Early marine carbonate cementation in a relict shelf-edge coral reef North of Miami, Florida: Pseudo-coupled depositional and diagenetic modeling

Abstract

Carbonate depositional and early diagenetic processes overlap in time because of the high chemical reactivity of calcite. Previous studies have modeled early diagenesis in a static depositional framework. They followed a rule-based modeling approach instead of applying rigorous thermodynamics and reaction kinetics.This study has developed a pseudo-coupled approach based on a dynamic depositional framework and reactive transport modeling for diagenesis. It has been tested for the “Pompano” reef north of Miami, Florida. The model includes five reef parasequences deposited over 9.0 kyr with five facies zones. After deposition of the first parasequence, diagenetic processes are modeled. The resulting framework forms the starting condition for depositing the next parasequence. Subsequently, its diagenetic overprint and the continued overprint in the underlying parasequence(s) are modeled. These workflow steps are repeated until all five parasequences are covered.The results show the spatial and temporal development of calcite cementation and porosity distribution. During the reef catch-up phase, cement mainly developed at the depositional surface (up to 10% of the total sediment volume). During the keep-up phase, cement abundance increases to a maximum value of ∼17%. After the reef's demise, cement forms a crust at the sediment-water interface with up to 38% of the total sediment volume. In general, controlling factors of cement distribution include facies-specific flow velocities, reef facies, relative sea-level changes, depositional gaps, and seawater salinity.The modeling results of this study are well aligned with the actual cement and porosity distribution in the Pompano reef and with other sub-recent and ancient examples described in the literature. Pseudo-coupled depositional-diagenetic modeling represents a suitable approach for quantitative porosity prediction in comparable depositional and diagenetic settings. It reduces uncertainties in prediction at inter-well to prospect scale for oil and gas exploration, geothermal exploration, and subsurface storage of CO2.