Name __________________________________________________
Per. _____
Lab - Stratigraphy and Lithologic Correlation
Geologists study sequences of sedimentary rocks on a bed-by-bed basis. They measure the
thickness of each bed, record the physical, chemical, and biological characteristics of the
rock, and note the nature of the contacts (or bedding planes) between beds. Using these data,
the geologist draws up a stratigraphic section for a particular sequence of rock. A stratigraphic
section is a graphical or pictorial representation of the sequence of rock units. Standard
symbols (called lithologic symbols) are used to refer to each rock type:
Geologists can draw stratigraphic sections for several outcrops (or cores) in an area, and then
trace beds from one section to another. This is called lithologic correlation . Basically,
correlation demonstrates the equivalency of rock units across an area. The sections being
correlated are commonly miles apart. Basically, a correlation is a hypothesis that units in two
widely separated sequences are equivalent. Clearly, the more unique characteristics that two
sections share, the greater the probability that the correlation is correct.
Lithologic correlation
Unconformity causing beds to be missing from a sequence
Exercise
In this exercise, you will practice lithologic correlation and will construct stratigraphic sections from geologic
data. To correlate the sections, you will draw lines connecting correlative contacts as shown on page 1. Use a
ruler and be as neat as possible. On the last question where you construct and correlate two stratigraphic
sections, you will need to use graph paper, and you may also wish to use colored pencils. Be certain that the
thicknesses of all of the units are to scale.
1.
a. Draw lines between the three stratigraphic sections below to connect the geologic contacts between
similar lithologies. Each column is a stratigraphic section. Each unit can be regarded as a bed.
b. How many beds can be correlated across all three sections? _________
c. How thick is the thickest stratigraphic section (or column of rocks)?
d. A bed of coal is present in sections B and C. How deep would you have to drill in section A (starting at
the top of the section, up near the letter A) to reach the buried coal seam? ________
2.
a. Draw lines to correlate the two sections below.
b. Which section (A or B) contains an unconformity? __________
c. Which units are missing from that section because of the unconformity? (Give rock types).
_______________________________
d. Label the position of the unconformity with an arrow and the word "unconformity".
e. What type of unconformity is it? ________________________
3. Using the data below from the western and eastern sections in the boxes below, do the following:
 Draw two stratigraphic sections on graph paper using the rock type and thickness data provided.
o Draw a horizontal line across the top of your paper to represent the ground surface. You will
draw the sections below this line.
o Draw the western section on the left and the eastern section on the right, about 4 inches apart.
 Locate the positions of all unconformities in the two sections (look for abrupt or erosional contacts in
the section descriptions). Mark the positions of the unconformities on your sections by using a wavy
line, and then, correlate the unconformities by extending the wavy line between the two sections. Label
your wavy lines "UNCONFORMITY", for clarity.
 Correlate the two sections by drawing lines to connect the contacts between equivalent units.
Western section – 690 ft total (strata are listed top down)
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100 ft Shale; dark gray, fissile; rare ammonoid fossils; lower contact abrupt - probably erosional.
40 ft Basalt with vesicles. (Lava flow).
35 ft Conglomerate; red to brown; no fossils.
100 ft Sandstone; white to pale red; dominantly quartz sandstone, very well sorted, rounded sand grains,
cross-bedded; no fossils.
75 ft Dolostone; tan to light gray; a few gastropod fossils present.
40 ft Limestone; light gray; oolitic limestone.
25 ft Limestone; medium gray; fossiliferous limestone; tabulate corals, crinoids, and bryozoans abundant.
Lower contact abrupt.
50 ft Conglomerate and breccia; brown to red matrix; no fossils.
75 ft Sandstone, with some conglomerate beds; brown to red; plant fossils and rare bones present.
100 ft Siltstone (brown to green) with rare coal beds; plant fossils and some bivalves.
50 ft Shale; green to gray or brown; trilobites and brachiopods present.
Eastern section – 675 ft total (top down)
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100 ft Shale; dark gray; fissile; rare ammonoid fossils present; lower contact abrupt - probably erosional.
40 ft Basalt with vesicles. (Lava flow).
75 ft Sandstone; white; dominantly quartz sandstone, very well sorted, rounded sand grains; cross-bedding
present; fossils absent.
100 ft Dolostone; tan to gray; a few gastropod fossils present.
60 ft Limestone; light gray; cross-bedded, oolitic limestone.
25 ft Limestone; medium gray; fossiliferous limestone with abundant tabulate corals.
20 ft Limestone; dark gray micrite limestone; lower contact abrupt - apparently erosional.
65 ft Sandstone with local conglomerate beds; brown to red.
50 ft Siltstone (brown, green, and gray), with rare coal beds; plant fossils present.
40 ft Shale; gray to brown; fissile; trilobite fossils present.
100 ft Limestone; gray; micrite limestone; rare brachiopods and bryozoans.
Staple your graph to this lab.