Abstract: Relationship Between Sedimentary Facies and Ground Water Flow in the Suwannee Formation, Upper Floridan Aquifer, West-Central Florida

N. T. Loizeaux, David A. Budd

The uppermost transmissive unit in the Upper Floridan aquifer corresponds to limestones of the lower Oligocene Suwannee Formation. Flow of ground water from this unit is generally assumed to be related to karst or fracture conduits associated with subaerial exposure at the end of Suwannee deposition. Core descriptions and ground-water flow-meter were compared in order to evaluate this assumption and to determine if there were any associations between facies patterns, stratigraphic subunits, and fluid flow.

The Suwannee consists of three subunits, numbered megacycle (MC) 1, 2, and 3, with the oldest being MC 1. Each megacycle can be can be further subdivided into component depositional facies. Ten facies have been recognized and represent depositional environments ranging from supratidal (facies 1) to deep outer ramp (facies 10). Porosities are high in all facies as the rocks are poorly lithified.

The comparison of facies and flow-meter logs indicates that proximity to the top of the Suwannee does relate to fluid flow. however, there is also a reasonable correlation to facies, thus conduits are not the sole control on flow. The best facies for fluid flow are subtidal lagoon and back-shoal facies which yield fluid from >65% of their total occurrences. The worst facies are supratidal and deep outer-ramp facies which yield fluids from <40% of their occurrences. These associations are probably related to original sorting and grain size; the good flow facies are higher energy deposits than the poorer flow facies.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994