Water-rock interactions in a modern coastal mixing zone

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The chemical evolution of ground water and the diagenetic history of the rocks in a modern saline-fresh-water mixing zone were investigated to test the hypothesis that this zone is a chemically active environment in which carboante mineral diagenesis occurs. The field site was in the unconfined section of the upper Floridan aquifer system. The mixing zone, marked by a steep concentration gradient, is >90 m thick at the study site in New Port Richey, Pasco County, Florida. At the petrographic scale, there is little evidence of diagenesis related to the modern mixing zone. Calcite crystals from the lower section of the cored interval have isotopic signatures that are different than those from the upper section, suggesting that the latter has undergone more water-rock interactions. The paragenetic sequence includes marine micritization and cementation; meteoric mineralogic stabilization; dissolution enhancement of porsity; phreatic, equant calcite cements; and echinoderm overgrowths, all typical of the region and not unique to the mixing zone. -from Authors

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Geological Society of America Bulletin

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