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

Subsurface Characterization

Kingsley Lake. Black lines show profile locations.

Profile A-A' (see below) illustrates the strata in and around the primary sinkhole within the lake. An abrupt change in the lake bottom slope can be seen on the flanks of the sinkhole. This is a filled, collapse-sinkhole with steep flanks overlain by offlapping fill and slumps. The fill is acoustically transparent with few low-amplitude reflections discernible. This is to be expected since the source of the fill is primarily clean quartz sands brought in from the adjacent Trail Ridge deposits. Plotted on the Kingsley Lake survey track map are the karst features identified from seismic profiles; Types 1, 2, 3, and 6 (for definition of types, see Fig. 16 or Trackmap) karst features were found. Features 1 and 2 represent the primary sinkhole surrounded by Type 6 undisturbed depositional layers.

The Type 1, 3 feature seen in profile B-B' (see below) appears to be a secondary collapse feature that occurred after the formation of the main doline shown in profile A-A' (see Profile A-A' below). Unlike the main doline, this feature is not completely filled with sediment. The data does not indicate that the feature extends through the surficial and Hawthorn Group sediments into the Floridan aquifer (>95 m).

Profile A-A'

Profile B-B'

There is only limited borehole data available to correlate the seismic data. Interpolating from the nearest borehole C-0478 (Index Map A) the top of the Hawthorn Group is seen along the shallow flanks of the lake at approximately 10 ms. In profile A-A' (see Profile A-A' above) the top of the Hawthorn Group is shown to be steeply dipping towards the center of Lake Kingsley due to the sinkhole collapse. It is estimated that the top of the Floridan aquifer should be seen in the data at approximately 150 ms. None of the profiles contained data that was resolvable at that depth however.

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