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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 Dias
Putman County, Florida

Introduction | Subsurface Characterization

Subsurface Characterization

Lake Dias
Lake Dias. Black lines show profile locations.
Seismic profiles from Lake Dias are predominantly obscured at depth. A strong bottom reflection leads to multiples seen throughout the data that obscure some of the record in the deeper portions of the lake (C-C' below). The record is also partially obscured in areas where the lake bottom nears the surface (A-A', B-B' below). In general the lake is characterized as a single large depression comprising most of the lake (Distribution of Features, blue line, below). Deep reflections tend to drop prior to becoming obscured near the central portions of the lake (B-B', blue lines). This suggests that deep structures influence the lake bathymetry. Low-amplitude, near surface reflections in some of the profiles near the fringes of the lake have a hummocky appearance (index map, type 4 feature, A-A', B-B', red lines, below). The reflections may represent smaller subsidence features in the fill overlying the deeper subsidence. Profile C-C' also shows some low angle, offlap type reflections (type 6 , red lines) that may represent subsequent fill during subsidence of the lake.

Profile A-A'
Profile A-A'

Profile B-B'
Profile B-B'

Profile D-D' (below) shows a feature seen in the extreme northeastern portion of the lake. Pronounced high angle reflections (red lines), overlain by fill-type horizontal reflections (orange lines) may represent a collapse structure (type 3). A chaotic signal below the horizontal reflections could be block fill associated with the initial collapse, which was subsequently overlain by fluvial fill. This is the only area throughout the lake where this type feature is present and could represent a major breach in the confining material overlying the aquifer.

Profile C-C'
Profile C-C'

Profile D-D'
Profile D-D'

Distribution of Features Map
Lake Dias Distribution of Features
(noted from seismic profiles)

Interpretations of gamma profiles from wells surrounding the lake (Index Map D, gamaa log cross-section C-C') show the top of the Ocala Limestone to be between -9 and -15 m (-20 and -50 ft) NGVD. This would correspond to between 26 and 35 milliseconds depth in the profiles, using an averaged sound velocity of 1500 m/s. This depth would suggest that the blue lines seen in the profiles (A-A', B-B', above) represent horizons near the top of the Ocala Limestone. Dissolution in the Ocala Limestone at depth would cause subsidence in the overlying material and fill.

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 May 06, 2013 @ 09:24 AM (JSS)