FAUNAL CHANGES IN BENTHIC FORAMINIFERA AT PALEOGENE PROVINCIAL AND INTERNATIONAL STANDARD STAGE BOUNDARIES IN THE GULF COASTAL PLAIN OF THE UNITED STATES

Five distinct neritic benthic foraminiferal faunas are recognized in the Paleogene section of the Gulf Coastal Plain of the United States. These are the Midway fauna of Paleocene and early Eocene age, the Claiborne fauna of middle Eocene age, the Jackson fauna of late middle, late Eocene and earliest Oligocene age, the Vicksburg fauna of early Oligocene age, and the Chickasawhay fauna of late Oligocene age. These benthic foraminiferal faunas consist of distinct species and are characteristic of the Gulf Coast provincial stages of the same name. Only the Sabinian Stage of late Paleocene-early Eocene age does not have a distinct fauna. The Midway fauna is cosmopolitan and has been recognized in neritic rocks worldwide.

The boundaries of the Gulf Coast provincial stages are unconformities throughout the region. Major changes in benthic foraminiferal faunas appear to occur at times of low sea level with one notable exception. The Midwayan-Sabinian boundary, which represents a major lowstand and the base of the Tejas supersequence, has only small-scale changes in benthic foraminifera.

The boundaries of the Paleogene international standard stages in the Gulf Coastal Plain show little change in benthic foraminiferal faunas. Of special interest is the Paleocene-Eocene (Thanetian-Ypresian) boundary, which is marked globally by a bathyal benthic foraminiferal extinction. In the Gulf Coastal Plain, this boundary is marked by the appearance of Nonionella wilcoxensis and Alabamina obtusa rather than a significant extinction.

It is not yet clear if the benthic foraminifera in the type areas of the international standard stages have a similar pattern of faunal change at stage boundaries as do those of the Gulf Coastal Plain. Determining if the Gulf Coast benthic foraminiferal faunal changes are regional or cosmopolitan events will provide the potential for inter-regional correlation based on benthic foraminifera.