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Diversity-equitability analysis of microfaunal data as used by Beerbower and Jordan shows promise of being a rapid and useful technique for mapping paleoenvironmental gradients. It may even provide a more satisfactory definition of environmental boundaries than biofacies analysis based on taxonomic composition.
Faunal diversity is calculated as Shannon's information theory average uncertainty measure. Using this diversity measure, a few equally common taxa can yield as high a diversity index as many unequally common taxa. Lloyd and Ghelardi's equitability index may be used to separate these two diversity components and refine seemingly homogeneous data.
Recent microfaunal data from Barnstable Harbor, Massachusetts, and the northern Gulf of Mexico have been subjected to diversity-equitability analysis. From Barnstable Harbor, contours based on the equitability index can be related rather clearly to tidal action within the harbor. A diversity-equitability plot of published Holocene Gulf of Mexico data reveals that some environments may be characterized by a unique D/E range. Although these results must be considered preliminary, an analysis of parts of the lower Miocene sequence in Block 24 field, High Island area, offshore Texas, shows that the technique merits further consideration and is potentially a very useful tool for both identifying and mapping ancient environments.
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