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Gravimetry Of The Anderson Bedrock Valley Of Central Indiana
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, 17th EEGS Symposium on the Application of Geophysics to Engineering and Environmental Problems, Feb 2004, cp-186-00001
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Abstract
Gravity was measured at 173 stations in 30 km of profiles near Middletown in central Indiana to<br>map the Anderson bedrock valley and direct test drilling to the deepest part of that valley. The valley fill<br>includes coarse-grained aquifers and fine-grained aquatards of lakebed sediments and tills that overlie<br>Silurian and Ordovician strata dominated by carbonate rocks. Available maps derived from seismic<br>refraction profiles and scattered water, oil, gas, and test wells have generally provided insufficient detail<br>to suitably locate test wells. Two test wells were recently drilled at sites adjacent to relative gravity<br>minima in the profiles of the present survey. These wells penetrated the bedrock surface near the<br>thalweg of the Anderson bedrock valley at elevations of 175 to 176 m above sea level or about 23 m<br>deeper than was previously penetrated by wells in the area. The maximum thickness of unconsolidated<br>strata is about 120 m. Seismic refraction records were reinterpreted using hidden layers and dipping<br>bedrock refractors.