[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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