Episodic reef development in a mixed carbonate-siliciclastic system, Pliocene/Pleistocene of Costa Rica; Geological Society of America, 28th annual meeting

A recently completed integrated stratigraphic study of the mixed sediments on the Caribbean side of the Isthmus of Panama (Limon, Costa Rica) has delineated two phases of reef proliferation that were controlled by changes in eustatic sea level. The older one, latest Early Pliocene, originated on siliciclastics of a prograded, shallow-marine shelf unit (Rio Banano Fm.), and corresponds with closure of the Central American isthmus. Although heavily stressed by siliciclastic input, the depositional conditions were supportive enough to stimulate origination of several modern reef-building corals. Most notably, the first occurrence of Acropora palmata is now placed significantly earlier at about approximately 3.6-4.0 Ma. The younger episode of reef development occurred around the Plio/Pleistocene boundary and is separated from the older reef unit by coarse-grained sands and gravel (Pueblo Nuevo Sands, Moin Fm.) associated with a marine regression. This younger reef sequence, also heavily sediment stressed, shows that most modern reef species were established by this time (1.9-1.6 Ma) and that accelerated extinction occurred between the two reef episodes. This sequence of reef development is coincident with several third-order sea level events, as recently documented from the Bahamas record. Relatively high sea levels in the Early Pliocene, a mid-Pliocene fall related to onset of northern hemisphere glaciation, and a highstand at the Plio/Pleistocene boundary are correlated respectively to the first reef phase, shallow marine sands, and the second reef event. Subsequent to the second reef phase, the Limon region was uplifted at least 50 m.