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Kansas Geological Survey, Open File Report 96-49

GPR Study of The Drum Limestone, part 9 of 9


High-resolution ground-penetrating radar was only partially successful at imaging the Drum Limestone, being limited to very shallow penetration depths (< 3 m) due to rapid signal attenuation and instrument noise. A lack of dielectric constant contrasts at deeper levels may also have contributed to the paucity of reflections. The lack of signal penetration in the Drum Limestone, particularly in areas of high near surface reflectivity, may be due to high conductivity layers at shallow depths combined with the high-frequency nature of the signal being used. The quality of the GPR data was best from near the surface to depths of 1 m, with some bounding surfaces and cross-beds appearing as high-amplitude reflections. Although lower in reflection strength, dipping clinoforms and other bounding surfaces were also imaged 1-3 m below the surface. The geometry of these reflections correlated fairly well with beds exposed along the highwall of the quarry at depths and station locations where the usable outcrop and GPR data overlapped. GPR data along line D2, which is perpendicular to the outcrop face was also useful because it allowed 3-D correlation of the bed forms imaged on line D1 into the outcrop face. The combined GPR interpretation confirmed the strike and dip direction of cross-beds measured on the limestone surface behind the outcrop, indicated the strike and dip direction of cross-beds not exposed at the surface behind the outcrop, and indicated the trend and dip of a channel-like feature which was covered along the outcrop face.

Results from this site suggest that high-resolution GPR is an excellent tool for imaging the internal stratigraphy of limestones near the surface, provided that high-conductivity soils or rock units above the limestone do not significantly attenuate the signal. Full-wavelength resolution with this technique is on the order of a few decimeters (depending on the velocity of the unit), and penetration depths can reach at least 3 m depending on lithology. Signal penetration in other areas and other limestone formations may be slightly deeper with a 500 MHz antenna as indicated by results at other limestone sites (Kruger et al., 1995; Martinez et al., 1995a, b). High-resolution GPR is also useful for imaging the near-surface structure of limestones, as indicated by the transition from dipping to relatively horizontal beds along the profile. These aspects suggest that GPR can be used to extend stratigraphic and structural information from a limestone unit away from the outcrop exposure, and if needed, create a grid of data to achieve a 3-D image of the unit in question. The correlations between geology and GPR in this report also suggest that GPR can be used as a remote sensing tool, even when outcrop information is sparse or unavailable.


We would like to thank Dr. Neil Anderson from the University of Missouri-Rolla, for the use of UMR's GPR equipment. We would also like to thank Mike Shoemaker for assisting in GPR data collection, Tim Carr for making Kansas Geological Survey funds available for the survey, and the Heartland Cement Co. for allowing access to the quarry site.
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Kansas Geological Survey, Open-File Report 96-49
Placed online Jan. 1997
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