Eocene and Oligocene stratigraphy and erosional unconformities in the Gulf of Mexico and Gulf Coast.

Population studies of planktonic foraminifers in the Gulf of Mexico Site 94 and E67-128 and classical Gulf Coast sections in Alabama and Mississippi are analyzed with respect to stratigraphy, paleoenvironment and erosional unconformities. The Eocene- Oligocene boundary in the Gulf Coast sections is placced in the lower part of the Shubuta Member of the Yazoo Formation in agreement with nannofossil stratigraphy, and in contrast to the common placement of this boundary at the top of the Shubuta. Overlying strata of the Shubuta Member, Bumpnose and Red Bluff formations are tentatively assigned to the Pseudohastigerina micra Zone. A major middle-late Eocene (43.0-39.5 Ma) unconformity appears to be present throughout the Gulf of Mexico and North Atlantic and may correspond to global cooling and a sea-level lowstand at about 40 Ma. A probable late Eocene hiatus occurs at about 37.5-38.5 Ma (P15-P16) and marks the onset of generally cooler latest Eocene and Oligocene global paleoclimatic conditions. The middle Oligocene maximum cooling (c29 Ma) and sea-level lowstand correspond to a hiatus in shallow (less than 3000 m) deep-sea sections, but is not found in deeper low-latitude DSDP sites.-Author