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Abstract: Biostratigraphy and Paleoecologic Tolerances of Oligocene Through Paleocene Foraminiferal Assemblages of the Gulf Coast Basin

S. Q. Breard, M. J. Nault, A. D. Callender

Operationally oriented biostratigraphic and paleoecologic models are developed for Paleocene, Eocene, and Oligocene foraminifera of the Gulf Coast Basin. This paper is a companion to Breard et al. (1993 GCAGS Transactions, p. 493-502), which describes models of significant paleoecologic and biostratigraphic foraminifera of the Miocene through Pleistocene of this region.

Key benthic paleoenvironmental markers for particular depth zones of the Paleogene are graphically presented, along with an updated biostratigraphic chart. Estimates of environmental ranges for optimal stratigraphic utility are listed for all marker species.

Several trends are noted when comparing Paleogene to Neogene and younger foraminiferal assemblages. Pre-Oligocene planktic diversity tends to be high, and many planktic species range as high as the inner shelf, which is considerably shallower than most Neogene occurrences. This is probably a result of higher paleotemperatures during the Eocene and Paleocene. Because the Paleogene zonation was derived from both well and outcrop studies, the biostratigraphy of that time can be tied to Gulf Coast lithostratigraphy, whereas the Neogene of the Gulf Coast shelf section is known almost entirely from the subsurface.

Recognition of finer environmental subdivisions is more difficult with increasing geologic time when biostratigraphic and environmental resolution become more broad. Reliance on similar morphotypes replaces the use of living fauna for determining environmental tolerances, especially in pre-Oligocene strata.

Combination of data from these charts with Breard et al. (1993) will allow explorationists to estimate environmental tolerances for the entire Cenozoic biostratigraphic column. This should serve as a predictive tool for foraminiferal studies useful in the exploration and production of oil and gas for the post-Mesozoic strata of the Gulf Coast Basin and beyond.

AAPG Search and Discovery Article #90983©1994 GCAGS and Gulf Coast SEPM 44th Annual Meeting, Austin, Texas, October 6-7, 1994