Interpretation of Paleogene-to-Neogene Paleokarst Features Using Newly Acquired Marine High-Resolution Seismic-Reflection Data, Biscayne Bay, Florida

In southeastern Florida during 2007 and 2008, about 125 km of marine, multichannel, high-resolution, seismic-reflection data were acquired almost entirely inside Biscayne National Park at water depths ranging from about 0.9 to 100 m. Fifteen profiles were acquired between the shoreline of the Florida peninsula and a series of small keys that separate Biscayne Bay from the Atlantic Ocean. Additionally, three profiles were collected eastward of the islands with two extending seaward of the present-day shelf margin and its discontinuous reefs. The set of seismic images from the 18 profiles is providing recognition of intriguing geologic features interpreted to be related to Paleogene-to-Neogene paleokarst beneath and beyond Biscayne Bay. Many of the seismic profiles exhibit disturbances in parallel seismic reflections that correspond to the rocks of the Floridan aquifer system and overlying intermediate confining unit. Many of the structural characteristics are interpreted to be related to collapsed paleocaves or collapsed-paleocave systems, and include fractures, faults, vertical sag structures, and km-scale suprastratal deformation. The seismic structures provide clues as to the sealing capacity of confining units above a highly permeable zone (Boulder Zone) in the lower part of the Floridan aquifer system used on the southeastern Florida peninsula for deep well injection of treated wastewater. The presence of these seismic disruptions through confining units suggests groundwater could flow across confinement. Combined, the structures could act as a regional seal bypass system. If this bypass system allows cross-stratal fluid migration, it could provide many pathways for upward directed groundwater flow with leakage to higher hydrostratigraphic levels. Future research plans to include acquisition of additional marine seismic profiles.