--> Abstract: Multiple Outlier-Reef Tracts off a Carbonate Platform: A New Type of Windward Margin (South Florida), by B. H. Lidz, A. C. Hine, and E. A. Shinn; #91004 (1991)

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Multiple Outlier-Reef Tracts off a Carbonate Platform: A New Type of Windward Margin (South Florida)

LIDZ, BARBARA H., U.S. Geological Survey, St. Petersburg, FL, ALBERT C. HINE, University of South Florida, St. Petersburg, FL, and EUGENE A. SHINN, U.S. Geological Survey, St. Petersburg, FL

A new set of sidescan-sonar imagery and high-resolution seismic-reflection profiles provides enhanced definition of a system of multiple outlier-reef tracts off the lower Florida Keys. The reefs occur approximately 0.5 to 1.5 km seaward of the south Florida bank margin. The system comprises a massive, outer, main reef tract of high (28 m) unburied relief that parallels the margin, and at least two narrower, discontinuous reef tracts of lower relief between the main tract and the shallow platform-margin reefs. The outer tract is approximately 0.5 to 1 km wide and extends a distance of about 57 km. A single pass divides the outer tract into two main reefs. This outlier-reef system developed in response to sea-level fluctuations and apparently formed on antecedent, low-gradient to flat o fbank surfaces, which are interpreted to be Pleistocene beaches that formed terrace-like features now in 30 and 40 m of water. Radiocarbon dates of a coral core from the outer tract confirm a pre-Holocene age.

The multiple outlier-reef system represents a new type of windward margin that presents a significant, unique mechanism for progradation of carbonate platforms during periods of sea-level fluctuation. Infilling of the backreef basins would create new, submerged, terraced headlands and would extend or "step" the platform seaward for hundreds of meters. Subsequent outlier-reef development would be dependent upon sea-level fluctuations and would result in laterally accumulating sequences. Implications are that similar subsurface outlier-reef systems may exist and that these systems could become clearly defined hydrocarbon reservoirs.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)