal
Sl. Brackish
Brackish
Brackish
Fresh
Extreme
Very
Moderate
Slight
Clear
SALINITY
Marine
DEPTH
Dry
Fresh
Supratidal
Intertidal
20
V. Shallow
Shallow
200
Mod.
Shallow
Mod. Deep
Deep
V. Deep
2000
0
3. Summarize information from the assemblage by answering Y, maybe or N:
Area of rapid sedimentation? _____
Fresh water? ______ Only normal marine salinity? ______
Dry land? ______
Intertidal _____ or supratidal zone? _________
4. It looks like Purple Cliff could possibly form in fresh water. What specific things should you look for to
see if this is true?
5. What would carefully recording the orientation of the current ripples help us to determine?
6. Best choice(s) for facies:
Hand in
ENVIRONMENTAL INTERPRETATION WORKSHEET
#4 AVOCADO VALLEY SHALE
1. Read about lycopods in your text (p. 262-264).
What are they?
How did they reproduce?
Are they more like algae, ferns, or flowering plants?
Lycopods suggest what environmental conditions when Dav was deposited (check as many as apply):
_____ Salt water
_____ Fresh water
_____ Moist to wet terrestrial climate
_____ Dry terrestrial climate
_____ Glaciation
2. What does #99 represent:
Compacted mud or compacted plant material?
3. Match the sedimentary structures with the descriptions and name them below:
Letter / #
Name
__R_
________________________
__148_
________________________
__B___
________________________
4. Review the age of this unit (see Geologic Column lab). Would finding amphibian tracts in Avocado
valley be a likely event (skim text for information about animal life during this period)? Explain.
5. How did conditions change between the deposition of Purple Cliff (Dpc) and Avocado Valley (Dav)?
6. Best choice(s) for facies:
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ENVIRONMENTAL INTERPRETATION WORKSHEET
#5 RED RIDGE CLEAN SANDSTONE
1. Identification
Fossils and Trace Fossils
# / Letter
Name
3
6
12
No sample:
Calcareous worm (annelid) tubes
Trace:
Sedimentary Structures
# / Letter
Name
35
26
A
C
No more
2. Use the turbidity, salinity and depth information posted with the rock to predict likely, possible and
unlikely conditions for the entire assemblage. Use solid and dashed lines on the summary tables below.
TURBIDTY
20
30
40
50
60
Hypersaline
Hypersaline
Sl.
Hypersaline
Normal
Sl. Brackish
Brackish
Brackish
Fresh
Extreme
Very
Moderate
Slight
Clear
SALINITY
Marine
DEPTH
Dry
Fresh
Supratidal
Intertidal
20
V. Shallow
Shallow
200
Mod.
Shallow
Mod. Deep
Deep
V. Deep
2000
0
3. Summarize information from the assemblage by answering Y, maybe or N:
Area of rapid sedimentation? _____
Fresh water? ______ Only normal marine salinity? ______
Dry land? ______
Intertidal _____ or supratidal zone? _________
4. How did you solve the problem of there being no good overlap of salinity conditions for this
assemblage?
5. Which organism, trace fossil or sedimentary structure is most useful in narrowing down your choices of
sedimentary environments for this formation? Explain your choice.
6. Best choice(s) for facies:
Hand in
ENVIRONMENTAL INTERPRETATION WORKSHEET
#6 GREEN POND DIRTY SHALE
1. Identification
Fossils and Trace Fossils
# / Letter
Name
6
9
12
17
Trace:
Sedimentary Structures
# / Letter
Name
No sample: Bioturbation
No more
No more
No more
No more
2. Use the turbidity, salinity and depth information posted with the rock to predict likely, possible and
unlikely conditions for the entire assemblage. Use solid and dashed lines on the summary tables below.
TURBIDTY
20
30
40
50
60
Hypersaline
Hypersaline
Sl.
Hypersaline
Normal
Sl. Brackish
Brackish
Brackish
Fresh
Extreme
Very
Moderate
Slight
Clear
SALINITY
Marine
DEPTH
0
3. Summarize information from the assemblage by answering Y, maybe or N:
Area of rapid sedimentation? _____
Fresh water? ______ Only normal marine salinity? ______
Dry land? ______
Intertidal _____ or supratidal zone? _________
4. Do you think that you are likely to find oscillation ripples in association with the Green Pond fossil
assemblage? Explain.
5. What does bioturbation tell us about this environment?
6. Best choice(s) for facies:
Dry
Fresh
Supratidal
Intertidal
20
V. Shallow
Shallow
200
Mod.
