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Regional Quaternary submarine geomorphology in the Florida Keys

Barbara H. Lidz
Christopher D. Reich
Eugene A. Shinn

U.S. Geological Survey, 600 Fourth Street South, St. Petersburg, Florida 33701, USA

Posted with permission from Lidz, Barbara H.; Reich, Christopher D.; Shinn, Eugene A. GSA Bulletin; July 2003; v. 115; no. 7; p. 845-866; 15 figures; 1 table. Copyright 2003 Geological Society of America. Note: Paper is also available from the Geological Society of America Bulletin website (journal subscription is required)


Introduction & Background
PDF version
High-quality seismic reflection profiles fill a major gap in geophysical data along the south Florida shelf, allowing updated interpretations of the history of the Quaternary coral reef system. Incorporation of the new and existing data sets provides the basis for detailed color maps of the Pleistocene surface and thickness of overlying Holocene accretions. The maps cover the Florida Keys to a margin-wide upper-slope terrace (30 to 40 m deep) and extend from The Elbow Reef (north Key Largo) to Rebecca Shoal (Gulf of Mexico). The data indicate that Pleistocene bedrock is several meters deeper to the southwest than to the northeast, yet in general, Holocene sediments are ~3 to 4 m thick shelf-wide. The Pleistocene map demonstrates the significance of a westward-dipping bedrock surface to Holocene flooding history and coral reef evolution. Seismic facies show evidence for two possible Holocene stillstands.

Aerial photographs provide information on the seabed surface, much of which is below seismic resolution. The photographs define a prominent, regional nearshore rock ledge that extends ~2.5 km seaward from the keys' shoreline. They show that bands of rock ridges exist along the outer shelf and on the upper-slope terrace. The photographs also reveal four tracts of outlier reefs on the terrace, one more than had been documented seismically. Seismic and photographic data indicate the tracts are >200 km long, nearly four times longer than previously thought. New interpretations provide insights into a youngest possible terrace age (ca. 175 ka?) and the likelihood that precise ages of oxygen isotope substage 5e oöid tidal-bar and coral reef components may differ. The tidal-bar/reef complex forms the Florida Keys.

Keywords: contour maps, coral reefs, Florida Keys, geophysical investigations, outliers, regional sea-level changes.

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† E-mail: blidz@usgs.gov.

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