EOCENE-OLIGOCENE MOLLUSCAN EXTINCTIONS AND FIRST APPEARANCE DATA ACROSS THE NORTH ATLANTIC IN THE NORTH AMERICAN GULF COASTAL PLAIN AND EUROPE

In March of 1846, Charles Lyell visited the type Jackson Group locality in Jackson, Mississippi, and recognized the locality to be of Eocene age and to be younger than the type Claiborne Group section (Eocene) on the Alabama River at Claiborne, Alabama, and older than the type Vicksburg Group section (Oligocene) at Vicksburg, Mississippi. These early correlations were based largely on molluscan faunas, which, because of synchronously-timed extinctions and first appearances of species across the northern Atlantic Ocean, proved to contain excellent guide fossils for the determination of geologic time. The end of the Eocene is marked by the extinction of the Venericardia planicosta (marine bivalve) stock and the demise of several strombid (marine gastropod) taxa. Coinciding with this is the absence of the solitary coral Flabellum in the Oligocene of the northern Gulf and the absence of all corals in northern Europe at latitudes above that of the Aquitaine Basin of southwestern France. Many Oligocene molluscan species of the northern Gulf show little relationship to the local Eocene faunas but closely resemble those of the Aquitaine Basin of France. This French-North American Oligocene molluscan connection indicates that ocean currents were effective in the trans-Atlantic transport of planktotrophic molluscan larvae.