Shallow
Mod. Deep
Deep
V. Deep
2000
Hand in
ENVIRONMENTAL INTERPRETATION WORKSHEET
#7 WHITE PEAK OOLITIC LIMESTONE
1. Identification
Fossils and Trace Fossils
# / Letter
Name
3
19
Trace:
Sedimentary Structures
# / Letter
Name
F
Round objects in jar:
No more
2. Use the turbidity, salinity and depth information posted with the rock to predict likely, possible and
unlikely conditions for the entire assemblage. Use solid and dashed lines on the summary tables below.
TURBIDTY
20
30
40
50
60
Hypersaline
Hypersaline
Sl.
Hypersaline
Normal
Sl. Brackish
Brackish
Brackish
Fresh
Extreme
Very
Moderate
Slight
Clear
SALINITY
Marine
DEPTH
Dry
Fresh
Supratidal
Intertidal
20
V. Shallow
Shallow
200
Mod.
Shallow
Mod. Deep
Deep
V. Deep
2000
0
3. Summarize information from the assemblage by answering Y, maybe or N:
Area of rapid sedimentation? _____
Fresh water? ______ Only normal marine salinity? ______
Dry land? ______
Intertidal _____ or supratidal zone? _________
4. What evidence helps you decide whether the oolites were washed in from elsewhere or were formed in
the actual environment in which White Peak was deposited?
5.Compare the posted sieve data histogram for White Peak with those in your lab manual. Which of the
graphs in your manual is most like White Peak?
Which of the two is better sorted?
6. Best choice(s) for facies:
Hand in
ENVIRONMENTAL INTERPRETATION WORKSHEET
#8 GRAY LEDGE LIMESTONE
1. Identification
Fossils and Trace Fossils
# / Letter
Name
Blue green algae (See sed. struc. I)
No sample: Ostracodes
No more
Trace: Unidirectional crawling tracks
Sedimentary Structures
# / Letter
Name
184
I
W
Indicate form of stromatolites *:_____________
* Stromatolite forms: wavy, columnar, oncolites.
2. Use the turbidity, salinity and depth information posted with the rock to predict likely, possible and
unlikely conditions for the entire assemblage. Use solid and dashed lines on the summary tables below.
TURBIDTY
20
30
40
50
60
Hypersaline
Hypersaline
Sl.
Hypersaline
Normal
Sl. Brackish
Brackish
Brackish
Fresh
Extreme
Very
Moderate
Slight
Clear
SALINITY
Marine
DEPTH
Dry
Fresh
Supratidal
Intertidal
20
V. Shallow
Shallow
200
Mod.
Shallow
Mod. Deep
Deep
V. Deep
2000
0
3. Summarize information from the assemblage by answering Y, maybe or N:
Area of rapid sedimentation? _____
Fresh water? ______ Only normal marine salinity? ______
Dry land? ______
Intertidal _____ or supratidal zone? _________
4. Briefly explain why stromatolites forming at different points on the shoreline have different shapes (see
examples and extra reading in lab).
5. Why do you think that there are few types of fossils found in this formation?
6. Best choice(s) for facies:
Hand in
FACIES DETERMINATION:
In this section organize and present your ideas INDEPENDENTLY from those of your
teammates.
Choose the two formations that you feel most confident about. You should have narrowed their
environments of deposition to one or two possible facies. Using all available information from this lab,
previous labs, lab manual, etc., explain how you arrived at your answers, and if you end up with more than
one possible facies, suggest what further evidence would help you decide between the two environments.
Give your answers some thought as you will be graded on how complete and convincing your explanations
are. Use this sheet to make notes, but please hand in a typed report.
Formation _______________________
Formation ______________________
Facies___________________________
Facies____________________________
Explanation:
Explanation:
Hand in
PART THREE: Q SEDIMENT IDENTIFICATION AND INTERPRETATION
1. Identification
You can identify the Q sediments on the basis of :
(1) textural information (either review earlier labs, Rocks and Sediments of Rainbow Quadrangle, and
Textural Analysis of Rainbow Quadrangle Units, or reexamine the samples today),
(2) sedimentary structures you will see today, and
(3) information in your lab manual (Guide to Identifying Q Sediments, p. 52) and graphs beginning on p.
46.
Use all this information to fill in the table below.
Q
Symbol
Qt
Age from
Geol. Col. lab
(+/- 330 y.)
14,000
Sedimentary
Structures Seen in
Lab Exhibit
Q44: Describe
surface of pebble:
Sed. Struct.
Mentioned in Lab
Exhibit
Massive
Qow
Not available
None
1. Large cross beds
2. Thick graded beds
None
1. Large cross beds
2. Current ripples
None
Massive
Qv
Describe layers:
No others
Qao
V=
Laminar beds
Qd
Ql
12,900
Q Identity
Briefly How Q Forms
(In your own words)
Z=
Qap
Qap 1 (plaster
cast)=
Cross beds, tool marks,
load casts
211=
2. Look at the attached map Surficial Geology of Rainbow Quadrangle. It shows where different Q
sediments are found at the earth’s surface today. Please type a summary of the distribution of Q sediments..
