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Abstract: Hurricane Control on Modern Reef Development.

BLANCHON, PAUL, Dept. of Geological Sciences, Indiana University, Bloomington IN47405. E-mail: [email protected]

Recent work on modern reefs around Grand Cayman has identified a significant connection between hurricanes and reef development. By analyzing the architecture and anatomy of breakwater reefs around Grand Cayman, I discovered that the reef core consists not of coral framework, but of coral-rudstone layers whose large, abraded clasts clearly implicate hurricanes as the major controlling agent. I also discovered that the reef-crest is located a uniform distance (~300 m) from a mid-shelf scarp — a distance that is proportional to the power and carrying capacity of hurricane waves. In addition to breakwater reefs, I also analyzed architectural variation in a submerged shelf-edge-reef system. This analysis showed that inter-marginal variation in shelf-edge-reef architecture results from the varying intensity of buttress pruning and sand flushing during hurricanes. Furthermore, it showed that intra-marginal variation in architecture is controlled by the angle of hurricane wave approach. This connection between modern reef development and hurricanes makes several testable predictions. First, the relation between breakwater-reef position and shelf width predicts that reefs should migrate along shore as sea-level rises and should therefore show lateral variation in reef initiation dates. Second, breakwater reef architecture should also vary as frictional interaction between storm waves and shelf changes during sea-level rise. Third, submerged shelf-edge reefs should show a predominance of lateral accretion on margins exposed to fully-developed storm waves and a proportionally greater vertical component as margins become more protected. Fourth, the correlation between hurricane intensity and shelf-edge reef architecture should also be reflected in the ecological diversity of coral associations. And finally, breakwater reefs and submerged shelf-edge reefs developed outside areas of hurricane influence should have significantly different styles of development.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah