250 Miles of Reef History: Reefs from Ft. Lauderdale to Dry Tortugas

E. A. Shinn, B. H. Lidz, and T. D. Hickey
USGS, St. Petersburg, FL

Mapping combined with coring indicates a diverse Holocene history off south Florida. Reef distribution is controlled mainly by pre-Holocene topography. Age of this topography ranges from mid- to late Pleistocene. Composition includes oolite, coral reefs, and siliciclastics. Geomorphology off the middle and lower Florida Keys was determined by high-resolution seismics and aerial photography. Northern areas off Ft. Lauderdale were characterized by lidar. Geomorphology, dredged outcrops, and core drilling off Miami and Ft. Lauderdale indicate parallel reefs grew on drowned coastal accretions. Coring off the Florida Keys shows linear reefs initiated on late Pleistocene coral reefs that probably formed on earlier coastal accumulations. Eight parallel reef lines can be discerned on the lower Keys outer shelf, whereas four can be defined on the narrower shelf off Ft. Lauderdale. Nearshore dune-based reefs near Ft. Lauderdale are a few meters thick. The outermost reef there is at least 12 m thick. Coral reefs that kept pace with rising sea level are restricted to the Florida Keys and Dry Tortugas and are up to 14 m thick. No reefs north of Miami have kept pace with Holocene sea-level rise. The area of actively accreting reefs is surprisingly low throughout the entire area. Less than 1% of Florida Keys coral reef area is classified as live. Senile reefs amount to about 2%.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005