PALEOGENE CHRONOSTRATIGRAPHY IN THE EASTERN GULF COASTAL PLAIN AND THE GLOBAL STRATOTYPE SECTIONS AND POINTS (GSSPS)

Chronostratigraphic correlation in the Paleogene of the eastern Gulf Coastal Plain has traditionally been facilitated through the use of numerous regional stages. Biostratigraphic zonations based on marine invertebrates and benthic foraminifera enabled regional correlation of both surface and subsurface sections throughout the Gulf Coastal Plain. The application of calcareous nannofossil and planktonic foraminiferal biostratigraphy to the Gulf Coastal plain has enabled correlation to the global geologic time scale and the recognition of Paleogene standard stages. These correlations were made before the establishment of GSSPs which define the Paleogene stages. Of the 9 ratified or proposed GSSPs, 3 (the Ypresian, the Rupelian, and the proposed Chattian) require a change in the correlation of those stages with the eastern Gulf Coastal Plain.

The Ypresian GSSP is in the Dabibaya section in Egypt at base of the Carbon Isotope Excursion (CIE) which characterizes the Paleocene-Eocene Thermal Maximum. The Paleocene-Eocene boundary in the Gulf Coast region has traditionally been placed above the highest occurrence (HO) of the planktonic foraminiferan Morozovella velascoensis at a level corresponding to the Tuscahoma-Hatchetigbee lithostratigraphic boundary. The HO of M. velascoensis occurs above the CIE at Dabibaya.

The Rupelian GSSP (Eocene-Oligocene boundary) is in the Massignano section, Italy at the HO of the planktonic foraminiferan Hantkenina alabamensis. The Eocene-Oligocene boundary in the eastern Gulf Coastal Plain has traditionally been placed at the Yazoo-Red Bluff/Forest Hill contact. Biostratigraphic work on the Mossy Grove and St. Stephens cores shows that the Rupelian GSSP correlates to a horizon within the upper Yazoo Clay.

The proposed Chattian GSSP will be in the Monte Cagnero section in Italy and will likely correspond to the O4/O5 planktonic foraminiferal zone boundary. In the Gulf Coastal Plain, the Rupelian-Chattian boundary has traditionally been placed at the Byram-Chickasawhay lithostratigraphic contact. Magnetostratigraphy in the St. Stephens core suggests this contact is below the proposed Chattian GSSP. Planktonic foraminifera in the Paynes Hammock Formation indicate an age no older than late Rupelian but cannot be correlated directly with the proposed Chattian GSSP.