Timing of latest Eocene molluscan extinction patterns in Mississippi

Molluscs removed from 12 bulk samples of the Yazoo Formation (zipper Eocene), exposed in a quarry at Cynthia, Mississippi, are similar in composition and diversity to those found in the underlying upper Eocene Moodys Branch Formation, when differences in outcrop area are considered (74% of the Yazoo species are also found in the Moodys Branch). This suggests there was no significant extinction during the late Eocene (at the P15/P16 biozone boundary) as has been reported for planktic foraminifera. Only 11.4% of the species from the Yazoo extend into the Oligocene Red Bluff Formation, suggesting a large molluscan extinction. at or near the Eocene-Oligocene boundary The presence in the lowermost Red Bluff of an assemblage with a relatively high diversity dominated by suspension-feeding bivalves suggests that the molluscan fauna had recovered from the extinction by the earliest Oligocene.