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Open-File Report 2012–1095

Holocene Core Logs and Site Methods for Modern Reef and Head-Coral Cores: Dry Tortugas National Park, Florida

By Todd D. Hickey, Christopher D. Reich, Kristine L. Delong, Richard Z. Poore, and John C. Brock

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Introduction

The Dry Tortugas are a series of islands, banks, and channels on a carbonate platform off the west end of the Florida Keys. Antecedent topography of the Dry Tortugas reflects carbonate accumulations of the last interglacial (marine isotope substage 5e, ~ 125,000 years ago, ka) when sea level was ~ 6 to 7 meters (m) higher than present (Schrag and others, 2002). The substage 5e surface was subsequently lithified and modified during subaerial exposure associated with lower sea level from ~ 120 ka to 8 ka. The lithified late Pleistocene carbonates are known as the Key Largo Limestone, a coral reef (Hoffmeister and Multer, 1964; Multer and others, 2002), and the Miami Limestone, a tidal-bar oolite (Sanford, 1909; Hoffmeister, 1974). The Holocene and modern sediments and reefs of the Dry Tortugas then accreted during the rise of sea level associated with the end of the last glacial and the start of the current interglacial (marine isotope Stage 1).

With the exception of a half dozen or so islands, the Dry Tortugas region has been submerged for approximately 8,000 years, allowing conditions suitable for coral reef formation once again. The Holocene reef accumulation varies in thickness due to the antecedent topography. The reefs are composed of massive head corals such as species of Montastraea, Siderastrea, and Diploria (Swart and others, 1996; Cohen and McConnaughey, 2003) and rest atop the Pleistocene Key Largo Limestone high (Shinn and others, 1977). The coral reefs within the Dry Tortugas represent a windward reef margin relative to dominant wind and wave energies (Hine and Mullins, 1983; Mallinson and others, 1997; Mallinson and others, 2003).

First posted March 5, 2013

For additional information contact:
U.S. Geological Survey
St. Petersburg Coastal and Marine Science Center
600 4th Street South
St. Petersburg, Florida 33701
http://coastal.er.usgs.gov/

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Suggested citation:

Hickey, T.D., Reich, C.D., Delong, K.L., Poore, R.Z., and Brock, J.C., 2013, Holocene core logs and site methods for modern reef and head-coral cores – Dry Tortugas National Park, Florida: U.S. Geological Survey Open-File Report 2012–1095, 27 p., available at http://pubs.usgs.gov/of/2012/1095.



Contents

Introduction

Methods

Results and Summary

Acknowledgments

References Cited

Appendix 1. Photographs of cored corals, Dry Tortugas National Park, Florida.

Appendix 2. Lithologic logs and core photographs, Dry Tortugas National Park, Florida.


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