Abstract: High Resolution Biostratigrapic Component of Sequence Stratigraphic Analysis: Key to Correlation of Paleogene Strata in the Eastern Gulf Coastal Plain

Ernest A. Mancini, Berry H. Tew

The biostratigraphic component of an integrated geochronologic, biostratigraphic, and sequence stratigraphic approach is critical for correlation of marginal marine strata to lithofacies equivalent and genetically related marine shelf and deeper marine deposits. In general, the occurrence of age diagnostic calcareous nannoplankton and planktonic foraminifera necessary for biozonal assignment is confined to glauconitic sand and marl beds of the transgressive systems tracts and condensed sections of third-order, unconformity-bounded depositional sequences in the Paleogene strata of the eastern Gulf Coastal Plain. In addition to chronostratigraphic information provided by biostratigraphy, potentially useful geochronologic data based on radiometric age determinations can be derived from a thigenic glauconite contained in these marine strata. Age data acquired from transgressive systems tract and condensed section rocks can be used in conjunction with chronostratigraphically significant physical surfaces associated with depositional sequences to provide a framework within which to correlate lithologically diverse strata representing various depositional settings during a specific interval of time. Physical surfaces that are associated with a depositional sequence and have chronostratigraphic significance include the upper and lower sequence bounding unconformities, the initial flooding surface or transgressive surface, and the maximum flooding surface or surface of maximum transgression. These bracketing physical surfaces can be used as constraints to interpret relative ti e lines at various points within a sequence. The maximum flooding surface within a depositional sequence is an important datum for correlation because this surface represents an essentially isochronous horizon. This physical surface is the turnaround point in sedimentation from retrogradation or aggradation (transgressive systems tract) to progradation (highstand systems tract). The lower and upper bounding surfaces of a depositional sequence, as well as the first transgressive surface, are useful for both physical correlation and as chronostratigraphic constraints. Although these physical surfaces are diachronous along their traces, they are event markers and in all cases separate older rocks below from younger rocks above. Thus, an integrated approach using biostratigraphy, geochronolo y, and sequence stratigraphy provides a useful mechanism for correlation of marginal marine to marine shelf and deeper marine strata within a physically constrained framework that can be directly correlated to existing chronostratigraphic schemes.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994