Laboratory Manual for Introductory Geology 4e

EXERCISE 12.9
Correlation (continued)
Name:
Course:
Section:
Date:
During field mapping last year, trilobite fossils were found in limestone units in both areas (see the figure below).
Paleontologists reported that these trilobites were identical index fossils from a narrow span of Middle Cambrian time.
(c) Using this additional information, draw lines indicating matching layers on the figure.
(d) Why does the presence of index fossils make correlation more accurate than correlation based on lithologic and
sequence similarities alone?
Lithologic correlation of two sequences assisted by index fossils.
Western sequence
250 miles Eastern sequence
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Siltstone
Shale
Sandstone
Conglomerate
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322 CHAPTER 12 INTERPRETING GEOLOGIC HISTORY