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.
Ground water in north-central Tennessee
This report describes briefly the physiography, stratigraphy, and geologic structure and the sources and chemical character of the ground water in a region covering 5,800 square miles on the northwest slope of the Nashville dome, in northcentral Tennessee. It includes Cheatham, Davidson, Dickson, Houston, Humphreys, Montgomery, Roberfcson, Rutherford, Stewart, Sumner, Williamson, and Wilson Counties. The region includes parts of two physiographic districts, the Nashville Basin and the Highland Rim plateau, both of which are sections of the Interior Low Plateaus province. The Highland Rim plateau comprises remnants of a regional peneplain, which was formed in the interval between late Upper Cretaceous and early upper Oligocene time and was subsequently arched and uplifted. Its present altitude within the region described is between 1,350 and 600 feet above sea level. The Nashville Basin is an elliptical depression 85 miles long by 50 miles wide formed by stream planation in the Ordovician limestones on the crest of the Nashville dome, and its floor is 700 to 550 feet above sea level. The period of stream planation has been ascribed to the middle Pleistocene. The principal streams are now intrenched 100 feet or more below the floor of the Nashville Basin. The primary structural feature of the region is the Nashville dome, the southerly one of two domes on the axis of the Cincinnati geanticline. The Nashville dome is a flat elliptical flexure whose major axis strikes N. 20°-30° E. across the eastern part of the region. From the apex of the dome, in the southeast corner of the region, the axis plunges northward and southward between 5 and 10 feet to the mile. The flanks dip about 15 feet to the mile within 50 miles of the apex, but the western flank flattens in the more remote parts of the region. Superposed upon the Nashville dome are many secondary anticlines, synclines, and domes, which generally are less than 5 miles long and 100 feet high. Where the secondary folding is most intense the rocks are much jointed. One of the two principal sets of joints is approximately parallel and the other normal to the major axis of the Nashville dome. In the northwestern part of the region the rocks are complexly faulted and folded in an area which is roughly circular in plan and about 8 miles in diameter; this is the Wells Creek uplift. The deformation that produced the Nashville dome began at least as early as the Lower Ordovician and recurred as late as upper Oligocene time. The oldest consolidated rock of the region is a cherty magnesian limestone of Lower Ordovician (Beekmantown?) age, which crops out only in the center of the Wells Creek Basin. The rocks exposed elsewhere on the Nashville dome range in age from Lower Ordovician (Chazy) to upper Mississippian, and each of the geologic systems within this range is represented. However, the geologic column is broken by one major unconformity, the complete hiatus including the Upper Ordovician and all of the Silurian and Devonian. At least 16 minor stratigraphic breaks occur. With the exception of the Chattanooga and Ridgetop shales, the strata are limestones, massive and thin bedded, pure, earthy, and cherty. Many of these limestones did not cross the axis of the Nashville dome, so that they overlap one another most complexly. The total maximum thickness of the exposed strata is about 2,530 feet, although the actual thickness in any one section is much less. A well drilled near the apex of the Nashville dome penetrates sandstone from 610 to 620 feet below the surface; the remaining strata include limestone, dolomite, and chert to a depth of 1,930 feet. The unconsolidated rocks include sand and gravel of Upper Cretaceous age, which rest upon the Highland Rim plateau in a few small areas, stream terrace deposits, and the alluvium that forms the present flood plains. vn ABSTRACT Most of the rocks, being dense limestone, are devoid of original interstices, so that in general the ground water circulates in joints and openings formed by solution. The number and capacity of water-bearing openings are dependent upon the number and continuity of open joints, the solubility of the limestone, and the positions of the several strata with respect to present and past equilibrium profiles of solution channeling. Therefore, as many of the limestones are essentially equal in solubility, the occurrence of ground water is not related to stratigraphy but rather to geomorphologic history. No large body of cavernous limestone has been depressed with relation to the water table so as to become saturated with water. A few discontinuous beds of permeable sandstone exist. Ground-water supplies adequate for domestic use can be obtained at most places from the limestone by drilled wells less than 200 feet deep, although some wells are dry, and comparatively few yield more than 10 gallons a minute. The largest wells that tap cavernous limestone yield