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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 3 Geography Sector-Specific Studies Geologic Highlights Tennessee Reef Tennessee Reef: Tennessee Reef is the only named Holocene buildup on the Pleistocene shelf-margin reef in the Tile 3 sector (Figs. 56B, 58, 67). The reef occupies an isolated bedrock high ~8 to 10 m below sea level that is surrounded by a vast sand prairie (see Benthic Ecosystems for Tile 3). Bedrock depth beneath the sand is ~10 to 14 m below sea level. It is not known whether corals became established on either side of the isolated Pleistocene reef at the time the reef began growth. If they did, they were not able to keep pace with rising sea level (e.g., Neumann and Macintyre, 1985) and are now concealed beneath sand. Benthic Ecosystems for Tile 3 [larger version] Figure 67. Aerial photo (1975) shows seafloor morphology in vicinity of Tennessee Reef (middle Keys, Fig. 56B; from Lidz et al., 2003; compare with interpreted Benthic Ecosystems for Tile 3). 'Tripod' symbol represents location of Tennessee Reef Light. Bedrock depth below sea level on the shelf behind Tennessee Reef is similar to bedrock depth under Hawk Channel (see Bedrock Surface map). This area of the shelf margin may represent a major low-elevation bedrock connection to four of the inshore channels on either side of Lower Matecumbe Key (Figs. 57, 58). Coral-rock ridges can be traced along the shelf margin (dotted lines) and at the seaward edge of the upper-slope terrace (arrows). Ovals mark areas of patch reefs on the landward ridge. Note absence of outlier reefs on the upper-slope terrace. [larger version] Contours of Pleistocene bedrock elevations in the Tile 3 sector indicate there may have been a significant connection from depressions beneath tidal channels in the middle Keys, across the bedrock low under Hawk Channel, to the low-elevation area surrounding Tennessee Reef. Tennessee Reef is southwest of the prominent depressions under Channels Two and Five, an unnamed channel, and Indian Key Channel on either side of Lower Matecumbe Key. These depressions may represent extensions of Pleistocene riverbeds that led from the Taylor Slough area to the shelf edge (Fig. 57; Davies, 1980; E.A. Shinn, USGS unpublished data). Region-wide contours indicate the connection, if it existed, may have been the largest in the keys (see Bedrock Surface map). continue to: Tile 4

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