Early oligocene palynosequences in the eastern Gulf Coast, U.S.A.

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Abstract
Palynomorph data from two localities in southwestern Alabama and southeastern Mississippi have been used to interpret the palynofloral succession of six of the seven lithostratigraphic units of the Vicksburg Group, to test the current sequence stratigraphic framework for the area, and to infer paleoclimatic conditions during the Early Oligocene. The samples group statistically by multivariate methods according to sporomorph types and relative frequencies, and two broad groups of high and low diversity assemblages have been identified. Quercoidites, Carya, Momipites, Siltaria sp. cf. S. scabriextima, Cupressacites hiatipites and Cupuliferoipollenites dominate the high diversity assemblage in the Bumpnose Limestone, Red Bluff Clay, Forest Hill Sand and Bucatunna Clay. These lithostratigraphic units have previously been interpreted as deposits of a highstand systems tract. The main difference between the Bucatunna sporomorph assemblage and that of the other units is the absence of the two taxodiaceous conifer pollen species resembling Sequoia. The Mint Spring Marl, which is considered the lower part of a transgressive systems tract, is slightly less diverse than the highstand deposits, but the assemblage is rich in the two Sequoia type pollen species. In southwestern Alabama, nonmarine palynomorphs outnumber marine palynomorphs in this unit, whereas the marine palynomorphs are the dominant constituents in southeastern Mississippi. This a reflection of transgression progressing from southeast to northwest that resulted in a thinner, older and more marginal Mint Spring facies in Alabama. The low diversity assemblage is present in the transgressive Marianna Limestone and highstand Glendon Limestone. The Marianna Limestone has fewer sporomorphs than the underlying Mint Spring Marl, with Sequoia type pollen also accounting for >70% of counted sporomorphs, but the unit is much richer in marine palynomorphs than nonmarine palynomorphs. The Glendon Formation has the poorest recovery of nonmarine and marine palynomorphs among the sediments, and this poor recovery may be related to diagenetic processes.