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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 6 Geography Sector-Specific Studies Geologic Highlights Saddlebunch Keys West Washerwoman American, Maryland, and Pelican Shoals Eastern Sambo Eastern Sambo: Eastern Sambo and Maryland Shoal flank Pelican Shoal (Fig. 91B). A single, moderately well developed outlier-reef tract is positioned at the seaward terrace edge off Eastern Sambo (Fig. 89, line 2) and Maryland Shoal (Fig. 95) but is absent off Pelican Shoal (Fig. 94A). Instead, a low-relief, bedrock dune-ridge type of accretion is present in the same location off Pelican Shoal. The low-relief feature is clearly part of the outlier-reef tract but a part that simply never experienced Pleistocene coral growth, as is judged from the smoothly rounded seismic reflection. Compare its smoothness (Fig. 94A) with the jaggedness of reflections over areas of known Holocene shelf-edge coral reefs (for example, Fig. 95). There is no seismic evidence that outlier reefs ever grew off Pelican Shoal. Lidz (2004) referred to the Pelican Shoal feature as a poorly developed reef or paleoshoreline beach-dune ridge. If the Pelican Shoal terrace feature does represent a beach-dune ridge, its presence would support the hypothesis (Lidz et al., 1997a) that beach-dune ridges served as nuclei for outlier-reef development. Confirmation of the origination of this feature would require coring. continue to: Tile 7/8

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