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Taxonomic Uniformitarianism in Gulf of Mexico Basin Cenozoic Foraminiferal Paleoecology: Is the Present Always the Key to the Past?
Taxonomic uniformitarianism, the application of recent foraminiferal data to reconstruction of ancient paleoenvironments (paleoecology), is an important, widely-used biostratigraphic tool in Gulf of Mexico Basin Cenozoic petroleum exploration. However, the application of recent data to ancient faunas has decreased utility through time. For example, faunal turnover renders Cenozoic models useless for Mesozoic paleobathymetry. Species-based models provide greater reconstruction accuracy than genera-based models, as illustrated by environmental range data from three foraminifera, Bolivina, Cibicides, and Uvigerina. Faunal assemblages are shown to be more accurate ecologic predictors than individual marker taxa.
Selected case histories of several foraminifera indicate migrations from shallow to deeper environments have occurred. Examples from invertebrate groups (mollusks and corals), vertebrates (coelacanth), and trace fossils indicate this phenomenon is not limited to foraminifera. Because of evolutionary changes in foraminiferal biofacies, it is determined that more age-specific models for paleoenvironments provide greater interpretation potential than previously published generalized models.
Paleozonation shifts do not always indicate a change in depth, but may signal some geologic event worthy of investigation. Large increases in faunal diversity and abundance may indicate other events besides paleobathymetric increases or condensed zones. These include salt gouge and rafting, unconformities, faults, flood surfaces, and clear-water events. Faunal declines may indicate shallowing, unconformities, faults, increased turbidity or rapid rates of sedimentation.
Ecologic morphotypes are frequently substituted for younger marker taxa upon extinction. However, similar shapes do not alway prove ecological compatibility. The concept of taxonomic uniformitarianism in paleoecological reconstruction using foraminifera and other groups is therefore supported, primarily as an interpretive tool for Late Cenozoic strata, but with several important caveats.
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