Data file: alveolinid.dat

Drobne (1977) compiled the occurrences of 15 species of Alveolina (a large foraminiferan) in 11 sections in the lower Eocene of Slovenia. Following Guex (1991), we will use this data set as an example of biostratigraphical correlation with the method of Unitary Associations.

Alveolina (A.) moussoulensis, 3.9 mm long. Photograph by Ralf Gietl (used with permission).

Open the file alveolinid.dat, and look at the data. The samples, in rows, are grouped by section using colors. Within each section, samples are entered in stratigraphical order from bottom to top. Try first to correlate the sections 'by eye', using for example index species of your choice. If you are several students carrying out this exercise, compare your results.

Choose 'Unitary associations' in the 'Strat' menu, and look at the statistics. View the unitary associations and the correlation. How does this correlation compare to your 'subjective' attempt? Also look at the reproducibility matrix to see which unitary associations can be identified in the different sections. Are any of the unitary associations weakly reproducible (observed in only a few sections)?

View the graph of superpositional relationships between maximal cliques, and identify cliques that occur in cycles. What does the presence of cycles imply?

Horizon 4 of section 1 contains a number of reworked specimens. Do you get a better result if you run the analysis again without this horizon?

More information about unitary association analysis can be found in the manual.

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