Welcome to the December 2024 edition of the Florida Geological Survey (FGS) News and Research. You will notice a slightly different layout to this newsletter. Our news items, including current happenings, recent publications, project developments and outreach events, are now compiled in a list. I hope this new format will allow us to better communicate all the things we do at the FGS.
The most noteworthy news item in this issue is the departure of Dr. Christopher Williams, who has been part of our FGS family for 16 years. Christopher has taken a new position with the Maryland Geological Survey, and we wish him all the best in his new role.
We are excited to report that Wakulla Spring was recognized internationally this August by the International Union of Geological Sciences (IUGS). The IUGS designated Wakulla Spring as one of the most outstanding geological heritage sites on Earth. Learn about this designation and more in our FGS News section below.
The FGS Research portion of the newsletter contains longer articles that focus on our ongoing research projects and items of geological interest. When possible, many of the articles within a newsletter will explore a similar topic, theme or region. Given the significance of the IUGS designation of Wakulla Spring, we dedicate a portion of this newsletter to exploring the geology of the Eastern Panhandle-Big Bend region. We revisit favorite places in the region, like Wakulla Spring, and examine them more deeply. Cave diving, underwater robotics and dye traces have allowed researchers to map the extent of the Wakulla Springs cave system, which is the longest mapped underwater cave system in the United States. FGS researchers have employed ground-penetrating radar (GPR) to create images of the subsurface, including the karst features within the Leon Sinks Geological Area. This innovative mapping deepens our understanding of karst systems and highlights the complexity of surface water-groundwater interactions in the region.
Another impressive collection of karst features can be found along the Aucilla Sinks portion of the Florida Trail, where water flows through a series of swallets and rises in the upper Floridan aquifer. I had the pleasure of showing faculty and students from the Florida State University (FSU) Department of Earth, Ocean, and Atmospheric Sciences (EOAS) this amazing part of our state. Collaborations between the FGS and FSU-EOAS are mutually beneficial and strengthen both organizations. In our news section, we highlight a recent collaborative project to create publicly accessible 3D images of FGS fossils, scanned and housed by FSU.
Exciting recent museum donations were a hit at this year’s open house. We featured our skull cast collection, including a Pleistocene giant beaver skull and a saber-tooth cat skull donated by Dr. Bruce Means. We appreciate all our donors and partners and look forward to expanding our museum displays to include a large amethyst geode and megalodon shark material.
The FGS 2024 open house was a success despite the passing of three hurricanes prior to the October event. Though many people don’t associate hurricanes with sinkhole formation, we report on the uptick in sinkhole reports after weather events. October was a tough month for our state and a busy one for the FGS.
Finally, the FGS STATEMAP team has been hard at work. This fall they published geologic maps of the United States Geological Survey (USGS) 30 x 60 minute Fort Myers and Naples quadrangles. They also started geologic mapping in the USGS 30 x 60 minute Fort Lauderdale quadrangle. Our mapping efforts result in a more detailed understanding of lithologies and geologic resources present near the land surface throughout the state. In previous newsletters, we shared some of this information through our Featured Formation series. This issue we highlight the Quaternary undifferentiated sediments and other undifferentiated Quaternary surficial geologic units in Florida.
In the next FGS News and Research, we will focus on the region containing the newest designated State Geological Site. Stay tuned for an announcement to be released this spring on Florida’s ninth State Geological Site.
As always, thank you for your continued support of our organization.
Sincerely,
Guy “Harley” Means
Director and State Geologist Florida Geological Survey Florida Department of Environmental Protection
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Dr. Christopher Williams
After 16 years of dedicated service to the State of Florida, Christopher Williams has taken a new position as Program Chief of Coastal and Environmental Geology with the Maryland Geological Survey. Christopher was hired at the FGS in 2008. During his 16-year tenure, he authored or coauthored 31 FGS publications and was involved in numerous outreach and education events. He was the lead author of Special Publication 59, Florida Geomorphology Atlas, published in 2022. It is the most comprehensive work on Florida’s geomorphology ever published. Christopher’s contributions to the understanding of Florida’s geology will leave a lasting scientific legacy. He will no doubt make a similar contribution in his new role with the Maryland Geological Survey. We wish him all the best.
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Wakulla Spring Recognized Internationally
This August, the International Union of Geological Sciences (IUGS) announced The Second 100 IUGS Geological Heritage Sites at the 37th International Geological Congress (IGC) in Busan, Republic of Korea. Wakulla Spring was recognized by the IUGS as one of the most outstanding geological places on Earth. The IUGS announcement states that these sites “are the world’s best demonstrations of geologic features and processes” and that the “recognition and visibility of the “Second 100” by IUGS can lead to their further appreciation, to their use as educational resources, and, most importantly, to their preservation.” Learn more about the impressive designation here. Read about the geology of the Edward Ball Wakulla Springs State Park in our article below.
