FLORIDA GEOLOGICAL SURVEY


problems were worked out during that project and data gathered during the project proved
invaluable in its completion.

 GEOLOGIC SUMMARY

 The near surface geology of the western portion of the USGS 1:100,000 scale Perry
quadrangle is composed of a complex mixture of Eocene to Holocene carbonate and siliciclastic
sediments. A combination of factors, including fluvio-deltaic deposition, marine deposition,
dissolution of underlying carbonates, erosion of sediments as a result of eustatic changes in sea
level and structural features, have influenced the geology of the study area.
 Much of the western portion of the Perry quadrangle is located within the Aucilla and
Econfina River basins (Figure 2). In this area, the Aucilla, Econfina, Fenholloway, and Wacissa
rivers and their tributaries contain numerous documented springs, including one first magnitude
spring and 24 lesser magnitude springs. A first magnitude spring is defined as having a minimum
average flow of 100 cubic feet per second, or 64.6 million gallons per day. Many of these springs
have evidenced significant increases in pollutants in the last few decades, particularly nitrate
(Scott et al., 2002). Detailed geologic mapping of lithostratigraphic units in this area provides
critical data needed for future assessments of the vulnerability of the aquifer systems and these
springs to contamination. The recharge areas for many of these springs are believed to be located
in and around the current study area. Understanding the surficial geology of the map area is a
key factor in developing management and protection plans, not only for the springs, but for the
unconfined portions of the Floridan aquifer system (FAS).

 Structure

 Several structural variables have affected the geology of the region. The Peninsular Arch
(Figure 3), a structurally high area which affected deposition from the Cretaceous to the early
Cenozoic, is the dominant subsurface feature in the Florida peninsula (Applin, 1951; Puri and
Vernon, 1964; Williams et al., 1977; Schmidt, 1984; Miller, 1986; Scott, 1997). The axis of the
Peninsular Arch extends from southeastern Georgia to the vicinity of Lake Okeechobee in
southern Florida in a general northwest to southeast trend. The crest of the arch passes beneath
Alachua County south and east of the study area and is highest in Union and Baker Counties east
of the study area. The arch was a topographic high during most of the Cretaceous Period and had
Upper Cretaceous sediments deposited over it (Applin, 1951). It formed a relatively stable base
for Eocene carbonate deposition except during times of periodic land emergence due to lowered
sea levels (Williams et al., 1977). The arch did not affect late Tertiary to Holocene sediment
deposition (Williams et al., 1977; Scott, 1997).
 The Ocala Platform is the most prominent structure affecting the near surface
depositional and post-depositional environments within the map area. Hopkins (1920) originally
named this feature the Ocala Uplift. Vernon (1951) described the Ocala Uplift as a gentle flexure
developed in Tertiary sediments with a northwest-southeast trending crest. Because there is
continuing uncertainty about the origin of this feature, Scott (1988) used the term Ocala
Platform, rather than Ocala Uplift or Ocala Arch, since it does not have a structural connotation.
 The Ocala Platform exerted its influence on late Tertiary sediment deposition, and
Miocene sediments of the Hawthorn Group are thought to have been deposited across the
platform (Scott, 1981a; Scott, 1988). Post-Miocene erosion, however, has removed sediments of