GROUND WATER IN NORTH-CENTRAL TENNESSEE
GROUND WATER IN NORTH-CENTRAL TENNESSEE
GROUND WATER IN NORTH-CENTRAL TENNESSEE
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OCCURRENCE OP <strong>GROUND</strong> <strong>WATER</strong> <strong>IN</strong> LIMESTONE 60,<br />
<strong>GROUND</strong> <strong>WATER</strong><br />
OCCURRENCE OF <strong>GROUND</strong> <strong>WATER</strong> <strong>IN</strong> LIMESTONE<br />
TYPES AND ORIO<strong>IN</strong> OF <strong>WATER</strong>-BEAR<strong>IN</strong>Q OPEN<strong>IN</strong>GS<br />
As Meinzer 39 has pointed out, no rock differs more radically with<br />
Tespect to yield of water than limestone. In some regions limestone<br />
ranks among the most productive water-bearing rocks; in other<br />
regions it is as unproductive as shale. These differences are related<br />
in part to differences in the mode of origin of limestone and in part to<br />
differences in the history of the rocks after they were laid down as<br />
calcareous sediment.<br />
The pore space of any rock may be termed continuous if the voids<br />
are connected with one another or discontinuous if the voids are not<br />
connected.40 Continuous pore space is that which renders the rock<br />
permeable to water or to other fluids; discontinuous pore space,.<br />
although it may aggregate a considerable part of the total volume<br />
of the rock, does not impart permeability. Both types of porosity<br />
are common in limestone.<br />
The pore space of a rock may also be termed primary if it existed<br />
in the sediment from which the rock was formed by consolidation,<br />
or secondary if it has been formed after the consolidation of the rock.<br />
Newly deposited calcareous sediment may contain many interstices<br />
and have considerable aggregate porosity. However, during com<br />
paction and lithification of the sediment, calcite generally crystallizes<br />
between many of the grains, so that the original interstices tend to<br />
become filled. Hence such primary pore space as remains in the<br />
consolidated rock may be largely discontinuous and may not render<br />
the rock permeable. The pure thick-bedded limestones of the older<br />
rock systems, such as those of Paleozoic age in central Tennessee, are<br />
generally very dense and contain no primary pore space visible to the<br />
eye other than minute openings in bedding planes. According to<br />
Howard 41 the pure calcareous rocks that have appreciable primary<br />
porosity are chalk, oolitic limestone, primary crystalline limestone<br />
and dolomite, and coral limestone. Such rocks are not common in<br />
north-central Tennessee. The earthy limestones and those that are<br />
interbedded with shale are also commonly without continuous<br />
primary pore space that might store and transmit water. The<br />
sandy limestones and calcareous sandstones, on the other hand, may<br />
have considerable primary porosity if the original interstices between<br />
the sand grains are not entirely filled with calcareous cement.<br />
!» Meinzer, O. E., The occurrence of ground water in the United States: IT. S. Qeol.<br />
Paper 489, pp. 131-137, 1923.<br />
* Murray, A. N., Limestone oil reservoirs of the northeastern United States and of Ontario,. Canada^<br />
Econ. Geology, vol. 25, No. 5, p. 453, 1930.<br />
« Howard, W. V., A classification of limestone reservoirs: Am. Assoc. Petroleum Geologists Bull,,, vol.<br />
12, p. 1155, 1928.