Florida Geological Survey


 LITHOSTRATIGRAPHY

 General Stratigraphy

 Cretaceous to Holocene strata in Brevard County consist of a thick sequence of interbedded limestone and dolostone overlain by a veneer of siliciclastic sediment. The Floridan aquifer system is characterized by Paleocene to Upper Eocene limestones and dolostones (Figure 10) that form part of an extensive carbonate platform that existed from late Cretaceous through Late Oligocene.

 Dunham's (1962) carbonate classification system is utilized in the following discussion of the Floridan aquifer system lithostratigraphy. Carbonate rocks, based on Dunham's method, are classified according to depositional texture with the primary emphasis on the presence or absence of carbonate mud and the abundance of carbonate grains (allochems). The classification system also distinguishes between mudsupported and grain-supported rocks which is the criteria used to separate wackestone from packstone and grainstone.

 Paleocene Cedar Keys Formation

 The Cedar Keys Formation is a sequence of interbedded dolostones and evaporites unconformably overlying the undifferentiated Cretaceous Lawson Formation and conformably underlying the Lower Eocene Oldsmar Formation (Chen, 1965). The top of the Cedar Keys Formation was described by Chen (1965) as a "distinct lithology consisting of a gray, microcrystalline, slightly gypsiferous and rarely fossiliferous dolomite (dolostone)." Anhydrite with "chicken wire" texture is commonly interbedded with gray to tan dolostone in the lower two-thirds of the Cedar Keys Formation (Miller, 1986). The formation commonly contains the foraminifera species Borelis gunte1ri except in the highly recrystallized dolostones of the upper Cedar Keys section (Miller, 1986).


 The top of the Cedar Keys Formation according to Miller (1986) ranges from approximately
-2,200 feet NGVD in northern Brevard County to
-3,000 feet NGVD in southern Brevard County. The Merritt Island, Harris #2, South Beaches, and Port Malabar wells were drilled within this depth range and could have penetrated the upper Cedar Keys Formation. Examination of cuttings over these intervals show a change from grayish and yellowish-brown dolostones characteristic of the lower Oldsmar to a gray dolostone that could be interpreted as Cedar Keys Formation. However, a definitive Cedar Keys Formation top was not identified in these wellbores.

 Lower Eocene Oldsmar Formation

 Miller (1986) defined the Oldsmar Formation as "the sequence of white to gray limestone and interbedded tan to light-brown dolomite (dolostone) that lies between the pelletal, predominantly brown limestone and brown dolomite (dolostone) of the Middle Eocene and the gray, coarsely crystalline dolomite (dolostone) of the Cedar Keys Formation." The contacts with both the underlying Cedar Keys Formation and the overlying Avon Park Formation are unconformable (Braunstein, et al, 1988). In Brevard County, the Oldsmar Formation top is indicated by a white to light gray, glauconitic, moderately indurated wackestone or packstone which contrasts with the cherty, brown dolostones of the overlying Avon Park Formation. The glauconitic zone has a characteristic gamma-ray and sonic log signature that is correlative between all the injection wells (Plates 1 and 2) and serves as an excellent datum for stratigraphic and structural analyses. Helicostegina gyrali is a common faunal constituent of the glauconitic interval. The top of the Oldsmar Formation ranges from
-1,667 feet NGVD at the Merritt Island site to
-1,918 feet NGVD at the Harris #2 site (Figure 7).

 Overall, the Oldsmar Formation consists of an upper section of interbedded packstone, wacke-