Reassessment of the Bahamas Fracture Zone

BALL, MAHLON M., U.S. Geological Survey, Evergreen, CO

The Bahamas Fracture Zone trends northwestward across south Florida and the Western Florida shelf, and it appears to connect with the Gilbertown-Pickens-Pollard portion of the circum-Gulf of Mexico fault system. Along the fracture zone's trend, seismic reflection data reveal normal displacement in the Late Jurassic section of a kilometer, on a down-to-the-west fault, 9 km east of the east end of Destin dome in the Apalachicola basin. This fault was active in Late Jurassic and Early Cretaceous time during the gulf spreading event. The Middle Jurassic Louann Salt thins abruptly to the east across this fault. Toward the southeast, where the fracture zone crosses the Florida peninsula, gravity data have previously been interpreted to indicate coincidence of the Bahamas Fracture Zone with "hinge zone" attended by relief on the Mohorovicic discontinuity. This interpretation is an artifact resulting from the use of erroneously low densities for the sedimentary fill of the South Florida basin. The inclusion of a nonexistent negative component for the basin's sedimentary fill necessitated the inclusion of an equally nonexistent positive contribution from relief on the Moho in order to match the observed anomaly. Although northwestward-trending faults do cross south Florida and the Western Florida shelf, the role of the Bahamas Fracture Zone as a boundary between continental and transitional or oceanic crust is insupportable.

AAPG Search and Discovery Article #91004 © 1991 AAPG Annual Convention Dallas, Texas, April 7-10, 1991 (2009)