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FGS 2024 Open House
"Earth Science Everywhere" was the theme of this year's open house, held on Tuesday, Oct. 15. The FGS hosted 171 visitors, and showcased museum updates as well as several new stations, including Geophysical Investigations, Aquifer Exploration and Fluorescent Minerals. As always, our microscopes, drill rig and geologic time scale were crowd-pleasers. Our open house was highlighted on the Florida Channel beginning at the 26:45 mark.
Southeastern Atlantic Coastal Plain Stratigraphic Nomenclatural Equivalency and Reconciliation Project
The South Carolina Geological Survey was recently awarded funding from the United States Geological Survey (USGS) to lead the "Southeastern Atlantic Coastal Plain Stratigraphic Nomenclatural Equivalency and Reconciliation Project (2023-2025)." State partners that received sub-awards to participate include the Florida, South Carolina, North Carolina and Virginia geological surveys. The project seeks to provide updates and revisions to the regional lithostratigraphy and resolve stratigraphic issues across state boundaries. The project deliverables will include updates to the USGS Geolex catalog (a national compilation of names and descriptions of geologic units) and updated regional stratigraphic correlation charts and notes.
Museum Donations
The Walter Schmidt Museum recently received several generous donations. The first two donations described below were showcased during the 2024 open house. We anticipate highlighting the second two donations in upcoming events.
The skull cast collection, donated by Dr. Bruce Means, includes a Pleistocene giant beaver (Castoroides dilophidus) skull and a saber-toothed cat (Smilodon fatalis) skull. They join the pampathere skull (Holmesina floridanus) donated by Harley Means.
"Ice Age River Fossils" is a touchable exhibit donated by the Florida Museum of Natural History (FLMNH). On display for many years at the FLMNH, it includes casts of Pleistocene fossils and images of the FGS employees who uncovered the fossils in Florida rivers. Additional interpretive signage created by the FGS highlights the process of paleontological discovery. Artwork by FGS geoscientist Amanda Kubes displays what many of the animals may have looked like when alive.
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The FLMNH recently retired their traveling “Megalodon: Largest Shark that Ever Lived” display. The FGS received cases and interpretive material and was loaned several impressive megalodon teeth to display at our next open house.
A large amethyst geode was donated by Jackie Lloyd in memory of long-time FGS geologist Paulette Bond. Lloyd and Bond worked at the FGS for decades and were life-long friends. The amethyst was one of Paulette's prized possessions; her husband, Per Arne Rikvold, gifted it to Jackie on Paulette's passing. We look forward to displaying it in our museum for many years to come.
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3D Scanning of Fossils
To increase access to delicate fossils for use in research and outreach, the FGS is collaborating with Dr. Scott Evans and Matthew Hunter of Florida State University. Evans’ paleontology students and Hunter’s library sciences team are using Artec 3D scanners to image FGS fossils. They will then compile data from the scans and house them on FSU’s Institutional Repository. Once these scans are posted, scientists, outreach groups, teachers and the public can access the scans to print replicas of the fossils and to examine them in detail.
FGS Outreach Events
The FGS continues to provide support for learning in science, technology, engineering and mathematics (STEM) fields. Below is an example of our recent outreach to educators and our community.
Discovery STEM 7th and 8th grade students from Maclay School were among this year’s open house visitors. The students, led by teachers Cameron Barton and Jessica Stewart, have been using ArcGIS as a tool to explore watersheds, soil types, landcover and the effects of recent storms.
The FGS was invited to provide outreach at the Governor’s Mansion during the Oct. 25 Halloween Celebration. Families affected by recent hurricanes were among the approximately 800 guests in attendance.
In collaboration with Dr. Amanda Tazaz of FSU’s Learning Systems Institute, the FGS led 15 youth from the Boys and Girls Club of the Big Bend to explore karst features at Leon Sinks Geological Area.
Walter Schmidt Museum tours have been in high demand. FGS welcomed many visitors to the museum, including employees of the Division of State Lands, invitees from the Tallahassee Senior Center and FSU Faculty. We also offered virtual tours to classrooms around the state.
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Recently Released FGS Publications
Dyer, S.B., 2024, Spring and River Reconnaissance, Rodman Reservoir Drawdown 2019-2020: Florida Geological Survey Information Circular 113, 30 p., https://doi.org/10.35256/IC113.
Fowler, G.D., III, and Lupo, M.E., 2024, Potentiometric Surface of the Upper Floridan Aquifer September 2021: Florida Geological Survey Map Series 165, scale 1:900,000, https://doi.org/10.35256/MS165.
Green, R.C., Hall, N.P., Earley, P.A., Hebets, C.L., Jones, S.A., and Williams, C.P., 2024, Geologic map of the USGS Fort Myers 30 x 60 minute quadrangle, southwestern Florida: Florida Geological Survey Open-File Map Series 116, scale 1:100,000, 2 pl., https://doi.org/10.35256/OFMS116.
