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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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Lake Kerr
Marion County, Florida

Introduction | Subsurface Characterization
Lake Kerr
Lake Kerr. Black lines show profile locations.

Subsurface Characterization

Lake Kerr is characterized by numerous subsidence depressions (type 2) tens to hundreds of meters in width (A-A', B-B' below). Parallel to low angle reflections within the depressions indicate active infilling during subsidence. The low-angle reflections appear to dip toward the southeast when present in the record (black dip symbols, Index Map D). This infilling gives the lake a smooth bathymetry (brown line contour map), unlike the highly irregular subsurface in which the subsidence occurs (blue line contour maps and 2-D profiles). The reflective horizons that were digitized to produce the contour maps are shown on the seismic examples. The north and south cross sections, derived from the gridded contour data sets, shows this contrast very well and may indicate that subsidence had matured prior to deposition of the nearsurface sediments.

Seismic Profile A-A'
Profile A-A'

Seismic Profile B-B'
Profile B-B'

Noise in the seismic record decreases in the eastern part of the lake and deeper reflective horizons can be seen (A-A', red line). The acoustic signal in the lower horizons is more chaotic and contains very high angle reflections, whereas the upper horizons have lower angle, intact reflections. It seems apparent in the seismic profiles that more solution-type collapse has occurred in the lower horizons and that it has influenced a more gradual subsidence in the overlying material (blue line). During subsidence the depressions were filled, possibly during migration of paleo-dunes that define this physiographic region.

Vertical Exaggeration 87:1. Contours are in meters from lake level.

Vertical Exaggeration 87:1.

The contact between the Ocala Limestone and the Hawthorn Group, as interpreted from gamma log profiles, is deeper than resolvable depth in the seismic profiles. However, changes in gamma counts in a well northeast of the lake (well M-0149, Index Map D) within the Hawthorn Group may correlate with the reflective horizons within profile A-A' at about 12 m.

Coastal & Marine Geology Program > Center for Coastal & Regional Marine Studies > Geologic Characterization of Lakes and Rivers of Northeast Florida > OFR 00-180 U. S. Department of the Interior | U.S. Geological Survey
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Updated December 05, 2016 @ 11:25 AM (JSS)