Hawthorn Group, Undifferentiated

The undifferentiated Hawthorn Group occurs at or near the surface near the southern flank of the Ocala Platform from Gilchrist County southward to Pasco County with isolated occurrences in Pinellas County. Correlation of these sediments to the formations of the Hawthorn Group exposed to the east and in the subsurface is uncertain. There is little to no phosphate present in these sediments and fossils are rare. Ages have not been documented but stratigraphic position suggests inclusion in the Hawthorn Group. These sediments may be residual from the weathering and erosion of the Hawthorn Group. The Hawthorn Group sediments on the Brooksville Ridge are deeply weathered and in some outcrops look like Cypresshead Formation siliciclastics. The undifferentiated Hawthorn Group sediments are light olive gray and blue gray in unweathered sections to reddish brown in deeply weathered sections, poorly to moderately consolidated, clayey sands to silty clays and relatively pure clays. These sediments are part of the intermediate confining unit/aquifer system and provide an effective aquitard for the FAS, except where perforated by karst features. Hard-rock phosphate deposits are associated with the undifferentiated Hawthorn Group sediments on the eastern flank of the Brooksville Ridge. The hard rock phosphate deposits were formed by the dissolution of phosphate in the Hawthorn sediments and redeposition in karst features.
State Florida
Name Hawthorn Group, Undifferentiated
Geologic age Miocene
Lithologic constituents
Major
Unconsolidated > Coarse-detrital > SandLight olive gray and blue gray in unweathered sections to reddish brown in deeply weathered sections, poorly to moderately consolidated, clayey sands to silty clays and relatively pure clays.
Unconsolidated > Fine-detrital > ClayLight olive gray and blue gray in unweathered sections to reddish brown in deeply weathered sections, poorly to moderately consolidated, clayey sands to silty clays and relatively pure clays.
Incidental
Sedimentary > Chemical > PhosphoriteHard-rock phosphate deposits are associated with the undifferentiated Hawthorn Group sediments on the eastern flank of the Brooksville Ridge.
References

Scott, T.M., Campbell, K.M., Rupert, F.R., Arthur, J.D., Missimer, T.M., Lloyd, J.M., Yon, J.W., and Duncan, J.G., 2001, Geologic Map of the State of Florida, Florida Geological Survey & Florida Department of Environmental Protection, Map Series 146, scale 1:750,000.

Scott, Thomas M.P.G. #99, Text to Accompany the Geologic Map of Florida, Open-file Report 80, Florida Geological Survey, 2001.

NGMDB product
Counties Alachua - Citrus - Gilchrist - Hernando - Hillsborough - Levy - Marion - Pasco - Pinellas