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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

Introduction: Table of Contents Project Overview Project Objective Geologic Setting Primary Datasets Primary Products - Overview Maps & Evolution Overview: Introduction 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 Organization of Report Tiles: 1, 2, 3, 4, 5, 6, 7/8, 9/10, 11 Summary Acknowledg- ments References Disclaimer Related Publications

Tile 9/10 Geography Sector-Specific Studies Geologic Highlights Boca Grande Key, Boca Grande Channel, and the Marquesas Keys Cosgrove Shoal and Coalbin Rock Cosgrove Shoal and Coalbin Rock: Cosgrove Shoal and Coalbin Rock form a linear hardground at the shelf edge east of well site A and south of Boca Grande Key and the Marquesas Keys (Fig. 117; see Benthic Ecosystems for Tile 10). The shoals are essentially senescent (non-accreting) bank-edge reefs that are exposed to cold, turbid Gulf and Florida Bay waters. Water depth and turbidity in the area preclude clear delineation of bottom features in aerial photographs. Water visibility over these hardgrounds is seldom more than 14 m and is usually much less due to suspended mud and silt and dark green color (Shinn et al., 1990). Chlorophyll causes the color and is indicative of high-nutrient content. Other than the 1988 well-site investigation, no specific studies have been devoted to this part of the reef tract. However, judging from the well-site data, surface accretions on Cosgrove Shoal and Coalbin Rock are probably Holocene and likely consist of encrusting species typical of the hardbottom communities documented at well sites A (Fig. 124A, 124C), C (Fig. 125B, 125C, 125D), and B (Fig. 126A, 126B). continue to: Tile 11

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