PALYNOMORPH BIOZONES IN THE CONTEXT OF CHANGING PALEOCLIMATE, MIDDLE EOCENE TO LOWER OLIGOCENE OF THE NORTHWEST GULF OF MEXICO
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abstract
Cooling paleoclimates over the period ca. 42 Ma to ca. 33 Ma were the driving force for the gradual disappearance of tropical and subtropical elements and the appearance of cooler elements in the palynofloras of east Texas. As a consequence, 11 palynomorph assemblage zones, one range zone and three biohorizons are recognized in 209 samples from 15 sections of the Crockett, Yegua, Caddell, Manning and Catahoula formations. From oldest to youngest, the succession of biozones is: middle Eocene Nuxpollenites crockettensis Assemblage Zone, Bombapollis texensis Assemblage Zone, Bursera Assemblage Zone, Friedrichipollis claibornensis Assemblage Zone, and Reticuloidosporites pseudomurus Assemblage Zone; late Eocene Sequoiapollenites Assemblage Zone, Rhizophora FAD, Rhizophora Assemblage Zone (which contains an ancestral Mutisieae pollen type in its lower part here designated the Mutisiapollis FAD and Mutisiapollis Zone), Nudopollis terminalis Assemblage Zone, Nudopollis terminalis LAD, Bombacacidites Assemblage Zone, and Pseudolaesopollis ventosus Assemblage Zone; and the early Oligocene Hypoxylonites Assemblage Zone. The age of the lower Catahoula Formation is early Oligocene based on the occurrence of Kallosphaeridium biornatum from a locality northwest of Huntsville, Texas. A short-term cooling event near the end of the Eocene set the stage for further changes in the early Oligocene. Use of these assemblage zones greatly increases the age resolution available for late middle Eocene to early Oligocene strata of the Gulf Coast.
