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.
56 <strong>GROUND</strong> <strong>WATER</strong> <strong>IN</strong> <strong>NORTH</strong>-<strong>CENTRAL</strong> <strong>TENNESSEE</strong><br />
crystalline beds may occur at any horizon in the section; further<br />
more, their composite thickness is generally between one-third and<br />
two-thirds the thickness of the formation. The platy layers are<br />
separated by very thin seams of calcareous shale, which weathers<br />
rapidly and allows the rock to disintegrate into a mass of loose slabs.<br />
In general the Pierce limestone is lithologically very similar to the<br />
Lebanon limestone, although it is much thinner; it also resembles<br />
platy facies of the Murfreesboro and Kidley limestones.<br />
The fossil fauna of the Pierce limestone is rich in the number of<br />
species and of specimens alike. The bryozoans are especially abun<br />
dant and valuable as stratigraphic guides. The most common and<br />
characteristic species are Nicholsonella pulchra, N. frondvfera, Anolo-<br />
tichia explanata, Stictoporella cribttina, Pianodema stonensis, and<br />
Batostoma, sp.<br />
The Pierce limestone, which is from 23 to 28 feet thick, crops out in<br />
narrow peripheral bands surrounding the minor structural domes that<br />
expose the Murfreesboro limestone in central Rutherford County.<br />
(See pi. 4.) Even though the outcrops are narrow usually less than<br />
a quarter of a mile wide complete sections are exposed for study at<br />
only a few localities.<br />
MURFREESBOBO LIMESTONE<br />
The Pierce limestone is underlain by the Murfreesboro limestone,<br />
the oldest formation to crop out at the apex of the Nashville dome,<br />
whose type locality 20 is the vicinity of the city of Murfreesboro<br />
Rutherford County. The contact between the two seems to be<br />
strictly conformable except at a point half a mile west of Lofton,<br />
Rutherford County, where the upper 10 feet of the Murfreesboro is<br />
missing. The Murfreesboro limestone is generally a thick-bedded<br />
dense, brittle, dark bluish-gray or drab limestone, which emits a bitu<br />
minous odor when freshly broken and contains much disseminated chert.<br />
The individual beds are from 6 inches to 4 feet thick and in some sec<br />
tions are separated by thin partings of shale or sand. This facies of<br />
the formation is lithologically almost identical with the Ridley lime<br />
stone, which lies above it. On Bradleys Creek at Lascassas, however,<br />
a shore phase of the formation is exposed, the lower 15 feet of the 27<br />
feet of beds that crop out being sandy, laminated, sun-cracked, and<br />
ripple-marked limestone that contains laminated chert nodules.<br />
The Murfreesboro limestone contains few fossils other than fucoids<br />
(?), but silicified forms are abundant at some places in the chert<br />
debris that remains after advanced weathering. The most common<br />
and diagnostic species are Salterella billingsi, Lophospira perangulata,<br />
Liospira abrupta, Helicotoma tennesseensis, H. declivis, and Leperditia<br />
fabulites.<br />
» Safford, J. M., and Killebrew, J. B., op. cit., p. 125.