Green, R.C., Hall, N.P., Earley, P.A., Hebets, C.L., Jones, S.A., and Williams, C.P., 2024, Text to accompany geologic map of the USGS Fort Myers 30 x 60 minute quadrangle, southwestern Florida: Florida Geological Survey Open-File Report 113, 36 p., https://doi.org/10.35256/OFR113.
Green, R.C., Hall, N.P., Earley, P.A., Hebets, C.L., Jones, S.A., Williams, C.P., Davis, B.L., and McMahan, E.L., 2024, Geologic map of the USGS Naples 30 x 60 minute quadrangle, southwestern Florida: Florida Geological Survey Open-File Map Series 117, scale 1:100,000, 2 pl., https://doi.org/10.35256/OFMS117.
Green, R.C., Hall, N.P., Earley, P.A., Hebets, C.L., Jones, S.A., Williams, C.P., Davis, B.L., and McMahan, E.L., 2024, Text to accompany geologic map of the USGS Naples 30 x 60 minute quadrangle, southwestern Florida: Florida Geological Survey Open-File Report 114, 36 p., https://doi.org/10.35256/OFR114.
Contact: Mabry Gaboardi Calhoun, Ph.D.
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The images and quoted text below were originally published by the FGS in 1996 within the poster displayed in Figure 1, “Earth Systems: The Foundation of Florida’s Ecosystems,” by Ed Lane and Frank Rupert. To explore the relationship between Florida’s ecology and its underlying geology, the authors divided Florida into five regions. To celebrate the upcoming 30th anniversary of this often-requested poster, we will focus on one region per newsletter. The focus of this newsletter is the Eastern Panhandle-Big Bend Region. The Big Bend region of Florida is informally defined as the portion of the state that includes the transition from the Panhandle to the Peninsula. It is sometimes described as the land within Florida to the east of the Apalachicola River and west of the Suwannee River, from the coastline to the state’s border with Georgia. Figure 2 displays the geology, surface features and vegetation representative of this region. The figures and quoted text below are original, as published in 1996. The links, footnotes and notes in bold are additions, relating the original text to updated information in the Florida Geomorphology Atlas, or providing further information about the geology and surface features of the area.
"The distance from the Georgia-Florida border in the north to the Gulf of Mexico in the south is about 50 miles. This landscape is naturally divided into two distinct areas by the east-west oriented Cody Scarp, an ancient shoreline feature which stretches from the western panhandle almost to Jacksonville. The Cody Scarp is a prominent feature that can rise as much as 150 feet in elevation over a mile of horizontal distance. The higher, rolling hills north of the Cody Scarp are in the Northern Highlands geomorphic province1, with elevations ranging from about 300 ft above sea level (ASL) near the Georgia/Florida border to about 75 feet ASL at the toe of the scarp. The flat region that gradually slopes down from the toe of the scarp to sea level at the Gulf is the Gulf Coastal Lowlands2. (Reminder: In the Florida Geomorphology Atlas, the FGS refined the mapping of geomorphic districts and their provinces. Please see the footnotes for current district and province names.)
The Northern Highlands are underlain by sediments of the Miocene Hawthorn Group, composed of interbedded quartz sands, clays, and carbonates. Except for a few areas where they crop out at the surface, these sediments usually underlie the younger Pliocene siliciclastic sediments of the Miccosukee Formation (reddish-orange clays, silts, and sands, described on pages 78-87 of FGS Bulletin 47). These heterogeneous sediments form loamy soils that are rich in nutrients. They support lush, natural vegetation, and make good farming soils. The rolling hills have been dissected by stream erosion, creating steep-walled channels in the weekly cemented, sandy sediments. Steepheads3 are distinctive erosional features that result from spring-fed streams eroding headward and etching narrow, steep ravines. These ravines form isolated environments that have specialized ecosystems of ferns, other sensitive plants, and amphibians.
Many large lake basins4 are the result of dissolution of buried limestone, which has caused slight subsidence of the overlying siliciclastic sediments. These lakes are only a few feet deep and usually have extensive marshes or wetlands associated with them. Due to the high clay content and the thickness of the Hawthorn Group and Miccosukee Formation sediments, which act as confining units, this region has low potential for recharge to the groundwater aquifer, the Floridan aquifer system, which is developed in the underlying limestones.
The upland ecosystems are based on the plant communities that are supported by the nutrient-rich sediments, and are dependent on the local stratigraphy and hydrology. Important elements in these ecosystems are the mixed hardwood and conifer forests, containing both temperate and subtropical species. Extensive stands of large, mature hardwoods (oak, maple, beech, hickory, magnolia), conifers (pine, cedar, cypress), and palms form the foundation and protective canopy for lush undergrowth. Together, these elements create rich and varied ecosystems.
