[Coral-List] Lower Keys ooids

Gene Shinn eshinn at marine.usf.edu
Thu May 18 11:27:42 EDT 2006

Dear Martin,  Of course I would love to have a sample of the ooid 
sand you described. I am a little suspicious that they may not be 
true ooids, at least in the Bahamian sense. Many geologists have 
called the sands on White Banks off Key Largo ooids but they are 
mainly just polished ovoid-shaped Halimeda sands with a superficial 
oolitic coating. The water at white banks is far more similar to 
water on the Bahama banks where ooids are forming than water in 
Florida Bay. One of the great mysteries  is why we have not found 
real ooids anywhere in the Florida Keys before.  For example, the 
tidal currents currents and bed forms on the "Quicksands," west of 
the Marquesas, are exactly like those in the ooid forming areas of 
the Bahamas. The difference is that the sands are 90%  Halimida 
flakes and there are no ooids.  We really looked for them. The large 
submarine sand dunes move back and forth several meters with each 
tidal change just like ooid sands in the Bahamas. The major visual 
difference is the water is green and visibility is seldom greater 
than 30 ft if that much. The  Pleistocene limestone underlying the 
Quicksands, however, is oolite. So for unknown reasons ooid sands 
were forming  during the Pleistocene, (when sea level was 20 feet 
higher than today) and creating the tidal sand bars that became  the 
lower Florida Keys of today. Ooids also formed and created beaches 
that are now 300 ft below present sea level off the keys. They formed 
during lowered  sea level  during the last glacial period about 
10-18ka.  So there are still some great mysteries  to be solved. If 
you have true ooids forming off your dock that would really be 
something. Please send sample to address below. Best Wishes, Gene

No Rocks, No Water, No Ecosystem (EAS)
------------------------------------ -----------------------------------
E. A. Shinn, Courtesy Professor
University of South Florida
Marine Science Center (room 204)
140 Seventh Avenue South
St. Petersburg, FL 33701
<eshinn at marine.usf.edu>
Tel 727 553-1158---------------------------------- 

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