Biostratigraphic Application and Ecology of Agglutinated Foraminifera in Gulf of Mexico Basin Cenozoic Exploration

By

Breard, S.Q., Callender, A.D., and Nault, M.J.

Applied Biostratigraphix, Houston, TX

Agglutinated foraminifera, the most primitive of all foraminiferal groups, have a long history of application in Gulf Basin exploration. Agglutinated taxa used as regional biostratigraphic markers of the neritic zone include species of Bigenerina, Clavulinoides and Textularia. Bathyal agglutinated markers include species of Cyclammina, Eggerella, Haplophragmoides, Matanzia and Tritaxilina. Both agglutinated extinctions (LADs) and agglutinant-dominated biofacies have been employed for regional as well as local correlation. A renaissance in the study of agglutinated foraminifera since the mid-1980s has contributed greatly to this application.

Ecologically, agglutinated foraminifera are found in marginal, neritic, bathyal and abyssal environments. Agglutinated biofacies are concentrated in marginal settings (brackish marsh, deltaic), more scattered throughout the shelf, and progressively more common in the bathyal zone (slope). Acme zones of selected bathyal species are especially useful in local correlation.

Biofacies dominated by agglutinated foraminifera are virtually unknown form the Gulf Basin Pleistocene, common in Pliocene and Miocene, rare, with the exception of the Hackberry Sequence, in the Oligocene, and common in the Wilcox (lower Eocene-upper Paleocene). Probable factors in the development of agglutinant-dominated biofacies include high depositional rates, water turbidity, restricted basin circulation and presence of organic-rich, fine-grained sediments. Pitfalls in application of agglutinated biofacies include improper taxonomic evaluation, taphonomic problems, habitat change through time, biofacies evolution and unknown stratigraphic ranges of agglutinated taxa.