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Coastal & Marine Geology Program > Center for Coastal & Regional Marine Studies > Geologic Characterization of Lakes and Rivers of Northeast Florida > OFR 00-180

Subsurface Characterization of Selected Water Bodies in the St Johns River Water Management District, Northeast Florida

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Identification of Karst Features from Seismic Patterns
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Lake Dixie
Lake County, Florida

Introduction | Subsurface Characterization

Subsurface Characterization

Lake Dixie
Lake Dixie. Black likes show profile locations.
Seismic profiles from Lake Dixie show a hard bottom reflection, possibly from well sorted sands, infilling a deeper karst surface (feature 6, A-A'). The strong bottom reflection leads to multiples seen throughout the data that obscure some of the record. Noise below the topographic lows in the profiles also obscure some of the record (green lines, B-B'). This noise could be a result of the accumulation of organic material in the depressions which attenuates the acoustic signal. Despite the noise in the acoustic record, the proximity of the underlying karst surface to the lake bottom allows for a variety of solution and subsidence type features to be seen. The subsurface is characterized by numerous small depressions with high angle reflections dipping toward their center (C-C'). The high angle reflections may extend to depth in the profile. These features may represent solution pipes dissolved into the karst subsurface. Larger subsidence features can also be seen in the profiles (type 3, A-A'). A plot of their distribution (blue line) shows three distinct areas of subsidence and their influence on the lake's bathymetry (blue line).

Profile A-A'
Profile A-A'

Profile B-B'
Profile B-B'

Profile C-C'
Profile C-C'

Distribution of Features
Lake Dixie Distribution of Features
(noted from seismic profiles)
A deeper, strong reflection can be seen in many of the subbottom profiles (red line, A-A', B-B'). The highly jagged appearance of this reflection is indicative of an erosional (karst) surface seen in profiles throughout the region. Interpretations of a gamma log acquired from a well located approximately 1.5 km (.9 mi) southeast of the lake (Index Map G, well L-0677) shows the top of the Ocala Limestone to be around 15 m (50 ft) NGVD. This correlates well with the horizon seen in the profiles. Differential dissolution in the Ocala Limestone could lead to subsequent subsidence in the overlying sediments of the Hawthorn Group and the undifferentiated fill.

Coastal & Marine Geology Program > Center for Coastal & Regional Marine Studies > Geologic Characterization of Lakes and Rivers of Northeast Florida > OFR 00-180

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Updated December 02, 2016 @ 11:25 AM (JSS)