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Summary: GEOLOGY, February 2008 151
Closure of the Central American Seaway in the Pliocene isolated
the Caribbean and Pacific Basins and contributed to a pulse of extinc-
tion and origination of species of shallow-marine fauna on both sides
of Central America (Jackson et al., 1996). Studies aimed at calculating
evolutionary rates associated with this event require not only detailed
paleontological assessment, but also robust chronologies of sedimentary
units deposited prior to, during, and after the closure. One limitation to
such studies has been insufficient age control on some fossil-bearing
lithologies that has introduced significant uncertainty into the rates
of change of marine communities (Budd et al., 1996; McNeill et al.,
2000). The Cibao Valley of the Dominican Republic (Fig. 1) contains
an ~3-m.y.-long record of well-preserved fossil taxa that existed in the
Caribbean prior to final closure of the Central American Seaway. One
thoroughly studied unit in this area is the Gurabo Formation, which was
deposited prior to final closure of the Central American Seaway, but the
precise age of the Gurabo Formation remains the subject of debate. In
fact, over the past 90 yr, 19 studies have reported various and disparate
ages for Cibao Valley units; these ages have ranged from the middle


Source: Asmerom, Yemane - Department of Earth and Planetary Sciences, University of New Mexico


Collections: Geosciences