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A Giant Sediment Trap in the Florida Keys

Eugene A. Shinn & Christopher D. Reich
U.S. Geological Survey, St. Petersburg, Florida
and
Stanley D. Locker & Albert C. Hine
University of South Florida
Department of Marine Sciences
St. Petersburg, Florida

Abstract

Aerial photography, high resolution seismic profiling, coring and jet probing have revealed a large sediment-filled sinkhole in the Key Largo National Marine Sanctuary off Key Largo, Florida. The 600-m-diameter feature straddles coral reef and carbonate-sand facies and contains >55 m of marine lime sand and aragonite mud. Bulk 14C age determinations of mud from a 30-m sediment core indicate infilling rates exceeding 20m/ka between 3 and 5.6 ka. The total thickness and nature of the sediment near the base of the sinkhole are not known.

Location Map Modified marine navigation chart (depths in feet). Sinkhole is located in the Key Largo National Marine Sanctuary about 1 mile (1.8 km) from Key Largo Dry Rocks reef.
Introduction

The purpose of this project is to describe a large newly discovered sediment-filled sinkhole on the Florida reef tract and to speculate on the climatic information it may contain. The figure to the right shows the location of a circular feature discovered in 1991 while examining aerial photographs of the Florida reef tract. The 600-m-diameter feature lies beneath 5-7 m of water and is bordered by Holocene reefs to the east and marine grass and gorgonian-populated carbonate sand to the west. Patches of marine grass grow on carbonate sands within the circular feature, but coral are absent. The circular feature initially suggested two possible origins: (1) a sinkhole or (2) a bolide impact crater. The bolide origin was based mainly on size and the lack of sinkholes in south Florida. Sinkholes or "blueholes" this large have not been described in the marine environment of Florida or the Bahamas.

Figures

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U.S. Department of the Interior, U.S. Geological Survey, St. Petersburg Coastal and Marine Science Center
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Updated: 21 April, 1998@12:10:35 PM (THF)