EARTH SCIENCE
Name: ____________
CROSS-SECTION CORRELATION
Period:
Date:
Task: To construct a geologic cross-section from three different outcrops
Purpose:
1. To reinforce the concepts of superposition, cross-cutting relations, and the correlation of similar rocks
and fossils.
2. To learn how geologists make cross-sections by correlating rocks and fossils. - . .
Vocabulary:
 Correlation - Connecting rock layers from different outcrops that are the same in rock type
and fossils present
 MYBP -Million Years Before Present
 Cross-section - A geologic picture of a slice of the earth
 Outcrop - An exposure of rock at the earth's surface
 Pinchout - When a rock bed present in one outcrop is missing in another
Procedure:
1. Work individually.
2. Label each outcrop according to the following top to bottom descriptions:
o Outcrop A- 20 meters of limestone, 30 meters oflava (l00 MYBP), 20 meters of reptile
shale, 30 meters of sandstone, 40 meters of conglomerate, and 20 meters of lava (250
MYBP)
o Outcrop B - 40 meters of limestone, 10 meters of lava (100 MYBP), 20 meters of reptile
shale, 20 meters of conglomerate, 30 meters oftrilobite/brachiopod shale, and 40 meters of
lava (250 MYBP)
o Outcrop C - 10 meters of limestone, 60 meters of reptile shale, 10 meters of conglomerate,
and 80 meters of trilobite/brachiopod shale.
3. Cut out the outcrops and glue them to a sheet of white paper in the following order:
o A on the left, B in the middle, C on the nght
o Make sure that you line up the volcanic dike that cuts each outcrop
o The tops of the outcrops will not be at the same elevation
o Space the outcrops about 1 inch apart, and remember to leave room at the bottom for a
legend
4. Correlate the outcrops in the following way:
o Locate the top of a rock layer, then draw a line to the top of the same rock layer in the next
outcrop (see picture on the next page).
o Draw a similar line between the two bottoms.
o Sometimes a bed of rock will have no corresponding bed in an adjacent outcrop. This is
called a pinchout. Just ignore it and connect the lines for the beds above and below.
5. In the areas between the outcrops sketch in the appropriate pattern: dots for sandstone, blocks for
limestone, etc.
6. Color each bed according to the following:
o Limestone: Yellow
o Shale: Gray
o Conglomerate: Orange
o Extrusive volcanic lava: Red
o Igneous intrusion: Pink
o Sandstone: Tan
o Fossils: Yellow
7. Construct a legend at the bottom that shows the pattern, color, and name of each rock type and fossil.
Analysis Questions (use complete responses):
1. Is the 100 MYBP lava older or younger than the shale with reptile fossils in it? Which relative dating
concept supports this?
2. What law would you use to support this statement: "The igneous intrusion could be the youngest event
on your cross-section"?
3. Give two lines of evidence (principles of relative dating) that supports this statement: "The reptile shale
is younger than the brachiopod/trilobite shale".
4. What factors might cause a rock layer to form a pinchout?
5. Why are there no trilobite fossils in the layer of shale with the reptile fossils? Which principle of
relative dating applies?