subsurface geology and coal resources of the pennsylvanian system ...

SHOAL CREEK
LIMESTONE
WEST FRANKLIN
LIMESTONE
COALUNO 7 '
COAL NO 6
COAL NO 5A
COAL NO 5
COAL"N0 4"
COAL8'N0 2"
DEKOVEN COAL
---
DAVIS COAL
STONEFORT(?
LIMESTONE
FIG. 26. - Generalized
partial section of the
Pennsylvanian system
shewing certain key
beds of the lower part
of the McLeansboro, of
the Carbondale, and of
the upper part of the
Tradewater groups in
Richland County.
It is also generally given this name by drill-a
ers and oil geologists working in this
county. The interval between West Franklin
limestone and Herrin (No. 6) coal bed
in the county varies from 180 to about 250
feet. In most parts of the county the interval
is about 225 feet. At one locality at
least (drill hole No. 56, sec. 2, T. 3 N., R.
9 E.) only 180 feet of interval is recorded
(fig. 27). The limestone and underlying
shale cuttings collected by the company from
this drill hole ss7ere found to correspond
closely with the West Franklin limestone
and underlying shale as described below.
Drill cuttings and various types of drilling
records indicate that the West Franklin
limestone in Richland County usually consists
of two benches of light gray, finely
crystalline, dense, moderately f ossilif erous
limestone, commonly separated by 1 to I
feet of light gray micaceous clay shale (fig.
28). Locally 6 inches to 1 foot of black shale
is found at the top of the gray shale. The
upper bench of limestone averages 5 feet
in thickness, but locally this bench is as much
as 10 feet thick. The lower bench is fairly
uniformly 8 to 10 feet thick. In places
only one bench is present, but whether this
represents the upper or lower bench or both
is not kno,wn.
The upper bench shows moderately high
resistivity (80-100 ohm-meters) in the
normal curve in most logs (fig. 29), the
third curve generally having a reverse
(negative) peak. The potential of this
bench in some holes was high for a
limestone (No. 1, fig. 29; Nos. 126 and
128, fig. 27), indicating high permeability,
but in many holes the potential was not high.
The lower, more massive bed of limestone
is distinguished by a very pronounced peak
in both the normal resistivity and the
third curve, and a potential varying to
about the same degree as the upper limestone
bench.
As elsewhere when onlp one bench of
limestone is present or onlp one high resistivity
peak is shown, identification of
the limestone as the upper or lower bench
is highly conjectural. This is the condition
in several .localities in the county, notably