DID INITIAL CONSTRAIN OF THE CENTRAL AMERICAN SEAWAY INDUCE PALEOPRODUCTIVITY CHANGES IN THE SOUTHERN PROTO-CARIBBEAN DURING THE EARLY MIOCENE?

The formation of the Panama Isthmus played a major role in the reorganization of global ocean circulation and modified oceanographic conditions on both sides of the gateway. Tectonic collision between the Panama microplate and the South American plate began at ~25 Ma, leading to the (1) final closure of the Central American Seaway (CAS) during the late Miocene (~12–10 Ma), and (2) full emergence of the Panama Isthmus during the middle Pliocene (~4.2–3.5 Ma). Although several paleontological studies have assessed the role of the formation of the Panama Isthmus in primary productivity during the Late Neogene, few studies have quantified the distribution and abundance of primary producers throughout the Neogene. Here, we present novel data on early Miocene (~24.1–17.3 Ma) dinoflagellate cysts (dinocysts) from the southern proto-Caribbean. Our results reveal a conspicuous shift from peridinioid-dominated (mostly heterotrophic) to gonyaulacoid-dominated (mostly autotrophic) dinocyst communities near the Aquitanian–Burdigalian boundary (~20.7 Ma). This decline in paleoproductivity does not appear to be related to taphonomy, local tectonics, changes in local precipitation, or terrestrial runoff. We hypothesize that this reduction in marine primary productivity may have been driven by the initial constriction of the CAS. Additional studies of Neogene sequences in the eastern equatorial Pacific and Caribbean are required to better understand the response of primary producers to the formation of the Panama Isthmus.