GROUND WATER IN NORTH-CENTRAL TENNESSEE
GROUND WATER IN NORTH-CENTRAL TENNESSEE
GROUND WATER IN NORTH-CENTRAL TENNESSEE
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
62 <strong>GROUND</strong> <strong>WATER</strong> <strong>IN</strong> <strong>NORTH</strong>-<strong>CENTRAL</strong> <strong>TENNESSEE</strong><br />
GEOLOGIC STRUCTURE<br />
NASHVILLE DOME<br />
The major feature of geologic structure in central Tennessee is the<br />
Nashville dome. This is a very broad elliptical flexure whose axis<br />
trends N. 20°-30° E. and passes near Fosterville and Lascassas, in<br />
eastern Rutherford County, and close to Norene, in southeastern<br />
Wilson County. At the apex of the dome, which is approximately<br />
at the center of the southern boundary of Rutherford County, about<br />
2 miles south of Fosterville (pi. 4), the top of the Chattanooga shale<br />
the most reliable horizon marker of the area is 1,300 feet above<br />
sea level. From its apex the axis of the dome plunges northward and<br />
southward between 5 and 10 feet to the mile. The transverse dips<br />
are generally slightly steeper, however, and are about 15 feet to the<br />
mile within 50 miles of the apex. This average dip is so slight that it<br />
is likely to be undeterminable in any one outcrop.<br />
The top of the Chattanooga shale or the projected original posi<br />
tion of that stratum prior to the erosion of the Nashville Basin is<br />
between 1,100 and 1,300 feet above sea level in most of Rutherford<br />
County, which occupies the highest part of the dome. On the east<br />
flank of the dome this horizon marker is about 700 feet above sea<br />
level at McMinnville and at Celina, which are approximately at the<br />
respective centers of Warren and Clay Counties. On the west flank<br />
of the dome on which lies the greater part of the region covered by<br />
this report the Chattanooga shale slopes northwestward and is<br />
about 900 feet above sea level at Franklin and Columbia, the principal<br />
cities of Williamson and Maury Counties, respectively. It is between<br />
350 and 400 feet above sea level at most places in the central part of<br />
Dickson County and in the vicinity of Ashland, in Cheatham County.<br />
Farther west, however, the average dip of the strata is either very<br />
flat or else reverses in a shallow syncline, for the Chattanooga shale<br />
crops out at several places along the Tennessee River (pi. 4) between<br />
325 and 400 feet above sea level. These outcrops are the only known<br />
exposures of the Chattanooga shale west of Williamson and Cheatham<br />
Counties within the region covered by this report. Furthermore,<br />
very few deep wells have been drilled to this shale in the intervening<br />
area, and the thickness and stratigraphy of the overlying beds have not<br />
been worked out in any detail. Consequently the data at hand are<br />
inadequate to show accurately even the general features of the struc<br />
ture in that part of the region that lies west of the Highland Rim<br />
escarpment.<br />
The Nashville dome is the southerly one of two major structural<br />
domes on the crest of the Cincinnati arch, a geanticline whose axis<br />
appears from beneath Cretaceous and Tertiary rocks in northeastern<br />
Mississsippi and northwestern Alabama and trends about N. 30° E.