KARST CONTROL OF THE BISCAYNE AQUIFER GROUNDWATER FLOW PATTERNS (Invited Presentation)

Karst developed during the five transgressive-regressive deposition cycles in the Pleistocene strata that host the Biscayne Aquifer influences, if not controls, groundwater flow patterns. Karst activity began when the marine carbonates became exposed during regression but was greatest during low sea level stands when vertically-downward percolating ground waters created solution pipes, phreatic tubes and minor horizontal dissolution along bedding planes and paleo-exposure horizons. With the return of transgression, the ground water table rose in response to rising sea level. As sea level approached the platform surface, ground waters began to move horizontally, producing cavernous zones in ooids and very high porosity zones in skeletal deposits along areas at the vadose-phreatic boundary. At least seven horizontal cavernous zones exist which are interconnected by vertical conduits that are associated with subaerial exposure surfaces. The resulting complex combinations of vertical and horizontal conduits dominate ground water flow patterns.

Orientation of surface features is used to recognize these subsurface conduits in the upper portion of the Aquifer, the Miami Formation. Features recognized include the orientation and alignment of karst valleys, dolines (often tree islands), erosion remnants (hardwood hammocks), springs, seeps, and cave systems with connections to the surface. Core samples provide evidence for concentration of karst process along disconformities. In addition, such patterns are expected to exist in the lower Pleistocene deposits along exposure horizons similar to what is observed on the present surface. Karst pathways developed in this manner will dictate the patterns and enhance the rate of salt water encroachment as sea level rises or freshwater consumption increases.