THE EARLY-MIDDLE EOCENE TRANSITION IN THE NORTHWESTERN CARIBBEAN: STUDIES FROM CUBA, JAMAICA, AND THE CAYMAN RISE

The early to middle Eocene transition (EMET) represents a time between 50 and 48 mybp when the Earth had a warm, but not extreme, climate. It follows an event of intense global warmth, the Early Eocene Thermal Maximum, at approximately 55 mybp and precedes the development of the first Antarctic glaciation at approximately 40 mybp. The EMET, however, does not represent a simple transition from “greenhouse” to “icehouse” climate modes. Rather, it represents a transitional episode with a reorganization of global climate patterns and ocean circulation. The Caribbean Basin is an important region to study the EMET as the development of oceanic gateways in this province during the Eocene may have played a role in the reconfiguration of ocean currents influencing climate change.

Planktonic foraminifera from three sections containing the EMET in the northwestern Caribbean were studied. In the Calle G section of Cuba, early to middle Eocene age chalks of the Universidad Group contained planktonic foraminiferal assemblages dominated by subbotinids and acarininids. Oxygen isotopes through the EMET in the Calle G section show widely fluctuating values during the latest Ypresian with the development of cooler, stable conditions into the middle Eocene. In the Rio Sambre section in northeastern Jamaica, shales of the Langley Member of the Richmond Formation produced a diverse assemblage of planktonic foraminifera. The planktonic assemblages in the Ypresian are dominated by morozovellids while those in the earliest Lutetian are dominated by subbotinids indicating a transition from warmer to cooler water conditions. A similar pattern was seen through the EMET in thin-sections from ODP site 998 on the Cayman Rise.

The results suggest an important paleoceanographic change occurred in the western Caribbean Basin during the EMET. The presence of warm but fluctuating conditions in the latest Ypresian followed by slightly cooler but more stable conditions may be related to a change in circulation patterns through the Caribbean. Foraminiferal records from piston cores on Beata Ridge during this interval show a transition from a pelagic environment to a neritic environment. It seems likely that Beata Ridge developed as a positive feature during the EMET and may have functioned as an oceanic gateway into the late Eocene.