DIVERGENCE OF LATE MIOCENE CARIBBEAN AND EASTERN PACIFIC TROPICAL BENTHIC FORAMINIFERA: EVIDENCE FROM ECUADOR AND CARIBBEAN PANAMA
The Rio Indio facies of the Chagres Formation, which crops out near the Caribbean entrance to the Panama Canal, is middle neritic. Benthic foraminiferal assemblages are dominantly Atlantic in affinity or cosmopolitan, and include few taxa that are or were primarily Pacific.
The Angostura Formation, NW coast of Ecuador, includes middle neritic and shallow outer neritic facies exposed along the Rio Santiago and Punta Verde, respectively. Unlike most of the Miocene neritic sediments of Panama and Colombia, these were well oxygenated and contained diverse faunas, allowing direct comparison with those of the Caribbean. The deeper assemblage of benthic foraminifera contains more endemic species (e.g., Epistominella sandiegoensis, Hanzawaia evansi) than does the shallower assemblage, but many of the species were still transisthmian in the Late Miocene.
The species distributions indicate a stage of developing endemism in Late Miocene, Eastern Pacific faunas. The deeper, outer neritic faunas of the Angostura Formation show greater divergence with the Caribbean than shallower, middle neritic faunas. Deeper faunas should have been affected first by the rise of the sill that severed the connection between tropical Atlantic and Eastern Pacific faunas.