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Free Content Geologic History of Grecian Rocks, Key Largo Coral Reef Marine Sanctuary

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Two transects, consisting of seven 8- to 14-m deep core holes, were drilled across the major ecologic zones of Grecian Rocks (25°06′06″N, 80°18′03″W) in the Key Largo Coral Reef Marine Sanctuary to determine its internal anatomy and age. Approximately 750 by 200 m in size, the reef accumulation was found to be controlled by a local Pleistocene topographic feature. Facies in the underlying Pleistocene correspond closely with the various coral facies in the overlying Holocene reef.

Grecian Rocks Reef is composed of five major ecologic zones: (1) a deep seaward rubble zone ranging in depth from 6–8 m; (2) a poorly developed spur and groove zone composed of massive head corals and Millepora (4–6 m water depth); (3) a characteristic high-energy oriented Acropora palmata zone extending from the surface down to 4 m; (4) a distinct broad reef flat composed of in situ A. palmata and coral rubble, followed by (5) a narrow low-energy back-reef zone of unoriented A. palmata, thickets of A. cervicornis, and various massive head corals in water 0–3 m deep. An extensive grass-covered carbonate sand flat 3–4 m deep extends in a landward direction from zone 5.

Cores revealed that all the zones except the massive coral head zone are superficial coatings over a carbonate sand and rubble accumulation. A thin 1-m thick layer of lime mud and peat was found 11.5 m below sea level on the Pleistocene bedrock beneath the sand and rubble in the reef flat core hole. Carbon-14 analyses of coral from 7 m below the reef surface indicate that the reef began growing approximately 6,000 years before present.

Document Type: Research Article

Publication date: July 1, 1980

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  • The Bulletin of Marine Science is dedicated to the dissemination of high quality research from the world's oceans. All aspects of marine science are treated by the Bulletin of Marine Science, including papers in marine biology, biological oceanography, fisheries, marine affairs, applied marine physics, marine geology and geophysics, marine and atmospheric chemistry, and meteorology and physical oceanography.
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