Geologic Correlation Activity Objective:

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Name:_________________________

Date:____________ Period:_______

Geologic Correlation Activity

Objective: To be able to construct a geologic cross-section from information provided from three different outcrops and interpret the geologic history based on the rock record.

Purpose: 1) To demonstrate understanding of the processes that form different geologic units and how they are interrelated.

2) To reinforce the concepts of superposition, original horizontally, and cross- cutting relationships.

3) To learn how geologists evaluate geologic history by correlating rock units and fossil assemblages.

Geologic Information: The following information has been determined by interpreting rock outcrops. The descriptions start at the top and work down the geologic section.

OUTCROP A:

20 meters of limestone, 30 meters of lava (dated at 100 mybp), 20 meters of shale with reptile fossils, 30 meters of sandstone, 40 meters of conglomerate with an interbedded igneous dike (dated at 50 mybp), and 20 meters of lava (dated at 250 mybp).

OUTCROP B:

40 meters of limestone , 10 meters of lava (dated at 100 mybp), 20 meters of shale with reptile fossils, 20 meters of conglomerate with an interbedded igneous dike, 30 meters of shale with trilobite/ brachiopod fossils, and 40 meters of lava (dated at 250 mybp).

OUTCROP C:

10 meters of limestone, 60 meters of shale with reptile fossils (this unit has been cut by an igneous dike), 10 meters conglomerate, and 80 meters of shale with trilobite fossils.

Procedure:

1. Work individually and identify each outcrop based on the information provided above. Cut out the outcrops and glue or tape them to a sheet of plain paper in the following order: Section A on the left, Section B in the middle, and Section C on the right. Label each of the sections at the top of the column. Make sure that you line up the volcanic dike that cuts through each unit. The tops of each unit will not necessarily be at the same elevation.

2. Space the three outcrops approximately one (1) inch apart on the paper. Make sure to leave room to place the legend you will create at the bottom of the page.

3. Correlate the three outcrops and evaluate the geologic history that is presented in the rock record. Start at the bottom of Section A and correlate the units between section A and Section B (section B should be to the right of Section A) as you work your way up the section of rock.

Remember, not all units need to be present in both sections in order to correlate the sections.

Sometimes a rock unit will have no corresponding unit in an adjacent outcrop, this is called a pinchout. This indicates that somewhere between the two areas the unit was either never deposited or was eroded away after deposition.

This activity meets Jeffco Science Content Standard 4.1 “know and understand the composition of Earth, its history, and the natural processes that shape it”;

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4. Draw lines between the sections to indicate where the different units are between them. In the areas between the outcrops, sketch in the appropriate pattern; dots for sandstone, blocks for limestone, etc. See example below.

5. Color each bed on your geologic cross section according to the following:

 Limestone = Yellow

 Shale = Gray

 Conglomerate = Orange

 Sandstone = Tan

 Igneous Dike = Pink

 Lava = Red

6. Construct a legend near the bottom of the page that shows the pattern, color, and type of each rock unit.

7. On a separate piece of paper, answer the analysis questions below.

Analysis Questions

1. Identify and describe the oldest and the youngest rock units identified in the three outcrops.

2. Is the 100 mybp lava unit older or younger than the shale with the reptile fossils? Explain why?

3. Explain why the 50 mybp igneous dike may or may not be the youngest unit in your cross-section?

Explain your answer.

4. Which set of fossils are older, the trilobites or the reptiles? Explain why?

5. Which geologic concept, or law, would you use to support this statement: “The igneous dike is younger than the shale unit with reptile fossils.” Explain your answer.

6. Which type of age dating would support the statement: “The two lava flows are separated by 150 million years of time”?

7. What explanation do you have for the 100 mybp lava being present in Outcrop A and B, but not in Outcrop C?

8. In your own words explain the terms; Law of Superposition, Law of Original Horizontality, and the Law of Cross-Cutting relationships.

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Name:__________________________

Date: ______________ Period: _____

Additional Honors Earth Science Questions (Required)

After completing the outcrop comparison activity and answering the analysis questions on page 2, complete the following questions:

9. Earth scientists take information about the rock units from as many locations (outcrops) as possible and try to develop a regional geologic setting. In this way, they are able to understand HOW the rocks were formed in the geologic past at that location and predict (using their

knowledge of geologic processes) what types of rocks might be associated with the processes which formed the rock units they have observed.

Using the regional geologic setting block diagram, complete the following table to indicate the rock types present, the classification of the rock unit, and the type of geologic environment in which each was formed.

Rock Type

(from outcrop columns) Rock Classification

(sedimentary, metamorphic, igneous) Environment of Formation

(description of geologic setting where rock unit may have been formed)

Limestone

Shale

Sandstone

Conglomerate

Igneous Dike

Lava Flow

10. On your outcrop correlation page (3-geologic columns), write the word WEST on the upper left corner and write the word EAST on the upper right corner. Based on the outcrop patterns you have observed answer the following questions:

a) If you were looking for the volcano which produced the 250 mybp and 100 mybp lava flows, which direction would you look. Fully explain your answer.

b) Based on sedimentary depositional models where sandstone might be deposited in a near- shore (beach) environment and shale is deposited in deep-ocean basins, which direction would you go if you wanted to find

 more continental rock units? ____________________________________________________

 more marine (deep-ocean) deposits? ___________________________________________

(hint: the sandstone unit is present in outcrop A and not present in outcrop’s B & C)

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11. Starting at the bottom of your geologic cross-section complete the description of the geologic history of this area started in the prompt below.

Approximately 250 million years before present, a lava flow was deposited in the area we are

studying. A marine shale unit with trilobite and bivalve shells was deposited next indicating that sea level rose or the land with the lava flow on it subsided, following the deposition of the shale ________

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