Biostratigraphic correlation is usually accomplished by means of biozones, defined as bodies of rock strata that are characterized by their distinctive association of fossils species. The assumption is that a given biozone in one region is approximately the same age as the same biozone in a separate region, even if the regions are quite distant from one another. Many kinds of biozones are recognized. The most widely used are the taxon range biozone, concurrent range biozone, and interval biozone.
• Taxon range biozone – body of strata corresponding to the total stratigraphic range of a specified fossil taxon (e.g., species or genus)
• Concurrent range biozone – body of strata corresponding to the overlapping stratigraphic ranges of two or more specified fossil taxa
• Interval biozone – body of strata corresponding to the interval between any two specified evolutionary events (e.g., interval between two extinction events; interval between two origination events; interval between an origination event and an extinction event). Examples of these kinds of biozones are illustrated in Figure 2.
5) Illustrations of Paleozoic brachiopods, along with their known stratigraphic ranges, are given on the following two pages. Use the information on these pages to help you complete Table 1. Using pencil, shade in the stratigraphic range of each brachiopod genus listed then answer the questions on the next page. (10 points) A few notes.
· Just do the brachiopods listed on the chart. There are more brachiopods in the pictures than there are on the chart.
· Some of the brachiopods have ranges that extend off the top of the chart (say into the Jurassic) just take them to the end of the Permian.
· If a range goes from the Silurian to the Permian, for example, that includes all of the Silurian through the end of the Permian. As an example I’ve done Chonetes for you.
6) Identiy a taxon range biozone, concurrent range biozone and an interval biozone. Circle them and label them on the chart. (5 points)
7) Which would be more useful for determining the age of a rock, the taxon range zone for Stringocephalus or Chonetes? (5 points) Why? (3 points)
8) How old is a rock that contains Derbyia? (3 points)
9) How old is a rock that contains Leptaena? (3 points)
10) How old is a rock that contains Derbyia AND Leptaena? (3 points)
11) Given your answers to 7, 8 and 9 why is it usually better to do biostratigraphy with fossil assemblages (groups of fossils) than individual fossils? (5 points)
12) On the next page there is a very simple map, the lines represent boundaries between different rocks. Fossils have been collected from each of the rocks. Fill in the chart with the ages of the rocks, then label the map with the age of the rocks. (9 points)