The Gulf Coastal Lowlands of the eastern panhandle-Big Bend area are underlain by thick sections of near-surface carbonate rocks of Oligocene age (Suwannee Limestone) and Miocene age (St. Marks Formation). These limestones have been deeply weathered by dissolution. These limestones also extend to the north under the Northern Highlands.
Karstification is largely a chemical erosion process that occurs in carbonate rocks. Because most of Florida is underlain by carbonate rocks, such as limestones or dolomitic rocks, karstification is one of the most important geological processes that historically and continually modifies the state's landforms. Here on the karst plain, karst has created extensive interconnected cavities and cavernous porosity; some caverns are over 100-feet wide and high. Saturated with fresh water to hundreds-of-feet deep, they constitute a vast and prolific upper part of the Floridan aquifer system.
Pleistocene and Recent quartz sands cover the limestones in a veneer, usually less than 20-feet thick. The sands are clean, very porous and permeable, and allow rain to infiltrate rapidly to the underlying limestone. This karst plain acts locally as a high recharge area or as a regional discharge area, depending on the quantity and extent of local rains, typically reflecting seasonal variation. Surface drainage is poor; most drainage takes place in the underground karst drainage systems. The karst plain is characterized by caves, natural bridges, disappearing streams, and springs, such as Wakulla Springs5. Sinkholes6 are ubiquitous throughout the karst plain, numbering in the thousands. Most sinkholes are only a few feet deep and intercept the shallow, local water table, creating many small lakes and wetland ecosystems, such as cypress stands. In places, the plain is crossed in an east-west direction by low, linear sand dunes7, left behind by higher stands of ancient sea levels.
The sands are whitish-gray, clean quartz, and have very few nutrients or minerals that are needed by plants. Consequently, the vegetation and the ecosystems of this area are less diverse than those of the Northern Highlands. The dominant plants of the karst plain are stunted oaks (blackjack and turkey oak) and spindly longleaf pine. Undergrowth is sparse, with scattered wiry grasses and palmettoes. In contrast, there are many places throughout the karst plain where dissolution has lowered the land surface, intercepting the water table to form ponds. These perennially wet or boggy environments support dense growths of hardwoods, cypress, palms, and undergrowth, similar to ecosystems found on the uplands.
The coastal environment is very dynamic and subject to the ceaseless geologic processes of shoreline erosion and accretion. Ecosystems in this zone range across fresh-to-brackish-to-salt water types; e.g., fresh-water streams discharge into brackish estuaries and tidal marshes, which interact with open Gulf waters8. The onshore dune systems and the offshore barrier islands9, with their own special ecosystems of grasses and ground cover, are significant components of coastal ecosystems, because they provide irreplaceable protection from erosion by storms."
Footnotes
- In the Florida Geomorphology Atlas, the FGS refined the mapping of geomorphic districts and their provinces. This area is now included in the Tifton Upland District. Please see the Atlas for more information about districts and their provinces.
- Now included in the Ocala Karst District.
- Steepheads: Located near the Apalachicola River, steepheads can be explored in this WFSU blog.
- Karst Lake: Lake Jackson is a well-known karst lake in north Leon County, which is naturally drained by sinkholes. The periodic drying events observed at Lake Jackson are documented in this video. More information can be found in the Lake Jackson FAQs and this FGS article.
- Springs: Explore the geology of Edward Ball Wakulla Springs State Park in this newsletter and in FGS Open File Report 22. Learn about research to trace the source of water for Wakulla Springs in FGS Special Publication 56. Further east, discover Madison Blue Spring State Park. Read about the FGS finding previously undocumented springs in the Big Bend Area. A Guide to Identifying Springs and Seeps in Florida provides additional information.
- Sinkholes: The geology of Leon Sinks Geological Area, located south of Tallahassee on US 319, is described in this newsletter and in FGS Open File Report 20. For more information about sinkholes in general, see FGS Leaflet 20.
- Ancient Sand Dunes: The Munson Sandhills are relict sand dunes deposited during times of higher sea levels.
- Estuary: St. Marks National Wildlife Refuge extends along the coastline through Taylor, Jefferson, and Wakulla Counties and includes the mouth of the St. Marks River.
- Offshore Barrier Island and Modern Dune System: Julian G. Bruce St. George Island State Park is a classic example of a barrier island with a modern dune system. To explore barrier island geology, please refer to FGS Leaflet 13.
Additional resources
Knight G.R., Oetting J., and Cross L., eds., 2011, Atlas of Florida's Natural Heritage: Biodiversity, Landscapes, Stewardship, and Opportunities: Tallahassee, Florida, Institute of Science and Public Affairs, Florida State University, 162 p.
Scott, T.M., 2001, Text to accompany the Geologic Map of Florida: Florida Geological Survey Open-File Report 80, 29 p., https://doi.org/10.35256/OFR80.
