ABSTRACT

The Wilcox Group is a reservoir-prone system containing over 3,000 ft of dominantly sandy section that records the rapid seaward progradation of a siliciclastic shelf/slope wedge onto a foundering Cretaceous surface. It is locally divided into Upper and Lower Wilcox units by an interval called the Big Shale. Biostratigraphic work has placed the upper part of the wedge in the Lower Eocene and the lower part in the Upper Paleocene. However, our examination of detailed planktonic foraminiferal and calcareous nannofossil data has shown that in some locales the entire nominal Wilcox section lies within the Eocene. The occurrence of Hantkenina spp. and planktonics characteristic of Zone P9, throughout the log-correlated upper and lower wedge, specify a Middle Eocene age. Nannofossils indicating Middle Eocene Zone NP14 (Carrizo equivalent age) confirm this assessment. Lower Eocene planktonics, no older than Zone P8, occur below the nominal Wilcox within a shaley interval containing several minor sands which may be equivalent to type Upper Wilcox (Sabinian). Because Discoaster binodosus was not seen in place, we were unable to confirm the presence of the Wilcox age nannofossil Zone, NP13. Paleocene microfossils were encountered only in a condensed marly Zone immediately overlying the Cretaceous. Our work suggests that, locally, the nominal Wilcox of southern Louisiana might be an expanded, down-dip equivalent of the Carrizo Formation, perhaps a canyon fill unit associated with the 49.5 MY sequence boundary.