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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 11 Geography Geologic Highlights The Marquesas-Quicksands Ridge Ellis Rock and New Ground Shoal Halfmoon Shoal Rebecca Shoal The Quicksands Halfmoon Shoal: Halfmoon Shoal is a bedrock high on the southwest end of the Marquesas-Quicksands ridge (Fig. 117). No cores have been drilled at Halfmoon Shoal. The shoal lies on the same trend along the south side of the ridge as the Marquesas Keys, where cores showed that Holocene sands overlie Pleistocene oolite. Scattered rock samples, collected west of the Marquesas Keys by hand, indicate that the oolite extends westward and may reach as far as Halfmoon Shoal (Shinn et al., 1990). As elsewhere along the Florida shelf, evidence of sedimentary processes can be envisioned when sediment thickness is measured. Sand is piling up in front of rock barriers (e.g., east of Halfmoon Shoal; Fig. 135) and is accumulating in topographic lows (e.g., northwest of New Ground Shoal; Fig. 136). Figure 136. Sediment isopach map of The Quicksands area derived from seismic data (from Shinn et al., 1990). Note general sediment thickness of 1 to 4 m and two areas of thick accretions (bold arrows): 8 m in south-central area and 12 m at Halfmoon Shoal. Sands are migrating westward (as shown on Fig. 135). V = vibracore site. [larger version] continue to: Rebecca Shoal

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