Abstract
The Floridan aquifer has often been proposed as a system of extensive meteoric carbonate diagenesis and mixing zone dolomitization. However, the dominance of marine isotope (C, O, {sup 87}Sr/{sup 86}Sr) and trace element (Sr, Fe, Mn) compositions in dolomites and limestones in the Eocene Avon Park Formation, Floridan aquifer, suggests that the very active low temperature meteoric groundwater system has, over the past 40 m.y., been an inefficient mechanism of diagenesis. {delta}{sup 18}O values of all but two replacement dolomites sampled range from +2.0 to +5.1 (PDB) with high Sr concentrations (90-325 ppm), indicating dolomitization by near-normal marine water involving no significant interaction with meteoric groundwater. The two {delta}{sup 18}O-depleted (0.0 {plus minus} 1) dolomites have low Sr concentrations ({approximately}100 ppm) suggesting limited recrystallization in meteoric water. Several dolomite samples have radiogenic {sup 87}Sr/{sup 86}Sr compositions (0.70810-0.70883 {plus minus} 2), but have heavy oxygen isotope compositions (> +2.0) and high Sr concentrations (<200 ppm) suggesting precipitation from cold Miocene age or younger seawater that circulated through the Florida platform. Most limestone stable isotope compositions cluster around marine values (({delta}{sup 18}O = {minus}1 to +1, PDB) {delta}{sup 13}C = +0.5 to +2.5) and have Eocene seawater {sup 87}Sr/{sup 86}Sr compositions (0.70775more » {plus minus} 2 to 0.70779 {plus minus} 2) with 400 to 500 ppm Sr. Isotopic compositions of limestones from the east coast of Florida are all within these ranges. Only some limestones from central Florida and the west coast contain depleted stable isotopic compositions and low Sr concentrations. The sample with the most depleted stable isotope values has a radiogenic {sup 87}Sr/{sup 86}Sr composition (0.70870 {plus minus} 2), suggesting that diagenetic meteoric water migrated through post-Miocene strata.« less
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