Outcrops of upper Miocene to upper Pliocene sediments in the Bocas del Toro Basin contain a record of the emergence of the southern Central American isthmus. Paleodepths and characteristics of past sedimentary regimes within the basin were determined from benthic foraminiferal species assemblages. The present Valiente Peninsula shallowed from upper bathyal depths of about 300-500 m to outer neritic depths of 150-200 m between latest Miocene (5.6-6.5 Ma) and middle Pliocene (3.5-3.6 Ma) times. Outer neritic assemblages from about 100-150 m paleodepth on the island of Escudo de Veraguas indicate negligible emergence through the late Pliocene, and their present sea-level altitude suggests rapid Quaternary shallowing. Middle neritic foraminiferal assemblages of Cayo Agua island shallowed from depths of about 40-80 m to 20-40 m between early (4.5-5.0 Ma) and middle (3.5-3.6 Ma) Pliocene times. Cayo Agua assemblages indicate establishment of a carbonate regime in the southwestern Caribbean region prior to complete closure of the Caribbean-East Pacific seaway around 3.5 Ma. -Author
