Tectonically Induced Fracturing, Folding, and Groundwater Flow in South Florida

Thomas M. Missimer and Robert G. Maliva
Camp Dresser & McKee, Inc., Fort Myers, Florida

Groundwater flow in the confined aquifers of South Florida is strongly influenced by the diagenesis and structural deformation of aquifer rock. Fractured dolomites are often the main flow zones. Deformation observed in post-Paleocene-aged rocks has often been attributed to karstic collapse related to the dissolution of Paleogene carbonates or Paleocene and Late Cretaceous evaporates. Seismic and borehole stratigraphic data from scattered locations in Florida reveal that regional folding is more common than previously recognized. The typical continuity of strata and paucity of steep-sided collapsed structures suggest that the folding is related to regional compressional events rather than karstic collapse.

The most widespread compressional event occurred in the late Miocene and early Pliocene, towards the end of the deposition of the Hawthorn Group. The subsurface folding has maximum relief on the order of 70 meters. Seismic surveys from both the east and west coasts of Florida, and stratigraphic correlations across wellfields in Lee and Collier County, show that latest Miocene to recent sediments buried the folds. The late Miocene compressional event correlates with a regional tectonic event. The stratigraphic distribution of fractured dolomites and subsurface stratigraphic data document earlier structural events. The combination of a paleohydrogeologic control over the geometry of dolomite bodies and a potential tectonically controlled preferred orientation of fractures introduces considerable anisotropy to aquifers, which may be at least qualitatively predictable.

AAPG Search and Discovery Article #90032©2004 GCAGS 54th Annual Convention, San Antonio, Texas, October 10-12, 2004