USGS Home
Contact USGS
Search USGS

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 7/8 Geography Sector-Specific Studies Geologic Highlights Margin Evolution Flooding the Florida Shelf Addendum Introduction New Evidence for Interpretation of the Nearshore Rock Ledge New Coral Reef Nuclei When Did the Upper-Slope Terrace Form? Why Did the Pleistocene Reefs Become So Imposing? Age of the Marquesas - Quicksand Ridge Ephemeral Islands and Lighthouses New Coral Reef Nuclei: Four types of coral reef nuclei in the Florida reef record are now known: outer-shelf beach-dune ridges and antecedent coral reefs (Perkins, 1977; Shinn et al., 1977a; Multer et al., 2002), the nearshore oolite-and-coral ledge (Marsalek, 1977), and inner-shelf topographic troughs (Lidz et al., 2006). The trough edges underlie prominent patch-reef clusters at Mosquito Bank, East Turtle Shoal, East Washerwoman Shoal, and West Washerwoman. Discovery of the trough-edge nuclei also yielded other 'firsts' in the Florida record. (1) The troughs and their edges are presumed to consist of grainstone/packstone (cemented carbonate sands of different size fractions), such as are found elsewhere in the bedrock beneath Hawk Channel (Reich et al., 2002; Multer et al., 2002). This type of substrate differs from those of beach-dune ridges and antecedent reefs and oolite. (2) The seagrass/lime-mud habitat is restricted to and extends throughout Hawk Channel, including within and around the troughs (Figs. 75, 78A, 87A, 87B; see Benthic Ecosystems map). This habitat also differs from that of the dune ridges, which would have been bare beach-sand limestone until coral colonization, and from that of the antecedent reefs and oolite, which would have been reefal and oolitic hardbottoms. (3) Beach dunes and antecedent reefs and tidal bars would have been elevated above surrounding topography. The trough edges, though higher than depths within the troughs, are at the same relative depth as substrate elsewhere along the axis of the bedrock depression beneath Hawk Channel (Lidz et al., 2006). (4) Trough locations within Hawk Channel are along the seaward side of the inner shelf. With the exception of the nearshore rock ledge, which is believed to consist of the Key Largo Limestone reef and the Miami Limestone oolite (Lidz et al., 2006) and whose outer edge harbors individual patch reefs (Figs. 87A, 87B, 104), no other discrete inner-shelf reef nuclei are known. The beach-dune and antecedent-reef nuclei are found along the outer shelf. Thus, the topographic troughs, seagrass/lime-mud habitat, grainstone/packstone substrate, and inner-shelf sites for coral reef nuclei each constitute new information in the well-studied reef record of Florida. Depositional controls throughout the stratigraphic record were fluctuating sea level, highstand apices, surf-zone location, antecedent topography, and precursor substrate type (Lidz, in press; Lidz et al., in press). continue to: When Did the Upper-Slope Terrace Form?

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