Abstract: High-Resolution Sequence Stratigraphy of Santonian-Maastrichtian Strata in Surface Exposures of the Eastern Gulf of Mexico Area, USA

Ernest A. Mancini, T. Markham Puckett, Berry H. Tew, Charles C. Smith

Since the publication of a global coastal onlap cycle chart in 1988, much discussion has resulted regarding the validity of application of these hypothesized global cycles to Cretaceous strata. Field mapping and lithostratigraphic and biostratigraphic correlation of Upper Cretaceous (Santonian to Maastrichtian) strata in the eastern Gulf Coastal Plain area has demonstrated that three genetically related, unconformity-bounded, depositional sequences of 1 to 12 million years' duration, their component systems tracts, and their defining surfaces can be recognized and traced for over a distance of 320 km. The time duration of the depositional cycles does not appear significant in that the component systems tracts can be recognized in each of these sequences regardless of dura ion. Eustasy is postulated as the major controlling factor of the cyclicity recorded in these strata, but the mechanism driving the development of parasequences within particular systems tracts appears to be the episodic introduction of siliciclastic sediment into the area.

Only the maximum flooding surface and/or condensed section strata have significance for chronostratigraphic correlation. The isochronous nature of these strata is illustrated by these beds resting within a given biostratigraphic zone throughout the eastern Gulf Coastal Plain area. Sequence boundaries and transgressive surfaces are diachronous. The transgressive deposits and their associated fauna and flora are impacted by the character of the sea level change, the rates of sedimentation and subsidence and the duration of the hiatus, resulting in these beds being assigned to different biostratigraphic zones as the strata onlap from the basin proper to the basin margin. For example, the transgressive deposits of these depositional sequences span at least two biostratigraphic zones from he deeper to the shallow parts of the basin. Depositional cycles should be dated by the synchronous maximum flooding surface rather than a diachronous sequence boundary or transgressive surface. Three such maximum flooding events are evident in these Santonian to Maastrichtian strata. They occur in lower Campanian, upper Campanian, and middle Maastrichtian strata. The availability of high resolution biostratigraphy and the establishment of standard sections is vital for comparative sequence stratigraphic analysis.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France