2008 Joint Meeting of The Geological Society of America, Soil Science Society of America, American Society of Agronomy, Crop Science Society of America, Gulf Coast Association of Geological Societies with the Gulf Coast Section of SEPM

Paper No. 6
Presentation Time: 2:45 PM

Association of Paleoenvironment and Evolutionary Grade of Reef Constructors through the Phanerozoic

JOHNSON, Claudia C., Geological Sciences, Indiana University, 1001 E. 10th Street, Bloomington, IN 47405, claudia@indiana.edu

The Phanerozoic record of reef development and recovery after extinctions is examined through greenhouse and icehouse climate states and warm and cool thermal modes. Reef composition is examined for grade of evolution of major skeletal constructors. Results indicate that changes in climate states and climate modes are reflected in the grade of evolution of bioconstructors in the geological record of reefs. During icehouse intervals, reefs developed from cellular to tissue grade of evolution. Geologically older greenhouse reefs evolved to tissue grade whereas younger greenhouse state reefs had relatively advanced organ system grade of constructors. The biologically most advanced reef constructors, those with organ system grade of evolution, occurred during the warm climate modes of greenhouse climate states. Quaternary icehouse reefs consisted of tissue grade of evolution of the major coral skeletal constructors. In terms of biotic composition and reef numbers, transitions between icehouse and greenhouse, and greenhouse and icehouse climate states were abrupt. Transitions from warm to cool climate modes were subtle, while transitions from cool to warm climate modes represented relatively larger changes in composition and numbers of reefs. The greatest number of reefs occurred during the warm mode of the greenhouse climate when reefs were constructed by cellular and tissue grades of bioconstructors.