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The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 40 (1990), Pages 767-776

The Nature and Significance of Condensed Sections in Gulf Coast Late Neogene Sequence Stratigraphy

Bernard L. Shaffer (1)

ABSTRACT

Because it lends itself to predictable interpretations, sequence stratigraphy is gaining acceptance as a unifying concept in stratigraphy in general and in exploration in particular. Any regional seismic stratigraphic study must be predicated on a sound chronostratigraphic framework. Among the components of stratigraphic sequences and depositional systems, the condensed section is probably the most fundamental stratigraphic unit. Condensed sections are relatively thin, highly fossiliferous hemi-pelagic beds that form at the time of maximum transgression. Most reliable biostratigraphic datums occur within them, and, being regionally widespread, they are excellent chronostratigraphic markers. Since they are the only consistent tangible stratigraphic unit which ties deep water and shelf environments, they are of paramount importance in delineating sequence boundaries and systems tracts.

This paper discusses various criteria for recognizing condensed sections, and documents 20 seismically resolvable condensed sections in the pre-Wisconsin Plio-Pleistocene to uppermost Miocene of the Gulf Coast. They are recognized by abundance and species diversity peaks, and are calibrated in terms of the foraminiferal and calcareous nannofossil datums within them. All of these condensed sections are associated with an increase in paleo-water depth. As indicated by the chronostratigraphic control provided by planktonic datums, they are not random events and can be shown to be regionally correlative.

The scheme presented here has been developed in conjunction with seismic sequence studies and has been integrated with regional seismic grids. Sixteen of these condensed sections are maximum flooding events; four of them have been found to develop between lowstand slope fans and lowstand prograding wedges.

The characteristics of condensed sections in various paleo-environmental settings are discussed, and the Miocene/Pliocene transition of the Gulf Coast is related to global eustatic events.


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