When correlations are done over great distances, geologists use fossils and the

Question

When correlations are done over great distances, geologists use fossils and the principle of faunal succession to help determine relative ages. While finding one good index fossil may help in correlation, it is best if one can use an assemblage of fossils. If we know that age range for each fossil, it is possible to determine the period of time in which all of the fossils coexisted. Geologists use fossil assemblages was well as the first occurrence and/or the last occurrence of particular fossils to make biostratigraphic correlations. a. Look at Figure 2 on the next page and the file fossil-rock-time-range.xls correlate the stratigraphic sections using fossil assemblages. To correlate stratigraphic sections, first determine which units are equivalent. To do this, it is best to look at the sequences of beds and then draw lines from contact to contact. In this case, instead of using the rock units alone, you'll also be incorporating the fossil age ranges. You may print out Figure 2 to complete the work or use your computer software. When completed, upload the tfile for grading. b. What is the age of the units containing the trilobites, nautiloids, brachiopods, and graptolites? What is the age of the units containing the crinoids, blastoids, and conodonts? c. d. What is the age of the units containing the conodonts and fusilinids?

Explanation / Answer

B. The age of the units containing the Trilobites, Graptolites, Brachipods and Nautiloids were approximately 345 to 570myrs ago. These are all from late Paleozoic Era. Trilobites and Graptolites are from Cambrian and Ordovician periods. Brachipods are from Devonian period.

C. The age of the units containing the Crinoids,Blastoids are from Late Paleozoic era(Devonian period), approximately 395 myrs ago.

D. The Conodonts are from Cambrian period(Paleozoic era) approximately 570 myrs ago and Fusilinids from Caeboniferous period(Mesozoic era) approximately 345 myrs ago.

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