MICROPALEONTOLOGICAL EVIDENCE FOR CLOSURE OF THE CENTRAL AMERICAN SEAWAY

The earliest evidence for a Central American Seaway that connected tropical Atlantic and Pacific waters was Joseph Cushman’s 1929 observation that Miocene assemblages of foraminifera of Venezuela and Ecuador were identical. Since that time, the best evidence for the presence of the seaway, its constriction and complete closure has come from the micropaleontological records of speciation and extinction events, biogeographic changes, paleobathymetric studies of land-based formations of Central and South America, and geochemistry.

During Paleogene time, the Caribbean Current flowed westward through the Central American Seaway, driven by the trade winds. The rise of the Central American volcanic arc began by the early Miocene and land had emerged from North America southward to what is now central Panama. The gap between Central and South America extended to lower bathyal to abyssal depths, allowing free exchange between the tropical Atlantic and Pacific. By the la~~~~ middle Miocene, emergence of the Central American arc had begun in central Panama to southern Costa Rica. By 9 million years ago, an Atlantic-Pacific strait extended only to upper bathyal depths. Despite a regional deepening about 6 million years ago, which was probably eustatic, the deepest strait was upper bathyal. Thus, severe and protracted constriction of the Central American Seaway occurred several million years before its complete closure about 4 million years ago.