The Bureau of Economic Geology The University of Texas at Austin Jackson School of Geosciences

 

Cedar Keys/Lawson, Central Florida Region

General Setting

Central Florida is underlain by a thick (>2,500 m) sequence of Cretaceous and Tertiary carbonates (Randazzo, 1997). This carbonate sequence consists of a variety of lithologies, including limestone, dolostone, mudstones, and evaporites. Subsequent to deposition of the Tertiary carbonates, extensive dissolution cavities developed, which now form the Floridan aquifer (Miller, 1986, 1997). Particularly prominent, cavernous intervals and/or Boulder Zones have been reported in the Lower Cretaceous Pine Key and/or Lawson and the Tertiary Cedar Keys and Avon Park Formations (Miller, 1997; J. Haberfeld, Florida Department of Environmental Protection, personal communication, 2000). Note that in the correlation chart of Randazzo and Jones (1997, inside back cover), the Lawson Formation correlates with the upper Pine Key Formation In this report, we will refer to the porous hydrostratigraphic interval as the Cedar Key/Lawson Dolomite.

Injection wells are used in several places in Florida to dispose of municipal and industrial wastes (Miller, 1997). The wastes are mostly injected into highly permeable zones in the lower Floridan aquifer, known as the Boulder Zone. About 208 Mgal/d was injected in 1988; Boulder Zone depths in south central Florida are typically 1,500 to 2,000 ft. Some wells, such as those in Polk County, inject wastes into the permeable, Upper Cretaceous Cedar Keys and Lawson Dolomites, which are below the Floridan aquifer. The Cedar Keys and Lawson Dolomites are generally 4,000 to 5,000 ft deep in central Florida.

Information Search and Selection

Central Florida is the focus of the this regional assessment because the lower Cedar Keys and Lawson Dolomites appear to contain a laterally extensive porous zone that is overlain by an anhydrite-dolomite sequence in the middle Cedar Keys Formation that is about 700 ft thick, forming an effective top seal (J. Haberfeld, Florida Department of Environmental Protection, personal communication, 2000). Currently the lateral extent of this potential CO2 reservoir is not known. Winston (1977) indicated that southwestern Florida was a vast back-barrier reef area during deposition of the Lawson and Cedar Keys Dolomites, which implies that the lithologies within these mixed carbonate and evaporite units are laterally extensive.

The Boulder Zones of the lower Floridan Aquifer are not presented in the GIS because they are generally too shallow, and the confining horizon within the middle and upper Oldsmar and lower Avon Park Formations generally has too high a leakage rate to be expected to retain gases (J. Haberfeld, Florida Department of Environmental Protection, personal communication, 2000), particularly along fracture zones.

The Floridan aquifer, which generally comprises the Paleocene upper Cedar Keys, the Eocene Oldsmar, Avon Park and Ocala, and the Oligocene Suwannee Formations, has been extensively studied (Miller, 1986, 1997). However, little has been published on the Cretaceous Cedar Keys and Lawson Dolomites below the Floridan aquifer (Winston, 1994, 1996). There is oil and gas production from the Lower Cretaceous Sunniland Limestone in southeastern Florida, but no information has been published on the overlying Lawson and Cedar Keys Dolomites. However, geophysical logs from this area, or any area in Florida where the Lower Cretaceous has been drilled can provide information regarding the physical properties of the Lawson and Cedar Keys Dolomites. In general, however, there is currently very little information available. Nonetheless, Florida is a rapidly developing area, and the Lawson and Cedar Keys Dolomites are potential reservoirs for CO2 sequestration, and, therefore, the information that is currently available for these Cretaceous strata are presented in the GIS.

Comments on Geologic Parameters

References

Applin, P. L., and Applin, E. R., 1944, Regional subsurface stratigraphy and structure of Florida and southern Georgia: American Association of Petroleum Geologists, v. 28, p. 1673-1753.

___________ 1967, The Gulf Series in the subsurface in northern Florida and southern Georgia: U.S. Geological Survey, Professional Paper 524-G, 35 p., 8 plates.

Blackwell, D. W., Wisian, K. W., and Steele, J. L., 2000, Geothermal resource/reservoir investigations based on heat flow and thermal gradient data for the United States

Chen, S. C., 1965, The regional stratigraphic analysis of Paleocene and Eocene rocks of Florida: Florida Geological Survey Bulletin No. 45, 105 p.

Kinney, D. M., ed., 1976, Geothermal gradient map of North America: American Association of Petroleum Geologists and U.S. Geological Survey, Publication G74014, 2 maps.

Meyer, F. W., 1989, Hydrogeology, ground-water movement, and subsurface storage in the Floridan Aquifer system in southern Florida: U.S. Geological Survey, Professional Paper 1403-G, 59 p.

Miller, J. A., 1986, Hydrogeologic framework of the Floridan Aquifer system in Florida and in parts of Georgia, Alabama, and South Carolina: U.S. Geological Survey, Professional Paper 1403-B, 91 p., 33 plates.

___________ 1997, Hydrogeology of Florida, in Randazzo, A. F., and Jones, D. S., eds., The geology of Florida: Tallahassee, University of Florida Press, p. 69-88.

National Imagery and Mapping Agency, 2000, Digital terrain elevation data (DTED Level 0)

Randazzo, A. F., 1997, The sedimentary platform of Florida: Mesozoic to Cenozoic, in Randazzo, A. F., and Jones, D. S., eds., The geology of Florida: Tallahassee, University of Florida Press, p. 39-56.

Randazzo, A. F., and Jones, D. S., eds., 1997, The geology of Florida: Tallahassee, University of Florida Press, 327 p.

Smith, D. L., and Lord, K. M., 1997, Tectonic evolution and geophysics of the Florida basement, in Randazzo, A. F., and Jones, D. S., eds., The geology of Florida: Tallahassee, University of Florida Press, p. 13-26.

Vernon, R. O., 1951, The geology of Citrus and Levy counties, Florida: Florida Geological Survey Bulletin 33, 256 p.

___________ 1970, The beneficial uses of zones of high transmissivities in the Florida subsurface for water storage and waste disposal: Florida Geological Survey, Information Circular No. 70, 39 p.

Winston, G. O., 1977, Cotype wells for the five classic formations in peninsular Florida: Gulf Coast Association of Geological Societies Transactions, v. 27, p. 421-427.

___________ 1994, The Paleogene of Florida, v. 3. Lithostratigraphy of the Cedar Keys Formation of the Paleocene and Upper Cretaceous age-Peninsular Florida and environs: Miami Geological Survey, 52 p.

___________ 1996, The Boulder Zone dolomites of Florida, v. 2, Paleogene zones of the southwestern peninsula: Miami Geological Society, 62 p.

Prepared by Andrew Warne.

 
 
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