Scott, T.M., Campbell, K.M., Rupert, F.R., Arthur, J.D., Green, R.C., Means, G.H., Missimer, T.M., Lloyd, J.M., Yon, J.W., and Duncan, J.G., 2001, Geologic Map of the State of Florida: Florida Geological Survey Map Series 146, scale 1:750,000, https://doi.org/10.35256/MS146.
Whitney, E.N., Means, D.B., Rudloe, A., and Jadaszewski, E. (Illustrator), 2014, Florida's Uplands: Sarasota, Florida, Pineapple Press, 166 p.
Whitney, E.N., Means, D.B., and Rudloe, A., 2014, Florida's Waters: Sarasota, Florida, Pineapple Press, 142 p.
Whitney, E.N., Means, D.B., Rudloe, A., and Jadaszewski, E. (Illustrator), 2014, Florida's Wetlands: Sarasota, Florida, Pineapple Press, 166 p.
Williams, C.P., Scott, T.M., and Upchurch, S.B., 2022, Florida Geomorphology Atlas: Florida Geological Survey Special Publication 59, 238 p., https://doi.org/10.35256/SP59.
Please use the Online FGS Publication Search to explore the geology of individual counties or geologic units within this area.
Contact: Mabry Gaboardi Calhoun, Ph.D.
Suggested citation for poster: Lane, E., and Rupert, F.R., 1996, Earth Systems: The Foundation of Florida’s Ecosystems: Florida Geological Survey Poster 6, Color, 40” x 60”, https://doi.org/10.35256/P06.
Link for this article: https://content.govdelivery.com/accounts/FLDEP/bulletins/3c6d3e0#link_1
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Edward Ball Wakulla Springs State Park, located in northern Florida, features Wakulla Spring, one of the largest artesian springs in the United States and perhaps in the world (Figure 1). The park is located in the Woodville Karst Plain Province of the Ocala Karst District, and contains numerous springs, sinkholes and other karst features. The spring is connected to a vast network of conduits that extend both to the north and south of the spring and are part of the longest mapped underwater cave system in the United States. As of January 2023, cave divers had explored and mapped approximately 45 miles of cave passage in what is called the Wakulla Springs cave system. More than 30 entrances, through sinkholes and springs, to the Wakulla Springs cave system are known and more than 22 miles of cave passage exceed a depth of 190 feet.
Wakulla Spring, the main source of water for the Wakulla River, discharges approximately 300 million gallons per day from the upper Floridan aquifer. Groundwater discharging from the spring can fill a 660,000 gallon Olympic-size swimming pool every eight minutes! The watershed that supplies water to Wakulla Spring is estimated to be 975 square miles and encompasses parts of North Florida and South Georgia. Water discharging from Wakulla Spring is a mix of older and younger groundwater. Surface water that recharges rapidly via multiple large swallets located throughout the watershed is later discharged at Wakulla Spring as young groundwater. Dye trace studies conducted in the Wakulla Spring watershed have verified that water flowing into four major swallets later discharges at Wakulla Spring. Because of the complex interplay between surface water and groundwater within the Wakulla Spring watershed, Wakulla Spring has one of the largest observed ranges in discharge of any spring in Florida.
Geology of Wakulla Spring
The geologic strata exposed in the cave beneath Wakulla Spring are limestone and dolostone carbonate rocks that were deposited over millions of years and are slowly being dissolved by naturally acidic water. The cave system that sustains the flow of water to the spring is primarily developed in the Oligocene Suwannee Limestone. The Suwannee Limestone was deposited in a shallow, warm sea that inundated Florida between 34 and 28 million years ago. The Suwannee Limestone is typically a white to pale orange limestone composed of sand-sized carbonate particles and frequently contains molds of larger fossil marine organisms. In some areas, the Suwannee Limestone is comprised of layers of tan to light brown dolostone, a rock formed by the alteration of limestone by magnesium-rich water.
The top of the Suwannee Limestone is encountered at a depth of 90 feet below the water surface at the spring vent. Overlying the Suwannee Limestone is the Miocene St. Marks Formation. This formation is 23 to 20 million years old and is exposed between 10 and 90 feet below the water surface. It is a white to pale orange, fossil-rich, sandy limestone. Although this formation is found below the water surface, there are several places where this formation can be observed at the surface along the nature trails within the park, at Cherokee Sink, and in the bed of the Wakulla River.
The Suwannee Limestone and St. Marks Formation are the geologic units that comprise the upper Floridan aquifer in this part of Florida. These limestone units contain many interconnected holes, like a sponge, that transmit water through the network of conduits to the spring. Wakulla Spring is one of hundreds of springs throughout Florida that act as discharge (flow) points for the upper Floridan aquifer.
