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Davis Lake
Volusia County, Florida
Introduction | Subsurface Characterization
Geologic Characterization
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| Davis Lake. Black lines show profile locations. |
The quality of the seismic profiles obtained from Davis Lake is poor. Multiples of the bottom reflection are seen throughout the data and 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, as shown midway in profile A-A'. The multiples may be a result of lithologically homogeneous, hard packed sands near surface which tend to set up ringing in the acoustic return, accumulation of organic material at the lake bottom may also attenuate the signal. Profile A-A' does show one area of potential disturbance (red dashed line). The high angle reflections, that become obscured by the multiples, may represent a dissolution feature which would indicate a breach in the overburden.
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| Profile A-A' |
The parabolic return (left-most feature bracketed by red dashed lines) unfortunately is also a pattern commonly associated with submerged pipelines. Three other lines that cross the same area are shown below (B-B', C-C', D-D'). The data is obscured by multiples, but inconsistencies in the acoustic return at depth may indicate a subsurface disturbance. Gamma-log profiles in the area (wells V-0346 and P-0146, Index Map D) show the contact between the Ocala Limestone and the overlying Hawthorn Group rising from about 21 m (70 ft) below mean sea level to the southwest, to 15 m (50 ft) below mean sea level north of the lake. This corresponds to approximately 20 m (-65.6 ft) below lake bottom, using an averaged sound velocity of 1500 m/s. This depth puts the top of the aquifer-bearing Ocala Limestone very near the surface. A breach through the overburden would increase the potential for contact between the surface waters and the aquifer.
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| Profiles A-A', B-B', and C-C' |
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U. S. Department of the Interior | U.S. Geological Survey
