ABSTRACT: Taxonomic Uniformitarianism in Gulf of Mexico Basin Cenozoic Foraminiferal Paleoecology: Is the Present Always the Key to the Past?

BREARD, SYLVESTER Q., ARDEN D. CALLENDER, RICHARD A. DENNE, and MICHAEL J. NAULT , Applied Biostratigraphix, Houston, TX

Taxonomic uniformitarianism, the application of recent foraminiferal distribution data to reconstruction of ancient paleoenvironments, is an important, widely-used biostratigraphic tool in Gulf Coast 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 paleoecology. 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 suggest this phenomenon is not limited to foraminifera. Because many factors affect foraminiferal biofacies, it is determined that more age-specific models for paleoenvironments provide greater interpretation potential than previously published generalized models.

Large increases in faunal diversity and abundance may indicate other events besides paleodepth increases, including gouge, unconformities, flood surfaces, clear-water events or condensed zones. Faunal declines may indicate shallowing, increased turbidity or rapid sedimentation. Paleozonation shifts do not always indicate a change in depth, but may signal some geologic event worthy of investigation. Ecologic morphotypes are frequently substituted for younger marker taxa upon extinction. However, similar shapes do not always 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.

AAPG Search and Discovery Article #90908©2000 GCAGS, Houston, Texas