ABSTRACT

In south-central Arkansas, sediments of the lower Eocene Wilcox group rest on the eroded upper surface of the Midway group of Paleocene age. An investigation of the palynomorphs present in these stratigraphic units disclosed a sharp change in spores, pollen and dinoflagellates across the Midway-Wilcox boundary.

The most abundant pollen in the Porters Creek Clay of the Midway group is a Taxodium-like form. Triporate pollen and psilate, monolete spores are also common. Aquilapollenites and Classopollis, genera common in Cretaceous rocks, are also present in the Porters Creek Clay. Dinoflagellates are abundant, but hystrichosphaerids are rare. A varied palynomorph assemblage is present in the Wilcox sediments of the area. Tricolporate pollen, a type rare in the Porters Creek Clay, is the most abundant form. The Wilcox pollen flora has a more modern aspect than that of the Porters Creek Clay. Aquilapollenites and Classopollis have not been found. Dinoflagellates and hystrichosphaerids are rare in the Wilcox sediments.

The sharp change in palynomorphs across the Midway-Wilcox boundary in this area apparently reflects both evolutionary changes in Tertiary floras and changes in the nature of the environment.