Chapter 6
Interpreting Sedimentary Environments and
Global Change
Chapter Outline:
I.
Modern and Ancient Sedimentary Environments
a. Using Sediments to Interpret Sedimentary Environments
b. Sedimentary Structures
c. Walther’s Law of Facies
II.
Interpreting Ancient Sedimentary Environments
a. Nonmarine Environments
b. Transitional Marine/Nonmarine Environments
c. Marine Environments
III. Using Carbon and Oxygen Isotopes to Interpret Global Climatic
and Oceanographic Change
a. Carbon Isotopic Ratios through Time
b. Oxygen Isotopic Ratios through Time
Key Terms:
facies
grain-size
sorting
roundness
bedding
bioturbation
ripples
cross-bedding
graded bedding
mudcracks
geopetal structures
stromatolites
concretions
paleosols
Walther’s Law of facies
transgression
continental shelf
regression
alluvial fans
barrier island
reef
continental slope
greenhouse gases
In-Class Activities:
Instructor Notes for In-Class Activity 1
Title:
Sedimentary structures: Clues to past environmental conditions
Time:
5-10 minutes prep; 50 – 60 minutes in class (or can assign research between
class periods)
Materials:
Internet required. Print instruction sheets as handouts.
Handouts:
A list of questions for students to research and discuss using recommended
websites. The textbook section called “Sedimentary Structures” is a useful
reference for answering the handout questions. In addition to the textbook,
the following websites are also useful references.
http://www.geology.pitt.edu/GeoSites/sedstructures.htm
http://people.uncw.edu/dockal/GLY312/sedstruct/sedstruct.htm
http://facstaff.gpc.edu/~pgore/geology/historical_lab/sedstructureslab.php
Have the students answer the following questions:
Examine the following photo:
http://www.geologyrocks.co.uk/system/files/u2/robinhoodsbay037.jpg
1) What type of sedimentary structure is depicted in the photo?
2) What inferences can a geologist make if he/she finds such structures
in rocks (as it pertains to current direction)?
Watch the following video and answer the following questions:
http://www.youtube.com/watch?v=WUqldSl0jAI
3) How do conglomerates form in the shore zone?
4) Are these conglomerates formed in a low or high-energy
environment? Why?
5) What types of sedimentary structures commonly form in beach
environments?
6) Do beaches have structure? If they do, describe it. If they do not
explain why.
7) What types of features and structures are produced by wind near
beaches?
Examine the following photo:
http://www.geo.cornell.edu/geology/classes/geol326/images/modernmud.gif
8) What type of sedimentary structure is shown in the above photo, and
what does it indicate about the environmental conditions during the
time of deposition?
Examine the following image:
http://www.geology.ohio-state.edu/~vonfrese/gs100/lect11/xfig11_21.jpg
9) What type of sedimentary structure is depicted in the image?
10) Can this structure be used to determine stratigraphic up? Explain.
Procedures:
Divide class into groups of 3-4. Have the students read the section of the
textbook called “Sedimentary Structures” in Ch. 6 of their textbook. In
addition to this part of their textbook students can also use the following
websites to answer the questions contained within this in-class exercise.
http://www.geology.pitt.edu/GeoSites/sedstructures.htm
http://people.uncw.edu/dockal/GLY312/sedstruct/sedstruct.htm
http://facstaff.gpc.edu/~pgore/geology/historical_lab/sedstructureslab.php
Have the students answer the 10 questions listed in the above handout
section. The students should neatly write their answers down and hand
them in to their instructor for grading. Knowledge of this information will
be useful in preparing for both a future quiz and test.
The goal of this in-class exercise is to study how geologists use sedimentary
Student
Instructions: structures to make inferences about the conditions that existed during the
deposition process. Today, you will have the opportunity to see what these
features look like, and how they form.
Specific
Suggestions:
Objectives:
At some later time during the semester, the instructor should provide the
students with the opportunity to student sedimentary structures in the field.
Students should become familiar with some of the common types of
sedimentary structures and what they tell geologists about the environment
of deposition for sedimentary rocks.
Students should be able to recognize common sedimentary structures by
sight (visually).
Students should become familiar with some of the common indicators of
stratigraphic up.
In-Class Activity 1: Handout
Read the textbook section called “Sedimentary Structures”. In addition to the textbook,
the following websites are also useful references.
http://www.geology.pitt.edu/GeoSites/sedstructures.htm
http://people.uncw.edu/dockal/GLY312/sedstruct/sedstruct.htm
http://facstaff.gpc.edu/~pgore/geology/historical_lab/sedstructureslab.php
Answer the following questions as a group, write down your answers and submit them
upon completion to your instructor for grading. By answering these questions you will
be preparing for a future quiz and test.
