--> Abstract: Profile of a Modern Coastal Mixing Zone in Tertiary Carbonate Rocks of the Floridan Aquifer, Pasco County, Florida, by J. L. Jee, A. F. Randazzo, C. M. Wicks, and J. S. Herman; #91004 (1991)

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Profile of a Modern Coastal Mixing Zone in Tertiary Carbonate Rocks of the Floridan Aquifer, Pasco County, Florida

JEE, JONATHAN L., and ANTHONY F. RANDAZZO, University of Florida, Gainesville, FL, and CAROL M. WICKS and JANET S. HERMAN, University of Virginia, Charlottesville, VA

Rock-core and ground-water samples from the Floridan aquifer mixing zone were studied to assess diagenesis and porosity and permeability development. This zone occurs in the Ocala Limestone (Eocene) and Suwannee Limestone (Oligocene); shallow-marine lithofacies thereof are grouped into eight informal lithologic units, five in the Ocala and three in the Suwannee.

Most diagenetic features relate to episodic sea-level fluctuations throughout the lesser than 50 my postdepositional history. Paragenesis includes marine micritization and cementation, meteoric mineralogic stabilization, dissolution enhancement of porosity, and phreatic, equant calcite cements and echinoderm overgrowths. Dolomitization of selected intervals occurred relatively late in the paragenetic sequence and dolomite crystals show no evidence of subsequent alteration.

Calcite cements are noncathodoluminescent and have C(13) and O(18) values higher in the Ocala and lower in the Suwannee. Dolomite crystals are nonstoichiometric and thinly zoned, alternating noncathodoluminescent and red-orange cathodoluminescent. Microprobe analysis revealed no systematic variations in Ca and Mg and concentrations of Mn, Fe, Sr, and Na below reliable limits. Dolomite stable isotope value ranges are -1.30 to +0.85 C(13) (PDB) and +0.274 to +2.651 O(18) (PDB).

The modern regional meteoric aquifer is a mature, mineralogically stable carbonate sequence. Aqueous geochemical data indicate supersaturation with respect to stoichiometric calcite and dolomite, and slight supersaturation with respect to aragonite. Bulk solubility measurements show that observed water compositions are in approximate equilibrium with respect to aquifer rocks and there is little evidence of water/rock interaction in this modern mixing zone.

 

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)