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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

Primary Datasets Introduction Seismic Profiles—Data Acquisition and Processing Seismic Profiles—Data Integration Aerial Photomosaics Thin Sections of Surface Sediments Introduction: Three primary types of data sources were used in this regional project: seismic profiles (Figs. 6C, 10), aerial photomosaics (Lidz et al., 2003), and thin sections of surface sediments (e.g., Lidz and Hallock, 2000). Radioisotope dates on corals, soilstone crust, and mangrove peat recovered in cores aided interpretations of how and when features accumulated that are now visible in the seismic profiles and photos (e.g., Shinn et al., 1977a; Robbin, 1981, 1984). All datasets except thin-section results were correlated with sea-level fluctuation data from the reef tract and elsewhere (e.g., Toscano and Lundberg, 1999; Chappell and Shackleton, 1986). Figure 10. Example of the high-quality seismic profiles (1997) used in this project. This profile crossed the shelf margin and upper-slope terrace at The Elbow (upper Keys, Fig. 6C, Tile 1). Note presence of a backreef trough in the bedrock (deep "W" shape in reflection of bedrock surface under the name of the reef). The trough has been filled with Holocene reefs and sediments and has no topographic expression in the present-day sea floor. Reflections in a seismic record represent a change in acoustic (sound-wave) impedance across contacts between rock layers having different acoustic properties. In other words, seismic reflections indicate the presence of subsurface rock surfaces or stratigraphic horizons within the rock record. In this case, the stratigraphic horizon is the unconformity between Pleistocene and Holocene limestones (see Fig. 7B). Latitude and longitude in degrees and decimal minutes based on GPS coordinates. Hours (military time) below coordinates serve as navigational correlation points along seismic line. (Figure modified from Lidz et al., 2003). [larger version] continue to: Seismic Profiles—Data Acquisition and Processing

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