DIAGENESIS AND COMPACTION OF LIMESTONES ASSOCIATED WITH EARLY BURIAL AND METEORIC AND SEA WATER INFILTRATIONS: A BASIN.RTM SIMULATION OF THE FLORIDA CARBONATE PLATFORM

The mechanisms driving permeability destruction in limestones during early burial is studied using Basin.RTM and a 600 meter-thick section of the Floridan Aquifer. Of particular interest is a 20-meter interval of Middle Eocene Avon Park Formation, of which there are ample petrographic observations and permeability measurements for calibration.

Basin.RTM is a Reaction-Transport-Mechanical (RTM) process-oriented finite-element simulator that accounts for diagenesis (including pressure solution), fluid flow, advective and diffusive mass-transfer, textural evolution, and mechanical compaction. Varying conditions of meteoric and sea-water influx were imposed to study diagenetic pathways and related sensitivity of permeability.

The 20 m Avon Park interval is subdivided into 11 bioclastic facies of varying thickness and composition. Lower- and over-lying sediments are divided into generalized formation-scale units. Lithologic compositions are described using 7 minerals, including various aragonites, magnesium calcites, calcite, and a dolomite.

Simulation results include: 1) Aragonite disappears from the sediments within the first 2 to 4 my after deposition with that CaCO3 becoming either calcite or being fluxed out of the system. 2) Depending on the composition and influx rate of water, dolomite can become an important byproduct of mineral reprecipitation process. 3) Finer-grained lithologies compact more extensively than coarser grained ones. 4) Pressure solution can be an important mechanism for diffusion-controlled mass transfer between lithologies when the water infiltration rate is low.

The results provide the timing and extent of compaction and composition changes over 40 Myr of geologic time. This evolving profile illustrates the interdependence of RTM basin processes, sediment composition and texture, and burial/recharge history that are responsible for producing highly cemented and/or compacted lithologies in heterogeneous basin sediments. Though difficult to summarize the findings in a few rules that apply to a wide range of carbonate systems, the modeling shows that the effects of early diagenesis and compaction in carbonates can be assessed with a quantitatively and process-oriented model.