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Thermal convection may be a significant dolomitizing ground-water flow process in active carbonate platforms. In platform margins there is an upward transfer of seawater from the surrounding ocean depths. This motion is induced by the strong horizontal density gradient that exists between the warmer platform interior (warmed by geothermal heat flux) and the cold surrounding ocean waters. The cold dense seawater flows inward displacing the platform pore waters upward. This flow process was discovered and studied in south Florida by Francis Kohout. Here these upwelling waters discharge from well-known submarine springs on the shelf and shelf edge. The waters are of seawater composition but with increased Ca/Mg suggesting that they have acted as dolomitizing fluids. In Flori a this flow pattern is distorted by and mixed with the large regional flow of the Floridan aquifer. In isolated platforms this distortion should not occur. To test the idea that this kind of convection might be an important diagenetic agent in platform settings in general, I have used ground-water flow theory to model this process in isolated platforms. Approximate theory suggests that Darcy velocities of 1 m/yr (3 ft/yr) occur. I am using boundary layer theory to determine the fully developed flow pattern and the distance from the margin to which the flow penetrates. The rate of dolomitization that could be developed by this process is comparable to and may exceed that of other flow processes in active platforms. I conclude that this "Kohout convection" is a large-scale flow process tha appears capable of pervasive dolomitization of platform margins.
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