the rocks under illinois - wordpress.com · 2010. 6. 17. · illinois state museum geology online...

Illinois State Museum Geology Online – http://geologyonline.museum.state.il.us

The Rocks Under Illinois Grade Level: 9 – 12 This lesson builds upon ISM Geology Online lesson 12.3, How Old is Illinois? http://geologyonline.museum.state.il.us/tools/lessons/12.3/index.html Purpose: The purpose of this activity is to draw the rock layers under the surface of Illinois between Rock Island and Chicago using the ages determined in ISM Geology Online lesson 12.3. Suggested Goals: The goal of drawing the rock layers will be met by teaching your students what the law of superposition is and how it can be used to predict the arrangement of the strata beneath the surface. Students will practice drawing layers and then create a three dimensional drawing complete with the appropriate symbols for the rocks. Targeted Objectives: Illinois is covered with thick layers of sedimentary rocks. In many places they are piled layer upon layer until they reach thicknesses of thousands of feet. In this activity students will use the rock layers that are visible at the surface to predict how the layers are arranged far underground where they cannot see. They will use the data from ISM Geology Online lesson 12.3 to make a cross section of Illinois between Rock Island and Chicago.

1. Students will learn the law of superposition 2. Students will learn how sedimentary rocks are arranged 3. Students will learn how to predict the arrangement and inclination of rock layers

far underground using clues at the surface. 4. Students will learn the common geologic symbols for sedimentary rocks. 5. Students will make a cross section using the common symbols for sedimentary

rocks to label them. 6. Students will learn how the rock layers of northern Illinois are arranged.

Background: Material called sediment spreads out evenly over the ocean floor so that a layer of sand or mud covers miles and miles of the sea bottom in roughly horizontal layers. If tectonic forces (mountain building) raise the continent the flow rate will increase and larger particles will reach farther out into the ocean covering the original sediment so that a new bed of coarser sediment might form on top of the first. For hundreds of millions of years, layer after layer settle on top of each other. The great thicknesses of sediment are compressed by their own weight and calcium carbonate, which is abundant in the sea, and change the layers to sedimentary rocks. Since new sediments are deposited on top of those that are already there, we know that the bottom layers are older. This principle, called the Law of Superposition states that the oldest rocks are on the bottom. It is one of the most important principles in the field


of geology. Another principle called the Law of Horizontality states that originally the sedimentary rocks were laid down in flat horizontal layers. These two principles will be used in this activity to determine how the rock layers are arranged under Illinois. Materials:

• Colored pencils • Ruler

Preparation: To begin this lesson, there should be a discussion of the Law of Superposition. Compare the rock layers to someone building a brick house. Which layer did the bricklayer lay first? How do we know? It is the same way with the rock layers. The bottom layer of brick and rock had to have been there before the others. Remind the students that sedimentary rocks are laid down horizontally but that forces in the earth often fold them. Tell them that Illinois is covered with thousands of feet of rock from times when there the area was covered by ocean or the delta of a great river. Begin the stratigraphy activity by telling the students that now they are going to learn how to tell how the rock layers are situated thousands of feet underground without leaving the surface. Tell them that they did the hard part already when they did ISM Geology Online lesson 12.3. Pass out copies of the pages labeled “Rules.” And go over each rule with your students. Draw the following on the board and ask if any student can draw the layers:

The correct answer will be Devonian on top of the Silurian.

Continue putting examples on the board. I usually let a student attempt to do all of a puzzle until they make a mistake and then I let the student who caught the error come up and try to finish the layers. At first it may be hard to get volunteers, but in a short time your students will be begging you to let them go to the board.


