LINEAMENTS AND FRACTURE TRACES, DECATUR COUNTY, INDIANA By Theodore K. Greeraan U.S. GEOLOGICAL SURVEY
Lineanents and fracture traces have been mapped throughout Decatur County, Indiana. These lineaments and fracture traces may indicate that solutionenlarged vertical fractures in the limestone and dolonite aquifers underlie most of the county. The use of lineament and fracture-trace maps in selecting bedrock-drilling sites results in a significant increase in the number of usable sites. Bedrock wells drilled on or near mapped lineaments and fracture traces have a higher average yield than veils drilled into interfracture areas. Parts of Decatur County and several adjacent counties are economically restricted by inadequate water supplies. The Greensburg ffanicipal Water Works, supplying 35 percent of the county's population, obtains 25 percent of its water from six wells in Greensburg. The remaining 75 percent is pumped from the Flat Rock River. This water is piped 8.25 miles and lifted 183 feet to the treatment station. Although the Flatrock River has adeduate flow to supply Greensburg's water needs, a ground-water supply can probably be developed nearer the treatment plant. Pleistocene till covers most of the nearly horizontal bedrock. Although averaging about 50 feet thick, this unconsolidated unit does not seem to inhibit the mapping of lineaments and fracture traces. Bedrock is middle Paleozoic limestone, dolomite, and shale. Two sequences of limestone and dolomite, separated by a thin shale unit, constitute the principal aquifer. The extremely variable well yields from this aquifer indicate that the bedrock permeability is also variable. Well placement is important in a fractured bedrock terrane, as fractures are a principal source of water to the well. Here, the most productive bedrock wells are at the mapped intersection of two or more fracture traces or lineaments and at the lowest local altitude. Use of a fracture-trace map will not guarantee a sufficient supply of ground water but will reduce the chance of drilling an inadequate well.
Significant Multiple Pre-Illinoian Till Exposure in Southeastern Indiana
Five tills are exposed in a stream cut south of the Wisconsinan glacial boundary in Decatur County, southeastern Indiana. All tills are mineralogically or texturally distinct. The uppermost till is leached 7 ft and is regarded as Illinoian. Because there is a thick paleosol (7 ft of leaching and 11 ft of oxidation) in the surface of the till immediately below the Illinoian till, four of the tills in this section are considered pre-Illinoian in age. This is the largest number of pre-Illinoian tills known east of the state of Illinois. On the basis of lithologic characteristics and fabric, all tills appear to have been deposited by ice moving from a northerly or westerly direction. The chert-rich basal till of this section is very distinctive and, where described from other localities in southeastern Indiana, always is the lowermost till of the section. For this reason, and because the till contains a high percentage of weathered chert pebbles and non-calcareous “red” clay material, it is regarded as representing the first ice advance into southeastern Indiana. Although no definite age can be assigned to the pre-Illinoian tills, it seems that because of their textural and mineralogical differences they represent (1) deposition by nearly contemporary ice sheets advancing from slightly different directions and/or (2) deposition by non-contemporaneous ice sheets which advanced from a common direction after erosion had modified the pre-existing surface enough to expose new source materials.
Archaeological Survey of Dangoyama Kofun by 3DGPR
We presented a three-dimensional ground penetrating radar (3DGPR) system for the archeological investigation in a harsh site, where we have to deal with many trees and/or great topographic variations. This system consists of a commercial GPR system with a laser positioning system. With this system, we can move the GPR antenna freely, on which a positioning detector can record accurate position for each GPR data trace. We applied our 3DGPR system at Dangoyama Kofun, a burial mound, in Fukushima prefecture, Japan. A lot of trees and bushes covered the survey area and cannot be cut. We acquired six datasets in two days in this area. We successfully imaged the boundary between the original surface of the burial mound and the covering soil clearly at about 0.3 m depth around the mound. Furthermore, we found some strong reflections appeared at 0.8 m depth in the top area of the mound, which can be from the artificial parts of the burial mound. The results would greatly aid the following archaeological excavation. In addition, we compared the non-interpolated depth slice with interpolated depth slice at same position and demonstrated that the interpolation process on threedimensional GPR data may introduce some artifacts which might mislead our interpretation.