DEFINITION OF LITHO- AND HYDRO-STRATIGRAPHIC ELEMENTS OF THE MIAMI OOLITIC CARBONATES WITH 3-D GROUND PENETRATING RADAR

The Pleistocene Miami Oolite hosts a highly porous and permeable vadose zone. Fluid flow is controlled by heterogeneous bedform stratigraphy and cross-cutting dissolution features. Hydrologists struggle to understand infiltration and flow from only borehole data and scattered outcrops. Non-invasive methods provide valuable insights for accurately determining 3-D architecture and dynamic properties in the vadose zone. These insights can lead to more realistic flow models and solve problems related to groundwater recharge, contaminant migration, carbonate diagenesis and biochemical processes.

A high-resolution 3-D 100MHz Ground Penetrating Radar (GPR) pilot survey was acquired on a dense grid of 10x20 cm covering an area of 24x46m, imaging the internal anatomy of the Miami Oolite to a depth of 7m. The 3-D migrated data can be partitioned into 3 major units: 1) soil zone with anthropogenic traces, 2) prograding oolitic barrier bar, and 3) ooid shoal complex. Each unit is characterized by three-dimensional patterns: Linear trenches and foundations, foresets with bifurcations, mottled chaotic facies and sand waves with rapidly changing directions, respectively. These features are most prominent on animated horizontal slices scanning through the data volume.

Computerized connectivity analysis of the GPR cube reveals three-dimensional continuous geobodies within the main units that may represent individual flow units. Lithologic information and 4-D repeat GPR surveys help distinguish hydrologically conductive and non-conductive zones. The classified bodies can then be used as real data input for flow modeling. A series of extensive 2-D, and local 3-D/4-D GPR surveys, in combination with verification boreholes, are needed to define characteristic elements of a regional litho- and hydrostratigraphic model of the Miami Oolite vadose zone system.