At the conclusion of the practice session, I put a sequence from one end of the board to the other with about twenty time periods on it. Just remember that it is easiest for you to make the sequences if you do not skip any periods. If you start with Ordovician then the next period should be either Cambrian or Silurian. In nature periods of time are often missing but for ease in the practice time it is best not to do that at least not at first. When you feel your students are adept at figuring out the rock layers, pass out the sheet labeled “Stratigraphy Worksheet” and have them try to finish it. I usually assign one at a time and then walk around to see who has the correct answer first. You might want to reward the first person to get each correct. Pass out the sheet labeled “A Block of Illinois” and tell your students that this sheet has the rock ages on it that they found when they did their fossil assemblage in ISM Geology Online lesson 12.3. It shows the ages of the rock layers between Rock Island and Chicago. Tell them that now they are going to predict what the rocks are like under their state. Have the students do the same thing on the front of the block as they did in the preceding exercise. Have them draw the layers lightly, in case they make a mistake. If they draw the layers correctly hey will create a sequence of layers sitting on top of Cambrian rocks. When they have completed the layers have them draw the sides as shown on the top of their sheet. Draw the layers back parallel to the top and bottom lines on the side to create a 3-D view. Pass out the sheet that has the rock symbols on it and briefly go over them. Then explain how to draw the layers of limestone, dolomite, and shale so that they are parallel to the bedding plain (bottom of the layer above). It is fortunate for Illinois that it has so much limestone and dolomite but it would have been better for this assignment if the Silurian rock would have been something else since there is a sequence of limestone dolomite limestone which all have pretty much the same symbol on the Illinois Block. This problem is reduced when the students lightly color the different periods of rock creating a very professional looking product. Discussion: 1. Do the rock layers in northern Illinois appear to be folded upward or downward?

Upward 2. What other information about the land would be helpful that the model does not

have since it is flat on top? It would be good to know the contour of the surface. 3. There is a fault on the east side of the Cambrian rock, which side rose the east

side or the west side? The west rose because it brought older rock to the surface.

4. Oil is often found in rock that forms an anticline (upward fold) if there is a layer of sandstone between two layers of shale. This model does show an anticline. Is there any place on the cross section that would likely have oil and why? No


because there is no place where sandstone is between two layers of shale. Oil is usually found in rock layers much younger than the ones in northern Illinois.

5. The Silurian and Ordovician rock appear to be rising on the left side of the map and then reappear on the right side. If they were once joined, why is there a break in the layers? Weathering and erosion have carried away the top of the anticline since it was highest up and thus more vulnerable to erosion by streams and wind.

6. Why is there no coal deposits in the eastern half of Illinois shown by the cross section? There is no Pennsylvanian or Mississippian rock in the western part. They are the periods when coal was formed.

7. Dinosaur fossils are found in Mesozoic age rocks which includes the Triassic, Jurassic, and Cretaceous. Why will there never be a dinosaur found in northern Illinois? There is no Mesozoic age rock in northern Illinois

Assessment: 1. One assessment would be the number of students that raise their hand to go to

the board to try their hand at drawing the layers. 2. Observe the students’ work as you walk around the class while they are working

on the two sheets. 3. Collect the pages of student work, “Stratigraphy Worksheet” and “Block of

Illinois.” 4. Give a quiz with several of the stratigraphy puzzles on it. Begin with some short

easy ones and work toward much more difficult ones. Correct them to see how well the students do on them.

5. Students’ responses to the discussion questions would be a good indicator of student understanding of the concept.

Extensions

• Have your students create a cross section from Cairo to Rockford. The bottom of Illinois is a basin syncline (basin) appropriately named the Illinois Basin.

• Visit a rock outcrop or a park where layers are visible. If this is not possible, show your students pictures of rock strata such as the Grand Canyon.

• Make an actual 3-D model of the rock layers of Northern Illinois. The Illinois State Geological Survey sells such a model of Illinois that would be perfect to show after your students have completed this lesson.

• Look at an Illinois Geologic Map to learn where the various age rocks can be found.

Web Resources

• ISM Geology Online GeoGallery http://geologyonline.museum.state.il.us/geogallery/

• This Website has geologic maps of all fifty states http://geology.tqn.com/cs/geomapssusstates


• This is the Website for the Illinois Geological Survey http://www.isgs.uiuc.edu/

• An Illinois Geologic Map from the Illinois State Geological Survey http://www.isgs.uiuc.edu/servs/pubs/edxhome.htm

Lesson Specifics:

• Students should have completed ISM Geology Online lesson 12.3. • Duration: two days. • It is best for each student to create a drawing of their own but students can work

together while doing their individual pictures. Illinois State Board of Education Goals and Standards:

• 11A: Know and apply the concepts, principles and processes of scientific inquiry.

• 12B: Know and apply concepts that describe how living things interact with each other and with their environment.

• 12E: Know and apply concepts that describe the features and processes of the Earth and its resources.