as much as 300 gallons a minute perennially. It is generally inadvisable to drill much more than 350 feet in search of water, because of the tightness of the rocks and of the inferior chemical character of the water at great depths. In many parts of the region the most reliable sources of water are the large springs, especially those that issue from solution channels in the limestone. Twelve such springs within the region are known to discharge 1,000 gallons a minute or more each, and one, Hurricane Rock Spring, discharges about 27,000 gallons a minute from a single solution channel. Generally the unconsolidated rocks other than the alluvium are drained and are not promising as sources of large supplies of water. The alluvium underlies flood plains that are subject to overflow, so that extensive development of its ground water is generally not feasible, even though some of its beds may be rather highly permeable. Rowing artesian wells in the vicinity of Nashville tap the St. Peter (?) sandstone, but the area of artesian flow covers only the lower land along the Cumberland River, the water is inferior in chemical character, and the specific capacities of the wells seem to be small. Moreover, this stratum is itself discontinuous, so that it is not a source of water over an extensive area. Flowing wells also exist in several other small areas, all of which are below the Highland Rim plateau and most of which are on or below the Nashville Basin peneplain. In at least one area the artesian flow is assisted if not caused by the presence of gas in the water. Usually it is not possible to predict the depth or location at which flowing wells can be obtained. In general most of the waters fall into three classes, according to the amount and kind of dissolved mineral matter. One class includes the calcium bicarbonate waters, which contain 50 to 500 parts per million of total solids and 30 to 300 parts per million of carbonate hardness and are essentially free from iron and hydrogen sulphide. Such are the waters which circulate freely through permeable beds and channeled limestone and issue from most of the springs and from wells less than 200 feet deep. A second class includes those highly concentrated calcium or calcium-magnesium sulphate waters with considerable noncarbonate hardness, and the third includes the brines or sodium chloride-sulphate waters. The waters of the last two classes can not be sharply discriminated. They occur both in deeply buried permeable beds and in slightly permeable beds at moderate depth; they issue from a few springs and from some wells less than 50 feet deep but generally occur in strata more than 100 feet below the surface. So far as is known they occur in all strata more than 350 feet below the surface. The dissolved solids range from 1,000 to 26,000 parts per million. Many of the moderately and highly concentrated sulphate waters, especially those in which magnesium is relatively concentrated, contain large quantities of hydrogen sulphide gas. There seems to be no relation between the stratigraphic position of most water-bearing beds and the chemical character of the ground water.Most of the rocks, being dense limestone, are devoid of original interstices, so that in general the ground water circulates in joints and openings formed by solution. The number and capacity of water-bearing openings are dependent upon the number and continuity of open joints, the solubility of the limestone, and the positions of the several strata with respect to present and past equilibrium profiles of solution channeling. Therefore, as many of the limestones are essentially equal in solubility, the occurrence of ground water is not related to stratigraphy but rather to geomorphologic history. No large body of cavernous limestone has been depressed with relation to the water table so as to become saturated with water. A few discontinuous beds of permeable sandstone exist. Ground-water supplies adequate for domestic use can be obtained at most places from the limestone by drilled wells less than 200 feet deep, although some wells are dry, and comparatively few yield more than 10 gallons a minute. The largest wells that tap cavernous limestone yield as much as 300 gallons a minute perennially. It is generally inadvisable to drill much more than 350 feet in search of water, because of the tightness of the rocks and of the inferior chemical character of the water at great depths. In many parts of the region the most reliable sources of water are the large springs, especially those that issue from solution channels in the limestone. Twelve such springs within the region are known to discharge 1,000 gallons a minute or more each, and one, Hurricane Rock Spring, discharges about 27,000 gallons a minute from a single solution channel. Generally the unconsolidated rocks other than the alluvium are drained and are not promising as sources of large supplies of water. The alluvium underlies flood plains that are subject to overflow, so that extensive development