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Numerous sinkholes in the area are developed in the Suwannee Limestone and St. Marks Formation. Overlying the St. Marks Formation is a thin, discontinuous layer of Pleistocene to Holocene sand and sandy clay deposited over the past 2.6 million years. Most of these sediments are marine deposits left behind during times when sea level was higher during Florida’s geological past. There are also fresh-water shell deposits found in the Wakulla River and its floodplain that were deposited during times when the Wakulla River was flowing (Figure 2). Where the Wakulla River exposes these shelly deposits, it is not uncommon to find the fossilized bones of extinct animals eroding out. The fossil remains of mammoths, mastodons, giant sloths, llamas, bison and saber-tooth cats have been found in Wakulla Spring and in the Wakulla River (Figure 3).
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Wakulla Spring is one of the most studied spring systems in the United States. Early scientific work conducted at Wakulla Spring led to the discovery and excavation of mastodon remains by the FGS in the 1930’s. Numerous skeletal remains from extinct Pleistocene megafaunal animals have since been discovered along with archaeological evidence of the first people that inhabited Florida. Today, ongoing research using cutting-edge SCUBA technology and autonomous underwater vehicles is revealing more information about this world-class artesian spring.
Designations
Wakulla Spring is an Outstanding Florida Spring, a designation made by the Florida Legislature to limit groundwater withdrawals deemed harmful to springs. Wakulla Spring is also a Florida State Geological Site designated by the State Geologist of Florida in 2018 as an outstanding example of a Florida spring. With its recent recognition by the International Union of Geological Sciences (IUGS) as a Geological Heritage Site, Wakulla Spring is now also an internationally recognized site of scientific and cultural importance.
Additional resources
Rupert, F.R., 1988, The Geology of Wakulla Springs: Florida Geological Survey Open-File Report 22, 18 p., https://doi.org/10.35256/OFR22.
Contact: Harley Means, P.G.
Suggested Citation
Means, G.H., 2024, Geology in the Real Florida: Edward Ball Wakulla Springs State Park: FGS News and Research December 2024 edition. https://content.govdelivery.com/accounts/FLDEP/bulletins/3c6d3e0#link_6.
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The Leon Sinks Geological Area (LSGA), part of the Apalachicola National Forest, is a protected karst area south of Tallahassee with trails, dry and wet sinkholes, swallets, natural bridges and caves (Figure 1). The LSGA is located in the Woodville Karst Plain Province and contains excellent examples of the region’s karst features.
FGS borehole W-18480 allows us to examine the stratigraphy at the site (Figure 2). Within the borehole, the upper 39 feet are undifferentiated sands and clays (UDSC). This is underlain by the Miocene sands and mudstones of the Torreya Formation (Hawthorn Group) to a depth of 50 feet. Limestone of the St. Marks Formation occurs from 50 to 115 feet below land surface. The Miocene St. Marks Formation is underlain by the Oligocene Suwannee Limestone from a depth of 115 ft to the total depth of the well.
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The geology of the area is favorable for sinkhole formation because of the thin overburden, or sediments, overlying limestone formations with cavernous porosity. Sinkhole types include cover subsidence and cover collapse, with their origin dependent on the underlying geology. The percentage of clay in the overburden is a primary factor that determines the nature of the subsidence. Sandy overburden will subside less dramatically than cohesive sediment containing minor amounts of clay, which can lead to the formation of cover collapse sinkholes like Big Dismal Sink at LSGA. The well-known and extensively mapped Wakulla Springs cave system tracks beneath, and is connected to, several of the sinks within the park, including Big Dismal. The southern portion of the LSGA has much less overburden. The water table is at or very near the surface in the southern extent of the LSGA, creating a swamp, as seen on the Gum Swamp Trail in Figure 1.
Ground-penetrating radar (GPR) data were collected in LSGA in 2018 along the path shown in Figure 3. Sections from the GPR radargrams that pass by several of the distinct karst features within the park are displayed in Figure 4. Marker numbers in Figures 3 and 4 correspond. Brighter colors in the radargrams indicate lithological contrast in the subsurface. Examples include the transition from sand to clayey sand, or the transition from dry clayey sand to saturated clayey sand. Marker 1 in Figures 3 and 4 is adjacent to Big Dismal Sink and is interpreted as an area with a thin veneer of sand or clayey sand atop a saturated clayey sand that may be forming the more competent layer that is visible within the sink.
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In the shallow surface, darker colors in the radargram are indicative of homogeneity in sediments. Marker 2 (Figures 3 and 4) is where the trail passes by Big Eight Sink. The trail lowers in elevation into the sink here and at this point in the radargram the buried karst feature can be seen as a grouping of high contrast reflectors within a “depression shaped” feature in the subsurface. This is interpreted as homogeneous sands (dark, no contrast) above a heterogeneous mix of saturated sand, clay and clayey sand that have collapsed into the depression created by the dissolution of the underlying limestone. Marker 3 (Figures 3 and 4) is where the trail passes by Magnolia Sink and, like marker 2, the high contrast features in the subsurface show mixed overburden sediments deposited in a conical depression. Similarly, marker 4 (Figures 3 and 4), which passes by Black Sink, demonstrates another excellent example of what the edge of a karst feature can look like in a GPR radargram. The conical depression in the subsurface with high contrast is again representative of a sinkhole.