Examine the following photo:
http://www.geologyrocks.co.uk/system/files/u2/robinhoodsbay037.jpg
1) What type of sedimentary structure is depicted in the photo?
2) What inferences can a geologist make if he/she finds such structures in rocks (as it
pertains to current direction)?
Watch the following video and answer the following questions:
http://www.youtube.com/watch?v=WUqldSl0jAI
3) How do conglomerates form in the shore zone?
4) Are these conglomerates formed in a low or high-energy environment? Why?
5) What types of sedimentary structures commonly form in beach environments?
6) Do beaches have structure? If they do, describe it. If they do not explain why.
7) What types of features and structures are produced by wind near beaches?
Examine the following photo:
http://www.geo.cornell.edu/geology/classes/geol326/images/modernmud.gif
8) What type of sedimentary structure is shown in the above photo, and what does it
indicate about the environmental conditions during the time of deposition?
Examine the following image:
http://www.geology.ohio-state.edu/~vonfrese/gs100/lect11/xfig11_21.jpg
9) What type of sedimentary structure is depicted in the image?
10) Can this structure be used to determine stratigraphic up? Explain.
If time remains, have the students in your group discuss some of the other sedimentary
structures that can be used to infer stratigraphic up.
Instructor Notes for In-Class Activity 2
Title:
Walther’s Law: A powerful tool for studying the lateral distribution of
paleoenvironments
Time:
5 – 10 Minutes prep; 40 – 60 minutes in class (or can assign research between
class periods)
Materials:
Internet required. Print instruction sheets as handouts.
Handouts:
A list of websites and questions to be answered. Students will find Ch. 6
“Walther’s Law of Facies” to be useful in answering some of the questions.
Also, students will find the following websites particularly useful:
http://video.google.com/videosearch?q=walthers+law&hl=en&emb=0&aq=f#
http://strata.geol.sc.edu/terminology/walther.html
http://facstaff.gpc.edu/~pgore/geology/historical_lab/stratigraphy.php
Procedures:
Hand out instruction sheets. Instruct the students to use the websites listed
above and Ch. 6 “Walther’s Law of Facies” in their textbook as references to
answer the following questions:
1) Neatly draw a series of pictures to show how facies shift vertically
with a sea-level drop (regression). Is a coarsening upward or a fining
upward sequence produced?
2) Now draw a series of pictures to show what happens to these facies
with a sea-level rise (transgression). Is a coarsening upward or a
fining upward sequence produced?
3) What effect would unconformities have on Walther’s Law? Why?
4) Would dune facies migrate towards the onshore or offshore during a
transgression? Explain.
5) How might Walther’s Law be used to determine whether global
warming or cooling was occurring in the past?
Student
Instructions: See above
Specific
Suggestions:
Objectives:
The instructor should emphasize that a future lab quiz and lecture exam will
contain questions to test the students understanding of Walther’s Law.
The student should be able to show how Walther’s Law works by drawing
detailed diagrams.
Students should become familiar with the way facies shift with transgressions
and regressions.
Students should become aware of how Walther’s Law might be useful in
studying past climate change.
In-Class Activity 2: Handout
Walther's Law of Facies, named after the geologist Johannes Walther, states that the
vertical succession of facies reflects lateral changes in environment. It also states that
when a depositional environment "migrates" laterally, sediments of one depositional
environment come to lie on top of another. A classic example of this law is the vertical
stratigraphic succession that typifies marine trangressions and regressions. However, the
law is not applicable where the contact between different lithologies is non-conformable
(i.e. sedimentation was not continuous), or in instances of rapid environmental change
where non-adjacent environments may replace one another.
The purpose of today’s in-class exercise is to familiarize you with Walther’s Law. Use
the section on “Walther’s Law” in your textbook as a reference. Then watch the
following video with the rest of your group.
http://video.google.com/videosearch?q=walthers+law&hl=en&emb=0&aq=f#
The following two websites should also be useful as reference in answering the below
questions.
http://strata.geol.sc.edu/terminology/walther.html
http://facstaff.gpc.edu/~pgore/geology/historical_lab/stratigraphy.php
Use a pencil to complete the following (since you will be making detailed drawings, and
may need to do some erasing).
1) Neatly draw a series of pictures to show how facies shift vertically with a sealevel drop (regression). Is a coarsening upward or a fining upward sequence
produced?
2) Now draw a series of pictures to show what happens to these facies with a sealevel rise (transgression). Is a coarsening upward or a fining upward sequence
produced?
3) What effect would unconformities have on Walther’s Law? Why?
4) Would dune facies migrate towards the onshore or offshore during a
transgression? Explain.
5) How might Walther’s Law be used to determine whether global warming or
cooling was occurring in the past?
By completing this in-class exercise you will be preparing for a future lab quiz and
lecture exam.