Title

Backstepping of Holocene Reefs Along Florida's East Coast

Event Name/Location

9th International Coral Reef Symposium, Bali, Indonesia, Oct 23-27

Document Type

Conference Proceeding

Publication Date

2000

Keywords

Coral Reefs, Florida

Abstract

The northern end of the Florida Reef Tract is comprised of numerous shore-parallel ridges and terraces that crest at depths of about 15m, 10m, and 5m. The deepest ridge is most distinct and the shallow terraces are often more gradational. A hardbottom community of octocorals, sponges and corals characterizes the present-day surfaces of these bathymetric highs. By contrast, exposures in at least two of these ridges indicate that they were formed by rapidly accreting, shallow water facies dominated by Acropora palmata. In the 1970’s the construction of a sewage outfall near Hillsboro Inlet, exposed a cross-section of the deepest ridge. Earlier studies have shown that radiocarbon dates of corals from the lower ridge range from 8900+95 to 7145+80 ybp. In 1993 a submarine ran aground on a more shallow terrace near Dania Beach, exposing a 3m deep by 28m long trench. Radiocarbon dates of corals collected from this exposure at depths of 9.8m to 7.8m yielded dates ranging from 6520+60 to 5950+90 ybp. When compared with well-established sea-level curves for the western Atlantic, the dates from these exposures show these shallow-water reefs intermittently tracked the rising sea. There appears to be a backstepping pattern of the reefs, possibly related to local or global stresses from a variety of causes. Inimical conditions related to these events could have abruptly halted reef growth. As more hospitable conditions returned, a ‘new’ reef apparently formed in a shallower, shoreward position from its predecessor.

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