A geochemical model for evaluating theories on the genesis of Florida's sedimentary phosphate deposits |
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| Authors: | Martha W Gilliland |
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| Institution: | (1) Department of Environmental Engineering Sciences, University of Florida, 32601 Gainesville, Florida, USA;(2) Present address: Science and Public Policy Program, University of Oklahoma, 73069 Norman, Oklahoma, USA |
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| Abstract: | Present ionic concentrations of Ca
++,HCO
3
-
,and HPO
4
=
in surface and groundwater runoff in Florida indicate that phosphorus is being concentrated in rock through dissolution and reprecipitation, with calcium phosphate increasing at the expense of calcium carbonate. Analog computer simulation of a systems model of this process suggests that significant enrichment can occur in 20 million years. The degree of enrichment depends on the supply of new phosphorus to Florida through rain and oceanic exchange processes. If the calcium phosphate content of original rock is 0.5 to 1.0 percent (0.52 to 1.05 percent P
2
O
5),a formation with 10 to 20 percent calcium phosphate (CaPO
4
or 10.5 to 21.0 percent P
2
O
5)as in the Hawthorn Formation (Miocene)may result. Nutrient upwelling along the continental slope coupled with transport to the estuaries by lateral eddy diffusion can supply an additional 400 mg P|m
2
|yr which, if deposited, would result in a sediment with a 4.3 percent CaPO
4 (4.5 percent P
2
O
5)content. If this is enriched later by resolution, 40 percent CaPO
4 (42 percent P
2
O
5)results. Through geologic time, the ocean may be considered as a source of phosphorus to the land through rain or estuarine sediment. |
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| Keywords: | analog computer simulation geochemistry phosphorus phosphate deposits |
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