Title

Palynological Patterns in Uppermost Eocene to Lower Oligocene Sedimentary Rocks in the U.S. Gulf Coast

Abstract

Climate, vegetation, sediment supply, and burial conditions play important roles in the diversity and abundance of palynomorphs transported into and preserved in depositional sequences. Preserved palynological assemblages (spores, pollen, dinoflagellate cysts, and palynofacies) can be used to recognize past vegetation patterns, climates, and sea-level fluctuations, and such a model is used here to interpret the upper Eocene to lowermost Oligocene Pachuta and Shubuta Members of the Yazoo Formation, and the lower Oligocene Vicksburg Group in southeastern Mississippi and southwestern Alabama. Of the 260 spore and pollen taxa identified, eleven groups representing about 50% of the taxa have been recognized on the basis of abundance, occurrence in most samples and ecological significance. The most prominent groups are Sequoiapollenites-Cupressacites, Momipites, Carya, Quercoidites, Cupuliferoipollenites, Cyrillaceaepollenites, and Siltaria. Statistical analysis on presence-absence data produced five significant cluster groups that were dominated by species of the 11 groups, as well as by Ulminpollenites thompsonianus and Salixipollenites parvus. These cluster groups show some ecological significance because they appear to represent upland, swamp, and marsh taxa that were either preserved in the nearshore sediments or dispersed into the shallow-marine environment. The prominence of Quercoidites, Sequoiapollenites, Cupressacites, and Cyrillaceaepollenites in the rich pollen assemblage, which contains some tropical to subtropical elements, such as Psilatricolporites operculatus and Nyssapollenites pulvinus, suggests a warm-temperate paleoclimate during the early Oligocene in the study area. Although Momipites was generally more abundant in the Eocene and Quercoidites increased during the Oligocene, there was no significant paleofloristic change across the Eocene/Oligocene boundary. The major floral turnover along the Gulf Coast occurred well before the deposition of the Vicksburg units during the early Oligocene, probably in the middle Eocene. This observation is confirmed by dinoflagellate cyst (dinocyst) data that do not show any significant change in standing diversity, or in turnover rates across the Eocene/Oligocene boundary. A combination of dinocyst paleoecology, palynofacies, and lithofacies formed the basis of sequence stratigraphic interpretations. In southern Mississippi, we identified a latest Eocene maximum flooding surface in the middle of the Shubuta Clay, but this surface was identified at the top of the Shubuta Clay in southern Alabama, where the Eocene/Oligocene boundary was placed within a condensed interval. This condensation, which was identified at the Shubuta Clay-Vicksburg Group contact, is equivalent to the accumulation of the upper Shubuta Clay and Red Bluff Clay in southern Mississippi.

Department(s)

Geosciences and Geological and Petroleum Engineering

Library of Congress Subject Headings

Eocene-Oligocene boundary
Eoceno
Fauna marinha
Marine animals, fossil -- North America
Oligoceno

Geographic Coverage

U.S. Gulf Coast

Time Period

Eocene
Oligocene

International Standard Book Number (ISBN)

9780231127165

Document Type

Book - Chapter

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2003 Columbia University Press, All rights reserved.

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