Tell where each Q sediment is located and why you think it is found where it is. Comparing the attached
map with the topographic map may help. For example, was a particular Q-sediment initially only deposited
in a limited geographical location--if so why, or is it part of an initially more extensive unit that has either
been buried by younger sediments or been partially removed by subsequent erosion? This report should be
attached to your bedrock facies interpretation.
Write your answer INDEPENDENTLY from your teammates.
Surfc
Surficial Geology of a Portion of Rainbow Quadrangle
Map Scale: 1/10” = 200’
B = Areas predominantly bedrock
Qa = Undifferentiated Qao and Qap
Note that Qow is not found at the surface here. From your
cross section you know that it is beneath some of the other
Q sediments.
HISTORICAL GEOLOGY
RAINBOW QUADRANGLE TECTONIC SETTINGS
We can determine the tectonic setting in which sediments were originally deposited by
looking at the rock types produced and by looking at other evidence, including types of igneous
rocks of the same age as the sediments, and at metamorphism, folding and faulting (again, only if
they happened at the same time as deposition of the sediments).
I. INTRODUCTION
1. Review descriptions of these tectonic settings from lecture and see summary in lab manual (p. 3940)
A. mid-ocean ridges
B. island arc subduction zones
C. other subduction zones
D. passive margins
E. continental rift zones
2. Label an example of each type of setting on this schematic diagram:
Check key before continuing on next page of lab.
II. USE OF GEOCHEMICAL DATA
The chemical composition of basalt magma varies with the tectonic setting in which it is
produced. Geochemical analysis reveals differences in "trace elements" (elements that occur in very
small amounts). We will use the trace elements zirconium and yttrium. Refer to the graph in your
lab manual, "Trace elements and tectonic settings". This graph is based on the analysis of many
samples of modern basalts whose tectonic setting can be clearly observed.
1. If the graph is of modern basalts, what principle makes it applicable to Rainbow Quadrangle
rocks?
2. Using the graph, Deer Mountain Basalt has a Zr/Y ratio of 7.2 and contains 205 ppm. of Zr. What
type of basalt is it? (Circle)
mid-ocean ridge
island arc
continental rift
passive margin
3. Given your answer to #2, which of the following sedimentary rocks would you expect to find
associated with Deer Mountain Basalt? (If uncertain, review the lab) (Circle one)
carbonates
terrestrial
clastic rocks
ophiolites
marine
shales
4.a. What Rainbow Quadrangle rock unit is geographically and chronologically associated with
Deer Mountain basalt? ________________________
b. Is it a carbonate, terrestrial clastic, ophiolitic, or marine shale unit?
_________________________
Note that the basalt geochemical data should agree with what we know about the surrounding
sedimentary rocks. If your answers to questions 3 and 4 do not support one another, you have either
misinterpreted the geochemistry or you have not retrieved the correct sedimentary information from
previous labs.
HISTORICAL GEOLOGY: RAINBOW QUADRANGLE FINAL ANALYSIS
INSTRUCTIONS FOR CLASS DISCUSSION AND TEAM ORAL REPORTS
PREPARATION FOR CLASS DISCUSSION
Re-read the introduction to the Rainbow Project. What did we hope that the project would
teach you about historical geology? Review the questions concerning the geologic history Rainbow
Quadrangle. Which can you now answer? What techniques and principles did you use to answer
them? Which remain unanswered, and why?
GENERAL FORMAT
You will report the results of your analysis of your assigned expert bedrock formation. Go
through all your labs looking for references to your formation. Teams will report on the rocks in the
order in which they formed. As a group we will discuss formation of igneous rocks and events
producing folding and faulting, and place the events in a larger context. Each team member is
expected to contribute to the oral report. You will be given feedback on the report, both as a group
and an individual, but will not be formally graded. It will count towards your overall class
participation in lab.
All of the lab samples will be available for you to use in your presentation. You may also
use the overhead projector, slide projector, blackboard, Power Point etc. Overheads available
include three Rainbow maps (topography, bedrock, and surficial), W-E and N-S cross sections,
textural analysis graphs (histograms and cumulative curves), block diagram of facies, and blanks to
make your own overheads. Reports should take about five minutes for each formation, then the
remainder of the lab will be spent on applications to new situations.
SPECIFIC INFORMATION TO INCLUDE IN ORAL REPORT
1. Formation name (rock type and geographical name). Age of rock unit as precisely as known
from all available evidence (relative ages from superposition, etc. and from fossil assemblages, and
absolute ages of igneous rocks).
2. Discussion of conditions of its deposition, specifically:
a. Best facies and reasons for your choice.
