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Neogene Changes in Caribbean Paleoproductivity and Paleobathymetry of Deep-Sea Benthic Foraminifera, With Implications for the Gulf of Mexico

Abstract

The Miocene to Pliocene closure of the Central American Seaway had a profound impact on marine habitats and organisms in both the Caribbean Sea and the tropical eastern Pacific Ocean. With the gradual emergence of the Isthmus of Panama, a barrier between the Caribbean and Eastern Equatorial Pacific (EEP) was erected, preventing flow between the two regions. This study examines paleoproductivity values determined from deep-sea benthic foraminifera from the late Oligocene (~26 Ma) to early Pleistocene (~2.5 Ma), and tests the hypothesis that paleoproductivity values prior to closure of the Central American Seaway are similar in both the Caribbean and EEP, and then diverge around the time of early shoaling of the Isthmus of Panama. Benthic foraminiferal data from Caribbean ODP Site 999 are examined in conjunction with previously published data from the Caribbean (DSDP Site 502) and EEP (DSDP Sites 503, 568, and 569). Prior to the differentiation in the bottom-water source for the Caribbean and EEP (~16 Ma), they showed similar trends in organic carbon flux as measured by the Benthic Foraminiferal Accumulation Rate (BFAR). The time of the initial differentiation in bottom water is marked in the Caribbean with a sharp decrease in BFAR, followed by a large increase. When significant constriction of the seaway occurred approximately 8 Ma, Caribbean values of paleoproductivity (as recorded by increases in oligotrophic indicator species) markedly decreased and diverged from EEP values. With complete closure of the Central American Seaway (~4 Ma), the Caribbean sites showed a decrease in BFAR values and thus paleoproductivity, supporting the conclusion that without surface exchange with the nutrient-rich EEP, and together with a projected decrease in Caribbean circulation and upwelling, the Caribbean Sea established its modern oligotrophic regime. Later studies have found that the species composition and dominant species in the Caribbean were very similar to that of deep waters in the Gulf of Mexico, so that the Gulf of Mexico should yield similar results. Paleobathymetric and paleoenvironmental reconstructions were also conducted for the Caribbean samples, based on known benthic foraminiferal preferences that are also currently in use in the Gulf of Mexico.