Contradictory Trends in the History of Cenzoic Corals and Coral Reefs: Oceanographic Change and Biotic Response

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9909485JacksonA fundamental question in paleontology concerns the consistency of biotic responses to environmental perturbations that occur repeatedly but in different contexts in earth history. The aim of this research project is to document the response of Cenozoic Caribbean reef coral communities to changes in paleoceanographic conditions during two episodes of rapid biotic change. Large numbers of coral species became extinct during both the Early Miocene and Early Pleistocene, and extensive reef tracts disappeared from the Caribbean during the Early Miocene transition and did not return until after the Early Pleistocene extinction. Therefore, the regional development of constructional coral reef ecosystems is apparently not correlated with coral species diversity. This paradox suggests that these two episodes were associated with alternating paleoceanographic conditions. One model proposes a switch from predominant benthic to planktonic productivity during the Early Miocene followed by a switch back to more oligotrophic conditions during the Pleistocene. We will explore this hypothesis through rigorous documentation of the changing patterns of reef-coral diversity and by regional analysis of the biotic component of sediments.Exposures of Late Oligocene to Middle Miocene coral bearing rocks will be examined along an east-west transect extending from the gulf coast of North America to the windward isles. Large new collections of fossil corals will be made to supplement existing museum collections and a new database of species level occurrences will be compiled. This database will be added to the existing Late Neogene data to determine rates of species appearance and disappearance in the Northern Caribbean. The relative contribution of heterotrophic and phototrophic/mixotrophic organisms to near shore sediments provide a proxy for paleoproductivity that is independent of coral diversity. This will be evaluated using lithological samples from each of the study sites.