9. Application of Sequence Stratigraphy to Delineate Heterogeneous Ground-Water Flow in Karstic Platform Carbonates
Karst subsurface formations host some of the most prolific and economically important aquifers. In 1990, the Floridan aquifer alone supplied an estimated 3.4 billion gallons of fresh water per day. Approximately 25 percent of the world's population lives above or depends on karst aquifers for potable water. In the United States, 40 percent of the ground water used for drinking comes from karst aquifers. These karst aquifers are particularly vulnerable to inadequate or poor ground-water management practices because of rapid recharge and fast ground-water flow through conduits characteristic to karst aquifers.
In general terms, karst aquifers contain complex, interconnected networks of solution-enlarged conduits that permit high-velocity ground-water flow over large distances in relatively short periods of time. Because of these flow characteristics; the U.S. Environmental Protection Agency has recognized that karst aquifers are highly susceptible to bacterial and chemical contamination.
In southern Florida, the USGS has been successful in implementing sequence stratigraphy as one of several tools for providing an accurate means of mapping karstic preferential flow zones. Results are (1) offering insight into the potential limitations of assumptions of numerical modeling karst aquifers as porous media, granular filtration theory, and risk assessment models applied to municipal wellhead protection; and (2) improving the conceptualization of ground-water seepage in areas critical to the restoration of the Florida Everglades, and fresh ground-water flows from coastal areas to ecologically sensitive estuaries and marine bays.
Sequence stratigraphy, hydrology, paleontology, geochronology, and borehole geophysics are being integrated to construct a conceptual aquifer model for the karstic Biscayne aquifer of southern Florida that is suitable for ground-water flow simulation. The model is being built by using vertical lithofacies successions constrained by high-frequency cycle boundaries. The vertical lithofacies successions contain (1) lower rock properties that produce preferential ground-water flow zones and, (2) middle units that are characterized by diffuse-carbonate flow, and (3) upper units that are leaky, low-permeability zones. Accurate horizontal and vertical correlation of these hydraulic parameters allows for construction of a sophisticated, high-resolution conceptual aquifer model. Additionally, similar research concepts have been integrated for characterization of the karstic Floridan aquifer.
The Mendenhall Fellow will work closely with experienced USGS geologists and hydrologists, and will conduct studies that integrate carbonate sequence stratigraphy, hydrology, paleontology, geochronology, and borehole geophysics of karstic Tertiary carbonates on the Florida platform. The candidate will be encouraged to expand on existing use of borehole geophysical tools, especially flowmeters, for quantification of aquifer parameters to be used for numerical ground-water model simulations.
Proposed Duty Station: St. Petersburg, and/or Miami, FL
Areas of Ph.D.: Geology, stratigraphy, geophysics
Qualifications: Applicants must meet one of the following qualifications: Research Geologist, Research Geophysicist
(This type of research is performed by those who have backgrounds for the
occupations stated above. However, other titles may be applicable depending
on the applicant's background, education, and research proposal. The final
classification of the position will be made by the Personnel specialist.)
Research Advisor(s): Gene Shinn, (727) 803-8747 x 3030, eshinn@usgs.gov; Kevin J. Cunningham, (305) 717-5813, kcunning@usgs.gov
Personnel Office contact: Rosetta Alexander, (703) 648-7468, ralexand@usgs.gov
U.S. Department of the Interior, U.S. Geological Survey
URL: http://geology.usgs.gov/postdoc/2006/opps/opp9.html
Direct inquiries to Rama K. Kotra at rkotra@usgs.gov
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Last modified: 12:05:20 Tue 24 Aug 2004
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