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Seismic Stratigraphy of the Central Indian River Region
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Stratigraphy of the Indian River Region
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Stratigraphy of the Indian River Region
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Jim Flocks
  Analysis of seismic data and natural gamma logs from wells within the study area indicate the Hawthorn Group to be dipping to the southeast in response to subsidence or dissolution in the underlying carbonate rock. Fluid migration and rock movement and dissolution along a deeper fault zone is a possible mechanism for the subsidence. Bermes (1958) and Schiner and others (1988) used well logs and water quality data to infer the presence of a fault system within the area. The fault system would predate the Miocene since the seismic profiles show no evidence of faulting within the Hawthorn Group.

Comparison of trends in contours generated from the seismic data with the cross section from the natural gamma logs show good correlation. Correlating measured depths on the gamma logs with depth-to-horizon on the seismic profiles indicate an average sound velocity of 1,955 m/s through the Hawthorn Group. This estimate is within the range of velocities suggested from other studies of the Miocene sediments in Florida. Absolute correlation between gamma log depth and two way travel time could not be established since the gamma log cross section did not intersect the seismic profiles.

Other features identified in the seismic profiles include three collapse sinkholes within the Hawthorn Group sediments. Two are located north of Johns Island in the Intracoastal Waterway on profile SB_2 (Fig. 11, S1 & S2). The other is located about one mile offshore east of the city of Vero Beach on profile SB_1 (Fig. 12).

Acknowledgments

The authors would like to express their thanks to the Governing Board of the St. Johns River Water Management District (SJRWMD),and Douglas A. Munch of SJRWMD, for continuing support of high-resolution seismic reflection studies within the District. Thanks to William Osborn, P.G. and David Toth, P.G. for assistance in planning and technical review. We would also like to recognize Dana Wiese (USGS) for operating the seismic equipment, Micah Weltmer (USGS) for graphics support, and Shane Dossat (SJRWMD) for his support in the field.

References

Bermes, B.J. , 1958, Interim report on geology and ground-water resources of Indian River County, Florida: Florida Geological Survey Information Circular 18, 74 p.

Brooks, H.K., and Merrit, J.M., 1981, Guide to the physiographic divisions of Florida: Florida Cooperative Extension Service Institute of Food and Agricultural Sciences, University of Florida, Gainesville. 1 map 150x105 cm and text 16 p.

Kindinger, J.L., Davis, J.B., Flocks, J.G., 1994, High-Resolution Single-Channel Seismic Reflection Surveys of Orange Lake and other selected sites of North Central Florida: U. S. Geological Survey Open File Report 94-616, 48 p.

Miller, J.A., 1986, Hydrogeologic framework of the Floridan Aquifer system in Florida and parts of Georgia, Alabama, and South Carolina: U. S. Geological Survey Professional Paper 1403-B, B91 p.

Sacks, L.A., Lee, T.M., and Tihansky, A.B., 1991, Hydrogeologic setting and preliminary data analysis for the hydrologic budget assessment of Lake Barco, an acidic seepage lake in Putnam County, Florida: U. S. Geological Survy Water-Resources Investigations Report 91-4180.

Schiner, G.R., Laughlin, C.P. , and Toth, D.J. , 1988, Geohydrology of Indian River County, Florida: U. S. Geological Survy Water-Resources Investigations Report 88-4073, 110 p.

Scott, T.M., 1988, The lithostratigraphy of the Hawthorn Group (Miocene) of Florida: Florida Geological Survey Bulletin 59, 148 p.

Wiener, J.M. ,1982, Geologic modeling in the Lake Wauberg-Chacala Pond vicinity utilizing seismic refraction techniques. University of Florida M.S. thesis. 94 p.

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