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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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Cow Pond Lake
Valusia County, Florida

Introduction | Subsurface Characterization

Subsurface Characterization

Cow Pond Lake
Cow Pond Lake. Black lines show profile locations.
The quality of the seismic profiles obtained from Cow Pond Lake is generally poor. A strong bottom reflection leads to multiples, seen throughout the data, that obscure some of the record in the deeper portions of the lake. The record is also partially obscured in areas where the lake bottom nears the surface (B-B', C-C' below). Areas above the first multiple show sediment fill (type 6, C-C') and evidence of near surface subsidence (type 1, A-A' below). These patterns are identical by down-dipping reflections on the flanks of a zone of obscured record. The type 1 features extend to depth in the profiles and occur in numerous, constrained areas throughout the lake.
Seismic Profile A-A'
Profile A-A'

Seismic Profile B-B'
Prolife B-B'

Seismic Profile C-C'
Profile C-C'

Distribution of features map showing that the lake is comprised of small solution/subsidence features rather than one predominant subsidence as seen in other lakes.
Cowpond Lake Distibution of Features
(noted from seismic profiles)
Areal extent of features noted from the seismic profiles can be seen in the map above. The Distribution of Features map shows that the lake is comprised of small solution/subsidence features rather than one predominant subsidence as seen in other lakes. Most of the type 1 reflection patterns seen in the lake extend to depth from the near lake bottom. Two areas of the lake, however, show deeper solution/subsidence type features (red numbers,Track Map) that do not extend entirely to the surface. These features may have evolved on a different time scale (earlier and infilled, or later and not fully developed) or hydrologic regime than the other type 1 features. Throughout the seismic profiles, segments of a strong reflection can be seen at depth where the record is not obscured (blue lines). These reflections may represent the karst surface of the Ocala Limestone. Interpretations of gamma logs from wells in the vicinity (Index Map D, wells P-0416, V-0346, V-0184) infer the top of the Ocala Limestone to range from -15 to -22 m (-50 to -75 ft) below sea level. The depth corresponds to 36 to 46 ms below the lake surface, using an averaged sound velocity of 1500 m/s. This correlates with the strong reflection seen in profile C-C'. The material above the Ocala Limestone could be the sands and clays of the Hawthorn Group and subsidence fill from the Plio-Pleistocene ridge sediments.

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 05, 2016 @ 11:25 AM (JSS)