As the trail proceeds, elevation again drops towards the south where there are more wetlands. Markers 5 and 6 (Figures 3 and 4) are Lost Stream Sink and Fisher Creek Sink, respectively. The radargrams here have a much different look than the previous sites. That is because these features are active or semi-active swallets (a sinkhole that receives surface water) that are at times taking large volumes of water from Fisher Creek. At markers 5 and 6, the radargrams depict the tell-tale sign of flowing water because of GPR signal attenuation. In general, water attenuates or decreases GPR signal strength producing little to no data. Small amounts of water may aid in identifying lithologic contrast in the subsurface, but larger quantities of water will tend to obscure the subsurface lithology. However, even though we cannot “see” the lithology, we can still interpret that water is likely flowing beneath the trail at these locations.
Leon Sinks Geological Area is a great location to see a variety of Florida’s famous karst features. As such, it provides us the opportunity to enhance our understanding of what GPR data indicate and refine our ability to interpret subsurface features using ground-penetrating radar.
Contact: Casey Albritton, P.G.
Suggested Citation
Albritton, C.K., 2024, The Geology of Leon Sinks Geological Area: FGS News and Research December 2024 edition. https://content.govdelivery.com/accounts/FLDEP/bulletins/3c6d3e0#link_8.
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In November, State Geologist Harley Means led Florida State University (FSU) faculty and students from the Department of Earth, Ocean, and Atmospheric Sciences (EOAS) on a hike along the Aucilla Sinks Trail (Figure 1). This portion of the Florida Trail, located in the Middle Aucilla Wildlife Management Area, allows many opportunities to observe karst features and surface water-groundwater interactions between the Aucilla River and the upper Floridan aquifer.
According to FSU-EOAS Professor Danny Goddard, “The interactions between FSU-EOAS and the FGS have broadened our faculty's understanding of the amazing and unique geology we have right here in our own backyard. The trips are great adventures for all of us here in the department and I think that excitement and information make its way into our research and our classrooms.”
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This article is the second in a multi-part series discussing Quaternary undifferentiated sediments in Florida. Scott et al. (2001) divided Florida’s Quaternary deposits into informal geomorphically defined units to better describe the geologic character and evolution of the mapped units. The Quaternary beach ridge and dune (Qbd) and the Quaternary alluvium (Qal) divisions of the Quaternary undifferentiated sediments are the focus for this edition. Scott et al., (2001) defines Holocene sediments as those found at an elevation generally less than 1.5 meters and along the coast. In the following paragraphs, you will learn about the defined differences between these informal geologic units, and some exceptions.
The extent of the Qbd has been defined in two ways. The first includes Pleistocene shoreline deposits comprised of quartz sand, silt or clay with variable amounts shell material. These have the characteristics of linear beach ridges and dunes like those that form along the coastlines of the Atlantic Coast and Gulf of Mexico coast today. Importantly, similar Holocene linear beach ridge and dune deposits, like False Cape of the Cape Canaveral region, are mapped as Holocene sediments (Qh), even though they have the same morphology as Qbd. As with the Holocene beach ridge and dune deposits, lidar can be used to map the extent of Qbd. Holocene beach ridge and dune deposits are rarely found above 10 meters. Qbd can include some regions higher than 10 meters in elevation. Holocene beach ridges have distinct, clear edges. Beach ridges of the Qbd have less distinct lines and edges that reflect the effects of weathering and shell dissolution over geologic time. Figure 1 shows a comparison between Holocene and Pleistocene beach ridge and dune deposits.
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The second way of defining Qbd deposits is by the more distinctive aeolian characteristics, such as transverse, barchan or parabolic dunes. They do not have the ridge and swale characteristics of shoreline deposits. Aeolian dunes have more irregular and non-linear forms than dunes generated as part of shoreline deposits. Most of these deposits are found in interior parts of Florida, not adjacent to the modern coastlines. They typically consist of quartz sand with minor amounts of silt or clay.
Florida’s mapped Qal deposits are alluvial in origin. They are not like alluvial fans from locations in the western United States. In the Florida context, these are sediments within river valleys, also known as fluvial or floodplain deposits. In the past, Qal mapping has been restricted to floodplains of larger river valleys in Florida, specifically in the Panhandle. Qal consists of quartz sand, silt, clay and organics. Lidar is used to locate landforms typical of river floodplains, like ridges and swales formed by stream channel migration, and oxbow lakes, lakes formed when streams cut off their own curved meanders. Qal is mapped based on these landforms and on sediment composition.
There are examples of Qal deposits geomorphically defined in floodplains that could be mapped in parts of Florida outside of the Panhandle. Many of these examples highlight the importance of consistency when dividing undifferentiated Quaternary sediments.