Don't just read all the data you have, but pick the most diagnostic bits of information, which
will vary for each unit: one formation might have several critical sedimentary structures,
backed up by trace fossil evidence, another might have one or two key fossils and a unique
structure. Textural analysis may be more useful for some units than for others.
b. Place the facies in a larger context:
(1) Climate of region (temperature and humidity, if known).
(2) Position relative to shoreline at that time:
Is unit terrestrial, transitional, or marine?
How close to actual shore?
How does it fit relative to units older and younger-- is sea level rising or falling,
climate changing, a normal progression in sedimentation occurring?
(3) What is the plate tectonic setting for your formation? (We will have better
information for some units than for others.)
(4) Is the environment hospitable to diverse and abundant life forms? (A desert, for
instance, is an inhospitable environment.) If you have some especially interesting
fossils in your formation, tell something about their lifestyles (see me for reference
books related to paleoecology).
(5) What were some of the "big events" in the earth's history at the time your rock
was deposited? For example, in the Late Ordovician you might mention the earliest
land plants, or that glaciation occurred in Gondawanaland. Make use of information
learned in lecture or from your text.
HISTORICAL GEOLOGY
RAINBOW QUADRANGLE FINAL ANALYSIS
I. INTRODUCTION: Today’s lab has two parts: one deals with what you did in the Rainbow Project and
the other gives you a chance to apply principles and techniques learned in the project to something entirely
new.
II. REFLECTIONS ON THE RAINBOW QUADRANGLE PROJECT
Work on the questions that follow on your own. Use any books or lab materials you wish, but do
not consult other students.
1. Questions from the first day of lab – we posed several questions pertaining to Rainbow Quadrangl.
Answer one of the three choices (a) or (b) or (c) below. (Obviously, if you missed the first day
lab, do either alternative (b) or (c).) Your answer should be about one paragraph long.
Choice a. Choose one of the questions listed in the introduction to the term project that requires
more than a one or two word answer, answer the question and briefly explain what lab techniques were
used to answer it. If in doubt whether a question is a good choice, ask.
Choice b. What questions remain unanswered about Rainbow Quadrangle? Choose one and
suggest how you might gather the information needed to answer it.
Choice c. Look at the displays on level one of the museum. What facies seem to be depicted?
What seems most distinctive to you about life in what is now Iowa, first in the Ordovician, then in the
Silurian?
2. Reflections on methodology:
Choose one of the following three questions. Be sure you address all parts of the question. You
will be graded on correctness and thoroughness of your answers and on how well written they are.
Organize your thoughts before beginning. You should be able to answer each question in about one typed
page
Choice a.
Describe the reasoning behind the use of assemblages of fossils and sedimentary structures rather than
single examples. Were assemblages equally effective for determining ages and facies in different
formations? What are some weaknesses of using either fossils or sedimentary structures for determining
facies? Use specific examples to back up your opinions whenever possible.
Choice b.
The principle of uniformitarianism is one of the key elements of historical geology. Describe how
uniformitarianism was used to provide information in at least three different situations in the Rainbow
Project. For each example, what was the modern phenomenon being observed, how was it applied to study
of the past, what assumptions had to be made, did those assumptions weaken the value of your
conclusions?
Choice c.
One of my goals in the course was to help you learn to visualize the earth and its materials in three
dimensions. Choose at least two labs which helped to accomplish this goal, describing how the lab
exercises helped you meet this goal. How did “seeing” Rainbow Quadrangle in three dimensions also help
you see the historical events that have taken place in Rainbow? Discuss one or two practical applications
of this skill in non-geological settings.
III. APPLYING WHAT YOU HAVE LEARNED TO SOMETHING NEW
Choose a new partner, someone not on your Rainbow Project team. Look at the list of geologic
maps and choose a map that you think might be interesting.
Working with your partner, use the map and accompanying column and cross section to
reconstruct as much of the history of the area as you can. The questions asked in the introduction to the
Rainbow Quadrangle may give you some ideas if you don’t know where to begin. Consult your text or me
for help with unfamiliar terms, etc. All maps and cross sections must stay in the lab as they are part of
a set, and lost or damaged pieces will be impossible to replace.
Each of you will write a separate discussion of some aspect of the information shown on the map.
Your discussion should be at least one page long. Do not try to cover everything that the map shows in
just a page or two. Choose something that you find interesting. Your instructor will give you some
guidance if you are unsure what to choose.
Inferences and speculations are welcome so long as you provide evidence to back them up. If
something you say is incorrect, but is a reasonable mistake for someone at your level of expertise, you will
not be penalized. You will be graded on both content (application of principles of historical geology at an
introductory level) and writing (organization, grammar, spelling, etc.). If you consult outside sources,
including your textbook, be sure to cite them.