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Coastal & Marine Geology Program > Center for Coastal & Watershed Studies > Professional Paper 1751

Systematic Mapping of Bedrock and Habitats along the Florida Reef Tract—Central Key Largo to Halfmoon Shoal (Gulf of Mexico)

USGS Professional Paper 1751

by Barbara H. Lidz, Christopher D. Reich, and Eugene A. Shinn

Table of Contents
Project Overview
Project Objective
Geologic Setting
Primary Datasets
Primary Products - Overview Maps & Evolution Overview:
Bedrock Surface map.
Depth to Pleistocene Bedrock Surface
Reef & Sediment Thickness
Benthic Ecosystems & Environments
Sedimentary Grains in 1989
Summary Illustration Index Map
Evolution Overview
Tile-by-Tile Analysis
Satellite image of the Florida Keys showing location of tiles.
Organization of Report
Tiles: 1, 2, 3, 4,
5, 6, 7/8, 9/10,

Tile 1

Molasses Reef and Little Molasses Island: Molasses Reef is a major reef that juts out from the margin in the Tile 1 sector (Fig. 33A, 33B). When the Gulf Stream meanders close to the shelf edge, Molasses Reef becomes vulnerable to ship groundings. One of the most damaging and best-documented groundings in the Florida Keys occurred at Molasses Reef in August 1984, when the M/V Wellwood ran hard aground and caused extensive damage. The ship pulverized ~5,000 m2 of reef (e.g., Hudson and Diaz, 1988). The Marine Sanctuary received $6.5 million in compensation in 2002. One year after hollow cement modules were placed on the site as "artificial reefs," they were encrusted with corals and sea whips and populated with fish and crustaceans. It has taken 19 years to achieve mitigation through renewed growth of the benthic community, but it has been suggested that the site is not likely to return to its pre-collision state within the next 100 years (J.H. Hudson, personal communication, 2003).

Little Molasses Island is no longer an island but the name remains. The reef is adjacent to and just north of Molasses Reef (Fig. 33A). Perkins (1977) recovered ~32.7 m of coralline limestone belonging to the Q4 and Q5 Units in a 45-m-long core drilled from a truck-mounted drill rig at Little Molasses Reef. The bottom of the Q4 Unit was not penetrated. The site represents the thickest Q4-Q5 section cored in south Florida.

Coastal & Marine Geology Program > Center for Coastal & Watershed Studies > Professional Paper 1751

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