Abstract

Continuous cores recently collected from the Pliocene Tamiami Formation, part of the highly productive surficial aquifer system in southern Florida, are composed of mixed siliciclastic-carbonate rocks that contain a heterozoan carbonate-particle association (terminology of James, 1997). The heterozoan carbonate particles of the Tamiami Formation accumulated in a mixed siliciclastic-carbonate ramp depositional system and may have been produced at non-tropical bottom-water paleotemperatures. An upwelling of nutrients and increased siliciclastic influx and runoff might have contributed to relatively high rates of heterozoan carbonate-particle production. Evidence for a non-tropical paleotemperature is indicated by: (1) an abundance of benthic carbonate particles produced by organisms that are light independent; (2) a lack of hermatypic corals, calcareous algae and non-skeletal grains such as ooids; (3) low to moderate amounts of carbonate mud; (4) absent to rare reefal structures; and (5) low amounts of marine cementation

The pore types of the Tamiami Formation, linked to a heterozoan carbonate-particle association, are mainly intergrain and separate-vug (skeletal-moldic) pore spaces. The intergrain pore space is contained in three classes of rock fabric that include grainstone, grain-dominated packstone and mud-dominated packstone. Aquifer tests and semi-quantitative core analyses performed on the rocks of the Tamiami Formation indicate that rock-fabric and associated pore space combine to form an interconnected pore system capable of producing high values of hydraulic conductivity. Values of hydraulic conductivity more than 100 feet/day are common; they are lowest in areas of the ramp overwhelmed by siliciclastic input.

The assemblage of heterozoan carbonate particles and associated pore system in the Tamiami Formation provides a potential analogue for other Tertiary aquifers deposited in a mixed siliciclastic-carbonate ramp depositional system.

James, N.P., 1997, The cool-water carbonate depositional realm, in James, N.P., and Clarke, J.A.D., eds., Cool-water carbonates: SEPM Special Publication No. 56, p. 1-20.

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