ABSTRACT

Agglutinated (arenaceous) foraminifera, the most primitive of all foraminiferal groups, have a long history of application in Gulf of Mexico (GOM) 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 or LAD's (Last Appearance Datum's or First Down Hole Occurrence) 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-1980's 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 from the Gulf of Mexico Basin Pleistocene, common in Pliocene and Miocene, rare, with the exception of the Oligocene Hackberry Sequence, and common in the Wilcox (lower Eocene-upper Paleocene). Probable factors in the development of agglutinant dominated biofacies include lack of calcium carbonate, high depositional rates, increased 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.