To accurately determine the thickness of these units, a high density of borehole data and detailed lithologic descriptions are needed. The Qh, Qbd and Qal are typically drawn on two-dimensional maps based upon surficial morphology. In many cases, the underlying materials cannot be assessed for age or depositional setting. The base of these units in geologic cross sections is interpreted down to the top of the first named geologic formation.
This article describes our efforts to better understand and map Florida’s young, complex, Quaternary geology, particularly the Qbd and Qal deposits. Part one of the series is available here. In the next edition, the historical mapping of the Trail Ridge sands (Qtr) on Trail Ridge and the Baywood Promontory in northeastern Florida will be contrasted with new research on heavy mineral deposits in the Cypresshead Formation in the region.
References Cited
Scott, T.M., 2001, Text to accompany the Geologic Map of Florida: Florida Geological Survey Open-File Report 80, 29 p., https://doi.org/10.35256/OFR80.
Scott, T.M., Campbell, K.M., Rupert, F.R., Arthur, J.D., Green, R.C., Means, G.H., Missimer, T.M., Lloyd, J.M., Yon, J.W., and Duncan, J.G., 2001, Geologic Map of the State of Florida: Florida Geological Survey Map Series 146, scale 1:750,000, https://doi.org/10.35256/MS146.
Contact: Clint Kromhout, P.G.
Suggested Citation
Williams, C.P., 2024, Featured Formation: Quaternary Undifferentiated Sediments and other Undifferentiated Quaternary Units in Florida, Part II: FGS News and Research December 2024 edition. https://content.govdelivery.com/accounts/FLDEP/bulletins/3c6d3e0#link_4.
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According to the National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Information (2024), North Atlantic tropical cyclone activity during 2024 exceeded the 30-year average (1991-2020) levels, with three hurricanes making landfall in Florida by the end of October. With storms come geohazards, including storm surges and flooding. In Florida, these short duration, high rainfall events can also result in sinkhole formation.
Sinkholes in Florida are primarily a result of limestone dissolution. Limestone dissolution at the surface can form solution sinkholes. Limestone dissolution below the surface causes cavities. These can range in size from microscopic pockets to caves that extend for miles. Often these cavities are overlain by deposits of sand and clay. The ground surface above can be relatively flat and appear unaffected by the void space below. If the sediments above the cavity become too heavy, they can gradually infill the cavity. This appears on the ground surface as a circular depression with a modest slope and is called a cover subsidence sinkhole. Sediments can also collapse into the cavity. This is called a cover collapse sinkhole. Heavy rainfall events, particularly after prolonged dry periods, can cause these cover subsidence and cover collapse sinkholes by increasing the weight of the overlying sediments. There are exceptions to how each of the different types of sinkholes form. If you have questions, we encourage you to contact the FGS or a licensed Florida professional geologist in your area.
The FGS provides a Sinkhole Helpline to clarify the information presented in DEP's Sinkholes FAQ, answer any additional sinkhole questions and provide verbal guidance relating to a sinkhole situation. The FGS also created and maintains a Subsidence Incident Reports database. Currently, most of the database records come from the Florida Department of Emergency Management’s State Watch Office, which is a statewide dispatch for emergency response calls.
Figure 1 shows the relationship between the number of reported subsidence incidents in Florida and major weather events from January 2000-October 2024. This year, after Hurricanes Debby, Helene and Milton, there was a clear uptick in subsidence incidents reported in Florida. Historically, there is precedence for an increase in the number of reports after storm events, such as after Tropical Storm Debby in June of 2012.
Interestingly, other weather events can impact the number of reported subsidence incidents. In January 2010, Plant City, Florida, experienced 11 consecutive days of below freezing weather. To preserve agricultural crops, emergency groundwater pumping occurred. This lowered the water level in the aquifer locally, causing previously water-filled cavities to empty. These empty voids could no longer support the weight of overlying sediments, resulting in an increase in sinkhole development.
Although sinkholes are not often thought of as an obvious result of weather-related events, they clearly can be. By changing the amount of water at the ground surface or in the underlying aquifer, sinkholes can be triggered. This relationship is evident in Florida, with its history of tropical storms, hurricanes and karst geology.
References Cited
NOAA National Centers for Environmental Information, 2024, Monthly Tropical Cyclones Report for October 2024, published online November 2024: https://www.ncei.noaa.gov/access/monitoring/monthly-report/tropical-cyclones/202410 (accessed December 2024).
Contact: Clint Kromhout, P.G.
Suggested Citation:
Gaboardi Calhoun, M.M., Kromhout, C.K., and Means, G.H., 2024, Hurricane Season and Associated Uptick in Reported Sinkholes: FGS News and Research December 2024 edition. https://content.govdelivery.com/accounts/FLDEP/bulletins/3c6d3e0#link_3.
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