EOGENETIC KARST AQUIFERS AFTER A DECADE OF INVESTIGATION

In 2002 a signature paper by Len Vacher and John Mylroie in Carbonates and Evaporites brought the concept of ‘eogenetic’ into the forefront of karst research, building upon Jerry Lucia’s 1968 concept of porosity-fabric and Phil Choquette and Lloyd Pray’s 1970 idea of time-porosity stages, both referring to the characterization of carbonate reservoirs. Borrowing from this literature, Vacher and Mylroie sought to place the porosity and permeability framework of eogenetic carbonates in the hydrologic perspective of an equivalent porous media. The stress upon the relatively high ‘matrix’ porosity and permeability of eogenetic carbonates emphasizes the importance of a dual-media (conduit/fracture and matrix) approach to understanding ground-water flow in karst.

As eogenetic karst is linked to the early stages of carbonate diagenesis, aquifers in eogenetic karst are largely distributed near the warm, low-latitude, siliciclastic-deprived, marine waters where carbonate sediments are forming now, or the “net depositional realm” according to Choquette and Pray. One such location is the Florida Platform, where the Karst Waters Institute hosted a symposium in 2002 dedicated to the hydrology and biology of Post-Paleozoic carbonate aquifers such as the Floridan, the Yucatan, and the Edwards. Rapid urbanization in these regions increases the risk of anthropogenic contamination. Additionally, freshwater resources in eogenetic karst can be severely limited by saltwater intrusion or relatively thin freshwater lenses.

In the decade following 2002, a wealth of research has highlighted the importance of eogenetic karst worldwide, and in an exciting twist, has stimulated revisions to the origin and morphology of paleokarst and reservoir characterization models. With vast exposures of Tertiary carbonates in North America, Australia, and the Middle East, we may ultimately come to view eogenetic karst with equal importance to classical karst in older, diagentically mature carbonates.