REVISED SEQUENCE STRATIGRAPHIC INTERPRETATION OF THE EOCENE-OLIGOCENEBOUNDARY INTERVAL, MISSISSIPPI AND ALABAMA, GULF-COAST BASIN, USA

Examination of regional stratigraphic relationships and graphic correl ation of biostratigraphic data from two important localities has resul ted in a new interpretation of the sequence stratigraphy of the Eocene -Oligocene boundary interval in Mississippi and Alabama. The much-stud ied section at St. Stephens Quarry in southwestern Alabama does not co ntain all of the components of the depositional sequence. At St. Steph ens, the highstand systems tract is missing and is represented by a ma rine hiatus (condensed section) at the top of the Upper Eocene Shubuta Clay. As a consequence, the surface of maximum starvation and the ove rlying sequence boundary are merged. Lowermost Oligocene sediments, wh ich were deposited in the lowstand systems tract, rest on this maximum flooding surface / sequence boundary. These findings agree with those from other parts of the Gulf Coast where the Eocene-Oligocene boundar y has been recognized as a sequence boundary associated with a subaeri al unconformity and a downward shift in coastal onlap. Revision of the sequence stratigraphic interpretation at St. Stephens Quarry alleviat es much of the confusion concerning the relationship between the Eocen e-Oligocene boundary and the sequence boundary. This new interpretatio n shows that not all sections contain all components of a particular d epositional sequence and that caution is warranted when sequence strat igraphic interpretations are used to evaluate observations. The sequen ce stratigraphic interpretation of the section at St. Stephens has und ergone revision as new observations have become available.