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

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SUBSURFACE GEOLOGY OF RICHLAND COUNTY
RAYMOND SIEVER AND GILBERT H. CADY
INTRODUCTION
HIS REPORT presents the results of
T a preliminary study of the Pennsylvanian
formations encountered in drilling
for oil in Richland County (figs. 1 and
25). The study was undertaken in
order to obtain information concerning the
depth, thickness, and distribution in the
county of mineable coal beds, and concerning
the occurrence of key beds that
might be useful as stratigraphic markers
and as structural datum planes.
The sources of information were drillingtime
and sample-study logs of nine control
drill holes compiled by the Coal Division
of the Geological Survey, about 350 electric
logs of rotary-drill holes, and drillers' logs
of two cable-tool holes. Only a few drillers'
logs and company sample-study logs
were used, as they were generally found to
be unsatisfactory for identifying Pennsylvanian
formations.
The coal beds generally of mineable thickness
(30 inches at 1000 feet or less, 3 feet
at more than 1000 feet)' are Herrin (No.
6) and Harrisburg (No. 5), which lie at
depths between 950 and 1200 feet below
the surf ace (fig. 26). A lower bed which
in places at least seems to be 3 feet or more
in thickness was penetrated in three control
drill holes from 1300 to 1400 feet below
the surface. The depth and thickness of
all these coal beds make very slight the
probability of their being mined in the near
future.
KEY BEDS
Shoal Creek limestone.-The youngest
Pennsylvanian sedimentary unit identifiable
over a considerable part of Richland County
10il. Gas and Coal Conservati?~~ .Act, Rules and Regulations:
p. 15 (Rule IS), Ill~nols Dept. Mines and
Minerals Division of Oil and Gas Conservation, 1941.
(New r;les adopted October 18, 1945, set 30 inches down
to 1000 feet as the limit of mineab~llty.)
C11-11
is the one designated here as the Shoal Creek
limestone. It appears to be the same limestone
as that similarly named in northeastern
Wayne County2 by Sims and co-authors,
who suggested its probable correlation with
the type Shoal Creek limestone exposed in
Bond C~untp.~ The interval between the
Shoal Creek limesto,ne and Herrin (No. 6)
coal bed in Richland County is between
338 and 456 feet in the tabulated drill
holes.
In six control drill holes, the cuttings consisted
of white to buff, very finely crystalline,
dense, and fairly pure limestone. Certain
zones in which the limestone has a
grayish mottled appearance were indicated
by the cuttings. Fragments of marine fossils,
including crinoid fragments, were
sparsely distributed through these mottled
cuttings. Directly beneath the limestone is
usually 1 to 3 feet of black "slate" underlying
which is commonly a thin bed of coal
underlain by 1 to 2 feet of light gray underclay.
Because this limestone cannot be definitely
recognized in more than forty percent
of the logs, it was not satisfactory here as
a datum plane for structural delineation as
it was in Wayne County.
West Franklin limestone.-More persistent
than the Shoal Creek limestone is a
second limestone which lies about 180 to
190 feet lower. The position and lithology
of this limestone is similar to that of the
West Franklin limestone of Indiana,4 which
outcrops near Evansville, Vanderbuq
County, and with which it is correlated.
Sims, Paul K., Payne, J. Norman, and Cady, Gilbert
H., Pennsylvanian key beds of Wayne County and the
structure of the "Sboal Creek" limestone and Herrin (No.
fbdyal bed: Illino~a Geol. Survey Rept. Inv. 93, p. 28,
Wdden, Jon A., Notes on Shoal Creek limestone: Illinois
Geol. Survey Bull. 8, p. 117, 1908.
Shrock, Robert R., and Malott, Clyde A., Structural
features of the West Franklin formation of southwestern
Indiana: Bull. Amer. Assoc. Pet. Geol. vol. 13, No. 10, pp.
1301-1315, 1929. See also the report on Gallatin County
in present volume, p. 69.