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Abstract

The seaward slope of the north coast of Jamaica is a region of variable reef geomorphology and marked biotic gradients. Several distinctive structural and ecological zones occur: the fore-reef, the tore-reef slope, and the deep fore-reef. Two well-defined breaks in slope are convenient reference points to define these zones and to extend reef zonation to below the limit of hermatypic scleractinian coral framework construction (Goreau, 1959). A fore-reef “escarpment,” extending from between —12 and —15 meters to —25 to —35 meters, separates the fore-reef from the fore-rec’f slope, and a pronounced dropoff at between —55 and —65 meters delineates the top of the deep fore-reef. These large scale geomorphic features are viewed as Pleistocene terraces mantled by recent reef growth to depths of less than 10 meters.

Submarine lithification by precipitation of Mg-calcite is a widespread and rapid process which adds to the solidarity of the reef and permits the existence of vertical to overhanging precipices. Submarine drilling and excavation demonstrate a vertical rate of reef growth of approximately 1.2m/1000 years at a depth —25m, which precludes the fore-reef escarpment and drop off from originating as constructional features of Holocene reef growth. Small scale geomorphic features at all depths are modified by channels of clastic dispersal which permit unconsolidated sediments to drain downslope. The scleractinian communities are self-cleansing and adapted to permit the abundant clastic debris which is produced to be shed effectively.

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