Resistivity, Oolites And A Fresh Water Lens

We have conducted a series of resistivity soundings and azimuthal resistivity surveys<br>across North Andros Island, Bahamas. The fresh water lens was mapped from a<br>combination of well data and resistivity soundings. The carbonate aquifer is dominated by<br>oolitic limestone and is known to have extensive karst development as evidenced by the<br>existence of blue holes. Charlies Blue Hole, which is several kilometers from the ocean, as<br>well as boreholes, exhibit clearly recognizable tidal fluctuations with small time lags<br>suggesting subsurface connection to the ocean, perhaps via fractures. Azimuthal resistivity<br>surveys allow us to evaluate the effects of preferred orientation of fractures.<br>Borings and surface sampling revealed changes in depositional environments across the<br>island. The resistivity surveys coupled with lithologic information from various locations,<br>allow us to draw a clearer picture of how the island geology is linked to the island<br>hydrology.