Florida Geological Survey


miliolids. The top of the Ocala Limestone is identifiable on gamma-ray logs as a sharp decrease in radioactivity relative to the overlying phosphatic Hawthorn Group sediments (Plates
1 and 2).

 The top of the Ocala Limestone marks the top of the Floridan aquifer system in Brevard County (Miller, 1986). Porosity and permeability are generally high throughout the formation since most prImary pore space remains open and well connected. Porosity is both intergranular and moldic, with intergranular as the dominant form. The top of the Ocala Limestone ranges from
-104 feet NGVD at the Merritt Island site to -308 feet NGVD at the Harris Corporation site. Ocala Limestone thickness averages 130 feet.

 Miocene Hawthorn Group

 The Hawthorn Group in Brevard County overlies the Ocala Limestone and consists of interbedded olive to yellowish-gray, poorlyindurated calcareous clay, quartz sand, wackestone and dolostone. Phosphatic sand- and gravel-sized grains are characteristic accessory minerals of the Hawthorn sediments in the study area. Clay beds of the Hawthorn Group function as the upper confining unit for the Floridan aquifer system in Brevard County (Brown et al., 1962).

 Hawthorn Group thickness is highly variable ranging from 20 feet at the Merritt Island site to 235 feet at the Harris Corporation site. The Hawthorn Group thins to the north and west with closer proximity to the Brevard Platform and Sanford High (Scott, 1988). The top of Hawthorn Group ranges from -55 feet NGVD at the Grant Street site to -134 feet NGVD at the D. B. Lee site.

 Pliocene Holocene Undifferentiated

 Overlying the Hawthorn Group is a sequence of unconsolidated shell beds, clays, and quartz sands that range from Pliocene to Holocene


(Brown et al., 1962). Constraining the age of these sediments is beyond the scope of this study. Total thickness of the Pliocene-Holocene section varies from 90 feet at the Harris Corporation site to 160 feet at the West Melbourne site.

 DEPOSITIONAL ENVIRONMENTS

 The thick sequence of limestones and dolostones comprising the Floridan aquifer system was deposited on an extensive carbonate platform that existed from Late Cretaceous through Oligocene. Carbonate sediments are intrabasinal deposits and are primarily the product of carbonate-precipitating organisms that thrive in warm, shallow tropical seas. Depositional environments on carbonate platforms are highly variable and as a result vertical and lateral facies can change over very short distances.

 Cores offer the optimum means for depositional environment interpretations in terms of subsurface studies. Cuttings are less useful because of their small size and because of the uncertainty associated with cavings. The lack of core in general, and the lack of stratigraphicallyequivalent cored intervals in the available cores, poses severe limitations on the degree to which reasonable lower Floridan depositional environment interpretations can be made. Observations regarding depositional environments for the purposes of this study were based entirely on information derived from core and thin section examination. Core was available for the Merritt Island, West Melbourne, Harris, and South Beaches injection wells and, consequently, environmental interpretive efforts focused on these sites. Depositional environment interpretations focus on the Oldsmar and Avon Park Formations due to the availability of core and emphasis of this study on the geologic framework of the lower Floridan aquifer system.