Symbols: Each variety of rock has its own symbol when drawn on a stratigraphic (rock layer) drawing. Also look at pictures on ISM Geology Online web site. Limestone is drawn like several layers of bricks on top of each other. Sandstone is easy to remember because it is shown with dots that resemble sand. Shale is shown with dashes. Each new line of dashes is indented slightly so that it is below the open spaces in the line of dashes above it. Conglomerate is made of gravels so it is easy to remember its symbol since it is tiny circles, that look like gravel, spread throughout the layer. Dolomite is very similar to limestone except that is contains the mineral magnesium. Its symbol is also very much like limestone but the sides of the bricks are diagonals producing rows of parallelograms. When drawing a layer of limestone, conglomerate or shale, it is important to draw them correctly. If a layer of either is inclined, then the symbol will be drawn parallel to the bedding plain which means the limestone will look like bricks that were laid on the layer under it. The dashes for shale will also be parallel to the layer above and below. This is what a layer of limestone and a layer of shale would look like if the layer they are in is folded.


Quaternary Tertiary Cretaceous Jurassic Triassic Permian Pennsylvanian Devonian Silurian Ordovician

NO

Procedure RULES to Follow when drawing Rock Layers Once the age of rock layers is determined, as was done in ISM Geology Online lesson 12.3, it is a simple matter and even a fun one, to predict what the subsurface orientation of the rock layers is. The rules to follow when determining the arrangement of the rocks are as follows:

1. Start by determining which layer is the youngest and draw that bed on top. If these are several layers of the same age, draw each of them on top. The youngest layer is the Mississippian.

2. The next youngest layer is usually right next to the youngest one and it should be drawn under the younger layer that is already

drawn on top. The Devonian would be under the Mississippian. 3. If there are other layers of that age that are not adjacent to the younger layer, draw then on top like you did in rule one. 4. It is never possible for lines marking the bottom of two layers to touch one another. In the following example if you draw the Ordovician under the large Silurian you can not bring it to the surface without touching the other Silurian so it is necessary to dip under that layer, too.

NO


5. When you draw a layer you should always keep it the same thickness. Do not make it thick in one place and thin somewhere else. The new layers should be drawn parallel to the layers above them. 6. If there is not enough room to put all of a layer on the drawing, bring it down as far as you can and then let it run off of the drawing. 7. If a layer is on the edge and it needs to be drawn on top, you may draw it either of the following ways.

YES

NO

YES


8. Do not draw a bottom to the lowest layer. Let it fill all of the space that remains at the bottom of the diagram.

NO YES


Quaternary Tertiary Cretaceous Jurassic Triassic Permian Pennsylvanian Devonian Silurian Ordovician

NO

Procedure RULES to Follow when drawing Rock Layers KEY Once the age of rock layers is determined, as was done in ISM Geology Online lesson 12.3, it is a simple matter and even a fun one, to predict what the subsurface orientation of the rock layers is. The rules to follow when determining the arrangement of the rocks are as follows:

1. Start by determining which layer is the youngest and draw that bed on top. If these are several layers of the same age, draw each of them on top. The youngest layer is the Mississippian.

2. The next youngest layer is usually right next to the youngest one and it should be drawn under the younger layer that is already

drawn on top. The Devonian would be under the Mississippian. 3. If there are other layers of that age that are not adjacent to the younger layer, draw them on top like you did in rule one. 4. It is never possible for lines marking the bottom of two layers to touch one another. In the following example if you draw the Ordovician under the large Silurian you can not bring it to the surface without touching the other Silurian so it is necessary to dip under that layer, too.

NO

like the youngest layer


5. When you draw a layer you should always keep it the same thickness. Do not make it thick in one place and thin somewhere else. The new layers should be drawn parallel to the layers above them. 6. If there is not enough room to put all of a layer on the drawing, bring it down as far as you can and then let it run off of the drawing. 7. If a layer is on the edge and it needs to be drawn on top, you may draw it either of the following ways.

YES

NO

YES


8. Do not draw a bottom to the lowest layer. Let it fill all of the space that remains at the bottom of the diagram.

NO YES


Stratigraphy Worksheet

Name_________________________ Period_____ Determine how the rock layers would be arranged in each of the following: 1. 2. 3. 4.


5. 6. 7.


Stratigraphy Worksheet KEY Determine how the rock layers would be arranged in each of the following: 1. 2. 3. 4.


5. 6. 7.

the rocks under illinois - wordpress.com · 2010. 6. 17. · illinois state museum geology online...

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