Profile of a modern coastal mixing zone in Tertiary carbonate rocks of the Floridan aquifer, Pasco County, Florida

Conference · Fri Mar 01 04:00:00 EST 1991 · AAPG Bulletin (American Association of Petroleum Geologists); (United States)

OSTI ID:5739182

Jee, J L; Randazzo, A F ^[1]; Wicks, C M; Herman, J S ^[2]

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1. Univ. of Florida, Gainesville (United States)
2. Univ. of Virginia, Charlottesville (United States)

Rock-core and ground-water samples from the Floridan aquifer mixing zone water 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 {le} 50 my post depositional 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 {delta}{sup 13}C and {delta}{sup 18}O 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 {minus}1.30 to +0.85 {delta}{sup 13}C (PDB) and +0.274 to +2.651 {delta}{sup 18}O (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.

• OSTI ID: 5739182
• Report Number(s): CONF-910403--
• Conference Information: Journal Name: AAPG Bulletin (American Association of Petroleum Geologists); (United States) Journal Volume: 75:3
• Country of Publication: United States
• Language: English

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58 GEOSCIENCES
580000* -- Geosciences
AQUIFERS
BUILDING MATERIALS
CARBONATE ROCKS
CATHODOLUMINESCENCE
CEMENTS
CENOZOIC ERA
CHEMISTRY
DEVELOPED COUNTRIES
DIAGENESIS
DISSOLUTION
DRILL CORES
FLORIDA
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC HISTORY
GROUND WATER
HYDROGEN COMPOUNDS
ISOTOPE RATIO
LIMESTONE
LITHOLOGY
LUMINESCENCE
MATERIALS
MINERALOGY
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OXYGEN COMPOUNDS
PARAGENESIS
PERMEABILITY
POROSITY
ROCK-FLUID INTERACTIONS
ROCKS
SATURATION
SEDIMENTARY ROCKS
TERTIARY PERIOD
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WATER