FORAMINIFERAL PALEOECOLOGY ACROSS THE EARLY-MIDDLE EOCENE TRANSITION (EMET) IN THE WESTERN CARIBBEAN

Foraminiferal faunas across the early to middle Eocene transition (EMET) were studied from two sections in the western Caribbean. The goal was to identify similarities and differences in the foraminiferal faunas from two distinct localities: the Calle G section in Cuba and ODP site 998 on the Cayman Rise.

The Calle G (Avenida de los Presidentes) section in northwestern Cuba consists of early to middle Eocene age chalks of the Universidad Group. Biostratigraphy of radiolaria, foraminifera, and nannofossils shows the section spans the EMET. The Universidad Group contains a diverse foraminiferal assemblage dominated by planktonics. The planktonic foraminiferal fauna is characterized by quantitatively abundant subbotinids and acarininids but contains no morozovellids. Oxygen isotopes were obtained from the planktonic foraminiferan Acarinina collactea across the EMET. The resultant curve shows widely fluctuating values during the early portion of the EMET with more stable values occurring in the middle Eocene. The benthic foraminiferal assemblage throughout is characterized by species of Chrysalogonium, Siphononodosaria, Nutallides, Gyroidinoides, and Cibicidoides. Values for the foraminiferal paleoecologic index tau through the Calle G section produces a curve similar to the oxygen isotope curve.

ODP site 998 on the Cayman Rise contains a series of foraminiferal limestones across the EMET. Unlike the Calle G section, this interval at site 998 contains an abundant planktonic foraminifera fauna including Morozovella. The Morozovella:Acarinina ratio studied at site 998 shows high, fluctuating values in the early part of the EMET with low, stable values in the middle Eocene.

The presence of fluctuating values of oxygen isotopes, tau, and the Morozovella:Acarinina ratio followed by stable values across the EMET may be related to a change in circulation patterns through the Caribbean caused by a developing oceanic gateway. The widely fluctuating oxygen isotope values in the latest Ypresian may also be related to an influx of freshwater in the North Atlantic associated with the coeval Azolla event in the Arctic Ocean. On-going studies at ODP site 999 and along the Rio Sambre in Jamaica may resolve the origin of this signal.